JP7558630B1 - Radio receiving device and burst detection method - Google Patents

Abstract

A wireless receiving device and a burst detection method are provided that improve noise resistance while maintaining frequency offset resistance in burst detection.
[Solution] In a wireless communication device, a burst detection unit 87 includes a first frequency shift unit that shifts the frequency of a received signal in a first direction to generate a first frequency-shifted signal, an LPF that extracts a preamble signal from the first frequency-shifted signal, a first power calculation unit that calculates signal power of the preamble signal extracted from the first frequency-shifted signal and obtains its average value, a second frequency shift unit that shifts the frequency of the received signal in a second direction opposite to the first direction to generate a second frequency-shifted signal, an LPF having the same signal extraction characteristics as the LPF and extracts the preamble signal from the second frequency-shifted signal, and a second power calculation unit that calculates signal power of the preamble signal extracted from the second frequency-shifted signal and obtains its average value.
[Selected figure] Figure 5

Description

The present invention relates to a wireless receiving device and a burst detection method for detecting data frames transmitted in bursts.

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 the wireless receiving device does not know when it will receive the signal. For this reason, wireless receiving devices that perform burst communication perform burst detection to detect the burst-transmitted signal (see, for example, Patent Document 1).

As shown in Figure 11 (A), a data frame used in burst communication consists 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.

As shown in FIG. 11(B), burst detection involves an LPF (Low-pass filter) 100 extracting a CW signal from the received signal output upon receiving a data frame and suppressing noise, a power calculation unit 101 calculating the signal power of the CW signal, and an averaging unit 102 calculating the average value of the signal power. As shown in FIG. 11(C), 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.

JP 2000-134274 A

In conventional burst detection, the received signal is input into an LPF to suppress noise as a measure to prevent 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 resistance to noise becomes, but on the other hand, narrowing the bandwidth of the LPF reduces the magnitude of the tolerable frequency offset.

The present invention aims to provide a wireless receiving device and a burst detection method that can improve noise resistance while maintaining frequency offset resistance in burst detection.

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, and a burst detection means for detecting the arrival of the data frame by detecting the preamble signal from the received signal, the burst detection means including a first frequency shifting means for shifting the frequency of the received signal in a first direction to generate a first frequency-shifted signal, a first signal extraction means for extracting the preamble signal from the first frequency-shifted signal, a first power calculation means for calculating a first signal power, which is the signal power of the preamble signal extracted from the first frequency-shifted signal, and calculating the average value of the first signal power, and a second power calculation means for shifting the frequency of the received signal in a direction opposite to the first direction. This wireless receiving device is characterized by comprising: a second frequency shifting means for shifting in a second direction to generate a second frequency-shifted signal; a 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; a second power calculation means for calculating a second signal power, which is the signal power of the preamble signal extracted from the second frequency-shifted signal, and obtaining its average value; a power comparison means for comparing the average value of the first signal power with the average value of the second signal power and outputting the larger of the two; and a determination means for comparing the average value of the signal power output from the power comparison means with a power threshold and determining that the preamble signal has been detected if the average value of the signal power is greater than the power threshold.

The invention described in claim 2 is characterized in that, in the wireless receiving apparatus described in claim 1, the burst detection means includes normalization means for normalizing an amplitude of the received signal prior to generating the first frequency shifted signal and prior to generating the second frequency shifted signal .

The invention of claim 3 is characterized in that in the wireless receiving device of claim 2, the burst detection means comprises a third frequency shifting means for shifting the frequency of the amplitude-normalized received signal so that it does not fall within the range of the signal extraction characteristics of the first signal extraction 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 determining its average value, 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 invention described in claim 4 is a burst detection method for detecting the arrival of a data frame transmitted in a burst, comprising: receiving the data frame, which is transmitted in a burst with a preamble signal added to the beginning of the data signal; outputting a received signal; shifting the frequency of the received signal in a first direction to generate a first frequency-shifted signal; shifting the frequency of the received signal in a second direction opposite to the first direction to generate a second frequency-shifted signal; extracting the preamble signal from the first frequency-shifted signal; extracting the preamble signal from the second frequency-shifted signal; The method is characterized in that it calculates a first signal power, which is the signal power of the preamble signal extracted from the first frequency shift signal, and calculates its average value, and calculates a second signal power, which is the signal power of the preamble signal extracted from the second frequency shift signal, and calculates its average value, compares the average value of the first signal power with the average value of the second signal power, outputs the larger of the two, compares the output average value of the signal power with a power threshold, and if the average value of the signal power is greater than the power threshold, determines that the preamble signal has been detected, and detects the arrival of the data frame.

According to the inventions described in claims 1 and 4, the frequency of the received signal is shifted to generate two types of frequency-shifted signals, and the preamble signal is extracted from each of the two types of frequency-shifted signals by the signal extraction means, thereby narrowing the bandwidth of the signal extraction means. Therefore, it is possible to improve noise resistance while maintaining the same frequency offset resistance as in the past. In addition, since burst detection is performed by comparing the average signal power of the received signal with the power threshold, it is possible to perform burst detection with high accuracy by setting the power threshold to a value that obtains, for example, a desired SNR (Signal-to-Noise Ratio).

In addition, according to the invention described in claim 2, the level adjustment by AGC (Automatic Gain Control), which was conventionally performed when the signal level of the received signal was low, is no longer necessary, so it is possible to suppress detection delays and improve the throughput of frame data.

Furthermore, according to the invention described in claim 3, the power threshold required to achieve the desired SNR is calculated from the noise power and used for burst detection, so that even if the amplitude of the received signal is normalized when no burst signal is being received, the SNR remains low, making it possible to prevent erroneous detection.

1 is a diagram showing a schematic configuration of a wireless communication system according to a first embodiment of the present invention; 2 is a functional block diagram showing a schematic configuration of a transmission unit of the wireless communication device shown in FIG. 1 . 2 is a functional block diagram showing a schematic configuration of a receiving system of the wireless communication device shown in FIG. 1 . 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. 1 is a functional block diagram showing a schematic configuration of a burst detection unit according to a first embodiment of the present invention; 6 is a diagram showing a frequency spectrum of a received signal when a burst is detected by the burst detection unit shown in FIG. 5 . 6 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 5 . 10 is a functional block diagram showing a schematic configuration of a burst detection unit according to a second embodiment of the present invention; FIG. 9 is a diagram showing a frequency spectrum of a received signal when a burst is detected by the burst detection unit shown in FIG. 8 . 9 is a flowchart showing a procedure of burst detection by the burst detection unit shown in FIG. 8 . 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.

The present invention will be described below based on the illustrated embodiment. Note that the following describes the characteristic configuration of the present invention, and omits a description of the conventional mechanism for wireless communication.

(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 the wireless communication transmitting and receiving stations that make up 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.

First, in this embodiment, we will explain the general configuration of the wireless communication device 2, which corresponds to the wireless receiving device of the present invention.

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

Here, the wireless communication device 2 is a device equipped with a transmission mechanism and a reception mechanism for transmitting and receiving. In the following description, the wireless communication device 2 when performing processing related to transmission using the transmission mechanism is referred to as the "transmission side," and the wireless communication device 2 when performing processing related to reception using the reception mechanism is referred to as the "reception side."

The interface unit 5 mainly comprises a data circuit-terminating device 51 (including devices called data communication devices and data circuit devices). The interface unit 5 receives input of transmission data for communication, and outputs this transmission data to the transmission unit 6 via the data circuit-terminating device 51.

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.

The transmitter 6 converts the digitally modulated data frame into an analog signal, converts the frequency of the signal to 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).

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) via the wireless line 4 to the antenna 3 of the wireless communication device 2 (in other words, the receiving side in this communication), the antenna 3 converts the received radio waves into an electrical signal (received signal) and outputs it.

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

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 whose phases are mutually orthogonal. In the following explanation, the in-phase component and the quadrature component will not be distinguished from each other except when it is necessary to focus on each of them separately, and will be explained as if both are common. In the drawings, the in-phase component signal and the quadrature component signal are represented by a single signal line.

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, the receiving unit 8 performs frequency offset correction, clock error correction, phase correction, etc. on the received data frame. The receiving unit 8 then separates the preamble signal from the data frame that has been subjected to various corrections, performs demapping processing on the data signal to generate transmission data, and outputs it to the interface unit 5.

The wireless communication system according to the first embodiment 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 with a narrower bandwidth, and performs burst detection by comparing the one of the two extracted CW signals with the greater signal power with a power threshold. This makes it possible to improve noise resistance while maintaining the same frequency offset resistance as before.

Figure 2 is a functional block diagram showing the 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.

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 using the so-called first-in, first-out method.

The mapping unit 62 performs mapping processing on the binary data string of the transmission data so that it has a predetermined signal point arrangement, generates a data signal consisting of a symbol string, and outputs it to the combining unit 64. The CW signal generating 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 generating unit 63b generates an alternating signal used to correct clock errors, and outputs it to the combining unit 64.

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. 4A) and outputs it to the transmission ROF 65. The transmission 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.

The quadrature modulation unit 66 superimposes a carrier signal of a predetermined frequency onto 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.

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.

The power amplifier 610 amplifies the transmission signal that has been 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 radio waves 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.

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

The antenna 3 converts the received radio waves into an electrical signal (received signal) and outputs it to the channel filter 81. A 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 with 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.

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

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 an in-phase component (Ich) baseband signal and a quadrature component (Qch) baseband signal whose phases are mutually orthogonal.

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, which has received the detection flag, outputs an enable signal to each module to cause it to process the data frame DF.

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 it 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 it to the symbol recovery unit 811.

The symbol recovery unit 811 corrects the clock error using the alternating signal included in the data frame DF of the baseband signal input from the reception ROF 810, and outputs the result 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 result to the separation unit 813.

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

Fig. 5 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the first 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, and a determination unit (determination means) 875.

As shown in FIG. 4B, when the amplitude of the signal power of the received signal is less than 1, the normalization unit 871 may normalize the amplitude to 1. In this embodiment, an example of normalizing the amplitude will be described.

In conventional burst detection, when the signal power of the received signal is lower than the rated power, the signal power of the received signal is amplified by AGC before burst detection is performed. Therefore, when the signal power of the received signal is lower than the rated power, it takes time for the signal power of the CW signal to exceed the power threshold, as shown in FIG. 11(C), and a delay occurs in burst detection, resulting in a decrease in throughput. Therefore, in burst detection according to this 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 a preamble signal has been detected. This makes it possible to detect the CW signal without waiting for the completion of level adjustment by AGC, which was previously performed when the signal power of the received signal is lower than the rated power, thereby reducing detection delays and improving frame data throughput.

Figure 6 (A) shows the spectrum of the received signal with normalized amplitude. The first frequency shifter 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 the expected frequency offset Δf of the received signal, as shown in Figure 6 (B).

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. 6(D).

As shown in FIG. 6(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 shift 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 this embodiment 1, a Δf that is half of 2Δf is used.

As shown in FIG. 6(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 shift 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.

In this way, in this embodiment 1, the frequency of the received signal R is shifted to generate two types of frequency-shifted signals Rs1 and Rs2, and the CW signal is extracted from each of these two types of frequency-shifted signals Rs1 and Rs2 using an LPF, thereby making it possible to reduce the bandwidth of the LPF to half that of the conventional method.

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 finds the average value of the signal power calculated by the power calculation unit 873A and outputs it to the power comparison unit 8711.

Similar to the above, 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 finds the average value of the signal power calculated by the power calculation unit 873B, and outputs it to the power comparison unit 8711.

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 determination 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.

The determination unit 875 compares the average signal power input from the power comparison unit 8711 with a preset power threshold, and determines that a CW signal has been detected when the average signal power is equal to or greater than the power threshold, as shown in FIG. 4(B).

Next, the operation of the burst detection unit 87 in the above-mentioned embodiment 1 will be explained based on the flowchart in FIG.

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).

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 by 1/2 the frequency offset Δf. Similarly, the second frequency shift unit 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 S2).

The LPF 872A of the burst detection unit 87 extracts a CW signal from the first frequency shift signal Rs1 and suppresses noise, and the LPF 872B extracts a CW signal from the second frequency shift signal Rs2 and suppresses noise (step S3).

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 S4).

The power comparison unit 8711 compares the average signal power of the first frequency shift signal Rs1 input from the averaging unit 874A with the average 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 S5).

The determination unit 875 compares the average signal power input from the power comparison unit 8711 with the power threshold read from memory and input, and determines that a CW signal has been detected if the average signal power is greater than the power threshold, and outputs a detection flag to the timing control unit 88 (step S6).

As described above, according to the wireless communication system 1 of the first embodiment, the frequency of the received signal R is shifted to generate two types of frequency-shifted signals Rs1 and Rs2, and the LPF extracts the CW signal for each of the two types of frequency-shifted signals Rs1 and Rs2, thereby making it possible to reduce the bandwidth of the LPF by half compared to the conventional method. Therefore, it is possible to improve the noise resistance while maintaining the same frequency offset resistance as the conventional method. In addition, when the amplitude of the received signal is normalized, a CW signal exceeding the power threshold can be detected without waiting for the AGC to adjust the reception level, 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.

(Embodiment 2)
Next, a wireless communication system according to a second embodiment of the present invention using a wireless receiving device and a burst detection method will be described. The wireless communication system according to the second embodiment differs from the first embodiment in that a power threshold is calculated from noise power when burst detection is performed from a received signal whose amplitude has been normalized. 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.

In the burst detection unit 87 of the first embodiment, the amplitude of the received signal is normalized when a burst signal is not being received, which may result in erroneous detection. Therefore, in the burst detection of the second embodiment, a power threshold required to achieve 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 a burst signal is not being received, the SNR remains low, making it possible to prevent erroneous detection.

Figure 8 is a functional block diagram showing a schematic configuration of a burst detection unit 87 of the wireless communication system 1 according to the second 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). 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.

As in the first embodiment, the normalization unit 871 normalizes the amplitude to 1 when the amplitude of the signal power of the received signal is less than 1, as shown in FIG. 4(B).

Figure 9 (A) shows the spectrum of the received signal with normalized amplitude. The first frequency shifter 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 the expected frequency offset Δf of the received signal, as shown in Figure 9 (B).

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. 9(D).

As shown in FIG. 9(C), the LPF 872A has a filter characteristic (signal extraction characteristic) indicated by the dashed line in the figure, extracts a CW signal from the first frequency shift signal Rs1, suppresses noise, and outputs the signal to the power calculation unit 873A.

As shown in FIG. 9(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 shift 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.

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 finds the average value of the signal power calculated by the power calculation unit 873A and outputs it to the power comparison unit 8711.

Similar to the above, 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 finds the average value of the signal power calculated by the power calculation unit 873B, and outputs it to the power comparison unit 8711.

The power comparison unit 8711 compares the average signal power of the first frequency shift signal Rs1 input from the averaging unit 874A with the average 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.

As shown in FIG. 9(F), the third frequency shifter 876 shifts 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), to generate a third frequency-shifted signal Rs. As shown by the dashed line in FIG. 9(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.

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).

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), the 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)

The determination unit 875 compares the average signal power input from the power comparison unit 8711 with the power threshold input from the power threshold calculation unit 8710, and determines that a CW signal has been detected if the average signal power is equal to or greater than the power threshold, and outputs a detection flag to the timing control unit 88.

Next, the operation of the burst detection unit 87 in the second embodiment will be explained with reference to the flowchart in FIG.

In the second embodiment, steps S1 to S5 are performed in the same manner as in the first embodiment, but the third 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 to generate a frequency-shifted signal (step S7). The LPF 877 extracts a noise signal from the frequency-shifted signal (step S8).

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 S9).

The power threshold calculation unit 8710 calculates a power threshold based on the noise power input from the averaging unit 879 and the desired SNR threshold, and outputs it to the determination unit 875 (step S10).

The determination unit 875 compares the average signal power input from the power comparison unit 8711 with the power threshold input from the power threshold calculation unit 8710, and determines that a CW signal has been detected if the average signal power is equal to or greater than the power threshold, and outputs a detection flag to the timing control unit 88 (step S6).

As described above, according to the wireless communication system 1 of the second embodiment, the power threshold required to achieve 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 being received.

Furthermore, according to the wireless communication system 1 of the second embodiment, as in the first embodiment, a CW signal exceeding the power threshold can be detected without waiting for the AGC to adjust the reception level, so that it is possible to improve the throughput of burst communication by suppressing the detection delay that occurs while waiting for the reception signal level to be adjusted.

Furthermore, according to the wireless communication system 1 of the second embodiment, as in the first embodiment, the frequency of the received signal R is shifted to generate two types of frequency-shifted signals Rs1 and Rs2, and the LPF is used to extract the CW signal from each of the two types of frequency-shifted signals Rs1 and Rs2. This makes it possible to reduce the bandwidth of the LPF by half compared to the conventional case. Therefore, it is possible to improve noise resistance while maintaining the same frequency offset resistance as the conventional case.

The above describes an embodiment of the present invention, but the specific configuration is not limited to the above embodiment, and even if there are design changes that do not deviate from the gist of the present invention, they are included in the present invention.

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 throughput is improved.

REFERENCE SIGNS LIST 1 Wireless communication system 2 Wireless communication device 5 Transmitter 8 Receiving unit (receiving means)
87 Burst detection unit (burst detection means)
871 Normalization unit (normalization means)
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)
874A, 874B, 879 Averaging section 875 Judgment section (judgment means)
876 Third 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 (4)

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 burst detection means for detecting the arrival of the data frame by detecting the preamble signal from the received signal,
The burst detection means includes:
a first frequency shifting means for shifting the frequency of the received signal in a first direction to generate a first frequency shifted signal;
a first signal extraction means for extracting the preamble signal from the first frequency shifted signal;
a first power calculation means for calculating a first signal power, which is the signal power of the preamble signal extracted from the first frequency shift signal, and calculating an average value of the first signal power;
second frequency shifting means for shifting the frequency of the received signal in a second direction opposite to the first direction to generate a second frequency-shifted signal;
a 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;
a second power calculation means for calculating a second signal power, which is the signal power of the preamble signal extracted from the second frequency shift signal, and calculating an average value thereof;
power comparison means for comparing the average value of the first signal power with the average value of the second signal power and outputting the larger of the two;
a determination means for comparing an average value of the signal power output from the power comparison means with a power threshold, and determining that the preamble signal has been detected when the average value of the signal power is greater than the power threshold;
A wireless receiving device comprising: The burst detection means includes:
Prior to generating the first frequency shifted signal and prior to generating the second frequency shifted signal,
2. The radio receiving apparatus according to claim 1, further comprising: a normalization unit for normalizing the amplitude of the received signal. The burst detection means includes:
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;
3. The wireless receiving device according to claim 2, further comprising: 1. A burst detection method for detecting the arrival of a burst-transmitted data frame, comprising:
receiving the data frame which has been burst-transmitted with a preamble signal added to the beginning of the data signal, and outputting the received signal;
shifting the frequency of the received signal in a first direction to generate a first frequency-shifted signal and shifting the frequency of the received signal in a second direction opposite the first direction to generate a second frequency-shifted signal;
extracting the preamble signal from the first frequency shifted signal and extracting the preamble signal from the second frequency shifted signal;
calculating a first signal power, which is the signal power of the preamble signal extracted from the first frequency shift signal, and calculating an average value thereof, and calculating a second signal power, which is the signal power of the preamble signal extracted from the second frequency shift signal, and calculating an average value thereof;
comparing the average value of the first signal power with the average value of the second signal power and outputting the larger one;
comparing an average value of the output signal power with a power threshold, and determining that the preamble signal has been detected if the average value of the signal power is greater than the power threshold, thereby detecting the arrival of the data frame;
13. A burst detection method comprising: