1.
Explain the relationship between the transport layer and QoS in wireless
sensor networks.
2. Elaborate the Quality of service/reliability in wireless sensor network.
3. Explain in detail about Coverage and deployment with example
Ans: Many wireless sensor networks are tasked with surveillance of certain geographical
areas, for example, to detect intruders, wildfires, or rare animals in a habitat. such an event
can only be detected if there are sensors close enough that can actually sense the event. Two
important questions arise:
a) Which points of this area are close enough to sensors such that an event taking place
at this point can be sensed (Coverage)
b) Given an area to be observed and some coverage requirements, what number of
sensors is needed and where should they be placed? (Deployment problem)
Coverage and deployment have a second important implication besides QoS. If there is some
overprovision of sensors, it might be possible to switch some sensors into sleep mode without
compromising coverage. This allows to save energy and to prolong the lifetime of the overall
network.
For example, in applications like wildfire detection or habitat monitoring, large areas have to
be observed with large numbers of sensors, and in such a situation, sensor deployment will
often only be a loosely controlled process.
(Explain the points below in brief is more content needed)
● Sensing models
● Coverage measures
● Uniform random deployments: Poisson point processes
● Coverage of random deployments: Boolean sensing model
● Coverage of random deployments: general sensing model
● Coverage determination
● Coverage of grid deployments
4. Describe the role of transport protocol in the context of WSNs.
Ans: The different tasks commonly attributed to transport protocols are:
• Reliable data transport: This task requires the ability to detect and repair losses of packets
in a multihop wireless network; appropriate mechanisms working on different layers are
discussed in more detail in Section 13.3.
• Flow control: The receiver of a data stream might temporarily be unable to process incoming
packets because of lack of memory or processor power. Flow control has so far not been a
research issue in sensor networks; some of the reasons have been discussed in Section 6.1
in the context of the link layer.
• Congestion control: Congestion occurs when more packets are created than the network
can carry and the network starts to drop packets. Dropping packets is a waste of energy and
counteracts any efforts to achieve reliability or information accuracy. Congestion-control
schemes try either to avoid this situation or to react to it in a reasonable manner. One important
way to avoid congestion is to control the rate at which sensor nodes generate packets.
Congestion control and rate control are discussed in Section 13.6.1
• Network abstraction: The transport layer offers a programming interface to applications,
shielding the latter from the many complexities and vagaries of data transport. Since there is
yet no standard transport protocol in sensor networks, there is no consensus on such an
interface.
5. What is coverage? How is it important in the context of sensors being
deployed in a region? How is area coverage different from node coverage?
Ans:
We are given a sensor deployment, that is a particular placement of sensors over a certain
geographical area. Which points of this area are close enough to sensors such that an event
taking place at this point can be sensed. Asked differently: which points are covered?
Coverage is thus an important aspect of QoS in sensor networks.
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• The node coverage fn describes the percentage of nodes whose sensing range can be fully
covered by the sensing ranges of other nodes. When the overlapping neighbours are awake,
such a node can be safely switched into sleep mode without reducing the area coverage.
6. What are sensing models? Describe Boolean sensing model in detail.
&
9. Explain the Coverage of random deployments: Boolean sensing model.
Ans: A sensor transforms environmental stimuli into electrical signals. The quality (signal
strength, noise) of the resulting signal depends, among other factors, on the distance between
the sensor and the actual event.
A second aspect of sensing quality is directionality. In an idealised scenario, a sensor has the
same sensitivity in all directions; however, in practice, often certain directions are preferred.
This can be either by construction (for example, video cameras) or as a result of sensor
deployment, when, for example, a node’s acoustic sensor is obstructed by other node
components.
A third aspect is constituted by the possibility that the same sensor can generate different
outputs for the same environmental stimulus at different times, for example, due to
temperature variations the sensing circuitry is exposed to.
● In the Boolean sensing model, all sensors of the same sensor modality (temperature,
humidity) have a common sensing range r. Events within this sensing range are
detected reliably, and events outside this range are not detected at all. Accordingly,
the sensor output signal for a sensor node at position p observing an event at position
q has strength:
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7. Differentiate between Boolean sensing model and general sensing model.
Ans:
8. Explain Uniform random deployment in detail. Determine area coverage for
Poisson point process.
Ans:
10. Explain the Coverage of random deployments: general sensing model
Ans:
With respect to detectability, it is demonstrated in [510] that there exists a threshold density
λc, such that an intruder wishing to move from q0 to q1 is almost surely detected when the
distance between q0 and q1 is large and λ > λc holds. This is shown by turning the general
sensing model into a Boolean one, such that the coverage area of the Boolean sensing model
is a subset of the area covered under the general sensing model. Since there exists a
threshold density λc under the Boolean sensing model such that for λ > λc detection is almost
sure, this must carry over to the general sensing model with its even larger area covered.
11. Explain coverage determination using k-coverage.
Ans:
12. Write short notes on Reliable data transport.
13. Explain the Single packet delivery using single path and the multi path in
detail.
Single packet delivery
14. Write a short note on the HHB and HHBA.
Refer Q 13
