Tech Report 035

An Introduction To Time-Frequency Slicing

This report is an introduction to Time-Frequency Slicing (TFS). TFS is a DVB technique that can combine multiple frequency channels into a single wider channel in order to improve the efficiency and robustness of DTT transmissions.

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This report is intended to be an accessible introduction to Time-Frequency Slicing (TFS). It pulls together the results of a number of theoretical studies and considers them in conjunction with measurements taken in the field to see how they compare. It also provides relevant background to the technique, including statistical multiplexing, and it assesses coverage scenarios which may particularly benefit from TFS.

Other aspects of TFS are also considered, such as how it might be deployed in practical networks, potential time frames for its introduction, as well as the benefits and drawbacks of the technique for consumers and broadcasters.
TFS is a DVB technique that enables multiple frequency channels to be combined into a single wider channel in order to improve the efficiency and robustness of DTT transmissions. Improvements come from two main areas:

· Frequency diversity gains. Variations between one RF channel and another in the transmission chain can be harnessed in order to improve the system’s performance (e.g. differences in antenna diagrams, receiving antenna gains, interference and the transmission channel).
· Larger statistical multiplexing (stat-muxing) pools that come from a wider frequency channel.

Simulations, supported by field measurements, indicate that combining four to six RF channels may achieve, for standard fixed rooftop reception, a capacity gain of some 20 - 25%. In addition, stat-muxing gains in the order of 15% for high- and ultra-high definition (HD and UHD) programmes are expected. These gains could, as is common, be used to improve the DTT proposition by introducing more services, or improving their quality. Furthermore these gains could make the delivery of UHD more practical.

Alternatively, TFS could be used to improve the coverage and/or robustness of DTT transmissions. For example, coverage deficiencies in one or more multiplexes caused by unequal interference could potentially be regained. Providing identical coverage for all the services in the TFS signal would also be possible in order to simplify the DTT proposition.