Wireless Sensor Networks
Written Examination
2021-09-24
Problem 1: (5p)
The figure shows a simple energy model for power consumption. Assuming a sensor node is only in
transmit and receive modes with the following assumptions: Energy to run circuitry = 60 nJ/bit and
Energy for radio transmission = 120 pJ/bit/m2.
Determine the energy consumption if 1 Mbit of information is transferred from the source to the sink,
where the source and sink are separated by 90 meters and the broadcast radius of each node is 3
meters.
Problem 2: (5p)
A cellular radio network is deployed in a Canadian sub-urban region. The installed base station
antenna height is 100 m, where the transmitter generates 10 W e.i.r.p. on 800 MHz in a 30 kHz
bandwidth. Nominal transmission distance is 5 km. The receivers are mounted in vehicles, moving at
up to 80 km/h, with the antenna height 2 m.
a) Using the Hata model, find the nominal propagation loss in dB.
b) Find the received power in Watt and dBm when the distance between the base station and the
vehicle increases to 10 km.
Problem 3: (5p)
A geostationary satellite is orbiting at the altitude 39,000 km above an earth station. The satellite is
transmitting a 40 dBm digital signal with 36 MHz bandwidth, which requires a signal-to-noise ratio of
12 dB for detection in the earth station receiver.
The transmitting antenna is a parabolic dish with a diameter of 80 cm. Assume that the aperture
efficiencies for both transmitting and receiving antennas η = 0.75.
a) Determine the minimum receiver threshold, in dBm, when the noise temperature of the receiving
system is 160 K.
b) Determine the minimum diameter of the receiving antenna given that the transmitting frequency is
11.2 GHz.
Hint: Free space propagation loss is calculated as:
1 (2)
𝜆𝜆 2
� dB
4𝜋𝜋𝜋𝜋
𝐿𝐿𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 = −10 log �
Wireless Sensor Networks
Written Examination
2021-09-24
Question 1:
(1p)
In the first lecture some WSN applications were described. Briefly describe the basic idea of the
following projects:
a) ZebraNet
b) Habitat Monitoring
Question 2:
(1p)
A sensor node in a WSN is capable of performing some processing, gathering sensory information and
communicating with other connected nodes in the network. Write 6 requirements and constraints that a
sensor node should satisfy.
Question 3:
(1p)
What is the definition of a “Node Degree” when studying scalability in WSN.
Question 4:
(1p)
Interleaving is a mechanism that helps the receiver either to identify bit errors to initiate
retransmission or correct a limited number of bits in case of errors. Explain how this mechanism
works.
Question 5:
(2p)
List and briefly explain three contention-based protocols for WSNs.
Question 6:
(1p)
HARQ (Hybrid ARQ) get advantages from ARQ and FEC techniques. Explain the difference between
HARQ Type I and HARQ Type II.
Question 7:
(2p)
Name and explain three disadvantages using Flooding and Gossiping techniques in WSNs.
Question 8:
(2p)
How is TPSN (Timing-Sync Protocol for Sensor Networks) used in WSNs?
Question 9:
(1p)
Describe how the ToA (Time of Arrival) technique works in WSNs.
Question 10:
(2p)
The path loss exponent is an important parameter when calculating a link budget. Use Friis’ free space
formula to identify the path loss exponent and explain its function.
Question 11:
(1p)
What is inter-symbol interference?
Question 12:
(2p)
Diversity is a common technique to compensate for fading in the radio channel. Name the two main
types of spatial diversity, and explain briefly how they work.
2 (2)
Path loss according to the Hata model
The Hata Model is an empirical formulation of the graphical path loss data provided by Okumura, and
is valid from 150 – 1500 MHz).
Urban Areas
The standard formula for median path loss in urban areas is given by:
𝐿𝐿50(𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢)(𝑑𝑑𝑑𝑑) = 69.55 + 26.16 log 𝑓𝑓𝑐𝑐 − 13.82 log h𝑡𝑡𝑡𝑡 − a(ℎ𝑟𝑟𝑟𝑟 ) + �44.9 − 6.55log(h𝑡𝑡𝑡𝑡 )�𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙
where
fc =
hte =
hre =
d=
150 – 1500 MHz (Communication frequency, [MHz])
30 – 200 m (Base station effective antenna height, [m])
1 – 10 m (Mobile station effective antenna height, [m])
1 km – 20 km (T-R separation distance, [km])
a(hre) is a correction factor for effective mobile antenna height.
For small to medium sized cities, the mobile antenna correction factor is calculated by:
𝑎𝑎(ℎ𝑟𝑟𝑟𝑟 ) = (1.1𝑙𝑙𝑙𝑙𝑙𝑙𝑓𝑓𝑐𝑐 − 0.7)ℎ𝑟𝑟𝑟𝑟 − (1.56𝑙𝑙𝑙𝑙𝑙𝑙𝑓𝑓𝑐𝑐 − 0.8) dB
While for large cities the factor is given by:
𝑎𝑎(ℎ𝑟𝑟𝑟𝑟 ) = 8.29(𝑙𝑙𝑙𝑙𝑙𝑙1.54ℎ𝑟𝑟𝑟𝑟 )2 − 1.1 dB for fc ≤ 300MHz
𝑎𝑎(ℎ𝑟𝑟𝑟𝑟 ) = 3.2(𝑙𝑙𝑙𝑙𝑙𝑙11.75ℎ𝑟𝑟𝑟𝑟 )2 − 4.97 dB for fc ≥ 300 MHz
Suburban Areas
To obtain the path loss in suburban areas a correction factor is added to the standard formula:
Open Rural Areas
𝐿𝐿50(𝑑𝑑𝑑𝑑) = 𝐿𝐿50(𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢) − 2[log(𝑓𝑓𝑐𝑐 ⁄28)]2 − 5.4
To obtain the path loss in open rural areas other correction factors are added to the standard
formula:
𝐿𝐿50(𝑑𝑑𝑑𝑑) = 𝐿𝐿50(𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢) − 4.78(log 𝑓𝑓𝑐𝑐 )2 + 18.33 log f𝑐𝑐 − 40.94