WO2008153359A2

WO2008153359A2 - Power allocation method and mobile communication system using the same

Info

Publication number: WO2008153359A2
Application number: PCT/KR2008/003357
Authority: WO
Inventors: Dong-Soo Choo
Original assignee: KTFreetel Co Ltd
Current assignee: KTFreetel Co Ltd
Priority date: 2007-06-13
Filing date: 2008-06-13
Publication date: 2008-12-18
Anticipated expiration: 2009-12-13
Also published as: WO2008153359A3

Abstract

Provided are a power allocation method and a mobile communication system using the same. The power allocation method includes: measuring a load factor of a cell; and allocating power to a high-speed downlink packet access (HSDPA) channel of the cell by using a power value which is provided by any one of a base station and a radio network controller based on the measured load factor.

Description

POWER ALLOCATION METHOD AND MOBILE COMMUNICATION SYSTEM USING THE SAME

Technical Field

[1] The present invention relates to mobile communication, and more particularly, a power allocation method for high-speed downlink packet access (HSDPA) and a mobile communication system using the power allocation method. Background Art

[2] A high-speed downlink packet access (HSDPA) standard, which offers a data transmission rate of up to 10 Mbps, is currently being developed to provide HSDPA service in a mobile communication environment. The HSDPA service uses the same frequency band as Release 99 and Release 4 of a third generation partnership project (3GPP). However, the HSDPA service uses a different channel from Release 99 and Release 4 of the 3GPP to perform high-speed packet data transmissions without affecting an existing system.

[3] In order to increase the transmission speed of the HSDPA service, high power must be allocated to a channel used for the HSDPA service. However, if high power is allocated to the channel, there may occur interference between adjacent cells. In addition, since there is a limit to power that can be allocated by a base station, if high power is allocated to the channel used for the HSDPA service, interference may occur between the channel and other channels within the same cell. Besides, the problem of power distribution may arise. In this regard, power allocation technology for the channel used for the HSDPA service is required. Disclosure of Invention

[4] Aspects of the present invention provide a power allocation method and a mobile communication system using the same, in which any one of a base station and a radio network controller is dynamically determined as a power value controller according to a traffic channel occupancy rate of a cell and determines a power value that is to be allocated to a channel used for high-speed downlink packet access (HSDPA) service.

[5] Aspects of the present invention also provide a power allocation method and a mobile communication system using the same, in which any one of a base station and a radio network controller is dynamically determined as a power value controller according to an orthogonal variable spreading factor (OVSF) code occupancy rate of a cell and determines a power value that is to be allocated to a channel used for HSDPA service.

[6] However, aspects of the present invention are not restricted to the one set forth herein. The above and other aspects of the present invention will become more apparent to one of ordinary skill in the art to which the present invention pertains by referencing the detailed description of the present invention given below.

[7] According to an aspect of the present invention, there is provided a power allocation method including: measuring a load factor of a cell; and allocating power to an HSDPA channel of the cell by using a power value which is provided by any one of a base station and a radio network controller based on the measured load factor.

[8] According to another aspect of the present invention, there is provided a mobile communication system including: a radio network controller which determines a power value controller for an HSDPA channel of a cell based on a load factor of the cell; and a base station which allocates power to the HSDPA channel of the cell according to a power value provided by the power value controller which was determined by the radio network controller.

[9] Advantages and features of the present invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of exemplary embodiments and the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the present invention will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification.

[10] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings.

[11] FIG. 1 illustrates a mobile communication system 100 according to an exemplary embodiment of the present invention. The mobile communication system 100 may include a radio access network (RAN) 10 and a core network 20. In the mobile communication system 100, a terminal 130 may be connected to the core network 20 by the RAN 10. That is, the terminal 130 is a communication device that can perform radio communications by using the mobile communication system 100. An example of the terminal 130 is a mobile phone. However, since the development of digital technology has blurred the boundaries between digital devices, examples of the terminal 130 are not limited to mobile phones. Therefore, the terminal 130 can be implemented as various types of handheld digital devices such as personal digital assistants (PDAs) and notebook computers.

[12] The RAN 10 may include first through third base stations 110-1 through 110-3 and a radio network controller 120. Each of the first through third base stations 110-1 through 110-3 may serve as a contact point between the RAN 10 and the terminal 130. The radio network controller 120 manages and controls the first through third base stations 110-1 through 110-3 which are connected thereto. In FIG. 1, three base stations, i.e., the first through third base stations 110-1 through 110-3, are connected to the radio network controller 120, which is, however, a mere example. The present invention is not limited by the number of base stations connected to the radio network controller 120.

[13] The RAN 10 may cover a geographical region which can be divided into a plurality of cells, each cell being a radio communication area that can be supported by a corresponding one of the first through third base stations 110-1 through 110-3. An example of the RAN 10 may be a universal mobile telecommunications terrestrial radio access network (UTRAN). The UTRAN may be based on wideband code division multiple access (W-CDMA).

[14] The RAN 10 may support a circuit- switching service and a packet-switching service.

Specifically, when the RAN 10 supports the circuit- switching service, the radio network controller 120 may be connected to a public switched telephone network (PSTN) and an integrated services digital network (ISDN) by a mobile switching center (MSC) 22. On the other hand, when the RAN 10 supports the packet-switching service, the radio network controller 120 may be connected to a packet-switched network (such as Internet or an X-25 external network) by a serving general packet radio service support node (SGSN) 24 and a gateway general packet radio service support node (GGSN) (not shown).

[15] In an embodiment of the present invention, the mobile communication system 100 may support high-speed downlink packet access (HSDPA). To this end, an HSDPA channel may be used between each of the first through third base stations 110-1 through 110-3 and the terminal 130. Examples of the HSDPA channel according to the present invention may include a high-speed dedicated physical control channel (HS-DPCCH), a high-speed physical downlink shared channel (HS-PDSCH), and a high-speed shared control channel (HS-SCCH).

[16] Specifically, the HS-DPCCH is an uplink channel that is used by the terminal 130 to transmit feedback information to each of the first through third base stations 110-1 through 110-3. The feedback information may include modulation information and coding information which are suitable for channel conditions between the terminal 130 and each of the first through third base stations 110-1 through 110-3. In addition, the feedback information may include information (acknowledgement (ACK) and non- acknowledgement (NACK)) indicating whether packet data sent by each of the first through third base stations 110-1 through 110-3 has been successfully received. The HS-PDSCH is a downlink channel that is used by each of the first through third base stations 110-1 through 110-3 to transmit packet data to the terminal 130 at high speed. The HS-SCCH is a downlink channel that is used by each of the first through third base stations 110-1 through 110-3 to transmit control information to the terminal 130. In this case, the control information may include control information, which is needed by the terminal 130 to receive packet data through the HS-PDSCH, and control information for other purposes.

[17] The mobile communication system 100 may control a power value that is to be allocated to the HSDPA channel of each cell. According to an embodiment of the present invention, a power value that is to be allocated to the HSDPA channel may be controlled by each of the first through third base stations 110-1 through 110-3 or the radio network controller 120. Which of the first through third base stations 110-1 through 110-3 and the radio network controller 120 will function as a power value controller (which determines a power value to be allocated to the HSDPA channel) may be dynamically determined by a load factor of each cell (hereinafter, referred to as a "cell load factor").

[18] In the present invention, a cell load factor includes at least one of a traffic channel occupancy rate and an orthogonal variable spreading factor (OVSF) code occupancy rate. The traffic channel occupancy rate may denote the proportion of a power value allocated to channels (e.g., channels used for voice communication service or video communication service based on Release 99 of a third generation partnership project (3GPP)), which exclude the HSDPA channel from among a plurality of channels used in each cell, in a maximum power value that can be supported by each of the first through third base stations 110-1 through 110-3.

[19] The process of determining a power value controller based on a traffic channel occupancy rate and the process of determining a power value that is to be allocated to the HSDPA channel are as follows.

[20] In order to determine a power value controller for the HSDPA channel, each of the first through third base stations 110-1 through 110-3 may measure a traffic channel occupancy rate in a cell under its control and provide the measured traffic channel occupancy rate to the radio network controller 120, which will now be described in detail with reference to FIG. 2.

[21] FIG. 2 is a flowchart illustrating the process of setting up an HSDPA call according to an exemplary embodiment of the present invention. In FIG. 2, a base station 110 can be any one of the first through third base stations 110-1 through 110-3 illustrated in FIG. 1. In the present and subsequent embodiments, reference numeral "110" will be used to indicate a base station in general.

[22] The terminal 130, which has obtained necessary system information in a cell selection process, may make a connection request to a radio network controller 120 via the base station 110 (operations S205 and S210). To this end, the terminal 130 may use a Radio Resource Control (RRC) Connection Request message.

[23] When receiving the connection request from the terminal 130, the radio network controller 120 may determine whether to allow access of the terminal 130. If the radio network controller 120 determines to allow access of the terminal 130, it may notify the terminal 130 via the base station 110 that it will allow access of the terminal 130 (operations S215 and S220). To this end, the radio network controller 130 may use an RRC Connection Setup message.

[24] After allowed to access the radio network controller 120, the terminal 130 may notify the radio network controller 120 via the base station 120 that it has accessed the radio network controller 120 (operations S225 and S230). To this end, the terminal 130 may use an RRC Connection Setup Complete message.

[25] Then, the terminal 130 may request the radio network controller 120 via the base station 110 to set up an HSDPA call (Operations S235 and S240). To this end, the terminal 130 may use an Initial Direct Transfer message.

[26] When requested by the terminal 130 to set up the HSDPA call, the radio network controller 120 may request the core network 20 to set up the HSDPA call (operation S245). Then, the core network 20 may transmit a Radio Access Bearer (RAB) Assignment Request message to the radio network controller 120 in order to request the radio network controller 120 to form a radio bearer with the terminal 130 (operation S250).

[27] Accordingly, the radio network controller 120 may transmit a Radio Link Setup

Request message to the base station 110 in order to instruct the base station 110 to set up a radio link (operation S255). Thus, the base station 110 may set up the radio link and transmit a Radio Setup Response message to the radio network controller 120 in order to notify the radio network controller 120 that the radio link has been set up (operation S260).

[28] The radio network controller 120 may transmit a Radio Bearer Setup message to the terminal 130 via the base station 110 in order to instruct the terminal 130 to set up a radio bearer (operations S265 and 270).

[29] Accordingly, the terminal 130 may set up the radio bearer and transmit a Radio

Bearer Setup Complete message to the radio network controller 120 via the base station 110 in order to notify the radio network controller 120 that the radio bearer has been set up (operations 275 and S280).

[30] Next, the radio network controller 120 may transmit an RAB Assignment Response message to the core network 20 in order to notify the core network 20 that the terminal 130 has formed the radio bearer (operation 285).

[31] Then, the base station 110 may measure a traffic channel occupancy rate in a cell under its control (operation S290) and transmit the measured traffic channel occupancy rate to the radio network controller 120 (operation S295).

[32] As described above, the traffic channel occupancy rate may denote the proportion of a power value allocated to all channels, which excludes the HSDPA channel, in a maximum power value that can be supported by the base station 110. Operations S290 and S295 in which the base station 110 measures the traffic channel occupancy rate and transmits the measured traffic channel occupancy rate to the radio network controller 120 may be periodically performed while the HSDPA call is maintained. However, there can be an embodiment in which operations S290 and S295 are periodically performed even after the HSDPA call is terminated. The cycle at which the traffic channel occupancy rate is measured may vary according to embodiments.

[33] Operations S290 and S295 of FIG. 2 may not necessarily be performed whenever a new terminal sets up an HSDPA call. If there are one or more terminals that have already set up an HSDPA call in a cell under the control of the base station 110, operations S290 and S295 may be continuously performed due to the presence of the terminals and regardless of the HSDPA call setup of a new terminal.

[34] In an embodiment of the present invention, the base station 110 may perform operations S290 and S295 even when there are no terminals that have formed an HSDPA call.

[35] When an HSDPA session is formed after the process of FIG. 2, the radio network controller 120 may transmit packet data received from the core network 20 to the base station 110, and the base station 110 may transmit the packet data to the terminal 130 using the HSDPA channel.

[36] The radio network controller 120, which receives the measured traffic channel occupancy rate from the base station 110, may determine a power value controller for the HSDPA channel in the cell under the control of the base station 110 based on the received traffic channel occupancy rate.

[37] FIG. 3 is a flowchart illustrating the process of determining a power value controller for an HSDPA channel according to an exemplary embodiment of the present invention.

[38] Referring to FIG. 3, when receiving a traffic channel occupancy rate from the base station 110 (operation S310), the radio network controller 120 may determine whether the received traffic channel occupancy rate is greater than a preset threshold value (operation S320).

[39] If determining that the traffic channel occupancy rate is greater than the preset threshold value, the radio network controller 120 may determine itself to be a power value controller for an HSDPA channel in a cell under the control of the base station 110 (operation S330).

[40] However, if determining in operation S320 that the traffic channel occupancy rate is not greater than the preset threshold value, the radio network controller 120 may determine the base station 110 to the power value controller for the HSDPA channel in the cell under the control of the base station 110 (operation S340).

[41] After the power value controller is determined, the radio network controller 120 may transmit information about the determined power value controller to the base station 110 (operation S350).

[42] The operations in FIG. 3 may be repeated. When the operations in FIG. 3 are repeated, operation S350 may be omitted if a newly determined power value controller is identical to a previously determined power value controller. For example, while the base station 110 is functioning as a power value controller, if the base station 110 is determined to be the power value controller again in operation S340, operation S350 may be omitted. However, if the radio network controller 120 is determined to be the power value controller in operation S330, operation S350 may be performed.

[43] In the exemplary embodiment of FIG. 3, the radio network controller 120 determines a power value controller for a specific cell based on a traffic channel occupancy rate of the specific cell. In this case, the radio network controller 120 may independently determine a power value controller for a cell under the control of each base station connected thereto.

[44] However, the present invention is not limited to the exemplary embodiment of FIG.

3. According to an embodiment of the present invention, the radio network controller 120 may determine a power value controller for an HSDPA channel in each cell under the control of a corresponding one of a plurality of base stations by comprehensively considering traffic channel occupancy rates received from the base stations.

[45] For example, in the mobile communication system 100 of FIG. 1, if a first traffic channel occupancy rate received from the first base station 110-1 is not greater than a first threshold value, the radio network controller 120 may determine the first base station 110-1 to be a power value controller for the HSDPA channel in a first cell under the control of the first base station 110-1. If the first traffic channel occupancy rate is greater than a second threshold value (which is greater than the first threshold value), the radio network controller 120 may determine itself to be the power value controller for the HSDPA channel in the first cell.

[46] However, if the first traffic channel occupancy rate is greater than the first threshold value but less than the second threshold value, the radio network controller 120 may determine the power value controller for the HSDPA channel in the first cell based on a second traffic channel occupancy rate received from the second base station 110-2 which controls a second cell adjacent to the first cell. If the second traffic channel occupancy rate is greater than the second threshold value or is not reported, the radio network controller 120 may determine itself to be the power value controller for the HSDPA channel in the first cell. However, if the second traffic channel occupancy rate is not greater than the second threshold value, the radio network controller 120 may determine the first base station 110-1 to be the power value controller for the HSDPA channel in the first cell.

[47] While the radio network controller 120 was determined to be the power value controller for the HSDPA channel in the first cell because the first traffic channel occupancy rate is greater than the first threshold value, if the first traffic channel occupancy rate becomes closer to the first threshold value, the radio network controller 120 may increase a power value without considering the conditions of the adjacent cell (i.e., the second cell). Consequently, the possibility of interference between the first and second cells can be reduced.

[48] A case where a power value controller is separately determined for the HSDPA channel of each cell has been described above. However, the present invention is not limited thereto. According to an embodiment of the present invention, the radio network controller 120 may simultaneously determine power value controllers for the respective HSDPA channels of all cells. For example, if the sum of respective traffic channel occupancy rates of a plurality of cells in the RAN 10 is less than a preset threshold value or if a ratio of the number of cells, whose respective traffic channel occupancy rates are less than a preset threshold value, to the total number of cells is equal to or greater than a predetermined ratio, the radio network controller 120 may simultaneously determine the first through third base stations 110-1 through 110-3 to be the power value controllers for the HSDPA channels in all cells within the RAN 10, respectively. On the contrary, if the sum of the respective traffic channel occupancy rates of the cells in the RAN 10 is equal to or greater than the preset threshold value or if the ratio of the number of cells, whose respective traffic channel occupancy rates are less than the preset threshold value, to the total number of cells is less than the predetermined ratio, the radio network controller 120 may determine itself to be the power value controller for the HSDPA channel of each cell.

[49] Various other embodiments, in which a power value controller for an HSDPA channel is dynamically determined based on a traffic channel occupancy rate of each cell, may be implemented and construed as being within the scope of the present invention.

[50] Once a power value controller is determined, the process of allocating power to an

HSDPA channel may be performed. Specifically, if the radio network controller 120 is determined to be the power value controller, the base station 110 may allocate power to the HSDPA channel based on a power value determined by the radio network controller 120. That is, the base station 110 may allocate power to the HSDPA channel within the range that does not exceed the power value determined by the radio network controller 120. Thus, a maximum power value that can be supported by the base station 110 may be changed to the power value determined by the radio network controller 120.

[51] If the base station 110 is determined to be the power value controller, it may determine a power value to be allocated to the HSDPA channel. Specifically, the base station 110 may allocate a maximum power value, which has been assigned thereto, to the HSDPA channel. Alternatively, the base station 110 may adjust a power value with reference to the measured traffic channel occupancy rate and allocate the adjusted power value to the HSDPA channel. Here, the maximum power value assigned to the base station 110 may be a value preset by a mobile communication system administrator.

[52] FIG. 4 is a flowchart illustrating a power allocation process according to an exemplary embodiment of the present invention. In the present embodiment, it is assumed that the base station 110 is a power value controller.

[53] The radio network controller 120 may transmit information about the power value controller to the base station 110 (operation S410). Then, the base station 110 may learn from the information that it has to determine a power value.

[54] The base station 110 may measure a traffic channel occupancy rate in a cell at preset intervals (operation S420). In addition, the base station 110 may determine the power value that is to be allocated to an HSDPA channel based on the measured traffic channel occupancy rate (operation S430).

[55] Then, the base station 110 may allocate power to the HSDPA channel based on the power value determined in operation S430 (operation S440).

[56] In FIG. 4, operation S420 may not necessarily be performed between operation S410 and operation S430. For example, if the cycle of measuring a traffic channel occupancy rate has not come around, operation S420 after operations S410 may be omitted, and the base station 110 may use a previously measured traffic channel occupancy rate in operation S430. Since the traffic channel occupancy rate can be measured periodically, operations S420 through S440 may be repeated if the power value controller is not changed to the radio network controller 110.

[57] Although not shown in FIG. 4, the base station 110 may transmit the traffic channel occupancy rate measured in operation S420 to the radio network controller 120. Then, the radio network controller 120 may determine the power value controller again by using the received traffic channel occupancy rate. If the radio network controller 120 is determined to be the power value controller, operations of FIG. 5 may be performed.

[58] FIG. 5 is a flowchart illustrating a power allocation process according to another exemplary embodiment of the present invention. In the present embodiment, it is assumed that the radio network controller 120 is a power value controller. [59] Referring to FIG. 5, the radio network controller 120 may transmit information about the power value controller to the base station 110 (operation S510). Then, the base station 110 may learn from the information that it cannot determine a power value.

[60] Since the radio network controller 120 is the power value controller, the base station

110 may wait for a power value transmitted from the radio network controller 120. The radio network controller 120 may determine a power value that is to be allocated to an HSDPA channel based on a traffic channel occupancy rate received from the base station 110 (operation S520).

[61] Next, the radio network controller 120 may transmit the power value determined in operation S520 to the base station 110 (operation S530), and the base station 110 may allocate power to the HSDPA channel based on the power value received from the radio network controller 120.

[62] Although not shown in FIG. 5, the base station 110 may periodically measure the traffic channel occupancy rate and transmit the measured traffic channel occupancy rate to the radio network controller 120. By using the received traffic channel occupancy rate, the radio network controller 120 may repeatedly perform operations S520 and S530.

[63] As described above with reference to FIG. 3, the radio network controller 120 may determine a power value controller by using a traffic channel occupancy rate received from the base station 110. If the base station 110 is determined to be the power value controller, the operations of FIG. 4 may be performed.

[64] A power value to be allocated to an HSDPA channel may be determined by a traffic channel occupancy rate. Specifically, as the traffic channel occupancy rate increases, the power value to be allocated to the HSDPA channel may be reduced. On the contrary, as the traffic channel occupancy rate decreases, the power value to be allocated to the HSDPA channel may be increased. Information about the power value that is to be allocated to the HSDPA channel according to the traffic channel occupancy rate may be experimentally set in the base station 110 and the radio network controller 120 to a value that enables efficient utilization of radio resources.

[65] If the base station 110 determines a power value that is to be allocated to an HSDPA channel, the base station 110 may use a traffic channel occupancy rate in a cell under its control. However, if the radio network controller 120 determines a power value that is to be allocated to an HSDPA channel, the radio network controller 120 may use not only a traffic channel occupancy rate in a specific cell but also a traffic channel occupancy rate in a cell adjacent to the specific cell.

[66] For example, based on the first traffic channel occupancy rate received from the first base station 110-1, the radio network controller 120 may determine a power value to be allocated to the HSDPA channel in the first cell under the control of the first base station 110-1. Then, the radio network controller 120 may correct the power value determined for the HSDPA channel of the first cell based on the second traffic channel occupancy rate which is received from the second base station 110-2 adjacent to the first base station 110-1. Here, the radio network controller 120 may reduce the initially determined power value if the second traffic channel occupancy rate is low. For example, if the second traffic channel occupancy rate is greater than a preset threshold value, the initially determined power value may be used. If the second traffic channel occupancy rate is not greater than the preset threshold value, the initially determined power value may be reduced by a predetermined value. Here, the value by which the initially determined power value is reduced based on the preset threshold value or the second traffic channel occupancy rate may be experimentally set to a value that can minimize the interference between cells or between channels within a cell.

[67] An example of parameters that can be used to implement the above embodiments is shown in Table 1. [68] Table 1 [Table 1] [Table ]

[69] From the parameters shown in Table 1, the "Automatic Control" parameter indicates whether a power value controller for an HSDPA channel is to be dynamically set. If the "Automatic Control" parameter is activated, the power value controller may be dynamically changed to a base station or a radio network controller according to a traffic channel occupancy rate. On the contrary, if the "Automatic Control" parameter is deactivated, any one of the base station 110 and the radio network controller 120 may continuously determine a power value as in the prior art.

[70] The "Report Level" parameter indicates a report unit of the traffic channel occupancy rate. For example, if the "Report Level" is set to 10 %, the base station 110 may report the traffic channel occupancy rate to the radio network controller 120 in units of 10 %.

[71] Each of the "Maximum Power" parameter and the "Minimum Power" parameter indicates the power value range. Therefore, a power value controller may determine a power value within the range of a value of the "Minimum Power" parameter to a value of the "Maximum Power" parameter.

[72] The "Periodic Report" parameter indicates whether the base station 110 is to periodically report the traffic channel occupancy rate to the radio network controller 120. The "Cycle" parameter indicates intervals at which the traffic channel occupancy rate is to be reported. If the "Periodic Report" parameter is set to "On" and if the "Cycle" parameter is set to 10, the base station 110 may transmit the traffic channel occupancy rate to the radio network controller 120 every 10 seconds.

[73] The above parameters may be set in the base station 110 and the radio network controller 120 by the mobile communication system administrator. The parameters shown in Table 1 are mere examples. Thus, only some of the parameters in Table 1 may be set, or new parameters may be set in addition to those in Table 1.

[74] Table 2 is an example of an information table that can be used to determine a power value. The information table (Table 2) is based on the assumption that the "Report Level" parameter of Table 1 is set to 10 %, that the "Maximum Power" level is set to 430 *0.1dB, and that the "Minimum Power" is set to 380 *0.1dB. The base station 110 or the radio network controller 120 may determine a power value by using the information table below.

[75] Table 2 [Table 2] [Table ]

[76] Determining a power value that is to be allocated to the HSDPA channel of each cell by using a traffic channel occupancy rate has been described above. However, as described above, the mobile communication system 100 according to the exemplary embodiment of the present invention may also control a power value that is to be allocated to an HSDPA channel according to an OVSF code allocation rate.

[77] FIG. 6 illustrates OVSF code occupancy according to an exemplary embodiment of the present invention.

[78] An OVSF refers to a set of spreading codes induced from a set of orthogonal codes and is used for channelization. An OVSF code is allocated as a unique value to each terminal that intends to transmit data. Therefore, a plurality of terminals existing in the same cell can transmit or receive data while having orthogonality to channels.

[79] That is, the OVSF code causes channels within a radio cell to have orthogonality to each other. In order to maintain orthogonality between forward channels, each terminal adjusts a transmission time according to its OVSF code and transmits data accordingly.

[80] Referring to FIG. 6, OVSF codes are generated and disposed in a tree structure composed of spreading factor (SF) layers. When an OVSF code is generated, it is assigned to a terminal, so that the terminal can perform orthogonal transmissions by using the OVSF code.

[81] When an OVSF code is occupied by a specific terminal, all OVSF codes in layers lower than a layer in which the OVSF code is disposed cannot be occupied by any terminal. For example, if a "C = 1 1" code 610 is occupied by a specific terminal, a "C = 1 1 1 1" code 620 and all OVSF codes in layers lower a layer in which the "C ch,4,0

= 1 1 1 1" code 620 is disposed cannot be occupied by any terminal. In addition, a "C ch,4,l = 1 1 -1 -1" code 630 and all OVSF codes in lay ^J ers lower a lay ^J er in which the

"C = 1 1 -1 -1" code 630 is disposed cannot be occupied by any terminal.

[82] The mobile communication system administrator may determine an SF layer for each terminal or each type of data that is to be transmitted. In an SF layer, occupied codes and unoccupied codes may coexist.

[83] OVSF codes for each radio cell are generated and managed by a corresponding base station or a radio network controller. Which of the first through third base stations 110-1 through 110-3 and the radio network controller 120 will function as a power value controller (which determines a power value to be allocated to an HSDPA channel) may be dynamically determined by an OVSF code occupancy rate of each cell.

[84] The OVSF code occupancy rate is a ratio of the number of OVSF codes occupied by terminals that intend to transmit or receive data to the total number of OVSF codes generated. OVSF codes (hereinafter, referred to target OVSF codes) which are used to calculate the OVSF code occupancy rate may be determined by the mobile communication system administrator. For example, if there is a dedicated OVSF code to an HSDP channel, OVSF codes excluding the dedicated OVSF code may be determined to be target OVSF codes. Then, a ratio of the number of target OVSF codes occupied by terminals to the total number of target OVSF codes may be calculated as the OVSF code occupancy rate. The target OVSF codes may be OVSF codes that exist in all SF layers or OVSF codes that exist in a specific SF layer. [85] FIG. 7 illustrates OVSF codes that are or are not dedicated to an HSDPA channel according to an exemplary embodiment of the present invention.

[86] The mobile communication system administrator may divide OVSF codes in each SF layer into a plurality of groups. Then, the mobile communication system administrator may allocate a specific group 710 of OVSF codes as a group of dedicated OVSF codes to an HSDPA channel and allocate the remaining group 720 of OVSF codes 720 as a group of OVSF codes for channels other than the HSDPA channel. In this case, an OVSF code having a specific number of codes may be allocated as a dedicated OVSF code to the HSDPA channel. However, the standards for allocating an OVSF code as a dedicated OVSF code to an HSDPA channel may vary according to an SF layer.

[87] In FIG. 7, OVSF codes are divided into the two groups 710 and 720. However, the

OVSF codes may be divided into three, four or more groups, and at least one of the groups may be allocated as being dedicated to the HSDPA channel.

[88] In order to determine a power value controller for an HSDPA channel, each of the first through third base stations 110-1 through 110-3 may measure an OVSF code occupancy rate in a cell under its control and provide the measured OVSF code occupancy rate to the radio network controller 120.

[89] Based on the OVSF code occupancy rate from the base station 110, the radio network controller 120 may determine the power value controller for the HSDPA channel in the cell under the control of the base station 110.

[90] FIG. 8 is a flowchart illustrating the process of determining a power value controller for an HSDPA channel according to another exemplary embodiment of the present invention.

[91] Referring to FIG. 8, when receiving an OVSF code occupancy rate from the base station 110, the radio network controller 120 may determine whether the OVSF code occupancy rate is greater than a preset threshold value (operation S820).

[92] If the OVSF code occupancy rate is greater than the preset threshold value, the radio network controller 120 may determine itself to be a power value controller for an HSDPA channel in a cell under the control of the base station 110 (operation S830).

[93] However, if it is determined in operation S820 that the OVSF code occupancy rate is not greater than the preset threshold value, the radio network controller 120 may determine the base station 110 to be the power value controller for the HSDPA channel in the cell under the control of the base station 110 (operation S840).

[94] After the power value controller is determined, the radio network controller 120 may transmit information about the determined power value controller to the base station 110 (operation S850).

[95] The operations in FIG. 8 may be repeated. When the operations in FIG. 8 are repeated, operation S850 may be omitted if a newly determined power value controller is identical to a previously determined power value controller. For example, while the base station 110 is functioning as a power value controller, if the base station 110 is determined to be the power value controller again in operation S840, operation S850 may be omitted. However, if the radio network controller 120 is determined to be the power value controller in operation S830, operation S850 may be performed.

[96] In the exemplary embodiment of FIG. 8, the radio network controller 120 determines a power value controller for a specific cell based on an OVSF code occupancy rate of the specific cell. In this case, the radio network controller 120 may independently determine a power value controller for a cell under the control of each base station connected thereto.

[97] However, the present invention is not limited to the exemplary embodiment of FIG.

8. According to an embodiment of the present invention, the radio network controller 120 may determine a power value controller for an HSDPA channel in each cell under the control of a corresponding one of a plurality of base stations by comprehensively considering OVSF code occupancy rates received from the base stations.

[98] For example, in the mobile communication system 100 of FIG. 1, if a first OVSF code occupancy rate received from the first base station 110-1 is not greater than a first threshold value, the radio network controller 120 may determine the first base station 110-1 to be a power value controller for the HSDPA channel in the first cell under the control of the first base station 110-1. If the first OVSF code occupancy rate is greater than a second threshold value (which is greater than the first threshold value), the radio network controller 120 may determine itself to be the power value controller for the HSDPA channel in the first cell.

[99] However, if the first traffic channel occupancy rate is greater than the first threshold value but less than the second threshold value, the radio network controller 120 may determine the power value controller for the HSDPA channel in the first cell based on a second OVSF code occupancy rate received from the second base station 110-2 which controls the second cell adjacent to the first cell. If the second OVSF code occupancy rate is greater than the second threshold value or is not reported, the radio network controller 120 may determine itself to be the power value controller for the HSDPA channel in the first cell. However, if the second OVSF code occupancy rate is not greater than the second threshold value, the radio network controller 120 may determine the first base station 110-1 to be the power value controller for the HSDPA channel in the first cell.

[100] While the radio network controller 120 was determined to be the power value controller for the HSDPA channel in the first cell because the first OVSF code occupancy rate is greater than the first threshold value, if the first OVSF code occupancy rate becomes closer to the first threshold value, the radio network controller 120 may increase a power value without considering the conditions of the adjacent cell (i.e., the second cell). Consequently, the possibility of interference between the first and second cells can be reduced.

[101] A case where a power value controller is separately determined for the HSDPA channel of each cell has been described above. However, the present invention is not limited thereto. According to an embodiment of the present invention, the radio network controller 120 may simultaneously determine power value controllers for the respective HSDPA channels of all cells. For example, if the sum of respective OVSF code occupancy rates of a plurality of cells in the RAN 10 is less than a preset threshold value or if a ratio of the number of cells, whose respective OVSF code occupancy rates are less than a preset threshold value, to the total number of cells is equal to or greater than a predetermined ratio, the radio network controller 120 may simultaneously determine the first through third base stations 110-1 through 110-3 to be the power value controllers for the HSDPA channels in all cells within the RAN 10, respectively. On the contrary, if the sum of the respective OVSF code occupancy rates of the cells in the RAN 10 is equal to or greater than the preset threshold value or if the ratio of the number of cells, whose respective OVSF code occupancy rates are less than the preset threshold value, to the total number of cells is less than the predetermined ratio, the radio network controller 120 may determine itself to be the power value controller for the HSDPA channel of each cell.

[102] Various other embodiments, in which a power value controller for an HSDPA channel is dynamically determined based on an OVSF code occupancy rate of each cell, may be implemented and construed as being within the scope of the present invention.

[103] Once a power value controller is determined, the process of allocating power to an

HSDPA channel may be performed. Specifically, if the radio network controller 120 is determined to be the power value controller, the base station 110 may allocate power to the HSDPA channel based on a power value determined by the radio network controller 120. However, if the base station 110 is determined to be the power value controller, it may determine a power value to be allocated to the HSDPA channel.

[104] A power value to be allocated to an HSDPA channel may be determined by an OVSF code occupancy rate. Specifically, as the OVSF code occupancy rate increases, the power value to be allocated to the HSDPA channel may be reduced. On the contrary, as the OVSF code occupancy rate decreases, the power value to be allocated to the HSDPA channel may be increased. Information about the power value that is to be allocated to the HSDPA channel according to the OVSF code occupancy rate may be experimentally set in the base station 110 and the radio network controller 120 to a value that enables efficient utilization of radio resources. [105] Since the process of controlling a power value according to an OVSF code occupancy rate is similar to the process of controlling a power value according to a traffic channel occupancy rate which has been described above with reference to FIGS. 4 and 5, a detailed description thereof will be omitted.

[106] If the base station 110 determines a power value that is to be allocated to an HSDPA channel, the base station 110 may use an OVSF code occupancy rate in a cell under its control. However, if the radio network controller 120 determines a power value that is to be allocated to an HSDPA channel, the radio network controller 120 may use not only an OVSF code occupancy rate in a specific cell but also an OVSF code occupancy rate in a cell adjacent to the specific cell. The radio network controller 120 which also uses an OVSF code occupancy rate in an adjacent cell is similar to the radio network controller 120 which also uses a traffic channel occupancy rate in an adjacent cell. Thus, a detailed description of the radio network controller 120 which also uses an OVSF code occupancy rate in an adjacent cell will be omitted.

[107] Controlling a power value to be allocated to an HSDPA channel of each cell by using a traffic channel occupancy rate or an OVSF code occupancy rate has been described above. However, the mobile communication system 100 according to the exemplary embodiment of the present invention may determine a power value controller based on a combination of a traffic channel occupancy rate and an OVSF code occupancy rate to control a power vale that is to be allocated to an HSDPA channel.

[108] For example, the sum of a traffic channel occupancy rate and an OVSF code occupancy rate may be compared to a predetermined threshold value. Alternatively, the sum of a weighted traffic channel occupancy rate and a weighted OVSF code occupancy rate may be compared to a preset threshold value. Then, a power value controller may be determined based on the comparison result and determine whether to increase or decrease a power value that is to be allocated to an HSDPA channel.

[109] A threshold value according to an embodiment of the present invention may be a value that can be set by the mobile communication system administrator. The mobile communication system administrator may arbitrarily change the threshold value according to its administration direction. Here, the threshold value may be an integer or a decimal fraction or may have a positive or negative value. When the threshold value has a negative value, its absolute value may be used to determine a power value controller.

[110] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. The exemplary embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the following claims, and all differences within the scope will be construed as being included in the present invention.

Brief Description of the Drawings [111] FIG. 1 illustrates a mobile communication system according to an exemplary embodiment of the present invention; [112] FIG. 2 is a flowchart illustrating the process of setting up a high-speed downlink packet access (HSDPA) call according to an exemplary embodiment of the present i nvention; [113] FIG. 3 is a flowchart illustrating the process of determining a power value controller for an HSDPA channel according to an exemplary embodiment of the present invention; [114] FIG. 4 is a flowchart illustrating a power allocation process according to an exemplary embodiment of the present invention; [115] FIG. 5 is a flowchart illustrating a power allocation process according to another exemplary embodiment of the present invention; [116] FIG. 6 illustrates orthogonal variable spreading factor (OVSF) code occupancy according to an exemplary embodiment of the present invention; [117] FIG. 7 illustrates OVSF codes that are or are not dedicated to an HSDPA channel according to an exemplary embodiment of the present invention; and [118] FIG. 8 is a flowchart illustrating the process of determining a power value controller for an HSDPA channel according to another exemplary embodiment of the present invention.

Industrial Applicability [119] As described above, a power allocation method and a mobile communication system using the same according to the present invention can allocate appropriate power to a high-speed downlink packet access (HSDPA) channel while reducing the possibility of interference between channels within a cell or between cells.

Claims

[I] A power allocation method comprising: measuring a load factor of a cell; and allocating power to a high-speed downlink packet access (HSDPA) channel of the cell by using a power value which is provided by any one of a base station and a radio network controller based on the measured load factor.

[2] The method of claim 1, wherein the power value is provided by the radio network controller when the load factor is greater than a predetermined threshold value, and the power value is provided by the base station when the load factor is equal to or less than the predetermined threshold value.

[3] The method of claim 1, wherein the load factor comprises at least one of a traffic channel occupancy rate and an orthogonal variable spreading factor (OVSF) code occupancy rate.

[4] The method of claim 3, wherein the traffic channel occupancy rate is a proportion of power allocated to channels, which exclude the HSDPA channel from among a plurality of channel used in the cell, in maximum power that can be supported by the base station.

[5] The method of claim 3, wherein the OVSF code occupancy rate is a ratio of the number of OVSF codes occupied by terminals to the total number of OVSF codes which are allocated to the channels excluding the HSDPA channel.

[6] The method of claim 5, wherein the OVSF codes are included in a preset spreading factor (SF) layer.

[7] The method of claim 3, wherein the OVSF code occupancy rate is a ratio of the number of OVSF codes occupied by terminals to the total number of OVSF codes which are included in the preset SF layer.

[8] The method of claim 1, wherein the allocating of power to the HSDPA channel comprises: determining any one of the base station and the radio network controller to be a power value controller for the HSDPA channel based on the load factor; and allocating power to the HSDPA channel according to the power value which is provided by the determined power value controller.

[9] The method of claim 1, wherein the power value is reduced as the load factor increases and increased as the load factor decreases.

[10] The method of claim 1, wherein the radio network controller determines the power value to be allocated to the HSDPA channel based on the load factor of the cell and a load factor of another cell adjacent to the cell.

[I I] A mobile communication system comprising: a radio network controller which determines a power value controller for an HS DPA channel of a cell based on a load factor of the cell; and a base station which allocates power to the HSDPA channel of the cell according to a power value provided by the power value controller which was determined by the radio network controller.

[12] The system of claim 11, wherein the power value is provided by the radio network controller when the load factor is greater than a predetermined threshold value, and the power value is provided by the base station when the load factor is equal to or less than the predetermined threshold value.

[13] The system of claim 11, wherein the load factor comprises at least one of a traffic channel occupancy rate and an OVSF code occupancy rate.

[14] The system of claim 13, wherein the traffic channel occupancy rate is a proportion of power allocated to channels, which exclude the HSDPA channel from among a plurality of channel used in the cell, in maximum power that can be supported by the base station.

[15] The system of claim 13, wherein the OVSF code occupancy rate is a ratio of the number of OVSF codes occupied by terminals to the total number of OVSF codes which are allocated to the channels excluding the HSDPA channel.

[16] The system of claim 15, wherein the OVSF codes are included in a preset SF layer.

[17] The system of claim 13, wherein the OVSF code occupancy rate is a ratio of the number of OVSF codes occupied by terminals to the total number of OVSF codes which are included in the preset SF layer.

[18] The system of claim 11, wherein the base station measures the load factor, and the radio network controller determines the power value controller which is to provide the power value based on the measured load factor.

[19] The system of claim 11, wherein the power value is reduced as the load factor increases and increased as the load factor decreases.

[20] The system of claim 11, wherein the radio network controller determines the power value to be allocated to the HSDPA channel based on the load factor of the cell and a load factor of another cell adjacent to the cell.