IEEE C80216m-09/0264
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Proposed Text for the DL MIMO Section (Differential Codebook Feedback) of the IEEE
802.16m Amendment
Date
Submitted
2009-01-07
Source(s)
Hosein Nikopourdeilami, Mo-Han
Fong, Sophie Vrzic, Robert Novak,
Dongsheng Yu, Kathiravetpillai
Sivanesan
Email:
hosein@nortel.com
mhfong@nortel.com
Nortel Networks
Re:
802.16m amendment working document, IEEE 802.16m-08/053r1
Abstract
The contribution proposes the text for the DL MIMO section to be included in the 802.16m
amendment working document.
Purpose
To be discussed and adopted by TGm for the 802.16m amendment.
Notice
Release
Patent
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Proposed Text for the DL MIMO Section
(Differential Codebook Feedback) of the IEEE 802.16m Amendment
Hosein Nikopourdeilami, Mo-Han Fong, Sophie Vrzic, Robert Novak, Dongsheng Yu, Kathiravetpillai
Sivanesan
Nortel Networks
1. Introduction
The contribution proposes the text for the DL MIMO section (Differential Codebook Feedback) to be included
in the 802.16m amendment. The proposed text is developed so that it can be readily combined with IEEE
P802.16 Rev2/D8 [1], it is compliant to the 802.16m SRD [2] and the 802.16m SDD [3], and it follows the style
and format guidelines in [4]. The simulation results supporting the proposed scheme for differential feedback is
provided in [5, 6].
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IEEE C80216m-09/0264
2. References
[1] IEEE P802.16 Rev2/D8, “Draft IEEE Standard for Local and Metropolitan Area Networks: Air Interface
for Broadband Wireless Access,” Dec. 2008.
[2] IEEE 802.16m-07/002r6, “802.16m System Requirements”
[3] IEEE 802.16m-08/003r6, “The Draft IEEE 802.16m System Description Document”
[4] IEEE 802.16m-08/043, “Style guide for writing the IEEE 802.16m amendment’
[5] C80216m-08/1074r1, “Evaluation of Codebook and Differential Feedback for DL Closed-Loop SU-MIMO”
[6] IEEE C802.16m-08/347, “Proposal for IEEE 802.16m Differential Encoding/Decoding for CL-MIMO
Codebook Feedback”
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3. 4. Text proposal for inclusion in the 802.16m amendment
-------------------------------------- Start of the text proposal
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[Add the following text to page 30, line 22 of IEEE 802.16m-08/050]
15.3.x DL MIMO Transmission Scheme
15.3.x.1 DL MIMO Architecture and Data Processing
15.3.x.2 Transmission for Data Channels
15.3.x.2.1 Single-user MIMO
15.3.x.2.1.1 Open-loop SU-MIMO
15.3.x.2.1.2 Closed-loop SU-MIMO
15.3.x.2.1.2.1 Precoding Technique
15.3.x.2.1.2.2 Feedback for SU-MIMO
In FDD systems and TDD systems, a mobile station may feedback some of the following information in Closed
loop SU-MIMO mode:
 Rank (Wideband or sub-band)
 Sub-band selection
 CQI (Wideband or sub-band, per layer)
 PMI (Wideband or sub-band for serving cell and/or neighboring cell)
 Long-term CSI
For codebook based precoding, three different feedback modes for the PMI are supported:

The standard mode: The PMI feedback from a mobile station shall represent an entry of the base
codebook. It shall be sufficient for the base station to determine a new precoder.

The adaptive mode: The PMI feedback from a mobile station shall represent an entry of the transformed
base codebook according to long term channel information.

The differential mode: the feedback from a mobile station provides a differential knowledge of the
short-term channel information. This feedback represents information that is used along with other
feedback information known at the base station for determining a new precoder. Details of differential
CSI feedback is described in section 15.3.x.2.3.
Mobile station shall support the standard, differential, and adaptive modes. The feedback information may be
transmitted via a physical layer control channel or via a higher layer signaling message.
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In TDD systems, a mobile station may transmit a sounding signal on the uplink.
15.3.x.2.2 Multi-user MIMO
15.3.x.2.2.1 Precoding technique
15.3.x.2.2.2 Unification with SU
15.3.x.2.2.3 Feedback for MU-MIMO
15.3.x.2.2.3.1 CQI feedback
15.3.x.2.2.3.2 CSI feedback
Channel state information feedback may be employed for MU-MIMO. Codebook-based feedback is supported
in both FDD and TDD. Sounding-based feedback is supported in TDD.
For codebook based precoding, three different feedback modes for the PMI are supported:

The standard mode: the PMI feedback from a mobile station shall represent an entry of the base
codebook. It shall be sufficient for the base station to determine a new precoder.

The adaptive mode: The PMI feedback from a mobile station shall represent an entry of the transformed
base codebook according to long term channel information.

The differential mode: the feedback from a mobile station provides a differential knowledge of the
short-term channel information. This feedback represents information that is used along with other
feedback information known at the base station for determining a new precoder. Details of differential
CSI feedback is described in section 15.3.x.2.3.
Mobile station shall support the standard, differential, and adaptive modes. The unified codebook for SU and
MU is employed. The MU MIMO codebook contains subsets of the unified codebook (including full set) to
support both unitary and non-unitary precoding. When codebook-based feedback is used, the ABS indicates
which codebook subset (including full set) will be used explicitly or implicitly.
An enhanced UL sounding channel is used to feedback CSI-related information by the AMS to facilitate vendorspecific adaptive closed-loop MIMO precoding. For sounding-based precoding, the enhanced UL sounding
channel can be configured to carry a known pilot signal from one or more AMS antennas to enable the ABS to
compute its precoding/beamforming weights by leveraging TDD reciprocity. The sounding waveform can be
configured to occupy portions of the frequency bandwidth in a manner similar to the sounding waveform used in
the legacy system. To facilitate analog-feedback-based precoding, the enhanced UL sounding channel can be
configured to carry unquantized CSI-related information (e.g., an unquantized encoding of the DL spatial
covariance matrix or an unquantized encoding of the eigenvectors of the DL spatial covariance matrix). The
unquanitized CSI-related information can be specific to a particular specified portion of the band (narrowband
feedback) or specific to the entire bandwidth (wideband feedback).
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15.3.x.2.3 Differential CSI Feedback for Closed-loop Single-user and Multi-user MIMO
Differential encoding is used to reduce amount of feedback overhead and/or improve the performance of closedloop MIMO mode. If the channel variation is slow in the time domain, the sequence of the channel codewords is
highly correlated. Therefore, instead of the codeword index (PMI), one can transmit only the offset of the
codeword index.
15.3.x.2.3.4 Codebook Description
Assume C as a codebook with M codewords denoted by ci , i  0,1,, M  1 . The codebook used for
standard mode PMI feedback is a subset of the codebook C . The codebook C is defined in section 15.3.x.2.3.
15.3.x.2.3.5 Differential Codebook Subsets
Corresponding to each codeword ci  C , there is a differential subset of codewords S (ci )  {cik }kL10 . The subset
contains L < M distinct codewords. The differential subsets are defined in section 15.3.x.2.3.
15.3.x.2.3.6 Differential Encoder
Consider ci (n) as a codeword selected from the codebook C for the time index n . For the next feedback
report at time n  1 , the codeword is selected among the differential subset S (ci (n)) which contains only
L elements. Therefore, the differential PMI kn 1 can be repressed by log 2 ( L) bits which is less than the
original log 2 (M ) bits of the codebook C .
15.3.x.2.3.9 Differential Decoder
Consider ciˆ ( n) as the estimate of the codeword at time n . When decoder receives the differential PMI kn 1
at time n  1 , it searches among the differential subset S (ciˆ (n)) to pick kn 1 ’th element as the received
codeword of the time n  1 . If estimate of time n is with error, the error propagates to the PMI estimation of
the time n  1 , as well.
15.3.x.2.3.7 Initialization of Differential Encoder
For the first feedback report, MS must encode the absolute PMI. The differential encoding is applied after the
first PMI report. The first PMI can be selected form a subset of the original codebook C . The subset codebook
is called coarse codebook and contains D  M elements. If the size of coarse book and the differential subset
are identical ( D  L) , the feedback rate does not change from time to time. The coarse codebook is defined in
section 15.3.x.2.3.
15.3.x.2.3.8 Reset of Differential Encoder
To eliminate effect of differential error propagation, the differential encoder must be reset after P encoding
stage. After resetting, the encoder start encoding over from coarse codebook and continues by differential
encoding for P  1 time, until the next reset occurs.
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