Application of Low Crest Factor Modulation in Radio Communication Systems

Introduction. Radio communication systems for small Earth-orbiting objects possess a number of specific features associated with their application area, thus being expected to meet conflicting requirements. These include, on the one hand, provision of a high data transfer rate (up to 20 Mbps) and, on the other, operation at large distances of up to 150 km or more, while having small dimensions and power consumption (usually no more than 5…20 W). The main share of energy required by onboard radio communication systems of small Earth-orbiting objects is consumed by the power amplifier. Therefore, such communication systems should use modulation with the lowest possible crest factor.

Aim. To investigate the effect of the parameters and operating modes of the amplifier on those of the radio communication system, such as its output power, efficiency, out-of-band transmitter radiation, and receiver sensitivity for signals with different types of modulation and different crest factor values.

Materials and methods. The laboratory bench consisted of pseudo-random sequence and carrier generators; QPSK, OQPSK, and SR-FQPSK transmitters; amplifier; QPSK, OQPSK, and SR-FQPSK receivers; attenuators; spectrum analyzer; power meter; and error meter. The parameters were measured using the methods embedded in the devices: spectrum analyzer, power meter, and error meter.

Results. The conducted experiments showed that operation of the amplifier in a nonlinear mode leads to an increase in the efficiency and output power in the field of compression. The out-of-band power is maximum for a QPSK modulated signal. The closer to the compression region the amplifier works and the larger the crest factor of the signal, the lower the sensitivity of the receiver.

Conclusion. The use of a low crest factor modulation (SR-FQPSK in the case of this study) ensures the maximum output power of the amplifier, the maximum efficiency, and the minimum level of out-of-band radiation. This increases the energy efficiency of radio communication systems and extends the communication range, thus allowing a more efficient use of frequency separation channel

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