Channel Characteristics Variations from Switching Between Narrow Beams

Sammanfattning: The demand for higher throughput and lower latency in telecommunication systems is growing. Upcoming telecommunication systems will operate at higher frequencies (above 15 GHz) compared with previous systems (below 6 GHz). Antenna arrays will be employed in upcoming systems for increased link budget (coverage) and multiple input multiple output channels. This implies that narrow beams will be used. Beam tracking and beam steering is necessary to follow the user equipment. It is hypothesised that changing beam direction changes the channel condition for the communication link. In this work beam changes in data gathered with a 5G testbed is analysed at both 15 GHz and 28 GHz. The results show that the channel is indeed affected by beam changes. Statistical results of the conducted analysis are presented followed by specific examples on how the channel is affected by the beam changes. Knowledge on how the channel is affected by beam changes is of interest when designing systems for beam selection. The results show a nearly threefold increase of rank changes immediately after a beam change at 15 GHz. The probability for a rank change up or down is found to be equal. At 28 GHz the metric used for channel richness is singular value ratio. The statistical results show that the difference in singular value ratio before and after a beam change is increased by a factor 2. It is also shown that grating lobes may have a significant effect on the channel richness when changing beam direction.