Gains and Limits of MIMO Technology for Safety-Critical PLC Applications

Many Power Line Communication (PLC) systems operate on top of multi-conductor infrastructures, which allows for the adoption of Multiple Input Multiple Output (MIMO) techniques. Current channel models for MIMO PLC do not consider terminal conditions and are focused on optimizing the average case. For safety-critical applications, however, the line terminations are important, as system performance has to be guaranteed for any conditions-including the worst case. In this paper, we present an analytical and a SPICE1-simulated channel model based on transmission line theory that is capable of incorporating terminal networks. Further, we evaluate the channel capacity and compare three different systems that could be deployed in a multi-conductor environment: A Single Input Single Output (SISO) system, multiple parallel SISO systems and a MIMO system. With our channel model we show that the terminal conditions have an impact on the overall signal attenuation, but also that they affect the relative cross-talk level compared to direct channels. Although we can confirm existing findings that MIMO techniques do provide performance gains, our results show that this is only true above a certain signal-to-noise ratio (SNR). For low SNRs, these gains decrease and in worst case, the gains over a SISO system are lost. Also, parallel SISO systems do not offer robust performance gains over single SISO systems, which discourages their use for safety-critical applications.