Data Rate Performance
Data Rate Performance
As mentioned earlier in this White Paper, the overall data rate requirement for different applications varies greatly. The extent to which different technologies can respond to the requirements of these applications depends on the data rate that they can provide.
Technology data rate capabilities are usually quoted in terms of the maximum physical data available, that is to say the speed with which the technology transmits binary data onto the channel. Whilst this provides a basic means of comparing different technologies, it does not take into account the fact that not all the data transmitted is actually used by the application. In all cases extra data must be transmitted for synchronisation, error correction, flow control and network management, which reduces the proportion of useful "application" data that can be transmitted onto the channel, by a factor of 20 to 40 per cent. In addition it should be born in mind the fact that the quoted maximum physical data rate for all technologies is that achieved under ideal conditions. In the section on coverage we will discuss the real world data rates that can be achieved in typical conditions. Despite all these caveats on comparing physical data rates, for simplicity's sake the number is the most often used for communicating technology capabilities, where DS2 can claim a far high speed than any wireless technology or any other technology for powerline or phone cables.
By looking at the different "usage scenarios" for the digital home, it is relatively straightforward to calculate the levels of data rate that will be required for the digital home. It is easy to conclude that technologies which cannot consistently provide data bandwidths in the range 35 to 55 Mbps will not be able to fulfil the needs of the digital home.
Home Network Coverage
To provide consumers with a problem free, out of the box experience, it is not enough to provide a high enough data rate for any particular application. It is important to provide coverage, which provides the required data bandwidth in a high percentage of potential connections throughout the whole home.
The diagram above shows the application data rate achieved in an independent test undertaken by C't magazine (the raw results can be seen below)
The wireless system only achieves 10Mbps in 52 per cent of cases, which means that only half of the home can be covered with a 10Mbps service. This makes it evident that video service with the best standard wireless solution available today is not a possibility.
A little better, the Homeplug 85Mbps Turbo solution can more or less guarantee a 10Mbps application bandwidth, but 20Mbps coverage for HDTV or multiple media services is patchy and 30Mbps is only possible in rare occasions.
For a true digital home, complete coverage at data rates anticipated in the usage scenarios mentioned earlier in this document, the only option is DS2 200Mbps technology, which can achieve 20Mbps in 100 per cent of cases, 30Mbps in 96 per cent of cases, 40Mbps in 91 per cent of cases and 50Mbps in 68 per cent of cases.