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2 g&3g planning & optimization

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2 g&3g planning & optimization

  1. 1. 2G, 3G Planning & Optimization ventinel Page 1 2G, 3G Planning & Optimization Part - 2
  2. 2. 2G, 3G Planning & Optimization ventinel Page 2 Contents 2 GSM Radio Network Planning ............................................................................................................... 4 2.1 Overview ........................................................................................................................................... 4 2.2 Planning Foundation .......................................................................................................................... 5 2.2.2 Performance Target Confirmation ............................................................................................... 6 2.3 Coverage Analysis .............................................................................................................................. 6 2.3.1 Area Division ............................................................................................................................... 6 II. Define the field strength at coverage area edges .......................................................................... 7 2.4 Network Structure Analysis ................................................................................................................ 8 2.4.1 Middle-Layer Station ................................................................................................................... 8 II. Advantages .................................................................................................................................. 8 III. Distance between stations .......................................................................................................... 9 IV. Challenges .................................................................................................................................. 9 2.4.2 High-Layer Station....................................................................................................................... 9 II. Functions ..................................................................................................................................... 9 2.4.3 Low-Layer Station ....................................................................................................................... 9 II. Other considerations.................................................................................................................. 10 2.5 Traffic Analysis ................................................................................................................................. 10 2.5.1 Traffic Prediction and Cell Splitting ............................................................................................ 10 II. Cell splitting ............................................................................................................................... 11 2.5.2 Voice Channel Allocation........................................................................................................... 13 II. Relationship between carrier number and bearable traffic ......................................................... 14 III. Example .................................................................................................................................... 14 2.5.3 Control Channel Allocation........................................................................................................ 15 II. CCCH allocation.......................................................................................................................... 15 2.6 Base Station Number Decision ......................................................................................................... 16 2.6.1 Characteristics of 3-sector base stations in urban areas ............................................................ 16 2.6.2 References for Design of Base Station Parameters .................................................................... 17 2.6.3 Uplink and Downlink Balance .................................................................................................... 17 I. Link budget model ...................................................................................................................... 18 II. Bass station sensitivity ............................................................................................................... 19
  3. 3. 2G, 3G Planning & Optimization ventinel Page 3 2.6.4 Cell Coverage Estimation........................................................................................................... 22 2.6.5 Base Station Address Planning .................................................................................................. 24 II. Planning methods ...................................................................................................................... 24 2.7 Design of Base Station Address ........................................................................................................ 25 2.7.1 Address design .......................................................................................................................... 25 I. Environment for antenna installation .......................................................................................... 28 II. Antenna isolation in GSM system ............................................................................................... 29 IV. Installation distance between antennas .................................................................................... 32 2.8 Location Area Design ....................................................................................................................... 34 2.8.1 Definition of Location Area ....................................................................................................... 34 2.8.2 Division of location areas .......................................................................................................... 35 II. Calculating coverage area and capacity of a location area .......................................................... 35 2.9 Dual-Band Network Design .............................................................................................................. 38 2.9.1 Necessity for Constructing Dual-Band Network ......................................................................... 38 2.9.2 GSM 1800MHz Coverage Solutions ........................................................................................... 38 2.10 Design of Indoor Coverage System ................................................................................................. 44 2.10.5 Traffic Control ......................................................................................................................... 48 2.11 Tunnel Coverage ............................................................................................................................ 49 2.11.4 Tunnel Coverage Based on Leaky Cable System ....................................................................... 53 2.12 Repeater Planning ......................................................................................................................... 57 2.12.2 Working Principles of Repeater ............................................................................................... 60 VII. Repeater adjacent cell planning ............................................................................................... 65 2.13 Conclusion ..................................................................................................................................... 66
  4. 4. 2G, 3G Planning & Optimization ventinel Page 4 2 GSM Radio Network Planning 2.1 Overview The design of radio network planning (RNP) is the basis of the construction of a wireless mobile network. The design level of network planning decides the future layout of a network. During network planning, the documents concerning base station distribution, channel assignment, and cell data must be outputted. And the major tasks involved are as follows: 1) Analyze carriers’ requirements on network coverage, capacity and quality. 2) Analyze the coverage and capacity features of the candidate mobile communication systems and bands, and then analyze the investment feasibility through estimating the network scale. 3) Decide the network structure and base station type based on further analysis. First analyze whether to construct a layering network according to user distribution, propagation conditions, city development plan and existed network conditions, and then analyze the sites within this area to decide whether to use omni antennas or directional antennas to meet the requirements on coverage and capacity. 4) Estimate the number of base stations Before estimating the number of base stations, estimate the coverage distance of base stations of various types in various coverage areas. The factors deciding the effective coverage area of a base station include: - Valid transmit power of the base station - Working bands to be used (900 MHz or 1800 MHz) - Antenna type and installation position - Power budget - Radio propagation environment - Carriers’ indexes on coverage Then through calculating the coverage distance and dividing the coverage areas, you can obtain a rough number of base stations for various coverage areas. 5) Plan an ideal base station address according to cellular structures. According to geographic maps or administrative maps and with the help of on-the-spot surveys, you can have a full understanding of the areas to be planed, and then mark the area where the number of users is large as a target address. After that, mark the addresses of other base stations according to the ideal cellular structure and the result of link budget. 6) Calculate the number of channels of the cells of each base station - Estimate the traffic of a base station according to its ideal location, and then obtain the number of carriers and channels needed by each base station by checking Erl table according to the indexes of call loss rate. - Decide the frequency reuse mode according to band width, network quality requirement, and equipment supportability. - Estimate the maximum base station configuration type according to the frequency bandwidth and reuse mode provided by the construction carriers. If the system capacity in some areas cannot be met, you need to add more base stations or cells to the system according to cell splitting principles and actual conditions. After that, reselect an ideal base station address on the map and re-estimate the number of channels required by the base station. 7) Predict the coverage area and decide the project data, namely, perform the preliminary emulation. The specific tasks are as follows: - Select the design indexes
  5. 5. 2G, 3G Planning & Optimization ventinel Page 5 Select the minimum received power and the penetration ratio index at the coverage area edge. - Select the design parameters, which includes: Antenna height (above the ground), antenna azimuth angle, antenna gain, antenna tilt angle, base station height above sea level, base station type, feeder length, antenna feeder system loss, combining and distribution modes, transmitter output power, receiver sensitivity, base station diversity reception, and diversity gains. - Predict the coverage area of each cell according to the propagation models in different areas, and then give the opinions on adjusting the base station address, antenna direction, antenna tilt angle, and antenna height in the areas where dead zones may be present and signals are poor. Finally, provide the project data. 8) Select actual base station address and decide base station type: Perform filed examination according to the ideal base station addresses, and then record the possible addresses according to various construction conditions (including power supply, transmission, electromagnetic background, and land taken over). Finally, recommend a suitable address based on integrated consideration of the deviation from the ideal base station address, the effect on future cell splitting, economic benefits, and coverage prediction. After the base station address is selected, decide the actual base station type according to the number of base station channels. After the base station type is decided, you need to make a scheme for antenna configuration. For moving a network, if you intend to provide a best combination scheme for the antenna feeders, you must fully investigate the combination of the antenna feeders of the original carriers, plan the future expansion of the base station, and design the combination of the antenna feeders supported by current equipments. 9) Plan frequency and adjacent cell Decide the frequency and adjacent planning according to the actual base station distribution and type. 10) Make cell data To ensure that the network runs stably, you must design the parameters relative to performance for each cell. These parameters include system information parameters, handover parameters, power control algorithm parameters, and so on. - Note: For the selection of handover bands, the handover algorithms to be enabled, and whether to use frequency hopping, power control, and DTX, they must be decided in coverage prediction and frequency planning, because the related parameters will be used in emulation. In addition, sections 2.9 and that later introduce the solutions to the planning of dual-band network and the planning in special occasions. 2.2 Planning Foundation 2.2.1 Coverage and Capacity Target Confirmation Before planning a network, you must confirm the network coverage and capacity target and relative specifications from carriers. They are specified as follows: - Definition of coverage areas - Specific division of the service quality in coverage areas - Grade of service (GoS) at Um interface - Prediction of network capacity and subscriber growth rate
  6. 6. 2G, 3G Planning & Optimization ventinel Page 6 - Available bands and restrictions on using bands - Restrictions on base station address and the number of carriers - Penetration loss in cars or indoor environment - Performance and sensitivity of base stations - Rules on base station naming and numbering - Information of the base stations in the existing network Engineers perform the network planning and guide the subsequent construction work according to the previous technical specifications. Because any change of these specifications will affect network construction, you must discuss these specifications with carriers and get their confirmation. 2.2.2 Performance Target Confirmation Carriers emphasize much on the future network quality. Therefore, network planning engineers must judge the indexes concerning network performance according to construction difficulty and experience, and then cooperate with carriers to design a reasonable solution. Generally, the performance of voice services can be judged according to KPI indexes. The KPI indexes vary slightly with carriers. The mean opinion score (MOS) is divided into five levels. - The call whose quality is above level 3 can access the mobile communication network. - The call whose quality is above level 4 can access the public network. 2.3 Coverage Analysis 2.3.1 Area Division I. Types of coverage area The signal propagation models are applied in accordance with the propagation environments in areas of different types. The signal propagation models decide the design principles, network structures, grade of services and frequency reuse modes for the radio networks in coverage areas. In order to decide the cell coverage area, you can the radio coverage areas into the following four types: - Big city - Middle-sized city - Small town - Countryside Big city - Dense population - Developed economy - Large traffic - Dense high buildings and mansions distributed in center areas - Flourishing shopping centers
  7. 7. 2G, 3G Planning & Optimization ventinel Page 7 Middle-sized city - Relatively dense population - Relatively developed economy - Relatively large traffic - Dense buildings distributed in center areas - Active and promising shopping centers Small town - Relative large population - Promising economic development - Moderate traffic - Relative dense buildings distributed in center areas - A certain scale of shopping centers but with great potentiality Countryside - Scattered population - Developing economy - Low traffic In addition, you must consider the coverage of the areas at the intersections and various transport arteries, including: - Express way - National high way - Provincial highway - Railway - Sea-route - Roads in mountain areas Generally, it is recommended to apply omni base stations in the countries plains and the areas with restricted landforms. In big cities, middle-sized cities, and along expressways, it is recommended to apply directional base stations. II. Define the field strength at coverage area edges When defining the field strength of the uplink edges of a service area, you must consider the factors: Mobile station sensitivity -102 dBm Fast fading protection 4 dB (3 dB for countryside) Slow fading protection 8 dB (6 dB for countryside) Noise (environmental noise and interfering noise) protection 5 dB Remark: - To ensure the indoor coverage in big and middle-sized cities, you can consider 15dB for the average penetration loss between buildings and consider adding 5dB to the protection margin. - Generally, the propagation loss of GSM 1800MHz signals is 8 dB greater than that of the GSM 900MHz signals in average.
  8. 8. 2G, 3G Planning & Optimization ventinel Page 8 - Radio links have two directions, namely, uplink direction and downlink direction, and the coverage area is defined by the direction in which the signals are poor, so you must consider the uplink and downlink balance. Therefore, if you intend to plan an ideal network, you must make a good power control budget so that the uplink and downlink can be as balance as possible. III. Define coverage probability The definition of coverage probability varies with the coverage areas, and the coverage probability is gradually improved along with the construction of the network. Generally, a call must be ensured to access the network at 90% of the places and 99% of the time within the coverage area. - For the outdoor environment in big cities, the two ratios must be greater. - For the areas in countryside, the two ratios can be lower. - For transport arteries, different standards are applied, and the coverage probability can be defined in accordance with the types of the arteries. 2.3.2 Radio Environment Survey Through surveying radio propagation environments, you can get familiar with the overall landforms, estimate the rough antenna height, and select the proper radio propagation model, among which the radio propagation model helps you estimate the number of base station when predicting the coverage. If necessary, you must adjust the propagation model. 2.4 Network Structure Analysis When considering the layout of base stations, you must deeply analyze network structure. Generally, according to network layers, a network can be divided into middle-layer, high-layer, and low-layer. The base stations at the middle-layer bear the greatest traffic in a network 2.4.1 Middle-Layer Station I. Definition and application A middle-layer station in big and middle-sized cities is defined as follows: - The antenna is installed on building tops. - The antenna height ranges from 25 to 30 meters, which is greater than the average height of the buildings. - It covers several blocks. In small towns and countryside areas, except the high-layer stations are designed for controlling traffic flow or for landform reasons, most of the base stations are middle-layer stations. II. Advantages Compared with high-layer stations, middle-layer stations can utilize frequency resources more efficiently. Compared with low-layer stations, middle-layer stations can absorb traffic more efficiently.
  9. 9. 2G, 3G Planning & Optimization ventinel Page 9 Therefore, the middle-layer stations bear the greatest traffic in a network. III. Distance between stations The average distance between most middle-layer stations range from 0.6 to 5 km except in countryside areas. In big cities, the distance between some middle-layer stations is shorter than 0.6 km. However, it is suggested that the distance between middle-layer stations in big cities cannot be shorter than 0.4 km. If this distance is too short, the buildings will produce strong interference against the signals of the base stations. In this case, to control the coverage area is quite demanding. IV. Challenges Because no suitable ground objective is available, to ensure the quality of service of a network is quite demanding. According to the experience on project construction and maintenance, great challenge is present in the selection of base station address, station design, project construction, network maintenance, and network quality. 2.4.2 High-Layer Station I. Definition and application A high-layer station in big and middle-sized cities is defined as follows: - The antenna height ranges from 10 to 50 meters, which is far greater than the average height of the buildings. - Its coverage areas contain the areas covered by multiple middle-layer stations. Because the high-layer stations make poor use of the frequency resources, they are mainly applied to the traffic networks where people move fast in big and middle-sized cities. In addition, to control construction cost and meet coverage requirements, you can install some high- layer stations in suburban areas, highroads, small towns, and countryside areas. II. Functions The high-layer stations must be as fewer as possible but be as effective as possible. They mainly provide services to the fast-moving subscribers in cities. & Note: The coverage of high buildings is realized by indoor distribution systems. 2.4.3 Low-Layer Station I. Definition and application A low-layer station is defined as follows: - The antenna height is shorter than 20 meters, which is shorter than the average height of the buildings. - The antenna can be installed on the outer walls of the lower floors of a building, on the top of lower
  10. 10. 2G, 3G Planning & Optimization ventinel Page 10 roofs, or in the rooms of a building. Generally, at the early stage of the network construction, signal network design is applied, so most of the base stations are middle-layer stations. After the basic network is established, you must adjust the base stations and add new base stations according to traffic and coverage requirements. For populated commercial areas where the traffic is heavy, you can use low-layer stations, which are constructed with micro cell layer and distributed antenna system. In this case, not only the requirements on indoor coverage are met, but also the interference and difficulties of base station selection caused by short distance between stations are avoided. With the development of the network, the low-layer stations will develop into the layering network structure. II. Other considerations The coverage area of a low-layer station is small, so it can fully use frequency resources but cannot absorb the traffic efficiently. As a result, ideal traffic cannot be ensured if the base station deviates far away from the areas where the traffic is heavy. Therefore, when constructing a low-layer station, you must consider whether the base station is used to make up coverage or solve the problem of heavy traffic, because the construction purpose is directly related to the selection of the address and type of the base station. & Note: A layering network cost much frequency resource, so it is not recommended for the networks where the frequency resource is inadequate. 2.5 Traffic Analysis 2.5.1 Traffic Prediction and Cell Splitting I. Traffic prediction The network construction requires the consideration of economic feasibility and rationality. Therefore, a reasonable investment decision must be based on the prediction of the network capacity of the early and late stage. When predicting network capacity, you must consider the following factors: - Population distribution - Family income - Subscription ratio of fixed telephone - Development of national economy - City construction - Consumption policy After predicting the total network capacity, you must predict the density of subscriber distribution. Generally, base stations are constructed in urban areas, suburban areas, and transport arteries. Therefore, you can use the percentage of prediction method. At the early stage of construction, the subscribers in cities account for a larger percentage of the total predicted subscribers. With the development of the network construction, the percentage of the
  11. 11. 2G, 3G Planning & Optimization ventinel Page 11 subscribers in suburban areas and transport arteries grows. The traffic of each subscriber is 0.025 Erl in urban areas and 0.020 Erl in suburban areas. The formula calculating traffic is: A = (n × T) / 3600 Here, - “n” is the call times in busy hour - “T” is the duration of each call, in the unit of second. In this way, the number of voice channels needed for a base station can be obtained through predicting the traffic. & Note: When estimating the number of voice channels needed for a base station in the future, you must consider the effect caused by cell splitting. In a GSM system, you can use Erl model to calculate the traffic density that the network can bear. The call loss can be 2% or 5% depending on actual conditions. Because restrictions on cell coverage area and the width of the available frequencies are present, you must plan the cell capacity reasonably. If good voice quality is ensured, you must enhance the channel utilization ratio as much as possible. In actual networking, if the network quality is ensured at a certain level, two capacity solutions are available, namely, a few stations with high-level configuration and multiple stations with low-level configuration. Both the advantages and disadvantages of the two solutions are apparent, so which one should be used depending on the actual conditions of an area. For network construction, you can expand the capacity either through adding base stations or through expanding the base station capacity. The expansion strategies adopted must be in accordance with the traffic density in an area. For example, the strategies such as adding 1800 MHz base stations, expanding sector capacity, adding micro cells, or improving indoor coverage can be used to expand network capacity. II. Cell splitting Cell splitting is quite effective for the expansion of network capacity. An omni base station can split into multiple sectors, and a sector can split into multiple smaller cells. In other word, you must plan cell radius in accordance with the traffic density of an area. Cell splitting means more base station and greater cost are needed. Therefore, when planning a network, you must consider the following factors: - The rules and diagrams of frequency reuse are repeatable. - The original base stations can still work. - The transition cells must be reduced or avoided. - The cell can split without effect. Cell splitting is quite important in a network. The followings further describe the cell splitting based on 1-to-4 splitting.
  12. 12. 2G, 3G Planning & Optimization ventinel Page 12 Cell splitting is used to split a congested cell into multiple smaller cells. Through setting the new cells whose radiuses are smaller than the original cells and placing them among the original cells, you can increase the number of channels in a unit area, thus increasing channel reuse times. In this case, system capacity is expanded. Through adjusting the project parameters relative to antenna feeders and reducing transmitter power, you can narrow the coverage area of a cell. Error! Reference source not found. shows that a cell splits into four smaller cells by half of its radius. Smaller cells are added without changing the frequency reuse mode. They are split proportional to the shape of the original cell clusters. In this case, the coverage of a service area depends on the smaller cells, which are 4 times outnumber of the original cells. To be more specifically, you can take a circle with the radius R as an example, the coverage area of the circle with the radius R is 4 times that of a circle with the radius R/2. After cell splitting, the number of cell clusters in the coverage area increases. Thus the number of channels in this coverage area increases and the system capacity is expanded accordingly. You can adjust the coverage area of the new cells through reducing the transmit power. For the transmit power of the new cells whose radiuses are half of that of the original cell, you can check the power “Pr” received at the new cell edge and at the original cell edge, and make them equal. However, you must ensure that the frequency reuse scheme of the new micro cells is the same as that of the original cell. As for Figure 5-1, - Pr [at the edge of the original cell] = Pt1R-n, and, - Pr [at the edge of the new cell] = Pt2 (R/2)-n Here, Pt1 and Pt2 are the transmit power of the base stations of the original cell and the new cell, and n is path fading exponent. If make n = 4, make the received power at the edge of the new and original cell equal, the following equation can be obtained: Pt2 = Pt1/16 That is to say, if the micro cells are used to cover the original coverage area and the requirement of S/I is met, the transmit power must be reduced by 12 dB. Not all cells need splitting. In fact, it is quite demanding for carriers to find out a perfect cell splitting scheme. Therefore, many cells of different scales exist in a network simultaneously. As a result, the minimum distance among intra-frequency cells must be maintained, which further complicate frequency allocation. In addition, you must pay attention to the handover because success handover ensure the all subscribers to enjoy good quality of service regardless of moving speed. When two layers of cells are present within an area but their coverage scale is different, according to the formula Pt2 = Pt1/16, neither all new cells can simply apply the original transmit power, nor all original cells can simply apply the new transmit power. If all cells apply great transmit power, the channels used by smaller cells cannot be separated from the intra-frequency cells. If all cells apply lower transmit power, however, some big cells will be exclusive from the service areas. For the previous reason, the channels in the original cells can be divided into two groups. One group
  13. 13. 2G, 3G Planning & Optimization ventinel Page 13 meets the reuse requirement of the smaller cells, and the other group meets the reuse requirement of the bigger cells. The bigger cells are applied to the communication of fast-moving subscribers, which requires a fewer handover times. The power of the two channel groups decides the progress of cell splitting. At the early stage of cell splitting, the channels in the low-power group are fewer. As the requirement grows, more channels are needed in low-power group. The cell splitting does not stop until all channels within this area are applied in the low-power group. In this case, all cells in this area have split into multiple smaller cells, and the radius of each cell is quite small. & Note: Commonly, you can restrict cell coverage area through adjusting the project parameters of the base station. 2.5.2 Voice Channel Allocation I. Voice channel decision The base station capacity refers to the number of channels that must be configured for a base station or a cell. The calculation of the base station capacity is divided into the calculation of the number of radio voice channels and the calculation of the number of radio control channels. According to the information of base stations and cells and the density distribution of subscribers, you can calculate the total number of the subscribers. Then according to the radio channel call loss ratio and traffic, you can obtain the number of voice channels that must be configured by checking Erl B table. Generally, you can decide the number of voice channels as follows: 1) According to the bandwidth and the reuse mode allowed by current GSM networks within the areas to be planned, you can obtain the maximum number of carriers that can be configured for a base station. 2) Each carrier has 8 channels. You can obtain the maximum number of voice channel numbers that can be configured for a base station by detracting the control channels from the 8 channels. 3) According to the number of voice channels and call loss ratio (generally 2% dense traffic areas and 5% for other areas), you can obtain the maximum traffic (Erl number) that the base station can bear through checking Erl B table. 4) Through dividing the Erl number by the average busy-hour traffic of subscribers, you can obtain the maximum number of subscribers that the base station can accommodate. 5) According to the data of subscriber density, you can obtain the coverage area of the base station. 6) After the areas are specified based on the subscriber density, according to the area of an area and the actual coverage area of the base station, you can calculate the number of needed base stations. 7) For important areas, you must consider back up stations and the cooperation between carriers. For example, an important county needs at least two base stations and three important carriers. 8) For the areas where burst traffic is possible, such as the play ground and seasonal tourism spots, you must prepare the equipments (such as carriers and micro cells) and frequency resources for future use. 9) The dynamic factors, such as roaming ratio, subscriber mobility, service development, industry competition, charging rate change, one-way charge, and economic growth, must be considered.
  14. 14. 2G, 3G Planning & Optimization ventinel Page 14 10) To configure a base station, you must consider the transmission at the Abis interface so that the capacity can be met while saving transmission. For example, the application and concatenation of the Abis interface 15:1 and 12:1 should be considered. 11) For indoor coverage and capacity, you can use micro cells and distributed antenna systems. For the coverage in countryside areas and highroads, you can use economical micro base stations. For the transmission in countryside areas and highroads, you can use HDSL because it is cost effective. 12) Prepare the some carriers, micro cells, and micro base stations for new coverage areas and future optimization. 13) In some special areas, you can use the base stations consisting of omni and directional cells, but you must consider the isolation between omni antennas and directional antennas. For traffic control, you can use the algorithm in terms of network layers. 14) For some highroads which require a little traffic by large coverage, you can use the two networking modes. They are: - (A micro base station with single carrier) + (0.5 + 0.5 cell with two set of directional antennas) - A micro base station with single carrier + 8-shaped antenna II. Relationship between carrier number and bearable traffic Erl traffic model can calculate the traffic that a network can bear. The call loss ratio can be 2% or 5% according to actual conditions. Table 5-7 describes the relationship between the number of carriers and the traffic that a network can bear according to Erl B table. According to Erl B table, the larger the number of carriers and the call loss ratio are, the greater the traffic that each TCH bear, and the greater the TCH utilization ratio is (the channel utilization ratio is an important indicator of the quality of network planning and design). If the number of subscribers of a base station is small, you can consider delaying the construction. Because restrictions on the coverage area of a cell and the bandwidth of the available frequencies, you must plan a reasonable capacity for the cell. If good voice quality is ensured, you must take measures to enhance the channel utilization ratio as much as possible. For the construction of the dual-band network, you can use the frequencies with wider bands to enhance channel utilization ratio, which is helpful for traffic sharing. In actual applications, when the traffic on each TCH accounts for 80-90% of total given by Erl B table (the call loss ratio is 2%), the congestion ratio in this cell rise greatly. Therefore, we generally calculate the traffic that a network can bear by taking the 85% of the traffic given by Erl B table as a reference. III. Example The capacity of a local network needs to be expanded. According to the service development, population growth and mobile popularity, the subscribers in this area are expected to reach 100,000 in 2 years. If only the followings are considered: - Roaming factor (according to the development trend of traffic statistics) = 10%. - Mobile factor (the subscriber moves slightly within the local network instead of roaming) = 10%.
  15. 15. 2G, 3G Planning & Optimization ventinel Page 15 - Dynamic factor (with burst traffic considered) = 15%. The network capacity = 100000 * (1 + 10% + 10% + 15%) = 135,000. However, because the congestion is present, we generally calculate the traffic that a network can bear by taking the 85% of the traffic given by Erl B table as a reference. As a result, the network capacity must be designed as follows: The network capacity = 135, 000/85% = 158,800, about 160,000. 2.5.3 Control Channel Allocation I. SDCCH allocation Stand-alone dedicated channel (SDCCH) is an important channel in a GSM network. Mobile station activities, such as location update, attach and detach, call setup and short message, are performed on SDCCH. The SDCCH is used to transmit signaling and data. It is difficult to induce a traffic model for the SDCCH; especially it even becomes impossible after the large-scale application of layering networks and short messages. Moreover, the equipments of some carriers support SDCCH dynamic allocation function. As a result, the traffic model for SDCCH must be adjusted according to actual conditions. The advantages of the SDCCH dynamic function are as follows: - Adjusting SDCCH capacity dynamically - Reducing SDCCH congestion ratio - Reducing the effect of initial SDCCH configuration against system performance - Making SDCCH and TCH configuration more adaptive to the characteristics of cell traffic - Optimizing the performance of the systems under the same carrier configuration. In conclusion, the SDCCH dynamic allocation function is divided into two types, namely, - Dynamic allocation from SDCCH to TCH - Dynamic recovery from SDCCH to TCH II. CCCH allocation Common control channels (CCCH) contain access grant channel (AGCH), paging channel (PCH) and random access channel (RACH). The function of a CCCH is sending access grant message (immediate assignment message) and paging message. All traffic channels in each cell share the CCCH. The CCC can share a physical channel (a timeslot) with SDCCH, or it can solely occupy a physical channel. The parameters relative to the CCCH include CCCH Configure, BS AG BLKS PES, and BS PA MFRMS. Here, - CCCH Configure designates the type of CCCH configuration, namely, whether the CCCH shares one physical channel with the SDCCH. If there are 1 or 2 TRX in a cell, it is recommended that the CCCH occupies a physical channel and share it with the SDCCH. If there are 3 or 4 TRXs, it is recommended that the CCCH solely occupies a physical channel. If there are more than 4 TRX, it is recommended to calculate the capacity of the paging channels in the CCCH according to actual conditions first, and then you can perform the configuration.
  16. 16. 2G, 3G Planning & Optimization ventinel Page 16 - BS AG BLKS PES indicates that the number of CCCH message blocks reserved to the AGCH. After CCCH configuration is done, this parameter, in fact, decides allocates the ratio of AGCH and PCH in CCCH. Some carriers can set sending priority for the “access grant message and “paging message”. When the former message set to be prior to the later one, the BS AG BLKS PES can be set to 0. - BS PA MFRMS indicates the number of multi-frames that can be taken as a cycle of paging sub- channels. In fact, this parameter decides the number of paging sub-channels that a cell can be divided into. & Note: In CCCH configuration, the location area planning, paging modes and system flow control must be considered. 2.6 Base Station Number Decision After traffic and coverage analysis, according to the selected base station equipments and parameters, you can obtain the coverage areas of various base stations through link budget. The coverage area helps you calculate the number of base stations required by each area. Then you decide the base station configuration according to traffic distribution. Finally, you must perform emulation using relative planning software so that coverage, capacity, carrier-to-interference ratio can be assured and interference can be avoided. 2.6.1 Characteristics of 3-sector base stations in urban areas Cellular communication is named because the coverage areas of base stations are extruded through small cellular-shaped blocks. In urban areas, for the purpose of capacity expansion and radio frequency optimization, mainly 3-sector base stations are used. This section explains some basic concepts of a 3- sector base station. This is a standard 3-sector cellular layout. Thedistance between two 3-sector base stations is R + r, here R = 2r. However, “R” is mainly used in cell radius estimation because the direction along “R” is the direction of the major lobe of the directional antenna. In the design for cellular layout, however, “r” indicates the cell radius. In a cellular cell, if the included angle between a direction and the direction of the major lobe of the antenna, the coverage distance along this direction is r = R/2, and the path loss along this direction is about 10dB less than that along the direction of the major lobe of the antenna (for the deduction, it is introduced in the following), namely, the equivalent isotropic radiated power (EIRP) along this direction can be about 10dB less than that along the major lobe. According to this feature, in the cellular layout of this kind, you can adopt the directional antenna whose azimuth beam width ranges from 60 to 65 degrees because their horizontal lobe gain diagram also meets this feature. If “R” is the cell radius, the cell area is S = 0.6495 × R × R. Sometimes the “r” is used as cell radius, so the cell area is S = 2 5981×r×r. Therefore, when calculating the cell area, you must make clear whether “r” or “R” is used. The followings deduce the EIRP required along “R” direction and “r” direction.
  17. 17. 2G, 3G Planning & Optimization ventinel Page 17 As shown in Figure 5-3, the coverage distance along “r” direction is half of that along “R” direction, namely, r = R/2. To keep even coverage, you must make the field intensity at the edges of the cell equal, namely, RxlvelB = RxlevelC. Suppose that the EIPR transmitted from cell A is EIRPR and EIRPr along “R” direction and “r” direction respectively, and the city HATA mode is used for path loss, the path loss from point A and B is expressed as equation (1) : EIRPR – RXLEVB = 69.55 + 21.66lgf - 13.82lgh1 + (44.9 - 6.55lgh1) lgR (1) And the path loss from point A to point C is expressed as equation (2): EIRPr- RXLEVc = 69.55 + 21.66lgf - 13.82lgh1 = (44.9 - 6.55lgh1) lgr (2) Subtract (2) from (1), the equation (3) is expressed as follows: EIRPR - EIRPr =(44.9 - 6.55lgh1)×(lgR – lgr) =(44.9 - 6.55lgh1) × lg (R/r) (3) Introduce R = 2r, the equation (4) is obtained as follows: EIRPR - EIRPr = 0.3 × (44.9 - 6.55lgh1) (4) When the antenna height “h1” increases from 5m to 100m, the values of (EIRPR - EIRPr) decrease from 12 to 9.5, which can be roughly treated as 10dB. 2.6.2 References for Design of Base Station Parameters When estimating the number of base stations, you must perform uplink and downlink budget. Based on the coverage division and propagation environment survey, you can obtain some project parameters and apply them to link budget. 2.6.3 Uplink and Downlink Balance After base station parameters are specified, you can perform link budget to estimate the coverage area of the base station. In addition, you must consider the sensitivity of the base station equipments at this time. In a mobile communication system, radio links are divided into two directions, namely, uplink and downlink. For an excellent system, you must perform a good power budget so that the balance is present between uplink signals and downlink signals. Otherwise, the conversation quality is good for one party but bad for the other party at the edges of the cell. If uplink signals are too bad, the mobile station cannot start a call even if signals are present. However, the because the fading for uplink channels and downlink channels is not totally the same and the other factors such as the difference of the performances of receivers are present, the calculated uplink and downlink are not absolute, but the there a fluctuation of 2 to 3 dB. The measurement report on uplinks and downlinks at the Abis interface can tell whether the uplink and downlink reach a balance. In addition, dialing tests in actual network can also tell whether the balance between uplinks and downlinks are reached. If the conversation quality on downlinks uplinks becomes poor simultaneously, it means that the downlinks and uplinks are balance. & Note: Some carriers provide the traffic statistics on uplink and downlink measurement, which can also tell
  18. 18. 2G, 3G Planning & Optimization ventinel Page 18 whether the balance between uplinks and downlinks are reached. I. Link budget model When calculating uplink and downlink balance, you must consider the functions of the tower amplifier first. In a base station receiving system, the thermal movement of the active parts and radio frequency (RF) conductors cause thermal noise, which reduces the signal-to-noise ratio of the receiving system. In this case, the receiving sensitivity of the base station is restricted and the conversation quality is reduced. To improve the receiving performance of the base station, you can add a low-noise amplifier under the receiving antenna. And this is the principle of the tower amplifier. The contributions of the tower amplifier to uplinks and downlinks are judged according to the performance of its low-noise amplifier and gain. In fact, it is the tower amplifier that reduces the noise coefficient of the base station receiving system. The power amplifier can improve the coefficients for the uplink receiving system (start from the output end of the receiving antenna). However, if the functions of the tower amplifier are quantified by this, the uplink improved value can be represented by the NFDelta (it is the reduced value of the noise coefficient of the receiving system) after a tower amplifier is added to the system. (1) No tower amplifier When there is no tower amplifier, the sensitivity of the equipments at the duplexer input interface at the top of the base station cabinet are taken as a reference. For downlink signals, if, Mobile station receiver output power = Poutm Base station diversity received gain = Gdb Base station receiving level = Pinb Base station side noise deterioration = Pbn Antenna receiving gain = antenna transmitting gain (according to reciprocity theorem) The following equation can be obtained: Pinb + Mf = Poutm + Gam – Ld + Gab + Gdb – Lfb – Pbn Generally, Pmn is almost equal to Pbn, so the following equation can be obtained: Poutb = Poutm + Gdb + (Pinm – Pinb) + Lcb (2) With tower amplifier If a tower amplifier is present, the improved value of the noise coefficients of the uplink receiving system can be represented by NFDelta, so the equation Poutb = Poutm + Gdb + (Pinm – Pinb) + Lcb can be developed into the following equation: Poutb = Poutm + Gdb + (Pinm - Pinb) + Lcb + NFDelta The two equations, Poutb = Poutm + Gdb + (Pinm – Pinb) + Lcb and Poutb = Poutm + Gdb + (Pinm - Pinb) + Lcb + NFDelta are used to calculate base station transmit power when the uplinks and downlinks are balance. Here, Pinb is the base station receiving sensitivity Pinm is the mobile station receiving sensitivity Gdb (antenna diversity receiving gain) is 3.5dB
  19. 19. 2G, 3G Planning & Optimization ventinel Page 19 According to the requirements in protocols GSM05.05, the mobile station transmit power and the reference receiving sensitivity of the mobile station and base station are specified in Table 5-10. At present, however, the sensitivities in actual systems are greater than the reference values listed in the following table. II. Bass station sensitivity This section further introduces the base station sensitivity and the functions of the tower amplifier. Receiver sensitivity refers to the minimum signal level needed to by the input end of the receiver when the certain bit error rate (BER) is met. The receiver sensitivity detects the performances of the following components: Receiver analog RF circuit Intermediate frequency circuit and demodulation Decoder circuit Three parameters are used to measure the receiver bit error performance. They are frame expurgation rate (FER), residual bit error rate (RBER), and bit error rate (BER). When a fault is detected in a frame, this frame is defined as deleted one. Here, FER indicates the ratio of the deleted frames to the total received frames. For full rate voice channels, the FER is present when the 3-bit cyclic redundancy check (CRC) detects errors or bad error indication (BFI) is caused. For signaling channels, the FER is present when the fire code (FIRE) or other packet codes detect errors. The FER is not defined in data services. FBER indicates the BER that are not announced as deleted frames, namely, it is the ratio of the bit errors in the frame detected as “good” to the total number of bits transmitted in “good” frames. BER indicates the ratio of the received error bits to all transmitted bits. Because BER occurs at random, the statistical measurement is mainly applied to measure receiver error rate. That is, sample multiple measuring points on each channel and when the number of measuring points is certain, if the BER of each measurement is within the required limit, the BER of this channel meets the BER as required. However, the number of sampled measured points and the limit value of the BER must meet the following conditions: For each independent sampled measuring point, the times for it to pass a “bad” unit must be as fewer as possible, that is, the probability must be smaller than 2%. For each independent sampled measuring point, the times for it to pass a “good” unit must be as more as possible, that is, the probability must be greater than 99.7%. The measurement has vivid statistical features. The measuring time must be reduced to the minimum. As a result, you can measure the receiver sensitivity through measuring whether the receiver BER has reached the requirement while entering sensitivity level to the receiver. Enter the reference sensitivity level to the receiver in various propagation environments. For the data produced after receiver demodulation and channel decoding, the indexes for FER, RBER.
  20. 20. 2G, 3G Planning & Optimization ventinel Page 20 The requirements on BCCH, AGCH, PCH, and SACCH are the same as that on SDCCH. The value of “a” in this table depends on the channels. It is 1 for base stations, and 1 to 1.6 for mobile stations. III. Contributions of tower amplifier to base station sensitivity In terms of technical principles, the tower amplifier reduces the noise coefficients of the base station receiving system, which is helpful for improving the sensitivity of the base station receiving system. In an actual system, to improve the receiving performance of the base station, you can add a low-noise amplifier near the feeder of the receiving antenna. In a mobile communication system, the receiver sensitivity = noise spectrum intensity (dBm/Hz) + bandwidth (dBHz) + noise coefficient (dB) + C/I (dB). Here the noise spectrum intensity, bandwidth, and noise coefficient are system thermal noise. C/I is the signal-to-noise ratio required at the Um interface. In a narrow band system, C/I indicates the modulation performance required by the receiver baseband, and it is a positive number. In a spreading communication system, because spread spectrum gain is present, the value of C/I is far beyond the requirement of the modulation performance of the receiver baseband, and it is a negative number. When there are n* cascaded receivers, the equivalent noise coefficient is as follows: Here, Gn indicates the receivers gain at each level (including the loss at each level). Fn indicates the noise coefficient of the receivers at each level. The noise coefficient of the passive device is equal to its loss, and the gain of the passive device is the reciprocal of the loss. According to the previous equation, the noise coefficient of the cascading system is determined by the receivers at the first level. It must be pointed out that the linear values of the parameters must be applied in the previous equation, so the “F” is a linear value, which must be converted into a logarithm. Moreover, according to this equation, the noise the cascaded receivers are determined by the noise coefficient (F1) of the receivers at the first level. However, when the tower amplifier stops working, because the loss is present on duplexer and bypass connectors, about 2dB of redundant loss is introduced on reverse link. According to the equation , the following two assumptions conclude the regularity of the effect of tower amplifier on the base station system. (1) Assumption 1 Hereunder is a series of assumptions: F1 = 2.5 dB (1.7783), noise coefficient of the tower amplifier F2 = 4.5 dB (2.8184), noise coefficient of the base station G = 2 (15.849) dB, tower amplifier gain Loss of the feeder and other passive devices = 3 dB (2) Gain of the feeder and other passive devices G0 = –3 dB (1/2) Noise coefficient of the feeder and other passive devices F0 = 1/G0
  21. 21. 2G, 3G Planning & Optimization ventinel Page 21 When the tower amplifier is not added, the noise coefficient of the base station receiving system with the antenna output end as reference point is as follows: F = F0 + (F2–1)/G0 = 10*log (2 + (2.8184–1)/0.5) =7.5dB When the tower amplifier is added, the noise coefficient of the base station receiving system with the antenna output end as reference point is as follows: F = F1 + (F0 – 1)/G + (F2 – 1)/(G*G0) = 10*log(1.7783 + (2 – 1)/15.849 + (2.8184 – 1)/(15.849 × 0.5) = 3.2dB At this time, the added tower amplifier improves the noise coefficient, and FDelta is 4.3dB, that is, the uplink is improved by 4.3 dB. (2) Assumption 2 Hereunder is a series of assumptions: F1 = 2.2 dB (1.6596), noise coefficient of the tower amplifier F2 =2.3 dB (1.6982), noise coefficient of the base station G = 12 (15.849) dB, tower amplifier gain Loss of the feeder and other passive devices = 3 dB (2) Gain of the feeder and other passive devices G0 = –3 dB (1/2) Noise coefficient of the feeder and other passive devices F0 = 1/G0 When the tower amplifier is not added, the noise coefficient of the base station receiving system with the antenna output end as reference point is as follows: F = F0 + (F2 – 1)/G0 = 10*log (2 + (1.6982 – 1)/0.5) = 5.3dB When the tower amplifier is added, the noise coefficient of the base station receiving system with the antenna output end as reference point is as follows: F = F1 + (F0 – 1)/G + (F2 – 1)/(G*G0) = 10*log(1.6596+(2 – 1)/15.849 + (1.6982 – 1)/(15.849 × 0.5)) = 2.6dB At this time, the added tower amplifier improves the noise coefficient, and FDelta is 2.7 dB, that is, the uplink is improved by 2.7 dB. According to the previous calculation, the following conclusions can be obtained: The tower amplifier improves the noise coefficient of the base station receiving system, thus improving the receiving sensitivity of the base station. The tower amplifier improves uplink signals effectively, which is also helpful for improving the receiving sensitivity of the base station. The gain of the antenna amplifier reduces the effect of the components installed behind the tower amplifier against noise coefficient. When the feeder is long and the loss of the feeder is great, if the tower amplifier is added, the noise coefficient of the base station receiving system and the uplink signals will be greatly improved. The smaller the noise coefficient of the tower amplifier is, if the tower amplifier is added, the greater the noise coefficient of the base station receiving system is improved. However, if the noise coefficient of the tower amplifier is too great, it may cause the noise coefficient of the base station receiving system to deteriorate. When the receiving sensitivity of the base station is great and the feeder is short, the tower amplifier makes a little improvement on the noise coefficient of the base station.
  22. 22. 2G, 3G Planning & Optimization ventinel Page 22 If the tower amplifier improves the base station sensitivity, the base station is more sensitive to outside interference. 2.6.4 Cell Coverage Estimation In actual project planning, the effective coverage area of a base station largely depends on the following factors: Effective base station transmit power Working band (900MHz or 1800MHz) to be used Antenna type and location Power budget Radio propagation environment Carriers; coverage requirements Based on the indexes of QoS for the mobile network and the actual applications, this section introduces the coverage area of the base station in different environments theoretically. If the following assumptions are present: The antenna height of GSM 900MHz and GSM 1800MHz base stations are 30 meters. The sensitivities of the GSM900 MHz 2W (33 dBm) mobile station and GSM 1800MHz 1W (30 dBm) mobile station are -102 dBm and -100 dBm respectively. The mobile station height is 1.5 meters and the gain is 0 dB. When the combiner and divider unit (CDU) is used, the sensitivities of the 900MHz base station and 1800MHz base station are -110dBm and -108dBm respectively. The CDU loss is 5.5dB, and the SCU loss is 6.8dB. The gain of the 65-degree directional antenna is 13dBd for the 900 MHz mobile station and 16dBd for the 1800MHz mobile station. The feeder is 50m in length. For 900MHz signals, the feeder loss is 4.03dBm/100m. For 1800MHz signals, the feeder loss is 5.87dB/100m. In general cities, select Okumura propagation model. No tower amplifier and the downlinks are restricted according to the calculation of the uplink and downlink balance. According to the previous assumptions, the calculated results are as follows: (1) Outdoor coverage radius of the 900 MHz base station in urban areas The minimum received level of the mobile station dBm. The coverage radius is calculated according to the maximum TRX transmit power. The maximum TRX transmit power for the 900 MHz base station W (46 dBm). The EIRP of the base station antenna is: (dBm) Here, LCOM indicates the combiner loss Lbf indicates the feeder loss Gab indicates the antenna gain of the base station
  23. 23. 2G, 3G Planning & Optimization ventinel Page 23 And the allowed maximum propagation loss is: (dB) According to the Okumura propagation model introduces earlier, Here, indicates the antenna height of the base station. indicates the antenna height of the mobile station. “f” = 900 MHz. (dB) According to the previous known number, the outdoor coverage radius of the 900 MHz base station in urban areas can be obtained, that is, d = 2.8km. (2) Coverage radius of the 900 MHz base station in urban buildings The minimum received level of the mobile station (dBm). (dB) Therefore, the coverage radius of the 900 MHz base station in urban buildings can be obtained, that is, d = 0.75km. If the previous assumptions are present, this indicates that the 900 MHz base station can cover the outdoor areas 2.8 km away, but for the subscribers on the first floor of the buildings 750 m away, the quality of the received signals is not satisfying. (3) Coverage radius of the 900 MHz base station in suburban areas The minimum received level of the mobile station (dBm). (dB) The Okumura propagation model in suburban areas must be modified as follows: Therefore, the coverage radius of the 900 MHz base station in urban areas can be obtained, that is, d = 5.4km, so it is obvious that the coverage radius of the base station with the same configuration is larger in suburban areas that in urban areas. (4) Outdoor coverage radius of the 1800 MHz base station in urban areas The minimum received level of the mobile station (dBm). Because the maximum transmit power of the 1800 MHz TRX is 40W (46dBm), the coverage radius is calculated based on this maximum transit power. (dBm) (dB) For the 1800 MHz base station, the Okumura propagation model is: In addition, f = 1800 MHz and (dB). According to the previous known number, the outdoor coverage radius of the 1800 MHz base station in urban areas can be obtained, that is, d = 1.7km. (5) Coverage radius of the 1800 MHz base stations in urban buildings The minimum received level of the mobile station (dBm). (dB) If the previous assumptions are present, this indicates that the 1800 MHz base station can cover the outdoor areas 1.7km away, but for the subscribers on the first floor of the buildings 500m away, the quality of the received signals is not satisfying.
  24. 24. 2G, 3G Planning & Optimization ventinel Page 24 2.6.5 Base Station Address Planning I. Overview When planning base station addresses, first you must estimate the number of the base stations needed in various coverage areas according to the coverage distance and the divisions of the coverage areas. For the convenience of prediction and emulation, you must plan an initial layout the base station addresses with the help of maps and the estimated results. II. Planning methods The base station address can be planned based on standard girds, or it can be planned from a specific area. (1) Plan base station address based on standard grids First you set the base stations in the coverage areas according to the distance of the standard grids, and then adjust the address layout and project parameters according to the estimated coverage results to meet the coverage requirement. After that, continue the planning according to the following instructions: If a satisfying address layout is obtained, you must analyze the capacity of the base stations to be planned according to this layout, and determine the reasonable number of base stations. When designing the capacity, you must calculate the number of TRXs needs to be configured for each base station, and then analyze and adjust the configuration of the base station according to the number of the configured TRXs. The adjustment of the configuration of the base station is determined by subscriber distribution. If the number of base stations in some areas does not meet capacity requirement, another base stations must be added. (2) Plan base station address based on a specific area According to this method, you are required to start the planning from the areas where the subscribers are most densely distributed or the planning work is quite hard to be performed. As a result, you must fully survey the subscriber distribution, landforms, and ground objectives within the coverage area to position the key coverage area where the center base stations should be planned. And these center base stations function as ensuring the coverage and capacity in important areas. After the layout of these center base stations is determined, you can plan other base station addresses according to coverage and capacity target. And this is how the final layout of the base station addresses come from. After the overall solution is determined, the subsequent steps are performed according to the first planning method. & Note: The difference of the traffic intensity and the abnormality of the landforms and ground objectives result in irregularity of the radio coverage. Therefore, the distance between base stations varies. Generally, this distance is smaller in the areas where traffic intensity is great. In some hot areas, you can ensure the system capacity by using micro cells and distributed antennas to provide multi-layer coverage. For restrictions from frequency resources are present, you must consider avoiding interference while
  25. 25. 2G, 3G Planning & Optimization ventinel Page 25 ensuring system capacity. There is no standard available for the layout of the base station addresses. A good planning solution is selected based on the integrated performance of the network. 2.6.6 Coverage Prediction The coverage prediction is to predict the coverage of the network to be constructed according to the selected base station addresses, designed base station types, suitable electronic maps, and network planning tools to judge whether the coverage meet the requirements of the subscribers. The coverage of a base station is determined by the following factors: Indexes of QoS Output power of transmitters Available sensitivity of receivers Direction and gain of antennas Working bands Propagation environment (such as landforms, city constructions) Application of diversity reception If the predicted results of the network coverage fail to meet the requirements, you can take the following adjusting measures: When there are subscribers distributing beyond the cell coverage area, but it is not economical for you to install a base station, you can use a repeater to ensure the requirement of those subscriber. When the signals are weak or blind zones are present within the coverage area, you can consider whether to use micro cells according to actual conditions. If a large blank area is present between neighbor cells, you can increase the antenna height and add base stations according to the principles of cell splitting. When the cell coverage area fails to meet the co-channel interference index, you can adjust the frequency configuration of the cell, adjust base station addresses, or adjust design of the parameters, such as antenna specification, antenna height, azimuth angle, tilt angle, and transmit power. & Note: When taking these adjusting measures, you must consider the mutual effect between base stations. 2.7 Design of Base Station Address 2.7.1 Address design Generally, in GSM radio network planning, the base station address is designed according to the following requirements: The address must serve to the reasonable cell structure. Based on the comprehensive analysis of the electronic maps and paper maps, you can select several candidate addresses from the perspective of coverage, anti-interference, and traffic balance. In actual conditions, carriers are required to discuss the selected addresses with owners. Generally, the addresses must be located within the area 1/4 radius of the cellular base station.
  26. 26. 2G, 3G Planning & Optimization ventinel Page 26 During the early construction stage when only a few base stations are installed, the base stations must be located in the center of the areas where subscribers are densely populated. For the selection of the base station addresses, the priority must be given to the important areas, such as government offices, airports, train stations, news center, and great hotels so that good conversation quality can be assured. Furthermore, overlapped coverage must be avoided in these areas. For other coverage areas, the base station addresses are designed according to standard cellular structures. For the suburban areas, highroads, and countryside areas, the design of base station addresses has little relation with cellular structures. Without affecting the layout of base stations, you can select the telecommunication buildings and post offices as the base station addresses so that the facilities, such as the equipment room, power supplier, and iron tower can be fully utilized. The direction of antenna major lobe must be in accordance with the area where the traffic intensity is great. In this case, the signal strength of the area can be enhanced, so does the conversation quality. Meanwhile, the direction of the antenna major lobe must be deviated from intra-frequency cells so that the interference can be controlled efficiently. In urban areas, it is recommended that the overlapped depth of the antennas in adjacent sectors cannot excel 10%. In suburban areas and small towns, the overlapped depth between coverage areas cannot be too great, and the included angle between sectors must be equal to or higher than 90°. In addition, for actual design, you must consider the mapping relationship between carrier number and cells. Generally, more carriers are configured for the cells with high intensity. The azimuth angle must be designed according to not only the traffic distribution in the areas around the base stations, but also the performance of the overall network. Generally, it is recommended to adopt the same azimuth angle for the 3-sector base stations in urban areas so that the complicated network planning can be avoided after cell splitting in the future. Moreover, the antenna major lobe cannot directly point to the straight streets in populated urban areas, because it can cause cross-coverage. In the areas connecting urban and suburban areas, and along transport arteries, you must adjust the azimuth angle according to coverage target. Generally, the base station address is not considered on the high mountains in urban and suburban areas. To be more specifically, the high mountains are those over 200 to 300 meters higher than above the sea-level). Otherwise, not only strong interference and weak signals may be present within the coverage area, but also the base stations are hard to be installed and maintained on high mountains. New base stations must be installed at the spots where the traffic is convenient, the power supply is available, and the environment is secure. In contrast, new base stations must not be installed at the spots near the radio transmit stations with high power, radar stations, and other equipments which produces great interference, because the interference-field intensity cannot be greater than that defined by the base station. The base station addresses must be far away from forests or woods to keep the receiving signals from fading. The transmission between base station controllers must be considered in the design of the base station address.
  27. 27. 2G, 3G Planning & Optimization ventinel Page 27 When selecting a base station address from high buildings in urban areas, you can divide the network into several layers with the help of the building height. The antenna height of major base stations must be a little higher than the average height of buildings. Generally, the antenna height of the base stations in populated urban areas ranges from 25 to 30 meters. In suburban areas (or the antenna points to suburban areas), the antenna height ranges from 40 to 50 meters. Along highroads or in mountain areas, the base station address is selected based on full survey of the landforms. For example, the address can be determined in an open area or at the turns of the highroads. When selecting a base station address from the cities characterized by mountains and hills and from the areas where high buildings are constructed with metals, you must consider the effect of time dispersion. In this case, the base station address must near reflected objectives. When the base station is far away from reflected objectives, you must adjust the directional antenna to the reverse direction of the reflected objectives. Caution: Time dispersion mainly refers to the intra-frequency interference arising from the time difference between the master signal and other multipath signal arriving at the receiver in terms of space transmission. According to the requirements in GSM protocols, the equalizer of the receiver must carry the time window with 16μs (equivalent to 4.8 km). The multipath signal with time difference greater than 16 μs is regarded as intra-interference signal. In this case, you must consider whether the level difference between the master signal and multipath signal meet the carrier-to-interference ratio (C/I), namely, the master signal is 12 dB greater than the multipath signal at least. 2.7.2 Project Parameter Decision After finishing designing a base station address, you must decide the project parameters needed for the base station installation. These parameters include: Latitude and longitude of the location of base station antenna Antenna height Directions of the antenna Antenna gain Azimuth angle Tilt angle Feeder specifications Transmit power for each cell of the base station And the previous parameters are decided through field survey. Before beginning field survey, you must familiarize yourself with the overall project and collect the materials and tools relative to the project. They are: All types of project documents Background information Information about the existing network Local map Configuration lists required in contracts Relative tools (including digital camera, GPS, compass, ruler, and laptop computer)
  28. 28. 2G, 3G Planning & Optimization ventinel Page 28 & Note: Make sure that all the materials and tools are usable before setting out. The following items must be emphasized before field survey: The GPS must be placed in an open land to position the latitude and longitude of a base station Make a detailed record of the surroundings around the base station, such as the distribution of the buildings, facilities with strong interference, and the equipments sharing the same base station address. It is better to record the previous information with a camera. Prevent the compass from magnetizing, because the magnetization will cause great deviation during the measurement. Field survey determines the layout of the base station addresses ultimately. The field survey for the base station includes optical measurement, spectrum measurement, and base station address survey. They are specified as follows: Optical measurement Measure if a barrier that may reflect electrical waves around the base station, such as high buildings. Spectrum measurement Check if the electromagnetic environments around the base stations are normal at present or in recent days. Base station address survey Check the installation conditions of antenna and equipments, power supply, and natural environment. The following sections introduce the design for antenna installation. I. Environment for antenna installation The environment for antenna installation can be divided into the environment near the antenna and the base station. For the environment near the antenna, you must consider the isolation between antennas and the effect of iron tower and buildings against the antenna. For the environment near the base station, you must consider the effect the high buildings within 500 meters against the base station. However, if the height of the buildings is properly used, you can obtain the intended coverage area. If a directional antenna is installed on the wall, the radiation direction of the antenna is perfectly perpendicular to the wall. If its azimuth angle must be adjusted, the included angle between the radiation direction and the wall is required to be greater than 75°. In this case, if the front-to-back ratio of the antenna is greater than 20 dB, the effect of the signals reflected by the wall in reverse direction against the signals in the radiation direction is quite slight. When installing an antenna, you must consider whether large shadows will be present within the coverage area of the antenna. The shadows are produced mainly because the base station is surrounded by some huge barriers, such as high buildings and great mountains. Therefore, the antenna must be installed in the areas with no such barriers. When a directional antenna is installed on building roofs, you must prevent the building edges from barring the radiation of antenna beams. Therefore, to reduce or ease the shadow, you can install the antenna near building edges.
  29. 29. 2G, 3G Planning & Optimization ventinel Page 29 Because the building roofs are diversified and complicated, if an antenna must be installed far away from building edges, the antenna must be installed higher than the roof. In this case, the wind load of the antenna must be considered. II. Antenna isolation in GSM system To avoid inter-modulation interference, you must leave certain isolation between the receiver and transmitter of the GSM base station, namely, Tx - Rx: 30 dB and Tx -Tx: 30 dB. They are applicable to the situation that a GSM 900MHz base station and a GSM 1800MHz base station share the same address. The antenna isolation depends on the radiation diagram, space distance, and gain of the antenna. Generally, the attenuation introduced by the voltage standing wave ratio (VSWR) is not considered. The antenna isolation is calculated as follows: For vertical arrangement, Lv = 28 + 40lg (k/λ) (dB) For horizontal arrangement, Lv =22 + 20lg (d/λ) – (G1+G2) – (S1 + S2) (dB) Here, Lv indicates the required isolation. λ indicates the length of carrier waves. k indicates the vertical isolation distance. d indicates the horizontal isolation distance. G1 indicates the gains of the transmitter antenna in the maximum radiation direction, in the unit of dBi. G2 indicates the gains of the receiver antenna in the maximum radiation direction, in the unit of dBi. S1 indicates the levels of the side lobes of the transmitter antenna in the 90° direction, in the unit of dBp, and it is a negative value relative to the main beam. S2 indicates the levels of the side lobes of the receiver antenna in the 90° direction, in the unit of dBp, and it is a negative value relative to the main beam. The followings introduce the requirements on the antenna mount in GSM 900MHz and GSM 1800MHz. (1) Directional antenna In one system, the following requirements must be met in terms of isolation: The horizontal distance between two antennas in the same sector must be equal to or greater than 0.4m. The horizontal distance between two antennas in different sectors must be equal to or greater than 0.5m. In different systems, the following requirements must be met when two antennas are in the same sector and direction: The horizontal distance between the two antennas must be equal to or greater than 1m. The vertical distance between the two antennas must be equal to or greater than 0.5m. The distance between the bottom of the antennas and the enclosing wall of building roof must be equal to or greater than 0.5m. The included angle between the line connecting the bottom of the antenna to the antenna-facing roof and the horizontal direction must be greater than 15°.
  30. 30. 2G, 3G Planning & Optimization ventinel Page 30 The bands of the two systems are close to each other, the interference against each other will easily occur. Mostly, the transmission of CDMA2000 1X base station will interfere with the reception of GSM 900MHz base station. The disclosure signals of the CDMA band falling into the channels of the GSM base station receivers will enhance the noise level of the GSM receivers. In this case, the GSM uplinks become weak, which will reduce the coverage area of the base station and worsen the quality of the network. If there is not enough isolation between base stations or the transmitting filter interfering base stations does not provide enough out-of-band attenuation, the signals falling into the band of the interfered base station receiver may strong, which will increase the noise level of the receiver. The deterioration of the system performance is closely related to the strength of interference signals, and the strength of interference signals is determined by the factors, such as the performance of the transmitting elements of the interfering base stations, the performance of the receiving elements of the interfered base stations, the distance between bands, and the distance between antennas. The signal from the amplifier of the interfering base station is first sent to the transmitting filter, and then it attenuate due to the isolation between the two base stations. Finally, it is received by the receiver of the interfered base station. The power of the spurious interference arriving at the antenna end of the interfered base station can be expressed by the following equation: Here, Ib indicates the interference level received at the antenna receiving end of the interfered base station, in the unit of dBm. PTX-AMP indicates the output power at the amplifier of the interfering base station, in the unit of dBm. Pattenuation indicates the out-of-band suppression attenuation at the transmitting filer. Iisolation indicates the isolation between the antennas of the two base stations, in the unit of dB. WBinterfered indicates the bandwidth of the signals at the interfered base station. WBinterfering indicates the measurable bandwidth of the interfering signals, or it can be understood as the bandwidth defined by spurious radiation. Regulate the previous equation and the following equation can be obtained: Suppose the transmit channel number of CDMA2000 1X is the last one on its working band, that is, 878.49MHz, the spurious signal level on the band of 890-915MHz must be equal to or lower than - 13dBm/100kHz. If you intend to put this assumption into practice, you can filter and combine each transmitted channel number by using band-limited filter with a bandwidth of only 1.23MHz. The band- limited filter of this type has great out-of-band attenuation, which can reach 56 dB at 890 MHz and 80 dB at 909 MHz. Here you must consider the worst situation, that is, the frequencies at the highest end of the CDMA system interfere with the frequencies at the lowest end of the GSM system. In this case, Iisolation = (-13dBm/100kHz) - 56 - Ib + 10lg (200kHz/100kHz) Here Ib indicates the highest interference level (dBm) allowed by the receiving end of the interfered base station. If the receiving sensitivity of the interfered base station is ensured, the outside interference level are required to be 10 dB lower than the back noise of the receiver. In this case, the sensitivity affected only accounts to about 0.5 dB. The back noise of the GSM receiver is the sum of the noise intensity, bandwidth, and noise coefficient. If the noise coefficient is 8 dB, the back noise is -174+noise coefficient+10lg (200000) = -174+8+53 = -113
  31. 31. 2G, 3G Planning & Optimization ventinel Page 31 (dBm). Therefore, the maximum spurious interference allowed is -113-10 = -123 (dBm/200kHz). As a result, the spurious interferences from other systems falling at the GSM receivers are required to be smaller than -123 (dBm/200kHz); otherwise, the spurious interferences will seriously affect the GSM system. Therefore, Iisolation = (-13dBm/100kHz) – 56 - Ib + 10lg (200kHz/100kHz) = -13- 56- (-123dBm/200kHz) + 10lg (200kHz/100kHz) = 57 dBm/200kHz. That is, according to the assumption, the isolation between a CDMA antenna and GSM 900MHz antenna must be at least 57dB regardless whether they share the address or not. Many ways can be used to reduce the interference. For example, you can adopt the following ways: Design enough distance between antennas Filter the out-of-band interference of the transmitter Add different equipments to the filter, such as receiver, duplexer, and divider. According to the requirements in TIA/EIA-97 protocols, the spurious interference from the CDMA antenna interface falling within the GSM 900MHz receiving bands must be less than -13 dBm/100kHz. Therefore, the problems, such as mutual interference and co-address construction must be considered in the initial design. To be specific, you can filter and combine each transmitted channel number using a limited-band filter with the bandwidth of only 1.23 MHz. The band-limited filter of this type has great out-of-band attenuation, thus the space distance between the antennas of the CDMA system and GSM system must be shortened. In addition, to minimize the interference, you must keep suitable isolation between the antennas of the CDMA system and GSM system. The antenna isolation is calculated according to the following two formulas, which has been introduced earlier: For vertical arrangement, Lv = 28 + 40lg (k/λ) (dB) For horizontal arrangement, Lv =22 + 20lg (d/λ) – (G1+G2) – (S1 + S2) (dB) According to the two formulas, the requirements on the isolation between the antennas of CDMA system and GSM 900 MHz system are specified in the following three circumstances. The antennas of the CDAM system and GSM 900MHz system do not share the same address, with the antennas horizontally opposite to each other, or the antennas of the two systems share the same address, with the antenna type of omni antenna. Suppose the effective gains of the antennas of the two systems in the maximum radiation direction are 10 dBi (with the feeder loss considered), and the interference signals are 890MHz, according to previous analysis, the isolation between the CDMA system and GSM system is required at least 57dB. Therefore, the following equation can be obtained according to the previous formula: 57 = 22 + 20lg (Dh/λ) – (10 + 10) The antennas of the CDMA and GSM 900 MHz system share the same address (the antennas are installed on the same platform and horizontally separated), with the antenna type of directional antenna. Suppose that the two antennas are horizontally placed, and their tilt angle is 65°, and that the effective gains of the two antennas in the radiation direction are 15dBi.
  32. 32. 2G, 3G Planning & Optimization ventinel Page 32 And if the side lobe of the 65°antenna is -18dB in the horizontal plane, the effective gain of the antenna in this direction is (15 – 18) dBi = -3 dBi. Therefore, 57=222+0lg (Dh/λ) - {(15+15) + [(-18) + (-18)]}. According to the previous equation, the horizontal distance between the two antennas are d = 9.5m. The antennas of the CDMA and GSM 900 MHz antennas share the same address (the antennas are not installed on the same platforms of the iron tower and vertically separated), with the antenna types of directional antenna and omni antenna. In this case, the equation 57=28 + 40 lg (k/λ) is present. According to this equation, the vertical distance between the two antennas is d = 1.8m. & Note: The previous descriptions are just theoretical detections. In actual networking, other types of antennas may be installed at the same address. In this case, some equipment indexes must be considered, among which the important ones are spurious radiation, the interference power of the interfering signals to interfered signals, and the antenna isolation. IV. Installation distance between antennas Diversity technology is the most anti-fading effective. When two signals are irrelevant to each other, the horizontal distance between the diversity antennas must be 0.11 times that of the valid antenna height. The higher place the antenna is installed, the larger the horizontal distance between diversity antennas is. When the distance between diversity antennas is equal to or greater than 6m, however, the antenna is hard to be installed on an iron tower. In addition, the distance required by vertical diversity antennas is 5 to 6 times that of the horizontal diversity antennas when the same coverage is ensured. Therefore, the vertical diversity antenna is seldom used in actual projects, but antennas are often vertically installed to meet isolation requirement, especially omni antennas are vertically installed. In addition, for highroad coverage, the line connecting two receiving antennas must be perpendicular to the highroad. If space diversity is used, the diversity distance is the perpendicular. Isolation requirement: Tx-Tx, Tx - Rx: 30 dB The installation for GSM 900MHz and GSM 1800MHz antennas is flexible, but no matter what specifications are used, they must meet the requirements on isolation and distance. In addition, in actual projects, barriers are present between antennas. For example, a tower is always present between two omni antennas, so you must shorten the horizontal distance between them. V. Design of base station parameters in residential areas A large number of residential areas are distributed in urban areas, so this section introduces the design of base station parameters in these areas. (1) Features of residential areas Building intensity
  33. 33. 2G, 3G Planning & Optimization ventinel Page 33 Great-intensity residential areas: the distance between buildings is within 10 meters. Middle-intensity residential areas: the distance between buildings ranges from 10 to 20 meters. Low-intensity residential areas: the distance between buildings is larger than 20 meters. Construction material The walls of the residential areas are constructed with concretes. The walls of the residential areas are constructed with bricks and concretes. The walls of the residential areas are constructed with hollow blocks. Notes: The thickness of the buildings varies with the regions and climates. Three specifications are available, namely, 24m, 47m, and 49m. Generally, the walls are thicker in southern parts and thinner in northern parts. (2) Antenna installation in residential areas The address where the antenna should be installed in residential areas is hard to be determined. Generally, when adopting micro cells, you can install the antenna within a residential area near to the target coverage area. In this case, the antenna can be installed in the following spots: On outer walls (not roofs) of a building On pillars Install a micro cell in underground garages If the antenna is installed at a wall corner, the major lobe of the antenna can radiate the space between buildings. Generally, the major lobe of the antenna cannot face the walls of the buildings nearby directly. If frequencies are reusable among these micro cells, the directions of antennas must be consistent with each other. In addition, you can also use the cell splitter to enable a cell to coverage the areas in two directions. In this case, however, the frequency utilization ratio may decrease and extra power splitter will introduce loss of 3 dB. For the residential areas with regular arrangement, the directional antennas whose horizontal beam width is 90° to 120° and vertical beam width is greater than 30° are recommended. Under certain conditions, the micro cell antenna can be installed on the pillars within a residential area. For the residential areas with irregular arrangement, the antenna can be installed on the walls of a building, so the reflected waves can coverage the walls of opposite buildings. In this case, the antennas whose horizontal beam width is greater than 120°and vertical beam width is greater than 30°are recommended. (3) Antenna selection When the walls of a building is selected as an installed position, you can use the build-in antenna of the micro cell directly, or other antennas with small size. According to coverage features of residential areas, when selecting the specifications for the micro cell antennas to be used, you must consider the following factors: Antenna gain Horizontal beam width
  34. 34. 2G, 3G Planning & Optimization ventinel Page 34 Vertical beam width Polarization mode Visual effect (antenna size, shape, and weight) The antenna gain is recommended less than 9 dBi for micro cell antennas. Because the coverage area of a micro cell antenna is small and the installed position is near to the coverage area, the antenna gain can be adjusted to a smaller value, especially if the gain of an antenna is greater than 10dBi, its size is large, which may cause opposition from residents. The selection of the horizontal and vertical beam width for an antenna is related to radio environment. If a micro cell antenna is installed on a wall, the antenna height is lower than the average height of surrounded buildings. In this case, if both the indoor coverage of lower floors and higher floors can be assured, you must select the antennas with greater vertical beam width. According to the height of buildings, you can select the directional antennas whose vertical beam width ranges from 35°to 80°. The selection of the horizontal beam width of the micro cell antenna and the installed position of the antenna are related to coverage target. In this case, you can select the directional antennas whose beam width ranges from 60° to 150°, or you can choose omni antennas or bi-directional antennas (8-shaped antennas). Both vertical polarization antennas and dual polarization antennas can be selected for a micro cell. The coverage area of a micro cell in urban areas is small, so the diversity reception is unnecessary. In this case, a vertical polarization antenna can meet the coverage requirements in residential areas. As for the dual polarization antenna, however, it is expensive and large in size, so it is not recommended. The visual effect must be emphasized for the micro cell antennas installed in residential areas. They must be small and moderate. In addition, they must be light for installation convenience. If the contract between the color of the antenna and that of the surrounded buildings is great, you must color the antenna with the same color of the buildings. In some cases, you should consider adopting dual-band antennas. When selecting a small-sized antenna, you should consider whether its maximum output power can bear the micro cell output power. When adopting short jumpers instead of 7/8 feeders, you should consider whether the antenna connector (N- shaped male/female, 7/16 DIN header) matches the jumper connector. 2.8 Location Area Design 2.8.1 Definition of Location Area In GSM protocols, a mobile communication network is divided into multiple service areas according to the codes of location areas. Thus the network pages a mobile subscriber through paging its location area. Location area is the basic unit of paging areas in a GSM system. That is, the paging message of a subscriber is sent in all cells of a location area. A location area contains one or more BSCs, but it belongs to one MSC only. Figure 5-13 shows the division of service areas.
  35. 35. 2G, 3G Planning & Optimization ventinel Page 35 Figure 5-1 Division of service areas 2.8.2 Division of location areas The coverage area of each GSM PLMN is divided into multiple location areas, in which an MS is positioned. The size of a location area, namely, the area covered by a location area code (LAC), plays a key role in a GSM system. Therefore, this section mainly introduces the principle for planning location areas. I. Dividing the location area according to the distribution and behaviour of mobile subscribers The distribution of location areas in cities and suburbs is different. Generally, suburban areas or counties occupy independent location areas. In cities, the distribution of location areas is similar to a concentric circle. (The areas in the internal circle can be divided into several location areas due to the requirements on capacity. The concentric circle can be divided into several fragments.) In addition, if two or more location areas are present simultaneously in a big city of great traffic, the landforms, such as mountains and rivers within this city can be used as edges of the location areas. In this case, the overlapped depth between the cells of the two location areas can be reduced. If no such landforms available within this city, the areas (such as streets and shopping centers) with great traffic cannot be used as edges of the location areas. Generally, the edge of a location area is oblique instead of parallel or perpendicular to streets. In the intersected areas of urban areas and suburban areas, to avoid frequent location update, you must design the edges of location areas near the outer base stations instead of the base stations just installed at the intersections. II. Calculating coverage area and capacity of a location area If the coverage area of a location area is too small, the mobile station will perform frequent location update. In this case, the signaling flow in the system will increase. If the coverage of a location area is too larger, however, the network will send a paging message in multiple cells until the mobile station is paged. In this case, the PCH will be overloaded and the signaling flow at the Abis interface will increase. The calculation of location areas varies with the paging strategies designed by different carriers. During early network construction stage, the traffic is not great, so a location area can accommodate more TRXs. However, it is still necessary for you to monitor the PCH load and traffic growth. When the traffic grows great, you can enhance the PCH capacity by adding a BCCH to the system, but the number of voice channels can be added is reduced by one accordingly. Generally, the capacity of a location area is calculated as follows: The number of paging blocks sent in each second × the number of paging messages sent in each paging block = the maximum paging times in each second. As a result, the number of paging times in each hour, the traffic allowed in each location area, and the number of carriers supported in each location area can be deducted. The followings introduce the items present in the previous paragraph respectively. (1) The number of paging blocks sent in each second

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