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Spectral efficiency

A convergence of different technologies means the wireless communications industry is continually pushed to do more with less.

Consumers, industry and government are all contributing to an explosion in sensing, communications and big data processes and applications.

This insatiable need for more data, faster speeds and lower latency is pushing semiconductor companies to develop new technologies that can keep pace with demand. Danish Aziz is a Staff Field Applications Engineer at Analog Devices (ADI) and helps design connectivity architectures that can meet shifting requirements.

Aziz explains, “In mobile communications, spectrum is a precious resource and you don’t have unlimited capabilities. If you want to increase capacity, then you have to either increase power consumption or the channel bandwidth.”

One technology that is gaining a lot of momentum is massive multiple-input, multiple-output (MIMO). In massive MIMO systems, more typical eight transmitter, eight receiver systems can be scaled to a much larger number of antennas, such as within 64T64R systems.
Aziz says, “Massive MIMO technology was developed to improve capacity despite bandwidth limitations. One of the key driving needs is to make more bandwidth efficient or spectrally-efficient systems by using multiple antennas.”

In simple terms, using spectrum more efficiently means more data can be sent over the available spectrum. Those 64T64R systems, for example, have been shown to deliver up to five times more capacity.

Tackling interference
Increasing the number of antennas, however, doesn’t only mean the system can handle more cellular traffic – more antennas also means more potential interference. As such, massive MIMO systems often make use of beamforming techniques to increase the effectiveness of the transmission.

Beamforming is emerging as a key element of 5G network development. Instead of blasting signals out in every direction, beamforming can direct and adjust radio waves to make them more powerful and targeted. This can transmit data directly to a user and even extend the range of RF transmissions.

Radar applications have used beamforming since the 1960s, but its use in communications has demanded some adaptions. Aziz explains that a radar system could use a “totally analogue beamforming system” because there were no size constraints. “It could take up a whole building if necessary. With communications equipment, that’s not feasible.”

As such, Aziz says, analogue is not an option and most 5G networks that use beamforming will likely use hybrid beamforming techniques. Aziz adds, “The most efficient and beneficial would be to have a system with completely digital beamforming but, at the moment, we are limited because of the hardware that is available.”

Designing the right products
Towards the end of last year, ADI added a wideband transceiver to its RadioVerse portfolio. Aziz explained that the ADRV9026 is designed to support base station applications, massive MIMO and small cell systems. What is unique about that transceiver, Aziz says, is that “in the past, we kept the number of channels the same but increased the bandwidth. Here, we have kept the bandwidth the same, but we have increased the number of channels from three to four.”

He adds, “At the same time, we changed the process technology. Usually, increasing the number of channels in a given system means the power consumption also increases. We based this product on 28-nanometer CMOS technology as changing the process technology means we can also reduce or maintain the power consumption.”

The ADRV9026 is also designed to be synchronisable. This is essential, Aziz says, as “when we talk about multi-antenna or multi-channel systems, one of the most important things is the synchronisation durability. We can synchronise multiple backends through a digital interface, which is sometimes called multi-chip synchronisation.”

5G networks will also make use of mmWave, the band of spectrum between 30 and 300 GHz. There was a need for a single platform that could cover the entire 5G mmWave band. Analog Devices developed the ADMV1013 up-converter and ADMV1014 down-converter to meet this need. These integrate I/Q mixers with an on-chip programmable quadrature phase shifter, configurable for direct conversion to or from baseband from DC to 6 GHz or an IF between 800 MHz and 6 GHz. The up-converter contains a transmit power amplifier driver, while the down-converter includes a receive LNA.

Above: Different frequencies are typically used for different applications

These are designed to support all broadband services and ultra-wide bandwidth transceiver applications. Aziz explains, “Whatever application is being examined in the mmWave space, we have integrated and individual components targeted to that application.”

The path from 4G to 5G
The rollout of 5G networks is creating new opportunities for small cells. Network operators are densifying their networks by using small cells to reuse spectrum more frequently. This means small cells are increasingly being deployed to provide capacity improvements, and that trend looks set to continue with small cells acting as building blocks in the transition from 4G to 5G.

As Aziz explains, “Our integrated transceivers have special features that help vendors set up a small cell very easily and cheaply. One of those is digital pre distortion (DPD), which is required when a base station is operating at high power.”

DPD shapes the data before it gets to the power amplifier (PA) to counteract the distortions the PA will produce. DPD technology has historically been used in FPGAs and ASICs, but Analog Devices has incorporated it into the transceiver. This lowers power consumption, as well as enabling the use of other technologies that enhance wireless network coverage and capacity.

The range of integrated designs offered by Analog Devices aims to simplify system design, shorten time to market, and provide performance for the range of short-range wireless systems, from LTE up to emerging 5G networks.

As 5G networks mature, and data generation and processing increases, there will continue to be pressure to use spectrum more efficiently. Through making use of these technologies, operators can reuse spectrum and improve capacity to keep pace with demand.

Author
Charlotte Hathway

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