MICROW AVE SIGNAL GENERATION IN OPTICAL DOMAIN FOR RADIO OVER OPTICAL FIBER BASED BROADBAND WIRELESS ACCESS

Abstract

Bandwidth requirements due to media applications are increasing and Radio over Fiber (ROF) is becoming an attractive choice for design and implementation of high speed wireless network. This technology increases the overall bandwidth and total number of users in a wireless system. Radio signal can be generated in electrical domain; however, opt ical generation is more efficient as it overcomes the electrical bandwidth limitations. In this thesis, radio signal has been generated in optical domain by beating two closely spaced wavelengths. Two lasers are used in this scheme and the output is Amplitude Shift Keying (ASK) signal. Optical switches have been used to implement the frequency hopping and the operating frequency of the scheme can be changed by controlling the optical switch. The DWDM ROF (Dense Wave Division Multiplexed Radio over Fiber) system with capability to change the operating frequency is presented. DWDM ring has also been simulated with frequency plan to assign the wavelength in DWDM ROF scenario. Performance analysis of the system is done in the presence of different transmissio n impairment and optimization is done to achieve the best performance of the system. A signal with data rate of 4 Gbps has been successfully transmitted up to distance of 125 km. Wavelength used for beating and generation of the down link signal is reused at Remote Antenna Unit (RAU). Erbium Doped Fiber Amplifier (EDFA) has been used to amplify the light signal; different algorithms have been developed and simulated to find the exact value of EDFA gain and number of amplifiers to be used. These algorithms can provide the exact placement of EDFAs in the DWDM ring. It has been verified that if gain is properly adjusted and EDFAs are properly placed, the Continuous Wave (CW) can be reused and uplink signal can be transmitted iiito Central Station (CS) using this wavelength. After simulation of the algorithm, DWDM ring is simulated to verify the algorithms and bit error rate and eye diagram analysis is done to compare the performance of the system. Ultra-wide band (UWB) signals have been generated using optical biasing, optical delay line and optical subtractor. UWB impulses are generated and their bandwidth has been optimized by controlling the relative delay. DWDM UWB rings are simulated and single UWB generator with capability to generate monocycle; doublet and triplet are presented. The effects of nonlinearities on UWB pulses are also studied. Multiple access technique is incorporated with this solution. A Next Generation Multi Service Access Gateway (NG-MSAG) is presented for Radio over Fiber. The architecture of this NG-MSAG allows the convergence of fixed, wireless, voice and data services. This convergence will decrease the overall deployment and operational cost of telecom operators especially those operators which are new in the industry and interested in deploying nation-wide fixed and wireless networks. The transport layer is based on IP/DWDM, Radio layer on ROF and services core is based on Next Generation Networks (NGN). The connectivity of NG-MSAG with telecom node is simulated. The Performance analysis is conducted and results are optimized which reveal the best performance when dispersion is kept in the range of +2 to +4 ps/(nm.km).