Waveform Research On Integration Of Radar And Communication

Born in the Second World War, the airborne warning and control system(AWACS) plays a very important role in the modern national defense. And, AWACS’s functions will arrive at a higher degree with the conversion that the modern war is coming into the systems’ rivalry. But in order to be adapted for different missions, a lot of electronic equipments are installed to AWACS. Thus a series of problems appear: first, the worse of the electromagnetism condition; second, the increase of the antenna’s kind makes it very difficult to be distributed; third, the worse of the AWACS’s endurance due to the energy’s consume of electronic equipment. Furthermore, because of the restriction of communication radio station’s transmitting power, the communication distance is limited; the transmission rate is very slow; anti-interference is not very well. So, when it’s necessary to transmit the large data in time, the drawback is very obvious.A practicable course of action to solve the above problems is that the communication function is inserted into the phased array radar system based on the high gain and the wide frequency band of the phased array radar. Furthermore, the fast development of the digital circuits results in a more and more high digital level of the radar system. Especially, the development of the solid-state active module, the high-speed multi-digital A/D convertor, the direct digital synthesizer(DDS), and universal use of the high-speed digital signal processor provide a good basis of the integration of radar and communication.Based on the above information, researches on the integration of radar and communication were carried out.Many multiplexing modes were available. But, this paper considered the wave multiplexing as the better mode by comparing and analyzing. Two apsects were given on the reason of choosing the linear frequency modulation(LFM) and the minimum shift keying(MSK) or the gaussian minimum shift keying(GMSK) as the integrated waveform: first, the MSK and GMSK had the more quickly declining rate, more lower sidelobes and more better bit error rate(BER) compared to the PSK, FSK and so on; second, the integrated waveform which was composed by LFM and MSK or LFM and GMSK had more less spectrum’s extension.By the compared analyzing of the integrated waveform’s spectrums, the parper proposed: in designing the integrated waveform, the modulated waveform should have the characteristic of the continuous phase and the constant envelop.The Doppler’s impact on the integrated waveform was analyzed in two aspects. Inpase correction and out-of-phase correction of I channel and Q channel were analyzed under the case that the Doppler only had effect on the carrier frequency and the case that the Doppler only had effect on all phases. Under the case that the Doppler only had effect on the carrier frequency, because of the Doppler’s existence, the non-orthogonality would be appearing between I channel and Q channel. The Doppler could result in the improvement of BER. For solving the above problem, the double iterative linear prediction method was proposed to estimate the Doppler frequency and the simulation results proved the proposed method correctness.The problem on the LFM_MSK’s spectrum’s enengy leak was analyzed. A detailed deduction on the time-frequecy result of LFM_MSK was carried out. The spectrum of the integrated waveform distribulted along the line 0f ?f ?? ?t. According to the time-frequecy result, solving the problem of the spectrum’s enengy leak was proposed, namely, the modulated data which was at the beginning could be set as +1 and the modulated data which was at the ending could be set as-1, and the amount is both ? ?21 4 ?? ?T. According to the analyzing results, BER of the integrated waveform was the same to the case when the only MSK signal was used in the communication system under the condition that the enery had no leak.The ambiguity function of the waveform LFM_MSK was analyzed. The ambiguity function of LFM_MSK was more near to the form of the thumbtack compared to that of the LFM signal. Therefore, it had the advantage of detecting. However, the ambiguity function of LFM_MSK was more disperse. The reason of the dispersion was explained. By analyzing, the Doppler slice was the same between the integrated waveform and the LFM. Moreover, the resolution of the integrated waveform’s Doppler slice was only depending on the radar’s pulse width, and was independent of the modulated data. The time-delay slice was deduction in two limited cases and a value bound of the time-delay resolution was given. After analyzing, the time-delay resolution was relative to the integrated waveform’s bandwidth, radar’s pulse width and the amount of the modulated data. The sidelobes of the time-delay slice were very high compared to that in LFM.A windowed deconvolution method was proposed to restrain the sidelobes. The tolerance on the bits’ error was very bad by the analysis on the matching filter of the integrated waveform. The reference signal should use the same modulation date that were modulated in the transmitted signal. Compared to the false alarm probability of the LFM, there was no change in the integrated waveform. But, the detection probability of the integrated waveform could decline. The decline of the detection probability could be solved by the codes’ s adjustment. An operating mode of the integrated system was proposed based on the integerated waveforms which had the positive and negative frequency modulation rates. In this operating mode, the radar system used the integerated waveform which had the positive frequency modulation rate, while the communication system used the integerated waveform which had the negative frequency modulation rate. Because of the quasi-orthogonal property, the integerated waveforms which had the positive and negative frequency modulation rates had very small interference with each other.