Research On Subband Frequency Hopping OFDM System Based On Cognition

In this thesis,the communication system focuses on a wireless communication network with strong narrow-band interference in the scenario.The network has a star topology,and all sub-nodes communicate directly with the central node,and there is almost no randomness in the traffic processes in the network.The central node of the network has the function of interference cognition.This system is mainly designed around to suppress narrow-band interference in the communication environment.At the same time,the system must meet the anti-interception demand.In order to solve the communication problem in this special scenario,this thesis designs a sub-band frequency hopping OFDM(Orthogonal Frequency Division Multiplexing)system based on interference cognition.A two-channel structure system is designed in this thesis.The control channel achieves anti-interference,low-intercepted and reliable transmission with low transmission power and low transmission rate.The traffic channel implements high-rate transmission through sub-band frequency hopping OFDM based on interference cognition,which improves the anti-interference and anti-interception abilities of this system.The work of this thesis is listed as follows:1.The sub-band frequency hopping OFDM system and its key technical solutions have been designed,including pilot signal design,frequency hopping sequence design and control channel protocol design.2.Sub-band frequency hopping OFDM system platform is established.Each function module is completed to ensure the correctness of the simulation platform and the effectiveness of the simulation results with certain simulation assumptions and simulation parameters.3.With the help of interference cognition information provided by the center node,some anti-interference technology schemes in sub-band frequency hopping OFDM system are further designed and studied,including subcarrier adaptive scheduling and frequency hopping sequence selection based on channel capacity.This paper simulates the impact of different narrow-band interference on the system performance,which can be concluded that it is difficult for OFDM system to meet practical communication requirements in narrow-band interference environment with some bandwidth and power degree.Then the paper simulates the performance of the adaptive subcarrier scheduling algorithm.The subcarrier scheduling makes the system performance in narrow-band interference environment approach none-interference OFDM system.Then two frequency hopping sequence selection algorithms are designed,and the effect of different frequency hopping sequence selection algorithms to OFDM system performance are simulated and evaluated.The frequency hopping sequence selection algorithm based on channel capacity standard has better anti-interference performance and higher system capacity compared with traditional random frequency hopping sequence selection,while frequency hopping sequence selection algorithm based on LRU(Least Recently Used)effectively guarantee the randomness of hopping sequence with almost little loss of performance,compared with frequency hopping sequence selection algorithm based on maximum channel capacity,which ensures a better anti-interception ability of system.