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7 October 1998 Coherent optical pulse CDMA systems based on I-Q noncoherent demodulation of M-ary orthogonal signals
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Abstract
Coherent optical pulse CDMA systems based on noncoherent demodulation of M-ary orthogonal signals are proposed. Each of the J information bits is encoded and transmitted as a M (equals2J) symbol word of a family of Hadamard-Walsh orthogonal sequences. A pulsed laser is employed at the transmitter, modulated by the symbol sequence and encoded by an optical tapped delay-line encoder to generate a unique optical pseudo-random sequence (bipolar code). At the receiver, a pulsed local oscillator followed by a tapped delay-line encoder is employed to produce the optical code sequence of the intended user. Correlation between the received signal and the local code is executed through a coherent optical correlator comprising a 3 dB coupler and balanced detector. Noncoherent demodulation of the M-ary orthogonal signals based on the maximum-likelihood criterion is used to recover the information bits. After a description of the network implementation, the performance of the system is theoretically analyzed and its numerical evaluation given. It is shown that the ratio of the number of available users to the practical code gain at a BER equals 10-9 is approximately 3.7% - 5%. Although a fewer number of users can be supported compared to full coherent reception (10%), the system no longer requires phase locking whilst keeping the advantages of the coherent approach. Hence the linewidth requirement of the laser sources is relaxed. The performance and the implementation of the system are still significantly better than conventional incoherent optical pulse CDMA systems utilizing unipolar codes.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Wei Huang and Ivan Andonovic "Coherent optical pulse CDMA systems based on I-Q noncoherent demodulation of M-ary orthogonal signals", Proc. SPIE 3531, All-Optical Networking: Architecture, Control, and Management Issues, (7 October 1998); https://doi.org/10.1117/12.327088
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