  Current and emerging mobile devices are omni directional in wireless
communication. Such omni directionality not only limits device energy
efficiency but also poses a significant challenge toward the capacity of
wireless networks through inter-link interference. In this work, we seek to
make mobile clients directional with beamsteering. We first demonstrate that
beamsteering is already feasible to mobile devices such as Netbooks and eBook
readers in terms of form factor, power efficiency, and device mobility. We
further reveal that beamsteering mobile clients face a unique challenge to
balance client efficiency and network capacity. There is an optimal operating
point for a beamsteering mobile client in terms of the number of antennas and
transmit power that achieve the required capacity with lowest power. Finally,
we provide a distributed algorithm called BeamAdapt that allows each client to
closely approach its optimal point iteratively without central coordination. We
also offer a cellular system realization of BeamAdapt. Using Qualnet-based
simulation, we show that BeamAdapt with four antennas can reduce client power
consumption by 55% while maintaining a required network throughput for a
large-scale network, compared to the same network with omni directional mobile
clients.
