Wireless receiving device and frame synchronization timing generation method

Abstract

To provide a wireless receiving device and a frame synchronization timing generation method capable of generating frame synchronization timing without reducing the throughput of burst communication.SOLUTION: A search interval setting unit 8172 sets a search interval using the timing at which a preamble signal is detected from a received signal as a reference. A correlation value calculation unit 8173 calculates the correlation value between a received signal in the search interval and a known signal. A maximum value search unit 8174 searches for the maximum correlation value. A synchronization timing calculation unit 8175 calculates frame synchronization timing based on the timing at which the search interval ends, the timing at which the correlation value becomes maximum, and the delay adjustment amount of the received signal.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a wireless receiving apparatus and a frame synchronization timing generating method for detecting data frames transmitted in bursts and generating frame synchronization timing. [Background technology]

[0002] In burst communication used in TDM (Time Division Multiplexing) communication, etc., discontinuous signals are transmitted at irregular intervals (hereinafter also referred to as burst transmission), so a wireless receiving device does not know when it will receive the signal. Therefore, a wireless receiving device that performs burst communication receives a signal transmitted in bursts, detects a preamble signal from the received signal, and performs burst detection to detect the arrival of a data frame included in the received signal.

[0003] On the other hand, the wireless receiving device performs frame synchronization processing on the received data frame. Frame synchronization is a process of generating the timing of any section (frame synchronization timing) using a known signal in order to extract signals of each section that constitute the frame format of the data frame from the received signal.

[0004] In conventional frame synchronization processing, as shown in frame synchronization circuit 100 in FIG. 27, a correlation value between a received signal including a data frame and a previously set known signal is calculated by correlation value calculation section 101. The data frame is added with a preamble signal and a known signal. Next, a threshold comparison section 102 compares the calculated correlation value with a previously set threshold, and generates frame synchronization timing if the correlation value is equal to or greater than the threshold (see, for example, Patent Document 1). In addition, forward and backward guard stages are provided to improve the probability of frame synchronization from a received signal with a low CNR (Career-to-Noise Ratio). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-252061 Summary of the Invention [Problem to be solved by the invention]

[0006] In burst communication, burst signals may be transmitted from multiple wireless transmission devices to one wireless reception device, and the destination station that transmitted the burst signal may be different for each received burst signal. Therefore, in burst communication, frame synchronization timing must be generated from one burst signal, and it is not possible to provide a forward protection stage number and a backward protection stage number. In burst communication, in order to ensure the frame synchronization probability from a received signal with a low CNR, it is sufficient to lengthen the known signal added to the data frame, but this causes a problem of reduced throughput.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS It is therefore an object of the present invention to provide a wireless receiving apparatus and a frame synchronization timing generating method capable of generating frame synchronization timing without reducing the throughput of burst communication. [Means for solving the problem]

[0008] The applicant has noticed that the relationship between the correlation value of correct frame synchronization timing and the correlation value of incorrect frame synchronization timing does not change even when the CNR of the received signal is low, and the correlation value of correct frame synchronization timing is often larger than the correlation value of incorrect frame synchronization timing. The invention described in is a wireless receiving device comprising: receiving means for receiving a data frame that is burst-transmitted with a preamble signal and a known signal added to the beginning of a data signal, and outputting a received signal; burst detection means for detecting the arrival of the data frame by detecting the preamble signal from the received signal; and frame synchronization means for generating frame synchronization timing for synchronizing with the data frame from the received signal using the known signal, wherein the frame synchronization means calculates a correlation value between the received signal and the known signal stored in advance, searches for a maximum value of the correlation value, and calculates the frame synchronization timing based on the maximum correlation value.

[0009] The invention described in claim 2 is characterized in that, in the wireless receiving device described in claim 1, the frame synchronization means comprises: delay adjustment means for performing delay adjustment of a predetermined number of symbols on the received signal and outputting the result; search section setting means for setting a search section for the frame synchronization timing for the received signal that has not been subjected to delay adjustment based on a frame format of the data frame, using as a reference the timing at which the burst detection means detects the preamble signal from the received signal; correlation value calculation means for calculating a correlation value between the received signal and the known signal stored in advance; maximum value search means for searching for a maximum value of the correlation value within the search section; and synchronization timing calculation means for calculating the frame synchronization timing based on the timing at which the search section ends, the timing at which the correlation value becomes maximum, and the delay adjustment amount.

[0010] The invention described in claim 3 is characterized in that, in the wireless receiving device described in claim 2, the search section setting means sets the search section to a section obtained by adding the number of symbols of the preamble signal and the number of symbols of the known signal, based on a burst detection pulse output by the burst detection means when the preamble signal is detected from the received signal.

[0011] The invention described in claim 4 is characterized in that, in the wireless receiving device described in claim 2 or 3, the synchronization timing calculation means calculates the delay adjustment amount and the difference in the number of symbols between the number of symbols from when the correlation value becomes maximum to when the search period ends, and sets the timing after the difference in the number of symbols from the timing when the search period ends as the frame synchronization timing.

[0012] The invention as recited in claim 5 is characterized in that, in the wireless receiving device as recited in claim 1, the preamble signal is an alternating signal.

[0013] The invention described in claim 6 is characterized in that, in the wireless receiving device described in claim 5, the burst detection means comprises: frequency shifting means for generating a frequency-shifted signal by shifting the frequency of the received signal so that the frequency of one of the spectra of the alternating signal matches the center frequency of the alternating signal; first signal extraction means for extracting the one of the spectra of the alternating signal from the frequency-shifted signal; power calculation means for calculating the signal power of the one of the spectra of the alternating signal extracted from the frequency-shifted signal and obtaining an average value thereof; and determination means for comparing the average value of the signal power of the one of the spectra of the alternating signal with a power threshold and determining that the alternating signal has been detected if the average value of the signal power of the one of the spectra of the alternating signal is greater than the power threshold.

[0014] The invention as set forth in claim 7 provides the wireless receiving device as set forth in claim 5, wherein the burst detection means includes first frequency shifting means for shifting the frequency of the received signal to generate a first frequency-shifted signal so that the frequency of one spectrum of the alternating signal becomes a first frequency in a positive direction with respect to a center frequency of the alternating signal, first signal extraction means for extracting one spectrum of the alternating signal from the first frequency-shifted signal, and a first power calculation means for calculating a first signal power, which is the signal power of one spectrum of the alternating signal extracted from a received signal, and calculating an average value of the first signal power; a second frequency shift means for shifting the frequency of the received signal so that the frequency of the one spectrum of the alternating signal becomes a first frequency in a negative direction with respect to a center frequency of the alternating signal to generate a second frequency-shifted signal; a second signal extraction means having the same signal extraction characteristic as the first signal extraction means and extracting one spectrum of the alternating signal from the second frequency-shifted signal; a second power calculation means for calculating a second signal power, which is the signal power of one spectrum of the alternating signal extracted from the second frequency-shifted signal, and calculating an average value of the second signal power; a power comparison means for comparing the average value of the first signal power with the average value of the second signal power and outputting the larger of the two; and a determination means for comparing the average value of the signal power outputted from the power comparison means with a power threshold and determining that the alternating signal has been detected when the average value of the signal power is greater than the power threshold.

[0015] An eighth aspect of the present invention is the wireless receiving device according to the sixth or seventh aspect, wherein the burst detection means includes normalization means for normalizing the amplitude of the received signal.

[0016] The invention recited in claim 9 is characterized in that, in the wireless receiving apparatus recited in claim 8, the burst detection means comprises third frequency shifting means for generating a third frequency-shifted signal by shifting a frequency of one spectrum of the alternating signal so that it does not fall within a range of signal extraction characteristics of the first signal extraction means, third signal extraction means having the same signal extraction characteristics as the first signal extraction means and extracting a noise signal from the third frequency-shifted signal, third power calculation means for calculating signal power of the noise signal and obtaining an average value thereof, and power threshold calculation means for calculating the power threshold based on the average value of the signal power of the noise signal.

[0017] The invention described in claim 10 is a frame synchronization timing generation method comprising the steps of receiving a data frame which has a preamble signal and a known signal added to the beginning of a data signal and transmitted in a burst, and outputting the received signal; detecting the arrival of the data frame by detecting the preamble signal from the received signal; and generating frame synchronization timing for synchronizing with the data frame from the received signal using the known signal, wherein the frame synchronization timing generation step calculates a correlation value between the received signal and the known signal stored in advance, searches for a maximum value of the correlation value, and calculates the frame synchronization timing based on the maximum correlation value. Effect of the Invention

[0018] According to the inventions described in claims 1 and 10, the correlation value between the received signal and a previously stored known signal is calculated, the maximum correlation value is searched for, and the frame synchronization timing is calculated based on the maximum correlation value, so that it is possible to improve the frame synchronization probability even if the CNR of the received signal decreases and the variation in the correlation value increases. Also, since it is not necessary to lengthen the known signal in response to a received signal with a low CNR as in the conventional technology, it is possible to suppress a decrease in the throughput of burst communication.

[0019] According to the invention recited in claim 2, a search section for frame synchronization timing is set for the received signal, and the frame synchronization timing is calculated based on the maximum correlation value between the received signal in the search section and a known signal, thereby making it possible to prevent the time required to calculate the frame synchronization timing from becoming long.

[0020] According to the invention described in claim 3, a section obtained by adding the number of symbols of the preamble signal and the number of symbols of the known signal is searched for based on a burst detection pulse indicating the detection of a burst signal. Since the frame synchronization timing is set as a search section, it is possible to prevent the time required for calculating the frame synchronization timing from becoming long.

[0021] According to the invention described in claim 4, the delay adjustment amount of the received signal and the difference in the number of symbols between the number of symbols from when the correlation value becomes maximum to the end of the search period are calculated, and the timing after the difference in the number of symbols from the timing when the search period ends is calculated as the frame synchronization timing, so that it is possible to prevent the time required to calculate the frame synchronization timing from becoming long.

[0022] According to the invention as recited in claim 5, since it becomes unnecessary to add a CW signal for burst detection to a data frame, it is possible to improve the throughput of the data frame.

[0023] According to the invention described in claim 6, a frequency-shifted signal is generated by shifting the frequency of the received signal so that the frequency of one of the spectra of the alternating signal coincides with the center frequency of the alternating signal, and one of the spectra of the alternating signal is extracted from the frequency-shifted signal, so that an alternating signal having a pair of spectra can be accurately detected from the received signal.

[0024] According to the invention described in claim 7, the frequency of the received signal is shifted to generate two types of frequency-shifted signals, and one of the alternating signal spectra is extracted by the signal extraction means for each of the two types of frequency-shifted signals, thereby narrowing the bandwidth of the signal extraction means. Therefore, it is possible to improve the noise resistance while maintaining the frequency offset resistance at the same level as in the past.

[0025] Furthermore, according to the invention described in claim 8, the amplitude of the received signal is normalized before the frequency of the received signal is shifted. This eliminates the need for level adjustment by AGC, which has been conventionally performed when the signal level of the received signal is low. This makes it possible to suppress detection delays and improve the throughput of burst communication.

[0026] In addition, according to the invention described in claim 9, a power threshold required to satisfy a desired SNR (Signal-to-Noise Ratio) is calculated from the noise power and used for burst detection. Therefore, even if the amplitude of the received signal is normalized when no burst signal is being received, the SNR remains low, making it possible to prevent erroneous detection. [Brief description of the drawings]

[0027] [Figure 1] 1 is a diagram showing a schematic configuration of a wireless communication system according to a first embodiment of the present invention. [Diagram 2] 2 is a functional block diagram showing a schematic configuration of a transmission unit of the wireless communication device shown in FIG. [Diagram 3] 2 is a functional block diagram showing a schematic configuration of a receiving system of the wireless communication device shown in FIG. [Figure 4] FIG. 1A shows the frame structure of a conventional data frame, FIG. 1B shows a schematic configuration of a conventional burst detection unit, and FIG. 1C is an explanatory diagram showing conventional burst detection. [Diagram 5] 4A shows the frame structure of a data frame according to the present embodiment, FIG. 4B shows a schematic configuration of the burst detection unit shown in FIG. 3, and FIG. 4C is an explanatory diagram showing burst detection using an alternating signal. [Figure 6] 4 is a block diagram showing a schematic configuration of a frame synchronization unit shown in FIG. 3. [Figure 7] 7 is a timing chart showing a calculation state of frame synchronization timing by the frame synchronization unit shown in FIG. 6. [Figure 8] FIG. 25 is a block diagram showing a simulation system for the conventional frame synchronization unit shown in FIG. 24. [Figure 9] 12 is a table showing setting values ​​used in a simulation system of the frame synchronization unit shown in FIGS. 8 and 11. [Figure 10] 9 is a graph showing the relationship between the correlation value and the CDF obtained in the simulation system shown in FIG. 8 . [Figure 11] FIG. 7 is a block diagram showing a simulation system for the frame synchronization unit shown in FIG. 6. [Figure 12] 7 is a graph showing the relationship between the correlation difference and the CDF obtained in the simulation system shown in FIG. 6. [Figure 13] 6 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 5(B). [Figure 14] 7 is a flowchart showing a calculation procedure of frame synchronization timing performed by a frame synchronizer shown in FIG. 6. [Figure 15] 10 is a functional block diagram showing a schematic configuration of a burst detection section according to a second embodiment of the present invention; FIG. [Figure 16] 16 is a diagram showing a frequency spectrum of an alternating signal whose frequency has been shifted by the frequency shift unit shown in FIG. 15. FIG. [Figure 17] 16 is a flowchart showing a procedure for burst detection by the burst detection unit shown in FIG. 15. [Figure 18] FIG. 11 is a functional block diagram showing a schematic configuration of a burst detection section according to an embodiment 3 of the present invention. [Figure 19] 19 is a diagram showing a frequency spectrum of an alternating signal whose frequency has been shifted by the frequency shift unit shown in FIG. 18. FIG. [Figure 20] 19 is a flowchart showing a procedure for burst detection by the burst detection unit shown in FIG. 18. [Figure 21] FIG. 11 is a functional block diagram showing a schematic configuration of a burst detection section according to a fourth embodiment of the present invention. [Figure 22] 22 is an explanatory diagram showing burst detection using an alternating signal normalized by the normalization unit shown in FIG. 21. [Figure 23] 22 is a flowchart showing a procedure for burst detection by the burst detection unit shown in FIG. 21. [Figure 24] FIG. 13 is a functional block diagram showing a schematic configuration of a burst detection section according to an embodiment 5 of the present invention. [Diagram 25] 25 is a diagram showing a frequency spectrum of an alternating signal whose frequency has been shifted by the frequency shift unit shown in FIG. 24. FIG. [Figure 26]25 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 24. [Figure 27] FIG. 1 is a block diagram showing a schematic configuration of a conventional frame synchronization unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention will be described below based on the embodiments shown in the drawings. Note that, in the following, only the characteristic configuration of the present invention will be described, and a description of the same mechanism as the conventional one for performing wireless communication will be omitted.

[0029] 1 is a diagram showing a schematic configuration of a wireless communication system 1 using a wireless communication device (wireless receiving device) 2 according to an embodiment of the present invention. A wireless communication device 2 and an antenna 3 are arranged in each of wireless communication transmitting and receiving stations constituting the wireless communication system 1. The wireless communication devices 2 are connected to each other by a wireless line 4 via the antenna 3. Note that a communication satellite or the like may be used as a relay station in the wireless line 4.

[0030] First, in this embodiment, a schematic configuration of a wireless communication device 2 corresponding to a wireless receiving device according to the present invention will be described.

[0031] The wireless communication device 2 includes an interface unit 5, a transmitter 6, a splitter 7, and a receiver 8 (see the lower part of FIG. 1).

[0032] Here, the wireless communication device 2 is a device that is equipped with a transmission mechanism and a reception mechanism and transmits and receives data. In the following description, the wireless communication device 2 when performing processing related to transmission using the transmission mechanism is referred to as the "transmitting side," and the wireless communication device 2 when performing processing related to reception using the reception mechanism is referred to as the "receiving side."

[0033] The interface unit 5 mainly includes a data circuit-terminating device 51 (including devices called data communication devices and data circuit devices). The interface unit 5 receives transmission data to be transmitted, and outputs the transmission data to the transmission unit 6 via the data circuit-terminating device 51.

[0034] The transmitter 6 receives the transmission data output from the interface 5, generates a data frame by combining a data signal obtained by mapping the transmission data with an alternating signal used to correct a clock error, and further superimposes a carrier signal of a predetermined frequency on the data frame to perform digital modulation. Note that the modulation method used in the wireless communication system 1 is not limited to a specific method, but for example, quadrature amplitude modulation (QAM) is used.

[0035] The transmitter 6 converts the digitally modulated data frame into an analog signal, converts the frequency of the signal into a high-frequency signal higher than a predetermined frequency, and outputs the signal as a transmission signal after amplifying it with a power amplifier. The transmission signal is guided from the transmitter 6 to the antenna 3 via the splitter 7, and is transmitted in bursts as radio waves from the antenna 3 via the wireless line 4 to the antenna 3 of the other wireless communication device 2 (in other words, the receiving side in this communication).

[0036] In addition, when a transmission signal is transmitted in bursts as radio waves from the antenna 3 of the other wireless communication device 2 (in other words, the transmitting side in this communication) to the antenna 3 of the wireless communication device 2 (in other words, the receiving side in this communication) via wireless line 4, the antenna 3 converts the received radio waves into an electrical signal (received signal) and outputs it.

[0037] The received signal output from the antenna 3 is guided to the receiving unit 8 via the branching filter 7. The receiving unit 8 receives the received signal, passes it through a channel filter that passes only signals in a predetermined frequency band, and converts it into a signal with a frequency lower than the high frequency. The receiving unit 8 further converts the frequency-converted received signal into a digital signal and outputs it.

[0038] The receiver 8 performs quadrature detection processing (demodulation) on the digital received signal to generate an in-phase component (Ich) baseband signal and a quadrature component (Qch) baseband signal, the phases of which are orthogonal to each other. In the following explanation, the in-phase component and the quadrature component will not be particularly distinguished from each other and will be explained as being common to both, except when it is necessary to focus on the in-phase component and the quadrature component separately, and in the drawings, the in-phase component signal and the quadrature component signal are represented by a single signal line.

[0039] The receiver 8 performs burst detection based on the demodulated baseband signal. When the arrival of a data frame is detected by this burst detection, the receiver 8 performs frequency offset correction, clock error correction, frame synchronization processing, phase correction, etc. on the received data frame. The receiver 8 then extracts a data signal from the data frame that has been subjected to various corrections and processing, performs demapping on the data signal to generate transmission data, and outputs it to the interface 5.

[0040] 2 is a functional block diagram showing a schematic configuration of the transmission unit 6. The transmission unit 6 includes a FIFO memory 61, a mapping unit 62, an alternating signal generation unit 63, a known signal generation unit 64, and a combining unit 65. The RF modulator 65 includes a transmission ROF 66 , a quadrature modulation unit 67 , a DAC (Digital Analog Converter) 68 , a mixer 69 , a local oscillator 610 , and a power amplifier 611 .

[0041] The FIFO memory 61 is a memory that temporarily stores the transmission data output from the interface unit 5 and outputs it to the mapping unit 62, and transfers the transmission data to the mapping unit 62 on a so-called first-in first-out basis.

[0042] The mapping unit 62 performs mapping processing on the binary data string of the transmission data so that it has a predetermined signal point arrangement, generates a data signal consisting of a symbol string, and outputs it to the combining unit 65. The alternating signal generating unit 63 generates an alternating signal (an alternating pattern of "1" and "0") used to correct clock errors, and outputs it to the combining unit 65. The alternating signal corresponds to a preamble signal of the present invention. The known signal generating unit 64 generates a signal of a known pattern used for frame synchronization, and outputs it to the combining unit 65.

[0043] The combining unit 65 combines the alternating signal input from the alternating signal generating unit 63 and the known signal input from the known signal generating unit 64 to the beginning of the data signal input from the mapping unit 62 to generate a data frame DF (see FIG. 5(A)), and outputs it to the transmitting ROF 66. The transmitting ROF 66 has a roll-off filter function, and performs band limiting processing on the data frame DF input from the combining unit 65, and outputs it to the orthogonal modulation unit 67.

[0044] The quadrature modulation unit 67 superimposes a carrier signal of a predetermined frequency on the data frame DF input from the transmission ROF 66, digitally modulates it, and outputs it to the DAC 68. Note that the modulation method used in the quadrature modulation unit 67 is not limited to a specific method, but for example, quadrature amplitude modulation is used.

[0045] The DAC 68 converts the data frame DF input from the quadrature modulation unit 67 into an analog transmission signal and outputs it to the mixer 69. The local oscillator 610 generates a local oscillation signal having a predetermined fixed frequency and outputs the generated local oscillation signal to the mixer 69. The mixer 69 mixes the local oscillation signal with the transmission signal input from the DAC 68 to convert it into a signal with a higher frequency than the predetermined frequency.

[0046] The power amplifier 611 amplifies the transmission signal frequency-converted by the mixer 69 and outputs it to the antenna 3. The antenna 3 transmits the transmission signal amplified by the power amplifier 611 as a radio wave to the antenna 3 of the other wireless communication device 2 (in other words, the receiving side in this communication). Although not shown, a splitter 7 is connected between the power amplifier 611 and the antenna 3.

[0047] As shown in Fig. 5(A), the transmitter 6 of this embodiment transmits a data frame DF consisting of an alternating signal, a known signal, and a data signal. The alternating signal is used not only for correcting clock errors but also for burst detection. In conventional burst communications, an unmodulated CW signal is added to the beginning of the alternating signal for burst detection, but in this embodiment, the alternating signal is used for burst detection, making the CW signal unnecessary, and thus improving throughput.

[0048] 3 is a functional block diagram showing a schematic configuration of the receiving unit 8. The receiving unit 8 includes a channel filter 81, a mixer 82, a local oscillator 83, a variable ATT (attenuator) 84, an ADC (Analog Digital Converter) 85, a quadrature detection unit 86, a burst detection unit 87, a timing control unit 88, an AFC (Automatic frequency control) 89, a receiving ROF 810, a symbol recovery unit 811, an APC (Automatic Phase Control) 812, a separation unit 813, a demapping unit 814, an AGC 815, a DAC 816, and a frame synchronization unit (frame synchronization means) 817.

[0049] The antenna 3 converts the received radio waves into an electric signal (received signal) and outputs it to the channel filter 81. The splitter 7 is connected between the antenna 3 and the channel filter 81. The channel filter 81 passes a predetermined frequency band of the received signal input from the antenna 3 and outputs it to the mixer 82. The local oscillator 83 generates a local oscillation signal having a predetermined fixed frequency and outputs the generated local oscillation signal to the mixer 82. The mixer 82 mixes the local oscillation signal with the received signal input from the channel filter 81 to convert it into a signal with a frequency lower than the predetermined frequency, and outputs it to the variable ATT 84.

[0050] The variable ATT 84 includes an attenuator, and adjusts the attenuation amount of the received signal output from the mixer 82 in response to an external signal to attenuate the signal and output the attenuated signal to the ADC 85. The attenuation amount in the variable ATT 84 changes based on a control signal of the AGC 815 supplied via the DAC 816.

[0051] The ADC 85 converts into a digital signal the received signal input from the variable ATT 84. The quadrature detection unit 86 performs quadrature detection processing on the received signal to generate an in-phase component (Ich) baseband signal and a quadrature component (Qch) baseband signal whose phases are orthogonal to each other.

[0052] The burst detection unit 87 performs burst detection from the baseband signal input from the quadrature detection unit 86. When the burst detection unit 87 detects the arrival of a data frame DF by burst detection, it outputs a burst detection pulse to the timing control unit 88 and the frame synchronization unit 817. The timing control unit 88, to which the burst detection pulse has been input, outputs an enable signal for causing each module to process the data frame DF, based on the frame synchronization timing calculated by the frame synchronization unit 817 and the burst detection pulse.

[0053] In response to an enable signal from the timing control unit 88, the AFC 89 performs frequency offset correction on the data frame DF of the baseband signal and outputs the result to the receive ROF 810. The receive ROF 810 has a roll-off filter function, and performs band limiting processing on the baseband signal input from the AFC 89 and outputs the result to the symbol recovery unit 811.

[0054] The symbol recovery unit 811 corrects the clock error using an alternating signal included in the data frame DF of the baseband signal input from the reception ROF 810 , and outputs the corrected clock error to the frame synchronization unit 817 .

[0055] The frame synchronization unit 817 performs delay adjustment of a predetermined number of symbols on the data frame DF of the baseband signal input from the symbol recovery unit 811, and outputs the result to the APC 812. In addition, the frame synchronization unit 817 uses the delay adjustment time to calculate frame synchronization timing and outputs the same to the timing control unit 88.

[0056] The APC 812 performs phase correction on the data frame DF of the baseband signal input from the frame synchronization unit 817 and outputs the corrected data to the separation unit 813 .

[0057] The separator 813 separates the data signal from the data frame DF and outputs the data signal to the demapping unit 814. The demapping unit 814 performs demapping processing (decoding processing) on ​​the signal (each of the in-phase component and the quadrature component) consisting of the symbol sequence data input from the separator 813, converts the symbol sequence data into transmission data of a binary data sequence, and outputs the transmission data to the interface unit 5.

[0058] Before describing the details of the burst detector 87 according to the present embodiment, Burst detection will now be explained. In the data frame DF used in conventional burst communication, as shown in Fig. 4(A), an unmodulated CW signal is added before an alternating signal as a preamble signal.

[0059] As shown in Fig. 4(B), in conventional burst detection circuit 200, LPF (Low-pass filter) 201 extracts a CW signal from the received signal output upon receiving a data frame and suppresses noise, power calculation section 202 calculates the signal power of the CW signal, and averaging section 203 obtains the average value of the signal power. As shown in Fig. 4(C), determination section 204 compares the average value of the signal power with a preset power threshold, and detects the arrival of a data frame when the average value of the signal power of the CW signal is greater than the power threshold (see, for example, Japanese Patent Application Laid-Open No. 2000-134274).

[0060] However, in conventional burst communications, the CW signal added for burst detection increases the amount of data, resulting in a decrease in throughput. Therefore, in this embodiment, the addition of a CW signal to the data frame DF is omitted, and burst detection is performed using an alternating signal.

[0061] 5A shows the frame format of the data frame DF according to this embodiment, in which only an alternating signal is added as a preamble signal. FIG. 5B is a functional block diagram showing a schematic configuration of a burst detector 87 according to this embodiment. The burst detector 87 includes an LPF 872, a power calculator 873, an averaging unit 874, and a determination unit 875.

[0062] The LPF 872 extracts an alternating signal from the received signal, suppresses noise, and outputs the signal to a power calculation unit 873. The power calculation unit 873 calculates the signal power of the received signal input from the LPF 872, and outputs the calculated signal power to an averaging unit 874. The averaging unit 874 obtains the average value of the signal power calculated by the power calculation unit 873, and outputs the average value to a determination unit 875.

[0063] The determination unit 875 compares the average value of the signal power input from the averaging unit 874 with a preset power threshold and outputs the detection result. When the detection result of the determination unit 875 determines that the average value of the signal power is greater than the power threshold as shown in Fig. 5(C), the burst detection unit 87 outputs a burst detection pulse to the timing control unit 88 and the frame synchronization unit 817. Note that the power threshold is a value that allows a desired SNR to be obtained, is preset, is stored in a memory (not shown), and is output to the determination unit 875.

[0064] 6 is a functional block diagram showing a schematic configuration of a frame synchronizer 817 according to this embodiment. The frame synchronizer 817 includes a delay adjuster (delay adjuster means) 8171, a search interval setting unit (search interval setting means) 8172, a correlation value calculator (correlation value calculator means) 8173, a maximum value searcher (maximum value searcher means) 8174, and a synchronization timing calculator (synchronization timing calculator means) 8175.

[0065] The delay adjustment unit 8171 performs delay adjustment of a predetermined number of symbols on the received signal input from the symbol recovery unit 811, and outputs the signal to the APC 812. The frame synchronization unit 817 uses the delay adjustment time generated by the delay adjustment unit 8171 to calculate frame synchronization timing.

[0066] The search interval setting unit 8172 sets a search interval for the frame synchronization timing for a received signal that has not been subjected to delay adjustment, based on the frame format of the data frame DF, using as a reference the timing at which the burst detection unit 87 detects a preamble signal (alternating signal in this embodiment) from the received signal. More specifically, The burst detection pulse output when a preamble signal is detected from the burst detection pulse generator is used as a reference, and a section obtained by adding the number of symbols of the preamble signal and the number of symbols of the known signal is set as a search section.

[0067] The correlation value calculation unit 8173 calculates a correlation value for each symbol between the received signal in the search section and a known signal stored in advance in a memory (not shown) or the like. The correlation value is calculated using the following formula 1. Note that in the following formula 1, the correlation between the received signal and the known signal is calculated as is, but the correlation may be found using the differential detection results of the received signal and the known signal. R(n): Correlation value M: Length of known signal x(n): Received signal p(n): known signal

[0068]

number

[0069] The maximum value search unit 8174 compares the correlation values ​​calculated in the search interval and searches for the maximum correlation value. When the CNR of the received signal is low, the variation in the correlation value between the received signal and the known signal increases, causing frame synchronization errors. For this reason, in the conventional technology, the known signal is made longer to ensure the frame synchronization probability.

[0070] On the other hand, the applicant has noticed that the relationship between the correlation value of correct frame synchronization timing and the correlation value of incorrect frame synchronization timing does not change even when the CNR of the received signal is low, and the correlation value of correct frame synchronization timing is often larger than the correlation value of incorrect frame synchronization timing. Therefore, in this embodiment, the correlation values ​​calculated in the search section are compared with each other to find the maximum correlation value.

[0071] The synchronization timing calculation unit 8175 calculates the frame synchronization timing based on the timing when the search interval ends, the timing when the correlation value becomes maximum, and the delay adjustment amount. More specifically, the delay adjustment amount and the difference in the number of symbols between the number of symbols from when the correlation value becomes maximum to the end of the search interval are calculated, and the timing after the difference in the number of symbols from the timing when the search interval ends is set as the frame synchronization timing. The synchronization timing calculation unit 8175 outputs the calculated frame synchronization timing to the timing control unit 88.

[0072] 7 shows an example of a timing chart when the frame synchronization timing is calculated by the above-mentioned frame synchronization unit 817. In the example shown in this figure, the number of symbols of the preamble signal is 500 symbols, the number of symbols of the known signal is 57 symbols, and the number of symbols of the data signal is 5000 symbols.

[0073] When the burst detector 87 detects a preamble signal from the received signal, it outputs a burst detection pulse. A detection delay occurs in the output of the burst detection pulse as shown in FIG.

[0074] The delay adjustment unit 8171 performs delay adjustment of the received signal input from the symbol recovery unit 811 by a delay adjustment amount β of a predetermined number of symbols (for example, 250 symbols), and outputs the signal to the APC 812 .

[0075] The search interval setting unit 8172 sets the 5th period of the preamble signal based on the burst detection pulse. A section of 557 symbols obtained by adding the 00 symbol and the 57 symbols of the known signal is set as the search section.

[0076] The correlation value calculation unit 8173 uses the above-mentioned formula 1 to calculate the correlation value for each symbol between the received signal in the search section and a pre-stored known signal.

[0077] The maximum value search unit 8174 compares the correlation values ​​calculated in the search interval and searches for the maximum correlation value.

[0078] The synchronization timing calculation unit 8175 calculates the difference in the number of symbols (β-α) between the delay adjustment amount β and the number of symbols α from when the correlation value becomes maximum to when the search interval ends, and sets the timing after the difference in the number of symbols from the timing when the search interval ends as the frame synchronization timing. For example, if the delay adjustment amount β is 250 symbols and the number of symbols α from when the correlation value becomes maximum to when the search interval ends is 10 symbols, the difference in the number of symbols (β-α) is 240 symbols, and the timing after 240 symbols from the timing when the search interval ends as the frame synchronization timing. By appropriately setting the delay adjustment amount β, the end timing of the known signal of the received signal after the delay adjustment coincides with the frame synchronization timing.

[0079] Here, the results of a simulation comparison between the erroneous frame synchronization probability of the conventional frame synchronization circuit 100 shown in FIG. 27 and the erroneous frame synchronization probability of the frame synchronization section 817 of this embodiment will be described.

[0080] Fig. 8 shows a simulation system 300 of the conventional frame synchronization circuit 100 shown in Fig. 27. The simulation system 300 includes a known signal generating section 301, a data signal generating section 302, a combining section 303, a noise adding section 304, a correlation value calculating section 305, a synchronous timing latch circuit 306, and an asynchronous timing latch circuit 307. Fig. 9 shows each setting value used in the simulation system 300.

[0081] The known signal generator 301 generates and outputs a known signal having a length of 57 symbols and a modulation method of pi / 2 shift BPSK. The data signal generator 302 generates and outputs a data signal having a length of 500 symbols and a modulation method of QPSK. The known signal generator 301 and the data signal generator 302 continue to output signals alternately.

[0082] The combining unit 303 combines the known signal input from the known signal generating unit 301 and the data signal input from the data signal generating unit 302 to generate a data frame. The noise adding unit 304 sets the CNR of the generated data frame. The correlation value calculating unit 305 calculates a correlation value for each symbol between the known signal generated by the known signal generating unit 301 and the data frame generated by the combining unit 303, and outputs the correlation value to the synchronous timing latch circuit 306 and the asynchronous timing latch circuit 307. For example, the above-mentioned formula 1 is used to calculate the correlation value.

[0083] The synchronous timing latch circuit 306 outputs the correlation value at the synchronous timing among the correlation values ​​input from the correlation value calculation unit 305. The asynchronous timing latch circuit 307 outputs the correlation value at a timing other than the synchronous timing among the correlation values ​​input from the correlation value calculation unit 305. In the graph shown in Fig. 10, the relationship between the correlation value output from the synchronous timing latch circuit 306 and the CDF (Cumulative Distribution Function) of the correlation value (frame synchronization leakage probability) is shown by a solid line, and the relationship between the correlation value output from the asynchronous timing latch circuit 307 and the CDF of the correlation value (frame mis-synchronization probability) is shown by a dashed line. The frame synchronization leakage probability indicates the probability that the correlation value at the correct frame synchronization timing is not synchronized, and the frame mis-synchronization probability indicates the probability that the correlation value at the incorrect frame synchronization timing is synchronized.

[0084] As can be seen from the graph shown in Fig. 10, if the threshold is set so that the frame synchronization leakage probability is reduced, the frame mis-synchronization probability increases. Conversely, if the threshold is set so that the frame mis-synchronization probability is reduced, the frame synchronization leakage probability increases. In other words, there is a trade-off between the frame synchronization leakage probability and the frame mis-synchronization probability. Therefore, in the conventional frame synchronization circuit 100, in order to achieve both the frame synchronization leakage probability and the frame mis-synchronization probability, the threshold is set to a value at which the two intersect. In the example shown in Fig. 10, the threshold is set to 0.355, and the frame synchronization leakage probability and the frame mis-synchronization probability are both approximately 0.8%.

[0085] 11 shows a simulation system 400 of the frame synchronization unit 817 of this embodiment. The simulation system 400 includes a known signal generation unit 401, a data signal generation unit 402, a combination unit 403, a noise addition unit 404, a correlation value calculation unit 405, a synchronous timing latch circuit 406, an asynchronous timing latch circuit 407, a delay adjustment unit 408, and a difference circuit 409.

[0086] The known signal generating section 401, the data signal generating section 402, the combining section 403, the noise adding section 404, the correlation value calculating section 405, the synchronous timing latch circuit 406, and the asynchronous timing latch circuit 407 of the simulation system 400 have the same configurations as the known signal generating section 301, the data signal generating section 302, the combining section 303, the noise adding section 304, the correlation value calculating section 305, the synchronous timing latch circuit 306, and the asynchronous timing latch circuit 307 of the conventional simulation system 300 described above, and therefore detailed explanations will be omitted.

[0087] The delay adjustment unit 408 of the simulation system 400 adjusts the delay of the correlation value output from the latch circuit for asynchronous timing 407 so that the correlation value output from the latch circuit for synchronous timing 406 and the most recent correlation value are output from the latch circuit for asynchronous timing 407, and so that the difference between the correlation value output from the latch circuit for synchronous timing 406 and the correlation value output from the latch circuit for asynchronous timing 407 can be calculated by the difference circuit 409.

[0088] 12 is a graph showing the relationship between the correlation value output from the synchronous timing latch circuit 406 and the correlation value output from the asynchronous timing latch circuit 407, and the CDF for the correlation value difference, when the simulation system 400 is operated based on the set values ​​shown in FIG. 9. In this embodiment, when the correlation value difference is greater than 0, frame synchronization is successful, and when it is equal to or less than 0, frame synchronization is unsuccessful. Therefore, the CDF when the correlation value difference becomes 0 is the frame erroneous synchronization probability. Note that the frame synchronization unit 817 of this embodiment calculates the timing at which the correlation value becomes maximum, so as long as burst detection is performed appropriately, no synchronization leak occurs. Therefore, the graph shown in FIG. 12 shows only the frame erroneous synchronization probability corresponding to the correlation value difference.

[0089] 12, the frame erroneous synchronization probability of this embodiment is 0.03%. In this way, by using the frame synchronization unit 817 according to this embodiment, it is possible to obtain a frame erroneous synchronization probability that is significantly smaller than the frame erroneous synchronization probability of 0.8% of the conventional simulation system 300 described above, and it is possible to improve the frame erroneous synchronization probability in burst communication at a low CNR.

[0090] Next, the burst detection process performed by the burst detector 87 in the above embodiment will be described with reference to the flowchart of FIG.

[0091] When the received signal of the data frame DF is input from the quadrature detection unit 86, the burst detection unit 87 extracts an alternating signal from the received signal by the LPF 872 and suppresses noise (step S 1).

[0092] The power calculation unit 873 of the burst detection unit 87 calculates the signal power of the alternating signal input from the LPF 872, and the averaging unit 874 calculates the average value of the signal power input from the power calculation unit 873 (step S2).

[0093] The judgment unit 875 of the burst detection unit 87 compares the average value of the signal power input from the averaging unit 874 with the power threshold value read from the memory and input, and if the average value of the signal power is greater than the power threshold value, it determines that an alternating signal has been detected and outputs a detection flag to the timing control unit 88 (step S3).

[0094] As described above, according to the wireless communication system 1 of the embodiment, it is not necessary to add a CW signal to the data frame DF, and therefore the throughput of burst communication is improved.

[0095] Next, the frame synchronization process performed by the frame synchronization unit 817 in the above embodiment will be described with reference to the flowchart of FIG.

[0096] The delay adjustment unit 8171 performs delay adjustment of a predetermined number of symbols on the received signal input from the symbol recovery unit 811, and outputs the result to the APC 812 (step S51).

[0097] When a burst signal is detected by the burst detection unit 87 and a burst detection pulse is input (YES in step S52), the search section setting unit 8172 sets a search section to be a section obtained by adding the number of symbols of the preamble signal and the number of symbols of the known signal, based on the input burst detection pulse (step S53).

[0098] The correlation value calculation unit 8173 calculates a correlation value between the received signal in the search section and the known signal for each symbol (step S54).

[0099] The maximum value search unit 8174 compares the correlation values ​​calculated in the search interval and searches for the maximum correlation value (step S55).

[0100] The synchronization timing calculation unit 8175 obtains the delay adjustment amount and the difference in the number of symbols between the number of symbols from when the correlation value becomes maximum to when the search interval ends, and calculates the timing after the difference in the number of symbols from the timing when the search interval ends as the frame synchronization timing. The synchronization timing calculation unit 8175 outputs the calculated frame synchronization timing to the timing control unit 88 (step S56).

[0101] As described above, according to the wireless communication system 1 of the embodiment, the correlation value between the received signal and the pre-stored known signal is calculated, the maximum correlation value is searched for, and the frame synchronization timing is calculated based on the maximum correlation value, so that it is possible to improve the frame synchronization probability even if the CNR of the received signal decreases and the variation in the correlation value increases. Also, since it is not necessary to lengthen the known signal in response to a received signal with a low CNR as in the conventional technology, it is possible to suppress a decrease in the throughput of burst communication.

[0102] According to the wireless communication system 1 of the embodiment, a search section for frame synchronization timing is set for a received signal, and the frame synchronization timing is calculated based on the maximum correlation value between the received signal in the search section and a known signal, thereby making it possible to prevent the time required to calculate the frame synchronization timing from becoming long.

[0103] According to the wireless communication system 1 of the embodiment, a search section is set to a section obtained by adding the number of symbols of the preamble signal and the number of symbols of the known signal based on a burst detection pulse indicating the detection of a burst signal, thereby making it possible to prevent the time required for calculating the frame synchronization timing from becoming long.

[0104] According to the wireless communication system 1 of the embodiment, the delay adjustment amount of the received signal and the difference in the number of symbols between the number of symbols from when the correlation value becomes maximum to the end of the search period are calculated, and the timing after the difference in the number of symbols from the timing when the search period ends is calculated as the frame synchronization timing, so that it is possible to prevent the time required to calculate the frame synchronization timing from becoming long.

[0105] According to the above embodiment, as long as burst detection is performed properly, frame synchronization leakage will not occur. Therefore, burst detection using alternating signals needs to be performed more accurately. In the following, other examples of burst detection using alternating signals will be described. Note that the burst detection described in the above embodiment is referred to as embodiment 1, and in the following, embodiments 2 to 5, which have different configurations and methods from embodiment 1, will be described.

[0106] (Embodiment 2) The burst detection unit 87 according to the second embodiment differs from the first embodiment in that, in order to accurately detect an alternating signal having a pair of spectra from a received signal, the burst detection unit 87 shifts the frequency of the received signal so that the frequency of one spectrum of the alternating signal coincides with the center frequency of the alternating signal, extracts one spectrum of the alternating signal from the frequency shifted signal, and performs burst detection using the signal power of the one spectrum of the alternating signal extracted from the frequency shifted signal. Note that, in the following, the same reference numerals are used for the same configuration as the wireless communication system 1 according to the first embodiment, and detailed description thereof will be omitted.

[0107] 15 is a functional block diagram showing a schematic configuration of a burst detection unit 87 according to embodiment 2. The burst detection unit 87 includes a frequency shift unit (frequency shift means) 876, an LPF (first signal extraction means) 872, a power calculation unit (power calculation means) 873, an averaging unit (power calculation means) 874, and a determination unit (determination means) 875.

[0108] 16(A) shows the spectrum of the received signal output from the quadrature detection unit 86. Since the leading portion of the received signal is an alternating signal, the spectrum of the received signal has a spectrum f1 of fsym / 2 (fsym: symbol frequency) in the positive direction relative to the center frequency fc of the alternating signal, and a spectrum f2 of -fsym / 2 in the negative direction.

[0109] The frequency shifter 876 shifts the frequency of the received signal by −fsym / 2 so that one spectrum of the alternating signal, for example the frequency of spectrum f1, matches the center frequency fc of the alternating signal, as shown in FIG. 16(B), to generate a frequency-shifted signal.

[0110] 16(C), extracts the spectrum f1 of the alternating signal from the frequency shifted signal, suppresses noise, and outputs the spectrum f1 to the power calculation unit 873. Note that, when the expected frequency offset of the received signal is ±Δf, the filter characteristic of the LPF 872 normally uses 2Δf, which is a bandwidth twice the frequency offset Δf.

[0111] The power calculation unit 873 calculates the signal power of the spectrum f1 of the alternating signal input from the LPF 872, and outputs the calculated signal power to the averaging unit 874. The averaging unit 874 obtains the average value of the signal power calculated by the power calculation unit 873, and outputs the average value to the determination unit 875.

[0112] The judgment unit 875 compares the average value of the signal power of the spectrum f1 of the alternating signal input from the averaging unit 874 with a preset power threshold, and judges that an alternating signal has been detected if the average value of the signal power is greater than the power threshold.

[0113] Next, the operation of the burst detection section 87 in the second embodiment will be described with reference to the flowchart in FIG.

[0114] When the received signal of the data frame DF is input from the quadrature detection unit 86, the burst detection unit 87 shifts the frequency of the received signal using the frequency shift unit 876 so that the frequency of one of the spectra of the alternating signal matches the center frequency fc of the alternating signal, thereby generating a frequency shifted signal (step S5).

[0115] The LPF 872 of the burst detection unit 87 extracts one spectrum of the alternating signal from the frequency shifted signal and suppresses noise (step S1).

[0116] The power calculation unit 873 of the burst detection unit 87 calculates the signal power of one spectrum of the alternating signal input from the LPF 872, and the averaging unit 874 calculates the average value of the signal power input from the power calculation unit 873 (step S2).

[0117] The judgment unit 875 of the burst detection unit 87 compares the average value of the signal power input from the averaging unit 874 with the power threshold value read from the memory and input, and if the average value of the signal power is greater than the power threshold value, it determines that an alternating signal has been detected and outputs a detection flag to the timing control unit 88 (step S3).

[0118] As described above, according to the wireless communication system 1 of the second embodiment, a frequency-shifted signal is generated by shifting the frequency of the received signal so that the frequency of one of the spectra of the alternating signal matches the center frequency fc of the alternating signal, and one of the spectra of the alternating signal is extracted from the frequency-shifted signal, so that it is possible to accurately detect an alternating signal having a pair of spectra from the received signal.

[0119] (Embodiment 3) Next, the burst detection unit 87 according to the third embodiment will be described. The burst detection unit 87 according to the third embodiment differs from the first and second embodiments in that it shifts the frequency of the received signal to generate two types of frequency-shifted signals, extracts alternating signals from each of the two types of frequency-shifted signals using an LPF, and performs burst detection by comparing the one of the two types of extracted alternating signals with the greater signal power with a power threshold. Note that, in the following, the same components as those of the burst detection unit 87 according to the first and second embodiments will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0120] In the burst detector 87 of the first embodiment, the received signal is input to an LPF to suppress noise as a measure against degradation of burst detection accuracy when the CNR of the received signal is low. In this case, the narrower the bandwidth of the LPF, the higher the noise resistance becomes, but on the other hand, narrowing the bandwidth of the LPF reduces the allowable frequency offset. Therefore, in the burst detection of the third embodiment, the frequency of the received signal is shifted to generate two types of frequency-shifted signals, and an alternating signal is extracted for each of the two types of frequency-shifted signals using an LPF with a narrower bandwidth, thereby improving noise resistance while maintaining the frequency offset resistance at the same level as in the second embodiment.

[0121] 18 is a functional block diagram showing a schematic configuration of a burst detection unit 87 according to the third embodiment. The burst detection unit 87 includes a first frequency shift unit (first frequency shift means) 87. 6A, an LPF (first signal extraction means) 872A, a power calculation unit (first power calculation means) 873A, an averaging unit (first power calculation means) 874A, a second frequency shift unit (second frequency shift means) 876B, an LPF (second signal extraction means) 872B, a power calculation unit (second power calculation means) 873B, an averaging unit (second power calculation means) 874B, a power comparison unit (comparison means) 8711, and a judgment unit (judgment means) 875.

[0122] 19(A) shows the spectrum of the received signal output from the quadrature detection unit 86. Since the leading portion of the received signal is an alternating signal, the spectrum of the received signal has a spectrum f1 of fsym / 2 (fsym: symbol frequency) in the positive direction relative to the center frequency fc of the alternating signal, and a spectrum f2 of -fsym / 2 in the negative direction.

[0123] As shown in Fig. 19(B), the first frequency shifter 876A shifts the frequency of the received signal so that the frequency of one spectrum (e.g., spectrum f1) of the alternating signal becomes Δf / 2 (first frequency) in the positive direction with respect to the center frequency fc of the alternating signal, thereby generating a first frequency-shifted signal. That is, the first frequency shifter 876A shifts the received signal by -fsym / 2+Δf / 2. Δf is an expected frequency offset and is also the bandwidth of LPF 872A and LPF 872B.

[0124] Similarly, the second frequency shifter 876B shifts the frequency of the received signal so that the frequency of one spectrum (for example, spectrum f1) of the alternating signal becomes Δf / 2 (first frequency) in the negative direction with respect to the center frequency fc of the alternating signal, as shown in Fig. 19(D) to generate a second frequency-shifted signal. That is, the second frequency shifter 876B shifts the received signal by -fsym / 2-Δf / 2.

[0125] 19(C), the LPF 872A has a filter characteristic (signal extraction characteristic) indicated by a dashed line in the figure, extracts an alternating signal spectrum f1 from the first frequency shift signal, suppresses noise, and outputs the spectrum to the power calculation unit 873A. When the expected frequency offset of the received signal is ±Δf, the filter characteristic of the LPF 872A normally uses 2Δf, which is a bandwidth twice the frequency offset Δf, but in the third embodiment, Δf, which is half of 2Δf, is used.

[0126] 19(E), the LPF 872B has a filter characteristic (signal extraction characteristic) indicated by a dashed line in the figure, extracts the spectrum f1 of the alternating signal from the second frequency shift signal, suppresses noise, and outputs the spectrum f1 to the power calculation unit 873B. The filter characteristic of the LPF 872B is the same as that of the LPF 872A, and the bandwidth is Δf.

[0127] In this manner, in the third embodiment, the frequency of the received signal is shifted to generate a first frequency-shifted signal and a second frequency-shifted signal, and one of the alternating signal spectra is extracted by the LPF for each of these two types of frequency-shifted signals, thereby making it possible to reduce the bandwidth of the LPF to half that of the conventional embodiment (second embodiment).

[0128] The power calculation unit 873A calculates a first signal power, which is the signal power of the first frequency shifted signal input from the LPF 872A, and outputs the calculated first signal power to the averaging unit 874A. The averaging unit 874A obtains an average value of the first signal power calculated by the power calculation unit 873A, and outputs the average value to the power comparison unit 8711.

[0129] Similarly to the above, the power calculation unit 873B calculates the second signal power, which is the signal power of the second frequency shifted signal input from the LPF 872B, and outputs the calculated second signal power to the averaging unit 874B. The averaging unit 874B obtains an average value of the second signal power calculated by the power calculation unit 873B, and outputs the average value to the power comparison unit 8711.

[0130] Power comparison unit 8711 compares the average value of the first signal power input from averaging unit 874A with the average value of the second signal power input from averaging unit 874B, and outputs the larger one to determination unit 875. That is, when the frequency offset of the received signal is in the negative direction, the average value of the first signal power is greater than the average value of the second signal power. Also, when the frequency offset of the received signal is in the positive direction, the average value of the second signal power is greater than the average value of the first signal power.

[0131] The judgment unit 875 compares the average value of the signal power input from the power comparison unit 8711 with a preset power threshold, and judges that an alternating signal has been detected when the average value of the signal power is equal to or greater than the power threshold, as shown in Figure 5 (A).

[0132] Next, the operation of the burst detector 87 in the third embodiment will be described with reference to the flowchart of FIG.

[0133] The first frequency shifter 876A generates a first frequency-shifted signal by shifting the frequency of the received signal by -fsym / 2+Δf / 2. Similarly, the second frequency shifter 876B generates a second frequency-shifted signal by shifting the frequency of the received signal by -fsym / 2-Δf / 2 (step S6).

[0134] The LPF 872A of the burst detection unit 87 extracts one spectrum f1 of the alternating signal from the first frequency shifted signal to suppress noise, and the LPF 872B extracts one spectrum f1 of the alternating signal from the second frequency shifted signal to suppress noise (step S1).

[0135] The power calculation unit 873A of the burst detection unit 87 calculates a first signal power which is the signal power of the first frequency shifted signal input from the LPF 872A, and the averaging unit 874A calculates the average value of the first signal power input from the power calculation unit 873A. Similarly, the power calculation unit 873B calculates a second signal power which is the signal power of the second frequency shifted signal input from the LPF 872B, and the averaging unit 874B calculates the average value of the second signal power input from the power calculation unit 873B (step S2).

[0136] The power comparison unit 8711 compares the average value of the first signal power input from the averaging unit 874A with the average value of the second signal power input from the averaging unit 874B, and outputs the larger one to the determination unit 875 (step S7).

[0137] The judgment unit 875 compares the average value of the signal power input from the power comparison unit 8711 with the power threshold value read from the memory and input, and if the average value of the signal power is greater than the power threshold value, it judges that an alternating signal has been detected and outputs a detection flag to the timing control unit 88 (step S3).

[0138] As described above, the burst detector 87 according to the third embodiment shifts the frequency of the received signal to generate the first and second frequency-shifted signals, and extracts one of the spectra of the alternating signals for each of the two types of frequency-shifted signals using an LPF, thereby making it possible to reduce the bandwidth of the LPF to half that of the conventional one. Therefore, it is possible to improve the noise resistance while maintaining the frequency offset resistance equivalent to that of the second embodiment. Also, as in the first embodiment, it is no longer necessary to add a CW signal to the data frame DF, thereby improving the throughput of burst communication.

[0139] (Embodiment 4) Next, the burst detector 87 according to the fourth embodiment will be described. The burst detector 87 differs from that of the third embodiment in that it normalizes the amplitude of the received signal before detecting the alternating signal. In the following description, the same components as those of the burst detector 87 of the third embodiment are denoted by the same reference numerals and will not be described in detail.

[0140] In conventional burst detection, when the signal power of the received signal is lower than the rated power, the signal power of the received signal is amplified by AGC before burst detection is performed. Therefore, when the signal power of the received signal is lower than the rated power, as shown in Fig. 5(C), it takes time for the signal power to exceed the power threshold, causing a delay in burst detection and reducing throughput. In the fourth embodiment, the amplitude of the received signal is normalized to suppress the delay in burst detection.

[0141] 21 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of a wireless communication system 1 according to embodiment 4. In the burst detection unit 87, a normalization unit (normalization means) 871 is connected before a first frequency shift unit 876A and a second frequency shift unit 876B.

[0142] As shown in Fig. 22, the normalization unit 871 normalizes the amplitude of the signal power of the received signal to 1, and outputs the amplitude-normalized received signal to the first frequency shift unit 876A and the second frequency shift unit 876B. As shown in the flowchart of Fig. 23, when the received signal of the data frame DF is input from the quadrature detection unit 86, the burst detection unit 87 normalizes the amplitude of the received signal by the normalization unit 871 (step S8), and then generates the first and second frequency shift signals by the first frequency shift unit 876A and the second frequency shift unit 876B (step S6). After the first frequency shift unit 876A and the second frequency shift unit 876B, detection of an alternating signal is performed based on the received signal whose amplitude has been normalized.

[0143] As described above, according to the burst detection unit 87 of the fourth embodiment, the amplitude of the received signal is normalized, so that an alternating signal exceeding a power threshold can be detected without waiting for adjustment of the received level by AGC. This makes it possible to suppress the detection delay that occurs while waiting for adjustment of the level of the received signal, and improve the throughput of burst communication.

[0144] The normalization of the amplitude of the received signal can also be applied to the first and second embodiments. When applied to the first embodiment, in the burst detection unit 87 shown in FIG. 5(B), a normalization unit 871 is connected before the LPF 872. Also, in the flowchart shown in FIG. 13, the amplitude of the received signal is normalized (step S8) before the alternating signal is generated (step S1). Similarly, when applied to the second embodiment, in the burst detection unit 87 shown in FIG. 15, a normalization unit 871 is connected before the frequency shift unit 876. Also, in the flowchart shown in FIG. 17, the amplitude of the received signal is normalized (step S8) before the frequency shift (step S6). This makes it possible to suppress detection delays caused by level adjustment of the received signal in the first and second embodiments as well.

[0145] (Embodiment 5) Next, the burst detection unit 87 according to the fifth embodiment will be described. The burst detection unit 87 according to the fifth embodiment differs from the fourth embodiment in that it calculates and uses a power threshold value from noise power when performing burst detection from a received signal whose amplitude has been normalized. Note that, in the following, the same components as those in the burst detection unit 87 according to the fourth embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0146] In the burst detection unit 87 of the fourth embodiment, when no burst signal is received, the amplitude of the received signal is normalized, which may cause erroneous detection. Therefore, in the burst detection of the fifth embodiment, the power threshold required to satisfy the desired SNR is calculated from the noise power and the burst is detected. This makes it possible to prevent false detection because the SNR remains low even if the amplitude of the received signal is normalized when no burst signal is received.

[0147] 24 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the fifth embodiment. The burst detection unit 87 includes a normalization unit (normalization means) 871, a first frequency shift unit (first frequency shift means) 876A, an LPF (first signal extraction means) 872A, a power calculation unit (first power calculation means) 873A, an averaging unit (first power calculation means) 874A, a second frequency shift unit (second frequency shift means) 876B, an LPF (second signal extraction means) 872B, and a power calculation unit (second power calculation means). The power converter includes a first power calculating unit (second power calculating means) 873B, an averaging unit (second power calculating means) 874B, a power comparing unit (comparison means) 8711, a third frequency shift unit (third frequency shifting means) 876C, an LPF (third signal extracting means) 872C, a power calculating unit (third power calculating means) 873C, an averaging unit (third power calculating means) 874C, a power threshold calculating unit (power threshold calculating means) 8710, and a determining unit (determining means) 875.

[0148] As in the fourth embodiment, the normalization unit 871 normalizes the amplitude of the signal power of the received signal to 1, as shown in FIG.

[0149] Fig. 25(A) shows the spectrum of the received signal output from the quadrature detection unit 86. As shown in Fig. 25(B), the first frequency shift unit 876A shifts the frequency of the received signal so that the frequency of one spectrum (e.g., spectrum f1) of the alternating signal becomes Δf / 2 in the positive direction with respect to the center frequency fc of the alternating signal, thereby generating a first frequency-shifted signal. Similarly, as shown in Fig. 25(D), the second frequency shift unit 876B shifts the frequency of the received signal so that the frequency of one spectrum f1 of the alternating signal becomes Δf / 2 in the negative direction with respect to the center frequency fc of the alternating signal, thereby generating a second frequency-shifted signal.

[0150] 25(C), the LPF 872A has a filter characteristic (signal extraction characteristic) indicated by a dashed line in the figure, extracts an alternating signal spectrum f1 from the first frequency shift signal, suppresses noise, and outputs the spectrum to the power calculation unit 873A. When the expected frequency offset of the received signal is ±Δf, the filter characteristic of the LPF 872A normally uses 2Δf, which is a bandwidth twice the frequency offset Δf, but in the third embodiment, Δf, which is half of 2Δf, is used.

[0151] 25(E), the LPF 872B has a filter characteristic (signal extraction characteristic) indicated by the dashed line in the figure, extracts the spectrum f1 of the alternating signal from the second frequency shift signal, suppresses noise, and outputs the spectrum f1 to the power calculation unit 873B. The filter characteristic of the LPF 872B is the same as that of the LPF 872A, and the bandwidth is Δf.

[0152] The power calculation unit 873A calculates a first signal power, which is the signal power of the first frequency shifted signal input from the LPF 872A, and outputs the calculated first signal power to the averaging unit 874A. The averaging unit 874A obtains an average value of the first signal power calculated by the power calculation unit 873A, and outputs the average value to the power comparison unit 8711.

[0153] Similarly to the above, the power calculation unit 873B calculates the second signal power, which is the signal power of the second frequency shifted signal input from the LPF 872B, and outputs the calculated second signal power to the averaging unit 874B. The averaging unit 874B obtains an average value of the second signal power calculated by the power calculation unit 873B, and outputs the average value to the power comparison unit 8711.

[0154] The power comparison unit 8711 compares the average value of the first signal power input from the averaging unit 874A with the average value of the second signal power input from the averaging unit 874B, and outputs the larger one as the determination unit. Output to 875.

[0155] As shown in Fig. 25(F), the third frequency shifter 876C generates a third frequency-shifted signal by shifting the amplitude-normalized received signal to a frequency that does not fall within the bandwidth Δf of the LPF 877, for example, -fsym / 4 (fsym: symbol frequency). As shown by the dashed line in Fig. 25(G), the LPF 872C has the same filter characteristics as the LPFs 872A and 872B, and extracts a noise signal from the third frequency-shifted signal.

[0156] The power calculation unit 873C calculates the signal power of the noise signal input from the LPF 872C, and the averaging unit 874C calculates the average value of the signal power input from the power calculation unit 873C (hereinafter also referred to as noise power).

[0157] The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 874C, and outputs the power threshold to the determination unit 875. Here, the SNR is calculated by the following formula (1). Therefore, as shown in the following formula (2), a power threshold required to obtain the SNR threshold is calculated by multiplying the noise power by a target SNR (hereinafter, referred to as the SNR threshold). SNR = signal power / noise power (1) Power threshold = SNR threshold × noise power (2)

[0158] The judgment unit 875 compares the average value of the signal power input from the power comparison unit 8711 with the power threshold input from the power threshold calculation unit 8710, and if the average value of the signal power is greater than or equal to the power threshold, judges that one of the spectra f1 of the alternating signal has been detected, and outputs a detection flag to the timing control unit 88.

[0159] Next, the operation of the burst detection section 87 in the above-mentioned fifth embodiment will be described with reference to the flowchart in FIG.

[0160] In the fifth embodiment, steps S8, S6, S1, S2, S7, and S3 are performed in the same manner as in the fourth embodiment, while the third frequency shifter 876C of the burst detector 87 shifts the frequency of the amplitude-normalized received signal to a position that does not fall within the bandwidth Δf of the LPF 872C to generate a third frequency-shifted signal (step S9). The LPF 872C extracts a noise signal from the third frequency-shifted signal (step S10).

[0161] The power calculation unit 873C calculates the signal power of the noise signal input from the LPF 872C, and the averaging unit 874C calculates the average value (noise power) of the signal power input from the power calculation unit 873C (step S11).

[0162] The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 874C and a desired SNR threshold, and outputs the power threshold to the determination unit 875 (step S12).

[0163] The judgment unit 875 compares the average value of the signal power input from the power comparison unit 8711 with the power threshold input from the power threshold calculation unit 8710, and determines that an alternating signal has been detected if the average value of the signal power is greater than or equal to the power threshold, and outputs a detection flag to the timing control unit 88 (step S3).

[0164] As described above, according to the wireless communication system 1 of the fifth embodiment, the power threshold required to satisfy the desired SNR is calculated from the noise power and used for burst detection. This makes it possible to prevent erroneous detection because the SNR remains low even if the amplitude of the received signal is normalized when no burst signal is received.

[0165] The method of calculating a power threshold from a noise signal and detecting a burst can also be applied to the first and second embodiments. When applied to the first embodiment, in the burst detection unit 87 shown in FIG. 5(A), a normalization unit 871 is connected before the LPF 872, a third frequency shift unit 876C, an LPF 872C, a power calculation unit 873C, an averaging unit 874C, and a power threshold calculation unit 8710 are connected to the normalization unit 871, and the power threshold calculated by the power threshold calculation unit 8710 is output to the determination unit 875. 15, a normalization unit 871 is connected before the frequency shift unit 876, a third frequency shift unit 876C, an LPF 872C, a power calculation unit 873C, an averaging unit 874C, and a power threshold calculation unit 8710 are connected to the normalization unit 871, and the power threshold calculated by the power threshold calculation unit 8710 is output to a determination unit 875. According to this, in the first and second embodiments as well, it is possible to suppress false detection that occurs when the amplitude of the received signal is normalized.

[0166] Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes and the like within the scope of the gist of the present invention, they are included in the present invention. [Explanation of symbols]

[0167] 1. Wireless communication systems 2. Wireless communication devices 6. Transmitter 8 Receiving unit (receiving means) 87 Burst detection unit (burst detection means) 871 Normalization unit (normalization means) 872, 872A LPF (first signal extraction means) 872B LPF (second signal extraction means) 872C LPF (third signal extraction means) 873 Power calculation unit (power calculation means) 873A Power Calculation Unit (First Power Calculation Means) 873B power calculation unit (second power calculation means) 873C Power calculation unit (third power calculation means) 874, 874A, 874B, 874C Averaging section 875 Judgment unit (judgment means) 846, 876A First frequency shift unit (first frequency shift means) 876B Second frequency shift unit (second frequency shift means) 876C Third frequency shift unit (third frequency shift means) 8710 Power threshold calculation unit (power threshold calculation means) 8711 Power comparison section (power comparison means) 817 Frame synchronization unit (frame synchronization means) 8171 Delay adjustment unit (delay adjustment means) 8172 Search section setting unit (search section setting means) 8173 Correlation value calculation unit (correlation value calculation means) 8174 Maximum value search unit (maximum value search means) 8175 Synchronization timing calculation unit (synchronization timing calculation means) DF Data Frame

Claims

1. a receiving means for receiving a data frame which is burst-transmitted with a preamble signal and a known signal added to the beginning of the data signal, and outputting a received signal; a burst detection means for detecting the arrival of the data frame by detecting the preamble signal from the received signal; a frame synchronization means for generating a frame synchronization timing for synchronizing with the data frame from the received signal by using the known signal, The frame synchronization means Calculating a correlation value between the received signal and the known signal stored in advance; Searching for a maximum value of the correlation value; calculating the frame synchronization timing based on the maximum correlation value; A radio receiving device comprising:

2. The frame synchronization means a delay adjustment means for performing delay adjustment of a predetermined number of symbols on the received signal and outputting the result; a search interval setting means for setting a search interval of the frame synchronization timing for the received signal that has not been subjected to delay adjustment based on a frame format of the data frame, using as a reference the timing at which the burst detection means detects the preamble signal from the received signal; a correlation value calculation means for calculating a correlation value between the received signal and the known signal stored in advance; a maximum value search means for searching for a maximum value of the correlation value within the search interval; a synchronization timing calculation means for calculating the frame synchronization timing based on a timing at which the search section ends, a timing at which the correlation value becomes maximum, and the delay adjustment amount; 2. The wireless receiving device according to claim 1, further comprising:

3. the search interval setting means sets, as the search interval, an interval obtained by adding the number of symbols of the preamble signal and the number of symbols of the known signal, based on a burst detection pulse output by the burst detection means when the preamble signal is detected from the received signal.

3. The wireless receiving device according to claim 2.

4. the synchronization timing calculation means calculates a difference in the number of symbols between the delay adjustment amount and the number of symbols from when the correlation value becomes maximum to when the search section ends, and determines the timing after the difference in the number of symbols from the timing when the search section ends as the frame synchronization timing.

4. The radio receiving device according to claim 2, wherein the first and second inputs are connected to the first and second inputs.

5. The preamble signal is an alternating signal.

2. The wireless receiving device according to claim 1,

6. The burst detection means includes: a frequency shifting means for shifting the frequency of the received signal so that the frequency of one spectrum of the alternating signal coincides with the center frequency of the alternating signal to generate a frequency-shifted signal; a first signal extraction means for extracting one spectrum of the alternating signal from the frequency shifted signal; a power calculation means for calculating a signal power of one spectrum of the alternating signal extracted from the frequency shift signal and calculating an average value thereof; a determination means for comparing an average value of the signal power of one spectrum of the alternating signal with a power threshold, and determining that the alternating signal has been detected when the average value of the signal power of one spectrum of the alternating signal is greater than the power threshold; 6. The wireless receiving device according to claim 5, further comprising:

7. The burst detection means includes: a first frequency shifting means for shifting a frequency of the received signal so that a frequency of one spectrum of the alternating signal becomes a first frequency in a positive direction with respect to a center frequency of the alternating signal, thereby generating a first frequency shifted signal; a first signal extraction means for extracting one spectrum of the alternating signal from the first frequency shift signal; a first power calculation means for calculating a first signal power, which is a signal power of one spectrum of the alternating signal extracted from the first frequency shift signal, and calculating an average value thereof; a second frequency shifting means for shifting the frequency of the received signal so that a frequency of one spectrum of the alternating signal becomes a first frequency in a negative direction with respect to a center frequency of the alternating signal, thereby generating a second frequency-shifted signal; a second signal extraction means having the same signal extraction characteristics as the first signal extraction means and extracting one spectrum of the alternating signal from the second frequency shift signal; a second power calculation means for calculating a second signal power, which is a signal power of one spectrum of the alternating signal extracted from the second frequency shift signal, and calculating an average value thereof; power comparison means for comparing the average value of the first signal power with the average value of the second signal power and outputting the larger of the two; a determination means for comparing an average value of the signal power output from the power comparison means with a power threshold, and determining that the alternating signal has been detected when the average value of the signal power is greater than the power threshold; 6. The wireless receiving device according to claim 5, further comprising:

8. the burst detection means includes a normalization means for normalizing the amplitude of the received signal; 8. The radio receiving device according to claim 6, wherein the first and second inputs are connected to the first and second inputs.

9. The burst detection means includes: a third frequency shifting means for shifting the frequency of the received signal so that the frequency of one spectrum of the alternating signal does not fall within a range of the signal extraction characteristic of the first signal extracting means, thereby generating a third frequency shifted signal; a third signal extraction means having the same signal extraction characteristics as the first signal extraction means and extracting a noise signal from the third frequency shifted signal; a third power calculation means for calculating the signal power of the noise signal and obtaining an average value thereof; a power threshold calculation means for calculating the power threshold based on an average signal power of the noise signal; 9. The wireless receiving device according to claim 8, further comprising:

10. receiving a data frame in which a preamble signal and a known signal are added to the beginning of a data signal and transmitted in a burst manner, and outputting the received signal; detecting the arrival of the data frame by detecting the preamble signal from the received signal; generating frame synchronization timing for synchronizing with the data frame from the received signal using the known signal; The step of generating frame synchronization timing includes: calculating a correlation value between the received signal and the known signal stored in advance, searching for a maximum value of the correlation value, and calculating the frame synchronization timing based on the maximum value of the correlation value; A frame synchronization timing generation method comprising:

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