Networks in Embedded Systems - DAIICT Intranet

Networks in Embedded Systems
200401066 – Ravi Varma
200401240 – Rahul Reddy

http://www-net.cs.umass.edu/cs791_sensornets/
http://www.isi.edu/scadds/papers/ICASSP-2001.ps
http://wwwnet.cs.umass.edu/cs791_sensornets/papers/akyildiz2.pdf

Introduction.
Sensing tasks and applications.
Characteristics of a Sensor Network.
Factors Influencing Sensor Network Design.
Communication architecture for sensor networks
Different types of network
Considerations for designing protocols and
Mechanisms.
Conclusions.

Recent advancement in wireless communications and electronics has
enabled the development of low-cost sensor networks. The sensor
networks can be used for various application areas (e.g., health, military,
home)
In this we discuss on distributed, wireless, sensor networks which
the signal processing is distributed along with the sensing.

Imagine:
high-rise buildings self-detect structural faults (e.g., weld
cracks)
schools detect airborn toxins at low concentrations, trace
contaminant transport to source
buoys alert swimmers to dangerous bacterial levels
earthquake-rubbled building infiltrated with robots and
sensors: locate survivors, evaluate structural damage.
ecosystems infused with chemical, physical, acoustic, image
sensors to track global change parameters.
battlefield sprinkled with sensors that identify track
friendly/foe air, ground vehicles, personnel.

Different types of sensors: seismic, low sampling rate
magnetic, thermal, visual, infrared, acoustic and radar, able
to monitor:
temperature,
humidity,
vehicular movement,
lightning condition,
pressure,
soil makeup,
noise levels,
the presence or absence of certain kinds of objects,
mechanical stress levels on attached objects, and
the current characteristics such as speed, direction, and size of an
object.

Intelligent
Highways
Seismic
Structure
response
Marine Micro
organisms
Collaborative
Robots
Wildlife
Monitoring
Many more
applications……..

Streams of data
Uncertain data
Large number of nodes
Multi-hop network
No global knowledge about the network
Node failure and interference is common
Energy is the scarce resource
Limited memory

Data dissemination Data collection

fault tolerance
scalability
production costs
operating environment
sensor network topology
hardware constraints
transmission media and
power consumption.

Failures:
lack of power,
physical damage in harsh environment
Interference by other objects (e.g. radios) and other
sensors.
Fault tolerance: the ability to sustain sensor network
functionalities without any interruption due to failures
The environment is important to the fault tolerance of
algorithms and protocols

# of sensors: hundreds, thousands, to millions, depending on the type of
applications.
Density can be expressed as:
μ(R) = (N π R 2 ) / A
where N is the number of scattered sensor nodes in region A; and R,
the radio transmission range. Basically, μ(R) gives the number of nodes
within the transmission radius of each node in region A.
Note: often we consider 2-dimensional space.
Density also depends on the applications.

Per node cost is important for large sensor networks. It has to be kept
low.
Bluetooth radio system: $5 now, but still too expensive for sensors.
PicoNode: targeted to be < 50c.
More challenging, with large amount of functionalities

All components must be contained in a “matchbox”
Limited energy
Low speed (MHz) and small OS kernel (KBs)
Small memory (KBs)
Transceiver (kbps, short range, feet-meters)

topology maintenance a challenging task due to
# of nodes, failures, dynamics etc
Pre-deployment and deployment phase: no careful planning.
considerations:
the installation cost,
no need for any pre-organization and pre-planning,
the flexibility of arrangement, and
better self-organization and fault tolerance.
Post-deployment phase
topology changes are due to change in position, reachability (due to
jamming, noise, moving obstacles, etc.), available energy,
malfunctioning, etc
How to maintain the topology change?
Re-deployment of additional nodes phase
Adding new sensors

In a multihop sensor network, communicating nodes are linked by a
wireless medium. These links can be formed by radio, infrared, or optical
media.
To enable global operation of these networks, the chosen transmission
medium must be available worldwide.

Sensor node lifetime shows a strong dependence on battery lifetime
sensing, communication, and data processing.
Communication
A sensor node expends maximum energy in data
communication. This involves both data transmission and
reception.
the active power + the start-up power consumption
Data processing
Much less, local data processing is crucial in minimizing power
consumption in a multi-hop sensor network.

distributed computing platform:
PE
network
PEs may be CPUs or ASICs.
PE
communication link
PE

PE
more processing
initial processing
PE sensor
PE actuator

How to program ?
A single computer
Parallel computers
Networks of computers
Networks of Embedded Systems (NES):-
How to program NES to perform distributed tasks ?

Higher performance at lower cost.
Physically distributed activities---time constants may not allow
transmission to central site.
Improved debugging---use one CPU in network to debug others.
May buy subsystems that have embedded processors.

When the precise location of a signal of interest is unknown in a
monitored region, distributed sensing allows one to place the sensors
closer to the phenomena being monitored than if only a single sensor
were used.
This yields higher SNR, and improved opportunities
for line of sight. While SNR can be addressed
in many cases by deploying one very large sensitive sensor,
line of sight, and more generally obstructions, cannot
be addressed by deploying one sensor regardless of its sensitivity.
Thus, distributed sensing provides robustness to environmental
obstacles.

Many different types of networks:
topology;
scheduling of communication;
routing

One source, one or more destinations, no data switching (serial port):
PE 1 PE 2 PE 3
link 1 link 2

Common physical connection:
PE 1 PE 2 PE 3 PE 4
header address data ECC packet format

Fixed: Same order of resolution every time.
Fair: every PE has same access over long periods.
round-robin: rotate top priority among Pes.
fixed A B C A B C
round-robin
A,B,C
A B C B C
A
A,B,C

in1 in2 in3 in4
out4
out3
out2
out1

Non-blocking.
Can handle arbitrary multi-cast combinations.
Size proportional to n 2 .

Use several stages of switching elements.
Often blocking.
Often smaller than crossbar.

Transport layer provides message-based programming interface:
send_msg(adrs,data1);
Data must be broken into packets at source, reassembled at
destination.
Data-push programming: make things happen in network based on
data transfers.

Designed for low-cost, medium data rate applications.
Characteristics:
serial;
multiple-master;
fixed-priority arbitration.
Several microcontrollers come with built-in I 2 C controllers.

Multiple DSPs are often connected by high-speed networks for
signal processing:
DSP DSP
DSP DSP

Timeliness of the processes directly tied to the application
requirements or the user perception
Usage of communication bandwidth, since in a radio
environment bandwidth will always be scarce
Complexity of the protocols and procedures: layer less?,
less layers? different layers?
Energy awareness

In conclusion, wireless sensor networks present fascinating
challenges for the application of distributed signal processing and
distributed control. These systems will challenge us to apply
appropriate techniques and metrics in light of the technology
opportunities (cheap processing and sensing nodes) and challenges
(energy constraints).