Effects of correlated interference on the potential linear antenna gain in CDMA macrodiversity systems

It is reported by Hanly (see IEEE Trans. Commun., vol.44, no.2, p.247-56, 1996) that in the reverse link of a CDMA macrodiversity system a remarkable L-fold capacity (throughput) increase can be attained by using L antenna elements (AEs) provided that the spread spectrum bandwidth approaches infinity. In a finite-bandwidth system, however, the increase in capacity as a result of the utilization of multiple AEs will be less than linear due to the presence of the correlated interference effects. In this paper, a spatial correlated interference analysis is presented in order to investigate the effects of the system parameters on the severity of the correlated interference. The results presented indicate that the parameter which we defined as the chiplength ([speed of light]/[chip rate]) plays a role in macrodiversity systems (in regards to the correlation effects) similar to the role of the carrier wavelength in microdiversity systems. It is observed that in systems where the size of the service region is large enough to enable inter-AE distances many times larger than the chiplength, significant (close to linear) capacity gains can be achieved by employing macrodiversity with many AEs. If, on the other hand, the service region size is not large enough with respect to the chiplength, the returns due to macrodiversity will not be as high