JP5569790B2 - Communication apparatus and communication system - Google Patents

Communication apparatus and communication system Download PDF

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JP5569790B2
JP5569790B2 JP2010083168A JP2010083168A JP5569790B2 JP 5569790 B2 JP5569790 B2 JP 5569790B2 JP 2010083168 A JP2010083168 A JP 2010083168A JP 2010083168 A JP2010083168 A JP 2010083168A JP 5569790 B2 JP5569790 B2 JP 5569790B2
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communication
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terminal
information
communication device
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JP2011217108A (en
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威生 藤井
海燕 鄭
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国立大学法人電気通信大学
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  The present invention relates to a communication apparatus and a communication system. For example, when MC-CDMA signals are transmitted to the same apparatus through two communication paths, the bit error rate of the signal received by the apparatus is sufficiently improved. The present invention relates to a communication apparatus and a communication system that can be made to operate.

  MC-CDMA (Multi-Carrier Code Division Multiple Access) is one of the multi-carrier communications, OFDM (Orthogonal Frequency Division Multiplexing) with high tolerance to delayed waves, and CDMA (Code Division with high frequency utilization efficiency). (Multiple Access) method.

  In this MC-CDMA system, the same data symbol is duplicated over a plurality of frequencies, and a spread code is multiplied in the subcarrier direction to be spread and transmitted. As a result, the MC-CDMA scheme can realize a cellular network that is resistant to propagation delay and has high frequency utilization efficiency.

  Further, in the MC-CDMA system, when a plurality of user signals are transmitted simultaneously from the same base station, synchronization is ensured in all user signals. Furthermore, since signals are received through the same communication path in the same receiver, there is little interference between the signals of each user when the spreading codes used when transmitting the signals of each user are orthogonal. Demodulation can be performed satisfactorily.

  However, when MC-CDMA signals transmitted from a plurality of transmitters are combined at the receiver, signals affected by different channels are combined at the receiver. Therefore, even if the extension codes used at the time of signal transmission of each user are orthogonal, the orthogonality is lost at the time of combining, and a large interference called multi-access interference (MAI (Multiple Access Interference)) is given.

  Such multi-access interference is not necessarily considered when communication is originally performed by multiplexing from the base station, but is considered when a relay station is provided between the base station and the receiver. There is a need.

  Specifically, in the cellular system, the communication quality at the receiver at the cell edge away from the base station is greatly degraded. Therefore, a relay station may be provided between the base station and the receiver in order to improve the level and quality of the received signal at the receiver. In this case, the relay station improves the level and quality of the received signal at the receiver by amplifying the received signal and retransmitting it to the receiver. As a result, the reach of the transmission signal can be expanded and the throughput can be improved.

  However, when a relay station is provided in an MC-CDMA cellular system, the receiver receives two signals from the base station through the relay path and the direct communication path from the base station. . That is, the signal transmitted from the relay station and the signal transmitted from the base station are received under the influence of different channels. As a result, when an orthogonal code having high frequency sharing characteristics is used as an extension code when transmitted from the same base station, the orthogonality of the spread code of the received signal is lost and large multi-access interference occurs. As a result, the bit error rate (BER) sometimes increases by using the relay station.

  Therefore, the present inventor has determined that the entire band of the transmission signal transmitted from the relay station to the receiver is based on the state of the channel (communication path) from the base station to the receiver and the state of the channel from the relay station to the receiver. Therefore, we proposed a relay station that suppresses multi-access interference at the receiver by weighting the transmission signal so that the channel state of the transmission signal is the same as the channel state from the base station to the receiver ( For example, refer nonpatent literature 1).

  With such a relay station, it is possible to effectively use the relay station even in an MC-CDMA cellular system.

  On the other hand, for MC-CDMA cellular systems equipped with relay stations, orthogonal codewords are allocated to base stations and relay stations, and at this time, the relay stations and receivers are grouped to consume a large number of orthogonal codes. Has been devised (see, for example, Patent Document 1). However, a method for suppressing multi-access interference that occurs at the receiver when both the base station and the relay station transmit signals has not been considered.

  Also, in a wireless relay transmission system comprising a transmitting station, one or more relay stations, and a destination station, each station estimates a transfer function of a path between the local station and another station, and the transfer function estimated by the relay station is transmitted to the transmitting station. It has been devised to transmit to (for example, see Patent Document 2 and Patent Document 3).

JP 2005-252677 A JP 2010-11128 A JP 2010-11349 A

Tatsumi Kaoru, Takeo Fujii, "A Study on Channel Compensation Methods for Relay Stations for MC-CDMA Relay Systems", IEICE Society Conference, 2009-9, B-5-120

  However, when the relay station described in Non-Patent Document 1 is used in a cellular system such as the MC-CDMA system, the relay station compensates the channel state of the transmission signal in units of all bands. Diversity gain obtained by utilizing and transmitting cannot be obtained. As a result, the bit error rate cannot be sufficiently improved.

  The present invention has been made in view of such circumstances, and when a signal such as the MC-CDMA system is transmitted to the same device via two communication paths, the bit error of the signal received by the device The rate can be sufficiently improved.

The communication device according to the first aspect of the present invention includes a signal receiving unit that receives a communication signal from a first other communication device, the first other communication device, and the first other communication device. First communication path information, which is information indicating the state of the first communication path to the second other communication apparatus that receives the communication signal, and the first communication path information from the own communication apparatus to the second other communication apparatus. The second communication of each subband obtained by dividing all subcarriers of the communication signal into a plurality of subbands based on the second communication path information that is information indicating the state of the two communication paths. Determining means for determining the weight of each subcarrier so that the state of the path is the same as the state of the first communication path of the subband;
Weighting means for weighting a transmission signal that is a signal to be transmitted to the second other communication device among the communication signals of the subcarrier based on the weight of each subcarrier determined by the determination means; And a transmission means for transmitting the transmission signal weighted by the weighting means to the second other communication apparatus.

  In the first aspect of the present invention, a communication signal is received from a first other communication device, and the communication signal is received from the first other communication device from the first other communication device. 1st communication path information which is the information showing the state of the 1st communication path to 2 other communication apparatuses, and the state of the 2nd communication path from an own communication apparatus to said 2nd other communication apparatus The state of the second channel of each subband obtained by dividing all subcarriers of the communication signal into a plurality of subbands based on the second channel information that is information indicating The weight of each subcarrier is determined so as to be the same as the state of the first communication path of the subband, and based on the determined weight of each subcarrier, Transmission that is a signal to be transmitted to the second other communication device Weighting is performed in No., weighted the transmission signal is transmitted to the second other communication apparatus.

  The communication system according to the second aspect of the present invention is a communication system including a second communication device and a third communication device that receive a communication signal from the first communication device, wherein the second communication device includes: First signal receiving means for receiving the communication signal from the first communication device, and information representing a state of a first communication path from the first communication device to the second communication device. Information transmission means for transmitting the communication path information to the third communication device, wherein the third communication device is a second signal receiving means for receiving the communication signal from the first communication device; , Information receiving means for receiving the first communication path information from the second communication apparatus, the first communication path information received by the information receiving means, and the second from the third communication apparatus. Is information indicating the state of the second communication path to the communication device And the state of the second communication path of each subband obtained by dividing all the subcarriers of the communication signal into a plurality of subbands based on the communication path information of the first subband. Based on the weight of each subcarrier determined by the determining means, the determining means for determining the weight of each subcarrier so as to be the same as the state of the communication path, and among the communication signals of the subcarrier A communication system comprising weighting means for weighting a transmission signal that is a signal to be transmitted to the second communication apparatus, and transmission means for transmitting the transmission signal weighted by the weighting means to the second communication apparatus. is there.

  In a second aspect of the present invention, a second communication device that receives a communication signal from the first communication device receives the communication signal from the first communication device, and receives the communication signal from the first communication device. The first communication path information, which is information indicating the state of the first communication path to the second communication apparatus, is transmitted to the third communication apparatus that receives the communication signal from the first communication apparatus. The third communication device receives the communication signal from the first communication device, receives the first communication path information from the second communication device, and receives the received first communication. Based on the path information and the second communication path information that is information indicating the state of the second communication path from the third communication apparatus to the second communication apparatus, all subcarriers of the communication signal are The weight of each subcarrier is set so that the state of the second communication path of each subband obtained by dividing into a plurality of subbands is the same as the state of the first communication path of the subband. Based on the determined weight of each subcarrier, the transmission signal that is a signal to be transmitted to the second communication device among the communication signals of the subcarrier is weighted, and the weighted transmission Send the signal to the second communication device To.

  According to the present invention, when a signal of MC-CDMA system or the like is transmitted to the same device through two communication paths, the bit error rate of the signal received by the device is sufficiently improved.

It is a figure which shows the structural example of one Embodiment of the communication system to which this invention is applied. FIG. 2 is a block diagram illustrating a configuration example of a relay station in FIG. 1. FIG. 3 is a block diagram illustrating a configuration example of a terminal signal demodulation unit in FIG. 2. It is a block diagram which shows the structural example of the transmission control part of FIG. It is a block diagram which shows the structural example of the transmission part of FIG. It is a figure which shows the structure of the subband in simulation. It is a figure which shows the conditions of simulation. It is a figure which shows the bit error rate when weighting is not performed. It is a figure which shows the bit error rate by the method described in the nonpatent literature 1. It is a figure which shows the bit error rate in the communication system of FIG. It is a flowchart explaining the resending process by the communication system of FIG. It is a figure explaining the signal of a subcarrier.

<One embodiment>
[Configuration example of one embodiment of communication system]
FIG. 1 is a diagram showing a configuration example of an embodiment of a communication system to which the present invention is applied.

  The communication system 10 in FIG. 1 includes a base station 11 (first other communication device, first communication device), a terminal 12 (second other communication device, second communication device), and a relay station 13 ( Communication device, third communication device). In the communication system 10, when a signal for a plurality of terminals including the terminal 12 (hereinafter referred to as a “multiple terminal signal”) is transmitted from the base station 11 and the terminal 12 fails to receive the multiple terminal signal, a plurality of signals are transmitted from the base station 11. The terminal signal is retransmitted and a signal for terminal 12 is transmitted from relay station 13.

  Specifically, the base station 11 of the communication system 10 performs multi-user communication by transmitting a plurality of terminal signals using the MC-CDMA scheme.

  In addition to the MC-CDMA method, MC-DS-CDMA (Multi-Signal) is a method that enables multi-user communication by spreading the signal when transmitting the signal divided into multiple subcarriers. There is also a Carrier Direct Sequence Code Division Multiple Access method.

  The MC-CDMA system is a system in which a signal is spread with a spreading code in the frequency direction, and has an advantage that a frequency diversity gain can be obtained even when encoding is not performed. The MC-CDMA system can obtain high quality and large capacity when used in the downlink.

  On the other hand, the MC-DS-CDMA system is a system in which a signal is serial-parallel converted and then spread with a spreading code in the time direction, and it is easy to maintain code orthogonality even in an environment with a large delay spread. is there. The MC-DS-CDMA system is assumed to be used on the uplink.

  The base station 11 transmits a plurality of terminal signals using the MC-CDMA scheme of the MC-CDMA scheme and the MC-DS-CDMA scheme as described above. Further, when a retransmission request signal is transmitted from the terminal 12, the base station 11 retransmits the multiple terminal signal.

  The terminal 12 receives the multiple terminal signal transmitted from the base station 11 and acquires the signal for the terminal 12 included in the multiple terminal signal. Further, when the terminal 12 fails to receive a plurality of terminal signals transmitted from the base station 11, the terminal 12 transmits a retransmission request signal to the base station 11, and also transmits a retransmission request signal, base station channel information, and relay station channel information. Is transmitted to the relay station 13.

  Note that the base station channel information (first communication path information) is information indicating the channel status between the base station 11 and the terminal 12, and here, the channel from the base station 11 to the terminal 12 of each subcarrier. It is assumed that it is a propagation path estimated value of (first communication path). This base station channel information is obtained using, for example, pilot symbols of a plurality of terminal signals transmitted from the base station 11.

  Further, the relay station channel information (second communication path information) is information indicating the status of the channel between the relay station 13 and the terminal 12, and here, the channel from the relay station 13 to the terminal 12 of each subcarrier. It is assumed that this is a propagation path estimated value of (second communication path).

  The terminal 12 receives a plurality of terminal signals transmitted from the base station 11 in response to the retransmission request and a signal for the terminal 12 transmitted from the relay station 13. Then, the terminal 12 combines the signal for the terminal 12 among the plurality of terminal signals and the signal for the terminal 12 from the relay station 13 and obtains the signal as the signal for the terminal 12.

  The relay station 13 receives a plurality of terminal signals transmitted from the base station 11. Based on the retransmission request signal transmitted from the terminal 12, the relay station 13 extracts a signal for the terminal 12 from the received multiple terminal signals. Further, the relay station 13 determines the state of the channel from the base station 11 to the terminal 12 for each subband composed of a plurality of subcarriers based on the base station channel information and the relay station channel information transmitted together with the retransmission request signal. And the weight of each subcarrier is determined so that the channel states from the relay station 13 to the terminal 12 are the same. The relay station 13 then weights the signal for the terminal 12 based on the determined weight for each subcarrier, and transmits the resulting signal to the terminal 12. Note that the number of subcarriers constituting the subband is an integral multiple of the spreading gain SF of the MC-CDMA system.

[Configuration example of relay station]
FIG. 2 is a block diagram illustrating a configuration example of the relay station 13 of FIG.

  As shown in FIG. 2, the relay station 13 includes a base station receiver 31, a terminal receiver 32, a transmission controller 33, a transmitter 34, an RF (Radio Frequency) converter 35, and a transmission antenna 36. The

  The base station reception unit 31 (signal reception means) includes a reception antenna 41, an IF (Intermediate Frequency) conversion unit 42, a terminal signal demodulation unit 43, and a storage unit 44.

  The receiving antenna 41 receives an RF signal of a plurality of terminal signals transmitted from the base station 11 of FIG.

  The IF conversion unit 42 converts the RF signal of the plurality of terminal signals supplied from the receiving antenna 41 into an IF signal and holds it.

  When the information for specifying the terminal 12 that has transmitted the retransmission request signal is supplied from the transmission control unit 33, the terminal signal demodulation unit 43 reads the multiple terminal signals held in the IF conversion unit 42. Then, the terminal signal demodulator 43 demodulates the signal for the terminal 12 out of the read plural terminal signals based on the information for specifying the terminal 12. The terminal signal demodulation unit 43 supplies a signal for the terminal 12 obtained as a result of demodulation to the storage unit 44.

  The accumulation unit 44 stores the signal for the terminal 12 supplied from the terminal signal demodulation unit 43.

  The terminal receiving unit 32 (information receiving unit) includes a receiving antenna 51, an IF converting unit 52, a retransmission request signal demodulating unit 53, and a storage unit 54.

  The reception antenna 51 receives the retransmission request signal, the base station channel information, and the RF signal of the relay station channel information transmitted from the terminal 12 in FIG.

  The IF converter 52 converts the retransmission request signal, base station channel information, and relay station channel information RF signals supplied from the receiving antenna 51 into IF signals and supplies them to the retransmission request signal demodulator 53.

  The retransmission request signal demodulator 53 demodulates the retransmission request signal, base station channel information, and relay station channel information supplied from the IF converter 52, and the retransmission request signal, base station channel information, and relay station obtained as a result thereof The channel information is supplied to the storage unit 54.

  The accumulation unit 54 stores the retransmission request signal, base station channel information, and relay station channel information supplied from the retransmission request signal demodulation unit 53.

  The transmission control unit 33 reads out the retransmission request signal from the storage unit 54 and supplies information identifying the terminal 12 that has transmitted the retransmission request signal to the terminal signal demodulation unit 43 based on the retransmission request signal. Specifically, for example, the retransmission request signal includes a signal indicating the retransmission request and a signal for specifying the terminal 12 that is the retransmission request source, and the transmission control unit 33 receives the retransmission request signal from the retransmission request signal. A signal specifying a certain terminal 12 is extracted, and information specifying the terminal 12 is supplied to the terminal signal demodulator 43.

  The transmission control unit 33 (determination unit) reads base station channel information and relay station channel information from the storage unit 54. Based on the base station channel information and the relay station channel information, the transmission control unit 33 determines that the channel state from the base station 11 to the terminal 12 in each subband is the channel from the relay station 13 to the terminal 12 in the subband. The weights of the subcarriers are determined so as to be the same as the state.

Specifically, the transmission control unit 33, using the following equation (1), determines a weight W k for each subcarrier.

W k = β m H rk * H dk
... (1)

In Equation (1), k represents a subcarrier number, and m represents a subband number. Β m represents a normalization coefficient for making the transmission power of the signal for the terminal 12 constant for each subband, and is defined by the following equation (2). Further, in equation (1), H rk represents relay station channel information, and H dk represents base station channel information. In the formula (1), * represents a complex conjugate. The same applies to the following description.

  In Equation (2), K represents the total number of subcarriers, and M represents the total number of subbands. The same applies to the following description.

The transmission controller 33 supplies the weight W k of each subcarrier determined as described above to the transmitter 34.

The transmission unit 34 (weighting means) reads the signal for the terminal 12 from the storage unit 44. Transmission unit 34, based on the weight W k of each subcarrier supplied from the transmission control unit 33, performs weighting to a signal terminal 12 of the sub-carrier.

Specifically, the transmission unit 34, by the following equation (3), with respect to the signal of the terminal 12 of each subcarrier, performs weighting using the weight W k of the subcarrier.

S k = W k S rk
... (3)

In Equation (3), S k represents the signal for terminal 12 after weighting of the kth subcarrier, and S rk represents the signal for terminal 12 before weighting of the kth subcarrier. Yes. The same applies to the following description.

When the signal for terminal 12 weighted by equation (3) as described above is transmitted to terminal 12, signal R k for terminal 12 of each subcarrier received by terminal 12 is (4)

R k = H rk β m H rk * H dk S rk = β m | H rk | 2 H dk S rk
... (4)

According to Equation (4), the signal R m for the terminal 12 received from the relay station 13 in the terminal 12 is subjected to the same frequency selective fading as the multiple terminal signals received from the base station 11 in subband units. Received signal. As a result, the orthogonality of the signal for each terminal acquired by the terminal 12 is not greatly degraded in subband units. Therefore, an increase in bit error rate due to multi-access interference can be suppressed.

Also, β m is a normalization coefficient defined by the above-described equation (2) for making the transmission power constant for each subband, so that for terminal 12 received from relay station 13 at terminal 12 The signal has a channel characteristic from the relay station 13 to the terminal 12 in the entire band. As a result, a diversity effect can be obtained.

  The transmission unit 34 supplies the signal for the terminal 12 weighted for each subcarrier by the above-described equation (3) to the RF conversion unit 35.

  The RF conversion unit 35 converts the signal for the terminal 12 that is an IF signal supplied from the transmission unit 34 into an RF signal, and supplies the RF signal to the transmission antenna 36.

  The transmission antenna 36 (transmission means) transmits the RF signal supplied from the RF conversion unit 35 to the outside. This RF signal is received by the terminal 12, for example.

  In FIG. 2, the receiving antenna 41 and the receiving antenna 51 are provided separately, but the receiving antenna 41 and the receiving antenna 51 may be integrated.

[Example of demodulator configuration]
FIG. 3 is a block diagram showing a configuration example of the terminal signal demodulator 43 of FIG.

  As shown in FIG. 3, the terminal signal demodulation unit 43 includes a GI removal unit 61, an FFT (Fast Fourier Transform) unit 62, multiplication units 63-1 to 63-K, demodulation units 64-1 to 64-K, and A P / S (Parallel / Signal) conversion unit 65 is included.

  The GI removal unit 61 of the terminal signal demodulation unit 43 removes the guard interval (GI) from the plurality of terminal signals supplied from the IF conversion unit 42 (FIG. 2) and supplies the guard interval (GI) to the FFT unit 62.

  The FFT unit 62 performs an FFT on the signal supplied from the GI removal unit 61, that is, a plurality of terminal signals from which the guard interval has been removed, and multiplies each of the K signals obtained as a result by the multiplication units 63-1 to 63-. Supply to K respectively.

  Each of the multipliers 63-1 to 63-K obtains a code necessary for extracting a signal for the terminal 12 based on information specifying the terminal 12 supplied from the transmission control unit 33 (FIG. 2). The signal supplied from the FFT unit 62 is multiplied. Thereby, each of the multipliers 63-1 to 63-K extracts the signal for the terminal 12 from the plurality of terminal signals supplied from the FFT unit 62. The multipliers 63-1 to 63-K supply the extracted signals for the terminal 12 to the demodulation units 64-1 to 64-K, respectively.

  The demodulating units 64-1 to 64-K demodulate the signals for the terminal 12 supplied from the multiplying units 63-1 to 63-K, respectively, and supply the resulting signals to the P / S converting unit 65. .

  The P / S conversion unit 65 serializes the signals for the K terminals 12 supplied from the demodulation units 64-1 to 64-K into signals for one terminal 12, and stores them in the storage unit 44 of FIG. Supply.

  In addition, although FIG. 3 demonstrated the structure of the terminal signal demodulation part 43, the resending request signal demodulation part 53 of FIG. 2 is comprised similarly.

[Configuration example of transmission control unit]
FIG. 4 is a block diagram illustrating a configuration example of the transmission control unit 33 in FIG.

  As illustrated in FIG. 4, the transmission control unit 33 includes an acquisition unit 71, an acquisition unit 72, and a weight calculation unit 73.

  The acquisition unit 71 of the transmission control unit 33 reads and acquires the retransmission request signal from the storage unit 54 of FIG. The acquisition unit 71 supplies information identifying the terminal 12 that has transmitted the retransmission request signal to the terminal signal demodulation unit 43 based on the retransmission request signal.

  The acquisition unit 72 reads out and acquires base station channel information and relay station channel information from the storage unit 54 and supplies the base station channel information and relay station channel information to the weight calculation unit 73.

Weight calculation unit 73, based on the relay station channel information with the base station channel information, determines a weight W k of each subcarrier by the formula (1) described above. The weight calculation unit 73 supplies the weights W k of the total number of subcarriers K obtained as a result to the transmission unit 34 in FIG.

[Configuration example of transmitter]
FIG. 5 is a block diagram illustrating a configuration example of the transmission unit 34 of FIG.

  As illustrated in FIG. 5, the transmission unit 34 includes an S / P (Signal / Parallel) conversion unit 81, duplication units 82-1 to 82-P, multiplication units 83-1 to 83-K, and multiplication units 84-1 to 84-1. 84-K, modulators 85-1 to 85-K, an IFFT (Inverse Fast Fourier transform) unit 86, and a GI insertion unit 87.

  The S / P conversion unit 81 of the transmission unit 34 reads out the signal for the terminal 12 serialized by the P / S conversion unit 65 of the terminal signal demodulation unit 43 of FIG. 3 from the storage unit 44 of FIG. The S / P converter 81 parallelizes the signal for the terminal 12 into a signal for P terminals 12. Note that P is a value obtained by dividing the MC-CDMA spread gain SF from the total number of subcarriers K. The S / P conversion unit 81 supplies the signals for the P terminals 12 one by one to the duplication units 82-1 to 82-P.

  Each of the duplication units 82-1 to 82-P duplicates the signal for the terminal 12 supplied from the S / P conversion unit 81 by the spreading gain SF times. The total K (= SF × P) terminal 12 signals generated by the duplicating units 82-1 to 82-P are supplied to the multiplying units 83-1 to 83-K one by one.

  Each of the multipliers 83-1 to 83-K multiplies a signal for the terminal 12 supplied from any of the duplication units 82-1 to 82-P by a predetermined code, and the terminal 12 obtained as a result thereof. Are supplied to the multipliers 84-1 to 84-N.

The multipliers 84-1 to 84-K receive the subcarrier weights W k corresponding to the multipliers 84-1 to 84-K from the transmission control unit 33 in FIG. The multipliers 84-1 to 84-K supply the signal for the terminal 12 supplied from the multipliers 83-1 to 83-K as Srk from the transmission control unit 33 according to the above equation (3). performing weighting using the weight W k to be. Then, multiplying unit 84-1 to 84-K is a signal S k for terminal 12 the weighted resultant, respectively, and supplies the modulation unit 85-1 to 85-K.

Modulation unit 85-1 to 85-K, respectively, to modulate the signal S k for terminal 12 supplied from the multiplication unit 84-1 to 84-K, and supplies to the IFFT unit 86.

  IFFT section 86 performs IFFT on the signals for K terminals 12 supplied from modulation sections 85-1 to 85 -K, and supplies the resulting signals for terminal 12 to GI insertion section 87. .

  The GI insertion unit 87 inserts a guard interval into the signal for the terminal 12 supplied from the IFFT unit 86, and supplies the signal for the terminal 12 obtained as a result to the RF conversion unit 35 (FIG. 2).

[Explanation of effects of communication system]
6 to 10 are diagrams for explaining the effects of the communication system 10 of FIG.

  In order to explain the effect of the communication system 10, the applicant formed subbands as shown in FIG. 6 and performed simulations under the conditions shown in FIG.

  That is, in the simulation, as shown in FIG. 6, the total number of subcarriers K is 128, the 128 subcarriers are divided into 16, and the divided 8 subcarriers are set as subbands. Specifically, as shown in FIG. 6, the 1st to 8th subcarriers are the 1st subband, and the 9th to 16th subcarriers are the 2nd subband. Thereafter, a subband is formed for each of the eight subcarriers in order, and finally, the 121st to 128th subcarriers are set as the 16th subband.

  In the simulation, as shown in FIG. 7, the modulation method is a QPSK (Quadrature Phase Shift Keying) method, and the number of subcarriers (The number of carriers) is 128 as described above. The number of packets is 1000, and the length of guard interval is 24. Further, the spreading gain SF (Spreading Factor) is 8, and the spreading code (Short spreading code) is Walsh Hadamard code (Walsh_Hadamard code). Further, the signal encryption method (Long scrambling code) is a random method (Random code), and the combining method (Combing method) in the terminal 12 is an equal gain combining method (EGC (Equal Gain Combining)).

  Further, in the simulation, it is assumed that the multi-terminal signal received by the relay station 13 is complete, and the multi-terminal signal is a signal for three terminals including the terminal 12.

  FIG. 8 shows an example of the terminal signal acquired by the terminal when the relay station transmits the terminal signal without weighting in the MC-CDMA communication system configured similarly to the communication system 10. It is a figure which shows a bit error rate.

  In FIG. 8, the horizontal axis represents the SN ratio (SNR), and the vertical axis represents the bit error rate (BER). Further, a is a value obtained by normalizing the amplitude of the signal received from the relay station at the terminal with the amplitude of the signal received from the base station. That is, when a = 0, the amplitude of the signal received from the relay station is 0, and when a = 1, the amplitude of the signal received from the relay station is the amplitude of the signal received from the base station. It is shown that it is the same. The same applies to FIGS. 9 and 10 described later.

  From the graph of FIG. 8, the bit error rate increases as the value a increases, that is, as the amplitude of the signal received from the relay station normalized by the amplitude of the signal received from the base station increases. Recognize.

  This is because the signal transmitted from the base station and the signal transmitted from the relay station undergo different frequency selective fading, and multi-access interference occurs in the terminal.

  The occurrence of such multi-access interference is caused by the fact that the transfer function of the channel is not flat in the frequency direction, that is, has frequency selectivity. Such frequency selectivity occurs when the delay spread of the channel is large, and the influence becomes larger as the symbol length becomes longer.

Therefore, in order to compensate for such a difference in frequency selectivity, a method described in Non-Patent Document 1 has been devised. In this method, the weight W k ′ for each subcarrier is determined by the following equation (5).

W k ′ = βH rk * H dk
... (5)

  Note that β in Expression (5) is a normalization coefficient for making the transmission power of the signal for the terminal constant in the entire band, and is defined by Expression (6) below.

  FIG. 9 is obtained at the terminal when the relay station transmits a signal for the terminal by the method described in Non-Patent Document 1 in the MC-CDMA communication system configured similarly to the communication system 10. It is a figure which shows the bit error rate of the signal for terminals.

  In the graph of FIG. 9, the solid line represents the bit error rate when the relay station illustrated in FIG. 8 transmits a signal for the terminal without weighting, and the dotted line represents the relay station in Non-Patent Document 1. It represents a bit error rate when a signal for a terminal is transmitted by the described method.

  According to the graph of FIG. 9, when the relay station transmits a signal for a terminal without weighting, the bit error rate increases as the value a increases, but the relay station is described in Non-Patent Document 1. When transmitting a signal for a terminal by the method, it can be seen that as the value a increases, the effect of the relay station appears and the bit error rate decreases. Thus, it can be seen that the method described in Non-Patent Document 1 is an effective method for reducing multi-access interference.

  However, in the method described in Non-Patent Document 1, since β is a normalization coefficient for making transmission power constant in the entire band, defined by the above-described equation (5), it is transmitted from the relay station. The channel state of the signal is compensated in the whole band unit. Therefore, diversity gain, which is one of the typical effects of using a relay station, cannot be obtained. As a result, the bit error rate is not sufficiently reduced.

  FIG. 10 is a diagram illustrating a bit error rate of the signal for the terminal 12 acquired by the terminal 12 in the communication system 10.

  In the graph of FIG. 10, a dotted line represents a bit error rate when the relay station illustrated in FIG. 9 transmits a signal for a terminal by the method described in Non-Patent Document 1, and a one-dot chain line represents a communication line. The bit error rate of the signal for the terminal 12 acquired by the terminal 12 in the system 10 is represented.

  From the graph of FIG. 10, it can be seen that the bit error rate of the signal for the terminal 12 acquired by the terminal 12 is reduced as compared with the case where the method described in Non-Patent Document 1 is used.

  This is because the bit error rate is significantly reduced by increasing the amplitude of the signal for the terminal 12 transmitted from the relay station 13 by obtaining both the effect of suppressing the multi-access interference and the diversity effect. .

  Note that the bit error rate tends to decrease as the number of subbands increases. However, if the relay station 13 performs spreading so that the subbands are different in the middle of the spreading code, the bit error rate increases rapidly.

[Description of communication system processing]
FIG. 11 is a flowchart for explaining retransmission processing by the communication system 10 of FIG.

  In step S11 of FIG. 11, the base station 11 (FIG. 1) transmits an RF signal of a plurality of terminal signals by the MC-CDMA system.

  In step S21, the terminal 12 receives an RF signal of a plurality of terminal signals transmitted from the base station 11 in step S11. In step S22, the terminal 12 determines whether or not the reception of the multiple terminal signal transmitted from the base station 11 in step S11 is successful.

  If it is determined in step S22 that reception of a plurality of terminal signals has been successful, the process ends. On the other hand, if it is determined in step S22 that reception of a plurality of terminal signals has not been successful, the terminal 12 transmits an RF signal of a retransmission request signal to the base station 11 in step S23. In step S24, the terminal 12 acquires base station channel information and relay station channel information, and transmits the base station channel information and relay station channel information to the relay station 13 as an RF signal together with a retransmission request signal.

  On the other hand, in step S31, the reception antenna 41 (FIG. 2) of the relay station 13 receives the RF signal of the multi-terminal signal transmitted from the base station 11 in step S11 and supplies it to the IF conversion unit. In step S32, the IF conversion unit 42 converts the RF signal of the plurality of terminal signals supplied from the receiving antenna 41 into an IF signal and holds it.

  In step S33, the receiving antenna 51 of the relay station 13 receives the retransmission request signal, the base station channel information, and the RF signal of the relay station channel information transmitted from the terminal 12 in step S24, and supplies them to the IF conversion unit 52. To do. The retransmission request signal, base station channel information, and relay station channel information RF signals supplied to the IF conversion unit 52 are converted into IF signals, demodulated by the retransmission request signal demodulation unit 53, and stored in the storage unit 54. . The acquisition unit 71 (FIG. 4) of the transmission control unit 33 supplies information specifying the terminal 12 that has transmitted the retransmission request signal to the terminal signal demodulation unit 43 based on the retransmission request signal stored in the storage unit 54. To do.

  In step S <b> 34, the terminal signal demodulator 43 extracts a terminal signal from the plurality of terminal signals held in the IF converter 42 based on the information specifying the terminal 12 supplied from the transmission controller 33. Demodulated and supplied to the storage unit 44 for storage.

In step S35, the weight calculation unit 73 of the transmission control unit 33 performs the calculation of the above-described equation (1) based on the base station channel information and the relay station channel information acquired from the storage unit 54 by the acquisition unit 72, determining the weight W k for each subchannel. The transmission control unit 33 supplies the weight W k of each subchannel to the transmission unit 34.

In step S36, the transmitting unit 34, by the equation (3) described above, based on the weight W k of each subcarrier supplied from the transmission control unit 33, the terminal 12 stored in the storage unit 44 of the sub-carrier The signal for weighting is weighted. The weighted signal for the terminal 12 is converted into an RF signal by the RF converter 35 and supplied to the transmission antenna 36.

  In step S <b> 37, the transmission antenna 36 transmits the weighted signal for the terminal 12 supplied from the RF conversion unit 35 to the terminal 12.

  On the other hand, in step S12, the base station 11 receives the retransmission request signal transmitted from the terminal 12 in step S23. In step S13, the base station 11 retransmits the multiple terminal signals by the MC-CDMA scheme.

  In step S25, the terminal 12 receives the multiple terminal signal retransmitted from the base station 11 in step S13, and receives the signal for the terminal 12 transmitted from the relay station 13 in step S37. In step S <b> 26, the terminal 12 combines the signal for the terminal 12 among the plurality of terminal signals received from the base station 11 in step S <b> 25 and the signal for the terminal 12 received from the relay station 13. Then, the process ends.

  In addition, after the process of step S26, the terminal 12 determines whether reception of the multiple terminal signal transmitted from the base station 11 and the signal for the terminal 12 transmitted from the relay station 13 is successful, and the reception is performed. If it is determined that the process has not succeeded, the process may return to step S23 and the subsequent processes may be repeated.

  As described above, in the communication system 10, the relay station 13 determines that the channel state from the relay station 13 to the terminal 12 in each subband is based on the relay station channel information and the base station channel information. The weight of each subcarrier is determined so as to be the same as the channel state from the station 11 to the terminal 12, and the signal for the terminal 12 transmitted to the terminal 12 is weighted based on the weight. Thereby, the channel state from the relay station 13 to the terminal 12 is compensated in subband units, and the channel characteristics from the relay station 13 to the terminal 12 are maintained in the entire band. As a result, the terminal 12 can suppress multi-access interference and obtain a diversity effect.

  Therefore, by applying the communication system 10 to a next-generation cellular system, it is possible to realize future mobile communication with higher quality and higher data rate.

  In the above description, the relay station channel information is transmitted from the terminal 12 to the relay station 13. However, the relay station channel information may be acquired by the relay station 13.

  The present invention is not limited to the MC-CDMA system that spreads in the frequency direction with the spread gain SF, but also the OFC DM (Orthogonal Frequency Code Division Multiplexing) in which the spread gain is determined by dividing the spread gain PG in the frequency direction and the time direction. It can also be applied to a method or the like. In this case, SF subcarrier signals output from the multipliers 83-1 to 83-K (FIG. 5) of the transmitter 34 are as shown in FIG. That is, SF signals are spread in the frequency direction and PG-SF signals are spread in the time direction.

  Further, the present invention can be applied to a next-generation cellular system that performs communication using the MC-CDMA system, a next-generation wireless LAN (Local Area Network) road-to-vehicle communication system, a high-speed wireless system used by a plurality of users, and the like.

  In the present embodiment, one base station 11, one terminal 12, and one relay station 13 are provided in the communication system 10, but a plurality of base stations 11, terminals 12, and relay stations 13 may be provided.

  In the present specification, each step of the flowchart includes not only processing that is performed in time series in the order described, but also processing that is not necessarily performed in time series but is executed in parallel or individually. It is a waste.

  Further, in this specification, the system represents the entire apparatus constituted by a plurality of apparatuses.

  Furthermore, the embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  DESCRIPTION OF SYMBOLS 10 Communication system, 11 Base station, 12 Terminal, 13 Relay station, 31 Base station receiving part, 32 Terminal receiving part, 33 Transmission control part, 34 Transmitting part, 36 Transmitting antenna

Claims (5)

  1. Signal receiving means for receiving a communication signal from the first other communication device;
    1st communication which is the information showing the state of the 1st communication path from said 1st other communication apparatus to the 2nd other communication apparatus which receives the said communication signal from said 1st other communication apparatus Based on the path information and the second communication path information that is the information indicating the state of the second communication path from the own communication apparatus to the second other communication apparatus, all subcarriers of the communication signal are The weight of each subcarrier is set so that the state of the second communication path of each subband obtained by dividing into a plurality of subbands is the same as the state of the first communication path of the subband. A decision means to decide;
    Weighting means for weighting a transmission signal that is a signal to be transmitted to the second other communication device among the communication signals of the subcarrier based on the weight of each subcarrier determined by the determination means; ,
    A transmission device comprising: transmission means for transmitting the transmission signal weighted by the weighting means to the second other communication device.
  2. The determining means includes a normalization coefficient for making the transmission power of the transmission signal constant for each subband, a propagation path estimation value of the first communication path of each subcarrier of the subband, and the The communication apparatus according to claim 1, wherein the complex conjugate of the propagation path estimation value of the second communication path is multiplied, and the resultant multiplication value is determined as the weight of the subcarrier.
  3. The communication apparatus according to claim 1, wherein the number of subcarriers in the subband is an integral multiple of a spreading gain of the communication signal.
  4. The communication apparatus according to claim 1, further comprising: an information receiving unit that receives the first communication path information from the second communication apparatus.
  5. In a communication system including a second communication device and a third communication device that receive communication signals from the first communication device,
    The second communication device is:
    First signal receiving means for receiving the communication signal from the first communication device;
    Information transmitting means for transmitting, to the third communication device, first communication channel information that is information indicating a state of the first communication channel from the first communication device to the second communication device. ,
    The third communication device is:
    Second signal receiving means for receiving the communication signal from the first communication device;
    Information receiving means for receiving the first communication path information from the second communication device;
    The first communication path information received by the information receiving means and the second communication path information which is information indicating the state of the second communication path from the third communication apparatus to the second communication apparatus And the state of the second communication path of each subband obtained by dividing all the subcarriers of the communication signal into a plurality of subbands is the state of the first communication path of the subband. Determining means for determining the weight of each subcarrier to be the same as
    Weighting means for weighting a transmission signal that is a signal to be transmitted to the second communication device among the communication signals of the subcarrier based on the weight of each subcarrier determined by the determination means;
    A transmission unit comprising: a transmission unit configured to transmit the transmission signal weighted by the weighting unit to the second communication device.
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