System Description and Operation Principles for IEEE 802.22 WRANs November 2005 doc.: IEEE 802.22-05/0094r0 January 2006 System Description and Operation Principles for IEEE 802.22 WRANs IEEE P802.22 Wireless RANs Date: 2005-11-07 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. > Ying-Chang Liang, Institute for Infocomm Research Y.-C. Liang, Inst. for Infocomm Research

November 2005 doc.: IEEE 802.22-05/0094r0 January 2006 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 & 8MHz) 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 Ying-Chang Liang, Institute for Infocomm Research Y.-C. Liang, Inst. for Infocomm Research

WRANs Operate in the VHF/UHF TV bands using cognitive radio technology January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Two-Layer OFDMA How? Advantages: January 2006 Two-Layer OFDMA How? 1st Layer: FDMA -- User allocation to TV channels 2nd 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 Ying-Chang Liang, Institute for Infocomm Research

OFDMA A group of subcarriers is defined as a subchannel January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

OFDMA January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Scalable Design Each CPE supports one TV channel usage January 2006 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, 7MHz and 8MHz TV channels BS supports the usage of multiple TV channels, either contiguous or discontiguous Two-layer OFDMA for BS Ying-Chang Liang, Institute for Infocomm Research

Variable Bandwidths within one TV Channel January 2006 Variable Bandwidths within one TV Channel Parameters Values Channel bandwidth 1.25 MHz 2.5 MHz 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 kHz Useful OFDMA symbol interval 179.2 μs * Oversampling factor of 8/7 Ying-Chang Liang, Institute for Infocomm Research

Support Variable TV Channel Bandwidths of 6, 7 & 8MHz January 2006 Support Variable TV Channel Bandwidths of 6, 7 & 8MHz Option A: Fixed sampling frequency Adding variable number of nulls Option B: Variable sampling frequency Keeping same number of useful subcarriers Ying-Chang Liang, Institute for Infocomm Research

Option A for Variable TV Bandwidth January 2006 Option A for Variable TV Bandwidth TV channel bandwidth 8 MHz 7 MHz 6 MHz Sampling frequency 7.5MHz*8/7 = 8.5714 MHz FFT size 1536 Number of useful subcarriers 1249 1145 937 Data/pilot subcarriers per subchannel 48/4 Number of subchannels 24 22 18 Ying-Chang Liang, Institute for Infocomm Research

Option A with Variable CP Length January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Option A: Minimum Peak Rates January 2006 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 No of subchannels per user 2 Minimum peak rates 1.513 Mbps (QPSK, ¾ rate, 1/16 CP factor) 504 kbps (QPSK, ½ rate, 1/16 CP factor) Ying-Chang Liang, Institute for Infocomm Research

Option B for Variable TV Bandwidth January 2006 Option B for Variable TV Bandwidth TV channel bandwidth 8 MHz 7 MHz 6 MHz Sampling Frequency 8/7*8 = 9.14MHz 8/7*7 = 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) Ying-Chang Liang, Institute for Infocomm Research

Option B: System Parameters January 2006 Option B: System Parameters Ying-Chang Liang, Institute for Infocomm Research

TDD as the Duplex Mode Why TDD? Drawback of TDD Our proposals January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Basic TDD Frame Structure January 2006 Basic TDD Frame Structure Ying-Chang Liang, Institute for Infocomm Research

DL Subframe DL Preamble January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Adaptive TDD Frame Structure January 2006 Adaptive TDD Frame Structure Near-by users are allowed to transmit earlier than far-away users Reduced BS TTG for increased throughput Ying-Chang Liang, Institute for Infocomm Research

CPE3 is the nearest user while CPE2 and CPE4 are the farthest user. January 2006 Adaptive TDD S1 S2 S3 S4 S5 S6 S7 S8 S9 CPE1 G pre data CPE2 CPE3 CPE4 CPE5 time CPE3 is the nearest user while CPE2 and CPE4 are the farthest user. Ying-Chang Liang, Institute for Infocomm Research

Channel Sensing and Adaptive TDD January 2006 Channel Sensing and Adaptive TDD TTG2 TTG1 BS DL Subframe Sense UL 1 UL 2 TRS Tss CPE1 DL Subframe Sense UL 1 DL1 DS1 Tss SSRTG DL1 CPE2 DL Subframe Sense UL 2 DL2 DS2 Tss SSRTG DL2 T ss = n * Tb, n = 1, 2, 3… TTG1 > TRS + Tss TTG2 – TTG1 = k * Ts, k = 1, 2, 3… A sensing slot after DL subframe for BS and CPEs to sense the channel Ying-Chang Liang, Institute for Infocomm Research

Other Channel Sensing Options January 2006 Sensing Duration = 100 ~ 200 us Sensing Frequency = 200~300Hz Other Channel Sensing Options CPE Sensing BS Sensing Ying-Chang Liang, Institute for Infocomm Research

Other Channel Sensing Options January 2006 Other Channel Sensing Options Sensing Duration = 100 ~ 200 us Sensing Frequency = 200~300Hz CPE Sensing (at distributed subcarrier positions) BS Sensing (at distributed subcarrier positions) Ying-Chang Liang, Institute for Infocomm Research

Channel Sensing Using Null Subcarriers January 2006 Channel Sensing Using Null Subcarriers Ying-Chang Liang, Institute for Infocomm Research

OFDMA Transmitter for BS January 2006 OFDMA Transmitter for BS Preamble Pilot Data 1 Randomizer FEC Interleaver Symbol Pre-transform Mapper Two-layer OFDMA Windowing Encoder . & Pulse . Shaping . Formulator Data K Randomizer FEC Interleaver Symbol Pre-transform Encoder Mapper Ying-Chang Liang, Institute for Infocomm Research

OFDMA Transmitter for CPE January 2006 OFDMA Transmitter for CPE Preamble/ Pilot Data Randomizer FEC Interleaver Symbol Pre-transform OFDMA Windowing Encoder Mapper . Formulator & Pulse . Shaping . Zeros Ying-Chang Liang, Institute for Infocomm Research

January 2006 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. Ying-Chang Liang, Institute for Infocomm Research

FEC Encoder: Convolutional Code (CC) January 2006 FEC Encoder: Convolutional Code (CC) Native code: Rate ½ with constraint length: 7 Generator polynomials: 171oct, 133oct Other coding rates through puncturing 2/3, ¾, 5/6 Ying-Chang Liang, Institute for Infocomm Research

FEC Encoder: Block Turbo Code (BTC) January 2006 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) Ying-Chang Liang, Institute for Infocomm Research

Parity Check Matrices for Hamming Codes January 2006 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. Ying-Chang Liang, Institute for Infocomm Research

Shortened Block Turbo Code (SBTC) Structure January 2006 Shortened Block Turbo Code (SBTC) Structure Ying-Chang Liang, Institute for Infocomm Research

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

January 2006 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(16i / Ncbps)) mod s i = 0,1,… Ncbps – 1 Ying-Chang Liang, Institute for Infocomm Research

Localized or distributed mapping Applicable to both UL and DL January 2006 Pre-Transforms P/S IFFT (size N) S/P Transform (size M) Cyclic Prefix Localized or distributed mapping Applicable to both UL and DL Ying-Chang Liang, Institute for Infocomm Research

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

Adaptive Modulation and Coding (AMC) January 2006 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) Ying-Chang Liang, Institute for Infocomm Research

Variable Throughput (1.25MHz, Downlink) January 2006 Variable Throughput (1.25MHz, Downlink) Modulation Code rate Data rate (in Mpbs) for different CP factor 3/8 1/4 1/8 1/16 QPSK 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 1.587 1.681 16-QAM 1.558 1.714 1.905 2.017 2.078 2.286 2.540 2.689 2.338 2.571 2.857 3.025 2.597 3.175 3.361 64-QAM 3.117 3.429 3.810 4.034 3.507 3.857 4.286 4.538 3.896 4.762 5.042 256-QAM 4.156 4.571 5.079 5.378 4.675 5.143 5.714 6.050 5.195 6.349 6.723 minimum downlink peak rate Ying-Chang Liang, Institute for Infocomm Research

Variable Throughput (1.25MHz, Uplink) January 2006 Variable Throughput (1.25MHz, Uplink) Modulation Code rate Data rate (in Mpbs) for different CP factor 3/8 1/4 1/8 1/16 BPSK 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 0.397 0.420 QPSK 0.390 0.429 0.476 0.504 0.520 0.571 0.635 0.672 0.584 0.643 0.714 0.756 0.649 0.794 0.840 16-QAM 0.779 0.857 0.952 1.008 1.039 1.143 1.270 1.345 1.169 1.286 1.429 1.513 1.299 1.587 1.681 64-QAM 1.194 1.559 1.715 1.905 2.017 1.754 1.929 2.143 2.269 1.948 2.381 2.521 minimum uplink peak rate Ying-Chang Liang, Institute for Infocomm Research

Transmit Power Control (TPC) January 2006 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 dB, 1 dB steps, and ± 0.5 dB accuracy. Transmit power control will be supported on link-by-link basis Ying-Chang Liang, Institute for Infocomm Research

Preamble and Pilot Design January 2006 Preamble and Pilot Design DL preamble Time synchronization, frequency synchronization and channel estimation UL preamble channel estimation DL and UL pilot allocations in each OFDMA symbol for channel parameter estimation and tracking Preamble and pilot design avoiding interference to primary users Ying-Chang Liang, Institute for Infocomm Research

DL Preamble The first OFDMA symbol of DL subframe January 2006 DL Preamble The first OFDMA symbol of DL subframe Periodic with period N/2 in time domain The locations of active subcarriers are: 2k, 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 Ying-Chang Liang, Institute for Infocomm Research

January 2006 UL Preamble UL preamble may be not necessary if pre-equalization 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 Ying-Chang Liang, Institute for Infocomm Research

Pre-Equalization for Uplink January 2006 Pre-Equalization for Uplink The wireless channel usually changes slowly, we can use the channel estimated based on the downlink preamble to do pre-equalization 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) Ying-Chang Liang, Institute for Infocomm Research

January 2006 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: 52k+1 and N/2+(3N/32)+52k+1, k=0,1,…,N/128-1. (N/16-N/64) variable-location pilots (3 for each subchannel) Locations: 13k+3(L mod 4)-5 and N/2+(3N/32)+13k+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 Ying-Chang Liang, Institute for Infocomm Research

DL Pilot Subcarrier Allocation (N =256) January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

January 2006 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. Ying-Chang Liang, Institute for Infocomm Research

Multiple Antenna Technologies January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Cyclic Delay Transmission January 2006 Cyclic Delay Transmission Frequency diversity achieved by FEC ! Ying-Chang Liang, Institute for Infocomm Research

Space-Frequency Coding (SFC) January 2006 Space-Frequency Coding (SFC) Subcarrier 1 Subcarrier 2 Ant 1 S(1) -S*(2) Ant 2 S(2) S*(1) Ying-Chang Liang, Institute for Infocomm Research

Switched-beam Beamforming + CDT/STBC January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Interference Avoidance to Primary Users (PUs) January 2006 Interference Avoidance to Primary Users (PUs) Beamforming to avoid interference to PU Use geographic knowledge of the primary user Frequency planning CPE2 uses frequencies unoccupied by PU for communication Frequencies occupied by PU can be allocated to CPE1& CPE3 Ying-Chang Liang, Institute for Infocomm Research

Delay Spread Reduction January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Basic Transmit Beamforming (BTB) January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Advanced Transmit Beamforming (ATB) January 2006 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. Ying-Chang Liang, Institute for Infocomm Research

ATB Reflector 1 Or repeater CPE Reflector 2 Local scatters January 2006 ATB Reflector 1 Or repeater Reflector 2 CPE Local scatters Beam 1 Beam 2 Delay 1 T1 = τ1+ D1 Delay 2 T2 = τ2+ D2 Overall Delay |T1-T2| +δ Pre-alignment & beamforming Stream 1 Stream 2 By adjusting timings D1 and D2, the overall delay of the channel can be changed. Ying-Chang Liang, Institute for Infocomm Research

ATB: Channel Shortening and Lengthening January 2006 ATB: Channel Shortening and Lengthening Ying-Chang Liang, Institute for Infocomm Research

January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Random Beamforming for MIMO January 2006 Random Beamforming for MIMO BS 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 Ying-Chang Liang, Institute for Infocomm Research

Random Beamforming for MIMO January 2006 Random Beamforming for MIMO Pilot Data … Pp Sp(n) xp(n) H1 Q1H u1(n) y1(n) z1(n) . HM QMH uM(n) yM(n) zM(n) Sk(n) xk(n) Hk QkH uk(n) yk(n) zk(n) Pilot mode Data mode: User k is scheduled for transmission DFE Ying-Chang Liang, Institute for Infocomm Research

Random Beamforming: Pilot Mode January 2006 Random Beamforming: Pilot Mode CPE BS Random beamformer generator ZF-GDFE receiver Training sequences Random beamformer SINR measurement SINR calibration using power control Proportional fairness scheduling Feedback requested rate & power allocations Ying-Chang Liang, Institute for Infocomm Research

Sectorization Each cell is divided into multiple sectors January 2006 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 Ying-Chang Liang, Institute for Infocomm Research

Inter-Sector Diversity January 2006 Inter-Sector Diversity Ying-Chang Liang, Institute for Infocomm Research

Sensing Mechanism Two-step sensing November 2005 doc.: IEEE 802.22-05/0094r0 January 2006 Sensing Mechanism Two-step sensing Step 1: energy detection If EP > TH1, then decide that PU present If EP < TH2, then decide that PU absent If TH2≤EP≤TH1, then proceed to step 2 Step 2: cyclostationary detection Compute SCD at selected cyclic frequencies If average energy of SCD, EC > TH3, then decide PU present Tentative decisions perform at the sensing unit. Decision fusion performed at the decision unit. Ying-Chang Liang, Institute for Infocomm Research Y.-C. Liang, Inst. for Infocomm Research

Frame Structure for Non-continuous Sensing January 2006 Frame Structure for Non-continuous Sensing Distributed (non-continuous) sensing Super frame = n * frames DL Frame 0 Frame 1 Frame n UL Sensing DL/S/UL Ying-Chang Liang, Institute for Infocomm Research

OFDMA with Block Spreading January 2006 OFDMA with Block Spreading Transmitter (frequency domain implementation) P/S IFFT (size = NFFT) Mapped Symbols from SS Cyclic Prefix Block Spread Ying-Chang Liang, Institute for Infocomm Research

OFDMA with Block Spreading January 2006 OFDMA with Block Spreading Transmitter (time domain implementation) Mapped Symbols from SS Phase Rotation Cyclic Prefix Block Spread Repetition Ying-Chang Liang, Institute for Infocomm Research

OFDMA with Block Spreading January 2006 OFDMA with Block Spreading OFDM Block Spreading Code c1 P/S CP CP Block 1 c2 CP CP CP Block 2 Block 1 Block K cK CP Block K Ying-Chang Liang, Institute for Infocomm Research

OFDMA with Block Spreading January 2006 OFDMA with Block Spreading Reference Receiver FFT Frequency domain Processing Received Signal Remove cyclic Prefix Block Despread Ying-Chang Liang, Institute for Infocomm Research

OFDMA with Block Spreading January 2006 OFDMA with Block Spreading Block de-spreading in Reference Receivers P/S c1 CP CP CP CP Block 1 Block K cK CP Ying-Chang Liang, Institute for Infocomm Research

MAC Enhancement January 2006 Ying-Chang Liang, Institute for Infocomm Research

January 2006 References [1] IEEE 802.22 Wireless RAN, Functional Requirements for the 802.22 WRAN Standard, IEEE 802.22-05/0007r46, 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 EN300 744 V1.5.1 (2004-11) Digital Video Broadcasting (DVB): Framing structure, channel coding and modulation for digital terrestrial television Ying-Chang Liang, Institute for Infocomm Research