BASIC Digital Communication TRANSFORMATIONS
The basic signal processing functions that may be considered as transformations are divided into nine categories.
1. Formatting and Source Coding:
Formatting and source coding are both data digitalization procedures. In addition to digitization, source coding includes data compression.
2. Baseband Signaling
The creation of PCM waveforms or line codes is a part of the baseband signaling process.
3. Bandpass signaling
When the references used during demodulation are a measure of all the signal properties (including phase), the technique is referred to be coherent. The procedure is called non-coherent when phase information is not utilized.
4. Equalization
In systems where channel-induced ISI (Intersymbol interference) can cause signal distortion, an equalization filter is required.
5. Channel Coding
The two approaches of channel coding are waveform coding and structured sequencing. The usage of new waveforms is a part of waveform coding. Redundant bits are employed in structured sequences.
6. Multiplexing and multiple access
Resource sharing is at the heart of both multiplexing and multiple access. Local multiplexing occurs, whereas distant multiple access occurs.
7. Spreading
In military applications, spreading is used to defend against interference and provide privacy. Signals can travel in frequency, time, or both directions.
8. Encryption
The main aims of encryption and decryption are communication privacy and authentication. Maintaining privacy entails preventing unwanted individuals from collecting information from the channel (eavesdropping). Authentication prevents unauthorized individuals from inserting false signals (spoofing) into the channel.
9. Synchronization
The estimate of both time and frequency is required for synchronization. In both frequency and phase, coherent systems must synchronize their frequency reference with the carrier. Phase synchronization is not required for non-coherent systems.
The digital communication transformations are shown in the figure.
Signals that represent numbers are sent across a digital communication system. The recipient knows a priori that these digits make up a finite set or alphabet. The probability of wrongly detecting a digit or of mistake is a figure of merit for digital communication systems (Pe).
