Comparison of receiver training methods in joint iterative channel estimation and decoding in flat fading channels | IEEE Conference Publication | IEEE Xplore

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


Abstract:

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...Show More

Abstract:

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.
Date of Conference: 07-10 September 2003
Date Added to IEEE Xplore: 19 February 2004
Print ISBN:0-7803-7822-9
Conference Location: Beijing, China

I. Introduction

Receivers that are designed to work in unknown time-selective correlated fading channels perform channel estimation for reliable communications. The quality of channel estimation is an important factor that affects the receiver performance. Most current mobile communication systems use constant envelope phase modulations. For this class of modulation schemes, estimation of the phase component of the channel response is essential and poses a great challenge for the receiver design, especially at high fading rates. Usually, to achieve reasonable precision in phase estimation, explicit periodic training bits are inserted among channel symbols. These bits are predetermined and convey no detectable information. The main advantage of this method is that during the training period good precision of channel estimation is attainable. Explicit training drawbacks are summarized as:

The receiver does not get any supervision between the training periods and if the channel state changes during this interval, performance is degraded.

Better channel estimation precision in the training period does not necessarily result in better channel estimation in the tracking period. In fact we have recently shown that the precision of channel state information degrades exponentially for two-state Markov channels as we move further from the last training bit [10].

References

References is not available for this document.