Timing detection method, communication system, and receiving device

Abstract

A transmission device in the present invention intermittently transmits a physical frame of a transmission signal. A receiving device therein is equipped with a correlation calculation unit and a determination unit. The correlation calculation unit calculates the correlation between a received signal and a correlation sequence which has been subjected to doppler shifts of various types of shift amounts. The determination unit determines that a physical frame has been received when any of the calculation results from the correlation calculation unit exceeds a threshold.

Description

[Technical Field]

[0001] The present invention relates to a timing detection method, a communication system, and a receiving device. [Background technology]

[0002] In a communication system that transmits and receives packets, it is necessary to accurately locate the beginning position of a physical frame in order to perform synchronization processing. However, because impulsive noise exists in water, timing of the impulsive noise is often mistakenly detected. To prevent incorrect timing detection in an environment with impulsive noise, a relatively long correlation sequence is embedded in the received signal, and frame timing detection is performed by cross-correlation (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] M. Stojanovic, JA Catipovic and JG Proakis, "Phase-coherent digital communications for underwater acoustic channels," in IEEE Journal of Oceanic Engineering, vol. 19, no. 1, pp. 100-111, Jan. 1994, doi: 10.1109 / 48.289455 Summary of the Invention [Problem to be solved by the invention]

[0004] The longer the correlation sequence, the lower the possibility of erroneously detecting impulsive noise as frame timing. On the other hand, the longer the correlation sequence, the lower the cross-correlation value between the Doppler-shifted received signal and the correlation sequence.

[0005] FIG. 6 illustrates the detection performance of the conventional technology. FIG. 6 shows the relationship between the moving speed and the cross-correlation value when detecting the reception of a physical frame in the conventional technology as the detection performance. A normalized SNR (Signal-to-Noise Ratio) is used for the cross-correlation value. The symbol L represents the detectable level. When the cross-correlation value exceeds the detectable level L, the reception of a physical frame can be detected. The symbol G11 represents the cross-correlation value when the sequence length is 25 ms, and the symbol G12 represents the detectable range when the sequence length is 25 ms. The symbol G21 represents the cross-correlation value when the sequence length is 100 ms, and the symbol G22 represents the detectable range when the sequence length is 100 ms. As shown in FIG. 6, a longer sequence length results in a larger cross-correlation value near a moving speed of 0 m / s, improving the SNR. This indicates higher resistance to impulsive noise. On the other hand, a longer sequence length narrows the range of moving speeds at which the reception of a physical frame can be detected.

[0006] In this way, if the correlation sequence is lengthened to increase the resistance to impulsive noise, timing detection becomes difficult in a mobile environment.

[0007] In view of the above circumstances, an object of the present invention is to provide a timing detection method, a communication system, and a receiving device that improve the detection accuracy of a received signal in a mobile environment while preventing a decrease in resistance to impulsive noise. [Means for solving the problem]

[0008] A timing detection method according to one aspect of the present invention includes a transmitting step in which a transmitting device intermittently transmits physical frames of a transmission signal; a correlation calculation step in which a receiving device calculates the correlation between the received signal and each of correlation series to which a Doppler shift of a plurality of shift amounts has been applied; and a determination step in which the receiving device determines that a physical frame has been received if any of the calculation results in the correlation calculation step exceeds a threshold value.

[0009] A timing detection method according to one aspect of the present invention includes a correlation calculation step of calculating the correlation between a received signal and each of correlation sequences to which a Doppler shift of a plurality of shift amounts has been applied, and a determination step of determining that a physical frame transmitted from a transmitting device that intermittently transmits physical frames of a transmission signal has been received if any of the calculation results in the correlation calculation step exceeds a threshold value.

[0010] One aspect of the present invention is a communication system having a transmitting device and a receiving device, wherein the transmitting device intermittently transmits signal frames, and the receiving device includes a correlation calculation unit that calculates the correlation between the received signal and each of correlation series that have been subjected to Doppler shifts of multiple shift amounts, and a determination unit that determines that a physical frame has been received if any of the calculation results by the correlation calculation unit exceeds a threshold value.

[0011] A receiving device according to one embodiment of the present invention includes a correlation calculation unit that calculates the correlation between a received signal and each of correlation sequences to which a Doppler shift of a plurality of shift amounts has been applied, and a determination unit that determines that a physical frame transmitted from a transmitting device that intermittently transmits physical frames of a transmission signal has been received if any of the calculation results by the correlation calculation unit exceeds a threshold value. [Effects of the Invention]

[0012] According to the present invention, it is possible to improve the detection accuracy of received signals in a mobile environment while preventing a decrease in resistance to impulsive noise. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a communication system according to an embodiment of the present invention. [Figure 2] 1 is a block diagram showing a configuration of a timing detection device according to an embodiment. [Figure 3] 10 is a flowchart showing a reception timing detection process of the timing detection device according to the embodiment. FIG. [Figure 4]FIG. 10 is a diagram illustrating the relationship between SNR and the amount of Doppler shift. [Figure 5] 10A and 10B are diagrams illustrating detection performance of a timing detection device according to an embodiment. [Figure 6] FIG. 1 is a diagram showing detection performance according to the prior art. [Figure 7] FIG. 1 is a block diagram showing the configuration of a conventional timing detection device. [Figure 8] FIG. 10 is a flowchart showing a reception timing detection process of a conventional timing detection device. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] The communication system of this embodiment improves the detection accuracy of physical frame reception in a mobile environment without shortening the correlation sequence and without reducing the impulsive noise resistance, thereby enabling the communication system of this embodiment to accurately detect the reception timing of a physical frame of a signal even in an environment where impulsive noise is present.

[0016] 1 is a diagram showing the configuration of a communication system 1 according to an embodiment of the present invention. The communication system 1 includes a transmitter 10 and a receiver 20. The communication system 1 is, for example, an underwater communication system that performs underwater communication. When performing underwater communication, the receiver 20 receives a signal that is transmitted from the transmitter 10 and transmitted underwater.

[0017] The transmitter 10 intermittently transmits physical frames of a transmission signal from an antenna. The physical frame includes a payload and a correlation sequence. The correlation sequence is set at a predetermined position in the physical frame. In this embodiment, the correlation sequence is set at the beginning of the physical frame. The correlation sequence is known.

[0018] The receiver 20 receives, by an antenna, the physical frames intermittently transmitted from the transmitter 10. The receiver 20 includes a timing detection device 21, a demodulation device 22, and a shift amount calculation device .

[0019] The timing detection device 21 calculates the correlation between the received signal received by the antenna and each of the correlation sequences to which a Doppler shift of a plurality of Doppler shift amounts has been applied, and detects the reception of a physical frame based on the calculation results. The timing detection device 21 notifies the demodulation device 22 of the received signal and the detected position of the physical frame in the received signal.

[0020] The demodulator 22 identifies the position of the payload in the received signal based on the detected position of the physical frame detected by the timing detector 21. If the correlation sequence is included in the beginning of the physical frame, the detected position notified by the timing detector 21 indicates the beginning of the physical frame in the received signal. The demodulator 22 obtains the information transmitted by the transmitter 10 by demodulating the portion of the received signal corresponding to the payload of the physical frame.

[0021] The shift amount calculation device 23 calculates a plurality of types of Doppler shift amounts to be applied to the correlation sequence used by the timing detection device 21. The shift amount calculation device 23 may be provided outside the receiver 20. Also, the receiver 20 does not need to include the shift amount calculation device 23. In this case, the timing detection device 21 uses a plurality of predetermined types of Doppler shift amounts that are set in advance.

[0022] Here, the prior art will be described. Fig. 7 is a diagram showing the configuration of a conventional timing detection device 91. The timing detection device 91 has a correlator 911 and a threshold determination unit 912. The correlator 911 calculates the correlation value between the received signal and the correlation sequence. The threshold determination unit 912 detects the reception of a physical frame by comparing the correlation value with a threshold.

[0023] 8 is a flow diagram showing the reception timing detection process of the timing detection device 91. The correlator 911 receives a received signal (step S91). The correlator 911 calculates the cross-correlation between the received signal and a known correlation sequence (step S92). The threshold determination unit 912 determines whether the correlation value of the cross-correlation calculated in step S92 is greater than a threshold (step S93).

[0024] If the threshold value determination unit 912 determines that the correlation value is equal to or less than the threshold value (step S93: NO), it repeats the process from step S91 for the received signal at the next timing. If the threshold value determination unit 912 determines that the correlation value is greater than the threshold value (step S93: YES), it detects the reception of a physical frame. If the correlation sequence is at the beginning of a physical frame, the threshold value determination unit 912 notifies the subsequent stage of the beginning position of the received signal input in step S91 as the detected position of the physical frame (step S94).

[0025] In the case of timing detection device 91, in principle, the longer the correlation sequence, the more difficult it is to detect a Doppler-shifted received signal.

[0026] Next, timing detection device 21 of this embodiment will be described. Fig. 2 is a diagram showing the configuration of timing detection device 21. Timing detection device 21 has branching section 211, N (N is an integer of 2 or more) correlators 212, and threshold determination section 213. N correlators 212 will be referred to as correlators 212-1 to 212-N, respectively.

[0027] Branching section 211 branches the received signal into N branches, and inputs the N branched received signals to correlators 212-1 to 212-N, respectively. Correlator 212-n (n is an integer between 1 and N) calculates the received signal and the correlation sequence A with a frequency shift amount f n Correlation sequence A with Doppler shift of [Hz] n Correlation value C with n Calculate the frequency shift amount f1~f N are different values. nmay be 0. For example, the frequency shift amount f1 of the correlator 212-1 is set to 0. In this case, the correlation sequence A is used as the correlation sequence A1 as it is. In this embodiment, the correlation value C n The normalized SNR is used as

[0028] The threshold value determination unit 213 calculates the correlation values ​​C1 to C2 calculated by the correlators 212-1 to 212-N, respectively. N If any of the above exceeds the threshold, the threshold decision unit 213 detects the reception of a physical frame. The threshold decision unit 213 outputs the received signal and the detected position of the physical frame to the demodulation device 22.

[0029] 3 is a flow chart showing the reception timing detection process of timing detection device 21. Branching unit 211 receives a reception signal received by an antenna (step S11). Branching unit 211 branches the reception signal into N, and inputs the N branched reception signals to correlators 212-1 to 212-N, respectively.

[0030] The correlator 212-n compares the portion of the received signal from the beginning to the length of the correlation sequence A with the known correlation sequence A by f n [Hz] Doppler shifted correlation sequence A n Correlation value C with n (Step S12-n). Here, the correlator 212-1 uses the correlation sequence A as the correlation sequence A1 as it is. The correlator 212-n calculates the calculated correlation value C n is output to the threshold value determination unit 213.

[0031] The threshold value determination unit 213 calculates the correlation values ​​C1 to C2 calculated by the correlators 212-1 to 212-N in steps S12-1 to S12-N, respectively. N The threshold value determining unit 213 inputs the correlation values ​​C1 to C N It is determined whether any of the above exceeds a threshold value (step S13).

[0032] The threshold value determination unit 213 calculates the correlation values ​​C1 to C NIf it is determined that all of the correlation values ​​C1 to C2 are equal to or less than the threshold value (step S13: NO), the process from step S11 is repeated for the received signal at the next timing. N If it is determined that any of the above exceeds the threshold (step S13: YES), the reception of a physical frame is detected. If the correlation sequence is at the beginning of a physical frame, the threshold determination unit 213 notifies the demodulation device 22 of the beginning position of the received signal input in step S11 as the detected position of the physical frame (step S14).

[0033] As described above, the timing detection device 21 calculates the cross-correlation between the received signal and a known correlation sequence, as well as the cross-correlation between the received signal and a Doppler-shifted correlation sequence in parallel, thereby enabling detection of a Doppler-shifted received signal without sacrificing detection accuracy.

[0034] Next, a method for calculating the frequency shift amounts set in the correlators 212-1 to 212-N of the timing detection device 21 by the shift amount calculation device 23 will be described.

[0035] (First calculation method) The first calculation method can eliminate undetectable Doppler frequencies. Since the Doppler frequency changes depending on the moving speed, it can also be said that it can eliminate undetectable moving speeds.

[0036] M is the length of the correlation sequence, f d is the Doppler frequency, T s is the symbol rate, σ s 2 is the signal power of the received signal, σ n 2 is the noise power of the received signal. The Doppler frequency is the amount of change between the frequency affected by the Doppler effect and the frequency before it is affected. The signal power S(f d ) is expressed by the following formula (1):

[0037]

number

[0038] Equation (1) is the value when a correlation sequence with a Doppler shift of 0 is used. The noise power N(f d ) is expressed by the following equation (2).

[0039]

number

[0040] The SNR at the time of detecting the reception of a physical frame is calculated by the following equation (3) using equations (1) and (2).

[0041]

number

[0042] Doppler frequency f d is expressed as the following equation (4).

[0043]

number

[0044] In this case, the signal power S(f d )=0. That is, the Doppler frequency f d =k / (MT s ) [Hz], the SNR at the time of detecting the reception of a physical frame is 0, and therefore signal detection is not possible. FIG. 4 is a diagram showing the relationship between the correlation value and the Doppler shift amount at the time of detecting a physical frame. Since the SNR, which is the correlation value, is 0 at the Doppler shift amounts fa and fb, signal detection is not possible. Therefore, the shift amount calculation device 23 calculates the Doppler frequency f d =1 / (MT s ) [Hz] and set in each correlator 212. That is, the correlators 212-1 to 212-N are set to f d =1 / (MT s) and calculate the correlation value with the received signal using each correlation sequence Doppler-shifted by 1 / 2. This makes it possible to eliminate Doppler frequencies where SNR=0.

[0045] As described above, in the first calculation method, the amount of Doppler shift of each of the plurality of types is calculated based on the sequence length M of the correlation sequence and the symbol rate T of the physical frame. s Product MT s The reciprocal of 1 / (MT s ) is an integer multiple of the correlation series. The number is The detection threshold is determined based on the range of movement speeds expected for the communication device including the transmitter 10 and receiver 20, i.e., the amount of Doppler shift expected from that range of movement speeds. The detection threshold is set based on the receiver operating characteristic (ROC) in accordance with the risk level (significance level) and detection power required by the system.

[0046] (Second calculation method) The shift amount calculation device 23 determines the frequency shift amount in the following procedure: This method can ensure the SNR at the lower limit of detection.

[0047] (Step 1) Shift amount calculation device 23 generates correlation sequence A with Doppler frequency=0, and sets it as correlation sequence A1. Shift amount calculation device 23 sets correlation sequence A1 in correlator 212-1. This corresponds to using one Doppler shift amount (0 in this case) from among multiple types of Doppler shift amounts as a reference, and setting the correlation sequence of the reference Doppler shift amount in correlator 212-1.

[0048] (Step 2) The shift amount calculation device 23 determines the detection threshold value TH for the received signal with Doppler frequency = 0 based on the general ROC characteristics. The shift amount calculation device 23 calculates the SNR at the detection threshold value TH for the received signal with Doppler frequency = 0, and calculates C min Let's say.

[0049] (Step 3) When a signal having a correlation sequence set at the beginning of a physical frame is received, the shift amount calculation device 23 calculates a Doppler frequency ±f that satisfies the condition shown in the following equation (5). d1 Ask for.

[0050]

number

[0051] That is, Doppler frequency ±f d1 The signal power S(f d ) and noise power N(f d ) is the ratio C of the signal power to noise power of the received signal at the detection threshold, calculated using the correlation sequence of the reference Doppler shift. min Matches.

[0052] (Step 4) The shift amount calculation device 23 calculates the correlation sequence A1 at the Doppler frequency ±f d1 The shifted correlation sequences A2 and A3 are set in the correlators 212-2 and 212-3, respectively. Furthermore, the shift amount calculation device 23 calculates the Doppler frequency ±2×f d1 The shifted correlation sequences A4 and A5 are set in the correlators 212-4 and 212-5, respectively. Thereafter, the shift amount calculation device 23 repeats this process up to the correlator 212-N. As a result, the multiple types of shift amounts are calculated based on the Doppler frequency f d1 The value is shifted by one.

[0053] FIG. 5 shows the detection performance of timing detection device 21 through computer simulation. For comparison, FIG. 5 also shows the detection performance of a conventional timing detection device 91. In this simulation, the correlation sequence length of the physical frame transmitted from transmitter 10 was 100 ms, and the carrier frequency was 20 kHz. Timing detection device 21 also includes three correlators 212, with correlator 212-1 using a correlation sequence shifted by 0 Hz, correlator 212-2 using a correlation sequence shifted by 10 Hz, and correlator 212-3 using a correlation sequence shifted by -10 Hz. Correlator 911 of timing detection device 91 also used a correlation sequence shifted by 0 Hz. The detectable SNR during detection was set to -10 dB.

[0054] The symbol L is the detectable level. When the SNR is greater than the detectable level L, it is possible to detect the reception of a physical frame. R11 indicates the detected SNR in correlator 212 of this embodiment, and R12 indicates the detectable range in correlator 212 of this embodiment. R21 indicates the detected SNR in conventional correlator 911, and R22 indicates the detectable range in conventional correlator 911. It can be seen from FIG. 5 that this embodiment widens the range of moving speeds at which physical frames can be detected, and makes it possible to improve the accuracy of frame detection in a moving environment without sacrificing sequence length.

[0055] Some of the functions of the receiver 20 in the above-described embodiment may be realized by a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit) reading and executing a program from a recording medium such as a memory. Also, some of the functions of the receiver 20 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0056] According to the above-described embodiment, the communication system includes a transmitting device and a receiving device. For example, the transmitting device corresponds to the transmitter 10 of the embodiment, and the receiving device corresponds to the receiver 20 of the embodiment. The transmitting device intermittently transmits physical frames of a transmission signal. The receiving device includes a correlation calculation unit and a determination unit. The correlation calculation unit corresponds to, for example, the correlator 212 of the embodiment. The correlation calculation unit calculates the correlation between the received signal and each of the correlation sequences to which a Doppler shift of a plurality of shift amounts has been applied. The received signal may be a signal transmitted underwater. The determination unit corresponds, for example, to the threshold determination unit 213 of the embodiment. The determination unit determines that a physical frame has been received if any of the calculation results by the correlation calculation unit exceeds a threshold.

[0057] The multiple shift amounts are determined by the sequence length M of the correlation sequence and the symbol rate T of the physical frame. s Product MT s The reciprocal of (1 / MT s ) is an integer multiple of

[0058] Alternatively, the plurality of types of shift amounts may be set to a predetermined Doppler frequency f d1 When one of the multiple shift amounts is used as a reference, the Doppler frequency f d1 The signal power S(f d ) and noise power N(f d ) is the ratio of the signal power of the received signal to the noise power at the detection threshold calculated using the correlation sequence of the reference shift amount, and is the SNR (for example, C min ) matches.

[0059] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0060] 1. Communication Systems 10 Transmitter 20 Receiver 21, 91 Timing detection device 22 Demodulator 23 Shift amount calculation device 211 Branch 212-1~212-N, 911 correlator 213, 912 Threshold value judgment unit 911 Correlator

Claims

1. a transmitting step in which a transmitting device intermittently transmits physical frames of a transmission signal; a correlation calculation step in which the receiving device calculates the correlation between the received signal and each of the correlation sequences to which a Doppler shift of a plurality of shift amounts has been applied; a determining step in which the receiving device determines that a physical frame has been received when any of the calculation results in the correlation calculation step exceeds a threshold value; and the number of types of shift amounts is determined according to a range of moving speeds of the transmitting device or the receiving device; Timing detection method.

2. A correlation calculation step of calculating correlations between a received signal received by a receiving device and each of correlation sequences to which a Doppler shift of a plurality of shift amounts has been applied; a determining step of determining that a physical frame transmitted from a transmitting device that intermittently transmits physical frames of a transmission signal has been received when any of the calculation results in the correlation calculation step exceeds a threshold value; and the number of types of shift amounts is determined according to a range of moving speeds of the transmitting device or the receiving device; Timing detection method.

3. A communication system having a transmitting device and a receiving device, the transmitting device intermittently transmits signal frames; The receiving device a correlation calculation unit that calculates the correlation between the received signal and each of the correlation sequences that have been subjected to Doppler shifts of a plurality of shift amounts; a determination unit that determines that a physical frame has been received when any of the calculation results by the correlation calculation unit exceeds a threshold value; the number of types of shift amounts is determined according to a range of moving speeds of the transmitting device or the receiving device; Communication system.

4. a correlation calculation unit that calculates the correlation between the received signal and each of the correlation sequences that have been subjected to Doppler shifts of a plurality of shift amounts; a determination unit that determines that a physical frame transmitted from a transmitting device that intermittently transmits physical frames of a transmission signal has been received when any of the calculation results by the correlation calculation unit exceeds a threshold value; Equipped with the number of types of shift amounts is determined according to a range of moving speeds of the transmitting device or the own device; Receiving device.

5. A correlation calculation unit that calculates the correlation between the received signal and each of the correlation sequences that have been subjected to Doppler shifts of multiple shift amounts; a determination unit that determines that a physical frame transmitted from a transmitting device that intermittently transmits physical frames of a transmission signal has been received when any of the calculation results by the correlation calculation unit exceeds a threshold value; Equipped with each of the plurality of types of shift amounts is a value obtained by multiplying an inverse number of a product of a sequence length of the correlation sequence and a symbol rate of the physical frame by an integer; Receiving device.

6. A correlation calculation unit that calculates the correlation between the received signal and each of the correlation sequences that have been subjected to Doppler shifts of multiple shift amounts; a determination unit that determines that a physical frame transmitted from a transmitting device that intermittently transmits physical frames of a transmission signal has been received when any of the calculation results by the correlation calculation unit exceeds a threshold value; Equipped with the plurality of types of shift amounts are values ​​shifted by a predetermined Doppler frequency, When one of the plurality of types of shift amounts is used as a reference, the ratio of signal power to noise power of the received signal calculated using the correlation sequence of a predetermined Doppler frequency coincides with the ratio of signal power to noise power of the received signal at a detection threshold calculated using the correlation sequence of the reference shift amount. Receiving device.

7. The received signal is a signal transmitted underwater.

7. The receiving device according to claim 4, wherein the receiving device is a receiving unit.

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