JP4684308B2 - Demodulator - Google Patents

Description

The present invention, an orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing; abbreviation: OFDM) relates to the demodulation equipment scheme.

  As a means of estimating the transmission path condition of information by the broadcast in the reception of orthogonal frequency division multiplexing (hereinafter referred to as “OFDM”) type digital broadcast that uses a large number of carriers and transmits information in a distributed manner, Calculation of a delay profile representing the characteristics of the delay wave reception power amount is given. This delay profile can be used to know the current incoming path (transmission path) environment. For this reason, for example, a multipath environment in which delayed waves due to reflections from mountains, etc. are mixed, or a single frequency network (Single Frequency Network). In a multipath environment generated by abbreviation: SFN), the components of the delay path do not cause intersymbol interference, that is, all the path components fall within the range of the guard interval (Fast Fourier Transform; (Abbreviation: FFT) can be used as means for determining the start position of the window. Examples of conventional techniques related to the delay profile include the following.

  As an example of the prior art, this technology aims to obtain the propagation conditions of an information transmission path using existing radio waves without using special radio waves or receivers. Is subjected to FFT processing to be converted to a frequency axis signal, and a scattered pilot (SP) signal for amplitude / phase equalization is arranged on the frequency axis from the frequency axis signal output from the FFT calculator. (Hereinafter referred to as “pilot signal”) is extracted by a pilot signal extractor. Subsequently, the amplitude / phase frequency characteristic detector interpolates the pilot signal for amplitude / phase equalization to generate and output respective frequency characteristic signals related to the amplitude and phase. An inverse fast Fourier transform (abbreviation: IFFT) computing unit obtains a time axis signal of the output of the amplitude / phase frequency characteristic detector, and detects a delay wave reception power amount with respect to a delay time. The power amount detected in this way is displayed as a delay profile on a display device in a predetermined format, and if necessary, stored in a data storage device (see, for example, Patent Document 1).

Japanese Patent No. 3654646

  The conventional delay profile generation technique or delay profile utilization technique in the reception of OFDM digital broadcasting is configured as described above, and the propagation condition of the information transmission path can be obtained without using a special radio wave or receiver. However, since the pilot signal is inserted only every 12 subcarrier components, when only a known SP signal is used, the multipath detection range using the delay profile result is an observable time range. Is very short compared to the symbol length.

The present invention relates to a multi-path detection range is wide, and an object thereof is to provide a configurable demodulation equipment time window position for the Fourier transform to the optimum position.

The demodulator according to the present invention includes a Fourier transform unit that performs Fourier transform on the received OFDM signal and outputs a subcarrier component obtained as a result of the Fourier transform, and the subcarrier component output from the Fourier transform unit. A pilot signal extraction unit that extracts a pilot signal, a known signal generation unit that generates and outputs a known signal corresponding to the pilot signal, and the pilot signal extracted by the pilot signal extraction unit A first division unit that calculates a transmission line characteristic corresponding to the pilot signal by dividing by the known signal output from the first transmission part, the transmission line characteristic of the pilot signal calculated by the first division part, and the Fourier A delay profile based on a result obtained by performing an inverse Fourier transform on the subcarrier component output from the converter; Generate and output a signal corresponding to the maximum delay time that is the arrival time of the most delayed arrival wave in the delay profile and a signal corresponding to the minimum delay time that is the arrival time of the most preceding arrival wave in the delay profile The transmission path characteristics of the pilot signal calculated by the profile generator and the first division section are interpolated in the time direction and the frequency direction, and the transmission path characteristics corresponding to the subcarrier components are output. An interpolation filter unit, and a timing synchronization unit that outputs a timing signal for controlling the timing of performing the Fourier transform in the Fourier transform unit based on the signal corresponding to the minimum delay time output from the delay profile generation unit; The subcarrier component output from the Fourier transform unit is converted into the interpolation filter unit. And a second division unit that outputs a demodulated signal by dividing by a transmission path characteristic corresponding to the subcarrier component output from the subcarrier component, the Fourier transform unit performs the Fourier transform according to the timing signal, The interpolation filter unit sets a passband of a frequency interpolation filter used for interpolation in the frequency direction based on a signal corresponding to the maximum delay time, and uses the frequency interpolation filter to set the frequency There line interpolation in the direction, the delay profile generator, said transmission channel characteristic of said pilot signal calculated in said first division unit, among the subcarrier component output from the Fourier transform unit, A result obtained by performing an inverse Fourier transform on the subcarrier component included in a symbol different from the symbol including the pilot signal for which the transmission characteristic is calculated by the first division unit. The delay profile is generated based on the results .

  According to the demodulator of the present invention, the received OFDM signal is Fourier transformed by the Fourier transform unit, and the subcarrier component is output. The pilot signal included in the subcarrier component is extracted by the pilot signal extraction unit, and the extracted pilot signal is divided by the first division unit by the known signal output from the known signal generation unit and transmitted corresponding to the pilot signal. Road characteristics are calculated. A delay profile is generated by the delay profile generator based on the transmission path characteristics of the pilot signal and the result of the inverse Fourier transform of the subcarrier component output from the Fourier transformer, and corresponds to the maximum delay time in the delay profile. A signal corresponding to the signal and the minimum delay time is output.

  In this way, the delay profile generator generates a pilot signal included in a subcarrier component obtained by Fourier transform of the received OFDM signal, that is, a pilot signal after Fourier transform, and all of the subcarrier components, that is, after Fourier transform. Since the delay profile is generated using all the received signals, the multipath detection range can be expanded compared to the case where the delay profile is generated using only the pilot signal after the Fourier transform. As a result, the delay profile can be accurately generated over a wide range.

  Since the pass band of the frequency interpolation filter is set by the interpolation filter unit based on the signal corresponding to the maximum delay time in such a delay profile, the pass band of the frequency interpolation filter is prevented from becoming excessively wide. be able to. Also, based on the signal corresponding to the minimum delay time in the delay profile, the timing synchronization unit outputs a timing signal, and the Fourier transform is performed by the Fourier transform unit in accordance with this timing signal, so the Fourier transform unit performs the Fourier transform. The pass band of the frequency interpolation filter can be controlled while adjusting the synchronization timing. Accordingly, since the pass band of the frequency interpolation filter can be minimized, the time window position for Fourier transform can be set at an optimum position. That is, the synchronization timing can be optimally controlled.

  Using such a frequency interpolation filter, the pilot signal transmission path characteristics calculated by the first division unit are interpolated in the frequency direction by the interpolation filter unit. Can be prevented from passing through the frequency interpolation filter. In this way, the interpolation in the frequency direction and the interpolation in the time direction are performed, and the transmission path characteristic corresponding to the subcarrier component is output from the interpolation filter unit, and the transmission path for this subcarrier component By characteristics, the subcarrier component output from the Fourier transform unit is divided by the second division unit, and a demodulated signal is output. Therefore, it is possible to reduce the deterioration in reception performance due to unnecessary noise components passing through the frequency interpolation filter.

In addition, the delay profile generation unit includes the pilot signal whose transmission characteristic is calculated by the first division unit among the transmission path characteristic of the pilot signal calculated by the first division unit and the subcarrier component output from the Fourier transform unit. A delay profile is generated based on a result obtained by performing an inverse Fourier transform on a subcarrier component included in a symbol different from the included symbol. Thus, by performing the delay profile generation process in time series over two symbols, it is possible to downsize the delay profile generation unit and downsize the demodulation device.

  Hereinafter, an application example of the present invention will be described by way of an embodiment, but before that, an OFDM transmission system will be described.

  In the OFDM transmission method, transmission data is modulated and transmitted by a transmission device using a plurality of carriers whose frequencies are orthogonal to each other (hereinafter also referred to as “subcarrier components”), and the transmission data is received and demodulated by a reception device. Transmission method.

  In a system using the OFDM transmission method, transmission data is allocated to signal point arrangements according to the modulation method of each subcarrier component in a transmission device. Next, an inverse Fourier transform is performed on each subcarrier component, and a plurality of subcarrier components whose frequencies are orthogonal to each other are multiplexed to generate a signal. Thereafter, a part of the tail of the multiplexed signal (hereinafter referred to as “multiplexed signal”) is added to the head of the multiplexed signal as a guard interval. Then, the multiplexed signal to which the guard interval is added is frequency-converted into a predetermined frequency band and transmitted.

  On the other hand, a receiving apparatus in a system using the OFDM transmission scheme frequency-converts the received OFDM signal into a predetermined frequency band, specifies the position of the guard interval, and establishes synchronization. Next, after removing a signal corresponding to the guard interval length for each symbol in the OFDM signal, Fourier transform is performed on the symbol to calculate each subcarrier component, and each subcarrier component is demodulated to transmit transmission data. Reproduce.

  The demodulation of the subcarrier component is performed by calculating the amount of change in amplitude and phase in the subcarrier component and reproducing the signal point arrangement at the time of transmission based on the calculation result. In order to facilitate the calculation of the amount of change in amplitude and phase, a known method for transmitting a known signal, ie, a pilot signal, which is a reference for calculating the amount of change using a specific subcarrier component is widely used. For example, in the digital terrestrial television broadcasting system in Japan, pilot signals are periodically inserted every 12 subcarrier components in the frequency direction and every 4 symbols in the time direction. The receiving apparatus calculates amplitude and phase variations based on the pilot signal and demodulates the subcarrier component. In the terrestrial digital television broadcasting system in Japan, the pilot signal is referred to as a scattered pilot signal. Hereinafter, for convenience of explanation, a pilot signal inserted into an OFDM signal in a transmission apparatus is referred to as a “transmission pilot signal”, and a pilot signal in the OFDM signal received in a reception apparatus is also referred to as a “reception pilot signal”.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of a demodulating apparatus 100 according to the first embodiment of the present invention. The demodulating device 100 includes a receiving antenna 1, a tuner unit 2, an A / D (Analog / Digital) conversion unit 3, an orthogonal demodulation circuit unit 4, an FFT circuit unit 5, a timing synchronization circuit unit 6, a fixed phase rotation removal unit 7, a delay Adjustment circuit unit 8, pilot extraction circuit unit 9, first division circuit unit 10, known signal generation circuit unit 11, time interpolation filter unit 12, delay profile generation circuit unit 13, frequency interpolation filter unit 14, second division circuit Unit 15 and data reproduction unit 16. The demodulation method which is a reference form of the present invention is executed by the demodulation device 100.

  The tuner unit 2 selects a desired OFDM digital broadcast from the broadcast radio wave (RF signal) input from the receiving antenna 1 and converts it into an intermediate frequency (abbreviation: IF) signal of a predetermined frequency and a predetermined level. . The tuner unit 2 gives the IF signal to the A / D conversion unit 3. The A / D conversion unit 3 converts the IF signal given from the tuner unit 2 from an analog signal to a digital signal, and gives the digital signal to the quadrature demodulation circuit unit 4.

  The quadrature demodulation circuit unit 4 performs quadrature demodulation on the digital signal supplied from the A / D conversion unit 3 and outputs a quadrature demodulated signal divided into an I signal (in-phase component) and a Q signal (quadrature component). The quadrature demodulation circuit unit 4 gives an I signal and a Q signal, which are quadrature demodulation signals, to the FFT circuit unit 5 and the timing synchronization circuit unit 6.

  The FFT circuit unit 5 which is a Fourier transform unit performs a fast Fourier transform on the I signal and the Q signal given from the orthogonal demodulation circuit unit 4 from a time axis signal to a frequency axis signal. More specifically, the FFT circuit unit 5 performs fast Fourier transform on the quadrature demodulated signal supplied from the quadrature demodulator circuit unit 4 based on a timing signal input from the timing synchronization circuit unit 6 described later, and is included in the quadrature demodulated signal. The subcarrier component to be transmitted is given to the fixed phase rotation removing unit 7. The step of performing the fast Fourier transform by the FFT circuit unit 5 and outputting the subcarrier component corresponds to the Fourier transform step.

  The fixed phase rotation removal unit 7 removes, for each subcarrier component given from the FFT circuit unit 5, a fixed value phase rotation component proportional to the frequency of the subcarrier component. The fixed phase rotation removal unit 7 gives the subcarrier component from which the fixed value phase rotation component has been removed to the delay adjustment circuit unit 8, the pilot extraction circuit unit 9, and the delay profile generation circuit unit 13.

  The delay adjustment circuit unit 8 includes a subcarrier component given from the fixed phase rotation removal unit 7, a pilot extraction circuit unit 9, a first division circuit unit 10, a known signal generation circuit unit 11, a time interpolation filter unit 12, a delay profile. The signal corresponding to the subcarrier component processed in the generation circuit unit 13 and the frequency interpolation filter unit 14 is delayed by a predetermined time so as to be input to the second division circuit unit 15 at the same timing, and then fixed phase. The subcarrier component given from the rotation removing unit 7 is given to the second division circuit unit 15. A pilot extraction circuit unit 9, which is a pilot signal extraction unit, extracts a received pilot signal included in the subcarrier component given from the fixed phase rotation removal unit 7 and gives it to the first division circuit unit 10. The step of extracting the received pilot signal included in the subcarrier component by the pilot extraction circuit unit 9 corresponds to the pilot signal extraction step.

  In demodulator 100, the transmission pilot signal inserted in the OFDM signal in the transmitter is set in advance as a known signal. Therefore, demodulator 100 compares the transmitted pilot signal, which is a known signal, with the received pilot signal. Thus, the transmission path characteristic corresponding to the received pilot signal can be calculated.

  Specifically, in the known signal generation circuit unit 11 that is a known signal generation unit, a transmission pilot signal that is a known signal is generated and output at a timing synchronized with the output of the reception pilot signal in the pilot extraction circuit unit 9, The first division circuit unit 10 is given. The step of generating and outputting a transmission pilot signal, which is a known signal, by the known signal generation circuit unit 11 corresponds to a known signal generation step. The first division circuit unit 10, which is the first division unit, divides the reception pilot signal given from the pilot extraction circuit unit 9 by the transmission pilot signal given from the known signal generation circuit unit 11, thereby obtaining each reception pilot signal. The transmission path characteristic corresponding to the signal is calculated, and the transmission path characteristic is given to the time interpolation filter unit 12 and the delay profile generation circuit unit 13. The step of dividing the reception pilot signal by the transmission pilot signal by the first division circuit unit 10 to calculate the transmission line characteristic corresponding to each reception pilot signal corresponds to the first division step.

  Since the channel characteristics calculated by the first divider circuit unit 10 are obtained only for the received pilot signal, interpolation processing by filtering is required to obtain channel characteristics for all subcarrier components. Become. Below, the necessity of the interpolation process by filtering is demonstrated concretely.

  FIG. 2 is a diagram showing an arrangement of pilot signals. FIG. 2 shows the arrangement of pilot signals in the OFDM signal used in the Japanese terrestrial digital television broadcasting system. In FIG. 2, the left-right direction toward the paper surface represents the frequency direction, and the up-down direction represents the time direction. Also, the black circles in FIG. 2 represent pilot signals, and the white circles represent subcarrier components other than pilot signals. 2 represents the k (k is a natural number) subcarrier, the part surrounded by a broken line represents the i (i is a natural number) symbol, and the part surrounded by the solid line And the portion surrounded by the broken line represent the k-th subcarrier component in the i-th symbol.

  As shown in FIG. 2, the pilot signal is inserted every 12 subcarrier components in the frequency direction and every 4 symbols in the time direction. Therefore, in order to calculate the transmission path characteristics for all subcarrier components from the transmission path characteristics calculated based on this pilot signal, interpolation processing in the time direction and the frequency direction is generally required.

  The time interpolation filter unit 12 which is an interpolation filter unit is configured to interpolate in the time direction in the interpolation process with respect to the transmission path characteristic corresponding to the received pilot signal given from the first division circuit unit 10. Process. The time interpolation filter unit 12 interpolates the transmission path characteristics corresponding to the received pilot signal in the time direction, thereby obtaining transmission path characteristics corresponding to each of the subcarrier frequency components including the pilot signal. The time interpolation filter unit 12 gives the frequency interpolation filter unit 14 the result of performing the interpolation process in the time direction.

  Among the interpolation processes, the frequency-direction interpolation process is performed in the frequency interpolation filter unit 14. Here, as a filter characteristic of the frequency interpolation filter unit 14, it is sufficient if there is a pass band through which an incoming wave component passes. When the pass band is unnecessarily wide, unnecessary noise components also pass through the filter. As a result, the demodulation performance deteriorates. In order to prevent such degradation of the demodulation performance, it is necessary to minimize the passband of the interpolation filter in the frequency direction. For this purpose, optimization of the timing (hereinafter referred to as “synchronization timing”) for performing fast Fourier transform in the FFT circuit unit 5 and optimization of the pass band of the frequency interpolation filter used for interpolation in the frequency direction are performed. It is effective to do this together.

  The optimization of the synchronization timing can be performed based on the symbol position of the incoming wave that has arrived the earliest for the receiving apparatus and the time difference between the symbol position of the incoming wave that has arrived the latest and the synchronization timing. Optimization of the pass band of the frequency interpolation filter can be performed based on the synchronization timing and the delay time of the arrival wave having the largest time difference from the synchronization timing. Therefore, a signal necessary for the optimization is generated by the delay profile generation circuit unit 13. Note that the amplitude and phase of each subcarrier component output from the FFT circuit unit 5 depend not only on multipath in the transmission path, phase noise and residual frequency error in the receiving apparatus, but also on the timing at which the fast Fourier transform is performed. Hereinafter, the synchronization timing and the delay time that are the basis of the signal generated in the delay profile generation circuit unit 13 will be described.

  FIG. 3 is a diagram for explaining the synchronization timing and delay time in the demodulator 100. In the following description, for ease of understanding, two different arrival waves, i.e., the arrival time to the receiving device, i.e., the time until the signal transmitted from the transmitting device arrives at the receiving device and is received, i.e., Assume that a first incoming wave and a second incoming wave are received. The first and second incoming waves are each composed of a guard interval and an i-th symbol. In the receiving apparatus, since a signal obtained by adding each incoming wave becomes a received wave, fast Fourier transform is performed at a timing such that interference between adjacent symbols (hereinafter also referred to as “inter-symbol interference”) does not occur. There is a need to do. First, the timing for performing the Fourier transform, that is, the setting of the synchronization timing will be described with reference to FIG.

  FIG. 3A is a diagram schematically showing first and second incoming waves and received waves received at different arrival times. FIG. 3A shows a received wave as a signal obtained by adding the first incoming wave and the second incoming wave. The front and rear shaded portions are portions where intersymbol interference occurs. For this reason, the data sections for performing the fast Fourier transform that does not interfere with adjacent symbols are, for example, the first data section, the second data section, and the third data section as shown in FIG. Each section length of the first to third data sections is a symbol length before adding the guard section, and the start point of the section is determined by the synchronization timing.

  For example, in the case of the first data period, the boundary at which no inter-symbol interference occurs between the (i−1) -th symbol and the i-th symbol in the received wave is set as the synchronization timing. In the case of the third data section, the last timing of the guard section in the first incoming wave is set as the synchronization timing. The tail end of the third data section is located at a boundary where no intersymbol interference occurs between the i + 1-th symbol and the i-th symbol in the received wave. The synchronization timing corresponding to the second data interval is provided between the synchronization timing corresponding to the first data interval and the synchronization timing corresponding to the third data interval. In this way, the synchronization timing is not uniquely determined, and may be within a time range depending on the arrival time difference of the incoming waves under the condition that no intersymbol interference occurs. Therefore, for example, in FIG. 3A, the synchronization timing of the second data interval may be provided anywhere between the synchronization timing of the first data interval and the synchronization timing of the third data interval.

  Next, a delay profile corresponding to a signal obtained by performing fast Fourier transform on data included in the first to third data sections in FIG. FIG. 3B is a diagram schematically showing a delay profile corresponding to a signal obtained by fast Fourier transforming data included in the first data section. FIG. 3C is a diagram schematically showing a delay profile corresponding to a signal obtained by fast Fourier transforming data included in the second data section. FIG. 3D is a diagram schematically showing a delay profile corresponding to a signal obtained by fast Fourier transforming data included in the third data section. 3 (b), 3 (c), and 3 (d), the horizontal axis indicates the tail end of the guard interval of each incoming wave with respect to the start point of the data interval for performing fast Fourier transform, that is, the start position of the i-th symbol. The corresponding delay time is represented, and the vertical axis represents the power corresponding to each incoming wave.

  The delay profile refers to information corresponding to a delayed wave in a multipath environment, for example, a delay time, a power value, etc. In this embodiment, a transmission path from the transmission device to the output of the FFT circuit unit 5 The delay time and received power corresponding to the received signal that has passed through are handled as the delay profile.

  In FIG. 3B, the difference a between the synchronization timing corresponding to the first data interval and the last guard interval in the first incoming wave is the delay time with respect to the synchronization timing of the first incoming wave, and the spectrum of the first incoming wave Appears at the position of the delay time a. Similarly, in FIG. 3C, the difference b between the synchronization timing corresponding to the second data interval and the last guard interval in the first arrival wave is the delay time of the first arrival wave with respect to the synchronization timing, and the first arrival time is reached. The wave spectrum appears at the position of the delay time b. In FIG. 3 (d), since the synchronization timing corresponding to the third data interval coincides with the end of the guard interval in the first incoming wave, the spectrum of the first incoming wave appears at the position of the delay time 0, The spectrum of the second incoming wave appears at a position separated by an amount t corresponding to the arrival time difference of each incoming wave. Note that, also in the first data section and the second data section, the spectrum of the second incoming wave appears at a position away from the spectrum of the first incoming wave by t.

  The delay profile generation circuit unit 13 serving as a delay profile generation unit generates a signal corresponding to the data transmitted from the transmission device based on the transmission path characteristics of the pilot signal supplied from the first division circuit unit 10. The delay time vs. received power corresponding to the transmission path up to the output is calculated, and the delay time vs. received power is calculated based on the subcarrier component given from the fixed phase rotation removing unit 7. A signal necessary for the optimization is output based on the received power.

  FIG. 4 is a block diagram showing a configuration of the delay profile generation circuit unit 13 according to the first embodiment of the present invention. The delay profile generation circuit unit 13 includes a signal sorting unit 21, a first inverse Fourier transform unit 22a, a second inverse Fourier transform unit 22b, a first relative level calculation unit 23a, a second relative level calculation unit 23b, and an incoming wave determination unit 24. The maximum delay wave determination unit 25, the maximum delay time calculation unit 26, and the synchronization timing offset calculation unit 27 are configured.

  The signal sorting unit 21 arranges the transmission path characteristics of the pilot signals given from the first division circuit unit 10 in order from the highest frequency to the lowest frequency. However, when the pilot signal arrangement is offset for each symbol as shown in FIG. 2, the frequency of the received pilot signal changes depending on the received symbol. Therefore, in such a case, the pilot signal of the symbol received before the current received symbol is also used so that the frequency of the received pilot signal does not change at the output of the signal sorting unit 21. For example, when pilot signals are arranged every four symbols in the time direction as shown in FIG. 2, the pilot signals for the past four symbols including the current received symbol are sorted.

  The first inverse Fourier transform unit 22a performs inverse Fourier transform on the transmission line characteristics corresponding to the pilot signals arranged in the order of high frequency or low frequency by the signal sorting unit 21, and corresponds to the result of the inverse Fourier transform. The signal is given to the first relative level calculator 23a.

  The first relative level calculation unit 23a calculates the amplitude of the signal given from the first inverse Fourier transform unit 22a, that is, the signal corresponding to the transmission path characteristic of the pilot signal, or the square value of the amplitude, and calculates the result of the calculation. This is given to the arrival wave determination unit 24. Here, the output of the first relative level calculator 23a, that is, the amplitude or the square value of the amplitude corresponds to delay time versus received power in the delay profile.

  The incoming wave determination unit 24 calculates a component larger than a predetermined threshold among the calculation results given from the first relative level calculation unit 23a, that is, the amplitude or the square value of the amplitude, as a component corresponding to the incoming wave. (Hereinafter also referred to as “arrival wave component”), and the relative time difference between the position on the time axis where the incoming wave component exists and the synchronization timing is provided as a delay time to the maximum delay wave determination unit 25. However, in the present embodiment, when the Fourier transform is performed with the earliest arrival wave as the synchronization timing in FIG. 3A, the last wave of the guard interval in the first arrival wave in FIG. 3A, the earliest arrival wave has the most delay time. It is detected as a small incoming wave. In the present embodiment, if there is an incoming wave obtained with a negative delay time value, it means that intersymbol interference with the (i + 1) th symbol has occurred.

  The second inverse Fourier transform unit 22 b performs inverse Fourier transform on all the subcarrier components output from the fixed phase rotation removal unit 7. More specifically, the second inverse Fourier transform unit 22b cancels the phase rotation component that differs for each subcarrier, and the square value of the I signal (in-phase component) of the subcarrier component and 2 of the Q signal (quadrature component). Inverse Fourier transform is performed using a value obtained by adding the multiplier value. The fixed phase rotation removal unit 7 removes the fixed phase rotation component of the subcarrier component. The second inverse Fourier transform unit 22b gives a signal corresponding to the result of the inverse Fourier transform to the second relative level calculation unit 23b.

  The second relative level calculation unit 23b calculates the amplitude of the signal corresponding to the result of the inverse Fourier transform for all the subcarrier components given from the second inverse Fourier transform unit 22b or the square value of the amplitude, and performs the calculation. Is given to the maximum delay wave determination unit 25. Here, the output of the second relative level calculator 23b, that is, the amplitude or the square value of the amplitude corresponds to delay time versus received power in the delay profile.

  Since the original signal of the inverse Fourier transform in the second inverse Fourier transform unit 22b, that is, the subcarrier component output from the fixed phase rotation removal unit 7, is not a known signal, the square value of the I signal (in-phase component) and Q It is difficult to specify a clear multipath position from the result of the inverse Fourier transform performed using the square value of the signal (orthogonal component). However, since the frequency of the signal subjected to the inverse Fourier transform is higher in the second Fourier transform unit 22b than in the case of performing the inverse Fourier transform using only the pilot signal as in the first inverse Fourier transform unit 22a, the pilot signal It is possible to obtain information about a wider frequency band than in the case of performing inverse Fourier transform using only. For example, when the transmission path characteristics of the pilot signals for the past four symbols sorted by the signal sorting unit 21 are given to the first inverse Fourier transform unit 22a, the pilot signal is periodic every 12 subcarrier components in the frequency direction. Therefore, from the result of the inverse Fourier transform in the second inverse Fourier transform unit 22b, it is possible to obtain information about the frequency band three times that in the case of performing the inverse Fourier transform using only the pilot signal. is there. Therefore, since the multipath detection range can be expanded, the FFT time window position can be set at an optimum position.

  In the first inverse Fourier transform unit 22a, there is a possibility that the aliasing component of the multipath signal detected from the result of the inverse Fourier transform performed using the pilot signal is observed from the characteristics of the digital signal.

  Therefore, the maximum delay wave determination unit 25 obtains the arrival wave component having the longest delay time based on the delay time given from the arrival wave determination unit 24, and at the position of the delay time corresponding to the aliasing component of the arrival wave component, It is determined whether or not there is a component that seems to be a peak based on the delay time versus received power given from the second relative level calculator 23b. When it is determined that a component that seems to be a peak exists at a position corresponding to the aliasing component of the arrival wave component, the maximum delay wave determination unit 25 receives the arrival wave having the delay time next to the arrival wave component having the longest delay time. A component is obtained and, as described above, it is determined whether or not a component that seems to be a peak exists at the position of the delay time corresponding to the folded component. This determination is continued until it is determined that a component that seems to be a peak does not exist at a position corresponding to the aliasing component of the incoming wave component.

  If the maximum delay wave determination unit 25 determines that there is no peak component at a position corresponding to the aliasing component of the arrival wave component, the maximum delay wave determination unit 25 determines that the arrival wave component is the maximum delay wave component, and sets the determination result to the maximum The delay time calculation unit 26 and the synchronization timing offset calculation unit 27 are given. The maximum delay wave determination unit 25 supplies the delay time given from the arrival wave determination unit 24 to the maximum delay time calculation unit 26 and the synchronization timing offset calculation unit 27 as they are.

  Based on the determination result given from the maximum delay wave determination unit 25, the maximum delay time calculation unit 26 has the longest delay time among the delay times given from the arrival wave determination unit 24 via the maximum delay wave determination unit 25. A signal corresponding to the delay time of the large maximum delay wave component (hereinafter also referred to as “filter band control signal”) is applied to the frequency interpolation filter unit 14.

  The synchronization timing offset calculation unit 27 determines the minimum delay wave component that has the shortest delay time based on the delay time given from the arrival wave determination unit 24 via the maximum delay wave determination unit 25, and A signal corresponding to the delay time of the minimum delay wave component (hereinafter also referred to as “timing offset adjustment signal”) is applied to the timing synchronization circuit unit 6. Note that the relationship between the delay time and the magnitude of the filter band control signal, such as power value, current value, and voltage value, or the delay time and the magnitude of the timing offset adjustment signal, such as power value, current value and The relationship with the voltage value or the like can be set to be a proportional relationship, for example.

  In this way, the delay profile generation circuit unit 13 generates a delay profile based on the transmission path characteristics of the pilot signal and the result obtained by performing inverse Fourier transform on the subcarrier component, and corresponds to the maximum delay time. And a step of outputting a signal corresponding to the minimum delay time corresponds to a delay profile generation step.

  The frequency interpolation filter unit 14, which is an interpolation filter unit, was interpolated in the time direction in the time interpolation filter unit 12 based on the filter band control signal given from the maximum delay time calculation unit 26. For the transmission line characteristics corresponding to each subcarrier component of the same frequency, an interpolation filter having the narrowest passband among the filters necessary and sufficient for the incoming wave corresponding to the maximum delay time to pass is used. select. Then, interpolation processing in the frequency direction is performed based on the selected interpolation filter. The steps of performing the time direction interpolation process and the frequency direction interpolation process on the transmission line characteristics corresponding to the received pilot signal by the time interpolation filter unit 12 and the frequency interpolation filter unit 14 are the interpolation process. It corresponds to.

  Through the interpolation processing in the time interpolation filter unit 12 and the frequency interpolation filter unit 14 described above, transmission path characteristics for all subcarrier components can be obtained. Note that the above-described frequency interpolation filter unit 14 can be configured by, for example, a low-pass filter that passes through a low band.

  The timing synchronization circuit unit 6, which is a timing synchronization unit, is information corresponding to the timing at which Fourier transform is performed according to the orthogonal demodulated signal given from the orthogonal demodulation circuit unit 4 and the timing offset adjustment signal given from the synchronization timing offset calculation unit 27. And a signal corresponding to the information is given to the FFT circuit unit 5 as a timing signal. The step of generating information corresponding to the timing at which Fourier transform is performed by the timing synchronization circuit unit 6 and outputting a signal corresponding to the information as a timing signal corresponds to a timing synchronization step.

  The second division circuit unit 15, which is the second division unit, divides each subcarrier component delayed by the delay adjustment circuit unit 8 by a transmission path characteristic corresponding to the subcarrier component output from the frequency interpolation filter unit 14. Then, each subcarrier component is demodulated. The second division circuit unit 15 divides each subcarrier component delayed by the delay adjustment circuit unit 8 by a transmission path characteristic corresponding to the subcarrier component output from the frequency interpolation filter unit 14 to obtain a demodulated signal. The output process corresponds to the second division process. The data reproduction unit 16 reproduces the transmission data from the signal point arrangement of the subcarrier component demodulated by the second division circuit unit 15 and outputs the transmission data as reproduction data.

  As described above, according to the present embodiment, the delay profile generation circuit unit 13 performs the pilot signal included in the subcarrier component obtained by Fourier transform of the received OFDM signal by the FFT circuit unit 5, that is, after the Fourier transform. Since the delay profile is generated using the pilot signal and all of the subcarrier components obtained by the Fourier transform in the FFT circuit unit 5, that is, all the received signals after the Fourier transform, only the pilot signal after the Fourier transform is generated. The multipath detection range can be expanded as compared with the case where a delay profile is generated by using. As a result, the delay profile can be accurately generated over a wide range.

  Since the pass band of the frequency interpolation filter is set by the frequency interpolation filter unit 14 based on the signal corresponding to the maximum delay time in such a delay profile, the pass band of the frequency interpolation filter becomes excessively wide. Can be prevented. Further, based on the signal corresponding to the minimum delay time in the delay profile, the timing synchronization circuit unit 6 outputs a timing signal, and the FTT circuit unit 5 performs Fourier transform in accordance with this timing signal. The pass band of the frequency interpolation filter can be controlled while adjusting the synchronization timing for performing the Fourier transform. Accordingly, since the pass band of the frequency interpolation filter can be minimized, the time window position for Fourier transform can be set at an optimum position.

  Using such a frequency interpolation filter, the frequency interpolation filter unit 14 performs interpolation in the frequency direction on the transmission path characteristics of the pilot signal calculated by the first division circuit unit 10. It is possible to suppress unnecessary noise components from passing through the frequency interpolation filter. In this manner, the frequency interpolation filter unit 14 performs interpolation in the frequency direction, and the time interpolation filter unit 12 performs interpolation in the time direction, so that the transmission path characteristic corresponding to the subcarrier component is obtained. Is output. The subcarrier component output from the FFT circuit unit 5 is divided by the second divider circuit unit 15 by the transmission path characteristic for the subcarrier component, and a demodulated signal is output. Therefore, it is possible to reduce the deterioration in reception performance due to unnecessary noise components passing through the frequency interpolation filter.

<Second Embodiment>
FIG. 5 is a block diagram showing a configuration of the delay profile generation circuit unit 13A in the second embodiment of the present invention. Since the configuration of the delay profile generation circuit unit 13A of the present embodiment is similar to the configuration of the delay profile generation circuit unit 13 of the first embodiment described above, only the different parts will be described and the corresponding parts will be described. Are denoted by the same reference numerals and redundant description is omitted.

  In the first embodiment described above, the pilot signal processing and the processing using all subcarriers in the delay profile generation by the delay profile generation circuit unit 13 are performed on the same symbol, but the transmission path distortion fluctuations Is not steep, it is not necessary to perform the pilot signal processing and the processing using all subcarriers in the delay profile generation for the same symbol. Therefore, in the present embodiment, delay profile generation processing using a pilot signal and delay profile generation processing using all received subcarrier components are performed using different symbols. Specifically, the delay profile generation circuit unit 13A in the present embodiment includes the transmission path characteristics of the pilot signal calculated by the first division circuit unit 10 and the subcarrier components output from the FFT circuit unit 5. A delay profile is generated based on a result obtained by performing inverse Fourier transform on a subcarrier component included in a symbol different from the symbol including the pilot signal whose transmission characteristic is calculated by the first divider circuit unit 10.

  The delay profile generation circuit unit 13A includes a signal sorting unit 21, an inverse Fourier transform unit 22, a relative level calculation unit 23, an incoming wave determination unit 24, a maximum delay wave determination unit 25, a maximum delay time calculation unit 26, and a synchronization timing offset calculation unit. 27 and an input signal changeover switch section 28.

  The input signal changeover switch unit 28 includes two input terminals, that is, first and second input terminals 28a and 28b and one output terminal 28c. The pilot signal output from the signal sorting unit 21 is input to the first input terminal 28a, and each subcarrier component output from the fixed phase rotation removing unit 7 is input to the second input terminal 28b. The input signal changeover switch unit 28 is connected to the first input terminal 28a and the output terminal 28c in accordance with a switching signal given from the maximum delay wave determination unit 25A described later, and the second input terminal 28b and the output terminal. 28c is switched to the state where it is connected.

  In a state where the first input terminal 28a and the output terminal 28c are connected, a pilot signal from the signal sorting unit 21 is given to the inverse Fourier transform unit 22, and the second input terminal 28b and the output terminal 28c are connected. Then, each subcarrier component from the fixed phase rotation removing unit 7 is given to the inverse Fourier transform unit 22.

  When the pilot signal from the signal sorting unit 21 is given to the inverse Fourier transform unit 22, the inverse Fourier transform unit 22 and the relative level calculation unit 23 are the first in the delay profile generation circuit unit 13 of the first embodiment described above. The same processing as that of the 1 inverse Fourier transform unit 22a and the first relative level calculation unit 23a is performed. As a result, the calculation result of the amplitude of the signal corresponding to the transmission path characteristic of the pilot signal or the square value of the amplitude, that is, the delay time versus received power in the delay profile is given to the arrival wave determination unit 24.

  The incoming wave determination unit 24 performs the same processing as in the first embodiment, and uses the relative time difference between the position on the time axis where the incoming wave component exists and the synchronization timing as the delay time, This is given to the determination unit 25A. When the relative time difference is given as a delay time from the incoming wave judgment unit 24, the maximum delay wave judgment unit 25A gives the input signal changeover switch unit 28 a switching signal for switching the connection state in the input signal changeover switch unit 28. In the input signal changeover switch unit 28, the state is switched from the state in which the first input terminal 28a and the output terminal 28c are connected to the state in which the second input terminal 28b and the output terminal 28c are connected in accordance with the switching signal. .

  Further, when each subcarrier component from the fixed phase rotation removal unit 7 is given to the inverse Fourier transform unit 22, the inverse Fourier transform unit 22 and the relative level calculation unit 23 generate the delay profile of the first embodiment described above. The same processing as the second inverse Fourier transform unit 22b and the second relative level calculation unit 23b in the circuit unit 13 is performed. Thereby, the calculation result of the amplitude of the signal corresponding to the result of the inverse Fourier transform for all the subcarrier components or the square value of the amplitude, that is, the delay time versus the received power in the delay profile is given to the maximum delay wave determination unit 25A. .

  Based on the delay time given from the incoming wave judgment unit 24 and the delay time versus the received power given from the relative level calculation unit 23, the maximum delay wave determination unit 25A, that is, the arrival wave component having the longest delay time, that is, the maximum delay wave And the determination result is given to the maximum delay time calculator 26 and the synchronization timing offset calculator 27. When the relative time difference is given as the delay time from the incoming wave judgment unit 24, the maximum delay wave judgment unit 25A gives the input signal changeover switch unit 28 a switching signal for switching the connection state in the input signal changeover switch unit 28. . In the input signal changeover switch unit 28, the state is switched from the state in which the second input terminal 28b and the output terminal 28c are connected to the state in which the first input terminal 28a and the output terminal 28c are connected in response to the switching signal. .

  As described above, according to the demodulating device of the present embodiment, the delay profile generation circuit unit 13A includes the transmission path characteristics of the pilot signal calculated by the first division circuit unit 10 and the sub-channels output from the FFT circuit unit 5. Based on a result obtained by performing inverse Fourier transform on a subcarrier component included in a symbol different from the symbol including the pilot signal whose transmission characteristic is calculated by the first divider circuit unit 10 among the carrier components, a delay profile is obtained. Is generated. That is, in the present embodiment, the delay profile generation process using the pilot signal and the delay profile generation process using all the received subcarrier components are performed on different symbols.

  Thus, by performing the delay profile generation process in time series over two symbols, the delay profile generation circuit unit 13A can be downsized, and the demodulator can be downsized. For example, as in the present embodiment, one inverse Fourier transform unit 22 and one relative level calculation unit 23 can be provided, and a signal input by the input signal changeover switch unit 28 can be switched. Compared to the delay profile generation circuit unit 13 in the embodiment, the number of inverse Fourier transform units 22 and relative level calculation units 23 can be reduced to 1/2 (1/2), and the circuit scale can be reduced to half. 1 (1/2). Since the delay profile generation circuit unit 13A can be miniaturized as described above, the demodulator can be miniaturized.

It is a block diagram which shows the structure of the demodulation apparatus 100 in the 1st Embodiment of this invention. It is a figure which shows arrangement | positioning of a pilot signal. 4 is a diagram for explaining synchronization timing and delay time in a demodulator 100. FIG. It is a block diagram which shows the structure of the delay profile generation circuit part 13 in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the delay profile production | generation circuit part 13A in the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Reception antenna, 2 Tuner part, 3 A / D conversion part, 4 Orthogonal demodulation circuit part, 5 FFT circuit part, 6 Timing synchronous circuit part, 7 Fixed phase rotation removal part, 8 Delay adjustment circuit part, 9 Pilot extraction circuit part 10 first division circuit unit, 11 known signal generation circuit unit, 12 time interpolation filter unit, 13, 13A delay profile generation circuit unit, 14 frequency interpolation filter unit, 15 second division circuit unit, 16 data reproduction unit, 21 signal sorting unit, 22 inverse Fourier transform unit, 22a first inverse Fourier transform unit, 22b second inverse Fourier transform unit, 23 relative level computation unit, 23a first relative level computation unit, 23b second relative level computation unit, 24 Arrival wave determination unit, 25, 25A Maximum delay wave determination unit, 26 Maximum delay time calculation unit, 27 Synchronization timing offset calculation unit, 28 Signal changeover switch unit, 100 demodulation device.

Claims (1)

A Fourier transform unit that performs a Fourier transform on the received OFDM signal and outputs a subcarrier component obtained as a result of the Fourier transform;
A pilot signal extraction unit that extracts a pilot signal included in the subcarrier component output from the Fourier transform unit;
A known signal generator for generating and outputting a known signal corresponding to the pilot signal;
A first divider that divides the pilot signal extracted by the pilot signal extractor by the known signal output from the known signal generator to calculate a transmission line characteristic corresponding to the pilot signal;
Generating a delay profile based on the transmission path characteristics of the pilot signal calculated by the first division unit and a result obtained by performing an inverse Fourier transform on the subcarrier component output from the Fourier transform unit; A delay profile generation unit that outputs a signal corresponding to the maximum delay time that is the arrival time of the most delayed arrival wave in the delay profile and a signal corresponding to the minimum delay time that is the arrival time of the most preceding arrival wave in the delay profile When,
An interpolation filter unit that performs interpolation in the time direction and the frequency direction on the transmission channel characteristics of the pilot signal calculated by the first division unit, and outputs a transmission channel characteristic corresponding to the subcarrier component; ,
A timing synchronization unit that outputs a timing signal for controlling the timing of performing the Fourier transform in the Fourier transform unit based on the signal corresponding to the minimum delay time output from the delay profile generation unit;
A second divider that divides the subcarrier component output from the Fourier transform unit by a transmission path characteristic corresponding to the subcarrier component output from the interpolation filter unit and outputs a demodulated signal;
The Fourier transform unit performs the Fourier transform according to the timing signal,
The interpolation filter unit sets a pass band of a frequency interpolation filter used for interpolation in the frequency direction based on a signal corresponding to the maximum delay time, and uses the frequency interpolation filter, There line interpolation in the frequency direction,
The delay profile generation unit includes the transmission characteristic of the pilot signal calculated by the first division unit and the transmission characteristic of the subcarrier component output from the Fourier transform unit by the first division unit. A demodulating apparatus that generates the delay profile based on a result obtained by performing inverse Fourier transform on the subcarrier component included in a symbol different from the symbol including the pilot signal calculated .

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