JP4980293B2 - Monitor cell list notification method and communication system - Google Patents

Description

  The present invention relates to a monitor cell list notification method and a communication system for notifying cell information of a handover destination candidate of a mobile terminal.

  In recent years, in cellular systems such as UMTS (Universal Mobile Telecommunications System), femtocells that are generated by installing ultra-small wireless base stations in homes and commercial facilities in order to expand wireless coverage indoors have attracted attention. ing. Since femtocells provide indoor wireless communication, the wireless coverage is small and the number of terminals that can communicate simultaneously in the cell is small, but the wireless transmission capability is the same as that of a macro cell that covers the outdoors, and limited wireless resources are limited. Can be used exclusively in the designated space / terminal. For this reason, the femtocell can improve the radio transmission speed per terminal and is expected to serve as a hot spot.

  In order to provide higher-quality wireless communication in a communication system including a femto cell, it is better to hand over a terminal from a macro cell to a femto cell in an area where the femto cell can be used, and to use the femto cell as much as possible. In consideration of user convenience, handover from a macro cell to a femto cell or from a femto cell to a macro cell is desirably performed automatically without the user being aware of it. In a conventional cellular system, for example, UMTS, a terminal measures the radio quality of a cell in communication and a cell existing in the vicinity thereof, and performs handover so that good communication quality is always maintained using the measurement result. Techniques for performing this have been standardized (see Non-Patent Document 1 and Non-Patent Document 2 below). According to such a conventional technique, the network notifies the terminal of a list of handover destination candidate cells (monitor cell list) using a notification message or a measurement request message, and measures the radio quality of the monitor cell and reports the result to the terminal. Instruct. Then, for example, when the radio quality of the cell with which the terminal is communicating falls below the highest quality measurement result reported from the terminal, the network hands over the terminal to the highest quality cell. .

  Further, in Patent Document 1 below, when there is another wireless communication system that provides a hot spot within the coverage area of a specific wireless communication system, the hot spot is not transmitted to a terminal that is communicating with the specific wireless communication system. A technique for smoothly performing handover between different wireless communication systems by notifying existence is disclosed.

Special table 2007-534222 gazette 3GPP, “RRC protocol specification”, TS25.331, V6.16.0, 2007-12 3GPP, “UE procedures in idle mode and procedures for cell reselection in connected mode”, TS25.304, V6.9.0, 2006-3

  The coverage area of the macro cell is larger than the coverage area of the femto cell in order to efficiently cover the outdoor communication area, and generally, a large number of femto cells may exist in or around the macro cell. On the other hand, the number of cells in which the terminal measures the radio quality for handover is limited due to the measurement load of the terminal and restrictions on measurement accuracy, and is defined as 32 in UMTS, for example. Therefore, the radio quality of all femtocells in and around the macrocell may not be measured. In order to hand over a terminal from a macro cell to a femto cell in such an environment, a cell (monitor cell) that identifies the position of the terminal in the macro cell, selects a femto cell existing around the terminal, and measures radio quality Need to be notified to the terminal.

  However, the conventional cellular system does not disclose any method for selecting a monitor cell to be notified according to the position of the terminal. For this reason, there is a problem in that a terminal that is communicating in a macro cell cannot be handed over even though a femto cell is nearby, and continues to communicate in the macro cell, so that the radio band of the femto cell cannot be used effectively. It was. In addition, when the terminal moves from the outdoor to the indoor, there is a problem that the handover from the macro cell to the femto cell cannot be performed properly, and communication is disconnected during indoor movement.

  On the other hand, in the above-mentioned Patent Document 1, by notifying a terminal of the presence of a hot spot of a different wireless communication system existing in or around a cell of the wireless communication system, regardless of the type of the wireless communication system, the different types of wireless communication of the terminal Inter-system handover can be facilitated. However, there is no disclosure about how to acquire information about whether or not a hot spot exists around the terminal. For this reason, there has been a problem that information about cells existing near the terminal cannot always be obtained.

  The present invention has been made in view of the above, and when there are a large number of femto cells in or around a macro cell, a monitor cell list notification that allows a terminal to perform a smooth handover from the macro cell to the femto cell The object is to obtain a method and a communication system.

  In order to solve the above-described problems and achieve the object, the present invention provides a terminal, a standard cell in communication with the terminal, and a small cell having a cell radius smaller than that of the standard cell in or around the coverage of the standard cell. In order to hand over the terminal to the small cell, the standard cell provides the terminal with a monitor cell list including information for measuring reception quality of a candidate cell that is a candidate for a handover destination. A method of notifying a monitor cell list in the case of notifying, wherein a landmark placement step of placing a landmark cell that overlaps at least a part of the coverage with the small cell; and a measurement request transmitted from the standard cell by the terminal A landmark cell reception quality measuring step for measuring the reception quality of the landmark cell based on the received signal, and the terminal Receiving quality reporting step, the standard cell selecting a landmark cell having the best receiving quality based on the report, and the standard cell selecting the selected land. And a monitor cell list notifying step of notifying the terminal by including information on the small cell overlapping at least a part of the coverage with the mark cell in the monitor cell list.

  According to the present invention, femto cells are grouped based on the positions of femto cells in or around the macro cell coverage, and the terminal determines which group the terminal is near by measuring the radio quality of the landmark cell. Since the landmark cell is arranged so that the macro cell can select the femto cell to be included and transmitted in the monitor cell list based on the radio quality measured by the terminal, the terminal can smoothly move from the macro cell to the femto cell. The effect that it is possible to perform simple handover.

  Embodiments of a monitor cell list notification method and a communication system according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a first embodiment of a communication system according to the present invention. As shown in FIG. 1, in the communication system according to the present embodiment, the mobile terminal 1 is generated by a mobile terminal 1 that is movable, a macro cell 200 generated by a general base station, and a small base station. Femtocells 300 to 304, and landmark cells 400 and 401, which are cells having a cell radius smaller than that of the macro cell and larger than that of the femtocells 300 to 304, are included. The coverage of the femtocells 300 to 304 exists within the coverage of the macrocell 200 or at a position that partially overlaps the coverage of the macrocell 200.

  The landmark cells 400 and 401 of the present embodiment are cells that are arranged in advance in a predetermined position within the coverage of the macro cell 200 or around the macro cell 200. In the present embodiment, it is assumed that the femto cell 300 exists in the coverage of the landmark 400 cell, and the femto cell 301 exists in a position partially overlapping with the coverage of the landmark cell 400. Further, it is assumed that the femtocell 302 exists inside the landmark cell 401.

  In the present embodiment, it is assumed that the positional relationship between the landmark cells 400 and 401 and the femtocells 300 to 304 is grasped when the landmark cells 400 and 401 are arranged and held in the macrocell 200 (for example, Etc., held by the base station of the macro cell 200).

  Next, the operation of the present embodiment will be described. Here, it is assumed that the terminal 1 exists within the coverage of the macro cell 200 and the coverage of the femto cell 300, and a case where the terminal 1 performs handover from the macro cell 200 to the femto cell 300 will be described.

  First, the macro cell 200 notifies the terminal 1 of the monitor cell list including the information of the landmark cells 400 and 401 in order to cause the terminal 1 to measure the communication quality of the landmark cells 400 and 401. The monitor cell list is a list for designating a cell to be measured by the terminal, and for a cell to be measured by the terminal 1, a cell ID (Identifier), a frequency, and a CDMA (Code Division Multiple Access) corresponding to each cell. The information necessary for the terminal to measure the radio quality, such as the code in the case of In the monitor cell list, the base station that generates the macro cell 200 may broadcast the same information to all the terminals located in the cell using the broadcast channel, or the radio cell established individually with each terminal. Individual information may be notified to each terminal using a channel.

  Next, the terminal 1 measures the radio quality of the landmark cells 400 and 401 based on the information of the landmark cells 400 and 401 included in the monitor cell list notified from the macro cell 200. Then, the terminal 1 reports the measurement results of the radio quality of the landmark cells 400 and 401 to the macro cell 200 in accordance with the measurement result reporting conditions and period specified by the macro cell 200. In the present embodiment, it is assumed that the report condition and cycle of the measurement result are included in the monitor cell list, but the present invention is not limited to this, and the terminal is separated from the monitor cell list using a broadcast channel or an individually established radio channel. 1 may be notified. The measurement result reporting conditions indicate the conditions for measurement. However, when high measurement accuracy is required, the reporting conditions are stricter (for example, increasing the amount of received signals used for measurement, statistical processing The reporting conditions may be relaxed when it is required to perform measurement quickly.

  As illustrated in FIG. 1, the terminal 1 is located within the coverage of the landmark cell 400 and is not located within the coverage of the landmark 401. Therefore, the terminal 1 reports to the macro cell 200 the measurement result that the landmark 400 has good radio quality and the landmark cell 401 has poor radio quality or cannot be measured.

  Then, the macro cell 200 recognizes that the terminal 1 is located within the coverage of the landmark cell 400 because the radio quality of the landmark cell 400 is good based on the measurement result reported from the terminal 1. Therefore, the macro cell 200 uses the information of the femtocells 300 and 301 existing in the vicinity of the landmark cell 400 (in the coverage of the landmark cell 400 or at a position where the coverage overlaps with the landmark cell 400) as the monitor cell. Including terminal 1 is notified.

  The terminal 1 measures the radio quality of the femtocells 300 and 301 based on the information of the femtocells 300 and 301 included in the monitor cell list notified from the macrocell 200. Then, the measurement result is notified to the macro cell 200 according to the report condition and cycle of the measurement result designated from the macro cell 200. Since terminal 1 is located within the coverage of femtocell 300 as shown in FIG. 1 and is not located within the coverage of femtocell 301, terminal 1 has good radio quality for femtocell 300, and femtocell For 301, a measurement result indicating that the radio quality is poor or measurement is impossible is reported to the macro cell 200.

  Then, it is appropriate for the macro cell 200 to grasp that the terminal 1 is located in the vicinity of the femto cell 300 based on the measurement result reported from the terminal 1, and to hand over the terminal 1 from the macro cell 200 to the femto cell 300. It can be judged that there is.

  It should be noted that the measurement result reporting conditions and the period specified by the macro cell 200 to the terminal 1 may be different between the case of measuring the landmark cells 400 and 401 and the case of measuring the femto cells 300 to 304. For example, the notification condition in the case of grasping the position of the terminal 1 based on the measurement results of the landmark cells 400 and 401 may be set more loosely than the reporting condition of the measurement results of the femtocells 300 to 304. Further, the reporting period of the measurement results of the landmark cells 400 and 401 may be set shorter than the reporting period of the measurement results of the femtocells 300 to 304. As described above, the speed of grasping the position of the terminal 1 using the landmark cell can be improved by relaxing the reporting condition or shortening the reporting cycle.

  The landmark cells 400 and 401 have communication means and are configured so that the terminal 1 can perform normal communication in the landmark cell in the same manner as other cells (macro cell 200 and femtocells 300 to 304). May be. The landmark cells 400 and 401 are provided with a minimum function for grasping the position of the terminal 1 so that the terminal 1 cannot perform normal communication within the coverage of the landmark cells 400 and 401. Also good. In the latter case, since radio resources (bandwidth, code, etc.) are not used effectively, it is desirable to minimize the number of landmark cells 400 and 401 to be arranged.

  The example shown in FIG. 1 is an example in which the number of landmark cells to be arranged is minimized with respect to the positional relationship between the macro cell 200 and the femto cells 300 to 304. In FIG. 1, there are femtocells 303 and 304 that are not located within the coverage of the landmark cells 400 and 401. For example, when the terminal 1 is located within the coverage of the femtocell 303, the terminal 1 has a measurement result that the radio quality is poor or the measurement is impossible for both the landmark cells 400 and 401. When the macro cell 200 reports a measurement result indicating that the radio quality is poor or measurement is impossible for any of the landmark cells 400 and 401 from the terminal 1, the macro cell 200 determines which of the landmark cells 400 and 401 Judge that it is not located in the coverage. In this case, the macro cell 200 notifies the terminal 1 of a monitor cell list including information on the femto cells 303 and 304. Then, the terminal 1 measures the radio quality of the femtocells 303 and 304 based on the notified monitor cell list, and reports the measurement result that the radio quality of the femtocell 303 is good to the macro cell 200. Therefore, the macro cell 200 can determine that it is appropriate to hand over the terminal 1 from the macro cell 200 to the femto cell 303 based on the reported measurement result.

  Even when the terminal 1 is not located in any coverage of the femtocells 300 to 304, the measurement results of the radio quality of both the landmark cells 400 and 401 are bad or cannot be measured. Also in this case, the monitor cell list including information of the femtocells 303 and 304 is notified from the macro cell 200, but the measurement results of the radio quality for the femtocells 303 and 304 reported from the terminal 1 are both bad or measured. It becomes impossible. In this case, the macro cell 200 may determine that there is no appropriate femto cell as a handover destination, and continue communication by the macro cell 200.

  Landmarks can be arranged in this way, for example, by dividing femtocells within the coverage of a macrocell or with some overlapping coverage into several groups according to location, and arranging landmark cells so that the groups can be distinguished. Good.

  As described above, in the present embodiment, the femtocells are grouped based on the positions of the femtocells 300 to 304 in or around the coverage of the macrocell 200 (positions where the coverage partially overlaps), and the terminal 1 , 401 are measured so that the landmark cells 400 and 401 are arranged so that it can be determined which group the terminal is near. Then, the macro cell 200 finds a group in which the terminal 1 is determined to be nearby based on the measurement result of the radio quality, and includes information on femtocells belonging to the group in the monitor cell list and notifies the terminal 1 of the information. . For this reason, even when there are more femto cells in and around the macro cell 200 than the number of cells in which the terminal 1 can measure the radio quality, the macro cell 200 can appropriately select the handover destination candidate of the terminal 1, and the macro cell Can be smoothly handed over to the femtocell.

Embodiment 2. FIG.
FIG. 2 is a diagram illustrating a configuration example of the second embodiment of the communication system according to the present invention. As shown in FIG. 2, in the present embodiment, the landmark cells 400 and 401 are deleted from the communication system of the first embodiment, but the rest is the same as in the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted. Also, the reachable range 100 shown in FIG. 2 is the reachable range of the transmission signal of the terminal 1, and the receiving device 2 is a device having a receiving function such as a base station located at the center of the macro cell 200. The terminal 1 includes an omni-type antenna and forms a signal reachable range such as the reachable range 100. Note that the terminal 1 may include an antenna other than the omni-type antenna. In that case, although the shape of the reachable range changes according to the characteristics of the antenna, the operation of the present embodiment can be similarly performed.

  In the first embodiment, landmark cells are arranged in advance and the position of the terminal 1 is determined. However, in this embodiment, a radio signal transmitted from the terminal 1 without using the landmark cell is transmitted to the periphery of the terminal 1. To determine the position of the terminal 1.

  The macro cell 200 requests the femto cells 300 to 304 located in and around the macro cell 200 to measure the transmission signal from the terminal 1 when communication with the terminal 1 is established. This request includes information necessary for measuring the transmission signal from the terminal 1, measurement contents, report conditions, and report contents. The information necessary for measuring the terminal transmission signal is, for example, a code used by the terminal 1 to be measured in the case of a system that performs multiple access by CDMA, and time division multiplexing by TDD. In the system in use, this is the time slot used by the measurement terminal. The measurement contents can include, for example, the reception level of the transmission signal from the terminal 1 in the femtocell, the path loss, and the like. Here, the reception level is the measurement content.

  As the reporting condition, here, as an example, “when the reception level of the transmission signal from the terminal 1 exceeds and falls below the reception level of the terminal 1 in the macro cell 200 (hereinafter referred to as a reference reception level)” is set. I decided to. However, when the reception level of the transmission signal from the terminal 1 is larger than the reference reception level, it is always reported if there is a report request when the report condition “exceeds”, but the reception level of the transmission signal from the terminal 1 is If it is smaller than the reference reception level, it is not reported if it is smaller than the reference reception level from the beginning, and is reported only when the state has changed from “above” to “below”. The reference reception level is notified from the macro cell 200 to each femto cell. The report contents include an event “beyond” or “below” the reference reception level and the reception level of the transmission signal from the terminal 1.

  On the other hand, when the femtocells 300 to 304 receive the measurement request as described above from the macrocell 200, the femtocells 300 to 304 must receive a transmission signal from the terminal 1 while performing communication with the terminals under its own cell. A terminal in communication with the femtocells 300 to 304 transmits a signal with power sufficient to reach the signal in the femtocell with a small coverage, whereas the terminal 1 transmits to the receiving device 2 of the macrocell 200 with a large coverage. The signal is transmitted with large power so that the signal reaches. For this reason, when the reception sensitivity of the femtocells 300 to 304 is lowered so as to receive the transmission signal of the terminal communicating with the own cell, the reception quality of the transmission signal of the terminal 1 deteriorates. On the other hand, if the reception sensitivity is increased to receive the transmission signal of the terminal 1, the reception quality of the transmission signal of the terminal communicating with the own cell deteriorates.

  In order to deal with such a problem, the macro cell 200 may transmit the femtocells 300 to 304 by including the transmission power information of the terminal 1 in the measurement request. As the transmission power information at this time, the transmission power value transmitted by the terminal 1 (when the terminal 1 transmits its own transmission power value to the macro cell 200), the transmission power value from the terminal 1 received by the receiving device 2 of the macro cell 200 is received. It is possible to use a transmission power value of a terminal predicted from values such as a reception level and a propagation delay of a transmission signal, or a value such as a reception level and a propagation delay. Then, each femtocell switches the sensitivity of the receiver between receiving a signal from the terminal in communication with itself and receiving a signal transmitted from the terminal 1 based on the transmission power information of the terminal received from the macro cell. Thus, it is possible to prevent the reception quality of both the terminal communicating with itself and the terminal 1 from being deteriorated. In addition, when the femtocells 300 to 304 include a plurality of receivers and one of the receivers can be used for reception quality measurement of the transmission signal of the terminal 1, the transmission power information of the terminal 1 received from the macrocell 200 Based on the sensitivity setting of the receiver.

  As described above, when receiving the measurement request from the macro cell 200, the femtocells 300 to 304 start measuring the transmission signal from the terminal 1 based on the measurement request. Here, since the measurement content is the reception level, the reception level is measured. The reception level is higher in the cell located closer to the terminal 1. In the example of FIG. 2, the center part of the femtocells 300 and 301 (there is a receiving unit such as a base station) is closer to the terminal 1 than the receiving device 2 of the macrocell 200. For this reason, the femtocells 300 and 301 report to the macrocell 200 from the reporting condition of reporting when “the reception level of the transmission signal of the terminal in each femtocell is above and below the reference reception level”. An event “beyond the reference reception level” and the reception level of the transmission signal of the terminal 1 are reported. The femtocells 302 to 304 report nothing to the macrocell 200 because the reception level of the transmission signal from the terminal 1 is lower than the reference reception level from the start of measurement. Here, although it has been described that the receiving unit is at the center of the femto cell, the receiving unit does not have to be located at the center of the coverage of each cell. Think of it as a part.

  When the macro cell 200 receives a report from the femtocells 300 and 301 that the reception level of the transmission signal from the terminal 1 exceeds the reference reception level, the macrocell 200 can determine that the terminal 1 is in the vicinity of the femtocells 300 and 301. The information of the cells 300 and 301 is included in the monitor cell list and notified to the terminal 1. In the example of FIG. 2, only the femtocells 300 and 301 exist in the reachable range 100, but a large number of femtocells exist in the reachable range 100, and the reception level of the transmission signal from the terminal 1 is the reference reception level. It is also conceivable that the number of femto cells above the number exceeds the number of cells that can be included in the monitor cell list. In such a case, the macro cell 200 selects, for example, femto cells to be included in the monitor cell list in descending order of reception level included in the received report.

  Next, the terminal 1 notified of the monitor cell list from the macro cell 200 subsequently measures the radio quality of the femto cells 300 and 301 according to a predetermined handover procedure and reports it to the macro cell 200. The handover procedure at this time may be any handover procedure as long as it is normally performed. Here, the terminal 1 notifies the macro cell 200 of the cell with the best measured radio quality.

  For example, when the terminal 1 is located within the coverage of the femtocell 300, the terminal 1 reports the measurement result of the radio quality of the femtocells 300 and 301 to the macrocell 200 according to a predetermined handover procedure, and the macrocell 200 based on this report The terminal 1 can be handed over to the femtocell 300 with good radio quality.

  On the other hand, when the terminal 1 is located in the vicinity of the femtocell 300 but not within the coverage, or when the terminal 1 moves away from the femtocell 300 due to movement (in the process up to the monitor cell list transmission, the femtocell In the handover procedure, the handover to the femtocell 300 is not performed when the handover procedure is out of the coverage of the femtocell 300), and other handover destination femtocells are determined. A monitor cell list update operation is performed. FIG. 3 is a diagram for explaining the monitor cell list update operation when the terminal 1 moves. The monitor cell list update operation will be described below with reference to FIG.

  Assume that the terminal 1 moves from the vicinity of the femtocell 300 and is located within the coverage of the femtocell 303. It is assumed that transmission power control is performed between the macro cell 200 and the terminal 1 so that communication is performed with the minimum transmission power necessary for the transmission signal from the terminal 1 to reach the reception device 2. At this time, since the distance between the terminal 1 and the receiving apparatus 2 is small and the radio propagation environment is good, the transmission signal reachable range 100 of the terminal 1 is a minimum range including the receiving apparatus 2 as shown in FIG. Become.

  As a result of the transmission power control as described above, the transmission signal from the terminal 1 can reach only the macro cell 200 and the femto cell 303. Therefore, in the femtocells 300 and 301 that have received the transmission signal from the terminal 1 before that, the reception level of the transmission signal of the terminal 1 cannot be measured or becomes very small. For this reason, the femtocells 300 and 301 report to the macrocell 200 the event that the reference reception level has been lowered and the reception level of the transmission signal of the terminal 1.

  Based on the report from the femtocells 300 and 301, the macro cell 200 determines that the terminal 1 has moved to a position away from the vicinity of the femtocells 300 and 301, and deletes the femtocells 300 and 301 from the monitor cell list. On the other hand, in the femtocell 303, since the terminal 1 moves into the coverage of its own cell and the reception level of the transmission signal of the terminal 1 becomes higher than the reference reception level, an event that the reference reception level is exceeded and the reception level of the terminal 1 Is reported to the macro cell 200. Here, as shown in FIG. 3, it is assumed that terminal 1 has moved to a position closer to the center of femtocell 303 than receiving apparatus 2.

  Next, the macro cell 200 determines that the terminal 1 is located in the vicinity of the femtocell 303 based on the report from the femtocell 303, and creates a new monitor cell list including information on the femtocell 303. Notify In the monitor cell list notified at this time, the femtocells 300 and 301 are deleted based on the report that the reference reception level from the above-described femtocells 300 and 301 is below.

  After receiving the new monitor cell list, the terminal 1 measures the radio quality of the femtocell 303 in accordance with a predetermined handover procedure and reports it to the macrocell 200. Here, since the terminal 1 is located within the coverage of the femtocell 303, the terminal 1 reports the measurement result of the radio quality of the femtocell 303 to the macrocell 200, and the macrocell 200 transmits the terminal 1 to the femto based on this report. Handover to the cell 303 can be performed.

  In the above description, the reception level is the measurement content in order to use the reception level in each femtocell of the transmission signal of the terminal as an index for knowing the positional relationship between each femtocell and the terminal. Any device can be used as long as it can relatively determine the positional relationship between the terminal and the terminal. For example, a path loss may be used.

  As described above, in the present embodiment, the macro cell 200 causes the femto cells 300 to 304 to measure the reception level of the transmission signal from the terminal 1 and report the measurement result. Then, the macro cell selects a femto cell to be included in the monitor cell list based on the report. Therefore, the macro cell 200 can appropriately select a femto cell located in the vicinity of the terminal 1 and include it in the monitor cell list, and can appropriately select a handover destination.

Embodiment 3 FIG.
FIG. 4 is a diagram illustrating a configuration example of the third embodiment of the communication system according to the present invention. As shown in FIG. 4, the communication system of the present embodiment includes a terminal 1 (not shown in FIG. 4) similar to that of the first embodiment, femtocells 301 to 303, 310 to 312, 320, 330, 340 to 342, 350 to 352, 360, and 370, and macro cell 200 similar to that of the first embodiment. The femtocells 301 to 303, 320, 330, 340 to 342, 350 to 352, 360, and 370 are the same cells as the femtocells 300 to 304 of the first embodiment although the positional relationship is different from that of the first embodiment. Although many femtocells exist in or around the macrocell 200, femtocells that are not used in the description are omitted in FIG. The receiving device 2 is the same as the receiving device 2 of the second embodiment. Hereinafter, constituent elements having the same functions as those in the first embodiment or the second embodiment are denoted by the same reference numerals as those in the first or second embodiment, and the description thereof is omitted.

  In the second embodiment, the femtocells 300 to 304 receive the transmission signal of the terminal 1 communicating with the macrocell 200, and the femtocell with a good measurement result of the transmission signal reception quality is included in the monitor cell list. In the present embodiment, in addition to the femtocells with good reception quality measurement results of transmission signals of terminal 1, femtocells existing around these femtocells are also included in the monitor cell list.

  It is assumed that the terminal 1 is communicating with the macro cell 200. In the present embodiment, among the femtocells that exist in large numbers in or around the macrocell 200, femtocells 310, 320,..., 370 indicated by black circles in FIG. Limited to. In the present embodiment, these femtocells that measure the transmission signal from the terminal 1 are referred to as landmark cells. In the first embodiment, the landmark cell transmits a signal, and the terminal 1 receives the signal, so that the macro cell 200 grasps the position of the terminal 1. On the other hand, in the present embodiment, the landmark cell measures the transmission signal from the terminal 1, and the macro cell 200 grasps the position of the terminal 1 based on the measurement result.

  In this embodiment, femtocells are grouped into a plurality of groups based on their positions. Regions 600 to 608 indicated by a one-dot chain line in FIG. 4 are virtual regions that define a group of femtocells. For example, femtocells 301 to 303 existing in region 600 form one group, and femtocells 310 to 312 existing in region 601 form another group. Similarly, in other regions, femtocells included in the region are grouped into one group. If there is a femto cell that exists across the boundary of the region, for example, the femto cell may be included in a group having a larger portion where the region and cell coverage overlap. Then, one of the femtocells included in the group is selected as a landmark cell.

  Here, the area is divided as shown in FIG. 4, but the landmark cell (including the receiving device 2 as described later) can be used regardless of where the terminal 1 exists in the coverage of the macro cell 200. May be divided in any way as long as the transmission signal of the terminal 1 can be received without omission and the number of femtocells belonging to the region is the same. Moreover, it is not necessary to divide each area | region so that it may have simple shapes, such as a circle | round | yen and a fan shape, and a complicated shape may be sufficient by the deviation of arrangement | positioning of actual topography, a structure, and femtocell. Moreover, each area | region may mutually overlap.

  Next, the operation of the present embodiment will be described. Hereinafter, since the operation differs depending on the position of the terminal 1, (1) when the terminal 1 exists near the center of the macro cell 200, (2) when the terminal 1 exists in the middle part of the macro cell 200, (3) the terminal 1 The description will be divided into three cases where the macro cell 200 exists in the peripheral portion.

  First, (1) the case where the terminal 1 exists near the center of the macro cell 200 will be described. FIG. 5 is an enlarged view of an area 600 near the center of the macro cell 200, and the transmission range 100 of the transmission signal of the terminal 1 when the terminal 1 communicating with the macro cell 200 is located in the vicinity of the receiving device 2. And the positional relationship between each femtocell.

  As shown in FIG. 5, when the terminal 1 is located in the vicinity of the receiving device 2, the reachable range 100 is the minimum range including the receiving device 2 by transmission power control. In some cases, the transmission signal of the terminal 1 cannot be received. Therefore, no landmark cell is provided in the region 600 including the receiving device 2 of the macro cell 200. Instead, the receiving device 2 itself (the macro cell 200 itself) measures the reception quality of the transmission signal of the terminal 1 and determines whether or not the terminal 1 exists in the area 600. In this case, the macro cell 200 itself can be considered as a landmark cell. When the macro cell 200 determines that the terminal 1 exists in the area 600, the macro cell 200 includes information on the femto cells 301 to 303 belonging to the group corresponding to the area 600 in the monitor cell and notifies the terminal 1 of the information. Thereafter, a predetermined handover procedure is performed as in the second embodiment.

  Next, (2) a case where the terminal 1 is located in the middle part of the macro cell 200 (a case where the terminal 1 is located in the areas 601 to 604 in FIG. 4) will be described. The macro cell 200 calculates the approximate distance between the receiving device 2 and the terminal 1 based on the reception quality of the transmission signal of the terminal 1, and determines that the terminal 1 is located in any one of the areas 601 to 604. And Since the terminal 1 is movable, there is a possibility that the terminal 1 is moving in the direction of the area 600, and conversely, there is a possibility that the terminal 1 is moving toward the areas 605 to 608. Therefore, the macro cell 200 includes the landmark cells 310, 320, and 330 in the areas 601 to 604 that are determined to be present when the approximate distance from the terminal 1 is calculated, and the area 600 in which the terminal 1 may move. And the landmark cells 340, 350, 360, and 370 in the areas 605 to 608 are requested to measure the reception quality of the transmission signal from the terminal 1 in the same manner as requested to each femtocell in the second embodiment. . In the area 600, since the receiving device 2 of the macro cell 200 has the role of a landmark cell as described above, there is no need to transmit a request, and the macro cell 200 measures the reception quality of the transmission signal from the terminal 1 by itself. To do.

  At this time, the reporting condition for reporting from each landmark to the macro cell 200 is “when the reception level of the transmission signal from the terminal 1 is above and below a predetermined threshold”, and the predetermined threshold is the macro cell A value lower by a certain amount than the reception quality of the terminal 1 at 200 is set. The set threshold value is notified from the macro cell 200 to each landmark. Notification may be included in the measurement request. In the present embodiment, the threshold value is determined in this manner in the monitor cell list as described later, in addition to the landmark cell whose reception quality is measured based on the request, as well as other femto areas to which the landmark cell belongs. This is because cells are also included and other femtocells may have better reception quality of transmission signals from terminal 1 (other femtocells may be closer to terminal 1 than landmark cells).

  Each landmark cell measures the reception quality of the transmission signal of the terminal 1 in accordance with the measurement request from the macro cell 200, and reports the reception quality to the macro cell 200 when the reception quality satisfies the above reporting condition. Since the subsequent operations differ depending on the position of the terminal 1, further (a) when the terminal 1 is located near the center of the area, (b) the terminal 1 is located near the boundary between the areas 600, 601, and 602. This will be described using two typical examples.

  First, (a) the case where the terminal 1 is located near the center of the area will be described. FIG. 6 is a diagram illustrating a positional relationship between the reach 100 and the femtocell when the terminal 1 is located near the center of the region 601. Here, description will be made assuming a positional relationship as shown in FIG. The landmark cell 310 measures the reception quality of the transmission signal of the terminal 1 in accordance with the measurement request from the macro cell 200 described above, and reports the measurement result to the macro cell 200 because the measurement result exceeds the threshold value. In landmark cells other than the landmark 310, the reception quality of the transmission signal from the terminal 1 is not measurable or very poor and does not satisfy the threshold value. When the reception quality of the terminal 1 reported from the landmark cell is better than the reception quality of the terminal 1 measured by the macro cell 200, the macro cell 200 displays information on the femtocells 310 to 312 belonging to the area 601 to which the landmark cell 310 belongs. The monitor cell list including this is transmitted to the terminal 1.

  FIG. 7 is a diagram illustrating an example of a reception quality profile reported in the arrangement example illustrated in FIG. 6. The threshold A indicates a threshold for the above-described report (a value lower than the reception quality of the terminal 1 in the macro cell 200 by a certain amount). In this way, in the example of FIG. 6, the reception quality of the terminal 1 at the landmark cell 310 is higher than the reception quality at the macro cell 200, so the macro cell 200 includes the monitor cell list including information on the femto cells 310 to 312. Is transmitted to the terminal 1.

  Next, (b) the case where the terminal 1 is located near the boundary between the regions 600, 601, and 602 will be described. FIG. 8 is a diagram showing the positional relationship between the reach 100 and each femtocell when the terminal 1 is located near the boundary of three regions (regions 600, 601, and 602). In the positional relationship shown in FIG. 8, landmark cells 310 and landmark cells 320 are landmark cells that can measure the reception quality of the transmission signal of terminal 1. Therefore, the macro cell 200 receives the reception quality report from the landmark cells 310 and 320.

  FIG. 9 is a diagram showing an example of a reception quality profile reported in the arrangement example shown in FIG. As shown in FIG. 9, since the reception quality is the same in the landmark cell 310, the landmark cell 320, and the macro cell 200, the reception device 2 of the landmark cells 310, 320 and the macro cell 200 belongs to the macro cell 200. Information on femtocells 301 to 303, 310 to 312 and 320 belonging to areas 600 to 602 is included in the monitor cell list and transmitted to terminal 1. Note that the condition for determining that reception qualities are equal may be included not only when the numerical values completely match but also when the difference in reception qualities is within a predetermined range.

  When femtocells included in the monitor cell list extend over a plurality of regions as in this example, the number of candidate femtocells may exceed the maximum number of cells that can be included in the monitor cell list. In that case, any number of femtocells that can be included in the monitor cell list may be selected and included in the monitor cell list, or the femtocell to be included in the monitor cell list may be implemented. A request for measurement may be made in the same manner as in mode 2, and a monitor cell list to be included in the monitor cell list may be selected.

  After the monitor cell list is transmitted to the terminal 1 as described above, a predetermined handover procedure is executed as in the second embodiment.

  Next, (3) a case where the terminal 1 is located in the periphery of the macro cell 200 will be described. The macro cell 200 calculates the approximate distance between the macro cell 200 and the terminal 1 based on the reception quality of the transmission signal of the terminal 1 as in the case where the terminal 1 is located in the middle part of the macro cell 200 (2). Then, the macro cell 200 determines that the terminal 1 is located in any one of the areas 605 to 608 based on the calculated distance. Since the terminal 1 is movable, it may move in the direction of the regions 600 to 603, and conversely, may move in a direction away from the coverage of the macro cell 200.

  In the case of (3), unlike the case of (2) above, when the terminal 1 is moving in a direction away from the coverage of the macro cell 200, it is not necessary to perform handover to the femto cell in the macro cell 200. Another macro cell adjacent to the macro cell 200 becomes a handover destination candidate. Therefore, the macro cell 200 includes the landmark cells 340, 350, 360, and 370 in the areas 605 to 608 where the terminal 1 is supposed to exist when the distance is calculated, and the areas 601 to 604 in which the terminal 1 may move. The landmark cells 310, 320, and 330 are requested to measure the reception quality of the terminal 1 as in the second embodiment.

  At this time, the condition for reporting from each femtocell to the macrocell 200 is “when the reception level of the transmission signal from the terminal 1 exceeds and falls below a predetermined threshold”. Unlike the case of (2), the predetermined threshold value is set to a value higher than the reception quality of the terminal 1 in the macro cell 200 by a certain amount. The set threshold value is notified from the macro cell 200 to each landmark. Notification may be included in the measurement request. In the case of (3) where transmission power control is performed, the threshold value is set in this way, among the femtocells existing in the areas 605 to 608 and 601 to 604, the transmission signal of the terminal 1 is set. This is because, in any femtocell that arrives, the reception quality does not fall below the reception quality of the transmission signal of the terminal 1 in the macro cell 200.

  Each landmark cell measures the reception quality of the transmission signal of the terminal 1 in accordance with the measurement request from the macro cell 200, and reports the reception quality to the macro cell 200 when the reception quality satisfies the above reporting condition. Since subsequent operations differ depending on the position of the terminal 1, further (c) when the terminal 1 is located near the center of the area 605, (d) the terminal 1 is located near the boundary between the areas 601 and 605. A description will be given using two typical examples.

  First, (c) the case where the terminal 1 is located near the center of the area 605 will be described. FIG. 10 is a diagram illustrating the positional relationship between the reach 100 and the femtocell when the terminal 1 is located near the center of the region 605. At this time, the landmark cells 310 and the landmark cells 340 have good reception quality of the transmission signal of the terminal 1. Therefore, the macro cell 200 receives the reception quality report from the landmark cells 310 and 340. FIG. 11 is a diagram showing an example of a reception quality profile reported in the arrangement example shown in FIG. As shown in FIG. 11, since the reception quality at the landmark cell 340 is higher than the reception quality at the landmark cell 310, the macro cell 200 includes information on the femtocells 340 to 342 belonging to the region 605 to which the landmark cell 340 belongs. The monitor cell list is transmitted to the terminal 1.

  Next, (d) the case where the terminal 1 is located near the boundary between the areas 601 and 605 will be described. FIG. 12 is a diagram illustrating a positional relationship between the reach 100 and the femtocell when the terminal 1 is located near the boundary between the region 601 and the region 605. At this time, landmark cells 310 and landmark cells 340 have good reception quality of the transmission signal of the terminal 1. Therefore, the macro cell 200 receives the reception quality report from the landmark cells 310 and 340. FIG. 13 is a diagram showing an example of a reception quality profile reported in the arrangement example shown in FIG. As shown in FIG. 13, the reception quality at the landmark cell 340 is the best, and the difference between the reception quality of the landmark cell 310 and the reception quality of the landmark cell 340 is within a predetermined range (a large difference). Therefore, the macro cell 200 transmits to the terminal 1 a monitor cell list including information on the femtocells 340 to 342 and 310 to 312 belonging to the areas 605 and 601 in the monitor cell list.

  As described above, when the number of femto cells to be included in the monitor cell list exceeds a maximum number that can be included in the monitor cell list when the number of femto cells to be included in the monitor cell list exceeds a plurality of areas, the same as (2) above. A femto cell may be selected.

  After the monitor cell list is transmitted to the terminal 1 as described above, a predetermined handover procedure is executed as in the second embodiment.

  As described in the examples (1) to (3) above, in the present embodiment, the method for determining the femtocell to include information in the monitor cell list varies depending on the distance between the receiving device 2 and the terminal 1. The macro cell 200 measures the reception quality of the terminal 1 (the macro cell 200 communicates with the terminal 1 and can therefore always measure the reception quality), and calculates the distance between the macro cell 200 and the terminal 1 based on the measurement result. The measurement may be performed at a predetermined cycle or irregularly. Then, depending on the calculated distance, it is determined which of the operations described in the above (1) to (3) is to be performed. When the distance between the receiving device 2 and the terminal 1 changes, the operation procedure is switched according to the distance. In addition, when the terminal 1 moves without changing the distance with the macro cell 200, for example, when the cell that reports the reception quality of the transmission signal of the terminal 1 moves within the intermediate units 601 to 604 of the macro cell 200 changes. Therefore, the monitor cell list update operation may be performed as in the second embodiment.

  In the present embodiment, the distance between the macro cell 200 and the terminal 1 is calculated and the operation procedure is switched based on the calculation result. However, the reception quality is not calculated without calculating the distance between the macro cell 200 and the terminal 1. Information on femtocells belonging to an area to which a landmark cell exceeding a predetermined threshold belongs may be included in the monitor cell list. In this case, since the femtocell in the area considering the movement of the terminal 1 is not notified, when the terminal 1 moves after the monitor cell list notification and before the handover, the same as in the second embodiment. A monitor cell list update operation may be performed.

  Also in this embodiment, each femtocell may measure the terminal 1 while communicating with the terminal that is communicating with the own cell. The transmission power information of the terminal 1 may be included in the measurement request and transmitted to the femtocell so that the reception sensitivity of each femtocell can be switched.

  As described above, in the present embodiment, femto cells existing inside and around the macro cell 200 are grouped based on the position, and one femto cell in the group is selected as a landmark cell. Then, the macro cell 200 measures the reception quality of the transmission signal of the terminal 1 communicating with the own cell, calculates the distance of the receiving device 2 based on the measurement result, and determines the operation procedure based on the distance. . Further, in each operation procedure, the macro cell 200 estimates a group that the terminal 1 is supposed to exist on the basis of the reception quality of the terminal 1 measured by the landmark cell, and the femto belonging to the group and a group around the group. The cell is included in the monitor cell list and notified to the terminal 1. For this reason, even when there are more femto cells in and around the macro cell 200 than the number of cells in which the terminal 1 can measure the radio quality, the macro cell 200 can appropriately select the handover destination candidate of the terminal 1, and the macro cell Can be smoothly handed over to the femtocell.

  In this embodiment, the landmark cells are fixed. However, a set of a plurality of landmark cells may be defined, and a set of landmark cells used for each terminal that performs handover control may be used properly. In this case, the load for measuring the reception quality for updating the monitor cell list can be distributed.

  As described above, the monitor cell list notification method and the communication system according to the present invention are useful for a communication system for notifying mobile terminals of cell information of handover destination candidates, and in particular, a large number of femtocells in and around a macro cell. Suitable for including communication systems.

It is a figure which shows the structural example of Embodiment 1 of the communication system concerning this invention. It is a figure which shows the structural example of Embodiment 2 of the communication system concerning this invention. It is a figure for demonstrating the monitor cell list update operation | movement when a terminal moves. It is a figure which shows the structural example of Embodiment 3 of the communication system concerning this invention. It is the figure which expanded the area | region near the center of a macrocell. It is a figure which shows the positional relationship of the reachable range and femtocell when a terminal is located near the center of an area | region. It is a figure which shows an example of the profile of the reception quality reported by the example of arrangement shown in FIG. It is a figure which shows the positional relationship of the reachable range and each femtocell when a terminal is located near the boundary of three area | regions. It is a figure which shows an example of the profile of the reception quality reported by the example of arrangement | positioning shown in FIG. It is a figure which shows the positional relationship of the reachable range and femtocell when a terminal is located near the center of an area | region. It is a figure which shows an example of the profile of the reception quality reported by the example of arrangement shown in FIG. It is a figure which shows the positional relationship of the reachable range and femtocell when a terminal is located in the boundary vicinity of an area | region. It is a figure which shows an example of the profile of the reception quality reported by the example of arrangement shown in FIG.

Explanation of symbols

1 Terminal 2 Receiving Device 100 Reaching Range 200 Macro Cell 300 to 304, 311, 312, 341, 342, 351, 352 Femto Cell 310, 320, 330, 340, 350, 360, 370, 400, 401 Landmark Cell 600 to 608 Area A Threshold

Claims (13)

In a communication system in which a terminal, a standard cell in communication with the terminal, and a small cell having a cell radius smaller than the standard cell exist in or around the coverage of the standard cell, the standard cell moves the terminal to the small cell. A monitor cell list notification method for notifying the terminal of a monitor cell list including information for measuring reception quality of a candidate cell that is a candidate for a handover destination,
A landmark placement step of placing a landmark cell that overlaps at least part of the coverage with the small cell;
A landmark cell reception quality measurement step in which the terminal measures reception quality of the landmark cell based on a measurement request transmitted from the standard cell;
A reception quality reporting step in which the terminal reports the reception quality to the standard cell;
A landmark cell selecting step in which the standard cell selects a landmark cell having the best reception quality based on the report;
A monitor cell list notifying step of notifying the terminal of the standard cell, including information on the small cell that overlaps at least part of the coverage with the selected landmark cell, in the monitor cell list;
A method of notifying a monitor cell list, comprising:   The measurement content requested by the measurement request, the report condition, and the report cycle are set so that the measurement result based on the measurement request is reported in a shorter cycle than the measurement result report based on the monitor cell list. The monitor cell list notification method according to claim 1. In a communication system in which a terminal, a standard cell in communication with the terminal, and a small cell having a cell radius smaller than the standard cell exist in or around the coverage of the standard cell, the standard cell moves the terminal to the small cell. A monitor cell list notification method for notifying the terminal of a monitor cell list including information for measuring reception quality of a candidate cell that is a candidate for a handover destination,
A measurement instruction step in which the standard cell transmits a measurement instruction to instruct the small cell to measure the reception quality of the terminal;
A reception quality measuring step in which the small cell measures the reception quality of the terminal based on the measurement instruction;
A reception quality reporting step in which the small cell reports the reception quality to the standard cell;
A small cell selection step in which the standard cell selects the candidate cell based on the reception quality;
A monitor cell list notifying step in which the standard cell includes the candidate cell information in the monitor cell list and notifies the terminal;
A method of notifying a monitor cell list, comprising:   4. The monitor cell list notification method according to claim 3, wherein, in the small cell selection step, a small cell whose reception quality exceeds a predetermined threshold is selected as the candidate cell.   The small cell selection step selects a predetermined number of small cells in order of good reception quality from among the small cells whose reception quality exceeds a predetermined threshold as the candidate cells. 4. The monitor cell list notification method according to 3. Dividing the standard cell into a plurality of areas, and selecting one landmark cell for each of the areas from the small cells;
In the measurement instruction step, the transmission target of the measurement instruction is the landmark cell,
In the small cell selection step, a landmark cell whose reception quality exceeds a predetermined threshold and a small cell that belongs to the same area as the landmark cell and is not selected as a landmark cell are selected as the candidate cell. The monitor cell list notification method according to claim 3, wherein the monitor cell list notification method is selected. The standard cell measures the reception quality of the terminal, and calculates a distance to the terminal based on the measurement result;
An area estimation step in which the standard cell obtains an area where a terminal may exist based on the distance as an estimation area from the plurality of areas;
Further including
7. The monitor cell according to claim 6, wherein in the measurement instruction step, the transmission target of the measurement instruction is a landmark cell belonging to the estimation area and a landmark cell adjacent to the estimation area. List notification method. A terminal reception quality measurement step in which the standard cell measures reception quality of the terminal;
Further including
7. The monitor cell list notification method according to claim 4, wherein the standard cell determines the threshold based on the reception quality measured in the terminal reception quality measurement step. .   8. The monitor cell list notification method according to claim 7, wherein the standard cell determines the threshold based on the reception quality measured in the distance calculation step.   The standard cell transmits measurement information necessary for measuring the reception quality of the terminal to small cells in or around the coverage of the standard cell. The monitor cell list notification method described. The measurement information includes the transmission power information of the terminal received by the standard cell from the terminal,
11. The monitor cell list notification method according to claim 10, wherein in the reception quality measurement step, the small cell adjusts reception sensitivity based on the transmission power information. There is a terminal, a standard cell in communication with the terminal, and a small cell having a cell radius smaller than that of the standard cell in or around the coverage of the standard cell, and the standard cell hands over the terminal to the small cell. Therefore, a communication system for notifying the terminal of a monitor cell list including information for measuring reception quality of a candidate cell that is a candidate for a handover destination,
A landmark cell that overlaps at least part of the coverage with the small cell,
The terminal measures the reception quality of the landmark cell based on a measurement request transmitted from the standard cell, and reports the reception quality to the standard cell;
The standard cell selects a landmark cell having the best reception quality based on the report, and includes information on the small cell that overlaps at least a part of the coverage with the selected landmark cell in the monitor cell list. A communication system characterized by notifying a terminal. There is a terminal, a standard cell in communication with the terminal, and a small cell having a cell radius smaller than that of the standard cell in or around the coverage of the standard cell, and the standard cell hands over the terminal to the small cell. Therefore, a communication system for notifying the terminal of a monitor cell list including information for measuring reception quality of a candidate cell that is a candidate for a handover destination,
The small cell measures the reception quality of the terminal based on an instruction from the standard cell, and reports the reception quality to the standard cell;
The communication system, wherein the standard cell selects the candidate cell based on the reception quality, includes the information on the candidate cell in the monitor cell list, and notifies the terminal.

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