JP2010045431A - Transmission path response estimator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission path response estimator for improving estimation precision in a transmission path response. <P>SOLUTION: The transmission path response estimator is used by a receiver of a radio system for receiving a signal of which a frame is disposed continuously or discontinuously, where a known pattern in which a specified code sequence is extended cyclically, is inserted periodically. The transmission path response estimator includes: a correlator 1 for calculating time correlation between a reception signal and the known pattern; a delay profile estimator 2 for generating a delay profile of the reception signal including one delay wave or more by recording time correlations in time series; an image path discrimination circuit 3 for identifying time position of pseudo delay waves in the delay profile; an image replica generator 4 for generating a pseudo replica to the delay waves in the delay profile; and a subtractor 5 for subtracting the pseudo replica from the delay profile. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a channel response estimator, and more particularly to a channel response estimator used for a receiver of a wireless system having a frame configuration in which a specific known pattern in which a code sequence is cyclically extended is periodically inserted.

  Generally, in a communication / broadcasting system using radio, a radio signal transmitted from a transmitter / broadcast station is reflected, scattered, or diffracted by terrain or a feature while reaching a receiver. A signal waveform may be distorted by combining a plurality of radio waves with each other. This phenomenon is generally called multipath. Note that the path followed by the transmission signal when this multipath occurs is called a multipath transmission path.

  Therefore, the receiver performs processing (equalization processing) for extracting the original waveform of the radio signal transmitted from the transmitting station / broadcasting station from the received signal whose waveform is distorted. The equalization processing is often performed by digital signal processing, and it is important to accurately estimate the distortion component received from the multipath transmission path.

  In general, the distortion component generated in a multipath transmission line becomes a filter response when an impulse is used as an input signal, and a transmission line impulse response (delay profile) that represents propagation delay, intensity attenuation, and phase rotation of each path in the time domain. ) Or frequency characteristics of intensity and phase in the frequency domain, and can be expressed using a transmission line frequency response. Therefore, the accuracy of the equivalent processing of signal distortion in the receiver largely depends on the estimation accuracy of these transmission line responses.

  Conventionally, as a channel response estimator in a receiver of a wireless system, there is one that calculates a complex time correlation between a received signal and a reference signal that is a known signal sequence, and calculates a delay profile by arranging these in time series. It is known (for example, refer nonpatent literature 1).

  However, the conventional channel response estimator cannot identify only the path that actually arrives for the received signal having the frame structure in which the unique word is inserted because the image path is generated in the delay profile. There was a problem that the estimation accuracy of the road response was significantly deteriorated.

  In order to avoid the detection of an image path, a transmission path response estimator that estimates a transmission path response in the frequency domain instead of obtaining a correlation in the time domain has been proposed (for example, Non-Patent Document 2). reference).

The above-described transmission path response estimator can realize equalization in the frequency domain without being conscious of the existence of an image path. However, when the PN sequence is long or when the delay time due to multipath is long, FFT and IFFT with a large number of points are required, which causes a problem that the circuit scale becomes very large.
Takuro Sato, “From Basics to Applications of CDMA Technology”, Realize Inc., Chapter 1, Section 1.11 Zhixing Yang, etc., “Channel estimation of DMB-T,” IEEE International conference on Communications, Circuits and Systems 2002, June 2002, vol.2, pp.1069-1072

  The present invention has been made in view of the above points, and an object of the present invention is to provide a transmission path response estimator that can improve the estimation accuracy of the transmission path response.

  A channel response estimator according to an aspect of the present invention receives a signal in which frames having a configuration in which a known pattern signal obtained by cyclically extending a specific code sequence is periodically inserted are arranged continuously or intermittently. A channel response estimator used in a receiver of a wireless system, wherein a correlation unit that calculates a time correlation between the signal and the known pattern signal, and the time correlation is recorded in time series, and one or more A delay profile estimation unit that generates a delay profile of the signal including a delay wave, an identification unit that identifies a time position of a pseudo delay wave based on a partial correlation between the received signal and the known pattern signal in the delay profile, and In the delay profile, a pseudo replica generation unit that generates a pseudo replica for the delayed wave, and subtracts the pseudo replica from the delay profile Similar to the delay wave removal unit, characterized by comprising a.

  The estimation accuracy of the transmission line response can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
First, the configuration of a transmission path response estimator according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic block diagram for explaining the configuration of a transmission path response estimator according to the first embodiment of the present invention.

  As shown in FIG. 1, the transmission path response estimator according to the first embodiment of the present invention includes a correlator 1 that calculates a complex time correlation between a received signal and a reference signal, and delays the calculated correlation value. A delay profile estimator 2 that records every time and calculates a delay profile h (τ), and an image path identification as an identification unit that identifies a time position of an image path that is a pseudo correlation peak from the delay profile h (τ). 3, an image replica generator 4 as a pseudo replica generation unit that generates a replica signal p (τ) of an image path, and a pseudo delay wave removal by subtracting the replica signal p (τ) from the delay profile h (τ) And a subtractor 5 as a part.

  A method of generating a true delay profile by removing an image path from the delay profile h (τ) in the transmission path response estimator configured as described above will be described. First, the configuration of a cyclically expanded unique word that is a reference signal will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating the configuration of a frame having a cyclically expanded unique word.

  As shown in FIG. 2, the unique word 10 includes a prefix code 101 (for example, 82 bits), a PN sequence 102 (for example, 255 bits) that is a specific code sequence, and a suffix code 103 (for example, 83 bits). Yes. Since the length of the unique word can be expressed as the sum of the lengths of these codes, for example, 82 + 255 + 83 = 420 bits. Here, the front code 101 is composed of the same code string as the end area 102c (for example, 82 bits) of the PN sequence, and the post code 103 is composed of the same code string as the head area 102a (for example, 83 bits) of the PN sequence.

  Next, in a received signal having a configuration in which a unique word periodically inserted as shown in FIG. 2 is arranged continuously or intermittently, an image path is removed from the delay profile h (τ) and the result is true. A method for estimating the delay profile will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 is a schematic diagram for explaining the transition of the estimated delay profile in the transmission line response estimator according to the first embodiment of the present invention. 3, the vertical axis represents the signal (complex) amplitude, and the horizontal axis τ represents the delay time. FIG. 3 shows only the time positions of the delay path and the image path, and FIG. 4 is a flowchart for explaining a procedure for removing the image path from the delay profile.

  First, in step S1, the correlation value between the received signal and the reference signal calculated in the correlator 1 is stored in a memory or the like for each delay time in the delay profile estimator 2 to generate a delay profile h (τ).

As shown in FIG. 3A, the true delay profile includes three delay paths a ₁ , a ₂ , and a ₃ . On the other hand, the delay profile h (τ) generated by the delay profile estimator 2 in step S1 has five delay paths b ₁ , b ₂ , b ₃ , b ₄ as shown in FIG. , and a _{b 5.}

  As shown in FIG. 2, in the unique word, the prefix code 101 and the end region 102c of the PN sequence are the same code sequence, and the start region 102a of the PN sequence and the post code 103 are configured by the same code sequence. . That is, in the received signal and the reference signal, the partial correlation is obtained at the time when the prefix code 101 and the end region 102c of the PN sequence overlap each other and at the time when the head region 102a of the PN sequence overlaps the postcode 103. The resulting image path is generated.

  In other words, no image path is generated in the intermediate region 102b of the PN region. Therefore, a time region (for example, a time region of 0 <= t <165) from the head of the prefix code 101 to the tail of the PN sequence head region 102a, and the head of the PN sequence tail region 102c to the tail of the postcode 103 Since the image path is generated only for the time region up to (for example, the time region of 255 <= t <420), the image path is removed only for this time region.

  In the following description, the profile of the time region from the beginning of the prefix code 101 to the end of the beginning region 102a of the PN sequence is A (t), and from the beginning of the tail region 102c of the PN sequence to the end of the suffix code 103 The time domain profile is denoted by B (t). A time domain profile corresponding to the intermediate area 102b of the PN sequence is denoted as X (t).

Next, in step S2, in the delay profile h (τ) obtained in step S1, the delay paths b ₁ and b ₂ existing in A (t) are identified by the image path discriminator 3, and these two For the delay paths b ₁ and b ₂ , the replica signal b (τ) is generated in the image replica generator 4.

  Specifically, the generation of the replica signal b (τ) is performed by calculating the autocorrelation characteristics of the PN sequence in advance and using the autocorrelation coefficient (Cacor) for the image path as a delay profile for which the replica signal is to be generated. Obtained by multiplying.

That is, a replica signal having _two paths c ₁ and c ₂ of b (t) is generated by A (t) × Cacor as shown in FIG. The path c ₁ is a replica of the delay path b ₁ , and the path c ₂ is a replica of the delay path b ₂ . Further, in FIG. 3C, the two generated replicas (paths c ₁ and c ₂ ) are shown with opposite signs. (Similarly, in the subsequent drawings, the generated replicas are shown with the signs reversed.)
Next, in step S3, the replica signal b (τ) generated in step S2 is subtracted from B (t) of the delay profile h (τ). Then, as shown in FIG. 3D, the delay path b ₄ is removed by the path c ₁ generated as a replica. That is, the delay path b ₄ is estimated to be the image path delay path b _1. On the other hand, the path c ₂ generated as a replica remains as a delay path c ₂ ′ because there is no delay path to be subtracted at the same time. A profile of the B (t) region after removing the image path by subtracting the replica signal b (τ) is newly set as B ′ (t).

Subsequently, in step S4, B'obtained in step S3 the delay path exists in the _{(t) b 5, c 2} ' identified in image path discriminator 3, these two delay path _b 5, c _With respect to ₂ ′, the image replica generator 4 generates a replica signal a (τ). That is, a replica signal a (τ) having two paths c ₃ and c ₄ of a (t) is generated by B ′ (t) × Cacor as shown in FIG. The path c ₃ is a replica of the delay path b ₅ and the path c ₄ is a replica of the delay path c ₂ ′.

Next, in step S5, the replica signal a (τ) generated in step S4 is subtracted from A (t) of the delay profile h (τ). Then, as shown in FIG. 3F, the delay path b ₂ is removed by the path c ₃ generated as a replica. That is, the delay path b ₂ is estimated to be image path delay path b _5. On the other hand, the path c ₄ generated as a replica remains as a delay path c ₄ ′ because there is no delay path to be subtracted at the same time. A profile of the A (t) region after the image path is removed by subtracting the replica signal a (τ) is newly set as A ′ (t).

  Finally, by combining the profile A ′ (t), the profile X (t) obtained in step S5, and the profile B ′ (t) obtained in step S3, the delay profile after image path removal is obtained. Obtain (step S6).

In order to reduce the influence of the cross-correlation noise, a path below a predetermined threshold Th1 (for example, −20 dB of the maximum delay path power) that is set in advance is replaced with zero for the combined delay profile. Good. By adding this process, by setting an appropriate threshold, the case of FIG. 3, can be replaced 3 (f) delay paths c ₂ in _', c _4' to zero, and finally, The same profile as the true delay profile shown in FIG.

  As described above, in the present embodiment, for the delay profile obtained from the received signal and the reference signal, a replica of the profile in the delay time region where the image path occurs is generated, and the replica is subtracted from the previous delay profile. Since the image path can be removed to obtain a profile substantially equal to the true delay profile, the estimation accuracy of the transmission path response can be improved.

  Also, by using a delay profile with improved estimation accuracy, it is possible to improve equalization performance when there are multipaths. Furthermore, when determining the frame synchronization of the received signal at the peak position of the delay profile, it is possible to pull in the synchronization with high accuracy and high speed. Furthermore, by using a delay profile with high estimation accuracy, there is an advantage that stability is improved even when tracking clock synchronization or frame synchronization.

  In this embodiment, image path identification / detection and replica generation / removal are repeated, but the delay profile has already been estimated from the previously processed frame, and the position and strength of the image path are If it is known, replica generation / removal may be simultaneously performed on all image paths existing in the delay profile. By parallelizing the image path removal processing, it is possible to shorten the calculation time until the final delay profile is estimated.

  Further, as a reference signal, it is preferable to use the entire unique word (eg, 420 bits) in order to increase the noise resistance of the correlation result, but for example, a PN sequence (eg, 255 bits) or a partial sequence of the PN sequence may be used. .

  Furthermore, in this embodiment, in step S1, the delay profile estimator 2 stores all the correlation peak sequences output from the correlator 1 and outputs them as a delay profile h (τ). Only the path may be extracted. For example, a predetermined threshold value Th2 may be set in advance, and only a path having power greater than or equal to the threshold value Th2 may be extracted and output as a delay profile h (τ).

  That is, when multipath equalization processing is performed based on the delay profile, only paths having power levels that affect reception quality are extracted, and other paths are excluded from the delay profile in advance. This threshold Th2 is determined by, for example, the modulation scheme, coding rate, required error rate, multipath distortion level, and the like. By using the delay profile formed by extracting only significant paths, the processing after step S2 can be performed, so that the amount of memory used and the amount of calculation can be reduced, and the processing time can be shortened.

  A method of eliminating paths other than a significant path (true delay path) from all paths existing in the delay profile h (τ) in the process of estimating the true delay profile as well as after step S1. A modification of the first embodiment will be described below.

  A modification of the transmission path response estimator of the present embodiment will be described with reference to FIGS. FIG. 5 is a schematic diagram for explaining the transition of the estimated delay profile in the transmission path response estimator according to the modification of the first embodiment of the present invention. 5, the vertical axis represents the signal (complex) amplitude, and the horizontal axis τ represents the delay time. FIG. 6 is a flowchart illustrating a procedure for removing an image path from the delay profile.

  In the following description, the same constituent elements and the same procedures as those of the first embodiment described with reference to FIGS. 1 to 4 are denoted by the same reference numerals, and the description thereof is omitted. The frame structure of the received signal and the structure of the unique word used for the reference signal are the same as those in the first embodiment described with reference to FIG.

First, a delay profile h (τ) is generated. (Step S1; see FIG. 5A) In the subsequent step S2 ′, the delay paths b ₁ and b ₂ existing in A (t) in the delay profile h (τ) obtained in step S1 are identified as image paths. The unit 3 discriminates and compares these two delay paths b ₁ and b ₂ with a predetermined threshold value Th ₂ set in advance. As described above, the threshold Th2 is a value determined by, for example, a modulation scheme, a coding rate, a required error rate, a degree of multipath distortion, and the like. As a result of comparison, the replica signal b ′ (τ) is generated in the image replica generator 4 only for the path determined to be equal to or greater than the threshold Th2 (delay path b _{1 in} the case of FIG. 5) (FIG. 5B). reference).

Next, in step S3, the replica signal b ′ (τ) generated in step S2 ′ is subtracted from B (t) of the delay profile h (τ). Then, as shown in FIG. 5C, the delay path b ₄ is removed by the path c ₁ generated as a replica. That is, the delay path b ₄ is estimated to be an image path of the delay path b ₁ . A profile of the B (t) region after the image path is removed by subtracting the replica signal b ′ (τ) is newly set as B ″ (t).

  Subsequently, in step S31, it is determined whether or not a path having a threshold value Th3 (for example, −10 dB of the maximum delay path power) or more exists in B ″ (t). If not present in B ″ (t), the process proceeds to step S6, and the image path removal is performed by combining the profile A (t), the profile X (t), and the profile B ″ (t) obtained in step S3. Get a later delay profile.

As shown in FIG. 5 (d), since the delay path _{b 5} is the threshold Th3 or more, step S31 odor, it is determined that the threshold Th3 or more paths exist B "(t). In this case, Proceeding to step S4 ′, the replica signal a ′ (τ) is generated in the image replica generator 4 only for the path of the threshold Th3 or more among the delay paths existing in B ″ (t) obtained in step S3. That is, in FIG. 5D, a replica is generated in the image replica generator 4 with respect to the delay path b ₅ existing in B ″ (t) (see FIG. 5E).

Next, in step S5 ′, the replica signal a ′ (τ) generated in step S4 ′ is subtracted from A (t) of the delay profile h (τ). Then, the delay path b ₂ is removed by the path c ₃ generated as a replica. That is, the delay path b ₂ is estimated to be image path delay path b _5. A profile of the A (t) region after the image path is removed by subtracting the replica signal a ′ (τ) is newly set as A ″ (t).

  Finally, the process proceeds to step S6, and the image path is obtained by combining the profile A ″ (t), the profile X (t) obtained in step S5 ′, and the profile B ″ (t) obtained in step S3. A delay profile after removal is obtained (see FIG. 5F).

  In the above-described modification, since a replica is generated by selecting a significant path in the process of estimating a true delay profile, it is possible to prevent a replica from being generated from noise and an image path, and Response estimation accuracy can be improved.

It can be seen that the configuration of the present application is more effective in comparison with a conventional transmission path response estimator. The conventional transmission path response estimator stores the result of the following equation (1) in a memory and outputs it as a delay profile in time series, where r (t) is a received signal and c (t) is a reference signal. To do.

In Equation (1), Ts indicates the sequence length of the reference signal c (t). The integration of equation (1) can be transformed into the following equation (2) in the discrete-time digital signal domain.

  In the equation (2), Δt indicates a sample interval. Therefore, the expression (2) can be realized by hardware using an FIR filter with an N-tap delay line. In general, in a CDMA (Code Division Multiple Access) system or a wireless system including a specific known pattern, hardware is realized by a sliding correlator or a matched filter.

  On the other hand, depending on the radio system, a specific code sequence (for example, a PN (Pseudo random noise) sequence) is cyclically expanded before and after a specific code sequence that includes a cyclic prefix and a cyclic postfix. May be inserted periodically. (Hereinafter, such a known pattern is referred to as a unique word.) That is, in a unique word, the same code string is included in the prefix code and the end area of the PN sequence, and the prefix code and the start area of the PN sequence are included. The same code string is included.

  Here, if a signal frame is composed of a unique word and a frame body, and frames having the same structure are arranged continuously or intermittently, a conventional transmission line response as shown in Non-Patent Document 1 described above. When a delay profile is calculated by obtaining a correlation between a received signal and a reference signal (unique word) using an estimator, pseudo peaks (hereinafter referred to as images) due to these partial correlations at times other than the time when a true delay path exists. Will be generated).

  That is, the time when the prefix code of the unique word included in the received signal and the end area of the PN area included in the reference signal overlap, the end area of the PN area included in the received signal and the front of the unique word included in the reference signal The time at which the code overlaps, the time at which the postfix code of the unique word included in the received signal overlaps the head area of the PN area included in the reference signal, and the head area and reference of the PN area included in the received signal An image pass occurs at the time when the postfix code of the unique word included in the signal overlaps.

  As described above, the transmission path response estimator cannot identify only a path that actually arrives for a received signal having a frame structure in which a unique word is inserted, because an image path is generated in the delay profile. There was a problem that the estimation accuracy of the road response was significantly deteriorated. This problem is solved in the present application.

  In order to avoid the detection of an image path, a transmission path response estimator that estimates a transmission path response in the frequency domain, instead of obtaining a correlation in the time domain, is used.

In this transmission path response estimator, since the received signal is a convolution of the PN sequence and the transmission path impulse response, the received signal converted to the frequency domain is converted to the time domain again by dividing by the known PN sequence. Thus, a transmission path impulse response can be obtained (see the following equation (3)).

  The above-described transmission path response estimator can realize equalization in the frequency domain without being conscious of the existence of an image path. However, when the PN sequence is long or when the delay time due to multipath is long, FFT and IFFT with a large number of points are necessary, and the circuit scale becomes very large. This problem is also solved in the present application.

(Second Embodiment)
Next, the configuration of a transmission path response estimator according to the second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic block diagram illustrating the configuration of a transmission path response estimator according to the second embodiment of the present invention.

  In the first embodiment, an image path is detected by creating one delay profile from a received signal and one type of reference signal. On the other hand, in the present embodiment, two types of delay profiles are created for received signals using two different types of reference signals a and b, and an image path is detected using these differences. Different.

  As in the first embodiment, the reference signal a is composed of the entire unique word including the code cyclic unit (the prefix code 101, the PN sequence start area 102a, the PN sequence end area 102c, and the postcode 103). Has been. Since the code length is long, the estimation accuracy of the delay profile is high, but the estimation result includes an image path. On the other hand, the reference signal b is composed only of a portion obtained by removing the code cyclic part from the unique word, that is, only the intermediate region 102b of the PN sequence. Since the code length is short, the estimation accuracy of the delay profile is rough, and the noise floor of the cross-correlation varies greatly, but the image path is not included.

  Based on these characteristics, the transmission path response estimator of the present embodiment detects an image path based on the difference between both delay profiles, and the image is obtained from the delay profile obtained as a correlation result between the reference signal a and the received signal. Eliminate the path.

  As shown in FIG. 7, the transmission path response estimator according to the second embodiment of the present invention is calculated with the first correlator 11a that calculates the complex time correlation between the received signal and the reference signal a. And a first delay profile estimator 12a for calculating a delay profile h1 (τ) by recording a correlation value for each delay time. Also, a second correlator 11b for calculating a complex time correlation between the received signal and the reference signal b, and a second delay for calculating the delay profile h2 (τ) by recording the calculated correlation value for each delay time. It also has a profile estimator 12b.

  The delay profile h1 (τ) and the delay profile h2 (τ) are input to the peak comparator 13, and the peak position is compared with the power value (see FIG. 8). FIG. 8 is a diagram illustrating a difference between the delay profile h1 (τ) and the delay profile h2 (τ). In FIG. 8, the horizontal axis represents the delay time, and the vertical axis represents the correlation power.

  In FIG. 8, the delay profile h1 (τ) generated from the correlation result with the received signal with the entire unique word as the reference signal a is indicated by a dotted line as the profile 201a, and the portion obtained by removing the code cyclic part from the unique word is referred to. The delay profile h2 (τ) generated from the correlation result with the received signal as the signal b is indicated by a solid line as the profile 201b.

As shown in FIG. 8, in the profile 201a, the correlation power level is almost zero except for the three peak positions of the paths d ₁ , d ₂ , and d ₃ . On the other hand, although the profile 201b has a certain correlation power level as a whole due to the influence of noise, two peak positions of the paths d ₁ and d ₂ are detected.

Now comparing the profiles 201a and profile 201b by paying attention to the peak position, the path _{d 3} is detected only in the profile 201a. As described above, the profile 201a would be detected image path in addition to the true delay path, since only true delay path is detected in the profile 201b, the path d ₃ and an image path estimation can do.

More specifically, the image path is estimated by the image path discriminator 14. That is, the power difference D (τ) between the two delay profiles h1 (τ) and h2 (τ) input from the peak comparator 13 is obtained (see the following formula (4)), and is set in advance as D (τ). The predetermined threshold Th4 is compared, and it is determined that an image path exists at time τ when D (τ)> Th4.

The threshold Th4, for example, the maximum power path in the delay profile h1 (tau) (e.g., the path _{d 2} in FIG. 8) is -10dB of being set. In this way, by comparing the power difference and the threshold Th4, it is possible to estimate the image path without overlooking the true delay path and image path that are not buried in the cross-correlation noise floor.

  Using the image path estimated by the image path discriminator 14, the image replica generator 15 generates an image path replica signal in the same manner as in the first embodiment, and the subtractor 16 determines the delay profile h1 (τ). By subtracting the generated replica signal, a delay profile after image path removal is obtained.

  Thus, in the present embodiment, two types of reference signals are used, that is, a reference signal a configured from the entire unique word and a reference signal b configured from a portion obtained by removing the code cyclic unit from the unique word. By comparing two types of delay profiles obtained from the reference signal and the received signal, the detection accuracy of the image path can be further improved, and the estimation accuracy of the transmission path response is improved. Even when the delay times of the image path and the true delay path coincide, the image path component can be detected accurately.

  As a modification of the second embodiment, a transmission path response estimator having the configuration shown in FIG. 9 can be considered. FIG. 9 is a schematic block diagram illustrating the configuration of a transmission path response estimator according to a modification of the second embodiment of the present invention.

  In the second embodiment described above, the reference signals a and b are input to the two correlators 11a and 11b, respectively, and the complex time correlation with the received signal is calculated. In the modification shown in FIG. By controlling the correlation integration interval calculated by the correlator 11 ′ by the gate signal generated by the gate circuit 17, the delay profile h 1 (τ) and the delay profile h 2 (τ) are simultaneously calculated from one correlator 11 ′. Then, the respective calculation results are output to the first delay profile estimator 12a and the second delay profile estimator 12b.

  The correlator 11 ′ has a configuration shown in FIG. 10, for example. FIG. 10 is a schematic circuit diagram illustrating the configuration of the correlator 11 ′. That is, the received signal is input to shift registers 1001a to 1001 (N-1), and complex multiplication of each tap output and the reference signal sequence {C1, C2, C3,..., CN} is performed by adders 1002a to 1002N, respectively. Are added by adders 1003a to 1003 (N-1).

  With the configuration as shown in FIG. 10, all the multiplier outputs and the adder outputs are used for the delay profile h1 (τ), and the multiplier outputs and adders at the necessary locations are used for the delay profile h2 (τ). The output can be extracted and used.

  Thus, the circuit scale can be reduced by sharing the correlator 11 ′ for calculating the complex time correlation between the reference signal and the received signal and controlling the timing of taking out the correlation output by the gate circuit 17.

(Third embodiment)
Next, the configuration of a transmission path response estimator according to the third embodiment of the present invention will be described with reference to FIG. FIG. 11 is a schematic block diagram illustrating the configuration of a transmission path response estimator according to the third embodiment of the present invention.

  In the first embodiment, a replica is generated with respect to a path having a delay time at which a delay path is detected, and the image path is removed by subtracting this from the delay profile. On the other hand, in the present embodiment, the position of the image path (delay time) is identified with respect to the path of the delay time at which the delay path is detected, and the image path is removed by replacing the time profile with zero. Is different.

  In an environment where the delay spread is small, there is no true delay path with high power at the position of the delay time at which the image path occurs. Therefore, in such an environment, a correlation peak appearing there can be recognized as an image path. The transmission path response estimator of the present embodiment is applicable to such an environment. In the following description, the same components as those in the transmission path response estimator according to the first embodiment shown in FIG.

  As shown in FIG. 11, the transmission path response estimator according to the third embodiment of the present invention includes an image replica generator 4 for generating an image path replica signal, and a replica signal from a delay profile h (τ). Instead of the subtracter 5 to be subtracted, a path replacer 21 as a replacement unit is provided.

  That is, the correlator 1 calculates the complex time correlation between the received signal and the reference signal, and the delay profile estimator 2 records the calculation result for each delay time to obtain the delay profile h (τ). In the subsequent image path discriminator 3, the position (delay time) of the image path in the delay profile h (τ) is identified, and the signal value at that time in the delay profile h (τ) is replaced with zero by the path replacer 21. The final delay profile after image path removal is obtained.

  As described above, in this embodiment, since the signal value at the time when the image path is detected is replaced with zero, a circuit for replica generation becomes unnecessary, the circuit configuration is easy, and the circuit scale and consumption are reduced. Electric power can be reduced.

  In addition, the estimation accuracy of paths with relatively high power is degraded due to the effects of thermal noise and various distortions (phase noise, frequency offset, IQ imbalance, etc.) generated in the analog front end and clock shift of the digital part. If the image path replica is generated using this result, an error may be artificially added rather than removing the image path for error propagation. In such a case, it is possible to prevent deterioration of the estimation accuracy of the delay profile by directly replacing the signal at the time when the image path is identified with zero.

  Note that the concept of the present embodiment can also be applied to the transmission path response estimator of the second embodiment. That is, as shown in FIG. 12, after the image path is detected by the peak comparator 13 and the image path discriminator 14 using the difference between the outputs of the two types of correlators 11a and 11b, the image path is replaced by the path replacer 21. The signal at the detection time is replaced with zero. FIG. 12 is a schematic block diagram illustrating the configuration of a transmission path response estimator according to a modification of the third embodiment of the present invention. With such a configuration, the position of the image path can be specified more accurately, and the image path can be removed by signal zero replacement, and the estimation accuracy can be prevented from being deteriorated with a simple configuration.

  Further, when the concept is further expanded, a channel response estimator having a configuration including both an image replica generator and a path replacer can be considered. That is, according to the estimation result of the delay profile estimator and the identification result of the image path discriminator, if the maximum delay time of a significant path is shorter than the predetermined image path occurrence time, the image path is Replace with zero. Conversely, if the maximum delay time of a significant path is longer than a predetermined image path generation time, an image path replica is generated and removed using an image replica generator. In this way, either the image replica generator or the path replacer can be used by switching according to the situation.

  In all the embodiments of the transmission path response estimator of the present invention, in an environment where the delay spread of the transmission path is large, the amount of leakage of the previous frame signal delayed into the unique word portion of the subsequent frame is large. The peak accuracy of the correlator output may be somewhat weakened. In this case, the result of estimating the delay profile of the previous frame using the channel response estimator of the present invention and the signal obtained by remodulating the demodulation result of the frame body (data part) of the previous frame are used to leak to the next frame. By generating a replica of the delayed signal and subtracting the replica of the delayed signal before estimating the delay profile in the next frame, it is possible to prevent institutional degradation of the transmission path response estimation.

  In the above-described three embodiments, a case has been described in which a prefix code and a postcode that are cyclically extended before and after a specific code sequence are included as a frame structure of a unique word. The channel response estimator of the present invention can also be applied to the case of a unique word having a configuration that includes only a prefix code that is cyclically expanded before that. In this case, the appearance range of the image path is limited to the latter half of the delay profile.

  Similarly, the channel response estimator of the present invention can also be applied to the case of a unique word having a configuration including only a specific code sequence and a postcode that is cyclically extended thereafter. In this case, the appearance range of the image path is limited to the first half area of the delay profile.

  Further, although a PN sequence has been described as a specific code sequence, an arbitrary code string having high autocorrelation characteristics and low cross-correlation characteristics may be used as code characteristics.

  Note that the present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the scope of the present invention. In addition, various configurations can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, you may delete some components from all the components shown by the above-mentioned embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined.

1 is a schematic block diagram illustrating a configuration of a transmission path response estimator according to a first embodiment of the present invention. Schematic explaining the structure of the frame which has the unique word extended cyclically. Schematic explaining transition of the estimated delay profile in the transmission line response estimator according to the first embodiment of the present invention. 9 is a flowchart for explaining a procedure for removing an image path from a delay profile. Schematic explaining transition of the delay profile estimated in the transmission line response estimator concerning the modification of the 1st Embodiment of this invention. 9 is a flowchart for explaining a procedure for removing an image path from a delay profile. The schematic block diagram explaining the structure of the transmission line response estimator concerning the 2nd Embodiment of this invention. The figure explaining the difference between delay profile h1 (τ) and delay profile h2 (τ). The schematic block diagram explaining the structure of the transmission line response estimator concerning the modification of the 2nd Embodiment of this invention. The schematic circuit diagram explaining the structure of correlator 11 '. Schematic block diagram for explaining the configuration of a transmission path response estimator according to the third embodiment of the present invention The schematic block diagram explaining the structure of the transmission line response estimator concerning the modification of the 3rd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Correlator, 2 ... Delay profile estimator, 3 ... Image path discriminator, 4 ... Image replica generator, 5 ... Subtractor,

Claims (5)

A channel response estimator used in a receiver of a wireless system that receives a signal in which frames having a configuration in which a known pattern signal in which a specific code sequence is cyclically extended is periodically inserted are arranged continuously or intermittently Because
A correlation unit for calculating a time correlation between the signal and the known pattern signal;
A delay profile estimator that records the time correlation in time series and generates a delay profile of the signal including one or more delay waves;
An identification unit for identifying a time position of a pseudo-delay wave by partial correlation between the received signal and the known pattern signal in the delay profile;
In the delay profile, a pseudo replica generation unit that generates a pseudo replica for the delayed wave;
A pseudo-delayed wave removing unit that subtracts the pseudo-replica from the delay profile;
A transmission path response estimator characterized by comprising:   The pseudo replica generation unit identifies the delayed wave having power exceeding a predetermined threshold from the delay profile as a true delayed wave, and generates the pseudo replica for the true delayed wave. Item 2. A channel response estimator according to Item 1. A channel response estimator used in a receiver of a wireless system that receives a signal in which frames having a configuration in which a known pattern signal in which a specific code sequence is cyclically extended is periodically inserted are arranged continuously or intermittently Because
A first correlation unit for calculating a time correlation between the signal and the known pattern signal;
A second correlation unit for calculating a time correlation between the signal and a part of the known pattern signal;
A first delay profile estimator that records the time correlation output from the first correlator in time series and generates a first delay profile of the signal including one or more delayed waves;
A second delay profile estimator that records the time correlation output from the second correlator in a time series and generates a second delay profile of the signal including one or more delayed waves;
A peak comparison unit that compares the position of the delayed wave in the first delay profile with the position of the delayed wave in the second delay profile;
An identification unit for identifying a position of a pseudo delayed wave based on a partial correlation between the received signal and the known pattern signal based on a comparison result in the peak comparison unit;
A pseudo replica generation unit that generates a pseudo replica for the delayed wave in the first delay profile;
A pseudo-delayed wave removing unit that subtracts the pseudo-replica from the first delay profile;
A transmission path response estimator characterized by comprising:   The identification unit calculates a difference between the first delay profile and the second delay profile for each time, and identifies that a pseudo delay wave exists at a time position where the difference exceeds a predetermined threshold. The transmission line transponder according to claim 3, wherein A channel response estimator used in a receiver of a wireless system that receives a signal in which frames having a configuration in which a known pattern signal in which a specific code sequence is cyclically extended is periodically inserted are arranged continuously or intermittently Because
A correlation unit for calculating a time correlation between the signal and the known pattern signal;
A delay profile estimator that records the time correlation in time series and generates a delay profile of the signal including one or more delay waves;
An identification unit for identifying a time position of a pseudo-delay wave by partial correlation between the received signal and the known pattern signal in the delay profile;
In the delay profile, a replacement unit that replaces the signal value at the time position of the pseudo delay wave with zero;
A transmission path response estimator characterized by comprising:

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