JP3667240B2 - Automatic gain control device for CDMA receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic gain control apparatus used for a receiver of a CDMA (Code Division Multiple Access) system using spread spectrum communication technology.
[0002]
[Prior art]
FIG. 3 is a block diagram showing a schematic configuration of a receiver employing a conventional CDMA system.
As shown in FIG. 3, a conventional CDMA receiver receives a CDMA signal transmitted from a base station by an antenna 301 of a mobile device, amplifies the received signal by an RF amplifier 302, and then a frequency converter 303. Is converted from a radio frequency to a baseband frequency, and digitized by an A / D (analog / digital conversion) unit 305. Based on the digitized signal, an AGC (automatic gain control) unit 304 performs gain control on the RF amplification unit 302.
[0003]
The digitized signal is passed to the despreading unit 307 and the path search unit 306 for searching the timing of the path to be received. Then, the timing is extracted by the path search unit 306, the spectrum is despread by the despreading unit 307 using the information, and is passed to the demodulation unit 309 and the AFC unit 308. The signal demodulated by the demodulating unit 309 is subjected to error correction by the error correcting unit 310 to obtain a desired received signal. On the other hand, the AFC unit 308 detects a frequency error between the base station and the mobile device and controls the frequency conversion unit 303 to reduce the frequency error.
[0004]
In the AGC system in the CDMA receiver using such spread spectrum communication technology, the sum of noise power, interference wave power, and desired wave power is made constant by automatically controlling the gain of the spread spectrum received signal. It was.
[0005]
According to the conventional AGC control method, since automatic gain control is performed on a received signal composed of a desired wave signal and an undesired wave signal (primary AGC), there is a problem that the desired wave power is not constant. In response to this problem, Japanese Patent Laid-Open No. 10-107765 (AGC circuit for CDMA) proposes a method for outputting a stable desired wave level to a demodulator based on an output from an analog correlator.
[0006]
[Problems to be solved by the invention]
In current communication devices, it is indispensable to reduce power consumption. For this purpose, it is necessary to integrate LSIs having individual functions.
In the AGC circuit for CDMA described in Japanese Patent Laid-Open No. 10-107765, a configuration using an analog correlator has been proposed, but most of the other circuits are generally configured by digital circuits. Therefore, since it is difficult to configure the digital circuit and the analog circuit with the same LSI, it is disadvantageous for integration.
[0007]
When a circuit (secondary AGC unit) that performs AGC on the despread signal in addition to the primary AGC as a problem in a normal communication device, the pull-in time of the secondary AGC is generally A large difference occurs depending on the initial value. As a further problem, in the case of an apparatus that performs error correction after demodulation, if the gain of AGC is not constant within a certain code block, the input signal level becomes non-uniform and the error correction capability decreases.
[0008]
As another problem, the signal subjected to automatic gain control is passed to the demodulation unit and the AFC unit. The optimum gain control cycle for controlling the AFC unit and the code block cycle when performing error correction after demodulation are as follows. Because they are not necessarily equal, the input signal level becomes non-uniform, and the error correction capability decreases. The same applies to the target value for gain control.
[0009]
The present invention has been made in view of the above-described circumstances, and by performing automatic gain control on a signal obtained by spectrum despreading in a digital despreader, the desired wave power is made constant, and the error correction unit and the AFC unit An object of the present invention is to provide an automatic gain control device for a CDMA receiver in which the gain control period and target value are optimal and LSI integration is easy.
[0010]
[Means for Solving the Problems]
An automatic gain control apparatus for a CDMA receiver according to the present invention performs automatic gain control on a spread spectrum received signal, and then performs automatic gain control on a despread spectrum signal in a digital despreader. An automatic gain control apparatus for a CDMA receiver, comprising: an AGC circuit that alternately performs gain control for a demodulation unit and gain control for an automatic frequency control unit in a time-sharing process, wherein the AGC circuit is automatically connected to the demodulation unit. The gain control target value is read and set from each storage unit storing the gain control target value of the frequency control unit, and the control period in the gain control of the demodulation unit is made equal to the code block period of error correction, Within the code block, the gain is controlled to be constant, and the gain is updated at the head of the next code block.
[0011]
The automatic gain control apparatus of the CDMA receiver can be configured to control the gain by bit-shifting the signal output from the digital despreader.
[0012]
Further, the automatic gain control device of the CDMA receiver has a circuit that allows an upper limit target value and a lower limit target value to be set as target values of the comparator, and allows a target value width to be set as an output of the comparator. It is possible to configure.
[0016]
In the automatic gain control apparatus of the CDMA receiver, the target value for gain control can be changed between gain control for the demodulation unit input and gain control for the automatic frequency control unit input.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an automatic gain control apparatus for a CDMA receiver according to the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a CDMA receiver using an automatic gain control apparatus according to an embodiment of the present invention.
As shown in FIG. 1, a CDMA receiver using an automatic gain control apparatus according to an embodiment of the present invention includes a CDMA reception antenna 101, an RF amplification unit 102, a frequency conversion unit 103, a primary AGC unit 104, an A / D Unit 105, path search unit 106, despreading unit 107, arithmetic unit 108, secondary AGC unit 109, AFC unit 110, demodulation unit 111, and error correction unit 112.
[0018]
In this receiver, the CDMA signal transmitted from the base station is received by the CDMA receiving antenna 101 of the mobile device, amplified by the RF amplifier 102, and then converted from a radio frequency to a baseband frequency by the frequency converter 103. , And digitized by the A / D unit 105.
Then, based on the digitized signal, the gain of the RF amplification unit 103 is controlled by the primary AGC unit 104.
[0019]
The digitized signal is transferred to the despreading section 107 and the path search section 106, the timing is extracted by the path search section 106, and the spectrum is despread by the despreading section 107 using the information. The signal subjected to the spectrum despreading is gain-controlled by the secondary AGC unit 109 and passed to the demodulation unit 111 and the AFC unit 110. The signal demodulated by the demodulation unit 111 is transferred to the error correction unit 112 and returned to the transmitted information. On the other hand, the AFC unit 110 detects a frequency error between the base station and the mobile device, and controls the frequency conversion unit 103 to adjust the frequency to the base station. As described above, the receiving apparatus according to the present embodiment has a configuration in which the secondary AGC unit 109 performs automatic gain control on the signal whose spectrum is despread by the despreading unit 107.
[0020]
Next, the secondary AGC unit in the automatic gain control device of the present embodiment will be described in detail.
FIG. 2 is a block diagram showing a detailed configuration of the secondary AGC unit in the automatic gain control apparatus of the present embodiment.
In the automatic gain control apparatus of the present embodiment, the gain control period can be changed between the demodulator input that performs error correction in the subsequent stage and the AFC unit input that does not perform error correction, so that it is optimal for each input. The gain control period can be set.
For this purpose, two AGC circuits may be provided. However, as shown in FIG. 2, by providing switches 211, 212, 213, 214, and 215 and performing time-sharing processing, the circuit scale is increased. Can be reduced. Hereinafter, the output to the demodulation unit 111 will be described, but the output to the AFC unit 110 is the same except for the gain control period.
[0021]
First, the initial value of the secondary AGC unit 109 will be described.
The initial value of the secondary AGC unit 109 set in the demodulation unit storage unit 210 may be set to a minimum value, a maximum value, or an intermediate value thereof. In this embodiment, the initial value is set to the path search unit 106. Estimate from the signal level measured in step 1.
That is, since the signal level measured by the path search unit 106 and the signal level measured by the despreading unit 107 are in a proportional relationship, the signal level measured by the path search unit 106 is multiplied by a constant in the calculation unit 108. And set in the demodulation unit storage unit 210. The signal level measured at this time may be time averaged.
As described above, by estimating the initial value of the secondary AGC unit 109 from the signal level measured by the path search unit 106, the pull-in time in the secondary AGC unit 109 can be shortened.
[0022]
Next, a procedure for updating the stored value in the demodulating unit storage unit 210 by comparing the power that has been gain-controlled based on the initial value set in the demodulating unit storage unit 210 and the target value will be described.
At this time, the switches 211 to 214 are set to the A side in FIG. In the case of output to the AFC unit 110, the switches 211 to 214 are set to the B side in FIG.
The signal level of the signal from the despreading unit 107 may be adjusted using a multiplication circuit based on the value of the demodulation unit storage unit 210. However, in the automatic gain control device of this embodiment, the despreading is performed. The signal from the unit 107 is bit-shifted by the demodulator bit shift unit 201 to adjust the signal level. By adopting such a method, the circuit scale can be reduced.
Further, the power is measured based on the signal whose level is adjusted by the power calculation unit 203, and the measured power is averaged by the averaging unit 204.
[0023]
The averaging period may be irrelevant to the error correction code block period. However, in the automatic gain control apparatus according to the present embodiment, the averaging period in the averaging unit 204 is the error correction code block period, and the gain control period is It is made equal to the code block period. The case where the error correction unit 112 uses soft decision Viterbi of the error correction method will be described as an example.
In soft decision Viterbi, transmission information is decoded based on the sign of a signal output from the despreading section 107 and absolute value information.
In this case, if the gain is controlled within the period of the code block, the absolute value information is distorted. Therefore, within the same error correction code block, the gain is controlled to be constant, and the gain is updated at the head of the next code block.
[0024]
At this time, the averaging storage unit 205 for the demodulation unit is used for averaging, and the averaging storage unit 206 for the AFC unit is used for the output for the AFC unit.
The averaged power is compared with the target value by the comparator unit 207 and evaluated as one of large (+1), small (−1), and equal (0).
[0025]
The automatic gain control device of the present embodiment is configured such that the comparator unit 207 compares the upper limit target value with the lower limit target value as the target value, and the range that is evaluated to be equal to the target value can be changed.
That is, when the upper limit target value <measured power, it is evaluated as “large”, when the lower limit target value> measured power, it is evaluated as “small”, and in other cases, “equal”. evaluate.
[0026]
This target value may be set the same for the demodulator and the AFC unit. However, in the automatic gain control device of the present embodiment, the target value is separately provided for the demodulator and the AFC unit. Is configured to set.
This target value is set as an upper limit target value and a lower limit target value in the demodulator target value storage unit 216 and the AFC unit target value storage unit 217, respectively, and is switched to time division by the switch 215. Compared.
[0027]
The output of the comparator unit 207 is subtracted from the previous value stored in the demodulation unit storage unit 210 by the subtractor 208 to update the stored value in the demodulation unit storage unit 210 and to store the stored value. Based on the value, the demodulator bit shift unit 201 is controlled to adjust the output of the despreading unit 107 to a target power level.
The direction of bit shift at this time is a direction in which the output of the despreading unit 107 is controlled to be large when the value of the demodulation unit storage unit 210 is large, and the output of the despreading unit 107 is also controlled to be small when the value is small. And
The control of the AFC bit shift unit 202 is performed in the same manner.
[0028]
【The invention's effect】
Since the automatic gain control apparatus for a CDMA receiver according to the present invention has the above-described configuration, the following effects can be obtained. That is, according to the CDMA receiver of the present invention, the desired signal power can be made constant by automatically controlling the gain of the spectrum despread signal in the digital despreader, and the LSI can be easily integrated. Become.
[0029]
Further, according to the automatic gain control device of the CDMA receiver of the present invention, the signal scaled up from the circuit using the multiplication circuit is controlled by gain control of the signal output from the digital despreader by bit shift. Can be reduced.
[0030]
Further, according to the automatic gain control device of the CDMA receiver of the present invention, the upper limit target value and the lower limit target value can be set as the target value of the comparator, and the range of the target value can be set as the output of the comparator. It becomes difficult to be affected.
[0034]
Further, according to the automatic gain control apparatus of the CDMA receiver of the present invention, the target value for gain control can be changed between the demodulator input for performing error correction at the later stage and the AFC unit input for which error correction is not performed. As a result, it is possible to set the optimum gain control target value for each.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a CDMA receiver using an automatic gain control apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a detailed configuration of a secondary AGC shown in FIG.
FIG. 3 is a block diagram showing a schematic configuration of a conventional CDMA receiver.
[Explanation of symbols]
101, 301 Antenna 102, 302 RF amplification unit 103, 303 Frequency conversion unit 304 AGC unit 104 Primary AGC unit 105, 305 A / D unit 106, 306 Path search unit 107, 307 Despreading unit 108 Operation unit 109 Secondary AGC Units 110 and 308 AFC units 111 and 309 Demodulating units 112 and 310 Error correcting unit 201 Bit shift unit for demodulating unit 202 Bit shift unit for AFC unit 203 Power calculating unit 204 Averaging unit 205 Average storage unit for demodulating unit 206 AFC unit Average storage unit 207 Comparator unit 208 Subtractor 209 AFC unit storage unit 210 Demodulation unit storage unit 211, 212, 213, 214, 215 Switch 216 Demodulation unit target value storage unit 217 AFC unit target value storage unit

Claims (4)

An automatic gain control device for a CDMA receiver that performs automatic gain control on a spread spectrum received signal and then performs automatic gain control on a despread spectrum signal in a digital despreader,
An AGC circuit that alternately performs gain control on the demodulation unit and gain control on the automatic frequency control unit by time division processing,
The AGC circuit reads and sets the gain control target value from each storage unit storing the gain control target values of the demodulation unit and the automatic frequency control unit, and makes an error in the control cycle in the gain control of the demodulation unit An automatic gain control apparatus for a CDMA receiver, wherein the gain is made equal to the code block period of correction, the gain is controlled to be constant in the code block, and the gain is updated at the head of the next code block.   2. The automatic gain control apparatus for a CDMA receiver according to claim 1, wherein gain control is performed by bit-shifting a signal output from the digital despreader.   2. The CDMA receiver according to claim 1, further comprising a circuit capable of setting an upper limit target value and a lower limit target value as target values of the comparator, and capable of setting a range of the target value as an output of the comparator. Automatic gain control device.   2. The automatic gain control apparatus for a CDMA receiver according to claim 1, wherein a target value for performing gain control can be changed between gain control for the demodulator input and gain control for the automatic frequency control unit input.

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