IEEE Communications Magazine,vol. 48, no. 5, pp. 112-118, May 2010.
Link adaptation is a way to increase data rates in wireless systems by adapting transmission parameters such as the modulation and coding rate to changing channel conditions. While link adaptation is a relatively mature concept, its application to multiple-input multiple-output (MIMO) communication links, present in several emerging wireless standards, has been challenging. The main reason is that the space-time transmission strategy can also be adjusted in MIMO links, requiring adapting between different multiplexing and diversity strategies with the same overall rate or fixed target error rate. This article reviews a recently proposed framework for adaptive MIMO architectures and shows how to use this framework to reduce adaptive control overhead. Practical implementation issues are discussed. Simulations in an IEEE 802.16 framework illustrate potential improvements in data rates.