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Correct option is (b) False

To elaborate: If the analog signal is not USED in the feedback path to adapt the EQUALIZER, the equalization is linear. On the other hand, if it is FED back to change the SUBSEQUENT OUTPUTS of the equalizer, the equalization is non-linear.

The CORRECT answer is (b) Baseband or at IF in a receiver

The explanation is: An equalizer is implemented at baseband or at IF in a receiver. Since the baseband COMPLEX envelope EXPRESSION can be used to represent bandpass WAVEFORM, the channel response, the demodulated SIGNAL and adaptive equalizer algorithm are usually simulated and implemented at baseband.

The correct CHOICE is (b) Sequential DECODING

To elaborate: FANO’s algorithm involves sequential decoding. It searches for the most probable path through the trellis by EXAMINING one path at a time.

Right choice is (a) Cellular Digital Packet Data

The best explanation: CDPD (Cellular Digital Packet Data) is a wide area MOBILE data service which USES unused bandwidth. It was mostly used in AMPS phones. Reed SOLOMON code in US CDPD uses m=6 bits per code SYMBOL.

Right answer is (a) LINEAR, non linear

The explanation: EQUALIZATION techniques can be classified into linear and non linear techniques. These CATEGORIES are DETERMINED from how the output of an adaptive equalizer is used for subsequent control of the equalizer.

Right option is (c) Coherence bandwidth

Easiest EXPLANATION: The rationale BEHIND the FREQUENCY diversity is that frequencies separated by more than the coherence bandwidth of the channel will be uncorrelated. Thus, they will not experience the same FADE.

The correct ANSWER is (B) False

For explanation: In comparison to Fano’s algorithm, the STACK algorithm is computationally simpler SINCE there is no retracting over the same path. But stack algorithm REQUIRES more storage than Fano’s algorithm.

Right option is (a) LMS GRADIENT DFE

To explain: Advantages of LMS gradient DFE ALGORITHM are low computational complexity and simple programming. While fast tranversal filter (FTF) algorithm, Fast KALMAN DFE and gradient lattice DFE uses complex programming.

Right CHOICE is (B) False

To explain I would SAY: The convergence rate of the LMS algorithm is SLOW. It is slow due to the FACT that it uses only one parameter i.e. step size that control the adaptation rate.

Correct choice is (b) Amplification of noise

The best explanation: The ZERO FORCING algorithm has the DISADVANTAGE that the inverse filter may EXCESSIVELY amplify noise at FREQUENCIES where the folded channel spectrum has high attenuation.

Right choice is (c) Linear transversal equalizer

Best explanation: The most COMMON equalizer structure used for EQUALIZATION is linear transveral equalizer (LTE). It is made up of tapped DELAY lines, with the tappings speed a symbol period APART.

The correct choice is (d) Small delays

Explanation: In comparison to Viterbi decoding, SEQUENTIAL decoding has a SIGNIFICANTLY larger delay. In ADVANTAGE over Viterbi decoding is that it requires less storage, and THUS CODES with larger constraint lengths can be employed.

Right option is (b) False

For explanation I would say: Fano’s ALGORITHM SEARCHES for the most probable path through the trellis diagram by examining one path at a time. The error rate PERFORMANCE of Fano’s algorithm is comparable to Viterbi’s algorithm.

The CORRECT option is (a) Added

To EXPLAIN I would say: In block codes, parity bits are added to the block of MESSAGE bits to MAKE codewords or code BLOCKS. They enable a limited number of errors to be detected and corrected without retransmission.

Right choice is (d) Coherence time

Easiest explanation: The correlation coefficient is determined by three factors, polarization angle, OFFSET angle from the main beam direction of the DIVERSITY ANTENNA, and the cross polarization discrimination. The correlation coefficient generally becomes higher as offset angle becomes large.

Right option is (d) MEAN SQUARE ERROR algorithm

Explanation: Three classic equalizer algorithm are zero forcing (ZF) algorithm, least mean squares (LMS) algorithm and recursive least squares (RLS) algorithm. They offer fundamental insight into algorithm DESIGN and operation.

Right OPTION is (a) Antenna diversity

The explanation is: Space diversity is also known as antenna diversity. It is one of the POPULAR forms of diversity used in wireless communications. Signals received from the spatially separated antenna on the MOBILE would have essentially uncorrelated ENVELOPES for antenna separation.

The correct answer is (b) Least mean square algorithm

Easiest EXPLANATION: The minimization of the MSE is carried out recursively, and it can be performed by the USE of stochastic GRADIENT algorithm. This more commonly called the least mean square (LMS) algorithm.

Right choice is (c) Slow convergence rate

For EXPLANATION: Recursive LEAST square (RLS) ALGORITHM uses fast convergence rate as opposed to LMS algorithms. They are powerful, albeit complex, adaptive signal processing TECHNIQUES which significantly improves the convergence of adaptive equalizer.

The correct choice is (d) LINEAR matrix

For explanation: Linear matrix is not a way to represent convolution code. Various ways of representing convolution codes are GENERATOR matrix, generator polynomial, logic TABLES, state DIAGRAM, tree diagram and trellis diagram.

The CORRECT OPTION is (d) Code distance

The explanation: The ABILITY of a block code to correct errors is a function of the code distance. Block codes can be USED to improve the performance of communication systems when other MEANS of improvement are impractical.

Correct option is (a) TIME

To elaborate: INTERLEAVING is used to obtain time diversity in a DIGITAL communication system without ADDING any overhead. It provides rapid proliferation of digital speech coders which transform ANALOG voices into efficient digital messages.

Correct ANSWER is (a) Modulation

To explain: Equalization, DIVERSITY and channel CODING are the three techniques which are used to improve received SIGNAL quality and link performance over small scale times and distance. But, the approach, cost, complexity and EFFECTIVENESS varies in wireless communication system.

Right choice is (c) Diversity

The best I can explain: RAKE receiver is a diversity receiver. Diversity is provided by the fact that the multipath components are practically uncorrelated from one another when their relative propagation DELAYS EXCEED CHIP PERIOD.

Correct OPTION is (B) False

Easiest explanation: In CDMA spread spectrum systems, the chip rate is typically MUCH GREATER than the flat fading bandwidth of the channel. Whereas conventional modulation techniques require an equalizer to undo intersymbol interference between adjacent channels.

Right option is (a) Receiver

Best explanation: In virtually all applications, diversity decisions are MADE by the receiver and are unknown to the transmitter. Diversity exploits the RANDOM nature of radio propagation by FINDING INDEPENDENT signal paths for COMMUNICATION.

Correct answer is (b) False

Explanation: ZF is not OFTEN used in wireless links as it neglects the effect of noise altogether. However, it PERFORMS WELL for static channels with high SNR, such as local wired telephone links.

Right option is (c) Equalization techniques

The best I can EXPLAIN: General operating modes of an adaptive equalizer includes training and tracking. A known fixed length training sequence is sent by the transmitter so that the RECEIVER’s equalizer may adapt to a proper setting for minimum BIT error RATE DETECTION.

Correct answer is (a) Search WINDOW

Easy EXPLANATION: The RANGE of time delays that a particular correlator an search is called a search window. RAKE RECEIVER attempts to collect the time shifted version of the original signal by providing a separate correlation receiver for each of the MULTIPATH signal.

Right ANSWER is (a) Structural properties

Explanation: The PERFORMANCE of an algorithm is determined by various factors. These factors are rate of CONVERGENCE, COMPUTATIONAL complexity and numerical properties. The performance of algorithm does not depend on structural properties.

The CORRECT answer is (c) Minimum SQUARE error detection

Best explanation: Decision feedback equalization, maximum likelihood SYMBOL detection and maximum likelihood sequence detection OFFERS non-linear equalization. They offer improvements over linear equalization TECHNIQUES and are used in most 2G and 3G systems.

Right answer is (b) False

Easy explanation: Convolution code can achieve a larger coding gain that can be achieved using a block coding with the same complexity. Their mapping is highly structured, ENABLING a DECODING method considerably DIFFERENT from block CODES.

Right answer is (c) Correlation RECEIVER

The BEST I can explain: RAKE receiver uses separate correlation receivers to PROVIDE the time shifted version of the original signal for each of the multipath signal. CDMA receivers combine these time shifted versions of the original signal to transmission in ORDER to improve the signal to noise RATIO of the receiver.

The correct ANSWER is (a) TIME shifted

The best explanation: RAKE receiver ATTEMPTS to COLLECT the time shifted versions of the original signal. It is due to the fact that there is useful information PRESENT in the multipath components.

Right answer is (d) Coherence TIME

The best I can explain: Time DIVERSITY repeatedly transmits information at time spacings that exceed coherence time of the channel. Thus, multiple repetitions of the signal will be received with independent fading CONDITIONS, THEREBY providing for diversity.

Correct option is (b) False

For EXPLANATION I would say: UNLIKE equalization, diversity requires no training overhead since a training sequence is not REQUIRED by the transmitter. Diversity is a powerful COMMUNICATION receiver technique that provides wireless LINK improvement at a relatively low cost.

Right choice is (c) Number of operations

Easy explanation: Computational complexity is the number of operations required to MAKE ONE COMPLETE iteration of the algorithm. It helps in comparing the performance with other algorithms.

Correct choice is (a) Error signal

Easy explanation: The adaptive algorithm is controlled by the error signal. The error signal is derived by comparing the output of the EQUALIZER and some signal which is either an exact scaled REPLICA of the transmitted signal or represents a PROPERTY of transmitted signal.

Correct option is (b) False

To explain I WOULD say: In a RAKE receiver, if the output from one correlator is corrupted by fading, the others may not be. And the corrupted SIGNAL may be discounted through WEIGHTING PROCESS.

The correct ANSWER is (a) CDMA

The best I can explain: RAKE receiver is essentially a DIVERSITY receiver which is used specifically for CDMA. It uses the fact that the MULTIPATH components are practically uncorrelated from ONE another when their RELATIVE propagation delays exceed a chip period.

Correct CHOICE is (B) False

To EXPLAIN I would say: Selection diversity uses m demodulators to PROVIDE m diversity branches. Their gain is adjusted to provide the same average SNR for each branch.

The correct option is (C) Rapid

For explanation: Small scale fades are characterized by deep and rapid fluctuations. They occur as the mobile system moves over distances of just a few wavelengths. These fades are CAUSED by multiple REFLECTIONS from the SURROUNDING in the vicinity of the mobile.

Correct CHOICE is (b) Blind algorithms

The best explanation: Blind algorithms exploit the characteristics of the transmitted SIGNAL and do not require TRAINING SEQUENCE. These TYPE of algorithm are able to acquire equalization through property restoral techniques of transmitted signal.

The correct choice is (b) Intersymbol interference

To elaborate: Equalization compensate the intersymbol interference (ISI) created by multipath WITHIN time dispersive channels. An EQUALIZER within a receiver compensates for the average RANGE of the expected channel AMPLITUDE and delay CHARACTERISTICS.