The unmanned aerial vehicles (UAVs) can serve for key applications in wireless communications. Cellular systems can be assisted by UAVs to provide ubiquitous coverage and additional capacity to overloaded base- stations. In this paper, we present the performance analysis of UAV assisted wireless communication system for ubiquitous coverage. In the considered system, the source and the destination terminals have single transmit and receive antennas, on the other hand the UAV node has multiple transmit and receive antennas. The closed form expression of the bit error rate (BER) performance for the considered system over generalized two-wave with diffused power (TWDP) fading is derived in particular. The performance analysis is done considering direct line of sight (LOS) and multi-path components between source-UAV- destination links. The results are analyzed for Rician and Rayleigh fading channel as a specific case of TWDP distribution. Moreover, in order to get the better insights of the system, we also perform the asymptotic analysis for the considered system. Simulation results are presented for different scenarios and it is observed that simulation results shows excellent agreement with the analytical results.