CN100518047C - A Signal Acquisition Method Against Large Delay Spread Channels - Google Patents

Abstract

The invention discloses a signal capture method that can resist big time delay spreading signal channel. After the self-correlated operation on the signal, a first time point is searched where the self-correlated output extent value is greater than an extent threshold Tamp in the self-correlated extent waveform; and then, a time slice with certain length like T2/2 is delayed from the first time point to decide a second time point where the self-correlated output extent value is less than the threshold value Tamp. after the second time point, the time slice that is less than and equal to a signal period T2 is searched until a wave crest is found that has an greater extent value than the threshold value Tamp, and the waveform width of the wave crest, which is above the threshold value Tamp, should be greater than a width threshold value Twid. And then the corresponding time point of the wave crest is the coarse synchronizing position. The signal capture method of the invention can resist big time delay spreading signal channel, and improves the efficiency of signal capture in real time.

Description

A Signal Acquisition Method Against Large Delay Spread Channels

technical field

The invention relates to a synchronous receiving technology in the technical field of communication, in particular to a signal acquisition method capable of resisting large delay extension channels.

Background technique

The so-called signal acquisition refers to the initial synchronization process of receiving system signals. The receiving system can only ensure that the receiving system obtains real signal synchronization by performing fine synchronization after obtaining initial synchronization, and continuously performing synchronization tracking during the process of receiving signals. Therefore, obtaining the initial synchronization of the signal is the first processing step of the receiver synchronization system, and it is also a very important processing step. The purpose of signal acquisition is to obtain a rough signal sync position, not an exact signal sync position. And due to the diversity of wireless channels, it is difficult for a certain signal acquisition method to ensure that the exact signal synchronization position can be obtained in all channel environments; or, for some channel conditions, the algorithm can obtain the exact signal synchronization position, but For other channel conditions, the algorithm may even fail. Therefore, one of the most important characteristics of the signal acquisition algorithm is that it should be universal, that is, it can obtain the rough synchronization position of the receiving system under any channel conditions. Further, after the rough synchronization is obtained, the fine synchronization can be used to obtain a more accurate signal synchronization position.

The European DVB (Digital Video Broadcasting, Digital Video Broadcasting) system adopts multi-carrier OFDM (Orthogonal Frequency Division Multiplexing, Orthogonal Frequency Division Multiplexing) channel transmission technology. The signal acquisition method of the DVB system utilizes the cyclic prefix (CP, Cyclic Prefix) part of the OFDM symbol. Since the length of the CP part is relatively short, for example, the shortest CP length in 2K mode in the DVB system is only 7 microseconds, so the robustness of the signal acquisition algorithm cannot be guaranteed; and, since the CP part cannot accurately identify the origin of each signal frame Therefore, even if the starting position of a certain OFDM symbol can be obtained, the receiving system cannot quickly and accurately find the starting position of each signal frame.

In order to avoid the synchronization dilemma faced by the DVB system, China's CMMB (China MobileMultimedia Broadcasting, China Mobile Multimedia Broadcasting) system proposes a new frame structure, which sets a beacon at the beginning of each time slot, thus ensuring The receiver may not use the CP part of the OFDM symbol for synchronization, but only use the beacon part to obtain the synchronization position of the signal.

As shown in Figure 1, a schematic diagram of the frame structure of the physical layer of the CMMB system is given. In the frame structure of the physical layer of the CMMB system, 1 second is divided into 40 time slots, and each time slot is composed of 1 beacon and 53 OFDM symbols.

As shown in FIG. 2 , a schematic diagram of the composition and structure of beacons in each time slot of the frame structure of the physical layer of the CMMB system is given. In each time slot, each beacon consists of a TxID (transmitter identification sequence) and two identical synchronization signals (SYNC, Synchronous signal). The time length of each synchronization signal is 204.8 microseconds, which is far greater than the CP length (51.2 microseconds) of an OFDM symbol.

For a system with a frame structure similar to the above CMMB, the commonly used signal acquisition method is to use two same synchronization (SYNC) signals for processing. The specific steps are: first, perform autocorrelation on the input signal; then, find the autocorrelation output The maximum value of the value amplitude is used to obtain the rough synchronization position of the signal. As shown in FIG. 3 , it describes the waveform diagram of the amplitude of the autocorrelation output value obtained by the traditional signal acquisition method, wherein the time T is much shorter than the time T2. For example, in the CMMB system, T2 corresponds to the length of one time slot. The waveform shown in Figure 3 is characterized by only one peak per time slot (T2).

However, from another point of view, SYNC, that is, too long synchronization signal will affect the transmission capacity of the system. Therefore, in a system that is more sensitive to transmission capacity, in order to increase the transmission capacity of the system, it will have to consider reducing the length of the SYNC signal; and, theoretically speaking, the delay spread of the wireless channel must be greater than that of the SYNC signal length. When the delay extension of the wireless channel is greater than the length of the synchronization signal, the waveform of the autocorrelation output value amplitude will appear multiple peaks (as shown in Figure 4) in each T2 (such as time slot), which leads to the traditional The signal catch method will no longer work.

To sum up, since the current signal capture method does not consider the situation of the large delay spread channel, a signal capture method that can resist the large delay spread channel is needed.

Contents of the invention

The technical problem to be solved by the present invention is to provide a signal acquisition method that can resist extended channels with large delays. In the case of extended channels with large delays, the signal acquisition can be realized quickly and accurately, that is, the rough synchronization can be determined quickly and accurately during the synchronization process. Location.

The technical scheme adopted in the present invention is:

The present invention provides a signal acquisition method, which is used to capture the synchronization position of signals with two identical synchronization signals in each beacon in each time slot during the signal synchronization process, including the following steps:

A, configuration setting the threshold T _amp of the autocorrelation output amplitude and the width threshold T _wid of the autocorrelation output amplitude waveform;

B, carry out autocorrelation calculation to described signal, search and determine the first time point that an autocorrelation output amplitude value is greater than threshold T _amp ;

C. After delaying the first time period from the first time point, it is determined that the autocorrelation output amplitude value is less than the second time point of the threshold T _amp ;

D. Search backward from the second time point in the second time period less than or equal to the signal period T ₂ until a peak is found, if the amplitude of the peak is greater than the threshold T _amp and the amplitude waveform of the peak is within the threshold T If the width of the waveform above _amp is greater than the width threshold T _wid , it is determined that the time point corresponding to the peak is the roughly synchronous position of the signal.

Further, the method further includes:

E. If the amplitude value of the peak is not found greater than the threshold T _amp and the amplitude waveform of the peak is above the threshold T _amp and the width of the waveform is greater than the peak width threshold T _wid , return to step B and perform the signal acquisition process again.

The method further comprises:

E1. If the amplitude value of the peak is not found greater than the threshold T _amp and the amplitude waveform of the peak is above the threshold T _amp and the waveform width is greater than the peak width threshold T _wid , then return to step A and perform the signal acquisition process again.

The method further comprises:

When the signal acquisition process is re-performed, in the step B, the peak time point whose amplitude is greater than the threshold T _amp obtained in the last search is taken as the first time point in the re-performed signal acquisition process this time.

The first time period in step C is half of the signal period. In step A, the threshold T _amp of the autocorrelation output amplitude is set according to the average power of the signal, and the width threshold T _wid of the autocorrelation output amplitude waveform is set by multipath delay.

Since the current signal acquisition method does not consider the situation of the extended channel with a large delay, in comparison, the signal acquisition method of the present invention aims at the characteristics of the signal of the extended channel with a large delay, by determining the search period including a signal, Using the peak judgment condition can quickly and accurately find a qualified peak from the extended signal, so as to locate the coarse synchronization position. Therefore, it can resist the channel environment with large delay extension and improve the efficiency of signal synchronization acquisition.

Description of drawings

Fig. 1 is the frame structure schematic diagram of CMMB system physical layer in the background technology of the present invention;

Fig. 2 is a schematic diagram of the composition structure of beacons in each time slot of the frame structure shown in Fig. 1;

Fig. 3 is the oscillogram of the autocorrelation output value magnitude that traditional signal capture method obtains;

Fig. 4 is when the delay extension of wireless channel is greater than the length of synchronous signal, the oscillogram of autocorrelation output value amplitude;

Fig. 5 is a flow chart of a signal acquisition method against a large delay spread channel in an embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be described in more detail below with reference to the drawings and embodiments.

Aiming at the situation that the current signal acquisition method does not consider the large delay expansion channel, the invention proposes a signal acquisition method which can resist the large delay expansion channel. More precisely, the signal acquisition method proposed by the present invention can process the waveform of the autocorrelation output value amplitude as shown in Figure 4, wherein, the time T is much smaller than the time T ₂ , and at each T ₂ (such as time slot) Multiple peaks will appear within the time interval (only two peaks are exemplarily shown in FIG. 4 , but not limited thereto).

The signal capture method that the present invention proposes, as shown in Figure 5, is made up of following processing steps:

Step 1: according to the system parameters, set the threshold T _amp of the autocorrelation output amplitude, and set the width threshold T _wid of the autocorrelation output amplitude waveform;

For the receiving system, there are usually automatic gain control AGC equipment or processing methods, and the automatic gain control AGC directly affects the setting of the threshold value, but the AGC of different systems may be different again, thus, for the automatic gain control The threshold T _amp of the correlation output amplitude and the width threshold T _wid of the autocorrelation output amplitude waveform can be adaptively set according to system performance requirements and power status during implementation.

When setting the threshold value of the actual system, it is generally set according to the simulation results. For example, according to the output waveform of the simulation, set a threshold value, and then run the simulation program to see whether the threshold value is valid. If it is invalid, modify the corresponding threshold value. Generally speaking, the amplitude threshold value is related to the average power of the signal. The larger the average power, the larger the amplitude threshold value, and the smaller the amplitude threshold value; and the waveform width threshold value is related to the delay of multipath It is related to the time extension, the greater the delay extension, the larger the waveform width threshold, and the smaller the waveform width threshold is.

Step 2: Carry out an autocorrelation operation on the signal, and search for a time point in the autocorrelation amplitude waveform, which is recorded as the first time point, and the autocorrelation output amplitude value corresponding to the time point is greater than the threshold T _amp ;

Step 3: Delay a certain length of time from the first time point, such as T ₂ /2, to ensure that the autocorrelation output amplitude value corresponding to the delayed time point (recorded as the second time point) is less than the threshold T _amp ; then, search backward from the second time point (the search length is less than or equal to T ₂ ), until a peak is found, its amplitude value should be greater than the threshold T _amp , and the amplitude waveform where the peak is located is within the threshold T _amp The waveform width on should be greater than the width threshold T _wid .

If the above conditions are satisfied, the signal capture process is completed, and the time point corresponding to the peak is the rough synchronization position of the signal.

If the above conditions are not met, go to step 1 and reset the parameters T _amp and T _wid , and then perform the signal capture process again; or directly return to step 2, keep the parameters T _amp and T _wid unchanged, and then perform signal capture again process. Wherein, a convenient method may be to use the peak time point whose amplitude is greater than the threshold T _amp obtained in this search as the first time point in the next signal acquisition process. That is to say, for a process that is not the first search, the peak time point of the last search can be used as the first time point in this signal acquisition process.

Since the current signal acquisition method does not consider the situation of the extended channel with a large delay, in comparison, the signal acquisition method of the present invention aims at the characteristics of the signal of the extended channel with a large delay, by determining the search period including at least one signal , using the peak judgment condition can quickly and accurately find a qualified peak from the extended signal, so as to locate the coarse synchronization position, thus, it can resist the channel environment with large delay extension and improve the efficiency of signal synchronization acquisition.

Of course, the present invention can also have other various embodiments, and those skilled in the art can make various corresponding changes and deformations according to the present invention without departing from the spirit and essence of the present invention, but these corresponding Changes and deformations should belong to the scope of protection of the appended claims of the present invention.

Claims (7)

1, a kind of signal acquisition methods is used in the signal Synchronization process, catches the sync bit that has the signal of two same synchronizing signals in each beacon of each time slot, it is characterized in that, comprises the steps:

The thresholding T of A, configuration settings auto-correlation output amplitude _AmpAnd the width threshold T of auto-correlation output amplitude waveform _Wid

B, described signal is carried out auto-correlation computation, search and determine that an auto-correlation output amplitude value is greater than thresholding T _AmpVery first time point;

C, after postponing very first time section backward, very first time point determines that auto-correlation output amplitude value is less than thresholding T _AmpSecond time point;

D, be less than or equal to signal period T since second time point ₂Second time period in search backward, until finding a crest, if the range value of this crest is greater than thresholding T _AmpAnd the amplitude wave-shape at this crest place is at thresholding T _AmpOn the waveform width greater than width threshold T _Wid, determine that then this crest time corresponding point is the coarse synchronization position of signal.

2, signal acquisition methods as claimed in claim 1 is characterized in that, described method further comprises:

E, if do not search the range value of this crest greater than thresholding T _AmpAnd the amplitude wave-shape at this crest place is at thresholding T _AmpOn the waveform width greater than width threshold T _WidCrest, then return step B and carry out the signal capture process again.

3, signal acquisition methods as claimed in claim 1 is characterized in that, described method further comprises:

E1, if do not search the range value of this crest greater than thresholding T _AmpAnd the amplitude wave-shape at this crest place is at thresholding T _AmpOn the waveform width greater than width threshold T _WidCrest, then return steps A and carry out the signal capture process again.

4, signal acquisition methods as claimed in claim 2 is characterized in that, described method further comprises:

When carrying out the signal capture process again, in described step B, will search for the amplitude of acquisition last time greater than thresholding T _AmpThe crest time point carry out first time point in the signal capture process again as this.

5, signal acquisition methods as claimed in claim 1 is characterized in that, the very first time section among the described step C is half of signal period.

6, signal acquisition methods as claimed in claim 1 is characterized in that,

In the steps A, the thresholding T of described auto-correlation output amplitude _AmpBe to set according to the average power of signal.

7, signal acquisition methods as claimed in claim 1 is characterized in that,

In the steps A, the width threshold T of described auto-correlation output amplitude waveform _WidThe time-delay that is multipath is set.

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