Optimisation of channel capacity for multiple-input multiple-output smart antenna using a particle swarm optimiser

In this study, the channel capacity of indoor multiple-input multiple-output ultra-wide band (MIMO-UWB) transmission for a smart antenna is described. A particle swarm optimiser (PSO) is used to synthesise the radiation pattern of the directional circular arc array to maximise the capacity performance in an indoor MIMO-UWB communication system. The UWB impulse responses of the indoor channel for any transmitter-receiver location are computed by applying shooting and bouncing ray/image techniques, inverse fast Fourier transform and Hermitian processing. By using the calculated frequency response, the capacity performance of the synthesised antenna pattern on an MIMO-UWB system can be computed. Based on the topography of the circular antenna array and the capacity formula, the array pattern synthesis problem can be reformulated into an optimisation problem and solved by the PSO algorithm. PSO optimisation is applied to a high-order non-linear optimisation problem. The novelties of our approach are not only choosing capacity as the cost function instead of the sidelobe level of the antenna pattern, but also considering the antenna feed length effect of each array element. The cost function for the problem is non-smooth and discontinuous with respect to the antenna pattern. It is difficult to solve by gradient methods, since the derivative is hard to derive. The strong point of the PSO algorithm is that it can find out the solution even if the performance index cannot be formulated by simple equations. The simulation results show that the synthesised antenna array pattern is effective to focus maximum gain on the line-of-sight path which scales as the number of array elements.