Effects of HPA-Nonlinearity on a 4-DPSK/OFDM-Signal for a Digital Sound Broadcasting System.

Orthogonal Frequency Division Multiplexing (OFDM) in conjunction with a 4-DPSK modulation format has been proposed for the future digital audio broadcasting system (DAB), that should provide compact disk sound quality in portable, vehicular and fixed receivers. With properly chosen parameters, this system should be appropriate for both terrestrial and satellite transmission. In this paper the influence of the nonlinear distortions introduced by the high power amplifier (HPA) of the transmitter is examined. In particular, the degradation in power efficiency due to intermodulation effects and backoff operating, as well as spectral degradations are investigated.It is shown for three different kinds of limiting amplifier models, that even with an output backoff (OBO) in the region of 5-6 dB, the degradation of, e.g., a 512-carrier 4-DPSK/OFDM system relative to the linear case is below 1.7 dB, while the regenerated sidelobes of the transmitted spectrum are kept below -20 dB.