MCM system, with a plurality of data streams, each with its own transmission parameters

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to, for example, a transmission method for digital television broadcasting, and in particular, an orthogonal frequency division multiplex transmission method (hereinafter, OFDM) in which data is transmitted by orthogonal frequency division multiplex digital modulation / demodulation processing (hereinafter, referred to as OFDM (Orthogonal Frequency Division Multiplexing)). It relates to a transmission method) and a transmission device and a reception device using the transmission method.

【0002】

[Conventional technology]

Conventionally, in order to further enhance television broadcasting services, there is an increasing demand for digital broadcasting in terrestrial broadcasting and the like. Especially in the transmission method of terrestrial digital broadcasting, the OFDM transmission method that is strong against multipath (ghost in broadcasting) is regarded as promising.

【0003】

This OFDM transmission method is a kind of multi-carrier modulation method, and as shown in FIG. 8, the transmission signal is a combination of a large number (tens to thousands) of digitally modulated waves (carrier waves 1 to k). .. As the modulation method of each carrier, QPSK, 16QAM, 64QAM and the like are used.

【0004】

Data transmission by the OFDM transmission method is performed in units of the transmission symbols shown in FIG. Each transmission symbol consists of a valid symbol period and a period called a guard interval. The valid symbol period is the signal period that is substantially required for data transmission. The guard interval is a redundant signal period for reducing the influence of multipath, and the signal waveform of the effective symbol period is cyclically repeated.

【0005】

When the frequency interval between each carrier is equal to the inverse of the length of the effective symbol period, the zero point of the frequency spectrum of each digital modulated wave is one with the carrier frequency of the adjacent modulated wave, as shown in FIG. 9 (a). However, there is no mutual interference between the carriers. At this time, the carrier waves are said to be orthogonal to each other. As shown in FIG. 9B, the spectrum of the OFDM signal has a shape close to a rectangle as a whole. Assuming that the length of the effective symbol period is ts and the number of carriers is K, the frequency interval between each carrier is 1 / ts and the transmission bandwidth is K / ts.

【0006】

In the OFDM transmission method, several tens to several hundreds of transmission symbols shown in FIG. 8 are collected to form one transmission frame. A configuration example of the OFDM transmission frame is shown in FIG. In addition to the data transmission symbol, the OFDM transmission frame may include a frame synchronization symbol, a service identification symbol, and the like, if necessary.

【0007】

FIG. 11 shows the conceptual configuration of the transmitting device A and the receiving device B when the above OFDM transmission method is adopted. First, in the transmission device A, binary transmission data is divided into data blocks for each fixed number of bits, and each data block is input in a state of being converted into one complex numerical value. Then, the series-parallel converter A1 gives one complex numerical value Ci (i = 1 to N) for each carrier frequency, and the inverse discrete Fourier transform circuit unit A2 performs inverse discrete Fourier transform on the time axis. As a result, a sample value of the time axis waveform is generated, and a time-continuous baseband analog signal waveform is obtained from this sample value series. The baseband analog signal waveform is converted to the transmission frequency by the frequency converter A3 and transmitted.

【0008】

The number of sample values on the time axis generated by the inverse discrete Fourier transform is typically 2 per valid symbol period.ⁿ (n is a positive integer). Therefore, r_G If = (guard interval length) / (effective symbol length) is defined, 2 per transmission symbolⁿ (1 + r_G ) Sample values are generated. The length of each transmission symbol is usually an integral multiple of the time interval of the sample points.

【0009】

In the receiving apparatus B, base reception signal by frequency conversion by the frequency converter B1 after obtaining the baseband signal waveform samples in the same sample rate as the transmitter. Then, this sample value series is discrete Fourier transformed on the frequency axis by the discrete Fourier transform circuit unit B2, the value of the received data is obtained by calculating the phase and amplitude of each carrier frequency component, and the series is serialized by the parallel series converter B3. Convert to and output.

【0010】

By the way, the reception form of television broadcasting is roughly classified into fixed reception and mobile reception (including mobile reception), and it is important to enable good reception in any case. However, in the conventional OFDM method, the effective symbol length, guard interval length, and number of carrier waves of the data transmission symbol are determined based on the fixed reception, which is in high demand, and fading is a problem in mobile reception. It is expected to be.

【0011】

[Problems to be Solved by the Invention]

As described above, in the conventional OFDM transmission method and the transmission device and the reception device using the same, the effective symbol length, guard interval length, and number of carrier waves of the data transmission symbol are set so as to be suitable for a plurality of reception modes. It was not possible to do so, and we had to make a decision based on the reception form, which is in high demand.

【0012】

An object of the present invention is to solve the above problems, provide an OFDM transmission method capable of receiving well in any case regardless of the receiving form, and further provide a transmitting device and a receiving device using the method. It is in.

【0013】

[Means for solving problems]

In the OFDM transmission method of the present invention that solves the above problems, the time interval between OFDM sampling points is T, and the effective symbol length is Ni T (Ni is positive) for the i-th data transmission symbol in the OFDM transmission frame. (Integer), the guard interval length is Mi T (Mi is zero or a positive integer), the number of carriers is Ki (Ki is a positive integer), and Ki / Ni T is a constant value W (W is determined by the bandwidth of the transmission line). The values of Ni, Mi, and Ki are arbitrarily selected on the condition that they are always smaller than the positive real number), and at least one of the values of Ni and Mi is set in one OFDM transmission frame. It is characterized by switching from one value to another one or more times.

【0014】

That is, in the OFDM transmission method according to the present invention, two or more kinds of values are used as the effective symbol length and the guard interval length of the data transmission symbol in one OFDM transmission frame, and each symbol length is used as an OFDM digital signal. The frequency bandwidth of the OFDM transmission signal is set to an integral multiple of the sampling period, which is the basic unit of processing, and is set to a value smaller than a constant value determined by the bandwidth of the available transmission line.

【0015】

As a result, even if a plurality of data transmission symbols having different effective symbol lengths and guard interval lengths are multiplexed in one transmission channel, mutual interference between carriers does not occur. Therefore, by using the OFDM transmission method of the present invention, it is possible to deal with various transmission conditions in one broadcasting channel without lowering the frequency utilization efficiency and without causing mutual interference between carriers. It becomes.

【0016】

In particular, within one broadcast channel, it becomes possible to simultaneously send an OFDM transmission symbol suitable for fixed reception and an OFDM transmission symbol suitable for mobile reception without deteriorating frequency utilization efficiency.

【0017】

BEST MODE FOR CARRYING OUT THE INVENTION

First, the idea of the present invention will be described. As a technique for sending an OFDM transmission symbol suitable for fixed reception and an OFDM transmission symbol suitable for mobile reception in one broadcasting channel, as shown in FIG. 12, the OFDM signal is divided into two frequency blocks on the frequency axis. It is divided, a guard band is provided between frequency blocks so that carrier interference does not occur between blocks, the symbol length and guard interval length are set to different values for each frequency block, and the two frequency blocks are used for fixed reception and mobile reception, respectively. The method to use is conceivable.

【0018】

However, in the method of dividing into a plurality of frequency blocks as described above, since the effective symbol length of OFDM and the carrier frequency interval are different in each frequency block, it is not possible to maintain the orthogonality between the carriers between the frequency blocks. Therefore, in order to prevent mutual interference between carriers between frequency blocks, a guard band having a considerable width must be provided between the frequency blocks. Therefore, there is a drawback that the frequency utilization efficiency is lowered by the amount of this guard band, and the bit rate that can be transmitted in one broadcasting channel is reduced.

【0019】

Therefore, in the present invention, mutual interference between carriers is prevented from occurring even if a guard band is not provided, thereby preventing data transmission suitable for fixed reception in one broadcasting channel without lowering frequency utilization efficiency. Allows you to send symbols and data transmission symbols suitable for mobile reception.

【0020】

Here, in the OFDM transmission method, in the discrete Fourier transform in the demodulator, an FFT window having the same length as the effective symbol period is set in each data transmission symbol period, and the FFT window is included in the FFT window.ⁿ Discrete Fourier transform of the sample points on the frequency axis.

【0021】

In this case, if the FFT window is set to the rearmost position of each transmission symbol, and if the delay time of multipath (ghost signal in television broadcasting) is shorter than the length of the guard interval, it will be adjacent to the FFT window of the demodulator. Since the ghost of the symbol does not invade, the characteristic deterioration due to multipath can be made much smaller than that of the single carrier method. Therefore, in general, the longer the guard interval is, the longer the delay time can be dealt with, and the stronger the transmission characteristic for multipath can be obtained.

【0022】

Next, the relationship between the OFDM symbol length and the guard interval length suitable for each reception mode of fixed reception and mobile reception will be described. In general, it is an important technical issue to reduce the influence of multipath in the fixed reception of OFDM, and as described above, it is advantageous to lengthen the guard interval in order to obtain transmission characteristics strong against ghosts. ..

【0023】

However, if a long guard interval is added, the transmission capacity (bit rate) decreases by the ratio of the guard interval length to the total symbol length. Therefore, in order to prevent the bit rate from decreasing even if the guard interval is increased, The effective symbol length needs to be increased by the same proportion as the guard interval length, and in the end, the total symbol length needs to be increased.

【0024】

On the other hand, in mobile reception, the transmission line characteristics change with time due to fading. Therefore, if the OFDM symbol length is made too long, the transmission line characteristics change so much even within one transmission symbol period, and the bit error rate. Becomes larger. That is, for fading at the time of mobile reception, increasing the guard interval and the symbol length acts in a disadvantageous direction. In the case of mobile reception, it is considered that the characteristic is intermediate between fixed reception and mobile reception.

【0025】

In this way, when using the OFDM transmission method, when setting transmission parameters such as the guard interval length and effective symbol length, the optimum parameter value differs depending on the reception mode assumed by the broadcasting system, so there is one type. It turns out that it is extremely difficult to support both fixed reception and mobile reception with a parameter set. Therefore, when it is desired to send information for both fixed reception and mobile reception within a certain broadcasting channel, it is necessary to use the OFDM transmission method according to the present invention.

【0026】

Hereinafter, embodiments of a transmitting device and a receiving device that employ the OFDM transmission method of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a block circuit diagram showing a configuration of a transmission device according to an embodiment of the present invention. This transmitter includes a series / parallel converter 111 ~ 11L, an inverse discrete Fourier converter 121 ~ 12L, a parallel / series converter 131 ~ 13L, a time sample series switch 14, and a symbol / synchronization for data transmission. Symbol switch 15, synchronization symbol waveform memory 16, D / A converter 17, low-pass filter 18, frequency converter 19, frame pulse generator 20, symbol pulse generator 21, and sampling clock generation. A device 22 and a local oscillator 23 are provided.

【0027】

In the transmission device having the above configuration, the L data series D1 to DL to be the transmission data are input to the L series / parallel converters 111 to 11L, respectively. The L transmission data series D1 to DL correspond to L types of parameter sets (effective symbol length, guard interval length, number of carrier waves).

【0028】

The series / parallel converters 111 to 11L convert series data into parallel data and assign it to each carrier wave of OFDM. The inverse discrete Fourier transforms 121 to 12L determine the phase and amplitude of each carrier wave in the symbol period from the transmission data assigned to each carrier wave, and regard the phase and amplitude as complex number data on the frequency axis to perform inverse discrete Fourier transform. The transform is performed and the sample value of the transmission waveform on the time axis is output. The parallel / series converters 131 to 13L convert the time sample values output in parallel for each symbol into a series sample value series.

【0029】

On the other hand, the sampling clock generator 22 generates a sampling clock based on the original vibration frequency signal output from the local oscillator 23. The frame pulse generator 20 and the symbol pulse generator 21 generate a frame pulse and a symbol pulse from the sampling clock, respectively. The sampling clock, frame pulse, and symbol pulse are supplied to each part of the transmitter and used for timing generation.

【0030】

The time sample sequence switcher 14 selectively switches L types of time sample sequences using frame pulses and symbol pulses, converts them into a single time sample sequence, and outputs the sequence. The synchronization symbol waveform memory 16 outputs a sample value of the frame synchronization symbol waveform. The data transmission symbol / synchronization symbol switch 15 is a time sample series of data transmission symbols output from the time sample series switch 14 and a waveform sample value of the frame synchronization symbol output from the synchronization symbol waveform memory 16. By switching the series, it is converted into a time sample value series of the baseband OFDM signal and output.

【0031】

The D / A converter 17 converts the time sample value series into an analog signal, and the low-pass filter 18 removes the high frequency component of the analog signal and outputs an analog baseband OFDM signal. The frequency converter 19 upconverts the baseband OFDM signal to an intermediate frequency or a radio frequency and outputs it as a transmission signal.

【0032】

FIG. 2 is a block circuit diagram showing a configuration of a receiving device according to an embodiment of the present invention. This receiver includes a band-passing filter 31, a frequency converter 32, a synchronization symbol waveform memory 33, a synchronization symbol position detector 34, an oscillation frequency control signal generator 35, a local oscillator 36, and a sampling clock. Generator 37, frame pulse generator 38, symbol pulse generator 39, A / D converter 40, series / parallel converter 411 to 41L, discrete Fourier converter 421 to 42L, demodulation / parallel / It is equipped with a series converter 431 to 43L.

【0033】

In the receiving device according to the above configuration, the band-passing filter 31 removes the out-of-band component of the received signal, and the frequency converter 32 down-converts the intermediate frequency or radio frequency OFDM signal to the baseband. The A / D converter 40 samples the baseband OFDM signal and converts it into a digital sample value sequence. The output is supplied to the series / parallel converters 411 to 41L and also to the synchronization symbol position detector 34.

【0034】

The synchronization symbol position detector 34 calculates the cross-correlation value between the sample value series of the baseband OFDM signal and the sample value series of the synchronization symbol waveform stored in the synchronization symbol waveform memory 33, and calculates the frame start position. Is detected, and the switching position of the transmission symbol and the FFT window position are determined.

【0035】

The oscillation frequency control signal generator 35 generates a signal for controlling the oscillation frequency of the local oscillator 36 based on the frame period detected by the synchronization symbol position detector 34. The details of the local oscillation frequency control method using the frame period are described in Japanese Patent Application No. 6-138386 Clock Frequency Automatic Control Method and Transmitter and Receiver Device Used for It.

【0036】

The sampling clock generator 37 generates a sampling clock based on the original vibration frequency signal output from the local oscillator 36. The frame pulse generator 38 and the symbol pulse generator 39 generate a frame pulse and a symbol pulse, respectively, based on the frame head position information and the sampling clock output from the synchronization symbol position detector 34. The sampling clock, frame pulse, and symbol pulse are supplied to each part of the receiving device and used for various timing generations.

【0037】

The series / parallel converters 411 to 41L convert the baseband sample value series into parallel data and supply it to the discrete Fourier transformers 421 to 42L. The discrete Fourier transformers 421 to 42L convert the sample values on the time axis into a spectrum for each carrier frequency. The demodulation / parallel / series converters 431 to 43L estimate the phase and amplitude of each carrier wave from the value of the frequency spectrum, obtain the value of the received data from the value of the phase and amplitude, and further receive the received data series D1 to DL in series. Convert to and output. L received data series D1 to DL correspond to L types of parameter sets.

【0038】

In the above system configuration, in the inverse discrete Fourier transform 12i (i is 1 to L) and the discrete Fourier transform 42i (i is 1 to L), the sampling clock interval is T and the effective symbol length in the frame is Ni T (. Ki / Ni T is determined by the bandwidth of the transmission line, where Ni is a positive integer), the guard interval length is Mi T (Mi is zero or a positive integer), and the number of carriers is Ki (Ki is a positive integer). Arbitrarily select the values of Ni, Mi, and Ki on the condition that they are always smaller than the constant value W (W is a positive real number).

【0039】

Further, in the time sample sequence switch 14, data transmission symbols having the same effective symbol length and guard interval length are made continuous on the time axis, and at least one of the effective symbol length and the guard interval length is different for data transmission. The data transmission symbols are switched in the order in which the number of switching points where the symbols are adjacent to each other is minimized.

【0040】

That is, various transmission orders can be considered for the order in which the transmission symbols corresponding to the data series D1 to DL are sent, but the data transmission symbol corresponding to one data series (one parameter set) is , The most basic method is to transmit in a continuous order on the time axis. In this case, the number of switching points where transmission symbols having different parameter sets are adjacent to each other is the minimum. Figure 3 shows an example of the frame configuration.

【0041】

As a specific example, when L = 2 and the transmission data series D1 is for fixed reception and the transmission data series D2 is for mobile reception, the parameter sets of the inverse discrete Fourier transforms 121 and 122 are for fixed reception and mobile reception, respectively. If set to, good reception is possible in any reception mode.

【0042】

Therefore, if the OFDM transmission method of the present invention is used, mutual interference does not occur between carriers even if a guard band is not provided, so that one broadcasting channel can be used for various transmission conditions without deteriorating frequency utilization efficiency. In particular, it is possible to send an OFDM transmission symbol suitable for fixed reception and an OFDM transmission symbol suitable for mobile reception within one broadcasting channel without deteriorating the frequency utilization efficiency.

【0043】

In the configuration of FIG. 1, L inverse discrete Fourier transforms 121 to 12L are used for L types of parameter sets, but inverse discrete Fourier transforms capable of supporting a plurality of types of FFT points are used. Therefore, it is possible to correspond to L kinds of symbol lengths with one piece.

【0044】

The modulation method for each carrier of OFDM is determined by the type of phase value and amplitude value assigned to each carrier as complex values on the frequency axis in the inverse discrete Fourier converters 121 to 12L, but corresponds to different parameter sets. It is also possible to use different modulation methods for each transmission data series D1 to DL, such as delayed detection QPSK, synchronous detection 16QAM, and synchronous detection 64QAM.

【0045】

On the other hand, in the configuration of FIG. 2, L discrete Fourier transformers 421 to 42L are used for L types of parameter sets, but by using discrete Fourier transformers that can handle a plurality of FFT points, It is also possible to support L types of parameter sets with one.

【0046】

In addition, among the L data series D1 to DL, for example, using the data series D1 and the corresponding transmission symbol, the effective symbol length, guard interval length, and number of carrier waves of the transmission symbol corresponding to the data series D2 to DL, respectively. It is also possible to send information about the carrier modulation method from the transmitting side to the receiving side.

【0047】

Generally speaking, the effective symbol length Na T (Na is a positive integer), guard interval length Ma T (Ma is zero or a positive integer), and the number of carrier waves of a specific data transmission symbol in the OFDM transmission frame. Ka (Ka is a positive integer) is set as a known value on the receiving side, the modulation method of each carrier wave of the specific symbol is also known on the receiving side, and the specific symbol of the OFDM transmission frame including the specific symbol is excluded. For data transmission by transmitting at least a part of the effective symbol length, guard interval length, number of carrier waves, and modulation method of each carrier wave of other data transmission symbols from the transmitting side to the receiving side using the specific symbol. The parameter set of the symbol can be changed.

【0048】

By the way, in the above embodiment, when the average transmission power of the i-th data transmission symbol in the OFDM transmission frame is Pi, as shown in FIG. 4, the value of Ni that defines the effective symbol length in the frame is set to the value of Ni. Determine the Pi value accordingly, and make the Ni value and the Pi value have a one-to-one correspondence. Here, when the number of possible values of Ni is L, the number of possible values of Pi is also L, and the average transmission power value Pi is set according to the effective symbol length Ni T of each data transmission symbol. Change.

【0049】

Using this method, for example, different service areas are set for the fixed reception layer and the mobile reception layer by setting the average transmission power to different values for the fixed reception layer and the mobile reception layer in each transmission frame. It becomes possible.

【0050】

Further, in the above embodiment, when the possible values of Ni are A1, A2, ..., AL, and the maximum value among A1, A2, ..., AL is Amax, then A1, A2 ,. .., AL are all divisors of Amax. That is, when the possible values of the effective symbol length Ni T are A1 T, A2 T, ..., ALT, and the maximum value among A1 T, A2 T, ..., ALT is Amax T. , A1 T, A2 T, ..., ALT are all divisors of Amax T.

【0051】

In this case, a part of the carrier frequency used in each data transmission symbol can be commonly used in all the data transmission symbols. Therefore, by using these carrier waves, for example, phase information, control information, and the like for synchronous detection can be sent.

【0052】

Further, in the above embodiment, the possible value of Mi that defines the guard interval length is one. That is, a plurality of values are used as the effective symbol length Ni T of the data transmission symbol, and one value is used for the guard interval length Mi T. In this case, for example, the fixed reception layer and the mobile reception layer in each transmission frame can have the same characteristics against intersymbol interference due to multipath.

【0053】

Further, in the transmission symbol in the OFDM transmission frame, the carrier frequency is changed at a predetermined frequency interval at regular time intervals. That is, the carrier wave of the transmission symbol (mobile reception symbol) having a small number of carrier waves is changed by the carrier frequency interval of the transmission symbol (fixed reception symbol) having a large number of carrier waves or a frequency that is an integral multiple thereof.

【0054】

According to this configuration, it is possible to send, for example, phase information for synchronous detection of a fixed reception symbol and information for equalizing a transmission line by using the carrier wave of the mobile reception symbol. Specifically, there are cases where the frequency is shifted in the RF band and cases where the frequency is shifted in the baseband. FIG. 5 shows a configuration example in the former case, and FIG. 6 shows an arrangement example of the carrier frequency in the latter case. In FIG. 5, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals.

【0055】

(1) When shifting the frequency in the RF band Figure 5 (a) shows the configuration on the transmitter side. The frequency-variable local oscillator 24 switches the oscillation frequency according to the transmission symbol by using the frame pulse and the symbol pulse from the frame pulse generator 20 and the symbol pulse generator 21 of FIG. By driving the frequency converter 19 of FIG. 1 with the switched oscillation frequency, it is possible to generate a signal whose frequency is shifted in time series.

【0056】

Figure 5 (b) shows the configuration on the receiving device side. The frequency-variable local oscillator 44 switches the oscillation frequency according to the transmission symbol by using the frame pulse and the symbol pulse from the frame pulse generator 38 and the symbol pulse generator 39 of FIG. By driving the frequency converter 32 of FIG. 2 with this switched oscillation frequency, the OFDM signal of the intermediate frequency or the radio frequency is down-converted to the baseband.

【0057】

(2) When shifting the frequency in the baseband FIG. 6 (a) shows an example of arranging the carrier frequency of the mobile reception symbol, and FIG. 6 (b) shows an example of arranging the carrier frequency of the fixed reception symbol (when m = 10 and n = 40). ..

【0058】

First, in the mobile reception symbol, when the number of carrier waves of the mobile reception symbol is m and the number of carrier waves of the fixed reception symbol is n, an inverse discrete Fourier transform of n points is used for both mobile and fixed. ..

【0059】

Here, the frequency slot numbers of the inverse discrete Fourier transform are set from 1 to n, the time series are set to 1, 2, 3, ..., and in the time series 1, the inverse discrete is every (m / n) from the slot number 1. Set the data in the Fourier transform. Next, in time series 2, data is set every (m / n) from slot number 2. Similarly, the data is set in the discrete Fourier transform while shifting the first slot number. As a result, as shown in FIG. 6A, it is possible to generate a signal whose frequency is shifted in time series.

【0060】

On the other hand, in the case of a fixed reception symbol, as shown in FIG. 6 (b), data may be set at all n points and an inverse discrete Fourier transform may be performed. Similarly, the demodulator side uses an n-point discrete Fourier transform. In this case, when demodulating the mobile reception symbol, information can be reliably extracted by selecting only the necessary slots of the signal whose frequency shifts in time series.

【0061】

Further, in the above embodiment, as shown in FIG. 7, a data transmission symbol for mobile reception having a relatively short effective symbol length and guard interval length is transmitted at a fixed time interval within one frame. In this case, it is possible to have the effect of time-axis interleaving on the fading that occurs during mobile reception. Therefore, errors that occur in bursts can be reduced, and the amount of memory required for interleaving can be reduced.

【0062】

Further, in the above embodiment, using a specific data transmission symbol, transmission parameters such as effective symbol length, guard interval length, number of carrier waves, and modulation method are changed for each OFDM transmission frame, and the amount of information to be transmitted is set in frame units. By changing with, it becomes possible to use it for ATM communication in which the amount of information to be transmitted fluctuates with time, and for an information source coding device using a variable length code. In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made.

【0063】

[Effect of the invention]

As described above, according to the present invention, it is possible to provide an OFDM transmission method capable of receiving well in any case regardless of the receiving form, and further to provide a transmitting device and a receiving device using the method.

[Simple explanation of drawings]

[Figure 1]

The block circuit diagram which shows the structure of one Embodiment of the transmission device using the OFDM transmission system of this invention.

[Figure 2]

The block circuit diagram which shows the structure of one Embodiment of the receiving apparatus using the OFDM transmission system of this invention.

[Fig. 3]

The figure which shows the structural example of the transmission frame of the OFDM transmission system of this invention.

[Fig. 4]

In order to explain another embodiment of this invention, the figure which shows the relationship between the effective symbol length in an OFDM transmission frame and the average transmission power.

[Fig. 5]

As another embodiment of the present invention, a configuration for changing the carrier frequency at predetermined frequency intervals at regular time intervals is shown, where (a) is on the transmitting device side and (b) is on the receiving device side. The block circuit diagram which shows the structure of.

[Fig. 6]

As another embodiment of the present invention, an example of arranging the carrier frequency in the case of shifting the frequency in the baseband in order to change the carrier frequency at predetermined frequency intervals at regular time intervals is shown. The figure which shows the arrangement example in the case of a) is a symbol for mobile reception, and (b) is a symbol for fixed reception.

[Fig. 7]

As another embodiment of the present invention, a diagram showing a state in which a data transmission symbol for mobile reception having a relatively short effective symbol length and guard interval length is transmitted at a fixed time interval within one frame.

[Fig. 8]

The figure which shows the transmission signal waveform and transmission symbol of an OFDM transmission system.

[Fig. 9]

The figure which shows the frequency spectrum of the OFDM transmission system.

[Fig. 10]

The figure which shows the structural example of the transmission frame of the OFDM transmission system.

[Fig. 11]

A block circuit diagram showing a conceptual configuration of a transmitter and a receiver using a conventional OFDM transmission method.

[Fig. 12]

The figure which shows the example of the frequency spectrum when the fixed reception frequency block and the mobile reception frequency block are provided in one broadcasting channel.

[Explanation of symbols]

111 ~ 11L ... Series / Parallel Converter 121 ~ 12L ... Inverse Discrete Fourier Transformer 131 ~ 13L ... Parallel / series converter 14 ... time sample sequence switch 15 ... Symbol for data transmission / Symbol switch for synchronization 16 ... Symbol waveform memory for synchronization 17 ... D / A converter 18 ... low pass filter 19 ... Frequency converter 20 ... frame pulse generator 21 ... Symbol pulse generator 22 ... Sampling clock generator 23 ... Local oscillator 24 ... Variable Frequency Local Oscillator 31 ... Bandpass filter 32 ... Frequency converter 33 ... Symbol waveform memory for synchronization 34 ... Symbol position detector for synchronization 35 ... Oscillation frequency control signal generator 36 ... Local oscillator 37 ... Sampling clock generator 38 ... Frame pulse generator 39 ... Symbol pulse generator 40 ... A / D converter 411 ~ 41L ... Series / Parallel Converter 421 ~ 42L ... Discrete Fourier Transformer 431 ~ 43L ... Demodulation / parallel / series converter 44 ... Variable Frequency Local Oscillator