CN103117769B

CN103117769B - Method for improving signal-to-noise ratio of de-spreading noises in satellite spread spectrum communication receiver, and receiver

Info

Publication number: CN103117769B
Application number: CN201310030584.2A
Authority: CN
Inventors: 徐晓书; 朱德民
Original assignee: First Research Institute of Telecommunication Technology
Current assignee: First Research Institute of Telecommunication Technology
Priority date: 2013-01-25
Filing date: 2013-01-25
Publication date: 2014-11-26
Anticipated expiration: 2033-01-25
Also published as: CN103117769A

Abstract

The invention relates to a method for improving signal-to-noise ratio of de-spreading noises in a satellite spread spectrum communication receiver, and a receiver. The method includes: generating QPSK (quadrature phase shift keying) baseband copied signals according to QPSK signal demodulation data, and using the QPSK baseband copied signals to counteract QPSK baseband signal components in baseband signals. Therefore, the signal-to-noise ratio of spread spectrum signals after de-spreading is increased and spread spectrum communication quality is improved. While spread spectrum gain of spread spectrum signals is unchanged, transmitting power of a spread spectrum transmitter can be lowered, the influence of spread spectrum signals on QPSK signals can be reduced, and invisibility of the spread spectrum signals can be improved. While signal-to-noise ratio of the spread spectrum signals after de-spreading is unchanged, spreading coefficient of the spread spectrum signals can be decreased, and transmission rate of a spread spectrum communication system can be increased.

Description

Method for improving signal-to-noise ratio of despread signal of satellite spread spectrum communication receiver and receiver

Technical Field

The invention relates to the fields of satellite communication, wireless communication, spread spectrum communication and modulation and demodulation.

Background

In the satellite communication system shown in FIG. 1, s₁(t) is the QPSK modulated uplink signal transmitted by transmitter 1, s₂(t) is the spread spectrum modulated uplink signal transmitted by the transmitter 2. s₁(t) and s₂(t) occupy substantially the same frequency and bandwidth, but s₂(t) amplitude ratio s₁(t) is much lower, thereby ensuring s₂(t) to s₁(t) the effect of the transmission is small. FIG. 2 is a hypothetical s₁(t) amplitude ratio s₂(t) amplitudeSignal power spectrum at 20 times higher (26 dB higher power). s₁(t)、s₂(t) after the frequency conversion of the signal by the communication satellite transponder, forming QPSK modulation downlink signal r₁(t) and spread spectrum modulated downlink signal r₂(t)，r₁(t)、r₂(t) also occupies substantially the same frequency and bandwidth, the sum s being maintained₁(t)、s₂(t) same signal amplitude relationship.

QPSK modulated downlink signal r₁Is represented by formula 1:

(formula 1)

Where a is the amplitude of the QPSK modulated signal, which has a positive value; a is_Ik、a_QkRespectively, data information transmitted by an I path and a Q path in the QPSK modulation signal takes the value of +/-1; h is₁(t-kT₁) Is the impulse response of the transmitted signal, and the corresponding frequency response function is that the roll-off coefficient is alpha₁Square root raised cosine function of alpha₁The value range of (1) is between 0 and 1; t is₁Is a_IkAnd a_QkSymbol period of (1/T)₁Is the baud rate of the QPSK signal; omega₁＝2πf₁Is the angular frequency of the QPSK carrier signal.

Spread spectrum modulated downlink signal r₂Is expressed by equation 2:

(formula 2)

Wherein B is the amplitude of the spread spectrum modulated signal, which is always positive; b_Ik、b_QkThe data information transmitted by the spread spectrum modulation signal path I and the path Q respectively has the value of +/-1; m is_i(t)、m_q(t) is the spread spectrum sequence of the path I and the path Q of the spread spectrum modulation signal, the value is +/-1, and the nominal rate and r thereof₁A of (t)_IkAnd a_QkThe same; m is_i(t)、m_qThe rate of (t) is much greater than b_Ik、b_QkVelocity of (1), m_i(t)、m_q(t) and b_Ik、b_QkThe ratio of the rates is called the spreading factor k (or spreading gain); h is₂(t-kT₂) Is the impulse response of the transmitted signal, which corresponds to a frequency response function ofThe roll-off coefficient is alpha₂Square root raised cosine function of alpha₁The value range of (1) is between 0 and 1; t is₂Is m_i(t)、m_qSymbol period of (T), 1/T₂Is its baud rate, its nominal value and T₁The same; omega₂=2πf₂Is the angular frequency of the signal, its nominal value and omega₁The same is true. The receiver input signal r (t) is shown in equation 3:

r(t)=r₁(t)+r₂(t) + n (t) (formula 3)

Where n (t) is Gaussian noise. Receiving a spread spectrum modulated signal r₂(t) the wideband QPSK modulated signal may be r₁(t) is equivalent to gaussian noise. If the spread spectrum modulation signal r is demodulated in a conventional manner₂(t), the signal-to-noise ratio after despreading is shown as formula 4.

(formula 4)

Where k is the spreading factor. As can be seen from formula 4, in order to increase r₂(t) the signal-to-noise ratio after despreading can be increased by k and r₂(t), or decreasing r₁(t), n (t). Increasing k decreases the transmission rate of the spread spectrum system; increase r₂The magnitude of (t) affects r₁(t) a transmission quality; when the noise coefficient of the receiving system is determined, n (t) is a determined value and cannot be reduced randomly; if a method could be found to reduce r without changing the existing parameters₁(t) can be increased₂(t) signal-to-noise ratio after despreading.

Disclosure of Invention

The invention aims to improve the signal-to-noise ratio of a despread signal of a satellite spread spectrum receiver and improve the communication spread spectrum quality under the condition of covering a QPSK large signal occupying the same frequency and the same frequency band.

To solve the above problems, the present invention provides a method for improving a signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver by generating a QPSK baseband replica signal by demodulating data of a QPSK signal and then canceling a QPSK baseband signal component in the baseband signal with the QPSK baseband replica signal, comprising:

an input signal splitter of the receiver acquires an input signal, and divides the input signal into two paths of equal input signals, wherein each path of input signal is the sum of a QPSK modulation downlink signal, a spread spectrum modulation downlink signal and Gaussian noise, and the QPSK modulation downlink signal is far greater than the spread spectrum modulation downlink signal;

a local oscillator carrier generated by a local oscillator of the receiver is synchronous with a carrier of a QPSK modulated downlink signal, the local oscillator frequency is equal to the carrier frequency of the QPSK modulated downlink signal, and an orthogonal local oscillator signal output by the local oscillator is multiplied by each path of input signals respectively to output an I path of difference frequency and sum frequency signal and a Q path of difference frequency and sum frequency signal;

a first QPSK signal matched filter and a second QPSK signal matched filter of the receiver respectively filter an I path difference frequency signal, a Q path difference frequency signal and a Q path sum frequency signal in the I path difference frequency signal, the Q path difference frequency signal and the Q path sum frequency signal, the I path difference frequency signal and the Q path difference frequency signal are output to be used as an I path baseband signal and a Q path baseband signal, the I path baseband signal and the Q path baseband signal are the sum of a QPSK baseband signal, a spread spectrum baseband signal and Gaussian noise, and the amplitude of the QPSK baseband signal is far greater than that of the spread spectrum baseband signal;

a QPSK demodulator of the receiver respectively outputs QPSK demodulation data of the I path and the Q path according to the I path and Q path baseband signals;

a third QPSK matched filter and a fourth QPSK matched filter of the receiver respectively output QPSK regenerated baseband signals of an I path and a Q path according to the QPSK demodulated data of the I path and the Q path;

an amplitude adjusting circuit of the receiver outputs a first, a second and a third pair of QPSK baseband replica signals according to the QPSK regenerated baseband signals of the I path and the Q path and the first, the second and the third amplitude adjusting parameters, and takes the second pair of QPSK baseband replica signals as the best compensation QPSK baseband replica signals, the first pair of QPSK baseband replica signals are used as over compensation QPSK baseband replica signals, and the third pair of QPSK baseband replica signals are used as under compensation QPSK baseband replica signals;

a signal delay module of the receiver respectively performs fixed time delay on the I path baseband signal and the Q path baseband signal, so that the delayed I path baseband signal and Q path baseband signal are matched with the QPSK baseband replica signal in time;

a signal cancellation module of the receiver respectively subtracts delayed I-path and Q-path baseband signals from the first, second and third pairs of QPSK baseband replica signals and outputs first, second and third pairs of spread spectrum baseband signals;

a signal-to-noise ratio module of the receiver despreads the first, second and third pairs of spread spectrum baseband signals, and calculates and outputs signal-to-noise ratios of the first, second and third despread signals;

and a control logic circuit of the receiver adjusts the first, second and third amplitude adjustment parameters according to the signal-to-noise ratios of the first, second and third despread signals, and controls the signal-to-noise ratio module to adjust the signal-to-noise ratios of the corresponding first, second and third despread signals until the signal-to-noise ratio of the second despread signal is the maximum value and the signal-to-noise ratios of the first and second despread signals are equal.

Further, in the above method, if the QPSK signal data information is processed by error correction coding, the step of outputting the I path QPSK regenerated baseband signal and the Q path QPSK regenerated baseband signal by the third QPSK matched filter and the fourth QPSK matched filter according to the I path QPSK demodulated data and the Q path QPSK demodulated data respectively includes:

and a channel error correction decoder of the receiver performs error correction decoding on the I path QPSK demodulation data and the Q path QPSK demodulation data and then encodes the I path QPSK demodulation data and the Q path QPSK demodulation data to generate I path and Q path recoding data, and the third QPSK matched filter and the fourth QPSK matched filter output I path and Q path QPSK regeneration baseband signals according to the I path and Q path recoding data. Since the error-correction decoded re-encoded data has a lower error rate (typically more than 3 orders of magnitude lower) than the demodulated data, the regenerated baseband signal generated therefrom has less distortion.

Further, in the above method, the formula of the input signal is as follows:

the formula of the input signal is as follows:

+ n (t)

= r_{1} (t) + r_{2} (t) + n (t)

where r (t) is the input signal, r₁For QPSK modulation of the downlink signal, r₂Modulating a downlink signal for spread spectrum, wherein n (t) is Gaussian noise;

r₁the formula of (1) is as follows:

a is the amplitude of the QPSK modulated signal, which has a positive value; a is_Ik、a_QkRespectively, data information transmitted by an I path and a Q path in the QPSK modulation signal takes the value of +/-1; h is₁(t-kT₁) Is the impulse response of the transmitted signal, and the corresponding frequency response function is that the roll-off coefficient is alpha₁Square root raised cosine function of alpha₁The value range of (1) is between 0 and 1; t is₁Is a_IkAnd a_QkSymbol period of (1/T)₁Is the baud rate of the QPSK signal; omega₁=2πf₁Is the angular frequency of the QPSK carrier signal, t is time, in seconds,

r₂the formula of (1) is as follows:

b is the amplitude of the spread spectrum modulated signal, which is always positive; b_Ik、b_QkThe data information transmitted by the spread spectrum modulation signal path I and the path Q respectively has the value of +/-1; m is_i(t)、m_q(t) is the spread spectrum sequence of the path I and the path Q of the spread spectrum modulation signal, the value is +/-1, and the nominal rate and r thereof₁A of (t)_IkAnd a_QkThe same; m is_i(t)、m_qThe rate of (t) is much greater than b_Ik、b_QkVelocity of (1), m_i(t)、m_q(t) and b_Ik、b_QkThe ratio of the rates is called the spreading factor k; h is₂(t-kT₂) Is the impulse response of the transmitted signal, which corresponds to a frequency response function with a roll-off factor of alpha₂Square root raised cosine function of alpha₂The value range of (1) is between 0 and 1; t is₂Is m_i(t)、m_qSymbol period of (T), 1/T₂Is its baud rate, its nominal value and T₁The same; omega₂=2πf₂Is the angular frequency of the signal, its nominal value and omega₁The same is true.

Further, in the above method, the formula of the I-baseband signal is as follows:

+ n_{i} (t)

= u_{i} (t) + v_{i} (t) + n_{i} (t)

the formula for the Q baseband signal is as follows:

+ n_{q} (t)

= u_{q} (t) + v_{q} (t) + n_{q} (t)

wherein x is_i(t) is I road baseband signal, x_q(t) Q-band baseband signals, u_i(t)、u_q(t) baseband components of the I and Q paths of the QPSK signal, v_i(t)、v_q(t) are the baseband components of the I and Q paths of the spread spectrum signal,n_i(t)、n_q(t) is Gaussian noise of path I and path Q, the baseband component of QPSK signal is far greater than that of spread spectrum signal, i.e. u_i(t)>>v_i(t),u_q(t)>>v_q(t) due to ω₁、ω₂Substantially equal, v_i(t)、v_qThe amplitude of (t) will vary slowly, A' is u_i(t)、u_q(t) an amplitude component, a' is proportional to a; b' is v_i(t)、v_qThe amplitude component of (t), B', is proportional to B.

Further, in the above method, the formula of the QPSK regenerated baseband signals of the I path and the Q path is:

wherein u'_i(t) is the I-line QPSK regenerated baseband signal, u'_q(t) is Q-path QPSK regenerated baseband signal, a'_IkIs line I QPSK demodulated data, a'_QkFor path I QPSK demodulated data, h₁(t-kT₁) Is the impulse impact response of the third QPSK matched filter and the fourth QPSK matched filter, and A 'is u'_i(t)、u′_q(t) amplitude component.

Further, in the above method, the first, second and third pairs of QPSK baseband replica signals are formulated as follows:

wherein, u "_in(t) first, second and third different amplitude path I QPSK baseband replica signals, u "_qn(t) Q-way QPSK baseband complex with first, second and third different amplitudesSystem signal, p₁、p₂、p₃Respectively a first, a second and a third amplitude adjustment parameter, p₁>p₂>p₃，p₁-p₂=p₂-p₃Δ, the control logic circuit adjusts p according to the signal-to-noise ratio after despreading the spread spectrum signal₁、p₂、p₃So that the second pair of QPSK baseband copies signal u "_i2(t)、u"_q2(t) baseband component u most approximate to paths I and Q of QPSK signal_i(t)、u_q(t)。

Further, in the above method, the first, second and third pairs of spread spectrum baseband signals are formulated as follows:

wherein, y_in(t) is the I-path spread spectrum baseband signal, y_qn(t) is Q-path spread spectrum baseband signal, Δ u_in(t)=u_i(t)-u"_in(t) is the residual component of the I-path QPSK baseband signal component, Δ u_qn(t)＝u_q(t)-u"_qn(t), is the residual component of the Q-path QPSK baseband signal component.

Further, in the above method, the snr module calculates and outputs snrs of the first, second, and third despread signals according to the following formula:

wherein,signal-to-noise ratio, m, of the first, second and third despread signals, respectively_i(t) is the local spreading sequence of path I, m_q(t) is Q local spread spectrum sequences, and the spread spectrum coefficient is k, z_i1(t)、z_q1(t)、z_i2(t)、z_q2(t) spreading the baseband signal y by the I route_in(t) Q path spread spectrum baseband signal y_qn(t) are each associated with said local spreading sequence m_i(t) and m_q(t) performing a modulo two addition to generate, S_{Despreading n}To de-spread the signal energy, N_{Despreading n}To de-spread signal noise energy, de-spread signal energy S is generated when local I and Q spreading sequences are synchronized with the input signal spreading sequence_{Despreading n}A peak is reached.

Further, in the above method, in the step of adjusting the first, second and third amplitude adjustment parameters by the control logic circuit of the receiver according to the snr of the first, second and third despread signals, when the first, second and third amplitude adjustment parameters are adjusted by the control logic circuit of the receiver, the control logic circuit of the receiver is configured to adjust the first, second and third amplitude adjustment parameters according to the snr of the first, second and third despread signalsWhen, p is decreased_n(ii) a When in useWhen p is increased_n(ii) a When in useAnd isWhen it is maximum, consider u "_i2(t)、u"_q2(t) is adjusted to optimum, p_nThe values were unchanged.

According to another aspect of the present invention, there is provided a receiver for improving a signal-to-noise ratio of a despread signal of satellite spread spectrum communication, the receiver comprising:

the system comprises an input signal splitter, a signal processing unit and a signal processing unit, wherein the input signal splitter is used for acquiring an input signal and dividing the input signal into two paths of equal input signals, each path of input signal is the sum of a QPSK modulation downlink signal, a spread spectrum modulation downlink signal and Gaussian noise, and the QPSK modulation downlink signal is far larger than the spread spectrum modulation downlink signal;

the local oscillator is used for generating orthogonal local oscillator signals required by demodulation, the local oscillator carrier is synchronous with the carrier of the QPSK modulated downlink signals, the local oscillator frequency is equal to the carrier frequency of the QPSK modulated downlink signals, and the orthogonal local oscillator signals output by the local oscillator are multiplied by each path of input signals respectively to output I path difference frequency, sum frequency signals and Q path difference frequency and sum frequency signals;

the first QPSK signal matched filter and the second QPSK signal matched filter are used for respectively filtering an I path difference frequency signal, a Q path difference frequency signal and a Q path sum frequency signal in the I path difference frequency signal, the Q path difference frequency signal and the Q path sum frequency signal, the I path difference frequency signal and the Q path difference frequency signal are output to be used as an I path baseband signal and a Q path baseband signal, the I path difference frequency signal and the Q path baseband signal are the sum of a QPSK baseband signal, a spread spectrum baseband signal and Gaussian noise, and the amplitude of the QPSK baseband signal is far greater than that of the spread spectrum baseband signal;

the QPSK demodulator is used for respectively outputting QPSK demodulation data of the I path and the Q path according to the I path and Q path baseband signals;

the third QPSK matched filter and the fourth QPSK matched filter are used for outputting QPSK regenerated baseband signals of the path I and the path Q according to the QPSK demodulated data of the path I and the path Q respectively;

an amplitude adjusting circuit, which is used for outputting a first, a second and a third pair of QPSK baseband reproduction signals according to the I path Q path QPSK reproduction baseband signal and a first, a second and a third amplitude adjusting parameters, and taking the second pair of QPSK baseband reproduction signals as the best compensation QPSK baseband reproduction signals, the first pair of QPSK baseband reproduction signals as over compensation QPSK baseband reproduction signals, and the third pair of QPSK baseband reproduction signals as under compensation QPSK baseband reproduction signals;

the signal delay module is used for respectively carrying out fixed time delay on the I-path baseband signals and the Q-path baseband signals, so that the delayed I-path baseband signals and Q-path baseband signals are matched with the QPSK baseband replica signals in time;

the signal cancellation module is used for subtracting delayed I-path baseband signals and delayed Q-path baseband signals from the first, second and third pairs of QPSK baseband replica signals respectively and outputting first, second and third pairs of spread spectrum baseband signals;

a signal-to-noise ratio module for despreading the first, second and third pairs of spread spectrum baseband signals, respectively, and calculating and outputting signal-to-noise ratios of the first, second and third despread signals;

and the control logic circuit is used for adjusting the first amplitude adjustment parameter, the second amplitude adjustment parameter and the third amplitude adjustment parameter according to the signal-to-noise ratios of the first despread signal, the second despread signal and the third despread signal, and controlling the signal-to-noise ratio module to adjust the signal-to-noise ratios of the corresponding first despread signal, the second despread signal and the third despread signal until the signal-to-noise ratio of the second despread signal is the maximum value and the signal-to-noise ratios of the first despread signal and the second despread signal.

Further, in the above receiver, the receiver further includes a channel error correction decoder, configured to perform error correction decoding on the I-path and Q-path QPSK demodulated data and then re-encode the I-path and Q-path QPSK demodulated data to generate I-path and Q-path re-encoded data, where the third QPSK matched filter and the fourth QPSK matched filter are configured to output I-path and Q-path QPSK regenerated baseband signals according to the I-path and Q-path re-encoded data.

Further, in the above receiver, the formula of the input signal is as follows:

+ n (t)

= r_{1} (t) + r_{2} (t) + n (t)

r₁the formula of (1) is as follows:

r₂the formula of (1) is as follows:

Further, in the above receiver, the formula of the input signal is as follows:

+ n (t)

= r_{1} (t) + r_{2} (t) + n (t)

r₁the formula of (1) is as follows:

r₂the formula of (1) is as follows:

Further, in the above receiver, the formula of the QPSK regenerated baseband signals of the I path and the Q path is:

Further, in the above receiver, the formula of the first, second and third pairs of QPSK baseband replica signals is as follows:

wherein, u "_in(t) first, second and third different amplitude path I QPSK baseband replica signals, u "_qn(t) Q-way QP of first, second and third different magnitudesSK baseband replica signal, p₁、p₂、p₃Respectively a first, a second and a third amplitude adjustment parameter, p₁>p₂>p₃，p₁-p₂=p₂-p₃= delta, the control logic adjusts p according to the signal-to-noise ratio after despreading the spread spectrum signal₁、p₂、p₃So that the second pair of QPSK baseband copies signal u "_i2(t)、u"_q2(t) baseband component u most approximate to paths I and Q of QPSK signal_i(t)、u_q(t)。

Further, in the above receiver, the formula of the first, second and third pairs of spread spectrum baseband signals is as follows:

wherein, y_in(t) is the I-path spread spectrum baseband signal, y_qn(t) is Q-path spread spectrum baseband signal, Δ u_in(t)=u_i(t)-u"_in(t) is the residual component of the I-path QPSK baseband signal component, Δ u_qn(t)=u_q(t)-u"_qn(t), is the residual component of the Q-path QPSK baseband signal component.

Further, in the above receiver, the snr module calculates and outputs snrs of the first, second, and third despread signals according to the following formula:

Further, in the above receiver, in the step of adjusting the first, second and third amplitude adjustment parameters according to the snr of the first, second and third despread signals by the control logic of the receiver, when the first, second and third amplitude adjustment parameters are adjusted by the control logic of the receiver, the second and third despread signals are received by the receiverWhen, p is decreased_n(ii) a When in useWhen p is increased_n(ii) a When in useAnd isWhen it is maximum, consider u "_i2(t)、u"_q2(t) is adjusted to optimum, p_nThe values were unchanged.

Under the condition of covering QPSK large signals occupying the same frequency and the same frequency band, compared with the prior art, the invention can improve the signal-to-noise ratio of despread signals of a satellite spread spectrum receiver and improve the communication spread spectrum quality; under the condition that the requirement of the spread spectrum gain of the spread spectrum signal is not changed, the transmitting power of a spread spectrum transmitter can be reduced, the influence of the spread spectrum signal on a QPSK signal is reduced, and the concealment of the spread spectrum signal is improved; under the condition that the signal-to-noise ratio requirement is unchanged after the spread spectrum signal is despread, the spread spectrum coefficient of the spread spectrum signal can be reduced, and the transmission rate of a spread spectrum communication system is improved.

Drawings

Fig. 1 is a schematic diagram of a spread spectrum satellite communication system under QPSK large signal masking conditions occupying the same frequency and the same frequency band;

FIG. 2 shows a QPSK modulated signal S₁Spread spectrum modulated signal S₂A schematic spectrum diagram of (a);

FIG. 3 is a flow chart of a method for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver in accordance with an embodiment of the present invention;

FIG. 4 is a schematic diagram of a receiver operation according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of an embodiment of the present invention for decoding and then encoding encoded information to improve distortion of a QPSK regenerated baseband signal;

FIG. 6 is a schematic diagram of the signal-to-noise ratio calculation of a despread signal in accordance with an embodiment of the present invention;

fig. 7 is a QPSK baseband component cancellation flow diagram according to an embodiment of the present invention;

fig. 8 is a diagram illustrating a signal-to-noise ratio after despreading a spread spectrum signal in a conventional manner;

fig. 9 is a diagram illustrating the signal-to-noise ratio of a spread spectrum signal after despreading according to an embodiment of the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Example one

For the satellite spread spectrum communication system under the same frequency and same bandwidth QPSK large signal mask as shown in fig. 1, the present embodiment provides a method for improving the signal-to-noise ratio of the despread signal of the satellite spread spectrum communication receiver as shown in fig. 3 and 4, the basic principle of the method of the present embodiment is to generate a QPSK baseband replica signal by QPSK demodulating data, and then cancel the QPSK baseband signal component in the baseband signal by using the QPSK baseband replica signal, thereby improving the signal-to-noise ratio of the signal after despreading the spread spectrum signal, the method includes:

step S1, the input signal splitter 1 obtains an input signal, and divides the input signal into two equal paths of input signals, where each path of input signal is a sum of a QPSK modulated downlink signal, a spread spectrum modulated downlink signal, and gaussian noise, where the QPSK modulated downlink signal is far greater than the spread spectrum modulated downlink signal.

Specifically, the input signal is as follows:

+ n (t)

= r_{1} (t) + r_{2} (t) + n (t)

(formula 5)

Where r (t) is the input signal, r₁For QPSK modulation of the downlink signal, r₂For spread spectrum modulation of the downlink signal, n (t) is Gaussian noise, according to the conditions described in the background, spread spectrum modulation signal r₂(t) has a much smaller amplitude than the QPSK modulated signal r₁(t) amplitude (typically less than 1/20), spread spectrum modulated signal r₂(t) does not affect QPSK modulated signal r₁Normal demodulation of (t).

r₁As shown in formula 1:

(formula 1)

Where a is the amplitude of the QPSK modulated signal, which has a positive value; a is_Ik、a_QkRespectively are data information transmitted by an I path and a Q path in a QPSK modulation signal,the value is +/-1; h is₁(t-kT₁) Is the impulse response of the transmitted signal, and the corresponding frequency response function is that the roll-off coefficient is alpha₁Square root raised cosine function of alpha₁The value range of (1) is between 0 and 1; t is₁Is a_IkAnd a_QkSymbol period of (1/T)₁Is the baud rate of the QPSK signal; omega₁＝2πf₁Is the angular frequency of the QPSK carrier signal, t is time, in seconds.

r₂As shown in formula 2:

(formula 2)

Wherein B is the amplitude of the spread spectrum modulated signal, which is always positive; b_Ik、b_QkThe data information transmitted by the spread spectrum modulation signal path I and the path Q respectively has the value of +/-1; m is_i(t)、m_q(t) is the spread spectrum sequence of the path I and the path Q of the spread spectrum modulation signal, the value is +/-1, and the nominal rate and r thereof₁A of (t)_IkAnd a_QkThe same; m is_i(t)、m_qThe rate of (t) is much greater than b_Ik、b_QkVelocity of (1), m_i(t)、m_q(t) and b_Ik、b_QkThe ratio of the rates is called the spreading factor k; h is₂(t-kT₂) Is the impulse response of the transmitted signal, which corresponds to a frequency response function with a roll-off factor of alpha₂Square root raised cosine function of alpha₂The value range of (1) is between 0 and 1; t is₂Is m_i(t)、m_qSymbol period of (T), 1/T₂Is its baud rate, its nominal value and T₁The same; omega₂=2πf₂Is the angular frequency of the signal, its nominal value and omega₁The same is true.

Step S2, a local oscillator carrier generated by a local oscillator 2 of the receiver is synchronized with the carrier of the QPSK modulated downlink signal, the local oscillator frequency is equal to the carrier frequency of the QPSK modulated downlink signal, and the local oscillator carrier is localThe orthogonal local oscillation signal output by the oscillator is multiplied by each path of input signal respectively to output the I path of difference frequency and sum frequency signal and the Q path of difference frequency and sum frequency signal. Specifically, after the QPSK modulated signal is normally demodulated, the local oscillator carrier of the receiver is synchronized with the carrier of the QPSK signal under the control of the carrier synchronization circuit, and the local oscillator frequency ω of the receiver is₀Equal to the carrier frequency omega of the input QPSK modulated signal₁。

Step S3, the first QPSK signal matched filter 3 and the second QPSK signal matched filter 4 of the receiver filter the I-path difference frequency, the sum frequency signal and the Q-path difference frequency, the I-path sum frequency signal and the Q-path sum frequency signal respectively, and output the I-path difference frequency signal and the Q-path difference frequency signal as the I-path and Q-path baseband signal x_i(t)、x_qAnd (t), the baseband signals of the I path and the Q path are the sum of QPSK baseband signals, spread spectrum baseband signals and Gaussian noise, wherein the amplitude of the QPSK baseband signals is far greater than that of the spread spectrum baseband signals.

Specifically, the I-band signal is as follows:

+ n_{i} (t)

= u_{i} (t) + v_{i} (t) + n_{i} (t)

(formula 6)

The Q-band signals are as follows:

+ n_{q} (t)

= u_{q} (t) + v_{q} (t) + n_{q} (t)

(formula 7)

Wherein x is_i(t) is I road baseband signal, x_q(t) Q-band baseband signals, u_i(t)、u_q(t) baseband components of the I and Q paths of the QPSK signal, v_i(t)、v_q(t) baseband components of the I and Q paths of the spread spectrum signal, n_i(t)、n_q(t) Gaussian noise of I path and Q path respectivelyThe baseband component of the QPSK signal is much larger than the baseband component of the spread spectrum signal, i.e. u_i(t)>>v_i(t),u_q(t)>>v_q(t) due to ω₁、ω₂Substantially equal, v_i(t)、v_qThe amplitude of (t) will vary slowly, A' is u_i(t)、u_q(t) an amplitude component, a' is proportional to a; b' is v_i(t)、v_qThe amplitude component of (t), B', is proportional to B.

Step S4, a QPSK demodulator 5 of the receiver outputs QPSK demodulation data a 'of I-path and Q-path respectively according to the I-path and Q-path baseband signals'_Ik、、a'_Qk。

Specifically, after QPSK signal demodulation, I-path QPSK demodulation data a 'are output'_IkAnd Q-path QPSK demodulated data a'_QkThe value is +/-1; most of a 'except a few bit errors'_IkAnd a'_QkData information a transmitted with QPSK signal_IkAnd a_QkThe same is true.

Step S5, outputting QPSK regenerated baseband signals u 'for the I path and Q path according to the QPSK demodulated data for the I path and Q path by using a third QPSK matched filter 6 and a fourth QPSK matched filter 7 of the receiver respectively'_i(t)、u'_q(t)。

Specifically, QPSK demodulated data a'_IkAnd a'_QkRespectively input impulse response of h₁A third QPSK matched filter and a fourth QPSK matched filter of (t-kT) for generating an I-path QPSK regenerated baseband signal u ' and a Q-path QPSK regenerated baseband signal u ' of the formula 8 '_i(t) and u'_q(t)。

(formula 8)

If the QPSK signal data information is subjected to the error correction coding process, step S5 includes:

a channel error correction decoder 13 of the receiver performs error correction decoding on the I path and Q path QPSK demodulation data and then encodes the decoded data to generate I path and Q path re-encoded data, and the third QPSK matched filter and the fourth QPSK matched filter output I path and Q path QPSK regeneration baseband signals according to the I path and Q path re-encoded data.

Specifically, to reduce QPSK demodulated data a'_Ik、a'_QkBit error-induced reproduced baseband signal u'_i(t)、u'_q(t) distortion if QPSK signal data information a_Ik、a_QkThe demodulated data a 'can be processed by error correction coding'_Ik、a'_QkError correction decoded and re-encoded to produce re-encoded data a'_Ik、a"_QkThen encodes the data a "_IkAnd a "_QkRespectively input impulse response of h₁(t-kT₁) Generates QPSK demodulated data reproduction baseband signal u 'of the formula 9'_i(t) and u'_q(t) (see FIG. 5). Due to and'_Ik、a'_QkCompared with, a "_Ik、a"_QkWith lower error rates (typically more than 3 orders of magnitude lower), denoted by a "_Ik、a"_QkU's of production'_i(t)、u'_q(t) has less distortion.

(formula 9)

In step S6, an amplitude adjustment circuit 8 of the receiver outputs first, second, and third pairs of QPSK baseband replica signals according to the I-path QPSK regenerated baseband signal, the Q-path QPSK regenerated baseband signal, and the first, second, and third amplitude adjustment parameters, and uses the second pair of QPSK baseband replica signals as best compensation QPSK baseband replica signals, the first pair of QPSK baseband replica signals as over-compensation QPSK baseband replica signals, and the third pair of QPSK baseband replica signals as under-compensation QPSK baseband replica signals.

Specifically, QPSK regenerated baseband signal u'_i(t) and u'_q(t) forming three pairs of QPSK baseband signal replicas through the amplitude adjustment circuit, the first, second and third pairs of QPSK baseband replica signals having the equation 10.

(formula 10)

Wherein, u "_in(t) first, second and third different amplitude path I QPSK baseband replica signals, u "_qn(t) for the first, second and third different amplitude Q-way QPSK baseband replica signals, p₁、p₂、p₃Respectively a first, a second and a third amplitude adjustment parameter, p₁>p₂>p₃，p₁-p₂=p₂-p₃Δ, the control logic circuit adjusts p according to the signal-to-noise ratio after despreading the spread spectrum signal₁、p₂、p₃So that the second pair of QPSK baseband copies signal u "_i2(t)、u"_q2(t) baseband component u most approximate to paths I and Q of QPSK signal_i(t)、u_q(t) when the second way isWhen the optimal compensation is performed, the despreading signal-to-noise ratio reaches the maximum value; at the moment, the first pair is over-compensated, and the despreading signal-to-noise ratio of the first pair is smaller than that of the second pair; the third path is under-compensated, and the de-spread signal-to-noise ratio is smaller than that of the second pair; the first, second and third pairs of despread signal-to-noise ratios form a peak to determine whether optimum compensation has been achieved.

Step S7, a signal delay module 9 of the receiver respectively performs fixed delay on the I path baseband signal and the Q path baseband signal, so that the delayed I path baseband signal and Q path baseband signal are matched with the QPSK baseband replica signal in time.

In particular, to compensate for u "_i1(t)～u"_i3(t)，u"_q1(t)～u"_q3(t) forming the required time delay, I path, Q path baseband signal x_i(t)、x_q(t) subject to a respective fixed delay, the delayed signal being x'_i(t)、x'_q(t) represents.

Step S8, a signal cancellation module 10 of the receiver subtracts the delayed I-path baseband signal and the delayed Q-path baseband signal from the first, second, and third pairs of QPSK baseband replica signals, and outputs first, second, and third pairs of spread spectrum baseband signals.

Specifically, x'_i(t) are each independently of u "_i1(t)、u"_i2(t)、u"_i3(t) minus, x'_iU in (t)_iThe (t) components are cancelled out to produce three I-path spread spectrum modulation baseband signals y_i1(t)、y_i2(t)、y_i3(t)；x'_q(t) are each independently of u "_q1(t)、u"_q2(t)、u"_q3(t) minus, x'_qU in (t)_qThe (t) components are cancelled out to generate three Q paths of spread spectrum modulation baseband signals y_q1(t)、y_q2(t)、y_q3(t) of (d). The first, second and third pairs of spread spectrum baseband signals are as in equation 11.

(formula 11)

In step S9, a signal-to-noise ratio module 11 of the receiver despreads the first, second, and third pairs of spread baseband signals, respectively, and calculates and outputs signal-to-noise ratios of the first, second, and third despread signals.

Specifically, the first, second, and third pairs of orthogonal spread spectrum baseband signals are despread respectively and the despread signal-to-noise ratio is calculated, and if the spreading factor is k, the despread signal-to-noise ratio of the spread spectrum signal is represented by formula 12:

(formula 12)

When QPSK baseband copies signal u "_in(t) and u "_qn(t) when perfectly matched with QPSK baseband signal,. DELTA.u_fin(t)、Δu_qn(t) tends to zero, and the signal-to-noise ratio after despreading the spread signal is represented by equation 13:

(formula 13)

Wherein, [ kv (t)]²=[kv_i(t)]²+[kv_q(t)]²Is the despread signal energy, [ n (t) ]]²=[n_i(t)]²+[n_q(t)]²Is the despread noise energy. Compared with the signal-to-noise ratio of the despread signal of the spread spectrum receiver in the conventional mode as in the formula 4, the signal-to-noise ratio of the despread signal obtained by the embodiment is obviously improved.

Specifically, the snr of the first, second, and third despread signals is calculated by equations 14, 15, and 16.

(formula 14)

(formula 15)

(formula 16)

Wherein,for the first, second and third despread signals signal-to-noise ratio, y_in(t)、y_qn(t) is a spread spectrum modulated baseband signal, m_i(t) is the local spreading sequence of path I, m_q(t) is Q local spread spectrum sequences, and k is a spread spectrum coefficient; as shown in FIG. 6, z_i1(t)、z_q1(t)、z_i2(t)、z_q2(t) spreading the baseband signal y by the I route_in(t) and Q-path spread spectrum baseband signal y_qn(t) local spread spectrum sequences m respectively corresponding to paths I and Q of spread spectrum modulation signals_i(t) and m_q(t) performing modulo two addition to generate; s_{Despreading n}To de-spread the signal energy, N_{Despreading n}To de-spread signal noise energy; when the local I path and Q path spread spectrum sequences are synchronous with the input signal spread spectrum sequence, the energy S of the de-spread signal_DespreadingA peak value is reached; n estimated by equation 16_DespreadingIn contains delta u_i(t)、Δu_q(t)、v_i(t)、v_q(t)，n_i(t)、n_q(t) component due to v in general_i(t)、v_qThe (t) component being much smaller than n_i(t)、n_q(t) component, v_i(t)、v_qThe effect of (t) is negligible.

Step S10, a control logic circuit 12 of the receiver adjusts the first, second, and third amplitude adjustment parameters according to the snrs of the first, second, and third despread signals, and controls the snr module to adjust the snrs of the corresponding first, second, and third despread signals until the snr of the second despread signal is the maximum and the snrs of the first and second despread signals are equal.

Specifically, the delayed baseband signal x'_i(t)、x'_q(t) and QPSK baseband replica signal u "_in(t)、u"_qn(t) (n =1, 2, 3) by subtraction, x'_i(t)、x'_q(t) QPSK baseband component reduction, producing first, second and third pairs of spread baseband signals y_in(t)、y_qn(t) (n =1, 2, 3). Calculating spread spectrum baseband signal y from equations 14, 15, and 16_in(t)、y_qn(t) (N =1, 2, 3) signal-to-noise ratio (S/N) after despreading_{Despreading n}(n =1, 2, 3). According to (S/N)_{Despreading n}Varying the amplitude adjustment parameter p_nNumerical values of (n =1, 2, 3) (flow chart shown in fig. 7): when in useWhen, p is decreased_n(ii) a When in useWhen p is increased_n(ii) a When in useAnd isWhen it is maximum, consider u "_i2(t)、u"_q2(t) is adjusted to optimum, p_nThe values were unchanged. By continuously adjusting p_nFinally, x'_i(t)、x'_qThe QPSK baseband components in (t) are cancelled out to obtain the maximum despread signal-to-noise ratio (S/N)_{Despreading 2}. When the second path is in the best compensation, the de-spread signal-to-noise ratio reaches the maximum value; at the moment, the path 1 is over-compensated, and the de-spread signal-to-noise ratio is small compared with the second path; the 3 rd path is under-compensated, and the de-spread signal-to-noise ratio is smaller than that of the second path; the signal-to-noise ratios of the first, second and third despread signals form a peak to determine whether optimum compensation is achieved.

Fig. 8 and fig. 9 show simulation results of the signal-to-noise ratio after despreading the QPSK modulation signal with a spreading factor of 127 (power of 26 dB) which is 20 times higher than the amplitude of the spread-spectrum modulation signal, and the signal-to-noise ratio of the received signal is 20 dB; wherein fig. 8 is the signal-to-noise ratio after despreading the spread spectrum signal in the conventional manner, and fig. 9 is the signal-to-noise ratio after despreading the spread spectrum signal in the present invention; in fig. 8 and 9, the horizontal axis is time, the vertical axis is power (in dB), the white line in the upper half of the graph is power after despreading the spread signal, and the white area in the lower half of the graph is noise, and it can be seen that the signal-to-noise ratio of the spread signal is improved by more than 10dB by the method of this embodiment.

By adopting the method of the embodiment in the satellite communication system shown in fig. 1, under the same transmission condition as the conventional manner, the signal-to-noise ratio of the spread spectrum signal after despreading can be improved, and the transmission quality of spread spectrum communication can be improved; under the condition that the requirement of the spread spectrum gain of the spread spectrum signal is not changed, the transmitting power of a spread spectrum transmitter can be reduced, the influence of the spread spectrum signal on a QPSK signal is reduced, and the concealment of the spread spectrum signal is improved; under the condition that the signal-to-noise ratio requirement is unchanged after the spread spectrum signal is despread, the spread spectrum coefficient of the spread spectrum signal can be reduced, and the transmission rate of a spread spectrum communication system is improved.

Example two

As shown in fig. 4, the present invention also provides another receiver for improving the signal-to-noise ratio of a despread signal of satellite spread spectrum communication, which includes an input signal splitter 1, a local oscillator 2, a first QPSK signal matched filter 3, a second QPSK signal matched filter 4, a QPSK demodulator 5, a third QPSK matched filter 6, a fourth QPSK matched filter 7, an amplitude adjusting circuit 8, a signal delay module 9, a signal cancellation module 10, a signal-to-noise ratio module 11, and a control logic circuit 12.

The input signal splitter 1 is configured to obtain an input signal, and divide the input signal into two equal paths of the input signal, where each path of the input signal is a sum of a QPSK modulated downlink signal, a spread spectrum modulated downlink signal, and gaussian noise, and the QPSK modulated downlink signal is far greater than the spread spectrum modulated downlink signal.

Specifically, the input signal is as follows:

+ n (t)

= r_{1} (t) + r_{2} (t) + n (t)

(formula 5)

r₁As shown in formula 1:

(formula 1)

Where a is the amplitude of the QPSK modulated signal, which has a positive value; a is_Ik、a_QkRespectively, data information transmitted by an I path and a Q path in the QPSK modulation signal takes the value of +/-1; h is₁(t-kT₁) Is the impulse response of the transmitted signal, and the corresponding frequency response function is that the roll-off coefficient is alpha₁Square root raised cosine function of alpha₁The value range of (1) is between 0 and 1; t is₁Is a_IkAnd a_QkSymbol period of (1/T)₁Is the baud rate of the QPSK signal; omega₁＝2πf₁Is the angular frequency of the QPSK carrier signal, t is time, in seconds.

r₂As shown in formula 2:

(formula 2)

The local oscillator 2 is used for generating orthogonal local oscillator signals required by demodulation, the local oscillator carrier is synchronous with the carrier of the QPSK modulated downlink signals, the local oscillator frequency is equal to the carrier frequency of the QPSK modulated downlink signals, and the orthogonal local oscillator signals output by the local oscillator are multiplied by each path of input signals respectively to output I path difference frequency, sum frequency signals and Q path difference frequency and sum frequency signals. Specifically, after the QPSK modulated signal is normally demodulated, the local oscillator carrier of the receiver is synchronized with the carrier of the QPSK signal under the control of the carrier synchronization circuit, and the local oscillator frequency ω of the receiver is₀Equal to the carrier frequency omega of the input QPSK modulated signal₁。

A first QPSK signal matched filter 3 and a second QPSK signal matched filter 4 for respectivelyFiltering the I path difference frequency and sum frequency signals and the Q path difference frequency and sum frequency signals in the I path difference frequency and sum frequency signals, and outputting the I path difference frequency signals and the Q path difference frequency signals as I path difference frequency and Q path baseband signals x_i(t)、x_qAnd (t), the baseband signals of the I path and the Q path are the sum of QPSK baseband signals, spread spectrum baseband signals and Gaussian noise, wherein the amplitude of the QPSK baseband signals is far greater than that of the spread spectrum baseband signals.

Specifically, the I-band signal is as follows:

+ n_{i} (t)

= u_{i} (t) + v_{i} (t) + n_{i} (t)

(formula 6)

The Q-band signals are as follows:

+ n_{q} (t)

= u_{q} (t) + v_{q} (t) + n_{q} (t)

(formula 7)

Wherein x is_i(t) is I road baseband signal, x_q(t) Q-band baseband signals, u_i(t)、u_q(t) baseband components of the I and Q paths of the QPSK signal, v_i(t)、v_q(t) baseband components of the I and Q paths of the spread spectrum signal, n_i(t)、n_q(t) is Gaussian noise of path I and path Q, the baseband component of QPSK signal is far greater than that of spread spectrum signal, i.e. u_i(t)>>v_i(t),u_q(t)>>v_q(t) due to ω₁、ω₂Substantially equal, v_i(t)、v_qThe amplitude of (t) will vary slowly, A' is u_i(t)、u_q(t) an amplitude component, a' is proportional to a; b' is v_i(t)、v_qThe amplitude component of (t), B', is proportional to B.

The QPSK demodulator 5 is used for outputting QPSK demodulated data a 'of the I path and the Q path respectively according to the baseband signals of the I path and the Q path'_Ik、、a'_Qk。

Specifically, after QPSK signal demodulation, I-path QPSK demodulation data a 'are output'_IkAnd Q-path QPSK demodulated data a'_QkThe value is +/-1; except a small amountExcept for bit errors, most of a'_IkAnd a'_QkData information a transmitted with QPSK signal_IkAnd a_QkThe same is true.

A third QPSK matched filter 6 and a fourth QPSK matched filter 7 for outputting an I-path QPSK regenerated baseband signal u ' and a Q-path QPSK regenerated baseband signal u ' according to the I-path QPSK demodulated data and the Q-path QPSK demodulated data '_i(t)、u'_q(t)。

(formula 8)

Wherein u'_i(t) is the I-line QPSK regenerated baseband signal, u'_q(t) is Q-path QPSK regenerated baseband signal, a'_IkIs line I QPSK demodulated data, a'_QkFor path I QPSK demodulated data, h₁(t-kT₁) Is the impulse shock response of the third QPSK matched filter 6 and the fourth QPSK matched filter 7, and A 'is u'_i(t)、u′_q(t) amplitude component.

If the QPSK signal data information is processed by error correction coding, the receiver further includes a channel error correction decoder 13 for error correction decoding the I path and Q path QPSK demodulated data and then re-encoding to generate I path and Q path re-encoded data, and the third QPSK matched filter 6 and the fourth QPSK matched filter 7 output I path and Q path QPSK regenerated baseband signals according to the I path and Q path re-encoded data.

(formula 9)

The amplitude adjusting circuit 8 is configured to output first, second, and third pairs of QPSK baseband replica signals according to the I-path Q-path QPSK regenerated baseband signal and the first, second, and third amplitude adjustment parameters, and use the second pair of QPSK baseband replica signals as best compensation QPSK baseband replica signals, the first pair of QPSK baseband replica signals as over-compensation QPSK baseband replica signals, and the third pair of QPSK baseband replica signals as under-compensation QPSK baseband replica signals.

(formula 10)

Wherein, u "_in(t) first, second and third different amplitude path I QPSK baseband replica signals, u "_qn(t) for the first, second and third different amplitude Q-way QPSK baseband replica signals, p₁、p₂、p₃Respectively a first, a second and a third amplitude adjustment parameter, p₁>p₂>p₃，p₁-p₂=p₂-p₃Δ, the control logic circuit adjusts p according to the signal-to-noise ratio after despreading the spread spectrum signal₁、p₂、p₃So that the second pair of QPSK baseband copies signal u "_i2(t)、u"_q2(t) baseband component u most approximate to paths I and Q of QPSK signal_i(t)、u_q(t) when the second path is at the optimum compensation, the despread signal-to-noise ratio reaches a maximum value; at the moment, the first pair is over-compensated, and the despreading signal-to-noise ratio of the first pair is smaller than that of the second pair; the third path is under-compensated, and the de-spread signal-to-noise ratio is smaller than that of the second pair; the first, second and third pairs of despread signal-to-noise ratios form a peak to determine whether optimum compensation has been achieved.

The signal delay module 9 is configured to perform fixed delay on the I path baseband signal and the Q path baseband signal, respectively, so that the delayed I path baseband signal and Q path baseband signal are matched with the QPSK baseband replica signal in time.

In particular, to compensate for u "_i1(t)～u"_i3(t)，u"_q1(t)～u"_q3(t) forming the required time delay, I path, Q path baseband signal x_i(t)、x_q(t) is subjected to a corresponding fixing delayTime delayed by the rear signal x'_i(t)、x'_q(t) represents.

The signal cancellation module 10 is configured to subtract the delayed I-path baseband signal and the delayed Q-path baseband signal from the first, second, and third pairs of QPSK baseband replica signals, and output a first, second, and third pairs of spread spectrum baseband signals.

(formula 11)

The snr module 11 is configured to despread the first, second, and third pairs of spread spectrum baseband signals, respectively, and calculate and output snr of the first, second, and third despread signals.

(formula 12)

When QPSK baseband copies signal u "_in(t) and u "_qn(t) when perfectly matched with QPSK baseband signal,. DELTA.u_in(t)、Δu_qn(t) tends to zero, and the signal-to-noise ratio after despreading the spread signal is represented by equation 13:

(formula 13)

Wherein, [ kv (t)]²=[kv_i(t)]²+[kv_q(t)]²Is the despread signal energy, [ n (t) ]]²=[n_i(t)]²+[n_q(t)]²Is the despread noise energy. Compared to the signal-to-noise ratio of the despread signal of the spread spectrum receiver in the conventional manner as in equation 4,

the signal-to-noise ratio of the despread signal obtained by the embodiment is obviously improved.

(formula 14)

(formula 15)

(formula 16)

The control logic circuit 12 is configured to adjust the first, second, and third amplitude adjustment parameters according to the signal-to-noise ratios of the first, second, and third despread signals, and control the signal-to-noise ratio module to adjust the signal-to-noise ratios of the corresponding first, second, and third despread signals until the signal-to-noise ratio of the second despread signal is the maximum value and the signal-to-noise ratios of the first despread signal and the second despread signal are equal.

Specifically, the delayed baseband signal x'_i(t)、x'_q(t) and QPSK baseband replica signal u "_in(t)、u"_qn(t) (n =1, 2, 3) by subtraction, x'_i(t)、x'_q(t) QPSK baseband component reduction, producing first, second and third pairs of spread baseband signals y_in(t)、y_qn(t) (n =1, 2, 3). Calculating spread spectrum baseband signal y from equations 14, 15, and 16_in(t)、y_qn(t) (N =1, 2, 3) signal-to-noise ratio (S/N) after despreading_{Despreading n}(n =1, 2, 3). According to (S/N)_{Despreading n}Varying the amplitude adjustment parameter p_nNumerical value of (n =1, 2, 3) (flow chart)As shown in fig. 7): when in useWhen, p is decreased_n(ii) a When in useWhen p is increased_n(ii) a When in useAnd isWhen it is maximum, consider u "_i2(t)、u"_q2(t) is adjusted to optimum, p_nThe values were unchanged. By continuously adjusting p_nFinally, x'_i(t)、x'_qThe QPSK baseband components in (t) are cancelled out to obtain the maximum despread signal-to-noise ratio (S/N)_{Despreading 2}. When the second path is in the best compensation, the de-spread signal-to-noise ratio reaches the maximum value; at the moment, the path 1 is over-compensated, and the de-spread signal-to-noise ratio is small compared with the second path; the 3 rd path is under-compensated, and the de-spread signal-to-noise ratio is smaller than that of the second path; the signal-to-noise ratios of the first, second and third despread signals form a peak to determine whether optimum compensation is achieved.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A method for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver, comprising:

an input signal splitter of the receiver acquires an input signal and divides the input signal into two equal paths of input signals, wherein each path of input signal is the sum of a QPSK modulation downlink signal, a spread spectrum modulation downlink signal and Gaussian noise, and the QPSK modulation downlink signal is greater than the spread spectrum modulation downlink signal;

a first QPSK signal matched filter and a second QPSK signal matched filter of the receiver respectively filter an I path difference frequency signal, a Q path difference frequency signal and a Q path sum frequency signal in the I path difference frequency signal, the Q path difference frequency signal and the Q path sum frequency signal, the I path difference frequency signal and the Q path difference frequency signal are output to be used as an I path baseband signal and a Q path baseband signal, the I path baseband signal and the Q path baseband signal are the sum of a QPSK baseband signal, a spread spectrum baseband signal and Gaussian noise, and the amplitude of the QPSK baseband signal is greater than that of the spread spectrum baseband signal;

2. The method of claim 1, wherein if the QPSK signal data is error correction coded, the steps of outputting I-path QPSK regenerated baseband signals and outputting Q-path QPSK regenerated baseband signals by the third QPSK matched filter and the fourth QPSK matched filter according to the I-path QPSK demodulated data and the Q-path QPSK demodulated data respectively comprise:

and a channel error correction decoder of the receiver performs error correction decoding on the I path QPSK demodulation data and the Q path QPSK demodulation data and then encodes the I path QPSK demodulation data and the Q path QPSK demodulation data to generate I path and Q path recoding data, and the third QPSK matched filter and the fourth QPSK matched filter output I path and Q path QPSK regeneration baseband signals according to the I path and Q path recoding data.

3. The method for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver of claim 1, wherein the input signal is of the formula:

r₁the formula of (1) is as follows:

a is the amplitude of the QPSK modulated signal, which has a positive value; a is_Ik、a_QkAre respectively provided withThe data information transmitted by the path I and the path Q in the QPSK modulation signal takes the value of +/-1; h is₁(t-kT₁) Is the impulse response of the transmitted signal, and the corresponding frequency response function is that the roll-off coefficient is alpha₁Square root raised cosine function of alpha₁The value range of (1) is between 0 and 1; t is₁Is a_IkAnd a_QkSymbol period of (1/T)₁Is the baud rate of the QPSK signal; omega₁＝2πf₁Is the angular frequency of the QPSK carrier signal, t is time, in seconds,

r₂the formula of (1) is as follows:

b is the amplitude of the spread spectrum modulated signal, which is always positive; b_Ik、b_QkThe data information transmitted by the spread spectrum modulation signal path I and the path Q respectively has the value of +/-1; m is_i(t)、m_q(t) is the spread spectrum sequence of the path I and the path Q of the spread spectrum modulation signal, the value is +/-1, and the nominal rate and r thereof₁A of (t)_IkAnd a_QkThe same; m is_i(t)、m_q(t) has a rate greater than b_Ik、b_QkVelocity of (1), m_i(t)、m_q(t) and b_Ik、b_QkThe ratio of the rates is called the spreading factor k; h is₂(t-kT₂) Is the impulse response of the transmitted signal, which corresponds to a frequency response function with a roll-off factor of alpha₂Square root raised cosine function of alpha₂The value range of (1) is between 0 and 1; t is₂Is m_i(t)、m_qSymbol period of (T), 1/T₂Is its baud rate, its nominal value and T₁The same; omega₂＝2πf₂Is the angular frequency of the signal, its nominal value and omega₁The same is true.

4. The method for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver of claim 3, wherein the I-baseband signal is formulated as follows:

the formula for the Q baseband signal is as follows:

wherein x is_i(t) is I road baseband signal, x_q(t) Q-band baseband signals, u_i(t)、u_q(t) baseband components of the I and Q paths of the QPSK signal, v_i(t)、v_q(t) baseband components of the I and Q paths of the spread spectrum signal, n_i(t)、n_q(t) Gaussian noise of path I and path Q, the baseband component of QPSK signal is greater than that of spread spectrum signal, i.e. u_i(t)>>v_i(t),u_q(t)>>v_q(t) due to ω₁、ω₂Equal, v_i(t)、v_qThe amplitude of (t) will vary slowly, A' is u_i(t)、u_q(t) an amplitude component, a' is proportional to a; b' is v_i(t)、v_qThe amplitude component of (t), B', is proportional to B.

5. The method of claim 4, wherein the formula for the I and Q QPSK regenerated baseband signals is as follows:

6. The method for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver as recited in claim 5, wherein the first, second and third pairs of QPSK baseband replica signals are formulated as follows:

wherein, u "_in(t) first, second and third different amplitude path I QPSK baseband replica signals, u "_qn(t) for the first, second and third different amplitude Q-way QPSK baseband replica signals, p₁、p₂、p₃Adjusting parameters for the first, second and third amplitudes, respectivelyNumber, p₁>p₂>p₃，p₁-p₂＝p₂-p₃Δ, the control logic circuit adjusts p according to the signal-to-noise ratio after despreading the spread spectrum signal₁、p₂、p₃So that the second pair of QPSK baseband copies signal u "_i2(t)、u"_q2(t) baseband component u most approximate to paths I and Q of QPSK signal_i(t)、u_q(t)。

7. The method for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication receiver of claim 6, wherein the equations for the first, second and third pairs of spread spectrum baseband signals are as follows:

wherein, y_in(t) is the I-path spread spectrum baseband signal, y_qn(t) is Q-path spread spectrum baseband signal, Δ u_in(t)＝u_i(t)-u"_in(t) is the residual component of the I-path QPSK baseband signal component, Δ u_qn(t)＝u_q(t)-u"_qn(t), is the residual component of the Q-path QPSK baseband signal component.

8. The method for improving the snr of despread signals of a satellite spread spectrum communication receiver of claim 7, wherein the snr module calculates and outputs the snrs of the first, second and third despread signals according to the following formula:

9. The method of improving the signal-to-noise ratio of despread signals of a satellite spread spectrum communication receiver of claim 8, wherein in the step of adjusting the first, second and third amplitude adjustment parameters by the control logic of the receiver based on the signal-to-noise ratios of the first, second and third despread signals, when the control logic of the receiver adjusts the first, second and third amplitude adjustment parameters based on the signal-to-noise ratios of the first, second and third despread signals When, p is decreased_n(ii) a When in useWhen p is increased_n(ii) a When in use When it is maximum, consider u "_i2(t)、u"_q2(t) is adjusted to optimum, p_nThe values were unchanged.

10. A receiver for improving the signal-to-noise ratio of a despread signal of a satellite spread spectrum communication, the receiver comprising:

the system comprises an input signal splitter, a signal processing unit and a signal processing unit, wherein the input signal splitter is used for acquiring an input signal and dividing the input signal into two equal paths of input signals, each path of input signal is the sum of a QPSK modulation downlink signal, a spread spectrum modulation downlink signal and Gaussian noise, and the QPSK modulation downlink signal is larger than the spread spectrum modulation downlink signal;

the first QPSK signal matched filter and the second QPSK signal matched filter are used for respectively filtering an I path sum frequency signal and an I path sum frequency signal in the I path difference frequency signal and a Q path sum frequency signal in the Q path difference frequency signal and outputting the I path difference frequency signal and the Q path difference frequency signal as an I path baseband signal and a Q path baseband signal, the I path baseband signal and the Q path baseband signal are the sum of a QPSK baseband signal, a spread spectrum baseband signal and Gaussian noise, and the amplitude of the QPSK baseband signal is greater than that of the spread spectrum baseband signal;