Delay profile measuring device, signal cancellation device, and program

Abstract

To obtain a delay profile that accurately reflects the frequency characteristics in the actual radio wave propagation environment. [Solution] The delay profile measuring device 1 comprises a frequency characteristic calculation unit 30a that calculates the frequency characteristics of a received signal, and a delay profile calculation unit 40 that calculates a delay profile in the time domain. The delay profile calculation unit 40 includes an FFT unit 50 that generates a feedback signal obtained by converting the delay profile to the frequency domain, an IFFT unit 43 that converts the error signal between the frequency characteristics and the feedback signal to the time domain, a first threshold processing unit 44 that sets to zero any signals in the time domain whose amplitude is less than or equal to a first threshold, and an adder unit 46 that updates the delay profile by adding the signal processed by the first threshold processing unit 44 to the delay profile.

Description

Technical Field

[0001] The present invention relates to a delay profile measurement device, a signal cancellation device, and a program.

Background Art

[0002] Generally, in wireless communication, knowing the radio wave propagation situation is an important issue. A delay profile is an indicator of the radio wave propagation situation. The delay profile indicates the time and electric field strength of the radio wave arriving at the reception point, and a measurement device equipped with a function for measuring this is widely used.

[0003] Over 20 years have passed since the start of terrestrial digital broadcasting, and the need for renewal due to the aging deterioration of transmission facilities has been increasing. On the other hand, in recent years, studies on transmission methods for next-generation terrestrial broadcasting have been underway. In such next-generation terrestrial digital broadcasting methods, it is required to provide high-function and high-quality services such as super high-definition broadcasting instead of conventional high-definition broadcasting. However, it is not easy to shift terrestrial digital broadcasting, which is also an important social infrastructure, to next-generation terrestrial broadcasting.

[0004] Therefore, in Patent Document 1, the applicant proposed a method to increase the information rate that can be transmitted without increasing the current number of broadcast channels (frequency bands) while maintaining backward compatibility for receiving terrestrial digital broadcasts using the ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system, which is the current broadcasting method for terrestrial digital broadcasting. Furthermore, Patent Document 2 shows a technology that enables a smooth transition when moving from current broadcasting to next-generation broadcasting in terrestrial digital broadcasting. Both of these are achieved by reducing the transmission power of the ISDB-T broadcast wave (first broadcast wave) and instead multiplexing a second broadcast wave with a transmission power that does not interfere with the reception of the ISDB-T broadcast wave. When multiplexing two different broadcast waves by sharing power, two methods can be considered: a synchronous multiplexing method in which power is adjusted and multiplexed after primary modulation as shown in Figure 15, and an asynchronous multiplexing method in which power is adjusted and multiplexed after secondary modulation as shown in Figure 16. In synchronous multiplexing, the secondary modulation is common to both terrestrial digital broadcasting and the second broadcast wave. Therefore, the use of more advanced technologies in the second broadcast wave than in terrestrial digital broadcasting is limited to the primary modulation, i.e., carrier modulation and error correction codes. On the other hand, in asynchronous multiplexing, the terrestrial digital broadcast wave and the second broadcast wave are independent signals. Therefore, more advanced technologies than those used in terrestrial digital broadcasting can be used in both the primary and secondary modulation.

[0005] Next, considering the reception of broadcast waves, in order to receive not only the ISDB-T broadcast wave but also the second broadcast wave, it is necessary to cancel the ISDB-T broadcast wave from the received signal. In a synchronous multiplexing system, if the ISDB-T broadcast wave can be received, demodulation processing for the second-order modulation is performed and converted to the frequency domain as shown in Figure 17. Since an orthogonal relationship is established between carrier waves in the frequency domain, it is possible to accurately cancel the ISDB-T broadcast wave from the received signal for each carrier wave.

[0006] On the other hand, in asynchronous multiplexing, the terrestrial digital broadcast and the second broadcast wave use different methods and are not synchronized. Therefore, as shown in Figure 18, it is necessary to generate a replica of the received signal of the ISDB-T broadcast wave from the received signal in the time domain and cancel it out. This is achieved by the replica generation unit 23 and subtraction unit 24 in Patent Document 1, and the signal cancellation device 17 in Patent Document 2. If the replica generated here is not sufficiently identical to the received signal of the actual ISDB-T broadcast wave only, it will be difficult to receive the second broadcast wave. However, paragraph 0049 of Patent Document 1 only states, "The replica generation unit 23 modulates the demodulated signal a' demodulated by the first demodulation unit 22 with the same transmission parameters as the first modulation unit 11 of the transmitting device 1 to generate a broadcast wave A' which is a replica of the broadcast wave A received by the first receiving antenna 41." The frequency characteristics included in the received signal are not considered. In other words, the replica generated by the replica generation unit 23 does not include frequency characteristics. Furthermore, the signal cancellation device 17 in Patent Document 2 is described in paragraph 0037 as follows: "The signal cancellation device 17 is a device that, when the receiver is set to select 4K broadcasting, inverts the phase of the signal decoded by the 2K signal decoding device 16 with respect to the signal sent from the high-frequency demodulator 15, and cancels out the signal for 2K broadcasting from the signal output from the high-frequency demodulator 15." In this way, it only inverts the phase and similarly does not take frequency characteristics into consideration. Therefore, the technologies described in Patent Documents 1 and 2 have the problem that the replica will be different from the received signal of only the actual ISDB-T broadcast wave, and it will not be possible to accurately cancel the ISDB-T broadcast wave component from the received signal, or the cancellation residual will be large.

[0007] Furthermore, in a same-channel interference environment, identifying the source of interference to the desired wave is also an important issue in wireless communication. For this reason, Patent Document 3 describes a technique for canceling the desired wave from the received signal and extracting the interference wave without interrupting the radio wave. The interference wave extraction device shown in Patent Document 3 differs from the replica generation unit 23 and subtraction unit 24 in Patent Document 1, or the signal cancellation device 17 in Patent Document 2, in that the target of cancellation or cancellation is either a second broadcast wave broadcast in addition to terrestrial digital broadcasting, or an interference wave that causes interference when receiving terrestrial digital broadcasting. However, it can also be used for the purpose of canceling ISDB-T broadcast waves from the received signal as described above. This is achieved by the transmission path characteristic addition unit 12 and the desired wave cancellation unit 14. Frequency characteristics (transmission path characteristics in Patent Document 3) are taken into consideration here. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6462289 [Patent Document 2] Patent No. 6542739 [Patent Document 3] Patent No. 5814070 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, paragraph 0033 of Patent Document 3 only states that "the transmission path characteristic addition unit 12 receives a desired wave signal from the desired wave extraction unit 10, receives transmission path characteristics from the transmission path characteristic calculation unit 11, adds transmission path characteristics to the desired wave signal, generates a desired wave replica signal, and outputs the desired wave replica signal to the desired wave cancellation unit 14," and does not clarify the specific procedure for adding transmission path characteristics. Furthermore, paragraph 0032 states that "the transmission path characteristic calculation unit 11 receives a received signal in which the desired wave and interference waves are mixed, calculates the transmission path characteristics using the received signal and a preset reference signal (a signal whose modulation content during transmission is known, also called a pilot signal (SP signal)), and outputs the obtained transmission path characteristics to the transmission path characteristic addition unit 12," and it is considered that the method for calculating the transmission path characteristics is a general method using a pilot signal.Therefore, if there is a difference between the frequency characteristics in the actual radio wave propagation environment and the transmission path characteristics added by the transmission path characteristic addition unit 12, the problem of a large cancellation residual will not be solved.

[0010] Figure 19 shows a conventional delay profile measurement device 1'. Generally, OFDM (Orthogonal Frequency Division Multiplexing) signals have fewer carriers than the size of the IFFT, which is the means of realizing second-order modulation. For example, in the ISDB-T system, second-order modulation is realized by an 8,192-point IFFT, but the number of carriers is 5,617. Therefore, the frequency band corresponding to 8,192 - 5,617 = 2,575 carriers is not used for signal transmission, and the frequency characteristics in this frequency band cannot be known. Thus, when obtaining a delay profile by converting the frequency characteristics obtained using SP (Scattered Pilot) in the ISDB-T system to the time domain, for example, the result obtained is one in which the sinc function is convolved into the path in the radio wave propagation environment. However, in the actual radio wave propagation environment, the sinc function is not convolved, so there is a difference from the frequency characteristics in the actual radio wave propagation environment, and as a result there is a problem that the broadcast wave component of the ISDB-T system cannot be canceled from the received signal, or the cancellation residual becomes large.

[0011] In view of these circumstances, the objective of the present invention is to obtain a delay profile that accurately reflects the frequency characteristics in an actual radio wave propagation environment. [Means for solving the problem]

[0012] The gist of the present invention, which solves the above problems, is as follows.

[0013] (1) A delay profile measuring device comprising: a frequency characteristic calculation unit for calculating the frequency characteristics of a received signal; and a delay profile calculation unit for calculating a delay profile in the time domain, wherein the delay profile calculation unit includes: an FFT unit for generating a feedback signal obtained by converting the delay profile to the frequency domain; an IFFT unit for converting the error signal between the frequency characteristics and the feedback signal to the time domain; a first threshold processing unit for setting to zero any signals in the time domain whose amplitude is less than or equal to a first threshold; and an addition unit for updating the delay profile by adding the signal processed by the first threshold processing unit to the delay profile.

[0014] (2) The delay profile measuring apparatus according to (1), wherein the delay profile calculation unit includes a normalization unit that calculates the average value of the frequency characteristics and performs normalization processing by dividing the frequency characteristics by the average value, and a multiplication unit that multiplies the delay profile by the average value.

[0015] (3) The delay profile measuring device according to (1) or (2), wherein the delay profile calculation unit has a second threshold processing unit that sets to zero signals whose amplitude is less than or equal to a second threshold among the delay profiles updated by the summing unit.

[0016] (4) The delay profile measuring device according to (3), wherein the delay profile calculation unit has a leak processing unit that reduces the absolute value by adding or subtracting a small positive amount to the signal processed by the second threshold processing unit.

[0017] (5) The delay profile measuring device according to any one of (1) to (4), wherein the frequency characteristic calculation unit performs channel equalization, carrier demodulation and carrier modulation on the frequency domain signal obtained by converting the received signal to the frequency domain, and calculates the frequency characteristic by dividing the frequency domain signal by the carrier-modulated signal.

[0018] (6) The frequency characteristic calculation unit performs channel equalization, carrier demodulation, error correction decoding, error correction encoding, and carrier modulation on the frequency domain signal obtained by converting the received signal into the frequency domain, and calculates the frequency characteristics by dividing the frequency domain signal by the signal obtained by performing carrier modulation on the frequency domain signal. The delay profile measurement device according to any one of (1) to (4).

[0019] (7) The delay profile measurement device according to (5), inserts a pilot signal into the carrier-modulated signal, converts it into the time domain, adds a guard interval to generate a time domain signal, and performs filter processing on the time domain signal using the delay profile calculated by the delay profile calculation unit as a filter coefficient to generate a replica signal. A replica generation unit, and a replica removal unit that subtracts the replica signal from the delayed received signal. A signal cancellation device comprising.

[0020] (8) The delay profile measurement device according to (6), inserts a pilot signal into the carrier-modulated signal, converts it into the time domain, adds a guard interval to generate a time domain signal, and performs filter processing on the time domain signal using the delay profile calculated by the delay profile calculation unit as a filter coefficient to generate a replica signal. A replica generation unit, and a replica removal unit that subtracts the replica signal from the delayed received signal. A signal cancellation device comprising.

[0021] (9) A program for causing a computer to function as the delay profile measurement device according to any one of (1) to (6).

[0022] (10) A program for causing a computer to function as the signal cancellation device according to (7) or (8).

Effect of the Invention

[0023] According to the present invention, a delay profile accurately reflecting frequency characteristics in an actual radio wave propagation environment can be obtained. Further, using this delay profile, a main signal component can be accurately canceled from a received signal.

Brief Description of Drawings

[0024] [Figure 1] It is a block diagram showing the configuration of a delay profile measurement device according to a first embodiment of the present invention. [Figure 2] It is a block diagram showing the configuration of a normalization unit in a delay profile measurement device according to a first embodiment of the present invention. [Figure 3] It is a block diagram showing the configuration of a first threshold processing unit in a delay profile measurement device according to a first embodiment of the present invention. [Figure 4] It is a block diagram showing the configuration of a second threshold processing unit in a delay profile measurement device according to a first embodiment of the present invention. [Figure 5] It is a block diagram showing the configuration of a leak processing unit in a delay profile measurement device according to a first embodiment of the present invention. [Figure 6] It is a block diagram showing the configuration of a real leak processing unit in a delay profile measurement device according to a first embodiment of the present invention. [Figure 7] It is a block diagram showing the configuration of a delay profile measurement device according to a second embodiment of the present invention. [Figure 8] It is a block diagram showing the configuration of a delay profile measurement device according to a third embodiment of the present invention. [Figure 9] It is a block diagram showing the configuration of a signal cancellation device according to a fourth embodiment of the present invention. [Figure 10] It is a block diagram showing the configuration of a signal cancellation device according to a fifth embodiment of the present invention. [Figure 11] It is a diagram showing a system of computer simulation. [Figure 12] It is a diagram showing transmission characteristics of a second broadcast wave when a Gaussian noise environment is used as a channel. [Figure 13] This figure shows the transmission characteristics for a second broadcast wave when a multipath environment is used as the channel. [Figure 14] This figure shows the required C / N and the equivalent C / N due to the cancellation residual. [Figure 15] This is a block diagram showing a transmitter in a conventional synchronous multiplexing system. [Figure 16] This is a block diagram showing a transmitter in a conventional asynchronous multiplexing system. [Figure 17] This is a block diagram showing a receiving device in a conventional synchronous multiplexing system. [Figure 18] This is a block diagram showing a receiving device in a conventional asynchronous multiplexing system. [Figure 19] This is a block diagram showing the configuration of a conventional delay profile measurement device. [Figure 20] This is a block diagram showing the configuration of a conventional signal cancellation device. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described in detail below with reference to the drawings. In each figure, the same components are given the same reference numeral and their descriptions are omitted as appropriate. In this embodiment, the OFDM method is used for secondary modulation.

[0026] <Delay profile measuring device according to the first embodiment> A delay profile measuring device is a device for understanding the arrival conditions of radio waves when receiving broadcast waves for terrestrial digital broadcasting. Figure 1 shows the configuration of a delay profile measuring device according to the first embodiment of the present invention. The delay profile measuring device 1 shown in Figure 1 comprises a GI (Guard Interval) removal unit 10, an FFT (Fast Fourier Transform) unit 20, a frequency characteristic calculation unit 30a, and a delay profile calculation unit 40. The delay profile measuring device 1 receives a received signal from an external source.

[0027] The GI removal unit 10 removes GI from the received signal input from outside the delay profile measuring device 1 and outputs the time-domain signal of the valid symbol interval to the FFT unit 20.

[0028] The FFT unit 20 converts the time-domain signal of the valid symbol interval input from the GI removal unit 10 into a frequency-domain signal and outputs it to the frequency characteristic calculation unit 30a.

[0029] The frequency response calculation unit 30a calculates the frequency characteristics of the frequency domain signal input from the FFT unit 20 and outputs it to the delay profile calculation unit 40. The frequency response calculation unit 30a includes a channel estimation unit 31 that determines the frequency characteristics using a pilot signal. That is, the channel estimation unit 31 determines the frequency characteristics by dividing the frequency domain signal by a pilot signal known at the receiving end. For example, in terrestrial digital broadcast waves, SP (Scattered Pilot) signals known at the receiving end are multiplexed at intervals of 3 carriers in the frequency direction and 4 symbols in the time direction, and this can be used for that purpose. The frequency characteristics of carriers and symbols where data carriers other than SP are multiplexed can be determined by interpolating the channel estimation value obtained using SP in the frequency and time directions.

[0030] (Delay Profile Calculation Unit) The delay profile calculation unit 40 calculates a delay profile in the time domain. The delay profile calculation unit 40 includes a normalization unit 41, a subtraction unit 42, an IFFT (Inverse Fast Fourier Transform) unit 43, a first threshold processing unit 44, a multiplication unit 45, an addition unit 46, a second threshold processing unit 47, a leak processing unit 48, a delay unit 49, an FFT unit 50, and a multiplication unit 51. The delay profile calculation unit 40 does not necessarily have to include the normalization unit 41 and the multiplication unit 51. Also, the delay profile calculation unit 40 does not necessarily have to include the second threshold processing unit 47 and the leak processing unit 48.

[0031] The normalization unit 41 calculates the average value of the frequency characteristics input from the frequency characteristics calculation unit 30a and outputs it to the multiplication unit 51. The normalization unit 41 also performs normalization by dividing the frequency characteristics by the average value and inputs it to the subtraction unit 42. Details of the normalization unit 41 will be described later.

[0032] The subtraction unit 42 subtracts the feedback signal input from the FFT unit 50 from the normalized frequency characteristics input from the normalization unit 41 to obtain an error signal in the frequency domain, and outputs it to the IFFT unit 43.

[0033] The IFFT unit 43 converts the error signal in the frequency domain, input from the subtraction unit 42, into a time domain signal and outputs it to the first threshold processing unit 44.

[0034] The first threshold processing unit 44 performs a first thresholding process on the time-domain error signals input from the IFFT unit 43, reducing signals with an amplitude less than or equal to the first threshold to zero, and outputs this to the multiplication unit 45. Details of the first threshold processing unit 44 will be described later.

[0035] The multiplication unit 45 multiplies the error signal in the time domain, which has undergone the first thresholding process, by an adaptation coefficient (step size) and outputs it to the addition unit 46. Here, the step size should be a value sufficiently smaller than 1.

[0036] The adder 46 adds the time-domain error signal input from the multiplier 45 to the delay profile input from the delay unit 49 to update the delay profile and outputs it to the second threshold processing unit 47.

[0037] The second threshold processing unit 47 performs a second threshold processing on the updated delay profile input from the summing unit 46, setting signals with an amplitude less than or equal to the second threshold to zero, and outputs this to the leak processing unit 48. Details of the second threshold processing unit 47 will be described later.

[0038] The leak processing unit 48 applies a leak processing to the real and imaginary parts of the delay profile, which has undergone second threshold processing, by adding or subtracting a predetermined small positive amount to reduce their absolute values, and outputs the results to the delay unit 49 and the multiplication unit 51. Details of the leak processing unit 48 will be described later.

[0039] The delay unit 49 delays the delay profile input from the leak processing unit 48 by a time corresponding to the interval at which the frequency characteristic calculation unit 30a calculates the frequency characteristic, for example, by 1 OFDM symbol, and outputs it to the FFT unit 50.

[0040] The FFT unit 50 converts the delay profile input from the delay unit 49 into a frequency domain signal and outputs it to the subtraction unit 42 as a feedback signal.

[0041] The multiplication unit 51 generates a delay profile by multiplying the delay profile that has undergone second threshold processing, input from the leak processing unit 48, by the average value of the frequency characteristics input from the normalization unit 41, and outputs it to the outside of the delay profile measuring device 1.

[0042] (Normalization part) Figure 2 shows the configuration of the normalization unit 41. The normalization unit 41 shown in Figure 2 comprises a sum calculation unit 411, a multiplication unit 412, and a division unit 413. The frequency characteristics input to the normalization unit 41 are divided into two parts: one is input to the division unit 413, and the other is input to the sum calculation unit 411.

[0043] The sum calculation unit 411 calculates the sum of the frequency characteristics input from the frequency characteristic calculation unit 30a and outputs it to the multiplication unit 412.

[0044] The multiplication unit 412 calculates the average value of the frequency characteristics by multiplying the sum of the frequency characteristics input from the sum calculation unit 411 by the reciprocal of the number of frequency characteristics (number of carriers). The average value of the frequency characteristics output by the multiplication unit 412 is divided into two parts: one is output to the outside of the normalization unit 41, and the other is input to the division unit 413.

[0045] The division unit 413 performs normalization by dividing the frequency characteristics input from the frequency characteristics calculation unit 30a by the average value (scalar value) of the frequency characteristics input from the multiplication unit 412 for each carrier, and outputs the frequency characteristics after normalization to the outside of the normalization unit 41.

[0046] (First threshold processing unit) Figure 3 shows the configuration of the first threshold processing unit 44. The first threshold processing unit 44 shown in Figure 3 comprises an amplitude calculation unit 441, a maximum value calculation unit 442, a multiplication unit 443, a comparison unit 444, and a switching unit 445. The time-domain error signal input from the IFFT unit 43 is divided into two parts: one is input to the switching unit 445, and the other is input to the amplitude calculation unit 441.

[0047] The amplitude calculation unit 441 calculates the amplitude of the time-domain error signal input from the IFFT unit 43. The amplitude value of the time-domain error signal output by the amplitude calculation unit 441 is divided into two parts: one is input to the comparison unit 444 and the other is input to the maximum value calculation unit 442.

[0048] The maximum value calculation unit 442 determines the maximum value of the amplitude of the error signal in the time domain input from the amplitude calculation unit 441 and outputs it to the comparison unit 444.

[0049] The multiplication unit 443 calculates a first threshold value by multiplying the maximum amplitude value of the time-domain error signal input from the maximum value calculation unit 442 by an adaptation coefficient (constant) of 1 or less, and outputs it to the comparison unit 444.

[0050] The comparison unit 444 compares the amplitude value of the time-domain error signal input from the amplitude calculation unit 441 with the magnitude of the first threshold input from the multiplication unit 443 for each time sample. If the value is larger, it outputs true (1) to the switching unit 445 as the comparison result; if it is smaller, it outputs false (0).

[0051] The switching unit 445 outputs an error signal in the time domain input from the IFFT unit 43 based on the comparison result input from the comparison unit 444 for each time sample, if it is true (1), and outputs zero if it is false (0). The output of the switching unit 445 is output to the outside of the first threshold processing unit 44 as the error signal after the first threshold processing. The first threshold processing unit 44 makes it possible to remove the sinc function that is convolved into the delay profile.

[0052] (Second threshold processing unit) Figure 4 shows the configuration of the second threshold processing unit 47. The second threshold processing unit 47 shown in Figure 4 comprises an amplitude calculation unit 471, a comparison unit 472, and a switching unit 473. The updated delay profile input from the summing unit 46 is divided into two parts: one is input to the switching unit 473 and the other is input to the amplitude calculation unit 471.

[0053] The amplitude calculation unit 471 calculates the amplitude of the updated delay profile input from the summing unit 46 and outputs it to the comparison unit 472.

[0054] The comparison unit 472 compares the amplitude value of the updated delay profile input from the amplitude calculation unit 471 with a predetermined constant, the second threshold, for each time sample. If the value is larger, it outputs true (1) to the switching unit 473 as the comparison result; if it is smaller, it outputs false (0).

[0055] The switching unit 473 outputs the updated delay profile input from the summing unit 46 based on the comparison result input from the comparison unit 472 for each time sample, if it is true (1), and outputs zero if it is false (0). The output of the switching unit 473 is output to the outside of the second threshold processing unit 47 as an error signal after the second threshold processing. The second threshold processing unit 47 makes it possible to remove noise components included in the delay profile.

[0056] (Leakage compensation) Figure 5 shows the configuration of the leak processing unit 48. The leak processing unit 48 shown in Figure 5 comprises a real part extraction unit 481, an imaginary part extraction unit 482, a first real number leak processing unit 483, a second real number leak processing unit 484, and a complex number constructor 485. The delay profile after the second threshold processing input from the second threshold processing unit 47 is divided into two parts: one is input to the real part extraction unit 481 and the other to the imaginary part extraction unit 482.

[0057] The real part extraction unit 481 extracts the real part of the delay profile after the second threshold processing input from the second threshold processing unit 47 and outputs it to the first real number leak processing unit 483.

[0058] The imaginary part extraction unit 482 extracts the imaginary part of the delay profile after the second threshold processing input from the second threshold processing unit 47 and outputs it to the second real number leak processing unit 484.

[0059] The first real number leak processing unit 483 and the second real number leak processing unit 484 each perform real number leak processing on the real and imaginary parts of the delay profile, and output the results to the complex number constructor 485.

[0060] The complex number constructor 485 constructs a complex number using the real part of the delay profile that has undergone real number leakage processing input from the first real number leakage processing unit 483 as the real part, and the imaginary part of the delay profile that has undergone real number leakage processing input from the second real number leakage processing unit 484 as the imaginary part, and outputs the leakage-processed delay profile to the outside of the leakage processing unit 48. The leakage processing unit 48 makes it possible to remove alias components and other such components that are accidentally mixed into the measurement results of the delay profile due to calculation errors or other factors that do not exist in the actual radio wave propagation environment.

[0061] (Real number leak processing unit) Since the configurations of the first real number leak processing unit 483 and the second real number leak processing unit 484 are identical, they are collectively referred to as real number leak processing units 483 and 484. Figure 6 shows the configurations of the real number leak processing units 483 and 484. The real number leak processing units 483 and 484 shown in Figure 6 include a sign calculation unit 421, an absolute value calculation unit 422, a first multiplication unit 423, a comparison unit 424, a second multiplication unit 425, and a subtraction unit 426. The real part of the delay profile input from the real part extraction unit 481, or the imaginary part of the delay profile input from the imaginary part extraction unit 482, is divided into three parts and input to the subtraction unit 426, the sign calculation unit 421, and the absolute value calculation unit 422, respectively.

[0062] The sign calculation unit 421 outputs the sign of the real or imaginary part of the delay profile input from the real part extraction unit 481 or the imaginary part extraction unit 482, i.e., +1 if positive and -1 if negative, to the first multiplication unit 423.

[0063] The first multiplication unit 423 multiplies the sign of the real or imaginary part of the delay profile input from the sign calculation unit 421 by a predetermined constant (leakage constant) and outputs it to the second multiplication unit 425. The leakage constant is a small positive quantity, and can be, for example, the value represented by the LSB of a fixed-point number.

[0064] The absolute value calculation unit 422 calculates the absolute value of the real or imaginary part of the delay profile input from the real part extraction unit 481 or the imaginary part extraction unit 482, and outputs it to the comparison unit 424.

[0065] The comparison unit 424 compares the absolute value of the real or imaginary part of the delay profile input from the real number leak processing units 483 and 484 with the leak constant, and outputs true (1) if the value is larger, and false (0) if the value is smaller, to the second multiplication unit 425.

[0066] The second multiplication unit 425 multiplies the multiplication result input from the first multiplication unit 423 by the comparison result (1 or 0) input from the comparison unit 424 and outputs it to the subtraction unit 426.

[0067] The subtraction unit 426 subtracts the value input from the second multiplication unit 425 from the real or imaginary part of the delay profile input from the real part extraction unit 481 or the imaginary part extraction unit 482, and outputs the real or imaginary part of the delay profile after real leak processing to the real leak processing units 483 and 484.

[0068] <Delay profile measuring device according to the second embodiment> Figure 7 shows the configuration of the delay profile measurement device according to the second embodiment. The delay profile measurement device 2 shown in Figure 2 differs from the delay profile measurement device 1 shown in Figure 1 in the configuration of the frequency characteristic calculation unit. Specifically, while the frequency characteristic calculation unit 30a of the delay profile measurement device 1 includes a channel estimation unit 31 that uses a pilot signal, the frequency characteristic calculation unit 30b of the delay profile measurement device 2 includes, in addition to the channel estimation unit 31, a channel equalization unit 32, a deinterleaving unit 33, a carrier demodulation unit 34, a carrier modulation unit 35, an interleaving unit 36, and a division unit 37. The frequency domain signal input from the FFT unit 20 is divided into three parts and input to the channel equalization unit 32, the channel estimation unit 31, and the division unit 37. Note that if the carrier modulation method in the carrier demodulation unit 34 and the carrier modulation unit 35 is defined, the delay profile measurement device 2 does not need to include the deinterleaving unit 33 and the interleaving unit 36.

[0069] The channel estimation unit 31, similar to the first embodiment, determines the frequency characteristics using a pilot signal and outputs it to the channel equalization unit 32.

[0070] The channel equalization unit 32 divides the frequency domain signal input from the FFT unit 20 by the frequency characteristics input from the channel estimation unit 31, and outputs the equalized frequency domain signal to the deinterleaving unit 33.

[0071] The deinterleaving unit 33 applies deinterleaving processing to the equalized frequency domain signal input from the channel equalization unit 32 and outputs it to the carrier demodulation unit 34.

[0072] The carrier demodulation unit 34 receives the deinterleaved frequency domain signal from the deinterleaving unit 33, performs carrier demodulation, and outputs an integer value to the carrier modulation unit 35.

[0073] The carrier modulation unit 35 receives an integer value from the carrier demodulation unit 34, modulates it using carrier modulation, converts it back into a frequency domain signal, and outputs it to the interleaving unit 36.

[0074] The interleaving unit 36 ​​applies interleaving processing to the frequency domain signal input from the carrier modulation unit 35 to obtain a remodulated signal, which is then output to the division unit 37.

[0075] The division unit 37 divides the frequency domain signal input from the FFT unit 20 by the remodulated signal input from the interleaving unit 36 ​​and outputs the frequency characteristic to the delay profile calculation unit 40.

[0076] <Delay profile measuring device according to the third embodiment> Figure 8 shows the configuration of a delay profile measuring device according to the third embodiment. The delay profile measuring device 3 shown in Figure 8 differs from the delay profile measuring device 2 shown in Figure 7 in the configuration of its frequency characteristic calculation unit. Specifically, the frequency characteristic calculation unit 30c of the delay profile measuring device 3 includes an error correction decoding unit 38 and an error correction coding unit 39 in addition to the configuration of the frequency characteristic calculation unit 30b of the delay profile measuring device 2. The integer value output by the carrier demodulation unit 34 is input to the error correction decoding unit 38.

[0077] The error correction decoding unit 38 converts the integer value input from the carrier demodulation unit 34 into a bit sequence, performs error correction decoding processing, and outputs it to the error correction encoding unit 39.

[0078] The error correction coding unit 39 takes the error-corrected and decoded bit sequence input from the error correction decoding unit 38, performs error correction coding on it again to convert the bit sequence into an integer value, and outputs it to the carrier modulation unit 35. The delay profile measuring device 3 can correct demodulation errors by error correction processing using the carrier demodulated integer value. As a result, it is possible to calculate a more accurate frequency characteristic, and consequently, a more accurate delay profile.

[0079] <Signal cancellation device according to the fourth embodiment> A signal cancellation device is a device that cancels the main signal component from a received signal in which two signals are multiplexed and extracts the secondary signal component. Figure 9 shows the configuration of a signal cancellation device according to the fourth embodiment. The signal cancellation device 4 shown in Figure 9 includes a replica generation unit 60 and a replica removal unit 70 in addition to the configuration of the delay profile measurement device 2 shown in Figure 2. The received signal input from outside the signal cancellation device 4 is split into two, one of which is input to the GI removal unit 10 and the other to the replica removal unit 70. The remodulation signal output by the interleaving unit 36 ​​of the frequency characteristic calculation unit 30b is split into two, one of which is input to the division unit 37 and the other to the replica generation unit 60.

[0080] The replica generation unit 60 includes a pilot insertion unit 61, an IFFT unit 62, a GI addition unit 63, and an FIR (Finite Impulse Response) unit 64. The replica removal unit 70 includes a delay unit 71 and a subtraction unit 72.

[0081] The pilot insertion unit 61 inserts a pilot signal into the remodulation signal input from the interleaving unit 36 ​​and outputs it to the IFFT unit 62.

[0082] The IFFT unit 62 converts the remodulated signal input from the pilot insertion unit 61 into a time-domain signal and outputs it to the GI addition unit 63.

[0083] The GI addition unit 63 adds GI to the time-domain remodulation signal input from the IFFT unit 62 and outputs it to the FIR unit 64.

[0084] The FIR unit 64 applies a filter to the time-domain remodulation signal input from the GI addition unit 63, using the delay profile input from the delay profile calculation unit 40 as the filter coefficient, to generate a replica signal, which is then output to the subtraction unit 72.

[0085] The delay unit 71 delays the received signal by the amount of time required from the time the received signal is input until the replica generation unit 60 generates the replica signal, and outputs it to the subtraction unit 72.

[0086] The subtraction unit 72 subtracts the replica signal input from the replica generation unit 60 from the delayed received signal input from the delay unit 71, and outputs the result to the outside of the replica removal unit 70.

[0087] <Signal cancellation device according to the fifth embodiment> Figure 10 shows the configuration of the signal cancellation device according to the fifth embodiment. The signal cancellation device 5 shown in Figure 10 differs from the signal cancellation device 4 shown in Figure 9 in the configuration of the frequency characteristic calculation unit. The configuration of the frequency characteristic calculation unit 30c of the signal cancellation device 5 is the same as that of the frequency characteristic calculation unit 30c of the delay profile measurement device 3 shown in Figure 8. The processing of each component has been described above, so a description is omitted here.

[0088] <Computer Simulation> Next, the results of the computer simulation are shown. The computer simulation was performed using the system shown in Figure 11, and a second broadcast wave was synthesized by delaying the terrestrial digital broadcast wave by one symbol and then reducing its transmission power by 20 dB. Table 1 shows the transmission parameters. Note that error correction decoding was not performed. [Table 1]

[0089] The signal cancellation device 5 shown in Figure 10 was used as the signal cancellation device according to the present invention, and the signal cancellation device 5' shown in Figure 20 was used as the conventional signal cancellation device. Figure 12 shows the transmission characteristics for the second broadcast wave when a Gaussian noise environment (AWGN environment) is used as the channel. Figure 13 shows the transmission characteristics for the second broadcast wave when a multipath environment is used as the channel. From the results of this computer simulation, it can be seen that the signal cancellation device 5 according to the present invention obtains a delay profile that accurately reflects the frequency characteristics in the radio wave propagation environment and accurately cancels terrestrial digital broadcast waves, resulting in superior transmission characteristics in both BER (Bit Error Rate) and MER (Modulation Error Ratio) characteristics compared to the conventional signal cancellation device 5' in both environments.

[0090] Figure 14 shows the required BER set to 10 -2 The required C / N (Carrier to Noise Ratio) and the equivalent C / N due to the cancellation residual are shown. When using the conventional signal cancellation device 5', the required BER is not reached in a multipath environment, but when using signal cancellation device 5, the required BER is obtained with a C / N of 33.8 dB. The equivalent C / N value due to the cancellation residual is 40 dB or more, which is considered to be a sufficiently small value.

[0091] As described above, according to the present invention, by converting a delay profile, which is a time-domain signal, into the frequency domain, calculating the error between the current measured value and the radio wave propagation environment in the frequency domain, and accumulating this error in the time domain, it is possible to obtain a delay profile that accurately reflects the frequency characteristics in the actual radio wave propagation environment. Furthermore, the main signal component can be accurately canceled from the received signal using this delay profile.

[0092] <Program> To enable the aforementioned delay profile measuring devices 1, 2, and 3, and signal cancellation devices 4 and 5, it is also possible to use computers capable of executing program instructions. Here, the computer may be a general-purpose computer, a dedicated computer, a workstation, or a PC (Personal Computer). The program instructions may be program code, code segments, etc., for executing the required tasks.

[0093] A computer comprises a processor, a memory unit, an input unit, and an output unit. The processor may be a CPU (Central Processing Unit), MPU (Micro Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), SoC (System on a Chip), etc., and may be composed of multiple processors of the same or different types. The processor controls each of the above components and performs various calculations by reading and executing programs from the memory unit. At least a part of these processes may be implemented in hardware. The input unit is an input interface that receives user input operations and acquires information based on user operations, such as a pointing device, keyboard, microphone, etc. The output unit is an output interface that outputs information, such as a display, speaker, etc.

[0094] The program may be recorded on a computer-readable recording medium. Using such a medium, the program can be installed on the computer. The recording medium on which the program is recorded may be a non-transitory recording medium. Non-transitory recording media are not particularly limited, but may include, for example, CD-ROMs, DVD-ROMs, or USB (Universal Serial Bus) memory. Alternatively, the program may be downloaded from an external device via a network.

[0095] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments described above, and various modifications or changes are possible without departing from the scope of the claims. For example, it is possible to integrate multiple component blocks shown in the configuration diagram of the embodiments, or to divide a single component block. [Explanation of symbols]

[0096] 1,2,3 Delay Profile Measurement Device 4,5 Signal Cancelling Device 10 GI removal section 20 FFT section 30a, 30b, 30c Frequency response calculation unit 31 Channel Estimation Unit 32 Channel Equalization Unit 33 Deinterleaving Section 34. Career Recovery Department 35 Carrier Modulation Section 36 Interleaving Section 37 Division part 38 Error Correction and Decoding Unit 39 Error Correction Encoding Unit 40. Delay Profile Calculation Unit 41 Normalization section 42 Subtraction Unit 43 IFFT section 44. First threshold processing unit 45 Multiplication section 46 Addition section 47. Second Threshold Processing Unit 48 Leakage Processing Unit 49 Delay section 50 FFT section 51 Multiplication part 60 Replica generation unit 61 Pilot insertion section 62 IFFT section 63 GI Addition Part 64 FIR section 70 Replica removal section 71 Delay section 72 Subtraction Unit 411 Sum Calculation Unit 412 Multiplication part 413 Division part 421 Sign calculation unit 422 Absolute Value Calculation Unit 423 First Multiplication Section 424 Comparison Section 425 Second Multiplication Section 426 Subtraction Unit 441 Amplitude Calculation Unit 442 Maximum value calculation unit 443 Multiplication part 444 Comparison Section 445 Switching section 471 Amplitude Calculation Unit 472 Comparison Section 473 Switching section 481 Real part extraction unit 482 Imaginary part extraction part 483 First Real Number Leakage Processing Unit 484 Second Real Number Leakage Processing Unit 485 Complex Number Construction Section

Claims

1. A frequency characteristics calculation unit that calculates the frequency characteristics of the received signal, It includes a delay profile calculation unit that calculates a delay profile in the time domain, The aforementioned delay profile calculation unit, An FFT unit that generates a feedback signal by converting the aforementioned delay profile into the frequency domain, An IFFT unit that converts the error signal of the frequency characteristics and the feedback signal into the time domain, A first threshold processing unit that sets to zero any error signals in the time domain whose amplitude is less than or equal to a first threshold, An adder unit updates the delay profile by adding the signal processed by the first threshold processing unit to the delay profile, A delay profile measuring device having the following features.

2. The aforementioned delay profile calculation unit, A normalization unit calculates the average value of the frequency characteristics and performs a normalization process by dividing the frequency characteristics by the average value, A multiplication unit that multiplies the delay profile by the average value, A delay profile measuring device according to claim 1, having the following features.

3. The aforementioned delay profile calculation unit, A second threshold processing unit, which reduces the signals with amplitudes below the second threshold to zero among the delay profiles updated by the summing unit, A delay profile measuring device according to claim 1, having the following features.

4. The aforementioned delay profile calculation unit, The leakage processing unit reduces the absolute value of the signal processed by the second threshold processing unit by adding or subtracting a small positive amount. A delay profile measuring device according to claim 3, having the following features.

5. The frequency characteristic calculation unit is, The delay profile measuring device according to claim 1, wherein the frequency characteristics are calculated by performing channel equalization, carrier demodulation, and carrier modulation on the frequency domain signal obtained by converting the received signal into the frequency domain, and dividing the frequency domain signal by the carrier-modulated signal.

6. The frequency characteristic calculation unit is, The delay profile measuring device according to claim 1, wherein channel equalization, carrier demodulation, error correction decoding, error correction coding, and carrier modulation are performed on the frequency domain signal obtained by converting the received signal to the frequency domain, and the frequency characteristics are calculated by dividing the frequency domain signal by the carrier-modulated signal.

7. The delay profile measuring device according to claim 5, A replica generation unit generates a replica signal by inserting a pilot signal into the carrier-modulated signal to convert it to the time domain, adding a guard interval, and then applying a filter to the time domain signal using the delay profile calculated by the delay profile calculation unit as the filter coefficient. A replica removal unit that subtracts the replica signal from the delayed received signal, A signal cancellation device equipped with the following features.

8. The delay profile measuring device according to claim 6, A replica generation unit generates a replica signal by inserting a pilot signal into the carrier-modulated signal to convert it to the time domain, adding a guard interval, and then applying a filter to the time domain signal using the delay profile calculated by the delay profile calculation unit as the filter coefficient. A replica removal unit that subtracts the replica signal from the delayed received signal, A signal cancellation device equipped with the following features.

9. A program for causing a computer to function as a delay profile measuring device according to claim 1.

10. A program for causing a computer to function as a signal cancellation device according to claim 7 or 8.

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