LONDON: Britain's Independent Television Commission (ITC) yesterday amended its technical standards to authorise those digital broadcasters who wish to broadcast in '16-QAM' transmission mode to press ahead. This follows the readvertising of licences for three digital terrestrial multiplexes and the success of tenders based on the '16-QAM' transmission mode.

In the light of technical assessments, including laboratory trials, and following the licence awards the ITC has said it is minded to mandate '16-QAM' as the transmission mode for all DTT services. A consultation on this proposition closed on 12 September.

Proponents of a change to '16-QAM' argued strongly that the benefits in terms of coverage and signal robustness justifies making '16-QAM' the mandatory transmission standard. Other respondents argued strongly that the research evidence for this was not strong enough to outweigh the disbenefit of reducing the number of services available.

The ITC has decided to commission an independent study to undertake tests in dual mode, '64-QAM' and '16-QAM' transmission in October when both modes will be in use.

The ITC will shortly be announcing field trials and research to provide practical in-home evidence of the performance of the two transmission modes. The most critical issue to assess will be the potential for differential performance between the public service channels carried at '64-QAM', and those at '16-QAM', in poor reception areas and in the presence of impulse interference (e.g. from thermostats, car ignitions, refrigerators etc).

This research will allow the Freeview service to launch with its preferred mode and the industry to assess the impact of transmission mode change based on real evidence. The ITC is minded to choose the '16-QAM' transmission mode but intends to make a final decision on this issue for the New Year based on the outcome of this research.

BBC and Crown Castle, who between them operate four of the six digital terrestrial television multiplexes, plan to move to a '16-QAM' transmission mode from the launch of their new service, known as 'Freeview'. The remaining two multiplex operators, Digital 3 and 4 and SDN, will be permitted to continue transmission at '64-QAM' during this interim period.