Cambridge Consultants claims first for “all-digital radio transmitter”
The concept is that digital circuitry – logic – generates a binary pattern with edge and pulse timing that directly forms the RF spectral output required; imposing modulated content is entirely carried out in the digital space. Similar ideas have been proposed for some time, and (somewhat) related activity has seen a great deal of effort go into area such as ultra-wideband signal generation or “impulse radio”, where very fast pulse edges in the time domain equate to signals at or below noise level that spread across a wide part of the spectrum.
CCL’s announcement describes digital circuitry directly feeding an antenna, but it seems reasonable to assume that for any significant RF power output an RF power amplifier would be required; but given the nature of the signal chain, not necessarily a linear amplifier.
CCL clarifies, “Unlike ‘software-defined radio’ (SDR), it’s not a mixture of analogue and digital components – for the first time, the radio is completely digital, which can enable new ways of using spectrum intelligently.” CCL is not new to RF innovation, having spun off the group that became Cambridge Silicon Radio (CSR) and that was first to develop a workable single-chip Bluetooth radio.
This development is codenamed Pizzicato (“plucking with the finger, the strings of a violin or other stringed instrument” – an allusion, presumably, to generating spectral content with a pulsed stimulus) and CCL sees it as a route to “unlock the potential of the IoT”. “It opens the door to a new dynamic way in which the predicted billions of IoT devices can operate together in a crowded radio spectrum. And it will enable the creation of 5G systems, with multiple radios and antennas.”
The Pizzicato digital radio transmitter consists of an integrated circuit outputting a single stream of bits, and an antenna – with no conventional radio parts or digital-to-analogue converter. Algorithms perform the necessary ultra-fast computations in real time, making it possible for standard digital technology to generate high-frequency radio signals directly.
“Our first trial of the technology has created 14 simultaneous cellular base station signals,” said Monty Barlow, director of wireless technology at Cambridge Consultants. “But it is the potential which is so exciting. Like mainstream microprocessing, a Pizzicato-based radio would directly benefit from Moore’s Law – shrinking in cost, size and power consumption with each new generation of silicon fabrication.
“If we’re going to get high-speed broadband to every mobile phone in the world, we’ll need lots of tiny, high-performance radios in those phones. The radios will be squashed together in a way that analogue just doesn’t tolerate. Whereas a Pizzicato-like digital radio can follow Moore’s Law to smaller size and lower power consumption.
“It could also be programmed to generate almost any combination of signals at any carrier frequencies, nimbly adapting its behaviour in a way that is impossible in conventional radios. It is early days for this technology but we believe radio design has reached a turning point.”
In recent decades, CCL adds, wireless design teams have employed digital techniques in radios – and such SDRs have provided a tenfold improvement in the data rate that can be squeezed into a radio channel. “But a more dramatic improvement is needed to cope with the growth in mobile broadband and the IoT.”
Greater efficiency requires the use of dynamic or ‘cognitive wireless’ techniques to sense the radio environment and switch parameters on the fly. This could give access to more of the estimated 90% of the allocated spectrum which is not in use at any one time.
Making use of the higher carrier frequencies of 10GHz and beyond, however, will require techniques such as meshing and beamforming to circumvent the inherently poor range – and the analogue parts of radios are becoming an increasing bottleneck.
“Crowding 50 analogue radios together on one chip, switching their operational parameters every few microseconds and expecting them to work at 60 GHz is an analogue designer’s nightmare,” said Barlow. “With Pizzicato, we have created a glimpse of future disruptive technology – a radio built purely from computing power.”
Cambridge Consultants; https://www.cambridgeconsultants.com
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