Packet scheduling algorithm to improve throughput and fairness in SDM system using adaptive antenna array

This paper investigates several downlink packet scheduling algorithms in OFDM based systems for space division multiplexing (SDM) with adaptive antenna array beam forming. The packet scheduling algorithm, which generates directional beams toward accessing users in accordance with the priority based on received signal-to-interference plus noise power ratio (SINR) have been proposed. However, the algorithm can generate few directional beams due to the increase of inter beam interference. As a result, the improvement of overall capacity is limited. In this paper, we propose an algorithm to increase total throughput by increasing the number of directional beams. In our algorithm, difference of angle and interference among directional beams are considered. It is shown that the proposed algorithm can increase the sector throughput by 13 % as compared to the conventional SINR-priority based algorithm. Moreover, we investigate the effect to take into account the channel quality and waiting time of each user in the proposed algorithm from the viewpoint of the sector throughput and the fairness of transmission slot assignment probability. Simulation results show that the proposed algorithm with taking into account the received SINR averaged over the scheduled users improves the sector throughput by 5 - 10% as compared to the original proposed algorithm. It is also shown that, additionally taking into account the waiting time of the users, although the sector throughput is degraded by 12%, the number of users who have the transmission slot assignment probability of less than 0.1 is reduced by 26% compared to the original proposed algorithm.