JP4313154B2 - COMMUNICATION SYSTEM, RECEPTION DEVICE, TRANSMISSION DEVICE, RECEPTION METHOD, TRANSMISSION METHOD, AND PROGRAM - Google Patents

Description

  The present invention relates to a communication system, a receiving device, a transmitting device, a receiving method, a transmitting method, and a program for realizing these on a computer.

  Conventionally, wireless communication techniques using systems such as the IMT 2000 W-CDMA system, the lCDMA2000 system, and the wireless LAN IEEE 802.11b have been proposed. In such wireless communication, CDMA (Code Division Multiple Access) is used in order to use the same frequency band for a plurality of communication connections.

  In CDMA, by spreading and modulating communication information using different spreading codes, a plurality of communication connections can be put into the same frequency band, and desired communication connections can be separated from the same frequency band.

In addition, a technique is known in which a number sequence obtained by applying an appropriate FIR (Finite Impulse Response) filter to a random number sequence is used as a spreading code. The following documents disclose such techniques.
JP 2001-292129 A JP 2002-290274 A MBPursley, Performance Evaluation for Phase-Coded Spread-Spectrum Multiple-Access Communication, Part I: System Analysis, IEEE Trans.on Communications, Vol.com-25, No.8, 1977

  The FIR filter used in the technology disclosed in [Patent Literature 1] and [Patent Literature 2] obtains a plurality of signals from one input signal and sums them, and the i th of the plurality of signals. Assuming that the delay time of the signal with respect to the input signal is D [i] and the amplification factor is A [i], the sequences D [0], D [1], D [2],. [0], A [1], A [2],... Are geometric sequences with a common ratio r (-1 <r <1).

  Then, using the same D, r and initial values of different recurrence formulas in a plurality of transmission / reception systems, the random number sequence generated by the recurrence formula using the Chebyshev polynomial is used to obtain a numeric sequence using the above FIR filter, It has been found that when a sequence is used as a spreading code, the bit error rate is improved.

  On the other hand, [Non-Patent Document 1] discloses a method of calculating interference noise between users when a certain set of spreading codes is used in code division multiplexing communication using spreading codes.

  However, in the technique using the FIR filter as described above, there is a demand for a technique for preferentially improving the communication quality indicated by the bit error rate or the like for any one system in an environment where a plurality of transmission / reception systems exist simultaneously. ing.

  It is an object of the present invention to provide a communication system, a receiving apparatus, a transmitting apparatus, a receiving method, a transmitting method, and a program for realizing these on a computer, which are suitable for performing such communication.

  In order to achieve the above object, the following invention is disclosed in accordance with the principle of the present invention.

The communication system according to the first aspect of the present invention includes at least one receiving device and K (K> 1) transmitting devices, and for each of the K transmitting devices, i (i = Correlation parameter r _i (−1 <r _i <1) is assigned to the (0,..., K−1) -th transmitting apparatus, and the configuration is as follows.

That is, when information is transmitted from an arbitrary transmitting device (hereinafter, this is the i-th transmitting device) among the K transmitting devices to the receiving device, the receiving device and the i-th transmitting device Is
The correlation parameter r _i ,
A random number sequence x ⁽ⁱ⁾ of length N + M (N> 1, M> 1) shown in [Equation 34] and satisfying the relationship shown in [Equation 35];
From [Equation 36] [Equation 37] [Equation 38] [Equation 39] and performing modulation / demodulation using a sequence N ⁽ length ⁾ of length N shown in [Equation 40] as a spreading code, Transmission is performed by asynchronous code division multiple access communication.

On the other hand, in the case where information is transmitted from an arbitrary transmitting device among the K transmitting devices (hereinafter, this is the k-th transmitting device) to the receiving device, the correlation assigned to the other transmitting device. Ρ (−1 <ρ <1) that minimizes the function f (ρ) defined by [Equation 41] and [Equation 42] from the parameters r _i (i = 0,..., K−1, where i ≠ k). ) Is a correlation parameter r _k (−1 <r _k <1) to be assigned to the k-th transmitter.

Then, i = k in [Equation 34], i = k in [Equation 36 [Equation 37] and [Equation 38], and [Equation 39] and the assigned correlation parameter r _k are used. In [Formula 40], modulation / demodulation is performed using a spreading code a ^(k) of length N with i = k, and transmission is performed by asynchronous code division connection communication.

Further, in the communication system of the present invention, each random number sequence x ⁽ⁱ⁾ is configured to be calculated by a recursion formula [Equation 44] based on a Chebyshev polynomial [Equation 43] of p (p ≧ 2) order. be able to.

  In the communication system of the present invention, the receiving apparatus includes a receiving unit, a parameter calculating unit, a spreading code calculating unit, and a demodulating unit, and can be configured as follows.

  That is, the receiving unit receives the sum of the modulated signals transmitted from the K transmitting devices.

On the other hand, the parameter calculation unit calculates the correlation parameter r _k.

Further, the spreading code calculation unit calculates the spreading code a ^(k) of the length N from the calculated correlation parameter r _k and the random number sequence x ^(k) .

Then, the demodulating unit demodulates the signal transmitted from the k-th transmission device from the sum of the received modulated signals, using the calculated spreading code a ^(k) of length N.

  In the communication system of the present invention, the k-th transmission device includes a signal reception unit, a parameter calculation unit, a spreading code calculation unit, a modulation unit, and a transmission unit, and is configured as follows. be able to.

  That is, the signal receiving unit receives a signal to be transmitted to the receiving device.

On the other hand, the parameter calculation unit calculates the correlation parameter r _k.

Further, the spreading code calculation unit calculates the spreading code a ^(k) of the length N from the calculated correlation parameter r _k and the random number sequence x ^(k) .

Then, the modulation unit modulates the received signal with the spread code a ^(k) having the calculated length N.

  On the other hand, the transmission unit transmits the modulated signal to the receiving device.

  A receiving device according to another aspect of the present invention is a receiving device of the communication system.

  A transmission device according to another aspect of the present invention is a reception device of the communication system.

A reception method according to another aspect of the present invention communicates with K (K> 1) transmission devices, and for each of the K transmission devices, the i (i = 0,..., K−1) th A correlation parameter r _i (−1 <r _i <1) is allocated to the transmission device, and includes an allocation process and a transmission reception process, and is configured as follows.

That is, when receiving transmission of information from any of the K transmitting devices (hereinafter, this is assumed to be the i-th transmitting device), the i-th transmitting device,
The correlation parameter r _i ,
A random number sequence x ⁽ⁱ⁾ of length N + M (N> 1, M> 1) shown in [Equation 34] and satisfying the relationship shown in [Equation 35];
From [Equation 36] [Equation 37] [Equation 38] [Equation 39] and performing modulation / demodulation using a sequence N ⁽ length ⁾ of length N shown in [Equation 40] as a spreading code, Transmission is performed by asynchronous code division multiple access communication.

On the other hand, when receiving information transmission from any of the K transmission devices (hereinafter, this is assumed to be the k-th transmission device), in the assignment step, the information is assigned to another transmission device. From the correlation parameters r _i (i = 0,..., K−1, i ≠ k), ρ (−1 <ρ <) that minimizes the function f (ρ) defined by [Equation 31] and [Equation 32]. Let 1) be a correlation parameter r _k (−1 <r _k <1) assigned to the k-th transmission device.

In the transmission acceptance step, i = k in [Equation 34], i = k in [Equation 36] [Equation 37] and [Equation 38], [Equation 39], and the assigned correlation parameter r _k . , Are used to demodulate using a spread code a ^(k) of length N with i = k in [Equation 40], and receive transmission by asynchronous code division connection communication.

Further, in the receiving method of the present invention, each random number sequence x ⁽ⁱ⁾ is configured to be calculated by a recursion formula [Equation 44] by a P (p ≧ 2) degree Chebyshev polynomial [Equation 43]. be able to.

  In the reception method of the present invention, the transmission reception step includes a reception step, a parameter calculation step, a spreading code calculation step, and a demodulation step, and can be configured as follows.

  That is, in the receiving step, the sum of the modulated signals transmitted from the K transmitting devices is received.

On the other hand, in the parameter calculation process to calculate the correlation parameter r _k.

Further, in the spreading code calculation step, the spreading code a ^(k) of the length N is calculated from the calculated correlation parameter r _k and the random number sequence x ^(k) .

Then, in the demodulation step, the signal transmitted from the k-th transmitter is demodulated from the sum of the received modulated signals using the calculated spreading code a ^(k) of length N.

A transmission method according to another aspect of the present invention is used in any one of K (K> 1) transmission devices communicating with at least one reception device, and for each of the K transmission devices, i A correlation parameter r _i (−1 <r _i <1) is assigned to the (i = 0,..., K−1) -th transmission device, and includes an assignment step and a transmission step. Constitute.

That is, when transmitting information from an arbitrary transmission device among the K transmission devices (hereinafter, this is the i-th transmission device) to the reception device, the reception device, the i-th transmission device, Is
The correlation parameter r _i ,
A random number sequence x ⁽ⁱ⁾ of length N + M (N> 1, M> 1) shown in [Equation 34] and satisfying the relationship shown in [Equation 35];
From [Equation 36] [Equation 37] [Equation 38] [Equation 39] and performing modulation / demodulation using a sequence N ⁽ length ⁾ of length N shown in [Equation 40] as a spreading code, Transmission is performed by asynchronous code division multiple access communication.

On the other hand, when information is transmitted from any one of the K transmitting devices (hereinafter, this is assumed to be the kth transmitting device) to the receiving device, in the allocation step, the other transmitting devices are transmitted. Ρ (−1) that minimizes the function f (ρ) defined by [Equation 41] and [Equation 42] from the assigned correlation parameters r _i (i = 0,..., K−1, where i ≠ k). Let <ρ <1) be a correlation parameter r _k (−1 <r _k <1) to be assigned to the k-th transmission apparatus.

Further, in the transmission step, i = k in [Equation 34], i = k in [Equation 36] [Equation 37] and [Equation 38], [Equation 39], the assigned correlation parameter r _k , Then, modulation is performed using a spreading code a ^(k) of length N with i = k in [Equation 40], and transmission is performed by asynchronous code division connection communication.

Further, in the transmission method of the present invention, each random number sequence x ⁽ⁱ⁾ is configured to be calculated by a recursion formula [Equation 44] using a p (p ≧ 2) degree Chebyshev polynomial [Equation 43]. be able to.

  In the transmission method of the present invention, the transmission process includes a signal reception process, a parameter calculation process, a spreading code calculation process, a modulation process, and a transmission process, and can be configured as follows.

  That is, in the signal receiving step, a signal to be transmitted to the receiving device is received.

On the other hand, in the parameter calculation process to calculate the correlation parameter r _k.

Further, in the spreading code calculation step, the spreading code a ^(k) of the length N is calculated from the calculated correlation parameter r _k and the random number sequence x ^(k) .

Then, in the modulation step, the received signal is modulated by the spread code a ^(k) having the calculated length N.

  On the other hand, in the transmission step, the modulated signal is transmitted to the receiving device.

  A program according to another aspect of the present invention receives a computer (including an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), and other various software radios) as described above. It is configured to function as a device or a transmission device, or to cause a computer to execute the above reception method or transmission method.

  The program of the present invention can be recorded on a computer-readable information recording medium (including a compact disk, flexible disk, hard disk, magneto-optical disk, digital video disk, magnetic tape, or semiconductor memory).

  A program of the present invention is stored in a general-purpose computer, a mobile phone, a PHS (Personal Handyphone System) device, a portable terminal such as a game device, an information processing device such as a parallel computer, an ASIC, and the like. , DSP, FPGA, etc., the above receiving device, transmitting device, receiving method, and transmitting method can be realized.

  Independent of these devices, the information recording medium of the present invention can be distributed and sold in stores, or the program of the present invention itself can be distributed and sold via a computer communication network.

  According to the present invention, in an environment in which a plurality of transmission / reception systems exist simultaneously, a reception device, a transmission device, a reception method, a transmission method, and the like suitable for preferentially improving communication quality for any one system, A program realized on a computer can be provided.

  Embodiments of the present invention will be described below. The embodiments described below are for illustrative purposes and do not limit the scope of the present invention. Accordingly, those skilled in the art can employ embodiments in which each or all of these elements are replaced with equivalent ones, and these embodiments are also included in the scope of the present invention. . In the following, first, the theoretical background of the present invention will be described, and then detailed embodiments will be described.

(Theoretical background)
In an environment with multiple users, the i-th user is a spreading code with a code length of N.
a ⁽ⁱ⁾ = a ⁽ⁱ⁾ ₀ , a ⁽ⁱ⁾ ₁ , ..., a ⁽ⁱ⁾ _N-1
Is used, the standard deviation σ _I of interference noise from other users with respect to the user i can be obtained as [Equation 45] according to [Non-Patent Document 1].

The partial correlation coefficient C _{k, i} (m) used here is defined as [Equation 46].

  Here, reviewing [Equation 45] reveals that only the subscripts of the partial correlation coefficient are k, k or i, i.

Where random number sequence
x ^(k) ₀ , x ^(k) ₁ , x ^(k) ₂ ,…
(See [Equation 34]). It is assumed that the average of this random number sequence is μ ^(k) and the standard deviation is σ ^(k) (see [Equation 37] and [Equation 39]).

A sequence of numbers used for spreading codes using such random numbers
a ^(k) ₀ , a ^(k) ₁ , a ^(k) ₂ ,…
(See [Equation 36]).

Then, the partial correlation coefficient C _{k, k} (m) can be obtained as [Equation 47].

Therefore, the expected value E [C _{k, k} {(m)] is obtained as in [Equation 48] using the function e (•, •) defined by [Equation 41].

  This can be specifically determined according to M. For example, the case of M = 1 is shown in [Formula 49], and the case of M = 2 is shown in [Formula 50].

In this way, for any M, E [C _{k, k} ] (m) = e (r _k , m) can be obtained as a function that can be described specifically analytically.

  Now, in order to make it easier to read, if the right side of [Equation 45] is rewritten using the function e (.,.), It will become [Equation 51].

As described above, this value corresponds to the expected value of the variance value of interference noise that user k receives from other users. Therefore, if select r _k that minimizes this, it becomes possible to minimize the interference noise user k receives.

Therefore, when rewriting as r _k → ρ, m → h and omitting the coefficient 1 / 6N from [Equation 51] as a function f (ρ), [Equation 52] is obtained.

This is the same function as [Formula 42] above. Using r _i used by users other than user k, search for ρ that minimizes the function f (ρ) in the range of -1 <ρ <1, and adopt the obtained ρ as r _k In this case, the interference noise of the user k is minimized.

  Since f (ρ) is a rational polynomial function that can be concretely described analytically (which can be described by four arithmetic operations of polynomials), the minimum ρ may be obtained by differentiating it, It is also possible to perform a numerical calculation and draw a graph to obtain a minimum approximate value of ρ.

  When calculation is performed specifically using the technique of differentiation and omitting the minute term, if M = 1, and if the value of [Equation 53] is positive, ρ → −1 is the optimum parameter, 53] is negative, ρ → + 1 is the optimum parameter.

Further, if M → ∞ and N is sufficiently larger than 1, omitting a minute term may adopt ρ that minimizes [Equation 54] as r _k . Since [Equation 55] is obtained by differentiating [Equation 54] with respect to ρ, the optimum ρ can be analytically determined from these.

  FIG. 1 is an explanatory diagram showing a graph drawn by actually conducting a numerical calculation experiment.

In the numerical calculation experiment, when M → ∞, the number of users K = 10, and the code length N is sufficiently longer than 1, the amplification factors used by the other nine users are -0.2, -0.1, 0.0, It is a graph corresponding to [Formula 53] when 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6. As described above, an environment in which the amplification factor (which is equal to the correlation parameter) of the FIR filter for each user is different is called a “heterogeneous environment”. The horizontal axis corresponds to ρ (r _{1 in the} figure), the vertical axis corresponds to the value of [Equation 53], and represents the value of E [σ _I ]. That is, the value of [Equation 53] is appropriately scale-converted while maintaining the magnitude relationship, and corresponds to the graph of this figure.

The optimum parameter value obtained in this experiment is ρ≈0.566005, and the expected value E [σ _I ] of the standard deviation of the interference noise at this time is approximately 2.55072N.

On the other hand, in the technique disclosed in [Patent Document 1] and [Patent Document 2] (the technique under “homogeneous environment” in which the amplification factors of all users' FIR filters are equal), the optimal parameter value is ρ = 2−3. ^1/2 ≒ 0.267949, and when the expected value E [σ _I ] of the standard deviation of interference noise at this time is obtained in this environment, it was about 2.59808N.

  As described above, according to the above principle, even in a heterogeneous environment, the optimum value of the amplification factor to be used can be obtained from the amplification factor value of the FIR filter used by other users. When this is used, the interference noise becomes smaller than in the prior art.

  In addition, when all the users employ the above-mentioned optimum parameter value as the correlation parameter (FIR filter amplification factor), the environment is homogeneous and corresponds to a special parameter example of the heterogeneous environment.

  FIG. 2 is a schematic diagram showing a schematic configuration of the communication system according to the embodiment of the present invention. Hereinafter, a description will be given with reference to FIG.

  The communication system 201 includes K (K> 1) transmission devices 231 and at least one reception device 251. Each of the plurality of transmission devices 231 generates a spreading code from a random number sequence by appropriately determining the amplification factor of the FIR filter, and performs code division multiplexing communication. Then, the receiving device 251 receives the sum total of the radio signals (modulated signals) emitted from the respective transmitting devices 231 that have arrived through the radio wave propagation path as a received signal.

  In such an environment, when the receiver 251 receives information transmitted from the k (0 ≦ k <K) -th transmitter 231, the present invention is used when it is desired to minimize the influence of interference noise. The principle can be applied.

(Transmitter)
FIG. 3 is a schematic diagram illustrating a schematic configuration of the k-th transmission device 231 according to the present embodiment. Hereinafter, a description will be given with reference to FIG.

  The transmission apparatus 231 includes a signal reception unit 301, a parameter calculation unit 302, a spreading code calculation unit 303, a modulation unit 304, and a transmission unit 305, and is configured as follows.

  That is, the signal receiving unit 301 receives a signal to be transmitted to the receiving device.

On the other hand, the parameter calculation unit 302 is an amplification factor of an FIR filter used by another transmission device (this is equal to the correlation parameter of the other transmission device) r _i (0 ≦ i <K, i ≠ k). And the optimum correlation parameter r _k is calculated according to the principle described above. That is, for the function of [Equation 42], a value ρ that takes the minimum value analytically using a technique of mathematical expression processing is obtained, or a specific numerical value is input to the function of [Equation 42]. It takes the minimum value calculate by performing Te calculated values [rho, employing the [rho} as r _k.

Further, the spreading code calculation unit 303 calculates the spreading code a ^(k) of the length N from the correlation parameter r _k calculated using the FIR filter and the random number sequence x ^(k) .

As the random number sequence x ^(k) , it is desirable that the expected value is 0, but when it is not 0, if the expected value μ ^(k) is subtracted from the elements included in the sequence, the input sequence is used. good. That is,
x ^(k) ₀ -μ ^(k) , x ^(k) ₁ -μ ^(k) , x ^(k) ₂ -μ ^(k) ,…
Is input to the FIR filter for obtaining the spreading code a ^(k) .

In addition, it is preferable that the random number sequence x ^(k) is independent for each user. In other words, it is preferable to adopt one that satisfies [Equation 35]. As a typical example of such a random number sequence, there is a method for obtaining a random number sequence x ^(k) by a recurrence formula [Equation 44] using a Chebyshev polynomial [Equation 43]. The resulting random number sequence behaves like a chaos and is independent of each other if the initial values are different. The period is infinite if the calculation is performed with infinite precision, and the period is extremely long even when the calculation is performed with finite precision. Therefore, the expected value and variance can be calculated analytically.

  FIG. 4 is a schematic diagram showing a schematic configuration of the FIR filter used here.

  The FIR filter 401 includes M delay units 402, M amplifiers 403, and an adder 404.

Here, each of the delay devices 402 delays the input signal (corresponding to the random number sequence x ^(k) ) by a predetermined time D. As D, a clock unit or the like used in an electronic circuit including the FIR filter 401 may be employed.

On the other hand, each of the amplifiers 403 receives the delay signal output from the delay unit 402, and when the delay time of the delay signal with respect to the input signal is T, the amplifier 403 amplifies to (−r ^(k) ) ^{T / D} times. And output.

  Further, the adder 404 sequentially obtains the total sum of the signals output from the amplifier 403 and uses this as an output signal.

The output signal obtained in this way needs to be properly normalized by the variance of the input random number sequence x ^(k) , and the result after this normalization is used as a spreading code. Specifically, the values σ ^(k) and β _k defined by [Equation 38] and [Equation 39] are used, and normalization is performed by sequentially multiplying the obtained output signal by β _k .

  For the FIR filter 401, the last length M sequence is adopted when a length N + M sequence is input. A mathematical expression of such calculation is [Equation 36].

Then, the modulation unit 304 modulates the received signal with the calculated spreading code a ^(k) of length N. The spread modulation performed by the modulation unit can be applied directly to the technology used in the code division multiplexing communication system.

  Finally, the transmitting unit 305 transmits the modulated signal to the receiving device.

(Receiver)
FIG. 5 is a schematic diagram illustrating a schematic configuration of a reception device 251 that receives information transmitted from the k-th transmission device 231 according to the present embodiment. Hereinafter, a description will be given with reference to FIG.

  The reception device 251 includes a reception unit 501, a parameter calculation unit 302, a spreading code calculation unit 303, and a demodulation unit 502, and can be configured as follows.

  That is, the receiving unit 501 receives the sum of the modulated signals transmitted from the K transmitting devices that have reached the receiving device 251 due to the influence of the radio wave propagation path.

On the other hand, the parameter calculating unit 302 calculates the correlation parameter r _k. Further, the spreading code calculation unit 303 calculates the spreading code a ^(k) of the length N from the calculated correlation parameter r _k and the random number sequence x ^(k) . The calculations performed by the parameter calculation unit 302 and the spreading code calculation unit 303 are the same as the calculations performed by the k-th transmission device 231.

Then, the demodulation unit 502 demodulates the signal transmitted from the k-th transmission device from the sum of the received modulated signals, using the calculated spreading code a ^(k) of length N. The spread demodulation performed by the demodulator can directly apply the technology used in the code division multiplexing communication system. For example, it is possible to apply a technique in which the correlation between the sum of the modulated signals and the spread code a ^(k) is calculated by sliding the window to synchronize and a transmission signal is obtained from the result of the synchronization.

  According to the present invention, a communication system, a receiving apparatus, a transmitting apparatus, a receiving method, a transmitting method suitable for preferentially improving communication quality for any one system in an environment where a plurality of transmitting / receiving systems exist simultaneously, and A program for realizing these on a computer can be provided, and can be applied to the field of communication technology.

It is explanatory drawing which shows the graph drawn by performing numerical calculation experiment with respect to the principle of this invention. It is explanatory drawing which shows schematic structure of the communication system which concerns on embodiment of this invention. It is explanatory drawing which shows schematic structure of the kth transmission apparatus of this embodiment. It is explanatory drawing which shows schematic structure of a FIR filter. It is explanatory drawing which shows schematic structure of the receiver which receives the information transmitted from the kth transmitter of this embodiment.

Explanation of symbols

201 Communication System 231 Transmitting Device 251 Receiving Device 301 Signal Accepting Unit 302 Parameter Calculation Unit 303 Spreading Code Calculation Unit 304 Modulating Unit 305 Transmitting Unit 401 FIR Filter 402 Delay Unit 403 Amplifier 404 Adder 501 Receiving Unit 502 Demodulating Unit

Claims (14)

A communication system having at least one receiving device and K (K> 1) transmitting devices, each of the K transmitting devices being i (i = 0, ..., K-1) th. Correlation parameter r _i (-1 <r _i <1) is assigned to
(A) When information is transmitted from an arbitrary transmission device (hereinafter, this is the i-th transmission device) among the K transmission devices to the reception device, the reception device and the i-th transmission device The transmitter of
The correlation parameter r _i ,
A random number sequence x ⁽ⁱ⁾ of length N + M (N> 1, M> 1) shown in [Equation 1] and satisfying the relationship shown in [Equation 2];
From [Equation 3] [Equation 4] [Equation 5] [Equation 6] and performing modulation / demodulation using the sequence N ⁽ length ⁾ of length N shown in [Equation 7] as a spreading code, Performs transmission by asynchronous code division multiple access communication,

(B) When information is transmitted from the arbitrary transmitting device among the K transmitting devices (hereinafter, this is the k-th transmitting device) to the receiving device,
From the correlation parameters r _i (i = 0,..., K−1, where i ≠ k) assigned to other transmitters, the function f (ρ) defined by [Equation 8] and [Equation 9] is minimized. Ρ (−1 <ρ <1) to be a correlation parameter r _k (−1 <r _k <1) assigned to the k-th transmitter,

[Equation 1] i = k, [Equation 3] [Equation 4] [Equation 5] i = k, [Equation 6] and the assigned correlation parameter r _k , [7] A communication system that performs modulation / demodulation using a spreading code a ^(k) of length N with i = k and performs transmission by asynchronous code division connection communication. The communication system according to claim 1,
Each of the random number sequences x ⁽ⁱ⁾ is calculated by a recursion formula [Equation 11] based on a Chebyshev polynomial [Equation 10] of p (p ≧ 2) order.

The communication system according to claim 1 or 2,
The receiving device is
A receiver that receives the sum of the modulated signals transmitted from the K transmitters;
A parameter calculation unit for calculating the correlation parameter r _k ;
From the calculated correlation parameter r _k and the random number sequence x ^(k) , a spreading code calculation unit for calculating the spreading code a ^(k) of the length N;
A demodulator that demodulates a signal transmitted from the k-th transmitter by the calculated spreading code a ^(k) of length N from the sum of the received modulated signals;
Characterized by comprising.   The receiving device in the communication system according to claim 3. The communication system according to any one of claims 1 to 3,
The k-th transmitter is
A signal receiving unit for receiving a signal to be transmitted to the receiving device;
A parameter calculation unit for calculating the correlation parameter r _k ;
From the calculated correlation parameter r _k and the random number sequence x ^(k) , a spreading code calculation unit for calculating the spreading code a ^(k) of the length N;
A modulation unit that modulates the received signal by the calculated spreading code a ^(k) of length N;
A transmitting unit for transmitting the modulated signal to the receiving device;
Characterized by comprising.   The transmission apparatus in the communication system according to claim 5. A receiving method for communicating with K (K> 1) transmitting devices,
For each of the K transmitting devices, a correlation parameter r _i (−1 <r _i <1) is assigned to the i (i = 0,..., K−1) -th transmitting device,
When receiving transmission of information from any of the K transmission devices (hereinafter, this is assumed to be the i-th transmission device), the i-th transmission device,
The correlation parameter r _i ,
A random number sequence x ⁽ⁱ⁾ of length N + M (N> 1, M> 1) shown in [Equation 12] and satisfying the relationship shown in [Equation 13];
From [Expression 14], [Expression 15], [Expression 16], and [Expression 17], the sequence a ⁽ⁱ⁾ of length N shown in [Expression 18] is used as a spreading code, and modulation / demodulation is performed. Perform transmission by asynchronous code division multiple access communication,

When receiving transmission of information from any of the K transmission devices (hereinafter, this is assumed to be the kth transmission device),
From the correlation parameters r _i (i = 0,..., K−1, where i ≠ k) assigned to other transmitters, the function f (ρ) defined by [Equation 19] and [Equation 20] is minimized. Ρ (-1 <ρ <1) to be assigned as a correlation parameter r _k (-1 <r _k <1) to be assigned to the k-th transmitter,

In [Equation 12], i = k, and in [Equation 14], [Equation 15], and [Equation 16], i = k, and using [Equation 17] and the assigned correlation parameter r _k , 18], using a spreading code a ^(k) of length N with i = k, and receiving a transmission by asynchronous code division connection communication;
A receiving method comprising: The reception method according to claim 7, comprising:
The random number sequence x ⁽ⁱ⁾ is calculated by a recursion formula [Equation 22] based on a Chebyshev polynomial [Equation 21] of p (p ≧ 2) degree.

The reception method according to claim 7 or 8, comprising:
The transmission acceptance step includes
A receiving step of receiving a sum of modulated signals transmitted from the K transmitting devices;
A parameter calculation step for calculating the correlation parameter r _k ;
A spreading code calculating step of calculating a spreading code a ^(k) of the length N from the calculated correlation parameter r _k and the random number sequence x ^(k) ;
A demodulation step of demodulating a signal transmitted from the k-th transmission device from the sum of the received modulated signals by the calculated spreading code a ^(k) of length N;
A method comprising the steps of: A transmission method used in any one of K (K> 1) transmitters communicating with at least one receiver,
For each of the K transmitting devices, a correlation parameter r _i (−1 <r _i <1) is assigned to the i (i = 0,..., K−1) -th transmitting device,
When transmitting information from any of the K transmitting devices (hereinafter, this is the i-th transmitting device) to the receiving device, the receiving device, the i-th transmitting device, Is
The correlation parameter r _i ,
A random number sequence x ⁽ⁱ⁾ of length N + M (N> 1, M> 1) shown in [Equation 23] and satisfying the relationship shown in [Equation 24];
From [Equation 25] [Equation 26] [Equation 27] [Equation 28] and performing modulation / demodulation using a sequence N ⁽ length ⁾ of length N shown in [Equation 29] as a spreading code, Perform transmission by asynchronous code division multiple access communication,

When transmitting information to the receiving device from any one of the K transmitting devices (hereinafter, this is assumed to be the kth transmitting device),
The function f (ρ) defined by [Equation 30] and [Equation 31] is minimized from the correlation parameters r _i (i = 0,..., K−1, where i ≠ k) assigned to other transmitters. Ρ (-1 <ρ <1) to be assigned as a correlation parameter r _k (-1 <r _k <1) to be assigned to the k-th transmitter,

In [Equation 23], i = k, in [Equation 25], [Equation 26], and [Equation 27], i = k, and using [Equation 28] and the assigned correlation parameter r _k , 29] in which a modulation is performed using a spreading code a ^(k) of length N with i = k, and transmission is performed by asynchronous code division connection communication;
A transmission method comprising: The transmission method according to claim 10, comprising:
The random number sequence x ⁽ⁱ⁾ is calculated by a recursion formula [Equation 33] using a Chebyshev polynomial [Equation 32] of p (p ≧ 2) order.

The transmission method according to claim 10 or 11,
The transmission step includes
A signal receiving step for receiving a signal to be transmitted to the receiving device;
A parameter calculation step for calculating the correlation parameter r _k ;
A spreading code calculating step of calculating a spreading code a ^(k) of the length N from the calculated correlation parameter r _k and the random number sequence x ^(k) ;
A modulation step of modulating the received signal by the calculated spreading code a ^(k) of length N;
A transmitting step of transmitting the modulated signal to the receiving device;
A method comprising the steps of:   A program for causing a computer to function as the receiving device according to claim 4.   A program causing a computer to function as the transmission device according to claim 6.

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