Broadband MIMO Couplers Characterization and Comparison

THIS paper focuses on MIMO Power Line Communication (PLC) to provide increased performance. In MIMO PLC, appropriate coupling methods are necessary in order to enable the effective injection of the signal through the broad band PLC channel so that high data rates can be achieved [1], [2], [3]. In the literature, different kind of couplers are proposed [4],[5]. In this paper, we want to characterize in an analytic way strengths and weaknesses of each coupler design (topology) from an electrical circuit perspective. We dwell on the description and analysis of the three main and common configurations used for the MIMO couplers: star (S), triangle (∆) and T. For each configuration, we study different connection formats for the input generators and output loads: star, triangle and T. Furthermore, we consider MIMO 2x3, 2x4, 3x3, 3x4 architectures, where the fourth received signal is referred to as common mode signal. The purpose in this study is to clearly define the equations that describe the output signals as a function of the input signals and the impedances present in the circuit. This is achieved analyzing the transfer function of the circuit under survey. A model is presented to be able to identify how much the nonidealities of components, such as, uncoupling/protection devices and filters, affect the coupling and cross coupling between signals. All these components add, inside the transmission chain, undesired effects in the signal of interest. Our aim is to define a procedure that, knowing the characteristics of these nonideal components, allows us to compensate this effects working on circuit parts and signals. Moreover, the effect of the line impedance variation on the coupled voltage is investigated. This is an important aspect since the line impedance may have a time variant behavior as a result of network loads that are time variant [6]. In particular, we consider the impedance mismatch problem [7] under a source load constraint with distinct coupler topologies: star, triangle and T. Finally, a comparison of the best combination of TX-RX coupler configurations is carried out.