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3 THE FREEVIEW SYSTEM
3.1 Introduction
This section describes the key features of the Freeview system and its terminology from the perspective of OpenVix tuning.
3.2 Regions & Transmitter Groups
The term “region” has a specific meaning in the context of Freeview – it is the area served by one of the regional variants
of BBC 1 & ITV. Unfortunately the two organisations sometime have different regional boundaries (typically one organisation
dividing the other’s region into 2), so transmitters are divided into “Transmitter Groups”, in which each transmitter transmits a
particular combination of regional variants.
In many areas it is possible to receive signals from transmitters for two or more groups, with the aerial orientation and type
determining which give the best signal at the PVR. The term “your region” or similar therefore would be more pedantically
expressed as something like “the Region associated with the best signals received by your PVR”.
There are ~15 Freeview (UK) Regions with varying in size from high hundreds of square Km to tens of thousands of Square Km
to reflect different population densities. The Regions and Transmitter Groups associated with each transmitter can be found from
the spreadsheets referenced here.
3.3 Service Numbering
Freeview Services have a “Logical Channel Number” (LCN) that is universally used in televisions and programme listings in
newspapers etc. There are substantial gaps in the numbering, allowing Services of similar types to have adjacent numbers,
and thus allowing automatic removal of some Service types (e.g. Adult) or automatic generation of bouquets for particular
Service types (e.g. Children’s) based purely on LCN. The gaps allow new Services to be added without invalidating such logic.
Further gaps appear when the receiver is incapable of processing certain Service types (e.g. internet-based & text Services in
the case of OpenVix). A list of Services can be found at https://www.radioandtelly.co.uk/freeviewchannels.html.
The LCNs are only employed in the user-interface, and the actual selection of Services is by a parameter known as
“Service Id” (SvId), which is unique across the network, so regional variants of Services have the same LCN but different SvIds.
N.B. LCNs in the range 690-699 are used for test & other temporary Services.
3.4 EPG Data
Each mux carries all the EPG data for all the Services in its Transmitter Group, but not for Services in other Transmitter Groups.
This allows single tuner devices such as televisions to display the EPG data on Services on muxes other than that currently in use.
Thus if not all muxes are received, the full set of schedule information for the Region is still available, which is somewhat confusing
to the user if the irrelevant information is not suppressed in some way. Data for individual Services is identified by SvId, avoiding
the regional ambiguities in the use of LCNs.
As it is impractical to transmit all the EPG data in one data frame, the EPG data is transmitted as individual events, with an Event
Number to allow correlation between subsequent transmissions of the same data. I suspect different Transmitter Groups use
different Event Numbers for the same programme.
3.5 Mux Names & Ids.
The principal Freeview muxes are designated PSB1, PSB2, PSB3, COM4, COM5, COM6, COM7, & COM8, and are supplemented in
populous areas by local muxes. The contents of the muxes can be found at sites such https://ukfree.tv/transmitters/multiplexes,
though as with so much information on the internet it is difficult to find reliable and guaranteed up-to-date sources. The principal
mux names are not affected by regional variations in BBC 1 & ITV, so the mux names need to be qualified if you wish to refer to
just one regional variant (e.g. “PSB1” refers to a mux including any regional variant of BBC 1, and PSB1 (Anglia) refers to the
variant transmitted in the Anglia region).
The muxes are allocated Transport Stream Identities (TsId’s) which reflect any variation in Service content, but not variations in
ancillary information such as EPG data and transmitter details. Thus PSB1 & PSB2’s TsIds vary by region, (as of August 2018)
PSB3 has one TsId for London and another for elsewhere, and COM5-8 have the same TsIds nationwide.
3.6 Mux Types
Freeview uses originally used just the DVB-T standard and only included Standard Definition (SD) video, and then introduced
the DVB-T2 standards on an additional mux (PSB3) to carry High Definition (HD) video without a major reduction in the number
of Services that could be carried. As a result the muxes are often referred to as SD and HD respectively, even though the DVB-T2
muxes include some SD Services and DVB-T could carry HD video. When the COM7, COM8, & local muxes were added the more
efficient DVB-T2 standard was adopted. I believe there has been talk of upgrading all the muxes to DVB-T2 to allow additional
Services or reduce the number of muxes (and hence spectrum utilisation) required, but such a move would make many televisions
useless so is likely to be some time away.
3.7 Freeview Transmitters
Freeview has three “levels” of transmitter, as follows:
• Freeview Extra, which transmit muxes PSB1, PSB2, PSB3, COM4, COM5, COM6 at high power plus some combination
of COM7, COM8 and local muxes generally at a lower power. Different local muxes may be transmitted on the same frequency
using directional aerials to limit interference – the term “petal” is used to describe these transmissions.
• Full Freeview which transmit PSB1, PSB2, PSB3, COM4, COM5, COM6 only.
• Freeview Light, which transmit PSB1, PSB2, and PSB3 only.
The Freeview Light transmitters are divided into groups together with one Full or Extra Transmitter, and transmit precisely the
same data streams as the “parent”. Among other things, this means that the programme guide etc information for Services on
the missing muxes is still available. These transmitters generally perform a “fill-in” role, transmitting at low power to cover a
gap in the parent transmitter coverage such as a town in a steep-sided valley. Some users on the edge of the cover may also
be able to receive COM4/5/6 from the parent “Full” transmitter while receiving a better signal for PSB1/2/3 from the
Light transmitter.
3.8 Mixing Signals From Different Transmitter Groups
In some areas it is possible to receive signals from more than one Transmitter Group. While receiving different muxes from different
groups will not affect the audio and video, there will be problems with the EPG (at least). Take the case where the PSB muxes are
obtained from Transmitter Group 1, and the COM muxes from Transmitter Group 2, then:
• If the EPG data is obtained from a PSB mux, all will be OK, as the COM muxes contain the same services with the same SvIds
as they would if they were received from group 1.
• If the EPG data is obtained from a COM mux, then it will refer to the regionalised Services using the SvIds appropriate to Transmitter
Group 2, but these will not exist in the Service list or any bouquet, and so the BBC1, ITV and possibly BBC1 HD, EPG data will be missing,
and the EPG display will be omit these services completely.
As the mux being used to collect EPG data is not under user control and affected by recordings starting, for the non-expert the regionalised
Service EPG would appear to come and go in a random fashion.
If the numbering of common elements of the EPG data is not identical between Transmitter Groups (as would seem likely), it would probably
be necessary to clear all the EPG data when changing the source mux.
3.9 Transmitter Frequencies
You can find the current frequencies, planned changes and muxes of transmitters serving your location by entering your postcode at
http://www.digitaluk.co.uk/coveragechecker. Which of those transmitters is optimum for you will depend on factors such as aerial
orientation (which may not be obvious with a communal aerial system) or very localised obstructions (e.g. a bungalow with adjacent
tall buildings). You may wish to use a non-optimum transmitter tin order to receive its regional programmes, but this will normally
require re-orientation of your aerial and perhaps use of a different aerial optimised for the new frequencies.
3.10 Interactive Services
The “Interactive” Services in the UK and Eire are provided using “MHEG”, which is described in some detail here. It is used in
several ways:
1) To implement the BBC’s “Red Button” facility on BBC TV Services.
2) To provide information on current programme beyond that in the EPG on Radio Services.
3) To provide some text + crude graphic Services which have no audio or video.
4) To allow broadcast of information such as need to retune.
5) Implement the Freeview “IPTV” Services which look to the user like normal Services having EPG etc entries, but use
the internet rather than the transmitted signals as the source of video and audio.
Of these, implementation of 1-4 appear to be universal on UK market televisions sets, but 5 seems to be unusual in my limited
experience. However none are implemented by OpenVix.
Though the BBC “Red button” Services are intended to be accessed by the Interactive facilities, they are in fact normal TV Services
which can be accessed by any TV or PVR (including OpenVix) via the LCN etc.
3.11 Changes
There are two types of change that affect use of every Freeview receiver as follows:
1) Very infrequent changes of transmitted frequency or the addition of new muxes, which in the past have probably averaged
once per ~3 years for most transmitters, possibly nearer one per year for the Extended Freeview transmitters. As of August 2018
we are ~half way through a period of revised frequency allocations to free up some of the frequency band for mobile telephone
use (see here for more information) – those that have not had their frequencies changed recently can expect them to change in
the next 2 years.
2) Changes to the mux contents, which have occurred at irregular intervals, perhaps averaging ~2 months. These changes
have included Service name changes, LCN changes, movement of Services between muxes, and the addition & removal of Services.
LCN changes and new Services potentially invalidate automatic processes to generate bouquets, or hide, categories of Services
where these are based on the LCN numbering system.
When Services are moved between muxes, they normally continue to be transmitted on the old mux with an LCN in the 690’s for
a few weeks. Until a rescan is performed the change of LCN will not be recognised so all will appear normal till the old version is
discontinued. A warning to rescan is normally transmitted via the Interactive facilities, but will not be visible on OpenVix PVRs
(see para 3.10 above).
Originally Posted by abu baniaz
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