**1. Introduction**

492 Wireless Communications and Networks – Recent Advances

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Today's communication network deployment is driven by the requirement to send, receive, hand off, and deliver voice, video, and data communications from one end-user to another. Current deployment strategies result in end-to-end networks composed of the interconnection of networks each of which can be classified as falling into one of three main categories of network: core, metropolitan and access network. Each component network of the end-to-end communication network performs different roles. Nowadays, the increase in the number and size of access networks is the biggest contributor to the rapid expansion of communication networks that transport information such as voice, video and data from one end-user to another one via wired, wireless, or converged wired and wireless technologies. Such services are commonly marketed collectively as a triple play service, a term which typically refers to the provision of high-speed Internet access, cable television, and telephone services over a single broadband connection. The metropolitan networks perform a key role in tripleplay service provision in delivering the service traffic to a multiplicity of access networks that provide service coverage across a clearly defined geographical area such as a city over fiber or wireless technologies infrastructure. The core networks or long haul networks are those parts of the end-to-end communication network that interconnect the metropolitan area networks. The core network infrastructure includes optical routers, switches, multiplexers and demultiplexers, used to deliver triple play service traffic to the metropolitan networks and route traffic from one metropolitan network to another.

Fig. 1, shows a simplified diagram of network connecting tripleplay service providers to end-users of the service. In this network, the uplink traffic from the end-users is input to the network via wireless or wired access network connections in the user's home. The packets associated with this traffic are multiplexed together and forwarded to the local metropolitan network for delivery to a long haul network for transporting to the service providers' access network and hence to the service provider. The downlink traffic from different service providers which is typically traffic corresponding to requested services is input to the network via local access network connections in the service provider premises. The downlink traffic from a particular access network is multiplexed together and delivered to the local metropolitan network for forwarding to a core network (or in some cases another metropolitan network) and hence to the end-users access networks for delivery to the end users. As many access networks are connected to a metropolitan network the traffic data rates throughout a metropolitan network are significantly higher than those throughout an access network. As many metropolitan networks feed traffic into a core network the traffic handling capabilities of a core network are significantly higher than those of a metropolitan network. The network traffic on core networks is expected to reach the order of hundreds exabytes in the near future, (Laskar et al., 2007). The rapidly changing face of networked communications has seen a continued growth in the need to transfer enormous amounts of information across large distances. A consequence of this is that technologies that are used extensively for transferring information such as coaxial cable, satellite, and microwave radio are rapidly running out of spare capacity, (Mcdonough, 2007).

Fig. 1. Near term future network capacity requirements.

Therefore, transportation of the traffic volumes that will be demanded by users in the near future will require significantly greater network transmission bandwidth than that provided by the current infrastructure. Consequently, in the near term each category of component network of existing end-to-end networks will face different and increasingly difficult challenges with respect to transmission speed, cost, interference, reliability, and delivery of the demanded traffic to or from end-users. Currently, super-broadband penetration and the on-going growth in the internet traffic to and from business and home users are placing a huge bandwidth demand on the existing infrastructure.

Broadband wireless sits at the confluence of two of the most remarkable growth stories of the telecommunication industry in recent years. Wireless and broadband have each enjoyed rapid mass-market adoption. Wireless mobile services grew from 11 million subscribers worldwide in 1990 to more than 5 billion by the end of 2010. The world's largest manufacturer of mobile phones has forecast that the number of mobile users accessing the internet via mobile broadband will grow to over 2 billion globally by the end 2014. Fixed broadband subscribers numbered only 57,000 in 1998 and rapidly increased to 555 million subscribers by the end of 2009. The number of fixed broadband subscribers is projected to exceed 720 million by 2015 despite the current economic situation, (OASE, 2010; ITU, 2011). The growth in the numbers of mobile telephone

network the traffic data rates throughout a metropolitan network are significantly higher than those throughout an access network. As many metropolitan networks feed traffic into a core network the traffic handling capabilities of a core network are significantly higher than those of a metropolitan network. The network traffic on core networks is expected to reach the order of hundreds exabytes in the near future, (Laskar et al., 2007). The rapidly changing face of networked communications has seen a continued growth in the need to transfer enormous amounts of information across large distances. A consequence of this is that technologies that are used extensively for transferring information such as coaxial cable, satellite, and microwave radio are rapidly running out

Therefore, transportation of the traffic volumes that will be demanded by users in the near future will require significantly greater network transmission bandwidth than that provided by the current infrastructure. Consequently, in the near term each category of component network of existing end-to-end networks will face different and increasingly difficult challenges with respect to transmission speed, cost, interference, reliability, and delivery of the demanded traffic to or from end-users. Currently, super-broadband penetration and the on-going growth in the internet traffic to and from business and home users are placing a

Broadband wireless sits at the confluence of two of the most remarkable growth stories of the telecommunication industry in recent years. Wireless and broadband have each enjoyed rapid mass-market adoption. Wireless mobile services grew from 11 million subscribers worldwide in 1990 to more than 5 billion by the end of 2010. The world's largest manufacturer of mobile phones has forecast that the number of mobile users accessing the internet via mobile broadband will grow to over 2 billion globally by the end 2014. Fixed broadband subscribers numbered only 57,000 in 1998 and rapidly increased to 555 million subscribers by the end of 2009. The number of fixed broadband subscribers is projected to exceed 720 million by 2015 despite the current economic situation, (OASE, 2010; ITU, 2011). The growth in the numbers of mobile telephone

of spare capacity, (Mcdonough, 2007).

Fig. 1. Near term future network capacity requirements.

huge bandwidth demand on the existing infrastructure.

subscribers, broadband and internet users over the last decade and the projections for the growth in these numbers are depicted in Fig. 2.

Fig. 2. Worldwide subscriber growth in the numbers of mobile telephony, internet, and broadband access users.

It follows that the demand for use of the available radio spectrum is very high, with terrestrial mobile phone and broadband internet systems being just one of many types of access technology vying for bandwidth. Mobile telephony and internet applications require the systems that support them to operate reliably in non-line-of-sight environments with a propagation distance of 0.5-30 km, and at velocities up to 100 km/h or higher. These operating environment constraints limit the maximum radio frequency the systems can use as operating at very high frequencies, i.e. approaching microwave frequencies, results in excessive channel path loss, and excessive Doppler spread at high velocity. This limits the spectrum suitable for mobile applications making the value of the radio spectrum extremely high. As an example, in Europe auctions of 3G licenses for the use of radio spectrum began in 1999. In the United Kingdom, 90 MHz of bandwidth was auctioned off for £22.5 billion (GBP). In Germany, the result was similar, with 100 MHz of bandwidth raising \$46 billion (US). This represents a value of around \$ 450 million (US) per MHz. The duration of these license agreements is 20 years. Therefore, it is vitally important that the spectral efficiency of the communication system should be maximized, as this one of the main limitations to providing low cost high data rate services, (OMEGA ICT Project, 2011; Yuen et al., 2004). By deploying converged fiber and wireless communication (Fi-Wi) technologies, network operators and service providers can meet the challenges of providing low cost high data rate services to wireless users. Only the relatively huge bandwidth of a fiber-optic access network can currently support low cost high data rate services for wired and wireless users.

This chapter makes the case for radio over fiber (RoF) networks as a future proof solution for supporting super-broadband services in a reliable, cost-effective, and environmentally friendly way.

This chapter is organized as follows: In Section II, the evolution of Internet traffic driven by the growth in wired and wireless subscribers worldwide is discussed. In Section III, solutions for cost effective transportation of traffic volumes in line with the demand expected as a result of anticipated growth in interactive video, voice communication and data services are presented. In Section IV, the radio over fiber (RoF) network as a future proof solution for supporting super-broadband services is described as a reliable, costeffective and environmentally friendly technology. Finally, concluding remarks are given in Section V.
