Study On Dynamic Spectrum Access Based Transform Domain Communication System And Related Key Technologies

With the rapid development of wireless communication technologies, broadbandmultimedia technologies and internet technologies, wireless communication servicesincrease continuously. These lead to the large amount of the electromagneticspectrum resources. However, the existing spectrum resources have not been fullyutilized and there are largely unoccupied frequency bands among the spectrum mostof the time and the space. The traditional wireless communication systems aredesigned based on the system framework of independent resources optimization andstatic spectrum management mode. On this basis, the developments of the relatedtechnologies have been restricted gradually and the spectrum utilization cannot beimproved. To improve the using efficiency of radio spectrum fundamentally and tosolve the constraints of the existing technologies on the utilization of the limitedspectrum resources, a new series of broadband wireless communication theories mustbe established which can acquire the usage of the spectrum and wait for anopportunity to select the unoccupied frequency bands to communicate without anyinterference to other users.As a new intelligent communication technology, CR is an effective solution tothe problems of limited spectrum resources and the low spectrum efficiency since itcan detect the unoccupied frequency bands in the authorized spectrum. According tothe definition of CR, it can sense and monitor the varying radio transmissionenvironment and exploit the methodology of understanding-by-building to learn fromthe environment. The CR equipment adapts the statistical variations in the incomingRF stimuli by modifying the specific parameters of the system in real-time. The primary objectives of CR are highly reliable communications whenever and whereverneeded and efficient utilization of the radio spectrum. Hence, CR technology providesa new spectrum managing mode for the communication managers and operators and avariety of CR based DSA technologies is emerging.As one of the DSA technologies of CR, TDCS has been investigated by scholarsin recent decades. On one hand, TDCS can sense the rapid changes of theelectromagnetic environment and find the spectrum holes and use them timely. Onthe other hand, TDCS verifies the system parameters adaptively and designs thecommunication waveform with the properties of low property of intercept and lowproperty of detect according to the statistical characteristics of the communicationenvironment. It accomplishes the DSA and the share of radio spectrum resourceswithout interfering with other users.From the perspective of DSA, this dissertation studies the fundamental theoriesand the rekated key technologies of TDCS which includes the spectrum access andbasic function generation algorithms, the phase coding algorithms, the modulationand demodulation algorithms and the signal detection algorithms in multipath fadingchannels. The main work and research results are listed as follows:(1) We describe the basic framework of the TDCS transceiver systematically andelaborate the function and principle of each module. On this basis, we study themodulation and demodulation techniques of TDCS. This dissertation derive themodels of the TDCS transmission signal and the related bit error rate based onantipodal signaling modulation, orthogonal modulation and biorthogonal modulation,respectively. The system performances of TDCS based on different modulationtechnologies are simulated and analyzed. Finally, the transmission rate and thebandwidth efficiency of the TDCS based on the multidimensional signalingmodulation are analyzed and discussed.(2) The spectrum access and basis function generation algorithms of TDCS arestudied. According to the types and features of the interference signal in the wireless communication environment, three algorithms are studied, which are based onwavelet transform, wavelet packet transform and fractional Fourier transformrespectively. The system performances of TDCS based on different algorithms areanalyzed and verified in the AWGN channel. Finally the channel capacity of TDCS isderived and the channel capacity and the efficiency of frequency bands are analyzedand compared under different interference conditions.(3) The phase coding algorithms and the multiple access capability of TDCS arestudied. Firstly, the principle of the random phase coding is elaborated. Thecorrelation functions of the basic function are derived and the multiple accesscapability is analyzed. Under different spectrum access conditions, the systemperformances of TDCS for single user communication and multiuser communicationare simulated and analyzed. Furthermore, a TDCS scheme based on spread phasecoding technology is proposed. The principle of the SPC-TDCS is introduced; thespread phase parameters and the system performances of SPC-TDCS are studied.Finally, the multiple access capabilities of SPC-TDCS and the conventional TDCSbased on random phase coding are compared and analyzed.(4) The signal detection algorithms of TDCS under multipath fading channel arestudied. Firstly, the multipath fading channel is modeled and the statistical features ofthe channel are analyzed. According to the features of the channel, the TDCS signaldetection algorithms based on channel equalization and cyclic prefix algorithm areproposed respectively. The transceiver structures and signal designs based ondifferent detection algorithms are analyzed. Finally, the system performances ofTDCS based on the two algorithms are analyzed and verified in different multipathfading channels.In the end, we summarize the main works of the dissertation and discuss thepossible research works in the future.