The D3&4 Multiplex
Through an ingenious engineering solution, we were able to facilitate the introduction of new services to the D3&4 multiplex whilst helping to reduce Opex.
The D3&4 terrestrial TV multiplex is one of the most watched multiplexes in the UK. It includes all the commercial Public Service Broadcasters (PSBs); ITV, Channel 4, Channel 5, S4C in Wales, STV in Scotland and UTV in Northern Ireland. With 47 television services, 20 regional variations for ITV 1, a single radio service and six different regional outputs apiece for Channels 4 and 5; the D3&4 multiplex is one of the most complex DTT multiplexes in the world.
D3&4 approached Arqiva and requested that we re-engineer the multiplex to help solve a number of outstanding challenges. The first technical challenge was to add an additional ninth service to the multiplex whilst maintaining picture quality for existing services. The second was to reduce the operational cost of running the multiplex.
What we did
Before any engineering work could commence, we had to first identify the most technologically suitable compression equipment available on the market. By running a supplier evaluation programme we were able to review all the key players in the MPEG and broadcast compression business, examine technology roadmaps and features, and perform a comprehensive picture quality ‘shoot-out’.
We also built a picture viewing area at Crystal Palace, the main transmitter site in London, and set up a Picture Quality Experts Group (PQEG). The PQEQ assessed the picture quality produced by the compression equipment from all leading suppliers.
To reduce operational costs we proposed introducing an advanced technique known as Remote Statistical Multiplexing; a first for the UK. Remote statistical multiplexing uses the advantage of an IP connection between the encoders and the multiplexers that allows the encoders to be installed at the playout sites and the multiplexers at the mux sites. This means the bandwidth between playout sites and multiplex sites is of the order of 3 or 4Mbits/s per service rather than 270Mbits/s for uncompressed material. It also removes the requirement for the contribution feeds to be compressed and therefore improves the picture quality by eliminating concatenation effects.
To test the performance of the remote statistical multiplexing system, we built a test network between Winchester and Ipswich with MPEG encoders at one end and multiplexers at the other. We used this proof of concept, not only to test the equipment, but also to verify the impact of network performance characteristics such as latency and jitter. Using our knowledge and the aforementioned system trial, we were able to optimise the design to provide best performance. Due to technology taking a nascent form, we were required to develop a network performance specification with our customer, our equipment supplier and the network provider.
We successfully introduced a new state-of-the-art compression system and enabled the addition of a ninth service to the multiplex without compromising picture quality of existing services. The new compression system uses remote statistical multiplexing to reduce the operational costs and eliminate the need for contribution encoders and decoders.
“We are very pleased with the engineering work carried out by Arqiva; they have designed and implemented an ingenious solution, which has delivered significant operational efficiencies”