Joint Fractional Time Allocation and Beamforming for Downlink Multiuser\n MISO Systems

It is well-known that the traditional transmit beamforming at a base station\n(BS) to manage interference in serving multiple users is effective only when\nthe number of users is less than the number of transmit antennas at the BS.\nNon-orthogonal multiple access (NOMA) can improve the throughput of users with\npoorer channel conditions by compromising their own privacy because other users\nwith better channel conditions can decode the information of users in poorer\nchannel state. NOMA still prefers that the number of users is less than the\nnumber of antennas at the BS transmitter. This paper resolves such issues by\nallocating separate fractional time slots for serving the users with similar\nchannel conditions. This enables the BS to serve more users within the time\nunit while the privacy of each user is preserved. The fractional times and\nbeamforming vectors are jointly optimized to maximize the system's throughput.\nAn efficient path-following algorithm, which invokes a simple convex quadratic\nprogram at each iteration, is proposed for the solution of this challenging\noptimization problem. Numerical results confirm its versatility.\n