On the Performance of Downlink Beamforming with Synchronized Beam Cycles

The next generation of wireless networks (e.g.,) will use multiple techniques to improve channel spectral efficiencies. In this paper we focus on one such technique, beamforming, in the downlink channel. In each sector, a number of fixed beams are used to serve UEs (User Equipment). For each frame, the scheduler chooses a beam and then schedules one or more UEs that lie within that beam. Since the power is focused on a narrow beam then the served UEs can achieve higher rates and the sector coverage is also increased. However, this beam causes more interference in adjacent sectors. If a neighboring sector schedules a UE that lies within the coverage of this beam then the rate for that UE will be low. The neighboring sectors must therefore schedule UEs outside of the beam or at least know of the interference that will be experienced. The first approach (interference avoidance) requires coordination among the sectors with the associated communication overheads and delays. In this paper we follow the second approach and assume no coordination among sectors except for the fact that they all use the same beam cycle period. Although all NBs use the same beam cycle period, they may occasionally change the specific beam schedule based on local factors such as the geographical distribution of UEs within its beams. Such changes should be made infrequently since the approach is based on the assumption that the interference experienced by a UE repeats with the beam cycle period.