JPH08335928A - Receiver - Google Patents

Abstract

PURPOSE: To reduce an error rate in the demodulation state by the reduction in the power level of a signal from each station by reducing the fluctuation in the signal power of each station in the demodulation state by the increase in the number of channels so as to keep the quantization accuracy constant in the receiver for a mobile communication system where simultaneous speech is conducted among mobile stations based on the code division multiple address communication system. CONSTITUTION: Analog signals sent from plural mobile stations are multiplexed in air and the multiplexed signal is received by an antenna 10. The frequency of the signal received by the antenna 10 is decreased up to a base band frequency at a reception section 20. The signal with the base band frequency is converted into a signal whose maximum amplitude is constant by an AGC 30. An output signal S30 of the AGC 30 is A/D-converted by an A/D converter 40 and outputted to a demodulation power controller 50. The demodulation power controller 50 normalizes the power of the signal of each station and outputs to a demodulation section 60. The demodulation section 60 uses a spread code for each station to take correlation for the demodulation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to code division multiple access (Co
The present invention relates to a receiver of a mobile communication system using a de Devision Multiple Access (hereinafter referred to as CDMA) system.

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, some documents were described in the following documents. References: IEICE Transactions , J77-B-II [1
1] (1994-11), Atsushi Fukasawa, Takuro Sato, Manabu Kawabe, Shinichi Sato and Daiki Sugimoto, "Structure and characteristics of interference canceller based on propagation path estimation using pilot signal", P.628-
640 In a conventional CDMA modulator / demodulator, transmission data is spread over a wide band by a user-specific spreading code, and the spread signal is converted into a high frequency signal by a wireless device (transmitter).
The signal converted to a high frequency signal is transmitted from the antenna,
This transmitted signal becomes one channel of CDMA.

In CDMA, a plurality of transmitting stations use the same frequency band, but since the transmitting stations have different spreading codes, simultaneous communication is possible. Normally, in synchronous CDMA,
Since an orthogonal code (that is, a code having a correlation value between codes of 0) is used as the spreading code, interference between the codes can be ignored. However, in the actual CDMA system, especially in the uplink from the mobile station to the base station (that is, the reverse link), each mobile station system operates with its own clock, so the receiving side becomes an asynchronous system. In a non-synchronous system, if a non-orthogonal code such as a pseudo-random code is used as the spreading code, inter-code interference occurs between the channels of each station when the number of stations communicating at the same time increases, and errors during demodulation occur. Will increase. In order to solve this problem, the CDMA modulator / demodulator described in the above document is provided with an interference canceling unit for canceling inter-code interference between channels. The interference removing unit removes inter-code interference and enables demodulation with few errors.

[0004]

SUMMARY OF THE INVENTION However, the conventional
The CDMA modem has the following problems. That is,
One of the causes of an error at the time of CDMA demodulation, particularly at the time of demodulation using an interference canceller, is deterioration of quantization accuracy due to a decrease in signal power. In CDMA, there is a technique (that is, power control) that controls the transmission power so that the power of each station received at the receiving side becomes the same, but this is adjusted so that the power level of each mobile station does not vary. It is a technology. By using this power control technique, the receiving station can receive a signal of the same power level regardless of the distance between the receiving station and each mobile station. However, there are also the following problems.

That is, the analog signal received by the antenna is multiplexed with the channels of a plurality of mobile stations. This signal generally passes through an automatic gain controller (hereinafter referred to as AGC), and an analog-to-digital converter (hereinafter referred to as ADC).
Is converted into a digital signal. At this time, the signal output from the AGC is output as a signal whose maximum amplitude value is fixed regardless of the amplitude of the input signal. Therefore, in the signal after the output signal of the AGC, the power of the signal per station changes due to the change in the number of stations. Therefore,
When the number of stations is small, there is no problem, but when the number of stations is large, the power per station decreases, so the accuracy of quantization in the interference canceller may deteriorate depending on the number of quantization bits. However, there is a problem that the error rate during demodulation becomes large. The object of the present invention is to keep the accuracy of quantization constant by reducing the fluctuation of the signal power of each mobile station at the time of demodulation due to the change of the number of channels (the number of stations), and This is to reduce the error rate at the time of demodulation due to the reduction.

[0006]

In order to solve the above-mentioned problems, the first invention receives an analog signal in which signals of a plurality of mobile stations are multiplexed and converts the analog signal into a signal of a baseband frequency. A receiving unit, an AGC that controls the gain according to the amplitude of the signal of the baseband frequency and converts the output signal to a constant maximum amplitude value, and an output signal of the automatic gain control unit from an analog signal to a digital signal. The mobile station includes an ADC for converting into a signal and a demodulation section for performing demodulation by correlating the output signal of the ADC and the spreading code for each mobile station, and each mobile station based on a code division multiple access communication system. The following devices are provided in a receiving device of a mobile communication system for performing simultaneous calls between two devices. That is, the AD
A demodulation power controller for estimating the power of the signal of each mobile station from the output signal of C and normalizing the power of the signal of each mobile station is provided.

In a second aspect of the invention, the demodulation power control device of the first aspect of the invention uses a signal power calculator for calculating the signal power of each mobile station from the output signal of the ADC, and a signal power of each mobile station. It comprises a first average value calculation unit for obtaining the average power of all mobile stations, and a normalization unit for normalizing the power of each station using the overall average power of each mobile station. Further, the signal power calculation unit includes a correlation calculation unit that obtains a correlation value between the output signal of the ADC and a spread code for each path of the desired station among the mobile stations, and the correlation calculation unit for each path of the desired station. A correlation value power calculation unit for synthesizing correlation values to obtain the correlation value power of the desired station, and a second average value calculation unit for averaging the correlation value powers of the desired station to obtain the signal power of the desired station. Is prepared. According to a third invention, the receiving unit of the first invention, the AGC of the first invention, and the ADC of the first invention.
An interference canceling unit that cancels an interference component of each path of each mobile station of a signal in which signals of the plurality of mobile stations are multiplexed, an output signal of the interference canceling unit, and a spreading code of each mobile station. A demodulation power control device of the second invention is provided in front of the interference removal part in a reception device provided with a demodulation part for performing correlation by using and to perform demodulation.

[0008]

According to the first and second aspects of the invention, since the receiving apparatus is configured as described above, the signal power of each mobile station is calculated from the output signal of the ADC in the signal power calculation section. next,
The first average value calculation unit calculates the average power of all mobile stations from the signal power of each mobile station. Further, the normalizing unit normalizes the power of each mobile station by using the average power of all the mobile stations. Therefore, the fluctuation of the signal power of each station at the time of demodulation due to the change of the number of stations becomes small, and the error rate due to the quantization error in the demodulation unit decreases. According to the third invention,
The signal power calculator calculates the signal power of each mobile station from the output signal of the ADC. Next, the first average value calculation unit calculates the average power of all mobile stations from the signal power of each mobile station. Further, the normalizing unit normalizes the power of each mobile station by using the average power of all the mobile stations. Therefore, the fluctuation of the signal power of each station at the time of demodulation due to the change of the number of stations becomes small, and the error rate due to the quantization error in the interference canceller decreases. Therefore, the above problem can be solved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a block diagram of the configuration of a receiving apparatus showing a first embodiment of the present invention. This receiving device has an antenna 10 for receiving an analog signal in which signals of a plurality of mobile stations are multiplexed, and is connected to a receiving section 20. The receiver 20 has a function of converting an analog signal from the antenna 10 into a signal S20 having a baseband frequency. The output side of the receiver 20 is connected to the input side of the AGC 30. AGC3
0 controls the gain according to the amplitude of the signal of the baseband frequency, and the maximum value of the amplitude is always constant in the output signal S30.
It has the function of converting to. The output side of AGC30 is
It is connected to an ADC 40 that converts the output signal S30 of the AGC 30 from an analog signal to a digital signal. ADC
The output side of 40 is connected to the input side of the demodulation power control device 50. The demodulation power control device 50 has a function of estimating the power of the signal of each mobile station from the output signal S40 of the ADC 40 and normalizing the power of the signal of each mobile station. The output side of the demodulation power control device 50 is connected to a demodulation section 60 which performs demodulation by correlating the output signal S50 of the demodulation power control device 50 and the spreading code of each mobile station.

FIG. 2 is a block diagram showing an example of the demodulation power control device shown in FIG. This demodulation power control device has an input terminal i for inputting an output signal S40 of the ADC 40
have n. The input terminal in has a correlation calculator 51-1.
To 51-n are connected to the respective input terminals. However, n is the number of stations on the transmission side. Also, each station on the transmission side has a different spreading code sequence. Correlation calculator 51-
The output terminals 1 to 51-n are connected to the average power calculator 52-
1 to 52-n are connected to the respective input terminals.
Correlation calculation units 51-1 to 51-n and average power calculation unit 5
A signal power calculator is composed of 2-1 to 52-n. Each output terminal of the average power calculation units 52-1 to 52-n is connected to a first average value calculation unit 53 that calculates an average value of all stations from 1 station to n stations. The output terminal of the average value calculation unit 53 is connected to the normalization unit 54. The output signal S40 is input to the normalizing section 54. The normalization unit 54 has a function of normalizing the output signal S40 using the output signal S53 of the average value calculation unit 53.

FIG. 3 is a configuration block diagram showing an example of the correlation calculator 51-1 in FIG. The correlation calculator has an input terminal IN for data Din. Input terminal IN
Is the multiplication units 51C1 to 51C1 to 51 corresponding to 1 to m paths.
It is connected to each first input terminal of Cm. The correlation calculator also includes a spread code generator 51A. The spread code generating section 51A is connected to the respective input terminals of the delay sections 51B1 to 51Bn corresponding to the 1st to mth paths. The output terminals of the delay units 51B1 to 51Bn are connected to the second input terminals of the multiplication units 51C1 to 51Cm. Each output terminal of the multiplication units 51C1 to 51Cm has a value of 1
Cumulative addition units 51D1 to 51D corresponding to paths to m paths
m is connected to each input terminal. Cumulative addition unit 51D1
Each output terminal of ~ 51Dm is connected to each input terminal of the normalization units 51E1 to 51Em corresponding to 1 path to m path. The output terminals of the normalization units 51E1 to 51Em are
Correlation value power calculation unit 51F corresponding to 1 to m paths
It is connected to each input terminal of 1 to 51 Fm. Each output terminal of the power calculators 51F1 to 51Fm is from one path to m
It is connected to the total power calculation unit 51G of all the paths. The correlation calculation units 51-2 to 51-n have the same configuration.

FIG. 4 shows the average power calculator 52- in FIG.
FIG. 3 is a configuration block diagram showing an example of No. 1. The average power calculation unit has a cumulative adder 52a that accumulates the output signal of the correlation calculation unit 51-1 and the output terminal of the cumulative adder 52a is connected to the input terminal of the divider 52b. Divider 5
2b has a function of calculating the average value of the output signal of the correlation calculation unit 51-1. The average power calculator 52-2
52-n have the same configuration.

FIG. 5 is a block diagram showing an example of the average value calculator 53 in FIG. This average value calculation unit 53
Is the output signal S of the average power calculation units 51-2 to 52-n.
It has an adder 53a for adding 51-2 to S52-n. The output terminal of the adder 53a outputs the output signal S51-2.
It is connected to the divider 53b which calculates the average value S53 of S52-n. FIG. 6 is a configuration block diagram showing an example of the normalization unit in FIG. This normalization unit outputs the output signal S
It is composed of a divider 54A that divides 40 by the average value S53. Next, the operation of the demodulation power control device of FIG. 2 will be described.
As an example, the operation of the first station will be focused on in the description. In the correlation calculator, the output signal S40 is correlated for each path with the spreading code of the first station, and the correlation value power Corr1 of the first station is obtained. Here, a detailed operation of the correlation calculation unit for obtaining the correlation value power Corr1 will be described.

As an example, the operation of the first pass will be described. The data Din input from the input terminal IN is the spread code codel obtained from the spread code generator 51A by the following equation (1).
Is multiplied by the multiplication unit 51C1 and the multiplication result R1 is input to the cumulative addition unit D1. R1 = Din · Codel (1) At this time, the delay B1 is adjusted so that the spreading code of the first path of the first station on the transmitting side and the spreading code codel generated on the receiving side are included in the data Din. Adjust the timing to be in sync. In the cumulative addition unit 51D1, the multiplication result R1
Is cumulatively added by a predetermined number (spreading gain number: PG) to obtain a cumulative addition value S1 and output to the normalization unit 51E1. S1 = ΣR1 (i) (i = 1 to PG) (2) In the normalization unit 51E1, the cumulative addition value S1 is divided by a predetermined number (spreading gain number) PG by the following equation (3). The correlation value Corr1P1 is obtained by normalization and output to the power calculation unit 51F1. Corr1P1 = S1 / PG (3) In the power calculation unit 51F1, the correlation value Corr1P is calculated by the following equation (4).
The power Corr1P1 of the correlation value is obtained by squaring 1 and output to the total power calculator 51G. PCorr1P1 = (Corr1P1) ² (4) Other paths (that is, the second to nth paths) similarly perform the above operation. In the total power calculation unit 51G, the following equation (5)
Then, all the powers PCorr1P1 to PCorr1Pn of the correlation values obtained from the power calculation units 51F1 to 51Fn of each path are added to obtain the correlation value power Corr1 of the first station. Corr1 = ΣPCcorr1P (i) (i = 1 to n) (5) This correlation value Corr1 represents the power of the signal of the first station. However, when the number of stations is large, the error included in the correlation value is large due to the influence of interference. Therefore, a better value can be obtained by using the average value for a long time. This correlation value Corr1 is shown in FIG.
It outputs to the inside average power calculation part 52-1. In the average power calculation unit 52-1 a fixed number of samples M (for example M =
The average value Ave (1) of 100) is calculated by the following equation (6) and output to the average value calculation unit 53. Ave (1) = {ΣCorr (i)} / M (i = 1 to M) (6) Other stations (second station to nth station) also perform the above operation in the same manner.

In this CDMA system, since the signals of the stations are power-controlled, it can be assumed that the received signals of the stations have almost the same power level. Therefore, the output signals S52- obtained from the average power calculation units 52-1 to 52-n
By averaging 1 to S52-n, more accurate power per station can be obtained. Average value calculator 53
Then, from the average values Ave1 to Aven of each station obtained from the average power calculation units 52-1 to 52-n, the average value Avetotal of the power of all the stations is calculated by the following equation (7) and output to the normalization unit 54. Avetotal = {ΣAve (i)} / n (7) (i = 1 to n) In the normalization unit 54, the average value of the power of all stations is calculated by the following equation (8).
Output signal S40 of ADC 40 in FIG. 1 using Avetotal
The digital received signal Din (t) is normalized and the normalized digital received signal DAve is obtained and output to the demodulation unit. DAve (t) = Din (t) / Avetotal (8) This received signal DAve is the output signal S of the demodulation power control device.
50. Next, the principle of normalizing the power of each station of the digital received signal DAve will be described by using mathematical expressions.

The power of the transmitting station (i-th station) is PS (i),
The gain of the AGC of the receiving station is Ga (t), and the signal power of the transmitting station (i-th station) after AGC is Pr (i). For simplicity, it is assumed that there is no noise component. The power Din of the reception signal of the antenna is expressed by the following equation (9) because the signals of the transmission stations of n stations are multiplexed. Din = ΣPS (i) (9) (i = 1 to n) The power DGin of the received signal after AGC is expressed by the following equation (10).
become that way. DGin = Din / Ga (t) = ΣPS (i) / Ga (t) (10) The power of the i-th station is expressed by the following equation (11). Pr (i) = PS (i) / Ga (t) (11) Therefore, the output value DAve is expressed by the following equation (12). DAve = Din / Avetotal = ΣPr (i) / Avetotal = n × Pra / Avetotal = n × Ns (12) However, Pra; ΣPr (i) / nNs; Pra / Avetotal Here, included in DAve The average power of l station is Pout
Then, Pout is expressed by the following equation (13). Pout = DAve / n = n × Ns / n = Ns (13)

As described above, Pra is the average value of the power of the received signal of each station, Ns is the ratio of Pra to Avetotal,
And Pout are the signal power of each station. In this way, the power of the signal of each station included in the output signal DAve is normalized to Ns. As shown in equation (6), Av
e (i) is a time average value of the power Corr (i) of the correlation value. Corr (i) represents the power of the signal at that time if the accuracy of the correlation is sufficient. Therefore, assuming that the accuracy of the correlation is sufficient, the relationship of the following expression (14) is established. Corr (i) = Pr (i) (14) Since Ave (i) represents the average power of the signal of the i-th station within a certain time, the relationship of the following expression (15) is established. Ave (i) = Pr (i) (15) Therefore, the average value Avetotal of the power of all stations is expressed by the following equation (16).
become that way. Avetotal = ΣPr (i) / n = Pra (16) From the above, the above equations (12) and (13) become the following equations (17) and (18), respectively. Dout = D / Avetotal = ΣPr (i) / Pra = n × Pra / Pra = n × 1 (17) Pout = n × 1 / n = 1 (18) Thus, the noise component is If there is no intersymbol interference, the output value Dout is normalized and output so that the power of each station is always a constant power "1". In a real system, noise components, intersymbol interference, and signal power variations at each station (due to imperfect power control)
For example, the correlation value Corr (i) deteriorates, and the relationship of Expression (14) is not always established. However, using the average-heavy method as detailed above, Avetot
By obtaining al, the relationship of Expression (16) is approximately established.

Next, the operation of FIG. 1 will be described. The analog signals transmitted from a plurality of mobile stations are multiplexed in the air and received by the antenna 10. Here, it is assumed that the signal transmitted from the mobile station is power-controlled.
The signal received by the antenna 10 is dropped to the baseband frequency by the receiver 20. This baseband signal is converted by the AGC 30 into a signal having a constant maximum amplitude value. The output signal S30 of the AGC 30 is analog / digital converted by the ADC 40 and output to the demodulation power control device 50. The demodulation power control device 50 normalizes the power of the signal of each station and outputs it to the demodulation unit 60. The demodulation unit 60 uses a spread code for each station to perform correlation and demodulates. As described above, in the first embodiment, the ADC 30
By providing the demodulation power control device 50 between the demodulation unit 60 and the demodulation unit 60, the fluctuation of the power per station is reduced, so that the calculation error in the demodulation unit 60 is reduced and the error rate due to the quantization error is reduced. Becomes smaller.

Second Embodiment FIG. 7 is a block diagram showing the configuration of a receiving apparatus according to a second embodiment of the present invention. Elements common to those in FIG. 1 are designated by common reference numerals. . In this receiving device, an interference removing unit 70 for removing an interference component of each path of each station is provided between the demodulation power control device 50 and the demodulation unit 60 in FIG. Next, the operation of FIG. 7 will be described. The operation up to the demodulation power control device 50 is the same as in the first embodiment. The signal in which the power of each station is normalized by the demodulation power control device 50 is output to the interference removing unit 70. The interference removing unit 70 performs an operation of removing the interference component of each path of each station, and outputs the data S70 from which the interference component of another station is removed to the demodulation unit 60. Here, by providing the demodulation power control device 50 on the output side of the ADC 40 as in the present embodiment, fluctuations in power per station of each station are reduced. Therefore, the precision with which the interference canceller 70 quantizes the signal is kept constant. As described above, in the second embodiment, by providing the demodulation power control device 50 between the ADC 40 and the interference removing unit 70, it is possible to reduce the power fluctuation per station. Therefore, the accuracy with which the interference canceller 70 quantizes the output signal S40 is kept constant.

[0020]

As described in detail above, according to the first and second aspects of the invention, the average power of the signal of each station is obtained from the baseband signal received by multiplexing a plurality of channels, and this average power is calculated. Since the signal power of each station is normalized by using it, the fluctuation of the signal power of each station at the time of demodulation due to the change in the number of stations can be reduced, and the error rate due to the quantization error in the demodulation unit can be reduced. it can. According to the third invention, the average power of the signal of each station is obtained from the baseband signal received by multiplexing a plurality of channels, and the power of the signal of each station is normalized using this average power. The power level of the signal of each station during demodulation due to the change in the number of stations is kept constant. Therefore, the accuracy of the quantization in the interference canceller can be kept constant, and the error rate due to the quantization error can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a receiving device showing a first embodiment of the present invention.

FIG. 2 is a configuration block diagram showing an example of a demodulation power control device in FIG.

FIG. 3 is a configuration block diagram showing an example of a correlation calculation unit in FIG.

4 is a configuration block diagram showing an example of an average power calculation unit in FIG.

5 is a configuration block diagram showing an example of an average value calculation unit in FIG. 2. FIG.

FIG. 6 is a configuration block diagram showing an example of a normalization unit in FIG.

FIG. 7 is a configuration block diagram of a receiving device showing a second embodiment of the present invention.

[Explanation of symbols]

 20 receiver 30 automatic gain controller 40 analog / digital converter 50 demodulation power controller 51-1 to 51-n correlation calculator 52-1 to 52-n average power calculator 53 average value calculator 54 normalizer 60 Demodulation unit 70 Interference removal unit

Claims (3)

[Claims] 1. A receiving unit for receiving an analog signal in which signals of a plurality of mobile stations are multiplexed and converting the analog signal into a signal of a baseband frequency, and a gain according to an amplitude of the signal of the baseband frequency. An automatic gain control unit that controls and converts an output signal whose amplitude maximum value is always constant; an analog / digital conversion unit that converts the output signal of the automatic gain control unit from an analog signal to a digital signal; A mobile station for simultaneous communication between the mobile stations based on a code division multiple access communication system, comprising a demodulation section for performing correlation using the output signal of the conversion section and the spread code for each mobile station. In a receiver of a communication system, demodulation for estimating the power of the signal of each mobile station from the output signal of the analog / digital converter and normalizing the power of the signal of each mobile station A force control device, the receiving apparatus characterized by comprising. 2. The demodulation power control device includes a signal power calculation unit that calculates the signal power of each mobile station from the output signal of the analog / digital conversion unit, and a total power of all mobile stations from the signal power of each mobile station. A first average value calculation unit that obtains average power; and a normalization unit that normalizes the power of each station using the overall average power of each mobile station, wherein the signal power calculation unit includes each of the mobile stations. A correlation calculation unit for obtaining a correlation value between the output signal of the analog / digital conversion unit and a spread code for each path of the desired station, and the desired station by combining the correlation value for each path of the desired station. And a second average value calculating section for averaging the correlation value powers of the desired station to obtain the signal power of the desired station. Item 1. The receiving device according to item 1. 3. A receiving unit according to claim 1, an automatic gain control unit according to claim 1, an analog / digital converting unit according to claim 1, and a signal obtained by multiplexing signals of the plurality of mobile stations. An interference removing unit that removes an interference component of each path of each mobile station, and a demodulating unit that performs correlation by performing demodulation using an output signal of the interference removing unit and a spreading code of each mobile station are provided. In the receiving device, the demodulation power control device according to claim 2 is provided before the interference removing unit.