COMNET Assignment (1)
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Lab 8
Lab 8.1 – Practice questions on Wireless Channel.
Question 1
Use the Okumura–Hata model to compute the path loss in dB for a suburban environment, with fc =
900 MHz, ht = 45 m, hr = 3 m, and d = 5 km.
{show your working}
{
L
dB
(
urban small
/
medium city
)
=
69.55
+
26.16log
f
c
−
13.82log
h
t
−
A
(
h
r
)
+
(
44.9
−
6.55log
h
t
)
log
d
Where:
A(
h
r
¿
: Correction factor for mobile unit antenna height
A
(
h
r
)
=
(
1.1log
f
c
−
0.7
)
h
r
−
(
1.56 log
f
c
−
0.8
)
dB
With frequency in MHz, heights in meters, and distance in Km}
Answer: LdB(urban) = 143.95 dB
LdB(suburban) = 134.01dB
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Question 2
Determine the height of an antenna for a TV station that must be able to reach customers up to 80 km
away. Use the Okumura–Hata model for a rural environment with fc = 76 MHz and hr = 1.5 m.
Transmit power is 150 kW and received power must be greater than 10
-13
W.
{
P
t
P
r
=
(
4
πfd
)
2
c
2
&
d
=
3.57
(
√
K h
1
+
√
K h
2
)
}
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Question 3
What is the thermal noise level of a channel with a bandwidth of 10 kHz carrying 1000 watts of
power operating at 50°C? Compare the noise level to the operating power.
{
N
=
kTB
¿
T
kelvin
=
T
celsius
+
273.15
}
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Question 4
The simplest form of flow control, known as stop-and-wait flow control, works as follows. A source entity
transmits a frame. After the destination entity receives the frame, it indicates its willingness to accept another
frame by sending back an acknowledgment to the frame just received. The source must wait until it receives
the acknowledgment before sending the next frame. The destination can thus stop the flow of data simply by
withholding acknowledgment. Consider a half-duplex point-to-point link using a stop-and-wait scheme, in
which a series of messages is sent, with each message segmented into a number of frames. Ignore errors and
frame overhead.
Watch Video:
https://www.youtube.com/watch?v=n09DfvemnTQ
a.
What is the effect on line utilization of increasing the message size so that fewer messages will be
required? Other factors remain constant.
Increasing the message size while keeping other elements constant can have an impact on line
utilization that is both beneficial and bad.
Positive Results:
Increased Throughput: Because more data is transferred in each message, larger message
sizes can result in increased throughput. This can lead to improved communication line
efficiency and utilization.
Negative Consequences:
Larger messages may take longer to transmit, resulting in higher latency. This may be an issue
in situations where low latency is critical, such as real-time communication systems.
Congestion Risk Increased: If the message size is greatly increased and the communication
connection has limited capacity, the risk of congestion increases. This can result in delays and
decreased overall performance.
Larger message sizes may reduce responsiveness in interactive systems. Reduced
responsiveness occurs because it takes longer for a complete message to be conveyed before
a response can be generated.
b.
What is the effect on line utilization of increasing the number of frames for a constant message size?
Increased frame count for a constant message size can have a major impact on line use. On the plus
side, this modification frequently results in increased throughput, especially if the communication
protocol supports parallel frame transmission. Breaking down a message into many frames also
allows for improved error handling at the frame level, improving overall data transfer dependability.
However, there are some disadvantages to consider. The increased number of frames adds overhead,
such as headers and trailers, which might limit the effective data transfer rate. Furthermore, sending
a message in many frames may increase latency because each frame must be transferred and
acknowledged independently.
c.
What is the effect on line utilization of increasing frame size?
Increasing frame size can impact line utilization in various ways. On the positive side, a larger frame
size often leads to improved efficiency and throughput, as more data is transmitted in each frame.
This can result in a reduction of overhead per unit of data, contributing to better overall line
utilization. However, there are potential drawbacks to consider. Larger frames may introduce higher
latency, especially in scenarios where real-time communication is crucial. Additionally, if errors occur
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in a large frame, the retransmission of the entire frame may lead to inefficiencies, impacting overall
reliability. The optimal frame size depends on the specific requirements of the communication
system, balancing the benefits of increased throughput against the potential drawbacks of higher
latency and error handling challenges.
Lab 8.2 – Antenna Systems - Types and Uses of Antennas.
Question 1:
Describe the characteristics of the following types of Antennas:
Antenna Type
Technical Characteristics
Uses
Physical Attributes
Omnidirectional
Antenna
- Frequency: Broad coverage across
multiple frequencies
- Wireless communication
- Typically compact
and lightweight
- Bandwidth: Moderate
- Wi-Fi, broadcasting,
mobile devices
- Directivity: Radiates and receives
signals in all directions
Yagi Antennas
- Frequency: Specific frequency
range
- Point-to-point
communication
- Array of elements on
a boom
- Bandwidth: Narrow
- TV reception, amateur
radio
- Moderate size and
weight
- Directivity: High directional focus
Parabolic Antennas
- Frequency: Wide range, depends on
the design
- Satellite communication,
radar
- Large dish reflector
- Bandwidth: High
- Deep space
communication, TV satellite
- Large size and
moderate weight
- Directivity: High directional focus
Horn Antennas
- Frequency: Wide range
- Microwave
communication, radar
- Horn-shaped structure
- Bandwidth: High
- Satellite ground stations,
weather radar
- Size varies, can be
bulky
- Directivity: Moderate to high
Question 2:
a)
What are Distributed Antenna Systems (DAS)? What are its components?
DAS are sophisticated networks designed to improve wireless coverage and capacity inside specific
geographic areas or structures. DAS, which consists of several components, strategically deploys
antenna nodes around a region to improve signal strength and reliability. The central hub, a critical
component, connects to the network of the wireless service provider and manages signal distribution
to the antenna nodes. A donor antenna can be used to capture strong wireless signals and feed them
into the DAS. Bi-Directional Amplifiers (BDAs) boost signals as they go across the network to preserve
signal strength and quality. The backhaul link connects the DAS to the service provider's network,
allowing signal transfer. Signals are carried between the central hub and spread antenna nodes via
the transmission medium, which can be fiber optic or coaxial cables. Additionally, passive
components such as splitters and combiners aid in the effective distribution and merging of signals.
DAS is used in locations where wireless coverage is difficult, such as huge buildings, stadiums, and
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Lab 8
airports, and it provides a solution to the limitations of typical wireless networks in high-density or
complicated structures.
b)
Where are they typically uses? Give 3 examples
Distributed Antenna Systems (DAS) are commonly utilized in contexts with wireless coverage and
capacity issues, particularly in large and complex structures. Here are three examples of common
uses:
DAS is frequently used in big public venues such as stadiums, arenas, and convention halls.
During events, these venues frequently see high-density user traffic, putting a strain on
typical wireless networks. DAS helps to offer dependable and stable wireless connectivity for
the huge number of attendees, enabling activities such as voice calls, data usage, and mobile
applications.
Office Buildings: Wireless signals may struggle to penetrate all regions in huge office buildings
with numerous stories and complex layouts. DAS is used to deliver continuous and
dependable wireless coverage across the facility, ensuring that employees and visitors can
stay connected regardless of their location. This is very crucial in modern organizations for
productivity and communication.
Airports are dynamic environments with a large flow of people and a variety of locations,
such as terminals, concourses, and parking buildings. In airports, DAS is utilized to address the
issues of providing seamless wireless connectivity throughout these diverse spaces. It helps
passengers communicate, makes airport operations easier, and allows people to stay
connected while waiting for planes.
c)
What is the difference between Active, Passive and Hybrid DAS?
The primary distinctions between Active, Passive, and Hybrid Distributed Antenna Systems (DAS) are
in their approaches to signal dispersion, amplification, and component use. Here's a quick rundown of
each:
DAS that is active:
Amplification: For signal distribution and amplification, active DAS employs active
components such as remote units and fiber optic cables. To magnify signals closer to the
antennas, remote units are strategically deployed across the coverage area.
Signal Strength: Because active DAS provides high-quality and consistent signal strength, it is
appropriate for big and complicated situations.
Flexibility: Active DAS is adaptable in terms of power levels and frequencies, allowing for efficient
signal distribution optimization.
DAS that is passive:
Amplification: For signal distribution, passive DAS uses passive components such as coaxial
cables, splitters, and combiners. It doesn't make advantage of powered amplification.
Signal Quality: While passive DAS is often less expensive, signal loss over longer cable runs
may occur, potentially resulting in signal quality changes.
DAS hybrid:
Combination: To enhance signal distribution, hybrid DAS integrates aspects of both active and
passive systems. It may use active components in some network segments while using
passive components in others.
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Flexibility and cost-effectiveness: Hybrid DAS strike a compromise between active systems'
flexibility and passive systems' cost-effectiveness. It is adaptable to exact coverage
requirements in a cost-effective manner.
d)
In the design and implementation of a DAS, what are 4-5 activities that you would need to carry out?
To guarantee optimal performance and coverage, designing and deploying a Distributed Antenna
System (DAS) entails several critical processes. Typically, the following activities would be carried
out:
1.
Site Survey and Analysis: This initial step sets the foundation for the entire project by
providing essential insights into the environment. Understanding coverage needs and
potential sources of interference is vital for designing an effective DAS.
2.
System Design: The planning phase involves translating the findings from the site survey
into a detailed layout for the DAS. This includes strategically placing antennas, planning
cabling routes, and determining the optimal location for equipment, ensuring a well-
designed and efficient system.
3.
Installation and Deployment: The physical installation is where the theoretical plans come
to life. Precise execution of antenna placement, cabling, and central hub installation is
crucial to realizing the intended coverage and performance goals.
4.
Testing and Optimization: The testing phase validates whether the implemented DAS
meets the specified requirements. Fine-tuning and optimizing the system based on
testing results ensure that it performs at its best, delivering reliable signal strength and
quality.
5.
Maintenance and Monitoring: Establishing a maintenance plan is essential for the long-
term reliability of the DAS. Regular monitoring and proactive maintenance help identify
and address issues promptly, ensuring consistent performance over time.
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