In variable rate modulation, maximisation of data rate can be achieved either by fixing the symbol rate with an adaptive control of the constellation size, or by fixing the constellation size and changing the symbol duration. It is proved that for joint optimal control of both types, they should be used separately: the constellation size changes under a constant maximal symbol rate, and when these opportunities have been exhausted the symbol rate adaptation should be used.

The article treats the potential and real efficiency of adaptive frequency scheduling procedure on instant data in group of radiolinks. The algoritmization problem is reduced to a well-known transport problem of linear programming. The figure-of-merit of performance is introduced and its potential bounds are determined. The methodology of how to take into consideration the influence of real factors on efficiency is proposed. An example with delay of communications is presented.

Frequency adaptation is one of the most powerful techniques which radio telecommunications can use to obtain suitable throughput when data transmission over radio channels with heavy fading and power interference. As adaptive transmission requires estimation of communication quality for each allocated channel, we consider the adaptive system with special sounding signals and determine how the inaccuracy of the channel estimation influences the communication quality. Our findings give also the dependence of the BER on the time elapsed after the moment of sounding and the influence of power narrow band interference on the BER.