A method for improving the signal-to-noise ratio of binary phase code baseband signals based on signal amplitude enhancement.

Abstract

This invention discloses a method for improving the signal-to-noise ratio (SNR) of binary phase-code baseband signals based on signal amplitude enhancement. It primarily addresses the problem in existing technologies where low signal amplitude at SNR below 0dB leads to increased baseband signal extraction bit error rate, impacting pulse compression performance. The method includes: using an orthogonal all-pass filter for orthogonal mixing to generate I-channel and Q-channel signals; performing four-channel parallel operations on these signals to obtain four intermediate signals; squaring, subtracting, and signing the Q-channel and I-channel signals to generate a frequency-offset second harmonic signal; and dividing the frequency by two to obtain the sine and cosine signals of the frequency offset; and mapping the three frequency offset signals and the four intermediate signals using a lookup table to obtain the baseband signal, thus completing pulse compression. This invention optimizes the signal processing paths at key nodes, enhancing the signal amplitude at 15 key nodes without increasing noise. While maintaining frequency offset adaptability, it can enhance the signal amplitude by more than 2 times, improve the SNR by more than 6dB, and reduce the bit error rate, making it suitable for scenarios with high signal quality requirements, such as radar detection and communication navigation.

Description

Technical Field

[0001] This invention belongs to the field of signal processing technology, and specifically relates to a method for improving the signal-to-noise ratio of baseband signals using radix-2 phase code, which can be applied to scenarios with high signal quality requirements such as radar detection and communication navigation. Background Technology

[0002] The radar emits a radio frequency (RF) signal to illuminate the target. The target reflects the echo, which the radar receives. The radar mixes the echo signal with its own local oscillator signal, down-converting it from an RF signal to an intermediate frequency (IF) signal. Then, the IF signal is sampled by an analog-to-digital converter (A / D converter) and digitally down-converted to a baseband signal. Finally, the baseband signal undergoes signal processing. Due to the relative motion between the radar and the target, the received echo signal experiences a Doppler frequency shift. Let the RF signal frequency be f0 and the local oscillator signal frequency be f. LO The intermediate frequency signal frequency is f I In theory, |f0-f LO |=f I However, the actual value of the output intermediate frequency signal frequency is f. IO The reason for this is the combined effect of factors such as the limited frequency stability of the signal itself and the Doppler frequency shift caused by the target motion, which resulted in a deviation between the actual and theoretical values ​​of the intermediate frequency signal. △ That is, |f I -f IO |=f △ This directly leads to a decrease in the radar's receiving gain and sensitivity, and in severe cases, it may be impossible to detect the target. A common way to solve this problem is to use a self-frequency modulation circuit in the radar to change the large difference frequency input into a small difference frequency output in a feedback manner. However, the difference frequency cannot be completely eliminated; it can only be made very small.

[0003] One type of transmitted signal waveform used by radar is a phase-coded signal. Radar transmits wide pulse signals to achieve high transmission energy and long range. The digital baseband signal is modulated onto the radio frequency carrier frequency for space transmission and target detection. At the transmitting end, a pseudo-random sequence code is used to phase-code a single pulse. At the receiving end, the received echo wide pulse signal is compressed to obtain a narrow pulse, achieving high range resolution. This narrow pulse is called the pulse compression peak. A pseudo-random sequence code contains multiple symbols. If the phase value of each symbol is limited to 0 and π, it is a binary phase-coded signal; otherwise, it is a polyphase-coded signal. The ambiguity function of phase-coded signals is "pinhead-shaped." Its advantages include good range resolution, high ranging accuracy, and low sidelobes. Its disadvantage is sensitivity to frequency offset between the received and transmitted signals. For this reason, the received signal is frequency-modulated, resulting in a frequency offset f between the received and transmitted signals. △This causes the phase of the baseband signal symbols obtained from demodulation to be inverted, reducing the number of matched symbols between received and transmitted signals and decreasing the amplitude of the pulse compression peak. If the amplitude does not exceed the decision threshold, the radar determines there is no target. Therefore, phase-coded signals are sensitive to frequency shifts and can only be used in scenarios where the target speed is low or the target speed is roughly known. The Doppler tolerance of binary phase codes is...

[0004] Patent application ZL202210692612.6 discloses a "Pulse Compression Method for Phase-Coded Signals with Adaptive Frequency Offset of Transceiver Signals." This method involves sampling and orthogonally transforming the received intermediate frequency (IF) signal at the receiving end to obtain I and Q signals. These two signals are then subjected to four-way parallel operations to obtain four intermediate signals. The sign bits of the I and Q signals are extracted to obtain the baseband signal with a frequency offset of 0. The I and Q signals are multiplied to obtain a second harmonic signal of the frequency offset. This signal is then divided to obtain sine and cosine signals of the frequency offset. Based on the sign of the frequency offset and the quadrant of the signal phase, the output is selected from the four intermediate signals to obtain baseband signals with frequency offsets greater than or less than 0. These are then subjected to parallel matched filtering to obtain the pulse compression peak. This method expands the Doppler tolerance of the binary phase code to 2π, meaning it is no longer limited by the Doppler tolerance. It can adaptively handle large dynamic and rapid changes in the frequency offset of the transmit and receive signals, making it suitable for situations where the target speed is high or unknown. However, this method normalizes the amplitudes of the 12 signals during the processing, without considering the impact of the actual signal amplitude on the signal-to-noise ratio. When the signal-to-noise ratio is below 0dB, the insufficient signal amplitude leads to an increase in the baseband signal extraction bit error rate, affecting the detection performance of the pulse compression system. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the existing technologies by proposing a signal-to-noise ratio (SNR) improvement method for binary phase code baseband signals based on signal amplitude enhancement. This method enhances the amplitude of the useful signal while maintaining the adaptive advantage of transmit and receive frequency offsets, and keeps the noise level constant, thereby improving the SNR, reducing the bit error rate, and enhancing the detection performance of the pulse compression system.

[0006] The technical idea of ​​this invention is to improve the signal amplitude without increasing noise by optimizing the signal processing paths of 15 nodes while maintaining the advantage of frequency offset adaptation, thereby improving the signal-to-noise ratio of the baseband signal and enhancing the detection performance of the pulse compression system.

[0007] Based on the above ideas, the implementation steps of the present invention include the following:

[0008] 1. A method for improving the signal-to-noise ratio of binary phase-coded baseband signals based on signal amplitude enhancement, which is an improvement on the digital signal generation scheme in the existing "Adaptive Transceiver Frequency Offset Phase-Coded Signal Pulse Compression Method", characterized by comprising:

[0009] (1) The transmitter transmits a signal, and the receiver receives the echo signal and down-converts it to an intermediate frequency signal.

[0010] (2) Perform A / D sampling on the intermediate frequency signal at a frequency of four times to obtain the digital signal of the intermediate frequency signal;

[0011] (3) Generate a pair of initial quadrature signals, including a cosine signal and a sine signal, through a numerically controlled oscillator (NCO);

[0012] (4) Input the digital signal into the orthogonal all-pass filter pair to generate a pair of orthogonal signals, and perform orthogonal mixing with the cosine signal and the sine signal respectively to generate four node signals. Add and subtract these four node signals to generate I-channel signals and Q-channel signals with an amplitude of twice that of the original digital signal. The original digital signal refers to the digital signal generated by the existing method.

[0013] (5) Perform four-way parallel addition and subtraction operations on the I-way signal and Q-way signal generated in step (4), extract the sign bit of the four-way operation results, generate four intermediate signals with amplitude amplified to twice that of the original digital signal, and use these four intermediate signals as data input for the baseband signal lookup table mapping.

[0014] (6) Extract the baseband signal with improved signal-to-noise ratio based on the frequency offset of the transmitted and received signals:

[0015] For cases where the frequency offset is zero, the sign bits of the I-channel and Q-channel signals are directly taken as the baseband signal, while keeping the noise unchanged, thereby improving the signal-to-noise ratio of the baseband signal to twice that of the original digital signal.

[0016] For cases where the frequency offset is not zero, the I-channel signal and Q-channel signal are first squared, subtracted, and the sign bit is taken to obtain the second harmonic signal AS0 of the transmit and receive signal frequency offset. Then, the second harmonic signal is divided by two to obtain the sine signal AS2 and the cosine signal AS1 of the transmit and receive signal frequency offset. Then, AS2, AS1, and AS0 are used as the address input for the baseband signal lookup table mapping and the noise is kept unchanged to obtain a baseband signal with a signal-to-noise ratio improved to twice that of the original digital signal.

[0017] (7) Matched filtering is performed on the baseband signals with improved signal-to-noise ratios obtained under different frequency offsets to complete pulse compression. Further, the pair of initial orthogonal signals generated by the numerically controlled oscillator (NCO) are represented as follows:

[0018] SQ = cos 2πfIn;

[0019] SI = sin2πfIn;

[0020] Where SQ is a cosine signal, SI is a sine signal, and f I Let n be the signal frequency and n be the signal sampling interval.

[0021] Furthermore, I-channel and Q-channel signals with amplitudes twice that of the original digital signal are generated, as shown below:

[0022] I = 2I′

[0023] Q = 2Q′

[0024] in, The I-channel signal is the original digital signal.

[0025] The Q-channel signal of the original digital signal.

[0026] A is the signal amplitude, f △ The frequency offset of the transmitted and received signals is θ, which represents binary phase modulation and takes the value 0 or π.

[0027] It is the phase difference between the received signal and the transmitted signal, ranging from 0 to 2π, where n is the sampling interval.

[0028] Furthermore, the four-way operations are represented as follows:

[0029]

[0030]

[0031] Where A1 is the result of the first operation, the sign bit of A1 is taken to obtain the first intermediate signal FLAG1;

[0032] R1 is the result of the second operation. Taking the sign bit of R1, we obtain the second intermediate signal FLAG2.

[0033] A2 is the inverted signal. The sign bit of the A1 signal is taken and passed through an inverter to obtain the third intermediate signal FLAG3.

[0034] R2 is the inverted subtraction signal. Take the sign bit of R1 and get the fourth intermediate signal FLAG4 through the inverter.

[0035] A is the signal amplitude, f △ The frequency offset of the transmitted and received signals is θ, which represents binary phase modulation and takes the value 0 or π.

[0036] It is the phase difference between the received signal and the transmitted signal, ranging from 0 to 2π.

[0037] β is the phase shift of the all-pass filter, and n is the sampling interval.

[0038] Furthermore, the second harmonic signal AS0, the sinusoidal signal AS2 and the cosine signal AS1 with frequency offset of the transmitted and received signals are respectively represented as follows:

[0039]

[0040] Where A is the signal amplitude, f △ For the frequency offset of the transmitted and received signals, It is the phase difference between the received signal and the transmitted signal, ranging from 0 to 2π, β is the phase shift of the all-pass filter, and n is the sampling interval.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] Firstly, this invention improves the signal-to-noise ratio and reduces the bit error rate because it uses a different signal processing path and amplitude signal than patent ZL202210692612.6, as shown in Table 1.

[0043] Table 1 Comparison of the solutions of the present invention and the prior art

[0044]

[0045] Secondly, this invention enhances the strength of 15 useful signals—namely, the I-channel signal, the Q-channel signal, I+Q, IQ, -(I+Q), QI, and I—by introducing orthogonal all-pass filter pairs and optimizing the signal processing path. FG Q FG The method uses FLAG1, FLAG2, FLAG3, FLAG4, AS2, AS1, and AS0, while maintaining constant noise, to improve the signal-to-noise ratio of 15 useful signals. Compared with the existing "Adaptive Transceiver Frequency Offset Phase-Coded Signal Pulse Compression Method", it increases the signal amplitude and improves the signal-to-noise ratio of the baseband signal, thereby improving the detection performance of the pulse compression system. The parameter comparison is shown in Table 2.

[0046] Table 2. Improvements in amplitude and signal-to-noise ratio of the present invention compared to the prior art.

[0047]

[0048] Simulation results show that, with a nominal signal-to-noise ratio of 0dB, the present invention improves the signal-to-noise ratio by 6dB and reduces the bit error rate by 97%. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0050] Figure 2 This is a schematic diagram of the generation of I-channel and Q-channel signals in this invention;

[0051] Figure 3 This is a schematic diagram illustrating the principle of generating intermediate signals and frequency offset signals in this invention;

[0052] Figure 4This is a schematic diagram of the principle of extracting baseband signals with negative frequency offset in this invention;

[0053] Figure 5 This is a schematic diagram of the principle of extracting baseband signals with positive frequency offset in this invention;

[0054] Figure 6 This is a schematic diagram of the baseband signal pulse compression principle in this invention. Detailed Implementation

[0055] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0056] Reference Figure 1 The implementation steps of this example include the following:

[0057] This example consists of the following two parts:

[0058] 1. The receiving end processes the received intermediate frequency signal to generate I-channel signal, Q-channel signal, 4 intermediate signals, 2 initial intermediate signals and 3 frequency offset signals.

[0059] Step 1: Generate I-channel signal and Q-channel signal.

[0060] Reference Figure 2 The implementation of this step includes the following:

[0061] 1.1) The receiving end receives the echo signal of the transmitted signal from the transmitting end, down-converts it to an intermediate frequency signal F(t), and applies the intermediate frequency signal to the intermediate frequency signal at a frequency f. S Perform a fourth-harmonic A / D sampling to obtain the digital signal IF(n) of the intermediate frequency signal:

[0062]

[0063] Among them, f I t is the intermediate frequency signal frequency, t is time; θ represents binary phase modulation, taking the value 0 or π.

[0064] f △ It is the frequency offset of the transmitted and received signals, and its value can be positive or negative; It is the phase difference between the received signal and the transmitted signal, ranging from 0 to 2π, where n = t × f S f is the sampling interval. S =4×f I ;

[0065] 1.2) Generate a pair of initial orthogonal signals consisting of a cosine signal SQ and a sine signal SI using a numerically controlled oscillator (NCO):

[0066] SQ=cos 2πf I n

[0067] SI = sin2πfI n

[0068] Where, when 2πf I n takes values ​​of 0, ... π At that time, the cosine signal cos2πf I The values ​​of n are 1, 0, -1, and 0 respectively, representing the sinusoidal signal sin2πf. I The values ​​of n are 0, 1, 0, and -1, respectively.

[0069] 1.3) Input the digital signal IF(n) into a pair of orthogonal all-pass filters to generate a pair of orthogonal signals IF. Q (n), IF I (n):

[0070]

[0071]

[0072] Where A is the signal amplitude and β is the additional phase shift of the orthogonal all-pass filter pair;

[0073] The orthogonal all-pass filter pair can be implemented in one of the following two ways.

[0074] The first is a 90° phase shifter group, which consists of two all-pass filters with identical topologies but different phase responses. Both filters have an additional phase shift of β, and one filter provides a 90° phase shift within its passband, outputting an IF... Q (n); another filter does not shift phase within the passband, and its output IF I (n);

[0075] Second, the Hilbert transform pair, which uses an FIR filter to implement the Hilbert transform;

[0076] The parameters of the two all-pass filter pairs mentioned above are shown in Table 3.

[0077] Table 3 Parameters of two all-pass filter pairs

[0078] Filter type IIR All-Pass Filter FIR full-pass filter order First or second order 6th to 10th order Passband range (normalized frequency) 0.1π～0.9π 0.05π～0.95π Phase error ±1° ±1° Group delay Linear phase response Linear phase response

[0079] 1.4) Mix the orthogonal signals to generate four node signals Y1 to Y4:

[0080] Will IF I (n) signal and cosine signal cos2πf I Multiplying n by n generates the first node signal Y1:

[0081]

[0082] Will IF I(n) signal and sinusoidal signal sin2πf I Multiplying n by n generates the second node signal Y2:

[0083]

[0084] Will IF Q (n) signal and cosine signal cos2πf I Multiplying n by n generates the third node signal Y3:

[0085]

[0086] Will IF Q (n) signal and sinusoidal signal sin2πf I Multiplying n by n generates the signal Y4 for the fourth node:

[0087]

[0088] 1.5) Add and subtract the signals from these four nodes to generate an I-channel signal and a Q-channel signal with an amplitude twice that of the original digital signal:

[0089] The original digital signal refers to the two digital signals generated in the "Adaptive Transceiver Signal Frequency Offset Phase-Coded Signal Pulse Compression Method" disclosed in patent ZL202210692612.6, which are represented as follows:

[0090] The I-channel signal is the original digital signal.

[0091] This is the Q-channel signal of the original digital signal.

[0092] The specific implementation of this example is as follows:

[0093] Add the first node signal Y1 and the fourth node signal Y4 to obtain the I-channel signal:

[0094]

[0095] Subtracting the second node signal Y2 from the third node signal Y3 yields the Q-channel signal:

[0096]

[0097] Step 2: Perform different operations on the I-channel signal and the Q-channel signal to obtain a pair of initial intermediate signals, four intermediate signals and three frequency offset signals.

[0098] Reference Figure 3 The implementation of this step includes the following:

[0099] 2.1) Take the sign bits of the I-channel and Q-channel signals to obtain a pair of initial intermediate signals I with amplitude amplified to twice that of the original digital signals. FG Q FG ;

[0100] 2.2) Perform four-way parallel processing, and extract the sign bit to obtain four intermediate signals with amplitude amplified to twice that of the original digital signal:

[0101] 2.2.1) Add the I-channel signal and the Q-channel signal to obtain the added signal A1:

[0102]

[0103] 2.2.2) Take the sign bit of A1 and pass it through a buffer to obtain the first intermediate signal FLAG1;

[0104] 2.2.3) Subtract the Q signal from the I signal to obtain the subtracted signal R1:

[0105]

[0106] 2.2.4) Take the sign bit of R1 and pass it through the buffer to obtain the second intermediate signal FLAG2;

[0107] 2.2.5) Invert A1 to obtain the inverted signal A2:

[0108]

[0109] 2.2.6) Take the sign bit of A1 and invert it to obtain the third intermediate signal FLAG3;

[0110] 2.2.7) Inverting R1 yields the inverse subtraction signal R2:

[0111]

[0112] 2.2.8) Take the sign bit of R1 and pass it through an inverter to obtain the fourth intermediate signal FLAG4;

[0113] 2.3) Through calculation and frequency division, three frequency offset signals AS0, AS1, and AS2 are obtained:

[0114] 2.3.1) Square the Q-channel signal and the I-channel signal respectively, then subtract them to generate the Y signal:

[0115]

[0116] 2.3.2) Take the sign bit of the Y signal to obtain the second harmonic signal AS0 of the transmit and receive signal frequency offset;

[0117] 2.3.3) A digital frequency divider is used to divide the frequency offset of the transmit / receive signal AS0 by two to obtain the cosine signal AS1 and the sine signal AS2 of the transmit / receive signal frequency offset:

[0118]

[0119] Second, extract the baseband signal with improved signal-to-noise ratio based on the frequency offset of the transmitted and received signals, and then perform matched filtering on it.

[0120] Step 3, for the frequency offset f of the transmit and receive signals △ If the value is less than 0, construct the first lookup table, and use the lookup table and the first 4-to-1 selector to output the baseband signal NCH with a negative frequency offset for both transmit and receive signals.

[0121] Reference Figure 4 The implementation of this step includes the following:

[0122] 3.1) Construct the first lookup table, which has 3 address input terminals and 2 value output terminals. It internally stores the 2-bit values ​​of the high-order SE1 and the low-order SE0, and selects the first 4-to-1 selector corresponding to it.

[0123] 3.2) The double frequency signal AS0, the frequency offset cosine signal AS1, and the frequency offset sine signal AS2 of the above-mentioned transmit and receive signals are used as the address input of the lookup table. The highest bit of the address input is AS2 and the lowest bit is AS0. The value output of the lookup table is connected to the address input of a 4-to-1 selector.

[0124] 3.3) Use the first intermediate signal FLAG1, the second intermediate signal FLAG2, the third intermediate signal FLAG3, and the fourth intermediate signal FLAG4 as the data inputs of the 4-to-1 selector;

[0125] 3.4) For the frequency offset f of the transmit and receive signals △ In the case of negative values, through phase The quadrant in which the table is located determines the value of the first lookup table input address AS2 AS1 AS0, and different internal preset values ​​SE1 SE0 are selected:

[0126] like If it is in the first quadrant, the input address AS2AS1 AS0 of the first lookup table is 111, and the preset value SE1 SE0 inside it is 00.

[0127] like If it is in the second quadrant, the input address AS2AS1 AS0 of the first lookup table is 010, and its internal preset value SE1 SE0 is 01.

[0128] like If it is in the third quadrant, the input address AS2AS1 AS0 of the first lookup table is 001, and its internal preset value SE1 SE0 is 10.

[0129] like If it is in the fourth quadrant, the input address AS2AS1 AS0 of the first lookup table is 100, and its internal preset value SE1 SE0 is 11.

[0130] 3.5) Based on the internal preset values ​​SE1 and SE0 output from the first lookup table, the first 4-to-1 selector outputs the corresponding intermediate signal to obtain the transmit / receive signal frequency offset f. △ When the signal-to-noise ratio is negative, the improved baseband signal NCH is:

[0131] When the first lookup table outputs SE1 and SE0 as 00, the first 4-to-1 selector outputs the first intermediate signal FLAG1 while maintaining the noise level, thus obtaining the transmit / receive signal frequency offset f. △ When the value is negative, the signal-to-noise ratio of the baseband signal NCH is improved to twice that of the original digital signal;

[0132] When the first lookup table outputs SE1 and SE0 as 11, the first 4-to-1 selector outputs the fourth intermediate signal FLAG4 while maintaining the noise level, thus obtaining the transmit / receive signal frequency offset f. △ When the value is negative, the signal-to-noise ratio of the baseband signal NCH is improved to twice that of the original digital signal;

[0133] When the first lookup table outputs SE1 and SE0 as 10, the first 4-to-1 selector outputs the third intermediate signal FLAG3 while maintaining the noise level, thus obtaining the transmit / receive signal frequency offset f. △ When the value is negative, the signal-to-noise ratio of the baseband signal NCH is improved to twice that of the original digital signal;

[0134] When the first lookup table outputs SE1 and SE0 as 01, the first 4-to-1 selector outputs the second intermediate signal FLAG2 while maintaining the noise level, thus obtaining the transmit / receive signal frequency offset f. △ When the value is negative, the signal-to-noise ratio of the baseband signal NCH is improved to twice that of the original digital signal.

[0135] Step 4, for the frequency offset f of the transmit and receive signals △ If the value is greater than 0, construct a second lookup table, and use this lookup table and a second 4-to-1 selector to output a baseband signal PCH with a positive frequency offset for both transmit and receive signals.

[0136] Reference Figure 5 The specific implementation of this step is as follows:

[0137] 4.1) Construct a second lookup table. This lookup table has 3 address input terminals and 2 value output terminals. It internally stores the 2-bit values ​​of the high-order SE1 and the low-order SE0, and selects the corresponding second 4-to-1 selector.

[0138] 4.2) The double frequency signal AS0, the frequency offset cosine signal AS1, and the frequency offset sine signal AS2 of the above-mentioned transmit and receive signals are used as the address input of the lookup table. The highest bit of the address input is AS2 and the lowest bit is AS0. The value output of the lookup table is connected to the address input of a 4-to-1 selector.

[0139] 4.3) Use the first intermediate signal FLAG1, the second intermediate signal FLAG2, the third intermediate signal FLAG3, and the fourth intermediate signal FLAG4 as the data inputs of the 4-to-1 selector;

[0140] 4.4) For the frequency offset f of the transmit and receive signals △ When the value is positive, through phase The quadrant in which the table is located determines the value of the input address AS2 AS1 AS0 in the second lookup table, and different internal preset values ​​SE1 and SE0 are selected:

[0141] like If it is in the first quadrant, the input address AS2AS1 AS0 of the second lookup table is 111, and the preset value SE1 SE0 inside it is 00.

[0142] like If it is in the second quadrant, the input address AS2AS1 AS0 of the second lookup table is 100, and its internal preset value SE1 SE0 is 01.

[0143] like If it is in the third quadrant, the input address AS2AS1 AS0 of the second lookup table is 001, and its internal preset value SE1 SE0 is 10.

[0144] like If it is in the fourth quadrant, the input address AS2AS1 AS0 of the second lookup table is 010, and its internal preset value SE1 SE0 is 11.

[0145] 4.5) Based on the internal preset values ​​SE1 and SE0 output from the second lookup table, the second 4-to-1 selector outputs the corresponding intermediate signal to obtain the transmit / receive signal frequency offset f. △ When the signal-to-noise ratio (SNR) of the baseband signal PCH is positive, it is improved to twice that of the original digital signal.

[0146] When the second lookup table outputs SE1 and SE0 as 00, the second 4-to-1 selector outputs the first intermediate signal FLAG1, while maintaining the noise level to obtain the transmit / receive signal frequency offset f.△ When the value is positive, the baseband signal PCH has a signal-to-noise ratio improved to twice that of the original digital signal;

[0147] When the second lookup table outputs SE1 and SE0 as 01, the second 4-to-1 selector outputs the second intermediate signal FLAG2, while maintaining the noise level to obtain the transmit / receive signal frequency offset f. △ When the value is positive, the baseband signal PCH has a signal-to-noise ratio improved to twice that of the original digital signal;

[0148] When the second lookup table outputs SE1 and SE0 as 10, the second 4-to-1 selector outputs the third intermediate signal FLAG3, while maintaining the noise level to obtain the transmit / receive signal frequency offset f. △ When the value is positive, the baseband signal PCH has a signal-to-noise ratio improved to twice that of the original digital signal;

[0149] When the second lookup table outputs SE1 and SE0 as 11, the second 4-to-1 selector outputs the fourth intermediate signal FLAG4, while maintaining the noise level to obtain the transmit / receive signal frequency offset f. △ When the value is positive, the signal-to-noise ratio of the baseband signal PCH is improved to twice that of the original digital signal.

[0150] Step 5, for the frequency offset f of the transmit and receive signals △ If the value is zero, directly use the pair of initial intermediate signals I obtained in step 2. FG Q FG As the frequency offset of the transmit and receive signals f △ The two baseband signals are set to 0, and the noise remains unchanged, so that the signal-to-noise ratio of the baseband signal is improved to twice that of the original digital signal.

[0151] Step 6: Perform matched filtering on the obtained baseband signal to obtain the pulse compression peak.

[0152] Reference Figure 6 The specific implementation of this step is as follows:

[0153] 6.1) Four matched filters are used. The baseband signal NCH with a negative transmit / receive frequency offset is input to the first matched filter, the baseband signal PCH with a positive transmit / receive frequency offset is input to the second matched filter, and the two baseband signals I when the transmit / receive frequency offset is 0 are input to the second matched filter. FG Q FG The signals are input to the third and fourth matched filters respectively, and these four channels perform matched filtering in parallel to obtain their respective pulse compression peaks;

[0154] 6.2) An OR gate is used to combine four channels to output a single pulse compression peak, thereby completing the pulse compression of the phase-coded signal. The amplitude of the pulse compression peak is not lost, thus realizing the pulse compression of the phase-coded signal with adaptive frequency offset of the transmit and receive signals.

[0155] The effects of this invention can be further illustrated by the following simulation results:

[0156] The bit error rate is defined as the proportion of baseband signal symbols that are incorrectly identified.

[0157] Calculate the bit error rate of the BPSK modulated signal using the bit error rate formula. Where Q(x) is the Gaussian Q-function, It's the signal-to-noise ratio (SNR), which is the energy per bit (E). b The ratio of the noise power spectral density N0.

[0158] The simulation parameters were set as follows: BPSK modulation, baseband signal symbol length of 1024, additive white Gaussian noise (AWGN) channel, and hard decision method, i.e., symbol bit decision. Monte Carlo simulation experiments were conducted to simulate the bit error rate of the present invention and the prior art 1000 times respectively. The results are shown in Table 4.

[0159] Table 4 Comparison of Bit Error Rates between the Invention and Existing Technologies

[0160]

[0161] As shown in Table 4, by introducing an orthogonal all-pass filter pair and optimizing the signal processing path, the actual signal-to-noise ratio of this invention is the nominal signal-to-noise ratio plus the improved gain, which increases the signal amplitude by 2 times and improves the gain by 6dB. When the nominal signal-to-noise ratio is 0dB (SNR=0dB), the actual signal-to-noise ratio of this invention is 6dB, and the bit error rate is reduced by 97%.

[0162] The above description is merely a specific example of the present invention and does not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A method for improving the signal-to-noise ratio of binary phase code baseband signals based on signal amplitude enhancement, characterized in that, include: (1) The transmitter transmits a signal, and the receiver receives the echo signal and down-converts it to an intermediate frequency signal; (2) The intermediate frequency signal is sampled by an A / D converter at a frequency of four times to obtain the digital signal of the intermediate frequency signal; (3) A pair of initial orthogonal signals, including a cosine signal and a sine signal, are generated by a numerically controlled oscillator (NCO); (4) The digital signal is input into a pair of orthogonal full-pass filters to generate a pair of orthogonal signals, which are then orthogonally mixed with the cosine signal and the sine signal to generate four node signals. These four node signals are added and subtracted to generate an I-channel signal and a Q-channel signal with an amplitude twice that of the original digital signal. The original digital signal refers to the digital signal generated by the low-pass filtering method. (5) Perform four-way parallel addition and subtraction operations on the I-way signal and Q-way signal generated in step (4), and extract the sign bit of the four-way operation results to generate four intermediate signals with amplitude amplified to twice that of the original digital signal. Use these four intermediate signals as the data input for the baseband signal lookup table mapping. (6) Extract the baseband signal with improved signal-to-noise ratio based on the frequency offset of the transmitted and received signals: For cases where the frequency offset is zero, the sign bits of the I-channel and Q-channel signals are directly taken as the baseband signal, while keeping the noise unchanged, thereby improving the signal-to-noise ratio of the baseband signal to twice that of the original digital signal. For cases where the frequency offset is not zero, the I-channel and Q-channel signals are first squared, subtracted, and then the sign bit is taken to obtain the frequency offset of the transmit and receive signals, which is twice the frequency offset of the transmit and receive signals. The frequency of the second harmonic signal is then divided by two to obtain a sinusoidal signal with the frequency offset of the transmit and receive signals. Sum and cosine signals Then , , The address input is used as the baseband signal lookup table mapping address, and the noise remains unchanged, resulting in a baseband signal with a signal-to-noise ratio improved to four times that of the original digital signal. The aforementioned lookup table mapping involves constructing two lookup tables to map the three frequency offset signals. , , As the address input for the two lookup tables, the four intermediate signals FLAG1, FLAG2, FLAG3, and FLAG4 are used as the data input for the two lookup tables. The two lookup tables select the corresponding input data according to the input address to obtain the baseband signal PCH with a positive frequency offset for the transmit and receive signals and the baseband signal NCH with a negative frequency offset for the transmit and receive signals. (7) Match filtering is performed on the baseband signals with improved signal-to-noise ratio obtained under different frequency offsets to complete pulse compression.

2. The method according to claim 1, characterized in that, The pair of initial orthogonal signals generated by the numerically controlled oscillator (NCO) in step (3) are represented as follows: ； ； Where SQ is a cosine signal and SI is a sine signal. Let n be the signal frequency and n be the signal sampling interval.

3. The method according to claim 1, characterized in that, The orthogonal all-pass filter pair mentioned in step (4) is either a 90° phase-shifting filter bank or a Hilbert transform pair.

4. The method according to claim 1, characterized in that, In step (4), an amplitude twice that of the original digital signal is generated. Road signals and The road signals are represented as follows: ； ； in, The I-channel signal is the original digital signal. ， A represents the signal amplitude. For the frequency offset of the transmitted and received signals, Represents two-phase modulation, with a value of 0 or , It is the phase difference between the received signal and the transmitted signal, ranging from 0 to... , where n is the sampling interval.

5. The method according to claim 1, characterized in that, The four-way operations in step (5) are represented as follows: ； ； ； ； Where A1 is the result of the first operation, the sign bit of A1 is taken to obtain the first intermediate signal FLAG1; R1 is the result of the second operation. Taking the sign bit of R1, we obtain the second intermediate signal FLAG2. A2 is the inverted signal. The sign bit of the A1 signal is taken and passed through an inverter to obtain the third intermediate signal FLAG3. R2 is the inverted subtraction signal. Take the sign bit of R1 and get the fourth intermediate signal FLAG4 through the inverter. A represents the signal amplitude. For the frequency offset of the transmitted and received signals, Represents two-phase modulation, with a value of 0 or ; It is the phase difference between the received signal and the transmitted signal, ranging from 0 to... ; Let n be the phase shift of the all-pass filter, and n be the sampling interval.

6. The method according to claim 1, characterized in that, The second harmonic signal obtained in step (6) The sinusoidal signal with frequency offset of the transmitted and received signals Sum and cosine signals They are represented as follows: ； ； ； Where A is the signal amplitude. For the frequency offset of the transmitted and received signals, It is the phase difference between the received signal and the transmitted signal, ranging from 0 to... , Let n be the phase shift of the all-pass filter, and n be the sampling interval.

7. The method according to claim 1, characterized in that, The two lookup tables respectively select the corresponding input data according to the input address to obtain the baseband signal PCH with a positive transmit / receive signal frequency offset and the baseband signal NCH with a negative transmit / receive signal frequency offset. The implementation includes: Frequency offset of transmitting and receiving signals When <0, the address is mapped according to the first lookup table. , , The value of the base is determined With signal NCH; Frequency offset of transmitting and receiving signals When >0, the address is mapped according to the second lookup table. , , The value of the base is determined PCH with signal; The first lookup table and the second lookup table have the same structure, both having 3 address input terminals and 2 value output terminals, and internally storing the high-order bits. and low position This is a 2-bit value.

8. The method according to claim 7, characterized in that, The frequency offset of the transmit and receive signals When <0, the address is mapped according to the first lookup table. , , The value of NCH determines the baseband signal, which includes: When the first lookup table mapping address , , When the value is 111, the first intermediate signal FLAG1 is output as the baseband signal NCH with a negative frequency offset for the transmit and receive signals; When the first lookup table mapping address , , When the value is 010, the second intermediate signal FLAG2 is output as the baseband signal NCH with a negative frequency offset for the transmit and receive signals; When the first lookup table mapping address , , When the value is 001, the third intermediate signal FLAG3 is output as the baseband signal NCH with a negative frequency offset for the transmit and receive signals; When the first lookup table mapping address , , When the value is 100, the fourth intermediate signal FLAG4 is output as the baseband signal NCH with a negative frequency offset for the transmit and receive signals.

9. The method according to claim 7, characterized in that, The frequency offset of the transmit and receive signals When >0, the address is mapped according to the second lookup table. , , The value of PCH determines the baseband signal PCH, which includes: When the second lookup table mapping address , , When the value is 111, the first intermediate signal FLAG1 is output as the baseband signal PCH with a positive frequency offset for the transmit and receive signals; When the second lookup table mapping address , , When the value is 100, the second intermediate signal FLAG2 is output as the baseband signal PCH with a positive frequency offset for the transmit and receive signals; When the second lookup table mapping address , , When the value is 001, the third intermediate signal FLAG3 is output as the baseband signal PCH with a positive frequency offset for the transmit and receive signals; When the second lookup table mapping address , , When the value is 010, the fourth intermediate signal FLAG4 is output as the baseband signal PCH with a positive frequency offset for the transmit and receive signals.

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