JP2006135369A - Multiple communication system using multiple gold code and pseudo random number sequence - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission/reception system extracting desired information with low noise by reducing the cross-correlation between gold codes in the case of inverse spread processing at reception when a plurality of gold codes are used to multiple transmission information and transmitting the multiplexed information in a direct spread system in a spread spectrum communication system. <P>SOLUTION: A multiple communication system includes: a transmission system for multiplexing digital information items 1 to U by the gold codes 1 to U and transmitting the multiplexed information items; and a reception system for receiving the signals transmitted from the transmission system, using any of the gold codes 1 to U to extract intended digital information among the digital information items 1 to U. The transmission system in the multiple communication system adopting the direct spread system is configured to use the gold codes 1 to U whose cross-correlation values are minimized and prescribed values to apply spread processing to the digital information items 1 to U and transmitting the multiplexed information items. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a direct spread multiplex communication system among spread spectrum communication systems, and more particularly to a multiplex communication system using a multiple gold code, for example, a central station using a direct spread system and a plurality of local stations. Such one-to-many communication can be used for communication from the central station to each local station, and each local station can receive a desired signal from the central station with low noise. Furthermore, the present invention relates to a pseudo-random number sequence in which the cross-correlation value is zero.

  Spread spectrum communication using the direct spreading method to realize stable communication even under the influence of noise and interference in various wireless communications, or to allow multiple communications to be multiplexed with only a combination of PN (pseudo-random number) codes The method is adopted. FIG. 6 shows an outline of a multiplexed spread spectrum communication system using the direct spreading method.

In the transmission system in FIG. 6, the primary modulation signals from the oscillators 10 ₁ to 10 _U are multiplied by the multipliers 11 _{1 to} 11 _U with respect to the respective digital information ₁ to _U , and further the multipliers 11 _{1 to} 11 _U. PN codes ₁ to _U as secondary modulation signals are multiplied by multipliers 12 _{1 to} 12 _U , respectively, and the multiplication results of the multipliers 12 _{1 to} 12 _U are added by an adder 13. Then, the addition result by the adder 13 passes through the band pass filter BPF, where a transmission signal in a required frequency band is selected and radiated as a transmission radio wave from the transmission antenna 14.

  Here, the modulation is performed in two stages, the first modulation is called primary modulation, and the modulation that expands the subsequent frequency band is called secondary modulation or spread modulation (actually, primary modulation and secondary modulation are interchanged). In some cases, a plurality of primary modulation units and secondary modulation units are combined in parallel to enable multiplexing of transmission signals. In FIG. 6, BPSK (Binary Phase Shift Keying), which is most frequently used in the direct spreading method, is used as an example of primary modulation.

Receiving system in FIG. 6 is the U installed corresponding to each of the digital information I through U, the first receiving system for receiving a digital information 1, the received signal received by receiving antenna 20 ₁ band A high-frequency signal in a required frequency band is selected through the pass filter BPF ₁ , multiplied by the same PN code 1 as that on the transmission side by a multiplier 21 ₁ , and demodulated as digital information 1 by a demodulator 22 ₁ . Similarly, in the U-th receiving system for receiving the digital information U, the received signal received by the receiving antenna 20 _U passes through the band-pass filter BPF _U, and a high-frequency signal in a required frequency band is selected and multiplied. Multiplier 21 _U multiplies the same PN code U as that on the transmission side, and demodulator 22 _U demodulates it as digital information U.

  FIG. 7 shows the relationship between the digital information and the digital transmission signal, and this digital transmission signal represents +1 when the digital information and the PN code have the same value, and represents −1 when the digital information and the PN code have the same value. Here, in the digital information and the PN code, +1 or −1 is used, but both express the logical value “+1” as −1 and the logical value “0” as +1. A digital transmission signal is obtained by arithmetically multiplying digital information and a PN code in terms of time. The transmission signal (transmission signal radiated from the antenna) for each digital transmission signal is sin (2πft) with respect to +1, and −sin (2πft) with respect to −1. The transmission signal including it will be described using a digital transmission signal.

  The PN code used in the secondary modulation is referred to as a spreading code, and this spreading code is desired to have a strong autocorrelation and a weak cross-correlation in consideration of multiplexing of transmission signals. When a PN code with a wide choice of code length is used, it is generally a Gold code, and the Gold code is used in multiplex communication using many direct spreading schemes.

The Gold code prepares two preferred pair M-sequence generation circuits (in FIG. 8, M sequences a (t) and b (t) having a code length of 31 are generated in FIG. 8) that satisfy certain conditions as shown in FIG. It is obtained by adding the outputs (exclusive OR for each bit). In FIG. 8, a _{0 to} a ₄ indicate the stages of the 5-stage shift register for generating the M sequence a (t), and b _{0 to} b ₄ indicate the stages of the 5-stage shift register for generating the M sequence b (t). Shows the stage. If one of the outputs of the two M-sequence generators is shifted in time, each becomes a completely different sequence, and a large number of Gold codes can be generated. That is, even though there is a cyclic code overlap, the initial values A and B of each M sequence are not both (0, 0,..., 0) and the generated sequence is “conventional Gold code. Is. In particular, as a property of the conventional Gold code generated from the M sequence of two preferred pairs, the cross-correlation values are −1, −K, L (K according to the time lag (cyclic time lag). And L take one of three values (see FIG. 8).

FIG. 9 shows an outline of a multiplexed spread spectrum communication system using a conventional Gold code as the PN code of FIG. 6, except that Gold codes 1 to U are used instead of PN codes 1 to U. 6 and the same or corresponding parts are denoted by the same reference numerals. In order to extract the digital information spread by the desired Gold code V from the multiplexed U transmission signals, the receiving side in FIG. 9 performs despreading by the Gold code V. . When synchronization between the digital transmission signal V using the Gold code V and the Gold code V on the receiving side is established, the correlation value between the two is N (= 2 ⁿ -1, where n: shift of the M sequence generation circuit It is possible to restore the transmitted digital information and receive the information, but between the other digital transmission signals, one of the three values of cross-correlation values −1, −K, and L. Therefore, the total correlation value is ± N ± Q ₁ ± Q ₂ ±... ± Q _U-1 . Here, Q ₁ , Q ₂ ,..., Q _U−1 are any one of the absolute values of the three values of the cross-correlation values (for example, 1 when the number n of shift registers of the M-sequence generation circuit is 5). 7 or 9), and the combination of ± signs in the correlation value sum is arbitrary. The reason why each correlation value is ± is that the value of the digital information to be diffused takes either +1 or −1. At the time of despreading at the time of reception, a signal spread by another Gold code becomes noise, which is the greatest factor that deteriorates reception performance.

  As described above, the cross-correlation values of different Gold codes have only three values of −1, −K, and L (see FIG. 8 for K and L). Therefore, the problem to be solved by the present invention is that these cross-correlation values may take a value of ± depending on the value of digital information, but in order to suppress the influence of the cross-correlation value that becomes noise, The cross-correlation value between the Gold codes used for spreading the signal is minimized (−1).

  Furthermore, another problem is to generate a new pseudo random number code with a cross-correlation value of 0 by partially modifying each Gold code with the minimum cross-correlation value.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

In order to achieve the above object, the invention of claim 1 is characterized in that a plurality of digital information is transmitted by multiplexing a plurality of digital codes, a signal transmitted by the transmission system is received, In a multiplex communication system using a direct spreading system including a receiving system for extracting intended digital information from the plurality of digital information using any of the Gold codes,
Correlation values between the plurality of Gold codes are minimum and constant values, and the transmission system synchronizes the bits of the plurality of digital information, and sets a plurality of bits in the same time zone to the plurality of Gold codes. It is characterized in that each code is spread in synchronism using a code, and these spread transmission signals are added and transmitted.

  The pseudo-random number sequence according to the invention of claim 2 is characterized in that 1 bit is added to the plurality of gold codes whose absolute values of mutual correlation values are minimum and constant values so that the cross-correlation value becomes 0. Yes.

  A multiplex communication system according to a third aspect of the invention is characterized in that, in the multiplex communication system according to the first aspect, the pseudo random number sequence according to the second aspect is used instead of the Gold code.

  According to the multiplex communication system using the multiple gold code according to the present invention, a plurality of digital information is multiplexed using a plurality of gold codes whose absolute values of mutual correlation values are minimum and constant values to form one channel. Although it is transmitted together, it uses the Gold code that has the smallest absolute value of the correlation value when receiving the desired digital information. The performance can be improved. As a result, the present invention has a great effect on multiplexed communication by the direct spreading method using the Gold code in various communication fields such as cellular phone communication, satellite communication, and wireless communication.

  In addition, the pseudo-random number sequence according to the present invention is such that one bit is added to the plurality of Gold codes whose absolute values of the mutual correlation values are minimum and constant so that the cross-correlation value becomes zero. Since there is a short length to a long length as in the M series and only 1 bit is added, the characteristics from the aspect of the random number are pseudo-random numbers that are almost similar to the Gold code. A pseudo-random number sequence having a cross-correlation value of 0 is widely used in communication systems (including the communication system described in the item of [Technical field]), the image / signal processing field, and the like that conventionally used the Gold code. Therefore, it has a great effect on the industrial field using communication and image / signal processing.

  Hereinafter, as a best mode for carrying out the present invention, an embodiment of a multiplex communication system using a multi-Gold code and a pseudo-random code will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a multiplex communication system using a multi-Gold code according to the present invention (spread spectrum communication system using a multiplexed direct spreading system), and FIG. 2 shows a multi-Gold code used in this embodiment. FIG. 3 shows a gold code generation circuit in which the absolute value of the cross-correlation value of the gold code, which is a key point of the present invention, is minimized.

  In the multiplex communication system of FIG. 1, it is used for spreading digital information so that a cross-correlation value with a signal other than a desired received signal is −1 on the receiving side among multiplexed transmission signals. The code order of each Gold code is aligned. That is, in the multiplex communication system according to the present embodiment, only the gold code that minimizes the absolute value of the cross-correlation value generated using the generation circuit of FIG. However, unlike the multiplexed communication system of FIG. 9, the other configurations are the same, and the same or corresponding parts are denoted by the same reference numerals.

  The multiple Gold code in FIG. 2 is generated by the generation circuit in FIG. 3 so that the absolute value of the cross-correlation value is minimum (the cross-correlation value is −1).

  With reference to FIG. 3, a method for generating a Gold code having a cross-correlation value of -1 will be described. This explanatory diagram shows that when an initial value and an output value of one M-sequence code generation circuit M1 belonging to each Gold code generation circuit are made the same, and an initial value of the other M-sequence code generation circuit M2 is made different, both The cross-correlation value of the gold code is −1, indicating that the absolute value is minimum.

One Gold code is generated by adding the outputs a (t) and b (t) of the two M-sequence generation circuits M1 and M2 (taking an exclusive OR). Here, the initial value of the circuit M1 that outputs a (t) of one of the two M-sequence generation circuits is set to a certain fixed value. That is, the output value of one M-sequence generation circuit M1 belonging to any Gold code generation circuit is set to be the same. The initial value of the other circuit M2 that outputs b (t) is changed for each Gold code generation circuit. In general, since the value of the M series has periodicity, even if the initial value is different from the circuit that outputs b (t), in a different circuit, a certain time shift τ (≠ 0) (= 1, 2, 3,... ) Having the value b (t−τ) is output. Therefore, the cross-correlation value X (τ) between the Gold codes generated in FIG. 3 is as follows.

Thus, if a (t) is made common and the initial value of b (t) is changed to generate a plurality of Gold codes, the absolute value of the cross-correlation value can be minimized. If n is the number of shift register stages, the initial value B can be set to 2 ⁿ −1 ([1 0 0... 0], [0 1 0... 0],..., [1 1 1... 1]). There are 2 ⁿ −1 such gold codes. Using the gold code generated as shown in FIG. 3, the transmitting side spreads digital information in synchronization and transmits it, and the receiving side that receives it despreads the desired digital signal with the spread gold code. By doing so, it becomes possible to receive low noise while minimizing the influence of other multiplexed signals.

の中から、Ｕ個のゴールド符号を取り出し、送信したい各ディジタル情報１〜Ｕを当該Ｕ個のゴールド符号１〜Ｕにより拡散、多重化し、その多重化された信号を受信し、その中から所望のディジタル情報Ｖを低雑音で抽出する送信系及び受信系を示している。この際、ディジタル情報を拡散する各ゴールド符号は、時間的に相互相関値が−１になるよう同期がとれていることが必要である。また、ディジタル情報１，２，…，Ｕの各ビットの始端、終端は揃っており、ゴールド符号の１周期に対応していることが必要である。つまり、送信系では、Ｕ個のディジタル情報１〜Ｕのビット間の同期を合わせ、同時間帯の複数個のビットを前記ゴールド符号１〜Ｕを用いて同期を合わせてそれぞれ拡散し、これらの拡散した送信信号を加算して送信する。 In the embodiment of FIG. 1, each Gold code generated in this way according to the multiplexing number U of digital information to be transmitted.

The U gold codes are extracted from the digital information 1 to U to be transmitted, spread and multiplexed by the U gold codes 1 to U, the multiplexed signal is received, and the desired information is received from the received signals. 2 shows a transmission system and a reception system for extracting the digital information V of the above with low noise. At this time, each Gold code for spreading the digital information needs to be synchronized so that the cross-correlation value becomes −1 in terms of time. Also, the start and end of each bit of the digital information 1, 2,..., U must be aligned and correspond to one period of the Gold code. That is, in the transmission system, synchronization between U digital information 1 to U bits is synchronized, and a plurality of bits in the same time zone are synchronized using the Gold codes 1 to U, respectively. The spread transmission signals are added and transmitted.

  Further, when the digital information is +1, the cross-correlation value is -1, and when the digital information is -1, the cross-correlation value is +1, and the value of the cross-correlation value changes according to the digital information. Assuming that each piece of digital information to be multiplexed is independent, probabilistically, +1 and -1 are approximately half, and when extracting the intended digital information on the receiving side, the overall cross-correlation value other than the intended digital information is Therefore, it becomes almost 0, and the reduction of the multiplexing noise can be actually achieved. If the independence of each digital information is not ensured, scramble is inserted before each digital information to ensure the independence of each digital information.

  Next, a method for generating a pseudo-random number sequence in which the cross-correlation value is 0 will be described with reference to FIGS.

Assuming that each Gold code generated as shown in FIG. 3 is Ci = (c _i0 , c _i1 ,...) (I = 1 to 2 ⁿ −1), the cross-correlation value between an arbitrary Ci and Cj (i ≠ j) Since −1 is −1, a sequence in which +1 or −1 is added to the end of this Gold code (in the following description, +1 is added to the end of the sequence Ci as shown in FIG. 4) Di = (c _{If i0} , c _i1 ,..., 1), the cross-correlation value between Di and Dj (i ≠ j) is zero. Since the last bit is fixed at +1, in order to balance +1, -1 of this last value and to secure mutual randomness, the sign of half of the series Di is inverted. New pseudo-random number sequence Ei = (c _i0 , c _i1 ,..., 1) or (−c _i0 , −c _i1 ,..., −1) (i = 1 to 2 ⁿ −1 is half of Is the former and half is the latter), the cross-correlation value between any Ei and Ej (i ≠ j) is zero. For example, for a gold code of length 31, the result is as shown in FIG.

  Such a pseudo-random number sequence can replace the Gold code used in the embodiment of FIG. 1, and can be used in the multiplex communication system targeted by the present invention. That is, if the U pseudo-random number sequences generated as shown in FIGS. 4 and 5 are used instead of the Gold codes 1 to U in FIG. 1, the cross-correlation value of these pseudo-random sequence is 0. It can be expected to receive low noise equivalent to or better than when using the Gold code.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

1 is a block diagram of both a transmission system and a reception system according to an embodiment of a multiplex communication system using a multiplex gold code according to the present invention. In the embodiment of the present invention, it is a waveform diagram showing an example of a Gold code having a minimum and constant cross-correlation value used for spreading digital information. In the embodiment of the present invention, it is a block diagram showing a gold code generation circuit in which the absolute value of the cross-correlation value of the gold code as a key point becomes a minimum and constant value. FIG. 5 is a block diagram showing a generation circuit for generating a pseudo-random number sequence based on a Gold code having a length of 31 generated in FIG. 3, which is an embodiment of a pseudo-random number sequence having a cross-correlation value of 0 according to the present invention. is there. FIG. 5 is an explanatory diagram illustrating a process of generating a pseudo random number sequence Ei by inverting the sign of half of the pseudo random number sequence Di generated by the generation circuit of FIG. 4. It is a block diagram of a spread spectrum communication system using a direct spreading method. It is explanatory drawing which shows the relationship on the time-axis of the digital transmission signal which wants to transmit, the PN code for spreading | diffusion, and the digital transmission signal which carried out arithmetic multiplication of both of these. It is a block diagram which shows the structural example of the production | generation circuit of the Gold code | cord | chord using two M series of the period length 31. FIG. FIG. 2 is a block diagram of a multiplex communication system using a gold code as a spread code, which is a spread spectrum communication system using a direct spreading method.

Explanation of symbols

10 ₁ to 10 _U oscillator 11 _{1 to} 11 _U , 12 _{1 to} 12 _U , 21 _{1 to} 21 _U multiplier 13 adder 14 transmitting antenna BPF, BPF _{1 to} BPF _U band pass filter 20 _{1 to} 20 _U receiving antenna
22 _{1 to} 22 _U demodulator M1, M2 M-sequence generation circuit

Claims (3)

A transmission system that multiplexes and transmits a plurality of digital information with a plurality of Gold codes, and receives a signal transmitted by the transmission system, and uses one of the plurality of Gold codes to In a multiplex communication system using a direct spreading system including a receiving system for extracting intended digital information from
The absolute value of the correlation value between the plurality of Gold codes is a minimum and constant value, and in the transmission system, the plurality of bits of the digital information are synchronized, and the plurality of bits in the same time zone are A multiplex communication system characterized in that a plurality of gold codes are used for spreading in synchronization, and the spread transmission signals are added and transmitted.   A pseudo-random number sequence, wherein one bit is added so that the cross-correlation value becomes 0 to the plurality of Gold codes having a minimum and constant cross-correlation value.   The multiplex communication system according to claim 1, wherein the pseudo random number sequence according to claim 2 is used instead of the gold code.

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