1 / 17

Mathematical Analysis of Throughput Bounds in Random Access with ZigZag Decoding

Mathematical Analysis of Throughput Bounds in Random Access with ZigZag Decoding. Jeongyeup Paek, Michael J. Neely University of Southern California CSI Seminar Series - June 2, 2009 (To Appear in WiOpt 2009). ZigZag.

kosey
Download Presentation

Mathematical Analysis of Throughput Bounds in Random Access with ZigZag Decoding

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. Mathematical Analysis of Throughput Bounds in Random Access with ZigZag Decoding Jeongyeup Paek, Michael J. Neely University of Southern California CSI Seminar Series - June 2, 2009 (To Appear in WiOpt 2009)

  2. ZigZag • “ZigZag Decoding: Combating Hidden Terminals in Wireless Networks”, Shyamnath Gollakota and Dina Katabi, SIGCOMM 2008. • 802.11 receiver design that allows successful reception of packets despite collision Ha! Then can we get better max. throughput? By how much?

  3. AP Bob Alice 802.11 MAC and Collision Collision Repeatedly collide … with some random jitter CSMA is not perfect…

  4. ∆1- ∆2 AP ∆1 ∆2 Bob Alice ZigZag Decoding 1st collision 2nd collision 0 Pa 1 3 Pa 1 3 Pb 2 4 2 Pb 4 Can reconstruct both packets Pa and Pb!!

  5. …. …. System Models • Three Idealized Multi-Access Models(Bertsekas and Gallager, Data Networks) • [1] Slotted random access • [2] Slotted Aloha (stabilized) • [3] Slotted CSMA (with mini-slot ) • Common assumptions • Slotted time (t{0,1,2,…}) • Fixed size packets • TX time 1 slot • Collided packets must be retransmitted • If only one node sends a packet in a slot, the packet is always received correctly

  6. Definitions and Assumptions • ‘Collision’ : when 3 or more users transmit in a slot • ‘ZigZag’ : if exactly 2 users transmit in a slot • Decodable using ZigZag decoding • ‘0’, ‘1’, ‘Zigzag’,or ‘C’ immediate feedback • If ‘ZigZag’ occurs in a slot, • That slot is automatically extended into 2 slots • Two colliding users retransmit in the next slot, and others never retransmit in the next slot • Exactly 2 packets are perfectly received at the receiver during 2 slots  throughput during this period = 1pkt/slot • Ignore decoding failure and 3 packet decoding

  7. …. …. [1] Slotted Random Access • N-users with infinite backlog of data to send • Transmit with probability ‘q’ N

  8. Slotted Random Access Using Renewal Theory, 81.8% improvement compared to the bound without Zigzag (e-1 = 0.3678)

  9. Slotted Random Access Max Throughput qN Numerical solution matches the derived bound for N 

  10. [2] Slotted Aloha • New users arrive at Poisson rate , and immediately transmit in the next slot • Backlogged users transmit with probability q(i) Using “Drift Theorem” for system stability… … better than the bound w/o Zigzag (e-1 = 0.3678) But not as good as hoped!

  11. Slotted Aloha - Modified • New users arriving during the ZigZag frame does not transmit in the second slot of ZigZag frame • Listen for feedback and become backlogged if in Zigzag 81.8% improvement compared to the bound without Zigzag (e-1 = 0.3678) Simulation result (0.6675) matches the bound

  12. [3] Slotted CSMA with mini-slots • New users arriving during mini-slot transmit in the next slot • New users arriving during transmission slot are backlogged • Backlogged users transmit with probability q(i) Exact µ* given in terms of q(i) A bit too complicated to find closed form formula for optimal q(i) and optimal throughput….

  13. CSMA - Numerical Better throughput Transmit more aggressively! Curve fitted ZigZag w/o ZigZag Max Throughput N * qN

  14. CSMA - Simulation Result Simulation results match the numerically solved bound ~20% ZigZag decoding improves maximum throughput by ~20%

  15. Experimental Results from the original ZigZag paper [Gollakota and Katabi] • Implementation • GNU Radio, 14-node 802.11b testbed • 10% of sender-receiver pairs are hidden terminal,10% sense each other partially. • Only receiver (AP) modifications. • Results • Avg. loss rate (over 20% pairs): 72.6%  0.7% • Avg. throughput (over all pairs): improved by 25.2%

  16. Conclusion • ZigZag decoding improves maximum throughput significantly.

  17. Thank you.

More Related