Results of simulation of
probability of
QAM and APSK
signals transmission errors caused by
nonlinearity of Q-band transmitter

**A. M. Ripak**^{ 1,2}, M. K. Lebedev^{ 1,2}, V. B. Khaikin^{ 1,2}

^{1 }Special Astrophysical Observatory of Russian Academy of
Sciences, Sankt-Petersburg Branch, Pulkovskoe shosse 65, Sankt-Petersburg
196140, Russia

^{2 }Scientific-Production Firm "Aisberg-NT"
Ligovskiy prospekt 195, Sankt-Petersburg 192007, Russia

The paper is received on May 30, 2017

**
Abstract. **
The multichannel QAM and APSK signal transmission in the Q band is
considered. The analysis has been performed of the mutual interference of
channels when passing QAM and APSK signals through the amplifier with a
nonlinear transfer characteristic. We consider two mechanisms of the
intermodulation distortion effect on the probability of the error in symbol
transmission, namely effect of in-phase intermodulation components on the
signal in the given channel, and effect of additive in power components caused
by the interaction between two or three channels other than the given one. In
order to estimate the effect of the second mechanism the central limit theorem
was used. We obtained a top estimate for the probability of the signal transfer
error arising due the mutual channels interference caused by the amplifier
nonlinearity as a function of gain compression level, modulation index, and
number of channels. The OIP3 value was taken as a parameter that affects the
probability of the erroneous signal transfer. In order to validate the results
obtained, the Simulink model of the multichannel QAM signal transfer was built
and the results of the modeling had been studied. The model accounts for three
mechanisms of interference due to the power amplifier nonlinearity. The first
one is the intermodulation mechanism, the second one is the signal
constellation distortion caused by the difference in the amplification for the
constellation points with different amplitudes, and the third one is the
mismatch of filters in the transmitter and the receiver as the transmitting power
increases, leading to the increase in intersymbol interference and the
constellation points “blur”. The latter two mechanisms manifest themselves in
both multichannel and single-channel systems. In this work the intermodulation
mechanism is studied in detail. All the calculations performed for the power
amplifier IC MAAP-010512 manufactured by MACOM with *P*_{1dB} = 27 dBm
and *P*_{OIP3} = 38 dBm
and the input signal power levels corresponding to the gain compression of
0.5–1 dB.

**
Key words:** Q band, transmitter, QAM, APSK, intermodulation, error probability.

References

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**
For citation:**

A. M. Ripak, M. K.
Lebedev, V. B. Khaikin.
Results of simulation of
probability of
QAM and APSK signals transmission
errors caused by nonlinearity of Q-band transmitter.
Zhurnal Radioelektroniki - Journal of Radio Electronics,
2017, No. 6. Available at http://jre.cplire.ru/jre/jun17/2/text.pdf.
(In Russian)