Airplay: Sector antennas, improved spectrum analysis elevate data rates significantly. Sector antennas that concentrate signal coverage have helped to elevate data rates for the UNH TV White Space trial.
Rouzbeh Yassini, the Executive Director of UNH BCoE, said the results “demonstrate real potential for TVWS networks to make broadband connectivity available in rural and unserved areas of the country.”
UNH BCoE is working with Carlson Wireless Technologies of Arcata, Calif., in Phase 2 of a TVWS trial that originated late in 2013. In the initial testing, downstream data rates languished in the sub-2 Mbps range, with occasional to frequent signal interruptions and difficulties establishing connectivity at some locations.
But changes involving antennas, network configuration, modulation and other approaches have triggered significant improvements.
For example, the new network implementation achieved a downstream rate of 5.66 Mbps and an upstream rate of 1.67 Mbps over the link connecting the directional antenna mounted on the Kingsbury Hall rooftop (see photo) to the Barrington, N..H. Public Library roughly 8 miles away. Within the more concentrated UNH campus footprint, downstream data rates approached 10 Mbps.
Also, a separate link was successful in establishing and maintaining a symmetrical 1 Mbps signal between the Stoke Hall antenna site and the Lee, N.H. library, where connectivity previously could not be achieved.
Here are some of the modifications the UNH BCoE team implemented in conjunction with Carlson Wireless to help lift the performance:
- Improved signal-to-noise: The electronics are now connected with a short RF cable pigtail, and the radio is connected to a base station inside a control room by CAT-5 cable. (In the previous iteration, all the electronics were mounted in a single box that was connected using 100 feet of RF cable, with its inherent losses.)
- Higher transmitting power: The use of a sector antenna with a coverage area of roughly 120 degrees provided additional gain to designated receive areas and minimized interference from other areas. Changing from an omnidirectional antenna to a sector antenna pointed from Stoke Hall to the Durham, N.H. Public Library led to a dramatic improvement in data rates, to 4.9/1.5 Mbps (downstream/upstream) from 0.81/0.15 Mbps.
- Higher-quality receivers: The use of client antennas with improved gain characteristics over original antennas has contributed to improved signal performance.
- Network planning: The UNH BCoE team has implemented more detailed review of the available spectrum characteristics in advance, coupled with ongoing signal monitoring post-installation. Additionally, proprietary tools provided by Carlson allowed signal measurement at the client sites, plus fine-tuning of antenna orientation.
- Advanced field tools: The use of an accurate electronic compass application running on a smartphone provided more precise directional data for antenna optimization.
The UNH BCoE TVWS network delivers signals over channels 22 and 23 within the over-the-air television spectrum. Testing by UNH BCoE found strong propagation characteristics, along with low noise and ingress, in these channels. (TVWS implementations rely on FCC-approved dynamic databases to indicate available channels by TV market.)
UNH BCoE will continue experimenting with TVWS technology through the fall of 2014.
Written by Stewart Schley.
Original article can be found here: http://unhbcoe.org/broadband-initiatives/broadband-unh/phase-2-tvws-trial-shows-promise