``Exploiting idle communication power to improve wireless network performance 
and energy efficiency" 

Lei Guo, Xiaoning Ding, Haining Wang, Qun Li, Songqing Chen, and Xiaodong Zhang

Proceedings of INFOCOM'06, Barcelona, Spain, April 23-29, 2006.  


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 separately and is far from being satisfactory.  On
one end, due to varying channel conditions, WLANs have to provide multiple
data 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, TCP is not
energy efficient running on 802.11.  In a TCP session, a wireless network
interface (WNI) has to stay awake to generate timely acknowledgments, and
hence, the energy is wasted by 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 improve the throughput and energy
efficiency of stations in WLANs with multiple channel rates.  We
characterize the energy efficiency as energy per bit, instead of energy
per second.  Based on modeling and analysis, we propose a data forwarding
mechanism and an energy-aware channel allocation mechanism.  In such a
system, a high channel rate station relays data frames between its
neighboring stations with low channel rates and the Access Point,
improving their throughput and energy efficiency.  Different from
traditional relaying approaches, our scheme compensates for the energy
consumption for data forwarding.  The forwarding station obtains
additional channel access time from its beneficiaries, leading to the
increase of its own throughput without compromising its energy efficiency.
We implement a prototype of our proposed system and evaluate it through
extensive experiments. Our results show significant performance
improvements for both low and high channel rate stations.