There’s substantial demand for 5G connectivity, so much so that available spectrum is already in short supply. Spectrum is broadly split into three main ranges of frequencies - low band (1 GHz and below), mid band (1 to 7 GHz), and high band (24 GHz and above). That high band is also known as millimeter wave (mmWave), and is rapidly becoming one of the big battlegrounds for researchers and developers in the 5G universe. 3GPP Release 16 and beyond contain a wide variety of capability, performance, and efficiency provisos that make mmWave increasingly practical.
What and why mmWave?
Millimeter wave or mmWave is so called because the wavelengths in these high-frequency bands are measured peak to peak in millimeters, with wavelengths ranging from ten to one millimetres. Research into their use dates right back to 1894, when Indian physicist Jagadish Chandra Bose recorded transmission and reception of 60 GHz waves.
"High frequency mmWave has seen rising interest due to its capability to offer data speeds akin to terrestrial fibre."
Martin Keenan, Avnet Abacus.
High frequency mmWave has seen rising interest due to its capability to offer data speeds akin to terrestrial fibre, especially in focussed environments. Common examples might be in Fixed Wireless Access (FWA), offering broadband connections to a small community by using mmWave as the often prohibitively expensive ‘last mile’ connection, lowering costs for the whole community. Other key applications are for providing large numbers of high-speed mobile connections in a specific space, such as stadiums, concert halls, airports, venues, train stations, and dense urban areas.
Barriers to uptake
While the promise of ultra-wide bandwidth in the mmWave frequencies has drawn much attention, there are a range of barriers that have made practical applications challenging. Indeed, for many years mobilising mmWave was widely held to be ‘impossible’ by key researchers. A key starting challenge is the fact that mmWave frequencies have high atmospheric attenuation, they are absorbed by atmospheric humidity, and conditions such as rain can have a dramatic impact on range.
A further complication is that mmWave devices face significant additional power and thermal performance challenges over standard, traditional cellular systems. This is because they are operating at much wider bandwidths, for example 400/800 MHz. Fortunately 3GPP Release 16 and 17 introduce a multitude of power saving features such as reduced signaling overhead and faster link feedback that will help to mitigate this issue.
Solutions in the ether
The key to bringing mmWave to the market has been a huge body of research into sidestepping that attenuation problem, much of which has been on the antenna side. Mobile 5G phones using mmWave would theoretically be blocked by a human hand, so reference designs contain multiple antennas on different sides, operating on the assumption that the whole phone surface won’t be covered.
"At the base station end, the proliferation of antennas - 32 in Release 15, and rising through later releases - has led to the term Massive MIMO."
Martin Keenan, Avnet Abacus.
At the base station end, the proliferation of antennas - 32 in Release 15, and rising through later releases - has led to the term Massive MIMO or mmIMO. In addition, techniques such as beamforming - which uses multiple antenna elements to focus energy in one direction using a narrow beam - and scanning techniques have transformed possible throughput and connection densities. This is particularly significant as it enables a solid data connection without direct line of sight, using the reflective properties of mmWave signals to bounce off nearby objects, such as the interior walls of a shopping mall or sporting stadium.
Such indoor deployments are likely to become increasingly popular in the future - a recent economic study conducted by GSMA Intelligence found that an indoor office space deployment generated cost savings between 5% and 20% when a significant share of data traffic needs to be supported by indoor 5G services.
City-wide C-V2X with mmWave?
Inevitably, the fact that these initial challenges have been solved has spurred more innovation. One recent example being Movandi’s May 2021 demonstration of mmWave repeaters to create a vehicle-to-everything (C-V2X) communications network. According to the company, an mmWave repeater installed inside a car enabled greater than 10x performance gains with an average throughput of 1.5 gigabits per second (Gbps) on the Verizon 5G Ultra Wideband network.
This is particularly significant as the demonstration overcomes the assumption that fast-moving cars are poor candidates for mmWave due to the signal blocking properties of steel and glass. According to a recent Gartner report, the attach rate of 5G interfaces in embedded automotive telematics will increase from near-0 per cent in 2019 to 51 per cent by 2029, reaching just under 180 million connections in connected cars by 2029.
Another boost for mmWave comes courtesy of Qualcomm, which announced successful 5G data call trials in April 2021 that combine mmWave with FDD or TDD sub-6GHz spectrum by utilising 5G Standalone (SA) mode Dual Connectivity. This combination should allow newer 5G devices to use whichever radio frequency offers the best data rate at the time, optimising speeds and minimising contention at busy locations or areas of limited coverage.
Future potential is unlimited
It is clear that the future potential of mmWave is vast, and is already a cornerstone in 5G network provision. The next 5G standard release, Release 17, will expand the reach of mmWave to lower-tier devices such as IIoT sensors and small wearables, thanks to 5G NR-Light, as well as a focus on beam management for mmWave bands, multi-transmission-point operations and higher mobility.
Release 17 is currently scheduled for completion in 2022, with a freeze in March 2022, followed by a coding protocols freeze in June 2022.
