Implementation Of Cognitive OFDM Multiple Access Based On USRP

In recent years,with the rapid development of wireless communication technology,and the increasing demand for communication speed,the demand for spectrum and bandwidth of wireless communication is also increasing gradually.However,the traditional frequency resource allocation by way of a fixed spectrum assignment will reduce the utilization rate of the frequency,resulting in a large number of frequency resources not used in a lot of time,has become a bottleneck restricting the development of the next generation of wireless communication network.With the development of software defined radio,Dr.Joseph Mitola developed the concept of Cognitive Radio,a programmable and dynamically configured radio,which selects the best wireless channel nearby,also makes people see a method to solve the scarcity of frequency resource.Under the circumstances that unlicensed users does not affect the licensed user,temporarily enter the licensed band for communication,through the collection of spectrum pool information,then analysis and reasoning,according to the result of communication,complete complex operations in a time slot,finish the communication timely and avoid the licensed user.Based on the cognitive algorithm,the orthogonal frequency division multiplexing(OFDM)technology with high speed transmission,efficient spectrum utilization and anti multipath and other advantages,has been adopted in various standards in recent years,and because of the carrier itself configuration flexibility,can be automatically adjusted according to the available bandwidth,dynamic spectrum allocation will be used for secondary users,so this paper researches and implements a cognitive module OFDM multiple access technology,achieve the cognitive access with a spectrum sensing,avoidance and communication process.This paper is aiming at the problem of low rate of radio frequency and usage of scarce spectrum resources,developed a method based on energy detection to idle sub-channels,then using OFDM blind detection to distinguish between licensed and unlicensed users,and run on the universal software radio peripheral(USRP)platform.The signal synchronization on the physical layer is accomplished by maximum likelihood(ML)estimation,the slot ALOHA access mechanism is used and avoid the licensed user during the transmission on the Media Access Control(MAC)layer,and gives the simulation analysis of system throughput performance while the primary user is presented.The experimental results show that the proposed method can improve the spectral efficiency of a given frequency band and realize the efficient utilization of the spectrum.