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Physical Layer of 3GPP W-CDMA

Physical Layer of 3GPP W-CDMA. Dec. 2000 IMT-2000 System R&D Team Samsung Electronics Co. , LTD. CONTENTS. Modem Chipset Technology Spread Spectrum Principles Basic Concept of 3GPP W-CDMA Benefits of 3GPP W-CDMA Synchronization of 3GPP Vocoder Layer 1 Channels of 3GPP W-CDMA

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Physical Layer of 3GPP W-CDMA

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  1. Physical Layerof 3GPP W-CDMA Dec. 2000 IMT-2000 System R&D Team Samsung Electronics Co. , LTD

  2. CONTENTS • Modem Chipset Technology • Spread Spectrum Principles • Basic Concept of 3GPP W-CDMA • Benefits of 3GPP W-CDMA • Synchronization of 3GPP • Vocoder • Layer 1 Channels of 3GPP W-CDMA • Transport Channels • Downlink Physical Channels • Uplink Physical Channels • Study Items in 3GPP • Overview of 3GPP BS modem

  3. 1. Modem Chipset Technology • Considerations in Defining a Modem Chipset • Modem ASICs, DSPs, or Microcontrollers? • The use of DSP in Spread-Spectrum Receivers • Cost Criteria • Tradeoffs in Modem Chipset • Modem ASIC Technology • 0.5u ® 0.35u ® 0.25u ® 0.18u • Lower Power Consumption • High Speed & High Density • Low Cost

  4. 2. Spread Spectrum Principles • Analog-Digital Interface • Gain Control • Resolution Bits for ADC • Resolution Bits for DAC • Spectrum • Power Control • Digital Signal Processing Requirements • Fading Environments

  5. 2.1 Spectrum processing gain N Spectrum of wideband CDMA Narrowband CDMA Narrowband CDMA processing gain N1 processing gain N1 Spectrum of FDMA/CDMA hybrid scheme

  6. 2.2 Power Control • In a CDMA system, the signal from one personal station interferes with the signals from all the other personal stations in the system. • The capacity of a CDMA system under very accurate power control • The capacity equation is only true if the received power from each personal station is the same. • If the received power from a particular personal station is too low, the quality of communication for that personal station will be unacceptable.

  7. 2.2 Power Control (Continued) • If the received power is too high, communication quality for that personal station will be acceptable, but the interference caused by the personal station may result in unacceptable communication quality for other personal stations. • Because power control ensures that all personal station signals are received with the same power, it thus combats fading (the RAKE receiver is another method to combat fading). • In order to combat fading, the power control scheme must be able to track the changes in received power at the cell site. • The average personal station transmit power can be found by solving the link budget using the received power at the personal station.

  8. 2.2 Power Control (Continued) • The performance of a power control system depends on the power control algorithm, speed of the adaptive power control system, dynamical range of the transmitter, spatial distribution of users, and propagation statistics. • The allowable number of users is approximated by where b=0.1*ln10 m : mean of the lognormal power control s2 : variance of the lognormal power control

  9. 2.3 Digital Signal Processing Requirements • Received the Pilot Ec/No and Traffic Eb/No • Modulation/Demodulation • Synchronization • Searcher Engine ( Acquisition: coarse synchronization ) • Detection Probability based on Detector Threshold Values • False-Alarm Probability based on Detector Threshold Values • Rake Finger (Tracking: fine synchronization) • Chip synchronization • Carrier phase locking (for coherent systems) • Automatic Frequency Control • Average Time to Loss of Lock • Combining Algorithm (MRC, EGC, etc) • Transmit Diversity Techniques • Viterbi/Turbo Decoder

  10. 2.4 Fading Environments • Short-Term Fading (Multipath Fading) • Caused by mainly by multipath reflections by local scatters • Sum of Multipath reflected waves • Usually Rayleigh distribution

  11. 2.4 Fading Environments(Continued) • Long-Term Fading(Shadowing) • Caused mainly by terrain and man made environment • Envelop of the fading signal • Log-normal distributed, Standard deviation of 6~8dB

  12. 3. Benefits of 3GPP W-CDMA • Flexible, High-Rate Data Services/High Quality • Multi-rate services (AMR voice - 2Mbps) • High-Resolution video in addition to voice/fax • High-speed internet connection • Ability to send up to 384Kbps High speed data while moving • Up to 2Mbps throughput for fixed applications • Improved Multi-path resolution - High Capacity • High spectral efficiency due to better frequency diversity • Lower transmit power control error through Rake diverstiy • 5MHz BW is more immune to fading • No accurate base station synchronization needed

  13. 3.1 Basic Concept of 3GPP W-CDMA • Carrier Spacing : 5Mhz (Nominal) • Downlink RF Channel Structure : Direct Spread • Roll-off Factor for Chip Shaping : 0.22 • Radio Frame Length : 10msec • Spreading Factors : 4-256(UL), 4-512(DL) • Power Control : Open, Inner-Loop, Outer-Loop • Coherent Detection : Pilot Symbols/Channel

  14. Access scheme : Direct-Sequence Code Division Multiple Access (DS-CDMA) • FDD (Frequency Division Duplex) • Channel coding and interleaving : Convolutional Coding, Turbo Coding, No Coding • Spreading Modulation : QPSK • Data Modulation : QPSK(DL), BPSK(UL)

  15. Spreading • FDD mode: Gold codes with 10 ms period (38400 chips at 3.84 Mcps) used, with the actual code itself length 218-1 chips • Physical layer procedures • Cell Search • Physical layer measurements • Radio characteristics including FER, SIR, Interference power, etc., are measured and reported to higher layers and network.

  16. Radio interface protocol architecture around the physical layer

  17. FDD layer 1 functions relationships by specification

  18. 3.2 Synchronization of 3GPP • Timing • The 3GPP system has two timing modes: • Asynchronous operation - Original Mode • GPS Synchronized - Added after Harmonization • Asynchronous Mode : • Eliminates need for GPS Satellite Receivers • Allows Operation in Tunnels, Building, and Subways where Satellite reception is difficult • Requires greater search time, more difficult Handovers • GPS Synchronized Mode: • Simpler, Faster Searching to ease soft handover • Requires BS to receive GPS Satellite signals

  19. Synchronization Issues • Network Synchronization • relates to the stability of the clocks • Node Synchronization • relates to the estimation and compensation of timing differences among UTRAN nodes. • Transport Channel Synchronization • Defines synchronization of the frame transport between RNC and Node B, considering radio interface timing. • Radio Interface Synchronization • Relates to the timing of the radio frame • Time Alignment Handling • Minimize the buffer delay in RNC

  20. Synchronisation Issues Model

  21. 4. Vocoder • Waveform Coder • PCM • A/m -law PCM(G.711): Toll Quality, 64Kbps • ADPCM(G.726) : 32Kbps • LD-CELP (G.728) : 16Kbps • CS-ACELP(G.729) : 8Kbps • Q-CELP : 8Kbps, 13Kbps • EVRC : 8Kbps • AMR : 12.2/10.2/7.95/7.4/6.7/5.9/5.15/4.75Kbps

  22. General Description of AMR • Frame size: 20ms • 8 different bit rates, capable of switching every 20 ms • Source controlled rate operation: battery, average bit rate • Voice activity detector • Comport noise generator • Evaluation of the acoustic background noise • the noise parameter encoding/decoding (SID frames) • generation of the comfort noise in the receiver • Error concealment of lost frames • receiving the indication of lost frames • use predicted parameters from the previous ones • muting in case of several subsequent lost frames

  23. AMR(Ordering of Bits) • The bits delivered by the speech encoder are rearranged according to subjective importance before they are sent to the RAN • Class A • Data protected with the internal CRC and Error Protection scheme 1 (EP1). • Class B • Data protected with Error Protection scheme 2 (EP2). • Class C • Data protected with Error Protection scheme 3 (EP3).

  24. · Example for AMR with Source Controlled Rate UMTS_AMR GSM_EFR GSM_AMR RAB sub-flows Total size of bits/RAB sub-flows combination (Mandatory) Source rate RFCIExample 1 RFCIExample 2 RFCIExample 3 RAB sub- Flow 1 Optional) RAB sub- Flow 2 (Optional) RAB sub- Flow 3 (Optional) 2 2 42 53 0 95 AMR 4.75kbps 3 49 54 0 103 AMR 5.15kbps 4 3 55 63 0 118 AMR 5.9kbps 5 58 76 0 134 AMR 6.7kbps 6 4 61 87 0 148 AMR 7.4kbps 7 75 84 0 159 AMR 7.95kbps 8 5 65 99 40 204 AMR 10.2kbps 9 2 81 103 60 244 AMR 12.2kbps 1 1 39 0 0 39 AMR SID 1 47 0 0 47 GSM EFR SID 0 0 0 0 NO DATA

  25. 5. Layer 1 Channels of 3GPP W-CDMA • Transport Channels • Downlink Physical Channels • Uplink Physical Channels

  26. 5.1 Transport Channels • Transport Channels • Dedicated channels, using inherent addressing of UE • Common channels, using explicit addressing of UE if addressing is needed • Dedicated Channels • DCH : Dedicated Channel • downlink or uplink transport channel • Common Channels • Six types of common transport channels: BCH, FACH, PCH, RACH, CPCH and DSCH

  27. BCH(Broadcast channel) • Downlink transport channel • Used to broadcast system and cell-specific information • Transmitted over the entire cell with a low fixed bit rate • FACH(Forward Access Channel) • Downlink transport channel • Used to carry control information from the BS to the UE • Transmitted over the entire cell or over only a part of the cell using e.g. beam-forming antennas.

  28. PCH(Paging Channel)) • Downlink transport channel • Used to carry control information to a UE • Transmitted over the entire cell • Associated with the transmission of physical layer generated Paing Indicators to support efficient sleep-mode procedures • RACH(Random Access Channel) • Uplink transport channel • Used to carry control information from a UE to the BS • Received from the entire cell • Characterized by a collision risk

  29. CPCH(Common Packet Channel) • Uplink transport channel • Associated with a dedicated channel on the downlink which provides power control and CPCH control commands for the uplink CPCH • Used to carry small and medium sized packets • Characterized by initial collision risk • DSCH(Downlink Shared Channel) • Downlink transport channel • Associated with one or several downlink DCH • Transmitted over the entire call or over only a part of the cell using e.g. beam-forming antennas.

  30. Transport-channel to physical-channel mapping

  31. 5.2 Downlink Physical Channels • CPICH(Common Pilot Channel) • P-CCPCH(Primary Common Control Physical Channel) • S-CCPCH(Secondary Common Control Physical Channel) • SCH(Synchronization Channel) • AICH(Acquisition Indication Channel) • AP-AICH(CPCH Access Preamble Acquisition Indicator Channel)

  32. CD/CA-ICH(CPCH Collision Detection/Channel Assignment Indicator Channel) • PICH(Page Indication Channel) • PDSCH(Physical Downlink Shared Channel) • DPCH(Dedicated Physical Channel)

  33. CPICH • The CPICH is a fixed rate (30 kbps, SF=256) downlink physical channel that carries a pre-defined bit/symbol sequence. • Primary Common Pilot Channel (P-CPICH) • The same channelization code is always used for the P-CPICH. • The P-CPICH is scrambled by the primary scrambling code • There is one and only one P-CPICH per cell • The P-CPICH is broadcast over the entire cell.

  34. Secondary Common Pilot Channel (S-CPICH) • An arbitrary channelization code of SF=256 is used for the S-CPICH. • A S-CPICH is scrambled by either the primary or a secondary scrambling code • There may be zero, one, or several S-CPICH per cell • A S-CPICH may be transmitted over the entire cell or only over a part of the cell • A Secondary CPICH may be the reference for the Secondary CCPCH and the downlink DPCH

  35. Frame structure for Common Pilot Channel

  36. Modulation pattern for Common Pilot Channel (with A = 1+j)

  37. P-CCPCH • A fixed rate (30 kbps, SF=256) downlink physical channel • Used to carry the BCH transport channel • No TPC commands • No TFCI • No Pilot bits • Not transmitted during the first 256 chips of each slot • P-SCH and S-SCH are transmitted during this period

  38. Frame structure for Primary Common Control Physical Channel

  39. STTD encoding for the data bits of the P-CCPCH

  40. S-CCPCH • Used to carry the FACH and PCH • Two types of S-CCPCH • include TFCI • not include TFCI

  41. Frame structure for Secondary Common Control Physical Channel

  42. SCH • A downlink signal used for cell search • Consists of two sub channels : Primary and Secondary SCH • P-SCH • Constructed as a so-called generalized hierarchical Golay sequence • Is chosen to have good aperiodic auto correlation properties • S-SCH • Used to find frame synchronization and identify the code group of the cell

  43. Structure of Synchronisation Channel (SCH)

  44. Structure of SCH transmitted by TSTD scheme

  45. PSC • Define a = <x1, x2, x3, …, x16> = <1, 1, 1, 1, 1, 1, -1, -1, 1, -1, 1, -1, 1, -1, -1, 1> • The PSC is generated by repeating the sequence a modulated by a Golay complementary sequence, and creating a complex-valued sequence with identical real and imaginary components • The PSC Cpsc is defined as Cpsc = (1 + j)  <a, a, a, -a, -a, a, -a, -a, a, a, a, -a, a, -a, a, a>

  46. SSC • The 16 secondary synchronization codes (SSCs), {Cssc,1,…,C ssc,16}, are complex-valued with identical real and imaginary components, and are constructed from position wise multiplication of a Hadamard sequence and a sequence z, defined as: z=<b, b, b, -b, b, b, -b, -b, b, -b, b, -b, -b, -b, -b, -b> b=<x1, x2, x3, x4, x5, x6, x7, x8,-x9,-x10,-x11,-x12,-x13,-x14,-x15,-x16> • The k:th SSC, Cssc,k, k = 1, 2, 3, …, 16 is then defined as: Cssc,k = (1 + j)  <hm(0) z(0), hm(1) z(1), hm(2) z(2), …, hm(255) z(255)> where m = 16(k – 1)

  47. Primary & Secondary Sync

  48. PDSCH • Used to carry the Downlink Shared Channel • All the PDSCHs under the same PDSCH root channelization are operated with radio frame synchronization • PDSHs allocated to the same UE on different radio frames may have different spreading factors. • For PDSCH the allowed spreading factors may vary from 256 to 4.

  49. Frame structure for the PDSCH

  50. AICH • A fixed rate (SF=256) physical channel used to carry acquisition indicators • Acquisition Indicator AIs corresponds to signature s on the PRACH • The real valued symbols a0,…,a31 are given by where AIs, taking the values +1, -1, and 0, is the acquisition indicator corresponding to signature s and the sequence bs,0, …, bs,31

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