1. ARQ block generation method in IEEE 802.16m
Document Number:
IEEE S802.16m-08/996r1
Date Submitted:
Source:
Doo-hyun Sung
Voice:
LG Electronic Inc
LG R&D Complex, 533 Hogye-1dong,
Dongan-gu, Anyang-shi, , Korea
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Venue:
Kobe, Japan
Base Contribution:
IEEE C802.16m-08/996r2
Purpose:
To be discussed and adopted by TGm for use in the IEEE m SDD
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2. ARQ Block Generation in IEEE 802.16e
Parameters
ARQ_BSN_MODULUS
Equal to the number of unique BSN values, i.e. 211 (=2048).
ARQ_WINDOW_SIZE
Maximum number of ARQ blocks with consecutive BSN in the sliding window of ARQ blocks.
Less than or equal to half of the ARQ_BSN_MODULUS, i.e. =< 210 (=1024).
ARQ_BLOCK_SIZE
Length used for partitioning an SDU into a sequence of ARQ blocks prior to transmission.
Range: 16, 32, 64, 128, 256, 512, 1024 bytes
Features
Logical partitioning of a MAC SDU into several ARQ blocks based on ARQ_BLOCK_SIZE.
Individual BSN (Block Sequence Number) allocated to each ARQ block.

3. ARQ Block Generation in IEEE 802.16e (cont’)
Drawbacks
1. Possibility to append unnecessary padding sequences
If ARQ_BLOCK_SIZE is 32 bytes and there remains 31 bytes of available space, there is no way but to append the padding sequence even though there exists MAC SDUs to transmit. (Refer to the figure below.)
2. Possibility to trigger ARQ Feedback IE message for refreshing ARQ window
As ARQ_BLOCK_SIZE gets smaller, the number of allocated BSNs to 1 MAC PDU gets larger.
Frequent ARQ Feedback IE transmissions for refreshing ARQ window.

4. Proposed ARQ Block Generation Method
ARQ block should be adaptive to the size of available MAC PDU payload.
Proposal 1: One MAC SDU or one of its fragments is defined as one ARQ block. One MAC SDU is fragmented when the available length of a MAC PDU payload is not enough to accommodate the MAC SDU.

5. Proposed ARQ Block Generation Method (cont’)
Two options on how BSNs would be allocated to ARQ blocks as below.
Option 2a: ARQ blocks derived from one MAC SDU are allocated one BSN
Option 2b: ARQ blocks derived from one MAC SDU are allocated consecutive BSNs
Main difference is whether fragments of one MAC SDU share the common BSN or not.
Option 2a
Option 2b

6. Proposed ARQ Block Generation Method (cont’)
Overhead comparison
Option 2a
Option 2b
BSN aspect
Better than 16e method (Slightly better than option 2b)
Better than 16e method
Signaling aspect
Additional fields are required to identify fragments of a MAC SDU on ARQ feedback message
No impact on ARQ feedback message
Proposal 2: ARQ blocks derived from one MAC SDU are allocated consecutive BSNs.(Option 2b)

7. Conclusion We propose the followings & SDD text proposal: Proposal 1
One MAC SDU or one of its fragments is defined as one ARQ block. One MAC SDU is fragmented when the available length of a MAC PDU payload is not enough to accommodate the MAC SDU.
Proposal 2
ARQ blocks derived from one MAC SDU are allocated consecutive BSNs.

8. Text Proposal for SDD
Start of the Text
10. Medium Access Control Sub-Layer
10.x. Data Plane Function
10.x.y. ARQ Mechanism
10.x.y.z. ARQ Block Usage
One MAC SDU or one of its fragments is defined as one ARQ block. One MAC SDU is fragmented to fit when the available length of a MAC PDU payload is not enough to accommodate the MAC SDU. ARQ block sequence numbers (BSNs) are allocated to each ARQ block. ARQ blocks derived from one MAC SDU are allocated consecutive BSNs. Detailed formats of related GMH & subheader (packing and/or fragmentation) are FFS.
End of the Text