||With the explosive grow of modern technology, mobile devices along with high quality multi-media services have grown beyond imagination. In order to match the demand of high speed interactive multi-media mobile applications, improving wireless network capacity is considered great challenge to modern communication technology. The key points toward multi-gigabits communications are to increase bandwidth and spectral efficiency of communication system. Higher carrier frequency provides much more bandwidth. For instance, around 60-GHz band, 7 GHz bandwidth has been declared licensed-free by several countries. However, higher carrier frequency signal suffers high transmission loss in both conventional cable and air-link transmission and leads to a limitation on transmission distance. In this thesis, Radio-over-Fiber (RoF) system is used to distribute Orthogonal Frequency Division Multiplexing (OFDM) signal from central station (CS) to base station (BS). Taking advantage of the characteristic that subcarriers of OFDM signal are orthogonal to each other, the 7 GHz bandwidth can be used more efficiently. Moreover, high frequency signal can enjoy low transmission loss with utilizing fiber as transmission medium.|
Multiple-Input Multiple-Output (MIMO) technology is another critical technique to improve spectral efficiency. By adding numbers of transmitter and receiver antennas and deliver independent signal through each transmitter antenna, data throughput can be increased because of the reuse of spectrum at the same time. Our group has successfully demonstrated simple RoF system using intensity-modulation direct detection scheme using electrical-absorption modulator (EAM). Although the architecture was simple, the fiber transmission distance is limited to 500 m by strong dispersion induced power fading. The single-drive mach-zehnder modulator (SD-MZM) is used to replace the EAM for being a more efficient modulator for the system. By adjusting the signal frequency and beating carrier frequency appropriately, the fiber transmission distance can be extended. However, in order to avoid signal-to-signal beat interference (SSBI), the extended distance is only 4 km. In this thesis, the frequency arrangement is selected appropriately to reduce dispersion induced power fading and the fiber transmission distance is successfully extended to 12 km. The integration with MIMO technology and the use of bit-loading algorithm further improve the spectral efficiency and achieved utmost data rate of 56 Gb/s at back-to-back transmission.