17 - Distributed power control

Summary

In the previous chapters, we have introduced optimal distributed medium access control (MAC) schemes, which are essentially distributed scheduling approaches that schedule the transmissions of all users on orthogonal resources (time slots) in a decentralized way while exploiting multi-user diversity in both channels and interference environments. Users are usually spatially separated and more than one user may be granted channel access and transmit data at the same time on the same frequency. Because of frequency reuse, the transmissions of different users will interfere with each other. To simplify the MAC designs, we have assumed collision channel models and once a collision, i.e. interference, exists, the transmission fails. In practice, a more realistic SINR channel model can be used. The signal to interference plus noise ratio (SINR) accounts for the cumulative interference level. A signal transmission succeeds if the SINR perceived by the receiver exceeds an SINR threshold. It is a more natural channel model for deciding packet decoding success. SINR is determined by both channel gains as well as transmitter powers of all users in the network. While channel gains are usually fixed depending on user locations, transmitter power control can be used to determine the transmission power of transmitters in wireless networks and thus control network interference to achieve good SINR performance. It is a fundamental component of wireless resource management. It has the benefit of reducing interference, increasing network capacity, and reducing energy consumption.