Advanced demodulation techniques for digital audio broadcast signals over fast fading channels.

Abstract

The Canadian digital audio broadcast (DAB) system uses a multicarrier modulation technique known as coded orthogonal frequency division multiplexing (COFDM). Several modes of operation are available. Mode IV, which has the longest symbol duration, allows transmitting antennas to be spaced more widely than other modes of operation providing a saving in broadcast infrastructure. However, the longer symbol duration also causes partial loss of coherence in subsequent symbol epochs that can cause a noticeable degradation in audio quality at velocities exceeding 92 km/hr in a typical urban propagation environment. This thesis identifies several advanced demodulation techniques that can be used in a receiver that will operate at higher vehicle velocities. One of these techniques, an iterative decision directed linear predictive receiver, has not been previously discussed in the literature. Simulation results indicate that the maximum vehicle velocity can be increased to 144 km/hr using this new receiver design.