Optimization of Multi-Basestation Codebook Beamforming for mmWave Connections to High Speed Trains

The exploration of mmWave technology for future public broadband communications is set to mitigate congestion in the lower spectra bands and is poised to provide multi-Gigabit radio access to urban users, as well as road and rail passengers. However, due to the unique and challenging propagation characteristics experienced in the mmWave bands, and particularity those in rail environments, a large number of trackside Base Stations (BSs) may be required to provide continuous coverage. This paper uses advanced simulation techniques to quantify the minimum number of required trackside BSs, and hence to minimise the capital and operational costs of the network. Our simulation results are supported by real-world track-to-train measurements captured on the UK test track. By combining detailed 3D geographic databases with mmWave propagation models and accurate simulations of the beamforming antenna arrays and mmWave data modems we present an analysis of the theoretic coverage along a 1.9km section of UK rail track. Simulated data rates are presented for each of the 36 potential trackside sites. All studies are performed using a carrier frequency of 60 GHz. The beamforming codebooks used in this work were taken from the mmWave modems used in the rail trials. The codebook choices at the trackside and on-train modems were optimally selected to minimise the number of required BS. Statistical analysis is provided for two different Effective Isotropic Radiated Powers (EIRP). For the higher EIRP level (60dBm), results show that an inter-BS spacing of just under 1000m is viable. This allows Gigabit data rates to be delivered along the entire 1.9km test track using just two trackside mmWave BSs.