CN101242259A - Frame synchronization detection method and device for OFDM system - Google Patents

Abstract

A frame synchronization detecting method in an orthogonal frequency division multiplex system comprises: conjugating correlation calculation to data signals in a fore and aft conjugate correlation window of data signal in a data signal sequence to obtain a correlation calculation accumulate result by accumulating; calculating an average energy of data signals in the fore and aft conjugate correlation window; taking a metric value of a data signal as a ratio between the correlation calculation accumulate result and the average energy, and in a detecting period, such as in a length of 1.5 frame, determining a frame starting time based on a data signal with a metric value maximal. The method, based on a character that predecessor using BPSK modulate conjugates symmetry, performs a frame synchronization detect, solves the synchronization problem in the orthogonal frequency division multiplex system.

Description

Frame synchronization detection method and device in the ofdm system

Technical field

The present invention relates to the data transmission technology in the field of wireless communication, be meant frame synchronization detection method and device in a kind of OFDM (Orthogonal Frequency Division Multiplexing is called for short " OFDM ") system especially.

Background technology

In the development of wireless communication devices course, the problem that the shortage of radio spectrum resources and the multipath of wireless channel in time become the transmission signals decline that characteristic causes is limiting further developing of wireless communication technology all the time.Corresponding with it, therefore the OFDM technology becomes the focus of wireless communication technology research because its availability of frequency spectrum height and the multipath characteristics that can overcome wireless channel well.

The OFDM technology was proposed first in middle 1960s, was mainly used in military wireless high-frequency communication system at that time.This technology proposes to realize multi-carrier modulation with discrete Fourier transform (Discrete Fourier Transform is called for short " DFT ").At transmitting terminal, data waiting for transmission are modulated at respectively on the subcarrier of a plurality of quadratures then through coding back demultiplexing parallel data, at last this multichannel modulation signal addition are sent; Sample at first to received signal at receiving terminal, use a plurality of identical subcarriers to carry out multi-channel demodulator then, again with this multi-channel demodulator signal and string output, the signal that reproduction sends.But, do not form large-scale the application owing to run into a lot of insoluble problems at that time.After this, people propose to optimize to the DFT algorithm, make that the modulation and demodulation in the OFDM technology can be respectively by contrary fast discrete Fourier conversion (InverseFast Discrete Fourier Transform, be called for short " IFFT ") and fast discrete Fourier conversion (FastDiscrete Fourier Transform, abbreviation " FFT ") finish.To the eighties in 20th century, the development of large scale integrated circuit technology has solved the problem of implementation of FFT, and the OFDM technology begins to be tending towards practicability, obtains promoting.At present, OFDM is mainly used in digital audio broadcasting (Digital Audio Broadcasting, be called for short " DAB "), digital video broadcasting (Digital Video Broadcasting, be called for short " DVB "), two-forty DSL (High-rate Digital Subscriber Loop, HDSL), ADSL (Asymmetric Digital Subscriber Line) (Asymmetric Digital Subscriber Line, ADSL), WLAN (wireless local area network) (Wireless Local Area Network, be called for short " WLAN ") 802.11 and wireless MAN (WirelessMetropolis Area Network, be called for short " WMAN ") in the fields such as 802.16, people have classified it as the core technology in the 4th generation mobile radio telecommunications, are used for realizing surpassing mobile wireless multimedia and the data communication of 2Mbps.

Figure 1 shows that each part of ofdm communication system.Transmitting terminal is at first encoded data, the line number of going forward side by side tone of Chinese characters system.Common modulator approach has: biphase phase shift keying (Binary Phase Shift Keying, abbreviation " BPSK "), quarternary phase-shift keying (QPSK) (Quadrature Phase Shift Keying, be called for short " QPSK ") and quadrature amplitude modulation (Quadra ture amplitude modulation is called for short " QAM ").Data flow segmentation after ovennodulation is gone here and there and is changed, and every segment data is through IFFT, and just the data to be transmitted of process coding is modulated to time-domain information as frequency domain information with frequency domain information.The time-domain signal segmentation is modulated, and adds Cyclic Prefix in the front of every segment signal (Cyclic Prefix is called for short " CP "), sends to communication channel by sending module afterwards.Receiving terminal then carries out corresponding anti-operation.Wherein.Add that last segment that the processing of CP is every section time-domain signal copies to the front, make multidiameter delay under length prerequisite, avoid intersymbol interference (Inter Symbol Interference less than Cyclic Prefix, be called for short " ISI "), significantly reduce the sensitiveness of ofdm communication system, resist the infringement of multidiameter delay effectively timing error.

Because what OFDM adopted is a kind of special multi-carrier modulation, requires all subcarriers must satisfy quadrature, if orthogonality worsens, then the performance of whole system can seriously descend, and produces between the distinctive subcarrier of OFDM and crosstalks.And in real work, because the time variation of wireless fading channel tends to cause frequency dispersal, cause doppler shift effect, thereby influence the carrier frequency orthogonality, so the precise synchronization that how to realize subcarrier has become a difficult point in the OFDM technology.

In the OFDM simultaneous techniques, frame synchronization detects, and judges promptly when the OFDM frame arrives, and is first link of whole synchronizing process, and remaining timing synchronous (comprising that sign synchronization and sampling clock are synchronous) and carrier synchronization all depend on frame synchronization and detect the quality of finishing.

In general, frame synchronization detects two kinds of methods: a kind of is the energy achieve frame synchronous detecting of utilizing received signal, and relatively typical method is two sliding window energy measuring methods; Another kind is to utilize preamble structure achieve frame synchronous detecting, and relatively typical method is to utilize the delay Autocorrelation Detection method of the repetitive structure of leading (Preamble).

Because communication system, special leading as being provided with among the 802.16e, therefore can adopt the method for utilizing preamble structure achieve frame synchronous detecting.In the 802.16e system, leadingly occupy an OFDM symbol since the unique texture of preceding pilot field caused it time domain have three sections pseudoperiod characteristic.Therefore propose in the prior art to utilize leading three sections pseudoperiod characteristic realize that in conjunction with postponing autocorrelative method downlink frame detects.This method has reasonable performance really under the situation of not considering inter-sector interference, but when sector interference is apparent in view, since sector interference destroyed leading three sections pseudoperiod characteristic, the detection performance of this method can reduce greatly, under extreme case even lost efficacy.

In view of the foregoing, the present invention proposes method and the device that a kind of new frame synchronization detects.

Summary of the invention

In order to address the above problem, the present invention proposes to utilize leading conjugation symmetry characteristic achieve frame detection method and device, and this method and device still can obtain good performance under the situation that sector interference exists.

Frame synchronization detection method in a kind of ofdm system of the present invention, this method comprise that the data-signal of symmetry carries out the conjugation correlation computations before and after the data-signal in the data taken signal sequence, add up the correlation computations accumulation result; Calculate this symmetrical data-signal energy; The metric of getting this data-signal is this correlation computations accumulation result and this energy ratio, detecting in the period, determines the initial moment of frame according to the data-signal of metric maximum.

This method further comprises conjugation correlation window size is set, get in this data signal sequence before and after this data-signal in conjugation associated window data-signal of symmetry and carry out the conjugation correlation computations and add up, calculate the data-signal energy of symmetry in the conjugation associated window of described front and back.

This conjugation correlation computations and the formula that adds up are

$C\left(d\right)=\underset{i=1}{\overset{W}{\mathrm{\Σ}}}r(d-i)r(d+i)$

Wherein, r (n) is described data signal sequence, and W is described conjugation correlation window size, and C (d) is described correlation computations accumulation result.

The data-signal energy that calculates symmetry in this front and back conjugation associated window is a calculated data signal averaging energy, and formula is

$P\left(d\right)=0.5\left[\underset{i=1}{\overset{W}{\mathrm{\Σ}}}({\left|r(d-i)\right|}^2+{\left|r(d+i)\right|}^2\right]$

Wherein, r (n) is described data signal sequence, and W is described conjugation correlation window size, and P (d) is a described data-signal average energy in the conjugation associated window of front and back.

In the detection period, determine that according to the data-signal of metric maximum the formula in the initial moment of frame is $d_{\mathrm{frame}\_\mathrm{start}}=\arg \underset{d}{\max }\left[M\left(d\right)\right],$ Wherein M (d) is the metric of a described data-signal.

The present invention also provides frame synchronization checkout gear in a kind of ofdm system, and this device comprises data storage cell, and storage is used for the data signal sequence that frame synchronization detects; Arithmetic element, before and after data memory module reads a data-signal the described data signal sequence data-signal of symmetry carry out the conjugation correlation computations, add up the correlation computations accumulation result, calculate this symmetrical data-signal energy, the metric of getting this data-signal is this correlation computations accumulation result and this energy ratio, determines the initial moment of frame according to the data-signal of metric maximum in the detection period.

Wherein, this device further comprises a parameter set unit, this parameter set unit is provided with conjugation correlation window size, arithmetic element is got before and after the data-signal described in the described data signal sequence in the conjugation associated window data-signal of symmetry and is carried out the conjugation correlation computations and add up, and calculates the data-signal energy of symmetry in the conjugation associated window of described front and back.

Further, this data storage cell comprises the first storage subelement and the second storage subelement, data-signal in the first storage subelement in described data-signal of storage and the front and back conjugation associated window thereof, the storage of the second storage subelement is with stored data signal in the first storage subelement of the mirror image symmetry of a described data-signal symmetry axis.

The present invention detects a kind of new method that provides for the frame synchronization of ofdm system.This method is based on the leading inherent characteristic that adopts the BPSK modulation, utilize the characteristics of leading conjugation symmetry to carry out the frame synchronization detection, therefore under the inter-sector interference serious situation, still can well work, thereby realize OFDM frame synchronization, solve the stationary problem in the ofdm system.

Description of drawings

To the description of one embodiment of the invention, can further understand purpose, specific structural features and the advantage of its invention by following in conjunction with its accompanying drawing.Wherein, accompanying drawing is:

Figure 1 shows that the ofdm communication system structural representation;

Figure 2 shows that the flow chart of frame synchronization detection method of the present invention;

Figure 3 shows that reception buffer structural representation in the embodiment of the invention;

Figure 4 shows that frame synchronization checkout gear structural representation of the present invention.

Embodiment

For making purpose of the present invention, technical scheme and advantage clearer, the present invention is described in further detail below in conjunction with drawings and Examples.

At wireless communication system, in the 802.16e system, agreement regulation targeting signal adopts the BPSK modulation, can get according to the principle of modulation technique, and targeting signal is a real number at frequency domain, and therefore after through the IFFT conversion, targeting signal has conjugate symmetry in time domain.Because agreement is stipulated simultaneously, have only targeting signal to adopt the BPSK modulation system in the data-signal, and other data-signals does not adopt this modulation system, therefore this conjugation symmetrical structure is that targeting signal institute is peculiar.The present invention promptly utilizes these characteristics to carry out frame synchronization and detects.

As shown in Figure 2, frame synchronization detection method carries out related operation to the OFDM data-signal and adds up in the ofdm system of the present invention, calculate data-signal energy in the conjugation symmetry window, and carry out the tolerance of data-signal according to related operation accumulation result and data-signal energy value, carry out peak value according to the tolerance result and detect, find frame start position.

The concrete steps of frame synchronization detection method of the present invention are described below:

Step a, reception OFDM data-signal are designated as sequence r (n).Get the size that W is the conjugation correlation window, w≤(FFT_size)/2.The big or small W of this conjugation correlation window is regulated at will as required.

Step b, get among the OFDM data signal sequence r (n) a signal r (d) and be symmetrical centre,

As shown in Equation (1), to being symmetrical centre, being that the front and back data-signal of scope is made the conjugation correlation computations with r (d) among the sequence r (n) with the W size, and add up conjugation correlation computations accumulation result C (d).

$C\left(d\right)=\underset{i=1}{\overset{W}{\mathrm{\Σ}}}r(d-i)r(d+i)---\left(1\right)$

The energy P (d) of data-signal in step c, the calculating conjugation associated window.Usually, in preferable mode, as shown in Equation (2), calculated energy is the average energy of two conjugation symmetry windows in this step.

$P\left(d\right)=0.5\left[\underset{i=1}{\overset{W}{\mathrm{\Σ}}}({\left|r(d-i)\right|}^2+{\left|r(d+i)\right|}^2\right]---\left(2\right)$

Steps d, as shown in Equation (3) is according to data-signal energy P (d) and correlation computations accumulation result C (d) computing metric M (d).

M(d)＝C(d)/P(d) (3)

Step e, carry out peak value according to metric M (d) and detect.As shown in Equation (4), detect in the period, calculate the metric of OFDM data-signal, corresponding constantly being the initial moment of frame of data-signal institute of metric maximum certain.

$d_{\mathrm{frame}\_\mathrm{start}}=\arg \underset{d}{\max }\left[M\left(d\right)\right]---\left(4\right)$

Need to prove step b and step c, usually, on flow process, there is not precedence relationship, can calculate the energy P (d) of data-signal in the conjugation associated window in the actual treatment earlier, calculate correlation computations accumulation result C (d) again, the sequential processes of describing before perhaps adopting can realize goal of the invention of the present invention.

Realize that approach of the present invention has a lot, can adopt field programmable gate array (FieldProgrammable Gate Array, abbreviation FPGA) carrying out hardware realizes, also can adopt digital signal processor (Digital Signal Processing, be called for short DSP) carry out the software realization, perhaps adopt FPGA and DSP in conjunction with realization.Respectively the present invention is described further below in conjunction with these three kinds of situations.

Embodiment one: utilize FPGA to realize detecting based on the frame synchronization of leading conjugation symmetry characteristic.

As shown in Figure 3, two reception buffer Rx Buff1 and Rx Buff2 are set, length is 2w+1 (w is a conjugation correlation window size, satisfies w≤(FFT_size)/2).

The OFDM data-signal is via analog to digital converter (AD Converter is called for short ADC) conversion back serial input reception buffer Rx Buff1.When Rx Buff1 fill full after, get that data r (d) makes the mirror image symmetry operation for symmetry axis in the buffer, with the storage after the operation to Rx Buff2.Usually, because buffering area half or data are still less only used in actual computing, therefore, the buffer Rx Buff2 among the present invention also can utilize the remainder of Rx Buff1 to replace.For convenience, still adopt two buffers among the present invention.

Utilize the data among buffer Rx Buff1 and the Rx Buff2 to carry out the frame synchronization detection calculations, detailed process is as follows:

Get the first half among Rx Buff1 and the Rx Buff2, promptly data r (d-w) data r (d+w) to r (d-1) and the Rx Buff2 carries out correspondingly multiplying each other and suing for peace to r (d+1) among the Rx Buff1, has calculated the correlation computations accumulation result C (d) in the formula (1).

Get the first half of Rx Buff1 and Rx Buff2,, so just obtain the average energy P (d) of the conjugation symmetry window in the formula (2) with square summation of each data delivery and divided by 2.

Utilize formula (3) to calculate metric M (d).

(in the length such as 1.5 frames) utilizes formula (4) in certain hunting zone, and in the pairing moment of the data-signal of computing metric maximum, this is the initial moment of frame constantly, so can the achieve frame synchronous detecting.

Whole operation process in the present embodiment is a unit with the clock from the ADC serial data normally, for instance, Rx Buff 1 fill full in, the data of whenever coming in just need carry out once above-mentioned operation.Can accomplish real-time data are handled like this, but bigger to the demand of hardware resource.

Embodiment two: utilize DSP to realize detecting based on the frame synchronization of leading conjugation symmetry characteristic.

The OFDM data-signal is placed in the memory after being changed by ADC, the data of taking out 2w+1 length in the time of each calculating from memory are placed among the register Rx Buff1, then to Rx Buff1 carry out with the intermediate data be the mirror image operation of symmetry axis and will operate after deposit data in Rx Buff2.Register Rx Buff1 is identical with reception buffer structure shown in Figure 3 with Rx Buff2 structure.

Utilize the data among Rx Buff1 and the Rx Buff2 to carry out the downlink frame detection calculations according to formula (1)-(4) then, detailed process is identical with embodiment one, so do not give unnecessary details.

It should be noted that, utilize the difference of FPGA Calculation Method to be that mainly FPGA can carry out concurrent operation among the embodiment two among computational methods and the embodiment one, therefore can realize real-time computing (each serial data comes in then just can finish the computing of a metric function).And the method for utilizing DSP can not realize such concurrent operation, therefore also just can't realize real-time search.For the method that adopts DSP, can consider the data in certain hunting zone (such as the data of 1.5 frames) all are cached in the memory, carry out non real-time computing then, so just can in this hunting zone, determine the original position of frame.

Embodiment three: utilize FPGA+DSP to realize detecting based on the frame synchronization of leading conjugation symmetry characteristic.

Utilize FPGA+DSP to realize to realize that based on the frame detection of leading conjugation symmetry characteristic one of search speed and hardware resource consumption is traded off.Adopt the calculating process of this method identical with top two kinds of methods, the key here is the division to the FPGA+DSP task.Concrete division can be implemented as required, only provides an example here.

The data that read certain hunting zone are placed in the memory, are carried out the preparation of window data Rx Buff1 and Rx Buff2 by DSP.Carry out concrete computing according to formula (1)-(4) for FPGA these data passes then, and operation result is fed back to DSP.So just can in this hunting zone, determine the original position of frame.

Generally speaking, with regard to the realization that OFDM frame synchronization of the present invention detects, frame synchronization checkout gear in a kind of ofdm system as shown in Figure 4, comprises a data storage cell and an arithmetic element usually at least.The data storage cell storage is used for the data signal sequence that frame synchronization detects.Arithmetic element, data-signal before and after data memory module reads a data-signal the described data signal sequence in the conjugation correlation window carries out the conjugation correlation computations, add up the correlation computations accumulation result, calculate the data-signal energy in the conjugation correlation window of described front and back, the metric of getting this data-signal is this correlation computations accumulation result and this energy ratio, determines the initial moment of frame according to the data-signal of metric maximum in the detection period.

This device can further include a parameter set unit and Data Receiving unit, and this parameter set unit can be provided with conjugation correlation window size, and data storage cell receives data and storage from the Data Receiving unit.

In addition, data storage cell comprises the first storage subelement and the second storage subelement, data-signal in the first storage subelement in this data-signal of storage and the front and back conjugation associated window thereof, the storage of the second storage subelement is with stored data signal in the first storage subelement of the mirror image symmetry of this data-signal symmetry axis.

The present invention detects a kind of new method that provides for the frame synchronization of ofdm system.This method is based on the leading inherent characteristic that adopts the BPSK modulation, utilize the characteristics of leading conjugation symmetry to carry out the frame synchronization detection, therefore under the inter-sector interference serious situation, still can well work, thereby realize OFDM frame synchronization, solve the stationary problem in the ofdm system.

Be understandable that the frame synchronization that the present invention is not only applicable to the 802.16e system detects, can also be widely used in all and adopt the leading frame synchronization that has the leading ofdm system of conjugate symmetry in other words of BPSK modulation to detect.For those of ordinary skills, can be equal to replacement or change according to technical scheme of the present invention and inventive concept thereof, and all these changes or replacement should belong to all within the present invention's scope required for protection.

Claims (10)

1. frame synchronization detection method in the ofdm system is characterized in that this method comprises: in the data taken signal sequence before and after the data-signal data-signal of symmetry carry out the conjugation correlation computations, add up the correlation computations accumulation result; Calculate the data-signal energy of described symmetry; The metric of getting this data-signal is this correlation computations accumulation result and this energy ratio, detecting in the period, determines the initial moment of frame according to the data-signal of metric maximum.

2. frame synchronization detection method in the ofdm system as claimed in claim 1, it is characterized in that: this method further comprises conjugation correlation window size is set, get before and after the data-signal described in the described data signal sequence in the conjugation associated window data-signal of symmetry and carry out the conjugation correlation computations and add up, calculate the data-signal energy of symmetry in the conjugation associated window of described front and back.

3. frame synchronization detection method in the ofdm system as claimed in claim 2 is characterized in that: described conjugation correlation computations and the formula that adds up are

$C\left(d\right)=\underset{i=1}{\overset{W}{\mathrm{\Σ}}}r(d-i)r(d+i)$

Wherein, r (n) is described data signal sequence, and W is described conjugation correlation window size, and C (d) is described correlation computations accumulation result.

4. frame synchronization detection method in the ofdm system as claimed in claim 2 is characterized in that: the data-signal energy of symmetry is a calculated data signal averaging energy in the conjugation associated window of the described front and back of described calculating, and formula is

$P\left(d\right)=0.5[\underset{i=1}{\overset{W}{\mathrm{\Σ}}}{\left(\right|r(d-i)|}^2+{\left|r(d+i)\right|}^2]$

Wherein, r (n) is described data signal sequence, and W is described conjugation correlation window size, and P (d) is a described data-signal average energy in the conjugation associated window of front and back.

5. frame synchronization detection method in the ofdm system as claimed in claim 1 is characterized in that: describedly determine that according to the data-signal of metric maximum the formula in the initial moment of frame is detecting in the period $d_{\mathrm{frame}\_\mathrm{start}}=\arg \underset{d}{\max }\left[M\left(d\right)\right],$ Wherein M (d) is the metric of a described data-signal.

6. frame synchronization detection method in the ofdm system as claimed in claim 1 is characterized in that: this method can be carried out hardware by FPGA and be realized, perhaps can adopt DSP to carry out software and realize, perhaps adopts FPGA and DSP in conjunction with realization.

7. frame synchronization checkout gear in the ofdm system, it is characterized in that: this device comprises data storage cell, storage is used for the data signal sequence that frame synchronization detects; Arithmetic element, before and after data memory module reads a data-signal the described data signal sequence data-signal of symmetry carry out the conjugation correlation computations, add up the correlation computations accumulation result, calculate the data-signal energy of described symmetry, the metric of getting this data-signal is this correlation computations accumulation result and this energy ratio, determines the initial moment of frame according to the data-signal of metric maximum in the detection period.

8. frame synchronization checkout gear in the ofdm system as claimed in claim 7, it is characterized in that: this device further comprises a parameter set unit, this parameter set unit can be provided with conjugation correlation window size, arithmetic element is got before and after the data-signal described in the described data signal sequence in the conjugation associated window data-signal of symmetry and is carried out the conjugation correlation computations and add up, and calculates the data-signal energy of symmetry in the conjugation associated window of described front and back.

9. frame synchronization checkout gear in the ofdm system as claimed in claim 8, it is characterized in that: described data storage cell comprises the first storage subelement and the second storage subelement, data-signal in the first storage subelement in described data-signal of storage and the front and back conjugation associated window thereof, the storage of the second storage subelement is with stored data signal in the first storage subelement of the mirror image symmetry of a described data-signal symmetry axis.

10. frame synchronization checkout gear in the ofdm system as claimed in claim 7 is characterized in that: this device further comprises the Data Receiving unit, and described data storage cell receives data and storage from the Data Receiving unit.

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