JP2008277900A - Ofdm communication device and adaptive speed control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique relating an OFDM communication device and adaptive speed control that adaptively control a communication speed according to the quality of a communication line without using a training signal. <P>SOLUTION: The OFDM communication device 1 sections a plurality of carriers into a plurality of blocks as unit block wherein adjacent carries are put together, generates an OFDM symbols for header information by using the same modulation systems for all the blocks, and generates a transmission frame by adding an error detection code so that code error detection can be performed by the blocks, thereby transmitting the transmission frame to an OFDM communication device as a communication opposite side. Then a result of error detection is received from the OFDM communication device as the opposite side, and a header analyzing unit 116 extracts the result of error detection and transmits it as reception possible/impossible state information 52 to a speed power control unit 117, which determines modulation systems by the blocks based upon the reception possible/impossible state information 52 and the S/N of the received signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an OFDM communication apparatus that uses an OFDM (Orthogonal Frequency Division Multiplexing) communication system to adaptively control a communication speed according to the quality of a communication channel, and to a technique related to adaptive speed control.

  The OFDM communication system is a system in which a plurality of carriers are arranged at equal intervals on the frequency axis with a minimum frequency interval that can be demodulated, and each carrier is modulated by data for communication. Since the frequency utilization efficiency, which is the ratio between the communication speed and the used frequency bandwidth, is high, it is widely adopted as a communication method such as ADSL (Asymmetric Digital Subscriber Line) and wireless LAN (Local Area Network).

  By the way, the environment surrounding the communication path is changing every moment. In wired communication, noise from a noise generation source is superimposed on a communication signal, the signal-to-noise ratio (S / N ratio) varies, or the type or number of devices connected to the communication path changes. Quality (attenuation amount frequency characteristic) of the communication signal is changed, and the received power intensity of the communication signal varies. Such fluctuations in the S / N ratio and received power intensity occur similarly in the case of wireless communication. That is, noise is superimposed on a communication signal, or a multipath is formed by the appearance of an object that interrupts radio propagation, or reflection on a wall surface of a building, thereby changing the S / N ratio or the received power intensity.

Therefore, a method for controlling the communication speed in accordance with the quality of the communication path has been considered.
For example, before transmitting data, a training signal that is known data is transmitted, and a code error rate, a received power intensity, and an S / N ratio relating to the training signal are measured on the receiving side. Then, a method is disclosed in which those results are returned to the transmission side, and on the transmission side, the communication speed is changed for each carrier or a plurality of carriers based on the returned measurement result. (See Patent Document 1)
Japanese Patent Laying-Open No. 2006-25067 (see paragraphs 0013 to 0014)

  However, according to the method using the training signal described above, data cannot be transmitted while the training signal is being transmitted, so that there is a problem in that a communication waiting time occurs and efficiency is deteriorated.

  Accordingly, the present invention has been made to solve the above-described problem, and there is no need to transmit a training signal, and an OFDM communication apparatus and adaptive speed control that adaptively control the communication speed according to the quality of the communication path. It is an object to provide technology related to the above.

  The adaptive speed control method according to the present invention is configured to change the data modulation method (speed) for each block unit in which a plurality of carriers are combined. For each block, control is performed to adaptively change the speed of data to be transmitted based on the S / N ratio calculated from the code error rate and the received power intensity. The code error rate is obtained by detecting whether or not data has been received correctly (whether or not it has been received correctly) for each block of the received communication signal on the communication partner side without using a training signal. Is stored in an Ack signal (response to reception) and returned. The received power intensity (S) and noise power intensity (N) are calculated from the received communication signal.

  According to the present invention, since it is not necessary to transmit a training signal, a decrease in efficiency can be prevented or efficiency can be improved as communication waiting time occurs. In addition, since the communication speed is adaptively controlled according to the quality of the communication channel, it is possible to prevent a decrease in efficiency due to data retransmission.

  Next, the best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described in detail with reference to the drawings as appropriate.

(Embodiment)
A hardware configuration of the OFDM communication apparatus according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a hardware configuration of the OFDM communication apparatus 1.
As shown in FIG. 1, the OFDM communication device 1 includes a processing unit 10, an input / output unit 20, and a storage unit 30.

  The processing unit 10 includes a central processing unit (CPU) 11 that executes arithmetic processing, and a main memory 12 that is a storage unit that the CPU 11 uses for arithmetic processing. The main memory 12 is realized by a RAM (Random Access Memory) or the like. Then, an application program stored in a storage unit 30 such as a ROM (Read Only Memory), a flash memory, or a hard disk device (not shown) is developed in the RAM, and the CPU 11 implements various processes by executing it.

  The input / output unit 20 includes an input / output interface 21 and an AD / DA converter 22. In the case of a wired connection, the input / output interface 21 takes in or outputs a communication signal to a communication path (not shown). In the case of wireless, signal input / output is performed via an antenna (not shown). Then, the level of the input / output signal is appropriately adjusted by the amplifier. The AD / DA converter 22 converts the analog signal received from the input / output interface 21 into a digital signal and converts it into a signal that can be processed by the processing unit 10 of the OFDM communication apparatus 1, or vice versa. The data (digital signal) generated by the processing unit 10 is converted into an analog signal and output from the input / output interface 21 to a communication path (not shown).

  The storage unit 30 stores various data and calculation results used by the CPU 11 for calculation processing, or data transmitted and received by the input / output unit 20 in the database 31 and the like. The storage unit 30 is realized by a flash memory or a hard disk device.

(Function of OFDM communication device)
Next, functions of the OFDM communication apparatus 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing the expanded function of the OFDM communication apparatus 1.
The OFDM communication apparatus 1 includes a processing unit 10, an input / output unit 20, and a storage unit 30, as shown in FIG.

  The input / output unit 20 includes a DA converter 106 that DA-converts the signal generated by the processing unit 10, a transmission amplifier 107 that adjusts the magnitude (gain) of the output signal of the DA converter 106, and a communication path (not connected). A reception amplifier 110 that adjusts the magnitude (gain) of a signal received from the figure, and an AD converter 111 that AD converts the output of the reception amplifier 110.

  The processing unit 10 includes a synchronization signal generation unit 101, a header generation unit 102, a mapper unit 103, an IFFT (Inverse Fast Fourier Transform) unit 104, a GI (Guard Interval) addition unit 105, and data used when transmitting data. Synchronization signal removal section 112, GI removal section 113, FFT (Fast Fourier Transform) section 114, demapper section 115 and header analysis section 116, and OFDM communication speed (modulation method) control and transmission power It is comprised by the speed electric power control part 117 which produces | generates the information for control.

The synchronization signal generation unit 101 is activated when transmission data is stored in a buffer memory (not shown), and outputs a synchronization signal. The synchronization signal may be generated every time it is activated, or a synchronization signal that has already been generated may be read from the storage unit 30.
The header generation unit 102 generates header information related to a source address, a destination address, a modulation scheme type (speed), and the like.
The mapper unit 103 converts the data to be transmitted into IQ coordinate (orthogonal coordinate) values (IQ data) using the modulation method determined by the speed power control unit 117.
The IFFT unit 104 performs inverse Fourier transform on the IQ data converted by the mapper unit 103 to convert it into a time signal.
GI adding section 105 adds a signal in the guard interval section between the signal (symbol) converted by IFFT section 104 and the next signal (symbol). For example, in a wireless transmission path, when not only a direct wave but also an indirect wave by a multipath is received in a superimposed manner, the effect of adding this guard interval is noticeable. That is, since the guard interval is added, even if the indirect wave is delayed and superimposed on the direct wave, the preceding and succeeding signals (symbols) are not mixed and can be demodulated correctly.

The synchronization signal removal unit 112 performs synchronization signal detection and removes the synchronization signal.
The GI removal unit 113 removes the interval of the guard interval from the signal.
The FFT unit 114 converts the signal into IQ data.
The demapper unit 115 converts the IQ data calculated by the FFT unit 114 into a digital signal (received data) using the modulation method determined by the speed power control unit 117.
The header analysis unit 116 extracts a header stored in the received data.

  The speed power control unit 117 obtains necessary information and performs a predetermined calculation in order to determine the type (speed) of the modulation method and the magnitude of the transmission power, thereby performing the predetermined calculation. Determine the transmission power intensity. Based on the result, information necessary for processing in each unit is output to the mapper unit 103, the demapper unit 115, and the like.

  The database 31 of the storage unit 30 stores data to be transmitted and received, data necessary for calculation by the speed power control unit 117, functions necessary for calculation by the processing unit 10, and the like.

(Processing flow in OFDM communication apparatus)
Next, the flow of processing in the OFDM communication apparatus 1 will be described with reference to FIGS. FIG. 3 is a diagram illustrating signal transmission / reception in the OFDM communication apparatus 1. FIG. 4 is a diagram showing a flow of processing in the OFDM communication apparatus (transmission side) 1a.

As shown in FIG. 3, in the embodiment of the present invention, the OFDM communication apparatus (transmission side) 1a transmits a transmission signal 44, and the OFDM communication apparatus (reception side) 1b that receives the transmission signal 44 responds to the reception. By sending back an Ack signal 45, data transmission / reception is realized.
Since the communication path between the transmission side 1a and the reception side 1b is assumed to change the quality of the communication path every moment, the reception side 1b determines whether the received transmission signal 44 is received correctly or not. Thus, the quality of the communication path is transmitted to the transmission side 1a by storing the reception correct / incorrect information in the Ack signal 45 and returning it.

  The configuration of the OFDM communication apparatus 1 is not different between the transmission side 1a and the reception side 1b, but the processing is slightly different between the transmission side 1a and the reception side 1b. That is, on the transmission side 1a, the transmission signal 44 modulated transmission data is transmitted to the communication path, the Ack signal 45 is received, and information on the quality of the communication path (reception correct / incorrect information) is received from the Ack signal 45. Processing to obtain is performed. On the other hand, on the receiving side 1b, processing for receiving the transmission signal 44 and acquiring data, processing for determining whether the received transmission signal 44 is received correctly, and storing and returning the reception accuracy information in the Ack signal 45 Is done.

  Therefore, the processing flow will be described below separately for the transmitting side 1a and the receiving side 1b.

(Transmission processing of transmission signal 44 on the transmission side)
First, the processing flow of the OFDM communication apparatus (transmission side) 1a will be described with reference to FIG. FIG. 4 is a diagram showing a processing flow of the OFDM communication apparatus (transmission side) 1a.
The transmission data 40 is temporarily stored in a buffer memory (not shown), and processing is started. First, the synchronization signal generation unit 101 reads an already created synchronization signal from the storage unit 30 (see FIG. 2). The synchronization signal is converted into an analog signal via the DA converter 106 and stored in a buffer memory (not shown), and then the signal level is adjusted by the transmission amplifier 107 and output to the communication path 70. The synchronization signal may be newly generated by the synchronization signal generation unit 101.
Next, the header generation unit 102 extracts header information of the transmission data 40 (for example, a transmission source address or a transmission destination address), and further, speed setting information 51 determined by the speed power control unit 117, that is, modulation. Information related to the type (speed) of the method is added to generate a header. Then, the mapper unit 103 converts the header into an IQ coordinate (orthogonal coordinate) value (IQ data). For the header, the mapper unit 103 modulates all carriers by QPSK (Quadrature Phase Shift Keying) that performs 2-bit modulation. Then, the IQ data is subjected to inverse Fourier transform by the IFFT unit 104, a guard interval is added by the GI adding unit 105, DA converted by the DA converter 106, and stored in a buffer memory (not shown), and then a transmission amplifier. The signal level is adjusted by 107 and sent to the communication path 70.
Next, the process for the transmission data 40 is almost the same as the process for the header. The difference is that the mapper unit 103 is adaptively modulated by the modulation scheme determined by the speed power control unit 117.
The signal level is adjusted based on the transmission power intensity information 55 determined by the speed power control unit 117. The signal level is adjusted by the mapper unit 103 and the transmission amplifier 107.

Here, the modulation method in the mapper unit 103 will be described in more detail with reference to FIG. 5 (see FIG. 4 as appropriate). FIG. 5 is a diagram illustrating an example in which a plurality of carriers are grouped into one block.
FIG. 5 shows, as an example, a case where four blocks are grouped with the number of carriers set to 8 when the number of carriers is 32. In the embodiment of the present invention, the modulation method is determined in units of blocks. That is, for each block, the carrier is modulated by the same modulation scheme.
Modulation methods include QPSK for 2-bit modulation, 16QAM (Quadrature Amplitude Modulation) for 4-bit modulation, and 64QAM for 6-bit modulation.
The modulation method to be used is determined by the speed power control unit 117 in units of blocks and output as speed setting information 51.
Again, for the header, QPSK is used as the modulation method for all blocks, and for the transmission data 40, the modulation method assigned to each block is used.
Note that a method of determining a modulation scheme in the speed power control unit 117 will be described later.

Next, an example of the frame format of the transmission signal 44 (see FIG. 3) will be described with reference to FIG. FIG. 6 is a diagram illustrating an example of the frame format of the transmission signal 44.
The order in which the frames are stored is the synchronization 301, the header portion 302 (302a, 302b), and the data portion 303 (303a, 303b,... 303n). Here, synchronization 301, header a (302a), header b (302b), data a (303a), data b (303b),... Data n (303n) each represent a unit called an OFDM symbol.
In FIG. 6, the header section 302 is shown for the case where there are two OFDM symbols. However, if all header information can be stored in one OFDM symbol, the header section 302 may include only the header a (302a). Further, the header information may be stored in three or more OFDM symbols.
Note that “corresponding to a predetermined position” described in the claims corresponds to the header portion 302 in the embodiment of the present invention. That is, it is predetermined that QPSK is used as a modulation method for all blocks for the header portion 302 stored after the synchronization 301. If the OFDM symbol “corresponding to a predetermined position” is determined in advance in the data unit 303, the “predetermined position” is stored in the storage unit 30. The “predetermined position” may be read out and the corresponding position may be determined in the processing unit 10.

Next, an example of the frame format of the header portion 302 of the transmission signal 44 (see FIG. 6) will be described using FIG. 7 (see FIGS. 4 and 6 as appropriate). FIG. 7 is a diagram illustrating an example of the frame format of the header portion 302 of the transmission signal 44.
In FIG. 7, the header section 302 stores a source address 311 and a destination address 312 read from the transmission data 40. Next, the speed setting information 313 of the data portion, which is the modulation method (speed) determined by the speed power control unit 117, is stored. Next, communication control information 314 such as transmission power intensity other than the speed setting information 313 in the data portion is stored. A CRC (Cyclic Redundancy Check) code 315 is stored at the end of the frame in order to detect errors in units of blocks. However, other error detection codes may be used as long as error detection can be performed.

  In addition, in order to know whether each block is received correctly (whether it has been received correctly or whether a code error has been detected), it is necessary to transmit the information of the header section 302 by all the blocks. Therefore, the information of the same header part 302 is transmitted by all the blocks.

(Reception processing of Ack signal on transmission side)
Next, processing for the received Ack signal will be described with reference to FIGS. FIG. 8 is a diagram illustrating an example of a frame format of the Ack signal 45 (see FIG. 3). FIG. 9 is a diagram illustrating an example of a frame format of the header 402 of the Ack signal 45.
The frame format of the Ack signal 45 includes a synchronization 401 and a header 402 as shown in FIG.
As shown in FIG. 9, the information stored in the header 402 includes a source address 411, a destination address 412, a data portion speed setting information 413, a header portion reception correct / incorrect information 414, and a data portion reception correct / incorrect. Information 415 and CRC code 416. The reception correct / incorrect information 414 for each block in the header part and the reception correct / incorrect information 415 for the data part are extracted by the header analysis unit 116 (see FIG. 4).

  Returning to FIG. 4 (see 8, 9 as appropriate), the Ack signal 45 received via the communication path 70 is temporarily stored in a buffer memory (not shown). At this time, as shown in FIG. 8, since it is detected that the data portion is not included, it is determined that the signal is the Ack signal 45. Then, the signal level is adjusted by the receiving amplifier 110, converted to a digital signal by the AD converter 111, the synchronization signal is removed by the synchronization signal removal unit 112, and the guard interval is removed by the GI removal unit 113. Then, the FFT unit 114 converts the value into IQ coordinates (orthogonal coordinates) (IQ data) by Fourier transformation. Then, the demapper unit 115 demodulates all blocks by QPSK, and converts IQ data into received data 41. That is, the information of the header 402 stored in the Ack signal 45 is acquired.

The header analysis unit 116 extracts reception correct / incorrect information 414 for each block in the header part and reception correct / incorrect information 415 for the data part from the received data 41. Then, the reception correct / incorrect information 414 for each block of the header part is transmitted to the speed power control unit 117 as the reception correct / incorrect information 52.
Further, the data portion reception correct / incorrect information 415 indicates whether or not the data portion 302 (see FIG. 6) has been correctly received. If the data part 303 is not correctly received, the reliability of communication is ensured by retransmitting from the transmission side 1a.
In the speed power control unit 117, the reception correct / incorrect information 52 is accumulated for a predetermined number (or a predetermined period) to finally determine the speed setting information 51. Details will be described later.

(Reception processing on the receiving side)
First, processing when the transmission signal 44 (see FIG. 3) is received will be described using FIG. 10 (see FIGS. 6, 7, and 9 as appropriate).
The signal level of the transmission signal 44 (see FIG. 3) received via the communication path 70 is adjusted by the reception amplifier 110. Then, it is temporarily stored in a buffer memory (not shown). At this time, as shown in FIG. 6, since it is detected that the data portion 303 is included, it is determined that it is not the Ack signal 45.
The signal whose level is adjusted by the reception amplifier 110 is converted into a digital signal by the AD converter 111, the synchronization signal is removed by the synchronization signal removal unit 112, and the guard interval is removed by the GI removal unit 113. Then, the FFT unit 114 converts the value into IQ coordinates (orthogonal coordinates) (IQ data) by Fourier transformation. Then, the demapper unit 115 converts the IQ data, accumulates it in a buffer memory (not shown), and obtains it as received data 41.

The reception gain information 54 relating to the adjusted level is transmitted to the speed power control unit 117 for use in the calculation of the reception power intensity.
Further, the IQ data information 53 is transmitted to the speed power control unit 117 for use in calculation of received power intensity.
Further, in the demapper unit 115, the modulation scheme for the header unit 302 is defined as QPSK, so that all blocks (carriers) are demodulated by QPSK. On the other hand, for the data part 303, the speed setting information 313 of the data part extracted by the header analysis part 116 is transmitted to the speed power control part 117. Thereafter, the speed power control unit 117 transmits the speed setting information 51 to the demapper unit 115 and is used for demodulation of the data unit 303.
In addition, the header analysis unit 116 uses the CRC code 315 to perform error detection on the header unit 302 in units of blocks and detect whether there is an error in the received information of the header unit 302. For example, when no error is detected, no bit is set (bit is set to 0), and when an error is detected, a bit is set (bit is set to 1) to generate header as reception correct / incorrect information 52. To the unit 102. The reception correct / incorrect information 52 is stored in the header 402 of the Ack signal 45 (see FIG. 8) as reception correct / incorrect information 414 for each block of the header portion.
Further, the processing unit 10 detects a code error in the data unit 303 using a CRC code (not shown) added to the end of the data unit 303, and whether there is an error in the received information in the data unit 303. Detection is performed. For example, when no error is detected, no bit is set (bit is set to 0), and when an error is detected, a bit is set (bit is set to 1) to generate header as reception correct / incorrect information 52. To the unit 102. The reception correct / incorrect information 52 is stored in the header 402 of the Ack signal 45 as the reception correct / incorrect information 415 of the data portion.

(Ack signal transmission processing on the receiving side)
Processing for generating the Ack signal 45 (see FIG. 3) will be described with reference to FIG. 10 (see FIGS. 8 and 9 as appropriate). FIG. 10 is a diagram illustrating a processing flow of the OFDM communication apparatus (reception side) 1b.
The Ack signal 45 has a frame format as shown in FIG. 8, and includes only the synchronization 401 and the header 402.
First, in the reception process described above, when reception data 41 is accumulated in a buffer memory (not shown), the synchronization signal generation unit 101 reads an already created synchronization signal from the storage unit 30 (see FIG. 2). The synchronization signal is converted into an analog signal via the DA converter 106, stored in a buffer memory (not shown), and the signal level is adjusted by the transmission amplifier 107 and output to the transmission line 70. The synchronization signal may be newly generated by the synchronization signal generation unit 101.
Next, the header generation unit 102 acquires the transmission source address 411 and the transmission destination address 412 extracted from the reception data 41 by the header analysis unit 116 as the address information 56, and the speed setting information of the data unit from the speed power control unit 117. 413 is acquired, the reception correct / incorrect information 414 for each block of the header part and the reception correct / incorrect information 415 of the data part are acquired as the receive correct / incorrect information 52 from the header analysis unit 116, and a CRC code 416 is further added to the header 402. Generate. Then, the mapper unit 103 converts the value into IQ coordinates (orthogonal coordinates) (IQ data) by QPSK. The subsequent processing, which is performed in the IFFT unit 104, the GI adding unit 105, the DA converter 106, and the transmission amplifier 107, is the same as the transmission processing of the transmission signal 44 on the transmission side described above, and thus the description thereof is omitted. To do.

  Here, in the OFDM communication apparatus 1 according to the embodiment of the present invention, the processing of the header analysis unit 116 as the main part and the processing of the speed power control unit 117 will be described in detail.

(Processing of header analysis unit 116)
First, the processing of the header analysis unit 116 on the transmission side 1a will be described with reference to FIG. 4 (see FIG. 9 as appropriate).
The header analysis unit 116 extracts the header 402 stored in the Ack signal 45 (see FIG. 8). Then, with respect to the reception correct / incorrect information 414 for each block of the extracted header part, a CRC code is used to determine whether the reception is correct (no error is detected and received correctly) and whether or not the reception is correct (error is detected). Then, it is transmitted to the speed power control unit 117 as the reception correct / incorrect information 52.

Next, processing of the header analysis unit 116 on the receiving side 1b will be described with reference to FIG. 10 (see FIG. 7 as appropriate).
The header analysis unit 116 extracts the header unit 302 stored in the transmission signal 44 (see FIG. 6). The transmission source address 311 and the transmission destination address 312 are transmitted to the header generation unit 102 as address information 56 for storage in the Ack signal 45 (see FIG. 8). Further, the speed setting information 313 in the data part is transmitted to the speed power control unit 117 as the speed setting information 51 and used for demodulation in the demapper unit 115. Further, the header analysis unit 116 performs error detection for each block using the CRC code 315 and determines whether or not the reception is correct. The determination result is transmitted to the header generation unit 102 as reception correct / incorrect information 52 and stored in the Ack signal 45.

(Processing of speed power control unit 117)
Next, the processing of the speed power control unit 117 will be described with reference to FIG. 11 (see FIGS. 4 and 10 as appropriate). FIG. 11 is a diagram illustrating a method for calculating the speed setting information 51 in the speed power control unit 117.
In order to calculate the speed setting information 51, the speed power control unit 117 acquires reception correct / incorrect information 52 from the header analysis unit 116, IQ data information 53 from the FFT unit 114, and reception gain information 54 from the reception amplifier 110.
The reception correct / incorrect information 52 is input to a BER (Bit Error Rate) calculation unit 611 for each block. When a predetermined number (or a predetermined period) of reception correct / incorrect information 52 is input, the reception positive number (the number of correctly received) and the number of reception rejection (the number of detected errors) are separately blocked. The BER for each block is calculated by dividing the number of reception rejections by the total number of reception correct / incorrect information 52 that is accumulated every time and stored in the storage unit 30. The predetermined number (or predetermined period) described above is preferably set shorter than the span of the quality change of the communication path.

Further, the IQ data information 53 is input to the received power intensity calculation unit 613. Then, an amplitude value (power intensity) is obtained from the IQ data, the amplitude value is corrected by the reception gain information 54, and the reception power intensity is calculated. By this calculation, the received power intensity for each carrier is obtained.
However, the received power intensity obtained here is the power intensity of a signal on which noise is superimposed. Therefore, the received power intensity calculation unit 613 estimates the S / N ratio.

Next, the reception power intensity for each block calculated by the reception power intensity calculation unit 613 is input to the minimum S / N ratio calculation unit 614 for each block. Then, a minimum S / N ratio for each block is calculated.
For example, when it is estimated that there is little external noise (noise superimposed on the communication channel), the noise (N) included in the IQ data is dominated by the noise generated by the reception amplifier 110, the AD converter 111, and the like. It is considered to be appropriate. Therefore, the power intensity of the noise can be measured in advance and stored in the storage unit 30. When calculating the S / N ratio, it is possible to read the power intensity of this noise from the storage unit 30 and estimate the S / N ratio for each carrier.
On the other hand, when it is estimated that the noise from the outside is large, it is possible to calculate the S / N ratio using a method (known method) for estimating the S / N ratio from the modulation method and the BER. Become. That is, since the modulation scheme is QPSK and the BER is acquired from the BER calculation unit 611 for each block, it is possible to estimate the S / N ratio using these modulation schemes and BER. Note that a table or a mathematical expression in which the relationship between the modulation method, the BER, and the S / N ratio is associated is stored in the storage unit 30.

Then, the S / N ratio (first S / N ratio described in the claims) obtained for the case where it is estimated that the noise from the outside is small and the case where the noise from the outside is estimated to be large were obtained. A smaller S / N ratio is calculated by comparing the S / N ratio (the second S / N ratio described in the claims).
In this way, the minimum S / N ratio for each block is calculated by the minimum S / N ratio calculation unit 614 for each block.

Then, a BER for each block is input from the BER calculation unit 611 for each block, and a minimum S / N ratio for each block is input from the minimum S / N ratio calculation unit 614 for each block to the speed determination unit 612 for each block. The Here, the speed is determined using a method (known method) for determining the speed (modulation method) from the S / N ratio and the BER. In the embodiment of the present invention, since the minimum S / N ratio is input, it is possible to determine the speed (modulation method) on the safe side (it is difficult for a code error to occur).
In this way, the speed setting information 51 is generated by the speed power control unit 117.

(Modification)
Next, when communication is performed between OFDM communication apparatuses using a communication line, transmission is not performed using all blocks, but is selected according to the number of selected blocks. A method for controlling the power will be described with reference to FIGS. FIG. 12 is a diagram illustrating a state in which a plurality of OFDM communication apparatuses are connected to the communication line. (A) of FIG. 13 is a figure which shows the electric power in the case of transmitting all the blocks, (b) is a figure which shows the electric power in the case of transmitting some blocks.

Generally, as the communication line becomes longer (goes farther), the attenuation amount in the communication frequency band increases and the attenuation amount in the high frequency band becomes remarkably large. When the amount of attenuation increases, the S / N ratio decreases and the code error increases, so that the communication speed cannot be increased.
This will be described with reference to the case shown in FIG. The distance between the OFDM communication apparatus 701 and the OFDM communication apparatus 702 is shorter than the distance between the OFDM communication apparatus 701 and the OFDM communication apparatus 703. Therefore, the signal attenuation is small between the OFDM communication apparatus 701 and the OFDM communication apparatus 702, whereas the signal attenuation is large between the OFDM communication apparatus 701 and the OFDM communication apparatus 703. Therefore, if the OFDM communication apparatus 701 communicates with the OFDM communication apparatus 702 and communicates with the OFDM communication apparatus 703 with the same transmission power per block, the received power in the OFDM communication apparatus 703 is assumed. The strength is smaller than the received power strength in OFDM communication apparatus 702. Therefore, it is assumed that the OFDM communication apparatus 703 has a small (bad) S / N ratio and cannot receive normally.

  Therefore, when transmitting a signal to a distant point, select a block in the low frequency band as a block to be transmitted in advance, and set the transmission power of the selected block within the range of the maximum performance of the transmission amplifier. Then, control to raise.

  FIG. 13 schematically shows the control. FIG. 13A shows power when all the blocks are used. On the other hand, FIG. 13B shows a case where power is increased by selecting two low-frequency blocks.

For example, regarding the power control method described above, a table in which the number of blocks to be transmitted and transmission power are associated with each other is stored in the storage unit 30 in advance, and the table stored in the storage unit 30 by the speed power control unit 117 is stored. Therefore, it is conceivable that the transmission power corresponding to the number of blocks to be transmitted is read out and transmitted to the mapper unit 103 or the transmission amplifier 107 as transmission power intensity information 55 for control.
At this time, the relationship between the number of blocks to be transmitted and the transmission power may be related so that the transmission power is always constant, but is not limited to this.

It is a figure which shows the hardware constitutions of an OFDM communication apparatus. It is the figure which expanded and showed the function of the OFDM communication apparatus. It is a figure which shows transmission / reception of the signal in an OFDM communication apparatus. It is a figure which shows the flow of a process of an OFDM communication apparatus (transmission side). It is a figure which shows the example which grouped the some carrier into one block. It is a figure which shows the example of the frame format of a transmission signal. It is a figure which shows the example of the frame format of the header part of a transmission signal. It is a figure which shows the example of the frame format of an Ack signal. It is a figure which shows the example of the frame format of the header of an Ack signal. It is a figure which shows the flow of a process of an OFDM communication apparatus (reception side). It is a figure which shows the calculation method of the speed setting information in a speed electric power control part. It is a figure which shows the state by which the some OFDM communication apparatus is connected to the communication line. (A) is a figure which shows the electric power in the case of transmitting all the blocks, (b) is a figure which shows the electric power in the case of transmitting some blocks.

Explanation of symbols

1, 1a, 1b OFDM communication apparatus 10 processing unit 20 input / output unit 30 storage unit 44 transmission signal 45 Ack signal 51 speed setting information 52 reception correct / incorrect information 53 IQ data information 54 reception gain information 55 transmission power intensity information 56 address information 101 synchronization Signal generation unit 102 Header generation unit 103 Mapper unit 104 IFFT unit 105 GI addition unit 106 DA converter 107 Transmission amplifier 110 Reception amplifier 111 AD converter 112 Synchronization signal removal unit 113 GI removal unit 114 FFT unit 115 Demapper unit 116 Header analysis unit 117 Speed power control unit

Claims (5)

A plurality of carriers are arranged at equal intervals on the frequency axis, transmission data is modulated and converted into OFDM symbols, and a synchronization signal is arranged at the head, and then communication is performed using a frame configured by storing the OFDM symbols. In an OFDM communication device,
The OFDM communication apparatus includes a processing unit,
The processor is
Dividing the plurality of carriers into a plurality of blocks each having a block in which adjacent carriers are grouped together;
Modulate the carrier belonging to one of the blocks using the same modulation scheme,
If the position of the OFDM symbol stored in the frame corresponds to a predetermined position, generating the OFDM symbol using the same modulation scheme in all blocks for the transmission data;
An OFDM communication apparatus characterized by the above. An error detection code is added to the frame so that a code error can be detected for each block with respect to the OFDM symbol corresponding to the predetermined position,
The processor is
When a frame with the error detection code added is received, error detection is performed,
Returning the error detection result to the OFDM communication apparatus of the communication partner;
The OFDM communication apparatus according to claim 1. The processor is
Obtaining the error detection results until a predetermined number or period is reached, accumulating the number of error detections, and dividing by the number of the acquired error detection results to calculate a code error rate;
Using the code error rate and the modulation scheme used to modulate the OFDM symbol corresponding to the predetermined position, the relationship between the code error rate, the modulation scheme, and the S / N ratio stored in the storage unit By calculating the first S / N ratio by referring to the information associated with
The received power intensity is calculated from the IQ data before demodulation, the power intensity of the analog noise of the reception system of the OFDM communication apparatus measured in advance stored in the storage unit is read, and the received power intensity from the IQ data is read And calculating the ratio of the power intensity of the analog noise of the receiving system to calculate the second S / N ratio,
By comparing the first S / N ratio and the second S / N ratio, the smaller S / N ratio is calculated,
By using the smaller S / N ratio and the code error rate, by referring to the information associated with the relationship between the code error rate, the modulation scheme, and the S / N ratio stored in the storage unit, Determining a modulation scheme for each block for the transmission data other than the OFDM symbol corresponding to the predetermined position;
The OFDM communication apparatus according to claim 2. The processor is
Select the number of one or more blocks to be used for transmission,
By referring to the information associated with the number of blocks to be transmitted and the transmission power stored in the storage unit,
Raising the transmission power of the carrier belonging to the block used for transmission above the transmission power of the carrier when all blocks are transmitted;
The OFDM communication apparatus according to any one of claims 1 to 3, wherein: A plurality of carriers are arranged at equal intervals on the frequency axis, transmission data is modulated and converted into OFDM symbols, and a synchronization signal is arranged at the head, and then communication is performed using a frame configured by storing the OFDM symbols. An adaptive speed control method used in an OFDM communication apparatus, comprising:
The OFDM communication apparatus includes a processing unit and a storage unit,
The processor is
Dividing the plurality of carriers into a plurality of blocks each having a block in which adjacent carriers are grouped together;
Modulate the carrier belonging to one of the blocks using the same modulation scheme,
When the position of the OFDM symbol stored in the frame corresponds to a predetermined position, for the transmission data, generate an OFDM symbol using the same modulation scheme in all blocks,
In the frame, an error detection code is added so that a code error can be detected for each block with respect to the OFDM symbol corresponding to the predetermined position, and transmitted to the OFDM communication apparatus of the communication partner,
Receiving the error detection result from the communication partner OFDM communication device;
Obtaining the error detection results until a predetermined number or period is reached, accumulating the number of error detections, and dividing by the number of the acquired error detection results to calculate a code error rate;
Using the code error rate and the modulation scheme used for modulation of the OFDM symbol corresponding to the predetermined position, the code error rate, modulation scheme and S / N ratio stored in the storage unit By calculating the first S / N ratio by referring to the information associated with the relationship,
The received power intensity is calculated from the IQ data before demodulation, the power intensity of the analog noise of the reception system of the OFDM communication apparatus measured in advance stored in the storage unit is read, and the received power intensity from the IQ data is read And calculating the ratio of the power intensity of the analog noise of the receiving system to calculate the second S / N ratio,
By comparing the first S / N ratio and the second S / N ratio, the smaller S / N ratio is calculated,
By using the smaller S / N ratio and the code error rate, by referring to the information associated with the relationship between the code error rate, the modulation scheme, and the S / N ratio stored in the storage unit, Determining a modulation scheme for each block for the transmission data other than the OFDM symbol corresponding to the predetermined position;
An adaptive speed control method characterized by the above.

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