KR100436569B1 - Initial synchronization acquisition circuit and method for reducing doppler frequency effect in spread spectrum communications system - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an initial synchronization acquisition circuit and method of a spreading communication system. In particular, the spreading communication system reduces the influence of the Doppler frequency without reducing the received energy by integrating a signal received during each section by dividing the integration time into N sections. An initial synchronization acquisition circuit and method are disclosed.

An initial synchronization acquisition circuit of a spreading communication system for reducing the Doppler frequency influence of the present invention includes: a plurality of in-phase integrators each integrating a received signal during each period obtained by dividing the integral time into N sections; An inverter for inverting the received signal by four minutes; A plurality of quadrature integrators for integrating the inverted signals, respectively, during each period in which integration time is divided into N sections; A first adder for summing integral values of the in-phase integrators; A second adder that sums integral values of the quadrature integrators; A reception voltage detector for generating a global receiving voltage by square-rooting the sum of the value of the first adder and the value of the second adder; A plurality of interval voltage detectors that square each squared sum of the integration values of the intervals and add a square root to generate a reception voltage of each interval; A third adder for adding up the received voltages of the sections; A first determination unit that determines that synchronization is obtained when the global reception voltage is greater than a first threshold value; And a second determiner that determines that synchronization is obtained when the value of the third adder is greater than the second threshold.

Description

INITIAL SYNCHRONIZATION ACQUISITION CIRCUIT AND METHOD FOR REDUCING DOPPLER FREQUENCY EFFECT IN SPREAD SPECTRUM COMMUNICATIONS SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an initial synchronization acquisition circuit of a spreading communication system. In particular, the present invention relates to an initial synchronization acquisition circuit, in which an integration time is divided into N sections to integrate signals received during each section, thereby reducing the influence of Doppler frequency without reducing the received energy. A synchronization acquisition circuit and method are disclosed.

1A shows an initial sync acquisition circuit 100 in a direct spreading-code distribution multiple access (DS-CDMA) system according to the prior art. The synchronization acquisition circuit 100 integrates and dumps the received signal Sp during the integration time T ( An in-phase integration and dump unit (10) generating a); An inverter (11) for inverting the received signal (Sp); A value obtained by integrating and dumping the inverted signal during an integration time T ( An orthogonal phase integrator and dump unit 12 for generating a) and; Above value ( ), ( ), Each detector is squared, summed, and compared to a square root and a threshold to determine synchronization.

1B illustrates an initial synchronization acquisition circuit 100 in a frequency hopping-code distribution multiple access (FH-CDMA) system according to the prior art. The synchronization acquisition circuit 100 of FIG. 1B has the same configuration as the synchronization acquisition circuit 100 of FIG. 1A.

The synchronization acquisition circuit 100 typically sets a long time as an integration section for a reliable acquisition, but the Doppler frequency influence cannot be ignored because a high carrier frequency is generated and a high Doppler frequency is generated in a fast moving body such as an aircraft. do.

2 shows a graph showing the reduction of received energy by Doppler frequency. That is, the integral time is fixed and the ratio of the amount of received energy detected as the Doppler frequency is increased. The line A of the graph shows that when the speed of the moving object is 1000 km / h and the carrier frequency is 8 GHz, in the DS-CDMA system, the chip rate is 8.192 MHz, the integral number of chips is 256, and the FH- In the case of a CDMA system, the integral time is fixed at 31.232 Hz, and the detected received energy gradually decreases from the normalization value 1 when there is no Doppler frequency, and the received energy decreases rapidly to 0 when the Doppler frequency continues to increase. [Sinc (f _d )] is a ^two- function relationship that increases and decreases again. In other words, each time the Doppler frequency becomes a multiple of the inverse of the integration time (except zero), the received energy is exactly zero. Therefore, even if the integration time is increased to increase the reception energy, the reception energy may be reduced and may become zero at any Doppler frequency. As can be seen from the line B, a method for reducing the influence of the Doppler frequency is to reduce the integration time by reducing the integration time. On the other hand, reducing the integration time also reduces the received energy.

FIG. 3A shows the waveform of a signal in the in-phase channel of the sync acquisition circuit 100 of FIG. 1A.

FIG. 3B shows the waveform of a signal in a quadrature channel of the synchronization acquisition circuit 100 of FIG. 1A.

FIG. 3C shows the waveform of the value integrating the signal in the in-phase channel of FIG. 3A.

FIG. 3D shows waveforms of in-phase integration and integral voltage values of the dump section 10 of FIG. 1A.

FIG. 3E shows waveforms of the quadrature integral and integral voltage values of the dump section 12 of FIG. 1A.

3F shows an output waveform of the detector 13 of FIG. 1A.

3A to 3F simulate a situation in which the synchronization acquisition circuit 100 processes a signal at a Doppler frequency of 15 kHz. As can be seen in FIG. 3f, an average energy of 0.457 was received and the remaining 0.543 energy was lost by the Doppler effect.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an initial synchronization acquisition circuit that reduces the influence of the Doppler frequency in a communication system of a moving object moving at a high speed.

It is also an object of the present invention to provide a circuit for preventing a reduction in received energy due to division of the integration time.

It is also an object of the present invention to further provide a circuit capable of predicting the Doppler frequency to improve the synchronization acquisition reliability in the initial synchronization acquisition circuit.

1A is a schematic diagram of an initial synchronization acquisition circuit 100 in a direct spreading-code distribution multiple access (DS-CDMA) system according to the prior art.

1B is a block diagram of an initial synchronization acquisition circuit 100 in a frequency hopping-code distribution multiple access (FH-CDMA) system according to the prior art.

2 is a graph showing a reduction in received energy due to Doppler frequency.

3A is a waveform of a signal in an in-phase channel of the synchronization acquisition circuit 100 of FIG. 1A.

3B is a waveform of a signal in a quadrature channel of the synchronization acquisition circuit 100 of FIG. 1A.

3C is a waveform of values obtained by integrating a signal in the in-phase channel of FIG. 3A.

3D is a waveform of in-phase integration and integral voltage values of the dump unit 10 of FIG. 1A.

3E is a waveform of an integral voltage value of the quadrature integral and dump unit 12 of FIG. 1A;

3F is an output waveform of the detector 13 of FIG. 1A.

4 is a block diagram of a synchronization acquisition circuit according to the present invention;

5 is a block diagram of a Doppler frequency detector according to the present invention.

6A is a waveform of a signal in an in-phase channel of the synchronization acquisition circuit of FIG.

6B is a waveform of a signal in a quadrature channel of the synchronization acquisition circuit of FIG.

6C is a waveform of values obtained by integrating a signal in the in-phase channel of FIG. 4.

6D is a waveform of voltage values of the first interval voltage detector 45_1 of FIG. 4.

6E is a waveform of a voltage value of the second interval voltage detector 45_2 of FIG. 4.

6F is an output waveform of the third adder 46 of FIG.

Fig. 7A is a graph of the relationship with the received energy ratio based on the Doppler frequency.

7B is a graph of the relationship with the Doppler frequency based on the received energy ratio.

The initial synchronization acquisition circuit of the spreading communication system which reduces the influence of the Doppler frequency of the present invention integrates a signal received during each of the first to Nth sections obtained by dividing the integral time into N sections. First to Nth in-phase integrators generating A four-minute phase inverter for inverting the received signal; Integrate the inverted signals by integrating the inverted signals during the first to Nth intervals by dividing the integral time into N sections. First to Nth quadrature integrators for generating the first to Nth quadrature integrators; A first adder for summing integral values of the in-phase integrators; A second adder that sums integral values of the quadrature integrators; A reception voltage detector for generating a global receiving voltage by square-rooting the sum of the value of the first adder and the value of the second adder; Integral value of the first to Nth intervals A first to N-th section voltage detector for generating a received voltage of each section by square- ing the sum by squared the sums of the sections; A third adder for adding up the received voltages of the sections; A first determination unit that determines that synchronization is obtained when the global reception voltage is greater than a first threshold value; And a second determiner that determines that synchronization is obtained when the value of the third adder is greater than the second threshold.

In addition, the initial synchronization acquisition method of the spreading communication system to reduce the influence of the Doppler frequency of the present invention by integrating the received signal during each of the first to the N-th period in which the integral time is divided into N intervals, the integral value Generating a; Phase inverting the received signal by four minutes; Integrate the four-minute phase-inverted signals for each of the first to Nth sections in which the integral time is divided into N sections to obtain an integral value. Generating a; The integral value A first summing step of adding up; The integral value A second summing step of summing; Generating a global reception voltage by square-rooting the sums of the first summation step and the second summation step, and then adding the square roots; Integral value of the same interval Generating a received voltage of each section by squares the sums of squares by the respective squares and adds the square roots; A third summing step of summing the received voltages of the respective sections; A first determining step of determining that synchronism has been obtained if the global received voltage is greater than a first threshold value; And a second determining step of determining that synchronization is obtained when the value of the third adding step is larger than a second threshold value.

4 shows a configuration diagram of a synchronization acquisition circuit according to the present invention. In a communication system composed of a receiver, a path, and a receiver, the receiver includes a synchronization acquisition circuit that receives a signal transmitted through the channel. In detail, the first to Nth phase integrating and dumping units 41_I1 to 41_IN for integrating and dumping the signal input to the in-phase channel during each period obtained by dividing the integral time T by N, and the input An inverter 42 for inverting the signal for four minutes; First to Nth quadrature integrating and dumping units 41_Q1 to 41_QN for integrating and dumping the inverted signal during each period in which the integral time T is divided by N; A first adder (43a) for adding up the first to Nth in-phase integrals and the integral values of the dump units (41_I1) to (41_IN); A second adder 43b for summing the first to Nth quadrature integrals and the integral values of the dump units 41_Q1 to 41_QN; A reception voltage detector (44) which squares and sums the values of the first and second adders (43a) and (43b), respectively, and squares them to generate a full-range reception voltage; The first to Nth period voltage detectors 45_1 to (n) that generate the received voltage of each period by square-rooting the sum of the integral values of the in-phase channel and the quadrature channel in the same section of the first to Nth sections, 45_N); A third adder (46) for adding the received voltages of the sections; A first determination unit (47a) for determining that synchronization is obtained when the global reception voltage is greater than a first threshold value; If the value of the third adder is larger than the second threshold value, the second determiner 47b determines that synchronization is obtained.

If the magnitude of the globally received signal is larger than the first threshold value in the in-phase channel, synchronization is considered to be obtained, and the clock is controlled to maintain synchronization.

If the magnitude of the received voltage of each section in the quadrature channel is greater than the second threshold value, it is considered that synchronization is obtained, and the clock is controlled to maintain synchronization.

When the Doppler frequency is 0, the received voltage detected after the summation of FIG. ) And the received voltage summed after detection ( The received energy by) is the same. However, if the Doppler frequency is low, considering the effect of noise, the received signal detected after the summation of FIG. 4 is less affected by the noise, and thus the reliability of the received energy is higher than that of the received received signal. That is, it is difficult to acquire synchronously with the received signals detected after summing without a signal. However, the received signals added after detection may be synchronously acquired with a mistake. Therefore, if a separate variable threshold is set so that the differential ratio of each channel energy can be applied for accurate synchronization acquisition, the reliability of synchronization acquisition can be obtained more. If the Doppler frequency is considerably large, the received energy summed after detection in Fig. 4 becomes much larger, and synchronization is obtained by the summed received energy after detection.

As shown in FIG. 2, when the Doppler frequency is the inverse of the integral time, the reception energy becomes zero. However, when the Doppler frequency is equal to the inverse of the integration time, the reception energy does not become zero when the Doppler frequency is equal to the inverse of the integration time.

FIG. 5 is a block diagram of a Doppler frequency detector according to the present invention, comprising: a first square circuit 51 which squares the global reception voltage of a synchronization acquisition circuit to generate global reception energy; A second square circuit 52 for generating a division interval received energy by squaring the value of the third adder 46; An energy ratio generating unit 53 for generating a ratio between the global reception energy and the division period reception energy; The memory 54 is configured to detect a pre-stored Doppler frequency through the ratio.

First, the basic principle of the Doppler frequency detector is as follows.

Based on the absence of the Doppler frequency, the ratio of the integral energy that can be received in a fixed time interval under the influence of the Doppler frequency is given by Equation 1. (CDMA principle of spread spectrum communication, Ant J. Viterbi Andrew J. Viterbi, 1995, Addison Wesley Longman Inc.

Where f _d is the Doppler frequency and T is the integration time.

Equation 1 shows the sinc square function, f _d the more or T is a value close to 1, the more the f _d T or greater can be seen that convergence to zero.

Integrating the energy (E _'b) from the equation (1) is as follows, when the 1-bit energy E _b la.

That is, it is K (f _b ) times smaller than E _{b to} be originally received.

In this case, when the absolute magnitude of the integrated voltage (V ₁ , that is, the output of the received voltage detector 44) is represented by the square root of the received energy, Equation 3 is obtained.

On the other hand, in the case of integrating the total integration time T by N and integrating for T / N time, the received energy ratio K (f _b ) 'is expressed by Equation 4.

Comparing Equation 4 and Equation 1, the ratio of the received energy of Equation 4 has a characteristic that is gently lowered compared to the size of f _d or T. That is, the integral voltage V _{2 (1 / N} ) (that is, the output of the first to Nth voltage detectors) during one section T / N is reduced to 1 / N as shown in Equation 5 below. .

The integral voltage (ie, the output of the third adder 46) of each section is expressed by Equation 6.

Although the magnitude of the integral voltage of each section is small, the sum of the integral voltages of all sections is restored to the original integral voltage.

The ratio of the integrated voltage (V ₁ ) obtained by integrating the entire period by the conventional method and divided into N equal intervals and then integrated, and then obtained is the ratio of the integrated voltage (V ₂ ) as shown in Equation (7).

The ratio of the squares of the integrated voltages is the ratio of the received energy according to the difference between the two paths, i.e., the square of Equation 7 is obtained.

For example, in the case of N = 2, Equation 8 is simplified as follows (if π f _d T / 2 is Θ).

When N is 2, a special case may be developed through the incidence and half angle formulas of the trigonometric function as shown in Equation 9, but when it is a natural number, the above and the liver are difficult to simplify. In general, N values are set in advance, and the actual values of several values are substituted in mathematics 8 to be calculated, and the results are stored in the memory 54 for use.

If the Doppler frequency is zero, there is no need to divide N equals. Rather, if divided N, the noise is further affected.

For example, an embodiment of the present invention will be described when N = 2. If the integral time is reduced to 15.616 Hz, which is half of the integration time (31.232 Hz) in the line A of Fig. 2, even if the Doppler frequency is 15 kHz, it is 1/2 of 0.832 which is the received energy of 7.5 kHz of the line B. Receive 0.416. Dividing the integration period into two and integrating each gives an energy of 0.416, and adding the two integration results to 0.832, which is two times 0.416. This shows a much improved characteristic compared to the received energy of the conventional synchronization acquisition circuit of 0.457. 6A to 6F below show graphs when N = 2 in the same situation as the embodiment of FIGS. 3A to 3F.

6A shows waveforms of signals in the in-phase channel of the synchronization acquisition circuit of FIG. 4.

FIG. 6B shows the waveform of a signal in a quadrature channel of the synchronization acquisition circuit of FIG. 4.

6C shows a waveform of values obtained by integrating signals in the in-phase channel of FIG. 4.

6D illustrates waveforms of voltage values of the first interval voltage detector 45_1 of FIG. 4.

FIG. 6E illustrates waveforms of voltage values of the second interval voltage detector 45_2 of FIG. 4.

FIG. 6F shows the output waveform of the third adder 46 of FIG. 4.

As can be seen from FIG. 6F, the reception energy of each section was about 0.832 as expected, and although the magnitude of the change was somewhat due to the influence of noise, the average reception energy was significantly increased from the conventional circuit.

7A shows a graph of the relationship with the received energy ratio based on the Doppler frequency. That is, it is a graph shown according to equation (9). In other words, when the signal-to-noise ratio is excellent, the approximate Doppler frequency is estimated by using the received energy ratio of each channel using the synchronization acquisition circuit of the present invention using the integration circuit which divides and integrates the conventional integration circuit and the integration section. Can be used.

7B shows a graph of the relationship with the Doppler frequency based on the received energy ratio. That is, it is assumed that the Doppler frequency is in the range of 0 to +/- 30 kHz or more, and the Doppler frequency is predictable by the ratio of received energy of two channels. However, although the Doppler frequency corresponding to the same energy ratio has one value in the range of 30 kHz or less, there may be another corresponding frequency in the range of 30 kHz or more. Doppler frequencies above 30 kHz are excluded because they are less likely to occur in real-world situations where the relative speed is greater than 4,050 km / h on an 8 GHz carrier. For example, in FIG. 7B, when the received energy ratio is 0.2, two frequencies (points A and B) of about 23 kHz and 42 kHz may be predicted as the predicted Doppler frequency values.

As described above, when there is a large Doppler frequency deviation, if the first or second threshold is set to 0.5 of the received energy of FIG. 2, the received energy at the Doppler frequency (30 kHz or more) is lower than 0.5, and thus is incorrect. Doppler frequency prediction can be prevented.

According to the present invention of the above-described configuration, the present invention has the effect that can be initially obtained by reducing the influence of the Doppler frequency in the communication system of a mobile moving at high speed. .

In addition, the present invention has the effect of preventing the reduction of the received energy due to the division of the integration time, and receiving higher received energy from the conventional synchronization acquisition cycle.

In addition, the present invention has the effect of improving the reliability of the received energy by applying a variable threshold value.

In addition, the present invention further provides a circuit capable of predicting the Doppler frequency, thereby improving the synchronization acquisition reliability in the initial synchronization acquisition circuit.

Claims (6)

Integrate the received signal by integrating the received signals during each of the first to Nth intervals by dividing the period into N intervals. First to Nth in-phase integrators generating An inverter for inverting the received signal; Integrate the inverted signals by integrating each of the inverted signals during the first to Nth intervals in which the period is divided into N sections. First to Nth quadrature integrators for generating the first to Nth quadrature integrators; A first adder for summing integral values of the in-phase integrators; A second adder that sums integral values of the quadrature integrators; A reception voltage detector for generating a global receiving voltage by square-rooting the sum of the value of the first adder and the value of the second adder; Integral value of the first to Nth intervals A first to N-th section voltage detector for generating a received voltage of each section by square- ing the sum by squared the sums of the sections; A third adder for adding up the received voltages of the sections; A first determination unit that determines that synchronization is obtained when the global reception voltage is greater than a first threshold value; And a second determining unit which determines that synchronization is obtained when the value of the third adder is larger than a second threshold value. 2. The apparatus of claim 1, wherein the initial synchronization acquisition circuit comprises: a first square circuit for generating global energy received squared by squaring the global received voltage; A second square circuit for generating division interval received energy by squaring the value of the third adder; An energy ratio generator configured to generate a ratio of the global energy received and the divided energy received; And a Doppler frequency detector comprising a memory configured to detect a pre-stored Doppler frequency through the ratio. 3. The Doppler frequency influence according to claim 1 or 2, wherein the first threshold value and the second threshold value can be varied to a predetermined value so that the Doppler frequency detector detects an optimal Doppler frequency. An initial synchronization acquisition circuit of a spreading communication system. Integrate the received signal by integrating the received signals during each of the first to Nth intervals by dividing the period into N intervals. Generating a; Inverting the received signal; Integrate the inverted signals by integrating the inverted signals during the first to Nth intervals by dividing the period into N sections. Generating a; The integral value A first summing step of adding up; The integral value A second summing step of summing; Generating a global reception voltage by square-rooting the sums of the first summation step and the second summation step, and then adding the square roots; Integral value of the same interval Generating a received voltage of each section by squares the sums of squares by the respective squares and adds the square roots; A third summing step of summing the received voltages of the respective sections; A first determining step of determining that synchronization is obtained when the global received voltage is greater than a first threshold; And a second determining step of determining that synchronization is obtained when the value of the third summing step is larger than a second threshold value. 5. The method of claim 4, wherein the initial synchronization acquisition method comprises: a first squared step of generating the global received energy by squaring the global received voltage; A second square step of generating a division interval received energy by squaring the value of the third summing step; Generating a ratio of the global reception energy and the division interval reception energy; And a Doppler frequency detection step comprising detecting a pre-stored Doppler frequency through the ratio. The Doppler frequency influence according to claim 4 or 5, wherein the first threshold value and the second threshold value can be varied to a predetermined value in order to detect an optimal Doppler frequency in the Doppler frequency detection step. Initial synchronization acquisition method of a spreading communication system that reduces the number of.