There is a continuous demand for increasing wireless access broadband services to the end users, especially with widespread high quality mobile devices. The Internet mobile applications and multimedia services are constantly hungry for broadband wireless bandwidth. In order to overcome this bandwidth limitation, a frequency band (57-64 GHz) has recently been assigned for short range indoor wireless broadband signals due to the large available bandwidth. However, the transmission at this band is limited to a few meters due to the high atmospheric absorption loss. Radio over Fiber (RoF) technology was considered an efficient solution to extend the distribution range and wireless capacity services. This chapter presents an introduction to RoF technology and its basic required optical components for indoor short range wireless millimeter waves (mm-waves). The limiting factors of RoF and its impairments are also described. Moreover, optical mm-wave generation solutions are explained and followed by the recent optical 60GHz activities and upcoming research areas such as THz and optical wireless.
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There is a global interest in wireless access broadband services based on optical fibers which provide a huge bandwidth needed for Internet users. Fiber to the home/premises (FTTH/FTTP) is also getting more and more attention to provide an ultimate solution for delivering different services to the customers’ premises. A FTTH network constitutes a fiber-based network, connecting a large number of end user to a central point. In the future, the access bitrate requirements will soon expected to increase more than 10Gbps (IDate Consulting and Reserach, 2013).
Wireless broadband services for the last few meters have also attracted much interest from many academic researchers and many companies such as Panasonic, Samsung, LG, and Toshiba. Services and multimedia applications such as Internet video, video communication, and video on demand are now available and need much greater bandwidth than that is offered today by available wireless channels. At the same time, new services such as high definition television (HDTV) and interactive video have been developed and are becoming commercially available in many countries (“WirelessHD Consortium,” 2013). These applications and services drive the need for new wireless connections that can carry the increased bitrates inside homes, or buildings. According to Edholm’s law, the wireless speed is being doubled for every 18 months over the last 25 years (Cherry, 2004). Therefore, in the next ten years, it is expected to reach to tens of Gbps. The use of 60 GHz radio techniques has become an enabler technology for many gigabit indoor applications that are constrained at lower frequency bands. These applications involve uncompressed Wireless HD streaming to wireless screens, wireless gigabit Ethernet that allows bidirectional Ethernet traffic and wireless docking stations that allow multiple peripherals to be connected without plugging and unplugging. A special frequency band in the 60 GHz has been globally allocated with 7 GHz of continuous spectrum for unlicensed use. The high path loss and the atmospheric absorption around 60 GHz make this band suitable for short range communication which mainly takes the form of the wireless local area network (WLAN), the wireless personal area network (WPAN), and the wireless body area network (WBAN). In addition, the short range coverage provides the cells with high security, anti-interference ability, and more densely packed communication links. The high available bandwidth and short range wireless signals enable broadband wireless access for in-building application such as HDTV and other multimedia services.
The combination of wireless and fiber optics was first introduced in the early 1980s for US military applications. This has been known as radio over fiber (RoF) technology and used also for RF distribution in cordless and mobile communication. The conventional way of RF signal distributions were transported via bulky copper cables and waveguides where all high frequency elements of a system have to be placed together to minimize the RF losses. The advantages of the low fiber losses, large bandwidth, and light weight features have enabled the optical fiber as an efficient transmission medium for transporting high frequency radio signals. Following this, many research centers and scientists across the world have developed new techniques to send wireless signals over fiber. RoF systems are now being used in many RF applications for transporting the radio signal from a central office (CO) to a remote antenna site such as cellular networks, indoor distributed antenna systems, and WLANs illustrated in Figure 1. The general RoF system is comprised of central location where the radio signal is generated and then distributed to a number of remote base stations using optical fibers in the building as shown in the Figure 1. Therefore, the most of the expensive and high frequency equipment have to be located at the central station where coding, modulation, multiplexing, and up-conversion are happening. Whereas, the remote antenna units (RAUs) should be simple, small in size, light and low cost (Jianjun et al., 2010).
Figure 1. Illustration diagram for fiber network distribution