Radio receiving device and burst detection method

Abstract

To provide a radio reception device and a burst detection method, capable of improving a through-put of a burst communication.SOLUTION: In a reception system of a radio communication device, a burst detection part 87 comprises: a first frequency shift part that shifts a frequency of a reception signal so that the frequency of a spectrum of an alternate signal having a pair of spectrums becomes a first frequency of a positive direction against a center frequency of the alternate signal; a power calculation part that calculates a first signal power as a power of the alternate signal of the first frequency shift signal; a second frequency shift part that shifts the frequency of the reception signal so that the frequency of one spectrum of the alternate signal becomes a first frequency of a negative direction against the center frequency of the alternate signal; a power calculation part that calculates a second signal power as a signal power of one spectrum of the alternate signal of the second frequency shift signal; and a determination part that determines that the alternate signal is detected in the case where the mean value of the signal power output from a power comparison part comparing both mean value of the first and second signal power is larger than the power threshold value.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a wireless receiving apparatus and a burst detection method for detecting data frames transmitted in bursts. [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 that a wireless receiving device does not know when it will receive the signal. Therefore, a wireless receiving device that performs burst communication performs burst detection to detect a signal transmitted in bursts (for example, see Patent Document 1).

[0003] As shown in Fig. 20(A), a data frame used in burst communication is composed of a data signal and a preamble signal added to the beginning of the data signal. The preamble signal contains an unmodulated CW signal used for burst detection and an alternating signal (an alternating pattern of "1" and "0") used for clock error correction.

[0004] As shown in Fig. 20(B), burst detection involves an LPF (Low-pass filter) 100 extracting a CW signal from the received signal output upon receiving a data frame and suppressing noise, a power calculation unit 101 calculating the signal power of the CW signal, and an averaging unit 102 calculating the average value of the signal power. As shown in Fig. 20(C), a determination unit 103 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-134274 A Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, in burst communication, it is common to add a CW signal and an alternating signal to the beginning of a data signal. However, adding a CW signal and an alternating signal to the data signal that should actually be transmitted increases the amount of data, resulting in 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 burst detection method capable of improving the throughput of burst communication. [Means for solving the problem]

[0008] In order to solve the above problem, the invention described in claim 1 comprises a receiving means for receiving a data frame transmitted in a burst with an alternating signal added to the beginning of a data signal, and outputting a received signal, and a burst detection means for detecting the arrival of the data frame by detecting the alternating signal from the received signal, the burst detection means including: a first frequency shifting means for generating a first frequency-shifted signal by shifting the frequency of the received signal so that the frequency of one spectrum of the alternating signal having a pair of spectra becomes a first frequency in a positive direction with respect to a center frequency of the alternating signal; a first signal extraction means for extracting one spectrum of the alternating signal from the first frequency-shifted signal; a first power calculation means for calculating a first signal power, which is the signal power of the one spectrum of the alternating signal extracted from the first frequency-shifted signal, and calculating an average value of the first signal power; a second frequency shift means for generating a second frequency-shifted signal by shifting the frequency of the received signal so that the frequency of a spectrum of the received signal becomes a first frequency in the negative direction with respect to the center frequency of the alternating 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-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 obtaining 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 output from the power comparison means with a power threshold and determining that the alternating signal has been detected if the average value of the signal power is greater than the power threshold.

[0009] The invention described in claim 2 is characterized in that, in the wireless receiving device described in claim 1, the burst detection means includes normalization means for normalizing the amplitude of the received signal before shifting the frequency of the received signal.

[0010] The invention recited in claim 3 is characterized in that, in the wireless receiving apparatus recited in claim 2, the burst detection means comprises third frequency shifting means for generating a third frequency-shifted signal by shifting the 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.

[0011] The invention described in claim 4 is a burst detection method used in a wireless receiving device that receives data frames transmitted in bursts, the method including the steps of receiving a data frame that has an alternating signal added to the beginning of the data signal and transmitted in bursts, and outputting a received signal, shifting the frequency of the received signal so that the frequency of one spectrum of the alternating signal having a pair of spectra becomes a first frequency in a positive direction with respect to a center frequency of the alternating signal to generate a first frequency-shifted signal, extracting one spectrum of the alternating signal from the first frequency-shifted signal, calculating a first signal power that is the signal power of the one spectrum of the alternating signal extracted from the first frequency-shifted signal and finding an average value of the first signal power, and calculating a first frequency shifted signal so that the frequency of the one spectrum of the alternating signal becomes a first frequency in a negative direction with respect to the center frequency of the alternating signal. a step of extracting one spectrum of the alternating signal from the second frequency-shifted signal, the step having the same signal extraction characteristics as the step of extracting one spectrum of the alternating signal from the first frequency-shifted signal; a step of 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 obtaining an average value thereof; a step of 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 step of comparing the average value of the larger signal power with a power threshold and determining that the alternating signal has been detected if the average value of the larger signal power is greater than the power threshold, thereby detecting the arrival of the data frame. Effect of the Invention

[0012] According to the inventions of claims 1 and 4, since it is not necessary to add a CW signal for burst detection to a data frame, it is possible to improve the throughput of the data frame.

[0013] According to the inventions of claims 1 and 4, 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.

[0014] Furthermore, according to the invention described in claim 2, 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.

[0015] In addition, according to the invention described in claim 3, 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]

[0016] [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] 3 is a diagram showing a frame structure of a data frame transmitted from a transmitting unit shown in FIG. 2. [Diagram 5] 4 is a functional block diagram showing a schematic configuration of a burst detection unit shown in FIG. 3. [Figure 6] FIG. 5 is an explanatory diagram showing burst detection using the data frame shown in FIG. [Figure 7]6 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 5. [Figure 8] 10 is a functional block diagram showing a schematic configuration of a burst detection unit of a wireless communication system according to embodiment 2 of the present invention. [Figure 9] 9 is a diagram showing a frequency spectrum of an alternating signal whose frequency has been shifted by the frequency shift unit shown in FIG. 8. FIG. [Figure 10] 9 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 8. [Figure 11] 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 12] 12 is a diagram showing a frequency spectrum of an alternating signal whose frequency has been shifted by the frequency shift unit shown in FIG. 11. FIG. [Figure 13] 12 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. [Figure 14] 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 15] 15 is an explanatory diagram showing burst detection using an alternating signal normalized by the normalization unit shown in FIG. 14. [Figure 16] 15 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 14. [Figure 17] 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. [Figure 18] 18 is a diagram showing a frequency spectrum of an alternating signal whose frequency has been shifted by the frequency shift unit shown in FIG. 17. FIG. [Figure 19] 18 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 17. [Figure 20] FIG. 1A shows the frame structure of a data frame used in conventional burst communication, FIG. 1B shows a schematic configuration of a conventional burst detection unit, and FIG. 1C is an explanatory diagram showing burst detection using a CW signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the present invention will be described 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. (Embodiment 1) 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.

[0018] 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.

[0019] 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).

[0020] 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."

[0021] 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 transmitting unit 6 via the data circuit-terminating device 51.

[0022] 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.

[0023] 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).

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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, phase correction, etc. on the received data frame. The receiver 8 then separates the alternating signal from the data frame that has been subjected to various corrections, performs demapping on the data signal to generate transmission data, and outputs it to the interface 5.

[0028] In the burst detection according to the present embodiment, a data frame to which an alternating signal is added as a preamble signal is burst-transmitted from the wireless communication device 2 on the transmitting side, and the arrival of the data frame is detected by detecting the alternating signal from the receiving means that receives and outputs the data frame. This eliminates the need to add a CW signal to the data frame, thereby improving the throughput of burst communication.

[0029] 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 combining unit 64, a transmission ROF 65, a quadrature modulation unit 66, a DAC (Digital Analog Converter) 67, a mixer 68, a local oscillator 69, and a power amplifier 610.

[0030] 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.

[0031] The mapping unit 62 performs mapping processing on the binary data string of the transmission data so as to form a predetermined signal point arrangement, generates a data signal consisting of a symbol string, and outputs the data signal to the combining unit 64. The alternating signal generating unit 63 generates an alternating signal used to correct the clock error, and outputs the alternating signal to the combining unit 64.

[0032] The combining unit 64 combines the alternating signal input from the alternating signal generating unit 63 with 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 65. The transmitting ROF 65 has a roll-off filter function and performs band limiting processing on the data frame DF input from the combining unit 64 and outputs it to the orthogonal modulation unit 66.

[0033] The quadrature modulation unit 66 superimposes a carrier signal of a predetermined frequency on the data frame DF input from the transmission ROF 65, digitally modulates it, and outputs it to the DAC 67. Note that the modulation method used in the quadrature modulation unit 66 is not limited to a specific method, but for example, quadrature amplitude modulation is used.

[0034] The DAC 67 converts the data frame DF input from the quadrature modulation unit 66 into an analog transmission signal and outputs it to the mixer 68. The local oscillator 69 generates a local oscillation signal having a predetermined fixed frequency and outputs the generated local oscillation signal to the mixer 68. The mixer 68 mixes the local oscillation signal with the transmission signal input from the DAC 67 to convert it into a signal with a higher frequency than the predetermined frequency.

[0035] The power amplifier 610 amplifies the transmission signal frequency-converted by the mixer 68 and outputs it to the antenna 3. The antenna 3 transmits the transmission signal amplified by the power amplifier 610 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 610 and the antenna 3.

[0036] As shown in FIG. 4, the transmitting unit 6 of this embodiment transmits a data frame DF consisting of an alternating signal and a data signal, thereby improving the throughput of burst communication compared to the conventional case in which a CW signal is added.

[0037] 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 separator 813, a demapping unit 814, an AGC 815, and a DAC 816.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 detection flag to the timing control unit 88. The timing control unit 88, to which the detection flag has been input, outputs an enable signal to each module to cause it to process the data frame DF.

[0042] 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.

[0043] 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 signal to the APC 812. The APC 812 performs phase correction on the data frame DF of the baseband signal input from the symbol recovery unit 811, and outputs the corrected signal to the separation unit 813.

[0044] 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.

[0045] 5 is a functional block diagram showing a schematic configuration of the burst detection unit 87 according to the present embodiment 1. The burst detection unit 87 includes an LPF 872, a power calculation unit 873, an averaging unit 874, and a determination unit 875.

[0046] 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.

[0047] The determination unit 875 compares the average value of the signal power input from the averaging unit 874 with a preset power threshold, and determines that an alternating signal has been detected when the average value of the signal power is greater than the power threshold, as shown in Fig. 6. Note that the power threshold is a value that allows a desired SNR to be obtained, which is preset and stored in a memory (not shown) and output to the determination unit 875.

[0048] Next, the operation of the burst detection section 87 in the above-mentioned first embodiment will be described with reference to the flowchart in FIG.

[0049] 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 S1).

[0050] 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).

[0051] 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).

[0052] As described above, according to the wireless communication system 1 according to the first embodiment, it is not necessary to add a CW signal to the data frame DF, and therefore the throughput of burst communication is improved. (Embodiment 2) Next, a wireless communication system according to a second embodiment using a wireless receiving device and a burst detection method of the present invention will be described. The wireless communication system 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, a frequency-shifted signal is generated by 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, one spectrum of the alternating signal is extracted from the frequency-shifted signal, and burst detection is performed using the signal power of 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.

[0053] 8 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the 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.

[0054] 9(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.

[0055] As shown in FIG. 9B, the frequency shifter 876 shifts the frequency of the received signal by −fsym / 2 so that the frequency of one spectrum of the alternating signal, for example spectrum f1, matches the center frequency fc of the alternating signal to generate a frequency-shifted signal.

[0056] 9(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.

[0057] 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. 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.

[0058] Next, the operation of the burst detector 87 in the second embodiment will be described with reference to the flowchart of FIG.

[0059] 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).

[0060] 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).

[0061] 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).

[0062] 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).

[0063] 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. (Embodiment 3) Next, a wireless communication system according to a third embodiment using the wireless receiving device and burst detection method of the present invention will be described. The wireless communication system according to the third embodiment shifts the frequency of a 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 one having the greater signal power with a power threshold. In the following, the same components as those in the wireless communication system 1 according to the first and second embodiments are denoted by the same reference numerals and detailed description thereof will be omitted.

[0064] In the burst detection unit 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 (Career-to-Noise Ratio) 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.

[0065] 11 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the present embodiment 3. The burst detection unit 87 includes 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, 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 determination unit (determination means) 875.

[0066] 12A 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.

[0067] As shown in Fig. 12(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.

[0068] Similarly, the second frequency shifter 876B 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 negative direction with respect to the center frequency fc of the alternating signal, as shown in Fig. 12(D) to generate a second frequency-shifted signal. That is, the second frequency shifter 876B shifts the received signal by -fsym / 2-Δf / 2.

[0069] 12(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.

[0070] 12(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.

[0071] 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).

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 6.

[0076] Next, the operation of the burst detector 87 in the above-mentioned third embodiment will be described with reference to the flowchart in FIG.

[0077] 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).

[0078] 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).

[0079] 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).

[0080] 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).

[0081] 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).

[0082] As described above, according to the wireless communication system 1 of the third embodiment, the frequency of the received signal is shifted to generate the first and second frequency-shifted signals, and one of the spectra of the alternating signals is extracted by the LPF for each of the two types of frequency-shifted signals, thereby making it possible to reduce the bandwidth of the LPF to half that of the conventional system. 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 not necessary to add a CW signal to the data frame DF, thereby improving the throughput of burst communication. (Embodiment 4) Next, a wireless communication system according to a fourth embodiment using the wireless receiving device and burst detection method of the present invention will be described. The wireless communication system according to the fourth embodiment differs from the third embodiment in that the amplitude of the received signal is normalized before detecting an alternating signal. In the following, the same components as those in the wireless communication system 1 according to the third embodiment are denoted by the same reference numerals and detailed description thereof will be omitted.

[0083] 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. 20(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 delay in burst detection is suppressed by normalizing the amplitude of the received signal.

[0084] 14 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the 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.

[0085] As shown in Fig. 15, when the amplitude of the signal power of the received signal is less than 1, the normalization unit 871 normalizes the amplitude 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. 16, 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 amplitude-normalized received signal.

[0086] As described above, according to the wireless communication system 1 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 the reception level to be adjusted by AGC. This makes it possible to improve the throughput of burst communication by suppressing the detection delay that occurs while waiting for the level adjustment of the received signal.

[0087] 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, a normalization unit 871 is connected before the LPF 872. Also, in the flowchart shown in FIG. 7, before the detection of the alternating signal (step S1), normalization of the amplitude of the received signal (step S8) is performed. Similarly, when applied to the second embodiment, in the burst detection unit 87 shown in FIG. 8, a normalization unit 871 is connected before the frequency shift unit 876. Also, in the flowchart shown in FIG. 10, normalization of the amplitude of the received signal (step S8) is performed 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. (Embodiment 5) Next, a wireless communication system according to a fifth embodiment using the wireless receiving device and burst detection method of the present invention will be described. The wireless communication system according to the fifth embodiment differs from the fourth embodiment in that a power threshold is calculated from noise power and used when burst detection is performed from a received signal whose amplitude has been normalized. Note that, in the following, the same components as those in the wireless communication system 1 according to the fourth embodiment are denoted by the same reference numerals and detailed description thereof will be omitted.

[0088] In the burst detection unit 87 of the fourth embodiment, the amplitude of the received signal is normalized when no burst signal is received, which may cause erroneous detection. Therefore, in the burst detection of the fifth embodiment, a power threshold required to satisfy a desired SNR is calculated from the noise power and used for burst detection. As a result, even if the amplitude of the received signal is normalized when no burst signal is received, the SNR remains low, making it possible to prevent erroneous detection.

[0089] 17 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.

[0090] As in the fourth embodiment, as shown in FIG. 15, when the amplitude of the signal power of the received signal is less than 1, the normalization unit 871 normalizes the amplitude to 1.

[0091] Fig. 18(A) shows the spectrum of the received signal output from the quadrature detection unit 86. As shown in Fig. 18(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. 18(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.

[0092] 18(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.

[0093] 18(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.

[0094] 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.

[0095] 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.

[0096] The power comparison section 8711 compares the average value of the first signal power input from the averaging section 874A with the average value of the second signal power input from the averaging section 874B, and outputs the larger one to the determination section 875.

[0097] As shown in Fig. 18(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. 18(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.

[0098] 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).

[0099] 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).

[0100] SNR = signal power / noise power (1) Power threshold = SNR threshold × noise power (2) 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.

[0101] 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.

[0102] 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).

[0103] 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).

[0104] 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).

[0105] 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).

[0106] 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.

[0107] The method of calculating a power threshold from a noise signal and detecting a burst can also be applied to embodiments 1 and 2. When applied to embodiment 1, in the burst detection unit 87 shown in FIG. 5, 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 a determination unit 875. Similarly, when applied to the second embodiment, in the burst detection unit 87 shown in Fig. 8, 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 the determination unit 875. According to this, also in the first and second embodiments, it is possible to suppress false detection that occurs when the amplitude of the received signal is normalized.

[0108] 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]

[0109] 1. Wireless communication systems 2. Wireless communication devices 5. 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) DF Data Frame

Claims

1. a receiving means for receiving a data frame in which an alternating signal is added to the head of the data signal and transmitted in bursts, and outputting a received signal; a burst detection means for detecting the arrival of the data frame by detecting the alternating signal from the received signal, 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 having a pair of spectra 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; A wireless receiving device comprising:

2. the burst detection means comprises normalization means for normalizing the amplitude of the received signal before shifting the frequency of the received signal.

2. The wireless receiving device according to claim 1,

3. 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; 3. The wireless receiving device according to claim 2, further comprising:

4. A burst detection method for use in a wireless receiving device that receives burst-transmitted data frames, comprising: receiving the data frame which has an alternating signal added to the beginning of the data signal and is burst-transmitted, and outputting the received signal; a step of shifting a frequency of the received signal so that a frequency of one spectrum of the alternating signal having a pair of spectrums 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; extracting one spectrum of the alternating signal from the first frequency shifted signal; 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 step of shifting a 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; extracting one spectrum of the alternating signal from the second frequency shifted signal, the one spectrum having the same signal extraction characteristics as the step of extracting one spectrum of the alternating signal from the first frequency shifted signal; 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; comparing the first average signal power with the second average signal power and outputting the larger one; a step of comparing the average value of the larger signal power with a power threshold, and determining that the alternating signal has been detected if the average value of the larger signal power is greater than the power threshold, thereby detecting the arrival of the data frame; A burst detection method comprising:

Images