1. Network Coding Retransmission Design with Common Feedback Channel
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IEEE C802.16m-09/0437
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Hung-Yu Wei, Ching-Chun Chou Voice: [Telephone Number (optional)]
Department of Electrical Engineering,
National Taiwan University
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In response to Call for SDD comments
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2. Basic Idea Observation Basic idea
Given an MBS group and a set of packets for transmission
Transmission error could occur on any packets/nodes
If there is only 1 or no packet loss, 1 XOR-coded retransmission could recover the transmission error.
This holds for every MSj in the MBS group
Basic idea
1 XOR-coded retransmission packet for an MBS group with only 1 or no packet loss.
Feedback design
Use E-MBS common feedback channel to transmit NACK
NACK feedback when 2 packet loss occurs

3. E-MBS with Common Feedback Channel
Network-Coding based retransmission
Common feedback channel to transmit NACK
X: Erroneous reception
The XOR-coded retransmission packet could repair packet losses from P1 to P5.
P1+P2+P3+P4+P5
Next batch starts from P6. P1 P2 P3 P4 P5 P6 x BS
MS1
MS2
MS3
Uplink feedback
More than 1 packet loss for MS1 & MS3

4. NACK Common Feedback and XOR retransmission
BS transmits MBS packets P1, P2, …
If there is exactly 1 packet loss among previous transmitted packet P1~P(k-1) for MSj .
When packet Pk is lost, MSj sends NACK through common feedback channel
After receiving NACK, BS retransmits network coded packet
R=(P1…  P(k-1))
The next batch starts
BS transmits Pk, P(k+1), ….

5. Proposed Text 14.3.3 E-MBS Operation with Retransmission
Details on E-MBS Operation with HARQ retransmission is FFS. An ABS may use a network-coding based retransmission scheme that does not require a feedback channel.
Modify the text marked in red as
An ABS may use a network-coding based retransmission scheme with or without E-MBS common feedback channel.