Cooperative Spectrum Sensing over Generalized Fading Channels Based on Energy Detection

This paper analyzes the unified performance of energy detection(ED) of spectrum sensing(SS) over generalized fading channels in cognitive radios(CRs). The detective performance of SS will be obviously affected by fading channels among communication nodes, and ED has the advantages of fast implementation, no requirement of priori received information and low complexity, so it is meaningful to investigate ED over various fading channels. The probability density function(p.d.f.) of α-κ-μ distribution is derived to evaluate energy efficiency for sensing systems.The detection probability with Marcum-Q function has been derived and the close-form expressions with moment generating function(MGF) method are deduced to achieve SS.Furthermore, exact closed-form analytic expressions for average area under the receiver operating characteristics curve( AUC) also have been deduced to analyze the performance characteristics of ED over α-κ-μ fading channels.Besides, cooperative spectrum sensing(CSS) with diversity reception has been applied to improve the detection accuracy and mitigate the shadowed fading features with OR-rule. At last, the results show that the detection capacity of ED will be evidently affected by α-κ-μ fading channels, but appropriate channel parameters can improve sensing performance. In addition, the establishedED-fading pattern is approved by simulations,and it can significantly enhance the detection performance of proposed algorithms.

The Study on Heterodyne and Phase Diversity Coherent Optical Fiber Communication Systems and Their Components

The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.