Ofdm communication device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) type communication device that performs transmission diversity, and more particularly to an OFDM type communication device that performs retransmission control.

【0002】

[Conventional technology]

A conventional OFDM type communication device that performs transmission diversity will be described with reference to FIG. FIG. 4 is a block diagram showing a configuration of a base station device provided with a conventional OFDM type communication device that performs transmission diversity. Note that FIG. 4 shows the configuration when the number of branches is 2.

【0003】

Hereinafter, the retransmission control by the base station device equipped with the conventional OFDM type communication device that performs transmission diversity will be taken as an example in the case where the base station device performs wireless communication with the mobile station device having the configuration as shown in FIG. explain. FIG. 5 is a block diagram showing a configuration of a base station device provided with a conventional OFDM type communication device that performs transmission diversity and a mobile station device that performs wireless communication. Here, when the base station apparatus transmits a signal to the mobile station apparatus and there is an error in the signal transmitted by the base station apparatus, the base station apparatus sends this erroneous signal to the mobile station apparatus. The case of transmitting (retransmitting) again will be described.

【0004】

The signal transmitted by the mobile station apparatus shown in FIG. 5 is received by the base station apparatus shown in FIG. With reference to FIG. 4, in the receiving system, the signals (received signals) received through the antenna 16 and the antenna 17, that is, the received signal from the branch 1 and the received signal from the branch 2, are the FFT unit 18 and the FFT unit 18, respectively. The FFT unit 19 performs an FFT (Four Fourier transform) process. The FFT unit 18 and the FFT unit 19 output signals arranged in each subcarrier in branch 1 and branch 2 to the receiving diversity unit 20, respectively.

【0005】

In the reception diversity unit 20, reception diversity processing is performed on the signals arranged in each subcarrier in branch 1 and branch 2. As this reception diversity processing, the reception diversity unit 20 selects, for example, the reception signal in the branch having a high reception level for each signal of each subcarrier, or synthesizes the reception signal in each branch.

【0006】

The signal that has undergone the reception diversity processing is demodulated and error-corrected by the demodulation / error correction unit 21. The signal that has undergone demodulation processing and error correction processing is sent to the retransmission control unit 11. If there is no error in the signal subjected to the demodulation processing and the error correction processing in the retransmission control unit 11, this signal is output as a reception signal.

【0007】

On the other hand, in the transmission system, the transmission signal is stored in the retransmission control unit 11. This transmission signal is a packet unit signal. The stored transmission signal is transmitted from the retransmission control unit 11 to the coding / modulation unit 12 according to the transmission timing.

【0008】

In the coding / modulation unit 12, the signal transmitted from the retransmission control unit 11 is coded and modulated. The coded and modulated signals are sent to the transmission subcarrier selection unit 13.

【0009】

By the way, the base station apparatus can usually perform transmission diversity when performing TDD-type communication with the mobile station apparatus. That is, the base station apparatus selects a signal to be transmitted for each branch based on the selection result by the reception diversity unit 20 among the signals arranged in each subcarrier.

【0010】

However, when the time interval between the uplink and the downlink is separated, or when the transmission signal is simultaneously received by a plurality of users (mobile stations) as in multicast communication, the base station apparatus is as described above. It becomes difficult to perform transmission diversity.

【0011】

Therefore, in the above case, the base station apparatus fixedly transmits the signal to be arranged in each subcarrier from any branch. That is, in the above case, the transmission subcarrier 13 performs the following processing.

【0012】

In the transmission subcarrier selection unit 13, a subcarrier to be fixedly transmitted is selected for each branch. For example, as the subcarrier to be transmitted for branch 1, the odd-numbered subcarrier is fixedly selected as shown in FIG. 6A. As shown in FIG. 6B, even-numbered subcarriers are fixedly selected as the subcarriers to be transmitted for branch 2.

【0013】

After that, the transmission subcarrier selection unit 13 outputs to the IFFT unit 14 only the signals arranged in the subcarrier to be transmitted for the branch 1 among the signals from the coding / modulation unit 12. Further, the transmission subcarrier selection unit 13 outputs to the IFFT unit 15 only the signals arranged in the subcarrier to be transmitted for the branch 2 among the signals from the coding / modulation unit 12.

【0014】

In the IFFT unit 14 and the IFFT unit 15, IFFT (inverse Fourier transform) processing is performed on the signal from the transmission subcarrier selection unit, respectively. The IFFT-processed signals by the IFFT unit 14 and the IFFT unit 15 are transmitted to the mobile station apparatus via the antenna 16 and the antenna 17, respectively.

【0015】

In the mobile station apparatus (FIG. 5), the signal received from the antenna 34 is subjected to FFT processing by the FFT unit 35. The signal subjected to the FFT processing is output to the retransmission control unit 31 after the demodulation processing and the error correction processing are performed by the demodulation / error correction unit 36.

【0016】

If there is no error in the signal subjected to the demodulation processing and the error correction processing in the retransmission control unit 31, this signal is output as a reception signal. On the contrary, when an error exists in the signal subjected to the demodulation processing and the error correction processing, this signal is stored in a predetermined memory.

【0017】

If there is an error in the signal that has undergone demodulation processing and error correction processing, the encoding / modulation unit 32 encodes the transmission including the packet requesting the base station device to retransmit this signal. And modulation processing, and after IFFT processing by the IFFT unit 33, the signal is transmitted to the base station device via the antenna 34.

【0018】

After that, in the base station device (FIG. 4), the retransmission control unit 11 transmits the packet requested to be retransmitted by the mobile station device to the coding / modulation unit 12 according to the retransmission timing. This packet is processed in the same manner as described above, and is retransmitted to the mobile station device via the antenna 16 and the antenna 17. As described above, the signal in which the error exists in the mobile station apparatus is retransmitted by the base station apparatus.

【0019】

[Problems to be Solved by the Invention]

However, the conventional OFDM type communication device that performs transmission diversity has the following problems. That is, in the mobile station apparatus described above, there may be a situation in which a signal in which poor quality signals are concentrated at a specific time is input as a signal for performing error correction processing.

【0020】

Here, in order to explain this situation concretely, FIG. 7 is referred to. FIG. 7 is a schematic diagram showing an example of the arrangement of subcarriers in a signal received by a mobile station device that performs wireless communication with a base station device provided with a conventional OFDM type communication device that performs transmission diversity. It is assumed that the transmission subcarrier selection unit 13 in the base station apparatus selects the subcarrier to be transmitted as shown in the above example.

【0021】

When the signal in which the subcarriers are arranged as shown in FIG. 7 is received by the mobile station apparatus (FIG. 5), the signals output by the FFT unit 35 are the subcarriers 1, the subcarriers 2, and the subcarriers 3. , Subcarriers 4, ..., and so on, the signals are extracted from each subcarrier in chronological order. Here, as is clear from FIG. 7, the signals arranged in each of the subcarriers 1, the subcarrier 2, the subcarrier 3, and the subcarrier 4 are of poor quality.

【0022】

As a result, the signal input to the demodulation / error correction unit 36 is a concentration of poor quality signals at a specific time, so that the effect of the error correction processing is reduced and the signal containing the error is retransmitted. It is often output to the control unit 31. As a result, the base station apparatus retransmits the same packet.

【0023】

Further, when the fluctuation of the line (transmission line) state is slower than the time interval for transmitting the same packet by the base station apparatus, the line state when the same packet is first transmitted and the same packet are different. The line state when transmitted (retransmitted) again is almost the same.

【0024】

In this case, when the signal including the retransmitted packet is received by the mobile station apparatus, the arrangement state of the subcarriers in the received signal is almost the same as that shown in FIG. Become. Therefore, in the mobile station device, there is a very high possibility that an error will occur in the packet retransmitted by the base station device, and further, the packet will be continuously erroneous. Therefore, it takes a long time for the mobile station device to receive a specific packet transmitted by the base station device without any error.

【0025】

The present invention has been made in view of this point, and an object of the present invention is to provide an OFDM communication device that performs transmission diversity capable of reducing the probability that the same transmission signal is continuously mistaken.

【0026】

[Means for solving problems]

The OFDM device of the present invention has a carrier wave selection means for selecting a carrier wave to be transmitted for each branch according to the number of retransmissions of a transmission signal, and an IFMT process for transmitting a transmission signal arranged on the carrier wave for each branch. It is characterized in that it is provided with a transmission means to be used.

【0027】

According to the present invention, when a certain transmission signal is first transmitted and when it is transmitted again, the carrier wave to be transmitted is changed for each branch. Therefore, when a specific transmission signal is erroneous, this specific transmission is performed. It is possible to shorten the time until the signal is received without error.

【0028】

The OFDM device of the present invention is characterized in that the carrier wave selection means selects a unique carrier wave for each unit frame.

【0029】

According to the present invention, since the line state can be changed while a certain transmission signal is received, the probability that the same transmission signal is continuously mistaken can be further reduced.

【0030】

The communication terminal device of the present invention is characterized by including any of the above OFDM communication devices. The base station device of the present invention is characterized by including any of the above OFDM communication devices.

【0031】

According to the present invention, there is provided a communication terminal device and a base station device capable of shortening the time until a specific transmission signal is received without an error when a specific transmission signal is erroneous. be able to.

【0032】

The OFDM communication method of the present invention includes a carrier wave selection step of selecting a carrier wave to be transmitted for each branch according to the number of retransmissions of the transmission signal, and IFFT processing of the transmission signal arranged on the carrier wave for each branch. It is characterized by comprising a transmission step of transmitting. [0033]

According to the present invention, when a certain transmission signal is first transmitted and when it is transmitted again, the carrier wave to be transmitted is changed for each branch. Therefore, when a specific transmission signal is erroneous, this specific transmission is performed. It is possible to shorten the time until the signal is received without error.

【0034】

BEST MODE FOR CARRYING OUT THE INVENTION

The gist of the present invention is to change the carrier wave to be transmitted for each branch according to the number of retransmissions of the transmission signal.

【0035】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the OFDM communication device that performs the transmission diversity according to the present invention will be described by taking the case where the OFDM communication device is mounted on the base station device as an example. However, the OFDM communication device that performs the transmission diversity according to the present invention will be described. The communication device can be mounted on the communication terminal device.

【0036】

(Embodiment) FIG. 1 is a block diagram showing a configuration of a base station apparatus including an OFDM communication apparatus for performing transmission diversity according to an embodiment of the present invention. Note that FIG. 1 shows a configuration when the number of branches is 2 as an example, but the number of branches is not limited.

【0037】

Hereinafter, regarding retransmission control by a base station device (hereinafter, simply referred to as base station device) provided with an OFDM type communication device that performs transmission diversity according to the present embodiment, this base station device wirelessly communicates with the mobile station device. Will be described by taking the case of performing the above as an example. Here, when the base station apparatus transmits a signal to the mobile station apparatus and there is an error in the signal transmitted by the base station apparatus, the base station apparatus sends this erroneous signal to the mobile station apparatus. A case of transmitting (resending) again will be described. The mobile station device can be realized by, for example, the configuration shown in FIG.

【0038】

The signal transmitted by the mobile station device is received by the base station device shown in FIG. Referring to FIG. 1, in the receiving system, the signals (received signals) received through the antenna 109 and the antenna 110, that is, the received signal from the branch 1 and the received signal from the branch 2, are the FFT unit 111 and the received signal, respectively. The FFT process is performed by the FFT unit 112. The FFT section 111 and the FFT section 112 output signals arranged in each subcarrier in branch 1 and branch 2 to the receiving diversity section 113, respectively.

【0039】

In the reception diversity unit 113, reception diversity processing is performed on the signals arranged in each subcarrier in branch 1 and branch 2. As this reception diversity process, the reception diversity unit 113 selects, for example, a reception signal in a branch having a high reception level for each subcarrier signal, or synthesizes a reception signal in each branch for each subcarrier signal. ..

【0040】

The signal that has undergone the reception diversity process is demodulated and error-corrected by the demodulation / error correction unit 114. The signal that has undergone demodulation processing and error correction processing is sent to the retransmission control unit 101. If there is no error in the signal subjected to the demodulation processing and the error correction processing in the retransmission control unit 101, this signal is output as a reception signal.

【0041】

On the other hand, in the transmission system, the transmission signal is stored in the retransmission control unit 101. As the transmission signal, for example, a packet unit signal is used. The stored transmission signal or the packet-by-packet transmission signal requested to be retransmitted by the mobile station apparatus is transmitted to the encoding / modulation unit 102 by the retransmission control unit 101 according to the transmission timing or the retransmission timing, respectively.

【0042】

In the coding / modulation unit 102, the signal transmitted from the retransmission control unit 101 is coded and modulated. The coded and modulated signals are sent to the first transmission subcarrier selection unit 103 and the second transmission subcarrier selection unit 104.

【0043】

In the first transmission subcarrier selection unit 103, a subcarrier (carrier wave) to be fixedly transmitted is selected for each branch. For example, as the subcarrier to be transmitted for branch 1, the odd-numbered subcarrier is fixedly selected as shown in FIG. 6A. As shown in FIG. 6B, even-numbered subcarriers are fixedly selected as the subcarriers to be transmitted for branch 2.

【0044】

After that, the first transmission subcarrier selection unit 103 arranges the selector 105 in the subcarrier to be transmitted for branch 1 among the signals from the coding / modulation unit 102 based on the above selection result. Only the signal is output. Further, the first transmission subcarrier selection unit 103 arranges the selector 106 in the subcarrier to be transmitted for branch 2 among the signals from the coding / modulation unit 102 based on the selection result. Only the signal is output.

【0045】

In the second transmission subcarrier selection unit 104, a subcarrier (carrier wave) to be fixedly transmitted is selected for each branch. However, the subcarriers selected for each branch by the second transmission subcarrier selection unit 104 are different from the subcarriers selected for each branch by the first transmission subcarrier selection unit 103 described above.

【0046】

For example, as the subcarrier to be transmitted for branch 1, the even-numbered subcarrier is fixedly selected as shown in FIG. 2 (a). Further, as the subcarrier to be transmitted for the branch 2, the odd-numbered subcarrier is fixedly selected as shown in FIG. 2 (b).

【0047】

After that, the second transmission subcarrier selection unit 104 arranges the selector 105 in the subcarrier to be transmitted for branch 1 among the signals from the coding / modulation unit 102 based on the selection result. Only the signal is output. Further, the second transmission subcarrier selection unit 104 arranges the selector 106 in the subcarrier to be transmitted for branch 2 among the signals from the coding / modulation unit 102 based on the selection result. Only the signal is output.

【0048】

In the selector 105 and the selector 106, the signal output by either the first transmission subcarrier selection unit 103 or the second transmission subcarrier selection unit 104 is output to the transmission OFDM unit 105 according to the control by the retransmission control unit 101.

【0049】

Specifically, depending on the number of retransmissions of the transmission signal (packet) transmitted by the retransmission control unit 101, that is, here, is the transmission signal transmitted by the retransmission control unit 101 the signal transmitted for the first time? A control signal indicating that either the signal from the first transmission subcarrier selection unit 103 or the signal from the second transmission subcarrier selection unit 104 should be output to the IFFT unit depending on whether the signal is retransmitted. Is output from the retransmission control unit 101 to the selector 105 and the selector 106, respectively.

【0050】

In the present embodiment, when the signal transmitted by the retransmission control unit 101 is the signal transmitted for the first time, the first transmission subcarrier selection unit is selected from the selector 105 and the selector 106 with respect to the IFFT unit. If the signal from 103 is output and is a signal to be retransmitted, the control signal output from the retransmission control unit 101 is set so that the signal from the second transmission subcarrier selection unit 104 is output. It is assumed that it has been done.

【0051】

According to the control signal as described above, the selector 105 outputs the signal arranged in the subcarrier to be transmitted for the branch 1 to the IFFT unit 107, and the selector 106 outputs the signal arranged to the IFFT unit 108 to the IFFT unit 108. The signal placed on the subcarrier to be transmitted for branch 2 is output.

【0052】

The signals output from the selector 105 and the selector 106 are subjected to IFFT processing by the IFFT unit 107 and the IFFT unit 108, respectively, and then transmitted to the mobile station apparatus via the antenna 109 and the antenna 110, respectively.

【0053】

Here, in the base station apparatus, the state of the signal received by the mobile station apparatus is changed by changing the subcarrier to be transmitted for each branch between the first transmission and the retransmission of a certain transmission signal. Explain how it changes.

【0054】

When a specific packet is received by the mobile station device for the first time and the line condition is as shown in FIG. 7, the signals FFTed by the mobile station device are subcarrier 1 and subcarrier 2. , Subcarrier 3, subcarrier 4, ..., The signals are extracted from each subcarrier in chronological order. The signal extracted in this way is a signal in which errors are concentrated at a specific time because the quality of the signals arranged in each of the subcarriers 1, subcarrier 2, subcarrier 3 and subcarrier 4 is poor. Become.

【0055】

On the other hand, when the base station apparatus retransmits the specific packet, as described above, the subcarrier to be transmitted for each branch is made different from that at the time of the first transmission of the specific packet. Therefore, the line when the base station apparatus first transmits the specific packet and the line when the base station apparatus transmits the specific packet again are completely independent lines, that is, lines that are different from each other.

【0056】

Therefore, when the specific packet is received again by the mobile station apparatus, the state of the line may be different from the state of the line when the specific packet is first received, as shown in FIG. Highly sex. In this case, as is clear from FIG. 3, the FFT signal in the mobile station device is a signal having a low quality and a low possibility that errors are concentrated at a specific time.

【0057】

Therefore, even when the line state of the first transmission and the second transmission of a specific packet by the base station device hardly changes, an error occurs in the packet retransmitted by the base station device in the mobile station device. Very unlikely. That is, in the above case, it is possible to avoid a situation in which a specific packet is continuously mistaken.

【0058】

As described above, according to the present embodiment, when a certain packet is first transmitted and when it is transmitted again, the subcarrier (carrier wave) to be transmitted is changed for each branch, so that the packet is arranged in the subcarrier. The signals transmitted from each branch are different from each other in each of the above cases. As a result, the line states in each of the above cases are independent of each other, so that it is possible to reduce the probability that the same packet will be mistaken in succession. Therefore, when a specific packet is incorrect, the time until the specific packet is received without error can be shortened.

【0059】

In the present embodiment, the case where two types of combinations for selecting the subcarriers to be transmitted are used has been described, but the present invention is not limited to this, and the number of combinations for selecting the subcarriers to be transmitted is not limited to this. It is also applicable to the case of increasing. The present invention is also applicable when a combination for selecting a subcarrier to be transmitted is arbitrarily set.

【0060】

Further, the present invention is also applicable when the combination for selecting the subcarriers to be transmitted is set independently for each unit frame. As a result, the line state can be changed while a certain packet is received, so that the probability that the same packet is continuously mistaken can be further reduced.

【0061】

Further, in the present embodiment, the case where the subcarrier to be transmitted for each branch is changed according to the number of retransmissions of a certain packet has been described, but the present invention is not limited to this, and the present invention is not limited to this, and for each branch. It is also applicable when the combination of subcarriers to be transmitted is changed according to various conditions such as line quality.

【0062】

Further, the OFDM communication device that performs transmission diversity according to the embodiment of the present invention can be mounted on a communication terminal device or a base station device in a digital mobile communication system.

【0063】

[Effect of the invention]

As described above, according to the present invention, the carrier wave to be transmitted is changed for each branch according to the number of retransmissions of the transmission signal, so that the probability that the same transmission signal is continuously mistaken is reduced. It is possible to provide an OFDM communication device that performs transmission diversity capable.

[Simple explanation of drawings]

[Figure 1]

A block diagram showing a configuration of a base station apparatus including an OFDM communication apparatus for performing transmission diversity according to an embodiment of the present invention. [Figure 2]

(a) Schematic diagram showing an example of the arrangement of subcarriers selected at the time of retransmission for branch 1 in a base station apparatus provided with an OFDM communication apparatus for performing transmission diversity according to the above embodiment. (b) Schematic diagram showing an example of the arrangement of subcarriers selected at the time of retransmission for branch 2 in a base station apparatus provided with an OFDM communication apparatus for performing transmission diversity according to the above embodiment. [Fig. 3]

Schematic diagram showing an example of the arrangement of subcarriers in a signal received by a base station apparatus provided with an OFDM communication apparatus for transmitting diversity and a mobile station apparatus for wireless communication according to the above embodiment. [Fig. 4]

A block diagram showing the configuration of a base station device equipped with a conventional OFDM type communication device that performs transmission diversity. [Fig. 5]

A block diagram showing the configuration of a mobile station device that performs wireless communication with the conventional base station device shown in FIG. [Fig. 6]

(a) Schematic diagram showing an example of the arrangement of subcarriers selected for branch 1 in a base station apparatus equipped with an OFDM communication apparatus for transmission diversity. (b) Schematic diagram showing an example of the arrangement of selected subcarriers for branch 2 in a base station device equipped with an OFDM communication device that performs transmission diversity. [Fig. 7]

Schematic diagram showing an example of the arrangement of subcarriers in the signal received by the mobile station device that wirelessly communicates with the conventional base station device shown in FIG. [Explanation of symbols]

101 Retransmission control unit 102 Coding / modulation section 103 1st transmission subcarrier selection unit 104 2nd transmission subcarrier selection section 105,106 selector 107,108 IFFT section 111,112 FFT section 113 Receiving Diversity Department 114 Demodulation / error correction section