CN101207594B

CN101207594B - Method for implementing frequency coarse synchronizing using energy detection technique

Info

Publication number: CN101207594B
Application number: CN2006101477117A
Authority: CN
Inventors: 朱峻杰; 林森凌; 王立宁
Original assignee: DINGXIN COMMUNICATION Co Ltd SHANGHAI
Current assignee: Dingxin Communication Co., Ltd., Shanghai
Priority date: 2006-12-21
Filing date: 2006-12-21
Publication date: 2010-12-15
Anticipated expiration: 2026-12-21
Also published as: CN101207594A

Abstract

The invention discloses a frequency rough synchronization method utilizing an energy detection technology. The method comprises the following steps: step one: the energy of a subcarrier of a quanta is measured and the range of integer time frequency deviation is determined; step two: a correlator searches and determines exactly the integer time frequency deviation by using the relevant characteristic of a phase referential code element to complete the rough synchronization of a frequency. The invention utilizes the relevant characteristic of the phase referential code element to improve the rough synchronization process of the frequencies, thereby achieving the object of algorithm simplification and performance improvement.

Description

A kind of energy detection technique that utilizes is realized the synchronous method of frequency rough

Technical field

The present invention relates to digital audio broadcasting (DAB, Digital Audio Broadcasting) system, particularly relate to the frequency coarse synchronizing method in a kind of digital audio broadcast system.

Background technology

Digital audio broadcast system is by ETSI (European TelecommunicationsStandards Institute, ETSI) a kind of digital audio broadcast system of Ti Chuing, the modulation system that it has adopted OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexi) to combine with DQPSK (difference quadrature phase shift keying modulation).For carrier frequency synchronization, very high because each subchannel bandwidth of OFDM is less to the sensitivity of carrier frequency offset, therefore need point-device carrier synchronization.Present carrier synchronization process is divided into two kinds of patterns: synchronously thick and synchronously thin.In thick synchronous mode, synchronizer is reduced to a small range with the big initial deviation of parameter; In thin synchronous mode, synchronizer further reduces the remainder error of parameter, improves the precision of estimating.

In ofdm system, in fact frequency departure can be decomposed into two parts: integer part and fractional part, integer part here and fractional part are for subcarrier spacing.So-called integer part is that a part of frequency departure that equals the integral multiple of subcarrier spacing; Fractional part is meant that a part of frequency departure less than subcarrier spacing.

As communication system, be to obtain the preceding very important step of information synchronously, the quality of synchronized algorithm design directly has influence on the power consumption and the performance of product, and particularly the many modes with integrated circuit of product realize now, so this problem is more outstanding.

The Frequency Synchronization of DAB system is primary process.In Frequency Synchronization, frequency slightly be again wherein very important part synchronously.Existing frequency coarse synchronizing method has following 2 kinds:

With the phase reference code that receives (Phase Reference Symbol, PRS) be FFT (fast fourier transform) after, with the PRS conjugate multiplication that this locality produces, then multiplied result is done the IFFT conversion.When phase reference code aligns with local PRS strictness, have peak value and occur.

The phase reference code PRS that receives is relevant with the local PRS through after the IFFT conversion that produces 2..If received signal is Domain Synchronous, have peak value after relevant and occur.

More than two kinds of synchronous methods of frequency rough all have separately shortcoming, specific as follows:

Method one: operand is excessive.Peak value detects each time all needs to do conjugate multiplication and be IFFT.And have only when phase reference code aligns with local PRS strictness, just there is peak value to occur.So must all possible frequency deviation of traversal, and step-searching greatly.So this method power consumption is bigger, is not suitable for hardware and realizes.

Method two: the effective precondition harshness of algorithm.Because this method is to detect frequency deviation information on time domain, so precondition is to want earlier precise synchronization on time domain.This has increased the difficulty of Domain Synchronous.From the angle of system is the algorithm of having simplified certain aspect, has but increased algorithm difficulty on the other hand greatly.Lose more than gain.

Though above method all is feasible for general ofdm system, has all ignored the particularity of DAB system.In the DAB system, as shown in Figure 1: an ofdm signal is made up of channel distortion experienced that mediates and the gap carrier wave that is in the edge, therefore the edge of channel distortion experienced can obtain by the method for similar energy measuring, thereby obtains the scope of carrier deviation.

Summary of the invention

In view of this, the technical problem to be solved in the present invention has been to provide a kind of energy detection technique that utilizes to realize the synchronous method of frequency rough.Can quick lock in frequency deviation region and and then further definite accurate integer frequency offset by this method.

Technical scheme of the present invention is as follows:

A kind of energy detection technique that utilizes is realized the synchronous method of frequency rough, comprises the steps:

Step 1: measure the subcarrier energy, determine the integer frequency offset scope;

Step 2: according to described integer frequency offset scope, correlator utilizes the phase reference code correlation properties to seek and determines accurate integer frequency offset, and it is synchronous to finish frequency rough.

Further, this method also has following characteristics, and described step 1 specifically comprises the steps:

Step 1.1: from left to right measure subcarrier energy through fast fourier transform;

Step 1.2: when detecting the channel distortion experienced edge, calculate through energy calculator, if the energy sum of 32 subcarriers in front is less than thresholding 1 desired level, and the energy sum of 32 subcarriers in back is greater than thresholding 2 desired levels, then

Step 1.3: integral times bias frequency range is defined in first subcarrier of 32 subcarriers of last subcarrier and back of 32 subcarriers in front, and in 3～5 subcarriers of adjacent sub-carrier.

Further, this method also has following characteristics, and described step 2 specifically comprises the steps:

Step 2.1: according to the indication that the channel distortion experienced edge is detected, thresholding determining device output enable signal is opened correlator;

Step 2.2: correlator slides 32 subcarriers of phase reference code of receiving and 32 subcarriers of local phase reference code relevant, and the window's position when then obtaining correlation peak is accurate integer frequency offset.

As from the foregoing, the inventive method search speed is fast, by mensuration to the energy value of subcarrier, with 2 threshold value quick lock in frequency deviation regions, and the effective precondition of algorithm satisfies easily, its needs carry out the frequency deviation detection at frequency domain rather than in time domain, and the requirement to time synchronized just is not so strict like this.In addition, algorithm is more accurate, the easier frequency that searches frequency deviation.

Concrete beneficial effect is as shown in Figure 2: Fig. 2 has shown the correlation of 32 phase reference codes, wherein has 4 relevant peaks, except maximum correlation peak 0 o'clock, all the other relevant peaks are all beyond ± 16.But the algorithm by front edge detects can not carry out PRS to these scopes and be correlated with, and therefore the relevant method that combines with PRS of rim detection is had only in theory a relevant peaks to occur, and this has not only saved operand, and has reduced the synchronous probability of mistake.So the present invention has utilized the characteristic of PRS, and frequency rough is improved synchronously, has reached shortcut calculation, improve the purpose of performance.

Description of drawings

Fig. 1 is an OFDM frame signal structural representation in the prior art;

Fig. 2 is the schematic diagram data of 32 phase reference code correlations in the inventive method;

Fig. 3 is the flow chart of steps of the inventive method;

Fig. 4 is the schematic diagram of the inventive method;

Fig. 5 is an explanation schematic diagram of determining the integer frequency offset scope in the inventive method;

Fig. 6 is the enforcement schematic diagram of the embodiment of the invention.

Embodiment

Below with reference to accompanying drawing, core concept of the present invention and each preferred embodiment are carried out further detailed description and explanation.

The invention provides a kind of energy detection technique that utilizes and realize the synchronous method of frequency rough, its core concept is: by the mensuration to the energy value of subcarrier, on the basis with 2 threshold value quick lock in frequency deviation regions, carry out relevant with local 32 phase reference codes 32 phase reference codes that receive, further determine integer frequency offset behind the window's position when obtaining correlation peak, finish thick synchronizing process.

Below with reference to Fig. 3, Fig. 4 and Fig. 5 core concept of the present invention is further set forth.

Fig. 3 is the flow chart of steps of the inventive method, and as shown in Figure 3, this method comprises two steps: step 1: measure the subcarrier energy, determine the integer frequency offset scope; Step 2: according to described integer frequency offset scope, correlator utilizes the phase reference code correlation properties to seek and determines accurate integer frequency offset, and it is synchronous to finish frequency rough.

Fig. 4 is the schematic diagram of the inventive method, as shown in Figure 4: the sliding window index signal that the window selector is used for the receiving phase reference symbols sn and is fed back by the thresholding determining device; Energy calculator is used to calculate carrier energy and the thresholding that the result inputs to thresholding determining device and setting is compared, and the thresholding determining device enables correlator work or the sliding window index signal is fed back to the window selector according to judged result; Correlated results detects the output frequency deviation through peak detector.

Fig. 5 is an explanation schematic diagram of determining integer frequency offset in the inventive method, as shown in Figure 5: show thresholding 1, thresholding 2 energy relationship with 32 subcarriers in front and 32 subcarriers in back respectively; Show simultaneously integral times bias frequency range be defined in before and after in the scope of two groups of subcarriers.

According to Fig. 3, Fig. 4 and Fig. 5, the inventive method specifically describes as follows: from left to right measure the subcarrier energy through fast fourier transform; When detecting the edge of channel distortion experienced, calculate through energy calculator, if the energy sum of 32 subcarriers in front is less than the thresholding 1 that sets, and the energy sum of 32 subcarriers in back is greater than thresholding 2, then integral times bias frequency range is defined in first subcarrier of 32 subcarriers of last subcarrier and back of 32 subcarriers in front, and in 3～5 subcarriers of adjacent sub-carrier, promptly in the zone that the two vertical lines of Fig. 5 show; After integer frequency offset was determined, the thresholding determining device was opened the output enable signal with correlator, and correlator will utilize the correlation properties of PRS to seek accurate integer frequency offset in the scope that integer frequency offset is determined.Simultaneously, in order to save computing time and energy, only need to use 32 subcarriers that receive PRS relevant just passable with 32 subcarriers of local PRS, the window's position when obtaining correlation peak is integer frequency offset, finishes thick synchronizing process.

Fig. 6 is the enforcement schematic diagram of the embodiment of the invention, and as shown in Figure 6, specific implementation process is as follows: at first, and with the value delivery addition of 1～No. 32 register in the register, simultaneously with the value delivery addition of 33～No. 64 registers.Compare with the mould value of 1～No. 32 register with the set point of thresholding 1 then, if less than thresholding 1, output 1, otherwise export 0; With the value delivery addition of 33～No. 64 registers, as if set point greater than thresholding 2, output 1, otherwise export 0.According to the output of the multiplier after comparator result, if 0, then the PRS window moves right 1, and device quits work in the square frame 1, otherwise window is motionless, and device is started working in the square frame 1.If device is started working in the following square frame 1, then that the conjugation of 33～No. 64 registers and preceding 32 symbols of local PRS is relevant and detect relevant peaks, as if greater than the setting thresholding, then Ci Shi PRS the window's position is integer frequency offset.If less than thresholding, then adjust PRS the window's position, it is relevant and whether detect relevant peaks greater than the step of setting thresholding to repeat above-mentioned preceding 32 symbol conjugation with 33～No. 64 registers and local PRS, up to finding relevant peaks, finishes synchronously thick.

Should be understood that above-mentioned description at specific embodiment is comparatively detailed, can not therefore think the restriction to scope of patent protection of the present invention, scope of patent protection of the present invention should be as the criterion with claims.

Claims

1. one kind is utilized energy detection technique to realize the synchronous method of frequency rough, comprises the steps:

Step 2: according to described integer frequency offset scope, correlator utilizes the phase reference code correlation properties to seek and determines accurate integer frequency offset, and it is synchronous to finish frequency rough;

Wherein, step 1 specifically comprises step:

2. a kind of energy detection technique that utilizes according to claim 1 is realized the synchronous method of frequency rough, it is characterized in that described step 2 further comprises: