Wireless receiving device and burst detection method

Abstract

To provide a radio receiver capable of improving throughput of frame data by suppressing detection delay.SOLUTION: A burst detection part 87 in a reception part includes: a normalization part 871; a first frequency shift part 876A; a low-pass filter (LPF) 872A; first power calculation means 873A, 874A for calculating an average value of first signal power; a second frequency shift part 876B; an LPF 872B; second power calculation means 873B, 874B for calculating an average value of second signal power; a power comparison part 8711 for outputting the greater from the average value of the first signal power and the average value of the second signal power; a third frequency shift part 876; an LPF 877 for extracting a noise signal from the third frequency shift signal; third power calculation means 878, 879 for calculating an average value of the signal power of the noise signal; a power threshold value calculation part 8710 for calculating a power threshold value based on the average value of the signal power of the noise signal; and a determination part 875 for determining that a preamble signal has been detected if the average value of the signal power is greater than the power threshold value.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] The present invention relates to a wireless receiving device and a burst detection method for detecting a data frame transmitted in a burst.

Background Art

[0002] In burst communication used in TDM (Time Division Multiplexing) communication or the like, since discontinuous signals are transmitted irregularly (hereinafter also referred to as burst transmission), a wireless receiving device does not know when to receive the signals. Therefore, in a wireless receiving device that performs burst communication, burst detection for detecting a signal transmitted in a burst is performed (see, for example, 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 head of the data signal. The preamble signal includes an unmodulated CW signal used for burst detection and an alternating signal (alternating pattern of "1" and "0") used for correcting clock error.

[0004] As shown in FIG. 16(B), in burst detection, the CW signal is extracted from the received signal output by receiving the data frame by an LPF (Low-pass filter) 100 to suppress noise, the signal power of the CW signal is calculated by a power calculation unit 101, and the average value of the signal power is obtained by an averaging unit 102. A determination unit 103 compares the average value of the signal power with a preset power threshold value, and determines that the CW signal has been detected when the average value of the signal power is equal to or greater than the power threshold value.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In conventional burst detection, when the signal power of the received signal is lower than the rated value, the signal power of the received signal is amplified by AGC (Automatic Gain Control) and then burst detection is performed. Therefore, when the signal power of the received signal is lower than the rated value, as shown in FIG. 16(C), it takes time until the signal power of the CW signal exceeds the power threshold, and there is a problem that a delay occurs in burst detection and the throughput decreases.

[0007] Therefore, an object of the present invention is to provide a wireless receiving apparatus and a burst detection method capable of improving the throughput of burst communication.

Means for Solving the Problems

[0008] In order to solve the above problems, the invention according to claim 1 includes: receiving means for receiving a data frame in which a preamble signal is added to the head of a data signal and burst-transmitted, and outputting a received signal; normalization means for normalizing the amplitude to 1 when the amplitude of the demodulated received signal is less than 1; and 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: first frequency shift means for shifting the frequency of the received signal whose amplitude has been normalized in a first direction to generate a first frequency shift signal; first signal extraction means for extracting the preamble signal from the first frequency shift signal; first power calculation means for calculating the first signal power, which is the signal power of the preamble signal extracted from the first frequency shift signal, and obtaining its average value; second frequency shift means for shifting the frequency of the received signal whose amplitude has been normalized in a second direction opposite to the first direction to generate a second frequency shift signal; second signal extraction means having the same signal extraction characteristics as the first signal extraction means and extracting the preamble signal from the second frequency shift signal; second power calculation means for calculating the second signal power, which is the signal power of the preamble signal extracted from the second frequency shift signal, and obtaining its average value; power comparison means for comparing the average value of the first signal power and the average value of the second signal power and outputting the larger one; 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 preamble signal has been detected when the average value of the signal power is greater than the power threshold; third frequency shift means for shifting the frequency of the received signal whose amplitude has been normalized so as not to fall within the range of the signal extraction characteristics of the first signal extraction means to generate a third frequency shift signal; 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 shift signal; third power calculation means for calculating the signal power of the noise signal and obtaining its average value; and power threshold calculation means for calculating the power threshold based on the average value of the signal power of the noise signal. A wireless receiving apparatus is characterized by comprising the above components.

Advantages of the Invention

[0009] According to the invention described in claim 1, when the signal level of the received signal is low, the level adjustment by AGC conventionally performed becomes unnecessary, so it is possible to suppress detection delay and improve the throughput of frame data.

[0010] Furthermore, according to the invention described in claim 1, the frequency of the received signal is shifted to generate two types of frequency-shifted signals, and for each of these two types of frequency-shifted signals, the preamble signal is extracted by the signal extraction means, whereby the bandwidth of the signal extraction means can be narrowed. Therefore, it is possible to improve the noise tolerance while maintaining the frequency offset tolerance equivalent to the conventional level.

[0011] Also, according to the invention described in claim 1, since the power threshold required to satisfy the desired SNR is calculated from the noise power and used for burst detection, even if the amplitude of the received signal is normalized when no burst signal is being received, the SNR remains low, so it is possible to prevent false detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0012]

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Figure 16

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described based on the illustrated embodiments. In the following, the characteristic configurations of the present invention will be described, and the description of the same mechanism as in the prior art when performing wireless communication will be omitted.

[0014] (Embodiment 1) FIG. 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 the transmitting and receiving stations of the wireless communication constituting the wireless communication system 1. The wireless communication devices 2 are mutually connected 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.

[0015] First, in this embodiment, a schematic configuration of the wireless communication device 2 corresponding to the wireless receiving device according to the present invention will be described.

[0016] The wireless communication device 2 includes an interface unit 5, a transmission unit 6, a demultiplexer 7, and a reception unit 8 (see the lower part of FIG. 1).

[0017] Here, the wireless communication device 2 is a device that performs transmission and reception with both a transmission mechanism and a reception mechanism. In the following description, when performing processing related to transmission using the transmission mechanism, the wireless communication device 2 is referred to as the "transmission side", and when performing processing related to reception using the reception mechanism, the wireless communication device 2 is referred to as the "reception side".

[0018] The interface unit 5 mainly includes a data line terminating device 51 (including devices called data communication devices and data line devices). The interface unit 5 receives the input of the transmission data of the communication target and outputs this transmission data to the transmission unit 6 via the data line terminating device 51.

[0019] The transmitting unit 6 receives the input of the transmission data output from the interface unit 5, combines a data signal obtained by performing mapping processing on the transmission data and a preamble signal arranged at the head of the data signal to generate a data frame, and further superimposes a carrier signal of a predetermined frequency on the data frame to perform digital modulation. Note that the preamble signal includes an unmodulated CW signal used for burst detection and an alternating signal used for correction of clock error. Also, although the modulation method used in the wireless communication system 1 is not limited to a specific method, for example, quadrature amplitude modulation (QAM) is used.

[0020] The transmitting unit 6 converts the digitally modulated data frame into an analog signal, then converts the frequency to a high-frequency signal higher than a predetermined frequency, amplifies it with a power amplifier, and outputs it as a transmission signal. The transmission signal is led from the transmitting unit 6 to the antenna 3 via the diplexer 7, and is burst-transmitted as radio waves from the antenna 3 to the antenna 3 of the other wireless communication device 2 (in other words, the receiving side in this communication) via the radio link 4.

[0021] Also, when a transmission signal is burst-transmitted 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 said wireless communication device 2 (in other words, the receiving side in this communication) via the radio link 4, the antenna 3 converts the received radio waves into an electrical signal (received signal) and outputs it.

[0022] The received signal output from the antenna 3 is led to the receiving unit 8 via the diplexer 7. The receiving unit 8 receives the input of the received signal, passes the received signal through a channel filter that allows only signals in a predetermined frequency band to pass, and then converts it into a signal having 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.

[0023] The receiving unit 8 performs quadrature detection processing (demodulation) on the digital received signal to generate a baseband signal of the in-phase component (Ich) and a baseband signal of the quadrature component (Qch) whose phases are orthogonal to each other. In the following description, unless it is necessary to focus on each of the in-phase component and the quadrature component separately, the in-phase component and the quadrature component will be described as common content without particularly distinguishing them, and in the drawings, the signal of the in-phase component and the signal of the quadrature component are represented by one signal line.

[0024] The receiving unit 8 performs burst detection based on the demodulated baseband signal. When the arrival of a data frame is detected by this burst detection, frequency offset correction, clock error correction, phase correction, etc. are performed on the received data frame. Then, the receiving unit 8 separates the preamble signal from the data frame subjected to various corrections, performs demapping processing on the data signal to generate transmission data, and outputs it to the interface unit 5.

[0025] In the burst detection according to the present embodiment, the amplitude of the received signal is normalized, and the arrival of the data frame is detected by detecting the preamble signal from the received signal whose amplitude is normalized. More specifically, the amplitude of the received signal is normalized, the preamble signal is extracted from the received signal whose amplitude is normalized, the signal power of the extracted preamble signal is calculated, and its average value is obtained. Then, the average value of the signal power of the preamble signal is compared with a preset power threshold, and when 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. As a result, when the signal power of the received signal is lower than the rated value, the CW signal can be detected without waiting for the completion of the level adjustment by AGC that has been conventionally performed, so that the detection delay can be suppressed and the throughput of the frame data can be improved.

[0026] FIG. 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 combining unit 64, a transmission ROF 65, an orthogonal modulation unit 66, a DAC (Digital Analog Converter) 67, a mixer 68, a local oscillator 69, and a power amplifier 610.

[0027] 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 by the so-called first-in first-out method.

[0028] The mapping unit 62 performs mapping processing on the binary data sequence of the transmission data so as to have a predetermined signal point arrangement, generates a data signal composed of a symbol sequence, and outputs it to the combining unit 64. The CW signal generation unit 63a generates a CW signal, which is an unmodulated continuous wave used for burst detection, and outputs it to the combining unit 64. The alternating signal generation unit 63b generates an alternating signal used for correcting the clock error and outputs it to the combining unit 64.

[0029] The combining unit 64 combines the CW signal input from the CW signal generation unit 63a and the alternating signal input from the alternating signal generation unit 63b at the head of the data signal input from the mapping unit 62, generates a data frame DF (see FIG. 5(A)), and outputs it to the transmission ROF 65. The transmission ROF 65 has a function of a roll-off filter, performs band-limiting processing on the data frame DF input from the combining unit 64, and outputs it to the orthogonal modulation unit 66.

[0030] The orthogonal 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. Although the modulation method used in the orthogonal modulation unit 66 is not limited to a specific method, for example, quadrature amplitude modulation is used.

[0031] The DAC67 converts the data frame DF input from the quadrature modulation unit 66 into a transmission signal of an analog 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 DAC67 and converts it into a signal having a frequency higher than a predetermined frequency.

[0032] 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 to the antenna 3 of the other wireless communication device 2 (in other words, the receiving side in this communication) as radio waves. Although not shown in the figure, a diplexer 7 is connected between the power amplifier 610 and the antenna 3.

[0033] FIG. 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 ROF810, a symbol reproduction unit 811, an APC (Automatic Phase Control) 812, a separation unit 813, a demapping unit 814, an AGC815, and a DAC816.

[0034] Antenna 3 converts the received radio wave into an electrical signal (received signal) and outputs it to the channel filter 81. A demultiplexer 7 is connected between the antenna 3 and the channel filter 81. The channel filter 81 passes a predetermined frequency band among the received signals 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, converts it into a signal having a frequency lower than a predetermined frequency, and outputs it to the variable ATT 84.

[0035] The variable ATT 84 includes an attenuator, attenuates the received signal output from the mixer 82 by adjusting the attenuation amount according to an external signal, and outputs it to the ADC 85. The attenuation amount in the variable ATT 84 changes based on the control signal of the AGC 815 supplied via the DAC 816.

[0036] The ADC 85 converts the received signal input from the variable ATT 84 into a digital signal. The quadrature detection unit 86 performs quadrature detection processing on the received signal to generate a baseband signal of an in-phase component (Ich) and a baseband signal of a quadrature component (Qch) whose phases are orthogonal to each other.

[0037] 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 the data frame DF by burst detection, it outputs a detection flag to the timing control unit 88. The timing control unit 88 that receives the detection flag outputs an enable signal for causing each module to perform processing on the data frame DF.

[0038] The AFC 89 performs frequency offset correction on the data frame DF of the baseband signal according to the enable signal from the timing control unit 88 and outputs it to the received ROF 810. The received ROF 810 has the function of a roll-off filter, performs band-limiting processing on the baseband signal input from the AFC 89, and outputs it to the symbol reproduction unit 811.

[0039] The symbol reproduction unit 811 corrects the clock error using the alternating signal included in the data frame DF of the baseband signal input from the received ROF 810, and outputs it to the APC 812. The APC 812 performs phase correction on the data frame DF of the baseband signal input from the symbol reproduction unit 811 and outputs it to the separation unit 813.

[0040] The separation unit 813 separates the data signal from the data frame DF and outputs it to the demapping unit 814. The demapping unit 814 performs demapping processing (decoding processing) on the signals (each of the in-phase component and the quadrature component) composed of the symbol string data input from the separation unit 813, converts the symbol string data into transmission data of a binary data string, and outputs it to the interface unit 5.

[0041] FIG. 4 is a functional block diagram showing the 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.

[0042] As shown in FIG. 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 the CW signal from the received signal to suppress noise and outputs it 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 obtains the average value of the signal power calculated by the power calculation unit 873 and outputs it to the determination unit 875.

[0043] The determination unit 875 compares the average value of the signal power input from the averaging unit 874 with a preset power threshold, and as shown in FIG. 5(B), determines that the CW signal has been detected when the average value of the signal power is equal to or greater than the power threshold. The power threshold is a value set in advance so as to obtain a desired SNR and is stored in a memory (not shown) and output to the determination unit 875.

[0044] Next, the operation of the burst detection unit 87 in the above embodiment will be described based on the flowchart of FIG. 6.

[0045] When the reception signal of the data frame DF is input from the quadrature detection unit 86 to the burst detection unit 87, the normalization unit 871 normalizes the amplitude of the reception signal (step S1).

[0046] The LPF 872 of the burst detection unit 87 extracts the CW signal from the reception signal whose amplitude has been normalized and suppresses noise (step S2).

[0047] 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).

[0048] 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 read from the memory and input, and determines that the CW signal has been detected when the average value of the signal power is greater than the power threshold, and outputs the detection flag to the timing control unit 88 (step S4).

[0049] As described above, according to the wireless communication system 1 according to the present embodiment, a CW signal exceeding the power threshold can be detected without waiting for the adjustment of the reception level by the AGC. Therefore, it is possible to suppress the detection delay that occurred while waiting for the level adjustment of the reception signal and improve the throughput of burst communication.

[0050] (Embodiment 2) Next, a wireless communication system according to Embodiment 2 using the wireless receiver and burst detection method of the present invention will be described. The wireless communication system according to Embodiment 2 is different from Embodiment 1 in that when performing burst detection from a received signal whose amplitude is normalized, a power threshold is calculated from the noise power and used. In the following, for the same configurations as those of the wireless communication system 1 according to Embodiment 1, the same reference numerals will be used and detailed descriptions thereof will be omitted.

[0051] In the burst detection unit 87 of Embodiment 1, when a burst signal is not being received, the amplitude of the received signal may be normalized and false detection may occur. Therefore, in the burst detection of Embodiment 2, a power threshold necessary to satisfy a desired SNR is calculated from the noise power and used for burst detection. As a result, even when the amplitude of the received signal is normalized when a burst signal is not being received, the SNR remains low, so that false detection can be prevented.

[0052] FIG. 7 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to 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.

[0053] Similar to Embodiment 1, as shown in FIG. 5(B), the normalization unit 871 normalizes the amplitude to 1 when the amplitude of the signal power of the received signal is less than 1.

[0054] FIG. 8(A) shows the spectrum of the received signal R with its amplitude normalized. As shown in FIG. 8(B), the LPF 872 has filter characteristics (signal extraction characteristics) indicated by the broken line in the figure, extracts the CW signal from the received signal with its amplitude normalized to suppress noise, and outputs it to the power calculation unit 873. Note that, when the assumed frequency offset of the received signal R is ±Δf, the filter bandwidth of the LPF 872 is usually 2Δf, which is twice the frequency offset Δf.

[0055] Similar to Embodiment 1, 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 the average value of the signal power calculated by the power calculation unit 873, and outputs it to the determination unit 875.

[0056] As shown in FIG. 8(C), the frequency shift unit 876 shifts the received signal R with its amplitude normalized 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 shift signal (third frequency shift signal) Rs. As shown by the broken line in FIG. 8(D), the LPF 877 has the same filter characteristics as the LPF 872, and extracts the noise signal from the frequency shift signal Rs.

[0057] 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 (hereinafter also referred to as noise power) input from the power calculation unit 878.

[0058] The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 879, and outputs it to the determination unit 875. Here, the SNR is obtained by the following formula (1). Therefore, as shown in the following formula (2), by multiplying the noise power by the target SNR (hereinafter referred to as SNR threshold), the power threshold required to obtain the SNR threshold is obtained. SNR = signal power / noise power ····· (1) Power threshold = SNR threshold × noise power ··· (2)

[0059] 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. When the average value of the signal power is equal to or greater than the power threshold, it determines that a CW signal has been detected, and outputs a detection flag to the timing control unit 88.

[0060] Next, the operation of the burst detection unit 87 in the above-described Embodiment 2 will be described based on the flowchart of FIG. 9.

[0061] When the reception signal of the data frame DF is input from the quadrature detection unit 86 to the burst detection unit 87, the normalization unit 871 normalizes the amplitude of the reception signal (step S1).

[0062] The LPF 872 of the burst detection unit 87 extracts a CW signal from the reception signal with the amplitude normalized and suppresses noise (step S2).

[0063] 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).

[0064] On the other hand, the frequency shift unit 876 of the burst detection unit 87 shifts the frequency to a position where the reception signal with the amplitude normalized does not fall within the bandwidth 2Δf of the LPF 877 to generate a frequency shift signal (step S5). The LPF 877 extracts a noise signal from the frequency shift signal (step S6).

[0065] 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 (noise power) input from the power calculation unit 878 (step S7).

[0066] 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 it to the determination unit 875 (step S8).

[0067] 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. When the average value of the signal power is equal to or greater than the power threshold, it determines that a CW signal has been detected, and outputs a detection flag to the timing control unit 88 (step S4).

[0068] As described above, according to the wireless communication system 1 according to the second embodiment, the power threshold required to satisfy the desired SNR is calculated from the noise power and used for burst detection. As a result, when a burst signal is not being received, even if the amplitude of the received signal is normalized, the SNR remains low, so false detection can be prevented. Also, similar to the first embodiment, a CW signal exceeding the power threshold can be detected without waiting for the adjustment of the reception level by the AGC, so the detection delay that occurred while waiting for the adjustment of the received signal level can be suppressed, and the throughput of burst communication can be improved.

[0069] (Embodiment 3) Next, a wireless communication system according to Embodiment 3 using the wireless reception apparatus and burst detection method of the present invention will be described. The wireless communication system according to Embodiment 3 shifts the frequency of the received signal to generate two types of frequency-shifted signals, extracts CW signals by an LPF for each of these two types of frequency-shifted signals, and compares the one with the larger signal power among the two extracted CW signals with the power threshold to perform burst detection, which is different from Embodiment 1. In the following, for the same configurations as those of the wireless communication system 1 according to Embodiment 1, the same reference numerals will be used and detailed descriptions will be omitted.

[0070] In the burst detection unit 87 of Embodiment 1, as a countermeasure against deterioration in burst detection accuracy when the CNR (Carrier-to-Noise Ratio) of the received signal is low, the received signal is input to an LPF to suppress noise. At this time, the narrower the bandwidth of the LPF, the higher the resistance to noise. On the other hand, when the bandwidth of the LPF is narrowed, the allowable frequency offset magnitude becomes smaller. Therefore, in the burst detection of this Embodiment 3, the frequency of the received signal is shifted to generate two types of frequency-shifted signals, and for each of these two types of frequency-shifted signals, a CW signal is extracted by an LPF with a narrowed bandwidth, so that it is possible to improve the noise resistance while maintaining the frequency offset tolerance equivalent to that of Embodiment 1.

[0071] FIG. 10 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of a wireless communication system 1 according to this 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.

[0072] Similar to Embodiment 1, as shown in FIG. 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.

[0073] FIG. 11(A) shows the spectrum of the received signal whose amplitude has been normalized. As shown in FIG. 11(B), the first frequency shift unit 876A generates a first frequency-shifted signal Rs1 by shifting the frequency of the received signal in the positive direction (first direction) by 1 / 2 of the assumed frequency offset Δf of the received signal.

[0074] Similarly, as shown in FIG. 11(D), the second frequency shift unit 876B generates a second frequency shift signal Rs2 in which the frequency of the received signal is shifted in the minus direction (the second direction opposite to the first direction) by 1 / 2 of the frequency offset Δf.

[0075] As shown in FIG. 11(C), the LPF 872A has filter characteristics (signal extraction characteristics) indicated by a broken line in the figure, extracts a CW signal from the first frequency shift signal Rs1 to suppress noise, and outputs it to the power calculation unit 873A. The filter characteristics of the LPF 872A are usually a bandwidth of 2Δf, which is twice the frequency offset Δf, when the assumed frequency offset of the received signal is ±Δf. However, in the second embodiment, Δf, which is half of 2Δf, is used.

[0076] As shown in FIG. 11(E), the LPF 872B has filter characteristics (signal extraction characteristics) indicated by a broken line in the figure, extracts a CW signal from the second frequency shift signal Rs2 to suppress noise, and outputs it to the power calculation unit 873B. The filter characteristics of the LPF 872B are the same as those of the LPF 872A, and its bandwidth is Δf.

[0077] Thus, in the third embodiment, the frequency of the received signal R is shifted to generate two types of frequency shift signals Rs1 and Rs2, and by extracting the CW signal from each of these two types of frequency shift signals Rs1 and Rs2 using an LPF, the bandwidth of the LPF can be made half of that in the conventional case (the first embodiment).

[0078] Similar to the first embodiment, the power calculation unit 873A calculates the signal power of the first frequency shift signal Rs1 input from the LPF 872A and outputs the calculated signal power to the averaging unit 874A. The averaging unit 874A obtains the average value of the signal power calculated by the power calculation unit 873A and outputs it to the power comparison unit 8711.

[0079] Similarly, the power calculation unit 873B calculates the signal power of the second frequency shift signal Rs2 input from the LPF 872B, and outputs the calculated signal power to the averaging unit 874B. The averaging unit 874B obtains the average value of the signal power calculated by the power calculation unit 873B, and outputs it to the power comparison unit 8711.

[0080] The power comparison unit 8711 compares the average value of the signal power of the first frequency shift signal Rs1 input from the averaging unit 874A with the average value of the signal power of the second frequency shift signal Rs2 input from the averaging unit 874B, and outputs the larger one to the determination unit 875. That is, when the frequency offset of the received signal R is in the minus direction, the average value of the signal power of the first frequency shift signal Rs1 is larger than the average value of the signal power of the second frequency shift signal Rs2. Also, when the frequency offset of the received signal R is in the plus direction, the average value of the signal power of the second frequency shift signal Rs2 is larger than the average value of the signal power of the first frequency shift signal Rs1.

[0081] The determination unit 875 compares the average value of the signal power input from the power comparison unit 8711 with a preset power threshold, and as shown in FIG. 5(B), 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.

[0082] Next, the operation of the burst detection unit 87 in the above-described Embodiment 3 will be described based on the flowchart of FIG. 12.

[0083] When the received signal of the data frame DF is input from the quadrature detection unit 86 to the burst detection unit 87, the normalization unit 871 normalizes the amplitude of the received signal (step S1).

[0084] The first frequency shift unit 876A generates a first frequency shift signal Rs1 in which the frequency of the received signal is shifted in the plus direction by 1 / 2 of the frequency offset Δf. Similarly, the second frequency shift unit 876B generates a second frequency shift signal Rs2 in which the frequency of the received signal is shifted in the minus direction by 1 / 2 of the frequency offset Δf (step S10).

[0085] The LPF 872A of the burst detection unit 87 extracts the CW signal from the first frequency shift signal Rs1 to suppress noise, and the LPF 872B extracts the CW signal from the second frequency shift signal Rs2 to suppress noise (step S2).

[0086] The power calculation unit 873A of the burst detection unit 87 calculates the signal power of the first frequency shift 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 shift 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).

[0087] The power comparison unit 8711 compares the average value of the signal power of the first frequency shift signal Rs1 input from the averaging unit 874A with the average value of the signal power of the second frequency shift signal Rs2 input from the averaging unit 874B, and outputs the larger one to the determination unit 875 (step S11).

[0088] The determination unit 875 compares the average value of the signal power input from the power comparison unit 8711 with the power threshold read from the memory and input. When the average value of the signal power is larger than the power threshold, it determines that the CW signal has been detected, and outputs a detection flag to the timing control unit 88 (step S4).

[0089] As described above, according to the wireless communication system 1 according to the third embodiment, the frequency of the received signal R is shifted to generate two types of frequency-shifted signals Rs1 and Rs2, and for each of these two types of frequency-shifted signals Rs1 and Rs2, the CW signal is extracted by the LPF, so that the bandwidth of the LPF can be made half of that in the conventional case (Embodiment 1). Therefore, it is possible to improve the noise tolerance while maintaining the frequency offset tolerance equivalent to that in Embodiment 1. Also, similar to Embodiment 1, since a CW signal exceeding the power threshold can be detected without waiting for the adjustment of the reception level by the AGC, it is possible to suppress the detection delay that occurred while waiting for the level adjustment of the received signal and improve the throughput of burst communication.

[0090] (Embodiment 4) Next, a wireless communication system according to Embodiment 4 using the wireless receiving apparatus and the burst detection method of the present invention will be described. The wireless communication system according to Embodiment 4 is a combination of Embodiment 1, Embodiment 2, and Embodiment 3. That is, the burst detection unit 87 of the present Embodiment 4 normalizes the amplitude of the received signal that has received the data frame DF, calculates the power threshold from the noise portion of the received signal whose amplitude has been normalized, shifts the frequency of the received signal to generate two types of frequency-shifted signals, performs extraction of the CW signal by the LPF for each of these two types of frequency-shifted signals, and compares the larger of the signal powers of the two types of extracted CW signals with the power threshold to perform burst detection. Hereinafter, for the same configurations as those of the wireless communication system 1 according to Embodiment 1, Embodiment 2, and Embodiment 3, the same reference numerals will be used and detailed description thereof will be omitted.

[0091] FIG. 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, a 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 determination unit (determination means) 875.

[0092] Similar to the first embodiment, as shown in FIG. 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.

[0093] FIG. 14(A) shows the spectrum of the received signal whose amplitude is normalized. As shown in FIG. 14(B), the first frequency shift unit 876A generates a first frequency shift signal Rs1 in which the frequency of the received signal is shifted in the positive direction (first direction) by 1 / 2 of the assumed frequency offset Δf of the received signal.

[0094] Similarly, as shown in FIG. 14(D), the second frequency shift unit 876B generates a second frequency shift signal Rs2 in which the frequency of the received signal is shifted in the negative direction (second direction opposite to the first direction) by 1 / 2 of the frequency offset Δf.

[0095] As shown in FIG. 14(C), the LPF 872A has filter characteristics (signal extraction characteristics) indicated by a broken line in the figure, extracts a CW signal from the first frequency shift signal Rs1 to suppress noise, and outputs it to the power calculation unit 873A.

[0096] As shown in Fig. 14(E), LPF872B has filter characteristics (signal extraction characteristics) indicated by the dashed line in the figure, extracts a CW signal from the second frequency shift signal Rs2 to suppress noise, and outputs it to the power calculation unit 873B. The filter characteristics of LPF872B are the same as those of LPF872A, and its bandwidth is Δf.

[0097] The power calculation unit 873A calculates the signal power of the first frequency shift signal Rs1 input from LPF872A, and outputs the calculated signal power to the averaging unit 874A. The averaging unit 874A obtains the average value of the signal power calculated by the power calculation unit 873A, and outputs it to the power comparison unit 8711.

[0098] Similarly to the above, the power calculation unit 873B calculates the signal power of the second frequency shift signal Rs2 input from LPF872B, and outputs the calculated signal power to the averaging unit 874B. The averaging unit 874B obtains the average value of the signal power calculated by the power calculation unit 873B, and outputs it to the power comparison unit 8711.

[0099] The power comparison unit 8711 compares the average value of the signal power of the first frequency shift signal Rs1 input from the averaging unit 874A with the average value of the signal power of the second frequency shift signal Rs2 input from the averaging unit 874B, and outputs the larger one to the determination unit 875.

[0100] As shown in Fig. 14(F), the third frequency shift unit 876 shifts the received signal R with normalized amplitude to a frequency that does not fall within the bandwidth Δf of LPF877, for example, -fsym / 4 (fsym: symbol frequency), to generate a third frequency shift signal Rs. As shown by the dashed line in Fig. 14(G), LPF877 has the same filter characteristics as LPF872A and 872B, and extracts a noise signal from the frequency shift signal Rs.

[0101] 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).

[0102] The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 879 and outputs it to the determination unit 875, in the same manner as in the second embodiment.

[0103] The determination 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. When the average value of the signal power is equal to or greater than the power threshold, it determines that a CW signal has been detected, and outputs a detection flag to the timing control unit 88.

[0104] FIG. 15 is a flowchart showing the processing procedure of the burst detection unit 87 in the fourth embodiment described above. The flowchart shown in FIG. 15 is a combination of the processing procedures of the first embodiment shown in FIG. 6, the processing procedures of the second embodiment shown in FIG. 9, and the processing procedures of the third embodiment shown in FIG. 12. Since the same processing is denoted by the same reference numerals, detailed description thereof is omitted.

[0105] As described above, according to the wireless communication system 1 according to the fourth embodiment, similar to the first embodiment, a CW signal exceeding the power threshold can be detected without waiting for the adjustment of the reception level by the AGC. Therefore, it is possible to suppress the detection delay that occurred while waiting for the level adjustment of the received signal and improve the throughput of burst communication.

[0106] Also, according to the wireless communication system 1 according to the fourth embodiment, similar to the second embodiment, the power threshold required to satisfy the desired SNR is calculated from the noise power and used for burst detection. As a result, even when the amplitude of the received signal is normalized when no burst signal is being received, the SNR remains low, so false detection can be prevented.

[0107] Furthermore, according to the wireless communication system 1 according to the fourth embodiment, similar to the third embodiment, the frequency of the received signal R is shifted to generate two types of frequency-shifted signals Rs1 and Rs2, and for each of these two types of frequency-shifted signals Rs1 and Rs2, the CW signal is extracted by the LPF, so that the bandwidth of the LPF can be made half of that in the conventional case (Embodiment 1). Therefore, it is possible to improve the noise tolerance while maintaining the frequency offset tolerance equivalent to that in Embodiment 1.

[0108] As described above, the embodiments of the present invention have been explained. However, the specific configuration is not limited to the above embodiments, and even if there are design changes and the like within the scope not departing from the gist of the present invention, they are included in the present invention.

[0109] For example, in the above embodiment, the CW signal is used as the preamble signal for burst detection. However, signals other than the CW signal, such as alternating signals, may be used. In this case, since the CW signal can be omitted from the preamble signal, the data amount of the preamble signal becomes smaller and the throughput is improved.

Explanation of Reference Numerals

[0110] 1 Wireless communication system 2 Wireless communication device 5 Transmission unit 8 Receiver (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 unit 875 Determination unit (determination means) 876 Frequency shift unit (third frequency shift means) 876A First frequency shift section (first frequency shift means) 876B Second frequency shift section (second frequency shift means) 877 LPF (third signal extraction means) 878 Power calculation section (third power calculation means) 8710 Power threshold calculation section (power threshold calculation means) 8711 Power comparison section (power comparison means) DF Data frame

Claims

【Claim 1】 Receiving means for receiving a data frame in which a preamble signal is added to the head of a data signal and burst-transmitted, and outputting a received signal; Normalizing means for normalizing the amplitude to 1 when the amplitude of the received signal after demodulation is less than 1; 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, comprising: The burst detection means: First frequency shift means for shifting the frequency of the received signal whose amplitude has been normalized in a first direction to generate a first frequency-shifted signal; First signal extraction means for extracting the preamble signal from the first frequency-shifted signal; First power calculation means for calculating the first signal power which is the signal power of the preamble signal extracted from the first frequency-shifted signal and obtaining its average value; Second frequency shift means for shifting the frequency of the received signal whose amplitude has been normalized in a second direction opposite to the first direction to generate a second frequency-shifted signal; Second signal extraction means having the same signal extraction characteristics as the first signal extraction means and extracting the preamble signal from the second frequency-shifted signal; Second power calculation means for calculating the second signal power which is the signal power of the preamble signal extracted from the second frequency-shifted signal and obtaining its average value; Power comparison means for comparing the average value of the first signal power and the average value of the second signal power and outputting the larger one of them; 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 preamble signal has been detected when the average value of the signal power is greater than the power threshold; Third frequency shift means for shifting the frequency of the received signal whose amplitude has been normalized so as not to fall within the range of the signal extraction characteristics of the first signal extraction means to generate a third frequency-shifted signal; 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 the signal power of the noise signal and obtaining its average value; Power threshold calculation means for calculating the power threshold based on the average value of the signal power of the noise signal; A wireless receiving apparatus, characterized by comprising the above.

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