Title: PART I: IEEE 802.15.4, a novel MACPhy layer for the Zigbee stack
1PART I IEEE 802.15.4, a novel MAC/Phy layer for
the Zigbee stack
Adaptive Information Cluster (AIC) Group,
University College Dublin, Ireland.
2Summary
- 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
3Energy-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.
4Some WSN applications
- Remote area monitoring
- Object location
- Industry machinery monitoring
- Disaster prevention
- Wireless medical systems
Monitoring nesting patterns of Storm Petrels.
medical systems
5Wireless 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
6WSN 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
7Sensor node prototypes
Mica2 mote
Tyndall sensor
Eyes node prototype
Philips sand nodes
8General sensor node architecture
- Any layer try to achieve the task using the
smallest amount of energy possible
9The 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
10Stack 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
11Protocol 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
12Z-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
13Z-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
14Z-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
15Zigbee 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
16Architecture of the Z-NWK layer
- ZigBee Device Types
- Stack Profile, Network Rules
- Network Management and Addressing
- Message Routing
- Route Discovery and Maintenance
- Security
17Network formation modalities
Star topology
Mesh topology
Tree topology
18NWK 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
19Network 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
20Network 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
21Transmitting 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
22IEEE 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
23Zigbee 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
24Ad-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
25The 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.
26THE 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
27Operating 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
28Concurrent 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
29IEEE 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
30PHY 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
31Device 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
32IEEE 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
33Beacon/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
34The superframe structure
- Becons, transmitted by FFDs, contain a superframe
specification
35IEEE 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.
36The 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
37End of PART I
38PART II MERLIN over IEEE 802.15.4 routing
capabilities without Zigbee
Adaptive Information Cluster (AIC) Group,
University College Dublin, Ireland.
39Network 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
40Step 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
41Step 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
42Step 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
43Step 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
44Step 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
45Step 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
46Other 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
47Other 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
48Issue 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
49Issue 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
50Question
- 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
51Can 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!
52How 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
53TICOSS 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
54The 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
55Timezone data traffic scheduling
Local broadcast Packets reach all neighbours.
No forwarding performed
Sleeping
56Global 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.
57Accessing 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)
58TICOSS 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
59The 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
60Packet 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
61Routing 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
62Routing 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
63TICOSS/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
64MERLIN Assessment
Simulation tool OmNet Framework EU EYES
project Evaluation of MERLIN against
SMACESR Experiments Philips Sand node
implementation Evaluation of TICOSS in progress
65Scenario 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
66V 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.
67V scheduling setup time
- V scheduling can be setup in less than 10 seconds
up to 250 nodes/100m2 of network density.
68End-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.
69Low traffic 2-hops scenario
70High traffic 2-hops scenario
71Multihop scenario Lifetime
Note These graphs have little relevance if not
related to the EtoE latency
72Multihop scenario Latency/energy
Given a certain sustainable latency, MERLIN
consumes between 2 and 2.5 times less
energy than SMACESR
73Total packet overhead
The MAC routing integrated nature MERLIN results
in a smaller packet overhead than SMAC ESR.
74Conclusion
- 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
75Thank you!
www.csi.ucd.ie/research (Prism LAB web
site) www.adaptiveinformation.ie (AIC project)
76An application for TICOSS
- Sensor-based wireless medical systems
77Appendix MERLIN MAC features
78Intra-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?
79Burst 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
80Asynchronous 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
81Disadvantages
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
82Something more about the work that we do at the
PRISM group
83Autonomic 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
84Agent 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
85An example Network anomaly intervention
Possible solution Multiple Notification messages
(High energy consuming)
Proposed solution Migrating agent
(Moderate energy consuming)
86Contribution 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
87Intelligence-aided sensor network
- Opportunistic power management
- Intelligent coverage
- Intelligent routing
88Opportunistic 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
89Intelligent 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
90Intelligent 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