A technique for detecting AMPS intermodulation distortion in an IS-95 CDMA mobile

When IS-95 CDMA mobiles are close to an AMPS base station, the radio frequency portion of the mobile often produces product signals in the baseband CDMA signal. In some cases, AMPS products will decrease the demodulation performance causing the IS-95 CDMA mobile to drop a call. To minimize the impact to existing mobile receiver designs, a technique is described for reducing intermodulation products by first detecting when the products are significant and then switching the low noise amplifier in the IS-95 CDMA mobile between a high and low gain state. This paper presents a detector for AMPS intermodulation products and the performance of this detector using data collected in CDMA networks in Los Angeles.