JP4280233B2 - Wireless communication system, wireless communication device, and method for changing guard interval length of wireless communication device - Google Patents

Description

  The present invention relates to the field of mobile communication, and more particularly, to a radio communication system, a radio communication system using a communication scheme that uses an adaptive modulation scheme that makes a transmission rate variable, and that provides a guard interval to suppress reception quality performance degradation due to multipath delay A communication device and a method for changing a guard interval length in the wireless communication device.

  In wireless communication using OFDM (Orthogonal Frequency Division Multiplex) used in wireless LANs and the like, interference due to multipulse delay waves is avoided by inserting a signal called a guard interval (GI) into a data signal. ing. Since the guard interval is a redundant signal, it is known that the transmission efficiency is improved by setting the length short depending on the state of the transmission path (see Patent Document 1).

The technique disclosed in Patent Document 1 is to adaptively control the guard interval length by detecting multipath. However, since multipath detection needs to have a detection range wider than the guard interle length, a special multipath detection signal must be added. There is also a problem from the viewpoint of detection time and power consumption.
JP 2002-374223 A

  In wireless communication systems that detect the multipath and adaptively control the guard interval length, the multipath detection requires a wider detection range than the guard interle length. Or add other signals. There is also a problem from the viewpoint of detection time and power consumption. The present invention has been made in order to solve the above-described problem, and does not require troublesome multipath detection that takes time and consumes power, and adaptively controls the guard interval length by a simple method. Accordingly, an object of the present invention is to provide a wireless communication system, a wireless communication apparatus, and a method for changing a guard interval length in the wireless communication apparatus, in which communication throughput is improved.

  In order to solve the above problem, a wireless communication system according to the present invention is a wireless communication system including a first wireless station that transmits a data signal to which a guard interval is added and a second wireless station that receives the data signal. Means for acquiring information indicating communication quality at the second radio station when communication is performed using a modulation method having a maximum transmission rate, and communication quality acquired by the acquisition means is predetermined. In the case where the quality is higher than the quality, guard interval length changing means for setting the length of the guard interval shorter than the currently set length is provided.

  The wireless communication device of the present invention is a wireless communication device that transmits a data signal with a guard interval added thereto to a communication partner wireless station, wherein the wireless station performs communication using a modulation method with a maximum transmission rate. Means for obtaining information indicating the communication quality of the radio station, and if the communication quality at the wireless station obtained by the obtaining means is equal to or higher than a predetermined quality, the length of the guard interval is set to a currently set length. And a guard interval length changing means for setting a shorter interval.

  Further, the method for changing the guard interval length in the wireless communication device of the present invention is the method for changing the guard interval length in the wireless communication device that communicates the data signal with the guard interval added thereto to the communication partner wireless station. Information indicating communication quality at the wireless station when performing communication using a modulation method is acquired, and when the acquired communication quality at the wireless station is equal to or higher than a predetermined quality, the guard interval It is characterized in that the length is set shorter than the currently set length.

  Furthermore, the wireless communication device of the present invention is a wireless communication device that transmits a data signal with a guard interval added thereto to a communication partner wireless station, and a directional antenna and means for determining the direction of arrival of radio waves from the wireless station; Means for setting the beam width of the directional antenna based on the determined direction of arrival, and if the set beam width is narrower than a predetermined range, the length of the guard interval is currently set Guard interval length changing means for setting the length shorter than the length is provided.

According to another aspect, the wireless communication device of the present invention is a wireless communication device that transmits a data signal to which a guard interval is added to a communication partner wireless station.
Means for determining the direction of arrival of radio waves from the radio station, and the tilt angle of the directional antenna can be controlled, and the tilt angle is set based on the determined direction of arrival of radio waves from the radio station And a guard interval length changing means for setting a length of the guard interval shorter than a currently set length when the set tilt angle is larger than a predetermined angle. It is characterized by.

  According to the present invention, it is possible to adaptively control the guard interval length by a simple method without requiring troublesome multipath detection.

  Embodiments of the present invention will be described below with reference to the drawings. The present invention is applicable to a cellular system composed of a base station and a mobile station, a wireless LAN system composed of an access point and a station, or an ad hoc wireless LAN system that communicates between stations without an access point. .

  FIG. 1 shows the configuration of a wireless device employing the present invention. FIG. 2 shows a second radio employing the present invention. The radio shown in FIG. 1 describes the transmitting side in detail, and the radio shown in FIG. 2 describes the receiving side in detail. Has a corresponding receiver / transmitter. In this embodiment, a cellular system composed of a base station and a mobile station will be described as an example. Therefore, description will be made assuming that the first radio shown in FIG. 1 is the base station side and the second radio shown in FIG. 2 is the mobile station side.

  This system transmits signals by OFDM communication. As shown in FIG. 1, in the OFDM scheme, first, error correction using turbo code is performed on data to be transmitted by the turbo encoding unit 101. An error correction code other than the turbo code may be used.

  The data modulation unit 102 performs primary modulation on the data subjected to error correction coding. The serial / parallel conversion unit 103 divides the data to be transmitted into the number of subcarriers, and the inverse Fourier transform unit 104 performs inverse Fourier transform processing to synthesize a modulated signal. Here, the primary modulation is variable according to the state of the transmission path, and is selected from BPSK, QPSK, 16-value QAM, and 64-value QAM. Although BPSK has a low transmission rate, it is excellent in noise / interference. Although 64-value QAM has a high transmission rate, it is vulnerable to noise and interference.

  In the combined signal, the guard interval adding unit 105 inserts a guard interval into the data so as to be strong against multipath. The digital OFDM signal to which the guard interval is added is converted into an analog signal by the radio unit 106, converted to an intermediate frequency radio signal, converted to a high frequency signal, amplified by the amplifying unit 107, and then transmitted from the antenna 108. Is done.

  A signal transmitted from the antenna 108 is received by the mobile device shown in FIG. 2, and a process reverse to the transmission process in FIG. 1 is performed. A signal is received by the antenna 201, and a high frequency is converted into a baseband signal by the wireless unit 202. The output of the radio unit 202 is sent to the time synchronization unit 203, where the guard interval insertion location is detected and sent to the GI removal unit 205. The guard interval is removed by the GI removal unit 205, the subcarrier signal is demultiplexed by the Fourier transform unit 206, and the digital signal is demodulated by the data demodulation unit 208 via the parallel / serial conversion unit 207. The demodulation result is subjected to error correction decoding by the turbo decoder 209. On the other hand, the quality of the received signal is measured by the quality measurement unit 210 based on the demodulation result, and information indicating the quality value is returned to the base station in FIG. 1 as FBI (Feedback Information) bits.

  The base station in FIG. 1 recognizes the communication quality of the current mobile station from the received FBI bit, and if it determines that the quality is excessive, the base station can change the modulation method to a method that can be sent at a higher transmission rate. Then, so-called adaptive control for reducing the transmission power is performed.

  FIG. 3 shows a modulation scheme and a transmission power control parameter set used in the adaptive control. Assume that communication is currently being performed in accordance with INDEX4 (modulation method: QPSK / transmission power: high). Suppose that quality is measured with a mobile device and it is detected that the quality is very good and the margin is 10 dB or more. In other words, if it is detected that there is no problem in quality even if the gain further decreases by 10 dB, the FBI bit indicating that the quality is excessive is generated by the FBI generation unit 211 of FIG. Sent back to the base station.

  The base station in FIG. 1 demodulates the received signal by the demodulation unit 109, extracts the FBI bit by the FBI bit extraction processing unit 110, recognizes that there is an excessive quality, and can communicate at another higher transmission rate. A data modulation unit that determines that it is possible and controls the modulation scheme control unit 111 with a control signal from the FBI bit extraction unit processing unit 110 and transmits the next packet by INDEX3 (modulation scheme: 16QAM / transmission power: large) 102 parts are controlled. When it is determined that the transmission power is excessive from the FBI bit sent back from the base station by performing communication with INDEX3 (it is assumed that the distance between the mobile station and the base station is close), INDEX2 (Modulation method: 64QAM / transmission power: small). Specifically, the TPC control unit (transmission power control unit) 112 controls the power amplifier 107 by a control signal from the FBI bit extraction processing unit 110.

  On the other hand, in communication using INDEX3, when the communication quality at the mobile station is poor and there are many data errors, INDEX5 (modulation method: BPSK / transmission power: large), which is resistant to noise and interference, although the transmission speed is one step lower. ) To communicate. By performing adaptive modulation, transmission is performed at different data rates, and communication at a variable transmission rate is performed.

  By combining the adaptive modulation method that adaptively changes the modulation method and the transmission power control that switches the transmission power according to the quality, a larger amount of data is transmitted when the quality is higher, and the amount of data is reduced when the quality is lower. As a modulation scheme resistant to noise / interference, reliable data transmission can be performed.

  In the present invention, a function for adaptively controlling the guard interval (GI) length is added here. As shown in FIG. 1, a GI length control unit 113 is provided which receives a modulation scheme and a transmission power control value as input and further inputs an FBI bit. As shown in FIG. 3, the combination that obtains the maximum transmission rate in the system when the adaptive modulation scheme that adaptively changes the modulation scheme and the transmission power control that switches the transmission power according to the quality is the most transmitted. When the transmission power control is set to the lowest power (INDEX1) and the result is that the quality is still excessive, the GI length is shortened from the next packet. A new INDEX0 for performing communication is provided. In this embodiment, when it is notified that the modulation method is the maximum rate, the transmission power is the minimum, and there is a margin in quality with the FBI bit, communication is performed with the GI length shortened from the next packet.

  FIG. 4 shows a simple signal format. (A) is a signal format corresponding to INDEX1 to INDEX5 in FIG. 3, and transmission is performed by adding GI (signal length T2) to the data symbol (signal length T1). FIG. 6B shows a signal format corresponding to INDEX0, and transmission is performed by adding a GI having a signal length of T3, which is ½ the signal length of FIG. In (a) and (b), although the same number of symbols is transmitted, (b) can be transmitted in a short time, and the transmission rate is equivalently high.

  The GI length is set in consideration of a multipath delay amount (delay time) that can be considered in a normal system. It is obvious that the transmission rate can be increased by shortening the GI length. However, if the GI length is shortened unnecessarily, the reception quality is significantly deteriorated due to the influence of multipath delay. In the present invention, the GI length is determined based on the transmission power value by transmission power control or the modulation scheme selection of adaptive modulation. The ability to transmit at a high transmission rate is an environment with good transmission conditions in which the base station and the mobile station are in the vicinity. Also, a small transmission power value is equivalent to an environment with good transmission conditions, that is, the base station and the mobile station are in the vicinity. The fact that the base station and the mobile station are in the vicinity and the transmission conditions are good means that there is a very high probability that the influence of the multipath delay is small, and in this case, the GI length is excessively given. Is equivalent. In the present invention, since the transmission condition is recognized from the transmission power value by transmission power control or the modulation scheme selected by adaptive modulation, it is not necessary to perform troublesome multipath detection to control the GI length. When the transmission conditions are good, the transmission speed and throughput can be improved by controlling to eliminate unnecessary GI sections.

  When the GI length is variable on the base station side, reception must be performed with the GI length changed on the mobile station side. For this, a method similar to the conventional adaptive modulation method can be used. In adaptive modulation, the control signal notifies in advance at which timing the modulation scheme is to be changed, and at the time, the mobile station and the base station simultaneously change the data, as shown in the signal format of FIG. This is a method of determining at the head of a packet which modulation method is used in the preamble attached before the symbol, and immediately receiving in a different reception format in the data symbol portion. As described above, if a method conventionally used in adaptive modulation is used, it is possible to change the format used for communication.

  In this embodiment, the determination of GI length switching is based on the selection of the modulation method for the maximum transmission rate and the transmission at the minimum transmission power, but the present invention is not limited to the maximum or minimum event. When there are a plurality of modulation schemes, for example, there are five modulation schemes A, B, C, D, E, A, B and C, D, E are divided into groups, and A, B, In addition, when it is determined that the quality is excessive, the GI length can be shortened. Further, when the transmission power has a dynamic range of −70 DBM to +10 DBM, it is also possible to provide a threshold value for −50 DBM, and to control the GI length to be shortened when the transmission power becomes equal to or less than the threshold value.

  In this embodiment, the control of the GI length is determined by the combination of the modulation method and the transmission power control. However, in the system having only the transmission power control without performing the adaptive modulation, the determination of the GI length is performed only by the transmission power value. It is also possible to perform GI length determination only by selecting the other modulation method. The INDEX is not limited to the example shown in FIG. For example, an example as shown in FIG. 5 is also possible.

  In the example of FIG. 3, the GI length is changed when INDEX1 is shifted to INDEX0. On the other hand, in FIG. 5, the GI length is changed from INDEX2 to INDEX1. Then, the transmission power is changed from INDEX1 to INDEX0, and finally INDEX for controlling the transmission power is set. First, when it is determined that the quality is better by changing the GI length, transmission power control should be performed last. When it is determined that the quality is excessive in INDEX2, the transmission power as shown in FIG. 3 is controlled to be small, the interference to other users is reduced, and the GI length of the user is controlled to be short. Although the method shown in FIG. 5 for increasing the speed is conceivable, the method shown in FIG. 5 can increase the probability that the transmission speed of the user can be increased as compared with the method shown in FIG. It is selected from FIG. 3 and FIG. 5 whether priority is given to increasing the capacity of the entire system by suppressing interference to other users or priority is given to increasing the transmission speed of a specific user.

  In the examples of FIGS. 3 and 5, the modulation scheme and transmission power control are used as the parameter set, but the coding rate of the error correction code may be added. In this way, finer adaptive modulation becomes possible.

  Next, another embodiment will be described with reference to FIG.

  FIG. 6 is a block diagram of the base station side showing another embodiment. The base station 600 is characterized by including an antenna (directional antenna 601) capable of adaptively controlling directivity. The same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  The directivity determining unit 602 determines from which direction the radio wave is coming based on the signal from the mobile station. The directivity determining unit 602 estimates and determines from which direction the radio wave is received from the time difference or the phase of the signal received by each antenna of the directional antenna 601. As a determination method, a MUSIC method known as a radio wave arrival direction estimation technique may be used. The directivity determining unit 602 determines what directivity the directional antenna should have from the determination result, supplies a control signal to the directivity control unit 603, and forms the antenna directivity.

  Further, the directivity determining unit 602 supplies information on what directivity the antenna has to the GI length control unit 113, and the GI length control unit 113 determines the degree of directivity formed for the mobile device. To control the GI length. If the beam width when the directional beam is formed is equal to or smaller than a predetermined threshold value (angle), it is determined that an antenna with high directivity is used, and the GI length is set short. With respect to the beam width of the directional beam, an angle at which the level is, for example, 20 dB lower than the maximum gain is defined on both sides around the angle having the maximum gain, and the number of angles between them is calculated. For example, if the angle is 30 degrees or less, the GI length is short, and if the angle is 30 degrees or more, the GI length is not changed and remains long. That is, when transmission is performed from the base station to the mobile station with directivity having a narrow beam width, reflection from others is reduced. In other words, the mobile station has a very high probability that the multipath delay wave will be reduced. In this case, this is equivalent to an excessive GI length. For example, a table as shown in FIG. 7 is prepared in the GI length control unit 113. When the beam width is narrow (less than 30 degrees in FIG. 7), the guard interval is set so that the GI length control unit 113 shortens the GI length. The adding unit 105 is controlled.

  In the above embodiment, the GI length is controlled based on the beam width. However, the GI length may be controlled by the tilt angle of the antenna. As shown in FIG. 8, when a base station (access point) is installed on the ceiling in the room, the directional antenna receives the direction from which the radio wave comes by controlling the tilt angle of the antenna. The directivity determining unit 602 determines from the radio wave. When the tilt angle is small (θ1), there is a high possibility of communication with a distant mobile station (STA1). In this case, multipulses from distant reflectors are assumed. On the other hand, when the tilt angle is large (θ2), it is determined that the mobile station (STA2) is at a position close to the position immediately below. In such a situation, there is less reflection from others. In other words, the mobile station has a very high probability that the multipath delay wave will be reduced. In this case, this is equivalent to an excessive GI length. For example, a table as shown in FIG. 9 is prepared in the GI length control unit 113, and when the tilt angle is large (30 degrees or more in FIG. 9), the GI length control unit 113 guards to shorten the GI length. The interval adding unit 105 is controlled.

  Also in this embodiment, it is not necessary to perform troublesome multipath detection in order to control the GI length. When the transmission conditions are good, control is performed so as to eliminate unnecessary GI sections, so that the transmission speed can be improved and the throughput can be improved.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram which shows schematic structure of the base station by which this invention is used. The block diagram which shows the outline of the mobile station by which this invention is used. The table | surface which shows the parameter set used when performing adaptive control. The figure which shows the signal format containing a guard interval (GI). The table | surface which shows another example of the parameter set used when performing adaptive control. The schematic block diagram of the base station which shows the other Example of this invention. The table | surface which shows the correspondence of beam width and GI length to set. The figure which shows the tilt angle in case the base station (access point) is installed in the ceiling in the room. The table | surface which shows the correspondence of a tilt angle and GI length to set.

Explanation of symbols

100, 600 ... Base station.
102: Data modulation unit.
105: A guard interval adding unit.
110: FBI bit extraction processing unit.
112: Transmission power control unit.
113... GI length control unit.
200: Mobile station.
210: Quality measurement unit.

Claims (6)

In a wireless communication system comprising a first wireless station that transmits a data signal with a guard interval added and a second wireless station that receives the data signal,
Means for obtaining information indicating communication quality at the second wireless station when communication is performed using a modulation method having a maximum transmission rate;
When the communication quality acquired by the acquisition means is equal to or higher than a predetermined quality, the guard interval length changing means is provided for setting the length of the guard interval to be shorter than the currently set length. Wireless communication system. The first radio station further includes transmission power control means, and when the communication quality at the second radio station when the transmission power is set to the minimum is equal to or higher than a predetermined quality, the guard 2. The wireless communication system according to claim 1, wherein the interval length changing means sets the length of the guard interval to be shorter than the currently set length.   The radio communication system according to claim 1, wherein the first radio station performs adaptive control using the type of the modulation scheme and a set value of transmission power by the transmission power control means as parameters.   4. The wireless communication system according to claim 3, wherein the parameter includes a coding rate value of an error correction code. In a wireless communication device that transmits a data signal to which a guard interval is added to a communication partner wireless station,
Means for acquiring information indicating communication quality at the wireless station when performing communication using a modulation method having a maximum transmission rate;
Guard interval length changing means for setting the length of the guard interval shorter than the currently set length when the communication quality at the wireless station acquired by the acquiring means is equal to or higher than a predetermined quality. A wireless communication device characterized by the above. In the method for changing the guard interval length in the wireless communication device for communicating the data signal with the guard interval added to the wireless station of the communication partner,
Obtaining information indicating the communication quality at the wireless station when performing communication using the modulation method with the maximum transmission rate,
A method of changing a guard interval length, characterized in that, when the acquired communication quality at the wireless station is equal to or higher than a predetermined quality, the guard interval length is set shorter than a currently set length.

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