A method and system for CP design and compensation of carrier frequency offset for wideband PLC-OFDM system

Abstract

The application relates to a CP design and carrier frequency distortion compensation method and system for a wideband PLC-OFDM system, which comprises the following steps: optimizing and designing a cyclic prefix length; realizing offsetting of a multipath effect caused by a channel, avoiding inter-symbol interference, improving the anti-interference capability of the PLC-OFDM system, and accommodating a longer channel delay. Fractional frequency offset (FFO) and integer frequency offset (IFO) estimation based on a cyclic prefix solve carrier frequency distortion. A CP-based decomposition carrier frequency compensation method accurately estimates the carrier frequency distortion amount of a receiving end signal, eliminates transmission-caused CFO, completes synchronization compensation of a transmitting-receiving system, and ensures the continuity and stability of signal transmission. The application improves the transmission real-time transmission performance of a wideband power line carrier communication system and plays an important role in the fields of home entertainment, monitoring and smart home, etc.

Description

Technical Field

[0001] This invention relates to the fields of FPGA signal processing, broadband power line carrier communication systems, and data processing technology. Specifically, it relates to a CP design and carrier frequency distortion compensation method and system for broadband PLC-OFDM systems. Background Technology

[0002] With the rapid development of home automation systems, vehicle communication systems, smart grid systems, and internet technology, the demands for data transmission in daily life and production are constantly increasing. Traditional communication systems require dedicated communication lines, resulting in high deployment and subsequent management costs. Compared to traditional communication systems, power line communication utilizes existing, widely distributed power lines as the communication medium, reducing construction costs while achieving broad coverage. Furthermore, with optimizations using technologies such as spread spectrum, OFDM, and multidimensional grid coding, power line communication offers advantages such as stable transmission and high transmission speeds.

[0003] However, the application of OFDM technology in broadband power line carrier communication systems still faces some challenges and has significant room for improvement. For example, power line channels are subject to noise, frequency-selective fading, and various types of interference, making transmission complex. Furthermore, multipath interference accompanying parallel transmission poses numerous difficulties for signal transmission. In OFDM systems, to counteract multipath effects caused by the channel and avoid inter-symbol interference, existing methods involve adding a cyclic prefix (CP) to the guard interval between subcarrier symbols. However, in practical communication, considering the complex transmission conditions in power lines, Doppler frequency offset, and the inherent physical characteristics of oscillators, it is difficult to maintain consistent subcarrier frequencies, posing challenges to subsequent demodulation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method for CP design and carrier frequency distortion compensation in broadband PLC-OFDM systems.

[0005] The number of subcarriers and the CP length are determined based on the characteristics of the power line channel. A CFO (FFO, IFO) estimation algorithm based on the cyclic prefix is ​​proposed. The original signal is compensated by estimating the fractional multiple of the frequency offset FFO and the integer multiple of the frequency offset IFO respectively, thereby improving the above problems.

[0006] This invention also proposes a CP design and carrier frequency distortion compensation system for broadband PLC-OFDM systems.

[0007] Terminology Explanation:

[0008] 1. PLC, or Power Line Communication, is a communication method that uses power lines to transmit data and media signals. This technology loads high-frequency information onto an electric current, transmits the information via power lines, and at the receiving end, a filter obtains the modulated signal, which is then demodulated to obtain the original communication signal, thus realizing information transmission.

[0009] 2. OFDM, orthogonal frequency division multiplexing, uses frequency division multiplexing to convert high-speed serial data into low-speed parallel data. The core idea of ​​OFDM is to divide the channel into several orthogonal sub-channels, thereby converting the high-speed signal into multiple parallel low-speed signals, which are then modulated onto each sub-channel for transmission. The orthogonality between the carriers allows them to transmit at the same time and frequency, significantly improving data transmission rate and spectral efficiency. Furthermore, OFDM effectively addresses frequency-selective fading and multipath fading, improving channel capacity and system performance while reducing distortion during transmission.

[0010] 3. CP, Cyclic Prefix. In an OFDM system, CP refers to the prefix of a symbol on a subcarrier signal. Inserting CP between the guard intervals of symbols, essentially copying a portion of the sampling points following each OFDM symbol and adding it to the beginning, ensures that the number of waveform periods in the delayed copy of the OFDM symbol is an integer multiple of the number of FFT periods, guaranteeing the orthogonality of the subcarriers. This solves the ISI and ICI problems caused by delay spread.

[0011] 4. Power Line Channels: Power lines are not dedicated communication lines. In practical applications, power lines as a communication transmission medium face problems such as high noise, interference, and attenuation, making it difficult to establish an accurate power line channel model. The usual approach is to repeatedly measure the parameters of the power lines and gradually build a relative model of the power line channel under specified conditions based on the test data.

[0012] 5. ISI, Inter-Symbol Interference. In OFDM systems, due to multipath effects, the previous symbol may fall into the sampling range of the current symbol, causing symbol overlap and severely interfering with signal transmission.

[0013] 6. ICI, Inter-Channel Interference. In the theoretical model of OFDM systems, the carriers of multiple channels strictly satisfy orthogonality, allowing for successful demodulation of multiple channel carriers at the receiver. However, in practical applications, the presence of ICI in multi-carrier systems disrupts the orthogonality between subcarriers, causing difficulties for subsequent demodulation.

[0014] 7. IFFT, Inverse Fourier Transform.

[0015] 8. QAM is an abbreviation for Quadrature Amplitude Modulation, which involves simultaneous changes in amplitude and phase, belonging to non-constant envelope two-dimensional modulation. QAM is a combination of quadrature carrier modulation technology and multilevel amplitude shifting.

[0016] The technical solution of this invention is as follows:

[0017] A method for CP design and carrier frequency distortion compensation in a broadband PLC-OFDM system includes:

[0018] Optimize the design of the loop prefix length;

[0019] Carrier frequency distortion is addressed by fractional frequency offset (FFO) and integer frequency offset (IFO) estimation based on cyclic prefix.

[0020] According to a preferred embodiment of the present invention, the cyclic prefix length is optimized; including:

[0021] Taking into account both bit error rate and power line channel conditions, the tolerable delay, cyclic prefix delay, and number of bits carried by each sub-band symbol are set.

[0022] Based on channel characteristics, the conditions for determining the number of subcarriers are set;

[0023] The cyclic prefix length is set based on channel characteristics, multipath delay range, and bandwidth efficiency.

[0024] Determine the IFFT length for communication;

[0025] Pilot symbols are generated using random codes, and QAM is used to modulate the pilot symbols. The subcarriers are traversed, pilot symbols are inserted at the pilot positions, and data symbols are copied to non-pilot positions to complete the allocation of data and pilot symbols.

[0026] Based on the allocated modulation symbol sequence, the IFFT operation is used to generate the transmission symbol sequence in the broadband power line carrier communication system;

[0027] The transmission symbol with the added cyclic prefix is ​​obtained by truncation and splicing based on the calculated cyclic prefix length and the transmission symbol sequence.

[0028] According to a preferred embodiment of the present invention, the method for resolving carrier frequency distortion based on fractional and integer multiples of frequency offset using a cyclic prefix includes:

[0029] Symbol synchronization processing is performed on the transmitted signals through the broadband PLC-OFDM system;

[0030] The position of the cyclic prefix is ​​determined based on the transmitted signal after the symbol synchronization problem has been resolved;

[0031] The fractional frequency offset is estimated using a cyclic prefix; the integer frequency offset is estimated using the start and end positions of the FFT and a cyclic shift judgment method.

[0032] Based on the obtained fractional and integer frequency offsets, the carrier frequency distortion is compensated to obtain the corrected transmission signal sequence.

[0033] Further preferably, the tolerable delay, cyclic prefix delay, and number of bits carried by each sub-band symbol are set, including:

[0034] Set the tolerable delay T d =0.0001, Cyclic prefix delay T cp =4*T d The number of bits carried by each sub-band symbol per Sub-belts =4.

[0035] A further preferred approach is to set the subcarrier number determination condition as follows: carrier count This refers to the number of subcarriers; bit per sym This refers to the number of bits to be transmitted in the symbol preceding the subband division;

[0036] A further preferred embodiment is to set the cyclic prefix length based on power line channel characteristics, multipath delay range, and bandwidth efficiency settings as follows: Where N is the subcarrier number selection ratio, specifically set as follows: interval sub-belts For subband bandwidth interval, delay CP This is the cyclic prefix delay.

[0037] Further preferably, based on the determined number of subcarriers, the IFFT length for communication is determined as follows: IFFT length =2∧nextpow2(carrier) count ); where 2∧nextpow2() implements taking the smallest power of 2 that is not less than the number of subcarriers.

[0038] A further preferred embodiment involves inserting QAM-modulated pilot symbols at pilot intervals, copying data symbols to non-pilot positions, and combining this with the obtained IFFT. length The resulting combination sequence of data and pilot symbols is: Where k is the length, and is the IFFT. length An integer sequence; X pmod The result of QAM modulation of the pilot symbols; Nps is the pilot spacing; bit prep For transmitting data symbol sequences; bit add pilot(k,:) is the symbol sequence after adding pilot signals; To round down the result of k divided by Nps, i.e., to calculate the index of the pilot symbol corresponding to the current position; n takes the value of a natural number.

[0039] A further preferred embodiment, based on the allocated modulation symbol sequence, uses IFFT operations to generate the transmission symbol sequence in a broadband power line carrier communication system as follows:

[0040] A further preferred embodiment is that, based on the calculated cyclic prefix length and the transmission symbol sequence, the transmission symbol after adding the cyclic prefix is ​​obtained by truncation and concatenation: signal CP =[signal(end-CP)] length +1: end, :); signal].

[0041] A further preferred method involves estimating the fractional octave offset using a cyclic prefix, including:

[0042] Set the sample range used when estimating the frequency bias to the obtained cyclic prefix length;

[0043] Store the sampled values ​​at different locations within the sample range used when estimating the frequency deviation;

[0044] The fractional octave frequency offset (FFO) is estimated using the phase difference between two times within this estimation range, as shown in equation (1):

[0045]

[0046] Among them, R x data This is the signal sequence received after transmission via a broadband power line carrier communication system.

[0047] A further preferred method is to estimate the integer multiples of the frequency offset using a cyclic shift judgment, including:

[0048] The received signal is compensated by performing fractional-fold frequency offset compensation on the obtained fractional-fold frequency offset to obtain the initially compensated signal Y. FFO As shown in equation (2):

[0049]

[0050] Where, ε f For fractional frequency offset FFO, N is the IFFT. length ;

[0051] The signal Y after initial compensation FFo Perform an FFT transform in the frequency domain to obtain the frequency domain representation Y. FFO FFT ;

[0052] Using frequency domain representation of Y FFo FFT The correlation sequence r is calculated using the cross-correlation method with the obtained symbol sequence after adding pilots, as shown in equation (3):

[0053] r = |IFFT{FFT(Y) FFO FFT )*(FFT(bit add pilot ))*}| (3)

[0054] The integer multiple of the frequency offset is obtained by determining the index of the peak of the correlation sequence r.

[0055] A further preferred embodiment is the corrected transmission signal sequence shown in equation (4):

[0056]

[0057] Where, ε i For integer multiples of frequency offset IFO, N is the IFFT. length .

[0058] A CP design and carrier frequency distortion compensation system for a broadband PLC-OFDM system includes an analog front-end, a processor, a storage device, a communication device, an I / O interface, and a display device;

[0059] The analog front end includes an analog-to-digital converter (ADC) and a power line coupler; it is used to extract transmitted signals from a broadband PLC-OFDM system and convert them into digital information that can be processed by a computer or digital circuit devices.

[0060] The processor is used to process digital signals; it optimizes the design of the cyclic prefix length; and it solves carrier frequency distortion based on fractional and integer multiples of the cyclic prefix frequency offset estimation.

[0061] Storage devices are used to perform the function of saving data;

[0062] The I / O interface is used to connect I / O circuits and peripheral devices through the broadband PLC-OFDM system bus, and is used for data and information exchange and control between external devices, the broadband PLC-OFDM system bus and the processor;

[0063] The communication device is used to realize the communication function of exchanging data with external devices, and the data is transmitted to the display device through the communication device.

[0064] A field-programmable gate array (FPGA) was selected as the processor.

[0065] The beneficial effects of this invention are as follows:

[0066] 1. The present invention designs a cyclic prefix adapted to the characteristics of power line channels to cancel out the multipath effect caused by the channel, avoid inter-symbol interference, improve the anti-interference capability of the system, and accommodate longer channel delays.

[0067] 2. The CP-based decomposed carrier frequency compensation method accurately estimates the carrier frequency distortion of the received signal, eliminates the CFO caused by transmission, completes the synchronization compensation of the transceiver system, and ensures the continuity and stability of signal transmission.

[0068] 3. This invention improves the real-time transmission performance of broadband power line carrier communication systems, playing an important role in fields such as home entertainment, monitoring, and smart homes. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the process for optimizing the cyclic prefix length according to the present invention;

[0070] Figure 2 This is a schematic diagram of the decomposition compensation process for carrier frequency distortion based on fractional frequency offset (FFO) and integer frequency offset (IFO) estimation of the cyclic prefix in this invention.

[0071] Figure 3 This is a schematic diagram of the CP design and carrier frequency distortion compensation system for a broadband PLC-OFDM system according to the present invention.

[0072] Figure 4 This is a constellation diagram of the original signal received from the power line channel in an embodiment of the present invention;

[0073] Figure 5 This is a constellation diagram of the received signal after CFO decomposition and compensation by the method of the present invention in an embodiment of the present invention. Detailed Implementation

[0074] The present invention will be further described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Those skilled in the art can make various modifications or alterations to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0075] Example 1

[0076] A method for CP design and carrier frequency distortion compensation in a broadband PLC-OFDM system includes:

[0077] The cyclic prefix length is optimized to offset the multipath effect caused by the channel, avoid inter-symbol interference, improve the anti-interference capability of the PLC-OFDM system, and accommodate longer channel delays.

[0078] Carrier frequency distortion is addressed by fractional frequency offset (FFO) and integer frequency offset (IFO) estimation based on cyclic prefix.

[0079] Example 2

[0080] The difference between the CP design and carrier frequency distortion compensation method for a broadband PLC-OFDM system described in Example 1 and the following is:

[0081] Optimize the design of the loop prefix length; such as Figure 1 As shown, it includes:

[0082] Taking into account both bit error rate and power line channel conditions, the tolerable delay, cyclic prefix delay, and number of bits carried by each sub-band symbol are set.

[0083] Based on channel characteristics, the conditions for determining the number of subcarriers are set;

[0084] The cyclic prefix length is set based on channel characteristics, multipath delay range, and bandwidth efficiency.

[0085] Determine the IFFT length for communication;

[0086] Pilot symbols are generated using random codes, and QAM is used to modulate the pilot symbols. The subcarriers are traversed, pilot symbols are inserted at the pilot positions, and data symbols are copied to non-pilot positions to complete the allocation of data and pilot symbols.

[0087] Based on the allocated modulation symbol sequence, the IFFT operation is used to generate the transmission symbol sequence in the broadband power line carrier communication system;

[0088] The transmission symbol with the added cyclic prefix is ​​obtained by truncation and splicing based on the calculated cyclic prefix length and the transmission symbol sequence.

[0089] Configure tolerable latency, cyclic prefix latency, and the number of bits carried by each sub-band symbol, including:

[0090] Set the tolerable delay T d =0.0001, Cyclic prefix delay T cp =4*T d The number of bits carried by each sub-band symbol per Sub-belts =4.

[0091] The conditions for determining the number of subcarriers are set as follows: carrier count This refers to the number of subcarriers; bit per sym This refers to the number of bits to be transmitted in the symbol preceding the subband division;

[0092] Based on the characteristics of the power line channel, the multipath delay range, and bandwidth efficiency, the cyclic prefix length is set as follows: Where N is the subcarrier number selection ratio, specifically set as follows: interval Sub-belts For subband bandwidth interval, delay CP This is the cyclic prefix delay.

[0093] Based on the determined number of subcarriers, the IFFT length for communication is determined as follows: IFFT length =2∧nextpow2(carrier) count ); where 2∧nextpow2() implements taking the smallest power of 2 that is not less than the number of subcarriers.

[0094] The QAM-modulated pilot symbols are inserted at the pilot intervals, and the data symbols are copied to non-pilot positions. This is combined with the IFFT obtained from the above calculations. length The resulting combination sequence of data and pilot symbols is: Where k is the length, and is the IFFT. length An integer sequence; X pmod The result of QAM modulation of the pilot symbols; Nps is the pilot spacing; bit prep For transmitting data symbol sequences; bit add pilot (k,:) is the symbol sequence after adding pilot signals; To round down the result of k divided by Nps, i.e., to calculate the index of the pilot symbol corresponding to the current position; n takes the value of a natural number.

[0095] Based on the allocated modulation symbol sequence, the transmission symbol sequence in a broadband power line carrier communication system is generated using IFFT operations as follows:

[0096] Example 3

[0097] The difference between the CP design and carrier frequency distortion compensation method for a broadband PLC-OFDM system described in Example 2 is as follows:

[0098] Carrier frequency distortion can be addressed by estimating fractional and integer multiples of frequency offset based on cyclic prefixes, such as... Figure 2 As shown, it includes:

[0099] Symbol synchronization processing is performed on the transmitted signals through the broadband PLC-OFDM system;

[0100] The position of the cyclic prefix is ​​determined based on the transmitted signal after the symbol synchronization problem has been resolved;

[0101] Carrier frequency distortion is decomposed into fractional and integer multiples of frequency offset. The fractional multiple of frequency offset is estimated using a cyclic prefix; the integer multiple of frequency offset is estimated using the start and end positions of the FFT and a cyclic shift method.

[0102] Based on the fractional and integer frequency offsets obtained from the above calculations, the carrier frequency distortion is compensated to obtain the corrected transmission signal sequence.

[0103] Based on the calculated cyclic prefix length and the transmission symbol sequence, the transmission symbol after adding the cyclic prefix is ​​obtained by truncation and concatenation: signal CP =[signal(end-CP)] length +1: end, :); signal].

[0104] Estimating fractional octave frequency offset using cyclic prefixes includes:

[0105] Set the sample range used when estimating the frequency bias to the obtained cyclic prefix length;

[0106] Store the sampled values ​​at different locations within the sample range used when estimating the frequency deviation;

[0107] The fractional octave frequency offset (FFO) is estimated using the phase difference between two times within this estimation range, as shown in equation (1):

[0108]

[0109] Among them, R x data This is the signal sequence received after transmission via a broadband power line carrier communication system.

[0110] Estimating integer multiples of frequency offset using a cyclic shift method includes:

[0111] The received signal is compensated by performing fractional-fold frequency offset compensation on the estimated fractional-fold frequency offset to obtain the initially compensated signal Y. FFo As shown in equation (2):

[0112]

[0113] Where, ε f For fractional frequency offset FFO, N is the IFFT. length ;

[0114] The signal Y after initial compensation FFo Perform an FFT transform in the frequency domain to obtain the frequency domain representation Y. FFo FFT ;

[0115] Using frequency domain representation of Y FFO FFTThe correlation sequence r is calculated using the cross-correlation method with the previously obtained symbol sequence after adding pilots, as shown in equation (3):

[0116] r = |IFFT{FFT(Y) FFO FFT )*(FFT(bit add pilot ))*}| (3)

[0117] The integer multiple of the frequency offset is obtained by determining the index of the peak of the correlation sequence r.

[0118] The corrected transmission signal sequence is shown in equation (4):

[0119]

[0120] Where, ε i For integer multiples of frequency offset IFO, N is the IFFT. length .

[0121] Figure 4 This is a constellation diagram of the original signal received from the power line channel in an embodiment of the present invention; Figure 5 This is a constellation diagram of the received signal after CFO decomposition and compensation by the method of the present invention in an embodiment of the present invention.

[0122] Example 4

[0123] A CP design and carrier frequency distortion compensation system for a broadband PLC-OFDM system, such as Figure 3 As shown, it includes an analog front-end, processor, storage device, communication device, I / O interface and display device;

[0124] The analog front end includes an analog-to-digital converter (ADC) and a power line coupler; it is used to extract transmitted signals from a broadband PLC-OFDM system and convert them into digital information that can be processed by a computer or digital circuit devices.

[0125] The processor is used to process digital signals; it also has certain control functions over other devices, enabling the orderly scheduling and operation of equipment. It optimizes the design of the cyclic prefix length; and solves carrier frequency distortion based on fractional and integer multiples of the cyclic prefix frequency offset estimation.

[0126] Storage devices are used to save data; they mainly include temporary storage of intermediate quantities necessary for calculations, or persistent storage of data signals, whether processed or unprocessed, compensated or uncompensated.

[0127] The I / O interface is used to connect I / O circuits and peripheral devices through the broadband PLC-OFDM system bus, and is used for data and information exchange and control between external devices, the broadband PLC-OFDM system bus and the processor;

[0128] The communication device is used to enable the communication function of exchanging data between this device and external devices, and the data is transmitted to the display device through the communication device.

[0129] For simplicity, a Field Programmable Gate Array (FPGA) is used as the processor in this description. Specifically, the FPGA calculates the IFFT length based on the determined number of subcarriers. The FPGA generates pilot signals using a random sequence and inserts modulated pilot signals into each subcarrier. Subsequently, pilot symbols and data are allocated according to the IFFT length, and symbols for transmission in the broadband power line carrier communication system are generated using IFFT operations. Finally, the prefix symbol is generated through CP calculation. For the CP-based FFO and IFO estimation process, the processor sets the sample range used for estimating the frequency deviation based on the cyclic prefix length, and samples and stores values ​​at different positions within the sample range. The processor solves for the FFO using the phase difference between two moments within the estimation range, and further obtains the IFO through operations such as convolution and multiplication. After obtaining the necessary information, the starting and ending positions of the FFT are used to determine the shift position for compensation. After decomposition compensation, the received signal after carrier frequency distortion compensation and channel distortion correction is obtained. The processing utilizes the parallel computing characteristics of the FPGA, resulting in low latency and high efficiency in data processing. It should be noted that the processor refers to any device capable of performing calculations and processing on digital signals. Apart from the FPGA used in the example above, it can be composed of one or more small- or medium-scale digital circuit chips, general-purpose central processing units, application-specific integrated circuits, digital signal processors, complex programmable logic devices, microprocessors, microcontrollers, or other electronic components to perform the above-mentioned calculations and processing.

[0130] Storage devices include volatile and non-volatile memory. They can be NAND Flash, Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), Read-Only Memory (ROM) (including erasable ROM), magnetic storage, optical discs, etc.

[0131] Communication methods include wired and wireless communication. Wired communication methods include fiber optic cables, USB data cables, network cables, etc., while wireless communication methods include Wi-Fi, Bluetooth, and 3G, 4G, 5G, or one or more combinations thereof.

[0132] A display device is a device used to convert data into physical quantities that can be perceived by humans. In this device, the display outputs compensated, low-distortion data, ensuring a high signal-to-noise ratio. This data can include text messages, characters, images, audio, video, etc. Therefore, the display methods are diverse, which determines the diversity of display devices. Display devices can be simple speakers, LED arrays, digital tubes, or even projectors, displays, and other multimedia components.

[0133] The above description is merely a partial set of typical embodiments of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., that can be readily conceived within the technical scope stated in the present invention should be included within the protection scope of the present invention. The scope of the present invention is defined by the appended claims and other equivalents.

Claims

1. A method for CP design and carrier frequency distortion compensation in a broadband PLC-OFDM system, characterized in that, include: Optimize the design of the loop prefix length; including: Taking into account both bit error rate and power line channel conditions, the tolerable delay, cyclic prefix delay, and number of bits carried by each sub-band symbol are set. Based on channel characteristics, the conditions for determining the number of subcarriers are set; The cyclic prefix length is set based on channel characteristics, multipath delay range, and bandwidth efficiency. Determine the IFFT length for communication; Pilot symbols are generated using random codes, and QAM is used to modulate the pilot symbols. Subcarriers are traversed, pilot symbols are inserted at pilot positions, and data symbols are copied to non-pilot positions to complete the allocation of data and pilot symbols. Based on the allocated modulation symbol sequence, the IFFT operation is used to generate the transmission symbol sequence in the broadband power line carrier communication system; Based on the calculated cyclic prefix length and the transmission symbol sequence, the transmission symbol with the added cyclic prefix is ​​obtained by truncation and concatenation. Carrier frequency distortion can be addressed by estimating fractional and integer multiples of frequency offset based on cyclic prefixes. Estimating fractional octave frequency offset using cyclic prefixes includes: Set the sample range used when estimating the frequency bias to the obtained cyclic prefix length; Store the sampled values ​​at different locations within the sample range used when estimating the frequency deviation; The fractional octave frequency offset is estimated using the phase difference between two times within this estimation range. As shown below: ； in, This is the received signal sequence after transmission via a broadband power line carrier communication system; This refers to the length of the cyclic prefix; This refers to the IFFT length; Estimating integer multiples of frequency offset using a cyclic shift method includes: The received signal is compensated by performing fractional-fold frequency offset compensation on the obtained fractional-fold frequency offset to obtain the initially compensated signal. As shown below: ； in, For fractional-harmonic frequency offset FFO, N is ; The signal after initial compensation Perform an FFT transform in the frequency domain to obtain the frequency domain representation. ; Using frequency domain representation The correlation sequence r is calculated using the cross-correlation method with the obtained symbol sequence after adding pilots, as shown below: ； The integer multiple of the frequency offset is obtained by determining the index of the peak of the correlation sequence r. The corrected transmission signal sequence is shown below: ； in, For an integer multiple of the frequency offset IFO, N is... , The value can be a natural number; Carrier frequency distortion is addressed by estimating fractional and integer multiples of frequency offset based on cyclic prefixes, including: Symbol synchronization processing is performed on the transmitted signals through the broadband PLC-OFDM system; The position of the cyclic prefix is ​​determined based on the transmitted signal after the symbol synchronization problem has been resolved; The fractional frequency offset is estimated using a cyclic prefix; the integer frequency offset is estimated using the start and end positions of the FFT and a cyclic shift judgment method. Based on the obtained fractional and integer frequency offsets, the carrier frequency distortion is compensated to obtain the corrected transmission signal sequence.

2. The method for CP design and carrier frequency distortion compensation in a broadband PLC-OFDM system according to claim 1, characterized in that, Configure tolerable latency, cyclic prefix latency, and the number of bits carried by each sub-band symbol, including: Set tolerable latency Cyclic prefix delay The number of bits carried by each subband symbol ; The conditions for determining the number of subcarriers are set as follows: ; This refers to the number of subcarriers; This refers to the number of bits to be transmitted in the symbol preceding the subband division; Based on the characteristics of the power line channel, the multipath delay range, and bandwidth efficiency, the cyclic prefix length is set as follows: Where N is the subcarrier number selection ratio, specifically set as follows: , Subband bandwidth spacing For cyclic prefix delay; Based on the determined number of subcarriers, the IFFT length for communication is determined as follows: ;in, To achieve the smallest power of 2 that is not less than the number of subcarriers.

3. The method for CP design and carrier frequency distortion compensation in a broadband PLC-OFDM system according to claim 2, characterized in that, The QAM-modulated pilot symbols are inserted at the pilot intervals, and the data symbols are copied to the non-pilot positions. The resulting... The resulting combination sequence of data and pilot symbols is: Where k is the length, and is sequence of integers; The result after QAM modulation of the pilot symbols; Pilot spacing; For transmitting data symbol sequences; The symbol sequence after adding pilot signals; To round down the result of k divided by Nps, we calculate the index of the pilot symbol corresponding to the current position.

4. The method for CP design and carrier frequency distortion compensation in a broadband PLC-OFDM system according to claim 3, characterized in that, Based on the allocated modulation symbol sequence, the transmission symbol sequence in a broadband power line carrier communication system is generated using IFFT operations as follows: ; Based on the calculated cyclic prefix length and the transmission symbol sequence, the transmission symbol after adding the cyclic prefix is ​​obtained by truncation and concatenation: .

5. A CP design and carrier frequency distortion compensation system for a broadband PLC-OFDM system, used to implement the CP design and carrier frequency distortion compensation method for a broadband PLC-OFDM system as described in any one of claims 1-4, characterized in that, This includes analog front-end, processor, storage device, communication device, I / O interface, and display device; The analog front end includes an analog-to-digital converter and a power line coupler; it is used to extract transmitted signals from a broadband PLC-OFDM system and convert them into digital information that can be processed by a computer or digital circuit devices. The processor is used to process digital signals; it implements optimized design for the cyclic prefix length. Carrier frequency distortion can be addressed by estimating fractional and integer multiples of frequency offset based on cyclic prefixes. Storage devices are used to perform the function of saving data; The I / O interface is used to connect I / O circuits and peripheral devices through the broadband PLC-OFDM system bus, and is used for data and information exchange and control between external devices, the broadband PLC-OFDM system bus and the processor; The communication device is used to realize the communication function of exchanging data with external devices, and the data is transmitted to the display device through the communication device; A field-programmable gate array (FPGA) was selected as the processor.

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