Randomizer

In telecommunication, a randomizer has the following meanings:

1. An algorithm that converts an input string into a seemingly random output string of the same length (e.g., by pseudo-randomly selecting bits to invert), thus avoiding long sequences of bits of the same value; in this context, a randomizer is also referred to as a scrambler.
2. An analog or digital source of unpredictable (i.e., high entropy), unbiased, and usually independent (i.e., random) output bits. A "truly" random generator may be used to feed a (more practical) deterministic pseudo-random random number generator, which extends the random seed value.

Scrambling

Scramblers are primarily used for two reasons:

1. For energy dispersal on the carrier, reducing inter-carrier signal interference.
2. To enable accurate timing recovery on receiver equipment without resorting to redundant line coding.

Scramblers are essential components of physical layer system standards besides interleaved coding and modulation. They are usually defined based on linear feedback shift registers (LFSRs) due to their good statistical properties and ease of implementation in hardware.

It is common for physical layer standards bodies to refer to lower-layer (physical layer and link layer) encryption as scrambling as well. This may well be because (traditional) mechanisms employed are based on feedback shift registers as well. Some standards for digital television, such as DVB-CA and MPE, refer to encryption at the link layer as scrambling.

See also

• Random number generation
• Scrambler

References

 This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).