CommScope enhances operator flexibility for DAS and PIM testing

CommScope’s unveiled new DAS and Small Cell products, along with a new CPRI PIM test solution at Mobile World Congress. Samuel Buttarelli and Colin Bryce explain the benefits of these latest offerings for mobile operators to Wireless editor James Atkinson

CommScope enhances operator flexibility for DAS and PIM testing

Highlighting a recent change in the in-building coverage market, Samuel Buttarelli, VP of Distributed Coverage and Capacity Solutions Sales, Europe at CommScope, (pictured below) says: ‘In general, we are finding that there is a lot of requirement for more flexibility now in the in-building market. DAS is a well known technology and it’s proven and effective for LTE, as we’ve seen in the US market. But now more flexibility is being required in multiple areas.’

He points to the need to support multiple frequency bands, particularly in Europe where there is a demand for high capacity in-building coverage. Carrier aggregation (CA) is being seen as a big play to bring more capacity into in-building solutions, so there is a lot of activity in Europe to support CA for in-building, he suggests.

‘There is a need for flexibility in the frequency bands suppliers are providing. In the past DAS was designed for in-building coverage and you just install a system and forget about it. But now there is a need to manage capacity too,’ he notes.

‘So, we have to think more about how to upgrade a DAS system in the future, how to install DAS most effectively inside the building, how to change the banding of the building, how to change the banding of the building, so that capacity can be changed or moved around a building to meet changing end users demand patterns.’

Buttarelli adds that another key issue demanding an effective solution is how to co-ordinate in-building and outdoor mobile networks to make sure the in-building system can work seamlessly with the outdoor macro network, ensuring interference issues are limited. But this needs to be monitored and managed in real time using automated processes, so there are a lot of discussions going on around self-organising networks (SON).

ION-U DAS enhancements
‘We are responding to changes in the flexibility of spectrum bands with our ION-U product,’ says Buttarelli, citing the recent addition of five European mobile frequencies – (see story here). ‘We’ve added the 800,900, 1800, 2100 and 2600MHz frequency bands, plus tri-band MIMO configurations over a single fibre to enhance the capacity and traffic load.

‘For high capacity we are also testing 4x4 MIMO as an alternative to carrier aggregation, but there is a lot of doubling of infrastructure, especially cabling with MIMO inside buildings. However, carrier aggregation gives you the downlink throughput you want (180Mbps) without this need for additional infrastructure,’ he points out.

The ION-U product, first introduced in 2013, is a combination low- and high-power DAS solution with the ability to provide wireless coverage and capacity to indoor and outdoor spaces or both in one compact head-end. It is specifically designed to simplify deployments when used in conjunction with planning, commissioning and optimisation tools.

Operator backing for ION-E system
CommScope’s newer ION-E system, announced in 2014, is a low-power unified wireless infrastructure solution that converges wired and wireless networks on economical Cat6A and fibre-optic cable. It is designed to be flexible enough to adapt changing end user capacity demands and has the capability to add new operators, bands or technologies without having to install new hardware.

Buttarelli reports that Telecom Italia has deployed an ION-E system in its HQ and has approved it, giving the product the fillip of major mobile operator endorsement. ‘We make indoor coverage systems much more IT friendly with ION-E, as you are able to re-direct capacity in a much more flexible way,’ he explains.

There has been much discussion over the last year on the subject of evolving go to market models for in-building coverage solutions, most notably around who pays. Buttareli observes: ‘It is still a carrier driven investment at the moment, but we see difficulties in some areas for carriers. They tell us it is clear what they have to do for small buildings.’

But what’s the best technical solution and business model? For residential properties, the femtocell is the answer. For very large venues and sprawling outdoor spaces it is also clear that DAS is the way to go. ‘But everything in between is causing a lot of debate,’ reports Buttarelli.

‘The traditional business case is not always working. Enterprises see in-building coverage as a key requirement, but they really want to see a multi-operator system. So, here we are seeing a more enterprise driven approach and they are willing to pay for it. Hence, our ION-E product, which is designed to be much easier for IT people to understand and manage.’

New go-to-market models
The point here is that traditional DAS systems require careful design and planning by experienced RF engineers and usually the installation of new cabling – requirements well beyond the capabilities of enterprise IT staff. ION-E on the other hand is a much easier solution to grapple with for IT departments.

‘We think enterprise and building owners are keener to pay for in-building systems now because they can see the need for better wireless coverage. Hospitals and universities have been leading the way here. Often the costs are split with a carrier, but the model still has to be sorted and cost divisions agreed,’ says Buttarelli.

Colin Bryce, Director for Business Development, EMEA and APAC at CommScope, adds: ‘That new business model is emerging and enterprises are looking to procure systems, but the operator still has to be involved. They are responsible for radio emissions and so on, so now operators are certifying ION-E type solutions. But they will want a credible RF installer to do the system, as they still require a degree of diligence, design and RF competence.’

Buttarelli agrees. ‘Usually third party installers are known and trusted by operator and of course you still have to have on-going maintenance agreements and service level agreements that have to be agreed and monitored.’

Metro cell deployment issues
Bryce (pictured below) points to another key area - the small cell. ‘We call it metro cell. We are not talking femtocells or in-building, low power coverage cells. Nor are we necessarily talking about deployment of remote radio heads (RRH) over a distance from a central ‘hotel’, although we can do outdoor coverage with a DAS system of course; it is still one option.’

What Bryce is referring to are outdoor metro cells in the 5-10W output category being provided by OEMs. ‘In this market niche we have everything but the radio strategy. We are talking to North American and European carriers and their strategy is to deploy these metro cells for underlay networks beneath the macro layer as part of a heterogeneous network (HetNet)

‘But operators are concerned about the way these offerings are being made to the market. OEMs sell the metro cells and then everything else is built around that almost on a one-off basis: i.e. sell the radio, then worry about finding the location, the power, the backhaul, etc. You can take this approach in the US, but in most cases you would not get away with US style deployment in Europe because of the planning laws,’ explains Bryce.

The issue here is that metro cells are placed below the standard height of traditional macro network, not on towers or rooftop, but down at street level on lampposts, bus shelters, advertising billboards and the like.

Bryce explains that CommScope has developed a two-part approach to dealing with the planning and installation issues associated with metro cell deployment: the first involves antenna design; and the second concerns small cell deployment housing innovations.

Harnessing antenna skills
Building on its antenna skills, it has worked with some key players in academia, radio planning companies, and a couple of mobile operators to look at what RF deployment really means at the street level layer.

‘There was a bit of an assumption that you didn’t need to worry too much about the RF,’ recalls Bryce. ‘Just stick up the cell, add the antenna and so on. But our studies show you lose circa 30% of impact and capacity, because you are basically broadcasting loads of RF energy where you don’t need it to go. And any RF energy going where you don’t want it, is going to be causing interference to the rest of the network.

CommScope’s new antennas are designed to provide a good coverage pattern using directional control and down-tilt capabilities, which enables the operator to focus RF energy where it needs it to be. ‘What you’d find is that when you shape the elevation radiation pattern of the small cell the upper side lobe suppression is good, which provides a lot of capacity in the sub-layer of the HetNet, but you are also broadcasting up into the macro layer, causing interference up there.’

The antennas are primarily targeted at high band frequencies, but Bryce reports that slightly surprisingly there has been quite a bit of interest in low band ones too.

To provide greater flexibility in the sub-layer, CommScope has ensured its antennas can be arranged in different configurations, such as quasi-omni dual band small cell antenna, which effectively sectorise the signal using phase adjustments in the antenna. ‘The good thing is that only one radio is needed not three, but if you need more capacity you just add more radios,’ says Bryce.

Alternatively, panel, bi-sectional antennas can be used to supply coverage up and down a road, for example. ‘You can have two antennas mounted on a wall like a doughnut. But the key thing is that I think operators realise they need to put more RF planning into these arrangements.’

Metro Cell Concealment Solution
CommScope’s second response to aiding metro cell deployment is its new two-piece design for mounting small cells on light poles – (see story here). ‘What we have come up with a well designed system enclosure supported by a services wrap. It is a good enclosure package to take to planning authorities and get a broad blessing for deploying the solution in the local authority region,’ says Bryce.

The CommScope Metro Cell Concealment solution offers a range of enclosures, which can be wrapped around lampposts with the radio half way up and antennas at the top. ‘There’s a lot of interest in this,’ reports Bryce. ‘Metro cell deployment is a big problem for operators, as it takes just as long to get planning permission as macro site, but there are far more metro cells. It’s the length of the process that makes it costly.’

Bryce says metro cell deployments are being handled both by MNOs and neutral host companies. ‘It is still early days for metro cells, especially in Europe, but in the next 12-24 months we expect something to happen in major European cities.’

He also notes that there is a demand from MNOs for lower frequencies for small cells for extending coverage to the suburbs and to rural areas. Demand is dictated by what frequencies they hold, but low frequencies do create an antenna size problem, because the laws of physics dictate that the lower the frequency the larger the antenna required.

In July 2014, CommScope acquired the Alifabs Cabinets & Ancillaries unit based in Yorkshire, UK, which is a specialist at deploying monopoles and specialist types, so it has been keen to exploit the company’s skills. ‘We have a very controlled partner programme, which enables us to offer a services wrap in key markets with highly trained people,’ says Bryce.

CPRI PIM tester
CommScope other main offering announced at Mobile World Congress in March was its Optical PIM (passive intermodulation) Tester – (see story here). ‘We have developed some core technology which allows us to interconnect with CPRI (Common Public Radio Interface) which defines the interface between the radio equipment in the baseband of the base station and the local or remote radio units.

Bryce explains that the base station used to be in a single box or cabinet, but this is often extended now by siting the RF portion at the top of tower, leaving the base band unit below. The CPRI interface is usually connected by fibre. CPRI was designed as an open interface and was developed by a number of major OEMs and chip companies

The trouble is it is not quite completely open. Bryce explains: ‘The synchronisation and radio modulation part are a common standard, but the operations and maintenance part is usually proprietary to the operator. It concerns how they connect the radio head and change channels and so on.

What CommScope’s new tester does is synchronise with the CPRI to connect to the radio head without having to deal with all the proprietary operations and maintenance part. A single technician can connect directly to the base band unit at the bottom of the tower and perform a truly active PIM test over CPRI.

The user interface is accessible from a smartphone, tablet or notebook computer. In short, there is no need to disconnect the coaxial cables from the antenna (potentially introducing new PIM in the test process!) and climb the tower to access the RF head. No climbers or cherry-pickers means PIM testing can be greatly speeded up and done by just one technician.

‘PIM is becoming a huge problem for operators,’ says Bryce. ‘If you mix two carriers or broadband downlink paths, or if there is any problem in the radio head part due to bad workmanship or whatever, then the bad bits will mix and create PIM. If these spurious emissions fall within the received path of the emissions it causes interference and you dramatically reduce the capacity of the cell site by up to 20-30%

‘Historically, operators got round it by being very careful in choosing the up and downlink path. But now with the very wide range of frequency bands that have to be accommodated, they can’t do that anymore, so PIM has become a very big problem and it is also harder to test,’ says Bryce

LTE Best Practice Book
CommScope’s final recent contribution to the industry is a new eBook called LTE Best Practices – a follow up to its Understanding the RF Path from a couple of years ago. The new eBook is a practical guide to LTE covering 10 best practices: noise mitigation; interference mitigation; co-siting; how to avoid PIM; FTTA implementation; implementing DAS; outdoor site construction; antenna selection; microwave backhaul; and small cells.

Summing up, Bryce says: ‘We still see huge opportunities for DAS. The floor for DAS will come down and the ceiling for small cells will rise and they’ll meet in the middle somewhere. But many users will want multiple carrier and multiple bands and that suits DAS.’

Regarding the buzz at Mobile World Congress, Bryce comments: ‘I didn’t see any major trends, although Cloud RAN and network virtualisation were probably the biggest themes. People are beginning to think Cloud RAN is actually deployable in some scenarios. There was a lot of talk around the Internet of Things and 5G, but they are still defining the use cases for that. But there is a lot of life in LTE still, which has been a much bigger success than 3G was in way, and LTE-A will bring more.’

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