Electronic signal processing for Optical Code Division Multiple Access Networks

Abstract

This work demonstrates the potential of electronic signal processing for applications in Optical Code Division Multiple Access Networks. The proposed designs are based in distributed topologies allowing operation at speeds close to the cut-off frequency of the transistors employed. We discuss structures capable of encoding and decoding time-domain and multiwavelength Optical CDMA signals. A scheme for mitigating of the impact of Group Velocity Dispersion in multi-wavelength OCDMA systems is also analysed.

Spectral-amplitude encoding CDMA system based on high-speed electronic encoder/decoder structures

“…For instance; when using Gold sequences of length 7 a correlation peak ratio of the order of 2:1 can be obtained theoretically. The method based on decoding unipolar pulses shows a slightly better correlation peak (theoretically a correlation peak ratio of 3:1 [3]). The use of Gold codes of length 7 can create potentially up to 7 quasi-orthogonal channels.…”

“…However, the processing gain of the CDMA receiver based on the 7-tap DTF is low in comparison with the cross-correlation variance of Gold codes. On the other hand, for a truly asynchronous operation, the cardinality of Optical Orthogonal Codes [10] applied to the DTF method in [3] yields 2 simultaneous users for a cross-correlation peak constrained to 1.…”

“…based transversal filters (DTF's) [2,3] has been considered as a technique to employ in multi-Gbps asynchronous networks. Besides the low-cost incurred in its deployment, the electronic technique avoids optical losses featured in optical matched filters and it relies on optical devices solely for transport functions and signal distribution.…”

“…Early work on the filter method confirmed the practicality of symbol-rate DTF design by achieving zero inter-symbol interference (ISI) in the reception of high-rate sequences [4]. In other proposal, time-domain encoding of unipolar pulses was considered in [3] as a method by which code is impressed on variable delays between consecutive pulses. Nonetheless, the span time of the filter taped delay line is highly constrained by filter design considerations.…”