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Pseudorandom Noise Sequence(PN sequence) Basics

PN sequence is widely used in CDMA systems for the following reasons.
•  spread the bandwidth of baseband modulated signal to the much larger bandwidth before transmission
•  to distiguish between different users by allocating unique PN sequences to them.

PN sequence generation

PN sequence stands for Pseudorandom Noise Sequence. Though the name suggests they are random sequences; but they are not random. PN sequences are deterministic and periodic in nature. The same pattern repeats after some duration. Following are important properties of a PN sequence.
•  Relative frequencies of one and zero are each equal to one half.
•  For 1s and 0s; half of all run lengths are of length 1; 1/4 are of length 2;1/8 are of length 3 and so on.
•  If new sequence is generated by shifting original sequence by nonzero elements than equal number of aggrements and also disaggrements exist between these two sequences.

PN sequences are generated by combining outputs of feedback shift registers. One such circuit is depicted in the figure.

PN sequence MATLAB code

%%PN Sequence Generator in matlab of length 1023
h = commsrc.pn('GenPoly', [[8 2 0]], 'Mask', [1 0 0 0 0 0 1 0]);
set(h, 'NumBitsOut', 1023);
pnseq = generate(h);
for k=1:length(pnseq)
if(pnseq(k) == 0)
pnseq(k) = -1;
end
end
maxpeak = xcorr(pnseq,pnseq);
plot(maxpeak);

Useful Links to MATLAB codes

Refer following as well as links mentioned on left side panel for useful MATLAB codes.
PTS for PAPR reduction
OFDM Preamble generation
Time off estimation corr
Freq off estimation corr
channel estimation
11a WLAN channel
11g WLAN channel
15.3 UWB channel
15.4a UWB channel
16d SUI Channel
16e wimax channel
Rician channel
Rayleigh channel
SC-FDMA
PN sequence generation
3D plotting
AM FM PM modulation
CRC8 CRC32

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