Directional Cell Search Delay Analysis for Cellular Networks with Static Users

TL;DR

This paper analyzes the delay in directional cell search for cellular networks with static users, revealing conditions under which the delay is infinite and demonstrating beam-sweeping's effectiveness in reducing delay.

Contribution

It provides a closed-form expression for mean cell search delay in Poisson networks and identifies phase transition phenomena related to antenna beam numbers.

Findings

Mean cell search delay is infinite in noise-limited networks with NLOS path loss exponent > 2.

A phase transition in delay exists based on the number of BS antennas in interference-limited networks.

Beam-sweeping significantly reduces cell search delay, especially at cell edges.

Abstract

Cell search is the process for a user to detect its neighboring base stations (BSs) and make a cell selection decision. Due to the importance of beamforming gain in millimeter wave (mmWave) and massive MIMO cellular networks, the directional cell search delay performance is investigated. A cellular network with fixed BS and user locations is considered, so that strong temporal correlations exist for the SINR experienced at each BS and user. For Poisson cellular networks with Rayleigh fading channels, a closed-form expression for the spatially averaged mean cell search delay of all users is derived. This mean cell search delay for a noise-limited network (e.g., mmWave network) is proved to be infinite whenever the non-line-of-sight (NLOS) path loss exponent is larger than 2. For interference-limited networks, a phase transition for the mean cell search delay is shown to exist in terms of the number of BS antennas/beams $M$: the mean cell search delay is infinite when $M$ is smaller than a threshold and finite otherwise. Beam-sweeping is also demonstrated to be effective in decreasing the cell search delay, especially for the cell edge users.