Performance Analysis of UAV Uplink Communication Technology

In order to meet the reliability and anti-jamming requirements of UAV communication system, the anti-jamming performance of the up-link communication technology is analyzed by comparing the influence of different jamming on the signal and the influence of Rice channel on the signal on the basis of in-depth study of the communication mechanism of the low-altitude UAV communication link. The simulation results show that the anti-jamming performance of the signal is better when the interference is added in the upstream communication technology, and the anti-broadband interference of the signal is better than other interference types when the channel is added.

with bipolarity by encoder, spreads the information codes with a group of pseudo-random sequences generated randomly by the pseudo-random code generator, and finally multiplies and modulates the carrier signals of a specific frequency by the carrier generator, and transmits the generated signals through the transmitter. At the receiving end, the signal is received by the receiver, filtered by the filter and demodulated by the local modulator, which generates the same carrier frequency as the center frequency of the transmitter, and the same pseudocode sequence is also generated for despreading. Finally, the source signal is decomposed.

Rice Channel
The transmitted signal decays through the Rice channel and obeys the Rice distribution. Suppose that the complex envelope of the signal propagating in Rice channel is as follows: ( ) S t is a signal for ground station, ( ) f c is the carrier frequency of the transmitted signal [6]. If the position of the transmitter of the ground station is relative to that of the receiver of the UAV, the received signal at the receiving end can be expressed as: It can be seen that the transmission function is independent of the frequency f because the channel impulse response is independent of the delay τ , and the attenuation of all bands is the same. n a has the greatest influence on the function. Because n a is the amplitude coefficient of the scattering path, not a fixed value, it can be changed by the Rice factor K [7]. Rice factor K can be expressed as: In the formula, Rice factor K can also be said to be the power ratio of the direct component and the ∈ is the variance of the scattering process of the zero-mean orthogonal component of the desired signal.

Simulation Process and Analysis
The simulation parameters of DSSS signal are: carrier amplitude 1 V, pseudo code rate 40.96 Mbps, carrier frequency 80 MHz, sampling frequency 10 MHz, symbol number 160, simulation time 0.05 s, initial phase 0. In this paper, the Anti-jamming Analysis of DSSS signal is carried out by adding Rice channel and jamming signal. When the Rice factor K equals 10dB, the channel noise is set, and three kinds of interference signals are set, including full-band interference, partial-band interference and multi-band interference. Fig.3 and Fig.4 are power spectrograms of signals without interference and channel, which are convenient for comparison and analysis when interference is added below.

Performance analysis of full-band interference
Full-band interference is to add the white Gaussian noise after band-pass filtering to the spread spectrum signal, so that the noise of the signal is relatively high, so as to achieve the purpose of antiinterference of the measured signal [8].
The time domain expression of full-band interference signal is: The power spectrum images of DSSS signal and interference signal are obtained by simulation as shown in Fig.5 and Fig.6. As can be seen from Fig.5, the central frequency is 10M and the bandwidth is 2M. Fig.6 is a signal superimposed by the interference signal and the original signal. The power spectrum image of the original signal in Fig.4 is covered by the interference signal in Fig.5. From  Fig.6, it can be seen that the power spectrum of the original arc has become a power spectrum image of broadband interference.  Fig.8 show the BER curves of signals with full-band interference. The figure shows that the bit error rate increases with the increase of the signal to signal ratio. When the dry-to-signal ratio is 0 dB, the BER of DSSS signal decreases to 0; when the dry-to-signal ratio is 19 dB, the BER of the system is 0.38. Fig.7 shows the BER curve of a signal with or without channel interference. Compared with Fig.8, although there is no effect on the signal when only channel interference is present, the bit error rate of the superposition of channel and interference signal increases after adding interference.

Performance analysis of partial band interference
Partial band interference is to interfere with spread spectrum signals in some communication bands. Part-band interference is similar to full-band interference, but part-band interference is half or a quarter of full-band interference. The power spectrum image of DSSS signal and the power spectrum image of partial band white Gaussian noise interference signal are shown in Fig.9 and Fig.10. As can be seen from Fig.9, it is a partial band interference with a center frequency of 10M and a bandwidth of  Fig.10 is a signal superimposed on the original signal. The power spectrum of the original signal in Fig.4 above is partially wrapped by the interference signal in Fig.9. From Fig.10, it can be seen that the power spectrum of the original arc has been partially transformed into the power spectrum of the partial interference, while the signal without interference is still the power spectrum of the signal.  Fig.12 show the BER curves of the signal with partial band interference. The figure shows that the bit error rate increases with the increase of the signal to signal ratio. The error rate is 0 when the dry-to-signal ratio is 0 dB and 0.44 when the dry-to-signal ratio is 19 dB. Fig.11 is the BER curve of the signal with or without channel interference. Compared with Fig.12, although it has no effect on the signal with only Rice channel interference, the BER of the superposition of channel and interference signal is higher than that of the simple addition of interference.

Performance analysis of multifrequency jamming
Multifrequency interference, commonly known as comb spectrum interference, is the interference of multiple frequencies on the originally transmitted signal. The time domain expression of multifrequency interference signal can be expressed as: In the formula, 1 2 , , n P P P  is the power of the multi-frequency interference signal, 1 2 , , n ϕ ϕ ϕ  is the initial phase of the multi-frequency interference signal, 1 2 , , n f f f  is the carrier frequency of the multi-frequency interference signal. In general, 1 2 , , n f f f  is determined by the frequency band range of the interfered signal detected by its own side [9].
In this paper, the frequency of multi-frequency interference signal is set to 5, and the carrier frequencies are 9.2 MHz, 9.6 MHz, 10 MHz, 10.4 MHz and 10.8 MHz, respectively. The power spectral density of spread spectrum signal and multi-frequency interference signal are shown in Fig.13 and Fig.14. From Fig.13, we can see that the center frequency is the same as the set frequency. Fig.14 is a signal superimposed on the original signal. The power spectrum of the original signal in Fig.4 above is partially covered by the interference signal in Fig.13. From Fig.14, it can be seen that the power spectrum of the original arc has been partially transformed into the power spectrum of the multi-frequency interference, while the undisturbed signal is still the power spectrum of the signal.  Fig.16 show the BER curves of signals with multi-frequency interference. The figure shows that the bit error rate increases with the increase of the signal to signal ratio. The error rate is 0 when the dry-to-signal ratio is 0 dB and 0.39 when the dry-to-signal ratio is 19 dB. Fig.15 is the BER curve of the signal with or without channel interference. Compared with Fig.16, although it has no effect on the signal with only Rice channel interference, the BER of the superposition of channel and interference signal is higher than that of the simple addition of interference. emphatically. At the same time, the BER curves of different ICR are established by comparing Rice channels under different interference conditions, and the comparison and analysis are carried out. The simulation results show that the anti-jamming performance of the signal is good by comparing the BER curves of the three kinds of jamming after adding the jamming to the signal. When adding the Rice channel, the BER of the original jamming signal obviously increases. Compared with the three kinds of jamming, the display signal in the graph is better than other jammings after passing through the Rice channel.