Performance of Multicarrier CDMA Rake System over Rayleigh Fading Channel

Based on the theory of multicarrier(MC) technique and the Rake receiver, a multicarrier DS-CDMA Rake system is proposed, where a data sequence multiplied by a spreading sequence modulates multiple carriers. The receiver provides a Rake for each subcarrier, and the outputs of the Rakes are combined by a maximal-ratio combiner. The average probability of error of the system is derived from an uncorrelated subcarrier and frequency-selective fading channel model. The system performances are evaluated over Rayleigh fading channel with an exponential multipath intensity profile(MIP) and with a rectangular MIP, respectively, when multipath interference is present. It is found that this kind of model has larger superiority in an exponential MIP than in a rectangular MIP.

Small Signal Circuit Model of Double Photodiodes

The transmission delay of photogenerated carriers in a CMOS-process-compatible double photodiode (DPD) is analyzed by using device simulation.The DPD small signal equivalent circuit model which includes transmission delay of photogenerated carriers is given.From analysis on the frequency domain of the circuit model the device has two poles.One has the relationship with junction capacitance and the DPD’s load,the other with the depth and the doping concentration of the N-well in the DPD.Different depth of the N-well and different area of the DPDs with bandwidth were compared.The analysis results are important to design the high speed DPDs.

Threshold Current Characteristics of Intracavity-contacted Vertical-cavity Surface-emitting Laser

Threshold current characteristics of intracavity-contacted oxide-confined vertical-cavity surface-emitting laser had been investigated in detail. Threshold current characteristics not only were depended on the size of oxide-aperture, but also were also strongly affected by the mismatch of its lasing mode and gain peak. For the same degree detuning of the gain peak and lasing mode at room temperature, the threshold current was approximately proportional to the square of the oxide-aperture diameter of above 5μm. For the same oxide-aperture device, the larger the detuning degree of the lasing mode shifted to the shorter wavelength of the gain peak at room temperature was, the lower the minimum threshold current was. The wavelengths of the lasing mode and gain peak were ±N×10nm detuning at 300K, The temperature of the minimum threshold current was changed to be about ±N×40K(N real number). The calculated results were consistent with the experimental ones.

Strip Waveguide Directional Coupling Modulator with Equivalent Refractive Index

The equivalent refractive index（ERI） method is employed to analyze the function of the strip waveguide directional coupling modulator（SWM）. Through deducing the diagnostic equation of the Exmn mode of the four-layer media film waveguide equivalent to the SWM,the transmission constant of the symmetrical mode of the positive phase and negative one and the coupling length of powerful transference are obtained. The veracity of ERI is validated with the example of Ex11 basal mode under conditions of comparing the three results of ERI,EIM and Marcatili.