EQUALIZATION OF OFDM OVER DOUBLY SELECTIVE CHANNELS

Abstract

Orthogonal Frequency-Division Multiplexing (OFDM) is now regarded as a feasible alternative to the conventional single carrier modulation techniques for high data rate communication systems, mainly because of its inherent equalization simplicity. It is well known fact that orthogonal frequency division multiplexing (OFDM) provides a practical solution to counter the inter symbol interference problem imposed by the frequency selective fading channel. The application of OFDM in fast frequency selective fading multipath channels is fraught with several difficulties many of which have not been practically treated in the literature. Current trends in broadband wireless communication system dictate that channel time variation will soon play an -important role in OFDM system. The primary advantage of cyclic prefix OFDM in time invariant frequency selective fading channels i.e. The absence of inter symbol interference and inter carrier interference do not carry over to time and frequency selective i.e. doubly selective channels. As a result the standard zero forcing and minimum mean square error equalization techniques will become prohibitively complex. Block linear equalizers and serial linear equalizers are normally designed to combat doubly selective fading. The implementation of block linear equalizers, which collect and process all the available data in the received frame in blocks, leads to an unsustainable computational complexity. On the other hand, serial linear time varying (LTV) equalizers, which process few data at a time, exhibit a good tradeoff between complexity and performance. In this dissertation work the performance of block linear and serial linear equalizers are evaluated for a single input multi output (SIMO) and multi input multi output (MIMO) systems for block transmission over. doubly selective channels. These approaches are extended for the equalization of OFDM system