CN1163038C - A phase stagger method to reduce the peak-to-average ratio of multi-carrier signals - Google Patents

Abstract

The present invention relates to a phase staggered method for reducing the peak-average ratio of a multi-carrier signal. Initial phases of all carriers are arranged, and the arrangement times of the iteration are N; multi-carrier compound envelopes are built up by using the initial phases; the multi-carrier compound envelopes are sampled so that a discrete envelope is obtained; a time-domain signal of the discrete envelope carries out the clipping so that a sampling point which carries out the clipping is obtained; the sampling point is used as the input of the discrete fourier transform so as to carry out the discrete fourier transform, and then a fourier frequency spectrum is obtained. A multi-carrier initial phase of which the iteration time is 1 can be obtained by the calculation of the fourier frequency spectrum, the process is repeated until the iteration times are N, and the initial phase is obtained, namely an initial phase to be obtained.

Description

A phase stagger method to reduce the peak-to-average ratio of multi-carrier signals

technical field

The invention relates to a phase stagger method for reducing the peak-to-average ratio of multi-carrier signals.

Background technique

At present, the main methods to reduce the peak-to-average ratio (the ratio of peak power to average power) of multi-carrier composite signals include probability clipping, signal compensation and phase staggering. Among them, the implementation of probability clipping is relatively simple, but the signal distortion caused by clipping often introduces spurs to the system. Although signal compensation will not cause signal distortion, the introduction of the compensation signal will inevitably increase the transmission power of the signal. The phase stagger avoids the above-mentioned defects and is widely used.

Phase staggering methods can be roughly divided into two categories, one is suitable for multi-carrier signal synthesis with equal amplitude and frequency interval, and the other is suitable for signal synthesis with different amplitude and frequency interval.

Generally speaking, to use the method of phase staggering to compress the signal envelope, the easiest thing to think of is to use the exhaustive search method to find a group of optimal phase groups. However, the exhaustive search method is only suitable for applications with a relatively small number of carriers and low real-time requirements due to the large amount of calculation. In order to solve the phase stagger problem when the number of carriers is large, empirical formula (1), empirical formula (2) and semi-empirical formula (3) are obtained from a large number of experiments.

θ _k = π(k-1)(k-1)/N (1)

θ _k = πk·k/N (2)

θ _k = π(k-1)(k-2)/N (3)

In the above formulas, θ _k is the initial phase of each carrier used for staggering; N is the number of carriers; The k values of the carriers are 1, 2, 3, 4...15 respectively.

In addition to the limitation of application conditions of equal amplitude and equal interval, the various phase stagger algorithms mentioned above require a large number of carriers (usually more than a dozen carriers) to obtain a good stagger effect.

Compared with the former, the phase staggering of multi-carrier signal synthesis with variable amplitude and unequal intervals is much more complicated. Due to the variation of the amplitude and the uncertainty of the frequency interval, it is difficult to obtain an analytical solution of the initial phase, so an iterative algorithm is usually used. At present, the representative algorithms are: Schroeder method, Patrick method and time-frequency domain exchange algorithm. Among the three algorithms, the time-frequency domain exchange algorithm is widely used because of its obvious effect, simple implementation and fast algorithms for the main operations involved.

As shown in Figure 1, it is a functional block diagram of the time-frequency domain exchange algorithm. The algorithm adopts the idea of backward deduction, and it starts from the purpose of compressing the peak value of the envelope to solve the initial phase value of each carrier. First, the initial phase of each carrier is set, and then the Fourier spectrum is constructed from the initial phase and amplitude, and the inverse discrete Fourier transform (IDFT) is used to obtain the time-domain waveform, the time-domain waveform is sampled, and the sampled time-domain waveform signal is clipped, and Discrete Fourier transform (DFT) is then performed to calculate the initial phase. This is repeated for many times to obtain the required initial phase of each carrier. Here, the range of clipping can be selected as 75%~95% of the maximum value of the envelope of the original synthesized signal. It is not easy to converge when you shave too little, and the phasing effect obtained by shaving too much is not good. In this algorithm, discrete Fourier transform is used to solve the initial phase of each carrier.

From the above description, it can be seen that the main computational load of the time-frequency domain exchange algorithm consists of three parts: discrete Fourier transform DFT, inverse discrete Fourier transform IDFT and the construction of Fourier spectrum from the initial phase and amplitude. Although DFT and IDFT have corresponding fast algorithms, when the number of sampling points is large, the amount of calculation is still relatively large. In addition, in the above algorithm, since the initial phase of each carrier is randomly set, it is necessary to increase the number of iterative algorithms to achieve the required initial phase of each carrier, thus increasing the amount of calculation and increasing the cost of the system.

Contents of the invention

The purpose of the present invention is to provide a phase staggering method for reducing the peak-to-average ratio of multi-carrier signals, which reduces the system cost by reducing the total calculation amount.

The purpose of the present invention is achieved in this way, a phase stagger method for reducing the peak-to-average ratio of multi-carrier signals, comprising the following steps: setting the initial phase of each carrier, and setting the number of iterations as N; using the above-mentioned initial phase to construct multi-carrier Synthetic envelope of the multi-carrier composite envelope; the discrete envelope is obtained by sampling the multi-carrier synthetic envelope; the clipping of the time domain signal of the discrete envelope is obtained after clipping; the sample point after the clipping is used as the discrete Fourier transform Input, perform discrete Fourier transform to obtain the Fourier spectrum; calculate from the Fourier spectrum, obtain the initial phase of the multi-carrier with the number of iterations N equal to 1; repeat the above process until the number of iterations is N, the obtained initial phase is the desired initial phase.

Due to the adoption of the above method, the two modules of Fourier spectrum construction and IDFT used in the existing phase staggering method are replaced by direct sampling of the synthetic envelope. This improvement can reduce the amount of calculation by half without changing the algorithm. effect, and use the coarse and fine search method to obtain a more suitable initial phase, speed up the convergence speed of the iterative operation, thereby reducing the total amount of calculation in the whole process, and reducing the cost of system implementation.

The present invention will be further described below in conjunction with the embodiments and accompanying drawings.

Description of drawings

Fig. 1 is the functional block diagram of existing time-frequency domain exchange algorithm;

Fig. 2 is a process block diagram of the phase shift method of the present invention.

Detailed ways

As shown in Figure 2, the present invention, that is: a phase stagger method that reduces the peak-to-average ratio of multi-carrier signals, comprises the following steps:

Step 1: For any k carriers to be combined:

x _i ＝A _i (cosw _i t+θ _i ) (4)

Wherein, i=0, 1, . . . , k-1. Firstly, the initial phase θ _i of each carrier is set, and the number of iterations is set to N. Among them, the setting process of the initial phase of each carrier is:

a. Use a random number generator to generate M groups of random phase groups: [θ ₀ ^j , θ ₁ ^j , . . . θ _k-1 ^j ], j=0, 1, . . . , M-1. Then, these M phase groups are respectively substituted into the formula (4), and a group of phases with the smallest synthetic envelope peak value is obtained as the result of the initial search.

b. Find out the one with the largest energy among the above k carriers (here set as the m-th carrier for the convenience of description). And put a group of phase values obtained from the above initial search as the initial phase into (4) formula.

c. Adjust the initial phase θ _m of the carrier m (the adjustment range is 2π/n, and the number of adjustments is n), and substitute the adjusted phase θ _m ^l (l=0, 1, n-1) into formula (4) middle.

d. Synthesize the maximum energy carrier m after the initial phase adjustment and other carriers into a new envelope, and find a group of phase groups corresponding to the lowest peak value of the synthesized envelope.

Step 2: Construct a composite envelope of multi-carriers using the group of initial phases finely selected above: y=∑yi.

Step 3: Sampling the multi-carrier synthesis envelope to obtain a discrete envelope: z=[z ₀ , z ₁ , . . . , z _i ].

Step 4: clipping the time-domain signal of the discrete envelope, and obtaining sample points after clipping: z′=[z ₀ ′, z ₁ ′, . . . , z _i ′].

Step 5: Use the sample points after clipping as the input of discrete Fourier transform, and perform discrete Fourier transform to obtain Fourier spectrum: y=[Y ₀ , Y ₁ , . . . , Y _i ].

Step 6: From the Fourier spectrum, the initial phase of the multi-carrier with the number of iterations equal to 1 can be obtained by calculation: [ψ ₀ , ψ ₁ , . . . , ψ _k-1 ].

Repeat the above steps from the second to the sixth until the number of iterations is N, and the obtained initial phase is the desired initial phase.

Claims (1)

1. A phase stagger method that reduces the peak-to-average ratio of multi-carrier signals, is characterized in that, comprises the following steps: Set the initial phase of each carrier, and set the number of iterations to N; Constructing a multi-carrier synthetic envelope using the above initial phase; Sampling the multi-carrier composite envelope to obtain a discrete envelope; Clip the time-domain signal of the discrete envelope to obtain clipped samples; The sample point after the clipping is used as the input of the discrete Fourier transform, and the discrete Fourier transform is performed to obtain the Fourier spectrum; Calculated from the Fourier spectrum to obtain the initial phase of the multi-carrier with the number of iterations N equal to 1; Repeat the above process until the number of iterations is N, and the obtained initial phase is the desired initial phase.