AT&T Laboratories is asking the FCC for permission to conduct tests in the 3.5 GHz band in Plano, Texas, using multiple new radio systems with integrated adaptive antennas. The purpose is to evaluate the performance of a novel short distance microwave radio digital communications network from several suppliers.
Similar to previous experiments, the radios will be installed and tested by AT&T Labs personnel using microwave radio and digital communications test equipment. Each radio unit weighs 33 pounds and is housed in a weatherproof outdoor enclosure. Each radio unit consists of a transmitter, a receiver and an integrated adaptive beamforming antenna. AT&T says the maximum transmit power of the radio unit will not exceed 47 dBm/10 MHz EIRP.
The tests sound similar to 3.5 GHz non-line-of-sight (NLOS) experiments the company was granted approval to do in Cumming, Georgia, just outside Atlanta, but those tests involve radio units that weighed about 12 pounds.
AT&T says testing in Plano will occur between base radio units deployed on masts on the roof top of the AT&T facility at 3400 W. Plano Parkway and prototype fixed user equipment located within a five kilometer radius of the facility. The ground elevation around the location is 218 meters above mean sea level, and no more than three radio transmitters will be operated simultaneously. Radios will be mounted on rigid masts on the building rooftop and will not exceed a height of 65 feet above ground level.
Depending on how it’s configured, each radio will use a digitally modulated 10 MHz, 20 MHz or 40 MHz channel in the 3550-3650 MHz band.
Interestingly, AT&T as a whole has not always been so gung-ho about the 3.5 GHz, or Citizens Broadband Radio Services (CBRS) band in the United States as it’s configured for sharing. Along with other carriers, AT&T was concerned about license terms providing sufficient time and assurance for operators to realize a return on investment. However, since the final CBRS rules were put into place and progress made in the 3.5 GHz ecosystem, AT&T, as well as Verizon, Sprint and T-Mobile, have joined the CBRS Alliance, which is focused on evangelizing the 3.5 GHz space.
AT&T is also interested in conducting more experiments in other bands, including the 3.7-4.2 GHz band, where the propagation characteristics are similar to those of the 3.5 GHz band and the 3.55-4.2 GHz range. The 3.5 GHz range is being considered in other regions of the world for 5G, increasing its chances for proving spectrum for international harmony.