KR20040018873A - Hand over apparatus and method for mobile communication system - Google Patents

Abstract

PURPOSE: A handover device of a mobile communication system is provided to exactly detect and output RSCP(Received Signal Code Power) values according to channel changes, and to cope with the channel changes caused when a moving speed of a terminal changes, thereby performing an exact handover process without adding a Doppler estimator. CONSTITUTION: A multi-path searcher(10) receives signals from 2 transmission antennas, and obtains an RSCP. A DSP buffer(20) stores values produced from the multi-path searcher(10). A moving average calculator(100) obtains moving averages as many as main window sections and sub window sections at proper intervals for values outputted through the DSP buffer(20). A history buffer(200) sequentially stores values outputted from the moving average calculator(100), and finds out changing history of the moving averages. A calibrating coefficient calculator(300) obtains calibrating coefficients by using changes of history buffer values and differences between RSCP values of each window. An RSCP calculator(400) substitutes the RSCP values and the calibrating coefficients for a mathematical formula, and obtains a new RSCP.

Description

HAND OVER APPARATUS AND METHOD FOR MOBILE COMMUNICATION SYSTEM}

The present invention relates to a handover device and a method of a mobile communication system, and in particular, in response to a change in a time-changed channel occurring when a moving speed of a terminal changes, an accurate handover is performed according to a moving speed without adding a Doppler estimator. The present invention relates to a handover device and a method for a mobile communication system.

When the mobile terminal moves out of the serving cell area to another target cell, changing the call path to the moved cell in order to maintain the call is hand-off or hand over. It is called.

That is, the mobile communication terminal compares the threshold value for the pilot channel strength received from the base transceiver station (BTS) with another neighboring BTS pilot channel strength that is continuously measured, and the comparison value of these measurements is a value that requires handover. Is reported to the system, and handover is performed under the control of the corresponding system according to the type of handover.

In this case, how to set the add and drop level for handover between two base stations affects the load and call quality of the system.

More specifically, in order to determine the optimal handover time, it is very important to obtain measurement results that adequately mitigate the effects of fast fading and deep fading. The performance reduction by 'deep fading' depends on the speed, and the moving average should be determined to overcome this.

For example, if the filtering length according to the speed is set to 100 ms, it operates at the desired performance at a speed of 50 to 60 km / h, but at a slow speed of about 3 km / h, the moving average duration is short, which causes a very large measurement error. The indicating signal is frequent.

As described above, when the moving average section is set according to the speed of the predetermined section, there is a problem in that unnecessary handover occurs at a slower speed, and in order to solve this problem, the filtering period is set very long (about 1 second). In this case, it is possible to provide an accurate value, but in this case, when the vehicle passes the micro cell at high speed due to the delay of the handover, a sudden rise peak occurs at the Node-B of the target cell to be moved. Defects occur.

Therefore, in order to solve the above problems and obtain an optimal filtering effect, a Doppler estimator must be installed in the terminal to properly adjust the filtering interval according to the speed, but the addition of such additional functions is a considerable burden on the terminal modem. There is a problem that can give.

Hereinafter, a conventional method for measuring a parameter (RSCP) for handover will be described with reference to FIG. 1.

Once received, the received signal code power (RSCP) can be obtained from a multi-path searcher that receives and processes signals from two transmit antennas.

First, when a cell searcher assigns a slot sync for a detected path and an initial value of a scramble code to a reference finger, an automatic frequency controller (AFC) In operation, the slot sync value after the delay lock loop (DLL) is locked is applied to the multi-path searcher (MP Searcher) 10.

Accordingly, the multi-path searcher 10 receives a common pilot channel (CPICH) while searching for a window size determined based on the slot sync, and the received signal is orthogonally variable with the scrambling code descrambler 10a. It passes through a spreading factor (OVSF) code spreader (10b) used for channel allocation such as subscriber and synchronization signals in a wireless section.

Next, the signal of the TD (Transmit Diversity) is decoded, and a coherent sum is performed through the accumulator 10c to multiply each 'I-arm' and 'Q-arm' by a multiplier ( After squared through 10d), a non-coherent sum is performed by the accumulator 10e.

Accordingly, the final values from the multipath searcher 10 are sent to a digital signal processing processor (DSP) connected to the terminal modem, and the DSP stores these values in the internal buffer 20, and then the moving average calculation unit. 30, a moving average is taken at every appropriate period and transmitted to the base station Node-B, and the handover is determined when the number of active sets becomes two or more according to the value. do.

However, since the parameter measurement for the handover as described above, since the moving average period is the same regardless of the moving speed of the terminal, there is a problem that the reliability of the handover is inferior, in order to solve the Doppler estimator In addition, there is a problem that can put a significant burden on the terminal modem.

Accordingly, the present invention has been created to solve the above-mentioned conventional problems, and responds to a change in time change channel generated when the movement speed of the terminal changes, so that the correct hand according to the movement speed is not required without adding a Doppler estimator. It is an object of the present invention to provide a handover apparatus and method of a mobile communication system that can perform an over.

The present invention for achieving the above object is a multi-path searcher (Multi-path Searcher) for receiving a signal from two transmit antennas to obtain a received signal code power (RSCP); A DSP buffer for storing values from the multipath searcher; A moving average calculating unit which obtains a moving average for the value output through the DSP buffer by a main window and a sub window section at appropriate intervals; A history buffer configured to sequentially store the values output from the moving average calculator to determine a change history of the moving average value; A correction coefficient calculator for calculating correction coefficients 1, 2 (α, β) by using a difference (△) of the RSCP values of the respective windows and a change trend of the history buffer values; After dividing the difference (△) of the RSCP value of each window by the size ratio (N) of the main window and the sub-window ( ), Multiplied by the correction factor 1,2 * α * β) plus the previous RSCP (RSCP + * alpha * beta) It is characterized by including the RSCP calculation unit for obtaining a new RSCP.

Another object of the present invention for achieving the above object is a first step of further setting a main window (Main measurement filtering window) and a smaller sub-window (sub-window) in size; Obtaining a RSCP value from a signal received through a multi-path, and obtaining a moving average value for each window section with a predetermined period with respect to the RSCP value; And a third step of calculating correction coefficients (α, β) by referring to the change in the moving average value and the RSCP difference value (△) of each window, and calculating a new RSCP value by using the correction coefficients. do.

1 is a block diagram showing the configuration of a device for conventional handover determination.

Figure 2 is an exemplary view comparing the size of the main window and the sub-window when setting two windows in accordance with the present invention.

Figure 3 is an exemplary view for explaining a method for measuring a parameter by the difference between the two windows in accordance with the present invention.

Figure 4 is a block diagram showing the configuration of an apparatus for handover decision according to the present invention.

5 is a flowchart illustrating a process of calculating RSCP for handover according to an embodiment of the present invention.

6 is an exemplary view showing accumulated values in a history buffer of a handover device according to the present invention.

*** Description of the symbols for the main parts of the drawings ***

100: moving average calculation unit 200: history buffer

300: correction coefficient calculation unit 400: RSCP calculation unit

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In this case, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings.

In addition, many specific details are set forth in the following description in order to provide a more general understanding of the invention, and it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. . In addition, detailed description of well-known functions and structures which are determined to unnecessarily obscure the subject matter of the present invention will be omitted.

The present invention provides a function similar to that of a Doppler estimator with minimal addition of a function, and accurately detects and outputs a parameter (RSCP) value, which has a significant effect on handover performance, according to a change in channel change according to a moving speed. It is characterized by.

That is, in the conventional case, the difference in the filtering time interval is large according to the speed, and in order to overcome this, the Doppler estimator needs to change the interval of the filtering time by measuring the speed, but this method has a problem of additionally having a Doppler estimator. there was.

Accordingly, in the present invention, as shown in FIG. 2, a main window and a sub-window having smaller sizes are additionally set, and the values of the two windows are stored for a predetermined period of time. The present invention relates to a method of determining a parameter by referring to the change trend.

Referring to FIG. 3, if the main window and sub-windows about 1/4 to 1/6 of the window size are additionally set, and the values of the two windows are stored in the buffer for 1 sec intervals at intervals of 100 msec, A total of 20 values are stored, 10 each.

In this case, the moving average (MA) operation using the sub-window may operate only at the measurement reporting interval, and at each reported time interval or at a predetermined multiple thereof, the value of the main window (dBm) With reference to the comparison value (ΔdB) with respect to the value of the subwindow (dBm), it is possible to know whether or not the 'fast fading' or 'deep fading'.

In addition, the signal strength data during the 1sec period of the two previous windows can be used to determine whether the signal has been in deep fading for a long time.

This helps to set a correction value, especially in a low speed (0 to 6 Km / h) environment. When the comparison value (ΔdB) is larger than a certain value, the signal strength of the main window is corrected.

That is, the difference value of the window (average value of the main window minus the average value of the sub-window = ΔdB) for each reporting period is compared to correct the corresponding value when the difference exceeds the predetermined reference value.

3 shows the difference between the values of the two windows. Based on this value, an improved parameter (Modified RSCP) according to the present invention can be obtained by Equation 1 below.

* α * β

Δ: difference between the main window and the sub-window measurement value.

α: correction coefficient 1 (coefficient multiplied according to the magnitude of the Δ value).

β: correction factor 2 (coefficient multiplied by 1 sec history).

N: Size ratio of main window and sub window (generally 4-6).

Hereinafter, a method of measuring a parameter (RSCP) for handover of the present invention will be described with reference to FIG.

That is, the present invention provides a multi-path searcher (10) for receiving signals from two transmit antennas and obtaining a received signal code power (RSCP); A DSP buffer 20 for storing values from the multipath searcher 10; A moving average calculation unit (100) which takes a moving average for the value output through the DSP buffer (20) for each period of the main window and sub window; A history buffer 200 for sequentially storing the values output from the moving average calculator 100 to know the change history of the moving average value; A correction coefficient calculation unit (300) for obtaining correction coefficients 1, 2 (α, β) by using a difference (△) of the RSCP values of the respective windows and a change trend of the history buffer values; The RSCP calculation unit calculates a new RSCP by substituting the RSCP and the correction coefficients 1 and 2 into Equation 1, and the operation and operation effects thereof will be described as follows.

Once received, the received signal code power (RSCP) can be obtained from a multi-path searcher (Multi-path Searcher) that receives and processes signals from two base station transmit antennas.

Next, when a cell searcher assigns a slot sync for a detected path and an initial value of a scramble code to a reference finger, an automatic frequency controller (AFC) In operation, the slot sync value after the delay lock loop (DLL) is locked is applied to the multi-path searcher (MP Searcher) 10.

Accordingly, the multi-path searcher 10 receives a common pilot channel (CPICH) while searching for a window size determined based on the slot sync, and the received signal is orthogonally variable with the scrambling code descrambler 10a. It passes through a spreading factor (OVSF) code spreader (10b) used for channel assignment such as subscriber and synchronization signals in a wireless section.

Next, the signal of the TD (Transmit Diversity) is decoded, and a coherent sum is performed through the accumulator 10c to multiply each 'I-arm' and 'Q-arm' by a multiplier ( After squared through 10d), a non-coherent sum is performed by the accumulator 10e.

Accordingly, the final values from the multipath searcher 10 are sent to a digital signal processing processor (DSP) connected to the terminal modem, and the DSP stores these values in the internal buffer 20, and then the moving average calculation unit. The moving average is taken by the main window and the sub-window section at appropriate intervals by the 100.

Next, after looking at the difference (△) of the RSCP value of each window obtained above and the change trend of the history buffer 200 values, the correction coefficient 1 is multiplied according to the magnitude of the value △ through the correction coefficient calculation unit 300. The value of the coefficient α and the correction coefficient 2 (the coefficient multiplied according to 1 sec history) is determined, and the RSCP calculation unit 400 substitutes the correction coefficient into Equation 1 to obtain a 'Modified RSCP'.

Accordingly, the present invention periodically transmits a parameter value (Modified RSCP) detected by Equation 1 to the base station (Node-B), to determine the handover according to the value.

Here, the correction coefficients 1 and 2 should be obtained through simulation, which is set by looking at the magnitude of the value of △ and the change trend of the history buffer, and by applying different weights to the correction coefficients 1 and 2 to obtain more accurate values. It becomes possible.

Next, FIG. 5 is a flowchart illustrating a process of calculating an RSCP for handover according to an embodiment of the present invention, and obtaining a received signal code power (RSCP) value by signals received from two base station transmitting antennas (S101 to S103). )Wow; Obtaining a moving average value corresponding to the RSCP value by a main window and sub window intervals at appropriate intervals (S104); Obtaining correction coefficients 1, 2 (α, β) by using the change average of the moving average value and the RSCP difference value (△) of each window (S105); After dividing the RSCP difference value? Of each window by the size ratio N of the main window and the sub-window, ), Multiplied by the correction factor 1,2 * α * β) plus the previous RSCP (RSCP + * α * β) to obtain a new RSCP (S106), the operation and operation of the present invention made as described above are as follows.

First, a terminal receiving a signal from each base station transmit antenna is to measure the RSCP through the multi-path searcher, in order to achieve this, in the present invention, in addition to the single window (main window) for the conventional cell search, the sub-window is smaller than that. Further, the moving average value is obtained for the main window and the sub-window section at predetermined intervals by buffering the RSCP value of each window.

Next, with reference to the change in the RSCP difference value (△) and the moving average value of the main window and the sub-window, the coefficient (α) multiplied by the size of the RSCP difference value (△) of each window through a simulation and a predetermined period (1sec) determines the value of the coefficient β multiplied by the RSCP history value (moving average value), and divides the RSCP difference value (△) of each window by the size ratio (N) of the main window and the subwindow ( ) By adding the previous RSCP to the value multiplied by the correction factor (RSCP + * α * β) A new RSCP is calculated and periodically transmitted to the base station Node-B, and handover is determined according to the value.

For reference, FIG. 6 is an exemplary view showing accumulated values in the history buffer according to the present invention. When the average value of the values stored in the histo buffer is taken, the depth of the terminal is changed to 'deep fading' when the moving speed of the terminal is low. You can see the status of missing signals.

Therefore, the setting of the correction coefficient 2 may set the size of the correction value by dividing the case where the overall signal increases, when the signal fluctuates within a certain range, and when the overall signal decreases.

The correction coefficient 1 can be set by looking at the difference (△) of the result value of the two windows, and when the difference is more than a predetermined difference, the correction coefficient 1 is reflected.

This coefficient can also be used selectively depending on the magnitude of the difference (eg, after setting two or three values, depending on the degree of difference).

As described above, the handover apparatus and method of the mobile communication system according to the present invention accurately respond to a movement speed without adding a Doppler estimator in response to a change in time change channel occurring when the movement speed of the terminal changes. This has the effect of being able to perform.

Claims (9)

A multi-path searcher for receiving signals from two transmitting antennas and obtaining a received signal code power (RSCP); A DSP buffer for storing values from the multipath searcher; A moving average calculator configured to obtain a moving average for a value output through the DSP buffer by a main window and a sub window interval every predetermined period; A history buffer configured to sequentially store the values output from the moving average calculator to determine a change history of the moving average value; A correction coefficient calculator for calculating correction coefficients 1, 2 (α, β) by using a difference (△) of the RSCP values of the respective windows and a change trend of the history buffer values; And a RSCP calculation unit for dividing the difference (△) of the RSCP value of each window by the ratio of the size of the main window to the sub-window and then adding the previous RSCP to a value obtained by multiplying the correction coefficients 1 and 2 to obtain a new RSCP. Handover device in mobile communication system. The mobile communication system according to claim 1, wherein the correction coefficients 1 and 2 are set through simulation using a difference (△) between the RSCP values of the main window and the sub window and a change trend of the moving average value stored in the history buffer. Handover device. The method of claim 1, wherein the sub window is set to about 1/4 to 1/6 of the size of the main window, and the values of the main window and the sub window are stored in the history buffer for several seconds at intervals of several milliseconds. Handover device of a mobile communication system characterized in that. The handover apparatus of claim 1, wherein the signal strength of the main window is corrected when a comparison value between the value of the main window and the value of the sub window differs by more than a predetermined reference value. . In detecting a Received Signal Code Power (RSCP) value for performing handover according to the moving speed, A first step of additionally setting a main measurement filtering window and a sub-window having a smaller size; Obtaining a RSCP value from a signal received through a multi-path, and obtaining a moving average value for each window section with a predetermined period with respect to the RSCP value; And a third step of calculating correction coefficients (α, β) by referring to the change in the moving average value and the RSCP difference value (△) of each window, and calculating a new RSCP value by using the correction coefficients. Handover method of a mobile communication system. The method of claim 5, wherein the new RSCP calculation process by the correction coefficient, After dividing the RSCP difference value? Of each window by the size ratio N of the main window and the sub-window, ), Multiplied by the correction coefficients (α, β) ( * α * β) plus the previous RSCP (RSCP + * α * β) handover method of a mobile communication system, characterized in that it is configured to calculate. 6. The handover method of claim 5, wherein the correction coefficient is set through a simulation using a change trend of the RSCP difference (△) and the moving average value of the main window and the sub-window. 6. The handover method of claim 5, wherein the sub window is set to about 1/4 to 1/6 of the main window size. The method of claim 5, wherein the moving average value is measured by a value accumulated for several seconds at intervals of several milliseconds.