MIMO-OFDM for Beyond Third Generation Communication

Multiple-input multiple-output (MIMO) wireless communication is a fundamental technology that will play an essential role in beyond third generation (a.k.a. fourth generation) communication systems. The key to MIMO communication technology is the use of multiple antennas at both transmitter and receiver to create a propagation channel with additional spatial degrees of freedom that can be exploited to improve the quality, capacity, and coverage -problems faced by all wireless cellular systems. MIMO technology is at various stages of adoption or deployment in third generation cellular systems, broadband fixed wireless access systems, high-speed wireless local area networks, and mobile ad-hoc networks for battlefield networks. In all cases, obtaining the benefits of MIMO technology requires careful system design and necessitates additional hardware and perhaps processing penalties.

Even with capacity-multiplying MIMO technology, it is anticipated that beyond third generation communication systems will still require large bandwidths to provide data rates of hundreds of megabits per second. Large bandwidth systems will require extensive equalization to compensate for frequency selectivity due to multi-path in the channel. OFDM (orthogonal frequency division multiplexing) is a digital modulation technique that dramatically reduces equalization complexity by enabling equalization in the frequency domain. The marriage of OFDM modulation and MIMO technology is natural and beneficial since OFDM enables support of more antennas and larger bandwidths since it simplifies equalization dramatically in MIMO systems. MIMO-OFDM, as the union is called, is expected to be the prime contender for fourth generation (4G) mobile cellular.

MIMO-OFDM is under intensive investigation by researchers in the WNCG and at academic institutions and industries throughout the world. Recently, Prof. Robert W. Heath Jr. delivered a tutorial at The 8th International Conference on Cellular and Intelligent Communications (CIC), in Seoul, Korea, on beyond third generation communication. While there has been a substantial amount of development on MIMO-OFDM, the general conclusion of this tutorial was that the design space for fourth generation MIMO-OFDM cellular systems is still wide open. Prof. Heath and his students are actively researching this area using a mixture of theoretical development combined with prototyping on a National Instruments based software radio platform.