Pseudorandom noise
In
noise which satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a deterministic sequence of pulses that will repeat itself after its period.[2]
In cryptographic devices, the pseudorandom noise pattern is determined by a key and the repetition period can be very long, even millions of digits.
Pseudorandom noise is used in some electronic musical instruments, either by itself or as an input to subtractive synthesis, and in many white noise machines.
In
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 narrow band 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
chip rate; compare bit rate and symbol rate
.
In a
FCC Part 15
mandates at least 50 different channels and at least a 2.5 Hz hop rate for narrow band frequency-hopping systems.
GPS satellites broadcast data at a rate of 50 data bits per second – each satellite modulates its data with one PN bit stream at 1.023 million
chips per second
and the same data with another PN bit stream at 10.23 million chips per second.
GPS
receivers correlate the received PN bit stream with a local reference to measure distance. GPS is a receive-only system that uses relative timing measurements from several satellites (and the known positions of the satellites) to determine receiver position.
Other
range-finding applications involve two-way transmissions. A local station generates a pseudorandom bit sequence and transmits it to the remote location (using any modulation technique). Some object at the remote location echoes this PN signal back to the location station – either passively, as in some kinds of radar and sonar systems, or using an active transponder at the remote location, as in the Apollo Unified S-band system.[3]
By correlating a (delayed version of) the transmitted signal with the received signal, a precise round trip time to the remote location can be determined and thus the distance.
PN code
A pseudo-noise code (PN code) or pseudo-random-noise code (PRN code) is one that has a spectrum similar to a
See also
- Barker code
- Gold Codes
- Maximum length sequence
- Zadoff–Chu sequence
- Pseudorandom number generator
- Pseudorandomness
- White noise
References
- ^ "Change Topic: Pseudorandom Noise (PRN) Expansion" (PDF). GPS.GOV. Archived (PDF) from the original on October 9, 2022. Retrieved July 13, 2011.
- ^
This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on January 22, 2022. (in support of MIL-STD-188).
- ^ "The Apollo Unified S Band System"
- ^ "PN Sequences". Archived from the original on May 12, 2006. Retrieved March 24, 2006.
