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Abstract
The effects of turbo-coding on the coherence multiplexed optical PPM CDMA systems are shown by evaluating bit error rate (BER) with respect to system parameters such as interleaver length (K), number of simultaneous users (N), code length (f), initial pulsewidth (t0) and normalized threshold (I¸) by including the effects of thermal noise and shot noise. Turbo-codes increase the number of simultaneous users besides reducing the BER for a decreasing normalized threshold. As the initial pulsewidth reduces from 7ps to 5ps the BER reduces from 1.6392x10-17 to 7.0167x10-18. For a fixed number of simultaneous users (N=20), an initial pulsewidth, (t0 = 5ps) and a normalized threshold (I¸ = 0.84), it is seen that the turbo-codes of interleaver length 10 reduces BER in the order 10-10, 10-18 and 10-32 for the code length varying as 63, 127 and 255 respectively. On comparison with the direct detection it is found that the balanced detection could accommodate an additional number of 8 users at a reduced BER of 10-16.
Highlights
Optical code division multiple access (OCDMA) technique is an emerging technology which permits multiple users to be multiplexed asynchronously at same wavelength through their unique signature sequences[1]
From the above analysis it is seen that as the code length increases, bit error rate (BER) decreases with turbo-codes applied to coherence-multiplexed PPM CDMA system and the BER is found to reduce to half that of the uncoded system
It was shown that the balanced detection could accommodate more number of users besides reducing BER compared to direct detection
Summary
Optical code division multiple access (OCDMA) technique is an emerging technology which permits multiple users to be multiplexed asynchronously at same wavelength through their unique signature sequences[1]. The advantages of a coherence multiplexed CDMA network and turbo-coded optical PPM CDMA system are combined in order to achieve a lower BER and more number of users than that of a direct-detection scheme with APD detectors.
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