The quest for higher-frequency communications

Researchers are developing measurement tools for tomorrow’s cell phone systems.

To help solve the wireless spectrum crowding conundrum and support the next generation of mobile technology - 5G cellular - researchers at the US National Institute of Standards and Technology (NIST) are developing measurement tools for channels that are new for mobile communications and that could offer more than 1000 times the bandwidth of today’s cell phone systems.

Mobile devices such as cell phones, consumer Wi-Fi devices and public safety radios mostly operate below 3 GHz. But some devices are starting to use fast silicon-germanium radio chips operating at millimetre wavelengths above 10 GHz. Researchers at NIST and elsewhere are eyeing channels up to 100 GHz and even beyond.

The metrology infrastructure for telecommunications at these frequencies is incomplete. NIST’s challenge is to develop tools and test methods that are far more precise than today’s versions to optimise device performance.

Wireless communications frequencies. Credit: Irvine/NIST

Because high-speed digital circuits can easily distort millimetre wave signals, even tiny errors can result in erroneous bits of information. In addition, millimetre waves don’t travel around corners as well as lower frequency waves, so channel models will be complex.

Possible solutions include development of complex antenna arrays that may provide novel capabilities such as beam steering - the capability to transmit in many different directions to point the beam directly at the receiving device, and even track mobile devices. This would strengthen signals and cause less interference to neighbouring devices.

“This work can advance the state of the art in telecommunications and help meet the expected increases in demand for wireless capacity,” NIST Project Coordinator Kate Remley said.

To support wireless communications at higher frequencies offering more channel capacity, NIST engineer Kate Remley led development of a new 94 gigahertz calibrated signal source for testing receivers and other devices. Credit: NIST

So far, Remley and her colleagues have developed a calibrated, modulated signal source to test millimetre wave instruments such as receivers and ‘channel sounders’ to support modelling of millimetre wave communications channels in indoor and outdoor environments.

Other NIST researchers have demonstrated a new probe for making the first calibrated measurements of electric fields above 100 GHz and a new facility for characterising antennas operating above 100 GHz.

The new calibrated signal source, demonstrated at 44 and 94 GHz, enables measurements of modulated signals to be traced to fundamental physical quantities. The source is based on commercial parts so that companies and other users can easily put together their own systems.

NIST researchers developed this directional 16-antenna array to support modelling of wireless communications channels at 83 gigahertz. Credit: NIST

The mobile channel sounder, demonstrated at 83 GHz so far, provides calibrated received signal strength and additional data for analysis of signal scattering and reflections, to help researchers develop network protocols that account for distortions.

As part of the same project, NIST researchers are also developing a millimetre wave instrument to measure the nonlinear characteristics of the transistors and amplifiers that will be used in millimetre wave receivers, transmitters and other devices.