Generating UWB-OFDM signal using sigma-delta modulator
In this paper we study the implementation issues of ultrawideband orthogonal frequency division multiplexing (UWB-OFDM) communication systems. Like narrowband OFDM, it is desirable to accomplish all modulation and demodulation process digitally in the base band. Designing such a transmitter and receiver for UWB-OFDM signal requires very fast and high-resolution digital-to-analog (D/A) and analog-to-digital (A/D) converters that operate on a very large frequency band. A modified version of sigma-delta modulator, which we call an N-tone sigma-delta, can be used for this purpose. This new structure introduces N zeros at N properly selected frequencies in the quantization noise spectrum and can be used anytime there are gaps in the spectrum of the transmitted signal. A digital transmitter and receiver for UWB-OFDM signal is proposed using this structure and its performance is studied in multipath fading channel.