Work On Radio Over Fiber Wireless Access System

With the information step of the world, setting up the Ubiquitous Network Society (UNS) is proposed and it is made of the most important national plan by many countries in the world. Now since the rapid growth of wireless internet data services, the demand for RF bandwitdth is increasing. Due to the limited availability of the RF band, wireless access systems would be moved to millimeter-wave band. This trend leads to micro/picocell systems. On the other hand, the further access network should have the ability to support of several different radio standards simultaneous. Since China has been embarking on U-China program, wireless high-speed data transmission and in-building coverage will be the key problems that must be resolved. Microwave radio-frequency transport over fiber is a novel approach which allows the radio functionality of several base stations to be integrated in a centralized headend unit. It offers a wireless access with a radio-independent fiber access network. A common problem of the optical transmissions is the link nonlinearity, especially the laser diode nonlinearity. The nonlinearity of the microcavity semiconductor laser is analyzed and the network architecture based radio over fiber for wireless telemedicine monitoring system is designed in this dissertation. The works included in this dissertation are:Nonlinear effect of microcavity semiconductor laser is analyzed using Volterra transfer function in analog modulation. Effects of the modulation frequency, bias current, the photon lifetime, spontaneous emission factor and spontaneous emission lifetime on third harmonic and third-order intermodulation distortions are investigated. The results show that nonlinear effect depends on spontaneous emission parameters. It is proven that control of nonlinear effect, expandation of modulation frequency and improvement of performance and application of ROF system based on microcavity semiconductor laser can be achieved by manipulating the spontaneous emission parameters of vertical cavity surface emitting lasers.The second harmonic, third harmonic and third-order intermodulation distortions of vertical cavity surface emitting laser (VCSEL) at analog modulation are calculated using Volterra transfer function with the help of the rate equations. Effects of the mirror reflectivity, the active material thickness and the optical confine factor on SHD, THD and IMD3 of VCSEL are analyzed considering the microcavity effects. The results show that high mirror reflectivity, low thickness of active material and small optical confine factor can decrease the harmonic and intermodulation distortions of VCSEL. The dependence of modulation response of a vertical cavity surface emitting semiconductor laser on its spontaneous parameters is investigated subject to direct current modulation. And the nonlinear distortion of Orthogonal Frequency-Division Multiplex (OFDM) signals caused by semiconductor laser in a Radio-over-Fiber link is also analyzed. The expression of in-band noise due to nonlinear distortion is then derived. Moreover, the relation of carrier-to-noise ratio with optical modulation index, average optical power is analyzed. The analytical method is applicable for nonlinearity analysis.A radio over fiber network has been proposed for providing wireless access to telemedicine services. The data uplink is of primary concern in this proposed architecture. Transmitter module, which consists of many tuning-transmitter based on wavelength-division multiplexing (WDM) technology, is used for the radio signal distribution so that the BS is simple. It has been proved that this architecture is economical and suitable for telemedicine system..