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LTE Long Term Evolution for future mobile services


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LTE, Long Term Evolution, the successor to UMTS and HSPA is the way forwards for high speed cellular services.In its first forms it was a 3G or 3.99G technology, but with further additions the technology fulfilled the requirements for a 4G standard. In this form it was referred to as LTE Advanced.
There has been a rapid increase in the use of data carried by cellular services. To cater for this and the increased demands for increased data transmission speeds and lower latency, further development of cellular technology have been required. The UMTS cellular technology upgrade has been dubbed LTE - Long Term Evolution. The idea is that 3G LTE will enable much higher speeds to be achieved along with much lower packet latency, a growing requirement for many services these days. 3GPP LTE will enable cellular communications services to move forward to meet the needs for cellular technology to 2017 and well beyond.

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LTE Long Term Evolution for future mobile services

  2. 2. LTE INDEX • INTRODUCTION • LTE-Basic Specification • Duplex Schemes • LTE Frames and Subframes • LTE Channel Types • LTE UE Catagories • Main LTE Technologies • OFDM • MIMO • SAE • LTE Self Organising Networks • Voice over LTE • SRVCC • LTE Security • 4G Aim, Features and Requirements • LTE Advance • LTE Advance Technologies
  3. 3. INTRODUCTION • Developed by the 3GPP(3rd Generation Partnership Project). • Specified in Release 8 and Release 9 document series. • For wireless communication of high-speed data for mobile phones and data terminals. • Based on the GSM/EDGE and UMTS/HSPA network technologies. • Increased capacity and speed using different radio interfaces together with core network improvements. • LTE is natural upgrade path for carriers with both GSM/UMTS networks and CDMA2000 networks. • Different LTE frequencies and bands used in different countries.-- • Only multi-band phones will be able to use LTE in all countries where it is supported. • 4G LTE does not satisfy the technical requirements of 3GPP LTE advance. • Originally set forth by ITU-R in IMT advance specification. • Due to marketing pressures and the significant advancements, LTE with WiMax etc. called 4G.
  4. 4. 3G LTE evolution • Also LTE is an all IP based network, supporting both IPv4 and IPv6. • Originally there was no provision for voice. • Voice over LTE(VoLTE) was chosen by GSMA as standard. 3GPP: 3rd Generation Partnership Project WCDMA: Wideband CDMA HSPA: High Speed Packet Access HSDPA/HSUPA: High Speed Downlink/Uplink Packet Access UMTS: Universal Mobile Telecommunication System WCDMA (UMTS) HSPA HSDPA / HSUPA HSPA+ LTE Max downlink speed bps 384 k 14 M 28 M 100M Max uplink speed bps 128 k 5.7 M 11 M 50 M Latency round trip time approx 150 ms 100 ms 50ms (max) ~10 ms 3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8 Approx years of initial roll out 2003 / 4 2005 / 6 HSDPA 2007 / 8 HSUPA 2008 / 9 2009 / 10 Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA
  5. 5. 3G LTE-Basic Specification LTE BASIC SPECIFICATIONS PARAMETER DETAILS Peak downlink speed 64QAM (Mbps) 100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO) Peak uplink speeds (Mbps) 50 (QPSK), 57 (16QAM), 86 (64QAM) Data type All packet switched data (voice and data). No circuit switched. Channel bandwidths (MHz) 1.4, 3, 5, 10, 15, 20 Duplex schemes FDD and TDD Mobility 0 - 15 km/h (optimised), 15 - 120 km/h (high performance) Latency Idle to active less than 100ms Small packets ~10 ms Spectral efficiency Downlink: 3 - 4 times Rel 6 HSDPA Uplink: 2 - 3 times Rel 6 HSUPA Access schemes OFDMA (Downlink) SC-FDMA (Uplink) Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink)
  6. 6. Duplex Schemes • Cellular communications system must be able to transmit in both directions simultaneously. • It is necessary to specify direction of transmission. • Two links are differentiated based on amount of data carried, transmission format and channels implemented. The two links are defined: • Uplink: transmission from UE or user equipment to eNodeB or base station. • Downlink: transmission from eNodeB or base station to UE or user equipment. • To be able to transmit in both directions, UE or base station must have a duplex scheme FDD/TDD.
  7. 7. LTE VARIANTS (Duplex Schemes) • Long-Term Evolution Time-Division Duplex (LTE-TDD),or Time-division Long-Term Evolution (TD-LTE) co-developed by an international coalition of companies. • Developed with idea of migration to 4G from 3G TD-SCDMA. • Frequency-Division Long-Term Evolution (LTE-FDD). • Differences between LTE-TDD and LTE-FDD: • How data is uploaded and downloaded. • What frequency spectra the networks are deployed in.
  8. 8. LTE VARIANTS (Duplex Schemes) • LTE-FDD • Uses paired frequencies to upload and download data. • Works better at lower frequencies. • LTE-TDD • Uses a single frequency to upload and download data alternatively. • The ratio between uploads and downloads changes dynamically based on load. • Works better at higher frequencies. (1850 MHz to 3800 MHz) • Spectrum is cheaper to access and has less traffic. • With bands overlapping WiMAX, later can be easily upgraded to support LTE-TDD. • Handshaking- • Despite the differences, TE-TDD and LTE-FDD share 90 percent of their core technology. • Makes it possible for the same chipsets and networks to use both versions of LTE.
  9. 9. Advantages / disadvantages of LTE TDD and LTE FDD PARAMETER LTE-TDD LTE-FDD Paired spectrum Does not require as both transmit and receive occur on the same channel. Requires with sufficient frequency separation to allow simultaneous transmission and reception. Hardware cost Lower. No diplexer needed to isolate Tr. and Recr. Lower cost of UEs. Diplexer is needed and cost is higher. Channel reciprocity Channel propagation same in both directions using one set of parameters. Channel characteristics different in both directions as use different frequencies. UL / DL asymmetry Possible to dynamically change UL and DL capacity ratio to match demand. UL / DL capacity determined by frequency allocation. Not possible to change dynamically to match capacity. Regulatory changes would be required and capacity is same in either direction. Guard period / guard band Required to avoid uplink and downlink transmissions clash. Large guard period will limit capacity. Larger guard period required if distances increased to accommodate larger propagation times. Guard band required to provide sufficient isolation between uplink and downlink. Large guard band does not impact capacity. Discontinuous transmission Required to allow both uplink and downlink transmissions. Can degrade performance of RF power amplifier in the transmitter. Continuous transmission is required. Cross slot interference Base stations need to be synchronized with uplink and downlink transmission times. If neighboring base stations use different uplink and downlink assignments and share same channel, interference may occur between cells. Not applicable
  10. 10. LTE TDD / TD-LTE and TD-SCDMA • With advantages of using LTE TDD / TD-LTE with TD-SCDMA, there needs to be a 3.9G and later a 4G successor to the technology. • With unpaired spectrum allocated for TD-SCDMA and UMTS TDD, upgrade path will benefit from vastly increased speeds and improved facilities of LTE. • Subframe structure adopted within LTE TDD / TD-LTE is upgrade path for TD-SCDMA. • Although LTE TDD has significant advantage of higher spectrum efficiency, it is anticipated that LTE FDD will be more widespread. • It is also anticipated that phones will be able to operate using either LTE FDD or LTE-TDD (TD-LTE) modes. • LTE UEs will be dual standard phones and able to operate in any country. • The main problem will then be the frequency bands that the phone can cover.
  11. 11. LTE Frame And Sub-Frame • 3G LTE system has a defined LTE frame and subframe structure for the E-UTRA, the air interface for 3G LTE (Evolved UMTS Terrestrial Radio Access) so that: • 3G LTE system can maintain synchronization. • System is able to manage different types of information carried between the base-station or eNodeB and UE. • The frame structures differ for TDD and FDD modes as there are different requirements on segregating the transmitted data. • There are two types of LTE frame structure: • Type 1: used for the LTE FDD mode systems. • Type 2: used for the LTE TDD systems.
  12. 12. Type 1 LTE Frame Structure • The basic type 1 LTE frame has an overall length of 10ms. • Length divided into 20 individual slots. • LTE Subframes consist of two slots. • Hence there are ten LTE subframes within a frame.
  13. 13. Type 1 LTE Frame Structure
  14. 14. Type 2 LTE Frame Structure • The 10ms frame comprises just two half frames, each 5ms long. • The LTE half-frames are further split into five subframes, each 1ms long.
  15. 15. Type 2 LTE Frame Structure • The subframes divided into standard subframes of special subframes consisting of three fields; • DwPTS - Downlink Pilot Time Slot. – (End of downlink) • GP - Guard Period • UpPTS - Uplink Pilot Time Slot. – (Beginning of uplink) • The total length of all three together must be 1ms. (E.g. Frame 2, 6). • Allows dynamic change of up and downlink balance. • These are also used within TD-SCDMA. • They have been carried over into LTE TDD (TD-LTE) and thereby help the upgrade path. • The fields are individually configurable in terms of length.
  16. 16. Sub-Frame Allocation • LTE TDD allows dynamic change of up and downlink balance and characteristics to meet the load conditions. • To achieve it in an ordered fashion, a total of seven up / downlink configurations have been set within the LTE standards. • These use either 5ms or 10ms switch periodicities. • 5ms switch periodicity:- Special subframe exists in both half frames. • 10ms switch periodicity:- Special subframe exists in first half frame only. • Subframes 0, 5 and DwPTS are always reserved for the downlink. • UpPTS and subframe immediately following special subframe are always reserved for uplink transmission.
  17. 17. Sub-Frame Allocation • D is a subframe for downlink transmission • S is a "special" subframe used for a guard time • U is a subframe for uplink transmission UPLINK- DOWNLINK CONFIGURATION DOWNLINK TO UPLINK SWITCH PERIODICITY SUBFRAME NUMBER 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D
  18. 18. Type 2 LTE Frame Structure • Example
  19. 19. 3G LTE Frequency Bands Allocations • FDD and TDD LTE frequency bands • FDD spectrum requires pair bands, one of the uplink and one for the downlink. • TDD requires a single band for Uplink and downlink but time separated. • Band allocations for TDD and FDD may overlap. • UE will need to detect whether a TDD or FDD transmission is being made on that particular LTE band in its current location. • LTE frequency bands are allocated numbers. • Currently the LTE bands between 1 & 22 are for paired spectrum, i.e. FDD. • LTE bands between 33 & 41 are for unpaired spectrum, i.e. TDD.
  20. 20. LTE Channel Types • To transport data across LTE radio interface, various "channels" are used. • Segregates different types of data to be transported across radio access network in an orderly fashion. • Provides interfaces to higher layers within the LTE protocol structure. • Various data channels are grouped in Three categories :- • Physical channels: Transmission channels that carry user data and control messages. • Transport channels: The physical layer transport channels offer information transfer to Medium Access Control (MAC) and higher layers. • Logical channels: Provide services for the Medium Access Control (MAC) layer within the LTE protocol structure. • LTE physical channels vary between the uplink and the downlink as each has different requirements and operates in a different manner.
  21. 21. 3G LTE Physical channels-Downlink • Physical Broadcast Channel (PBCH): • Carries system information for UEs to access the network. • Only carries Master Information Block (MIB) messages. • The modulation scheme is always QPSK. • Information bits are coded and rate matched. • Bits are then scrambled using a scrambling sequence specific to the cell to prevent confusion with data from other cells. • The MIB message on the PBCH is mapped onto the central 72 subcarriers or six central resource blocks regardless of the overall system bandwidth. • A PBCH message is repeated every 40ms, i.e. one TTI of PBCH includes four radio frames. • The PBCH transmissions has 14 information bits, 10 spare bits, and 16 CRC bits.
  22. 22. 3G LTE Physical channels-Downlink • PBCH • 3 bits for system bandwidth • 3 bits for PHICH information, • 1 bit to indicate normal or extended PHICH • 2 bit to indicate the PHICH Ng value • 8 bits for system frame number for initial sychronization and periodic sync. • 10 bits are reserved for future use • CRC also conveys number of transmit antennas used by eNodeB. • MIB CRC is scrambled or XORed with antenna specific mask. • Generation periodicity –duration 40 ms between two consecutive MIB information generated by the higher layers for physical layer. • System frame number within each MIB,- a rolling number between 0-255. • Changesg every MIB but other contents may or may not change. • Transmission periodicity – duration between two consecutive PBCH transmission by the physical layer. • Contents within 4 consecutive PBCH remains same as PBCH carries MIB. • MIB can change only after 40 milliseconds since first PBCH transmission.
  23. 23. 3G LTE Physical channels-Downlink • Physical Broadcast Channel (PBCH):
  24. 24. 3G LTE Physical channels-Downlink PBCH Transmission • CRC Generation – 16 bit CRC by CRC module, scrambled with antenna specific mask. • CRC attachment to MIB – CRC is attached to MIB payload total 40 bits (24 bit of MIB + 16 bit of CRC) • Convolution encoding – Tail bit convolution encoding performed over 40 bits. • Output is 3 streams of 40 bits each(120 bits) • Rate matching – Repetition coding, 120 bits repeated 16 times to get 1920 bits. • MIB is a very vital information, UE cannot afford to lose. • Scrambling – These 1920 bits are scrambled with a scrambling sequence as long as 1920 bits • Modulation (QPSK) – A QPSK performed over 1920 bits to obtain 960 complex QPSK symbols
  25. 25. 3G LTE Physical channels-Downlink PBCH Transmission • PBCH has to be transmitted every 10 milliseconds on subframe 0 of all radio frames. • PBCH modulation buffer is divided into 4 sub-buffers each 240 complex symbols. • By the time last sub buffer is transmitted on PBCH, a new MIB is arrived from higher layer. • 4 consecutive radio frames transmit same MIB information. • UE has to find 4 consecutive system frame numbers that are same to understand 40 millisecond boundary. • UE can decode MIB & 40 millisecond boundary in 40 milliseconds for the best case and 70 milliseconds for the worst case.
  26. 26. 3G LTE Physical channels-Downlink • Physical Control Format Indicator Channel (PCFICH) : • PCFICH informs UE about the format of the signal being received. • It indicates number of OFDM symbols used for PDCCHs (1, 2, or 3). • Information within PCFICH is essential because the UE does not have prior information about the size of the control region. • A PCFICH is transmitted on the first symbol of every sub-frame and carries a Control Format Indicator, CFI field. • The CFI contains a 32 bit code word that represents 1, 2, or 3. • CFI 4 is reserved for possible future use. • The PCFICH uses 32,2 block coding which results in a 1/16 coding rate and 16 symbols. • QPSK modulation to ensure robust reception. • PCFICH carried by 4 REGs evenly distributed across whole band regardless of B/W. (Resource Element Group) • Exact position of PCFICH determined by cell ID and bandwidth.
  27. 27. 3G LTE Physical channels-Downlink • PDCCH: Physical downlink control channel • PDSCH: Physical downlink shared channel
  28. 28. 3G LTE Physical channels-Downlink • Physical Downlink Control Channel (PDCCH) : • Main purpose of this channel is to carry scheduling information of different types: • Downlink resource scheduling • Uplink power control instructions • Uplink resource grant • Indication for paging or system information • PDCCH contains message Downlink Control Information,. • DCI carries control information for a particular UE or group of UEs. • The DCI format has different types defined with different sizes. • The different format types include: Type 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A, and 4.
  29. 29. 3G LTE Physical channels-Downlink • Physical Downlink Shared Channel (PDSCH) : Main data bearing channel allocated to users on a dynamic basis. • Also used to transmit broadcast information not transmitted on the PBCH e.g. System Information Blocks (SIB) and paging & RRC signalling messages. • PDSCH is also used to transfer application data. • QPSK, 16QAM, 64QAM modulation types. • QPSK is most robust, used for transmission of SIB and Paging. • RBs are shared among all active connections. • Paging messages-Broadcast using PDSCH channel. • LTE UE in RRC IDLE mode monitor PDCCH for paging indications. • It decodes paging message carried in PDSCH RBs. • Downlink RRC Signalling messages-Carried by PDSCH. • Signalling Radio Bearers(SRB) will use PDSCH. • Every connection usually will have its own set of SRB.
  30. 30. 3G LTE Physical channels-Downlink CP- Cyclic Prefix
  31. 31. 3G LTE Physical channels-Downlink • Physical Hybrid ARQ Indicator Channel (PHICH) : • Channel is used to report the Hybrid ARQ status. • It carries the HARQ ACK/NACK signal indicating whether a transport block has been correctly received. • The HARQ indicator is 1 bit long – • "0" indicates ACK, "1" indicates NACK. • The PHICH is transmitted within the control region of the subframe. • It is typically only transmitted within the first symbol. • If the radio link is poor, then the PHICH is extended to a number symbols for robustness.
  32. 32. 3G LTE Physical channels-Uplink • Physical Uplink Control Channel (PUCCH) : • Provides various control signalling requirements. • Number of different PUCCH formats defined to enable channel to carry required information in most efficient format for particular scenario encountered. • Includes ability to carry SRs, Scheduling Requests. PUCCH FORMAT UPLINK CONTROL INFORMATION MODULATION SCHEME BITS PER SUB- FRAME NOTES Format 1 SR N/A N/A Format 1a 1 bit HARQ ACK/NACK with or without SR BPSK 1 Format 1b 2 bit HARQ ACK/NACK with or without SR QPSK 2 Format 2 CQI/PMI or RI QPSK 20 Format 2a CQI/PMI or RI and 1 bit HARQ ACK/NACK QPSK + BPSK 21 Format 2b CQI/PMI or RI and 2 bit HARQ ACK/NACK QPSK + BPSK 22 Format 3 Provides support for carrier aggregation.
  33. 33. 3G LTE Physical channels-Uplink • Physical Uplink Shared Channel (PUSCH) : • Uplink counterpart of PDSCH • Physical Random Access Channel (PRACH) : • Used for random access functions. • The only non-synchronised transmission that the UE can make within LTE. • The downlink and uplink propagation delays are unknown when PRACH is used. • Therefore it cannot be synchronised. • PRACH instance is made up from two sequences: • a cyclic prefix • a guard period. • The preamble sequence may be repeated to enable the eNodeB to decode the preamble when link conditions are poor.
  34. 34. 3G LTE Physical channels-Uplink
  35. 35. 3G LTE Transport channels-Downlink • Downlink: • Broadcast Channel (BCH) : Maps to Broadcast Control Channel (BCCH) • Downlink Shared Channel (DL-SCH) : Main channel for downlink data transfer. • Used by many logical channels. • Paging Channel (PCH) : To convey the PCCH • Multicast Channel (MCH) : Used to transmit MCCH information to set up multicast transmissions. • • Uplink: • Uplink Shared Channel (UL-SCH) : Main channel for uplink data transfer. • Used by many logical channels. • Random Access Channel (RACH) : Used for random access requirements.
  36. 36. 3G LTE Logical channels • Cover the data carried over the radio interface. • Service Access Point, SAP between MAC sublayer and the RLC sublayer provides the logical channel. • Control channels: Carry the control plane information: • Broadcast Control Channel (BCCH) : Provides system information to all mobile terminals connected to the eNodeB. • Paging Control Channel (PCCH) : Used for paging information when searching a unit on a network. • Common Control Channel (CCCH) : Used for random access information, e.g. for actions including setting up a connection. • Multicast Control Channel (MCCH) : Used for Information needed for multicast reception. • Dedicated Control Channel (DCCH) : Used for carrying user- specific control information, e.g. for controlling actions including power control, handover, etc..
  37. 37. 3G LTE Logical channels • Traffic channels: Carry the user-plane data: • Dedicated Traffic Channel (DTCH) : Used for the transmission of user data. • Multicast Traffic Channel (MTCH) : Used for transmission of multicast data.
  38. 38. 3G LTE Downlink channels
  39. 39. 3G LTE Downlink channels
  40. 40. 3G LTE UE Category • LTE categories define standards to which a particular handset, dongle or other equipment will operate. • Needed to ensure that base station can communicate correctly with user equipment. • LTE category defines overall performance and capabilities of UE. • The eNB communicates using UE capabilities and not beyond. • 9 different LTE UE categories are defined with wide range in the supported parameters and performance. • Example: • LTE category 1 does not support MIMO, but LTE UE category 5 supports 4x4 MIMO. • UE class 1 does not offer performance offered by that of HSPA. • LTE UE categories are capable of receiving transmissions from up to four antenna ports.
  41. 41. 3G LTE UE Category • Headline data rates for category 8 exceed the requirements for IMT-Advanced by a considerable margin. • Headline rates show the maximum data rates achievable. HEADLINE DATA RATES FOR LTE CATEGORIES LTE UE CATEGORY LINK 1 2 3 4 5 6 7 8 Downlink 10 50 100 150 300 300 300 1200 Uplink 5 25 50 50 75 50 150 600
  42. 42. 3G LTE UE Category ULAND DL PARAMETERS FOR LTE UE CATEGORIES LTE CATEGORY PARAMETER LTE CAT 1 LTE CAT 2 LTE CAT 3 LTE CAT 4 LTE CAT 5 LTE CAT 6 LTE CAT 7 LTE CAT 8 Max number of DL-SCH transport block bits received in a TTI 10 296 51 024 102 048 150 752 302 752 299 552 299 552 1 200 000 Max number of bits of a DL- SCH block received in a TTI 10 296 51 024 75 376 75 376 151 376 TBD TBD TBD Total number of soft channel bits 250 368 1 237 248 1 237 248 1 827 072 3 667 200 3 667 200 TBD TBD Maximum number of supported layers for spatial multiplexing in DL 1 2 2 2 4 Max number of bits of an UL- SCH transport block received in a TTI 5 160 25 456 51 024 51 024 75 376 TBD TBD TBD Support for 64-QAM in UL No No No No Yes No Yes, up to RAN 4 Yes • DL-SCH = Downlink shared channel • UL-SCH = Uplink shared channel • TTI = Transmission Time Interval
  43. 43. 3G LTE UE Category 0 • LTE category needed focusing on developing technologies: • Internet of Things(IoT) • General machine to machine(M2M) communications. • Requirements are • much lower data rates, • short bursts, • remote device to be able to draw low current levels. • LTE Category 0 has a reduced performance requirement. • Meets the needs of many machines while significantly reducing complexity and current consumption. • In spite of reduced specification, it complies with LTE system requirements. • New LTE Cat 0 was introduced in Rel 12 of the 3GPP standards.
  44. 44. 3G LTE UE Category 0 • One major advantage of LTE Category 0: • Modem complexity is considerably reduced when compared to other LTE Categories. • 50% that of a Category 1 modem. LTE CATEGORY 0 PERFORMANCE SUMMARY PARAMETER LTE CAT 0 PERFORMANCE Peak downlink rate 1 Mbps Peak uplink rate 1 Mbps Max number of downlink spatial layers 1 Number of UE RF chains 1 Duplex mode Half duplex UE receive bandwidth 20 MHz Maximum UE transmit power 23 dBm
  45. 45. Main LTE Technologies - 1 1. OFDM (Orthogonal Frequency Division Multiplex): • Enables high data bandwidths to be transmitted efficiently. • High degree of resilience to reflections and interference. • Differ between the uplink and downlink: • OFDMA (Orthogonal Frequency Division Multiple Access )– downlink. • SC-FDMA(Single Carrier - Frequency Division Multiple Access) - uplink. • Specialized FDM with all carrier signals orthogonal to one another. • Crosstalk between sub-channels eliminated and inter-carrier guard bands not required. • Unlike conventional FDM, a separate filter for each sub-channel is not required.
  46. 46. Main LTE Technologies- -OFDM • OFDM (Orthogonal Frequency Division Multiplex): • But multiple signals arising from the many reflections. • Limits use of OFDM in high-speed vehicles. • FDM requires very accurate frequency synchronization between receiver and transmitter. • OFDMA is a multi-user version of OFDM. • Multiple access achieved by assigning subsets of subcarriers to individual users. • Allows simultaneous low data rate transmission from several users. • SC-FDMA interpreted as linearly precoded OFDMA scheme. • Assigns multiple users to a shared communication resource. • SC-FDMA has small peak to average power ratio. • Desirable for uplink wireless transmission where transmitter power efficiency is of paramount importance. • More constant power enables high RF power amplifier efficiency in mobile handsets.
  47. 47. Main LTE Technologies - 2 2. MIMO (Multiple Input Multiple Output): • Additional signal paths due to reflections are used to advantage. • Increase the throughput. • Multiple antennas to enable different paths to be distinguished. • 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used at base station. • Dimensions of user equipment limit number of antennas to be place at least half wavelength apart. • Improves performance of system. • Provides LTE with ability to improve its data throughput and spectral efficiency above OFDM. • Enables far high data rates and much improved spectral efficiency. • MIMO an integral part of LTE.
  48. 48. LTE MIMO Basics • Transmitter and Receiver have more than one antenna. • Provide improvements in data rate and efficiency. • MIMO has been a cornerstone of the LTE standard. • Initially, in releases 8 and 9 multiple transmit antennas on the UE was not supported as only interested in power reduction. • Rel. 10 has number of new schemes introduced. • Closed loop spatial multiplexing for SU-MIMO as well as multiple antennas on the UE.
  49. 49. LTE MIMO Modes • MIMO modes depend on equipment used and channel functions. • Single antenna: • Used on most basic wireless links. • Single data stream transmitted by one antenna and received by one or more antennas. • SISO or SIMO dependent upon the antennas used. • SIMO is also called Receive Diversity. • Transmit diversity: • Utilizes transmission of same information stream from multiple antennas. • Information is coded differently using Space Frequency Block Codes. • Provides an improvement in signal quality at reception but does not improve the data rate. • Used on Common Channels as well as Control and Broadcast channels.
  50. 50. LTE MIMO Modes • Open loop spatial multiplexing: • Sends two information streams transmitted over two or more antennas. • No feedback from the UE. • TRI, Transmit Rank Indicator transmitted from the UE can be used by the base station to determine the number of spatial layers. • Close loop spatial multiplexing : • Similar to open loop version, but has feedback incorporated to close the loop. • PMI, Pre-coding Matrix Indicator is fed back from the UE to the base station. • Enables transmitter to pre-code data to optimize transmission. • Enable receiver to more easily separate different data streams.
  51. 51. LTE MIMO Modes • Closed loop with pre-coding: • Single code word is transmitted over a single spatial layer. • Used as a fall-back mode for closed loop spatial multiplexing. • May also be associated with beamforming as well. • Precoding matrix selection at receiver and precoding operation at transmitter. • Achieves good tradeoff between system complexity and performance gain given by closed-loop transmission. • Multi-User MIMO, MU-MIMO: space-division multiple access • Enables the system to target different spatial streams to different users. • Set of users each with one or more antennas communicate with each other. • Multiple access (multi-user) capabilities to MIMO
  52. 52. LTE MIMO Modes • Beam-forming: • Most complex of the MIMO modes. • Likely to use linear arrays that will enable the antenna to focus on a particular area. • This will reduce interference, and increase capacity as the particular UE will have a beam formed in their particular direction. • A single code word is transmitted over a single spatial layer. • A dedicated reference signal is used for an additional port. • The terminal estimates the channel quality from the common reference signals on the antennas.
  53. 53. Main LTE Technologies - 3 3. SAE (System Architecture Evolution): • For very high data rate and low latency, system architecture is evolved for improved performance. • Number of functions handled by core network transferred to periphery. • Provides a much "flatter" form of network architecture. • Latency times can be reduced and data can be routed more directly to its destination. • Fully compatible with LTE Advanced. • Based on GSM / WCDMA core networks to enable simplified operations and easy deployment.
  54. 54. SAE-Advantages • Improved data capacity: With 3G LTE data rates 100 Mbps and focus on mobile broadband, network should handle greater levels of data. • Hence necessary system architecture must be adopted. • All IP architecture: With 3G evolution, voice evolved from circuit switched to IP data. • New SAE schemes have adopted an all IP network configuration. • Reduced latency: SAE concepts evolved to ensure levels of latency reduced to 10ms for increased interaction and much faster responses. • Ensure applications using 3G LTE will be sufficiently responsive. • Reduced OPEX and CAPEX: Any new design reduces capital expenditure and the operational expenditure. • Flat architecture of SAE means only two node types are used. • A high level of automatic configuration is introduced to reduce set-up and commissioning time.
  55. 55. SAE-Basics • Based on GSM / WCDMA core networks to enable simplified operations and easy deployment. • SAE network brings major changes to allow more efficient effective transfer of data. • Several common principles used in the development of LTE SAE network: • Common gateway node and anchor point for all technologies. • Optimized architecture for user plane with only two node types. • All IP based system with IP based protocols used on all interfaces. • Split in control plane / user plane between mobility management entity (MME) and gateway. • Radio access network / core network functional split similar to that used on WCDMA / HSPA. • Integration of non-3GPP access technologies (e.g. cdma2000, WiMAX, etc) using client as well as network based mobile-IP.
  56. 56. LTE SAE-Evolved Packet Core • Evolved Packet Core or EPC is main element of the LTE SAE network. • This connects to eNodeBs. • LTE SAE EPC consists of four main elements as :
  57. 57. LTE SAE-EPC Elements • Mobility Management Entity, MME: Main control node for LTE SAE access network. • Handles features: • Idle mode UE tracking • Bearer activation / de-activation • Choice of SGW for a UE • Intra-LTE handover involving core network node location • Interacting with HSS to authenticate user on attachment • Implements roaming restrictions • Acts as a termination for Non-Access Stratum (NAS) • Provides temporary identities for UEs • Acts as termination point for ciphering protection for NAS signaling. • Also handles security key management. • It is the point at which lawful interception of signaling may be made. • Paging procedure • The S3 interface terminates in the MME thereby providing the control plane function for mobility between LTE and 2G/3G access networks. • Also terminates the S6a interface for the home HSS for roaming UEs. • Overall provides a considerable level of overall control functionality.
  58. 58. LTE SAE-EPC Elements • Serving Gateway, SGW: It is a data plane element within LTE SAE. • Main purpose: • Manage user plane mobility. • Acts as main border between the Radio Access Network, RAN and core network. • Maintains data paths between eNodeBs and PDN Gateways. • Forms interface for data packet network at E-UTRAN. • Serves as mobility anchor ensuring data path when UEs move across areas served by different eNodeBs. • PDN Gateway, PGW: Provides connectivity for the UE to external packet data networks • Fulfills function of entry and exit point for UE data. • UE may have connectivity with more than one PGW for accessing multiple PDNs. (Packet Data Network)
  59. 59. LTE SAE-EPC Elements • Policy and Charging Rules Function, PCRF: Generic name for entity within the LTE SAE EPC. • Detects the service flow. • Enforces charging policy. • For applications requiring dynamic policy or charging control, a network element Applications Function, AF is used.
  60. 60. LTE Self Organising Networks • LTE requires smaller cell sizes for greater data traffic to be handled. • Need to reduce costs by reducing manual input. • Results in more complicated networks. • Difficult to plan and manage the network centrally. • Need self organising networks. • LTE major driver behind self-organising network, SON philosophy. • 3GPP developed requirements for LTE SON alongside basic functionality of LTE. • Standards for LTE SON are embedded within the 3GPP standards.
  61. 61. LTE SON-Major Elements • Self configuration: • To enable new base stations to become "Plug and Play" items. • Should need as little manual intervention in the configuration process as possible. • Be able to organise RF aspects. • Configure backhaul. • Self optimisation: • After set up, enables base station to optimise operational characteristics to best meet the needs of the overall network. • Self-healing: • Enables network to self-heal. • By changing characteristics of the network to mask the problem until it is fixed. • For example, the boundaries of adjacent cells can be increased by changing antenna directions and increasing power levels, etc..
  62. 62. Voice Over LTE –Why? • Originally- • LTE - IP cellular system for data, • 2G / 3G systems or VoIP for voice • Leads to: • Fragmentation and incompatibility, not allowing all phones to communicate with each other. • Reduced voice traffic. • SMS services still widely used, reducing revenue from voice calls and SMS. • Viable and standardised scheme needed to provide voice and SMS services to protect this revenue.
  63. 63. LTE – Options for Voice • CSFB, Circuit Switched Fall Back: Standardised under 3GPP specification 23.272. • Uses variety of processes and network elements for fall back to the 2G or 3G connection (GSM, UMTS, CDMA2000 1x) before a circuit switched call is initiated. • Allows SMS using an interface SGs allowing messages to be sent over an LTE channel. • SV-LTE - Simultaneous Voice LTE: Allows packet switched LTE services to run simultaneously with a circuit switched voice service. • Has disadvantage, two radios to run at the same time within the handset with serious impact on battery life. • VoLGA, Voice over LTE via GAN: 3GPP Generic Access Network aims for consistent set of voice, SMS and other circuit-switched services as they transit between GSM, UMTS and LTE access networks. • For mobile operators, aims to provide low-cost and low-risk approach for bringing primary revenue generating services (voice and SMS) onto the new LTE network deployments. • Voice over LTE, VoLTE: Chosen by GSMA for use on LTE. • Standardised method for providing SMS and voice over LTE.
  64. 64. V0LTE – Basics • IP Multimedia Subsystem, IMS-based specification. • Enables system integration with suite of applications available on LTE. • Cut down version reduced number of entities required in IMS network, but simplified interconnectivity focusing on VoLTE elements. • Entities within the reduced IMS network used for VoLTE: • HSS: Home subscriber server • P-CSCF: Proxy-Call Session Control Function • I-CSCF: Interrogating-Call Session Control Function • S-CSCF: Serving-Call Session Control Function • IP-CAN : IP connectivity access network • AS: Application server
  65. 65. V0LTE – Basics • IP-CAN, IP Connectivity Access Network: Consists of EUTRAN and MME. • P-CSCF, Proxy Call State Control Function: User to network proxy. • All SIP signalling to/ from user runs via P-CSCF whether in home / visited network. • I-CSCF, Interrogating Call State Control Function: Used for forwarding an initial SIP request to the S-CSCF when initiator does not know which S-CSCF should receive the request. • S-CSCF, Serving Call State Control Function: Undertakes variety of actions within overall system. • Has number of interfaces to communicate with other entities within the overall system. • AS, Application Server: Handles voice as an application. • HSS, Home Subscriber Server: Main subscriber database used within IMS. • Provides details of subscribers to other entities within IMS network, to be granted access or not dependent upon their status.
  66. 66. V0LTE – Basic operation • The IMS calls for VoLTE are processed by subscriber's S-CSCF in the home network. • The connection to the S-CSCF is via P-CSCF. • Dependent upon network in use and overall location within a network, the P-CSCF will vary. • Hands back to circuit switched legacy networks in a seamless manner, while only having one transmitting radio in the handset to preserve battery life. • A system known as SRVCC - Single Radio Voice Call Continuity is required for this.
  67. 67. SRVCC- Single Radio Voice Call Continuity • It is level of functionality, required within VoLTE systems for packet domain calls on LTE to be handed over to legacy circuit switched voice systems like GSM, UMTS and CDMA 1x in a seamless manner. • SRVCC enables: • Inter Radio Access Technology, Inter RAT handover, • handover from packet data to circuit switched data voice calls. • Handovers made while- • maintaining existing quality of service, • ensuring that call continuity meets critical requirements for emergency calls. • Requires single active radio in the handset and some upgrades to the supporting network infrastructure.
  68. 68. SRVCC- Network Architecture • SRVCC originally included in 3GPP Rel 8. • 3GPP Rel 10 implemented later as this ensures a considerably lower level of voice interruption and dropped calls. • SRVCC demands software upgrades to MSS, Mobile SoftSwitch subsystem in MSC, IMS subsystem and LTE/EPC subsystem. • No upgrades required for radio access network of the legacy system. • Majority of legacy system remains unaffected. • Upgrades to MSC are relatively easy to manage. • MSC centrally located and not dispersed around the network. • Makes upgrades easier to manage. • Dedicated MSC may be used that has been upgraded to handles the SRVCC requirements.
  69. 69. SRVCC- Working • Controls transfer of calls in both directions. • LTE to legacy network handover Required when user moves out of LTE coverage area. • Handover undertaken in two stages: • Radio Access Technology transfer: Handover for the radio access network. • Well-established protocol e.g. transfers from 3G to 2G. • Session transfer: New element required for SRVCC. • To shift access control and voice media anchoring from Evolved Packet Core, EPC of packet switched LTE network to legacy circuit switched network. • During handover, CSCF in IMS architecture maintains control of whole operation.
  70. 70. SRVCC- Working • Voice handover using SRVCC on LTE
  71. 71. SRVCC- Working • The SRVCC handover process takes place in a number of steps: • Process initiated by a request for session transfer from IMS CSCF. • The IMS CSCF responds simultaneously with two commands, • one to the LTE network, • other to the legacy network. • LTE network receives radio Access Network handover execution command through MME and LTE RAN. • This instructs user device to prepare to move to a circuit switched network for the voice call. • The destination legacy circuit switched network receives a session transfer response preparing it to accept the call from the LTE network. • After all the commands have been executed and acknowledged, the call is switched to the legacy network with the IMS CSCF still in control of the call.
  72. 72. SRVCC- Working • Legacy network to LTE When returning a call to the LTE network much of same functionality is again used. • To ensure VoLTE device return to LTE RAN from legacy RAN, there are two options the legacy RAN can implement to provide a swift and effective return: • Allow LTE information to be broadcast on the legacy RAN so the LTE device is able to perform the cell reselection more easily. • Simultaneously release the connection to the user device and redirect it to the LTE RAN.
  73. 73. SRVCC- Interruption performance • One of key issues with VoLTE and SRVCC is interruption time of handover from LTE RAN to legacy RAN. • Time reduces if simultaneously performs redirections of RAN and session. • User experience is maintained. • Actual interruption time is not unduly noticeable. • Session redirection is the faster of the two handovers, • therefore necessary for overall handover methodology to accommodate the fact that there are difference between the two. • USIM: For LTE, SIM upgraded to USIM- UMTS Subscriber Identity Module may be used. • Gives more functionality, has a larger memory. • Older SIM cards are not compatible and may not be used.
  74. 74. LTE Security • LTE security requirements: • Must provide at least same level of security that was provided by 3G services. • Should not affect user convenience. • Should provide defense from attacks from the Internet. • Should not affect the transition from existing 3G services to LTE. • The USIM currently used for 3G services should still be used. • Changes required to implement level of LTE security are : • Hierarchical key system introduced, keys changed for different purposes. • Security functions for Non-Access Stratum, NAS, and Access Stratum, AS have been separated. • The NAS functions - functions for which processing is accomplished between core network and mobile terminal UE. • The AS functions - communications between - network edge, i.e. eNB and UE. • Concept of forward security introduced for LTE security. • Security functions introduced between existing 3G and LTE network.
  75. 75. 4G - AIM • Upgrading of 3G UMTS to 4G mobile communications technology. • Simplifying the architecture of the system. • Transitions from existing UMTS circuit/packet switching combined network to all-IP flat architecture system.
  76. 76. 4G - FEATURE • Peak download rates - 299.6 Mbit/s and upload rates - 75.4 Mbit/s depending on the user equipment. • Five different terminal classes defined from audio to peak data rates. • All terminals will be able to process 20 MHz bandwidth. • Lower latencies for data transfer, handover and connection setup time than before. • Improved support for mobility up to 350 km/h or 500 km/h depending on the frequency band. • OFDM access for the downlink, single carrier FDMA for the uplink to conserve power. • Support for both FDD and TDD, also half-duplex FDD communication systems with the same radio access technology.
  77. 77. 4G - FEATURE • Increased spectrum flexibility: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz wide cells are standardized. • Support for cell sizes from tens of meters radius (femto and Pico cells) up to 100 km radius macrocells. • Lower frequency bands to be used in rural areas for, • 5 km is the optimal cell size, • 30 km having reasonable performance, • and up to 100 km cell sizes supported with acceptable performance. • In city and urban areas, higher frequency bands are used to support high speed mobile broadband for cell sizes 1 km.
  78. 78. 4G - FEATURE • Supports at least 200 active data clients in every 5 MHz cell. • Simplified architecture with network side of E-UTRAN composed only of eNODE-Bs. • Support for inter-operation and co-existence with legacy standards like GSM/EDGE, UMTS and CDMA2000. • Packet switched audio interface. • Support for MBSFN(Multicast Broadcast Single Frequency Network) • Can deliver services such as Mobile TV using the LTE infrastructure, • Is a competitor for DVB-H-based TV broadcast (Digital Video Broadcasting – Handheld) • Does not provide backward compatibility to previous standard such as 2G and 3G.
  79. 79. 4G - Requirements  Support for all frequency bands currently used by IMT systems by ITU-R.  It must be an all IP-based packet switching network.  Must provide data peak rates of up to approximately:  100 Mbit/s for highly mobile access.  1 Gbit/s for low mobility  User-friendly applications, services, and equipment  Dynamically use and share resources network to support more simultaneous users per cell.  Must be able to provide a scalable channel BW of 5–20 MHz .  High QOS that supports next generation multimedia services .
  80. 80. 4G- WiMAX • Wimax-Worldwide interoperability for Microwave access • IP based wireless broadband telecommunication technology. • Aimed at providing high speed data, voice, video, also digital wireless communication to mobile. • Initially designed to provide up to 30 - 40 Mbit/s data rate upgraded to 1 Gbit/s. • Developed as an alternative to DSL (digital subscriber line) • Sometimes referred as Wifi on steroids , provides VoIP, IPTV and other internet based services. • Two standards to Wimax: Fixed Wimax and Mobile Wimax. • Fixed Wimax: IEEE 802.16-2004 or IEEE 802.16d; • Fixed wireless access technology. • Aimed at servicing fixed and mobile applications. • Purpose is to replace the Subscriber digital line (DSL)standard and to serve as backhaul for wifi access points or for mobile networks, and subsequently provide basic voice and broadband access. • Mobile Wimax- • Mobile wireless access standard • Only capable to work on NLOS environments. • For fixed and mobile applications with a greater indoor penetration.
  81. 81. 4G- LTE • Though originally sold as 4G, LTE didn't satisfy the ITU-R technical requirements. • Due to marketing pressures and advancements of LTE, ITU later decided LTE as 4G technology. • LTE is a first-generation 4G technology to reach speeds of around 100Mbit/s. • Originally lacked in download speed, uplink spectral efficiency and speed. • Uplink spectral efficiency is efficiency of upload and transmit data rate from smartphone. • Falls short of true 4G capacity because – • lack of carrier aggregation • phones not having many antennae. • Better carrier aggregation and MIMO leads to 'true' 4G: LTE Advanced.
  82. 82. 4G LTE - LTE Advance • 4G technology, IMT Advanced developed under 3GPP termed LTE Advanced. • ITU-R started development for terrestrial components of IMT Advanced radio interface in competition with LTE Advanced solution. • Key milestones for ITU-R IMT Advanced evaluation KEY MILESTONES ON THE DEVELOPMENT OF 4G LTE-ADVANCED MILESTONE DATE Issue invitation to propose Radio Interface Technologies. March 2008 ITU date for cut-off for submission of proposed Radio Interface Technologies. October 2009 Cutoff date for evaluation report to ITU. June 2010 Decision on framework of key characteristics of IMT Advanced Radio Interface Technologies. October 2010 Completion of development of radio interface specification recommendations. February 2011
  83. 83. 4G LTE - LTE Advance COMPARISON OF LTE-A WITH OTHER CELLULAR TECHNOLOGIES WCDMA (UMTS) HSPA HSDPA / HSUPA HSPA+ LTE LTE ADVANCED (IMT ADVANCED) Max downlink speed bps 384 k 14 M 28 M 100M 1G Max uplink speed bps 128 k 5.7 M 11 M 50 M 500 M Latency round trip time approx 150 ms 100 ms 50ms (max) ~10 ms less than 5 ms 3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8 Rel 10 Approx years of initial roll out 2003 / 4 2005 / 6 HSDPA 2007 / 8 HSUPA 2008 / 9 2009 / 10 2014 / 15 Access methodology CDMA CDMA CDMA OFDMA / SC- FDMA OFDMA / SC-FDMA
  84. 84. LTE Advance - Key Features • LTE Advanced aims for : • Peak data rates: downlink - 1 Gbps; uplink - 500 Mbps. • Spectrum efficiency: 3 times greater than LTE. • Peak spectrum efficiency: downlink - 30 bps/Hz; uplink - 15 bps/Hz. • Spectrum : ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used. • Latency: from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for individual packet transmission. • Cell edge user throughput to be twice that of LTE. • Average user throughput to be 3 times that of LTE. • Mobility: Same as that in LTE • Compatibility: LTE Advanced shall be capable of interworking with LTE and 3GPP legacy systems.
  85. 85. LTE Advance - Technologies • Orthogonal Frequency Division Multiplex, OFDM : Forms basis of radio bearer. • OFDMA with SC-FDMA used in hybrid format. • Multiple Input Multiple Output, MIMO: Other key enabler for LTE Advanced. • Enables data rates to be increased beyond what basic radio bearer would normally allow. • Additional antennas to enable additional paths at cost of overheads and return per additional path • Beamforming may be used to enable antenna coverage to be focused where it is needed.
  86. 86. LTE Advance - Technologies • Carrier Aggregation, CA: Operators are able to utilise multiple channels either in the same bands or different areas of the spectrum to provide the required bandwidth. • Coordinated Multipoint : Interference from adjacent cells along with poor signal quality lead to a reduction in data rates and poor performance at the cell edges. • Coordinated multipoint has been introduced. • LTE Relaying: Enables signals to be forwarded by remote stations from a main base station to improve coverage. • Device to Device, D2D: Enables fast swift access via direct communication. • Facility essential for emergency services on the scene of an incident.
  87. 87. Reference • • between-4g-lte-3605656/ • phones/4G-and-LTE-everything-you-need-to- know/articleshow/38880546.cms • 1-0300.pdf • ommunication • term-evolution