Performance driven symbol adaptation for precoded downlink and point-to-point MIMO systems

This paper proposes a dynamic symbol adaptation scheme for downlink and point-to-point multiple input multiple output (MIMO) systems aiming at the minimization of the overall system bit error rate. The proposed scheme adaptively changes the order or the values of the symbols to be transmitted within a sub-frame of symbols with the objective to enhance the received symbols´ power. The adaptation is based on the instantaneous interference between the symbols taking into account the channel´s characteristics as well as the actual symbol values. This procedure is targeted to optimizing, rather than strictly minimizing the interference between the symbols. In this way, constructive instantaneous interference is utilized in enhancing the decision variables at the receiver on a symbol-by-symbol basis, so that detection is made more reliable. The proposed scheme can be used in conjunction with various conventional MIMO precoding and detection techniques. The presented simulations show that it provides significant benefits to the corresponding conventional system´s error rate performance.