Abstract

Two novel optimized delay diversity (ODD) schemes for suboptimum equalization are proposed in this thesis. ODD was first proposed based on the Chernoff bound on the pairwise error probability (PEP) for maximum-likelihood sequence estimation (MLSE). It was shown that the MLSE-ODD scheme outperforms the generalized delay diversity (GDD) scheme in frequency-selective fading channels. However, the MLSE scheme is too complex for most practical applications. Therefore, low-complexity equalization schemes such as decision-feedback equalization (DFE) or even linear equalization (LE) have to be used.

In this work, two novel ODD schemes are investigated. The ODD transmit filters of the two novel schemes are optimized for correlated multiple-input multiple-output (MIMO) frequency-selective Rayleigh fading channels with suboptimum DFE or LE employed at the receiver, respectively. An equivalent discrete-time channel model containing the DD transmit filters, the pulse shaping filters, the mobile channel, and the receiver input filters is first given. Then, the worst-case pairwise error probabilities (PEPs) for both DFE and LE are derived based on the discrete-time channel model and the error variances of the two schemes. Finally, a stochastic gradient algorithm for optimization of the ODD filter coefficients is proposed. The algorithm assumes knowledge of the channel impulse response (CIR) at the receiver while only the statistics of the CIRs are required at the transmitter. The proposed algorithm takes into account the equivalent discrete-time channel, the operating signal-to-noise ratio (SNR), the modulation scheme, the length of the ODD transmit filters as well as the correlations of the transmit and receive antennas.

The resulting ODD filters are applied to Global System for Mobile Communication (GSM) and Enhanced Data Rates for GSM Evolution (EDGE). Simulation results show that the ODD filters proposed in this thesis significantly outperform the previously proposed MLSE-ODD filters when DFE and LE are used at the receiver, respectively.