JP4359902B2 - OFDM signal modulation apparatus and OFDM signal modulation method - Google Patents

Description

  The present invention relates to an OFDM signal modulation apparatus and an OFDM signal modulation method for wirelessly transmitting packetized data (information signal) to a communication network, and more particularly to IEEE (The Institute of Electrical and Electronics Engineers, Inc./American Institute of Electrical and Electronics Engineers). The wireless LAN (Local Area Network) standard that is standardized in IEEE Std 802.11 is related to the improvement of the utilization efficiency of the MAC (Medium Access Control) layer of IEEE Std 802.11.

  Conventionally, an access control method in the IEEE 802.11 MAC layer has been used as a method for wirelessly transmitting packetized data. In the transmission method using radio waves as a transmission medium, unlike the wired communication method, when data is simultaneously transmitted from a plurality of transmission terminals, they interfere with each other and interfere with communication. That is, data collision is an unavoidable problem.

  That is, when the transmitting side terminal is performing data transmission, the power received by the transmitting station is larger than the power received and transmitted from other transmitting terminals. Cannot detect that is being sent. Therefore, IEEE 802.11 uses an access control method called CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) to avoid collision between transmitted data.

FIG. 17 shows an example of MAC access control when the number of terminals is 3 in connection with conventional data collision avoidance.
In the figure, the terminal 1 transmits data until the time indicated by (1). The terminal 2 and the terminal 3 hold data to be transmitted and are on standby.

  The terminal 2 and the terminal 3 execute the carrier sense of the line from the time point (1) when the terminal 1 has finished transmitting data, and check whether it is busy, that is, whether another terminal is using the line. When a state in which there is no energy on the line is continuously detected, it is randomly given differently for each terminal and a fixed period called DIFS (Distributed Coordination Function Inter Frame Spacing) whose detection time is 34 μsec. Wait for backoff period.

  Both the terminal 2 and the terminal 3 wait for a DIFS period at the same time. After that, it waits for different backoff periods given by random numbers for each terminal. Since the back-off period of the terminal 2 shown here is shorter than that of the terminal 3, the terminal 2 transmits data from (2) at the end point.

  Terminal 3 checks the line after the end of backoff. However, since the transmission power of the terminal 2 is detected, no transmission is performed. Then, the terminal 3 waits for the DIFS and the newly selected backoff period from (3) after the transmission of the terminal 2 is completed, and when it is detected that there is no energy on the line at time (4), You can send for the first time.

  Here, since different values are used for each terminal during the backoff period, even if the terminals detect no carrier on the line at the same time, transmission is performed from different times. Since it starts, the possibility of collision of packets transmitted on the line is kept low.

That is, each terminal selects a random time from a time range of 0 to CW based on the current CW (Contention Window) parameter of each terminal, and uses the selected time as a back-off period.
FIG. 18 shows values of CW parameters conventionally used.

  In the figure, the horizontal axis represents the number of retransmissions, and the vertical axis represents the upper limit value of the CW coefficient. That is, a random value generated between 0 and 7 is used at the first transmission. A back-off time based on a random number generated between 0 and 15 for the second time, 0 to 31 for the third time, and 0 to 255 for the sixth and subsequent times is used. The back-off time is a time obtained by multiplying the coefficient value by 9 microseconds which is a slot time.

  As described above, in the conventional access control method based on CSMA / CA, a long back-off time is set for each retransmission, and a long time is required for transmission. However, there is a case where the terminal 3 is located away from the terminal 2 and the reception environment is not preferable. In that case, the terminal 3 cannot receive the signal transmitted from the terminal 2 and starts transmission after a predetermined back-off time has elapsed. A signal emitted from the terminal 3 interferes with a signal emitted from the terminal 2, and the target data cannot be delivered.

In the IEEE802.11 MAC access control system, a mechanism for returning an ACK (Acknowledgment) from the receiving terminal side to the transmitting terminal side is specified in order to confirm whether or not the data has been delivered.
FIG. 19 shows a procedure for confirming delivery by ACK in the conventional IEEE802.11 MAC access control system.

  The transmitting side terminal confirms that the DIFS period line is not used and starts data transmission. When the receiving terminal confirms that the data is addressed to itself, it waits for 16 μsec SIFS (Short Inter Frame Space) period after receiving the data. If the data can be received normally, an ACK indicating that is received. Reply (Acknowledgment).

  Since SIFS is set to 16 μsec and is shorter than DIFS (34 μsec) before starting normal data, ACK is transmitted with priority over other data communications. On the other hand, other terminals cannot access the line while the transmitting terminal and the receiving terminal are transmitting. That is, it is defined that other terminals can enter a transmission waiting state due to backoff in the contention section for the first time after confirming that the DIFS section line is not busy after the ACK is returned.

When a plurality of types of media data are multiplexed and transmitted from the transmission-side device to the reception-side device, retransmission is performed according to the characteristics of each medium as a method for restricting retransmission processing according to the characteristics of each medium. The transmission side device having the function of regulating the processing is configured such that the block generation unit divides each media data into blocks and attaches error detection codes, and these are mixed and arranged by the multiplexing unit and transmitted by the transmission unit. The data retransmitting means includes a method of retransmitting block data notified from the receiving side apparatus.
Further, in the receiving side device, the separation means separates the block data sequence received by the receiving means for each medium, the reproducing means reproduces each media data, and the retransmission request means detects a transmission error by the error detecting means. This block is notified to the transmission side device. Also, at least one of the transmission side device and the reception side device has a retransmission setting means for setting whether or not to perform retransmission processing for each medium, and restricts retransmission processing for each medium based on this setting. There is a method of transmitting and receiving media data including a retransmission control means (see, for example, Patent Document 1).

JP-A-10-341217

  However, in the conventional access control in IEEE802.11, when an ACK is not returned from the receiving terminal within a predetermined time after the end of transmission, and when a NAK (Negative Ack) indicating that reception has failed is received. The already transmitted data is retransmitted. The retransmission protocol is operated so as to be completed within the seven layers of the OSI model.

  And, in response to an ACK signal in wireless communication, unlike a wired reply, a weak received signal transmitted from a receiving terminal immediately after transmission often includes burst error data. Even if a received signal is detected, it is impossible to obtain even information as to which terminal the signal is sent to. Therefore, there is a problem that the transmission terminal deteriorates the bandwidth utilization rate, for example, it repeats retransmission even if the reception terminal normally completes reception.

  Therefore, in the present invention, the receiving terminal does not always return an ACK signal, and returns a NAK signal only when normal reception is not possible. When the transmitting terminal does not receive the NAK signal immediately after transmission, it is considered that the transmitting terminal has transmitted normally, and the transmitting terminal continues to transmit the next data, thereby improving the bandwidth utilization rate. Therefore, for transmission of the NAK signal, a code indicating the transmission destination is transmitted by a transmission method with excellent radio tolerance. The NAK information transmitted only when the receiving terminal cannot perform normal reception is more important information than ACK, and the transmitted NAK information is reliably transmitted to the transmitting terminal.

  In this case, the receiving terminal that transmits the NAK information is a hidden terminal with respect to the third transmitting terminal, and the third terminal is in a carrier-free state even though the NAK information is transmitted. Even if there is a signal to be transmitted, the transmitting terminal transmits the NAK signal to its own terminal by transmitting the NAK signal transmitted from the receiving terminal by a digital modulation method having radio tolerance. To provide an OFDM signal modulation apparatus and an OFDM signal modulation method that prevent the transmission of data from being regarded as being normally received despite the transmission of NAK information. To do.

In order to solve the above problems, the OFDM signal modulation apparatus of the present invention is provided with a MAC header, a payload storing digital data to be transmitted, and a frame check sequence for performing error detection of the digital data. While the frame divided into a plurality of segments is digitally modulated, a unique ID for identifying each segment is provided at the beginning of each of the plurality of segments, and at least the PHY (Physical) is provided at the beginning of the frame. OFDM having a structure in which a header and transmission destination information are provided, and the unique ID, PHY (Physical) header, and transmission destination information are digitally modulated by a modulation scheme having a higher radio tolerance than the digital modulation scheme of the frame OFDM to receive and demodulate signal from OFDM signal modulator An apparatus for demodulating a signal, wherein the frame included in the OFDM signal is digitally demodulated to restore the digital data, and the frame check sequence included in the OFDM signal is used to generate an error for each segment. Error correction means for performing correction processing, and error correction processing for each segment using the frame check sequence in the error correction means, and detecting an error correction impossible signal indicating a segment for which error correction processing was impossible Error correction impossible signal detection means, the unique ID included in the OFDM signal, a PHY (Physical) header, destination information and PHY header / destination information demodulation means for digital demodulation, and the PHY header / destination information The unique ID digitally demodulated by the demodulator and the destination information A transmission destination / unique ID confirmation means to be recognized; and a unique ID of a segment in which the error correction impossible signal is detected and error correction processing is impossible is obtained from the transmission destination / unique ID confirmation means and set in a NAK signal, NAK signal generation means for transmitting to the OFDM signal modulation device.
The OFDM signal modulation method of the present invention includes a plurality of segments each provided with a MAC header, a payload storing digital data to be transmitted, and a frame check sequence for detecting an error in the digital data. While the divided frames are digitally modulated, a unique ID for identifying each segment is provided at the head of each of the plurality of segments, and at least a PHY (Physical) header and transmission destination information are provided at the head of the frame. An OFDM signal having a structure in which the unique ID, PHY (Physical) header, and transmission destination information are digitally modulated by a modulation scheme having higher radio tolerance than the digital modulation scheme of the frame. An OFDM signal demodulation method for receiving and demodulating from an apparatus. Digitally demodulating the frame included in the OFDM signal to restore the digital data; performing error correction processing for each segment using the frame check sequence included in the OFDM signal; Performing error correction processing for each of the segments using the frame check sequence, detecting an error correction impossible signal indicating a segment for which error correction processing was impossible, the unique ID included in the OFDM signal, and PHY (Physical) header, transmission destination information and digital demodulation step, confirmation step of digitally demodulated unique ID and transmission destination information, and error correction impossible signal detected and error correction processing was impossible The unique ID of the segment is set in the NAK signal, and the OFDM signal An OFDM signal modulation method and a step of transmitting to the adjustment device.

  According to the OFDM signal modulation apparatus and the OFDM signal modulation method of the present invention, when a frame included in an OFDM signal is digitally demodulated to restore digital data, an error is detected for each segment using a frame check sequence included in the OFDM signal. A correction process is performed, an error correction process is performed for each segment using a frame check sequence, and an error correction impossible signal indicating a segment for which the error correction process cannot be performed is detected, while a unique ID included in the OFDM signal and a PHY (Physical) header, transmission destination information and digital demodulation, digital demodulated unique ID and transmission destination information are confirmed, and error correction impossible signal is detected and error correction processing cannot be performed. Since it is set to signal and transmitted to the OFDM signal modulator, On the side, when the OFDM signal demodulation, it is possible to easily recognize the segment which can not be error corrected.

It is a figure which shows schematic structure of the radio | wireless packet data transmission system based on the Example of this invention. It is a figure which shows schematic structure of the transmitter which transmits the OFDM signal based on the Example of this invention. It is a figure which shows schematic structure of the receiver which receives the OFDM signal based on the Example of this invention. It is a block diagram which shows the structure of the OFDM signal transmitter based on the Example of this invention. It is a figure which shows the structure of the data frame of the OFDM signal based on the Example of this invention. It is a block diagram which shows the structure of the OFDM signal receiver based on the Example of this invention. It is a figure which shows the frame structure of the MAC part of a NAK signal based on the Example of this invention. It is a figure which shows the structure of the OFDM signal transmitter by the 1st modification based on implementation of this invention. It is a figure which shows the structure of the data frame by the 1st modification based on implementation of this invention. It is a figure which shows the structure of the OFDM signal receiver by the 1st modification based on implementation of this invention. It is a figure which shows the frame structure of the NAK signal by the 1st modification based on implementation of this invention. It is a figure which shows the signal transmitted from the transmitter and receiver based on implementation of this invention. It is a figure which shows the structure of the OFDM transmitter by the 2nd modification based on implementation of this invention. It is a figure which shows the structure of the data frame by the 2nd modification based on implementation of this invention. It is a figure which shows the structure of the OFDM signal receiver by the 2nd modification based on implementation of this invention. It is a figure which shows the frame structure of the NAK signal by the 2nd modification based on implementation of this invention. It is a figure which shows the outline of operation | movement of the wireless packet data transmission system based on a prior art example. It is a figure which shows the value of a CW parameter based on a prior art example. It is a figure which shows the procedure of the delivery confirmation by ACK based on a prior art example.

According to the wireless packetized data receiving method and the wireless packetized data transmission system according to the embodiment of the present invention, the following effects 1) or 2) can be provided.
That is,
1) Obtain a sender identification code for identifying the sender from the received packetized information signal, and digitally modulate the obtained sender identification code and the position information of the packetized information signal to be retransmitted with a small multi-valued number. Since the transmitted NAK signal is transmitted, the band utilization rate can be increased more than the transmission of the ACK signal indicating normal reception. Furthermore, since the retransmission request transmitted from the reception side to the transmission side is transmitted using a modulation scheme with high radio tolerance, the transmission side can easily recognize that the NAK signal is transmitted to the own station. A method of receiving wireless packetized data can be realized.
2) A wireless packet data transmission system in which a first period immediately after the end of transmission of a packetized signal is a transmission period of a NAK signal, and when transmission of the NAK signal is not detected, another terminal transmits the signal. The NAK signal is transmitted by a radio-resistant digital modulation method, and therefore a wireless packetized data transmission system capable of easily recognizing that the NAK signal is transmitted to the own station is provided on the transmission side. realizable.

Hereinafter, preferred embodiments of the OFDM signal modulation apparatus and OFDM signal modulation method according to the present invention will be described.
FIG. 1 shows a schematic configuration of the wireless packet data transmission system, which will be described with reference to the drawings.

  The wireless packet data transmission system shown in FIG. 1 includes an access point (hereinafter abbreviated as AP or sometimes referred to as a parent device) 1 and terminals A2a, B2b, and C2c. The terminals A2a to C2c and AP1 are connected to each other via a wireless network. The terminals A2a and B2b perform wireless communication while being controlled by the AP1, and transmit desired packetized digital data from the terminal A2a via the wireless network, and the terminal B2b receives it.

  Here, the information transmitted from the terminal A2a is data continuously transmitted, such as a digital video signal, and the continuous data is divided into predetermined sizes, and an error correction code is added to the divided data. Sent as packetized data.

  The transmitted packetized data is received by the terminal B2b, and an error detection calculation is performed on the received packetized data. When the received data includes error data, the error signal is corrected using the attached error correction code. When the received packetized data does not include an error signal and when correction processing is performed, the terminal B2b does not particularly transmit the ACK signal that the packetized data is normally received.

  After transmitting packetized data, terminal A2a recognizes that normal reception has been made, particularly when no ACK signal is returned from terminal B2b, and transmits the next packetized data during the next data transmission period. The divided packetized data are transmitted one after another.

  When the terminal B2b receives packetized data including an error that cannot be corrected, a NAK (Negative Ack) signal designating the transmitting terminal A2a as the receiving terminal is returned, and a retransmission of the packet signal that cannot be normally received is requested. The NAK signal is modulated and transmitted by a modulation method having a strong radio tolerance compared to the digital modulation performed on the packetized data transmitted by the terminal A2a.

  When the digital modulation scheme performed by the terminal A2a is, for example, 16QAM (16-quadrature amplitude modulation), the digital modulation of the terminal B2b is QPSK (quadrature phase shift keying) or BPSK (bi-phase shift keying) for the following reason. Modulated and transmitted.

  That is, the period during which the terminal B2b is permitted to transmit the NAK signal is from the time when SIFS (Short Inter Frame Space) that is, for example, 16 μs has elapsed since the end of transmission of the terminal A2a. It is necessary to start transmission by the time point (Point Inter Frame Space) has elapsed. Terminal B2b starts transmitting a NAK signal after SIFS has elapsed. Terminal A2a starts receiving the NAK signal and does not transmit packetized data during that period.

  On the other hand, consider a case where the terminal C2c tries to transmit some request signal (REQ) to the AP1. In this case, the transmission time of the request signal is permitted from the time when RRIFS (Recovery / Request Inter Frame Space) of 24 μs, for example, has elapsed after the transmission of the other terminal is completed.

  Here, when the terminal B2b is in a hidden terminal state with respect to the terminal C2c, that is, when the terminal C2c cannot receive the NAK signal transmitted from the terminal B2b, the terminal C2c cannot detect the carrier signal after the terminal A2a transmission ends. Then, the transmission of the request signal waiting for transmission is started from the time when the RRIFS period has elapsed after the end of transmission of the terminal A2a.

The terminal A2a receives both the NAK signal transmitted from the terminal B2b and the request signal transmitted from the terminal C2c at the same time.
Of the two signals received, the NAK signal with the earlier transmission start time is a signal that should be preferentially received. Since the NAK signal is transmitted as a radio-resistant signal, the transmitting terminal A2a filters the received signal and attenuates the distortion component of the demodulated signal, thereby easily decoding the NAK signal.

  If the NAK signal is decoded here, the data retransmission between the terminal A2a and the terminal B2b and the subsequent communication are normally performed. Then, the request signal from the terminal C2c is transmitted again at a time when the terminal C2c is granted a normal transmission permission.

  As described above, since the terminal B2b that receives the packetized data does not send back an ACK signal particularly during normal reception, it is possible to save time related to the transmission of the ACK signal.

  Furthermore, since the terminal B2b transmits the NAK signal only when data reception fails, the terminal B2b can be retransmitted with error data and the terminal B2b becomes a hidden terminal. Even if there is a signal to be transmitted because other terminals do not sense the carrier, the signal transmitted by the terminal B2b is highly likely to be decoded and communication may be continued. high.

  Even if the terminal B2b does not become a hidden terminal, the code indicating the transmission destination is transmitted by a transmission method with high radio tolerance, so that the terminal that receives the signal is transmitted to its own station. Whether the received signal is a transmitted signal or a signal transmitted to another station. By this, when the signal transmitted to the local station is surely received, the local station transmits a CTS (Clear To Send) command, for example, thereby suppressing the transmission of the signal transmitted due to the hidden terminal problem. can do. As a result, it is possible to realize a wireless packet transmission system in which the transmission frequency is low and an important NAK signal is reliably received.

The overview of the wireless packet transmission system using the NAK method has been described above.
Next, the configuration and operation of each transmitting apparatus and receiving apparatus included in each terminal apparatus that performs these operations will be described.
FIG. 2 shows a schematic configuration of a transmission apparatus that generates an OFDM (Orthogonal Frequency Division Multiplexing) signal, and the operation will be described with reference to the drawings.

  The OFDM signal transmission apparatus shown in the figure includes an error correction signal adding unit 32, a mapping unit 33, an inverse Fourier transform unit 34, a guard interval adding unit 35, a high frequency signal processing unit 36, a transmission control unit 38, and transmission destination information / NAK. The information generating unit 39 is configured.

  First, the information signal supplied to the error correction signal adding unit 32 is a signal that is continuously transmitted like a digital video signal, for example. The error correction signal adding unit 32 adds a correction code for correcting error data generated during transmission. Next, the digital data to be transmitted by the mapping circuit 33 is mapped onto a plurality of QAM (Quadrature Amplitude Modulation) planes.

  The respective data mapped to the plurality of QAM planes are subjected to inverse Fourier transform by an inverse Fourier transform unit 34, and a plurality of orthogonal frequency division modulated signals modulated as signals of the respective QAM planes are generated. A guard interval for reducing multipath distortion is added to the orthogonal frequency division signals by the guard interval adding unit 35.

  The orthogonal frequency division signal to which the guard interval is added is subjected to predetermined signal processing for radiating to the spatial transmission path by the high-frequency signal processing unit 36, and is transmitted to the wireless network via the antenna circuit in a time zone during which transmission is permitted. Is output.

  In addition to the information signal, the signal transmitted from the transmitter includes error data in the information signal received by the receiver described later, and if the error data is not corrected, the transmitted information signal is normal. NAK information indicating that it has not been received is generated, the transmitting terminal is designated as the receiving destination, and the information is returned.

  The NAK information and a signal indicating the transmission destination of the information signal are generated by the transmission destination information / NAK information generation unit 39 and supplied to the mapping 33. Here, the QAM plane mapped by the mapping unit is, for example, a quaternary QAM mapping plane having a small degree or a BPFS plane.

  The mapped signal is subjected to inverse Fourier transform by an inverse Fourier transform unit 34, a guard interval is added by a guard interval adding unit 35, and transmitted via a high frequency signal processing unit 36. The transmission timing is the time designated by SIFS as the timing for transmitting the NAK information.

FIG. 3 shows a schematic configuration of a receiving apparatus that receives an OFDM (Orthogonal Frequency Division Multiplexing) signal, and its operation will be described with reference to the drawings.
The OFDM signal receiver shown in the figure includes a high-frequency signal processing unit 41, a carrier sense unit 42, a guard interval removal unit 44, a Fourier transform unit 45, a demapping unit 46, an error signal correction processing unit 47, and transmission destination information / NAK. An information acquisition unit 49 is included.

  First, a signal on the wireless network, which is a spatial transmission path acquired by the antenna circuit, is amplified by the high frequency signal processing unit 41. A part of the amplified signal is supplied to the carrier sense unit 42 and the other part is supplied to the guard interval removing unit 44.

The carrier sense unit 42 detects whether or not a carrier signal exists on the wireless network, and the detected result is supplied to the transmission control unit 38.
In the guard interval removing unit 44, the guard interval adding unit 35 removes the signal of the added guard interval unit.

  Next, the orthogonal frequency division multiplexed signal from which the guard interval portion is removed by the Fourier transform unit 45 is Fourier transformed, and as a result, signal point information on the QAM plane is obtained. The demapping unit 46 performs an operation complementary to that performed by the mapping unit 33 to obtain the transmitted digital information.

When the transmitted information signal includes error data, the error signal correction processing unit 47 corrects the error data and outputs the obtained digital information signal.
On the other hand, transmission destination information / NAK information transmitted from other transmission terminals is subjected to predetermined signal processing by the high-frequency signal processing unit 41, the guard interval removal unit 44, and the Fourier transform unit 45, and is supplied to the demapping unit 46. Is done. In this case, for example, a quaternary QAM mapping plane or a BPFS plane having a small order is used to acquire transmission destination information and NAK information.

  The acquired NAK information is transmitted to the OFDM signal transmitting apparatus, and the packetized information signal that has failed to be received is transmitted again. When the retransmitted information signal is normally received, the receiving terminal does not return an ACK signal, but returns a NAK signal only when reception of the packetized information signal fails.

  The configuration of the OFDM signal transmitting apparatus and the OFDM signal receiving apparatus and their operations have been outlined above.

Next, a configuration example is shown for the transmission procedure and the reception procedure used in the wireless packet transmission system, and the operation will be described in detail.
FIG. 4 shows the configuration of the OFDM signal transmission apparatus, which will be described with reference to the drawings.

  The OFDM signal transmission apparatus shown in the figure includes a MAC frame creation unit 31a, a reference signal unit 31b, a transmission destination information extraction unit 31c, a PHY (Physical) header unit 31d, an FEC (Forward Error Correction) interleaving unit 32, and a mapping unit 33. , IFFT (Inverse fast Fourier transform) 34, guard interval (GI) adding unit 35a, preamble adding unit 35b, and high frequency amplification processing unit 36. The mapping unit 33 includes a MAC frame modulation unit 33a, a reference modulation unit 33b, and a PHY header / destination information modulation unit 33c.

  First, the input information signal is generated as a MAC frame signal together with the MAC header by the MAC frame creation unit 31a, and after the error correction code is added by the FEC interleaving unit 32, the MAC frame modulation of the mapping unit 33 is performed. Mapping to the QAM plane is performed by the unit 33a.

  In addition, the transmission destination information extraction unit 31c extracts a region describing the transmission destination from the input MAC header, and supplies it to the PHY header / destination information modulation unit 33c together with the PHY header generated by the PHY header unit 31d. In this case, mapping to the QAM plane is performed for modulation using a modulation scheme with strong radio tolerance.

  The reference modulation unit 33b of the mapping unit 33 performs mapping of the reference signal for performing the synchronization operation of the receiving device supplied from the reference signal unit 31b. The mapping point is for a predetermined signal point defined on the QAM plane.

  The above-mentioned signal subjected to QAM mapping is supplied to the inverse Fourier transform unit 34, where it is generated as, for example, 52 subcarrier signals constituting the OFDM signal. A guard interval signal for reducing multipath distortion is added to the generated signal by the guard interval adding unit 35a. Next, a preamble signal is added by the preamble adding unit 35b, and signal processing such as high frequency signal amplification is performed by the high frequency amplification processing unit 36, which is supplied to an antenna (not shown) and transmitted to the wireless network.

FIG. 5 shows and describes the format of a data frame of an OFDM signal transmitted to the wireless network.
The first part of the signal to be transmitted is a preamble, a PHY header, and a destination, and this part is mapped by the PHY header / destination information modulator 33c. The signal generated by mapping is the first part of the OFDM signal that is digitally modulated by a radio-resistant modulation scheme.

  Next, a MAC header to which description areas such as frame control, duration ID, address 1, address 2, address 3, and sequence control are assigned is transmitted, followed by a payload for transmitting an information signal, and transmitted. An FCS (Frame Check Sequence) for detecting an error in the received signal is transmitted. The MAC header, payload, and FCS are signals used in IEEE 802.11, which is a wireless LAN standard, for example.

  Then, MAC frames such as the MAC header, payload, and FCS are signals that are mapped and modulated by the MAC frame modulation unit 33a, and are so-called normal radio resistance modulation signals.

  Accordingly, a signal based on the MAC frame is transmitted after the information signal is modulated at, for example, 64QAM at a normal transmission rate. The signal part transmitted first has a transmission capacity lower than that of the MAC frame, and is transmitted using a scheme that is strong in radio tolerance, such as QPSK or BPSK.

  As described above, in the data frame described above, the area describing the transmission destination is provided independently of the MAC header and is arranged behind the PHY header. At that time, as with the PHY header, transmission is performed using a modulation scheme with strong radio tolerance, so that even if the transmission path condition is bad, the destination information should be received by the receiver with a higher probability than the conventional scheme. It is aimed.

Next, a receiving apparatus that receives a signal transmitted from the transmitting apparatus according to the first embodiment will be described.
FIG. 6 shows the configuration of the OFDM signal receiving apparatus, and its operation will be described with reference to the drawings.

  The OFDM signal receiving apparatus shown in the figure includes a high-frequency signal processing unit 41, a preamble detection synchronization processing unit 43a, a guard interval removal unit 44, a Fourier transform unit 45, a reference signal demodulation 43b, a demapping unit 46, and an error signal correction processing unit 47. , An uncorrectable signal detector 47a, a PHY header / destination information demodulator 48a, a destination information confirmation unit 48b, and a NAK signal generator 49a.

  First, a signal radiated into the space is obtained by an antenna circuit (not shown), and the obtained OFDM signal including, for example, 52 subcarriers is amplified by the high frequency signal processing unit 41. Next, the preamble portion of the data frame is detected by the preamble detection synchronization processing unit 43a. A synchronization signal for demodulating the OFDM signal is generated.

  Based on the generated synchronization signal, the guard interval removal unit 44 removes the signal of the guard interval unit attached by the transmission device. The signal from which the guard interval portion has been removed is input to the Fourier transform unit 45, and the position of the signal point on the QAM plane related to each subcarrier signal is detected.

  The reference signal demodulator 43b demodulates the reference signal level for demapping based on the signal point information of the subcarrier assigned as the reference signal. The demapping unit 46 performs demapping of each subcure area based on the reference signal level, and the obtained digital data is supplied to the correction processing unit 47.

  An information signal in which an error is detected and corrected using FCS is output as an information signal output, and an uncorrectable error signal is detected as uncorrectable by the uncorrectable signal detector 47a and supplied to the NAK signal generator 49a. Is done.

  The NAK signal generation unit 49a demodulates the transmission destination information transmitted by the PHY header / destination information demodulation unit 48a using a modulation scheme with strong radio tolerance, and the transmission destination information confirmed by the transmission destination information confirmation unit 48b. Supplied. Then, the fact that an uncorrectable MAC frame has been received is transmitted to the transmitting terminal that transmitted the MAC frame, and a request is made to retransmit the data including the error.

  By inserting the destination address obtained by demodulation into the NAK signal requesting retransmission, the terminal device that transmitted the information signal can recognize that the data sent by itself has not been received, and can be sure. Can respond to re-transmission.

FIG. 7 shows a frame configuration of only the MAC part of the NAK signal.
In the figure, areas of frame control, duration ID, transmission destination address, and error correction code (FCS) are allocated from the top. In addition, when transmitting data, not only the transmission destination but also the transmission source is transmitted by a modulation scheme with strong radio tolerance.

  In that case, the terminal that should receive the NAK signal can be specified by inserting the received source address to form the NAK signal. Here, the transmission destination is a transmission destination address that is first transmitted together with data.

  The frame data transmission method has been described above in which the data frame is transmitted and the data frame is retransmitted when the received data includes uncorrectable error data by transmitting the NAK signal designating the transmission destination. Here, the NAK signal is a signal for requesting retransmission only when there is an error in the received information signal, and when there is no signal error, no NAK signal is returned.

  In other words, during normal use with good transmission path conditions, the ACK signal indicating that the signal has been normally received is not transmitted, so that the band utilization efficiency is improved including the SIFS period set for that purpose, Throughput on data transmission is improved.

  Then, when the transmitted data is transmitted in a state where the transmission path is bad and the error correction is impossible, the NAK signal clearly specifying the transmission source of the local station by the modulation scheme having strong radio tolerance is received from the terminal receiving the data. Since the sending terminal receives and recognizes that at least the data frame has been sent to itself, the sending terminal can reliably respond to the retransmission request.

  In particular, when the ACK signal is not always returned and the NAK signal is returned only at the time of abnormality, it is necessary to reliably receive the returned NAK signal and respond to the retransmission. Even if the receiving terminal that returned the NAK signal becomes a hidden terminal with respect to the third terminal, it is determined that the line is not busy, and thus the third signal is transmitted. There is a high probability that a NAK signal by a modulation scheme with strong radio tolerance is decoded at the transmitting terminal. Therefore, it is possible to avoid a situation where the receiving terminal cannot perform normal reception without retransmitting the entire data frame.

The configurations of the OFDM signal transmitting apparatus and the OFDM signal receiving apparatus according to the first modification of the embodiment will be described below and their operations will be described. The same functional parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
FIG. 8 shows a configuration of an OFDM signal transmission apparatus according to the first modification.

  In this figure, compared to the configuration shown in FIG. 4 described above, an ID counter 31d is arranged, a frame generation 31e is arranged instead of the MAC frame creation unit 31a, and a PHY header / destination The difference is that a PHY header / destination information / unique ID modulator 33d is provided instead of the information modulator 33c. An error correction signal addition unit 32a is used instead of the error correction signal addition unit 32, and the signal flow is different.

FIG. 9 shows the structure of a data frame according to the first modification.
Compared to FIG. 5 described above, the MAC header, payload, and FCS differ in that segment-structured data having a smaller data amount than the MAC frame is divided into a plurality of segments.

  The MAC frame is divided into segment configuration data and transmitted, and the head portion of the segment data has a data configuration in which transmission destination information transmitted by a modulation scheme with high radio tolerance is attached. Each segment is assigned a unique ID so that it can be identified.

  Then, the unique ID is modulated by a method with strong wireless tolerance. The data transmitted next to the transmission destination is composed of a set of an ID modulated by a method with strong radio tolerance and data composed of a segment modulated by normal radio tolerance. There are multiple data.

  FIG. 10 shows a configuration of an OFDM signal receiving apparatus according to the first modification. The OFDM signal receiving apparatus shown in the figure is different from the OFDM signal receiving apparatus shown in FIG. 6 in that the transmission destination information confirmation unit 48b is a transmission destination / unique ID confirmation unit 48c.

  Accordingly, the OFDM signal receiving apparatus shown in FIG. 6 requests retransmission of the entire MAC frame including the error portion even if there is an error in a part of the received data. The OFDM signal receiving apparatus in the first modification adds only a unique ID including an error to the NAK signal and returns it to the transmitting apparatus. It is requested to retransmit only the segments that could not be corrected.

FIG. 11 shows a frame configuration of the NAK signal according to the first modification.
Compared to the frame configuration shown in FIG. 7 described above, the unique ID 1, unique ID 2,... Are inserted. The number of unique IDs inserted is the same as the number of segments including error data.

  FIG. 12 shows the state of data that is actually transmitted. Suppose that when a data frame divided into four segments is sent from the transmitter, the second and fourth segments of which cannot be corrected and reception fails. The receiver returns a destination address and unique IDs of the second and fourth segments by a NAK signal.

  Here, if data is transmitted not only at the transmission destination but also at the transmission source by a modulation scheme with strong radio tolerance, the retransmitted data is received by forming the NAK signal by inserting the address. You can specify the terminal that should be sent. Here, the transmission destination indicates the transmission destination address sent together with the data.

  In the above example, NAK information is transmitted immediately after transmission is completed. On the other hand, when data to be transmitted is arranged with a long interleave length and error correction processing is performed, error correction may be performed by rearranging MAC frame data transmitted multiple times. In the case of performing error correction by performing computation while returning the interleave, it is detected that there is an uncorrectable error at the time delayed according to the interleave length.

  That is, in the case of performing error correction processing by interleaving processing for a long time, a segment including an uncorrectable data error is detected after all error correction processing is performed, and retransmission of the detected segment portion is requested. . In this case, it is difficult to specify the destination partner because the transmission is performed after a predetermined time has elapsed, unlike when the data retransmission is requested immediately after the transmission is completed.

  In particular, when the state of the transmission path is poor, it is difficult to determine whether the transmitting terminal that has received the retransmission request is its own station or another station. At this time, by adding the transmission destination address demodulated by the receiving terminal and the unique ID of the segment that cannot be corrected to the NAK signal, the transmission source that has transmitted the data in the past is the data transmitted by itself. It can recognize things and respond to retransmissions.

The characteristic points of the configuration and the operation in the first modification have been described above. Other operations are the same as the configuration and operation of the above-described embodiment.
Next, characteristic points of the configuration and operation according to the second modification will be described.

  FIG. 13 shows a configuration of an OFDM transmission apparatus according to the second modification. Compared with the first modification, this apparatus is not provided with an ID counter 31d, and instead of a PHY header / destination information / unique ID modulation unit 33d, a PHY header / destination information modulation unit 33c is arranged. Is different.

FIG. 14 shows the structure of a data frame according to the second modification.
Compared to the data frame according to the first modified example shown in FIG. 9 described above, there is a difference in that there is no ID transmitted by a modulation scheme with strong radio tolerance.

  FIG. 15 shows a configuration of an OFDM signal receiving apparatus according to the second modification. Compared with the OFDM signal receiving apparatus according to the first modification shown in FIG. 10 described above, a transmission destination information confirmation unit 48b is provided instead of the transmission destination / unique ID confirmation unit 48c, and a counter 47b and a memory 47c is newly arranged.

  Here, the counter 47b counts the number of segments transmitted subsequent to the transmission destination transmitted as a radio-resistant modulation scheme, and when the received segment data error correction is disabled, the count number is stored in the memory. 47c is stored. Accordingly, the number of segments to be requested for retransmission is stored in the memory.

FIG. 16 shows a frame configuration of the NAK signal according to the second modification.
Compared to transmitting the unique ID that needs to be retransmitted in the frame configuration of the NAK signal shown in FIG. 11, the information related to the error segment number is transmitted in the frame configuration of the NAK signal according to the second modification.

  The difference between the configurations and operations of the OFDM signal transmitting apparatus and the OFDM signal receiving apparatus according to the second modification has been described above. Other operations are the same as those shown in the embodiment and the first modification.

The technical contents shown in the above-described embodiments and the first and second modifications can be summarized as the following items 1) to 12).
1) In a wireless communication system that transmits packets to each other,
In the packet to be transmitted, an area to which a transmission destination is assigned and an area to which information is assigned are prepared, and each of them is modulated by a different wireless method. A wireless terminal device that transmits using a modulation method with strong wireless tolerance.
2) In a packet to be transmitted, an area to which a transmission destination is assigned and an area to which information and an error detection code for the information are assigned are prepared, and each is modulated by a different wireless system. In a wireless communication system that performs packet transmission with each other, including a wireless terminal device that transmits a region using a modulation method that is the same as or stronger than the information unit,
Demodulate the area to which the destination is assigned, transmitted using a more robust modulation method, and continue to demodulate the area to which the information is assigned if the destination is addressed to you. A wireless terminal device that performs error detection using the error detection code and generates and transmits an ACK packet notifying reception failure when an error is detected.
3) In the wireless communication system according to the above item 2), including a wireless terminal device that generates and transmits an ACK packet notifying that an error has been detected, and performing packet transmission with each other.
A wireless terminal device that receives an ACK packet, generates a packet assigned information to be transmitted again, and transmits the packet.
4) A wireless communication system configured using the above items 1) to 3).
5) In a wireless communication system that performs packet transmission between each other,
In a packet to be transmitted, an area to which a transmission destination is assigned and an area to which information is assigned are prepared, and each of them is modulated by a different wireless method. Transmitting using a robust modulation scheme,
Furthermore, the information part is divided into a plurality of segments, and a segment-specific ID and an error detection code are assigned to each segment, and the ID part is the same as the information part or using a modulation method having a higher wireless tolerance. A wireless terminal device for transmission.
6) In a packet to be transmitted, an area to which a transmission destination is assigned and an area to which information is assigned are prepared, and each of them is modulated by a different wireless method. It is to be transmitted using a modulation method with stronger radio tolerance, and the information part is further divided into a plurality of segments, and an ID unique to the segment and an error detection code are assigned to each segment, and the ID part is In a wireless communication system that includes a wireless terminal device that transmits using a modulation method that is the same as or stronger than the information unit, and performs packet transmission with each other,
Demodulate the area to which the destination is assigned, transmitted using a more robust modulation method, and continue to demodulate each segment area in the area to which the information is assigned if the destination is addressed to you. At that time, each segment unique ID transmitted using a more robust modulation method is demodulated, and an error is detected and an error is detected using an error detection code incorporated in each segment. In this case, a wireless terminal device that holds an ID specific to the segment, generates an ACK packet to which all the IDs specific to the segments that have failed to be received are generated, and transmits the ACK packet.
7) In a wireless communication system configured to include a wireless terminal device that generates and transmits an ACK packet to which all of the segment-specific IDs in which errors have been detected are allocated, as described in 6) above, and performs packet transmission with each other,
A wireless terminal device that receives and demodulates an ACK packet, generates only a piece of information corresponding to a segment-specific ID indicated in the packet, and transmits the packet.
8) A wireless communication system configured by the above items 5) to 7) 9)
In a packet to be transmitted, an area to which a transmission destination is assigned and an area to which information is assigned are prepared, and each of them is modulated by a different wireless method. Transmitting using a robust modulation scheme,
Furthermore, the information part is divided into a plurality of segments, and a wireless terminal device that assigns and transmits an error detection code for each segment.
10) In a packet to be transmitted, an area to which a transmission destination is assigned and an area to which information is assigned are prepared, and each of them is modulated by a different wireless method. The transmission is performed using a modulation scheme with higher radio tolerance, and the information section is further divided into a plurality of segments, and includes a radio terminal device that allocates and transmits an error detection code for each segment. In a wireless communication system that performs packet transmission between each other,
Demodulate the area to which the destination is assigned, transmitted using a more robust modulation method, and continue to demodulate each segment area in the area to which the information is assigned if the destination is addressed to you. At that time, a counter and a memory are provided, and each segment is demodulated, and an error is detected using an error detection code incorporated in the segment. Is a wireless terminal device that generates and transmits an ACK packet to which all the positional information corresponding to the segment that has failed to be received is stored.
11) In the wireless communication system that performs packet transmission between each other, including a wireless terminal device that generates and transmits an ACK packet in which all the position information of the segment in which the error is detected is allocated, described in 10) above,
A wireless terminal device that receives and demodulates an ACK packet, generates only a packet by connecting only information corresponding to position information of a segment indicated in the packet, and transmits the packet.
12) A wireless communication system configured by using the wireless terminal device described in 9) to 11) above.

  The present invention can be used to realize a wireless packet data transmission system applicable to a wireless LAN that connects a plurality of terminal devices to the Internet.

1 Access point 2a Terminal A
2b Terminal B
2c Terminal C
31a MAC frame creation unit 31b Reference signal unit 31c Destination information extraction unit 31d PHY header unit 32 Error correction signal addition unit 32a FEC interleaving unit 33 Mapping unit 33a MAC frame modulation unit 33b Reference modulation unit 33c PHY header / destination Information modulation unit 33d PHY header / destination information / unique ID modulation unit 34 Inverse Fourier transform unit 35, 35a Guard interval addition unit 35b Preamble addition unit 36 High frequency amplification processing unit 37 Transmission order table unit 38 Transmission control unit 39 Destination information / NAK information generation unit 41 High frequency signal processing unit 43a Preamble detection synchronization processing unit 43b Reference signal demodulation 44 Guard interval removal unit 45 Fourier transform unit 46 Demapping unit 47 Error signal correction processing unit 47a Uncorrectable signal Out section 47b counter 47c memory 48a PHY header destination information demodulation section 48b destination information confirmation unit 48c destination-specific ID confirmation unit 49 transmits destination information, NAK information acquisition unit 49a NAK signal generator

Claims (2)

A frame divided into a plurality of segments each provided with a MAC header, a payload storing digital data to be transmitted, and a frame check sequence for detecting an error in the digital data is digitally modulated. , A unique ID for identifying each segment is provided at the head of each of the plurality of segments, and at least a PHY (Physical) header and transmission destination information are provided at the head of the frame, and the unique ID and PHY ( OFDM signal demodulating device for receiving and demodulating an OFDM signal having a structure in which a physical header and transmission destination information are digitally modulated by a modulation scheme having higher radio tolerance than the digital modulation scheme of the frame. Because
Frame demodulation means for digitally demodulating the frame included in the OFDM signal to restore the digital data;
Error correction means for performing error correction processing for each segment using the frame check sequence included in the OFDM signal;
An error correction impossible signal detection means for performing an error correction process for each segment using the frame check sequence in the error correction means, and detecting an error correction impossible signal indicating a segment in which the error correction process is impossible;
The unique ID included in the OFDM signal, a PHY (Physical) header, destination information and PHY header / destination information demodulating means for digital demodulation;
A destination / unique ID confirmation unit for confirming the unique ID digitally demodulated by the PHY header / destination information demodulation unit and the destination information;
NAK signal generation for acquiring the unique ID of the segment in which the error correction impossible signal is detected and error correction processing is impossible from the transmission destination / unique ID confirmation means, setting it as a NAK signal, and transmitting to the OFDM signal modulator Means,
An OFDM signal modulation device. A frame divided into a plurality of segments each provided with a MAC header, a payload storing digital data to be transmitted, and a frame check sequence for detecting an error in the digital data is digitally modulated. , A unique ID for identifying each segment is provided at the head of each of the plurality of segments, and at least a PHY (Physical) header and transmission destination information are provided at the head of the frame, and the unique ID and PHY ( OFDM signal demodulating method for receiving and demodulating an OFDM signal having a structure in which a (Physical) header and destination information are digitally modulated by a modulation scheme having higher radio tolerance than the digital modulation scheme of the frame Because
Digitally demodulating the frame contained in the OFDM signal to restore the digital data;
Performing error correction processing for each segment using the frame check sequence included in the OFDM signal;
Performing an error correction process for each of the segments using the frame check sequence, and detecting an error correction impossible signal indicating a segment for which the error correction process was impossible;
Digitally demodulating the unique ID included in the OFDM signal, a PHY (Physical) header, destination information,
Confirming the digitally demodulated unique ID and destination information;
Setting the unique ID of the segment in which the error correction impossible signal is detected and error correction processing is impossible to the NAK signal, and transmitting to the OFDM signal modulation device;
An OFDM signal modulation method comprising: