JPH06232871A - Radio communication system - Google Patents

Abstract

PURPOSE:To provide a radio communication system for properly transmitting a target bit sequence even at the time of retransmission even when a partial carrier frequency disables communication by the influence of frequency selection fading or the like. CONSTITUTION:A transmission source radio terminal receiving a retransmission request packet from a destination radio terminal generates a retransmission packet by judging the bit sequence to be retransmitted from retransmission request carrier information in the same packet and sends it to a reception radio terminal by using the communication enable carrier frequency judged from normal reception carrier information. At such a time, when there is one bit sequence to be retransmitted, the transmission source radio terminal parallelly sends the retransmission packets by using all the communication enable carrier frequencies. When there are two bit sequence to be retransmitted and there is one communication enable carrier frequency, these bit sequences are sent while being divided twice by using one communication enable carrier frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system for high-speed data transmission represented by a local area network.

[0002]

2. Description of the Related Art A coaxial cable is used in an information transmission system such as a campus.
LAN (Local Area Network)
Is often used. Such a wired LAN
However, since it takes time and cost to re-install when a layout change or the like occurs from the initial installation state, a wireless LAN is strongly required. Especially in Japan, IEEE8 is widely used as a wired LAN.
02.3 standard 10 Mbps CSMA / CD (Carrie
r Sense Multiple Access with Collision Detection)
A method for ensuring compatibility with the method is being studied.

One of the points for realizing this wireless LAN is to realize efficient high-speed data communication on a wireless transmission line affected by frequency selective fading. In the presence of frequency selective fading, for example, even at a frequency at which high-speed data communication can be normally performed up to now, the received signal level is extremely lowered due to a subtle change in the reflection condition of the surroundings such as movement of a person. In many cases, communication is suddenly disabled, and throughput is greatly reduced. To overcome such problems, Japanese Patent Application No. 3-21
1886, Japanese Patent Application No. 3-211887, Japanese Patent Application 3-2
No. 92588, a "multi-carrier transmission system" in which a redundant bit for error correction is added to data to be transmitted, and then part or all of the transmission data is divided and sent to a plurality of carriers having different frequencies. Is proposed. In this system, even if the data of some carriers on the receiving side become incommunicable due to the frequency selective fading described above, or if a large number of errors occur, other carriers that are normally received and demodulated It is possible to recover all the transmission data from the data of the above by error correction.

However, since wireless communication in a room is strongly affected by fixed obstacles such as walls and moving obstacles such as people, when the transmission quality temporarily becomes extremely poor due to frequency selective fading. There is also. Therefore, a sufficient transmission quality cannot be obtained only by combining the above-mentioned multicarrier transmission method and error correction.

A retransmission method is one of the methods for improving the transmission quality. However, if the data is not correctly received, even if the data is retransmitted immediately, the influence of frequency selective fading and the like still remains, and it is likely that the error cannot be completely corrected in the same manner.

[0006]

As described above, the retransmission method is one of the methods for improving the transmission quality. However, if the data is not correctly received, even if the data is retransmitted immediately, the influence of frequency selective fading and the like still remains, and it is likely that the error cannot be completely corrected in the same manner.

The present invention has been made to solve such a problem, and even in a situation where some carrier frequencies are incommunicable due to the influence of frequency selective fading or the like, a target bit string is retransmitted. It is an object of the present invention to provide a wireless communication system capable of correctly transmitting the data.

[0008]

In order to achieve the above-mentioned object, a wireless communication system of the present invention divides at least a part of a data sequence forming a packet into a plurality of bit strings, and each bit string is different. Using carrier frequency,
In a wireless communication system in which wireless transmission is performed between a plurality of wireless terminals, each wireless terminal can check whether or not each bit string of the received packet addressed to itself can be correctly received, and the wireless terminal can correctly receive each bit string by the checking means. If a bit string that did not exist is determined and the number of the bit string satisfies the preset condition, a resend request for at least a part of the bit string is transmitted using the carrier frequency that can correctly receive the bit string. Retransmission request means to send to the original wireless terminal and, when a retransmission request is received, resend to resend the requested bit string to the retransmission request source wireless terminal using the carrier frequency that could correctly transmit the bit string And means.

[0009]

That is, in the present invention, the wireless terminal of the transmission source is
When the destination wireless terminal requests to retransmit the bit string,
Even if some carrier frequencies cannot be communicated due to frequency selective fading, etc., because the bit string requested to be retransmitted is retransmitted using the carrier frequency that was able to correctly transmit the bit string in the immediately preceding packet transmission. The target bit string can be correctly transmitted at the time of retransmission.

Furthermore, if the individual bit strings for which retransmission is requested are simultaneously transmitted using a plurality of carrier frequencies, the carrier frequency at which the state of the transmission line changes due to the movement of an obstacle such as a person and communication becomes impossible is a current event. Even in a situation where it changes moment by moment, it becomes possible to correctly retransmit the target bit string.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a wireless terminal in a wireless terminal system according to an embodiment of the present invention.

As shown in the figure, this wireless terminal has an interface unit (I / F) 1, a serial / parallel conversion unit (S / P) 2, a control packet transmission unit 3, an encoding unit 4, and a transmission unit. Carrier exchange section 5, random pulse transmission section 6, modulators (MOD) 7a, 7b, 7c, 7d, RF section 8, antenna 9, demodulators (DEM) 10a, 10b, 10c, 1
0d, collision detection unit 11, reception carrier replacement unit 12, decoding unit 13, parallel / serial conversion unit (P / S) 1
4, control packet receiving unit 15, interface unit (I /
F) 16 and a control unit 17 and the like.

The interface units 1 and 16 are provided for interfacing with external devices such as personal computers and workstations. For example, level conversion, timing adjustment, clock reproduction, clock. Has functions such as synchronization.

The serial / parallel conversion unit 2 divides the transmission data input from the external device via the interface unit 1 into a plurality of bit strings and performs speed conversion according to the encoding processing speed.

According to the instruction from the control unit 17, the control packet sending unit 3 assembles a control packet such as a resend request packet for requesting resending of a bit string that could not be correctly received and sends it to the serial / parallel conversion unit 2.

The encoding unit 4 includes a C1 encoder (outer encoder) and a C1 encoder.
2 encoders (inner encoders). The C1 encoder encodes each vertical block including at least one bit of a plurality of bit strings input from the serial / parallel conversion unit 2 to generate a new bit string for parity check. In this example, the C1 code is (4, 3, 2)
A parity check code is used. Specifically, as shown in FIG. 2, this C1 encoder has two exclusive OR circuits 2
1 and 22 are used. That is, in this C1 encoder, a parity check bit is calculated from each 1 bit of the three bit strings input from the serial / parallel conversion unit 2, and the result is output as the fourth bit string.

The C2 encoder calculates a check bit for error correction for each block of each bit string input from the C1 encoder, adds the check bit to the original bit string, and outputs it.

The C1 code shown in FIG.
2) The parity detection code is a C2 code (21, 1).
5, 4) An example of the packet structure when the extended Hamming code is applied is shown. Here, the address / user information i (i =
0, 1, 2) is, for example, a destination address, a self-address, a packet length, among the data series forming the packet,
User information, CRC (Cyclic Redundancy Code), and the like are divided into three bit strings of carriers 0 to 2, and the bit string is divided into 15 bits for each carrier to form a block. The parity check bit is an array of the parity check bits of the nth bit (n = 1 to 15) of each address / user information i (i = 0, 1, 2). The check bit i (i = 0, 1, 2) is a check bit for expanded Hamming code error correction of the address / user information i obtained by the C2 encoder. The check bit 3 is a check bit for expanding Hamming code error correction of the parity check bit, which is also obtained by the C2 encoder.

The transmission carrier replacement unit 5 holds the four bit strings received from the encoding unit 4, replaces the bit strings in accordance with the instruction from the control unit 17, and places an SFD (Start Frame Delimiter) at the beginning of each bit string. ) And packet identification information are added to the four modulators 7
a to 7d. Here, the SFD is a unique word for the receiving wireless terminal to perform packet synchronization, and a 16-bit pattern is determined for each system. The packet identification information includes information indicating the type of the relevant packet (normal packet / retransmission request packet / retransmission packet, etc.) instructed by the control unit 17 and carrier replacement information. The bit strings are replaced by, for example, in the case of a normal packet, the bit strings 0 to 3 are replaced with the carrier 0
To modulators 7a to 7d for 3 to 3. The four bit strings for one packet held in the sending carrier exchanging unit 5 are held until the bit string of the next packet starts to be input from the encoding unit 4, and when there is a retransmission request, an instruction from the control unit 17 is given. Send multiple times according to.

The random pulse generator 6 receives each bit string from the transmission carrier switcher 5, adds a collision detection window to the head of each bit string, and modulators 7a.
Send to ~ 7d. This collision detection window is used to detect the packet and interrupt the packet transmission when the packets are transmitted from a plurality of wireless terminals and collide with each other.

Each of the modulators 7a to 7d performs modulation for wirelessly transmitting the input bit string, and the IF (Interm)
ediate Frequency) signal is output. In this example, a 4-phase PSK modulation method is used as the modulation method.

The RF unit 8 converts the IF signal input from each of the modulators 7a to 7d, that is, the modulated carrier signal, into four different frequencies designated by the control unit 17, and outputs them to the antenna 9. Further, the RF unit 8 converts a carrier signal having a frequency designated by the control unit 17 from the signals input from the antenna 9 into a predetermined frequency and sends the carrier signal to the demodulators 10a to 10d.

The demodulators 10a to 10d demodulate the IF signal frequency-converted by the RF unit 9 to regenerate a clock, and send the regenerated clock and the received bit string to the collision detector 11. The demodulators 10a to 10d detect the level of the received signal, and when the received signal level is equal to or higher than the reference level of the data signal, the carrier detection signal is equal to or higher than the reference level of the random pulse. The random pulse detection signal is sent to the collision detection unit 11. If the two reference levels are the same, the detection signal may be common. Further, when the received signal level is extremely low due to the influence of frequency selective fading or the like, a signal indicating communication failure is output.

The collision detecting section 11 includes the random pulse transmitted by the random pulse transmitting section 6 and the demodulators 10a to 10a.
The random pulse detection signal input from 10d is compared, and if the random pulse detection signal is received at a timing not transmitted by itself, it is determined that a collision has occurred, and it passes through the interface section 16. Then, the collision information is output to the external device and the packet transmission from the wireless terminal itself is interrupted. If no collision is detected, the received bit string is sent as it is to the receiving carrier exchanging unit 12.

The reception carrier exchanging unit 12 synchronizes each reception bit string received from the four demodulators 10a to 10d with packet synchronization based on the SFD for each carrier and then 4
It holds one bit string and notifies the control unit 17 of the contents of the packet identification information. Also, the receiving carrier replacement unit 12
Replaces the four bit strings according to the instruction from the control unit 17 and outputs them to the decoding unit 13.

The decoding unit 13 comprises a C1 decoder (outer decoder) and a C2 decoder (inner decoder). The C2 decoder
A bit string that is an error correction result for the C1 decoder and has an error correction function that performs error correction on each block of the received bit string for each carrier and an error detection function that determines whether or not an error remains in the error correction result. And send an error detection signal.
In this example, the C2 decoder uses 1-bit error correction in a block divided into 21 bits for each carrier and 2 bits.
Bit error residual detection can be performed. In this example, the calculation of the error correction check bit for each block at the time of encoding and the calculation of the error correction and the error residual detection at the time of decoding are performed by the linear operation of the bits in the block. Therefore, as described above, as the C1 code, (2
1, 15, 4) The extended Hamming code is used to suppress the delays at the time of encoding and decoding to the same extent as the block length.

In the C2 decoder, a function of checking the CRC of the fixed pattern added to the packet or each block in the packet and outputting an error detection signal when there is an error is added. The error detection capability is further improved.

The C1 decoder determines a carrier that could not correctly receive the bit string based on the communication failure signal obtained from the demodulators 10a to 10d or the error detection signal from the C2 decoder, and determines the bit string of this carrier as Restoration is performed from the other carriers, that is, the bit string of each carrier that has correctly received the bit string.

In this embodiment, the recoverable bit string is up to one of the four carriers. That is, even if one of the bit strings modulated with four carrier frequencies becomes incapable of communication due to the influence of frequency selective fading or the like, the error rate of the bit strings modulated with the other three carrier frequencies is 2 If it is less than or equal to 8 × 10 ^{−5, the} packet discard rate for a packet with a length of 512 octets is less than or equal to 4.0 × 10 ^−5, which is provisionally determined by IEEE 802.11 and the wireless LAN standardization committee. Can meet the regulations that apply. In this case, it is assumed that the coding rate (the number of information bits / the number of transmission bits) is 0.56 and that the roll-off coefficient of the filter is 50% and the guard band is 10% by using the above-mentioned 4-phase PSK modulation. The physical transmission rate per bit string (that is, carrier) is 4.46 Mbps, the frequency bandwidth is about 3.68 MHz, and assuming a 4-system configuration, the total bandwidth is 6
It becomes 0 MHz.

If there are two or three carriers that could not correctly receive the bit string, the C1 decoder 13a notifies the control unit 17 of this fact. Receiving this notification, the control unit 17 instructs the control packet transmission unit 3 to generate a retransmission request packet.

FIG. 4 shows the structure of the normal packet and the retransmission request packet. As shown in the figure, the normal communication packet 40 includes a collision detection window 41 and a preamble 4
2, SFD 43, packet identification information 44, destination address 45, own address 46, packet length 47, user information 48, and CRC 49. In addition, the retransmission request packet 50 includes a collision detection window 51 and a preamble 5
2, SFD 53, packet identification information 54, destination address (address of source wireless terminal of original packet) 55, self address (address of destination wireless terminal of original packet)
56, packet length 57, normal reception carrier information 58, retransmission request carrier information 59, and CRC 60.

Here, the packet identification information 44, 54 includes information indicating the type of the packet (normal packet / retransmission request packet / retransmission packet, etc.) and carrier replacement information. In the case of a normal packet, information indicating that the data is divided into a plurality of carriers and transmitted is set as the carrier replacement information. Further, in the case of a retransmission request packet, information indicating that data of the same content is transmitted using all communicable carriers is set as carrier replacement information. Further, in the case of a retransmission packet, information indicating which carrier to exchange the retransmission data with for transmission is set as carrier exchange information. Further, the normal reception carrier information 58 in the retransmission request packet 50 indicates a list of carriers that have correctly received the bit string. The retransmission request carrier information 59 indicates a list of carriers of a bit string for which retransmission is requested, that is, a list of carriers for which the bit string was not correctly received.

The control packet receiving unit 15 reads the packet identification information in the received packet, and when the received packet is a control packet such as a resend request packet, the control packet receiving unit 15 notifies the control unit 17 of this fact.

Next, an operation represented by the wireless communication system of this embodiment will be described.

FIG. 5 shows a communication procedure of a normal packet, a retransmission request packet and a retransmission packet between wireless terminals.

As shown in the figure, the source radio terminal first divides a part of the transmission data sequence into three bit strings,
A total of four bit strings including a parity check bit string are assigned to four carriers each having a different frequency, and a normal packet is transmitted.

The wireless terminal receiving the normal packet demodulates each received bit string, and then the C2 decoder 13b of the decoding unit 13
Error correction is performed in block units. When this error correction determines two or three bit strings whose errors cannot be completely corrected, or when two or three carriers are incommunicable due to the extremely low received signal level in the demodulators 10a to 10d. If it is determined that one of the bit strings has not been correctly received, the receiving wireless terminal generates a retransmission request packet having a content for requesting the retransmission of the bit string except for one that was not correctly received, and sends this packet to the source wireless terminal. At this time, the receiving wireless terminal sends out a retransmission request packet using all carrier frequencies for which the bit string was correctly received.

The source wireless terminal that has received the retransmission request packet determines a bit string to be retransmitted from the retransmission request carrier information in the packet to generate a retransmission packet, and determines this retransmission packet from the normal reception carrier information. It is sent to the receiving wireless terminal using a carrier frequency that enables communication.

At this time, as shown in FIG. 6, when there is one bit string to be retransmitted (when there are two communicable carriers), retransmitted packets are transmitted in parallel using all communicable carrier frequencies. Further, as shown in FIG. 7, when there are two bit strings to be retransmitted (when there is one communicable carrier), these bit strings are separately transmitted twice using one communicable carrier frequency.

Thus, according to the wireless communication system of this embodiment, when the wireless terminal of the packet transmission source receives the retransmission request, it retransmits the target bit string using the carrier frequency at which the data could be correctly transmitted in the immediately preceding packet transmission. I do. Therefore, even when some carrier frequencies are incommunicable due to frequency selective fading or the like, the target bit string can be correctly transmitted at the time of retransmission. Also, if the individual bit strings for which retransmission is requested are sent simultaneously using multiple carrier frequencies, the state of the transmission line will change due to the movement of obstacles such as people, and the carrier frequency at which communication becomes impossible will change from moment to moment. Even in such a situation, the target bit string can be retransmitted correctly.

In the present embodiment, one of the four bit strings is restored by transmitting the parity check bit string as the fourth bit string, thereby reducing the number of bit strings for which retransmission is requested by one. However, it goes without saying that the present invention can be applied to a system that does not have such a restoration function. That is, the present invention can be applied to the case of requesting retransmission of all bit strings that could not be correctly received.

The carrier requesting retransmission may be selected on the receiving side, or a list of all carriers for which the receiving side has correctly received the bit string is sent to the retransmitting side as normal reception carrier information and retransmitted. The side may select the carrier to be actually retransmitted from among them.

Further, in the present embodiment, the case where the packet is transmitted using four carriers has been described, but the present invention can be applied as long as the packet is transmitted using a plurality of different carrier frequencies.

[0045]

As described above, according to the wireless communication system of the present invention, when the wireless terminal of the packet transmission source receives the retransmission request from the destination wireless terminal, the carrier frequency at which the data can be correctly transmitted in the immediately preceding packet transmission. Since the target bit string is retransmitted by using, the target bit string can be correctly transmitted at the time of retransmission even in a situation where some carrier frequencies are incommunicable due to frequency selective fading or the like.

Further, if a method of simultaneously transmitting individual bit strings for which retransmission is requested by using a plurality of carrier frequencies, the state of the transmission line changes due to the movement of an obstacle such as a person and communication becomes impossible. It is possible to correctly retransmit the target bit string even in a situation where the carrier frequency that changes is constantly changing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wireless terminal in a wireless terminal system according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration sequence of a C1 encoder.

FIG. 3 is a diagram showing a configuration of a packet obtained through an encoding unit.

FIG. 4 is a diagram showing configurations of a normal packet and a retransmission request packet.

FIG. 5 is a diagram showing a communication procedure of a normal packet, a retransmission request packet, and a retransmission packet between wireless terminals.

FIG. 6 is a diagram showing an operation when there is one bit string to be retransmitted (when there are two communicable carriers).

FIG. 7 is a diagram showing an operation when there are two bit strings to be retransmitted (one communicable carrier).

[Explanation of symbols]

1, 16 ... Interface section, 2 ... Serial / parallel conversion section, 3 ... Control packet sending section, 4 ... Encoding section, 5 ...
Transmission carrier switching unit, 6 ... Random pulse transmission unit, 7
a, 7b, 7c, 7d ... Modulator, 8 ... RF section, 9 ... Antenna, 10a, 10b, 10c, 10d ... Demodulator, 11
... Collision detection section, 12 ... Reception carrier replacement section, 13 ... Decoding section, 14 ... Parallel / serial conversion section, 15 ... Control packet receiving section, 17 ... Control section.

Claims (5)

[Claims] 1. A wireless communication system in which at least a part of a data sequence forming a packet is divided into a plurality of bit strings, and a different carrier frequency is used for each bit string to perform wireless transmission between a plurality of wireless terminals. The wireless terminal, check means for checking whether or not each bit string of the received packet addressed to itself has been correctly received, and the bit string which has not been correctly received by the checking means, and the number of the bit strings When satisfies a preset condition, a retransmission request means for transmitting a retransmission request for at least a part of the bit string of the bit string to a wireless terminal which is a transmission source by using a carrier frequency that can correctly receive the bit string, and , When the retransmission request is received, the bit string requested to be retransmitted is a carrier that can correctly transmit the bit string. Wireless communication system, characterized by comprising a retransmitting means for retransmitting the retransmission request source wireless terminal addressed with wavenumber. 2. The wireless communication system according to claim 1, wherein the retransmitting means transmits individual bit strings requested to be retransmitted,
A wireless communication system characterized in that a plurality of carrier frequencies capable of correctly transmitting a bit string are used to retransmit at the same time to the wireless terminal of the retransmission request source. 3. The wireless communication system according to claim 1, wherein the retransmitting means retransmits each bit string requested to be retransmitted when the number of bit strings requested to be retransmitted is greater than the number of bit strings successfully transmitted. A wireless communication system, wherein the wireless communication system is characterized in that it is retransmitted to a wireless terminal that is the source of the retransmission request in a plurality of times by using a carrier frequency that has correctly transmitted a bit string. 4. The wireless communication system according to claim 1, wherein the re-transmission requesting unit sends, together with the re-transmission request, information indicating a carrier frequency at which a bit string was correctly transmitted, to the radio terminal of the transmission source. Wireless communication system. 5. A wireless communication system in which at least a part of a data sequence forming a packet is divided into a plurality of bit strings, and a different carrier frequency is used for each bit string to perform wireless transmission between a plurality of wireless terminals. In the data retransmission method, the wireless terminal receiving the packet checks whether each bit string of the packet has been correctly received, and as a result, the bit string that cannot be correctly received is determined,
When the number of the bit strings satisfies the preset condition, a resend request for at least a part of the bit strings of the bit string is transmitted to the wireless terminal of the transmission source by using the carrier frequency at which the bit string was correctly received. Then, the wireless terminal receiving the retransmission request, the bit string requested to be retransmitted,
A method of retransmitting data in a wireless communication system, comprising: retransmitting to a wireless terminal of a retransmission request source, using a carrier frequency that can correctly transmit a bit string.