CN1640039A - Method and device for multipath search and tracking - Google Patents

Abstract

The invention provides a method and a device for multipath searching and tracking, which de-spreads a received signal by adopting a matched filter; when the local code word in the matched filter is aligned with a certain path signal of the received signal, the matched filter outputs a correlation peak value; the energy of different time delay signals is obtained after the square addition of signals of I, Q two branches, the maximum value is selected as the strongest path signal, the strongest path signal is subtracted from the output of the matched filter, and the maximum energy is selected from the residual signals as the other path signal; the position information of the two paths is sent to the RAKE receiving unit. To find the strongest signal in the downlink synchronization channel signal.

Description

A method and device for multipath search and tracking Technical field

The present invention belongs to the technical field of wireless communication, and in particular relates to the realization of multipath search in the downlink synchronization subsystem of a CDMA system, specifically a method and device for multipath search and tracking. Background technique

In a CDMA communication system, multipath search and tracking is to search and select an appropriate path among the received signals arriving at the mobile station through multiple paths after the mobile station obtains frame synchronization, code synchronization and carrier synchronization, and determines the target cell. Provided to the RAKE receiver.

In the mobile communication environment, the signal sent by the transmitter reaches the receiver through different paths. The signals of each path experience different random amplitude attenuation and phase rotation, as well as different time delays. After these signals arrive at the receiver, they are superimposed on each other, causing the fading of the composite signal. The presence of signals on these paths is also random, that is, they exist at some moments, disappear at some moments, are stronger than other paths at some moments, and may have stronger path signals at some moments.

In a CDMA communication system, a RAKE receiver including multiple branches can be used to combat fading. The RAKE receiver utilizes multiple paths with strong signals detected by a search unit and assigns them to each branch. Each branch is responsible for synchronizing with a path signal, demodulating the signal therein, and then merging the path information according to certain rules.

The specific tasks of the multipath search unit include:

search for the location of the strongest path signal (timing);

Accurately track signal timing of each path and report to RAKE receiver;

Detect the quality of each path signal;

Search for a new, more suitable path.

Contents of the invention

The object of the present invention is to provide a multipath search and tracking method and device for finding the signal with the strongest energy among the downlink synchronization channel signals. Technical scheme of the present invention is:

A method for multipath search and tracking, comprising the following steps:

Using a matched filter to despread the received signal;

When the local codeword in the matched filter is aligned with a certain path signal of the received signal, the matched filter outputs a correlation peak value;

The energy of signals with different delays is obtained by adding the squares of the signals of the I and Q branches, and the maximum value is selected as the strongest path signal, and the strongest path signal is subtracted from the output of the matched filter, and then obtained from the remaining signal Select the maximum energy as another path signal;

Send the location information of the two paths to the RAKE receiving unit.

The use of the matched filter to despread the received signal refers to: 4/ before the start of the D-SYNCH (downlink synchronization channel); the matched filter despreads the received signal.

In the method of the present invention, the steps may further include:

Before the D-SYNCH (downlink synchronization channel) starts, the N matched filter despreads the received signal, and N is the sampling frequency;

Save the data within the range of RANGE near the D-SYNCH synchronization position, and accumulate the signals of consecutive N_FRAMES-Acc frames; the initial synchronization position comes from the frame boundary detection unit, and the subsequent positions can be the first one found in the previous multipath search. radial position;

Find the maximum value in the accumulated RANGE long signal, which can represent a path; record the maximum value and the maximum position

The average V of the currently selected maximum value and the maximum value of the previous AVERAGE-COUNTER frame. For comparison, if V^Kx V ₀ , the RAKE receiver uses the path position of the previous frame and does not update; otherwise, uses P;

Calculating the energy of the other samples corresponding to the path, subtracting from the accumulated A ¾" long corresponding signal;

Search for the maximum value V ₂ and the position P ₂ within the RANAGE window;

则 P₂代表第二条路径， 否则被看作噪声； 将 W if

Then P ₂ represents the second path, otherwise it is regarded as noise; W

P ₂ is sent to the RAKE receiver;'

If LOSS—COUNTER W times in a row, notify the synchronous capture to work again;

Comparing P ₂ , the signal arriving first is taken as the first path, and the signal arriving later is taken as the second path, namely: P mirKP P ₂ ), P ₂ =raax (P _l5 P ₂ ).

The selection of the RANGE should consider clock error and multipath search error.

The selection of the N-FRAMES-Acc should consider the clock error.

The selection of said N-FRAMES-Acc will consider the clock error including:

When the initial clock error is 3ppm, 3 frames can be accumulated; when the clock error is corrected to less than 0.3ppm, 10 frames can be accumulated.

The present invention also provides a multipath search and tracking device, which includes: a matched filter, a square addition module, a storage module, a path search module, and a synchronization acquisition module;

The matched filter despreads the received signal;

The despread signal is input to the described square addition module;

Inputting the output signal of the square addition module into the storage module;

The output signal of the storage module is input into the path search module and the synchronization capture module, and the synchronization capture module is coupled with the path search module;

The output signal of the path search module is sent to the RAKE receiving unit.

The matched filter includes: the sampling rate is: N _c ; the rate of the matched filter is: N/ _c . The output signal of the path search module includes: the position of the first path and the position of the second path.

The effect of the present invention is that, by providing a multipath search and tracking method and device, it can find the signal with the strongest energy among the downlink synchronization channel signals.

Description of drawings

FIG. 1 is a subframe structure diagram of a downlink synchronization channel;

Figure 2a is the waveform diagram of the output signal of the matched filter under the condition of no noise and multipath; Waveform diagram of output signal with filter;

FIG. 2c is a waveform diagram of the output signal of the matched filter when the two signals exist at the same time and the output signals are superimposed after passing through the code matched filter;

Figure 3 is a waveform data diagram;

Fig. 4 is a structural block diagram of the device of the present invention;

Figure 5 is a flowchart of the method of the present invention.

Detailed ways

The present invention provides a method and device for multipath search and tracking. The following is combined with the accompanying drawings, and the implementation of multipath search in the downlink synchronization subsystem of the TD-LAS system designed according to the physical layer specification of the TD-LAS system is taken as an example , to describe specific embodiments of the present invention.

W 其中： A = (+j + + + -) , B = (- } - + + -) , C = (-7 _— +) , D = (-} - + + -) In the TD-LAS system, the structure of the downlink synchronization channel is shown in Figure 1; the downlink synchronization physical channels of all cells use the same LS spreading code (see Table 1), and different modulation code groups to distinguish cells. The downlink synchronization subframe has 8 time slots in total. Refer to Table 2 for the length of each time slot. Each time slot transmits a downlink synchronization pulse with a length of 72Chips, including 24chips of C code and 24chips of S code. The protection of 24chips is reserved in the middle The downlink sync pulse is transmitted at the beginning of each time slot. The LS code used for the downlink synchronization channel is a complex code, and the corresponding spreading and despreading are similar to QPSK, as shown in Table 4. The 8 time slots of the downlink synchronous subframe can transmit 8 modulation symbols, and a total of 8 bipolar mutually orthogonal code sequences can be obtained, such as each row or column of the 8 X 8Walsh matrix, in the TD-LAS system These code sequences are called LA polar sequences in (see Table 3). 8 orthogonal LA polarity sequences can support a network of 8 cells/sectors; to support a larger network scale, it can be combined with other cell identification methods such as continuous pilot cell identification, and can also Make different cell/sector clusters use different LA guard intervals, and expand the D-SYNPCH signal set. Table 1. Spreading code (LS code) of the downlink synchronization channel (j = V^I )

W where: A = (+j + + + -) , B = (- } - + + -) , C = (-7 _— +) , D = (-} - + + -)

表 3. 下行同步信道的 LA极性码

表 4. 下行同步信道的 LA极性码 Table 2. Subframe slot length of downlink synchronization channel

Table 3. LA Polarity Codes for Downlink Sync Channels

Table 4. LA Polarity Codes for Downlink Sync Channels

Multipath search and tracking is to select an appropriate path among the received signals arriving at the mobile station through multiple paths after the mobile station obtains frame synchronization, code synchronization and carrier synchronization, and determines the target cell, and provides it to the RAKE receiver.

In the mobile communication environment, the signal sent by the transmitter reaches the receiver through different paths. The signals of each path experience different random amplitude attenuation and phase rotation, as well as different time delays. After these signals arrive at the receiver, they are superimposed on each other, causing the fading of the composite signal. The presence of signals on these paths is also random, existing at some moments, disappearing at some moments, stronger than other path signals at some moments, and possibly stronger path signals at some moments.

In a CDMA communication system, a RAKE receiver including multiple branches can be used to combat fading. The RAKE receiver utilizes multiple paths with strong signals detected by a search unit and assigns them to each branch. Each branch is responsible for synchronizing with a path signal, demodulating the signal therein, and then merging the path information according to certain rules.

Specifically, the tasks of the multipath search unit include: 1) Search for the position of the strongest path signal (timing);

2) Accurately track the signal timing of each path and report to the RAKE receiver;

3) Detect the quality of each path signal;

4) Search for a new and more suitable path;

In the TD-LAS system, the downlink multipath search uses a matched filter with a rate of 4 to perform matched filtering on the downlink synchronous channel signal, and find the signal with the strongest energy among them after multi-frame averaging.

In the present invention, the rate of the received signal is 4 ¾ first despreading through a code-matched filter. Due to the zero-correlation window characteristic of the code word, the waveform of the output signal of the matched filter is shown in Figure 2a under the condition of no noise and multipath.

When another signal goes through a different path, the time delay is 1 chip, and the output waveform of the code-matched filter is shown in Figure 2b. As a result, when the two signals exist at the same time, after passing through the code-matched filter, the output signals are superimposed, and the waveform is shown in Figure 2c.

Assuming that the signal power of the first path is stronger than the signal power of the second path, the position of the maximum value in the output waveform of the matched filter is the position of the signal of the first path. The maximum output value of the detector can determine the synchronization position of the first path signal, or the time delay, which is assigned to a RAKE branch. In order to determine the time delay of the second path, the component of the matched filter output by the first path signal is subtracted from the entire output to form a waveform as shown in Figure 2b, in which the maximum value is searched, and the second path is detected synchronization position.

Since only the maximum output value can be obtained when the first path signal is detected, the output amplitudes at other sample value moments need to be calculated. For example, Figure 3 shows the output of the matched filter ideally after adding the baseband shaping filter, which has been normalized to the maximum value. As long as the maximum energy is known, the actual energy values at other sample moments can be calculated by using the waveform data in Fig. 3,

E„, is the maximum energy value, is the energy value at time /. is the maximum position, and S(i) is the waveform at time i. As shown in Figure 4 and Figure 5, the specific implementation of the present invention is as follows:

The search unit starts to work after the synchronous acquisition obtains the rough position of the downlink synchronous channel. The 4-rate matched filter despreads the received signal. When the local codeword in the matched filter is aligned with a certain path signal of the received signal, the matched filter output correlation peak. The energy of signals with different delays is obtained by adding the squares of the signals of the I and Q branches, and the maximum value is selected as the strongest path signal, which is subtracted from the output of the matched filter, and then the maximum energy is selected from the remaining signal As the second path signal, the position information of the two paths is sent to the RAKE receiving unit. The steps of algorithm implementation are as follows:

After the downlink synchronization initial acquisition algorithm is completed, the initial position of the D-SYNCH channel is sent, and the multipath search unit starts to work:

1) Before D-SYNCH starts, 4 matched filters despread the received signal;

2) Save the data in the vicinity of the D-SYNCH synchronization position, and perform continuous

The signals of N-FRAMES-Acc frames are accumulated. The initial synchronization position comes from the frame boundary detection unit, and the subsequent position can be the first path position found in the previous multipath search.

Note: The selection of α should consider the clock error and the error of multipath search.

^— ^KS^cc selection should also consider the clock error. When the initial clock error is 3ppm, 3 frames can be accumulated; when the clock error is corrected to be less than 0.3ppm, 10 frames can be accumulated.

3) Find the maximum value in the accumulated long signal, which represents a path. Record the maximum value and the maximum position P].

4) The currently selected maximum value is compared with the average ^ of the maximum value of the previous A VERAGE_COUNTER frame, if <Γχ V ₀ , the RAKE receiver uses the path position of the previous frame and does not update it, otherwise uses P,

5) Calculate the energy of other samples corresponding to the Λ path, and subtract it from the accumulated corresponding signal of ^W length;

6) Search the maximum value and position Ρ ₂ ' in the RANAGE window,

7) If V V^ TH—Pa tl^, then represents the second path, otherwise it is regarded as noise. Send ^, to the RAKE receiver.

8) If the consecutive LOSS—COUNTER times ^ ₀ , notify the synchronous capture to work again.

9) For comparison, P ₂ , the signal that arrives first is taken as the first path, and the signal that arrives later is taken as the second path. That is, P ≧ min CP ₇ , P , P ₂ = x (Ρ _1: Ρ.

The I/O and related parameters of the present invention are as follows: The parameters of multipath search and tracking are shown in Table 5, and the input and output parameters are shown in Table 6.

Table 5. Parameters for Multipath Search and Tracking

表 6. 多径搜索和跟踪的输入和输出

Table 6. Inputs and outputs for multipath search and tracking

本发明的效果在于， 通过提供一种多径搜索和跟踪的方法及装置， 其 能够在下行同步信道信号中寻找出能量最强的信号。

The effect of the present invention is that, by providing a multipath search and tracking method and device, it can find the signal with the strongest energy among the downlink synchronous channel signals.

The above specific embodiments are only used to illustrate the present invention, but not to limit the present invention.

Claims (9)

Rights request 1. A method for multipath search and tracking, comprising the following steps: Using a matched filter to despread the received signal; When the local codeword in the matched filter is aligned with a certain path signal of the received signal, the matched filter outputs a correlation peak value; The energy of signals with different delays is obtained by adding the squares of the signals of the I and Q branches, and the maximum value is selected as the strongest path signal, and the strongest path signal is subtracted from the output of the matched filter, and then obtained from the remaining signal Select the maximum energy as another path signal; Send the two path position information to the RAKE receiving unit. 2. The method according to claim 1, wherein said using a matched filter to despread the received signal refers to: N <sub>c</sub before the start of D-SYNCH (downlink synchronization channel) >The matched filter despreads the received signal. 3. The method according to claim 1, wherein the steps may further comprise: despreading the received signal by the Nf_c matched filter before the D-SYNCH (downlink synchronization channel) starts; Save the data within the range of RANGE near the D-SYNCH synchronization position, and The signal of N_FRAMES_Acc frame is accumulated; the initial synchronization position comes from the frame boundary detection unit, and the subsequent position can be the first path position found in the previous multipath search; Find the maximum value in the accumulated RANGE long signal, which can represent a path; record the maximum value and the maximum position The currently selected maximum value is compared with the maximum average value V _Q of the previous AVERAGE-COUNTER frame, if the V^Kx V^RAKE receiver is set to use the path position of the previous frame, no update is made; otherwise, P ₁ is used to calculate the corresponding Pi path Other sample energies, subtracted from the accumulated JUW long corresponding signals; Search for the maximum value ^ and position P ₂ within the RANAGE window; If /V^TH—Pa th" then P ₂ represents the second path, otherwise it is regarded as noise; Send P ₂ to the RAKE receiver; If continuous LOSS—COUNTER times<V ₀ , then notify the synchronous capture to work again; To compare Ρ ₂ , the signal arriving first is taken as the first path, and the signal arriving later is taken as the second path, namely: P mii PP ₂ ), P ₂ =max (P ₁₋ P ₂ ). 4. The method according to claim 3, wherein the selection of the RANGE takes into account clock errors and multipath search errors. 5. The method according to claim 3, characterized in that, the selection of the N_FRAMES-Acc takes clock error into consideration. 6. The method according to claim 5, characterized in that, the selection of N-FRAMES_Acc to consider the clock error includes: When the initial clock error is 3ppm, 3 frames can be accumulated; when the clock error is corrected to less than 0.3ppm, 10 frames can be accumulated. 7. A multipath search and tracking device, including: a matched filter, a square addition module, a storage module, a path search module, and a synchronization acquisition module; The matched filter despreads the received signal; The despread signal is input to the described square addition module; Inputting the output signal of the square addition module into the storage module; The output signal of the storage module is input into the path search module and the synchronization capture module, and the synchronization capture module is coupled with the path search module; The output signal of the path search module is sent to the RAKE receiving unit. 8. The device according to claim 7, wherein the matched filter comprises: a sampling rate of N; a matched filter rate of N/_c. 9. The device according to claim 7, wherein the output signal of the path search module includes: the position of the first path and the position of the second path.