Due to non linearity of the front end RF components in a WCDMA Receiver, the modulation of the leaked transmitter (TX) signal can get transferred to a blocker, resulting in cross-modulation. If the blocker is close to the desired channel, the cross-modulation spectrum would contaminate the desired channel. Previous published work has analyzed cross-modulation but only for the cases when the leaked TX signal has one or infinite number of physical channels. In this paper, we perform more exhaustive analysis, and derive a closed form expression for the distortion as a function of a generic (N) number of channels in the leaked TX signal. This analysis is also supported with measurements on a WCDMA chip.
In WCDMA Receivers, WCDMA modulated adjacent channel interferers (ACI) can distort the useful signal due to non linearity of the front end RF components. Non linearity of the RF front end transfers the modulation of the transmitter (TX) leakage onto the ACI, resulting in crossmodulation distortion. In addition to this, if the ACI signal is strong, it would undergo spectral Re-Growth and some fraction of its power will leak into the adjacent desired channel. The Adjacent Channel Selectivity (ACS) scenarios in the 3GPP RX specification outline the performance requirement for the receiver in the presence of a strong as well as a weak ACI signal. For the ACS high power scenario (in which the ACI signal is strong), the distortion due to ACI leakage is much more significant compared to the crossmodulation distortion. Therefore, understanding the ACI leakage distortion becomes important, in order to ensure reliable receiver performance. In this paper, we analyze and report observations of the ACI leakage phenomenon on a WCDMA Receiver chip. Measurement results have also been reported for the 3GPP ACS high power scenario. The chip measurements are supported with time-domain simulation results.I.
In this paper we analyze and measure the distortion due to self-mixing of transmitter (TX) leakage in WCDMA mobile receivers (RX). The self-mixing is primarily due to the second order non linearity of the mixer, which is very significant in WCDMA receivers due to the high power of the TX leakage signal. Existing published work has analyzed the dependence of this distortion, on the TX leakage power and second order non-linearity of the Mixer. We go one step further and derive closed form expression for this distortion as a function of the power level of the TX, the second order nonlinearity of the mixer, and the number of equal power WCDMA channels in the TX leakage signal. This is also verified against measurements on a WCDMA receiver Chip.
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