JP2014003512A - Ofdm signal transmission and reception system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an image data transmission method capable of maintaining favorable image quality regardless of a state of a transmission path, and having good transmission efficiency.SOLUTION: On the basis of an occurrence state of transmission errors and an image quality evaluation result that are detected by a receiver (201), a transmitter (101) changes a modulation system of each carrier. The modulation system of a carrier with many transmission errors is changed to one with a smaller modulation multilevel number. An encoding parameter is changed on the basis of the modulation system of each carrier and the image quality evaluation result. When the image quality is low, it is determined that the number of the transmission errors is large, and the encoding parameter is made larger.

Description

  The present invention relates to an OFDM signal transmission / reception system that transmits data in a digital format using an OFDM modulation method.

  As a multi-carrier modulation scheme for transmitting large-capacity digital data at high speed, there is an Orthogonal Frequency Division Multiplexing (OFDM) scheme. In this method, data to be transmitted is divided into a number of data parts, different carriers are assigned to the respective data parts, and the assigned carriers are modulated by the data parts and multiplexed to perform multicarrier transmission. . Each carrier is modulated by, for example, PSK or QAM. The OFDM method prevents interference between carriers by maintaining orthogonality between all carriers.

  However, when an error occurs in the transmission process due to noise on the transmission path, an error occurs in the received data. This is a factor that degrades video quality, for example, when transmitting video. In particular, when an error occurs in highly important frame data in the video data, the video quality deteriorates greatly.

  Therefore, in Patent Document 1 as a conventional OFDM modulation device, the data is classified into highly important data and low data, an error correction code is added to the former, and the error rate of the highly important data is low in importance. It has been proposed to improve transmission quality by keeping it lower than data.

  Further, in Patent Document 2, data to be transmitted is classified according to the importance of the data to be transmitted, error correction coding is performed at different coding rates, and modulated by different multilevel modulation methods and transmitted. Proposed. For example, a multi-level modulation method with a low error correction coding rate is applied to those with high importance and a small amount of information per symbol, and an error correction coding rate is applied to those with low importance. Is applied, and a multilevel modulation method with a large amount of information per symbol is applied.

Japanese Patent Laid-Open No. 9-46314 International Publication No. 1996/07260

ITU-T Recommendation P.M. 910, “Subjective video quality assessment methods for multimedia applications”

  Non-patent document 1 will be described later.

However, the OFDM modulation apparatus disclosed in Patent Document 1 cannot correct errors that occur due to noise in the transmission path for less important data. In either of Patent Document 1 and Patent Document 2, data with high importance is not necessarily transmitted on a carrier that does not generate an error. For example, when impulse noise is generated on a specific carrier, the carrier on which noise is concentrated In some cases, the data cannot be correctly demodulated on the receiving side due to the transmission of data, and the error cannot be completely corrected by error correction decoding. In addition, since the reception status such as the error occurrence status when receiving data on the receiving side is not reflected on the transmitting side, even if the transmission path status is relatively good overall (for highly important data While the error coding rate is low, an error correction code is not added to data with low importance, and therefore there is a problem that even if an error occurs in data with low importance, the error cannot be corrected. In these cases, the transmission object is H.264. In the case of image data encoded by H.264 or the like, the corresponding decoder cannot correctly decode the data, and the reproduced video is disturbed, resulting in a decrease in image quality.
Therefore, it is desired to realize a transmission method of image data that can maintain a good image quality regardless of the condition of the transmission path and that has a high transmission efficiency.

The OFDM signal transmission / reception system of the present invention comprises:
An OFDM signal transmission / reception system that modulates image data and transmits it from a transmitter to a receiver,
The transmitter is
An encoder that generates a bitstream in which the image data is information-compressed based on an encoding parameter;
After performing error correction coding on the bitstream, the bitstream is divided into a plurality of data portions, and different carriers are modulated by the respective carrier modulation schemes in the respective data portions obtained by the division. An OFDM modulator for generating an OFDM modulated signal;
A carrier controller that determines the carrier modulation scheme based on reception state information and outputs information indicating the determined carrier modulation scheme;
An encoding controller that determines the encoding parameter from an image quality evaluation result included in the reception state information and outputs information indicating the determined encoding parameter;
The receiver is
Demodulate the OFDM signal received from the transmitter, generate a bitstream, perform error correction processing on the OFDM signal, and output error detection information indicating an error position detected by the error correction processing An OFDM demodulator;
From the error detection information, a transmission path evaluator that generates and outputs data representing an error occurrence state in each of the carriers that can be used for transmission of the image data;
An image quality evaluator that evaluates image quality based on the bitstream from the OFDM demodulator and outputs data representing an image quality evaluation result;
A reception state evaluator that generates the reception state information including data representing the error occurrence state from the transmission path evaluator and data representing the image quality evaluation result from the image quality evaluator, and outputs the reception state information to the transmitter It is characterized by providing.

  According to the present invention, it is possible to suppress the occurrence of data errors that affect image quality regardless of the condition of the transmission path, to maintain good image quality, and to transmit image data efficiently. .

It is a block diagram which shows the OFDM signal transmission / reception system which concerns on Embodiment 1 of this invention. It is a figure which shows an example of allocation of the modulation system with respect to each carrier with a table format. It is a block diagram which shows the structural example of the transmission evaluator of FIG. It is a figure which shows an example of the value of the error generation parameter | index about each carrier in a table format. (A)-(c) is a figure which shows the example of generation | occurrence | production of an error, a change of an error generation parameter | index, and generation | occurrence | production of the error flag whose value accompanying this is "1". (A)-(c) is a figure which shows the example of generation | occurrence | production of an error, the change of an error generation parameter | index, and generation | occurrence | production of the error flag whose value accompanying this is "0". It is a figure which shows an example of a data structure of the reception status information transmitted to the transmitter from the receiver of FIG. It is a block diagram which shows the structural example of the image quality evaluator which concerns on FIG. It is a block diagram which shows the structure of the transmission line evaluator 211 which concerns on Embodiment 2 of this invention. It is a block diagram which shows the OFDM signal transmission / reception system which concerns on Embodiment 4 of this invention.

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

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a first embodiment of an OFDM signal transmission / reception system according to the present invention. The illustrated OFDM signal transmission / reception system includes a transmitter 101 and a receiver 201.

The transmitter 101 generates an OFDM signal Sm from the input image data Id and outputs the OFDM signal Sm to the receiver 201 via the transmission path 401.
The transmission line 401 is formed by a one-to-one wired connection such as a metal wire. However, the present invention is also applicable when the transmission path 401 is formed by wireless connection.

  The receiver 201 demodulates the received OFDM signal Sm, generates a bit stream Srb, and outputs the bit stream Srb to the display 301.

  The display 301 generates image data by decoding into a predetermined format based on the bit stream Srb from the receiver 201, and displays an image represented by the image data.

The receiver 201 aggregates the occurrence status of errors detected when the OFDM signal Sm is demodulated, evaluates the image quality based on the generated bit stream Srb, and receives the aggregation result and the reception status information reflecting the evaluation result Srs is generated and output to the transmitter 101.
Based on the reception state information Srs from the receiver 201, the transmitter 101 determines or switches (resets) encoding parameters in image data encoding, and determines or switches (resets) the modulation scheme of each carrier in OFDM modulation. Set).

  The transmitter 101 includes an encoder 102, an OFDM modulator 103, a carrier controller 104, and an encoding controller 105.

  The encoder 102 encodes the image data Id based on the encoding parameter Sqs input from the encoding controller 105, generates a bit stream Ssb in which information is compressed by encoding, and outputs the bit stream Ssb to the OFDM modulator 103. A quantization step used for quantization in the process of encoding the image data Id is determined based on the encoding parameter Sqs input from the encoding controller 105. Here, the image data Id is still image data or video data (moving image data). The encoder 102 is, for example, JPEG or H.264. It shall correspond to a predetermined format such as H.264.

The OFDM modulator 103 performs OFDM modulation on the bit stream Ssb from the encoder 102 to generate an OFDM signal Sm. The generated OFDM signal Sm is transmitted to the receiver 201.
The OFDM modulator 103 divides the bit stream Ssb into a plurality of data portions, assigns the respective data portions to the respective carriers, and modulates the assigned carriers by the respective modulation schemes by the respective data portions. Each data part consists of one or more bits and is also called a block. Hereinafter, the modulation scheme applied to each carrier is referred to as a carrier modulation scheme.

  As the carrier modulation method, for example, BPSK, QPSK, 8PSK, 16QAM, 32QAM, 64QAM, 128QAM, 256QAM, 512QAM, and 1024QAM are used.

  The OFDM modulator 103 includes an error correction encoder 103a, and when performing OFDM modulation, the error correction encoder 103a detects the position of a bit including an error, such as a Reed-Solomon code, for the bit stream Ssb. Predetermined possible error correction coding is performed, and the bit stream subjected to the error correction coding is divided into a plurality of data parts and modulated.

  Based on the reception state information Srs from the receiver 201, the carrier controller 104 allocates data indicating the method of dividing the bit stream Ssb, the allocation of each data portion generated by the division, and the modulation scheme of each carrier. Information Sca is output to OFDM modulator 103, which performs OFDM modulation according to carrier allocation information Sca.

  Since the carrier allocation information Sca is not only used in OFDM modulation in the OFDM modulator 103 but also required in OFDM demodulation in the receiver 201, it is transmitted from the transmitter 101 to the receiver 201. . For example, the carrier allocation information Sca is also transmitted as a part of the OFDM signal Sm by the OFDM modulator 103 using one or more carriers.

  The carrier controller 104 also calculates the amount of information that can be transmitted on all the carriers that can be used for transmission of the image data Id based on the modulation scheme of each carrier, and outputs it as a transmission data amount estimated value Agi. The amount of transmission information per symbol in all carriers can be obtained by integrating the amount of information that can be transmitted in each carrier over all carriers. The amount of information (number of bits) that can be transmitted per symbol in each carrier is proportional to the logarithm of the modulation multi-level number of the modulation scheme applied to each carrier.

  The encoding controller 105 determines the encoding parameter Sqs from the estimated transmission data amount Agi output from the carrier controller 104 and the image quality evaluation result Sqp included in the reception state information Srs, and determines the determined encoding parameter. The information Sqs shown is output.

  The receiver 201 includes an OFDM demodulator 202, a transmission path evaluator 211, an image quality evaluator 221, and a reception state evaluator 231.

  The OFDM demodulator 202 receives the OFDM signal Sm transmitted from the transmitter 101, performs OFDM demodulation on the OFDM signal Sm, performs error correction decoding on the demodulated signal, generates a bit stream Srb, and Output to the evaluator 221 and the display 301. At this time, the transmitter 201 first demodulates the carrier used for transmission of the carrier allocation information Sca, and demodulates other carriers according to the demodulated carrier allocation information Sca.

  In addition, the OFDM demodulator 202 includes a deinterleaver that can reproduce the original order before being changed by the interleaver of the OFDM modulator 103 when the OFDM modulator 103 includes an interleaver. In the OFDM demodulation, deinterleaving is performed. The OFDM demodulator 202 includes an error correction decoder 202a. The error correction decoder 202a decodes the error correction code applied by the error correction encoder 103a to the deinterleaved bit stream, and error correction is performed. The position of the error bit detected by the processing is specified, error detection information Seb indicating the occurrence of the error and the position of the error is generated, and output to the transmission path evaluator 211. Further, the error correction decoder 202a generates a bit stream Srb in which an error is corrected, and outputs the bit stream Srb to the image quality evaluator 221 and the display 301.

  The transmission path evaluator 211 determines the error occurrence status in each of the carriers used in OFDM modulation from the error detection information (data indicating the error occurrence status detected during demodulation) Seb from the OFDM demodulator 202. The data Sef and Scn to represent are generated and output. Of these, data Sef indicates that transmission errors frequently occur or that the frequent occurrence of transmission errors has been resolved, and is referred to as an error flag. Data Scn is the corresponding carrier (transmission errors occur frequently). Or the carrier from which the frequent occurrence of transmission errors has been resolved), and is referred to as a control target carrier number. As will be described in detail below, the error flag Sef and the control target carrier number Scn are used as information requesting to change the transmission conditions by the transmitter 101, for example, the modulation scheme of each carrier.

  The image quality evaluator 221 evaluates the image quality based on the bit stream Srb from the OFDM demodulator 202 and outputs an estimated image quality value (data indicating Sqp) as an image quality evaluation result.

  The reception state evaluator 231 is a summary of the data Sef and Scn representing the error occurrence status in each carrier from the transmission path evaluator 211 and the image quality evaluation result (representing data) Sqp from the image quality evaluator 221. Is sent to the transmitter 101 as reception state information Srs.

Transmission of the reception state information Srs to the transmitter 101 may be performed via the same transmission path as that of the OFDM signal Sm, or another transmission means such as a wireless LAN may be used.
When transmitting wirelessly, the reception state evaluator 231 transmits reception state information Srs as a control signal separately from the transmission path 401 used by the transmitter 101 and the receiver 201 for transmission of the OFDM signal Sm. Wireless signal transmitter 231a (indicated by a dotted line in FIG. 1).

  While the amount of information transmitted as the reception status information Srs is not large, it plays an important role in control, so it is desirable to transmit it with a reliable transmission means.

  Error correction coding may be performed when transmitting the reception status information Srs. In this case, an error correction decoding circuit (not shown) is required for the transmitter 101. However, an error can be prevented from occurring in the reception state information Srs due to the occurrence of a transmission error, and the transmitter 101 can be reliably controlled.

  In a system in which a plurality of receivers (not shown) are provided and receive OFDM signals transmitted from the transmitter 101 via the same transmission path, a transmission path evaluator 211 and an image quality evaluator are provided for all receivers. For example, only one or a part of the receivers may include the transmission path evaluation unit 211, the image quality evaluation unit 221, and the reception state evaluation unit 231. That is, it is possible to transmit image data with good image quality without evaluating the transmission path and image quality in all receivers.

The display 301 includes a decoder 302 and an image player 303.
The decoder 302 decodes the bit stream Srb from the receiver 201 into a predetermined format, generates image data Od, and outputs the image data Od to the image player 303.
The image reproducer 303 reproduces the image data Od from the decoder 302 and displays an image represented by the reproduced image data Od.

  The method of dividing the bit stream Ssb into the data portion, the allocation of the data portion to each carrier, and the modulation scheme to be used in each carrier in the OFDM modulator 103 are based on the transmission error occurrence status detected by the receiver 201. Determined. For example, for a carrier in which transmission errors occur frequently or frequently, the carrier is switched to a modulation method with a smaller number of modulation multi-values, and a data portion consisting of fewer bits is allocated. On the other hand, for a carrier with a small transmission error, switching to a modulation scheme having a larger number of modulation multi-values is made, and a data portion consisting of more bits is allocated.

  The evaluation of the occurrence status of transmission errors is performed for each frame or every plurality of frames in units of frames of image data received by the receiver 201. The switching of the modulation method in the transmitter 101 is performed between frames and frames. At the break.

As described above, the carrier allocation information Sca is also transmitted from the transmitter 101 to the receiver 201 as part of the OFDM signal Sm.
For transmission of the carrier allocation information Sca, one or more carriers are used according to the modulation multi-level number. The modulation method of the carrier used for transmission of the carrier allocation information Sca is not changed and remains fixed.

  Hereinafter, of the operation of the transmitter 101, the modulation scheme control in the OFDM modulator 103 and the encoding parameter control in the encoder 102 will be described in more detail.

In the OFDM modulator 103, the data part transmitted by each carrier (data part used for modulation of the carrier) and the modulation method of each carrier are designated by the carrier allocation information Sca from the carrier controller 104 as described above. Is done.
FIG. 2 shows an example of assignment of modulation schemes for the carrier numbers C1 to CN in a table format. In the example shown in FIG. 2, “0” is written in the carrier number C1 to indicate that the carrier is not used.

  Data (setting value) indicating a carrier modulation scheme designated for each carrier is a value indicating one of a plurality of carrier modulation schemes that can be implemented in the OFDM signal transmission / reception system. The initial value of the set value is a value indicating the carrier modulation scheme having the largest number of modulation multi-values among the carrier modulation schemes that can be implemented in the OFDM signal transmission / reception system, for example, 1024QAM.

The modulation scheme of each carrier is determined so that the data transmission amount per symbol by all carriers becomes a desired value. The amount of information transmitted on all carriers is controlled by the carrier allocation information Sca.
The content of the carrier allocation information Sca is determined or changed (reset) by the carrier controller 104 based on the error flag Sef and the control target carrier number Scn included in the reception state information Srs.

  The carrier allocation information Sca is an array composed of a number of elements equal to the number of carriers that can be used for transmission of image data, and indicates a carrier modulation scheme that is applied to each carrier that can be used in order from the top of the array. Data (setting values) are arranged. In other words, the carrier allocation information Sca output from the carrier controller 104 does not include the carrier number in FIG. 2 and is configured by arranging the data indicating the modulation scheme in the order of the carrier number (array).

The carrier modulation scheme applied to each carrier is determined based on the error flag Sef included in the reception state information Srs and the previous carrier modulation scheme.
For example, when the error flag Sef included in the reception status information Srs is “1” indicating that transmission errors frequently occur, the amount of transmission information per symbol is smaller than the modulation scheme applied last time (modulation). The carrier modulation scheme having a smaller multi-value number is reset as a new modulation scheme applied to the carrier, and a value (setting value) representing the modulation scheme is used as an element of the array of the carrier allocation information Sca.

  On the other hand, when the error flag Sef included in the reception status information Srs is “0” indicating that the frequent occurrence of transmission errors has ended or disappeared, the transmission information amount per symbol is greater than the carrier modulation scheme applied last time. Is reset as a new modulation scheme applied to the carrier, and a value (setting value) representing the modulation scheme is set in the array of the carrier allocation information Sca. Element.

  In this way, the carrier controller 104 determines the carrier modulation scheme for the carrier used for image data transmission, outputs the carrier allocation information Sca including the determined carrier modulation scheme, and determines each carrier. Based on the carrier modulation method, the amount of information that can be transmitted by all carriers in one symbol is calculated, and is output to the encoding controller 105 as a transmission data amount estimated value Agi. The carrier controller 104 also outputs the image quality estimation value Sqp included in the reception state information Srs transmitted from the reception state evaluator 231 of the receiver 201 to the encoding controller 105.

  The encoding controller 105 outputs the image quality estimation value Sqp (image quality evaluation result included in the reception state information Srs transmitted from the receiver 201) supplied from the carrier controller 104 and the carrier controller 104. The transmission data estimated value Agi (information amount that can be transmitted in one symbol) is input to determine an encoding parameter Sqs to be used when the encoder 102 encodes, and data indicating the determined encoding parameter Sqs is stored in the encoder 102. Output to.

Here, the encoding parameter Sqs indicates an information compression rate by encoding. The larger the value of the encoding parameter Sqs, the higher the compression rate. The compression rate represents the degree of compression, and is defined by, for example, compression rate = (information amount before compression−information amount after compression) / information amount before compression.

  When encoding is performed according to JPEG, the encoding parameter Sqs is the quantization scale QS and the encoding is H.264. When performed according to H.264, the encoding parameter Sqs is the quantization parameter qP.

  The encoding controller 105 determines that the image quality estimated value Sqp (represented by the image quality evaluation result Sqp from the receiver 201) of the image displayed based on the received bit stream Ssb is a predetermined reference value (image quality reference value) Qb. The encoding parameter Sqs is determined so as to be the above.

For example, when the image quality evaluation result Sqp included in the reception state information Srs is greater than or equal to the reference value Qb, the encoding controller 105 determines the transmission data amount estimated value Agi (information that can be transmitted with one symbol) calculated by the carrier controller 104. The encoding parameter Sqs is calculated based on the (quantity). More specifically, when the estimated image quality value Sqp is equal to or greater than the reference value Qb and the estimated transmission data amount Agi is increased, the encoding parameter Sqs is decreased, and the estimated image quality value Sqp is equal to or greater than the reference value Qb. When the estimated transmission data amount Agi decreases, the encoding parameter Sqs is not changed (the current state is maintained).
On the other hand, when the image quality evaluation result Sqp is lower than the reference value Qb, the encoding parameter Sqs is set to a larger value.

  In order to reduce the encoding parameter Sqs, for example, the previous value is multiplied by a predetermined value smaller than 1, for example, 0.8. On the other hand, when the encoding parameter Sqs is increased, for example, the previous value is multiplied by a predetermined value greater than 1, for example 1.2.

  As an initial value of the encoding parameter Sqs, a value that gives the maximum amount of data that can be transmitted by the OFDM signal transmission / reception system in an ideal transmission path (no transmission error occurs) is given.

The encoding parameter determination method is expressed by the following equation (1).

The encoding parameter determination method assumes that the influence of image noise due to a transmission error is larger than the influence of encoding noise due to encoding as a cause of reducing the image quality estimation value Sqp.
When the estimated image quality Sqp is lower than the reference value Qb, it is considered that a large amount of image noise is generated in the demodulated and decoded data due to a transmission error occurring in the transmission process to the receiver 201. Therefore, the amount of transmitted data is reduced by increasing the encoding parameter Sqs, that is, by increasing the compression rate. On the other hand, the amount of data transmitted on each carrier is controlled by the carrier controller 104. By reducing the amount of data transmitted on the carrier on which transmission errors frequently occur, transmission errors on that carrier can be reduced. Therefore, it is possible to prevent image quality deterioration due to transmission errors.

  In determining the encoding parameter Sqs, a numerical model indicating the relationship between the encoding parameter Sqs and the bit rate, and the relationship between the encoding parameter Sqs and the image quality is used. It is also possible to calculate an optimal encoding parameter Sqs that is equal to or less than the estimated value Agi (data amount that can be transmitted by the set modulation method) and that the image quality estimated value Sqp is equal to or greater than the reference value Qb. In this case, it is necessary to prepare a numerical model in advance. However, since the encoding parameter Sqs is calculated using the relationship between the encoding parameter Sqs, the bit rate, and the image quality, optimal encoding is performed on the image data Id according to the reception state. Can be applied.

Next, generation of the reception state information Srs in the receiver 201 will be described in more detail.
As described above, the OFDM demodulator 202 performs error correction processing upon OFDM demodulation for the OFDM signal Sm, generates error detection information Seb indicating the occurrence and position of the detected error, and outputs the error detection information Seb to the transmission path evaluator 211. To do. From the information indicating the position of the error, it is possible to specify the error bit and the data portion including the error bit.

If no error is detected when error correction decoding is performed, a signal representing invalid data is generated and output as error detection information Seb.
If no error is detected, the error detection information Seb may not be output. However, when an error is detected, data indicating the error occurrence status such as the error detection information Seb is determined at a predetermined period (determined periodic It is preferable to output only at a proper timing. By doing so, the transmitter 101 only needs to perform processing to cope with transmission errors only at periodic timing.

  Based on the error detection information Seb for each frame of the received data, which is output from the OFDM demodulator 202, the transmission path evaluator 211 determines the carrier in which the transmission error frequently occurs and the carrier in which the frequent transmission error situation has been resolved. A number to be specified (control target carrier number) Scn and an error flag Sef indicating that a transmission error has frequently occurred for the carrier or that the frequent occurrence state of the transmission error has been generated are generated and output.

  For example, as shown in FIG. 3, the transmission path evaluator 211 includes an error detection carrier specifying unit 212 and a carrier analyzer 213.

  Based on the error detection information Seb from the OFDM demodulator 202, the error detection carrier specifying unit 212 is configured when a data portion including a bit corresponding to the error position indicated by the information Seb is modulated by the OFDM modulator 103 during transmission. Then, the carrier to which the data part is assigned (modulated by the data part) is specified, and the number indicating the carrier is output to the carrier analyzer 213 as the error detection carrier number Sen.

  When the OFDM modulator 103 is provided with an interleaver, the error detection carrier specifying unit 212 uses the same interleaver as the OFDM modulator 103 to generate a bit stream Sm of bits corresponding to the error position indicated by the information Seb. Reproduce the position (rank) at. As a result, it is possible to specify the carrier on which the data portion including the bit is transmitted.

  When the error detection information Seb is invalid data, the error detection carrier identifying unit 212 generates a signal representing invalid data as the error detection carrier number Sen and outputs it.

  The carrier analyzer 213 receives the error detection carrier number Sen output from the error detection carrier specifying unit 212, and counts the number of detected errors and continuity over the predetermined period for each carrier for each predetermined period. And analyze. The predetermined period (error detection cycle) is, for example, a period corresponding to one frame of image data to be transmitted or an integral multiple thereof.

  The aggregation for each carrier is performed by determining whether or not an error has occurred in each of all the carriers that can be used for transmitting image data during a predetermined period, and corresponding error occurrence indices EI1 to EIN are determined according to the determination result. Control over the value. Of the carriers that can be used in the present OFDM signal transmission / reception system, errors are not counted for carriers that are not used for image data transmission, and therefore the value of the error occurrence index EIn is maintained at “0”. .

  An example of the values of the above error occurrence indices EI1 to EIN is shown in FIG. 4 in a table format in association with the carrier number. The numerical value that each index EIn (any of n = 1 to N) can take is divided into three types of 1 or more, 0, or −1, and when it is 1 or more, it indicates the number of times an error has occurred continuously, When it is 0, it indicates that no error has occurred, and when it is −1 or less, it indicates the number of consecutive frames in which an error has occurred but has been eliminated and thereafter no error has occurred.

The error detection information Seb output from the OFDM demodulator 202 is not invalid data (indicating that an error has been detected), and the carrier number Sen that specifies the carrier in which the error is detected is output by the error detection carrier specifying unit 212. In this case, the carrier analyzer 213 performs the following processing according to the value of the error occurrence index EIn for the carrier specified by the carrier number Sen.
(A1) If the value of the index EIn is “0” or more, the value of the index EIn is incremented by 1.
(A2) If the value of the index EIn is “−1” or less, it is set to “1”.

For carriers in which no error has been detected, that is, carriers other than the carrier identified by the error detection carrier number Sen output from the carrier analyzer 213, depending on the value of the error occurrence index EIn for the carrier, Perform proper processing.
(B1) If the value of the index EIn is “0”, it remains “0”.
(B2) When the value of the index EIn is “1” or more, it is set to “−1”.
(B3) When the value of the index EIn is “−1” or less, the value of the index EIn is decremented by 1.

  The carrier analyzer 213 generates an error flag Sef having a value “1” when the value of the error occurrence index EIn for each carrier is a positive first value Eat, for example, 5 or more, and is negative. An error flag Sef having a value of “0” is generated when the value falls below a second predetermined value Ebt, for example, −5.

The value of the error flag Sef being “1” indicates that errors frequently occur in the corresponding carrier, and it is necessary to change to a modulation scheme with a smaller number of modulation multilevels.
The value of the error flag Sef being “0” indicates that the frequent occurrence of errors has been resolved in the corresponding carrier, so that it is possible to change to a modulation scheme with a larger number of modulation multilevels.
The error flag Sef and the control target carrier number Scn are supplied to the reception state evaluator 231 in association with each other.

  The carrier number corresponding to the carrier having the error occurrence index EIn smaller than the first threshold Hth and larger than the second threshold Lth is not output to the reception state evaluator 231.

  The reception state evaluator 231 generates the error flag Sef output from the carrier analyzer 213, the control target carrier number Scn, and the image quality estimation value Sqp output from the image quality evaluator 221 as reception state information Srs, and transmits the reception state information Srs. To the device 101.

  FIGS. 5A to 5C and FIGS. 6A to 6C show changes in the error occurrence index EIn according to the rules (A1), (A2), and (B1) to (B3), and An example of the generation of the error flag Sef having a value “1” or a value “0” is shown. 5 (a) to (c) and FIGS. 6 (a) to (c), the occurrence of an error is checked every frame period. In FIGS. 5 (a) and 6 (a), A frame period in which an error has occurred is indicated by “1”, and a frame period in which no error has occurred is indicated by “0”. A change in the error occurrence index EIn depending on whether or not an error has occurred in each frame period shown in FIGS. 5A and 6A occurs in the next frame period.

In the example shown in FIG. 5B, as a result of detecting the occurrence of errors continuously over five frame periods from the frame period f15 to the frame period f19, the value of the error occurrence index EIn is “5” in the next frame period f20. Therefore, as shown in FIG. 5C, the error flag Sef having the value “1” is generated in the frame period f20. Further, since an error has occurred after the frame period f19, the value of the error occurrence index EIn continues to increase to “6” and “7”, and the error flag Sef having the value “1” is continuously generated. ing.
The error flag Sef having the value “1” is transmitted to the transmitter 101 together with the corresponding control target carrier number Scn.
A predetermined upper limit value may be provided for the value of the error occurrence index EIn. The upper limit value is obtained by adding the first threshold value Hth and the number of selectable carrier modulation schemes other than the carrier modulation scheme set as the initial value for each carrier. When an error continues to occur in a certain carrier, the error occurrence index EIn stops incrementing when it reaches the upper limit value and maintains the upper limit value.

In the example shown in FIG. 6B, the occurrence of an error was detected in the frame periods f32 and f33, but the occurrence of the error was not detected over 5 frame periods from the frame period f34 to f38 following the frame period f33. It becomes “−1” in the frame period f35, and the value of the error occurrence index EIn reaches “−5” in the frame period f39. Therefore, as shown in FIG. 6C, the value becomes “0” in the frame period f39. Error flag Sef is generated and transmitted to the transmitter 101 together with the corresponding control target carrier number Scn.
When the error flag Sef having the value “0” is transmitted to the transmitter 101, the error occurrence index EIn is reset to “0” in the next frame period f40.

  The data relating the error flag Sef and the control target carrier number Scn output from the transmission path evaluator 211 or the reception status evaluator 231 does not need to be in the table format shown in FIG. It may be in the form of a side-by-side array.

  For example, when there are a plurality of control target carrier numbers Scn having the same value of the error flag Sef, the control target carrier numbers Scn having the same value of the error flag Sef are collectively transmitted for one error flag Sef value. The For example, as shown in FIG. 7, data indicating that the value of the flag Sef is “1” is positioned at the head, and thereafter, the value of the error flag Sef is “1”. An array in which the control target carrier number Scn (that is, the number of the carrier in which the transmission error is frequently detected) is arranged, and data indicating that the value of the flag Sef is “0” is positioned at the beginning, Thereafter, an array in which one or two or more control target carrier numbers Scn (that is, carrier numbers in which the frequent occurrence of transmission errors have been resolved) in which the value of the error flag Sef is “0” is arranged is output.

  In the transmitter 101, as described above, the carrier allocation information is reset based on the error flag Sef and the control target carrier number Scn transmitted from the receiver 201.

  As described above, the image quality evaluator 221 evaluates the image quality based on the bit stream Srb from the OFDM demodulator 202, and outputs the image quality estimation value Sqp (data indicating the image quality evaluation result). For example, as shown in FIG. 8, the image quality evaluator 221 includes a decoder 222, a feature amount calculator 223, and an objective evaluator 224.

  The decoder 222 receives the bit stream Srb from the OFDM demodulator 202, decodes it into a predetermined format, and outputs the image data Sid obtained by the decoding to the feature quantity calculator 223.

  The feature quantity calculator 223 calculates a plurality of image feature quantities from the image data Sid, and the objective evaluator 224 objectively evaluates the image quality from the image feature quantities calculated by the feature quantity calculator 223. Sqp is output.

  The feature quantity calculator 223 includes an intra-frame feature quantity calculator 223a and an inter-frame feature quantity calculator 223b.

  The in-frame feature value calculator 223a calculates an in-frame feature value Ssi that is an image feature value for each frame based on the image data Sid from the decoder 222. As the intra-frame feature quantity Ssi, for example, the spatial feature quantity SI (Spatial Information) described in Non-Patent Document 1 is used in order to extract noise due to a transmission error.

The in-frame feature quantity Ssi may be calculated in units of one frame, or may be calculated in units obtained by dividing one frame into blocks each composed of a plurality of pixels.
In the case of calculation in units of frames, the in-frame feature amount Ssi is composed of data Ssi _d (d = 1) representing one value. In the case of calculation in units of blocks, the in-frame feature quantity Ssi is composed of data Ssi _d (d = 1 to D (D ≧ 1)) representing one or a plurality of values. Data Ssi _d may be, for example, consist of data representing the characteristic quantity of each corresponding block.
Furthermore, it may be composed of data representing one or more kinds of statistical values obtained based on the feature values of each block, and the combination of the statistical values and the feature values calculated in units of frames. There may be.
Examples of the statistical value include the maximum value, the minimum value, and the average value of the feature values of each block.
In this way, the accuracy of image quality determination can be improved by using a statistical value or a combination of a statistical value and a feature quantity in units of frames.
The in-frame feature quantity Ssi is output to the objective evaluator 224.

  As the intra-frame feature quantity in units of frames or blocks calculated by the intra-frame feature quantity calculator 223a, another index representing the feature of the image may be used instead of the spatial feature quantity SI.

  The inter-frame feature quantity calculator 223b includes two or more frames of image data (including the image data Sid of each frame and one before and / or after) including the image data Sid of each frame from the decoder 222. Based on the image data (Sid), an inter-frame feature quantity Sti, which is an image feature quantity in a plurality of frames, is calculated. When each frame image data Sid and the subsequent frames are used, after the “after frame” data is output from the decoder 222, the feature amount of the frame is calculated. For this purpose, a frame buffer (not shown) is provided in the inter-frame feature quantity calculation unit 223b.

Inter-frame feature value Sti _e to calculate, as well it used as an index for measuring the smoothness in movement of a video, which are used to extract the block-shaped noise superimposed by transmission errors, for example, of the The temporal feature amount TI (Temporal Information) described in Non-Patent Document 1 can be used.

The inter-frame feature quantity Sti may be calculated in units of one frame, or may be calculated in units obtained by dividing one frame into blocks each composed of a plurality of pixels.
When the calculation is performed in units of frames, the inter-frame feature value Sti includes data Sti _e (e = 1) representing one value. When calculating in block units, the inter-frame feature quantity Sti is composed of data Sti _e (e = 1 to E (E ≧ 1)) representing one or a plurality of values. Data Sti _e may be, for example, consist of data representing the characteristic quantity of each corresponding block.
Furthermore, it may be composed of data representing one or more kinds of statistical values obtained based on the feature values of each block, and the combination of the statistical values and the feature values calculated in units of frames. There may be.
Examples of the statistical value include the maximum value, the minimum value, and the average value of the feature values of each block.
In this way, the accuracy of image quality determination can be improved by using a statistical value or a combination of a statistical value and a feature quantity in units of frames.
The inter-frame feature quantity Sti is output to the objective evaluator 224.

  The interframe feature quantity calculated by the interframe feature quantity calculator 223b is not the temporal feature quantity TI, but another index representing the feature of the image calculated from the image data of a plurality of frames. It may be used.

  The objective evaluator 224 evaluates the image quality based on the in-frame feature value Ssi and the inter-frame feature value Sti output from the feature value calculator 223, and outputs the image quality estimation value Sqp as a result.

  The objective evaluator 224 objectively evaluates the quality of the image data Sid based on the image feature amounts Ssi and Sti calculated by the feature amount calculator 223, and generates and outputs an image quality estimated value Sqp. For the quality of the image data Sid, a subjective evaluation value may be measured in advance by a subjective evaluation experiment, but in the present embodiment, a result of a subjective evaluation experiment performed on a plurality of still images or videos that are not processing targets. By reflecting in the objective evaluation of the image to be processed, an objective evaluation value having a high correlation with the subjective evaluation value is obtained for the image to be processed.

With the image feature amounts Ssi and Sti as inputs, the image quality is determined by the following equation (2), for example, and an image quality estimated value Sqp in which subjective image quality is estimated from the image feature amounts is derived. In the equation (2), the estimated image quality value Sqp is calculated as F type (F ≧ 1) types of in-frame feature values Ssi _f (f = 1 to F) and inter-frame feature values Sti constituting the in-frame feature value Ssi. It is obtained by the sum of the G types (G ≧ 1) of inter-frame feature quantities Sti _g (g = 1 to G) to be configured.
Incidentally, the characteristic values Ssi _f and Sti coefficient according to _{g α f, β g} and constant C is carried out in advance, which is derived by a subjective evaluation experiment for a plurality of still images or video, thereby the image quality estimation value Sqp takes a value from 0 to 5, for example. The numbers α _f and β _g and the constant C are integers of 1 or more. The image quality estimation value Sqp obtained in this way indicates that the larger the value, the better the image quality, and the smaller the value, the worse the image quality. Here, the output of the image quality estimation value Sqp to the reception state evaluator 231 described later can be output for each frame, but may be performed for each of a plurality of frames. In the latter case, for example, a maximum value, a minimum value, an average value, or the like is used for the image quality estimation value Sqp calculated for each frame.

For example, the evaluation is performed such that the range of values that the image quality estimation value can take is 0.0 to 0.5 as described above, and the reference value Qb is set to 3.5, for example. In this case, the encoding parameter Sqs is determined so that the image quality of the image displayed by the received image data Id is 3.5 or more.
Note that the evaluation may be performed so that the range of values that the image quality estimation value Sqp can take is not the above 0.0 to 5.0 but wider. For example, when 0.0 to 10.0 is set, more detailed image quality evaluation can be performed, and the degree of image quality adjustment can be controlled more precisely.

  The reception state evaluator 231 receives data from the transmission path evaluator 211 indicating an error occurrence state in a carrier that can be used for transmission of image data, that is, the error flag Sef and the control target carrier number Scn, and the image quality evaluator 221. The image quality estimation value Sqp as the image quality evaluation result is received, and the reception status information Srs is generated together and transmitted to the transmitter 101.

  Hereinafter, the process of changing the modulation scheme and resetting the encoding parameter in the transmitter 101 based on the evaluation result of the transmission error in the receiver 201 will be described more specifically.

  The carrier controller 104 of the transmitter 101, for the carrier specified by the control target carrier number Scn included in the reception state information Srs, the value of the error flag Sef set for the control target carrier number Scn and The following processing is performed according to the modulation method applied to the carrier last time.

  When the error flag Sef is “1”, the number of modulation multi-values is smaller for the carrier specified by the control target carrier number Scn than the modulation scheme applied last time, and therefore transmission information per symbol. Determine a modulation scheme with a smaller amount. For example, when the setting value of the previous carrier modulation scheme specifies 64QAM, the carrier modulation scheme applied this time is 32QAM, which has a smaller transmission information amount than 64QAM.

  Here, in all carriers, the amount of reduction in the amount of transmission information per symbol by changing the carrier modulation method may be uniform, and an error occurrence index (or other index that reflects the number of times an error has occurred continuously). ) May be different depending on.

  In order to make the amount of reduction uniform, for example, it may be determined to be a carrier modulation method with the least amount of transmission information after the carrier modulation method applied last time, and this makes it complicated to change the carrier modulation method. It is not necessary to mount a complicated circuit, and the circuit scale can be reduced. At this time, the carrier modulation scheme previously applied to a carrier is the carrier modulation scheme with the least amount of transmission information per symbol among a plurality of carrier modulation schemes that can be implemented in this OFDM signal transmission / reception system, and the carrier When the corresponding error flag Sef is “1”, the carrier modulation scheme may not be changed, the carrier may not be used, and another carrier may be used instead.

  On the other hand, when the amount of decrease in the amount of transmission information is made different, for example, the carrier modulation scheme is determined such that the amount of decrease in the amount of transmission information per symbol is larger as the error occurrence index value is larger. For example, if the carrier modulation scheme applied last time is 64QAM and the error occurrence index EIn is equal to or less than a predetermined value Hts (a value larger than the first threshold value Hth), the error occurrence index is changed to 32QAM as described above. If EIn is larger than the above-mentioned predetermined value Hts, it is changed to 16QAM having a smaller modulation multi-value number than 32QAM. In this case, it is necessary to record an error occurrence index for all the carriers that can be used for transmission of image data, but this reduces errors that occur in data transmitted on carriers that are prone to transmission errors. it can.

  Among the carriers specified by the control target carrier number Scn indicating the frequent occurrence of transmission errors, there are cases where the transmission error occurrence status is unstable (for example, the occurrence and elimination of frequent error occurrence states are repeated), and others If a sufficient amount of transmission can be secured with this carrier, the carrier can be changed so as not to be used. As a result, the possibility of errors occurring in the data to be transmitted can be reduced.

  When the error flag Sef is “0”, the number of modulation multivalues is larger for the carrier specified by the control target carrier number Scn than the previously applied modulation scheme, and therefore transmission per symbol is performed. A modulation scheme with a larger amount of information is determined. For example, when the setting value of the previous carrier modulation scheme specifies 64QAM, the carrier modulation scheme applied this time is 128QAM, which has a larger transmission information amount than 64QAM.

  Here, in all carriers, the amount of increase in the amount of transmission information per symbol may be uniform by changing the carrier modulation method, and an error occurrence index (or other error does not continuously occur after the occurrence of an error). It may be different depending on the index reflecting the number of times.

  In order to make the increase range uniform, for example, it may be determined to be a carrier modulation method having the next largest amount of transmission information after the carrier modulation method applied last time, and this makes it difficult to change the carrier modulation method. It is not necessary to mount a complicated circuit, and the circuit scale can be reduced. At this time, the carrier modulation scheme previously applied to a certain carrier is the carrier modulation scheme having the largest amount of transmission information per symbol among a plurality of carrier modulation schemes that can be implemented in this OFDM signal transmission / reception system, and the carrier When the error flag Sef for is “0”, the carrier modulation scheme may not be changed.

  On the other hand, when the increase amount of the transmission information amount is made different, for example, as the error occurrence index is small, the carrier is determined to be a carrier modulation scheme in which the increase amount of the transmission information amount per symbol is large. For example, if the previously applied carrier modulation scheme is 64QAM and the error occurrence index EIn is equal to or greater than a predetermined value Lts (a value smaller than the second threshold Lth), the error occurrence index is changed to 128QAM as described above. If EIn is smaller than the predetermined value LTs, it is changed to 256QAM having a larger modulation multi-value number than 128QAM. In this case, it is necessary to record an error occurrence index for all the carriers that can be used for transmission of image data, but this makes it possible to increase the amount of data transmitted on a carrier that is unlikely to cause a transmission error as much as possible. , Transmission efficiency can be increased.

  After determining the carrier modulation method to be applied to each carrier, the carrier controller 104 outputs carrier allocation information Sca indicating the determined carrier modulation method, and the carrier controller 104 calculates the transmission data amount estimate value Agi, and the transmission data amount estimate value Agi. And the image quality estimated value Sqp are generated and output to the encoding controller 105. As an initial value of the transmission data amount estimated value Agi, a value that gives the maximum data amount that can be transmitted by the OFDM signal transmission / reception system in an ideal transmission path (a transmission path in which no transmission error occurs) is given.

  In the above example, it is determined whether or not the modulation method needs to be changed based on the error occurrence indices EI1 to EIN generated by the method described with reference to FIGS. 4 to 6C. However, the present invention is not limited to this. In short, the data indicating the error occurrence status such as the number of error occurrences is used as information for requesting the change of the modulation method, and the modulation method is changed based on this information. That's fine.

As a result of the above control, the modulation method is changed as long as it is possible to reduce the occurrence of transmission errors by changing the modulation method, and there are still many transmission errors even in the modulation method having the smallest number of modulation multi-values. In this case, since the image quality deteriorates accordingly, processing for changing the code parameter to a larger value is performed.
As described above, the modulation method of each carrier is changed based on the transmission error occurrence status, and the coding parameters are changed based on the carrier modulation method and the image quality evaluation value in real time. Efficiency can be kept as high as possible.

  As described above, instead of changing the modulation scheme applied to each carrier using the error flag Sef as information requesting the change of the modulation scheme, the change of the carrier modulation scheme applied to each carrier is changed to the reception state information. You may perform according to the image quality estimated value Sqp contained in Srs. In this case, the carrier controller 104 needs to input the same image quality reference value Qb as that of the encode controller 105 (indicated by a dotted line in FIG. 1). The image quality reference value Qb is set to a value corresponding to the minimum quality required for the image displayed by the received image data. The image quality estimation value Sqp and the image quality reference value Qb indicate that the larger the value, the better the image quality.

  For example, when the image quality estimation value Sqp included in the reception state information Srs is lower than the reference value Qb, the carrier is set so as to reduce the amount of data to be transmitted all at once or sequentially (for example, in a predetermined order). When the modulation method is changed and the estimated image quality value Sqp is equal to or greater than the reference value Qb, the carrier modulation method is changed so as to increase the amount of data to be transmitted all at once or sequentially (for example, in a predetermined order). I decided to.

  In this case, the modulation method may be changed based on the estimated image quality value Sqp independently of the change (resetting) of the modulation method based on the error flag Sef and the control target carrier number Scn. The modulation method may be changed based on the combination of the flag Sef and the estimated image quality Sqp.

  When the image quality estimation value Sqp included in the reception state information Srs is equal to or greater than the reference value Qb, the amount of data to be transmitted is increased in order to maintain the current state even if the error flag Sef indicates the elimination of the frequent occurrence of transmission errors. Thus, the carrier modulation scheme may not be changed. As a result, when the receiver 201 obtains sufficiently high image quality, the delay time due to processing for changing the carrier modulation scheme by the transmitter 101 can be eliminated.

  In the example of FIG. 1, the display 301 includes the decoder 302. However, as illustrated in FIG. 8, when the receiver 201 includes the decoder 222, the decoder 302 is included in the display 301. It does not have to be. In this case, for example, the image data Sid output from the decoder 222 of the receiver 201 may be input to the image regenerator 303.

Embodiment 2. FIG.
The overall configuration of the OFDM transmission / reception system according to the second embodiment is the same as that shown in FIG. 1, but is different in that the transmission path evaluator 211 is configured as shown in FIG.
The transmission path evaluator 211 of FIG. 9 is different from the configuration of the transmission path evaluator 211 of FIG. 3 in that an error occurrence period predictor 214 is additionally provided. 9, components having the same reference numerals as those in FIG. 3 are the same in configuration and operation as those in the first embodiment, and thus description thereof is omitted.

The error occurrence period predictor 214 performs at least once every predetermined period in each of all the carriers that can be used for transmission of image data from the error flag Sef and the control target carrier number Scn output from the carrier analyzer 213. It is determined whether or not an error has occurred, and the determination result is recorded in association with each period.
In this case, only when an error is detected at least once in each predetermined period, the time (representing the time) in which the error is detected (for example, the start time of the period) is recorded as the error occurrence time. May be.
Information indicating the error occurrence time is obtained for each carrier, but this information may not be in a table format but may be in an array format.

The error occurrence period predictor 214 determines the presence or absence of error periodicity for each carrier from the above-mentioned recording, and when the error occurrence has periodicity, information (periodicity information) Sce indicating the periodicity is obtained. Generate and output. This periodicity information includes information indicating the length of the period and information indicating a time difference from a reference time (for example, current time) to a timing at which an error is predicted to occur next.
The output period information Sce is transmitted by the reception state evaluator 231 as a part of the reception state information Srs.
Note that whether to transmit the periodicity information Sce to the transmitter 101 as the reception state information Srs may be selectable by setting.

  The carrier controller 104 uses the periodicity information Sce to reset the carrier allocation information Sca so that the carrier is not used at the time when the error is predicted to occur and the time zone before and after the time.

  With the configuration of the first embodiment, a delay occurs from the occurrence of a transmission error until the reflection to the carrier allocation information Sca. However, with the configuration of the second embodiment, the modulation scheme is prior to the timing at which the transmission error occurs. Since the change (reassignment of carrier allocation) is performed, the occurrence of a transmission error can be prevented and more stable transmission can be performed.

  In order to obtain periodicity information, the occurrence of an error may be observed continuously or intermittently. When performing intermittently, observe every predetermined period (observation execution cycle), and once the periodicity information is obtained in each observation, continue to use the obtained periodicity information until the next observation It is also good. The observation execution cycle is longer than the error detection cycle described above. Each observation is made long enough to determine the presence or absence of periodicity and to obtain information necessary for calculating the length of the period and the above time difference. If the above observation is performed continuously, it is advantageous in that it is possible to respond quickly even when the error generation period changes.

  Note that instead of including the periodicity information Sce in the reception status information Srs, the error occurrence period predictor 214 causes the frequent occurrence of errors prior to the timing at which frequent occurrence of expected errors is expected for a carrier in which transmission errors occur frequently. May be transmitted to the transmitter 101 together with the control target carrier number Scn indicating the carrier where the error is expected to occur frequently.

  In this case, the reception state evaluator 231 and the transmitter 101 of the receiver 201 can cope with the expected frequent occurrence of errors by performing the same processing as in the first embodiment. In other words, the transmitter 101 treats the flag that predicts the frequent occurrence of the error as a substitute for the error flag Sef with the above value “1”, and changes to a modulation method with a smaller number of modulation multi-values. When the timing at which frequent occurrence is expected has passed, the original modulation system is restored. Since the configuration of the reception state evaluator 231 and the transmitter 101 may be the same as that of the first embodiment, it is possible to prevent transmission errors from occurring without increasing the circuit scale.

  For example, when the system of the present invention is applied to a bus or train that circulates on a predetermined route, when there is noise in a specific frequency band at a specific place, a periodic transmission error can be suppressed in advance. For example, in the case of a train, this is an effective measure against transmission errors caused by noise from the pantograph.

Embodiment 3 FIG.
The configuration of the OFDM transmission / reception system according to Embodiment 3 is shown in FIG.
The OFDM transmission / reception system shown in FIG. 10 is generally the same as the transmission / reception system of FIG. 1, but instead of the reception status evaluator 231, the carrier controller 104, and the encoding controller 105 of FIG. The difference is that a carrier controller 114 and an encode controller 115 are provided. 10 having the same reference numerals as those in FIG. 1 are the same in configuration and operation as those in the first embodiment, and thus description thereof is omitted. The reception state evaluator 241 may include a wireless signal transmitter 231a, similar to the reception state evaluator 231 of FIG.

Unlike the reception state evaluator 231 in FIG. 1, the reception state evaluator 241 outputs an image quality flag Sr as a part of the reception state information Srs instead of the image quality estimation value Sqp, and the carrier controller 114 outputs the image quality estimation value Sqp. The reception state information Srs including the image quality flag Sr is received instead of the image quality flag Sr, and the image quality flag Sr is output instead of the image quality estimation value Sqp. The encoding controller 115 is based on the image quality flag Sr instead of the image quality estimation value Sqp. Reset the encoding parameters.
The image quality flag Sr indicates whether or not the carrier controller 114 or the encoding controller 115 needs to reset the modulation scheme or the encoding parameter, and requests the transmission condition to be changed in the same manner as the error flag Sef. It is used as information.

The reception state evaluator 241 determines the value of the image quality flag Sr based on the image quality reference value Qb and the image quality estimated value Sqp. This image quality reference value Qb is the same as that used in the encoding controller 105 in the system of FIG.
For example, if the estimated image quality value Sqp is lower than the reference value Qb, the value of the image quality flag Sr is set to a first value, for example “1”; otherwise, the value of the image quality flag Sr is set to a second value, for example “ 0 ”.
The reception state evaluator 241 transmits, as reception state information Srs, a collection of the error flag Sef and the control target carrier number Scn indicating the error occurrence state from the transmission path evaluator 211 and the internally generated image quality flag Sr. To the device 101.

  When only the determination of the encoding parameter Sqs in the encoding controller 115 is controlled by the image quality flag Sr, for example, when the image quality flag Sr is “1”, the image quality estimation value Sqp in the first embodiment is greater than the reference value Qb. If the image quality flag Sr is “0”, the control may be performed in the same manner as in the case where the estimated image quality value Sqp is equal to or greater than the reference value Qb.

When the change of the modulation method in the carrier controller 114 is controlled by the image quality flag Sr, as described in the modification of the first embodiment, when the image quality flag Sr is “1”, all carriers are controlled. When the modulation scheme is changed so as to decrease the number of modulation multilevels simultaneously or sequentially (for example, in a predetermined order) and the image quality flag Sr is “0”, all carriers are simultaneously or sequentially (for example, predetermined The modulation scheme may be changed to increase the modulation multi-level number (in order).
In this case, the modulation method may be changed based on the image quality flag Sr independently of the change (resetting) of the modulation method based on the error flag Sef and the control target carrier number Scn, and the control target carrier number Scn and the error flag may be changed. The modulation method may be changed based on the combination of Sef and the image quality flag Sr.

If the image quality flag Sr is “0”, the carrier controller 114 generates new carrier allocation information Sca (reset the carrier allocation information Sca) to improve transmission efficiency, and the image quality flag Sr. If the value of “1” is “1”, an improvement in image quality is desired. Therefore, the encoding controller 115 may calculate (recalculate) a new encoding parameter Sqs.
In this case, the carrier controller 114 and the encode controller 115 may reset the carrier allocation information Sca or recalculate the encoding parameter Sqp only when the image quality flag Sr has one of the values. It is possible to shorten the time from when the change occurs until the processing for responding to the change is performed.

When resetting is requested only to one of the carrier controller 114 and the encoding controller 115 by the image quality flag Sr, the image quality flag can be expressed by 1 bit.
For example, as described above, when the image quality flag Sr is “0”, it indicates a reset request to the carrier controller 114, and when the image quality flag Sr is “1”, it indicates a reset request to the encode controller 115. It's also good.

  When the image quality flag Sr has a value that requires resetting the carrier controller 104, the carrier controller 114 can calculate each of the error flags Sef included in the reception state information Srs and the control target carrier number Scn. Based on the amount of information that can be transmitted by the carrier, the modulation scheme of each carrier is determined, and carrier allocation information Sca is generated. The carrier modulation scheme applied to each carrier needs to be determined so that the modulation multi-level number is equal to or greater than the modulation multi-level number of the previously applied modulation scheme. After determining the carrier modulation method, the transmission data amount estimate value Agi is calculated, and the image quality flag Sr included in the reception state information Srs and the transmission data amount estimate value Agi are output to the encoding controller 115.

The encoding controller 115 can uniquely determine the encoding parameter Sqs based on the image quality flag Sr from the carrier controller 114 and the transmission data amount estimated value Agi. An example of determining the encoding parameter Sqs in the encoding controller 115 is shown in Expression (3). Sq _n-1 and Sqs in the formula (3) indicate that the smaller the value, the lower the compression rate.

  If the reception status information Srs clearly indicates that it is a reset request for either the carrier controller 114 or the encode controller 115, the transmitter 101 calculates the calculation cost for analyzing the reception status information Srs. The transmitter 101 can reduce the delay time from when the reception state information Srs is received until it is applied to the carrier controller 114 and the encode controller 115.

  When resetting is performed in both the carrier controller 114 and the encoding controller 115, the image quality flag Sr may be configured with 2 bits. Since the image quality flag Sr can be uniquely determined simply by comparing the image quality reference value Qb and the image quality estimated value Sqp, the image quality flag Sr can be calculated easily in a short time.

  As described above, the configuration for changing the modulation scheme in the carrier controller 114 and / or changing the encoding parameter in the encoding controller 115 using the image quality flag Sr as information for requesting the change of the transmission condition has been described. The reception state evaluator 241 of the device 201 requests a change in the transmission conditions (modulation scheme and coding parameters) in the transmitter 101 based on the data Sef and Scn indicating the error occurrence status in each carrier and the image quality evaluation result Sqp. Information is generated, and the information is transmitted from the receiver 201 to the transmitter 101, and the transmitter 101 changes the modulation scheme in the carrier controller 114 and / or the encoding parameter in the encoding controller 115 based on this information. What is necessary is just to be the structure which changes.

    101 transmitter, 102 encoder, 103 OFDM modulator, 104 carrier controller, 105 encoding controller, 114 carrier controller, 115 encoding controller, 201 receiver, 202 OFDM demodulator, 211 transmission path evaluator, 212 error detection Carrier identifier, 213 carrier analyzer, 214 error generation period predictor, 221 image quality evaluator, 222 decoder, 223 feature quantity calculator, 223a intra-frame feature quantity calculator, 223b inter-frame feature quantity calculator, 224 objective evaluator 231 reception state evaluator, 241 reception state evaluator, 301 display unit, 302 decoder, 303 image player.

Claims (10)

An OFDM signal transmission / reception system that modulates image data and transmits it from a transmitter to a receiver,
The transmitter is
An encoder that generates a bitstream in which the image data is information-compressed based on an encoding parameter;
After performing error correction coding on the bitstream, the bitstream is divided into a plurality of data portions, and different carriers are modulated by the respective carrier modulation schemes in the respective data portions obtained by the division. An OFDM modulator for generating an OFDM modulated signal;
A carrier controller that determines the carrier modulation scheme based on reception state information and outputs information indicating the determined carrier modulation scheme;
An encoding controller that determines the encoding parameter from an image quality evaluation result included in the reception state information and outputs information indicating the determined encoding parameter;
The receiver is
Demodulate the OFDM signal received from the transmitter, generate a bitstream, perform error correction processing on the OFDM signal, and output error detection information indicating an error position detected by the error correction processing An OFDM demodulator;
From the error detection information, a transmission path evaluator that generates and outputs data representing an error occurrence state in each of the carriers that can be used for transmission of the image data;
An image quality evaluator that evaluates image quality based on the bitstream from the OFDM demodulator and outputs data representing an image quality evaluation result;
A reception state evaluator that generates the reception state information including data representing the error occurrence state from the transmission path evaluator and data representing the image quality evaluation result from the image quality evaluator, and outputs the reception state information to the transmitter An OFDM signal transmission / reception system comprising: The carrier controller can transmit with one symbol by all carriers available for transmission of the image data from a carrier modulation scheme determined for each of the carriers available for transmission of the image data. Calculate the amount of information,
The encoding controller determines the encoding parameter based on the amount of information that can be transmitted by the one symbol, calculated by the carrier controller, when the image quality evaluation result is equal to or greater than a predetermined reference value.
The OFDM signal transmission / reception system according to claim 1, wherein the encoding controller sets the encoding parameter to a larger value when the image quality evaluation result is lower than the reference value. The carrier controller is
The carrier modulation scheme of a carrier in which errors frequently occur among the available carriers is changed to a modulation scheme with a smaller number of modulation multi-values based on data representing the occurrence status of the error. Item 3. The OFDM signal transmission / reception system according to Item 1 or 2.   4. The carrier controller according to claim 1, wherein the carrier controller determines not to use a carrier whose error occurrence state is indicated by data representing the error occurrence state. 5. The OFDM signal transmission / reception system described.   2. The carrier controller according to claim 1, wherein, when the image quality evaluation result is lower than a predetermined reference value, the carrier controller changes the carrier modulation scheme to a carrier modulation scheme with a smaller number of modulation multilevels. OFDM signal transmission / reception system.   6. The OFDM signal transmission / reception system according to claim 1, wherein the OFDM demodulator outputs the error detection information only at a timing for each predetermined period.   7. The transmission path evaluator records the error occurrence status, detects a periodically occurring error, and generates information indicating the periodicity of the error occurrence. The OFDM signal transmission / reception system described in 1.   8. The transmission path evaluator records the occurrence state of the error at a predetermined time, and generates information indicating the periodicity from a recording result at the predetermined time. OFDM signal transmission / reception system.   The reception state evaluator generates and outputs information requesting a change of the carrier modulation scheme or the encoding parameter based on data indicating the error occurrence status and data indicating the image quality evaluation result. The OFDM signal transmission / reception system according to any one of 1 to 8.   The reception status evaluator is a radio for transmitting the reception status information to the transmitter on a transmission path different from a transmission path used for transmission of the image data from the transmitter to the receiver. The OFDM signal transmission / reception system according to claim 1, further comprising a signal transmitter.

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