JP2006217541A - Unique word detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a unique word detection circuit which has a simple configuration and surely detects a unique word UW by simple processing. <P>SOLUTION: An inputted baseband signal and a delay signal delayed from the baseband signal by one symbol are subjected to a complex conjugate operation to generate an I signal component Icc and a Q signal component Qcc. An I signal correlation processing part 21 performs correlation processing of a plurality of reference signals and the I signal component Icc respectively, and a Q signal correlation processing part 22 performs correlation processing of a specific reference signal and the Q signal component Qcc. An absolute value operating part 3 performs an absolute value operation of these correlation processing signals Icf and Qcf to generate I signal correlation data ABS (Icf). A UW timing detecting part 7 compares a multiplication result of maximum I signal correlation data ABS (Icf) and data being prescribed times as large as correction Q signal correlation data ABS (Q'cf) and also its inverse number with a threshold and outputs a time point where the multiplication result exceeds the threshold as UW detection timing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a unique word detection circuit for detecting a unique word of a digital modulation signal, and in particular, a unique word detection of a digital modulation signal in which a unique word (hereinafter referred to as “UW”) is equivalently BPSK modulated. It relates to the circuit.

  In a system that transmits and receives information using a digital modulation signal, UWs set with a specific bit length are arranged at the same position in each frame in order to demodulate the digital modulation signal. An apparatus for demodulating a digital modulation signal in such a system, that is, a digital communication signal receiver, synchronizes and demodulates the digital modulation signal by detecting the UW.

  As described above, since detection of UW is an essential condition for demodulation of a digital modulation signal, various unique word detection circuits that detect UW accurately and reliably have been conventionally devised. In these conventional unique word detection circuits, a method of correlating UW to the baseband signal of the digital modulation signal and a method of correlating UW to the I signal and Q signal of the baseband signal of the digital modulation signal are used. ing.

Among them, as a unique word detection circuit that stably detects UW under a low C / N0, Patent Document 1 discloses an I signal and a Q signal generated by orthogonal baseband demodulation of a digital modulation signal. A method is disclosed in which square calculation is performed, and UW is detected using a signal having a larger amplitude among the amplitudes of the squared signals.
JP 11-341096 A

  When UW is directly correlated with a baseband signal by a conventional unique word detection circuit, if there is a frequency shift, the UW detection error becomes large. In addition, when the UW is correlated with the complex conjugate signal (I signal, Q signal) of the baseband signal with the conventional unique word detection circuit, the reference threshold value cannot be dynamically changed. Unless the setting is changed for each device, UW cannot be detected accurately.

  The unique word detection circuit shown in Patent Document 1 compares and selects the I signal and the Q signal, and performs normal rotation and inversion processing of the selected I signal and Q signal according to the frequency shift direction. The signal processing becomes complicated and the processing circuit becomes complicated.

  Therefore, an object of the present invention is to provide a unique word detection circuit that can detect a unique word UW accurately and reliably with a simple configuration and simple processing.

The present invention provides a unique word detection circuit for detecting a unique word from a digital modulation signal in which at least the unique word is equivalently BPSK modulated.
A baseband signal generating means for generating a baseband signal by symbol-synchronizing the digital modulation signal, a baseband signal, and a complex conjugate of the delayed signal obtained by delaying the baseband signal by one symbol, Complex conjugate calculation signal generation means for generating a conjugate calculation signal; reference signal generation means for generating a plurality of reference signals each having a different bit pattern used for a unique word of a digital modulation signal; and I of the complex conjugate calculation signal I signal correlation processing means for performing correlation processing between a signal component and an arbitrary type of reference signal, and I signal correlation data generating means for generating an I signal correlation data by calculating an absolute value of an output signal of the I signal correlation processing means I signal correlation data comparing means for comparing each I signal correlation data and outputting the most correlated I signal correlation data; Q signal correlation processing means for correlating the Q signal component of the combination calculation signal and an arbitrarily selected reference signal, and calculating the absolute value of the output signal of the Q signal correlation processing means to generate Q signal correlation data Q signal correlation data generation means, and timing detection means that uses the timing at which the I signal correlation processing data exceeds the determination reference value based on the Q signal correlation processing data as a unique word detection timing. .

  The unique word detection circuit of the present invention is characterized in that the I signal correlation processing means performs correlation processing on the I signal component of the complex conjugate calculation signal and all of the reference signals.

  In this configuration, a baseband signal is generated by quadrature baseband demodulation of the digital modulation signal. At this time, the baseband signal is symbol-synchronized at the same time. The symbol-synchronized baseband signal and the 1-symbol delayed signal of this baseband signal are subjected to complex conjugate multiplication.

  A baseband signal at a certain time point t is r (t), a baseband I signal that is a real component of the baseband signal is I (t), and a baseband Q signal that is an imaginary component of the baseband signal is Q ( t)

It is represented by

  When the frequency offset is Δf, the amplitude at time t is A (t), and the phase is θ (t), the baseband I signal I (t) and the baseband Q signal Q (t) are respectively

It is expressed.

  Since the baseband signal r (t) is symbol-synchronized, it can be expressed discretely,

It becomes. Therefore, the complex conjugate multiplication operation of the discretized baseband signal r [n] and the one-symbol delayed signal r [n−1] of this baseband signal is

It becomes. Here, Ts is a constant symbol rate, and Δθ is a differential value of θ [n].

  Here, since UW is equivalently a BPSK modulation signal, the amplitude is constant, and Δθ can be ignored because it takes only “0” or “π”.

  As a result, the UW and its timing do not change between the complex conjugate operation signal calculated by this complex conjugate multiplication operation and the baseband signal as the original signal, and the frequency shift component is canceled and does not depend on the frequency shift component. A complex conjugate operation signal is generated.

  Next, a plurality of reference signals each having a different bit pattern are subjected to correlation processing, one by one, with the I signal component Icc, which is the real part of the complex conjugate operation signal. One arbitrarily selected reference signal among the plurality of reference signals is correlated with the Q signal component Qcc, which is the imaginary part of the complex conjugate calculation signal.

  The correlation processing signal Icf between the plurality of reference signals and the I signal component Icc of the complex conjugate calculation signal is calculated as an absolute value. The I signal correlation data for each reference signal generated by this processing is compared, and the I signal correlation data having the largest absolute value is extracted.

  Further, the correlation processing signal Qcf between the specific reference signal and the Q signal component Qcc of the complex conjugate calculation signal is subjected to an absolute value calculation to generate Q signal correlation data.

  Next, a ratio of the extracted I signal correlation data to a predetermined value based on the Q signal correlation data is calculated, and it is determined whether or not this ratio exceeds a preset criterion value. Then, the timing at which this ratio exceeds the determination reference value is detected as the timing of the last symbol of UW. Thereby, the timing of UW is detected.

  The I signal correlation data comparison means of the unique word detection circuit of the present invention is characterized in that the reference signal used for the I signal correlation data having the strongest correlation is detected as UW.

  In this configuration, the I signal correlation data is maximized because the correlation between the UW included in the I signal Icc of the complex conjugate calculation signal and the reference signal is maximized, that is, the UW and the reference signal match. Since this is an agreement, the reference signal at this time is detected as UW.

  Further, the Q signal correlation processing means of the unique word detection circuit according to the present invention performs a filter operation for removing a high frequency component of the correlation signal Qcf between the Q signal component Qcc of the complex conjugate calculation signal and the specific reference signal. It is said.

  In this configuration, by removing the high frequency component of the correlation processing signal Qcf between the Q signal component Qcc of the complex conjugate calculation signal and the specific reference signal, the noise component of the correlation processing signal Qcf is removed, and the substantial Q signal component A criterion value based on is obtained.

  Also, the unique word detection circuit of the present invention provides a correlation processing signal Icf between the I signal component Icc of the complex conjugate calculation signal and the reference signal, which is the I signal correlation data having the strongest correlation at the timing detected by the timing detection means. And a frequency detection means for detecting the frequency of the digital modulation signal by using an arctangent calculation of a ratio of the Q signal component Qcc of the complex conjugate calculation signal and the specific reference signal to the correlation processing signal Qcf. Yes.

  In this configuration, the correlation processing signal Icf between the specific reference signal identified as UW and the I signal component Icc of the complex conjugate calculation signal, and the correlation processing of this specific reference signal and the Q signal component Qcc of the complex conjugate calculation signal Using the signal Qcf, based on (Equation 4),

From which Δf is obtained. The frequency of the received digital modulation signal can be obtained by using this Δf.

  According to the present invention, it is possible to detect UW timing and UW with a simple processing operation circuit and a simple processing arithmetic circuit.

  Further, according to the present invention, by filtering the Q signal component, the determination reference value becomes more accurate, and UW can be detected more accurately and reliably.

  In addition, according to the present invention, UW timing and UW can be detected, and the frequency of the received digital modulation signal can be detected.

A unique word (UW) detection circuit according to an embodiment of the present invention will be described with reference to FIGS. In this embodiment, a UW detection circuit of a receiver that uses a digital communication signal in which at least UW is equivalently BPSK modulated as a digital communication signal will be described.
FIG. 1 is a schematic block diagram showing a part of a digital communication signal receiver including a UW detection circuit according to this embodiment.
In the digital communication signal receiver, first, an IF signal obtained by converting the received digital communication signal into an intermediate frequency is input to the mixer 101 and the mixer 102. The mixer 101 receives a local oscillation signal having a predetermined frequency from a voltage controlled oscillator (VCO) 103, and the mixer 101 mixes the local oscillation signal with the IF signal to generate an intermediate frequency I signal. The mixer 102 receives a π / 2 delayed local oscillation signal obtained by delaying the local oscillation signal by a π / 2 phase by the π / 2 phase circuit 104. The mixer 102 adds a π / 2 delayed local portion to the IF signal. The oscillation signal is mixed to generate an intermediate frequency Q signal.

  The low-pass filter (LPF) 105 removes the harmonic component of the intermediate frequency I signal and outputs it to the down converter 107, and the low-pass filter (LPF) 106 removes the harmonic component of the intermediate frequency Q signal and outputs the down converter 108. Output to.

  The symbol timing detection circuit 109 detects the symbol timing based on the intermediate frequency I signal and the intermediate frequency Q signal, and outputs the symbol timing signal to the down converters 107 and 108.

  The down converter 107 generates a baseband I signal based on the input intermediate frequency I signal and the symbol timing signal, and the down converter 108 generates a baseband I signal based on the input intermediate frequency Q signal and the symbol timing signal. A Q signal is generated. The I signal and the Q signal that are symbol-synchronized and down-converted to baseband are input to the UW detection circuit 100.

  The UW detection circuit 100 detects the last timing of the UW (unique word) and the UW type Fuw, that is, the code constituting the UW, by the configuration and method described later. Then, the UW detection circuit 100 outputs the UW detection timing Tuw to the frequency estimation circuit 110. The frequency estimation circuit 110 calculates a frequency shift amount Δf by a method described later using the input UW detection timing Tuw, and estimates the frequency of the received digital communication signal.

FIG. 2 is a block diagram showing a schematic configuration of the UW detection circuit 100 shown in FIG.
FIG. 3 is a block diagram showing a schematic configuration of the complex conjugate calculation unit 1 shown in FIG.
FIG. 4 is a block diagram showing the UW detection circuit shown in FIG. 2 in units of functional blocks.

  The UW detection circuit 100 includes a complex conjugate calculation unit 1, a correlation processing unit 2, an absolute value calculation unit 3, a maximum value detection unit 4, a determination reference generation unit 5, a mixer 6, a UW timing detection unit 7, a UW type detection unit 8, A filter 9 and a reference signal storage unit 10 are provided.

The complex conjugate calculation unit 1 includes a 1-symbol delay processing unit 11, a complex conjugate processing unit 12, and a mixer 13.
When the baseband signal r [n], that is, the baseband I signal I [n] and the baseband Q signal Q [n], are input to the complex conjugate computing unit 1, they are distributed to two systems, respectively. The signal is input to the symbol delay processing unit 11 and the mixer 13. The 1-symbol delay processing unit 11 outputs a 1-symbol delayed signal r [n−1] obtained by delaying the input baseband signal r [n] by one symbol to the complex conjugate processing unit 12.

  The complex conjugate processing unit 12 calculates the complex conjugate of the input 1-symbol delayed signal r [n−1] and outputs it to the mixer 13. The mixer 13 multiplies the baseband signal r [n] by the complex conjugate r * [n−1] of the one-symbol delayed signal, and outputs a complex conjugate operation signal r [n] r * [n−1]. . At this time, the complex conjugate processing unit 12 converts the I signal component Icc of the complex conjugate calculation signal, which is the real part of the complex conjugate calculation signal r [n] r * [n−1], to the I signal correlation processing unit of the correlation processing unit 2. 21, and outputs the Q signal component Qcc of the complex conjugate calculation signal, which is the imaginary part of the complex conjugate calculation signal r [n] r * [n−1], to the Q signal correlation processing unit 22 of the correlation processing unit 2.

  The reference signal storage unit 10 stores a reference signal composed of the same code as the UW used for the digital communication signal received by the digital communication signal receiver. Usually, a plurality of UWs are set, and these UWs are set to have different codes and are not correlated with each other or have a very weak relationship. The reference signal storage unit 10 stores reference signals respectively corresponding to the plurality of UWs. For example, in the example of FIG. 2 (FIG. 4), nine reference signals corresponding to the correlations F0 to F8 are stored.

When the I signal component Icc of the complex conjugate calculation signal is input, the I signal correlation processing unit 21 sequentially reads out the reference signal from the reference signal storage unit 10, and performs correlation processing (correlation) between each reference signal and the I signal component Icc. F0 to correlation F8) are sequentially performed to generate correlation processing signal Icf ₀ to correlation processing signal Icf ₈ . Then, the I signal correlation processing unit 21 outputs these correlation processing signals Icf _{0 to} Icf ₈ to the I signal absolute value calculation unit 31 of the absolute value calculation unit 3.

When the Q signal component Qcc of the complex conjugate calculation signal is input, the Q signal correlation processing unit 22 reads a specific reference signal (for example, a reference signal corresponding to the correlation F0) from the reference signal storage unit 10, and this reference signal a correlation processing between the Q signal component Qcc performed (correlation Fn), generates the correlation processing signals Qcf _n. Then, the Q signal correlation processing unit 22 outputs the correlation processing signal Qcf _n to the filter 9. At this time, the reference signal to be used may be any reference signal. This is because the Q signal component Qcc corresponds to the noise component with respect to the actual signal, and even if any reference signal is used, the correlation is low and hardly changes.

The filter 9 includes, for example, a first-order IIR filter that removes high frequency components, and the corrected correlation processed signal Q′cf _{n from} which the harmonic component of the correlation processed signal Qcf _n has been removed is used as the absolute value of the Q signal of the absolute value calculation unit 3. The result is output to the calculation unit 32. By performing such filtering can remove the harmonic component or noise in the correlation signal Qcf _n underlying the judgment reference value to be described later, to obtain an accurate determination reference value.

The I signal absolute value calculation unit 31 calculates the absolute value of the input correlation processing signals Icf _{0 to} Icf ₈ and outputs I signal correlation data ABS (Icf ₀ ) to ABS (Icf ₈ ) to the maximum value detection unit 4. To do.

The maximum value detection unit 4 detects the maximum value from the input I signal correlation data ABS (Icf ₀ ) to ABS (Icf ₈ ), and outputs the I signal correlation data ABS (Icf) that is the maximum value to the mixer 6. To do. Further, the maximum value detection unit 4 outputs the corresponding reference signal to the UW type detection unit 8 assuming that the reference signal corresponding to the I signal correlation data ABS (Icf) having the maximum value corresponds to UW. Here, the I signal absolute value calculation unit 31 corresponds to the “I signal correlation data generation unit” of the present invention, and the maximum value detection unit 4 corresponds to the “correlation data comparison unit” of the present invention.

  The UW type detection unit 8 detects the corresponding UW from the input reference signal and outputs UW type data Fuw set in advance. Subsequent UW detection is executed based on the UW type data Fuw set in this way.

The Q signal absolute value calculation unit 32 calculates the absolute value of the input corrected correlation processing signal Q′cf _n and outputs the corrected Q signal correlation data ABS (Qcf _n ) to the determination reference generation unit 5. Here, the Q signal absolute value calculation unit 32 corresponds to “Q signal correlation data generation means” of the present invention.

The criterion generation unit 5 performs an operation indicated by 50 in FIG. 4, that is, a fixed multiplication (for example, 10 times as shown in FIG. 4) on the input corrected Q signal correlation data ABS (Q′cf _n ). Reciprocal calculation is performed and the result is output to the mixer 6 as a determination reference value.

  The mixer 6 multiplies the I signal correlation data ABS (Icf) input from the maximum value detection unit 4 by the determination reference value output from the determination reference generation unit 5, and sends the operation data to the UW timing detection unit 7. Output.

The UW timing detection unit 7 compares the calculation data input from the mixer 6 with a threshold stored in advance, detects a timing at which the calculation data exceeds the threshold, and uses this timing as the UW detection timing to detect timing detection data. Outputs Tuw. This timing corresponds to the last symbol timing of UW. At this time, the threshold value is set as follows. For example, when the ratio of the actual signal to noise is set to 10 times, as shown in FIG. 4, the corrected Q signal correlation data ABS (Q′cf _n ) of the corrected correlation processing signal Q′cf _n corresponding to the noise is obtained. In the case of using a judgment reference value multiplied by 10, the threshold value may be set to “1”. The threshold value and the determination reference value may be appropriately set according to a desired determination reference.

  The frequency estimation circuit 110 receives timing detection data Tuw output from the UW timing detection unit 7 and UW type data Fuw output from the UW type detection unit 8. The frequency estimation circuit 110 extracts a correlation processing signal Icf between the reference signal corresponding to the UW type data Fuw and the I signal component Icc of the complex conjugate calculation signal from the I signal correlation processing unit 21 at the input timing of the timing detection data Tuw. At the same time, the correlation processing signal Qcf is extracted. Then, the frequency estimation circuit 110 calculates the frequency shift Δf by applying these correlation processed signals Icf and Qcf to the above-described (Equation 5). Then, the frequency of the received digital modulation signal is estimated using this frequency shift Δf. Thereby, frequency estimation can be performed while detecting the timing of UW and UW.

  Next, specific simulation results using the configuration of the present embodiment will be described.

  5 to 9 are graphs showing the ratio of the correlation processing result between the reference signal and UW to noise. 5 to 9, the result indicated by “same UW pattern correlation result” indicates that the reference signal and UW match, and the result indicated by “other UW pattern correlation result” indicates that the reference signal and UW match. This is equivalent to the I signal correlation data ABS (Icf) in the above description. The “evaluation noise value” corresponds to the corrected Q signal correlation data ABS (Q′cf) described above. 5 to 9, Eb / N is different, FIG. 5 shows a case where Eb / N is 0 dB, FIG. 6 shows a case where Eb / N is 5 dB, FIG. 7 shows a case where Eb / N is 10 dB, FIG. 8 shows a case where Eb / N is 15 dB, and FIG. 9 shows a case where Eb / N is 20 dB. Further, in each of FIGS. 5 to 9, the upper diagram shows the case where the frequency offset, that is, the frequency shift Δf is 0 Hz, and the lower diagram shows the case where the frequency shift Δf is 3 kHz (3000 Hz).

  This simulation uses 16QAM as a modulation / demodulation method, has a frame length of 2688 symbols, and a symbol rate of 33.6 ksymbol / sec. It was done in.

  Further, in this simulation, when the ratio of the correlation processing result between the reference signal and the UW to the noise becomes 10 times, the UW is detected as being detected.

  As can be seen from FIGS. 5 to 9, even when Eb / N is 0 dB, that is, the digital modulation signal having information is buried in noise and the frequency shift is 3 kHz, 95.8% UW can be detected with a probability of. If there is no frequency shift, UW can be detected at approximately 100% regardless of Eb / N. Furthermore, if Eb / N is 5 dB or more, UW can be detected with approximately 100% even if the frequency shift is 3 kHz.

  As described above, by using the UW detection circuit of the present invention, UW can be reliably and accurately detected even when there is a frequency shift and Eb / N is low.

Schematic configuration block diagram showing a part of a digital communication signal receiver including the UW detection circuit of the present embodiment 1 is a block diagram showing a schematic configuration of the UW detection circuit 100 shown in FIG. The block diagram which shows schematic structure of the complex conjugate calculating part 1 shown in FIG. The block diagram which shows the UW detection circuit shown in FIG. 2 in a functional block unit A graph showing the ratio of the correlation processing result between the reference signal and UW to noise (Eb / N = 0 dB) A graph showing the ratio of the correlation processing result between the reference signal and UW to noise (Eb / N = 5 dB) A graph representing the ratio of the correlation processing result between the reference signal and UW to noise (Eb / N = 10 dB) Graph showing the ratio of correlation processing result between reference signal and UW to noise (Eb / N = 15 dB) A graph representing the ratio of the correlation processing result between the reference signal and UW to noise (Eb / N = 20 dB)

Explanation of symbols

100-UW detection circuit 1-complex conjugate calculation unit 2-correlation processing unit 21-I signal correlation processing unit 22-Q signal correlation processing unit 3-absolute value calculation unit 31-I signal absolute value calculation unit 32-Q signal absolute value Calculation unit 4-Maximum value detection unit 5-Decision reference generation unit 6-Mixer 7-UW timing detection unit 8-UW type detection unit 9-Filter 11-1 symbol delay processing unit 12-Complex conjugate processing unit 13-Mixer 101 102-mixer 103-voltage controlled oscillator (VCO)
104-π / 2 phase circuit 105, 106-LPF
107, 108-down converter 109-symbol timing detection circuit 110-frequency estimation circuit

Claims (5)

In a unique word detection circuit for detecting a unique word from a digital modulation signal in which at least the unique word is equivalently BPSK-modulated,
Baseband signal generation means for generating a baseband signal by symbol-synchronizing the digital modulation signal;
A complex conjugate calculation signal generating means for generating a complex conjugate calculation signal by performing a multiplication operation of the baseband signal and the complex conjugate of the delayed signal obtained by delaying the baseband signal by one symbol;
A reference signal generating means for generating a plurality of reference signals each having a different bit pattern used for a unique word of the digital modulation signal;
I signal correlation processing means for correlating the I signal component of the complex conjugate calculation signal with any kind of reference signal;
I signal correlation data generating means for generating an I signal correlation data by performing an absolute value calculation of an output signal of the I signal correlation processing means;
I signal correlation data comparing means for comparing each I signal correlation data and outputting the most correlated I signal correlation data;
Q signal correlation processing means for performing correlation processing between the Q signal component of the complex conjugate calculation signal and an arbitrarily selected reference signal;
Q signal correlation data generating means for calculating the absolute value of the output signal of the Q signal correlation processing means to generate Q signal correlation data;
A unique word detection circuit comprising: timing detection means for setting a timing at which the I signal correlation processing data exceeds a criterion value based on the Q signal correlation processing data to detect a unique word.   The unique word detection circuit according to claim 1, wherein the I signal correlation processing unit performs correlation processing on the I signal component of the complex conjugate operation signal and all of the reference signals.   3. The unique word detection circuit according to claim 1, wherein the I signal correlation data comparison unit detects a reference signal used for the I signal correlation data having the strongest correlation as a unique word.   The said Q signal correlation process means performs the filter calculation which removes the high frequency component of the correlation process signal of the Q signal component of the said complex conjugate calculation signal, and a specific reference signal. Unique word detection circuit.   At the timing detected by the timing detection means, the Q signal component of the complex conjugate operation signal of the correlation signal between the I signal component of the complex conjugate operation signal and the reference signal that is the most correlated I signal correlation data is specified. 5. The unique word detection circuit according to claim 1, further comprising frequency detection means for detecting a frequency of the digital modulation signal from an arctangent calculation of a ratio of the signal to the correlation signal with respect to the reference signal.

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