Capacity reduction of WCDMA downlink in the presence of interference from adjacent narrow-band system

One of the main challenges when implementing the future mobile multimedia networks is the cost-effective network evolution from second- to third-generation systems. This evolution path may include the use of different technologies at the same frequency band. The performance of the wide-band code-division multiple-access (WCDMA) downlink is studied in the case when there are narrow-band (NB) interference sources at the adjacent frequencies. A simple, analytical method to calculate the downlink capacity reduction of the WCDMA macrocell in this case is presented. The analysis takes into account different downlink interference mechanisms: wide-band noise from the transmitter as well as adjacent channel interference, intermodulation, and cross-modulation originating in the mobile receiver. The effect of each interference component to the capacity of the WCDMA macrocellular network has been evaluated with numerical examples. The analysis shows that capacity per cell is sensitive to the cell size, and therefore very careful network planning is needed in order to operate the WCDMA networks efficiently. The results of this paper can be utilized when implementing the WCDMA system to the same band with existing narrow-band systems, for instance, with the PCS 1900 band in United States and GSM 1800 band in Europe.