CN103209067B - A kind of power line OFDM pilot symbol generation method and device - Google Patents

Abstract

The invention discloses a kind of power line OFDM pilot symbol generation method and device.Its method comprises the steps: frequency pilot sign generation step, generates sequence of pilot symbols；Symbol mapping step, is respectively mapped to data symbol and described sequence of pilot symbols on effective subcarrier, thus forms the Frame comprising multiple OFDM symbol being made up of data symbol and frequency pilot sign.Owing to have employed above-mentioned pilot tone generating mode, it is fully able to the OFDM technology adapting to apply data length variable in electric lines of force, simultaneously under the power line environment of strong interference, it is possible to obtain the communication efficiency of high-quality.

Description

A kind of power line OFDM pilot symbol generation method and device

[technical field]

Field of power line communication of the present invention, particularly relates to a kind of power line OFDM pilot symbol generation method and device.

[background technology]

Power line carrier (Power Line Carrier) communication technology is called for short PLC, refers to utilize electric lines of force as information A kind of communication mode that transmission medium carries out data transmission.It can make full use of existing distribution network infrastructure, it is not necessary to Any wiring, it becomes possible to provide the user data communication services.Utilize existing electric lines of force to realize data communication, can save greatly Save the construction cost of communication network.Along with domestic intelligent grid and intelligent home network are constantly risen, power line carrier communication is won To have a fast-developing period.

But the factor of impact and restriction power line carrier communication development is a lot, letter complicated on topmost or electric lines of force Road.The feature of voltage Power Line Carrier Channel environment: various noises, various noise jamming (certain frequency, irregular, unpredictable), Various impulse disturbances (irregular, unpredictable), and time-varying decay (irregular, unpredictable so that communication distance is confined to 1000 Within meter), the multipath (maximum delay < 3us) that reflection causes.As can be seen here, voltage Power Line Carrier Channel has time variation, and impedance becomes Changing big, decay is relatively big (when especially electrical load is capacitive, to multicarrier communication signal near short circuit), and various interference noises are multiple Miscellaneous.

What domestic application was more at present is narrowband modulation technology, i.e. uses general, traditional carrier modulation technique by number The spectrum modulation of word signal, in higher carrier frequency, mainly includes amplitude keying (ASK), frequency keying (FSK) and phase place Keying (PSK) technology.But these traditional modulation techniques all have a disadvantage in that 1) capacity of resisting disturbance is more weak；2) arrowband The data rate of modulation technique is the lowest.Therefore current technology cannot meet growing power line carrier communication demand.

OFDM (Orthogonal Frequency Division Multiplexing, be abbreviated as OFDM) is A kind of special multi-carrier signal modulator approach, the significant advantage of this technology be can effective contrary frequency Selective intensity, And the availability of frequency spectrum is high compared with the transmission of Traditional parallel data.OFDM has been successfully applied in wireless communication field, and achieves Good effect.Such as digital audio broadcasting (DAB), DVB (DVB), wireless local area network (WLAN) are all applied OFDM technology, ofdm system is typically to utilize some subcarrier pilot symbol transmitted in some moment, then utilizes time-frequency domain Correlation properties carry out interpolation to obtain the frequency domain response of whole channel.

Abroad power line communication technology is studied the most for a long time, formulated some standards (such as Prime standard, ERDF G3 Standard), OFDM is introduced power line communication, this ofdm system the most only has coding module and inverse Fourier transform module. But, show through a series of field test, this OFDM technology or products application on China Power line, poor effect.Warp Crossing to research and analyse internal power line channel circumstance and learn, there is following characteristic in it: 1, due to densely populated, power network is close Cloth, electromagnetic interference ratio is stronger；2, the electromagnetic radiation of most of electrical equipment of China's application exceeds standard, and the electromagnetism brought to power network is done Disturb the strongest.External OFDM standard cannot follow the tracks of the variation characteristic of channel, thus it is under strong electromagnetic environment, it is impossible to Obtain the communication efficiency of high-quality.It addition, current pilot tone inserted mode is only applicable to the pilot tone of fixed data length, at electric lines of force In communication, especially in the electric lines of force of strong electromagnetic interference, the length of data needs constantly according to the data volume of actual transmissions Adjusting, in the case, the pilot tone inserted mode in the existing field such as wireless cannot play a role.

[summary of the invention]

The electric power environmental strong in order to adapt to electromagnetic interference, the invention provides a kind of power line OFDM pilot symbol generation method And device.

A kind of power line OFDM pilot symbol generation method, comprises the steps:

Frequency pilot sign generation step, generates sequence of pilot symbols；

Symbol mapping step, is respectively mapped to data symbol and described sequence of pilot symbols on effective subcarrier, thus Form the Frame comprising multiple OFDM symbol being made up of data symbol and frequency pilot sign.

Preferably, each OFDM symbol of described Frame has frequency pilot sign；After certain symbol period, Sub-carrier positions residing for the frequency pilot sign of rear OFDM symbol is consistent with in front OFDM symbol.

Preferably, described symbol period is N_f, in the i-th OFDM symbol of Frame, the son residing for frequency pilot sign carries Ripple position is j,

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

Wherein, i=1,2 ..., N_s, k is coefficient, N_sThe number of the OFDM symbol that the Frame of expression transmission is comprised, N_startRepresent the initial subcarrier sequence number of effective subcarrier of each OFDM symbol, N_endRepresent effective son of each OFDM symbol The terminator carrier wave sequence number of carrier wave, effective subcarrier comprises pilot sub-carrier and data subcarrier；Wherein operative symbolRepresent The maximum integer of the numerical value being not more than in this operative symbol, % represents remainder.

Preferably, described sequence of pilot symbols generates according to following algorithm: $\underset{K=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(K\right)c^{*}{(K+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.,$ Wherein * represents that complex conjugate, the cycle of c (K) are that N, c (K) represent sequence of pilot symbols k-th frequency pilot sign, and τ is Arbitrary Digit.

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

Preferably, described symbol mapping step includes:

Pilot tone inserting step, inserts between the described data symbol of serial by described frequency pilot sign, and the data of formation serial/ Pilot symbol stream；

Serioparallel exchange step, changes the circulation of described data/pilot symbol into parallel data/pilot symbols；

And subcarrier mapping step, described data/pilot symbols is mapped on subcarrier, forms OFDM symbol.

A kind of electric lines of force OFDM pilot tone generating means, including:

Frequency pilot sign generating means, is used for generating sequence of pilot symbols；

Symbol mapping device, for data symbol and described sequence of pilot symbols are respectively mapped to effective subcarrier, Thus form the Frame comprising multiple OFDM symbol being made up of data symbol and frequency pilot sign.

Preferably, each OFDM symbol of described Frame has frequency pilot sign；After certain symbol period, rear Sub-carrier positions residing for the frequency pilot sign of OFDM symbol is consistent with in front OFDM symbol.

Preferably, described symbol period is N_f, in the i-th OFDM symbol of Frame, the son residing for frequency pilot sign carries Ripple position is j,

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

Wherein, i=1,2 ..., N_s, k is coefficient, N_sThe number of the OFDM symbol that the Frame of expression transmission is comprised, N_startRepresent the initial subcarrier sequence number of effective subcarrier of each OFDM symbol, N_endRepresent effective son of each OFDM symbol The terminator carrier wave sequence number of carrier wave, effective subcarrier comprises pilot sub-carrier and data subcarrier；Wherein operative symbolRepresent The maximum integer of the numerical value being not more than in this operative symbol, % represents remainder.

Preferably, described sequence of pilot symbols generates according to following algorithm: $\underset{K=0}{\overset{N-1}{\mathrm{\&Sigma;}}}c\left(K\right)c^{*}{(K+\mathrm{\&tau;})}_{\mathrm{mod}N}=\left\{\begin{array}{c}N,\mathrm{\&tau;}=0\\ 0,\mathrm{\&tau;}\&NotEqual;0\end{array}\right.,$ Wherein * represents that complex conjugate, the cycle of c (K) are that N, c (K) represent sequence of pilot symbols k-th frequency pilot sign, and τ is Arbitrary Digit.

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

Preferably, described symbol mapping device includes:

Pilot tone insertion apparatus, between the described data symbol that described frequency pilot sign inserts serial, forms serial Data/pilot symbol stream；

Serioparallel exchange device, for changing the circulation of described data/pilot symbol into parallel data/pilot symbols；

And subcarrier mapping device, for described data/pilot symbols being mapped to subcarrier, form OFDM symbol Number.

In existing pilot configuration, the position of frequency pilot sign more disperses, and owing to it applies the data in regular length Under form, its position is also relatively fixed, and in the power line environment of intense electromagnetic interference, data length the most constantly adjusts, and leads Respective change is also wanted in frequency symbol position, thus, have employed this most intensive and there is periodic pilot interposition method, complete Entirely can adapt to the OFDM technology applying data length variable in electric lines of force, simultaneously under the power line environment of strong interference, It is obtained in that the communication efficiency of high-quality.

[accompanying drawing explanation]

Fig. 1 is a kind of specific embodiment of the electric lines of force OFDM pilot tone generating means of the present invention；

Fig. 2 is that the frequency pilot sign of the present invention inserts a kind of detailed description of the invention in data fit block；

Fig. 3 is a kind of concrete structure schematic diagram of the Frame of the present invention；

Fig. 4 is the another kind of concrete structure schematic diagram of the Frame of the present invention.

[detailed description of the invention]

Below in conjunction with specific embodiment, this explanation is expanded on further.Should be understood that this embodiment is merely to illustrate the present invention Rather than restriction the scope of the present invention.For general technical staff of the technical field of the invention, without departing from this On the premise of inventive concept, it is also possible to make some simple deduction or replace, all should be considered as belonging to protection scope of the present invention.

A kind of specific embodiment of power line OFDM pilot symbol generation method, comprises the steps:

Frequency pilot sign generation step, generates sequence of pilot symbols；

Symbol mapping step, is respectively mapped to data symbol and described sequence of pilot symbols on effective subcarrier, thus Form the Frame comprising multiple OFDM symbol being made up of data symbol and frequency pilot sign.

A kind of specific embodiment of electric lines of force OFDM pilot tone generating means, including: frequency pilot sign generating means, it is used for generating Sequence of pilot symbols；

Symbol mapping device, for data symbol and described sequence of pilot symbols are respectively mapped to effective subcarrier, Thus form the Frame comprising multiple OFDM symbol being made up of data symbol and frequency pilot sign.

CAZAC sequence is the nonbinary sequence of complex numbers of the good characteristic having possessed permanent width, zero autocorrelation.CAZAC sequence Row have the property that

(1) good autocorrelation (following shift characteristics), after i.e. moving cyclic shift to arbitrary original series with it Sequence is orthogonal；

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

(3) permanent amplitude characteristic, the i.e. arbitrarily constant amplitude of CAZAC sequence；

(4) low peak average ratio characteristic, the i.e. arbitrarily peak value of the time-domain signal of CAZAC sequence composition are the lowest with average ratio value；

In power line environment, in order to be able to obtain channel-estimation information accurately, the pilot frequency sequence of power line carrier system, Need to possess following characteristic:

(1) being the new estimation realizing unbiased, all of subcarrier need to i.e. need pilot frequency sequence to exist through identical excitation Frequency domain possesses the characteristic of permanent amplitude；

(2) for can carry out channel estimation and synchronization more accurately, pilot frequency sequence need to possess good autocorrelation with mutual Guan Xing；

(3) require that pilot frequency sequence has less peak-to-average force ratio；

Based on above-mentioned analysis, the present invention has selected CAZAC sequence as pilot frequency sequence.

Cycle is that the auto-correlation function of CAZAC sequence c (k) of N is

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

This sequence can be taken as

c(k)=exp[jrπk²/ N], r with N is relatively prime

How to construct the inserted mode of good pilot tone, need to consider following factor:

(1) interval inserted with the coherence bandwidth of channel (relevant with maximum multipath time delay), coherence time (with the most general Strangle frequency displacement relevant) relevant；

(2) placement of pilot tone must make channel estimator can with upper signal channel response change；

(3) reduce the overhead brought because placing pilot tone as far as possible；

In fields such as radio communications, pilot configuration mainly has block structure, pectinate texture, square structure and dispersed structure.

And the channel circumstance of electric lines of force is complicated, its transmission feature has: time variation is big, and impedance transformation is big, and decay is relatively big, Various interference noises are complicated.In order to preferably follow the tracks of the time-varying of channel, pilot configuration such as Fig. 2 institute of this specific embodiment design Show possess following characteristic:

(1) each frequency pilot sign meets Nyquist sampling theorem in direction, frequency domain territory；

(2) mark space of the adjacent pilot symbols on frequency axis direction is N_f, i.e. exist between adjacent pilot symbols N_fIndividual data symbol, and(τ_maxExtending for maximum delay, Δ F is the frequency interval between adjacent sub-carrier),

(3) N_sThe number of the OFDM symbol that the Frame of expression transmission is comprised, N_startRepresent having of each OFDM symbol The initial subcarrier sequence number of effect subcarrier, N_endRepresent the terminator carrier wave sequence number of effective subcarrier of each OFDM symbol.Wherein Effectively subcarrier comprises pilot sub-carrier and data subcarrier.

(4) between adjacent OFDM symbol, there is shifted relationship in pilot frequency locations, is returned to initial bit through certain symbol period Putting, i.e. pilot frequency locations cyclic shift, herein, symbol period is numerically all N with mark space_f.Therefore, pilot data can be with table It is shown as P_i,j, wherein:

i=1,2,...,N_s

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

Wherein,Represent the maximum integer being not more than itself.As:

Assuming adjacent sub-carrier frequencies interval delta F=5kHz of system, the maximum time domain that system considers expands to τ_max=20us, therefore presses According to the pilot interposition method of the present invention, the frequency interval between adjacent pilot symbols need to meet The problems such as the accuracy that the expense of the system considered and channel are estimated, can be by N_f=5。

Frequency pilot sign uses CAZAC sequence c (K)=exp [jr π K²/ N], (r Yu N is relatively prime), can be by r=1, N=10, i.e. pilot tone The generation expression formula of sequence is c (K)=exp [j π K²/10]。

As it is shown in figure 1, be the another kind of specific embodiment of pilot tone generating means of the present invention.Insert including the pilot tone being sequentially connected Enter device, serioparallel exchange device, subcarrier mapping device and IFFT converting means, data symbol generating means and CAZAC sequence Generating means is connected with pilot tone insertion apparatus respectively.

Data symbol generating means generates data symbol waiting for transmission；

CAZAC sequence generator is to generate CAZAC sequence c (K)=exp [j π K²/ 10], as the pilot tone symbol being inserted into Number sequence；

Pilot tone insertion apparatus, inserts pilot symbols in data symbol block according to structure shown in Fig. 2, the number of composition serial According to/pilot symbol stream；

Owing to effective subcarrier number of OFDM is (N_end-N_s+ 1) individual, when enter serioparallel exchange device serial data/ Frequency pilot sign number reaches (N_end-N_s+ 1) time individual, i.e. constituting one group of data/pilot symbol, serioparallel exchange device will this group number It is converted into parallel one group data/pilot symbol according to/frequency pilot sign；So repeat, until producing N_sGroup data/pilot symbol Number；As seen from Figure 2, at the frequency pilot sign of rear data/pilot symbols in the relative position residing for this group, with front data/ The frequency pilot sign of frequency pilot sign group is in the relative position consistency residing for this group.

Subcarrier mapping device, is mapped to often organizing parallel data/pilot symbol on subcarrier, forms an OFDM symbol Number, multiple OFDM symbol then constitute OFDM data frame, as it is shown on figure 3, total N_sIndividual OFDM symbol constitutes a Frame； As seen from Figure 3, through some cycles, the frequency location residing for the frequency pilot sign of posterior OFDM symbol, with preceding Frequency location residing for the frequency pilot sign of OFDM symbol is identical.

This OFDM data frame, again through IFFT changeable device, does inverse discrete Fourier's series operation, changes to time domain, enter Row sends.

As shown in Figure 4, Frame is in the sub-carrier positions of the frequency pilot sign of i-th OFDM symbol jth subcarrier For P_i,j, use following algorithm:

i=1,2,...,N_s

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

N_f=5, N_sWhen=13, during 13 OFDM symbol one OFDM data frames of composition, the distribution feelings of its data/pilot symbol Condition.By Fig. 4 figure it can be seen that through cycle N_f=5, the frequency location residing for the frequency pilot sign of posterior OFDM symbol, and front The frequency location residing for frequency pilot sign of OFDM symbol identical.

Claims (8)

1. a power line OFDM pilot symbol generation method, is characterized in that, comprises the steps:

Frequency pilot sign generation step, generates sequence of pilot symbols；

Symbol mapping step, is respectively mapped to data symbol and described sequence of pilot symbols on effective subcarrier, thus is formed Comprise the Frame of multiple OFDM symbol being made up of data symbol and frequency pilot sign；

Each OFDM symbol of described Frame has frequency pilot sign；After certain symbol period, in rear OFDM symbol The sub-carrier positions residing for frequency pilot sign consistent with in front OFDM symbol；

Described symbol period is N_f, in the i-th OFDM symbol of Frame, the sub-carrier positions residing for frequency pilot sign is j,

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

Wherein, i=1,2 ..., N_s, k is coefficient, N_sThe number of the OFDM symbol that the Frame of expression transmission is comprised, N_startTable Show the initial subcarrier sequence number of effective subcarrier of each OFDM symbol, N_endRepresent effective subcarrier of each OFDM symbol Terminator carrier wave sequence number, effective subcarrier comprises pilot sub-carrier and data subcarrier；Wherein operative symbolRepresent and be not more than The maximum integer of the numerical value in this operative symbol, % represents remainder；N is there is between adjacent pilot symbols_fIndividual data symbol, andτ_maxExtending for maximum delay, Δ F is the frequency interval between adjacent sub-carrier.

2. power line OFDM pilot symbol generation method as claimed in claim 1, is characterized in that: described sequence of pilot symbols is according to such as Lower algorithm generates:Wherein * represents that complex conjugate, the cycle of c (K) are N, c (K) Representing sequence of pilot symbols k-th frequency pilot sign, τ is Arbitrary Digit.

3. power line OFDM pilot symbol generation method as claimed in claim 2, is characterized in that:

C (K)=exp [jr π K²/ N], wherein, r with N is relatively prime, and j represents imaginary unit, and r is integer.

4. power line OFDM pilot symbol generation method as claimed in claim 3, is characterized in that, described symbol mapping step includes:

Pilot tone inserting step, inserts described frequency pilot sign between the described data symbol of serial, forms the data/pilot of serial Symbol stream；

Serioparallel exchange step, changes the circulation of described data/pilot symbol into parallel data/pilot symbols；

And subcarrier mapping step, described data/pilot symbols is mapped on subcarrier, forms OFDM symbol.

5. an electric lines of force OFDM pilot tone generating means, is characterized in that, including:

Frequency pilot sign generating means, is used for generating sequence of pilot symbols；

Symbol mapping device, for data symbol and described sequence of pilot symbols are respectively mapped to effective subcarrier, thus Form the Frame comprising multiple OFDM symbol being made up of data symbol and frequency pilot sign；

Each OFDM symbol of described Frame has frequency pilot sign；After certain symbol period, in rear OFDM symbol Sub-carrier positions residing for frequency pilot sign is consistent with in front OFDM symbol；

Described symbol period is N_f, in the i-th OFDM symbol of Frame, the sub-carrier positions residing for frequency pilot sign is j,

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

Wherein, i=1,2 ..., N_s, k is coefficient, N_sThe number of the OFDM symbol that the Frame of expression transmission is comprised, N_startTable Show the initial subcarrier sequence number of effective subcarrier of each OFDM symbol, N_endRepresent effective subcarrier of each OFDM symbol Terminator carrier wave sequence number, effective subcarrier comprises pilot sub-carrier and data subcarrier；Wherein operative symbolRepresent and be not more than The maximum integer of the numerical value in this operative symbol, % represents remainder；N is there is between adjacent pilot symbols_fIndividual data symbol, andτ_maxExtending for maximum delay, Δ F is the frequency interval between adjacent sub-carrier.

6. electric lines of force OFDM pilot tone generating means as claimed in claim 5, is characterized in that: described sequence of pilot symbols is according to such as Lower algorithm generates:Wherein * represents that complex conjugate, the cycle of c (K) are N, c (K) Representing sequence of pilot symbols k-th frequency pilot sign, τ is Arbitrary Digit.

7. electric lines of force OFDM pilot tone generating means as claimed in claim 6, is characterized in that:

C (K)=exp [jr π K²/ N], wherein, r with N is relatively prime, and r is integer.

8. electric lines of force OFDM pilot tone generating means as claimed in claim 6, is characterized in that, described symbol mapping device includes:

Pilot tone insertion apparatus, between the described data symbol that described frequency pilot sign is inserted serial, the data of formation serial/ Pilot symbol stream；

Serioparallel exchange device, for changing the circulation of described data/pilot symbol into parallel data/pilot symbols；

And subcarrier mapping device, for described data/pilot symbols being mapped to subcarrier, form OFDM symbol.