CN104301277B - OFDM symbol synchronization capture method based on acoustic communication - Google Patents
OFDM symbol synchronization capture method based on acoustic communication Download PDFInfo
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- CN104301277B CN104301277B CN201410500398.5A CN201410500398A CN104301277B CN 104301277 B CN104301277 B CN 104301277B CN 201410500398 A CN201410500398 A CN 201410500398A CN 104301277 B CN104301277 B CN 104301277B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
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Abstract
The invention discloses a kind of OFDM symbol synchronization capture method based on acoustic communication, comprise the following steps, 1）A region is selected as DFT demodulation windows from the DAB symbol received；2）Seizure is synchronized to each OFDM symbol, if in the absence of intersymbol interference is produced, correct demodulation, synchronization catch is successful；If there is intersymbol interference, synchronization catch failure is demodulated, it is necessary to DFT demodulation windows are slided backward by sliding unit again, so as to correct demodulation, synchronization catch success；3）The data frame that successfully each OFDM symbols are constituted will be caught, enter row decoding, be reduced into initial data.The OFDM symbol synchronization capture method based on acoustic communication of the present invention, when carrying out DFT Fourier transformations, slided using by DFT demodulation windows by sliding unit, it is ensured that DFT demodulation windows capture symbol in the absence of intersymbol interference, the communication quality of sound wave is improved, is had a good application prospect.
Description
Technical field
The present invention relates to a kind of OFDM symbol synchronization capture method based on acoustic communication, belong to wireless communication technology neck
Domain.
Background technology
Frequency of sound wave can make full use of existing video/audio playback equipment and reception device in below 24kHz, without
To the loudspeaker and microphone of specific customization, the frequency that human ear can not be discovered easily, will not to daily life produce compared with
Many influences, therefore, sound wave communication is widely applied.
In acoustic communication processing procedure, in order to ensure that the energy when data frame switches (is not reduced to the leakage of other frequencies
Noise), it is necessary to data frame signal is extended, but the data frame signal after extension, when carrying out DFT Fourier transformations,
Easily cause DFT demodulation windows to be difficult to capture data frame and data-frame sync, so as to influence the communication quality of sound wave.
The content of the invention
In overcoming data frame to extend, DFT demodulation windows are difficult to capture data frame and data
Frame synchronization, so that the problem of influenceing the communication quality of sound wave.The OFDM symbol synchronization catch side based on acoustic communication of the present invention
Method, when carrying out DFT Fourier transformations, is slided, it is ensured that DFT demodulation windows are caught using by DFT demodulation windows by sliding unit
Data frame and data-frame sync are grasped, the communication quality of sound wave is improved, has a good application prospect.
In order to achieve the above object, the technical solution adopted in the present invention is：
A kind of OFDM symbol synchronization capture method based on acoustic communication, it is characterised in that：Comprise the following steps,
Step (1), a region is selected as the DFT demodulation windows of Fourier transformation from the DAB symbol received
Mouthful；
Step (2), DFT Fourier transformations are carried out to each OFDM symbol, and carry out synchronization catch, provided with two kinds of seizure feelings
Condition,
(1) if the sample value that the DFT demodulation windows of step (1) are included is the value in corresponding OFDM symbol, do not deposit
Producing intersymbol interference, correct demodulation, synchronization catch success；
(2) if the sample value that the DFT demodulation windows of step (1) are included includes the value of next OFDM symbol, deposit
In intersymbol interference, synchronization catch failure, it is necessary to which DFT demodulation windows are slided backward by sliding unit, demodulate again, with
Just correct demodulation, synchronization catch success；
Step (3), will catch the data frame that successfully each OFDM symbols are constituted, enters row decoding, be reduced into initial data.
The foregoing OFDM symbol synchronization capture method based on acoustic communication, it is characterised in that：It is described by DFT demodulation windows
Slided backward by sliding unit, the calculating process of slide displacement is,
(1) length for generating sample of signal provided with DFT units is L, then the length of data is 2.75L after extending；
The transitional region of (2) two OFDM symbols is overlapping together, and transitional region is 0.25L, then two OFDM symbol heads
The spacing in portion is 2.75L-0.25L=2.5L；
(3) DFT demodulation windows length is L, and sliding distance is 2.5L/2=1.25L.
The foregoing OFDM symbol extended method based on acoustic communication, it is characterised in that：The step (1), from receiving
DAB symbol select the region as the DFT demodulation window selection courses of Fourier transformation to be, from the numeral received
Access amount in audio signal beginning is used as demodulation window for the sample of L length.
The beneficial effects of the invention are as follows：The OFDM symbol synchronization capture method based on acoustic communication of the present invention, is being carried out
During DFT Fourier transformations, slided using by DFT demodulation windows by sliding unit, first demodulation success rate is high (50%), average
Demodulate number of times few (average only to need 1.5 times), it is ensured that DFT demodulation windows capture symbol in the absence of intersymbol interference, improve sound wave
Communication quality, have a good application prospect.
Brief description of the drawings
Fig. 1 is the flow chart of the OFDM symbol synchronization capture method based on acoustic communication of the present invention.
Fig. 2 is that the original position of the DFT demodulation windows of the present invention falls the synchronization catch schematic diagram in cyclic prefix.
Fig. 3 is that the original position of the DFT demodulation windows of the present invention falls the synchronization catch schematic diagram outside cyclic prefix.
Fig. 4 is the schematic diagram of the signal extension of one embodiment of the invention.
Fig. 5 is the synchronization catch of one embodiment of the invention and the schematic diagram slided.
Fig. 6 is the schematic diagram of the demodulation DFT demodulation windows of one embodiment of the invention.
Embodiment
Below in conjunction with Figure of description, the invention will be further described.Following examples are only used for clearly
Illustrate technical scheme, and can not be limited the scope of the invention with this.
As shown in figure 1, the OFDM symbol synchronization capture method based on acoustic communication of the present invention, comprises the following steps,
Step (1), a region is selected as the DFT demodulation windows of Fourier transformation from the DAB symbol received
Mouthful, the selection course of the DFT demodulation windows of Fourier transformation is, is L length from the digital audio and video signals beginning access amount received
The sample of degree is used as demodulation window.
Step (2), DFT Fourier transformations are carried out to each OFDM symbol, and carry out synchronization catch, provided with two kinds of seizure feelings
Condition, timing slip during demodulation is τ sampling,
(1) as shown in Fig. 2 the original position of DFT demodulation windows falls in cyclic prefix, DFT demodulation windows are included
Sample value is the value in this OFDM symbol, then in the absence of intersymbol interference is produced, correct demodulation, synchronization catch is successful；
(2) as shown in figure 3, the original position of DFT demodulation windows falls outside cyclic prefix, DFT demodulation windows are included
Sample value contains the value of next OFDM symbol, then there is intersymbol interference, synchronization catch failure is, it is necessary to which DFT is demodulated
Window is slided backward by sliding unit, is demodulated again, so as to correct demodulation, synchronization catch success；
Step (3), will catch the data frame that successfully each OFDM symbols are constituted, enters row decoding, be reduced into initial data.
Described to slide backward DFT demodulation windows by sliding unit, the calculating process of slide displacement is,
(1) length for generating sample of signal provided with IDFT units is L, then the length of data is 2.75L after extending, specifically
For the afterbody 0.5L of replicating original signal is used as preceding transitional region and protection interval+complete primary signal+duplication of duplication 2L
The head 0.25L of primary signal is used as rear transitional region；
The transitional region of (2) two OFDM symbols is overlapping together, and transitional region is 0.25L, then two OFDM symbol heads
The spacing in portion is 2.75L-0.25L=2.5L；
(3) DFT demodulation windows length is L, and sliding distance is 2.5L/2=1.25L.
Each OFDM symbol is equipped with a Barker code, and Barker code is sequentially stored into shift register, displacement deposit
The length of device is equal to the length of Barker code, and when the sharp peaks of the microphone decision level of receiving terminal occur, judgment frame starts
With end position, frame synchronization is realized.
When signal is not present, demodulation failure, the original position of demodulation window constantly slides backward 1.25L sample, directly
Occur to signal；In the presence of signal, then the probability for having 50% is demodulated successfully, the start bit of demodulation window if demodulation is unsuccessful
Put and slide backward 1.25L sample, you can 100% demodulates successfully, original position, in fact without selection, is exactly from opening Mike
Wind, it is that demodulation fails always certainly when demodulation is not having signal to receive just continuous after digital audio and video signals, and constantly slip exists
In the presence of signal, success can be demodulated by most catching twice.
According to the OFDM symbol synchronization capture method based on acoustic communication of the present invention, a specific embodiment is introduced,
Assuming that sending 256bit original sound datas (1024bit is expanded to after channel coding) per frame, 16 data are used
Subcarrier is transmitted, using QPSK planispheres (2bit), then there are 32 OFDM symbols (1024/16/2=32) per frame data, numeral
The sampling precision of audio signal is that 16bit, sample frequency are 44.1kHz, using 640 sampled points as an OFDM symbol, then per frame
The length of signal is:32*640/44100 ≈ 0.4644 (second), data-frame sync catch process be,
(1) signal extension
The digital audio and video signals that 256 points are generated by IDFT units, do mode as shown in Figure 4 and extend,
(2) synchronization catch is with sliding
When making DFT units using 256 sample windows and demodulating, demodulation window position drop point in fact, as shown in fig. 6, solution
It can be demodulated when adjusting the original position of DFT demodulation windows between A and B with correct, as shown in figure 5, can not be correct between C and D
Demodulation, AB=CD, i.e., the first probability for having 50% that catches is caught successfully, when first seizure failure, only need to slide backward 320
Sample 100% can be caught successfully, catch for average 1.5 times and sign synchronization can be achieved, sign synchronization efficiency high, here by
Specific numerical value introduces the situation of sign synchronization, i.e. the sample length of IDFT generations is x, is x+x+x/ by the length after extension
2+x/4=2.75x, because the transitional region of front and rear 2 OFDM symbols is overlapping together, therefore the spacing on 2 OFDM symbol heads
For 2.75x-x/4=2.5x, the DFT demodulation windows length demodulated every time is x, and sliding distance is 2.5x/2=1.25x, is lifted above
Numerical value in example is according to this ratio setting, it is possible to reaches average 1.5 times and catches the effect that sign synchronization can be achieved.
(3) frame synchronization
When being subsequently received the 13rd OFDM symbol of frame in, there are sharp peaks in Barker code, just can determine whether that frame starts according to this
With end position.
General principle, principal character and the advantage of the present invention has been shown and described above.The technical staff of the industry should
Understand, the present invention is not limited to the above embodiments, the original for simply illustrating the present invention described in above-described embodiment and specification
Reason, without departing from the spirit and scope of the present invention, various changes and modifications of the present invention are possible, these changes and improvements
It all fall within the protetion scope of the claimed invention.The claimed scope of the invention is by appended claims and its equivalent circle
It is fixed.
Claims (1)
1. the OFDM symbol synchronization capture method based on acoustic communication, it is characterised in that：Comprise the following steps,
Step (1), a region is selected as the DFT demodulation windows of Fourier transformation, tool from the DAB symbol received
It from the digital audio and video signals beginning access amount received is the sample of L length as DFT demodulation windows that body, which is,；
Step (2), DFT Fourier transformations are carried out to each OFDM symbol, and carry out synchronization catch, there is two kinds of seizure situations,
(1) if the sample value that the DFT demodulation windows of step (1) are included is the value in corresponding OFDM symbol, in the absence of production
Raw intersymbol interference, correct demodulation, synchronization catch success；
(2) if the sample value that the DFT demodulation windows of step (1) are included includes the value of next OFDM symbol, there is symbol
Interference between number, synchronization catch failure is demodulated, so as to just, it is necessary to DFT demodulation windows are slided backward by sliding unit again
Really demodulation, synchronization catch success；
Step (3), will catch the data frame that successfully each OFDM symbol is constituted, enters row decoding, be reduced into initial data,
Described to slide backward DFT demodulation windows by sliding unit, the calculating process of slide displacement is,
(1) length of DFT units generation sample of signal is L, then the length of data is 2.75L after extending；
The transitional regions of (2) two OFDM symbols is overlapping, and transitional region is 0.25L together, then two OFDM symbol heads
Spacing is 2.75L-0.25L=2.5L；
(3) DFT demodulation windows length is L, and sliding distance is 2.5L/2=1.25L.
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| CN102694763A (en) * | 2012-05-31 | 2012-09-26 | 重庆邮电大学 | Method for assessing integer frequency offset of TD-LTE system |
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| 一种基于OFDM循环前缀的符号定时算法;陈曦等;《无线电工程》;20050131;第35卷(第1期);第1-2页 * |
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