CN103209067A - Power line OFDM (Orthogonal Frequency Division Multiplexing) pilot symbol generation method and device - Google Patents

Abstract

The invention discloses a power line OFDM pilot symbol generation method and device. The power line OFDM pilot symbol generation method comprises the following steps: pilot symbol generation step: generating a pilot symbol sequence; and symbol mapping step: respectively mapping a data symbol and the pilot symbol sequence to effective subcarriers to form a data frame which comprises a plurality of OFDM signals and consists of the data symbol and the pilot symbol. By utilizing the power line OFDM pilot symbol generation method, the application to the power line of the OFDM technology with changeable data length can be completely adapted to, and meanwhile, excellent communication effect can be obtained in a power line environment with strong interference.

Description

Power line OFDM pilot frequency generation method and device

[ technical field ] A method for producing a semiconductor device

The invention belongs to the field of power line communication, and particularly relates to a power line OFDM pilot frequency generation method and device.

[ background of the invention ]

A Power Line Carrier (PLC) communication technology refers to a communication method for data transmission using a Power Line as an information transmission medium. The data communication system can fully utilize the existing distribution network infrastructure, and can provide data communication service for users without any wiring. The existing power line is utilized to realize data communication, and the construction cost of a communication network can be greatly saved. With the continuous rise of domestic smart grids and smart home networks, the power line carrier communication has won a period of rapid development.

However, there are many factors that influence and restrict the development of power line carrier communication, and most importantly, complex channels are also provided on the power line. Characteristics of the power line carrier channel environment: various noises, various clutter interferences (certain frequency, irregular and unpredictable), various impulse interferences (irregular and unpredictable), time-varying attenuation (irregular and unpredictable, so that the communication distance is limited within 1000 meters), and multipath caused by reflection (maximum delay <3 us). Therefore, the power line carrier channel has time-varying property, large impedance transformation, large attenuation (especially when the power load is capacitive, the carrier communication signal is approximately short-circuited), and various interference noises are complicated.

At present, the domestic application is mostly narrow-band modulation technology, that is, a general and traditional carrier modulation technology is adopted to modulate the frequency spectrum of a digital signal to a higher carrier frequency, and the technology mainly comprises amplitude keying (ASK), frequency keying (FSK) and phase keying (PSK). However, these conventional modulation techniques have the following disadvantages: 1) the anti-interference capability is weak; 2) the data rate of the narrowband modulation technique is low. Therefore, the current technology cannot meet the requirement of power line carrier communication which is increasingly developed.

Orthogonal Frequency Division Multiplexing (OFDM) is a special method for modulating multicarrier signals, and the technology has the significant advantages of being capable of effectively resisting Frequency selective fading and having high spectrum utilization rate compared with the traditional parallel data transmission. OFDM has been successfully applied in the field of wireless communications with good results. Such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), and Wireless Local Area Network (WLAN), all employ OFDM technology, and OFDM systems usually transmit pilot symbols at certain time instants by using certain subcarriers, and then use the correlation characteristics of the time-frequency domain to perform interpolation to obtain the frequency domain response of the whole channel.

Foreign research on power line communication technology has been long, and standards (e.g., Prime standard, ERDF G3 standard) have been established to introduce OFDM into power line communication, which OFDM system basically has only an encoding module and an inverse fourier transform module. However, a series of field tests show that the OFDM technology or the product has poor effect when applied to the power line in china. Through research and analysis on the domestic power line channel environment, the following characteristics exist: 1. the population is dense, the power grid is dense, and the electromagnetic interference is strong; 2. the electromagnetic radiation of most electrical appliances applied in China exceeds the standard, and the electromagnetic interference brought to a power grid is strong. The foreign OFDM standard cannot track the variation characteristics of the channel, and thus cannot obtain a good communication effect in a strong electromagnetic environment. In addition, the conventional pilot insertion method is only applicable to a pilot with a fixed data length, and in power line communication, particularly in a power line with strong electromagnetic interference, the length of data needs to be adjusted continuously according to the data amount actually transmitted.

[ summary of the invention ]

The invention provides a power line OFDM pilot frequency generation method and device in order to adapt to a power environment with strong electromagnetic interference.

A power line OFDM pilot frequency generation method comprises the following steps:

a pilot symbol generation step of generating a pilot symbol sequence;

and a symbol mapping step of mapping the data symbols and the pilot symbol sequence to effective subcarriers respectively, thereby forming a data frame comprising a plurality of OFDM symbols consisting of the data symbols and the pilot symbols.

Preferably, each OFDM symbol of the data frame has a pilot symbol; after a certain symbol period, the position of the sub-carrier where the pilot symbol of the following OFDM symbol is located is consistent with that of the preceding OFDM symbol.

Preferably, the symbol period is N_fIn the ith OFDM symbol of the data frame, the position of the sub-carrier where the pilot symbol is located is j,

j=N_start-1+(i%N_f)+(k-1)N_f

wherein i =1,2_sK is a coefficient, N_sIndicating the number of OFDM symbols contained in the transmitted data frame, N_startDenotes the starting subcarrier number, N, of the active subcarriers of each OFDM symbol_endIndicating the number of the terminal sub-carrier of the effective sub-carrier of each OFDM symbol, the effective sub-carrier contains the pilot sub-carrierWave and data subcarriers; wherein the operation sign

Denotes the largest integer not greater than the value within the operator,% denotes the remainder.

Preferably, the pilot symbol sequence is generated according to the following algorithm: $\underset{K=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(K\right)c^{*}{(K+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.,$ where denotes the complex conjugate, the period of c (K) is N, c (K) denotes the kth pilot symbol of the pilot symbol sequence, and τ is an arbitrary number.

Preferably, c (K) = exp [ jr π K²/N]Wherein r is prime to N, j represents an imaginary unit, and r is an integer.

Preferably, the symbol mapping step includes:

a pilot insertion step of inserting the pilot symbols between the serial data symbols to form a serial data/pilot symbol stream;

a serial-to-parallel conversion step of converting the data/pilot symbol stream into a parallel data/pilot symbol group;

and a sub-carrier mapping step, wherein the data/pilot frequency symbol group is mapped to the sub-carrier to form the OFDM symbol.

A power line OFDM pilot generation apparatus comprising:

pilot symbol generating means for generating a pilot symbol sequence;

and the symbol mapping device is used for respectively mapping the data symbols and the pilot symbol sequences onto the effective subcarriers so as to form a data frame comprising a plurality of OFDM symbols consisting of the data symbols and the pilot symbols.

Preferably, each OFDM symbol of the data frame has a pilot symbol; after a certain symbol period, the position of the sub-carrier where the pilot symbol of the following OFDM symbol is located is consistent with that of the preceding OFDM symbol.

Preferably, the symbol period is N_fIn the ith OFDM symbol of the data frame, the position of the sub-carrier where the pilot symbol is located is j,

j=N_start-1+(i%N_f)+(k-1)N_f

wherein i =1,2_sK is a coefficient, N_sIndicating the number of OFDM symbols contained in the transmitted data frame, N_startDenotes the starting subcarrier number, N, of the active subcarriers of each OFDM symbol_endThe serial number of a termination subcarrier of an effective subcarrier of each OFDM symbol is represented, and the effective subcarrier comprises a pilot subcarrier and a data subcarrier; wherein the operation sign

Denotes the largest integer not greater than the value within the operator,% denotes the remainder.

Preferably, the pilot symbol sequence is generated according to the following algorithm: $\underset{K=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(K\right)c^{*}{(K+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.,$ where denotes the complex conjugate, the period of c (K) is N, c (K) denotes the kth pilot symbol of the pilot symbol sequence, and τ is an arbitrary number.

Preferably, c (K) = exp [ jr π K²/N]Wherein r and N are relatively prime, and r is an integer.

Preferably, the symbol mapping means comprises:

pilot insertion means for inserting said pilot symbols between said data symbols in series to form a serial data/pilot symbol stream;

a serial-to-parallel conversion means for converting the stream of data/pilot symbols into a parallel set of data/pilot symbols;

and subcarrier mapping means for mapping the data/pilot symbol groups onto subcarriers to form OFDM symbols.

In the existing pilot frequency structure, the positions of pilot frequency symbols are scattered, and because the positions of the pilot frequency symbols are relatively fixed when the pilot frequency symbols are applied to a data format with fixed length, the data length is often continuously adjusted in a power line environment with strong electromagnetic interference, and the positions of the pilot frequency symbols are also correspondingly changed, therefore, the pilot frequency inserting method which is dense and has periodicity is adopted, the method can be completely suitable for applying the OFDM technology with variable data length in the power line, and meanwhile, the high-quality communication effect can be obtained in the power line environment with strong interference.

[ description of the drawings ]

Fig. 1 is a specific embodiment of a power line OFDM pilot generation apparatus of the present invention;

FIG. 2 is an embodiment of pilot symbol insertion into a data symbol block according to the present invention;

FIG. 3 is a diagram of a specific structure of a data frame according to the present invention;

fig. 4 is another specific structure diagram of the data frame of the present invention.

[ detailed description ] embodiments

The description is further illustrated below with reference to specific examples. It should be understood that this example is only for illustrating the present invention and is not intended to limit the scope of the present invention. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

A specific embodiment of the power line OFDM pilot generation method includes the following steps:

a pilot symbol generation step of generating a pilot symbol sequence;

and a symbol mapping step of mapping the data symbols and the pilot symbol sequence to effective subcarriers respectively, thereby forming a data frame comprising a plurality of OFDM symbols consisting of the data symbols and the pilot symbols.

A specific embodiment of the power line OFDM pilot generation apparatus includes: pilot symbol generating means for generating a pilot symbol sequence;

and the symbol mapping device is used for respectively mapping the data symbols and the pilot symbol sequences onto the effective subcarriers so as to form a data frame comprising a plurality of OFDM symbols consisting of the data symbols and the pilot symbols.

CAZAC sequences are non-binary complex sequences having excellent characteristics of constant amplitude and zero autocorrelation. CAZAC sequences have the following characteristics:

(1) good autocorrelation (cyclic shift characteristic), that is, the arbitrary original sequence and the sequence after cyclic shift are not correlated;

(2) good cross-correlation, i.e. cross-correlation and partial correlation values close to zero;

(3) constant amplitude characteristics, i.e. the amplitude of any CAZAC sequence is constant;

(4) low peak-to-average ratio (i.e., the ratio of the peak value to the average value of a time domain signal composed of any CAZAC sequence is very low);

in a power line environment, in order to obtain accurate channel estimation information, a pilot sequence of a power line carrier system needs to have the following characteristics:

(1) in order to realize unbiased new estimation, all subcarriers need to be excited identically, that is, a pilot frequency sequence is required to have a constant amplitude characteristic in a frequency domain;

(2) in order to more accurately perform channel estimation and synchronization, the pilot sequence needs to have good autocorrelation and cross correlation;

(3) the pilot frequency sequence is required to have smaller peak-to-average ratio;

based on the above analysis, the present invention selects CAZAC sequence as the pilot sequence.

The autocorrelation function of a CAZAC sequence c (k) of period N is

$\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(k\right)c^{*}{(k+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.$

The sequence may be taken as

c(k)=exp[jrπk²/N]R is coprime to N

How to construct a good pilot insertion method needs to consider the following factors:

(1) the interval of the insertion is related to the coherence bandwidth (related to maximum multipath delay) and the coherence time (related to maximum doppler shift) of the channel;

(2) the placement of the pilots must be such that the channel estimator can keep up with the changes in the channel response;

(3) the system overhead caused by pilot frequency placement is reduced as much as possible;

in the fields of wireless communication and the like, the pilot frequency structure mainly comprises a block structure, a comb structure, a square structure and a dispersion structure.

The channel environment of the power line is complex, and the channel transmission characteristics are as follows: the time-varying property is large, the impedance transformation is large, the attenuation is large, and various interference noises are complex. In order to better track the time variation of the channel, the pilot structure designed in this embodiment is as shown in fig. 2, and has the following characteristics:

(1) each pilot frequency symbol satisfies the Nyquist sampling theorem in the direction of a frequency domain;

(2) the symbol interval of adjacent pilot symbols in the direction of the frequency axis is N_fI.e. there is N between adjacent pilot symbols_fA data symbol, and

（τ_maxfor maximum delay spread, af is the frequency spacing between adjacent subcarriers),

（3）N_sindicating the number of OFDM symbols contained in the transmitted data frame, N_startDenotes the starting subcarrier number, N, of the active subcarriers of each OFDM symbol_endAnd a terminal subcarrier number indicating an effective subcarrier of each OFDM symbol. Wherein the active subcarriers include pilot subcarriers and data subcarriers.

(4) Between adjacent OFDM symbols, pilotThe position has a shift relation and returns to the initial position after a certain symbol period, i.e. the pilot frequency position is circularly shifted, wherein the symbol period is equal to the symbol interval in value N_f. Thus, the pilot data may be denoted as P_i,jWherein:

i=1,2,...,N_s

j=N_start-1+(i%N_f)+(k-1)N_f

wherein,

representing the largest integer no greater than itself. Such as:

assuming that the adjacent subcarrier frequencies of the system are spaced apart by Δ F =5kHz, the maximum time domain spread considered by the system is τ_max=20us, therefore, according to the pilot insertion method of the present invention, the frequency spacing between adjacent pilot symbols needs to be satisfied

Considering the overhead of the system and the accuracy of the channel estimation, N may be used_f=5。

The pilot symbols adopt CAZAC sequence c (K) = exp [ jr pi K²/N](r is prime to N), r =1, N =10, i.e. the generation expression of the pilot sequence is c (K) = exp [ j π K =²/10]。

Fig. 1 shows another embodiment of the pilot generation apparatus of the present invention. The device comprises a pilot frequency insertion device, a serial-parallel conversion device, a subcarrier mapping device and an IFFT conversion device which are connected in sequence, wherein a data symbol generation device and a CAZAC sequence generation device are respectively connected with the pilot frequency insertion device.

The data symbol generating device generates a data symbol to be transmitted;

the CAZAC sequence generator generates a CAZAC sequence c (K) = exp [ j π K²/10]As a pilot symbol sequence to be inserted;

pilot insertion means for inserting pilot symbols into the data symbol blocks according to the structure shown in fig. 2 to form a serial data/pilot symbol stream;

the number of effective subcarriers of OFDM is (N)_end-N_s+1, when the number of serial data/pilot symbols entering the serial-to-parallel conversion device reaches (N)_end-N_s+1), a group of data/pilot symbols is formed, and the serial-parallel conversion device converts the group of data/pilot symbols into a parallel group of data/pilot symbols; repeating the above steps until the Nth step is generated_sGroup data/pilot symbols; as can be seen from fig. 2, the relative positions of the pilot symbols of the following data/pilot symbol group in the group are identical to the relative positions of the pilot symbols of the preceding data/pilot symbol group in the group.

A sub-carrier mapping device, which maps each group of parallel data/pilot frequency symbols to sub-carriers to form an OFDM symbol, and a plurality of OFDM symbols form an OFDM data frame, as shown in FIG. 3, the total number of N_sThe OFDM symbols constitute a data frame; as can be seen from fig. 3, after a certain period, the frequency position of the pilot symbol of the following OFDM symbol is the same as the frequency position of the pilot symbol of the preceding OFDM symbol.

The OFDM data frame is processed by an IFFT changing device to do inverse discrete Fourier changing operation, and is changed to a time domain to be sent.

As shown in fig. 4, the sub-carrier position of the pilot symbol in the jth sub-carrier of the ith OFDM symbol in the data frame is P_i,jThe following algorithm is used:

i=1,2,...,N_s

j=N_start-1+(i%N_f)+(k-1)N_f

N_f=5，N_sif =13, the data/pilot symbols are distributed when 13 OFDM symbols constitute one OFDM data frame. As can be seen from the graph of FIG. 4, over a period N_f=5, the frequency position where the pilot symbol of the following OFDM symbol is located is the same as the frequency position where the pilot symbol of the preceding OFDM symbol is located.

Claims (12)

1. A power line OFDM pilot frequency generation method is characterized by comprising the following steps:

a pilot symbol generation step of generating a pilot symbol sequence;

and a symbol mapping step of mapping the data symbols and the pilot symbol sequence to effective subcarriers respectively, thereby forming a data frame comprising a plurality of OFDM symbols consisting of the data symbols and the pilot symbols.

2. The method for generating power line OFDM pilot as claimed in claim 1, wherein: each OFDM symbol of the data frame has a pilot symbol; after a certain symbol period, the position of the sub-carrier where the pilot symbol of the following OFDM symbol is located is consistent with that of the preceding OFDM symbol.

3. The method for generating power line OFDM pilot as claimed in claim 2, wherein: the symbol period is N_fIn the ith OFDM symbol of the data frame, the position of the sub-carrier where the pilot symbol is located is j,

j=N_start-1+(i%N_f)+(k-1)N_f

wherein i =1,2_sK is a coefficient, N_sIndicating the number of OFDM symbols contained in the transmitted data frame, N_startDenotes the starting subcarrier number, N, of the active subcarriers of each OFDM symbol_endThe serial number of a termination subcarrier of an effective subcarrier of each OFDM symbol is represented, and the effective subcarrier comprises a pilot subcarrier and a data subcarrier; wherein the operation sign

Denotes the largest integer not greater than the value within the operator,% denotes the remainder.

4. A power line OFDM pilot generation method as claimed in any one of claims 1 to 3, wherein: the pilot symbol sequence is generated according to the following algorithm: $\underset{K=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(K\right)c^{*}{(K+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.,$ where denotes the complex conjugate, the period of c (K) is N, c (K) denotes the kth pilot symbol of the pilot symbol sequence, and τ is an arbitrary number.

5. The power line OFDM pilot generation method of claim 4, wherein: c (K) = exp [ jr π K²/N]Wherein r is prime to N, j represents an imaginary unit, and r is an integer.

6. The power line OFDM pilot generation method as claimed in claim 4, wherein said symbol mapping step comprises:

a pilot insertion step of inserting the pilot symbols between the serial data symbols to form a serial data/pilot symbol stream;

a serial-to-parallel conversion step of converting the data/pilot symbol stream into a parallel data/pilot symbol group;

and a sub-carrier mapping step, wherein the data/pilot frequency symbol group is mapped to the sub-carrier to form the OFDM symbol.

7. A power line OFDM pilot generation apparatus, comprising:

pilot symbol generating means for generating a pilot symbol sequence;

and the symbol mapping device is used for respectively mapping the data symbols and the pilot symbol sequences onto the effective subcarriers so as to form a data frame comprising a plurality of OFDM symbols consisting of the data symbols and the pilot symbols.

8. The power line OFDM pilot generation apparatus as claimed in claim 7, wherein: each OFDM symbol of the data frame has a pilot symbol; after a certain symbol period, the position of the sub-carrier where the pilot symbol of the following OFDM symbol is located is consistent with that of the preceding OFDM symbol.

9. The power line OFDM pilot generation apparatus as claimed in claim 8, wherein: the symbol period is N_fIn the ith OFDM symbol of the data frame, the position of the sub-carrier where the pilot symbol is located is j,

j=N_start-1+(i%N_f)+(k-1)N_f

wherein i =1,2_sK is a coefficient, N_sIndicating the number of OFDM symbols contained in the transmitted data frame, N_startDenotes the starting subcarrier number, N, of the active subcarriers of each OFDM symbol_endThe serial number of a termination subcarrier of an effective subcarrier of each OFDM symbol is represented, and the effective subcarrier comprises a pilot subcarrier and a data subcarrier; wherein the operation sign

Denotes the largest integer not greater than the value within the operator,% denotes the remainder.

10. The power line OFDM pilot generation apparatus as claimed in any of claims 7 to 9, wherein: the pilot symbol sequence is calculated as followsGenerating: $\underset{K=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(K\right)c^{*}{(K+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.,$ where denotes the complex conjugate, the period of c (K) is N, c (K) denotes the kth pilot symbol of the pilot symbol sequence, and τ is an arbitrary number.

11. The power line OFDM pilot generation apparatus as claimed in claim 10, wherein: c (K) = exp [ jr π K²/N]Wherein r and N are relatively prime, and r is an integer.

12. The power line OFDM pilot generating device as claimed in claim 10, wherein said symbol mapping means comprises:

pilot insertion means for inserting said pilot symbols between said data symbols in series to form a serial data/pilot symbol stream;

a serial-to-parallel conversion means for converting the stream of data/pilot symbols into a parallel set of data/pilot symbols;

and subcarrier mapping means for mapping the data/pilot symbol groups onto subcarriers to form OFDM symbols.

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