# Digital Communication Assignment Words: 1448

The transmission of digitally encoded analog signals requires significantly more bandwidth than simply transmitting the original analog signal. Analog signal must be converted to digital codes prior to transmission and converted back to analog form at the receiver, thus necessitating additional encoding and decoding circuitry. 3. Define data Signaling Rate. Data signaling rate is defined as the rate measured in terms bits per second(b/s) at which data are transmitted. Data signaling rate Rub=l/Tab Where Tab=bit duration. 4. Define modulation rate.

It is defined as the rate at which signal level is changed depending On the nature of the format used to represent the digital data. T is measured in Bauds or symbols per second. 5. Why do we go for Gram-Schmidt Articulation’s procedure? Consider a message signal m. The task of transforming an incoming message mi=l into a modulated wave is(t) may be divided into separate discrete time & continuous time operations. The Justification for this separation lies in the Gram-Schmidt articulation’s procedure which permits the representation of any set of M energy signals, {is(t)}, as linear combinations of N orthogonal basis functions 6.

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What is called processing gain ? Processing Gain (PIG) is defined as the ratio of the bandwidth f spread message signal to the bandwidth of unsurpassed data signal ‘e). BOW (spreader signal) Processing Gain ? (Unsurpassed signal) 7. What is called Jamming effect ? In the frequency band of the interest, somebody else transmits the signals intentionally since these signals the in the frequency band of transmission, they interface the required signal. Hence it becomes difficult to detect the required signals. This is called Jamming effect. 8. What is Anti Jamming ?

With the help of spread spectrum method, the transmitted signals are spread over the mid frequency band. Hence these signals appear as noise. Then it becomes difficult for the Summers to send Jamming signals. This is called intimating. 9. How are the predictor coefficients determined? For the adaptation of the predictor coefficients the least mean square (ALMS) algorithm is used. 10. Define adaptive suburban coding? It is a frequency domain coder, in which the speech signal is divided in to number of suburban and each one is coded separately. It uses non masking phenomenon in perception for a better speech quality.

The noise shaping is done by the adaptive bit assignment. 11 . Define a since else. Since pulse is a signal waveform that produces zero SIS and is defined by P (t) = sin (.NET)/.NET = since (AWT) 12. What are the practical difficulties in a since pulse? The amplitude characteristics of the since pulse should be flat from -W to W And zero elsewhere. This is physically unrealizable because of the abrupt Transitions at the band edges В±W. The function decreases as 1 It for large t, resulting in a slow rate of decay. There is practically no margin of error in sampling times in the receiver. 14.

Define Bandwidth Bandwidth is simply a measure of frequency range. The range of regencies contained in a composite signal is its bandwidth. 15. What are the two characteristics of a channel? Bandwidth Power 16. Name the channels considered in digital communication Telephone channels, coaxial cables, optical fibers, microwave radio, and satellite channels. . Define pulse code modulation. In pulse code modulation, analog signal is sampled and converted to fixed length, serial binary number for transmission. The binary number varies according to the amplitude of the analog signal.

This sample variable amplitude pulse is digitized by the analog to digital converter. . What is the purpose of the sample and hold circuit? The sample and hold circuit periodically samples the analog input signal and converts those samples to a multilevel PAM signal. 3. What is the Iniquity sampling rate? Iniquity sampling rate states that, the minimum sampling rate is equal to twice the highest audio input frequency. 4. Define overload distortion. If the magnitude of sample exceeds the highest quantization interval, overload distortion occurs. 5. Define quantization.

Quantization is a process of approximation or rounding off. Assigning PC codes to absolute magnitudes is called quantizing. 6. Define dynamic range. Dynamic range is the ratio of the largest possible magnitude to the smallest possible magnitude. Mathematically, dynamic range is DRY= Vamping 7. Define Quantization error? The difference between the instantaneous values of the quantized signal and the input signal is called as quantization error. 8. What are the three types of quantities? Midstream quantities Modifier quantities Biased quantities 9. Define commanding. Commanding is the process of compressing and expanding.

With commanded systems, the higher amplitude analog signals are compressed prior to transmission and then expanded at the receiver. 0. Define slope overload. How it is reduced. The slope of the analog signal is greater than the delta modulator can maintain, and is called slope overload. Slope overload is reduced by increasing the clock frequency and by increasing the magnitude of the minimum step size. 1 1 . Define granular noise. How it is reduced. When the original input signal has relatively constant amplitude, the reconstructed signal has variations that were not present in the original signal.

This is called granular noise. Granular noise can be reduced by decreasing the step size. 12. Define adaptive delta modulation. Adaptive delta modulation is a delta modulation system where the step size of the AC is automatically varied depending on the amplitude characteristics of the analog input signal. 13. Define delta modulation. It transmits only one bit per sample. It compared the value with the previous sample value. It is used to reduce the signaling rate and transmission bandwidth. 14. What are two main disadvantages of delta modulation? Slope overload distortion Granular noise 1 5. What are two types of commanding? -law commanding A-law commanding 16. What is DEEP? DEEP is nothing but differential pulse code adulation where the differences in the amplitude of the two successive samples are transmitted rather than the actual sample. 17. Define TDMA. The signals to be multiplexed are transmitted sequentially one after the other. Each signal occupies a short time slot. 18. Define crosstalk and guard time. Crosstalk nears interference between the adjacent TDMA channels. It is the unwanted coupling of information from one channel to the other. Guard time is the spacing introduced between the adjacent TDMA channels. 19.

Define Iniquity rate. The sampling rate of AH samples per second, for a signal of bandwidth of W Hertz, is called Iniquity rate. 0. What is Aliasing? Aliasing is the phenomenon of a high frequency component in the spectrum of the signal taking on the identity of a lower frequency in the spectrum of its sampled version. This effect is due to the sampling rate less than the Iniquity rate. 21 . What are the measures to combat the effect of aliasing? (I). Prior to sampling, a low pass filter is used to attenuate those high frequency Components of the signal that are not essential to the information being Conveyed by the signal. He filtered signal is sampled at a rate slightly higher than the Iniquity rate. 24. What is Pulse Amplitude Modulation? 2. What is natural sampling? In Natural sampling, the sampled signal consists of a sequence of pulses of varying amplitude whose tops are not flat but follow the waveform of the message signal m (t). 23. What is flat top sampling? In flat top sampling, the duration of each sample is lengthened to T, to avoid the use of an excessive transmission bandwidth, since bandwidth is inversely proportional to pulse duration. 24. Define Aperture effect.

In flat top sampling, due to the lengthening of the sample, amplitude distortion as well as a delay oft/2 was introduced. This distortion is referred to as Aperture effect. 25. How signal is recovered through holding? In signal recovery through holding, the sample pulses are extended; that is, the sample value of each individual baseball signal is held until the occurrence of the next sample of that same baseball signal. The output waveform consists of up and down staircase waveform with no blank intervals. These voltage transitions are rounded as the capacitor charges and discharges exponentially. 26. What is Pulse Width Modulation?

In Pulse Width Modulation, the width of regularly spaced pulses is varied in proportion to the corresponding sample values of a continuous message signal. 27. What is Pulse Position Modulation? In Pulse Position Modulation, the positions of regularly spaced pulses are varied in proportion to the corresponding sample values of a continuous message signal. 28. How channel synchronization is done in PAM systems? In PAM systems, channel synchronization is done by transmitting a marker pulse in addition to the message bearing pulses. This marker pulse can be identified by making its amplitude exceed that of all possible message pulses.

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