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IEEE 802.15.4

IEEE 802.15.4

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IEEE 802.15.4

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  1. IEEE 802.15.4 Taekyoung Kwon

  2. 802.15.4 • Wireless MAC and PHY layer specifications for Low-rate Wireless Personal Area Networks (LR-WPANs) • Short distance • Little or no infrastructure • Small • Power-efficient • inexpensive

  3. Application spaces • Home Networking • Automotive Networks • Industrial Networks • Interactive Toys • Remote Metering

  4. INDUSTRIAL & COMMERCIAL CONSUMER ELECTRONICS PERSONAL HEALTH CARE PC & PERIPHERALS TOYS & GAMES HOME AUTOMATION More specifically… TV VCR DVD/CD remote monitors sensors automation control mouse keyboard joystick ZigBee LOW DATA-RATE RADIO DEVICES monitors diagnostics sensors PETsgameboys educational security HVAC lighting closures

  5. Application topology • Cable replacement - Last meter connectivity • Virtual Wire • Wireless Hub • Stick-On Sensor Mobility Ease of installation

  6. requirements Thousands of sensors in a small space  Wireless but wireless implies Low Power! and low power implies Limited Range. Of course all of these is viable if a Low Cost transceiver is required

  7. Basic characteristics

  8. 802.15.4 PHY • DSSS • 250 Kbps at 2.450 GHz (ISM) • 16-ary quasi-orthogonal modulation • 4 bit -> 1 symbol • 32 chip sequence • 1 symbol -> 32 chips • O-QPSK • 2.0Mchip/s • 62.5ksymbol/s * FEC

  9. 802.15.4 PHY: Packet structure • PHY Packet Fields • Preamble (32 bits) – synchronization • Start of Packet Delimiter (8 bits) • PHY Header (7 bits) – PSDU length • PSDU (0 to 1016 bits) – Data field Start of Packet Delimiter PHY Header PHY Service Data Unit (PSDU) Preamble 6 Octets 0-127 Octets

  10. 802.15.4 PHY

  11. service primitive • user services provided by a layer are implemented as a set of service primitives • the primitive name includes details of its type and identity of layer providing service

  12. 4 primitives • For confirmed service, there are 4 primitives request - entity wants service to do some work indication - entity is informed about event response - entity wants to respond to event confirm - entity is to informed about its request • For unconfirmed service, the first 2 primitives

  13. 4 primitives

  14. 802.15.4 PHY: primitives PHY Data Service • PD-DATA – exchange data packets between MAC and PHY PHY Management Service • PLME-CCA – clear channel assessment • PLME-ED - energy detection • PLME-GET / -SET– retrieve/set PHY PIB parameters • PLME-SET-TRX-STATE – enable/disable transceiver

  15. details

  16. details

  17. Constants

  18. PIB attributes

  19. 802.15.4 PHY revisited • Receiver sensitivity: -85 dBm at 2.4GHz • dB = 10 log p/p_ref • dBm = 10 log p/1mW • LQI • Word file • www.rfdh.com • How about 802.15.4a? • UWB • Any more parameter?

  20. 802.15.4 MAC • Extremely low cost • Ease of implementation • Reliable data transfer • Short range operation • Very low power consumption Simple but flexible protocol

  21. Traffic types • Periodic data • Application defined rate (e.g. sensors) • Intermittent data • Application/external stimulus defined rate (e.g. light switch) • Repetitive low latency data • Allocation of time slots (e.g. mouse)

  22. 802.15.4 MAC

  23. MAC • Full function device (FFD) • Any topology • Network coordinator capable • Talks to any other device • Reduced function device (RFD) • Limited to star topology • Cannot become a network coordinator • Talks only to a network coordinator • Very simple implementation

  24. MAC: star topology PAN Coordinator Master/slave Communications flow Full function device Reduced function device

  25. MAC: peer-to-peer Cluster tree Point to point Full function device Communications flow

  26. MAC: combined topology Clustered stars - for example, cluster nodes exist between rooms of a hotel and each room has a star network for control. Communications flow Full function device Reduced function device

  27. General frame format • 4 Types of MAC Frames: • Data Frame • Beacon Frame • Acknowledgment Frame • MAC Command Frame

  28. Data transfer model • To a coordinator • From a coordinator • Between peer-to-peer entities

  29. Communication in beacon mode (from device to coordinator) Slotted CSMA-CA

  30. Communication in non-beacon mode (from device to coordinator) unslotted CSMA-CA

  31. Communication in beacon mode (from coordinator to device) slotted CSMA-CA Indirect transmission

  32. Communication in non-beacon mode (from coordinator to device) Indirect transmission unslotted CSMA-CA

  33. How about peer-to-peer mode? • In a peer-to-peer PAN, every device may communicate with every other device in its radio sphere of influence. In order to do this effectively, the devices wishing to communicate will need to either receive constantly or synchronize with each other. In the former case, the device can transmit data using unslotted CSMA-CA mode. In the latter case, other measures need to be taken in order to achieve synchronization. Such measures are beyond the scope of this standard.

  34. Superframe: CSMA-CA + TDMA GTS 2 GTS 1 Total 16 slots Contention Access Period Contention Free Period 15ms * 2n where 0  n  14 Transmitted by network coordinator. Contains network information, frame structure and notification of pending node messages. Network beacon Beacon extension period Space reserved for beacon growth due to pending node messages Contention period Access by any node using CSMA-CA Guaranteed Time Slot Reserved for nodes requiring guaranteed bandwidth [n = 0]. up to 7 GTSes

  35. Superframe structure • macBeaconOrder (BO) • Interval between beacons • Beacon Interval (BI) • BI = aBaseSuperframeDuration * 2BO • macSuperframeOrder (SO) • Length of active portion of the superframe • Superframe duration (SD) • SD = aBaseSuperframeDuration * 2SO • aBaseSuperframeDuration = 16 * aBaseSlotDuration • 0<=SO<=BO<=14 • If BO = SO = 15, no beacon -> unslotted CSMA-CA

  36. Example of superframe

  37. Inter-frame spacing (IFS)

  38. Illustration (2.4GHz) • A minimum size slot: 30 bytes • 60 symbols, 0.96ms • If MPDU’s size < 18 octet, SIFS = 6 octet • Otherwise, LIFS = 20 octets • aUnitBackoffPeriod = 10 octets

  39. CSMA-CA • CSMA-CA is not for beacon, ACK, data frames in CFP

  40. Unslotted version macMinBE = 3

  41. aMaxBE = 5 macMaxCSMABackoff = 4

  42. MAC addressing • All devices have IEEE addresses (64 bits) • Short addresses (16 bits) can be allocated • Addressing modes • PAN identifier (16 bits)+ device identifier (16/64 bits) • 0xffff: PAN ID, short address • Beacon frame: no destination address

  43. General frame format • 4 Types of MAC Frames: • Data Frame • Beacon Frame • Acknowledgment Frame • MAC Command Frame

  44. General MAC frame

  45. Frame control field

  46. Addressing mode

  47. src Beacon frame BSN Superframe spec.