Code properties: influences on the performance of a quaternary CDMA system

By considering a virtual set of codes this paper determines what features of the crosscorrelation spectra influence performance in a Q-CDMA system. A set of virtual codes is a family of codes that has only its properties (e.g. crosscorrelation, randomness) defined as desired. Virtual codes are considered because of the problems that exist in drawing conclusions when an actual set of codes is used. An examination of the influence of code phase for a small set of actual codes shows that the performance call vary over a magnitude or more at larger bit-energy to noise ratios and smaller user numbers, thus making conclusions drawn from an actual set of codes potentially subjective. This paper employs a virtual set of codes to develop a technique that will allow the influence of properties, such as the peak crosscorrelation value, and the occurrence of values and adjacent pairs of values of the discrete-time correlation, on the performance of the system to be observed. Such analysis whilst approximate, provides a valuable insight into code properties that should be considered when selecting a subset of codes for use in a Q-CDMA system, or in designing code generation methods