CN101778064B - Transmitter and method for handling peak-to-average power - Google Patents

Abstract

The invention discloses a transmitter for processing a power peak-to-average value and a method thereof, which can be applied to a communication system based on orthogonal frequency division multiplexing or other multi-carriers. The transmitter uses N subcarriers, where L subcarriers are reserved for signal power peak-to-average reduction (L is less than N). The method comprises the following steps: the original frequency domain data symbols are sent to the reserved sub-carrier symbol generator after being generated. And these subcarriers can be generated by signal processing in a pure frequency domain. The combination of these generated reserved sub-carrier symbols and the original data symbols results in a transmission signal with reduced power peak-to-average value. The reduced power peak-to-average transmitted signal may be repeatedly sent to the reserved sub-carrier symbol generator to generate updated reserved sub-carrier symbols. After several times of repeated processing, the original data symbols and the reserved sub-carrier symbols are combined to obtain the transmission signal with the lowest power peak-to-average value.

Description

Transmitter and method for handling peak-to-average power

technical field

The present invention relates to a transmitter and its method for obtaining peak-to-average power, and in particular to a transmitter and its method for processing peak-to-average power in the frequency domain.

Background technique

In an Orthogonal frequency division multiplexing (OFDM) communication system, excessive signal power peak-to-average power ratio (PAPR) will reduce the quality of the transmitted signal or affect the transmitter transmission power efficiency. The reason is that the transmitter usually has a non-linear radio frequency (RF) front-end circuit, such as a power amplifier. FIG. 1 is a graph showing the relationship between input power Pin and output power Pout of a power amplifier. When the power peak value of the input power Pin reaches the nonlinear region NL, the output signal of the power amplifier will be distorted and the quality of the transmitted signal will be reduced. If the input power Pin is reduced so that it falls in the linear region of the power amplifier, the efficiency of transmitting power will be reduced.

In a multi-carrier (Multi-carrier) transmission system, such as the Orthogonal Frequency-Division Multiple Access (OFDMA) mode of the IEEE 802.16e standard, the base station (Base-station, BS) can reserve some Carrier (sub-carrier), and use these sub-carriers to reduce the above phenomenon that the PAPR is too large. Please refer to FIG. 2 , which is a schematic diagram of a traditional method for reducing PAPR. x(t) is the original signal to be transmitted in the time-domain. It can be seen from FIG. 2 that the original signal x(t) to be transmitted has two peaks exceeding the threshold TH. In the traditional method, the peak reduction signal P(t) is generated through the reserved subcarriers, and P(t) is cyclically shifted on the time axis to the time points ni and nj respectively to generate Signals P _ni (t) and P _nj (t). Multiply P _ni (t) and P _nj (t) by the phase parameter and amplitude parameter respectively, that is, β _i and μ _i and β _j and μ _j , and then add them to the signal x(t) to obtain the peak power The reduced corrected signal x'(t) to be transmitted.

However, in the traditional method, at least two Inverse FastFourier transform (IFFT) circuits are required to generate the signals x(t) and P(t) respectively. Moreover, in order to maintain the expected low-power peak-to-average effect of the signal x'(t) to be transmitted, the traditional method usually needs to over-sample the signal by more than four times, and then perform the above-mentioned PAPR reduction. deal with.

Contents of the invention

In view of this, an example of the present invention is to provide a transmitter and its method, which can be achieved without multiple inverse Fourier transforms and without over-sampling by performing processing in the frequency domain.

According to another example of the present invention, it is applied in a transmitter of an OFDM communication system. The transmitter uses N subcarriers, and L subcarriers in the N subcarriers are reserved subcarriers, and L is smaller than N. The method includes the following steps: receiving a data signal, the packet power of the data signal can be decomposed into a fixed power and a disturbance power. L reserved subcarrier symbols located on L subcarriers of the reserved subcarriers are generated. The L reserved subcarrier symbols are updated according to the data signal, and a signal to be combined is generated accordingly. Combining the signal to be combined with the data signal in the frequency domain.

According to another aspect of the present invention, a transmitter is provided, which is applied in an OFDM communication system. The transmitter uses N subcarriers, and L subcarriers in the N subcarriers are reserved subcarriers, and L is smaller than N. The transmitter includes a modulating unit, a reserved subcarrier symbol generating unit and a combining unit. The modulation unit is used to output a data signal, and the packet power of the data signal has a fixed power and a disturbance power. The reserved subcarrier symbol generation unit is used to generate L reserved subcarrier symbols located at L reserved subcarrier positions, update the L reserved subcarrier symbols according to the data signal, and generate a signal to be combined accordingly. The combining unit is used for combining the signal to be combined with the data signal in the frequency domain.

In order to make the above-mentioned content of the present invention more comprehensible, a plurality of embodiments are specifically cited below, together with the accompanying drawings, and are described in detail as follows.

Description of drawings

FIG. 1 is a graph showing the relationship between input power Pin and output power Pout of a power amplifier.

FIG. 2 is a schematic diagram of a conventional method for reducing PAPR.

FIG. 3 is a block diagram of a transmitter for reducing peak-to-average power of data signals according to an embodiment of the present invention.

FIG. 4 shows an example of ||ρ|| ² when the number of reserved subcarriers is assumed to be 3 and the reserved subcarrier symbols are X _a , X _b , and X _c .

FIG. 5 is a graph showing a simulation result of the embodiment of FIG. 3 .

FIG. 6 is a block diagram of a transmitter for reducing peak-to-average power of data signals according to another embodiment of the present invention.

FIG. 7 is a graph showing a simulation result of the embodiment of FIG. 6 .

FIG. 8 is a block diagram of a transmitter according to yet another embodiment of the present invention.

[Description of main component symbols]

300, 600, 800: Teleporter

302, 602: modulation unit

304, 604, 804: reserved subcarrier symbol generation unit

306, 606, 806: merge units

308, 608, 808: conversion unit

310, 610: reserved subcarrier index value generator

312: switch

502, 504, 506, 508, 702, 704, 706: curve

612, 614: Switcher

816: filter

818: First multiplier

820: second multiplier

Detailed ways

The present invention proposes a method for obtaining peak-to-average power, which is applied to a transmitter of a multicarrier (Multicarrier) transmission system. The transmitter uses N subcarriers, and L subcarriers in the N subcarriers are reserved subcarriers, and L is smaller than N. The method includes the following steps. A data signal is received, and the packet power of the data signal has a fixed power and a disturbance power. L subcarrier symbols located on the reserved subcarriers are generated. The L subcarrier symbols are updated according to the data signal, and a signal to be combined is generated accordingly. The signal to be combined is combined with the data signal in the frequency domain, so that the disturbance power corresponding to the updated data signal becomes smaller, thereby reducing the peak-to-average power of the transmission signal. An embodiment is given below to further describe in detail as follows.

Please refer to FIG. 3 , which is a block diagram of a transmitter for reducing peak-to-average power of a data signal according to an embodiment of the present invention. The aforementioned multi-carrier transmission system is, for example, an OFDM communication system. The transmitter 300 includes a modulation unit 302 , a reserved subcarrier symbol generation unit 304 , and a combining unit 306 . The modulation unit 302 is used to output a data signal Data, and the power of the data signal Data has a fixed power and a disturbance power. The reserved subcarrier symbol generating unit 304 is used to generate L reserved subcarrier symbols located in the reserved subcarrier, update the L reserved subcarrier symbols according to the data signal Data, and generate a signal Cmb to be combined accordingly. The combining unit 306 is used for combining the signal Cmb to be combined and the data signal Data in the frequency domain, so that the disturbance power corresponding to the adjusted data signal Data' becomes smaller, thereby reducing the peak-to-average power of the transmission signal.

Further, assuming that the subcarrier index values of the N subcarriers used by the transmitter 300 are 0 to N-1, the set of L subcarrier index values of the reserved subcarriers in the N subcarriers is U, U={k ₀ , k ₁ , . . . k _L-1 }. The data signal Data has N data symbols X ₀ , X ₁ , . . . , X _N-1 located on N subcarriers. _Define a ^data vector X= _[ X ₀ , X ₁ , . In order to prevent the transmission signal from being interfered by the reserved subcarrier symbols, we assume that before the data is combined with the reserved subcarrier symbols, when i∈U, _Xi = 0, but the method of the present invention reduces the peak-to-average power of the data signal are not limited by this assumption.

并定义保留子载波符元向量为 $X_R={[X_{k_0},X_{k_1},...X_{k_{L-1}}]}^T.$ 假设上述的待合并信号Cmb具有N个合并符元C₀，C₁，...，C_N-1，定义合并向量C＝[C₀，C₁，...，C_N-1]^T，C_i为第i个合并符元。同样地，当 $i\∉U$ 或i∈U^C时，C_i＝0，然而本发明的降低数据信号的功率峰均值的方法不受限于此假设。In addition, the above L reserved subcarrier symbols are defined as

And define the reserved subcarrier symbol vector as $x_R={[x_{k_0},{\mathrm{<figure-callout\; id="1"\; label="x\; k"\; filenames="H2009100022300E00011.png,H2009100022300E00061.png"\; state="\{\{state\}\}">x</figure-callout>}}_{k_{}},...x_{k_{L-1}}]}^T.$ Assuming that the above-mentioned signal to be combined Cmb has N combining symbols C ₀ , C ₁ , ..., C _N-1 , define a combining vector C=[C ₀ , C ₁ , ..., C _N-1 ] ^T , C _i is the ith combined symbol. Similarly, when $i\&NotElement;u$ Or when ^i∈UC , C _i =0, however, the method for reducing the peak-to-average power of the data signal of the present invention is not limited to this assumption.

This embodiment can be illustrated by the following formula (1):

find out make $\hat{C}=\arg \underset{C}{\min }{\left|\right|x+c\left|\right|}_{\&infin;}=\arg \underset{C}{\min }{\left|\right|f(x+C)\left|\right|}_{\&infin;}---\left(1\right)$

Wherein, x and c respectively represent the data signal Data in the time domain and the signal Cmb to be combined. F represents the N×N IFFT matrix, where:

${\left\{f\right\}}_{\mathrm{no},k}={\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H2009100022300E00061.png"\; state="\{\{state\}\}">e</figure-callout>}}^j$ for n, k=0, 1, . . . , N-1.

Equation (1) means that after adding all possible c and x respectively, find out the value of c when the maximum of all absolute values (norm) of all elements of the vector x+c is the minimum among all c. Such c can minimize the peak power of x+c, and reduce the peak power of the data signal Data', so as to reduce the value of PAPR. The requirement to find c that meets this condition can be achieved by finding the corresponding C.

A method for obtaining the above-mentioned C will be described below.

The time domain signal x(t) of OFDM data signal Data is defined as:

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="k\; e\; j"\; filenames="H2009100022300E00061.png"\; state="\{\{state\}\}">k</figure-callout></span><figure-callout\; id="2"\; label="k\; e\; j"\; filenames="H2009100022300E00061.png"\; state="\{\{state\}\}">\; </figure-callout>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{}{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; t</span>}}^{}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Wherein, 0≤t≤T and T represents symbol duration. The envelope power of the signal x(t) is defined as:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; |</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="k\; e\; j"\; filenames="H2009100022300E00061.png"\; state="\{\{state\}\}">k</figure-callout></span><figure-callout\; id="2"\; label="k\; e\; j"\; filenames="H2009100022300E00061.png"\; state="\{\{state\}\}">\; </figure-callout>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{}{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; t</span>}}^{}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; \{</span>\underset{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="H2009100022300E00061.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; u</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, define

$\mathrm{\&rho;}\left(u\right)=\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{x}_k{x}_{k+u}^{*}$ for 1≤u≤N-1

ρ(μ) is called the aperiodic autocorrelation function (Aperiodic Auto-correlationFunction, AACF) of {X _k } ₀ ^N-1 .

为固定功率，

为扰动(fluctuation)功率。由于为固定功率，不会随着时间t而改变，所以P_x(t)的大小将会由会随着时间t而改变的

的大小所决定。因此，如果要最小化P_x(t)，可通过最小化扰动功率

的值来达成。一般而言，要将会随时间变化的扰动功率最小化并不容易，因此我们转而希望AACF的p-绝对值(也即是p次方的绝对值)的和

能越小越好。其中，p＞0或为正整数。Hereby define formula (3)

is a fixed power,

is the disturbance power. because As a fixed power, it will not change with time t, so the size of P _x (t) will be changed with time t by

determined by the size. Therefore, if P _x (t) is to be minimized, the perturbation power can be minimized by

value to achieve. In general, it is not easy to minimize the time-varying perturbation power, so we instead want the sum of the p-absolute values (that is, the absolute values to the pth power) of the AACF

The smaller the better. Wherein, p>0 or a positive integer.

可以最小化的话，那么我们就可预期扰动功率会因此而降低。以下将以p值等于2为例说明的，然而本实施例并不限于此。其中，本实施例是通过改变{X_k}₀ ^N-1中，对应至被保留子载波的保留子载波符元来使

最小化。本实施例是以陡降法(steepest descent)来改变保留子载波符元

的值，以使最小化。As long as a set of {X _k } ₀ ^N-1 can be obtained, such that

can be minimized, then we can expect the perturbation power to be reduced as a result. In the following, the p value equal to 2 will be described as an example, but this embodiment is not limited thereto. Among them, in this embodiment, by changing {X _k } ₀ ^N-1 , the reserved subcarrier symbols corresponding to the reserved subcarriers to make

minimize. In this embodiment, the reserved subcarrier symbols are changed by steepest descent

value so that minimize.

Hereby describe in detail as follows. By calculation, we can get

${<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; *</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

After partial differentiation of equation (4), we can get

$\frac{<span\; class="notranslate">\; \&PartialD;</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{<span\; class="notranslate">\; *</span>}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}}{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Where i=0, 1, . . . , L−1 and _u +1≦ki≦Nu−1.

)。因此，可以得到AACF向量的偏微分为Next, define the AACF vector as ρ=[ρ(1), ρ(2), . . . , ρ(N-1)] ^T . The square of the absolute value of the vector defining ρ (ie ||ρ|| ² ) is equal to |ρ(1)| ² +|ρ(2)| ² +...+|ρ(N-1)| ² (also Right now

). Therefore, the partial differential of the AACF vector can be obtained as

$\frac{<span\; class="notranslate">\; \&PartialD;</span>}{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{<span\; class="notranslate">\; *</span>}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>}{<span\; class="notranslate">\; \&PartialD;</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{<span\; class="notranslate">\; *</span>}}\underset{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}\underset{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}}{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

举例来说，可通过下式更新：In addition, the reserved subcarrier symbol vector is defined as $x_R=[x_{k_0},{\mathrm{<figure-callout\; id="1"\; label="x\; k"\; filenames="H2009100022300E00011.png,H2009100022300E00061.png"\; state="\{\{state\}\}">x</figure-callout>}}_{k_{}},...,x_{k_{L-1}}{]}^T.$ The above-mentioned steep drop method for changing X _R is to update the L reserved sub-carrier symbols according to the gradient (gradient) of the reserved sub-carrier symbol vector X _R according to the square of the vector absolute value of the AACF vector (||ρ|| ² ) Yuan

For example, it can be updated by:

This embodiment minimizes ||ρ|| ² by iteratively calculating X _R . n represents the number of updates. X _R ⁽ⁿ⁺¹⁾ represents X _R after the n+1th update, and X _R ⁽ⁿ⁾ represents X _R before the n+1th update. When n=0, it represents the unupdated X _R ⁽⁰⁾ , for example, it can be equal to the original X _R , but X _R ⁽⁰⁾ can also be other values. μ is the step unit (step size).

Afterwards, the reserved subcarrier symbol generating unit generates the combined signal Cmb according to X _R ⁽ⁿ⁺¹⁾ . Among the N combined symbols C ₀ , C ₁ , ..., C _N-1 of the combined signal Cmb, for the symbol C _i , when i∈U, $C_i=x_i^{(\mathrm{no}+1)}.$ Then, the combining unit 306 combines the signal Cmb to be combined into the data signal Data in the frequency domain to generate the adjusted data signal Data′. The data signal Data' can be represented by Y ₀ , Y ₁ , . . . , Y _N-1 . For symbol Y _i , when i∈U, Y _i =C _i . when $i\&NotElement;u$ , Y _i =X _i . The transmitter 300 has a conversion unit 308 for converting the data signal Data′ processed by the combining unit 306 to generate a transmission signal Data” in the time domain correspondingly for transmission. The conversion unit 308 is, for example, an IFFT converter.

For example, the transmitter 300 further includes a switch 312, which is used to enable the reserved subcarrier symbol generation unit 304 to calculate the updated value of X _R according to the adjusted data signal Data' when calculating X _R recursively, and The data signal Data' is updated. Then, X _R is updated again with the updated data signal Data' until the number of updates reaches the predetermined number of recursions.

In addition, the transmitter 300 also has a reserved subcarrier index value generator 310 for generating the index values of the L subcarriers of the reserved subcarriers mentioned above. The generated index value will be output to the reserved subcarrier symbol generating unit 304 .

The physical meaning of formula (7) is explained as follows. Please refer to FIG. 4 , which shows an example of ||ρ|| ² when the number of reserved subcarriers is assumed to be 3 and the reserved subcarrier symbols are X _a , X _b , and X _c .

来求X_R ⁽ⁿ⁺¹⁾的话，所得到的X_R ⁽ⁿ⁺¹⁾将会比X_R ⁽ⁿ⁾更接近||ρ||²的极值，例如是P点。因此，通过找出

来更新X_R，可以得到使||ρ||²的值更接近P点的保留子载波符元X_a、X_b、及X_c，而合乎所求。If X _R ⁽ⁿ⁾ is known, let the vector $\stackrel{\&Right\; Arrow;}{G}={\&dtri;}_{x_R}{\left|\right|\mathrm{\&rho;}\left|\right|}^2{|}_{x_R^{\left(\mathrm{no}\right)}}.$ due to vector It can be regarded as the direction in which the value of ||ρ|| ² changes the most. Therefore, according to

If X _R ⁽ⁿ⁺¹⁾ is calculated, the obtained X _R ⁽ⁿ⁺¹⁾ will be closer to the extreme value of ||ρ|| ² than X _R ⁽ⁿ⁾ , such as point P. Therefore, by finding

To update X _R , the reserved subcarrier symbols X _a , X _b , and X _c that make the value of ||ρ|| ² closer to point P can be obtained, which meets the requirement.

In addition, the above-mentioned step unit μ is a value that allows equation (7) to converge. The method of μ can be obtained by referring to a preset look-up table, for example. The look-up table can be set according to various communication parameters of the transmitter, such as the number N of subcarriers used, or the size of the fast Fourier transform (FFT).

Please refer to FIG. 5 , which shows a simulation result diagram of this embodiment. In this simulation, the FFT size is 1024, the number N of subcarriers used by the transmitter is 1024, the number L of reserved subcarriers is 72, and the subcarrier index value of the reserved subcarriers is randomly optimized (Random optimized) selection, over-sampling rate (Over-sampling Rate) is 4, the internal difference method uses frequency domain zero-padding (Frequency domain zero-padding), and the number of recursions is set to 4 times for simulation.

In Figure 5, the horizontal axis represents PAPR, and the vertical axis represents the complementary cumulative distribution function (Complementary cumulative distribution function, CCDF). CCDF refers to the sum of probabilities of values greater than the corresponding PAPR. The smaller the CCDF value, the smaller the peak-to-average power of the transmitted signal. Curves 502 and 504 in FIG. 5 are CCDF values of the original data signal Data, and curves 506 and 508 are CCDF values of the data signal Data' after performing the method for reducing the PAPR of the data signal in this embodiment. Curves 502 and 506 are simulation results after oversampling, while curves 504 and 508 are simulation results at Nyquist sampling rate. It can be seen from FIG. 5 that after being processed by the method of this embodiment, the PAPR value can be reduced by approximately 2dB, so the peak-to-average power of the data signal Data' to be transmitted can be reduced and the signal quality can be improved.

Please refer to FIG. 6 , which is a block diagram of a transmitter 600 for reducing the peak-to-average power of a data signal according to another embodiment of the present invention. Different from the previous embodiment, in this embodiment, the L reserved subcarrier symbols are divided into multiple groups of reserved subcarrier symbols. In this embodiment, when updating the L reserved sub-carrier symbols, the L reserved sub-carrier symbols are updated by sequentially updating the multiple groups of reserved sub-carrier symbols.

In the transmitter 600 , the switch 614 is selectively electrically connected to the modulating unit 602 and the combining unit 606 , and the switch 612 is selectively electrically connected to the converting unit 608 and the combining unit 606 .

By making the reserved subcarrier index value generator 610 respectively output the index values of different groups of reserved subcarrier symbols in sequence, the reserved subcarrier symbol generating unit 604 is only updated for a certain group of reserved subcarrier symbols, to generate the combined signal Cmb_1. If there are still reserved subcarrier symbols that have not been updated, the switches 612 and 614 will feed back the data signal Data'_1 output by the combining unit 606 to the reserved subcarrier symbol generating unit 604, so that the reserved subcarrier symbols The generating unit 604 updates the symbols of the next group of reserved subcarriers. And when the reserved subcarrier symbols of all groups are updated, the switcher 612 will output the data signal Data'_1 to the conversion unit 608 .

Please refer to FIG. 7 , which shows a simulation result diagram of this embodiment. The curve 702 is the simulation result when the L reserved subcarrier symbols are divided into one group and the number of recursion is 2 times. Curve 704 is the simulation result when the L reserved subcarrier symbols are divided into one group and the number of recursion is 4 times. The curve 706 is the simulation result when the L reserved subcarrier symbols are divided into four groups, and the number of recursion is 4 times. It can be seen from the curve 706 that the method of dividing the L reserved subcarrier symbols into multiple groups of reserved subcarrier symbols and sequentially updating these groups of reserved subcarrier symbols will further reduce the peak-to-average signal power.

In addition, in yet another embodiment of the present invention, the above L reserved subcarrier symbols may also be divided into multiple groups of reserved subcarrier symbols. In this embodiment, when updating the L reserved sub-carrier symbols, the L reserved sub-carrier symbols are updated by updating the multiple groups of reserved sub-carrier symbols in parallel. During parallel processing, unprocessed reserved subcarrier symbols may be treated as non-reserved subcarrier symbols for processing.

Please refer to FIG. 8 , which shows a block diagram of a transmitter 800 according to another embodiment of the present invention. Different from the embodiment in FIG. 3 , the transmitter 800 further has a filter 816 , a first multiplier 818 and a second multiplier 820 . The filter 816 has a frequency response function H, and Hk represents the frequency response coefficient value of the kth subcarrier. The first multiplier 818 is used to multiply the N data symbols by corresponding frequency response coefficients Hk respectively. The reserved subcarrier symbol generating unit 804 updates the L reserved subcarrier symbols according to the N data symbols multiplied by Hk, and generates the signal Cmb_2 to be combined. The second multiplier 820 is used to multiply the signal Cmb_2 to be combined by 1/Hk and output it to the combining unit 806 . The converting unit 808 is configured to convert the data signal Data'_2 processed by the merging unit 806 to generate a time-domain transmission signal Data"_2 correspondingly, and output it to the filter 816.

In this embodiment, since the data signal referred to in the process of updating the L reserved subcarrier symbols is equivalent to the data signal processed by the filter 816, the updated L subcarrier symbols generated by this embodiment Reserving the subcarrier symbols can further eliminate the possible influence of the filter 816 on the peak of the packet power of the data signal.

The method for reducing the peak-to-average power of the data signal in the above-mentioned embodiments of the present invention is implemented in the frequency domain, so multiple Fourier transforms are not required as in the traditional method.

In summary, although the present invention has been disclosed as above with an embodiment, it is not intended to limit the present invention. Those skilled in the art of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope defined by the claims.

Claims (12)

1. A method applied in a transmitter of a multi-carrier transmission system, wherein the transmitter uses N subcarriers, and L subcarriers in the N subcarriers are reserved subcarriers, and L is less than N, its characteristics That is, the method includes: receiving a data signal, the packet power of the data signal has a fixed power and a disturbance power; generating L reserved subcarrier symbols located on L subcarriers of the reserved subcarriers; Updating the L reserved subcarrier symbols according to the data signal, and generating a signal to be combined accordingly; and combining the signal to be combined in the data signal in frequency domain. 2. The method according to claim 1, wherein the data signal has N data symbols located at N subcarriers, and the N data symbols are corresponding to an aperiodic autocorrelation function vector, so The L reserved subcarrier symbols are corresponding to the reserved subcarrier symbol vectors, and in the step of updating the L reserved subcarrier symbols, the square of the absolute value of the vector according to the aperiodic autocorrelation function vector For the gradient of the reserved subcarrier symbol vector, update the L reserved subcarrier symbols, or update according to the pth power of the vector absolute value of the aperiodic autocorrelation function vector, where p is greater than 0 . 3. The method according to claim 1, wherein the step of updating the L reserved subcarrier symbols comprises recursively updating the L reserved subcarrier symbols. 4. The method according to claim 1, wherein the L reserved subcarrier symbols are divided into multiple groups of reserved subcarrier symbols, and in the step of updating the L reserved subcarrier symbols, The L reserved subcarrier symbols are updated by sequentially updating the multiple groups of reserved subcarrier symbols. 5. The method according to claim 1, wherein the L reserved subcarrier symbols are divided into multiple groups of reserved subcarrier symbols, and in the step of updating the L reserved subcarrier symbols, The L reserved subcarrier symbols are updated by updating the multiple groups of reserved subcarrier symbols in parallel. 6. method according to claim 1 is characterized in that, described transmitter has filter, and the frequency response function of described filter is H, and Hk represents the frequency response coefficient value of the kth subcarrier, and described data The signal has N data symbols located on N subcarriers, and the step of updating the L reserved subcarrier symbols includes: multiplying the N data symbols by corresponding Hk respectively; Updating the L reserved subcarrier symbols according to the N data symbols multiplied by Hk, and correspondingly generating the signal to be combined; and multiplying the signal to be combined by 1/Hk; Wherein, the signal to be combined multiplied by 1/Hk is used as the signal to be combined to be combined with the data signal in the combining step. 7. A transmitter, applied in an OFDM communication system, the transmitter uses N subcarriers, L subcarriers in the N subcarriers are reserved subcarriers, and L is less than N, It is characterized in that the transmitter includes: A modulating unit for outputting a data signal, the packet power of the data signal has a fixed power and a disturbance power; The reserved subcarrier symbol generation unit is used to generate L reserved subcarrier symbols located in the L subcarriers of the reserved subcarriers, update the L reserved subcarrier symbols according to the data signal, and generate the L reserved subcarrier symbols accordingly. Merge signals; The combining unit is used for combining the signal to be combined into the data signal in the frequency domain. 8. The transmitter according to claim 7, wherein said data signal has N data symbols located at N subcarriers, said N data symbols being corresponding to aperiodic autocorrelation function vectors, The L reserved subcarrier symbols are corresponding to the reserved subcarrier symbol vectors, and the modulation unit is based on the square of the vector absolute value of the aperiodic autocorrelation function vector for the reserved subcarrier symbol vectors to update the L reserved sub-carrier symbols, or update according to the p-th power of the vector absolute value of the aperiodic autocorrelation function vector, where p is greater than 0. 9. The transmitter according to claim 7, wherein the modulating unit recursively updates the L reserved subcarrier symbols. 10. The transmitter according to claim 7, wherein the L reserved subcarrier symbols include multiple groups of reserved subcarrier symbols, and the modulation unit updates the multiple groups of reserved subcarrier symbols sequentially subcarrier symbols to update the L reserved subcarrier symbols. 11. The transmitter according to claim 7, wherein the L reserved subcarrier symbols include multiple groups of reserved subcarrier symbols, and the modulation unit updates the multiple groups of reserved subcarrier symbols in parallel Carrier symbols are used to update the L reserved subcarrier symbols. 12. The transmitter according to claim 7, wherein the data signal has N data symbols located on N subcarriers, and the transmitter further has: The filter has a frequency response function H, and Hk represents the frequency response coefficient value of the kth subcarrier; The first multiplier is used to multiply the N data symbols by Hk respectively, and the reserved subcarrier symbol generating unit updates the L reserved subcarriers according to the N data symbols multiplied by Hk Carrier symbols, and correspondingly generate the signal to be combined; a second multiplier, configured to multiply the signal to be combined by 1/Hk and output to the combining unit; The converting unit is configured to convert the data signal processed by the merging unit to correspondingly generate a transmission signal in the time domain, and output it to the filter.

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