Spread spectrum communication is an effective and commonly used anti-jamming communication method. It is the main means of military communication. It is divided into basic technologies such as direct sequence spread spectrum, frequency hopping, linear frequency modulation and time hopping, and hybrid technologies composed of a combination of basic technologies. All technologies The design of the pseudo code is related to the anti-interference performance of the system. The pseudo-random sequences commonly used in existing spread spectrum communication systems are m-sequence, Gold-sequence, Walsh-sequence, M-sequence, and C / A codes (coarse / intercepted codes) and fine codes (P codes) commonly used in satellite communications. In these sequences, the P code has excellent performance and the longest code period. At a clock rate of 10.23 MHz, the code time period is about 266 days. Based on the study of the principle of P code, this paper proposes a pseudo-random sequence generation method with longer period and good security performance, which can be used in the wartime satellite measurement and control communication.
1 PN code design principle
1.1 Design principles
In the spread spectrum anti-jamming communication system, the design of the code mainly considers the performance of the relevant characteristics of the code, the confidentiality of the code (complexity of the code), and code capacity. Specific requirements are as follows:
(1) Strong autocorrelation characteristics
The code synchronization in the system is often realized by the correlation characteristics of the code, which requires the autocorrelation performance of the code to have sharp autocorrelation distribution characteristics.
With two sequences {ai} and {bi} of length N, i = O, 1, ..., N-1, the autocorrelation function of the sequence is defined as:
In practical applications, the autocorrelation function of the pseudo-random sequence in spread spectrum communication is required to be binary, that is, the autocorrelation function Ra (j) is:
(2) Weak cross-correlation characteristics In the wireless communication system, in order to reduce multipath interference and achieve multiple access communication, on the basis of autocorrelation performance, the cross-correlation value between different codes is also required to be low, so in multi-user systems often use mutually orthogonal PN sequence. For the sequences {ai) and {bi}, i = O, 1, ..., N-1, orthogonal is defined as: It can be known from the above analysis that in a multi-user system, the number of orthogonal codes determines the system capacity, so it is hoped that when designing the spreading code, a code sequence with a large capacity should be selected. (4) Good confidentiality Spread spectrum communication systems are often used in military communications, so when designing codes, the following methods are often used: to reduce the DC power of the code, to make the number of "O" and "1" in the code balanced; increase the period of the code; use nonlinear shift The register implements the code sequence. 1.2 Basics of code sequence design The generation of pseudo-random sequences can be achieved through linear or nonlinear shift registers. Because m-sequences have good pseudo-randomness, small m-sequences are used in the design of GOLD, C / A, P and other PN sequences, so m-sequences are the basic sequence of spread spectrum communication. The m sequence is a code sequence with a period of N = 2n-1 generated by the n-level linear shift register, is the abbreviation of the longest linear shift register sequence, and has excellent autocorrelation characteristics. Its generating principle is shown in FIG. 1. Air Mattresses With Pump,Airbed With Pump,Double Airbed With Built In Pump,Air Bed With Built In Pump SHENZHEN SMARTNEWO TECHNOLOGY CO,. LTD , https://www.newopump.com
In the formula: N is the sequence autocorrelation peak, which is equal to the sequence period, that is, N = 2n-1; σ is the sequence autocorrelation sidelobe value, which satisfies σ < 
(3) Large code capacity 
The characteristic polynomial is: 
In the formula: ci is called the feedback coefficient, and the value is 0 or 1; 1 means to participate in the feedback; O means not to participate in the feedback. Whether the shift register can generate m sequences is determined by the value of the feedback coefficient; the code period is determined by the number of shift registers; the linear complexity of the sequence directly determines the security performance of the spread spectrum system, and the principle of linear generation of m sequences is analyzed As long as the continuous 2n-1 symbols of the sequence can be intercepted, the value of the coefficient ci can be given, so that the m sequence is completely deciphered. In practical systems, the output of several stages of the shift register or the output of several different m-sequences are often combined in a non-linear manner to produce a non-linear sequence that is difficult for the jammer to crack. In this paper, this method is used, referring to the construction principle of P code, a method of generating a spreading sequence code with a long period and high complexity is proposed.