CS263 Wireless Communications and Sensor Networks Matt Welsh Lecture 6 Bluetooth and 802 15 4 October 12 2004 2004 Matt Welsh Harvard University 1 Today s Lecture Bluetooth Standard for Personal Area Networks PANs IEEE 802 15 4 New standard for Low Power Wireless Networks 2004 Matt Welsh Harvard University 2 Bluetooth basics Short range high data rate wireless link for personal devices Originally intended to replace cables in a range of applications e g Phone headsets PC PDA synchronization remote controls Operates in 2 4 GHz ISM band Same as 802 11 and 802 15 4 Frequency Hopping Spread Spectrum across 80 channels Somewhat bulky application interfaces Not just simple byte stream data transmission Rather complete protocol stack to support voice data video file transfer etc Bluetooth operates at a higher level than 802 11 and 802 15 4 2004 Matt Welsh Harvard University 3 Bluetooth basics cont d Maximum data rate of up to 720 Kbps But requires large packets 300 bytes Class 1 Up to 100mW 20 dBm transmit power 100m range Class 1 requires that devices adjust transmit power dynamically to avoid interference with other devices Class 2 Up to 2 4 mW 4 dBm transmit power Class 3 Up to 1 mW 0 dBm transmit power Security is optional Many devices on the market do not take security seriously 2004 Matt Welsh Harvard University 4 Usage Models Wireless audio e g Wireless headset associated with a cell phone Requires guaranteed bandwidth between headset and base No need for packet retransmission in case of loss Cable replacement Replace physical serial cables with Bluetooth links Requires mapping of RS232 control signals to Bluetooth messages LAN access Allow wireless device to access a LAN through a Bluetooth connection Requires use of higher level protocols on top of serial port e g PPP File transfer Transfer calendar information to from PDA or cell phone Requires understanding of object format naming scheme etc Lots of competing demands for one radio spec 2004 Matt Welsh Harvard University 5 Protocol Architecture Service Discovery UDP TCP IP Telephony Control Audio Object Exchange PPP RFCOMM Cable Replacement Logical Link Control and Adaptation Protocol L2CAP Baseband Specification Physical Radio Spec 2004 Matt Welsh Harvard University 6 Piconet Architecture One master and up to 7 slave devices in each Piconet Master controls transmission schedule of all devices in the Piconet Time Division Multiple Access TDMA Only one device transmits at a time Frequency hopping used to avoid collisions with other Piconets 79 physical channels of 1 MHz each hop between channels 1600 times a sec 2004 Matt Welsh Harvard University 7 Scatternets Combine multiple Piconets into a larger Scatternet Device may act as master in one Piconet and slave in another Each Piconet using different FH schedule to avoid interference Can extend the range of Bluetooth can route across Piconets 2004 Matt Welsh Harvard University 8 Baseband Specification 79 1 MHz channels defined in the 2 4 GHz ISM band Gaussian FSK used as modulation 115 kHz frequency deviation Frequency Hopping Spread Spectrum Each Piconet has its own FH schedule defined by the master 1600 hops sec slot time 0 625 ms Time Division Duplexing Master transmits to slave in one time slot slave to master in the next TDMA used to share channel across multiple slave devices Master determines which time slots each slave can occupy Allows slave devices to sleep during inactive slots 2004 Matt Welsh Harvard University 9 Time slots master slave f1 f2 f3 f4 f4 f6 Each time slot on a different frequency According to FH schedule Packets may contain ACK bit to indicate successful reception in the previous time slot Depending on type of connection e g Voice connections do not use ACK and retransmit Packets may span multiple slots 2004 Matt Welsh Harvard University 10 Physical and Logical Links Bluetooth supports two types of physical links Synchronous Connection Oriented SCO Slave assigned to two consecutive slots at regular intervals Just like TDMA No use of retransmission why Asynchronous Connectionless ACL Allows non SCO slots to be used for on demand transmissions Slave can only reply if it was addressed in previous slot by master SCO Link A SCO Link B ACL Link master slave A slave B 2004 Matt Welsh Harvard University 11 Packet Formats Bluetooth supports 14 different payload formats Different formats for control voice and data packets Frames can span 1 3 or 5 slots Different levels of error coding No coding 1 3 or 2 3 FEC 72 54 232 Access Header code bits 0 2745 624 624 624 624 Payload What is the maximum bandwidth that Bluetooth can achieve Counting only application payload bytes no CRC or FEC 5 slot packet no protection 341 payload bytes Total time 5 0 625 ms 3 125 ms But need to count an extra slot from the master for ACK Total bandwidth is therefore 341 bytes 6 0 625 ms 710 kbps Most texts say either 721 or 723 kbps is the max This depends on definition of kilobit I use 1024 bits Stallings text claims DH5 packet has 341 bytes of payload Appears to be only 339 plus 2 byte CRC 2004 Matt Welsh Harvard University 12 IEEE 802 15 4 and ZigBee Emerging standard for low power wireless monitoring and control Scale to many devices Long lifetime is important contrast to Bluetooth 10 75m range typical Designed for industrial process monitoring control medical devices etc High data rate for small packets 200 Kbps for 75 byte packets IEEE 802 15 4 Physical and MAC layer Combination of CSMA and TDMA schemes ZigBee Network and application layer on top of 802 15 4 Still emerging standard not yet available outside of ZigBee Alliance 2004 Matt Welsh Harvard University 13 Chipcon Ember CC2420 Single chip 802 15 4 radio transceiver 5 Incorporated into the Telos motes you are going to use in this class 1 8V supply consumes 19 7 mA receiving 17 4 mA transmit Easy to integrate Open source software drivers Supports 802 15 4 PHY and encryption in hardware MAC still implemented in software 2004 Matt Welsh Harvard University 14 802 15 4 PHY 802 15 4 defines several frequency ranges 16 channels in the 2 4 GHz band 5 MHz per channel 10 channels in the 915 MHz band 2 MHz per channel 1 channel in the 868 MHz band Direct Sequence spreading used for 2 4 GHz band Each 4 bit nibble mapped onto quasi orthogonal 32 bit chipping code Modulated using offset QPSK Data transmitted at a rate of 2 million chips sec 32 bit chip maps onto 4 bit raw data symbol So effective data rate is 2 000 000 32 4 250 000 bits