Signal Processing and Recognition Technology and Simulation of Radar Communication Integrated System

: The integrated radar communication system combines the functions of radar and communication systems. It has attracted wide attention because of its advantages in effectively reducing electromagnetic interference between equipment and reducing equipment volume. However, there is no complete radar communication integrated signal design scheme so that the radar and communication system can operate well at the same time to achieve better detection and communication performance. In order to achieve better results for the integration of radar communication, this article summarizes and analyzes the existing research on integration of radar communication, and summarizes the realization of two design ideas of superimposed signal and single signal. The basic system composition of pulse radar and continuous wave radar, the working mechanism of radar speed and distance measurement and the basic composition of communication system are described. Research has proved that through the integration of radar communication, signal processing and identification are greatly improved, the signal transmission strength is more than 30% stronger than that without integration, and the transmission distance is 20% higher. Moreover, there are also great differences between the different integration methods. The fuzzy function used in this article is better than other experimental methods. This shows that the integrated radar communication system is the trend of future research on signal processing and recognition.

measurement as much as possible. Communication equipment is used for the exchange of battlefield information under the premise of low probability of interception. Since World War II, the improvement of communication equipment is more reflected in the convenience and the improvement of battery life [3]. By realizing the integration of the radar communication system, the communication system can use the high transmission power of the radar system to carry more energy and transmit a longer distance; the narrow beam directional antenna of the radar can provide good concealment for the communication signal, only Information can only be received within the radar antenna beam range, thereby reducing the possibility of being detected by the enemy; and the integration of the two reduces the size of the equipment, and reduces the load and cost of equipment that require high mobility such as aircraft and ships. , It is of great help to improve the overall combat performance. In view of this, the research on the integration of radar communication is very necessary [4].
RALPHH.CAGER and others designed a Ku-band radar communication fusion system for NASA's orbiter. This system can work as a radar system when converging with other orbiters, and it can also work through the orbit and data relay satellite system. The two-way communication between the track and the ground realizes the purpose of radar and communication [5]; scholars such as Shrawan C. Surender use ad-hoc networks, wireless communication and random waveforms in radar sensors to meet the demand for covert situational awareness, using ultra-wideband Random noise radar has the characteristics of low interception probability and low detection probability. A notch filter is used to cut part of the radar signal spectrum, and the communication data is cleverly embedded in it for transmission [6]. Xu.S.J proposed a radar communication fusion system based on direct sequence spread spectrum ultra-wideband radar (DS-UWB). The system adopts the idea of CDMA, using two orthogonal pseudo-random (PN) codes to spread the radar signal and the communication signal separately to avoid mutual interference [7].
Scholars such as AboulnarHassanien proposed a "dual-function radar communication system" based on the idea of space division multiplexing. The system uses beamforming technology to make the main lobe of the antenna radiation signal used for the radar, and the communication information is located in the side lobe. When there is a multi-user situation Multiple side lobes can be used for communication [8].
In view of the more or less limitations and deficiencies in the current implementation of radar communication integration, this paper proposes a conversion method to derive the ambiguity function of the proposed radar communication integration waveform. The ambiguity function is similar to the traditional The ambiguity function of FM continuous wave radar has similar forms and properties. The design plan of radar communication integration is reviewed. The analysis concludes that the integration is mainly divided into two ways: superimposed waveform and integrated waveform, and pointed out the advantages and disadvantages of the respective solutions. Using their properties, the sine waveform in communication can be used For radar speed and range measurement, communication and radar functions will be basically unaffected. The implementation process is explained in detail through necessary simulation analysis, and the correctness of the theoretical derivation is verified.

Radar
The working principle of radar is very similar to the principle of acoustic reflection. If you send a sound to an object that reflects the sound, you will get an echo. When the speed of sound is known, the time required for the echo to return can be converted into the distance and approximate direction of the object [9][10]. Radar emits electromagnetic waves in a very similar way. The signal emitted by the radio frequency front end of the radar transmitter is transmitted to the reflecting object and reflected from the transmitting object back to the radar receiver. The radar uses a small part of the energy of the reflected echo to determine the direction and distance of the reflecting object.
According to the type of waveform emitted by the radar, the radar can be divided into pulse radar and continuous wave radar system. The pulse radar transmitter and receiver share the antenna, the radar transmits a high-power pulse signal in a short time, and the rest of the time waits to receive the reflected echo [11]; while the continuous wave radar uses a separate transmitter and receiver, Thus, the reflected echo from the target can be received while continuously transmitting a continuous radar waveform.
Pulse radar is a radar device that transmits short and high-power pulses. It receives echo signals during the silent period (that is, when the pulse is not transmitted). Before the measurement is completed, the radar transmitter is turned off [12].The characteristic of this method is that the radar pulse modulation has a very short transmitting pulse. The duration of the transmitting pulse is recorded as  , and there are very large pulses between the transmitting pulses   T , which is called the receiving time. When the radar is fixed somewhere or stationary, the distance of the reflecting target is determined by the measured round-trip time between the received echo and the transmitted echo. The transmitted signal of pulse radar can be simply expressed as: The function A(t) is the amplitude change with respect to time, that is, amplitude modulation. In the simplest case, the transmitter is turned on for a short period of time (time  ), and remains off (time   T ) for the rest of the pulse repetition interval. Since the radar only emits energy within a pulse period, and waits for the echo to be received in the silent state during the remaining time, the duty factor can be defined The average transmit power of the radar can be expressed as: Among them t P is the peak transmit power of the radar. Single pulse energy: After the radar transmits a pulse, there needs to be enough waiting time to receive the target echo before the next pulse is transmitted. The maximum round-trip delay that will not cause distance ambiguity is T, and the corresponding maximum non-ambiguity distance is defined as Ru, which can be expressed as: We define Pu as the power reflected from the target to the radar. The total power transmitted to the radar receiver can be expressed as: In actual operation, the echo signal received by the radar receiver is not only the reflected echo of the target, but also random noise. Then the radar equation can be expressed as: The pulse radar antenna concentrates electromagnetic energy in a narrow beam. When the center of the antenna beam is exactly at the target, the target reflects the most energy and the radar receives the strongest echo signal; when the antenna beam deviates from the target, the target reflects The energy is reduced, and the intensity of the echo signal is weakened [13][14]. Therefore, when the received echo signal has the strongest energy, the direction of the antenna beam is the direction of the target relative to the radar. If you need to improve the accuracy of radar angle measurement, you can choose a larger antenna to emit a narrower beam. The radar operation framework is shown in Figure 1

Communication Principle
The radar system uses the emitted electromagnetic waves to propagate in free space, and the received echo is obtained after being reflected by the target to extract state information such as the range and speed of the target [15]. The wireless communication system uses electromagnetic radiation energy to transmit information from the transmitter to the receiver. The information to be transmitted is processed by the communication transmitter and converted into a waveform suitable for transmission in free space. The radiated electromagnetic energy is transmitted to the receiver after the influence of the channel, and the receiver performs a series of processing on the received signal to restore the transmitted data.
The baseband transmission signal of the communication system can be simply expressed as: This is completely consistent with the form of the radar signal. The difference is that the and of the communication system  respectively represent the amplitude, frequency and phase of the signal, which contains the communication information to be transmitted. The way of embedding communication data corresponds to amplitude modulation, frequency modulation and phase modulation respectively. In the transmission process, a suitable modulation method can be selected according to the performance index requirements of the system [16]. For the digital bandpass transmission system, using the discrete value characteristics of the digital signal, the modulation mode corresponds to the discrete form, expressed as amplitude keying (ASK), frequency shift keying (PSK) and phase shift keying (PSK).
In the case of binary, information is characterized by "0" and "1", which can be mapped into binary amplitude, frequency or phase states during modulation [17][18].
Since the modulation and demodulation of the chirp signal is difficult to implement in hardware in actual operation, it is difficult to directly apply the chirp signal to the communication system. An interesting fact is that the fractional Fourier transform of a sinusoidal signal is a chirp signal, so it is possible to consider using the sinusoidal signal in communication as the integrated waveform of radar communication.
The signal generated by the transmitter can not only realize the radar function but also communicate, and completely integrate the radar and the communication, and no longer need two sets of signal generation equipment and superimpose [19]. The receiving end uses a power divider to divide the received signal into radar and communication channels, and perform signal processing respectively to extract relevant information. Obviously, the idea of "combining two into one" is more in line with the needs of radar communication integration, and future research directions will also work towards it.

Integrated System
One of the problems in realizing the integration of radar communication is how to introduce integrated signals on the basis of existing systems and equipment, and gradually update and upgrade the system, so as to achieve that the current equipment can be put into use with a small amount of modification and reduce To achieve the purpose of cost. One of the solutions is to select the traditional radar waveform or communication waveform for the integrated waveform design of radar communication, that is, modulate the communication data based on the radar waveform or realize the function of the radar based on the communication waveform [20][21]. In terms of system structure, the radar transmitter performs power amplifier and other equipment on the generated waveform and then transmits it through the antenna, and the receiver performs matched filtering processing on the received signal to obtain target information. The distortion of the signal waveform does not affect the radar detection; the communication system is due to The waveform contains information, which requires operations such as encoding, modulation, decoding, and demodulation of the signal. Waveform distortion will undoubtedly lead to information errors and affect communication performance. When the integration of radar communication is realized based on radar waveforms, a series of communication modules for improving the effectiveness and reliability of the system need to be added to the radar equipment, and the system has a high degree of complexity [22]. When the integration of radar communication is realized based on the communication waveform, the focus is on how to make the communication waveform have the function of radar. If this function can be achieved, the integrated system does not need to add additional radar modules, and the implementation complexity is relatively low [23].
Since the transmission waveform of the integrated radar communication system is in the form of a communication waveform, the transmitted waveform does not contain radar information, so the communication receiver can complete normal communication reception without modification. The realization of the radar function is based on the communication signal. After performing the fractional Fourier transform on the above, the principle of linear frequency modulation is used to obtain the target range speed information [24][25]; the communication receiver and the radar receiver perform different signal processing on the received signal to extract the signal contained The two receiving systems do not interfere with each other, and the radar and communication share the power and other resources of the entire transmitter, so the radar system will not interfere with the communication system. However, since the realization of the fractional domain chirp continuous wave radar requires continuous phase of the transmitted waveform, it is necessary to select a suitable modulation method to meet the requirements when modulating communication data.
In the choice of the transmitted signal waveform, pulse radar usually modulates A(t) and f(t) in the formula. A(t) is a rectangular wave with a narrow time width, and f(t) is used to transmit a narrow pulse signal, which corresponds to a large bandwidth in the frequency domain, thereby achieving high range resolution. f(t) usually uses linear frequency modulation, namely: for signals that increase linearly with time, there is actually no essential difference in the detection mechanism of radar.

Signal Processing Recognition Model
Chirp signals are widely used by radar designers to improve the relationship between the resolution and range of radar systems. When applied to communication systems, they can have anti-interference and anti-multipath fading characteristics. The frequency of the chirp signal changes linearly with time, but in actual operation, it is difficult to implement the modulation and demodulation of the chirp signal in hardware, so it is difficult to directly apply the chirp signal to the communication system [26].
Which a  represents the fractional frequency operator, and its time domain expression is: In the formula,  is a time operator and  is frequency operator. Using the relationship between the Hermite operator and the instantaneous variable, the instantaneous fractional frequency u of the signal s(t) can be expressed as: The signal s(t) can be expressed in the form of amplitude and phase, that is and   t  are the amplitude and phase of s(t) respectively, and both are differentiable functions.
Substituting into the formula can get: The signal form transmitted by the integrated radar communication system can be expressed as:   (13) Regarding the time domain of the single-frequency sinusoidal signal transmitted continuously, the time and frequency of the signal are not related, so that the time delay and frequency shift information in the echo reflected by the moving target cannot be obtained, and the ranging analysis cannot be performed. When the time of the signal is related to the frequency, the frequency can correspond to a specific point in time, that is, the "time scale". The time scale allows the system to accurately calculate the transmission and reception time difference and convert it into a distance, thereby reflecting the time delay in the echo And Doppler frequency shift can also be obtained accordingly.

Subjects
This article integrates different communication methods through different methods and compares the differences between them. Perform data statistics through relevant literature, questionnaire surveys, yearbooks, etc., and use models to digitize to obtain relevant parameter values. Compare the differences between the parameters and find out the changes between the integration for signal processing and recognition.

Integrated Approach
The radar communication is integrated through the integrated waveform ambiguity function, which can be defined from the perspective of distance-velocity two-dimensional resolution and matched filter output. Assuming that the amplitudes of the two targets are the same, the received echoes of the two targets can be expressed as: The mean square error of the two can be expressed as The ambiguity function is an effective tool for the design and analysis of radar waveforms, which is determined by the characteristics of the transmitted waveform and the filter. By analyzing the ambiguity function, the resolution and ambiguity of the radar under different design waveforms can be studied.

Determine the Evaluation Weight
The index weight is a numerical index indicating the importance and function of the index. In the indicator system of the evaluation plan, the weight of each indicator is different. Even if the indicator level is the same, the weight is different. Index weight is also called weight and is usually represented by a. It is a number greater than zero but less than 1, and the sum of the weights of all first-level indicators must be equal to 1, that is, satisfy the conditions 0 <a <1 and ∑a-1.

Statistics
All data analysis in this article uses SPSS19.0, statistical test uses two-sided test, significance is defined as 0.05, and p <0.05 is considered significant. The statistical results are displayed as mean±standard deviation (x±SD). When the test data complies with the normal distribution, the double-T test is used as the comparison within the group, and the independent sample P test is used as the comparison between the groups. If the regular distribution is not sufficient, two independent samples and two related samples will be used for inspection.

Development of Communication Radar
Through the methods of literature and interviews, we collected changes in various parameters of radar and communication in recent years, compared their development and changes, and studied their development trends. The changes in radar parameters are shown in Table 1:   Table 2:  Figure 3:

Figure 3. Changes in communication parameters
From the figure, we can see that the change range of communication is slightly smaller than that of radar, and the change range is generally around 0.2. The change range has not been large in recent years.
Among them, the detection speed has changed the most, and the increase range is around 0.35.

Different Methods to Detect Sample Differences
We detect a certain amount of cars in different ways, and compare the accuracy of the object shape after it is detected, which can effectively understand the good points of each detection method, as shown in Figure 4 and

Different Algorithm Recognition Situation
Through previous experiments, we have collected various parameters of radar, communication, and integrated recognition under different conditions, as shown in Table 3: In the same chart, we can see that after the integration of the system, the identification parameters are much higher than those of the non-integrated system, and the transmission efficiency and transmission speed have greatly changed. However, the waveform integration system used in the experiment in this article has relevant parameters not only higher than those of radar and communication, but also due to the integration of the system using traditional methods. In order to verify the validity of the test data, we have performed multiple simulations on the system and obtained relevant data, as shown in Figure 6:

Conclusion
At present, the integration of radar communication has been widely studied by scholars at home and abroad due to its advantages such as reducing the volume of equipment and electromagnetic interference.
The integration of radar communication systems is of great significance in the civil and military fields.
How to design the signal waveform of radar communication integration so that it can achieve better radar and communication performance at the same time is the difficulty in achieving integration. The basic system composition of pulse radar and continuous wave radar and the principle of speed and range measurement are described; the basic composition and principle of the communication system are given.
On this basis, the problem of selecting the transmission waveform of the integrated radar communication system is brought out. The sinusoidal signal in the communication will have the nature of the chirp signal after proper transformation domain processing. This paper studies the continuous wave radar detection of integrated radar communication signals in the fractional domain. It can be applied to the integration of vehicle, shipboard, and airborne radar communication, but it is difficult to play a role in large-distance scenarios. Pulse radar can detect longer distances due to its high transmitting power, so that it can analyze the pulse radar system of the integrated signal of radar communication in the fractional domain, and broaden its application range.