Despite four days of conference presentations at Small Cell World Summit 2016 (London, 9-12 May), there was precious little discussion about backhaul. Steve Greaves, CEO of small cell backhaul specialist CCS (pictured), understandably wondered whether the industry thought the issue had been solved. ‘It hasn’t,’ was his emphatic comment on that.
CCS was showcasing its combined small cell with integrated backhaul prototype, first seen at this year’s MWC. ‘Everybody still wants to know about site acquisition and backhaul – they are still the big issues that need solving – at least in some regions,’ said Greaves.
‘The concept of small is good still holds and we are promoting the combined unit (pictured) and moving forward with serious trials with some small cell vendors in Cambridge, UK and another one in the US.’
The 8kg combined unit weighs around 8kg – the maximum load allowed on lampposts in the UK (some small cells alone without the backhaul can weight 18-20kg). ‘It makes for one attachment, it’s aesthetically pleasing and it’s a low load,’ explained Greaves.
‘The problem with a lot of small cells vendors is they want to mimic macro with products that are between 20-90W power. They are really mini-macros, and yes, they cover wider areas and support more customers, but physically they still have to be installed somewhere. If they are high power units, you need a big box to cool it,’ Greaves pointed out.
Potential of shared spectrum models
Greaves said he was very interested in the spectrum sharing model being developed for the 3.5GHz band in the US. ‘That model gives you the ability to deploy networks quickly without barriers and change plans in a very quick timescale and that’s quite radical.’
He added that Cambridge University wants to build its own network as there are a lot of not-spots that the MNOs can’t or won’t do anything about. ‘But it doesn’t want the hassle of running its own network. However, you could take that local traffic out to a third-party hosted EPC that could be based in China, for example
‘You could buy a core service and deploy small cells, but where do you get your spectrum? Shared spectrum models could be the answer. But all solutions still need backhaul so that is great for us,’ said Greaves with a smile. ‘Villages could run their own networks: that is the vision anyway. The question is: can it scale technically?’
Returning to the theme of site planning as a major hindrance to urban small cell deployments, CCS has published a short report called: ‘Making the urban small cell happen’, which looks at some of the issues.
Small cell deployment report
The report argues that there are limited sites available for small cell deployments and they are often not ideal from a radio planning perspective as they can be affected by line of sight (LOS) issues and unpredictable multipath interference. In addition, getting agreement between councils, contractors, small cell vendors, mobile operators and their managed service providers can be a major headache.
CCS’s view is that people better get used to planning around making ‘second-best sites’ viable. CCTV poles, for example, have less planning restrictions attached to them compared with lampposts, but they are generally 6m high, as opposed to 8m, so LOS becomes more challenging.
The company argues its multipoint to multipoint (MPTMP) Metnet solution gives it an advantage here. Each node (operating in 26GHz and 28GHz) delivers a 270-degree field of view, generating a high number of viable connections.
The system’s self-organisation sequence identifies all the possible links and selects the strongest ones – cycling through this process continuously to adapt to changing RF conditions. The support for multiple connections means Metnet can operate on some non-line of sight links – up to 350m in a recent Cape Town trial.
‘That’s our key differentiator,’ said Greaves. ‘We are able to monitor interference at a local level and turn it into a schedule.’ The ability of Metnet nodes to self-configure and optimise eliminates the need for radio planning and manual antenna alignments, meaning nodes can be deployed temporarily if a site is not immediately available and easily re-deployed later.
Small cell timing issues
Tight timing synchronisation is also vital to ensure a seamless handover between small cell and macro layer to minimise interference and deliver maximum capacity. But if accurate frequency and phase timing (1588v2 and SynchE) are not available, the GPS is required to provide local synchronisation.
CCS has conducted some small cell deployments in Fujian, China where narrow streets and tall buildings limit the view of the sky, affecting GPS quality. Metnet backhaul nodes have an integrated GPS antenna, which is able to provide a source of local master synchronisation to the small cell. Just one Metnet node needed to see the sky and it could then pass timings on to the rest of the small cell network.
Returning to the Cambridge trial of the integrated small cell with backhaul unit, Greaves said the operator wants it to run as a neutral host solution to see whether it does work, and if its current form factor needs altering.
‘We want to sort out the small cell side, package it and find the right flavour of technology to enable neutral host solutions. That is our hope for this combined unit this year. It is not commercially available; it is kite flying really for proof of concept,’ said Greaves, who also revealed that CCS has a Gigabit backhaul product coming out later this year.