Generalised link-layer adaptation with costly power 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 the case of costly power. The cost can be interpreted in the common economic sense, or can be a signal to encourage efficient resource use in a decentralised matter; furthermore, it may simply be a “Lagrange multiplier” in a centralised optimisation. When the symbol rate is flexible, the result under pricing is similar to the costless scenario: a set of possible link configurations can be ranked by the slope of a tangent line from the origin to the graph of a scaled version of the PSRF: the steeper the tangent the better the configuration. However, if the “effective price” — the power price divided by the noise-normalised channel gain — is sufficiently high, it is optimal for the terminal not to operate. If the symbol rate is fixed, the optimal configuration depends on the effective price.