Question 1

Which modulation scheme is preferred for direct sequence spread spectrum process?
A)bpsk
B)qpsk
C)bpsk & qpsk
D)none of the mentioned

Accepted Answer

Direct Sequence Spread Spectrum (DSSS) can effectively use both Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) as modulation schemes. These schemes are preferred because they provide a good balance between complexity, performance, and bandwidth efficiency, making them suitable for the spread spectrum process.

Question 2

The processing gain is given as_________  modulation scheme.
A)wss/r
B)r/wss
C)wss/2r
D)r/2wss

Accepted Answer

Processing gain is given as the ratio of the spread spectrum signal bandwidth (wss) to the bandwidth of the original signal (r), hence the correct formula is wss/r.

Question 3

The minimum spacing between consecutive hop positions gives the
A)minimum number of chips necessary
B)maximum number of chips necessary
C)chip rate
D)none of the mentioned

Accepted Answer

The minimum spacing between consecutive hop positions gives the minimum number of chips necessary because it determines the number of chips that are required to represent each symbol in the spread spectrum signal.

Question 4

Which system allows larger processing gain?
A)direct sequence
B)frequency hopping
C)direct sequence & frequency hopping
D)none of the mentioned

Accepted Answer

The answer of Which system allows larger processing gain?
A)direct sequence
B)frequency...

Question 5

In which technique is phase coherence hard to maintain?
A)direct sequence
B)frequency hopping
C)direct sequence & frequency hopping
D)none of the mentioned

Accepted Answer

Frequency hopping involves changing the carrier frequency over time in a pseudorandom sequence, making it difficult to maintain phase coherence due to the rapid changes in frequency.

Question 6

Which type of demodulator is used in the frequency hopping technique?
A)coherent
B)non coherent
C)coherent & non coherent
D)none of the mentioned

Accepted Answer

Non-coherent demodulators are typically used in frequency hopping techniques because they do not require phase synchronization, making them more suitable for rapidly changing frequencies.

Question 7

Robustness gives the inability of a signal to withstand the impairments.

Accepted Answer

Robustness refers to the ability of a signal to withstand or overcome impairments, not the inability.

Question 8

Chips are the
A)repeated symbols
B)non repeated symbols
C)smallest length symbols
D)none of the mentioned

Accepted Answer

Chips are the repeated symbols.

Question 9

Slow frequency hopping is
A)several hops per modulation
B)several modulations per hop
C)several symbols per modulation
D)none of the mentioned

Accepted Answer

Slow frequency hopping involves several modulations per hop, meaning the frequency changes less frequently, allowing multiple bits (or symbols) to be transmitted within one frequency before hopping to the next.

Question 10

Fast frequency hopping is
A)several modulations per hop
B)several modulations per symbol
C)several symbols per modulation
D)none of the mentioned

Accepted Answer

The answer of Fast frequency hopping is
A)several modulations per hop
B)several...

Question 11

Which duration is shorter?
A)hop duration
B)symbol duration
C)chip duration
D)none of the mentioned

Accepted Answer

The answer of Which duration is shorter?
A)hop duration
B)symbol duration
C)chip duration
D)none...

Question 12

Frequency division multiple access (FDMA) assigns_________  channels to_________     users.
A)individual, individual
B)many, individual
C)individual, many
D)many, many

Accepted Answer

FDMA assigns individual channels to individual users, allowing each user to have a dedicated frequency band for communication.

Question 13

If the FDMA channel is not in use, it can be used by other users.

Accepted Answer

FDMA (Frequency Division Multiple Access) assigns a specific frequency band to each user within a larger frequency spectrum, and these allocations are typically fixed, not allowing other users to utilize the channel when it's not in use by the primary user.

Question 14

The bandwidth of FDMA channel is
A)wide
B)narrow
C)large
D)zero

Accepted Answer

FDMA (Frequency Division Multiple Access) channels are characterized by narrow bandwidths allocated for individual users or signals, allowing multiple users to share the same communication medium by using different frequency bands.

Question 15

Which of the following is not true for FDMA systems as compared to TDMA systems?
A)low complexity
B)lower cell site system cost
C)tight rf filtering
D)narrow bandwidth

Accepted Answer

FDMA (Frequency Division Multiple Access) systems typically have higher cell site system costs compared to TDMA (Time Division Multiple Access) systems due to the need for multiple receivers and transmitters to handle the separate frequency channels, making choice B incorrect.

Question 16

__________     is undesired RF radiation.
A)intermodulation frequency
B)intermediate frequency
C)instantaneous frequency
D)instrumental frequency

Accepted Answer

Intermodulation frequency is undesired RF radiation that occurs when two or more signals mix together, creating additional signals at frequencies that are not present in the original signals. This can lead to interference in communication systems.

Question 17

__________     is based on FDMA/FDD.
A)gsm
B)w-cdma
C)cordless telephone
D)amps

Accepted Answer

AMPS (Advanced Mobile Phone System) is based on FDMA/FDD (Frequency Division Multiple Access/Frequency Division Duplex).

Question 18

In US AMPS, 416 channels are allocated to various operators with 10 kHz guard band and channel between them is 30 kHz. What is the spectrum allocation given to each operator?
A)12.5 khz
B)30 khz
C)12.5 mhz
D)30 mhz

Accepted Answer

Each operator is allocated 12.5 MHz of spectrum. This is calculated by considering the total number of channels (416) and the bandwidth of each channel (30 kHz), along with the guard bands. The total spectrum is divided among operators, typically two, resulting in 12.5 MHz per operator.

Question 19

TDMA systems transmit in a continuous way.

Accepted Answer

TDMA (Time Division Multiple Access) systems transmit in a non-continuous way, allocating unique time slots to each user within each channel, thus sharing the same frequency channel by dividing the signal into different time slots.

Question 20

__________     are utilized to allow synchronization of the receivers between different slots and frames.
A)preamble
B)data
C)guard bits
D)trail bits

Accepted Answer

The answer of __________     are utilized to allow synchronization of the...

Quiz 10: Modulation Schemes and Access Techniques for Spread Spectrum Systems

Which modulation scheme is preferred for direct sequence spread spectrum process?

The processing gain is given as_________ modulation scheme.

The minimum spacing between consecutive hop positions gives the

Which system allows larger processing gain?

In which technique is phase coherence hard to maintain?

Which type of demodulator is used in the frequency hopping technique?

Robustness gives the inability of a signal to withstand the impairments.

Chips are the

Slow frequency hopping is

Fast frequency hopping is

Which duration is shorter?

Frequency division multiple access (FDMA) assigns_ channels to_ users.

If the FDMA channel is not in use, it can be used by other users.

The bandwidth of FDMA channel is

Which of the following is not true for FDMA systems as compared to TDMA systems?

__________ is undesired RF radiation.

__________ is based on FDMA/FDD.

In US AMPS, 416 channels are allocated to various operators with 10 kHz guard band and channel between them is 30 kHz. What is the spectrum allocation given to each operator?

TDMA systems transmit in a continuous way.

__________ are utilized to allow synchronization of the receivers between different slots and frames.

Quiz 10: Modulation Schemes and Access Techniques for Spread Spectrum Systems

Which modulation scheme is preferred for direct sequence spread spectrum process?

The processing gain is given as_________ modulation scheme.

The minimum spacing between consecutive hop positions gives the

Which system allows larger processing gain?

In which technique is phase coherence hard to maintain?

Which type of demodulator is used in the frequency hopping technique?

Robustness gives the inability of a signal to withstand the impairments.

Chips are the

Slow frequency hopping is

Fast frequency hopping is

Which duration is shorter?

Frequency division multiple access (FDMA) assigns_________ channels to_________ users.

If the FDMA channel is not in use, it can be used by other users.

The bandwidth of FDMA channel is

Which of the following is not true for FDMA systems as compared to TDMA systems?

__________ is undesired RF radiation.

__________ is based on FDMA/FDD.

In US AMPS, 416 channels are allocated to various operators with 10 kHz guard band and channel between them is 30 kHz. What is the spectrum allocation given to each operator?

TDMA systems transmit in a continuous way.

__________ are utilized to allow synchronization of the receivers between different slots and frames.

Frequency division multiple access (FDMA) assigns_ channels to_ users.