2-bit HARQ Feedback
Document Number: IEEE C802.16m-09/1139
Date Submitted: 2009-05-02
Source:
Yujian Zhang
Jong-kae (JK) Fwu
Hujun Yin
[email protected]
[email protected]
[email protected]
Intel Corporation
Re:
Venue:
Category: AWD-Comments / Area: Chapter 15.3.9 (UL-CTRL)
“Comments on AWD 15.3.9 UL-CTRL”
IEEE Session#61, Cairo
Base Contribution: None
Purpose: Discussion by TGm
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1
2-bit HARQ Feedback
•
2-bit HARQ feedback scheme in AWD is as follows :
Sequence
index
0
1
2
3
Orthogonal sequence
[+1 +1 +1 +1]
[+1 -1 +1 -1]
[+1 +1 -1 -1]
[+1 -1 -1 +1]
1-bit Feedabck
Even numbered channel ACK
Even numbered channel NACK
Odd numbered channel ACK
Odd numbered channel NACK
2-bit Feedback
ACK/ACK
ACK/NACK
NACK/ACK
NACK/NACK
2
Impact from Missing A-MAP (1)
• A-MAP reliability requirement is 1% PER, which means that there is 1%
probability that AMS misses one A-MAP.
– Assuming 2 A-MAPs are independent, the probability that 1 A-MAP is correct while
another A-MAP in error is 2*0.99*.0.01=0.0198
– In this scenario, there is a NACK->ACK error; note that the related error requirement is
0.001.
3
Impact from Missing A-MAP (2)
• Can the permutation of 2-bit feedback assignments solve the problem?
• Without loss of generality, we fix the order for 1-bit feedback, and vary the
order for 2 bit feedback.
– Sequence 0 can only be ACK/NACK. The rationale is: when only A-MAP 2 is
in error,
• ACK/ACK introduces NACK->ACK error for data 2
• NACK/ACK introduces ACK->NACK error for data 1, and NACK->ACK error for
data 2
• NACK/NACK introduces ACK->NACK error for data 1.
– Similarly, sequence 2 can only be NACK/ACK, in consideration of A-MAP 1
error.
– Then ACK/ACK and NACK/NACK are allocated for sequence 1 and 3.
• However, no matter ACK/ACK is assigned to sequence 1 or 3, there is NACK>ACK error due to A-MAP error.
• In conclusion, no matter how the mapping table is generated, 2-bit
feedback scheme has the problem of NACK->ACK (i.e. increase NACK>ACK probability to 1 magnitude over 0.001).
4
Recommended Solution
• When HARQ feedback channels in one subframe are related to
transmissions from more than one subframes, they are transmitted
independently from different regions.
• An example for TDD 5:3 ratio.
5