| CRAHNs have spectrum sensing function,can avoid interference and crowded frequency bands,are convenient and fast for networking,have strong resistance to damage,and do not depend on network infrastructure.Disaster relief,field operations,and military applications have good application prospects.This dissertation studies the adaptive scheme based on OFDM modulation in the physical layer of CRAHN network,proposes a set of physical layer adaptive scheme based on OFDM modulation,and implements an important module for FPGA implementation.In this paper,the research status of cognitive radio Ad-Hoc network and the development of adaptive OFDM technology are introduced.Then the principle,technical difficulties and some classical algorithms of OFDM adaptive modulation are introduced.After that,this paper introduces the research progresses of this thesis on channel coding,puts forward the main channel coding method using Turbo coding as the OFDM adaptive research scheme,and carries out FPGA implementation and simulation testing.Then,based on the design idea of cross-layer,this dissertation develops a scheme of OFDM adaptive communication system design by using FPGA +MCU hardware platform,studies and designs the overall framework of this system,and gives the physical layer Protocol Data Unit(PPDU)format and MAC layer frame structure.Finally,based on all of the above preliminary work,this paper combines the actual situation of FPGA development platform,using Verilog HDL,select the Altera company provides,with high performance,low power consumption,low cost Cyclone III series,this The architecture and some core modules of the overall system of the thesis are implemented in detail in FPGA.These core modules include: channel coding module,constellation mapping module,pilot insertion module,insertion cyclic prefix module,leading sequence structure and modulation module And interpolation filter module.After that,we also simulated the core modules.The simulation results show that the system has a certain reliability and meets the design requirements.The implemented system can receive the MAC data frame from the MAC layer and use our OFDM adaptive modulator to modulate the data according to the adaptive parameters in the MAC data frame structure.The adaptive transmission under wireless Ad-Hoc network with multipath Doppler is realized,which isvery flexible in practical application. |
