This study was commissioned by the European Commission to examine whether spectrum could be used more effectively by controlling interference itself, rather than relying on the traditional method for achieving this: limiting the technical parameters of transmitters. The project, managed by Eurostrategies sprl and LS Telcom, has yet to come to final conclusions but initial findings suggest that this alternative approach has its limitations.
Techniques to control interference itself (known as interference management) do not 'produce an all-encompassing improvement in the efficiency or effectiveness of spectrum use' nor are they a replacement for standard techniques, says Richard Womersley of InterConnect (a Eurostrategies partner). However, 'the application of such techniques in some circumstances does provide alternative and additional tools to the spectrum manager which inform and encourage more flexible access to the radio spectrum,' he adds.
Potential for spectrum release
One of these interference management techniques is to regulate receivers as well as transmitters and the project team found that in some circumstances this produced impressive benefits, while in others it had no effect. In the case of point-to-point microwave links in 7GHz, 13GHz, 18GHz and 23GHz reasonable expectations of improvement in receiver performance didn't free up significant amounts of spectrum. However, in GSM the introduction of Single Antenna Interference Cancellation (SAIC) trialled in a 2004 study would, the team estimated, produce a reduction in spectrum requirements of up to 15%. Hugh Collins of InterConnect analysed the economic implications for each technology and said that introducing SAIC would cost only a few euros per terminal, way below the break-even level of €15-46 per terminal which represents the economic value of the spectrum savings. So this he argued, was a 'very worthwhile change to make.'
But the most striking improvements in spectrum efficiency could be achieved by modifying terrestrial digital television (DVB-T) receivers to incorporate antenna diversity i.e. having two or more antennas. This would allow the creation of a higher modulation scheme with six instead of four programmes per channel, potentially releasing 78MHz.
Hugh Collins estimated that this spectrum would be worth €49 billion to the mobile industry, but required the modification of 181 million fixed TV receivers and 124 million mobile TV receivers, producing a break even modification cost per terminal of €158. 'So that's very likely to be worthwhile as well,' he told the audience at a seminar to discuss the interim findings in Brussels this month.
However, broadcasters pointed out that releasing this amount of spectrum wasn't currently possible because this wasn't how the allocations has been planned at RRC-06, nor could fixed receivers necessarily take advantage of the diversity technique, a point accepted by the project team. They said this was a scenario intended to stimulate debate.
No need for regulation
One mobile operator pointed out that if the economic incentives were already there to improve receiver performance, there was no need for regulatory intervention. If a company can improve its own spectrum efficiency through receiver modification these incentives certainly exist, but that isn't the case if the improvements depend on the actions of others. Jan Outters from the German broadcasting research Institute, IRT said consumers wouldn't update their TV receivers in the cause of spectrum efficiency: 'People don't change [their set top boxes] every 18 months like their phones. If we need to change these to release spectrum there is nothing to motivate the users.'
The project team said they weren't in favour of compulsory regulation of receivers, rather they wanted policies which encouraged beneficial modifications, like a secondary market for spectrum licences. 'In a spectrum trading environment there would be an incentive for an operator to pay to change those set top boxes,' said Hugh Collins.
Confusing definitions
Having ruled out regulation of receivers the main controversy in the team's draft proposals comes in suggestions to tighten up definitions and administrative procedures.
Particularly contentious is a proposal to remove the specific reference to 'safety services' in the Authorisation and R&TTE Directives. These currently define harmful interference as that "which endangers the functioning of a radionavigation service or of other safety services or seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service operating in accordance with the applicable Community or national regulations." The team argue that this wording is unclear. "Endangering" and "obstructing" could mean that no actual harm is caused to the service; "repeatedly" could mean just two instances.
They also question the need for a specific reference to radionavigation or safety services as there is no list of what these are in either Directive. Almost anything could be considered a safety service, including GSM phones, so it is better to ensure equal treatment for every service. The project team has proposed a new definition: "Harmful interference means interference which degrades or interrupts radiocommunication to an extent beyond that which would reasonably be expected when operating in accordance with the applicable Community or national regulations."
Richard Womersley says this doesn't diminish the protection for safety of life: considering the range of services now used for that purpose the new definition may increase the protection. Furthermore, by introducing the concept of reasonableness it recognises that a certain level of interference is unavoidable and there needs to be a rational debate about whether these unwanted signals are actually causing harm.
The project team also argues that the way harmful interference is treated under the relevant Commission decisions and EU Directives is confusing. The Authorisation Directive doesn't need to mention these at all, they argue, because they are addressed elsewhere, like in the R&TTE Directive. This should incorporate the new definition discussed above and clarify that harmful interference is in fact a subset of electromagnetic disturbance, and can arise from sources other than radio equipment.
Technical studies too slow?
At the Brussels seminar the most controversial issue was criticism of the compatibility studies carried out by the European regulator's organisation, CEPT. Respondents to a survey carried out by the project team said CEPT was too slow in carrying these out; insufficiently transparent; and some studies carried out by member states were not objective. These claims were hotly disputed by many delegates at the seminar, with the support for CEPT coming from the public sector, corporate and regulators alike. This highlighted an apparent contradiction between what spectrum stakeholders say in public and what they say in anonymous surveys.
The project team suggested that the current arrangement could be improved by allowing organisations other than CEPT to carry out or to validate these studies under the direction of the Commission. The standards body, ETSI, the European Radiocommunications Office (ERO), and private sector test labs were all mentioned as possibilities, with one favoured option being to delegate technical work to a department of the European Commission, the Joint Research Centre.
The report is expected to be published by the Commission in December.•
26.10.07
By Martin Sims |
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