WO2001073993A1 - Communication device and communication method - Google Patents

Abstract

A despreading unit carries out despreading of the received signal with a spreading code unique to a mobile station device. A switch judges on the basis of the correlation level of the despread signal for each mobile station device whether it outputs a channel estimate determined for each mobile station device to a reset unit or JD unit. The JD unit carries out joint detection calculation using the channel estimate from the reset unit or the channel estimate from the switch and generates a matrix used for performing interference elimination of the received signal. The received signal delayed by a predetermined time is multiplied by the matrix from the JD unit, and thus data from which interference is eliminated is obtained for each mobile station device.

Description

 Description Communication device and communication method

 The present invention relates to a communication device and a communication method used in communication of a code division multiple access (CDMA) system. Background art

 In a conventional digital mobile communication system using the CDMA system, a base station device performs wireless communication with a plurality of mobile station devices. The base station device receives a signal in which a signal transmitted by each mobile station device is multiplexed in the same frequency band. The base station apparatus uses a technique called joint detection (Joint Detection; hereinafter referred to as “JD”) from a received signal (received signal) to perform interference due to multipath fading, interference between symbols, and multiple factors. Various interference such as connection interference is removed, and demodulated data for each mobile station device is extracted. JD l'tele 'Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code-Division Multiple-Access Channels "(Klein A., Kaleh GK, Baier PW, IEEE Trans.Vehicular Technology, vol. 45, pp. 276-287, 1996.).

 Here, wireless communication performed between the base station device and a plurality of mobile station devices will be briefly described. The mobile station device transmits to the base station device according to a frame format as shown in FIG. FIG. 1 is a schematic diagram showing an example of a frame format used by a mobile station device in a digital mobile communication system to which JD is applied.

The mobile station device converts the information signal spread by the spreading code unique to the mobile station device into the data portion 101 and the data portion 101 in the frame format shown in FIG. The data is transmitted to the base station apparatus using the data section 103. Also, the mobile station device transmits a known signal unique to the mobile station device to the base station device using the midamble section 102 in the frame format.

 The base station apparatus receives a signal obtained by multiplexing a signal transmitted from each mobile station apparatus in the same frequency band using the frame format shown in FIG. First, the base station apparatus uses the signal corresponding to the midamble section 102 in the received signal (received signal) and a known signal unique to each mobile station apparatus to obtain a channel for each mobile station apparatus. Get an estimate. Second, the base station apparatus generates a coefficient used for interference removal processing on a received signal using a channel estimation value for each mobile station apparatus and a spreading code unique to each mobile station apparatus. Third, the base station apparatus multiplies the data part 101 and the data part 103 of the received signal by the generated coefficient to generate a demodulated signal that minimizes the interference component. obtain. Lastly, the base station apparatus can perform a hard decision on the obtained demodulated signal, thereby obtaining demodulation data for each mobile station apparatus.

 In the wireless communication as described above, the mobile station apparatus is transmitted by the data section 101 and the data section 103 in the frame format shown in FIG. 1 in order to reduce interference with other mobile station apparatuses. If there is no information signal available, only the midamble 102 in the above frame format is transmitted. That is, when the mobile station device has no information signal to be transmitted, the mobile station device performs communication called DTX that transmits only the midamble portion 102 in the frame format.

However, the conventional digital mobile communication system using JD has the following problems. That is, if a mobile station device that performs DTX (hereinafter referred to as “target mobile station device”) does not transmit any information indicating that DTX is to be performed to the base station device, the base station device performs The station equipment cannot recognize that DTX is being performed. Therefore, the base station apparatus recognizes that the target mobile station apparatus is transmitting the data section 101 and the data section 103, and To generate the coefficients. Therefore, since the generated coefficients include errors, the demodulated signal obtained by multiplying the generated coefficients by the received signal also includes the error power S. As a result, the accuracy of the demodulated data obtained using the demodulated signal deteriorates.

 In addition, the base station apparatus demodulates the information signal about the target mobile station apparatus which is not originally included in the received signal so as to extract the information signal from the received signal. As a result, in the base station device, an abnormal operation of the entire device occurs. Disclosure of the invention

 An object of the present invention is to provide a communication device (base station device) that maintains good demodulated data quality irrespective of DTX by a transmitting device (mobile station device). The purpose of this is to receive a signal in which signals transmitted by a plurality of transmitting devices are multiplexed in the same frequency band, and to use the spreading code unique to the transmitting device for the received signal (received signal). This is achieved by performing interference cancellation on a received signal by using a despread signal for each of the plurality of transmitting-side devices obtained by performing the spreading process. BRIEF DESCRIPTION OF THE FIGURES

 Fig. 1 is a schematic diagram showing an example of a frame format used by a mobile station device in a digital mobile communication system to which JD is applied;

 FIG. 2 is a block diagram illustrating a configuration of the communication device according to the embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 The base station device including the communication device according to the present embodiment performs wireless communication of the CDMA system with a plurality of mobile station devices (transmitting devices).

As described above, each mobile station device follows the frame format shown in FIG. Then, transmission to the base station apparatus is performed. Specifically, each mobile station device uses the data part 101 and the data part 103 in the frame format shown in FIG. 1 to convert the information signal spread by the spreading code unique to the mobile station device. And transmits it to the base station apparatus. In addition, the mobile station device transmits a known signal unique to the mobile station device to the base station device using the midamble section 102 in the frame format.

 The base station device receives a signal in which a signal transmitted by each mobile station device is multiplexed in the same frequency band. This base station apparatus removes various interferences from a received signal using joint detection and extracts demodulated data for each mobile station apparatus.

 Next, the configuration of a base station device including the communication device according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration of a base station device provided with a communication device according to an embodiment of the present invention. In the present embodiment, a case will be described where the number of mobile station devices that perform wireless communication with the base station device is n.

 In FIG. 2, a delay unit 201 delays a received signal by a predetermined time and sends it to a multiplication unit described later. The channel estimating units 202-1-2 to 202-n extract the channel estimation values for the mobile station devices l to n by correlating using the received signals, and switch the extracted channel estimation values respectively. 2 0 5 1 Send to 1 2-5—n.

 The despreading sections 203-1 to 203-n respectively perform despreading processing using the received signals and spreading codes specific to the mobile station apparatuses 1 to n, and are obtained by the despreading processing. The signal is sent to the control unit 204.

The control unit 204 uses the signals obtained by the despreading processing in the despreading units 203-l to 203-n to determine whether each of the mobile station devices l to n applies DTX. Determine whether or not. The control section 204 sends a control signal according to the result of the determination to the switches (SW) 205-5-1 to 205-n. Switches 205 to 1 to 205-n respectively calculate the channel estimation values from the channel estimator 202 to 1 to 202 based on the control signal from the controller 204. , Reset section 206-1-2 to 06-n or joint detection (hereinafter referred to as “JD”) section 207. The reset sections 206-1-1 to 206-11 reset the channel estimation values from the switches 205-1-205-n, respectively, and output them to the JD section 207.

 The JD unit 207 performs a matrix operation using the channel estimation values from the switches 205-1 to 205-n or the reset units 206-:! To 206-n. And outputs the result of the matrix operation to the multiplication unit 208.

 The multiplication unit 208 multiplies the result of the matrix operation from the JD unit 207 by the received signal from the delay unit 201, and sends the multiplication result to the discriminator 209. The classifier 208 performs hard decision on the result of the multiplication from the multiplication unit 209, and extracts demodulated data.

Next, the operation of the base station apparatus having the above configuration will be described. Here, the signals transmitted by each mobile station apparatus according to the above-described frame format are multiplexed on the same frequency band and received by an antenna (not shown). A signal (received signal) received by the antenna is subjected to predetermined reception processing such as frequency conversion by a radio unit (not shown). The received signal subjected to the reception processing is used as a received signal shown in FIG. 2 as a delay unit 201, a channel estimating unit 202——! To 202—n, and a despreading unit 203__1 ~ 203-sent to n. The received signal delayed by the predetermined time by the delay unit 201 is sent to the multiplication unit 208. In the channel estimating units 202-1-2 to 202-n, respectively, the correlation between the signal corresponding to the midamble part of the received signal and the known signal unique to each of the mobile station devices l to n is assumed to be the maximum possible. It is taken in the range of the delay width. As a result, channel estimation sections (202-1 to 202-2-n) obtain channel estimation values (matrices) for mobile station apparatuses l to n, respectively. Note that the channel estimation value is represented by a complex number composed of an I component and a Q component. Channel estimation unit The channel estimation values obtained from 202-1-2 to 205-n are sent to switches 205-1-205-n, respectively.

 The despreading sections 203-1-2 to 203-n respectively perform despreading processing on signals corresponding to the data portion of the received signal using spreading codes unique to the mobile station apparatuses 1 to n. Done. The spreading codes unique to the mobile station devices l to n correspond to the spreading codes used by the mobile station devices 1 to n when performing the spreading process on the information signal.

 Despreading part 2 0 3—:! A signal obtained by the despreading process (hereinafter, simply referred to as a “despread signal”) will be described. Here, as an example, we focus on the despread signal obtained by despreading unit 203_i (l≤i≤n).

 When the mobile station apparatus i applies DTX, the mobile station apparatus i transmits the spread-processed information signal to the data portion 1 in the frame format shown in FIG.

No transmission is performed using 01 and the data part 103. Therefore, the despread signal obtained by despreading section 203-i is equivalent to the despread signal obtained when mobile station apparatus i is not present. That is, the level of the despread signal obtained by the despreading unit 203-i becomes very small.

 Conversely, when the mobile station apparatus i does not apply DTX, the mobile station apparatus i transmits the spread information signal to the data section 101 and the data section 1 in the frame format shown in FIG. It is transmitted using 03. Therefore, the level of the despread signal obtained by the despreading section 203-i has a certain level.

 Therefore, to determine whether or not a certain mobile station device applies DTX, a signal (level) obtained by despreading a received signal using a spreading code unique to this mobile station device is detected. It can be said that it can be recognized.

Reverse scatter part 2 0 3—:! The despread signal obtained by 22 0 3—n is Output to 04.

 The control section 204 determines whether or not each of the mobile station apparatuses 1 to n uses DTX using the despread signal from the despreading section 203-to 203-n. That is, based on the despread signals from despreading sections 203_1 to 203-n, it is determined whether or not mobile station apparatuses l to n respectively apply DTX. Specifically, for example, when the level of the despread signal from despreading section 203—i (1≤i≤n) is equal to or higher than the threshold, mobile station apparatus i does not apply DTX Is determined. Conversely, if the level of the despread signal from despreading section 203-i (1≤ί≤n) is less than the threshold, it is determined that mobile station apparatus i applies DTX. The threshold value is determined by, for example, performing a despreading process using a spreading code unique to the predetermined mobile station device on a received signal in which a signal transmitted by the predetermined mobile station device is reliably multiplexed. It can be set using the level of the obtained despread signal.

 In the control unit 204, based on the determination result, the switch 205— :! Control signals for ~ 205-n are generated. Specifically, when it is determined that the mobile station device i (1≤i≤n) applies DTX, the channel estimation value from the channel estimation unit 202-i is determined for the switch 205-i. A control signal to be sent to the reset unit 206—i is generated. Conversely, if it is determined that the mobile station apparatus i does not apply DTX, a control signal indicating that the channel estimation value from the channel estimation section 202 -i is sent to the JD section 207 for the switch 205 -i Is generated. The control signal generated in this way is a switch 205— :! ~ 205— sent to n.

In the switches 205-1 to 205-n, the channel estimation value is output based on the control signal from the control unit 204. Specifically, in switch 205-i, which has received a control signal to output the channel estimation value from channel estimation section 202-i to reset section 207, the channel estimation value is output to reset section 206-i. Is done. Conversely, the channel from the channel estimation unit 202—i In the switch 205 i receiving the control signal indicating that the channel estimation value is output to the JD unit 207, the above channel estimation value is output to the JD unit 207 instead of the reset unit 206-i Is done.

 The reset units 206-1-2 to 206-n reset the channel estimation values from the switches 205-1-205-n, respectively. The reset channel estimation value is sent to JD section 207. Note that the channel estimation value reset by the reset unit 2061-i is equivalent to the channel estimation value for the mobile station device i when the mobile station device i does not exist.

 In the JD unit 207, the channel estimation value from the switch 205-1-2 to 205-n or the channel estimation value from the reset unit 206-1-206-n and each mobile station A matrix operation using a spreading code unique to the device is performed. When this matrix operation is performed, a channel estimation value for a mobile station device to which DTX is applied is treated as a channel estimation value for a nonexistent mobile station device. That is, a mobile station device to which DTX is applied is treated as a nonexistent mobile station device. Specifically, the JD unit 207 performs the following matrix operation. That is, first, the channel estimation value for each mobile station device, the spreading code unique to each mobile station device, and the convolution operation are performed to obtain the convolution operation result (matrix ) Is obtained.

 As a result, a matrix (hereinafter, referred to as a “system matrix”) in which the convolution operation results for each user are regularly arranged is obtained. Here, for simplicity of explanation, the system matrix is expressed as [A].

 Further, a matrix [B] is obtained by performing a matrix multiplication according to the following equation (1) using the system matrix.

[B] = ([A] ^H · [A])- ¹ · [A] ^H- one (1)

Here, [A] ^H is the conjugate transpose of the system matrix, and ([Α] ^Η · [Α])- ¹ is the inverse matrix of [Α] ^Η · [Α].

The matrix [B] obtained by the above matrix operation is sent to the multiplication unit 208. You. In the multiplication unit 208, a multiplication process is performed between the signal corresponding to the data part in the received signal transmitted from the delay unit 201 and the matrix transmitted from the JD unit 207, and The data for each mobile station device from which the interference has been removed can be obtained. That is, in the multiplication unit 208, interference is removed from the received signal transmitted from the delay unit 201. The obtained data for each mobile station device is sent to the discriminator 209. In the discriminator 209, demodulated data is obtained by making a hard decision on the data for each mobile station apparatus sent from the multiplication unit 208. As described above, in the present embodiment, first, a despreading process is performed on a received signal using a spreading code unique to the mobile station device, thereby generating a despread signal for the mobile station device. I do. Further, based on the generated despread signal, the mobile station device detects whether or not DTX is applied. Thereafter, as a channel estimation value for the mobile station apparatus determined to apply DTX, when this mobile station apparatus does not exist instead of the actually generated channel estimation value for the mobile station phase apparatus A matrix operation is performed using the channel estimation for this mobile station device in.

 By this means, it is possible to prevent a matrix ([B] in the present embodiment) used for interference removal obtained by this matrix operation from containing an error. Therefore, the accuracy of the demodulation can be kept good.

 According to the present embodiment, the base station apparatus can perform an accurate matrix operation without transmitting information indicating that DTX has been applied to the base station apparatus from the mobile station apparatus to which DTX has been applied. Therefore, the accuracy of the obtained demodulated data can be kept good. In addition, since the mobile station device can reduce transmission power by applying DTX, interference with other mobile station devices can also be reduced.

Note that, in the present embodiment, a case has been described where the base station device is equipped with the communication device according to the present invention in order to disclose the best embodiment. That is, now In the digital mobile communication system to which the CDMA method is applied, in the present embodiment, in consideration of the fact that the base station apparatus receives signals transmitted by a plurality of mobile station apparatuses, the base station apparatus The case where the communication device according to the present invention is mounted has been described.

On the other hand, in a digital mobile communication system in which a mobile station device receives signals transmitted by a plurality of base station devices (or a plurality of transmitting devices), the communication device according to the present invention is used as a mobile station device. It can be mounted. In this case, the mobile station device equipped with the communication device according to the present invention can keep good demodulation quality of each base station device (each transmitting device). In this case, regarding the specific actions and operations in this case, “mobile station device (communication terminal device)” is replaced with “base station device” and “base station device” is replaced with “mobile station device ( (Communication terminal device) ”can be easily derived by reading it, so detailed description is omitted. As described above, according to the present invention, a signal in which signals transmitted by a plurality of transmitting apparatuses are multiplexed in the same frequency band is received, and the received signal (received signal) is unique to the transmitting apparatus. Since the interference removal for the received signal is performed by using the despread signal for each of the plurality of transmitting devices obtained by performing the despreading process using the spreading code, the transmitting device (mobile station device) ), It is possible to provide a communication device (base station device) that maintains good demodulated data quality regardless of DTX. As will be apparent to those skilled in the art, the present invention can be implemented using a general-purpose commercially available digital computer and microprocessor programmed according to the techniques described in the above embodiments. Things. As will be apparent to those skilled in the art, the present invention encompasses a convenience program created by those skilled in the art based on the technology described in the above embodiments. A computer program product that is a recording medium containing instructions that can be used to program a computer that implements the present invention is within the scope of the present invention. This recording medium corresponds to a disk such as a floppy disk, an optical disk, a CD-ROM and a magnetic disk, a ROM, a RAM, an EPROM, an EEPROM, a magneto-optical card, a memory card or a DVD, but is not particularly limited thereto. is not. The JD used in the present embodiment includes not only the technology disclosed in “Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code-Division Multiple-Access Channels” described above, but also this technology. Can be used as appropriate. This description is based on Japanese Patent Application No. 2000-089360 filed on Mar. 28, 2000. This content is included here. Industrial applicability

 INDUSTRIAL APPLICABILITY The present invention is suitable for use in the field of communication devices and communication methods used in code division multiple access communication.

Claims

The scope of the claims  1. Receiving means for receiving a signal in which signals transmitted by a plurality of transmitting apparatuses are multiplexed in the same frequency band, and using a spreading code unique to the transmitting apparatus for the signal received by the receiving means. A despreading unit that performs a despreading process, and generates a despread signal for each of the plurality of transmission-side devices; and a signal received by the reception unit based on the generated despread signal. And a demodulating means for removing interference with respect to each of the plurality of transmitting-side devices and extracting demodulated data for each of the plurality of transmitting-side devices.  2. The demodulation means, when the level of the reverse strip signal for a predetermined transmitting device is less than a predetermined value, performs interference cancellation as a transmitting device that does not include the predetermined transmitting device. The communication device according to 1.  3. A base station device including a communication device, wherein the communication device includes: a receiving unit that receives a signal in which signals transmitted by a plurality of communication terminal devices are multiplexed in the same frequency band; Despreading means for performing a despreading process on the received signal using a spreading code unique to the communication terminal device, and generating a despread signal for each of the plurality of communication terminal devices; And demodulating means for removing interference with respect to the signal received by the receiving means based on the despread signal and extracting demodulated data for each of the plurality of communication terminal apparatuses. 4. A communication terminal device that performs wireless communication with a base station device equipped with a communication device, wherein the communication device multiplexes signals transmitted by a plurality of communication terminal devices including the communication terminal device in the same frequency band. Receiving means for receiving the received signal; performing inverse spreading processing on the signal received by the receiving means using a spreading code unique to the communication terminal apparatus; and performing inverse spreading on each of the plurality of communication terminal apparatuses. A despreading means for generating a spread signal; and a demodulation for removing interference with respect to the signal received by the receiving means based on the generated despreading means and extracting demodulated data for each of the plurality of communication terminal apparatuses. Means. 5. Signals multiplexed in the same frequency band with signals transmitted by multiple transmitters Receiving a signal, performing despreading processing on the signal received in the receiving step using a spreading code unique to the transmitting device, and despreading a despread signal for each of the plurality of transmitting devices. A despreading step of generating, and a demodulation step of removing interference with respect to the signal received by the receiving means based on the generated despreading signal, and extracting demodulated data for each of the plurality of transmission-side devices, A communication method comprising: