Comparison of receiver training methods in joint iterative channel estimation and decoding in flat fading channels

In this paper we compare two different methods for receiver training in flat fading channels. The first method is the traditional way in which periodic training sequences are sent to the receiver (explicit training). In the second method, recently proposed, the information source emits bits with unequal probabilities of being ´0´ and ´1´. This method is called implicit training, since the training is implied in the non-symmetrical source structure. BPSK signaling is used as the simplest example of constant-envelope phase modulations. We map the phase component of the flat fading channel response to a simple two-state Markov model. Then joint iterative trellis-based maximum a posteriori probability (MAP) method is used for channel state estimation and decoding. The results of computer simulations for the receiver bit error rate (BER) performance in various channel fading rates and information rates are presented. The results indicate superior performance of implicit training. In slow fading conditions, the gain is 4 dB at information rate of 0.15 bits/channel use and 1.2 dB for information rate of 0.25 bits/channel use.