JP2003051770A - Wireless communication system, wireless communication equipment and wireless communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To pull in a frequency errors each times it is caused by a change in the center frequency of a received signal from each wireless communication terminal. SOLUTION: A RAM113 provided to a loop filter 77 stores a frequency error correction value for each transmission terminal. A controller 69 discriminates a transmission terminal on the basis of a polling packet and reservation information. An address corresponding to the transmission terminal is sent to the RAM113 by a switching signal generated by a changeover circuit 79. Thus, the frequency error correction value is switched depending on the wireless communication terminal transmitting the signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless LAN (Loca
l Area Network), a wireless communication system for performing mutual communication between a plurality of wireless stations, a wireless communication device, and a wireless communication method. Especially, when there are a plurality of wireless communication terminals, The present invention relates to a wireless communication system, a wireless communication device, and a wireless communication method that perform frequency error correction that reintroduces a frequency error that occurs when the center frequency of a received signal changes.

More specifically, the present invention relates to a radio communication system for detecting a frequency error using a synchronization symbol (preamble) provided at the beginning of a transmission frame for frequency error correction, and performing the frequency error correction, The present invention relates to a wireless communication device and a wireless communication method, and more particularly, to a wireless communication system, a wireless communication device, and a wireless communication method for correcting a frequency error due to switching of a wireless terminal for transmission with high accuracy without being affected by noise.

[0003]

2. Description of the Related Art As computers have become more sophisticated, a plurality of computers have been connected to form a LAN (Local Area Network).
Are often used to share information such as files and data, to share peripheral devices such as printers, and to exchange information such as transfer of electronic mail and data.

In the conventional LAN, each computer is connected by wire using an optical fiber, a coaxial cable, or a twisted pair cable. However, such a wired LAN requires construction work for connection, which makes it difficult to construct the LAN easily and complicates the cable. Further, even after the LAN is constructed, the movement of the device is limited by the cable length, which is inconvenient.

Therefore, a wireless LAN is drawing attention as a system that relieves the user from the wiring of the conventional wired LAN. According to this type of wireless LAN, most of the wired cables can be omitted in a work space such as an office, so a personal computer (P
A terminal such as C) can be moved relatively easily.

In particular, in recent years, information has become more and more multimedia, and data such as image data and audio data, which has a large amount of data and which requires high-speed transmission, is often handled. For this reason, wireless communication interfaces such as IEEE 1394 and IEEE 802 are drawing attention, and these IEEE 1394 and I
A wireless LAN capable of wirelessly transmitting data specified by EEE 802 is being realized.

When constructing a wireless LAN, for example,
A wireless communication unit may be locally connected as one of peripheral devices to a general computer system such as a personal computer (PC), and the connection may be performed via each wireless communication unit. The wireless communication unit modulates and demodulates data by a predetermined modulation method so that the data can be wirelessly transmitted between the wireless communication terminals, and transmits and receives data, and controls the data transmission procedure and the transmission timing between the wireless communication terminals. ing. As such a wireless LAN control method, for example, CSMA / CA (Carrier Sense Multiple Access wi
th Collision Avoidance) method is known. CSM
According to the A / CA method, the transmitting station confirms the presence / absence of other communication, starts data transmission if it is not in communication, and shifts the timing and retransmits when a collision with other communication is detected.

Conventionally, in such a wireless LAN, when there are a plurality of wireless communication terminals, the center frequency of the received signal from each wireless communication terminal changes, so that the wireless communication terminal of the other party for data transmission changes. It is necessary to reintroduce the frequency error every time. Therefore, conventionally, a symbol for frequency error correction is provided at a predetermined position in the transmission frame, and the frequency error correction is performed by detecting this symbol.

FIG. 14 shows the structure of a transmission frame applied in a conventional wireless LAN. As shown in the figure, a synchronization symbol (preamble) for frequency error correction is provided at the beginning of one frame.
Following this, the data body is transmitted. 15 to 1
7 schematically shows the preamble structure for each of the cases of IEEE 802.11a, BRAN, and wireless 1394.

In the wireless communication unit constituting each wireless communication terminal, when a signal from the wireless communication terminal is received, the preamble at the beginning of one frame is detected and AGC (Automa
ticGain Control), the frequency error is detected from the received signal of the synchronization symbol for frequency error correction. Then, the frequency error correction is performed by multiplying the received signal by the sine wave generated by the NCO so that the frequency error value of the received signal becomes zero. By such frequency error correction, the frequency error of the received signal is controlled so as to approach 0, and the data is received.

As described above, in the conventional wireless LAN, the wireless communication unit constituting each wireless communication terminal detects the frequency error value in order to correct the frequency error each time the signal is received. However, the detection of this frequency error value has a drawback that the accuracy is poor due to variations caused by noise. Particularly, in multi-level modulation such as 64QAM, the required accuracy is about 0.5 ppm, which is extremely high accuracy, and even slight noise is affected, which causes a transmission error.

In particular, IEEE 1394 and IEEE 8
Wireless L that wirelessly transmits data specified by 02.
In the AN, high speed is required. Therefore, if the accuracy of the frequency error detection value is poor, the overhead such as retransmission increases and the throughput decreases.

Further, the frequency error is more important than that of the AGC. Because the signal strength changes from moment to moment, it is necessary to correct again using the signal strength of the preamble even when referring to the past setting value of the AGC gain. This is because there is almost no change for each wireless communication terminal.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is, when there are a plurality of wireless communication terminals, a frequency error that reintroduces a frequency error caused by a change in the center frequency of a received signal from each wireless communication terminal. An object of the present invention is to provide an excellent wireless communication system, wireless communication device, and wireless communication method that preferably perform correction.

A further object of the present invention is to perform frequency error correction by detecting a frequency error using a synchronization symbol (preamble) provided at the beginning of a transmission frame for frequency error correction. An object is to provide an excellent wireless communication system, wireless communication device, and wireless communication method.

A further object of the present invention is to provide an excellent wireless communication system, wireless communication device and wireless system capable of highly accurately correcting a frequency error due to switching of a wireless communication terminal for transmission without being affected by noise. To provide a communication method.

[0017]

The present invention has been made in consideration of the above problems, and a first aspect thereof is a wireless communication system in which a plurality of wireless communication terminals perform time division communication. Therefore, each of the wireless communication terminals described above includes a frequency error correction unit that corrects the frequency error of the received signal, and a correction value storage that stores the frequency error correction value obtained by the frequency error correction unit for each wireless communication terminal. Means and a transmitting terminal determining means for determining the transmitting wireless communication terminal, and the frequency error correction value corresponding to the wireless communication terminal specified by the transmitting terminal determining means is retrieved from the correction value storage means. The radio communication system is applied as a correction value of the frequency error correction means.

In a wireless LAN system in which a plurality of wireless communication terminals communicate with each other in a time division manner,
Since the center frequency of the received signal from each wireless communication terminal changes, a frequency error may occur.

According to the wireless communication system of the first aspect of the present invention, each wireless communication terminal stores the frequency error correction value for the wireless communication terminals other than itself and performs the wireless communication. The frequency error correction is performed by determining the terminal and using the corresponding frequency correction value based on the result of the determination to reintroduce the frequency error. Therefore, even if the wireless communication terminal that is transmitting is changed, the frequency error correction can be accurately performed.

Here, the frequency error correction means may detect a frequency error value in a slot of a predetermined control area in the radio frame.

Alternatively, the frequency error correction means may detect a frequency error value in a predetermined user area slot in the radio frame.

Alternatively, the frequency error correction means may detect a frequency error value of a predetermined synchronization signal in the radio frame.

Further, the transmitting terminal determining means may determine the transmitting wireless communication terminal based on the polling information.

Alternatively, the transmitting terminal determining means may determine the transmitting wireless communication terminal based on the reservation information for node allocation. Of course, the transmitting terminal determining means may determine the wireless communication terminal that is transmitting based on the combination of polling information and reservation information for node allocation.

In the wireless communication system according to the first aspect of the present invention, each wireless communication terminal controls the AGC control means for controlling the level of the received signal to a predetermined level, and each wireless communication partner. It further comprises control value storage means for storing the control value obtained by the AGC control means for each communication terminal, wherein the control means stores the frequency correction value corresponding to the wireless communication terminal specified by the transmission terminal determination means. Along with taking out from the correction value storing means, the corresponding control value is also taken out from the control value storing means, and the correction value of the frequency error correcting means and the AGC are respectively obtained.
You may make it apply as a control value of a control means.

With this configuration, each wireless communication terminal can correct both the AGC and the frequency error according to the communication partner.

Compared to AGC, frequency error is even more important. Since the signal strength changes from moment to moment, even if the past setting value of the AGC gain is referred to, it is necessary to correct again by using the signal strength of the preamble. However, regarding the frequency error, the wireless communication with the communication partner becomes necessary. This is because it hardly changes from terminal to terminal. The Doppler frequency is as small as several tens of Hz, and the amount of correction of the frequency error hardly changes each time it is received. Rather, since it is affected by an error due to noise or the like, it is possible to perform a highly accurate correction by storing the past correction amount and referring to the stored value.

As another method for keeping the accuracy of the frequency error correction high, there is a method of referring to the correlation value of the last area (C area) of the preamble. FFT in C area
In order to perform FFT, it is necessary to wait for a signal without performing FFT for two symbols for calculating the frequency error before FFT. A signal delay circuit (buffer) for this is required, and the demodulation processing delay time increases by 2 symbols in addition to the increase in circuit scale. Therefore, in order to secure a quick response, it is necessary to speed up the response processing circuit in the upper layer after demodulation, which causes the circuit to be complicated. On the other hand, according to the present invention in which the amount of frequency correction is stored in advance, the accuracy of frequency error correction can be increased, the delay time of demodulation processing can be short, the circuit scale can be small, and the manufacturing can be performed at low cost. You can

A second aspect of the present invention is a wireless communication device operating on a wireless communication network which communicates with each other in a time division manner, or a wireless communication method for controlling communication operation. Transmitting / receiving means or step for transmitting / receiving, frequency error correcting means or step for correcting frequency error of received signal, and correction for storing the frequency error correction value obtained by the frequency error correcting means or step for each wireless communication terminal Value storing means or step, transmitting terminal determining means or step for determining the wireless communication terminal that is transmitting, and frequency error correction value corresponding to the wireless communication terminal specified by the transmitting terminal determining means or step And a control unit or step applied as a correction value for the frequency error correction. Or a wireless communication method.

In a wireless LAN system in which a plurality of wireless communication terminals communicate with each other in a time division manner,
Since the center frequency of the received signal from each wireless communication terminal changes, a frequency error may occur.

According to the wireless communication device or the wireless communication method of the second aspect of the present invention, each wireless communication terminal operating on the wireless LAN system stores the frequency error correction value for the wireless communication terminals other than itself. In addition, it is possible to perform the frequency error correction in which the wireless communication terminal that is transmitting is determined and the frequency error is reintroduced using the corresponding frequency correction value based on the determination result. Therefore, the wireless communication device to which the present invention is applied can accurately perform frequency error correction even if the wireless communication terminal that is transmitting changes.

Here, the frequency error correction means or step may detect a frequency error value in a slot of a predetermined control area in the radio frame.

Alternatively, the frequency error correction means or step may detect a frequency error value in a predetermined user area slot in the radio frame.

Alternatively, the frequency error correction means or step may detect a frequency error value of a predetermined synchronization signal in the radio frame.

The transmitting terminal determining means or step may determine the transmitting wireless communication terminal based on the polling information.

Alternatively, the transmitting terminal determining means or step may determine the wireless communication terminal transmitting based on the reservation information for node allocation.
Of course, the transmitting terminal determining means or step may determine the wireless communication terminal that is transmitting based on a combination of polling information and reservation information for node allocation.

The radio communication apparatus or radio communication method according to the second aspect of the present invention includes AGC control means or step for controlling the level of the received signal to be a predetermined level, and each radio as a communication partner. It further comprises control value storage means or step for storing the control value obtained by the AGC control means or step for each communication terminal, wherein the control means or step is the wireless communication terminal specified by the transmission terminal determination means or step. While taking out the frequency correction value corresponding to, also taking out the corresponding control value,
It may be applied as the correction value of the frequency error correction means or step and the control value of the AGC control means or step, respectively.

With this configuration, each wireless communication device can correct both the AGC and the frequency error according to the communication partner.

Frequency error is even more important than in AGC. Since the signal strength changes from moment to moment, even if the past setting value of the AGC gain is referred to, it is necessary to correct again by using the signal strength of the preamble. However, regarding the frequency error, the wireless communication with the communication partner becomes necessary. This is because it hardly changes from terminal to terminal. The Doppler frequency is as small as several tens of Hz, and the amount of correction of the frequency error hardly changes each time it is received. Rather, since it is affected by an error due to noise or the like, it is possible to perform a highly accurate correction by storing the past correction amount and referring to the stored value.

Still other objects, features and advantages of the present invention are as follows.
It will be clarified by a more detailed description based on embodiments of the present invention described below and the accompanying drawings.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 schematically shows the configuration of a wireless LAN system 1 according to an embodiment of the present invention.

The wireless LAN system 1 shown in the figure comprises a plurality of wireless communication terminals 1A, 1B, 1C .... Each of the wireless communication terminals 1A, 1B, 1C ... Is a general data terminal 3A, 3B such as a personal computer (PC),
The wireless communication units 4A, 4B, 4C, ... Are locally connected to the 3C.

One of these wireless communication terminals 1A, 1B, 1C operates as a control station (coordinator) provided with a control function for maintaining communication order in the wireless LAN system 1, and the others. The wireless communication terminal of becomes the terminal station. In the example shown in FIG. 1, the wireless communication terminal 1C operates as a control station, and the other wireless communication terminals 1A, 1A
It is assumed that B ... Are operating as terminal stations.

Each of the wireless communication units 4A, 4B, 4C ... Equipped on the side of the wireless communication terminals 1A, 1B, 1C ..
11C ... and a receiving unit 12A that receives and processes wireless data,
12B, 12C, ..., Control units 13A, 13B, 13C.

In this embodiment, the transmitters 11A, 11B,
11C ..., and receivers 12A, 12B, 12C ...
Is an OFDM (Orthogonal Frequency Division Multip
lexing: Orthogonal frequency division multiplexing) is used for wireless data communication. The OFDM system is a kind of multi-carrier (multi-carrier) transmission system, and modulates and transmits data by using a plurality of orthogonal carrier waves.

Further, each wireless communication terminal 1A, 1B, 1C ...
Between TDMA (Time Division Multip
le Access: data transmission is performed by the time division multiple access method. One frame has a length of 4 milliseconds, for example, and is composed of a control area AR1 and a user area AR2, as shown in FIG.

The control area AR1 is provided for transmitting control data between the terminals. A synchronization symbol MS is assigned to the head of the control area AR1. Following this, control slots S1, S2, S3, ... For exchanging control data between the wireless communication terminals are assigned.

The user area AR2 is used for transmitting user data (payload) between the wireless communication terminals. For example, a wireless 1394 system (ARIB STD-T7) which is a wireless standard of IEEE 1394.
In 2), isochronous transmission mode and isochronous transmission mode are supported.
In the isochronous transmission mode, signals are exchanged in a uniform timing relationship between transmission and reception, so that a delay time is guaranteed and it is used for high-speed data transmission such as video data and audio data. Further, in the asynchronous mode, data transfer is performed only when there is data to be transferred, and it is used for data transfer that requires reliable transmission, although delay time such as a command does not matter. Also, in the high-speed wireless access system (ARIB STD-T71), the frame length is 2 milliseconds, and the wireless 13
Similar to the 94 system, it is divided into a control area and a user area.

As data is transmitted by such a wireless 1394 system, the user area AR2 is
Isochronous data area D-ISO and asynchronous data area DA
It is divided into SYNC. Isochronous data area D-ISO
In the allocation of the asynchronous data area D-ASYNC, the bandwidth of the isochronous data area D-ISO is first secured so that the user area can be effectively used, and the remaining bandwidth is allocated as the asynchronous data area D-ASYNC.

In the wireless LAN system 1 shown in FIG.
The wireless communication terminal 1C functions as a control station that controls the entire system 1, and the other wireless communication terminals 1A, 1B ... Operate as terminal stations. When configuring the wireless LAN system 1, first, when the power is turned on, the wireless communication terminals 1A and 1A are connected.
When the operations of B, 1C, ... Are started, information is exchanged between the wireless communication terminals using the control slots S1, S2, S3 ,. Then, in the resource information memory 15 equipped in the wireless communication terminal 1C designated by the control station, the information of each wireless communication terminal 1A, 1B, ... Constituting the wireless LAN system 1 is registered.

At this time, the wireless communication terminals 1A, 1
B, 1C ... Wireless communication units 4A, 4B, 4
Frequency error correction is performed in the reception units 12A, 12B, 12C, ... The pulling in of the frequency error correction is completed for each received slot. That is, when the reception of one slot is completed, the frequency error correction is newly performed again when the next radio slot is received.

Here, as illustrated in FIG. 3, each control slot S1, S2, S3 ... Included in the control area AR1.
Are equivalent to slots of control signals transmitted from the wireless communication terminals 1A, 1B, 1C, ...

The radio communication terminal 1A first performs frequency error correction using the frequency error value of the signal in the control slot S2. As shown in FIG. 4, the frequency error correction value at this time is the frequency error correction value S of the signal from the wireless communication terminal 1B.
-Import as FERR2. Then the control slot S
Frequency error correction is performed using the reception frequency error value of the signal of No. 3, and the frequency error correction value at this time is used as the wireless communication terminal 1C.
The frequency error correction value S-FERR3 of the signal from is taken in. In this way, the wireless communication terminal 1A includes the other wireless communication terminals 1B, 1C in the wireless LAN system 1.
Frequency error correction value S-F when the signal from ... Is received
ERR2, S-FERR3 ... Are sequentially taken in.

Similarly, the wireless communication terminal 1B has a control area A
When the frequency error correction is performed using the reception frequency error value of the signal of each control slot S1, S3 ... In R1, and the frequency error value at this time is received from the wireless communication terminals 1A, 1C. Frequency error correction value S-FERR
1, S-FERR3 ... Similarly, in the wireless communication terminal 1C, frequency error correction is performed using the frequency error values of the signals of the control slots S1, S2 ... In the control area AR1, and signals from the wireless communication terminals 1A, 1B. Error correction value S-FER when receiving
Take in as R1, S-FERR2 ...

When data is transmitted between the wireless communication terminals in the wireless LAN system 1, the wireless terminal 1C serving as a control station allocates slots and secures bands. In addition, each wireless communication terminal 1A, 1B,
In 1C, since the frequency error correction value when the signal from the wireless communication terminal other than itself is received is already accumulated by the above-described processing procedure, the wireless communication terminal from which the received signal comes. The frequency error correction value can be switched depending on whether or not the wireless data is received.

According to the storage means as shown in FIG. 4 described above, both AGC and frequency error correction can be used in combination by simultaneously referring to the AGC set value and the frequency error value of the terminals 1B and 1C. . That is, the AGC setting value is read at the same time as the frequency error correction value stored in each address according to the wireless communication terminal as the communication partner, and the frequency error correction value is read by the frequency error correction circuit and the AGC set value is read by the AGC amplifier. By giving it, the initial synchronization acquisition in the preamble can be performed more reliably.

However, the frequency error is more important than the AGC. Since the signal strength changes from moment to moment, even if the past setting value of the AGC gain is referred to, it is necessary to correct again by using the signal strength of the preamble. However, regarding the frequency error, the wireless communication with the communication partner becomes necessary. This is because it hardly changes from terminal to terminal. The Doppler frequency is as small as several tens of Hz, and the amount of correction of the frequency error hardly changes each time it is received. Rather, since it is affected by an error due to noise or the like, it is possible to perform a highly accurate correction by storing the past correction amount and referring to the stored value.

However, it is appropriate that the AGC set value waits at the immediately preceding set value. Wireless L that is generally used in a quasi-static communication environment such as in an office or home
In the AN, the change in signal strength with time is relatively gradual, so that it is effective to wait at the set value of the AGC gain set immediately before for a short time.

When the set value of the AGC amplifier is unknown, the gain of the AGC amplifier is temporarily set to a proper value, and the arrival of a signal is waited in that state. If this gain is too small, a situation may occur in which the arrival of a signal of low signal strength is not noticed. On the other hand, if the gain is too large, signal deterioration occurs due to signal saturation, and arrival of the preamble cannot be detected, that is, synchronization error occurs. Normally, the AGC gain is set to a relatively large value, and the correlator is made so that the signal can be detected even when the AGC amplifier is saturated. However, the signal detection performance is improved when noise or interference waves are present. As a result of the deterioration, the packet error rate deteriorates. In this way, it is desirable that the AGC gain waits at the desired gain as much as possible.

As another method of keeping the accuracy of frequency error correction high, there is a method of referring to the correlation value of the last area (C area) of the preamble. However, in this method, since the FFT is performed on the C region, the FF
FFT during two symbols to calculate the frequency error before T
Need to wait for the signal without doing. A signal delay circuit (buffer) for this is required, and the demodulation processing delay time increases by 2 symbols in addition to the increase in circuit scale. Therefore, in order to secure a quick response, it is necessary to speed up the response processing circuit in the upper layer after demodulation, which causes the circuit to be complicated. On the other hand, according to the above-described frequency correction method in which the frequency correction amount is stored in advance, the accuracy of frequency error correction can be increased, the demodulation processing delay time is short, the circuit scale is small, and the cost is low. Can be manufactured.

FIG. 5 exemplifies how the frequency error correction value switching control is performed in the case of a polling packet. In the example shown in the figure, the wireless communication terminal 1B
It is assumed that the frequency error correction processing in FIG.

In this example, it is assumed that the wireless communication terminal 1B first receives a signal from the wireless communication terminal 1C which is the control station. In this signal reception period, the frequency error correction value is the correction value S-FERR3 when the wireless communication terminal 1C which is the control station is received.

Then, it is assumed that a polling packet is received at timing F1. The destination is described in the polling packet, and the next communication is transmitted from the wireless communication terminal indicated by the destination. In the example shown in FIG. 5, the polling packet at the timing F1 includes the wireless communication terminal 1
A is written as the destination. Therefore, in this case, the correction value for the next frequency error correction is the wireless communication terminal 1A.
To the correction value S-FERR1 when the signal from is received.

As described above, in the case of the polling packet, the polling packet is received, and the frequency error correction value is switched based on the destination written in the polling packet to transmit the radio packet. The frequency error correction value can be switched according to the communication terminal. Of course, at the same time as switching the frequency error correction location, A
The AGC set value in the GC amplifier may be switched.

FIG. 6 shows an example of frequency error correction value switching control when node allocation is performed. In the example shown in the figure, it is assumed that the frequency error correction processing in the wireless communication terminal 1B is shown.

It is assumed that the wireless communication terminal 1B has received a signal from the wireless communication terminal 1C, which is a control station, until then. In this signal reception period, the frequency error correction value is the correction value S-FERR3 when the wireless communication terminal 1C is received. Then, it is assumed that the reservation information is received at the timing F11. In this reservation information, it is assumed that it is described that the wireless communication terminal 1A transmits at the time points t1 to t2 and the wireless communication terminal 1B transmits at the time points t2 to t3.

In such a case, the next frequency error correction value is set according to the contents written in the reservation information, and at the time points t1 to t2, the frequency error correction value is received by the wireless communication terminal 1A. The correction value S-FERR1 at that time is switched to. Further, at subsequent time points t2 to t3, since the wireless communication terminal station 1B itself performs transmission, the frequency error correction value is not set.

As described above, in the case of the node allocation method, the wireless communication transmitting the signal by receiving the reservation information and switching the frequency error correction value based on the content described in the reservation information. The frequency error correction value can be switched according to the terminal. And
Of the control slots included in the control area AR1, frequency error correction is performed from the frequency error detection value of the signal in the control slots S1, S3, ... Of the terminal transmitting the signal, and the frequency error correction value is updated accordingly. . Of course, at the same time as switching the frequency error correction location, A in the AGC amplifier is changed.
The GC setting value may be switched.

In this case, as shown in FIG.
The frequency error correction follows every 4 milliseconds corresponding to a frame. It can be considered that the frequency error value of each wireless communication terminal 1A, 1B, 1C ... Is almost constant over the use time, and therefore does not change once the frequency error correction value converges. There is no problem if the frequency error value is updated only once for each frame. Of course, in addition to this, the frequency error correction may be performed using the signal of the user area AR2.
Alternatively, the frequency error of the synchronization symbol MS may be detected.

As described above, in the case of polling, the wireless communication terminal on the receiving side can use the polling information to determine the wireless communication terminal to be transmitted, and
In the case of the node allocation method, it is possible to determine the wireless communication terminal that transmits using the reservation information. Of course, the terminal that transmits may be determined by combining the polling information and the reservation information.

For example, a wireless LAN system (ARIB STD) specified in IEEE 802.11a
-T70), the frame length is not always a fixed value,
The next transmitting terminal can be determined in advance based on the polling signal transmitted by the access point (control station).

FIG. 7 shows wireless communication terminals 1A, 1B, 1C.
1 schematically shows a hardware configuration of a device applied as the wireless communication units 4A, 4B, 4C ...

In the wireless communication unit 4 shown in FIG.
The transmission data is input via the communication controller 51. The transmission data from the communication controller 51 is supplied to the mapping circuit 52. QPSK (Quadrature Phase Shift K
eying: four-phase phase shift keying). QPSK
Are orthogonal I and Q channels with the same carrier frequency f _c
This is a system in which two-value transmission is performed independently for each channel, and four-value transmission is performed as a whole.

The output of the mapping circuit 52 is serial /
It is supplied to the parallel conversion circuit 53. The serial / parallel conversion circuit 53 converts serial data into parallel data. The output of the serial / parallel conversion circuit 53 is supplied to an IFFT (Inverse Fast Fourier Transform) circuit 54. IFFT circuit 5
4, the transmission data is converted into frequency domain data, which is inverse Fourier transformed and converted into time domain data. The output of the IFFT circuit 54 is supplied to the parallel / serial conversion circuit 55.

Serial / parallel conversion circuit 53, IFF
The T circuit 54 and the parallel / serial conversion circuit 55 are OF
DM (Orthogonal Frequency Division Multiplexing)
The transmission data is converted into a multi-carrier signal according to the method.

The output of the parallel / serial conversion circuit 55 is supplied to the frequency conversion circuit 57. The frequency conversion circuit 57 includes a PLL (Phase Lock Loop) synthesizer 5
The local oscillation signal output from 8 is supplied. The transmission signal is converted into a predetermined frequency by the frequency conversion circuit 57.

The output of the frequency conversion circuit 57 is supplied to the power amplifier 59. The transmission signal is power-amplified in the power amplifier 59. By switching to the terminal 60A side of the switch circuit 60, the output of the power amplifier 59 is supplied to the antenna 61, and the output of the switch circuit 60 is supplied to the antenna 61.
It is sent as wireless data.

On the other hand, the received signal from the antenna 61 is supplied to the switch circuit 60. When receiving data, the switch circuit 60 is switched to the terminal 60B side. The output of the switch circuit 60 is the LNA (Low Noise Am
plifier) 62 and then supplied to the frequency conversion circuit 63.

A local oscillation signal is supplied from the PLL synthesizer 58 to the frequency conversion circuit 63. The frequency conversion circuit 63 converts the received signal into an intermediate frequency signal.

The output of the frequency conversion circuit 63 is AGC (Au
to the gain control circuit 64. AGC
The circuit 64 detects the signal level of the received signal, compares the signal level of the received signal with the reference level, and controls so that the signal level of the received signal becomes constant.

The output of the AGC circuit 64 is supplied to the serial / parallel conversion circuit 65 via the frequency error correction circuit 70. The frequency error correction circuit 70 corrects the frequency error of the received signal. The correction pull-in is completed for each slot to be received, and when the reception of one slot is completed,
When the next wireless slot is received, a new frequency error correction is performed again. For example, in the case of a polling packet, the frequency error correction value is switched according to the destination described in the polling packet, thereby performing the frequency error correction according to the terminal on the transmitting side. Further, in the case of node allocation, the frequency error correction value is switched based on the description content of the reservation information, thereby performing the frequency error correction according to the terminal on the transmitting side. Of course, it is also possible to specify the wireless communication terminal on the transmitting side by the combination of the polling information and the reservation information and perform the frequency error correction according to the terminal.

The output of the frequency error correction circuit 70 is supplied to the serial / parallel conversion circuit 65 and the serial data is converted into parallel data. The output of the serial / parallel conversion circuit 65 is an FFT (Fast Fourier Trans
form) circuit 66. The output of the FFT circuit 66 is supplied to the parallel / serial conversion circuit 67, and the parallel data is converted into serial data.

Serial / parallel conversion circuit 65, FFT
The circuit 66 and the parallel / serial conversion circuit 67 are OFD.
M-mode demodulation is performed.

The output of the parallel / serial conversion circuit 67 is supplied to the demapping circuit 68. In the demapping circuit 68, QPSK demodulation processing is performed. The output of the demapping circuit 68 is supplied to the communication controller 51, and the received data is output from the output of the communication controller 51 to the data terminal.

The overall operation of the wireless communication unit 4 is controlled by the controller 69 as a whole. That is, the transmission of data and the reception of data are controlled by the communication controller 51 based on a command from the controller 69.

FIG. 8 shows the internal structure of the frequency error correction circuit 70 in detail. In the figure, the AGC circuit 6
The intermediate frequency signal output by 4 is supplied to the input terminal 71. The intermediate frequency signal from the input terminal 71 is supplied to the frequency converter 72. The local oscillation frequency of the frequency converter 72 is changed according to the set value output from the loop filter 77 (described later).

The output of the frequency converter 72 is the output terminal 73.
And is supplied to the frequency error detector 74. The frequency error detection circuit 74 detects the frequency error value of the received signal and outputs the detected value of this frequency error as a digital value.

The frequency error detection circuit 74 is, for example, as shown in FIG.
As shown in, a correlator 82 for detecting the correlation of the intermediate frequency signal from the input terminal 81 and a phase difference detector 84 for detecting the frequency error value from the phase rotation amount of this correlation value are provided. The signal is sent from the output terminal 85.

Alternatively, the frequency error detector 74 is shown in FIG.
It can also be configured as shown in. In this case, an A / D converter 92 that digitally converts the intermediate frequency signal from the input terminal 91, a digital correlation circuit 93 that digitally detects the correlation of the intermediate frequency signal, and a frequency error value from the phase rotation amount of this correlation value. And a correction value calculator 94 for detecting the detection signal, and sends a detection signal from the output terminal 95.

Alternatively, the frequency error detector 74 is shown in FIG.
It can also be configured as shown in. In this case, a quadrature demodulation circuit 102 that demodulates the intermediate frequency signal from the input terminal 101 into an I signal and a Q signal, and an A / D converter 103 that digitizes the demodulated I signal and the Q signal, respectively.
A and 103B, a digital complex correlation circuit 104 that digitally detects the correlation between them, and a phase difference detector 105 that detects a frequency error value from the phase rotation amount of the correlation value.
The detection signal is sent from the output terminal 107.

In FIG. 8, a value obtained by adding a negative sign to the frequency error value detected by the frequency error detection circuit 74 is output.
This value corresponds to the correction value of the frequency error correction circuit 70. A value obtained by adding a negative sign to the frequency error value is supplied to the loop filter 77.

FIG. 12 shows the internal structure of the loop filter 77 in detail. The loop filter 77 includes a multiplication circuit 111 and a limiter circuit 11 as shown in FIG.
2, RAM 113, and an adder circuit 114.

A value obtained by adding a negative sign to the frequency error value is input to the input terminal 110. A value obtained by adding a negative sign to the frequency error value is supplied to the addition circuit 114 via the multiplication circuit 111. The adder circuit 114 includes a RAM (Random Access).
Memory) 113 output is supplied. In the adder circuit 114, the input signal passed through the multiplier circuit 111 and the RAM 11
The outputs of 3 are added.

The output of the adder circuit 114 is the limiter circuit 11.
2 is supplied to the RAM 113. The output of the RAM 113 is output from the output terminal 116 and fed back to the adder circuit 114.

As described above, the value obtained by adding a negative sign to the frequency error value from the input terminal 110 is multiplied by the gain in the multiplication circuit 111, and this value is accumulated to form a loop.
The filter 77 is configured. This accumulated value is stored in the RAM 11
Accumulated in 3. The value stored in the RAM 113 becomes the local oscillation frequency of the frequency error correction circuit 70.

An address is given to the RAM 113 from the terminal 115. The storage area in the RAM 113 is set by this address. Therefore, by switching the address for the RAM 113, the frequency error correction value can be switched according to the transmitting wireless communication terminal.

In FIG. 8, the output of the loop filter 77 is supplied to the frequency conversion circuit 72. The oscillation frequency in the frequency conversion circuit 72 is the loop filter 77.
It is set according to the output of.

As described above, the loop filter 77 is provided with the RAM 113, and the RAM 113 stores the frequency error correction value for each transmitting radio communication terminal. The controller 69 determines the wireless communication terminal transmitting the signal based on the polling packet and the reservation information. With this switching signal,
A switching signal is generated in the switching circuit 79. The switching signal is sent from the switching circuit 79 to the RAM 11 by this switching signal.
The corresponding address is sent to 3. This allows
The frequency error correction value is switched according to the wireless communication terminal transmitting the signal.

As described above, if the frequency error correction value is digitized and stored in the RAM 113, the control value can be easily switched for each wireless communication terminal on the transmitting side only by switching the address. Of course, the frequency error correction may be performed in an analog manner, the frequency error correction value may be stored in the integrator for each wireless communication terminal, and each integrator may be switched by the switch circuit.

In the above-described embodiment, the frequency error correction value is switched according to the wireless communication terminal transmitting the signal, but the AGC control value may be switched at the same time. . Further, when the diversity antenna is used, the AGC control value may be switched for each antenna used.

It is appropriate to wait for the AGC set value at the immediately preceding set value. In a wireless LAN where a quasi-static communication environment such as in an office or home is common,
Since the change in signal strength over time is relatively gradual, it is effective to wait for the set value of the AGC gain set immediately before for a short time.

When the set value of the AGC amplifier is unknown, the gain of the AGC amplifier is temporarily set to a certain value, and the arrival of a signal is waited in that state. If this gain is too small, a situation may occur in which the arrival of a signal of low signal strength is not noticed. On the other hand, if the gain is too large, signal deterioration occurs due to signal saturation, and arrival of the preamble cannot be detected, that is, synchronization error occurs. Normally, a correlator is made so that the signal can be detected even if the AGC amplifier is saturated and the AGC gain is set to a relatively large value. However, if noise or an interference wave is present, the signal detection performance is improved. As a result of the deterioration, the packet error rate deteriorates. In this way, it is desirable that the AGC gain waits at the desired gain as much as possible.

FIG. 13 illustrates a mechanism for performing gain control of the AGC amplifier and antenna switching control based on the information of the wireless communication terminal on the transmission side. In the example shown in the figure, the wireless communication unit 4A (4B, 4C) outputs the gain control information 123A, 123B, 123C, ... Of the corresponding AGC amplifier according to which antenna 121A, 121B, 121C. It is designed to be taken out and used.

In the above description, the value input to the loop filter 77 is a value obtained by adding a negative sign to the frequency error value, but the frequency error value is input to the loop filter 77.
A negative sign may be added on the output side. RAM
Although the value stored in 113 is the frequency error correction value, the frequency error value may be stored and a negative sign may be added to the frequency error value in the frequency error correction circuit.

[Supplement] The present invention has been described in detail with reference to the specific embodiments. However, it is obvious that those skilled in the art can modify or substitute the embodiments without departing from the scope of the present invention. That is, the present invention has been disclosed in the form of exemplification, and the contents of this specification should not be construed in a limited manner. In order to determine the gist of the present invention, the section of the claims described at the beginning should be taken into consideration.

[0107]

As described above in detail, according to the present invention,
When there are a plurality of wireless communication terminals, the frequency error correction is preferably performed to reintroduce the frequency error that occurs because the center frequency of the received signal from each wireless communication terminal changes.
An excellent wireless communication system, wireless communication device, and wireless communication method can be provided.

Further, according to the present invention, it is possible to detect the frequency error by using the synchronization symbol (preamble) provided at the head of the transmission frame for frequency error correction and perform the frequency error correction. It is possible to provide a wireless communication system, a wireless communication device, and a wireless communication method.

Further, according to the present invention, an excellent radio communication system, radio communication device and radio which can highly accurately correct a frequency error due to switching of a radio communication terminal for transmission without being influenced by noise. A communication method can be provided.

Further, according to the present invention, the wireless communication terminal is
Both AGC and frequency error can be corrected according to the communication partner. Compared to AGC, the frequency error is even more important. Since the signal strength changes from moment to moment, it is necessary to correct again using the signal strength of the preamble even if the past setting value of the AGC gain is referred to. This is because it hardly changes from terminal to terminal. The Doppler frequency is as small as several tens of Hz, and the amount of correction of the frequency error hardly changes each time it is received. Rather, since it is affected by an error due to noise or the like, it is possible to perform a highly accurate correction by storing the past correction amount and referring to the stored value.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a wireless LAN system according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a configuration of a transmission frame exchanged between the wireless terminals 1A, 1B, 1C ...

3 is a diagram showing a specific configuration example of the transmission frame shown in FIG. 2, in which the control slots S1, S2, S3 ... Included in the control area AR1 are wireless communication terminals 1A, 1 respectively.
It is the figure which showed the example corresponded to the slot of the control signal transmitted from B, 1C ...

FIG. 4 is a diagram showing a case where the wireless communication terminal 1A performs frequency error correction using the frequency error values of the signals of the control slots S2, S3 ... In the control area AR1, and the other wireless communication terminals 1B, 1C.
It is the figure which showed a mode that it was taken in as a frequency error correction value.

FIG. 5 shows an example of switching control of a frequency error correction value in the case of a polling packet.

FIG. 6 is a diagram showing an example of frequency error correction value switching control when node allocation is performed.

FIG. 7 is a diagram schematically showing a hardware configuration of an apparatus applied as wireless communication units 4A, 4B, 4C ... Equipped in wireless communication terminals 1A, 1B, 1C.

FIG. 8 is a diagram showing in detail an internal configuration of a frequency error correction circuit 70.

FIG. 9 is a diagram showing in detail an internal configuration example of a frequency error detector 74.

FIG. 10 is a diagram showing in detail another example of the internal configuration of the frequency error detector 74.

FIG. 11 is a diagram showing in detail another example of the internal configuration of the frequency error detector 74.

FIG. 12 is a diagram showing in detail the internal configuration of a loop filter 77.

FIG. 13 is a diagram showing AGC based on information of a wireless communication terminal on the transmitting side.
It is a figure showing the mechanism for performing gain control of an amplifier, and antenna switching control.

FIG. 14 is a diagram showing a configuration of a transmission frame applied in a conventional wireless LAN.

FIG. 15 is a diagram schematically showing a configuration of a preamble of a transmission frame according to IEEE 802.11a.

FIG. 16 is a diagram schematically showing the structure of a preamble of a transmission frame according to BRAN.

FIG. 17 is a diagram schematically showing a configuration of a preamble of a transmission frame according to wireless 1394.

[Explanation of symbols] 1 ... Wireless LAN system 1A, 1B, 1C ... Wireless communication terminal 3A, 3B, 3C ... Data terminal 4A, 4B, 4C ... Wireless communication unit 11A, 11B, 11C ... Transmitter 12A, 12B, 12C ... Receiving unit 13A, 13B, 13C ... Control unit 15 ... Resource information memory 51 ... Communication controller 52 ... QPSK modulation circuit 53 ... Serial / parallel conversion circuit 54 ... IFFT circuit 55 ... Parallel / serial conversion circuit 57 ... Frequency conversion circuit 58 ... PLL synthesizer 59 ... Power amplifier 60 ... Switch circuit 61 ... antenna 62 ... LNA 63 ... Frequency conversion circuit 64 ... AGC circuit 65 ... Serial / parallel conversion circuit 66 ... FFT conversion circuit 67 ... Serial / parallel conversion circuit 68 ... Demapping circuit 69 ... Controller 70 ... Frequency error correction circuit 71 ... Input terminal 72 ... Frequency converter 73 ... Output terminal 74 ... Frequency error detector 77 ... Loop filter 81 ... Input terminal 82 ... Correlator 84 ... Phase difference detector 85 ... Output terminal 91 ... Input terminal 92 ... A / D converter 93 ... Digital correlation circuit 94 ... Correction value calculator 95 ... Output terminal 101 ... Input terminal 102 ... Quadrature demodulation circuit 103 ... A / D converter 104 ... Digital complex correlation circuit 105 ... Output terminal 110 ... Input terminal 111 ... Multiplier circuit 113 ... RAM 114 ... Adder circuit 116 ... Output terminal

Claims (24)

[Claims] 1. A wireless communication system in which a plurality of wireless communication terminals perform time-division communication, wherein each of the wireless communication terminals serves as a frequency error correction means for correcting a frequency error of a received signal, and a communication partner. A correction value storage unit that stores the frequency error correction value obtained by the frequency error correction unit for each wireless communication terminal, a transmission terminal determination unit that determines the wireless communication terminal that is transmitting, and the transmission terminal determination unit A frequency error correction value corresponding to the wireless communication terminal specified by the above-mentioned correction value storage means and applied as a correction value of the frequency error correction means. . 2. The radio communication system according to claim 1, wherein the frequency error correction means detects a frequency error value in a slot of a predetermined control area in the radio frame. 3. The wireless communication system according to claim 1, wherein the frequency error correction means detects a frequency error value in a predetermined user area slot in the wireless frame. 4. The radio communication system according to claim 1, wherein the frequency error correction means detects a frequency error value of a predetermined synchronization signal in a radio frame. 5. The wireless communication system according to claim 1, wherein said transmitting terminal judging means judges a wireless communication terminal transmitting based on polling information. 6. The wireless communication system according to claim 1, wherein said transmitting terminal judging means judges a wireless communication terminal transmitting based on reservation information for node allocation. 7. The transmission terminal determining means determines a wireless communication terminal transmitting based on a combination of polling information and reservation information for node allocation. Wireless communication system. 8. Each wireless communication terminal controls AGC control means for controlling a level of a received signal to a predetermined level, and a control value obtained by the AGC control means for each wireless communication terminal as a communication partner. Further comprising a control value storage means for storing the frequency correction value corresponding to the wireless communication terminal identified by the transmission terminal determination means from the correction value storage means, and also the corresponding control value. The radio communication system according to claim 1, wherein the radio communication system is extracted from the control value storage means and applied as a correction value of the frequency error correction means and a control value of the AGC control means, respectively. 9. A wireless communication device operating on a wireless communication network for time-divisionally communicating with each other, comprising: transmitting / receiving means for transmitting / receiving a signal; frequency error correcting means for correcting a frequency error of a received signal; Correction value storage means for storing the frequency error correction value obtained by the frequency error correction means for each of the partner wireless communication terminals; transmission terminal determination means for determining the wireless communication terminal that is transmitting; A frequency error correction value corresponding to the wireless communication terminal specified by the terminal determination means, taken out from the correction value storage means, and applied as a correction value of the frequency error correction means. Wireless communication device. 10. The radio communication apparatus according to claim 9, wherein the frequency error correction means detects a frequency error value in a slot of a predetermined control area in the radio frame. 11. The wireless communication apparatus according to claim 9, wherein the frequency error correction means detects a frequency error value in a slot of a predetermined user area in the wireless frame. 12. The wireless communication device according to claim 9, wherein the frequency error correction means detects a frequency error value of a predetermined synchronization signal in a wireless frame. 13. The wireless communication apparatus according to claim 9, wherein said transmitting terminal judging means judges a wireless communication terminal transmitting based on polling information. 14. The wireless communication apparatus according to claim 9, wherein the transmitting terminal determining means determines a wireless communication terminal transmitting based on reservation information for node allocation. 15. The transmission terminal determining means determines a wireless communication terminal transmitting based on a combination of polling information and reservation information for node allocation. Wireless communication device. 16. An AGC control means for controlling a received signal level to a predetermined level, and a control value storage for storing a control value obtained by the AGC control means for each wireless communication terminal as a communication partner. Further comprising means for extracting the frequency correction value corresponding to the wireless communication terminal specified by the transmitting terminal determination means from the correction value storage means, and also outputting the corresponding control value from the control value storage means. The wireless communication device according to claim 9, wherein the wireless communication device is extracted and applied as a correction value of the frequency error correction unit and a control value of the AGC control unit, respectively. 17. A wireless communication method for controlling a communication operation on a wireless communication network that performs time-division communication with each other, comprising a frequency error correction step of correcting a frequency error of a received signal, and each of the communication partners. A correction value storage step of storing the frequency error correction value obtained in the frequency error correction step for each wireless communication terminal, a transmission terminal determination step of determining the wireless communication terminal that is transmitting, and a transmission terminal determination step of A communication control step of extracting a frequency error correction value corresponding to the specified wireless communication terminal and applying it as a correction value for frequency error correction. 18. The wireless communication method according to claim 17, wherein in the frequency error correction step, a frequency error value in a slot of a predetermined control area in the wireless frame is detected. 19. The wireless communication method according to claim 17, wherein the frequency error correction step detects a frequency error value in a slot of a predetermined user area in the wireless frame. 20. The radio communication method according to claim 17, wherein the frequency error correction step detects a frequency error value of a predetermined synchronization signal in a radio frame. 21. The wireless communication method according to claim 17, wherein in the transmitting terminal determining step, the wireless communication terminal that is transmitting is determined based on polling information. 22. The wireless communication method according to claim 17, wherein in the transmitting terminal determining step, the transmitting wireless communication terminal is determined based on reservation information for node allocation. 23. The transmitting terminal determining step determines a wireless communication terminal transmitting based on a combination of polling information and reservation information for node allocation.
18. The wireless communication method according to claim 17, wherein: 24. An AGC control step for controlling the level of a received signal to a predetermined level, and a control value storage for storing the control value obtained by the AGC control step for each wireless communication terminal as a communication partner. In the communication control step, the frequency correction value corresponding to the wireless communication terminal identified in the transmission terminal determination step is extracted, and the corresponding control value is extracted in the communication control step. The wireless communication method according to claim 17, wherein the wireless communication method is applied as a value and a control value of the AGC control means.