A nonlinear OFDM information transmission method and system based on frequency domain symbol block modulation

Abstract

The present invention discloses a nonlinear OFDM information transmission method and system based on frequency domain symbol block modulation. The information sending part uses frequency domain symbol blocks to carry bit information. The relative amplitude and phase state of two symbols in the frequency domain symbol block are used to load bit information and meet power constraints. The frequency domain symbol block is modulated by OFDM to form an OFDM time domain signal and performs time domain upsampling, iterative clipping and filtering, and digital pre-distortion to reduce the interference of the nonlinear power amplifier output signal to adjacent channels; the information receiving part uses the frequency domain symbol block constraint and signal distortion characteristics to perform nonlinear signal reconstruction on the peak distorted received signal, and then performs OFDM demodulation, detection and frequency domain symbol block demapping on the reconstructed signal to restore the transmitted bit information. The present invention can improve the adjacent channel interference performance and information transmission performance of the power amplifier under nonlinear conditions, reduce the power back-off requirements of the power amplifier, and thus improve the energy efficiency of the OFDM system.

Description

Technical Field

[0001] The present invention belongs to the technical field of nonlinear wireless communication, and relates to a nonlinear orthogonal frequency division multiplexing (OFDM) information transmission method and system based on frequency domain symbol block modulation. Background Art

[0002] With the rapid development of wireless communication technology, the energy consumption of massive communication base stations and devices will increase greatly in the future. In order to comply with the sustainable development concept of green energy conservation, energy efficiency is crucial in the research of future wireless communication networks. The energy consumption of wireless communication systems is mainly generated by communication base stations, and the power amplifier is the most energy-consuming device in the base station, accounting for more than half of the energy consumption of the base station. Therefore, the key to high-efficiency wireless communication networks lies in improving the power efficiency of power amplifiers.

[0003] However, for power amplifiers, there is usually an inherent contradiction between power efficiency and traditional communication performance. High power efficiency often means stronger power amplifier nonlinearity. On the one hand, this nonlinearity will cause spectrum leakage in adjacent channels at the transmitter, seriously interfering with RF activities based on adjacent channels; on the other hand, it will seriously distort the modulated signal and deteriorate the information demodulation and recovery performance at the receiver. This effect is more prominent in wireless communications based on high peak-to-average ratio modulation signal transmission such as orthogonal frequency division multiplexing. Therefore, traditional OFDM transmission requires higher power back-off to ensure high linearity of the power amplifier output, but the power efficiency is extremely low.

[0004] In order to achieve good information transmission performance in the high power efficiency area, the transmitter power amplifier linearization technology, peak-to-average ratio reduction technology, nonlinear receiving technology, etc. have been developed successively. However, the power amplifier linearization technology is still limited by the high peak-to-average ratio characteristics of OFDM, the peak-to-average ratio reduction technology usually comes at the cost of signal distortion or information rate reduction, and the nonlinear receiving technology can improve the information demodulation performance of the receiving end, but it will produce bad adjacent channel interference at the transmitting end. Summary of the invention

[0005] Purpose of the invention: In view of the problems in the prior art, the present invention aims to provide a method, device and system related to nonlinear OFDM information processing based on frequency domain symbol block modulation, so as to achieve low adjacent channel interference performance and error-free information transmission under the nonlinear state of the power amplifier.

[0006] Technical solution: To achieve the above-mentioned invention object, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a nonlinear OFDM information transmission method based on frequency domain symbol block modulation, comprising the following steps:

[0008] Frequency domain symbol block modulation is used to transmit bit information mapping. Each frequency domain symbol block contains two frequency domain symbols. The relative amplitude and phase state of the two frequency domain symbols in the frequency domain symbol block are used to load the bit information. The two frequency domain symbols in the modulated frequency domain symbol block meet the set power constraint.

[0009] The mapped frequency domain signal is modulated by OFDM to form an OFDM time domain signal, and two frequency domain symbols in the frequency domain symbol block are respectively loaded onto two pre-set subcarriers;

[0010] The OFDM time domain signal is subjected to time domain upsampling and iterative clipping and filtering (CAF) to obtain a clipped signal;

[0011] The clipped signal is subjected to digital pre-distortion (DPD) to correct the linearity of the output signal of the nonlinear power amplifier; the digitally pre-distorted signal is passed through the nonlinear power amplifier to form a transmission signal.

[0012] Based on the nonlinear OFDM information transmission method described in the first aspect, for a power amplifier working in a nonlinear region, based on frequency domain symbol block modulation, iterative CAF and digital predistortion, the RF transmission signal output by the power amplifier nonlinearly has a low adjacent channel leakage ratio (ACLR). Loading the bit information stream into the frequency domain symbol block with intrinsic constraints can achieve error-free information recovery at the receiving end under clipping and power amplifier nonlinearity.

[0013] In a second aspect, the present invention provides a method for receiving nonlinear OFDM information based on frequency domain symbol block modulation, comprising the following steps:

[0014] Acquire a received signal, where the received signal is a peak distorted received signal obtained by frequency domain equalization, phase windowing and time domain downsampling of a transmitted signal captured by a wireless channel;

[0015] The received signal is nonlinearly reconstructed using the frequency domain symbol block constraint and the signal distortion characteristic, wherein the nonlinear signal reconstruction includes frequency domain reconstruction and time domain reconstruction and is implemented through time-frequency domain reconstruction iteration; the frequency domain reconstruction is performed based on two frequency domain symbols in the frequency domain symbol block satisfying the set power constraint, and the time domain reconstruction is performed based on the distortion characteristic of the clipping signal;

[0016] The reconstructed signal is demodulated by OFDM to obtain a frequency domain symbol block;

[0017] The relative amplitude and phase states of two frequency domain symbols within a frequency domain symbol block are demapped into bit information.

[0018] Based on the nonlinear OFDM information receiving method described in the second aspect, the received signal is nonlinearly reconstructed in the time-frequency domain based on the frequency domain symbol block constraints and signal distortion characteristics, which can achieve error-free information recovery and support superior information transmission performance with high power efficiency.

[0019] In a third aspect, the present invention provides a nonlinear OFDM information transmission method based on frequency domain symbol block modulation, comprising the steps of the nonlinear OFDM information sending method described in the first aspect; and the steps of the nonlinear OFDM information receiving method described in the second aspect.

[0020] Based on the nonlinear OFDM information transmission method described in the third aspect, the adjacent channel interference problem caused by nonlinearity and the signal distortion problem are decoupled. The transmitter uses frequency domain symbol blocks to carry bit information, uses iterative CAF to reduce the peak-to-average ratio of OFDM time domain signals, and combines level digital pre-distortion to reduce the interference of the nonlinear power amplifier output signal to adjacent channels; the receiver uses a nonlinear signal reconstruction method based on frequency domain symbol block constraints to reconstruct the distorted signal, then performs OFDM demodulation, frequency domain symbol block demapping, and restores the transmitted bit information. Low adjacent channel interference performance and error-free information transmission in the nonlinear state of the power amplifier are achieved.

[0021] In a fourth aspect, the present invention provides a nonlinear OFDM information sending device based on frequency domain symbol block modulation, comprising:

[0022] A frequency domain symbol block modulation module is used to send bit information mapping, each frequency domain symbol block contains two frequency domain symbols, the relative amplitude and phase state of the two frequency domain symbols in the frequency domain symbol block are used to load the bit information, and the two frequency domain symbols in the frequency domain symbol block after modulation meet the set power constraint;

[0023] An OFDM modulation module is used to convert the mapped frequency domain signal into an OFDM time domain signal, and two frequency domain symbols in the frequency domain symbol block are respectively loaded onto two preset subcarriers;

[0024] The time domain upsampling and CAF module is used to perform time domain upsampling, iterative clipping and filtering on the OFDM time domain signal to obtain a clipped signal;

[0025] A digital pre-distortion module is used to correct the linearity of the output signal of the nonlinear power amplifier;

[0026] The nonlinear power amplifier is used to perform nonlinear power amplification on the time domain signal to form a transmission signal.

[0027] In a fifth aspect, the present invention provides a nonlinear OFDM information receiving device based on frequency domain symbol block modulation, comprising the following steps:

[0028] The signal receiving and processing module is used to obtain a peak distorted receiving signal by performing frequency domain equalization, phase windowing, time domain downsampling and matched filtering on the transmission signal captured by the wireless channel;

[0029] A signal reconstruction module, used to perform nonlinear signal reconstruction on the received signal by using the frequency domain symbol block constraint and the signal distortion characteristic, wherein the nonlinear signal reconstruction includes frequency domain reconstruction and time domain reconstruction, and is implemented by iterative reconstruction in the time and frequency domains; the frequency domain reconstruction is performed based on two frequency domain symbols in the frequency domain symbol block satisfying a set power constraint, and the time domain reconstruction is performed based on the distortion characteristic of the clipping signal;

[0030] OFDM demodulation module, used for demodulating the reconstructed signal through OFDM to obtain frequency domain symbol blocks;

[0031] The frequency domain symbol block modulation and demapping module is used to demap the relative amplitude and phase state of two frequency domain symbols in the frequency domain symbol block into bit information.

[0032] In a sixth aspect, the present invention provides a nonlinear OFDM information transmission system based on frequency domain symbol block modulation, comprising the transmitting device described in the fourth aspect and the receiving device described in the fifth aspect.

[0033] In a seventh aspect, the present invention provides a computer program product, comprising a computer program / instruction, which, when executed by a processor, implements the steps of the method described in the first aspect and the second aspect.

[0034] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: (1) The OFDM nonlinear information transmission method and system based on frequency domain symbol block modulation proposed in the present invention has the advantage of being able to decouple the adjacent channel interference problem and the nonlinear information transmission problem, and to process them separately at the transmitting end and the receiving end. The transmitting end improves the ACLR performance based on iterative CAF and digital predistortion, and the receiving end improves the information transmission performance based on the constraint characteristics of frequency domain symbol block modulation. (2) The frequency domain symbol block modulation scheme with intrinsic symbol power constraint proposed in the present invention, and the reconstruction method of nonlinear distorted received signals based on symbol power constraint, have the advantage of being able to achieve error-free information recovery at the receiver side under clipping and power amplifier nonlinearity, and support superior information transmission performance under high power efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a nonlinear OFDM information sending method based on frequency domain symbol block modulation according to an embodiment of the present invention.

[0036] Figure 2 It is a flow chart of a nonlinear OFDM information receiving method based on frequency domain symbol block modulation according to an embodiment of the present invention.

[0037] Figure 3 It is a flowchart of a transmitter and a receiver of a nonlinear OFDM information transmission method based on frequency domain symbol block modulation according to an embodiment of the present invention.

[0038] Figure 4 It is a flowchart of nonlinear OFDM signal reconstruction in an embodiment of the present invention.

[0039] Figure 5 1 is a comparison diagram of transmitter performance in an embodiment of the present invention, wherein (a) is the complementary cumulative distribution function of the peak-to-average ratio of the power amplifier input signal, and (b) is a comparison of the variation curves of the ACLR performance of the transmitted signal with the power amplifier input power back-off.

[0040] Figure 6 It is a nonlinear signal reconstruction convergence curve diagram in an embodiment of the present invention, showing the change of the received error vector magnitude (Error Vector Magnitude, EVM) with the number of reconstruction iterations.

[0041] Figure 7 2 is a comparison diagram of the information transmission performance of the receiver in the embodiment of the present invention, wherein (a) and (b) are comparison diagrams of the EVM and bit error rate (BER) performance of the reconstructed and non-reconstructed processing under different input power back-offs, and (c) and (d) are comparison diagrams of the EVM and BER performance of the reconstructed and non-reconstructed processing under different signal-to-noise ratios. DETAILED DESCRIPTION

[0042] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0043] Figure 1 is a flow chart of a nonlinear OFDM information sending method based on frequency domain symbol block modulation disclosed in an embodiment of the present invention, such as Figure 1 As shown, the nonlinear OFDM information sending method includes the following steps:

[0044] Step S101, frequency domain symbol block modulation: frequency domain symbol block modulation is used to send bit information mapping, each frequency domain symbol block contains two frequency domain symbols, the relative amplitude and phase state of the two frequency domain symbols in the frequency domain symbol block are used to load the bit information, and the two frequency domain symbols in the modulated frequency domain symbol block meet the set power constraint.

[0045] In this step, the bit information stream is loaded into a frequency domain modulated signal composed of frequency domain symbol blocks with intrinsic constraints. In one possible implementation, the power difference between two frequency domain symbols is , phase and And the phase difference For bit information loading, power and Set to a fixed value as a frequency domain symbol block constraint.

[0046] For example, two frequency domain symbols and The amplitude and phase of are expressed as:

[0047]

[0048] and Meeting power constraints: .

[0049] Step S102, OFDM modulation: the mapped frequency domain signal is subjected to OFDM modulation to form an OFDM time domain signal, and two frequency domain symbols in the frequency domain symbol block are respectively loaded onto two preset subcarriers.

[0050] This step implements orthogonal frequency division multiplexing transmission, converting the frequency domain modulated signal transmitted based on multiple subcarriers into a time domain modulated signal.

[0051] Exemplarily, in OFDM modulation, the OFDM time domain symbol is expressed as:

[0052]

[0053] in N is the number of frequency domain symbol blocks contained in an OFDM symbol, and the OFDM symbol length is 2 N , n is the time domain index, k is the frequency domain symbol block index, and Respectively represent k The subcarrier index values ​​of the two frequency domain symbols in the OFDM symbol within the frequency domain symbol block, j Represents the imaginary part of a complex number.

[0054] Step S103, time domain upsampling and CAF: the OFDM time domain signal is subjected to time domain upsampling, iterative clipping and filtering to obtain a clipped signal.

[0055] In this step, the spectrum leakage caused by nonlinearity is observed and the peak-to-average power ratio (PAPR) of the time-domain modulated signal is reduced. In one possible implementation, a multi-stage clipping rate and filter configuration is used, and the time-domain modulated signal is first clipped by a clipper with a lower clipping rate, then upsampled and filtered simultaneously by a root raised cosine pulse shaping filter, and then iterative CAF processing is performed using a clipper with a higher clipping rate and a low-pass filter.

[0056] Step S104, digital predistortion: the clipping signal is subjected to digital predistortion to correct the linearity of the output signal of the nonlinear power amplifier and reduce the ACLR of the nonlinear region of the power amplifier; the digitally predistorted signal is passed through the nonlinear power amplifier to form a transmission signal.

[0057] In this step, digital predistortion includes amplitude predistortion and phase predistortion, and the predistorter parameter configuration is related to the nonlinear characteristics of the subsequent power amplifier.

[0058] In the nonlinear OFDM information sending method based on frequency domain symbol block modulation described in this embodiment, the power amplifier operates in a nonlinear region, and the transmitting end is based on frequency domain symbol block modulation, iterative CAF and digital predistortion, and the RF transmission signal output by the nonlinear power amplifier has a low ACLR.

[0059] Figure 2 is a flow chart of a nonlinear OFDM information receiving method based on frequency domain symbol block modulation disclosed in an embodiment of the present invention, such as Figure 2 As shown, the nonlinear OFDM information receiving method comprises the following steps:

[0060] Step S201, obtaining a received signal.

[0061] In this step, the received signal is the transmitted signal captured by the wireless channel, and the peak distorted received signal is obtained by frequency domain equalization, phase windowing and time domain downsampling. The signal reception processing part is realized by the existing technology, mainly including signal capture, channel estimation and channel equalization, phase windowing and downsampling processing.

[0062] Step S202, nonlinear signal reconstruction: nonlinear signal reconstruction is performed on the received signal using the frequency domain symbol block constraints and signal distortion characteristics. The nonlinear signal reconstruction includes frequency domain reconstruction and time domain reconstruction, and is implemented through time-frequency domain reconstruction iterations. The frequency domain reconstruction is performed based on two frequency domain symbols in the frequency domain symbol block satisfying the set power constraints, and the time domain reconstruction is performed based on the distortion characteristics of the clipping signal.

[0063] This step implements iterative reconstruction of the distorted received time domain signal in the time-frequency domain based on the intrinsic constraints and nonlinear distortion characteristics of the frequency domain symbol block. In one possible implementation, the frequency domain reconstruction first converts the time domain signal to the frequency domain using the fast Fourier transform, and then normalizes the power of each symbol block according to the received power of the frequency domain symbol block, so that the sum of the symbol power in each symbol block is equal, and then the frequency domain signal is reconverted to the time domain; the time domain reconstruction first estimates the amplitude distortion threshold of the received signal based on the known clipping rate, and then performs inverse clipping processing based on the threshold and the received time domain signal after frequency domain reconstruction; the transmitted time domain modulation signal is restored by iterative time-frequency domain reconstruction. Finally, the reconstructed time domain signal is converted to the frequency domain as the input of the signal detection to restore the original transmitted signal.

[0064] Step S203, OFDM demodulation: the reconstructed signal is subjected to OFDM demodulation to obtain a frequency domain symbol block.

[0065] Corresponding to the OFDM modulation in the sending method, exemplarily, the symbols in the receiving frequency domain symbol block and Reconstructing the time domain signal After Fourier transform, it is expressed as:

[0066]

[0067] Step S204, frequency domain symbol block modulation and demapping: demapping the relative amplitude and phase state of two frequency domain symbols in the frequency domain symbol block into bit information.

[0068] In the nonlinear OFDM information receiving method based on frequency domain symbol block modulation described in this embodiment, the distorted signal is reconstructed based on the intrinsic constraint characteristics of the frequency domain symbol block, and the information is demodulated based on the reconstructed received signal, thereby achieving error-free information transmission under nonlinear distortion.

[0069] The following example uses nonlinear OFDM information transmission based on 256 subcarriers to illustrate the effectiveness and superiority of the proposed method in adjacent channel interference suppression and nonlinear information transmission. First, in this example, the nonlinearity of the power amplifier is mainly characterized by the AM-AM effect and the AM-PM effect. The specific Saleh model is expressed as follows:

[0070]

[0071] in Input signal for the power amplifier, The output signal of the power amplifier is and They are and phase. , , and is the power amplifier Saleh model parameter. Exemplarily, the power amplifier model parameters and wireless transmission parameter configurations are shown in Table 1.

[0072]

[0073] Based on the above parameter configuration, a nonlinear OFDM information transmission method based on frequency domain symbol block modulation disclosed in an embodiment of the present invention is described in detail below.

[0074] First, the nonlinear OFDM information transmission part is used in the transmitter. Figure 3 The left side shows a flowchart of the implementation process of the low ACLR nonlinear OFDM information transmission method, which realizes the conversion from the bit information stream to the low ACLR RF signal, including the following steps:

[0075] Step S301, frequency domain symbol block modulation: two adjacent symbols in the frequency domain are taken as a frequency domain symbol block X. The bit information stream is mapped to the frequency domain symbol block X, which is expressed as:

[0076]

[0077] Where c is the transmitted bit vector, is the label function, which is the mapping of the bit information stream to the frequency domain symbol block. The complex signal of two symbols in the symbol block X is expressed as:

[0078]

[0079] in and are two frequency domain symbols in a symbol block, , , and Represents the frequency domain symbol and The relative state of , and Respectively and The phase sum, phase difference and power difference between are used to load bit information. Different parameter combinations represent different bit information streams. Frequency domain symbol block modulation maps bit information to frequency domain symbol amplitude and phase characterized by relative states. Represents the mth combination of three parameters. For a modulation order of 64, There are 64 states corresponding to 6 bits of information. For example, when the bit information stream is Mapping ,at this time . It remains fixed and unchanged as the constraint state of the frequency domain symbol block. Represents the frequency domain symbol and The total power of the symbol block is expressed as:

[0080]

[0081] Based on the method, bit information is loaded into a frequency domain symbol block with constraints.

[0082] Step S302, OFDM modulation: convert the symbol block into a multi-carrier time domain transmission signal. Assume that the number of OFDM subcarriers is 2 N , then an OFDM symbol contains at most N First, the serial input frequency domain symbol blocks are grouped, each group contains N A frequency domain symbol block, two frequency domain symbols in the symbol block are loaded onto two pre-set subcarriers, and then a time domain signal is obtained based on an inverse discrete Fourier transform. In this embodiment, two frequency domain symbols in the symbol block are loaded onto two adjacent subcarriers as an example. At this time, the first n The time domain signal is expressed as:

[0083]

[0084] Finally, the parallel time domain signals are converted to serial output.

[0085] Step S303, time domain upsampling and CAF. Clipping and filtering are used to reduce the peak-to-average ratio of the OFDM signal and suppress out-of-band leakage. At the same time, upsampling is used to observe the signal spectrum including out-of-band. First, the input high peak-to-average ratio OFDM time domain signal is clipped, and the clipped signal is expressed as:

[0086]

[0087] in is the clipping level. , then the signal amplitude at this moment is set to , Phase Remains unchanged if the time domain signal amplitude does not exceed , the original signal is kept. The clipping level is usually characterized by the clipping rate, expressed as:

[0088]

[0089] in It is expressed as the average power of the calculated signal. The lower the clipping rate, the lower the peak value of the signal after clipping, and the lower the peak-to-average ratio, but the difference with the original signal is also greater. At the same time, the nonlinearity of clipping leads to serious out-of-band leakage. The first clipping uses a clipping rate of 1.3 dB to obtain a lower peak-to-average ratio. Then, the clipping signal is upsampled and matched filtered. The matched filter uses a root raised cosine filter to filter out the out-of-band leakage caused by clipping. The present invention is demonstrated by taking the upsampling multiple of 4 and the raised cosine factor of 0.25 as an example. The matched filter output signal is expressed as:

[0090]

[0091] in represents the convolution operator, Represents the filter impulse response. Although the matched filter can suppress out-of-band leakage, it also increases the signal peak-to-average ratio. Then, iterative CAF is further used for clipping and filtering. Subsequently, a 2dB clipping rate and a FIR filter based on the Kaiser window function are used. The CAF is iterated twice and finally output by the filter. The output time domain signal is characterized as:

[0092]

[0093] The operator Represents iterative CAF processing. Time domain signal It has a lower peak-to-average ratio and out-of-band leakage, but is similar to the original time domain signal. In comparison, there is nonlinear distortion in amplitude and phase.

[0094] It should be noted that the filter used in this step is only an example. In some other embodiments, those skilled in the art can make a reasonable selection as needed.

[0095] Step S304, lightweight digital pre-distortion: generate the amplitude and phase inverse response of the power amplifier to suppress the ACLR of the nonlinear power amplifier output signal. In this example, a lightweight pre-distortion method characterized by Sigmoid nonlinearity is adopted. First, the Sigmoid nonlinear model is used to characterize the AM-AM effect of the power amplifier, which is characterized as:

[0096]

[0097] in is the power amplifier nonlinear gain, is the linear gain of the power amplifier, Input signal power to the power amplifier. and Characterize the nonlinearity of the power amplifier, respectively:

[0098]

[0099] in and is the input saturation power and input 1dB compression point power of the power amplifier. For digital predistortion based on Sigmoid nonlinear characterization, the input signal With output signal The relationship can be characterized as:

[0100]

[0101] According to the known input signal Solve the output signal amplitude in the above equation to perform amplitude predistortion. Then, based on the predistorted amplitude, perform phase predistortion. The phase of the predistorted output signal is expressed as:

[0102]

[0103] in To predistort the input signal The phase of is the estimated power amplifier phase offset, expressed as:

[0104]

[0105] in , and are the model parameters related to the AM-PM effect of the power amplifier, is the signal amplitude after amplitude predistortion The predistortion output signal is expressed as:

[0106]

[0107] In this embodiment, the iterative CAF method is used to greatly reduce the peak-to-average ratio of the OFDM signal, and the DPD based on the Sigmoid nonlinear characterization is proposed to improve the linearity of the power amplifier output. The combination of the two reduces the ACLR under the nonlinear state of the power amplifier. The advantage is that, under the premise of ensuring the ACLR performance, the transmitter based on CAF and DPD has a lower power back-off requirement and supports superior adjacent channel interference performance under high power efficiency. In some other embodiments, those skilled in the art can reasonably select a digital predistorter according to the specific power amplifier.

[0108] Step S305, nonlinear power amplification and transmission: The output time domain signal of the digital predistortion is input into the RF power amplifier after undergoing RF processes such as digital-to-analog conversion and up-conversion. This embodiment ignores the influence of other hardware damages and uses the predistorted output signal as the input signal of the power amplifier. The nonlinear power amplifier characterized by the aforementioned Saleh model, the output signal of the power amplifier is expressed as:

[0109]

[0110] Through the RF antenna, Output signal for power amplifier The phase of Sent into the wireless channel, sending the signal It has lower ACLR characteristics and less interference to adjacent channel-based communication activities, but has severe amplitude and phase nonlinear distortion.

[0111] Then, the nonlinear OFDM information receiving part is used in the receiver. Figure 3 The right side shows a flowchart of the implementation of the nonlinear OFDM information receiving method based on frequency domain symbol block constraints, which realizes the process of recovering the transmitted bit information stream from the received nonlinear signal, including the following steps:

[0112] Step S401, signal capture: first capture the transmitted signal from the wireless channel. Due to the multipath effect and noise of the wireless channel, the received signal captured by the receiving antenna Sending a signal There is a difference between them, and the relationship between them is expressed as:

[0113]

[0114] in is the impulse response of the wireless channel, is Gaussian white noise.

[0115] Step S402: Channel estimation and channel equalization: Assume that the estimated channel frequency response is , first receive the signal Converted into frequency domain signal through Fourier transform , zero-forcing equalization is used to eliminate the influence of wireless channels.

[0116] Step S403: Phase windowing: Since the FIR filter used in the iterative CAF at the transmitting end is based on the Kaiser window function and presents a linear phase offset within the band, phase windowing is required. The frequency domain signal output after channel equalization and phase windowing is:

[0117]

[0118] in p is the number of CAF iterations after matched filtering at the transmitter, is the filter in-band phase response. Then, the frequency domain signal Reconvert to time domain signal .

[0119] Step S404: Downsampling: To recover the transmitted bit stream, the receiver should perform downsampling and matched filtering corresponding to the upsampling and root raised cosine filtering at the transmitting end. The output signal of the matched filtering is:

[0120]

[0121] in is a matched filter.

[0122] Step S405: Reconstruction of nonlinear signal based on frequency domain symbol block constraints: Due to the clipping processing at the transmitting end and the residual power amplifier nonlinearity, the received time domain signal OFDM time domain signal at the transmitter There are significant differences. This difference is not only due to the Gaussian noise in the channel and the irrationality of channel equalization, but also mainly due to the nonlinear distortion of the signal caused by the transmitter clipping processing and the residual nonlinearity of the power amplifier. Based on the frequency domain symbol block modulation constraints and the nonlinear characteristics of the clipping processing, the received signal is After iterative reconstruction, the reconstructed time domain signal is expressed as:

[0123]

[0124] in represents a nonlinear reconstruction operator. For the specific implementation process, please refer to steps S501 to S505 below.

[0125] Step S406: Frequency domain symbol block modulation and demodulation: The reconstructed received time domain signal By grouping by the number of subcarriers, we get parallel OFDM time domain symbols, and then use Fourier transform to get the received frequency domain symbol block, which is expressed as:

[0126]

[0127] Then, based on maximum likelihood detection, the transmitted symbol block is estimated:

[0128]

[0129] Where S is the frequency domain symbol block modulation state space, , To receive two frequency domain symbols in a frequency domain symbol block, , Indicates the calculation of the 2-norm. After signal detection, the frequency domain symbol block is inversely mapped into a bit information stream, which is expressed as:

[0130]

[0131] in is the inverse labeling function, which is represented as the mapping from frequency domain symbol blocks to bit information streams.

[0132] The following is an example of a specific implementation of nonlinear signal reconstruction, that is, the nonlinear reconstruction operator in step S405 The construction of Figure 4 The figure shows a flowchart of the steps of nonlinear OFDM signal reconstruction with frequency domain symbol block constraints. The nonlinear signal reconstruction includes the following steps:

[0133] Step S501, initializing the reconstructed signal: setting the initial value of the nonlinear reconstructed signal .

[0134] Step S502, estimating the frequency domain symbol block power: Based on the characteristic that the low power part of the clipping signal maintains good linearity, using The first quartile of estimates the frequency domain symbol block power. For the transmitter, the frequency domain symbol block power OFDM time domain signal The ratio of the first quartile of power is a constant value, expressed as:

[0135]

[0136] in For OFDM signal The first quartile of power. At the receiving end, based on the power ratio Estimate the received frequency domain symbol block power, expressed as:

[0137]

[0138] in To receive OFDM time domain signals The first quartile of power.

[0139] Step S503: frequency domain symbol reconstruction: First, l Iterations, for each OFDM symbol, Using Fourier transform, we get N ×2-dimensional frequency domain symbol block vector , symbol block vector Depend on N dimensional frequency domain symbol vector and Then the total power of the two frequency domain symbols in each frequency domain symbol block is calculated to obtain NDimensional power vector , expressed as:

[0140]

[0141] Next, use Pair symbol vector And symbol vector Power normalization is performed to satisfy the constraint of consistent power of frequency domain symbol blocks, expressed as:

[0142]

[0143] After frequency domain reconstruction, k frequency domain symbol blocks, the total symbol power in the block is calculated as:

[0144]

[0145] After symbol reconstruction, the power of each symbol block is 1, satisfying the constraint of consistent power of frequency domain symbol blocks. Finally, the frequency domain symbol block vector after frequency domain reconstruction is According to the inverse Fourier transform process of the symbol block, it is converted into a time domain signal .

[0146] Step S504, time domain signal reconstruction: first estimate the time domain signal amplitude reconstruction level threshold, which is related to the transmitter clipping rate and also includes the residual power amplifier effect. l The time domain reconstruction level threshold of the iteration is estimated as:

[0147]

[0148] Based on the reconstruction level threshold estimate and signal distortion characteristics, l The signal after iterative time domain reconstruction It is expressed as:

[0149]

[0150] Step S505, iteration: calculation and The vector error between them is determined to be smaller than the error between them in the previous iteration, which is expressed as:

[0151]

[0152] like If it is greater than 0, the time domain reconstruction signal is output. ;like If it is less than 0, the above steps S503 to S505 are repeated.

[0153] Transmitter and receiver performance results using the proposed method:

[0154] Figure 5 The transmitter peak-to-average ratio performance and ACLR performance are given; Figure 5 (a) is the complementary cumulative distribution function of the peak-to-average ratio of the power amplifier input signal. It can be seen that the original OFDM signal has a peak-to-average ratio of up to about 12dB. After iterative clipping filtering, the peak-to-average ratio is reduced to about 4dB. Figure 5 (b) is a comparison of the ACLR performance of the transmitted signal with the input power back-off of the power amplifier. Taking the ACLR requirement of 45dBc as an example, it can be seen that the unprocessed transmitted signal requires at least 17.8dB of input power back-off. Using DPD based on Sigmoid nonlinear characterization, the ACLR performance requirement for input power back-off is reduced to 8dB, and further using iterative clipping and filtering, the input power back-off requirement is reduced to 2.8dB. The proposed transmission method effectively improves the ACLR performance of the power amplifier's nonlinear operation.

[0155] Figure 6 The convergence performance of nonlinear signal reconstruction is given, and the decrease of the received EVM with the number of reconstruction iterations is shown by taking the signal-to-noise ratio of 30dB and the input back-off power of 2.8dB as an example. It can be seen that the unreconstructed signal has obvious distortion, and the received EVM is only about -12.5dB, which cannot meet the demodulation requirements of the 64-order information modulation scheme. After multiple frequency domain and time domain reconstruction iterations, the received EVM drops below -30dB, and the EVM performance is improved by about 18dB.

[0156] Figure 7 The receiver information transmission performance is given, where Figure 7(a) and (b) are the EVM and BER performance comparison diagrams of the reconstructed and unreconstructed signals under different input power back-offs, with a signal-to-noise ratio of 30 dB. It can be seen that for the received EVM, the signal without nonlinear reconstruction has a higher EVM, with the lowest value being only about -12.5 dB, and it decreases slowly with the increase of input power back-off. The signal distortion is mainly caused by transmitter clipping. After signal reconstruction, the EVM decreases rapidly, with the lowest value reaching below 30 dB, and the maximum input power only needs to be backed off by 3 dB. Correspondingly, the unreconstructed signal has an extremely high bit error rate, and error-free information transmission cannot be achieved. After signal reconstruction, error-free information transmission can be achieved by backing off the input power by more than 2 dB, and the input power back-off requirement is greatly reduced. (c) and (d) are the EVM and BER performance comparison diagrams of the reconstructed and unreconstructed signals under different signal-to-noise ratios, with an input power back-off of 2.8 dB. It can be seen that the received EVM and BER of the unreconstructed signal are difficult to reduce with the increase of the signal-to-noise ratio, and there is a high error floor. After the signal is reconstructed, the received EVM decreases linearly with the increase of the signal-to-noise ratio. 25dB meets the signal-to-noise ratio requirement and can achieve error-free information transmission in the nonlinear region of the power amplifier. By comparison, it can be found that the method of the present invention can effectively reduce the adjacent channel interference performance under the nonlinearity of the power amplifier, improve the information transmission performance of the receiver, and reduce the power back-off requirements.

[0157] An embodiment of the present invention discloses a nonlinear OFDM information sending device based on frequency domain symbol block modulation, comprising:

[0158] A frequency domain symbol block modulation module is used to send bit information mapping, each frequency domain symbol block contains two frequency domain symbols, the relative amplitude and phase state of the two frequency domain symbols in the frequency domain symbol block are used to load the bit information, and the two frequency domain symbols in the frequency domain symbol block after modulation meet the set power constraint;

[0159] An OFDM modulation module is used to convert the mapped frequency domain signal into an OFDM time domain signal, and two frequency domain symbols in the frequency domain symbol block are respectively loaded onto two preset subcarriers;

[0160] The time domain upsampling and CAF module is used to perform time domain upsampling, iterative clipping and filtering on the OFDM time domain signal to obtain a clipped signal;

[0161] A digital pre-distortion module is used to correct the linearity of the output signal of the nonlinear power amplifier;

[0162] The nonlinear power amplifier is used to perform nonlinear power amplification on the time domain signal to form a transmission signal.

[0163] An embodiment of the present invention discloses a nonlinear OFDM information receiving device based on frequency domain symbol block modulation, comprising:

[0164] The signal receiving and processing module is used to obtain a peak distorted receiving signal by performing frequency domain equalization, phase windowing, time domain downsampling and matched filtering on the transmission signal captured by the wireless channel;

[0165] A signal reconstruction module, used to perform nonlinear signal reconstruction on the received signal by using the frequency domain symbol block constraint and the signal distortion characteristic, wherein the nonlinear signal reconstruction includes frequency domain reconstruction and time domain reconstruction, and is implemented by iterative reconstruction in the time and frequency domains; the frequency domain reconstruction is performed based on two frequency domain symbols in the frequency domain symbol block satisfying a set power constraint, and the time domain reconstruction is performed based on the distortion characteristic of the clipping signal;

[0166] OFDM demodulation module, used for demodulating the reconstructed signal through OFDM to obtain frequency domain symbol blocks;

[0167] The frequency domain symbol block modulation and demapping module is used to demap the relative amplitude and phase state of two frequency domain symbols in the frequency domain symbol block into bit information.

[0168] Exemplarily, the signal receiving and processing module includes: a signal capture unit, which is used to capture the transmission signal from the wireless channel. A channel estimation and channel equalization unit, which is used to estimate the wireless channel according to the received pilot signal, and to equalize the original received frequency domain signal based on the estimated wireless channel to obtain the equalized received frequency domain signal; the channel estimation is based on the pilot signal. Compared with the modulation, the pilot signal has a lower power and works in the linear region of the power amplifier. The nonlinearity of the power amplifier does not affect the accuracy of the channel estimation. A zero-forcing (ZF) equalizer is used in the channel equalization, and the phase offset of the transmitter low-pass filter on the received frequency domain signal is eliminated in the frequency domain. A phase windowing unit: used to remove the influence of the filter in the iterative CAF at the receiving end on the phase offset of the received signal; a downsampling unit, which is used to downsample the equalized received time domain signal and perform inverse filtering corresponding to the transmitter shaping filter to obtain the received time domain signal. Due to the clipping on the transmitter side and the nonlinearity of the power amplifier, the received time domain signal is severely distorted, and the transmission bit information cannot be directly restored by demodulation.

[0169] A computer program product disclosed in an embodiment of the present invention includes a computer program / instruction, which, when executed by a processor, implements the steps of the above-mentioned nonlinear OFDM information sending method and receiving method based on frequency domain symbol block modulation.

[0170] The program / instruction code for implementing the method of the embodiment of the present invention can be written in any combination of one or more programming languages. These programs / instruction codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program / instruction code, when executed by the processor or controller, causes the steps of the method of the present invention to be implemented. The program / instruction code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0171] It should be noted that, for the above-mentioned method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0172] The descriptions of the various embodiments provided by the present invention can refer to each other, and the descriptions of the various embodiments have different focuses. For parts that are not described in detail in a certain embodiment, refer to the relevant descriptions of other embodiments. For the convenience and simplicity of description, for example, the functions and execution steps of each device provided in the embodiment of the present invention can refer to the relevant description of the method embodiment of the present invention, and the various method embodiments and the various device embodiments can also refer to, be combined with or quoted from each other.

[0173] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A nonlinear OFDM information transmission method based on frequency domain symbol block modulation, characterized in that: The following steps are involved: Frequency domain symbol block modulation is used to transmit bit information mapping. Each frequency domain symbol block contains two frequency domain symbols. The relative amplitude and phase state of the two frequency domain symbols in the frequency domain symbol block are used to load the bit information. The two frequency domain symbols in the modulated frequency domain symbol block meet the set power constraint. The mapped frequency domain signal is modulated by OFDM to form an OFDM time domain signal, and two frequency domain symbols in the frequency domain symbol block are respectively loaded onto two pre-set subcarriers; The OFDM time domain signal is subjected to time domain upsampling, iterative clipping and filtering to obtain a clipped signal; The clipping signal is subjected to digital pre-distortion to correct the linearity of the output signal of the nonlinear power amplifier; the digitally pre-distorted signal is passed through the nonlinear power amplifier to form a transmission signal; In frequency domain symbol block modulation, the power difference, phase sum, and phase difference between two frequency domain symbols are used for bit information loading, and the power sum is set to a constant value as a frequency domain symbol block constraint.

2. The nonlinear OFDM information transmission method based on frequency domain symbol block modulation according to claim 1, characterized in that: The OFDM time domain signal is subjected to time domain upsampling, iterative clipping and filtering to obtain a clipped signal, including: the OFDM time domain signal is first clipped, then subjected to time domain upsampling and matched filtering, and then subjected to a second iterative clipping and filtering process; a multi-level clipping rate is used, and the clipping rate of the first clipping is lower than the clipping rate of the second clipping.

3. A nonlinear OFDM information receiving method based on frequency domain symbol block modulation, characterized in that: The following steps are involved: Acquire a received signal, wherein the received signal is a transmitted signal captured by a wireless channel, and a peak distorted received signal is obtained by frequency domain equalization, phase windowing, and time domain downsampling; The received signal is nonlinearly reconstructed by using the frequency domain symbol block constraint and the signal distortion characteristics. The nonlinear signal reconstruction includes frequency domain reconstruction and time domain reconstruction and is implemented by iterative reconstruction in the time and frequency domains. The frequency domain reconstruction is performed based on the power constraint of the symbol block imposed by the frequency domain symbol block modulation at the transmitting end, and the time domain reconstruction is performed based on the distortion characteristics of the clipping signal. In the frequency domain symbol block modulation, the power difference, phase sum and phase difference between two frequency domain symbols are used for bit information loading, and the power sum is set to a constant value as the frequency domain symbol block constraint. The reconstructed signal is demodulated by OFDM to obtain a frequency domain symbol block; The relative amplitude and phase states of two frequency domain symbols within a frequency domain symbol block are demapped into bit information.

4. The nonlinear OFDM information receiving method based on frequency domain symbol block modulation according to claim 3, characterized in that: The frequency domain reconstruction first converts the time domain signal to the frequency domain, then normalizes the power of each symbol block according to the received power of the frequency domain symbol block to make the sum of the symbol powers in each symbol block equal, and then reconverts the frequency domain signal to the time domain; the time domain reconstruction first estimates the amplitude distortion threshold of the received signal based on the known clipping rate, and then performs inverse clipping processing based on the threshold and the received time domain signal after frequency domain reconstruction; and the transmitted time domain modulated signal is restored by iterative time-frequency domain reconstruction.

5. A nonlinear OFDM information transmission method based on frequency domain symbol block modulation, characterized in that: The method comprises the steps of a nonlinear OFDM information sending method based on frequency domain symbol block modulation according to any one of claims 1-2; and the steps of a nonlinear OFDM information receiving method based on frequency domain symbol block modulation according to any one of claims 3-4.

6. A nonlinear OFDM information sending device based on frequency domain symbol block modulation, characterized in that: include: A frequency domain symbol block modulation module is used to send bit information mapping, each frequency domain symbol block contains two frequency domain symbols, the relative amplitude and phase state of the two frequency domain symbols in the frequency domain symbol block are used to load the bit information, and the two frequency domain symbols in the frequency domain symbol block after modulation meet the set power constraint; in the frequency domain symbol block modulation, the power difference, phase sum and phase difference between the two frequency domain symbols are used to load the bit information, and the power sum is set to a constant value as a frequency domain symbol block constraint; An OFDM modulation module is used to convert the mapped frequency domain signal into an OFDM time domain signal, and two frequency domain symbols in the frequency domain symbol block are respectively loaded onto two preset subcarriers; The time domain upsampling and CAF module is used to perform time domain upsampling, iterative clipping and filtering on the OFDM time domain signal to obtain a clipped signal; A digital pre-distortion module is used to correct the linearity of the output signal of the nonlinear power amplifier; The nonlinear power amplifier is used to perform nonlinear power amplification on the time domain signal to form a transmission signal.

7. A nonlinear OFDM information receiving device based on frequency domain symbol block modulation, characterized in that: The following steps are involved: The signal receiving and processing module is used to obtain a peak distorted receiving signal by performing frequency domain equalization, phase windowing, time domain downsampling and matched filtering on the transmission signal captured by the wireless channel; A signal reconstruction module is used to perform nonlinear signal reconstruction on a received signal by using a frequency domain symbol block constraint and a signal distortion characteristic, wherein the nonlinear signal reconstruction includes frequency domain reconstruction and time domain reconstruction and is implemented through iterative reconstruction in the time and frequency domains; the frequency domain reconstruction is performed based on a power constraint between two frequency domain symbols in a frequency domain symbol block imposed by a frequency domain symbol block modulation at a transmitting end, and the time domain reconstruction is performed based on the distortion characteristic of a clipped signal; in the frequency domain symbol block modulation, a power difference, a phase sum, and a phase difference between two frequency domain symbols are used for bit information loading, and the power sum is set to a constant value as a frequency domain symbol block constraint; OFDM demodulation module, used for demodulating the reconstructed signal through OFDM to obtain frequency domain symbol blocks; The frequency domain symbol block modulation and demapping module is used to demap the relative amplitude and phase state of two frequency domain symbols in the frequency domain symbol block into bit information.

8. A nonlinear OFDM information transmission system based on frequency domain symbol block modulation, characterized in that: It comprises the transmitting device according to claim 6 and the receiving device according to claim 7.

9. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

Images