A new metric for BER evaluation in APP decoders with space diversity

We propose a new metric which summarizes in a single parameter most of the information required to infer the BER of a turbo code (TC) in a Rayleigh multiple-input multiple-output (MIMO) channel. This metric relies on the measurement of the mean and variance of the log-likelihood ratios (LLRs) at the TC output and it is shown to provide a one-to-one relationship with the BER. Thus, this metric can be used to monitor the quality-of-service (QoS) and detect the need of changing the transmission mode in a reconfigurable system with adaptive modulation and coding (AMC).