MCC-Assignment 1

1. What is Multiplexing and explain types of it.
Multiplexing is the process of combining multiple signals into one signal, over a shared
medium. If analog signals are multiplexed, it is Analog Multiplexing and if digital signals are
multiplexed, that process is Digital Multiplexing.
Types of Multiplexing:
There are mainly two types of multiplexers, namely analog and digital. They are further divided
into FDM, WDM, and TDM.
Analog Multiplexing
The analog multiplexing techniques involve signals which are analog in nature. The analog
signals are multiplexed according to their frequency (FDM) or wavelength (WDM).
Frequency Division Multiplexing (FDM)

In analog multiplexing, the most used technique is Frequency Division Multiplexing FDM. This
technique uses various frequencies to combine streams of data, for sending them on a
communication medium, as a single signal.
Wavelength Division Multiplexing (WDM)

Wavelength Division Multiplexing is an analog technique, in which many data streams of
different wavelengths are transmitted in the light spectrum. If the wavelength increases, the
frequency of the signal decreases.
Digital Multiplexing
The term digital represents the discrete bits of information. Hence the available data is in the
form of frames or packets, which are discrete.
Time Division Multiplexing (TDM)

In TDM, the time frame is divided into slots. This technique is used to transmit a signal over a
single communication channel, with allotting one slot for each message. Of all the types of
TDM, the main ones are Synchronous and Asynchronous TDM.
Synchronous TDM
In Synchronous TDM, the input is connected to a frame. If there are ‘n’ number of connections,
then the frame is divided into ‘n’ time slots. One slot is allocated for each input line. In this
technique, the sampling rate is common to all signals and hence same clock input is given.
The mux allocates the same slot to each device at all times.
Asynchronous TDM
In Asynchronous TDM, the sampling rate is different for each of the signals and the clock
signal is also not in common. If the allotted device, for a time-slot, transmits nothing and sits
idle, then that slot is allotted to another device, unlike synchronous.
2. Advantages of Cellular System.
– Higher Capacity : it allows frequency reuse

– less transmission power : for BS its OKAY but for Mobile power is serious issue.
– local interference only : Having long distances between sender and receiver
results in even more interference problems.
– Robustness : Cellular systems are decentralized and so, more robust against the
failure of single components
3. Explain signal propagation and its range?
 Like wired networks, wireless communication networks also have senders and
receivers of signals.
 However, in connection with signal propagation, these two networks exhibit
considerable differences.
 In wireless networks, the signal has no wire to determine the direction of
propagation.
 Whereas signals in wired networks only travel along the wires.
 As long as the wire is not interrupted or damaged, it typically exhibits the same
characteristics at each point.
1) Transmission range
Within a certain radius of the sender transmission is possible, i.e., a receiver
receives the signals with an error rate low enough to be able to communicate
and can also act as sender.
2) Detection range
Within a second radius, detection of the transmission is possible, i.e., the
transmitted power is large enough to differ from background noise.
However, the error rate is too high to establish communication
3) Interference range
Within a third even larger radius, the sender may interfere with other
transmission by adding to the background noise. A receiver will not be able to
detect the signals, but the signals may disturb other signals.
4. Frequency Division Multiplexing.
FDM describes schemes to subdivide the frequency dimension into several non-
overlapping frequency bands.
Each channel ki is now allotted its own frequency band as indicated. Senders using a
certain frequency band can use this band continuously.
Again, guard spaces are needed to avoid frequency band overlapping (also called
adjacent channel interference).
This scheme is used for radio stations within the same region, where each radio station
has its own frequency.
This very simple multiplexing scheme does not need complex coordination between
sender and receiver: the receiver only has to tune in to the specific sender.
5. Explain Cellular system with three and seven cell clusters?
 Cellular systems implements Space Division Multiplexing Technique (SDM).
 Each transmitter is called a base station and can cover a fixed area called a cell.
 fixed area may be different for different locations.
 The shape of cells are never perfect circles or hexagons
• To avoid interference :
– Two possible models to create cell patterns with minimal interference.
– Cells are combined in clusters on the left side three cells form a cluster, on the
right side seven cells form a cluster.
– All cells within a cluster use disjointed sets of frequencies.
– The hexagonal pattern is chosen as a simple way of illustrating the model.
• To reduce interference even further sectorized antennas can be used.
• Figure shows the use of three sectors per cell in a cluster with three cells.
• Typically, it makes sense to use sectorized antennas instead of omni-directional
antennas for larger cell radii.

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1. What is Multiplexing and explain types of it.

Frequency Division Multiplexing (FDM)

Wavelength Division Multiplexing (WDM)

Time Division Multiplexing (TDM)

2. Advantages of Cellular System.

– Higher Capacity : it allows frequency reuse

3. Explain signal propagation and its range?

4. Frequency Division Multiplexing.

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