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01 principles of the wcdma system

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01 principles of the wcdma system

  1. 1. Internal Principles of the WCDMA System www.huawei.comHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
  2. 2. Preface  Now, the most popular term in the mobile communication field is WCDMA!  What is WCDMA? And what is its benefit?  Today, let’s go to know about WCDMA!HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 2
  3. 3. Objectives  After studying this course, you should be able to:  Know the basic knowledge of the CDMA system.  Master advantages of the CDMA technology comparing with other multiple access technologies.  Know technical features of WCDMA FDD.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 3
  4. 4. Contents Chapter 1 WCDMA Principle Chapter 2 Technical Features of WCDMA FDDHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 4
  5. 5. Overview of CDMA Principles  Radio Propagation Environment  Multiple Access Technology and Duplex Technology  CDMA Principles and Rake ReceiverHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 5
  6. 6. Multipath EnvironmentTransmitted signal Strength of the received signal TimeHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 6
  7. 7. Fading Transmitted data Received data 0 -5 -10 -15dB -20 -25 -30 -35 -40HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 7
  8. 8. Fading Rx power (dBm) -20 Fast fading Slow fading -40 -60 Distance (m) 10 20 30HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 8
  9. 9. Frequency-Selective Fading P(f) P(f) FadingNarrowband System f f Transmit Signal Received Signal P(f) P(f) Fading Broadband System f f Transmit Signal Received SignalHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 9
  10. 10. Classification of Typical Radio Mobile Channels  Static channel  Pedestrian channel in typical urban areas (TU3)  Vehicle mounted channel in typical urban areas (TU30)  Vehicle mounted channel in rural areas (RA50)  Vehicle mounted channel on the highway (HT120)HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 10
  11. 11. Overview of CDMA Principles  Radio Propagation Environment  Multiple Access Technology and Duplex Technology  CDMA Principles and Rake ReceiverHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 11
  12. 12. Duplex Technology – Distinguish User’s UL andDL Signal – FDD Frequency division duplex (FDD) : Distinguish the uplink and downlink according to the frequencies.  Adopted by the WCDMA, CDMA2000 and GSM  Advantage: It can be easily implemented.  Disadvantage: The spectrum utilization is low when the uplink and downlink services (mainly the data services) are asymmetrical.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 12
  13. 13. Duplex Technology – Distinguish User’s UL andDL Signal – TDD Time division duplex (TDD) : Distinguish the uplink and downlink according to the timeslots.  Adopted by the TD-SCDMA  Advantage: The uplink and downlink can be allocated with different numbers of timeslots when the uplink and downlink services are asymmetrical. Therefore, the spectrum utilization is high.  Disadvantage: − It cannot be easily implemented and needs precise synchronization. In the CDMA system, GPS synchronization is needed. − When it is used with the CDMA technology, it is difficult to control interference between the uplink and the downlink.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 13
  14. 14. Multiple Access Technology - Distinguish Different Users CDMA Traffic channels: different users are assigned unique code and transmitted over Power the same frequency band, for example, WCDMA and Time ncy Freque CDMA2000 TDMA Power Traffic channels: different time slots cy are allocated to different users, for en Tim qu example, DAMPS and GSM FDMA e Fre Us U U s er ePower U s ser r U s er Traffic channels: different frequency bands er cy are allocated to different users,for example, en u Tim eq e Fr AMPS and TACSHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 14
  15. 15. Characteristics of CDMA System  High Spectral Efficiency  Frequency multiplex coefficient is 1.  Soft capacity  Quality  Coverage  Interference  Self-interference system  A UE transmission power is interference for another UE.  Wideband systemHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 15
  16. 16. Overview of WCDMA Principles  Radio Propagation Environment  Multiple Access Technology and Duplex Technology  CDMA Principles and Rake ReceiverHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 16
  17. 17. Questions  Why does the WCDMA system have enhanced anti- interference performance?  Why is the WCDMA system more secure?  Why are the WCDMA handsets more environment protective?HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 17
  18. 18. Common Terms  Bit, symbol and chip  Bit (bps): the data that is obtained upon source coding and contains information.  Symbol (sps): the data obtained upon channel coding and interleaving.  Chip (cps): the data obtained upon final spreading. − The spreading rate of WCDMA is: 3.84 Mcps  Processing gain  It refers to the ratio of the final spreading rate to the bit rate (cps/bps).  In the WCDMA system, the processing gain depends on the specific service.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 18
  19. 19. Spreading Factor and Service Rate  Chip rate = symbol rate × spreading factor  For WCDMA, if the chip rate is 3.84 MHz and the spreading factor is 4, the symbol rate is 960 Kbps.  For CDMA2000-1x, if the chip rate is 1.2288 MHz and the spreading factor is 64, the symbol rate is 19.2 Kbps.  Symbol rate = (service rate + check code) × channel code ×repetition or punching rate  For WCDMA, if the service rate is 384 Kbps and the channel code is 1/3 Turbo, the symbol rate is 960 Kbps.  For CDMA2000-1x, if the service rate is 9.6 Kbps and the channel code is 1/3 convolutional code, the symbol rate is 19.2 Kbps.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 19
  20. 20. Basic Diagram of the WCDMA System Channel RF Source coding and Spreading Scrambling Modulation transmission coding interleaving Radio link Channel Source deinterleaving RF decoding and De-spreading De-scrambling Demodulation decoding reception de-interleavingHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 20
  21. 21. Source Coding in WCDMA  The WCDMA system adopts the adaptive multi-rate (AMR) speech coding.  A total of eight coding modes are available. The coding rate ranges from 12.2 Kbps to 4.75 Kbps.  Multiple voice rates are compatible with the coding modes used by current mainstream mobile communication systems. This facilitates the design of multi- mode terminals.  The system automatically adjusts the voice rate according to the distance between the user and the NodeB, thus reducing the number of handovers and call drop.  The system automatically decreases the voice rate of some users according to the cell load, thus saving power and containing more users. Channel Source RF Interleaving Spreading coding and Scrambling Modulation coding transmission interleavingHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 21
  22. 22. Channel Coding in WCDMA  Channel coding can enhance symbol correlation to recover signals in the case of interference. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25  Code type  Voice service: Convolutional code (1/2 and 1/3).  Data service: Turbo code (1/3). Channel Source RF Interleaving coding Spreading Scrambling Modulation coding transmission interleavingHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 22
  23. 23. Interleaving  Interleaving is used to damage symbol correlation and reduce the impact caused by fast fading and interference of the channel. 1 2 3 4 5 6 7 8 ... ... 452 453 454 …… Ist interleaving B0 B1 B2 B3 B4 B5 B6 B7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 . . . . . . . . .... . . . . . . . . .... . . . . . . . . 449 450 451 452 453 454 455 456 2nd interleaving {A4,B0} {A5,B1} {A6,B2} {A7,B3} {B4,C0} {B5,C1} {B6,C2} {B7,C3}HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 23
  24. 24. Self Correlation and Mutual Correlation of Code Words  Different users adopt different spreading code words, such as x1(t) , x2(t) ….  Self correlation determines multipath interference.  Mutual correlation determines multiple access interference.  Self-correlation function  R(τ) =<x1(t) , x1(t+τ) >  Mutual-correlation function  V(τ) =<x1(t) , x2(t+τ) > 1, when x1=x2 , and x = y Note: <x1(x) , x2(y)> = 0, othersHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 24
  25. 25. Spreading Principle  Users who need to send information: UE1, UE2 and UE3  UE1 uses c1 for spreading: UE1 x c1  UE2 uses c2 for spreading: UE2 x c2  UE3 uses c3 for spreading: UE3 x c3  c1, c2 and c3 are orthogonal to each other  Information sent: UE1 x c1 + UE2 x c2 + UE3 x c3 Channel RF Source Interleaving Scrambling coding and Spreading Modulation transmission coding interleavingHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 25
  26. 26. De-spreading Principle  UE1 uses c1 for de-spreading.  (UE1 x c1 + UE2 x c2 + UE3 x c3) x c1 = UE1 x (c1 x c1) + UE2 x (c2 x c1) + UE3 x (c3 x c1) = UE1 x 1 + UE2 x 0 + UE3 x 0 = UE1  In the same way, UE2 uses c2 for de-spreading and UE3 uses c3 for de-spreading to get their own signals.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 26
  27. 27. Spreading Principle ____________ UE1: +1 -1 1 _____________ UE2: -1 +1 c1: +1 -1 +1 -1 +1 -1 +1 -1 c2: +1 +1 +1 +1 +1 +1 +1 +1 UE1xc1: +1 -1 +1 -1 -1 +1 -1 +1 UE2xc2: -1 -1 -1 -1 +1 +1 +1 +1 UE1xc1 + UE2xc2: 0 -2 0 -2 0 +2 0 +2HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 27
  28. 28. De-spreading Principle UE1×c1 + UE2×c2 : 0 -2 0 -2 0 +2 0 +2 UE1 de-spreading with c1: +1 -1 +1 -1 +1 -1 +1 -1 De-spreading result: 0 +2 0 +2 0 -2 0 -2 Integral: +4 -4 Decision: +4/4 = +1 -4/4 = -1 UE2 de-spreading with c2: +1 +1 +1 +1 +1 +1 +1 +1 De-spreading result: 0 -2 0 -2 0 +2 0 +2 Integral: -4 +4 Decision : -4/4 = -1 +4/4 = +1 Question: How to generate those orthogonal codes like c1 and c2?HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 28
  29. 29. OVSF & Walsh Cch,4,0 =(1,1,1,1) Cch,2,0 = (1,1) Cch,4,1 = (1,1,-1,-1)Cch,1,0 = (1) Cch,4,2 = (1,-1,1,-1) Cch,2,1 = (1,-1) Cch,4,3 = (1,-1,-1,1) SF = 1 SF = 2 SF = 4 OVSF codes (Walsh) are completely orthogonal and their mutual correlation is zero.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 29
  30. 30. Why CDMA system is a self interference system?  Since all the users use orthogonal code, where does the self interference come from?  Comes from the code error during the transfer.  If there are some code error on one user’s information, it misses some orthogonal to others. Then interference comes.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 30
  31. 31. Sample of code error UE1xc1 + UE2xc2 : 0 -2 0 -2 0 +2 0 +2 UE1xc1 + UE2xc2 error : 2 -2 0 -2 1 +2 0 +2 c1: +1 -1 +1 +1 +1 -1 +1 -1 Result: 2 +2 0 +2 0 -2 0 -2 Integral: +6 -4 Decision: +6/4 = 1.5 -4/4=-1 C2 +1 +1 +1 +1 +1 +1 +1 +1 Result: 2 -2 0 -2 0 +2 0 +2 Integral: -2 +4 Decision: -2/4=-0.5 +4/4=1HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 31
  32. 32. Scrambling in the WCDMA System  Downlink: Different cells have different downlink scrambling codes.  Each cell is configured with a unique downlink scramble. The UE identifies a cell based on the scramble.  The OVSF code is used to distinguish different users in a cell.  Uplink: Scrambles are used to distinguish different users.  In one cell, each user is configured with a unique uplink scrambling code.  The OVSF code is used to distinguish the services of a user. Channel Source RF Interleaving coding and Spreading Scrambling Modulation coding transmission interleavingHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 32
  33. 33. Spreading and Scrambling Chips after spreadingSymbols 3.84Mcps and xx sps 3.84M scrambling OVSF code Scrambling code 3.84McpsHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 33
  34. 34. Code Generation Technologies in CDMA  Random sequence (Bernoulli sequence)  It consists of 0’s and 1’s only, with the number of 0’s equal to that of 1’s.  The probability of continuous 1 or 0 is as follows: 1/2 for one continuous 0 or 1, 1/4 for two continuous 0 or 1, 1/8 for three continuous 0 or 1….  One half of the shift sequence is the same as the original sequence and the other half is different.  m sequence - scrambling code used in the CDMA2000 system  It is generated by the shift register.  As the longest linear shift register sequence, its period is 2n-1, where “n” stands for the length of the shift register.  When the delay is 0, the self-correlation function has a maximum value. In other cases, the function value is always -1.  It meets the Bernoulli sequence.  Its disadvantages are: Only one sequence is available and different users are distinguished by different phases. So it has a high requirement for synchronization.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 34
  35. 35. Gold Sequence — Scrambling Code in the WCDMA System  Gold sequence  It consists of two preferred m sequences on the Exclusive-OR basis.  Its self-correlation function has multiple values, which is worse than the m sequence.  It exceeds the m sequence in quantity.  The Gold sequence is used to distinguish the cells and users in the WCDMA system owing to its good self correlation.  Good self correlation determines the Gold sequences can be used to distinguish users, thus the multiple access function is realized.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 35
  36. 36. Advantages and Disadvantages of the Gold Sequence  Advantages: The Gold sequence needs no GPS synchronization and features high system flexibility and security.  The NodeB can work in asynchronous mode.  It is easy to realize indoor coverage.  Disadvantages: The Gold sequence has greater inter-code interference than the m sequence.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 36
  37. 37. Spreading/De-spreading Principle — Explanationsfor Frequency Domain Eb / No = Ec / Io × gain Power spectrum a2Tbit = Ebit Demodulation Allowed maximum interference threshold level of the system Gain Power that all the users can share Interference signals from other users EchipHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 37
  38. 38. Spectrum Change in CDMA Spreading code P(f) P(f) f Broadband signal P (f) f Narrowband signal f Noise Separation of signals and noise P (f) Signal combination Noise + broadband signal P (f) f Spreading code f The CDMA broadband spreading technology effectively avoids frequency-selective fading of radio channels.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 38
  39. 39. Rake Receiver Correlator 1 The Correlator 2 Combiner combined signal Receive set Correlator 3 Searcher Calculate the correlator time delay and signal strength s(t) s(t) t t RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the systemHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 39
  40. 40. Summary - Advantages of CDMA  RAKE receiver is adopted  The time diversity effect generated by channel coherence time is efficiently used.  Frequency diversity  Wideband frequency spectrum  Higher interference tolerance and security performance  Low signal transmission power  Great flexibility in carrying multiple services with largely different bit rate and QoS requirement.  Different spreading factors for different services with different data rates  High spectral efficiency  All users can share the same frequency spectrum simultaneously.  Supporting soft handover and softer handover.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 40
  41. 41. Contents Chapter 1 WCDMA Principle Chapter 2 Technical Features of WCDMA FDDHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 41
  42. 42. Characteristics of WCDMA FDD  Channel bandwidth: 5MHz  Chip rate: 3.84Mcps  Frame length: 10ms  Voice coding: AMR (Adaptive Multi-Rate)  Uplink and downlink modulation: QPSK/QPSK  Coherence demodulation aided with pilot  Fast closed loop power control: 1500Hz  Handover: soft/hard handover  Support synchronous and asynchronous NodeB operationHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 42
  43. 43. Characteristics of WCDMA FDD  Satisfy the minimum performance requirement of IMT2000  Compatible with GSM-MAP core network  Comparatively steady version R99 has been released  Support open loop and closed loop transmit diversity mode  Support Common Packet Channel(CPCH) and Downlink Share Channel, adapt to Internet data access mode  Support macro diversity, selection diversity of NodeB location  Support different fast power control algorithms and open loop, out loop power control  Fully support UE locating servicesHUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 43
  44. 44. Differences Between the WCDMA and GSM onthe Air Interface WCDMA GSM Carrier spacing 5 MHz 200 KHz Frequency reuse coefficient 1 1-18 Power control frequency 1500 Hz 2 Hz or lower Through network planning QoS control Through the RRM algorithm (frequency planning) The 3.84 MHz bandwidth enables the air interface to use Frequency diversity Frequency hopping the rake receiver for multipath diversity. Timeslot-based scheduling Packet data Load-based packet scheduling in GPRS Supported by the protocol to Not supported by the Downlink transmit diversity improve downlink capacity standard but can be applied.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 44
  45. 45. Conclusion  This course describes the WCDMA system.  This course first describes some key technologies. Then, describes the basic principles of CDMA and the WCDMA FDD mode.  After studying this course, we can have a preliminary understanding of WCDMA, thus laying a good foundation for subsequent study.HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 45
  46. 46. Thank You ! www.huawei.com

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