JP4390636B2 - OFDM signal frame generator, transmitter, signal transmission system, and OFDM signal frame generation method - Google Patents

OFDM signal frame generator, transmitter, signal transmission system, and OFDM signal frame generation method Download PDF

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JP4390636B2
JP4390636B2 JP2004174644A JP2004174644A JP4390636B2 JP 4390636 B2 JP4390636 B2 JP 4390636B2 JP 2004174644 A JP2004174644 A JP 2004174644A JP 2004174644 A JP2004174644 A JP 2004174644A JP 4390636 B2 JP4390636 B2 JP 4390636B2
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ofdm signal
pilot
amplification factor
power amplification
transmission
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JP2005027294A (en
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繁 冨里
武史 山田
啓正 藤井
哲士 阿部
博人 須田
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株式会社エヌ・ティ・ティ・ドコモ
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00Arrangements affording multiple use of the transmission path
    • H04L5/003Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048Allocation of pilot signals, i.e. of signals known to the receiver
    • H04L5/005Allocation of pilot signals, i.e. of signals known to the receiver of common pilots, i.e. pilots destined for multiple users or terminals
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00Arrangements for detecting or preventing errors in the information received
    • H04L1/0001Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0006Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format

Description

  The present invention relates to generation of a transmission signal frame according to an orthogonal frequency division multiplexing (hereinafter referred to as “OFDM”) transmission scheme, and relates to an OFDM signal frame generator, transmitter, signal transmission system, and OFDM The present invention relates to a signal frame generation method.

  In recent years, the OFDM transmission method has been put into practical use in wireless LAN systems such as IEEE 11a, and application of the OFDM transmission method is also being studied in terrestrial digital broadcasting and cellular communication. The OFDM signal transmission method does not require equalization of multipath interference caused by a propagation path, and is suitable for wideband signal transmission.

  In general, in wireless communication, since the propagation path condition changes according to the position of the receiving terminal, an adaptive modulation / demodulation technique that changes the transmission rate on the transmission side according to the propagation path condition is used. When performing adaptive modulation / demodulation, the transmitter acquires a reception quality value from the reception side, and changes the transmission rate according to the reception quality value. The reception quality value is determined on the reception side using the received signal power value, the received signal-to-noise power ratio, the Doppler frequency, etc., and the desired received quality value (desired frame error rate).

  FIG. 1 shows an example of a conventional OFDM signal frame generator 93 to which an adaptive modulation / demodulation technique is applied. The transmission unit includes a frame generator 93, an OFDM modulator 92, and an RF unit 91.

  Among these, in the frame generator 93, the rate information determiner 94 determines rate information using the reception quality value. The rate information may include not only the number of information bits, the coding rate, the modulation multi-level number, and the spreading factor, but also other information or only a part of them. A data symbol sequence is generated by the data symbol sequence generator 95 according to the rate information. When the receiving side needs rate information for demodulation, rate information is also included in the information symbol series. Pilot symbol generator 96 generates pilot symbols. The multiplexer 97 places the generated data symbols and pilot symbols in the time / frequency slots, and generates a transmission signal frame. The OFDM modulator 92 performs OFDM modulation on the signal in the frame. The OFDM-modulated signal is frequency-converted by the RF unit 91 and transmitted.

  FIG. 2 shows a block diagram of an OFDM transceiver using a conventional frame generator. The data symbol generator 95 in the transmitter 90 includes an encoder 95A, a mapper 95B that performs multilevel modulation symbol generation, and a spreader 95C.

  One receiver 80 includes an RF unit 81, an OFDM demodulator 82, a transmission path estimator 83, a reception quality determiner 85, and a despreading / demapping / decoding unit 84. The received signal is down-converted by the RF unit 81 and OFDM demodulated by the OFDM demodulator 82. The transmission path estimator 83 performs transmission path estimation using the OFDM demodulated signal and pilot symbols. The transmission path estimator 83 estimates the transmission path values (amplitude and phase) of all subcarriers used for transmission and the power value of noise applied to the receiving antenna. Reception quality determiner 85 calculates a received signal-to-noise power ratio from the transmission path estimation value and the noise power estimation value. The reception quality value is determined using this value and the desired reception quality value. Despreading / demapping / decoding unit 84 demodulates the information symbol sequence using the channel estimation value and the OFDM demodulated signal.

  FIG. 3 shows an example of a transmission frame to be generated. Detailed OFDM signal parameters are shown in FIG. The pilot data arrangement format is such that four pilot symbols are arranged before and after the frame for each subcarrier, and twelve data symbols are arranged at the center of the frame. FIG. 13 shows a correspondence table of reception quality values, rate information (coding rate, modulation multi-level number, spreading factor, number of information bits) and transmission rate when the pilot data arrangement format of FIG. 3 is used. ing. The rate determiner determines the rate information using the information in the correspondence table of FIG. 13 corresponding to the reception quality values “1 to 3” fed back by the receiver 80. For example, when the reception quality value is “1”, 12 bits of CRC (Cyclic Redundancy Check) bits are added to the input information symbol sequence “945 bits” to obtain 957 bits (about 960 bits). On the other hand, FEC (Forward Error Correction) at a coding rate of “1/2” and “QPSK (Quadrature Phase Shift Keying)” at 2 bits / hertz are applied and spread. By spreading at a rate of “1”, 960 symbols of data symbols are generated as symbols after coding, modulation and spreading.

  In demodulation of OFDM signal transmission, it is necessary to estimate transmission path values of all subcarriers used for transmission on the receiving side. Here, as a simple and highly accurate transmission path estimation method, it is assumed that the transmission path is estimated by synchronously adding a total of 8 pilot symbols in each subcarrier (the transmission path fluctuation in one frame is very small). Suppose there is.)

  Pp / Pi in FIG. 3 indicates a pilot symbol power (Pp) per subcarrier and a power ratio per modulation symbol after despreading. Generally, in order to obtain good channel estimation accuracy, this value (Pp / Pi) is preferably about 6 to 10 dB. In the case of FIG. 3, Pp / Pi is about 9 dB. In the transmission signal frame generated by the conventional frame generator, the pilot data arrangement format and the number of pilot symbols are fixed regardless of the reception quality value.

  However, a technique for stably performing OFDM communication by adaptively changing the number of pilot symbols according to the transmission environment has been proposed (see Patent Document 1 below).

JP 2000-151548 A

  However, in the above-described conventional frame generator, the pilot data arrangement format is fixed. If the pilot data arrangement format is fixed, the channel estimation accuracy is limited. Therefore, in the OFDM transmission system using the conventional frame generator, the reception quality is very poor (that is, the signal-to-noise power ratio is low). ) Even if an attempt is made to reduce the transmission rate sufficiently using the adaptive modulation / demodulation technique on the transmission line, there is a problem that communication becomes impossible due to a channel estimation error.

  For example, FIG. 4 shows an example in which the transmission rate is reduced to 4 kbps using a conventional frame generator when the reception quality value is very poor. In this example, the transmission rate is reduced by setting the spreading factor to 240. Pi gain of FIG. 4 has shown the increment of Pi in the structure of FIG. 4 with respect to Pi of the structure of FIG. That is, by spreading and reducing the transmission rate, a gain of about 24 dB per modulation symbol can be obtained when despreading is performed on the receiving side. However, in this case, Pp / Pi decreases to “−14 dB”, and the channel estimation accuracy deteriorates.

  The present invention has been made to solve the above-described problem, and an OFDM signal frame generator, a transmitter, a signal transmission system, and a signal transmission system capable of avoiding a situation in which communication is impossible even in a communication channel with very poor reception quality. An object is to provide an OFDM signal frame generation method.

In order to achieve the above object, an OFDM signal frame generator according to the present invention, based on a reception quality value at the receiver related to an OFDM signal received by the receiver, as described in claim 1, Rate determining means for determining rate information of the OFDM signal, pilot data arrangement format determining means for determining the pilot data arrangement format of the OFDM signal based on the reception quality value, and the OFDM based on the reception quality value Pilot symbol number determining means for determining the number of pilot symbols of the signal, power amplification factor determining means for determining the power amplification factor of the OFDM signal based on the reception quality value, transmission based on the rate information and the power amplification factor Data symbol generating means for generating a generated data symbol sequence, and the generated data symbols and pilot symbols Le number, and based on pilot data arrangement format, the transmission signal frame and a generation unit, the pilot data arrangement format determining means for generating a transmission signal frame of the OFDM signal to be transmitted, corresponds to the first transmission rate The pilot data allocation format of the OFDM signal is determined from among the first pilot data allocation format and the second pilot data allocation format corresponding to the second transmission rate lower than the first transmission rate. When the second pilot data arrangement format is determined as the pilot data arrangement format of the OFDM signal, the pilot symbol number determining means is smaller than the first pilot symbol number corresponding to the first transmission rate and The number of second pilot symbols corresponding to the second transmission rate is set as the number of pilot symbols of the OFDM signal. And / or the power gain determining means determines a second power gain greater than the first power gain corresponding to the first transmission rate and corresponding to the second transmission rate, as an OFDM signal. The power amplification factor is determined .

  A transmitter according to the present invention is a transmitter for transmitting an OFDM signal as described in claim 8, and includes the OFDM signal frame generator according to any one of claims 1 to 7. It is characterized by comprising.

A signal transmission system according to the present invention is a signal transmission system comprising a transmitter for transmitting an OFDM signal and a receiver for receiving the OFDM signal as described in claim 9. The receiver comprises reception quality value determining means for determining a reception quality value at the receiver related to the received OFDM signal, and feedback means for feeding back the determined reception quality value to the transmitter. , Rate determining means for determining rate information of the OFDM signal based on the reception quality value obtained by feedback, and pilot data allocation format for determining the pilot data allocation format of the OFDM signal based on the reception quality value And determining the number of pilot symbols for determining the number of pilot symbols of the OFDM signal based on the reception quality value And a power amplification factor determination means for determining the power amplification factor of the OFDM signal based on the received quality value, and a data symbol generation means for generating a data symbol sequence to be transmitted based on the rate information and the power amplification factor When, the generated data symbol, the number of pilot symbols, and based on pilot data arrangement format, e Bei and transmission signal frame generating means for generating a transmission signal frame of the OFDM signal to be transmitted, pilot data arrangement format determining The means includes a first pilot data arrangement format corresponding to the first transmission rate and a second pilot data arrangement format corresponding to the second transmission rate lower than the first transmission rate. The pilot data arrangement format of the OFDM signal is determined, and the second pilot data arrangement format is the pilot of the OFDM signal When determined as the data arrangement format, the pilot symbol number determining means determines the second pilot symbol number smaller than the first pilot symbol number corresponding to the first transmission rate and corresponding to the second transmission rate, The number of pilot symbols of the OFDM signal is determined, and / or the power amplification factor determination means is a second higher than the first power amplification factor corresponding to the first transmission rate and corresponding to the second transmission rate. The power amplification factor is determined as the power amplification factor of the OFDM signal .

Furthermore, the OFDM signal frame generation method according to the present invention is the OFDM signal frame generation method of generating a transmission signal frame of the OFDM signal at the transmitter for transmitting the OFDM signal to the receiver as described in claim 10. A rate determining step for determining rate information of the OFDM signal based on a reception quality value at the receiver related to the OFDM signal received by the receiver, and based on the reception quality value, A pilot data arrangement format determining step for determining the pilot data arrangement format, a pilot symbol number determining step for determining the number of pilot symbols of the OFDM signal based on the reception quality value, and the OFDM based on the reception quality value Power amplification factor determination step for determining the power amplification factor of the signal, based on the rate information and the power amplification factor A data symbol generation step for generating a data symbol sequence to be transmitted, and a transmission signal for generating a transmission signal frame of an OFDM signal to be transmitted based on the generated data symbols, the number of pilot symbols, and a pilot data arrangement format have a frame generation step, the pilot data arrangement form determining step, corresponding to the first pilot data arrangement format and the slower second rate than the first transmission rate corresponding to the first transmission rate If the pilot data arrangement format of the OFDM signal is determined from the second pilot data arrangement format to be performed, and the second pilot data arrangement format is determined as the pilot data arrangement format of the OFDM signal, the pilot In the symbol number determining step, a first pilot symbol corresponding to the first transmission rate A second pilot symbol number smaller than the second transmission rate and corresponding to the second transmission rate is determined as the number of pilot symbols of the OFDM signal, and / or in the power amplification factor determination step, the second pilot symbol number corresponding to the first transmission rate is determined. The second power gain that is greater than the power gain of 1 and that corresponds to the second transmission rate is determined as the power gain of the OFDM signal .


  According to these inventions, based on the received quality value at the receiver related to the OFDM signal received by the receiver, the rate information of the OFDM signal, the pilot data arrangement format of the OFDM signal, the pilot of the OFDM signal The number of symbols and the power amplification factor of the OFDM signal are respectively determined. Further, a data symbol sequence to be transmitted is generated based on the rate information and the power amplification factor, and a transmission signal of the OFDM signal to be transmitted is generated based on the generated data symbols, the number of pilot symbols, and the pilot data arrangement format A frame is generated.

  As described above, according to the present invention, a transmission signal frame of an OFDM signal can be generated by changing the pilot data arrangement format, the number of pilot symbols, and the power amplification factor according to the reception quality value. As a result, even in transmission channels with poor reception quality, the transmission rate is sufficiently reduced using adaptive modulation technology, and at the same time, the number of pilot symbols and the pilot data arrangement format are changed to maintain good channel estimation accuracy. Thus, it is possible to avoid a situation in which communication is impossible.

  As for the generation of the transmission signal frame of the OFDM signal, pilot symbols corresponding to the number of pilot symbols may be generated once, and then the generated pilot symbols and data symbols may be combined according to the pilot data arrangement format. Alternatively, data symbols and pilot symbols corresponding to the number of symbols may be combined in the combining process according to the pilot data arrangement format.

  By the way, in the above, it is desirable that the reception quality value is fed back to the OFDM signal frame generator by the receiver as described in claim 2. By feeding back the received quality value from the receiver to the OFDM signal frame generator, the OFDM signal frame generator changes the pilot data arrangement format and the number of pilot symbols according to the appropriate received quality value, and the OFDM signal Transmission signal frames can be generated.

  Further, as described in claim 3, the pilot data arrangement format may be determined with respect to the subcarrier number to be used, the number of pilot symbols and the number of data symbols in the subcarrier to be used. In this case, a transmission signal frame of the OFDM signal can be generated based on the generated data symbols, the number of pilot symbols, and the pilot data arrangement format.

  In such a pilot data arrangement format, the subcarrier number to be used may be selected at regular intervals on the frequency slot of the transmission signal frame, as described in claim 4. In this case, a frequency diversity effect can be obtained by using a plurality of subcarriers selected at regular intervals on the frequency slot, fading can be reduced, and communication quality can be improved.

  Further, as described in claim 5, the subcarrier number to be used may be changed according to the frame number. In this case, since different subcarriers are used in different transmission frames (different times), the frequency Diversity gain can be obtained.

  Also, in the pilot data arrangement format, it is desirable that the frame length is variable according to the reception quality value, as described in claim 6. In this case, the degree of freedom in generating the transmission signal frame is increased, and flexible control is possible. For example, when the fluctuation of the transmission line is very small within one frame and can be regarded as constant (no fluctuation of the transmission line), the gain of power used for the data symbol can be increased by increasing the frame length. Further, it is desirable that the pilot data arrangement format determining means designates a subcarrier to which the pilot data arrangement format is applied for each block based on the reception quality value. Specifically, when there is little fluctuation in the propagation path, there are situations where it is possible to receive the same propagation path estimation value for 10 frames, for example. In such a case, for example, the first frame is an arrangement format including only the pilot, and the second to tenth frames are the data only arrangement format. The amount of data can be increased.

  According to the present invention, a transmission signal frame of an OFDM signal can be generated by changing the pilot data arrangement format, the number of pilot symbols, and the power amplification factor according to the reception quality value. As a result, even in transmission channels with poor reception quality, the transmission rate is sufficiently reduced using adaptive modulation technology, and at the same time, the number of pilot symbols and the pilot data arrangement format are changed to maintain good channel estimation accuracy. Thus, it is possible to avoid a situation in which communication is impossible.

  Embodiments according to the present invention will be described below.

[Device configuration]
FIG. 5 shows a block diagram of an OFDM signal frame generator 13 in the present embodiment. Differences from the conventional frame generator 93 of FIG. 1 are as follows. That is, the frame generator 13 of FIG. 5 has a pilot / data arrangement format determiner 20 and makes the pilot / data arrangement format variable according to the reception quality value. Also, a pilot symbol number determiner 19 is provided, and the number of pilot symbols is variable according to the reception quality value. Further, a power amplification factor determiner 18 is provided, and the power amplification factor is variable according to the reception quality value.

  FIG. 6 shows a block diagram of an OFDM signal transmission system 1 using the frame generator 13 described above. The OFDM signal transmission system 1 includes a transmitter 10 including the frame generator 13 of FIG. 5 and a receiver 30. The configuration of the receiver 30 is the same as the configuration of the receiver 80 shown in FIG.

  The OFDM signal transmission system 1 is characterized by the configuration of the frame generator 13 provided in the transmitter 10. The rate information determiner 14 in the frame generator 13 determines rate information (coding rate, multi-level number, spreading factor) according to the reception quality value, as in the conventional type. At this time, the correspondence table between reception quality values and rate information shown in FIG. 14 is used. In FIG. 14, low rate information of 4 kbps is added as rate information corresponding to the reception quality value 0.

  The pilot data arrangement format determiner 20 determines the pilot data arrangement format using the correspondence table between the reception quality values and the pilot data arrangement format shown in FIG. As is clear from FIG. 15, when the reception quality value is 0 (in the case of low rate transmission), a different pilot data arrangement format is used than when the reception quality value is other than 0 (1 to 3).

  The pilot symbol number determiner 19 determines the number of pilot symbols using the correspondence table between the reception quality value and the number of pilot symbols shown in FIG. When the reception quality value is 0 (in the case of low-rate transmission), a different number of pilot symbols is used than when the reception quality value is other than 0 (1 to 3).

  The power amplification factor determiner 18 determines the power amplification factor using the correspondence table between the reception quality value and the power amplification factor shown in FIG. This power amplification factor is used when only some subcarriers are used as a pilot data arrangement format (details will be described later). For example, when only half of the available subcarriers are used and the total transmission power is concentrated on the half of the subcarriers, the power amplification factor is 2. When power amplification is not performed, the power amplification factor may be fixed to 1.

[OFDM signal frame generation processing]
Next, an OFDM signal frame generation process executed in the frame generator 13 of FIG. 5 will be described based on FIG.

  First, in S1, based on the reception quality value at the receiver 30 regarding the OFDM signal received by the receiver 30, the rate information of the OFDM signal to be transmitted, the pilot data arrangement format of the OFDM signal, the OFDM The number of pilot symbols of the signal and the power amplification factor of the OFDM signal are determined. At this time, the rate information is determined by the rate information determiner 14, the pilot data allocation format is determined by the pilot data allocation format determiner 20, the number of pilot symbols is determined by the pilot symbol count determiner 19, and the power amplification factor is determined by the power amplification factor determiner. 18 respectively. The reception quality value is a value fed back from the receiver 30 to the transmitter 10.

  Next, in S2, a data symbol sequence and a pilot symbol are generated. At this time, the data symbol sequence generator 15 generates a data symbol sequence by processing the input information symbol sequence according to the rate information and power amplification factor determined in S1. The pilot symbol generator 16 generates as many pilot symbols as the determined number of pilot symbols.

  In S3, the transmission data frame of the OFDM signal is generated by combining the generated data symbol and the pilot symbol based on the pilot data arrangement format.

  Thus, in this embodiment, it is possible to generate a transmission signal frame of an OFDM signal by changing the pilot data arrangement format, the number of pilot symbols, and the power amplification factor according to the reception quality value. As a result, even in transmission channels with poor reception quality, the transmission rate is sufficiently reduced using adaptive modulation technology, and at the same time, the number of pilot symbols and the pilot data arrangement format are changed to maintain good channel estimation accuracy. Thus, it is possible to avoid a situation in which communication is impossible.

[Various examples of pilot data arrangement format for low-speed transmission corresponding to reception quality value 0]
In the following, various examples of the pilot data arrangement format for low-speed transmission (4 kbps) corresponding to the reception quality value 0 will be described. Here, a guideline for determining a pilot data arrangement format for realizing low-speed transmission under the following assumptions is shown.

(Assumption)
1) A pilot symbol is inserted for each carrier used for transmission, and channel estimation is performed.
2) Let P be the transmission power used to transmit one frame.
3) Let N be the number of data symbols after multi-level modulation / spreading sent in one frame transmission.
4) Let Pi be the power used for the data symbols.
5) Let Pp = P-Pi be the power used for the pilot symbols.
6) Let K be the number of subcarriers used for transmission.

As described above, in general, in order to obtain good channel estimation accuracy in signal transmission, it is necessary to maintain a constant (about 8 dB) power ratio between pilot symbol power used per carrier and one modulated data symbol before spreading. There is. When this power ratio is D, the above condition can be expressed as the following equation (1).

When this equation (1) is solved for P i , the following equation (2) is obtained.

Reception quality (received signal power to noise power ratio) is in a poor transmission channel, it is necessary to increase the P i. For this reason, it can be seen from equation (2) that the number of subcarriers K is desirably smaller. However, in the fading channel, if the number of subcarriers K is reduced, there is a trade-off that it is difficult to obtain quality improvement due to the frequency diversity effect during demodulation.

  Therefore, from the above consideration, in low-speed transmission, it is possible to configure the transmission signal frame so that the number of subcarriers to be used is reduced and the power is concentrated on the small number of subcarriers to such an extent that the frequency diversity effect can be obtained. desirable.

  FIG. 7 shows a first example of a low-speed transmission pilot data arrangement format provided using the above guidelines. The information symbol sequence modulation flow at this time is, for example, as follows. 2 bits of CRC bits are added to the input information symbol sequence “2 bits” to obtain 4 bits. On the other hand, by performing FEC at a coding rate “4/7” using a BCH code of a rate “4/7” and “QPSK” at 2 bits / hertz, and spreading at a spreading factor “4” A 16-chip data symbol is generated as a symbol after encoding, modulation and spreading.

  In FIG. 7, four subcarriers used for transmission are selected in advance, and only four subcarriers are used for transmission of one frame. In this case, since the total power is concentrated on the four subcarriers, the power amplification factor is 20. Considering that the spreading factor is 4, in this case, the Pi gain compared with FIG. 3 is 80 (20 × 4), that is, about 19 dB, and Pp / Pi can be maintained at about 6 db. . In addition, frequency diversity gain can be obtained by using four subcarriers. Note that the number of carriers used above may be four or more.

  FIG. 8 shows a second example of the low-speed pilot data arrangement format provided by the present invention. In FIG. 8, only one subcarrier is used for transmission, and all transmission power is concentrated on the single subcarrier (power amplification factor is 80). The information symbol sequence modulation flow at this time is, for example, as follows. 2 bits of CRC bits are added to the input information symbol sequence “2 bits” to obtain 4 bits. On the other hand, by performing FEC at a coding rate “4/7” using a BCH code of a rate “4/7” and “QPSK” at 2 bits / hertz, and spreading at a spreading factor “2” A data symbol of 8 chips is generated as a symbol after encoding, modulation and spreading. In this case, Pi gain can be increased to about 22 dB, and Pp / Pi can be increased to about 8 dB. However, in this case, since a single subcarrier is used, frequency diversity at the time of demodulation cannot be obtained. However, when the receiver has a plurality of reception antennas, the loss of frequency diversity can be compensated by the reception diversity gain.

  FIG. 9 shows a third example of the low-speed pilot data arrangement format provided by the present invention. In FIG. 9, the number of the subcarrier used for transmission (one subcarrier in FIG. 9) is switched according to the frame number. As a switching reference, a pattern known in advance by the receiver can be used. If this configuration is used, since different subcarriers are used in different transmission frames (different times), a frequency diversity effect can be expected. Note that the modulation flow of the information symbol sequence in this example is the same as in the second example.

  FIGS. 10 and 11 show fourth and fifth examples of pilot data arrangement formats provided by the present invention, respectively. Compared with the first to third examples (configurations of FIGS. 7 to 9) described above, the OFDM signal parameters are changed. FIG. 18 showing the details shows that the Pi gain can be increased by increasing the frame length. In this case as well, it is assumed that the fluctuation of the transmission path due to fading within one frame is very small. Also, the modulation flow of the information symbol sequence in the fourth example of FIG. 10 is as follows, for example. 3 bits of CRC bits are added to the inputted information symbol series “8 bits” to become 11 bits. On the other hand, FEC using a 4-bit BCH code and “QPSK” at 2 bits / hertz are applied and spread at a spreading factor of “8”, so that data of 64 chips is obtained as a symbol after code, modulation, and spread. A symbol is generated. On the other hand, the modulation flow of the information symbol sequence in the fifth example of FIG. 11 is as follows, for example. 3 bits of CRC bits are added to the inputted information symbol series “8 bits” to become 11 bits. On the other hand, by performing FEC using a 4-bit BCH code and “QPSK” at 2 bits / hertz and spreading at a spreading factor of “4”, data of 32 chips is obtained as a symbol after code / modulation / spreading. A symbol is generated.

  From the first to fifth examples (FIGS. 7 to 11) described above, a plurality of frame configurations can be listed as candidates for the frame configuration for transmission at low speed. Therefore, it is only necessary to select one of these and set the pilot data arrangement format in FIG. 15 to “0”. Also, in the pilot data arrangement format “0”, the modulation multi-level number, coding rate, and spreading rate can be diversified, and a plurality of rate information other than 4 kbps can also be included. Furthermore, the number of pilot data arrangement formats can be increased.

  Further, as can be seen from the second and third examples (FIGS. 8 and 9), when the transmission path variation is very small within one frame and can be regarded as constant (no transmission path variation), the frame length By increasing the length, Pi gain can be increased. Therefore, it is also possible to use pilot data arrangement formats having different frame lengths in FIG. The number of pilot symbols is determined at the same time as the pilot / data arrangement format is determined. For example, when the pilot data arrangement format is determined to be “0”, the reception quality value is “0” and the number of pilot symbols is “48”, as is apparent from the correspondence relationship in FIGS.

  The pilot data arrangement format described in the above embodiment may be a case of designating a part of subcarrier blocks (for example, blocks of subcarrier numbers 1 to 5) among all subcarriers. For example, it is conceivable that subcarriers are divided into blocks in advance and designated for each block. Specifically, when there is little fluctuation in the propagation path, there are situations where it is possible to receive the same propagation path estimation value for 10 frames, for example. In such a case, for example, the first frame is an arrangement format including only the pilot, and the second to tenth frames are the data only arrangement format. The amount of data can be increased.

  As described above, according to the present invention, a transmission signal frame of an OFDM signal can be generated by changing the pilot data arrangement format, the number of pilot symbols, and the power amplification factor according to the reception quality value. As a result, even in transmission channels with poor reception quality, the transmission rate is sufficiently reduced using adaptive modulation technology, and at the same time, the number of pilot symbols and the pilot data arrangement format are changed to maintain good channel estimation accuracy. Thus, it is possible to avoid a situation in which communication is impossible.

  In the above-described embodiment, an example is shown in which both the pilot signal arrangement and the data signal arrangement are variable. However, as shown in FIG. 20, only the data portion arrangement format can be made variable. .

  Further, in the above-described embodiment, the embodiment based on the frame configuration using both the head and the tail pilot has been shown. However, in the present invention, the frame configuration using only one of the head and the tail pilot, or the scattered pilot is used. It can be easily applied to the frame structure to be used.

It is a block diagram of the conventional frame generator. It is a block diagram of an OFDM signal transmission system using a conventional frame generator. It is a figure which shows the example of a conventional frame structure. It is a figure which shows the example of a conventional low-speed frame structure. It is a block diagram of the frame generator in embodiment of invention. 1 is a block diagram of an OFDM signal transmission system using a frame generator in an embodiment of the invention. It is a figure which shows the 1st example of a pilot data arrangement | positioning format. It is a figure which shows the 2nd example of a pilot data arrangement | positioning format. It is a figure which shows the 3rd example of a pilot data arrangement | positioning format. It is a figure which shows the 4th example of a pilot data arrangement | positioning format. It is a figure which shows the 5th example of a pilot data arrangement | positioning format. It is a table | surface which shows the 1st example of the parameter of an OFDM signal. It is a table | surface which shows the example of a response | compatibility with the reception quality value and rate information which are used with the conventional rate determiner. It is a table | surface which shows the example of a response | compatibility with the reception quality value and rate information used with the rate determiner of embodiment. It is a table | surface which shows the example of a response | compatibility with the reception quality value and pilot data arrangement | positioning format which are used with the pilot arrangement | positioning format determiner of embodiment. It is a table | surface which shows the example of a response | compatibility with the reception quality value and pilot symbol number which are used with the pilot symbol number determination device of embodiment. It is a table | surface which shows the example of a response | compatibility with the reception quality value used with the power amplification factor determiner of embodiment, and a power amplification factor. It is a table | surface which shows the 2nd example of the parameter of an OFDM signal. It is a flowchart which shows the content of an OFDM signal frame production | generation process. It is a figure which shows the example to which only the arrangement | positioning format of the data part was made variable.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... OFDM signal transmission system, 10 ... Transmitter, 11 ... RF part, 12 ... OFDM modulator, 13 ... Frame generator, 14 ... Rate information determiner, 15 ... Data symbol sequence generator, 15A ... Encoder, 15B DESCRIPTION OF SYMBOLS ... Mapping device, 15C ... Spreader, 16 ... Pilot symbol generator, 17 ... Multiplexer, 18 ... Power amplification factor determiner, 19 ... Pilot symbol number determiner, 20 ... Pilot data arrangement format determiner, 30 ... Receiver , 31 ... RF section, 32 ... OFDM demodulator, 33 ... transmission path estimator, 34 ... despreading / demapping / decoder, 35 ... reception quality determiner.

Claims (10)

  1. Rate determining means for determining rate information of the OFDM signal based on a reception quality value at the receiver related to the OFDM signal received by the receiver;
    Pilot data arrangement format determining means for determining a pilot data arrangement format of the OFDM signal based on the received quality value;
    Pilot symbol number determining means for determining the number of pilot symbols of the OFDM signal based on the reception quality value;
    Power amplification factor determination means for determining a power amplification factor of the OFDM signal based on the reception quality value;
    Data symbol generation means for generating a data symbol sequence to be transmitted based on the rate information and the power amplification factor;
    The generated data symbols, the number of pilot symbols, and on the basis of the pilot data arrangement format, Bei example a transmission signal frame generating means for generating a transmission signal frame of the OFDM signal to be transmitted, and
    The pilot data allocation format determining means includes a first pilot data allocation format corresponding to a first transmission rate and a second pilot data allocation rate corresponding to a second transmission rate that is lower than the first transmission rate. From the data allocation format, determine the pilot data allocation format of the OFDM signal,
    When the second pilot data arrangement format is determined as the pilot data arrangement format of the OFDM signal, the pilot symbol number determining means is more than the first pilot symbol number corresponding to the first transmission rate. The second pilot symbol number that is small and corresponds to the second transmission rate is determined as the pilot symbol number of the OFDM signal, and / or the power amplification factor determination means corresponds to the first transmission rate. An OFDM signal frame generator , wherein a second power amplification factor that is larger than the first power amplification factor and that corresponds to the second transmission rate is determined as a power amplification factor of the OFDM signal.
  2.   The OFDM signal frame generator according to claim 1, wherein the reception quality value is fed back to the OFDM signal frame generator by the receiver.
  3.   The OFDM signal frame generator according to claim 1 or 2, wherein the pilot data arrangement format is determined with respect to a subcarrier number to be used, and the number of pilot symbols and the number of data symbols in the subcarrier to be used. .
  4.   The OFDM signal frame generator according to claim 3, wherein the subcarrier numbers to be used are selected at regular intervals on a frequency slot of a transmission signal frame.
  5.   The OFDM signal frame generator according to claim 3, wherein the subcarrier number to be used is changed according to a frame number.
  6.   6. The OFDM signal frame generator according to claim 1, wherein in the pilot data arrangement format, a frame length is variable according to the reception quality value.
  7.   7. The pilot data arrangement format determination means designates a subcarrier to which a pilot data arrangement format is applied for each block based on the reception quality value. An OFDM signal frame generator as described.
  8. A transmitter for transmitting an OFDM signal,
    A transmitter comprising the OFDM signal frame generator according to any one of claims 1 to 7.
  9. A signal transmission system configured to include a transmitter for transmitting an OFDM signal and a receiver for receiving the OFDM signal,
    The receiver
    Reception quality value determining means for determining a reception quality value at the receiver related to the received OFDM signal;
    Feedback means for feeding back the determined received quality value to the transmitter;
    The transmitter is
    Rate determining means for determining rate information of an OFDM signal based on a reception quality value obtained by feedback;
    Pilot data arrangement format determining means for determining a pilot data arrangement format of the OFDM signal based on the received quality value;
    Pilot symbol number determining means for determining the number of pilot symbols of the OFDM signal based on the reception quality value;
    Power amplification factor determination means for determining a power amplification factor of the OFDM signal based on the reception quality value;
    Data symbol generation means for generating a data symbol sequence to be transmitted based on the rate information and the power amplification factor;
    The generated data symbols, the number of pilot symbols, and on the basis of the pilot data arrangement format, Bei example a transmission signal frame generating means for generating a transmission signal frame of the OFDM signal to be transmitted, and
    The pilot data allocation format determining means includes a first pilot data allocation format corresponding to a first transmission rate and a second pilot data allocation rate corresponding to a second transmission rate that is lower than the first transmission rate. From the data allocation format, determine the pilot data allocation format of the OFDM signal,
    When the second pilot data arrangement format is determined as the pilot data arrangement format of the OFDM signal, the pilot symbol number determining means is more than the first pilot symbol number corresponding to the first transmission rate. The second pilot symbol number that is small and corresponds to the second transmission rate is determined as the pilot symbol number of the OFDM signal, and / or the power amplification factor determination means corresponds to the first transmission rate. A signal transmission system , wherein a second power amplification factor larger than the first power amplification factor and corresponding to the second transmission rate is determined as a power amplification factor of the OFDM signal .
  10. An OFDM signal frame generation method for generating a transmission signal frame of an OFDM signal in a transmitter that transmits the OFDM signal to a receiver,
    A rate determining step for determining rate information of the OFDM signal based on a reception quality value at the receiver related to the OFDM signal received by the receiver;
    A pilot data arrangement format determining step for determining a pilot data arrangement format of the OFDM signal based on the received quality value;
    A pilot symbol number determining step of determining the number of pilot symbols of the OFDM signal based on the reception quality value;
    A power amplification factor determination step for determining a power amplification factor of the OFDM signal based on the reception quality value;
    A data symbol generation step of generating a data symbol sequence to be transmitted based on the rate information and the power amplification factor;
    The generated data symbols, the number of pilot symbols, and based on the pilot data arrangement format, have a, a transmission signal frame generating step of generating a transmission signal frame of the OFDM signal to be transmitted,
    In the pilot data allocation format determination step, a first pilot data allocation format corresponding to a first transmission rate and a second pilot data allocation corresponding to a second transmission rate that is lower than the first transmission rate. From the data allocation format, determine the pilot data allocation format of the OFDM signal,
    When the second pilot data arrangement format is determined as the pilot data arrangement format of the OFDM signal, in the pilot symbol number determining step, it is more than the first pilot symbol number corresponding to the first transmission rate. The second pilot symbol number that is small and corresponds to the second transmission rate is determined as the number of pilot symbols of the OFDM signal, and / or the power amplification factor determination step corresponds to the first transmission rate. A method of generating an OFDM signal frame , comprising: determining a second power amplification factor that is greater than the first power amplification factor and that corresponds to the second transmission rate as the power amplification factor of the OFDM signal.
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JP4899554B2 (en) * 2006-03-16 2012-03-21 日本電気株式会社 Wireless communication system, wireless communication method, and signal processing program thereof
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