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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.