KR20020057593A - Method for alternative digital modulation/demodulation - Google Patents

Abstract

PURPOSE: A method for applying variably a digital modulation/demodulation method in a mobile communication system is provided to switch the digital modulation/demodulation method to a 16QAM method according to a measured result by measuring an S/N(Signal to Noise) ratio of a received signal. CONSTITUTION: A call service is connected in mobile communication(S11). A data transmission and reception process is performed between terminals and an S/N ratio of a signal received from the terminal is measured(S13). A state of a radio channel is checked by comparing the measured value of the S/N ratio with a reference value stored in the terminal(S15,S17). An existing QPSK digital modulation/demodulation method is maintained if the radio channel is in the normal state(S19). The existing QPSK digital modulation/demodulation method is switched to 16QAM if the radio channel is in the abnormal state(S21).

Description

Variable application method of digital modulation and demodulation method in mobile communication system {Method for alternative digital modulation / demodulation}

The present invention relates to a digital modulation and demodulation method in a mobile communication system, and more particularly, by applying a digital modulation and demodulation method variably according to the environment of a wireless channel, so that high-speed data can be transmitted and received stably regardless of the influence of external interference. The present invention relates to a variable application method of a digital modulation and demodulation method in a mobile communication system.

In general, digital modulation methods include phase shift keying, frequency shift keying, and the like.

Phase Shift Keying is a method of loading data on the phase of a sine wave used as a carrier wave. The phase shift keying method divides a carrier phase of a constant frequency and a constant amplitude into two equal parts (180 ° phase difference), four equal parts (90 ° phase difference), or It is a modulation method that divides into 8 equal parts (45 ° phase difference) and assigns 0 or 1 to different phases, or assigns 2 bits or 3 bits to each other and sends them to the other party.

The phase shift of the carrier is 90 degrees, called Quadrature Phase Shift Keying (QPSK), and is generally used in the field of CDMA cellular communication services, WLL, and iridium communication.

The digital modulation of the QPSK method is a method in which the digitally processed data in the baseband is divided into I (In phase) and Q (Quadrature phase) channels, and then each channel is combined into one symbol with different phase energy.

Fig. 1 (a) is a block diagram of a general QPSK modulated signal generator.

As shown, a serial-to-parallel converter 10 for converting serially input binary data into binary parallel data, and the serial-to-parallel converter 10 generates a level of a signal separated into I and Q channel data, respectively. A first level generator 11 and a second level generator 12, a delay element 13 for delaying the Q channel signal to simultaneously modulate the I and Q channel signals passing through the level generator, and the I channel signal. A carrier generator 14 for mixing carriers, a phase shifter 15 for shifting the phase of the carrier generated by the carrier generator by 90 °, a signal output from the first level generator, and the carrier generation A first mixer 16 for mixing the carriers generated from the unit, and a second mixer for mixing the Q-channel signal output from the delay element 13 and the carriers phase shifted by 90 degrees from the phase shifter 15 17 and above 1 consists of a mixer 16 and second mixer 17. The I channel signal and a summing amplifier 18 for summing the Q channel signal output from.

The operation of the QPSK modulated signal generator configured as described above is as follows.

The binary data input to the serial-to-parallel converter 10 is converted into parallel data in a non-return to zero (NRZ) format, divided into one for each of the I and Q channels, and simultaneously modulated with the I and Q channels. In this case, in order to perform simultaneous modulation with phase difference, the delay element 13 is placed to delay the Q channel signal, and the phase of the carrier is shifted and mixed with the delayed Q channel signal.

When the modulation signal generator changes from 0 to 1 or 1 to 0, the phase of the I channel balance modulator output is or Is inverted to, and the output of the Q channel is or If the sum of the two trigonometric signal by the summer (18), , , , or We have one of four values with the same frequency but only 90 degrees out of phase. That is, since the I and Q channels are orthogonal to each other, there is no interference even when synthesized through the summer 18.

FIG. 1 (a) is a diagram illustrating an embodiment of the signal flow of FIG. 1 (a).

As shown, reference numeral 20 denotes a binary data signal input to the QPSK signal modulator, and reference numerals 21 and 22 denote I and Q channels of data separated into I and Q channels through the serial-to-parallel converter of FIG. 23 is a modulated signal that has passed through the summer of FIG.

An input signal sequence of 22 is an example, and is 1,1,0,1,1,0,0,0,1,1,1,0. When this signal passes through a serial-to-parallel converter, the binary data are alternately separated into I and Q channels. Therefore, the signal of the I channel becomes 1,0,0,0,1,1 which is an odd number of the input data. The binary data 1 has a phase of 0 ° and the binary data 0 has a phase of 180 °.

Similarly, binary data divided into Q channels are 1, 1, 0, 0, 1, 0, which are even numbers of the input data.

The sum of the signals of the I channel and the Q channel with the phase difference is 11, 01, 10, 00, 11, 10, and the phase is a result of the trigonometric summation of the I and Q channel signals, as shown at 23. 45 °, 135 °, 315 °, 225 °, 45 °, 315 °.

FIG. 1 (a) is a signal constellation diagram of QPSK modulation and demodulation method, and as shown in FIG. 1A, four two-bit digital signals of 00, 01, 10, and 11 can be transmitted, and each two-bit digital signal has a phase difference of 90 °. Have.

However, as described above, the QPSK digital modulation method has a low data transmission rate and low influence of external interference, so that a high-speed transmission / reception of a large amount of data such as transmission and reception of a video other than a voice call is impossible in a mobile communication system.

Therefore, the present invention has been proposed to solve the above problems according to the prior art,

An object of the present invention is to measure the signal-to-noise ratio of the received signal during the wireless data transmission and reception of the terminal from time to time, and whenever a reference value is not reached, the digital modulation and demodulation method is switched to 16QAM to reliably transmit and receive high-speed data regardless of the influence of external interference The present invention provides a variable application method of a digital modulation and demodulation method in a mobile communication system.

Features of the present invention for achieving the above object,

When the call is connected and data transmission and reception of the terminal are started, measuring a signal-to-noise ratio of the received signal received by the terminal, and comparing the measured value with a preset reference value to determine whether the state of the wireless channel is good;

As a result of the determination, if the state of the radio channel is good, maintaining the existing QPSK digital modulation and demodulation method, and if the state of the radio channel is not good, characterized in that it comprises a step of switching the digital modulation and demodulation method to 16QAM.

1 (a) is a block diagram of a general QPSK modulated signal generator,

Figure 1 (a) is a view showing an embodiment of the signal flow of Figure 1 (a),

1 (a) is a signal constellation diagram of the QPSK modulation and demodulation method,

Figure 2 (a) is a block diagram of the configuration of the 16QAM modulated signal generator applied to the present invention,

FIG. 2 (b) is a diagram showing an embodiment of the signal flow of FIG. 2 (a),

Figure 2 (c) is a signal constellation diagram of the 16QAM modulation and demodulation method applied to the present invention

3 is a flowchart illustrating a variable application method of a digital modulation and demodulation method in a mobile communication system according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: serial-to-parallel converter

14: carrier generation unit

15: phase shifter

Hereinafter, a preferred embodiment of the variable application method of the digital modulation / demodulation method in the above-described mobile communication system will be described in detail with reference to the accompanying drawings.

Prior to describing an embodiment of the present invention, the 16QAM modulation and demodulation method applied to the present invention will be described.

Quadrature Amplitude Modulation (QAM) modulation and modulation is a method of classifying a digital signal by a predetermined amount and modulating it while changing a carrier signal and a phase. Unlike BPSK, QAM uses not only phase but also size, so it can transmit more digital data simultaneously.

In 16-QAM, 16 levels of quantized digital signals are distributed and modulated by 16 coordinates in the I and Q channels. In other words, it is possible to send a binary digital signal of 4 bits per coordinate through 16 signal spaces of different phases and magnitudes. The receiving end observes in which area the received signal is located based on a boundary line separating 16 signal coordinates and demodulates the original signal.

FIG. 2 (a) is a block diagram of a 16QAM modulated signal generator according to the present invention.

As shown, the first modulator 30 and the second modulator 40 which receive binary input data in order of 2 bits and modulate the I and Q channels, and the first modulator and the second modulator. And a summer 50 for summing the negative outputs.

Since the configuration and operation of the first modulator 30 and the second modulator 40 are the same as those of the QPSK modulated signal generator, a description thereof will be omitted.

The first modulator 30 The carrier frequency of is inputted and puts a phase difference of 90 ° again in the Q channel of the first modulator 30, and the second modulator 40 The carrier frequency of is inputted to put a phase difference of 90 ° again in the Q channel of the second modulator 40.

Therefore, the modulated signal output from the 16QAM modulated signal generator is transmitted simultaneously with 4 bits per symbol, which means that the data rate is twice that of QPSK.

In the 16QAM modulated signal generator, four I values and four Q values are used. According to the present invention, since the apparatus is switched to QPSK and 16QAM, only the upper first modulator is used when operating in the QPSK mode, and both the first modulator and the second modulator are used when the system operates in 16QAM. That is, four I and Q channels are used.

FIG. 2B is a diagram illustrating an embodiment of the signal flow of FIG. 2A.

As shown, reference numeral 70 denotes binary data input in serial form to the first and second modulators, and is 1,1,0,1,1,0,0,0,1,1,1,0. The data of, 0,1,0,1,1,0,0,1 are input in order. Reference numeral 71 and reference numeral 72 denote data flows of I and Q channels in 2-bit binary data input to the first modulator in FIG. 2 (a), and 73 and 74 denote second data in FIG. 2 (a). It is a data flow of I and Q channels from 2-bit binary data input to the modulator. That is, alternately two bits are input to the first modulator and the second two bits are input to the second modulator, and the data input to each modulator is separated by one bit according to the I and Q channels. Will be.

Reference numeral 75 shows the summed output of the modulated signals in the four I and Q channels as described above, and it can be seen that data is transmitted by 4 bits as 1101, 1000, 1110, 0101, 1001.

Figure 2 (c) is a signal constellation diagram of the 16QAM modulation and demodulation method applied to the present invention, it is demodulated to the original signal based on the position of the data shown in a total of 16 signal coordinates of four each.

The QPSK modulation and demodulation technique determines the signal value using only the phase information, and the 16QAM method uses two values of phase and magnitude simultaneously to determine the signal value. The method is much higher, but the data rate is better than QPSK.

The present invention measures the terminal received signal-to-noise ratio and determines whether to switch the 16QAM scheme according to the value. The signal-to-noise ratio refers to the analogy between signal and noise, and the larger the value, the better the state of the wireless channel. This state can be transmitted in a very secure state because there are no other interference waves on the radio channel. In this case, the 16QAM modulation scheme is used to improve the data rate without affecting external interference, i.e., to transmit a large amount of data quickly when the radio channel is in good condition.

3 is a flowchart illustrating a variable application method of a digital modulation and demodulation method in a mobile communication system according to the present invention.

First, when a call of mobile communication is connected (S11), when data transmission and reception of the terminal is started, the signal-to-noise ratio of the received signal received by the terminal is measured (S13), and the measured value and the reference value pre-stored in the terminal are compared with each other. It is determined whether the state is good (S15).

As a result of the determination, if the state of the wireless channel is good, the existing QPSK digital modulation / demodulation method is maintained (S19). If the state of the wireless channel is not good, the digital modulation / demodulation method is switched to 16QAM (S21).

The process of FIG. 3 is frequently performed throughout the call to actively respond to changes in the wireless channel environment so that whenever a wireless channel environment is good, the modulation / demodulation method is changed to 16QAM so that a large amount of data can be transmitted.

The variable application method of the digital modulation and demodulation method in the mobile communication system according to the present invention as described above has the effect of enabling high-speed data transmission without being affected by channel interference by frequently switching the digital modulation and demodulation method according to the radio channel environment. .

In addition, since the modulation / demodulation conversion is determined based on the signal-to-noise ratio, error-free data transmission and reception are possible.

Claims (3)

In the digital modulation and demodulation method of a mobile communication system, When a call is connected and data transmission and reception of the terminal are started, measuring a signal-to-noise ratio of the received signal received by the terminal and comparing the measured value with a reference value previously stored in the terminal to determine whether the state of the wireless channel is good; In the mobile communication system comprising the step of maintaining the existing QPSK digital modulation and demodulation method when the state of the wireless channel is good, and converting the digital modulation and demodulation method to 16QAM when the state of the wireless channel is not good. Variable application method of digital modulation and demodulation method. The method of claim 1, If the state of the radio channel is good, maintaining the existing QPSK digital modulation and demodulation method, and if the state of the radio channel is not good, the step of switching the digital modulation and demodulation method to 16QAM is whether or not the state of the radio channel from time to time during the data transmission and reception of the terminal And a digital modulation / demodulation method in a mobile communication system, wherein the digital modulation / demodulation method is switched from time to time according to the channel environment. The method of claim 1, Measuring the signal-to-noise ratio of the received signal received by the terminal and comparing the received signal-to-noise ratio using the energy of the symbol detected in the baseband and the strength of the received signal, as a result And storing a table in a memory of a terminal and comparing the received signal with a signal received during a terminal call.