Parameter Estimation Of Time-frequency Overlapped Signals For Underlay Spectrum Sharing

Underlay mode in cognitive radio plays a promising role to effective and reliable spectrum utilization by detecting the real-time spectrum condition and adopting spectrum allocation intelligently.SUs access the spectrum only if the interference caused by them remains below an acceptable level to prevent the PUs transmission from destructive interference.PUs and SUs can co-exist at the same spectrum,so the communication signals in Underlay are time-frequency overlapped.Underlay is now catching more and more attention with the development of novel technology and growing demand to spectrum.Parameter estimation including carrier frequency and symbol rate which has significant influence to the measurement of interference temperature,can provide reference to subtle feature analysis,modulation type identification,and signal demodulation.This paper is concerned with the estimation of carrier frequency and symbol rate for signals in Underlay spectrum sharing system.The whole work is orgnized as follows:In order to solve the problem estimating carrier frequency of time-frequency overlapped MASK for Underlay spectrum sharing signals,a novel method based on diagonal slice spectra of cyclic bispectrum is proposed.Firstly,after analyzing the diagonal slice spectra of cyclic bispectrum of MASK theoretically,information relating to carrier frequency in the f=0 slice is found.Then peak extraction is carried out from f=0slice by use of norm theory and adaptive threshold which,as a result,eliminates the clutter lines caused by noise and other interference to a large extent.Finally,carrier frequency belonging to each component is obtained respectivly.The Cramer-Rao Bound(CRB)is also developed Mathematically for carrier frequency estimation of time-frequency overlapped signals to characterize its estimation performance.Simulation results show that the normalized mean square error(NMSE)is only10-6when SNR is-9d B.The method we proposed performs well in the estimation of carrier frequency,though it is time-frequency overlapped.The author also devotes to symbol rate estimation of time-frequency overlapped MPSK in Underlay spectrum sharing.Single MPSK's Teager Energy Operator(TEO)is studied first,and is found to have impulse information relating to symbol rate.After continous anlysis of overlapped MPSK's TEO,we draw the conclusion that symbol rates of time-frequency overlapped signals can be detected by the change of TEO.Finally,a scheme estimating symbol rates of overlapped MPSK respectively based on TEO is proposed,which maps the signals into the energy domain since they are overlapped in time and frequency domain.CRB of overlapped MPSK's symbol rate estimation is also derived and compared with the simulation results,which nearly matches the theoretically predicted lower limits.The scheme proposed needs no prio knowledge of carrier frequency and is also computational efficient.The estimation performance of proposed algorithm is testified by sumulations which finally confirms our method's robustness to SNR,the spectrum overlapped ratio,and power ratio.