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Wireless LANs and PANs

Chapter 15. Wireless LANs and PANs. Outline. Introduction Wireless Local Area Networks (WLANs) Enhancement for IEEE 802.11 WLANs Wireless Metropolitan Area Networks (WMANs) using WiMAX and Mesh Networks Mesh Networks Wireless Personal Area Networks (WPANs ) Summary.

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Wireless LANs and PANs

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  1. Chapter 15 Wireless LANs and PANs

  2. Outline • Introduction • Wireless Local Area Networks (WLANs) • Enhancement for IEEE 802.11 WLANs • Wireless Metropolitan Area Networks (WMANs) using WiMAX and Mesh Networks • Mesh Networks • Wireless Personal Area Networks (WPANs) • Summary

  3. Scope of Various WLAN and WPAN Standards WMN 802.16* 802.16 WiMAX Power consumption Complexity 802.11n* 802.11a HiperLAN 802.11g* WMAN 802.11b 802.11 WLAN 802.15.I Bluetooth * Standard in progress 802.15.4 WPAN Data rate

  4. Wireless Local Area Networks (WLANs) • IEEE group published a standard for WLANs named as IEEE 802.11 (now known as IEEE 802.11a) • Higher bit rates at 2.4GHz ISM band resulted in high-speed standard called the IEEE 802.11b (popularly known as Wi-Fi) • Can be used to have an ad hoc network using peer-to-peer mode, • Or, as a client/server wireless configuration Ad hoc Client/server

  5. IEEE 802.11 • It is the standard for wireless LANs. • It specifies MAC procedures and operate in 2.4 GHz range with data rate of 1Mbps or optionally 2Mbps. • User demand for higher bit rates and international availability of 2.4 GHz band has resulted in development of a high speed standard in the same carrier frequency range. • This standard called 802.11b, specifies a PHY layer providing a basic data rate of 11 Mbps and a fall-back rate of 5.5 Mbps.

  6. IEEE 802.11 • In the ad hoc network mode, as there is no central controller, the wireless access cards use the CSMA/CA protocol to resolve shared access of the channel. • In the client/server configuration, many PCs and laptops, physically close to each other (20 to 500 meters), can be linked to a central hub [AP] • A larger area can be covered by installing several APs • The access points track movement of users and make decisions on whether to allow users to communicate • WLAN cards could be operated in continuous aware mode (radio always on) and power saving polling mode (radio in sleep state to extend battery life)

  7. Distributed Wireless Network Wired network Station Access point Access point Distributed system Station Access point Station Station

  8. IEEE 802.11 and variants • IEEE 802.11a • With a throughput up to 54Mbps • IEEE 802.11a operates on 5GHz • It has less interference as compared to IEEE 802.11b/g since 2.4GHz band is heavily used • Uses orthogonal frequency-division multiplexing (OFDM)with 52 subcarriers spanning over a 20MHz spectrum • IEEE 802.11b (WiFi) • Operates on 2.4GHz band with thruput of up to 11Mbps • Direct-sequence spread spectrum DSSS on PHY layer • IEEE 802.11g • Operates on 2.4G using either DSSS or OFDM • Can achieve higher throughput of up to 54Mbps • IEEE 802.11n • Multiple-input multiple-output (MIMO) technology • Bandwidth can be 40MHz in 2.4GHz and 5GHz

  9. Enhancement for IEEE 802.11 WLANs • The keys behind all the above networks are the wireless cards and wireless LAN access points • In an ad hoc network mode, there is no central controller, the wireless access cards use CSMA/CA protocol to resolve shared access • MAC layer access uses one of following methods: distributed coordination function (DCF), point coordination function (PCF), and hybrid coordination function (HCF) • DCF is carrier sense multiple access with collision avoidance (CSMA/CA) and senses the medium before sending frame

  10. Issues in MAC Protocol • Challenges security related and support of multicast and location management • Many mobile applications require support for group communication • Location-based services include providing listings of local restaurants or movie theaters, emergency services, and vehicle tracking • Scalability is a major concern to WLANs • In client server model, many PC’s or laptops physically close to each other (20-500m) can be linked to a central hub (access point) which acts as a bridge between the wireless and wired network • A large area can be covered by installing several access points in the building

  11. IEEE 802.11a (the enterprise wireless) • 5-GHz band with data rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps • Uses orthogonal frequency division multiplexing (OFDM) • Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAM • Equipment was more expensive that consumer equipment for 802.11b • 802.11a on 5 GHz is not interoperable with 802.11 b/g that operate on 2.4 Ghz although dual-band capable equipment is becoming more common for the consumer market. • 5 GHz band is less crowded than 2.4 GHz (thus less degradation due to conflicts, interference, etc) but physically has less range since it is absorbed more readily by walls and other solid objects in the LOS path • OFDM has fundamental propagation advantages in a high multipath environment while the higher frequencies enable smaller antennas with higher gain which counteract the disadvantage of a higher frequency. • The increased number of usable channels (at least in the US) and the near absence of other interfering systems (microwave ovens, cordless phones, baby monitors) give 802.11a significant aggregate bandwidth and reliability advantages over 802.11b/g (you get what you pay for)

  12. 802.11 b/g/n • IEEE 802.11b • Provides data rates of 5.5 and 11 Mbps at 2.4 GHz, a very crowded band • Complementary code keying (CCK) modulation scheme • Suffers interference from other products operating in the 2.4 GHz band microwave ovens, Bluetooth devices, baby monitors & cordless telephones • IEEE 802.11g • 2.4 GHz, up to 54 Mbps, OFDM same as 802.11a • Still has the interference problems of the 2.4 GHz band • .11g and .11b can operate simultaneously but with an .11b user in the cell the wireless network will degrade the .11g performance (AP must do translation for .11b) but still much faster than .11b alone. It is a myth that the entire network downmodes to .11b • Dual-band, or dual-mode Access Points and Network Interface Cards (NICs) that can automatically handle a and b/g are now common in all the markets, and very close in price to b/g only devices • IEEE 802.11n – new top dog on the block, IEEE standard just ratified

  13. Wireless Range Considerations

  14. Wireless Range Factors

  15. 802.11n Lessons Learned • .11n has realized better rate versus range • Backward compatible with 802.11 a/b/g stations • Mixed Mode (normal default for legacy compatibility) • Legacy Mode – AP behaves like 802.11 a/g device with improved performance but disabling .11n operation • 802.11n Mode - .11n stations only, avoids air time consumption from legacy devices (802.11b) • Tools – monitoring, diagnosis, compliance • Needed to solve tough interference problems • Key Design Parameters: site surveys, device placement, security and wired network

  16. 802.11n Lessons Learned • Live site surveys the only way to determine true coverage • 802.11n signal propagation more dependent on the environment than 802.11a/b/g • 802.11n has 8X more bandwidth at 5 GHz but propagation characteristics are very different from 2.4 GHz band thus one must perform site surveys in both bands; at a minimum survey at 5 GHz • Although .11n has greater signal propagation than 802.11a/b/g, distant stations and too many stations per AP will lower performance

  17. Wireless Metropolitan Area Networks (WMANs) • IEEE 802.16 based WiMAX • Offers less expensive opportunity • Supports point-to-multipoint broadband wireless access • Very high bit rates in the range of 3.5 MHz • Support a variety of backhaul requirements, including both ATM and packet-based protocols • Convergence sublayers are used to map the transport-layer–specific traffic to a MAC and offers features such as payload header suppression, packing, and fragmentation • Supports 99.999 percent link availability • MAC supports automatic repeat request (ARQ)

  18. Wireless Mesh Network Internet Backbone IGW 1 IGW 2 MR2 MR3 MR1 MR4 MR6 MR5 Mesh Clients Figure 15.9 Illustration of a Wireless Mesh Network (WMN)

  19. Wireless Mesh Network • Comprise of: • Internet Gateways (IGWs) • Mesh Routers (MRs) • Mesh Clients (MCs) • Multi-hop WMN, traffic is predominantly oriented towards IGWs from MRs • Traditional routing solutions of MANETs are not adequate for WMNs • TCP could result in excessive packet delays • Vulnerable to variety of security attacks

  20. Wireless Personal Area Network • Bluetooth initially conceived to replace RS232 cables, is the only WPAN technology to be commercially available • Since 2002, its presence has become visible in devices ranging from laptops to wireless mouse to cameras, to headsets, to printers and cell phones • IEEE 802.15.x protocols to address needs of WPANs with varied data rates • Bluetooth has adopted as IEEE 802.15.1 (medium rate) while the IEEE 802.15.3 (high rate) and 802.15.4 (low rate) are also available

  21. IEEE 802.15 Task Groups • IEEE 802.15 WPAN/Bluetooth TG1 • IEEE 802.15 Coexistence TG2: TG2 (the IEEE 802.15.2) is developing recommended practices to facilitate coexistence of WPANs (the IEEE 802.15) and WLANs (the IEEE 802.11). • IEEE 802.15 WPAN/High Rate TG3: The TG3 for WPANs is chartered to draft a new standard for high-rate (20Mbps or greater) WPANs • IEEE 802.15 WPAN/Low Rate TG4: The goal is to provide a standard for ultra-low complexity, cost, and power for low-data-rate (200 kbps or less) wireless connectivity among inexpensive fixed, portable, and moving devices

  22. Bluetooth • It is named after the King of Denmark that unified different factions in Christianity through the country. • It is a short range RF communication. • Low cost, low power, radio based wireless link eliminates the need for short cable. • Bluetooth radio technology built into both the cellular telephone and the laptop would replace the cable used today to connect a laptop to cellular phone. • Printers, desktops can all be wireless. • It also provides a universal bridge to existing data networks (Fig 14.11).

  23. Figure 14.9 Use of Bluetooth to connect notebook Bluetooth Cellular Link Base Station

  24. Figure 14.10 Bluetooth connecting printers, PDA’s, desktops, fax machines, keyboards, joysticks and virtually any other digital device

  25. Figure 14.11 Bluetooth providing a universal bridge to existing data networks Fixed Line

  26. Bluetooth: A mechanism to form ad hoc networks of connected devices away from fixed network infrastructures Bluetooth Personal Ad hoc Network

  27. Bluetooth • The ultimate goal is to make small products (PC/Laptops) have only one wire attached to power cord. • In case of PDA, the power cord is also eliminated. • A simple application of Bluetooth is updating the phone directory of the PC from a mobile telephone. • A typical Bluetooth has a range of 10 m.

  28. Features • Fast frequency hopping to reduce interference. • Adaptive output power to minimize interference. • Short data packets to maximize capacity. • Fast acks allowing for low coding overhead for links. • Flexible packet types that support a wide application range. • CVSD (Continuous Variable Slope Delta Modulation) voice coding that can withstand high bit error rates. • Transmission/reception interface tailored to minimize power consumption

  29. Architecture of Bluetooth System and Scatternet S2,3 Piconet 2 S3,1 S3,2 S2,2 M2 S3,3 M3 S2,1 S2,4 /S3,4 Piconet 3 S1,2 /S2,5 M1 M4 S4,1 S1,1 S 1,3 /S 4,4 S1,5 Piconet 4 S1,4 S4,2 Piconet 1 S4,3

  30. Bluetooth Technological Characteristics

  31. Architecture • Bluetooth radio typically hops faster and uses shorter packets as compared to other systems operating in the same frequency band. • Use of FEC (Forward Error Correction) limits the impact of random noise. • As the interference increases, the performance decreases.

  32. Architecture (cont’d) • Bluetooth devices can interact with other Bluetooth devices. • One of the devices acts as a master and others as slaves. • This network is called “Piconet”. • A single channel is shared among all devices in Piconet. • There can be up to seven active slaves in the Piconet. • Each of the active slaves has an assigned 3 bit Active Member address. • A lot of other slaves can remain synchronized to the Master through remaining inactive slaves, referred to as parked nodes. • A parked device remains synchronized to the master clock and can become active and start communicating in the Piconet anytime.

  33. Architecture (cont’d) • If Piconets are close to each other, they have overlapping areas • The scenario where the nodes of two or more Piconets mingle is called Scatternet • Before any connections in the Piconet are created all devices are in STDBY mode • In this mode an unconnected unit periodically “listens” for message every 1.28 seconds • Each times a device wakes up, it tunes on the set of 32 hop frequencies defined for that unit

  34. IEEE 802.15.4 • Some applications that require high data rates such as shared Internet access, distributed home entertainment, and networked gaming • However, there is an even bigger market for home automation, security, and energy conservation applications • IEEE 802.15.4 defines specification for low-rate, low-power WPANs • Application areas include industrial control; agricultural, vehicular, and medical sensors; and actuators

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