Signal encoding techniques pdf

If the above example is considered, as there is a long sequence of constant voltage level and the clock synchronization may be lost due to the absence of bit interval, it becomes difficult for the receiver to differentiate between 0 and 1. There is a change in the polarity of the signal, only when the incoming signal changes from 1 to 0 or from 0 to 1.

It is the same as NRZ, however, the first bit of the input signal should have a change of polarity. If a 1 occurs at the incoming signal, then there occurs a transition at the beginning of the bit interval. For a 0 at the incoming signal, there is no transition at the beginning of the bit interval. NRZ codes has a disadvantage that the synchronization of the transmitter clock with the receiver clock gets completely disturbed, when there is a string of 1s and 0s.

Hence, a separate clock line needs to be provided. The signal level is checked twice for every bit time, both initially and in the middle. Hence, the clock rate is double the data transfer rate and thus the modulation rate is also doubled. The clock is taken from the signal itself.

The bandwidth required for this coding is greater. In this type of coding, the transition is done at the middle of the bit-interval. The transition for the resultant pulse is from High to Low in the middle of the interval, for the input bit 1. While the transition is from Low to High for the input bit 0. In this type of coding, there always occurs a transition in the middle of the bit interval. If there occurs a transition at the beginning of the bit interval, then the input bit is 0.

If no transition occurs at the beginning of the bit interval, then the input bit is 1. The number of bits are processed in different manners, in both of these processes. In Manchester encoding, to send the data, the clocks with double speed is required rather than NRZ coding. Here, as the name implies, 4 bits of code is mapped with 5 bits, with a minimum number of 1 bits in the group.

The clock synchronization problem in NRZ-I encoding is avoided by assigning an equivalent word of 5 bits in the place of each block of 4 consecutive bits. These 5-bit words are predetermined in a dictionary.

The basic idea of selecting a 5-bit code is that, it should have one leading 0 and it should have no more than two trailing 0s. Hence, these words are chosen such that two transactions take place per block of bits. We have used two voltage levels to send a single bit over a single signal. But if we use more than 3 voltage levels, we can send more bits per signal. Quadrature PSK More efficient use by each signal element representing more than one bit e.

Analog Data, Digital Signal Digitization Conversion of analog data into digital data Digital data can then be transmitted using NRZ-L Digital data can then be transmitted using code other than NRZ-L Digital data can then be converted to analog signal Analog to digital conversion done using a codec Pulse code modulation Delta modulation. Pulse Code Modulation PCM 1 If a signal is sampled at regular intervals at a rate higher than twice the highest signal frequency, the samples contain all the information of the original signal Proof - Stallings appendix 4A.

Pulse Code Modulation PCM 2 4 bit system gives 16 levels Quantized Quantizing error or noise Approximations mean it is impossible to recover original exactly. Nonlinear Encoding Quantization levels not evenly spaced Reduces overall signal distortion Can also be done by companding. Delta Modulation Analog input is approximated by a staircase function Move up or down one level at each sample interval Binary behavior Function moves up or down at each sample interval. Analog Data, Analog Signals Why modulate analog signals?

Higher frequency can give more efficient transmission Permits frequency division multiplexing chapter 8. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous. Carousel Next. What is Scribd? Explore Ebooks. Bestsellers Editors' Picks All Ebooks. Explore Audiobooks. Bestsellers Editors' Picks All audiobooks. Explore Magazines. Editors' Picks All magazines. Explore Podcasts All podcasts. Difficulty Beginner Intermediate Advanced. Explore Documents.

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