Wi Max Phy Introduction V0.3
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Wi Max Phy Introduction V0.3

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  • 1. Understanding WiMAX PHY BP Tiwari beyond4g.org 1
  • 2. Agenda  OFDMA  WiMAX Frame  Sub channels and Permutations  Smart Antenna Systems  Summary of WiMAX PHY features Beyond 4G 2 WIMAX Series – Understanding PHY
  • 3. Lets understand fading in wireless communications Frequency selective fading ( Fading (Delay Spread) MULTIPATH FADING CHANNELS Delay Spread) Delay Spread) Time Selective Fading ( Doppler ) Multiple copies of signal arrive at the receiver, offset in time Beyond 4G 3 WIMAX Series – Understanding PHY
  • 4. WiMAX Addresses Fading Frequency selective fading ( Fading (Delay Spread) Delay Spread) OFDMA Diversity Schemes Multiple Antenna Systems Multiple copies of signal arrive at the receiver, offset in time Cyclic Prefix ( ISI ) Forward Error Correction Beyond 4G 4 WIMAX Series – Understanding PHY
  • 5. Concept of OFDM Subcarrier  In OFDM available  OFDM is robust to fading bandwidth is divided  High spectral efficiency into N (large number  Eliminate Inter-symbol of) orthogonal sub- Interference (ISI) by the carriers introduction of the cyclic  Each sub-carrier is prefix (CP) individually modulated  Sensitivity to frequency (QAM) at 1/N total offset data rate  Higher Peak to average  FFT implementation power ratio(PAPR) (fast and efficient) Beyond 4G 5 WIMAX Series – Understanding PHY
  • 6. OFDM vs. OFDMA  Subcarrier SC – Type: Data, Pilot, null (guard and DC)• – Number: 128, 512, 1024, OFDM 2048 (at least one) OFDMA Subcarrier  Subchannel – A set of sub carriers forms a subchannel – The sub carriers may and may not be adjacent Subchannels – Distributed allocation (diversity) – Contiguous allocation (selectivity) Beyond 4G 6 WIMAX Series – Understanding PHY
  • 7. OFDMA Advantages •Orthogonality of users are maintained A A E E using large symbol duration and cyclic prefix SUBCHANNEL B B B B C C C C •Users concentrate transmit power over partial bandwidth D D D D •High granularity in resource allocation TIME & power control •Inherent resistance to multi-path • Users/bursts are scheduled (OFDM) across both frequency (subchannels)and time (symbols) •Flexible Sub-channelization • Per burst modulation, coding •Distributed (pseudo-random) and TX power permutations –frequency diversity • Higher granularity in resource •Contiguous (clustered) allocation permutations -> selectivity • More degrees of freedom in scheduling •Scalability of Channel Sizes • Improved fairness and QoS Beyond 4G 7 WIMAX Series – Understanding PHY
  • 8. OFDM Symbols and Cyclic Prefix  Pilots used for channel  Use Cycle Prefix (CP) as estimation and tracking guard interval  Interleaving (bits  Prepend segment of distributed across tones) OFDM symbol –> and error correcting overhead facilitates recovery under frequency selective fading  CP duration > max delay spread or narrow-band interference  Eliminates ISI  Retains orthogonally between sub-carriers (ICI) Beyond 4G 8 WIMAX Series – Understanding PHY
  • 9. OFDMA Frame Structure CQICH  Uplink and Downlink is s divided into time zones UL- Different Permutation UL BURST 3 S MAP DL BURST 4  U B P ACKCH ’s for downlink and uplink C R H A E A DL- – DL PUSC,AMC etc N – UL PUSC,AMC M MAP N P B C E e L DL BURST 1 D UL BURST 2 L ri S E M A o d – Activation STC/MIMO R CDMA Codes i DL BURST 3 A N C R  G a DL BURST 2 I N n g UL BURST 1 – Special allocation in G . uplink for ranging and BW Request S1 S2 Sn DOWNLINK TTG UPLINK  RTG Fast Feedback/CQICHs – SS measured CINR Beyond 4G 9 WIMAX Series – Understanding PHY
  • 10. Localized vs Distributed Sub channels Beyond 4G 10 WIMAX Series – Understanding PHY
  • 11. Subchannels in 16e  DL PUSC – 1 cluster = 14 adjacent subcarriers x 2 OFDM symbols – 1 subchannel = 28 subcarriers – 1 slot = 1 subchannel x 2 OFDM symbols – 1 slot = 56 subcarriers = 48 data subcarriers + 8 pilots  UL PUSC  DL/UL AMC2X3 – 1 tile = 4 subcarriers x 3 OFDM symbols – 1 bin = 9 subcarriers x 1 OFDM symbols – 1 subchannel = 6 tiles (frequency domain) – 1 subchannel = 2 bins (frequency domain) – 1 slot =1 subchannel x 3 OFDM symbols – 1 slot = 1 subchannel x 3 OFDM symbols – 1 slot = 72 subcarriers – 1 slot = 54 subcarriers = 48 data subcarriers + 24 pilots = 48 data subcarriers + 6 pilots Beyond 4G 11 WIMAX Series – Understanding PHY
  • 12. Permutation schemes in DL : PUSC Sym 2 Cluster Sym 2 Sym 2 Sym 2 Sym 2 Beyond 4G 12 WIMAX Series – Understanding PHY
  • 13. Permutation schemes in UL : PUSC Tile Structure 3 SYMBOLS • 4 Sub carrier X 3 Symbol • 4 Pilot + 8 Data Pilot Sym 3 Sym 3 Sym 3 Sym 3 Beyond 4G 13 WIMAX Series – Understanding PHY
  • 14. PHY Data Rates  Without MIMO and overheads Beyond 4G 14 WIMAX Series – Understanding PHY
  • 15. Advanced Antenna Systems : STBC  STC gains vary from 5-10 db depending on channels condition Beyond 4G 15 WIMAX Series – Understanding PHY
  • 16. MIMO B : Spatial Multiplexing  SM can double throughput in theory by require very high CINR conditions of uncorrelated signal to achieve full advantages. 30% sector improvement in loaded conditions. Beyond 4G 16 WIMAX Series – Understanding PHY
  • 17. Beam forming  Beamforming can provide additional 5-6 db gains in downlink improving overall network quality.  Improves sector capacity by 20 to 25%  4Rx in uplink provides additional 3 db gain Beyond 4G 17 WIMAX Series – Understanding PHY
  • 18. UL Collaborative MIMO  Collaborative Spatial Multiplexing for two MSs with single transmit antenna  Two MS transmit on the same resource (sub channels)  For orthogonal zing – Orthogonal pilot patterns (pattern A, pattern B)  Multiple data detection – Using multiple receive antennas – Interference suppression: MMSE, ZF – Nonlinear interference cancellation: SIC, PIC Beyond 4G 18 WIMAX Series – Understanding PHY
  • 19. MIMO Summary Parameters Gain in Link Gain in Comments Budget Capacity MIMO A 5-10* MIMO A in low SINR condition improves channel fading. Switching between MIMO A and B is automatic and controlled by BTS. MIMO B Nil 30% in Average improvement of 30% in average full load , customers higher CINR or uncelebrated signals will take advantage of MIMO B DL-Beam 5-6 db in 20 to 25% BF helps in improving capacity Forming Downlink over MIMO and improve network quality. 4th order 3 db over 2nd Nil Improves cell radius by 3db in Diversity order uplink. diversity *STC + 2 Rx in receiver with possibility MRC combining Beyond 4G 19 WIMAX Series – Understanding PHY
  • 20. Mobile WiMAX PHY Summary Feature Support Scalable Channel TDD , 5 and 10 MHz , 20 (optional) Bandwidth Frame size and cyclic 5 ms , 1/8 prefix Sub-carrier allocations PUSC,AMC,FUSC Error correction and CC, CTC with HARQ HARQ Modulation Downlink :QPSK,16QAM,64QAM Uplink : QPSK, 16QAM Uplink Control channels Ranging , CQICH’s , ACKCH MIMO Downlink : 2x2 , STC , SM Uplink : 1X2 , Virtual SM BeamForming AMC or PUSC UL channel sounding Beyond 4G 20 WIMAX Series – Understanding PHY
  • 21. Thanks Beyond 4G 21 WIMAX Series – Understanding PHY