JP5787846B2 - Receiving device, spread spectrum communication device, and communication system - Google Patents

Description

  The present invention relates to a receiving device, a spread spectrum communication device, and a communication system.

  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. Direct spread spectrum, which is one of the spread spectrum techniques, is a high-speed comparison of a symbol rate signal that is primarily modulated by PSK (Phase Shift Keying) or FSK (Frequency Shift Keying) on the transmission side. It is spread over a wide band with a rate spreading code and transmitted. On the receiving side, synchronization acquisition can be established and a transmission information data sequence can be reproduced by despreading using the same spreading code as the spreading code used on the transmitting side and a sliding correlator (for example, the following patents) Reference 1).

Japanese Patent No. 3441301

  However, the conventional direct spread spectrum system has a problem in 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 primary modulation, it is necessary to prepare a sliding correlator for the number of modulation multilevels in the configuration described in Patent Document 1, and as the number of modulation multilevels increases in addition to the spreading code length, There has been a problem that the circuit scale of the correlator or the amount of calculation increases.

  The present invention has been made in view of the above, and provides a receiving apparatus, a spread spectrum communication apparatus, and a communication system that can realize synchronization supplement without increasing the circuit scale even when the modulation multi-level number increases. The purpose is to obtain.

  In order to solve the above-described problems and achieve the object, the present invention is a receiving apparatus that receives a spread code signal spread by a spread code on a transmission side as a reception signal, and the spread signal is spread with respect to the reception signal. A despreading unit that generates a despread signal by performing despreading based on a code; a replica generation unit that generates a replica of a transmission signal as a replica signal based on the despread signal; and the replica signal and the despreading A correlation value calculation unit that calculates a correlation value with a signal, and a synchronization determination unit that detects a synchronization timing for the spreading code based on the correlation value.

  According to the present invention, there is an effect that synchronization supplement can be realized without increasing the circuit scale even if the modulation multi-level number increases.

FIG. 1 is a diagram illustrating a functional configuration example of a spread spectrum communication apparatus according to the present invention. FIG. 2 is a diagram illustrating an example of the frequency arrangement of the FSK modulated signal in the spread spectrum communication apparatus. FIG. 3 is a diagram illustrating an example of a spectrum after spread modulation processing. FIG. 4 is a diagram illustrating a configuration example of the synchronization capturing unit. FIG. 5 is a diagram illustrating an arrangement example of carrier signals of 4FSK modulation. FIG. 6 is a diagram showing a time waveform of the Ich component in the FSK data carrier signal.

  Hereinafter, embodiments of a receiving device, a spread spectrum communication device, and a communication system according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment.
FIG. 1 is a diagram illustrating a functional configuration example of a spread spectrum communication apparatus according to the present invention. The spread spectrum communication device 1 (transmission device) is a transmission device, and the spread spectrum communication device 2 (reception device) is a reception device. Here, in order to explain an example in which transmission from the spread spectrum communication apparatus 1 to the spread spectrum communication apparatus 2 is performed, the component as a transmission apparatus is shown. In the spread spectrum communication apparatus 2, the component as a reception apparatus is shown. Show. In general, the spread spectrum communication apparatus often has a transmission / reception function. In this case, the spread spectrum communication apparatus 1 has a function as a reception apparatus in the same manner as the spread spectrum communication apparatus 2, and the spread spectrum communication apparatus 2 Similar to the spread spectrum communication apparatus 1, it also has a function as a transmission apparatus. In the case of having a transmission / reception function, a component having a portion that can be shared (for example, the spread code generation unit 12) may be shared as one component without being separately provided for transmission and reception.

  As shown in FIG. 1, the spread spectrum communication apparatus 1 includes an FSK modulation unit 11 that performs FSK modulation based on information data to be transmitted, a spread code generation unit 12 that generates and stores a spread code, and an FSK modulated signal. Are provided with a spread modulation unit 13 that performs spread modulation with a spread code, and a transmission processing unit 14 that transmits a spread modulation signal.

  The spread spectrum communication device 2 includes a reception processing unit 21 that receives a signal (spread modulation signal) transmitted from the spread spectrum communication device 1, a synchronization acquisition unit 22 that detects a synchronization timing of a spread code from the received signal, and a transmission side A spread code generator 23 that generates and stores the same spread code, a despreader 24 that performs despreading using the spread code, an FSK demodulator 25 that performs FSK demodulation using the despread signal, and .

FIG. 2 is a diagram showing an example of the frequency arrangement of the FSK modulated signal in the spread spectrum communication apparatus 1 of the present embodiment. Here, an example of quaternary FSK is shown, and as shown in FIG. 2, the FSK modulated signal has f ₀ , f ₁ , f ₂ , and f ₃ corresponding to the quaternary values in the spreading bandwidth Bw. It is arranged as FSK data carrier signals (FSK modulated carrier signals) 201, 202, 203, 204 of four frequencies (FSK modulated carrier frequencies).

  FIG. 3 is a diagram illustrating an example of a spectrum after spread modulation processing in the spread spectrum communication apparatus 1 of the present embodiment. In FIG. 3, a spectrum 300 shows an example of a spectrum after spread modulation.

  Next, the operation of the present embodiment will be described. Here, an example will be described in which FSK modulation is applied as primary modulation for an information sequence, and a direct spread spectrum method is used in which spreading is performed over a wide band using a spreading code. First, the operation of the transmission side (spread spectrum communication apparatus 1 in FIG. 1) will be described.

The FSK modulation unit 11 that performs primary modulation processing generates FSK modulation data by giving different carrier frequency transitions for each value of information data based on the information data a (t) (t indicates time). For example, as shown in FIG. 2, when four-value FSK is taken as an example, information data values 00, 01, 10, and 11 are associated with f ₀ , f ₁ , f ₂ , and f ₃ in the spreading bandwidth Bw, respectively. Then, frequency conversion is performed to generate FSK modulation data.

The spread code generation unit 12 generates a spread code c (t) and stores it in a memory or the like. The spread modulation unit 13 generates the spread modulation data s (t) as illustrated in FIG. 3 by multiplying the FSK modulation data b (t) and the spread code c (t) as shown in Expression (1). To do.
s (t) = b (t) × c (t) (1)

  Next, the operation of the receiving side (spread spectrum communication apparatus 2 in FIG. 1) will be described. The received signal r (t) is input to the synchronization acquisition unit 22 and the despreading unit 24. The synchronization acquisition unit 22 uses the received signal r (t) and the same spread code c (t) as that on the transmission side to extract the synchronization timing of the spread code multiplied by the received signal, and performs synchronization acquisition.

  FIG. 4 is a diagram illustrating a configuration example of the synchronization capturing unit 22 in the spread spectrum communication apparatus 1 of the present embodiment. As shown in FIG. 4, the synchronization acquisition unit 22 performs a despreading unit 31 that performs despreading on a received signal using a spreading code, and a primary modulation signal (transmission) transmitted using the despread received signal. A replica of the signal), a correlation power calculation unit (correlation value calculation unit) 33 that calculates correlation power between the received signal after despreading and the replica signal generated by the replica generation unit 32, A correlation power peak detection unit 34 that detects the maximum value of the correlation power and a synchronization determination unit 35 that performs synchronization determination of the spread code are provided.

The operation of the synchronization capturing unit 22 will be described with reference to FIG. The despreading unit 31 despreads the signal (despread signal) based on the received signal r (t) and the despread code c ^* (t) generated based on the spread code c (t) used on the transmission side. x ′ (t) is calculated.
x ′ (t) = r (t) × c ^* (t) (2)

  The replica generation unit 32 generates a replica signal rep (t) common to the FSK modulation signal used for synchronization acquisition, which is a point of the present embodiment, from the despread signal x ′ (t). The replica generation method will be described with reference to FIGS.

FIG. 5 is a diagram illustrating an arrangement example of carrier signals of 4FSK modulation. In FIG. 5, F ₀ represents a frequency bandwidth obtained by dividing the spreading bandwidth Bw into 16 equal parts, and frequency 0 represents the center frequency of the spreading bandwidth. In this embodiment, as shown in FIG. 5, the spread bandwidth Bw and 16F _0, carrier frequency -8F _0, -4F _0, 4 single FSK data carrier signal 0,4F ₀ 501,502,503,504 Is used.

  FIG. 6 shows a time waveform of the Ich component in each FSK data carrier signal when FSK modulation mapping is performed on the frequency axis in FIG. The vertical axis in FIG. 6 indicates the frequency, and the horizontal axis indicates time (a discrete value at one sample time). The spreading code length N indicates a sample length corresponding to the cycle of the spreading code. In the present embodiment, the replica observation period M is set to a period that is an integral multiple of each of the four carrier frequency periods. In the example of FIG. 6, the spreading code length N is divided into four replica observation periods M.

In the example of FIG. 6, it is assumed that the replica observation period M satisfies the following formula (3).
_{u 0 / f 0 = u 1} / f 1 = u 2 / f 2 = u 3 / f 3 ... (3)
Here, f ₀ = −8F ₀ , f ₁ = −4F ₀ , f ₂ = 0, f ₃ = 4F _0, and u _{0 to} u ₃ represent integers greater than zero. That is, each FSK data carrier signal is a repeated signal with the replica observation period M as a unit. Further, the Qch component is also a signal obtained by advancing the phase of the Ich component by π / 2, and the characteristic of being a repeated signal in the replica observation period M is not changed.

Using these features, the replica generation unit 32 performs calculations shown in the following equations (4) to (6) to generate a replica signal rep (n).
rep (n) = R (m) (4)
m = mod (n, M) (5)
R (m) = A (m) + B (m) + C (m) + D (m) (6)
Here, A (m), B (m), C (m), and D (m) are obtained by dividing the despread signal x ′ (t) for each repetition period in the replica observation period M. Further, n indicates a sample number in the spreading code period and 0 ≦ n ≦ N−1, and m indicates a sample number in the replica observation period M and 0 ≦ m ≦ M−1. mod (p, q) represents the remainder of p / q. As can be seen from the above equation (6), R (m) is the sum of the FSK data carrier signals for each replica observation period M, and corresponds to the average value of the FSK data carrier signals for each replica observation period M. The method for generating the replica signal is not limited to the above example, and any method may be used as long as it is generated based on the despread signal x ′ (t). For example, in the above equation (6), a weighted average may be applied as an averaging method. Further, by setting R (m) above as an average value of the phase difference of the FSK data carrier signal for each replica observation period M, a replica signal corresponding to the phase difference for each replica observation period M of the transmission signal before spreading is generated. can do.

  Here, an example in which FSK modulation is performed as primary modulation has been described, but the type of primary modulation is not limited to this. What is necessary is just to obtain | require the repetition period of a transmission signal based on the periodicity of a transmission signal, and to divide | segment despread signal x '(t) by making this repetition period into a replica observation period.

  The correlation power calculation unit 33 obtains a correlation value between the replica signal rep (t) and the despread signal x ′ (t), and calculates the power P (t). Here, assuming that t is expressed in units of sample time, rep (t) = rep (n).

P (t) = | x ′ (t) rep (0) + x ′ (t−1 / Bw) rep (1)
+ ... + x ′ (t− (N−1) / Bw) rep (N−1) | ² (7)

  The correlation power peak detection unit 34 has a sample time (correlation) corresponding to the highest correlation power (correlation power peak value) among the correlation powers at each sample time within the spreading code period calculated by the above equation (7). Power peak time) is detected. Here, a correlation power value normalized with received power or the like can be used as necessary.

  The synchronization determination unit 35 performs synchronization determination using the sample time corresponding to the correlation power peak value output from the correlation power peak detection unit 34. That is, the synchronization determination unit 35 detects the synchronization timing for the spreading code based on the correlation power peak value. Here, although there is no restriction on the synchronization determination method, for example, there is a method of determining a synchronization when a correlation power threshold value is provided and the correlation power peak value exceeds the threshold value. If it is determined to be synchronized, the sample time l corresponding to the correlation power peak value is output as the synchronization timing.

  The despreading unit 24 adjusts the phase of the received signal r (t) and the spread code c (t) according to the sample time l determined to be synchronized by the synchronization capturing unit 22, and the received signal r (t) after adjustment By using the spread code c (t), the same calculation as in the equation (2) is performed to obtain the despread signal x (t).

  The FSK demodulator 25 demodulates the despread signal x (t) and outputs demodulated data. There is no restriction on the FSK demodulation method implemented here, and general FSK demodulation may be performed.

  As described above, in the present embodiment, a common replica signal is generated from each received signal in each FSK data carrier signal in the multilevel FSK modulation applied in the primary modulation, and the correlation power peak between the replica signal and the despread signal is obtained. To detect. The synchronization timing of the spread code can be detected by performing synchronization determination using the correlation power peak. In other words, according to the present embodiment, synchronization acquisition of a spread code can be established without using a known signal such as a pilot signal. In the prior art, in multilevel FSK modulation, it is necessary to prepare in advance a matched filter for correlating the replica signal for each FSK data carrier corresponding to the multilevel number and the received signal. In addition, there is a problem that the circuit scale of the correlator or the amount of calculation increases as the number of modulation multilevels increases. On the other hand, in the present embodiment, one replica signal generated from the received signal is generated instead of the despread signal replica that is individually required for each FSK data carrier signal corresponding to the multivalued number. Since this replica signal can be commonly used for FSK data carrier signal synchronization acquisition, it is possible to achieve synchronization acquisition while greatly reducing the circuit scale or the amount of calculation of the matched filter used for synchronization acquisition. Can do.

  As described above, the receiving apparatus, the spread spectrum communication apparatus, and the communication system according to the present invention are useful for a communication system that performs direct spread spectrum, and are particularly suitable for a communication system with a large number of modulation multilevels.

  1, 2 spread spectrum communication apparatus, 11 FSK modulation unit, 12 spread code generation unit, 13 spread modulation unit, 14 transmission processing unit, 21 reception processing unit, 22 synchronization acquisition unit, 23 spread code generation unit, 24 despreading unit, 25 FSK demodulating unit, 31 despreading unit, 32 replica generating unit, 33 correlation power calculating unit, 34 correlation power peak detecting unit, 35 synchronization determining unit, 201-204, 501-504 FSK data carrier signal, 300 spectrum.

Claims (7)

A receiving device that receives a spread code signal spread by a spread code on the transmission side as a received signal,
A despreading unit that generates a despread signal by despreading the received signal based on the spread code;
A replica generation unit that generates a replica of a transmission signal as a replica signal based on the despread signal;
A correlation value calculation unit for calculating a correlation value between the replica signal and the despread signal;
A synchronization determination unit that detects a synchronization timing for the spreading code based on the correlation value;
A receiving apparatus comprising:   The replica generation unit divides the reception signal for one period of the spreading code for each repetition period of the transmission signal, and generates the replica signal based on an average value of the divided reception signals; The receiving device according to claim 1. The spread code signal is a signal that is first modulated by FSK modulation and then spread by the spread code,
The receiving apparatus according to claim 1, wherein the replica generation unit generates a replica of a primary modulation signal as the replica signal.   The receiving apparatus according to claim 3, wherein the frequency of the FSK modulation carrier in the FSK modulation is any two or more frequencies selected within a spreading bandwidth.   5. The receiving apparatus according to claim 3, wherein the repetition period is an integral multiple of the period of the FSK modulation carrier for each of the modulation carrier frequencies. 6. A spread spectrum communication apparatus comprising: a transmission unit that transmits a spread code signal spread by a spread code; and a reception unit that receives a spread code signal spread by the spread code received from another device as a reception signal;
The receiver is
A despreading unit that generates a despread signal by despreading the received signal based on the spread code;
A replica generation unit that generates a replica of a transmission signal as a replica signal based on the despread signal;
A correlation value calculation unit for calculating a correlation value between the replica signal and the despread signal;
A synchronization determination unit that detects a synchronization timing for the spreading code based on the correlation value;
A spread spectrum communication apparatus comprising: A transmission device for transmitting a spread code signal spread by a spread code;
A receiving device for receiving the spread code signal as a received signal;
A communication system comprising:
The receiving device is:
A despreading unit that generates a despread signal by despreading the received signal based on the spread code;
A replica generation unit that generates a replica of a transmission signal as a replica signal based on the despread signal;
A correlation value calculation unit for calculating a correlation value between the replica signal and the despread signal;
A synchronization determination unit that detects a synchronization timing for the spreading code based on the correlation value;
A communication system comprising:

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