Tone Reservation to Reduce the Envelope Fluctuations of Multicarrier Signals

In this paper we propose a method for reducing nonlinearity distortion by limiting the envelope fluctuations of an OFDM signal. The method is based on tone reservation, and the free tones are assigned in a way to limit the variations of the instantaneous power of the time domain signal. The problem is shown to be convex, and by adding an equality constraint, zero constellation error is guaranteed. We present an iterative solution for this problem, and show that the globally optimal point can be approached by only a few iterations. Both in-band and out-of-band distortions are reduced at the expense of a small increase in bandwidth of the signal. The corrected signal is less sensitive to nonlinearities, and therefore the distortion is reduced for all input backoff values.