Two strategies to increase the forward link capacity of CDMA systems are compared analytically, and by simulation, with a conventional CDMA system. The strategies are based on reducing the data rate of selected mobile connections. The impact of the propagation environment on the capacity gain of each method is discussed. The comparison shows that maximum capacity gain is achieved when there is large diference between powers allocated to dflerent mobile terminals in the cell.
KeywordsAdaptive data rate, Orthogonality factor, multipath fading.
INTRODUCTIONThe imbalance of data volume between the forward link and the reverse link is one reason, among many others, that the forward link is the capacity bottleneck of 3G CDMA systems [l]. This paper discusses two strategies to increase the capacity of the forward link of CDMA systems by degrading the QoS (reducing the data rate) of some of the mobile connections (MCs). This assumes the use of a variable rate vocoder that can operate satisfactorily at the lower data rate. Similar data rate reduction could be adapted for streaming video and other data formats. The impact of the propagation environment on capacity, and the improvement due to each of the two strategies will be assessed. General layout of CDMA system is shown in figure 1.
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