CN108632195B - Segmented companding algorithm for reducing peak-to-average power ratio of OFDM (orthogonal frequency division multiplexing) signal - Google Patents
Segmented companding algorithm for reducing peak-to-average power ratio of OFDM (orthogonal frequency division multiplexing) signal Download PDFInfo
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Abstract
The invention discloses a segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal, which relates to the field of wireless communication, and is characterized in that a companding parameter table is designed by utilizing the stability of the probability distribution of the amplitude of a time domain OFDM signal, namely when the number N of OFDM signal carriers is more than or equal to 64, the probability distribution of the amplitude of the time domain signal keeps stable, and OFDM time domain signals in different amplitude intervals are compressed in a segmented manner by utilizing the cumulative probability distribution function of the amplitude, so that the amplitude of the compressed OFDM time domain signal is uniformly distributed, and the peak-to-average power ratio of the time domain OFDM signal is reduced; and the receiving end reversely expands and restores the received OFDM time domain signal in an opposite mode, and further demodulates the original signal. The segmented companding algorithm has the advantages of small algorithm calculation amount and high processing efficiency; the algorithm fully utilizes the amplitude distribution characteristics of OFDM time domain signals to design a companding ratio, and has good adaptability to OFDM signals with different modulation orders and carrier numbers.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal.
Background
The OFDM (Orthogonal Frequency Division Multiplexing) technology has not only good anti-fading and anti-multipath interference performance, but also the advantages of high spectrum utilization rate and easy implementation, is widely applied in the field of wireless communication, and is one of the core technologies of 4G wireless communication systems.
Although the OFDM system has good multipath interference resistance, due to the characteristic of multi-carrier superposition, the OFDM time domain signal peak-to-average power ratio is relatively high, and the signal easily enters a nonlinear working area of an amplifying device, so that nonlinear distortion of the signal shown in fig. 1 is caused. In order to avoid signal nonlinear distortion and improve system performance, one solution is to improve the dynamic range of system components, but on one hand, the scheme improves the design complexity of the system and is not beneficial to the effective utilization of energy; the other solution is to reduce the peak-to-average power ratio of the OFDM time domain signal by taking effective measures, which on one hand reduces the complexity of system hardware, and at the same time can improve the energy utilization rate and prolong the endurance time of the mobile terminal battery.
At present, methods for reducing the peak-to-average power ratio of an OFDM signal can be roughly classified into four major categories, namely, an encoding method, a selective mapping method, a partial series transmission method, and a signal predistortion algorithm; the signal predistortion algorithm directly processes the OFDM time domain signal, has a simple principle and low cost, is very suitable for occasions with limited hardware, and is a common one in the predistortion algorithm, so that the companding method is widely concerned.
Disclosure of Invention
The invention aims to: in order to solve the problem that the peak-to-average power ratio of an OFDM time domain signal is too high, an amplifier is easy to enter a nonlinear region in the transmitting process, and nonlinear distortion of the signal is caused, the invention provides a segmented companding algorithm for reducing the peak-to-average power ratio of the OFDM signal.
The invention specifically adopts the following technical scheme for realizing the purpose:
a segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal comprises the following steps:
s1: after data to be transmitted is subjected to coding modulation processing at a transmitting end, an OFDM frequency domain signal is obtained, and the OFDM frequency domain signal is subjected to IFFT conversion and normalization processing to generate a normalized OFDM time domain signal;
s2: obtaining an accumulative probability distribution function F (x) of the amplitude of the OFDM time domain signal by carrying out statistical analysis on the OFDM time domain signal, and obtaining a companding parameter table by calculating the accumulative probability distribution function F (x);
s3: carrying out segmented compression on the OFDM time domain signal by using a companding parameter table, adding a protection interval, carrying out analog-to-digital conversion on the segmented and compressed OFDM time domain signal, and then sending the OFDM time domain signal to a receiving end;
s4: preprocessing a received signal by a receiving end to obtain a normalized OFDM time domain compressed signal;
s5: performing inverse expansion transformation on the OFDM time domain compressed signal by using the same companding parameter table as that in the S3, and expanding and restoring the OFDM time domain compressed signal into an OFDM time domain signal before compression;
s6: and demodulating and channel decoding the recovered OFDM time domain signal to obtain the transmitted data.
Further, the encoding and modulating process in S1 specifically includes: and carrying out channel coding and MQMA high-order modulation on data to be transmitted to obtain an OFDM frequency domain signal, and converting the OFDM frequency domain signal into an OFDM time domain signal through IFFT.
Further, a set of amplitude parameters a ═ a associated with the signal distribution law is obtained according to the cumulative probability distribution function f (x) in S20,A1,…,Am]The formula for calculating the amplitude parameter a is:
wherein m is the number of segments of the segmented companding algorithm, AiThe probability of occurrence is less than
Under the normalized condition, A0＝0，Am＝1。
Further, in S3, if the maximum amplitude level of the segmented compressed OFDM time-domain signal is v, the amplitude range of the segmented OFDM time-domain signal is [0, v ], and the amplitude span of each segment of the compressed OFDM time-domain signal is L, the calculation formula of L is:
if the OFDM time domain signal of the nth sample is x [ n ] within one OFDM time domain symbol, the calculation formula of x [ n ] is:
x[n]＝|x[n]|ejθ[n]
wherein, theta [ n ]]Representing the phase of the nth sample symbol, the transmitted OFDM time domain signal xt[n]The calculation formula of (2) is as follows:
further, the receiving end in S4 preprocesses the received compressed transmission signal, specifically: and carrying out sampling timing compensation, energy normalization, frequency offset compensation and the like on the received transmitted compressed signal in sequence to obtain a time domain signal for subsequent demodulation.
Further, in S5, the OFDM time-domain signal of the receiving end at the nth sampling time is:
yr[n]＝|yr[n]|ejθ[n]
wherein θ [ n ] represents the phase of the nth sampling symbol, the calculation formula of the OFDM time domain signal inverse spreading transform is:
wherein y [ n ] is the time-domain sample signal after expansion.
The working principle of the invention is as follows:
the method comprises the steps of utilizing the stability of the probability distribution of the amplitude of the OFDM time domain signal, namely when the number N of carriers of the OFDM time domain signal is larger than or equal to 64, keeping the accumulated probability distribution of the signal amplitude stable, utilizing the accumulated probability distribution function of the amplitude to design a companding parameter table, and compressing the OFDM time domain signals in different amplitude ranges in a segmented mode to enable the amplitude of the compressed OFDM time domain signal to be in a uniform distribution characteristic, and utilizing the reverse expansion reduction of the received signal by a receiving end in a reverse mode, so that the peak-to-average power ratio of the OFDM time domain signal is reduced.
The invention has the following beneficial effects:
1. the invention can make the amplitude of the compressed OFDM time domain signal be uniformly distributed, can effectively reduce the peak-to-average power ratio of the signal and reduce the nonlinear effect.
2. The invention utilizes the segmented companding algorithm, the algorithm has small calculation amount and high processing efficiency; the algorithm fully utilizes the amplitude distribution characteristics of OFDM time domain signals to design a companding ratio, and has good adaptability to OFDM signals with different modulation orders and carrier numbers.
3. According to the invention, the distribution characteristic of the OFDM time domain signal is kept stable, and the companding parameters of the OFDM time domain signal with the same parameters do not need to be repeatedly calculated, so that the algorithm implementation flow is simplified, and the operation efficiency is improved.
Drawings
Fig. 1 is a diagram of the nonlinear distortion of an OFDM signal.
Fig. 2 is a communication flow diagram of the present invention.
Fig. 3 is a comparison of the cumulative probability distribution of the OFDM signal amplitude with the cumulative probability distribution of the signal amplitude after the companding process.
FIG. 4 is a graph of amplitude mapping before and after compression in accordance with the present invention.
Detailed Description
For a better understanding of the present invention by those skilled in the art, the present invention will be described in further detail below with reference to the accompanying drawings and the following examples.
Example 1
The segmented companding algorithm for reducing the peak-to-average power ratio of the OFDM signal of the present embodiment is mainly applied to a wireless communication system adopting OFDM modulation, a wireless communication system is assumed to employ 16QAM amplitude modulation and 64 sub-carrier OFDM modulation, through statistical analysis, the cumulative probability distribution of the OFDM time domain signal amplitude is shown in FIG. 3, and it can be seen from the cumulative probability distribution curve that about 70% of the normalized signal amplitude is concentrated in the region of 0.2-0.6, while the probability of the signal appearing in the region of 0.6-1.0 is only about 10%, i.e. the probability of occurrence of large amplitude signals is low, and the probability distribution of signal amplitude is extremely uneven, which results in a signal with a high peak-to-average power ratio, therefore, the present embodiment performs companding algorithm processing on the OFDM signal related to the system, wherein the number m of segments is 10, and still obtain the normalized signal that the signal amplitude is 1 after companding, including the following step:
s1: as shown in fig. 2, after performing coding modulation processing on data to be transmitted at an information source, i.e., a transmitting end, an OFDM frequency domain signal is obtained, and the OFDM frequency domain signal is subjected to IFFT modulation transformation and normalization processing to generate a normalized OFDM time domain signal;
the code modulation processing specifically comprises: carrying out channel coding and MQMA high-order modulation on data to be transmitted to obtain an OFDM frequency domain signal;
s2: carrying out statistical analysis on OFDM time domain signals with the same modulation order and carrier number as the OFDM time domain signals to obtain an accumulative probability distribution function F (x) of the amplitude of the OFDM time domain signals, and calculating through the accumulative probability distribution function F (x) to obtain a companding parameter table;
a set of amplitude parameters a ═ a [ a ] related to the OFDM time domain signal distribution law is obtained through the cumulative probability distribution function f (x) in S10,A1,…,A10]Wherein A is0,A1,…,A10Correspondingly, the maximum amplitude corresponding to the cumulative probability distribution of the amplitude of the OFDM time domain signal at 10%, 20%, …, and 100% is represented, in this embodiment, the distribution parameter a is obtained by analyzing the OFDM signal of 16QAM and 64 subcarriers, [0,0.126,0.182,0.233,0.274,0.321,0.366,0.422,0.489,0.585,1]；
Calculating the compression multiple of the signal as B ═ B by using the obtained distribution parameters and the amplitude level of the companded signal0,b1,…,b10]，
By
It is understood that, in this embodiment, if L is 0.1, then
B＝[0.793,1.748,1.953,2.409,2.164,2.212,1.766,1.506,1.043,0.241]；
S3: uniformly compressing the OFDM time domain signal in a segmented manner according to the compression multiple, adding a protection interval, performing analog-to-digital conversion on the OFDM time domain signal after the segmented compression, transmitting the OFDM time domain signal to a receiving end through a radio frequency channel;
let the OFDM time domain signal of the nth sample be:
x[n]＝|x[n]|ejθ[n]
the transmitted OFDM time domain signal xt[n]The calculation formula of (2) is as follows:
xt[n]＝[(|x[n]|-Ai-1)bi+L(i-1)]ejθAi-1<|x[n]|<Ai,i∈[1,m]
as shown in fig. 4, for the amplitude mapping relationship before and after compression, the cumulative probability distribution of the amplitude of the signal after companding exhibits an approximate linear relationship, as shown in fig. 3, that is, the amplitude distribution of the signal tends to be uniform, thereby achieving the desired effect and effectively reducing the peak-to-average power ratio of the signal;
s4: after preprocessing the received signal by the receiving end, obtaining a normalized OFDM time domain compressed signal, wherein the preprocessing specifically comprises the following steps: carrying out sampling timing compensation, energy normalization and frequency offset compensation on the received signals in sequence;
s5: performing inverse expansion transformation on the OFDM time domain compressed signal by using the same compression multiple B as that in S3, and restoring the OFDM time domain compressed signal into an OFDM time domain signal before compression;
let the OFDM time domain compressed signal at the nth sampling time by the receiving end in S5 be:
yr[n]＝|yr[n]|ejθ[n]
the calculation formula of the OFDM time domain compressed signal inverse expansion transform is:
wherein y [ n ] is the extended sampling signal;
s6: and performing FFT demodulation transformation and channel decoding on the OFDM time domain signal which is subjected to the expansion recovery, obtaining the transmitted data and sending the data to an information sink.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention, the scope of the present invention is defined by the appended claims, and all structural changes that can be made by using the contents of the description and the drawings of the present invention are intended to be embraced therein.
Claims (5)
1. A segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal is characterized by comprising the following steps:
s1: after data to be transmitted is subjected to coding modulation processing at a transmitting end, an OFDM frequency domain signal is obtained, and the OFDM frequency domain signal is subjected to IFFT conversion and normalization processing to generate a normalized OFDM time domain signal;
s2: carrying out statistical analysis on OFDM time domain signal amplitude values with the same modulation order and carrier number as the OFDM time domain signals to obtain an accumulative probability distribution function F (x) of the OFDM time domain signal amplitude values, and calculating through the accumulative probability distribution function F (x) to obtain a companding parameter table;
specifically, a set of amplitude parameters a ═ a associated with the signal distribution law is obtained according to the cumulative probability distribution function f (x)0,A1,…,Am]The formula for calculating the amplitude parameter a is:
wherein m is the number of segments of the segmented companding algorithm, AiThe probability of occurrence is less than
Under the normalized condition, A0＝0，Am＝1；
S3: carrying out segmented compression on the normalized OFDM time domain signal by using a companding parameter table, adding a protection interval, carrying out analog-to-digital conversion on the segmented and compressed OFDM time domain signal, and then sending the OFDM time domain signal to a receiving end;
s4: preprocessing a received signal by a receiving end to obtain a normalized OFDM time domain compressed signal;
s5: performing inverse expansion transformation on the OFDM time domain compressed signal by using the same companding parameter table as that in the S3, and restoring the OFDM time domain compressed signal into an OFDM time domain signal before compression;
s6: and demodulating and channel decoding the OFDM time domain signal after the expansion recovery to obtain the transmitted data.
2. The segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal according to claim 1, wherein the coded modulation processing in S1 specifically comprises: and carrying out channel coding and MQAM high-order modulation on data to be transmitted to obtain an OFDM frequency domain signal, and converting the OFDM frequency domain signal into an OFDM time domain signal through IFFT.
3. The segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal according to claim 1, wherein in S3, assuming that the maximum amplitude level of the segmented compressed OFDM time domain signal is v, the amplitude range of the segmented OFDM time domain signal is [0, v ], and the amplitude span of each segment of the compressed OFDM time domain signal is L, and the calculation formula of L is:
if the OFDM time domain signal of the nth sample is x [ n ] within one OFDM time domain symbol, the calculation formula of x [ n ] is:
x[n]＝|x[n]|ejθ[n]
wherein, theta [ n ]]Representing the phase of the nth sample symbol, the transmitted OFDM time domain signal xt[n]The calculation formula of (2) is as follows:
4. the segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal according to claim 1, wherein the receiving end in S4 preprocesses the received signal, specifically: and carrying out sampling timing compensation, energy normalization, frequency offset compensation and the like on the received signals in sequence.
5. The segmented companding algorithm for reducing the peak-to-average power ratio of an OFDM signal according to claim 1, wherein the OFDM time domain signal at the nth sampling moment at the receiving end in S5 is:
yr[n]＝|yr[n]|ejθ[n]
wherein θ [ n ] represents the phase of the nth sampling symbol, the calculation formula of the OFDM time domain signal inverse spreading transform is:
wherein y [ n ] is the time-domain sample signal after expansion.
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