A low-complexity phase synchronization receiving system and method for MSK coded modulation system

Abstract

The present invention discloses a low-complexity phase synchronization receiving system and method for an MSK coding modulation system, and relates to the technical field of continuous phase modulation. On the one hand, the present invention encodes and modulates the original message by constructing a precoding method, and the receiving end uses phase decoupling frequency conversion processing to achieve the best sampling point extraction at the moment when the inter-code interference is minimum, converting MSK into BPSK-like modulation without oversampling processing, and can offset the modulation phase component of the receiving synchronization segment to achieve accurate estimation of Doppler phase and frequency, thereby improving the anti-Doppler capability. On the other hand, the real part of the signal after Doppler frequency deviation and phase deviation compensation is taken, and coherent demodulation soft information is directly output. The proposed demodulation algorithm has low complexity, and its performance is comparable to that of BPSK. It is significantly better than the MSK optimal demodulation receiver in the low signal-to-noise ratio area, and is particularly suitable for bit-interleaved coding modulation systems combined with channel coding, and can achieve reliable transmission under low signal-to-noise ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of continuous phase modulation, and in particular to a phase synchronization receiving system and method for a low-complexity MSK coding modulation system. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Minimum Shift Keying (MSK) is a special case of continuous phase modulation. Due to its high spectral and power efficiency, it achieves strong out-of-band rejection without filtering, while maintaining its inherent constant envelope characteristics, enabling it to operate in the nonlinear saturation region of high-power amplifiers, achieving high-power amplification. Consequently, MSK has been widely studied in fields such as satellite navigation, satellite communications, and deep-space communications, where both power and bandwidth are limited.

[0004] Compared to incoherent demodulation, coherent demodulation algorithms achieve performance close to theoretical values. Carrier synchronization is a crucial step in coherent reception processing, and the accuracy of Doppler frequency and phase estimation impacts the coherent demodulation performance of communication systems. To overcome the short-term fast fading introduced by dual-frequency channels, high-dynamic MSK burst communication systems typically evenly insert synchronization segments into the data frame structure. Data-assisted open-loop synchronization is used to rapidly estimate short-term Doppler frequency and phase variations, achieving carrier synchronization.

[0005] Due to the continuity of MSK phase, the unknown data segment will introduce an ambiguous initial phase to the subsequent synchronization segment, resulting in the inability to eliminate the MSK modulation phase of the synchronization segment and thus affecting the inability to accurately estimate the Doppler frequency. Although the frequency doubling method can be used as an effective solution, by amplifying the phase by integer multiples, the influence of the ambiguous initial phase can be eliminated and the frequency offset can be accurately estimated, but the Doppler frequency estimation range will decrease proportionally, and its phase estimation range is reduced to -π / 4~π / 4, and the frequency estimation range is reduced to ~ , not suitable for high dynamic and large Doppler scenes. Summary of the Invention

[0006] The purpose of the present invention is to address the problems existing in the prior art and provide a low-complexity phase synchronization receiving system and method for MSK coded modulation system. The system encodes and modulates the original message by constructing a precoding method. The receiving end uses phase decoupling and frequency conversion processing to achieve the best sampling point extraction at the time when the inter-code interference is minimum, converts MSK into BPSK-like modulation, decouples the phase between MSK symbols, and uses a data-assisted open-loop synchronization method without oversampling processing. Only the synchronization sequence is used to reconstruct the modulation phase of the best sampling point in each symbol to offset the modulation phase component of the received synchronization segment, so as to achieve accurate estimation of Doppler phase and frequency, effectively reduce the sampling signal processing length, and reduce processing delay. The MSK phase estimation range of this method is improved to -π~π, and the frequency estimation range is improved to ~ , with strong Doppler immunity. The demodulation module directly outputs coherent demodulation soft information after taking the real part of the signal. Compared with the MSK optimal demodulation receiver, the proposed demodulation algorithm has low complexity and performance comparable to BPSK. It significantly outperforms the MSK optimal demodulation receiver in low signal-to-noise ratio regions. It is particularly suitable for bit-interleaved coded modulation systems combined with channel coding, and can achieve reliable transmission under low signal-to-noise ratio conditions.

[0007] The technical solutions of the present invention are as follows:

[0008] A low-complexity phase synchronization receiving system for an MSK coded modulation system, comprising:

[0009] The transmitter encodes the service data and frames it with the synchronization sequence to generate a baseband pulse signal, which is then modulated by MSK precoding and output through the RF transmission link.

[0010] After the receiving end obtains the digital baseband signal through the RF receiving link, it performs phase decoupling processing in sequence to eliminate the phase correlation between bits to generate a BPSK-like signal, frame synchronization detection, channel estimation and zero-forcing equalization based on the synchronization sequence, and BPSK-like demodulation to extract the coded soft information, and finally recovers the service data through iterative decoding.

[0011] Furthermore, the transmitting end includes: an LDPC encoding module, a framing module, a precoding module, an MSK modulation module, a digital-to-analog conversion module, and an analog up-conversion module;

[0012] The LDPC encoding module outputs a coding sequence based on the service data;

[0013] The framing module inserts synchronization sequences before and after the coding sequence to generate a pulse signal;

[0014] The precoding module performs precoding based on all bits in the pulse signal and then outputs an MSK modulated signal through the MSK modulation module;

[0015] The digital-to-analog conversion module and the analog up-conversion module process the MSK modulated signal and radiate an MSK radio frequency signal.

[0016] Furthermore, the receiving end includes: an analog down-conversion module, an analog-to-digital conversion module, a phase decoupling frequency conversion module, a signal detection module, a channel estimation module, a channel equalization module, a BPSK-like demodulation module and an LDPC decoding module;

[0017] The analog down-conversion module and the analog-to-digital conversion module process the MSK radio frequency signal after noise interference and output a received digital baseband signal;

[0018] The phase decoupling and frequency conversion module performs matched filtering on the received digital baseband signal, then performs phase decoupling and frequency conversion on the filtered signal to eliminate the phase correlation between bits, and finally extracts the signal after phase decoupling and frequency conversion processing to output a BPSK-like signal with a bit sampling rate of 2 times;

[0019] The signal detection module performs correlation detection on the BPSK-like signal and realizes frame synchronization through peak search and threshold detection methods;

[0020] The channel estimation module reconstructs the modulation phase of the optimal sampling point of each bit through the synchronization sequence, and eliminates the MSK modulation phase of the received signal synchronization sequence;

[0021] The channel equalization module uses a zero-forcing algorithm to directly offset the channel fading response of the received signal pulse, and the equalized pulse signal outputs the coding sequence soft information through the BPSK-like demodulation module;

[0022] The LDPC decoding module iteratively decodes the soft information of the coding sequence to recover the service data.

[0023] The present invention also proposes a low-complexity phase synchronization receiving method for an MSK coding modulation system, based on the above-mentioned low-complexity phase synchronization receiving system for an MSK coding modulation system, comprising:

[0024] Step S1: The service data is encoded by the LDPC encoding module and then output as a coded sequence;

[0025] Step S2: The framing module inserts synchronization sequences before and after the coding sequence to generate a pulse signal;

[0026] Step S3: All bits in the pulse signal are pre-coded by the pre-coding module and then output as MSK modulated signals through the MSK modulation module;

[0027] Step S4: The MSK modulated signal is processed by the digital-to-analog conversion module and the analog up-conversion module to radiate an MSK radio frequency signal;

[0028] Step S5: The receiving platform receives the MSK radio frequency signal after noise interference through the analog down-conversion module and the analog-to-digital conversion module and outputs the received digital baseband signal;

[0029] Step S6: performing matched filtering on the received digital baseband signal through the phase decoupling and frequency conversion module, then performing phase decoupling and frequency conversion on the filtered signal to eliminate the phase correlation between bits, and finally decimating the signal after phase decoupling and frequency conversion to output a BPSK-like signal with a bit sampling rate of 2 times;

[0030] Step S7: The signal detection module performs correlation detection on the BPSK-like signal and realizes frame synchronization through peak search and threshold detection methods;

[0031] Step S8: The channel estimation module reconstructs the modulation phase of the optimal sampling point of each bit through the synchronization sequence, eliminates the MSK modulation phase of the received signal synchronization sequence, and realizes accurate estimation of the Doppler phase of the received synchronization sequence;

[0032] Step S9: The channel equalization module uses a zero-forcing algorithm to directly offset the channel fading response of the received signal pulse, and the equalized pulse signal is output through the BPSK-like demodulation module to output the coded sequence soft information;

[0033] Step S10: The LDPC decoding module iteratively decodes the soft information of the coding sequence to recover the service data.

[0034] Furthermore, the precoding method is as follows:

[0035]

[0036] Where, is the i-th precoded bit in the pulse, is the i-th bit and has a value of [0, 1] and , is the exclusive OR operation;

[0037] Precoded bits Dual polarization coding Then perform MSK modulation and output the MSK modulated signal, which is expressed as:

[0038]

[0039] Where, is the bit energy, T is the bit time, is the phase of the i-th bit, is the dual-polarization coding of the i-th bit, that is , j is the imaginary part identifier.

[0040] Furthermore, the phase decoupling frequency conversion module processing flow in step S6 is as follows:

[0041] Step S61: Perform matched filtering on the received digital baseband signal, namely:

[0042]

[0043] Where, is the nth sampling point of the matched filter signal, To receive the mth sampling point of the digital baseband signal, The matched filter coefficients;

[0044] Step S62: performing phase decoupling and frequency conversion processing on the matched filtered signal, namely:

[0045]

[0046] Where, is the signal after phase decoupling and frequency conversion processing, T is the bit time, and Ts is the sampling time.

[0047] Step S63: extract the signal after the phase decoupling and frequency conversion processing to output a quasi-BPSK signal with a bit sampling rate of 2 times, that is:

[0048]

[0049] Where, The nth sampling point of the BPSK-like signal with a bit sampling rate of 2 times.

[0050] Furthermore, the channel estimation module has a built-in Doppler frequency estimation algorithm and a phase estimation algorithm.

[0051] Furthermore, the Doppler frequency estimation algorithm includes:

[0052] Step A: After frame synchronization, the starting time of each MSK bit time is used as the time of minimum inter-symbol interference to extract the optimal sampling point, where the sampling time is the bit time, that is:

[0053]

[0054] Where, is the nth best sampling point of the BPSK-like signal, is the sampling point at the frame header moment.

[0055] Step B: Extract the preamble sequence and postamble sequence from the pulse signal, conjugate and multiply them with the local sequence, sum them, and take the phase to complete the phase estimation of the middle moment of the synchronization sequence, that is:

[0056] Doppler phase estimation of intra-pulse preamble sequence :

[0057]

[0058] In the formula For phase operation, L is the synchronization sequence symbol length. The value of the nth bit of the local synchronization sequence is:

[0059]

[0060] in, is the nth original bit of the synchronization sequence in the pulse and has a value of [0, 1];

[0061] Doppler phase estimation using intra-pulse postsynchronization sequence :

[0062]

[0063] Where, is the number of symbols between the start time of the preamble sequence and the start time of the postamble sequence;

[0064] Step C: Since the phase difference between the two synchronization segments has a 2π periodic ambiguity, the phase estimates of the two synchronization segments need to be corrected, namely:

[0065] when ,but ;

[0066] when ,but ;

[0067] Step D: Use the difference between the two synchronization segments to estimate the phase to achieve Doppler frequency estimation, that is:

[0068] .

[0069] Furthermore, the phase estimation algorithm includes:

[0070] Doppler frequency estimation and preamble sequence Doppler phase estimation , fit the channel Doppler phase of the pulse signal, that is:

[0071]

[0072] Where L is the synchronization sequence length, T is the bit time, Np is the number of pulse bits, and j is the imaginary part identifier.

[0073] Furthermore, the BPSK-like demodulation module processing flow in step S9 is as follows:

[0074] Step S91: After suppressing the channel fading response through the channel equalization module, the received equalized signal is extracted. The sampling period is the bit period, and T is the bit time, that is:

[0075]

[0076] Where Np is the number of pulse symbols, is the k-th bit observation information of the pulse;

[0077] Step S92: Equalize the signal The real part of is taken out as the k-th bit soft information of the pulse signal, that is:

[0078]

[0079] in, To take the real part operation, is the k-th bit soft information of the pulse signal.

[0080] Compared with the existing technology, the beneficial effects of the present invention are:

[0081] 1. Improve the anti-Doppler capability and reduce the complexity of receiving processing: A low-complexity phase synchronization receiving system and method for MSK coded modulation system are proposed. The transmitter constructs a precoding method, and the receiver extracts the optimal sampling point at the moment of minimum inter-code interference after phase decoupling and frequency conversion, converting MSK into BPSK-like modulation without oversampling. Only the synchronization sequence is used to reconstruct the modulation phase of the optimal sampling point in each symbol to offset the modulation phase component of the received synchronization segment, so as to achieve accurate estimation of Doppler phase and frequency, effectively reduce the length of sampling signal processing, and reduce processing delay and hardware overhead. Compared with the traditional frequency doubling method, the phase estimation range of this method is improved to -π~π, and the frequency estimation range is improved to ~ , with strong anti-Doppler capability, including The demodulation module processes only the optimal sampling point within the MSK symbol, takes the real part, and directly outputs the coherent demodulation soft information. Compared with the MSK optimal demodulation receiver, the complexity is significantly reduced.

[0082] 2. Improve demodulation and decoding performance: This method constructs a precoding method at the transmitter end, and achieves the optimal sampling point extraction at the moment when the inter-code interference is minimum after phase decoupling and frequency conversion at the receiver end, converting MSK into BPSK-like modulation. The demodulation module takes the real part of the signal and directly outputs coherent demodulation soft information. Its performance is comparable to that of BPSK, and is significantly better than the MSK optimal demodulation receiver in the low signal-to-noise ratio area. It is particularly suitable for bit-interleaved coded modulation systems combined with channel coding, and can achieve correct decoding performance under low signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 This is a schematic diagram of a phase synchronization receiving system and method for a low-complexity MSK coded modulation system;

[0084] Figure 2 This is the eye diagram of the MSK signal proposed by the present invention;

[0085] Figure 3 Schematic diagram of MSK phase decoupling proposed in the present invention;

[0086] Figure 4 The multi-frequency and phase estimation accuracy of the channel estimation module proposed in the present invention;

[0087] Figure 5 The demodulation performance of the coherent receiving method of the MSK demodulation module proposed in the present invention;

[0088] Figure 6 This is the decoding performance of the MSK coding modulation system proposed in the present invention. DETAILED DESCRIPTION

[0089] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0090] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0091] Example 1

[0092] See also Figure 1 , a low-complexity MSK coded modulation system phase synchronization receiving system, comprising:

[0093] The transmitter encodes the service data and frames it with the synchronization sequence to generate a baseband pulse signal, which is then modulated by MSK precoding and output through the RF transmission link.

[0094] After the receiving end obtains the digital baseband signal through the RF receiving link, it performs phase decoupling processing in sequence to eliminate the phase correlation between bits to generate a BPSK-like signal, frame synchronization detection, channel estimation and zero-forcing equalization based on the synchronization sequence, and BPSK-like demodulation to extract the coded soft information, and finally recovers the service data through iterative decoding.

[0095] In this example, specifically, the transmitting end includes: an LDPC encoding module, a framing module, a precoding module, an MSK modulation module, a digital-to-analog conversion module, and an analog up-conversion module;

[0096] The LDPC encoding module outputs a coding sequence based on the service data;

[0097] The framing module inserts synchronization sequences before and after the coding sequence to generate a pulse signal;

[0098] The precoding module performs precoding based on all bits in the pulse signal and then outputs an MSK modulated signal through the MSK modulation module;

[0099] The digital-to-analog conversion module and the analog up-conversion module process the MSK modulated signal and radiate an MSK radio frequency signal.

[0100] In this example, specifically, the receiving end includes: an analog down-conversion module, an analog-to-digital conversion module, a phase decoupling frequency conversion module, a signal detection module, a channel estimation module, a channel equalization module, a BPSK-like demodulation module and an LDPC decoding module;

[0101] The analog down-conversion module and the analog-to-digital conversion module process the MSK radio frequency signal after noise interference and output a received digital baseband signal;

[0102] The phase decoupling and frequency conversion module performs matched filtering on the received digital baseband signal, then performs phase decoupling and frequency conversion on the filtered signal to eliminate the phase correlation between bits, and finally extracts the signal after phase decoupling and frequency conversion processing to output a BPSK-like signal with a bit sampling rate of 2 times;

[0103] The signal detection module performs correlation detection on the BPSK-like signal and realizes frame synchronization through peak search and threshold detection methods;

[0104] The channel estimation module reconstructs the modulation phase of the optimal sampling point of each bit through the synchronization sequence, and eliminates the MSK modulation phase of the received signal synchronization sequence;

[0105] The channel equalization module uses a zero-forcing algorithm to directly offset the channel fading response of the received signal pulse, and the equalized pulse signal outputs the coding sequence soft information through the BPSK-like demodulation module;

[0106] The LDPC decoding module iteratively decodes the soft information of the coding sequence to recover the service data.

[0107] This embodiment further proposes a low-complexity phase synchronization receiving method for an MSK coding modulation system, based on the above-mentioned low-complexity phase synchronization receiving system for an MSK coding modulation system, including:

[0108] Step S1: The service data is encoded by the LDPC encoding module and then output as a coded sequence;

[0109] Step S2: The framing module inserts synchronization sequences before and after the coding sequence to generate a pulse signal;

[0110] Step S3: All bits in the pulse signal are pre-coded by the pre-coding module and then output as MSK modulated signals through the MSK modulation module;

[0111] Step S4: The MSK modulated signal is processed by the digital-to-analog conversion module and the analog up-conversion module to radiate an MSK radio frequency signal;

[0112] Step S5: The receiving platform receives the MSK radio frequency signal after noise interference through the analog down-conversion module and the analog-to-digital conversion module and outputs the received digital baseband signal;

[0113] Step S6: performing matched filtering on the received digital baseband signal through the phase decoupling and frequency conversion module, then performing phase decoupling and frequency conversion on the filtered signal to eliminate the phase correlation between bits, and finally decimating the signal after phase decoupling and frequency conversion to output a BPSK-like signal with a bit sampling rate of 2 times;

[0114] Step S7: The signal detection module performs correlation detection on the BPSK-like signal and realizes frame synchronization through peak search and threshold detection methods;

[0115] Step S8: After frame synchronization, the starting time of each MSK bit time is used as the time of minimum inter-symbol interference to extract the optimal sampling point, where the sampling time is the bit time. The channel estimation module reconstructs the modulation phase of each optimal sampling point through the synchronization sequence, eliminates the MSK modulation phase of the received signal synchronization sequence, and accurately estimates the Doppler phase of the received synchronization sequence. The phase of the synchronization sequence before and after the pulse signal is differentially processed to estimate the Doppler frequency and fit the channel fading response.

[0116] Step S9: The channel equalization module uses a zero-forcing algorithm to directly offset the channel fading response of the received signal pulse, and the equalized pulse signal is output through the BPSK-like demodulation module to output the coded sequence soft information;

[0117] Step S10: The LDPC decoding module iteratively decodes the soft information of the coding sequence to recover the service data.

[0118] In this embodiment, specifically, the precoding method is as follows:

[0119]

[0120] Where, is the i-th precoded bit in the pulse, is the i-th bit and has a value of [0, 1] and , is the exclusive OR operation;

[0121] Precoded bits Dual polarization coding Then perform MSK modulation and output the MSK modulated signal, which is expressed as:

[0122]

[0123] Where, is the bit energy, T is the bit time, is the phase of the i-th bit, is the dual-polarization code of the i-th bit, that is , j is the imaginary part identifier.

[0124] In this embodiment, specifically, the phase decoupling frequency conversion module processing flow in step S6 is as follows:

[0125] Step S61: Perform matched filtering on the received digital baseband signal, namely:

[0126]

[0127] Where, is the nth sampling point of the matched filter signal, To receive the mth sampling point of the digital baseband signal, The matched filter coefficients;

[0128] Step S62: performing phase decoupling and frequency conversion processing on the matched filter signal, namely:

[0129]

[0130] Where, is the signal after phase decoupling and frequency conversion processing, T is the bit time, and Ts is the sampling time.

[0131] Step S63: extract the signal after the phase decoupling and frequency conversion processing to output a quasi-BPSK signal with a bit sampling rate of 2 times, that is:

[0132]

[0133] Where, The nth sampling point of the BPSK-like signal with a bit sampling rate of 2 times.

[0134] In this embodiment, specifically, the channel estimation module has a built-in Doppler frequency estimation algorithm and a phase estimation algorithm.

[0135] In this embodiment, specifically, the Doppler frequency estimation algorithm includes:

[0136] Step A: After frame synchronization, the starting time of each MSK bit time is used as the time of minimum inter-symbol interference to extract the optimal sampling point, where the sampling time is the bit time, that is:

[0137]

[0138] Where, is the nth best sampling point of the BPSK-like signal, is the sampling point at the frame header moment.

[0139] Step B: Extract the preamble sequence and postamble sequence from the pulse signal, conjugate and multiply them with the local sequence, sum them, and take the phase to complete the phase estimation of the middle moment of the synchronization sequence, that is:

[0140] Doppler phase estimation of intra-pulse preamble sequence :

[0141]

[0142] In the formula For phase operation, L is the synchronization sequence symbol length. The value of the nth bit of the local synchronization sequence is:

[0143]

[0144] in, is the nth original bit of the synchronization sequence in the pulse and has a value of [0, 1];

[0145] Doppler phase estimation using intra-pulse postsynchronization sequence :

[0146]

[0147] Where, is the number of symbols between the start time of the preamble sequence and the start time of the postamble sequence;

[0148] Step C: Since the phase difference between the two synchronization segments has a 2π periodic ambiguity, the phase estimates of the two synchronization segments need to be corrected, namely:

[0149] when ,but ;

[0150] when ,but ;

[0151] Step D: Use the difference between the two synchronization segments to estimate the phase to achieve Doppler frequency estimation, that is:

[0152]

[0153] In this embodiment, specifically, the phase estimation algorithm includes:

[0154] Doppler frequency estimation and preamble sequence Doppler phase estimation , fit the channel Doppler phase of the pulse signal, that is:

[0155]

[0156] Where L is the synchronization sequence length, T is the bit time, Np is the number of pulse bits, and j is the imaginary part identifier.

[0157] In this embodiment, specifically, the BPSK-like demodulation module processing flow in step S9 is as follows:

[0158] Step S91: After suppressing the channel fading response through the channel equalization module, the received equalized signal is extracted. The sampling period is the bit period, and T is the bit time, that is:

[0159]

[0160] Where Np is the number of pulse symbols, is the k-th bit observation information of the pulse;

[0161] Step S92: Equalize the signal The real part of is taken out as the k-th bit soft information of the pulse signal, that is:

[0162]

[0163] in, To take the real part operation, is the k-th bit soft information of the pulse signal.

[0164] See Figure 2 and Figure 3 ,Depend on Figure 2 From the eye diagram of the MSK signal, we can see that the starting moment of the MSK bit time is the moment when the inter-symbol interference is minimum. Figure 3 In this method, the transmitter constructs a precoding method, and the receiver extracts the optimal sampling point at the moment when the inter-symbol interference is minimum after phase decoupling and frequency conversion. The phase of the signal after phase decoupling and frequency conversion at the starting moment within the bit time is the original bit information, realizing the transformation of MSK modulation into BPSK-like modulation.

[0165] See Figure 4 , the optimal sampling point of the signal after phase decoupling and frequency conversion is extracted at the starting moment within the bit time, where the sampling time is the bit time. The channel estimation module reconstructs the modulation phase of the optimal sampling point of each bit through the synchronization sequence, eliminates the MSK modulation phase of the received signal synchronization sequence, and realizes accurate estimation of the Doppler phase of the received synchronization sequence. The phases of the front and back synchronization sequences of the pulse signal are differentially processed to realize Doppler frequency estimation and fit the channel fading response. When the interval length of the front and back synchronization sequences is set to 20us and the synchronization segment length is 2us, the frequency estimation range of the frequency doubling method is -6.25kHz~6.25kHz, and the frequency estimation range of the algorithm proposed in this paper is -25kHz~25kHz. It can be seen from the figure that when the Doppler frequency is 5kHz, the frequency estimation accuracy of the algorithm in this paper is better than that of the frequency doubling method at low signal-to-noise ratio, and the accuracy of the two is comparable at high signal-to-noise ratio. When the Doppler frequency is 20kHz, since it exceeds the estimation range of the frequency doubling method, the estimated frequency deviation maintains a large error, but the frequency estimation accuracy of the algorithm of the present invention still maintains a high level. Therefore, the algorithm of the present invention can improve the Doppler frequency range and estimation accuracy, and has a strong anti-Doppler capability.

[0166] See Figure 5 Under ideal synchronization, the coherent reception method of the BPSK-like demodulation module proposed by the present invention for MSK is comparable to the theoretical performance of BPSK. At the same time, when a 20kHz Doppler frequency is present, the coherent demodulation performance after processing by the channel estimation module and channel equalization module of the present invention shows negligible performance degradation compared to the ideal synchronization performance. In addition, in the low signal-to-noise ratio region, the BPSK-like demodulation performance proposed by the present invention for MSK is significantly better than that of the MSK optimal demodulation receiver, and the reception complexity is significantly reduced. The MSK optimal demodulation receiver requires one filter and four phase states for maximum likelihood sequence detection, but the demodulation module of the present invention does not require oversampling. Each symbol is processed only at the optimal sampling time. After extracting the real part of the equalized signal, the coherent demodulation soft information is directly output, effectively reducing hardware overhead and processing delay, and facilitating engineering implementation.

[0167] See Figure 6Since the MSK demodulation performance of the present invention is comparable to the theoretical performance of BPSK, it is particularly suitable for bit-interleaved coded modulation systems combined with channel coding, and can achieve correct decoding performance under low signal-to-noise ratio. In the embodiment of the 1 / 4 code rate LDPC coding system, the decoding performance of the MSK coded modulation system proposed by the present invention is significantly better than that of the maximum likelihood demodulation MSK coded modulation system, and at a BER of 10 -6 It has a 2dB advantage, and the lower the bit rate, the greater the advantage.

[0168] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

[0169] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of the description in this section that did not constitute prior art at the time of filing are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A low-complexity phase synchronization receiving method for an MSK coded modulation system, characterized in that: include: Step S1: The service data is encoded by the LDPC encoding module and then output as a coded sequence; Step S2: The framing module inserts synchronization sequences before and after the coding sequence to generate a pulse signal; Step S3: All bits in the pulse signal are pre-coded by the pre-coding module and then output as MSK modulated signals through the MSK modulation module; Step S4: The MSK modulated signal is processed by the digital-to-analog conversion module and the analog up-conversion module to radiate an MSK radio frequency signal; Step S5: The receiving platform receives the MSK radio frequency signal after noise interference through the analog down-conversion module and the analog-to-digital conversion module and outputs the received digital baseband signal; Step S6: performing matched filtering on the received digital baseband signal through the phase decoupling and frequency conversion module, then performing phase decoupling and frequency conversion on the filtered signal to eliminate the phase correlation between bits, and finally decimating the signal after phase decoupling and frequency conversion to output a BPSK-like signal with a bit sampling rate of 2 times; Step S7: The signal detection module performs correlation detection on the BPSK-like signal and realizes frame synchronization through peak search and threshold detection methods; Step S8: The channel estimation module reconstructs the modulation phase of the optimal sampling point of each bit through the synchronization sequence, eliminates the MSK modulation phase of the received signal synchronization sequence, and realizes accurate estimation of the Doppler phase of the received synchronization sequence; Step S9: The channel equalization module uses a zero-forcing algorithm to directly offset the channel fading response of the received signal pulse, and the equalized pulse signal is output through the BPSK-like demodulation module to output the coded sequence soft information; Step S10: The LDPC decoding module iteratively decodes the soft information of the coding sequence to recover the service data; The method for extracting the optimal bit sampling point is as follows: After frame synchronization, the starting time of each MSK bit time is used as the time when the inter-symbol interference is minimum to extract the optimal sampling point, where the sampling time is the bit time, that is: Where, is the nth best sampling point of the BPSK-like signal, is the sampling point at the frame header moment.

2. The low-complexity phase synchronization receiving method for MSK coded modulation system according to claim 1, characterized in that: The precoding method is as follows: Where, is the i-th precoded bit in the pulse, is the i-th bit and has a value of [0, 1] and , is the exclusive OR operation; Precoded bits Dual polarization coding Then perform MSK modulation and output the MSK modulated signal, which is expressed as: Where, is the bit energy, T is the bit time, is the phase of the i-th bit, is the dual-polarization coding of the i-th bit, that is , j is the imaginary part identifier.

3. The low-complexity phase synchronization receiving method for MSK coded modulation system according to claim 2, characterized in that: The phase decoupling frequency conversion module processing flow in step S6 is as follows: Step S61: Perform matched filtering on the received digital baseband signal, namely: Where, is the nth sampling point of the matched filter signal, To receive the mth sampling point of the digital baseband signal, The matched filter coefficients; Step S62: performing phase decoupling and frequency conversion processing on the matched filter signal, namely: Where, is the signal after phase decoupling and frequency conversion processing, T is the bit time, and Ts is the sampling time; Step S63: extract the signal after the phase decoupling and frequency conversion processing to output a quasi-BPSK signal with a bit sampling rate of 2 times, that is: Where, The nth sampling point of the BPSK-like signal with a bit sampling rate of 2 times.

4. The low-complexity phase synchronization receiving method for MSK coded modulation system according to claim 3, characterized in that: The channel estimation module has a built-in Doppler frequency estimation algorithm and a phase estimation algorithm.

5. The low-complexity phase synchronization receiving method for MSK coded modulation system according to claim 4, characterized in that: The Doppler frequency estimation algorithm comprises: Step A: After frame synchronization, the starting time of each MSK bit time is used as the time of minimum inter-symbol interference to extract the optimal sampling point, where the sampling time is the bit time, that is: Where, is the nth best sampling point of the BPSK-like signal, is the sampling point at the frame header moment; Step B: Extract the preamble sequence and postamble sequence from the pulse signal, conjugate and multiply them with the local sequence, sum them, and take the phase to complete the phase estimation of the middle moment of the synchronization sequence, that is: Doppler phase estimation of intra-pulse preamble sequence : In the formula is the phase operation, L is the synchronization sequence symbol length; The value of the nth bit of the local synchronization sequence is: in, is the nth original bit of the synchronization sequence within the pulse and has a value of [0, 1]; Doppler phase estimation using intra-pulse postsynchronization sequence : Where, is the number of symbols between the start time of the preamble sequence and the start time of the postamble sequence; Step C: Since the phase difference between the two synchronization segments has a 2π periodic ambiguity, the phase estimates of the two synchronization segments need to be corrected, namely: when ,but ; when ,but ; Step D: Use the difference between the two synchronization segments to estimate the phase to achieve Doppler frequency estimation, that is: 。 6. The low-complexity phase synchronization receiving method for MSK coded modulation system according to claim 5, characterized in that: The phase estimation algorithm comprises: Doppler frequency estimation and preamble sequence Doppler phase estimation , fit the channel Doppler phase of the pulse signal, that is: Where L is the synchronization sequence length, T is the bit time, Np is the number of pulse bits, and j is the imaginary part identifier.

7. The low-complexity phase synchronization receiving method for MSK coded modulation system according to claim 6, characterized in that: The BPSK-like demodulation module processing flow in step S9 is as follows: Step S91: After suppressing the channel fading response through the channel equalization module, the received equalized signal is extracted. The sampling period is the bit period, and T is the bit time, that is: Where Np is the number of pulse symbols, is the k-th bit observation information of the pulse; Step S92: Equalize the signal The real part of is taken out as the k-th bit soft information of the pulse signal, that is: in, To take the real part operation, is the k-th bit soft information of the pulse signal.

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