Principles of Electronic Communication Systems

Principles of ElectronicCommunication Systems Third Edition Louis E. Frenzel, Jr.

Chapter 21 Wireless Technologies

Topics Covered in Chapter 21 • 21-1: Wireless LAN • 21-2: PANs and Bluetooth • 21-3: ZigBee and Mesh Wireless Networks • 21-4: WiMAX and Metropolitan-Area Networks • 21-5: Infrared Wireless • 21-6: Radio-Frequency Identification and Near-Field Communications • 21-7: Ultrawideband Wireless

21-1: Wireless LAN • In addition to cell phones, there are many more wireless systems and applications in common use today. • These are primarily short-range systems that have a range of a few inches up to several miles depending upon the application. • Each of these popular systems is defined by a specific industry standard and is identified with one or a few well-known applications.

21-1: Wireless LAN Figure 21-2: Types of WLANs. (a) Access point extension to a wired LAN. (b) Public access point via an Internet service provider (ISP).

21-1: Wireless LAN • Local-area networks (LANs) within a company or an organization are still interconnected mainly by CAT5 or CAT6 twisted pair. • Wireless extensions and even complete wireless LANs have become more common now that reliable, low-cost wireless modems are available. • Wireless is a great way to expand an existing network. • What makes the wireless LAN so appealing is that it offers flexibility, convenience, and lower costs.

21-1: Wireless LAN • Wireless access points (APs) are available not only within offices, but also in restaurants, coffee shops, airports, hotels, convention centers, and other public places. • Access points are more commonly known as “hot spots.” Some cities are installing municipal hot spots. • Anyone with a laptop equipped with a LAN modem interface can link up to the AP and access his or her e-mail or the Internet. There are hundreds of thousands of hot spots around the world.

21-1: Wireless LAN • As long as the computer is within the range of the AP, the connection is automatic. • Wireless LANs also serve our continuing need to be more mobile in our jobs and activities.

21-1: Wireless LAN • Another growing use of wireless LANs is in the implementation of home networks. • Installing a wireless LAN is fast, easy, and very inexpensive. A special box called a residential gateway or wireless router connects to the cable TV or DSL and serves as the access point. • This gateway or router uses a software approach called network address translation (NAT)to make it appear as if each networked PC has its own Internet address, when in reality only the one associated with the incoming broadband line is used.

21-1: Wireless LAN Hardware of Wireless LANs • The hardware devices in a wireless LAN are the access point or the gateway/router and the radio modems in the PCs. • The access point is a box containing a transceiver that interfaces to an existing LAN by way of CAT5/6 wiring. • It gets its dc operating power via the twisted-pair cabling. • The IEEE 802.3af standard related to furnishing dc power over the network cable is referred to as Power over Ethernet (PoE).

21-1: Wireless LAN Hardware of Wireless LANs • In a home network, the gateway or router is designed to attach to the DSL or cable TV modem with CAT5/6 cable. • It often attaches to one of the PCs in the home network by cable. • The other PCs link to the gateway/router wirelessly.

21-1: Wireless LAN Wireless LAN Standards • One standard for wireless LANs has emerged as the most flexible, affordable, and reliable. • Known as the IEEE 802.11 standard, it is available in multiple forms for different needs. • The earliest useful and most widely adopted version of the 802.11 standard is 802.11b. • It operates in 11 channels in the 2.4-GHz unlicensed ISM band. • This band extends from 2.4 to 2.4835 MHz for a total bandwidth of 83.5 MHz.

21-1: Wireless LAN Wireless LAN Standards • The access method is direct sequence spread spectrum (DSSS) so that multiple signals may share the same band. • The 802.11b standard specifies a maximum data rate to 11 Mbps. This rate is achieved only under the most favorable path conditions. • Increasing range or noise causes the rate to automatically drop off to 5.5, 2, or 1 Mbps, which helps ensure a reliable connection despite the lower speed.

21-1: Wireless LAN Wireless LAN Standards: IEEE 802.11n • The newest standard is the 802.11n version. • It uses the 2.4-GHz band and OFDM. • A primary feature of this standard is the use of multiple-input multiple-output (MIMO) antenna systems to improve reliability of the link. • APs for 802.11n use two or more transmit antennas and three or more receive antennas. The wireless nodes use a similar arrangement. In each case multiple transceivers are required for the AP and the node. • MIMO systems reduce multipath problems and extend the range and reliability of the wireless link.

21-1: Wireless LAN Wireless LAN Standards: Wireless Security • The 802.11 standard also includes provision for encryption to protect the privacy of wireless users. • Since radio signals can literally be picked up by anyone with an appropriate receiver, those concerned about privacy and security should use the encryption feature built into the system. • The basic security protocol is called Wired Equivalent Privacy (WEP)and uses the RC4 encryption standard and authentication.

21-1: Wireless LAN Wireless LAN Standards: Wireless Security • WEP may be turned off or on by the user. It does provide a basic level of security; however, WEP has been cracked by hackers and is not totally secure from the most high-tech data thieves. • Two stronger encryption standards called Wi-Fi Protected Access (WPA)and WPA2 are also available in several forms to further boost the encryption process. • The IEEE also has a security standard called 802.11i that provides the ultimate in protection.

21-2: PANs and Bluetooth • A personal-area network (PAN) is a very small network that is created informally or on an ad hoc basis. • A PAN typically involves two or three nodes, but some systems permit many nodes to be connected in a small area. • PANs can be wired, but today all are wireless. • The most popular wireless PAN system is Bluetooth, a standard developed by the cell phone company Ericsson for use as a cable replacement.

21-2: PANs and Bluetooth • Bluetooth is a digital radio standard that uses frequency-hopping spread spectrum (FHSS) in the unlicensed 2.4-GHz ISM band. • Three levels of transmission power have been defined, depending upon the application. • Bluetooth transceivers are available as single-chip transceivers that interface to the device to be part of a PAN.

21-2: PANs and Bluetooth • Bluetooth transceivers send out search signals and then listen for nearby Bluetooth-equipped devices. • If another Bluetooth device comes into range, the two Bluetooth devices automatically interconnect and exchange data. • These devices form what is called a piconet, the linking of one Bluetooth device that serves as a master controller to up to seven other Bluetooth slave devices. • Bluetooth devices can also link to other piconets to establish larger scatternets.

21-2: PANs and Bluetooth Figure 21-3: Bluetooth piconet with scatternet link. Up to seven devices can be actively connected.

21-2: PANs and Bluetooth • The main applications for Bluetooth are cordless headsets for cell phones, wireless connections between PCs, or laptop computers and PDAs. • Bluetooth applications include: laptop connections at meetings, wireless printer-to-PC connections, laptop-to-cell phone connections, wireless audio headsets, and wireless digital camera-to-TV set connections. • The Bluetooth standard is maintained by the Bluetooth Special Interest Group (SIG) and supported by more than 2000 manufacturers.

21-3: ZigBee and Mesh Wireless Networks • ZigBee is the commercial name for another PAN network technology based on the IEEE 802.15.4 wireless standard. • Like Bluetooth, it is a short-range technology with networking capability. • It was designed primarily for commercial, industrial, and home monitoring and control applications. • ZigBee is designed to operate in the license-free spectrum.

21-3: ZigBee and Mesh Wireless Networks • There are three basic bands and versions (below). • Data rates are low, but most applications are simply transmitting sensor data or making simple on/off operations.

21-3: ZigBee and Mesh Wireless Networks • ZigBee’s virtue is its versatile networking capability. • The standard supports three topologies: star, mesh, and cluster tree. The most commonly used are the star and mesh. • These network topologies are made up of three types of ZigBee nodes: • ZigBee coordinator (ZC) • ZigBee router (ZR) • ZigBee end device (ZED).

21-3: ZigBee and Mesh Wireless Networks • The ZC initiates a network formation. There is only one ZC per network. • The ZR serves as monitor or control device that observes a sensor or initiates off/on operations on some end device. • It also serves as a router as it can receive data from other nodes and retransmit it to other nodes. • The ZED is simply an end monitor or control device that only receives data or transmits it.

21-3: ZigBee and Mesh Wireless Networks Figure 21-4:Most common ZigBee network topologies. (a) Star. (b) Mesh.

21-3: ZigBee and Mesh Wireless Networks • In the mesh topology, most of the nodes are ZRs that can serve as monitor and control points and can also repeat or route data to and from other nodes. • The mesh topology can greatly extend the range of the network, and enhance its network reliability or robustness.

21-3: ZigBee and Mesh Wireless Networks • ZigBee can address a wide range of wireless needs. • It was designed primarily for monitoring and control. • Monitoring refers to looking at a wide range of physical conditions, especially temperature, humidity, pressure, the presence of light, speed, and position information. • Control refers to the sending of command signals to initiate some action. • Typically commands are used to turn things off and on, such as lights, motors, solenoids, relays, and other devices.

21-3: ZigBee and Mesh Wireless Networks • Popular applications of ZigBee include: • Monitoring and controlling lights; • Heating, ventilating, and air conditioning (HVAC) systems in large buildings; • Industrial monitoring and control in factories, chemical plants, and manufacturing operations. • Automatic electric and gas meter reading. • Medical uses, such as wireless patient monitoring. • Automotive sensor systems. • Military battlefield monitoring. • Consumer applications such as home monitoring and control, remote control of other objects, and security.

21-4: WiMAX and Metropolitan-Area Networks • Metropolitan-area networks (MANs) are primarily fiber-optic networks, most often SONET rings, that connect enterprise LANs to WANs or the Internet backbone. • Another typical MAN is a local cable TV network. • A new wireless contender for metropolitan-area networking is known as WiMAX. It is defined by the IEEE 802.16 standard.

21-4: WiMAX and Metropolitan-Area Networks • It was developed to provide a wireless alternative to consumers for broadband Internet connections. • These connections are now dominated by cable TV and DSL, but with the new WiMAX standard, wireless Internet service providers (WISPs)may soon be offering wireless broadband connections. • The primary standard is known as IEEE 802.16-2004 or 802.16d.

21-4: WiMAX and Metropolitan-Area Networks • Its primary applications will fit into two basic categories: point-to-point (P2P) or point-to-multipoint (PMP). • The P2P mode is for applications requiring the transfer of data between two points. • The PMP mode is a broadcast mode from a central base station to multiple surrounding nodes. In this mode WiMAX serves as a WISP for homes or businesses.

21-4: WiMAX and Metropolitan-Area Networks • WiMAX uses a 256-carrier OFDM system with adaptive modulation. • The OFDM method lessens the line-of-sight (LOS) problems that occur in serving a large area. • Reflections from buildings or signal absorption by trees and houses make reception poor or stop transmissions altogether.

21-4: WiMAX and Metropolitan-Area Networks • A mobile version of WiMAX is now available. The standard is IEEE 802.16e 2005. • It is designed to permit nodes to be mobile while maintaining contact with a base station. • WiMAX is especially attractive to developing countries where a wireless infrastructure is easier and less expensive to install than a traditional wired telephone or cable TV system.

21-5: Infrared Wireless • Perhaps the most widespread wireless system uses infrared (IR) light for short-distance data communication. • The most widely used is the wireless remote control on TV sets, VCRs, and DVD players and on most audio CD stereo systems. • Infrared has also been used for wireless LANs and PANs.

21-5: Infrared Wireless TV Remote Control • Almost every TV set sold these days, regardless of size or cost, has a wireless remote control. • Other consumer electronic products have remote controls including VCRs, cable TV converters, CD and DVD players, stereo audio systems, and some ordinary radios. • Generic remote controls are available to hook up to any device that you wish to control remotely.

21-5: Infrared Wireless TV Remote Control • All remote control devices work on the same principle. • A small handheld battery-powered unit transmits a serial digital code via an IR beam to a receiver that decodes it and carries out the specific action defined by the code. • A TV remote control is one of the more sophisticated of these controls, for it requires many codes to perform volume control, channel selection, and other functions.

21-5: Infrared Wireless TV Remote Control • The keyboard is a matrix of single-pole single-throw (SPST) pushbuttons. • The row and column connections are made to a keyboard encoder circuit inside the IC. • When a key is depressed, the pulses from one of the column outputs are connected to one of the row inputs. • The encoder circuit converts this input to a unique binary code representing a number for channel selection or some function such as volume control.

21-5: Infrared Wireless TV Remote Control • The serial output is generated by the shift register as data is shifted out. • A standard nonreturn to zero (NRZ)serial code is generated and applied to a serial encoder. • The serial bit stream turns a higher-frequency pulse source off and on. • The pulses modulate the IR light source by turning it off and on. • The IR source is usually one or more IR LEDs. Two or more LEDs are used to ensure a sufficient level of IR radiation to the receiver in the TV set.

21-5: Infrared Wireless Figure 21-5: IR TV remote control transmitter.

21-5: Infrared Wireless TV Remote Control • In an IR receiver, the PIN IR photodiode is mounted on the front of the TV set, where it picks up the IR signal from the transmitter. • Two or more high-gain amplifiers boost the signal level. • The incoming pulses are detected, shaped, and converted to the original serial data train. • This serial data is read by the control microcomputer that is usually part of the TV receiver. • The microcontroller inputs and decodes the incoming signal and issues output control signals to all other circuits.

21-5: Infrared Wireless Figure 21-7: The IR receiver and control microprocessor.

21-5: Infrared Wireless IR PANs • Besides remote control, the primary application for IR data communication is in short-distance links between computers, computers and printers, or ad hoc PANs. • Distance links are typically up to 1 m, however under some conditions, the distance can be extended to 9 m. • There must be a clear line of sight between the transmitter and receiver.

21-5: Infrared Wireless Figure 21-8: Common applications for IR data communication.

21-5: Infrared Wireless IR PANs • An IR transceiver connects to interface circuitry in the PC or PDA. • The interface is typically a small embedded controller inside the computer or PDA. • The encoder puts the serial digital data from the PC or PDA into the proper format for transmission. • A high-current bipolar transistor or MOSFET drives one or more IR LEDs.

21-5: Infrared Wireless IR PANs • The receiver consists of the PIN diode that picks up the IR light from a nearby transmitter. • The signal is amplified and shaped and then sent to the decoder, which recovers the original data. • Although many laptops and PDAs have a built-in transceiver, their use is often restricted by this need for line of sight. • A better arrangement is a transceiver dongle which consists of a cable attached to the interface in the PC or PDA and to the movable dongle containing the LED and PIN diode.

21-5: Infrared Wireless Figure 21-9: IR wireless LAN transceiver.

21-5: Infrared Wireless IrDA System • The most widely used IR data communication system was developed by Hewlett-Packard. • It has since become an international standard that is maintained by the Infrared Data Association (IrDA). • The complete interface and system are referred to as IrDA. • The systems are designed for a short range of between 20 to 30 cm and 1m. • The maximum usable range is 8.9 m.

21-5: Infrared Wireless IrDA System • Most systems use data speed rates of 4 Mbps, however, a 16-Mbps version is available. • IrDA does not use a modulated IR beam, but rather baseband transmission that requires encoding and decoding. • The standard NRZ serial data is converted into pulses especially encoded for IR operation. • The 4-Mbps version uses another encoding scheme, called 4PPM (pulse position modulation).

21-6: Radio-Frequency Identification and Near-Field Communications • Another growing wireless technique is radio frequency identification (RFID). • RFID uses thin, inexpensive tags or labels containing passive radio circuits that can be queried by a remote wireless interrogation unit. • The tags are attached to any item that is to be monitored, tracked, accessed, located, or otherwise identified.

Principles of Electronic Communication Systems