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

January 2007

Soo-Young Chang, Huawei TechnologiesSlide 1

doc.: IEEE 802.22-07/0041r0

Submission

IEEE P802.22 Wireless RANs Date: 2007-1-3Name Company Address Phone email

Vincent K. N. Lau HKUST Hong Kong, China 852-2358-7066 [email protected]

Wai Ho Mow HKUST Hong Kong, China 852-2358-7070 [email protected]

Roger S. Cheng HKUST Hong Kong, China 852-2358-7072 [email protected]

Ross D. Murch HKUST Hong Kong, China 852-2358-7044 [email protected]

Khaled Ben Letaief HKUST Hong Kong, China 852-2358-7064 [email protected]

Linjun Lu Huawei Technologies Shenzhen, China 0086-755-28973119 [email protected]

Soo-Young Chang Huawei Technologies Davis, CA, U.S. 1-916 278 6568 [email protected]

Jianwei Zhang Huawei Technologies Shanghai, China 86-21-68644808 [email protected]

Lai Qian Huawei Technologies Shenzhen, China 86-755-28973118 [email protected]

Jianhuan Wen Huawei Technologies Shenzhen, China 86-755-28973121 [email protected]

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 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 [email protected].>

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Submission

Name Company Address Phone email

Terry T.Y. Wu HKUST Hong Kong, China 852-2358-7086 [email protected]

S. M. Mok HKUST Hong Kong, China 852-2358-7086 [email protected]

Edward K. S. Au HKUST Hong Kong, China 852-2358-7086 [email protected]

Zhou Wu Huawei Technologies Shenzhen, China 86-755-28979499 [email protected]

Jun Rong Huawei Technologies Shenzhen, China 86-755-28979499 [email protected]

Jian Jiao Huawei Technologies Beijing, China 86-10-82882751 [email protected]

Meiwei Jie Huawei Technologies Shenzhen, China 86-755-28972660 [email protected]

Co-Authors:

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Submission

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.

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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 ch

anges, 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 sele

cted (spatial multiplexing or spatial diversity).

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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

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Submission

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.

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• 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 Cfb

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

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Submission

Transmitter Receiver

{R_1, Q_1, Mode_1};{R_2, Q_2, Mode_2};

.

.

.{R_N, Q_N, Mode_N}.

{feedback link}

Data Source

Precoding Matrix Q

Data rate / MCS (R);Selection of Modes (SD vs SM)

Online Adaptation Algorithm Combined MCS, Mode and Precoder with MIMO

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Submission

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.

• At a time slot, the receiver estimates the current CSI and determines which of the 16 regions it falls into.

• The receiver feeds back the region index (e.g. 3) to the transmitter via the 4-bit feedback link.

• The transmitter utilizes the MCS, Mode and Precoder from the 3rd entry in the table.

Low overhead (4 bits) and low complexity.

Online Adaptation Algorithm A Simple Illustrative Example

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Submission

• 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)

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Table 1: CFB-REQ message format

Table 2: CFB-REQ message body

Syntax Size Notes

CFB-REQ_Message_Format() {

Management Message Type = 60 8 bits

Message Body Variable Table 2

}

Syntax Size Notes

CFB-REQ_Message_Body() {

Frame Number 8 bits The least significant 8 bits of the number in which to start the measurement.

Number of Frames 7 bits The number of frames over which to measure.

Number of sub-channels, c 8 bits The number of sub-channels requested to estimate and feedback.

For i= 1:c {

sub-channel index 8 bits The index of the sub-channels requested to estimate and feedback.

}

reserved 1 bits Shall be set to zero

}


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Table 3: CFB-RSP message format

Table 4—CFB-RSP message body

Syntax Size Notes

CFB-RSP_Message_Format() {

Management Message Type = 61 8 bits

Message Body Variable Table 4

}

Syntax Size Notes

CFB-RSP_Message_Body() {

Number of sub-channels, c 8 bits The number of sub-channels requested to estimate and feedback.

For i= 1:c {

sub-channel index 8 bits The index of the sub-channels requested to estimate and feedback.

Feedback for the sub-channels 8 bits Index 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.

}

}


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Submission

MAC Management MessagesTiming and Message Flows (1)

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• 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 Message Description Connection

0-59 … … …

60 CFB-REQ MIMO Channel Feedback Request Basic

61 CFB-RSP MIMO Channel Feedback Response Basic

MAC Management MessagesTiming and Message Flows (2)

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Submission

Optimal Codebook Design2-by-2 system, 9dB SNR, 2 bits feedback

-0.6742 0.7385

-0.6674 + 0.3162i -0.6093 + 0.2887i

Codebook Entry

MCS (R)

Mode (M) Precoder (Q)

Modulation Encoding Rate

1 BPSK 3/4 2

216QAM 3/5

1 [-0.7059 -0.6581+0.2620i]T

316QAM 7/8

1 [-0.7048 -0.6556+0.2711i]T

464QAM 3/4

1 [-0.7073 -0.6537+0.2690i]T

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Submission

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.

[ ]

**[1] [2] [ ] [i]

** 2[1] 2 [1] [1] [1]

[

Without loss of generality, let { } are sorted in ascending order. ie

.... , the partition {H } below is an optimizing partition.

: log | |

i

N

nR nT H HM

i

R

R R R

H C P R

H

H H HH I Σ V V V V

** 2] [ ] 2 [ ] [ ] [ 1]

** 2[ ] 2 [ ] [ ] [ 1]

: log | | for [2,.., 1]

: log | |

nR nT H Hi M i i i

nR nT H HN M N N N

C R P R i N

H C P R

H H H

H H H

H I Σ V V V V

H I Σ V V V V

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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: 0.01

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Simulation Results (1)

0 5 10 150

1

2

3

4

5

62x1 (Correlation coefficient = 0.94)

SNR (dB)

Ave

rage

sys

tem

Goo

dput

(b/

s/H

z)2 bits feedback (Adaptive rate, mode and precoder)

Fixed rate, mode and precoder

Ergodic capacity with perfect CSIT

2 bits feedback (Design in draft)

Full CSIT

Proposed design

No CSIT

Design in standard draft chapter 8.10.1

Full CSIT

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Submission

Simulation Results (2)

0 5 10 150

1

2

3

4

5

6

72x2 (Correlation coefficient = 0.94)

SNR (dB)

Ave

rage

sys

tem

Goo

dput

(b/

s/H

z)2 bits feedback (Adaptive rate, mode and precoder)

Fixed rate, mode and precoder

Ergodic capacity with perfect CSIT

2 bits feedback (Design in draft)

Full CSIT

Proposed design

No CSIT

Design in standard draft chapter 8.10.1

January 2007


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Submission

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.

Documents

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