Reception device, reception method, control circuit, and storage medium

Abstract

A reception device (3) comprises: a correlation coefficient calculation processing unit (41) that calculates, for each frequency hopping channel and for each correlation observation period shorter than a symbol period of a reception signal, a correlation coefficient between the reception signal and a known signal; an inter-observation period phase-difference calculation unit (42) that calculates, on the basis of the correlation coefficient, a first average phase difference that is the average of the phase differences of correlation coefficients between different correlation observation periods; an inter-channel phase-difference calculation unit (43) that calculates, on the basis of the correlation coefficient, a second average phase difference that is the average of the phase differences of correlation coefficients between different frequency hopping channels; and a determination unit (47) that determines a head timing of a spread code on the basis of the average power in the symbol duration of the first average phase difference and the average power in the symbol duration of the second average phase difference.

Description

Receiving device, receiving method, control circuit and storage medium

[0001] The present disclosure relates to a receiving device, a receiving method, a control circuit, and a storage medium used in spread spectrum communication.

[0002] Spread spectrum is a technology for spreading wireless communication signals over a wide frequency band, and well-known examples include frequency hopping, which is used in the Bluetooth (registered trademark) standard, and direct spread spectrum, which is used in the wireless LAN (Local Area Network) standard (IEEE (Institute of Electrical and Electronics Engineers) 802.11b). Spread spectrum can reduce the effects of interference by spreading signals over a wide band and distributing the spectrum to a specific band, and is also used for long-distance wireless communication.

[0003] In direct spread spectrum communications, a sequence with good autocorrelation, such as a pseudo random noise (PN) code, is generally used as the spreading code. Specifically, a transmitter constituting a communication device on the sending side of direct spread spectrum communications multiplies a transmission signal by a spreading code to generate and transmit a spread spectrum signal with a wider bandwidth. A receiver constituting a communication device on the receiving side performs despreading by multiplying the received spread spectrum signal by the complex conjugate of the same spreading code as the transmitter, restoring the received spread spectrum signal to its original narrowband signal before spreading, and then demodulating it. Therefore, at the start of communications, the receiver must perform initial synchronization acquisition to synchronize with the spreading code included in the received signal. Initial synchronization acquisition involves calculating the correlation between the received signal and the same spreading code as the transmitter, detecting the correlation peak, determining the start timing of the spreading code, and establishing synchronization.

[0004] However, in spread spectrum, the higher the spreading rate, the lower the signal power density per time and frequency, i.e., the lower the SNR (Signal to Noise power Ratio), making it more difficult to synchronize the spreading code. In general, the SNR is improved by extending the observation time for calculating the correlation between the received signal and the spreading code, thereby achieving synchronization of the spreading code.

[0005] However, in a transmission path where a frequency offset exists, if the observation time for calculating the correlation between the received signal and the spreading code is extended, the correlation peak will decrease due to the influence of the frequency offset, resulting in a problem of degraded synchronization performance. To address this problem, for example, the initial synchronization acquisition method described in Patent Document 1 divides the received signal into multiple blocks at time intervals that reduce the influence of transmission path fluctuations, calculates the correlation with the spreading code for each block, and detects the peak of the average correlation power obtained by tallying the correlation power for each block, thereby mitigating the degradation of synchronization performance when a frequency offset exists in the received signal.

[0006] Furthermore, spread spectrum technologies that are resistant to frequency-selective fading environments are being studied. For example, the spread spectrum method described in Non-Patent Document 1 uses CHYB-DS-FFH CDMA (Coherent Hybrid-Direct Sequence-Fast Frequency Hopping Code Division Multiple Access), which combines coherent fast frequency hopping and direct sequence spreading, to improve frequency utilization efficiency and reception performance under frequency-selective transmission paths. The spread spectrum method described in Non-Patent Document 1 distributes a direct spread spectrum signal across multiple carrier frequencies by frequency hopping the signal at high speed within a symbol time, and transmits the signal in a spread-spectrum manner. The spread bandwidth can be expanded by increasing the spreading rate of the direct spread spectrum and the number of frequency hopping channels.

[0007] Japanese Patent Application Laid-Open No. 2003-152600

[0008] Shigeru Tomisato, Kazuhiko Fukawa, and Hiroshi Suzuki, "Coherent Hybrid DS-FFH CDMA System - Basic Transmission Characteristics in Mobile Radio," Transactions of the Institute of Electronics, Information and Communications Technology (B-II), Vol. J77-B-II, No. 1, pp. 1-10 (January 1994)

[0009] To achieve the communication described in Non-Patent Document 1, i.e., to achieve spread spectrum transmission by rapidly frequency hopping a direct spread spectrum signal within a symbol time, the receiver must simultaneously synchronize with the frequency hopping (hereinafter referred to as frequency hopping synchronization) and the spreading code of the direct spread spectrum. However, as the spreading factor of the direct spread spectrum signal and the number of frequency hopping channels increase, the signal power density per frequency carrier decreases and the frequency hopping pattern becomes more complex. Furthermore, if a frequency offset exists between the transmitter and the receiver, the signal detection performance of the receiver deteriorates, increasing the time required for synchronization processing. Furthermore, while the technology described in Patent Document 1 can mitigate the degradation of synchronization performance when a frequency offset exists in the received signal, there is a problem in that if the signal power density within the block decreases due to fast frequency hopping, the signal detection performance deteriorates and the time required for synchronization processing increases significantly.

[0010] The present disclosure has been made in view of the above, and aims to provide a receiving device capable of improving the performance of initial synchronization acquisition for receiving a signal generated by frequency hopping a direct spread spectrum signal.

[0011] In order to solve the above-mentioned problems and achieve the object, the present disclosure provides a receiving device that receives a signal that has been spectrum spread by applying direct spectrum spreading using a spreading code and frequency hopping, the receiving device comprising: a correlation coefficient calculation processing unit that calculates a correlation coefficient between a received signal and a known signal for each frequency hopping channel and for each correlation observation period that is shorter than the symbol period of the received signal; an observation period phase difference calculation unit that calculates a first average phase difference that is the average of the phase differences of the correlation coefficients between different correlation observation periods based on the correlation coefficient; an inter-channel phase difference calculation unit that calculates a second average phase difference that is the average of the phase differences of the correlation coefficients between different frequency hopping channels based on the correlation coefficient; and a determination unit that determines the start timing of the spreading code based on the power of the average value of the first average phase difference within a symbol time and the power of the average value of the second average phase difference within a symbol time.

[0012] The present disclosure provides an advantage in that it is possible to realize a receiving device capable of improving the performance of initial synchronization acquisition for receiving a signal generated by frequency hopping a direct spread spectrum signal.

[0013] FIG. 1 is a diagram showing a configuration example of a transmitting device according to a first embodiment; FIG. 2 is a diagram for explaining frequency hopping processing of spread signals in a transmission frequency conversion unit of a transmitting device according to a first embodiment; FIG. 3 is a diagram showing a configuration example of a receiving device according to a first embodiment; FIG. 4 is a diagram showing a configuration example of an initial synchronization acquisition unit provided in a receiving device according to a first embodiment; FIG. 5 is a diagram for explaining a correlation coefficient observation period in a correlation coefficient calculation unit constituting an initial synchronization acquisition unit of a receiving device according to a first embodiment;

[0014] Hereinafter, a receiving device, a receiving method, a control circuit, and a storage medium according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0015] First Embodiment This embodiment relates to a transmitter and a receiver constituting a communication device applied to a spread spectrum communication system that transmits and receives a direct spread spectrum signal by distributing it among a plurality of carrier frequencies, and will be described with reference to FIGS. 1 to 7.

[0016] Fig. 1 is a diagram showing an example of the configuration of a transmitting device 1 according to a first embodiment. As shown in Fig. 1, the transmitting device 1 according to the first embodiment includes a modulating unit 11, a spreading unit 12, a transmitting waveform shaping unit 13, a transmitting frequency converting unit 14, a digital-to-analog converting unit 15, a transmitting high frequency unit 16, and a transmitting antenna 17. A transmitting bit sequence 10 is input to the modulating unit 11.

[0017] The transmission bit sequence 10 input to the modulation section 11 is transmission information bits or a bit sequence obtained by encoding the transmission information bits.

[0018] The modulation unit 11 performs primary modulation on the transmission bit sequence 10 to convert it into a data symbol sequence. Examples of modulation methods used in the primary modulation include PSK (Phase Shift Keying) and FSK (Frequency Shift Keying). However, the modulation methods applied in this embodiment are not limited to these. The data symbol sequence output by the modulation unit 11 is input to the spreading unit 12.

[0019] The spreading unit 12 multiplies the spreading code by the data symbol sequence output from the modulation unit 11 to generate a spread signal. The spreading code is a sequence with a chip period for spreading the data symbol sequence, which is a modulated signal, and can be a code with good autocorrelation, such as a PN code, a GOLD code, or a phase rotation sequence in which the frequency changes over time but the amplitude remains constant. Here, for simplicity of explanation, the number of chips in the spread signal per symbol is assumed to be 128.

[0020] The transmission waveform shaping unit 13 upsamples the spread signal output from the spreading unit 12 and limits the band of the spread signal spectrum.

[0021] The transmission frequency converter 14 generates an intermediate frequency (IF) signal for each frequency hopping period, in accordance with a predetermined frequency hopping pattern, by converting the carrier frequency of the spread spectrum signal after transmission waveform shaping output from the transmission waveform shaping unit 13. For simplicity of explanation, the number of frequency channels for frequency hopping (hereinafter referred to as frequency hopping channels) is assumed to be eight. The frequency hopping period is assumed to be a one-chip period, assuming high-speed frequency hopping shorter than one symbol.

[0022] FIG. 2 is a diagram illustrating the frequency hopping process of a spread signal in the transmission frequency converter 14 of the transmitter 1 according to the first embodiment. In FIG. 2, the horizontal axis represents time. One square represents one chip period, and the chip number 200 of the spread signal is written below. Chips with chip numbers 200 of 0 to 127 represent symbol periods 201, during which one symbol is transmitted. Chips with chip numbers 200 of 128 and above transmit the next symbol. The symbol period 201 is also referred to as symbol time. Also, in FIG. 2, the vertical axis represents frequency. One square represents the frequency interval of frequency hopping channels 202, and the frequency hopping channel number 203 is written on the left side. In frequency hopping, the transmitter 1 according to the present embodiment uses eight channels with frequency hopping channel numbers 203 of 0 to 7, and selects one of these channels in each chip period. The transmission frequency converter 14 frequency-converts the spread signal to a predetermined frequency hopping channel in synchronization with the chip period according to a predetermined frequency hopping pattern. For example, at the time when the chip number is 128, a spread spectrum signal is assigned to frequency hopping channel 0 of hatched chip signal 204, and no spread spectrum signal is assigned to frequency hopping channels 1 to 7 of unhatched chip signal 205. In this way, transmission frequency converter 14 distributes the spread spectrum signal in both the time direction and the frequency direction to assign the spread spectrum signal.

[0023] The digital-to-analog converter 15 converts the digital signal output from the transmission frequency converter 14 into an analog signal.

[0024] The transmission high frequency unit 16 generates an RF (Radio Frequency) transmission signal by performing analog signal processing such as frequency conversion, amplification, and band limiting on the transmission analog signal output from the digital-to-analog conversion unit 15. In this embodiment, the transmission frequency conversion unit 14 generates an IF signal, but the IF signal may also be directly converted into an RF signal by digital signal processing.

[0025] The transmitting antenna 17 emits the radio frequency transmission signal generated by the high frequency transmitting unit 16 as a radio wave.

[0026] 3 is a diagram illustrating a configuration example of a receiving device 3 according to the first embodiment. As illustrated in FIG. 3, the receiving device 3 according to the first embodiment includes a receiving antenna 30, a high-frequency receiving unit 31, an analog-to-digital converting unit 32, a receiving frequency converting unit 33, a receiving waveform shaping processing unit 34 including a plurality of receiving waveform shaping units 340 to 347, an initial synchronization acquisition unit 35, a despreading unit 36, and a demodulating unit 37. The demodulating unit 37 outputs a receiving bit sequence 38. The receiving device 3 receives a signal transmitted by the transmitting device 1 described above, i.e., a signal that has been spectrum-spread using direct spectrum spreading and frequency hopping.

[0027] The receiving antenna 30 of the receiving device 3 receives the RF signal transmitted from the transmitting device 1 .

[0028] The high frequency receiving unit 31 generates an IF signal by performing frequency conversion, amplification, band limitation, etc. on the RF signal received by the receiving antenna 30. In this embodiment, the IF signal is generated by the high frequency receiving unit 31, but the IF signal may also be directly converted into a baseband spread signal, which will be described later.

[0029] The analog-to-digital converter 32 converts the received analog signal output from the high frequency receiver 31 into a received digital signal.

[0030] The reception frequency converter 33 receives the received digital signal from the analog-to-digital converter 32, converts the frequency of the IF signal for each frequency hopping channel, and generates a baseband spread signal. Here, it is assumed that eight frequency hopping channels are received, and the reception frequency converter 33 converts the IF signals for the eight channels into baseband spread signals.

[0031] The received waveform shaping sections 340 to 347 of the received waveform shaping processing section 34 downsample the baseband spread signals of each frequency hopping channel output by the received frequency conversion section 33, and perform band limitation to reduce noise using a low-pass filter. After downsampling and band limitation are performed in the received waveform shaping sections 340 to 347, the received signals for each frequency hopping channel are output to the initial synchronization acquisition section 35 and the despreading section 36.

[0032] When spreading code synchronization for direct spread spectrum signaling has not yet been established, the initial synchronization acquisition unit 35 estimates the spreading code synchronization timing of the direct spread spectrum signal and performs synchronization determination using the modulation signal pattern and a received pilot signal whose spreading code is known, and notifies the despreading unit 36 ​​of the estimated spreading code synchronization timing and the synchronization determination result.

[0033] Details of the initial synchronization acquisition unit 35 will be described with reference to Fig. 4. Fig. 4 is a diagram showing an example of the configuration of the initial synchronization acquisition unit 35 included in the receiving device 3 according to the first embodiment. As shown in Fig. 4, the initial synchronization acquisition unit 35 includes a pilot generation unit 40, a correlation coefficient calculation processing unit 41 including a plurality of correlation coefficient calculation units 410 to 417, an observation period phase difference calculation unit 42, an inter-channel phase difference calculation unit 43, a symbol averaging processing unit 44 including a plurality of symbol averaging units 441 to 448, a power calculation processing unit 45 including a plurality of power calculation units 451 to 458, a power addition unit 46, and a determination unit 47.

[0034] Pilot generation unit 40 generates a pilot pattern for each frequency hopping channel according to a predetermined modulation signal pattern, spreading code, and frequency hopping pattern that are the same as those of transmitter 1. Pilot generation unit 40 outputs each generated pilot pattern to correlation coefficient calculation units 410 to 417 corresponding to each frequency hopping channel. As described above, in this embodiment, there are eight frequency hopping channels, and pilot generation unit 40 generates pilot patterns for eight channels. The pilot pattern length is 128, the same as the spreading code length in transmitter 1. Here, the pilot pattern of chip signal 205 (see FIG. 2) to which no signal is assigned in the frequency hopping channel is set to 0. In this embodiment, the pilot pattern of chip signal 205 to which no signal is assigned in the frequency hopping channel is set to 0, but correlation coefficient calculation units 410 to 417, which will be described later, may be configured to hold only the pilot patterns of chip signals 204 to which signals are assigned (see FIG. 2), and may not perform any calculation on chip signals 205 to which no signal is assigned, instead of multiplying them by 0 in correlation coefficient calculation units 410 to 417. Furthermore, pilot patterns for eight predetermined channels may be stored in a ROM (Read Only Memory) or the like and used.

[0035] Correlation coefficient calculation sections 410 to 417 constituting the correlation coefficient calculation processing section 41 correspond to the outputs of the received waveform shaping sections 340 to 347 for each frequency hopping channel (0 to 7). The correlation coefficient calculation sections 410 to 417 respectively receive as input the received signals output by the received waveform shaping sections 340 to 347 and pilot patterns, which are known signals corresponding to each frequency hopping channel and are generated by the pilot generation section 40. The correlation coefficient calculation sections 410 to 417 calculate correlation coefficients by performing a product-sum operation on the received signals and the complex conjugates of the pilot patterns, and output the correlation coefficients to the observation period phase difference calculation section 42 and the inter-channel phase difference calculation section 43.

[0036] 5, the correlation coefficient calculation units 410 to 417 can be configured by a transversal filter including a shift register 50 corresponding to the pilot pattern length, a multiplier 51, and an adder 52. Note that FIG. 5 is a diagram showing an example of the configuration of the correlation coefficient calculation units 410 to 417 of the initial synchronization acquisition unit 35 included in the receiving device 3 according to the first embodiment.

[0037] The correlation coefficient calculation units 410 to 417 receive received signals with a sampling rate at least twice the spreading chip rate, and the delay elements constituting the shift register 50 delay the signals by the chip period, including the samples oversampled with respect to the spreading chip rate. The multiplier 51 multiplies the complex conjugate (c0) of the pilot pattern for 128 chips with respect to the spread signal for the spreading code length of 128 chips in one symbol period output from the shift register 50. * ~c127 * ) is multiplied.

[0038] The adder 52 combines the output signals of the multiplier 51, which have been divided into correlation observation period units determined within a range that allows the effect of frequency offset on the calculation of the correlation coefficient to be suppressed, and adds the combined signals for each correlation observation period. FIG. 6 is a diagram illustrating the correlation coefficient observation period in the correlation coefficient calculation units 410 to 417 constituting the initial synchronization acquisition unit 35 of the receiving device 3 according to the first embodiment. As in FIG. 2 , the horizontal axis of FIG. 6 represents time, and the lower row lists chip numbers (0 to 127) for 128 chips in one symbol period. The vertical axis of FIG. 6 represents frequency, and lists frequency hopping channel numbers (0 to 7) for eight channels. Here, as an example of a correlation observation period 600, one symbol is divided into 16-chip periods, and chip numbers 0 to 15 are defined as correlation observation period T1, chip numbers 16 to 31 as correlation observation period T2, ..., and chip numbers 112 to 127 as correlation observation period T8. The correlation coefficient calculation processing unit 41 (correlation coefficient calculation units 410 to 417) of the initial synchronization acquisition unit 35 calculates a correlation coefficient for each frequency hopping channel and for each correlation observation period. For example, the correlation coefficient for correlation observation period T1 of frequency hopping channel 0 is calculated using spread signals of chip numbers 0 to 15 of frequency hopping channel 0, which are included in range 601. Similarly, the correlation coefficient for correlation observation period T1 of frequency hopping channels 1 to 7 is calculated using spread signals included in ranges 602 to 608, respectively. The same is true for correlation observation periods T2 to T8. The adders 52 of the correlation coefficient calculation units 410 to 417 perform addition processing on the spread signals for correlation observation periods T1 to T8 in additions #1 to #8, and output correlation coefficients d1 to d8.

[0039] The observation period phase difference calculation unit 42 receives the correlation coefficients d1 to d8 for the correlation observation periods T1 to T8 of each channel calculated by the correlation coefficient calculation units 410 to 417. The observation period phase difference calculation unit 42 calculates the average phase difference of the correlation coefficients between a plurality of different correlation observation periods. There is no upper limit to the number of phase differences between observation periods calculated by the observation period phase difference calculation unit 42. For example, the average phase difference Φ of the correlation coefficients between one correlation observation period m,1 , the correlation coefficient between two correlation observation periods and the average phase difference Φ m,2 , the correlation coefficient between the three correlation observation periods and the average phase difference Φ m,3, and the correlation coefficient between the four correlation observation periods, the average phase difference Φ m,4 In the calculation of the above, they can be calculated by the following formulas (1) to (4). In the formulas (1) to (4), m is the frequency hopping channel number (0 to 7), d m,i is the correlation coefficient of the ith frequency hopping channel number m (i is 1 to 8), and * is the complex conjugate.

[0040]

[0041] The inter-channel phase difference calculation unit 43 receives the correlation coefficients d1 to d8 for the correlation observation periods T1 to T8 of each channel calculated by the correlation coefficient calculation units 410 to 417. The inter-channel phase difference calculation unit 43 calculates the average phase difference of the correlation coefficients between a plurality of different frequency hopping channels. The number of phase differences between channels to be detected depends on the number of frequency hopping channels. For example, m,1 , correlation coefficient between two channels, average phase difference Ψ m,2 , correlation coefficient between three channels, average phase difference Ψ m,3 , correlation coefficient between four channels, average phase difference Ψ m,4 In the calculation of the above, they can be calculated by the following formulas (5) to (8). In the formulas (5) to (8), m is the frequency hopping channel number (0 to 7), d m,i is the correlation coefficient of the ith frequency hopping channel number m (i is 1 to 8), and * is the complex conjugate.

[0042]

[0043] The symbol averaging processing unit 44 calculates a correlation observation period phase difference (Φ m,1 , Φ m,2 , Φ m,3 , Φ m,4), and the inter-channel phase difference (Ψ m,1 , Ψ m,2 , Ψ m,3 , Ψ m,4 ) are input to the symbol averaging units 441 to 444 of the symbol averaging processing unit 44. m,1 , Φ m,2 , Φ m,3 , Φ m,4 ) is input, and the inter-symbol averaging units 445 to 448 of the inter-symbol averaging processing unit 44 calculate the inter-channel phase difference (Ψ m,1 , Ψ m,2 , Ψ m,3 , Ψ m,4 ) is entered.

[0044] The inter-symbol averaging units 441 to 444 average the input correlation observation period phase differences at symbol time intervals, and the inter-symbol averaging units 445 to 448 average the input inter-channel phase differences at symbol time intervals. The averaging method is not particularly limited, but the inter-symbol averaging units 441 to 448 perform averaging, for example, by calculating as shown in the following equation (9) using an exponential moving average over multiple symbols. In equation (9), k is the input sample time, X(k) is the input to the inter-symbol averaging units 441 to 444 at time k, Y(k) is the output from the inter-symbol averaging units 441 to 444 at time k, and T sym represents the symbol time, and α represents the forgetting factor.

[0045]

[0046] The power calculation processing unit 45 receives the inter-symbol average phase differences calculated individually for a plurality of different correlation observation period phase differences and a plurality of different inter-channel phase differences by the inter-symbol averaging processing unit 44. The power calculation units 451 to 458 of the power calculation processing unit 45 each calculate the power (|Y(k)| 2 ) and outputs it to the power adding unit 46.

[0047] The power addition unit 46 adds the powers calculated by the power calculation units 451 to 458 to calculate the total power (hereinafter referred to as correlation power), and outputs it to the determination unit 47. Here, the power addition may be an arithmetic average or a weighted average.

[0048] The determination unit 47 receives the correlation power calculated by the power adder 46 for each input sample time interval of the received signal. The determination unit 47 detects the correlation power that is maximum within one symbol time and performs synchronization determination to estimate the start timing of the spreading code. While the synchronization determination process is not particularly limited, for example, a detection symbol count threshold is set, and the determination unit 47 observes the timing (input sample time) of the maximum correlation power among the input sample times within the symbol time over a predetermined number of symbol times. If the number of consecutive detections of the same timing exceeds the detection symbol count threshold, the detected timing is determined to be a synchronization timing candidate. If the correlation power value at the synchronization timing candidate is equal to or greater than the predetermined threshold, the determination unit 47 determines synchronization. If synchronization is determined, the determination unit 47 notifies the despreading unit 36 ​​of the synchronization determination result indicating this and also notifies the despreading unit 36 ​​of the detected timing as spreading code synchronization timing.

[0049] The above-described operation of the initial synchronization acquisition unit 35 can be shown in a flowchart as shown in Fig. 7. Fig. 7 is a flowchart showing an example of the operation of the initial synchronization acquisition unit 35 of the receiving device 3 according to the first embodiment.

[0050] Initial synchronization acquisition unit 35 first calculates the correlation coefficient between the received signal and the known signal in correlation coefficient calculation units 410 to 417 (step S11). As described above, correlation coefficient calculation units 410 to 417 calculate the correlation coefficient for each of a plurality of correlation observation periods generated by dividing one symbol for each of a plurality of frequency hopping channels.

[0051] The initial synchronization acquisition unit 35 then calculates a first average phase difference in the observation period phase difference calculation unit 42 (step S12). The observation period phase difference calculation unit 42 calculates the average phase difference (correlation observation period phase difference) of the correlation coefficients between the plurality of different correlation observation periods as the first average phase difference.

[0052] The initial synchronization acquisition unit 35 then calculates a second average phase difference in the inter-channel phase difference calculation unit 43 (step S13). The inter-channel phase difference calculation unit 43 calculates the average phase difference (inter-channel phase difference) of the correlation coefficients between the plurality of different frequency hopping channels as the second average phase difference.

[0053] Next, the initial synchronization acquisition unit 35 calculates the average value of the average phase difference within a symbol time in the inter-symbol averaging units 441 to 448 (step S14). The inter-symbol averaging units 441 to 444 average the first average phase difference over the symbol time interval, and the inter-symbol averaging units 445 to 448 average the second average phase difference over the symbol time interval.

[0054] Next, initial synchronization acquisition unit 35 calculates correlation power in power calculation units 451 to 458 and power addition unit 46 (step S15). Power calculation units 451 to 458 calculate the power of the average value within a symbol time of the average phase differences calculated by inter-symbol averaging units 441 to 448, respectively, and power addition unit 46 calculates correlation power by adding up the powers calculated by power calculation units 451 to 458.

[0055] The initial synchronization acquisition unit 35 then determines the leading timing of the spreading code in the determination unit 47 (step S16). As described above, the determination unit 47 determines the leading timing of the spreading code based on the correlation power of the received signal for each input sample time interval input from the power addition unit 46.

[0056] Returning to the description of FIG. 3 , the despreading unit 36 ​​receives the received signals, which are the outputs of the received waveform shaping units 340-347 for each frequency hopping channel (0-7), as well as the spreading code period timing and synchronization determination result from the initial synchronization acquisition unit 35. The spreading code synchronization timing indicates the leading timing of the spreading code. The despreading unit 36 ​​synchronizes the leading timing of the spreading code determined to be synchronized with the received signal and despreads the frequency hopping channel received signal within the symbol time according to a predetermined frequency hopping pattern and spreading code. Here, if the frequency spacing of the frequency hopping channels becomes wide, there is a possibility that differences in frequency response will occur between the channels. Therefore, the despreading unit 36 ​​can, for example, estimate the frequency response of each frequency hopping channel using a pilot signal, correct for the different frequency responses between the frequency hopping channels, and then despread the signal, thereby reducing degradation of the SNR after despreading. A general frequency diversity combining method can be applied as a method for combining these frequency hopping channels, and is not limited to this method. The output of the despreading unit 36 ​​is restored as a modulated symbol signal corresponding to the modulation method applied by the modulation unit 11 in the transmitting device 1 .

[0057] The demodulator 37 demodulates the modulated symbol signal restored by the despreader 36, and outputs a received bit sequence 38 obtained by the demodulation process.

[0058] Next, the hardware configuration of the receiving device 3 according to this embodiment will be described. The receiving high frequency unit 31, analog-to-digital conversion unit 32, receiving frequency conversion unit 33, received waveform shaping processing unit 34, initial synchronization acquisition unit 35, despreading unit 36, and demodulation unit 37 of the receiving device 3 are realized by processing circuits. This processing circuit may be dedicated hardware or a control circuit including a memory and a CPU (Central Processing Unit) that executes a program stored in the memory. Here, the memory may be, for example, a non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM, or flash memory, a magnetic disk, or an optical disk. When this processing circuit is a control circuit including a CPU, this control circuit may be, for example, a control circuit 70 configured as shown in FIG. 8. FIG. 8 is a diagram illustrating an example of the control circuit 70 that realizes the receiving device 3 according to the first embodiment.

[0059] As shown in Fig. 8, the control circuit 70 includes a processor 71, which is a CPU, and a memory 72. When the high-frequency receiving section 31, the analog-to-digital converting section 32, the receiving frequency converting section 33, the receiving waveform shaping processing section 34, the initial synchronization acquisition section 35, the despreading section 36, and the demodulating section 37 of the receiving device 3 are realized by the control circuit 70 shown in Fig. 8, programs for operating the high-frequency receiving section 31, the analog-to-digital converting section 32, the receiving frequency converting section 33, the receiving waveform shaping processing section 34, the initial synchronization acquisition section 35, the despreading section 36, and the demodulating section 37 of the receiving device 3 are stored in the memory 72, and the processor 71 reads and executes the programs stored in the memory 72 to realize the high-frequency receiving section 31, the analog-to-digital converting section 32, the receiving frequency converting section 33, the receiving waveform shaping processing section 34, the initial synchronization acquisition section 35, the despreading section 36, and the demodulating section 37 of the receiving device 3. The memory 72 is also used as a temporary memory for each process performed by the processor 71. It is also possible to implement some of the receiving high frequency section 31, analog-to-digital conversion section 32, receiving frequency conversion section 33, receiving waveform shaping processing section 34, initial synchronization acquisition section 35, despreading section 36, and demodulation section 37 of the receiving device 3 by dedicated hardware, with the remainder being implemented by the control circuit 70. The dedicated hardware here refers to a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a circuit that combines these.

[0060] As described above, the receiver 3 of the spread spectrum communication system according to this embodiment is a spread spectrum communication receiver having a function of performing initial synchronization acquisition on a spread spectrum transmission signal obtained by directly frequency-hopping the spread spectrum signal at high speed within a symbol time. The receiver divides the received signal into correlation observation periods of the spread spectrum code, which are time intervals in which the influence of time fluctuations in the transmission path due to frequency offsets is reduced, and calculates correlation coefficients for each frequency-hopping channel and each correlation observation period. The receiver then averages the phase differences of the correlation coefficients for multiple different correlation observation periods and the phase differences of the correlation coefficients for multiple different channel spacings within a symbol time, respectively, and then performs spread code synchronization timing estimation and synchronization determination based on the power of the average phase difference obtained by averaging the calculated results over the symbol time interval and multiple symbol times. In this way, the receiver 3 performs synchronization determination based on the phase differences of the correlation coefficients for multiple different correlation observation periods and multiple different channel spacings. This allows for averaging effects across multiple symbols while reducing the influence of transmission path fluctuations, even in transmission paths where time fluctuations in the transmission path due to frequency offsets and differences in frequency response between channels occur due to wider bandwidths. As a result, the accuracy of peak power detection is improved by improving the SNR, and the correlation of the spreading code with noise and erroneous timing other than the spreading code synchronization timing is reduced. This reduces detection errors in the spreading code synchronization timing and synchronization decision errors, thereby enabling faster initial synchronization acquisition.

[0061] Embodiment 2 In the above-described embodiment 1, the inter-symbol averaging processing unit 44, the power calculation processing unit 45, and the power adding unit 46 calculate values ​​obtained by averaging, within a symbol time, the average phase differences of the correlation coefficients for a plurality of different correlation observation periods and the average phase differences of the correlation coefficients for a plurality of different channel intervals, and then estimate the spreading code synchronization timing and perform synchronization determination based on the power of the average phase differences obtained by averaging the calculation results over the symbol time interval and over a plurality of symbol times.

[0062] In contrast, in embodiment 2, the phase differences of the correlation coefficients for a plurality of different correlation observation periods are averaged within a symbol time, and then the phase offset for one correlation observation period due to the frequency offset is estimated using the average phase difference obtained by averaging the calculation result over the symbol time interval and the plurality of symbol times.The phase is corrected based on the estimated phase offset for each of the average phase differences for the plurality of different correlation observation periods, and the arithmetic mean of the corrected average phase differences for the plurality of different correlation observation periods is taken to calculate the correlation power based on the phase difference during the observation period.Then, spreading code synchronization timing estimation and synchronization determination are performed based on the total power obtained by adding the correlation power based on the phase difference during the observation period and the correlation power based on the phase difference between channels.

[0063] This embodiment differs from embodiment 1 in the initial synchronization acquisition operation in the receiving device, so a description of the parts common to embodiment 1, i.e., parts other than the initial synchronization acquisition operation, will be omitted.

[0064] Fig. 9 is a diagram showing a configuration example of an initial synchronization acquisition unit 35a that realizes an initial synchronization acquisition operation in a receiving device according to the second embodiment. The receiving device according to the second embodiment has a configuration in which the initial synchronization acquisition unit 35 of the receiving device 3 according to the first embodiment is replaced with an initial synchronization acquisition unit 35a shown in Fig. 9. In Fig. 9, the same components as those in the initial synchronization acquisition unit 35 of the receiving device 3 according to the first embodiment shown in Fig. 4 are assigned the same reference numerals. Explanation of the components assigned the same reference numerals as those in the initial synchronization acquisition unit 35 of the receiving device 3 according to the first embodiment will be omitted.

[0065] The initial synchronization acquisition unit 35a of the receiving device according to the second embodiment has a configuration in which the power calculation processing unit 45 and the power adding unit 46 of the initial synchronization acquisition unit 35 of the receiving device 3 according to the first embodiment are replaced with a phase offset correction unit 80, a power calculation processing unit 81, and a power adding unit 82. The power calculation processing unit 81 is made up of power calculation units 811, 815 to 818.

[0066] The phase offset correction unit 80 receives the inter-symbol average values ​​of the correlation observation period phase differences calculated by the inter-symbol averaging units 441 to 444 of the symbol averaging processing unit 44. The phase offset correction unit 80 corrects for the phase offset due to the frequency offset using the inter-symbol average values ​​of the correlation observation period phase differences calculated by the inter-symbol averaging units 441 to 444, and then performs arithmetic averaging. If a frequency offset is present in the received signal, the carrier phase changes over time at a constant slope. Therefore, if a frequency offset is present, a constant phase offset amount is added to the received signal according to the correlation observation period. The observation period phase difference indicates the phase offset amount associated with the frequency offset in that correlation observation period. For example, a phase difference between two correlation observation periods is twice the phase difference between one correlation observation period. Similarly, a phase difference between three correlation observation periods is three times the phase difference between one correlation observation period, and a phase difference between four correlation observation periods is four times the phase difference between one correlation observation period. By utilizing this property, the phase offset correction unit 80 can correct the phase offset caused by the frequency offset, thereby enabling the phase differences between the correlation observation periods to be combined in phase. That is, by correcting the phase of the phase difference between two correlation observation periods to 1 / 2, the phase difference between three correlation observation periods to 1 / 3, and the phase difference between four correlation observation periods to 1 / 4, all of the phase differences can be aligned to the phase difference of one correlation observation period, and by taking their arithmetic mean, they can be combined in phase. The phase offset correction unit 80 outputs the average phase difference over one correlation observation period after arithmetic averaging (hereinafter referred to as the combined observation period phase difference) to the power calculation processing unit 81.

[0067] The power calculation processing unit 81 receives as input the combined observation period phase difference calculated by the phase offset correction unit 80 and the inter-symbol average phase difference of a plurality of different inter-channel phase differences calculated by the inter-symbol averaging units 445 to 448. The combined observation period phase difference is input to a power calculation unit 811, and the inter-symbol average phase differences calculated by the inter-symbol averaging units 445 to 448 are input to power calculation units 815 to 818. The power calculation units 811 and 815 to 818 of the power calculation processing unit 81 calculate the power of each of the input combined observation period phase difference and inter-symbol average phase difference, and output the calculated power to a power addition unit 82.

[0068] The power adder 82 adds the powers calculated by the power calculators 811, 815 to 818 and outputs the total power as correlation power to the decision unit 47. Here, the power addition may be an arithmetic average or a weighted average.

[0069] As described above, the initial synchronization acquisition unit 35a of the receiving device according to the second embodiment corrects the phase offset caused by the frequency offset for the phase differences between the correlation coefficients of a plurality of different correlation observation periods, and performs synchronization determination using the composite observation period phase difference calculated by averaging the phase differences after correction. This is expected to improve the SNR compared to the initial synchronization acquisition in the receiving device 3 according to the first embodiment, and therefore makes it possible to achieve faster initial synchronization acquisition even in a low SNR transmission path.

[0070] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0071] 1 Transmitting device, 3 Receiving device, 10 Transmitting bit sequence, 11 Modulation unit, 12 Spreading unit, 13 Transmitting waveform shaping unit, 14 Transmitting frequency conversion unit, 15 Digital-to-analog conversion unit, 16 Transmitting high frequency unit, 17 Transmitting antenna, 30 Receiving antenna, 31 Receiving high frequency unit, 32 Analog-to-digital conversion unit, 33 Receiving frequency conversion unit, 34 Receiving waveform shaping processing unit, 35, 35a Initial synchronization acquisition unit, 36 Despreading unit, 37 Demodulation unit, 38 Received bit sequence, 40 Pilot generation unit, 41 Correlation coefficient calculation processing unit, 42 Observation period phase difference calculation unit, 43 Inter-channel phase difference calculation unit, 44 Symbol-to-symbol averaging processing unit, 45, 81 Power calculation processing unit, 46, 82 Power addition unit, 47 Decision unit, 50 Shift register, 51 Multiplier, 52 Adder, 80 Phase offset correction unit, 340 to 347 Received waveform shaping unit, 410 to 417 correlation coefficient calculation units, 441 to 448 symbol average units, 451 to 458, 811, 815 to 818 power calculation units.

Claims

1. A receiving device for receiving a signal that has been spectrum spread by applying direct spectrum spreading using a spreading code and frequency hopping, comprising: a correlation coefficient calculation processing unit that calculates a correlation coefficient between a received signal and a known signal for each frequency hopping channel and for each correlation observation period that is shorter than the symbol period of the received signal; an observation period phase difference calculation unit that calculates a first average phase difference, which is the average of the phase differences of the correlation coefficients between different correlation observation periods, based on the correlation coefficient; an inter-channel phase difference calculation unit that calculates a second average phase difference, which is the average of the phase differences of the correlation coefficients between different frequency hopping channels, based on the correlation coefficient; and a determination unit that determines the start timing of the spreading code based on the average power of the first average phase difference within a symbol time and the average power of the second average phase difference within the symbol time.

2. The receiving device described in claim 1, characterized in that the observation period phase difference calculation unit calculates the phase difference of the correlation coefficient for each correlation observation period for each of a plurality of different combinations of the correlation observation periods and averages the calculated phase differences to obtain the first average phase difference, and the inter-channel phase difference calculation unit calculates the phase difference of the correlation coefficient for each correlation observation period for each of a plurality of different combinations of the frequency hopping channels and averages the calculated phase differences to obtain the second average phase difference.

3. The receiving device according to claim 1 or 2, further comprising: a phase offset correction unit that corrects a phase offset included in the first average phase difference based on the plurality of first average phase differences calculated by the observation period phase difference calculation unit; and wherein the determination unit determines the start timing of the spreading code based on the average power of the first average phase difference within the symbol time after the phase offset has been corrected by the phase offset correction unit and the average power of the second average phase difference within the symbol time.

4. A receiving method in which a receiving device receives a signal that has been spectrum spread by applying direct spectrum spreading using a spreading code and frequency hopping, comprising: a correlation coefficient calculation step in which the receiving device calculates a correlation coefficient between a received signal and a known signal for each frequency hopping channel and for each correlation observation period that is shorter than the symbol period of the received signal; an observation period phase difference calculation step in which the receiving device calculates a first average phase difference, which is the average of the phase differences of the correlation coefficients between different correlation observation periods, based on the correlation coefficient; an inter-channel phase difference calculation step in which the receiving device calculates a second average phase difference, which is the average of the phase differences of the correlation coefficients between different frequency hopping channels, based on the correlation coefficient; and a determination step in which the receiving device determines the start timing of the spreading code based on the average power of the first average phase difference within a symbol time and the average power of the second average phase difference within the symbol time.

5. A control circuit constituting a receiving device that receives a spectrum-spread signal by applying direct spectrum spreading using a spreading code and frequency hopping, the control circuit executing the following steps: a correlation coefficient calculation step that calculates a correlation coefficient between a received signal and a known signal for each frequency hopping channel and for each correlation observation period that is shorter than the symbol period of the received signal; an observation period phase difference calculation step that calculates a first average phase difference, which is the average of the phase differences of the correlation coefficients between different correlation observation periods, based on the correlation coefficient; an inter-channel phase difference calculation step that calculates a second average phase difference, which is the average of the phase differences of the correlation coefficients between different frequency hopping channels, based on the correlation coefficient; and a determination step that determines the start timing of the spreading code based on the average power of the first average phase difference within a symbol time and the average power of the second average phase difference within the symbol time.

6. A storage medium storing a program executed by a control circuit constituting a receiving device that receives a spectrum-spread signal by applying direct spectrum spreading using a spreading code and frequency hopping, the program causing the control circuit to execute the following steps: a correlation coefficient calculation step of calculating a correlation coefficient between a received signal and a known signal for each frequency hopping channel and for each correlation observation period that is shorter than the symbol period of the received signal; an observation period phase difference calculation step of calculating a first average phase difference, which is the average of the phase differences of the correlation coefficients between different correlation observation periods, based on the correlation coefficient; an inter-channel phase difference calculation step of calculating a second average phase difference, which is the average of the phase differences of the correlation coefficients between different frequency hopping channels, based on the correlation coefficient; and a determination step of determining the start timing of the spreading code based on the average power of the first average phase difference within a symbol time and the average power of the second average phase difference within the symbol time.

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