Orthogonality of UMTS codes in indoor channels

UMTS (Universal Mobile Telecommunications System) spreading codes are only truly orthogonal in the absence of multipath delay and time offsets. In all practical channels the loss of orthogonality will result in the generation of non-zero cross-correlation products that can compromise the error performance of code division multiple access (CDMA) systems. The practical level of cross-correlation produced in the uplink of multiuser applications at the base-station site and the effect of this interference on the RAKE receiver is investigated by means of wideband dual polar channel measurements from a field trials campaign, taken within the UMTS time division duplex (TDD) uplink (1910-1915 MHz). The results showed that 75% of the measurements in an indoor channel had normalised correlations less than 0.25.