Location dependent CDMA orthogonality in system level simulations

In system simulations of WCDMA radio networks, a constant value for the orthogonality factor is often assumed in the whole considered area of interest to determine the network performance. This factor is used to scale the intra-cell interference, which has an important impact on the network performance. However, the orthogonality factor is not constant, but depends on the individual channel profile between transmitter and receiver, as well as on the receiver implementation. Therefore, this factor is different for every particular user. In a new approach, the orthogonality factor is calculated dependent on the above parameters for each receiver point individually. Comparisons of this new approach with the simple constant value approach are presented. The results show that the assumption of a constant orthogonality factor within a cell may lead to unrealistic results in system level simulations, especially if interference sensitive high bit rate services are considered, e.g., the packet transmission technology HSDPA (high speed downlink packet access). Especially in the field of performance analysis for network planning and design, it is important to obtain an accurate performance estimate with a correlation to the predicted area, instead of average values for the whole simulation area.