1 / 18

TIM Compression

TIM Compression. Authors:. Date: 2012-03-11. Abstract.

arsenio-clements
Download Presentation

TIM Compression

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. TIM Compression Authors: Date: 2012-03-11 Haiguang Wang et. al, I2R, Singapore

  2. Abstract Considering that the data transmission rate of 802.11ah 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. Jaya Shankar et. al, I2R, Singapore

  3. Motivation • IEEE 802.11ah 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 802.11ah PHY can be as low as 150 kbps. • Itmay 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. Haiguang Wang et. al, I2R, Singapore

  4. 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 TIM IE Format Haiguang Wang et. al, I2R, Singapore

  5. 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. Problem with Current Partial Virtual Bitmap Partial Virtual Bitmap 00000000 00001000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 18 bytes 00000000 00000000 00000000 00000000 00000000 00001000 Haiguang Wang et. al, I2R, Singapore

  6. 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 TIM Compression Haiguang Wang et. al, I2R, Singapore

  7. 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. Using AID Directly in TIM Bitmap Number of bits for each AID AID 1 AID 2 . . . AID N Haiguang Wang et. al, I2R, Singapore

  8. 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 • ∆ AID_i = AID_i – AID_i-1, i = 2, …, n. • Transmit ∆ AID_1, ∆ AID_2, …, ∆ AID_n in the TIM IE. AID with Differential Encoding Number of bits for each AID AID 1 ∆ AID 2 . . . ∆ AID N Haiguang Wang et. al, I2R, Singapore

  9. Simulation Parameters • Simulator • Qualnet network simulator • Simulation parameters • DCF mode with 1 MHz bandwidth • With implemented power saving protocols. • PHY modulation: MCS0-REP2 defined by 802.11ah • Transmission range: 1 km • Basic parameters Haiguang Wang et. al, I2R, Singapore

  10. Topology Haiguang Wang et. al, I2R, Singapore

  11. Data packets from AP to 1000 stations follows Exponential distribution. The destination follows a uniform distribution among nodes associated with the AP. 2 packets, 20 bytes each per station per hour Traffic Model Haiguang Wang et. al, I2R, Singapore

  12. Performance Results: 2 pkts/station/hour * Statistics duration: from 300s – 3600s ** Compression Rate: using Partial Virtual Bitmap as a base Haiguang Wang et. al, I2R, Singapore

  13. TIM IE Size vs. Active AIDs Number of Active AIDs Haiguang Wang et. al, I2R, Singapore

  14. 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. Haiguang Wang et. al, I2R, Singapore

  15. References • [1] Chao-Chun Wang, “Supporting Large Number of STAs in 802.11ah”, IEEE 802.11-11/1019, July 2011. Haiguang Wang et. al, I2R, Singapore

  16. 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: Straw Poll (1) Haiguang Wang et. al, I2R, Singapore

  17. Do you agree to use the binary form representation of AIDs to help reduce the size of TIM IE? Y: N: A: Straw Poll (2) Haiguang Wang et. al, I2R, Singapore

  18. Do you agree to use differential encoding to further compress the binary form AIDs? Y: N: A: Straw Poll (3) Haiguang Wang et. al, I2R, Singapore

More Related