JP2006211096A - Radio communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication device capable of executing stable communication by reducing the probability of occurrence of determination errors of a symbol. <P>SOLUTION: The radio communication device 100 is provided with a modulation unit 160 which can be adapted to modulation systems of multiple dimensions and modulates a transmission signal by using a signal point on a constellation of each modulation system, and a modulation control unit 140 which switches the modulation in the modulation unit 160 to the modulation using a higher-order modulation system when reception quality on the reception side of the transmission signal is below a prescribed level, and also, switches to the modulation using a partial signal point having a distance between the signal points larger than that of in the modulation system before the switching in the signal points of the high-order modulation system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention particularly relates to a wireless communication apparatus that adjusts a modulation method.

  Conventionally, a method has been proposed in which a plurality of antennas are arranged on the transmission side and a required SNR (Signal to Noise Ratio) is reduced by making use of diversity gain. As such a method, for example, there is a space-time block coding method using orthogonality in the time axis direction as a design index (see Non-Patent Document 1). In this space-time coding scheme, signals with the same content are transmitted with a plurality of antennas shifted in time, so that maximum ratio combining is possible even when signals with the same content are in different fading states. Can be reduced.

As another example, in multi-level modulation, there is a method in which a high priority signal is arranged in high-reliability upper bits in a symbol (see Patent Document 1). In these methods, since a signal having a high priority is arranged in a high-reliability upper bit, the required SNR can be reduced.
JP-A-8-186606 “Space-Time Block Codes from Orthogonal Designs” IEEE Transactions on Information Theory, pp.1456-1467, vol.45, no.5, July 1999

  However, although the required SNR is reduced when performing space-time block coding as shown in Non-Patent Document 1, it is necessary to reduce the transmission power value per antenna in consideration of interference with other cells. Therefore, a situation where the SNR for each individual symbol is less than the required SNR is likely to occur, and a symbol determination error is likely to occur. In addition, even in a scheme in which the bit arrangement is devised as shown in Patent Document 1, a symbol near the determination axis tends to have a SNR that is less than the required SNR due to fading, resulting in a symbol determination error. Cheap.

  The present invention has been made in view of this point, and an object of the present invention is to provide a wireless communication apparatus that reduces the probability that a symbol determination error occurs and enables stable communication.

  The radio communication apparatus of the present invention can be adapted to a multi-dimensional modulation scheme, and has a modulation means for modulating a transmission signal using signal points on the constellation of each modulation scheme, and reception quality at a reception side of the transmission signal is predetermined When the level is less than the level, the modulation in the modulation means is switched to modulation using a higher-order modulation method, and the signal point distance in the modulation method before switching among the signal points of the higher-order modulation method. And a control means for switching to modulation using a part of signal points having a larger distance between signal points.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communication apparatus which reduces the probability that the determination error of a symbol will occur and enables stable communication can be provided.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  As illustrated in FIG. 1, the wireless communication device 100 includes an RF receiver 101, an RF receiver 102, a demodulator 110, an error correction decoder 120, a separator 130, a modulation controller 140, and an error correction. The encoder 150, the modulator 160, the space-time encoder 170, the RF transmitter 181 and the RF transmitter 182 are included.

  The RF receiving unit 101 receives a signal from the radio communication apparatus 200 described later, performs processing such as down-conversion on the received signal, and outputs the received signal to the demodulating unit 110. The same applies to the RF receiver 102.

  Demodulator 110 demodulates the output signals of RF receiver 101 and RF receiver 102 and outputs the demodulated received signal to error correction decoder 120.

  Error correction decoding section 120 receives the demodulated received signal, performs predetermined error correction processing, and outputs the result to demultiplexing section 130.

  Separating section 130 outputs the received signal after error correction processing as received data. In particular, reception quality information from radio communication apparatus 200 included in the reception data is output to modulation control section 140. This reception quality information is information relating to the reception quality in the wireless communication device 200 of the signal transmitted from the wireless communication device 100.

  The modulation control unit 140 performs control to switch the modulation method used when transmitting the transmission signal according to the value indicated by the reception quality information received from the separation unit 130. Specifically, when the reception quality is poor, that is, when the reception quality information is less than a predetermined threshold value, the modulation control unit 140 determines a higher order than the currently used modulation method according to the reception quality. Among the signal points in this modulation scheme, control is performed to switch to signal points that are less likely to cause a determination error than signal points in the current modulation scheme. In other words, when the reception quality on the receiving side of the transmission signal is less than a predetermined level, the modulation control unit 140 converts the signal point in the higher-order modulation scheme from the signal point in the modulation scheme of the predetermined modulation multilevel number. Is controlled to switch to a signal point that is less likely to cause a determination error than a signal point in the modulation scheme of the predetermined modulation multilevel number. The modulation control unit 140 performs control by outputting modulation scheme identification information indicating a modulation scheme to be used and signal point information indicating a signal point in the modulation scheme to the modulation section 160. Further, the modulation scheme identification information is output to the RF transmission unit 181 and the RF transmission unit 182 as a control signal for the wireless communication apparatus 100.

  For example, based on the transmission of 2 bits per symbol using a signal point of QPSK (Quaternary Phase Shift Keying), the reception quality information is set to a predetermined threshold when transmission is currently performed with QPSK. If not, control is performed using a signal point of 16QAM (Quadrature Amplirude Modulation) with Gray arrangement, which also uses a signal point having a smaller probability of determination error than the signal point of QPSK.

More specifically, as shown in FIG. 2A, when transmission is performed using QPSK signal points, when transmitting 4 consecutive bits (b ₁ b ₂ b ₃ b ₄ ), X ₁ : b ₁ b ₂ and X ₂ : b ₃ b ₄ are divided and transmitted after mapping. In this embodiment, the transmission is switched to transmission using 16QAM signal points according to the reception quality. At this time, a signal point group having a smaller determination error probability than the QPSK signal point is used. For example, as the distance between signal points increases, the probability of a determination error occurring decreases, so four points at four corners among 16QAM signal points are used (see FIG. 2B). Then, in order to perform mapping by converting from the QPSK signal points to the four corners of the 16QAM signal points, X ₁ : b ₁ b ₂ 00 and X ₂ : b ₃ b ₄ 00 are used. Good.

If the reception quality is even worse, a signal point group of 64QAM, which is a higher-order modulation method than 16QAM, is used (see FIG. 2C). Also at this time, as the distance between the signal points increases, the probability of occurrence of a determination error decreases. Therefore, four of the four QAM signal points are used. Then, in order to perform mapping by converting from the QPSK signal points to the four corners of the 64QAM signal points, X ₁ : b ₁ b ₂ 0000 and X ₂ : b ₃ b ₄ 0000 are used. Good.

  Also, for example, when transmission is performed at 16QAM based on transmission of 4 bits per symbol using 16QAM signal points in Gray arrangement, the reception quality information does not reach a predetermined threshold value. In such a case, control is performed using a 64QAM signal point in Gray arrangement, and a signal point having a smaller determination error probability than the 16QAM signal point.

More specifically, as shown in FIG. 3A, when transmission is performed using 16QAM signal points, continuous 8 bits (b ₁ b ₂ b ₃ b ₄ b ₅ b ₆ b ₇ b ₈ ) are used. When transmitting, X ₁ : b ₁ b ₂ b ₃ b ₄ and X ₂ : b ₅ b ₆ b ₇ b ₈ are respectively mapped and transmitted. In this embodiment, the transmission is switched to transmission using 16QAM signal points according to the reception quality. At this time, a signal point group having a smaller determination error probability than the QPSK signal point is used. For example, since the probability that a determination error will occur decreases as the distance between signal points increases, 16 signal points as shown in FIG. 3B are used from among 64 QAM signal points. In order to perform mapping by converting 16 QAM signal points into 64 signal points as shown in FIG. 3B out of 64 QAM signal points, X ₁ : b ₁ b ₂ b ₃ b ₄ b ₃ b ₄ and X ₂ : b ₅ b ₆ b ₇ b ₈ b ₇ b ₈ .

  Further, for example, when transmission is currently performed in BPSK based on transmission of 1 bit per symbol using a BPSK (Binary Phase Shift Keying) signal point, reception quality information is a predetermined threshold value. If it is less than the above, control is performed using a 16QAM signal point in Gray arrangement, and also using a signal point having a smaller probability of determination error than the BPSK signal point.

More specifically, as shown in FIG. 4 (a), when transmission is performed using BPSK signal points, when transmitting two consecutive bits (b ₁ b ₂ ), X ₁ : b ₁ and X _2: send by performing each mapping divided into a b _2. In this embodiment, the transmission is switched to transmission using 16QAM signal points according to the reception quality. At this time, a signal point group having a smaller determination error probability than the BPSK signal point is used. For example, since the probability that a determination error will occur decreases as the distance between signal points increases, two signal points as shown in FIG. 4B are used among the 16QAM signal points. In order to perform mapping by converting the signal points of BPSK into two signal points as shown in FIG. 4B among the signal points of 16QAM, X ₁ : b ₁ b ₁ 11 and X ₂ : b ₂ b ₂ 11 may be used.

If the reception quality is even worse, a signal point group of 64QAM, which is a higher-order modulation method than 16QAM, is used (see FIG. 4C). Also at this time, the probability that a determination error will occur decreases as the distance between the signal points increases, so two signal points as shown in FIG. 4C are used among the 64QAM signal points. In order to perform mapping by converting the signal points of BPSK into two signal points as shown in FIG. 4C among the signal points of 64QAM, X ₁ : b ₁ b ₁ 1 (b ₁ ) ^# 11 And X ₂ : b ₂ b ₂ 1 (b ₂ ) ^# 11. In this specification, (b ₁ ) ^# means inversion of b ₁ and is treated as (1) ^# = 0, (0) ^# = 1.

  The modulation unit 160 converts the modulation scheme identification information indicating the modulation scheme switched by the modulation control unit 140 according to the reception quality as described above and the signal point in the basic modulation scheme into the signal point in the modulation scheme after switching. The received signal point information is input, and the transmission signal after error correction encoding input from the error correction encoding unit 150 is modulated according to the information. Then, the modulated signal is output to space-time coding section 170.

The space-time coding unit 170 receives the modulated signal from the modulation unit 160, performs space-time coding, and sends the signal to the RF transmission unit 181 and the RF transmission unit 182 with equal power. Specifically, since radio communication apparatus 100 according to the present embodiment has two antennas and therefore has two RF transmission units 181 and 182, symbols X 1 and X that are continuously transmitted are included. 2 is sent out as follows. That is, X 1 and X 2 are transmitted while being shifted in this order in time to the RF transmitter 181, and − (X 2 ) * and (X 1 ) * are transmitted to the RF transmitter 182. In this order, they are sent out with a time shift. In the present specification, it denotes the complex conjugate of X 1 (X 1) * and.

  The RF transmission unit 181 and the RF transmission unit 182 up-convert the control signal from the modulation control unit 140 and the signal from the space-time coding unit 170, and the radio communication apparatus 200 via an antenna corresponding to each. Send to.

  As illustrated in FIG. 5, the wireless communication device 200 includes an RF receiver 201, an RF receiver 202, a space-time decoder 210, a control signal extractor 220, a demodulator 230, an error correction decoder 240, , Separation section 250, reception quality information generation section 260, error correction coding section 270, modulation section 280, RF transmission section 291 and RF transmission section 292.

  The RF reception unit 201 and the RF reception unit 202 receive a signal from the wireless communication apparatus 100, perform processing such as down-conversion, and send the processed signal to the space-time decoding unit 210 and the control signal extraction unit 220.

  The space-time decoding unit 210 receives signals from the RF receiving unit 201 and the RF receiving unit 202 and performs space-time decoding. Then, the space-time decoding unit 210 outputs the modulated signal to the demodulation unit 230 as a signal in the same state as the signal actually modulated by the modulation unit 160 of the wireless communication apparatus 100. .

  The control signal extraction unit 220 receives signals from the RF reception unit 201 and the RF reception unit 202, extracts a control signal from the wireless communication device 100 included in the signals, and outputs the control signal to the demodulation unit 230. This control signal includes modulation scheme identification information as described above.

Demodulation section 230 demodulates the output signal from space-time decoding section 210 according to the modulation scheme identification information from control signal extraction section 220. In other words, the demodulator 230 demodulates the signal transmitted from the wireless communication device 100 by a demodulation method corresponding to the modulation method actually applied in the wireless communication device 100. That is, the modulation scheme identification information indicates BPSK, QPSK, 16QAM, and 64QAM, and demodulation corresponding to each is performed. Specifically, taking the case described with reference to FIGS. 2A and 2B as an example, since the modulation scheme identification information indicates 16QAM, demodulation according to this is performed and X ₁ : b ₁ b ₂ 00 and X ₂ : b ₃ b ₄ 00 are obtained.

Further, demodulation section 230 outputs only “a signal portion actually necessary as data” to error correction decoding section 240 and reception quality information generation section 260. The “signal portion actually necessary as data” is X ₁ : b ₁ b ₂₀₀ and X ₂ : b ₃ , taking the case described with reference to FIGS. 2A and 2B as an example. Among b ₄₀₀ , the “b ₁ b ₂ ” part and the “b ₃ b ₄ ” part. As described above, in order to extract only “a signal portion actually necessary as data”, it is necessary to share information on a basic modulation scheme between the wireless communication device 100 and the wireless communication device 200. The sharing method is not particularly limited, and may be determined in advance, or information regarding a basic modulation method may be included in the control signal.

  Error correction decoding section 240 receives the “signal part actually necessary as data” output from demodulation section 230, performs error correction decoding, and outputs the result to separation section 250. The output signal is separated into various received data by the separation unit 250 and output to the functional unit to be output.

  Reception quality information generation section 260 measures the reception quality of the reception signal based on the output signal from demodulation section 230 and generates reception quality information. This reception quality information is transmitted to the radio communication apparatus 100 as described above and used as a modulation system switching reference.

  Error correction coding section 270 performs error correction coding on each of the transmission data and the reception quality information from reception quality information generation section 260 and outputs the result to modulation section 280.

  Modulation section 280 modulates the output signal from error correction coding section 270 using a predetermined modulation method, and sends the modulated signal to RF transmission section 291 and RF transmission section 292.

  The RF transmission unit 291 and the RF transmission unit 292 transmit the same signal output from the modulation unit 280 to the wireless communication apparatus 100 via an antenna connected to each.

  In the above description, the case where the reception quality is less than the predetermined threshold has been described. Here, a case where the reception quality is equal to or higher than a predetermined threshold will be described. In this case, the modulation control unit 140 performs normal adaptive modulation. That is, the higher-order modulation scheme is switched as the reception quality level increases. In this case, unlike the case where the above-described reception quality is less than the predetermined threshold value, all signal points on the constellation of each modulation method are used. By doing in this way, the modulation control unit 140, with a certain reception quality level as a boundary, performs normal adaptive modulation control and the current modulation among signal points in a higher-order modulation method than the currently used modulation method. It is possible to switch to control for switching to a signal point that is less likely to cause a determination error than the signal point in the system. At this time, even when modulation control is performed using signal points on the constellation of the same modulation method, the above-mentioned modulation using normal signal transmission using all signal points or only some signal points is used. It is necessary to include information that can distinguish whether the modulation is included in the control signal transmitted to the wireless communication apparatus 200 and the control signal for the modulation unit 160.

  In the above description, the case where each of the wireless communication device 100 and the wireless communication device 200 has two antennas has been described for the sake of simplicity. However, the present invention is not limited to this, and the number of antennas is not limited.

  In the above description, the reception quality is measured in radio communication apparatus 200 and the reception quality information is transmitted as it is to radio communication apparatus 100, and radio communication apparatus 100 switches the modulation method based on the reception quality information. As explained. However, the present invention is not limited to this, and radio communication apparatus 200 determines a modulation scheme to be switched according to reception quality, and transmits the determined switching modulation scheme information to radio communication apparatus 100. Also good. In this case, the modulation control unit 140 of the wireless communication apparatus 100 performs modulation using a modulation method signal point corresponding to the received switching modulation method information.

  As described above, according to the present embodiment, the radio communication apparatus 100 can adapt to a multi-dimensional modulation scheme, and modulates a transmission signal using a signal point on the constellation of each modulation scheme, and the transmission When the reception quality on the signal receiving side is less than a predetermined level, the modulation in the modulation section 160 is switched to modulation using a higher-order modulation scheme, and before switching among the signal points of the higher-order modulation scheme. And a modulation control unit 140 that switches to modulation using a part of signal points having a distance between signal points that is larger than the distance between signal points in the modulation method.

  By doing this, when the reception quality on the receiving side of the transmission signal is less than a predetermined level, the signal point distance is larger than the signal point distance in the modulation method before switching among the signal points of the higher-order modulation method. Since the modulation is switched to the modulation using some signal points, it is possible to provide the wireless communication apparatus 100 that reduces the probability of a symbol determination error and enables stable communication.

  Further, some signal points used in the modulation scheme after switching by the modulation control unit 140 are signal point groups having the largest distance between signal points on the constellation of the modulation scheme after switching.

  By doing so, it is possible to provide radio communication apparatus 100 that can ensure a sufficient inter-symbol distance, reduce the probability of a symbol determination error, and enable stable communication.

  Furthermore, the modulation control unit 140 switches signal points based on a control signal from the receiving side.

  By doing so, the number of processes in the wireless communication apparatus 100 is reduced, so that the structure of the wireless communication apparatus 100 can be simplified.

  A first aspect of the wireless communication apparatus of the present invention is adaptable to a multi-dimensional modulation system, and modulates a transmission signal using a signal point on a constellation of each modulation system, and a receiving side of the transmission signal When the reception quality in the signal does not reach a predetermined level, the modulation in the modulation means is switched to modulation using a higher-order modulation method, and among the signal points of the higher-order modulation method, And a control means for switching to modulation using a part of signal points having a distance between signal points larger than the distance between signal points.

  According to this configuration, when the reception quality on the receiving side of the transmission signal is less than a predetermined level, the signal point distance larger than the signal point distance in the modulation method before switching among the signal points of the higher-order modulation method is set. Since the modulation is switched to the modulation using some of the signal points, the probability that a symbol determination error occurs can be reduced and stable communication can be performed.

  The second aspect of the wireless communication apparatus of the present invention employs a configuration in which the partial signal points in the modulation scheme after switching by the control means are signal point groups having the longest distance between signal points.

  According to this configuration, a sufficient inter-code distance can be ensured, and the probability of occurrence of a symbol determination error can be reduced and stable communication can be performed.

  A third aspect of the wireless communication apparatus of the present invention employs a configuration in which the control means switches the modulation method based on a control signal from the receiving side.

  According to this configuration, since it is not necessary to determine whether the reception quality is at a predetermined level, the number of processes is reduced, so that the structure can be simplified.

  The wireless communication device of the present invention is useful as a device that reduces the probability that a symbol determination error occurs and enables stable communication.

The block diagram which shows the structure of the radio | wireless communication apparatus which concerns on embodiment of this invention The figure which uses for description of the switching method of the modulation system in the radio | wireless communication apparatus of FIG. The figure which uses for description of the other switching method of the modulation system in the radio | wireless communication apparatus of FIG. The figure which uses for description of the other switching method of the modulation system in the radio | wireless communication apparatus of FIG. The block diagram which shows the structure of the other radio | wireless communication apparatus which concerns on embodiment of this invention.

Explanation of symbols

100, 200 Wireless communication device 101, 102, 201, 202 RF receiver 110, 230 Demodulator 120, 240 Error correction decoder 130, 250 Separator 140 Modulation controller 150, 270 Error correction encoder 160, 280 Modulator 170 Space-Time Encoding Unit 181, 182, 291, 292 RF Transmitting Unit 210 Space-Time Decoding Unit 220 Control Signal Extraction Unit 260 Reception Quality Information Generation Unit

Claims (3)

Modulation means that can adapt to a multi-dimensional modulation scheme and modulates a transmission signal using signal points on the constellation of each modulation scheme;
When reception quality on the receiving side of the transmission signal is less than a predetermined level, the modulation in the modulation means is switched to modulation using a higher-order modulation method, and among the signal points of the higher-order modulation method Control means for switching to modulation using a part of signal points having a distance between signal points larger than the distance between signal points in the modulation method before switching;
A wireless communication apparatus comprising:   2. The radio communication apparatus according to claim 1, wherein the some signal points in the modulation scheme after switching by the control means are signal point groups having a longest distance between signal points.   2. The wireless communication apparatus according to claim 1, wherein the control unit switches a modulation method based on a control signal from the receiving side.

Images