WO2007056891A1

WO2007056891A1 - A up-link synchronization method in mobile communication system

Info

Publication number: WO2007056891A1
Application number: PCT/CN2005/001934
Authority: WO
Inventors: Meiling Ding
Original assignee: Zte Corporation
Priority date: 2005-11-16
Filing date: 2005-11-16
Publication date: 2007-05-24
Also published as: CN101185270A; CN101185270B

Abstract

A up-link synchronization method in mobile communication system, comprises the following steps: (1) performing initial synchronization between a base station and a user equipment, and initial synchronization adjusting amount information used by the user equipment is included in initial synchronization adjusted signal sent by the user equipment; (2) the base station compares the received timing of user signal and the timing required by the base station, if the timing difference is more than a preset threshold, then performing initial synchronization with the user equipment again, until the timing difference is less than the preset threshold; (3) performing synchronous tracking between the base station and the user equipment, the user equipment sends the signal keeping time sequence , or, passing the signal adjusted synchronistically and comprising the synchronization adjusting amount information used by the user equipment, and turning back to step (2). The present invention improves precision and stability of up-link synchronization, and improves capacity and performance of the system.

Description

Uplink synchronization method in mobile communication system

Technical field

The present invention relates to a mobile communication system, and more particularly to an uplink synchronization method in a mobile communication system. Background technique

Whether in an analog communication system or in a digital communication system, the establishment and maintenance of synchronization is the basis for the interaction between the two parties. In a mobile communication system, the establishment and maintenance of downlink synchronization is generally performed by the user equipment searching and tracking the downlink synchronization channel and the broadcast channel, and the establishment and maintenance of the uplink synchronization is performed by the base station device to search for an access signal (such as a prefix). And the uplink synchronization channel) and the timing adjustment of the uplink signal are completed. In order to facilitate the implementation of this process, the structure of the random access channel in the Wideband Code Division Multiple Access (WCDMA) mobile communication system has been specifically proposed. However, in this implementation case, the uplink synchronization is directed to a single-user device, and the user equipment at this time does not dynamically adjust its own transmission timing.

On the other hand, due to the lack of implementation urgency and application complexity, the requirements for the uplink signals of all user equipments to be synchronized at the base station are not well studied and discussed until CDMA (Code Division Multiple Access) technology. widely used. The CDMA system is a self-interference system. The synchronization of the uplink signal on the base station side is beneficial to improve the capacity and performance of the entire system, and the accuracy of synchronization is much higher than that of the GSM system. Based on this consideration, a method of reverse channel synchronization has been proposed. In this method, when the base station sends the forward synchronization signal to all of the mobile stations associated therewith, the mobile station separately transmits the reverse synchronization signal to the base station in synchronization with the received forward synchronization signal. Upon receipt of the reverse synchronization signal, the base station calculates the delay for these mobile stations and sends the relevant synchronization information to the respective mobile stations. Based on this information, the mobile station controls the synchronization of the channel signals sent to the base station, respectively. This method is used in an uplink synchronization transmission scheme in a WCDMA mobile communication system, a time division code division multiple access (TD-CDMA) mobile communication system, and an uplink synchronization technique in a time division synchronous code division multiple access (TD-SCDMA) mobile communication system. Both require the uplink signal to be synchronized on the base station side. As shown in FIG. 1, it is a schematic diagram of an implementation environment of an uplink synchronization technology that is focused on the present invention.

In general, the uplink synchronization technology includes two parts, initial synchronization and synchronous tracking, as shown in Figure 2. The schematic diagram of the implementation process of the existing uplink synchronization technology mainly includes the following steps: Step 21: The base station sends a downlink synchronization signal, so that the user equipment acquires downlink synchronization. Step 22: The user equipment sends an uplink initial synchronization signal according to the downlink synchronization situation. Step 23: The base station acquires and sends an initial synchronization adjustment amount of the user equipment, so that the user equipment adjusts the uplink transmission timing. Step 24: The user equipment adjusts and sends the initial synchronization adjusted signal according to the received initial synchronization adjustment amount, and In one step, the initial synchronization process is completed. Step 25: The base station evaluates whether the user equipment needs to perform synchronization adjustment. From this step, the uplink synchronization enters the synchronization tracking phase. If the user equipment needs to adjust the uplink timing, the process proceeds to step 26. Otherwise, proceed to step 28; Step 26, the base station sends a synchronization signal adjustment amount to the user equipment; Step 27, the user equipment adjusts and transmits the synchronously adjusted signal according to the synchronization signal adjustment amount, and the process proceeds to step 25; Step 28, the base station requests the user equipment Keep signal Timing, this process can be set by adjusting the amount of pre-approved value is achieved both; Step 29, the user equipment transmits the hold timing signal, the flow proceeds to step 25.

Through this process, it is not difficult to find that when the actual timing adjustment of the user equipment needs to be utilized on the base station side, the latter can only be used as the adjustment amount required by the base station. This will lead to at least two problems: First, the adjustment amount understood by the base station and the user equipment is different due to the quality of the communication; Second, the adjustment amount cannot meet the requirements of the base station due to the user equipment. The actual timing adjustment of the user equipment is undoubtedly the basis for the base station to further evaluate whether the user equipment needs to be synchronized. However, in this important step, the current methods do not complete the process, so that the implementation performance of the uplink synchronization is not improved. Summary of the invention

The technical problem to be solved by the present invention is to provide a method for uplink synchronization in a mobile communication system, so that a mobile communication system with uplink synchronization and uplink quasi-synchronization can obtain better uplink synchronization effects and improve the capacity and performance of the mobile communication system.

In order to solve the technical problem, the technical solution provided by the present invention includes the following steps -

(1) initial synchronization between the base station and the user equipment, and the initial synchronization adjustment information applied by the user equipment is included in the signal after the initial synchronization adjustment sent by the user equipment;

(2) The base station compares the timing of the received user signal with the timing required by the base station side. If the timing difference is greater than the preset threshold, the base device performs initial synchronization with the user equipment again until the timing difference is small. At a preset threshold;

(3) synchronous tracking between the base station and the user equipment, the user equipment sends a signal to maintain the timing, or a synchronously adjusted signal containing the synchronization adjustment amount information applied by the user equipment, and returns to step (2) to re-execute .

Step (1) includes:

(a) the base station transmits a downlink synchronization signal;

(b) the user equipment sends an uplink initial synchronization signal according to the downlink synchronization situation;

(c) the base station acquires and transmits an initial synchronization adjustment amount of the user equipment;

(d) The user equipment adjusts and transmits the initially synchronized adjusted signal according to the received initial synchronization adjustment amount, and the signal includes initial synchronization adjustment amount information applied by the user equipment.

Step (2) includes:

(el) determining a position of a signal path corresponding to a target value of the user signal timing received at the base station;

(e2) obtaining, from the user signal, a synchronization adjustment amount applied by the user equipment, and determining an actual synchronization adjustment amount of the user equipment according to the synchronization adjustment amount sent by the base station to the user equipment;

(e3) filtering the energy of the channel impulse response of the received signal by using a filter according to the actual synchronization adjustment amount to obtain a sequence (");

(e4) Using the noise energy and the energy of the strongest path in the sequence to post-process sequence ¹ » to distinguish the noise path from the effective path, and assign the value at the non-noise path position to the resulting sequence ⁵ ^ , ") The value at the remaining positions is set to 0;

(e5) searching in the sequence for the position of the signal path corresponding to the determined target value; (e6) confirming the searched path based on the comparison result of the actual RAKE energy on the path and the energy estimated by the channel estimation result if it is confirmed that the diameter of a false path, ^a ^ ( ") value is set to false then the radial position 0, and returns to step (E5), otherwise go to step (E7);

(e7) The timing of the path is compared with the timing required by the base station. If the timing difference is greater than the preset threshold, the base station requests the user equipment to perform initial synchronization again until the timing difference is less than the preset threshold.

Step (3) includes: (g) The base station evaluates whether the user equipment needs to perform synchronization adjustment, and if necessary, performs step (h); otherwise, proceeds to step (j);

(h) the amount of synchronization signal adjustment sent by the base station to the user equipment;

(i) The user equipment adjusts and transmits the synchronously adjusted signal according to the synchronization signal adjustment amount, and the signal includes the synchronization adjustment amount information applied by the user equipment, and returns to step (2) to re-execute;

(j) the base station requires the user equipment to maintain the signal transmission timing;

(k) The user equipment sends a signal to maintain the timing, and returns to step (2) to re-execute.

The invention uses a method of adding a feedback mechanism in the uplink synchronization process so that the base station end can accurately learn the timing adjustment amount of the user equipment, thereby eliminating the estimation deviation, and reducing the cause by the shift filtering, the wave technology and the path verification technology. The probability of introducing a false path due to noise, etc., greatly improves the accuracy and stability of the uplink synchronization, thereby improving the capacity and performance of the system. BRIEF abstract

1 is a schematic diagram of a cell of a mobile communication system;

2 is a flow chart of an existing uplink synchronization implementation;

3 is a schematic diagram of an uplink synchronization process according to an embodiment of the present invention;

FIG. 4 is a schematic flowchart of a base station evaluating whether a user equipment needs to perform initial synchronization again according to an embodiment of the present invention. Best Mode for Carrying Out the Invention

In order to improve the uplink synchronization performance, considering that the user transmission timing is dynamically adjusted, the present invention uses a method of adding a feedback mechanism in the uplink synchronization process so that the base station end can accurately learn the timing adjustment amount of the user equipment, so as to eliminate the estimation. Deviation, at the same time, the technique of shift filtering and the method of path verification are proposed to reduce the probability of introducing a false path due to noise and the like.

The uplink synchronization method proposed by the present invention can be applied to TD-CDMA, TD-SCDMA and

In mobile communication systems such as WCDMA. The implementation of the present invention in TD-SCDMA will be described below with reference to the accompanying drawings, thereby illustrating the technical features and functional features of the present invention. As shown in FIG. 3, the implementation steps of the present invention in TD-SCDMA are as follows:

Step 30: The base station sends a downlink synchronization signal by using a downlink synchronization channel (DwPCH), so that the user equipment acquires downlink synchronization.

Step 31: The user equipment sends an uplink initial synchronization signal by using an uplink synchronization channel (UpPCH.) according to the downlink synchronization.

Step 32: The base station acquires and sends an initial synchronization adjustment quantity of the user equipment by using a fast physical access channel (FPACH), so that the user equipment adjusts the uplink sending timing.

Step 33: The user equipment adjusts and sends the initial peer-adjusted signal according to the received initial synchronization adjustment amount, and the signal is transmitted through a physical random access channel (PRACH) or a dedicated physical channel (DPCH) according to a specific situation. In addition, the signal may carry initial synchronization adjustment amount information applied by the user equipment.

Step 34: The base station evaluates whether the user equipment needs to perform initial synchronization again. When evaluating the transmission timing of the user equipment, the base station needs to comprehensively consider the timing adjustment amount of the user equipment required last time and the actual timing adjustment amount fed back by the user equipment, if the base station needs the user. The timing adjustment performed by the device is greater than a certain threshold, and the process proceeds to step 35, otherwise proceeds to step 36.

Step 35: The base station requests the user equipment to perform initial initial synchronization by signaling, and the signaling may be carried on the DPCH or from the common control physical channel (S-CCPCH) or the like.

Step 36: The base station evaluates whether the user equipment needs to perform synchronization adjustment. If the synchronization timing adjustment performed by the user equipment in step 34 is greater than half of the synchronization timing adjustment step, the process proceeds to step 37, otherwise the process proceeds to step 39.

Step 37: The base station sends a command for adjusting the synchronization signal of the user equipment by using a synchronization offset (SS) field on a channel such as a downlink DPCH. This process can be implemented by setting the SS field to a value recognized by both parties in advance, for example, in QPSK modulation. The use of 00 indicates that the synchronization timing is adjusted forward by one step, and the use of 11 indicates that the synchronization timing is adjusted backward by one step.

Step 38: The user equipment adjusts and sends the synchronously adjusted signal according to the command of the synchronization signal adjustment, and the signal notifies the base station of the actual synchronization adjustment amount applied by the SS field on the channel such as the uplink DPCH, and the process proceeds to step 34.

Step 39: The base station requests the user equipment to maintain the signal transmission timing, and the process can be performed by using the SS The field is set to a value that is mutually agreed in advance, such as 01 for QPSK modulation and 011 for 8PSK.

Step 40: The user equipment transmits a signal that maintains the transmission timing, and fills the corresponding value in the SS field, and the flow proceeds to step 34.

The present invention further provides a method for improving the uplink synchronization performance by using the shift filtering and the path verification technology in the step of evaluating whether the user equipment needs to perform the initial synchronization again. The specific implementation steps may be as shown in FIG. 4:

Step 341: Determine a target value of the user signal timing received at the base station end, for example, it may be set to a position where the initial path of the signal is expected to be received, and the target values are equal for all user equipments.

Step 342: Obtain the synchronization adjustment amount applied by the user equipment from the user signal, and combine the synchronization adjustment amount sent by the base station to the user equipment, so as to obtain the real synchronization adjustment condition of the user equipment. In the specific implementation, the base station side can obtain the final approved adjustment amount by using ^{5 =} 5 _{1 +} (1-3)*, where is the timing adjustment amount required by the base station to request the user equipment last time, and the actual timing adjustment amount fed back by the user equipment, ³ is the filter coefficient, and the value range is [0, 1]. The actual value can be determined according to the signal-to-noise ratio of the communication link.

Step 343: Filtering the energy of the channel impulse response of the received signal by using a filter to obtain a sequence (ie, sequence 1 in FIG. 4), and considering the true synchronization adjustment of the user equipment during filtering. Assume that the output sequence of the last filter is:

Z,(«-l) Z ₂ ("-l) Z ₃ 0_1),..., Z - 1),..., Z,{n-\) where I is the length of the filter output sequence, generally greater than or equal to The value of the channel estimation window length; n is the sequence number of the nth filtering. For the first filtering, the output of the filter can be directly set to the value associated with the channel impulse response or even the channel impulse response itself.

If the energy sequence of the input channel impulse response is defined as ("), then in the case of an alpha Alpha filter:

Z,.(«) = ?* ("-l) + (l- i = l,2,-;I where ^ is the coefficient of the Alpha filter, the range of values is [0,1], in the filtered The first few frames can also be used to change the Alpha filter coefficients to improve convergence. Then, assuming that the true synchronization adjustment amount obtained in step 342 is reflected that the output sequence of the filter is forward, the definition sequence is -^" - where 1≤ ≤/ - and when / > /-, then ¹ ) is set To disturb the power of the signal; the true synchronization adjustment obtained in step 342 is reflected when the filter output sequence is shifted back by k, then the definition is - the sequence is = where l ≤ ≤ J, and at that time, ¹ ^" — ¹ ) Set to the power of the interfering signal; assume that the true sync adjustment obtained in step 342 is 0, ie no adjustment, then define the sequence; r(" - 1) = Z(" - 1). Step 344, using the noise energy and the energy pair of the strongest path in the sequence obtained above to perform post-processing to distinguish the noise path from the effective path, which is to be compared with the interference signal to distinguish the noise path from the effective path; The value at the non-noise path position is assigned to another sequence (ie, sequence 2 in Figure 4), which is actually a sequence of results, so there is nothing special about the results needed to carry the ^. Its size is the same. »The value at the remaining positions is set to 0. In practice, the threshold can be set by the noise energy and the strongest path energy, and the position in the sequence that is smaller than this threshold is the position of the noise path.

Step 345, searching for the position i of the first path in the sequence from the smallest to the largest, for step 346 to confirm.

In step 346, the first path is confirmed by using the comparison result of the actual RAKE energy and the estimated energy on the path. Using the first-path position obtained in step 345, the instantaneous channel estimation value on the path is found, and the energy ^p » of the RAKE on the path can be calculated by using the information such as the instantaneous channel estimation value and the spreading factor, and at the same time, The actual energy (") can also be obtained by directly performing RAKE processing on the path. If w < o) (where κ is a parameter and the value interval is (0, 1)), the path is considered to be a false path. And the value of the i position is set to 0 in the sequence (step 348 in the figure), and the process proceeds to step 345, otherwise, it is confirmed that the path is the first path of the user signal, and the process proceeds to step 347.

Step 347: Comparing the timing of the first path with the timing required by the base station. If the timing adjustment required by the user equipment by the base station is greater than the threshold T, the process proceeds to step 35 in FIG. 3, and the base station requests the user equipment to perform the signaling again. Initial synchronization; otherwise, the process proceeds to step 36 in FIG. 3, and the base station evaluates whether the user equipment needs to perform synchronization adjustment; wherein the threshold Τ value interval is (-16, 16) chips.

Claims

Claim

A method for implementing uplink synchronization in a mobile communication system, comprising the steps of:

(2) The base station compares the timing of the received user signal with the timing required by the base station side. If the timing difference is greater than the preset threshold, the base station performs initial synchronization with the user equipment again until the timing difference is small.

2. The method of claim 1 wherein said step (1) comprises:

(a) the base station transmits a downlink synchronization signal;

(d) The user equipment adjusts and transmits the initially synchronized adjusted signal according to the received initial synchronization adjustment amount, where the signal contains the initial synchronization adjustment amount information applied by the user equipment.

3. The method according to claim 1, wherein the step (2) comprises:

(e3) filtering, according to the actual synchronization adjustment amount, the energy of the channel impulse response of the received signal by using a filter to obtain a sequence;

(e4) post-processing the sequence using the energy of the noise and the energy of the strongest path in the sequence to distinguish the noise path from the effective path, and assign a sequence of values (") at the non-noise path position to the resulting sequence,

The value at the remaining positions is set to _0; (e5) searching, in the sequence "), a position of a signal path corresponding to the determined target value;

(e6) confirming the searched path based on the comparison result of the actual RAKE energy on the path and the energy estimated by the channel estimation result, and if the path is confirmed to be a false path, the ^(") value at the virtual path position is determined. Set to ₀ and return to step ( _e5 ), otherwise go to step (e7); (e7) compare the timing of the path with the timing required by the base station. If the timing difference is greater than the preset threshold, the base station requests the user equipment again. The initial synchronization is performed until the timing difference is less than the preset threshold.

4. The method according to claim 1, wherein the step (3) comprises:

(g) The base station evaluates whether the user equipment needs to perform synchronization adjustment, and if necessary, performs step (h); otherwise, proceeds to step (j);

(i) the user equipment adjusts and transmits the synchronously adjusted signal according to the synchronization signal adjustment quantity, where the signal contains the synchronization adjustment amount information applied by the user equipment, and returns to step (2) to re-execute; (j) the base station requests the user equipment to maintain Signal transmission timing

5. The method of claim 3, wherein the step (el) comprises: setting a target value of the user signal timing to a position of a first path of the desired received signal.

The method according to claim 3, wherein the step (e2) comprises: determining the actual adjustment amount by using = 3* + (1 - δ)*, where the base station requests the user equipment last time. The timing adjustment amount is the actual timing adjustment amount fed back by the user equipment, which is the filter coefficient.

7. The method according to claim 6, wherein the value range of the 3 is [0, 1], and the actual value can be determined according to a signal to noise ratio of the communication link.

8. The method according to claim 3, wherein the step (e3) comprises: setting the output sequence of the last filter to be: ^Z i (" - ^Z ^ ⁿ ~ ^l) , ^Z ^ ⁿ ~ ^l ..., ^Ζ '(", ,..., ^Ζ -^) , where I is the length of the filter output sequence, and η is the sequence number of the nth filter;

If the actual synchronization adjustment determined in step (e2) is reflected to the output sequence of the filter is forward k, Bay U defines "—the sequence is a ¹ ) ^{= z} ^("—丄), where i < ≤/- fe, and when -, sets -D to the power of the interfering signal;

If the actual synchronization adjustment amount determined in the step (e2) is reflected to the output sequence of the filter being the backward shift k, then the definition sequence is ^"- ¹ "^'-^^- ¹ ), where 1≤ ≤/, and then, then Set — to the power of the interference;

If the actual synchronization adjustment determined in step (e2) is 0 _3⁄4, then the sequence ¹ D ^{= z} is defined ("- The energy sequence of the input channel impulse response is set, then in the case of the Alpha filter, there are:

Z _i {n) = * Y _i (nl) +

= 1,2,—,/ where is the coefficient of the Alpha filter.

9. The method according to claim 3, wherein the step (e4) comprises: setting a threshold by using noise energy and a strongest path energy, and confirming a position in the sequence smaller than the threshold as a noise path. position.

The method according to claim 3, wherein the step (e5) comprises: searching for the position of the signal path corresponding to the determined target value in the sequence y» according to the order of the number from small to large.

The method according to claim 3, wherein the step (e6) comprises: searching for an instantaneous channel estimation value on the path according to the signal path position found in the step (e5); Channel estimation value, calculating the energy of RAKE on the path;

The actual energy O) is obtained by directly performing RAKE processing on the path;

If 3⁄4 (") < * ), where κ is a parameter, the path is considered to be a false path, and the value of the i position is set to 0 in the sequence, and proceeds to step (e5), otherwise proceeds to step (e7).

The method of claim 11, wherein the value interval of K is (0, 1).

13. The method according to claim 1, wherein the preset threshold of step (2) is (-16, 16) chips.

figure 2

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