Optimum receiver design for wireless broad-band systems using OFDM. I

Orthogonal frequency-division multiplexing (OFDM) is the technique of choice in digital broad-band applications that must cope with highly dispersive transmission media at low receiver implementation cost. In this paper, we focus on the inner OFDM receiver and its functions necessary to demodulate the received signal and deliver soft information to the outer receiver for decoding. The effects of relevant nonideal transmission conditions are thoroughly analyzed: imperfect channel estimation, symbol frame offset, carrier and sampling clock frequency offset, time-selective fading, and critical analog components. Through an appropriate optimization criterion (signal-to-noise ratio loss), minimum requirements on each receiver synchronization function are systematically derived. An equivalent signal model encompassing the effects of all relevant imperfections is then formulated in a generalized framework. The paper concludes with an outline of synchronization strategies.