KR20000026103A - Method for controlling adaptation auto gain - Google Patents

Abstract

PURPOSE: A method for controlling an adaptation auto gain is provided to change parameter Pth of a second auto electric power control unit according to Eb/No of a received signal. CONSTITUTION: A method for controlling an adaptation auto gain includes two steps. A first step is to vary the intensity of a critical receiving signal according to quality of a receiving signal demodulated. A second step is to control an electric power gain for a base band signal being inputted from the intensity of the varied critical receiving signal and the intensity of a receiving signal of a base band which is changed with a digital. In the step to vary the intensity of the critical receiving signal, the intensity of the critical receiving signal is varied in the direction getting out of a range of the quantization in a digital change.

Description

Adaptive automatic gain control method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus of a base station and a mobile terminal, and more particularly, to improve reception performance of a base station and a mobile terminal in a CDMA mobile communication system using quadrature phase shift keying (hereinafter, referred to as QPSK) modulation and demodulation scheme. A suitable adaptive automatic gain control method is provided.

In general, in a CDMA mobile communication system, a receiving apparatus of a base station or a mobile terminal first processes a high frequency signal introduced through an antenna into a first intermediate frequency signal and converts the first intermediate frequency signal into a second intermediate frequency signal. It has a down conversion function to process the second downlink frequency, and an automatic gain control function to maintain a constant level of a received signal.

In particular, since QPSK digital modulation carries information on the phase of a signal, it is necessary to provide a constant signal power to the digital demodulator by adjusting the power gain of the receiver according to the signal strength level of the received signal.

Therefore, all QPSK receivers developed so far have an automatic gain control circuit (AGC Circuit) for providing a constant signal power to the digital demodulator.

In addition, these QPSK receivers are provided with a down conversion circuit, and include a circuit configuration for spatial diversity and a circuit configuration for received signal strength indication (RSSI).

1 is a block diagram showing the configuration of a CDMA receiving apparatus using the QPSK demodulation scheme according to the prior art.

Referring to FIG. 1, in a QPSK receiver for down-frequency processing a high frequency signal introduced through an antenna, the RF end 10 has a low noise amplifier (LNA) 11 and a band pass that passes only a predetermined band. A filter (BPF) 12 and a power gain adjustment pad (PAD) 13 for adjusting the signal level of the output of the band pass filter 12 to a certain level.

Here, the output of the power gain adjustment pad 13 is synthesized with the first local signal in the first down conversion synthesizer 14 and then first down frequency converted into a first intermediate frequency signal.

A plurality of amplifiers 21, 22, 25, 28 and amplified intermediate frequency signals are included in the primary intermediate frequency stage 20 for converting a received signal converted into such a primary intermediate frequency signal to a secondary intermediate frequency signal. A power gain adjusting pad 23 and band pass filters 24 and 27 are provided to adjust the level of P to a constant level.

In addition, the secondary down-converting synthesizer 29 of the secondary intermediate frequency terminal 20 synthesizes the first intermediate frequency signal and the second local signal that have passed through the amplifier 28 to produce a secondary intermediate frequency signal. The secondary intermediate frequency signal passes through the plurality of amplifiers 31 and 33 and the band pass filter 32 of the secondary intermediate frequency terminal 30 and is output as a received signal of the baseband frequency.

Here, the output of the primary intermediate frequency 20 should be output at the same intensity as that of the initially received high frequency signal, but in the actual QPSK receiving apparatus, the deviation is generated for each device to output different received signal levels. The second intermediate frequency signal is extracted using a divider 34 provided in the second intermediate frequency terminal 30 and then provided to the first automatic gain control stage 40.

Received Signal Strength Indication (hereinafter abbreviated as RSSI) of the primary automatic gain control stage 40 The detector 41 is thus the level (dB) of the signal extracted from the secondary intermediate frequency terminal 30 Is detected and provided to the integrator 42, and the integrator 42 receives its critical RSSI level and the output level of the RSSI detector 41, and outputs its output to the attenuator 26 provided in the primary intermediate frequency section 20. By adjusting the first received signal power gain is adjusted.

Here, the integrator 42 outputs a control signal for controlling the attenuator 26 to reduce the power gain if the level of the signal extracted from the secondary intermediate frequency 30 is greater than the threshold RSSI level, and vice versa. If the level is less than the threshold RSSI level, then the attenuator 26 outputs a control signal for controlling the power gain.

Since the primary automatic gain control stage 40 is fundamentally measured by measuring the power of the analog signal, and may change with time, the digital demodulator 70 is provided by providing a secondary automatic power gain control stage 50 to solve this problem. ) To input a certain level of power.

The secondary automatic power gain control stage 50 calculates the power level of the baseband signal converted into the digital signal in the digital converter (ADC) 65 of the baseband frequency stage 60 by the automatic gain control calculator (AGC ROM) 51. Calculates the received signal strength, converts it to an analog signal in the analog converter (DAC) 52, and integrates the voltage control gain amplifier (VCA) 54 to control the integrated signal.

That is, in order to allow a certain level of power to be input to the digital demodulator 70, the automatic gain control calculator (AGC ROM) 51 controls the voltage when the strength of the received baseband signal is greater than the threshold received signal strength P _TH . Control in the direction of decreasing the power gain of the gain amplifier (VCA) 54; conversely, control in the direction of increasing the power gain of the voltage controlled gain amplifier 54 when the received signal strength is less than the threshold received signal strength P _TH . do.

Here, the automatic gain control calculator 51 has a look up table for calculating the strength of the baseband signal from the received I and Q signals quantized by 4 bits, respectively, The output of the automatic gain control calculator 51 is calculated.

2 (I ² + Q ² )-P _TH -------- Formula (1)

Therefore, the output of the integrator 53 becomes as shown in equation (2).

2 [E (I ² ) + E (Q ² )]-P _TH -------- Formula (2)

Where E is the energy per bit of the baseband signal.

2 is a phase shift diagram according to E _b / N ₀ of a conventional QPSK receiver.

2A is a phase shift diagram according to basic E _b / N ₀ , FIG. 2B is a phase shift diagram when N ₀ increases and E _b decreases, and FIG. 2C is a phase shift diagram when N ₀ decreases and E _b increases. .

Referring to FIG. 2, in the conventional second automatic power gain control stage, the digital standardized reception of the received signal including the normalized noise and the signal (hereinafter, abbreviated as S _normalized ) is made constant, thereby receiving the digital conversion. The power strength of the signal can be made constant.

In FIG. 2, the center points of the four circles having the same radius represent the phase of a signal that is digitally converted and input to the second automatic power gain control stage. In the QPSK modulation and demodulation mobile communication system, information is carried at the position of this center point. . Where the statistical standard deviation of the normalized received noise power density (hereinafter abbreviated as N _{0, normalized} ) is

As can be seen from this, all signals other than the call channel are recognized as noise.

In addition, the statistical standard deviation of the normalized desired signal (hereinafter abbreviated as E _{b, normalized} ) is As can be seen from this, the signal of the communication channel is included in the molecule.

In the related art, S _normalized = KP _TH = 1.0.

When comparing the phase shift diagram of FIG. 2B with FIG. 2A, N _{0, normalized} is increased, E _{b, normalized} is decreased, and S _normalized is the same. Therefore, the reception quality is worse than that of the phase shift diagram shown in FIG. 2A.

When comparing the phase shift diagram of FIG. 2C with FIG. 2A, N _{0, normalized} is decreased, E _{b, normalized} is increased, and S _normalized is the same. Thus, the reception quality is better than the phase shift diagram shown in FIG. 2A.

In other words, the reception quality changes as noise increases or decreases in the received signal _so that N _{0, normalized} increases or decreases.

According to the related art described above, the output equation 2 (I ² + Q ² ) -P _{TH of the} automatic gain control calculator (AGC ROM) and the output equation 2 [E (I ² ) + E (Q ² )] of the integrator. The I and Q signals used in P _TH are mixed with noise and QPSK modulated signals.

In addition, the statistical standard deviation of the received signal, including normalized noise and the signal, has a value defined as S _normalized = KP _TH = 1.0, so that the power-to-noise power spectrum density per bit of the received signal (hereinafter, E _b / N _0). It will have a fixed threshold received signal strength (P _TH ) regardless of.

Therefore, since S _normalized is fixed constantly, it is difficult to improve reception performance when noise is increased and reception quality is degraded.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and the quality of the received signal, that is, the received signal E _b / To provide an adaptive automatic gain control method for changing the parameter (P _TH ) of the secondary automatic power gain control stage in accordance with N ₀ .

According to an aspect of the present invention, there is provided an adaptive automatic gain control method, including: varying a threshold received signal strength according to a quality of a demodulated received signal, and varying the threshold received signal strength and digital conversion. Adjusting the power gain for the input baseband signal from the intensity of the received baseband received signal.

Preferably, in the step of varying the threshold received signal strength, the threshold received signal strength is varied in a direction that does not deviate from the quantization range during the digital conversion.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the configuration of a CDMA receiving apparatus using the QPSK demodulation method according to the prior art.

2 is a phase shift diagram according to E _b / N ₀ of a conventional QPSK receiver,

a) is the phase shift diagram according to the fundamental E _b / N ₀ .

b) is the phase shift when N ₀ increases and E _b decreases.

c) is the phase shift when N ₀ decreases and E _b increases.

3 is a block diagram showing a configuration of an adaptive automatic gain control circuit according to the present invention;

4 is a phase shift diagram according to E _b / N ₀ of the QPSK receiving apparatus according to the present invention.

a) is the phase shift diagram according to the fundamental E _b / N ₀ .

b) is the phase shift diagram when N ₀ increases.

c) is the phase shift diagram when N ₀ decreases.

5 is a state transition diagram of a state controller provided in the digital demodulator according to the present invention.

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

3 is a block diagram showing a configuration of an adaptive automatic gain control circuit according to the present invention.

Referring to FIG. 3, the adaptive automatic gain control circuit according to the present invention has a configuration similar to that of the secondary automatic power gain control stage in FIG. 1 described above, but conventionally makes the threshold received signal strength P _TH constant. On the other hand, in the present invention, the control signal for varying the threshold received signal strength (P _TH ) from the digital demodulator 300 according to the quality of the received signal is transferred to the automatic gain control calculator 110 to determine the threshold received signal strength (P _TH ). Will change.

Reference will be made to FIG. 4 to describe this.

4 is a phase shift diagram according to E _b / N ₀ of the QPSK receiver according to the present invention.

Referring to FIG. 4, in the phase shift diagram according to the present invention, E _{b and normalized} are constant and S _normalized is changed.

The radius of the circle related to this S _normalized is proportional to the square root of the critical received signal strength (P _TH ).

S _normalized = KP _TH (K is proportional constant) ----------- Equation (3)

4A, 4B and 4C are phase shift diagrams represented by equation (3).

Here, the center points (400, 500, 600) of the four circles of the same radius are located farthest from the origin within the allowable quantization range.

This indicates that the receiving device has the least sensitive reception performance to external noise because the distance between the center points 400, 500, 600 of the four circles is the longest.

In FIG. 4A, N _{0, normalized} is

,

E _{b, normalized} is to be.

In addition, S _normalized = KP _TH in the present invention, if the reception quality of the digital demodulator 300 is high, this is reduced, and if the reception quality is low, it is increased.

In FIG. 4B _, N _{0, normalized} is increased compared to FIG. 4A, but E _{b, normalized} is the same, and S _normalized is the same, and thus has the same reception quality as in FIG. 4A.

In FIG. 4C, since N _{0, normalized} is reduced compared to FIG. 4A, E _{b, normalized} is the same, and S _normalized is the same, and thus has the same reception quality as that of FIG. 4A.

In the present invention, drops than the received signal quality of the digital demodulator, the desired value to increase the received signal strength threshold (P _TH), the quality of the received signal is lowered permitting the received signal strength threshold (P _TH) than the desired value.

However, the CDMA received signal strength E _{b (normalized} ² ) should not be outside the quantization range of the digital converter 300. Accordingly, the digital demodulator 300 requires a state machine 310 in which the state changes depending on whether or not the four-way center points 400, 500, and 600 of the received signal quality and phase shift are in or out of the quantization range.

The state controller 310 outputs a control signal for changing the threshold received signal strength P _TH to the automatic gain control calculator 110.

5 is a state transition diagram of a state controller provided in the digital demodulator according to the present invention.

Referring to FIG. 5, the state transition diagram of the state controller provided in the digital demodulator is described as two items as follows.

First, if the received signal quality is smaller than the desired value and E _{b, normalized} does not deviate from the quantization range of the digital converter, the threshold received signal strength P _TH is increased (S1, S3).

Second, if the received signal quality is greater than the desired value, or if E _{b, normalized} is outside the quantization range of the digital converter, the threshold received signal strength P _TH is reduced (S2, S4).

Here, the input of the digital converter is said to be saturated when it is out of the quantization range, and the function for determining the saturation or desaturation is performed by the digital modem.

S _normalized ² = P _TH ² = N _{0, normalized} ² + E _{b, normalized} ² ------- Equation (4)

E _{b, normalized} ² / N _{0, normalized} ² = R ---------------------------- Equation (5)

Equation (4) shows that the power of the combined signal of the CDMA signal and the noise maintains a constant threshold received signal strength (P _TH ) as a characteristic of digital automatic gain control. Equation (5) is the value (R) found while recovering the pseudo noise signal of the digital demodulator.

Using these equations (4) and (5), N _{0, normalized} and E _{b, normalized} are expressed as follows.

E _{b, normalized} ² = (1 + (1 / R)) * P _TH ² -------------------- Equation (6)

N _{0, normalized} ² = ((1 + R) / R ² ) * P _TH ² -------------------- Equation (7)

As described above, the present invention changes the S _{normalized value} by adding or subtracting the critical received signal strength P _TH according to the received signal quality of the digital demodulator, thereby solving the degradation of the reception quality due to the noise increase. There is an effect that can improve the performance of.

Claims (2)

Varying the threshold received signal strength according to the quality of the demodulated received signal; And adjusting the power gain for the input baseband signal from the variable threshold received signal strength and the digitally converted baseband received signal strength. The method of claim 1, And in the step of varying the threshold received signal strength, the threshold received signal strength varies in a direction that does not deviate from the quantization range during the digital conversion.