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24 May 2022

BT’s atomic RF receiver could transform the economics of universal 5G

Antenna innovation has, naturally, always been fundamental to delivering on the promises of successive mobile network generations. In 5G, it has become particularly diverse and interesting. Technologies such as active antennas and Massive MIMO, which have been evolving for many years, are moving into the mainstream and now operator and vendor labs are looking towards the next wave of enablers of improved coverage and capacity. One effort is taking place within BT’s labs, and focuses on using ‘excited atomic states’ to support hyper-sensitive receivers that could boost 5G coverage, the operator speculates, by 100 times.

Such R&D is vital to continuing to stretch the capabilities of 5G to meet evolving user and industry requirements. The 3GPP’s 5G standards can only go so far in improving network performance and enabling new services. The subsets of the specifications that get implemented by vendors and operators are an important factor, as is the deployment of software to optimize the network and make it behave intelligently. Edge compute, potentially close to the cell sites, as noted in the editorial above, is a relatively new addition to the operator’s toolbox for making the most of 5G, and stretching its performance to new limits.

The techniques to get more out of a network are proliferating as RANs are virtualized and densified, but the choice of antenna technology remains one of the critical factors in deciding a network’s economic viability and the quality of experience it enables.

BT’s trial focuses on a new quantum antenna technology using atomic RF receiver technology. This aims to support increased sensitivity to picking up weak signals. The receiver design uses a quantum effect called ‘electromagnetically induced transparency’, which is highly sensitive to electric fields. BT Labs – in Martlesham, in eastern England – believes has the potential to boost sensitivity by over 100 times.

The represents the first time a digitally encoded message has been received on a 3.6 GHz 5G carrier frequency. Previously, simple audio has been received on frequencies above 3.5 GHz, but this test is significant because it supports digital modulation, and therefore full data transfer, on one of the most important commercial spectrum bands that BT’s mobile arm, EE, uses for 5G.

The atomic RF receiver can be embedded in a passive optical receiver in hard-to-reach locations to increase coverage further.

This new type of receiver also has the potential to reduce network energy consumption, says the BT team, which would be valuable in some of the broad-coverage IoT applications that are emerging in the 5G era, enabling devices to be cheaper and to last far longer.

All this work provides a tantalizing vision of how coverage could be improved by many times without incurring unsustainable costs, while greatly enhancing quality of service at the cell edge. Those benefits could, in turn, have a significant impact on the cost-effectiveness of delivering high quality connectivity to rural areas, or enabling truly ubiquitous coverage, of the kind required by many vehicular or tracking applications in the Industrial IoT. Applications such as smart agriculture, smart logistics and smart cities could become more cost-effective and straightforward to manage, as well as more capable.

A BT spokesperson told TelecomTV: “A conventional dipole antenna is a macroscopic solid conductor and subject to thermal noise as the billions of atoms jostle each other at room temperature. In a diffuse gas, the atoms interact much less, so thermal noise can be reduced, and the signal-to-noise ratio is reduced even for weak signals, especially in a narrow frequency band.”

The next phase of the work is to adapt the technology to be affordable to manufacture and implement, and to be small enough to be integrated into mass market equipment. The project is part of broader studies, by the BT Labs team, into the optimal RF modulation and signal processing that will deliver the full potential of future radio networks in 5G-Advanced or 6G phases.

The specific receiver technology will be part of a later phase, in large-scale commercial terms, and that’s assuming it succeeds in the rounds of tests and trials that lie ahead, and that it gains a critical mass of OEM and operator support. According to BT’s senior manager for network physics, Fraser Burton: “A commercial product is at least 3-5 years out, so network deployment within the decade is possible.”

But innovations like this will be critical to ensure that 5G can progressively deliver performance and coverage that is significantly different from what 4G could have enabled, had it continued to evolve – and therefore justify the investment in the 5G roadmap.

BT has secured a number of patents related to the implementation of the atomic RF receiver.

The operator’s CTO, Howard Watson, said in a statement: “BT’s investment in cutting edge R&D plays a central role in ensuring the UK remains a network technology leader. Our programme has huge potential to boost the performance of our next generation EE network and deliver an even better service to our customers. Although it’s early days for the technology, we’re proud to be playing an instrumental role in developing cutting edge science”.