Adaptive MIMO Transmission Techniques for Broadband Wireless Communication Systems

Link adaptation is a way to increase data rates in wireless systems by adapting transmission parameters such as the modulation and coding rate. While link adaptation in single antenna systems is now mature, its application to multiple-input multiple-output communication links, presented in several emerging wireless standards, has been challenging. The main reason is that the space-time transmission strategy can also be adjusted in MIMO communication links, introducing a new dimension for adaptation. This means that practical MIMO link adaptation algorithms must also provide a dynamic adaptation between diversity and multiplexing modes of operation. This article reviews a recently proposed framework for adaptive MIMO architectures and shows how to use this framework to reduce adaptive control overhead. We also discuss practical implementation issues. Simulations in an IEEE 802.16e (mobile WiMAX) system illustrate the framework's potential improvements in data rates.