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This chapter presents a select high-level overview of wireless communication.
2.1 Communication Systems
All wireless communication systems have the following components:
In short, the transmitter feeds a signal of encoded data modulated into RF waves into the antenna. The antenna radiates the signal through the air where it is picked up by the antenna of the receiver. The receiver demodulates the RF waves back into the encoded data stream sent by the transmitter.
2.2 Wireless Network Types
There are a number of different types of networks used in wireless communication. Network types are typically defined by size and location.
2.2.1 WPAN
A wireless personal area network (WPAN) is meant to span a small area such as a private home or an individual workspace. It is used to communicate over a relatively short distance. The specification does not preclude longer ranges being achieved with the trade-off of a lower data rate.
In contrast to other network types, there is little to no need for infrastructure with a WPAN.
Ad-hoc networking is one of the key concepts in WPANs. This allows devices to be part of the network temporarily; they can join and leave at will. This works well for mobile devices like PDAs, laptops and phones.
Some of the protocols employing WPAN include Bluetooth, ZigBee, Ultra-wideband (UWB) and IrDA. Each of these is optimized for particular applications or domains. ZigBee, with its sleepy, battery-powered end devices, is a perfect fit for wireless sensors. Typical ZigBee application domains include: agricultural, building and industrial automation, home control, medical monitoring, security and, lest we take ourselves too seriously, toys, toys and more toys.
2.2.2 WLAN
Wireless local area networks (WLANs) are meant to span a relatively small area, e.g., a house, a building, or a college campus. WLANs are becoming more prevalent as costs come down and standards improve.
A WLAN can be an extension of a wired local area network (LAN), its access point connected to a LAN technology such as Ethernet. A popular protocol for WLAN is 802.11, also known as Wi-Fi.
2.2.3 WWAN
A wireless wide area network (WAN) is meant to span a large area, such as a city, state or country. It makes use of telephone lines and satellite dishes as well as radio waves to transfer data. A good description of WWANs is found at: http://en.wikipedia.org/wiki/WWAN.
2.3 Wireless Network Topologies
This section discusses the network topologies supported by the IEEE 802.15.4 and ZigBee specifications. The topology of a network describes how the nodes are connected, either physically or logically. The physical topology is a geometrical shape resulting from the physical links from node to node, as shown in Figure 2.1. The logical topology maps the flow of data between the nodes.
IEEE 802.15.4 supports star and peer-to-peer topologies. The ZigBee specification supports star and two kinds of peer-to-peer topologies, mesh and cluster tree.
ZigBee-compliant devices are sometimes specified as supporting point-to-point and point-to-multipoint topologies.
2.4 Wireless Standards
The demand for wireless solutions continues to grow and with it new standards have come forward and other existing standards have strengthened their position in the marketplace. This section compares three popular wireless standards being used today and lists some of the design considerations that differentiate them.
Each wireless standard addresses the needs of a different market segment. Choosing the best-fit wireless standard is a crucial step in the successful deployment of any wireless application. The requirements of your application will determine the wireless standard to choose.
For more information on design considerations, see Technical Note 249, "Designing with Wireless Rabbits."
2.5 Security in a Wireless Network
This section discusses the added security issues introduced by wireless networks. The salient fact that signals are traveling through the air means that the communication is less secure than if they were traveling through wires. Someone seeking access to your network need not overcome the obstacle of tapping into physical wires. Anyone in range of the transmission can potentially listen on the channel.
Wireless or not, a network needs a security plan. The first thing to do is to decide what level of security is appropriate for the applications running on your network. For instance, a financial institution, such as a bank or credit union offering online account access would have substantially different security concerns than would a business owner offering free Internet access at a coffee shop.
2.5.1 Security Risks
After you have decided the level of security you need for your network, assess the potential security risks that exist.
Who is in range of the wireless transmissions?
Can unauthorized users join the network?
What would an unauthorized user be able to do if they did join?
Is sensitive data traveling over the wireless channel?
Network security is analogous to home security: You do not want your house to be a target so you do things to minimize your risk, whether that be outside lighting, motion sensors, or even just keeping bushes pruned back close to the house so bad guys have fewer hiding places.
Deterrence is the goal because nothing is guaranteed to be 100% safe in the real world.
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