JP2005252446A - Cell selection method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To select a communication cell optimum to a modulation-demodulation system of a communication channel under a multi-path environment. <P>SOLUTION: The cell selection apparatus includes: a delay profile generating section 101 for generating a delay profile; a reception level measurement section 102 for measuring a reception level from the delay profile; a reception level table 103 for storing the measured reception level; a multi-path information measurement section 104 for measuring multi-path information from the delay profile; a multi-path information table 105 for storing the measured multi-path information; a reception level correction section 106 for carrying out correction of changing a value of the measured reception level into a different value in accordance with the measured multi-path information measured by the modulation-demodulation system of the communication channel; and a cell selection section 107 for selecting a cell actually communicated depending on the reception level of all the cells after the correction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cell selection method and apparatus used in a mobile station in a code division multiple access (CDMA) type mobile communication system using spread spectrum codes.

  In a CDMA mobile communication system using a spread spectrum code, a wide service area is composed of a plurality of cells having a relatively narrow range, and one base station is provided in each cell. The mobile station moves in this wide service area while communicating with the base station. That is, as the mobile station moves, the optimal base station for communication changes from moment to moment. Therefore, the mobile station needs to perform so-called cell selection (cell determination) for appropriately selecting a base station optimal for communication.

  Therefore, conventionally, a mobile station receives a perch channel that is always transmitted by the base station of each cell and performs cell selection (for example, Patent Document 1). FIG. 3 is a block diagram showing a configuration example of a conventional cell selection device. Hereinafter, a conventional cell selection method will be described with reference to FIG.

  In FIG. 3, the conventional cell selection device includes a delay profile generation unit 301 to which a reception signal is input, a reception level measurement unit 302 that receives an output of the delay profile generation unit 301, and a reception that receives an output of the reception level measurement unit 302. The level table 303 includes a cell selection unit 304 that receives the output of the reception level table 303 and outputs a selected cell.

  The delay profile generation unit 301 receives the received signal and generates a delay profile for the perch channel for each cell to be measured. FIG. 2 is a diagram illustrating an example of a delay profile. FIG. 2A shows a case where the delay profile in the cell A is obtained as a single-path delay profile having only one path A-1. FIG. 2B shows a case where the delay profile in the cell B is obtained as a multipath delay profile of the path B-1 and the path B-2. The reception levels are path A-1> path B-1> path B-2.

  The reception level measurement unit 302 measures the reception level from the delay profile generated by the delay profile generation unit 301. In the reception level measuring unit 302, when there are a plurality of paths in consideration of the RAKE reception gain that is a feature of the CDMA system, the reception level measurement unit 302 measures the combination of the reception levels for each path. For example, in the case of the delay profile of cell B shown in FIG. 2B, the reception level of cell B is the sum of the reception levels of path B-1 and path B-2.

  The reception level table 303 manages the reception level for each cell by holding the result measured by the reception level measuring unit 302. At this time, in order to reduce the influence of a rapid environmental change such as fading and shadowing, the reception level is generally averaged using an IIR filter or the like.

The cell selection unit 304 reads the measurement results of all the cells from the reception level table 303, and selects a cell with a high reception level as a preferable cell for communication. For example, in FIG. 2 (a) and FIG. 2 (b), the reception level of the cell B held in the reception level table 303 is a combination of the path B-1 and the path B-2, Since it is higher than the reception level, the cell selection unit 304 selects the cell B.
Japanese Patent No. 2939117

  However, in a mobile communication system that uses different modulation / demodulation schemes depending on the channel to be communicated, the degree of influence on reception performance due to multipath interference may differ depending on the modulation / demodulation scheme. There is a problem that it is not an optimal cell selection method.

  That is, in the example shown in FIG. 2, as described above, the reception level for each cell is larger than that of the cell A by the cell B combining the two paths B-1 and B-2. Therefore, cell B is selected. However, when the modulation / demodulation method differs depending on the channel to be communicated, when the modulation / demodulation method is the method X, the reception performance is better in the cell B than in the cell A. There are cases where cell A is better than B.

  The present invention has been made in view of this point, and an object of the present invention is to provide a cell selection method and apparatus capable of selecting a communication cell optimal for a modulation / demodulation method of a channel for communication.

  In order to solve such a problem, the cell selection method of the present invention sequentially receives perch channels of cell candidates to be communicated to create a delay profile, and receives the perch channel reception level and multipath information from the delay profile. Measured for each cell, performs correction to change the measured reception level value to a different value according to the modulation / demodulation method of the channel for communication and measured multipath information, and communicates cells with higher reception level after the correction It was made to select as a cell.

  According to this method, the mobile station changes the reception level, which is an index to be selected, to a different value according to the modulation / demodulation method of the channel to be communicated and the measured multipath information. A cell can be selected. As a result, the mobile station can perform communication with good reception performance.

  In the cell selection method of the present invention, in the above-described invention, in the measurement of the multipath information, the number of multipaths measured in the past of the same base station is averaged.

  According to this method, correction for cell selection that does not react sensitively to environmental changes such as fading and shadowing can be performed, so that cell selection capable of stable communication can be realized as a whole.

  In the cell selection method of the present invention, in the above-described invention, in the correction of the measured reception level, the reception level is multiplied by a constant corresponding to the modulation / demodulation method of the channel to be communicated and the measured number of multipaths.

  According to this method, in a system in which a modulation / demodulation method that is easily affected by the number of multipaths and a modulation / demodulation method that is difficult to be affected are mixed, the correction constant is small in the former modulation / demodulation method, and the correction is reduced in the latter modulation / demodulation method. By increasing the constant for this, the optimum cell selection can be performed according to the modulation / demodulation method.

  The cell selection device according to the present invention sequentially receives the perch channels of cell candidates to be communicated to create a delay profile, and receives the perch channel reception level and multipath information from the created delay profile. A means for measuring each time, a means for correcting the value of the measured reception level to a different value according to the modulation / demodulation method of the channel for communication and the measured multipath information, and the reception level after the correction is larger And a means for selecting a cell as a communication cell.

  According to this configuration, the mobile station changes the reception level, which is an index to be selected, to a different value according to the modulation / demodulation method of the channel to be communicated and the measured multipath information. A cell can be selected. As a result, the mobile station can perform communication with good reception performance.

  According to the present invention, in a CDMA mobile communication system using a plurality of modulation / demodulation schemes having different influences on reception performance due to multipath interference, a mobile station can select a communication cell optimal for the modulation / demodulation scheme of a channel to be communicated. Therefore, communication with good reception performance can be made possible.

  The essence of the present invention is based on a measured number of paths per cell and a modulation / demodulation scheme of a channel to be communicated in a CDMA mobile communication system using a plurality of modulation / demodulation schemes having different degrees of influence on reception performance due to multipath interference. Then, a correction is made to the measured reception level for each cell so that a communication cell optimum for the modulation / demodulation method of the channel to be communicated can be selected.

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

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a cell selection device according to an embodiment of the present invention. 1 includes a delay profile generation unit 101 to which a reception signal is input, a reception level measurement unit 102 that receives an output of the delay profile generation unit 101, and a reception level table that receives an output of the reception level measurement unit 102. 103, the multipath information measurement unit 104 that receives the output of the delay profile generation unit 101, the multipath information table 105 that receives the output of the multipath information measurement unit 104, and the outputs of the reception level table 103 and the multipath information table 105 And a reception level correction unit 106 to which a demodulation method discrimination signal is input from the outside, and a cell selection unit 107 that receives the output of the reception level correction unit 106 and outputs a selected cell.

  Next, the operation of the cell selection device configured as described above will be described. In this cell selection device, the reception level and the number of paths of all cells are periodically measured, and the measured reception level for each cell is determined based on the measured reception level and number of paths for each cell and the modulation / demodulation method of the communication channel. A first operation for applying correction and a second operation for selecting a communication cell having a reception level optimal for the modulation / demodulation method of the channel to be communicated from the corrected reception levels when actually switching cells. . The first operation is realized by the delay profile generation unit 101 to the reception level correction unit 106, and the second operation is realized by the cell selection unit 107.

  That is, the delay profile generation unit 101 receives a received signal and generates a delay profile for the perch channel for each cell to be measured. FIG. 2 is a diagram illustrating an example of a delay profile. FIG. 2A shows a case where the delay profile in the cell A is obtained as a single-path delay profile having only one path A-1. FIG. 2B shows a case where the delay profile in the cell B is obtained as a multipath delay profile of the path B-1 and the path B-2. The reception levels are path A-1> path B-1> path B-2.

  The reception level measurement unit 102 measures the reception level from the delay profile generated by the delay profile generation unit 101. In the reception level measuring unit 102, when there are a plurality of paths in consideration of the RAKE reception gain that is a feature of the CDMA system, the reception level measurement unit 102 measures the combination of the reception levels for each path. For example, in the case of the delay profile of cell B shown in FIG. 2B, the reception level of cell B is the sum of the reception levels of path B-1 and path B-2.

  The reception level table 103 receives the reception level measured by the reception level measuring unit 102, and when there is a past measurement result, performs an averaging process and holds it. On the other hand, when there is no past measurement result, that is, in the case of a cell to be measured for the first time, the reception level is held as it is. The reception level table 103 sequentially outputs reception levels of necessary cells to the reception level correction unit 106 in response to a request from the reception level correction unit 106.

  The multipath information measurement unit 104 detects a path from the delay profile generated by the delay profile generation unit 101 and outputs the path to the multipath information table 105.

  The multipath information table 105 receives the number of paths measured by the multipath information measurement unit 104, and when there is a past measurement result, performs an averaging process and holds it. On the other hand, when there is no past measurement result, that is, in the case of a cell to be measured for the first time, the number of paths is held as it is. The multipath information table 105 sequentially outputs the required number of cell paths to the reception level correction unit 106 in response to a request from the reception level correction unit 106.

  The reception level correction unit 106 calculates a corrected reception level based on the reception level and the number of paths received from the reception level table 103 and the multipath information table 105, respectively, and the modulation / demodulation method discrimination signal input from the outside.

  Here, the modulation / demodulation method discrimination signal input from the outside will be described prior to the description of the operation of calculating the corrected reception level in the reception level correction unit 106. The degree of influence of the multipath environment on the reception performance is such that if only one-path reception is considered, the reception performance deteriorates significantly as the number of paths increases. This is because channels for other mobile stations and perch channels are orthogonal, but multipath components are not orthogonal, so the larger the number of multipaths for the mobile station, the greater the interference component. .

  There are various modulation / demodulation methods, but when the degree of influence of the multipath environment on the reception performance is compared between, for example, a quaternary QPSK method and a 16-value QAM method, even if the number of multipaths increases in the QPSK method. Although the influence of reception performance due to interference is relatively small, the influence of reception performance due to interference is larger in the QAM system than in the QPSK system. Therefore, the modulation / demodulation method discrimination signal input from the outside to the reception level correction unit 106 is assumed here to be a signal that specifies a QPSK method that has a small influence on reception performance in a multipath environment and a 16QAM method that has a large influence. Yes.

  The reception level correction unit 106 also includes a correction constant table TBL_QPSK [] for QPSK and a correction constant table TBL_16QAM [] for 16QAM, and correction constants used for correction in accordance with instructions from a modulation / demodulation method discrimination signal input from the outside. The table is switched and used.

  Here, in the correction constant table TBL_QPSK [] for QPSK and the correction constant table TBL_16QAM [] for 16QAM, if the number of paths is the same, the susceptible 16QAM is smaller than QPSK, that is, after correction. The reception level is a smaller value. The larger the number of paths, the smaller the value. Since the mounting characteristics regarding the reception performance of each mobile station are different for each mobile station, the contents of this table are different for each mobile station.

The reception level correction unit 106 determines the reception level and the number of paths received from the reception level table 103 and the multipath information table 105, and the modulation / demodulation method specified by the modulation / demodulation method determination signal input from the outside. Applying the equation (1), the operation of calculating the corrected reception level in each cell is performed.
VAL = VAL_REAL
× TBL [INT [AVE_PATH * STEP]] (1)

  In equation (1), VAL is the corrected reception level. VAL_REAL is a reception level before correction. TBL [] is the correction constant table TBL_QPSK [] or the correction constant table TBL_16QAM []. INT [] means truncation to an integer and is the same as the C language int function. AVE_PATH is the number of paths averaged and includes a decimal point. STEP is the resolution of the correction constant table based on the average number of passes. If the resolution is 10, one correction constant table is prepared for every 1/10 of the average number of passes.

  The cell selection unit 107 sequentially receives the corrected reception levels of all the cells from the reception level correction unit 106, and selects a cell having a large value from the corrected reception levels. It is possible to output a cell from which a high reception level is obtained as a selected cell. This will be specifically described with reference to FIG.

  As shown in FIG. 2A, cell A is received in a single path state, and as shown in FIG. 2B, cell B is received in a multipath number of two. In terms of path units, the reception levels are path A-1> path B-1> path B-2. The reception level for each cell is larger than that of the cell A by combining the two paths B-1 and B-2 with the reception level before correction.

  When the modulation / demodulation method is the QPSK method, since there is also a RAKE combining gain, the reception performance of the cell B where the multipath exists is better than the cell A of the single path. However, when the modulation / demodulation method is the 16QAM method, the reception performance of the cell A is better than that of the cell B.

  Therefore, in the present embodiment, the content of correction applied to the measured reception level is changed by the reception level correction unit 106 for each modulation / demodulation method / number of reception paths. That is, in the above example, when the modulation / demodulation method is the QPSK method, the reception level of the cell B is increased, and when the modulation / demodulation method is the 16QAM method, the reception level of the cell A is increased.

  As a result, the cell selection unit 107 selects a reception level having a large value from the reception levels corrected in this way. Therefore, when the modulation / demodulation method used in the communication channel is the QPSK method, the cell selection unit 107 selects cell B. In other words, when the 16QAM system is used, the cell A is selected.

  As described above, according to this embodiment, the correction content of the reception level is changed for each modulation / demodulation method / number of reception paths, and the influence of reception on the reception performance due to multipath interference is selected for the optimum cell selection for communication. In consideration of this, in a CDMA mobile communication system using a plurality of modulation / demodulation schemes having different degrees of influence on reception performance due to multipath interference, it is possible to select an optimum cell for the modulation / demodulation scheme of a channel to be communicated. The reception performance can be improved.

  Specifically, in the correction of the measured reception level, the modulation level of the channel to be communicated and the constant corresponding to the measured number of multipaths are multiplied by the received level, so that the modulation / demodulation system is easily influenced by the number of multipaths. In a system with a combination of modulation and demodulation systems that are difficult to receive, in the former modulation / demodulation system, the correction constant is small, and in the latter modulation / demodulation system, the correction constant is large, so that the optimal cell is selected according to the modulation / demodulation system. You will be able to choose.

  In the measurement of multipath information, the number of multipaths measured in the past by the same base station is averaged, so correction for cell selection that does not react sensitively to environmental changes such as fading and shadowing can be performed. Overall, cell selection capable of stable communication can be realized.

  INDUSTRIAL APPLICABILITY The present invention is suitable for selecting a communication cell optimal for a modulation / demodulation method of a channel to be communicated in a CDMA mobile communication system using a plurality of modulation / demodulation methods having different degrees of influence on reception performance due to multipath interference. . Therefore, it is useful as a cell selection method and apparatus in a mobile station that implements the HSDPA (High Speed Down Link Packet Access) method, which is a high-speed packet communication standardized by 3GPP.

The block diagram which shows the structure of the cell selection apparatus which concerns on one embodiment of this invention Diagram showing an example of a delay profile The block diagram which shows the structural example of the conventional cell selection apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Delay profile production | generation part 102 Reception level measurement part 103 Reception level table 104 Multipath information measurement part 105 Multipath information table 106 Reception level correction | amendment part 107 Cell selection part

Claims (4)

  A delay profile is generated by sequentially receiving perch channels of cell candidates to be communicated, and the reception level and multipath information of the perch channel are measured for each cell from the delay profile, and the measured reception level value is communicated. A cell selection method comprising: performing correction for changing to a different value according to a channel modulation / demodulation method and measured multipath information, and selecting a cell having a higher reception level after the correction as a communication cell.   The cell selection method according to claim 1, wherein the multipath information is measured by averaging the number of multipaths measured in the past by the same base station.   2. The cell selection method according to claim 1, wherein in the correction of the measured reception level, the reception level is multiplied by a constant according to a modulation / demodulation method of a channel to be communicated and the measured number of multipaths.   Means for sequentially receiving perch channels of cell candidates to be communicated to create a delay profile, means for measuring the reception level and multipath information of the perch channel from the created delay profile for each cell, and measurement Means for changing the received level value to a different value depending on the modulation / demodulation method of the channel for communication and the measured multipath information, and means for selecting a cell having a higher received level after the correction as a communication cell And a cell selection device.

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