18-03-2011, 06:24 PM
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 | M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
 Digital Transmission
Digital Transmission
* Line coding is the process of converting binary data to a digital signal. * The number of different values allowed in a signal is the signal level. The number of symbols that represent data is the data level. * Bit rate is a function of the pulse rate and data level. * Line coding methods must eliminate the dc component and provide a means of synchronization between the sender and the receiver. * Line coding methods can be classified as unipolar, polar, or bipolar. * NRZ, RZ, Manchester, and differential Manchester encoding are the most popular polar encoding methods. * AMI is a popular bipolar encoding method. * Block coding can improve the performance of line coding through redundancy and error correction. * Block coding involves grouping the bits, substitution, and line coding. * 4B/5B, 8B/10B, and 8B/6T are common block coding methods. * Analog-to-digital conversion relies on PCM (pulse code modulation). * PCM involves sampling, quantizing, and line coding. * The Nyquist theorem says that the sampling rate must be at least twice the highest-frequency component in the original signal. * Digital transmission can be either parallel or serial in mode. * In parallel transmission, a group of bits is sent simultaneously, with each bit on a separate line. * In serial transmission, there is only one line and the bits are sent sequentially. * Serial transmission can be either synchronous or asynchronous. * In asynchronous serial transmission, each byte (group of 8 bits) is framed with a start bit and a stop bit. There may be a variable-length gap between each byte. * In synchronous serial transmission, bits are sent in a continuous stream without start and stop bits and without gaps between bytes. Regrouping the bits into meaningful bytes is the responsibility of the receiver.
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