Praise for Fundamentals of WiMAX

C H A P T E R 5Multiple-AntennaTechniquesThe use of multiple antennas allows independent channels to be created in space and is oneof the most interesting and promising areas of recent innovation in wireless communications.Chapter 4 explained how WiMAX systems are able to achieve frequency diversity throughthe use of multicarrier modulation. The focus of this chapter is spatial diversity, which can be createdwithout using the additional bandwidth that time and frequency diversity both require. Inaddition to providing spatial diversity, antenna arrays can be used to focus energy (beamforming)or create multiple parallel channels for carrying unique data streams (spatial multiplexing). Whenmultiple antennas are used at both the transmitter and the receiver, these three approaches areoften collectively referred to as multiple/input multiple output (MIMO) communication 1 and canbe used to1. Increase the system reliability (decrease the bit or packet error rate)2. Increase the achievable data rate and hence system capacity3. Increase the coverage area4. Decrease the required transmit power1. Use of the term MIMO (pronounced “My-Moe”) generally assumes multiple antennas are at boththe transmitter and the receiver. SIMO (single input/multiple output) and MISO (multiple input/single output) refer, respectively, to only a single antenna at the transmitter or the receiver. Withoutfurther qualification, MIMO is often assumed to mean specifically the spatial multiplexingapproach, since spatial multiplexing transmits multiple independent data streams and hence hasmultiple inputs and outputs.149