Signal shaping for peak-power and dynamics reduction in transmission schemes employing precoding

Precoding, i.e., nonlinear pre-equalization, at the transmitter side has been proved to be a very efficient strategy for channel equalization in single-carrier digital transmission schemes. It enables the application of coded modulation in a seamless fashion. A drawback of precoding is that the signal at the input of the decision device exhibits a huge dynamic range. Based on dynamics shaping, a combined precoding/shaping technique introduced in the paper by Fischer et al. in 1995, a new shaping strategy is developed in this paper. This technique enables a flexible tradeoff among: 1) reduction of the average transmit power; 2) avoidance of peaks in the transmit signal in order to facilitate line driver implementation; and 3) restriction of the maximum amplitude at the receiver side to a prescribed value. Over a wide range, all three demands can be met simultaneously. As the scheme is fully compatible with Tomlinson–Harashima precoding, it can replace the precoder even in existing and standardized schemes. Simulation results for a typical digital subscriber line scenario show the achievable gains.