Method for generating a soft sequence for despreading in an iterative MSK-soft spreading system

Abstract

The application discloses a method for generating a despread soft sequence of an MSK-soft spread spectrum system based on iteration, and relates to the field of communication, and comprises the following steps: S1, constructing an MSK-spread spectrum signal receiving model; S2, receiving a received signal of a sampling point by the MSK-spread spectrum signal receiving model; and S3, under the assistance of an initial word C0 of a spread spectrum code stored in the MSK-soft spread spectrum system, other code phase code words are constructed by using a traditional spread spectrum code word based on a cyclic shift, and the characteristics that MSK signal phases change continuously symbol by symbol are used to construct a despread soft sequence of the MSK-soft spread spectrum system. The despread soft sequence of the MSK-CCSK is generated by the above method, so that the hardware RAM resource can be saved, and the design of an MSK-CCSK despreader is simplified. Compared with a traditional method, the application theoretically explains the corresponding relationship between the construction of the despread soft sequence of the MSK-CCSK and the construction of an MSK-CCSK spread spectrum sequence, and is helpful to further understanding of the principle of the MSK-CCSK system.

Description

Technical Field

[0001] This invention relates to the field of communications, and more particularly to an iterative method for generating soft sequences for despreading MSK-soft spread spectrum systems. Background Technology

[0002] MSK (Minimum Frequency Shift Keying) signals have characteristics such as constant envelope and low sidelobes, making them particularly suitable for wireless communication systems with limited power and severe nonlinear distortion.

[0003] Soft spread spectrum is a novel baseband spread spectrum technique developed by combining direct sequence spread spectrum (DSSS) with coding techniques. CCSK (Cyclic Code Shift Keying) is a special case of soft spread spectrum. It selects a spreading code with good autocorrelation properties as its base code, denoted as , with a code length of B. The B codewords obtained by cyclic shifting constitute the CCSK spreading code set. In implementation, each Kbit of information bits is used as an index to map to a B-bit output codeword for output. Compared to traditional direct spread spectrum systems, CCSK systems can achieve certain coding gains, making them particularly suitable for bandwidth-constrained applications requiring high communication rates.

[0004] Therefore, the spread spectrum system that combines MSK and CCSK has significant comprehensive advantages over the MSK-direct spread spectrum system and has broad application prospects in fields such as communication and data links.

[0005] Compared to ordinary QPSK (Quadrature Phase Shift Keying)-CCSK systems, due to the inherent characteristics of MSK signals, the spreading code and despreading soft sequence of CCSK are inconsistent. When despreading at the receiver, CCSK symbols cannot be traversed by simple cyclic shifting of the CCSK code set. Instead, it is necessary to combine the characteristics of the MSK signal itself to specially generate despreading soft sequence words for CCSK symbols.

[0006] In existing literature, the despreading soft sequence word of MSK-CCSK is stored in RAM after all the spreading code words of CCSK are modulated by MSK, and then read out during despreading to achieve fast despreading. When the spreading factor is high, it requires a large amount of RAM resources, and the data bit width operated on the RAM port is also wide, which causes a large timing constraint pressure. Summary of the Invention

[0007] The purpose of this invention is to design an iterative method for generating soft despreading sequences in an MSK-soft spread spectrum system in order to solve the above problems.

[0008] The present invention achieves the above objectives through the following technical solutions:

[0009] An iterative method for generating soft despreading sequences in MSK-soft spread spectrum systems includes:

[0010] S1. Construct the MSK-spread spectrum signal reception model;

[0011] S2, MSK - Spread spectrum signal receiving model receives the received signal at the sampling point;

[0012] S3. Initial spreading code word stored in the MSK-soft spread spectrum system With the assistance of traditional spread spectrum codewords, which are constructed based on cyclic shifting to create other codewords and the characteristic of MSK signal phase changing continuously symbol by symbol, a despreading soft sequence for the MSK-soft spread spectrum system was constructed.

[0013] The beneficial effects of this invention are as follows: generating the despreading soft sequence of MSK-CCSK using the above method can save hardware RAM resources and simplify the design of MSK-CCSK despreader; compared with traditional methods, this patent explains the correspondence between the construction of MSK-CCSK despreading soft sequence and the construction of MSK-CCSK spreading sequence from a principle perspective, which helps to further deepen the understanding of the principle of MSK-CCSK system. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the CCSK symbol despreading and demodulating unit based on the iterative MSK-soft spread spectrum system despreading soft sequence generation method of this invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0016] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0017] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0018] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0019] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0020] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] An iterative method for generating soft despreading sequences in MSK-soft spread spectrum systems includes:

[0023] S1. Construct the MSK-spread spectrum signal receiving model, represented as follows: Where A is the signal amplitude. For carrier frequency, The Doppler frequency shift is caused by the relative motion between the receiver and the transmitter. Channel noise; This is the nth information sequence before spreading. For the first in the spread spectrum sequence There are 1 code element, assuming the spread chip is 1. The symbol period before system spread spectrum is The spread symbol period is The system spread factor is ,Right now ; For the initial phase, for The phase value accumulated from all transmitted symbols at any given moment. ;

[0024] The S2 and MSK spread spectrum signal receiving models receive the received signal at the sampling points. The received signal is represented as follows: The received signal is transformed and represented as... Where M is the oversampling factor for each symbol, and j is the complex exponent. The sampling period is ;

[0025] S3. Initial spreading code word stored in the MSK-soft spread spectrum system With the assistance of traditional spreading codewords, which are constructed based on cyclic shifting to create other code phase codes and the characteristic of continuous symbol-by-symbol phase change of the MSK signal, a despreading soft sequence for the MSK-soft spreading system was constructed; specifically:

[0026] Initial codewords stored in the MSK-soft spread spectrum system With the assistance of [unclear], the current phase is generated by iteratively generating the despread soft sequence words of other phases one by one. The code Specifically, assuming the CCSK code pattern is CCSK(B, K), meaning K bits of information are mapped to B bits of spreading code. Assuming the spreading code for phase 0 is... The corresponding demodulation information is represented as 0 in decimal. Phase-corresponding codeword for The corresponding demodulation information is represented in decimal as follows: ,in These are code elements that have been renumbered and sorted;

[0027] Using code The despreading soft sequence for MSK modulation is represented as follows: During CCSK symbol matching, starting from phase 0 to... Phase matching is performed phase by phase, assuming one phase match is performed for each clock cycle; It possesses the characteristic of iterative generation, combined with and The generation methods are as follows: .

[0028] The working principle of the iterative MSK-soft spread spectrum system despreading soft sequence generation method of this invention is as follows:

[0029] The MSK-spread spectrum signal receiving model is

[0030]

[0031] Where A is the signal amplitude. For carrier frequency, The Doppler frequency shift is caused by the relative motion between the receiver and the transmitter. The channel noise is assumed here to be additive white Gaussian noise, and... ; This is the nth information sequence before spreading. For the first in the spread spectrum sequence There are 1 code element, assuming the spread chip is 1. The symbol period before system spread spectrum is: The spread symbol period is The system spread factor is ,Right now . The initial phase, i.e., the phase corresponding to time 0, can generally be assumed to be... , for The phase value accumulated from all transmitted symbols at any given moment. .

[0032] The signal at the optimal sampling point of the receiver (ignoring noise) can be expressed as:

[0033]

[0034] Where M is the oversampling factor for each symbol, The sampling period is .

[0035] To obtain the above signals directly without the influence of the spreading factor... The sequence requires further transformation of the above formula, expressed as:

[0036]

[0037] It can be found that in order to obtain The sequence needs to be constructed using the following despreading soft sequence.

[0038]

[0039] in, These are respectively for MSK spread spectrum signals. sequence sum Despreading soft sequences are actually sequences obtained by MSK modulation of the spread spectrum sequence. By performing correlation operations between this sequence and the received signal, the MSK spread spectrum signal can be directly despread.

[0040] For the MSK-CCSK system, the useful information of the CCSK symbol lies entirely in the spreading codeword. middle, It does not carry information (which can be considered as the CCSK system,) (Always 1). Therefore, for the MSK-CCSK system, only construction is required. Despreading can be completed by despreading a soft sequence.

[0041] Assume the CCSK code type is CCSK(B, K), meaning that K bits of information are mapped to B bits of spread spectrum codewords.

[0042] Assume the spreading codeword with 0 phase is The corresponding demodulation information is represented as 0 in decimal. The codeword corresponding to the phase is The corresponding demodulation information is represented in decimal as follows: ,in These are code elements that have been renumbered and sorted. The corresponding MSK modulation and despreading soft sequence is

[0043]

[0044] When performing CCSK symbol matching, starting from phase 0... Phase matching is performed phase-by-phase, assuming one phase match is performed for each clock cycle; to reduce storage requirements, it is necessary to... It also possesses the characteristic of being iteratively generated. Combined and The generation methods are as follows:

[0045] .

[0046] From the above formula, we can see that when we know... At that time, With the aid of typing, one can... The despreading soft sequence words for other phases are generated iteratively one by one, without the need to store all code words, thus simplifying the despreading implementation algorithm of the MSK-CCSK system.

[0047] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for generating despreading soft sequences for an MSK-soft spread spectrum system based on iteration, characterized in that, include: S1. Construct the MSK-spread spectrum signal receiving model, represented as follows: Where A is the signal amplitude. For carrier frequency, The Doppler frequency shift is caused by the relative motion between the receiver and the transmitter. Channel noise; This is the nth information sequence before spreading. For the first in the spread spectrum sequence There are 1 code element, assuming the spread chip is 1. The symbol period before system spread spectrum is The spread symbol period is The system spread factor is ,Right now ; For the initial phase, for The phase value accumulated from all transmitted symbols at any given moment. ; The S2 and MSK-spread spectrum signal receiving model receives the received signal at the sampling point, represented as follows: The received signal is transformed and represented as... Where M is the oversampling factor for each symbol, and j is the complex exponent. The sampling period is ; S3. Initial spreading code word stored in the MSK-soft spread spectrum system With the assistance of traditional spreading codewords, which are constructed based on cyclic shifting to create other codewords and the characteristic of continuous symbol-by-symbol phase change of the MSK signal, a despreading soft sequence for the MSK-soft spreading system was constructed; specifically including: Assuming the CCSK code pattern is CCSK(B,K), meaning K bits of information are mapped to B bits of spreading code, and assuming the spreading code for phase 0 is... The corresponding demodulation information is represented as 0 in decimal. Phase-corresponding codeword for The corresponding demodulation information is represented in decimal as follows: ,in These are code elements that have been renumbered and sorted; using codewords The despreading soft sequence for MSK modulation is represented as follows: During CCSK symbol matching, starting from phase 0 to... Phase matching is performed phase by phase, assuming one phase match is performed for each clock cycle; It possesses the characteristic of being iteratively generated, combined with despreading soft sequences and The generation methods are as follows: .

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