JP5439726B2 - Receiver synchronizer in spread spectrum direct communication system - Google Patents

Description

The present invention relates to a reception synchronization apparatus in a spread spectrum communication system using a direct spreading system.

FIG. 7 shows an example of the output vs. frequency characteristic of the correlator, and FIG. 8 shows an example of the circuit configuration of the demodulator in the conventional direct spectrum spread spectrum communication system.
In FIG. 8, the mixer 10 outputs a baseband spread spectrum signal by multiplying the received spread spectrum signal (SS received signal) converted from the high frequency signal into the intermediate frequency signal and the output of the voltage controlled oscillator (VCO) 11. . By passing this baseband spread spectrum signal through a low-pass filter (LPF) 12, harmonic components and aliasing noise (folding noise) are cut. The output of the LPF 12 is AD converted by sampling at a predetermined clock frequency by the AD converter 13 and becomes a digitized received spread spectrum signal. The digitized received spectrum spread signal is input to the correlator 14 and a correlation value is output by obtaining a correlation with a spread code pattern prepared in advance. For example, the output of the sweeper 16 configured by a counter controlled by the sweep controller 15 is converted into an analog voltage via the DA converter 17 and used as a control signal for the VCO 11. By sequentially increasing the output voltage of the sweeper 16 within a certain range and sweeping the frequency, the correlation value vs. frequency characteristic as shown in FIG. 7 is obtained from the correlator. After the correlation value is changed to electric power by the power converter 18, the maximum value of the correlation value is obtained by the maximum value detector 19, and the output frequency (fc) of the VCO 11 when the maximum value of the correlation value is obtained is When the initial pull-in is completed, the sweep is stopped and the despread timing is output from the correlator. If the despreading timing is acquired, the despreader 21 performs despreading at that timing.

However, when the S / N of the received signal is poor, there may be a case where the despread timing cannot be obtained accurately. Usually, when accurate despreading timing cannot be obtained by sweeping one diffusion cycle, a method of integrating the correlation voltage multiple times is used. FIG. 9 shows the configuration of a demodulator according to this method. In FIG. 9, an integrator is provided, and integration for N diffusion periods is performed by an integration number setting value N. In the integration of one spreading period, there may be a case where the noise voltage is higher than the correlation voltage value due to the phase matching of the spreading code, and the reliability of the obtained despreading timing is low. However, the input noise component can be regarded as white Gaussian noise, and since all frequency components are included with the same intensity, it is utilized that the voltage converges to zero by integration. Therefore, by integrating a plurality of times, the correlation voltage at the point where the phases of the spreading codes coincide with each other is strengthened, and the noise voltage portion converges to zero. This method improves S / N and makes it possible to increase the detection probability of despreading timing. However, if the frequency deviation cannot be ignored due to a low transmission rate, the integration effect cannot be obtained, or by integration. Conversely, problems such as cancellation of peak portions occur, and therefore it is necessary to remove the frequency deviation. (Examples of the effect of integration when there is no frequency deviation and examples where the integration effect is not obtained when there is a deviation are shown in FIGS. 10 and 11. FIG. 10 shows the case where the integration effect is obtained. By integrating the output voltage with the diffusion period, the correlation peak portion is emphasized, and the size of the peak is multiplied by the number of integrations. 11 shows the case where the integration effect cannot be obtained, as shown in the upper part of Fig. 11. In some cases, the correlation value in each diffusion period becomes a large positive value, and in other cases, the negative large value. Here, since the correlation value is expressed not by electric power but by voltage, it can be a negative value, so if integration is performed by adding these correlation values multiple times, the peak value can be obtained. The parts cancel each other and the integration effect cannot be obtained. If this happens, the peak value is detected by comparison with a predetermined threshold value, so that the peak value may be smaller than the threshold value. As a result, the peak value cannot be detected correctly, that is, the correct despreading timing cannot be obtained.

Further, as an example in which frequency deviation becomes a problem, the following satellite mobile phone system can be considered. This system is shown in FIG.
In FIG. 12, a signal called a common pilot channel (CPICH) is always transmitted from the base station, and the terminal performs frequency synchronization with reference to this channel. For this reason, if the satellite frequency deviation is ΔF, 2 × ΔF is received by the base station, and when the terminal transmission rate is low, the correlation value by despreading is integrated several times in the spreading period. If so, it becomes a problem. Here, the frequency deviation ΔF of the satellite is doubled at the base station because the signal passes through the satellite twice when reciprocating between the base station and the terminal, so that the frequency deviation of the satellite is received twice. Because it becomes. Furthermore, when burst frames are received by TDMA or the like, it is necessary to complete the detection of frequency synchronization and despreading timing within a limited time (such as within the first pilot of the frame). With the conventional sweep method, synchronization is completed. There is a problem because it takes a long time.

As the prior art, there are Patent Documents 1 to 3. Japanese Patent Laid-Open No. 2004-26883 discloses a reception that can obtain a high-quality demodulated signal by reducing the number of transfer bits of the signal from the receiving means to the demodulating means, reducing the size and power consumption of the apparatus, and eliminating phase fluctuations and gain control errors. An apparatus is disclosed. Patent Document 2 discloses a receiving apparatus that can accurately detect the reception timing of a correct path in a propagation path with multipath fading and shadowing. Patent Document 3 discloses a communication device that speeds up detection of codes in initial synchronization using a matched filter.
JP 2001-339455 A Japanese Patent Laid-Open No. 10-32523 Japanese Patent Laid-Open No. 11-340874

  An object of the present reception synchronization apparatus is to provide a reception synchronization apparatus capable of sufficiently obtaining the integration effect of the correlation value regardless of the frequency deviation and accurately performing the frequency control of the received signal and the acquisition of the inverse correlation timing.

  This reception synchronization apparatus is a reception synchronization apparatus of a direct spectrum spread communication system, and includes a reception means for receiving a radio signal, a phase rotation means for giving a phase rotation to the reception signal, and a correlation value of the phase-rotated reception signal. A correlation unit that takes the correlation value, an integration unit that integrates the correlation value, and a phase rotation that gives the maximum correlation value from a value obtained by converting the integral value of the correlation value of the received signal subjected to the phase rotation of a plurality of different phase rotation amounts. A maximum value detecting means for detecting the amount, a despreading means for despreading the received signal, and a phase rotation amount for giving the maximum correlation value are set in the phase rotating means, and this phase rotation is performed for the subsequent received signals. Give the amount and despread.

  According to this reception synchronization apparatus, it is possible to provide a reception synchronization apparatus that can sufficiently obtain the integration effect of the correlation value regardless of the frequency deviation and can accurately perform the frequency control of the received signal and the acquisition of the inverse correlation timing.

In this embodiment, the frequency deviation of the input signal is removed to the extent that a sufficient integration effect can be obtained. Here, it is assumed that the received signal is composed of multicarriers, and that a pilot signal is always transmitted in a certain subcarrier, and that adjustment of frequency deviation and detection of despreading timing are performed using the pilot signal.

The amount of frequency deviation with which a sufficient integration effect can be obtained is obtained from the diffusion period and the number of integrations, and the upper limit of the frequency deviation can be estimated from system factors such as frequency stability. Therefore, a signal necessary for integration is stored in a buffer, and the frequency deviation is canceled by giving the estimated frequency deviation amount with an opposite phase to the stored signal. Here, since it is unrealistic from the scale of hardware to give all possible frequency deviations,
Amount of frequency deviation with which sufficient integration effect can be obtained. Range of frequency deviation that can be taken below A [Hz] ..... -B [Hz] to B [Hz]
Then, a discrete value obtained by dividing the interval from B [Hz] to -B [Hz] at intervals of A [Hz] is given to the phase rotator. Here, the range of frequency deviations that can be taken is estimated by those skilled in the art from system design matters, and the amount of frequency deviation that can obtain a sufficient integration effect depends on the number of integrations, etc. Shall be determined.

As an example, consider the following system.
When the range of the frequency deviation that can take a frequency deviation amount of 10 [Hz] or less capable of obtaining a sufficient integration effect is −20 [Hz] to 20 [Hz],
For the signal stored in the buffer,
(1) -20 [Hz] is given, the correlation peak power value (2) -10 [Hz] obtained as a result of integrating the correlation value by despreading with the spreading period is given, and the correlation value by despreading is integrated with the spreading period The correlation peak power value (3) 0 [Hz] obtained as a result of the correlation is given, and the correlation peak power value (4) 10 [Hz] obtained as a result of integrating the correlation value due to despreading with the spreading period is given. Correlation peak power value (5) 20 [Hz] obtained as a result of integrating the value with the spreading period is given, and correlation peak power value (1) to (5) obtained as a result of integrating the correlation value by despreading with the spreading period Among these results, the phase rotation amount at which the highest correlation peak power value was obtained is the actual frequency deviation amount, and the integration effect can be obtained by canceling the deviation.

  In this method, it is possible to apply a plurality of estimated deviation amounts to a stored signal within the range of possible frequency deviations, and collectively compare the correlation peak power values due to each deviation amount. Since the detection of the diffusion timing can be completed at the same time, the time can be greatly reduced as compared with the conventional method.

FIG. 1 is a conceptual explanatory diagram of the integration effect when the frequency deviation is canceled according to the present embodiment.
FIG. 1A is a conceptual diagram of a correlation value before frequency deviation cancellation. Here, it is assumed that the diffusion period T is 4 ms and the frequency deviation is about 36 Hz. If there is a frequency deviation, the correlation value changes from a large positive value to a large negative value, and even if integration is performed as it is, an integration effect cannot be obtained. Therefore, as shown in FIG. 1B, it is assumed that a phase rotation of −36 Hz is given to the input signal to cancel the frequency deviation. Then, as shown in FIG. 1B, the correlation value becomes a large positive value, and when it is integrated, a state in which an integration effect is sufficiently obtained can be obtained.

FIG. 2 is a block diagram of a demodulator according to an embodiment of the present invention.
In FIG. 2, the same components as those in FIG. 9 are denoted by the same reference numerals.
In FIG. 2, the mixer 10 outputs a baseband spread spectrum signal by multiplying the received spread spectrum signal (SS received signal) converted from the high frequency signal into the intermediate frequency signal and the output of the voltage controlled oscillator (VCO) 11. By passing this baseband spread spectrum signal through a low-pass filter (LPF) 12, harmonic components and aliasing noise (folding noise) are cut. The output of the LPF 12 is AD converted by sampling at a predetermined clock frequency by the AD converter 13 and becomes a digitized received spread spectrum signal. The digitized received spectrum spread signal is input to the correlator 14 and a correlation value is output by obtaining a correlation with a spread code pattern prepared in advance. For example, the output of the sweeper 16 composed of a counter is converted into an analog voltage via the DA converter 17 to obtain a control signal for the VCO 11, and the output voltage of the sweeper 16 is sequentially increased within a certain range to increase the frequency. By sweeping, the correlation value vs. frequency characteristic as shown in FIG. (Here, the correlation value is an output obtained from a conventional matched filter.) The maximum value detector 19 obtains the maximum value of the correlation value, and sweeps at the VCO output frequency (fc) when the maximum value of the correlation value is obtained. Stop operation and complete frequency synchronization.

  Next, the operation proceeds to the operation of integrating the output of the correlator 14 with the diffusion period. When the frequency residual due to the initial sweep by the AFC (Automatic Frequency Control) 20 having the sweeper 16 and the sweep controller 15 for controlling the sweeper 16 or the frequency deviation of the satellite or the like affects the integration, the frequency deviation is caused by the phase rotator 31. Cancel. As for the phase rotation amount, the rotation amount control unit 32 acquires the correlation power value that is the output of the maximum value detector 19, and controls the phase rotation amount of the phase rotator so that the magnitude of the peak value becomes maximum. .

  The buffer 30 in FIG. 2 is a RAM that stores an input signal for an integration period, and holds the input signal until a final result is obtained. After storing the signal for the diffusion period, data reading from the buffer 30 and phase rotation for the read data are performed. Here, since it is necessary to cancel the deviation to a frequency deviation amount (A [Hz]) or less at which a sufficient integration effect can be obtained, the frequency deviation range assumed in the system is set at intervals of A [Hz]. The phase is sequentially rotated, the post-integration correlation peak powers obtained with the respective phase rotation amounts are compared, and the despread timing at which the highest value is obtained is adopted. Here, the rotation amount control unit 32 controls the phase rotation amount and compares the correlation power value according to each phase rotation amount.

The influence of the deviation can be canceled by the above operation, and the S / N improvement effect by integration can be surely obtained, so that the detection rate of the despreading timing can be improved.
FIG. 3 is a diagram showing a demodulator configuration when frequency synchronization operation is not necessary in the base station receiver of a system such as a satellite mobile phone.

3, the same components as those in FIG. 9 are denoted by the same reference numerals.
In this case, although the input signal (terminal transmission signal) is frequency-synchronized with the base station, it is necessary to remove the frequency deviation due to the satellite in order to obtain the effect of integration reliably.

  In FIG. 3, the mixer 10 outputs a baseband spread spectrum signal by multiplying the received spread spectrum signal (SS received signal) converted from the high frequency signal into the intermediate frequency signal and the output of the voltage controlled oscillator (VCO) 11. By passing the baseband spread spectrum signal through a low-pass filter (LPF) 12, harmonic components and aliasing noise (folding noise) are cut. The output of the LPF 12 is AD converted by sampling at a predetermined clock frequency by the AD converter 13 and becomes a digitized received spread spectrum signal.

Next, in order to integrate the input signal with the diffusion period, data for the integration period is stored in the buffer 30, and the input signal is held until a final result is obtained. After storing the signal for the diffusion period, data reading from the buffer 30 and phase rotation for the read data are performed. Here, since it is necessary to cancel the deviation to a frequency deviation amount (A [Hz]) or less at which a sufficient integration effect can be obtained, the frequency deviation range assumed in the system is set at intervals of A [Hz]. The phase is sequentially rotated, the post-integration correlation peak powers obtained with the respective phase rotation amounts are compared, and the despread timing at which the highest value is obtained is adopted. Here, the rotation amount control unit 32 controls the phase rotation amount and compares the correlation power value according to each phase rotation amount.

The influence of the deviation can be canceled by the above operation, and the S / N improvement effect by integration can be surely obtained, so that the detection rate of the despreading timing can be improved.
FIG. 4 is a diagram for explaining the operation of the phase rotator.

  The phase rotation unit performs a complex operation on the I and Q signals. The input signals Bi (t) and Bq (t) of the phase rotation unit in FIG. 4 can be expressed as follows.

Here, θ (t) is a phase difference, and D (t) is modulation data.
When Ri (t) and Rq (t) are Cos waves and Sin waves based on the set phase rotation amount, the calculation of the complex calculation unit (phase rotation unit) is

It becomes.
When the phase difference of the input signal and the set phase rotation amount are the same, Ri (t) and Rq (t) are

Substituting Equations (1), (2), (4), and (5) into Equation (3),

In the case of BPSK, the output signal is expressed as follows from equation (6).

FIG. 5 is a diagram showing a configuration example according to another embodiment when there is no buffer.
In FIG. 5, the same components as those in FIG. 9 are denoted by the same reference numerals.

  In FIG. 5, the mixer 10 outputs a baseband spread spectrum signal by multiplying the received spread spectrum signal (SS received signal) converted from the high frequency signal into the intermediate frequency signal and the output of the voltage controlled oscillator (VCO) 11. By passing the baseband spread spectrum signal through a low-pass filter (LPF) 12, harmonic components and aliasing noise (folding noise) are cut. The output of the LPF 12 is AD converted by sampling at a predetermined clock frequency by the AD converter 13 and becomes a digitized received spread spectrum signal. The digitized received spectrum spread signal is input to correlators 14-1 to 14-n, and a correlation value is output by obtaining a correlation with a spread code pattern prepared in advance. Here, in this embodiment, instead of storing data in the buffer and sequentially giving different phase rotation amounts to obtain correlation values, phase rotation control units 1 to n are provided for the number of types of phase rotation amounts to be given, Simultaneously and in parallel, different phase rotation amounts are given to the signals to obtain correlation values, and the maximum value detector 19 detects which phase rotation amount gives the largest correlation value and obtains a frequency deviation. Thereby, the same effect as the case where a buffer is provided without providing a buffer can be obtained.

  In the same way as described above, it is necessary to cancel the deviation to a frequency deviation amount (A [Hz]) or less that can obtain a sufficient integration effect, but the frequency deviation amount is unknown and is assumed on the system. The phase of the frequency deviation is rotated at intervals of A [Hz]. If the frequency deviation range assumed in the system is B [Hz], (B / A) number of phase rotators are required.

  By these operations, it becomes possible to reliably obtain the S / N improvement effect by canceling the frequency deviation and integrating, so that the detection rate of the despreading timing is remarkably improved. In addition, since frequency synchronization and despreading timing detection are completed in the same time, it is advantageous when operation within a limited time such as burst operation is required, and there is a merit that the operation rate decreases otherwise. .

FIG. 6 is a diagram illustrating an example of a TDMA burst frame.
Next, consider a case where a burst frame is received by TDMA or the like instead of a system in which a pilot signal is constantly transmitted. When receiving a burst frame, it is necessary to detect the frequency synchronization and despreading timing by the first pilot of each frame every frame, but the frequency deviation is a fluctuation centered on the deviation detected in the previous frame. Can be estimated.

For example, when the frequency deviation range is from −160 Hz to 160 Hz and phase rotation is performed at 10 Hz intervals, and a frequency deviation of +60 Hz is detected in the previous frame, the pilot deviation of the next frame is The amount of phase rotation to be given should be a deviation amount that can shift within one frame period centered on +60 Hz. Therefore, the amount of phase rotation to be applied can be reduced compared to the first time, the despreading timing detection time for the second and subsequent frames is shortened, and the operation rate of the circuit is reduced, so that low power consumption can be expected.

  According to the above embodiment, in the spread spectrum communication system using the direct spreading method, the frequency deviation of the input signal is removed without significantly changing the configuration from the conventional method, and the S / N improvement effect by the integration of the output voltage of the correlator is reliably obtained. This makes it possible to establish high-speed and accurate reception synchronization.

It is a conceptual explanatory drawing of the integration effect at the time of canceling a frequency deviation according to this embodiment. It is a block diagram of a demodulator according to an embodiment of the present invention. It is a figure which shows a demodulator structure when the operation | movement of a frequency synchronization is not required in the base station receiver of a system like a satellite mobile phone. It is a figure explaining operation | movement of a phase rotator. It is a figure which shows the structural example according to another embodiment when there is no buffer. It is a figure which shows the example of a TDMA burst frame. It is a figure of an example of the output vs frequency characteristic of a correlator. It is a figure of an example of the circuit structure of the demodulator in the spread spectrum direct communication system of a prior art example. It is a figure which shows the structure of the demodulator by the method of integrating a correlation voltage in multiple times. It is a figure which shows the example of an effect by integration when there is no frequency deviation. It is a figure which shows the example in which an integration effect is not acquired when there exists a frequency deviation. It is a figure explaining the system of a satellite mobile telephone.

Explanation of symbols

10 Mixer 11 VCO
12 Low-pass filter 13 A / D converter 14, 14-1 to 14-n Correlator 15 Sweep controller 16 Sweep controller 17 D / A converter 18, 18-1 to 18-n Power converter 19 Maximum value detection 20 AFC
21 Despreader 22, 22-1 to 22-n Integrator 30 Buffer 31, 31-1 to 31-n Phase rotator 32 Rotation amount control unit

Claims (3)

A spread synchronization communication type reception synchronization device,
Receiving means for receiving a radio signal;
Phase rotation means for applying phase rotation to a signal input from the reception means;
Correlation means for obtaining a correlation between a signal input from the phase rotation means and a predetermined spreading code pattern and outputting a correlation peak voltage value;
Integrating means for integrating the correlation peak voltage value with a diffusion period;
Power conversion means for power-converting an integral value obtained by the integration means;
Maximum value detection means for detecting the maximum value of the correlation peak power value input from the power conversion means;
A phase rotation amount control means for outputting a frequency deviation which is a discrete value determined as a phase rotation amount , based on the frequency deviation detected in the previous frame of the input signal, to the phase rotation means;
The phase rotation amount control means acquires a maximum phase rotation amount corresponding to a maximum value of the correlation peak power value when the phase rotation amount is changed within a predetermined range, and sends the phase rotation amount to the phase rotation means. Output,
The phase synchronizer provides phase rotation to a signal input from the receiver based on the maximum phase rotation amount. In the reception synchronization device of the spread spectrum communication system,
Receiving means for receiving a spread spectrum spread signal;
Phase rotation means for applying phase rotation to a signal input from the reception means;
Correlation means for obtaining a correlation between a signal input from the phase rotation means and a predetermined spreading code pattern and outputting a correlation peak voltage value;
Integrating means for integrating the correlation peak voltage value with a diffusion period;
Power conversion means for power-converting an integral value obtained by the integration means;
Maximum value detection means for detecting the maximum value of the correlation peak power value input from the power conversion means;
A phase rotation amount control means for outputting a frequency deviation which is a discrete value determined as a phase rotation amount , based on the frequency deviation detected in the previous frame of the input signal, to the phase rotation means;
Have
The phase rotation amount control means acquires a maximum phase rotation amount corresponding to a maximum value of the correlation peak power value when the phase rotation amount is changed within a predetermined range, and outputs the maximum phase rotation amount to the phase rotation means,
The phase synchronizer adds the maximum phase rotation amount to a signal input from the receiver. In the reception synchronization method of the spread spectrum communication method,
Receives a spread spectrum spread signal,
Giving a phase rotation amount to the spread signal,
Obtaining a correlation between the spread signal to which the phase rotation amount is given and a predetermined spread code pattern, and outputting a correlation peak voltage value;
Integrating the correlation peak voltage value with a diffusion period to obtain an integral value,
The integral value is converted into power to obtain a correlation peak power value,
Detecting the maximum value of the correlation peak power value;
Obtaining a maximum phase rotation amount corresponding to a maximum value of the correlation peak power value when the phase rotation amount is changed within a predetermined range;
A reception synchronization method, comprising: adding the maximum phase rotation amount, which is a frequency deviation which is a discrete value, determined based on a frequency deviation detected in a previous frame of an input signal, to the spread signal.