Dirty fibre, interference hunting and tower safety

As operators invest more and more in their networks, new solutions can reduce the operational cost - both financial and human - of maintaining cell sites.

With 4G availability on the rise in Europe, the investment operators have made in their networks is nothing short of staggering. Vodafone alone invested €23 billion in networks and services between 2014 and 2016. It’s been a massive upfront expenditure that only now is beginning to deliver a return. Western European mobile operator CAPEX per subscription stands at US$34, according to ABI Research.

Yet despite this initial outlay, operator thoughts are keenly trained on the maintenance of these expensively-assembled networks. For operators, keeping this infrastructure in tip top condition is akin to the cleaning of a house – it never ends. There are a whole multitude of problems to consider and working out the right response to fixing it isn’t always clear. However, if operators are to reduce churn and to maintain QoS, it’s crucial.

Keeping base stations sparkling

One of the many challenges operators face is dirty fibre. This is the collection of dust and particles floating through the air that can find its way onto the fibre optic connector endfaces. This can then either slow down or completely inhibit network traffic in extreme cases. As far back as 2001, a survey found contaminated fibre end-faces were the leading cause of fibre link failure, representing 85 per cent of failures. With traditional base station configurations and testing protocols, identifying and solving the issue is hugely time-intensive. Many operators simply see it as an acceptable loss.

Another common complaint of current network infrastructure is the level to which interference can reduce coverage, capacity, and throughput. This can have a major and more immediate impact on user QoE than dirty fibre. Whilst the problem is clear, finding its source isn’t always as easy. Indeed up until the recent past, the equipment used to scan for interference was incredibly weighty, clumsy, and often involved engineers using wheelbarrows to go around searching for the source of the interference.

This is particularly true in urban environments where geographical impediments can muddy the water when hunting for the source of interference. In addition to this, the presence of illegal, unlicensed, or unintentional signals, can show up in the network intermittently or persistently at different frequencies over time. It’s like looking for a needle in a haystack…with the needle constantly moving.

The human element

These are just two of the faults that can occur within base stations and why manpower can be one of the biggest outlays for keeping the ‘lights’ on. Despite evolutions of technology within the industry, when it comes to test and measurement this human element can also prove challenging in a different way, by presenting issues around safety. Many current base stations in the US use a Fibre to the Antenna (FTTA) approach, with the rationale of better coverage, power savings, better signal-to-noise ratio, and overall better network quality. These cell sites, which are beginning to be deployed in Europe asoperators race to meet aggressive LTE deployment schedules, use a distributed architecture with a remote radio head (RRH) connected via a fibre feed to sync with the base band unit (BBU), which is placed at the base of the tower.

What’s clear is that operators need to find a way to maintain the upkeep of their installations, solve more of the common problems that impact them, and look for opportunities to limit the amount of time engineers spend maintaining them.

One of the main benefits of this approach is that the fibre connection reduces the reliance on the coaxial connection in older base stations, with the subsequent reduction of the loss associated with coax cables serving to improve cell-site performance. However, the placement of the RRH at the top of a cell tower throws up its own issues from a test and maintenance point of view, ranging from an increase in tower climbs and safety concerns, to high maintenance costs.

Sending people up very tall pieces of infrastructure is loaded with potential risk. Sadly, an engineer in Iowa died earlier this year falling from a base station, and recent reports put the number of similar deaths in the US at five this year already. What’s clear is that operators need to find a way to maintain the upkeep of their installations, solve more of the common problems that impact them, and look for opportunities to limit the amount of time engineers spend maintaining them.

Making the link

As FTTA rollouts become more commonplace in next-generation cell sites in Europe, so new methods for signal testing must be harnessed to reduce the risk of infrastructure climbs. New ways of performing RF analysis from Common Public Radio Interface (CPRI) or Open Base Station Architecture Initiative (OBSAI) links on the ground instead of the top of the tower head are one way of avoiding unnecessary harm, as well as saving critical maintenance time.

Test and measurement methods that use CPRI or OBSAI protocols can capture and analyse RF metrics whether fronthaul is coax or fibre-based. Current testing methods for that setup require a tower climb, but the instrument with RF over CPRI (RFoCPRI) can be plugged into the BBU at the base of the tower, allowing engineers to get all the access to the RF signals and the spectrum over that, without having to climb the tower. Engineers can therefore instead perform tests from the safety of the ground, reducing the time they spend suspended from great heights.

Equally, a fibre connection allows for an immediate test of the fibre and highlights just how dirty it has become. New testing equipment can send a signal through a piece of fibre and analyse what bounces back. If there is a fault in the fibre, it can be detected to within a matter of centimetres. RFoCPRI technology also allows the performance of interference analysis without disrupting service. This is made possible by monitoring the CPRI signal derived from a passive optical coupler installed next to the BBU, at the base of the tower.

Turning up the volume

What these new methods and set-ups provide is less reliance on multiple site visits from multiple engineering teams. Instead, with RFoCPRI technology an increased volume of tests can take place in a shorter space of time and results can even be beamed back via the cloud to a remote control hub. If an onsite engineering team needs approvals to start the maintenance procedure, that can be given remotely instead of having to return at a later date to start all over again.

Operators juggling with the cost of current network infrastructure and managing expectation of 5G should be searching for the tools to reduce the operational expenditure they are faced with. This means the installation equipment, testing kits, and staff servicing them must be able to deliver more for operators. As margins continue to be squeezed, with competition showing no signs of easing in Europe, and while regulation hampers where infrastructure can be deployed persists, operators must get more from what they have at their disposal. European operators are going to have to be incredibly savvy about the current working practices they and their contracted workers are adopting, or the continual issues they face will go on eating into performance and profits.

About the author:
Kashif Hussain is marketing lead for CellAdvisor Solutions, Viavi Solutions.