Wireless and Mobile Networks CMPE 257 Spring 2006 Bluetooth

Announcements Access to QualNet. Two options: Get a CD from the helpdesk (BE 240). Contains license and necessary instructions. Or, remote access via ssh.

Today Bluetooth.

Bluetooth

Overview Cable replacement technology. Industry standard. Connect devices such as phone handsets, headsets, computer peripherals, etc. Industry standard. Allows wireless communication between devices.

Applications: Cable Replacement 1 Mb/s. Range ~10 meters. PANs Single chip radio. Low power & low cost. Why not use Wireless LANs? - power - cost

Applications: Synchronization Automatic synchronization of calendars, address books, business cards.

Applications: Cordless Headset Multiple device access. Hands-free operation.

More applications… Conference table. Cordless computer. Instant photo transmission. Cordless phone.

Bluetooth Origins Study by Ericsson Mobile Communications in 1994. Alternatives to cables connecting mobile phones to accessories. Use of radio links instead of infrared. Why? Transmission of data and voice. Result: Bluetooth spec. Named after Harald Blatand (Danish for Bluetooth). 10th century Viking king who united Denmark and Norway.

Bluetooth SIG History Early 1998: Bluetooth SIG is formed. Promoter company group: Ericsson, IBM, Intel, Nokia, Toshiba. Goal: develop license-free technology for universal wireless connectivity. Target: handheld market. Bluetooth spec: defines RF wireless communication interface and protocols.

Bluetooth SIG History May 1998: Public announcement of Bluetooth SIG. July 1999: 1.0A spec (>1,500 pages) published. December 1999: version 1.0B released. December 1999: promoters increases to 9. 3Com, Lucent, Microsoft, Motorola February 2000: 1,800+ adopters. February 2001: version 1.1 out.

More History… Recently, IEEE 803.15.1 standard for Wireless PANs (WPANs) Only MAC and PHY.

Goals Open spec. Low cost. Power efficiency. In order to replace cables, should have similar cost. Cell phone cable is ~ $10. Power efficiency. Lightweight and small form factor. Easy to use. Reliable and resilient to failures.

The Bluetooth Standard Defines a protocol stack to enable heterogeneous devices to communicate. The Bluetooth stack includes protocols for the radio layer all the way up to device discovery, service discovery, etc.

Bluetooth Protocol Stack Application Applications RFCOMM/SDP Presentation Layer L2CAP Session Layer Host Controller Interface Transport Layer Link Manager Network Layer Link Controller Data Link Layer Baseband PHY RF OSI/ISO

Bluetooth Layers Radio: physically transmits/receives data. Baseband/Link Controller: controls PHY. Link Manager: controls links to other devices. Host Controller:e2e communication. Logical Link Control: multiplexes/demultiplexes data from higher layers. RFCOMM: RS323-like serial interface. SDP: allows service discovery among Bluetooth devices.

The Bluetooth PHY

Radio Band 2.4 GHz license-free ISM band. Available worldwide. Industrial, Scientific, Medical (ISM) band. Unlicensed, globally available. Centered around 2.4 GHz. Resilient to interference. Frequency hopping. Range: 10, 20, and 100m. 1MB/s.

Unlicensed Radio Spectrum  33cm 12cm 5cm 26 Mhz 83.5 Mhz 125 Mhz 902 Mhz 2.4 Ghz 5.725 Ghz 928 Mhz 2.4835 Ghz 5.785 Ghz cordless phones baby monitors Wireless LANs 802.11 Bluetooth Microwave oven unused

Bluetooth Radio Link MA scheme: Frequency hopping spread spectrum. 1Mhz . . . 1 2 3 79 83.5 Mhz MA scheme: Frequency hopping spread spectrum. 2.402 GHz + k MHz, k=0, …, 78 1,600 hops per second. 1 Mb/s data rate.

BT Radio Link (Cont’d) Time-division duplex (TDD) Separation of Xmission and reception in time. Units alternate transmits and receives. Gaussian Frequency Shift Keying (G-FSK) modulation. ‘1’s as positive frequency deviations from carrier frequency; ‘0’s as negative deviations.

Multiple Access BT targets large number of independent communications active in the same area at the same time. Single FH channel: 1 Mb/s. Each 1Mb/s channel shared by limited number of participants. In target user scenarios, it’s unlikely that all units in-range will share data among all of them. 1 MB/s is reasonable. (is it?) Theoretically, total bandwidth is 79 Mb/s. In practice, < 79 Mb/s since codes are non-orthogonal.

Host Controller Interface Baseband Control end of baseband +link controller= Data link layer Applications RFCOMM/SDP L2CAP Host Controller Interface Link Manager Carries out MAC functions. Link Controller Baseband RF

Master and Slaves Communicating devices must agree on hopping sequence. BT devices can operate as masters or slaves. Master node defines sequence to be used. Slave units use master id to pick sequence. Master also controls when devices are allowed to transmit. Master allocates slots to slaves. Allocates total available bandwidth among slaves.

Piconets BT communication takes place over piconets. Piconet formation initiated by master. All other participants are slaves. Number of participants limited to 8 (1 master and 7 slaves). Channel capacity and addressing overhead. Each slave assigned a locally unique ID. Master/slave roles last for the duration of the piconet.

More on Piconets On a piconet, slaves only have direct links to master. Point-to-point or point-to-multipoint connections.

Piconets: Considerations Most target applications involve local communication among small group of devices. Piconets with up to 8 nodes match well. If many groups of devices active simultaneously, each group as separate piconet. Overlapping piconets can coexist.

Contention-Free MA Master and slaves. Master performs medium access control. Schedules traffic through polling. Time slots alternate between master and slave transmission. Master-slave: master includes slave address. Slave-master: only slave chosen by master in previous master-slave slot allowed to transmit. If master has data to send to a slave, slave polled implicitly; otherwise, explicit poll.

BT States Standby . Initially, all nodes in standby. . Node (master) can begin inquiry to find nearby devices. . Piconet is then formed. . Devices join by paging. Unconnected Inquiry Page Connecting Transmit Connected Active Sniff Park Hold Low power

Inquiry Device discovery Listeners respond with their address.

Paging Device enters paging to invite others to join its piconet. Master Active Slave Parked Slave Standby Device enters paging to invite others to join its piconet. Establishes links with nodes in proximity. Paging message unicast to selected receiver. Receiver sends ACK. Sender becomes master, receiver slave.

Piconet New Node Admission Master can actively try to discover new nodes or wait (in scan/listen mode) to be discovered. Communication in the current piconet suspended. Admission latency versus piconet capacity tradeoff.

Bluetooth Link Formation Point-to-point link: Master-slave relationship. m s s m Piconet: 8 units: channel capacity. Master (establishes piconet) can connect to up to 7 slaves. Master/slave relationship lasts while link/piconet lasts. No slave-to-slave communication.

Link Types 2 types of links: Synchronous (SCO) links: Point-to-point between master and slave. Link established by reserving slots in either direction periodically. Used to carry real-time traffic (voice). Asynchronous (ACL) links: Point-to-multipoint between master and slaves. Use remaining slots on channel. Traffic scheduled by master.

Error Control Supports both FEC and retransmission. FEC for SCO packets. ARQ for ACL traffic. If no ACKs, retransmit. Stop-and-wait ARQ. Fast-ARQ: ACK included in RX slot immediately following the TX slot in which packet was sent. CRC to check for errors.

Packet Format 72 bits 54 bits 0 - 2744 bits Access code Header Payload No CRC No retries Voice header Data CRC FEC (optional) Mention that over SCO link you cannot carry any other real-time traffic. There is no protocol-id field in the SCO header/payload. Is this really true? ARQ FEC (optional) 625 µs master slave

Access Code 72 bits Access Payload code Header Address of piconet master.

Packet Header m s Purpose Max 7 active slaves 54 bits Access code Header Payload Purpose Addressing (3) Packet type (4) Flow control (1) 1-bit ARQ (1) Sequencing (1) HEC (8) Max 7 active slaves 16 packet types (some unused) How useful is header protection when payload is unprotected Broadcast packets are not ACKed For filtering retransmitted packets Verify header integrity total 18 bits

Multiple Piconets Piconets may overlap in space and time. They can work independently. Each with its own hopping sequence. Packets with different access codes. Or they can overlap, i.e., nodes can participate in more than 1 piconet. “Time sharing”.

Scatternets Interconnection of multiple piconets. Slave Master

Scatternets (cont’d…) Interconnection by bridge nodes. Bridge nodes are members of piconets they interconnect. Bridge node “stay” in a piconet for some time, then switch to another piconet by changing hop sequence. Do this for all member piconets. Send and receive in each piconet. Forward from one piconet to another.

Link Controller and Link Manager Applications RFCOMM/SDP L2CAP Attaching/detaching slaves from piconet; power management; security. Host Controller Interface Link Manager Link Controller Carries out inquiry and paging operations; manages multiple links and different piconets. Baseband RF

Power Management Low-power modes: prolong battery life. Devices can be turned-off when idle. Devices wake up periodically to send/receive data.

Low-Power Operation 3 modes: Hold: node sleeps for specified interval. Master can put slaves in hold while searching for new members, attending another piconet, etc. No ACL packets. Sniff: slave low-duty cycle mode. Slave wakes up periodically to talk to master. Fixed “sniff” intervals. Park: Very low power state. Used to admit more than 7 slaves in piconet. Slave gives up its active member address. Receives “parked” member address. Wakes up periodically listening for broadcasts which can be used to “unpark” node.

Security Authentication and encryption. LMP provides mechanisms for negotiation of encryption modes, keys, etc.

Host Controller Interface Applications Optional interface layer between higher and lower layers of the BT stack. RFCOMM/SDP L2CAP Host Controller Interface Link Manager E.g., when lower- and higher BT layers run on different Devices: PCMCIA card and PC’s processor. Link Controller Baseband RF

Logical Link Control and Host Controller Interface L2CAP Applications RFCOMM/SDP Logical Link Control and Adaptation Protocol= Session Layer. L2CAP Host Controller Interface Link Manager Link Controller L2CAP provides Protocol multiplexing Quality of service negotiation Baseband RF

Host Controller Interface RFCOMM/SDP Applications RFCOMM/SDP L2CAP Service discovery, serial port interface. Host Controller Interface Link Manager Link Controller Baseband RF

References: Bluetooth papers in reading list. Johansson and Gerla’s Bluetooth Tutorial at Mobicom 2001. Bluetooth 1.1: Connect Without Cables, Bray and Sturman.

Bluetooth on the market: PC cards, Cell phones, Head sets, Chip sets,… Features Cost 20 dBm (~100 m) Point-to-multipoint No Scatternet Applications File Transfer, Dial-Up Networking LAN access, Fax, … 169 $ --- 200 $ 0 dBm (~10 m) Company Toshiba, Motorola, Digianswer IBM, TDK 3COM 10 m user-user; 100 m user-Base Station SW- & FW-upgradeable LAN access, Fax, E-mail Unconscious connection 149 $ Nokia Point-to-point Connectivity Battery for the cell phone Ericsson, Sigma Point-to-point; ARM processor; USB; RFCOMM ports Basic BT Radio stack Embedded or Host stack Programmable 500 $ 1500$