Why 60GHz mmWave is moving into the mainstream
If you think of the different radio frequencies that our modern technologies use, you may struggle to think of any widespread users of the 60GHz frequency. Why haven’t we seen more widespread use of 60GHz until recently? The emergence of new applications such as those demonstrated by Ainstein at the annual Consumer Electronics Show (CES) in Las Vegas promise to soon bring 60GHz into the mainstream.
Brief history and overview of 60GHz
The 60GHz frequency is an Extremely High Frequency (EHF) which falls in the V Band, as designated by the IEEE (which includes frequencies ranging from 40GHz to 75GHz). The 60GHz frequency is also considered a millimeter-wave (mmWave) frequency. As a mmWave frequency, 60GHz offers benefits that haven’t been easily accessible to civilian use until recently.
Few developers and engineers are familiar with 60GHz applications, as it has historically seen its greatest use in military and scientific research applications. However, the 60GHz frequency is unlicensed and open for all to use and develop applications for (provided those applications meet the same Federal Communications Commission rules of non-interference that all other radio frequency applications must).
Benefits and challenges of working with the 60GHz frequency
A few challenges remain from an engineering perspective that accompany the utilization of 60GHz frequency for radar systems.
One challenge exists at the edge of the field of view (FOV) wherein tracking a target can become difficult because the reflected signal strength is weaker than it is closer to the center of the FOV. This is a well-known challenge, however, and one that can be mitigated through the use of multiple radar system sensors.
Another challenge relates to the algorithm used by radar systems for deciding which objects are targets and which are clutter. Given a stationary target in a clutter rich environment (e.g., several people sitting for an extended period at a table), traditional Doppler domain processing may occasionally incorrectly classify a stationary target as clutter.
However, the potential benefits of radar systems designed for the 60GHz frequency may well outweigh these challenges.
The 60GHz frequency offers potential benefits to those who develop applications for it. Chief among these isn’t inherent to the frequency itself, but a fact of the success – and crowding – of applications utilizing other radio frequencies: 60GHz is a relatively uncongested frequency, compared to the lower 2.4GHz and 5GHz frequencies typically used for Wi-Fi networks, which increasingly suffer performance issues owing to high congestion on these frequencies. 60GHz is largely free of these congestion concerns, and as a result promises better signal integrity.
A related benefit is that the unlicensed 60GHz frequency offers up to 9GHz of spectrum – many times greater bandwidth than what is available in the lower unlicensed frequencies. This also supports the case for greater signal integrity in the 60GHz frequency. In an editorial note to ACM’s SIGCOMM Computer Communication Review, L. Lily Yang of Intel Corporation said “…the abundance of the bandwidth in the unlicensed 60GHz band is unmatched in any of the lower frequency bands.”
Much of the excitement around 60GHz in the past decade has centered around wireless communications. However, for domains such as radar systems, the large bandwidth available in the 60GHz frequency can provide a much more precise and accurate radar reading, lending itself to use cases for radar that previously haven’t been widely deployed – people counting, building automation, perimeter security, and workplace safety, to name a few.
Another benefit of the 60GHz frequency derives from its short wavelength. The short wavelength of the 60GHz frequency is less capable of moving through walls and buildings (as 2.4GHz Wi-Fi signals do, for example). Historically this has been seen as a drawback, since the frequency has been viewed mostly through the lens of communications systems where we seek radio signals that travel through walls and building (cellular networks and Wi-Fi networks, for example). Thus, in many cases, allowing a signal to pass through walls is desirable. But, with the proliferation of radio signals flying through our airwaves today, there is a growing need on the part of many users for signals which remain contained to a defined space.
There are several factors that affect whether a signal can penetrate a solid object, such as a building's wall. Many of these relate to the wavelength of the signal. Whether or not a physical barrier such as a building's wall can be penetrated by a wireless signal depends in large part on the material the wall is made of. As long as the wall isn't made of a highly conductive metal, or an extremely dense material (brick, concrete, etc.), there typically aren't any issues with a Wi-Fi signal traveling from one room to another in a home.
The most common RF and microwave signals -- AM/FM radio signals, television signals, cellular signals, and Wi-Fi signals, for example -- feature a relatively long wavelength on the order of a few meters down to 12mm for Wi-Fi signals. For signals with this order of wavelength, a typical building wall is effectively "transparent", allowing them to pass through as easily as light passes through glass. In the case of higher frequency signals, though, walls begin to act less like light through a glass window and more like a closed door.
Signal penetration depth is described by the Beer-Lambert law, which says:
The Beer-Lambert law is related to the signal attenuation constant as such:
Where deltap is the penetration depth of signal into a surface. Alpha is found by calculating the attenuation constant, which is affected by the signal wavelength (lambda). Thus, as a signal’s wavelength decreases (i.e. higher frequency signal), its attenuation constant becomes larger, and its penetration depth decreases.
A 2014 study commission by the UK Office of Communications (the UK’s equivalent of the US FCC) looked at signal loss in buildings for different building materials and different frequencies. Figure 2 summarizes some of the study's findings, which are consistent with what theory predicts: energy loss (as measured in dB) of a signal increases rapidly and directly in proportion to a signal’s frequency.
Figure 1. Signal loss in buildings for different building materials and different frequencies. (Source: UK Office of Communications/2014 Aegis Systems technical study)
Radar systems utilizing the 60GHz frequency enable sensors to accurately sense range, velocity and angle of objects in a scene, all while providing the high resolution needed for industrial environments.
One frequent challenge for moving vehicles -- construction machinery, mining equipment, and other specialty vehicles -- as well as for unmanned aerial vehicles (UAVs), and industrial settings is how to track targets in these difficult environments. A target may be something as simple as a boulder blocking the path in a large open-pit mine, or it could be a human being which must be avoided by heavy industrial machinery in a manufacturing setting.
A device that operates at a lower frequency requires a larger antenna to properly send and receive signals than a similar device operating at a higher frequency. Because of this principle, radar systems utilizing the 60GHz frequency can be miniaturized and made smaller than similar devices utilizing the lower 2.4GHz frequency. Doing so opens up new potential uses of radar systems and radar sensors that would otherwise be infeasible due to physical constraints of large radar systems.