WIB – A NEW SYSTEM CONCEPT
FOR DIGITAL TERRESTRIAL TELEVISION (DTT)
E. Stare (1), J.J. Giménez (2), P. Klenner (3)
(1) Teracom, Sweden (erik.stare@teracom.se)
(2) Universitat Politècnica de València, Spain (jorgigan@iteam.upv.es)
(3) Panasonic Europe Ltd, Germany (peter.klenner@eu.panasonic.com)
ABSTRACT
A new system concept for DTT, called “WiB”, is presented, where potentially all frequencies within the Ultra High Frequency (UHF) band are used on all transmitter (TX) sites (i.e. reuse-1). Interference, especially from neighbouring transmitters operating on the same frequency and transmitting different information, is handled by a combination of a robust transmission mode, directional discrimination of the receiving antenna and interference cancellation methods. With this approach DTT may be transmitted as a single wideband signal, covering potentially the entire UHF band, from a single wideband transmitter per TX site. Thanks to a higher spectrum utilisation the approach allows for a dramatic reduction in fundamental power/cost and about 37-60% capacity increase for the same coverage as with current DTT. High speed mobile reception as well as fine granularity local services would also be supported, without loss of capacity. The paper also outlines further possible developments of WiB, e.g. doubling the capacity via cross-polar Multiple In Multiple Out (MIMO), backward-compatible with existing receiving antennas, and adding a second, WiB-mobile, Layer Division Multiplexing (LDM) layer within the same spectrum, either as mobile broadcast or as mobile broadband.
Läs mer här (pdf)
Slides (pdf)
Länk till Teracom om WIB @ IBC och utdelning av pris som bästa konferansföredrag på IBC2016 i Amsterdam (8-12 september): https://www.teracom.se/omvarld/wib/
FAQ´s from Teracom web site https://www.teracom.se/omvarld/wib/faq-wib/
What does WiB stand for?
The acronym can be read as short for WideBand reuse-1 (with the ‘i’ symbolizing the ‘1’ in reuse-1). WiB should be pronounced as a word (similar to “rib”), i.e. not pronouncing each letter separately. ‘WideBand’ refers to the fact that the WiB signal extends far outside the normal 8 MHz channel and may cover up to the complete UHF band. ‘Reuse-1’ refers to the fact that all frequencies are used from all transmitter sites (in frequency planning terms referred to as reuse-1).
What are the main differences between WiB and existing DTT?
With WiB all frequencies are used from all transmitter sites (current DTT only uses about one 5th) which allows WiB to be transmitted as a single wideband signal using a robust modulation. This scheme allows both higher capacity and lower costs than existing DTT. WiB also includes interference cancellation, which in practice is only usable together with robust modulation (for the layers to be canceled) and therefore cannot be used with today’s DTT.
How much could WiB increase the total capacity per transmitter site in the UHF band?
Simulations of a regular network shows that capacity could be increased (compared to DVB-T2) in the range 37-60% for the most critical case with reception with 95% probability in the worst point (same distance to three adjacent transmitters) at the 1% worst time and for the case where a particular TX needs to be received. By using both polarisations (MIMO) the total capacity could potentially be doubled compared to the above figures. Please note that in contrast to earlier MIMO proposals the introduction of WiB-MIMO could be done in a way that is backward-compatible with legacy receiving antennas, see below.
In which sense, and why, could the introduction of WiB-MIMO be backward-compatible with existing receiver antennas?
With WiB one could start with e.g. using only horizontal polarization signals directed to existing horisontally polarised receiving antennas. One could later increase/double the capacity by adding also the vertical polarization. Users with a new antenna could access both polarisations (full capacity), whereas users with legacy horizontal-only antennas would continue to receive the horizontal polarization (same capacity as earlier) without being disturbed. The main reason why this is possible with WiB is the much higher robustness in the transmission with WiB (e.g. about 17 dB more robust with QPSK ½ compared to current 256-QAM 2/3). With this robustness the inherent ability of an existing receiving antenna to “attenuate” (discriminate) the unwanted polarization (16 dB is a normally assumed value) would then allow sufficient protection between the polarisations. Typical robustness of today’s DTT would not allow for this.
How is it possible to reduce the power consumption by 90% with WiB?
The underlying reason is that for a given used bandwidth the required power increases exponentially with capacity (according to the fundamental “Shannon law”). With existing DTT we have come pretty far up on the exponential curve, which means that there is a corresponding potential for saving if we can go in the other direction. With WiB we can exploit much more spectrum from each transmitter site (thanks to the reuse-1) and can therefore use a lower capacity per UHF channel and still have a high total capacity. The net effect of being in the more favourable part of the exponential curve and exploiting unused spectrum is a 90% power saving (for the same total capacity).
How does WiB work at country borders?
At any border, as long as the same system is used on both sides of the border, and in a synchronized way, WiB will work just as well at country borders as at any other content borders. In all such cases the interference cancellation process can be fully applied.
Do not Single Frequency Networks have the same reuse-1, they only use a single frequency on all sites, don’t they?
Yes, within a particular SFN this is the case, but at content borders (the border of the SFN) also the frequency must shift in a similar way as with a traditional Multi-Frequency Network (MFN). This results in a reuse also with SFN, e.g. reuse-4 and not reuse-1 as one may first believe. With WiB reuse-1 is really used.
Will WiB support U-HDTV services?
Thanks to the assumed wider tuner bandwidth, e.g. 32 MHz (4 UHF channels) the peak data rate could reach 28-40 Mbps, which should be a sufficient HEVC peak data rate for U-HDTV also with High Dynamic Range (HDR) and High Frame Rate (HFR) options used. WiB allows statistical multiplexing of video services using the full 200-300 Mbps capacity as the statmux pool. WiB would therefore allow close-to-ideal statmuxing of “many” U-HDTV services, especially considering that the average U-HDTV service data rates may be much lower than the mentioned peak data rates above.
When WiB uses all the frequencies everywhere there is no room anymore for white space usage – is this not a negative aspect of WiB?
Not really. With WiB “white spaces” can be implemented instead via LDM, i.e. with broadcast and mobile telecom using the same spectrum. In fact this is likely to be a much more efficient way of using white spaces than the traditional approach.
Today PMSE (Programme Making and Special Events), such as wireless microphones, can use unused UHF spectrum in a kind of “white space” way. If WiB uses all spectrum there is nothing left for PMSE. How could that issue be resolved?
First, due to the wideband nature of the WiB signal it becomes virtually insensitive to the use of PMSE (which is typical very narrow-band in spectrum). Second, from the point of view of WiB interfering into PMSE we can note that WiB transmits with a 17 dB lower signal level (per UHF channel) than current DTT and furthermore that most PMSE use is indoor. Both these facts should help co-habitation in the same spectrum very significantly. Of course there are cases when WiB could disturb PMSE and for such cases a solution must be found. One solution could be to use the end parts of the UHF spectrum where the WiB signal anyway needs to be highly attenuated due to spectrum mask requirements. A few MHz on each side of the spectrum could probably be used for PMSE without problems. Use in other bands is also a possibility. This is an important area which needs thorough study and the above considerations are only a starting point.
What about (frequency-shifting) transposers? Since WiB from main transmitters already uses all frequencies there seems to be no remaining frequencies left for transposers.
This would be true if all incoming services would need to be retransmitted via the transposer. Typically however only a (small) subset of all services need to be retransmitted via transposers, e.g. public services to get very high coverage. When less than 50% of all services need to be retransmitted it is however possible to cancel out services not be transmitted and instead use these slots as “freed-up” transposer space for the services to be retransmitted. In addition, of course one may of course use on-channel (SFN) repeaters similar to today, as well as separately fed small transmitters.
With the WiB supermux, would it be possible to still have several licenses, e.g. different multiplex operators?
Yes, WiB allows the total capacity to be arbitrarily divided into sub-parts which could have a constant and guaranteed capacity, with also guaranteed coverage etc. The capacity of each part could be operated (e.g. statmuxed) independently from the other parts. Content licenses or multiplex licenses could therefore be granted similar to today.
With WiB, would it be possible to let different services have different coverage?
Yes, it is possible to allocate different robustness and/or power to different services. Small stations and regenerative repeaters may even retransmit only a subset of the services without breaking the original statmux
With all these advantages, why did not anyone invent WiB earlier?
At the time of standardisation of DVB-T, and also of DVB-T2, a WiB system would have been too complex. For a system that would be introduced in the 2020’s the complexity of WiB should however not be an issue. It is also worth noting that WiB is radically different from existing DTT and it takes somebody to come up with a concrete proposal.
What could make the broadcast world and the mobile telecom world accept WiB principles as the basis for future standardization and implementation?
One reason could be that a combined system could allow both broadcast and mobile telecom to use the full UHF spectrum, if transmitted in LDM, and therefore allow a win-win situation. Ideally, this could put an end to the lengthy “tug of war” of spectrum that we see. Broadcasters could secure the 470-694 MHz spectrum for long term use and at the same time the mobile telecom industry could get access to the full spectrum long before they would otherwise be able to (if at all).
If broadcast and mobile telecom downlink could share the same spectrum, what then about the uplink?
Theoretically the same kind of interference cancellation could be applied also to allow downlink and uplink to share the same spectrum, but for the time being this looks practically unfeasible. What could be done is of course to allocate one portion of the spectrum to the uplink (in FDM or TDM). Another possibility would be to consider the WiB-based system just as a supplemental downlink system, which would need an anchor in other parts of the spectrum (for bi-directional services).