Part I: Mobile Networks Infrastructure: Getting the Signal Where It’s Needed

By Bradley Smith

Introduction

In my former articles I’ve written about the history of Australian telecommunications networks and how these have evolved over time, which has led into the topic of Smart Cities.

Believe it or not, there are a lot of smoke and mirrors used to get the signal to make your phone work properly. Those without adequate coverage often lament about their carrier of choice – how their “mobile phone doesn’t work” when they need it.

This article looks at the infrastructure that Carriers (Telstra/Optus/Vodafone/NBN/TPG) have used in past and present times to make your phones work. My next series of articles will look at the way the upcoming mobile network infrastructure will need to change in order to get the signal to the devices – not just phones or handsets, but the connected devices of the 5G age.

• Part I    Basic mobile infrastructure definitions
• Part II   The Smoke and Wires that hold together 2G / 3G and 4G services
• Part III  The new infrastructure required for 5G and beyond

Building a Mobile Network

Delivering signal to a mobile-hungry population is largely dependent on the population density. The aim of the mobile network operator (MNO) is to provide an RF solution that will benefit the most people or solve the largest issues with the least expense to the company. Let’s look at the various ways that mobile services are integrated into society.

MACRO sites – no doubt you would have seen the towers on the city landscape, in the suburbs or perhaps blended in to the landscape as best as possible on rooftops. These sites provide extensive footprint and coverage to large populations and simply “hose” an area with the signal that keeps your mobile actively connected. Macro sites typically share the infrastructure between the Carriers (Telstra, Optus, Vodafone, TPG, NBN, etc) to consolidate the number of sites that are present in our cities. Typically 2 or 3 Carriers will collocate on a single structure, which reduces the visibility on the landscape of this infrastructure.

However there are limits to how many Carriers can be supported on a single structure. A pole (or monopole, as they call it) has two points of assessment to determine how much equipment can be installed on it: the footings, and the tower structure itself. If the tower can’t be strengthened to cater for extra antennas from a second or third Carrier, then it can be swapped out. There are larger problems to address if the footing is at capacity, which generally means that the structure can’t be loaded any further; and in these cases another site location is generally required.

IN-BUILDING sites – the signal from Macro sites doesn’t always penetrate into certain areas as it can be limited by its location or shielding from the building itself. There is a large push by all Carriers to get more signal into the areas where it’s needed – for example on train station platforms, tunnels, underground shops and car park basements.

An in-building cell (IBC, for short) involves a series of low radiating power antennas that are scattered throughout the building or infrastructure, and designed to cover small areas. For instance it might be a floor of an office building, a rail platform for commuters and shopping centre malls.

The good old days of early IBC infrastructure deployment required long copper pipes like drain pipe to be meticulously designed by RF engineers, who had to determine the best combination of antennas, attenuators, and pipe lengths to provide an even coverage throughout the building. It was a work of art, to say the least. Nowadays, IBC’s are deployed simply with optic fibre and power runs that mean a signal can be placed right on top of the locations that it is required without too much concern for how long the cable runs need to be.

CoWs – as they are affectionately known – are “Cell on Wheels” which are temporary mobile phone sites that are designed for events (like the Commonwealth Games or V8 Supercars) which require additional capacity, as the standard mobile network wouldn’t be able to handle the extra influx of visitors. CoWs are deployed to provide the extra infrastructure and are typically removed after the event. The CoW is simply a transportable shelter on wheels or a skid, and a pump up mast or small pole or guyed structure that can take antennas and/or a microwave dish.

Some CoWs are deployed for “emergency coverage” situations, like bush fire relief, or where a site is no longer able to be maintained at an existing facility - for instance, the landlord might have terminated the lease. In these events, a CoW can provide mobile coverage for the season that a new site is required, which might take 2 to 3 years. CoWs are subject to council and landlord approval, and need to be “planned” into the network just like regular Macro sites.

The Situation in the Bush

Australia is a huge country. Deploying mobile infrastructure into remote areas, as well as developing areas off the city limits, requires careful planning. That’s why the Australian Government has introduced the Mobile Blackspot program, in order to expand mobile footprint into the bush, by offering to pay the Carrier around half of the cost of the site deployment costs.

Now this isn’t as easy as it seems. It’s not simply a matter of spending bucket loads of cash, as there are a number of requirements to build a site. First, the site needs to cover as much area as possible for it to be of benefit to as many users as possible. So we’re generally looking for the largest hill or high tower in the vicinity. That’s been my job as an RF Engineer. Second, once a few candidates have been identified with willing landlords there is a need to evaluate the sites in terms of access and power runs. It’s not always feasible to spend the entire site budget to build power and access runs, so the most suitable candidate is chosen that ticks a few more boxes from this angle. Third, the site typically has to get support from council or meet certain obligations that provide minimal impact on the landscape, which may all form part of the construction process. Getting council approval for a new site build can range from 3 months to several years, depending on who we are dealing with here. Incidentally, this process is the virtually same to build city sites, just as much as building rural sites.

Recap

Building mobile network infrastructure is a lengthy and costly process, and the process of acquiring sites takes time. Normally Carriers will build Macro sites to get as much coverage to the population as possible through poles and rooftop sites, then focus on supplying coverage in building and in areas where it’s required to meet population demands and expectations. The rural mobile network has its own series of challenges and will take years to get adequate mobile coverage that can meet the demands of the populations of people that live in those areas. CoWs can be deployed for special events and in times of crisis but these are intended for short term measures only and are not a final solution.

The next article in this series will focus on other types of technology and equipment that has been used to deliver mobile network services over the years. Some of it is now redundant, however it’s the smoke and mirrors bits that pique my interest in the industry of mobile networks from an engineering perspective as it results in a positive outcome to meet customer expectations.