Moving around in the beam space
One of the key features of cellular communication is mobility – this allows a mobile terminal to move around between cells while maintaining an uninterrupted connection to the network. Mobility is important in mmWave communication too and particularly so if mmWave communication is to be successful in offloading traffic from increasingly loaded sub 6 GHz carrier frequencies.
Current radio architectures used in mobile terminals for 5G-NR mmWave communication rely on analog beamforming. In analog beamforming the mobile terminal can only transmit or receive in one direction at a time. Therefore, when searching for neighbouring cells, the mobile terminal is allowed to carry out beam sweeping in which it uses up to 8 different beams for detecting signals from every possible direction around it. This translates into the neighbour cell detection time being up to 8 times longer than if the mobile terminal had been capable of receiving from multiple directions at the same time. The same principle applies to signal strength measurements on beams in the serving cell i.e. the mobile terminal is granted additional time for carrying out beam sweeping. Analog beamforming thus results in a less responsive system, where handover or beam change may take a longer time than desired and therefore may lead to reduced end-user experience (end-user throughput, latency, power consumption) and overall system performance (system throughput, capacity). Additionally, it may lead to the mobile terminal dropping the mmWave connection and falling back to sub 6 GHz where capacity is scarce.
In contrast, digital beamforming allows the mobile terminal to receive from any direction without first having to conduct beam sweeping, and further, to receive from more than one direction at a time, if needed. Therefore, digital beamforming results in a far more responsive system than when analog beamforming is used, leading to better end-user experience and stronger overall system performance by the mobile terminal being connected to the best cell and the best beam at any given time.
BeammWave’s mobility algorithms utilise the above mentioned beam scanning and beam tracking advantages, along with a digital beamforming architecture, to thereby enable a robust mobility operation for mmWave communication.
