CN105634651A - Method for reducing PAPR of OFDM system based on pre-coding and exponential companding technologies - Google Patents

Abstract

The invention relates to the technical field of wireless communication, and provides a method for reducing the PAPR of an OFDM system based on pre-coding and exponential companding technologies. The method comprises the following steps: S1, parallelizing serial data at a data sender, pre-coding and carrying out inverse fast Fourier transform on the parallel data, and adding a cyclic prefix; S2, carrying out parallel-serial conversion on the data obtained in S1, companding the data through an exponential companding algorithm, and sending the data; S3, exponentially de-companding and carrying out serial-parallel conversion on the received data, removing the cyclic prefix, and carrying out fast Fourier transform; and S4, carrying out parallel-serial conversion on the data obtained in S3 through a pre-decoder, and demodulating and outputting the data. According to the scheme of the invention, a pre-coding algorithm is adopted in the time domain of an OFDM transmitter, and an exponential companding algorithm is adopted in the frequency domain. Compared with the traditional method, the scheme not only effectively reduces the peak-to-average power ratio, but also has a small impact on the bit error rate of the system and can ensure that the system can get reliable bit error rate performance.

Description

A kind of precoding association index companding technology reduces the method for ofdm system PAPR

Technical field

The present invention relates to communication technical field, relate to a kind of method that precoding association index companding technology reduces ofdm system PAPR.

Background technology

OFDM technology is the key technology of forth generation mobile communication (4G) system, because it has the features such as availability of frequency spectrum height is strong with anti-multipath fading ability, is therefore widely used in mobile communication system. In wireless communications, the modulation system of signal is by the communication performance of decision systems, highspeed serial data stream can be converted to multi-path low speed sub data flow and be modulated in multiple orthogonal sub-carriers by OFDM modulation technique, widens code-element period, reduces the intersymbol interference that channel delay causes; Meanwhile, OFDM technology eliminates the multipath effect impact on communication system further by adding protection interval between each OFDM symbol. Therefore, use OFDM modulation technique can effectively reduce the impact that systematic function is caused by channel disturbance in a communications system, contribute to realizing the low-loss radio communication of high speed. But OFDM technology there is also some defects, one of them is exactly that the peak-to-average power ratio (Peak-to-AveragePowerRatio, PAPR) of ofdm system is too high. Communication system exists nonlinear device, too high PAPR value signal is once enter the nonlinear operation region of device, non-linear distortion can be caused, produce out-of-band radiation and Intermodulation Interference, this can be substantially reduced the operational efficiency of system, the communication performance of influential system, therefore reduces the PAPR of ofdm system and has very important significance for the performance of communication system.

Summary of the invention

Present invention solves the technical problem that and be: when ensureing low error rate, reducing the PAPR of ofdm system, thus improving the performance of communication system.

In order to solve above-mentioned technical problem, the present invention proposes a kind of method combining with index companding technology based on precoding and reducing ofdm system PAPR, comprises the following steps:

S1, at data sending terminal by serial data parallelization, parallel data precoding and inverse fast Fourier transform are processed, increase Cyclic Prefix;

S2, the data that S1 is obtained carry out parallel-serial conversion, by index companding algorithm, data are carried out companding, send data;

S3, to the data exponential solution companding received, remove Cyclic Prefix after serial to parallel conversion, then carry out fast Fourier transform;

S4, the data that S3 is obtained pass through pre decoder, carry out parallel serial conversion.

Technique scheme has the advantage that the time domain of OFDM transmitter adopts precoding algorithms, and frequency domain adopts the algorithm of index companding. Precoding algorithms reduces the PAPR of OFDM by reasonable employment null subcarrier, but the addition of null subcarrier causes out-of-band emission power and increases and efficiency of transmission reduction. The present invention proposes effectively to reduce peak-to-average power ratio based on precoding in conjunction with nonlinear exponent companding algorithm, simultaneously that the impact of error rate of system is less, it is possible to ensure that system obtains reliable bit error rate performance.

Accompanying drawing explanation

Fig. 1 is the system block diagram of the present invention;

Fig. 2 is the contrast simulation figure that the present invention and traditional method reduce PAPR;

Fig. 3 is the bit error rate performance comparison diagram of the present invention and traditional method.

Detailed description of the invention

Below in conjunction with accompanying drawing and example, the specific embodiment of the present invention is described in further detail. Following instance is used for the present invention is described.

The present invention is directed to the height power ratio of ofdm system in 4G communication, it is proposed to a kind of precoding association index companding technology reduces the method for ofdm system PAPR. The method, compared with traditional communication method, not only significantly reduces peak-to-average power ratio, and the impact of error rate of system is less, it is possible to ensure that system obtains reliable bit error rate performance.

As it is shown in figure 1, the present invention implements according to the following steps:

S1, include as shown in 4 parts before Fig. 1 (1) input traffic, (2) data modulation with coding, (3) serial to parallel conversion, (4) precoder. First pass through the data stream of input after QPSK modulation and serial to parallel conversion, obtain N subcarriers signal, then pass through precoder. In precoder, the element of pre-coding matrix is:

$P_{a,0}=\left\{\begin{array}{cc}\frac{{(-1)}^a}{\sqrt{N}}\sin \left(\frac{\mathrm{a\π}}{{2N}_P}\right)& 0\≤a\≤N_P\\ \frac{{(-1)}^a}{\sqrt{N}}& N_P\≤a\≤N\\ \frac{{(-1)}^a}{\sqrt{N}}\cos \left(\frac{(a-N)\mathrm{\π}}{{2N}_P}\right)& N\≤a\≤L-1\end{array}\right.,$ $P_{a,b}=P_{a,0}{e}^{-j2\mathrm{\π}\frac{\mathrm{ab}}{N}}$

Wherein P_{A, b}It it is the value of a sampled point of b subcarrier. Thus can release pre-coding matrix

Wherein L=N+Np, Np �� (0, N) is extension length, and matrix P meets P ' P=I, and matrix I is the unit matrix of N �� N, and P ' is the associate matrix of pre-coding matrix P.

S2, as shown in Figure 1, Cyclic Prefix, (7) parallel serial conversion, (8) index companding is increased, by the serial data stream after (5), (6), (7) step according to decompression function including (5) IFFT, (6):

$h\left(x\left(t\right)\right)=\mathrm{sgn}\left(x\left(t\right)\right)\sqrt[d]{\mathrm{\α}[1-\exp (-\frac{x{\left(t\right)}^2}{{\mathrm{\σ}}^2})]}$

The amplitude of serial signal is carried out corresponding companding to reduce PAPR, sends data then through emitter.

S3, comprise (9) index companding in Fig. 1, (10) serial to parallel conversion, (11) remove the part such as Cyclic Prefix, (12) FFT, at receiving terminal, being received the serial signal that receives of termination to carry out solving companding, it solves companding function and is:

$h^{-1}\left(x\left(t\right)\right)=\mathrm{sgn}\left(x\left(t\right)\right)\sqrt{-{\mathrm{\σ}}^2{\log }_e(1-\frac{x{\left(t\right)}^d}{\mathrm{\α}})}$

Data stream after decompression passes through (10), (11), (12) step, the time domain data of the N group obtained decompression.

S4, as shown in the 13rd to 16 part of Fig. 1 (13) include decoder, (14) serial to parallel conversion, the demodulation of (15) data and the part such as coding, (16) output stream. The N group decompression time domain data obtained through S3 process is decoded by decoder, and decoding matrix is the associate matrix P ' of encoder matrix P. Because P ' P=I is unit battle array, so recovery primary signal that can be complete after decompression. Decoded signal is after serioparallel exchange, and QPSK demodulates output.

Fig. 2 shows ofdm communication scheme that traditional ofdm system and the present invention combine with index companding algorithm based on the precoding reduction degree to PAPR. It can be seen that traditional ofdm communication scheme, the value of PAPR is significantly high, reaches about 10.1DB, and the present invention compares traditional scheme and is significantly improved, only about 3DB, reduces 7.1DB.

Fig. 3 shows the bit error rate performance of the ofdm communication scheme that traditional ofdm system and the present invention combine with index companding algorithm based on precoding. It can be seen that when signal to noise ratio is 12, the error performance of the present invention is best.

As can be seen from the above embodiments, the method of the present invention adopts precoding algorithms by the time domain in OFDM transmitter, frequency domain adopts the algorithm of index companding, compared with traditional method, the program not only significantly reduces peak-to-average power ratio, and the impact of error rate of system is less, it is possible to ensure that system obtains reliable bit error rate performance.

Claims (6)

1. the method that a precoding association index companding technology reduces ofdm system PAPR, it is characterised in that comprise the following steps:

S1, at data sending terminal by serial data parallelization, parallel data precoding and inverse fast Fourier transform are processed, increase Cyclic Prefix;

S2, the data that S1 is obtained carry out parallel-serial conversion, by index companding algorithm, data are carried out companding, send data;

S3, to the data exponential solution companding received, remove Cyclic Prefix, then fast Fourier transform after serial to parallel conversion;

S4, the data that S3 is obtained pass through pre decoder, carry out parallel serial conversion, demodulation output.

2. scheme according to claim 1, it is characterised in that in step S1, the data after base band mapping are through precoder, change initial data phase place and amplitude distribution situation, then carries out OFDM modulation and transmits.

3. scheme according to claim 1, it is characterised in that in step S1, primary signal is extended by the method for precoding, shares the power of N number of data in L data, and changes the PHASE DISTRIBUTION of each sampled point in original OFDM symbols.

4. scheme according to claim 1, it is characterised in that step S2 adopts index companding algorithm that the amplitude of signal is converted, and the amplitude adjusting small-signal and big signal reduces PAPR.

5. scheme according to claim 1, it is characterised in that step S3 and S4 is according to solving companding function h^-1The associate matrix transform data of (x (t)) and pre-coding matrix.

6. scheme according to claim 1, it is characterized in that, step S1, S2, S3, S4 adopt precoding algorithms in the time domain of OFDM transmitter, the algorithm of index companding is adopted at frequency domain, receiving terminal is due to index companding function strictly monotone, there is unique decompression function, and P ' P=1 is unit battle array, it is to avoid high bit-error.