802.15.4 Presentation.ppt

7/27/2019 802.15.4 Presentation.ppt

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Samer Shammaa

Telecommunications Eng. Dept.

Dr. Pramode Verma


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Outline Introduction

WSN Applications

TopologiesArchitecture

Physical Layer

MAC Layer

Superframe structure


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Introduction Until recently, the main concern in wireless

communication was on high throughput

Some applications need a different set of requirements Example: LR-WPAN applications

-Low cost communication network

-Limited power

-Low throughput

Require: reasonable battery life, extremely low cost,short range operation, reliable data transfer


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LR-WPAN ApplicationsHome

Automation

Heating, ventilation, air conditioning, security, lighting,

control of objects.

Industrial Detecting emergency situations, monitoring machines.

Automotive Automotive sensing such as time pressure monitoring.

Agriculture Sensing of soil moisture, pesticide, herbicide, PH levels.

Others Controlling consumer electronics, PC peripherals, etc.


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Solution? Existing standards not suitable for these applications

b/c of complexity, power consumption, and high cost.

Need a simple, flexible protocol IEEE 802.15.4 defines protocol via RF for PAN.

Provide a standard with ultra-low complexity, cost, andpower for low-data-rate wireless connectivity among

inexpensive fixed, portable, and moving devices.


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Wireless Protocols Comparison


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Comparison (2)


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Device Types Full function device (FFD)

Any topology PAN coordinator capable Talks to any other device Implements complete protocol set

Reduced function device (RFD) Limited to star topology or end-device in a peer-to-peer

network. Cannot become a PAN coordinator Very simple implementation Reduced protocol set


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Modes of OperationNetwork Device: An RFD or FFD implementation

containing an IEEE 802.15.4 medium access controland physical interface to the wireless medium.

Coordinator: An FFD with network devicefunctionality that provides coordination and otherservices to the network.

PAN Coordinator: A coordinator that is the principalcontroller of the PAN. A network has exactly one PANcoordinator.


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Network Topologies


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Combined Topology Ex: hotel where

cluster nodesexist betweenthe rooms of ahotel and eachroom has a starnetwork forcontrol.


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Star Network FormationAfter an FFD is activated, it can establish its own

network and become the PAN coordinator

Choose a PAN Identifier different from surroundingnetworks (within RF sphere of influence)

The PAN coordinator allows other devices, potentiallyboth FFDs and RFDs, to join its network.


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Peer-to-peer Network Formation Each device is capable of communicating with any

other device within its radio sphere of influence

One Device is nominated as the PAN coordinator

Form first cluster by choosing an unused PANidentifier and broadcasting beacon frames toneighboring devices.

A candidate device receiving a beacon frame may

request to join the network at the PAN coordinator. If the PAN coordinator permits the device to join, it

adds the new device as a child device in its neighborlist.


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Continued Newly joined device adds the PAN coordinator as its

parent in its neighbor list and begins transmittingperiodic beacons

Other candidate devices may then join the network atthat device.

Once predetermined application or network

requirements are met, the first PAN coordinator mayinstruct a device to become the PAN coordinator of anew cluster adjacent to the first one.

Other devices gradually connect and form a multi-

cluster network structure


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Cluster Tree Network


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Architecture


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Physical Layer Provides two services:

-PHY data service

-PLME-SAP providing dataand managementservices to upper layers.


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PHY Data Service Enables the transmission and reception of PHY

protocol data units (PPDUs) across the physical radiochannel

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

Channel switching


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Operating Band 2.4GHz band operates worldwide- offers 250kb/s

868 MHz band operates in Europe- offers 20 kb/s

915 MHz band operates in United States- offers 40kb/s


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PHY Frame Structure

The 32-bit preamble is used for synchronization

11100101 indicates start of packet

7 out of the 8 PHY header bits are used to indicate thelength of the PSDU

The PSDU has a variable length between 0 and 127bytes


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MAC Layer The MAC sublayer provides two services:

-MAC data service: enables the transmission andreception of MAC protocol data units (MPDUs) acrossthe PHY data service

-MLME-SAP: provides data and management services toupper layers


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MAC Sublayer Features Beacon management

Channel access

Guaranteed Time Slot (GTS) management Frame validation

Acknowledged frame delivery

Association

Disassociation

Provides means for implementing application-appropriate security mechanisms


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MAC Frame Format


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Frame Control Field


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MAC Frame Types IEEE 802.15.4 defines 4 types of MAC frames:

Beacon Frame

Data FrameAcknowledgment Frame

MAC Command Frame


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Beacon Frame Format


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Data Frame Format

Acknowledgment Frame Format


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Command Frame Format

Association request

Association response

Disassociationnotification

Data request

PAN ID conflictnotification

Orphan Notification Beacon request

Coordinatorrealignment

GTS request


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Superframe Structure

The active portion is divided into 16 equally sized slots

During the inactive portion, the coordinator may enter

a low-power mode The beacons are used to synchronize the attached

devices, to identify the PAN, and to describe thestructure of the superframes


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Superframe Structure


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Guaranteed Time Slots (GTSs) For low-latency applications or applications requiring

specific data bandwidth

PAN coordinator may dedicate portions of the activesuperframe to that application

PAN coordinator may allocate up to seven of theseGTSs, and a GTS may occupy more than one slot

period


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Questions?


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Data Transfer Three types of data transfer:

-Data transfer to a coordinator in which a devicetransmits the data

-Data transfer from a coordinator in which the devicereceives the data

-Data transfer between two peer devices

*In star topology only first two are used*The mechanisms for each transfer type depend on

whether the network supports the transmission ofbeacons


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Data Transfer to a Coordinator

Beacon-enabled PAN

Slotted CSMA-CA

Nonbeacon PAN

Unslotted CSMA-CA


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Data Transfer from a Coordinator

PAN indicates message is

pending in the beacon

Device request data at

application-defined rate


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Peer-to-peer Data Transfers Devices wishing to communicate will need to either

receive constantly or synchronize with each other

In the first case, the device can simply transmit its datausing unslotted CSMA-CA

In the latter case, other measures need to be taken inorder to achieve synchronization


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Improving Probability of

Successful Delivery The IEEE 802.15.4 LR-WPAN employs various

mechanisms to improve the probability of successful

data transmission: CSMA-CA mechanism

Frame acknowledgment

Data verification


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Unslotted CSMA-CA Mechanism Used by nonbeacon-enabled PANs

Each time a device wishes to transmit data frames orMAC commands, it waits for a random period

If the channel is found to be idle, following therandom backoff, the device transmits its data

If the channel is found to be busy following the

random backoff, the device waits for another randomperiod before trying to access the channel again

Acknowledgment frames are sent without using aCSMA-CA mechanism


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Slotted CSMA-CA Mechanism Used by beacon-enabled PANs

Backoff slots are aligned with the start of the beacontransmission

Device locates the boundary of the next backoff slotand then waits for a random number of backoff slots

If the channel is busy, following this random backoff,

the device waits for another random number ofbackoff

If the channel is idle, the device begins transmittingon the next available backoff slot boundary


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Frame AcknowledgmentA successful reception and validation of a data or MAC

command frame can be optionally confirmed with anacknowledgment

If the originator does not receive an acknowledgmentafter some period, it assumes that the transmissionwas unsuccessful and retries the frame transmission

When the acknowledgment is not required, theoriginator assumes the transmission was successful


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Data Verification-FCS Mechanism In order to detect bit errors, an FCS mechanism

employing a 16-bit International TelecommunicationUnionTelecommunication Standardization Sector

(ITU-T) cyclic redundancy check (CRC) is used todetect errors in every frame


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Approaches for Low Power The protocol has been developed to favor battery-

powered devices

Battery-powered devices will require duty-cycling toreduce power consumption

Thus will spend most of their operational life in a sleepstate

Each device periodically listens to the RF channel inorder to determine whether a message is pending

Higher powered devices have the option of listening tothe RF channel continuously


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Service Primitives The services of a layer are

the capabilities it offersto the user in the next

higher layer or sublayerby building its functionson the services of thenext lower layer


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Continued

Each event consists of passing a service primitive fromone layer to the other through a layer SAP associatedwith an N-user

Service primitives convey the required information byproviding a particular service

A service is specified by describing the service

primitives and parameters that characterize it


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Primitive Types Request: The request primitive is passed from the N-user to

the N-layer to request that a service is initiated.

Indication: The indication primitive is passed from the N-

layer to the N-user to indicate an internal N-layer event that issignificant to the N-user. This event may be logically related to aremote service request, or it may be caused by an N-layerinternal event.

Response: The response primitive is passed from the N-user to

the N-layer to complete a procedure previously invoked by anindication primitive.

Confirm: The confirm primitive is passed from the N-layer tothe N-user to convey the results of one or more associated

previous service requests.


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Data Transfer Message Sequence


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Indirect Data Transfer


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Association


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Disassociation


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Data Polling-No Data Pending


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Data Polling-Data Pending


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References -IEEE Std. 802.15.4-2006

-Marco Naeve, Eaton Corp., IEEE 802.15.4 MACOverview, 05/2004

-IEEE Std. 802.15.4 Enabling Pervasive Wireless SensorNetworks, Dr. Jose Gutierrez, Eaton Corp.

-

http://deneb.cs.kent.edu/~mikhail/classes/seminar.u04/praveen_lrwpan.ppt

- 140.117.169.69/course1/zigbee-802.15.4.ppt
http://deneb.cs.kent.edu/~mikhail/classes/seminar.u04/praveen_lrwpan.ppthttp://deneb.cs.kent.edu/~mikhail/classes/seminar.u04/praveen_lrwpan.ppthttp://deneb.cs.kent.edu/~mikhail/classes/seminar.u04/praveen_lrwpan.ppthttp://deneb.cs.kent.edu/~mikhail/classes/seminar.u04/praveen_lrwpan.ppt


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802.15.4 Presentation.ppt