JP2005130480A - Method of detecting carrier shift amount of digital transmission signal, method of correcting carrier shift amount, and receiving apparatus using these methods - Google Patents

Abstract

A frequency shift correction control can be normally performed even when the frequency shift received on a transmission line or the like is a carrier shift count of ± 1 or more.
In an OFDM transmission apparatus having a TMCC carrier, a TMCC carrier is demodulated from a received received signal, a relative carrier position of the demodulated TMCC carrier is detected, and a detected relative carrier position of the TMCC carrier and a normal TMCC carrier position are detected. Thus, the carrier frequency deviation is detected and the carrier frequency deviation is corrected and controlled based on the detected carrier deviation. Even when the frequency deviation is greater than or equal to ± 1 carrier deviation, it can be normally corrected.
[Selection] Figure 1

Description

  The present invention relates to improvement of transmission tolerance of a digital transmission apparatus, and more particularly to a carrier deviation amount detection method, a carrier deviation amount correction method, and a receiving apparatus using these methods.

  In recent years, orthogonal frequency division multiplexing (OFDM), which is characterized by being resistant to multipath fading and ghosting, is suitable for digital transmission for mobiles and terrestrial digital television broadcasting. Multiplex) method) is attracting attention.

The OFDM system is a kind of multi-carrier modulation system, and is a transmission system in which digital modulation is performed on n (n is several tens to several hundreds) carrier waves (carriers) orthogonal to each other.
The transmission signal from the transmission device of such a digital transmission device may cause a frequency shift due to fading or the like in the transmission path. When a signal with a frequency shift is received, the signal must be demodulated after correcting the frequency shift.

FIG. 1 shows a conventional example for correcting a frequency shift. A reception signal received by a reception high-frequency unit (not shown) of the reception device is frequency-converted into an IF (intermediate frequency) signal by the reception high-frequency unit. The IF signal from the reception high frequency unit is frequency converted into a baseband signal by the frequency conversion unit 1. The signal frequency-converted into the baseband signal is subjected to analog / digital conversion (hereinafter abbreviated as A / D conversion) by an AD (analog-to-digital) converter 3. The A / D converted digital signal is quadrature demodulated by the quadrature demodulator 4 into I-axis and Q-axis signals. The quadrature demodulated Q-axis signal is input to the error detection unit 8 to control the control voltage of a frequency control VCO (voltage controlled oscillator) 2 so that the value of the Q-axis signal becomes zero. By the above control, the frequency shift received on the transmission path is removed. Such a technique is disclosed in Patent Document 1, for example.
Japanese Patent Laid-Open No. 11-4209

  However, the frequency deviation correction control has the following problems. That is, in the above control, correction control cannot be performed normally unless the frequency deviation amount is within a certain range. The OFDM transmission signal has a multi-carrier structure as shown in FIG. That is, in the above control, when the frequency deviation of two or more carriers is in the positive or negative phase direction (here, such a case is defined as a case where the number of carrier deviations is ± 2 or more for convenience). Then, with reference to the position where the carrier position is shifted, correction control is performed so that the phase is matched with the carrier closest to the position. Therefore, in the case of a frequency shift of one carrier or less, the carrier can be adjusted to the correct position. However, in the case of a frequency shift of two or more carriers, there is a problem that the carrier cannot be adjusted to the correct position. .

  Thus, in the above-described prior art, when correcting the frequency deviation, if the number of carrier deviations is ± 1 or less, the frequency deviation can be corrected normally, but the number of carrier deviations is ± 2 or more. However, there is a problem that the frequency deviation cannot be corrected normally.

  An object of the present invention is to eliminate these drawbacks and to enable normal correction control of frequency deviation even when the frequency deviation is greater than or equal to ± 2 carrier deviations.

  In order to achieve the above object, the present invention demodulates the TMCC carrier from the received signal and detects the relative carrier position of the demodulated TMCC carrier in an OFDM transmission apparatus having a TMCC (Transmission and Multiplexing Configuration Control) carrier. The carrier shift amount is detected based on the detected TMCC carrier position.

  Further, a carrier deviation amount is detected from the detected relative carrier position of the TMCC carrier and a normal TMCC carrier position, and the carrier frequency deviation is corrected and controlled based on the detected carrier deviation amount.

  Further, when detecting the relative carrier position of the TMCC carrier, all the TMCC carrier data within one demodulated symbol period are added, and the above addition processing is performed within a range of ± M carriers (M is an integer of 2 or more) from the normal TMCC carrier position. Is to do.

  Further, the signal subjected to the addition process is further added between N symbols (N is an integer of 2 or more), and the peak of the signal added between the N symbols is detected. From the detected peak position and the normal TMCC carrier position, This detects the amount of carrier shift.

  According to the present invention, even when the frequency shift received on the transmission line or the like is more than ± 2 carrier shifts, it can be corrected normally, and transmission tolerance can be improved.

Hereinafter, a case where the present invention is applied to an OFDM transmission apparatus will be described.
Before describing the present invention, the carrier arrangement of an OFDM transmission apparatus will be described. As shown in FIG. 2, the OFDM transmission signal has a multicarrier structure. As described above, the carrier includes a main data carrier for sending main data and a sub data carrier for sending sub data arranged at a predetermined random position. As the sub data, for example, a CP (Continual Pilot) carrier arranged periodically (for example, every 8 carriers), a TMCC (Transmission and Multiplexing Configuration Control) carrier arranged at a predetermined random position, The AC (Auxiliary Channel) carrier arranged at a predetermined random position and the Null (Null) carrier arranged periodically (for example, every 420 carriers). Carriers other than these are main data carriers. In FIG. 2, the AC carrier and the null carrier are not shown.

Here, the CP carrier is used for synchronous reproduction, the TMCC carrier is used for mode identification such as a modulation scheme, and the main data carrier is used for video and audio transmission.
FIG. 3 is a diagram showing the arrangement of sub data carriers in the 2K half mode among carriers compliant with the ARIB STD-B33 standard. In the figure, the CP carrier is omitted.

In the following description of embodiments, an example using the 2K half mode will be described as an example.
Hereinafter, an embodiment of the present invention regarding a carrier deviation number (deviation amount) detection method and frequency deviation correction method will be described in detail with reference to FIG.

  A reception signal received by a reception high-frequency unit (not shown) of the reception device is frequency-converted into an IF signal by the reception high-frequency unit. The IF signal from the reception high frequency unit is frequency converted into a baseband signal by the frequency conversion unit 1. The signal frequency-converted to the baseband signal is A / D converted by the AD converter 3. The A / D converted signal is orthogonally demodulated into an I-axis signal and a Q-axis signal by the orthogonal demodulation unit 4. The orthogonally demodulated I-axis and Q-axis signals are input to FFT (Fast Fourier Transform) and subjected to Fourier transform. The Fourier-transformed I-axis and Q-axis signals are input to the TMCC carrier demodulator 6, and all TMCC carrier data are differentially demodulated (in the present invention, for example, DQPSK (Differential Quadrature Phase Shift Keying) demodulation).

  The differentially demodulated received signal (herein referred to as a TMCC carrier demodulated signal) is input to the TMCC carrier position detector 7. As described in detail below, the TMCC carrier position detection unit 7 adds all values sampled with a predetermined random arrangement position pattern of the TMCC carrier to the demodulated data within one symbol period. At this time, the above addition process is performed for each arrangement position pattern that is shifted by one carrier within a range of ± M carriers (for example, M = 20) from the normal TMCC carrier position.

  When the transmission signal has a specification of 7 GHz band or 10 GHz band, and the carrier interval is 20 kHz, the value of M is set to 20 when the frequency deviation specification is 7 PPM. However, in the present invention, the value of M is not limited to this.

  Here, FIG. 5 shows a specific configuration example of the TMCC carrier position detection unit 7, the N symbol addition unit 10, and the carrier shift amount detection unit 11, and the operation thereof will be described with reference to FIGS. 6A-6D. Note that the processing in these units 7, 10, and 11 may be software processed by a computer.

  The TMCC carrier position detection unit 7 includes an enable signal generator 71 and an addition unit 72. The enable signal generator 71 generates an enable signal Se corresponding to a predetermined random arrangement position pattern (see FIG. 3) of the TMCC carrier. Here, 2M + 1 enable signals Se (-M) to Se (0) to Se (+ M) are generated. That is, these enable signals Se (-M) to Se (0) to Se (+ M) are pulse signals synchronized with predetermined random positions of the TMCC carrier, and one carrier with reference to the enable signal Se (0). The phase of the signal is shifted by the position. The enable signal Se (-M) is delayed in phase by M units with respect to the enable signal Se (0), and the enable signal Se (+ M) is M units with respect to the enable signal Se (0). The phase is advanced.

In the figure, the enable signal Se (0) is drawn in synchronization with the TMCC carrier of the differentially demodulated signal (FIG. 6A) from the demodulator 6, but if it is synchronized with any carrier good.
In adder 72, one symbol of the differentially demodulated received signal (TMCC carrier demodulated signal) from demodulator 6 in synchronization with the pulses of enable signals Se (-M) to Se (0) to Se (+ M) Minutes are sampled and added, and output to the N symbol adder 10 as added values D (-M) to D (0) to D (+ M) for each symbol. That is, for example, one symbol of the differentially demodulated signal from the demodulator 6 is sampled and added in synchronization with the pulse of the enable signal Se (0), and the added value D (0) is output. The added value D (0) for one symbol is output for each symbol. Other addition values D (-M) to D (+ M) are similarly obtained and output for each symbol.

  The N symbol addition unit 10 performs addition between N symbols (for example, N = 10) for each addition value D (-M) to D (0) to D (+ M) for each symbol, and the addition value D ( -M) N to D (0) N to D (+ M) N are given to the carrier shift amount detection unit 11, respectively. That is, for example, the addition value D (0) for each symbol is added for N symbols and output as the addition value D (0) N. Other addition values D (−M) N to D (+ M) N are obtained in the same manner and provided to the carrier shift amount detection unit 11.

  Here, the value of N is determined as follows. In other words, the value of N varies depending on the range of transmission signals with which the C / N value is used to determine (detect) the carrier shift amount. Specifically, as the value of N is increased, the carrier shift amount can be determined even for a transmission signal having a lower C / N value. However, in this case, more time is required until the determination. For example, when the carrier shift amount is determined using a transmission signal up to C / N = −1 dB, N is about 50, and if one symbol length is about 50 μsec, the N symbol period is about 2.5 msec. Become. The value of N may be small if an attempt is made to determine the carrier shift amount with a transmission signal having a higher C / N value, while the value of N is determined if an attempt is made to determine the carrier shift amount with a transmission signal having a lower C / N value. The value must be set large.

  The carrier shift amount detection unit 11 detects the largest value (peak value) among these added values D (−M) N to D (0) N to D (+ M) N, and detects the corresponding carrier position. . That is, the largest value (peak value) among the addition values D (-M) N to D (0) N to D (+ M) N is obtained from the sampling of the TMCC carrier. Is the actual TMCC carrier position. For example, if the largest value (peak value) is D (+ M) N, it is determined that a TMCC carrier exists at the position in FIG. 6B.

  Thus, as shown in FIGS. 7A and 7B, the peak value, that is, the actual TMCC carrier position of the reception signal (FIG. 7B) is the TMCC of the transmission signal (FIG. 7A) even when there is a carrier deviation of ± 2 or more. It is detected at a position deviated from the carrier position (that is, a normal TMCC carrier position or a TMCC carrier position having no frequency deviation). Note that the TMCC carrier position of the transmission signal is predetermined at a predetermined position. Therefore, if there is no carrier shift, the TMCC carrier position can be recognized as the predetermined position.

  Therefore, the carrier deviation amount detection unit 11 detects the difference between the carrier position determined as the actual TMCC carrier position and the normal TMCC carrier position (difference in the number of carriers) as the carrier deviation number (deviation amount).

  The number of carrier deviations detected by the carrier deviation amount detection unit 11 is input to the offset value calculation unit 9, and an offset value for controlling the frequency control VCO 2 is calculated according to the detected number of carrier deviations. The calculated offset value is input to the error detection unit 8 and added as an offset value of the control voltage value of the VCO 2 to control the control voltage value of the VCO 2.

  As a result, even if there are ± 2 or more carrier shifts, the number of carrier shifts from the position where the carrier shifts correctly to the normal TMCC carrier position can be detected, and correction control of the frequency shift can be performed normally. it can.

  In the above embodiment, the carrier shift amount is continuously detected for each N symbol and the carrier frequency shift is corrected and controlled. However, the carrier shift amount is detected for each intermittent or discrete N symbol. Then, correction control of the carrier frequency deviation may be performed.

  In this embodiment, the transmission apparatus in which the transmission signal is an OFDM signal has been described. However, the present invention is not limited to this. The present invention is applicable to a transmission apparatus for transmission signals having a main data carrier for sending main data and a sub data carrier for sending sub data arranged at a predetermined random position. Here, the main data is data such as audio and video, and the sub data is auxiliary data other than the main data, and includes, for example, mode identification data such as a modulation method.

The block diagram which shows the structure of an example of the receiver of the OFDM transmission signal of a prior art. The schematic diagram which shows the carrier arrangement | positioning of an OFDM transmission signal. The figure which showed arrangement | positioning of the sub data carrier in 2K half mode. The block diagram which shows the structure of the receiver of the OFDM transmission signal by one Example of this invention. The block diagram which shows the structure of the TMCC carrier position detection part etc. of the receiver of FIG. The timing chart for demonstrating operation | movement of the TMCC carrier position detection part of FIG. The schematic diagram for demonstrating the TMCC carrier demodulation position in case there exists a +/- 2 or more carrier shift.

Claims (5)

In a digital transmission signal transmission system having a first carrier for sending main data and a second carrier arranged at a predetermined random position for sending sub data,
The second carrier is demodulated from the received digital transmission signal, the relative carrier position of the second carrier demodulated signal obtained by the demodulation is detected, and the detected relative carrier position of the second carrier demodulated signal is detected. A carrier shift detection method, comprising: detecting a carrier shift amount based on the above. In claim 1,
A carrier deviation detection method comprising: detecting a carrier deviation amount from the detected relative carrier position of the second carrier and a normal second carrier position; and correcting and controlling the carrier frequency deviation based on the detected carrier deviation amount. . In claim 1,
When detecting the relative carrier position of the second carrier demodulated signal, add a value obtained by sampling the second carrier demodulated signal within one symbol period with a predetermined arrangement pattern of the second carrier;
A carrier deviation detection method, wherein the addition is performed for each arrangement position pattern that is shifted by one carrier within a range of ± M carriers (M is an integer of 2 or more) from a normal second carrier position. In claim 3,
When detecting the relative carrier position of the second carrier demodulated signal, the signal obtained by the addition is added over N symbol periods (N is an integer of 2 or more),
The above addition is performed for each arrangement position pattern shifted by one carrier within a range of ± M carriers (M is an integer of 2 or more) from the normal second carrier position,
Detecting the maximum value from the added value of each of the arrangement position patterns, detecting the position of the arrangement position pattern corresponding to the maximum value as the relative carrier position;
A carrier deviation detection method, wherein a carrier deviation amount is detected from the relative carrier position and a normal second carrier position. In a transmission device for transmitting an OFDM signal having a TMCC carrier, in a reception device for an OFDM transmission signal,
A wave number conversion unit that converts the IF signal from the reception high-frequency unit into a baseband signal, an AD converter that converts the frequency-converted signal into a baseband signal, a digital signal from the AD converter, an I-axis signal, A quadrature demodulator that performs quadrature demodulation on the Q-axis signal;
FFT (Fast Fourier Transform) for Fourier transforming the orthogonally demodulated I-axis and Q-axis signals, and TMCC carrier demodulation for differentially demodulating the Fourier-transformed I-axis and Q-axis signals and outputting a TMCC carrier demodulated signal , A carrier position detection unit that detects a relative carrier position of the obtained TMCC carrier demodulated signal, a carrier shift amount detection unit that detects a carrier shift amount based on the detected relative carrier position, and the detected carrier shift A receiving apparatus comprising: a correction control unit that performs correction control of carrier frequency deviation based on the amount.