Wireless LANs are more commonly referred to by their trade name Wi-Fi. The terms Wi-Fi, WLAN, and 802.11 are used interchangeably in this text. Local-area networks (LANs) within a company, government agency, hospital or other organization typically use CAT5 or CAT6 unshielded twisted pair as the transport medium. However, more and more, wireless extensions to these LANs are becoming popular as are entirely wireless LANs. Low-cost wireless modems installed in personal computers and laptops make this possible. Three common configurations are shown in Fig. 21-2. Fig. 21-2(a) shows a wireless access point (AP) is connected to an existing wired LAN, usually through an Ethernet switch. This AP contains a transceiver that can cover a specific geographic area, usually inside a building. This area usually extends out to no more than about 100 m, but generally, the range is less due to the great signal attenuation of the walls, ceilings, floors, and other obstructions. PCs or laptops within that range and containing a radio modem can link up with the AP, which in turn connects the PC or laptop to the main LAN and any services generally available via that LAN such as e-mail and Internet access.
Another popular configuration is shown in Fig. 21-2(b). Here the AP is connected to the main LAN or more commonly to an Internet service provider (ISP) by way of a long-range interconnection such as a hardwired T1 or T3 line, fiber connection, or a microwave relay link such as WiMAX, as described later in this chapter. The AP is usually installed in a restaurant, coffee shop, airport, hotel, convention center, or another public place. It is more commonly known as a “hot spot.” Some cities are also 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.
What makes the wireless LAN so appealing is that it offers flexibility, convenience, and lower costs. To add a node to an existing wired LAN, the main problem is the new wiring. If such wiring is not in place already, it is time-consuming and expensive to pull cables through walls and ceilings and to install connectors. Moving computers within a building because of office reconfiguration is a huge problem and expense unless existing wiring can be reused. By using a wireless extension such problems essentially disappear.
Any computer can be located at any new point quickly and easily at no additional cost. As long as the computer is within the range of the AP, the connection is automatic. Wireless is a great way to expand an existing network.
Wireless LANs also serve our continuing need to be more mobile in our jobs and activities. The cell phone has given us the freedom to maintain communications anywhere, at any time, and virtually in any place. The wireless LAN also gives us that same portability for our computers, mainly laptops, which have essentially become the de facto PC form factor. Within an organization, a user can take her or his laptop to the conference room for a meeting, to a colleague’s office, or to the cafeteria for lunch. And with all the available hot spots, we can use our laptops almost anywhere, especially while we are traveling.
Another growing use of wireless LANs is in the implementation of home networks. See Fig. 21-2(c). As more and more families become users of multiple PCs, tablets, and smartphones, there is a need to interconnect each device to a broadband Internet connection such as a DSL or cable TV line. It allows each user to access e-mail or the Internet or to share a common peripherals such as a printer. Most homeowners do not want to wire their homes with CAT5/6 cable at great expense. Installing a wireless LAN is fast, easy, and very inexpensive these days. 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.
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 just a box containing a transceiver that interfaces to an existing LAN by way of CAT5/6 wiring. It typically gets its dc operating power via the twisted-pair cabling, because the dc supply voltage is superimposed on the data. The IEEE 802.3af standard related to furnishing dc power over the network cable is referred to as Power over Ethernet (PoE). The AP is usually mounted high on a wall or ceiling to give good coverage to a specific area. The antenna may be built into the box or maybe a separate array that gives directionality to the AP to ensure coverage of the desired area and minimum interference to other nearby WLANs.
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.
The radio modems for each PC take many forms. All are transceivers with an accompanying antenna. The transceivers are usually a single chip in most of the newer systems. In the older systems, the modem is contained on a plug-in card for the PC/PCImbus. Today, it is more common to have the radio modem built into the PC motherboard. For laptops and tablets, the modem is built in, so no special installation is needed.
Wireless LAN Standards
Over the years, a number of wireless LAN methods have been developed, tested, and abandoned. One standard 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 table shows the different versions of the standard and some technical details.
The earliest useful and most widely adopted version of the 802.11 standards 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. The center frequencies of each channel are given below.
Note that the channels are spaced 5 MHz apart over the spectrum. However, each channel is 22 MHz wide so that the channels overlap. Any given AP uses one of these channels.
The access method is direct sequence spread spectrum (DSSS) so that multiple signals may share the same band. Channel assignments are critical in facilities where multiple WLANs exist, so that interference is minimized.
The 802.11b standard specifies a maximum data rate of 11 Mbps. This rate is achieved only under the most favorable path conditions such as minimum range and minimum noise. Increasing range or noise causes the rate to automatically drop off to 5.5, 2, or 1 Mbps. This helps ensure a reliable connection despite the lower speed. At the 1- and 2-Mbps rates, the serial data signal is XORed with an 11-bit code called the Barker code to produce the DSSS signal. This particular bit sequence has unique properties that make it easy to receive and decode. The Barker sequence is 10110011000. Each serial data bit is XORed with this code. For modulation, 1 Mbps is achieved with DBPSK. For 2 Mbps, the modulation is DQPSK.
To achieve its faster rates of 5.5 and 11 Mbps, a different form of coding called complementary code keying (CCK) is used. The serial data signal is then modified by using one of 64 eight-bit codes to represent 6 bits of the serial data signal. The bit-coded bits are the chips. The modulation is differential quadrature phase-shift keying (DQPSK).
Four chips per 6-bit sequence are used to achieve the 5.5-Mbps rate. The use of CCK greatly improves the performance of the signal under noise and multipath conditions because the unique codes have properties that make them easier to identify and decode under adverse conditions.
As conditions degrade between the AP and the wireless node due to increased distance, noise, or number of obstacles, the transceiver automatically readjusts to the changing conditions by adjusting the data rate downward, first to 5.5 Mbps also using DQPSK/ CCK, then to 2 Mbps using DQPSK alone, and then to 1 Mbps using DBPSK. The maximum allowed equivalent isotropic radiated power (EIRP) is 1 W. Most IC transceivers produce an output of 100 mW. Gain antennas may be used as long as the output power plus the antenna gain is less than the 1-W EIRP allowed. A variety of power amplifier accessories and antennas are commercially available to customize each LAN.
The overall range depends upon environmental conditions. Indoors the range is typically less than 100 ft at 11 Mbps. It drops to 1 Mbps at about 300 ft. Outdoors with a clear line of sight and maximum EIRP, a range up to 8 km (about 12 mi) can be achieved.
The 802.11a standard was developed next. It uses the unlicensed 5-GHz band. There are three authorized segments: 5.15 to 5.25 GHz with 50-mW maximum power, 5.25 to 5.35 GHz with 250-mW maximum power, and 5.725 to 5.825 GHz at a maximum of 1 W of power. Each of these bands is divided into multiple nonoverlapping 20-MHz-wide channels. Each channel is designed to carry an OFDM signal made up of 52 subcarriers, 48 for data and the other 4 for error correction codes. Each of the subcarriers is about 300 kHz wide.
As with the 802.11b standard, the 802.11a version supports a wide range of data rates. The fastest is 54 Mbps. Other backoff rates usually include 48, 36, 24, 18, 12, 9, and 6 Mbps. Each uses a different modulation scheme. For 6 Mbps, BPSK is used. For 12 Mbps, QPSK is used. For the higher rates, QAM is used; 16-QAM gives 24 Mbps, while 64-QAM is used to achieve 54 Mbps. The standard provides for backoff data rates as the link conditions deteriorate due to increased range, noise, or multipath interference.
The key advantage of the 802.11a standard is that the frequency band is much less used than the busy 2.4-GHz band, which contains microwave ovens, cordless phones, Bluetooth wireless, and a number of other services, all of which can cause interference at one time or another, thereby producing interference that can block communications or at least decrease the range and data rate. With fewer interfering signals in the 5-GHz band, there is less interference and greater reliability.
The downside of this standard is its shorter range. As the frequency of operation increases, the given transmission range typically decreases. Indoor operation greatly reduces range because 5-GHz signals are more easily absorbed and reflected than 2.4-GHz signals. With 802.11a, the maximum range is about 50 m at the maximum data rate.
The 802.11g standard was an attempt to extend the data rate within the popular 2.4-GHz band. Using OFDM, this standard provides for a maximum data rate of 54 Mbps at 100 ft indoors. As with the 802.11a standard, there are low backoff rates, as described earlier, as the communications path degrades. The 802.11g standard also accommodates the 802.11b standards and so is fully backward-compatible. An 802.11b transceiver can talk to an 802.11g AP but at a lower data rate. An 802.11g transceiver can also talk to an 802.11b AP but also at a lower data rate.
The 802.11n version was developed to further increase the data rate. It also uses both the 2.4-GHz and 5-GHz bands and OFDM. A primary feature of this standard is the use of multiple-input multiple-output (MIMO) antenna systems to improve the 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. This arrangement permits a data rate in the 100- to the 600-Mbps range at a distance up to 100 m. MIMO systems greatly mitigate multipath problems and help extend the range and reliability of the wireless link. In all these standards, the carrier sense multiple access with collision avoidance (CSMA/CA) access method is used to minimize conflicts among those wireless nodes seeking access to the AP. Each transceiver listens before it transmits on a channel. If the channel is occupied, the transceiver waits a random period before attempting to transmit again. This process continues until the channel is free for transmission.
11n Wi-Fi dominates the wireless LAN space today, as it is commonly available in all smart phones, tablets, and laptops. And it is the wireless technology of all hot spots and access points, including the millions of home wireless routers. It is increasingly embedded in consumer electronic equipment. It is also backward-compatible with previous standards, allowing 802.11a/g equipment to be used.
One of the newest versions of the standard is 802.11ac. 11ac uses the 5-GHz ISM band only, for minimum interference and maximum available bandwidth. Furthermore, it continues the use of MIMO and OFDM. However, some key changes boost the theoretical data rate above 3 Gbps depending on modulation, channel bandwidth, and MIMO configuration.
the primary changes are 80- and 160-MHz-wide channels in addition to the usual 40-MHz channel. As the bandwidth increases, so do the number of OFDM subcarriers, to a maximum of 512 at 160-MHz bandwidth. OFDM also adds 256QAM, which further boosts the data rate. Finally, it defines a greater number of MIMO versions with a maximum of an 838 configuration. A multi-user version MU-MIMO is also defined. The standard also supports coexistence and compatibility with previous 11a and 11n devices. Transmit beamforming is also an option to extend the range and ensure link reliability.
Another version of Wi-Fi is 802.11ad. 11ad uses the 60-GHz ISM band. It is backward-compatible with all previous versions, including 11a/b/g/n/ac, as the media access control (MAC) layers of the protocol are similar. The 11ad version is also known by its trade name WiGig.
WiGig uses the unlicensed ISM 60-GHz band from 57 to 64 GHz. The technology divides this into four 2.16-GHz-wide bands. The primary modulation scheme is OFDM, which can support a data rate up to 7 Gbps, making it one of the fastest wireless technologies available. The standard also defines a single-carrier mode that uses less power; this is a better fit for some portable handheld devices. The single-carrier mode can deliver a data rate up to 4.6 Gbps. Both speeds permit transmission of uncompressed video. The WiGig specification also provides security in the form of the Advanced Encryption Standard (AES).
Because of the small antenna size at 60 GHz, gain antennas are normally used to boost signal power and range. The maximum typical range is 10 meters. WiGig products use on-chip phased array antennas that can provide beamforming. This adaptive beamforming permits beam tracking between transmitter and receiver to ensure that obstacles can be avoided and speed maximized even under changing environmental conditions. The primary disadvantage of 11ad is its short range. Remember that the higher frequencies travel shorter distances, as the wireless physics dictates. This disadvantage is generally overcome by the high-gain beamforming antennas.
The primary application of 11ad is the transport of video from one device to another over a short distance. One clever feature of the standard is the use of a protocol adaption layer (PAL). This is a software structure that talks to the MAC layer and allows simplified wireless implementation of other fast standard interfaces like USB, HDMI, DisplayPort, and PCIe.
Wi-Fi continues to be one of the most widely used wireless technologies in history. Many of the new devices in the works are related to consumer media products, health/ fitness/medical, automotive, smart meters, and automation products. Table 21-1 summarizes the most popular versions of Wi-Fi.
Related Wi-Fi Standards
The IEEE 802.11 Working Groups keep a running agenda of development. Those groups work on not only the next major standard versions but also many additions and improvements to the basic standards. Some of the most signifi cant past work does the following:
● 802.11e Provides Quality of Service (QoS) features that allow VoIP and other critical services to be carried over Wi-Fi.
● 802.11i Provides full security for Wi-Fi in the form of WEP, WPA, and WPA2.
● 802.11s Brings automatic ad hoc mesh networking to Wi-Fi.
● 802.11u Provides a protocol between access points and clients that permit inter-networking with support for authentication, authorization, and accounting with network selection, encryption policy enforcement, and resource management. Facilitates automatic connections and network handoffs. Allows Wi-Fi to be used for cellular handoff in small cells.
● 802.11y Brings Wi-Fi to the 3650–3700 MHz band.
One of the most interesting versions of Wi-Fi is the 802.11p standard that is to be deployed in V2x or vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) systems. These systems are part of the proposed Intelligent Telecommunications System (ITS) that provides safety and traffic information to vehicles using telematics. Called the Dedicated Short Range Communications (DSRC) wireless system, this standard is similar to the 802.11a Wi-Fi standard.
The Dedicated Short-Range Communications (DSRC) system uses the IEEE 802.11p standard and a protocol referred to as Wireless Access in Vehicular Environments (WAVE). The DSRC is assigned a 75-MHz segment of the spectrum from 5.85 to 5.925 GHz. There are seven 10-MHz channels designated by even numbers from 172 to 184. These channels are half the size of a standard 20-MHz 802.11 channel to minimize Doppler shift and multipath fading. A European version of the system is assigned 50 MHz of bandwidth for five channels.
The purpose of this spectrum is to allow vehicle and roadside unit (RSU) infrastructure radios to form vehicular ad hoc networks (VANETs). These networks will be dynamic and provide short-lived intermittent connectivity to implement various safety applications for collision avoidance and road safety. Connections are automatic. The 802.11p standard radio is half-duplex with a data rate in the 6- to 27-Mbps range and has an estimated maximum range of 300 meters (1 km).
The WAVE protocol uses the standard PHY and MAC layers of the 802.11a standard but uses the IEEE 1609 standard family for the upper layers, including a MAC extension, an LLC layer, network, and transport layers that include IPv6 with UDP and TCP, and an upper message application layer. Security is also provided by the 1609.2 standards. Several different types of short-message formats have been developed for different conditions.
Then there are projects still being developed in the various task groups. An example is 802.11ah. This is a modification to existing standards that would allow operation in sub-1-GHz bands to extend the range and implement applications such as smart meters. Another interesting new standard in development is 11af for the TV white space opportunity to be covered later.
The Wi-Fi Alliance
What makes Wi-Fi so good is the support, promotion, and development of the Wi-Fi Alliance (WFA), a trade association of companies developing and using the standard. Its key function is testing and certifying all chips and products to ensure full compatibility and interoperability. The WFA also develops its own standards and some excellent enhancements to the standards. Some examples are Wi-Fi Direct, HotSpot 2.0 and Passpoint, and Miracast. Typically these are software enhancements that can be included in standard chipsets and products.
Wi-Fi Direct is a modification of the basic standard to permit Wi-Fi-enabled devices to connect with one another without going through a traditional hot spot or router. This lets smartphones, laptops and tablets, cameras, printers, and other Wi-Fi-equipped devices automatically develop one-to-one communications. Many chips and devices are now enabled with Wi-Fi Direct.
HotSpot 2.0 is the WFA’s answer to linking Wi-Fi access points (APs) and eventually cellular networks. Passpoint is the certifying standard that provides an easier way to link up with a Wi-Fi network. It simplifies the finding and enabling of access to hot spots and access points. The location and linkup of hot spots are smoother and automatic and fully protected with WPA2 security.
The enabler of HotSpot 2.0 is the 802.11u standard. It allows devices and networks to negotiate and connect automatically. The user does not have to do anything. HotSpot 2.0 and Passpoint select the best nearby AP and connect without user interaction. They permit Wi-Fi roaming and pave the way to automatic handoff for implementing cellular data offload to Wi-Fi.
Miracast is the WFA’s solution for displaying video between devices wirelessly without going through an access point. It lets Miracast-enabled devices transfer video directly, such as from a laptop to a big-screen TV, or from a smartphone to a TV, or from a laptop to a larger video monitor in a docking station. Other possible uses are sending a laptop screen to a projector or allowing a tablet to display TV from a cable set-top box. Miracast uses Wi-Fi Direct to make the connection.
Even though Wi-Fi appears to be everywhere now, soon it will be even more widespread. It is already available in many airliners so that passengers can connect to the Internet in flight. It is used in printers and cameras. But that’s not all.
Another Wi-Fi target is the machine-to-machine (M2M) field and the Internet of Things (IoT). For example, Wi-Fi appears to be emerging as the wireless of choice in home networks and even appliances. Both ZigBee and Z-Wave wireless devices are already in the home, but they require some kind of gateway to make an Internet connection. Because many homes already have a Wi-Fi network, it is a natural choice for home networks.
Whirlpool, LG, and others use Wi-Fi to collect usage data on their refrigerators, washers, and other appliances. Some appliance makers offer a smartphone app that lets the owner see energy consumption, usage, maintenance, and other data on each connected appliance.
The 802.11 standard also includes a provision for encryption to protect the privacy of wireless users. Because 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. 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. It removes all doubt about the safety of data transmission for even the toughest applications. Another standard, 802.11x, provides a secure method of authentication for wireless transactions.
While the IEEE standards attempt to establish the technical specifications of the transceivers and their interfaces, different implementations of the standards by different semiconductor manufacturers have created interoperability problems. What this means is that even though each manufacturer has met the standard, some minor variation prevents the transceiver from communicating with the transceiver of another manufacturer. Such interoperability problems greatly limited the adoption during the early stages of 802.11b WLANs.
It was so bad that manufacturers banded together to form the Wi-Fi Alliance. Wi-Fi is short for wireless fidelity, and it has been adopted as the trademark of 802.11 products. The Wi-Fi Alliance set up testing and certification standards that all vendors had to meet to ensure full interoperability of all products. Any Wi-Fi-certified AP or wireless node will talk to any other Wi-Fi-certified products. The full interoperability brought about by the testing and certification process has made this wireless standard popular and very widely used.
PANs and Bluetooth
A personal-area network (PAN) is a very small wireless network that is created informally or on an ad hoc basis. It typically involves only two or three nodes, but some systems permit many nodes to be connected in a small area.
The most popular wireless PAN system is Bluetooth, a standard developed by the cell phone company Ericsson for use as a cable replacement. The objective was to provide hands-free cell phone operation by eliminating the cable connecting a cell phone to a headset. Today, this is one of the main applications of Bluetooth, but it also has other cable replacement applications.
Bluetooth is a digital radio standard that uses frequency-hopping spread spectrum (FHSS) in the unlicensed 2.4-GHz ISM band. It hops over 79 frequencies spaced 1 MHz apart from 2.402 to 2.480 GHz. The hop rate is 1600 hops per second. The dwell time on each frequency, therefore, is 1/1600 = 625 µs. During this time, digital data is transmitted. The total data rate is 1 Mbps, but some of that is overhead (headers, error detection and correction, etc.). The actual data rate is 723.2 kbps simplex or 433.9 kbps duplex. T e data, which may be voice or any other digitized information, is put into packets and transmitted sequentially in as many as fi ve time slots. The serial data signal is Gaussian-fi ltered, and then FSK is used for modulation. The frequency shift between binary 0 and 1 is +160 kHz.
Three levels of transmission power have been defined, depending upon the application. For short distances up to 10 m, class 3 power at 0 dBm (1 mW) is used. For longer distances or more robust operation in an environment with obstacles and noise, the higher-power class 2 can be used with 4 dBm or 2.5 mW. Maximum Bluetooth range is about 100 m and is achieved with class 1 power of 20 dBm or 100 mW.
Bluetooth transceivers are available as single-chip transceivers that interface to the device to be part of a PAN. These devices invariably contain some kind of embedded controller that handles the application. If voice is used, a vocoder is needed.
Bluetooth is set up so that the wireless transceiver constantly sends out a search signal and then listens for other nearby, similarly equipped Bluetooth devices. If another 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. Once the PAN has been established, the nodes can exchange information with one another. Bluetooth devices can also link to other piconets to establish larger scatter nets. See Fig. 21-3.
Another version 2.0 of Bluetooth is called Enhanced Data Rate (EDR). It has all the features described earlier but increases the overall data rate to 3 Mbps. The 3-Mbps rate includes all the headers and other overhead. The raw data rate is three times the 723 kbps rate mentioned earlier for a net rate of more than 2.1 Mbps. The new protocol still transmits at 1 Mbps using GFSK for accessing and recognizing inputs to establish a link and for the protocol headers. However, it uses a different modulation method to achieve a higher data rate in the data payload.
A gross data rate of 2.1 Mbps is achieved by using a form of QPSK called n/4- differential QPSK. It uses 908 spaced phase shifts of +1350, +450, -450, and -1350. It transmits 2 bits per symbol with a symbol rate of 1 Mbps.
To reach the 3-Mbps rate, an eight-phase differential phase-shift keying (8DPSK) modulation scheme is used. It transmits 3 bits per symbol. Otherwise, all other characteristics of the Bluetooth standard are the same.
The most recent version of Bluetooth is 4.0. It incorporates all the previous features of Bluetooth but adds Bluetooth Low Energy (BLE), a low-power variation of the original Bluetooth standard.
Bluetooth BLE is also called Bluetooth Smart. Smart uses a different set of technical and radio techniques to ensure very low power consumption. The data protocol was changed to make transmissions low-duty cycle or a very short transmission burst between long periods. The low-duty cycle, in addition to extremely low-power sleep modes, allows a Bluetooth Smart product to operate for many years on a coin cell. Bluetooth Smart provides a group of APIs to permit fast and easy application development.
Bluetooth Low Energy still operates in the same ISM (industrial-scientific-medical) license-free 2.4- to 2.483-GHz frequency band as standard Bluetooth. However, it uses a different frequency-hopping spread spectrum (FHSS) scheme. Standard Bluetooth hops at a rate of 1600 hops per second over 79 channels 1-MHz wide. BLE FHSS uses 40 channels 2-MHz wide to ensure greater reliability over longer distances. Standard Bluetooth offers gross data rates of 1, 2, or 3 Mbps. BLE’s maximum rate is 1 Mbps with a net throughput of 260 Kbps. GFSK modulation is used.
Other features of BLE are a power output of 0 dBm (1 mW) and a typical maximum range of 50 meters. Security is 128-bit AES. Link reliability is improved with the use of an adaptive frequency-hopping technique that avoids interference, a 24-bit CRC, and a 32-bit Message Integrity Check. The most common network configurations are P2P or star. Latency is only 6 ms.
A key point is that BLE is not compatible with standard Bluetooth, and it is a separate radio on standard Bluetooth 4.0 chips. If such interoperability is desirable, it could be implemented with a dual-mode device. This is an integrated circuit that contains both a standard Bluetooth radio and a BLE radio, where each can operate separately but not at the same time. They can share an antenna. It is also available as a separate device for low-power-only applications.
Just for clarification, here is the new Bluetooth terminology:
● Bluetooth Smart Ready – This refers to the dual-mode chips set of version 4.0. It handles any previous versions of classic Bluetooth in addition to BLE.
● Bluetooth Smart – This is BLE only. It will not connect any other version of Bluetooth except for Smart Ready 4.0 or other BLE devices.
● Bluetooth – This is Classic Bluetooth that is compatible with previous versions and Smart Ready devices. Will not connect with Smart devices.
Apple, Google, Android, and Microsoft (Windows 8) provide software support for the Bluetooth standards. That expedites connectivity with devices such as smart phones, tablets, and laptops.
An interesting Bluetooth application is Apple’s iBeacon wireless location service. It uses Bluetooth Low Energy (BLE) to implement beacons to send out a message that defines their location to nearby BLE smartphones. This new technology is bringing forth a whole new batch of uses.
The beacon is a BLE tag, sticker, or self-contained battery-powered gadget that is placed in a location that will allow it to reach nearby Bluetooth devices like iPhones or Android phones. The iBeacon tag has a range of around 40 to 50 feet in an indoor environment but could reach up to 100 feet or so in an outdoor setting with a clear line-of-sight path. The beacon pulses out a signal that is then received and acknowledged.
The beacon then sends out a desired message to the phone. The most mentioned application is ads for retail stores and restaurants. In a mall or other shopping area, you would automatically receive sales notices or menu selections once you are in the range of the store and if you have the appropriate iBeacon app. Any geo-fencing application can be applied to iBeacon. Geo-fencing uses the BLE range to define a virtual boundary. Once you are within that “fence,” you can take part in whatever applications are running.
Many phones already have BLE installed. All iPhones from 4S to current models are iBeacon-ready. So are many Android models, such as Samsung Galaxy. It is estimated that most smartphones will have BLE in the coming years. All you need are the apps to use iBeacon.
The main applications for Bluetooth are cordless headsets for cell phones and hands-free voice systems in cars and trucks. It is also the main connection between smartphones and the accessory smart watches. Bluetooth is also used in other wearables such as those for medical or fitness monitoring. Other uses include wireless human interface devices (HIDs) such as keyboards, mice, and game controllers. Any wireless connection over a short distance that is within the data rate capability of Bluetooth is a potential application.
The Bluetooth standard is maintained by the Bluetooth Special Interest Group (SIG) and supported by more than 2000 manufacturers. Bluetooth was also originally standardized by the IEEE as 802.15.1, but the standard is maintained by the Bluetooth SIG.
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. The 802.15.4 standard defines the so-called air interface, which is the physical layer (PHY or layer 1 of the OSI standard) and the media access control (MAC or layer 2) of the system. The ZigBee Alliance, an organization of chip, software, and equipment vendors of ZigBee products, specifies additional higher levels of layers including networking and security.
ZigBee is designed to operate in the license-free spectrum available in the world. This is defined by the FCC Part 15 in the United States. There are three basic bands and versions.
Even though the data rates are low, this is not usually an issue, because most applications are simply transmitting sensor data or making simple on/off operations. Transmission is by packets with a maximum size of 128 bytes, 104 of which is data. Both 16- and 64-bit addressing modes are available, although the maximum is considered to be up to 65,536 total nodes. The access method as with Wi-Fi is CSMA/CA. The most widely used version is the one operating in the 2.4-GHz band.
As for range, it varies considerably with the application and the environment. Using 2.4 GHz, the typical maximum indoor range is about 30 m. That can extend to 400 m outdoors with a clear line of sight. The maximum range is obtained at 868 or 900 MHz and can be as much as 1000 m with a line-of-sight path.
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, illustrated in Fig. 21-4. These network topologies are made up of three types of ZigBee nodes: a ZigBee coordinator (ZC), a ZigBee router (ZR), and ZigBee end device (ZED).
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. It does not repeat or route. The ZC and ZR nodes are called full-function devices (FFDs), and the ZED is known as a reduced-function device (RFD).
The star configuration in Fig. 21-4(a) is the most common, where a centrally located ZR accepts data from or distributes control data to other ZRs or ZEDs. The central ZR then communicates back to the ZC, which serves as the master controller for the system.
In the mesh topology, most of the nodes are ZRs, which can serve as monitor and control points but also can repeat or route data to and from other nodes. The value of the mesh topology is that it can greatly extend the range of the network. If a node lacks the power or position to reach the desired node, it can transmit its data through adjacent nodes that pass along the data until the desired location is reached. While the maximum range between nodes may be only 30 m or less, the range is multiplied by passing data from node to node over a much longer range and the wider area.
An additional feature of the mesh topology is network reliability or robustness. If one node is disabled, data can still be routed through other nodes over alternate paths. With redundant paths back to the ZC, a ZigBee mesh ensures that data reaches its destination regardless of unfavorable conditions. Many critical applications require this level of reliability.
As for applications, 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. Sensors generate an analog signal representing the physical variable that is amplified and otherwise conditioned and then converted to digital data that is transmitted back to the central monitoring location where decisions are made. This characteristic makes ZigBee a superior short-range telemetry system in what is being called wireless sensor networks.
Control refers to the sending of command signals to initiate some action. Typically commands are used to turn things off and on. Some examples are lights, motors, solenoids, relays, and other devices that perform some type of function.
Some popular applications include monitoring and controlling lights; heating, ventilating, and air conditioning (HVAC) systems in large buildings; and industrial monitoring and control in factories, chemical plants, and manufacturing operations. Automatic electric and gas meter reading is a major application. Other applications include medical uses such as wireless patient monitoring, automotive sensor systems, military battlefield monitoring, and a whole host of consumer applications such as home monitoring andncontrol, remote control of other objects, and security. Because ZigBee is so low-cost and battery-operated, it can be used in a wide range of situations, most of which probably have not been discovered yet.
WiMAX and Wireless 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. Now there is a wireless contender for metropolitan-area networking. Known as WiMAX, it is the wireless system defined by the IEEE 802.16 standard. 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. 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. Common examples are cell site backhaul from a base station to the switching office or Wi-Fi hot spot interconnections to the ISP. Both of these applications typically rely on hardwired T1 or T3 connections, which are very expensive. A wireless backhaul link is far less expensive, not to mention easier to install.
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. In both modes, the service is assumed to be fixed; i.e., none of the nodes are mobile.
WiMAX was designed to operate anywhere in the 2- to 6-GHz range wherever appropriate spectrum is available. The spectrum may be licensed or unlicensed depending upon its location and the host country. The most common bands are 2.3, 2.5, and 5.8 GHz in the United States and 3.5 GHz in Europe, Asia, and Canada.
The maximum data rate is 75 Mbps, but that is usually divided up among a large number of users. Speed is set by bandwidth, which can be anything from 1.75 to 20 MHz. The WISP will allocate bandwidth and speed to users based on their needs and charge accordingly. The maximum range of a single base station is about 30 mi, although in a practical system one base station will usually only cover a range of 2 to 10 km (3.2 to 6 mi). Full-duplex using time-division duplexing (TDD) or frequency-division duplexing (FDD) is supported by the standard. One or the other is chosen based on the application and the spectrum and service available.
WiMAX uses a 256-carrier OFDM system with adaptive modulation. OFDM is a superior method that mitigates the line-of-sight (LOS) problems that occur in serving a large area. Reflections from buildings and other structures cause multipath problems that can stop transmission. Trees and houses can absorb the signal, making reception poor or nonexistent. Yet OFDM helps to lessen these problems. The modulation method of each OFDM channel is selected automatically depending upon the range, noise, and data rate. The standard supports BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM. BPSK would be selected for longer range and lower speeds; 64-QAM or 256-QAM would be selected for shorter ranges to give higher speeds.
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. An example is a WiMAX-enabled laptop on a commuter train or in a car or truck. The maximum range is about 3 mi, but that will depend upon the environment and terrain. Speeds up to about 75 mi/h can be accommodated. Data rates are adaptable to the environment and range but can hit a maximum of 15 Mbps under ideal conditions. IEEE 802.16e uses 2048-channel OFDM to achieve these characteristics. The access method is OFDMA (access) where the 2048 channel OFDM signal is divided among multiple users. With 64 channels assigned to each subscriber, one OFDMA bandwidth can accommodate up to 32 users.
Although WiMAX is a well-developed and proven wireless technology, it has been eclipsed by LTE. LTE is similar in most respects to WiMAX, especially TD-LTE, as both use TDD and OFDMA. Most cellular companies and Internet service providers have chosen LTE, leaving WiMAX with an unsure future.
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