WIB – the next generation digital TV system?
Within the DVB-project Technical Module a study mission is currently in progress with the name WIB, Wideband Broadcasting. The task is to evaluate the feasibility of a new digital TV broadband transmission system.
The basic idea with WIB is to use all available UHF channels at all transmitters, in an ultra-wideband transmission. Using all frequencies at all sites, with different program content, is referred to a frequency reuse factor of one. This can be compared to the traditional frequency planning where a reuse factor between 4-6 is normally used.
A frequency reuse factor of one (1) may however result in interference between the service areas of the individual sites. The impact of the interference is reduced by choosing a very robust transmission mode. Instead of using 64QAM or 256QAM modulation, (requiring a C/N of about 20dB), QPSK modulation would be used, which can work with Carrier to Noise (C/N) close 0 dB, which would significantly reduce the impact of interference. Additionally, it is also suggested to use interference cancelling techniques, to further reduce the impact of interference.
Figure: WIB use all channels as the same time at all transmitters, (picture provided by Erik Stare, Teracom).
Potentially WIB could bring a number of benefits:
- The total emitted power for the wideband signal would be lower compared to the distribution of say 6 or 8 multiplexes using the “traditional” 8 MHz channel raster. This would reduce operational cost
- Using a very robust modulation would make it easier to provide portable and mobile DTT reception
- The large bandwidth used would also provide frequency diversity in the transmission which would improve reception, and increase the spectrum efficiency.
- Since total transmission capacity seen across the UHF band would increase, it would result in a larger statistical multiplexing gain. This could be important for example when broadcasting UHD services requiring high data rates
Most important in the light of the limited spectrum availability, is however, the expected increase in spectrum efficiency. Simulations indicate that within the full UHF band an increase in spectrum efficiency (bits/Hz) of between 30 and 60% compared to today’s situation, would be achievable, when providing the same coverage.
From a planning perspective two main questions are to be asked about WIB:
- How much would the data rate increase in the UHF band from channel 21-48 (470- 694 MHz), compared to the current 8MHz channelling using by DVB-T/T2 systems?
- How would the introduction/switchover be carried out, without interrupting the existing DTT services? This may perhaps be the most difficult question to deal with
The concept of WIB was first presented by Erik Stare at Teracom, in a paper at IBC 2016. More information about WIB may be found in the article in EBU technical Review.