Fiber-Optic Based Solutions for Long-Tunnels Radio Coverage and Surveillance

1. Introduction

The city of Mecca is a holy place that is surrounded by a number of huge mountains. It hosts millions of people throughout the year, where the peak time is during the annual pilgrimage event that is known as Hajj. During this event, the pilgrims have to visit several places around the city, where they pass through many long mountain tunnels (Simpson et al., 2014). The latest number of tunnels in Mecca is 66 tunnels including 56 for vehicles and 10 for pedestrians, and their lengths range from 0.5 km to 1.7 km. Therefore, emergency communications in such long, congested tunnels are vital especially in case of accidents.

Unfortunately, most of these tunnels still suffer from partial or total inaccessibility of wireless communication services such as global system for mobile communications (GSM), radio broadcasting and terrestrial trunked radio (TETRA) (Hrovat et al., 2009). This is due to the tunnel structure which typically consists of two curved parts at either tunnel entrance and a straight or semi-straight part in the middle. Such structure does not allow the use of conventional cellular base stations installed near the tunnel (Hrovat et al., 2010). Thus, internal coverage is impossible away from the tunnel edges where incidents are likely to happen (see Figure 1). This would imply that continuous monitoring and communication are lost, and plenty of people are at high risk.

Figure 1.

Tunnel structure and internal coverage situation

Several radio propagation models have already been presented to improve the communication ability inside different types of tunnels (Guan et al., 2013; Hrovat et al., 2014; Moridi et al., 2014; Sood et al., 2015; Qureshi et al., 2016). Such studies focused on enhancing the radio frequency (RF) signal propagation inside tunnels based on the conventional cellular network structure. This research focuses on enhancing the efficiency through upgrading the network structure, where it proposes fiber-optic based solutions for tunnel radio coverage and surveillance. The radio coverage includes personal communication via GSM and private communication via TETRA, while surveillance involves video communication through the mobile network. Both radio and surveillance projects are proposed to be connected to the same infrastructure; and the key component for both of them is the vertical micro-ducted fiber which is supposed to minimize the deployment cost and disruption (Nahas, 2015). Figure 2 shows a classification diagram of the overall manuscript and key subsections.

Figure 2.

The manuscript structure

This proposal is recommended to be considered by the Saudi Ministry of Interior (MOI), which is responsible for the safety and security of pilgrims. The TETRA and surveillance networks of the MOI can be therefore upgraded to cover the tunnels dead spots, hence minimal human risk.

The study is also useful for the local mobile network operators, which are interested to improve their quality of service to attract more customers during the Hajj season that is considered one of the biggest gathering occasions in the world.

In general, the proposed solutions are applicable for any similar closed environments such as rail tunnels, metros, underground stations, etc.

2. Coverage Solutions

The coverage solution can be divided into two parts: first, the internal coverage, which concerns how to cover the whole tunnel length; second, the access resource, which concerns how to get the external RF signal into the tunnel or how to connect the tunnel edge to the existing cellular backbone.