Wireless caught up with CommScope at Small Cells World Summit 2016 (9-12 May), where it was showcasing cell virtualisation technology on its OneCell system, the small cell solution it gained after acquiring Airvana in October last year.
Josh Adelson, director of Product Marketing, Small Cell at CommScope, explained that the old Airvana team now operates as a small cell unit within CommScope with the remit to develop the products.
‘It has helped us a lot to have access to CommScope’s resources and contacts with operators, as it’s a pretty resource heavy task to get a small cell certified by an operator,’ said Adelson.
The OneCell is a C-RAN split small cell solution where distributed access points are linked to a single baseband controller handling the LTE signalling: this just looks like a single physical cell as far as the operator’s network is concerned. The advantage of this approach is that there are no handover issues between cells and no cell border interference.
The downside is; how do you get more capacity out of only a single cell? The answer is you create multiple virtual cells dynamically within that single cell, which allows you to generate more capacity without introducing border interference issues.
Adelson described a scenario where four laptops are located within a 10MHz cell, each getting 60-70Mbps of throughput at the same time where the theoretical maximum for a 10MHz channel is 75Mbps. Using cell virtualisation, Adelson reports that CommScope is getting four times that in its lab.
The way LTE works is that it allocates the available spectrum to users through Physical Resource Blocks (PRBs), which is a way to split up the signal to service users at same time. A 10MHz channel has 50 PRBs.
Smart Reuse solution
What CommScope’s new product feature, called: Smart Reuse (cell virtualisation) does is extract 200 PRBs out of that 10 MHz channel instead of just 50. So, how does it work?
‘The first thing to understand is that we know where each user is within the cell in terms of RF space (not so much physical space), because we can tell the strength of the signal from their devices: it is strong if close, and weaker if they are further from the AP. By knowing these locations the system can define virtual sectors, which are non-overlapping areas that can serve each user in a particular time slot,’ explained Adelson.
What the Smart Reuse system does is that within PRB 1 it will send resources only to the radio points where the users are – say three devices A, B and C. So, it delivers three times the reuse on PRB 1, whereas before, only one user could use PRB 1 at any one time. All of this happens within a millisecond.
In the same millisecond, the network can define three completely different users D, E and F for PRB 2, again delivering three times the reuse on PRB 2. Incidentally, the formation of sectors is defined by who is calling for data at any given time and where they are in any given millisecond.
Smart Reuse also does more. ‘We can send resources to a user from one or more radio points so they get a better service. If the user is standing beneath one radio point they get a good service from that one alone. If someone is located between three radio points, none of which is providing a good signal, then we can combine the three radios to maintain quality of service levels,’ said Adelson.
A point to note: a user can be within more than one virtual sector so long as the sectors are not overlapping within a given PRB. If the users are in the same PRB within the same sector then they will experience interference.
‘If you do the same for all 50 PRBs within that 10MHz channel you get 300Mbps in a single OneCell. And then it all starts over again in the next millisecond,’ said Adelson, who adds that in real life deployments the radio points are often quite far apart and there are often things in between to block signals, so the opportunity for using this radio solution is pretty good.
A different architecture
He added that it is important to understand how this CommScope solution differs from normal small cell architecture. ‘Each cell operates in the same channel, so they are reusing the spectrum but each is acting independently. So, inevitably two cells will use same PRB sometimes and that is what creates interference. But by managing the PRBs intelligently and dynamically we can organise it so that we don’t pay the interference price.
‘And you don’t have to worry about exact spacing in terms of RF design so much, where if the radios get too close they create interference or are too far apart so you get a coverage hole. You want them to overlap.’
Adelson said the company is not aware of anybody else doing this yet, but he noted that it seems to echo what a lot of operators are talking about with 5G in terms of getting rid of the cell as the foundation of the architecture. ‘It seems to fit with what they are saying, not that we set out to do that, we are just trying to solve capacity issues economically.’
Another way to think about the process is self-virtualisation, according to Adelson. ‘Think about NFV; that’s about virtualising a hardware function and using it when you need it – pooling resources.’
CommScope has tested Smart Reuse with an MNO in the US, which it cannot name yet, but Adelson revealed that when they tried to measure the performance improvement for users it delivered a 220%-285% improvement in throughput speeds.
‘We are trialling with larger operators and it is ready to go, but the certification process that the operator has to go through and then integrate it with back end systems takes time. But in general, we think this product simplifies things.
‘It makes RF planning easier and that makes operators more comfortable when it comes to concerns over small cells impacting their macro network. There is a lot in this solution that makes that easier, so that should encourage them,’ said Adelson.