JPS636935A - Preamble detection circuit - Google Patents

Abstract

PURPOSE:To detect a top signal pattern in a preamble from an input signal at high accuracy by providing a 1st band pass filter including a frequency component in its pass band and a 2nd band pass filter excluding a frequency component in its pass band. CONSTITUTION:The BPF 1 has a pass band characteristic with its nonmodulation carrier frequency as a center, and the BPF 2 has the characteristic of a pass band in the vicinity of the nonmodulation carrier frequency excluding said nonmodulation carrier band. When signals of a channel including the BPFs 1 and 2 arrive in a burstlike shape, the signal passing through the BPF 1 includes a preample signal at a nonmodualtion carrier frequency. Since the pass band of the BPF 2 excludes the nonmodulation carrier frequency, the signal passing through the BPF 2 is constant according as the preamble signal is received or not. Out of two powers inputted to a comparator circuit 7 through power calculation circuits 3 and 4 and LPFs 5 and 6, the power passing through the BPF l increases, and an output from the comparator circuit 7 exceeds a reference value. Finally a preamble detection signal is outputted from a detection circuit.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to the beginning of a signal arriving in a burst on the receiving side of digital wireless communication using, for example, TDMA (time division multiple access VC) system. The present invention relates to a preamble detection circuit that detects a preamble signal present in a preamble signal.

(Prior Art) Satellite communications have come into widespread use today due to their various advantages such as broadcastability and uniformity of service over a wide area. In line with this, there is a strong demand for downsizing of earth stations (especially their antennas) from a practical standpoint, and it is also desired to keep the signal output of satellites as low as possible in order to save on satellite power.

However, as antennas are made smaller and the output power of LFR stars is reduced, the proportion of noise contained in the received signal becomes extremely large, making the input signal appear as if it were buried in noise. . For this reason, a problem has arisen in which, especially in noisy areas such as high latitude regions, it is erroneously detected that a signal has been input due to the influence of noise even though no signal has been input.

Furthermore, input detection of signals arriving in a burst is generally performed by detecting a preamble signal present at the beginning of the signal. Conventionally, this preamble detection has been performed by detecting that the input power exceeds a certain value.

However, in satellite communications, input power fluctuates hundreds of times due to weather, location, etc., so preamble detection is difficult with fixed level determination. On the other hand, AGC(A
Although it has been attempted to suppress the level fluctuations of the input signal, in this case, the noise level also fluctuates greatly, making it fundamentally difficult to detect the signal input by level determination.

(Problems to be Solved by the Invention) As described above, the conventional preamble detection method cannot sufficiently remove the influence of noise, resulting in problems such as false detection or no detection, especially in noisy regions. There has occurred.

The present invention has been made to solve these problems, and it is an object of the present invention to provide a preamble detection circuit that can accurately detect the signal pattern at the beginning of the preamble from an input signal.

[Structure of the Invention] (Means for Solving the Problems) The present invention includes a first band-pass filter whose pass band includes a frequency component corresponding to the signal pattern at the beginning of the preamble; a second bandpass filter that is within the same channel as the passband and whose passband does not include a frequency component corresponding to the signal pattern at the beginning of the preamble; and a second bandpass filter that calculates the power of the signal that has passed through each of these bandpass filters. the first and second power output means, a comparison means for determining the average difference between the outputs of both the power output means, and a detection means for outputting a preamble detection signal when the output of the comparison means exceeds a predetermined level. We are prepared.

(effect) The noise at the receiver is generally white noise.

The average power density of this white noise is approximately constant regardless of the band. Therefore, among the average powers of the frequency components corresponding to the signal pattern at the beginning of the preamble, the average power of the noise component is approximately equal to the average power of the other frequency components. The first bandpass filter passes the frequency component corresponding to the signal pattern at the beginning of the preamble, and therefore includes the power of the preamble signal and the m'11M power. but,
Since the second bandpass filter does not include the frequency component corresponding to the signal pattern at the beginning of the preamble, it passes only the noise power. Therefore, by determining the power of the signal that has passed through both band-pass filters and comparing the two, it is possible to detect the power valve of the preamble signal.

(Example) Examples of the present invention will be described below.

FIG. 1 is a diagram showing a preamble detection circuit provided in a receiving device that receives signals arriving in bursts in satellite communication. Here, a case will be explained in which the preamble signal located at the beginning of the received signal is composed of an unmodulated carrier wave. The received signal is passed through the first bandpass filter (
BPF) 1 and a second bandpass filter <BPF) 2. The first BPFl has a passband characteristic centered around the unmodulated carrier frequency, as shown in FIG. In addition, the second BPF2 is in the same channel as the pass band of the first BPF1, but the liquid-free FJ4 is
It has a passband characteristic that does not include the W1 transmission band and is preferably near the unmodulated carrier frequency. The output of the first BPFl is input to the first power calculation circuit 3. Further, the output of the second BPF 2 is input to the second power calculation circuit 4.

These power calculation circuits 3 and 4 calculate the signal power by performing square calculations, absolute value calculations, etc. on the signals that have passed through the BPFs 1 and 2. The outputs from these power calculation circuits 3.4 are smoothed by low-pass filters 5 and 6, respectively.
It is introduced into two inputs of the comparator circuit 7. Comparison circuit 7
can be constructed by a subtractor or a divider. The output from the comparison circuit 7 is input to the detection circuit 8. The detection circuit 8 is constituted by, for example, a comparator, and has the negative input inputted with the output from the comparison circuit 7, and the other input inputted with a predetermined reference value. Then, when the output from the comparison circuit 7 exceeds a predetermined reference value, a preamble detection signal is output.

Next, the operation of the preamble detection circuit according to this embodiment configured as described above will be explained. If there is no signal input,
BPF1, 2 passes noise components in their respective passbands. - In general, noise in the field of communications is often white noise.

The average power of white noise in a certain band is constant regardless of its frequency. Therefore, in a state where no signal arrives as described above, the noise components passing through BPF 1 and 2 are different band components, but their average powers are approximately equal. Therefore, the power calculation circuit 3.4 performs a squaring operation and converts it into power, and the average power of the two male and female tone components that is smoothed by the LPF 5.6 and input to the comparison circuit 7 becomes approximately equal. The output of 7 becomes smaller. In this case, since the output of the comparator circuit 7 is below the reference value, no detection signal is obtained from the detection circuit 8.

Next, when the signals of the channel including the 8PF1 and 2 arrive in a burst, the signal passing through BPF1 has no change U! A preamble signal with a 4V8 transmission frequency is included. - There is a black discoloration U in the passband of BPF2.
Since it does not include the A'm transmission frequency, the signal passing through the BPF 2 is constant regardless of whether or not the preamble signal is received. Therefore, the power calculation circuits 3 and 4 and the LPF 5
．． BP of both types of force inputted to the comparator circuit 7 via 6
Since the power passing through the FI increases, the output of the comparison circuit 7 exceeds the reference value. Therefore, the detection circuit 8 outputs a preamble detection signal.

As described above, according to this embodiment, the average power of noise is estimated by referring to the average power of a band in which it is known in advance that no signal will be input, so that the signal is not buried in a considerable amount of noise. Preamble components can be detected with high accuracy even when Note that the unmodulated carrier frequency mentioned above may fluctuate somewhat depending on the conditions of the transmission path, but by setting the passband width of the BPFL with some margin in anticipation of this fluctuation, it is possible to prevent the preamble signal from being detected. can be prevented.

FIG. 3 shows a preamble detection circuit according to another embodiment of the present invention. In the previous embodiment, the outputs from the power calculation circuits 3.4 were smoothed by the LPF 5.6 and compared, but in this embodiment, the outputs from the power calculation circuits 3 and 4 were subtracted by the subtracter 11 and then compared. , the output of the subtracter 11 is passed through the LPF 12
I try to smooth it with . The output of the LPF 12 is input to a determination circuit 13, which is a comparison means, and it is determined here whether or not it exceeds a predetermined reference value. When the determination circuit 13 determines that the input signal exceeds a predetermined reference value, the timer 14 is activated. If the determination circuit 13 determines that the reference value has been exceeded multiple times within the time set by the timer 14, the detection circuit 15 outputs a preamble detection signal.

With such a configuration, erroneous detection of the preamble signal can be prevented and detection accuracy can be further improved.

FIG. 4 shows a further embodiment of the present invention. This embodiment is an example in which the present invention is applied to each of two channels having a quadrature phase relationship. I signal is 8PF21 and BPF22
is input. Further, the Q signal, which is out of phase with the I signal by 90°, is input to the BPF 23 and the BPF 24. BPF
21. 23 is a first band pass filter whose pass band includes the frequency component of the preamble signal;
2 and 24 are second band-pass filters whose pass band does not include the frequency component of the preamble signal. Each of these B
The outputs of PF21-24 are sent to multipliers 25, 26, 27, respectively.
．． 28, are squared, and directly converted into electric power. Then, the first BPFs 21.23 are added together by the adder 29, and the second BPFs 21.23 are added together. The adder 30 adds together the PFs 22 and 24. The outputs of the adders 29 and 30 are respectively smoothed by LPFs 31 and 32 and input to a comparison circuit 33 which is comparison means. The subsequent detection procedure can be performed in the same manner as in each of the embodiments described above.

In this way, the preamble signal can be reliably detected by adding the same band components of the I and Q signals that have a quadrature phase relationship.

[Effects of the Invention] As described above, according to the present invention, focusing on the fact that white noise is approximately constant regardless of the band, the signal power of the band including the frequency component corresponding to the signal pattern at the beginning of the preamble,
Since the preamble signal is detected by comparing the signal power of a band that does not include this frequency component, it is possible to perform preamble detection with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a preamble detection circuit according to an embodiment of the present invention, and FIG.
FIG. 3 is a block diagram showing the configuration of a preamble detection circuit according to another embodiment of the present invention, and FIG. 4 is a diagram showing the passband characteristics of the second BPF. FIG. 2 is a block diagram showing the configuration of a preamble detection circuit. 1.21.23...1st BPF, 2.22°24.
...Second BPF, 3.4...Power calculation circuit, 5゜6
．． 12, 31.32...LPF, 7.33...Comparison circuit, 8.15...Detection circuit, 11...Subtractor, 1
3... Judgment circuit, 14... Timer, 25-28.
... Multiplier, 29.30 ... Adder.

Claims (4)

[Claims] (1) a first bandpass filter whose passband includes a frequency component corresponding to the signal pattern at the beginning of the preamble; and a first power calculation means for calculating the power of the signal that has passed through the first bandpass filter; a second band-pass filter that is within the same channel as the pass band of the first band-pass filter and whose pass band does not include a frequency component corresponding to the signal pattern at the beginning of the preamble; a second power calculation means for calculating the power of the passed frequency band; a comparison means for calculating the average difference between the output of the first power calculation means and the output of the second power output means; 1. A preamble detection circuit comprising: detection means for outputting a preamble detection signal when the output exceeds a predetermined level. (2) The preamble detection circuit according to claim 1, wherein the comparison means comprises a subtracter. (3) The preamble detection circuit as set forth in claim 1, wherein the comparison means comprises a divider. (4) The preamble detection circuit according to claim 1, wherein the detection means outputs a detection signal when the output from the comparison means continuously exceeds a certain value. .