What is TVWS?
TV Whitespace (TVWS) is the inactive or unused space found between channels actively used in UHF and VHF spectrum. TVWS frequency spans from 470 MHz - 790 MHz. Currently, TVWS radios are being deployed in rural communities by ISPs to provide broadband. In fact, the TVWS band performs best in the most rural service areas. This is due to the characteristics of TVWS, and how it's shared with powerful analog TV stations.
Access to the TVWS band is controlled by a Spectrum Access System (SAS) database. Having a band controlled by a SAS is a new model for the Service Provider industry. The SAS database provides channel availability to operators. All TVWS devices must be registered with the SAS. A benefit of the SAS is over time it will provide valuable data for predicting noise levels in service areas.
Diagram Above: Cognitive TVWS radios auto-adjust to utilize available spectrum and automatically register with the Spectrum Database you designate it to connect to.
What Are the Benefits of TVWS?
- NLOS Deployments: TVWS is perfect for NLOS deployments. Its low frequency can penetrate through trees and buildings.
- Long Range: TVWS can have a range up to 30 KM, including hilly terrain.
- Easy Mount CPEs: With excellent NLOS performance you will no longer need remote masts. You can mount right on an existing structure.
What to Consider before Deploying TVWS
Due to the properties of TVWS, certain testing is required before deploying. Here are a few items you might want to consider:
- TV Station Interference: TV broadcast megawatts of transmission power. Although analog TV stations are slowly disappearing, their signals carry a very long distance.
- Noise Floor: TV broadcasters are the most significant source of interference, but not the only ones. Industrial noise like high-power electric motors, SCADA operations and LMR systems can also cause interference.
- Higher is Not Always Better: In TVWS, it is often better to deal with obstructions than interference. Although lower heights cause foliage to have a negative impact your link budget, it will save you from destructive interference from high-power noise sources at greater heights.
- Leverage MIMO: TV broadcasters and other TVWS noise generators rarely use MIMO. In this case, use two single polarity antennas on the same pole, instead of a dual polarity antenna, will allow you to benefit from MIMO gain due to diversity and uncorrelated signals.
- RF Survey: An RF survey is a crucial step before determining if TVWS will work in your service area. Spectrum analyzers can be used to do spectrum sweeps. It is best to test at the height of your base station. Most TVWS equipment has built-in spectrum sweeps.
Tools to Use before Deployment
- The Microsoft ® Airband Initiative program for ISPs. Receive grant funding and other assistance as a strategic partner with Microsoft ® in connecting customers in rural areas.
- The Cavell, Mertz & Associates Google Earth FCC Info plug-in. This tool will show you the TV broadcasters in your service area.
- TV Fool website can be used to understand where you can get off-air TV. If your service area indicates poor off-air TV coverage, then it’s a good indication that TVWS will work well in that area.
- Nominet Channel Search engine: is the database administrator Redline has selected for its radio. Their site provides very valuable information.