In this work, we show a new design of analog equalizing network for N-stream strong Line-of-Sight MIMO communication, aiming at improved robustness. The design includes a core fixed equalizing network that equalizes ideal spatially orthogonal channels. Existing works show that the fixed equalizing network can equalize a spatially orthogonal MIMO system with parallel arrays. However, it is observed that such a fixed equalizing network is very sensitive to displacement errors. To make the system robust, state-of-the-art approaches use N2 fully controlled analog elements to perfectly equalize the channel via aligning the structured interferences. In this work, the terms causing the sensitiveness of fixed analog equalizing networks are identified. By compensating the tackled sensitive terms, the proposed design uses only 2N fully controlled analog elements and the robustness of the system is improved significantly. Meanwhile, by exploring the channel property, this work shows that if the spatially orthogonality is achieved by uniform rectangular arrays, the equalization can be applied with a new two-stage scheme. The scheme can be applied to spatially orthogonal MIMO systems with digital and/or analog equalization. Meanwhile, the computational complexity, required components number, as well as the complexity of the hardware design are significantly reduced.
['Xiaohang Song', 'Wolfgang Rave', 'Gerhard Fettweis']
Analog and successive channel equalization in strong line-of-sight MIMO communication