Amarjeet Singh February 7, 2012 References Bluetooth Protocol Architecture v.1 www.bluetooth.org http://www.tutorial-reports.com/wireless/bluetooth/
Slides from last class uploaded on the course website Student presentations: All papers linked on the website Tentative schedule in the spreadsheet Select your paper soon 1 hour presentation will send out the suggestive outline soon Details of Group Project on the website Feedback on demo of Assignment-3 Assignment-4 due coming friday
How is collision avoidance implemented in CAN? IEEE 802.15.4: Which two layers does the protocol define? What are the node types defined? What are the supported topologies? How many channels are available in 2.4 GHz range? Zigbee: How does it extend IEEE 802.15.4? What are different devices supported? What are the different addresses supported? What are different supported topologies? What are techniques employed for reliable communication? What are techniques employed for security of the data?
Program and Debug Interface (PDI): Atmel proprietary interface for external programming and on-chip debugging Supports programming of Non-volatile memory (NVM): Flash, EEPROM, Fuses, Lock bits Programming and Debugging possible through 2 physical interfaces: 2-pin PDI Interface (PDI_CLK, PDI_DATA) JTAG Interface
Uses bi-direction, synchronous, half duplex, serial receiver and transmitter Similar to? Physical layer includes start of frame detection, frame error detection, parity generation, parity error detection and collision detection
Can be used for two purposes: Boundary scan capability to test the PCB Programming the device through JTAG capability of PDI interface Boundary scan has the capability of driving and observing logic levels on I/O pins All microcontroller (or board) components having JTAG capabilities are connected serially by TDI/TDO signals External controller sets up the devices to drive values at their output pins and observes the input values received from other devices Received data is compared with the expected result
Low level serial communication over 4 lines TDI, TDO, TCK, TMS JTAGEN fuse must be programmed and JTAG disable bit in MCU control register must be cleared to enable JTAG interface Done by default JTAG PDICOM instruction sets JTAG to access PDI for external programming and on-chip debugging
Short range radio links intended to replace cables No line of sight required unlike IrDA Short range: 0-30 feet (10 meters) with power consumption of 4 dbm (2.5 mw) Distance can be increased by amplifying the power Operates in the unlicensed band at 2.4 GHz also used by other devices such as 802.11, garage door openers, microwave etc. Higher probability of interference Bluetooth channel is divided into time slots each 625 us in length Devices hop through these timeslots making 1600 hops per second
Uses 79 channels in the frequency range 2.402-2.480 GHz Uses Frequency Hop Spread Spectrum (FHSS) to avoid interference Transmitter hops between available frequencies according to specified algorithm Transmitter operates in sync with receiver A short burst of data is transmitted on a narrowband Transmitter then tunes to another frequency and transmits again - capable of hopping its frequency over a given bandwidth several times a second Requires much wider bandwidth than required to transmit the same information using one carrier frequency
Supports two kinds of links Asynchronous Connectionless (ACL) for data transmission Synchronous Connection Oriented (SCO) for audio/video Maximum effective rate around 700 kbps in asymmetric ACL link Symmetric ACL allows data rates of around 400 kbps
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: All units share the same channel Maximum of 7 slaves controlled by a master (3-bit addresses used) Bluetooth radios are symmetric - same device can act as both master and slave Slaves are not allowed to talk to each other directly Other operational states (low power) Parked: Device does not participate in the piconet, synchronized to the master and can be quickly reactivated Standby: Device does not participate in the piconet, occasionally monitoring, not synchronized
Operational States A piconet Master S SB SB Slave Parked* M P Standby* S * Low power states S SB S
Initially, devices know only about themselves No synchronization Everyone monitors in standby mode (performs inquiry or page scan for 10 ms every 1.28 seconds Power consumption in standby mode is reduced by over 98% All devices have the capability of serving as master or slave D E F A Devices in this illustration are in the same mode but are not synchronized or coordinated - listening at different times and on different frequencies H C B G
Unit establishing the piconet automatically becomes the master It sends an inquiry to discover other devices out there Inquiry procedure: Enables a device to discover which devices are in range and determine the addresses and clocks for devices Paging procedure: Establishes an actual connection; only bluetooth device address is required to setup the connection Master and slave exchange packet using channel access code and master clock 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
Note that a device can be Undiscoverable D F H G M N O J E I A K C B L P Q 10 meters
standby disconnected detach inquiry page connecting Transmit AMA Connected AMA active Park PMA Hold AMA Sniff AMA low power
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 standby Transmit AMA Park PMA inquiry Hold AMA page Connected AMA Sniff AMA
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 standby Transmit AMA inquiry page Connected AMA Park PMA Hold AMA Sniff AMA
Sniff state Slaves listen to the piconet at a reduced rate Master designates certain slots to transmit to slaves in sniff state Hold state Only internal timer is running 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 standby Transmit AMA Park PMA inquiry Hold AMA page Connected AMA Sniff AMA
Piconets with overlapping coverage use different hopping sequences Collisions may occur when multiple piconets use the same carrier frequency at the same time Higher probability of collision with more piconets 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
D F H G M N O J E I A K C B L P Q
Let us test the range of bluetooth devices we have Try looking for connection from my machine (AMARJEET-PC)
Developed by Bluetooth Special Interest Group (SIG) to support interoperability Bluetooth core protocols (radio, baseband, LMP, L2CAP, SD) are required by most bluetooth devices
Frequency Hop Spread Spectrum (FHSS) in 79 hops displaced by 1 MHz between 2.402-2.480 GHz Each device is classified into 3 power classes: Power class 1 - long range (~100 m), output power 20 dbm Power class 2 - medium range (~10 m), output power 4 dbm Power class 3 - short range (~10 cm), output power 0 dbm
Baseband is the physical layer of Bluetooth Manages physical channels and links apart from other services like error correction, flow control, synchronization and security Baseband protocol is implemented as a link controller that works with link manager to carry link level routines such as link connection and power control Baseband transceiver applies TDD (Time Division Duplex) Alternate transmit and receive - Master and slave transmit in even and odd number slots Device addressing: 4 types of addresses can be assigned to bluetooth units Bluetooth Device Address: Unique 48-bit device address Active Member Address: 3-bit number, valid as long as slave is active Parked Member Address: 8-bit master-local address for parked slaves Access Request Address: Specifies the slot when a parked slave is allowed to send access request
13 different types of packets defined in Baseband layer Each packet consists of 3 entities: Access Code (68/72 bits): Used for timing synchronization, inquiry etc. Header (54 bits): Contains information for packet acknowledgement, packet numbering, flow control, error check etc. Payload (0-2745 bits): Contains either voice field or data field or both
Link Manager discovers other remote LMs and communicates with them using Link Manager Protocol (LMP) LMP consists of different Protocol Data Units (PDU) sent from one device to another using Active Member Address; Some of these PDU include: Authentication: Verifier send LMP_au_rand PDU containing random number to claimant; claimant calculates response which is function of random number, its BD_ADDR and a secret key; response sent back to verifier Detach: Connection between two devices can be closed anytime by master or slave; A reason parameter is also included in the LMP_detach PDU Power Control: If RSSI value differs from preferred value, a request (LMP_incr_power_req, LMP_dec_power_req) is sent to increase/decrease the device s TX power
HCI Firmware: Located on actual bluetooth hardware device; implements the HCI commands for bluetooth hardware
HCI Driver: Located on the host (e.g. software entity); Host receives asynchronous notifications of HCI events; parses the received event packet to determine the event
HCI Controller Transport Layer: HCI Driver and Firmware communicates via HCI Controller Transport Layer; Should provide the ability to transfer data without knowledge about the data
Logical Link Control and Adaptation Layer Protocol (L2CAP): Provides connection-oriented and connectionless data services to upper layer protocols Permits higher level protocols and applications to transmit and receive L2CAP data packets up to 64 kb L2CAP specification is defined for only ACL links and no support for SCO links is planned RFCOMM Protocol: Transport Protocol that provides emulation of serial port (RS232) over L2CAP Supports up to 60 simultaneous connections between two devices
At Link level, a pair of devices share a secret key derived from Bluetooth passkey (also known as Personal Identification Number - PIN) Either built-in or entered in the user interface After authentication, devices can create shared link keys that can be used to encrypt traffic on a link Combination of authentication and creating link keys is called pairing Possibly accompanied by exchange of higher level security information
High-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 Typical range: 30 m at 11 Mbps, 90 m at 1 Mbps Frequency Selection using Direct Sequence Spread Spectrum (DSSS): Provides spreading gain against narrowband noise 13 channels available from 2.401-2.495 GHz each of width 22 MHz
Channel Freq. (MHz) US / Can Eur. Japan 1 2412 2 2417 3 2422 4 2427 5 2432 6 2437 7 2442 Channel Freq. US / Can Eur. Japan 8 2447 9 2452 10 2457 11 2462 12 2467 13 2472 14 2484
U.S. and Canada channel 1 channel 6 channel 11 f [MHz] 2412 2437 2462 22 MHz
Characteristic Bluetooth IEEE 802.11b IEEE 802.11a Spectrum 2.4 GHz Max Transmit 725 kbps Rate Frequency FHSS selection Medium Master access centralized Typical transmit 100 mw power 2.4 GHz 11 Mbps DSSS CSMA/CA 0.05/0.25/1 W 5 GHz 54 Mbps OFDM CSMA/CA 1/2.5/100 mw
Source: 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
BT uses 79 channels in the frequency range 2.402-2.480 GHz, using FHSS coding technique Simultaneous operation in the same frequency range as 802.11 b/g, microwave, cordless telephones BT device can be in one of the modes - active (master/slave), low power (hold/sniff/park), standby standby inquiry page Transmit AMA Connected AMA Park PMA Hold AMA Sniff AMA
Baseband protocol is implemented as a link controller that works with link manager to carry link level routines such as link connection and power control