An improved OCDMA/OCDMA scheme based on displaced orthogonal user sets

Author

Vanhaverbeke, Frederik ; Moeneclaey, Marc

Author_Institution

Dept. of Telecommun. & Inf. Process., Ghent Univ., Gent, Belgium

Volume

8

Issue

5

fYear

2004

fDate

5/1/2004 12:00:00 AM

Firstpage

265

Lastpage

267

Abstract

We introduce a new type of OCDMA/OCDMA for oversaturated channels, by displacing in time the orthogonal signature sets of the users. A displacement by an integer multiple of a chip period considerably improves the performance of iterative detection of the user data, as compared to quasi-orthogonal sequences (QOS) and conventional random O/O sequences. An additional displacement by half a chip period reduces the variance of the cross correlation between the users of the two sets by up to 50%, and results in an additional performance improvement for square root cosine rolloff chip pulses. This improved O/O system can accommodate a number of users equal to twice the spreading gain N, when N≥32. For a practical rolloff of 25% and N=128, the acceptable channel overload can almost be tripled with improved O/O as compared to conventional O/O.

Keywords

code division multiple access; interference suppression; iterative methods; random sequences; spread spectrum communication; telecommunication channels; OCDMA; channel overload; cross correlation; displaced orthogonal user set; integer multiple chip period; interference cancellation; iterative detection; orthogonal signature set; oversaturated channel; quasiorthogonal sequence; random orthogonal sequence; spreading gain; square root cosine rolloff chip pulse; user data; Detectors; Downlink; Fading; Information processing; Interference; Multiaccess communication; Proposals; Interference cancellation; oversaturated channels; quasi-orthogonal sequences;

fLanguage

English

Journal_Title

Communications Letters, IEEE

Publisher

ieee

ISSN

1089-7798

Type

jour

DOI

10.1109/LCOMM.2004.827453

Filename

1300572