1. July 2004
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Modified Delayed (Dly) Acknowledgement for IEEE Systems]
Date Submitted: [28th June , 2004]
Source: [Sanjeev K. Sharma and Jinwoo Hong] Company [Samsung Electronics]
Address [75 W. Plumeria Dr, San Jose, CA, 95134]
Voice:[ ], FAX: [ ],
Re: []
Abstract: [ Modified Delayed (Dly) Acknowledgement for IEEE Systems]
Purpose: [For discussion to modify delayed acknowledgement in Systems and include the proposed modified Dly ACK]
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
Sanjeev K. Sharma et al, Samsung

2. Modified Delayed (Dly) ACK for IEEE 802.15.3 Systems
July 2004
Modified Delayed (Dly) ACK for IEEE Systems
July 2004
Sanjeev K. Sharma et al, Samsung

3. July 2004
Problem Definition
To use Dly ACK as per current IEEE MAC draft,
Each MPDU received is Delay (Dly) ACKed using 2 Bytes for each MPDU
Size of Delayed (Dly) ACK frame increases with increase in number of MPDU blocks
Larger size of Delayed (Dly) ACK frame reduces the probability of its successful transmission, which may cause retransmission of all the frames causing bandwidth wastage
Sanjeev K. Sharma et al, Samsung

4. July 2004
Delayed (Dly) ACK in
Each MPDU needs two (2) bytes for Dly ACK
Size of Dly ACK increases with increase in MPDU Blocks
Figure 1: Fragmentation Control Field of IEEE MAC Header
octets: 4
FCS 2
MPDU ID
block-n …
block-2
block-1 1
MPDUs
ACKed
MAX
Frames
Burst 10
MAC header
bits: b15-b9
Fragment
Number
b8-b0
MSDU
Figure 2: Delayed (Dly) ACK for IEEE
Sanjeev K. Sharma et al, Samsung

5. Proposed Delayed (Dly) ACK
July 2004
Proposed Delayed (Dly) ACK
Proposed modified Dly ACK is shown in Figure 3
We need up to 16 bytes (128 bits as there are max 128 fragments) to Dly ACK each MSDU
First Fragment Number field is from where we want to start the Dly ACK
octets: 4
octets: 4
0~16
0~16 2 2 … …
0~16
0~16 2 2 1 1 1 1 1 1 10 10
octets: 4
octets: 4
0~16
0~16 2 2 … …
0~16
0~16 2 2 1 1 1 1 1 1 10 10
Bitmap for
Bitmap for
Bitmap for
Bitmap for
MPDUs
MPDUs
MAX
MAX
MAX
MAX
FCS
FCS
Bitmap for
Bitmap for
MSDU n
MSDU n … …
Bitmap for
Bitmap for
MSDU 1
MSDU 1
MPDUs
MPDUs
MAX
MAX
MAX
MAX
MAC header
MAC header
FCS
FCS
MSDU n
MSDU n
MSDU n
MSDU n … …
MSDU 1
MSDU 1
MSDU 1
MSDU 1
ACKed
ACKed
Frames
Frames
Burst
Burst
MAC header
MAC header
MSDU n
MSDU n
MSDU 1
MSDU 1
ACKed
ACKed
Frames
Frames
Burst
Burst
bits: b15
bits: b15 - - b9 b9 b8 b8 - - b0 b0
bits: b15
bits: b15 - - b9 b9 b8 b8 - - b0 b0
First Fragment
First Fragment
MSDU
MSDU
First Fragment
First Fragment
MSDU
MSDU
Number
Number
Number
Number
Number
Number
Number
Number
Figure 3: Proposed Modified Delayed (Dly) ACK for IEEE MAC
Sanjeev K. Sharma et al, Samsung

6. Example: Multiple MSDUs (1/2)
July 2004
Example: Multiple MSDUs (1/2)
Modified Dly ACK for Multiple MSDUs without any MSDU loss is shown in Figure 4. Delay ACKed are fragments 50~60 of MSDU1 and fragments 0~7 of MSDU2.
octets: 4
FCS
MSDU n
0~16
Bitmap for
MSDU 1 2 1
MPDUs
ACKed
MAX
Frames
Burst 10
MAC header
MSDU 2
ACKed (19)
bits: b15 - b9
Number b8 b0
MSDU
First Acked
Fragment
Number (50)
(1)
b15-b11
b00000
b10 b
bits: b7
Number (0)
(2)
1 byte
2 bytes
Figure 4: To ACK Multiple MSDUs using Proposed Dly ACK
Sanjeev K. Sharma et al, Samsung

7. Example: Multiple MSDUs (2/2)
July 2004
Example: Multiple MSDUs (2/2)
Modified Dly ACK for Multiple MSDUs with loss of one fragment (52) is shown in Figure 5. Delay ACKed are fragments 50~60 of MSDU1 and fragments 0~7 of MSDU2.
octets: 4
FCS
MSDU n
0~16
Bitmap for
MSDU 1 2 1
MPDUs
ACKed
MAX
Frames
Burst 10
MAC header
MSDU 2
ACKed (18)
bits: b15 - b9
Number b8 b0
MSDU
First Acked
Fragment
Number (50)
(1)
b15-b11
b00000
b10 b
bits: b7 b
Number (0)
(2)
1 byte
2 bytes
Figure 5: To ACK Multiple MSDUs with One Lost Fragment using Proposed Dly ACK
Sanjeev K. Sharma et al, Samsung

8. Performance Comparison
July 2004
Performance Comparison
Table: Performance Comparison
Excluding size of MAC header, Max Burst, Max Frames, and MPDUs ACKed, which is 17 bytes.
Saving = (529-53)/ %
Parameter Name
Dly ACK
Modified Dly ACK
Max number of MPDUs to be Dly ACKed
256
Max Number of Fragments
128
Size of Dly ACK frame body for 256 MPDUs (Max)
256*2 = 512 (bytes)
2*18 = 36 (bytes)
Size of Dly ACK Frame
= 529 (bytes)
36+17 = 53 (bytes)
Sanjeev K. Sharma et al, Samsung

9. July 2004
Advantages
We save Delay (Dly) ACK overhead significantly (up to 90%) by using the (proposed) bitmap fields.
Proposed scheme improves the throughput efficiency of the overall system.
Improves the chances of successful transmission of Dly ACK, which reduces the probability of retransmission of all frames.
In case of non-fragmented MSDUs, modified Dly ACK is identical to Dly ACK.
Easy to implement.
Sanjeev K. Sharma et al, Samsung

10. July 2004
Proposal to b
Adopt the modified Delayed (Dly) ACK mechanism in IEEE b
Sanjeev K. Sharma et al, Samsung

11. July 2004
References
Wireless Medium Access Control (MAC) and Physical (PHY) Layer Specifications for High Rate Wireless Personal Area Networks (WPAN), Draft P /D17, February 2003.
Sanjeev K. Sharma et al, Samsung