JP2013046373A - Communication system and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a communication system capable of synchronization acquisition with a small circuit scale.SOLUTION: In a communication system applying spread spectrum communication performing FSK modulation in primary modulation, a communication device on the reception side includes: synchronization timing detection means (spread code generation unit 21, synchronization acquisition unit 22) for generating a signal replica for synchronization acquisition on the basis of relationship of each carrier frequency used in the FSK modulation on the transmission side and an identical spread code to the code used in the spread modulation on the transmission side, and for determining synchronization timing of the spread code by performing correlation operation between the signal replica and a reception signal; based on the determined synchronization timing, a despreading unit 24 for despreading the reception signal using the spread code; and an FSK demodulation unit 25 for FSK demodulating the despread reception signal.

Description

  The present invention relates to a communication system that transmits and receives data using spread spectrum technology.

  Spread spectrum technology has excellent characteristics of anti-interference / disturbance and confidentiality, and is used not only for communication but also in various fields such as radar, distance measurement, and time synchronization. In the direct spread spectrum system, which is one of the spread spectrum techniques, the transmitting side compares a symbol rate signal that has been primarily modulated by PSK (Phase Shift Keying) or FSK (Frequency Shift Keying) with the symbol rate. It is spread over a wide band with a rate spreading code and transmitted. On the reception side, synchronization acquisition and reproduction of a transmission information data sequence can be performed by despreading using the same spreading code as the spreading code used on the transmission side and a sliding correlator (see, for example, Non-Patent Document 1). ). Non-Patent Document 2, which describes a W-CDMA mobile communication system using spread spectrum technology, describes that a pilot signal is subjected to spreading code multiplexing or time multiplexing.

Mitsuo Yokoyama "Spread Spectrum Communication System" Science and Technology Publishers Supervised by Keiji Tachikawa "W-CDMA mobile communication system" Maruzen Co., Ltd.

  However, the conventional direct spread spectrum system as described in Non-Patent Document 1 has a problem that the circuit scale of the sliding correlator used for synchronization acquisition increases as the spreading code length increases. In particular, when FSK modulation is used for the primary modulation, it is necessary to prepare all the sliding correlators for the number of modulation multi-levels in the conventional configuration. As the number of modulation multi-levels increases in addition to the spreading code length, There was a problem that the circuit scale increased. On the other hand, the circuit scale of the sliding correlator can be reduced by adopting a configuration in which synchronization acquisition is performed using a pilot signal as described in Non-Patent Document 2. However, when the pilot signal is multiplexed with the spreading code, the spreading code is assigned exclusively to the pilot, so that the number of multiplexing is consumed and the inter-code interference is increased. On the other hand, when the pilot signals are time-multiplexed, the above-mentioned problems do not occur, but synchronization acquisition can be performed only at the time when the pilot signals are inserted, and synchronization acquisition is required when the pilot insertion interval is widened. There was a problem that time would increase.

  The present invention has been made in view of the above, and in direct spectrum spreading using FSK modulation for primary modulation, synchronization acquisition can be realized with a small circuit scale regardless of an increase in the number of modulation multilevels. An object is to obtain a communication system. It is another object of the present invention to provide a communication system and a receiver that can shorten the time required for synchronization compared to the case where synchronization acquisition is performed using only pilot signals.

  In order to solve the above-described problems and achieve the object, the present invention is a communication system to which spread spectrum communication that performs FSK modulation with primary modulation is applied, in which a communication device on the reception side performs FSK modulation on the transmission side. A signal replica for synchronization acquisition is generated based on the relationship between the frequencies of the carriers used in the transmission and the same spreading code as that used in the spread modulation on the transmission side, and the correlation between the signal replica and the received signal is generated. Synchronization timing detection means for performing calculation and determining the synchronization timing of the spreading code, despreading means for despreading the received signal using the spreading code according to the determined synchronization timing, and despreading by the despreading means FSK demodulating means for FSK demodulating the spread received signal.

  According to the present invention, since a signal replica that can be commonly used for synchronization acquisition of a plurality of carriers is generated and synchronization acquisition of each carrier is performed, there is an effect that the scale of a circuit that performs synchronization acquisition processing can be reduced.

FIG. 1 is a diagram showing a configuration example of a first embodiment of a communication system according to the present invention. FIG. 2 is a diagram illustrating an example of the FSK modulation operation. FIG. 3 is a diagram illustrating an example of a transmission signal after execution of spread modulation. FIG. 4 is a diagram illustrating an example of a relative phase change of each carrier frequency of quaternary FSK modulation data. FIG. 5 is a diagram illustrating a configuration example of the synchronization capturing unit. FIG. 6 is a diagram illustrating a configuration example of the communication system according to the second embodiment of the present invention. FIG. 7 is a diagram illustrating a configuration example of the data synchronization capturing unit. FIG. 8 is a diagram illustrating a configuration example of a pilot synchronization acquisition unit. FIG. 9 is a diagram illustrating a configuration example of the third embodiment of the communication system according to the present invention.

  Embodiments of a communication system and a receiver according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a first embodiment of a communication system according to the present invention. The communication system according to the present embodiment includes a transmitter (a communication device on the data transmission side) including an FSK modulation unit 11, a spread code generation unit 12, and a spread modulation unit 13, a spread code generation unit 21, a synchronization acquisition unit 22, A receiver (communication device on the data receiving side) provided with a spread code generating unit 23, a despreading unit 24, and an FSK demodulating unit 25. In the communication system of this embodiment having such a configuration, FSK modulation is applied to primary modulation, and spreading is performed over a wide band using a spreading code.

  Hereinafter, the communication system of the present embodiment will be described in detail. First, the operation of the transmitter will be described.

In the transmitter, the FSK modulator 11 that performs primary modulation generates FSK modulated data b (t) based on the input information data a (t). That is, according to the value of the information data a (t), FSK modulation is performed by assigning carriers having different frequencies for each value to generate FSK modulated data. For example, when quaternary FSK is taken as an example, as shown in FIG. 2, the values 00, 01, 10, and 11 are set as frequencies in the spreading band Bw as f ₀ , f ₁ , f ₂ , and f ₃ , respectively. The FSK modulation data b (t) is generated by conversion.

  The spreading code generator 12 generates a spreading code used in the spreading process by the spreading modulator 13. For example, a predetermined spread code is generated and stored in a memory or the like, and is output to the spread modulation unit 13 at a predetermined timing.

The spread modulation unit 13 multiplies the FSK modulation data b (i) output from the FSK modulation unit 11 and the spread code c (k) output from the spread code generation unit 12 as shown in the following equation (1). The spread modulation data s (t) is generated. By this processing, the FSK modulation data b (k) as shown in FIG. 2 becomes the spread modulation data s (t) as shown in FIG.
s (k) = b (k) × c (k) (1)

  In Equation (1), k is an integer of 0 ≦ k ≦ L (L is a spreading code length) and indicates the order of spreading codes. This k corresponds to the chip rate period interval after spreading. The spread modulation data s (t) generated by the spread modulation unit 13 is transmitted toward the receiver. Here, t represents time.

  Next, the operation of the receiver will be described.

  The spread modulation data s (t) transmitted from the transmitter is received as a signal r (t), and this received signal r (t) is input to the synchronization acquisition unit 22 and the despreading unit 24.

  The spread code generator 21 generates a spread code used in the synchronization acquisition process by the synchronization acquisition unit 22. For example, a predetermined spreading code is generated and stored in a memory or the like, and is output to the synchronization capturing unit 22 at a predetermined timing.

Here, a method in which the spread code generation unit 21 generates a spread code will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of relative phase changes of the carrier frequencies f ₀ , f ₁ , f ₂ , and f ₃ of the quaternary FSK modulation data b (t) generated by the FSK modulation unit 11 of the transmitter. . Each carrier of the quaternary FSK modulation data b (t) has a timing corresponding to the relationship between the carrier frequencies, for example, φ (0), φ (1), φ (2) in the example shown in FIG. , Φ (3), φ (4), the phases coincide (the relative phase becomes 0 and the amplitudes of all carriers coincide with 0). Therefore, in the spread code generation unit 21, as shown in the following equation (2), from the same spread code used in the spread modulation of the transmitter, each timing (φ (0), A spreading code corresponding to φ (1), φ (2),...) is extracted to generate a spreading code d (k ′) that is a signal replica used for synchronization acquisition.
d (k ′) = c (φ _k ) (2)

In the formula (2), k ′ is an integer of 1 ≦ k ′ ≦ L ′. L ′ is the number of timings when the phases of the respective carriers of the FSK modulated data b (t) are all matched, and represents the code length of the signal replica d (k ′) generated by the spread code generating unit 21. d (k ′) is represented by a complex number. This signal replica d (k ′) can be commonly used in the synchronization acquisition process regardless of the carrier of the FSK modulation. Here, the timing at which the phases of the carriers coincide with each other depends on the relationship of the frequency arrangement of the carriers, and can be specified from the relationship of the carrier frequencies. Further, if each carrier is arranged so that the least common multiple of each carrier frequency is not as small as possible, the period in which the phases match is shortened. That is, the code length of the signal replica d (k ′) is increased. The longer the code length of the signal replica d (k ′), the shorter the time required for synchronization acquisition. For example, when the carrier frequency is set so that f ₁ = 2f ₀ , f ₂ = 3f ₀ , and f ₃ = 4f ₀ , the code length of the signal replica d (k ′) can be increased.

  Note that the spread code c (k) necessary for generating the signal replica d (k ′) may be held in advance by the spread code generation unit 21 or is appropriately acquired from the spread code generation unit 23 described later. You may make it do.

  The synchronization acquisition unit 22 performs a sliding correlation process with the received signal r (t) using the signal replica d (k ′) generated by the spreading code generation unit 21 to detect and determine the synchronization timing of the spreading code. . An operation example in the case of performing synchronization acquisition by detecting the peak position of the correlation power between the signal replica d (k ′) and the received signal r (t) will be described with reference to FIG. FIG. 5 is a diagram illustrating a configuration example of the synchronization acquisition unit 22. The synchronization acquisition unit 22 includes a delay unit 221, a multiplier 222, an adder 223, a correlation power calculation unit 224, a correlation peak position detection unit 225, and a threshold. A value determination unit 226 is provided.

As shown in FIG. 5, the synchronization acquisition unit 22 that performs sliding correlation processing can be realized by an FIR type product-sum operation circuit. In the synchronization acquisition unit 22, each delay unit 221 performs only the period T ′ of the timing at which the phases of the respective carriers of FSK modulation match, that is, the spread code generation unit 21 converts the spread code c (k) to the signal replica d (k The input signal r (t) is delayed by a time corresponding to the period for extracting '). The delay device 221 includes a FIFO, a memory, a register, and the like. The coefficient of each multiplier 222 is set to the synchronization signal replica d (k ′) generated by the spreading code generator 21, and each multiplier 222 multiplies the input signal r (t) by d (k ′), The adder 223 adds each multiplication result to calculate a correlation value q (t) between the input signal r (t) and the synchronization signal replica d (k ′). This process is expressed by the following equation (3). In the following formula (3), i ′ represents a received sample number. In the following formula (3), * indicates a complex conjugate.
q (i ′) = Σ {r (i ′ · T ′ + k ′ · T ′) × d ^* (k ′)} (3)

The correlation power calculation unit 224 calculates the power p (i ′) of the correlation value q (i ′) output from the adder 223 according to the following equation (4).
p (i ′) = q (i ′) ^* × q (i ′) (4)

  The correlation peak position detection unit 225 detects the timing at which the correlation power becomes maximum within the cycle of the spreading code sequence length, and stores it together with the maximum value of the correlation power.

  The threshold determination unit 226 compares the threshold with the correlation power at the timing detected by the correlation peak position detection unit 225 (the maximum value of the correlation power within the period of the spreading code sequence length), and determines the threshold as the correlation power. Is exceeded, it is determined that the timing is the correct synchronization timing of the spreading code, and the determined timing m (t) is output to the despreading unit 24 as the synchronization timing determination result. Here, when comparing the correlation power with the threshold value, the threshold power may be determined by normalizing the correlation power using the average power of the received signal.

  The spreading code generator 23 generates the same spreading code c (k) as that generated by the spreading code generator 12 of the transmitter.

The despreading unit 24 multiplies the reception signal r (t) and the complex conjugate of the spread code c (k) in accordance with the timing m (t) estimated by the synchronization acquisition unit 22 according to the following equation (5), and performs despreading. Perform diffusion.
x (k) = r (m (t) + k · T) × c ^* (k) (5)

  The FSK demodulator 25 performs demodulation corresponding to FSK on the despread signal x (t) output from the despreader 24 and outputs demodulated data y (t). In the present invention, the demodulation method for FSK modulation is not particularly limited.

  As described above, in the communication system according to the present embodiment, the communication device (transmitter) on the data transmission side performs FSK modulation on the data and further performs spread modulation to transmit the data. The communication device (receiver) on the data receiving side generates a spread code for synchronization acquisition based on the frequency relationship of each data carrier in M-value FSK modulation applied to primary modulation, and performs synchronization acquisition. did. Specifically, the timing at which the phase of each data carrier matches is identified based on the frequency relationship of each data carrier, and the spreading code corresponding to each timing at which the phase of each data carrier matches is extracted for synchronization acquisition. The spread code is generated, the signal is treated as a signal replica, and the received signal sample corresponding to each timing at which the phases of the data carriers match (the timing at which the signal replica is extracted from the spread code) is correlated with the signal replica, We decided to perform synchronous acquisition. Thereby, the circuit scale of the receiver can be reduced. When the conventional technique is applied, reception of an M-value FSK-modulated signal requires that a signal replica for synchronization acquisition be generated for each of M data carriers and a sliding correlation process be performed. There is a problem that the circuit scale increases as the number of multi-values increases. On the other hand, in the receiver according to the present embodiment, one signal replica can be commonly used for synchronization acquisition of M data carriers, so that the scale of a circuit that performs sliding correlation processing for synchronization acquisition is greatly reduced. it can. Accordingly, power consumption can be reduced. If the frequency of each data carrier is set so that the least common multiple of the frequency of each data carrier becomes small, synchronization acquisition can be completed in a shorter time.

Embodiment 2. FIG.
In the first embodiment described above, a communication system has been described in which synchronization acquisition is performed without using known data such as a pilot for a direct spread spectrum signal whose primary modulation is an FSK modulated carrier. In contrast, in this embodiment, when known data (for example, pilot data) can be used, in addition to the conventional synchronization acquisition using the known data included in the received signal, data other than the known data is used. A communication system that improves synchronization acquisition performance and shortens synchronization acquisition time by performing synchronization acquisition will be described. In the present embodiment, description will be made assuming that known data is pilot data.

  FIG. 6 is a diagram illustrating a configuration example of the communication system according to the second embodiment of the present invention. The communication system according to the present embodiment includes a transmitter including a pilot generation unit 31, an FSK modulation unit 32, a spread code generation unit 33, and a spread modulation unit 34, a spread code generation unit 41, a data synchronization acquisition unit 42, a spread code And a receiver including a generation unit 43, a pilot synchronization acquisition unit 44, a despreading unit 45, and an FSK demodulation unit 46. As in the first embodiment, an example in which the primary modulation is FSK modulation in the communication system of the present embodiment will be described.

  Hereinafter, the communication system of the present embodiment will be described in detail. First, the operation of the transmitter will be described.

In the transmitter according to the second embodiment, pilot generation unit 31 generates pilot data. The FSK modulation unit 32 that performs primary modulation generates FSK modulation data b (t) based on the input information data a (t) or the pilot data p (t) generated by the pilot generation unit 31. That is, different carrier frequencies are given to the information data a (t) or the pilot data p (t) to generate FSK modulation data, and the information data and pilot data are time-division multiplexed. For example, when quaternary FSK is taken as an example, for information data a (t), each value of 00, 01, 10, and 11 is set as shown in FIG. 2 as in the FSK modulator 11 of the first embodiment. FSK modulated data b (t) is generated by converting the frequency in the spread band Bw as in f ₀ , f ₁ , f ₂ , and f ₃ . For pilot data, as in the case of information data, any one of f ₀ , f ₁ , f ₂ , and f ₃ carrier frequencies may be selected to perform FSK modulation, or f ₀ , f ₁ , f ₂ , f FSK modulation may be performed by selecting a carrier frequency in a spread band Bw other than ₃ . Here, the latter method is adopted, and the carrier frequency on which pilot data is carried is assumed to be f _P. f _p is frequency f ₀ of the data carrier, _f 1, f _2, it is desirable to set the least common multiple so decreases with f _3.

  The spread code generation unit 33 and the spread modulation unit 34 are the same as the spread code generation unit 12 and the spread modulation unit 13 included in the transmitter according to Embodiment 1, and the spread modulation unit 34 is expressed by the above equation (1). Accordingly, the spread modulation data s (t) is generated by multiplying the FSK modulation data b (t) output from the FSK modulation unit 32 by the spread code c (k) generated by the spread code generation unit 33.

  Next, the operation of the receiver will be described.

  The spread modulation data s (t) transmitted from the transmitter is received as a signal r (t), and this received signal r (t) is sent to the data synchronization acquisition unit 42, pilot synchronization acquisition unit 44 and despreading unit 45. Entered.

  The spreading code generator 41 generates a spreading code similar to the spreading code generator 21 of the first embodiment. Here, a signal replica is generated by extracting from the spreading code (the same spreading code used in the spread modulation on the transmission side) that corresponds to the timing at which the phases of each carrier match, including the carrier of the pilot signal. Then, a common signal replica can be generated for data and pilot.

  The data synchronization acquisition unit 42 performs a sliding correlation process with the received signal r (t) using the signal replica d (k ′) generated by the spreading code generation unit 41, and determines the synchronization timing of the spreading code at each sample time. Calculate the likelihood. An operation example when calculating the correlation power between the signal replica d (k ′) and the received signal r (t) and calculating the likelihood of the synchronization acquisition timing will be described with reference to FIG. FIG. 7 is a diagram illustrating a configuration example of the data synchronization acquisition unit 42, and the data synchronization acquisition unit 42 includes a delay unit 421, a multiplier 422, an adder 423, and a correlation power calculation unit 424.

  As shown in FIG. 7, the data synchronization acquisition unit 42 that performs the sliding correlation process can be realized by an FIR type product-sum operation circuit. In the data synchronization acquisition unit 42, each delay unit 421 delays the input signal r (t) by a period of timing at which the phases of the respective carriers of FSK modulation match. The delay device 421 includes a FIFO, a memory, a register, and the like. The coefficient of each multiplier 422 is set to the synchronization signal replica d (k ′) generated by the spreading code generator 41, and each multiplier 422 multiplies the input signal r (t) by d (k ′), The adder 223 adds each multiplication result to calculate a correlation value q (t) between the input signal r (t) and the synchronization signal replica d (k ′). This process is expressed by the above-described equation (3).

  Correlation power calculation section 424 calculates power p (t) of correlation value q (t) output from adder 423 according to the above equation (4), similarly to correlation power calculation section 224 of the first embodiment. . The calculated correlation power p (t) is output to the pilot synchronization acquisition unit 44 as the likelihood of synchronization acquisition timing for each sample. This process can be operated regardless of data or pilot as an input signal. That is, correlation power calculation section 424 calculates the correlation value q (t) by executing the above process when the input signal r (t) is either information data or pilot data.

  The spread code generation unit 43 generates the same spread code c (k) as that generated by the spread code generation unit 33 of the transmitter and also uses the spread code c ′ (k) used in the synchronization acquisition process by the pilot synchronization acquisition unit 44. ) Is generated. The spreading code c ′ (k) is generated by multiplying the spreading code c (k) and the FSK modulation signal obtained by FSK modulation of the pilot data. The spread code generator 43 stores the spread codes c (k) and c ′ (k) in a memory or the like, and outputs them at predetermined timings. The spreading code c (k) is output to the despreading unit 45, and the spreading code c ′ (k) is output to the pilot synchronization capturing unit 44 as a signal replica for pilot synchronization.

The pilot synchronization acquisition unit 44 performs a sliding correlation process with the pilot reception signal using the pilot synchronization signal replica c ′ (k) generated by the spreading code generation unit 43, and detects and determines the synchronization timing of the spreading code. Do. The pilot reception signal is a reception signal corresponding to a signal component obtained by subjecting pilot data to FSK modulation and spread modulation in the reception signal r (t). An operation example in the case of performing synchronization acquisition by detecting the peak position of the correlation power between the pilot synchronization signal replica c ′ (k) and the pilot reception signal r (t) will be described with reference to FIG. In the following description, the pilot reception signal is denoted by r _p (t). FIG. 8 is a diagram illustrating a configuration example of the pilot synchronization acquisition unit 44. The pilot synchronization acquisition unit 44 includes a delay unit 441, a multiplier 442, an adder 443, a correlation power calculation unit 444, a correlation power synthesis unit 445, and a correlation. A peak position detection unit 446 and a threshold value determination unit 447 are provided.

As shown in FIG. 8, the pilot synchronization acquisition unit 44 that performs the sliding correlation process can be realized by an FIR type product-sum operation circuit. In the pilot synchronization acquisition unit 44, each delay unit 441 delays the pilot reception signal r _p (t) by the chip rate period. The delay device 441 includes a FIFO, a memory, a register, and the like. The coefficient of each multiplier 442 is set to the synchronization signal replica c ′ (k) generated by the spreading code generator 43, and each multiplier 442 multiplies the input signal r _p (t) by c ′ (k). Then, the adder 443 adds the multiplication results to calculate the correlation value q _p (t) between the input signal r _p (t) and the pilot synchronization signal replica c ′ (k). This process is expressed by the following equation (6).
q _p (i ′) = Σ {r _p (i ′ · T + k · T) × c ′ ^* (k)} (6)

Correlation power calculation section 444 calculates power p _p (t) of correlation value q _p (t) output from adder 443 according to the following equation (7).
p _p (i ′) = q _p (i ′) ^* × q _p (i ′) (7)

The correlation power combining unit 445 calculates the likelihood p (t) of the synchronization acquisition timing for each sample calculated by the data synchronization acquisition unit 42 and the correlation power calculated by the correlation power calculation unit 444 according to the following equation (8). _p (t) Add and synthesize.
p _SUM (i ′) = p _p (i ′) + p (i ′) (8)

Correlation peak position detection section 446 detects the timing at which p _SUM (t) calculated by correlation power combining section 445 is maximized within the period of the spread code sequence length, and the maximum value of combined correlation power p _SUM (t) Remember with it.

  The threshold determination unit 447 compares the threshold with the correlation power at the timing detected by the correlation peak position detection unit 446 (the maximum value of the combined correlation power within the period of the spreading code sequence length), and correlates the threshold. If the power exceeds, the timing is determined to be the correct spreading code synchronization timing, and the determined timing m (t) is output to the despreading unit 45. Here, when comparing the correlation power with the threshold value, the threshold power may be determined by normalizing the correlation power using the average power of the received signal.

  The despreading unit 45 is the same as the despreading unit 24 of the first embodiment, and the received signal r (t) and the spread code generating unit are synchronized with the timing m (t) estimated by the pilot synchronization capturing unit 44. Despreading is performed by multiplying the complex conjugate of the spreading code c (t) generated at 43.

  The FSK demodulator 46 performs demodulation corresponding to FSK on the despread signal x (t) output from the despreader 45 and outputs demodulated data y (t).

  As described above, in the communication system according to the present embodiment, the communication device (receiver) on the data reception side performs spreading corresponding to each timing at which the phases of the carriers in the M-value FSK modulation applied to the primary modulation match. A code replica is extracted to generate a signal replica, and a correlation operation is performed between the received signal sample corresponding to each timing (the timing at which the signal replica is extracted from the spread code) at which each carrier phase matches, and the signal replica is obtained as a result. The obtained correlation power is used as likelihood information as a guideline for determining the synchronization timing of the spreading code. Also, a synchronization acquisition process using known pilot data is executed to calculate correlation power in each sample, and this correlation power value and the likelihood information are combined to detect correlation peak (for synchronization timing determination). The correlation power value is generated. That is, the correlation power obtained by executing the correlation calculation similar to the correlation calculation performed by the spreading code generation unit 21 and the synchronization acquisition unit 22 included in the receiver according to the first embodiment is handled as the likelihood information, and the pilot. A correlation power value is calculated by executing a correlation operation using data, and a correlation power value with improved reliability is obtained by adding the likelihood information and the correlation power value. Thereby, the peak position detection accuracy of the correlation power value can be improved, and the performance can be improved as compared with the case where the synchronization acquisition is performed using only the pilot signal.

  In addition, when the correlation power obtained by performing the correlation calculation is cumulatively added and the synchronization timing is determined when the cumulative value exceeds the threshold, the synchronization acquisition is performed using only the pilot signal. Compared with the case where the process is performed, the time required until the synchronization detection can be shortened.

Embodiment 3 FIG.
In the first embodiment described above, a communication system has been described in which synchronization acquisition is performed without using known data such as a pilot for a direct spread spectrum signal whose primary modulation is an FSK modulated carrier. In contrast, in this embodiment, a communication system that not only performs synchronization acquisition without using known data but also realizes estimation of a carrier frequency offset and a transmission path impulse response from a received signal will be described.

  FIG. 9 is a diagram illustrating a configuration example of the third embodiment of the communication system according to the present invention. The communication system of the present embodiment includes a transmitter (a communication device on the data transmission side) provided with an FSK modulation unit 51, a spread code generation unit 52, and a spread modulation unit 53, a spread code generation unit 61, a synchronization acquisition unit 62, A receiver including a spread code generator 63, a frequency offset estimator 64, a transmission line response estimator 65, a signal corrector 66, a despreader 67, and an FSK demodulator 68. It consists of In the communication system of this embodiment having such a configuration, FSK modulation is applied to primary modulation, and spreading is performed over a wide band using a spreading code.

  Hereinafter, the communication system of the present embodiment will be described in detail. First, the operation of the transmitter will be described.

In the transmitter according to the third embodiment, the FSK modulation unit 51 is the same as the FSK modulation unit 11 included in the transmitter according to the first embodiment, and the FSK modulation unit 51 that performs primary modulation receives the input information. Based on the data a (t), FSK modulation data b (t) is generated. That is, according to the value of the information data a (t), FSK modulation is performed by assigning carriers having different frequencies for each value to generate FSK modulated data. For example, when quaternary FSK is taken as an example, as shown in FIG. 2, the values 00, 01, 10, and 11 are set as frequencies in the spreading band Bw as f ₀ , f ₁ , f ₂ , and f ₃ , respectively. The FSK modulation data b (t) is generated by conversion.

  The spread code generation unit 33 and the spread modulation unit 34 are the same as the spread code generation unit 12 and the spread modulation unit 13 included in the transmitter according to Embodiment 1, and the spread modulation unit 34 is expressed by the above equation (1). Accordingly, the spread modulation data s (t) is generated by multiplying the FSK modulation data b (t) output from the FSK modulation unit 32 by the spread code c (k) generated by the spread code generation unit 33.

  Next, the operation of the receiver will be described.

  The spread modulation data s (t) transmitted from the transmitter is received as a signal r (t), and this received signal r (t) is input to the signal correction unit 66. Although details of the signal correction unit 66 will be described later, the output r ′ (t) is input to the synchronization correction unit 62, the frequency offset estimation unit 64, the transmission path response estimation unit 65, and the despreading unit 67.

  The spread code generation unit 61 generates a spread code similar to the spread code generation unit 21 of the first embodiment.

  The synchronization acquisition unit 62 is the same as the synchronization acquisition unit 22 of the first embodiment, and uses the signal replica d (k ′) generated by the spread code generation unit 61 to output signals from the signal correction unit 66. A sliding correlation process with r ′ (t) is performed to detect and determine the synchronization timing of the spreading code. Details of the signal r ′ (t) will be described later.

  The spreading code generation unit 63 generates the same spreading code c (k) as that generated by the spreading code generation unit 53 of the transmitter.

The frequency offset estimation unit 64 uses the signal r ′ (t) and the signal replica d (k ′) generated by the spreading code generation unit 61 in accordance with the timing m (t) estimated by the synchronization acquisition unit 62. Estimate the frequency offset. The frequency offset estimated value is obtained according to the following equation (9), for example. In the following equation (9), arg represents a complex argument.
f _{T ′} (t) = arg [Σ [{r ′ (m (t) + k ′ · T ′) × d ^* (k ′)}
× {r ′ (m (t) + (k′−1) · T ′) × d ^* (k′−1)} ^* ]] (9)
Here, f _{T ′} (t) represents a frequency offset amount per time T ′ corresponding to the sample period of the signal replica d (k ′), and the signal r ′ (t) is expressed by the following equation (10). It can be converted into a frequency offset amount f _Ts per period T _S.
f _Ts (t) = f _{T ′} (t) × (T _S / T ′) (10)

The transmission path response estimation unit 65 uses the signal r ′ (t) and the signal replica d (k ′) generated by the spreading code generation unit 61 in accordance with the timing m (t) estimated by the synchronization acquisition unit 62. To estimate the transmission path impulse response. The estimated value of the transmission path impulse response is obtained according to the following equation (11), for example.
CIR (t) = Σ {r ′ (m (t) + k ′ · T ′) × d ^* (k ′)} (11)
Here, CIR (t) represents a transmission path impulse response.

The signal correction unit 66 uses the frequency offset estimation value estimated by the frequency offset estimation unit 64, that is, the frequency offset amount f _Ts per cycle T _S, and the transmission path impulse response estimation value CIR estimated by the transmission path response estimation unit 65. For example, the received signal r (t) is corrected according to the following equation (12), and the corrected received signal r ′ (t) is output. In the state immediately after the start of the reception operation, that is, in the state where the estimation results (f _Ts and CIR) by the frequency offset estimation unit 64 and the transmission path response estimation unit 65 are not obtained, the signal correction unit 66 receives the received signal r. (t) is output as r ′ (t) without correction.
r ′ (t) = r (t) × CIR ^* (t) × exp (j · f _Ts (t) × t / T _S ) (12)

  The despreading unit 67 is the same as the despreading unit 24 of the first embodiment, and the received signal r ′ (t) after correction and the spread are synchronized with the timing m (t) estimated by the synchronization capturing unit 62. Despreading is performed by multiplying the complex conjugate of the spreading code c (t) generated by the code generator 63.

  The FSK demodulator 68 performs demodulation corresponding to FSK on the despread signal x (t) output from the despreader 67 and outputs demodulated data y (t).

  As described above, in the communication system according to the present embodiment, the communication device (receiver) on the data reception side performs spreading corresponding to each timing at which the phases of the carriers in the M-value FSK modulation applied to the primary modulation match. A code replica is extracted to generate a signal replica, and the received signal sample corresponding to each timing at which the phases of the respective carriers coincide (the timing at which the signal replica is extracted from the spreading code) and the signal replica are used, and the frequency offset estimation value and A transmission line impulse response was obtained. That is, in addition to the function of the receiver of the first embodiment, the function of estimating the frequency offset and the transmission path impulse response is further provided. As a result, the frequency offset estimation value and the transmission path impulse response estimation value can be obtained without using the pilot signal, and the pilot signal is not required. Therefore, the frequency utilization efficiency is improved as compared with the case where the pilot signal is used. Can be planned. Moreover, the same effect as Embodiment 1 can also be acquired.

  As described above, the communication system according to the present invention is useful for a communication system to which spread spectrum is applied, and is particularly suitable for a communication system that performs FSK modulation as primary modulation.

11, 32, 51 FSK modulation unit 12, 21, 23, 33, 41, 43, 52, 61, 63 Spread code generation unit 13, 34, 53 Spread modulation unit 22, 62 Synchronization acquisition unit 24, 45, 67 Despreading Unit 25, 46, 68 FSK demodulation unit 31 pilot generation unit 42 data synchronization acquisition unit 44 pilot synchronization acquisition unit 64 frequency offset estimation unit 65 transmission path response estimation unit 66 signal correction unit 221 421 441 delay unit 222 222 442 Multiplier 223, 423, 443 Adder 224, 424, 444 Correlation power calculation unit 225, 446 Correlation peak position detection unit 226, 447 Threshold value determination unit 445 Correlation power synthesis unit

Claims (12)

A communication system applying spread spectrum communication that performs FSK modulation with primary modulation,
The communication device on the receiving side
Based on the relationship between the frequencies of the carriers used in the FSK modulation on the transmission side and the same spreading code as that used in the spread modulation on the transmission side, a signal replica for synchronization acquisition is generated, and the signal A synchronization timing detecting means for performing a correlation operation between the replica and the received signal and determining a synchronization timing of the spreading code;
Despreading means for despreading the received signal using the spreading code according to the determined synchronization timing;
FSK demodulating means for FSK demodulating the received signal despread by the despreading means;
A communication system comprising: The synchronization timing detection means includes
2. The communication system according to claim 1, wherein a part of codes in the spread code is extracted as the signal replica based on a relationship between frequencies of the carriers. The synchronization timing detection means includes
Based on the relationship between the frequencies of the carriers, the timing at which the phases of the carriers are all matched is identified, and a code corresponding to the identified timing is extracted from the spreading code to be the signal replica. The communication system according to claim 2. Estimating means for estimating a frequency offset and a transmission path impulse response based on the synchronization timing, the spreading code and the received signal;
The communication system according to claim 1, 2 or 3, further comprising: Signal correction means for correcting a received signal based on the frequency offset and the transmission path impulse response;
The communication system according to claim 4, further comprising: A communication system applying spread spectrum communication that performs FSK modulation with primary modulation,
The communication device on the receiving side
A first signal replica for acquisition of synchronization is generated based on the frequency relationship of each carrier used in the FSK modulation on the transmission side and the same spreading code used in the spread modulation on the transmission side Correlation calculating means for calculating a correlation between the first signal replica and the received signal;
A second signal replica for synchronization acquisition using known information is generated based on the spreading code, and the second signal replica and the known information contained in the received signal are obtained by FSK modulation and spreading modulation. A synchronization timing for performing a correlation calculation of the received signal, further combining the correlation calculation result and the correlation calculation result by the correlation calculation means, and determining a synchronization timing of the spreading code using the combined correlation calculation result Detection means;
Despreading means for despreading the received signal using the spreading code according to the determined synchronization timing;
FSK demodulating means for FSK demodulating the signal despread by the despreading means;
A communication system comprising: The correlation calculation means includes
The communication system according to claim 6, wherein a part of codes in the spread code is extracted as the first signal replica based on a relationship between frequencies of the carriers. The correlation calculation means includes
Based on the relationship between the frequencies of the carriers, the timing at which the phases of the carriers are all matched is identified, and a code corresponding to the identified timing is extracted from the spreading code and the first signal replica The communication system according to claim 7. The communication device on the sending side
9. The FSK modulation is performed by using a plurality of carriers in a relationship that can express the frequency of another carrier by multiplying the frequency of the carrier having the lowest frequency by an integer multiple. The communication system according to one. A receiver for receiving a signal whose data is FSK modulated and further spread modulated,
Based on the relationship between the frequencies of the carriers used in the FSK modulation on the transmission side and the same spreading code as that used in the spread modulation on the transmission side, a signal replica for synchronization acquisition is generated, and the signal A synchronization timing detecting means for performing a correlation operation between the replica and the received signal and determining a synchronization timing of the spreading code;
Despreading means for despreading the received signal using the spreading code according to the determined synchronization timing;
Demodulation means for FSK demodulating the signal despread by the despreading means;
A receiver comprising: Estimating means for estimating a frequency offset and a transmission path impulse response based on the synchronization timing, the spreading code and the received signal;
The receiver according to claim 10, further comprising: A receiver for receiving a signal whose known information and data are FSK modulated and further spread modulated,
A first signal replica for acquisition of synchronization is generated based on the frequency relationship of each carrier used in the FSK modulation on the transmission side and the same spreading code used in the spread modulation on the transmission side Correlation calculating means for calculating a correlation between the first signal replica and the received signal;
Based on the spreading code, a second signal replica for synchronization acquisition using the known information is generated, and the known information included in the second signal replica and the received signal is subjected to FSK modulation and spreading modulation. And the correlation calculation result and the correlation calculation result by the correlation calculation means are combined, and the synchronization timing of the spreading code is determined using the combined correlation calculation result. Synchronization timing detection means;
Despreading means for despreading the received signal using the spreading code according to the determined synchronization timing;
FSK demodulating means for FSK demodulating the signal despread by the despreading means;
A receiver comprising:

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