JP2016158048A - Frequency off set estimation apparatus and radio communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency off set estimation apparatus capable of capturing a carrier wave by adaptively optimizing estimated performance of offset and exactly estimating a frequency offset.SOLUTION: The frequency off set estimation apparatus receives a signal transmitted from transmission side at a fixed unique word interval, sequentially changes a correlation length among a group of predetermined values, executes erroneous detection by a CRC code, and identifies a correlation length used for estimation of a frequency offset in such a range as to set a transmission error at not more than a predetermined value according to a result of error detection.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a radio communication apparatus, and more particularly to a technique for detecting a frequency offset for carrier wave recovery.

  In wireless communication devices, there is a deviation between the frequency on the transmission device side and the frequency on the reception device side, and it is known that the bit error rate (BER) characteristics deteriorate due to the influence of this frequency deviation. Therefore, the receiving-side demodulator removes the frequency deviation between transmission and reception by an automatic frequency control (AFC) circuit or the like. Similarly, there is a phase error or phase shift between transmission and reception, and the demodulator removes the phase error by a carrier recovery (CR) circuit or the like.

  The AFC circuit constitutes an AFC loop composed of a phase rotator, a frequency discriminator, and a voltage controlled oscillator (local oscillator), and the frequency discriminating circuit obtains a frequency deviation component from the received modulation signal frequency-converted to the baseband band, A voltage controlled oscillator (VCO) generates an AFC reference signal having a frequency corresponding to the frequency deviation component, and a phase rotator performs phase rotation corresponding to the frequency deviation from the received modulation signal using the AFC reference signal. The frequency deviation component is to be removed.

  In such an AFC circuit, Patent Document 1 discloses a technique capable of detecting a synchronous / asynchronous state of the circuit and automatically establishing synchronization when the circuit is in an asynchronous state.

  Further, in Patent Document 2, in a wireless communication such as satellite communication or mobile communication, in a demodulation circuit that realizes synchronous detection, the AFC circuit and the CR circuit are converged with a phase error remaining, and in this converged state, The phase error removal circuit detects the remaining phase error by correlating the received modulation signal with the known pattern, and by correcting the detected phase error, the adjustment parameter for the feedback loop is reduced. A technique for simplifying the feedback loop is disclosed.

  On the other hand, in recent years, with the widespread use of wireless communication systems, a shortage of frequency resources has become apparent, especially in the microwave band, and transmission techniques for achieving high frequency utilization efficiency are required. The orthogonal polarization multiplexing technique pays attention to the wavefront direction of a radio wave radiated from an antenna, and transmits independent signals having wavefronts orthogonal to each other at the same frequency.

  When this orthogonal polarization multiplexing technology is applied, V and H polarization multiplexing using vertical (V) polarization and horizontal (H) polarization can be realized in the case of linear polarization used in fixed wireless communication or the like. In this case, the frequency utilization efficiency is doubled compared to the case where the orthogonal polarization multiplexing technique is not applied. The V and H polarization multiplexed signals can be transmitted and received by, for example, arranging two linear radiating elements orthogonally in a cross shape.

  Furthermore, in satellite communication, a polarization multiplexing method is known in which signals are multiplexed on three or more polarizations that are not necessarily orthogonal to improve frequency utilization efficiency (see, for example, Non-Patent Document 1). In this method, a bit is assigned to each polarization, and a signal point is obtained by multiplexing (synthesizing) values obtained by mapping each polarization component before synthesis onto the horizontal (H) / vertical (V) polarization IQ plane. Form. At this time, the signal point arrangement is optimized so that the minimum Euclidean distance between symbols on each polarization of H / V is maximized.

  In such satellite communication, since reception is generally performed with a low S / N ratio, a frequency error (frequency offset) between the transmission side and the reception side is detected and frequency deviation is removed (frequency reproduction). The circuit for performing (processing) is required to have high accuracy even in such a situation. In order to meet such a demand, in Non-Patent Document 2, when the frequency offset is detected based on the correlation of the unique word of a predetermined pattern inserted in the transmission signal, the interval D between the pilot symbols of the unique word is variable. The result of evaluating the bit error rate (BER) and the like is disclosed.

JP 2006-217054 A JP 2009-267714 A

Yafune, Webber, Yano, Ban, Kobayashi, "Proposal of Multi-Polarization Spatial Multiplexing Technology for Satellite Communications", IEICE Technical Report, Vol. 112, No. 191, pp.1-5, Aug. 2012. J. Webber, M. Yofune, K. Yano, H. Ban, and K. Kobayashi, “Performance of frequency recovery algorithms for a poly-polarization multiplexing satellite system”, 11th IEEE Malaysia International Conference on Communications (MICC2013), 27- 29th Nov. 2013.

  In general, if the interval D between the pilot symbols of the unique word is increased, the frequency offset can be estimated with a smaller number of frames (shorter acquisition period), but in this case, the range of the frequency offset that can be evaluated becomes narrow. On the other hand, in order to detect a coarse frequency offset, it is necessary to reduce the interval D between pilot symbols of unique words. However, reducing the interval D between the pilot symbols of the unique word causes an increase in the number of frames required for estimating the frequency offset.

  Here, the maximum allowable distance D is limited by an unknown frequency offset. Therefore, it is difficult to know in advance how to set the unique word symbol interval D in a general communication environment.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to adaptively optimize the offset estimation performance and accurately correct the frequency offset in a demodulation circuit that realizes synchronous detection. And providing a frequency offset estimation apparatus capable of capturing a carrier wave and a wireless communication apparatus using the same.

  According to one aspect of the present invention, there is provided a frequency offset estimating device for estimating a frequency offset between a carrier frequency and a local oscillation frequency of a received signal, wherein a plurality of unique words are arranged in each received signal. Including a correlator for calculating a correlation between a plurality of frames and an error detection code and a unique word with a received signal, and the correlator can calculate a correlation with a variable correlation length, Error detection for detecting transmission errors using an error calculation code and an offset calculation unit for calculating the estimated value of the frequency offset by integrating the calculated correlation over the number of frames of the set average frame size And a control unit for controlling the correlator, the offset calculation unit, and the error detection unit, the control unit i) between predetermined unique words And the error is detected by sequentially changing the correlation length among a set of predetermined values, and ii) the transmission error is less than or equal to a predetermined value according to the error detection result. In such a range, the correlation value used for estimating the frequency offset is specified.

  Preferably, the error detection code is provided over a plurality of frames, the error detection unit calculates error information by combining error detection results for the plurality of frames, and the control unit transmits a transmission error based on the error information. Among the correlation lengths corresponding to the frame having the smallest value, the maximum correlation length is specified.

  Preferably, the error detection code is provided over a plurality of frames, the error detection unit calculates error information by combining error detection results for the plurality of frames, and the control unit transmits a transmission error based on the error information. Among the correlation lengths corresponding to the frame having the minimum value, the minimum correlation length is specified.

  Preferably, the apparatus further includes a storage device for storing a correlation value used for calculating the frequency offset, and the control unit sets a correlation length for each frame of the number of received frame average sizes within a set of predetermined values. The correlation values calculated by sequentially changing are stored in the storage device, and the offset calculation unit calculates an estimated value of the frequency offset based on the correlation values stored in the storage device.

  According to another aspect of the present invention, there is provided a wireless communication apparatus for receiving a radio signal including a plurality of frames each having a plurality of unique words and an error detection code, wherein the radio signal is received and detected. For estimating the frequency offset between the carrier frequency of the received signal from the receiving means and the local oscillation frequency, and correcting the frequency error of the received signal based on the estimated frequency offset A carrier frequency reproducing means including a frequency offset estimating means for estimating a frequency offset, and the frequency offset estimating means includes a correlator for calculating a correlation with a received word and a unique word. The correlator can calculate the correlation with variable correlation length, and the calculated correlation is set to the set frame average size. An offset calculation unit for calculating the estimated value of the frequency offset, and an error detection unit for detecting a transmission error by using an error detection code, and a correlator, an offset calculation unit, and The control unit further includes a control unit for controlling the error detection unit. The control unit receives i) a signal transmitted at a predetermined unique word interval at a receiving side, and sets a correlation length among a set of predetermined values. Error detection is performed by sequentially changing, and ii) in accordance with the error detection result, a correlation value used for frequency offset estimation is specified within a range where the transmission error is equal to or less than a predetermined value, and corrected by the carrier frequency recovery means And a decoding means for performing a decoding process on the received signal.

  Preferably, the error detection code is provided over a plurality of frames, the error detection unit calculates error information by combining error detection results for the plurality of frames, and the control unit transmits a transmission error based on the error information. Among the correlation lengths corresponding to the frame having the smallest value, the maximum correlation length is specified.

  Preferably, the error detection code is provided over a plurality of frames, the error detection unit calculates error information by combining error detection results for the plurality of frames, and the control unit transmits a transmission error based on the error information. Among the correlation lengths corresponding to the frame having the minimum value, the minimum correlation length is specified.

  Preferably, the apparatus further includes a storage device for storing a correlation value used for calculating the frequency offset, and the control unit sets a correlation length for each frame of the number of received frame average sizes within a set of predetermined values. The correlation values calculated by sequentially changing are stored in the storage device, and the offset calculation unit calculates an estimated value of the frequency offset based on the correlation values stored in the storage device.

  According to the present invention, in a demodulation circuit that realizes synchronous detection, an optimum correlation length N is selected according to a propagation path state, so that a frequency offset can be adaptively accurately estimated and a carrier wave can be captured. It becomes possible.

It is a functional block diagram for demonstrating the structure of the transmitter 1000 of this Embodiment. It is a functional block diagram for demonstrating the structure of the receiver 2000 of this Embodiment. It is a figure for demonstrating arrangement | positioning of the symbol in a unique word. It is a functional block diagram for demonstrating the structure of the frequency offset estimation apparatus 2070 and the CRC decoding process part 216 in the carrier frequency reproduction | regeneration part 207. FIG. It is a figure which shows the simulation result of the relationship between correlation length N and the largest frequency offset which can be evaluated. It is a figure which shows the example of a different arrangement | positioning of the unique word in the unique word space | interval D and the correlation length N. It is a figure for demonstrating the aspect by which the unique word arrange | positioned by the different unique word space | interval D is arrange | positioned in the flame | frame of a transmission signal. It is a figure for demonstrating arrangement | positioning of the unique word and CRC code | symbol transmitted from a transmission side to a reception side. It is a conceptual diagram which shows evaluation of the adjustable maximum frequency offset at the time of changing the correlation length N adaptively. It is a figure which shows the simulation result of the relationship between bit energy to noise power density ratio Eb / No and bit error rate BER. It is another figure which shows the simulation result of the relationship between bit energy to noise power density ratio Eb / No and bit error rate BER. It is a flowchart for demonstrating the processing flow of adaptive correlation length. It is a figure which shows the relationship between the number of received frames and the remaining frequency offset. It is a conceptual diagram which shows the example of the correlation value stored in a memory | storage device.

  Hereinafter, a radio communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, components and processing steps given the same reference numerals are the same or equivalent, and the description thereof will not be repeated unless necessary.

  As will be described below, the radio communication system according to the present embodiment employs a polarization multiplexing scheme.

  Preferably, in the present embodiment, a communication device in a system that transmits information using two polarized waves is more suitable for use in a system system that does not stand out between transmission and reception, such as satellite communication. is there. Note that a communication device having only the transmission function can be configured to include only the transmission function of the present embodiment, and a communication device having only the reception function can be configured to include only the reception function of the present embodiment. The transceiver can also be configured to have a transmission / reception function.

  In addition, the wireless communication system of the present embodiment is a wireless communication device that simultaneously uses two orthogonal polarizations (which are orthogonal at a realistic level and the cross polarization component need not be 0) for information transmission. It is a target. However, in the transmitter, receiver, and transmitter / receiver of this embodiment, it is possible to temporarily stop the polarization multiplexing communication function as described below and switch to communication using the conventional communication method. It is also possible to configure the system.

  In addition, this embodiment can also be used in a polarization multiplexing system that multiplexes signals with three or more polarizations.

(Configuration of transmitter and receiver)
FIG. 1 is a functional block diagram for explaining the configuration of transmitter 1000 according to the present embodiment.

  Referring to FIG. 1, a transmitter 1000 receives a digital data signal (information bit) to be transmitted, and performs CRC (Cyclic Redundancy Check) encoding for a check calculated from data in order to catch a transmission error. A CRC encoding unit 100 to perform, and an error correction encoding processing unit 101 that performs error correction encoding processing on information bits from the CRC encoding unit 100 and converts them into transmission symbols are provided. In addition to the error correction coding process, an “interleave process” or the like may be executed.

  Transmitter 1000 further includes an S / P converter 102 for serial / parallel conversion (S / P conversion) of symbols to be transmitted, and a transmission symbol converted to a parallel signal in I / Q mapping data storage unit 106. V / H mapping processing for mapping each polarization component of horizontal polarization (H polarization) and vertical polarization (V polarization) to signal points in a signal space diagram (constellation) based on the retained information Unit 104.

  Here, the I component means an in-phase component in quadrature modulation, the Q component means a quadrature phase component in quadrature modulation, and I / Q mapping means I component and Q component. This means that signal points are arranged on a plane stretched by.

  Transmitter 1000 further includes a unique word insertion unit (hereinafter referred to as UW insertion unit) 107a for inserting a unique word into the I / Q component for V polarization from V / H mapping processing unit 104, and V / H. And a UW insertion unit 107b for inserting a unique word into the I / Q component for H polarization from the mapping processing unit 104.

  Transmitter 1000 further includes a quadrature modulation unit 108a that quadrature modulates the I / Q component for the V polarization from UW insertion unit 107a with a corresponding modulation scheme (for example, QPSK modulation scheme), and UW insertion unit 107b. A quadrature modulation unit 108b that quadrature modulates the I / Q component of the H polarization of the signal with a corresponding modulation method (for example, QPSK modulation method), and a D / A for digital / analog conversion of the output of the quadrature modulation unit 108a A conversion unit 110a and a D / A conversion unit 110b for digital / analog conversion of the output of the quadrature modulation unit 108b are provided.

  The output of the D / A conversion unit 110a is amplified by a power amplifier (not shown), subjected to filter processing for suppressing unnecessary frequency components by the transmission filter processing unit 112a, and then transmitted from the vertically polarized antenna 114a. The output of the D / A conversion unit 110b is amplified by a power amplifier (not shown), filtered by the transmission filter processing unit 112b, and then transmitted from the horizontal polarization antenna 114b.

  As will be described later, UW insertion sections 107a and 107b insert unique words into the transmission signal at intervals D of unique word symbols that are known in advance on the transmission side and reception side.

  Hereinafter, the “unique word symbol interval” is simply referred to as “unique word interval”.

  FIG. 2 is a functional block diagram for explaining the configuration of the receiver 2000 of the present embodiment.

  Referring to FIG. 2, receiver 2000 performs a reception filter for filtering a signal amplified by a low-noise amplifier (not shown) of a reception signal from vertical polarization antenna 200a, horizontal polarization antenna 200b, and vertical polarization antenna 200a. A processing unit 202a, a reception filter processing unit 202b for filtering a signal amplified by a low noise amplifier (not shown) from a reception signal from the horizontally polarized antenna 200b, and an analog-to-digital conversion for a signal from the reception filter processing unit 202a An analog-digital conversion unit (A / D conversion unit) 204a and an A / D conversion unit 204b for analog-digital conversion of a signal from the reception filter processing unit 202b are provided.

  Receiver 2000 further includes quadrature detectors 206a and 206b that receive signals from A / D converters 204a and 204b, respectively, and separate I / Q components on the constellation.

  The carrier frequency recovery unit 207 performs estimation of the value of the frequency offset with respect to the local oscillator, as will be described later, with respect to the signal from the quadrature detection unit 206a or the quadrature detection unit 206b. Based on the offset, the input signal is corrected to a state in which the frequency error is close to zero by the same configuration as the AFC circuit described above.

  Subsequently, the received modulation signal whose frequency error has been corrected by the carrier frequency reproducing unit 207 is input to the carrier phase reproducing unit 208. Since the frequency error remains even after correction of the frequency error in the carrier frequency reproduction unit 207, the received symbol point rotates slowly, resulting in deterioration of characteristics. Therefore, the carrier wave phase recovery unit 208 corrects the remaining frequency error (phase error). Carrier wave phase recovery section 208 brings the residual phase error in the received modulated signal after correction close to zero.

  The maximum likelihood determination processing unit 209 calculates the likelihood for a predetermined signal point on the signal space diagram for the signal from the carrier phase reproduction unit 208 based on the mapping information from the I / Q mapping data storage unit 210. Then, maximum likelihood decoding is performed by the MLD (Maximum Likelihood Detection) method. In the MLD method, a metric is calculated using all combinations of transmission signals that can be transmitted from a transmission antenna with respect to a reception signal. Then, a combination of transmission signals that gives the minimum distance is selected.

  The “signal point” refers to a reference position defined on the constellation by the modulation method, and the “symbol” is a unit of information that is modulated on the transmission side and transmitted by the reference clock. Means “sign”.

  The bit information of the transmission signal calculated by the maximum likelihood determination processing unit 209 is subjected to error correction by the error correction decoding processing unit 214 via the P / S conversion unit 212 that performs parallel / serial conversion (P / S conversion). Is output as received data.

  Note that the error correction decoding processing unit 214 may execute convolutional decoding or deinterleaving processing according to the configuration on the transmitter side.

Furthermore, the CRC decoding processing unit 216 performs CRC decoding processing on the received signal, detects whether or not a transmission error has occurred in the combination of the current unique word interval D and the correlation length N, and A frequency offset estimation process in the frequency reproduction unit 207 is controlled.
(Embodiment 1)
FIG. 3 is a diagram for explaining the arrangement of symbols in a unique word.

  In FIG. 3, the symbols are BPSK modulated.

  FIG. 3A is a diagram for explaining a situation where the phase is estimated.

  The received signal is expressed as follows.

Here, zn represents noise.

  At this time, the estimated frequency is expressed as follows.

As shown in FIG. 3A, the phase estimation value θ _iD hat of the unique word position (i-D) (hereinafter, when the symbol “^” is added on the letter X, “X hat” Let us consider a case where the phase estimation value θ _i hat of the unique word position i is obtained based on The estimated value θ _i hat includes additive white Gaussian noise Δe _i . At this time, in FIG. 3 (a), a region which varies by additive white Gaussian noise .DELTA.e _i is indicated by vertical arrows at the unique word position i. As shown in FIG. 3A, the phase estimation error due to noise becomes relatively smaller as the unique word interval D becomes larger, and the influence thereof becomes smaller.

  FIG. 3B shows the symbol position (symbol number) on the horizontal axis when the unique word interval D = 1 (when unique words are continuously arranged), and the symbol Pi along with the amplitude along the vertical axis. Although the estimation is possible even in a noisy environment and the offset range is large, the accuracy is lowered.

  FIG. 3C shows the symbol position (symbol number) on the horizontal axis and the symbol Pi along with the amplitude on the vertical axis when the unique word interval D = 4. Since the symbols are distributed over a wider range of frames, higher accuracy can be obtained, but the range of offsets that can be estimated is smaller.

  FIGS. 3B and 3C also illustrate a case where there are eight unique word symbols for simplicity.

  As shown in FIG. 3C, when the unique word interval D = 4, data symbols exist between the unique word symbols.

  On the other hand, in a noisy environment, a noise error will cause a phase estimation from one unique word symbol to the next unique word symbol. Therefore, as the unique word interval D increases, the influence of the noise error on the phase estimation decreases, and the frequency offset estimation accuracy improves.

  FIG. 4 is a functional block diagram for explaining the configuration of the frequency offset estimation device 2070 and the CRC decoding processing unit 216 in the carrier frequency reproduction unit 207.

  In the present embodiment, it is assumed that the unique word interval D is fixed as a large value in advance on the transmission side. Here, the “large value” means a value sufficient for the accuracy of the required frequency offset estimation, and is not particularly limited. For example, any one of D = {8, 16, 32} Set to a value. On the receiving side, as described below, the correlation length N is adaptively changed on the assumption that the unique word interval D is fixed.

  In estimating the frequency offset, the modified L & R (MLR) algorithm is a widely used and well-known frequency offset estimation algorithm in DVB-S2 satellite receivers. Such a modified L & R algorithm is based on calculating an average correlation for L frames in order to improve frequency estimation characteristics in a noisy environment.

  The modified L & R algorithm is disclosed in the following document.

Known Document 1: E. Casini, R. De Gaudenzi, and A. Ginesi, “DVB-S2 modem algorithms design and performance over typical satellite channels,” Proceedings of the Int. Journal of Sat. Commun. And Networking, pp. 281 --318, June 2004.
Known Document 2: M. Luise. And R, Reggiannini, “Carrier frequency recovery in all-digital modems for burst-mode transmissions,” IEEE Trans. Commun., Vol. 43, No. 2/3/4, pp. 1169 --1178, Feb-Apr. 1995.
Further, in the following literature, the inventor of the present patent application has proposed a scheme (DMLR scheme) modified so that the interval D between UW symbols can be 1 or more.

Known Document 3: J. Webber, M. Yofune, K. Yano, H. Ban, and K. Kobayashi, “Performance of frequency recovery algorithms for a poly-polarization multiplexing satellite system”, 11th IEEE Malaysia International Conference on Communications (MICC2013 ), 27-29th Nov. 2013.
Here, the frequency offset estimation apparatus 2070 is hardware for executing the “modified L & R algorithm modified so that the interval D between UW symbols can be 1 or more” as described above. Therefore, since the estimation of the frequency offset is detailed in the known document 3, the outline thereof will be described below.

  Frequency offset estimation apparatus 2070 receives received modulation signal Z and memory input from quadrature detection unit 206a or 206b (hereinafter, collectively referred to as quadrature detection unit 206), as will be described later, under the control of a control unit (not shown). The correlation with the unique word UW stored in the above is taken by a correlator 3020 having a correlation length N (N: natural number) according to the following formula, and this correlation value is obtained by a moving average size L (number of frames) by an integration processing unit 3030. Only).

That is, the integration processing unit 3030 integrates the correlation values over the L frames, and the offset calculation unit 3040 converts the integrated correlation values into a frequency offset f _LR-D hat according to the following equations (3) and (4). To do.

  Where l is the current frame number, m is the delay, Lp is the length of the unique word, N is the correlation length, L is the average frame size, and D is the unique word interval It is.

Z (k) means the product of the kth symbol of the lth frame and the conjugate of the kth symbol of a known unique word to be correlated. By taking the product with the conjugate of a known unique word, the influence of modulation can be removed. z ^* (k) is a complex conjugate of z (k).

  In the equation (1), this corresponds to taking a correlation between symbols shifted by m for the l-th frame. In equation (2), this means that the correlation values over the L frames are integrated.

The frequency offset f _LR-D hat is converted into complex frequency error information by a table or the like, and a complex multiplier (not shown) performs complex multiplication of the input received modulation signal and frequency error information to correct the frequency error. The received modulated signal is obtained. The carrier frequency reproduction unit 207 repeats the above operation to bring the residual frequency error in the corrected received modulated signal close to zero.

  On the other hand, the CRC decoding processing unit 216 operates in accordance with control of a control unit (not shown), the decoding unit 2162 performs CRC decoding processing on the received signal from the error correction decoding processing unit 214, and the CRC check unit 2164 The presence or absence of a transmission error is determined by the CRC code. The correlation length control unit 2166 detects whether or not an error has occurred in the current unique word interval D, the correlation length N, and the frame average size L, and updates the correlation length N according to the flow described later to obtain the optimum correlation length. N is determined. Note that the correlation length control unit 2166 updates the correlation length N by referring to a lookup table (LUT) 2168.

  In addition, since correlation values for different correlation lengths N can be calculated for the same set of received signals, a correlation value is set for the same set of received signals for each element of the set of preset correlation lengths N. By calculating and storing in the storage device, the correlation length control unit 2166 may be configured to determine the optimum correlation length N based on the correlation value stored in the storage device in this way. it can. With this configuration, when the L frame signal is received and the correlation value is calculated, the calculation of the correlation value for each element of the set of possible correlation lengths N is complete. It is possible to reduce the time required to determine the optimum correlation length N.

  In FIG. 4, the correlation length control unit 2166 and the control unit that controls the entire receiver 2000 have been described as being different from each other, but these may be integrated as one control unit.

  With this configuration, the transmission side transmits a signal having a fixed unique word interval D, as will be described in more detail later. On the receiving side, in the initial phase, a CRC check is performed by an algorithm controlled by the control unit while sequentially selecting a specific correlation length N from a set of values that can be taken by the correlation length N. The optimum correlation length N is specified in a range where the transmission error is equal to or less than a predetermined value.

  The error detection code is not limited to the CRC code, and other error detection codes may be used.

  FIG. 5 is a diagram illustrating a simulation result of the relationship between the correlation length N and the maximum frequency offset that can be evaluated.

  That is, FIG. 5 shows a change in the maximum frequency offset that can be drawn with respect to the correlation length N, using the unique word interval D as a parameter.

  In FIG. 5, the simulation is performed assuming that the number of unique word symbols is 32 and the data transfer rate is 10 MBd.

  As described above, for the same correlation length, the maximum frequency offset that can be evaluated decreases as the unique word interval D increases.

  On the other hand, when the unique word interval D is fixed, if the correlation length N is decreased, the maximum offset frequency that can be evaluated can be increased.

  Therefore, even when the transmission side is transmitting with the unique word interval D fixed, if the correlation length N is adaptively changed on the reception side, the maximum frequency offset that can be evaluated can be made variable. is there.

  FIG. 6 is a diagram illustrating examples of different arrangements of unique words with unique word intervals D and correlation lengths N. In FIG.

  FIG. 7 is a diagram for explaining a mode in which unique words arranged at different unique word intervals D are arranged in a frame of a transmission signal.

  Also in FIG. 5, the maximum frequency offset that can be evaluated is determined by two parameters of the unique word interval D and the correlation length N, as described above.

  Here, if the effective unique word interval D ′ is defined by D ′ = D · N, the maximum frequency offset that can be evaluated is the same for the same effective unique word interval D ′.

  In FIG. 6, the unique word symbols distributed and arranged in a predetermined area of the frame are indicated by diagonal lines. The unique word (UW) symbol index indicates the number of a certain unique word symbol starting from the first unique word symbol in the frame.

  For example, in the case of (D, N, D ′) = (1, 4, 4) as shown in FIG. 6A and (D, N, D ′) = (as shown in FIG. 6B. In the case of 4, 1, 4), the effective unique word interval D ′ is 4 and the maximum frequency offset that can be evaluated is the same.

  However, for offset evaluation, the interval between any two unique words needs to be set so that the corresponding phase difference is 2π or less, and the value of the unique word interval D has an upper limit.

  Next, referring to FIG. 7, as shown in the upper part of FIG. 7, when the unique word interval D = 1, a predetermined number of consecutive symbols (symbols here) are placed at the beginning of each predetermined number of frames. The predetermined number includes, for example, a portion (hereinafter referred to as UW portion) in which a unique word consisting of 64) is arranged.

  On the other hand, as shown in the lower part of FIG. 7, in the arrangement in which the unique word interval D exceeds 1, a predetermined unique word interval from the beginning of each frame (for example, D = 2 to 64 in the lower part of FIG. 7). The unique words of a predetermined number of symbols are arranged in a distributed manner.

  In the present embodiment, the unique word interval D is selected and fixed by the transmission side from a set of predetermined values, and the selected unique word interval is also used for data communication.

  Here, the number of symbols used as the unique word is not necessarily limited to the above value.

  Here, the unique word interval D = n (n: natural number) means that when the i-th symbol (UW symbol index = i) is a unique word, the (i + n) -th symbol is also a unique word. It means that there is.

  FIG. 8 is a diagram for explaining the arrangement of unique words and CRC codes transmitted from the transmission side to the reception side.

  FIG. 8A shows the arrangement of unique words distributed in one frame, and FIG. 8B shows the number L of frame average sizes, which is the number of frames for which frame average processing is performed in frequency offset evaluation. FIG. 8C shows another example of the arrangement of CRC codes, and FIG. 8C shows another example of the arrangement of CRC codes.

  As shown in FIG. 8B or FIG. 8C, a set of frames, which is a unit for error detection using a CRC code or the like, is called a block. In the present embodiment, the unique word interval D is assumed to be constant within the same block.

  As shown in FIG. 8A, unique words are distributed in one frame at a specified interval D.

  As shown in FIG. 8B, for example, a 16-bit CRC symbol can be arranged immediately after transmission of L frames (frame number l = 1 to L), which is an average frame size. .

Alternatively, as shown in FIG. 8 (c), immediately after transmission of L frames (frame number l = 1 to L), which is the average frame size, and for each subsequent L _N frames (L _N ≧ 0) For example, a 16-bit CRC symbol may be arranged.

However, the arrangement of the CRC symbols is not limited to the arrangement shown in FIG. 8B or FIG. 8C. For example, the CRC symbols may be provided in each frame, and more generally, reception is performed. On the side, at least one frame may be arranged at a position where transmission errors can be checked after receiving L frames having a predetermined unique word interval D. Desirably, (L _N +1) frames may be arranged at positions where transmission errors can be checked after receiving L frames having a predetermined unique word interval D. When (L _N +1) CRC codes are arranged, for example, error detection results for each of these CRC codes are integrated, and the presence / absence of an error is detected based on the integration result. The impact can be reduced.

  Therefore, for example, the following procedure can be used as a flow for adaptively changing the correlation length N on the receiving side.

  i) The average correlation is calculated by using the correlator shown in FIG.

  At this time, when the number of received frames is less than L, the correlation length N is set to a predetermined value stored in the lookup table 2168. By setting the initial value of the correlation length N in this way, the frequency offset can be evaluated with the correlation length N suitable for the unique word interval D fixed on the transmission side.

  ii) When the number of received frames becomes L or more, the value of the correlation length N is adaptively changed according to the result of error detection by the CRC code according to the flow described later.

At this time, when the CRC code is arranged as shown in FIG. 8C, the error detection result by the CRC code is processed (integrated or averaged) for (L _N +1) CRC codes. As described above, the influence of noise can be reduced.

  FIG. 9 is a conceptual diagram showing the evaluation of the adjustable maximum frequency offset when the correlation length N is adaptively changed.

  FIG. 9A shows the evaluation of the maximum frequency offset by the above-described conventional modified L & R (MLR) algorithm, and FIG. 9B shows the algorithm (fine adjustment DMLR algorithm in the present embodiment in a state with high accuracy. 9 (c) shows the evaluation of the maximum frequency offset, and FIG. 9 (c) shows the evaluation of the maximum frequency offset by the algorithm (coarse DMLR algorithm) in this embodiment in a state where the accuracy is low.

  It is assumed that the data transfer rate fsym is 10 MBd.

  As shown in FIG. 9A, in the conventional MLR algorithm, when (D, N, D ′) = (1, 16, 16), the maximum frequency offset Δfmax is ˜588 kHz.

  On the other hand, in the fine adjustment DMLR algorithm as shown in FIG. 9B, for example, 64 is set as a sufficiently large unique word interval D, and (D, N, D ′) = (64, 16, 1024). In this case, the maximum frequency offset Δfmax is ˜9.19 kHz. On the other hand, as shown in FIG. 9 (c), when the correlation length N is reduced and D, N, D ′) = (64, 2, 128) as the coarse adjustment DMLR algorithm, the maximum frequency offset Δfmax is , Up to ~ 52.1 kHz.

  FIG. 10 is a diagram showing a simulation result of the relationship between the bit energy to noise power density ratio Eb / No and the bit error rate BER.

  FIG. 10 shows a case where the unique word interval D and the correlation length N are changed as parameters.

  For the number of unique word symbols Nuw = 32, the correlation length employed in the conventional MLR algorithm is Nuw / 2 = 16.

  The modulation scheme is 8PSK for each of the two polarizations, the frequency offset is Δf = ± 2 kHz, the data transfer rate fsym is 10 MBd, the frame average size L = 256, and the forward error correction (FEC) is The simulation is performed under the condition that it is not performed.

  In FIG. 10, the results of the following algorithms are shown in comparison.

Conventional MLR algorithm: (D, N, D ′) = (1, 16, 16)
DMLR algorithm: (D, N, D ′) = (2, 16, 32)
(D, N, D ′) = (4, 16, 64)
(D, N, D ′) = (32, 16, 512)
Adaptive correlation length algorithm: (D, N, D ′) = (32, 8, 256)
(D, N, D ′) = (32, 4, 128)
The adaptive correlation length algorithm with (D, N, D ′) = (32,4,128) is larger than the DMLR algorithm with (D, N, D ′) = (32,16,512). The same degree of accuracy can be achieved while accommodating the maximum frequency offset.

  FIG. 11 is another diagram showing a simulation result of the relationship between the bit energy to noise power density ratio Eb / No and the bit error rate BER.

  The simulation conditions are the same as in the case of FIG.

  By setting the unique word interval D to 16, even when the correlation length N is decreased from 16 to 1, no significant deterioration in the BER is observed. In other words, setting D = 16 indicates that the correlation length N can be changed on the receiving side in order to make the maximum frequency offset variable.

  In actual communication, the variable range of the unique word interval D and the correlation length N can be set in advance so as to suit the communication environment by such simulation and experiment. 2168 can be stored.

  FIG. 12 is a flowchart for explaining the processing flow of the adaptive correlation length.

  As described above, in the present embodiment, the unique word interval D is fixed at a value fixed on the transmission side, and the correlation length N is changed on the reception side to specify the optimum correlation length N.

  As described below, the maximum correlation length N is specified by using the CRC check. Here, as an example of the arrangement of the CRC code, it is assumed that the arrangement is as shown in FIG.

  Referring to FIG. 12, first, as an initialization process, the transmission side sets the value of unique word interval D to a predetermined value, and this value D is held constant throughout the transmission. It is assumed that the unique word interval D is also known on the receiving side. Here, D = 16 (S100).

  Furthermore, as initialization processing, it is assumed that a combination Nset = {Nset (1), Nset (2),..., Nset (n)} that can be correlated is set in advance on the receiving side (S100). ).

  Here, as an example, Nset = {Nset (1), Nset (2),..., Nset (5)} = {1, 2, 4, 8, Nuw / 2 (= 16)}. Although not particularly limited, it is desirable that the elements of Nset are arranged in order from the smallest, as will be described below. In the following, it is assumed that the elements of Nset are arranged in ascending order.

N _N is the number of Nset elements to be tested. The frame average size L is assumed to be 256 as an example. It is assumed that L _N shown in FIG. Accordingly, the number Lc of error detections per block using the CRC code is Lc = (L _N +1). Further, n, which is a working variable for designating an element in Nset during processing, is initialized to n = 0.

Further, referring to FIG. 12, the receiving side receives (L + L _N ) frames containing unique words (S102).

  Subsequently, the value of n is incremented by 1, and the correlation length N is set to N = Nset (n) (S104).

A CRC check is performed on the first L frames and the subsequent L _N frames in total. If the CRC check is not passed, CRC (l) = 1 is set. If the CRC check is passed, CRC (l) = 0 is set (S106).

  The defect number index Fail (n) is calculated by the following formula (S108).

Next, it is determined whether the value of the current variable n is equal to or greater than the number N _N of elements in Nset (S110). If it is less than N _N , the process returns to step S104, and the value of n Is incremented by 1, the next value is set as the correlation length N (S104), and the subsequent processing is repeated.

On the other hand, in step S110, if n is greater than or equal to N _N , the maximum correlation length N is selected as the correlation length for evaluating the frequency offset among the correlation lengths having the smallest defect number index Fail (n). (S112).

  That is, when priority is given to accuracy, when two or more elements in Nset have the same defect number index value, it is desirable to select the element with the largest value of N.

  However, as the priority is given to the maximum frequency offset that can be evaluated, the minimum correlation length N is selected as the correlation length for evaluation of the frequency offset among the correlation lengths having the minimum defect number Fail (n). It is good also as a structure to be.

As described above, the defect index is defined as an integrated value of the error detection results for Lc = (L _N +1) times. Thereby, although the influence of noise or the like can be reduced, the index (error information) that indicates the error status in an integrated manner for a plurality of frames is not limited to this. For example, a method of determining whether or not the ratio is equal to or less than a predetermined value may be employed by using the ratio of the number of frames in which errors are detected with respect to Lc.

  FIG. 13 is a diagram illustrating the relationship between the number of received frames and the remaining frequency offset.

  FIG. 13 shows a case where the test is performed while sequentially changing the correlation length N from a smaller value to a larger value in the flowchart of FIG.

  The unique word interval D = 8, the frame average size L = 64, the bit energy to noise power density ratio Eb / No = 4.8 dB, the data transfer rate fsym is 5 MBd, and the initial frequency offset Δf = 64 kHz. .

  In the initial phase, as the correlation length N is sequentially increased from N = 1 to N = 8 according to the flowchart of FIG. 12, the remaining frequency offset decreases as a trend. However, when the correlation length N = 16, the value of the maximum frequency offset that can be evaluated becomes too small, and the residual frequency offset increases rapidly.

For this reason, the maximum correlation length N is selected as the optimum correlation length N _{OPT in} the range of N = 1 to N = 8 and the defect number index is the minimum, for example, and thereafter the correlation length in the communication phase. Will be used as.

  By adaptively setting the value of N in the initial operation start phase, stable communication can be performed in the subsequent communication phase.

(Storing correlation data in storage device)
In the following, when the optimum correlation length is determined by storing the correlation value in a storage device (not shown) while the optimum value of the correlation length is being evaluated on the receiving side, this is immediately handled. A configuration that allows the correlation value to be calculated to be calculated will be described.

That is, as the process for selecting the correlation length N, the process shown in FIG. 12 may be executed. However, after the correlation length N is selected, as described below, (L + L _N ) pieces are newly obtained. It is not always necessary to receive this frame. Such a configuration will be described below.

  FIG. 14 is a conceptual diagram illustrating an example of correlation values stored in the storage device.

In step S102 of FIG. 12, the frames are sequentially received while incrementing the frame number l by 1, and the correlator 3020 changes the correlation length N for the L frames from the frame l to the frame (l + L−1). The stored values are stored in a storage device (not shown in FIG. 4) as shown in FIG. At this time, the size of the data to be stored is a matrix of L rows and N _N columns.

If the optimum correlation length N _OPT is determined in step S112, the correlation value corresponding to this correlation length N _OPT is read from the storage device, integrated in the integration processing unit 3030, and the offset calculation unit 3040 It is possible to adopt a configuration for calculating. Thereby, in the evaluation of the frequency offset, l = 1 to L are targets for taking a moving average.

  As described above, during the operation start phase, the reception side selects a specific correlation length from a set of correlation lengths, transmits a predetermined number of frames, and the reception side performs CRC code decoding processing. The transmission error is evaluated, and the correlation length is specified in a range that minimizes the transmission error.

  At this time, if the maximum correlation length among the minimum transmission errors is selected as the correlation length for evaluating the frequency offset, the frequency offset can be estimated with high accuracy.

  Alternatively, if the smallest correlation length among the minimum transmission errors is selected as the correlation length for evaluating the frequency offset, the frequency offset range that can be evaluated can be as wide as possible.

  Of the above-mentioned correlation lengths that minimize the transmission error, whether the maximum or minimum correlation length is selected depends on the frequency band to be used, the modulation method to be used, the data transfer rate, and the assumed frequency offset. It shall be determined in advance according to the range.

  In the data communication phase, data reception is performed with the correlation length specified in this way, thereby maximizing the range of frequencies that can be acquired by the carrier frequency recovery unit on the receiving side, or estimating the frequency offset with high accuracy. It becomes possible to do. In this case, since the correlation length is selected so that the transmission error is minimized, the frequency offset can be estimated with a smaller number of frames (shorter acquisition period).

  Embodiment disclosed this time is an illustration of the structure for implementing this invention concretely, Comprising: The technical scope of this invention is not restrict | limited. The technical scope of the present invention is shown not by the description of the embodiment but by the scope of the claims, and includes modifications within the wording and equivalent meanings of the scope of the claims. Is intended.

  100 error correction coding processing unit, 102 S / P conversion unit, 104 V / H mapping processing unit, 106, 210 I / Q mapping data storage unit, 107a, 107b UW insertion unit, 108a, 108b orthogonal modulation unit, 110a, 110b D / A conversion unit, 112a, 112b Transmission filter processing unit, 114a, 200a Vertical polarization antenna, 114b, 200b Horizontal polarization antenna, 202a, 202b Reception filter processing unit, 204a, 204b A / D conversion unit, 206a, 206b Quadrature detection unit, 207 Carrier frequency recovery unit, 208 Carrier phase recovery unit, 209 Maximum likelihood determination processing unit, 212 P / S conversion unit, 214 Error correction decoding processing unit, 216 CRC decoding processing unit, 1000 transmitter, 2000 reception Machine.

Claims (8)

A frequency offset estimation device for estimating a frequency offset between a carrier frequency of a received signal and a local oscillation frequency,
The received signal includes a plurality of frames each having a plurality of unique words arranged therein, and an error detection code,
A correlator for calculating a correlation between the received signal and the unique word; the correlator can calculate the correlation with a variable correlation length;
An offset calculation unit for calculating the estimated value of the frequency offset by integrating the calculated correlation over a set number of frames of the average frame size; and
An error detection unit for detecting a transmission error by the error detection code;
A control unit for controlling the correlator, the offset calculation unit, and the error detection unit, the control unit,
i) A signal transmitted at a predetermined unique word interval is received at the receiving side, and the correlation length is sequentially changed among a set of predetermined values to perform error detection;
ii) A frequency offset estimation device that specifies a correlation value used for frequency offset estimation within a range in which a transmission error is equal to or less than a predetermined value according to the error detection result. The error detection code is provided over a plurality of frames;
The error detection unit calculates error information by combining error detection results for the plurality of frames,
The frequency offset estimation apparatus according to claim 1, wherein the control unit specifies a maximum correlation length among correlation lengths corresponding to a frame having a minimum transmission error based on the error information. The error detection code is provided over a plurality of frames;
The error detection unit calculates error information by combining error detection results for the plurality of frames,
The frequency offset estimation apparatus according to claim 1, wherein the control unit specifies a minimum correlation length among correlation lengths corresponding to a frame having a minimum transmission error based on the error information. A storage device for storing a correlation value used for calculating the frequency offset;
The control unit stores, in the storage device, a correlation value calculated by sequentially changing the correlation length among a set of predetermined values for each frame of the received number of average frame sizes,
The frequency offset estimation apparatus according to any one of claims 1 to 3, wherein the offset calculation unit calculates an estimated value of the frequency offset based on the correlation value stored in the storage device. A wireless communication device for receiving a plurality of frames each having a plurality of unique words and a wireless signal including an error detection code,
Receiving means for receiving and detecting the radio signal;
A carrier frequency reproducing means for estimating a frequency offset between a carrier frequency and a local oscillation frequency of the received signal from the receiving means, and correcting a frequency error of the received signal based on the estimated frequency offset; ,
The carrier frequency reproduction means includes frequency offset estimation means for estimating the frequency offset, and the frequency offset estimation means includes:
Including a correlator for calculating a correlation between the received signal and the unique word, wherein the correlator is capable of calculating the correlation with a variable correlation length;
An offset calculation unit for calculating the estimated value of the frequency offset by integrating the calculated correlation over a set number of frames of the average frame size; and
An error detection unit for detecting a transmission error by the error detection code;
The controller further includes a controller for controlling the correlator, the offset calculator, and the error detector.
i) A signal transmitted at a predetermined unique word interval is received at the receiving side, and the correlation length is sequentially changed among a set of predetermined values to perform error detection;
ii) In accordance with the result of the error detection, specify a correlation value to be used for frequency offset estimation within a range in which a transmission error is equal to or less than a predetermined value,
A wireless communication apparatus further comprising decoding means for performing decoding processing on the signal corrected by the carrier frequency reproduction means. The error detection code is provided over a plurality of frames;
The error detection unit calculates error information by combining error detection results for the plurality of frames,
The wireless communication apparatus according to claim 5, wherein the control unit specifies a maximum correlation length among correlation lengths corresponding to a frame having a minimum transmission error based on the error information. The error detection code is provided over a plurality of frames;
The error detection unit calculates error information by combining error detection results for the plurality of frames,
The wireless communication apparatus according to claim 5, wherein the control unit specifies a minimum correlation length among correlation lengths corresponding to a frame having a minimum transmission error based on the error information. A storage device for storing a correlation value used for calculating the frequency offset;
The control unit stores, in the storage device, a correlation value calculated by sequentially changing the correlation length among a set of predetermined values for each frame of the received number of average frame sizes,
The wireless communication apparatus according to claim 5, wherein the offset calculation unit calculates an estimated value of the frequency offset based on the correlation value stored in the storage device.