Engineers at the National Institute of Standards and Technology (NIST), US, have developed a new method to evaluate and select optimal antenna designs for 5G cellphones, wireless devices and base stations. They believe this could boost 5G wireless network capacity and also reduce costs.
5G systems will avoid crowded conventional wireless channels by using higher, millimeter-wave frequency bands. Transmissions at these frequencies lose a lot of energy along the way, which weakens received signal strength. One solution is “smart” antennas that can form unusually narrow beams—the area in space where signals are transmitted or received—and rapidly steer them in different directions. Antenna beam-width affects wireless system design and performance. NIST’s new measurement-based method allows system designers and engineers to evaluate the most appropriate antenna beam-widths for real environments.
According to NIST engineer Kate Remley, the new method could reduce costs by enabling greater success with initial network design, eliminating much of the trial and error that is now required. It would also foster the use of new base stations that transmit to several users either simultaneously or in rapid succession without one antenna beam interfering with another. This, in turn, would increase network capacity and reduce costs with higher reliability.
This is the first detailed measurement-based study of how antenna beam-width and orientation interact with the environment to affect millimeter-wave signal transmission. In the technique, NIST measurements covering a broad range of antenna beam angles are converted into an omnidirectional antenna pattern covering all angles equally. The omnidirectional pattern can then be segmented into narrower and narrower beam-widths. Users can evaluate and model how antenna beam characteristics are expected to perform in specific types of wireless channels.
An engineer could use the method to select an antenna that best suits a specific application. For example, the engineer may choose a beam-width that is narrow enough to avoid reflections off certain surfaces or that allows multiple antennas to coexist in a given environment without interference.
To develop the new method, the NIST team collected experimental data in a hallway and lobby of a NIST research building, using a special robot loaded with a customized channel sounder and other equipment. A channel sounder collects data that capture the signal reflections, diffractions and scattering that occur between a transmitter and receiver. Many such measurements can be used to create a statistical representation of the radio channel, to support reliable system design and standardization.
The study results confirm that narrow beams can significantly reduce signal interference and delays, and that an optimized beam orientation reduces energy loss during transmissions. For example, the time interval during which signal reflections arrive (a metric called RMS delay spread) dropped dramatically from 15 nanoseconds (ns) to about 1.4 ns as antenna beamwidth was reduced from omnidirectional (360 degrees) to a narrow 3 degrees or so-called pencil beam.
Future research will include extending the method to different environments and analysis of other wireless channel characteristics.
