Frequency Study Of Cognitive Radio System

At present, the utilization of the frequency resource in china shows a high degree of imbalance. On one hand, the interference problem is severe in the frequency bands which load heavy traffic. The variety of the communication devices and the overlap of the used spectrum caused the lack of related radio frequency, which poses great threat to the quality of the wireless communication services. On the other hand, there is plenty of frequency resource which bears little services, which causes great waste to the related frequency resources. Cognitive Radio, built on a Software-Defined Radio, is an intelligent wireless communication system that could be aware of its environment, and use the methodology of "understanding-by-building" to learn the environment, to efficiently improve the radio spectrum utilization and solve the problem of radio electromagnetic spectrum scarcity.Any wireless communication technique can't break away from the dependence of spectrum, and its practical performance and further development has a direct relationship with the spectrum allocation. In order to apply cognitive radio technology, we must select the appropriate frequency band and ensure the EMC between different wireless communication systems in the same geographical area for the maximum spectrum efficiency and utility.This thesis mainly studies on the appropriate frequency band of cognitive radio system under the existing frequency allocation standards of China. By comparing on the amounts of communication traffic of different frequency, and analyzing with characteristics of cognitive radio system, the suitable frequency bands:698-806MHz/2300-2400MHz are given. This thesis studies on the possible coexistence interference under different conditions between cognitive LTE system and digital TV system in the band 698-806MHz or radar system in the band 2300-2400MHz by theoretical analysis and Monte Carlo simulation analysis. According to the simulation results, the reasonable protection frequency bandwidth and isolation distances are given, and some useful methods of reducing the interference are proposed. On the basis of the main user in the band 2300-2400MHz: radar system, a new radar signal detection scheme is proposed. In this scheme, the radio signal is multiple cumulative detected at the cognitive LTE uplink time slot. And it effectively reduces the interference between different systems.This thesis is supported by National Science and Technology Major Project: The research of the key technologies in efficient use of spectrum based on WRC-11(2009ZX03007-004). It not only provides a useful basis for cognitive radio system spectrum allocation, but also provides technical analysis reserves for coexistence of multi-systems.