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Ultra-broadband Wireless Communications at True Terahertz

Case Studies

In the last several years, millimeter-wave (mmWave) technology has been a hot topic, in part because it is the focus of much 5G development. This unused, or underused, portion of the frequency spectrum is expected to help 5G deliver an enhanced user experience as it rolls out around the world.

Of course, researchers are already looking over the horizon at frequencies above 95 GHz, exploring and creating the communication technologies that come next.

In the US, the Defense Advanced Research Agency (DARPA) is researching electronic devices—transistors and power amplifiers—that can operate at frequencies above one terahertz. Similarly, the U.S. Federal Communications Commission (FCC) has issued a Notice of Proposed Rulemaking (NPRM) related to the frequency spectrum above 95 GHz.

At the University at Buffalo (New York), Dr. Josep Jornet works with his colleagues and students to explore the requirements of communication at terahertz frequencies. They identified two central challenges, and Keysight equipment is helping advance their research. One early result: the first ever successful wireless communication at 1 THz.

The Challenge: Developing Viable Terahertz Devices

For the University at Buffalo (UB) team, the focus of their research is determining the feasibility of ultra-broadband, ultra-fast wireless communications in the terahertz band, which covers 100 GHz to 10 THz. While others are investigating optical communications as the next step beyond mmWave, Jornet asks, “Why would anyone skip over 10 beautiful terahertz of bandwidth?”

The objective of the research is to establish the theoretical and experimental foundations of ultra-broadband communication networks in the terahertz band. This spans four key elements:

Materials and devices: generators, detectors, modulators, demodulators, and antennas

Channel: modeling the radio channel (e.g., path loss, noise) and analyzing its potential capacity

Communications: modulation, coding (i.e., security), synchronization, and ultra-massive multiple-input/multiple-output (UM-MIMO)

Networks: error and flow control; medium access control (MAC); relaying; and routing

In their terahertz work, UB researchers identified two significant challenges.

  1. The need to generate very high carrier frequencies and transmit them with sufficient power. Increasing the power efficiency of such devices is a crucial need for future commercialization.
  2. The necessity for devices capable of modulating those carrier signals on the transmitter side and companion devices capable of receiving and demodulating the transmitted signals. It is challenging to create high-power signal sources and high-sensitivity receivers that cover terahertz frequencies while operating at room temperature.

The Solution: Creating a Terahertz Testbed

In their research, Jornet and the UB team (Prof. Jonathan Bird, Prof. Erik Einarsson, Prof. Dimitris Pados, and Prof. Stella Batalama (the latter two are now in Florida Atlantic University)) began solving these problems by working at macroscale and nanoscale. Macroscale topics center on a variety of networking scenarios: wireless personal area networks (WPAN), wireless local area networks (WLAN), cellular systems, and satellite networks. The nanoscale work focuses on materials such as graphene, which forms into sub-wavelength antenna arrays and other new devices.

A measurement platform that enables them to benchmark and test their new devices was also a key requirement. Called the TeraNova testbed, the system’s block diagram illustrates what is recognizable as an over-the-air test configuration (Figure 1).

The Results: Achieving True Communication at 1.025 THz

Functionally, the system generates waveforms, encodes them, modulates the intermediate frequency (IF), upconverts, transmits and receives using tiny horn antennas, downconverts, and stores the signals. Using the Z-Series DSO, the researchers can then apply signal processing techniques and analyze the results.

To date, the system is the first ever to transmit and receive communications at 1.025 THz, applying zeros and ones to encode information onto the carrier. It is also the first to achieve ultra-broadband transmission — bandwidth in excess of 30 GHz — at 1 THz, error-free.

Going Forward

Given the recent progress in this field, Jornet expects to see “true” terahertz devices on the market between 2021 and 2023. If so, it seems terahertz connections will be part of “5G+” and future generations of wireless communication. In the meantime, there is lots of work to be done in four primary areas: devices, communications, government regulation, and industry standardization.

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