A-MAP Diversity Issues and Proposed Solution (15.3.5.3.2)
Document Number: IEEE C802.16m-09/2589
Date Submitted: 2009-11-06
Source:
Yi Hsuan
JK Fwu
Yang-seok Choi
Hujun Yin
yi.hsuan@intel.com
Intel Corporation
Re:
Venue:
Category: AWD-Comments / Area: Chapter 15.3.5.3.2 (DL physical structure)
“Comments on AWD 15.3.5.3.2 DL physical structure”
IEEE Session#64, Atlanta
Purpose: Discussion and Adoption by TGm
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1
DRU Subcarrier Permutation
• DRU subcarrier permutation is done in the following step:
– Suppose that there are LDRU,FPi DRUs in frequency partition i. There are
LDRU,FPi * 8 data tone pairs per OFDMA symbol in those DRUs.
– Renumber those data tone pairs as RSPFPi,l[u], where l is OFDMA symbol
index in the subframe and 0≤ u < LDRU,FPi*8.
– Apply the subcarrier permutation formula in the following to generate the
s-th DLRU, 0 ≤ s < LDRU,FPi
SPFPiLRUs,l[m]=RSPFPi,l[k], where m is the subcarrier pair index, 0 ≤ m < 8,
and
k = LDRU,FPi*f(m,s)+g(PermSeq(),s,m,l)
f(m,s)=(m+13*s)mod 8
g(PermSeq(),s,m,l)={PermSeq[(f(m,s)+s+l)mod
LDRU,FPi]+DL_PermBase}mod LDRU,FPi
2
Alloation of A-MAP Channels in DLRUs
• The permutation guarantees that for each OFDMA symbol any DLRU is
composed of tone-pairs from all DRUs (up to 8).
• However A-MAP channels are smaller in size than DLRU.
– NUS-A-MAP: 72 tones
– A-A-MAP: 56 tones
– HF-A-MAP: 16 tones
– PC-A-MAP: 4 tones
• In additional to size, A-MAP channels are formed in the time first manner.
• The diversity orders for A-MAP channels need to be investigated.
3
Example of a DLRU – Created from 4 DRUs
Time
Frequency
DRU 0 tone-pair
DRU 1 tone-pair
DRU 2 tone-pair
DRU 3 tone-pair
4
Some Pathological Cases of the Current
Permutation
• The pathological situation on the previous slide can happen in the following
cases:
– When DRU number is 4 in the frequency partition, there is no PRU
diversity for any given tone-pair index m over all symbols in a DLRU.
– When DRU number is 8 in the frequency partition, there is no PRU
diversity for any given tone-pair index m over all symbols in a DLRU.
• For other cases the problem is less pronounced but sacrifice in A-MAP diversity
is still unavoidable.
5
Diversity Order of A-MAP Channels
• The minimum diversity order of a A-MAP channel is the minimum number of
DRUs that its tones come from.
• Given a 6 symbol subframe, the minimum A-MAP channel diversity can be
derived from the permutation equation and A-MAP channel size.
NUS-A-MAP
A-A-MAP
HF-A-MAP
PC-A-MAP
Minimum diversity order with
2 DRUs
2
2
1
1
Minimum diversity order with
3 DRUs
3
2
1
1
Minimum diversity order with
4 DRUs
3
3
1
1
Minimum diversity order with
5 DRUs
4
3
1
1
6
Proposed DRU Subcarrier Permutation
f(m,s) needs to be modified, in order to make tone pairs in different
symbols with the same tone-pair index m come from different DRUs.
Modification:
f(m,s,l)=[m+13*(s+l)]mod 8
– l, the symbol index, is introduced in the equation in order to provide
enough offset such that tones from different DRUs can be selected
for different symbols.
7
Example of a modified DLRU – Created from 4
DRUs
Time
Frequency
DRU 0 tone-pair
DRU 1 tone-pair
DRU 2 tone-pair
DRU 3 tone-pair
8
Diversity Order of A-MAP Channels Using the
Modified DLRU
• HF-A-MAP diversity order equals the number of DRUs until 4 DRUs, which
provide about full diversity.
• Diversity order of 2 can be guaranteed for PC-A-MAP.
• Diversity order of NUS-A-MAP and A-A-MAP equals DRU numbers up until 5
DRUs.
NUS-A-MAP
A-A-MAP
HF-A-MAP
PC-A-MAP
Minimum diversity order with
2 DRUs
2
2
2
2
Minimum diversity order with
3 DRUs
3
3
3
2
Minimum diversity order with
4 DRUs
4
4
4
2
Minimum diversity order with
5 DRUs
5
5
4
2
9
Proposed AWD Text Change:
Modify Section 15.3.5.3.2, page 302, line 65 as follows
f(m,s) = [m + 13*(s+l) ] mod LSP,l
10