A frequency offset between the clocks in the digital-toanalog-converters (DAC's) in the transmitter and the analog-todigital-converters (ADC's) in the receiver would severely impact the performance of an OFDM communication system. The effect of the frequency offset can be approximated as a phase rotation for each sample of an OFDM symbol, where the amount of the rotation is proportional to the sub-channel index. In this paper, an algorithm for the compensation of such a frequency offset is proposed which uses the pilot tones present in each OFDM symbol. The required phase corrections for samples in all subcarriers are determined and applied. The proposed algorithm is tested on an OFDM communication system whose parameters are selected based on IEEE 802.11a standard for wireless local area networks (WLAN). Simulation results show that the algorithm works quite effectively even with large amounts of frequency offsets.

This paper aims to study the effects of three error sources on the modulation error ratio for a DRM broadcast system which uses an EER based power amplifier. The considered error sources are a) clipping and quantization of the envelope signal before digital to analog conversion, b) limiting the bandwidth of the envelope signal, and c) the time mismatch between the envelope and modulated phase signals. The study is based on the simulation results of a DRM broadcast system which is modeled by using SIMULINK.Index Terms -Digital radio, envelope elimination and restoration, error analysis, quantization, radio broadcast transmitters, power amplifiers.

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