Appendix 3B. Effective Interference Evaluation of Second-Order Distortion Products

The second-order distortion products of the AM transmission leakage are not all in the desired signal bandwidth as depicted in Fig. 3B.1. The second-order distortion IMD _{2 _Tx} that we concern mainly consists of a DC product IMD _{2_DC} and a low frequency product IMD _{2_LF} excluding all high-frequency distortion products. IMD _{2_Tx} is expressed by IMD _{2_DC} and IMD _{2_LF} as

(3B.1)

Figure 3B.1: Second-order distortion spectra of CDMA transmission leakage

To evaluate how much the second-order distortion product will really impact the CNR. The power ratios of the low-frequency distortion product to the overall IMD ₂_ _TX need be estimated. This estimation begins with the probability density function (PDF), p( x) of the AM transmission waveform. The average magnitude square of the transmission waveform is

(3B.2)

Normalizing the waveform magnitude square by the average magnitude we obtain x ² = or express it in dB

(3B.3)

The average of the normalized magnitude square is corresponding to the normalized DC product IMD _{2 _Dc}:

(3B.4)

The normalized low-frequency product of the second-order distortion IMD _{2 _LF} is

(3B.5)

Therefore, the normalized IMD _{2_Tx} is expressed in

(3B.6)

The power ratio of the low-frequency product IMD _{2 _LF} to the second order product IMD _{2 _Tx} can be expressed as

(3B.7)

As we have seen in Fig. 3B.1, only a portion of...