KR100317571B1 - Method and circuit for suppressing symbol interference in digital communication - Google Patents

Abstract

The present invention relates to a method and a circuit thereof for maximally suppressing intersymbol interference of a digital communication device. A feature of the intersymbol interference suppression method of a digital communication device according to the present invention is to detect a phase difference using a signal received at a receiver, compare it with a transmission signal, and transmit and receive a signal so that the phase of the transmission and reception signal is always maintained at 90 °. It is to suppress the intersymbol interference of the transmission and reception signals in a system by shifting the phase by a constant phase difference value.

Description

Interference Symbol Suppression Method and Circuit in Digital Communication System

The present invention relates to a method and a circuit for reducing an error of a signal caused by noise and inter-symbol interference in digital communication, and more particularly, a signal delay and error occurrence factor when a signal is modulated or demodulated. The present invention relates to a method and a circuit for accurately determining data by minimizing the size of the data to accurately recognize the data.

1 and 2 are block diagrams of a receiver 100 and a transmitter 200 for a digital communication system which are well known to date. For reference, general digital communications are described in Section 2.9.5 pages 92–95 of Berber sclar's “Digital Communication” and Section 3.3 pages 127–132 of the same textbook. In addition, the basic contents of digital communication are described in Section 8.10 Section 409 to Section 8.13 Section 422 of "Communication Systems" (3rd edition), published by Kang Chang-un and Cha Kyun-hyun, published in the Korean Air.

First, referring to the signal processing in the digital communication receiver 100 shown in FIG. 1, the RF signal received through the antenna is amplified by the low noise amplifier 101 and then input to the bandpass filter 102.

The RF signal filtered by the bandpass filter 102 is mixed with the output signal of the pseudo noise generator 105 by the first and second multipliers 103 and 104, respectively, to respectively an inphase signal and a quadrature signal. Output separated by.

Each of the in-phase and quadrature signals output from the first and second multipliers 103 and 104 is input to the third and fourth multipliers 107 and 108, and the in-phase signal is input to the cosine wave generator from the third multiplier 107. A 90 ° phase shifter 109 which is mixed with the cosine signal of the 106 and outputs the quadrature signal to a sine wave by shifting the output of the cosine wave generator 106 by 90 ° in a fourth multiplier 108. Is mixed with the sine wave output signal and output.

The outputs of the third and fourth multipliers 107 and 108 are integrated in the integrator 111 through the adder 110 and then passed through the low pass filter 112 to determine the received signal in the signal discriminator 113. The baseband signal is converted and output.

On the other hand, in the signal processing process in the digital communication transmitter 200 shown in Figure 2, the baseband input data signal is input to the serial-to-parallel converter 201, where it is separated into an in-phase signal and a quadrature signal After the first and second multipliers 202 and 203 are applied.

The in-phase and quadrature signals input to the first and second multipliers 202 and 203 are respectively mixed with the output signals of the pseudo noise generator 204 and filtered through the respective low pass filters 205 and 206.

The in-phase signal and quadrature signal filtered out by the low pass filters 205 and 206 are input to the first and second modulators 208 and 209. The in-phase signal is input to the cosine and generator in the first modulator 208. A 90 ° phase shifter 210 which is modulated by the cosine signal of 207 and outputs the quadrature signal to a sine wave by shifting the output of the cosine wave generator 106 by 90 degrees in the second modulator 209. Is modulated and output by a sine wave output signal.

The outputs of the first and second modulators 208 and 209 are transmitted to the outside through the antenna through the RF mixer 211.

Here, since the in-phase signal and the quadrature signal are logically orthogonal signals, the desired signal can be extracted even if the two signals are mixed without interfering with each other. Accordingly, digital modulation and demodulation modulates and demodulates using the orthogonality of these signals, and the orthogonality between the two signals is used to restore the original signal even during modulation and demodulation.

The orthogonality of such signals is to demodulate the information signal inputted from the demodulator and to place the signal point so that the signal can be accurately determined when the signal is discriminated. Create a signal point layout to help

On the other hand, the data information signal of the digital communicator is received in a mixed form of the in-phase signal and the quadrature signal, and is output in the form of the baseband information signal by signal discrimination according to the signal point arrangement. Accordingly, the transmission / reception system having a digital modulation / demodulation system has various arrangements of signal points according to the type of the system, and the transmission format is transmitted in various forms so that the arrangement of such signal points is maintained accurately.

As a kind of digital communication method of such a system, Binary Phase Shift Keying (BPSK), Quadrature Binary Phase Shift Keying (QPSK), π / 4 Quadrature Binary Phase Shift Keying (π / 4 QPSK), and Differential Quadrature Binary Phase Shift Keying (DQPSK) ), Offset Quadrature Binary Phase Shift Keying (OQPSK), Frequency Shift Keying (FSK), and M-ary Quadrature Amplitude Modulation (M-ary QAM).

General PSK (Phase Shift Keying) communication is a communication method using a phase shift modulation and demodulation method that transmits a signal having a different phase according to the type of input information signal.

The binary PSK (BPSK) system uses an antipodal, a pair of sinusoidal signals whose satellites have a 180 ° relative phase difference to represent binary symbols 1 and 0. Therefore, the binary PSK system has a signal point of one dimension and a signal arrangement point (M = 2) consisting of two information signal points.

This separation of signal space finds the midpoint of the line connecting two information signal points and draws a boundary line that separates the appropriate judgment area. The separated determination area is divided into symbols 0 and 1, respectively. If the received signal point falls in the 0 area, it is determined that 0 is transmitted. If it falls in the 1 area, it is determined that 1 is transmitted. Randomly judges among and 1.

An important objective in the design of digital communication systems is to provide low error probability and efficient use of channel bandwidth.

Quadrature multiplexing is used for efficient bandwidth utilization in digital communications. Typical examples include four-phase phase shift keying and QAM. QPSK, π / 4 QPSK, DQPSK, OQPSK, and M-ary QAM schemes, which have two-dimensional signal points, are used to represent four symbols of π / 4, 3π / 4, 5π / 4, and 7π / 4. One of the phases arranged at intervals is taken and the signal points on the plane are recognized by their respective coordinates and determined.

In order to define the decision rule for detecting two-dimensional signal data, the signal space is divided into four areas, each area being defined as a set of points closest to the information point represented by four signal vectors. The determination region is defined by the vertical bisectors that follow the information point.

The determination area defined in this way is a quadrant whose vertex is the origin and is determined by the value of the determination area according to the position where the received information signal falls.

In quadrature phase shift keying (QPSK) modulation, the response characteristics and phase shifter characteristics of a mixer that performs quadrature quadrature modulation generally affect the performance of the modulator. Due to the unbalance of the wave, the characteristics of the phase shifter have shown the phase unbalance, which has been the main cause of error in the decision by increasing the error rate in the real system.

With this decision rule, the received signal point is determined by each symbol according to the location where it falls, but this decision is not dropped to the range of the judgment area due to noise of the transmission channel or interference between adjacent symbols. You make a mistake that makes a mistake.

Therefore, in order to minimize the determination error that the information signal input to the receiver wrongly judges the original transmission signal due to noise of transmission channel or interference between adjacent symbols, the system which minimizes noise of transmission channel or interference between adjacent symbols should be designed. .

The purpose of the present invention is to minimize the noise and inter-symbol interference in a digital communication system to accurately determine the original signal, and to change the phase of the transmitted signal and the phase of the transmitted signal arbitrarily to eliminate the inter-symbol interference. To provide a method and a circuit for suppressing inter-cardiac interference.

Means for achieving the above object of the present invention, by using a signal received by the receiver detects the phase difference and compares it with the transmission signal, the phase of the transmission signal is fixed so that the phase of the transmission and reception signal is always maintained at 90 ° It is characterized by a method of minimizing the intersymbol interference of a transmission / reception signal in a system by transmitting by shifting a phase difference value and a circuit implementing the same.

1 shows a block diagram of a typical receiver 100 for a digital communication system.

2 shows a block diagram of a 200 of a transmitter for a conventional digital communication system.

3 is a circuit block diagram of a demodulation stage for suppressing inter-symbol interference according to the present invention.

FIG. 4 is a flowchart illustrating a method of minimizing inter-symbol interference through the demodulation circuit illustrated in FIG. 3.

FIG. 5 is an operation flowchart for explaining another method of minimizing inter-symbol interference through the demodulation circuit illustrated in FIG. 3.

※ Explanation of code for main part of drawing ※

314: Receiver Phase Meter

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a demodulation circuit for suppressing intersymbol interference according to the present invention.

As shown in FIG. 3, the baseband serial data input to the transmitter 300 is input to the serial and parallel converter 301 and separated into an in-phase signal and a quadrature signal, respectively. It is configured to be applied to the multipliers (302,303).

The in-phase and quadrature signals input to the first and second multipliers 302 and 303 are respectively processed as output signals of the pseudo noise generator 304 to be input to the first and second modulators 308 and 309.

The cosine wave signal output of the cosine wave generator 307 is input to the differential phase detector 313 where it is phase detected by the output of the receiver phase measurement logic 314 and then at the phase accumulator 312 to the cosine wave output. The phase accumulator is configured to accumulate, and the output of the phase accumulator 312 is configured to be applied as a direct modulation signal to the first modulator 308 side, and the 90 ° shifter 310 to the second modulator 309 side. It is configured to be applied as a modulated signal after the phase shift through. The outputs of the first and second modulators 308 and 309 are configured to be transmitted to the outside through the antenna through the RF mixer 311 and output.

An operation process of the demodulation circuit configured as described above is described in detail as follows.

Phase Shift Keying Modulation (PSK) and Quadrature Amplitude Modulation (QAM) transmitters of all digital communication systems select the transmission signal from a certain phase to be serialized.

This series of serial data is input to the serial-to-parallel converter 301 where the information signal is converted into a parallel signal of an in-phase signal and a quadrature signal, and then input to the first and second multipliers 302 and 303.

The pseudo noise generator 304 generates a constant orthogonal code and supplies a predetermined bit of data to the in-phase signal and quadrature signal of the first and second multipliers 302 and 303.

The multiplier 303 multiplies the input signal by a predetermined bit of data generated by the pseudo noise generator 304 to generate a new code signal. The new generation code generated in this way is passed through a lowpass filter for effective band limiting (omitted in the figure).

As such, the carrier frequency generated by the cosine wave generator 307 used to modulate the signals of the band-limited in-phase channel and the quadrature channel is used. The cosine wave carrier frequency is sine by the 90 ° phase shifter 310. It is converted into a (Sine) wave and provided as a carrier signal for modulation to the balanced modulators of the in-phase and quadrature channels, that is, the first and second modulators 308 and 309, respectively.

The cosine wave used for the modulation is compensated by the difference phase detector 313 detecting the change in phase change generated while the carrier of the input signal passes through the noise channel and added to the cosine wave in the phase accumulator 312 by the change. The signal is transmitted while maintaining a phase difference of 90 ° with the transmitted signal.

As a result, the phase difference between the transmission and reception signals is always maintained at 90 ° in one system, thereby minimizing the error of the determination of the information signal by protecting against transmission noise and interference between adjacent symbols.

At this time, in order to prevent an increase in error due to the accumulation of phase change, compensation for the phase change of the received signal is alternately compensated in the + and-directions to suppress the increase of the error due to the accumulation of the change, or to a certain amount. The phase change is accumulated and then the phase change accumulated at an appropriate level is deleted, and the compensation is continued until a certain amount of phase change is accumulated from the beginning. By repeating accumulation and deletion in this way, the phase difference of the transmitted / received signal can always be maintained at 90 degrees.

Meanwhile, the in-phase signal and quadrature signal modulation outputs of the first and second modulators are converted into RF signals by the RF mixer 311 and output.

The data transmitted from the transmitter uses a phase locked loop (PLL) to detect the phase error generated by passing through the noisy channel and detects the synchronization. The phase error detected from the phase locked loop is transferred to the carrier frequency generator of the transmitter. The phase error detected by the phase locked loop is added to the cosine wave, which is the carrier frequency of the transmitter, so that the received signal and the transmitted signal are always maintained at 90 °, or a separate phase detection circuit is added to the receiver to be used as a phase detection dedicated circuit. The phase error detected by the receiver is transmitted to the transmitter so that the transmitted signal and the received signal are always transmitted at 90 °.

FIG. 4 is a flowchart illustrating a method of minimizing symbolic interference through the demodulation circuit illustrated in FIG. 3.

The transmission signal passing through the noise channel is shifted out of phase with the original transmission signal due to the noise and arrives at the receiver. The arrived signal is a much weaker signal than the transmitted signal, which is subjected to very serious interference by the transmitted signal and thus affects the data determination of the received signal. Therefore, accurate phase control is required.

First, the phase signal 402 of the received signal subjected to phase interference by the transmitter is compared in the phase difference detection step 403 with the cosine wave phase 401 of the cosine generator of the transmitter to find a phase that is changed from the original phase. The value is detected. In general, one vector value representing a phase is defined as a sine wave and a cosine wave. The cosine wave represents real data, and the sine wave represents image data. In the present invention, the cosine wave phase 401 is used as a reference signal for detecting a change in the phase signal of the received signal.

The phase difference value detected in the phase difference detection step 403 is compared with an arbitrary value a set for the system in the phase difference comparison step 404. As a result of the comparison, when the phase difference value is larger than the set value a, the phase difference value is ignored and set to 0, and then added to the cosine wave (405) so that the cosine wave is output 406 as it is. Here, setting the phase difference value to 0 means that the phase difference value is too large to be treated as an error.

On the other hand, in the phase difference comparison step 404, if the phase difference value is smaller than the set value a, the step 407 of adding the phase difference value and the cosine wave is executed. The cosine wave added with the phase difference value in step 407 generates a sinusoidal wave 409 shifted by the phase difference through the 90 ° phase shift step 408 and is output to the receiver (not shown).

The sine wave output in step 409 has a phase shifted by the phase difference detected in step 403. The phase difference determined in step 403 is evidence that there is noise or inter-symbol interference in the course of reaching the receiver. As described above, when there is noise or inter-symbol interference in the transmission signal, the signal cannot be accurately determined because the phase is not accurate to the received signal. Thus, in the present invention, the phase difference detection step 403 is used to detect the phase difference. Then, the phase of the transmission signal is compensated for in advance by the detected phase difference and transmitted so that the phase of the transmission signal and the reception signal can be accurately maintained 90 degrees. For example, when the phase difference detected in step 403 is 2 °, the transmission signal is transmitted at 92 ° or 88 °, so that the transmission signal and the reception signal can have exactly 90 ° phase difference.

FIG. 5 is a flowchart illustrating another method of minimizing inter-symbol interference through the demodulation circuit illustrated in FIG. 3.

The phase 502 of the signal received by the receiver and the cosine wave phase 501 of the cosine wave generator which is a reference signal are detected through the phase difference detection step 503. The phase difference value detected in the detection step 503 is compared with the phase difference value allowed by the system, that is, the set value a in the comparison step 504. As a result of the comparison, if the phase difference value is greater than the set value a, the phase difference value is ignored and set to 0, and then added to the cosine wave (505) so that the cosine wave is output 506 as it is. Here, setting the phase difference value to 0 means that the phase difference value is too large to be treated as an error.

On the other hand, when the phase difference value is smaller than the setting value a, the phase difference value is accumulated 507 and then the accumulated phase difference value is compared with the setting value a (508). If it is larger than the set value a, the phase difference value is set to 0 as in the previous step, and the process proceeds to steps 505 and 506. If the set value is smaller than the set value a, the step 509 is added to the cosine wave. The new cosine wave in which the phase difference accumulation value and the cosine wave are combined generates a sinusoidal wave 511 shifted by the phase difference accumulated through the 90 ° phase shift 510 and is output to the receiver (not shown).

As described above, the present invention can minimize a determination error that incorrectly determines an original transmission signal due to noise of a transmission channel or interference between adjacent symbols in a digital communication system, thereby improving reliability of the communication system. .

Claims (3)

A method for maximally suppressing intersymbol interference of a transmitted / received signal in a system includes: Detects the phase difference of the signal received by the receiver and compares it with the transmitted signal to shift the phase of the transmitted signal by a constant phase difference value so that the phase of the transmitted and received signal is always maintained at 90 °. A difference detection step 403 for detecting a cosine wave phase; Comparing (404) the phase difference value detected in step (403) to a set value; In step 404, if the phase difference value is greater than the set value a, ignoring the phase difference value and setting it to 0 and adding it to the cosine wave, and if the phase difference value is less than the set value a, adding the phase difference value to the cosine wave as it is (407); In the step 407, the cosine wave to which the phase difference value is added is added to the received signal and the 90 degree phase difference by adding the sine wave whose phase is changed by 90 degrees through the 90 degree transition step 410 and the cosine wave having the phase difference value as it is in the step 407. Generating a signal having a step (414) comprising the inter-symbol interference suppression method of the digital communication. A method for maximally suppressing intersymbol interference of a transmitted / received signal in a system: Detects the phase difference of the signal received by the receiver and compares it with the transmission signal to shift the phase of the transmission signal by a certain phase difference value so that the phase of the transmission / reception signal is always maintained at 90 °. A phase difference detecting step 503 for detecting a cosine wave phase; Comparing (504) the phase difference value detected in step (503) to a set value; In step 504, setting the phase difference value to zero when the detected phase difference value is larger than the set value and accumulating the phase difference value when the detected phase difference value is smaller than the set value (506); Comparing the accumulated phase difference value in the step 506 with a set value again and setting the phase difference value to 0 if greater than the set value and adding the sum with a cosine wave if less than the set value; Generating a new cosine wave in which the cosine wave is added to the phase difference accumulation value in step 511, and generating a new sine wave in which the 90 ° phase is changed through the 90 ° transition step. Interference symbol suppression method of a digital communication device, characterized in that. In the intersymbol interference suppression circuit of a digital communicator to minimize the intersymbol interference of a transmission / reception signal in a system: Baseband serial data input to the transmitter 300 is input to the serial and parallel converter 301 and configured to be applied to the first and second multipliers 302 and 303, respectively, and to the first and second multipliers 302 and 303, respectively. The in-phase signal and the quadrature signal are respectively processed as output signals of the pseudo noise generator 304 and input to the first and second modulators 308 and 309, and the cosine wave signal output of the cosine wave generator 307 is differential. A phase accumulator 312 is inputted to the phase detector 313 and phase-detected by the output of the receiver phase measurement logic 314, and then phase-accumulated in the cosine wave output in the phase accumulator 312, and the output of the phase accumulator 312 Are respectively configured to be applied directly as a modulated signal to the first modulator 308 side and to be applied as a modulated signal after phase shifting through the 90 degree shifter 310 to the second modulator 309 side, respectively. The outputs of the two modulators (308, 309) are passed through the RF mixer (311). A configured to be sent to output to an external inhibiting interference between symbols in a digital communication device, characterized by a circuit.