An improved partial transmission sequence method for BPSK modulation

Abstract

The application is suitable for the field of wideband digital communication technology, and relates to an improved partial transmission sequence method for BPSK modulation. The method utilizes the signal characteristics of BPSK modulation, introduces a new phase factor selection scheme, simplifies the calculation process of the time domain candidate signal of the PTS scheme, and enables the transmitting end to not transmit any sideband information. With the help of the new phase factor sequence, the corresponding partial transmission sequence method of the BPSK modulation signal can effectively reduce the calculation complexity, and meanwhile, the same channel transmission performance as the traditional scheme is obtained without carrying sideband information. In addition, very excellent peak-to-average ratio performance can also be obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wideband digital communication, and particularly relates to an improved partial transmit sequence method for BPSK modulation. BACKGROUND

[0002] Orthogonal Frequency Division Multiplexing (OFDM) technology can realize high-speed data transmission with high spectrum utilization, can effectively combat multipath fading, and has low channel equalization process calculation complexity, and therefore is widely applied in the field of digital wideband communication, including LTE, 5G, digital audio broadcast (DAB), digital video broadcast (DVB), high-power line carrier (HPLC), etc. However, the problem of high peak-to-average power ratio (PAPR) of the transmitted signal caused by the multi-carrier system of OFDM will reduce the working efficiency of the power amplifier at the sending end, and puts forward higher requirements on the linear range of the amplifier, and increases the hardware cost of the system, and therefore the peak-to-average ratio reduction technology has always been one of the key technologies of the OFDM system.

[0003] Researchers have done a lot of research on the PAPR reduction problem of OFDM signals, and have proposed a series of solutions, which can be divided into signal distortion methods and signal non-distortion methods, wherein the signal distortion methods include clipping method, compression and expansion method, etc.; the signal non-distortion methods can be divided into grouping coding method, selective mapping, partial transmit sequence (PTS), etc. The PTS method is a commonly used peak-to-average ratio reduction algorithm, and the basic idea is to divide a frame of input OFDM symbols into V non-overlapping sub-sequences in the frequency domain, and multiply each sub-sequence by different weighting coefficients, and reduce the PAPR value of the combined sequence by selecting appropriate weighting coefficients. The core of this method is to generate a certain number of time-domain candidate signals, and then select the signal with the smallest PAPR value for transmission. The PTS technology will not cause distortion of the signal, and therefore will not cause loss of signal channel transmission performance, but has two shortcomings, one is high calculation complexity, and the other is the need to carry a certain amount of sideband information, and the peak-to-average ratio reduction performance is poor. Patent No. CN102075483B provides a method for reducing the peak-to-average ratio (PAPR) of OFDM signals, which preliminarily reduces the signal peak-to-average ratio by using SLM or PTS with a small number of groups, and then reduces the PAPR to a target value by setting the clipping rate by using the clipping method on the time-domain data output by the PTS or SLM. This method still has high calculation complexity in the process of reducing the peak-to-average ratio of OFDM signals, and also needs to carry sideband information, and still has the disadvantages of the prior art.

[0004] Therefore, how to reduce computational complexity while avoiding the carrying of sideband information to improve peak-to-average power ratio performance is a problem that urgently needs to be solved by researchers in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide an improved partial transmission sequence method for BPSK modulation, which solves the problems of high computational complexity in the selection process of the optimal signal in existing partial transmission sequence algorithms, as well as the need to carry sideband information, resulting in poor peak-to-average power ratio performance.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides an improved partial transmission sequence method for BPSK modulation, comprising the following steps:

[0008] S10. Let the original frequency domain signal be X = [X(0), X(1), ..., X(N-1)] T , where the symbol [.] T The transpose of a vector divides a signal X into V non-overlapping groups of signals. The matrix representing the combination of these groups is denoted as:

[0009]

[0010] S20. Let the numerical expression of the set of phase rotation factors corresponding to the V grouped signals be:

[0011]

[0012] S30. Calculate the V grouped frequency domain signals. The corresponding time-domain signal is expressed as:

[0013]

[0014] make

[0015] S40. Combining steps S20 and S30, we obtain M = 2. V One time-domain candidate signal;

[0016] S50, M = 2 calculated from step S40 V The signal with the smallest peak-to-average power ratio is selected from the candidate signals in the time domain and transmitted.

[0017] Furthermore, when using the set of phase rotation factors in the expression of step S20, the calculation process of multiplying each group signal by a complex factor with an amplitude of 1 can be completed without complex multiplication.

[0018] Further, the step S40 after optimization based on the recursive idea of the calculation process is as follows:

[0019] Let Then:

[0020]

[0021] Wherein the symbol represents the exhaustive addition of two sets, that is, set And Then

[0022] Further, the step S30 needs Complex number multiplication and Complex number addition, the step S40 does not need complex number multiplication, and the number of complex number additions is num_add v =2 v+1 (N-1), v=1, 2,..., V-1, and the sum of the number of complex number additions required to complete all the calculation processes is

[0023] Further, in the step S10, N / V is an integer greater than 1.

[0024] The improved partial transmission sequence method for BPSK modulation provided by the present application has at least the following beneficial effects compared with the prior art:

[0025] The existing PTS technology does not cause distortion of the signal, so it does not cause loss of signal channel transmission performance, but it has two disadvantages, one is high computational complexity, and the other is the need to carry a certain amount of sideband information, which has poor peak-to-average ratio performance. The present application uses the signal characteristics of BPSK modulation, simplifies the calculation process of the time-domain candidate signal of the PTS scheme by introducing a new phase factor selection scheme, and can make the transmitting end no longer need to transmit any sideband information. With the help of the new phase factor sequence, the corresponding partial transmission sequence method of the BPSK modulated signal can effectively reduce the computational complexity, and at the same time, without carrying sideband information, the same channel transmission performance as the traditional scheme is obtained, and very excellent peak-to-average ratio performance can also be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the scheme of the present application, the drawings required in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0027] Figure 1This is a schematic flowchart illustrating an improved partial transmission sequence method for BPSK modulation provided in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the signal processing flow of a traditional PTS solution;

[0029] Figure 3 This invention provides an improved partial transmission sequence method for BPSK modulation, which calculates all candidate signals based on a recursive approach.

[0030] Figure 4 A constellation point location diagram at the transmitter for each packet frequency domain signal in an improved partial transmission sequence method for BPSK modulation, provided as an embodiment of the present invention;

[0031] Figure 5 This is a performance comparison chart of the judgment error rate and packet error rate of the BPSK+1 / 2Turbo scheme under different N / Q values ​​in an AWGN channel for an improved partial transmission sequence method for BPSK modulation, provided in an embodiment of the present invention.

[0032] Figure 6 The image shows the signal CCDF curve of an improved partial transmission sequence method for BPSK modulation provided in this embodiment of the invention, and the signal CCDF curve of the prior art. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0035] This invention provides an improved partial transmission sequence method for BPSK modulation, applied to the PTS peak-to-average power ratio reduction technique for OFDM signals. The improved partial transmission sequence method for BPSK modulation includes:

[0036] S10. Let the original frequency domain signal be X = [X(0), X(1), ..., X(N-1)] T , where the symbol [.] Tdenotes the transposition of a vector, the signal X is divided into V non-overlapping group column signals, and the matrix of the group column signal combination is denoted as:

[0037]

[0038] S20, the phase rotation factor set corresponding to the V group signals is expressed as:

[0039]

[0040] S30, the time domain signal corresponding to the V group frequency domain signals is calculated, and the expression is denoted as:

[0041]

[0042] Let

[0043] S40, M=2 V time domain candidate signals are obtained by combining step S20 and step S30.

[0044] S50, from the M=2 V time domain candidate signals calculated in step S40, a signal with the minimum peak-to-average ratio value is selected for transmission.

[0045] The present application utilizes the signal characteristics of BPSK modulation, simplifies the calculation process of the time domain candidate signal of the PTS scheme by introducing a new phase factor selection scheme, and can make the transmitting end no longer need to transmit any sideband information. With the help of the new phase factor sequence, the corresponding partial transmission sequence method of the BPSK modulated signal can effectively reduce the calculation complexity, and at the same time, the same channel transmission performance as the traditional scheme is obtained without carrying sideband information. In addition, very excellent peak-to-average ratio reduction performance can also be obtained.

[0046] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings.

[0047] In an OFDM system with a subcarrier number of N, X=[X(0), X(1),..., X(N-1)] represents a frequency domain signal, x=[x(0), x(1),..., x(N-1)] represents a corresponding time domain signal, and the relationship between the two is as follows:

[0048]

[0049] The peak-to-average ratio value of the signal is defined as

[0050]

[0051] where max(x 2 ) denotes the square of the maximum amplitude of the elements in signal x, and E(x 2 ) denotes the average power of signal x.

[0052] Among the many techniques for reducing the peak-to-average ratio, the PTS algorithm does not cause distortion of the signal and has very good performance in reducing the peak-to-average ratio. The core idea of the algorithm is to group N subcarriers, then multiply each group of subcarriers by the same phase rotation factor, then combine, and through the selection of the rotation phase of each group, the purpose of reducing the peak-to-average ratio of the transmitted signal is achieved.

[0053] As shown in Figure 2 , the original frequency domain signal X = [X(0), X(1),..., X(N-1)] is divided into V non-overlapping group signals, denoted as {X0, X1,..., X V-1} and these group signals satisfy

[0054]

[0055] Then further add a phase rotation factor with an amplitude of 1 to each group signal , where each phase rotation factor is selected from a discrete set containing W elements, i.e. v,w θ v ∈ S v,1 = {0, s v,W-1 ,..., s V}.

[0056] Note: W elements in each phase rotation factor set, which must contain a 0 value element, which is used to generate the time domain signal corresponding to the original frequency domain signal.

[0057] Then calculate the generated time domain candidate signal set

[0058]

[0059] The above generates a total of W V time domain candidate signals, then through a certain selection algorithm, the signal with the smallest peak-to-average ratio is selected for transmission, i.e. the corresponding rotation phase factor is found, as follows:

[0060]

[0061] Based on the above process, it can be seen that if the exhaustive search scheme is adopted, the transmitting end needs to calculate the values of all W V time domain candidate signals, and the calculation process includes:

[0062] V IDFT operations of length N are performed to calculate x. v =IDFT(X) v ), v = 0, 1, ..., V-1;

[0063] Then regarding x v Multiplying each of v = 0, 1, ..., V⁻¹ by a complex rotation phase factor with an amplitude of 1 yields the calculated value. (Note: The first phase factor is 1 and does not need to be calculated);

[0064] Finally, these V complex signals of length N are added together to obtain a time-domain candidate signal.

[0065] The IDFT operation can use the Fast Fourier Transform (IFFT) algorithm. Completing one N-point IFFT operation requires... Multiplication of complex numbers and Complex number addition. In summary, calculate all of W. V The number of complex multiplications required for each time-domain candidate signal is The number of complex number additions is 1, while the number of complex number additions is 2. Therefore, it can be seen that as the values ​​of V and W increase, the computational load of the algorithm will increase rapidly, especially the number of complex number additions, which increases exponentially, resulting in high computational complexity.

[0066] In addition, to ensure that the receiver correctly interprets the received signal, the transmitter needs to carry log2W. V Each bit of sideband information is used to indicate the serial number of the transmitted signal to the receiver. Because this sideband information is crucial, reliable transmission requires significant channel resources, which reduces channel utilization, lowers data transmission rates, and increases system complexity.

[0067] BPSK modulation is the lowest order modulation scheme. Although it has the lowest spectral efficiency, it boasts the strongest noise immunity and the longest signal transmission distance under the same channel conditions. Therefore, it is a very commonly used modulation technique. For an OFDM signal with N subcarriers using BPSK modulation, such as... Figures 1 to 6 As shown, in this embodiment, the improved partial transmission sequence method for BPSK modulation includes the following steps:

[0068] S10. Let the original frequency domain signal be X = [X(0), X(1), ..., X(N-1)] T , where the symbol [.] T The transpose of a vector divides a signal X into V (N / V is an integer greater than 1) non-overlapping groups of signals. The matrix representing the combination of these groups is denoted as:

[0069]

[0070] S20, the phase rotation factor set corresponding to the V group signal is expressed as:

[0071]

[0072] S30, first calculate the time domain signal corresponding to the V group frequency domain signal , the expression is recorded as:

[0073]

[0074] Then let

[0075] In the case of using the phase rotation factor set of the expression in step S20, the calculation process of multiplying each group signal by a complex factor with an amplitude of 1 can be completed without complex multiplication, which can reduce the amount of calculation.

[0076] S40, in the case of using the phase rotation factor set of the expression in step S20, using the signal of the expression in step S30, a total of M=2 V Figure 3 Time domain candidate signals can be generated, combined with , the following is the optimized calculation process based on the recursive idea: let Then:

[0077]

[0078] Where the symbol represents the exhaustive addition of two sets, that is, let set And Then

[0079] S50, select a signal with the smallest peak-to-average ratio from the M=2 V Time domain candidate signals calculated in step S40 to send.

[0080] Further, the following is the calculation complexity analysis of the improved partial transmission sequence method provided by the embodiment of the application for BPSK modulation, wherein Complex multiplication is required to complete step S30, and Complex addition is required; and step S40 does not require any complex multiplication, and in terms of complex addition, based on the calculation process of step S40, the number of complex additions required for each calculation of a V-1 recursive calculation process is

[0081] num_add v =2 v+1(N - 1), v = 1, 2,..., V - 1

[0082] Therefore, the sum of the number of complex additions required to complete these calculation processes is:

[0083]

[0084] Table 1 summarizes the calculation complexity comparison between the conventional PTS scheme and the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application, where W = 2, V = 16, and N = 1024. Compared with the conventional phase sequence PTS scheme, the number of complex multiplications and complex additions of the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application can be reduced by 6.25% and 86.7%, respectively. Obviously, the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application can effectively reduce the calculation complexity.

[0085] Table 1

[0086]

[0087] Since the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application is to avoid carrying any sideband information at the transmitting end, the following is the signal processing mechanism at the receiving end. Let the received frequency domain signal after channel equalization be Y = [Y(0), Y(1),..., Y(N - 1)], and let:

[0088] Y v = [Y(0 + (v - 1)N / V), Y(1 + (v - 1)N / V),..., Y(N / V - 1 + (v - 1)N / V)]

[0089] where v = 0, 1,..., V - 1.

[0090] Without loss of generality, it is assumed that the channel estimation is ideal and error-free. The relationship between the received frequency domain sub-signals and the transmitted frequency domain sub-signals is as follows:

[0091]

[0092] where H v represents the noise term after channel equalization.

[0093] Since there is a restriction of not carrying sideband information, the receiving end needs to determine the specific value of the rotation phase corresponding to each group signal. Based on the expression of step S20, the receiving end only needs to determine whether the constellation point position of the frequency domain signal of each group signal is [-1, 1] or [j, -j], as shown in Figure 4 .

[0094] Then based on the above analysis, the constellation point position judgment mechanism of the receiving end is as follows:

[0095] Let

[0096] D v,1 = [Y(0+(v-1)N / V)-1, Y(1+(v-1)N / V)-1,..., Y(N / V-1+(v-1)N / V)].

[0097] D v,2 = [Y(0+(v-1)N / V)+1, Y(1+(v-1)N / V)+1,..., Y(N / V+1+(v-1)N / V)].

[0098] D v,3 = [Y(0+(v-1)N / V)-j, Y(1+(v-1)N / V)-j,..., Y(N / V-j+(v-1)N / V)].

[0099] D v,2 = [Y(0+(v-1)N / V)+j, Y(1+(v-1)N / V)+j,..., Y(N / V+j+(v-1)N / V)].

[0100] Let D v = [d v,0 , d v,1 ,..., d v,N / V-1 ] and wherein:

[0101] d v,k = min(|Y(k+(v-1)N / V)-1|, |Y(k+(v-1)N / V)+1|), k = 0, 1,..., N / V-1

[0102] and

[0103]

[0104] Calculate

[0105]

[0106] and

[0107]

[0108] Then the judgment mechanism is as follows

[0109]

[0110] After the receiving end completes the judgment of the above judgment mechanism, it respectively judges the received signal Y vv=0,1,...,V-1, and the received signal is equivalent to the original frequency domain signal with BPSK modulation constellation point [-1, 1].

[0111] Based on the above constellation point position judgment mechanism of the received end grouping signal, if the judgment result of a certain grouping signal is wrong, it is equivalent to introducing some phase interference noise of π / 2 to the corresponding N / Q received signals, thereby causing the overall decoding performance to decline. Therefore, it is necessary to ensure the high accuracy of the above judgment mechanism.

[0112] In an additive white Gaussian noise (AWGN) channel, Figure 5 The judgment error rate of the above judgment mechanism under different N / Q values and the performance comparison between the packet error rate and the BPSK+1 / 2 Turbo coding scheme are given. As can be seen from the results in the figure, under the same signal-to-noise ratio, with the increase of the value of N / Q, the above judgment mechanism quickly reduces, and the transmission error rate performance of the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application can be ensured to remain basically the same as that without using it under the condition of N / Q≥64.

[0113] Further, the time domain complementary cumulative distribution function (CCDF) is usually used to describe the distribution of the signal peak-to-average ratio (PAPR), and its mathematical calculation formula is:

[0114] Pr(PAPR>z)=1-Pr(PAPR≤z)

[0115] Let the number of subcarriers N=1024, V=16, and use the BPSK modulation technology, Figure 6 The CCDF curves of the signal after using the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application and the CCDF curves of the signal without using the patent scheme are given, and from Figure 6 As can be seen from the results, because the number of time domain candidate signals generated by the improved partial transmission sequence method for BPSK modulation provided by the embodiment of the present application is large, there is a large transmission signal peak-to-average ratio optimization space, and very excellent peak-to-average ratio reduction performance can be obtained.

[0116] Compared with the prior art, the improved partial transmission sequence method for BPSK modulation in the above embodiment does not cause signal distortion, thus does not cause loss of signal channel transmission performance, but has two shortcomings, one is high calculation complexity, and the other is that a certain amount of sideband information needs to be carried, and the peak-to-average ratio performance is poor. The present application utilizes the signal characteristics of BPSK modulation, simplifies the calculation process of the time-domain candidate signal of the PTS scheme by introducing a new phase factor selection scheme, and can make the transmitting end not need to transmit any sideband information. With the help of the new phase factor sequence, the corresponding partial transmission sequence method of the BPSK modulation signal can effectively reduce the calculation complexity, at the same time, the same channel transmission performance as the traditional scheme is obtained without carrying sideband information, and very excellent peak-to-average ratio performance can also be obtained.

[0117] Obviously, the above-described embodiments are only preferred embodiments of the present application, but not all the embodiments. The preferred embodiments of the present application are shown in the drawings, but do not limit the patent scope of the present application. The present application can be realized in many different forms, and contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive. Although the present application is described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing specific embodiments, or equivalently replace part of the technical features. Any equivalent structure made by using the content of the present application specification and drawings, directly or indirectly applied in other related technical fields, is also within the patent protection scope of the present application.

Claims

1. An improved partial transmission sequence method for BPSK modulation, characterized in that, Includes the following steps: S10. Let the original frequency domain signal be X = [X(0), X(1), ..., X(N-1)] T , where the symbol [.] T The transpose of a vector divides a signal X into V non-overlapping groups of signals. The matrix representing the combination of these groups is denoted as: S20. Let the numerical expression of the set of phase rotation factors corresponding to the V grouped signals be: When using the set of phase rotation factors in the expression of step S20, the calculation process of multiplying each group signal by a complex factor with an amplitude of 1 can be completed without complex multiplication; S30. Calculate the V grouped frequency domain signals. The time-domain signal corresponding to v = 0, 1, ..., V-1 is expressed as: make S40. Combining steps S20 and S30, we obtain M = 2. V One time-domain candidate signal; S50, M = 2 calculated from step S40 V The signal with the smallest peak-to-average power ratio is selected from the candidate signals in the time domain and transmitted.

2. The improved partial transmission sequence method for BPSK modulation according to claim 1, characterized in that, The optimized recursive-based calculation process in step S40 is as follows: make If v = 1, 2, ..., V-1, then: Among the symbols This represents the exhaustive summation of two sets.

3. The improved partial transmission sequence method for BPSK modulation according to claim 2, characterized in that, In step S30, it is necessary to Multiplication of complex numbers and The number of complex additions is num_add, which does not require complex multiplication in step S40. v =2 v+1 (N-1), v=1,2,...,V-1, the sum of the number of complex additions required to complete all calculations is:

4. The improved partial transmission sequence method for BPSK modulation according to claim 1, characterized in that, In step S10, N / V is an integer greater than 1.

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