CN113225292B - A Method for Reducing OFDM Peak-to-Average Ratio Using Pilot Blocking - Google Patents

Abstract

The invention provides a method for reducing OFDM peak-to-average ratio by pilot frequency block, which can effectively reduce the peak-to-average ratio of generated signals by dividing data and pilot frequency block and rotating phase, does not influence resource allocation, has no conflict with the existing system, does not increase extra devices, and is simple to realize. The invention does not need to change the existing communication system and standard, the transmitting end only needs to add simple extra calculation, and the receiving end does not need to add any extra processing, thus being applicable to OFDM system, FBMC system or GDMC system.

Description

A Method for Reducing OFDM Peak-to-Average Ratio Using Pilot Blocking

technical field

The invention relates to a transmitter technology suitable for OFDM (Orthogonal Frequency Division Multiplexing), which can reduce the Peak to Average Power Ratio (PAPR) of a transmitted signal, and belongs to the field of signal processing in a mobile communication system.

Background technique

At present, the standardization work of the fifth generation mobile communication system (5G) has been completed, and large-scale commercial use is starting. 5G still uses OFDM-based multi-carrier technology on the air interface. However, unlike the fourth generation mobile communication system (4G), since 5G supports rich service scenarios, each service scenario has different requirements for the bandwidth or interval of subcarriers. According to 5G technical specifications 3GPP TS 38.211 (V15.2.0) and 3GPP TS 38.212 (V15.2.0), the bandwidth of sub-carriers will be ²ⁿ multiples of 15kHz, such as: 15kHz, 30kHz, 60kHz, etc., while 4G only uses 15kHz A subcarrier spacing. When the carrier frequency is below 6GHz (FR1 band), the subcarrier bandwidth is 15kHz, 30kHz and 60kHz, and the signal bandwidth is up to 100MHz; while above 6GHz (FR2 band), the subcarrier bandwidth is 60kHz, 120kHz and 240kHz, and the signal bandwidth is up to 400MHz. .

5G supports up to 4096 subcarriers. The time domain signal of these subcarriers after inverse discrete Fourier transform (IDFT) presents a Gaussian distribution, and the peak-to-average power ratio (PAPR) of the signal is very large, which reduces the efficiency of the power amplifier (PA). In particular, the user end is unlikely to use expensive PA devices with better performance, so the problem of the peak-to-average ratio of the uplink transmission signal becomes particularly important. In order to reduce the peak-to-average ratio, 4G adopts DFT-s-OFDM technology in the uplink. However, this also brings problems such as inflexibility of uplink resource allocation. In view of these problems, the present invention proposes a peak-to-average ratio reduction method suitable for OFDM. By dividing the data and pilot frequency into blocks and rotating the phase, the method can effectively reduce the peak-to-average ratio of the generated signal, does not affect resource allocation, has no conflict with the existing system, does not add additional devices, and is simple to implement.

SUMMARY OF THE INVENTION

Technical problem: The purpose of the present invention is to reduce the peak-to-average ratio of the signal and improve the PA efficiency of the transmitting end by dividing the data and pilot frequency into blocks and rotating the phase for OFDM, and further provides a fast, reliable and low-complexity implementation. , A transmission method suitable for both OFDM and other multi-carrier technologies.

Technical scheme: in order to achieve the above object, the present invention adopts the following technical scheme:

Step 1) The transmitting end divides the N subcarriers of an OFDM symbol into M parts equally in the frequency domain, where 1≤M≤N and M is divisible by N;

和

表示第m个部分中的导频和数据；Step 2) respectively take N-dimensional vectors

and

represents the pilot and data in the mth part;

和

进行N点的离散傅里叶反变换(IDFT)，得到长度为N个采样的时域信号向量

和

并通过相加得到x_m，即

Step 3) for each part separately

and

Perform N-point inverse discrete Fourier transform (IDFT) to obtain a time-domain signal vector with a length of N samples

and

and get x _m by adding, i.e.

计算第i个候选序列

的值，共得到Q个候选序列；Step 4) Select a group

Calculate the ith candidate sequence

, a total of Q candidate sequences are obtained;

Step 5) Among the Q candidate sequences, find the sequence with the smallest PAPR value, and record its weight as

计算第i个候选序列

的值，共得到Q个候选序列；Step 6) Select a group

Calculate the ith candidate sequence

, a total of Q candidate sequences are obtained;

Step 7) Among the Q candidate sequences, find the sequence with the smallest PAPR value and send it directly as the sending sequence.

表示旋转因子，取值为集合

中的任一元素。由于b₀i通常设为1，所以共有Q＝W^M-1个候选序列。in,

Represents a twiddle factor, the value is a set

any element in . Since b ₀ i is usually set to 1, there are Q=W ^M-1 candidate sequences in total.

beneficial effect

1. The peak-to-average ratio reduction method of the present invention can be applied to the uplink and downlink of a multi-carrier modulation system.

2. This method does not need to change the existing communication system and standard, the sender only needs to add a simple extra calculation, and the receiver does not need to add any additional processing.

3. In addition to OFDM, new waveforms suitable for next-generation communication systems include filter bank multi-carrier (FBMC), generalized frequency division multiplexing (GDMC), etc. The peak-to-average ratio reduction method of the present invention is also applicable to these new waveform techniques.

Description of drawings

Fig. 1 is the principle diagram of the present invention;

Figure 2 shows the PAPR simulation results.

Detailed ways

The specific embodiments of the present invention will be described below with reference to the accompanying drawings, so that those skilled in the art can better understand the present invention. It should be noted that, in the following description, since the detailed description of some known technologies and functions may dilute the content of the present invention, these descriptions will be omitted here.

Consider an OFDM system, there are N subcarriers in total, each subcarrier bandwidth is Δf, and the total bandwidth is S=NΔf. Suppose X=[X(0), X(1),, X(N-1)] is the symbol vector to be transmitted, where X(k) represents the QPSK or QAM modulated symbol transmitted on the kth subcarrier . For channel estimation, pilot (Pilot) needs to be transmitted together with data. Practical systems, such as 5G, typically employ comb-type pilots. At this time, N _p pilots {P(m); 0≤m≤N _p -1} are uniformly inserted into X, and the occupied positions can be expressed as {k=mD _f ; 0≤m≤N _p -1}. Wherein, D _f =N/N _p represents the pilot interval, which is an integer. Therefore, the symbols transmitted on each subcarrier can finally be expressed as:

表示包含所有导频位置的集合。频域信号X经过IDFT变换后得到时域信号x，其采样周期为T＝1/S。在发送前，每个OFDM符号还需加上G个采样的循环前缀(CP)。为了去除符号间干扰。CP的长度需要大于信道的最大时延扩展τ_max，即此时GT>τ_max。所以，根据采样定理，导频间隔需满足：Wherein, D(k) represents the data symbol modulated onto the kth subcarrier;

Represents a set containing all pilot positions. After the frequency domain signal X is transformed by IDFT, the time domain signal x is obtained, and its sampling period is T=1/S. Before sending, each OFDM symbol also needs to add a cyclic prefix (CP) of G samples. To remove intersymbol interference. The length of the CP needs to be greater than the maximum delay extension τ _max of the channel, that is, GT>τ _max at this time. Therefore, according to the sampling theorem, the pilot interval needs to satisfy:

接下来，再将X_m分为导频部分

和数据部分

分别包含第m个子块在导频子载波和数据子载波上的符号，其它位置为零。比如，第0个子块的导频部分

可以表示为：In the proposed method, the transmitter first divides X into equal M discrete sub-blocks, where 1≤M≤N and M is divisible by N. The mth sub-block is represented by X _m =[X _m (0), X _m (1),, X _m (N-1)], and satisfies

Next, divide X _m into pilot parts

and data section

It contains the symbols of the mth sub-block on the pilot sub-carrier and the data sub-carrier, respectively, and the other positions are zero. For example, the pilot part of the 0th sub-block

It can be expressed as:

可以表示为：The data part of the 0th sub-block

It can be expressed as:

和

做N点的IDFT得到各自的时域信号

和

以及它们相加的和

其中0≤m≤M-1。separately for each

and

Do the IDFT of N points to get the respective time domain signals

and

and their sum

where 0≤m≤M-1.

First calculate the ith candidate sequence, namely:

表示第i个候选序列对第m个子块旋转的角度，取值为集合B中的任一元素。考虑到计算复杂度等问题，假设集合有W个元素，可将集合B设为：Among them, the subscript 1 represents the first selection.

Indicates the rotation angle of the i-th candidate sequence to the m-th sub-block, and takes the value of any element in the set B. Considering the computational complexity and other issues, assuming that the set has W elements, set B can be set as:

设为1，不改变最终结果，所以共有不相同的候选序列数为：due to the

Setting it to 1 does not change the final result, so the total number of different candidate sequences is:

Q=W ^M-1 [Formula 7]

即：Next, calculate the PAPR of each candidate sequence separately, find the sequence with the smallest PAPR value, and record its weight as

which is:

Then, keep the weight of the data part unchanged, and change the weight of the pilot part to get:

表示第i个候选序列对第m个导频部分旋转的角度，取值为与第一次选择相同的集合B中的任一元素。同理，计算每个候选序列的PAPR，并记录使PAPR值最小的权值为

Among them, the subscript 2 represents the second selection.

Indicates the rotation angle of the i-th candidate sequence to the m-th pilot part, and the value is any element in the same set B as the first selection. Similarly, calculate the PAPR of each candidate sequence, and record the weight value that minimizes the PAPR value.

Finally, choose

For the sending sequence, add the CP and send it out. The combination of weights used by the pilot and data or the sequence number of the candidate sequence can be told to the receiver through control signaling. Since the receiver knows the set B, the original signal when the phase is not rotated can be accurately recovered through this signaling.

Figure 2 presents the cumulative distribution function (CCDF) computer simulation results of PAPR. In the simulation, it is assumed that OFDM has 1024 subcarriers, adopts QPSK modulation, 128 pilots are uniformly inserted into the data sequence, M=2 and W=4. It can be seen from the simulation results that the proposed method greatly reduces the peak-to-average ratio compared to the traditional system (the curve marked as OFDM).

According to the above description, a method for reducing the peak-to-average ratio of an OFDM symbol by using pilot frequency blocks can be obtained. The implementation steps are as follows:

Step 1) The transmitting end divides the N subcarriers of an OFDM symbol into M parts equally in the frequency domain, where 1≤M≤N and M is divisible by N;

和

表示第m个部分中的导频和数据；Step 2) respectively take N-dimensional vectors

and

represents the pilot and data in the mth part;

和

进行N点的离散傅里叶反变换(IDFT)，得到长度为N个采样的时域信号向量

和

并通过相加得到x_m，即

Step 3) for each part separately

and

Perform N-point inverse discrete Fourier transform (IDFT) to obtain a time-domain signal vector with a length of N samples

and

and get x _m by adding, i.e.

计算第i个候选序列

的值，共得到Q个候选序列；Step 4) Select a group

Calculate the ith candidate sequence

, a total of Q candidate sequences are obtained;

Step 5) Among the Q candidate sequences, find the sequence with the smallest PAPR value, and record its weight as

计算第i个候选序列

的值，共得到Q个候选序列；Step 6) Select a group

Calculate the ith candidate sequence

, a total of Q candidate sequences are obtained;

Step 7) Among the Q candidate sequences, find the sequence with the smallest PAPR value and send it directly as the sending sequence.

表示旋转因子，取值为集合

中的任一元素。由于

通常设为1，所以共有Q＝W^M-1个候选序列。in,

Represents a twiddle factor, the value is a set

any element in . because

Usually set to 1, so there are Q=W ^M-1 candidate sequences.

Even the implementation method of the present invention described above, it should be pointed out: for those skilled in the art, under the premise of not departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as protection scope of the present invention.

Claims (3)

1. A method for reducing OFDM peak-to-average ratio by pilot frequency block is characterized by comprising the following steps:

step 1: the transmitting end equally divides N sub-carriers of OFDM into M discontinuous sub-blocks X in frequency domain_mWherein M is more than or equal to 1 and less than or equal to N, and M can be evenly divided by N, and M is more than or equal to 0 and less than or equal to M-1;

step 2: mixing X_mDivision into pilot parts

And a data part

Respectively containing symbols of the mth sub-block on a pilot frequency sub-carrier and a data sub-carrier, and the other positions are zero;

and step 3: to pair

And

respectively carrying out N-point inverse discrete Fourier transform to obtain time domain signal vectors with the length of N samples

And

and calculate

And 4, step 4: for x_mPerforming phase rotation for several times to obtain several candidate sequences, and finding the candidate sequence with the minimum PAPR value as the transmission sequence to directly transmitAnd (4) removing.

2. The method as claimed in claim 1, wherein the step 4 comprises the following steps:

step 4.1: selecting a group

Computing the ith candidate sequence

To obtain Q candidate sequences; wherein,

representing the angle of the rotation of the ith candidate sequence to the mth sub-block, and taking the value as a set

W is a natural number;

step 4.2: in Q candidate sequences, the sequence with the minimum PAPR value is searched, and the weight value is recorded as

Step 4.3: selecting a group

Computing the ith candidate sequence

To obtain Q candidate sequences;

step 4.4: and (4.3) searching the sequence with the minimum PAPR value as a sending sequence to be directly sent out from the Q candidate sequences obtained in the step (4.3).

3. The method of claim 1 for reducing peak-to-average power ratio of OFDM using pilot blockingIs characterized in that

Set to 1, then Q ═ W^M-1。

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