Technical Research On Faster-than-Nyquist

As the material basis of communication services, the radio spectrum constructs the whole framework for current mobile communications. But it is not inexhaustible public resources, the growing demands for radio spectrum resources and fierce competitions between all kinds of radio techniques and applications result in the increasing scarcity of radio spectrum. However, baseband transmission system without inter-symbol interference(ISI) must satisfy the Nyquist criterion, which is a constraint on the growth of spectral efficiency. Therefore, this paper mainly studies the signal design method beyond the Nyquist rate and utilizes the limited spectral resources to realize high-speed data transmission.FTN and Overlapped Time Domain Multiplexing(OVTDM) have broken the fetter of the Nyquist criterion. FTN is a technique based on the idea of interference cancellation, while OVTDM is a technique based on sequence detection. Essentially, both of them relax the requirement for no inter-symbol interference, resulting in higher spectral efficiency. In this paper, these two design schemes of transmission signals above Nyquist rate are studied respectively.Aiming at FTN technology, the scheme of combining multi-carrier FTN system with Turbo coding is studied. Due to the introduction of infinitely long and uncontrollable ISI at the transmitter, a parallel decoding structure combining serial interference cancellation(SIC) with Turbo decoding is designed at the receiver, which has low complexity and delay. Simulation results show that compared with convolutional codes,Turbo-coded FTN system can achieve about 3?6dB performance gain in the case of low spectral efficiency, and the gain is decreased when the spectrum efficiency is high.For OVTDM, the performance of OVTDM system with different multiplexing waveforms under different spectral efficiency is studied. As the IOTA function has excellent time-frequency localization(TFL) and low out-of-band signal energy, this paper designs a serial cascaded OVTDM system employing IOTA multiplexing waveform. Compared with the system using rectangular multiplexing waveform, the system also has a greater performance gain.