WO2020047984A1

WO2020047984A1 - Multiple repeated phase shift code shift keying modulation method and demodulation method therefor

Info

Publication number: WO2020047984A1
Application number: PCT/CN2018/113492
Authority: WO
Inventors: 王盾; 陈耀辉; 李东俊; 董启甲
Original assignee: 航天恒星科技有限公司
Priority date: 2018-09-07
Filing date: 2018-11-01
Publication date: 2020-03-12
Also published as: CN109039975B; CN109039975A

Abstract

The present invention relates to a multiple repeated phase shift code shift keying modulation method, and a demodulation method therefor. A set of messages consisting of several binary bits repeatedly modulate, with the same phase and by means of code shift keying, N identical pseudo-random sequences, sequentially connect said N identical pseudo-random sequences having the same initial phase so as to form a new modulation symbol, and complete multiple repeated phase shift code shift keying modulation; a receiving end uses a comb filter to superimpose the received N sets of pseudo-random sequence data within the same symbol into one set of pseudo-random sequence data, and then performs matching filtering with pseudo-random sequences locally generated by the receiving end, searches for pseudo-random sequence phases corresponding to correlation peaks, and completes R-CSK message demodulation. By comprehensively taking into account factors such as spreading gain, information transmission rate, bit error rate, and modulation and demodulation signal processing complexity, said method of the present invention has a better performance than the conventional CSK modulation method.

Description

Code-shift keying modulation method with multiple repeated phase shifts and its demodulation method

Technical field

The invention belongs to the technical field of communication and navigation signal design, and in particular relates to a code-shift keying modulation method and a demodulation method for repeated phase shifts.

Background technique

Compared with DSSS direct-sequence spread-spectrum method, the code-shift keying modulation method (referred to as CSK modulation method) can transmit more information bits while maintaining the relevant characteristics of the spread-spectrum pseudo-random sequence, which is widely used in spread-spectrum communication.

In the conventional CSK modulation method, the symbol time length T _{S of the} modulation message is generally equal to the cycle time T _{C of the} spread-spectrum pseudo-random sequence. For a spread spectrum pseudo-random sequence with a chip length of L and a cycle time of T _C , the maximum broadcastable message rate is R = K / T _S , where K is an integer that satisfies the condition of 2 ^K ≦ L. Limited by the signal transmission power or the signal power at the receiving end, to ensure a sufficiently low bit error rate for information transmission, the K value actually selected is often much smaller than the maximum K value that may be theoretically selected.

A method for improving the information transmission rate of the CSK modulation method is to increase the number of transmission information bits K in one symbol, increase the time length of the modulation message symbol, increase the energy of the signal symbol received by the receiving end, and improve the error rate of the information transmission. However, this method also simultaneously increases the cycle time T _C and chip length L of the spread-spectrum pseudo-random sequence, which results in an increase in the amount of CSK modulation and demodulation signal processing, which greatly increases the software and hardware costs of the demodulation CSK message at the receiving end. And power consumption. Another method to increase the information transmission rate of the CSK modulation method is to increase the number of transmitted information bits K in one symbol, increase the length of the modulation message symbol, reduce the chip rate of the spreading pseudo-random sequence, and increase the spreading frequency in synchronization. While the pseudo-random sequence period T _C is maintained, the chip length L of the spread-spectrum pseudo-random sequence is kept constant, thereby avoiding an increase in the amount of CSK modulation and demodulation signal processing, and maintaining the software and hardware costs and power of demodulating CSK messages at the receiving end. Consuming. However, reducing the chip rate of the spread-spectrum pseudo-random sequence will cause the signal spectrum spread width to decrease, which will lead to an increase in the signal power density at the receiving end, which is not suitable for areas such as satellite communications and satellite navigation that have strict restrictions on the signal landing power flux density .

The code-shift keying modulation method (referred to as R-CSK modulation method) and its demodulation method proposed by the present invention for multiple repeated phase shifts can improve the transmission rate of CSK modulation information while keeping the signal power density at the receiving end unchanged. Avoid greatly increasing the software and hardware costs and power consumption of the demodulation CSK message at the receiving end.

Summary of the Invention

The technical problem to be solved by the present invention is to provide a technical method capable of effectively improving the information transmission efficiency of the code shift keying modulation and demodulation method, which can be applied to the design of a message transmission signal and a signal receiver in a communication and navigation system.

In order to solve the foregoing technical problems, the present invention provides the following technical solutions:

A code shift keying modulation method with multiple repeated phase shifts, which is characterized in that:

Repeat the same phase code-shift keying modulation for a pseudo-random sequence within the same transmission symbol, including the following steps:

First, using a preset keying modulation method, code shift keying modulation is performed on a given set of transmission messages to obtain a pseudo-random sequence, wherein the phase of the pseudo-random sequence is controlled by the transmission message;

Secondly, the above code shift keying modulation process is repeated multiple times, and multiple pseudo-random sequences with the same initial phase are sequentially connected to form a modulated transmission symbol, that is, a baseband signal.

As a preferred technical solution of the present invention, in the above-mentioned code shift keying modulation method with multiple repeated phase shifts, a baseband signal is constructed as follows:

First, channel coding is performed on the message to obtain an encoded bit stream D (t);

Second, according to the symbol clock provided by the timing generator, 1-> K _R serial / parallel conversion is performed on the corresponding bit stream after the message encoding, to obtain a parallel data stream, where each K _R -bit parallel data duration (symbol time length) ) Equal to N times the cycle time of the pseudo-random sequence;

Then, according to the pseudo-random sequence periodic clock provided by the timing generator, the phase selection module generates a pseudo-random sequence phase offset corresponding to the parallel data stream;

Finally, according to the pseudo-random sequence cycle clock, pseudo-random sequence chip clock provided by the timing generator, and the phase offset corresponding to the parallel data stream, a preset keying modulation method is used to The pseudo-random sequence is repeatedly code-shift-keyed to obtain a modulated pseudo-random sequence.

This is the baseband signal S (t). As a preferred technical solution of the present invention, the symbol clock is an integer multiple of the periodic clock of the pseudo-random sequence and synchronized with the periodic clock of the pseudo-random sequence.

As a preferred technical solution of the present invention, in the above-mentioned code shift keying modulation method with multiple repeated phase shifts, a radio frequency transmission signal is constructed as follows:

First, perform carrier modulation on the generated baseband signal S (t) to generate an intermediate frequency carrier signal. The modulation uses BPSK, QPSK, FSK or other equivalent carrier modulation methods;

Second, up-convert the generated intermediate frequency carrier signal to the required transmission frequency to generate a radio frequency carrier signal;

Then, the generated RF carrier signal is power amplified and sent to the transmitting antenna.

In addition, the present invention also provides a demodulation method for the above-mentioned code shift keying modulation method with multiple repeated phase shifts. The following method is used to implement message demodulation:

First, the RF carrier signal received by the receiver antenna is processed by the RF front-end to output a digital intermediate frequency signal;

Second, the digital intermediate frequency signal is passed to the digital down conversion module. The digital down conversion module converts the digital intermediate frequency signal into IQ two under the action of the external input receiver's local intermediate frequency signal and the carrier Doppler frequency offset signal in the received signal. Orthogonal baseband signals;

Again, IQ quadrature baseband signal is transmitted to the two comb filter, the comb filter control symbol clock external input pseudo-random sequence and the cycle of the clock, the same symbol period length N of the time T _C The data block is superimposed and transformed into a data block with a time length T _C , and the result is output to the matched filtering module;

Then, under the control of the externally input symbol clock and pseudo-random sequence cycle clock, the matching filtering module performs correlation matching calculation on the received data block with a length of time T _C and the pseudo-random sequence generated by the local pseudo-random sequence generator. The correlation result is output to the correlation peak search module, which searches for the phase of the local pseudorandom sequence corresponding to the correlation peak, and converts the phase into bit data for output;

Finally, the bit data output by the correlation peak search module is used to obtain the transmitted message data through the channel decoding module.

As a preferred solution, in the demodulation method described above, the comb filter is implemented as follows:

First, the comb filter delays the input data sequentially by N-1 times under the control of a cycle clock of a pseudo-random sequence input externally, each time the pseudo-random sequence cycle time is T _C seconds, and then the N-1 times The delayed data and input data are superimposed and sent to the data interception module;

Secondly, the data interception module intercepts the input data stream under the control of an externally input symbol clock and a pseudo-random sequence cycle clock, and outputs data superimposed N times in the same symbol. The data time length is the pseudo-random sequence cycle time T _C seconds.

Compared with the prior art, the code shift keying modulation and demodulation method of the multiple repeated phase shifts of the present invention has the following technical effects:

The code-shift keying modulation and demodulation method provided by the present invention for multiple repeated phase shifts. As the message transmitting end adopts the code-shift keying modulation method for multiple repeated phase shifts, compared with the conventional CSK, it can ensure the effective information rate. Under the same circumstances, better information transmission bit error rate performance can be obtained; while increasing the CSK modulation information transmission rate, the signal power density of the receiving end can be kept unchanged, which can avoid a substantial increase in the software and hardware costs of demodulating CSK messages at the receiving end and Power consumption; the demodulation part uses a comb filter to superimpose the received N sets of pseudo-random sequence data in the same symbol into 1 set of pseudo-random sequence data, and the same rate of pseudo-random sequence is used, and the period of the pseudo-random sequence is equal to the present invention Compared with the conventional CSK modulation of the proposed symbol length, it can effectively reduce the demodulation cost of the receiver while ensuring the same demodulation performance. The method of the invention is applicable to the fields of communication, navigation system design and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a timing diagram of R-CSK modulation;

Figure 2 is a conventional CSK modulation timing diagram;

FIG. 3 is a schematic block diagram of a message transmitter according to the present invention;

4 is a schematic block diagram of a conventional CSK modulation message receiver;

5 is a schematic block diagram of a message receiver designed according to the present invention;

6 is a block diagram of a comb filter in a message receiver designed according to the present invention;

FIG. 7 is a comparison chart of the effect of the bit error rate of the R-CSK information transmission of the present invention and the bit error rate of the conventional CSK information.

detailed description

The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings of the description.

Figure 1 shows the timing diagram of the R-CSK modulation. The symbol time length T _{S, R of the} broadcast message is equal to N times the cycle time of the pseudo-random sequence T _C. One symbol is represented by K _R -bit, and the information rate R _R = K _R / T _{S, R} bps, K _R -bit corresponding to the initial phase of PRN expressed as a decimal value range is

That can represent at most

Phase, repeatedly modulate N identical pseudo-random sequences with the same phase (that is, the K _R -bit message (m) in FIG. 1 corresponds to N PRN (m)), and sequentially order N pseudo-random sequences with the same initial phase Connect to form a new modulation symbol, and complete the code-shift keying modulation with multiple repeated phase shifts. The correspondence between the K _R -bit message (m) and the PRN (m) in FIG. 1 is only one embodiment of the present invention, and may also be other correspondences.

Figure 2 shows the timing diagram of conventional CSK modulation. The symbol length T _{S of the} broadcast message is equal to the period length T _{C of the} pseudo-random sequence. K-bit is used to represent a symbol, and the information rate is R = K / T _S bps. K-bit corresponds The initial phase of PRN is expressed as a decimal value range of M = 0, 1, ..., 2 ^K -1, that is, it can represent a maximum of 2 ^K phases. The initial phase expressed in K-bit symbols modulates a pseudo-random sequence to complete CSK modulation. The correspondence between the K-bit message (m) and the PRN (m) in FIG. 2 is only one embodiment of the present invention, and may also be other correspondences.

A code shift keying modulation method designed by the present invention for multiple repeated phase shifts. In actual application, as shown in FIG. 3, the following method is used to implement message broadcast.

First, using a preset keying modulation method, code shift keying modulation is performed for a given set of transmission messages to obtain a pseudo-random sequence, wherein the phase of the pseudo-random sequence is controlled by the transmission message;

Secondly, the above code shift keying modulation process is repeated multiple times, and multiple pseudo-random sequences with the same initial phase are sequentially connected to form a modulated transmission symbol.

Build the baseband signal as follows:

Secondly, according to the symbol clock T _{S, R} provided by the timing generator _, 1-> K _R serial / parallel conversion is performed on the corresponding bit stream after the message encoding, to obtain a K _R -bit parallel data stream, where each K _R -bit The parallel data duration T _{S, R} (symbol time length) is equal to N times the cycle time T _C of the pseudo-random sequence;

Then, according to the pseudo-random sequence cycle clock (simplified as sequence cycle clock in the figure) and pseudo-random sequence chip clock (simplified as sequence chip clock in the figure) provided by the timing generator, the phase selection module generates a parallel data stream corresponding to The phase shift of the pseudo-random sequence of the N, because the symbol clock and the sequence cycle clock are synchronized, N identical phase shifts can be generated in the same symbol duration;

Finally, according to the sequence cycle clock, sequence chip clock provided by the timing generator, and N identical phase offsets corresponding to the parallel data stream, a preset keying modulation method is adopted to repeatedly generate the pseudo-random sequence generator. N pseudo-random sequences with the same initial phase are set to form N consecutive pseudo-random signals with the same initial phase

This is the baseband signal S (t).

Then, carrier modulation is performed on the generated baseband signal to obtain an intermediate frequency carrier signal, and then an up-conversion process is performed on the intermediate frequency carrier signal to obtain a radio frequency carrier signal, which is finally subjected to power amplification processing and transmitted to a transmitting antenna for broadcasting.

When using BPSK carrier modulation, the RF transmission signal is expressed as follows:

Among them, P _s represents the radio signal transmission power, and f _c represents the frequency of the transmitted signal. BPSK carrier modulation is only one application example of the present invention, and other carrier modulation methods such as QPSK and FSK can also be used.

Aiming at the code shift keying modulation method with multiple repeated phase shifts designed above, the present invention further designs a code shift keying modulation demodulation method with multiple repeated phase shifts. Figure 4 first shows a schematic block diagram of a conventional CSK modulated message receiver;

Secondly, in the digital down conversion module, the digital intermediate frequency signal is mixed with the external input local intermediate frequency signal and the carrier Doppler frequency offset signal of the received signal to complete the digital down conversion, and output the orthogonal IQ two-way baseband data. Two IQ data outputs to the matched filtering module;

Then, under the control of the externally input symbol clock and pseudo-random sequence cycle clock (simplified as the sequence cycle clock in the figure), the matched filtering module combines the received IQ data block with a time length of T _C with the pseudo-random sequence generator. Correlation matching calculation is performed on the pseudo-random sequence generated under the control of the sequence periodic clock and the pseudo-random sequence chip clock (simplified as the sequence chip clock in the figure), and the correlation result is output to the correlation peak search module to search the local pseudo-random sequence corresponding to the correlation peak Phase, and convert the phase to bit data output;

FIG. 5 shows a schematic block diagram of a message receiver designed according to the present invention.

Secondly, in the digital down conversion module, the digital intermediate frequency signal is mixed with the external input local intermediate frequency signal and the carrier Doppler frequency offset signal of the received signal to complete the digital down conversion, and output the orthogonal IQ two-way baseband data. Two IQ data outputs to the comb filter;

Third, the two data of the baseband IQ are passed to a comb filter, and the comb filter superimposes N sets of pseudo-random sequence data in the same symbol into 1 set of pseudo-random sequence data;

The block diagram of the comb filter is shown in Figure 6: under the control of an external input pseudo-random sequence cycle clock (simplified as the sequence cycle clock in the figure), the comb filter delays the input data sequence by N-1 times. Each delay pseudo random sequence cycle time T _C seconds, and then superimpose the N-1 delay data with the input data and send it to the data interception module. Second, the external control of the symbol clock and sequence cycle clock input by the data interception module. Next, the input data stream is intercepted, and the data with N times superimposed in the same symbol is output, and the data time length is the pseudo-random sequence cycle time T _C seconds. The intercepted data is sent to the matched filtering module.

Then, under the control of the externally input symbol clock and sequence cycle clock, the matched filtering module compares the received data block of length T _C with the pseudo-random sequence generator in the sequence cycle clock and pseudo-random sequence chip clock (in the figure). Correspond to the pseudo-random sequence generated under the control of sequence chip clock) for correlation matching calculation, and the correlation result is output to the correlation peak search module, which searches for the phase of the local pseudo-random sequence corresponding to the correlation peak, and converts the phase to bit data output;

In order to more intuitively reflect the effectiveness of the code-shift keying modulation and demodulation method proposed by the present invention for multiple repeated phase shifts, FIG. 7 shows the R-CSK information transmission error rate of the present invention and the conventional CSK information error rate. The effect comparison chart of the rate, the theoretical calculation of the bit error rate performance of the conventional CSK and R-CSK under the condition of the same transmission information rate, the related symbols and corresponding relationships are as follows:

In conventional CSK, the cycle time of the pseudo-random sequence is T _C , the chip length is L, and the symbol time length is T _S , where T _S = T _C , and a symbol is represented by K-bit, then the base M = 2 ^K , Information rate R = K / T _S ;

The formula for calculating the bit error rate of coherent demodulation symbols for conventional CSK modulation is as follows:

The formula converted to the information bit error rate is as follows:

In R-CSK, the cycle time of the pseudo-random sequence is T _C , the chip length is L, and the symbol time length is T _{S, R.} K _R -bit is used to represent a symbol, and the number of repetitions is N. In order to achieve the transmission with conventional CSK The information rate is consistent, and K _R = NK, T _{S, R} = NT _{S is required} , then the base M _R = 2 ^NK = M ^N , and the information rate R _R = K _R / T _{S, R} = NK / NT _C = K / T _S = R;

The R-CSK CSK modulation of M _R into coherent demodulation symbol error rate calculation formula can be obtained coherent demodulation symbol error rate calculation formula R-CSK:

The formula converted to the information bit error rate is as follows:

For the convenience of calculation and without loss of generality, K = 2 (ie M = 4) and N = 2 (ie M _R = 16) are used for simulation. The effect comparison chart is shown in Fig. 7. It can be seen that at the same information transmission rate With the same E _b / N _0- bit energy-to-noise density ratio, the coherent demodulation information bit error rate obtained by the R-CSK modulation method proposed by the present invention is higher than the coherent demodulation information bit error rate obtained by the conventional CSK modulation method. Low, better transmission performance. The same conclusion can also be obtained from the information bit error rate calculation formula of CSK modulation non-coherent demodulation. It can be inferred from FIG. 7 that under the condition that the information bit error rate is the same, the R-CSK modulation method proposed by the present invention requires less bit energy to transmit information. In other words, when the information bit error rate and the information bit energy are the same, the R-CSK modulation method proposed by the present invention can obtain a higher information transmission rate.

In a code shift keying modulation and demodulation method designed by the present invention with multiple repeated phase shifts, the message broadcast end can ensure that the When the effective information rate is the same, better information transmission bit error rate performance can be obtained; while the CSK modulation information transmission rate can be improved, the signal power density of the receiving end is kept unchanged, and the softness of the demodulated CSK message at the receiving end is greatly increased. Hardware cost and power consumption; the demodulation part uses a comb filter to superimpose the N sets of pseudo-random sequence data in the same symbol into a group of pseudo-random sequence data, which is the same as the rate of pseudo-random sequence and the period of the pseudo-random sequence. Compared with the conventional CSK modulation equal to the symbol length proposed by the present invention, the demodulation cost of the receiver can be effectively reduced while ensuring the same demodulation performance. The method of the invention is applicable to the fields of communication, navigation system design and the like.

The embodiments of the present invention have been described in detail above with reference to the drawings, but the present invention is not limited to the above embodiments, and can be made without departing from the spirit of the present invention within the scope of the knowledge possessed by a person of ordinary skill in the art. Various changes.

Claims

A code shift keying modulation method with multiple repeated phase shifts, which is characterized by repeating the same phase code shift keying modulation for a pseudo-random sequence within the same transmission symbol multiple times, including the following steps:

First, using a preset keying modulation method, code shift keying modulation is performed on a given set of transmission messages to obtain a pseudo-random sequence, wherein the phase of the pseudo-random sequence is controlled by the transmission message;

Then, the above code shift keying modulation process is repeated multiple times, and a plurality of pseudo-random sequences with the same initial phase are sequentially connected to form a modulated transmission symbol, that is, a baseband signal.
The code-shift keying modulation method with multiple repeated phase shifts according to claim 1, characterized in that the baseband signal is constructed as follows,

First, channel coding is performed on the message to obtain an encoded bit stream D (t);

Secondly, according to the symbol clock provided by the timing generator, 1-> K R serial / parallel conversion is performed on the corresponding bit stream after the message encoding, to obtain a parallel data stream, where each K R -bit parallel data duration, that is, symbol time The length is equal to N times of the cycle time of the pseudo-random sequence;

Then, according to the pseudo-random sequence periodic clock provided by the timing generator, the phase selection module generates a pseudo-random sequence phase offset corresponding to the parallel data stream;

Finally, according to the pseudo-random sequence cycle clock, pseudo-random sequence chip clock provided by the timing generator, and the phase offset corresponding to the parallel data stream, a preset keying modulation method is used to The pseudo-random sequence is repeatedly code-shift-keyed to obtain a modulated pseudo-random sequence.
This is the baseband signal S (t).
The code-shift keying modulation method of multiple repeated phase shifts according to claim 2, wherein the symbol clock is an integer multiple of a pseudo-random sequence cycle clock and synchronized with the pseudo-random sequence cycle clock.
The method of code shift keying modulation for multiple repeated phase shifts according to claim 2, characterized in that: the radio frequency transmission signal is constructed as follows:

First, perform carrier modulation on the generated baseband signal S (t) to generate an intermediate frequency carrier signal. The modulation uses BPSK, QPSK, FSK or other equivalent carrier modulation methods;

Second, up-convert the generated intermediate frequency carrier signal to the required transmission frequency to generate a radio frequency carrier signal;

Then, the generated RF carrier signal is power amplified and sent to the transmitting antenna.
A demodulation method for the code-shift keying modulation method with multiple repeated phase shifts according to claims 1 to 4, characterized in that, before the correlation matching demodulation message, a comb filter is used to superimpose the received baseband data To reduce the signal processing workload of the demodulation message at the receiving end,

First, the RF carrier signal received by the receiver antenna is processed by the RF front-end to output a digital intermediate frequency signal;

Second, the digital intermediate frequency signal is passed to the digital down conversion module. The digital down conversion module converts the digital intermediate frequency signal into IQ two under the action of the external input receiver's local intermediate frequency signal and the carrier Doppler frequency offset signal in the received signal Orthogonal baseband signals;

Again, IQ quadrature baseband signal is transmitted to the two comb filter, the comb filter control symbol clock external input pseudo-random sequence and the cycle of the clock, the same symbol period length N of the time T C The data block is superimposed and transformed into a data block with a time length T C , and the result is output to the matched filtering module;

Then, under the control of the externally input symbol clock and pseudo-random sequence cycle clock, the matching filtering module performs correlation matching calculation on the received data block with a length of time T C and the pseudo-random sequence generated by the local pseudo-random sequence generator. The correlation result is output to the correlation peak search module, which searches for the phase of the local pseudorandom sequence corresponding to the correlation peak, and converts the phase into bit data for output;

Finally, the bit data output by the correlation peak search module is used to obtain the transmitted message data through the channel decoding module.
The method according to claim 5, wherein the implementation of the comb filter is as follows:

First, the comb filter delays the input data sequentially by N-1 times under the control of a cycle clock of a pseudo-random sequence input externally, each time the pseudo-random sequence cycle time is T C seconds, and then the N-1 times The delayed data and input data are superimposed and sent to the data interception module;

Secondly, the data interception module intercepts the input data stream under the control of an externally input symbol clock and a pseudo-random sequence cycle clock, and outputs data superimposed N times in the same symbol. The data time length is the pseudo-random sequence cycle time T C seconds.