Multi-user networks can support a large number of users at the same time and the system resources need to be shared among different users. The system performance can be improved significantly by exploiting multi-user diversity in either centralized or distributed ways, which has been demonstrated in Parts II and III. Similarly, multi-user diversity can also be exploited to improve network energy efficiency. This will be the focus of this chapter and the next one. In this chapter, we will first provide an overview of centralized energy-efficient wireless resource management. To better understand the topic, we will later discuss in detail how to manage resources in orthogonal frequency division multiple access (OFDMA) networks so that the overall network achieves the highest energy efficiency.

Overview

Because of limited wireless resources, there exist intricate tradeoffs between individual performance and the whole network. For example, in a time division multiple access (TDMA) system, all users share a common frequency band. Lowering the rate of one user requires longer transmission duration and thus reduces the available time of other delay-sensitive users. This forces other users to increase modulation order to support higher data rate and consume more energy while potentially the transmission may still suffer from a higher bit error rate (BER). Flexible cross-layer optimization allowing each user to adapt to its environment will enable huge energy savings. Furthermore, the exploitation of diversity across all users will further reduce overall network energy consumption.