JP6511273B2 - OFDM transmitter and OFDM transmission method - Google Patents

Description

  The present invention relates to an OFDM transmitter and an OFDM transmission method used for communication of orthogonal frequency division multiplexing (OFDM).

  Conventionally, an OFDM transmitter that generates an OFDM signal in which the same transmission data is distributed to a plurality of carrier frequencies is known (for example, Patent Document 1).

  FIG. 1 is a diagram showing a conventional OFDM signal. In the conventional OFDM signal, as shown in FIG. 1, the same transmission data # 1 is transmitted to two carrier frequencies of carrier frequencies # 1 to #n and carrier frequencies # n + 1 to # 2n for all carrier frequencies. Each #n is distributed.

  Thus, by distributing the same transmission data to a plurality of carrier frequencies, it is possible to avoid interference due to the adjacent channel interference wave in the presence of the adjacent channel interference wave.

JP, 2006-74081, A

  However, in the conventional OFDM transmitter, since the same transmission data is distributed to all the carrier frequencies to generate OFDM signals, there is a problem that the frequency utilization efficiency is lowered.

  An object of the present invention is to provide an OFDM transmitter and an OFDM transmission method capable of avoiding interference without reducing frequency utilization efficiency and achieving both improvement in frequency utilization efficiency and avoidance of interference. It is.

The OFDM transmitter according to the present invention performs orthogonal frequency division multiplexing processing on transmission data composed of a plurality of bits, thereby selecting a predetermined number in order from the most significant digit of the bit string in which the plurality of bits are arranged. Orthogonal frequency division multiplexing means for generating an OFDM signal in which the upper bits which are a part of the bits are arranged on a single carrier frequency and the lower bits which are the remaining bits are arranged redundantly on a plurality of carrier frequencies; And transmitting means for transmitting the OFDM signal.

The OFDM transmission method according to the present invention performs orthogonal frequency division multiplexing processing on transmission data composed of a plurality of bits to select a predetermined number in order from the most significant digit of the bit string in which the plurality of bits are arranged. Generating an OFDM signal in which the upper bits which are a portion of the bits are arranged on a single carrier frequency and the lower bits which are the remaining bits are arranged redundantly on a plurality of carrier frequencies; And transmitting.

  According to the present invention, it is possible to avoid interference and increase frequency utilization efficiency as much as possible, and it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference.

Diagram showing a conventional OFDM signal A block diagram showing a configuration of an OFDM transmitter according to Embodiment 1 of the present invention A diagram showing an OFDM signal according to Embodiment 1 of the present invention Diagram showing the constellation of 8 PSK A block diagram showing a configuration of an OFDM transmitter according to Embodiment 2 of the present invention A diagram showing an OFDM signal according to Embodiment 2 of the present invention A diagram showing an OFDM signal according to Embodiment 3 of the present invention FIG. 14 is a block diagram showing the configuration of an OFDM transmission apparatus according to Embodiment 4 of the present invention The figure which shows the OFDM signal which concerns on Embodiment 4 of this invention. The block diagram which shows the structure of the OFDM transmitter which concerns on Embodiment 5 of this invention FIG. 16 is a flow chart showing the operation of the OFDM transmitting apparatus according to the fifth embodiment of the present invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

Embodiment 1
<Configuration of OFDM Transmitter>
The configuration of the OFDM transmitter 100 according to the first embodiment of the present invention will be described in detail below with reference to FIG.

  The OFDM transmission apparatus 100 includes a first selection unit 101, a first carrier arrangement unit 102, a second carrier arrangement unit 103, a second selection unit 104, a modulation unit 105, a Fourier inverse transform unit 106, and a transmission unit. And an antenna 108.

  The first selection unit 101 receives transmission data composed of a bit string in which a plurality of bits are arranged, and outputs, to the first carrier placement unit 102, upper bits selected by a predetermined number in order from the most significant digit of the bit string. The lower bits which are the remaining bits other than the upper bits in the bit string are output to the second carrier allocation unit 103. As a typical example, in the case of performing modulation of 3-bit 1 symbol such as 8 PSK, etc., the first selection unit 101 divides the bit string of transmission data into every 5 bits, and 3 bits as upper bits (first bit, second bit) And the remaining one bit is output to the second carrier arranging section 103 as the lower bit (third bit).

  The first carrier arranging unit 102 arranges the upper bits output from the first selecting unit 101 so as to be distributed to a predetermined single carrier frequency, and outputs the upper bits to the second selecting unit 104.

  Second carrier arranging section 103 arranges the lower bits output from first selecting section 101 so as to be distributed to a plurality of predetermined carrier frequencies, and outputs the result to second selecting section 104. For example, when performing modulation of 3-bit 1 symbol such as 8 PSK, the second carrier allocation unit 103 arranges each input lower bit so as to be distributed to two carrier frequencies.

  The second selection unit 104 outputs the upper bits output from the first carrier placement unit 102 and the lower bits output from the second carrier placement unit 103 to the modulation unit 105 at a predetermined timing.

  The modulation unit 105 performs multi-value modulation on the upper bits and the lower bits output from the second selection unit 104 to generate a modulation signal, and outputs the modulation signal to the inverse Fourier transform unit 106.

  The inverse Fourier transform unit 106 performs inverse Fourier transform, which is orthogonal frequency division multiplexing processing, on the modulation signal output from the modulation unit 105 to generate an OFDM signal, and outputs the OFDM signal to the transmission unit 107.

  The transmitting unit 107 performs RF processing on the OFDM signal output from the inverse Fourier transform unit 106 and transmits the signal from the antenna 108.

<Operation of OFDM transmitter>
The operation of the OFDM transmission apparatus 100 according to Embodiment 1 of the present invention will be described in detail below with reference to FIGS. 3 and 4. In FIGS. 3 and 4, the case where transmission data is 8PSK modulated will be described as an example. Further, in FIG. 3, “transmission data” is simply described as “data”, and “carrier frequency” is simply described as “carrier”.

  First, each bit of transmission data is divided by the first selection unit 101 into one disposed as the upper bits (first bit, second bit) and one disposed as the lower bits (third bit). The one arranged as the upper bits is output to the first carrier placement unit 102, and the one placed as the lower bits is output to the second carrier placement unit 103.

  Next, the higher-order bits are allocated by the first carrier allocation unit 102 so as to be distributed to a single carrier frequency of a frequency band (hereinafter referred to as “used frequency band”) F1 used for OFDM transmission. Further, the lower order bits are allocated by the second carrier allocation unit 103 to a plurality of (for example, two) carrier frequencies in the use frequency band F1.

  Next, the high order bit and the low order bit are output to the modulation unit 105 at a predetermined timing by the second selection unit 104 and subjected to multi-level modulation by the modulation unit 105 to become a modulation signal.

  Next, the multilevel modulation signal is subjected to inverse Fourier transform by the inverse Fourier transform unit 106 to be an OFDM signal.

  Next, the OFDM signal is subjected to RF processing by the transmission unit 107 and transmitted from the antenna 108.

  As shown in FIG. 3, such an OFDM signal is divided into the first bit #i (#i is an integer from 1 to 2 n) and the second bit #i, which are upper bits, to a single carrier frequency #i. The third bit #j (#j is an integer from 1 to n), which is the lower bit, is distributed to two carrier frequencies #j and # n + j.

In FIG. 3, the first to third bits are transmitted on the carrier frequency # 1, the next to third bits are transmitted on the carrier frequency # 2, and thereafter, three bits are transmitted on the same carrier frequency .

  In the 8 PSK constellation (I-Q plane) of FIG. 4, the interval of the determination threshold H2 of the third bit indicated by the broken line is narrower than the interval of the determination threshold H1 of the first bit and the second bit indicated by the solid line. Therefore, the third bit is more likely to be erroneous than the first and second bits.

  On the other hand, in the present embodiment, even in the environment where adjacent channel interference waves exist, by generating an OFDM signal in which lower bits that are more likely to be erroneous compared to higher bits are allocated to a plurality of carrier frequencies. The error rate of the third bit, which is the lower bit, can be reduced, and interference can be avoided. In addition, it is possible to suppress a decrease in frequency utilization efficiency by generating an OFDM signal in which upper bits less error prone than lower bits are allocated to a single carrier frequency. From this, according to the present embodiment, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference.

  In the present embodiment, although the case of using 8 PSK as the modulation scheme has been described, the present invention is not limited to 8 PSK, and any modulation scheme can be used as long as it can transmit information of 3 bits or more in one symbol. Modulation schemes (eg, 16 QAM, 64 QAM, 256 QAM, etc.). For example, in the case where the present invention is applied to 16 QAM, the third and fourth bits, which are lower bits, are arranged redundantly on a plurality of carriers.

  In the present embodiment, although the lower bit (for example, the third bit in the case of 8 PSK) is redundantly arranged on two carriers, the present invention redundantly arranges the same information. The number of carriers is not limited to two, and can be set to an arbitrary number of carriers. For example, the lower bits may be arranged redundantly to four carriers or the like. Of course, it is also possible to adaptively change the number of carriers in which the lower bits are redundantly arranged, depending on channel quality or the like (such as the level of the adjacent channel interference wave).

Second Embodiment
The configuration of the OFDM transmission apparatus 500 according to Embodiment 2 of the present invention will be described in detail below with reference to FIG.

  The OFDM transmitter 500 includes a turbo coding unit 501, a first selection unit 502, a first carrier arrangement unit 503, a second carrier arrangement unit 504, a second selection unit 505, a modulation unit 506, and a Fourier inverse. A converter 507, a transmitter 508, and an antenna 509 are included.

  The turbo coding unit 501 turbo-codes input data to generate transmission data including parity bit 1, parity bit 2 and systematic bits. Turbo coding section 501 outputs the generated parity bit 1, parity bit 2 and systematic bit to second selecting section 502.

  The first selection unit 502 outputs the parity bit 1 and the parity bit 2 which are partial bits output from the turbo coding unit 501 to the first carrier arrangement unit 503. The second selection unit 502 outputs systematic bits, which are the remaining bits output from the turbo coding unit 501, to the second carrier arrangement unit 504.

  The first carrier placement unit 503 places the parity bit 1 and the parity bit 2 output from the first selection unit 502 so as to be distributed to a predetermined single carrier frequency, and outputs the result to the second selection unit 505.

  The second carrier allocation unit 504 arranges the systematic bits output from the first selection unit 502 so as to be distributed to a plurality of predetermined carrier frequencies, and outputs the systematic bits to the second selection unit 505.

  The second selection unit 505 outputs the parity bit 1 and the parity bit 2 output from the first carrier placement unit 503 and the systematic bits output from the second carrier placement unit 504 to the modulation unit 506 at a predetermined timing. Do.

  The modulation unit 506 modulates the parity bit 1, the parity bit 2 and the systematic bit output from the second selection unit 505 to generate a modulation signal and outputs the modulation signal to the inverse Fourier transform unit 507.

  The inverse Fourier transform unit 507 performs inverse Fourier transform, which is orthogonal frequency division multiplexing processing, on the modulated signal output from the modulation unit 506 to generate an OFDM signal, and outputs the OFDM signal to the transmission unit 508.

  The transmitting unit 508 performs RF processing on the OFDM signal output from the inverse Fourier transform unit 507 and transmits the signal from the antenna 509.

<Operation of OFDM transmitter>
The operation of the OFDM transmission apparatus 500 according to Embodiment 2 of the present invention will be described in detail below with reference to FIG. In FIG. 6, "transmission data" is simply described as "data", and "carrier frequency" is simply described as "carrier".

  First, input data is turbo-coded by the turbo coding unit 501 to become transmission data composed of parity bit 1, parity bit 2 and systematic bits.

  Next, the parity bit 1 and the parity bit 2 are output to the first carrier placement unit 503 by the first selection unit 502, and the systematic bits are output to the second carrier placement unit 504 by the first selection unit 502.

  Next, parity bit 1 and parity bit 2 are arranged by first carrier arranging section 503 so as to be distributed to a single carrier frequency of use frequency band F2. Also, systematic bits are allocated by the second carrier allocation unit 504 to a plurality of carrier frequencies of the use frequency band F2.

  Next, the parity bit 1, the parity bit 2 and the systematic bit are output to the modulation unit 506 at a predetermined timing by the second selection unit 505, and are modulated by the modulation unit 506 to become a modulation signal.

  Next, the modulation signal is subjected to Fourier inverse transform by the inverse Fourier transform unit 507 to be an OFDM signal.

  Next, the OFDM signal is RF-processed by the transmitting unit 508 and transmitted from the antenna 509.

  In such an OFDM signal, as shown in FIG. 6, parity bit 1 # j (#j is an integer from 1 to n) is distributed to a single carrier frequency #j and parity bit 2 # j is single. As well as distributing to carrier frequency # n + j, systematic bit #j is distributed to two carrier frequencies #j and # n + j.

In FIG. 6, the first parity bit and systematic bit are transmitted on carrier frequency # 1, the next parity bit and systematic bit are transmitted on carrier frequency # 2, and thereafter, the pair of parity bit and systematic bit is on the same carrier frequency. Will be sent.

  In this embodiment, the error rate of systematic bits is generated even in the presence of adjacent channel interference waves by generating an OFDM signal in which systematic bits more important than parity bits are allocated to a plurality of carrier frequencies. Can be reduced and interference can be avoided. In addition, it is possible to suppress a decrease in frequency utilization efficiency by generating an OFDM signal in which parity bit 1 and parity bit 2 which are less important than systematic bits are allocated to a single carrier frequency. From this, according to the present embodiment, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference.

Third Embodiment
In the present embodiment, the configuration of the OFDM transmission apparatus is the same as that shown in FIG. Further, in the present embodiment, description will be made using the symbols of the OFDM transmitter of FIG.

<Operation of OFDM transmitter>
The operation of the OFDM transmitting apparatus 100 according to Embodiment 3 of the present invention will be described in detail below with reference to FIG. In FIG. 7, the case of using a 6-bit 1-symbol modulation scheme such as 64 QAM will be described as an example. Further, in FIG. 7, “transmission data” is simply described as “data”, and “carrier frequency” is simply described as “carrier”.

  In the OFDM signal of the present embodiment, as shown in FIG. 7, the upper bits 1st and 2nd bits are allocated to single carrier frequencies # 1 to # 4n, and the middle to lower bits are 3 The sixth to sixth bits are distributed to a predetermined number of carrier frequencies # 1 to #n and carrier frequencies # 3n + 1 to # 4n sequentially selected from the carrier frequency # 1 and the carrier frequency # 4n at both ends of the use frequency band F3. The carrier frequencies # 1 to #n and the carrier frequencies # 3 n + 1 to # 4 n carrier frequencies # n + 1 to # 2 n, which are the lower bits 5th and 6th bits, and the third to 6th bits. Carrier frequencies # 2n + 1 to # 3n are allocated.

  Specifically, the first and second bits of transmission data # 1 are distributed only to a single carrier frequency # 1, and the third to sixth bits, which are lower bits of transmission data # 1, are a plurality of carriers. It is distributed to frequency # 1 and carrier frequency # 3n + 1. The fifth and sixth bits of the transmission data # n + 1 are distributed to a plurality of carrier frequencies # n + 1 and 2n + 1. Transmission data # 2 to #n and transmission data # n + 2 and subsequent ones are also distributed in the same manner as transmission data # 1 and transmission data # n + 1.

  As described above, in this embodiment, the number of lower bits allocated to carrier frequencies # 1 to #n and carrier frequencies # 3n + 1 to # 4n, and carrier frequencies # n + 1 to # 2n and carrier frequencies # 2n + 1 to # 3n. Make the number of lower bits distributed to be different.

7, the first 1-6 bit is transmitted at the carrier frequency # 1, 1-6 bit of the next is transmitted at a carrier frequency # 2, since, 6 bits are transmitted at the same carrier frequency.

  In this embodiment, by generating an OFDM signal in which lower bits that are more likely to be erroneous compared to higher bits are allocated to a plurality of carrier frequencies, the lower bits can be generated even in the presence of adjacent channel interference waves. The error rate of the sixth bit from the bit can be reduced, and interference can be avoided. In addition, it is possible to suppress a decrease in frequency utilization efficiency by generating an OFDM signal in which upper bits less error prone than lower bits are allocated to a single carrier frequency. From this, according to the present embodiment, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference.

  Further, in the present embodiment, the carrier frequency to which the third and fourth bits are assigned as the number of carrier frequencies to which the fifth and sixth bits are assigned more easily than the third and fourth bits which are lower bits. The error rate of the 5th bit and the 6th bit can be improved by making it more than the number of n, and interference can be further avoided. Further, an OFDM signal is generated in which the number of carrier frequencies for distributing the third bit and the fourth bit, which is less likely to be erroneous than the fifth bit and the sixth bit, is smaller than the number of carrier frequencies for distributing the fifth bit and the sixth bit. Thus, it is possible to suppress a decrease in frequency utilization efficiency. From this, according to the present embodiment, it is possible to achieve further coexistence of improvement of frequency utilization efficiency and avoidance of interference.

  As described above, according to the present embodiment, the lower bits are composed of a plurality of bits by generating an OFDM signal in which the number of lower bits allocated to the plurality of carrier frequencies is made different for each of the plurality of carrier frequencies. Even in the case of multi-level modulation such as 64-value modulation, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference.

  Also in the present embodiment, the number of carriers in which the 5th bit and the 6th bit are overlapped can be set arbitrarily, and can be adaptively changed according to the channel quality or the like. The same applies to the third and fourth bits.

Embodiment 4
<Configuration of OFDM Transmitter>
The configuration of the OFDM transmission apparatus 800 according to Embodiment 4 of the present invention will be described in detail below with reference to FIG.

  The OFDM transmitter 800 includes a first selection unit 801, a first carrier allocation unit 802, a second carrier allocation unit 803, a second selection unit 804, a modulation unit 805, a Fourier inverse transform unit 806, and a transmission unit. And an antenna 808.

  Of the transmission data, the first selection unit 801 transmits to the first carrier arrangement unit 802 transmission data that can be distributed to carrier frequencies other than the carrier frequency at the end of the use frequency band (hereinafter referred to as “inner carrier frequency”). While outputting, the transmission data to be distributed to the carrier frequency at the end of the use frequency band (hereinafter referred to as “outside carrier frequency”) is output to the second carrier arrangement unit 803. Here, the carrier frequency at the end is not limited to one, and may be plural.

  The first carrier placement unit 802 places the transmission data output from the first selection unit 801 so as to be distributed to the inner carrier frequency, and outputs the transmission data to the second selection unit 804.

  The second carrier placement unit 803 places the transmission data output from the first selection unit 801 so as to be distributed to the outer carrier frequency, and outputs the transmission data to the second selection unit 804.

  The second selection unit 804 outputs the transmission data output from the first carrier placement unit 802 and the transmission data output from the second carrier placement unit 803 to the modulation unit 805 at a predetermined timing.

  The modulation unit 805 performs multi-level modulation on the transmission data output from the second selection unit 804 to generate a modulation signal, and outputs the modulation signal to the inverse Fourier transform unit 806.

  The inverse Fourier transform unit 806 generates an OFDM signal by performing inverse Fourier transform, which is orthogonal frequency division multiplexing processing, on the modulation signal output from the modulation unit 805, and outputs the OFDM signal to the transmission unit 807.

  The transmission unit 807 RF-processes the OFDM signal output from the inverse Fourier transform unit 806 and transmits it from the antenna 808.

<Operation of OFDM transmitter>
The operation of the OFDM transmitter 800 according to Embodiment 4 of the present invention will be described in detail below with reference to FIG.

  First, transmission data distributed to the inner carrier frequency is output to the first carrier arrangement unit 802 by the first selection unit 801. The transmission data distributed to the outer carrier frequency is output by the first selection unit 801 to the second carrier allocation unit 803.

  Next, the transmission data distributed to the inner carrier frequency is arranged by the first carrier arrangement unit 802 so as to be distributed to a single inner carrier frequency. Further, transmission data distributed to the outer carrier frequency is arranged by the second carrier allocation unit 803 so as to be distributed to a plurality of outer carrier frequencies.

  Next, the transmission data distributed to the inner carrier frequency and the transmission data distributed to the outer carrier frequency are output by the second selection unit 804 to the modulation unit 805 at a predetermined timing.

  Next, the transmission data is output to the modulation unit 805 at a predetermined timing by the second selection unit 804, and is modulated by the modulation unit 805 to be a modulation signal.

  Next, the modulation signal is subjected to Fourier inverse transform by the inverse Fourier transform unit 806 to be an OFDM signal.

  Next, the OFDM signal is RF-processed by the transmission unit 807 and transmitted from the antenna 808.

  In such an OFDM signal, as shown in FIG. 9, transmission data # 1 is distributed to a plurality of outer carrier frequency signals # 1 and outer carrier frequency signals # 2 n-1 of the use frequency band F4 and transmission data # 2 Are distributed to a plurality of outer carrier frequency signals # 2 and an outer carrier frequency signal # 2 n. Further, in the OFDM signal, transmission data # 3 to # 2n-2 are distributed to a single inner carrier frequency signal # 3 to # 2n-2.

  In this embodiment, an environment where adjacent channel interference waves exist is generated by generating an OFDM signal in which transmission data distributed to the outer carrier frequency susceptible to adjacent channel interference waves is divided into a plurality of outer carrier frequencies. Even the error rate can be reduced and interference can be avoided. In addition, it is possible to suppress a decrease in frequency utilization efficiency by generating an OFDM signal in which transmission data distributed to the inner carrier frequency is distributed to a single inner carrier frequency. From this, according to the present embodiment, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference.

Fifth Embodiment
<Configuration of OFDM Transmitter>
The configuration of the OFDM transmission apparatus 1000 according to Embodiment 5 of the present invention will be described in detail below with reference to FIG.

  The OFDM transmitter 1000 includes a first selection unit 1001, a first carrier arrangement unit 1002, a second carrier arrangement unit 1003, a second selection unit 1004, a modulation unit 1005, a Fourier inverse transform unit 1006, and a transmission unit. 1007, an antenna 1008, an antenna 1051, a receiving unit 1052, a level detection unit 1053, and a carrier placement control unit 1054.

  Among the transmission data, the first selection unit 1001 outputs, to the first carrier arrangement unit 1002, transmission data to be distributed to carrier frequencies other than the carrier frequency at the end of the use frequency band under the control of the carrier arrangement control unit 1054. The transmission data distributed to the carrier frequency at the end of the use frequency band is output to the second carrier arrangement unit 1003.

  First carrier arranging section 1002 arranges the transmission data outputted from first selecting section 1001 so that it can be distributed to carrier frequencies other than the carrier frequency at the end of the used frequency band, and outputs it to second selecting section 1004 .

  The second carrier allocation unit 1003 arranges the transmission data output from the first selection unit 1001 so as to be distributed to the carrier frequency at the end of the use frequency band, and outputs the transmission data to the second selection unit 1004.

  The second selection unit 1004 modulates the transmission data output from the first carrier allocation unit 1002 and the transmission data output from the second carrier allocation unit 1003 at a predetermined timing according to the control of the carrier allocation control unit 1054. Output to

  The modulation unit 1005 performs multi-level modulation on the transmission data output from the second selection unit 1004 to generate a modulation signal, and outputs the modulation signal to the inverse Fourier transform unit 1006.

  The inverse Fourier transform unit 1006 generates an OFDM signal by performing inverse Fourier transform, which is orthogonal frequency division multiplexing processing, on the modulation signal output from the modulation unit 1005, and outputs the OFDM signal to the transmission unit 1007.

  The transmitting unit 1007 RF-processes the OFDM signal output from the inverse Fourier transform unit 1006 and transmits it from the antenna 1008.

  The receiving unit 1052 performs RF processing on the received signal received from the antenna 1051 and outputs the processed signal to the level detection unit 1053.

  Level detection unit 1053 detects the interference wave level of the reception signal output from reception unit 1052, and outputs an electrical signal indicating the detection result to carrier placement control unit 1054.

  The carrier placement control unit 1054 sets the range of the carrier frequency to which the same transmission data is distributed, according to the detection result of the interference wave level indicated by the electric signal output from the level detection unit 1053. The carrier placement control unit 1054 controls the first selection unit 1001 and the second selection unit 1004 to distribute the same transmission data to the set carrier frequencies.

<Operation of OFDM transmitter>
The operation of the OFDM transmitter 1000 according to the fifth embodiment of the present invention will be described in detail below with reference to FIG. In the following description, the magnitude relationship between the values of the thresholds Th1, Th2, and Th3 is Th1>Th2> Th3.

  First, the level detection unit 1053 detects the interference wave level of the received signal (S1101).

  Next, the carrier placement control unit 1054 determines whether the interference wave level detected by the level detection unit 1053 is larger than the threshold Th1 (S1102).

  When the interference wave level is larger than the threshold Th1 (S1102: YES), the carrier allocation control unit 1054 selects the first selection unit 1001 and the second selection unit 100 to distribute the same transmission data to all carrier frequencies in the use frequency band. The unit 1004 is controlled (S1103).

  On the other hand, when the interference wave level is equal to or less than the threshold Th1 (S1102: NO), the carrier placement control unit 1054 determines whether the interference wave level detected by the level detection unit 1053 is larger than the threshold Th2 (S1104).

  When the interference wave level is larger than the threshold Th2 (S1104: YES), the carrier allocation control unit 1054 distributes the same transmission data to the outer carrier frequency of a half of the used frequency band. And control the second selection unit 1004 (S1105).

  On the other hand, when the interference wave level is equal to or less than the threshold Th2 (S1104: NO), the carrier placement control unit 1054 determines whether the interference wave level detected by the level detection unit 1053 is larger than the threshold Th3 (S1106).

  When the interference wave level is higher than the threshold Th3 (S1106: YES), the carrier allocation control unit 1054 distributes the same transmission data to the outer carrier frequency of 1⁄4 of the used frequency band. And control the second selection unit 1004 (S1107).

  On the other hand, when the interference wave level is less than or equal to the threshold Th3 (S1106: NO), the carrier allocation control unit 1054 distributes the first selection unit 1001 and the first selection unit 1001 to distribute one transmission data to all carrier frequencies in the use frequency band. The second selection unit 1004 is controlled (S1108).

  As described above, according to the present embodiment, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference by varying the number of carrier frequencies to which the same transmission data is distributed according to the interference wave level. Can.

  In the present embodiment, carrier arrangement control section 1054 may generate control information indicating the range of carrier frequencies to which the same transmission data is distributed, and cause the control information to be superimposed on the OFDM signal. As a result, the OFDM receiving apparatus at the other end of communication can easily know the carrier frequency to which the same transmission data is distributed, and can demodulate the received OFDM signal.

(Variation 1)
In the first embodiment described above, it is assumed that some bits are arranged on a single frequency carrier on the premise that the use frequency band is constant, but the present invention is not limited to this, and the use frequency band is When variable, and when the use frequency band is narrow, all bits may be arranged on a plurality of frequency carriers.

  Hereinafter, this variation will be described. In this variation, the configuration of the OFDM transmitter is the same as that shown in FIG.

  When the first selection unit 101 receives transmission data composed of a bit string in which a plurality of bits are arranged, all bits of the upper bits and the lower bits of the bit string are used as the second carrier when the use frequency band is equal to or less than a predetermined value. Output to arrangement section 103.

  When the use frequency band is equal to or less than a predetermined value, the first carrier arranging unit 102 does not operate because the upper bits and the lower bits are not input.

  The second carrier allocation unit 103 arranges the upper bits and the lower bits output from the first selection unit 101 so that they can be distributed to a plurality of carrier frequencies in the use frequency band when the use frequency band is less than or equal to a predetermined value. Output to the second selection unit 104.

  When the use frequency band is equal to or less than a predetermined value, the second selection unit 104 outputs the upper bits and the lower bits output from the second carrier arrangement unit 103 to the modulation unit 105 at a predetermined timing.

  When the frequency band to be used is larger than the predetermined value, the operation is the same as that of the first embodiment, and thus the description thereof is omitted.

  Thus, according to the present variation, in addition to the effects of the first embodiment, when the use frequency band is equal to or less than a predetermined value, an OFDM signal is generated in which all bits of a plurality of bits are divided into a plurality of carrier frequencies. By doing this, it is possible to achieve both improvement in frequency utilization efficiency and avoidance of interference when the frequency band to be used is narrow.

  This variation can also be applied to the second to fifth embodiments.

(Variation 2)
In the first embodiment, the case where some bits are arranged on a single frequency carrier has been described on the premise that the environment of the used frequency band is uniform, but the present invention is not limited to this. When a specific frequency band such as white space is included in the frequency band, more bits may be allocated to the carrier frequency of the specific frequency band than the other carrier frequencies. Further, all the bits may be redundantly arranged on the carrier frequency of the specific frequency band.

  The white space is a vacant frequency band provided as a gap for preventing interference between channels in the terrestrial television broadcast frequency band. In addition to the white space, there are discrete frequency bands that exist discretely in some areas, and these discrete frequency bands may be specified frequency bands as well as the white space.

  Hereinafter, this variation will be described. In this variation, the configuration of the OFDM transmitter is the same as that shown in FIG.

  When the first selection unit 101 receives transmission data composed of a bit string in which a plurality of bits are arranged, all bits of the high-order bit and the low-order bit of the bit string are transmitted to the second carrier arrangement unit 103 for a specific frequency band. Output.

  The first carrier placement unit 102 does not operate because the upper bit and the lower bit are not input for a specific frequency band.

  The second carrier allocation unit 103 arranges the upper bits and the lower bits output from the first selection unit 101 so as to be distributed to a plurality of carrier frequencies for a specific frequency band, and outputs the upper bits and the lower bits to the second selection unit 104. .

  The second selection unit 104 outputs the upper bits and the lower bits output from the second carrier allocation unit 103 to the modulation unit 105 at a predetermined timing for a specific frequency band.

  In addition, about frequency bands other than a specific frequency band, since it becomes the same operation | movement as said Embodiment 1, the description is abbreviate | omitted.

  As described above, according to the present variation, in addition to the effects of the first embodiment, the number of bits allocated to the carrier frequency of the specific frequency in the used frequency band is allocated to the carrier frequency of frequencies other than the specific frequency. By generating more OFDM signals, it is possible to lower the transmission level of the carrier frequency of a specific frequency, so interference to other communication devices can be reduced.

  This variation can also be applied to the second to fifth embodiments.

  The present invention is not limited to the above-described embodiment in the type, arrangement, number, etc. of members, and the constituent elements thereof may be appropriately replaced with ones having equivalent functions and effects without departing from the scope of the invention. Of course, it can be changed as appropriate.

  The present invention is suitable for use in an apparatus that performs OFDM communication.

100, 500, 800, 1000 OFDM transmitter 101, 502, 801, 1001 first selection unit 102, 503, 802, 1002 first carrier arrangement unit 103, 504, 803, 1003 second carrier arrangement unit 104, 505, 804 , 1004 second selection unit 105, 506, 805, 1005 modulation unit 106, 507, 806, 1006 Fourier inverse transform unit 107, 508, 807, 1007 transmission unit 108, 509, 808, 1008, 1051 antenna 501 turbo encoding unit 1052 receiver 1053 level detector 1054 carrier placement controller

Claims (5)

By performing orthogonal frequency division multiplexing processing on transmission data composed of a plurality of bits, upper bits that are partial bits selected by a predetermined number sequentially from the most significant digit of the bit string in which the plurality of bits are arranged And orthogonal frequency division multiplexing means for generating an OFDM signal in which the following are arranged on a single carrier frequency and the lower bits which are the remaining bits are arranged redundantly on a plurality of carrier frequencies.
Transmission means for transmitting the OFDM signal;
OFDM transmitter comprising. The orthogonal frequency division multiplexing means
Wherein the number of carrier frequencies that fallible some bits among the lower bits are arranged overlapping, errors hardly some bits of the lower bits is greater than the number of carrier frequencies arranged overlapping Generate an OFDM signal,
The OFDM transmitter according to claim 1. The orthogonal frequency division multiplexing means
When a frequency band used to transmit data is variable, when the frequency band is larger than a predetermined value, a predetermined number is selected in order from the most significant digit of the bit string in which the plurality of bits are arranged Generating the OFDM signal in which the upper bits, which are the bits of R, are placed on a single carrier frequency, and the lower bits, which are the remaining bits, are placed redundantly on a plurality of carrier frequencies.
The OFDM transmitter according to any one of claims 1 or 2. The orthogonal frequency division multiplexing means
When a frequency band used for transmitting an OFDM signal includes a discrete frequency band, the number of bits allocated to the carrier frequency of the vacant frequency band may be a carrier of a frequency other than the frequency band. Generate an OFDM signal with more than the number of bits placed in the frequency,
The OFDM transmitter according to any one of claims 1 or 2. By performing orthogonal frequency division multiplexing processing on transmission data composed of a plurality of bits, upper bits that are partial bits selected by a predetermined number sequentially from the most significant digit of the bit string in which the plurality of bits are arranged Generating an OFDM signal in which the first and second lower bits, which are the remaining bits, are placed redundantly on a plurality of carrier frequencies,
Transmitting the OFDM signal;
OFDM transmission method comprising.

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