ECE Colloquium: Jiwoong Jang(Ulsan College) “PN-Sequence”
Speaker : Jiwoong Jang
A pseudo noise sequence (PN sequence) or pseudo random sequence (PR sequence) is one that has a spectrum similar to a random sequence of bits but is deterministically generated.
In this talk, I introduce about PN sequence including generation methods, properties and application areas. In cryptography, PN sequence is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, PN seuqence consists of a deterministic sequence of pulses that will repeat itself after its period. In cryptographic devices, the pseudo random noise pattern is determined by a key and the repetition period can be very long, even millions of digits.
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 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 direct-sequence spread spectrum system, each bit in the binary PN sequence is known as a chip and the inverse of its period as chip rate; compare bit rate and symbol rate.
In a frequency-hopping spread spectrum sequence, each value in the PN sequence is known as a channel number and the inverse of its period as the hop rate.