- Pseudorandom noise
In spread-spectrum systems, the receiver correlates a locally generated signal with the received signal. Such spread-spectrum systems require a set of one or more "codes" or "sequences" such that
- Like random noise, the local sequence has a very low correlation with any other sequence in the set, or with the same sequence at a significantly different time offset, or with narrowband interference, or with thermal noise.
- Unlike random noise, it must be easy to generate exactly the same sequence at both the transmitter and the receiver, so the receiver's locally generated sequence has a very high correlation with the transmitted sequence.
In a frequency-hopping spread spectrum sequence, each value in the pseudorandom sequence is known as a channel number and the inverse of its period as the hop rate. FCC Part 15 mandates at least 50 different channels and at least a 2.5 Hz hop rate for narrowband frequency-hopping systems.
A pseudonoise code (PN code) is one that has a spectrum similar to a random sequence of bits but is deterministically generated. The most commonly used sequences in direct-sequence spread spectrum systems are maximal length sequences, Gold codes, Kasami codes, and Barker codes.
- ^ "Change Topic: Pseudorandom Noise (PRN) Expansion". GPS.GOV. http://www.gps.gov/technical/icwg/meetings/2011/09/13/WAS-IS-FINAL_PRN_Expansion_4May2011.pdf. Retrieved 13 July 2011.
- ^ "Pseudorandom Noise (PRN) Code Assignments". Los Angeles Air Force Base. http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=8618. Retrieved 13 July 2011.
- ^ This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
- ^ 
Spread spectrum in Digital Communications Main articles Spread spectrum Methods CDMA Schemes Major implementations Major concepts
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