JP2001268040A - OFDM signal mode determination device - Google Patents

Abstract

(57) [Problem] To reduce the number of transmission modes to one only from the frame length when there are transmission modes having the same frame length but different symbol lengths as in digital audio broadcasting (DAB). Can not. SOLUTION: A plurality of kinds of transmission modes are assumed for which a sliding correlation of a guard section length between a signal delayed with an effective symbol length and a signal not delayed is assumed, and a plurality of kinds of sliding modes are stored in storage means for a plurality of kinds of symbol lengths. Each correlation result is phase-synchronized and added. The transmission mode is determined by comparing the maximum values of the phase synchronization addition results and selecting the largest one. By this means, the transmission mode can be accurately and quickly determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining a transmission mode when receiving an OFDM signal in which a transmission mode varies depending on a symbol length and a guard signal is added at the beginning of an effective symbol.

[0002]

2. Description of the Related Art Conventionally, digital audio broadcasting (DA)
When there are transmission modes having the same frame length but different symbol lengths as in B), the transmission mode is first narrowed down by determining the frame length, and a discrete Fourier transform is performed in one of the assumed transmission modes. Attempt conversion. next,
A method has been used in which a result of the discrete Fourier transform is correlated with a known signal transmitted only once in a frame, and whether or not a desired transmission mode is set.

[0003] In this method, it is possible to make a determination only once per frame, it takes time for initial pull-in, and a long time from power-on to start of reception and a long seek time are required.

In a method of simply obtaining a correlation with a guard signal section, integrating the guard section length, filtering the result of integration, and analyzing the result by discrete Fourier transform, the received signal level is increased by fading as in mobile reception. If it fluctuates, it is difficult to determine the transmission mode appropriately and quickly.

FIG. 7 shows a configuration 1 of a conventional mode judging unit. The frame synchronizing unit 1 establishes frame synchronization using a non-signal (Null signal) section or the like, and then transmits the data in a frame length judging unit 2. Different frame lengths are determined depending on the mode, and when there is a possibility that the frame length has a plurality of transmission modes, the transmission mode provisional determination unit 3 provisionally determines any of the possible transmission modes.

The tentative determination result is input to the guard interval removing unit 4 through the switch 10, and the guard interval length determined by the frame synchronization timing from the frame synchronization unit 1 is removed from the received signal. After being converted into a signal, the signal is input to a discrete Fourier transform unit 6 to perform a discrete Fourier transform. The result of the discrete Fourier transform is input to the correlation operation unit 7 and is correlated with the known signal from the known signal generation unit 8.

[0007] The correlation result is input to a transmission mode determination unit,
If the correlation is large, the tentative decision result is correct and demodulation is performed as it is.If the correlation is small, the tentative decision is incorrect and the above operation is repeated in another possible transmission mode, and the correlation is sufficiently large. At this point, the transmission mode determination ends.

Next, FIG. 8 shows a configuration 2 of a conventional receiving apparatus. The received signal input from the tuner section is obtained by determining the correlation between the signal delayed by the effective symbol delay section 51 and the correlation operation section 52. Can be The correlation result is integrated by the integration section 53 by the guard section length, and the integration result is subjected to filtering or discrete Fourier transform to determine the mode. here,
When the received signal level fluctuates greatly due to fading, it is difficult to determine the mode.

[0009]

When there are transmission modes having the same frame length but different symbol lengths, such as digital audio broadcasting (DAB), the transmission mode is reduced to only one from the frame length alone. Can not.

Further, it is difficult to accurately and quickly determine a transmission mode even when a received signal fluctuates greatly due to fading during mobile reception. Here, the received signal cannot be demodulated unless the transmission mode is determined, which is a very important issue. An object of the present invention is to solve the above problems.

[0011]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention is implemented for a plurality of types of transmission modes in which a sliding correlation in a guard section is assumed, and a plurality of types of storage modes for a plurality of symbol lengths are stored. Are phase-synchronized and added.

The transmission mode is determined by comparing the maximum values of the results of the phase synchronization addition and selecting the largest one. By this means, the transmission mode can be accurately and quickly determined.

[0013]

The invention according to claim 1 is an apparatus for receiving an OFDM signal in which a transmission mode differs depending on a symbol length and a guard signal is added at the head of an effective symbol. Means for storing the signal for the assumed maximum symbol length, and obtaining a plurality of kinds of effective symbol time-delayed signals from the storage means, and performing a correlation operation with the signal not delayed A plurality of means; a plurality of sliding correlation means for integrating the correlation operation results by a plurality of assumed guard signal section lengths; and storing the plurality of sliding correlation results by a plurality of assumed symbol lengths. A plurality of storage means; a plurality of means for performing phase-synchronous addition of the integration result to a value stored in the storage means over a plurality of symbols; Means for selecting the largest one from the maximum value of the calculation results to determine the transmission mode, the transmission mode having the same frame length but different symbol lengths. Has the effect that the transmission mode can be determined accurately and at high speed even in the presence of.

According to a second aspect of the present invention, in the OFDM signal mode determining apparatus according to the first aspect, when storing the sliding correlation result, a binary value indicating whether the value is larger or smaller than a separately determined threshold value. The present invention relates to an OFDM signal mode determination device, characterized in that the circuit scale required as storage means can be reduced,
The determination device has an effect that the size can be reduced.

According to a third aspect of the present invention, in the OFDM signal mode determination apparatus according to the first aspect, the correlation operation means shifts the frequency of the effective symbol time-delayed signal. It is related to a signal mode determination device, even if the received signal has a frequency offset, and the sliding correlation value is small due to the difference between the guard section and the second half signal of the effective symbol, it is possible to cancel the frequency offset, The correlation between the delayed signal and the signal in the guard section is increased, and the mode can be accurately determined.

According to a fourth aspect of the present invention, in the OFDM signal mode determining apparatus according to the third aspect, a complex orthogonal signal is stored in the means for storing the received signal for an assumed longest symbol length. When the frequency of the signal delayed by the effective symbol time is shifted, a numerically controlled oscillator (NCO: Numerica) is added to the complex orthogonal signal.
ly Controlled Oscillator)
Characterized by complex multiplying a complex sine wave from
The present invention relates to a DM signal mode determination device, in which a signal after quadrature demodulation is stored only for the longest symbol length, and an orthogonal complex sine wave signal is used for frequency shift of a signal delayed by an effective symbol time. Since no image signal or the like is generated, there is no need for a filtering process, and as a result, the circuit scale can be reduced.

According to a fifth aspect of the present invention, in the OFDM signal mode determining apparatus according to the fourth aspect, the signal whose effective symbol time has been delayed has its frequency shifted in the negative direction and does not shift its frequency. The present invention relates to an OFDM signal mode determination device, which prepares a plurality of devices and a device that is shifted in the positive direction, and performs a correlation operation and phase synchronization addition for each to determine a transmission mode. Even when the direction of the frequency offset is unknown, it is possible to output a somewhat large sliding correlation value, so that it has the effect of enabling accurate transmission mode determination. Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 6.

(Embodiment 1) FIG. 1 shows Embodiment 1 using the present invention. In FIG. 1, the OFDM signal mode determining apparatus of the present invention employs the longest symbol length among a plurality of assumed symbol lengths. , A correlation calculating means # 1 13, a correlation calculating means # 2 13 ', a correlation calculating means # 3 13'', a correlation calculating means # 4 13''', a sliding correlation means # 1 14, a sliding correlation. Means # 2 14 ', Sliding correlation means # 3 1
4 ″, sliding correlation means # 4 14 ′ ″.
Phase synchronous addition means # 1 16 and phase synchronous addition means # 2 1
6 ′, phase synchronization addition means # 316 16 ″, phase synchronization addition means # 4 16 ′ ″..., Maximum value detection means # 116,
Maximum value detection means # 2 16 ', maximum value detection means # 31
6 ″, maximum value detection means # 4 16 ′ ″...

The received signal from the tuner section is delayed in the longest effective symbol length storage means 12 by an assumed symbol length. The plurality of delayed signals delayed by the assumed effective symbol length are correlated with signals that have not been delayed by the correlation calculation means # 1, correlation calculation means # 2, correlation calculation means # 3, correlation calculation means # 4,. An operation is performed. The respective calculation results are obtained by sliding correlator # 1, sliding correlator # 2, sliding correlator # 3,
In the sliding correlating means # 4,..., Integration is performed by the guard section length corresponding to each symbol.

Next, each sliding correlation result has a storage capacity corresponding to the symbol length corresponding to each sliding correlation result.
Also, a phase synchronization conversion unit # 1, a phase synchronization conversion unit # 2, a phase synchronization conversion unit # 3, a phase synchronization conversion unit # 4, which can add a new correlation result to a value already stored.
Are phase-synchronized and added. FIG. 2 shows the state of the above-described delayed signal, correlation calculation, sliding correlation, and phase-locked addition.
-(a) to Fig. 2- (d).

FIG. 2 shows one of the assumed plural symbol lengths (for example, only # 1). The same applies to other assumed plural symbol lengths.

Here, the effective symbol length delay signal shown in FIG. 2B is output from the longest effective symbol length storage means 12 in FIG. 1, and when a signal having a delay time shorter than the longest effective symbol length is output. By outputting a signal in the middle of the means, the delay circuit can be shared.

Next, in the maximum value detecting means # 1, the maximum value detecting means # 2, the maximum value detecting means # 3, the maximum value detecting means # 4,... For detecting the maximum value of each phase synchronous addition result. Is detected, the largest phase synchronous addition result is selected by the comparing means 17, and the transmission mode of the corresponding symbol length is determined.

If the above-mentioned mode determination method is adopted, only the phase synchronous adding means having the same symbol length as the received signal has the same sliding correlation value at the same phase, so that the maximum value of the phase synchronous adding means becomes large.

In the case of the phase synchronization adding means having a symbol length different from that of the received signal, since the sliding correlation value changes at random, the mode can be accurately determined without increasing the maximum value of the phase synchronization adding means. It can be carried out.

(Embodiment 2) FIG. 3 shows Embodiment 2 using the present invention. In FIG.
In addition to the first embodiment shown in FIG.
18, binarization means # 2 18 ', binarization means # 3 1
8 ″ is composed of binarizing means # 418 ′.

In the binarizing means, the output from the sliding correlation means is binarized by comparing it with a separately determined threshold value.

Here, it is also preferable that the threshold value is changed according to the magnitude of the received signal. By performing the binarization as described above, the required circuit scale can be reduced, and the mode determination device can be reduced in size.

(Embodiment 3) FIG. 3 shows Embodiment 3 using the present invention, and FIG. 3 shows Embodiment 2 using the present invention.
In FIG. 3, the receiving apparatus of the present invention includes a frequency shift unit 19 in addition to the first embodiment shown in FIG.

When a frequency offset occurs in the signal from the tuner section, even if the signal in the guard section is different from the latter half of the effective symbol, the frequency of the delayed signal is shifted to match the two. Therefore, a large sliding correlation value can be obtained, and the mode can be accurately determined.

(Embodiment 4) FIG. 5 shows Embodiment 4 using the present invention. In FIG. 5, both the in-phase component and the quadrature component are output from the tuner section.
Numerically controlled oscillator (NCO: N
Umerically ControlledOsci
llator) 20 and complex multiplying means 21 are used, and in the subsequent stage, in-phase component storage means 22 for delaying the in-phase component by the assumed maximum symbol length and quadrature component storage for delaying the orthogonal component by the assumed maximum symbol length Means 23. Here, correlation calculation means # 1, # 2, # 3, #
.. Are means for determining the correlation of the complex signal.

By using such a configuration, the frequency shift can be easily performed, and the mode can be accurately determined even when a frequency error exists.

(Embodiment 5) FIG. 6 shows Embodiment 5 using the present invention. In FIG. 6, the receiving apparatus of the present invention comprises a negative frequency shift means 24, a positive frequency shift means 25, a longest symbol. Storage means 26, 2
6 ′, 26 ′, correlation calculation groups 27, 27 ′, 27 ″, sliding correlation calculation groups 28, 28 ′, 28 ″, phase synchronization addition groups 29, 29 ′, 29 ″, maximum value detection group 3
0, 30 ', 30'', comparing means 31, 31', 3
1 '', a selecting means 32.

The signal frequency-shifted by the negative frequency shift means 24 is delayed by an assumed symbol,
Correlation with a signal which is not delayed is performed in the correlation operation group 27. Here, a plurality of types of correlation calculations are performed corresponding to the assumed plurality of types of symbol lengths.

Next, in the sliding correlation group 28, a sliding correlation for calculating the integral of the assumed guard section length is performed for a plurality of types of guard section lengths, and the phase synchronization addition of the corresponding symbol lengths is performed. Performed in group 29.

The maximum value detected by the maximum value detection group 30 for detecting the maximum value of the phase synchronous addition group is selected by the comparing means 31 at the symbol length having the largest value, and the maximum value is inputted to the selecting means 32. Similarly, if you do not shift the frequency,
Also, the case where the frequency shift is performed in the plus direction is performed, and the selecting means 32 compares the respective maximum values, selects the one with the largest value, and determines the symbol length.

By using the above-described configuration, even when it is unknown in which direction the frequency offset is, it may occur that the correlation with the guard interval becomes large by using a plurality of frequency-shifted delay signals, Accurate mode determination is possible.

When the frequency offset amount is known in advance, the correlation operation may be performed after performing control to cancel the frequency offset not only for the delayed signal but also for both correlated signals.

As a method of estimating the amount of frequency offset, there is a method of calculating the amount of phase rotation between the signal of the guard section, which should be the same signal, and the latter half of the effective symbol. Compensating the frequency offset amount in this way is preferable because highly accurate mode determination can be performed.

[0040]

As described above, according to the present invention, the reception level is greatly increased in the case of digital audio broadcasting (DAB) in which the symbol length is different even if the frame length is the same, or as in the case of mobile reception. Can be accurately determined even when the value fluctuates, and the time required at power-on or at the time of seeking can be reduced.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a configuration of an OFDM signal mode determination device according to a first embodiment of the present invention.

FIG. 2 is a diagram schematically illustrating a correlation operation, a sliding correlation, and a synchronous addition in the first embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a configuration of an OFDM signal mode determination device according to a second embodiment of the present invention.

FIG. 4 is a block circuit diagram showing a configuration of an OFDM signal mode determination device according to a third embodiment of the present invention.

FIG. 5 is a block circuit diagram showing a configuration of an OFDM signal mode determination device according to a fourth embodiment of the present invention.

FIG. 6 is a block circuit diagram showing a configuration of an OFDM signal mode determination device according to a fifth embodiment of the present invention.

FIG. 7 is a block circuit diagram showing a configuration 1 of an OFDM signal mode determination device according to a conventional embodiment.

FIG. 8 is a block circuit diagram showing a configuration 2 of an OFDM signal mode determination device according to a conventional embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frame synchronization part 2 Frame length judgment part 3 Transmission mode provisional judgment part 4 Guard section elimination part 5 Serial parallel conversion part 6 Discrete Fourier transformation part 7 Correlation operation part 8 Known signal generation part 9 Transmission mode judgment part 10 Switch 11 Parallel serial conversion Unit 12 longest symbol length storage means 13 correlation calculation means # 1, 13 'correlation calculation means # 2 13' 'correlation calculation means # 3 13' '' correlation calculation means # 4 14 sliding correlation means # 1 14 'sliding correlation means # 2 14 ″ sliding correlating means # 3 14 ′ ″ sliding correlating means # 4 15 phase synchronous adding means # 1 15 ′ phase synchronous adding means # 2 15 ″ phase synchronous adding means # 3 15 ′ ″ phase synchronous adding means # 4 16 Maximum value detection means # 1 16 'Maximum value detection means # 2 16' 'Maximum value detection means # 16 '' 'maximum value detecting means # 4 17 comparing means 18 binarizing means # 1 18' binarizing means # 2 18 '' binarizing means # 3 18 '' 'binarizing means # 4 19 frequency shift Means 20 Numerically controlled oscillator 21 Complex multiplication 22 In-phase component storage means 23 Quadrature component storage means 24 Negative frequency shift means 25 Plus frequency shift means 26, 26 ', 26' 'Longest symbol length storage means 27, 27', 27 ' 'Correlation operation group 28, 28', 28 '' Sliding correlation operation group 29, 29 ', 29' 'Phase synchronous addition group 30, 30', 30 '' Maximum value detection group 31, 31 ', 31' 'Comparison means 32 Selection means 51 Effective symbol length delay means 52 Correlation operation unit 53 Integrator

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kentoku Kunieda 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa F-term in Matsushita Giken Co., Ltd. 5K022 DD01 DD17 DD32

Claims (8)

[Claims] 1. An apparatus for receiving an OFDM signal in which a transmission mode differs according to the length of a symbol length and a guard signal is added at the beginning of an effective symbol. Means for storing, a plurality of means for obtaining a plurality of types of effective symbol time-delayed signals assumed from the storage means, and performing a correlation operation with a signal not delayed, and assuming the correlation operation result A plurality of sliding correlation means for integrating by a plurality of types of guard signal section lengths to be obtained; a plurality of storage means for storing the plurality of sliding correlation results for only a plurality of assumed symbol lengths; A plurality of means for phase-synchronizing addition of the integration result to a set value over a plurality of symbols; And a means for selecting a transmission mode to determine the transmission mode. 2. The OFD according to claim 1, wherein the value for storing the sliding correlation result is a binary value indicating whether the value is larger or smaller than a separately determined threshold value.
M signal mode determination device. 3. The OFDM signal mode judging device according to claim 1, wherein in the correlation operation means, the frequency of the signal delayed by the effective symbol time is shifted. 4. A means for storing a received signal for an assumed longest symbol length stores a complex orthogonal signal, and when shifting the frequency of a signal delayed by an effective symbol time, 4. The OFDM signal mode judging device according to claim 3, wherein a complex orthogonal signal is complex-multiplied by a complex sine wave from a numerically controlled oscillator. 5. A signal whose effective symbol time has been delayed is prepared by preparing a plurality of signals whose frequency is shifted in the negative direction, those whose frequency is not shifted, and those whose frequency is shifted in the positive direction. 5. The OFDM signal mode determination device according to claim 4, wherein the transmission mode is determined by performing a correlation operation and phase synchronization addition for each of them. 6. The OFDM according to claim 1, wherein
A broadcast wave receiving terminal device using a signal mode determination device. 7. The OFDM according to claim 1
A wireless communication receiving terminal device using a signal mode determination device. 8. The OFDM according to claim 1, wherein
A wired communication terminal device using a signal mode determination device.