The Transform Domain Communication System Based On Ofdm Modulation And Demodulation Techniques

The transform domain communication (TDC) is a new technology, which is based on the spread spectrum communication and the transform domain technology. The TDC possesses great ability in restraining the noise through the two methods, dynamically detecting spectrum holes and then changing its waveform. This technology can be regarded as an embranchment of the cognitive radio (CR), because it can use the spectrum neatly and gain higher spectral efficiency.This thesis proposes a modulation scheme of TDCS based on the orthogonal frequency division multiplexing (OFDM). This scheme uses the idea of multi-modulation switching and variable data rate transmission in TDCS, to meet the multiple needs for future communication. This scheme can be used to implement the switch among the MPSK and CSK by changing the phase parameter in the transmitter. We focus on the design of the BCSK flat modulation scheme and derive the error rate expression in the AWGN. The simulation results are in accord with the theoretical analysis. The results show that for small number of the subcarries (Ns<256), this new scheme can offer higher spectral efficiency and better BER performance. For the case of large Ns, the CSK and BCSK have almost the same performance. For adapting more different environments of communication, we also propose the scheme of TDCS by changing the date rate and evaluate the relationship between spectral efficiency and power efficiency for BER=10^-4. Finally, we give the application environment of this scheme.Furthermore, we investigate the performance of this system using the BCSK and CSK modulation under the variant multipath channel models. The results show that this system can handle the frequency selective fading effectively. Comparing with the traditional TDCS, the new system does not require the complex Rake receiver. For the case of good channel condition, BCSK can remain the excellent performance.