Robust Transmission over Frequency Selective Fast Fading Channels with Noncoherent Turbo Detection

Noncoherently detected frequency shift keying can be used in fast fading environments where it is difficult to track the channel. In this paper we present two methods to improve the performance of iteratively detected OFDM-MFSK. OFDM-MFSK is a combination of orthogonal frequency division multiplexing (OFDM) and noncoherent M-ary frequency shift keying (MFSK) that was developed as a robust transmission method for fast time varying channels. The first method increases the number of bits per label and therefore leads to an increased data rate, but also to an ambiguous mapping which has to be resolved by the channel decoder. In the second method, a precoder is inserted between the channel coder and the mapper, leading to a system of three serially concatenated codes. To analyze the iterative behavior of the receiver, we will use three dimensional EXIT charts, which allow us to predict the performance. The intention of both methods is to adapt the channel code to the modulation scheme in order to improve the performance of the iterative receiver.