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: A burst detection part 87 of a radio communication device comprises: a normalization part 871 that normalizes a fluctuation of a reception signal; an LPF 872 that extracts a preamble signal from the reception signal of which the fluctuation is normalized; a power calculation part 873 that calculates a signal power of the preamble signal extracted; and a comparison part 875 that compares a mean value of the signal power and a power threshold value, and determines that the preamble signal is detected when the mean value of the signal power is larger than the power threshold value.SELECTED DRAWING: Figure 4

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. 16(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] 16(B), burst detection involves an LPF (Low-pass filter) 100 extracting a CW signal from a 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. A determination unit 103 compares the average value of the signal power with a preset power threshold, and determines that a CW signal has been detected when the average value of the signal power is equal to or 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] 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 (Automatic Gain Control) before burst detection is performed. Therefore, when the signal power of the received signal is lower than the rated power, as shown in Fig. 16(C), it takes time for the signal power of the CW signal to exceed the power threshold, causing a delay in burst detection and reducing 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 that is burst-transmitted with a preamble signal added to the beginning of a data signal, and outputting a received signal; a normalizing means for normalizing the amplitude of the demodulated signal power to 1 when the amplitude of the demodulated signal power is less than 1; and a burst detecting means for detecting the arrival of the data frame by detecting the preamble signal from the amplitude-normalized received signal; the burst detection means comprises: a first signal extraction means for extracting the preamble signal from the amplitude-normalized received signal; a power calculation means for calculating the signal power of the preamble signal extracted by the first signal extraction means and obtaining an average value thereof; a determination means for comparing the average value of the signal power of the preamble signal with a power threshold and determining that the preamble signal has been detected when the average value of the signal power of the preamble signal is greater than the power threshold; a third frequency shift means for shifting the frequency of the amplitude-normalized received signal so that it does not fall within a range of the signal extraction characteristic of the first signal extraction means to generate a third frequency-shifted signal; a third signal extraction means having the same signal extraction characteristic 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; and a power threshold calculation means for calculating the power threshold based on the average value of the signal power of the noise signal. The present invention relates to a wireless receiving device comprising: Effect of the Invention

[0013] Claim 1 to According to the described invention, the level adjustment by AGC that was conventionally performed when the signal level of the received signal was low is no longer necessary, so that it is possible to suppress detection delays and improve the throughput of frame data.

[0014] Also, claims 1According to the invention described in the above, burst detection is performed by comparing the average signal power of the amplitude-normalized received signal with a power threshold. Therefore, by setting the power threshold to a value that provides a desired SNR (Signal-to-Noise Ratio), it is possible to perform burst detection with high accuracy.

[0016] Also, claims 1 According to the invention described in the above, the power threshold required to satisfy the desired SNR 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, thereby making it possible to prevent erroneous detection. [Brief description of the drawings]

[0017] [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] 4 is a functional block diagram showing a schematic configuration of a burst detection unit shown in FIG. 3. [Diagram 5] 3A shows the frame structure of a data frame transmitted from the transmitting unit shown in FIG. 2, and FIG. 3B shows burst detection in which the signal power of a received signal is normalized. [Figure 6] 4 is a flowchart showing a procedure of burst detection performed by the burst detector shown in FIG. 3; [Figure 7] 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 8] 8 is a diagram showing a frequency spectrum of a received signal when a burst is detected by the burst detection unit shown in FIG. 7. [Figure 9] 8 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 7. [Figure 10]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 11] 11 is a diagram showing a frequency spectrum of a received signal when a burst is detected by the burst detection unit shown in FIG. [Figure 12] 11 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. [Figure 13] 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 14] 14 is a diagram showing a frequency spectrum of a received signal when a burst is detected by the burst detection unit shown in FIG. 13. [Figure 15] 14 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 13. [Figure 16] 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 conventional burst detection using a CW signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 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.

[0019] (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.

[0020] 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.

[0021] 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).

[0022] 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."

[0023] 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.

[0024] 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 a preamble signal placed at the beginning of the data signal, and digitally modulates the data frame by superimposing a carrier signal of a predetermined frequency on the data frame. The preamble signal includes an unmodulated CW signal used for burst detection and an alternating signal used for correcting clock errors. 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.

[0025] 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).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 preamble 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.

[0030] In the burst detection according to the present embodiment, the amplitude of the received signal is normalized, and a preamble signal is detected from the amplitude-normalized received signal to detect the arrival of a data frame. More specifically, the amplitude of the received signal is normalized, a preamble signal is extracted from the amplitude-normalized received signal, and the signal power of the extracted preamble signal is calculated to obtain its average value. Then, the average value of the signal power of the preamble signal is compared with a preset power threshold, and if the average value of the signal power of the preamble signal is greater than the power threshold, it is determined that the preamble signal has been detected. This makes it possible to detect a CW signal without waiting for the completion of level adjustment by AGC, which has been conventionally performed when the signal power of the received signal is lower than the rated value, and therefore it is possible to suppress detection delay and improve the throughput of frame data.

[0031] 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, a CW signal generation unit 63a, an alternating signal generation unit 63b, a coupling 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.

[0032] 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.

[0033] The mapping unit 62 performs mapping processing on the binary data string of the transmission data so as to obtain 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 CW signal generating unit 63a generates a CW signal, which is an unmodulated continuous wave used for burst detection, and outputs the CW signal to the combining unit 64. The alternating signal generating unit 63b generates an alternating signal used for clock error correction, and outputs the alternating signal to the combining unit 64.

[0034] The combining unit 64 combines the CW signal input from the CW signal generating unit 63a and the alternating signal input from the alternating signal generating unit 63b 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 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 4 is a functional block diagram showing a schematic configuration of the burst detection unit 87. The burst detection unit 87 includes a normalization unit (normalization means) 871, 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.

[0047] 5(B), when the amplitude of the signal power of the received signal is less than 1, the normalization unit 871 normalizes the amplitude to 1. The LPF 872 extracts a CW signal from the received signal, suppresses noise, and outputs the signal to the 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 the averaging unit 874. The averaging unit 874 finds the average value of the signal power calculated by the power calculation unit 873, and outputs it to the determination unit 875.

[0048] 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 a CW signal has been detected when the average value of the signal power is equal to or greater than the power threshold, as shown in Fig. 5(B). Note that the power threshold is preset to a value that will provide a desired SNR, is stored in a memory (not shown), and is output to the determination unit 875.

[0049] Next, the operation of the burst detector 87 in the above embodiment will be described with reference to the flowchart of FIG.

[0050] When the received signal of the data frame DF is input from the quadrature detection unit 86, the normalization unit 871 of the burst detection unit 87 normalizes the amplitude of the received signal (step S1).

[0051] The LPF 872 of the burst detector 87 extracts a CW signal from the amplitude-normalized received signal and suppresses noise (step S2).

[0052] The power calculation unit 873 of the burst detection unit 87 calculates the signal power of the CW 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 S3).

[0053] The determination 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 determines that a CW signal has been detected if the average value of the signal power is greater than the power threshold value, and outputs a detection flag to the timing control unit 88 (step S4).

[0054] As described above, according to the wireless communication system 1 of this embodiment, a CW signal exceeding a power threshold can be detected without waiting for the reception level to be adjusted by AGC, so that it is 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.

[0055] (Embodiment 2) Next, a wireless communication system according to a second embodiment using the wireless receiving device and 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, when performing burst detection from a received signal whose amplitude has been normalized, a power threshold is calculated from noise power and used. Note that, in the following, the same components as those in the wireless communication system 1 according to the first embodiment are denoted by the same reference numerals and detailed description thereof will be omitted.

[0056] In the burst detection unit 87 of the first 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 second 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.

[0057] 7 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 2. The burst detection unit 87 includes a normalization unit (normalization means) 871, a frequency shift unit (third frequency shift means) 876, an LPF (third signal extraction means) 877, a power calculation unit (third power calculation means) 878, an averaging unit (third power calculation means) 879, a power threshold calculation unit (power threshold calculation means) 8710, and a determination unit (determination means) 875.

[0058] As in the first embodiment, when the amplitude of the signal power of the received signal is less than 1, normalization section 871 normalizes the amplitude to 1, as shown in FIG. 5(B).

[0059] Fig. 8(A) shows the spectrum of the amplitude-normalized received signal R. As shown in Fig. 8(B), the LPF 872 has a filter characteristic (signal extraction characteristic) shown by the dashed line in the figure, extracts a CW signal from the amplitude-normalized received signal, suppresses noise, and outputs the signal to the power calculation unit 873. Note that, when the expected frequency offset of the received signal R is ±Δf, the filter characteristic of the LPF 872 normally uses 2Δf, which is a bandwidth twice the frequency offset Δf.

[0060] As in the first embodiment, 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 the averaging unit 874. The averaging unit 874 obtains an average value of the signal power calculated by the power calculation unit 873, and outputs the average value to the determination unit 875.

[0061] 8(C), the frequency shifter 876 shifts the amplitude-normalized received signal R to a frequency that does not fall within the bandwidth 2Δf of the LPF 877, for example, −fsym / 4 (fsym: symbol frequency), to generate a frequency-shifted signal (third frequency-shifted signal) Rs. As shown by the dashed line in FIG. 8(D), the LPF 877 has the same filter characteristics as the LPF 872, and extracts a noise signal from the frequency-shifted signal Rs.

[0062] The power calculation unit 878 calculates the signal power of the noise signal input from the LPF 877, and the averaging unit 879 calculates the average value of the signal power input from the power calculation unit 878 (hereinafter also referred to as noise power).

[0063] The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 879, 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)

[0064] The determination unit 875 compares the average value of the signal power input from the averaging unit 874 with the power threshold input from the power threshold calculation unit 8710, and determines that a CW 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.

[0065] Next, the operation of the burst detection section 87 in the above-mentioned second embodiment will be described with reference to the flowchart in FIG.

[0066] When the received signal of the data frame DF is input from the quadrature detection unit 86, the normalization unit 871 of the burst detection unit 87 normalizes the amplitude of the received signal (step S1).

[0067] The LPF 872 of the burst detector 87 extracts a CW signal from the amplitude-normalized received signal and suppresses noise (step S2).

[0068] The power calculation unit 873 of the burst detection unit 87 calculates the signal power of the CW 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 S3).

[0069] Meanwhile, the frequency shifter 876 of the burst detector 87 shifts the frequency of the amplitude-normalized received signal to a position that does not fall within the bandwidth 2Δf of the LPF 877, thereby generating a frequency-shifted signal (step S5). The LPF 877 extracts a noise signal from the frequency-shifted signal (step S6).

[0070] The power calculation unit 878 calculates the signal power of the noise signal input from the LPF 877, and the averaging unit 879 calculates the average value (noise power) of the signal power input from the power calculation unit 878 (step S7).

[0071] The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 879 and a desired SNR threshold, and outputs the power threshold to the determination unit 875 (step S8).

[0072] The determination unit 875 compares the average value of the signal power input from the averaging unit 874 with the power threshold input from the power threshold calculation unit 8710, and determines that a CW 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 S4).

[0073] As described above, according to the wireless communication system 1 of the second 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. Also, as in the first embodiment, it is possible to detect a CW signal exceeding the power threshold without waiting for the reception level to be adjusted by the AGC, thereby suppressing the detection delay that occurs while waiting for the level adjustment of the received signal and improving the throughput of burst communication.

[0074] (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 differs from the first embodiment in that it shifts the frequency of a received signal to generate two types of frequency-shifted signals, extracts a CW signal from each of the two types of frequency-shifted signals using an LPF, and performs burst detection by comparing the one of the two extracted CW signals with the greater signal power with a power threshold. Note that, in the following, the same components as those in the wireless communication system 1 according to the first embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted.

[0075] 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 a CW signal is extracted for each of the two types of frequency-shifted signals using an LPF with a narrower bandwidth, thereby making it possible to improve noise resistance while maintaining the frequency offset resistance equivalent to that of the first embodiment.

[0076] 10 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 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, 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.

[0077] As in the first embodiment, when the amplitude of the signal power of the received signal is less than 1, normalization section 871 normalizes the amplitude to 1, as shown in FIG. 5(B).

[0078] Fig. 11(A) shows the spectrum of the received signal whose amplitude has been normalized. As shown in Fig. 11(B), the first frequency shifter 876A generates a first frequency shifted signal Rs1 by shifting the frequency of the received signal in the plus direction (first direction) by 1 / 2 the expected frequency offset Δf of the received signal.

[0079] Similarly, the second frequency shift unit 876B generates a second frequency shifted signal Rs2 by shifting the frequency of the received signal by 1 / 2 the frequency offset Δf in the negative direction (a second direction opposite to the first direction), as shown in FIG. 11(D).

[0080] 11(C), the LPF 872A has a filter characteristic (signal extraction characteristic) indicated by a dashed line in the figure, extracts a CW signal from the first frequency shifted signal Rs1, suppresses noise, and outputs the signal 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 second embodiment, Δf, which is half of 2Δf, is used.

[0081] 11(E), the LPF 872B has a filter characteristic (signal extraction characteristic) indicated by a dashed line in the figure, extracts a CW signal from the second frequency shifted signal Rs2, suppresses noise, and outputs the signal 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.

[0082] In this manner, in the third embodiment, the frequency of the received signal R is shifted to generate two types of frequency-shifted signals Rs1 and Rs2, and a CW signal is extracted from each of the two types of frequency-shifted signals Rs1 and Rs2 by an LPF, thereby making it possible to reduce the bandwidth of the LPF to half that of the conventional embodiment (first embodiment).

[0083] As in the first embodiment, the power calculation unit 873A calculates the signal power of the first frequency shifted signal Rs1 input from the LPF 872A, and outputs the calculated signal power to the averaging unit 874A. The averaging unit 874A obtains an average value of the signal power calculated by the power calculation unit 873A, and outputs the average value to the power comparison unit 8711.

[0084] Similarly to the above, the power calculation unit 873B calculates the signal power of the second frequency shifted signal Rs2 input from the LPF 872B, and outputs the calculated signal power to the averaging unit 874B. The averaging unit 874B obtains an average value of the signal power calculated by the power calculation unit 873B, and outputs it to the power comparison unit 8711.

[0085] The power comparator 8711 compares the average value of the signal power of the first frequency shifted signal Rs1 input from the averaging unit 874A with the average value of the signal power of the second frequency shifted signal Rs2 input from the averaging unit 874B, and outputs the larger one to the decision unit 875. That is, when the frequency offset of the received signal R is in the negative direction, the average value of the signal power of the first frequency shifted signal Rs1 is greater than the average value of the signal power of the second frequency shifted signal Rs2. Also, when the frequency offset of the received signal R is in the positive direction, the average value of the signal power of the second frequency shifted signal Rs2 is greater than the average value of the signal power of the first frequency shifted signal Rs1.

[0086] 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 a CW 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 (B).

[0087] Next, the operation of the burst detector 87 in the above-mentioned third embodiment will be described with reference to the flowchart of FIG.

[0088] When the received signal of the data frame DF is input from the quadrature detection unit 86, the normalization unit 871 of the burst detection unit 87 normalizes the amplitude of the received signal (step S1).

[0089] The first frequency shifter 876A generates a first frequency shifted signal Rs1 by shifting the frequency of the received signal in the positive direction by 1 / 2 the frequency offset Δf. Similarly, the second frequency shifter 876B generates a second frequency shifted signal Rs2 by shifting the frequency of the received signal in the negative direction by 1 / 2 the frequency offset Δf (step S10).

[0090] The LPF 872A of the burst detection unit 87 extracts a CW signal from the first frequency shifted signal Rs1 and suppresses noise, and the LPF 872B extracts a CW signal from the second frequency shifted signal Rs2 and suppresses noise (step S2).

[0091] The power calculation unit 873A of the burst detection unit 87 calculates the signal power of the first frequency shifted signal Rs1 input from the LPF 872A, and the averaging unit 874A calculates the average value of the signal power input from the power calculation unit 873A. Similarly, the power calculation unit 873B calculates the signal power of the second frequency shifted signal Rs2 input from the LPF 872B, and the averaging unit 874B calculates the average value of the signal power input from the power calculation unit 873B (step S3).

[0092] The power comparison unit 8711 compares the average value of the signal power of the first frequency shifted signal Rs1 input from the averaging unit 874A with the average value of the signal power of the second frequency shifted signal Rs2 input from the averaging unit 874B, and outputs the larger one to the judgment unit 875 (step S11).

[0093] 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 a CW signal has been detected and outputs a detection flag to the timing control unit 88 (step S4).

[0094] As described above, according to the wireless communication system 1 of the third embodiment, the frequency of the received signal R is shifted to generate two kinds of frequency-shifted signals Rs1 and Rs2, and the LPF extracts the CW signal from each of the two kinds of frequency-shifted signals Rs1 and Rs2. This makes it possible to reduce the bandwidth of the LPF to half that of the conventional system (first embodiment). Therefore, it is possible to improve the noise resistance while maintaining the frequency offset resistance equivalent to that of the first embodiment. Also, as in the first embodiment, it is possible to detect a CW signal exceeding the power threshold without waiting for the adjustment of the reception level by the AGC, so that it is possible to suppress the detection delay that occurs while waiting for the level adjustment of the received signal and improve the throughput of burst communication.

[0095] (Embodiment 4) Next, a wireless communication system according to a fourth embodiment using the wireless receiving device and the burst detection method of the present invention will be described. The wireless communication system according to the fourth embodiment is a combination of the first, second, and third embodiments. That is, the burst detection unit 87 according to the fourth embodiment normalizes the amplitude of a received signal that has received a data frame DF, calculates a power threshold from the noise portion of the amplitude-normalized received signal, shifts the frequency of the received signal to generate two types of frequency-shifted signals, extracts a CW signal from each of the two types of frequency-shifted signals using an LPF, and compares the one of the two types of extracted CW signals with a higher signal power with the power threshold to perform burst detection. In the following, the same components as those in the wireless communication system 1 according to the first, second, and third embodiments are denoted by the same reference numerals and will not be described in detail.

[0096] 13 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the fourth 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) 873C. The power converter includes a first power calculation unit (second power calculation means) 873B, an averaging unit (second power calculation means) 874B, a power comparison unit (comparison means) 8711, a third frequency shift unit (third frequency shift means) 876, an LPF (third signal extraction means) 877, a power calculation unit (third power calculation means) 878, an averaging unit (third power calculation means) 879, a power threshold calculation unit (power threshold calculation means) 8710, and a judgment unit (judgment means) 875.

[0097] As in the first embodiment, when the amplitude of the signal power of the received signal is less than 1, normalization section 871 normalizes the amplitude to 1, as shown in FIG. 5(B).

[0098] Fig. 14(A) shows the spectrum of the received signal whose amplitude has been normalized. As shown in Fig. 14(B), the first frequency shifter 876A generates a first frequency shifted signal Rs1 by shifting the frequency of the received signal in the plus direction (first direction) by 1 / 2 the expected frequency offset Δf of the received signal.

[0099] Similarly, the second frequency shift unit 876B generates a second frequency shifted signal Rs2 by shifting the frequency of the received signal by 1 / 2 the frequency offset Δf in the negative direction (a second direction opposite to the first direction), as shown in FIG. 14(D).

[0100] As shown in FIG. 14C, the LPF 872A has filter characteristics (signal extraction characteristics) indicated by the dashed line in the figure, extracts a CW signal from the first frequency shifted signal Rs1, suppresses noise, and outputs the signal to the power calculation unit 873A.

[0101] 14(E), the LPF 872B has a filter characteristic (signal extraction characteristic) indicated by a dashed line in the figure, extracts a CW signal from the second frequency shifted signal Rs2, suppresses noise, and outputs the signal 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.

[0102] The power calculation unit 873A calculates the signal power of the first frequency shifted signal Rs1 input from the LPF 872A, and outputs the calculated signal power to the averaging unit 874A. The averaging unit 874A obtains an average value of the signal power calculated by the power calculation unit 873A, and outputs it to the power comparison unit 8711.

[0103] Similarly to the above, the power calculation unit 873B calculates the signal power of the second frequency shifted signal Rs2 input from the LPF 872B, and outputs the calculated signal power to the averaging unit 874B. The averaging unit 874B obtains an average value of the signal power calculated by the power calculation unit 873B, and outputs it to the power comparison unit 8711.

[0104] The power comparison unit 8711 compares the average value of the signal power of the first frequency shifted signal Rs1 input from the averaging unit 874A with the average value of the signal power of the second frequency shifted signal Rs2 input from the averaging unit 874B, and outputs the larger one to the judgment unit 875.

[0105] As shown in Fig. 14(F), the third frequency shifter 876 generates a third frequency-shifted signal Rs by shifting the amplitude-normalized received signal R 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. 14(G), the LPF 877 has the same filter characteristics as the LPFs 872A and 872B, and extracts a noise signal from the frequency-shifted signal Rs.

[0106] The power calculation unit 878 calculates the signal power of the noise signal input from the LPF 877, and the averaging unit 879 calculates the average value of the signal power input from the power calculation unit 878 (hereinafter also referred to as noise power).

[0107] The power threshold calculation section 8710 calculates a power threshold based on the noise power input from the averaging section 879 , as in the second embodiment, and outputs the power threshold to the determination section 875 .

[0108] 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, it determines that a CW signal has been detected and outputs a detection flag to the timing control unit 88.

[0109] Fig. 15 is a flowchart showing the processing procedure of the burst detection unit 87 in the above-mentioned embodiment 4. Note that the flowchart shown in Fig. 15 is a combination of the processing procedure of the embodiment 1 shown in Fig. 6, the processing procedure of the embodiment 2 shown in Fig. 9, and the processing procedure of the embodiment 3 shown in Fig. 12, and the same processes are denoted by the same reference numerals, so detailed explanations will be omitted.

[0110] As described above, according to the wireless communication system 1 of the present embodiment 4, as in the embodiment 1, a CW signal exceeding a power threshold can be detected without waiting for the reception level to be adjusted by AGC, so that it is 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.

[0111] Furthermore, according to the wireless communication system 1 of the present embodiment 4, a power threshold required to satisfy a desired SNR is calculated from noise power and used for burst detection, as in the embodiment 2. This makes it possible to prevent erroneous detection, since the SNR remains low even if the amplitude of the received signal is normalized when no burst signal is received.

[0112] Furthermore, according to the wireless communication system 1 of the fourth embodiment, similarly to the third embodiment, the frequency of the received signal R is shifted to generate two kinds of frequency-shifted signals Rs1 and Rs2, and the LPF extracts a CW signal from each of the two kinds of frequency-shifted signals Rs1 and Rs2. This makes it possible to reduce the bandwidth of the LPF to half that of the conventional system (first embodiment). Therefore, it is possible to improve the noise resistance while maintaining the frequency offset resistance at the same level as the first embodiment.

[0113] 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.

[0114] For example, in the above embodiment, a CW signal is used as the preamble signal used for burst detection, but a signal other than a CW signal, such as an alternating signal, may be used. In this case, the CW signal can be omitted from the preamble signal, so the data amount of the preamble signal is reduced and the throughput is improved. [Explanation of symbols]

[0115] 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) 873 Power calculation unit (power calculation means) 873A First power calculation unit (first power calculation means) 873B second power calculation unit (second power calculation means) 874, 874A, 874B, 879 Averaging section 875 Judgment unit (judgment means) 876 Frequency shift unit (third frequency shift means) 876A First frequency shift unit (first frequency shift means) 876B Second frequency shift unit (second frequency shift means) 877 LPF (third signal extraction means) 878 Power calculation unit (third power calculation means) 8710 Power threshold calculation unit (power threshold calculation means) 8711 Power comparison section (power comparison means) DF Data Frame

Claims

[Claim 1] a receiving means for receiving a data frame which has a preamble signal added to the beginning of the data signal and is transmitted in bursts, and outputting a received signal; a normalization means for normalizing the amplitude of the demodulated signal power of the received signal to 1 when the amplitude is less than 1; a burst detection means for detecting the arrival of the data frame by detecting the preamble signal from the received signal whose amplitude has been normalized; The burst detection means includes: a first signal extraction means for extracting the preamble signal from the amplitude-normalized received signal; a power calculation means for calculating the signal power of the preamble signal extracted by the first signal extraction means and obtaining an average value of the signal power; a determination means for comparing an average value of the signal power of the preamble signal with a power threshold and determining that the preamble signal has been detected when the average value of the signal power of the preamble signal is greater than the power threshold; a third frequency shifting means for shifting the frequency of the amplitude-normalized received signal so as not to fall within a range of the signal extraction characteristic of the first signal extracting means, to generate 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; A wireless receiving device comprising:

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