Modification to OL Precoder Cycling
Document Number: IEEE S80216m-09_1918
Date Submitted: 2009-08-29
Source:
Kiran Kuchi, J. Klutto Milleth, Padmanabhan M S
CEWiT, India
Voice:
E-mail:
kkuchi@cewit.org.in,
klutto@cewit.org.in
Venue: Comments
on P802.16m/D1:
Base Contribution: IEEE C80216m-09_1918
Purpose: To discuss and adopt the proposed text in section 15.3.7.1.2.1
To discuss in TGm for appropriate action. Notice:
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Advantage of precoder cycling


Localized allocation uses N1 cycling i.e., same
precoder is applied in a subband and precoder
changes from subband to subband

N1 cycling artificially introduces peaks and nulls in
the channel

With best band scheduling high multi-user diversity
DRU and mini-band CRU uses SFBC or SM with
precoding

In channels with low frequency selectivity e.g.,
PED-A, precoder cycling increases the diversity
benefit
Current OL precoder cycling
specification

In the D1

OL precoder cycles every N1=4 PRUs


N1 cycling is optional in rank-1 OL region
The precoder to be applied in each PRU is
predetermined before permuting the subbands and
mini-bands
Problems with current precoder
cycling specification

With multiple frequency partitions,

In some cases, the subbands which are allocated in
the same frequency partition are contiguous in
frequency and they share the same precoder

If the channel does not change across contiguous
subbands, it adversely degrades best-band
scheduling gain when user is allocated in the same
frequency partition
Problems with current precoder
cycling specification contd.

In certain frequency partitions, the precoder
allocated in mini-band CRUs DRUs take the
same value

Loss in diversity advantage in channels with low
frequency selectivity such as PED-A

Even in channels with high frequency selectivity,
there will be loss in diversity advantage if the
allocated min-band CRUs are adjacent in frequency
Proposed Remedy



This problem is overcome if precoder cycling is specified in each
frequency partition separately
In each frequency partition (FP),

define a logically contiguous sub-band CRU index to all the
subbands and allocated in that FP

define a logically contiguous mini-band CRU index to all the
mini band CRUs allocated in that FP

define a logically contiguous mini-band DRU index to all the
mini band DRUs allocated in that FP
In each FP,

For subband CRUs, Precoder cycling based on logical sub-band index

For mini-band CRUs, Precoder cycling based on logical miniband-CRU
index

For mini-band DRUs, Precoder cycling based on logical miniband-DRU
index
Precoder cycling: illustration
Black color: precoder cycling before FP
Red color: logical index based cycling
Precoder allocation before FP
C(0), C(0)
C(1),
C(0)
C(1),
C(1)
C(1),
C(0)
C(0),
C(0
)
C(1
)
C(1)
C(1),
C(0)
C(1),
C(1)
C(1),
C(0)
C(1),
C(1)
C(0), C(0)
C(0
)
C(0), C(1)
C(1
)
C(0
)
C(1),
C(0)
C(1),
C(1)
C(1), C(0)
C(1),
C(1)
C(1
)
C(0), C(0)
C(0
)
C(0), C(1)
C(1
)
C(0
)
C(0),
C(0)
C(1), C(1)
C(1),
C(0)
C(1),
C(1)
C(1
)
C(0), C(0)
C(0
)
C(1), C(1)
C(1
)
C(1),
C(0)
C(1),
C(1)
C(1),
C(0)
C(1),
Precoder cycling illustration


In CRU(FP1), if precoder cycling is done before frequency
partition, two contiguous subbands are allocated with
same precoder C(0)

Loss in best-band scheduling gain if channel does not vary across
these sub-bands

With the proposed precoder cycling two distinct precoders will be
allocated in these subbands
In DRU(FP3), current method allocates same precoder
C(1) to all PRUs. The proposed method cycles between
C(0) and C(1) sequentially
Proposal


Adopt the text proposed in C80216m-09_1918
for OL precoder cycling in OL MIMO region
In OL region, the MS need not know the OL
precoder, the proposed solution does not
increase implementation complexity at AMS.