Performance evaluation of non-linear transmit power amplifiers for North American digital cellular portables

This paper discusses the system performance degradation resulting from using a non-linear transmit power amplifier (PA) in a North American digital cellular (NADC) portable radio. The NADC portables require a linear power amplifier for the spectrally efficient linear modulation scheme, π/4-DQPSK. It is well known that these PA´s can exhibit non-linear characteristics that degrade system performance. System degradation is measured using bit error rate (BER) as the figure of merit. The PA is modeled by its AM-AM and AM-PM characteristics; the receiver architecture contains the simple, yet robust, differential detector. Simulation results are presented for additive white Gaussian noise (AWGN), Rayleigh fading, and frequency selective fading environments, and compared to results for a truly linear PA. In addition, PA spectral regrowth is discussed as well as the potential use of a linearization technique to compensate for the PA effects