JP5014293B2 - MIMO-OFDM receiver - Google Patents

Description

  In the present invention, a guard interval is inserted before a data symbol, and a pilot (for example, CP: Continuous Pilot) carrier for estimating a propagation channel is inserted between data carriers so as to be orthogonal codes between transmission streams. More particularly, the present invention relates to a MIMO-OFDM receiver that appropriately corrects a frequency deviation that occurs between transmitting and receiving devices when a plurality of spatially multiplexed transmission streams are separated.

  As a system for transmitting program material from a relay site to a broadcasting station or the like, an orthogonal frequency division multiplexing (OFDM) digital wireless transmission system is summarized as the ARIB STD-B33 standard (Non-patent Document 1). Yes.

  Based on this standard, a technique called MIMO (Multi-Input Multi-Output) that dramatically improves frequency use efficiency by using a plurality of antennas for a transmitter and a receiver is being studied. For example, a system in which a pilot carrier is arranged at predetermined intervals on the frequency axis and each symbol on the time axis is modulated with a code orthogonal between transmission streams to form a MIMO-OFDM signal is disclosed (for example, a patent) Reference 1).

  In the OFDM transmission system, it is known that transmission characteristics deteriorate due to inter-carrier interference (ICI) in which orthogonality between subcarriers is lost due to frequency deviation between transmitter and receiver.

  Furthermore, in the conventional MIMO-OFDM wireless transmission in which a plurality of OFDM signals having different modulation signals are transmitted from the same number of antennas at the same frequency, an update period of propagation channel estimation required for separating each transmission stream There is a problem that separation / decoding characteristics are greatly degraded due to an increase in the phase rotation amount of each carrier due to a frequency deviation. In addition, the conventional MIMO-OFDM scheme improves the separation / decoding performance in an environment with many multipaths, but the accuracy of frequency deviation detection deteriorates.

  Thus, such frequency deviation detection and correction methods have been proposed in the OFDM system and the MIMO-OFDM system (see, for example, Non-Patent Document 2 and Patent Document 2).

  In addition, regarding the OFDM method, a phase tracking method for correcting a residual frequency deviation using a pilot signal is also disclosed (for example, see Non-Patent Document 3).

  Further, with respect to the MIMO-OFDM system, a method is disclosed in which a residual frequency deviation is estimated based on a phase difference between a modulation point and a received signal point, and a phase rotation corresponding to the deviation is corrected (for example, Patent Document 3). reference).

  Furthermore, with respect to detection of wideband frequency deviation, in the OFDM method, a method is known in which a frequency deviation of an integral multiple of the carrier interval is detected based on the correlation between adjacent symbols of subcarriers extracted after FFT calculation ( For example, see Patent Document 4).

JP 2005-124125 A JP 2006-135861 A JP 2006-186732 A JP 2002-280993 A "Portable OFDM digital radio transmission system for transmitting television broadcast program material", ARIB STD-B33 Seki, Taga, Ishikawa, “Examination of new frequency synchronization method using guard period in OFDM”, Television Society Technical Report, ITE Technical Report Vol.19, No.38, p.13-18 Morikura, Kubota, "802.11 High-Speed Wireless LAN Textbook", (Impress), p.215-216

  The methods proposed in Non-Patent Document 2 and Patent Document 2 can detect a frequency deviation within 1/2 of the subcarrier interval, but cannot detect a wideband frequency deviation exceeding that. Further, since the problem of residual frequency deviation occurs due to noise and other influences, it is not expected to detect a frequency deviation with high accuracy for performing highly accurate signal separation.

  In addition, in the phase tracking disclosed in Non-Patent Document 3, Patent Document 3, and the like, when the MIMO-OFDM method is used, pilot signals between different transmission streams are spatially multiplexed. It is not possible and is simply difficult to apply. Further, this phase tracking is performed at the final stage of demodulation, and the influence of the residual frequency deviation remains at the time of separation / decoding of the spatially multiplexed MIMO-OFDM signal.

  As proposed in Patent Document 1, when a pilot carrier is arranged at a predetermined interval on the frequency axis and each symbol on the time axis is modulated with a code orthogonal between transmission streams, a MIMO-OFDM signal is configured. There is a problem that a wideband frequency deviation cannot be detected only by a simple correlation calculation between adjacent symbols of subcarriers extracted after the FFT calculation. Another problem is that the frequency deviation detection accuracy deteriorates as compared with the conventional OFDM transmission method because the transmission streams, which are interference sources, are spatially multiplexed.

  Therefore, an object of the present invention is to provide a MIMO-OFDM receiver that appropriately corrects a frequency deviation that occurs between transmitting and receiving devices when a plurality of spatially multiplexed transmission streams are separated.

  A MIMO-OFDM receiver according to the present invention is a MIMO-OFDM receiver that receives an OFDM signal transmitted by spatially multiplexing a plurality of different transmission streams at the same frequency, and is a pilot signal that becomes an orthogonal code for each transmission stream. Is inserted between data carriers, and the OFDM signals of the plurality of transmission streams are demodulated, and two sets of subcarrier signals having different symbol numbers are extracted for each symbol corresponding to the length of the orthogonal code. And means for detecting the maximum correlation value of the correlation calculation obtained by shifting in the subcarrier direction in units of subcarriers using the combination of two sets of subcarrier signals having different symbol numbers. The deviation amount of the subcarrier interval specified from the combination is expressed as a frequency deviation that is an integral multiple of the subcarrier interval. Detecting Te, characterized in that it comprises a means for correcting the frequency deviation for each reception system.

  In the MIMO-OFDM receiver according to the present invention, the means for extracting two sets of subcarrier signals having different symbol numbers extracts a TMCC signal common to the plurality of transmission streams, and determines a frame head position from the TMCC signal. Means for detecting and extracting two sets of subcarrier signals having different symbol numbers from the detected frame head position for each symbol corresponding to the length of the orthogonal code, from an OFDM signal in which a plurality of transmission streams are spatially multiplexed. And two sets of subcarrier signals having different symbol numbers, where the orthogonal code length is 1, and the symbol number n satisfying mod (n, l) = 0 and the symbol preceding l symbols Number (n-1) subcarrier signals, and each receiving system has a frequency that is an integral multiple of the subcarrier interval. The means for correcting the deviation includes the subcarrier signal of the symbol number n and the subcarrier signal of the symbol number (n−1) one symbol earlier in the subcarrier direction in a subcarrier direction as a set of correlation operations. It is further characterized by further comprising correction means for detecting a maximum correlation value from a predetermined number of combinations of shifted correlation operations.

  Also, in the MIMO-OFDM receiver according to the present invention, the means for extracting two sets of subcarrier signals with different symbol numbers is assumed that the orthogonal code length is l and the symbol number n is mod (n, l) = r (0 When extracting two sets of subcarrier signals having different symbol numbers consisting of a subcarrier signal of symbol number n satisfying ≦ r <l−1) and a subcarrier signal of symbol number (n−1) preceding l symbols And a means for selecting a combination that maximizes the correlation value of the correlation calculation obtained by shifting in the subcarrier direction in units of subcarriers.

  Further, in the MIMO-OFDM receiver according to the present invention, the means for correcting a frequency deviation of an integral multiple of a subcarrier interval for each receiving system corrects the frequency deviation for each receiving system and then detects the detected correlation calculation. And a means for detecting a frequency deviation between the transmitters and receivers from a phase term of the maximum correlation value of the combination, and a means for correcting the detected frequency deviation between the transmitters and receivers for each reception system.

  Further, in the MIMO-OFDM receiver according to the present invention, means for detecting a frequency deviation within ½ of the subcarrier interval by performing a correlation operation between guard intervals obtained by copying a part of an effective symbol of the OFDM signal during the demodulation. And a means for correcting a frequency deviation that is an integral multiple of the subcarrier interval for each reception system includes 1 / of the detected subcarrier interval while the frequency deviation that is an integral multiple of the subcarrier interval is not corrected. A frequency deviation within 2 and a frequency deviation that is an integral multiple of the subcarrier interval are added, and the frequency deviation after the addition is corrected.

  Further, in the MIMO-OFDM receiver according to the present invention, the means for correcting a frequency deviation of an integral multiple of a subcarrier interval for each reception system includes a frequency deviation within 1/2 of the detected subcarrier interval and the subcarrier. After adding the frequency deviation of the integral multiple of the interval and correcting the frequency deviation after the addition, from the phase term of the maximum correlation value used to calculate the frequency deviation of the integral multiple of the subcarrier interval, It further comprises a correction means for detecting a correction amount for further correcting the frequency deviation and correcting the correction amount.

  Further, in the MIMO-OFDM receiver according to the present invention, the means for correcting a frequency deviation of an integral multiple of the subcarrier interval for each reception system is between guard intervals obtained by copying a part of the effective symbol of the OFDM signal during the demodulation. Regardless of whether or not a frequency deviation within 1/2 of the subcarrier interval is detected by performing correlation calculation, the frequency deviation within 1/2 of the subcarrier interval is corrected after correcting the frequency deviation of an integral multiple of the subcarrier interval. The correction amount in the means for correcting the frequency deviation is cyclically varied so that the frequency deviation of the subcarrier interval is minimized, and the correction amount is corrected so that the frequency deviation is equal to or less than a preset threshold value. And a correction means for performing the correction.

  In the MIMO-OFDM receiver according to the present invention, a known pilot pattern is defined in advance to correct a frequency deviation exceeding the carrier interval of the pilot signal, and is an integral multiple of the subcarrier interval for each reception system. The means for correcting the frequency deviation is to slide the correlation calculation of the subcarrier signal in the carrier direction when calculating the correlation between the subcarrier signal of symbol number n in the predetermined effective symbol section and the known pilot pattern. Repeatedly, an average value obtained by adding and averaging the correlation values at the same carrier position in the symbol direction is calculated, a means for extracting the maximum value from the average values, and a deviation of the receiving system in the extracted maximum average value And a means for correcting the quantity as a frequency deviation.

  According to the present invention, when MIMO-OFDM transmission is used in a mobile environment, it is possible to detect and correct a broadband and high-accuracy frequency deviation even in a severe propagation environment where the frequency deviation fluctuates over time. .

  First, the MIMO-OFDM receiver according to the first embodiment of the present invention will be described.

[Example 1]
The MIMO-OFDM receiving apparatus according to the first embodiment is an apparatus that receives an OFDM signal that is transmitted by spatially multiplexing a plurality of different transmission streams at the same frequency, and sets a guard interval before a data symbol between data carriers. It is configured as a receiving apparatus of a MIMO-OFDM transmission system that employs multicarrier modulation in which pilot (for example, CP: Continuous Pilot) carriers for propagation channel estimation are inserted so as to be orthogonal codes between transmission streams. Accordingly, the transmitter itself of the MIMO-OFDM transmission scheme is known, and detailed description thereof is omitted.

  In particular, the MIMO-OFDM receiver according to the first embodiment is configured to select a symbol to be extracted for frequency deviation detection using a TMCC signal.

  FIG. 1 shows a MIMO-OFDM receiver according to a first embodiment of the present invention. In the MIMO-OFDM transmission system, the transmission signal is not limited. For example, the transmission signal can be an OFDM system signal based on the ARIB STD-B33 standard, and a MIMO-OFDM system that spatially multiplexes a plurality of transmission streams. Therefore, the pilot signals are arranged so as to be orthogonal codes between transmission streams. In the present embodiment, the number of transmission streams is 2, the phase of both transmission stream 1 and transmission stream 2 is non-inverted in even symbols within one OFDM frame composed of symbol numbers 0 to 407, and phase of transmission stream 1 is in odd symbols. In the non-inverted transmission stream 2, it is assumed that a pilot signal having an orthogonal code whose phase is inverted is inserted between data carriers. Even when the number of transmission streams is 4, the present invention can be easily applied. In addition, such an arrangement of pilot signals is based on, for example, the ARIB STD-B33 standard, and for each transmission stream, each symbol is arranged every 8 from the position of subcarrier number 0 in the carrier arrangement direction. It shall be.

The MIMO-OFDM receiver 1 according to the first embodiment includes an antenna 2, a frequency converter (D / C) 3, an A / D converter 4, an orthogonal demodulator 5, a multiplier 6, an FIR filter (LPF ) 7, downsample processing (DS) 8, guard interval correlation (GI correlation) 9, FFT unit 10, TMCC detection unit 11, common processing unit 12 for detecting and correcting frequency deviation, and carrier extraction Unit 13, frame synchronization detection unit 14, and intersymbol carrier correlation unit 15, and a processing stage (not shown) for performing a known demodulation process and a decoding process for demodulating and decoding a received signal after TMCC detection. Can do. The common processing unit 12 includes a local oscillator (Lo) 16, a numerically controlled oscillator (NCO) 17, an adder 18, a selector unit 19, a first frequency deviation (Δf _n1 ) detection unit 20, A second frequency deviation (Δf _n2 ) detection unit 21, a third frequency deviation (Δf _w ) detection unit 22, and a peak detection unit 23 are provided.

  The antenna 2 receives a MIMO-OFDM OFDM signal that spatially multiplexes a plurality of transmission streams.

  The frequency converter (D / C) 3 down-converts the OFDM signal received by the antenna 2 to a frequency band where digital signal processing is possible.

  The A / D converter 4 converts the reception signal frequency-converted by the frequency converter (D / C) 3 into a digital signal.

  The orthogonal demodulator 5 multiplies the signal converted into the digital signal by the A / D converter 4 with a signal of a predetermined frequency from the local oscillator (Lo) 16, and a plurality of transmission streams are spatially multiplexed. Performs digital quadrature demodulation processing of the OFDM signal.

  The multiplier 6 multiplies the signal from the quadrature demodulator 5 by a predetermined correction signal for correcting the frequency deviation from the numerically controlled oscillator (NCO) 17, and the signal from the quadrature demodulator 5 has a frequency. Correct the deviation.

  The FIR filter (LPF) 7 functions as a low-pass filter that removes signal components in an undesired frequency band from the signal from the multiplier 6.

  The down-sampling process (DS) 8 has a function of resampling the signal in the frequency band of the signal from the FIR filter (LPF) 7 to a frequency that can be subjected to FFT conversion.

  The guard interval correlation (GI correlation) 9 has a function of specifying a range of effective symbols by performing correlation calculation between guard intervals in which a part of the effective symbols of the OFDM signal is copied on the transmission side.

  The FFT unit 10 removes a range corresponding to the guard interval, extracts a signal in the range of valid symbols, and performs an FFT operation on the extracted OFDM time domain signal.

  The TMCC detection unit 11 extracts a TMCC signal common to the plurality of transmission streams, and sends the TMCC signal to the frame synchronization detection unit 14.

  The carrier extraction unit 13 extracts two sets of subcarrier signals having different symbol numbers for each symbol corresponding to the length of the orthogonal code from the detected frame head position from an OFDM signal in which a plurality of transmission streams are spatially multiplexed. It has the function to do. A more detailed example will be described later.

  The frame synchronization detection unit 14 has a function of detecting the frame head position from the TMCC signal.

  The intersymbol carrier correlation unit 15 has a function of performing a correlation calculation using two sets of subcarrier signals with different symbol numbers as a combination of a set of correlation calculations. Preferably, the two sets of subcarrier signals having different symbol numbers have the orthogonal code length of l, the symbol number n satisfying mod (n, l) = 0, and the symbol code number n subcarrier signals before l symbols. In particular, when the orthogonal code length is l = 2, two sets of subcarrier signals having different symbol numbers have a symbol number n of mod (n, 2) = It consists of a subcarrier signal of symbol number n satisfying 0 and a subcarrier signal of symbol number (n-2) two symbols before.

  Based on the signal corresponding to the frequency deviation, the numerically controlled oscillator (NCO) 17 sends a signal having a frequency controlled by the control signal corresponding to the frequency deviation output from the adder 18 to the multiplier 6, and receives the reception system. The frequency deviation is corrected every time. In addition, the numerically controlled oscillator (NCO) 17 corrects the frequency deviation for each reception system, and further determines from the phase term of the maximum correlation value of the combination of correlation operations detected through the inter-symbol carrier correlation unit 15 between the transmitter and the receiver. This function has a function of detecting a frequency deviation between the transmitter and the receiver and detecting the frequency deviation between the transmitter and the receiver.

The adder 18 includes a signal of the first frequency deviation (Δf _n1 ) or the second frequency deviation (Δf _n2 ) from the selector unit 19 and a third frequency deviation (Δf _w ) from the third frequency deviation (Δf _w ) detection unit 22. _w )) and adding the signal to the numerically controlled oscillator (NCO) 17.

The selector unit 19 selects a signal having the first frequency deviation (Δf _n1 ) or the second frequency deviation (Δf _n2 ) according to a selection condition described later, and sends the signal to the adder 18. For example, the frequency deviation that is an integral multiple of the subcarrier interval as the third frequency deviation (Δf _w ) is adjusted to zero, and the frequency deviation within ½ as the first frequency deviation (Δf _n1 ) is set in advance. If it is less than the threshold value, a signal of the second frequency deviation (Δf _n2 ) is selected, and otherwise, the selection condition can be such that the first frequency deviation (Δf _n1 ) is selected. This is because when the third frequency deviation (Δf _w ) has been adjusted by the numerically controlled oscillator (NCO) 17 and the first frequency deviation (Δf _n1 ) is less than a preset threshold, the second frequency The deviation (Δf _n2 ) is corrected, and in other cases, the frequency deviation obtained by adding the first frequency deviation (Δf _n1 ) and the third frequency deviation (Δf _w ) is corrected. Alternatively, while the third frequency deviation (Δf _w ) is not corrected, the frequency deviation obtained by adding the first frequency deviation (Δf _n1 ) and the third frequency deviation (Δf _w ) may be corrected. .

The first frequency deviation (Δf _n1 ) detection unit 20 includes means for detecting a frequency deviation within 1/2 of the subcarrier interval after the guard interval correlation calculation from the strength of the mutual correlation.

The second frequency deviation (Δf _n2 ) detection unit 21 adds the detected first frequency deviation (Δf _n1 ) and the third frequency deviation (Δf _w ), corrects the frequency deviation after the addition, From the phase term of the maximum correlation value used for calculating the three frequency deviations (Δf _w ), a correction amount for further correcting the frequency deviation within ½ is detected.

The third frequency deviation (Δf _w ) detection unit 22 detects the deviation amount of the subcarrier interval specified from the detected combination of correlation calculations as a frequency deviation that is an integral multiple of the subcarrier interval.

  The peak detection unit 23 detects the maximum correlation value from a predetermined number of combinations of correlation operations shifted in the subcarrier direction in units of subcarriers (that is, detection of correlation peaks). Preferably, the subcarrier signal of symbol number n and the subcarrier signal of symbol number (n−2) two symbols before are a predetermined number of subcarriers shifted in the subcarrier direction as a combination of correlation operations. From the combination of correlation calculations, the one having the maximum correlation value is detected.

  Hereinafter, the operation of the MIMO-OFDM receiver according to the first embodiment will be described in more detail with reference to FIGS. 6 and 7.

  In FIG. 1, a signal received by one antenna 2 is down-converted by a frequency converter (D / C) 3 to a frequency band where digital signal processing is possible. Next, the frequency-converted received signal is converted into a digital signal by the A / D converter 4 and digital orthogonal demodulation processing is performed. In MIMO-OFDM transmission, since reception is usually performed using a plurality of antennas, there is a part where each antenna performs the same processing individually and a part where the processing can be made common. The signal processing received by the antenna will be mainly described, and details regarding processing when a plurality of antennas are used will be described later.

  In the transmitter / receiver, a frequency deviation occurs between transmitted and received signals due to individual differences of a local oscillator (not shown) used in the frequency converter (D / C) 3. A frequency deviation detected by a method described later is fed back to the signal after digital quadrature demodulation by the quadrature demodulator 5 (step S1), and the numerically controlled oscillator (NCO) 17 is controlled and multiplied by the output signal of the NCO 17 The frequency deviation is corrected (step S2). Here, it is assumed that the initial output of the NCO 17 at the start of operation is 1, that is, through. Thereafter, the output of the NCO 17 is updated every time a frequency deviation is detected.

Next, an operation for detecting a frequency deviation will be described. The frequency deviation is detected by dividing it into a narrow band frequency deviation (Δf _n1 ) within ½ of the subcarrier interval and a wide band frequency deviation (Δf _w ) with the subcarrier interval as a unit. In the initial operation, a narrow band frequency deviation is first detected by a method normally used in the OFDM system (for example, shown in Non-Patent Document 2). This will be briefly described below.

A signal that has undergone quadrature demodulation and frequency deviation correction processing (multiply by 1 and pass through during initial operation) is passed through an FIR filter (LPF) 7 and subjected to downsampling processing (DS) 8 (step S3). Then, a guard interval correlation (GI correlation) 9 is performed (step S4). From the phase term of the correlation peak in the guard interval correlation (GI correlation) 9, a narrow band frequency deviation Δf _n1 within ½ of the subcarrier interval is detected and fed back to the NCO 17 to correct the frequency deviation (step) S4). The detected frequency deviation is shown in equation (1).

_{C GI} in the formula (1) is a guard interval correlation peak value, _{T u} is the effective symbol length, symbol real and imag, respectively indicating the calculated value of the real part and the imaginary part of the numbers in parentheses. Up to this point, it is the same as detection of a narrow band frequency deviation in the conventional OFDM system.

In this method, the frequency deviation (Δf _n1 ) exceeding 1/2 of the carrier interval cannot be detected because the correlation value is not reliable, and the residual frequency deviation after correction at this time is determined as MIMO-OFDM. Depending on the demodulation method, the allowable range may be exceeded. Therefore, the following method (steps S5 to S8) detects a wideband frequency deviation (Δf _w ) that is an integral multiple of the carrier interval, and more accurately detects the frequency deviation (Δf _n2 ) (FIGS. 6 and 6). 7 "a", "b").

  An effective symbol is extracted at the cut-out position detected by the guard interval correlation (step S21), and after the FFT operation by the FFT unit 10, the TMCC signal that has been DBPSK modulated and inserted into the designated subcarrier is detected by the TMCC detection unit 11, for example. . Since the TMCC signal is common to the transmission stream 1 and the transmission stream 2, there is no problem in detection even if each stream is spatially multiplexed on the propagation channel. Various control information such as modulation scheme and error correction can be acquired from the TMCC signal, but in this embodiment, only the frame start position can be detected and used (step S22).

By detecting the frame synchronization word from the TMCC signal by the frame synchronization detection unit 14, the symbol number (0 to 407) after the FFT calculation can be grasped. Therefore, the carrier extraction unit 13 extracts, for example, the subcarrier signals C _{n, 8k} having the symbol number n satisfying mod (n, 2) = 0 from the symbol after the FFT calculation (step S23). Here, C _{n, 8k} indicates the signal value (complex number) of the subcarrier of symbol number n and carrier number 8k. That is, in this embodiment in which the number of transmission streams is 2, only the subcarriers of even-numbered symbols are extracted every 8 in the carrier arrangement direction. The reason for extracting every 8 lines is that the purpose is to extract subcarriers corresponding to the interval between pilot carriers.

  In the MIMO-OFDM scheme, odd-numbered symbols are inserted with inverted pilot signal values between transmission streams, and each transmission stream has substantially the same phase, such as when the transmission antenna interval is small with respect to the transmission / reception distance. In the case of reception, it is canceled out because the level drops and the detection accuracy deteriorates significantly. However, when there is a possibility that the phase of each transmission stream is in the opposite phase, such as when the transmission antenna interval is wide with respect to the transmission / reception distance, the method of Example 2 described later is used.

Next, the subcarrier signal C _{n, 8k of} symbol number n satisfying the extracted mod (n, 2) = 0 and the subcarrier signal of symbol number (n−2) two symbols before by the inter-symbol carrier correlation unit 15. C _n-2,8k correlation calculation is performed. Further, the inter-symbol carrier correlator 15 performs sub-carrier correlation calculation between symbols (hereinafter referred to as inter-symbol carrier correlation) for eight sets shifted in units of sub-carriers. Expression (2) shows the correlation calculation value γ _{n, m} of each group by a mathematical expression. Here, m (= an integer of 0 to 7) represents a shift amount, and * in the formula represents a conjugate complex number. 2 and 3 show examples of inter-symbol carrier correlation in the case of γ _{n, 0} and γ _{n, 2} when there is a frequency deviation of two subcarrier intervals between the transceivers. In FIG. 2, the sets 101-1 to 101-3 that correlate between symbols are selected. However, the correlation value is not high because it is not on the pilot signal (black circle). From this situation, By sequentially shifting in the carrier direction, the position where the correlation value is high can be found because it is on the pilot signal (black circle) (step S24). FIG. 3 shows a situation in which the sets 102-1 to 102-3 are selected as having inter-symbol carrier correlation.

If the group having the largest absolute value among the eight sets of correlation values γ _{n, 0 to} γ _{n, 7 in} the equation (2) is γ _{n, w} (step S25), the third frequency deviation (Δf _w ) The detection unit 22 detects a frequency deviation Δf _w (= wΔf _c ) that is w times the subcarrier interval Δf _c as a wideband frequency deviation (step S 26), and Δf _n (Δf _n1 or Δf _n2 ) via the selector unit 19. ) To the adder 18. However, the range of the detectable frequency deviation Δf _w is up to the adjacent CP carrier interval (= 8Δf _c ).

4 and 5 show examples of correlation absolute values of each set when γ _{n, w} = γ _{n, 2} . Figure 4 is a narrow-band frequency deviation (Delta] f _n1) is corrected case, FIG. 5 is a sufficient uncorrected case, the correction processing pre-stage here mentioned process narrowband frequency deviation (Delta] f _n1) Need to be done in.

The narrow-band frequency deviation Δf _n1 and the wide-band frequency deviation Δf _w detected by the method described above are added by the adder 18 via the selector unit 19 and fed back to the NCO as the total frequency deviation between transmission and reception to correct the frequency deviation. Is done.

  In MIMO transmission, which is a spatial multiplexing technique, a propagation channel is estimated on the receiving side, and signal processing such as separation / detection based on the result is performed. Since the propagation channel is usually obtained by averaging over several symbols, a phase difference occurs between the first half symbol and the second half symbol due to residual frequency deviation, and separation and decoding of signals spatially multiplexed by MIMO Since this affects the characteristics, it is necessary to correct the frequency deviation with higher accuracy in order to exhibit the decoding performance.

Therefore, a method of switching Δf _n1 that is detected from the phase difference of the guard interval correlation peak value and used for correction to a narrower frequency deviation Δf _n (Δf _n1 or Δf _n2 ) to a more accurate correction value Δf _n2. This will be described below.

The third frequency deviation (Δf _w ) detection unit 22 detects the correction value Δf _n2 with higher accuracy by detecting the correlation peak value γ _n detected by the inter-symbol carrier correlation when detecting the wideband frequency deviation (Δf _w ). _{, w} . γ _{n, w} is a complex number, and the frequency deviation Δf _n2 is detected from the phase angle according to the equation (3) (step S27).

T _u in equation (3) represents the effective symbol length. 2T _{u is} because the inter-symbol carrier correlation is performed at intervals of 2 symbols. For example, when the number of transmission streams is 4 and the pilot signals form orthogonal codes between the transmission streams over 4 symbols, 4T _u Become.

Or Delta] f _n2 is no wide frequency deviation of the subcarrier spacing, or corrected by Delta] f w _{= 0} becomes and if narrowband frequency deviation Delta] f _n1 detected from the guard interval correlation is less than the threshold f _th, Delta] f _n2 It is possible to detect the residual frequency deviation with higher accuracy. When this condition is satisfied, the selector unit 19 switches to Δf _n2 as the narrow band frequency deviation detection output Δf _n .

For example, the reference value of the threshold f _th is set to a value of about 10 to 20% of the subcarrier interval Δfc. If the frequency deviation increases due to deterioration in detection accuracy due to a decrease in the reception level or increase in the Doppler frequency due to movement, and Δf _n2 exceeds f _th , Δf _n1 is again set to Δf _n and the selector unit is switched again. Output. The Δf _n output from the selector unit 19 is added to the broadband frequency deviation detection value Δf _w by the adder 18 and fed back to the control of the NCO 17.

  By repeating the above processing, it is possible to always perform highly accurate correction of the frequency deviation even in a severe propagation environment in which the frequency deviation fluctuates with time due to the influence of the Doppler effect or the like.

  The above description has been given for the case of reception with one antenna. However, in MIMO transmission, since reception is usually performed with a plurality of antennas, an embodiment in which they are used for detection and correction of frequency deviation will be described.

A configuration example in the case of reception with two antennas is shown in FIG. Similar components are denoted by similar reference numerals, and further detailed description of similar components is omitted. That is, the MIMO-OFDM receiver 1 according to the modification of the first embodiment shown in FIG. 8 includes antennas 2-1, 2-2, frequency conversion units (D / C) 3-1, 3-2, A / D conversion units 4-1, 4-2, quadrature demodulation units 5-1, 5-2, multipliers 6-1, 6-2, FIR filters (LPF) 7-1, 7-2, down Sample processing (DS) 8-1, 8-2, guard interval correlation (GI correlation) 9-1, 9-2, FFT units 10-1, 10-2, TMCC detection units 11-1, 11- 2, carrier extraction units 13-1 and 13-2, frame synchronization detection unit 14, intersymbol carrier correlation units 15-1 and 15-2, local oscillator (Lo) 16, and numerically controlled oscillator (NCO) 17, an adder 18, a selector unit 19, a first frequency deviation (Δf _n1 ) detection unit 20, and a second frequency Although corresponding to each element of FIG. 1 in that it includes a deviation (Δf _n2 ) detection unit 21, a third frequency deviation (Δf _w ) detection unit 22, and a peak detection unit 23, a frame synchronization detection unit 14 and the peak detection unit 23 are different from each other in that they have an average process between receiving antennas and a peak detection / average process unit 24. However, the basic operation is the same as in FIG. 1 except for the following points.

  The configuration shown in FIG. 8 operates individually for each of the receiving antennas 2-1 and 2-2 except for the common processing unit 12 surrounded by a broken line in FIG. For the correlation peak values (GI correlation units 9-1 and 9-2, inter-symbol carrier correlation units 15-1 and 15-2) detected for each reception antenna system, the frame synchronization detection unit 14 and the peak detection unit 23, and The peak detection / average processing unit 24 can perform simple addition or addition with weighting according to the received signal level between the systems, thereby obtaining a highly reliable correlation value. However, in each receiving antenna system, it is assumed that the local oscillator 16 and the NCO 17 are synchronized by using the same signal source.

  According to the MIMO-OFDM receiver of the first embodiment, when MIMO-OFDM transmission is used in a mobile environment, a wide band and high-accuracy frequency deviation can be obtained even in a severe propagation environment in which the frequency deviation varies with time. It can be detected and corrected.

  Next, a MIMO-OFDM receiver according to Embodiment 2 of the present invention will be described.

[Example 2]
The MIMO-OFDM receiver according to the second embodiment is a further improvement of the MIMO-OFDM receiver according to the first embodiment, and particularly operates to adaptively select symbols to be extracted for frequency deviation detection.

  In the first embodiment, a symbol to be extracted for frequency deviation detection is specified by detecting the first frame using a TMCC signal (eg, even-numbered symbols). In most cases, the receiving apparatus of the first embodiment can detect and correct the frequency deviation with high accuracy. However, in rare cases, the transmission antenna interval is relatively large with respect to the distance between transmission and reception. It is possible that the propagation paths are different and are combined in opposite phases. In that case, degradation of detection accuracy is expected. Therefore, the MIMO-OFDM receiver according to the second embodiment does not fix the symbol numbers detected using the TMCC detection unit 11 and the frame synchronization detection unit 14, but adaptively assigns symbols for frequency deviation detection according to the propagation environment. Operate to select.

  FIG. 9 illustrates a MIMO-OFDM receiver according to the second embodiment. Components similar to those in the first embodiment will be described with the same reference numerals. The MIMO-OFDM receiver according to the second embodiment further includes a correlation comparison unit 26 and a combination selection unit 27 instead of using the TMCC detection unit 11 and the frame synchronization detection unit 14 as compared with the first embodiment. A difference is that a carrier extracting unit 25 for extracting carriers of all symbols is provided instead of the carrier extracting unit 13 for extracting carriers of designated symbols.

  In the first embodiment, an example in which only even-numbered symbols are extracted and inter-symbol carrier correlation is performed has been described. However, in the second embodiment, inter-symbol correlation is similarly performed on odd-numbered symbols. With respect to, a result obtained by comparing two sets of correlation values consecutive in the symbol direction is used. That is, the correlation comparison unit 26 has a function of sending, to the combination selection unit 27, the result of comparing two sets of correlation values consecutive in the symbol direction for each of the even and odd symbols.

  The combination selection unit 27 has a function of selecting a pair having the largest absolute value from the correlation value results compared by the correlation comparison unit 26 and sending the selected pair to the peak detector 23.

  FIG. 10 shows a flowchart for explaining the second embodiment. However, since the flowchart of Example 1 shown in FIG. 6 is common to Example 2, only the flowchart corresponding to FIG. That is, in the second embodiment, the same processing is performed until the FFT operation of the FFT 10 of the first embodiment (step S31). After the FFT calculation, the subcarriers of all symbols are extracted by the carrier extraction unit 25 (step S32), and the intersymbol carrier correlation shown in Expression (2) is performed by the intersymbol carrier correlation unit 15 (step S33). Here, n in the formula (2) does not need to satisfy mod (n, 2) = 0. By the functions of the inter-symbol carrier correlation unit 15 and the correlation comparison unit 26, 8 sets of correlation peak values are obtained for each symbol as in the first embodiment (steps S33 and S34). The group with the larger value is selected (step S35). The peak detector 23 performs an averaging process between the symbol direction and the receiving antenna system in order to improve the accuracy with respect to the selected set of correlation peaks. The subsequent processing is the same as that in the first embodiment (steps S36 and S37).

  As described above, when two sets of subcarrier signals having different symbol numbers as described in the first embodiment are extracted, the orthogonal code length is set to l and the symbol number n is detected without detecting the frame head position from the TMCC signal. Symbol number n satisfying mod (n, l) = r (0 ≦ r <l−1) and different symbol numbers consisting of the subcarrier signal of symbol number (n−1) before l symbols When two sets of subcarrier signals are extracted, the combination that maximizes the correlation value of the correlation calculation obtained by shifting in the subcarrier direction in units of subcarriers is selected. After performing the operation of the second embodiment, if the operation of the first embodiment is performed, the propagation paths for each transmission stream are different from each other and are prevented from being combined in opposite phases while including all the advantages of the first embodiment. Will be able to.

  Next, a MIMO-OFDM receiver according to Embodiment 3 of the present invention will be described.

[Example 3]
The MIMO-OFDM receiver according to the third embodiment operates so as to obtain the frequency deviations Δf _n and Δf _w from the result of inter-symbol carrier correlation without using Δf _n1 detected from the phase difference of the guard interval correlation peak value.

In order to obtain the frequency deviation Δf _n by inter-symbol carrier correlation, accurate detection cannot be performed unless the frequency deviation is equal to or smaller than the threshold f _{th in} the initial state. Therefore, in the first embodiment and the second embodiment, as a first step, a narrow band frequency deviation Δf _n1 is detected from the guard interval correlation, fed back to the NCO 17, and corrected until the frequency deviation becomes equal to or less than the threshold f _th , Thereafter, the method of switching to Δf _n2 in the second step has been described.

In this embodiment, a method of obtaining and correcting frequency deviations Δf _n and Δf _w by direct intersymbol carrier correlation without detecting frequency deviation due to guard interval correlation will be described with reference to FIG.

FIG. 11 shows a MIMO-OFDM receiver according to the third embodiment of the present invention. Moreover, the flowchart of Example 3 is shown in FIG. Similar components are denoted by similar reference numerals, and further detailed description of similar components is omitted. That is, as shown in FIG. 11, there is no detection and correction processing of the narrow band frequency deviation Δf _n1 due to the guard interval correlation, and the control signal for the peak detector 28 to directly control the NCO 17 based on two criteria described later. Except for transmission, the configuration is the same as that of the first embodiment up to inter-symbol carrier correlation and peak detection. The NCO 17 cyclically varies the control frequency for each period in which the inter-symbol carrier correlation is detected within the frequency range corresponding to the pilot carrier interval in the initial state (step S41).

For example, in the ARIB STD-B33 standard (Non-Patent Document 1), the variable amount of the control frequency is such that the subcarrier interval is Δfc = 20 kHz, the pilot carrier interval is Δfc = 160 kHz, and a narrow band frequency deviation is detected by inter-symbol carrier correlation. If the possible amount is f _th = 4 kHz or less, the amount is periodically varied, for example, in 2 kHz steps smaller than the detectable limit. That is, assuming that the original control frequency of the NCO is 80 MHz, the NCO is cyclically varied as 79.990 MHz, 79.992 MHz, 79.994 MHz,..., 80.06 MHz, 80.008 MHz. The process proceeds in the same manner as in the first embodiment while making the variable (steps S42 to S46). However, if the variable step is reduced, the detection accuracy is improved, but a delay occurs in the pull-in time, so an appropriate value is set.

Accordingly, in the initial state frequency deviation even greater than f _th, by varying cyclically the control frequency of the NCO 17, can be frequency deviation is to control the frequency of smaller than f _th NCO 17, the inter-symbol-carrier correlation The unit 15 can accurately detect the frequency deviations Δf _n and Δf _w . However, when the frequency deviation becomes smaller than f _th , it is necessary to detect this and stop the cyclic control frequency of the NCO 17. As the method, the first criterion is that the magnitude of the frequency deviation Δf _n detected by the inter-symbol carrier correlation is smaller than f _th and Δf _w = 0 (step S49), and the absolute value of the peak detection value Is added as a second criterion (steps S47 and S48), and when both conditions are satisfied, the periodic control frequency of the NCO 17 is stopped (step S50). ), Correction control of Δf _n and Δf _w is performed as in the first embodiment (step S51). The first determination criterion and the second determination criterion are constantly monitored by the peak detector 28. When the determination criterion is not satisfied, the periodic control frequency of the NCO 17 is resumed (step S41).

As a result, frequency deviations Δf _n and Δf _w can be obtained and corrected by direct inter-symbol carrier correlation without detecting frequency deviation due to guard interval correlation.

  Next, a MIMO-OFDM receiver according to Embodiment 4 of the present invention will be described.

[Example 4]
The MIMO-OFDM receiver according to the fourth embodiment operates to detect a wideband frequency deviation exceeding the pilot carrier interval.

  In the wideband frequency deviation detection method using the intersymbol carrier correlation of the first to third embodiments, a larger frequency deviation exceeding the pilot carrier interval cannot be detected. Therefore, a method for detecting a frequency deviation exceeding the pilot carrier interval will be described with reference to FIG.

FIG. 13 is a diagram partially illustrating the MIMO-OFDM receiver according to the third embodiment of the present invention. The steps up to the carrier extraction of the designated symbol are the same as those in the first embodiment, and are omitted. The MIMO-OFDM receiver according to the fourth embodiment is different in that it includes a known CP pattern transmission unit 29 that transmits a known pilot pattern, and includes a correlation comparison unit 26 instead of the intersymbol carrier correlation unit 15. The correlation comparator 26 repeats the correlation calculation with the known pilot pattern for the designated symbol subcarriers extracted by the carrier extractor 13 while sliding in the carrier direction, and adds and averages the correlation values at the same carrier position in the symbol direction. The average value is calculated, and the average value is sent to the peak position detector 23. The peak position detector 23 extracts the maximum value from the average value and sends it to the third frequency deviation (Δf _w ) detector.

  Here, as in the first embodiment, in the present embodiment in which the number of transmission streams is 2, only the carriers of even-numbered symbols are extracted every eight in the carrier arrangement direction, and the designated symbols are known. This is to perform correlation calculation with the pilot pattern. In the first to third embodiments, the inter-symbol carrier correlation is performed, but it is noted here that the calculation is a correlation with a known pilot pattern.

  As an example, FIG. 14 shows a correlation output when sliding over all carriers. In the case where the position where the absolute value of the correlation output in the figure is the maximum matches the known pilot pattern, the actual frequency deviation can be detected in units of carrier intervals from the deviation from the center.

  Therefore, in the MIMO-OFDM receiver of the fourth embodiment, a known pilot pattern is defined in advance to correct a frequency deviation exceeding the carrier interval of the pilot signal, and the subcarrier of symbol number n in a predetermined effective symbol period When calculating the correlation between the signal and the known pilot pattern, the correlation calculation of the subcarrier signal is repeated while sliding in the carrier direction, and the average value obtained by adding and averaging the correlation values at the same carrier position in the symbol direction is calculated. The maximum value is extracted from the average values, and the shift amount of the receiving system at the extracted maximum average value is corrected as a frequency deviation.

  From the above, it is possible to detect even a frequency deviation exceeding the pilot carrier interval by the method of the present embodiment, and by combining with the methods of the first to third embodiments, a wide band and highly accurate correction of the frequency deviation is realized. be able to.

  Although the above-described embodiments have been described as typical examples, it is obvious to those skilled in the art that many variations and substitutions can be made by combining the embodiments 1 to 4 within the spirit and scope of the present invention. . For example, the pilot signal has been described as using CP, but another reference signal may be transmitted on the transmission side and added to the TMCC information. Accordingly, the invention should not be construed as limited by the embodiments described above, but only by the claims.

  According to the present invention, it is possible to appropriately correct a frequency deviation that occurs between transmitting and receiving devices when a plurality of spatially multiplexed transmission streams are separated, which is useful for applications using a MIMO-OFDM receiver.

It is a figure which shows the MIMO-OFDM receiver of Example 1 by this invention. It is a figure which shows the example of the carrier correlation between symbols in the MIMO-OFDM receiver of Example 1 by this invention. It is a figure which shows the example of the carrier correlation between symbols in the MIMO-OFDM receiver of Example 1 by this invention. It is a figure which shows the example when a narrow band frequency deviation ((DELTA) _fn1 ) is correct | amended. It is a figure which shows the example in case a narrow band frequency deviation ((DELTA) _fn1 ) is not fully correct | amended. It is a flowchart explaining operation | movement of the MIMO-OFDM receiver of Example 1 by this invention. It is a flowchart explaining operation | movement of the MIMO-OFDM receiver of Example 1 by this invention. It is a figure which shows the MIMO-OFDM receiver of the modification of Example 1 by this invention. It is a figure which shows the MIMO-OFDM receiver of Example 2 by this invention. It is a flowchart explaining operation | movement of the MIMO-OFDM receiver of Example 2 by this invention. It is a figure which shows the MIMO-OFDM receiver of Example 3 by this invention. It is a flowchart explaining operation | movement of the MIMO-OFDM receiver of Example 3 by this invention. It is a figure which shows partially the MIMO-OFDM receiver of Example 4 by this invention. It is a figure which shows the example of a correlation output at the time of making it slide over all the carriers in the MIMO-OFDM receiver of Example 4 by this invention.

Explanation of symbols

1 MIMO-OFDM Receiver 2, 2-1, 2-2 Antenna 3, 3-1, 3-2 Frequency Converter (D / C)
4,4-1, 4-2 A / D converter 5,5-1,5-2 Quadrature demodulator 6,6-1,6-2 Multiplier 7,7-1,7-2 FIR filter (LPF )
8,8-1,8-2 Downsample processing (DS)
9, 9-1, 9-2 Guard interval correlation (GI correlation)
10, 10-1, 10-2 FFT unit 11, 11-1, 11-2 TMCC detection unit 12 Common processing unit 13, 13-1, 13-2 Carrier extraction unit 14 Frame synchronization detection unit 15, 15-1, 15-2 Intersymbol Carrier Correlator 16 Local Oscillator (Lo)
17 Numerically controlled oscillator (NCO)
18 Adder 19 Selector 20 First Frequency Deviation (Δf _n1 ) Detection Unit 21 Second Frequency Deviation (Δf _n2 ) Detection Unit 22 Third Frequency Deviation (Δf _w ) Detection Unit 23 Peak Detection Unit 24 Peak Detection / Average Processing Unit 25 Carrier extraction unit 26 Correlation comparison unit 27 Combination selection unit 28 Peak detector 29 Known CP pattern transmission unit

Claims (8)

A MIMO-OFDM receiver for receiving an OFDM signal transmitted by spatially multiplexing a plurality of different transmission streams at the same frequency,
Pilot signals that are orthogonal codes for each transmission stream are inserted between data carriers,
Means for demodulating OFDM signals of the plurality of transmission streams and extracting two sets of subcarrier signals having different symbol numbers for each symbol corresponding to the length of the orthogonal code;
Means for detecting a maximum correlation value of a correlation operation obtained by shifting in the subcarrier direction in units of subcarriers using a combination of two sets of subcarrier signals having different symbol numbers;
And a means for detecting a deviation amount of the subcarrier interval specified from the detected combination as a frequency deviation that is an integral multiple of the subcarrier interval and correcting the frequency deviation for each reception system. OFDM receiver. The means for extracting two sets of subcarrier signals having different symbol numbers extracts a TMCC signal common to the plurality of transmission streams, detects a frame head position from the TMCC signal, and the plurality of transmission streams are spatially multiplexed. Means for extracting two sets of subcarrier signals with different symbol numbers for each symbol corresponding to the length of the orthogonal code from the detected frame head position from the OFDM signal;
The two sets of subcarrier signals having different symbol numbers have an orthogonal code length of l, a symbol number n satisfying mod (n, l) = 0, and a symbol number of l symbols before ( n−1) subcarrier signals,
The means for correcting a frequency deviation that is an integral multiple of the subcarrier interval for each reception system includes a set of correlations between the subcarrier signal of the symbol number n and the subcarrier signal of the symbol number (n−1) before l symbols. The MIMO-OFDM receiver according to claim 1, wherein a combination having a maximum correlation value is detected from a predetermined number of combinations of correlation calculations shifted in the subcarrier direction in units of subcarriers. .   The means for extracting two sets of subcarrier signals having different symbol numbers is a symbol number n where the orthogonal code length is 1 and the symbol number n satisfies mod (n, l) = r (0 ≦ r <l−1). Are extracted in the subcarrier direction in units of subcarriers when two sets of subcarrier signals with different symbol numbers consisting of a subcarrier signal of 1 symbol and a subcarrier signal of symbol number (n−1) before l symbols are extracted. The MIMO-OFDM receiving apparatus according to claim 1, further comprising means for selecting a combination having a maximum correlation value of the obtained correlation calculation. Means for correcting a frequency deviation of an integral multiple of the subcarrier interval for each reception system,
After correcting the frequency deviation for each receiving system,
Means for detecting a frequency deviation between the transceivers from the phase term of the maximum correlation value of the combination of detected correlation operations;
The MIMO-OFDM receiver according to claim 1, further comprising: a unit that corrects the detected frequency deviation between the transceivers for each reception system. Means for performing a correlation operation between guard intervals obtained by copying a part of an effective symbol of an OFDM signal at the time of demodulation and detecting a frequency deviation within 1/2 of a subcarrier interval;
Means for correcting a frequency deviation of an integral multiple of the subcarrier interval for each reception system,
While the frequency deviation that is an integral multiple of the subcarrier interval is not corrected, a frequency deviation within ½ of the detected subcarrier interval and a frequency deviation that is an integral multiple of the subcarrier interval are added. The MIMO-OFDM receiver according to any one of claims 1 to 4, further comprising correction means for correcting the frequency deviation after the addition.   The means for correcting a frequency deviation that is an integral multiple of the subcarrier interval for each reception system adds a frequency deviation within ½ of the detected subcarrier interval and a frequency deviation that is an integral multiple of the subcarrier interval. Then, after correcting the frequency deviation after the addition, a correction amount for further correcting the frequency deviation within 1/2 is detected from the phase term of the maximum correlation value used to calculate the frequency deviation that is an integral multiple of the subcarrier interval. 6. The MIMO-OFDM receiving apparatus according to claim 5, further comprising correction means for correcting the correction amount. Means for correcting a frequency deviation of an integral multiple of the subcarrier interval for each reception system,
Regardless of whether or not a frequency deviation within 1/2 of the subcarrier interval is detected by performing a correlation operation between guard intervals obtained by copying a part of the effective symbol of the OFDM signal during the demodulation, an integer multiple of the subcarrier interval is used. After correcting the frequency deviation, the correction amount in the means for correcting the frequency deviation is cyclically varied so that the frequency deviation within ½ of the subcarrier interval is equal to or less than a preset threshold value, and the subcarrier interval is The MIMO-OFDM receiving apparatus according to claim 1, further comprising: a correction unit that detects a correction amount that minimizes the frequency deviation and corrects the correction amount. In order to correct the frequency deviation exceeding the carrier interval of the pilot signal, a known pilot pattern is defined in advance,
Means for correcting a frequency deviation of an integral multiple of the subcarrier interval for each reception system,
When performing a correlation calculation between the subcarrier signal of symbol number n in a predetermined effective symbol section and the known pilot pattern,
Means for calculating the average value obtained by adding and averaging the correlation values of the same carrier position in the symbol direction, and extracting the maximum value from the average values, by repeating the correlation calculation of the subcarrier signal while sliding in the carrier direction; ,
The MIMO-OFDM receiver according to any one of claims 1 to 7, further comprising means for correcting a deviation amount of the reception system at the extracted maximum average value as a frequency deviation.

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