Measuring single-tone desensitization for CDMA receivers

T CDMA cellular radio system was designed to operate within the same radio frequency spectrum as the older (preceding) advanced mobile phone system (AMPS ) system in the U.S. cellular band. The RF scheme for AMPS employs many closely spaced and relatively narrowband FM channels. By contrast, the RF scheme for CDMA employs fewer, and relatively wideband RF channels. As a result, CDMA channel planning has to consider existing AMPS channels, which act as interferers, degrading the CDMA link performance. We will discuss two primary mechanisms that impact the design and performance of a cellular band CDMA handset. Reciprocal mixing, where the local oscillator (LO) phase-noise ‘jams’ the desired incoming RF, and cross-modulation, where the transmitter leakage overdrives the receiver's low-noise amplifi er (LNA). To demonstrate good performance, the article provides measurements on an actual system.