ABSTRAm This paper describes an rf fiber-optic antenna remoting system designed to COMeCt a base station to a remote cell site with up to six sectors. This system has two major advantages over the current transmission systems using T1 lines or some other form of radio transmission. First, cost savings are realized only rf equipment, such as power amplifiers for the downlink and low noise amplifiers for the uplink, is required at the remote site, resulting in a considerable reduction in the physical size of remote cell site equipment. Thus, it is possible to house the entire remote cell site equipment in a small enclosure mounted at the base of the antenna supporting structure, resulting in great savings in real estate and building costs. Second, performance is enhanced: with the use of fiber-optic antenna remoting, all the system control functions and diversity management can be performed in one central location. In this paper, an entire fiber-optic link, from rf input at the laser to the rf output of the photodetector, is treated as a single rf component. The expressions for its gain and noise figure are derived. These expressions were then used in the cascading formula to predict the overall system performance when additional rf components, such as mixers and amplifers, were cascaded with the fiberoptic link. A discussion of the selection of intermediate frequencies for minimum intermodulation products was presented. Measured performance and curves for design tradeoffs were also included. INTRODUCI'IONIn a cellular mobile communication system, the coverage area is divided into cells, where the transmitting and receiving antennas and associated equipment are located. Each base station controls a number of cells through an interconnecting network of high-speed data and voice links between cells and the base station. Currently, T1 lines, 800-MHz radio links, or microwave radio links [I] are used between the base station and the cells. As traffic increases, a large cell may be split into smaller cells, requiring additional high-speed links to complete the network. In the present cellular mobile phone systems 121 , a data bank is installed at each end of the T1 carrier. The data bank converts 20 voice channels along with system control data into a 1.544 Mb/s data stream for transmitting by a TI cable. A reverse process is performed at the other end. The demultiplexed voice channels are then sent to the radio frame for final radiation by an antenna. A similar process is used for receiving. For a sixsector site supporting 90 radio channels (15 radio channels per sector], 4 '/z T1 cables are required for each direction. The disadvantage of using T1 cables is the large leasing costs. The microwave link works on the same principle as the T1 cables except that the cables are replaced by a modulated microwave carrier, and free space is used as the transmission medium. Though it has the capacity to transmit as many as 900 channels, it is subjected to the constraints of frequency coordination and outage due to multipath. Thi...
A cost-effective chromatic dispersion (CD) estimation method is proposed, which is based on the delay-tap sampling (DTS) technique in combination with periodic training sequences (PTS). By performing equivalent sampling of PTS, DTS-based CD estimation at ultra-low sampling rate can be realized, significantly reducing the cost and high-speed requirements of analog to digital converters (ADCs). In contrast to the existing Nyquist DTS-based CD estimation method, we construct the CD lookup table in the CD over-compensated region, which can be suitable for a dynamic range of OSNR conditions. The CD lookup table built from the simulation can be used in the experimental system with similar configurations directly, indicating that the suggested method is reasonable and highly feasible. Besides, with only 1.25 GSa/s sampling rate of ADCs (about 1/30 of the Nyquist sampling rate which is 40.28 GSa/s), both 20.14 GBaud quadrature-phase-shift-keying (QPSK) simulation and experimental systems demonstrate the feasibility of the method, with a 28 ps/nm maximum CD estimation error for the simulation and a 35 ps/nm maximum CD estimation error for the experiment when OSNR is fixed to 18 dB. Furthermore, we also investigate the robustness of our method under the condition of different amplifier spontaneous emission (ASE) noise and nonlinear noise. The proposed method shows great potential for making a remarkable cost reduction in CD monitoring. INDEX TERMS Metrology, chromatic dispersion, fiber optics, fiber nonlinear optics.
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