Coordinated Multi-BS SSB Beam Design for Enhanced Initial Access Coverage

TL;DR

This paper proposes a joint transmission strategy for synchronization signal blocks in 5G networks, enabling coherent combining at the UE to significantly improve initial access coverage.

Contribution

It introduces a repetition-based joint transmission method for SSBs that does not require channel state information, enhancing coverage with limited configurations.

Findings

Up to 6 dB SNR gain with 4 BSs using JT of SSBs

Repetition-based JT enables coherent combining without CSI

Limited configurations optimize coverage and reduce overhead

Abstract

Ensuring strong synchronization signal block (SSB) coverage is essential for reliable user equipment (UE) connection during initial access. While techniques such as power boosting and network densification are commonly used, this work explores joint transmission (JT) of SSBs as an alternative to enhance coverage. Although JT is widely applied in data transmission, its use for SSBs has not been explored due to the lack of channel state information, which prevents coherent signal alignment across base stations (BSs). To address this, we propose a repetition-based JT strategy using a small set of predefined phase configurations at the BSs. This enables the UE to coherently combine multiple SSB receptions and achieve constructive gain regardless of its location. To reduce overhead, a limited number of joint beam configurations is selected to maximize the coverage. Simulation results under the line-of-sight conditions show up to 6 dB relative SNR gain with JT of SSBs using 4 BSs, compared to independent SSB transmission under the same resource budget. These results highlight the potential of JT to improve the coverage of SSBs during the initial access.