Wireless# Guide to Wireless Communications. Objectives

Transcription

1 Wireless# Guide to Wireless Communications Chapter 6 High Rate Wireless Personal Area Networks 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 Wireless# Guide to Wireless Communications 2 1

2 High Rate WPAN Standards IEEE is currently working on two standards IEEE and IEEE 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 Wireless# Guide to Wireless Communications High Rate WPANs IEEE standard defines the MAC and PHY layers WiMedia Alliance Formed to support the development of any necessary higher-layer protocols And software specifications for Potential applications Connecting digital cameras to printers and kiosks Connecting laptops to multimedia projectors and sound systems Wireless# Guide to Wireless Communications 4 2

3 High Rate WPANs Application characteristics Require high throughput Transceiver should be low-power Cost should be low Require quality-of-service (QOS) capabilities Connections should be simple and automatic Devices should be able to connect to multiple other devices Security features should be included Wireless# Guide to Wireless Communications 5 WiMedia Protocol Stack 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 The lower two layers of the stack (MAC and PHY) Are implemented in hardware PHY layer Converts data bits into a modulated RF signal standard uses the ISM 2.4 GHz band Wireless# Guide to Wireless Communications 6 3

4 WiMedia Protocol Stack Wireless# Guide to Wireless Communications 7 WiMedia Protocol Stack PHY layer Supports two different channel plans A coexistence channel plan A high-density channel plan Channels are limited to 15 MHz bandwidth IEEE standard specifies five data rates 11 Mbps, 22 Mbps, 33 Mbps, 44 Mbps, and 55 Mbps Trellis code modulation (TCM) Encodes the digital signal so single bit errors can be detected and corrected Also called error correction (FEC) Wireless# Guide to Wireless Communications 8 4

5 WiMedia Protocol Stack Wireless# Guide to Wireless Communications 9 WiMedia Protocol Stack Modulation See Table 6-2 for modulation techniques Enhancements Passive scanning Dynamic channel selection Ability to request channel quality information Link quality and received signal strength indication Transmit power control An coexistence channel plan Lower transmit power Neighbor piconet capability Wireless# Guide to Wireless Communications 10 5

6 WiMedia Protocol Stack Wireless# Guide to Wireless Communications Network Topology Piconet coordinator (PNC) Role assumed by the first device in the area Provides all of the basic communications timing in a piconet PNC sends a beacon The piconet is peer-to-peer Devices can transmit data directly to each other The PNC is also responsible for managing QoS Devices can form a dependent piconet Wireless# Guide to Wireless Communications 12 6

7 Network Topology Wireless# Guide to Wireless Communications Network Topology Types of dependent piconets Child piconets Useful for extending the coverage of a piconet Neighbor piconets Allow coexistence with other piconets in the same area Wireless# Guide to Wireless Communications 14 7

8 Network Topology Wireless# Guide to Wireless Communications Network Topology Wireless# Guide to Wireless Communications 16 8

9 Additional MAC Layer Functionality The IEEE MAC layer functionality Connection time (association) is fast Devices associated with the piconet can use a short, one-octet device ID Devices can obtain information about the capabilities of other devices Peer-to-peer (ad hoc) networking Data transport with QoS Security Efficient data transfer using superframes Wireless# Guide to Wireless Communications 17 Additional MAC Layer Functionality Wireless# Guide to Wireless Communications 18 9

10 Additional MAC Layer Functionality IEEE superframe structure A beacon An optional contention access period (CAP) The channel time allocation period (CTAP) Communication in an piconet Beacon frame sent by the PNC includes a variable indicating the end of the CAP Devices can send asynchronous data in the CAP Devices can request channel time on a regular basis Requested channel time is called isochronous time Wireless# Guide to Wireless Communications 19 Additional MAC Layer Functionality Communication in an piconet Devices can also request channel time for asynchronous communications in the CTAP Communications use a time division multiple access (TDMA) scheme Power management devices can turn off completely for long periods of time Without losing their association with the piconet Wireless# Guide to Wireless Communications 20 10

11 Additional MAC Layer Functionality Power management power-saving methods Device synchronized power save (DSPS) mode Piconet synchronized power save (PSPS) mode Asynchronous power save (APS) mode Wake superframe Superframe designated by the PNC Devices that are in power save mode wake up and listen for frames addressed to them Wireless# Guide to Wireless Communications 21 Additional MAC Layer Functionality Wireless# Guide to Wireless Communications 22 11

12 Additional MAC Layer Functionality Power management Additional power-saving methods PNC can set a maximum transmit power level Devices request a reduction or an increase in their own transmit power General MAC frame format All MAC frames include a set of fields that are present in the same order in every frame Wireless# Guide to Wireless Communications 23 Additional MAC Layer Functionality Wireless# Guide to Wireless Communications 24 12

13 Mesh Networking ( ) Mesh networking Each device connects to all other devices within range Effectively creating multiple paths for transmission Enable WiMedia networks to span an entire building Wireless# Guide to Wireless Communications 25 Mesh Networking ( ) Wireless# Guide to Wireless Communications 26 13

14 Ultra Wide Band (UWB) Allows new transmission techniques based on UWB to coexist with other RF systems With minimal or no interference Characteristics It transmits low-power, short-range signals It transmits using extremely short low-power pulses lasting only about 1 nanosecond It transmits over a band that is at least 500 MHz wide UWB can send data at speeds of up to 2 Gbps Wireless# Guide to Wireless Communications 27 How UWB Works UWB PHY Digital signals need to be spread over a wide band Using techniques such as FHSS or DSSS UWB uses short analog pulses for signaling Does not rely on traditional modulation methods This technique is called impulse modulation Biphase modulation Most common modulation technique used by UWB Uses a half-cycle positive analog pulse to represent a 1 Wireless# Guide to Wireless Communications 28 14

15 How UWB Works Wireless# Guide to Wireless Communications 29 How UWB Works UWB PHY Direct-sequence UWB (DS-UWB) When transmitting pulses that are a nanosecond long Signal spreads over a very wide frequency band In the UWB case, the signal spreads over a band that is at least 500 MHz wide Orthogonal frequency division multiplexing (OFDM) Commonly referred to as MB-OFDM Frequency band is divided into five groups containing a total of 14 frequency bands Wireless# Guide to Wireless Communications 30 15

16 How UWB Works Wireless# Guide to Wireless Communications 31 How UWB Works Wireless# Guide to Wireless Communications 32 16

17 How UWB Works UWB PHY Orthogonal frequency division multiplexing (OFDM) Each frequency band is 528 MHz wide Further divided into 128 frequency channels Channels are orthogonal They do not interfere with each another Data bits are sent simultaneously (in parallel) Wireless# Guide to Wireless Communications 33 IEEE a Proposed enhancement to Uses UWB technology to support higher data rates For multimedia and imaging applications Protocol Adaptation Layer (PAL) Enables wireless FireWire at 400 Mbps Based on an a/WiMedia platform Wireless USB (WUSB) version 2 Based on the WiMedia specifications Transmits at 480 Mbps at a distance of up to 2 meters Wireless# Guide to Wireless Communications 34 17

18 WPAN Challenges Challenges Competition Among WPAN Standards HR WPAN Security Cost of WPAN Components Industry Support for WPAN Technologies Protocol Functionality Limitations Spectrum Conflict Wireless# Guide to Wireless Communications 35 Competition Among WPAN Standards IEEE and.3a are positioned to compete with Bluetooth for market share It will take a few years before products begin to appear on the market Wireless USB and wireless 1394 (FireWire) have the potential to quickly outpace Bluetooth Wireless# Guide to Wireless Communications 36 18

19 HR WPAN Security Bluetooth security Bluejacking Exploits a Bluetooth device s ability to discover nearby devices and send unsolicited messages Bluesnarfing Accesses contact lists and other information without the user s knowledge Denial-of-service (DoS) attacks Flood a Bluetooth device with so many frames that it is unable to communicate Wireless# Guide to Wireless Communications 37 HR WPAN Security Security for IEEE HR WPANs Based on the Advanced Encryption Standard (AES) Defines how any two devices can establish a secure communications session To protect both the information and the integrity of communications at the MAC and PHY layers also supports message integrity verification at the MAC layer Prevents a man-in-the-middle attack Wireless# Guide to Wireless Communications 38 19

20 Cost of WPAN Components Bluetooth currently supports more devices than other WPAN technologies Industry experts believe that price must be reduced to reach competitive advantage Does not make economic sense to use a chip that costs $15 to replace a cable that costs $7 Wireless# Guide to Wireless Communications 39 Industry Support for WPAN Technologies IrDA has had strong industry support for many years Bluetooth s support in the networking industry has been, at best, spotty Industry experts predict that new technologies will be more quickly embraced by manufacturers Such as and ZigBee Wireless# Guide to Wireless Communications 40 20

21 Protocol Functionality Limitations Bluetooth protocol suffers from its lack of hand-off capability between piconets Hand-off Ability to move from one master or PNC to another Without getting disconnected from the network In infrared, roaming is a limitation but not a concern Since this technology is designed for peer-to-peer communications Wireless# Guide to Wireless Communications 41 Spectrum Conflict Spectrum conflict Potential for technologies using the same frequency bands to interfere with each other Applying UWB technology may significantly reduce or eliminate this issue UWB can interfere with a networks ZigBee and WiMedia products should be able to coexist with b/g without any serious problems Wireless# Guide to Wireless Communications 42 21

22 Summary IEEE is a WPAN technology Optimized for multimedia voice and video signals The WiMedia protocol stack has two upper layers One for audio/video and one for data transfer applications The PHY layer supports two different channel plans Works in the same ISM band as b WLANs supports peer-to-peer or ad hoc networks piconets support child and neighbor piconets Wireless# Guide to Wireless Communications 43 Summary Efficient data transmission is accomplished by use of the superframe concept In , devices can be in one of several powersaving modes mesh networking standard extends the capabilities of networks Ultra Wide Band is a digital transmission technology Will soon support very high-speed transmissions at up to 100+ Mbps UWB transmissions: bandwidth of at least 500 MHz Wireless# Guide to Wireless Communications 44 22

23 Summary UWB transmits using very short pulses Challenges for WPANs include speed, security, cost, industry support, interference, and protocol limitations WPAN devices that are designed to be small and consume very little power have limited processing capabilities and storage Wireless# Guide to Wireless Communications 45 23