AWD Text Modification to Non-adaptive precoding in DL MIMO
Document Number: IEEE C80216m-09_0896
Date Submitted: 2009-04-27
Source:
Kiran Kuchi, J. Klutto Milleth, Vinod R, Dileep M K,
Divagar , Padmanabhan M S,
Bhaskar R, Giridhar K
Voice:
CEWiT, India
E-mail:
[email protected],
[email protected]
Venue: Call
for Comments on IEEE 802.16m-09/0010r1a IEEE 802.16m Amendment text/Area:
Chapter 15.3.7 (DL-MIMO)
Base Contribution: None
Purpose: To discuss and adopt the proposed text in amendment text
To discuss in TGm for appropriate action. Notice:
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Suggested modification to Nonadaptive precoding



The mandatory non-adaptive precoder which is defined in DL MIMO section 15.3.7.1.2.1 uses
N1 cycling and the precoder W is fixed in time.
The purpose of this method is to keep the precoder fixed for the duration of the sub-band and
enable best-M scheduling
With multiple frequency partitions, the number of sub-bands available in each frequency
partition is insufficient to implement N1-cycling+best-M scheduling . For example in 5 M Hz BW,
with 4-partitions, the number of subbands/partition is only one.

N1 cycling has no meaning in such scenarios

Proposed change:

For single frequency partition case, use N1 cycling


The precoder W does not depend on the subframe number

The precoder W changes every N1 PRUs in the same subframe
For multiple frequency partitions, use 1D and/or 2D-POD

The precoder W changes with the subframe number

The precoder W changes every N2 PRUs in the same subframe
1D Vs 2D POD with N2 cycling

For multiple frequency partitions, reduced amount of BW available in each partition

More users can be served if users are simultaneously scheduled over two subframes




“1D-POD in time” suitable diversity mode for low-medium bit-rate users who are allocated 1PRU in frequency, and allocation extended over two or more subframes.
“1D-POD in frequency” useful diversity mode when the user is given multiple PRUs in same
subframe
2D-POD gives extra diversity gain when resource allocation spans both frequency and time
2D-POD subsumes “1D-POD in time” and “1D-POD in frequency” as special cases. 2D-POD
can only provide a benefit

2D-POD facilitates robust CQI computation (by virtue of special property of the DFT code book)

2D-POD can be used in conjunction with best-band scheduling
Non-Adaptive precoder Text for DL
MIMO


With non-adaptive precoding, the precoding matrix is an NtX Mt matrix W(k), where Nt is the number of
transmit antennas, Mt is the number of streams, and k is the physical index of the subcarrier where W(k) is
applied. The matrix W(k) is selected from a subset of size Nw precoders of a base code book for a given Mt.
The matrix W changes every N Psc contiguous physical subcarriers according to equation (10). W belongs to
a subset of the base code book specified in section 15.3.7.2.6.6.2.4.1.
When a single frequency partition is used, the precoder W does not depend on the subframe number . The
value of N is equal N1. The NtX Mt precoding matrix W(k) applied on subcarrier k is selected as the code
word of index i in the open-loop codebook subset with Mt streams where i is given by


i=mod([k/(NPsc)]-1, Nw)
When the frequency band is split into multiple frequency partitions, in each partition, the value of N is set
equal to N2 , Psc=18. The precoder W changes with the subframe number. The W is computed as elementwise multiplication of two vectors/matrices as:
W=Cs(i).Cs(j) where i=mod([k/(NPsc)]-1, Nw) and j=mod(q,Nw) where q is the subframe number, and Cs is
open-loop subset code book of size Nw=4..
OL code book subsets for Nw=4

The base 2-Tx OL code book uses the following entries from the C(2,1,3) code book. The subsets for Nw=4 are given by the
entries of C(2,1,3,m) where the index m takes the following values m=0,4,6,2 in the specified order. The subset code book Cs
is represented in Tabular form as
index

0
1
2
3
0.7071
0.7071
0.7071
0.7071
0.7071
-0.7071
j0.7071
-j0.7071
4-Tx OL code book subset for Nw=4 uses the following entries from the C(4,1,6) code book. The subset a for Nw=4 are given by
the entries of C(4,1,6,m) where the index m takes the following values m=6,0,1, 2 in the specified order. The subset code book
Cs is represented in Tabular form as
index
0
1
2
3
0.5
0.5
-0.5
-0.5
0.5
-0.5
-0.5
0.5
0.5
0.5
0.5
0.5
0.5
-0.5
0.5
-0.5