Analog–digital precoding based on mutual coupling considering the actual radiation performance of MIMO antenna arrays

Mutual coupling among antenna array elements can have impacts on not only the elements’ mutual impedance but also the radiation characteristics, which is usually not considered appropriately in previous precoding researches. In this paper, an analog–digital precoding scheme based on mutual coupling is proposed considering the actual radiation performance of multiple-input multiple-output antenna arrays. Instead of reducing or eliminating the mutual coupling effect as in the conventional approach, this paper focuses on exploiting it to improve the system performance. Open-circuit radiation pattern is firstly introduced in the system model to further evaluate the effect of mutual coupling on the antenna radiation performance. Conventional linear precoding is applied in the digital domain. As for the analog domain, to minimize the noise amplification factor and thus maximize the receive signal-to-noise ratio of the system through exploiting the mutual coupling effect, the proper load impedances and antenna weighting coefficients are selected by convex optimization and Newton method. Simulation results show that the proposed scheme performs significantly better than the conventional one without mutual coupling in zero forcing and minimum mean square error systems. Besides, greater performance gain in MIMO systems with smaller antenna spacing, higher dimensionality and larger apparent power are observed.