Beamformed PRACH preamble transmission and multi-TRP reception in 6G systems

Abstract

The thesis investigates how to design the beamformers for preamble transmission and reception in a random access scenario with multiple Transmission and Reception Points (TRPs) to meet the coverage requirements of the co-located 5G and 6G site deployments. The primary objectives are i) to model and simulate the preamble transmission and reception with and without channel state information at the transmitter (CSIT) to compensate for the 6 dB increased path loss when deploying higher frequencies (7 GHz) on existing network optimized for lower frequencies (3.5 GHz), and ii) to evaluate the preamble detection performance for several 6G network deployment strategies.

The results show that the preamble transmission and reception with CSIT can meet the requirement of 6 dB gain. This can be achieved by designing a precoder based on strongest-eigenmode beamforming, and a combiner based on non-coherent weighted power combining. The transmit beamformer is the right singular vector which corresponds to the largest singular value of the aggregated channel matrix and defines the optimal spatial path for preamble transmission. An optimal usage of the aggregated DL measurements of the Synchronization Signal Block (SSB) allows efficient utilization of uplink beamforming for the Physical Random Access Channel (PRACH). The receive beamformer is expanded to cover the multi-TRP case, and it is a coordinated beamforming to jointly process the received signals from involved TRPs. In addition, the gain requirement is fulfilled in both single- and multi-TRP environments depending on the preamble transmit beamforming strategy chosen based on user-equipment antenna configuration and network deployment. The thesis contributes to the uplink coverage enhancement of PRACH preamble transmission and reception by proposing novel signal processing methods in a 6G multi-TRP environment.