RFUnderstanding Encoders and Decoders in Digital Electronics
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In digital electronics and information theory, an “encoder” and a “decoder” are devices or components used to convert data from one format or representation to another. Encoders transform data into a different format for efficient representation or transmission, while decoders reverse the process to retrieve the original data.
They play a crucial role in digital communication systems, data storage, and digital signal processing (DSP) applications. In wireless communication systems, encoders and decoders are critical in the physical layer to ensure reliable transmission of data over radio waves.
Encoder
An encoder is a device or circuit that takes an input signal, typically in the form of data or information, and converts it into a different format or code. The purpose of an encoder is to represent the input information in a more efficient or compact way or to prepare it for transmission or storage.
Encoders are often used to convert analog signals into digital format or compress data. They can also create error-detection codes for data integrity purposes. Examples of encoders are as follows:
- Digital encoders, which convert an analog voltage or position into a digital representation.
- Data encoders, which convert data from one format to another (e.g., ASCII to binary).
- Compression algorithms, which encode data to reduce its size for storage or transmission (e.g., JPEG for images or MP3 for audio).
In a wireless communication system, the encoder module changes the stream of input bytes into an output stream of bytes with added redundant bytes. It adds the redundancy and changes the formats of original data. Figure-1 depicts the encoder and decoder process and typical encoders and decoders available.
Examples of Encoders in Wireless Physical Layer:
Convolutional encoder, CTC (Convolutional Turbo Coder) encoder, LDPC (Low Density Parity Check) encoder, differential encoder. The primary function of these modules is known as Forward Error Correction.
A convolutional encoder is often used in wireless communication systems to add redundancy to the data before transmission. The Viterbi decoder is used to decode the convolutionally encoded data at the receiver. Turbo encoding is a more advanced technique that involves using two or more convolutional encoders in parallel. Turbo decoding involves using iterative algorithms at the receiver to decode the received signals.
Decoder
A decoder is the counterpart of an encoder. It takes an encoded or compressed signal and converts it back to its original format or representation. Decoders are used to retrieve and interpret data that has been encoded or compressed.
Decoders are commonly used in various applications such as data transmission, data storage, and multimedia playback. Examples of decoders are as follows:
- Video decoders, which take a compressed video stream (e.g., MPEG) and decode it for display.
- Audio decoders, which decode compressed audio data (e.g., MP3) for playback.
- Binary decoders, which convert binary data into various outputs based on specific binary patterns (e.g., binary-to-decimal decoders).
In a wireless communication system, the decoder module utilizes redundant information present in the erroneous received vector to recover the original information bits transmitted.
Examples of Decoders: Viterbi decoder, CTC decoder, LDPC decoder, differential decoder.
Difference between Encoder and Decoder
Let us compare encoder and decoder and derive differences between them in tabular form.
| Parameters | Encoder | Decoder |
|---|---|---|
| Function | Converts input data into a different format or code for efficient representation, transmission, or storage. | Converts encoded or compressed data back to its original format. |
| Purpose | Prepares data for transmission or storage by adding redundancy or converting to a more efficient format. | Retrieves and interprets data that has been encoded, compressed, or prepared for transmission. |
| Input | Accepts raw or unencoded data as input. | Accepts encoded, compressed, or prepared data as input. |
| Output | Produces encoded, compressed, or modified data as output. | Produces original data or a representation of it as output. |
| Common use cases | Data compression encoders (e.g., JPEG for images), Error correcting encoders (e.g., convolutional, LDPC for wireless communication). | Data compression decoders (e.g., JPEG for images), error correcting decoders (e.g., Viterbi, turbo, LDPC for wireless communication). |
| Inverse operation | The inverse operation of encoding is decoding. | The inverse operation of decoding is encoding. |
| Goal | To efficiently represent or transmit data. | To recover or interpret data. |
| Examples | Huffman encoder for text compression, Convolutional encoder for wireless communication. | Huffman decoder for text decompression, Viterbi decoder for wireless communication. |
Conclusion
In summary, the key difference between encoder and decoder lies in their functions. Encoders prepare data for transmission, compression, or error correction, whereas decoders retrieve and interpret encoded, compressed, or transmitted data.
Encoders typically take raw data as input, while decoders handle encoded or prepared data, aiming to efficiently represent data for transmission (encoder) or recover and interpret it (decoder).
Encoder Implementation
Refer to the convolutional encoder implementation and MATLAB code as per the diagram above. It produces 3 bits output for every one input bit. Hence the data output size will be three times the input data size. Puncturing is used to remove bits from desired positions to increase the bit rate.
