Design and Analysis of Transmit Beamforming for Millimetre Wave Base Station Discovery

TL;DR

This paper develops an analytical framework for initial access in mm-wave systems, proposing a beamforming strategy for base station discovery that balances narrow and wide beams to optimize detection performance.

Contribution

It introduces a hypothesis testing approach for BS discovery, characterizes detector behavior, and designs a sequential scanning method with a flexible codebook for improved initial access.

Findings

Narrow beams may not improve discovery performance due to scanning costs.

The proposed sequential scanning method effectively reduces miss-discovery probability.

Analytical results guide optimal beam pattern design for mm-wave initial access.

Abstract

In this paper, we develop an analytical framework for the initial access (a.k.a. Base Station (BS) discovery) in a millimeter-wave (mm-wave) communication system and propose an effective strategy for transmitting the Reference Signals (RSs) used for BS discovery. Specifically, by formulating the problem of BS discovery at User Equipments (UEs) as hypothesis tests, we derive a detector based on the Generalised Likelihood Ratio Test (GLRT) and characterise the statistical behaviour of the detector. The theoretical results obtained allow analysis of the impact of key system parameters on the performance of BS discovery, and show that RS transmission with narrow beams may not be helpful in improving the overall BS discovery performance due to the cost of spatial scanning. Using the method of large deviations, we identify the desirable beam pattern that minimises the average miss-discovery probability of UEs within a targeted detectable region. We then propose to transmit the RS with sequential scanning, using a pre-designed codebook with narrow and/or wide beams to approximate the desirable patterns. The proposed design allows flexible choices of the codebook sizes and the associated beam widths to better approximate the desirable patterns. Numerical results demonstrate the effectiveness of the proposed method.