# Digital Transmission A digital transceiver is a system composed of a collection of both digital and analog processes that work in concert with each other in order to handle the treatment and manipulation of binary information. The purpose of these processes is to achieve data transmission and reception across some sort of medium, whether it is a twisted pair of copper wires, a fiber optic cable, or a wireless environment. At the core of any digital transceiver system is the binary digit or bit, which is considered to be the fundamental unit of information used by a digital communication system. Therefore, a digital transceiver is essentially responsible for the translation between a stream of digital data represented by bits and [[Physical Layer#Maxwell's Equations|electromagnetic waveforms]] possessing physical characteristics that uniquely represent those bits. Since electromagnetic waveforms are usually described by sine waves and cosine waves, several physical characteristics of electromagnetic waveforms commonly used to represent digital data per time interval $T$ include the amplitude, phase, and carrier frequency of the waveform. However, there is much more going on in a digital transceiver than just a mapping between bits and waveforms, as shown in the figure below. In this illustration of the basic anatomy for a digital transceiver, we observe that there are several functional blocks that constitute a communication system. For instance, the mapping between bits and electromagnetic waveform characteristics is represented by the modulation and demodulation blocks. ![[Pasted image 20250114175222.png]] > [!Figure] > Generic representation of a digital communication transceiver. (source: #ref/Collins ) Additionally, there are the source encoding and source decoding blocks that handle the removal of redundant information from the binary data, channel encoding and channel decoding blocks that introduce a controlled amount of redundant information to protect the transmission for potential errors, and the radio frequency front end (RFFE) blocks that handle the conversation of baseband waveforms to higher carrier frequencies. One may ask the question, Why do we need all these blocks in our digital communication system? Notice in the figure above the presence of a channel between the transmitter and the receiver of the digital transmission system. The main reason why the design of a digital communication system tends to be challenging, and that so many blocks are involved in its implementation, is due to this channel. If the channel was an ideal medium where the electromagnetic waveforms from the transmitter are clearly sent to the receiver without any sort of distortion or disturbances, then the design of digital communication systems would be trivial. However, in reality a channel introduces a variety of random impairments to a digital transmission that can potentially affect the correct reception of waveforms intercepted at the receiver. For instance, a channel may introduce some form of noise that can obfuscate some of the waveform characteristics. Furthermore, in many real-world scenarios many of these non-ideal effects introduced by the channel are time-varying and thus difficult to deal with, especially if they vary rapidly in time. Thus, under real-world conditions, the primary goal of any digital communication system is to transmit a binary message $m(t)$ and have the reconstructed version of this binary message $\hat m(t)$ at the output of the receiver to be equal to each other.