OFDM satellite navigation signal modulation method based on phase hopping

Abstract

The invention provides an OFDM satellite navigation signal modulation method based on phase hopping. The method comprises the following steps: S1, determining an initial discrete phase vector; s2, obtaining a plurality of clusters; s3, a random number rand belongs to (0, 1) is set, if rand is smaller than p1, one cluster is randomly selected from the multiple clusters, and the step S4 is executed; otherwise, randomly selecting two clusters from the plurality of clusters, and turning to S5; s4, acquiring an updated discrete phase vector based on the first subcarrier phase selection vector, and turning to S6; s5, acquiring an updated discrete phase vector based on a second subcarrier phase selection vector, and turning to S6; s6, taking a discrete phase vector corresponding to a small value in the two PAPR values as a discrete phase vector output by the current cycle; s7, obtaining a discrete phase vector output by the first layer of circulation; s8, obtaining a discrete phase vector circularly output by the second layer; s9, obtaining a final discrete phase vector; and S10, performing phase hopping on each subcarrier of the OFDM original navigation signal vector to obtain an OFDM phase hopping signal vector.

Description

Technical Field

[0001] The invention relates to the field of satellite navigation technology, and in particular to a modulation method of an OFDM satellite navigation signal based on phase hopping. Background Art

[0002] The use of Orthogonal Frequency Division Multiplexing (OFDM) technology in low-orbit satellite navigation signals will bring advantages such as high-frequency band utilization and more flexible resource allocation. Traditional navigation signals are mostly constant envelope signals, and most of them use direct sequence spread spectrum systems, which are very different from OFDM modulation technology. In order to use OFDM technology on low-orbit satellites, it is necessary to solve the peak to average power ratio (PAPR) problem brought about by this technology. There are various means to deal with PAPR problems in terrestrial wireless networks, but the transmitter structure on the satellite is difficult to change, and the power is usually limited. At the same time, the accuracy of the service provided by the navigation signal must be taken into account, so the means to deal with PAPR problems in terrestrial wireless networks cannot be used. Summary of the invention

[0003] The invention provides a modulation method of an OFDM satellite navigation signal based on phase hopping, and solves the technical problem of high peak-to-average power ratio of OFDM navigation signals applied to low-orbit satellites.

[0004] The present invention provides a modulation method of an OFDM satellite navigation signal based on phase hopping, the method comprising:

[0005] S1, determining an initial discrete phase vector for phase hopping;

[0006] S2, performing kmeans clustering operation on the initial discrete phase vector to obtain several clusters;

[0007] S3. Set a random number rand∈(0,1). If rand<p1, randomly select one cluster from several clusters and go to S4. Otherwise, randomly select two clusters from several clusters and go to S5, where p1 is the probability of selecting a cluster.

[0008] S4. If rand<p 1c , the cluster center of the currently selected cluster is used as the first subcarrier phase selection vector; otherwise, an individual is randomly selected from the currently selected cluster as the first subcarrier phase selection vector; based on the first subcarrier phase selection vector, an updated discrete phase vector is obtained, and the process goes to S6, where p 1c is the probability of selecting the cluster center of a cluster;

[0009] S5. If rand<p 2c , then the second subcarrier phase selection vector is obtained based on the cluster centers of the two currently selected clusters; otherwise, a second subcarrier phase selection vector is obtained by randomly selecting an individual from each of the two currently selected clusters; an updated discrete phase vector is obtained based on the second subcarrier phase selection vector, and the process goes to S6, where p 2c is the probability of selecting the cluster centers in two clusters;

[0010] S6. Obtain the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector, and obtain the PAPR value of the OFDM original navigation signal vector based on the initial discrete phase vector under the constraint that the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector is the lowest; obtain the PAPR value of the OFDM original navigation signal vector based on the updated discrete phase vector; and use the discrete phase vector corresponding to the smaller value of the two PAPR values ​​as the discrete phase vector outputted by the current cycle;

[0011] S7, taking the discrete phase vector outputted by the current cycle as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the first layer of cycles is reached, and obtaining the discrete phase vector outputted by the first layer of cycles;

[0012] S8, taking the discrete phase vector output by the first layer loop as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the second layer loop is reached, and obtaining the discrete phase vector output by the second layer loop;

[0013] S9, taking the discrete phase vector output by the second cycle as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the third cycle is reached, obtaining the discrete phase vector output by the third cycle, and taking the discrete phase vector output by the third cycle as the final discrete phase vector;

[0014] S10. Perform phase hopping on each subcarrier of the OFDM original navigation signal vector based on the final discrete phase vector to obtain an OFDM phase hopping signal vector.

[0015] Preferably, in S4 of the present invention, the updated discrete phase vector is obtained by the following formula:

[0016] θ new =θ select +ξ·N(μ,σ 2 )

[0017] In the formula, θ new is the updated discrete phase vector, θ select is the first subcarrier phase selection vector, ξ is the first weight coefficient, N(μ,σ 2) is the Gaussian distribution function, μ is the mean, σ 2 is the variance.

[0018] Preferably, in S5 of the present invention, the updated discrete phase vector is obtained by the following formula:

[0019] θ new =θ′ select +ξ·N(μ,σ 2 )

[0020] θ′ select =w1θ select_1 +w2θ select_2

[0021] In the formula, θ′ select is the second subcarrier phase selection vector, θ select_1 ,θ select_2 They are the cluster centers of the two currently selected clusters or a randomly selected individual of each cluster, and w1 and w2 are the second and third weight coefficients respectively.

[0022] Preferably, the PAPR value of the OFDM original navigation signal vector is obtained by the following formula:

[0023]

[0024] in,

[0025] Where PAPR is the PAPR value of the OFDM original navigation signal vector, b is the proportional coefficient, is a constant, X is the OFDM original navigation signal vector, H is the conjugate transpose, T is the transpose, N is the number of subcarriers, i, l, h are different subcarrier indexes, and θ′[l] and θ′[h] are the discrete phases of the lth and hth subcarriers in the updated discrete phase vector.

[0026] Preferably, the OFDM phase-hopping signal vector is obtained by the following formula:

[0027] S PH =X⊙e θ

[0028] S PH =[s PH [0],s PH [1],...,s PH [N-1]]

[0029] in,

[0030] In the formula, S PHis the OFDM phase-hopping signal vector, X is the OFDM original navigation signal vector, θ is the final discrete phase vector, ⊙ is the Hadamard product operator symbol, s PH [k] is the kth OFDM phase-hopping signal in the OFDM phase-hopping signal vector, C[i] is the ranging code of the ith subcarrier, θ[i] is the discrete phase of the ith subcarrier in the final discrete phase vector, M is the number of OFDM symbols, and N is the number of subcarriers.

[0031] Preferably, the number of cycles of the first layer loop is the number of OFDM symbols, the number of cycles of the second layer loop is the total number of iterations, and the number of cycles of the third layer loop is the number of uniform segments of the initial discrete phase vector in the range of [0,2π].

[0032] By applying the technical solution of the present invention, the BSO algorithm is used to iteratively update the initial discrete phase vector to obtain the final discrete phase vector, and the phase of each subcarrier of the OFDM original navigation signal vector is jumped based on the final discrete phase vector to obtain the OFDM phase-hopping signal vector. The results show that this method significantly reduces the PAPR of the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A flow chart of a modulation method of an OFDM satellite navigation signal based on phase hopping provided according to an embodiment of the present invention is shown;

[0035] Figure 2 A schematic diagram of the time-frequency structure of an OFDM navigation signal provided according to an embodiment of the present invention is shown;

[0036] Figure 3 A schematic diagram of a curve showing PAPR obtained by a BSO algorithm under different subcarrier numbers provided by an embodiment of the present invention is shown;

[0037] Figure 4 A comparison diagram of PAPR obtained by an OFDM original navigation signal and an OFDM phase-hopping signal when the number of subcarriers provided according to an embodiment of the present invention is 32, 64, 128, 256;

[0038] Figure 5 A schematic diagram of a curve showing PAPR obtained under different iteration times provided by an embodiment of the present invention is shown;

[0039] Figure 6 A schematic diagram of a curve showing PAPR obtained under different phase hopping number conditions according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0042] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0043] like Figure 1 As shown, the present invention provides a modulation method of an OFDM satellite navigation signal based on phase hopping, the method comprising:

[0044] S1, determining an initial discrete phase vector for phase hopping;

[0045] S2, performing kmeans clustering operation on the initial discrete phase vector to obtain several clusters;

[0046] S3. Set a random number rand∈(0,1). If rand<p1, randomly select one cluster from several clusters and go to S4. Otherwise, randomly select two clusters from several clusters and go to S5, where p1 is the probability of selecting a cluster.

[0047] S4. If rand<p 1c , the cluster center of the currently selected cluster is used as the first subcarrier phase selection vector; otherwise, an individual is randomly selected from the currently selected cluster as the first subcarrier phase selection vector; based on the first subcarrier phase selection vector, an updated discrete phase vector is obtained, and the process goes to S6, where p 1c is the probability of selecting the cluster center of a cluster;

[0048] S5. If rand<p 2c , then the second subcarrier phase selection vector is obtained based on the cluster centers of the two currently selected clusters; otherwise, a second subcarrier phase selection vector is obtained by randomly selecting an individual from each of the two currently selected clusters; an updated discrete phase vector is obtained based on the second subcarrier phase selection vector, and the process goes to S6, where p 2c is the probability of selecting the cluster centers in two clusters;

[0049] S6. Obtain the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector, and obtain the PAPR value of the OFDM original navigation signal vector based on the initial discrete phase vector under the constraint that the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector is the lowest; obtain the PAPR value of the OFDM original navigation signal vector based on the updated discrete phase vector; and use the discrete phase vector corresponding to the smaller value of the two PAPR values ​​as the discrete phase vector outputted by the current cycle;

[0050] S7, taking the discrete phase vector outputted by the current cycle as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the first layer of cycles is reached, and obtaining the discrete phase vector outputted by the first layer of cycles;

[0051] S8, taking the discrete phase vector output by the first layer loop as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the second layer loop is reached, and obtaining the discrete phase vector output by the second layer loop;

[0052] S9, taking the discrete phase vector output by the second cycle as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the third cycle is reached, obtaining the discrete phase vector output by the third cycle, and taking the discrete phase vector output by the third cycle as the final discrete phase vector;

[0053] S10. Perform phase hopping on each subcarrier of the OFDM original navigation signal vector based on the final discrete phase vector to obtain an OFDM phase hopping signal vector.

[0054] The present invention uses the BSO algorithm to iteratively update the initial discrete phase vector to obtain the final discrete phase vector, and based on the final discrete phase vector, each subcarrier of the OFDM original navigation signal vector is phase-hopped to obtain the OFDM phase-hopping signal vector. The results show that this method significantly reduces the PAPR of the signal.

[0055] In this embodiment, the phase element θ=[θ[0] θ[1] … θ[N-1]] superimposed on the signal is used as the optimization target, and the optimization range needs to be determined first. Since the values ​​to be optimized are all e (·) The phase elements are in the form of , so the value range of θ is [0,2π], and the individuals are evenly distributed within this range.

[0056] Before performing the discrete phase vector cyclic update, first initialize various variables and constants, including the number of subcarriers N, the number of segments Size in the range of phase elements [0,2π], the number of OFDM statistical symbols RunMax, the maximum number of iterations GenMax, the probability of selecting a cluster p1, and the probability of selecting the cluster center of a cluster p 1c , the probability p of selecting the cluster center in two clusters 2c .

[0057] According to an embodiment of the present invention, in S4 of the present invention, the updated discrete phase vector is obtained by the following formula:

[0058] θ new =θ select +ξ·N(μ,σ 2 )

[0059] In the formula, θ new is the updated discrete phase vector, θ select is the first subcarrier phase selection vector, ξ is the first weight coefficient, N(μ,σ 2 ) is the Gaussian distribution function, μ is the mean, σ 2 is the variance.

[0060] According to an embodiment of the present invention, in S5 of the present invention, the updated discrete phase vector is obtained by the following formula:

[0061] θ new =θ′ select +ξ·N(μ,σ 2 )

[0062] θ′ select =w1θ select_1 +w2θ select_2

[0063] In the formula, θ′ select is the second subcarrier phase selection vector, θ select_1 ,θ select_2 They are the cluster centers of the two currently selected clusters or a randomly selected individual of each cluster, and w1 and w2 are the second and third weight coefficients respectively.

[0064] According to an embodiment of the present invention, the PAPR value of the OFDM original navigation signal vector is obtained by the following formula:

[0065]

[0066] in,

[0067] Wherein, PAPR is the PAPR value of the OFDM original navigation signal vector, b is the proportional coefficient, is a constant, X is the OFDM original navigation signal vector, H is the conjugate transpose, T is the transpose, N is the number of subcarriers, i, l, h are different subcarrier indexes, θ′[l], θ′[h] are the discrete phases of the lth and hth subcarriers in the updated discrete phase vector, and θ′[l] and θ′[h] are the elements in the phase vector of X generated in the process of expanding the formula.

[0068] Among them, the constraint condition of the above formula is that the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector is the lowest. The periodic integrated sidelobe level PISL of the periodic autocorrelation function of the OFDM original navigation signal vector is obtained by the following formula: x :

[0069]

[0070] Where n∈[-(N-1),N-1],n≠0, n is the signal vector index, X[n] is the nth frequency domain signal of the OFDM original navigation signal vector, is the nth periodic autocorrelation function of the OFDM original navigation signal vector. In order to optimize the PISL performance of the signal, this value should be as small as possible, so |X[n]|=1 should be set as a constraint in the signal design process.

[0071] The OFDM navigation signal vector will occupy the entire bandwidth within the available frequency band and the entire time slot within the available time slot. The time-frequency structure of the signal vector is as follows: Figure 2 As shown in the figure, it can be seen that the OFDM navigation signal vector is composed of a ranging code of length M×N, where M is the number of OFDM symbols and N is the number of subcarriers. The ranging code is divided into M segments, and each segment is placed on an OFDM symbol in the subcarrier index order of [1, N].

[0072] Each OFDM symbol (i.e., each OFDM navigation signal) can be expressed as:

[0073]

[0074] Phase-hopping modulation changes the phase on each subcarrier. Assuming that the discrete phase vector used for phase hopping on an OFDM symbol is θ = [θ[0] θ[1] … θ[N-1]], the OFDM phase-hopping signal can be expressed as

[0075]

[0076] The OFDM phase-hopping signal vector is obtained by the following formula:

[0077] S PH =X⊙e θ

[0078] S PH =[s PH [0],s PH [1],...,s PH [N-1]]

[0079] in,

[0080] In the formula, S PH is the OFDM phase-hopping signal vector, X is the OFDM original navigation signal vector, θ is the final discrete phase vector, ⊙ is the Hadamard product operator symbol, s PH [k] is the kth OFDM phase-hopping signal in the OFDM phase-hopping signal vector, C[i] is the ranging code of the ith subcarrier, θ[i] is the discrete phase of the ith subcarrier in the final discrete phase vector, M is the number of OFDM symbols, and N is the number of subcarriers.

[0081] According to one embodiment of the present invention, the number of cycles of the first layer loop is the number of OFDM symbols, the number of cycles of the second layer loop is the total number of iterations, and the number of cycles of the third layer loop is the number of uniform segments of the initial discrete phase vector in the range of [0,2π].

[0082] In summary, the present invention provides a modulation method for OFDM satellite navigation signals based on phase hopping, which uses the BSO algorithm to iteratively update the initial discrete phase vector to obtain the final discrete phase vector, and based on the final discrete phase vector, the phase of each subcarrier of the OFDM original navigation signal vector is jumped to obtain the OFDM phase hopping signal vector. The results show that this method significantly reduces the PAPR of the signal, specifically Figure 3-Figure 6 shown.

[0083] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0084] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modulation method for OFDM satellite navigation signals based on phase hopping, characterized in that: The method comprises: S1, determining an initial discrete phase vector for phase hopping; S2, performing kmeans clustering operation on the initial discrete phase vector to obtain several clusters; S3. Set a random number rand∈(0,1). If rand<p1, randomly select one cluster from several clusters and go to S4. Otherwise, randomly select two clusters from several clusters and go to S5, where p1 is the probability of selecting a cluster. S4. If rand<p 1c , the cluster center of the currently selected cluster is used as the first subcarrier phase selection vector; otherwise, an individual is randomly selected from the currently selected cluster as the first subcarrier phase selection vector; based on the first subcarrier phase selection vector, an updated discrete phase vector is obtained, and the process goes to S6, where p 1c is the probability of selecting the cluster center of a cluster; S5. If rand<p 2c , then the second subcarrier phase selection vector is obtained based on the cluster centers of the two currently selected clusters; otherwise, a second subcarrier phase selection vector is obtained by randomly selecting an individual from each of the two currently selected clusters; an updated discrete phase vector is obtained based on the second subcarrier phase selection vector, and the process goes to S6, where p 2c is the probability of selecting the cluster centers in two clusters; S6. Obtain the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector, and obtain the PAPR value of the OFDM original navigation signal vector based on the initial discrete phase vector under the constraint that the periodic integrated sidelobe level of the periodic autocorrelation function of the OFDM original navigation signal vector is the lowest; obtain the PAPR value of the OFDM original navigation signal vector based on the updated discrete phase vector; and use the discrete phase vector corresponding to the smaller value of the two PAPR values ​​as the discrete phase vector outputted by the current cycle; S7, taking the discrete phase vector outputted by the current cycle as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the first layer of cycles is reached, and obtaining the discrete phase vector outputted by the first layer of cycles; S8, taking the discrete phase vector output by the first layer loop as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the second layer loop is reached, and obtaining the discrete phase vector output by the second layer loop; S9, taking the discrete phase vector output by the second cycle as the initial discrete phase vector, and repeating S2 to S6 until the number of cycles of the third cycle is reached, obtaining the discrete phase vector output by the third cycle, and taking the discrete phase vector output by the third cycle as the final discrete phase vector; S10. Perform phase hopping on each subcarrier of the OFDM original navigation signal vector based on the final discrete phase vector to obtain an OFDM phase hopping signal vector.

2. The method according to claim 1, characterized in that: In S4 of the present invention, the updated discrete phase vector is obtained by the following formula: i new =θ select +ξ·N(μ,σ 2 ) In the formula, θ new is the updated discrete phase vector, θ select is the first subcarrier phase selection vector, ξ is the first weight coefficient, N(μ,σ 2 ) is the Gaussian distribution function, μ is the mean, σ 2 is the variance.

3. The method according to claim 1, characterized in that In S5 of the present invention, the updated discrete phase vector is obtained by the following formula: i new =θ′ select +ξ·N(μ,σ 2 ) θ′ select =w1θ select_1 +w2θ select_2 In the formula, θ′ select is the second subcarrier phase selection vector, θ select_1 ,θ select_2 They are the cluster centers of the two currently selected clusters or a randomly selected individual of each cluster, and w1 and w2 are the second and third weight coefficients respectively.

4. The method according to claim 1, characterized in that: The PAPR value of the OFDM original navigation signal vector is obtained by the following formula: in, Where PAPR is the PAPR value of the OFDM original navigation signal vector, b is the proportional coefficient, is a constant, X is the OFDM original navigation signal vector, H is the conjugate transpose, T is the transpose, N is the number of subcarriers, i, l, h are different subcarrier indexes, and θ′[l] and θ′[h] are the discrete phases of the lth and hth subcarriers in the updated discrete phase vector.

5. The method according to claim 1, characterized in that The OFDM phase-hopping signal vector is obtained by the following formula: S PH =X⊙e θ S PH =[s PH [0],s PH [1],...,s PH [N-1]] in, In the formula, S PH is the OFDM phase-hopping signal vector, X is the OFDM original navigation signal vector, θ is the final discrete phase vector, ⊙ is the Hadamard product operator symbol, s PH [k] is the kth OFDM phase-hopping signal in the OFDM phase-hopping signal vector, C[i] is the ranging code of the ith subcarrier, θ[i] is the discrete phase of the ith subcarrier in the final discrete phase vector, M is the number of OFDM symbols, and N is the number of subcarriers.

6. The method according to claim 1, characterized in that The number of cycles of the first loop is the number of OFDM symbols, the number of cycles of the second loop is the total number of iterations, and the number of cycles of the third loop is the number of uniform segments of the initial discrete phase vector in the range of [0,2π].

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