Digital dividend: cognitive access

Executive Summary

Executive summary

Background

1.1 Since its launch in 2005, our Digital Dividend Review (DDR) has considered how to make the spectrum freed up by digital switchover (DSO) available for new uses. This includes the capacity available within the spectrum that will be retained to carry the six digital terrestrial television (DTT) multiplexes after DSO. This is known as interleaved spectrum because not all this spectrum in any particular location will be used for DTT and so is available for other services on a shared (or interleaved) basis.

1.2 In our statement of 13 December 2007 on our approach to awarding the digital dividend, we considered the use of interleaved spectrum by licence-exempt applications (i.e. those exempted from the need to be licensed under the Wireless Telegraphy Act 2006 ). We concluded that we should allow cognitive access as long as we were satisfied that it would not cause harmful interference to licensed uses, including DTT and programme-making and special events (PMSE). This could potentially bring substantial benefits to citizens and consumers in the form of new devices and services.

1.3 Cognitive devices can detect spectrum that is otherwise unused and transmit without causing harmful interference. They have the potential to support a wide range of uses, including high-speed always-on broadband and are particularly suited to using interleaved spectrum precisely because significant capacity is often unused at any one location at least some of the time.

1.4 This document, which is largely technical in nature, consults on proposed parameters for licence-exempt cognitive devices using interleaved spectrum to prevent harmful interference to licensed uses.

Cognitive access to interleaved spectrum

1.5 In their simplest form, cognitive devices rely solely on spectrum-sensing capabilities to detect unused spectrum in which they can transmit. If they fail to detect licensed use of spectrum, harmful interference might occur. To prevent this, two key parameters must be set appropriately:

• The device must be able to determine with sufficiently certainty that the spectrum is not in use in the vicinity. Depending on how this is achieved, parameters such as sensing levels need to be set.
• The device must transmit with relatively low power such that its signal does not travel far from its location.

1.6 In an alternative form, cognitive devices measure their location and make use of a geolocation database to determine which channels they can use at their current location. In this case parameters such as locational accuracy and frequency of database enquiry are important.

1.7 Other parameters such as out-of-band performance and politeness of behaviour also need to be set to ensure optimal use of the spectrum.

1.8 While it is not possible to set parameters such that harmful interference will never occur, it is possible to set them such that there is an acceptably low probability of harmful interference.

Key device parameters

1.9 The main part of this document shows how we have derived the proposed key parameters for successful licence-exempt cognitive access to interleaved spectrum in the UK. Table 1 sets out those we believe necessary if cognitive devices are to use sensing alone. Transmit powers here and throughout this document are effective isotropic radiated power (EIRP) into an 8 MHz bandwidth.

Table 1. Key parameters for sensing

1.10 Table 2 sets out the key parameters that we believe necessary if cognitive devices use geolocation.

Table 2. Key parameters for geolocation

1.11 We have derived these parameters from a mix of theory and measurement. Where a range of acceptable parameters includes those adopted elsewhere in the world, we have proposed the values from the latter in the interest of promoting international economies of scale.

Question 1. The executive summary sets out our proposals for licence-exempting cognitive devices using interleaved spectrum. Do you agree with these proposals?

Next steps

1.12 This consultation closes on 1 May 2009. We recognise that it raises challenging technical and operational issues and therefore plan to engage with stakeholders on our proposals during the consultation period.

1.13 More information about next steps is set out in section 11.