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Title: PART I: IEEE 802.15.4, a novel MACPhy layer for the Zigbee stack


1
PART I IEEE 802.15.4, a novel MAC/Phy layer for
the Zigbee stack
  • A.G. Ruzzelli

Adaptive Information Cluster (AIC) Group,
University College Dublin, Ireland.
2
Summary
  • Wireless Sensor networks (WSNs)
  • Generality
  • Prototypes
  • Application Requirements
  • Zigbee generality
  • Overview of the stack
  • The components
  • The primitives
  • Zigbee NWK layer
  • The NWK layer architecture and services
  • The address assignment
  • The AODV protocol
  • IEEE 802.15.4
  • Generality
  • Superframe structure

3
Energy-Efficient Wireless Sensor Networks (WSNs)
  • A large number of tiny wireless devices to sense
    the environment
  • Sensor nodes
  • Few more powerful devices to collect the data
  • Gateways (or sinks or PAN coordinators)

PDA, laptop, PC etc.
4
Some WSN applications
  • Remote area monitoring
  • Object location
  • Industry machinery monitoring
  • Disaster prevention
  • Wireless medical systems

Monitoring nesting patterns of Storm Petrels.
medical systems
5
Wireless sensor characteristics
WSN manager
  • Sensors are of
  • Low cost
  • Low processing capability
  • ? System strength based on sensor collaboration
  • Large scale networks
  • Multihop communication
  • Sensors are battery operated for long unattended
    period
  • ? Saving energy is a primary objective

6
WSN issues
  • Large number of nodes
  • ?Scalability issues
  • High dynamic condition (number and position of
    nodes might change)
  • ? Network Reactivity and Self-organization
  • Power management
  • ?The network needs to be connected as long as
    possible
  • System reliability
  • ?The wireless signal needs to cope with
    interference
  • ?Coordination among node communication
  • Node synchronization (clock skew and offset)
  • ?To avoid sending to a sleeping node
  • Robustness
  • ?Subject to environmental variability (harsh
    condition)
  • ?Complex interoperability of network devices

7
Sensor node prototypes
Mica2 mote
Tyndall sensor
Eyes node prototype
Philips sand nodes
8
General sensor node architecture
  • Any layer try to achieve the task using the
    smallest amount of energy possible

9
The need of the Zigbee standard
  • An exponential increase of the interest on WSNs
  • No communication systems that addressed
  • Energy efficiency
  • Low cost devices
  • Low data rate per node
  • Very low duty cycle
  • Scalability (e.g. issues with Bluetooth)
  • WSN proprietary systems cause interoperability
    problems

10
Stack Reference Model
End developer applications, designed using
application profiles
ZA1
ZA2

ZAn
IA1
IAn
Application interface designed using general
profile
API
UDP
ZigBee NWK
IP
Topology management, MAC management, routing,
discovery protocol, security management
802.2 LLC
MAC (SSCS)
Channel access, PAN maintenance, reliable data
transport
IEEE 802.15.4 MAC (CPS)
Transmission reception on the physical radio
channel
IEEE 802.15.4 PHY
LLC logical link control SSCS Service specific
convergence sublayer
11
Protocol Stack Features
  • 8-bit microcontroller
  • Full protocol stack lt32 KB
  • Simple node-only stack 4KB
  • Coordinators require extra RAM
  • Node device database
  • Transaction table
  • Table of neighbours

APPLICATION
Customer
APPLICATION INTERFACE
NETWORK LAYER
DATA LINK LAYER
ZigBee Alliance
MAC LAYER
MAC LAYER
IEEE
PHY LAYER
Silicon
ZigBee Stack
Application
12
Z-NWK layer The components
Zigbee coordinator (ZC)
  • Only one ZC present in the network
  • Initiates the network formation (PAN ID, channel
    stack etc.)
  • It acts as PAN coordinator with FFD capability
  • It can act as a router to other nodes
  • It acts as interface between the user and the
    network

13
Z-NWK layer The components
Zigbee router (ZR)
  • Responsible for tree/mesh packet routing
  • Associates/disassociates node to the network
  • Coordinates communication to children nodes
  • It is in RX mode when idle
  • (no sleep mode implemeted)
  • Maintains a table of neighbours

14
Z-NWK layer The components
Zigbee end device (ZED)
  • It has reduced functionalities
  • It has reduced duty cycle regulated by the
    parent ZR
  • It can talk with the parent ZR only
  • It cannot associate other nodes

15
Zigbee primitives and services
  • Zigbee primitives are used to communicate between
    layers
  • 4 primitive types are present
  • Request/confirm
  • Indication/response
  • Layers communicate through the entitities of the
    Service Access Point (SAP)
  • e.g. NLDE-SAP network layer data entity-SAP

16
Architecture of the Z-NWK layer
  • ZigBee Device Types
  • Stack Profile, Network Rules
  • Network Management and Addressing
  • Message Routing
  • Route Discovery and Maintenance
  • Security

17
Network formation modalities
Star topology
Mesh topology
Tree topology
18
NWK Layer services
  • Layer management entity LME
  • allow requesting services and interfacing to
    other layers
  • Layer data entity LDE
  • Allow transmitting data

SAP Service access point
19
Network Initiation by ZCoordinator
  • NLME_NETWORK_DISCOVERY.request
  • Performs an Active Scan
  • Looks for other ZigBee networks on the channel
  • Selects a compatible network Stack Profile

20
Network Association ZR ZED
  • NLME_JOIN.request
  • Selects the highest acceptable router
  • Link Quality, with capacity
  • Associates with the router
  • Allocated an address on the network
  • Device authenticates with network
  • NLME_START_ROUTER.request
  • Updates Beacon Payload
  • Depth, Capacity
  • Starts a router
  • Updates Association Permit Status

21
Transmitting data
  • NLDE-DATA.request
  • Used by NHL for all data transmissions
  • Uni-casts and broadcasts
  • Accepts the following parameters
  • Destination Address
  • Radius
  • Discover Route
  • NLDE-DATA.indication
  • Reports the receipt of a data transmission
  • Includes the following parameters
  • Source Address

22
IEEE addressing
  • IEEE provides unique long address of 64bits for
    nodes that uses 802.15.4
  • Long addresses cause high data overhead if used
    for node communication
  • Communication relies on not-unique short address
    of 16bits
  • (65536 devices)
  • Short adrresses are forged by the Zigbee address
    assignment procedure

23
Zigbee Tree-structure address assignment
Router (FFD) at depth d1 Cskip(d) 1
Cm-Rm-CmRm(Lm-d-1)/(1-Rm) N-th end device
(RFD) An Aparent Cskip(d)Rmn
Note In order to assign addresses, it is
necessary to know a priori maxDepth, maxRouter
numbers and maxNumbChildren
24
Ad-Hoc on demand vector (AODV) routing
  • Route discovery
  • Find or update route between specific source and
    destination
  • Started if no active route present in routing
    table
  • Broadcast routing request (RREQ) packets
  • Generates routing table entries for hops to
    source
  • Endpoint router responds with Routing response
    (RREP) packet
  • Routes generated for hops to destination
  • Routing table entry generated in source device

25
The ADOV protocol
  • Route discovery
  • A routing table is required if a route already
    exists

2
1
3
5
2
1
4
RREQ
RREP
picture taken from ZigBee presentation by Jan
Dohl et al.
26
THE IEEE 802.15.4
  • Defined by the IEEE for low-rate, wireless
    personal area networks (WPANs).
  • Defines the physical layer Phy and the medium
    access control layer MAC.
  • low-power spread spectrum signal at

27
Operating Frequency Bands
Channel 0
Channels 1-10
2 MHz
868MHz / 915MHz PHY
868.3 MHz
928 MHz
902 MHz
2.4 GHz PHY
Channels 11-26
5 MHz
2.4 GHz
2.4835 GHz
28
Concurrent channel allocation
  • An example of Frequency Channel allocation for
    device classes

IEEE 802.11b channel in North America and Europe
Bluetooth cannels
IEEE 802.11b channel in Europe
2401
2402
2403
2481
2482
2483
2480
2400
picture taken from ZigBee Specifications v1.0
29
IEEE 802.15.4 PHY layer
  • 2400MHz Band specs
  • 4 Bits per symbol
  • DSSS with 32 Bit chips
  • O-QPSK modulation
  • Sine halfwave impulses

Medium
Bit to Symbol
QPSK Mod.
Symbol to Chip
Binary Data
picture taken from IEEE 802.15.4 Specification
30
PHY layer contd.
  • General specs and services
  • Error Vector Magnitude (EVM) lt 35
  • -3dBm minimum transmit power (500µW)
  • Receiver Energy Detection (ED)
  • Link Quality Indication (LQI)
  • Use ED LQI to reduce TX-power
  • Clear Channel Assessment (CCA) with 3 modes
  • Energy above threshold
  • Carrier sense only
  • Carrier sense with energy above threshold

31
Device types
  • In conformity with Zigbee devices, IEEE802.15.4
    are of 3 types
  • PAN coordinator
  • Act as network initiator
  • Only one allowed in the network
  • Full functional devices FFDs
  • That have all access control functionalities
    implemented (channel scan, beacon transmission,
    association etc.)
  • Reduced functional devices RFDs
  • That can only talk to the FFD that associated them

32
IEEE 802.15.4 MAC layer
  • Managing PANs
  • Channel scanning (ED, active, passive, orphan)
  • PAN ID conflict detection and resolution (in
    progress)
  • Starting a PAN
  • Sending beacons
  • Device discovery
  • Device association/disassociation
  • Synchronization (beacon mode)
  • Orphaned device realignment

33
Beacon/nonbeacon-enable modes
  • Beacon-enabled mode
  • Beacons are broadcasted periodically by the FDD
  • Beacons do not employ CSMA prior transmission
  • Beacons contain info related to superframe length
  • and GTS allocation details
  • ACK is optional
  • Nonbeacon-enabled mode
  • The MAC reduces to a simple unslotted CSMA-CA
  • No Superframe
  • No GTS
  • ACK is optional

34
The superframe structure
  • Becons, transmitted by FFDs, contain a superframe
    specification

35
IEEE 802.15.4 association phase
FFD
Coordinator
RFD
RFD Broadcast Beacon request
FFD Superframe spec.
RFD Association req..
FFD ACK with seq.
FFD Broadcast standard timezone packet
FFD Broadcast standard data packet
RFD Data request
FFD ACK with seq.
FFD Association response with short ID.
RFD ACK with seq.
36
The IEEE802.15.4 chip
  • IEEE802.15.4 is coded onto the chip CC2420
    (partially hard coded)
  • Zigbee licence must be bought separately
  • Zigbee compliancy might be lost if some change to
    the code is made
  • ? NOT very suitable for research purposes

37
End of PART I
38
PART II MERLIN over IEEE 802.15.4 routing
capabilities without Zigbee
  • A.G. Ruzzelli

Adaptive Information Cluster (AIC) Group,
University College Dublin, Ireland.
39
Network formation by the IEEE 802.15.4 MAC
  • One PAN coordinator
  • Zero or more coordinators
  • Zero or more end devices
  • First device starts the network as PAN
    coordinator
  • A new device can detect all coordinators (both
    the PAN coordinator and coordinators)
  • A device can join the network by associating with
    any coordinator in range
  • After joining a device can volunteer as
    coordinator

40
Step 1 Starting a new network
  • Device starts network scan (MLME_SCAN)
  • Detects no network
  • Starts new network as PAN coordinator (MLME_START
    with PANCoordinatorTRUE)
  • If PANCoord then other devices in range can
    discover device 1 by means of a network scan

1
41
Step 2 Second device joins the network
  • Device 2 starts network scan (MLME_SCAN)
  • Detects PAN coordinator device 1
  • Sends association request to device 1
    (MLME_ASSOCIATE)
  • Node2 is now and End device ? Other devices
    cannot discover device 2 by means of a network
    scan

1
2
range
42
Step 3 Device 2 becomes a coordinator
  • Device 2 starts serving as a coordinator of the
    existing network (MLME_START with
    PANCoordinatorFALSE, PANId channel parameters
    are ignored)
  • Node2 is now Other devices in range can now
    discover device 2 by means of a network scan

1
2
43
Step 4 Device 3 joins the network
  • Device 3 starts network scan (MLME_SCAN)
  • Detects coordinator device 2(assuming device 1
    is not in range of device 3)
  • Sends association request to device 2
    (MLME_ASSOCIATE)
  • Note Other devices cannot discover device 3 by
    means of a network scan

1
2
3
range
44
Step 5 Device 4 joins the network
  • Device 4 starts network scan (MLME_SCAN)
  • Detects two coordinators device 1 and device
    2(assuming device 1 and device 2 are in range
    of device 4)
  • Sends association request to device 1
    (MLME_ASSOCIATE)(alternatively it could join the
    network also through device 2)
  • Note Other devices cannot discover device 4 by
    means of a network scan

1
4
range
2
3
45
Step 6 Device 4 becomes a coordinator
  • Device 4 starts serving as a coordinator of the
    existing network (MLME_START with
    PANCoordinatorFALSE, PANId channel parameters
    are ignored)
  • Note Other devices in range can now discover
    device 4 by means of a network scan

1
4
2
3
46
Other devices can join in the same way
  • IEEE 802.15.4 allows only direct (single hop)
    communication between two devices that are in
    range of each other.
  • IEEE 802.15.4 leaves it to the higher layers to
    define how network-wide unique short MAC
    addresses are assigned by coordinators.
  • Extended MAC addresses can be used instead of
    short addresses ? High packet overhead

5
6
1
4
2
range
7
8
3
47
Other devices can join in the same way
  • A networking protocol (e.g. ZigBee) on top of
    IEEE 802.15.4 is required to allow communication
    between nodes that are not in range of each other
    by routing of packets via intermediate nodes
    (multi hop).
  • ZigBee defines how short NWK addresses are
    assigned to devices.
  • The short NWK addresses are used also as short
    MAC addresses.

5
6
1
4
2
range
7
8
3
48
Issue 1 The hidden association problem
  • The IEEE 802.15.4 does NOT provide coordination
    between coordinators
  • End devices (RFDs) can talk to its coordinator
    only
  • ? packet collisions might occur
  • 1) Eg. Node9 transmitting to node2 might generate
    collision at node8 that is receiving from node11.
  • 2) Eg. Either node10 and node7 transmission might
    prevent correct neighbouring node reception

5
6
1
4
9
2
range
7
8
10
3
11
49
Issue 2 Beacons are weak
  • Beacons are more prone to collide as transmitted
    without CSMA
  • If a beacon collides then no children RFD devices
    can transmit or receive.

1
4
9
Beacon
2
7
Beacon
Beacon
8
10
3
Tx
11
50
Question
  • Q.1 How can we avoid packet collisions?
  • A.1 By using RTS/CTS/ACK
  • Cons1 We lose the 802.15.4 compliancy
  • Cons2 Results show a very long delay when
    associated to low node duty cycle

1
9
2
8
RTS
CTS
ACK
11
51
Can we at least mitigate collisions without lose
the compliancy?
  • YES
  • 1)You let all nodes become full functional
    devices (FFDs)
  • PROS
  • FFDs can perform carrier sensing before
    transmitting a packet
  • Any node is free to talk to any other node ?
    peer-to-peer communication
  • CONS
  • IEEE 802.15.4 does not define any sleeping mode
    for FDDs
  • High energy consumption

5
6
1
4
9
2
range
7
8
10
3
11
A sleeping scheduling for FFD devices is needed!
52
How all nodes can become FFDs
  • void mlmeAssociateIndication(ADDRESS
    deviceAddress, BYTE capabilityInformation, BOOL
    securityUse, UINT8 aclEntry)
  • // We accept all association requests here.
  • if( gAF_ApplInfo.appCoordinator
    IAM_COORDINATOR
  • gAF_ApplInfo.appCoordinator
    IAM_COORD_W_BEACON
  • gAF_ApplInfo.appCoordinator
    IAM_ASSOCIATED_COORD ) //By Ruzzelli
  • void mlmeAssociateConfirm(WORD assocShortAddress,
    MAC_ENUM status)
  • if( status ! SUCCESS ) return
  • if( assocShortAddress 0xFFFD ) return
  • gAF_MyShortAddr assocShortAddress
  • gAF_ApplInfo.appCoordinator IAM_ASSOCIATED_COOR
    D //by Ruzzelli

53
TICOSS TImezone COOrdinated Sleeping Scheduling
for FFDs
  • We organize nodes in timezones (TZ) based on the
    number of hops to the PAN coordinator
  • We address nodes either
  • solely based on their TZ
  • using the short address provided by the Zigbee
    address procedure
  • We inject a sleeping scheduling table to
    coordinate FDDs activitiy

5
TZ 1
TZ 2
6
1
TZ 1
4
TZ 1
9
TZ 1
2
TZ 2
range
7
8
TZ 1
TZ 1
10
3
TZ 2
11
54
The origin of TICOSS
  • TICOSS is derived from the routing characteristic
    of MERLIN 1 adapted to the IEEE 802.15.4
  • DESIGN goals
  • MACRouting integration into a simple
    architecture
  • No usage of handshake mechanisms
  • No specific node addressing ? Upstream/downstream
    Multicast
  • Reduced latency along a very low energy
    consumption
  • Increasing communication reliability while
    limiting packet overhead

1 Ruzzelli, A.G., OHare, G.M.P., OGrady,
M.J., Tynan, R., MERLIN A synergetic integration
of MAC and routing protocol for distributed
sensor networks, In SECON06, Third Annual IEEE
Communication Society Conference on Sensor, Mesh
and Ad Hoc Communications and Networks Reston,
VA, USA, September 25-28, 2006
55
Timezone data traffic scheduling
Local broadcast Packets reach all neighbours.
No forwarding performed
Sleeping
56
Global allocation
Frame
Frame
Zone 1
Zone 2
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
The allocation of further zones can be obtained
by appending the same table.
The allocation of further frames is obtained by
flanking the same table.
57
Accessing the table
NZONE 4 NSLOT 9
To access the current slot in the table SLOT
GlobalTime/SLOTTIME currentSlot Mod(SLOT,
NSLOT)
Nodes in the same timezone contend the slot for
local broadcast only once each 4 frametimes If
Mod(FRAME, NZONE) Mod(myZone,NZONE)
58
TICOSS over 802.15.4
PAN coord
  • Nodes in the same zone share the same slot for
    activity
  • Intra-zone transmission is regulated by IEEE
    802.15.4
  • Inter-zone transmission is regulated by the
    scheduling

59
The network-wide unique address
  • Recall that with TICOSS as a routing protocol, we
    can
  • 1. Address nodes solely based on their TZ
    (MULTICAST)
  • ?a node transmits data packets only specifying
    the timezone of the receiver
  • PROS
  • Avoid problems of address conflicts
  • Avoid issues of running out short addresses
  • Reduce the actual byte transmitted (for special
    transmission I can still use the long address)
  • CONS
  • multiple copy of the same msg sent can be
    generated?
  • ?increase transmission overhead!
  • ACK not used
  • (the original MERLIN version uses burst tone
    instead)
  • 2. Use the Zigbee address assignment procedure
    to address a secific nodes (UNICAST)
  • ?a node transmits data packets to the node with
    highest cost link function

60
Packet ACK
  • In TICOSS, packet transmission can be
  • Multicasted to higher or lower timezones
  • No ACK is performed
  • Unicasted to a selected node that is chosen based
    on a tunable cost function
  • Successful reception are ACK by transmitting back
    the IEEE802.15.4 sequence packet number

61
Routing characteristics (I)
Controlled multipath
  • 3 small buffers of upstream, downstream and local
    broadcast are provided
  • Packets organised in multiple msgs of the same
    data traffic type
  • Packets contain a msg-ID index of included msgs
  • Nodes, which lose the contention, keep on
    listening to the beginning of the transmitted
    packet then go into sleep
  • Nodes discard from their buffer the msgs already
    fowarded.

Channel contention
P a c k e t
messages
Msg-index
Pro Reduce overhead in transmission! Con
Small increase of node activity Increase
complexity.
Discard msgs already forwarded from their queue
Listen to the packet index
62
Routing characteristics (II)
Timezone maintenance
  • Timezone update are sent periodically
  • Failed reception of timezone update from zone N-1
    node to zone N node triggers a upstream multicast
    of Timezone Update request (TUR)
  • N-1 node/s reply ? Connection reestablished
  • N-1 failed ? local broadcast TUR
  • At least one reply ? change of zoen to N1
  • N failed ? downstream broadcast TUR

2
2
1
1
2
2
1
1
3
3
3
3
4
4
2
4
4
6
TUR
4
TUR
5
3
63
TICOSS/MERLIN analogy
  • Similarities
  • Both protocols use same routing features
  • Both protocols use a slotted CSMA to access the
    channel
  • Differences
  • MERLIN is a proprietary integrated MAC and
    routing protocol, instead TICOSS uses the IEEE
    802.15.4 MACPhy features,
  • MERLIN uses burst ACK to notify correct incorrect
    receptions, instead TICOSS has two ACK
    modalities
  • Multicast with ACK disabled
  • Unicast with ACK enabled

64
MERLIN Assessment
Simulation tool OmNet Framework EU EYES
project Evaluation of MERLIN against
SMACESR Experiments Philips Sand node
implementation Evaluation of TICOSS in progress
65
Scenario and Setup
  • Scenarios
  • 5 nodes two-hops
  • 70 nodes Random
  • multihop
  • Metrics
  • Energy consumption per RX packet
  • Network lifetime
  • E-to-E latency
  • Total packet overhead
  • sleeping time
  • Parameters
  • Duty cycle (acting on CW and frametime size)
  • Low traffic conditions (12 packet/min)
  • High traffic conditions (60 packet/min)

Forwarder
Sources
Destinations
66
V scheduling Network lifetime.
V-scheduling
The network lifetime depends linearly on the
frame length
300
250
200
Network Lifetime (days)
150
100
50
0
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Frametime (sec)
1 Gateway 100
Nodes rand. Distributed. 800500 area network
Min signal strength(12 m) 50 msg/min sent
by 5 rand. nodes Static network
  • The network is considered to fail when 30 of
    nodes are depleted.
  • Lifetime calculated for a linear depletion of 2
    AA batteries.

67
V scheduling setup time
  • V scheduling can be setup in less than 10 seconds
    up to 250 nodes/100m2 of network density.

68
End-to-end packet delay
V-scheduling
  • The controlled multiple path mechanism may cause
    a lower delay for nodes farther from the gateway
  • An increase of latency at the intersection of
    data traffic flows due to periodical stop of
    nodes activity that go into sleep.
  • V-scheduling delay obtained for 2sec frametime
    length

Frametime length should be based upon application
requirements.
69
Low traffic 2-hops scenario
70
High traffic 2-hops scenario
71
Multihop scenario Lifetime
Note These graphs have little relevance if not
related to the EtoE latency
72
Multihop scenario Latency/energy
Given a certain sustainable latency, MERLIN
consumes between 2 and 2.5 times less
energy than SMACESR
73
Total packet overhead
The MAC routing integrated nature MERLIN results
in a smaller packet overhead than SMAC ESR.
74
Conclusion
  • PART I
  • The Zigbee stack has been presented
  • A focus on IEEE 802.15.4 has been given
  • PART II
  • We described how to build networking
    capabilities over IEEE 802.15.4
  • We presented TICOSS, which is derived from the
    MERLIN protocol, as a tree-based routing layer
  • MERLIN simulated results have been presented

75
Thank you!
www.csi.ucd.ie/research (Prism LAB web
site) www.adaptiveinformation.ie (AIC project)
76
An application for TICOSS
  • Sensor-based wireless medical systems

77
Appendix MERLIN MAC features
78
Intra-zone MAC features
Zone N1
Zone N
Zone N-1
  • Recall that
  • Nodes in the same zone share the same slot for
    activity
  • transmission in MERLIN (multicast) do not address
    a specific receiving node
  • How can simultaneous transmission be handled?
  • How can correct/incorrect receptions be
    notified?

79
Burst tones can help
  • Properties
  • Are signal impulse ?Do not contain any coded
    information
  • Are robust ? Several simultaneous burst can still
    be identified as one burst
  • They are shorter that a normal ACK
  • Utilization

80
Asynchronous transmission Mechanism
CCA
CCA
Sleep
Sleep
Tx1
Tc
Random
CCA
Listen
CCA
Sleep
Sleep
Tx2
Transmit
Burst
CCA
Random
Listen
Sleep
Sleep
Rx1
Burst
CCA
Listen
Sleep
Sleep
Rx2
S l o t l e n g t h
burstACK if local broadcast, burst NACK if
multicast
Tx1
Rx1
Rx1
Tx1
Tx2
Tx2
Rx2
Rx2
81
Disadvantages
1)MERLIN does not address a specific receiving
node ? multiple copy of the same msg sent can be
generated? ?increase overhead! 2) Some
collisions due to the Hidden Terminal Problem
(HTP)
Zone 3
A
?
B
82
Something more about the work that we do at the
PRISM group
83
Autonomic WSNs
  • Origin of autonomic computing by IBM
  • Relieve human of the burden of managing large
    scale computer systems
  • Autonomic WSNs properties
  • Self healing
  • Self protection
  • Self configuration
  • Self optimization
  • Self managing

84
Agent technology for autonomic WSNs
  • Agent properties
  • Sense-deliberate-act cycle
  • Sensing data is used as input for the decision
    making process
  • Mobility
  • Useful characteristic of agents that well map
    onto WSNs
  • Agent can migrate from one node to another
    processing data as it goes
  • Fault tolerance
  • Agents can still take decision if some data are
    missing

85
An example Network anomaly intervention
Possible solution Multiple Notification messages
(High energy consuming)
Proposed solution Migrating agent
(Moderate energy consuming)
86
Contribution of autonomic computing to WSNs
  • Self configuring nodes
  • (1) can set up a network
  • (2) might not be well positioned but still work
  • (3) can evaluate network gaps
  • (4) can decide communication schedule.
  • Self protection attribute
  • Migrating agents check channel condition and
    battery level before migrating
  • Self healing
  • Repair network damage due to hash work condition
  • Negotiating new routes
  • Activating redundant nodes
  • Ask for replacement of damaged nodes.
  • Self optimization
  • Quality of service
  • Network efficiency
  • Delay control and data prioritization

87
Intelligence-aided sensor network
  • Opportunistic power management
  • Intelligent coverage
  • Intelligent routing

88
Opportunistic power management (1)
  • Increase network longevity by deactivating
    redundant nodes node hibernation
  • Sensing Coverage
  • All points within the sensed area need to be
    covered by at least 1 sensor. Traditionally, a
    point is covered if it is within the sensing
    range of a given sensor.

Gateway
Redundant based on sensor coverage
89
Intelligent sensing coverage
  • It deals with the quality of sensory data
    provided to the application which is using it
  • Data sampling frequency at the node and
    surrounding nodes should be enough to have a
    certain detail of the phenomena of interest
  • Migrating agents control
  • Sensor sampling rate by tuning it
  • Might request an increase of node density in an
    area

90
Intelligent routing
  • By interacting with different layers the agent
    can check several parameters
  • A look-up table with neighbouring nodes
    parameters (RSSI, battery level, location) is
    provided
  • Even with incomplete data an agent can figure out
    the best neighbours to which to forward the data
    to

Routing
table
Route managing Agent
MAC
Physical
Antenna
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