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Innovation Briefing Issue 6 | Sponsored content: Who are cellXica?

  • 6 minute read
  • Published by Crispin Moller on 20 Sep 2021
  • Last modified 16 Sep 2021
There is a small British company in Cambridge that has been making mobile-phone base stations for ten years. Yet even people steeped in the industry have never heard of cellXica.

The combination of wavemobile and its sister company cellXica follow a kind of Russian-doll approach to mobile technology. Buried deep inside the base station is what cellXica most wants to improve; the hardest bit of mobile technology, known as the physical layer or layer 1. This is where the real radio engineering happens; where analogue meets digital and where the cleverest of clever people turn specifications and formulae into hardware. Wrapped around this is the software and hardware that make a mobile-phone base station. And wrapped around that are the services provided by wavemobile, which takes the cellXica equipment and builds it into an entire mobile network with 5G-capable cores from  Quortus and Attocore, spectrum licences and interconnection.

Chief Technology Officer at cellXica, Niro Mahasinghe, explains the relationship between cellXica and wavemobile:

“cellXica is a technology-driven company that does all the low-level modem design, and wavemobile develops real-world applications. We don’t typically sell things off the shelf. Hardware reference design licensing means we do one design, and license it to several manufacturers.”

There is something very Cambridge about cellXica. Products are 100% designed and engineered in the UK – the hardware, the stack, the physical layer, it’s all British. It’s a small company of just 22 people; and it doesn’t seek world domination or a stock-market listing. The company doesn’t even have a sales person. Instead, it concentrates on designs, which it licenses to other companies to manufacture in volume. There is a common theme among Cambridge companies: they are most interested in fundamental, deep-technology challenges. This is what makes the science parks around the city so inspiring to visit.

Soft Hardware

The company started in 2011 by developing 4G software-defined radio, or SDR. It was enabled by the development of the Zynq chip by Xilinx Inc. This chip is a FPGA with hardened ARM cores, a class of device that bridges the gap between hardware and software. It’s hardware, but the design of the hardware can be reprogrammed. Mahasinghe says: “That’s the exciting thing; at that time RF technology was locked into the chip design process, so Zynq came in at the right time. Based on ARM cores, it made it quite possible for us to have a chip which was more like a system-on-a-chip, you can have high-speed digital design on it. So we wrote all of the LTE base station physical layer and the protocol stack ourselves.”

The work was prescient. SDR is a technology that has spent decades being the next big thing - by the time cellXica was formed, many had written it off as a pipe-dream. Today it’s become the universal technology used for 5G.

As a niche product supplier, cellXica has some very special customers, with military or search and rescue comms being typical applications. This leads to interesting differences between cellXica and mobile network equipment vendors. When reliability is very much a matter of life and death, it concentrates the mind on the design priorities. When deployment means having a base station that can be flown, or carried by someone parachuting into harm’s way and which needs to run reliably on batteries, a lot of thought must go into efficiency. And when command and control is within a fairly small area, it has to be a private network with no need for backhaul.

To meet the demands of these customers, cellXica has taken its physical layer, protocol stack and equally impressive SDR and wrapped them up into a range of base stations with different features and form factors. Out of this has come a couple of units that have mainstream appeal for industry and private networks. The eXsite-M3Q is a small cell capable of supporting up to 32 users including limited LTE-M, while the eXsite-SC6 is its bigger brother, which uses the Marvell OCTEON Fusion-M SoC as the modem and can link 512 devices. Both are currently 4G; 5G is in the works.

The technology cellXica builds deviates a little from convention, which cellXica is not afraid to do in order to provide a practical solution to an otherwise unsolvable problem. For instance, the company has patented its GiLTE, pronounced “guilty”, technology, which stands for GSM-in-LTE. That’s GSM as in 2G and LTE as in 4G, which means that this radio can do both at the same time, with the GSM part embedded within the LTE carrier. That’s especially exciting in the UK when a company wants to use the shared access licence part of band 3. This is available to any organisation that wants to use it on a first-come first-served basis by stipulating a postcode within which it will be used and applying to Ofcom.

Flying the Flag

Spectrum liberalisation is a driver for a number of British innovations. It means more demand for units such as the SC6, and that in turn means increased volumes and so reduced prices. In particular, having honed the design using Zynq, cellXica can commit to the volumes necessary to produce a system-on-a-chip design.

While the start-up costs of making an SoC are very high, the individual component prices are low. Better still, they use less power.

Mahasinghe enthuses about the SC6. “It is our commercial-grade base station, for high capacity. Things like stadiums, for example, It’s perfect for that - where you don’t need lots of power, but there’s a lot of users in a very small area and for that, you can have four 90-degree sectors covering 128 uses in each sector.”

The spectrum it uses is flexible, up to 4GHz, which takes in half of the easily licensable N77 3.8GHz to 4.2GHz band. Bandwidth is up to 80MHz, which allows for very fast internet access.

As cellXica devices are technology-driven and contain GiLTE, they are ideal for the community radio projects typified by the 5G Testbeds and Trials, Rural Connected Communities projects. In many rural locations, there will be a long-term need to support 2G as well as 4G, so the GiLTE technology is a very flexible solution that solves a the “voice” problem.

The company is looking to grow its international business, again through wavemobile and similar partners, and in particular by supporting community radio projects that use the citizens’ broadband radio service. The company is working with partners to build OpenRAN systems by supplying hardware to vendors that integrate their own software.

Mahasinghe doesn’t take his work home with him - It’s already there. He has a cellXica base station at his house with full network connectivity. wavemobile

has the interconnect and spectrum licences, cellXica provides the hardware. Having a network for just one home would be a bit like having a private railway or power station - it’s significant infrastructure - but it’s a solution to the poor coverage he has in his back garden, which occurs despite the flat terrain around the city of Ely in the fen region of Cambridgeshire.