In-network Angle Approximation for Supporting Adaptive Beamforming

There is a great interest in utilizing P4 for in-network computing along with programmable data planes. This use is emerging as a new network paradigm that can not just reduce the complexity but the delay as well. Beamforming is now an integral feature of modern wireless communication systems and its implementation calls for an accurate beam alignment by estimating the direction of signal arrival. However, this estimation is computationally complex, especially in a dynamic environment where a user is constantly on the move. In this paper, we propose a user-assisted in-network method to optimally approximate the angle of arrival by segmenting the cell area into an exponentially binned grid and make use of the advantages offered by programmable data planes and their match-action table (MAT) logic. The method expects location messages periodically reported by user equipment, processes them in the network and reconfigures the base station antennas accordingly, implementing user-assisted in-network beam control. The proposed method is implemented in P4 and runs on a Tofino ASIC. Our evaluation proves a theoretical bound on the absolute error of the proposed MAT-based angle approximation and shows that it is in accordance with the empirical error distributions. Moreover, there is no significant increase in errors attributed to the latency of various control cycle times (less than 100ms) and the user's movement at moderate speeds (of less than 90km/h.) We also show that the resource usage is only affected by the size of the TCAM table used to store the angle approximation values and that the proposed method has no significant per-stage resource usage on the pipeline.