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Lecture 6 802.11b, Bluetooth and Coexistence

Wireless Networks and Mobile Systems. Lecture 6 802.11b, Bluetooth and Coexistence. Lecture Objectives. Discuss the operation of IEEE 802.11 and Bluetooth WLANs/WPANs Summarize standardization efforts and recommendations by IEEE 802.15 group

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Lecture 6 802.11b, Bluetooth and Coexistence

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  1. Wireless Networks and Mobile Systems Lecture 6802.11b, Bluetooth and Coexistence

  2. Lecture Objectives • Discuss the operation of IEEE 802.11 and Bluetooth WLANs/WPANs • Summarize standardization efforts and recommendations by IEEE 802.15 group • Discuss interference issues between IEEE 802.11 and BT and some suggested interference mitigation/ coexistence techniques 802.11b, Bluetooth and Coexistence 2

  3. Agenda • IEEE 802.11b • Characteristics • Channel layout (US) • Bluetooth • Characteristics • Piconets and scatternets • Comparison with 802.11 • IEEE 802.15 • Coexistence between BT and IEEE 802.11b • Types of coexistence • Examples of coexistence mechanisms 802.11b, Bluetooth and Coexistence 3

  4. Characteristics Channel assignment IEEE 802.11b

  5. Characteristics • Higher-speed physical layer extension of 802.11 in the 2.4 GHz band • Same MAC functions • Offers data rates of 11, 5.5, 2 and 1 Mbps • In practice, maximum achievable user data rate around 6-7 Mbps • DSSS • 1 and 2 Mbps use 11-bit Barker sequence and DBPSK and DQPSK, respectively (as in 802.11) • Higher data rates use 8-chip complementary code keying (CCK) 802.11b, Bluetooth and Coexistence 5

  6. Center Frequencies 802.11b, Bluetooth and Coexistence 6

  7. Channel Layout U.S. and Canada channel 1 channel 6 channel 11 f [MHz] 2412 2437 2462 22 MHz 802.11b, Bluetooth and Coexistence 7

  8. Wi-Fi • Wireless fidelity • The Wi-Fi Alliance certifies interoperability of 802.11-based products • Non-profit organization founded in 1999 • Over 200 members 802.11b, Bluetooth and Coexistence 8

  9. Introduction to Medium Access Arbitration • Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) • Station that desires to transmit senses the medium • If busy, backoff for a random period of time after the medium becomes idle • If idle, transmit after a mandatory minimum interframe spacing • No explicit collision detection, but if frame is not ACK’d, station assumes a collision has occurred and retransmits • Optionally, can reserve the channel through the exchange of RTS/CTS frames • More on that in a later lecture… 802.11b, Bluetooth and Coexistence 9

  10. Characteristics Piconets and scatternets Comparison with 802.11 Bluetooth

  11. Characteristics • Operates in the 2.4 GHz range, using FHSS • Short range • Up to 10 m • Asynchronous (data) and synchronous (voice) service available • Around 700 kbps • No need for infra-structure (ad hoc) • Low power consumption 802.11b, Bluetooth and Coexistence 11

  12. Piconets • Nodes can assume the role of master or slave • One or more slaves can connect to a master, forming a piconet • The master sets the hopping pattern for the piconet, and all slaves must synchronize to that pattern • Maximum of 7 slaves controlled by a master (3-bit addresses used) • Other operational states • Parked: device does not participate in the piconet, but is known to the master and can be quickly reactivated • Standby: device does not participate in the piconet 802.11b, Bluetooth and Coexistence 12

  13. Operational States Operational States A piconet SB Master S SB Slave M Parked* P S Standby* * Low power states S SB S 802.11b, Bluetooth and Coexistence 13

  14. Forming a Piconet (1) • Initially, devices know only about themselves • No synchronization • Everyone monitors in standby mode • All devices have the capability of serving as master or slave N F H D G P O E A M J B L Q I K C 802.11b, Bluetooth and Coexistence 14

  15. Forming a Piconet (2) • Unit establishing the piconet automatically becomes the master • It sends an inquiry to discover what other devices are out there • Addressing • Active devices are assigned a 3-bit active member address (AMA) • Parked devices are assigned an 8-bit parked member address (PMA) • Standby devices do not need an address 802.11b, Bluetooth and Coexistence 15

  16. Inquiry Note that a device can be “Undiscoverable” D F N H H G M A P B O E K J L Q I C 10 meters 802.11b, Bluetooth and Coexistence 16

  17. States standby disconnected detach inquiry page connecting Transmit AMA Connected AMA active Park PMA Hold AMA Sniff AMA low power 802.11b, Bluetooth and Coexistence 17

  18. standby inquiry page Transmit AMA Connected AMA Park PMA Hold AMA Sniff AMA Connecting to a Piconet • Device in standby listens periodically • If a device wants to establish a piconet, it sends an inquiry, broadcast over all wake-up carriers • It will become the master of the piconet • If inquiry was successful, device enters page mode • Devices in standby may respond to the inquiry with its device address • It will become a slave to that master 802.11b, Bluetooth and Coexistence 18

  19. standby inquiry page Transmit AMA Connected AMA Park PMA Hold AMA Sniff AMA Page and Connect States • After receiving a response from devices, the master can connect to each device individually • An AMA is assigned • Slaves synchronize to the hopping sequence established by the master • In active state, master and slaves listen, transmit and receive • A disconnect procedure allows devices to return to standby mode 802.11b, Bluetooth and Coexistence 19

  20. standby inquiry page Transmit AMA Connected AMA Park PMA Hold AMA Sniff AMA Low Power States • Sniff state • Slaves listen to the piconet at a reduced rate • Master designates certain slots to transmit to slaves in sniff state • Hold state • Slave stops ACL transmission, but can exchange SCO packets • Park state • Slave releases its AMA • Still FH synchronized and wakes up periodically to listen to beacon 802.11b, Bluetooth and Coexistence 20

  21. Scatternets (1) • Piconets with overlapping coverage use different hopping sequences • Collisions may occur when multiple piconets use the same carrier frequency at the same time • Devices can participate in multiple piconets simultaneously, creating a scatternet • A device can only be the master of one piconet at a time • A device may serve as master in one piconet and slave in another • A device may serve as slave in multiple piconets 802.11b, Bluetooth and Coexistence 21

  22. Scatternets (2) D F H N G M A B P O E K J L I Q C 802.11b, Bluetooth and Coexistence 22

  23. Protocol stack Source: Bluetooth Protocol Architecture v.1, white paper available at www.bluetooth.org 802.11b, Bluetooth and Coexistence 23

  24. Comparison with 802.11a/b Characteristic Bluetooth IEEE 802.11b IEEE 802.11a Spectrum 2.4 GHz 2.4 GHz 5 GHz Max Transmit Rate 725 kbps 11 Mbps 54 Mbps Frequency selection FHSS DSSS OFDM Medium access Master centralized CSMA/CA CSMA/CA Typical transmit power 100 mW 0.05/0.25/1W 1/2.5/100 mW 802.11b, Bluetooth and Coexistence 24

  25. Overview of WPAN efforts underway at IEEE IEEE 802.15

  26. IEEE 802.15 Working Group • Goal: development of consensus standards for PANs and short distance wireless networks • Publishes standards and recommended practices • Deals with issues of coexistence and interoperability with other wireless and wireline technologies • URL: http://grouper.ieee.org/groups/802/15/ Task Group 1: WPAN/Bluetooth Task Group 2: Coexistence Task Group 3: WPAN High Rate Task Group 4: WPAN Low Rate 802.11b, Bluetooth and Coexistence 26

  27. IEEE 802.15 Task Groups • IEEE 802.15.1 - Developed a standard based on, and compatible with Bluetooth 1.1 • Licensed technology from Bluetooth SIG, Inc. • IEEE 802.15.2 – Considering coexistence mechanism proposals • IEEE 802.15.3 – Chartered to develop a high data rate (200 Mbps) WPAN standard • Application: low cost, low power imaging and multimedia • IEEE 802.15.4 – Investigates a low data rate WPAN solution with very low complexity to allow multi-month to multi-year battery life • Application: sensors, interactive toys, remote controls, badges 802.11b, Bluetooth and Coexistence 27

  28. Types of coexistence Example of coexistence mechanisms Coexistence between Bluetooth and IEEE 802.11

  29. Overlapping Frequency Bands Source: Tim Godfrey, “802.11 and Bluetooth Coexistence Techniques,” National Wireless Engineering Conference, 2002 802.11b, Bluetooth and Coexistence 29

  30. Who interferes with whom? • Bluetooth interferes with 802.11b • 802.11b frames collide with Bluetooth packets (longer frames have a higher probability of collision) • Retransmissions increase delay • Impact can be severe, depending on the distance from the node equipped with 802.11b to the access point and to the Bluetooth nodes • 802.11b also interferes with Bluetooth • High power 802.11b transmitter can saturate the Bluetooth receiver • Can also cause increased errors if the bands are overlapping • Impact can be severe, depending on the power of the 802.11b nodes and the distance to them 802.11b, Bluetooth and Coexistence 30

  31. Types of Coexistence Mechanisms • Collaborative • Requires exchange of information among IEEE 802.11b and Bluetooth devices • Best when both WPAN and WLAN devices embedded in the same piece of equipment (e.g., a notebook with Bluetooth and 802.11 cards) • Examples: deterministic frequency nulling, TDMA of BT and 802.11 • Non-collaborative • Can be adopted by 802.11b or Bluetooth devices without explicit collaboration • Examples: adaptive frequency hopping, power control 802.11b, Bluetooth and Coexistence 31

  32. Adaptive Frequency Hopping • Bluetooth radio can detect some frequencies as “undesirable” (due to interference) and not use them in a hopping sequence • AFH in the process of standardization by the Bluetooth SIG • To be incorporated in Bluetooth 1.2 • Clearly, not effective if the entire band is subject to interference from 802.11 • Non-collaborative 802.11b, Bluetooth and Coexistence 32

  33. TDMA Approach • Designate separate intervals for BT and 802.11 • Can be based on 802.11 beacon interval • Clients and access points would need to be modified to incorporate this type of approach • Also, can be wasteful, since interference problem is localized, but this solution would be applied to the entire BSS • Collaborative 802.11 BT 802.11 BT time 802.11b, Bluetooth and Coexistence 33

  34. Other Approaches • Power control • 802.11 and/or BT devices limit their transmit powers to the lowest power needed to achieve the desired rate • Fragmentation • May attempt to reduce collision probability by reducing the size of 802.11 frames • Scheduling • BT devices schedule packet transmissions during hops that are outside the band of frequencies currently used by the WLAN and avoid transmitting while in-band 802.11b, Bluetooth and Coexistence 34

  35. Summary • IEEE 802.11b achieves transmission rates of up to 11 Mbps in the 2.4 GHz ISM band using DSSS • Bluetooth also operates in the 2.4 GHz ISM band, using FHSS • Master/slave architecture, where piconets are formed between one master and up to 7 slaves • Coexistence is an issue, to prevent BT nodes from acting (maybe unwittingly) as a rogue node in an IEEE 802.11 WLAN • Adaptive frequency hopping is the leading proposal to enable coexistence 802.11b, Bluetooth and Coexistence 35

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