Transmitter, receiver, transmission method, reception method, control circuit, and program storage medium

Abstract

A transmitter (1) has a frequency repetition modulation unit (18) that generates a signal in which an information symbol at which a signal in time domain becomes non-zero and a null symbol at which a signal in time domain becomes zero appear periodically, by generating a transmission spectrum in which: the spectrum of a modulated signal is continuously arranged on the frequency axis; the same transmission symbol is arranged at a predetermined subcarrier interval with respect to the spectrum of the modulated signal; and the spectrum on the high band side of the center frequency is equal to the spectrum on the low band side of the center frequency.

Description

Transmitter, receiver, transmitting method, receiving method, control circuit, and program storage medium

[0001] The present disclosure relates to a transmitter, a receiver, a transmitting method, a receiving method, a control circuit, and a program storage medium.

[0002] Unlicensed bands, such as the ISM (Industry-Science-Medical) band used in wireless standards such as wireless LAN (Local Area Network) and Bluetooth (registered trademark), are widely used in various systems because they do not require a license for wireless communication. Communication devices using unlicensed bands are installed in various indoor and outdoor locations, including offices and train stations. Therefore, if the communication devices use the same frequency band as another communication device, signals from other systems, including the other communication devices, can cause significant interference with the system including the communication device. Therefore, interference resistance is an important technology for stable communication using unlicensed bands.

[0003] One technique for improving interference resistance is interference avoidance technology. Interference avoidance technology is a technique for improving interference resistance by using a channel that is less affected by interference, and is a technique for switching the frequency channel used by a wireless system to a channel that is less affected by interference by measuring the degree of the impact of interference in advance or detecting an interference collision. Patent Document 1 discloses a method for measuring and evaluating the interference status of each channel that a wireless system can use, and determining a channel that is less affected by interference as a channel that the system will use preferentially.

[0004] Patent document 2 discloses a method in which a processing circuit for measuring interference conditions of channels that can be used by a wireless system in the 5 GHz band is provided separately from the processing circuit for communication, so that when a signal from another system is detected on a channel currently being used for communication, the channel to be used for communication is switched to a channel that has been previously evaluated by the processing circuit for measuring interference conditions as having less interference.

[0005] Patent No. 5895194 Patent No. 4886814

[0006] Applying the above-described interference avoidance techniques can reduce the probability of interference collisions, thereby improving the interference resistance of wireless systems. However, in environments where interference is numerous, such as the ISM band, it is not uncommon for interference from other systems to occur on all channels used by a wireless system. In other words, in environments where interference is numerous, interference collisions can occur even when interference avoidance techniques are applied, and when an interference collision occurs, the received packets that have been affected by the interference cannot be demodulated due to the effects of the interference.

[0007] The present disclosure has been made in view of the above, and aims to provide a transmitter that can transmit a signal that can be demodulated even in the event of interference collision.

[0008] In order to solve the above-mentioned problems and achieve the objectives, the transmitter according to the present disclosure has a frequency repetition modulation unit that generates a transmission spectrum in which the spectrum of the modulated signal is arranged continuously on the frequency axis, the same transmission symbol is arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side are equal to the center frequency, thereby generating a signal in which information symbols whose time-domain signal is non-zero and null symbols whose time-domain signal is zero appear periodically.

[0009] The transmitter according to the present disclosure has the advantage of being able to transmit a signal that can be demodulated even in the event of interference collision.

[0010] 7 is a diagram showing the configuration of a wireless system according to an embodiment; FIG. 8 is a diagram showing the configuration of a transmitter according to an embodiment; FIG. 9 is a diagram showing an example of a time waveform of a transmission signal when sampled every symbol time; FIG. 10 is a diagram showing the configuration of a receiver according to an embodiment; FIG. 11 is a diagram showing the configuration of a reception quality measurement unit of a receiver according to an embodiment; FIG. 12 is a diagram showing an image of the processing of a signal separation unit of a reception quality measurement unit of a receiver according to an embodiment; FIG. 13 is a diagram for explaining the operation of an interference information estimation unit of a reception quality measurement unit of a receiver according to an embodiment; FIG. 14 is a diagram showing the frequency spectrum characteristics in the interference arrival pattern of FIG. 7;

[0011] Hereinafter, a transmitter, a receiver, a transmitting method, a receiving method, a control circuit, and a program storage medium according to embodiments will be described in detail with reference to the drawings. In the following description, bold characters in mathematical expressions indicate vectors or matrices.

[0012] 1 is a diagram showing the configuration of a wireless system according to an embodiment of the present invention. The wireless system according to the embodiment of the present invention includes a transmitter 1 and a receiver 2.

[0013] 2 is a diagram showing the configuration of a transmitter 1 according to an embodiment. The transmitter 1 includes a modulation unit 11, a frequency repetition modulation unit 18 including a frequency repetition unit 12 and an IFFT (Inverse Fast Fourier Transform) unit 13, a CP (Cyclic Prefix) adding unit 14, a transmission filter unit 15, a transmission RF (Radio Frequency) unit 16, and a transmission antenna 17.

[0014] The modulation unit 11 performs an Orthogonal Frequency Division Multiplexing (OFDM) modulation process on the data sequence to be transmitted. Here, the number of subcarriers in the OFDM signal is N. In this case, the modulated symbol of the k-th subcarrier index is denoted by s ｋ Then, the OFDM modulated signal spectrum s is expressed by the following equation (1): In the following description, the output of the modulator 11 expressed by equation (1), i.e., the OFDM modulated signal spectrum, will be referred to as the reference spectrum.

[0015]

[0016] The frequency repetition unit 12 performs frequency repetition processing on the reference spectrum generated by the modulation unit 11. The procedure of the processing performed by the frequency repetition unit 12 is shown below. If the number of repetitions is M, the frequency repetition unit 12 performs frequency repetition processing so that M consecutive reference spectra are lined up in frequency, as shown in the following equation (2). At this time, in the allocation processing of each subcarrier performed by the frequency repetition unit 12, each subcarrier is allocated so that the same symbol is assigned at every N subcarrier interval, as shown in equation (2).

[0017]

[0018] Since the bandwidth of each subcarrier is the same as that of the reference spectrum, the bandwidth after repetition processing is expanded to M times the bandwidth of the reference spectrum. In the following description, the output of the frequency repetition unit 12 is referred to as the transmission spectrum.

[0019] The IFFT unit 13 performs an inverse fast Fourier transform on the transmission spectrum and outputs one block of time-domain transmission signals. The following equation (3) represents one block of transmission signals after the inverse fast Fourier transform.

[0020]

[0021] In formula (3), x ｎis the transmitted symbol at discrete time index n. Hereinafter, the discrete time index is called a symbol time. Here, the time domain transmitted signal x is expressed as x every symbol time interval M. ｎ A symbol with a value of ≠0 appears, and at other symbol times, x ｎ = 0, resulting in a transmission signal in which a null is formed in the time domain. FIG. 3 is a diagram showing an example of the time waveform of a transmission signal when sampled every symbol time. As shown in FIG. 3, the time waveform of the transmission signal has a non-zero pulse appearing every M symbol times, and becomes null at other symbol times. At a null, both the I value and Q value are 0. In the following, the transmission symbol x ｎ is non-zero, the information symbol is the transmitted symbol x ｎ is called a null symbol.

[0022] The CP adding unit 14 adds a predetermined number of samples at the end of one block of the transmission signal converted into the time domain to the beginning of the time-domain transmission signal as a guard interval. The transmission filter unit 15 performs filtering on the signal obtained by the CP adding unit 14 and outputs the generated transmission signal data to the transmission RF unit 16.

[0023] The RF transmission unit 16 performs digital-to-analog (DA) conversion on the generated transmission signal data, converts the baseband signal to a carrier frequency, amplifies the signal, and then outputs the signal to the transmission antenna 17 .

[0024] The transmitting antenna 17 radiates the signal from the RF transmitting unit 16 into the air.

[0025] Furthermore, in the transmitter 1, the frequency repetition unit 12 generates a transmission spectrum in which the spectrum of the modulated signal is continuously arranged on the frequency axis, the same transmission symbols are arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side with respect to the center frequency are equal. The IFFT unit 13 converts the transmission spectrum generated by the frequency repetition unit 12 into a time-domain signal, and generates and transmits a signal in which information symbols whose time-domain signal is non-zero and null symbols whose time-domain signal is zero appear periodically.

[0026] 4 is a diagram showing the configuration of a receiver 2 according to an embodiment of the present invention. The receiver 2 includes a receiving antenna 21, an RF receiving unit 22, a receiving filter unit 23, a CP removing unit 24, a receiving quality measuring unit 25, an FFT (Fast Fourier Transformation) unit 26, a frequency repetition combining and selecting unit 27, and a demodulating unit 28.

[0027] The receiver 2 has one receiving antenna 21, and receives radio waves radiated from the transmitter 1 by the receiving antenna 21. In the embodiment, the number of receiving antennas 21 is one, but the number of receiving antennas 21 is not limited to one, and the receiver 2 may have multiple receiving antennas 21. If the receiver 2 has multiple receiving antennas 21, the following processing may be performed for each signal received by each of the multiple receiving antennas 21, or the multiple signals received by the multiple receiving antennas 21 may be combined before the following processing is performed.

[0028] The RF receiver 22 adjusts the gain of the signal received by the receiving antenna 21, converts the gain-adjusted signal into a baseband signal, and then performs AD conversion. The receiving filter 23 performs filtering on the AD-converted signal. The CP remover 24 removes guard intervals from the received signal processed by the receiving filter 23. Here, it is assumed that the transmitter 1 and receiver 2 are synchronized, and that the receiver 2 knows the arrival timings of information symbols and null symbols in the desired signal being received. Equation (4) shows the time-domain received signal for one block after the CP removal by the CP remover 24.

[0029]

[0030] The received signal from which the guard interval has been removed by the CP removal unit 24 is output to the reception quality measurement unit 25 and the FFT unit 26 .

[0031] 5 is a diagram showing the configuration of the reception quality measurement unit 25 included in the receiver 2 according to the embodiment. The reception quality measurement unit 25 includes a signal separation unit 251, an interference information estimation unit 252, an information interval estimation unit 253, and a reception quality information integration unit 254.

[0032] The signal separator 251 separates information symbols and null symbols within one block of the received signal to measure the features of the information symbols and the features of the interference signals. The features refer to information about power, phase, and amplitude. The detailed operation is described below. Within one block of the interference-suppressed received signal, the signal separator 251 extracts an information symbol measurement interval and an interference signal measurement interval, with the information symbols periodically arranged in consideration of the effects of multipath on the communication path and the null symbols corresponding to the last several symbols of each information symbol as the information symbol measurement interval, and the remaining null symbols as the interference signal measurement interval. The signal separator 251 outputs the extracted symbols corresponding to the information symbol measurement interval to the information interval estimation unit 253 and the extracted symbols corresponding to the interference signal measurement interval to the interference information estimation unit 252. Figure 6 is a diagram illustrating an example of the processing performed by the signal separator 251 in the reception quality measurement unit 25 of the receiver 2 according to this embodiment. In FIG. 6, each information symbol and the following two null symbols are extracted from the received signal after CP removal as an information symbol measurement section, and the other null symbols are extracted as an interference signal measurement section.

[0033] The interference information estimation unit 252 estimates the feature quantity of the interference signal using the interference signal measurement period and estimates whether there is any change in the interference arrival pattern. Fig. 7 is a diagram for explaining the operation of the interference information estimation unit 252 provided in the reception quality measurement unit 25 of the receiver 2 according to the embodiment. The detailed operation of the interference information estimation unit 252 is shown in the following (i) to (iv) using as an example the case where interference A and interference B as shown in Fig. 7 arrive at different times. Fig. 8 is a diagram showing the frequency spectrum characteristics in the interference arrival pattern of Fig. 7.

[0034] (i) The interference information estimation unit 252 further divides the interference signal measurement period for one block of the received signal to measure the feature amount of interference. In the example of Fig. 7, the interference information estimation unit 252 divides the interference signal measurement period for one block of the received signal into first to eighth interference signal measurement periods, each M symbol time, and estimates the average value of the feature amount of the interference signal in each period.

[0035] (ii) Next, the interference information estimation unit 252 estimates whether there is a change in the interference situation. The interference information estimation unit 252 determines whether there is a significant difference based on the difference in the feature values ​​between adjacent interference signal measurement intervals, thereby determining whether there is a change in the interference situation. In the embodiment, the feature value is the average power of each measurement interval, but the feature value to be compared may be another feature value, such as phase. In the embodiment, the index used to determine the interference situation is the power difference, and the interference information estimation unit 252 determines that the interference situation has changed if the power difference is equal to or greater than a threshold. The interference information estimation unit 252 compares the feature values ​​in order from the earliest interval to the earliest interval. The interference information estimation unit 252 determines that there is no change in the interference situation between intervals where the power difference is less than the threshold, and determines that the interference situation has changed between intervals where the power difference is equal to or greater than the threshold. Figure 9 is an image diagram of average power. In the example of Figure 9, when comparing the first part from the first interference signal measurement section to the fourth interference signal measurement section and the second part from the fifth interference signal measurement section to the eighth interference signal measurement section, the power difference is less than the threshold in both the first and second parts, so it is determined that the interference situation is the same. On the other hand, when comparing the fourth interference signal measurement section with the fifth interference signal measurement section, the power difference is greater than the threshold, so it is determined that the interference situation has changed. In other words, in the example of Figure 9, it is observed that two types of interference patterns have arrived regarding the observed interference arrival situation: a first interference pattern from the first interference signal measurement section to the fourth interference signal measurement section and a second interference pattern from the fifth interference signal measurement section to the eighth interference signal measurement section. In Figure 9, P Ａ means the average power value in the first interference signal measurement period and the second interference signal measurement period, and P Ｂ means the average power value in the third and fourth interference signal measurement periods, and P Ｃ means the average power value in the fifth and sixth interference signal measurement periods, and P Ｄ means the average power value in the seventh interference signal measurement period and the eighth interference signal measurement period.

[0036] (iii) After estimating the interference situation, the interference information estimation unit 252 estimates the feature quantity of each interference pattern. When estimating the feature quantities, the interference information estimation unit 252 estimates the average feature quantity of all interference signal measurement intervals in which it is determined that the same interference has arrived. In the example of Fig. 9, the interference information estimation unit 252 estimates the average feature quantity for the first interference pattern using the interference signal measurement interval of 0 to 4M symbol times, and for the second interference pattern using the interference signal measurement interval of 4M to 8M symbol times.

[0037] (iv) After estimating the average feature value of each interference pattern, the interference information estimation unit 252 outputs information indicating the average feature value of each interference pattern and the interval of each interference pattern to the information interval estimation unit 253 and the reception quality information integration unit 254.

[0038] The information interval estimation unit 253 measures the average power of the information symbols from the information symbol measurement interval. When measuring the average power of the information symbols, the information interval estimation unit 253 measures the average power of the information symbols assigned to the interval corresponding to each interference pattern notified by the interference information estimation unit 252. For example, in FIG. 6, if it is determined that the interference measurement interval from symbol time 3 to symbol time M-1 and the interference measurement interval from symbol time M+3 to symbol time 2M-1 have the same interference pattern, the information interval estimation unit 253 measures the average power using the information symbols corresponding to each interference measurement interval, that is, the information symbols at symbol time 0 and symbol time M. The information interval estimation unit 253 performs this process on the information symbols corresponding to all interference patterns estimated within one block of the interference-suppressed received signal.

[0039] The reception quality information integrating unit 254 aggregates the interference information measured by the interference information estimating unit 252 and the information symbol information measured by the information interval estimating unit 253, and notifies the aggregated information to a subsequent module. The reception quality information integrating unit 254 determines the reception quality of the interference-suppressed received signal based on the interference measured by the interference information estimating unit 252 and the average power of the information symbol measured by the information interval estimating unit 253. In the embodiment, the reception quality information integrating unit 254 determines the reception quality by comparing the average power of the information symbol with the average power of the interfering signal for each interference arrival pattern measured by the interference information estimating unit 252. Hereinafter, the average power of the information symbol in a certain interference arrival pattern will be referred to as P ｄ and the average power of the interference signal is P ｉ An example of a method for determining reception quality in the embodiment is shown below. When no interference signal exists, the average power of the interference signal is relatively small compared to the average power of the information symbol. Therefore, when the power comparison result is P ｄ >P ｉ If this is the case, the reception quality information integrating unit 254 determines that the reception quality is "high". "High reception quality" means that the reception quality is relatively good. On the other hand, if a residual interference signal exists with a magnitude equal to or greater than a certain level, the power of the interference signal will be equal to or greater than the average power of the information symbol. Therefore, if the power comparison result is P ｉ >P ｄ If so, the reception quality information integrating unit 254 determines that the reception quality is "low." "Low reception quality" means that the reception quality is relatively poor. After completing the reception quality determination, the reception quality information integrating unit 254 outputs the interference information, the information symbol information, and the reception quality information to a subsequent module.

[0040] The FFT unit 26 performs a fast Fourier transform on one block of the received signal, converts the one block of the received signal into a frequency domain signal, and outputs the frequency domain signal. The interference-suppressed received symbol of the k-th subcarrier after the fast Fourier transform process is denoted by r ｋ The signal after fast Fourier transform is expressed as follows in equation (5): In the following description, the received signal converted into a frequency domain signal is referred to as the received signal spectrum.

[0041]

[0042] 10 is a diagram showing the configuration of the frequency repetition synthesis selection unit 27 included in the receiver 2 according to the embodiment. The frequency repetition synthesis selection unit 27 includes a subcarrier selection unit 271 and a repetition synthesis unit 272. The frequency repetition synthesis selection unit 27 performs a repetition synthesis process that combines spectra that are consecutively arranged in frequency by frequency repetition processing. When performing the repetition synthesis process, the frequency repetition synthesis selection unit 27 performs weighting taking into account the amount of interference of each subcarrier in order to reduce the influence of interference signals before combining.

[0043] The subcarrier selector 271 determines the weight of each subcarrier when performing frequency repetition combining processing. In the embodiment, as an example, a process flow for determining subcarrier weights during repetition combining using reception quality information measured by the reception quality measurement unit 25 in the case of FIG. 8 is shown. In the example of FIG. 8, it is assumed that interference A and interference B exist, and that the reception quality information for each interference pattern measured by the reception quality measurement unit 25 has both been determined to be "reception quality: low." If there is even one signal determined to be "reception quality: low" among the measured interference patterns, the subcarrier selector 271 searches for a subcarrier in the received signal spectrum where interference is concentrated. In the embodiment, the subcarrier selector 271 compares the average power of all subcarriers with the power of each subcarrier, and determines that interference exists in that subcarrier if the power of that subcarrier is greater than the average power by a certain amount. In the example of Figure 8, the power of a subcarrier where only interference B is present and the power of a subcarrier where both interference A and interference B are present are greater than the average power, so the subcarrier selection unit 271 determines that both the subcarrier where only interference B is present and the subcarrier where both interference A and interference B are present are subcarriers where interference is present.

[0044] Next, the subcarrier selection unit 271 determines a weight for each subcarrier. For subcarriers determined to have interference, the subcarrier selection unit 271 determines a weight for combining corresponding to the difference between the power of the subcarrier determined to have interference and the average power. In the example of FIG. 8 , the subcarrier selection unit 271 determines the weight for a subcarrier where only interference B exists and the weight for a subcarrier where both interference A and interference B exist, relatively small, and determines the weight for a subcarrier where no interference exists relatively large. Note that in this embodiment, when "reception quality: high" is determined, no interference search is performed, and the subcarrier selection unit 271 sets all the weights for combining to be the same. After determining the weights for all subcarriers, the subcarrier selection unit 271 outputs the weight for each subcarrier to the repetition combination unit 272.

[0045] The repetition synthesis unit 272 performs a repetition synthesis process that synthesizes spectra that are arranged consecutively in frequency by frequency repetition processing. At this time, the repetition synthesis unit 272 performs weighting using the weight determined by the subcarrier selection unit 271 and then performs synthesis processing. Since the same transmission symbol is arranged at every N subcarrier interval in the signal that has undergone frequency repetition processing according to equation (2), the repetition synthesis unit 272 synthesizes identical symbols when performing frequency repetition synthesis processing. In other words, the repetition synthesis unit 272 synthesizes received symbols at every N subcarrier interval. The weight of the k-th subcarrier in the received signal spectrum before synthesis is set to v ｋ Then, the received symbol R in the w-th subcarrier after repetition combining is ｗ is expressed by the following equation (6).

[0046]

[0047] In this embodiment, the output of the repetition combining unit 272 is referred to as the “repetition combined reception spectrum.” The number of subcarriers in the repetition combined reception spectrum is N, and the bandwidth of the repetition combined reception spectrum is the same as the bandwidth of the reference spectrum.

[0048] The demodulator 28 demodulates the received spectrum after repetition synthesis, and outputs the demodulated bits to a subsequent higher-level device.

[0049] Furthermore, the receiver 2 includes a frequency repetition synthesis selection unit 27 that performs frequency repetition synthesis processing on a received signal in which the same spectrum is consecutively arranged, by combining subcarriers containing the same symbol information to generate a single spectrum. When performing frequency repetition synthesis processing, the frequency repetition synthesis selection unit 27 adjusts the amount of synthesis of each subcarrier by weighting the subcarriers when combining them in accordance with the reception status of the received signal. For example, the reception quality measurement unit 25 extracts null symbols from the received signal in any interval, divides the extracted null symbols into intervals consisting of any number of null symbols, estimates the feature of the interference signal in each interval, compares the feature of adjacent intervals to determine changes in the arrival status of the interference signal, and estimates the feature of the interference signal for each arrival status of the interference signal using the null symbol corresponding to the determined arrival status of the interference signal. For example, the reception quality measurement unit 25 extracts information symbols from the received signal in any interval, estimates the feature of the information symbol using the extracted information symbol, and observes and evaluates the reception status using the estimated feature of the information symbol and the feature of the interference signal.

[0050] As described above, the transmitter 1 transmits a signal having such a characteristic that null symbols appear in the time domain signal by performing frequency repetition processing on the modulated signal. That is, the transmitter 1 can transmit a signal that allows demodulation even in the event of interference collision. The receiver 2 measures the interference situation using the characteristics of the received signal and performs spectrum synthesis processing with weighting corresponding to the interference situation, thereby enabling demodulation even in the event of interference collision. That is, the receiver 2 can demodulate the received signal even in the event of interference collision.

[0051] Each component of the transmitter 1 and the receiver 2 is realized by a processing circuit. The processing circuit may be realized by a dedicated circuit or by a control circuit using a CPU. When the processing circuit is realized by a dedicated circuit, each of the transmitter 1 and the receiver 2 has a processing circuit 30 shown in FIG. 11 , and each function of the transmitter 1 and the receiver 2 is realized by the processing circuit 30. FIG. 11 is a diagram showing the processing circuit 30 when each function of the transmitter 1 and the receiver 2 according to the embodiment is realized by the processing circuit 30. When the processing circuit is realized by a dedicated circuit, the processing circuit 30 is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof.

[0052] When the processing circuit is realized by a CPU, each of the transmitter 1 and the receiver 2 has a CPU 31 and a memory 32 shown in Fig. 12, and the functions of each of the transmitter 1 and the receiver 2 are written as a program, which is stored in the memory 32. The CPU 31 realizes the function corresponding to the program by reading and executing the program stored in the memory 32. Fig. 12 is a diagram showing the CPU 31 when each function of the transmitter 1 and the receiver 2 according to the embodiment is realized by the CPU 31. The CPU 31 may be replaced with a processing system, an arithmetic system, a microprocessor, or a DSP (Digital Signal Processor). The memory 32 is, for example, a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM (registered trademark)), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a digital versatile disk (DVD). Note that some of the multiple functions possessed by the transmitter 1 and the receiver 2 may be realized by dedicated circuits, and the remaining functions may be realized by a program and the CPU 92.

[0053] 13 is a diagram showing a control circuit 33 that controls the operation performed by the transmitter 1 according to the embodiment. Specifically, the control circuit 33 causes the transmitter 1 to perform an operation of generating a transmission spectrum in which the spectrum of a modulated signal is continuously arranged on the frequency axis, identical transmission symbols are arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side are equal to the center frequency, and an operation of transmitting a signal in which, based on the generated transmission spectrum, information symbols whose time-domain signals are non-zero and null symbols whose time-domain signals are zero periodically appear. The operation performed by the receiver 2 according to the embodiment may also be controlled by a control circuit equivalent to the control circuit 33. The control circuit that controls the operation performed by the receiver 2 causes the receiver 2 to perform a frequency repetition synthesis process for combining subcarriers containing identical symbol information to generate a single spectrum for a received signal in which the same spectrum is continuously arranged, and an operation of adjusting the amount of synthesis of each subcarrier by weighting the subcarriers when combining them in accordance with the reception status of the received signal when performing the frequency repetition synthesis process.

[0054] 14 is a diagram showing a program storage medium 34 storing a program for controlling the transmitter 1 according to the embodiment. The program causes the transmitter 1 to perform an operation of generating a signal in which information symbols whose time-domain signals are non-zero and null symbols whose time-domain signals are zero periodically appear by generating a transmission spectrum in which the spectrum of a modulated signal is continuously arranged on the frequency axis, the same transmission symbols are arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side are equal to each other with respect to a center frequency. The receiver 2 according to the embodiment may also be controlled by a program stored in a program storage medium equivalent to the program storage medium 34. The program causes the receiver 2 to perform a frequency repetition synthesis process for a received signal in which the same spectrum is continuously arranged, combining subcarriers containing the same symbol information to generate a single spectrum, and an operation of adjusting the amount of synthesis of each subcarrier by weighting the subcarriers when combining them in accordance with the reception status of the received signal when performing the frequency repetition synthesis process.

[0055] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0056] 1 transmitter, 2 receiver, 11 modulation unit, 12 frequency repetition unit, 13 IFFT unit, 14 CP addition unit, 15 transmission filter unit, 16 transmission RF unit, 17 transmission antenna, 18 frequency repetition modulation unit, 21 reception antenna, 22 reception RF unit, 23 reception filter unit, 24 CP removal unit, 25 reception quality measurement unit, 26 FFT unit, 27 frequency repetition synthesis selection unit, 28 demodulation unit, 30 processing circuit, 31 CPU, 32 memory, 33 control circuit, 34 program storage medium, 251 signal separation unit, 252 interference information estimation unit, 253 information interval estimation unit, 254 reception quality information integration unit, 271 subcarrier selection unit, 272 repetition synthesis unit.

Claims

1. A transmitter comprising a frequency repetition modulation unit which generates a transmission spectrum in which the spectrum of a modulated signal is arranged continuously on the frequency axis, the same transmission symbol is arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side of the center frequency are equal, thereby generating a signal in which information symbols where the time-domain signal is non-zero and null symbols where the time-domain signal is zero appear periodically based on the transmission spectrum.

2. A receiver comprising a frequency repetition synthesis selection unit that performs a frequency repetition synthesis process for generating a single spectrum by synthesizing subcarriers containing the same symbol information for a received signal in which the same spectrum is consecutively arranged, wherein the frequency repetition synthesis selection unit, when performing the frequency repetition synthesis process, adjusts the amount of synthesis of each subcarrier by weighting the subcarriers when synthesizing them in accordance with the reception conditions of the received signal.

3. The receiver according to claim 2, further comprising a reception quality measurement unit that extracts null symbols from the received signal in any interval, divides the extracted null symbols into intervals consisting of any number of null symbols, estimates features of the interference signal in each interval, compares the features of adjacent intervals to determine a change in the arrival status of the interference signal, and estimates the features of the interference signal for each arrival status of the interference signal using the null symbols corresponding to the determined arrival status of the interference signal.

4. The receiver according to claim 3, characterized in that the reception quality measuring unit extracts information symbols from the received signal at any interval, estimates features of the information symbols using the extracted information symbols, and observes and evaluates the reception status using the estimated features of the information symbols and the features of the interference signal.

5. A transmission method comprising: a step of generating a transmission spectrum in which the spectrum of a modulated signal is arranged continuously on a frequency axis, identical transmission symbols are arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side with respect to a center frequency are equal; and a step of transmitting a signal in which, based on the generated transmission spectrum, information symbols whose time-domain signal is non-zero and null symbols whose time-domain signal is zero appear periodically.

6. A receiving method comprising a step of performing a frequency repetition synthesis process for generating a single spectrum by synthesizing subcarriers containing the same symbol information for a received signal in which the same spectrum is consecutively arranged, wherein, in the step of performing the frequency repetition synthesis process, when performing the frequency repetition synthesis process, weighting is performed when synthesizing each subcarrier in response to the reception status of the received signal to adjust the amount of synthesis of each subcarrier.

7. The receiving method according to claim 6, further comprising the steps of: extracting null symbols from the received signal in any interval; dividing the extracted null symbols into intervals consisting of any number of null symbols; estimating a feature of the interference signal in each interval; comparing the feature of adjacent intervals to determine a change in the arrival state of the interference signal; and estimating the feature of the interference signal for each arrival state of the interference signal using the null symbol corresponding to the determined arrival state of the interference signal.

8. The receiving method according to claim 7, characterized in that in the step of estimating the characteristic amount, information symbols are extracted from the received signal in an arbitrary section, the characteristic amount of the information symbol is estimated using the extracted information symbol, and the receiving situation is observed and evaluated using the estimated characteristic amount of the information symbol and the characteristic amount of the interference signal.

9. A control circuit that causes a transmitter to perform the following operations: generating a transmission spectrum in which the spectrum of a modulated signal is arranged continuously on the frequency axis, the same transmission symbol is arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high-band side and the spectrum on the low-band side with respect to a center frequency are equal; and transmitting a signal in which, based on the generated transmission spectrum, information symbols whose time-domain signal is non-zero and null symbols whose time-domain signal is zero appear periodically.

10. A control circuit that causes a receiver to perform the following operations: a frequency repetition synthesis process for generating a single spectrum by synthesizing subcarriers containing the same symbol information for a received signal in which the same spectrum is consecutively arranged; and, when performing the frequency repetition synthesis process, a weighting operation is performed when synthesizing each subcarrier in response to the reception status of the received signal to adjust the amount of synthesis of each subcarrier.

11. A program storage medium storing a program for controlling a transmitter, the program causing the transmitter to execute the operation of generating a signal in which information symbols, where the time domain signal is non-zero, and null symbols, where the time domain signal is zero, appear periodically by generating a transmission spectrum in which the spectrum of a modulated signal is continuously arranged on the frequency axis, the same transmission symbol is arranged at regular subcarrier intervals in the spectrum of the modulated signal, and the spectrum on the high band side and the spectrum on the low band side are equal to a center frequency.

12. A program storage medium storing a program for controlling a receiver, the program causing the receiver to execute the following operations: a frequency repetition synthesis process for generating a single spectrum by synthesizing subcarriers containing the same symbol information for a received signal in which the same spectrum is consecutively arranged; and, when performing the frequency repetition synthesis process, a weighting operation is performed when synthesizing each subcarrier in response to the reception conditions of the received signal to adjust the amount of synthesis of each subcarrier.

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