Research On FQPSK Modulation Of Forest Fire Monitoring And Positioning System

At present, the commonly used method of monitoring forest fires in China is video surveillance, due to the seriousness of forest fires, efficient transporting of the forest fire point play an important role in extinguishing forest fires as soon as possible. Many forest fire monitoring systems adopt wirelessly transport the image signal, in order to reduce the construction cost of the equipment, the system uses solar energy as voltage supply, so power is severely limited, which puts forward a higher power efficiency requirements in power amplifier, then it makes the power amplifier to work in the state of saturation, which leads the communication channel to be nonlinear, so we should use the modulation mode with constant envelope or quasi-constant envelope. Besides, the use of band-pass filter in transceivers requires that the modulation must have a good spectrum performance, that is a narrow main lobe and a fast roll-off side lobe, so modulated signal can pass the filter through a very narrow bandwidth without distortion, which makes no change in the signal envelope to maintain its quasi-constant envelope, then meets the requirement of nonlinear forest communication channel.At first, the status of the forest fire prevention in the world as well as the domestic and study of FQPSK modulation mode are introduced in the paper, and the paper gives the hardware and software design of the forest fire prevention system. Then the paper study the FQPSK modulation of the forest fire image wireless transmission, including its modulation and demodulation scheme, envelope characteristics, spectral characteristics, constellation, power spectrum, bit error rate(BER), spectrum spreading in nonlinear channel, what’s more, the paper compare FQPSK with QPSK, OQPSK and IJF-OQPSK modulation, finds that FQPSK is best, because FQPSK modulation envelope is constant and roll-off fast, it’s best in power spectrum and its spectrum spreading is least in the band-limited nonlinear channel. Besides, the 5 d B power advantages of nonlinear amplifier gives FQPSK modulation a 33.35% advantage in broadcasting distance than QPSK. So, FQPSK modulation mode is an appropriate modulation technique in the forest fire image wireless transmission. Besides, due to the ordinary FQPSK has defects in the envelope, the paper puts forward an improved FQPSK trellis-coded modulation baseband waveform mapping method, which makes the envelope is strict constant, and the spectral side lobe attenuation faster as well, so the improved FQPSK modulation has a better performance than the ordinary FQPSK.