Applying Ad-Hoc Relaying to Improve Capacity, Energy Efficiency, and Immission in Infrastructure-Based WLANs

Abstract

In classical infrastructure-based wireless systems such as access point-equipped wireless LANs, all mobile terminals communicate directly with the access point. In order to improve the capacity or energy efficiency of such systems, the use of mobile terminals as intermediate relays has been proposed. The rationale is that intermediate relays reduce the communication distance and hence the emitted power. Therefore, relaying could also reduce electromagnetic immission. To assess these potential benefits, we study the effectiveness of various relaying algorithms in a uniform, HiperLAN/2-based system model that has been amended by relaying functionality. These algorithms jointly select intermediate relay terminals and assign transmission power as well as modulation to mobile terminals. The energy efficiency of a point-to-point communication is indeed improved by relaying, however, this effect only marginally transfers to scenarios taking into account several terminals. Nevertheless, it is still possible to extend the lifetime of a network by taking into account available battery capacities.

For a discussion of capacity improvements, two different modes of conceiving system fairness are identified. For both system modes, we present relaying algorithms. Moreover, adding an additional frequency to a cell is beneficial: Using two frequencies can almost double the cell capacity, and for one fairness mode, even relaying with one frequency can improve capacity by up to 30%.

In addition, all these algorithms reduce the immitted power averaged over the area of a cell. All algorithms show improvements, an additional algorithm specialized to reduce immission power can cut the average power almost in half.