A receiver-initiated MAC protocol with enhancements for multi-hop wireless networks
Balvinder Kaur Thind
Washington State University
Chair: Muralidhar Medidi
Multiple channel access interference is a major cause of throughput degradation in wireless
networks because of the shared channel. IEEE 802.11 MAC is a standard for medium access in
wireless LANs, but suffers from channel contention and co-channel interference and thus, performs
poorly. The focus of this thesis is to design and study a medium access control protocol that
mitigates the effect of multiple channel interference.
We propose to use a receiver-initiated MAC protocol, instead of the sender-oriented 802.11
MAC. Our protocol is based on carrier sensing and resolves collisions among senders based on a
deterministic tree splitting algorithm. By doing collision resolutions, we aim to use time efficiently
otherwise wasted in 802.11 MAC for random backoffs, particularly in cases when the channel
contention is high. Receiver-initiated based collision resolutions guarantee that, no data packets
collide at a receiver because of interference from its own senders: a major cause of hidden node
Further, the protocol is enhanced to have multiple subchannels by dividing the common communication
channel. All the subchannels serve the purpose for both control as well as data packets.
A subchannel assignment scheme is proposed to exploit the parallel transmissions that are possible
in multi-channel networks. This should help in reducing the co-channel interference and thereby,
improve the throughput.
In order to handle the unfairness issues associated with receiver-initiated protocols, we propose
a third enhancement: an adaptive approach of deliberate transitions between receiving and sending
modes. These mode transitions force nodes to spend fixed time in each mode, thereby giving a fair
chance to become a sender as well as a receiver.
We also present simulation results using ns2 simulator, varying several system parameters to
evaluate our approach and compare it with standard IEEE 802.11. The simulation results indicate
that collision resolution with multiple subchannel access provides throughput enhancement and
better packet delays than 802.11 MAC. We also observe that the maximum throughput is achieved
when the channel is divided into three or four subchannels irrespective of the size, shape of the
network, and traffic load. The results also indicate that we further improve on throughput by doing
deliberate transitions and, that the protocol has better fairness for QoS assurance as compared to
standard 802.11 MAC.
School:Washington State University
School Location:USA - Washington
Source Type:Master's Thesis
Keywords:computer network protocols wireless communication systems
Date of Publication: