Research On Multi-Carrier Transmission Via Efficient Modulations

In the wireless communication industry, more attention have been put on the crisis of the spectrum re-sources scarcity, and this crisis is intensified by the increasing of data access rates to satisfy the user demand for the high-quality information services. In order to address this problem, lots of research have been studied on the spectrum utilization and the power utilization energy ratio. Therefore, as the fundamental research on the wireless communication system, the efficient modulations and the based multi-carrier realizations can improve the spectrum and power utilization, and provide an efficient solution for this spectrum shortage. In the thesis, we mainly discuss the multi-carrier communication system based on the efficient modulation-s, including the separation of the mixed multi-carrier signals and the sophisticated demodulation methods. The enhancement of the spectrum utilization is attained, and the excellent communication performance is maintained.In the thesis, the general expression for the efficient modulations is firstly given and analyzed, where the different modulation methods are obtained by tuning the various parameters. To effectively demodulate this efficient waveforms, the demodulation methods via the special impacting filtering (SIF) have been discussed. Furthermore, we obtain the non-centresymmetry characteristic of the signals with the efficient modulations, which is utilized to guide the design of the transmit shaping filters. In the non-rectangular spectra partition model, according to the different demodulation methods, this thesis mainly discuss the following realizations of the multi-carrier communication system with the efficient modulations:1) The digital impacting filters bank based multi-carrier communication system with the efficient modula-tions Inspired by the idea of the sine signal suppression, we redesign the digital impacting filter utilized in the single carrier system with the efficient modulation signals. The impact-notch characteristic of the impact-ing filter is obtained by set zeros at the notch frequency. Hence, this proposed digital impacting filter can both impacting the received signals and suppressing the interference. The demodulation performance for the efficient modulation signals is improved by suppressing the interference. Furthermore, the efficient communication system is built based on this impact-notch filters bank, where the mixed signals without the guard intervals is transmitted, and this mixed signals is separated and demodulated by this filters bank.2) The narrowband filter based multi-carrier communication system with the efficient modulations Under the idea condition, we present the circuit model of the impacting filter and the reason of the impact-ing demodulation. When the working frequency of the input signal is at the steepest frequency of the filter frequency response curve, the phase change of the input signal gives the strong amplitude fluctuation of the output signal, and this amplitude fluctuation becomes obvious with the increasing of slope. We call this as the "slope-phase discrimination" characteristics of the impacting filter. Then the FIR narrowband filter, which has the natural "slope-phase discrimination" characteristics, is adopted as the receiver for the efficient modulation systems, where the transition regions at the left and right sides of the narrowband filter are utilized as the impacting filter to demodulate the two sub-carriers signal. Simulation results for this FIR filter demonstrate the effectiveness of the impacting characteristics, and the communication system based on the efficient modulation with the FIR filter is built and compared with the traditional one with the â…¡R digital filter. Results show that this two sub-carriers signal is separated efficiently by the FIR filter, which outperforms the IIR filter.3) The efficient communication system based on the random time hopping MPPSK (TH-MPPSK) modula-tion By using the random sequence to control the phase jump position of the MPPSK signal, we propose a novel efficient modulation method, namely time hopping MPPSK (TH-MPPSK) signal, and we built a multi-carrier system via the TH-MPPSK signal. Moreover, we propose three demodulation methods, namely the multi-carrier joint demodulation (MJD), the one-by-one (OBD) and Improved one-by-one detection (IOBD), by exploiting the correlation characteristics of the modulated signal with the random phase jump position. The simulation results show that, at lower SNR, we can use MJD to demodulation the signals without the complexity consideration, while at high SNR, the OBD and IOBD methods can be utilized. In addition, the same demodulation performance can be achieved when the number of sub-carriers increases. Therefore, the multi-carrier system with dense multi-carrier transmission can be realized by the proposed TH-MPPSK modulation.Finally, the performance of the efficient modulation system in the Rayleigh channel has been analyzed, and the results show that the simple techniques of the channel equalization cannot improve the performance significantly. As the MIMO technique can provide spatial diversity to anti multichannel fading and im-prove the system gain, we can utilize the MIMO technique to suppress the multi-path, the co-channel and the inter-symbol interference. Combining the MIMO technique, the channel equalization and the three pro-posed demodulation methods, the MJD demodulation and the TH-MPPSK modulation can perform well in the Rayleigh fading channel, and the system can work efficiently without the channel coding and the anti fading technique. The results demonstrate that the combination of the efficient modulations and the MIMO can further improve the spectrum utilization, and enhance the system capacity.