JP4425811B2 - OFDM transmission method, OFDM transmission apparatus, and OFDM transmission program - Google Patents

Description

  The present invention relates to an OFDM transmission method for improving frequency utilization efficiency by performing adaptive modulation in multicarrier communication, and a transmission apparatus, reception apparatus, and program thereof.

At present, transmission and access technologies in mobile communication systems are rapidly progressing in Japan, such as IMT-2000 (International Mobile Telecommunication 2000) service started in October 2001 for the first time in the world. In addition, technologies such as HSDPA (High Speed Down-link Packet Access) have been standardized, and practical application of data transmission at a maximum of about 10 Mbps is being promoted.
On the other hand, standardization for realizing broadband wireless Internet access targeting a transmission rate of 10 Mbps to 100 Mbps is also in progress, and various technologies have been proposed.

A requirement necessary for realizing wireless communication at a high transmission rate is to improve frequency utilization efficiency. Since the transmission rate and the bandwidth to be used are in a proportional relationship, increasing the transmission rate can be solved by widening the frequency bandwidth to be used. However, the frequency bands that can be used are tight, and it is difficult to consider that a sufficient bandwidth is allocated to construct a new wireless communication system. Therefore, it is necessary to increase the frequency utilization efficiency.
When wireless communication is performed using a single carrier, there is a problem that if the modulation speed is increased, the characteristics are greatly deteriorated when the propagation state of a part of the band is deteriorated due to factors such as multipath. In order to solve this problem, there is known a method of giving redundancy to a transmission line by using a multi-carrier method using a plurality of carriers. Among the multicarrier schemes, the scheme having the narrowest carrier spacing is OFDM (Orthogonal Frequency Division Multiplexing).

  OFDM is a method used in IEEE802.11a, which is a 5 GHz band wireless communication system, and digital terrestrial broadcasting. OFDM is a system in which tens to thousands of carriers are arranged at the minimum frequency interval where no theoretical interference occurs and are communicated simultaneously. Normally, this carrier is called a subcarrier in OFDM, and phase shift keying is performed by modulating each subcarrier such as PSK (Phase Shift Keying) and QAM (Quadrature Amplitude Modulation). To do. Further, by performing multi-level quadrature amplitude modulation in combination with an error correction method, modulation resistant to frequency selective fading can be performed. The configuration of a conventional OFDM transmitter and OFDM receiver will be described with reference to FIGS. In the following description, it is assumed that the number of subcarriers used for OFDM is 768 waves.

  FIG. 19 is a block diagram showing a configuration of an OFDM transmitter 300 used for OFDM. The OFDM transmitter 300 includes an error correction code unit 3001, an S / P (Serial / Parallel) conversion unit 3002, a mapping unit 3003, an IFFT (Inverse Fast Fourier Transform) unit 3004, a P / S. A (Parallel / Serial) conversion unit 3005, a GI (Guard Interval) insertion unit 3006, a D / A (Disital / Analog) conversion unit 3007, a wireless transmission unit 3008, and an antenna unit 3009 Have.

  The error correction coding unit 3001 performs error correction coding processing on the transmission data. S / P conversion section 3002 converts the data output from error correction coding section 3001 into data necessary for modulation of each subcarrier. For example, when the number of subcarriers is 768 waves and the modulation scheme of each subcarrier is QPSK (Quadrature Phase Shift Keying), the data is converted into 768 data in units of 2 bits. Mapping section 3003 performs modulation processing for each subcarrier on the data output from S / P conversion section 3002. The IFFT unit 3004 performs an inverse fast Fourier transform process on the data output from the mapping unit 3003. When generating a 768-wave OFDM signal, the number of points of the inverse fast Fourier transform that is normally used is 1024. The P / S conversion unit 3005 converts the data output from the IFFT unit 3004 from parallel data to serial data. The GI insertion unit 3006 inserts a guard interval into the data output from the P / S conversion unit 3005. The guard interval is inserted in order to reduce intersymbol interference when receiving an OFDM signal. The D / A conversion unit 3007 converts the data output from the GI insertion unit 3006 from a digital signal to an analog signal. The wireless transmission unit 3008 converts the data output from the D / A conversion unit 3007 into frequency data for transmission. The antenna unit 3009 transmits data output from the wireless transmission unit 3008.

  FIG. 20 is a block diagram showing a configuration of an OFDM receiver 305 used for OFDM. Basically, the OFDM receiving apparatus 305 performs the reverse process of the OFDM transmitting apparatus 300. The OFDM receiver 305 includes an error correction decoding unit 3051, a P / S conversion unit 3052, a propagation path estimation / demapping unit 3053, an FFT (Fast Fourier Transform) unit 3054, an S / P conversion unit 3055, and a GI removal. Unit 3056, synchronization unit 3060, A / D (Analog / Disital: analog / digital) conversion unit 3057, wireless reception unit 3058, and antenna unit 3059.

  The antenna unit 3059 receives a radio wave transmitted from the OFDM transmitter 300. The wireless reception unit 3058 converts the frequency of the radio wave received by the antenna unit 3059 into data in a frequency band in which analog / digital conversion is possible. The A / D conversion unit 3057 converts the data output from the wireless reception unit 3058 from analog data to digital data. The synchronization unit 3060 performs OFDM symbol synchronization on the data output from the A / D conversion unit 3057. The GI removal unit 3056 removes the guard interval from the data output from the synchronization unit 3060. Then, the S / P conversion unit 3052 parallelizes the data output from the GI removal unit 3056 into 1024 wave data. The FFT unit 3054 performs a 1024-point fast Fourier transform process on the data output from the S / P conversion unit 3055. The propagation path estimation / demapping unit 3053 demodulates 768 subcarriers for the data output from the FFT unit 3054. In general, in the propagation path estimation, the OFDM reception apparatus 305 estimates the propagation path by sending known data from the OFDM transmission apparatus 300 to the OFDM reception apparatus 305. The P / S conversion unit 3052 serializes the data output from the propagation path estimation / demapping unit 3053. Error correction decoding section 3051 performs error correction on the data output from P / S conversion section 3052 and demodulates the data transmitted from OFDM transmitting apparatus 300.

  There is an adaptive modulation technique as a technique for improving the frequency utilization efficiency of the multicarrier scheme including OFDM. This is a technique of grasping the propagation state for each subcarrier and using a high-speed modulation scheme for subcarriers with good propagation state to send more information. In addition, there is a method of changing the transmission power of each subcarrier according to the propagation state.

  One method of applying adaptive modulation to OFDM is to change the modulation parameter of each subcarrier according to the propagation situation. Usually, in OFDM, the amount of transmission is increased by multilevel modulation of each subcarrier. Normally, modulation such as BPSK (Binary Phase Shift Keying), QPSK, 16QAM, and 64QAM is performed on each subcarrier. Here, BPSK, QPSK, 16QAM, and 64QAM are used. In many cases, SNR (Signal to Noise power Ratio) or SINR (Signal to Interference and Noise power Ratio) is used as a reference for how many bits are allocated to subcarriers. Here, a case will be described where the OFDM transmission apparatus 300 side adopts a method of knowing SINR for each subcarrier obtained by the OFDM reception apparatus 305 side by some method. There are various methods for knowing the SINR. As an example, the OFDM receiving apparatus 305 notifies the OFDM transmitting apparatus 300 of the SINR. Suppose that BPSK, QPSK, 16QAM, 64QAM is used as the modulation scheme of each subcarrier, and the threshold values of SINR that can satisfy a desired error rate characteristic when each modulation scheme is used are TH_BPSK, TH_QPSK, TH_16QAM, This is expressed as TH_64QAM. The modulation parameter is set so that the amount of information that can be transmitted is maximized according to SINR for each subcarrier.

FIG. 21 is a graph showing the relationship between subcarriers and modulation schemes selected by SINR. Here, a case where the number of subcarriers is 10 (subcarrier numbers are 0 to 9) will be described. The vertical axis in FIG. 21 indicates SINR, and the horizontal axis indicates the subcarrier number. For example, when the subcarrier number is 3, the SINR exceeds TH_16QAM, which is a 16QAM threshold, but does not reach TH_64QAM, which is a 64QAM threshold. Therefore, 16QAM is selected as the modulation method.
By performing this operation each time the propagation path changes, it is possible to transmit information accurately with high frequency efficiency and even when the propagation path condition is deteriorated.

In addition, what is disclosed by patent document 1 is known as a technique which improves the efficiency of communication of a cellular system by performing adaptive modulation. This technique measures the power of a desired wave and an interference wave in units of subcarriers, and performs communication by selecting only subcarriers that can obtain a desired transmission rate.
On the other hand, a technique of MIMO (Multiple Input Multiple Output) is known as a technique for increasing the communication speed. MIMO is intended to improve throughput and reliability by preparing a plurality of antennas on the transmission side and reception side in a multipath environment and performing signal processing. Various MIMO schemes have been proposed, and the technique disclosed in Non-Patent Document 1 is known as an example.
JP 2003-304214 A Takeo Ohgane, Toshihiko Nishimura, Tomotaka Ogawa “Space Division Multiplexing and its Basic Characteristics in MIMO Channel” Proceedings of the Institute of Electronics, Information and Communication Engineers VOL.J87-B NO, 8 SEPTEMBER 2004

  However, when implementing adaptive modulation in actual equipment, the actual data handled in most cases is fixed length in order to implement ARQ (Automatic Repeat reQuest), FEC (Frame Error Correction), etc. Even if the amount of information that can be transmitted increases by several percent, the increased amount cannot be used in many cases. For example, when information is selected from three types in units of 256 bytes, 512 bytes, and 768 bytes and communication is performed, even if a transmission capacity of 500 bytes can be obtained by using adaptive modulation, bytes that can actually be transmitted The number is 256, and the channel capacity for 244 bytes is wasted.

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to improve an estimation accuracy of a propagation path and improve communication quality in wireless communication, an OFDM transmission method, a transmission apparatus, and a reception apparatus thereof And providing a program.

  The invention according to claim 1 is an OFDM transmission method for transmitting data of a fixed length using a plurality of symbols, and corresponds to the data of the fixed length when adaptive modulation is performed on a subcarrier by a control means. A first step of calculating the number of additional correction symbols, which is the number of symbols to be inserted into the fixed-length data, from the number of symbols to be transmitted and the number of symbols used for the actual transmission data; And a second step of inserting a correction symbol for estimating a propagation path characteristic for the symbol corresponding to the fixed-length data based on the number of additional correction symbols calculated by the means. This is an OFDM transmission method.

  The invention according to claim 2 is an OFDM transmission apparatus that transmits data of a fixed length using a plurality of symbols, and a symbol corresponding to the data of the fixed length when adaptive modulation is performed on a subcarrier. The number of additional correction symbols, which is the number of symbols to be inserted, from the number and the number of symbols used for the actual transmission data, and the fixed-length data based on the number of additional correction symbols calculated by the control unit. An OFDM transmission apparatus comprising: a propagation path estimation symbol creating means for inserting a correction symbol for estimating a propagation path characteristic for a corresponding symbol.

  The invention according to claim 3 is characterized in that the propagation path estimation symbol creating means inserts a correction symbol by a preamble into a symbol corresponding to the fixed length data. It is an OFDM transmitter.

  The invention according to claim 4 is characterized in that the propagation path estimation symbol creating means inserts a correction symbol by midamble into a symbol corresponding to the fixed-length data. OFDM transmission apparatus.

  The invention according to claim 5 is characterized in that the propagation path estimation symbol creating means inserts a correction symbol by postamble into a symbol corresponding to the fixed length data. OFDM transmission apparatus.

  According to a sixth aspect of the present invention, at least two or more of the propagation path estimation symbol creating means are configured by any one of a preamble, a midamble, and a postamble with respect to a symbol corresponding to the fixed length data. The OFDM transmitter according to claim 2, wherein the correction symbol is inserted.

  The propagation path estimation symbol creating means divides the additional correction symbol based on the number of antennas used for transmitting the fixed-length data, and the divided additional correction is performed. 7. The OFDM transmitter according to claim 2, wherein a correction symbol is inserted into a symbol corresponding to the fixed length data based on the symbol.

  The propagation path estimation symbol creating means may change the insertion pattern of the correction symbols to be inserted based on the divided additional correction symbols for each of the divided additional correction symbols. The OFDM transmitter according to claim 7, wherein

  In the invention according to claim 9, the propagation path estimation symbol creating means inserts a correction symbol for a symbol corresponding to the fixed-length data more than the number of the antennas. 8. The OFDM transmission apparatus according to claim 7, wherein the symbols are divided, and based on the divided additional correction symbols, correction symbols are inserted by interleaving with respect to symbols corresponding to the fixed-length data. is there.

  The invention according to claim 10 is an OFDM receiver that receives a fixed length of data using a plurality of symbols, and refers to the correction symbol included in the fixed length of data, thereby An OFDM receiver characterized by estimating the characteristics of a propagation path of data of a certain length.

  The invention according to claim 11 is an OFDM transmission program for transmitting data of a fixed length using a plurality of symbols, and a symbol corresponding to the data of the fixed length when adaptive modulation is performed on a subcarrier. The first step of calculating the number of additional correction symbols, which is the number of symbols to be inserted into the fixed-length data, from the number and the number of symbols used for actual transmission data, and the number of additional correction symbols calculated in the first step And a second step of inserting a correction symbol for estimating a propagation path characteristic for a symbol corresponding to the fixed-length data.

In the present invention, the number of symbols not used for transmission data is calculated from the fixed-length data transmitted from the OFDM transmission / transmission apparatus, and additional correction symbols for estimating propagation path characteristics are inserted.
As a result, it is possible to estimate the characteristics of the propagation path between the OFDM transmitter and the OFDM receiver by using the additional correction symbol, and the reception performance in the OFDM receiver can be improved.

Hereinafter, an OFDM transmission apparatus according to an embodiment of the present invention will be described with reference to the drawings.
In the present embodiment, a case will be described in which data is transmitted from an OFDM transmission apparatus to an OFDM reception apparatus by using OFDM. The OFDM transmission apparatus will be described on the assumption that the SINR characteristics for each subcarrier of the OFDM reception apparatus are known. Depending on the type of wireless communication system, it may be better to use SNR instead of SINR. In this embodiment, the case of using SINR will be described. Various methods can be considered as a method of knowing SINR characteristic information in the OFDM receiving apparatus on the OFDM transmitting apparatus side. For example, it is conceivable that the OFDM receiving apparatus transmits SINR characteristic information to the OFDM transmitting apparatus.

FIG. 1 is a diagram illustrating an example of a configuration of transmission data for OFDM transmission.
In the present embodiment, transmission data transmitted from an OFDM transmitter to an OFDM receiver has a frame structure with a fixed period as shown in FIG. An information slot d21 is arranged at the head of one frame d1, and data slots d3 (d31 to d37) are arranged behind it. The broadcast slot d2 (the broadcast slot d21 of one frame d1, the broadcast slot d22 of the next frame,...) Is transmitted using only a predetermined modulation scheme. The information slot d2 stores later-described information of the subsequent data slot d3. The information on the data slot d3 stored in the notification slot d2 includes the start time of the data slot d3, the preamble information of the data slot d3, the modulation scheme of the data slot d3, the information of the OFDM receiver that demodulates the data slot d3, and the like. included.
The intra-frame time reference position is expressed with reference to the start time of the notification slot d21. The OFDM receiving apparatus receives and demodulates the first broadcast slot d21 of the frame d1, demodulates the start time of the data slot d3 in this frame d1, the preamble information of the data slot d3, the modulation scheme of the data slot d3, and the data slot d3. The data slot d3 is demodulated using the information of the OFDM receiving apparatus to perform wireless communication by OFDM.

  In the present embodiment, a case where the number of subcarriers used for OFDM is C will be described. It is assumed that the transmission power of each subcarrier is equal to P when performing data transmission from the OFDM transmitter, and there are also subcarriers that are not used in transmission. Further, it is assumed that L (number of symbols corresponding to fixed length data) OFDM symbols are used in one data transmission. The L OFDM symbols are composed of k propagation path estimation symbols and d data symbols in which data payloads are stored. In this embodiment, it is assumed that at least two propagation path estimation symbols are compensated even if the data symbol modulation method is set to the slowest speed. That is, k ≧ 2.

FIG. 1B is a diagram illustrating an example of a data configuration transmitted by the OFDM transmitter according to the present embodiment. This data includes AGC (Auto Gain Control), AFC (Auto Frequency Control) symbol d4, a propagation path estimation symbol d5 which is a preamble for estimating the propagation path, and a modulation scheme for each subcarrier. It consists of an MLI (Modulation Level Information) symbol d6 and a data symbol d7.
AGC, AFC symbol d4, propagation path estimation symbol d5, and data symbol d7 correspond to broadcast slot d21 in FIG. The data symbol d7 corresponds to the data slot d3 in FIG.

  The number of bits of data to be transmitted in one communication is one of R1, R2, and R3, and R1, R2, and R3 are integer values that satisfy the relationship of R1 <R2 <R3.

The modulation scheme of each subcarrier is any one of BPSK, QPSK, 16QAM, and 64QAM, and the number of bits that can be transmitted is 1, 2, 4, and 6, respectively. Assuming that 16QAM is used for all subcarriers, the number of bits that can be transmitted in one data transmission is 4 × C × d bits.
As described above, the OFDM transmitter employs a method of knowing the SINR in the OFDM receiver in some way when transmitting the power of each subcarrier with P. In the present specification, the SINR of each subcarrier is expressed as SINR_cnum. Here, cnum is a subcarrier number, and is an integer value that satisfies the condition 1 ≦ cnum ≦ C. Further, the SINR necessary to communicate using each modulation method and satisfy a predetermined error rate is represented as TH_ (modulation method). That is, in the BPSK, QPSK, 16QAM, and 64QAM modulation schemes, the SINR required to satisfy a predetermined error rate is expressed as TH_BPSK, TH_QPSK, TH_16QAM, and TH_64QAM.

Next, the configuration of the OFDM transmitter 100 according to the first to seventh embodiments of the present invention will be described. FIG. 2 is a block diagram showing a configuration of OFDM transmission apparatus 100.
The OFDM transmitter 100 includes a control unit 1, a mapping unit 2, an IFFT unit 3, a P / S conversion unit 4, a GI insertion unit 5, a signal switching unit 6, a D / A conversion unit 7, a radio transmission unit 8, and an antenna unit 9. A modulation scheme determining unit 10, an SINR storage unit 11, a propagation path estimation symbol creating unit 12, an AGC / AFC symbol creating unit 13, a receiving unit 14, and an MLI creating unit 15.

Transmission data transmitted from the OFDM transmitter 100 to the OFDM receiver is input to the mapping unit 2.
The mapping unit 2 maps transmission data by allocating transmission data to each subcarrier based on the modulation scheme of each subcarrier determined by the modulation scheme determination unit 10 to be described later, and outputs it to the IFFT unit 3.
The IFFT unit 3 performs inverse fast Fourier transform processing on the data output from the mapping unit 2, and outputs the time waveform data of the OFDM signal to the P / S conversion unit 4.
The P / S conversion unit 4 converts the data output from the IFFT unit 3 from parallel data to serial data and outputs the data to the GI insertion unit 5.

The GI insertion unit 5 inserts a guard interval into the data output from the P / S conversion unit 4 and outputs the data to the signal switching unit 6. The guard interval is generated in order to reduce the intersymbol interference of the OFDM signal, and usually the signal after the OFDM signal is copied and added to the head.
The signal switching unit 6 switches between data output from the GI insertion unit 5 and data output from a propagation path estimation symbol creation unit 12 and an AGC / AFC symbol creation unit 13 described later, and a D / A conversion unit 7 is output.
The D / A conversion unit 7 converts the data output from the signal switching unit 6 from digital data to analog data and outputs the data to the wireless transmission unit 8.

The wireless transmission unit 8 converts the data output from the D / A conversion unit 7 into a frequency used for wireless communication, and outputs the frequency to the antenna unit 9.
The antenna unit 9 transmits the data output from the wireless transmission unit 8 on the radio wave to the OFDM receiver.
The modulation scheme determination unit 10 uses the data acquired from the reception unit 14 by the control unit 1 and applies modulation to each subcarrier based on the processing of flowcharts described in first to seventh embodiments described later. Determine the method. At this time, SINR data that is the reception characteristic of the OFDM receiver stored in the SINR storage unit 11 is used.
The AGC / AFC symbol creation unit 13 creates an AGC / AFC symbol based on the control of the control unit 1 and outputs the symbol to the signal switching unit 6.
The control unit 1 controls the modulation scheme determination unit 10, the SINR storage unit 11, the propagation path estimation symbol creation unit 12, the AGC / AFC symbol creation unit 13, the reception unit 14, the MLI creation unit 15, and the like. The control unit 1 uses the number of symbols corresponding to the fixed-length data when adaptive modulation is performed on the subcarrier and the number of symbols used for the actual transmission data to determine the fixed-length data that is transmission data transmitted from the OFDM transmitter 100. The number of additional correction symbols that is the number of symbols to be inserted into is calculated.

Based on the number of additional correction symbols calculated by the control unit 1, the propagation path estimation symbol creation unit 12 performs propagation path characteristics for symbols corresponding to fixed-length data that is transmission data transmitted from the OFDM transmitter 100. A correction symbol (preamble, midamble, and postamble) is estimated and inserted. Thereby, the propagation path estimation symbol is inserted into the transmission data transmitted from the OFDM transmitter 100.
The MLI creation unit 15 creates an MLI based on the control of the control unit 1 and outputs it to the mapping unit 2.

  Next, the OFDM receiver will be described. The OFDM receiving apparatus receives transmission data into which a propagation path estimation symbol is inserted from the OFDM transmission apparatus 100 (see FIG. 2), and estimates the propagation path characteristics of the transmission data with reference to the propagation path estimation symbol. . By performing such processing, it is possible to improve the reception characteristics of transmission data in the OFDM receiver.

Next, processing of the OFDM transmission apparatus 100 according to the first embodiment of the present invention will be described.
FIG. 3 is a flowchart showing processing of the OFDM transmitter 100 of this embodiment.
Here, a case where data of a certain length of data S (S> 0) bits is transmitted from the OFDM transmitter 100 to the OFDM receiver will be described.
First, the modulation scheme determination unit 10 compares SINR_cnum, which is the SINR of each subcarrier, with TH_ (modulation scheme), and among the modulation schemes with SINR_cnum equal to or greater than TH_ (modulation scheme), the number of transmission bits is the largest. A large modulation scheme is selected as CB_cnum (step S101). SINR_cnum is stored in advance in the SINR storage unit 11 or received by the reception unit 14 from the OFDM receiver and stored in the SINR unit 11. Then, the selected CB_cum is stored in the SINR storage unit 11. The process of step S101 is performed for all subcarriers. FIG. 4A shows a program for executing the process performed in step S101.

Next, the control unit 10 obtains the maximum number of bits Rm that satisfy a predetermined error rate and can communicate in one slot in communication from the OFDM transmitter 100 to the OFDM receiver (step S102). That is, CB_cnum obtained in step S101 is multiplied by the maximum number of data symbols dmax (dmax = L−2) in one slot for all subcarriers. FIG. 4B shows a program for executing the processing performed in step S102.
Next, the control unit 10 determines the number of bits Rr (actual transmission data) actually transmitted in one slot (step S103). Here, the number of bits Rr transmitted in one slot is determined from among R1, R2, and R3. Rm obtained in step S102 is compared with R1, R2, and R3, and the largest value smaller than Rm is selected from R1, R2, and R3. However, when the number of bits to be transmitted is smaller than Rm, S is compared with R1 to R3, and an appropriate Rr is selected. FIG. 4C shows a program for executing the processing performed in step S103.

Next, the control unit 10 determines whether the bit number Rr is not 0 (step S104). If Rr is 0, it indicates that transmission is not possible with the required error rate. Therefore, “NO” is determined in step S104, and the processing ends as “abnormal end”. In this case, the data transmission by the OFDM transmitter 100 is stopped and the change in the propagation path state is waited or the error rate set first is changed, and the processing from step S101 is started again.
On the other hand, if the bit number Rr is not 0, “YES” is determined in the step S104, and the process proceeds to a step S105. Then, the control unit 10 calculates the number of bits Rs (data of a certain length) that can be transmitted with one symbol (step S105).

Next, the control unit 10 calculates the number of symbols d (number of symbols used for actual transmission data) necessary to transmit the Rr bit using Rs (step S106). A value obtained by dividing Rr by Rs (rounded up after the decimal point) is calculated as d.
Next, the control unit 10 calculates the number k ′ of additional correction symbols as Ld (step S107).
Next, the propagation path estimation symbol creation unit 12 sets the number of additional preambles in the corresponding slot to be k ′ in the broadcast slot. (Step S108). Then, propagation path estimation symbol creating section 12 inserts k ′ preambles as correction symbols in symbols corresponding to transmission data transmitted from OFDM transmitting apparatus 100. The OFDM receiving apparatus can demodulate the corresponding slot by referring to k ′ preambles.
According to the first embodiment described above, the use of the preamble as a correction symbol for estimating the propagation path in the OFDM transmission apparatus 100 can improve the estimation accuracy of the propagation path. Reception performance can be improved.

Next, processing of the OFDM transmitter 100 according to the second embodiment of the present invention will be described.
In the present embodiment, a case will be described in which a correction symbol (midamble) for estimating a propagation path is inserted in the middle of a series of data symbols when surplus symbols are generated.
Normally, when demodulating OFDM, attenuation for each subcarrier is checked by a propagation path estimation symbol (preamble) added to the head of the frame, and the received signal is corrected and demodulated according to this result. However, if the data symbol continues for a certain length and the propagation path fluctuates over time due to fading or other reasons, the state of the propagation path differs from the beginning at the end of the data symbol, and the demodulation accuracy May get worse.

  FIG. 5 is a schematic diagram illustrating an example of data transmitted by the OFDM transmitter 100 according to the present embodiment. This data is composed of AGC, AFC symbol d4, MLI symbol d6, data symbol d71, propagation path estimation symbol d52 which is a midamble, and data symbol d72. In the first embodiment (see FIG. 1B), the propagation path estimation symbol d5, which is a surplus symbol, is used as a preamble. Instead, a propagation path estimation symbol d52 is inserted into the data symbol. Thus, it becomes possible to perform correction following the fluctuation of the propagation path.

FIG. 6 is a flowchart showing processing of the OFDM transmitter 100 according to this embodiment.
Here, a case will be described in which the OFDM transmitter 100 transmits data of a certain length of data S (S> 0) bits to the OFDM receiver.
First, the modulation scheme determination unit 10 compares SINR_cnum, which is the SINR of each subcarrier, with TH_ (modulation scheme), and among the modulation schemes with SINR_cnum equal to or greater than TH_ (modulation scheme), the number of transmission bits is the largest. A large modulation scheme is selected as CB_cnum (step S201). SINR_cnum is stored in advance in the SINR storage unit 11 or received by the reception unit 14 from the OFDM receiver and stored in the SINR unit 11. Then, the selected CB_cnum is stored in the SINR storage unit 11. The process in step S201 is performed for all subcarriers. FIG. 7A shows a program for executing the process performed in step S201.

Next, the control unit 10 obtains the maximum number of bits Rm that satisfy a predetermined error rate and can communicate in one slot in communication from the OFDM transmitter 100 to the OFDM receiver (step S202). That is, CB_cnum obtained in step S201 is multiplied by the maximum number of data symbols dmax (dmax = L−2) in one slot for all subcarriers. FIG. 7B shows a program for executing the process performed in step S202.
Next, the control unit 10 determines the number of bits Rr (actual transmission data) to be actually transmitted in one slot (step S203). Here, the number of bits Rr transmitted in one slot is determined from among R1, R2, and R3. Rm obtained in step S202 is compared with R1, R2, and R3, and the largest value smaller than Rm is selected from R1, R2, and R3. However, when the number of bits to be transmitted is smaller than Rm, S is compared with R1 to R3, and an appropriate Rr is selected. FIG. 7C shows a program for executing the process performed in step S203.

Next, the control unit 10 determines whether Rr is not 0 (step S204). If Rr is 0, the requested error rate indicates that transmission is not possible. Therefore, “NO” is determined in step S204, and the processing ends as “abnormal end”. In this case, the data transmission by the OFDM transmitter 100 is stopped and the process waits for the propagation path state to change or the initially set error rate is changed, and the processing from step S201 is started again.
If Rr is not 0, “YES” is determined in the step S204, and the process proceeds to a step S205. Then, the control unit 10 calculates the number of bits Rs (data of a certain length) that can be transmitted with one symbol (step S205).

Next, the control unit 10 calculates the number of symbols d (the number of symbols used for actual transmission data) necessary to transmit the Rr bit using Rs (step S206). A value obtained by dividing Rr by Rs (rounded up after the decimal point) is calculated as d.
Next, the control unit 10 calculates the number k ′ of additional correction symbols as Ld (step S207).
Next, the control unit 10 determines whether or not the number of additional correction symbols k ′ is greater than 0 (step S208). If the number of additional correction symbols k ′ is greater than 0, “YES” is determined and the process proceeds to step S209. If k ′ is 0 or less, “NO” is determined and the process proceeds to step S210.

In step S209, the propagation path estimation symbol creation unit 12 sets the k ′ symbols in the broadcast slot so as to use them as a midamble. Then, propagation path estimation symbol creation section 12 inserts k ′ midambles as correction symbols into symbols corresponding to transmission data transmitted from OFDM transmission apparatus 100. The OFDM receiver can demodulate the corresponding slot by referring to the k ′ midambles. The OFDM receiver can demodulate the corresponding slot by referring to the k ′ midambles. Various positions are conceivable as positions where the midamble is inserted. In this embodiment, it is assumed that the midamble is inserted at the position of the value obtained by dividing the number of data symbols by 2 (rounded down).
On the other hand, in step S210, the propagation path estimation symbol creation unit 12 sets in the broadcast slot so as not to use the midamble. As a result, the OFDM receiving apparatus knows that no midamble is used in the slot and can demodulate normally.
According to the second embodiment described above, the use of the midamble as a correction symbol for estimating the propagation path in the OFDM transmission apparatus 100 can improve the estimation accuracy of the propagation path. Reception performance can be improved.

Next, processing of the OFDM transmission apparatus 100 according to the third embodiment of the present invention will be described.
In this embodiment, a case will be described in which a correction symbol (postamble) for estimating a propagation path is added to the end of a series of data symbols when surplus symbols are generated.
Normally, when demodulating OFDM, the attenuation for each subcarrier is checked by a propagation path estimation symbol (preamble) added to the head of the frame, and the received signal is corrected and demodulated according to this result. However, if the data symbol continues for a certain length and the propagation path fluctuates over time due to fading or the like, the situation of the propagation path at the end of the data symbol is different from that at the beginning, and demodulation is performed. The accuracy may deteriorate.

FIG. 8 is a schematic diagram illustrating an example of data transmitted by the OFDM transmitter 100 according to the present embodiment. This data is composed of AGC, AFC symbol d4, MLI symbol d6, data symbol d73, and propagation path estimation symbol d53 which is a postamble. In the first embodiment (see FIG. 1B), the surplus symbol is used as a preamble, but instead, a propagation path estimation symbol d53 is added to the end of the data symbol to follow the fluctuation of the propagation path. Correction can be performed.
When using midambles, sequential processing may be used.However, when performing propagation path correction using postambles, data symbols between the preamble and postamble are temporarily stored and the preambles are used. Using the propagation path information obtained by using the postamble and the propagation path information at each symbol position. It is possible to improve the demodulation accuracy by using the correction.

FIG. 9 is a flowchart showing the processing of the OFDM transmitter 100 of this embodiment.
Here, a case will be described in which the OFDM transmitter 100 transmits data of a certain length of data S (S> 0) bits to the OFDM receiver.
First, the modulation scheme determination unit 10 compares SINR_cnum, which is the SINR of each subcarrier, with TH_ (modulation scheme), and has the largest number of transmission bits among the modulation schemes with SINR_cnum equal to or greater than TH_ (modulation scheme). The modulation method is selected as CB_cnum (step S301). SINR_cnum is stored in advance in the SINR storage unit 11 or received by the reception unit 14 from the OFDM receiver and stored in the SINR unit 11. Then, the selected CB_cnum is stored in the SINR storage unit 11. The process of step S301 is performed for all subcarriers. FIG. 10A shows a program for executing the process performed in step S301.

Next, the control unit 10 obtains the maximum number of bits Rm that satisfy a predetermined error rate and can communicate in one slot in communication from the OFDM transmitter 100 to the OFDM receiver (step S302). That is, CB_cnum obtained in step S301 is multiplied by the maximum number of data symbols dmax (dmax = L−2) in one slot for all subcarriers. FIG. 10B shows a program for executing the process performed in step S302.
Next, the control unit 10 determines the number of bits Rr (actual transmission data) actually transmitted in one slot (step S303). Here, the number of bits Rr transmitted in one slot is determined from among R1, R2, and R3. Rm obtained in step S302 is compared with R1, R2, and R3, and the largest value among the values smaller than Rm is selected from R1, R2, and R3. However, when the number of bits to be transmitted is smaller than Rm, S is compared with R1 to R3, and an appropriate Rr is selected. FIG. 10C shows a program for executing the processing performed in step S303.

Next, the control unit 10 determines whether Rr is not 0 (step S304). Here, when Rr is 0, it indicates that transmission is not possible with the required error rate. Therefore, “NO” is determined in step S304, and the processing ends as “abnormal end”. In this case, the data transmission by the OFDM transmitter 100 is stopped and the process waits for the propagation path state to change or the initially set error rate is changed, and the processing from step S301 is started again.
If Rr is not 0, “YES” is determined in the step S304, and the process proceeds to a step S205. Then, the control unit 10 calculates the number of bits Rs (data of a certain length) that can be transmitted with one symbol (step S305).

Next, the control unit 10 calculates the number of symbols d (number of symbols used for actual transmission data) necessary to transmit the Rr bit using Rs (step S306). A value obtained by dividing Rr by Rs (rounded up after the decimal point) is calculated as d.
Next, the control unit 10 calculates the number k ′ of additional correction symbols as L−d−2 (step S307).
Next, the control unit 10 determines whether or not the number of additional correction symbols k ′ is greater than 0 (step S308). If the number of additional correction symbols k ′ is greater than 0, “YES” is determined and the process proceeds to step S309. If k ′ is 0 or less, “NO” is determined and the process proceeds to step S310.

In step S309, the propagation path estimation symbol creation unit 12 sets in the broadcast slot so that k ′ symbols are used as the postamble. Then, propagation path estimation symbol creation section 12 inserts k ′ postambles as correction symbols in symbols corresponding to transmission data transmitted from OFDM transmitter 100. The OFDM receiver can demodulate the corresponding slot by referring to the k ′ midambles. The slot can be demodulated by referring to the k ′ postambles of the OFDM receiver.
On the other hand, in step S310, the propagation path estimation symbol creation unit 12 sets the broadcast slot so as not to use the postamble. As a result, the OFDM receiving apparatus knows that no postamble is used for the slot, and can normally demodulate.
According to the third embodiment described above, since the postamble is used as a correction symbol for estimating the propagation path in the OFDM transmission apparatus 100, the propagation path estimation performance can be improved. Performance can be improved.

Next, processing of the OFDM transmitter 100 according to the fourth embodiment of the present invention will be described.
In the first to third embodiments, when a surplus symbol is generated, only one of the preamble, midamble, and postamble is added as a correction symbol for estimating the propagation path. In the present embodiment, a case will be described in which propagation path estimation symbols are added as correction symbols to a plurality of positions. Any number of preambles, midambles, and postambles may be used. In this embodiment, a case where one preamble and one midamble are added will be described.
As shown in FIG. 11, the data transmitted by the OFDM transmitter 100 according to the present embodiment includes AGC, AFC symbol d4, propagation path estimation symbol d54 which is a preamble, MLI symbol d6, data symbol d74, mid It is composed of a propagation path estimation symbol d55 which is an amble and a data symbol d75.

FIG. 12 is a flowchart showing processing of the OFDM transmitter 100 according to the present embodiment.
Here, a case will be described in which data transmission of data S (S> 0) bits of a certain length occurs in the OFDM receiver in the OFDM transmitter 100.
First, the modulation scheme determination unit 10 compares SINR_cnum, which is the SINR of each subcarrier, with TH_ (modulation scheme), and has the largest number of transmission bits among the modulation schemes with SINR_cnum equal to or greater than TH_ (modulation scheme). The modulation method is selected as CB_cnum (step S401). SINR_cnum is stored in advance in the SINR storage unit 11 or received by the reception unit 14 from the OFDM receiver and stored in the SINR unit 11. Then, the selected CB_cnum is stored in the SINR storage unit 11. The process of step S401 is performed for all subcarriers. FIG. 13A shows a program for executing the processing performed in step S401.

Next, the control unit 10 obtains the maximum number of bits Rm that satisfy a predetermined error rate and can communicate in one slot in communication from the OFDM transmitter 100 to the OFDM receiver (step S402). That is, CB_cnum obtained in step S401 is multiplied by the maximum number of symbols dmax (dmax = L−2) in one slot for all subcarriers. FIG. 13B shows a program for executing the processing performed in step S402.
Next, the control unit 10 determines the number of bits Rr (actual transmission data) actually transmitted in one slot (step S403). Here, the number of bits Rr transmitted in one slot is determined from among R1, R2, and R3. Rm obtained in step S402 is compared with R1, R2, and R3, and the largest value smaller than Rm is selected from R1, R2, and R3. However, when the number of bits to be transmitted is smaller than Rm, S is compared with R1 to R3, and an appropriate Rr is selected. FIG. 13C shows a program for executing the processing performed in step S403.

Next, the control unit 10 determines whether Rr is not 0 (step S404). Here, when Rr is 0, the requested error rate indicates that transmission is not possible. Therefore, “NO” is determined in step S404, and the processing ends as “abnormal end”. In this case, the data transmission by the OFDM transmitter 100 is stopped and the change in the propagation path state is waited or the initially set error rate is changed, and the processing from step S401 is started again.
If Rr is not 0, “YES” is determined in the step S404, and the process proceeds to a step S405. Then, the control unit 10 calculates the number of bits Rs (data of a certain length) that can be transmitted with one symbol (step S405).

Next, the control unit 10 calculates the number of symbols d (number of symbols used for actual transmission data) necessary to transmit the Rr bit using Rs (step S406). A value obtained by dividing Rr by Rs (rounded up after the decimal point) is calculated as d.
Next, the control unit 10 calculates the number k ′ of additional correction symbols as L−d−2 (step S407).
Next, the control unit 10 determines whether or not the number of additional correction symbols k ′ is greater than 0 (step S408). If the number of additional correction symbols k ′ is greater than 0, “YES” is determined and the process proceeds to step S409. If k ′ is 0 or less, “NO” is determined and the process proceeds to step S414.

Next, in step S414, the propagation path estimation symbol creation unit 12 sets in the broadcast slot so as not to use the additional preamble / midamble. As a result, the OFDM receiver side knows that no additional preamble or midamble is used in the slot, and can normally demodulate.
On the other hand, in step S409, the propagation path estimation symbol creation unit 12 sets the number of additional preamble symbols kp and the number of additional mitoamble symbols km. Here, half the number of additional correction symbols is set for each, and when the number of additional correction symbols is not divisible by 2, one midamble is set more than the preamble.

Next, the propagation path estimation symbol creation unit 12 sets the km symbols in the broadcast slot so as to use them as a midamble (step S410). Here, since km is always 1 or more, the midamble is set to be used.
Next, the control unit 10 determines whether or not kp is larger than 0 (step S411). If kp is greater than 0, “YES” is determined and the process proceeds to step S412. If kp is 0 or less, “NO” is determined and the process proceeds to step S413.

In step S412, the propagation path estimation symbol creation unit 12 sets in the broadcast slot so that kp symbols are used as additional preambles.
On the other hand, in step S413, the propagation path estimation symbol creation unit 12 sets in the broadcast slot so as not to use the additional preamble. Then, propagation path estimation symbol creation section 12 inserts k ′ preambles and postambles as correction symbols in symbols corresponding to transmission data transmitted from OFDM transmission apparatus 100. The OFDM receiver can demodulate the corresponding slot by referring to the k ′ midambles. The slot can be demodulated by referring to the k ′ preamble and postamble of the OFDM receiver.
Various positions can be considered as the midamble insertion position. For example, it is possible to insert the midamble at the position of the value obtained by dividing the number of data symbols by 2 (rounded down).
According to the fourth embodiment described above, since the propagation path estimation performance can be improved by using the preamble and midamble as the correction symbol for estimating the propagation path, the reception performance in the OFDM receiver is improved. Can be made.

Next, processing of the OFDM transmitter 100 according to the fifth embodiment of the present invention will be described.
In this embodiment, a case will be described in which data is transmitted from the OFDM transmitter 100 to the OFDM receiver using MIMO. In this embodiment, MIMO with 3 outputs is described, but any number of outputs is possible. Here, it is assumed that the number of antennas on the OFDM receiver side is 3 or more.

As shown in FIG. 14A, data transmitted by the OFDM transmitter 100 according to the present embodiment includes AGC and AFC symbol d4, propagation path estimation symbols d55, d56, and d57, which are preambles, and MLI symbol d6. , A data symbol d75, an additional propagation path estimation symbol d8, and a data symbol d76.
In this embodiment, in order to estimate the propagation paths of the three antennas, propagation path estimation symbols d55, d56, and d57 corresponding to the three antennas (antenna a1, antenna a2, and antenna a3) are prepared. When transmitting the estimation symbol d55, it is transmitted only from the antenna a1, only when transmitting the propagation path estimation symbol d56, only from the antenna a2, and when transmitting the propagation path estimation symbol d57, it is transmitted only from the antenna a3. .
As a result, the propagation paths from the respective antennas a1 to a3 can be estimated on the OFDM receiver side, so that the received waves can be separated. For this reason, in this embodiment, the number of propagation path estimation symbols is at least 3.

FIG. 15 is a flowchart showing processing of the OFDM transmitter 100 of this embodiment.
Here, a case will be described in which data transmission of data S (S> 0) bits of a certain length occurs in the OFDM receiver in the OFDM transmitter 100.
First, the modulation scheme determination unit 10 compares SINR_cnum, which is the SINR of each subcarrier, with TH_ (modulation scheme), and has the largest number of transmission bits among the modulation schemes with SINR_cnum equal to or greater than TH_ (modulation scheme). The modulation method is selected as CB_cnum (step S501). SINR_cnum is stored in advance in the SINR storage unit 11 or received by the reception unit 14 from the OFDM receiver and stored in the SINR unit 11. Then, the selected CB_cnum is stored in the SINR storage unit 11. FIG. 16A shows a program for executing the process performed in step S501. The process in step S501 is performed for all subcarriers. Here, all of the subcarriers include three multiplexed parts.

  Next, in communication from the OFDM transmitter 100 to the OFDM receiver, the maximum number of bits Rm that satisfy a predetermined error rate and can communicate in one slot is obtained (step S502). That is, CB_cnum obtained in step S501 is multiplied by the maximum number of data symbols dmax (dmax = L−3) in one slot for all subcarriers. FIG. 16B shows a program for executing the processing performed in step S502.

  Next, the control unit 10 determines the number of bits Rr (actual transmission data) to be actually transmitted in one slot (step S503). The number of bits Rr to be transmitted in one slot is determined from among R1, R2, and R3. Rm determined in step S502 is compared with R1, R2, and R3, and the largest value smaller than Rm is selected from R1, R2, and R3. However, when the number of bits to be transmitted is smaller than Rm, S is compared with R1 to R3, and an appropriate Rr is selected. A program for executing the processing performed in step S503 is shown in FIG.

Next, the control unit 10 determines whether Rr is not 0 (step S504). When Rr is 0, the requested error rate indicates that transmission is not possible. Therefore, “NO” is determined in step S504, and the processing ends as “abnormal end”. In this case, the data transmission by the OFDM transmitter 100 is stopped, waiting for the propagation path state to change, or the error rate set first is changed, and the processing from step S501 is started again.
If Rr is not 0, “YES” is determined in the step S504, and the process proceeds to a step S505. Then, the control unit 10 calculates the number of bits Rs (constant length data) that can be transmitted in one symbol (step S505).

Next, the control unit 10 calculates the number of symbols d (number of symbols used for actual transmission data) necessary for transmitting the Rr bit using Rs (step S506). A value obtained by dividing Rr by Rs (rounded up after the decimal point) is calculated as d.
Next, the control unit 10 calculates the number k ′ of additional correction symbols as Ld−3 (step S507).
Next, the control unit 10 determines whether or not the number of additional correction symbols k ′ is greater than 0 (step S508). If the number of additional correction symbols k ′ exceeds 0, “YES” is determined and the process proceeds to step S509. If k ′ is 0 or less, “NO” is determined and the process proceeds to step S513.
Normally, MIMO performs propagation path estimation by preparing symbols for the number of outputs for propagation path estimation, but this embodiment also supports cases where the surplus symbols generated as a result of adaptive modulation cannot be secured for the output. Therefore, subcarriers used in OFDM are divided by the number of outputs, and separate antenna propagation path estimation symbols d55, d56, and d57 (see FIG. 14A) are transmitted to the respective bands. At this time, an additional correction symbol is transmitted from each antenna only in the corresponding band.

Next, in step S509, the propagation path estimation symbol creating unit 12 refers to the pattern of the additional propagation path estimation symbol d8 when transmitted last time. As shown in FIG. 14B, the additional propagation path estimation symbol 82, the additional propagation path estimation symbol 83, and the additional propagation path estimation symbol 84 are stored in the additional propagation path estimation symbol d8. The additional propagation path estimation symbol 82 is a propagation path estimation symbol for the antenna a1, the additional propagation path estimation symbol 83 is a propagation path estimation symbol for the antenna a2, and the additional propagation path estimation symbol 84 is a propagation path estimation symbol for the antenna a3. Contains information about.
Since there is no previous information at the time of the first transmission, the propagation path estimation symbol of the antenna a1 is added to the additional propagation path estimation symbol 82, the propagation path estimation symbol of the antenna a2 is added to the additional propagation path estimation symbol 83, and the additional propagation path A state where a propagation path estimation symbol of the antenna a3 is set in the estimation symbol 84 is used.

Next, the propagation path estimation symbol creation unit 12 generates an additional propagation path estimation symbol d8 to be used this time from the additional propagation path estimation symbol d8 at the previous transmission. In this embodiment, the band is divided and used by the number of outputs, so if only the same band is used, propagation path estimation errors other than that band increase, so the pattern is changed for each slot. To do.
There are various methods for changing the pattern. In this embodiment, the antennas a1, a2, and a3 to be assigned to the propagation path estimation symbols d55, d56, and d57 of the three bands are (antenna a1, antenna a2, and antenna a3). ) → (antenna a2, antenna a3, antenna a1) → (antenna a3, antenna a1, antenna a2) →...

  Next, the propagation path estimation symbol creation unit 12 sets the pattern of the additional propagation path estimation symbol d8 and the k ′ symbols in the broadcast slot so as to be used as a midamble (step S511). Then, propagation path estimation symbol creating section 12 inserts the pattern of additional propagation path estimation symbol d8 and k ′ symbols as midambles into the symbol corresponding to the transmission data transmitted from OFDM transmitting apparatus 100. The same k ′ midambles are used. As a result, the OFDM receiver can normally demodulate even if a midamble is inserted in the data symbol. There are various places where the midamble is inserted, but in this embodiment, the midamble is inserted at the position of the value obtained by dividing the number of data symbols by 2 (rounded down).

Next, the propagation path estimation symbol creation unit 12 stores the pattern of the additional propagation path estimation symbol d8 used this time, and generates a new additional propagation path estimation symbol d8 pattern in the next transmission. (Step S512).
Next, the propagation path estimation symbol creation unit 12 sets the broadcast slot so as not to use the midamble (step S513). As a result, the OFDM receiver knows that no midamble is used in the slot and can normally demodulate.
According to the fifth embodiment described above, the OFDM symbol transmission apparatus 100 can use surplus symbols as propagation path estimation symbols as correction symbols for estimating a propagation path, thereby improving propagation path estimation performance. Therefore, the reception performance in the OFDM receiver can be improved.

Next, processing of the OFDM transmission apparatus 100 according to the sixth embodiment of the present invention will be described.
In the fifth embodiment, even if there are a plurality of additional propagation path estimation symbols, the propagation path estimation symbols having the same contents are inserted. For this reason, an additional propagation path estimation symbol used by a certain antenna acts only on a specific band, and does not provide a correction effect over the entire band. In the sixth embodiment, a case will be described in which a correction effect is obtained over a plurality of bands or all bands by changing the transmission pattern for each symbol.

  FIG. 17 is a flowchart illustrating a part of the processing of the OFDM transmitter 100 according to the present embodiment. Since the processing according to the present embodiment overlaps with the processing of steps S501 to S508 and S513 of the fifth embodiment (see FIG. 12), description thereof is omitted. However, since the processing of steps S509 to S512 of the fifth embodiment is different in the present embodiment in that it is replaced by the processing according to the flowchart shown in FIG. 17, these processing will be described below.

First, the control unit 10 sets the value of the counter for internal processing to a value equal to the number k ′ of additional propagation path estimation symbols (step S601). Then, the propagation path estimation symbol creation unit 12 refers to the pattern of the additional propagation path estimation symbol used last time (step S602). Next, the propagation path estimation symbol creation unit 12 creates a new additional propagation path estimation symbol pattern from the previously used additional correction symbol pattern (step S603).
Next, the propagation path estimation symbol creation unit 12 generates one additional propagation path estimation symbol based on the newly created additional propagation path estimation symbol pattern (step S604). Then, the propagation path estimation symbol creation unit 12 records a newly used additional propagation path estimation symbol pattern (step S604).

Next, the control unit 10 decreases the value of the counter by 1 (step S606). Then, the control unit 10 determines whether or not the counter value is greater than 0 (step S607). If the value of the counter is greater than 0, “YES” is determined, and the process proceeds to step S602. On the other hand, if the value of the counter is 0 or less, “NO” is determined, and the process proceeds to step S608.
In step S608, the propagation path estimation symbol creation unit 12 sets the generated k ′ additional propagation path estimation symbols to be used as a midamble. Then, propagation path estimation symbol creation section 12 inserts k ′ additional propagation path estimation symbols as midambles in the symbols corresponding to the transmission data transmitted from OFDM transmission apparatus 100.
As a result, when a plurality of additional correction symbols can be used, correction symbols used for a signal from a certain antenna are transmitted in a plurality of bands, thereby enabling more accurate correction. FIG. 18A shows the case where k ′ = 2. In this figure, the additional propagation path estimation symbol is the additional propagation path estimation symbol 85 used for the signal from the antenna 1, the additional propagation path estimation symbol 86 used for the signal from the antenna 2, and the antenna 3. 2 are included for each of two additional propagation path estimation symbols 87 to be used for signals from.
According to the sixth embodiment described above, propagation path estimation performance for data transmitted from the OFDM transmitter 100 can be improved, and reception performance in the OFDM receiver can be improved.

Next, processing of the OFDM transmitter 100 according to the seventh embodiment of the present invention will be described.
In the fifth embodiment and the sixth embodiment, when assigning correction symbols for each antenna to additional propagation path estimation symbols, the band is divided by the number of outputs. On the other hand, in this embodiment, the band to be used is further divided finely, and additional propagation path estimation symbols used by each antenna are interleaved and assigned, so that all the bands used by each antenna are not rotated. It is possible to obtain correction information over a band. FIG. 18B shows an example in which the additional propagation path estimation symbols 82, 83, and 84 are divided into 12 parts. In this figure, the additional propagation path estimation symbol is the additional propagation path estimation symbol 85 used for the signal from the antenna 1, the additional propagation path estimation symbol 86 used for the signal from the antenna 2, and the antenna 3. Four additional propagation path estimation symbols 87 to be used for the signals from are included.
According to the seventh embodiment described above, the correction information can be obtained over the band used by the data symbol by extrapolating the correction information using the interleaved correction information on the OFDM receiver side. Therefore, more accurate correction can be performed.

  In the embodiment described above, a program for realizing the functions of the control unit 1, the modulation method determination unit 10, the AGC / AFC symbol creation unit 13, the MLI creation unit 15, and the like is recorded on a computer-readable recording medium. Then, the OFDM transmitter 100 may be controlled by causing the computer system to read and execute the program recorded on the recording medium. The “computer system” here includes an OS and hardware such as peripheral devices.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” dynamically holds a program for a short time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, it is also assumed that a server that holds a program for a certain time, such as a volatile memory inside a computer system that serves as a server or client. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

It is a figure which shows an example of the data structure transmitted from an OFDM transmitter. 1 is a block diagram showing a configuration of an OFDM transmission apparatus 100. FIG. It is a flowchart which shows the process of the OFDM transmitter 100 by the 1st Embodiment of this invention. It is a program for performing the process of the OFDM transmitter 100 by this embodiment. 2 is a diagram illustrating an example of a data configuration transmitted from an OFDM transmission apparatus 100. FIG. It is a flowchart which shows the process of the OFDM transmitter 100 by the 2nd Embodiment of this invention. It is a program for performing the process of the OFDM transmitter 100 by this embodiment. 2 is a diagram illustrating an example of a data configuration transmitted from an OFDM transmission apparatus 100. FIG. It is a flowchart which shows the process of the OFDM transmitter 100 by the 3rd Embodiment of this invention. It is a program for performing the process of the OFDM transmitter 100 by this embodiment. 2 is a diagram illustrating an example of a data configuration transmitted from an OFDM transmission apparatus 100. FIG. It is a flowchart which shows the process of the OFDM transmitter 100 by the 5th Embodiment of this invention. It is a program for performing the process of the OFDM transmitter 100 by this embodiment. 2 is a diagram illustrating an example of a data configuration transmitted from an OFDM transmission apparatus 100. FIG. It is a flowchart which shows the process of the OFDM transmitter 100 by the 6th Embodiment of this invention. It is a program for performing the process of the OFDM transmitter 100 by this embodiment. It is a flowchart which shows the process of the OFDM transmitter 100 by the 7th Embodiment of this invention. 2 is a diagram illustrating an example of a data configuration transmitted from an OFDM transmission apparatus 100. FIG. It is a block diagram which shows the structure of the OFDM transmitter 300 used for OFDM. It is a block diagram which shows the structure of the OFDM receiver 305 used for OFDM. It is a graph which shows the relationship between a subcarrier and the modulation system selected by SINR.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... OFDM transmitter, 1 ... Control part, 2 ... Mapping part, 3 ... IFFT part, 4 ... P / S conversion part, 5 ... GI insertion part, 6 ... Signal switching unit, 7 ... D / A conversion unit, 8 ... radio transmission unit, 9 ... antenna unit, 10 ... modulation method determination unit, 11 ... SINR storage unit, 12 ... Propagation path estimation symbol creation unit, 13 ... AGC / AFC symbol creation unit, 14 ... reception unit, 15 ... MLI creation unit, 300 ... OFDM transmission device, 3001 ... error correction Code unit, 3002... S / P converter, 3003... Mapping unit, 3004... IFFT unit, 3005... P / S converter, 3006. / A conversion unit, 3008 ... wireless transmission unit, 3009 ... antenna unit, 30 ... OFDM receiver, 3051 ... error correction decoding unit, 3052 ... P / S conversion unit, 3053 ... propagation path estimation / demapping unit, 3054 ... FFT unit, 3055 ... S / P conversion unit, 3056 ... GI removal unit, 3057 ... A / D conversion unit, 3058 ... wireless reception unit, 3059 ... antenna unit, 3060 ... synchronization unit

Claims (10)

An OFDM transmission method for transmitting data of a fixed length using a plurality of symbols,
An additional correction symbol that is the number of symbols inserted into the fixed-length data from the number of symbols corresponding to the fixed-length data and the number of symbols used for actual transmission data when adaptive modulation is performed on the subcarrier by the control means A first step of calculating a number;
Secondly, a propagation path estimation symbol creating means inserts a correction symbol for estimating propagation path characteristics for a symbol corresponding to the fixed-length data based on the number of additional correction symbols calculated by the control means. And the steps
An OFDM transmission method comprising: An OFDM transmitter that transmits data of a certain length using a plurality of symbols,
Control means for calculating the number of additional correction symbols, which is the number of symbols to be inserted, from the number of symbols corresponding to the fixed-length data when adaptive modulation is performed for subcarriers and the number of symbols used for actual transmission data;
Propagation path estimation symbol creating means for inserting a correction symbol for estimating propagation path characteristics for a symbol corresponding to the fixed length data based on the number of additional correction symbols calculated by the control means;
An OFDM transmitter characterized by comprising:   The OFDM transmission apparatus according to claim 2, wherein the propagation path estimation symbol creating means inserts a correction symbol by a preamble into a symbol corresponding to the fixed length data.   3. The OFDM transmission apparatus according to claim 2, wherein the propagation path estimation symbol creating means inserts a correction symbol by midamble into a symbol corresponding to the fixed length data.   The OFDM transmission apparatus according to claim 2, wherein the propagation path estimation symbol creating means inserts a correction symbol by a postamble into a symbol corresponding to the fixed length data.   The propagation path estimation symbol creating means inserts at least two or more correction symbols configured by any one of a preamble, a midamble, and a postamble with respect to a symbol corresponding to the fixed-length data. The OFDM transmitter according to claim 2.   The propagation path estimation symbol creating means divides the additional correction symbol based on the number of antennas used for transmitting the fixed-length data, and based on the divided additional correction symbol, corrects the correction symbol to the fixed-length symbol. The OFDM transmitter according to claim 2, wherein a symbol corresponding to the data is inserted.   8. The OFDM transmission according to claim 7, wherein the propagation path estimation symbol creating unit changes an insertion pattern of correction symbols to be inserted based on the divided additional correction symbols for each of the divided additional correction symbols. apparatus.   The propagation path estimation symbol creation means divides the additional correction symbol more than the number of antennas when inserting a correction symbol into a symbol corresponding to the fixed-length data, and the divided additional correction symbol 8. The OFDM transmission apparatus according to claim 7, wherein correction symbols are inserted by interleaving with respect to symbols corresponding to the fixed-length data based on the data. An OFDM transmission program that transmits data of a certain length using a plurality of symbols,
The number of additional correction symbols, which is the number of symbols to be inserted into the fixed-length data, is calculated from the number of symbols corresponding to the fixed-length data and the number of symbols used for actual transmission data when adaptive modulation is performed for the subcarrier. A first step;
A second step of inserting a correction symbol for estimating a propagation path characteristic for a symbol corresponding to the fixed-length data based on the number of additional correction symbols calculated in the first step;
An OFDM transmission program comprising:

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