1. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 1 IEEE P802.22 Wireless RANs Date: 2007-1-3 Authors: Combined MCS, Mode and Precoder Design for Point to Point MIMO in WRAN with Limited CSI Feedback 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 >

2. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 2 Co-Authors:

3. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 3 Existing Point to Point MIMO in WRAN [1] Existing mechanism in IEEE 802.22 (Annex C.6) –Channel State Information at Transmitter (CSIT) is important for MIMO.  It can be obtained through feedback in WRAN. –Limited feedback for channel state information (CSI) would be required despite TDD and slow fading because the US and DS subcarriers allocation may be different. –Limited feedback bits are used to design the precoding matrix,  e.g. 2(Nt-1) bits are feedback where Nt is the number of transmit antennas. –No mechanism defined in the current specification to drive the transmission rate / MCS (modulation and coding scheme). –The number of data streams (the transmission mode: spatial diversity vs. spatial multiplexing) is not determined by the CSIT.

4. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 4 Existing Point to Point MIMO in WRAN [2] Drawbacks of the current mechanism –Rate / MCS adaptation is very important for robust performance over slowly fading channels. –Rate / MCS adaptation based on ARQ only may have poor performance The ARQ feedback may be outdated when the data traffic is bursting. The user may not be operating on a fixed channel. When the channel for a user changes, the ARQ feedback is unable to predict the channel state in the new channel. –When the MIMO channel is spatial correlated, it is not sure which mode shall be selected (spatial multiplexing or spatial diversity).

5. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 5 Outstanding Issues Limited feedback for CSI would be required despite TDD and slow fading –The US and DS subcarriers allocation may be different Mode Selection, MCS and Precoder Issue –For ARQ-based scheme, the MCS cannot be driven to an optimal transmission setting in a short time  long delay to settle. –No precoder design can be applied with ARQ-scheme. –Subcarrier allocation to a user may change over time  cannot rely entirely on ARQ feedback to drive the rate / MCS. Antenna Correlation Issue –The issue of antenna correlation can be significant due to lower operating frequency. –Feedback bits should be used more efficiently

6. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 6 Proposed Solution Combined MCS, Mode and Precoder Adaptation A simple but efficient online adaptation framework for point-to-point MIMO system over slow fading correlated MIMO channels with  MCS adaptation  space-time (Spatial Diversity vs. Spatial Multiplexing tradeoff) adaptation  precoder (Q) adaptation MAC management message formats and message flows associated with the CSIT feedback and adaptation. The optimal codebook and channel partitioning rule.

7. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 7 Upon receiving data, the receiver estimates the instantaneous CSIR H and determines the partition H belongs to. Suppose H belongs to i-th partition, the receiver feeds back the index i with C fb feeback bits to the MIMO transmitter as the CSI. Once the transmitter receives the bits, the MCS, mode and precoder from the i-th entry of the codebook that will be used for data transmission can be obtained. Online Adaptation Algorithm Combined MCS, Mode and Precoder with MIMO

8. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 8 Online Adaptation Algorithm Combined MCS, Mode and Precoder with MIMO

9. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 9 Suppose we have 4 bits of CSI feedback, 3 transmit and 3 receive antennas. Transmitter: There is a table (with 16 entries) of Precoding Matrix (Q), MCS (R), Spatial Multiplexing vs. Spatial Diversity mode. Receiver: There is a partition (with 16 regions) of the CSIR space. 1.At a time slot, the receiver estimates the current CSI and determines which of the 16 regions it falls into. 2.The receiver feeds back the region index (e.g. 3) to the transmitter via the 4-bit feedback link. 3.The transmitter utilizes the MCS, Mode and Precoder from the 3 rd entry in the table.  Low overhead (4 bits) and low complexity. Online Adaptation Algorithm A Simple Illustrative Example

10. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 10 Suppose there are 4 bits feedback for a sub-channel, in which a CPE occupies 2 discontinuous sub-channels. –The BS shall use a message, CFB-REQ, to inform the CPE when feedback is needed on the 2 occupied sub-channels: The starting feedback frame Number of feedback frames The index of the sub-channels requiring feedback –When the CPE received the feedback requesting message, it shall use a message, CFB-RSP, to report limited feedback to the BS (4 bits per sub-channel): Index of the feedback sub-channels Limited feedback bits for these sub-channels. MAC Management Messages (1)

11. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 11 Table 1: CFB-REQ message format Table 2: CFB-REQ message body Syntax SizeNotes CFB-REQ_Message_Format() { Management Message Type = 608 bits Message BodyVariableTable 2 } SyntaxSizeNotes CFB-REQ_Message_Body() { Frame Number8 bitsThe least significant 8 bits of the number in which to start the measurement. Number of Frames7 bitsThe number of frames over which to measure. Number of sub-channels, c8 bitsThe number of sub-channels requested to estimate and feedback. For i= 1:c { sub-channel index8 bitsThe index of the sub-channels requested to estimate and feedback. } reserved1 bitsShall be set to zero } MAC Management Messages (2)

12. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 12 Table 3: CFB-RSP message format Table 4—CFB-RSP message body Syntax SizeNotes CFB-RSP_Message_Format() { Management Message Type = 618 bits Message BodyVariableTable 4 } SyntaxSizeNotes CFB-RSP_Message_Body() { Number of sub-channels, c8 bitsThe number of sub-channels requested to estimate and feedback. For i= 1:c { sub-channel index8 bitsThe index of the sub-channels requested to estimate and feedback. Feedback for the sub-channels8 bitsIndex of the partition that the CSI belongs to. Shall be feedback to the transmitter through the reverse link. The transmitter uses the parameters (rate, mode and precoder) within the codebook on the forward link. } } MAC Management Messages (3)

13. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 13 MAC Management Messages Timing and Message Flows (1)

14. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 14 CFB-REQ/RSP can be applied to both DS and US transmissions. It is not compulsory to set the maximum number of bits for each sub-channel as 8. The actual number of feedback bits can be smaller for a small codebook. Table 24 of the specification is revised as follows. Table 24: Management messages Type MessageDescriptionConnection 0-59……… 60CFB-REQMIMO Channel Feedback RequestBasic 61CFB-RSPMIMO Channel Feedback ResponseBasic MAC Management Messages Timing and Message Flows (2)

15. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 15 Optimal Codebook Design 2-by-2 system, 9dB SNR, 2 bits feedback Codebook Entry MCS (R) Mode (M)Precoder (Q) ModulationEncoding Rate 1BPSK 3/4 2 2 16QAM 3/5 1[-0.7059 -0.6581+0.2620i] T 3 16QAM 7/8 1[-0.7048 -0.6556+0.2711i] T 4 64QAM 3/4 1[-0.7073 -0.6537+0.2690i] T

16. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 16 Channel Partitioning Rule –R is the transmission rate that MCS can provide; –M is the transmission mode which denotes the number of data streams transmit simultaneously; –V is the right singular matrix of H; –P is the power constraint.

17. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 17 Simulation Settings Antenna spacing / wavelength = 1 –The calculation of the correlation matrix only needs the ratio –Since the TV operating band is 47-910MHz, the WRAN system can work on ~100MHz band with a wavelength of 3m. Number of scatters = 100 Angular spread (Transmit Correlation) = 20 (in degree) Feasible mode = 1 to Nr –Nt ≥ Nr, where Nr is the number of receive antennas) FER constraint:

18. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 18 Simulation Results (1)

19. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 19 Simulation Results (2)

20. doc.: IEEE 802.22-07/0041r0 Submission January 2007 Soo-Young Chang, Huawei TechnologiesSlide 20 Conclusion We proposed an integrated limited feedback design framework for point-to- point MIMO systems over slow fading correlated MIMO channels with (a) rate/modulation adaptation; (b) space-time (Spatial Diversity vs. Spatial Multiplexing tradeoff) adaptation (c) Q (precoder) adaptation The MIMO system goodput can be significantly enhanced by rate, mode and precoder adaptation. The codebook is obtained offline and the online adaptation algorithm is very simple. Hence the design is practical.