Cellular Networks MCQ Quiz in বাংলা - Objective Question with Answer for Cellular Networks - বিনামূল্যে ডাউনলোড করুন [PDF]

Correct answer is 2GImportant Points

• CDMA( Code Division Multiple Access)
• It is a channel access method with multiple access.
• Multiple access means sending multiple information to one communication channel.  

circuit switching is a method of implementing a telecommunication network in which two network nodes establish a dedicated communication channel (circuit) through the network before the nodes may communicate.

A local loop is a wired connection from a telephone company's central office with integrated services digital network (ISDN) or digital subscriber line (DSL) (option 3 is wrong)

A private branch exchange is a telephone system within an enterprise that switches calls between users on local lines while enabling all users to share a certain number of external phone lines.PBXS can include network switching systems that accommodate analog phones into the enterprise's digital PBX system. (option 1 is correct)

Private branch exchanges used analog technology originally. Today, PBXs use digital technology -- digital signals are converted to analog for outside calls on the local loop using plain old telephone service (POTS). A switching centre that directly supports subscribers is known as digital PBX.(option 2 is correct)

The signal to interference ratio for a mobile receiver in the functioning cell is given by:

\(\dfrac{S}{\sum_{i = 1}^P I_P}\)

S = Desired signal power from the desired base station

I_i = Interference power caused by the i^th interfering co-channel cell base station

i₀ = Number of co-channel interfering cells

The average received signal strength at any point decays as a power law of the distance of separation between a transmitter and receiver (Propagation measurements).

The average received power (P_r) at a distance (d) => R from the transmitting antenna is approximated by:

\(P_r=P_0(\frac{d}{d_0})^{-n}\)

CONCEPT:

minimum number of PN Bit required for each frequency hop = log₂ no. of distinct hop

where \(no.\;of\;distince\;hops = \frac{{Hopping\;Bandwidth}}{{step\;size}}\)

Solution:

given step size = 100 Hz

Hopping B.W. = 400 MHz

\(No.\;of\;distinct\;loops = \frac{{400 \times {{10}^6}}}{{100}} = 4 \times {10^6}\)

minimum no. of PM bits = log₂ 4 × 10⁶

≃ 22 Bits

ALOHA:

1) ALOHA is a simple communication scheme in which each source in a network sends its data whenever there is a frame to send without checking to see if any other station is active.

2) After sending the frame each station waits for an implicit or explicit acknowledgment.

3) If the frame surrounding reaches the destination, the next frame is sent.

4) Otherwise the frame is sent again.

CSMA:

1) With CSMA, a station wishing to transmit first listens to the medium to determine if another transmission is in progress.

2) If the medium is in use, the station must wait.

3) If the medium is idle, the station may transmit.

HANDOFF:

The hand-off is a process in which the connected cell or data session is transferred from one channel is another of the new base station.

It has two type

1. HARD-HANDOFF – It is based on the phenomenon of the break before make i.e. first existing radio link will be dropped then the new connection will be established.

2. SOFT-HANDOFF – It is based on the phenomenon of make before break i.e. the existing radio link will not be released until the new radio link is completely established.

Pseudorandom noise (PN) code: It is used in CDMA scheme-

It has two types:

1. PN long code – It is 42 bit in length

• Frequency re-use in non-adjacent cells allows a small bandwidth to be used by many subscribers.
• Now TDMA/CDMA allows further sharing, using spread spectrum technologies or (for TDMA) by dividing the available bandwidth into time slots for different users.
• Digital technology has led to these multiple access systems but on its own, digital technology didn't achieve simultaneous users.
• HLR in telecom is the reference database for subscriber parameters like customer ID, customer number, billing detail.
• VLR contains a copy of most of the data stored at the HLR.
• It is, however, temporary data that exists for only as long as the subscriber is “active” in the particular area covered by the VLR.

The correct answer is only (a).

Key Points

The global positioning system (GPS) is a network of satellites and receiving devices used to determine the location of something on Earth. Some GPS receivers are so accurate they can establish their location within 1 centimeter (0.4 inches). GPS receivers provide location in latitude, longitude, and altitude.

Global positioning system (GPS) uses CDMA.

Code division multiple access (CDMA):

• CDMA stands for Code Division Multiple Access.
• CDMA (Code Division Multiple Access) uses a digital modulation technique called Direct Sequence spread spectrum which spreads voice data over a very wide spectrum using a user or cell-specific pseudo-random codes.
• It is a wireless technology used in the transmission of signals from places with high security and Noise reduction.
• The principle of the spread spectrum is used to work with CDMA.
• CDMA is not frequency specific to each user, instead, every channel uses the full available spectrum.
• Each user in a CDMA system uses a different code to modulate their signal.

The correct answer is: 48 volts DC
Explanation:

In a traditional landline telephone system, the voltage present across the telephone, when it is on hook (i.e., when the handset is placed on the cradle and the line is not active), is typically around 48 volts DC. This DC voltage is applied by the central office or telephone exchange to maintain the circuit and detect when the handset is lifted off-hook, which decreases the circuit resistance and signals the exchange to provide a dial tone.

The other options describe different characteristics or conditions:

1) 48 volts, 20 hertz AC is not typically used for the on-hook condition. AC signals in telephone lines are more associated with ringing signals.

2) 90 volts DC is not the correct voltage for the on-hook condition. The telephone line conditions do not involve a 90-volt DC scenario.

3) 90 volts, 20 hertz AC is indicative of the ringing voltage supplied by the telephone exchange to cause the telephone to ring. This AC signal is applied in addition to the normal on-hook DC voltage when there is an incoming call.

Therefore, the typical voltage across a telephone when on the hook is 48 volts DC.

The correct option is 3

Explanation:

The Erlang is a dimensionless unit that is specifically used in telecommunications to measure traffic load or intensity. One erlang represents the intensity of one traffic unit during a continuous one-hour period. In simpler terms, if a group of circErlanguits or channels is being used continuously (100% of the time) for one hour, that represents 1 erlang of traffic. This measure is crucial in the planning and dimensioning of telephone networks as it allows for the calculation of the required capacity to handle a given amount of traffic with acceptable quality.

The other options given relate to various measurements, but not specifically to the measurement of traffic load in telephone systems:

Bells: A theoretical and historical unit related to the logarithmic scale of power ratios, but not used to measure load in telephone systems. The term "bell" is a tribute to Alexander Graham Bell but is not the unit for measuring telephone loads. Instead, we use "decibels," a tenth of a bell, for measuring power and signal levels.
Decibels (dB): A logarithmic unit used to express the ratio of two values of a physical quantity, often power or intensity. In telecommunications, decibels are used to measure signal levels, losses, or gains, but not the traffic load.
Watts: A unit of power in the International System of Units (SI) that measures the rate of energy transfer or consumption. In telecommunications, watts might be used to measure the power consumption of equipment but not the traffic load on the system.
Therefore, erlangs are the correct unit for expressing load in telephone systems, as they directly measure the amount of telecommunications traffic.