``PSM-Throttling: minimizing energy consumption for bulk data
communications in WLANs"

Enhua Tan, Lei Guo, Songqing Chen, and Xiaodong Zhang

Proceedings of the 15th International Conference on Network Protocols
(ICNP'07), Beijing, China, October 16-19, 2007.


While the 802.11 power saving mode (PSM) and its enhancements can
reduce power consumption by putting the wireless network interface
(WNI) into sleep as much as possible, they either require additional
infrastructure support, or may degrade the transmission throughput and
cause additional transmission delay. These schemes are not suitable for
long and bulk data transmissions with strict QoS requirements on
wireless devices. With increasingly abundant bandwidth available on the
Internet, we have observed that TCP congestion control is often not a
constraint of bulk data transmissions as bandwidth throttling is widely
used in practice.

In this paper, instead of further manipulating the trade-off between
the power saving and the incurred delay, we effectively explore the
power saving potential by considering the bandwidth throttling on
streaming/downloading servers. We propose an application-independent
protocol, called PSM-throttling. With a quick detection on the TCP flow
throughput, a client can identify bandwidth throttling connections with
a low cost. Since the throttling enables us to reshape the TCP traffic
into periodic bursts with the same average throughput as the server
transmission rate, the client can accurately predict the arriving time
of packets and turn on/off the WNI accordingly. PSM-throttling can
minimize power consumption on TCP-based bulk traffic by effectively
utilizing available Internet bandwidth without degrading the application
โค"os performance perceived by the user.  Furthermore, PSM-throttling
is client-centric, and does not need any additional infrastructure
support. Our lab-environment and Internet-based evaluation results show
that PSM-throttling can effectively improve energy savings (by up to
75%) and/or the QoS for a broad types of TCP-based applications,
including streaming, pseudo streaming, and large file downloading, over
existing PSM-like methods.