Transparent transport of wireless communication signals in radio-over-fibre systems

Abstract

The evolution of current wireless access communication networks, especially inside buildings, moves towards higher microwave carrier frequencies in order to support the ever-growing data traffic volumes. This causes significant infrastructure cost increments due to the complexity and increased number of antenna sites needed for a certain area of coverage. Radio-over-Fibre (RoF) distribution antenna systems can reduce costs by means of consolidating the radio access control and signal processing at a central site (CS), and delivering the radio signals transparently to the antenna sites (ASs). Employing the Optical Frequency Multiplication (OFM) technique, we show experimentally the feasibility of delivering different radio signal modulations (e.g., 16QAM, 64-QAM) with different data rates (from 24 to 78 Mbps) at 17.8 GHz, while maintaining the required optical link transparency. Additionally, the medium access control (MAC), duplexing schemes and multiple access methods of the different wireless systems put key requirements on the design of radioover-fibre distribution networks, since the additional propagation delay inserted by the optical link has to be considered from the central controller for supporting such systems. Centrally-scheduled radio MAC schemes, like the ones defined in IEEE 802.16, enable the accommodation of the fibre link between the CS and the AS in exchange for a reduction in the radio bandwidth utilization, which decreases linearly with the fibre length. Introduction Radio-over-Fibre (RoF) distribution antenna systems have been identified as a promising option for the access architecture of the emerging wireless access communication networks, specially inside buildings, as a means of reducing infrastructure cost and antenna site complexity, and generating high microwave carrier frequencies optically. In this approach, the insertion of an optical link between the central station (CS) and the antenna site (AS) lies within the physical layer of the wireless system to be supported, independently of the radio-over-fibre technique employed (Fig. 1). The optical distribution system behaves as an analogue transmission system that shall not modify the nature of the radio signal format, but deliver it with the best possible accuracy at the remote antenna location, which acts as a transparent analogue repeater-interface from the optical medium to the radio medium. Since the radio control is located at the central site, a remote radio medium access control has to be performed, thus converting the optical domain in an extension of the radio domain access. Therefore, the radio characteristics and the wireless system requirements set the boundaries and limitations for the optical distribution system design.