To let many users benefit from the high speed communication in an optical fiber, a way to share the channel is needed. One way to share the channel between the users is the multiple access technique of Code Division Multiple Access, CDMA. This technique is based on coding. By assigning the users different codewords, the receiver is able to distinguish the information sent from each user. One family of codes suitable to use in a fiber optic network is the constant weight Optical Orthogonal Codes, OOC. To influence the users interference tolerability it is possible to assign the users codewords of the same length but with different weights. By letting the users have codewords of different length it is possible to have different data rates in the system. These two versions of optical orthogonal codes, with variable length and weight, are investigated in this thesis for their cardinality. The variable weight and variable length codes were created by combining optical orthogonal codes with different parameters. I have found that for variable length OOC:s of weight 2 it seems to be possible to increase the cardinality of a code, but for codes with higer weights than that, it is better that all users are assigned codewords of the same length. But since an upper bound for the cardinality of these types of codes has not been found, it is not possible to verify if this conclusion is correct. For variable weight OOC:s it is found that it is only possible to increase the cardinality of small, not optimal, codes. For codes including many codewords it is rarely possible to include more codewords without breaking the conditions on cross correlation between the codewords.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:liu-7672 |
| Date | January 2006 |
| Creators | Isaksson, Erica |
| Publisher | Linköpings universitet, Institutionen för systemteknik, Institutionen för systemteknik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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