CN102202028A - Method for designing cognitive high-speed wireless communication system under discrete spectrum condition - Google Patents

Abstract

The invention discloses a design method of a cognitive high-speed wireless communication system under discrete frequency spectrum conditions. In particular, a high-speed cognitive wireless communication system and method under discrete frequency spectrum conditions are disclosed. The system includes an authorized frequency band analysis module, an unlicensed frequency band analysis module and a data modulation module. The authorized frequency band analysis module performs spectrum analysis on the authorized frequency band of the communication system to obtain the first available frequency band; the unlicensed frequency band analysis module analyzes other frequency bands other than the authorized frequency band of the communication system, or at least one other The authorized frequency band of the system is analyzed to obtain the second available frequency band; the data modulation module uses OFDM/OFDMA to modulate the data to be sent based on the first available frequency band and the second available frequency band.

Description

The cognitive high-speed radiocommunication system method for designing of discrete spectrum condition

Technical field

The application relates to the frequency spectrum perception technology in the wireless communication system.

Background technology

Be well positioned to meet in the 2G mobile communication under the condition of voice communication demand, the develop rapidly that remains unchanged of current wireless communication technology, its main target is exactly in order to satisfy growing high data rate demand.Time Division Multiplexing, code division multiplexing (CDM), frequency division multiplexing traditional multiplex techniques such as (FDM), and such as OFDM (OFDM), smart antenna, the integrated application of technology such as link circuit self-adapting is for the design of high-speed radiocommunication system provides allocation plan flexibly.

In these technology, because OFDM availability of frequency spectrum height, and can effectively overcome the advantages such as intersymbol interference that multipath effect causes, more and more be subjected to the favor of industry.At present, 3GPP and 3GPP2 have been defined as the OFDM technology key physical layer technology of 4G, and replace the CDM technology with this.

Measurement and analysis to communication spectrum and utilance thereof shows in recent years, and current frequency spectrum resource situation main cause in short supply is not that the physics frequency range is less, but cause owing to the availability of frequency spectrum of having authorized frequency range is very low.The measurement result to domestic a few quasi-representative scenes according to research institute of recent China Mobile wireless technology research institute shows, the reason that the availability of frequency spectrum is very low mainly contains: on the one hand, because the limitation of History Understanding and technology, the spectrum allocation may standard of continuing to use at present remain FCC in the nineteen twenty-seven promulgation.Because adopt the fixed frequency spectrum method of salary distribution, many practical efficiencies of frequency range that distributed are very low, make frequency spectrum shortage and frequency spectrum intensification of contradictions more than needed.On the other hand, to the deficiency of availability of frequency spectrum technological development efficiently, and this improves the extremely heavy approach of frequency spectrum resource short supply state just at present.Therefore, under existing spectrum allocation may mode caused situation that resource is not fully utilized, the new technology of actively developing high spectrum utilization effectively was particularly important.

Summary of the invention

According to the application's one side, a kind of data-modulated system is provided, comprising:

Authorize the frequency range analysis module, the mandate frequency range of communication system is carried out spectrum analysis, to obtain first available frequency band;

Unauthorized frequency range analysis module is analyzed other frequency range outside the mandate frequency range of described communication system or the mandate frequency range that is different from least one other system of described communication system, to obtain second available frequency band; And

The data-modulated module based on described first available frequency band and described second available frequency band, adopts the OFDM/OFDMA mode that the data that will send are modulated.

Described data-modulated module be configured to mode with zero padding with described data-modulated to the subcarrier of described first available frequency band and described second available frequency band.

As a kind of selection, described data-modulated module is configured to the cutting of dividing into groups of described first available frequency band and described second available frequency band, and with on described data-modulated each available frequency band after the grouping cutting.

According to the application on the other hand, provide a kind of data modulation method, having comprised:

The mandate frequency range of communication system is carried out spectrum analysis to obtain first available frequency band;

Other frequency range outside the mandate frequency range of described communication system or the mandate frequency range that is different from least one other system of described communication system are analyzed, to obtain second available frequency band; And

Based on described first available frequency band and described second available frequency band, adopt the OFDM/OFDMA mode that the data that will send are modulated.

Wherein, the described step that adopts the OFDM/OFDMA mode that the data that will send are modulated comprises:

With the mode of zero padding with described data-modulated to the subcarrier of described first available frequency band and described second available frequency band.

As a kind of selection, the step that described employing OFDM/OFDMA mode is modulated the data that will send can comprise:

First available frequency band and described second available frequency band are divided into groups to cut; And

On described data-modulated each available frequency band after the grouping cutting.

Brief Description Of Drawings

Fig. 1 shows the data-modulated system according to an execution mode of the application;

The discrete spectrum that Fig. 2 shows ideally distributes;

Figure 3 shows that the block diagram of the concrete parts of the unauthorized frequency range sensing module shown in Fig. 1;

The signal spectrum that is after direct OFDM modulates shown in Figure 4;

Figure 5 shows that the block diagram of the concrete parts of the modulating unit shown in Fig. 1;

Fig. 6 shows under desirable discrete spectrum condition, string character and modulated sub-carriers corresponding relation during N=19;

Fig. 7 shows under the discrete spectrum condition of reality, string character and modulated sub-carriers corresponding relation during N=19;

Fig. 8 also schematically shows according to demodulating unit the application, that use at data receiver;

Fig. 9 (a) shows according to a FFT embodiment of the application, that carry out OFDM data padding modulation at transmitting terminal and realizes; Fig. 9 (b) shows according to a FFT embodiment of the application, that carry out the data zero suppression at receiving terminal and realizes;

When Figure 10 shows OFDM radio frequency grouping modulation, string character and modulated sub-carriers corresponding relation when N=19;

Figure 11 shows under actual discrete frequency spectrum condition, OFDM radio frequency grouping modulation up-conversion stage schematic diagram; And

Figure 12 (a) and Figure 12 (b) show the FFT realization of carrying out OFDM radio frequency grouping modulation at transmitting terminal respectively, and the FFT realization of carrying out the data zero suppression at receiving terminal.

Embodiment

With reference to the accompanying drawings the data-modulated system according to the application's embodiment is described in detail.

Fig. 1 shows the data-modulated system 1000 according to an execution mode of the application.System 1000 comprises authorizes frequency range analysis module 10, unauthorized frequency range analysis module 20 and data-modulated module 30.

Authorize the mandate frequency range of 10 pairs of communication systems of frequency range analysis module to carry out spectrum analysis.Analyze the result who obtains and for example be labeled as f (A).

Unauthorized frequency range sensing module 20 is by measuring wireless energy signal on frequency domain, other frequency range outside the above-mentioned mandate frequency range of perception, for example, the situation of utilizing of the frequency range that departments such as electric power, amateur radio station, geological and mineral, water conservancy, meteorology, army are used is detected, and acquisition idling-resource wherein, for example be labeled as f (B).Frequency spectrum perception will determine whether on frequency domain that exactly signal takies, and finds available " cavity ".Based on the frequency spectrum perception of energy measuring, the receiver of communication system needn't be known the feature that any relevant main user transmits in advance.Successively by mould/number (A/D) conversion, make comparisons this result and threshold value, thereby judge whether current channel has main CU by the sampling summation with signal for receiver; This will be described in detail with reference to Fig. 2 below.By counting of increase sampling computing, or increase the time span of the each received signal of receiver, can increase the accuracy of energy measuring.

Data-modulated module 30 passes through to integrate above-mentioned all frequency resource f (A+B), and employing is modulated the data that will send based on the OFDM/OFDMA mode based on frequency resource f (A+B).In one embodiment, suppose frequency spectrum condition ideal, promptly as shown in Figure 2.At this moment, available discrete spectrum bounds just overlaps with experimental process carrier spectrum scope, and available frequency band is f0, f1, f2, f3, f (m), f (m+1), f (N-3), f (N-2) and f (N-1), shown in dark part among the figure, all the other white portions are represented unauthorized frequency range.Ideally this, if can partly transmit signal, and, just can realize effective utilization of frequency spectrum resource, and the availability of frequency spectrum can reach 100% in the not number of delivering a letter of white portion in dark color.

Figure 3 shows that the block diagram of unauthorized frequency range sensing module 20.The signal Y of 201 pairs of receptions of A/D converting unit that unauthorized frequency range sensing module 20 comprises is converted to digital signal Y[n].The digital signal Y[n of 202 pairs of conversions of energy calculation unit] summation of sampling.Here, suppose

H0：Y[n]＝W[n]；

H1：Y[n]＝h[n]*X[n]+W[n] 1)

In the following formula, H0 is the hypothesis of frequency range free time, and H1 is the busy hypothesis of frequency range.W is additive white Gaussian noise (AWGN), and X is main user's a transmission signal, and h is the channel filtering coefficient between main user and the cognitive user, can be undertaken that channel estimating is approximate to be drawn by each cognitive user.Y is the received signal of cognitive user.N=1,2 ..., N, wherein N is the sampling integer.

Suppose that additive white Gaussian noise has zero-mean and variance is σ _w ², then energy calculation unit 202 is calculated the signal statistics amount T that detects:

$T=\underset{n}{\mathrm{\Σ}}{\left(Y\right[n\left]\right)}^2---2)$

Detection threshold determination module 203 is used for determining detection threshold γ.The principle that detection threshold determination module 203 is followed when detection threshold γ is as follows.

Detection threshold determination module 203 is at first determined false alarm probability P _Af, the detection probability of calculating then under certain signal to noise ratio (snr) situation is weighed the detection performance.During the cognitive radio frequency spectrum, require to guarantee that as much as possible main user is interference-free, promptly the smaller the better to the interference of busy frequency range, and detection probability is the bigger the better.

In this embodiment, the approximate Gaussian Profile that meets of detection statistic T:

H0：T～Normal(Nσ _w ²，2Nσ _w ⁴)

3)

H1：T～Normal(N(σ _w ²+σ _x ²)，2N(σ _w ²+σ _x ²) ²)

Wherein, N is hits (detection time), σ _w ²Be white noise variance, σ _x ²Be average power signal.

Because under the H0 situation, T meets Gaussian Profile, P _Af=P (T＞γ | H0), then

$P_{\mathrm{af}}=Q\left(\frac{\mathrm{\γ}-N{\mathrm{\σ}}_w^2}{\sqrt{2N{\mathrm{\σ}}_w^4}}\right)---4)$

In the formula,

So by formula 4) know, as false alarm probability P _AfAfter determining, detection threshold has just determined thereupon that also promptly, detection threshold γ is

$\mathrm{\γ}={\mathrm{\σ}}_w^2(N+\sqrt{2N}{Q}^{-1}\left(P_{\mathrm{af}}\right))---5)$

In like manner, under the H1 condition, detection statistic also meets Gaussian Profile, so detection probability

$P_d=P(T>\mathrm{\γ}|H_1)=Q\left(\frac{\mathrm{\γ}-N({\mathrm{\σ}}_w^2+{\mathrm{\σ}}_x^2)}{\sqrt{{2N({\mathrm{\σ}}_w^2+{\mathrm{\σ}}_x^2)}^2}}\right)---6)$

With formula 5) the detection threshold substitution (3) that obtains can obtain detection probability, and wherein signal to noise ratio snr is

From top analysis as can be seen, when having determined P _AfAfter, under the known condition of noise variance, just can calculate detection threshold γ, with detection threshold γ substitution 6) formula, just can obtain the detection probability Pd under the current signal to noise ratio condition.

Judging module 204 compares statistic T and the detection threshold γ that tries to achieve, and exports usable spectrum in the unauthorized frequency range according to relatively result.Here, the higher detection probability means that not the user to busy frequency range produces interference, and lower false alarm probability means that we can make full use of idle frequency range.

By above-mentioned each module 201～204, can under the discrete spectrum condition, obtain current available discrete frequency range, and guarantee under the condition of higher detection probability and lower false alarm probability, to communicate.

To further describe the concrete work disposal of data-modulated module 30 referring to accompanying drawing below.

The bandwidth of supposing each available discrete frequency is greater than a subcarrier bandwidth, and outside each available discrete frequency point ranges, each subcarrier is necessary for zero, to avoid interference the unauthorized frequency range that has main telex network so.

Usually, no matter be under ideal or the non-ideality, the frequency spectrum situation all is arrowband, discrete, therefore directly uses the OFDM modulation also can produce modulation signal in unauthorized frequency range, disturbs thereby produce.The signal spectrum that is after direct OFDM modulates shown in Figure 4.Can see that by Fig. 4 the bandwidth of each sub-carrier signal is BW/N.Simultaneously, the shared total frequency band of this N subcarrier must be continuous, adjacent sub-carrier centre frequency interval delta f=1/NTs, (Ts is the string character Cycle Length to each subcarrier bandwidth 1/NTs, N is the parallel channel number, and NTs is an OFDM symbol period length), total bandwidth is BW.That is to say,, can not intactly carry out the OFDM modulation, otherwise also can produce modulation signal, disturb thereby produce in unauthorized frequency range for the symbols streams that will send.Therefore, in some communications applications, for example require to use in the OFDM High Speed Modulation mode continuous frequency range, that 4G communication (communication of the 4th generation) is adopted of one section broad, can not directly use the OFDM modulation.In order to satisfy the discrete spectrum condition, the application's data-modulated module 30 proposes two kinds of amended schemes, i.e. OFDM data padding modulation and OFDM radio frequency grouping modulator approach.

1.OFDM data padding modulation:

Modulate for the OFDM data padding, the functional module that in traditional OFDM modulation flow process, has added frequency spectrum perception and data padding, all pairing subcarriers of busy frequency spectrum that perceive are carried out data padding, thereby make through being fit to current discrete spectrum condition after the process of the data flow after the zero padding OFDM modulation.

As shown in Figure 5, data-modulated module 30 comprises digital coding unit 301, serial/parallel (S/P) converting unit 302, modulating unit 303 and sum unit 304.

Digital coding unit 301 is the serial bit stream of Rb bit/s from the transmitting terminal receiving velocity of ofdm system, then the bit stream that receives is encoded, so that every log2M bit is mapped as a symbol (M is the symbol numbers of symbol space), be the serial symbol stream of Rs=Rb/log2M symbol/s and produce speed:

Dn=a (n)+jb (n), wherein, symbol period Ts=1/Rs (s of unit).

Then, after these string characters are operated through data padding, be converted to N road parallel symbol by serial 302, in N the orthogonal sub-carriers in each symbol-modulated available frequency band one, modulating unit 303 is modulated to N road parallel symbol on the subcarrier of corresponding available frequency band, then, sum unit 304 will be modulated to data addition corresponding subcarrier, after N the modulation.

Can realize that by suitably choosing f0 and subcarrier spacing each subcarrier is mutually orthogonal, (Ts is the string character Cycle Length to get subcarrier spacing Δ f=1/NTs, N is the parallel channel number, NTs is an OFDM symbol period length), and f0=k/NTs (wherein k is the integer more than or equal to zero, generally get 0), fn=f0+n Δ f then can keep quadrature between each subcarrier in an OFDM symbol period.

In ofdm system, every N subcarrier sum can be called as an OFDM symbol (broad-band channel is divided into N narrowband subchannels).Specifically be expressed as:

$X\left(t\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}[a\left(n\right)\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000065163900021.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&pi;fnt}+b\left(n\right)\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HSA00000065163900021.png"\; state="\{\{state\}\}">sin</figure-callout>}2\mathrm{\&pi;fnt}]$

The concrete principle of string character zero padding is with reference to Fig. 6, for given serial symbol stream d (n)=a (n)+j*b (n), d (3) zero padding afterwards is some, pass d (4) again, d this moment (4) no longer modulates the 5th subcarrier, but modulate m+1 subcarrier (m=9), corresponding subcarrier frequency f (m).And the modulation symbol of corresponding the 5th subcarrier was zero at this moment, by the multiplication relation that modulating unit 303 is realized, and 0*cos (2 π * f (4))+0*sin (2 π * f (4))=0, promptly this moment, centre frequency was that the modulated subcarriers of f (4) also is to be 0 on frequency spectrum.Therefore, be equivalent to not take unauthorized frequency range, promptly satisfied unauthorized frequency range subcarrier under the discrete spectrum condition and be necessary for zero requirement.The frequency of back and subcarrier corresponding relation are analogized by this zero padding method.

By after the said method zero padding modulation, in one embodiment, for example again the OFDM symbol is sent into channel through up-conversion (multiply by a centre frequency be fc carrier wave) and transmit.

Can see, under desirable discrete spectrum condition, after OFDM data padding modulation, can effectively utilize each to authorize frequency range, and do not disturb for unauthorized frequency range.Under actual discrete frequency spectrum condition, the bandwidth of each frequency range can not all take with subcarrier, but should reserve some protection sidebands, to avoid interference unauthorized frequency range.This moment, the availability of frequency spectrum did not reach 100%.Schematic diagram under the actual discrete frequency spectrum condition as shown in Figure 7.

As seen, the centre frequency of each modulated subcarriers must guarantee that its sideband does not drop on outside the mandate frequency range, and this moment, the availability of frequency spectrum had decline slightly.

Regard the symbol sum on the synchronization parallel channel after the zero padding as an OFDM symbol X (t), X (t) sampled with the time interval of Δ t=Ts (Ts is the string character Cycle Length), can obtain its discrete form:

$X\left(\mathrm{mTs}\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}[a\left(n\right)\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000065163900021.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&pi;fn}\left(\mathrm{mTs}\right)+b\left(n\right)\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HSA00000065163900021.png"\; state="\{\{state\}\}">sin</figure-callout>}2\mathrm{\&pi;fn}\left(\mathrm{mTs}\right)]$

In the formula, m=0,1 ..., N-1.According to the Nyquist sampling theorem, we know, these components are carried out low-pass filtering with the Δ t time interval, promptly carry out the D/A conversion, then can reply again into original analog signal X (t).

With fn=f0+n Δ f substitution (wherein, f0=k/NTs, and get the integral multiple that k is N, general f0=0), then following formula can be write

$X\left(m\right)=\mathrm{Re}\left\{\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\right[a\left(n\right)+\mathrm{jb}\left(n\right)\left]e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA00000065163900021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;nm}/N}\right\},(m=\mathrm{0,1,2}...,N-1)$

Sequence x[n just in the braces { }]=a (n)+jb (n), (n=0,1 ..., discrete Fourier transform (DFT) N-1) (DFT).

As seen, the also available DFT of the modulation treatment that modulating unit 303 is realized (shown in the inner branch of the frame of broken lines of Fig. 5) realizes, get the real part of DFT output, can revert to original analog signal X (t) again through D/A conversion and reconstruction (smoothly) filtering again, can send into channel through up-conversion and transmit.

Correspondingly, Fig. 8 also schematically show according to the application, at the demodulating unit 401 that data receiver uses, be used for the modulation signal of demodulation from above-mentioned modulating unit 303.As shown in Figure 8, demodulating unit 401 receives N symbol of self-channel, and the data after the demodulation are carried out parallel/serial conversion by P/S converting unit 402.Then, string character is sent in the data decode unit 403 reverted to serial data.The available FFT of the demodulation process that demodulating unit 401 is carried out (shown in the inner branch of the frame of broken lines of Fig. 8) realizes.

Fig. 9 (a) shows according to a FFT embodiment of the application, that carry out OFDM data padding modulation at transmitting terminal and realizes.Shown in Fig. 9 (a), at step S101, digital coding unit 301 receives from bit stream for example user, the process chnnel coding.Among the step S102,, above-mentioned bit stream through chnnel coding is carried out the zero padding computing based on the usable spectrum resource f (A) and the f (B) that for example authorize frequency range analysis module 10 and unauthorized frequency range analysis module 20 to obtain.Then in step S103, the serial bit stream through the zero padding computing is converted to parallel bit stream, then in step S104, parallel bit stream is carried out IFFT (inverse Fourier transform fast).In step S105, will be converted to the bit stream of serial through the bit stream of inverse Fourier transform fast, in step S106, in bit stream, insert protection time slot, Cyclic Prefix then.In step S107, will be converted to analog signal through the slow bit stream of handling before the circulation, in step S108, launch then.

Fig. 9 (b) shows according to a FFT embodiment of the application, that carry out the data zero suppression at receiving terminal and realizes.Shown in Fig. 9 (b), after receiving terminal receives the signal that above-mentioned steps S108 sends, be converted into digital signal, then the signal of conversion is carried out Time and Frequency Synchronization operation (step S201～S203).Then, remove the Cyclic Prefix (step S204) that in above-mentioned steps S106, adds, carry out serial/parallel conversion (step S205) then, and then parallel Bitstream signal is carried out FFT.Signal behind the process FFT is converted into the signal of serial then, carries out the laggard line data decoding of data zero suppression (step S206) (that is, symbol de-maps) then, then carries out channel and separates (step S207).

2.OFDM radio frequency grouping modulation:

In the scheme of OFDM radio frequency grouping modulation, data-modulated module 30 is carried out continuous OFDM modulation earlier with customer traffic, and modulation principle as shown in Figure 5.In final radio frequency part, at first obtain each available frequency band by frequency spectrum sensing module, the cutting of the more continuous frequency range of ofdm modulation signal being divided into groups, modulation (moving) is to each available frequency band.

For available frequency band f0, f1, f2, f3, f (m), f (m+1), f (N-3), f (N-2), f (N-1), regard it as section continuous frequency spectrum, the subcarrier initial frequency is f0, and the adjacent sub-carrier centre frequency remains unchanged at interval, be still Δ f=1/NTs, so, for example 9 sub-carrier occupancy total bandwidths be 9 times frequency at interval, i.e. 9/NTs.Subcarrier centre frequency f (k)=f0+k/NTs (k=0,1 ... 8).

Carry out common OFDM modulation subsequently, only sub-carrier number is not N, but equals available frequency number.With N=19 is example, and available frequency is f0, f1, f2, f3, f9, f10, f16, f17, f18,9 altogether.This moment will be with serial symbol stream d (0), d (1) ... d (18) corresponds on 9 modulated sub-carriers successively.The corresponding f of d (0) (0), the corresponding f of d (1) (1) ... the corresponding f of d (8) (8), the corresponding again f of d (9) (0), the corresponding f of d (10) (1) ... be the corresponding f of d (k+9) (k).Figure 10 image has shown the corresponding relation of string character and modulated sub-carriers.

After such method modulation, consider actual discrete frequency spectrum condition, for fear of transmitting in unauthorized frequency range, will carry out respective handling in the up-conversion stage this moment.As shown in figure 11, with frequency spectrum shown in Figure 10 on frequency domain, multiply by respectively with (f0, f3), (f4, f5), (f6 f8) is 3 band pass filters of up-and-down boundary, it is fc that three sections frequency spectrums that obtain multiply by centre frequency more respectively, fc+7/NTs, and the carrier wave of fc+14/NTs carries out up-conversion.By such processing, the resultant signal frequency spectrum that transmits in space channel just can realistic discrete spectrum condition.

In like manner, receiving terminal also should be made corresponding adjustment.Be described in the FFT realization that transmitting terminal carries out OFDM radio frequency grouping modulation respectively with reference to Figure 12 (a) and Figure 12 (b) below, and the FFT realization of carrying out the data zero suppression at receiving terminal.

In Figure 12 (a), digital coding unit 301 receives from bit stream for example user, the process chnnel coding, and the serial bit stream with coding is converted to parallel bit stream (step S301 and S302) then.Then parallel bit stream is carried out IFFT (inverse fast Fourier transform), will be converted to the bit stream of serial, in bit stream, add the protection time slot then, before the circulation slow (step S303～305) through the bit stream of IFFT.In step S306, to be converted to analog signal through the slow bit stream of handling before the circulation, then in step S307, with signal process band pass filter, be cut into the plurality of sub-bands signal, again each sub-band signal frequency spectrum is modulated to respectively on the centre frequency of authorized frequency bands (making signal pass through multiplier), thereby avoids interference unauthorized frequency range.

Shown in Figure 12 (b), after receiving terminal receives the signal that transmitting terminal sends, with signal through band pass filter and the multiplier identical with transmitting terminal, thereby the analog baseband signal that obtains sending is converted into digital signal (step S401～S402) then.Then, digital signal after the conversion removes the Cyclic Prefix (step S404) that joins wherein after by Time and Frequency Synchronization (step S403), then, the signal of having removed Cyclic Prefix is carried out serial/parallel conversion (step S405), and then parallel Bitstream signal is carried out FFT (step S406).The laggard line data of signal (step S407) that is converted into serial through the signal behind the FFT is then decoded (that is, symbol de-maps) (step S408), then carries out channel-decoding (step S409).

From as can be seen above, OFDM data padding modulation is done an OFDM computing for whole frequency, and incoming bit stream has been carried out the zero insertion processing, computing is counted more, make operand bigger, but comparatively convenient in the last down-conversion stage, only need a carrier wave to finish; And the OFDM operand of OFDM radio frequency grouping modulation is less, and it is less to count, but will handle accordingly at the radio frequency place, need subcarrier be divided into groups, and several continuous sub-carriers make whole system radio-frequency module number increase with a radio-frequency module.

The concrete application

Below with the application that transform the above-mentioned embodiment of example explanation the present invention as of electric power 230MHz wireless communication system.

1. existing power 230MHz wireless communication system is introduced

Electric power 230MHz wireless communications mode is called for short 230 private networks, promptly adopt data radio station, the special-purpose duplexing frequency of 15 couple and the electric power private wireless communication systems of 10 pairs of single power frequency point structures in the 230MHz band limits of national radio committee electric load control approval.Digital Signal Processing, digital modulation and demodulation, forward error correction, equilibrium are adopted in digital radio transfer of data radio station, technology such as judgement, by GMSK, QPSK, modulation systems such as CPFSK, can make transmission rate reach 19.2kbps, receive and dispatch change-over time less than 10ms, transmission range reaches more than 70 kilometers.

The 230MHz radio communication can adopt the networking mode of point-to-multipoint, promptly sets up a base station in cities and counties electric company, forms a radial network, realizes the main website of system of power load management system and communicating by letter of terminal.Except the network construction form of point-to-multipoint, can also adopt relay networking, linear networking and division of cells to carry out modes such as many base station networkings.Radio station data and speech compatibility can work in single worker, half-duplex, TDD, full duplex mode, transmit-receive cofrequency or alien frequencies transfer networking.230MHz wireless system equipment is followed GB GB/T 16611-1996 " data radio station general specification ".

1991] No. 5 files, " as the professional frequency range of using such as remote measurement, remote control, transfer of data, wherein 229.0～235.0MHz frequency range is used for radio astronomy service in the Beijing area with 223.025～235.000MHz, and other business must not produce harmful interference to it." channel spacing is 25kHz.

Frequency planning is as follows:

1. single frequency network frequency range

As the single frequency network frequency range, channel spacing is 25KHZ with 228.025～230.000MHz frequency range.

Wherein, below the 10 pairs of single power frequency points be that power load monitoring system uses (seeing Table 1), these frequencies are discrete unequal interval and distribute.

228.075	228.125	228.175	228.250	228.325
					228.400	228.475	228.550	228.675	228.750

Table 1 power load monitoring system uses single power frequency point (MHz)

Double frequency networking frequency range

As double frequency networking frequency range, transmitting-receiving frequency is spaced apart 7MHz with 223.025～228.000MHz and 230.025～235.000MHz frequency range, and channel spacing is 25KHz.223.025～235.000MHz frequency range is used for main platform (main website or central station) emission; 223.025～228.000MHz frequency range is used to belong to platform (belonging to platform or terminal station) emission.

Wherein, below the 15 pairs of duplexing frequencies be that power load monitoring system uses (seeing Table 2), these frequencies are discrete unequal interval and distribute.

Main platform	230.525	230.675	230.725	230.850	230.950
						Belong to platform	223.525	223.675	223.725	223.850	223.950
Main platform	231.025	231.125	231.175	231.225	231.325
						Belong to platform	224.025	224.125	224.175	224.225	224.325
Main platform	231.425	231.475	231.525	231.575	231.650
						Belong to platform	224.425	224.475	224.525	224.575	224.650

Table 2 power load monitoring system uses duplexing frequency (MHz)

Used by majority net province company at present as information gathering of the large-scale special change user power utilization of electric power and monitoring.But shortcomings such as the 230MHz wireless private network still exists, and transmission rate is low, technical standard lags behind, frequency is discrete.

1991, State Radio Regulatory Commission issue state did not have [1991] No. 5 files of pipe, and 223.025～235.000MHz frequency range is distributed.Wherein, Ministry of Energy at that time distributes 10 pairs of single power frequency points of acquisition and 15 pairs of duplexing frequencies, amounts to 40 frequencies.These frequencies intersperse among in the 12MHz frequency range.Because traditional data radio station at synchronization, only is operated on a pair of frequency, this frequency point allocation scheme can reduce the interference between working frequency points, and the radio station frequency point allocation is had positive effect.

By above analysis as seen, the discrete spectrum condition of existing 230MHz power communication system and be not suitable for directly using the OFDM technology.State does not have [1991] No. 5 files specify of pipe, and 230MHz system frequency is 25kHz at interval, and necessary bandwidth is not more than 16kHz.Adopt the design of conventional wireless data radio station, have bigger protection (9kHz) at interval between frequency.If the employing continuous frequency spectrum uses the OFDM technology, then do not need to reserve protection between subcarrier at interval.Only consider that from protection design at interval band efficiency just can improve 36%.Though can use the OFDM technology under existing situation by the scheme of similar " spectrum aggregating ", systematic function can obtain very big lifting, but still the situation that can exist the part Radio Resource to be wasted.

2,230MHz power communication frequency range is undergone technological transformation

At first the wireless communication system by as shown in Figure 1 filters out current available discrete frequency range in the 230MHz system, then these frequency ranges is adopted OFDM data padding modulation or OFDM radio frequency grouping modulation, then can adapt to the discrete spectrum condition of this system.

Being modulated to example with the OFDM data padding carries out technology to 230MHz power communication frequency range and carries out modification scheme design.As table 1, shown in the table 2, electric power 230MHz system has 40 discrete frequency ranges can be for communication.Each frequency range has the continuous frequency spectrum of 25kHz.For these 40 discrete frequency ranges,, just mean at 40 different radio-frequency modules of radio frequency place needs, for total system cost costliness if adopt OFDM radio frequency grouping modulation this moment.Obviously, be more suitable for adopting OFDM data padding modulation herein, only launch, use a filter with a carrier wave at the radio frequency place.

Carry out the symbol zero padding after the sign map module, specific design is carried out according to these 40 discrete frequency ranges and subcarrier bandwidth in the quantity of zero padding and position, improves the availability of frequency spectrum as much as possible satisfying under the principle do not disturb unauthorized frequency range.Can have the technical indicator that performance index are come the design object system with reference to the LTE system.

The OFDM subcarrier width that the LTE system adopts is two kinds of 7.5kHz and 15kHz, and under the discrete frequency situation, the frequency of the current use of 230MHz system is spaced apart 25kHz, and necessary bandwidth is 16kHz.If adopt 7.5kHz as the goal systems subcarrier width, 25kHz can place 2 or 3 complete subcarriers as the frequency bandwidth at each frequency.Then compare the LTE system, the availability of frequency spectrum is between (2*7.5/25=60%)～(3*7.5/25=90%).If adopt 15kHz as the goal systems subcarrier width, at most only can place 1 complete subcarrier at each frequency.The part frequency can't be placed complete subcarrier, compares the LTE system, and the availability of frequency spectrum is below 46%.Therefore, the design of the subcarrier width of goal systems is advisable with 7.5kHz.

By table 1, the data of table 2 as can be known, the minimum frequency of whole 230MHz communications band is 223.525MHz, high frequency points is 231.650MHz, bandwidth is 231.325MHz-223.525MHz=7800kHz altogether, so the available subcarrier number is 7800kHz/7.5kHz=1040.Now, we carry out zero padding for the unauthorized frequency range in the entire spectrum.By the matlab sequential operation, we obtain the number and the corresponding center frequency point thereof of available subcarrier.As shown in table 3 below:

Table 3 data padding scheme (concrete digitized representation passes the center frequency point of data, the MHz of unit) (

In the LTE system, under the 20MHz bandwidth, descending peak rate 100Mbps (using the MIMO antenna of 2*2), up peak rate 50Mbps (using the MIMO antenna of 2*1).Therefore, the spectrum efficiency of LTE system is 2.5～5bps/Hz.We use the subcarrier frequency range of 7.5kHz herein, have 84 subcarriers and are used effectively, and the effective bandwidth after the polymerization is 630kHz (84*7.5kHz), and the availability of frequency spectrum has reached 63% under total bandwidth 40*25kHz=1000kHz.If press the efficiency index 2.5～5bps/Hz under the LTE continuous frequency spectrum, then our design spectrum efficiency can reach 1.575～3.15bps/Hz, and message transmission rate can reach 1.575～3.15bps Mbps under 40 discrete frequencies (1000kHz bandwidth).

Consider that from communication coverage the maximum communication scope of LTE system definition is in 50～100km (Plain), according to the different influences of topography and difference, coverage is littler in the city.At present, the domestic communication coverage of surveying in the big city is several kilometers.Because after LTE system works frequency range about 2GHz, mixed down to 230MHz, coverage can improve a lot (being up to about 20km), the city is expected to reach more than 20 kilometer coverage, and coverage is bigger under the landform such as Plain, suburb.

By above analysis, we sum up under the condition of the discrete frequency of 230MHz, and the performance index of goal systems are as shown in table 4.

Subcarrier width	(7.5kHz compatible LTE system)
		Frequency bandwidth	1000kHz(40*25kHz)
Spectrum efficiency	1.575～3.15bps/Hz
		Transmission rate	1.575～3.15Mbps
Coverage	Much larger than LTE system distance (50-100km), be subjected to the influence of topography and difference
		Business support	Support " three is distant " i.e. remote signalling, remote measurement, remote control

Table 4 goal systems performance index (230MHz disperse frequency)

By table 4 as seen, under the discrete spectrum condition, our design has strengthened the message transmission rate of system greatly.

The above only is a preferred implementation of the present invention; be not so limit claim of the present invention; every equivalent structure or equivalent flow process conversion that utilizes specification of the present invention and accompanying drawing content to be done; or directly or indirectly be used in other relevant technical field, all in like manner be included in the scope of patent protection of the present invention.

Claims (11)

1. A data modulation system comprising: The authorized frequency band analysis module performs spectrum analysis on the authorized frequency band of the communication system to obtain the first available frequency band; An unlicensed frequency band analysis module, which analyzes other frequency bands other than the licensed frequency band of the communication system, or the licensed frequency band of at least one other system different from the communication system, to obtain a second available frequency band; and The data modulation module modulates the data to be sent in OFDM/OFDMA based on the first available frequency band and the second available frequency band. 2. data modulation system as claimed in claim 1, wherein, described unlicensed frequency band analysis module comprises: The A/D conversion unit converts the received signal into a digital signal; an energy calculation unit, which calculates the energy of the converted digital signal; The judging module compares the calculated energy with the detection threshold, and obtains the second available frequency band according to the comparison result. 3. The data modulation system according to claim 1, wherein the data modulation module modulates the data onto the subcarriers of the first available frequency band and the second available frequency band in a zero padding manner. 4. The data modulation system according to claim 3, wherein the data modulation module further comprises: A serial/parallel conversion unit, which converts the serial symbol stream of the data into N parallel symbols, where N is a positive integer; a modulation unit, for modulating the N channels of parallel symbols onto the subcarriers of the corresponding available frequency bands of the first available frequency band and the second available frequency band; and The summing unit is configured to add the modulated parallel symbols to obtain OFDM data symbols. the 5. The data modulation system according to claim 4, wherein the data modulation module further comprises: a data encoding unit, receiving a serial bit stream of said data, and inserting at least one numerical zero at a predetermined position in said serial bit stream, Wherein, the modulation unit modulates the zero-inserted serial bit stream onto the sub-carrier of the corresponding available frequency band. 6. The data modulation system according to claim 1, wherein the data modulation module is configured to perform packet segmentation on the first available frequency band and the second available frequency band, and modulate the data into packet segmentation on each of the available frequency bands. 7. A data modulation method, comprising: performing spectrum analysis on the licensed frequency band of the communication system to obtain the first available frequency band; analyzing a frequency band other than the licensed frequency band of the communication system, or a licensed frequency band of at least one other system different from the communication system, to obtain a second usable frequency band; and Based on the first available frequency band and the second available frequency band, OFDM/OFDMA is used to modulate the data to be sent. 8. The method according to claim 7, the step of modulating the data to be sent by the OFDM/OFDMA mode comprises: The data is modulated onto the subcarriers of the first available frequency band and the second available frequency band in a zero padding manner. 9. The method according to claim 8, the step of modulating the data to be sent by the OFDM/OFDMA mode comprises: receiving a serial bit stream of said data; inserting at least one numerical zero at a predetermined position in said serial bit stream; and The serial bit stream after zero insertion is modulated onto the subcarriers of the corresponding available frequency bands of the first available frequency band and the second available frequency band. the 10. The method according to claim 8, the step of modulating the data to be sent by using OFDM/OFDMA mode comprises: dividing the first available frequency band and the second available frequency band into groups; and The data is modulated onto each available frequency band after packet segmentation. 11. The method according to claim 9, the step of modulating the data to be sent by using OFDM/OFDMA mode further comprises: The modulated data is up-converted to avoid transmission of the data in an unlicensed frequency band. the

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