Total optimisation of a media-streaming wireless terminal: Energy-efficient link adaptation under higher-layer criteria

It has long been recognised that a wireless communication system can be more efficient if link-layer parameters such as modulation order, symbol rate and packet size, are (adaptively) optimised. A common optimising criterion is to maximise spectral efficiency (bits per second per Hertz (bps/Hertz)) subject to a very low bit-error constraint. But a packet-oriented criterion for link adaptation seems more appropriate for practical communication networks fitted with strong error detection and a selective packet re-transmission mechanism. In recent work, we performed link optimisation for maximal bits per second or bits per Joule for data (delay-tolerant) traffic. In the present work, we extend our previous analysis to consider a (delay-sensitive) media streaming application (e.g. music, or video), which introduces yet another degree of freedom: the number of bits allocated to a second of the media signal (encoding rate). We consider any arbitrary combination of link-layer parameters, with the only restriction that the corresponding packet-success rate function (PSRF) is an S-curve. Under a very general optimisation criteria, we obtain a robust result for a media-streaming terminal with an adjustable symbol rate: the key is a tangent line from (0, 0) to a scaled graph of the PSRF, the steeper the line (greater slope) the better the configuration. Under additional reasonable assumptions, at the optimum, both throughput per unit SNR and “fidelity” per unit rate are maximal, which is intuitively appealing.