Method for low voltage broadband power line carrier communication

The present application is a National Stage entry under 35 U.S.C.371 of International Patent Application No. PCT/CN2018/079428, filed on Mar. 19, 2018, which claims priority from Chinese Patent Application No. CN 201710595937.1, filed Jul. 20, 2017, the entire contents of each of which are incorporated by reference herein.

The present disclosure relates to digital communications technologies, and more particularly relates to a method for low voltage broadband power line carrier communication.

As specified in the LVPLC (Low Voltage Broadband Power Line Carrier Communication) protocol of the State Grid, the physical layer (PHY) frame format includes a long preamble, a frame control, and a data payload, wherein the long preamble is for frequency offset compensation, automatic gain control, symbol synchronization and channel estimation. A long preamble-trained receiving system trained has an improved symbol synchronization property and frequency synchronization property, which may adjust voltage gains and estimate channel characteristics more accurately, thereby improving receiver performance. However, a certain number of long preambles take up a large portion of bandwidth and system processing overhead, resulting in a relatively large resource overhead and time overhead for the system to implement frequency offset compensation, automatic gain control, symbol synchronization and channel estimation.

The present disclosure provides a method for low voltage broadband power line carrier communication, which may quickly and accurately implement frequency offset compensation, automatic gain control, symbol synchronization, and channel estimation without sacrificing precision, thereby achieving quick convergence, reducing resource overheads and time overheads, and enhancing system performance.

To achieve the objective above, the method for low voltage broadband power line carrier communication according to the present disclosure comprises: modulating and transmitting, by a transmitter, a physical layer protocol frame; and receiving and processing, by a receiver, the physical layer protocol frame;

wherein the physical layer protocol frame includes: a plurality of short preambles, a plurality of long preambles, a plurality of frame control symbols, and a plurality of data payload symbols;

the modulating the physical layer protocol frame comprises steps of:

selecting a plurality of sub-carriers according to a fixed frequency interval to transmit the short preambles; and

transmitting, using all available sub-carriers, the long preambles, the frame control symbols, and the data payload symbols.

The receiving and processing the physical layer protocol frame comprises steps of:

Step S 1 : performing, by the receiver, direct-current (DC) estimation, automatic gain control, frequency offset compensation, symbol synchronization, and channel estimation with respect to the short preambles and long preambles received;

Step S 2 : processing, by the receiver, the frame control symbols and the data payload symbols after obtaining accurate channel information based on the outcomes from step S 1 to obtain correct data;

wherein processing the short preambles and long preambles in the physical layer protocol frame specifically comprises steps of:

Step S 1 . 1 : analog gain adjustment, wherein an analog gain module adjusts gain of the received analog signal;

Step S 1 . 2 : analog-to-digital conversion, wherein an analog-to-digital conversion module performs analog-to-digital conversion to the received short preambles or long preambles to produce a digital sampling signal for the short preambles or long preambles of time domain;

Step S 1 . 3 : automatic gain control, wherein an automatic gain control module performs energy estimation on the digital sampling signal for the short preambles or long preambles to obtain an energy gain parameter, the energy gain parameter acting on the analog gain module to implement energy gain coefficient adjustment;

Step S 1 . 4 : direct-current estimation, wherein a direct-current estimation module performs direct-current estimation on the digital sampling signal for the short preamble or long preamble to obtain a time-domain signal;

Step S 1 . 5 : frequency offset compensation, wherein a frequency offset compensation module performs coarse-grained frequency offset compensation for the short preambles or performs fine-grained frequency offset compensation for the long preambles;

Step S 1 . 6 : symbol synchronization, wherein a symbol synchronization module performs coarse-grained autocorrelation processing to the short preambles or performs fine-grained autocorrelation processing for the long preambles, thereby implementing symbol synchronization;

Step S 1 . 7 : fast Fourier transform, wherein a fast Fourier transform module performs fast Fourier transform to the short preambles and the long preambles and then converts the fast Fourier transformed short preambles and the fast Fourier transformed long preambles from time domain to frequency domain;

Step S 1 . 8 : channel estimation, wherein a channel estimation module performs channel estimation to the short preambles or the long preambles to obtain an estimated preamble value.

The automatic gain control comprises steps of:

Step S 1 . 2 . 1 : preamble detection, wherein if the short preambles or the long preambles are detected, a counter is started;

Step S 1 . 2 . 2 : counting, by a counter, the short preambles or the long preambles, and computing energies thereof;

Step S 1 . 2 . 3 : comparing, by a comparer, short preamble energy or long preamble energy with a system set threshold, wherein the outputted energy gain parameter acts on the analog gain module to perform adjustment energy for subsequent reception;

if energy<lower threshold, the outputted energy gain parameter is a positive value;

if energy> higher threshold, the outputted energy gain parameter is a negative value.

The frequency offset compensation comprises steps:

Step S 1 . 4 . 1 : determining preamble type; in the case of short preambles, simultaneously performing step S 1 . 4 . 2 and step S 1 . 4 . 4 ; in the case of long preambles, simultaneously performing step S 1 . 4 . 3 and step S 1 . 4 . 4 ;

Step S 1 . 4 . 2 : performing coarse-grained frequency offset compensation for the short preambles, and performing step S 1 . 4 . 5 ;

Step S 1 . 4 . 3 : performing fine-grained frequency offset compensation for the long preambles, and then performing step S 1 . 4 . 5 ;

Step S 1 . 4 . 4 : caching the short preambles and the long preambles for superimposing the outcomes of frequency offset compensation, and then performing step S 1 . 4 . 5 ;

Step S 1 . 4 . 6 : outputting the compensated data to the symbol synchronization module.

The symbol synchronization comprises steps of:

Step S 1 . 5 . 1 : determining preamble type; in the case of short preambles, simultaneously performing step S 1 . 5 . 2 and step S 1 . 5 . 4 ; in the case of long preambles, simultaneously performing step S 1 . 5 . 3 and step S 1 . 5 . 4 ;

Step S 1 . 5 . 2 : performing coarse-grained autocorrelation processing to the short preambles so as to quickly perform symbol synchronization with a relatively large step, and then performing step S 1 . 5 . 5 ;

Step S 1 . 5 . 3 : performing fine-grained autocorrelation processing to the long preambles so as to perform refined symbol synchronization with a relatively small step, and then performing step S 1 . 5 . 5 ;

Step S 1 . 5 . 4 : caching the short preamble and the long preamble for symbol synchronization, and then performing step S 1 . 5 . 5 ;

The channel estimation comprises steps of:

Step S 1 . 7 . 1 : determining preamble type; in the case of short preambles, performing step S 1 . 7 . 2 ; in the case of long preambles, performing step S 1 . 7 . 4 ;

Step S 1 . 7 . 2 : performing channel interpolation to the short preambles to obtain spectra of all available sub-carriers, and performing step S 1 . 7 . 3 ;

Step S 1 . 7 . 3 : performing interpolation and filtering to the short preambles to smooth the spectra, and then performing step S 1 . 7 . 4 ;

Step S 1 . 7 . 4 : performing channel filtering to the short preambles or long preambles and then performing step S 1 . 7 . 5 ;

Step S 1 . 7 . 5 : performing phase estimation to the short preambles or the long preambles to obtain an estimated preamble value.

In the present disclosure, when transmitting a physical layer protocol frame, short preambles are first transmitted to undergo automatic gain control, channel estimation, coarse-grained frequency offset compensation, and symbol synchronization; and then long preambles are transmitted to undergo automatic gain control, channel estimation, fine-grained frequency offset compensation, and symbol synchronization. Compared with the scheme of only transmitting long preambles, the present disclosure combines transmissions of short preambles and long preambles, which thus may quickly and accurately implement frequency offset compensation, automatic gain control, symbol synchronization, and channel estimation without sacrifice of precision, thereby achieving quick convergence, reducing resource overheads and time overheads, and enhancing system performance.

FIG. 1 is a structural schematic diagram of a physical layer protocol frame provided according to the present disclosure;

FIG. 2 is a sub-carrier modulation spectrum for short preambles;

FIG. 3 is a sub-carrier modulation spectrum for long preambles/frame control symbols/data payload symbols;

FIG. 4 is a flow diagram of a method for processing short preambles and long preambles in the physical layer protocol frame;

FIG. 5 is a flow diagram of automatic gain control;

FIG. 6 is a flow diagram of frequency offset compensation;

FIG. 7 is a flow diagram of symbol synchronization; and

FIG. 8 is a flow diagram of channel estimation.

Hereinafter, the preferred embodiments of the present disclosure will be illustrated in detail with reference to FIGS. 1-8 .

The present disclosure is applicable to the low voltage broadband power line carrier communication network of the State Grid and is also applicable to communications systems satisfying other standards for low voltage broadband power line carrier communication systems.

The method for low voltage broadband power line carrier communication according to the present disclosure comprises: modulating and transmitting, by a transmitter, a physical layer protocol frame; and receiving and processing, by a receiver, the physical layer protocol frame.

As shown in FIG. 1 , the physical layer protocol frame includes: a plurality of short preambles, a plurality of long preambles, a plurality of frame control symbols, and a plurality of data payload symbols.

Particularly, a short preamble refers to a segment of known sequence, which occupies specific sub-carriers of a carrier band with a fixed frequency interval; a long preamble refers to a segment of known sequence, which occupies all available sub-carriers of the carrier band; a frame control symbol includes control information of a frame, which occupies all available sub-carriers of the carrier band; and a data payload symbol includes valid data of the frame, which occupies all available sub-carriers of the carrier band.

The modulating the physical layer protocol frame comprises steps of:

selecting a plurality of sub-carriers according to a fixed frequency interval to transmit the short preambles; and

transmitting, using all available sub-carriers, the long preambles, the frame control symbols, and the data payload symbols.

As shown in FIG. 2 , when the short preambles are modulated, the initial sub-carrier frequency point M*f 0 is first selected; then, corresponding sub-carrier frequency points are selected with X*f 0 as a frequency interval; if the size of the short preamble is N+1, a group of sub-carriers {M*f 0 ,X*f 0 +M*f 0 ,2X*f 0 +M*f 0 , . . . ,N*X*f 0 +M*f 0 } are selected to transmit the short preambles, wherein f 0 denotes the fundamental frequency, N, X, and M are all natural numbers.

As shown in FIG. 3 , f 0 denotes the fundamental frequency, and the carrier bands for modulating the long preambles, the frame control symbols, and the data payload symbols are all available carrier bands. In actual use, if a certain sub-carrier is unavailable, the sub-carrier is not in the list of all available sub-carriers. It needs to be noted that the carrier bands for modulating short preambles are a subset of carrier bands for modulating long preambles.

The receiving and processing the physical layer protocol frame comprises steps of:

Step S 1 : performing, by the receiver, direct-current estimation, automatic gain control, frequency offset compensation, symbol synchronization, and channel estimation with respect to the short preambles and long preambles received;

Step S 2 : processing, by the receiver, the frame control symbols and the data payload symbols after obtaining accurate channel information based on the outcomes from step S 1 to obtain correct data;

wherein, as shown in FIG. 4 , the processing the short preambles and long preambles in the physical layer protocol frame specifically comprises steps of:

Step S 1 . 1 : analog gain adjustment, wherein an analog gain module adjusts gain of the received analog signal;

Step S 1 . 2 : analog-to-digital conversion, wherein an analog-to-digital conversion module performs analog-to-digital conversion to the received short preambles or long preambles to produce a digital sampling signal for short preambles or long preambles of time domain;

Step S 1 . 3 : automatic gain control, wherein an automatic gain control module performs energy estimation on the digital sampling signal for the short preambles or long preambles to obtain an energy gain parameter, the energy gain parameter acting on the analog gain module to implement energy gain coefficient adjustment;

Step S 1 . 4 : direct-current estimation, wherein a direct-current estimation module performs direct-current estimation on the digital sampling signal for the short preambles or long preambles to obtain a time-domain signal;

Step S 1 . 5 : frequency offset compensation, wherein a frequency offset compensation module performs coarse-grained frequency offset compensation for the short preambles or performs fine-grained frequency offset compensation for the long preambles;

Step S 1 . 6 : symbol synchronization, wherein a symbol synchronization module performs coarse-grained autocorrelation processing to the short preambles or performs fine-grained autocorrelation processing for the long preambles, thereby implementing symbol synchronization;

Step S 1 . 7 : fast Fourier transform, wherein a fast Fourier transform module performs fast Fourier transform to the short preambles and the long preambles and then converts the fast Fourier transformed short preambles and the fast Fourier transformed long preambles from time domain to frequency domain;

Step S 1 . 8 : channel estimation, wherein a channel estimation module performs channel estimation to the short preambles or the long preambles to obtain an estimated preamble value.

As shown in FIG. 5 , the automatic gain control comprises steps of:

Step S 1 . 2 . 1 : preamble detection, wherein if the short preambles or the long preambles are detected, a counter is started;

Step S 1 . 2 . 2 : counting, by a counter, the short preambles or the long preambles, and computing energies thereof;

Step S 1 . 2 . 3 : comparing, by a comparer, short preamble energy or long preamble energy with a system set threshold, wherein the outputted energy gain parameter acts on the analog gain module to perform adjustment energy for subsequent reception;

if energy<lower threshold, the outputted energy gain parameter is a positive value; if energy> higher threshold, the outputted energy gain parameter is a negative value.

Through multiple times of automatic gain control, energy gain coefficient adjustment may be implemented quickly and accurately.

As shown in FIG. 6 , the frequency offset compensation comprises steps:

Step S 1 . 4 . 1 : determining preamble type; in the case of short preambles, simultaneously performing step S 1 . 4 . 2 and step S 1 . 4 . 4 ; in the case of long preambles, simultaneously performing step S 1 . 4 . 3 and step S 1 . 4 . 4 ;

Step S 1 . 4 . 2 : performing coarse-grained frequency offset compensation for the short preambles, and performing step S 1 . 4 . 5 ;

based on the short preamble sub-carrier modulation spectrum shown in FIG. 2 , the coarse-grained frequency offset compensation may adjust the X*f 0 frequency offset to the utmost extent, and the coarse-grained frequency offset compensation may adjust the frequency till surrounding the subcarrier center frequency point quickly with a relatively large step;

Step S 1 . 4 . 3 : performing fine-grained frequency offset compensation for the long preambles, and then performing step S 1 . 4 . 5 ;

based on the subcarrier modulated spectra for long preambles shown in FIG. 3 , the fine grain may further narrow down the offset between the to-be-estimated frequency points and the central frequency point, thereby improving precision of frequency offset compensation;

Step S 1 . 4 . 4 : caching the short preambles and the long preambles for superimposing the outcomes of frequency offset compensation, and then performing step S 1 . 4 . 5 ;

Step S 1 . 4 . 6 : outputting the compensated data to the symbol synchronization module.

Through multiple times of frequency offset compensation, the frequency offset compensation may be implemented quickly and accurately.

As shown in FIG. 7 , the symbol synchronization comprises steps of:

Step S 1 . 5 . 1 : determining preamble type; in the case of short preambles, simultaneously performing step S 1 . 5 . 2 and step S 1 . 5 . 4 ; in the case of long preambles, simultaneously performing step S 1 . 5 . 3 and step S 1 . 5 . 4 ;

Step S 1 . 5 . 2 : performing coarse-grained autocorrelation processing to the short preambles so as to quickly perform symbol synchronization with a relatively large step, and then performing step S 1 . 5 . 5 ;

Step S 1 . 5 . 3 : performing fine-grained autocorrelation processing to the long preambles so as to perform refined symbol synchronization with a relatively small step, and then performing step S 1 . 5 . 5 ;

Step S 1 . 5 . 4 : caching the short preamble and the long preamble for symbol synchronization, and then performing step S 1 . 5 . 5 ;

Through multiple times of coarse/fine-grained symbol synchronization adjustment, symbol synchronization timing may be implemented quickly and accurately.

As shown in FIG. 8 , the channel estimation comprises steps of:

Step S 1 . 7 . 1 : determining preamble type; in the case of short preambles, performing step S 1 . 7 . 2 ; in the case of long preambles, performing step S 1 . 7 . 4 ;

Step S 1 . 7 . 2 : performing channel interpolation to the short preambles to obtain spectra of all available sub-carriers, and performing step S 1 . 7 . 3 ;

Step S 1 . 7 . 3 : performing interpolation and filtering to the short preambles to smooth the spectra, and then performing step S 1 . 7 . 4 ;

Step S 1 . 7 . 4 : performing channel filtering to the short preambles or long preambles and then performing step S 1 . 7 . 5 ;

Step S 1 . 7 . 5 : performing phase estimation to the short preambles or the long preambles to obtain an estimated preamble value.

The estimated value derived from channel estimation will be used in processing frame control symbols and data payload symbols.

In the present disclosure, when transmitting a physical layer protocol frame, short preambles (SP) are first transmitted to undergo automatic gain control, channel estimation, coarse-grained frequency offset compensation, and symbol synchronization; and then long preambles (LP) are transmitted to undergo automatic gain control, channel estimation, fine-grained frequency offset compensation, and symbol synchronization. Compared with the scheme of only transmitting long preambles, the present disclosure combines transmissions of short preambles and long preambles, which thus may quickly and accurately implement frequency offset compensation, automatic gain control, symbol synchronization, and channel estimation without sacrifice of precision, thereby achieving quick convergence, reducing resource overheads and time overheads, and enhancing system performance.

Although the contents of the present disclosure have been described in detail through the foregoing preferred embodiments, it is noted that the depictions above shall not be regarded as limitations to the present disclosure. After those skilled in the art having read the contents above, many modifications and substitutions to the present disclosure are all obvious. Therefore, the protection scope of the present disclosure should be limited by the appended claims.