Digital Communication

EC51-DIGITAL COMMUNICATION UNIT-1 DIGITAL COMMUNICATION SYSTEM 1. What are the advantages of digital transmission? The advantage of digital transmission over analog transmission is noise immunity. Digital pulses are less susceptible than analog signals to variations caused by noise. Digital signals are better suited to processing and multiplexing than analog signals. Digital transmission systems are more noise resistant than the analog transmission systems. Digital systems are better suited to evaluate error performance. 2.What are the disadvantages of digital transmission? 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 Signalling Rate. Data signalling rate is defined as the rate measured in terms bits per second(b/s) at which data are transmitted. Data signaling rate Rb=I/Tb Where Tb=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.It is measured in Bauds or symbols per second. 5.Why do we go for Gram-Schmidt Orthogonalization procedure? Consider a message signal m. The task of transforming an incoming message mi=1,2,…..M, into a modulated wave si(t) may be divided into separate discrete time & continuous time operations. The justification for this separation lies in the Gram-Schmidt orthogonalization procedure which permits the representation of any set of M energy signals, {si(t)}, as linear combinations of N orthonormal basis functions 6. What is called processing gain ? Processing Gain (PG) is defined as the ratio of the bandwidth of spread message signal to the bandwidth of unspreaded data signal ie). BW (spreaded signal) Processing Gain =