Microsoft PowerPoint - E1zigbee ppt

Size: px

Start display at page:

Download "Microsoft PowerPoint - E1zigbee ppt"

齐凌
6 years ago
Views:

1 ZigBee/IEEE Overview Y.-C. Tseng CS/NCTU 1

2 New trend of wireless technology Most Wireless industry focuses on increasing high data throughput A set of applications require simple wireless connectivity, relaxed throughput, very low power, short distance and inexpensive hardware. Industrial Agricultural Vehicular Residential Medical 2

3 What is ZigBee Alliance? An organization with a mission to define reliable, cost effective, low-power, wirelessly networked, monitoring and control products based on an open global standard Alliance provides interoperability, certification testing, and branding 3

4 IEEE working group 4

5 Comparison between WPAN 5

6 ZigBee/IEEE market feature Low power consumption Low cost Low offered message throughput Supports large network orders (<= 65k nodes) Low to no QoS guarantees Flexible protocol design suitable for many applications 6

7 ZigBee network applications monitors sensors automation control INDUSTRIAL & COMMERCIAL CONSUMER ELECTRONIC S TV VCR DVD/CD Remote control monitors diagnostics sensors PERSONAL HEALTH CARE ZigBee LOW DATA-RATE RADIO DEVICES PC & PERIPHERAL S mouse keyboard joystick consoles portables educational TOYS & GAMES HOME AUTOMATION security HVAC lighting closures 7

8 Wireless technologies Range Meters 10,000 GSM GPRS EDGE 3G , ZigBee b a/g Hiper Bluetooth 2.0 LAN/2 Bluetooth Bluetooth 1.5 WiMedia Bandwidth 10 kbps ,000 10, ,000 8

9 ZigBee/ architecture ZigBee Alliance 45+ companies: semiconductor mfrs, IP providers, OEMs, etc. Defining upper layers of protocol stack: from network to application, including application profiles First profiles published mid 2003 IEEE Working Group Defining lower layers of protocol stack: MAC and PHY 9

10 How is ZigBee related to IEEE ? ZigBee takes full advantage of a powerful physical radio specified by IEEE ZigBee adds logical network, security and application software ZigBee continues to work closely with the IEEE to ensure an integrated and complete solution for the market 10

11 IEEE overview 11

12 General characteristics Data rates of 250 kbps, 20 kbps and 40kpbs. Star or Peer-to-Peer operation. Support for low latency devices. CSMA-CA channel access. Dynamic device addressing. Fully handshaked protocol for transfer reliability. Low power consumption. Channels: 16 channels in the 2.4GHz ISM band, 10 channels in the 915MHz ISM band 1 channel in the European 868MHz band. Extremely low duty-cycle (<0.1%) 12

13 IEEE basics is a simple packet data protocol for lightweight wireless networks Channel Access is via Carrier Sense Multiple Access with collision avoidance and optional time slotting Message acknowledgement Optional beacon structure Target applications Long battery life, selectable latency for controllers, sensors, remote monitoring and portable electronics Configured for maximum battery life, has the potential to last as long as the shelf life of most batteries 13

14 IEEE Device Types There are two different device types : A full function device (FFD) A reduced function device (RFD) The FFD can operate in three modes by serving as Device Coordinator PAN coordinator The RFD can only serve as: Device 14

device (RFD) Limited to star topology Cannot become a network

15 FFD vs RFD 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 15

16 Star topology Network coordinator Master/slave Full Function Device (FFD) Reduced Function Device (RFD) Communications Flow 16

17 Peer to peer topology Point to point Tree Full Function Device (FFD) Communications Flow 17

18 Device addressing Two or more devices communicating on the same physical channel constitute a WPAN. A WPAN includes at least one FFD (PAN coordinator) Each independent PAN will select a unique PAN identifier Each device operating on a network has a unique 64-bit extended address. This address can be used for direct communication in the PAN A device also has a 16-bit short address, which is allocated by the PAN coordinator when the device associates with its coordinator. 18

19 IEEE physical layer 19

20 IEEE PHY overview PHY functionalities: Activation and deactivation of the radio transceiver Energy detection within the current channel Link quality indication for received packets Clear channel assessment for CSMA-CA Channel frequency selection Data transmission and reception 20

21 IEEE PHY Overview Operating frequency bands 868MHz/ 915MHz PHY Channel 0 Channels MHz 902 MHz 2 MHz 928 MHz 2.4 GHz PHY Channels MHz 2.4 GHz GHz 21

22 Frequency Bands and Data Rates The standard specifies two PHYs : 868 MHz/915 MHz direct sequence spread spectrum (DSSS) PHY (11 channels) 1 channel (20Kb/s) in European 868MHz band 10 channels (40Kb/s) in 915 ( )MHz ISM band 2450 MHz direct sequence spread spectrum (DSSS) PHY (16 channels) 16 channels (250Kb/s) in 2.4GHz band 22

23 PHY Frame Structure PHY packet fields Preamble (32 bits) synchronization Start of packet delimiter (8 bits) shall be formatted as PHY header (8 bits) PSDU length PSDU (0 to 127 bytes) data field Sync Header Preamble Start of Packet Delimiter PHY Header Frame Length (7 bit) Reserve (1 bit) PHY Payload PHY Service Data Unit (PSDU) 4 Octets 1 Octets 1 Octets Bytes 23

24 IEEE MAC 24

25 Superframe Beacon CAP CFP Beacon GTS 0 GTS 1 Inactive SD = abasesuperframeduration*2 SO symbols (Active) BI = abasesuperframeduration*2 BO symbols A superframe is divided into two parts Inactive: all station sleep Active: Active period will be divided into 16 slots 16 slots can further divided into two parts Contention access period Contention free period 25

26 Superframe Beacons are used for starting superframes synchronizing with other devices announcing the existence of a PAN informing pending data in coordinators In a beacon-enabled network, Devices use the slotted CSMA/CA mechanism to contend for the usage of channels FFDs which require fixed rates of transmissions can ask for guarantee time slots (GTS) from the coordinator 26

27 Superframe The structure of superframes is controlled by two parameters: beacon order (BO) : decides the length of a superframe superframe order (SO) : decides the length of the active potion in a superframe For a beacon-enabled network, the setting of BO and SO should satisfy the relationship 0 SO BO 14 For channels 11 to 26, the length of a superframe can range from msec to sec (= 3.5 min). 27

28 Superframe Each device will be active for 2 -(BO-SO) portion of the time, and sleep for 1-2 -(BO-SO) portion of the time Duty Cycle: BO-SO Duty cycle (%) <

Data Transfer Model (I) Data transferred from device to coordinator In a beacon-enable network, a device finds the beacon to synchronize to the superframe structure.

29 Data Transfer Model (I) Data transferred from device to coordinator In a beacon-enable network, a device finds the beacon to synchronize to the superframe structure. Then it uses slotted CSMA/CA to transmit its data. In a non-beacon-enable network, device simply transmits its data using unslotted CSMA/CA Communication to a coordinator In a beacon-enabled network Communication to a coordinator In a non beacon-enabled network 29

30 Data Transfer Model (II-1) Data transferred from coordinator to device in a beacon-enabled network: The coordinator indicates in the beacon that some data is pending. A device periodically listens to the beacon and transmits a Data Requst command using slotted CSMA/CA. Then ACK, Data, and ACK follow Communication from a coordinator In a beacon-enabled network 30

Data transfer model (II-2) Data transferred from coordinator to device in a non-beacon-enable network: The device transmits a Data Request using unslotted CSMA/CA.

31 Data transfer model (II-2) Data transferred from coordinator to device in a non-beacon-enable network: The device transmits a Data Request using unslotted CSMA/CA. If the coordinator has its pending data, an ACK is replied. Then the coordinator transmits Data using unslotted CSMA/CA. If there is no pending data, a data frame with zero length payload is transmitted. Communication from a coordinator in a non beacon-enabled network 31

32 Channel Access Mechanism Two type channel access mechanism: beacon-enabled networks slotted CSMA/CA channel access mechanism non-beacon-enabled networks unslotted CSMA/CA channel access mechanism 32

33 Slotted CSMA/CA algorithm In slotted CSMA/CA The backoff period boundaries of every device in the PAN shall be aligned with the superframe slot boundaries of the PAN coordinator i.e. the start of first backoff period of each device is aligned with the start of the beacon transmission The MAC sublayer shall ensure that the PHY layer commences all of its transmissions on the boundary of a backoff period 33

34 Slotted CSMA/CA algorithm (cont.) Each device maintains 3 variables for each transmission attempt NB: number of times that backoff has been taken in this attempt (if exceeding macmaxcsmabackoff, the attempt fails) BE: the backoff exponent which is determined by NB CW: contention window length, the number of clear slots that must be seen after each backoff always set to 2 and count down to 0 if the channel is sensed to be clear The design is for some PHY parameters, which require 2 CCA for efficient channel usage. Battery Life Extension: designed for very low-power operation, where a node only contends in the first 6 slots 34

35 Slotted CSMA/CA (cont.) need 2 CCA to ensure no collision 35

36 Why 2 CCAs to Ensure Collision-Free Each CCA occurs at the boundary of a backoff slot (= 20 symbols), and each CCA time = 8 symbols. The standard species that a transmitter node performs the CCA twice in order to protect acknowledgment (ACK). When an ACK packet is expected, the receiver shall send it after a t ACK time on the backoff boundary t ACK varies from 12 to 31 symbols One-time CCA of a transmitter may potentially cause a collision between a newly-transmitted packet and an ACK packet. (See examples below) 36

37 Why 2 CCAs (case 1) Backoff boundary Existing session New transmitter Backoff end here CCA Detect an ACK New transmitter CCA CCA Backoff end here Detect an ACK 37

38 Why 2 CCAs (Case 2) Backoff boundary Existing session New transmitter Backoff end here CCA Detect an ACK New transmitter CCA Backoff end here Detect an DATA 38

39 Why 2 CCAs (Case 3) Backoff boundary Existing session New transmitter Backoff end here CCA CCA Detect an ACK New transmitter CCA Backoff end here Detect a DATA 39

40 Unslotted CSMA/CA only one CCA 40

41 GTS Concepts (I) A guaranteed time slot (GTS) allows a device to operate on the channel within a portion of the superframe A GTS shall only be allocated by the PAN coordinator The PAN coordinator can allocated up to 7 GTSs at the same time The PAN coordinator decides whether to allocate GTS based on: Requirements of the GTS request The current available capacity in the superframe 41

42 GTS Concepts (II) A GTS can be deallocated At any time at the discretion of the PAN coordinator or By the device that originally requested the GTS A device that has been allocated a GTS may also operate in the CAP A data frame transmitted in an allocated GTS shall use only short addressing 42

43 GTS Concepts (III) Before GTS starts, the GTS direction shall be specified as either transmit or receive Each device may request one transmit GTS and/or one receive GTS A device shall only attempt to allocate and use a GTS if it is currently tracking the beacon If a device loses synchronization with the PAN coordinator, all its GTS allocations shall be lost The use of GTSs be an RFD is optional 43

44 Association Procedures (1/2) A device becomes a member of a PAN by associating with its coordinator Procedures Coordinator Device Association req. Scan channel ACK Make decision Beacon (pending address) Data req. ACK Association resp. ACK Wait for response 44

45 Association Procedures (2/2) In IEEE , association results are announced in an indirect fashion. A coordinator responds to association requests by appending devices long addresses in beacon frames Devices need to send a data request to the coordinator to acquire the association result After associating to a coordinator, a device will be assigned a 16-bit short address. 45

46 ZigBee Network Layer Protocols 46

47 ZigBee Network Layer Overview Three kinds of networks are supported: star, tree, and mesh networks 47

48 ZigBee Network Layer Overview Three kinds of devices in the network layer ZigBee coordinator: responsible for initializing, maintaining, and controlling the network ZigBee router: form the network backbone ZigBee end device: must be connected to router/coordinator In a tree network, the coordinator and routers can announce beacons. In a mesh network, there is no regular beacon. Devices in a mesh network can only communicate with each other in a peer-to-peer manner 48

49 Address Assignment In ZigBee, network addresses are assigned to devices by a distributed address assignment scheme ZigBee coordinator determines three network parameters the maximum number of children (C m ) of a ZigBee router the maximum number of child routers (R m ) of a parent node the depth of the network (L m ) A parent device utilizes C m, R m, and L m to compute a parameter called C skip which is used to compute the size of its children s address pools Cskip 1+ Cm ( Lm d 1), 1+ Cm Rm Cm Rm 1 Rm Lm d 1 ( d) =, if Rm = 1 Otherwise (a) (b) 49

50 C skip =31 Total:127 For node C If a parent node at depth d has an address A parent, the nth child router is assigned to address A parent +(n- 1) C skip (d)+1 nth child end device is assigned to address A parent +R m C skip (d)+n node A Cm=6 Rm=4 Lm=3 Addr = 30 Addr = C Addr = 38 Addr = 125 Addr = 1, Cskip = 7 B A Addr = 33, Cskip = 1 Addr = 39 C Addr = 64, Cskip = 1 Addr = 0, Cskip = 31 Addr = 32, Cskip = 7 Addr = 63, Cskip = 7 Addr = 92 Addr = 126 Addr = 40, Cskip = 1 Addr = ,126 50

51 ZigBee Routing Protocols In a tree network Utilize the address assignment to obtain the routing paths In a mesh network: Routing Capability: ZigBee coordinators and routers are said to have routing capacity if they have routing table capacities and route discovery table capacities There are 2 options: Reactive routing: if having routing capacity Tree routing: if having no routing capacity 51

52 ZigBee Tree Routing When a device receives a packet, it first checks if it is the destination or one of its child end devices is the destination If so, accept the packet or forward it to a child Otherwise, relay it along the tree Example: Cm=6 Rm=4 Lm=3 Addr = 30 Addr = 31 C Addr = 38 Addr = 125 Addr = 1, Cskip = 7 B A Addr = 33, Cskip = 1 Addr = 39 Addr = 64, Cskip = 1 Addr = 0, Cskip = 31 Addr = 32, Cskip = 7 Addr = 63, Cskip = 7 Addr = 92 Addr = 126 Addr = 40, Cskip = 1 Addr = 45 52

53 ZigBee Mesh Routing Route discovery by AODV-like routing protocol The cost of a link is defined based on the packet delivery probability on that link Route discovery procedure The source broadcasts a route request packet Intermediate nodes will rebroadcast route request if They have routing discovery table capacities The cost is lower Otherwise, nodes will relay the request along the tree The destination will choose the routing path with the lowest cost and then send a route reply 53

54 Routing in a Mesh network: Example 54

55 Summary of ZigBee network layer Pros Cons Star 1. Easy to synchronize 2. Support low power operation 3. Low latency 1. Small scale Tree 1. Low routing cost 2. Can form superframes to support sleep mode 3. Allow multihop communication 1. Route reconstruction is costly 2. Latency may be quite long Mesh 1. Robust multihop communication 2. Network is more flexible 3. Lower latency 1. Cannot form superframes (and thus cannot support sleep mode) 2. Route discovery is costly 3. Needs storage for routing table 55

Microsoft PowerPoint - Aqua-Sim.pptx

Microsoft PowerPoint - Aqua-Sim.pptx Peng Xie, Zhong Zhou, Zheng Peng, Hai Yan, Tiansi Hu, Jun-Hong Cui, Zhijie Shi, Yunsi Fei, Shengli Zhou Underwater Sensor Network Lab 1 Outline Motivations System Overview Aqua-Sim Components Experimental