Doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 1Jianwei Zhang, Huawei Channel Sensing and Radio Resourse Allocation Algorithms for WRAN Systems.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 1Jianwei Zhang, Huawei Channel Sensing and Radio Resourse Allocation Algorithms for WRAN Systems IEEE P802.22 Wireless RANs Date: 2006-03-29 Authors: 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 Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl 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.patcom@iee.org

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 2Jianwei Zhang, Huawei Co-Authors:

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 3Jianwei Zhang, Huawei PART I: CHANNEL SENSING 1. Guard intervals for extra quiet period in TDD WRAN system 2. Region-based Bayesian method for RF sensing in WRAN system 3. The MAC management message for channel sensing 4. Pilot design for channel estimation and interference detection in WRAN system PART II: RADIO RESOURCE ALLOCATION 1. Effective and flexible structure for CPE CSIT collection at base station for TDD/FDD OFDMA architecture 2. Downlink multiuser resource allocation algorithm for OFDMA-based QoS-enabled WRAN system 3. Joint dynamic frequency selection and power control with user specific transmit power mask constraints in uplink WRAN system using OFDMA scheme 3. Joint dynamic frequency selection and power control with user specific transmit power mask constraints in uplink WRAN system using OFDMA scheme

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 4Jianwei Zhang, Huawei INTRODUCTION In this contribution, some algorithms on channel sensing and radio resource allocation are suggested. These algorithms were briefly introduced during Mar. 2006 meeting in IEEE802-06/0030r3. However detailed description on these algorithms was requested from the floor of the working group because of lack of information on them in that document. Therefore this contribution is submitted with the corresponding MS Word format contribution. This contribution consists of two parts: –Part I: Channel Sensing –Part II: Radio Resource Allocation The first part has four algorithms and the second has three algorithms as shown in the next slide.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 5Jianwei Zhang, Huawei PART I: CHANNEL SENSING 1. Guard intervals for extra quiet period in TDD WRAN system 2. Region-based Bayesian method for RF sensing in WRAN system 3. The MAC management message for channel sensing 4. Pilot design for channel estimation and interference detection in WRAN system

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 6Jianwei Zhang, Huawei 1.Guard intervals for extra quiet period in TDD WRAN system 1. Guard intervals for extra quiet period in TDD WRAN system

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 7Jianwei Zhang, Huawei BACKGROUND Synchronous Quiet PeriodSynchronous Quiet Period  a period in which all WRAN devices stop transmission in all channels available in the system  used for sensing the signals in all channels of the system without interfering the system itself  useful to enhance awareness to the surrounding radio environment Can the sensing accuracy be further enhanced?

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 8Jianwei Zhang, Huawei FULL UTILIZATION OF GUARD INTERVALS Guard IntervalsGuard Intervals – When using OFDMA at the physical layer, guard intervals should be inserted at the switching points of transmission  OFDM symbols of different users can be synchronized at BS. –We can use these guard intervals as extra quiet periods for sensing! 1 CPE1 (d=0) CPE2 (d=R) GIDownlink sub-frame 23412341234 Uplink sub-frame 1 GIDownlink sub-frame 23412341234 Uplink sub-frame … … [R: cell radius]

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 9Jianwei Zhang, Huawei RELATED WORK BY I2R (1) All CPE should have a mandatory quiet period with fixed length at the switching point from downlink (DL) to uplink (UL). DL Subframe DL2 DL Subframe UL 2 SSRTG TRS Sense Tss Sense Tss Sense Tss UL 1 SSRTG TTG1 TTG2 UL 2UL 1 DL2 DL1 CPE2 CPE1 BS DS1 DS2

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 10Jianwei Zhang, Huawei RELATED WORK BY I2R (2) To be improvedTo be improved – Guard intervals from uplink to downlink have not been utilized. – Since a quiet period of fixed length is inserted to all CPEs (regardless of their distances to base station), for the CPEs at the edge of the cell in which guard intervals are usually not required, the uplink transmission of these CPEs will be deferred  can be improved 1 CPE1 (d=0) CPE2 (d=R) GIDownlink sub-frame 23412341234 Uplink sub-frame 1 GIDownlink sub-frame 23412341234 Uplink sub-frame … … [R: cell radius]

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 11Jianwei Zhang, Huawei FOR OUR PROPOSED DESIGN AssumptionsAssumptions – TDD (time division duplex) deployment – OFDMA (orthogonal frequency domain multiplexing access) is used in both uplink and downlink Main FeaturesMain Features – Adaptive Guard Interval Control – Asynchronous Quiet Period

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 12Jianwei Zhang, Huawei OUR PROPOSED DESIGN (1) Feature: Adaptive Guard Interval Control  Conventionally, CPE1 should wait for CPE2 during the uplink transmission such that their first uplink symbols are synchronized at BS.  We relax the above constraint: 1 CPE1 (d=0) CPE2 (d=R) GIDownlink sub-frame 23412341234 Uplink sub-frame 1 GIDownlink sub-frame 23412341234 Uplink sub-frame … … * CPE2’s first UL symbol is synchronized with CPE1’s second UL symbol

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 13Jianwei Zhang, Huawei ADANTAGES OF ADAPTIVE GI CONTROL  For those CPEs being close to BS: they can start transmission in advance (1) Length of guard intervals from DL to UL can be shortened (2) More OFDM symbols can be transmitted  For those CPEs being far away from BS (1) Uplink transmission will no longer be deferred (2) Number of transmitted OFDM symbols remains unchanged  If considering some practical limitations such as the hardware limitation or the delay spread of the multi-path channel, a gap should be guaranteed between the DL and UL sub-frame when operating the adaptive GI control. 1 Downlink sub-frame 23412341234 Uplink sub-frame … 5 1 Downlink sub-frame 23412341234 Uplink sub-frame … Without adaptive guard interval control With adaptive guard interval control CPE3 (0<d<R)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 14Jianwei Zhang, Huawei OUR PROPOSED DESIGN (2) Feature: Asynchronous Quiet Period  Guard intervals from UL to DL can also be used as extra quiet period for channel sensing.  Depending on the demand for sensing accuracy, some OFDM symbols can be replaced by the sensing period – Flexibility is ensured – BS notifies the assignment of such sensing periods to the CPEs by using the proposed Sensing Period Assignment (SPA) message. 1 Downlink sub-frame 23412341234 Uplink sub-frame … 5 With adaptive guard interval control CPE3 (0<d<R)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 15Jianwei Zhang, Huawei SPA MESSAGE FORMAT SyntaxNotes SPA_Message_Format() { Management Message TypeIndicates the type of SPA message Connection IDIndicates the user to whom the message is sent Start TimeIndicates the start time of the sensing period, in unit of OFDM symbols DurationIndicates the duration of the sensing period, in unit of OFDM symbols }

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 16Jianwei Zhang, Huawei CONCLUSION Adaptive Guard Interval ControlAdaptive Guard Interval Control  For CPEs being close to BS, more OFDM symbols can be transmitted  Guard intervals from DL to UL can be shortened  For CPEs being far away from BS, their uplink transmission will no longer be deferred  Performance Gain: Assume cell size is 33km and frame length is 5ms, the round-trip delay is 0.22ms  4.4% of bandwidth can be used! Asynchronous Quiet PeriodAsynchronous Quiet Period  Guard intervals from UL to DL can also be used for channel sensing  Flexibility: some OFDM symbols can be replaced by sensing period  Sensing Period Assignment (SPA) message: one kind of MAC management message

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 17Jianwei Zhang, Huawei 2.Region-based Bayesian method for RF sensing in WRAN system 2. Region-based Bayesian method for RF sensing in WRAN system

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 18Jianwei Zhang, Huawei BACKGROUND The WRAN system needs to detect the presence of incumbent systems and avoid the interference to the incumbent system Detection of Incumbents –Presence of the incumbents –Locations of the incumbents

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 19Jianwei Zhang, Huawei DETECTION OF INCUMBENTS Detect the presenceof the incumbentsDetect the presence of the incumbents –The subband needs to be vacated in the whole cell/sector –Lower spatial efficiency Detect the locations of the incumbentsDetect the locations of the incumbents –When the operation range of incumbent is small, the subband may be used without interfering to the incumbent. –Higher spatial efficiency –Complexity grows exponentially with the number of targets –Many previous work requires: knowledge of number of targets, knowledge of signatures, and detection of time of arrivals, etc.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 20Jianwei Zhang, Huawei REGION-BASED RF SENSING ALGORITHM Partition the cell/sector into a number of disjoint regions For each region, decide whether some incumbents exist  Higher spatial efficiency  The number of targets need not be known a priori  Complexity does not exponentially grow with the number of targets Control overhead  Each CPE feedbacks incumbent types and the corresponding subband

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 21Jianwei Zhang, Huawei THE BAYSIAN METHOD (1) Define d = The vector {d i } of all sensors and C ij = Cost of deciding H i (  ), given H j (  ) is true. The decision rule of the Bayesian method is where  is a subset of PIT* region iff i * (  ) = 1. Cost matrix example: * PIT: potential incumbent transmitter

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 22Jianwei Zhang, Huawei THE BAYSIAN METHOD (2) For simplicity, assume conditional independence,

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 23Jianwei Zhang, Huawei THE BAYSIAN METHOD (3) We assume the detection process of a sensor is modeled by Bernoulli trials.  Each IT within its detection region is an i.i.d. trial.  The probability of detecting a particular IT is independent of its position.  Flag di = 1, iff at least one IT is detected.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 24Jianwei Zhang, Huawei THE BAYSIAN METHOD (4)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 25Jianwei Zhang, Huawei ALGORITHM FLOW System Initialization Compute PIT (potential incumbent transmitter) region Compute Protection Region

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 26Jianwei Zhang, Huawei PIT REGION DISTRIBUTION 400 CPEs, 4 ITs (incumbent transmitters) Detection radius = 10 grids (Grid space = 50m) 5km by 5km square region y (grid point) Union Algorithm x (grid point) Region-based Algorithm

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 27Jianwei Zhang, Huawei REGION-BASED VS UNION ALGORITHMS (1) P F,i = 0.01 (per CPE per subband) Ratio of areas of PIT region CPE density (#CPE/km 2 ) Probability of miss

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 28Jianwei Zhang, Huawei REGION-BASED VS UNION ALGORITHMS (2) P F,i = 0.1 (per CPE per subband) Ratio of areas of PIT region CPE density (#CPE/km 2 ) Probability of miss

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 29Jianwei Zhang, Huawei SENSITIVITY TO ESTIMATE OF CPE DENSITY (1) P F,i = 0.1 (per CPE per subband) Actual average number of IT per km 2 = 0.16 IT/km 2 Ratio of areas of PIT region Expected number of IT per km 2 Probability of miss Expected number of IT per km 2

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 30Jianwei Zhang, Huawei Estimate of Black curve = Sum of three curves SENSITIVITY TO ESTIMATE OF CPE DENSITY (2)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 31Jianwei Zhang, Huawei Downlink System – Ideal antenna with 120-degree beam-width and front-to-back ratio G FB of 13dB. – Uniform gain within main beam and constant attenuation of 13dB outside. – Cell radius is 33km; path loss exponent in a cell, pl = 3. – 10 circular clusters of CPEs, with radius of 3km, center uniformly distributed – For every cluster, 100 CPEs are uniformly distributed within it. – P th = Maximum WRAN signal power allowed in the protection region – P Rmin = Minimum required receiving power of a CPE: P th + 3dB – D rr = The radius of the receivable region – D pro = The minimum distance between BS and protection region, D pro. REGION-BASED ALGORITHM: TRANSCEIVABLE REGION (1)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 32Jianwei Zhang, Huawei REGION-BASED ALGORITHM: TRANSCEIVABLE REGION (2) y (km) x (km)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 33Jianwei Zhang, Huawei COMPARISON OF USABLE SUBBANDS Average number of subbands available to the system: FDD – Region-based Algorithm: 32 subbands / base station –Union Algorithm: 12 subbands / base stationTDD –Region-based Algorithm: 31 subbands / base station –Union Algorithm: 12 subbands / base station

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 34Jianwei Zhang, Huawei COMPLEXITY COMPARISON Complexity Ratio of Region-based to Union Algorithm CPE density (#CPE/km 2 ) At a reasonable CPE density, the complexity of the region-based algorithm is about 10 times of the union algorithm and its complexity will converge to less than 14 times of the union algorithm.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 35Jianwei Zhang, Huawei CONCLUSION More efficient use of space for frequency reuseMore efficient use of space for frequency reuse –Smaller PIT and protection regions  larger transceivable region –CPEs inside the receivable region can use the channel –Noticeable gain in the number of usable channels per cell Compared with union algorithm: –Large reduction in PIT region –Small increase in probability of miss –The tradeoff can be controlled by the cost matrix Moderate Computation ComplexityModerate Computation Complexity Low overhead for sensing reportLow overhead for sensing report

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 36Jianwei Zhang, Huawei 3. The MAC management message for channel sensing

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 37Jianwei Zhang, Huawei PROPOSED DESIGN Design of MAC Management Messages for channel sensing of the CPE’s Our proposed RF sensing algorithm suggests the following information is sufficient for satisfactory performance in sensing report of CPE’s –Incumbent type –Channel occupied by the incumbent Design Criteria: Reduce control overhead

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 38Jianwei Zhang, Huawei MEASUREMENT REQUEST (MS-REQ) (1)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 39Jianwei Zhang, Huawei MEASUREMENT REQUEST (MS-REQ) (2)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 40Jianwei Zhang, Huawei SYSTEM TYPES

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 41Jianwei Zhang, Huawei Table 4. Interval-basis Channel List Table 3. Channel-basis Channel List CHANNEL- / INTERVAL-BASIS CHANNEL LISTS

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 42Jianwei Zhang, Huawei MEASUREMENT REPORT (MS-REP) Table 5. Measurement Report

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 43Jianwei Zhang, Huawei INCREMENTAL MEASURMENT REPORT Table 6. Incremental Measurement Report

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 44Jianwei Zhang, Huawei INCREMENTAL MEASURMENT REPORT Table 7. Full Measurement Report

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 45Jianwei Zhang, Huawei EXAMPLE

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 46Jianwei Zhang, Huawei CONCLUSION Compatible with IEEE802.16 MAC Management MessagesCompatible with IEEE802.16 MAC Management Messages –Flexible –Support various schemes of control channel assignment Design Criteria: Reduce control overheadDesign Criteria: Reduce control overhead –Interval-basis Channel List –Incremental Measurement Report

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 47Jianwei Zhang, Huawei 4. Pilot design for channel estimation and interference detection in WRAN system

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 48Jianwei Zhang, Huawei PROPOSED DOWNLINK PILOT DESIGN  ●    ●    ●    ●    ●    ●    ●    ●    ●   … Block 0  ●    ●    ●    ●    ●    ●    ●    ●    ●   … Block 1  ●    ●    ●    ●    ●    ●    ●    ●    ●   … Block 2  ●    ●    ●    ●    ●    ●    ●    ●    ●   … Block 3                                     … Block 4                                     … Block 5                                     … Block 6                                     … Block 7                                     … Block 8 ………………………………………. ●: Pilot subcarrier  : Data subcarrier Major consideration  The channel is slow varying  The subcarrier spacing is about several KHz  To facilitate the interference detection

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 49Jianwei Zhang, Huawei PROPOSED UPLINK PILOT DESIGN ●    ●    ●    ● Block 0              Block 1              Block 2 ……………… ●: Pilot subcarrier  : Data subcarrier Major consideration  The channel is slow varying  The subcarrier spacing is about several KHz  Subband-based OFDMA

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 50Jianwei Zhang, Huawei INTERFERENCE DETECTION Left graphs stands for the constellation of pilots on the same subcarriers of different OFDM blocks Right graphs stands for the constellation of corresponding received signals Interference  symmetric structure of the constellation will be destroyed No matter the interference varies or not No matter what constellation size used Channel Channel + Interference

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 52Jianwei Zhang, Huawei SIMULATION MODEL AND PARAMETERS Interference generated in time domain  more close to the real situation Interference on one subcarrier of different OFDM blocks varies False alarm probability is set to 0.01 Noise power is known a prior AWGN Filter Remove CP + signal FFT Noise Interference Frequency response of the filter.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 53Jianwei Zhang, Huawei SIMULATION RESULTS - 2 PILOTS

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 54Jianwei Zhang, Huawei SIMULATION RESULTS - 5 PILOTS Threshold does not change But use to do the hypothesis test

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 55Jianwei Zhang, Huawei CONCUSION – INTERFERENCE DETECTION Pilot design for both downlink and uplink Interference detection –Do not require extra overhead –No matter the interference is varying or not –No matter the constellation size used –Performance only depends on interference to noise ratio

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 56Jianwei Zhang, Huawei JOINT INTERFERENCE DETECTION & DECODING Existence of Narrowband Interference in WRAN Avoids Transmission in Interference Jammed Subcarriers –Transmitter may not know the existence of interference due to bursty nature of interference Receiver Detect Interference –Pilot based approaches –Data based approaches Based on estimated data Based on correlation of channel fading in frequency and time domain Existing Decoders Require Interference Knowledge –Performance determined by the accuracy of the interference detection

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 57Jianwei Zhang, Huawei SYSTEM MODEL For Each Codeword Parallel Channel

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 58Jianwei Zhang, Huawei EXISTING DECODING SCHEMES Optimal Maximum Likelihood DecodingOptimal Maximum Likelihood Decoding –Decoding metric is optimized differently for noise and interference –Require noise and interference statistics (position and power) Conventional DecodingConventional Decoding –Only require interference position; not require interference power –Ignore (erase) interference jammed symbols –Decoding metric is Euclidean distance (Optimal metric for AWGN) –Undetected interference corrupts decoder because of metric mismatch  all require interference detector

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 59Jianwei Zhang, Huawei JOINT ERASURE DECODING Given the number of erasures, search all possible codewords x with all possible erasure positions e Determine the number of erasures –Apply sufficiency criteria Achievable performance –Maximum Likelihood decoding with the exact knowledge of the noise and interference statistics

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 60Jianwei Zhang, Huawei IMPLEMENTATION – PRODUCT TRELLIS Erasure Indicator TrellisErasure Indicator Trellis Bit TrellisBit Trellis Product TrellisProduct Trellis

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 61Jianwei Zhang, Huawei SUFFICIENCY CRITERIA Error Checking Code BasedError Checking Code Based –Output the first candidate codeword that passes error checking and terminate decoding Path Metric Difference BasedPath Metric Difference Based –Calculate path metric difference of consecutive candidate codewords Metric difference is decreasing Metric difference is small after all interference are erased –If the metric difference is less than a threshold, then output the candidate codeword & terminate decoding

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 62Jianwei Zhang, Huawei COMPLEXITY REDUCTION Find the most likely path sequentially Demodulator marks symbol erasures –Erase the symbol if any of the corresponding bit is marked as an erasure by decoder –Erase the symbol based on the channel output detectable Undetectable  left to decoder

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 63Jianwei Zhang, Huawei SIMULATIONS – FIXED SIR OR JAMS (1) Rate-½ 64-state convolutional code 16QAM with Gray mapping 864 subcarriers Profile A multipath fading channel; constant over each packet Fixed SIR or number of jammed subcarriers Sufficiency criterion: path metric difference based Demodulator does not mark erasure based on channel output

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 64Jianwei Zhang, Huawei SIR=0dB, SNR=20dB 5 Jams, SNR=20dB The proposed decoder (1) almost achieves the performance of the optimal decoder (2) reduces sensitivity to the number of jammed subcarriers (3) is insensitive to interference power SIMULATIONS – FIXED SIR OR JAMS (2)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 65Jianwei Zhang, Huawei Optimal threshold of the path metric difference based sufficiency criterion is (1)almost independent of number of jammed subcarriers (2)almost independent of interference power  Threshold can be determined offline SIR=0dB, SNR=20dB 5 Jams, SNR=20dB SIMULATIONS – FIXED SIR OR JAMS (3)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 66Jianwei Zhang, Huawei SIMULATION – W/O INTERFERENCE DETECTOR (1) 864 subcarriers 20 OFDM symbols per packet One codeword per OFDM symbol 2 OFDM pilot symbols for –Interference detection –Frequency domain LS channel estimation 32 jammed subcarriers (wireless microphone) SIR uniformly distributed in [-20dB,10dB] Sufficiency criterion: path metric difference based

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 67Jianwei Zhang, Huawei ( 1) Without interference detector (red)  Great gain over conventional decoder for BER and PER  Complexity increase by 1.5 times for PER=0.1 relative to conventional (2) With interference detector (blue)  Smaller gain for BER but significant gain for PER  Complexity increase by 15% for PER=0.1 relative to conventional (3) Proposed decoder performs similarly with or without interference detector SIMULATION – W/O INTERFERENCE DETECTOR (2)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 68Jianwei Zhang, Huawei SIMULATION – W/O CHANNEL ESTIMATION ERROR (1) Random interference for each carrier with probability 0.04 SIR uniformly distributed in [-20dB,10dB] 2 OFDM pilot symbols for frequency domain LS channel estimation Each codeword is transmitted through 200 carriers and 10 OFDM symbols Each convolutional codeword is encoded by CRC Demodulator marks erasures Sufficiency criterion: CRC and path metric difference based –CRC generator polynomial is 435(octal )

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 69Jianwei Zhang, Huawei (1) Without channel estimation error (solid)  Joint erasure marking and decoding Performs closely to optimal decoder  Complexity increase by 50% for WER=0.01 relative to conventional decoder (2) With channel estimation error (dashed)  Joint erasure marking and decoding is less sensitive to channel estimation error than separate erasure marking and decoding using demodulator only  Complexity increases by twice for WER=0.01 relative to conventional decoder Gain of joint over separate (separate) (joint) (separate) (joint) SIMULATION – W/O CHANNEL ESTIMATION ERROR (2)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 70Jianwei Zhang, Huawei CONCLUSION The proposed decoding scheme almost achieves the optimal decoder performance without knowing the interference statistics Threshold of sufficiency criterion does not depend on interference characteristics and can be determined offline Complexity increase is reasonably small especially for high SNR or with an interference detector Performance loss due to channel estimation error is much smaller than that of conventional decoding scheme Therefore, it is robust and effective to combat unknown interference in practical situations

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 71Jianwei Zhang, Huawei PART II: RADIO RESOURCE ALLOCATION 1. Effective and flexible structure for CPE CSIT collection at base station for TDD/FDD OFDMA architecture 2. Downlink multiuser resource allocation algorithm for OFDMA-based QoS-enabled WRAN system 3. Joint dynamic frequency selection and power control with user specific transmit power mask constraints in uplink WRAN system using OFDMA scheme 3. Joint dynamic frequency selection and power control with user specific transmit power mask constraints in uplink WRAN system using OFDMA scheme

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 72Jianwei Zhang, Huawei 1. Effective and flexible structure for CPE CSIT collection at base station for TDD/FDD OFDMA architecture

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 73Jianwei Zhang, Huawei MOTIVATION Design good resource allocation algorithm to fully utilize the resource Radio resource is very scarce CSIT is a crucial input CSIT is a crucial input

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 74Jianwei Zhang, Huawei CSIT* ACQUISION Using the reciprocity of the uplink and downlink channelUsing the reciprocity of the uplink and downlink channel  CSIT of the excited subchannels of those currently uplink-active CPEs of TDD system Using feedbackUsing feedback  CSIT of the un-excited subchannels of those currently uplink- active CPEs of a TDD system  CSIT of the currently uplink-inactive CPEs of TDD system  CSIT of all the CPEs of FDD system Very important to design a good CSIT collection mechanism * CSIT: channel state information at transmitter

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 75Jianwei Zhang, Huawei FEATURES OF DOWNLINK WRAN SYSTEM BS knows the QoS requirements and queueing states of all the CPEs  BS can determine which CPEs have higher priority and are more urgent Maximum Doppler frequency is very small  The CSIT can be updated rather infrequently Variation of Doppler frequency among CPEs is limited  The CSIT update frequencies of CPEs are similar Polling-based CSIT feedback mechanism

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 76Jianwei Zhang, Huawei MAIN FEATURES OF PROPOSED STRUCTURE Centralized polling at the BSCentralized polling at the BS  BS decides which CPEs to poll based on QoS requirements, queueing states, etc.  BS decides for each selected CPE which subband to estimate based on power mask, history, etc.  BS decides for each selected CPE through which subchannels to convey CSIT Placement of the polling informationPlacement of the polling information  For currently active CPEs, the polling information is contained in the UL-MAP  For currently inactive CPEs, the polling information is contained in some broadcast channel

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 77Jianwei Zhang, Huawei CSIT COLLECTION REQUEST MESSAGE (1) SyntaxSize (bits)Remarks CSIT_Collection_Request() { N_DL_RCID8 N_DL_RCID is the number of selected downlink-active-only CPEs and both-downlink-and-uplink-active CPEs that are in this subband for i = 1: N_DL_RCID { Downlink RCID8 Feedback_Control( )variable } UL_RCID_flag1 0: no selected CPE is uplink-active-only 1: there are selected CPEs that are uplink-active-only If {UL_RCID_flag == 1}{ N_UL_RCID8 N_UL_RCID is the number of selected uplink-active-only CPEs that are in this subband for i = 1: N_UL_RCID { Uplink RCID8 Feedback_Control( )variable } } CSIT_Collection_Request for active CPEs (to be cont’d)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 78Jianwei Zhang, Huawei CID_flag1 0: no CID is used 1: CID is used If {CID_flag == 1}{ N_CID8 N_CID is the number of selected CPEs that are switched to this subband for i = 1: N_CID { CID16 Feedback_Control( )variable } } } CSIT COLLECTION REQUEST MESSAGE (2) CSIT_Collection_Request for active CPEs (Cont’d)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 79Jianwei Zhang, Huawei FEEDBACK CONTROL MESSAGE (1) SyntaxSize (bits)Remarks Feedback_Control() { Subband_change_flag1 0: estimate the downlink CSI of this subband 1: in the next frame estimate the downlink CSI of the subband specified by Subband Index If{Subband_ change_flag==1}{ Subband Index8At most 256 6MHz subband } Else{ Quantization_level_flag1 0: use default quantization level, L=a 1: use specified quantization level If{ Quantization_level_flag ==1}{ Quantization level, L=b2 Assume there are at most 4 additional quantization precision levels } Feedback_ch_constraint_flag1 0: use default number of subchannels, N=c 1: use specified number of subchannels If{ Feedback_ch_constraint_flag==1}{ Number of subchannels, N=d6Assume 64 subchannels in a subband } Feedback_Control Message (to be cont’d)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 80Jianwei Zhang, Huawei FEEDBACK CONTROL MESSAGE (2) Feedback_symb_constraint_flag1 0: use default number of OFDM symbols, M=e 1: use specified number of OFDM symbols If{Feedback_symb_constraint_flag==1}{ Number of OFDM symbols, M=f2 Assume at most 4 OFDM symbols can be used to do feedback } for j=1:N{ Subchannel Index6 } } } Feedback_Control Message (cont’d)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 81Jianwei Zhang, Huawei CSIT COLLECTION REQUEST MESSAGE (1) CSIT_Collection_Request for inactive CPEs (to be cont’d) SyntaxSize (bits)Remarks CSIT_Collection_Request() { N_CID8N_CID is the number of selected inactive CPEs for i = 1:N_CID{ CID16 Subband Index8At most 256 6MHz subband Quantization_level_flag1 0: use default quantization level, L=a 1: use specified quantization level If{ Quantization_level_flag ==1}{ Quantization level, L=b2 Assume there are at most 4 additional quantization precision levels } Feedback_ch_constraint_flag1 0: use default number of subchannels, N=c 1: use specified number of sub-channels If{ Feedback_ch_constraint_flag==1}{ Number of subchannels, N=d6Assume 64 subchannels in a subband }

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 82Jianwei Zhang, Huawei CSIT COLLECTION REQUEST MESSAGE (2) CSIT_Collection_Request for inactive CPEs (Cont’d) Feedback_symb_constraint_flag1 0: use default number of OFDM symbols, M=e 1: use specified number of OFDM symbols If{Feedback_symb_constraint_flag==1}{ Number of OFDM symbols, M=f2 Assume at most 4 OFDM symbols can be used to do feedback } for j=1:N{ Subchannel Index6 } } }

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 83Jianwei Zhang, Huawei Overhead reductionOverhead reduction  For currently active CPEs, 8-bit RCID is used instead of the 16-bit CID to identify CPEs FlexibilityFlexibility  Default constraint on the number of subchannels and the number of OFDM symbols that a CPE should use to do feedback is known to both the BS and the CPEs  BS has the option to allocate more or less subchannels and/or OFDM symbols for each CPE to do feedback, depend on the QoS requirement or the urgency of the downlink traffic  Default CSIT quantization level is known to both BS and CPEs  BS has the option to increase or decrease the quantization level to adjust the precision of the feedback FEATURES OF PROPOSED STRUCTURE (1)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 84Jianwei Zhang, Huawei FEATURES OF OUR PROPOSED STRUCTURE (2) CPEs decide which subchannel CSIT to feedback based on the channel conditionCPEs decide which subchannel CSIT to feedback based on the channel condition  Using predefined modulation and coding scheme, given the number of subchannels, OFDM symbols that are used to convey CSIT, and the CSIT quantization level, each CPE knows it can feedback the CSIT of say c number of subchannels  For FDD system, the CPE should choose c number of subchannels with the largest gains  For TDD system, the CPE should choose c number of un-excited subchannels with the largest gains } } x Subchannel Gain 6 Subchannel Index for i = 1:c { If Q-bit feedback is allowed, thenCSIT_Feedback_Format() { RemarksSize (bits)  )6(xQc  CSIT_Feedback_Format

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 85Jianwei Zhang, Huawei 2. Downlink multiuser resource allocation algorithm for OFDMA-based QoS-enabled WRAN system

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 86Jianwei Zhang, Huawei BACKGROUND What’s challenging for 802.22? (1)Interference Avoidance to Incumbent Users (IU) –No cooperation possible between incumbent & WRAN systems – No cooperation possible between incumbent & WRAN systems  Preventive measures should be chosen at the WRAN transmitter – Unknown BS-IU channels & incompatible system structure – Unknown BS-IU channels & incompatible system structure  Isotropic transmission reduces the effective cell coverage  Transmit-side interference pre-cancellation is impossible (2)Broad available spectrum for each cell: (~180MHz, 30 TV channels) – – covered by multiple OFDM symbols instead of one – – max. one subband per each CPE  Simultaneous multi-band channel estimation is not possible

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 87Jianwei Zhang, Huawei DEFINITIONS Concept of band, subband, subchannel and subcarriers

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 88Jianwei Zhang, Huawei PROPOSED ALGORITHM Features for (1) Interference Avoidance to Incumbent Users (IU) – Peak power constraint, namely power mask, for every subband. –Sectored antenna adopted for reducing the performance sensitivity to any nearby incumbent users (from a cell to only a sector). for (2) Broad available spectrum for each cell: (~180MHz, 30 TV channels) – Two-layer resource allocation algorithm: Layer-1: subband allocation – distribute users over subbands exploiting knowledge of power mask.  avoid over-congestion of subbands. Layer-2: in-subband subchannel and power allocation – maximize subband throughput: QoS-enabled, priorities allowed.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 89Jianwei Zhang, Huawei 2-LAYER ALGORITHM The two-layer structure of the multiuser resource allocation algorithm Layer-1 Allocation Subband Assignment Layer-2 Allocation In-subband Subchannel, Power and Rate Allocation Knowledge of transmit power mask on every subband in every sector Knowledge of channel gain of the assigned subband Dynamic Frequency Selection Block

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 90Jianwei Zhang, Huawei LAYER-1: SUBBAND ASSIGNMENT (1) Intuition: Subband with smaller allowed maximum transmit power should handle less CPEs Step 1: For each sector, eliminate those unserviceable subbands, defined as those subbands with the power mask value smaller than a threshold. Step 2: Define P mm,b,c as the average power mask per subchannel of subband b, i.e. the peak possible transmit power per subchannel, in sector c. Let K c be the total number of users in sector c. For each sector c, the number of users allocated to subband b, represented by K b, c, is done according to the following equation:

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 91Jianwei Zhang, Huawei LAYER-1: SUBBAND ASSIGNMENT (2) Step 2: (cont’d)where N b is the number of serviceable subbands and L is the number of sectors. Both and should be non-decreasing functions. Example functions: If the objective is to maximize the minimum average user data rate, we can use: (i) where  b can be set to the average channel power gain to noise ratio. (ii) - (i) approximates the rate of each subchannel in subband b of sector c. - (ii) reflects the relative number of possible subchannel allocation across different sectors for that subband b.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 92Jianwei Zhang, Huawei LAYER-1: SUBBAND ASSIGNMENT (3) Step 3:Randomly select K b,c users for subband b in sector c. Remarks:Step 3 is indeed up to the vendors. e.g. Assignment can be done based on user classes so that users of higher class may be distributed to a subband with larger power mask. Example: Advantages of exploiting one-dimensional (within sector) and two- dimensional (across sector & subband) power mask against equal user allocation. Objective: maximize the minimum average user data rate. System Settings: 3 sectors, 2 subbands, 40 subchannels per subband, 60 users per sector. (i)1-D (Single-sector) allocation (ii)2-D (Multi-sector) allocation

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 93Jianwei Zhang, Huawei LAYER-1: PERFORMANCE (1) Subchannel power masks in the example for the Layer-1 algorithm: Subchannel power masks in the example for the Layer-1 algorithm: Subband 1Subband 2 Subchannel Power Mask Sector 120 Sector 24020 Sector 3400

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 94Jianwei Zhang, Huawei LAYER-1: PERFORMANCE (2) Subchannel allocation and subchannel data rate for the Layer-1 algorithm example with 40 subchannels per subband: Sector Equal Allocation1-D (single-sector) Allocation 2-D (multi-sector) Allocation Subband 1Subband 2Subband 1Subband 2Subband 1Subband 2 #Sub- ch. Alloc- ated Data Rate per subch. #Sub- ch. Alloc- ated Data Rate per subch. #Sub- ch. Alloc- ated Data Rate per subch. #Sub- ch. Alloc- ated Data Rate per subch. #Sub- ch. Alloc- ated Data Rate per subch. #Sub- ch. Alloc- ated Data Rate per subch. 1 84.3923204.39238 204.39238 204.3923 2 165.3576204.3923165.3576204.3923165.3576204.3923 3 165.357600165.357600165.357600

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 95Jianwei Zhang, Huawei LAYER-1: PERFORMANCE (3) Effect of different user allocation algorithms on the subband data rate per user with 60 users per sector: (Differences are highlighted) Sector Equal Allocation1-D (single-sector) Allocation 2-D (multi-sector) Allocation Subband 1Subband 2Subband 1Subband 2Subband 1Subband 2 No. of users Alloc- ated Bits per User No. of users Alloc- ated Bits per User No. of users Alloc- ated Bits per User No. of users Alloc- ated Bits per User No. of users Alloc- ated Bits per User No. of users Alloc- ated Bits per User 1 301.1713302.9282301.1713302.9282172.0670432.0429 2 302.8574302.9282332.5976273.2536302.8574302.9282 3 302.8574300601.42870--601.42870--

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 96Jianwei Zhang, Huawei LAYER-1: PERFORMANCE (4) Advantage of 1-D allocation over Equal Allocation: - realized in Sector 3 - realized in Sector 3: min. average rate per user increases from 0 to 1.4287. Advantage of 2-D allocation over its 1-D counterpart (also Equal Allocation): - realized in Sector 1 - realized in Sector 1: min. average rate per user increases from 1.1713 to 2.0429.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 97Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (1) Objective: – Maximize subband throughput by subchannel (a group of pre-selected subcarriers) and power allocation. – Support differentiated-QoS service. – Allow flexible tradeoff between max. throughput and fairness among users. Problem Formulation: – divided into two cases: (i) individual subcarrier power gain is known. (ii)average channel power gain is known, – The proposed algorithm is optimal for case (i), and almost optimal for case (ii) if every subchannel is within the coherence bandwidth.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 98Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (2) Problem Formulation: subject to e.g. rate control (0   k  1) priority control (l QoS_Class (k)  0) #subchannels#users#subcarriers in subchannel i Power allocated to user k on subchannel i Power mask Subchannel Sharing Factor

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 99Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (3) Define the rate function as: where is a factor bridging the gap between ideal minimum power required (using mutual information) and actual required transmission power (using practical modulation schemes for a given rate) is the noise power, is the average channel power gain of subcarrier n(i) in subchannel i, and with

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 100Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (4) Proposed algorithm - by relaxing to, the problem becomes convex and method of Lagrangian can be applied to obtain the optimal solutions. Algorithm Details: Step 1: Initialization. Initialize. Step 2: Select the optimal CPE for each subcarrier for a given value of Ω CPE k is selected ( ) for subcarrier i according to the following criterion: where

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 101Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (5) with defined as Step 3:Compute the optimal allocated power for each CPE for a given value of The optimal average power for user k on subchannel i is:

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 102Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (6) Step 4: Coarse adjustment of If ( ), Set for some small. Go back to Step 2. Else Optimal solutions obtained; algorithm terminated. End Else If ( ),. Go to Step 2.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 103Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (7) Step 4 (Cont’d): Elseif ( ), Go to Step 5. Else Optimal solutions obtained; algorithm terminated. End Step 5: Fine adjustment of While ( ) for some predefined tolerance level,

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 104Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (8) Step 5 (Cont’d): Repeat Step 2 and 3. If ( ), Elseif ( ), End Repeat Step 2 and Step 3. End

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 105Jianwei Zhang, Huawei LAYER-2: IN-SUBBAND ALLOCATION (9) In case of oscillations between two assignment profiles, and, a time-sharing ratio ( : ) for these profiles can be calculated: where so that on average the total power constraint is satisfied.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 106Jianwei Zhang, Huawei LAYER-2: CHANNEL QUANTIZATION In our numerical results, the following simple channel quantization algorithm is used: Quantization lookup table construction: 1. Acquire the channel power gain distribution. 2. Identify the range of the channel power with a desirable probability of occurrence, say 90%. 3. Equally partition the corresponding range in the logarithm domain. 4. Set up the thresholds as the middle points of each interval in the logarithm domain. 5. Transform the thresholds into their corresponding thresholds in the original domain.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 107Jianwei Zhang, Huawei LAYER-2: RHO QUANTIZATION When time-sharing cannot be implemented, the following two algorithms can be used: Algorithm 1: Step 1:Select the assignment profile closest to the Total Power Constraint. Step 2:Perform optimal power allocation for that assignment set. Algorithm 2: (shown good enough through numerical evaluation) Select the assignment profile with the total power smaller than the Total Power Constraint. In practice, perfect channel information feedback may not be possible but limited number of bits is used instead.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 108Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (1) Sum rate comparison of (i) optimal SPA, (ii) random SA & optimal PA and (iii)random SA & equal PA with effects of channel quantization: Legend: - Perfect - 3-bit quantization - 1-bit quantization

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 109Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (2) Percentage loss of sum rate for the optimal subchannel and power allocation due to channel quantization:

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 110Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (3) Sum Rate Performance: Optimal Subchannel and Power Allocation: 3-bit Channel Quantization is sufficiently good (~ 1% loss). 1-bit Channel Quantization is fairly good (~ 9% loss). Random Subchannel Assignment with Optimal/Equal Power Allocation: Even 1-bit Channel Quantization gives apparently the same performance.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 111Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (4) Number of iterations required for convergence with 3-bit channel quantization and power constraint accuracy of 99.999998%:

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 112Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (5) Complexity Issue: Optimal Subchannel and Power Allocation (i) Number of operations 1  required: (Number of users)*(Number of subcarriers or subchannels 2 ) *(Number of iterations 3 ) Random Subchannel Assignment with Optimal Power Allocation: (i) Number of operations 1  required: (Number of subcarriers or subchannels 2 )*(Number of iterations 3 ) Random Subchannel Assignment with Equal Power Allocation: Two steps: random subchannel assignment + peak power clipping according to the Power Mask values. Remarks: 1. includes mainly the calculation of power and rate. 2. when the same channel gain and power mask are used in a subchannel. 3. fairly independent of the total number of users, of order O(log(FFT Size)) assuming same #subchannels for all FFT sizes.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 113Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (6) Percentage of the occurrence of subchannel sharing with the application of 3-bit channel quantization.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 114Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (7) Percentage loss of sum rate among the cases of subchannel sharing with sharing factor quantization for the optimal subchannel and power allocation:

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 115Jianwei Zhang, Huawei LAYER-2: PERFORMANCE (8) - Sharing rarely occurs (~2%). - Actual loss due to rho-quantization in total data rate is negligible (~0.01% loss with rho-quantization Algorithm 2 among scenarios with time-sharing).

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 116Jianwei Zhang, Huawei CONCLUSION Developed a two-layer resource allocation algorithm for the downlink IEEE 802.22 WRAN Systems, featuring – interference avoidance to incumbent users – user pre-distribution over subbands in a cell, avoiding over-congestion of subbands in a way that subband with a larger power mask (max. transmit power possible) should handle more CPEs – efficient in-subband subchannel and power allocation for: (i) maximizing subband throughput at affordable complexity, (ii)allowing QoS to be guaranteed, (iii) allowing prioritized transmission and flexible tradeoff between maximum throughput and fairness among users.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 117Jianwei Zhang, Huawei 3. Joint dynamic frequency selection and power control with user specific transmit power mask constraints in uplink WRAN system using OFDMA scheme

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 118Jianwei Zhang, Huawei BACKGROUND (1) Principles of WARN systemsPrinciples of WARN systems  shares the VHF/UHF TV bands between 47MHz-910MHz which are being used by the licensed operators and other license-exempt (LE) devices.  a main constraint is to avoid interference to incumbent services such as TV broadcasting (analog and digital) and Public Safety systems. Role of Dynamic Frequency SelectionRole of Dynamic Frequency Selection  performs multiple-access control to provide QoS-guaranteed services required in the WRAN standard while not disturbing the service quality of the licensed users.  involves user selection, rate adaptation as well as transmit power control (TPC).

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 119Jianwei Zhang, Huawei BACKGROUND (2) Role of Dynamic Frequency Selection Role of Dynamic Frequency Selection (Cont’)  The spectrum occupation information, called geographical spectrum state information (GSSI), is obtained by data fusion and acts as the input information for dynamic frequency selection (DFS). – Usually full GSSI may not be easy to obtain. – Instead of full GSSI, one possible form of partial GSSI is transmit power masks imposed on all WRAN transmitters. CPE 1 {n b, n c }={1, 1} × × × ×× × BS CPE 2 CPE 3 CPE k CPE n CPE j {n b, n c }={1, 6} {n b, n c }={2, 3} {n b, n c }={3, 7} {n b, n c }={5, 8} {n b, n c }={5, 5} n b : Index of subbands n c : Index of subchannels

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 120Jianwei Zhang, Huawei RELATED WORKS (1) · In patent US2005180354 “Method for allocating subchannels in an OFDMA mobile communication system”, Cho et al. proposed resource allocation algorithms to maximum the transmission rates of all users by allocating subchannels and bits. · The scheme introduced an adaptive modulation using linear programming into an existing scheme for a system including a single kind of users, thereby enabling simultaneous execution of the adaptive modulation for all users in a system including two kinds of users.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 121Jianwei Zhang, Huawei RELATED WORKS (2) · In paper “Multiuser OFDM with adaptive subcarrier, bit and power allocation,” Wong et al. considered a subcarrier, bit and power allocation problem in OFDM system. · The objective is to the minimize the total transmitted power, given the minimum data rate requirement of each user.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 122Jianwei Zhang, Huawei DRAWBACKS OF THE RELATED WORK For the patent US2005180354, the problem considered here is actually a rate adaptive problem which maximizes a lower bound of all users’ throughput with respect to a transmit power budget. Delay constraints and users’ priorities were not considered in this invention. It cannot be applied in WRAN systems since it does not employ any technique to guarantee free interference to the incumbent users. Subband allocation among multiple OFDM symbols was not investigated.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 123Jianwei Zhang, Huawei PROPOSED ALGORITHM Two-Layers’ Design Layer-1 Allocation Subband Assignment Layer-2 Allocation In-subband Subchannel, Power and Rate Allocation Knowledge of transmit power mask on every subband in every sector Knowledge of channel gain of the assigned subband Dynamic Frequency Selection Block

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 124Jianwei Zhang, Huawei LAYER 1 (SUBBAND ALLOCATION) (1) Method 1: (Sum-Rate-Max Strategy)Method 1: (Sum-Rate-Max Strategy) Step 1: Step 1: For each 6-MHz subband b, create a list of CPEs in descending order of their transmit power mask values. CPEs with power mask values smaller than a serviceable threshold predefined a priori are eliminated. Step 2: Step 2: Create a list of CPEs in descending order of their maximum power mask values across subbands. Define as the normalized power mask per subchannel of user k on subband b. For k = to where, (i) (ii) Remove CPE k from for all b’s except b k. End

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 125Jianwei Zhang, Huawei LAYER 1 (SUBBAND ALLOCATION) (2) (Cont’) The functions and should be non-decreasing functions. For example, where  b can be set to the average channel gain to noise ratio. Step 3 (Optional): Step 3 (Optional): Perform subband re-assignment starting from the CPE with minimum.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 126Jianwei Zhang, Huawei LAYER 1 (SUBBAND ALLOCATION) (3) Method 2: (Round-Robin-Max Strategy)Method 2: (Round-Robin-Max Strategy) Step 1: Step 1: For each 6-MHz subband b, create a list of CPEs in descending order of the transmit power mask values. CPEs with power mask values smaller than a serviceable threshold predefined a priori are eliminated. Step 2: Step 2: Sort the subbands in descending order of their maximum power mask. Starting from index 1, i.e. the subband with the largest maximum power mask, each subband takes turn to pick up one CPE with the maximum transmit power mask. Any CPE selected in the previous subband will be subtracted from the list of the latter subbands. Repeat Step 2 until the lists of all the subbands are empty.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 127Jianwei Zhang, Huawei AN EXAMPLE FOR LAYER-1 ALGORITHM (1) CPE Subband 1Subband 2 Subchannel Power Mask Approx. Subchannel Data Rate Subchannel Power Mask Approx. Subchannel Data Rate 1505.672500 2505.672500 3605.9307505.6725 4304.9542204.3923 5103.4594304.9542 6405.3576204.3923 Subchannel Power Masks and the Approximated Subchannel Data Rate

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 128Jianwei Zhang, Huawei Sum-Rate-MaxRound-Robin-MaxCPE-Max Subband 1Subband 2Subband 1Subband 2Subband 1Subband 2 CPE selected Data Rate per subch. CPE selected Data Rate per subch. CPE selected Data Rate per subch. CPE selected Data Rate per subch. CPE selected Data Rate per subch. CPE selected Data Rate per subch. --35.672535.9307--15.6725-- 1 ----54.954225.6725-- 2 --1 --35.9307-- 65.3576----44.392344.9542-- --44.392325.6725----54.9542 --5 64.392365.3576-- CPE Assignment and Corresponding Subchannel Data Rates AN EXAMPLE FOR LAYER-1 ALGORITHM (2)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 129Jianwei Zhang, Huawei Subchannel Allocation and Corresponding Subchannel Data Rates Sum-Rate-MaxRound-Robin-MaxCPE-Max Subband 1Subband 2Subband 1Subband 2Subband 1Subband 2 #Subch. allocate d Data Rate per subch. #Subch. allocate d Data Rate per subch. #Subch. allocate d Data Rate per subch. #Subch. allocate d Data Rate per subch. #Subch. allocate d Data Rate per subch. #Subch. allocate d Data Rate per subch. CPE Order --205.6725155.9307--9 (8.7)5.6725-- 14 (14.3) 5.6725---- 17 (17.2) 4.95429 (8.7)5.6725-- 14 (14.3) 5.6725-- 13 (12.5) 5.6725-- 10 (10.4) 5.9307-- 12 (11.4) 5.3576---- 12 (11.4) 4.39235 (5.2)4.9542-- --84.3923 12 (12.5) 5.6725----404.9542 --124.9542 11 (11.4) 4.392375.3576-- Min. CPE Rate 35.1448.3224.77 Sum Rate 431.16416.02421.85 AN EXAMPLE FOR LAYER-1 ALGORITHM (3)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 130Jianwei Zhang, Huawei LAYER-2 ALLOCATION Objective  maximize the weighted system capacity given the QoS requirements and power constraints Problem FormulationProblem Formulation subject to

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 131Jianwei Zhang, Huawei PROPOSED ALGORITHM (1) Our proposed algorithm to solve Layer-2 problem is described a follows:Our proposed algorithm to solve Layer-2 problem is described a follows: Step 1: Initialize all the Lagrangian multipliers to be zeros and set. Step 2: Selection of temporarily optimal CPE for each subchannel given the values of. For every subchannel and every CPE, compute where Then for each subchannel, we select the CPE such that and accordingly set

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 132Jianwei Zhang, Huawei PROPOSED ALGORITHM (2) Step 3: Compute the temporarily optimal power allocation. For each CPE in each subchannel, compute Step 4: Examine whether the total power limitation for each CPE is satisfied or not. Given the temporarily optimal values of and. If has been satisfied for each CPE, stop. The optimal solutions have been obtained. Else, go to Step 5. Step 5: Adjust the values of to satisfy the total power limitations. Denote as the precision of the power allocation within a tolerance error.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 133Jianwei Zhang, Huawei PROPOSED ALGORITHM (3) While haven’t been satisfied for all the CPE’s, Choose the CPE that exceeds the most the total power limitation. Set that the lower bound to be the current value and the upper bound to be, where Set and repeat step 2 and step 3 using. If, set ; Elseif, set. Repeat until is satisfied. End ( Cont’)

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 134Jianwei Zhang, Huawei CHANNEL QUANTIZATION · In practice, perfect channel information feedback may not be possible but limited number of bits is used instead. · A simple channel quantization algorithm is provided where the index of a quantization table based on the estimated channel power gain is used as the channel feedback. Quantization lookup table construction: Step 1: Step 1: Acquire the channel power gain distribution. Step 2: Step 2: Identify the range of the channel power with a desirable probability of occurrence, say 90%. Step 3: Step 3: Equally partition the corresponding range in the logarithm domain. Step 4: Step 4: Set up the thresholds as the middle points of each interval in the logarithm domain. Step 5: Step 5: Transform the thresholds into their corresponding thresholds in the original domain.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 135Jianwei Zhang, Huawei KEY RELATED WORK Paper [Wong99]C. Y. Wong, R. S. Cheng, K. B. Letaief, and R. Murch, “Multiuser OFDM with adaptive subcarrier, bit and power allocation,” IEEE Journal on Selected Areas of Communications, vol. 17, no. 10, pp. 1747-1758, Oct. 1999. US Patent [Li05]X. Li, H. Liu, K. Li, and W. Zhang, “OFDMA with Adaptive Subcarrier-Cluster Configuration and Selective Loading,” US Patent, US6947748 B2, Sep-20 2005. US Patent Application [Cho05]Y.-O. Cho, et al, “Method for Allocating Subchannels in an OFDMA Mobile Communication System,” US Patent Application, US2005/0180354 A1, Aug-18, 2005.

doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 136Jianwei Zhang, Huawei END

Doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 1Jianwei Zhang, Huawei Channel Sensing and Radio Resourse Allocation Algorithms for WRAN Systems.

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Doc.: IEEE 802.22-06/0048r0 Submission May 2006 Slide 1Jianwei Zhang, Huawei Channel Sensing and Radio Resourse Allocation Algorithms for WRAN Systems.

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