CN105141566B - A kind of PTS method reducing SCMA systems PAPR - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, in particular to an Orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) signal peak-to-average power ratio (Peak-to ‑average power ratio, PAPR) suppression method. A PTS method for reducing the PAPR of SCMA system, which uses the multiple access transmission characteristics of SCMA to perform phase rotation on time-domain resource blocks in the two dimensions of user and frequency point, and uses the sparseness of the codebook to perform a small number of low-dimensional IFFT operations More candidate sequences can be obtained.

Description

A PTS Method for Reducing PAPR of SCMA System

technical field

The invention belongs to the technical field of wireless communication, and in particular relates to a peak-to-average power ratio (Peak-to-average) signal peak-to-average power ratio (Peak-to-average) of a sparse code division multiple access (Sparse Code Multiple Access, SCMA) system (Orthogonal Frequency Division Multiplexing, OFDM) power ratio, PAPR) inhibition method.

Background technique

With the commercialization of the LTE system, in the face of the ever-increasing number of users, ubiquitous network access, and higher communication quality requirements, people began to study 5G.

The SCMA system has become a new research hotspot because of its better link transmission quality and doubled system capacity than the LTE system. However, like other OFDM-based systems, the OFDM-based SCMA system has a peak-to-average ratio (PAPR) problem, which causes nonlinear distortion of the signal after the power amplifier, which is too practical.

In the SCMA system, due to the large number of user signals, the defect of high PAPR is more obvious. Therefore, according to the signal transmission mode of the SCMA system, it is necessary to reduce the PAPR of the system. The traditional Partial Transmit Sequence (PTS) technology can still be applied to reduce the PAPR of OFDM signals in SCMA systems, but the computational complexity of this method is high, which affects the practical application of this method.

Contents of the invention

In order to solve the deficiencies of the prior art, the present invention combines the characteristics of the SCMA system to provide a PTS method for reducing the PAPR of the SCMA system. This method utilizes the multiple access transmission characteristics of SCMA to optimize the time domain resources in the two dimensions of users and frequency points. Blocks are phase rotated, and using the sparseness of the codebook, more candidate sequences can be obtained through a small number of low-dimensional IFFT operations.

A kind of PTS method that reduces SCMA system PAPR, concrete method is as follows:

S1. Process the frequency domain signal at the sending end, specifically:

S11. After mapping the signal bit stream of the i-th layer with a length of N/2 through the codebook E, a frequency-domain sequence _Xi with a length of N is obtained, where i=1, 2, 3, ..., J, J represent the signal number of bitstream layers;

S12. Interleave and divide X _i described in S11 into W frequency-domain sub-blocks with a length of N Wherein, W represents the number of non-zero elements in each codeword, w=1, 2, 3,..., W;

S13, remove the above mentioned in S12 After the zero element in the short sequence of length N/4 frequency domain is obtained

S2. Process the time-domain signal at the transmitting end to obtain a time-domain candidate sequence, specifically:

S22. According to the factor diagram of SCMA, the obtained J*W time-domain short sequences are obtained Combining to obtain K time-domain short sequences Among them, K represents the number of frequency points in the factor diagram, k=1, 2, 3,..., K;

W _k-1 = [1,exp(j2π(k-1)/N),...,exp(j2π(k-1)(N-1)/N)];

S25. Sub-blocks in the time domain Obtain alternative signals in time domain by superposition which is Thus, a plurality of different time-domain candidate signals can be obtained;

S3. Select the signal with the smallest PAPR from the candidate signals in the time domain, add a cyclic prefix after the parallel-to-serial conversion, and transmit through the D/A conversion unit, the HPA unit, and the up-conversion unit;

S4. Process the received time-domain signal at the receiving end to obtain a frequency-domain signal Y;

S5. Process the frequency domain signal Y described in S42 at the receiving end, specifically as follows:

S51. Interleaving and dividing the frequency domain signal Y described in S4 into K frequency domain sub-blocks Y _k ;

S52. Multiply each frequency-domain sub-block by a phase factor and superimpose to obtain a frequency-domain signal

S53. Rotate the codebook E described in S1 to obtain a new codebook

S6, the frequency domain signal obtained in S52 and the codebook E obtained in S53 are input to the MPA receiver, and finally the corresponding transmission signal of each layer is output.

Further, the frequency-domain signal Y obtained in S4 is specifically:

S41. After the received signal is down-converted and A/D conversion unit, the cyclic prefix is removed, and the time-domain signal y is obtained after serial-to-parallel conversion;

S42. Perform an FFT operation on the time-domain signal y described in S41 to obtain a frequency-domain signal Y.

The beneficial effects of the present invention are:

The present invention is applied in the 5G SCMA system, which can reduce the PAPR of the OFDM signal, fully utilize the multiple access transmission characteristics and codebook sparsity of the SCMA system, and perform phase rotation on the time domain resource block in the two dimensions of user and frequency point, More time-domain candidate signals are obtained through low-dimensional IFFT operation, which significantly reduces the PAPR of OFDM signals, and the complexity of the sending end is low.

The receiving end uses the codebook rotation to obtain a new codebook, which is used as the input of the MPA receiver to effectively recover the original transmitted signal.

Description of drawings

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

Figure 2 is the factor diagram of SCMA.

FIG. 3 is a flow chart of receiving end processing in the present invention.

Fig. 4 is a specific processing flowchart of the present invention.

Figure 5 is the PAPR performance curve.

Detailed ways

Introduce the specific embodiment of the present invention below in conjunction with accompanying drawing:

In this embodiment, the Matlab simulation platform is used for experiments, and the system parameters are as follows: the number of subcarriers is N=256, the number of layers J=6, the number of available frequency points K=4, the overload rate is 150%, and the phase rotation factor P _1,j , P _{2, k} ∈ [±1], the number of simulations is 105, and the codebook used is shown in Table 1:

Table 1 4*6 codebook set

Sender processing:

The binary bit stream with a length of 128 in each layer is mapped into a complex signal sequence with a length of 256 through its respective codebook, and these signal sequences are interleaved and segmented to obtain 12 subsequences with a length of 256, and then these subsequences are dezeroed to do 64-point IFFT to obtain short signals in the time domain.

Phase rotation of the time-domain signal produces candidate sequences.

After multiplying the time-domain sub-sequences of each layer by the phase factor P _1,j , these rotated sub-sequences are combined according to the SCMA factor diagram to obtain 4 signal sub-blocks with a length of 64, and then these time-domain sub-blocks are processed again The phase rotation of P _2,k , according to the IFFT property, obtains 4 sub-blocks with a length of 256, and finally adds these sub-blocks to obtain the time-domain candidate sequence.

Calculate the PAPR of each candidate sequence and select the smallest one.

Receiver processing:

After the received signal is down-converted and A/D conversion unit, the cyclic prefix is removed, and then the time-domain signal is obtained through serial-to-parallel conversion, and then the time-domain signal is subjected to FFT operation to obtain the frequency-domain signal Y.

The frequency domain signal Y is interleaved and divided into 4 frequency domain sub-blocks Y _k . Multiply the phase factor P _2,k for each frequency domain sub-block and then superimpose them to obtain the frequency domain signal Rotate the original codebook group by P _1,j to obtain a new codebook group

frequency domain signal and the new codebook set Input to the MPA receiver, and finally output the corresponding transmission signal of each layer.

The simulation test is carried out by adopting the method of the present invention. The PAPR performance of the method is compared with conventional PTS (including adjacent, random, interleaved partitions). As shown in Figure 5, the PAPR suppression performance of the present invention is similar to that of traditional PTS (random segmentation mode), and is better than the PAPR suppression performance of traditional PTS (interleaved or adjacent mode), yet, as shown in Table 2, the same In the case of alternative sequences, the number of complex multiplications and complex additions required by the present invention is much smaller than that of the traditional PTS method.

Table 2 Comparison of main sender complexity

Claims (1)

1. a kind of PTS method that reduces SCMA system PAPR is characterized in that, comprises the following steps: S1. Process the frequency domain signal at the sending end, specifically: S11. After mapping the signal bit stream of the i-th layer with a length of N/2 through the codebook E, a frequency-domain sequence _Xi with a length of N is obtained, where i=1, 2, 3, ..., J, J represent the signal number of bitstream layers; S12. Interleave and divide X _i described in S11 into W frequency-domain sub-blocks with a length of N Wherein, W represents the number of non-zero elements in each codeword; S13, remove the above mentioned in S12 After the zero element in the short sequence of length N/4 frequency domain is obtained S14, described in S13 Perform N/4-point IFFT operation to obtain short sequence in time domain which is S2. Process the time-domain signal at the transmitting end to obtain a time-domain candidate sequence, specifically: S21, the S14 said Multiply the phase rotation factor p _1,i to obtain the time-domain short sequence after phase rotation, namely Among them, P _1,i ∈{1,-1}; S22. According to the factor diagram of SCMA, the obtained J*W time-domain short sequences are obtained Combining to obtain K time-domain short sequences Among them, K represents the number of frequency points in the factor diagram, k=1, 2, 3,..., K; S23, the time domain short sequence Multiply the phase rotation factor p _2,k to obtain the time domain subsequence which is Among them, P _2,k ∈{1,-1}; S24. According to the nature of the IFFT operation, the time-domain short sequence A time-domain sub-block of length N is obtained after transformation which is in, W _k-1 = [1,exp(j2π(k-1)/N),...,exp(j2π(k-1)(N-1)/N)]; S25. Sub-blocks in the time domain Obtain alternative signals in time domain by superposition which is Thus, a plurality of different time-domain candidate signals can be obtained; S3. Select the signal with the smallest PAPR from the candidate signals in the time domain, add a cyclic prefix after the parallel-to-serial conversion, and transmit through the D/A conversion unit, the HPA unit, and the up-conversion unit; S4. Process the received time-domain signal at the receiving end to obtain a frequency-domain signal Y, specifically: S41. After the received signal is down-converted and A/D conversion unit, the cyclic prefix is removed, and the time-domain signal y is obtained after serial-to-parallel conversion; S42. Perform an FFT operation on the time-domain signal y described in S41 to obtain a frequency-domain signal Y; S5. Process the frequency domain signal Y described in S42 at the receiving end, specifically as follows: S51. Interleaving and dividing the frequency domain signal Y described in S4 into K frequency domain sub-blocks Y _k ; S52. Multiply each frequency domain sub-block by a phase rotation factor and then superimpose them to obtain a frequency domain signal S53. Rotate the codebook E described in S11 to obtain a new codebook S6, the frequency domain signal obtained in S52 and the codebook obtained in S53 Input to the MPA receiver, and finally output the corresponding transmission signal of each layer.