Abstract
The high capacity offered by the optical fiber, combined with the mobility and the flexibility of wireless access, either fixed or not, provides an efficient approach to alleviating the requirements posed by the envisaged provision of any-service, anytime and anywhere, next generation communication networks. The objective of this chapter is to present an overview of Radio-over-Fiber technology, as an emerging infrastructure for next generation, fiber-based, wireless access broadband networking. In particular, the fundamental concept of Radio-over-Fiber technology is reviewed and the partial components comprising it are discussed. Furthermore, the associated architectures are depicted and a short literature survey of trends and applications is considered.
TopIntroduction
Nowadays, it is well acknowledged that there has been a tremendous growth in communication technologies spanning from mobile telephony and wireless networks, to high definition television and satellite communications. Additionally, a great number of standards has been developed, setting the requirements and the specifications for this rapid expansion (ITU, 2002; IEEE, 1999; ETSI, 2001; IEEE, 2004). Despite this fact, there is an increased necessity for integration or, otherwise, collaboration of heterogeneous technologies, especially for mobile and wireless communications, into a universal backbone network being capable of providing mobile, broadband, reliable and ever-present services to end users. In other words, this rapid expansion is characterized by the ever increasing requirement for faster and mobile communications with enhanced Quality of Service (QoS). Next generation networks (NGNs) should have the ability to offer mobile multimedia (video, audio and Internet) services to end users, anytime and anywhere (Kim, 2003; Agrawal, 2004; Arroyo-Fernandez, 2003; Arroyo-Fernandez, 2004).
The issues of mobility and multimedia services are strictly connected with the development of wireless broadband networks and network access technologies. An overview of the development of past, current and future wireless communication systems is depicted in Figure 1. Compared to cable networks, broadband wireless networks offer not only user mobility, but also reduced installation and maintenance cost. On the other hand, cable access is still superior in terms of high-speed data delivery. Therefore, the potential of accomplishing similar capacities in wireless networks is of great interest. However, the development of advanced wireless broadband networks, being able to efficiently handle (in terms of NGN services) radio frequency (RF) signals at the mm-wave bands, entails many inherent difficulties that cannot be solved straightforwardly through mainstream microwave technology. In this new communication scenery, Radio-over-Fiber (RoF) technology has an augmented potential to be adopted as an emerging infrastructure for broadband, high-speed mobile/wireless communications.
Figure 1. The Mobile/Wireless communications landscape in terms of data rates, frequency bands and the most common applications
Key Terms in this Chapter
Central Station (CS): In Radio over Fiber, the Central Station is responsible for the generation and distribution of mm-wave signals and the general management of a group of Base Stations. The CS is connected to each BS through optical fiber. The CS is also known as Central Site or Control Station.
Base Station (BS): In Radio over Fiber topology, the Base Station is every individual access point to the underlying network, acting as the radio interface for the user and the optical interface for the network. The BS is also referred to as Remote Station or Remote Antenna Unit.
Sub-Carrier Multiplexing (SCM): A multiplexing scheme where each individual baseband signal is allocated to a different RF subcarrier.
Spurious Free Dynamic Range (SFDR): It refers to the dynamic range achieved up to the point where the signal power causes the intermodulation products to reach the noise power level or the noise floor.
Relative Intensity Noise (RIN): Intrinsic noise of a Laser diode due to spontaneous emission and relaxation oscillation.
Intensity Modulation / Direct Detection (IM/DD): A modulation scheme where the intensity of an optical source is modulated by the RF or mm-wave signal. Demodulation is achieved through direct detection of the optical carrier and conversion using a photodetector.
Orthogonal Frequency Division Multiple Access (OFDMA): Is an extension of OFDM for the case of multiuser systems for an efficient utilization of the spectrum resources. For example, OFDMA can be used as a multiple access scheme where groups of the subcarriers are allocated to different users.
Code Division Multiple Access (CDMA): A spread spectrum modulation technique and multiple access scheme as well, where each user or terminal is assigned a different (spreading) codeword.
Wavelength Division Multiplexing (WDM): A multiplexing scheme where each individual mm-wave signal or any information signal is assigned to a different wavelength optical source.