Research On Interference And Coexistence For Wideband And Data Transmission System Of 230MHz

Spectrum resources are extremely valuable for communication. However, the utilization ratio of the 230 MHz frequency band is low. In order to enhance the ratio, one general solution is applying the radio spectrum sharing scheme based on cognitive radio (CR) technology. The second users (SUs) must detect the unoccupied spectrum of primary users (PUs), and avoid the interference. It is possible to turn off the subcarriers in the cognitive system based on the spectrum sensing results using the NC-OFDM spectrum pool technology. However, some radiated power of other subcarriers within the PU’s band may still influence the authorized users’work. Therefore, the research of suppression algorithm of OFDM sidelobe interference is necessary.In this dissertation, a spectrum sharing technology based on CR has been proposed firstly. This technology retains the communication format with 25 kHz bandwidth in the 230 MHz band, and divides the band into a plurality of resource groups for spectrum sensing, so as to avoid interference in the occupied spectrum and achieve coexistence among multi-systems. In addition, some coexistence indicators based on the spectrum-sharing scheme, used to ensure the reliability for the authorized users and cognitive users, have been proposed as well.Secondly, the spectrum pooling technology-based NC-OFDM, and the principles and solutions of sidelobes interference has been introduced. Two active interference cancellation (AIC) methods which used to suppress the sidelobes in OFDM systems have been deeply studied. For the conventional AIC algorithms, because the cycle prefix will degrade the notching performance, a method of adding a window has been presented to solve this problem. The simulation results have been given to demonstrate the performances of this method. Then the power spectral density of active interference cancellation algorithms (PSD-AIC) model has been simulated, and an algorithm called α-PSD-AIC has been proposed to reduce the power glitch of cancellation subcarriers. Comparing with the existed optimization algorithms, this algorithm has about 5 dB improvements for the notch depth with the same power of cancellation subcarriers.Finally, two schemes used to verify the optimization algorithms based on the system coexistence indicators are proposed. The first scheme is the simulation of the broadband OFDM signal and discrete single-carrier narrowband signal in 230 MHz band using System Vue software, which can realize digital modulation, low pass filtering molding, conversion and power amplification, the corresponding demodulation process, and analysis of the bits error ratio (BER) of primary user signals; The second is the building of a semi-physical simulation platform, which includes digital radio transceivers, signal source and other hardware equipment to simulate the actual work environment. The semi-physical simulation results show that when the slot width equals to 8 subcarriers (64 kHz), the power at the slot is about-51.94 dBm which is less than the standard test result-46 dBm (reserved bandwidth of 75 kHz). The interference immunity and bandwidth efficiency have been significantly improved.