January 2006 doc IEEE 802 22 050094 r

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 System Description and Operation Principles for IEEE 802. 22 WRANs IEEE P 802. 22 Wireless RANs Date: 2006 -01 -16 Notice: This document has been prepared to assist IEEE 802. 22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802. 22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http: //standards. ieee. org/guides/bylaws/sb-bylaws. pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard. " Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802. 22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee. org. > Submission 1 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Abstract • • • • • OFDMA as the basic multiple-access scheme for both uplink and downlink Pre-transform for uplink to reduce peak-to-average power ratio (PAPR) TDD as the duplex mode, with adaptive guard time control to maximize the system throughput Distributed channel sensing using guard interval between dowlink subframe and uplink subframe The CPEs support the usage of single TV channel with variable channel bandwidth (6, 7 & 8 MHz) The BS supports the usage of multiple TV channels, either contiguous or discontiguous Scalable bandwidth ranging from 1. 25 MHz to 7. 5 MHz for each CPE Preamble and pilot design to avoid interference to primary users Shortened block Turbo codes (SBTC) with special parity check matrix design Supporting transmit power control (TPC) and adaptive modulation and coding (AMC) Adaptive antennas for interference avoidance and channel shortening Transmit diversity, random beamforming and virtual MIMO Cellular deployment and sectorization for enhanced channel capacity Sensing Mechanism using two-step sensing approach Frame structure for non-continuous sensing Block spreading for additional multiple access MAC Enhancement Submission 2 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 WRANs • Operate in the VHF/UHF TV bands using cognitive radio technology – Sensing before using – No fixed spectrum available • Co-exist with primary users, e. g. wireless microphone – Primary users have higher priority in channel usage • Coverage range as large as 100 km – Large delay spread – Long propagation delay Submission 3 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Two-Layer OFDMA • How? – 1 st Layer: FDMA -- User allocation to TV channels – 2 nd Layer: OFDMA -- Multiple access within each TV channel • Advantages: – Provide user orthogonality – Most suitable for irregular spectrum (discontiguous TV channels, partial TV channel) – Exploit multiuser diversity Submission 4 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA • A group of subcarriers is defined as a subchannel • Each user is allocated with one or more subchannels • Localized subchannel vs distributed subchannel • Localized subchannel preferable for avoiding interference to primary users Submission 5 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA Parameters Description B Chanel bandwidth N FFT size Number of used subcarriers, including DC subcarrier Oversampling factor Subcarrier spacing Tb Useful symbol duration Tc Cyclic prefix duration Ts =Tc+Tb OFDMA symbol duration Cyclic prefix factor Submission 6 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Scalable Design • Each CPE supports one TV channel usage – OFDMA – Scalable bandwidth ranging from 1. 25 MHz to 7. 5 MHz – Scalable for 6 MHz, 7 MHz and 8 MHz TV channels • BS supports the usage of multiple TV channels, either contiguous or discontiguous – Two-layer OFDMA for BS Submission 7 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Variable Bandwidths within one TV Channel Parameters Values Channel bandwidth 1. 25 MHz 2. 5 MHz 7. 5 MHz Sampling frequency* 1. 4286 MHz 2. 8571 MHz 5. 7143 MHz 8. 5714 MHz Sampling interval 0. 7 μs 0. 35 μs 0. 175 μs 0. 1167 μs FFT size 256 512 1024 1536 Subcarrier spacing 5. 5804 k. Hz Useful OFDMA symbol interval 179. 2 μs * Oversampling factor of 8/7 Submission 8 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Support Variable TV Channel Bandwidths of 6, 7 & 8 MHz • Option A: Fixed sampling frequency – Adding variable number of nulls • Option B: Variable sampling frequency – Keeping same number of useful subcarriers Submission 9 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Option A for Variable TV Bandwidth TV channel bandwidth 8 MHz 7 MHz Sampling frequency 7. 5 MHz*8/7 = 8. 5714 MHz FFT size 1536 6 MHz Number of useful subcarriers 1249 1145 937 Data/pilot subcarriers per subchannel 48/4 Number of subchannels 24 22 18 Submission 10 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Option A with Variable CP Length CP factor 1/16 1/8 1/4 3/8 * CP length 11. 2 μs 22. 4 μs 44. 8 μs 67. 2 μs OFDMA symbol interval 190. 4 μs 201. 6 μs 224 μs 246. 4 μs * optional, to support repeater applications Submission 11 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Option A: Minimum Peak Rates Downlink Uplink Channel bandwidth 1. 25 MHz Total No of subcarriers 256 No of used subcarriers 209 No of subchannels 4 No of data subcarriers per subchannel 48 No of pilot subcarriers per subchannel 4 No of subchannels per user 4 2 Minimum peak rates 1. 513 Mbps (QPSK, ¾ rate, 1/16 CP factor) 504 kbps (QPSK, ½ rate, 1/16 CP factor) Submission 12 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Option B for Variable TV Bandwidth TV channel bandwidth 8 MHz 7 MHz 6 MHz Sampling Frequency 8/7*8 = 9. 14 MHz 8/7*7 = 8 MHz 8/7*6 = 6. 86 MHz FFT size 1024 / 2048 Number of useful subcarriers 864 / 1728 CP length (28 / 14 / 7 us) / (56 / 28 / 14 us) Spectrum efficiency (With ~1/16 CP factor) 78% Number of subchannels 27 (32 / 64 subcarriers per subchannels) Submission 13 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Option B: System Parameters Submission 14 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 TDD as the Duplex Mode • Why TDD? – Difficult to identify paired spectrum for FDD • Drawback of TDD – Large BS TTG due to long propagation delay • Our proposals – Adaptive guard time control to increase system throughput – A sensing slot allocated for distributed channel sensing after DL subframe Submission 15 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Basic TDD Frame Structure Submission 16 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 DL Subframe • DL Preamble – transmitted in the first OFDMA symbol of the TDD frame – used by CPEs for time synchronization, frequency synchronization and channel estimation • FCH contains the Downlink Frame Prefix (DLFP) which specifies: – used subchannel bitmap, ranging channel indication, coding scheme for DL/UL-MAP, DL/UL-MAP length • DL-MAP specifies: – Frame duration (in # of OFDMA symbols) and frame number – Subchannel allocation for each DL burst (subchannel and symbol offsets). – Coding/modulation scheme used for each DL burst • UL-MAP specifies: – Subchannel allocation for each UL burst (subchannel and symbol offsets) – Coding/modulation scheme for each UL burst – UL-subframe start time for each burst (relative to the beginning of the frame) due to the use of adaptive TDD Submission 17 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 UL Subframe • Preamble is not necessary if pre-equalization is done at CPEs • Otherwise, the first OFDMA symbol of a UL burst is designed as the UL preamble • One subchannel can be assigned for ranging and BW request • A sensing slot after DL subframe is designed for BS and all CPEs to sense the primary users • Adaptive TDD is proposed to reduce required BS TTG Submission 18 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive TDD Frame Structure • Near-by users are allowed to transmit earlier than faraway users • Reduced BS TTG for increased throughput Submission 19 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive TDD S 1 S 2 S 3 S 4 S 5 S 6 CPE 1 G G pre G data G dat a CPE 2 G G G pre G data CPE 3 G pre G data CPE 4 G G CPE 5 G G pre S 7 S 8 S 9 G data G dat a G data G dat a G data G pre G data G dat a G dat a G data time CPE 3 is the nearest user while CPE 2 and CPE 4 are the farthest user. Submission 20 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Channel Sensing and Adaptive TDD TTG 2 TTG 1 BS DL Subframe TRS DL 1 CPE 2 UL 1 Sense DS 1 Tss SSRTG DL Subframe DL 2 DL 1 UL 2 Sense DS 2 Tss SSRTG DL 2 T ss = n * Tb, n = 1, 2, 3… TTG 1 > TRS + Tss TTG 2 – TTG 1 = k * Ts, k = 1, 2, 3… A sensing slot after DL subframe for BS and CPEs to sense the channel Submission UL 2 Tss DL Subframe CPE 1 UL 1 Sense 21 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Sensing Duration = 100 ~ 200 us Sensing Frequency = 200~300 Hz Other Channel Sensing Options CPE Sensing Submission BS Sensing 22 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Sensing Duration = 100 ~ 200 us Sensing Frequency = 200~300 Hz Other Channel Sensing Options CPE Sensing BS Sensing (at distributed subcarrier positions) Submission 23 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Channel Sensing Using Null Subcarriers Submission 24 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA Transmitter for BS Preamble Pilot Data 1 Data K Randomizer Submission FEC Encoder Interleaver Symbol Mapper Pre-transform. . . Symbol Mapper Two-layer OFDMA Formulator Windowing & Pulse Shaping Pre-transform 25 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA Transmitter for CPE Preamble/ Pilot Data Randomizer FEC Encoder Interleaver Symbol Mapper Pre-transform . . . OFDMA Formulator Windowing & Pulse Shaping Zeros Submission 26 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Randomizer • • Only information bits are randomized but preambles are not randomized Information of sub-channel offset and symbol offset are used to initialize the state of the randomizer for different data block. Submission 27 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 FEC Encoder: Convolutional Code (CC) • Native code: – Rate ½ with constraint length: 7 – Generator polynomials: 171 oct, 133 oct • Other coding rates through puncturing – 2/3, ¾, 5/6 Submission 28 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 FEC Encoder: Block Turbo Code (BTC) • Component code – Extended Hamming code • Native code: (16, 11), (32, 26) and (64, 57) • Other code rate through shortening – Parity check code • (8, 7) and (16, 15) Submission 29 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Parity Check Matrices for Hamming Codes N’ = 15 K’ = 11 N’ = 31 K’ = 26 N’ = 63 K’ = 57 Special parity check matrix design simplifies the decoding complexity. The syndrome value gives the error position, thus, look-up table is not needed. Submission 30 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Shortened Block Turbo Code (SBTC) Structure Submission 31 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Data Payload for One Subchannel: SBTC Modulation Scheme Encoding Rate QPSK ~1/2 ~2/3 6/1 ~3/4 16/3 23/4 ~5/6 ~1/2 ~2/3 16 -QAM ~1/2 ~2/3 ~3/4 64 -QAM ~5/6 ~1/2 12 20/2 25/3 16/1 16/2 25/2 35/4 24 20/1 16/1 23/2 Submission 25/1 36 48 35/2 60 31/5 40/6 Coded Bytes ~2/3 9/1 16/2 Allowed Data (Bytes) / No of symbols 8 PSK 40/4 40/3 32 40/2 72 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Interleaver s: half of the number of coded bits per subcarrier k: the index of the coded bit before the first permutation i: index after the first and before the second permutation j: index after the second permutation Ncbps: number of coded bits per encoded block • First permutation (Block interleaver) i = (Ncbps/16) (k mod 16) + floor(k/16) k = 0, 1, …, Ncbps – 1 • Second permutation (Interleaving within the modulated symbol) j = s × floor(i / s) + (i + Ncbps – floor(16 i / Ncbps)) mod s i = 0, 1, … Ncbps – 1 Submission 33 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Pre-Transforms 0 0 0 S/P Transform (size M) IFFT 0 0 (size N) P/S Cyclic Prefix 0 0 0 Localized or distributed mapping Applicable to both UL and DL Submission 34 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Pre-Transforms • Transform matrix: – DFT matrix multiplied by diag(1, α, …, α M-1), α = exp(-jπ/2 M) or 1 – Walsh-Hadamard matrix – Identity matrix • Uplink – Single carrier system if DFT matrix is used – Localized FDMA vs Interleaved FDMA – Low PAPR Interleaved FDMA A B C A B C Frequency Localized FDMA A B C Frequency Submission 35 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive Modulation and Coding (AMC) • Modulation schemes: – Downlink: QPSK, 16 -QAM, 64 -QAM, 256 QAM – Uplink: BPSK, QPSK, 8 -PSK, 16 -QAM, 64 QAM • Code rates (CC and BTC): – 1/2, 2/3, 3/4, 5/6 – Convolutional Codes (CC) and Block Turbo Codes (BTC) Submission 36 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Variable Throughput (1. 25 MHz, Downlink) Modulation 16 -QAM 64 -QAM 256 -QAM Submission Data rate (in Mpbs) for different CP factor 3/8 1/4 1/8 1/16 ½ 0. 779 0. 857 0. 952 1. 008 2/3 1. 039 1. 143 1. 270 1. 345 ¾ 1. 169 1. 286 1. 429 1. 513 5/6 1. 299 1. 429 1. 587 1. 681 ½ 1. 558 1. 714 1. 905 2. 017 2/3 2. 078 2. 286 2. 540 2. 689 ¾ 2. 338 2. 571 2. 857 3. 025 5/6 2. 597 2. 857 3. 175 3. 361 ½ 2. 338 2. 571 2. 857 3. 025 2/3 3. 117 3. 429 3. 810 4. 034 ¾ 3. 507 3. 857 4. 286 4. 538 5/6 3. 896 4. 286 4. 762 5. 042 ½ 3. 117 3. 429 3. 810 4. 034 2/3 4. 156 4. 571 5. 079 5. 378 ¾ 4. 675 5. 143 5. 714 6. 050 5/6 5. 195 5. 714 6. 349 6. 723 37 Ying-Chang Liang, Institute for Infocomm Research minimum downlink peak rate QPSK Code rate

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Variable Throughput (1. 25 MHz, Uplink) Modulation BPSK 16 -QAM 64 -QAM Submission Data rate (in Mpbs) for different CP factor 3/8 1/4 1/8 1/16 ½ 0. 195 0. 214 0. 238 0. 252 2/3 0. 260 0. 286 0. 318 0. 336 ¾ 0. 292 0. 321 0. 357 0. 378 5/6 0. 325 0. 357 0. 397 0. 420 ½ 0. 390 0. 429 0. 476 0. 504 2/3 0. 520 0. 571 0. 635 0. 672 ¾ 0. 584 0. 643 0. 714 0. 756 5/6 0. 649 0. 714 0. 794 0. 840 ½ 0. 779 0. 857 0. 952 1. 008 2/3 1. 039 1. 143 1. 270 1. 345 ¾ 1. 169 1. 286 1. 429 1. 513 5/6 1. 299 1. 429 1. 587 1. 681 ½ 1. 194 1. 286 1. 429 1. 513 2/3 1. 559 1. 715 1. 905 2. 017 ¾ 1. 754 1. 929 2. 143 2. 269 5/6 1. 948 2. 143 2. 381 2. 521 38 Ying-Chang Liang, Institute for Infocomm Research minimum uplink peak rate QPSK Code rate

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Transmit Power Control (TPC) • Objectives of TPC – Maintaining the reliability of communication when there are changes in channel and propagation conditions. – Conserving power while reducing interference. • Transmitters must support monotonic TPC with range of up to 30 d. B, 1 d. B steps, and ± 0. 5 d. B accuracy. • Transmit power control will be supported on link-bylink basis Submission 39 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Preamble and Pilot Design q DL preamble q Time synchronization, frequency synchronization and channel estimation q UL preamble q channel estimation q DL and UL pilot allocations in each OFDMA symbol for channel parameter estimation and tracking q Preamble and pilot design avoiding interference to primary users Submission 40 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 DL Preamble • The first OFDMA symbol of DL subframe – Periodic with period N/2 in time domain – The locations of active subcarriers are: 2 k, k=0, 1, …, N/2 -1. • If the subcarrier coincides with the DC or a guard subcarrier, or a subcarrier used by a primary user, set the value on the subcarrier to zero. • Use a PN sequence to generate the values for the active subcarriers. – Low PAPR consideration – Each cell uses a different PN Submission 41 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 UL Preamble • UL preamble may be not necessary if preequalization is done at CPE, otherwise, a preamble is needed for channel estimation • Each user sends a user dependent preamble to the BS to aid the estimation of channels at the BS. – Constructed from the basic preamble by setting all the subcarriers which are not allocated to the user as null subcarriers • If the subcarrier is used by a primary user, set the value on the subcarrier to zero. • Use a PN sequence to generate the values for the active subcarriers – Low PAPR consideration – Each cell uses a different PN Submission 42 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Pre-Equalization for Uplink • The wireless channel usually changes slowly, we can use the channel estimated based on the downlink preamble to do preequalization for uplink. • Let H(k, n) be the frequency domain channel response for user k at subcarrier n. The pre-equalized signal for user k is – where s(k, n): modulated symbol for user k at subcarrier n B(k): subcarrier index set for user k p(k, n): power constraint factor such that (C(k) is the power for user k) Submission 43 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 DL Pilot • There are N/16 pilot subcarriers spread over the whole spectrum • Two types of pilots – Fixed-location pilots: Subcarrier locations for the fixed location pilots remain unchanged in every OFDMA symbol. – Variable-location pilots: subcarrier locations for the variable location pilots change in every four OFDMA symbols. • N/64 fixed-location pilots (1 for each subchannel) – Locations: 52 k+1 and N/2+(3 N/32)+52 k+1, k=0, 1, …, N/128 -1. • (N/16 -N/64) variable-location pilots (3 for each subchannel) – Locations: 13 k+3(L mod 4)-5 and N/2+(3 N/32)+13 k+3(L mod 4)-5, k=0, 1, …, N/32 -1 (k is not divisible by 4). (L is the OFDMA symbol index. ) • In all cases, if the pilot subcarrier coincides with a subcarrier used by a primary user, set the value on the pilot subcarrier to zero Submission 44 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 DL Pilot Subcarrier Allocation (N =256) Fixed pilot 1 53 153 205 Variable pilot (symbol 0) 8 21 34 60 73 86 160 173 186 212 225 238 Variable pilot (symbol 1) 11 24 37 63 76 89 163 176 189 215 228 241 Variable pilot (symbol 2) 14 27 40 66 79 92 166 179 192 218 231 244 Variable pilot (symbol 3) 17 30 43 69 82 95 169 182 195 221 234 247 Submission 45 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 UL Pilot • The subcarriers are first divided into clusters with each cluster having 13 subcarriers. • Each cluster has one pilot subcarrier. • The pilot location is varying in three OFDMA symbols. – The location in a cluster is: 4(L mod 3)+3, L is the OFDMA symbol index. • If the pilot subcarrier coincides with a subcarrier used by a primary user, set the value on the pilot subcarrier to zero. Submission 46 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Multiple Antenna Technologies • Transmit diversity – Robustness to fading effect • Transmit beamforming – Range extension – Interference avoidance – Delay spread reduction • Spatial multiplexing – Increased throughput for dedicated users • Virtual MIMO and random beamforming – Increased system throughput Submission 47 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Cyclic Delay Transmission Frequency diversity achieved by FEC ! Submission 48 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Space-Frequency Coding (SFC) Submission Subcarrier 1 Subcarrier 2 Ant 1 S(1) -S*(2) Ant 2 S(2) S*(1) 49 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Switched-beam Beamforming + CDT/STBC • Downlink transmission (Localized) • Two eigenbeams (switched beams) transmitted at a time • Data transmitted at one beam cyclic delayed version at another beam • Achieve diversity and beamforming gain simultaneously Base CPE 1 Submission 50 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Interference Avoidance to Primary Users (PUs) • Beamforming to avoid interference to PU – Use geographic knowledge of the primary user – Frequency planning • CPE 2 uses frequencies unoccupied by PU for communication • Frequencies occupied by PU can be allocated to CPE 1& CPE 3 Submission 51 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Delay Spread Reduction • For channels with large delays – Repeater applications – Large cell size • Solutions – Basic transmit beamforming (BTB) and advanced transmit beamforming (ATB) – Exploits spatial domain as different reflectors usually have different direction of departure (DOD) w. r. t. transmitter Submission 52 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Basic Transmit Beamforming (BTB) • In DL, beamformer only directs transmission to the path/cluster with the strongest gain per user. • Other directions are suppressed – reducing overall delay • Frequency domain beamforming for each user (subchannel) – different directions Submission 53 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Advanced Transmit Beamforming (ATB) • More than one beam transmitted per user in DL. • If overall channel delay in excess of CP length, relatively delay of each beam may be adjusted to suit CP length. • Can also be used to increase delay diversity • A repeater behaves like an additional delay path with known direction – can use ATB to mitigate extra delay introduced by repeater. Submission 54 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 ATB Beam 1 Reflector 1 Or repeater. Delay 1 T CPE 1 = τ1+ D 1 Overall Delay |T 1 -T 2| +δ Stream 1 Stream 2 Pre-alignment & beamforming Beam 2 Reflector 2 Delay 2 T 2 = τ2+ D 2 Local scatters Or repeater By adjusting timings D 1 and D 2, the overall delay of the channel can be changed. Submission 55 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 ATB: Channel Shortening and Lengthening Submission 56 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Virtual MIMO • Uplink • Multiple Antennas at BS and single antenna at each CPE • Multiple CPEs share the same physical channel • Spectrum efficiency increase linearly with CPE number if the CPE number is less than the number of BS antennas Base CPE 1 CPE 2 Submission 57 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Random Beamforming for MIMO • Randomly pick up one beamforming matrix, it will hit somebody if there are many users within the cell! • When the user is hit and scheduled, it seems that the BS knows the CSI of that user. • Equal rate for all data streams using TPC • Multiuser diversity gain BS Submission 58 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Random Beamforming for MIMO Pilot Sp(n) Data Pp xp(n) Pp xk(n) Data u 1(n) H 1 Q 1 H … z 1(n) DFE y 1(n) . . . u. M(n) HM Pilot mode Sk(n) Pilot QMH z. M(n) DFE y. M(n) uk(n) Hk Qk H zk(n) DFE yk(n) Data mode: User k is scheduled for transmission Submission 59 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Random Beamforming: Pilot Mode Training sequences BS CPE Random beamformer generator ZF-GDFE receiver Random beamformer SINR measurement SINR calibration using power control Proportional fairness scheduling Submission Feedback requested rate & power allocations 60 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Sectorization • Each cell is divided into multiple sectors • Each sector is covered by one sector or more antennas • Frequency reuse 1 except sector edge users • Inter-sector diversity is achieved for sector edge users using CDT or STBC • If designed properly, sector-specific scrambling codes can be used to achieve frequency diversity Submission 61 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Inter-Sector Diversity Submission 62 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Sensing Mechanism • Two-step sensing – Step 1: energy detection • If EP > TH 1, then decide that PU present • If EP < TH 2, then decide that PU absent • If TH 2≤EP≤TH 1, then proceed to step 2 – Step 2: cyclostationary detection • Compute SCD at selected cyclic frequencies • If average energy of SCD, EC > TH 3, then decide PU present • Tentative decisions perform at the sensing unit. Decision fusion performed at the decision unit. Submission 63 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Frame Structure for Non-continuous Sensing • Distributed (non-continuous) sensing Super frame = n * frames DL/S/UL Frame 0 DL Submission DL/S/UL Frame 1 Frame n Sensing UL 64 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Advantages of Non-Continuous Sensing • Reduce data transmission latency/jitter due to sensing. • Detect incumbent users quicker. • Take advantage of time diversity to detect incumbent users more reliably. Submission 65 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA with Block Spreading • Relaxes stringent power amplifier requirement by making transmission continuous 0 Mapped Symbols from SS 0 0 IFFT P/S (size = NFFT) Cyclic Prefix Block Spread 0 0 0 Submission 66 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA with Block Spreading • Transmitter (time domain implementation) Mapped Symbols from SS Submission Repetition Phase Rotation 67 Cyclic Prefix Block Spread Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA with Block Spreading OFDM Block CP Spreading Code c 1 c 2 c. K Submission CP Block 1 CP Block 2 P/S CP Block 1 CP Block K 68 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA with Block Spreading • Reference Receiver Received Signal Submission Block Despread Remove cyclic Prefix 69 FFT Frequency domain Processing Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 OFDMA with Block Spreading • Block de-spreading in Reference Receivers CP CP Block 1 CP Block K P/S CP Submission c 1 70 c. K CP Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 MAC Enhancements to IEEE 802. 22 • Based on IEEE 802. 16 -2004 MAC Protocol • Enhancement: – Dynamic channel sensing slots allocations – Adaptive & rapid ARQ in dynamic virtual control channel Submission 71 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Sensing Requirements • The channel has to be sensed from time to detect whether the channel is being used by the TV broadcast. (required by the 802. 22) – Sensing Duration: 100 - 200 μs. – At least N samples within a required time duration T. • In the following design, we assume the TV signal is continuous wave. Submission 72 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Sensing Method • Periodical sensing with fixed interval. – Advantage: simple in design and implementation. – Shortcoming: not flexible. Submission 73 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Dynamic sensing slot allocation with deadline • Dynamic sensing – Perform the channel sensing more frequent when the channel is idle. – When channel is busy, the sensing interval must meet a predefined maximal value. – Advantage: can reduce the data packet delay and shorten the detection time. Submission 74 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Dynamic sensing slot allocation with deadline Submission 75 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive & Rapid MAC ARQ in Dynamic Virtual Control Channel • ARQ (Automatic Retransmission Request) is the means by which either end of the link can request the retransmission of part of a frames, generally as a result of it being received erroneously. • ARQ In General: - to overcome unreliable channel condition by performing retransmission to ensure reliable delivery to next hop entity. - optional mechanism in current 802. 16. - beneficial for delay sensitive frames which require timely delivery. ARQ = = Reliability & Timeliness Submission 76 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive & Rapid MAC ARQ in Dynamic Virtual Control Channel • Requirements for optimum ARQ mechanism: – Efficient - to utilize and reserve slots for ARQ transmission when necessary so as to be cost-effective. -Adaptive - to utilize resources efficiently e. g. to perform retransmission in an “intelligent” manner ARQ would be beneficial in fluctuating channel condition but not in permanent blockage scenario. - Responsive - to enable rapid retransmission to meet the delay Qo. S requirements, feedback to sender entity has to be fast and reliable Submission 77 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel • In summary, a good ARQ mechanism must have the following traits: Cost-Effective Intelligent Fast Reliable Submission 78 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel 802. 16 ARQ algorithm is not specified and is implementation specific. Possible methods to implement ARQ in mesh mode 802. 16: - Scheme A: Piggy-backed to schedule control messages, which will be send out regularly in the Control sub-frame, based on the holdoff exponent value configured. - Scheme B: Send as normal data in Data sub-frame which required Bandwidth Request/Grant/Confirm process. Submission 79 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel Deficiencies with 802. 16 ARQ: Scheme A: Piggy-backed method - Dependent on holdoff exponent values. With a high exponent value configured, the time interval between successive schedule control message will be large Slow-Responsiveness for ARQ. - Schedule control message size is limited by one time slot and the amount of information transmitted composed of Scheduling, Request, Grant and Time Slot Availability IEs (Information Elements). Embedding of ARQ information would be limited by the available resources and as a result will be delayed Slow Responsiveness for ARQ. - Schedule control message for each node is limited to once per frame. Thus, when an receiver entity receives data in a time slot after it has sent out its schedule control message (within the same frame), the receiver entity can only send out the ARQ information in the subsequent frame of the receiver entity’s schedule control message transmission. Slow Responsiveness for ARQ. Submission 80 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel Deficiencies with 802. 16 ARQ: Scheme B: Send as data - The overall process of securing the time slot for ARQ message transmission will go through the process of BW Request/Grant/Confirm. The delay encountered would be even more severe than Scheme A Slow Responsiveness of ARQ. Submission 81 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel • Deficiencies with 802. 16 ARQ: Common for both Scheme A & B - ARQ scheme of 802. 16 does not specify how to handle retransmission in a long fading environment. Currently, retransmission will be persistent for a fixed number of times with interval of retransmission based upon BW Request/Grant/Confirm process. In the case when the network is facing long fading, the aggressiveness of the ARQ should be reduced, so as to make efficient use of wireless resources intelligent ARQ. Submission 82 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel • Proposed ARQ for 802. 22 MAC adapted from 802. 16 specification: –A separate virtual control channel (VCC) to handle ARQ messages which will be adaptively allocated by the BS based upon the number of flows which require timely Qo. S. – When timely Qo. S is required by many SS, the BS will allocate more time slots for the virtual control channel. This is to ensure, the SS has faster responsiveness by ensuring faster slot allocation of the virtual control channel time slots. – When timely Qo. S is not required by all SS, the BS will release the virtual control channel timeslot back for normal data usage. In summary: VCC will ensure efficient usage of wireless resource by having the BS allocating resource intelligently. Submission 83 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel • Proposed ARQ for 802. 22 MAC adapted from 802. 16 specification: – Slot reservation of VCC resources will be made using existing 802. 16 Mesh Election or some other centralized algorithms which is more appropriate. Thus, no Bandwidth Request/Grant/Confirm is required. –An SS which is active (acting as receiver), would invoke Mesh Election to secure time slot in VCC to send back ARQ feedback. – An inactive node will not “bid” for the VCC resources. In summary: VCC will ensure efficient usage of wireless resource by having the SSs invoking VCC resource reservation intelligently and efficiently. Submission 84 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel • Proposed ARQ for 802. 22 MAC adapted from 802. 16 specification: – To ensure responsiveness, each SS can obtained more than one VCC time slot within a frame. As an SS received more traffic flows, the frequency of obtaining the VCC timeslot will be increased, so as to ensure rapid ARQ feedback can be made. In summary: VCC will ensure rapid ARQ feedback by adjusting the frequency of VCC slots acquisition based on traffic volume it is accepting. Submission 85 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 Adaptive and Rapid MAC ARQ in Dynamic Virtual Control Channel • Other ARQ enhancements: – To ensure efficient usage of data channel resource in scenario whereby an SS is facing blockage or experiencing long fading duration, the data channel reservation process will intelligently perform exponential backoff in sending out BW Request. This will ensure efficient resource utilization for the Schedule Control resources. Submission 86 Ying-Chang Liang, Institute for Infocomm Research

January 2006 doc. : IEEE 802. 22 -05/0094 r 4 References [1] IEEE 802. 22 Wireless RAN, Functional Requirements for the 802. 22 WRAN Standard, IEEE 802. 22 -05/0007 r 46, October 2005. [2] IEEE 802. 16 -2004. IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems, 2004. [3] ETSI EN 300 744 V 1. 5. 1 (2004 -11) Digital Video Broadcasting (DVB): Framing structure, channel coding and modulation for digital terrestrial television Submission 87 Ying-Chang Liang, Institute for Infocomm Research