``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.  


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.