Wireless Personal Area Networks are based on the IEEE 802.15 standard [3-4]. They permit communication in a very short range, of about 10 meters. Unlike other wireless networks, a connection made through a WPAN involves little or no infrastructure or direct connectivity to the world outside the link. This allows small, power-efficient, inexpensive solutions to be implemented for a wide range of devices such as a smartphone and a PDA.

These networks are characterized by low power demands and a low bit rate. Such kind of networks relay on technologies such as Bluetooth, IrDA, ZigBee or UWB. From an application point of view, Bluetooth is intended for a cordless mouse, keyboard, and hands-free headset, IrDA is intended for point-to-point links between two devices for simple data transfers and file synchronization, ZigBee is designed for reliable wirelessly networked monitoring and control networks and, UWB is oriented to high-bandwidth multimedia links.

• Bluetooth

Bluetooth corresponds to the IEEE 802.15.1 standard. Originally Bluetooth was designed for low power consumption, short range and omni-directional (point to multipoint) communications, and cheap devices, to be used as a cable replacement, linking devices through an ad hoc connection of radio waves. Nowadays developers are designing Bluetooth-enabled components and systems for a range of additional applications. This technology operates for three different classes of devices: Class 1, class 2 and class 3 where the range is about 100 meters, 10 meters and 1 meter respectively. Using the 2.4 GHz band, two devices within the coverage range of each other can share up to 720 Kbps of capacity or transfer rate. The most commonly used is class 2.

A Bluetooth network is also called a piconet, and is composed of up to 8 active devices in a master-slave relationship. The first Bluetooth device in the piconet is the master, and all other devices are slaves that communicate with the master. A piconet typically has a range of 10 meters, although ranges of up to 100 meters can be reached under ideal circumstances. To provide security, each link is encoded and protected against eavesdropping and interference. Two piconets can be connected to form a scatternet. A Bluetooth device may participate in several piconets at the same time, thus allowing for the possibility that information could flow beyond the coverage area of the single piconet. A device in a scatternet could be a slave in several piconets, but master in only one of them.

• IrDA

The Infrared Data Association (IrDA) specifies a complete set of infrared communications standards. IrDA refers to that set of standards and is used to provide wireless connectivity to devices that would normally use cables for connectivity. IrDA is a low-power, low-cost, unidirectional (point to point), narrow angle (< 30º) cone, ad hoc data transmission standard designed to operate over a distance of up to 1 meter and at speeds of 9600 bps to 4 Mbps (currently), 16 Mbps (under development). Some of the devices that use IrDA are notebooks, PDAs, printers and cameras.

• ZigBee

ZigBee is based on the IEEE 802.15.4 standard and was developed as an open global standard to address the unique needs of easy implementation, high reliability, low-cost, low-power and low-data rate wireless device networks. ZigBee operates the unlicensed bands including 2.4 GHz, 900 MHz and 868 MHz at a maximum transfer rate of 250 Kbps, enough to satisfy sensor and automation needs using wireless.

ZigBee also serves for creating larger wireless networks not demanding high data throughput. Two different device types can participate in a ZigBee network: Full-function devices (FFD) and reduced-function devices (RFD). FFDs can operate in three modes serving as a WPAN coordinator, coordinator or device. RFD is only intended for applications that are extremely simple, such as a light switch. ZigBee supports three different topologies: star, mesh, and cluster tree, which are shown in Figure 1.4. In the star topology, the communication is established between devices and a single central controller, called the WPAN coordinator. In the mesh topology, any device can communicate with any other device as long as they are in range of one another. Cluster-tree network is a special case of a mesh network in which most devices are FFDs and a RFD may connect to a cluster-tree network as a leaf node at the end of a branch. Any of the FFD can act as a router and provide synchronization services to other devices and routers. Only one of these routers is the WPAN coordinator.

• UWB

Based on the IEEE 802.15.3 standard, Ultra Wide Band (UWB) technology has recently attracted much attention as an indoor short-range high-speed wireless communications. UWB serves a very different purpose than the other technologies mentioned in this section. UWB enables the movement of massive files at high data rates over short distances. Thus, UWB has a data transfer over 110 Mbps up to 480 Mbps at distances up to few meters which can satisfy most of the multimedia applications such as audio and video delivery in home networking and it can also act as a wireless cable replacement of high speed serial bus such as USB 2.0 and IEEE 1394. In America, frequencies for UWB have been allocated in the 3.1 GHz to 10.6 GHz band. However, in Europe, the frequencies include two parts: from 3.4 GHz to 4.8 GHz and 6 GHz to 8.5 GHz.

UWB transmissions transmit information by generating radio energy at specific time intervals and occupying a large bandwidth, see Figure 1.5, thus enabling pulse-position or time modulation. The information can also be modulated on UWB signals (pulses) by encoding the polarity of the pulse, its amplitude and/or by using orthogonal pulses. UWB pulses can be sent sporadically at relatively low pulse rates to support time or position modulation, but can also be sent at rates up to the inverse of the UWB pulse bandwidth.