JPH05167630A - Unique word detector - Google Patents

Abstract

PURPOSE:To detect a unique word with a comparatively small circuit even when an input signal has a frequency error by applying delay detection to an input signal with a 1st delay detector, eliminating a frequency offset therefrom and inputting the result to a correlation device. CONSTITUTION:An input signal is subject to delay detection by a 1st delay detector 5 to eliminate a frequency offset included in an input signal and the unique word generated by a unique word generator 1 is subject to delay detection by a 2nd delay detector 6. Then the signals subject to delay detection respectively are given to a correlation device 2, in which the correlation is calculated and its output is converted into power by a power converter 4 and a level detector 3 is used to detect a maximum value thereby detecting the unique word. Thus, even when a large frequency uncertainty is in existing in the input signal, it is not required to use lots of the correlation devices arranged and the circuit scale is remarkably reduced. Furthermore, since only one input signal is required for the level detector 3, an error detection probability is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a unique word detector, and more particularly to a unique word detector as a signal detector when the input signal frequency has a large indefiniteness.

[0002]

2. Description of the Related Art Unique word detectors are roughly classified into two types according to their purpose. One is to establish frame synchronization, and a completely demodulated signal is input. The other one is for performing signal detection, and a quasi-synchronized demodulated signal is input. An example of the former is shown in FIG. The input signal R (t) is expressed by a complex number as a quadrature-modulated signal of two series, and a complex unique word pattern U (τ) of length T is inserted. The unique word generator 1 outputs a complex conjugate value U ^* (τ) of U (τ). The cross-correlator 2 outputs a cross-correlation value C (t) of R (t) and U ^* (τ).

[Equation 1]

Assuming that the unique word portion included in the input signal is received at time t = t _o ,

[Equation 2] Becomes However, N (t) is a noise component. For this reason,

[Equation 3] And takes the maximum value. However, n (t) is a contribution by the noise component. Therefore, the level detector 3 having C (t) as an input detects the maximum value C (t _o ) by comparing the value of C (t) with a predetermined threshold value, and the time t = You can know t _o .

An example of the latter is shown in FIG. In this case, since the input signal R (t) is a signal before demodulation, the input signal R (t _o + τ) at time t = t _o + τ
Is the residual frequency offset after quasi-synchronous demodulation is ω and the phase error is θ,

[Equation 4] Becomes Therefore, the cross-correlation output is also

[Equation 5] Becomes This is the absolute value | C when ω << 2 / T
(T _o) |, or the square (ie, power) takes a maximum value. Therefore, it can be dealt with by inserting a circuit for converting into electric power between the correlator and the level detector.

The problem is when ω has a larger value. As is clear from (Equation 5), | C (t _o ) | is s
This is because a term of in (ωT / 2) / ω is included, so that a sufficiently large output cannot be obtained when ω becomes large. Therefore, as shown in FIG. 3A, K unique K word detectors (blocks 1 to K) are arranged in parallel. As shown in FIG. 3 (b), each block inputs a signal whose frequency is shifted by the frequency converter 7 with respect to the input signal. The frequency to shift differs for each block.

For example, the signal Rk (t) given by (Equation 6) is input to the kth unique word detector.

[Equation 6] Then, the correlator output Ck (t) is, at the time of t = t _o,

[Equation 7] Therefore, if Δωk << 2 / T in any of the K unique word detectors, | Ck (t _o ) | has a sufficiently large maximum value. The level detector 3 determines that a signal is detected when any of the K input signals exceeds the threshold value.

[0007]

In the conventional unique word detector, the number K of individual word detectors and frequency converters required increases as the instability of the input signal frequency increases. There is a problem that the circuit scale becomes large. Further, when the number of input signals to the level detector increases, there is a problem that the probability of signal false detection increases. It is an object of the present invention to provide a unique word detector capable of detecting a unique word with a relatively small circuit even when an input signal has a frequency error.

[0008]

SUMMARY OF THE INVENTION A unique word detector of the present invention comprises a first differential detector for differentially detecting an input signal in which a unique word is inserted, and a unique word for generating a complex conjugate value of the unique word. A generator, a second differential detector that differentially detects the output of the unique word generator, a cross-correlator that cross-correlates the outputs of the first and second differential detectors, and a cross-correlator A power converter that squares the output to obtain the power, and a level detector that compares the output of the power converter with a predetermined threshold value and detects the maximum value thereof are provided.

[0009]

The input signal is delayed detected by the first differential detector to remove the frequency offset contained in the input signal, and the unique word pattern generated by the unique word generator is detected by the second differential detector. The differential detection is performed, the cross-correlator calculates the cross-correlation of each of the delay-detected signals, the output is converted into electric power, and the maximum value is detected by the level detector to detect the unique word.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. Figure 2
The same parts as those in the conventional configuration shown in FIG. 3 are designated by the same reference numerals. In addition to these configurations, here, a first delay detector 5 and a second delay detector 6 are provided, and then the output of the cross-correlator 2 is input to the power converter 4 and the level detector 3. ing.

In this configuration, the input signal R (t) is delay-detected by the first delay detector 5, and the signal D (t) represented by (Equation 8) is output.

[Equation 8] Therefore, at time t = t _o + τ, R (t _o + τ)
Considering that is expressed by (Equation 4),

[Equation 9] However, N ′ (t _o ) is a term including a noise component.

The output U of the unique word generator 1
^* (Τ) is also delayed and detected by the second differential detector 6 W (τ)
Is output.

[Equation 10] The cross-correlator 2 calculates the correlation value C between D (t) and W (τ).
Output (t).

[Equation 11] This means that when t = t _o , from (Equation 9) and (Equation 10),

[Equation 12] Therefore, the power | C (t _o ) | ² is constant regardless of the value of the frequency offset ω. Therefore, the correlator 2
Since the output obtained by converting the output of the above into the electric power by the power converter 4 always takes the maximum value at t = t _o (even if the value of ω is large),
By detecting this maximum value with the level detector 3, the signal can be detected and the time t = t _o can be known.

[0013]

As described above, according to the present invention, the input signal is delayed detected by the first delay detector to remove the frequency offset and then input to the correlator. Even if there is a possibility, it is not necessary to arrange a large number of correlators in parallel as in the conventional case, and it is possible to significantly reduce the circuit scale. Further, since there is only one input signal to the level detector, there is an effect that the false detection probability is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a unique word detector of the present invention.

FIG. 2 is a block diagram of an example of a conventional unique word detector.

FIG. 3 is a block diagram of another example of a conventional unique word detector.

[Explanation of symbols]

 1 Unique Word Generator 2 Cross Correlator 3 Level Detector 4 Power Converter 5 First Delay Detector 6 Second Delay Detector

Claims (1)

[Claims] 1. A first delay detector for delay-detecting the input signal, which is a signal obtained by quasi-synchronizing demodulation of a received signal in which a unique word is inserted, and a complex conjugate value of the unique word is generated. A unique word generator, a second differential detector for differentially detecting the output of the unique word generator, a cross-correlator for cross-correlating the outputs of the first and second differential detectors, and A power converter that squares the output of the correlator to obtain electric power, and a level detector that compares the output of this power converter with a predetermined threshold value and detects the maximum value thereof. Unique word detector to do.