Doubly Iterative Receiver for MIMO Amplify-And-Forward Relay Networks

In this paper we consider a Multi-Input Multi-Output (MIMO) wireless relay network which comprises of a source terminal, a destination terminal and a relay. The transmission from the source terminal to the destination is divided into two phases. During Phase I, the source terminal sends its signals to the relay. The relay only amplifies and forwards its received signals to the destination terminal during Phase II, i.e., the network works in the Amplify-and-Forward (AF) mode. In this mode, the noise elements at the relay at Phase I are also amplified and forwarded through a link (from the relay to the destination terminal). It makes the overall noises across antennas of the destination terminal correlated. This correlation is characterized by a noise covariance matrix. Hence, for the purpose of data detection at the destination terminal, we need to estimate channel coefficients as well as the noise covariance matrix. In the considered network, an error correcting code (ECC) is used. We propose a doubly iterative receiver to estimate channel information and decode transmitted signals. The estimation part is an application of the Expectation Conditional Maximization (ECM) algorithm. Turbo-equalization is used to provide soft information of transmitted signals to the ECM-based algorithm. Simulation results show that our doubly iterative receiver provides an excellent BER performance.