A Survey of Current and Emerging Radio-over-fibre Technologies for Wireless Communications Applica- Tions

This is an extended and updated version of the invited paper given at the International Topical Meeting on Microwave Photonics, 2002 (MWP2002), in which current and emerging radio over fiber technologies for cellular communications applications were described. INTRODUCTION Radio over fiber has recently emerged as a useful technology for providing specialized coverage of wireless communications services. It was first proposed and demonstrated by Cooper et al [1] in 1990 and now accounts for a significant market size. This relatively ‘niche’ market is expected to grow significantly in the future as new radio over fiber technologies emerge and their applications become more diverse and less costly. This paper reviews the current applications and technologies in this field, and explains why radio over fiber is attractive to providers of wireless network infrastructure. Emerging applications, trends and technologies are then described, in an attempt to show that radio over fiber is poised to become the dominant access transmission technology for low-power wireless networks. RADIO OVER FIBER Radio over fiber uses analogue fiber optic links to transmit and distribute radio signals from a central location where the base stations are situated to a number of remote locations where the antennas are placed. The basic radio over fiber sub-system is a bi-directional analogue fiber optic link and consists of a laser / photodiode pair at the central site, a laser / photodiode pair at the remote site and one or more optical fibers linking the two sites. Figure 1 shows the component parts of this basic fiber optic sub-system. In the majority of cases, the laser is directly (intensity) modulated by the input RF signal and the photodiode employs direct detection; this type of link is referred to as intensity modulated direct detection (IMDD).IMDD links can have good wideband performance depending on the individual component specifications and are the simplest and most cost-effective of the available link types. Figure 2 shows the operating principle of the IMDD link. The RF input power applied to the laser input impedance causes a modulation of the laser bias current (I), which in turn modulates the intensity of the output light (L). This intensity modulated lightwave signal is transmitted across the optical fiber to the photodiode. In the photodiode, the modulated light creates a A SURVEY OF CURRENT AND EMERGING RADIO-OVER-FIBRE TECHNOLOGIES FOR WIRELESS COMMUNICATIONS APPLICATIONS Dr. David Wake Highlights: Radio over fiber is poised to become the dominant access transmission technology for low-power wireless networks Radio over fiber uses analogue fiber optic links to transmit and distribute radio signals from a central location where the base stations are situated to a number of remote locations where the antennas are placed Several new radio over fiber technologies and enhancements are emerging, ultimately aimed at reducing the cost of deployment and greatly extending the market appeal of Radio over Fiber systems One of the major benefits of using radio over fiber technology is the centralization of the base station processing and radio functions This benefit can be greatly enhanced if a switching fabric is used to connect the base stations to the head-end optical transceivers This approach allows capacity to be allocated dynamically, which means that fewer base station transceivers are required for a given grade of service This architecture also has the ability to reconfigure which base stations are connected to which antennas. This is important for situations where network operators need to add or remove service to specific customers These are the core value propositions of Microwave Photonics Inc. and are currently being developed at their Advanced Technology Centre