Trellis ternary line coding scheme for asynchronous optical CDMA systems |
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Authors: | Maw-Yang Liu Hen-Wai Tsao Joe-Air Jiang |
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Affiliation: | aDepartment of Electrical Engineering, National Ilan University, 260 Ilan, Taiwan;bDepartment of Electrical Engineering, National Taiwan University, Taipei, Taiwan;cDepartment of Bio-Industrial Mechatronics Engineering, National Taiwan University, Taipei, Taiwan |
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Abstract: | In this paper, we investigate the employment of a ternary line coding technique based on Ungerboeck's trellis-coded method in asynchronous optical CDMA systems. The ternary coding we use is predicated upon the equal-weight orthogonal (EWO) scheme. Each user transmits two mutually orthogonal signature sequences to represent “+1” and “−1”, respectively, and nothing is transmitted for “0”. The receiver employs a maximum-likelihood soft-decoder to select the path with minimum Euclidean distance as the preferred path. This trellis ternary coding scheme applies set partitioning with partially overlapping subsets to increase the free Euclidean distance, which considerably improves system performance. Furthermore, due to line coding technique, such scheme comprises sufficient clock information, and thus benefits for baseband timing extraction (i.e. clock recovery). Numerical results reveal that the proposed trellis ternary coding scheme can significantly reduce the error floor and allow more active users to be accommodated in the network. |
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Keywords: | Optical CDMA Equal-weight orthogonal Prime codes Trellis ternary line coding |
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