CN113890811B - Subcarrier allocation method based on proportional greedy algorithm and ACE-PTS - Google Patents
Subcarrier allocation method based on proportional greedy algorithm and ACE-PTS Download PDFInfo
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Abstract
The invention discloses a subcarrier allocation method based on a proportional greedy algorithm and an ACE-PTS, which aims to solve the problem of inhibiting the loss system rate in the peak-to-average ratio of an OFDM system and the problem of higher complexity in the subcarrier allocation process. The subcarrier allocation method comprises the following steps: 1) Pre-allocating sub-carriers by using a proportional greedy algorithm; 2) Quadrature modulating subcarriers; 3) Allocating a position order to the subcarrier sequences by using an ACE-PTS method; 4) The recombined subcarrier sequences are optimized. The invention can effectively inhibit the peak-to-average ratio of signals, maximize the throughput of the system, reduce the complexity of subcarrier allocation, and can be used for subcarrier allocation in an Orthogonal Frequency Division Multiplexing (OFDM) system.
Description
Technical Field
The invention belongs to the technical field of communication, and further relates to a subcarrier allocation method based on a proportional greedy algorithm and a constellation diagram expansion-part transmission sequence ACE-PTS (Active Constellation Extension-Partial Transmit Sequence) in the field of wireless communication systems. The invention can be applied to an orthogonal frequency division multiplexing OFDM (Orthogonal Frequency Division Multiplexing) system for wireless communication, pre-distributes subcarrier resources, realizes maximization of system throughput and inhibition of Peak-to-average power ratio (PAPR-to-Average Power Ratio), ensures that the subcarrier can provide maximum link rate, ensures fairness among links, and can avoid signal distortion and system power efficiency loss caused by working in a nonlinear interval when the Peak-to-average power ratio signal passes through a power amplifier.
Background
In wireless communication, compared with a single carrier system, an Orthogonal Frequency Division Multiplexing (OFDM) system with multiple carriers has higher transmission efficiency and spectrum efficiency, and OFDM technology is widely used in the field of wireless communication. However, since the OFDM system adopts a multi-carrier modulation technique, when a plurality of subcarrier signals with the same or similar phases are superimposed in the time domain, a peak-to-average ratio PAPR problem of the signals will be caused. The signal peak to average ratio places higher linearity requirements on the wireless transmitter portion of the communication system, requiring costly power amplifiers to avoid distortion and loss of spectral and power efficiency of the system caused by operation in the nonlinear regime. Meanwhile, a certain rate difference is generated due to the fact that the sub-carriers are distributed on different links during modulation. The allocation scheme of the limited subcarrier resources has great influence on the performance of the system.
The university of electronics discloses a peak-to-average ratio suppression method of a subcarrier modulation OFDM system in the patent literature "a peak-to-average ratio suppression method of a subcarrier modulation OFDM system" (patent application No. 201610318530, application publication No. CN 106027444A) applied thereto. The method comprises the following steps: (1) And carrying out carrier index modulation on the signal to obtain a frequency domain signal, and representing the signal on a time domain through inverse Fourier transform. (2) And performing amplitude limiting processing on the time domain signal to obtain a peak value offset signal, and converting the peak value offset signal to the time domain to complete constellation diagram expansion. (3) Repeating iteration until the signal peak-to-average ratio reaches the peak-to-average ratio iteration threshold after the constellation diagram is expanded, stopping, and outputting a final signal. Finally, the effect of inhibiting the peak-to-average ratio is achieved. The method has the following defects: because only part of subcarriers are randomly selected for activation in carrier index modulation for transmitting data, subcarrier resources cannot be fully utilized, and part of rates are lost during system transmission.
Limian Gao et al in its published paper "Joint Optimization of Subcarriers Allocation and Tone Reservation PAPR Reduction for OFDMA System" (2012IEEE 14th International Conference on Communication Technology,2012, 1172-1176) propose a method of joint peak-to-average ratio suppression and throughput optimization based on subcarrier reservation. The method comprises the following steps: (1) And calculating the peak-to-average ratio of the data set at the reserved position by using a traversing method, and finding out the number of reserved subcarriers when the peak-to-average ratio is minimum. (2) Each user is pre-allocated with a subcarrier with the maximum channel gain, and the throughput of the system at this time is calculated. (3) And continuing to allocate the subcarriers according to the greedy algorithm, and updating the throughput after each allocation until all the subcarriers are allocated. Finally, the purposes of peak-to-average ratio suppression and throughput optimization are achieved. The method has the following defects: the number of allocated subcarriers is not set for each user, so that the channel gains of the subcarriers to all users need to be traversed when the subcarriers are allocated, and the complexity in the subcarrier allocation process is improved.
Disclosure of Invention
The invention aims to solve the problems of inhibiting the loss system rate in the peak-to-average ratio of an OFDM system and higher complexity in the subcarrier allocation process by providing a subcarrier allocation method based on a proportional greedy algorithm and an ACE-PTS aiming at the defects of the prior art.
The specific idea of the invention for achieving the above purpose is that by using a proportional greedy algorithm, in the subcarrier pre-allocation process, a subcarrier with the maximum channel gain value is allocated to each user, and since the system throughput is proportional to the channel gain value, the allocation of the subcarrier with the maximum channel gain value to the user can significantly increase the system throughput, and judge whether each user reaches the maximum total number of allocated subcarriers, if so, the subcarrier is not required to be allocated to the user. The subcarrier is pre-allocated by using a proportional greedy algorithm, users with the subcarrier capable of being allocated are updated after each judgment, the subcarrier is not allocated for the users reaching the maximum total number of the allocated subcarriers, the process of traversing the channel gain values of all users in allocation can be reduced, the complexity in the subcarrier allocation process is reduced, and the maximization of the throughput of the system is realized. The invention divides the sub-carrier into two parts according to the sub-carrier arrangement sequence in the sub-carrier distribution position sequence process by using an ACE-PTS method, and carries out amplitude limiting treatment and constellation diagram expansion on the part with large peak-average ratio, because the peak-average ratio of the part is larger, the peak-average ratio is reduced by using an amplitude limiting treatment and constellation diagram expansion method before the distribution position sequence, wherein the amplitude limiting treatment can reduce the appearance of high amplitude value in the signal, the constellation diagram expansion method can improve the error rate performance of the system and reduce the negative influence caused by the amplitude limiting treatment, therefore, the part with large peak-average ratio carries out amplitude limiting treatment and constellation diagram expansion, and carries out optimization and recombination for each sub-carrier adjustment phase, and the phase value corresponding to the sub-carrier is adjusted in the optimization and recombination process, so as to obtain a plurality of sub-carriers with minimum peak-average ratio, and the sub-carrier is selected from the sub-carriers after optimization and recombination. It can be seen that the allocation of subcarrier position order by using the ACE-PTS method, by reorganizing the subcarrier position order and adjusting the phase of each subcarrier, it is possible to increase the system transmission rate and reduce the system peak-to-average ratio without any loss of subcarrier resources.
The specific steps for realizing the invention are as follows:
step 1, pre-allocating sub-carriers by using a proportional greedy algorithm:
(1a) Selecting one untagged user from the K users; wherein K represents the total number of users, and K is more than or equal to 8;
(1b) Selecting a maximum channel gain value from different channel gain values of all unassigned subcarriers corresponding to the selected user;
(1c) Distributing the sub-carrier corresponding to the maximum channel gain value to the selected user, and deleting the sub-carrier in the sub-carriers;
(1d) Judging n k ＜N k If yes, executing the step (1 a), otherwise, marking the selected user as a forbidden user, and executing the step (1 e); wherein n is k Indicating that the kth selected user is assignedN, N k A constant is represented by a number of times,n represents the total number of sub-carriers, N is greater than or equal to 1024, G k A state value representing a transmission channel between the kth selected user and the antenna transmitting end;
(1e) Judging whether all sub-carriers are allocated, if yes, executing the step 2, otherwise, executing the step (1 a);
step 2, quadrature modulation subcarrier:
carrying out orthogonal modulation on each pre-allocated subcarrier in sequence according to the initial position sequence of the subcarrier to obtain a modulated subcarrier sequence consisting of all subcarriers subjected to orthogonal modulation;
step 3, allocating position order to the subcarrier sequences by using ACE-PTS method:
(3a) Respectively calculating the front in the subcarrier sequencesLength sequence and post->Peak-to-average ratio of the length sequence; wherein N represents the total length of the subcarrier sequence;
(3b) Converting the subcarrier sequence with large peak-to-average ratio into a time domain by utilizing P-point inverse fast Fourier transform, then carrying out amplitude limiting treatment, converting the signal subjected to the time domain amplitude limiting into a frequency domain by utilizing Q-point Fourier transform, and carrying out constellation diagram expansion on the signal subjected to the frequency domain amplitude limiting; wherein P represents the sampling point number in the inverse fast Fourier transform, Q represents the sampling point number in the Fourier transform, and the values of P and Q are equal to N;
(3c) Judging whether the frequency domain amplitude limiting signal after the constellation diagram expansion meets the convergence condition, if so, executing the step (3 d), otherwise, executing the step (3 b);
(3d) Converting the frequency domain limited signal after the constellation diagram expansion into a time domain by utilizing P point inverse fast Fourier transform to obtain a time domain signal after the constellation diagram expansion;
step 4, optimizing the recombined subcarrier sequence:
(4a) Dividing a sub-carrier sequence with small peak-to-average ratio into V continuous sub-sequences with equal length, and sequentially carrying out P-point inverse fast Fourier transform on each sub-sequence to obtain a time domain signal of the sub-sequence according to the dividing sequence; wherein V represents the total number of sub-sequences after segmentation,
(4b) By means ofAnd->Respectively adjusting the phase of each sub-sequence time domain signal and the time domain signal after constellation diagram expansion; wherein (1)>Representing the ith subsequence time domain signal after phase adjustment, i represents the sequence number of the subsequence time domain signal, i is more than or equal to 1 and less than or equal to V and X i Representing an ith sub-sequence time domain signal before phase adjustment, e jφ Representing the rotational phase factor, e (·) The index operation based on the natural number e is represented, j represents the imaginary unit symbol, phi represents the adjustable angle value in the rotary phase factor, the value interval is [0,2 pi ], and the value interval is +.>Pi represents the circumference ratio, < >>Representing the constellation spread time domain signal after phase adjustment, and Y represents the constellation spread time domain signal before phase adjustment;
(4c) Accumulating the phases of all the time domain signals after phase adjustment to obtain a time domain total signal, and storing the time domain total signal into a time domain total signal set;
(4d) JudgingIf the time domain total signal is the same as the time domain total signal set, executing step (4 e), otherwise, adding the adjustable angle value in the rotary phase factorPerforming step (4 b) afterwards;
(4e) Converting each time domain total signal in the time domain total signal set to a frequency domain by utilizing Q-point Fourier transform, and calculating the peak-to-average ratio of each subcarrier after changing the position order;
(4f) And selecting the subcarrier with the smallest peak-to-average ratio from all the subcarriers with changed position sequences as the subcarrier after optimization and recombination.
Compared with the prior art, the invention has the following advantages:
firstly, the invention pre-distributes sub-carriers by using a proportional greedy algorithm, distributes sub-carriers to users with the maximum gain value for each sub-carrier, does not distribute sub-carriers to users reaching the total number of the maximum sub-carrier distribution, overcomes the defect of excessively high complexity of sub-carrier distribution in the prior art, shortens the distribution time of each sub-carrier, improves the distribution efficiency and reduces the complexity in the distribution process.
Secondly, the invention utilizes ACE-PTS method to distribute position sequence to subcarrier sequence, and adjusts the phase of each subcarrier by recombining subcarriers, thereby reducing the appearance of high amplitude value in subcarriers, overcoming the defect of reducing system transmission rate by losing subcarrier resources in the prior art, making the invention fully utilize subcarrier resources in OFDM system, improving system transmission rate, maximizing system throughput and reducing system peak-to-average ratio.
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FIG. 1 is a flow chart of the present invention;
fig. 2 is an embodiment of a constellation expansion method in the present invention;
fig. 3 is a simulation diagram of the present invention.
Detailed description of the preferred embodiments
The invention is further described below with reference to the drawings and examples.
The steps of implementing the present invention will be further described with reference to fig. 1.
And step 1, pre-allocating sub-carriers by using a proportional greedy algorithm.
Firstly, selecting an unlabeled user from K users; wherein K represents the total number of users, and K is more than or equal to 8.
And secondly, selecting the maximum channel gain value from different channel gain values of all unassigned sub-carriers corresponding to the selected user.
And thirdly, distributing the subcarrier corresponding to the maximum channel gain value to the selected user, and deleting the subcarrier in the subcarriers.
The throughput of the ith user is calculated according to the following formula:
wherein R is i Indicating the throughput of the ith user, B indicating the bandwidth of the OFDM system, N indicating the total number of sub-carriers, N being greater than or equal to 1024, p indicating the transmission power of the system, H i,j Representing the channel gain of the ith user to the jth subcarrier;
accordingly, the sub-carrier corresponding to the maximum channel gain value is allocated to the selected user, and the throughput of the selected user can be maximized.
Fourth, judge n k ＜N k If yes, executing the first step of the step, otherwise, marking the selected user as a forbidden user and executing the fifth step of the step; wherein n is k Representing the total number of sub-carriers allocated to the kth selected user, N k A constant is represented by a number of times,G k representing the state value of the transmission channel between the kth selected user and the antenna transmitting end.
Said constant N k Representing the maximum total number of sub-carriers allocated to the kth user;
because each user is positioned at different positions and has different channel state values with the transmission channel between the wireless transmitting end, the total number of the allocated maximum subcarriers is set according to the channel state values of the users according to the throughput calculation formula, so that the users under good channel conditions can allocate more subcarriers, the system throughput is greatly improved, the users under bad channel conditions can allocate fewer subcarriers, and the negative influence of the bad channel conditions on the system throughput is reduced as much as possible.
And fifthly, judging whether all the subcarriers are allocated, if yes, executing the step 2, otherwise, executing the first step of the step.
And 2, quadrature modulating the subcarriers.
And carrying out orthogonal modulation on each pre-allocated subcarrier in sequence according to the initial position sequence of the subcarrier to obtain a modulated subcarrier sequence consisting of all subcarriers subjected to orthogonal modulation.
And step 3, allocating the position order to the subcarrier sequences by using an ACE-PTS method.
First, respectively calculating the front in the subcarrier sequenceLength sequence and post->Peak-to-average ratio of the length sequence; where N represents the total length of the subcarrier sequence.
Secondly, converting the subcarrier sequence with large peak-to-average ratio into a time domain by utilizing P-point inverse fast Fourier transform, then carrying out amplitude limiting treatment, converting the signal subjected to the time domain amplitude limiting into a frequency domain by utilizing Q-point Fourier transform, and carrying out constellation diagram expansion on the signal subjected to the frequency domain amplitude limiting; wherein P represents the sampling point number in the inverse fast Fourier transform, Q represents the sampling point number in the Fourier transform, and the values of P and Q are equal to N.
The constellation diagram expansion method has good effect of reducing the peak-to-average ratio, so the constellation diagram expansion method is used for the subcarrier sequence with large peak-to-average ratio.
Clipping the time signal according to the following steps:
wherein,representing the time domain signal after clipping processing, x n Representing an ungrounded time domain signal, |·| representing a modulo operation, a representing a clipping threshold, a=0.74|x n |，e (·) Represents an exponential operation based on a natural number e, j represents an imaginary unit symbol, arg [ · ]]Representing a phase fetch operation;
and the time domain signal is subjected to amplitude limiting treatment, so that the occurrence of high amplitude values in the time domain signal can be reduced, and the peak-to-average ratio of the system is reduced.
The constellation expansion method in the present invention is further described with reference to the embodiment of fig. 2:
the embodiment of the invention performs constellation diagram expansion on the frequency domain signal in an OFDM system with a modulation mode of 16 quadrature amplitude modulation QAM (Quadrature Amplitude Modulation). In fig. 2, black filled circles represent sixteen constellation points, each constellation point is obtained by mapping a single subcarrier to a vector diagram coordinate system through 16QAM modulation, a single dashed arrow indicates that the constellation point can only expand towards the direction, the value of the direction coordinate after expansion is a larger value in the absolute value of the direction coordinate corresponding to the constellation point and the absolute value of the direction coordinate corresponding to the constellation point after clipping, the dashed arrow perpendicular to each other indicates that the constellation point can expand towards the area pointed by the arrow, and the value of the horizontal coordinate and the vertical coordinate after expansion is a larger value in the absolute value of the real part and the imaginary part of the constellation point and the absolute value of the real part and the imaginary part of the constellation point after clipping respectively.
And constellation diagram expansion is carried out on the frequency domain signals, so that the error rate performance of the system can be improved, and negative influence caused by amplitude limiting processing is reduced.
And thirdly, judging whether the frequency domain amplitude limiting signal after the constellation diagram is expanded meets the convergence condition, if so, executing the fourth step of the step, and otherwise, executing the second step of the step.
The convergence condition refers to a case where the following two conditions are satisfied at the same time:
the amplitude of the frequency domain limited signal is not changed after the constellation diagram is expanded under the condition 1;
in condition 2, the phase of the frequency-domain limited signal is not changed after the constellation expansion.
And fourthly, converting the frequency domain amplitude limiting signal after the constellation diagram expansion into a time domain by utilizing P point inverse fast Fourier transform, and obtaining the time domain signal after the constellation diagram expansion.
Step 4, optimizing the recombined subcarrier sequence:
dividing a sub-carrier sequence with small peak-to-average ratio into V continuous sub-sequences with equal length, and sequentially carrying out P-point inverse fast Fourier transform on each sub-sequence to obtain a time domain signal of the sub-sequence according to the dividing sequence; wherein V represents the total number of sub-sequences after segmentation,
second step, utilizeAnd->Respectively adjusting the phase of each sub-sequence time domain signal and the time domain signal after constellation diagram expansion; wherein (1)>Representing the ith subsequence time domain signal after phase adjustment, i represents the sequence number of the subsequence time domain signal, i is more than or equal to 1 and less than or equal to V and X i Representing an ith sub-sequence time domain signal before phase adjustment, e jφ Represents the rotation phase factor, phi represents the adjustable angle value in the rotation phase factor, the value interval is [0,2 pi ], and the value interval is +.>Pi represents the rate of the circumference of a circle,representing the constellation spread time domain signal after phase adjustment, and Y represents the constellation spread time domain signal before phase adjustment.
Thirdly, accumulating the phases of all the time domain signals after phase adjustment to obtain a time domain total signal, and storing the time domain total signal into a time domain total signal set.
And the step of accumulating the phases of all the phase-adjusted time domain signals to obtain a time domain total signal is to reconstruct all the segmented subsequences into a new time domain total signal according to the optimization step, so that the peak-to-average ratio of the system can be reduced.
Fourth, judging whether the time domain total signal to be stored is the same as the time domain total signal set, if yes, executing the fifth step, otherwise, adding the adjustable angle value in the rotation phase factorThe second step of this step is then performed.
And fifthly, converting each time domain total signal in the time domain total signal set into a frequency domain by utilizing Q-point Fourier transform, and calculating the peak-to-average ratio of each subcarrier after changing the position order.
And sixthly, selecting the subcarrier with the smallest peak-to-average ratio from all the subcarriers with changed position sequences as the subcarrier after optimization and recombination.
The effects of the present invention are further described below in conjunction with simulation experiments:
1. simulation experiment conditions:
the hardware platform of the simulation experiment of the invention is: the processor is Intel i5-6400 CPU, the main frequency is 2.7GHz, and the memory is 16GB.
The software platform of the simulation experiment of the invention is: windows 10 operating system and MATLAB R2019a.
2. Simulation content and result analysis:
the simulation experiment of the invention adopts the invention and three prior arts (Root-Finding method, constellation expansion-convex set mapping method ACE-POCS (Active Constellation Extension-Projection onto Convex Sets) method and partial transmitting sequence PTS method) to respectively distribute 2048 subcarriers in the OFDM system with parameters set in the following table 1, and obtains the system throughput and signal peak-to-average ratio inhibition performance diagram. The simulation experiment parameter settings are shown in table 1:
table 1 list of experimental parameter settings
| Setting item | Value taking |
| Total number of sub-carriers | 2048 |
| Total number of users | [2，4，6，8，10，12，14，16] |
| Modulation order | 64QAM |
| System bandwidth | 1MHz |
| Number of constellation expansion map iterations | 200 |
| Total number of partial transmit sequence cut sub-blocks | 8 |
| Rotational phase factor | [-1，1] |
In simulation experiments, three prior art techniques employed refer to:
the Root-Finding method in the prior art refers to a subcarrier allocation method, abbreviated as the Root-Finding method, proposed by Zukang et al in "Optimal power allocation in multiuser OFDM systems, GLOBECOM'03.IEEE Global Telecommunications Conference (IEEE Cat. No. 03CH37489), san Francisco, calif., USA,2003, pp. 337-3411 Vol.1.
The prior art constellation extension-convex set mapping method ACE-POCS refers to a peak-to-average ratio suppression method, abbreviated as constellation extension-convex set mapping method ACE-POCS, proposed by Krongold et al in "PAR reduction in OFDM via active constellation extension,2003IEEE International Conference on Acoustics,Speech,and Signal Processing,2003.Proceedings" (ICASSP' 03), hong Kong, china,2003, pp.iv-525.
The prior art partial transmit sequence PTS method refers to a peak-to-average ratio suppression method, abbreviated as the partial transmit sequence PTS method, set forth in Seog Geun Kang et al, "A novel subblock partition scheme for partial transmit sequence OFDM, in IEEE Transactions on Broadcasting, vol.45, no.3, pp.333-338, sept.1999.
The effects of the present invention are further described below in conjunction with the simulation diagram of fig. 3.
Fig. 3 (a) is a graph showing the throughput performance comparison of two different methods, wherein the method is provided by the invention and a Root-Finding algorithm of a traditional Root-Finding algorithm, the number of sub-carriers allocated to each user and the corresponding channel gain value are obtained under the condition of increasing the total number of users accessing an Orthogonal Frequency Division Multiplexing (OFDM) system, and the throughput of the system under the condition of different total numbers of users of different methods is calculated by using a system throughput formula.
The system throughput for all users is calculated as follows:
where R represents the system throughput of all users, p i Indicating the power distributed by the wireless transmitting end to the ith user, H i Representing the total value of the channel gains for the i-th user. The system throughput in the case of different total users can be directly calculated as an evaluation index of fig. 3 (a) by using a system throughput formula.
The abscissa in fig. 3 (a) represents the number of users accessing the system, and the ordinate represents the overall throughput of the system in bits/Hz. The curve labeled "- + -" in fig. 3 (a) shows the system throughput performance curve under access to different numbers of users after allocation of subcarriers using the method of the present invention. The curve labeled "-" in fig. 3 (a) shows the system throughput performance curve under different numbers of users after the subcarriers are allocated by adopting the Root-filtering algorithm of the conventional Root-Finding algorithm.
Fig. 3 (b) is a graph showing the peak-to-average ratio performance contrast curves of three different methods, which are obtained by adjusting the position order of subcarriers in an OFDM system to obtain a plurality of subcarriers after optimization and recombination, and then calculating the complementary cumulative distribution function of the peak-to-average ratio of the system processed by the different methods by using a peak-to-average ratio calculation formula and the complementary cumulative distribution function.
The system peak-to-average ratio is calculated according to the following formula:
wherein PAPR represents the system peak-to-average ratio, max [. Cndot.]Indicating maximum operation, P (t) indicating subcarrier power, E [. Cndot.]Representing the desired operation of the fetch. The complementary cumulative distribution function of the peak-to-average ratio is P { PAPR > PAPR th And the average peak ratio after sampling is larger than the sum of the occurrence probabilities of the sampling values of the threshold value of the average peak ratio, wherein the value interval of the threshold value of the average peak ratio is [5,13 ]]Complementary accumulated points of peak-to-average ratio in the value interval are calculatedThe cloth function is used as an evaluation index in fig. 3 (b).
The abscissa in fig. 3 (b) represents the peak-to-average ratio threshold value of the orthogonal frequency division multiplexing OFDM system signal, and the ordinate represents the complementary cumulative distribution function. The curve denoted by "- -" in fig. 3 (b) represents a peak-to-average ratio performance curve calculated for a subcarrier signal at the transmitting end of an OFDM system without any optimization algorithm. The curve marked with "-" in fig. 3 (b) shows the peak-to-average ratio performance curve after processing the subcarrier signal of the transmitting end of the OFDM system by using the conventional partial transmit sequence PTS method. The curve denoted by "-" in fig. 3 (b) shows a peak-to-average ratio performance curve after processing a subcarrier signal at a transmitting end of an OFDM system by using a conventional constellation extension ACE-POCS method. The curve denoted by "- +" in fig. 3 (b) shows the peak-to-average ratio performance curve after processing the subcarrier signal at the transmitting end of the OFDM system by the method of the present invention.
As can be seen from the simulation experiment diagram of FIG. 3 (a), when the number of users accessing the system is 2, 4, 6, 8, 10, 12, 14 and 16 respectively, compared with the traditional root finding algorithm, the invention has the system throughput gain of nearly 0.1bits/Hz at the minimum and the system throughput gain of nearly 0.2bits/Hz at the maximum, thus obviously improving the system throughput in a large-bandwidth system.
As can be seen from the simulation experiment diagram of FIG. 3 (b), the present invention has a complementary cumulative distribution function value of 10 -3 When compared with an orthogonal frequency division multiplexing OFDM system, the system has a peak-to-average ratio gain of approximately 3.7dB, compared with a traditional partial transmission sequence PTS method, has a peak-to-average ratio gain of approximately 1.0dB, compared with a traditional constellation diagram expansion ACE method, has a peak-to-average ratio gain of approximately 0.9 dB. Therefore, the invention can obviously reduce the peak-to-average ratio of the transmission signals of the Orthogonal Frequency Division Multiplexing (OFDM) system.
The simulation experiment shows that: the method of the invention pre-distributes the sub-carriers by using a proportional greedy algorithm, distributes the position sequence to the sub-carrier sequences by using an ACE-PTS method, can realize the maximization of the throughput of the system, can inhibit the peak-to-average ratio of an Orthogonal Frequency Division Multiplexing (OFDM) system, solves the problems of lower throughput and higher complexity of the system caused by the fact that the sub-carriers are distributed to the users with the maximum channel gain one by one under the conditions of inhibiting the peak-to-average ratio and high-order modulation by using partial sub-carriers in the OFDM system in the prior art method, and is a practical sub-carrier distribution method.
Claims (2)
1. A subcarrier allocation method based on a proportional greedy algorithm and ACE-PTS is characterized in that subcarrier sets corresponding to each user are obtained after the subcarriers are pre-allocated by the proportional greedy algorithm; allocating a position order to the subcarrier sequences by using an ACE-PTS method; the subcarrier allocation method comprises the following specific steps:
step 1, pre-allocating sub-carriers by using a proportional greedy algorithm:
(1a) Selecting one untagged user from the K users; wherein K represents the total number of users, and K is more than or equal to 8;
(1b) Selecting a maximum channel gain value from different channel gain values of all unassigned subcarriers corresponding to the selected user;
(1c) Distributing the sub-carrier corresponding to the maximum channel gain value to the selected user, and deleting the sub-carrier in the sub-carriers;
(1d) Judging n k ＜N k If yes, executing the step (1 a), otherwise, marking the selected user as a forbidden user, and executing the step (1 e); wherein n is k Representing the total number of sub-carriers allocated to the kth selected user, N k A constant is represented by a number of times,n represents the total number of sub-carriers, N is greater than or equal to 1024, G k A state value representing a transmission channel between the kth selected user and the antenna transmitting end;
(1e) Judging whether all sub-carriers are allocated, if yes, executing the step 2, otherwise, executing the step (1 a);
step 2, quadrature modulation subcarrier:
carrying out orthogonal modulation on each pre-allocated subcarrier in sequence according to the initial position sequence of the subcarrier to obtain a modulated subcarrier sequence consisting of all subcarriers subjected to orthogonal modulation;
step 3, allocating position order to the subcarrier sequences by using ACE-PTS method:
(3a) Respectively calculating the front in the subcarrier sequencesLength sequence and post->Peak-to-average ratio of the length sequence; wherein N represents the total length of the subcarrier sequence;
(3b) Converting the subcarrier sequence with large peak-to-average ratio into a time domain by utilizing P-point inverse fast Fourier transform, then carrying out amplitude limiting treatment, converting the signal subjected to the time domain amplitude limiting into a frequency domain by utilizing Q-point Fourier transform, and carrying out constellation diagram expansion on the signal subjected to the frequency domain amplitude limiting; wherein P represents the sampling point number in the inverse fast Fourier transform, Q represents the sampling point number in the Fourier transform, and the values of P and Q are equal to N;
(3c) Judging whether the frequency domain amplitude limiting signal after the constellation diagram expansion meets the convergence condition, if so, executing the step (3 d), otherwise, executing the step (3 b);
(3d) Converting the frequency domain limited signal after the constellation diagram expansion into a time domain by utilizing P point inverse fast Fourier transform to obtain a time domain signal after the constellation diagram expansion;
step 4, optimizing the recombined subcarrier sequence:
(4a) Dividing a sub-carrier sequence with small peak-to-average ratio into V continuous sub-sequences with equal length, and sequentially carrying out P-point inverse fast Fourier transform on each sub-sequence to obtain a time domain signal of the sub-sequence according to the dividing sequence; wherein V represents the total number of sub-sequences after segmentation,
(4b) By means ofAnd->Respectively adjusting the phase of each sub-sequence time domain signal and the time domain signal after constellation diagram expansion; wherein (1)>Representing the ith subsequence time domain signal after phase adjustment, i represents the sequence number of the subsequence time domain signal, i is more than or equal to 1 and less than or equal to V and X i Representing an ith sub-sequence time domain signal before phase adjustment, e jφ Representing the rotational phase factor, e (·) The index operation based on the natural number e is represented, j represents the imaginary unit symbol, phi represents the adjustable angle value in the rotary phase factor, the value interval is [0,2 pi ], and the value interval is +.>Pi represents the circumference ratio, < >>Representing the constellation spread time domain signal after phase adjustment, and Y represents the constellation spread time domain signal before phase adjustment;
(4c) Accumulating the phases of all the time domain signals after phase adjustment to obtain a time domain total signal, and storing the time domain total signal into a time domain total signal set;
(4d) Judging whether the time domain total signal to be stored is the same as the time domain total signal set, if so, executing the step (4 e), otherwise, adding the adjustable angle value in the rotary phase factorPerforming step (4 b) afterwards;
(4e) Converting each time domain total signal in the time domain total signal set to a frequency domain by utilizing Q-point Fourier transform, and calculating the peak-to-average ratio of each subcarrier after changing the position order;
(4f) And selecting the subcarrier with the smallest peak-to-average ratio from all the subcarriers with changed position sequences as the subcarrier after optimization and recombination.
2. The sub-carrier allocation method according to claim 1, wherein the convergence condition in the step (3 c) is a condition that the following two conditions are satisfied at the same time:
the amplitude of the frequency domain limited signal is not changed after the constellation diagram is expanded under the condition 1;
in condition 2, the phase of the frequency-domain limited signal is not changed after the constellation expansion.
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