For Siso Fading Channels, Adaptive Modulation Threshold Optimization Technology Research

Adaptive modulation is one of key technologies in mobile wide-band communication systems. Its main principle is that the transmitters adaptively vary the transmitted power level, modulation schemes or some other parameters. Thus, without wasting power or sacrificing BER, this adaptive modulation provide a higher average spectral efficiency by taking advantage of flat fading channel. One of adaptive modulation schemes is well known as Fixed Threshold Method, or Fixed Mode-Switching-Level Method, in which a set of optimum mode-switching levels is derived at first. And then, the transmitter chooses the best modulation format based on the near-instantaneous channel-quality information perceived by the receiver, which is fed back to the transmitter. This method will be studied in this article. I will apply the Lagrangian optimization technique and Torrance optimization technique for deriving the optimized modulation-mode switching levels under some different BER constraints. Then, I finished the simulations in MC-SS system based on the derived optimum switching levels. The simulation results show that the average throughput of the system became better and the BER also satisfied the constraints. In the last part of this article, two-user scenario is considered, in which each user choose the best modulation format, under each BER constraint, to maximize the whole system average throughput.