Digital Television Yields to Broadband Wireless Access

November 4, 2011 | WireIE Holdings International | Content Marketing | Author

The digitization of US over-the-air television channels has afforded a twofold opportunity to expand broadband access in that country.

The most publicized was the reassigning of 108 MHz of spectrum at the ‘top’ of the former UHF analogue television band in what broadly became known as the 2008 700 MHz auction. The auction resulted in the coveted “B” (22 MHz) and “C” (12 MHz) blocks going to AT&T and Verizon respectively. The band will primarily be used for LTE as well as 3G overflow in the shorter term.

White Spaces And Cognitive Radio

The other wireless broadband access opportunity resulting from the digitization of broadcast television is arguably more abstract. The FCC recently ruled in favour on the somewhat contentious concept of using the remaining 222 MHz of UHF, and 42 MHz of VHF digital television broadcast spectrum on shared basis with a broadband access technology commonly referred to as White Spaces.

Also touted as “Wi-Fi on steroids”, White Spaces will be an unlicensed radio access technology in which wireless broadband sessions occur on digital television guard band frequencies. Unassigned digital television channels can also be used by White Spaces technology yielding throughputs of up to 11 Mbps per device.

The philosophy behind how White Spaces manage RF spectrum is what the FCC refers to as “opportunistic” under a mechanism known as Spectrum Sensing Cognitive Radio (IEEE 802.22). The protocol also allows for database querying in addition to RF sensing – thus giving television broadcasters a second layer of protection from potential interference. This works by the location of the White Spaces device (based on its GPS coordinates) being reconciled with digital television transmitter/antenna values in the database. RF interference threshold parameters dictate whether the White Spaces device can use the channel.

This highly dynamic, in-the-moment approach to RF spectrum assignment is intriguing in that spectrum utilization is continually optimized based on many key parameters in the RF environment. In fact, this could be a bellwether for current generation radio access technologies where demand for spectrum is outstripping available bandwidth.

While the 2008 spectrum auction has given the successful bidders access to the favourable propagation of 700 MHz, White Spaces is permitted to operate across the entirety of both digital television bands (174-216 MHz VHF and 470-698 MHz UHF). In light of the propagation characteristics unique to each of these bands, and the comparatively ad hoc nature of the White Spaces approach to spectrum utilization, radio access can be exposed to a number of propagation anomalies that will temporarily enhance or degrade performance. Fortunately, the Spectrum Sensing Cognitive Radio protocol should mitigate the degradations and exploit the enhancements in signal propagation.

Network Extensions Essential Piece of the Puzzle

As jurisdictions outside the US complete their transition to digital television, White Spaces will become broadly available as a new and innovative broadband wireless access technology. At that time, many regions will also be repurposing retired analogue television spectrum for 4G broadband wireless services. With these broadband access technologies based on IP, Ethernet Radio is an obvious choice for backhauling these dense access networks. WireIE is a leader in Network Extensions based on Ethernet Radio.