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Correct choice is (b) False

Explanation: Linear modulation techniques are bandwidth EFFICIENT. They are USED in WIRELESS communication systems when there is an INCREASING demand to accommodate more and more users WITHIN a limited spectrum.

Correct choice is (a) Angle modulation

The best explanation: FM is a PART of general class of modulation known as angle modulation. Angle modulation varies a sinusoidal CARRIER SIGNAL in such a way that the angle of the carrier is VARIED according to the amplitude of the modulating BASEBAND signal.

Right option is (b) Amplitude

Easiest explanation: FM is CALLED the constant envelope because amplitude of the carrier wave is kept constant. It is duo to the FACT that the envelope of the carrier does not change with changes in the MODULATING signal.

Correct option is (a) Fast, small

To explain: According to Nyquist, the impulse response of the overall communication SYSTEM should have fast DECAY with small magnitude for sample values not EQUAL to zero. If the channel is ideal then it should be possible to realize APPROXIMATE shaping filters at both transmitter and receiver.

The correct choice is (b) False

To elaborate: It is possible to have COLLISIONS in an FH SYSTEM where an UNDESIRED user transmits in the same channel at the same TIME as the desired user. Whenever an undesired signal occupies a particular hopping channel in FH, the noise and interference in the channel are translated in FREQUENCY.

The correct option is (b) False

To explain I would say: MSK has simple demodulation and SYNCHRONIZATION circuits. It has VARIOUS other ADVANTAGES like continuous phase property makes it highly DESIRABLE for highly reactive loads. Due to these advantages, MSK is a popular modulation scheme for mobile radio communication.

Correct option is (a) Amplitude

To EXPLAIN I would say: In linear MODULATION TECHNIQUE, the amplitude of transmitted signal varies linearly with MODULATING digital signal. It is a form of digital modulation technique.

The correct option is (b) False

Easy explanation: Nyquist FILTERS have zero crossings at ADJACENT symbol peaks and a truncated transfer FUNCTION. Gaussian filter does not FOLLOW Nyquist CRITERION and has a smooth transfer function with no zero crossings.

Correct OPTION is (a) Signal fading DUE to Doppler shift in the CHANNEL

Explanation: Doppler spread refers to signal fading due to Doppler shift in the channel. It is a MEASURE of spectral broadening caused by time rate of CHANGE of the mobile radio channel.

Correct option is (a) Twice

Best explanation: Quadrature phase shift keying (QPSK) has twice the BANDWIDTH of BPSK. It is because two bits are transmitted in a single modulation symbol. The phase of the carrier takes on one of the four equally SPACED VALUES, where each value of phase corresponds to a UNIQUE PAIR of message bit.

The correct option is (d) Nyquist

The explanation: Nyquist was the first to solve the problem of ISI. He OVERCOME the problem of ISI while keeping the transmission bandwidth low. He OBSERVED that ISI can be COMPLETELY nullified if at every instant, the response due to all symbols except the current symbol is EQUAL to zero.

Right answer is (d) Absolute bandwidth

To explain I would SAY: The absolute bandwidth is defined as the range of FREQUENCIES over which the signal has a non-zero power spectral density. For symbols REPRESENTED as rectangular baseband PULSES, the PSD profile extends over an infinite range of frequencies, and has an absolute bandwidth of infinity.

The correct answer is (B) Frequency

To EXPLAIN: Frequency hopping involves a periodic CHANGE of transmission frequency. A frequency hopping signal is regarded as a sequence of modulated data bursts with time varying, pseudo random carrier frequencies.

The correct choice is (c) Non DETERMINISTIC

Best explanation: Pseudo-Noise sequences are deterministic in nature. Certain characteristics of PN sequence are NEARLY equal number of 0s and 1S, very low correlation between shifted versions of the sequence, very low CROSS correlation between any two sequences.

The correct answer is (d) Frequency modulation

To elaborate: The modulation INDEX of an FSK signal is SIMILAR to FM modulation index. It is defined by (2∆F)/Rb. Here ∆F is the PEAK RF frequency and Rb is the BIT RATE.

Correct choice is (a) Identical

The EXPLANATION is: The spectrum of an OQPSK signal is identical to that of QPSK signal. Hence, both signals occupy the same bandwidth. The STAGGERED alignment of the even and odd BIT streams in OQPSK signal does not change the NATURE of spectrum.

The correct option is (a) Double sideband SUPPRESSED carrier amplitude modulated waveform

To elaborate: The BPSK signal is EQUIVALENT to a double sideband suppressed carrier amplitude modulated waveform, where cos(2πft) is applied as the carrier. Hence, a BPSK signal can be GENERATED using a balanced MODULATOR.

Right answer is (B) False

For explanation: Fast frequency HOPPING occurs if there is more than one frequency hop during each TRANSMITTED symbol. THUS, in fast frequency hopping the hopping rate equals or exceeds the information symbol rate.

Correct answer is (d) Total HOPPING bandwidth and INSTANTANEOUS bandwidth

Easiest EXPLANATION: The processing gain of frequency hopping (FH) systems is given by Bss/B. Here, Bss and B DENOTE the total hopping bandwidth and instantaneous bandwidth respectively.

The correct option is (a) True

To explain I would SAY: Yes, MSK can be thought of as a SPECIAL FORM of offset quadrature phase shift KEYING. The condition is that baseband RECTANGULAR pulses are replaced with half sinusoidal pulses.

Correct answer is (c) BPSK

The best EXPLANATION: In DPSK system, input binary sequence is FIRST differentially encoded and then MODULATED using a BPSK modulator. The differentially encoded sequence is generated from input binary sequence by complimenting their modulo-2 SUM.

The correct choice is (b) False

To ELABORATE: Raised cosine filter is the most popular pulse SHAPING filter used in MOBILE communication. It BELONGS to the class of FILTERS that satisfy Nyquist criterion.

Right answer is (d) Voltage CONTROLLED oscillators

The explanation: In direct method, VCOs are used to vary the frequency of the carrier signal in ACCORDANCE with the baseband signal amplitude variations. These oscillators use devices with REACTANCE that can be VARIED by the APPLICATION of a voltage.

Right choice is (b) False

Easy explanation: Frequency MODULATED SIGNAL is regarded as the phase modulated signal in which the modulating wave is integrated before modulation. This means that an FM signal can be generated by first integrating the MESSAGE signal and then using the result as an input to a phase modulator.

The correct option is (d) Base station

Best explanation: The mobile velocity, channel DELAY SPREAD, interference levels and modulation formats all independently impact the raw bit error rate in mobile COMMUNICATION systems. And simulation is a POWERFUL way to design or predict the PERFORMANCE of wireless communication links.

Correct option is (a) Hopset

Explanation: The set of possible carrier frequencies in FH-SS is called hopset. Hopping OCCURS of a FREQUENCY BAND that includes a number of CHANNELS. Each CHANNEL is defined as a spectral region with central frequency in the hopset.

Correct OPTION is (B) Time required for synchronization between the transmitter and the receiver

Explanation: COHERENCE time is the time required for synchronization between the transmitter and receiver. It is the over which a propagating wave is said to be COHERENT.

Right option is (a) Intersymbol interference

To EXPLAIN I would SAY: Frequency SELECTIVE fading is caused due to multipath delay spread which CAUSES intersymbol interference. It results in an irreducible BER FLOOR for mobile systems.

Correct option is (c) Multiplying

For explanation I WOULD say: A direct sequence spread SPECTRUM (DS-SS) system spreads the baseband data by directly multiplying the baseband data PULSES with a PSEUDO noise sequence. And the pseudo noise sequence is produced by a pseudo noise code generator.

The correct CHOICE is (d) 2^m-1

Easy explanation: There are EXACTLY 2^m-1 non-zero states for an m STAGE feedback shift register. Thus, the period of a PN sequence produced by a LINEAR m stage shift register cannot exceed 2^m-1.

Right option is (a) LARGE transmission bandwidth

Easy explanation: Spread spectrum systems are bandwidth INEFFICIENT for single users. But in spread spectrum systems, many users can simultaneously use the same bandwidth without significantly interfering with one ANOTHER. It is one of the advantages of spread spectrum.

Correct choice is (b) False

For EXPLANATION: M-ary QAM does not have constant ENERGY per SYMBOL. It also does not have constant distance between possible symbol states. It reasons that PARTICULAR values of M-ary QAM signal will be DETECTED with higher probability than others.

Correct choice is (b) SYMBOL

The EXPLANATION: In an M-ary signalling scheme two or more bits are grouped together to form SYMBOLS. And one of the M possible signals is transmitted during each symbol period of DURATION TS.

Right answer is (b) False

For explanation I would SAY: Modern mobile communication systems use digital MODULATION TECHNIQUES. Advancements in VLSI and digital signal processing technology have made digital modulation more cost effective than ANALOG TRANSMISSION systems.

Correct choice is (d) Generation and RECEPTION of signal is complicated

To elaborate: Tone-in-band SSB systems has the advantage of MAINTAINING the low bandwidth property of the SSB signals, while at the same time providing good adjacent channel protection. The tone in band system employs feedforward automatic GAIN and frequency control to mitigate the effects of multipath induced fading.

Correct answer is (d) Transmitted power

The explanation: The performance of modulation SCHEME is often measured in terms of its power efficiency and bandwidth efficiency. Other factors also AFFECT the choice of modulation scheme, such as COST and complexity of the subscriber receiver and modulation which is simple to DETECT.

The correct option is (d) Less bandwidth requirement

The explanation: DIGITAL modulation offer many ADVANTAGES over analog modulation. Some advantages include GREATER noise immunity and robustness. They provide EASIER MULTIPLEXING of various forms of information and greater security.

Correct answer is (c) INCREASES, increases

To EXPLAIN: The first null bandwidth of M-ary PSK signals decrease as M increases while Rb is HELD constant. Therefore, as the value of M increases, the bandwidth efficiency also increases.

The CORRECT OPTION is (d) Phase

To ELABORATE: In an M-ary PSK, the carrier phase takes ONE of the M possible values. The possible values of phase are θi=2(i-1)/M, where i=1,2,…….,M.