Understanding and Resolving Wireless Collision with PHY Techniques

PhD Thesis Proposal Defence


Title: "Understanding and Resolving Wireless Collision with PHY 
Techniques"

by

Mr. Xiaoyu JI


Abstract:

Due to the broadcast nature and lack of collision detection mechanism, 
wireless networks suffer from collision. Collision happens when two or 
more data packets overlap in the time domain at receiver and none of them 
can be received correctly. Collision increases packet delivery delay, 
decreases network throughput and incurs extra energy cost because of 
retransmissions. To tackle collision, researchers propose abundant 
protocols in Medium Access Control (MAC) layer. The essential idea behind 
these protocols is to properly coordinate multiple senders to access a 
shared channel and avoid the case where there are two or more senders 
accessing a shared channel simultaneously. While in recent years, an 
increasing number of protocols are invented to approach collision in the 
physical layer (PHY). PHY layer demonstrates promising properties, e.g., 
power indicator like RSSI, the effect of capture and constructive 
interference, which enable us resolve collision from its nature as 
wireless signals.

This proposal first draws a new logical roadmap along which we understand 
and deal with collision. The roadmap is: collision avoidance -> collision 
tolerance -> collision cancellation -> collision exploitation. We in the 
beginning avoid collision out of its harm, and then we can just tolerate 
them with some “powerful weapons”. After that, we try to cancel collision 
with more powerful techniques and finally we realize that collision could 
be utilized to assists us. Guided by this roadmap, the proposal mainly 
addresses collision to achieve energy-efficient scheduling and 
near-optimal channel utilization, respectively in the stages of collision 
avoidance and tolerance. For the former, we find an interesting stair-like 
pattern of RSSI constructed by colliding signals under constructive 
interference. By intentionally forming this stair pattern, receiver is 
able to distinguish colliding senders and further distinguish and schedule 
them in only one round. For the latter, we change the channel access 
method from an asynchronous way to a synchronous one based on the capture 
effect in PHY layer. With multiple users accessing a shared channel 
simultaneously yet guaranteeing with high probability that one of them can 
transmit successfully, the channel utilization can be improved and 
approximates its optimal value.


Date:			Monday, 12 May 2014

Time:                   10:00am - 12:00noon

Venue:                  Room 4475
                         lifts 25/26

Committee Members:	Dr. Yunhao Liu (Supervisor)
 			Dr. Ke Yi (Supervisor)
 			Dr. Pan Hui (Chairperson)
 			Prof. Gary Chan
 			Dr. Lei Chen


**** ALL are Welcome ****