12 Dec 2016
Dirty fibre and poor QoS – are operators about to trip on the first 5G hurdle?
Kashif Hussain, CellAdvisor Solutions Marketing at Viavi Solutions looks at 5G network infrastructure and the test solution requirements.
The 5G race is gathering pace. Barely a week goes by without another player throwing its hat in the ring. Just recently it’s been the EU, which alongside free Wi-Fi in public spaces, is proposing to fully deploy 5G mobile networks by 2025.
Nokia has announced the launch of 4.5G Pro, shortly followed by a tie-up with Optus. Ericsson, meanwhile, has stated it intends to start delivering technology powering the first 5G networks as early as 2017, and is also partnering with Orange on the development and test of 5G use cases.
LTE is becoming widespread, and it’s clear that operators are ramping up their investment in network infrastructure and 5G technology. Ovum predicts there will be 24 million 5G customers in the world by 2021.
Testing for success
Despite the huge potential for 5G it will not be without its challenges. In the UK in particular, it will necessitate the installation of new transmitters nationwide, the right regulation for a flourishing and competitive market, and the right skills and diagnostic tools to ensure proper management of the infrastructure. The industry needs help defining effective network evolution strategies to avoid the mistakes of yesteryear, and operators must be able to manage operational networks while gaining valuable analytics to inform future network plans.
The right test and measurement tools will help mobile network operators (MNOs) and network equipment manufacturers (NEMs) avoid the issues seen during the evolution of wireless networks to 4G, which resulted in the networks failing at times or running slowly. 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 quality of service (QoS), it’s crucial.
As data usage on wireless increases - predicted to grow 66% annually from 2012 to 2017, according to Cisco - these networks of today are being restricted not just by signal interference caused by so-called ‘dirty fibre’, but also the current time-intensive methods for testing base stations. How can we learn from past mistakes - patchy service, fading, weak signals and variable quality of experiences - to deliver a robust future network, fit for delivering the big connectivity ambitions of today’s telecoms companies, governments, businesses and consumers?
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 quality of experience (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.
Tackling dirty fibre
Already popular in the US, Fibre to the Antenna (FTTA) cell sites are beginning to make their presence felt here. These new installations fundamentally change the base station model: Instead of a component approach where an antenna is connected to a base band unit (BBU) via coaxial connection, this new breed of cell sites uses a distributed architecture approach. This involves a remote radio head (RRH), placed at the top of the tower, connected via a fibre feed to sync with the base band unit (BBU), which is placed at the base of the tower.
The older base stations using the coaxial connection always experienced a degradation of signal, and maintaining and testing them is a costly exercise. 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, and the resulting time it takes to maintain cell sites. 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 saving critical maintenance time.
New testing technologies for future networks
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 a test instrument with RF over CPRI (RFoCPRI) or RF over OBSAI can be plugged into the BBU at the base of the tower, allowing engineers to get access to the RF signals and spectrum, without having to climb the tower. Engineers can instead perform tests from the safety of the ground, reducing the time they spend on maintenance.
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.
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 sent 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. This all means the amount of time and therefore cost that needs to be dedicated to one site can be dramatically reduced, making the entire process far leaner than it has been in the past.
Tackling interference in dense environments
Interference in cellular networks is one of the most common problems in the radio access network (RAN). Different systems and services such as mobile communications, mobile radios, paging, wireless local area networks, and digital video broadcasting each use an assigned spectrum to avoid transmitting different services at the same frequency—causing signal collisions or interference.
We know that signal interference in wireless networks negatively affects transmission coverage and mobile network capacity, limiting overall network performance. Unfortunately, unavoidable signal interference is becoming more prevalent in wireless networks with the increasing number of active transmitters on the RF spectrum. In addition to the licensed systems, the spectrum is also occupied by unlicensed transmitters, while reflection due to dense urban environment can cause signal distortion. This is creating a very complex environment which must be routinely monitored in order to maximise service performance.
Testing and analysing to define and support a smoother evolution
There are ways to detect, manage and help ease the issue with interference using diagnostic tools to pinpoint where the issues are and what type of interference it is. Interference analysis has three main stages: detection — using metrics and RAN KPIs to identify the network performance issues that are related to interference anomalies; identification — having the ability to identify the type of interference signal through demodulation (for example, FM, AM, GSM) and finally location — performing directional measurements, recording the geographical coordinates used to triangulate, and find the intersection area which will represent the geographical location of the interferer.
Interference is typically intermittent, being active for short periods of time. This makes it difficult to identify and therefore, it is important to continuously record spectrum measurements, either as spectrum analysis or spectrogram measurements. RF test analysers have the ability to continuously monitor the spectrum, performing all interference analysis measurements including spectrum analysis, spectrogram, and RSSI, which can be executed unattended and for extended periods of time.
The most commonly used test method to detect interference is spectrum analysis, which performs measurements on frequency domain. This indicates the amount of energy or power transmitted at each frequency. RF test analysers perform spectrum analysis with configurable filters (for example, resolution bandwidth and video bandwidth) and power adjustments (for example, attenuation, averaging, and pre-amplification) for the proper characterisation of interference signals in the spectrum. These analysers also provide several tools for signal examination such as maximum hold, trace overlay, and power-limit masks, among others. All are very useful for detecting interference signals.
The more complex the RAN gets, the more operators need to minimise cost, time to market, downtime and risks to field technician safety in cell site installations. Base station analysers can be augmented with embedded baseband unit (BBU) emulation to enable comprehensive testing during remote radio head (RRH) installations at cell sites, to reduce the need for repeat site visits and tower climbs, speed up deployment times and cut operational expenses. 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.
Fundamental testing for 5G
The evolving fifth generation (5G) cellular wireless networks are envisioned to provide higher traffic capacity, enhanced end-user quality-of-experience (QoE) and ultra-high reliability, very low latency and energy optimization. 5G will feature many types of new technologies that require a new approach to test and measurement including spectrum reuse and use of different bands, (for example mmwave communication using 28~GHz and 38~GHz bands), multi-tier networks, D2D communication, CRAN, massive-MIMO, heterogeneous and multi-tier network M2M communication as well as self-organizing and cognitive networks. These are just some of the many new features 5G will offer. Interference analysis in wireless networks is a fundamental testing procedure to monitor the spectrum’s environment with several emerging technologies which will enable and define the 5G mobile communications standards.
Future 5G cellular wireless networks will definitely be a combination of different enabling technologies. However, the biggest challenge will be to integrate all the enabling technologies and make them all work together. Testing, analysing, defining and collaboration is the path to success in delivering the supercharged vision of future communication networks.
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About the author
Kashif Hussain is the CellAdvisor Solutions Marketing at Viavi Solutions (formerly JDSU) for the wireless business unit. He has more than 20 years of wireless industry experience. Kashif's expertise in RF, DAS, HetNets, and LTE comes from developing, managing, supporting, marketing and consulting on major mobile communications projects. Kashif's industry experience also includes various senior roles at MobileNet, Tektronix Communications, Ericsson and Nortel. He has also authored patent for wireless products.
Viavi is a global provider of network test, monitoring and assurance solutions to communications service providers, enterprises and their ecosystems, supported by a worldwide channel community including Viavi Velocity Solution Partners. The company delivers end-to-end visibility across physical, virtual and hybrid networks, enabling customers to optimize connectivity, quality of experience and profitability. Viavi is also a leader in high performance thin film optical coatings, providing light management solutions to anti-counterfeiting, consumer electronics, automotive, defense and instrumentation markets.
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