Wireless_ Guide to Wireless Communications by yantingting

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									Wireless# Guide to Wireless Communications   6-1




Chapter 6
High Rate Wireless Personal Area Networks

At a Glance

Instructor’s Manual Table of Contents
   Overview

   Objectives

   Teaching Tips

   Quick Quizzes

   Class Discussion Topics

   Additional Projects

   Additional Resources

   Key Terms

   Technical Notes for Hands-On Projects
Wireless# Guide to Wireless Communications                                                    6-2



Lecture Notes

Overview
        Chapter 6 defines a high rate wireless personal area network (HR WPAN). Students will
        learn about the different HR WPAN standards and their applications. Next, students will
        see how WiMedia and UWB work. Chapter 6 also outlines the issues facing WPAN
        technologies. Finally, students will review the security features of each HR WPAN
        technology.


Objectives
       Define a high rate wireless personal area network (HR WPAN)
       List the different HR WPAN standards and their applications
       Explain how WiMedia and UWB work
       Outline the issues facing WPAN technologies
       Describe the security features of each HR WPAN technology


Teaching Tips
High Rate WPAN Standards
    1. Mention that the IEEE is currently working on two additional standards for WPANs:
       the IEEE 802.15.3 and 802.15.5 standards.

    2. Explain that the IEEE 802.15.3 standard defines the specifications for HR WPANs
       supporting speeds of 11, 22, 33, and up to 55 Mbps in the 2.4 GHz ISM band.


Teaching        For more information about the IEEE 802.15.3 and 802.15.5 standards, visit:
Tip             http://grouper.ieee.org/groups/802/15/.


802.15.3 High Rate WPANs

    1. Mention that IEEE standard only defines the MAC and PHY layers for WPANs.

    2. Explain that the WiMedia Alliance was formed to support the development of any
       necessary higher-layer protocols and software specifications for 802.15.3. Describe
       some of the potential applications for this standard.
Wireless# Guide to Wireless Communications                                                  6-3

    3. Describe the characteristics required by 802.15.3 applications:
       a. Require high throughput
       b. Transceiver should be low-power
       c. Cost should be low
       d. Require quality-of-service (QOS) capabilities
       e. Connections should be simple and automatic
       f. Devices should be able to connect to multiple other devices
       g. Security features should be included


Teaching        For more information about the IEEE 802.15.3 standard, visit:
Tip             www.ieee802.org/15/pub/TG3.html.


WiMedia Protocol Stack

    1. Explain that the WiMedia group defined two different architectures for the upper layers
       of the protocol stack. One is used for multimedia audio/visual applications and the other
       for data transfer applications. Use Figure 6-1 to illustrate your explanation.

    2. Describe the 802.15.3 PHY layer. This layer is responsible for converting data bits into
       a modulated RF signal. The 802.15.3 standard uses the ISM 2.4 GHz band and supports
       two different channel plans:
          a. A coexistence channel plan
          b. A high-density channel plan

    3. Mention that the channels are limited to 15 MHz bandwidth. Use Table 6-1 to describe
       the supported channel plans.

    4. Explain that the IEEE 802.15.3 standard specifies five data rates: 11 Mbps, 22 Mbps, 33
       Mbps, 44 Mbps, and 55 Mbps. This standard uses trellis code modulation (TCM)
       technology that encodes the digital signal so single bit errors can be detected and
       corrected. This technique is also referred to as forward error correction (FEC).


Teaching        Read more about trellis code modulation at:
Tip             http://en.wikipedia.org/wiki/Trellis_modulation.


    5. Use Table 6-2 to describe the various modulation techniques supported by the IEEE
       802.15.3 standard.
Wireless# Guide to Wireless Communications                                                    6-4

    6. Mention that because 802.15.3 operates in the same 2.4 GHz unlicensed band as other
       standards, to prevent interference, the PHY layer includes a number of enhancements,
       including:
           a. Passive scanning
           b. Dynamic channel selection
           c. Ability to request channel quality information
           d. Link quality and received signal strength indication
           e. Transmit power control
           f. An 802.11 coexistence channel plan
           g. Lower transmit power
           h. Neighbor piconet capability

802.15.3 Network Topology

    1. Define a Piconet Coordinator (PNC) as a role assumed by the first device in the area
       that provides all of the basic communications timing in a piconet. The PNC is also
       responsible for managing QoS. Use Figure 6-2 to illustrate your explanation.

    2. Explain that devices can form a dependent piconet. Use Figure 6-3 and Figure 6-4 to
       describe the two types of piconets:
          a. Child piconet
          b. Neighbor piconet

Additional MAC Layer Functionality

    1. Describe the MAC layer functionality as explained in this section.

    2. Explain that efficient data transfer is accomplished using superframes. Use Figure 6-5
       to illustrate your explanation.

    3. Describe the structure of a superframe in the 802.15.3 standard.

    4. Explain the general communication process in an 802.15.3 piconet, as described in this
       section.

    5. Explain that one of the best power management methods included in the 802.15.3
       standard is the ability of devices to turn off completely for long periods of time without
       losing their association with the piconet.

    6. Describe the three main 802.15.3 power-saving methods:
          a. Device synchronized power save (DSPS) mode
          b. Piconet synchronized power save (PSPS) mode
          c. Asynchronous power save (APS) mode

    7. Define a wake superframe as a superframe designated by the PNC, in which devices
       that are in power save mode wake up and listen for frames addressed to them. Use
       Figure 6-6 to show the use of wake superframes.
Wireless# Guide to Wireless Communications                                                    6-5

    8. Describe the following two additional power-saving methods:
          a. PNC can set a maximum transmit power level
          b. Devices request a reduction or an increase in their own transmit power

    9. Explain that all MAC frames include a set of fields that are present in the same order in
       every frame. Use Figure 6-7 to show the general MAC frame format.

Mesh Networking (802.15.5)

    1. Define the IEEE 802.15.5 as a proposed standard for mesh networking, in which each
       device connects to all other devices within range, effectively creating multiple paths for
       transmission. Use Figure 6-8 to illustrate a mesh networking.


Quick Quiz 1
    1. The ____________________ was formed to support the development of any necessary
       higher-layer protocols and software specifications for 802.15.3 and to perform various
       other administrative functions.
       Answer: WiMedia Alliance

    2. ____________________ capabilities allow devices to request more channel access time
       in order to prioritize high-volume, time-sensitive traffic, such as voice stream.
       Answer: Quality-of-service (QOS)
                 Quality-of-service
                 QOS

    3. The ____________________ is the device that provides all of the basic
       communications timing in a piconet.
       Answer: piconet coordinator (PNC)
               piconet coordinator
               PNC

    4. The frame check sequence (FCS) is a 32-bit ____________________ field, a common
       technique for detecting data transmission errors.
       Answer: cyclic redundancy check (CRC)
               cyclic redundancy check
               CRC


Ultra Wide Band (UWB)
    1. Explain that UWB allows new transmission techniques based on UWB to coexist with
       other RF systems with minimal or no interference.
Wireless# Guide to Wireless Communications                                                6-6

    2. Describe some of the main characteristics of UWB, including:
       a. It transmits low-power, short-range signals
       b. It transmits using extremely short low-power pulses lasting only about 1
          nanosecond
       c. It transmits over a band that is at least 500 MHz wide
       d. UWB can potentially send data at speeds of up to 2 Gbps


Teaching        For more information about Ultra Wide Band, visit:
Tip             http://en.wikipedia.org/wiki/Ultra_wideband.


How UWB Works

    1. Mention that normally, digital signals need to be spread over a wide band using
       techniques such as FHSS or DSSS. UWB uses short analog pulses for signaling, and
       does not rely on traditional modulation methods. This technique is called impulse
       modulation. Define biphase modulation as the most common modulation technique
       used by UWB. Biphase modulation uses a half-cycle positive analog pulse to represent
       a 1. Use Figure 6-9 to illustrate the UWB impulse modulation and the biphase
       modulation.

    2. Describe the following two additional modulation techniques:
          a. Direct-sequence UWB (DS-UWB)
          b. Orthogonal frequency division multiplexing (OFDM)

    3. Explain that DS-UWB takes advantage of the fact that when transmitting pulses that are
       a nanosecond long, the signal naturally spreads over a very wide frequency band. In the
       UWB case, the signal spreads over a band that is at least 500 MHz wide. Use Figure 6-
       10 to illustrate your explanation.

    4. Explain that in orthogonal frequency division multiplexing (OFDM), commonly
       referred to as MB-OFDM, the frequency band is divided into five groups containing a
       total of 14 frequency bands. Use Table 6-3 to describe the MB-OFDM frequency band
       allocation.

    5. Mention that each frequency band is 528 MHz wide, further divided into 128 frequency
       channels. These channels are orthogonal, meaning that they do not interfere with each
       another.

Teaching
                Read more about OFDM at: http://en.wikipedia.org/wiki/OFDM.
Tip

IEEE 802.15.3a

    1. Define IEEE 802.15.3a as a proposed enhancement to 802.15.3 that uses UWB
       technology to support higher data rates for multimedia and imaging applications.
Wireless# Guide to Wireless Communications                                                  6-7

    2. Explain that the Protocol Adaptation Layer (PAL) enables wireless FireWire at 400
       Mbps, based on an 802.15.3a/WiMedia platform.

    3. Mention that the 802.15.3a standard also defines wireless USB (WUSB) version 2,
       based on the WiMedia specifications and transmitting at 480 Mbps at a distance of up to
       6 feet (2 meters).


Teaching        For more information about the IEEE 802.15.3a standard, visit:
Tip             www.ieee802.org/15/pub/TG3a.html.



WPAN Challenges
This section explains challenges faced by WiMedia and UWBWPAN technologies.

Competition Among WPAN Standards

    1. Explain that IEEE 802.15.3 and .3a are positioned to compete with Bluetooth for market
       share. It will take a few years before 802.15.3 products begin to appear on the market.

    2. Mention that wireless USB and wireless 1394 (FireWire) have the potential to quickly
       outpace Bluetooth.

HR WPAN Security

    1. Explain the following security problems that affect Bluetooth technology:
       a. Bluejacking
       b. Bluesnarfing
       c. Denial-of-Service (DoS) attack

Teaching
                Read more about Bluejacking at: http://en.wikipedia.org/wiki/Bluejacking.
Tip


Teaching        Read an article about the risks of Bluesnarfing at:
Tip             http://news.zdnet.co.uk/communications/wireless/0,39020348,39145881,00.htm.


    2. Explain that the security for IEEE 802.15.3 HR WPANs is based on the Advanced
       Encryption Standard (AES) and defines how any two devices can establish a secure
       communications session to protect both the information as well as the integrity of
       communications at the MAC and PHY layers.
Wireless# Guide to Wireless Communications                                                  6-8



Teaching        For more information about the Advanced Encryption Standard (AES), visit:
Tip             http://en.wikipedia.org/wiki/Advanced_Encryption_Standard.


    3. Mention that IEEE 802.15.3 also supports message integrity verification at the MAC
       layer that prevents a man-in-the-middle attack.

Cost of WPAN Components

    1. Describe the economic problems faced by Bluetooth technology, as explained in this
       section.

Industry Support for WPAN Technologies

    1. Explain that IrDA has enjoyed strong industry support for many years, while
       Bluetooth’s support in the networking industry has been, at best, spotty.

    2. Mention that industry experts predict that new technologies like 802.15.3 and ZigBee
       will be more quickly embraced by manufacturers.

Protocol Functionality Limitations

    1. Explain that Bluetooth protocol suffers from its lack of hand-off capability between
       piconets. Define hand-off as the ability of a device to move from one master or PNC to
       another without getting disconnected from the network.

    2. Describe the limitations in infrared communications. In infrared, roaming is a limitation
       but not a concern, since this technology is designed for peer-to-peer communications.

Spectrum Conflict

    1. Define spectrum conflict as the potential for technologies using the same frequency
       bands to interfere with each other. Applying UWB technology may significantly reduce
       or eliminate this issue.

    2. Mention that UWB can interfere with 802.11a networks. ZigBee and WiMedia products
       should be able to coexist with 802.11b/g without any serious problems.


Quick Quiz 2
    1. ____________________ attacks flood a Bluetooth device with so many frames that it is
       unable to communicate.
       Answer: Denial-of-service (DoS)
                Denial-of-service
                DoS
Wireless# Guide to Wireless Communications                                                   6-9

    2. ____________________ is a symmetric key encryption mechanism introduced by the
       National Institute of Standards and Technology (NIST) in the United States.
       Answer: Advanced Encryption Standard (AES)
               Advanced Encryption Standard
               AES

    3. ____________________ is the ability of a device to move from one master or PNC to
       another without getting disconnected from the network in a network that extends
       beyond the communications range of each device that controls the communications.
       Answer: Hand-off

    4. ____________________ is the potential for technologies using the same frequency
       bands to interfere with each other to the extent that they sometimes perform poorly
       when used within close range of each other.
       Answer: Spectrum conflict


Class Discussion Topics
    1. What is a piconet?

    2. What are the benefits of using message integrity verification at the 802.15.3 MAC
       layer?


Additional Projects
    1. Ask your students to write a one-page report listing various applications for ultra wide
       band (UWB).

    2. Ask your students to write a one-page report explaining a man-in-the-middle attack.
       They can use the Internet to research for information about this type of attack.


Additional Resources
    1. IEEE 802.15:
       http://en.wikipedia.org/wiki/IEEE_802.15.1

    2. WiMedia Alliance:
       www.wimedia.org/en/index.asp

    3. Ultra Wideband (UWB) Technology:
       www.intel.com/technology/comms/uwb/

    4. UWB Forum:
       www.uwbforum.org/
Wireless# Guide to Wireless Communications                                                  6-10

    5. Orthogonal Frequency Division Multiplexing (OFDM) Forum:
       www.caba.org/standard/ofdm.html

    6. EEE 802.15 Working Group for WPAN:
       http://grouper.ieee.org/groups/802/15/

    7. Bluejacking:
       www.bluejacking.info/index.html

    8. Bluesnarfing:
       http://en.wikipedia.org/wiki/Bluesnarfing

    9. Advanced Encryption Standard:
       www.utimaco.us/encryption/aes.html


Key Terms
     Advanced Encryption Standard (AES) — A symmetric key encryption mechanism
      introduced by the U.S. National Institute of Standards and Technology.
     biphase modulation — Modulation that uses a half-cycle positive analog pulse to
      represent a 1 and a half-cycle negative analog pulse to represent a 0.
     channel time allocation (CTA) — Periods of time allocated by the PNC to a specific
      device for prioritizing communications in a WPAN. See also management channel time
      allocation (MCTA).
     channel time allocation period (CTAP) — The superframe component used for
      communications between the PNC and other devices.
     child piconets — Separate piconets with their own ID; the child PNC is a member of
      the original or parent piconet.
     contention access period (CAP) — A mechanism used to communicate commands or
      any asynchronous data that may be present in a superframe. The CAP is also used to
      allow devices that are not yet part of a piconet to send a request to the PNC to join the
      piconet.
     cyclic redundancy check (CRC) — A common technique for detecting data
      transmission errors.
     denial-of-service (DoS) — A type of security attack on a networked device in which
      the attacker sends so many frames to a single device that the device is unable to
      communicate with other devices.
     hand-off — The ability of a device to move from one master or PNC to another without
      getting disconnected from the network in a network that extends beyond the
      communications range of each device that controls the communications.
     impulse modulation — A digital transmission technique employed by UWB in which
      the polarity of a single analog pulse (one-half of a sine wave) represents a binary digit 1
      or 0.
     isochronous — The channel time in synchronous transmissions.
     management channel time allocation (MCTA) — Time periods used for
      communication between the devices and the PNC.
Wireless# Guide to Wireless Communications                                                6-11

     man-in-the-middle attack — A security attack in which a hacker captures frames,
      alters them, and then retransmits them to the intended receiver or another device on the
      network.
     mesh networking — A network topography in which each device connects to all other
      devices within range.
     message integrity — A process of adding certain encrypted random data to each
      communications session so that the receiver can verify that the message has not been
      tampered with, after being transmitted.
     neighbor piconets — Separate piconets that have their own PNC, but that depend on
      the original piconet’s PNC to allocate a private block of time when their devices are
      allowed to transmit.
     orthogonal frequency division multiplexing (OFDM) — A transmission technique in
      which the frequency band is divided into a number of frequencies (called sub-
      frequencies or channels) that do not interfere with each other.
     piconet coordinator (PNC) — A device that provides all of the basic communications
      timing in an 802.15.3 piconet.
     Protocol Adaptation Layer (PAL) — A set of protocol implementation rules that will
      enable wireless FireWire at 400 Mbps, based on an 802.15.3a/WiMedia platform.
     quality of service (QoS) — A feature of some PANs that allows devices to request
      more channel access time in order to prioritize high-volume, time-sensitive traffic, such
      as a voice stream.
     spectrum conflict — The potential for technologies using the same frequency bands to
      interfere with each other to the extent that they sometimes perform poorly when used
      within close range of each other.
     superframe — A mechanism for managing transmissions in a piconet. The superframe
      is a continually repeating frame containing a beacon, contention access periods, channel
      time allocation periods, and management time allocation periods.
     trellis code modulation (TCM) — A method of encoding a digital signal in a way that
      permits single bit errors to be detected and corrected.
     wake superframe — The superframe designated by the PNC in which devices that are
      in power save mode will wake up and listen for frames addressed to them.
     WiMedia Alliance — An association of manufacturers and interested organizations
      formed to promote the implementation of the IEEE 802.15.3 standard and provide
      various support activities.


Technical Notes for Hands-On Projects
Project 6-1: This project requires a Web browser and an Internet connection.

Project 6-2: This project requires a Web browser and an Internet connection.

								
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