Binary De Bruijn sequences for DS-CDMA systems: analysis and results
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RESEARCH
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Binary De Bruijn sequences for DS-CDMA systems: analysis and results Susanna Spinsante*, Stefano Andrenacci and Ennio Gambi
Abstract Code division multiple access (CDMA) using direct sequence (DS) spread spectrum modulation provides multiple access capability essentially thanks to the adoption of proper sequences as spreading codes. The ability of a DSCDMA receiver to detect the desired signal relies to a great extent on the auto-correlation properties of the spreading code associated to each user; on the other hand, multi-user interference rejection depends on the crosscorrelation properties of all the spreading codes in the considered set. As a consequence, the analysis of new families of spreading codes to be adopted in DS-CDMA is of great interest. This article provides results about the evaluation of specific full-length binary sequences, the De Bruijn ones, when applied as spreading codes in DSCDMA schemes, and compares their performance to other families of spreading codes commonly used, such as msequences, Gold, OVSF, and Kasami sequences. While the latter sets of sequences have been specifically designed for application in multi-user communication contexts, De Bruijn sequences come from combinatorial mathematics, and have been applied in completely different scenarios. Considering the similarity of De Bruijn sequences to random sequences, we investigate the performance resulting by applying them as spreading codes. The results herein presented suggest that binary De Bruijn sequences, when properly selected, may compete with more consolidated options, and encourage further investigation activities, specifically focused on the generation of longer sequences, and the definition of correlation-based selection criteria. Keywords: Spreading code, De Bruijn sequence, DS-CDMA, Welch bound
Introduction It is well known that an efficient use of radio spectrum, and the delivery of high capacity to a multitude of final users may be achieved through the adoption of multiuser communication techniques. Among them, code division multiple access (CDMA) using direct sequence (DS) spread spectrum modulation is widely recognized as an efficient solution to allow uncoordinated access by several users to a common radio network, to resist against interference, and to combat the effects of multipath fading [1,2]. With respect to other possible techniques available to enable multiple access, CDMA may also provide intrinsically secure communications, by the selection of pseudonoise spreading codes [3]. In a CDMA system, the transmitted signal is spread over a frequency band much wider than the minimum bandwidth required to transmit the information. All users share the same frequency band, but each transmitter is * Correspondence: [email protected] D.I.B.E.T., Universitá Politecnica delle Marche Ancona, Italy
assigned a distinct spreading code. The selection of suitable spreading codes plays a fundamental role in determining the performance of a CDMA system. As a matter of fact, the multiple access capa
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