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Doc.: IEEE 802.11-12/0370r2 Submission January 2012 Haiguang Wang et. al, I2R, SingaporeSlide 1 TIM Compression Date: 2012-03-11 Authors:

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Presentation on theme: "Doc.: IEEE 802.11-12/0370r2 Submission January 2012 Haiguang Wang et. al, I2R, SingaporeSlide 1 TIM Compression Date: 2012-03-11 Authors:"— Presentation transcript:

1 doc.: IEEE /0370r2 Submission January 2012 Haiguang Wang et. al, I2R, SingaporeSlide 1 TIM Compression Date: Authors:

2 doc.: IEEE /0370r2 Submission January 2012 Jaya Shankar et. al, I2R, Singapore Slide 2 Abstract Considering that the data transmission rate of ah can be as low as 150 kbps, it is necessary to improve the media transmission efficiency. In this contribution, we propose a few methods to reduce the size of TIM bitmap and simulation results shows that the size of TIM IE can be reduced significantly.

3 doc.: IEEE /0370r2 Submission January 2012 Haiguang Wang et. al, I2R, SingaporeSlide 3 Motivation IEEE ah is required to support up to 6000 stations by a single AP [1]. The TIM bitmap can be as large as a few thousand bit in size. –The transmission speed of the ah PHY can be as low as 150 kbps. –It may take more than 6.7 milliseconds to transmit a TIM bitmap with a size of 1000 bits. The overhead may consume a significant portion of channel time. –Compression can help in reducing the time required for TIM bitmap transmission.

4 doc.: IEEE /0370r2 Submission TIM IE Format TIM IE Format (minimum 6 bytes) –Element ID and Length –DTIM count –DTIM Period –Bitmap control Bit 0: for multicast/broadcast Bit 1 – 7: partial bitmap offset –Partial Virtual Bitmap consists of octets numbered N1 through N2 of the traffic indication virtual bitmap –N1: the largest even number such that bits numbered 1 through (N1 × 8) – 1 in the bitmap are all 0. –N2 is the smallest number such that bits numbered (N2 + 1) × 8 through 2007 in the bitmap are all 0 March 2012 Haiguang Wang et. al, I2R, SingaporeSlide 4

5 doc.: IEEE /0370r2 Submission Problem with Current Partial Virtual Bitmap Encoding of TIM Bitmap with the partial virtual bitmap as specified in the current standard is not efficient. –Many zero octets may be included in the partial bitmap, which are unnecessary and can be removed with simple encoding method. March 2012 Haiguang Wang et. al, I2R, SingaporeSlide bytes Partial Virtual Bitmap

6 doc.: IEEE /0370r2 Submission TIM Compression TIM IE can be further compressed to reduce beacon transmission time. –Reduce the TIM IE from 6 bytes to 4 bytes when there is no packet in the buffer by excluding. Bitmap control field (one byte) One byte with all zeros for Partial Virtual Bitmap March 2012 Haiguang Wang et. al, I2R, SingaporeSlide 6

7 doc.: IEEE /0370r2 Submission Using AID Directly in TIM Bitmap When the number of bits being enabled (set to’1’) in the Partial Virtual Bitmap is sparse, representing AID directly in a binary form can reduce the size of TIM IE significantly. The scheme should include –A way to specify the number of bits required to encode AID. –All AIDs are encoded with the same number of bits. March 2012 Haiguang Wang et. al, I2R, SingaporeSlide 7 Number of bits for each AID AID 1 AID 2 AID N...

8 doc.: IEEE /0370r2 Submission AID with Differential Encoding Using differential encoding can further reduce the size of TIM IE when AIDs are encoded in binary. –E.g. Sort AIDs that need to be transmitted in the TIM IE in ascending order, denoted as AID 1, AID 2, …, AID n. –Compress the AID 1, AID 2, …, AID n with differential encoding as follows: ∆AID 1 = AID 1 -1 ∆ AID i = AID i – AID i-1 -1, i = 2, …, n. –Transmit ∆ AID 1, ∆ AID 2, …, ∆ AID n in the TIM IE. March 2012 Haiguang Wang et. al, I2R, SingaporeSlide 8 Number of bits for each AID ∆ AID 1 ∆ AID 2 ∆ AID n...

9 doc.: IEEE /0370r2 Submission Encoding TIM Bitmap with AID Differential Encoding + Partial Virtual Bitmap (PVTB) AID differential encoding can encode TIM Bitmap size efficiently when the 1’s in the bitmap is sparse and the PVTB encoding scheme is more efficient when the 1’s in the bitmap is dense. –The two encoding scheme can be used alternatively based on the density of 1’s in the bitmap. AP choose one of the schemes for TIM encoding by comparing the size of bitmap after encoding. –AP can derive the size of encoded bitmap based on calculation instead of create a bitmap. March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 9

10 doc.: IEEE /0370r2 Submission Performance Results Comparison with other TIM Bitmap encoding schemes –Partial Virtual Bitmap (PVTB): defined in the IEEE –Page-Block TIM encoding scheme: proposed in IEEE /0388r1. March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 10

11 doc.: IEEE /0370r2 Submission 64 Stations March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 11

12 doc.: IEEE /0370r2 Submission 256 Stations March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 12

13 doc.: IEEE /0370r2 Submission 512 Stations March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 13

14 doc.: IEEE /0370r2 Submission 1204 Stations March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 14

15 doc.: IEEE /0370r2 Submission 2048 Stations March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 15

16 doc.: IEEE /0370r2 Submission 8192 Stations March 2012 Jaya Shankar et. al, I2R, SingaporeSlide 16

17 doc.: IEEE /0370r2 Submission January 2012 Slide 17 Conclusions In this contribution, we propose a few methods to reduce the size of TIM IE. Firstly, we propose that the TIM IE may be transmitted with the DTIM count and DTIM period only when there is no data packet in the buffer of AP; Secondly, we propose to allow AIDs in TIM IE to be directly encoded in its binary form and using differential encoding on the list of binary form AIDs to further reduce the size of TIM IE. We have compared the AID with Differential Encoding with the Encoding algorithm proposed in [2] and the improvement can be as high as 40%. Haiguang Wang et. al, I2R, Singapore

18 doc.: IEEE /0370r2 Submission January 2012 Slide 18 References [1] Chao-Chun Wang, “Supporting Large Number of STAs in ah”, IEEE /1019, July [2] Minyoung Park, “TGah Efficient TIM Encoding”, IEEE /388, March Haiguang Wang et. al, I2R, Singapore

19 doc.: IEEE /0370r2 Submission Straw Poll (1) Do you agree that TIM IE should exclude the Bitmap Control field and Partial Virtual Bitmap when there is no data packet in the buffer of AP? Y: N: A: January 2012 Haiguang Wang et. al, I2R, SingaporeSlide 19

20 doc.: IEEE /0370r2 Submission Straw Poll (2) Do you agree to use the binary form representation of AIDs to help reduce the size of TIM IE? Y: N: A: March 2012 Haiguang Wang et. al, I2R, SingaporeSlide 20

21 doc.: IEEE /0370r2 Submission Straw Poll (3) Do you agree to use differential encoding to further compress the binary form AIDs? Y: N: A: March 2012 Haiguang Wang et. al, I2R, SingaporeSlide 21


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