roadcasting (radio, TV) or walkie-talkies. Alternatively communication may be bidirectional, such as communication between cellular base stations and mobile phones. Generally point to point communication is carried out using directional antennas, and point to multi-point using omnidirectional or sec- tor-directional antennas. Wireless communications may be carried out using different media and technologies: in the air (such as radio, TV, mobile communications, etc.), space (satellite communications), and even water (sonar, visible light). Usually the frequency of operation for each of these media is different and a function of the special characteristics of the particular medium. For example, communication within water must be at very low frequencies because of the conductive character of water. Similarly space communication can use very high frequencies, since line- of-sight can usually be established between the transmitter and receiver. In the context of broadband telecommunications services, this book focuses on terrestrial fixed-wireless and mobile communications. These systems usually operate within a frequency range of 450 MHz to 5.8 GHz as will be discussed below. Mobile Terrestrial Telecommunications Systems Mobile terrestrial telecommunications systems, used in public and private broadband service provision, are generally characterised as a star network, shown in Figure 10.4, where a central fixed device communicates with many moving subscriber devices. The central device may be called a base station or an access point. The subscriber device may be called user equipment or mobile phone/device (cell phone) depending on the wireless standard and functionality. The central device communicates with subscribers using an allocated frequency spectrum. Some standards operate within a licensed band, where the operating frequency band is allo- cated by the government through a specific process, such as an auction. Some systems operate within an unlicensed band, where all devices need to comply with government reg