Performance of multihop decode-and-forward and amplify-and-forward relay networks with channel estimation

This paper investigates the performance of three types of multihop relay systems with a single relay path from the source to the destination, using the relaying strategies: decode-and-forward (DF), fixed gain amplify-and-forward (AF), and variable gain AF, respectively. It is shown that, as the number of hops increases, the performance degradation of DF relay systems is due to error propagation, while that of AF relay systems comes from 1) noise propagation from each relay node, and 2) the statistical fading property of the AF compound channel. Although the performance degradation of a variable gain AF relay system mainly comes from noise propagation and its performance is robust in a cascaded AF fading channel, it is shown that a fixed gain AF relay system suffers from a large performance loss since the cascaded fixed gain AF fading channel gives more severe fading. As a result, the variable gain AF significantly outperforms the fixed gain AF and achieves comparable performance as the DF scheme. Furthermore, we study channel estimation techniques, such as the least squares (LS) and linear minimum mean square error (LMMSE) channel estimation in multihop, single path AF relay systems, where the mean squared error (MSE) of both channel estimators in a fixed gain AF relay system is derived, and the performance of the aforementioned three systems with channel estimation errors are simulated.