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Quantifying the Availability of TV White Spaces for Cognitive Radio Operation in the UK
Maziar Nekovee
TL;DR
Quantitative evidence on TV White Space opportunities outside the United States was limited. The paper combines DTV coverage maps and transmitter data to estimate UK availability, finding about 150 MHz on average for low-power cognitive radios, though availability is fragmented and adjacent-channel constraints reduce it.
Problem
Quantitative information on spectrum opportunities from cognitive access to TV bands outside the United States was limited.
Source: §1 · p. 3Method
The paper combines DTV coverage maps and transmitter data to estimate available TVWS frequencies across UK locations and examine location, transmit power, and adjacent-channel constraints.
Source: §1 · p. 3Results
∼150 MHz of TVWS is available on average for low-power cognitive radios, but availability is fragmented and adjacent-channel constraints drastically reduce it.
Source: §5 · pp. 12–13Takeaways & Limitations
Fragmentation makes pooling techniques such as NC-OFDM crucial for effective TVWS use, particularly for future high-bandwidth applications.
Source: §5 · p. 13The analysis focuses mainly on low-power access; aggregated interference among devices in one region and improved high-power estimates remain future work.
Source: §4 · p. 9, §5 · p. 13
Abstract
from arXiv · showhide
Cognitive radio is being intensively researched for opportunistic access to the so-called TV White Spaces (TVWS): large portions of the VHF/UHF TV bands which become available on a geographical basis after the digital switchover. Using accurate digital TV (DTV) coverage maps together with a database of DTV transmitters, we develop a methodology for identifying TVWS frequencies at any given location in the United Kingdom. We use our methodology to investigate variations in TVWS as a function of the location and transmit power of cognitive radios, and examine how constraints on adjacent channel interference imposed by regulators may affect the results. Our analysis provides a realistic view on the spectrum opportunity associated with cognitive devices, and presents the first quantitative study of the availability and frequency composition of TWVS outside the United States.
1 Introduction
Cognitive radio can opportunistically use licensed spectrum when and where incumbents are absent, and TV White Spaces have drawn growing research and regulatory attention. This paper addresses limited quantitative evidence beyond the United States with an analysis of UK availability.
1 Introduction
- Cognitive radio supports opportunistic spectrum access by sensing licensed bands and using frequencies when or where incumbents are absent.Access may be temporal or spatial; spatial access uses locations where a licensed band is unused without harmful interference to nearby incumbent operations.Source: §1 · p. 2
- US and UK regulators moved toward TVWS access, with the FCC establishing secondary-use rules and Ofcom proposing licence-exempt use of interleaved spectrum.The introduction also notes the emerging 802.22 standard for cognitive access to TV bands.Source: §1 · p. 2
- Quantitative evidence on global spectrum opportunities outside the United States remained limited, despite research on US cognitive access to TVWS.The authors identify this lack of evidence as the gap their UK study addresses.Source: §1 · p. 3
- The paper quantifies UK TV White Space availability using DTV coverage maps and transmitter data, examining location, transmit power, and adjacent-channel constraints.It presents the first quantitative study of TVWS availability and frequency composition outside the United States.Source: §1 · p. 3
2 Cognitive radio operation in TV bands
Digital switchover creates both cleared TV channels and geographically unused channels that can form TV White Spaces. These bands attract interest for their combination of bandwidth and coverage, while cognitive access must protect licensed users.
2 Cognitive radio operation in TV bands
- After digital switchover, some channels are cleared while others remain unused by DTV stations in particular areas, forming TV White Spaces or interleaved spectrum.Low-power devices may use vacant channels in locations where TV stations could not operate without interference; cognitive devices must avoid harmful interference to DTV and wireless microphones.Source: §2 · pp. 3–4
- TVWS interest stems from the combination of bandwidth and coverage, with TV-band signals traveling farther and penetrating buildings more readily than WiFi and 3G signals.Potential uses include broadband access and mobile or digital-home networks; the passage also notes the suitability of UHF wavelengths for small resonant antennas.Source: §2 · pp. 4–5
- The post-switchover UK spectrum is divided into interleaved (TVWS) and cleared channels across the VHF and UHF TV bands.Figure 1 depicts both channel categories [4].Source: Figure 1 · p. 5
3 Methodology
The methodology identifies location-specific TVWS by combining DTV coverage information with distance-based protection from interference. It treats low- and high-power cognitive radios differently when estimating available frequencies.
3 Methodology
- UK interleaved spectrum totals 256 MHz, but the proposed auction of channels 61 and 62 would leave 240 MHz for cognitive-device access.The available frequencies vary by location with the spatial arrangement and frequency planning of DTV transmitters.Source: §3 · p. 5
- The keep-out distance is derived from a path-loss model to protect TV receivers at the edge of a transmitter’s coverage area.A cognitive radio may use that station’s frequencies only when it is at least the specified distance away.Source: §3 · pp. 6–7
- Available TVWS frequencies are counted across DTV transmitters, excluding a transmitter’s frequencies when the cognitive radio is inside its keep-out distance.The method applies a distance condition at location r and sums over transmitters and DTV frequencies.Source: §3 · p. 7
- The DTV coverage maps used in the study are simulation-based and further validated and refined through measurements and DTV-user observations.They draw on location, transmit power, antenna height, and frequency data for the UK’s 81 main transmitters.Source: §3 · p. 7
- For low-power radios, the algorithm maps a UK location to the nearest coverage-map grid point and tags each transmitter’s frequencies occupied or vacant.It repeats this check across all 81 UK transmitters; the resulting vacancy list is an upper bound.Source: §3 · p. 8
- For high-power radios, the method approximates each transmitter’s coverage area with a minimum-area enclosing disk to reduce computational effort.The passage gives 4 Watts ERP as an example and estimates keep-out radii of 30–120 km.Source: §3 · pp. 8–9
4 Results
Across 18 UK population centres, low-power radios had at least 12 available channels, but channel availability and placement varied. Adjacent-channel exclusions sharply reduced access, and availability also fell as transmit power increased.
4 Results
- The analysis focuses mainly on low-power cognitive access; a full analysis of high-power devices is deferred elsewhere.Source: §4 · p. 9
4.1 TVWS availability and frequency composition
- At least 12 channels (96 MHz) were accessible to low-power cognitive devices at each location, with average available spectrum just over 150 MHz.Availability varied considerably across the 18 population centres.Source: §4.1 · p. 9, Figure 4 · p. 10
4.2 The impact of adjacent channel interference and transmit power
- Excluding vacant channels adjacent to occupied DTV channels drastically reduced availability; central London had none, and the across-location average was only ∼30 MHz.The constraint removes vacant channels whose immediate adjacent channels are occupied.Source: Figure 4 · p. 10, §4.2 · p. 12
4.1 TVWS availability and frequency composition
- Bristol and Liverpool had most available channels at 470–550 MHz, while Southampton’s were concentrated at 630–806 MHz; London had 16 MHz contiguous within 96 MHz total.Available channels could be highly non-contiguous, which may restrict technologies requiring contiguous spectrum.Source: §4.1 · pp. 10–11, Figure 5 · p. 11
4.2 The impact of adjacent channel interference and transmit power
- In Manchester, availability fell sharply above 100 mW, though 40 MHz remained available at 2 W, within the typical operation of future 802.22 devices.At or below 100 mW, up to 17 channels (136 MHz) were available.Source: §4.2 · p. 12
5 Conclusions
The study estimates UK TV White Space availability across 18 population centres and finds substantial low-power spectrum, often fragmented into non-adjacent channels. It concludes that pooling techniques are important for effective use, while adjacent-channel constraints sharply reduce availability.
5 Conclusions
- The 18-centre analysis found an average of ∼150 MHz of TVWS for low-power radios, but much of this bandwidth was fragmented across non-adjacent channels.Source: §5 · pp. 12–13
- Pooling techniques such as NC-OFDM are identified as crucial for effective TVWS use, particularly for future high-bandwidth applications.Source: §5 · p. 13
- Regulatory or standards-based adjacent-channel constraints drastically reduce the availability of TVWS.Source: §5 · p. 13
- Future work includes methods for estimating and controlling aggregate interference from multiple devices in one region and improved estimates for high-power use cases.Source: §5 · p. 13