CN101459648A - Method for lowering PAR of OFDM system based on virtual carrier preservation algorithm - Google Patents

Abstract

Translated fromChinese

本发明公开了无线通信技术领域中的一种基于虚载波预留算法降低OFDM系统峰均比的方法。技术方案是，将设定的特殊频域信号Cⁱ和承载有用信息的频域信号X经IFFT变换得到各自的时域信号cⁱ和x；计算x的初始PAPR值，记为PAPR_min，设定全零的时域信号c_final；计算x+c_final+cⁱ和x+c_final－cⁱ两个序列的PAPR值，并和PAPR_min比较，将最小的PAPR值存入PAPR_min，并且令此时满足最小PAPR值的特殊时域信号为c_temp，并更新c_final＝c_final+c_temp，直至i＝L；选择具有最小PAPR的组合并进行发送。本发明有效地降低了峰均比计算的复杂度和误码率，提高了系统的可靠性。

The invention discloses a method for reducing the peak-to-average ratio of an OFDM system based on a virtual carrier reservation algorithm in the technical field of wireless communication. The technical solution is to convert the set special frequency domain signal Cⁱ and the frequency domain signal X carrying useful information through IFFT to obtain respective time domain signals cⁱ and x; calculate the initial PAPR value of x, denoted as PAPR_min , set Set the all-zero time-domain signal c_final ; calculate the PAPR values of the two sequences x+c_final +^ci and x+c_final^-ci , and compare them with PAPR_min , store the smallest PAPR value into PAPR_min , and Let the special time-domain signal satisfying the minimum PAPR value at this time be c_temp , and update c_final =c_final +c_temp until i=L; select the combination with the minimum PAPR and send it. The invention effectively reduces the complexity and bit error rate of calculation of the peak-to-average ratio, and improves the reliability of the system.

Description

Translated fromChinese

基于虚载波预留算法降低OFDM系统峰均比的方法Method of Reducing Peak-to-Average Ratio of OFDM System Based on Virtual Carrier Reservation Algorithm

技术领域technical field

本发明属于无线通信技术领域，尤其涉及一种基于虚载波预留算法降低OFDM系统峰均比的方法。The invention belongs to the technical field of wireless communication, and in particular relates to a method for reducing the peak-to-average ratio of an OFDM system based on a virtual carrier reservation algorithm.

背景技术Background technique

随着人们对通信宽带化、个人化和移动化的需求越来越高，OFDM(Orthogonal Frequency Division Multiplexing，正交频分复用)技术在各个无线通信领域得到了广泛的应用。OFDM系统的一大缺点是有较高的峰值平均功率比，OFDM系统的发送信号是多个子载波上的发送信号相叠加而成的，当这些信号以同相相位相加时，所得信号的瞬时功率很大，远远超出信号的平均功率，导致系统产生较高的PAPR(Peak-to-Average Power Ratio，峰值平均功率比)。高PAPR对发射机和接收机内的功率放大器的线性范围提出了很高的要求，并且增加了A/D、D/A转换器等设备的复杂度。如果放大器的线性范围不能满足信号的动态变化范围，则信号会产生非线性畸变，导致频谱泄漏，各子载波间的正交性遭到破坏，产生载波间干扰，降低系统的性能。所以，峰值平均功率比问题是OFDM系统需要解决的重要问题。As people's demand for communication broadband, personalization and mobility is getting higher and higher, OFDM (Orthogonal Frequency Division Multiplexing, Orthogonal Frequency Division Multiplexing) technology has been widely used in various wireless communication fields. A major disadvantage of the OFDM system is that it has a high peak-to-average power ratio. The transmitted signal of the OFDM system is superimposed by the transmitted signals on multiple subcarriers. When these signals are added in the same phase, the instantaneous power of the obtained signal Very large, far exceeding the average power of the signal, resulting in a higher PAPR (Peak-to-Average Power Ratio, peak-to-average power ratio) in the system. High PAPR puts forward high requirements on the linear range of power amplifiers in transmitters and receivers, and increases the complexity of A/D, D/A converters and other equipment. If the linear range of the amplifier cannot meet the dynamic range of the signal, the signal will generate nonlinear distortion, resulting in spectrum leakage, the orthogonality between subcarriers will be destroyed, and inter-carrier interference will be generated, which will reduce the performance of the system. Therefore, the problem of peak-to-average power ratio is an important problem to be solved in the OFDM system.

在无线OFDM系统中，目前国内外降低PAPR的技术主要分为3类：信号预畸变类技术、信号扰码类技术、编码类技术。信号预畸变类技术的思想是直接对信号的峰值进行非线性操作，最直接，最简单。由于它采用的是非线性操作，产生了带内噪声和带外干扰，因此系统的误码率比较高。编码类技术的思想是只发送那些具有较低PAPR特性的码字，从而避免了发送那些会出现较高PAPR的码字。该类技术为线性过程，不会使信号产生畸变，因此也没有限幅类技术的缺点。但是，编码类技术的计算复杂度非常高，编解码都非常麻烦，更重要的是，这类技术的信息速率降低得很快，因此只适用于子载波数比较少的情况。信号扰码类技术，它的核心思想是降低大PAPR出现的概率，采用的也是线性变换，但是该类技术复杂度比较高，需要进行多次IFFT运算和搜索过程。In the wireless OFDM system, the technologies for reducing PAPR at home and abroad are mainly divided into three categories: signal pre-distortion technology, signal scrambling technology, and coding technology. The idea of signal predistortion technology is to directly perform nonlinear operations on the peak value of the signal, which is the most direct and simplest. Because it uses non-linear operation, it produces in-band noise and out-of-band interference, so the bit error rate of the system is relatively high. The idea of encoding-like techniques is to send only those codewords with lower PAPR characteristics, thereby avoiding sending those codewords that would have higher PAPR. This type of technology is a linear process and will not cause signal distortion, so it does not have the disadvantages of limiting technology. However, the computational complexity of encoding technology is very high, and encoding and decoding are very cumbersome. More importantly, the information rate of this type of technology decreases rapidly, so it is only applicable to the case where the number of subcarriers is relatively small. Signal scrambling technology, whose core idea is to reduce the probability of large PAPR, also uses linear transformation, but this type of technology is relatively complex and requires multiple IFFT operations and search processes.

发明内容Contents of the invention

本发明的目的在于，针对频率选择性衰落信道下的OFDM系统模型，在传统的虚载波预留算法降低峰值平均功率比(PAPR)的基础上，提出一种低复杂度的降低OFDM系统峰均比的方法，克服目前已有的降低OFDM系统峰均比的方法计算复杂度过高的缺陷。The purpose of the present invention is to propose a low-complexity reduction of OFDM system peak-to-average power ratio (PAPR) based on the traditional virtual carrier reservation algorithm for OFDM system models under frequency-selective fading channels. The ratio method overcomes the defect of high computational complexity of the existing methods for reducing the peak-to-average ratio of OFDM systems.

本发明的技术方案是，一种基于虚载波预留算法降低OFDM系统峰均比的方法，其特征是所述方法包括下列步骤：The technical scheme of the present invention is, a kind of method that reduces peak-to-average ratio of OFDM system based on virtual carrier reservation algorithm, it is characterized in that described method comprises the following steps:

步骤1：对L个设定的特殊频域信号Cⁱ(i＝1，2，...，L)进行IFFT变换，将变换后得到的时域信号cⁱ(i＝1，2，...，L)存入存储器中；其中，L为降低峰值载波的个数，降低峰值载波可选择的幅值取{0，±1}；Step 1: Perform IFFT transformation on L set special frequency domain signals Cⁱ (i=1, 2, ..., L), and transform the time domain signals Cⁱ (i=1, 2, . .., L) is stored in the memory; wherein, L is the number of reducing the peak carrier, and the optional amplitude of reducing the peak carrier is {0, ±1};

步骤2：将承载有用信息的频域信号X进行IFFT运算，得到时域信号，记为x；Step 2: Perform IFFT operation on the frequency-domain signal X carrying useful information to obtain a time-domain signal, denoted as x;

步骤3：计算x的PAPR值，记为PAPR_min；初始化i＝1，设定全零的时域信号c_final，用于存储最终要发送的特殊时域信号cⁱ；Step 3: Calculate the PAPR value of x, denoted as PAPR_min ; initialize i=1, set an all-zero time-domain signal c_final for storing the final special time-domain signal cⁱ to be sent;

步骤4：计算x+c_final+cⁱ和x+c_final-cⁱ两个序列的PAPR值，并和PAPR_min比较，将最小的PAPR值存入PAPR_min，并且令此时满足最小PAPR值的特殊时域信号为c_temp，并更新c_final＝c_final+c_temp；Step 4: Calculate the PAPR values of the two sequences x+c_final +^ci and x+c_final^-ci , and compare them with PAPR_min , store the minimum PAPR value into PAPR_min , and make the minimum PAPR value at this time The special time domain signal of is c_temp , and update c_final =c_final +c_temp ;

步骤5：令i＝i+1，重复上述步骤4，直至i＝L；Step 5: let i=i+1, repeat the above step 4 until i=L;

步骤6：将时域信号x和c_final相加得到最终的待发送的x_final，此时的PAPR_min就是最终的峰均比。Step 6: Add the time-domain signal x and c_final to obtain the final x_final to be sent, and the PAPR_min at this time is the final peak-to-average ratio.

所述特殊频域信号Cⁱ(i＝1，2，...，L)为第i个降低峰值载波位置处值为1，其余载波位置处值为0的序列。The special frequency domain signal Cⁱ (i=1, 2, . . . , L) is a sequence in which the i-th reduced peak carrier position has a value of 1 and the rest of the carrier positions have a value of 0.

本发明的效果是，在虚载波预留算法的基础上，降低OFDM系统峰均比，有效地降低了计算复杂度，实现了系统的适用性和系统复杂度之间的均衡，保证了OFDM系统的实际应用需求，同时无需另外发送边带信息，且不改变原序列的顺序和相位关系，因而在接收端不需要做任何多余的处理，不会对误码率产生影响，从而进一步提高了系统的可靠性和可用性。The effect of the present invention is that on the basis of the virtual carrier reservation algorithm, the peak-to-average ratio of the OFDM system is reduced, the computational complexity is effectively reduced, the balance between the applicability of the system and the complexity of the system is realized, and the OFDM system is guaranteed practical application requirements, without additional sending of sideband information, and does not change the order and phase relationship of the original sequence, so there is no need to do any redundant processing at the receiving end, and will not affect the bit error rate, thereby further improving the system reliability and availability.

附图说明Description of drawings

图1是适用本发明的OFDM系统收发框图。Fig. 1 is a block diagram of the transceiver of the OFDM system applicable to the present invention.

图2是虚载波预留算法的原理图。FIG. 2 is a schematic diagram of a virtual carrier reservation algorithm.

图3是本发明基于虚载波预留算法降低OFDM系统峰均比的方法流程图。Fig. 3 is a flowchart of a method for reducing the peak-to-average ratio of an OFDM system based on a virtual carrier reservation algorithm in the present invention.

图4是本发明基于虚载波预留算法降低OFDM系统峰均比的方法的CCDF曲线仿真图。Fig. 4 is a CCDF curve simulation diagram of the method for reducing the peak-to-average ratio of the OFDM system based on the virtual carrier reservation algorithm of the present invention.

具体实施方式Detailed ways

下面结合附图，对优选实施例作详细说明。应该强调的是，下述说明仅仅是示例性的，而不是为了限制本发明的范围及其应用。The preferred embodiments will be described in detail below in conjunction with the accompanying drawings. It should be emphasized that the following description is only exemplary and not intended to limit the scope of the invention and its application.

图1是适用本发明的OFDM系统收发框图。图1中，在发送端进行数据的成帧过程，由前导信息和数据信息构成，然后进行QAM的调制、IFFT变换、插入循环前缀后，进行并串变换，通过对生成的OFDM时域数据流信号转换为中频信号，发送出去。在接收端，首先就是要进行同步和信道估计的工作，进行FFT变换后根据估计的参数，解调出QAM符号，估计出误码率。Fig. 1 is a block diagram of the transceiver of the OFDM system applicable to the present invention. In Figure 1, the data framing process is performed at the sending end, which is composed of preamble information and data information, and then QAM modulation, IFFT transformation, and cyclic prefix insertion are performed, and parallel-serial transformation is performed, and the generated OFDM time-domain data flow is The signal is converted into an intermediate frequency signal and sent out. At the receiving end, the first step is to perform synchronization and channel estimation. After FFT transformation, the QAM symbols are demodulated and the bit error rate is estimated according to the estimated parameters.

图2是虚载波预留算法的原理图。图2中，利用虚载波预留算法降低PAPR的基本思想是：用一种具有特殊结构的频域信号和承载有用信息的频域信号进行叠加，使得前者经过IFFT运算后所得到的时域信号可以有效地降低后者所对应的时域信号的峰值，从而达到降低系统PAPR的目的。FIG. 2 is a schematic diagram of a virtual carrier reservation algorithm. In Figure 2, the basic idea of using the virtual carrier reservation algorithm to reduce PAPR is to superimpose a frequency-domain signal with a special structure and a frequency-domain signal carrying useful information, so that the time-domain signal obtained by the former after IFFT operation The peak value of the time-domain signal corresponding to the latter can be effectively reduced, thereby achieving the purpose of reducing the system PAPR.

定义特殊频域信号C中非零值的子载波为降低峰值载波，降低峰值载波的个数记为L。理论上，该L个降低峰值载波的幅度和相位可取任意值，但这样取值的集合规模较大，系统的计算量非常大。所以为了减少计算量，通常降低峰值载波只取特定范围，拿QAM来说，一般只取{0，±1，±i}。The subcarriers with non-zero values in the special frequency domain signal C are defined as reduced peak carriers, and the number of reduced peak carriers is denoted as L. Theoretically, the amplitudes and phases of the L peak-reduced carriers can take any value, but the scale of such a set of values is relatively large, and the calculation amount of the system is very large. Therefore, in order to reduce the amount of calculation, the peak carrier is usually reduced and only a specific range is taken. Taking QAM as an example, generally only {0, ±1, ±i} is taken.

定义R^N＝{0，1，2，...，N-1}为OFDM系统中所有N个子载波的位置序列。定义R^c＝{i₀，i₁，...，i_L-1}为OFDM系统中降低峰值载波在所有N个子载波中所处的位置序列，且0≤i₀<i₁<...<i_L-1<N。则定义R为R^N中去掉R^c后的集合，即R^c的补集：R＝R^N-R^c。频域信号X和C满足原始频域信号X取值为非零的子载波位置上，频域信号C取值为零；在原始频域信号X取值为零的子载波位置上，频域信号C取值为非零。即：Define R^N ={0, 1, 2, . . . , N-1} as the position sequence of all N subcarriers in the OFDM system. Define R^c ={i₀ , i₁ ,...,i_L-1 } as the position sequence of the reduced peak carrier in all N subcarriers in the OFDM system, and 0≤i₀ <i₁ <.. .<i_L-1 <N. Then define R as the set after removing R^c in R^N , that is, the complement of R^c : R=R^N −R^c . The frequency domain signals X and C satisfy the subcarrier position where the value of the original frequency domain signal X is non-zero, and the value of the frequency domain signal C is zero; at the subcarrier position where the value of the original frequency domain signal X is zero, the frequency domain Signal C has a value other than zero. Right now:

$\begin{array}{cc}{\mathrm{<span><span>X</span>x</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>=</span>=</span>\left\{\begin{array}{cc}{\mathrm{<span><span>X</span>x</span>}}_{\mathrm{<span><span>k</span>k</span>}}& \mathrm{<span><span>k</span>k</span>}<span><span>\&Element;</span>\&Element;</span>\mathrm{<span><span>R</span>R</span>}\\ \mathrm{<span><span>0</span>0</span>}& \mathrm{<span><span>k</span>k</span>}<span><span>\&Element;</span>\&Element;</span>{\mathrm{<span><span>R</span>R</span>}}^{\mathrm{<span><span>c</span>c</span>}}\end{array}\right.& {\mathrm{<span><span>C</span>C</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>=</span>=</span>\left\{\begin{array}{cc}\mathrm{<span><span>0</span>0</span>}& \mathrm{<span><span>k</span>k</span>}<span><span>\&Element;</span>\&Element;</span>\mathrm{<span><span>R</span>R</span>}\\ {\mathrm{<span><span>C</span>C</span>}}_{\mathrm{<span><span>k</span>k</span>}}& \mathrm{<span><span>k</span>k</span>}<span><span>\&Element;</span>\&Element;</span>{\mathrm{<span><span>R</span>R</span>}}^{\mathrm{<span><span>c</span>c</span>}}\end{array}\right.\end{array}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>)</span>)</span>$

定义采用虚载波预留算法的OFDM系统中的虚载波预留比(ToneReservation Ratio，TRR)为降低峰值载波数L与载波数N的比值，即TRR＝L/N。The virtual carrier reservation ratio (ToneReservation Ratio, TRR) in the OFDM system using the virtual carrier reservation algorithm is defined as the ratio of the number of peak carriers L to the number of carriers N, that is, TRR=L/N.

将具有特殊结构的频域信号C叠加到有用频域信号X上，用于降低OFDM系统的PAPR，叠加后所产生的时域信号x_T可以表示为：The frequency domain signal C with a special structure is superimposed on the useful frequency domain signal X to reduce the PAPR of the OFDM system. The time domain signal x_T generated after superposition can be expressed as:

x_T＝Q(X+C)＝Q(X)+Q(C)＝x+c                (2)x_T ＝Q(X+C)＝Q(X)+Q(C)＝x+c (2)

其中Q为离散傅立叶变换IFFT的数学描述。x、c分别表示频域信号X、C经过离散傅立叶变换IFFT所得到的时域信号。Q矩阵描述如下：Where Q is the mathematical description of the discrete Fourier transform IFFT. x and c respectively represent the time domain signals obtained by the frequency domain signals X and C through the discrete Fourier transform IFFT. The Q matrix is described as follows:

这样基于虚载波预留算法的OFDM系统的峰均比定义可以改为：In this way, the peak-to-average ratio definition of the OFDM system based on the virtual carrier reservation algorithm can be changed to:

$\mathrm{<span><span>PAPR</span>PAPR</span>}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>T</span>T</span>}}<span><span>)</span>)</span><span><span>=</span>=</span>\frac{\underset{\mathrm{<span><span>n</span>no</span>}}{\mathrm{<span><span>max</span>max</span>}}<span><span>\{</span>\{</span>{<span><span>|</span>|</span>\mathrm{<span><span>x</span>x</span>}<span><span>+</span>+</span>\mathrm{<span><span>c</span>c</span>}<span><span>|</span>|</span>}^{\mathrm{<span><span>2</span>2</span>}}<span><span>\}</span>\}</span>}{\mathrm{<span><span>E</span>E.</span>}<span><span>\{</span>\{</span>{<span><span>|</span>|</span>\mathrm{<span><span>x</span>x</span>}<span><span>+</span>+</span>\mathrm{<span><span>c</span>c</span>}<span><span>|</span>|</span>}^{\mathrm{<span><span>2</span>2</span>}}<span><span>\}</span>\}</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>4</span>4</span>}<span><span>)</span>)</span>$

而由于在采用虚载波预留算法的OFDM系统中，虚载波预留比(TRR)一般较小，所以E{|x+c|²}≈E{|x|²}，则上式可以简化为：In the OFDM system using the virtual carrier reservation algorithm, the virtual carrier reservation ratio (TRR) is generally small, so E{|x+c|² }≈E{|x|² }, then the above formula can be simplified for:

$\mathrm{<span><span>PAPR</span>PAPR</span>}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>T</span>T</span>}}<span><span>)</span>)</span><span><span>=</span>=</span>\frac{\underset{\mathrm{<span><span>n</span>no</span>}}{\mathrm{<span><span>max</span>max</span>}}<span><span>\{</span>\{</span>{<span><span>|</span>|</span>\mathrm{<span><span>x</span>x</span>}<span><span>+</span>+</span>\mathrm{<span><span>c</span>c</span>}<span><span>|</span>|</span>}^{\mathrm{<span><span>2</span>2</span>}}<span><span>\}</span>\}</span>}{\mathrm{<span><span>E</span>E.</span>}<span><span>\{</span>\{</span>{<span><span>|</span>|</span>\mathrm{<span><span>x</span>x</span>}<span><span>|</span>|</span>}^{\mathrm{<span><span>2</span>2</span>}}<span><span>\}</span>\}</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>5</span>5</span>}<span><span>)</span>)</span>$

所以可以通过选取信号C使得时域信号x_T的峰值最小，从而降低PAPR。可见该算法的核心是如何寻找可以有效降低OFDM系统中PAPR的频域信号C。从接收端来看，所接收的信号序列进行FFT运算后得到数据序列如下：Therefore, the PAPR can be reduced by selecting the signal C to minimize the peak value of the time domain signal x_T. It can be seen that the core of the algorithm is how to find the frequency domain signal C that can effectively reduce the PAPR in the OFDM system. From the perspective of the receiving end, the received signal sequence is subjected to FFT operation to obtain the data sequence as follows:

${\mathrm{<span><span>H</span>h</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>X</span>x</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>+</span>+</span>{\mathrm{<span><span>C</span>C</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>)</span>)</span><span><span>+</span>+</span>{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>=</span>=</span>\left\{\begin{array}{cc}{\mathrm{<span><span>H</span>h</span>}}_{\mathrm{<span><span>k</span>k</span>}}{\mathrm{<span><span>X</span>x</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>+</span>+</span>{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}}& \mathrm{<span><span>k</span>k</span>}<span><span>\&Element;</span>\&Element;</span>\mathrm{<span><span>R</span>R</span>}\\ {\mathrm{<span><span>H</span>h</span>}}_{\mathrm{<span><span>k</span>k</span>}}{\mathrm{<span><span>C</span>C</span>}}_{\mathrm{<span><span>k</span>k</span>}}<span><span>+</span>+</span>{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>k</span>k</span>}}& \mathrm{<span><span>k</span>k</span>}<span><span>\&Element;</span>\&Element;</span>{\mathrm{<span><span>R</span>R</span>}}^{\mathrm{<span><span>c</span>c</span>}}\end{array}\right.<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>6</span>6</span>}<span><span>)</span>)</span>$

鉴于传统的虚载波预留算法复杂度比较大，在此提出一种低复杂度的虚载波预留算法，着眼点在于降低系统的复杂度。在OFDM系统中，子载波数目N是已知的且一般不会变的，数据信息和导频信息所占的载波位置也基本是固定的。据此可以对传统的算法提出改进，本发明把降低峰值载波的幅度相位选择范围确定为{0，±1}，即K＝3。In view of the relatively high complexity of the traditional virtual carrier reservation algorithm, a low-complexity virtual carrier reservation algorithm is proposed here, with the focus on reducing the complexity of the system. In an OFDM system, the number N of subcarriers is known and generally does not change, and the carrier positions occupied by data information and pilot information are basically fixed. Based on this, the traditional algorithm can be improved. The present invention determines the amplitude and phase selection range for reducing the peak carrier as {0, ±1}, that is, K=3.

由傅立叶反变换的线性特性可知，可以先分别将X、C进行IFFT后再相加，效果等同于相加后再进行IFFT。改进算法的基本思想是：固定频域信号Cⁱ，i＝1，2，...，L，其中Cⁱ为第i个降低峰值载波位置处值为1，其余载波为0情况下扩展成的N点序列(本文中相位选择范围为{0，±1})，然后存储各固定频域信号Cⁱ，i＝1，2，...，L经过IFFT运算后所对应的时域信号cⁱ，i＝1，2，...，L，同时将所要传输的有用信号按要求扩展成为频域信号X，并对其进行IFFT运算，将得到时域信号记为x，再将时域信号x和固定时域信号cⁱ的组合进行迭代相加，从中得到PAPR最小的时域信号组合进行发送。From the linear characteristics of the inverse Fourier transform, it can be known that X and C can be IFFTed first and then added, the effect is equivalent to adding and then IFFT. The basic idea of the improved algorithm is: fixed frequency domain signal Cⁱ , i=1, 2, ..., L, where Cⁱ is 1 at the position of the i-th reduced peak carrier, and expands to N point sequence (in this paper, the phase selection range is {0, ±1}), and then store the corresponding time domain signals of each fixed frequency domain signal Cⁱ , i=1, 2, ..., L after IFFT operation cⁱ , i=1, 2,..., L, at the same time, expand the useful signal to be transmitted into frequency domain signal X as required, and perform IFFT operation on it, and denote the obtained time domain signal as x, and then time The combination of the domain signal x and the fixed time domain signal^ci is added iteratively, and the time domain signal combination with the minimum PAPR is obtained and sent.

图3是本发明基于虚载波预留算法降低OFDM系统峰均比的方法流程图。图3中，步骤301：先将L个特殊频域信号Cⁱ(i＝1，2，...，L)经过IFFT变换后的时域信号cⁱ(i＝1，2，...，L)存入存储器中。其中，降低峰值载波可选择的幅值取{0，±1}，L为降低峰值载波的个数。Fig. 3 is a flowchart of a method for reducing the peak-to-average ratio of an OFDM system based on a virtual carrier reservation algorithm in the present invention. In Fig. 3, step 301: Firstly, L special frequency domain signals Cⁱ (i=1, 2, ..., L) are transformed by IFFT to time domain signals cⁱ (i = 1, 2, ... , L) stored in memory. Wherein, the selectable amplitude for reducing the peak carrier is {0, ±1}, and L is the number of reduced peak carriers.

步骤302：将承载有用信息的频域信号X进行IFFT运算，得到的时域信号记为x。Step 302: Perform an IFFT operation on the frequency-domain signal X carrying useful information, and denote the obtained time-domain signal as x.

当确定特殊频域信号C的位置信息R^c后，就可以先确定L种固定的特殊频域信号Cⁱ，然后根据IFFT变换的线性特性IFFT(X+C)＝IFFT(X)+IFFT(C)得到特殊频域信号和有用频域信号经IFFT变换后各自的时域信号。After the location information R^c of the special frequency domain signal C is determined, L kinds of fixed special frequency domain signals Cⁱ can be determined first, and then according to the linear characteristic of IFFT transformation IFFT(X+C)=IFFT(X)+IFFT( C) Obtain respective time-domain signals of the special frequency-domain signal and the useful frequency-domain signal after IFFT transformation.

步骤303：计算x的PAPR值，记为PAPR_min；初始化i＝1，设定全零的时域信号c_final，用于存储最终要发送的特殊时域信号cⁱ。Step 303: Calculate the PAPR value of x, which is denoted as PAPR_min ; initialize i=1, and set an all-zero time-domain signal c_final for storing the final special time-domain signal cⁱ to be sent.

步骤304：计算x+c_final+cⁱ和x+c_final-cⁱ两个序列的PAPR值，并和PAPR_min比较，将最小的PAPR值存入PAPR_min，并且令此时满足最小PAPR值的特殊时域信号为c_temp，并更新c_final＝c_final+c_temp。Step 304: Calculate the PAPR values of the two sequences x+c_final +^ci and x+c_final^-ci , and compare them with PAPR_min , store the minimum PAPR value into PAPR_min , and make the minimum PAPR value satisfied at this time The special time domain signal of is c_temp , and update c_final =c_final +c_temp .

步骤305：令i＝i+1，重复上述步骤4，直至i＝L。Step 305: Let i=i+1, repeat the above step 4 until i=L.

在传统的采用虚载波预留算法的OFDM系统中，特殊结构的频域信号C是按照遍历搜索方式来选取的。基本思想为：在N个子载波中，有L个降低峰值载波，每个降低峰值载波的幅度相位有K(包括零)种可能的取值，通过搜索L个降低峰值载波的所有幅度相位的K^L种组合，最后从中选择一种最优组合，使得PAPR最小。In the traditional OFDM system using the virtual carrier reservation algorithm, the frequency domain signal C with a special structure is selected according to the traversal search method. The basic idea is: among the N subcarriers, there are L reduced peak carriers, and the amplitude phase of each reduced peak carrier has K (including zero) possible values, by searching the K of all amplitude phases of the L reduced peak carriers^L kinds of combinations, and finally choose an optimal combination to minimize PAPR.

在长为N-L的原有用频域信号数据X后直接补L个用于降低PAPR的控制数据，从而形成能够产生低PAPR的叠加信号X+C。对于原有用频域信号X而言，先将其与各个具有特殊结构的备选频域信号Cⁱ相加得到组合数据X+Cⁱ，该组合数据经过IFFT运算后得到时域信号xⁱ_T，最后再从这K^L种组合中选取PAPR最小的组合xⁱ_T，并将其作为最后的OFDM符号进行传输。可见，这种传统的子载波预留算法共需要进行K^L次IFFT运算，且随着子载波数N的增加，或者降低峰值载波数L的增加所需要进行的IFFT运算的次数也会明显增加，因此传统的子载波预留算法复杂度比较大。L pieces of control data for reducing PAPR are directly supplemented after the original frequency-domain signal data X of length NL, so as to form a superposition signal X+C capable of generating low PAPR. For the original frequency domain signal X, it is first added to each alternative frequency domain signal Cⁱ with a special structure to obtain the combined data X+Cⁱ , and the combined data is subjected to IFFT operation to obtain the time domain signal xⁱ_T , and finally select the combination xⁱ_T with the smallest PAPR from these K^L combinations, and transmit it as the last OFDM symbol. It can be seen that this traditional subcarrier reservation algorithm requires a total of K^L times of IFFT operations, and as the number of subcarriers N increases, or the number of IFFT operations required to reduce the peak carrier number L increases, the number of IFFT operations will also increase significantly. , so the complexity of the traditional subcarrier reservation algorithm is relatively large.

本发明就是利用特殊频域信号的可确定性来存储其对应的时域信号以降低系统的复杂性。在采用本发明的方法降低峰均比的OFDM系统，对每个频域信号X而言，只需要做一次对频域信号X的IFFT运算，而不需要对所有K^L种组合都进行IFFT运算，从而极大地减少了IFFT的运算次数，它仅需要额外的使用一个存储器来存储已经计算好的时域信号cⁱ，i＝1，2，...，L，降低了系统的复杂度。在求PAPR的过程中，采用迭代求次优解的方法，仅需要K×L次迭代，远小于遍历搜索法的K^L次迭代，进一步降低了系统的复杂度。该算法不需要传输边带信息，不需要逆运算，且不改变原序列的顺序和相位关系，因而在接收端不需要做任何多余的处理，不会对误码率产生很大影响，也是该算法的一个突出特点。The present invention utilizes the determinability of the special frequency domain signal to store its corresponding time domain signal to reduce the complexity of the system. In the OFDM system using the method of the present invention to reduce the peak-to-average ratio, for each frequency-domain signal X, only one IFFT operation on the frequency-domain signal X needs to be performed, and no IFFT operation needs to be performed on all K^L combinations , thereby greatly reducing the number of IFFT operations, it only needs to use an additional memory to store the calculated time domain signal cⁱ , i=1, 2, . . . , L, reducing the complexity of the system. In the process of calculating PAPR, the method of iteratively seeking the suboptimal solution only needs K×L iterations, which is much smaller than the K^L iterations of the traversal search method, which further reduces the complexity of the system. This algorithm does not need to transmit sideband information, does not need inverse operation, and does not change the order and phase relationship of the original sequence, so it does not need to do any redundant processing at the receiving end, and will not have a great impact on the bit error rate. A salient feature of the algorithm.

步骤6：将时域信号x和c_final相加得到最终的待发送的x_final，此时的PAPR_min就是最终的峰均比。Step 6: Add the time-domain signal x and c_final to obtain the final x_final to be sent, and the PAPR_min at this time is the final peak-to-average ratio.

图4是本发明基于虚载波预留算法降低OFDM系统峰均比的方法的CCDF曲线仿真图。图4中，仿真条件为：子载波数N＝512，调制方式QAM，幅度相位范围为{0，±1}，即K＝3，降低峰值载波数L＝16，L＝32和未经过任何处理(原始信号)三种情况下的互补累积概率分布函数(CCDF)曲线。从图4中的CCDF曲线可以看出，经过本发明的基于虚载波预留算法降低OFDM系统峰均比的方法处理的OFDM系统的PAPR特性较未经处理的OFDM系统的PAPR特性有一定的改善，在CCDF为10^-3处，采用降低峰值载波数L＝32的系统的PAPR值为8.2dB，而原始信号的PAPR值为11.2dB，且随着L的增大，改善效果越好，但系统的复杂性也就相应的增加，需要发送更多的功率，需要牺牲一定的频谱利用率，使得频谱利用率降低。可见该改进算法可以有效的降低OFDM系统的PAPR值，该仿真验证了该算法具有改善PAPR的作用，并且无须发送边带信息，复杂度很低。Fig. 4 is a CCDF curve simulation diagram of the method for reducing the peak-to-average ratio of the OFDM system based on the virtual carrier reservation algorithm of the present invention. In Figure 4, the simulation conditions are: the number of subcarriers N=512, the modulation method QAM, the range of amplitude and phase is {0, ±1}, that is, K=3, the number of peak carriers is reduced L=16, L=32 and without any Complementary cumulative probability distribution function (CCDF) curves for the three cases of processing (raw signal). As can be seen from the CCDF curve in Figure 4, the PAPR characteristics of the OFDM system processed by the method of reducing the peak-to-average ratio of the OFDM system based on the virtual carrier reservation algorithm of the present invention are improved to a certain extent compared with the PAPR characteristics of the unprocessed OFDM system , when the CCDF is 10^-3 , the PAPR value of the system with reduced peak carrier number L=32 is 8.2dB, while the PAPR value of the original signal is 11.2dB, and with the increase of L, the improvement effect is better, but The complexity of the system increases accordingly, more power needs to be sent, and a certain spectrum utilization rate needs to be sacrificed, which reduces the spectrum utilization rate. It can be seen that the improved algorithm can effectively reduce the PAPR value of the OFDM system. The simulation verifies that the algorithm can improve the PAPR, and there is no need to send side information, and the complexity is very low.

以上所述，仅为本发明较佳的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应该以权利要求的保护范围为准。The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of changes or modifications within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (2)

1, a kind of method based on virtual carrier preservation algorithm reduction ofdm system peak-to-average force ratio is characterized in that described method comprises the following steps:

Step 1: to L special frequency-region signal C that setsⁱ(i=1,2 ..., L) carry out the IFFT conversion, with the time-domain signal c that obtains after the conversionⁱ(i=1,2 ..., L) deposit in the memory; Wherein, L is for reducing the number of peak value carrier wave, reduce the selectable amplitude of peak value carrier wave get 0, ± 1};

Step 2: the frequency domain signal X that will carry useful information is carried out the IFFT computing, obtains time-domain signal, is designated as x;

Step 3: calculate the PAPR value of x, be designated as PAPR_MinInitialization i=1 sets complete zero time-domain signal c_Final, be used to store the special time-domain signal c that finally will send_i

Step 4: calculate x+c_Final+ cⁱAnd x+c_Final-cⁱThe PAPR value of two sequences, and and PAPR_MinRelatively, the PAPR value with minimum deposits PAPR in_Min, and the special time-domain signal that makes satisfy minimum PAPR value this moment is c_Temp, and upgrade c_Final=c_Final+ c_Temp

Step 5: make i=i+1, repeat above-mentioned steps 4, until i=L;

Step 6: with time-domain signal x and c_FinalAddition obtains final x to be sent_Final, the PAPR of this moment_MinIt is exactly final peak-to-average force ratio.

2, a kind of method based on virtual carrier preservation algorithm reduction ofdm system peak-to-average force ratio according to claim 1 is characterized in that described special frequency-region signal Cⁱ(i=1,2 ..., be that i reduction peak value carrier position place value is 1 L), all the other carrier position place values are 0 sequence.

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