ABSTRACT
Adaptive signaling, where transmission parameters are adjusted based on information about the current state of the channel, has the capability to significantly increase the throughput of wireless communication systems. Such adaptation can take many forms (power, code rate, modulation, etc.) and can be performed at many different timescales, depending on the system capabilities and the rate at which the channel state varies. After a general introduction to the adaptive signaling methodology, this chapter focuses on symbol-by-symbol adaptation of coded modulation in response to measurements of the multipath fading. In such systems, there are two key design decisions: (1) choosing the structure of the coded modulation on which adaptation will be performed, and (2) deciding how to adapt that structure based on available measurements. These two design problems are discussed in detail for systems where the transmitter and receiver each have a single antenna. Extensions to systems with multiple antennas at the transmitter or receiver, which is a problem of great current interest in the research community, are also discussed. Performance results confirm the significant gains achievable through adaptation of the coded modulation in wireless systems, and future directions in this important area are discussed.
