TR-07-3.pdf
``Cooperative Relay Service in a Wireless LAN"
Lei Guo, Xiaoning Ding, Haining Wang, Qun Li, Songqing Chen, and Xiaodong Zhang
IEEE Journal on Selected Areas in Communications, Vol. 25, No. 2, 2007,
pp. 355-368.
Abstract
As a family of wireless local area network (WLAN) protocols between physical
layer and higher layer protocols, IEEE 802.11 has to accommodate the features
and requirements of both ends. However, current practice has addressed the
problems of these two layers separately and is far from satisfactory. On
one end, due to varying channel conditions, WLANs have to provide multiple
physical channel rates to support various signal qualities. A low channel
rate station not only suffers low throughput, but also significantly degrades
the throughput of other stations. On the other end, the power saving
mechanism of 802.11 is ineffective in TCP-based communications, in which
the wireless network interface (WNI) has to stay awake to quickly acknowledge
senders, and hence, the energy is wasted on channel listening during idle
awake time.
In this paper, considering the needs of both ends, we utilize the idle
communication power of the WNI to provide a Cooperative Relay Service (CRS)
for WLANs with multiple channel rates. We characterize energy efficiency as
energy per bit, instead of energy per second. In CRS, a high channel rate
station relays data frames as a proxy between its neighboring stations with
low channel rates and the Access Point, improving their throughput and energy
efficiency. Different from traditional relaying approaches, CRS compensates
a proxy for the energy consumed in data forwarding. The proxy obtains
additional channel access time from its clients, leading to the increase of
its own throughput without compromising its energy efficiency. Extensive
experiments are conducted through a prototype implementation and ns-2
simulations to evaluate our proposed CRS. The experimental results show
that CRS achieves significant performance improvements for both low and high
channel rate stations.