A small British company in Cambridge has been making mobile-phone base stations for ten years. Yet even people steeped in the industry have never heard of cellXica.
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.
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.
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 is hardware, but the design of the hardware can be reprogrammed. 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 to have a chip which was more like a system-on-a-chip with a high-speed digital design. cellXica wrote all of the LTE base station physical layer and the protocol stack in-house.
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.
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.
The most recent design from cellXica is the M5Q, a 5G cell which was developed as part of the Future Networks Programmes that also sponsor the ONE Word project. The M5Q and M3Q will both be used by ONE WORD giving options for 2G, 4G and 5G. The M5Q is designed around the 3.8-4.2 GHz radio frequencies that are easily available from Ofcom although through the ONE Word programme there is an ambition to develop an 1800 MHz, Band 3, version.
Spectrum liberalisation is a driver for a number of British innovations. It means more demand for units such as the M5Q, 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.
As cellXica devices are technology-driven and contain GiLTE, they are ideal for the community radio projects typified by the ONE Word project. 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.
