The increasing bandwidth requirement of new wireless applications has lead to standardization of the millimeter wave spectrum for high-speed wireless communication. The millimeter wave spectrum is part of 5G and covers frequencies between 30 and 300 GHz corresponding to wavelengths ranging from 10 to 1 mm. Although millimeter wave is often considered as a communication medium, it has also proved to be an excellent 'sensor', thanks to its narrow beams, operation across a wide bandwidth, and interaction with atmospheric constituents. In this paper, which is to the best of our knowledge the first review that completely covers millimeter wave sensing application pipelines, we provide a comprehensive overview and analysis of different basic application pipeline building blocks, including hardware, algorithms, analytical models, and model evaluation techniques. The review also provides a taxonomy that highlights different millimeter wave sensing application domains. By performing a thorough analysis, complying with the systematic literature review methodology and reviewing 165 papers, we not only extend previous investigations focused only on communication aspects of the millimeter wave technology and using millimeter wave technology for active imaging, but also highlight scientific and technological challenges and trends, and provide a future perspective for applications of millimeter wave as a sensing technology.

The cellular industry's shift from long-distance radio signals to short-distance millimeter waves is one of the 5G era's biggest changes, expected to continue with submillimeter waves over the next decade. To more precisely direct millimeter wave and future terahertz-frequency signals toward user devices, Arizona State University researchers have developed ViWi-BT, a vision-wireless framework that improves beam tracking using computer vision and deep learning. Smartphones historically operated much like other long-distance radios, scanning the airwaves for omnidirectional tower signals and tuning into whatever was strongest and/or closest. But in the 5G and 6G eras, networks of small cells will use beamforming antennas to more specifically target their signals in a given direction toward discovered client devices, which may be contemplating connections from multiple base stations at once. ViWi-BT's goal is to use AI and a device's cameras or lidar capabilities to identify physical impediments and advantages for the beam targeting process, enabling "vision-aided wireless communications."

As 5G networks continue to expand in cities and countries across the globe, key researchers have already started to lay the foundation for 6G deployments roughly a decade from now. This time, they say, the key selling point won't be faster phones or wireless home internet service, but rather a range of advanced industrial and scientific applications -- including wireless, real-time remote access to human brain-level AI computing. That's one of the more interesting takeaways from a new IEEE paper published by NYU Wireless's pioneering researcher Dr. Ted Rappaport and colleagues, focused on applications for 100 gigahertz (GHz) to 3 terahertz (THz) wireless spectrum. As prior cellular generations have continually expanded the use of radio spectrum from microwave frequencies up to millimeter wave frequencies, that "submillimeter wave" range is the last collection of seemingly safe, non-ionizing frequencies that can be used for communications before hitting optical, x-ray, gamma ray, and cosmic ray wavelengths. Dr. Rappaport's team says that while 5G networks should eventually be able to deliver 100Gbps speeds, signal densification technology doesn't yet exist to eclipse that rate -- even on today's millimeter wave bands, one of which offers access to bandwidth that's akin to a 500-lane highway. Consequently, opening up the terahertz frequencies will provide gigantic swaths of new bandwidth for wireless use, enabling unthinkable quantities and types of data to be transferred in only a second.

The future depends on connectivity. From artificial intelligence and self-driving cars to telemedicine and mixed reality to as yet undreamt technologies, all the things we hope will make our lives easier, safer, and healthier will require high-speed, always-on internet connections. The FCC regulates who can use which ranges, or bands, of frequencies to prevent users from interfering with each other's signals. Low-Band Frequencies Bands below 1 GHz traditionally used by broadcast radio and television as well as mobile networks; they easily cover large distances and travel through walls, but those are now so crowded that carriers are turning to the higher range of the spectrum. Mid-Band Spectrum The range of the wireless spectrum from 1 GHz to 6 GHz, used by Bluetooth, Wi-Fi, mobile networks, and many other applications.

The Internet of Things is expected to grow quickly to tens of billions of connected devices, from smart refrigerators to smart showers to smart cruise ships. And pretty soon, it's going to extend to smart cars, Intel demonstrated at its recent autonomous cars event in San Jose, Calif. But Intel knows that we'll have to get data in and out of those cars at rates that are much faster than today's LTE mobile networks can handle. And that's why Rob Topol, general manager of Intel's 5G business and technology, believes that 5G wireless networking will be like the "oxygen" for self-driving cars. Intel is making 5G modem chips to transfer data at gigabits a second over wireless networks in the future, perhaps as early as 2020. Topol believes this wireless networking will enable self-driving cars to communicate with connected infrastructure. That infrastructure will help the cars process sensor, safety, and information for the car and return the results quickly to the cars.

Smartphone-based virtual reality headsets are great and all, but for the best games and experiences you need a dedicated facehugger tethered to a powerful PC like it's a diver's lifeline. Wireless hardware is one of the inevitable next steps for VR, and a company called TPCAST is already developing a cord-cutting peripheral for the Vive, supported by HTC's VR accelerator program. MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) is making headway in this area too, today releasing research into a wireless system that's both headset-agnostic and could address some unforeseen problems with peripherals like TPCAST's. MIT CSAIL's prototype system, known as MoViR, uses millimeter waves to send data from a transmitter that's hooked up to a computer to the headset's receiver. These high-frequency radio waves are capable of maintaining wireless connections at speeds over 6 Gbps -- enough bandwidth to stream the two, high-definition feeds required for VR -- but the signal doesn't penetrate objects well.