Lecture Objectives Wireless Networks and obile ystems Lecture 2 802.11 and Bluetooth technology Discuss the operation of IEEE 802.11 and Bluetooth WLANs/WANs ummarize 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 Agenda IEEE 802.11b Characteristics Channel layout (U) Bluetooth Characteristics iconets and scatternets Comparison with 802.11 IEEE 802.15 Coexistence between BT and IEEE 802.11b Types of coexistence Examples of coexistence mechanisms IEEE 802.11b Characteristics Channel assignment 802.11b, Bluetooth and Coexistence 3 Characteristics Center Frequencies Higher-speed physical layer extension of 802.11 in the 2.4 GHz band ame AC functions Offers data rates of 11, 5.5, 2 and 1 bps In practice, maximum achievable user data rate around 6-7 bps D 1 and 2 bps use 11-bit Barker sequence and DBK and DQK, respectively (as in 802.11) Higher data rates use 8-chip complementary code keying (CCK) Channel 1 2 3 4 5 6 7 Freq. (Hz) 2412 2417 2422 2427 2432 2437 2442 U / Can Eur. Japan Channel 8 9 10 11 12 13 14 Freq. 2447 2452 2457 2462 2467 2472 2484 U / Can Eur. Japan 802.11b, Bluetooth and Coexistence 5 802.11b, Bluetooth and Coexistence 6 1
Channel Layout Wi-Fi channel 1 U.. and Canada channel 6 channel 11 Wireless fidelity The Wi-Fi Alliance certifies interoperability of 802.11- based products Non-profit organization founded in 1999 Over 200 members f [Hz] 2412 2437 2462 22 Hz 802.11b, Bluetooth and Coexistence 7 802.11b, Bluetooth and Coexistence 8 Introduction to edium Access Arbitration Carrier ense ultiple Access/Collision Avoidance (CA/CA) tation 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 RT/CT frames ore on that in a later lecture Bluetooth Characteristics iconets and scatternets Comparison with 802.11 802.11b, Bluetooth and Coexistence 9 Characteristics Operates in the 2.4 GHz range, using FH hort 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 iconets 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 aximum of 7 slaves controlled by a master (3-bit addresses used) Other operational states arked: device does not participate in the piconet, but is known to the master and can be quickly reactivated tandby: device does not participate in the piconet 802.11b, Bluetooth and Coexistence 11 802.11b, Bluetooth and Coexistence 12 2
Operational tates Forming a iconet (1) Operational tates aster lave A piconet B B Initially, devices know only about themselves No synchronization Everyone monitors in mode All devices have the capability of serving as master or slave arked* tandby* * Low power states B O J D E F I A K H C B G L N Q 802.11b, Bluetooth and Coexistence 13 802.11b, Bluetooth and Coexistence 14 Forming a iconet (2) Inquiry Unit establishing the piconet automatically becomes the master It sends an to discover what other devices are out there Addressing Active devices are assigned a 3-bit active member address () arked devices are assigned an 8-bit parked member address (A) tandby devices do not need an address O D J 10 meters F E H A I K G C B Note that a device can be Undiscoverable L N Q 802.11b, Bluetooth and Coexistence 15 802.11b, Bluetooth and Coexistence 16 detach ark A tates disconnected connecting active low power 802.11b, Bluetooth and Coexistence 17 Connecting to a iconet Device in listens periodically If a device wants to establish a piconet, it sends an, broadcast over all wake-up carriers It will become the master of the piconet If was successful, device enters mode Devices in may respond to the with its device address It will become a slave to that master 802.11b, Bluetooth and Coexistence 18 ark A 3
age and Connect tates After receiving a response from devices, the master can connect to each device individually An is assigned laves 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 mode 802.11b, Bluetooth and Coexistence 19 ark A state Low ower tates laves listen to the piconet at a reduced rate aster designates certain slots to transmit to slaves in sniff state state lave stops ACL transmission, but can exchange CO packets ark state lave releases its till FH synchronized and wakes up periodically to listen to beacon 802.11b, Bluetooth and Coexistence 20 ark A catternets (1) catternets (2) iconets 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 O D J F E I H A K G C B L N Q 802.11b, Bluetooth and Coexistence 21 802.11b, Bluetooth and Coexistence 22 rotocol stack Comparison with 802.11a/b Characteristic Bluetooth IEEE 802.11b IEEE 802.11a pectrum 2.4 GHz 2.4 GHz 5 GHz ource: Bluetooth rotocol Architecture v.1, white paper available at www.bluetooth.org ax Rate Frequency selection edium access Typical transmit power 725 kbps FH aster centralized 100 mw 11 bps D CA/CA 0.05/0.25/1W 54 bps OFD CA/CA 1/2.5/100 mw 802.11b, Bluetooth and Coexistence 23 802.11b, Bluetooth and Coexistence 24 4
IEEE 802.15 Overview of WAN efforts underway at IEEE IEEE 802.15 Working Group Goal: development of consensus standards for ANs and short distance wireless networks ublishes 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: WAN/Bluetooth Task Group 2: Coexistence Task Group 3: WAN High Rate Task Group 4: WAN Low Rate 802.11b, Bluetooth and Coexistence 26 IEEE 802.15 Task Groups IEEE 802.15.1 - Developed a standard based on, and compatible with Bluetooth 1.1 Licensed technology from Bluetooth IG, Inc. IEEE 802.15.2 Considering coexistence mechanism proposals IEEE 802.15.3 Chartered to develop a high data rate (200 bps) WAN standard Application: low cost, low power imaging and multimedia IEEE 802.15.4 Investigates a low data rate WAN solution with very low complexity to allow multimonth to multi-year battery life Application: sensors, interactive toys, remote controls, badges Coexistence between Bluetooth and IEEE 802.11 Types of coexistence Example of coexistence mechanisms 802.11b, Bluetooth and Coexistence 27 Overlapping Frequency Bands Who interferes with whom? ource: Tim Godfrey, 802.11 and Bluetooth Coexistence Techniques, National Wireless Engineering Conference, 2002 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 29 802.11b, Bluetooth and Coexistence 30 5
Types of Coexistence echanisms Collaborative Requires exchange of information among IEEE 802.11b and Bluetooth devices Best when both WAN and WLAN devices embedded in the same piece of equipment (e.g., a notebook with Bluetooth and 802.11 cards) Examples: deterministic frequency nulling, TDA 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 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 IG 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 31 802.11b, Bluetooth and Coexistence 32 TDA 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 B Collaborative ower control Other Approaches 802.11 and/or BT devices limit their transmit powers to the lowest power needed to achieve the desired rate Fragmentation ay attempt to reduce collision probability by reducing the size of 802.11 frames cheduling 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 802.11 BT 802.11 BT time 802.11b, Bluetooth and Coexistence 33 802.11b, Bluetooth and Coexistence 34 ummary IEEE 802.11b achieves transmission rates of up to 11 bps in the 2.4 GHz I band using D Bluetooth also operates in the 2.4 GHz I band, using FH aster/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 6