JP4865655B2 - Wireless communication method - Google Patents

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method that are used for wireless packet communication and in which a transmission station realizes highly reliable communication with a destination station in cooperation with a relay station.

In a system that communicates wireless packets from a transmitting station to a destination station, due to the influence of noise or the like, the destination station may not be able to correctly demodulate the wireless packet, resulting in a reception error.
For this reason, in recent years, there is a communication system in which a relay station is newly added to the system. FIG. 9 is a configuration diagram of a communication system including a relay station. The communication system includes a transmission station 503, a destination station 505, and a relay station 507. The relay station 507 receives a radio packet transmitted from the transmission station 503 to the destination station 505 and relays it to the destination station 505, and the destination station 505 arrives from the relay station 507 and a radio packet that directly arrives from the transmission station 503. A radio packet is combined and demodulated. Thereby, a cooperative scheme for reducing the reception error rate in the destination station 505 has been proposed.
In the cooperative transmission method, there are two types of relay methods by the relay station 507: a non-regenerative relay method and a regenerative relay method.
FIG. 10 is a diagram illustrating a wireless packet (wireless signal) based on the non-regenerative relay method. In the non-regenerative relay system, the relay station 507 amplifies the radio signal and transmits it to the destination station 505 without demodulating the radio packet from the transmission station 503.
FIG. 11 is a diagram illustrating a wireless packet (wireless signal) based on the regenerative relay system. In the regenerative relay system, the relay station 507 demodulates the radio packet from the transmission station 503, regenerates the radio packet from the demodulated data, and transmits the regenerated radio packet to the destination station 505. (See Non-Patent Document 1)

(Aggelos Bletsas et al., `` Cooperative Diversity with Opportunistic Relaying '', IEEE WCNC 2006 Proceeding)

However, in the conventional non-regenerative relay system, the noise component added in the communication between the transmission station 503 and the relay station 507 is also amplified and relayed by the relay station 507 together with the signal component. There has been a problem that the effect of reducing the reception error rate due to is reduced.
On the other hand, in the conventional regenerative relay system, noise components added in communication between the transmission station 503 and the relay station 507 are removed. However, since the relay station 507 demodulates the radio packet from the transmission station 503 and relays it, there is a problem that the delay time until the relay station 507 relays the packet to the destination station 505 increases as shown in FIG.
The present invention has been made in view of the above points, and provides a wireless communication apparatus and a wireless communication method for efficiently reducing wireless packet reception error rate and delay time at a destination station and efficiently communicating wireless packets. The purpose is to provide.

In order to achieve the above-described object, the present invention provides a wireless communication method for relaying a wireless packet transmitted from a transmitting station to a destination station using one or a plurality of relay stations , the transmitting station comprising: A step of transmitting one wireless packet; a step of storing data of the first wireless packet; and a response signal transmitted by the destination station, when the response signal transmitted from the destination station is received, from the stored data of the first wireless packet Generating a second wireless packet that is the same as the first wireless packet and transmitting the second wireless packet to a destination station; and the relay station receives the first wireless packet from the transmitter station and performs non-regenerative relay to the destination station The first wireless packet is demodulated, and when demodulated correctly, the data of the demodulated first wireless packet is stored in a memory. When the first demodulation step for storing the signal waveform of the first wireless packet in the memory and the response signal transmitted from the destination station are received, the data of the wireless packet is stored in the memory Generates a third wireless packet from the data and transmits the third wireless packet to the destination station. On the other hand, when a signal waveform is stored in the memory, the transmitted from the transmitting station The second radio packet is transmitted by non-regenerative relay, and a combined wave of the second radio packet and the signal waveform stored in the first demodulation step is demodulated, and stored as data when correctly demodulated And a step in which the destination station demodulates a combined wave in which a wireless packet transmitted from the transmitting station and a wireless packet transmitted from the relay station are combined in space. , When the composite wave is not correctly demodulated, comprising the steps of: transmitting a response signal which is determined, a.

As described above, in the present invention, since the wireless packet is relayed by non-regenerative relay except when the wireless packet is retransmitted, the delay time does not increase unlike the conventional regenerative relay system. In addition, even when a radio packet is retransmitted without being demodulated correctly at the destination station, the error reception rate can be reduced because the data demodulated and stored at the relay station is used.
Also, in the present invention, as the modulation method of the wireless packet, using OFDM. Here, OFDM is called Orthogonal Frequency Division Multiplexing and is one of modulation schemes. That is, even if a plurality of radio stations transmit the same OFDM symbol at the same time, no interference occurs, and the reception error rate at the destination station can be reduced by the diversity effect.

  According to the present invention, it is possible to reduce the reception error rate and delay time of radio packets at the destination station, and to provide efficient radio packet communication.

  Hereinafter, preferred embodiments of a wireless communication apparatus and a wireless communication method according to the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, the same reference numerals are given to components having substantially the same functional configuration, and redundant description is omitted.

  FIG. 1 is a configuration diagram of a wireless communication system. The wireless communication system includes a transmission station 3, a destination station 5, and a relay station 7. In this embodiment, the relay station 7 is one station, but there may be a plurality of stations.

  The transmitting station 3 generates and transmits a wireless packet, a storage unit 32 that stores the generated transmission data, and a response signal (ACK (Acknowledgements) signal or NACK (Negative Acknowledgements) transmitted from the destination station 5. ) Signal).

  The destination station 5 includes a reception unit 51 that receives a wireless packet transmitted from the transmission station 3 and receives a wireless packet that is transmitted via the relay station 7, a demodulation unit 52 that demodulates the wireless packet, and a demodulation unit. 52 includes a transmission unit 53 that transmits a response signal (ACK signal or NACK signal) according to whether or not the signal was normally demodulated at 52.

  The relay station 7 includes a receiving unit 71 having a function of receiving a wireless packet from the transmitting station 3 and a function of receiving a response signal (ACK signal or NACK signal) from the destination station 5, and relay for relaying the wireless packet to the destination station 5. Unit 72, a demodulator 73 that demodulates the radio packet, and a storage unit 74 that stores the radio packet and data demodulated by the demodulator.

Next, the operation of the wireless communication system in the configuration of FIG. 1 will be described in order for the transmitting station 3, the destination station 5, and the relay station 7.
FIG. 2 is a flowchart showing the operation of the transmission station 3. The transmitting station 3 generates transmission data (step S101), generates a wireless packet (step S102), transmits the wireless packet (step S103), and stores the wireless packet data in its own memory (step S104). ). After transmitting the radio packet, the transmission station 3 waits for a response signal from the destination station 5 (step S105).

  When the transmitting station 3 receives the ACK signal from the destination station 5, that is, when the wireless packet is normally demodulated by the destination station 5, the transmitting station 3 discards the data of the wireless packet stored in the memory (step S106). In step S105, when the transmitting station 3 receives the NACK signal from the destination station 5, that is, when the wireless packet is not demodulated normally by the destination station 5, the wireless packet is determined from the wireless packet data stored in the memory. Is generated (step S107), and a wireless packet is transmitted (step S108).

  FIG. 3 is a flowchart showing the operation of the destination station 5. The destination station 5 receives the combined wave of the wireless packet transmitted from the transmitting station 3 and the wireless packet transmitted through the relay station 7 (step S201), and demodulates the wireless packet (step S202). Here, when the radio packet can be normally demodulated (step S203), the destination station 5 transmits an ACK signal (step S204). In step 203, if the radio packet cannot be demodulated normally (step S203), the destination station 5 transmits a NACK signal (step S205).

  FIG. 4 is a flowchart showing the operation of the relay station 7. The relay station 7 receives the radio packet transmitted from the transmission station 3 (step S301), relays the radio packet in a non-regenerative manner (step S302), demodulates the radio packet (step S303), and has it demodulated normally? It is determined whether or not (step S304).

  When the radio packet is normally demodulated, the relay station 7 stores the demodulated data in the memory (step S311) and waits for a response signal from the destination station 5 (step S312). When the ACK signal is received from the destination station 5 (step S312), the relay station 7 discards the data stored in the memory (step S313) and ends the process. When the NACK signal is received from the destination station 5 in step S312, the relay station 7 again generates a wireless packet from the data stored in the memory (step S314), and transmits the generated wireless packet to the destination station 5 (step S315). ) And waits for a response from the destination station 5 (step S312).

  If the radio packet is not demodulated normally in step S304, the relay station 7 stores the radio signal waveform of the radio packet signal in the memory (step S321) and waits for a response signal from the destination station 5 (step S322). . When the ACK signal is received from the destination station 5 (step S322), the relay station 7 discards the radio packet stored in the memory (step S323) and ends the process.

  In step S322, when a NACK signal is received from the destination station 5 (step S322), the relay station 7 receives the wireless packet transmitted from the transmitting station 3 again (step S324), and does not regenerate the received wireless packet. Relay (step S325), combine the radio signal waveform stored in the memory and the signal waveform of the radio packet received again, demodulate the synthesized wave (step S326), return to step S304, and the synthesized wave is correctly demodulated Determine whether or not. In this way, when correctly demodulated, the demodulated data is stored in the memory and prepared for the case where a response signal is sent from the next destination station.

  When the relay station 7 has a plurality of memories, the relay station 7 can store radio signal waveforms of a plurality of radio packets in the memory and use them at the time of demodulation. When there is one memory, the relay station 7 may store the wireless packet received again by overwriting the wireless packet currently stored, or may not store the wireless packet received again.

5, 6, and 7 are time charts showing a state of wireless packet transfer by the wireless communication apparatus of the present embodiment. The horizontal axis of FIGS. 5, 6, and 7 represents time.
FIG. 5 is a time chart showing a state of wireless packet transfer in each station when a NACK signal is not transmitted from the destination station 5 and a wireless packet is not retransmitted from the transmission station 3. The relay station 7 performs non-regenerative relay of the wireless packet received from the transmission station 3. The destination station 5 can receive a combined wave of a wireless packet that arrives directly from the transmitting station 3 and a wireless packet that is non-regeneratively relayed from the relay station 7 almost simultaneously. For this reason, there is no delay time due to relay as in the conventional regenerative relay system.

  FIG. 6 is a time chart showing a state of wireless packet transfer in each station when a NACK signal is transmitted from the destination station 5 and the relay station 7 can correctly demodulate the wireless packet during relay in step S304 shown in FIG. . The relay station 7 stores data acquired from the demodulated radio packet in its own memory. The destination station 5 transmits a NACK signal when it cannot correctly demodulate the combined wave of the wireless packet that arrives directly from the transmitting station 3 and the wireless packet that has been non-regeneratively relayed from the relay station 7.

The transmitting station 3 retransmits the radio packet as shown in step S107 shown in FIG. When the relay station 7 receives the NACK signal from the destination station 5, the relay station 7 does not perform non-regenerative relay of the wireless packet retransmitted from the transmission station 3, and reads the data stored in the memory as in step S314 shown in FIG. The radio packet is regenerated and retransmitted to the destination station 5.
As described above, according to this embodiment, unlike the conventional non-regenerative relay system, noise components generated in communication between the transmission station and the relay station are not added, so that the reception error rate of the radio packet at the destination station 7 is reduced. it can.

  FIG. 7 is a time chart showing a state of wireless packet transfer in each station when a NACK signal is transmitted from the destination station 5 and the relay station 7 cannot correctly demodulate the wireless packet at the time of relay in step S304 shown in FIG. is there. The destination station 5 transmits a NACK signal when it cannot correctly demodulate the combined wave of the wireless packet that arrives directly from the transmitting station 3 and the wireless packet that has been non-regeneratively relayed from the relay station 7.

  When receiving the NACK signal, the transmitting station 3 retransmits the radio packet as shown in step S107 shown in FIG. When the relay station 7 receives the NACK signal from the destination station 5, the relay station 7 performs non-regenerative relay of the wireless packet retransmitted by the transmission station 3, and the wireless packet stored in the memory and the retransmitted wireless packet as shown in step S 326 in FIG. 4. The packet is synthesized and the synthesized wave is demodulated. In this way, when correctly demodulated, as shown in step S311, the relay station 7 stores the demodulated data in the memory and prepares for re-transmission.

  FIG. 8 is a relationship diagram between a radio packet and an OFDM symbol. OFDM is called Orthogonal Frequency Division Multiplexing and is one of frequency multiplexing. When OFDM is used as a radio packet modulation scheme, a radio packet to be sent is divided into a plurality of OFDM symbols and transmitted. At this time, as shown in FIG. 8, even if the reception timings of the OFDM symbol from the transmission station 3 and the OFDM symbol from the relay station 7 are deviated within the range of the guard interval (GI), they do not interfere with each other. The OFDM symbol to which a guard interval (GI) is added has a characteristic that the station 5 can receive normally. At this time, the reception error rate at the destination station 5 is reduced due to the diversity effect.

  The preferred embodiments of the wireless communication apparatus and the wireless communication method according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

As described above, according to the present invention, the relay station can prevent an increase in delay time as in the conventional regenerative relay system by non-regeneratively relaying the wireless packet. In addition, the relay station demodulates the wireless packet that has been previously non-regeneratively relayed and stores the data in a memory. When the retransmission is performed, the data is read out, and the wireless packet is regenerated and retransmitted. Like the regenerative relay format, the influence of noise components generated in communication between the transmission station and the relay station is reduced, and the reception error rate of the destination station is reduced.
For this reason, according to the present invention, the average delay time of wireless packet communication is reduced, and highly accurate wireless packet communication is provided.

Configuration diagram of wireless communication network system Flow chart showing operation of transmitting station 3 A flowchart showing the operation of the destination station 5 Flow chart showing operation of relay station 7 Time chart showing a state of wireless packet transfer by the wireless communication device of the present embodiment Time chart showing a state of wireless packet transfer by the wireless communication device of the present embodiment Time chart showing a state of wireless packet transfer by the wireless communication device of the present embodiment Relationship diagram between wireless packet and OFDM symbol Configuration diagram of conventional communication system Time chart showing non-regenerative relay data transfer Time chart showing the state of regenerative relay data transfer

Explanation of symbols

3 ......... Transmitting station 5 ......... Destination station 7 ......... Relay station

Claims (2)

A wireless communication method for relaying a wireless packet transmitted from a transmission station to a destination station using one or more relay stations,
The transmitting station is
Transmitting a first wireless packet;
Storing the data of the first wireless packet;
Generating a second wireless packet that is the same as the first wireless packet from the stored data of the first wireless packet when the response signal transmitted by the destination station is received, and transmitting the second wireless packet to the destination station; ,
The relay station is
Receiving a first wireless packet from the transmitting station and transmitting to the destination station by non-regenerative relay;
When the first radio packet is demodulated and correctly demodulated, the demodulated first radio packet data is stored in the memory, and when the first radio packet is not demodulated correctly, the signal of the first radio packet is stored. A first demodulation step for storing the waveform in a memory;
When a response signal transmitted from the destination station is received and a wireless packet data is stored in the memory, a third wireless packet is generated from the data, and the third wireless packet is transmitted to the destination When the signal waveform is stored in the memory, the second wireless packet transmitted from the transmitting station is transmitted by non-regenerative relay, and the second wireless packet and the Demodulating a composite wave with the signal waveform stored in the first demodulation step, and storing it as data when correctly demodulated;
The destination station is
Demodulating a combined wave in which a wireless packet transmitted from the transmitting station and a wireless packet transmitted from the relay station are combined in space;
If the synthesized wave is not demodulated correctly, transmitting a determined response signal;
A wireless communication method. As the modulation scheme of the wireless packet, the wireless communication method of claim 1 using OFDM.

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