Impact of Dirty Devices on CDMA Network Coverage and Capacity

The introduction of cellphones with poor receiver sensitivity, known as dirty devices, to the Code Division Multiple Access (CDMA) cellular network results in a reduction in cell edge coverage, degraded capacity, and higher drop-call rates. This poor network performance has a negative impact on customer experience and satisfaction, which may result in increased churn for CDMA wireless carriers. Previous research on the impact of dirty devices has used computer-based simulations. This paper demonstrates the influence of dirty devices on a live commercial CDMA network using two distinct approaches. The first approach deploys dirty and non-dirty devices in a live commercial cell, and measures the impact on forward base transceiver station (BTS) power and forward link Ec/Io (Ec is the received pilot chip energy and Io is the spectral density of the total power seen by the device). A series of tests on a live CDMA network with known dirty devices shows an increase in BTS transmit power resources compared with non-dirty devices, leading to the degradation of forward link Ec/Io. The second approach uses a statistical study of the aggregated pilot strength measurement messages reported by the mobile to ascertain the impact of known dirty devices on the overall network Ec/Io of non-dirty devices.