JP2013059126A - Communication control device and communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a communication device to use a plurality of cell IDs.SOLUTION: A communication control device 300 includes control units 303, 304. The control unit 303 allows a communication device 200 to transmit a radio signal including a control channel region and an individual channel region of a first cell ID. The control unit 303 does not allow the communication device 200 to transmit a radio signal of the first cell ID in a portion of a resource element of the individual channel region of the first cell ID. The control unit 304 allows the communication device 200 to transmit a radio signal including the control channel region and the individual channel region of a second cell ID different from the first cell ID, in a manner to overlap the time position of the control channel region of the second cell ID with the time position of the individual channel region of the first cell ID.

Description

  Embodiments relate to wireless communication.

  In 3GPP (3rd Generation Partnership Project), a standard for a high-speed cellular radio communication system called LTE (Long Term Evolution) has been established. LTE employs Orthogonal Frequency Division Multiple Access (OFDMA) technology in downlink communication. OFDMA can increase multipath tolerance through the use of cyclic prefixes. That is, OFDMA is suitable for a technique that covers a wide service area by transmitting the same signal from a plurality of different transmission points at the same frequency. Such a technique is called “Single Frequency Network (SFN)”, but in the following description, the technique is referred to as “same frequency transmission” for convenience in order to distinguish it from SFN (System Frame Number).

  The number of sequences used in each LTE cell, and the sequences used for control channel and dedicated channel communication are determined by cell-specific ID (identification information) called cell ID (Cell-ID). For example, if a plurality of access points (radio signal transmission / reception points) use the same cell ID, a service by the same frequency transmission can be provided. In other words, handover does not occur even when the user terminal freely moves within the service areas of these access points. For example, even if the user terminal leaves the service area of a certain access point, communication can be continued without handover if the user terminal exists within the service area of the access point using the same cell ID. On the other hand, since the number of sequences used in each cell is determined by the cell ID as described above, there is an upper limit on the number of user terminals that can be accommodated by a single cell ID. That is, if a plurality of access points use different cell IDs, the number of user terminals that can be accommodated can be increased.

  However, it is difficult to change the cell ID used by the access point. For example, if the access point suddenly stops using the current cell ID, the user terminal accommodated in the access point by this cell ID is disconnected. On the other hand, changing the cell ID in a time zone with little traffic such as at night can alleviate the influence of the above problem, but the time zone in which the cell ID can be changed is limited. That is, it is difficult to change the cell ID flexibly. Moreover, even if the cell ID before the change and the cell ID after the change are used together as a transition measure, the interference between both becomes a problem.

JP 2010-226704 A

[Online], Internet <URL: http://www.3gpp.org/ftp/specs/latest/Rel-8> [Online], Internet <URL: http://www.wimaxforum.org/>

  Accordingly, an object of the embodiment is to make a communication device use a plurality of cell IDs.

  The communication control device includes a first control unit and a second control unit. The first control unit causes the communication device to transmit a radio signal including the control channel region and the dedicated channel region of the first cell ID. The first control unit does not cause the communication device to transmit the radio signal of the first cell ID in a part of the resource elements in the dedicated channel region of the first cell ID. The second control unit sends a radio signal including a control channel region and a dedicated channel region of the second cell ID different from the first cell ID to the communication device, and a time position of the control channel region of the second cell ID and the first Are transmitted so that the time positions of the individual channel areas of the cell IDs overlap.

1 is a block diagram illustrating a communication control device and a plurality of access points according to an embodiment. The figure which illustrates the 1st phase for cell ID change. The figure which illustrates the 2nd phase for cell ID change. The figure which illustrates the 3rd phase for cell ID change. The figure which illustrates the radio | wireless resource structure of LTE. The figure which illustrates the radio | wireless frame structure of the LTE of a TDD system. The figure which shows an example of allocation of the cell ID in each sub-frame. The figure which shows an example of allocation of the cell ID in each sub-frame. Explanatory drawing of operation | movement of the communication control apparatus which concerns on 4th Embodiment. Explanatory drawing of operation | movement of the communication control apparatus which concerns on 5th Embodiment. Explanatory drawing of operation | movement of the communication control apparatus which concerns on 6th Embodiment. Explanatory drawing of operation | movement of the communication control apparatus which concerns on 7th Embodiment. Explanatory drawing of operation | movement of the communication control apparatus which concerns on 8th Embodiment. Explanatory drawing of operation | movement of the communication control apparatus which concerns on 8th Embodiment.

Hereinafter, embodiments will be described with reference to the drawings. In each embodiment, the same or similar elements as those already described are denoted by the same or similar reference numerals, and redundant description is basically omitted. In addition, each embodiment is described mainly on the premise of LTE for concrete description, but each embodiment can be appropriately applied to other types of wireless communication systems.
(First embodiment)
A communication control device according to an embodiment controls at least one communication device. In the example of FIG. 1, the communication control apparatus 300 controls two access points (AP) 100 and 200, respectively. In the following description, in each embodiment, control of the cell ID of the access point 200 by the communication control device 300 will be mainly described. Of course, the communication control apparatus according to each embodiment may control two or more communication apparatuses in the same or similar manner.

  The Axpoint 100 includes an interface (I / F) 101, an L2 (layer 2) processing unit 102, an L1 (layer 1) processing unit 103, a radio unit 104, and an antenna 105. The access point 100 performs lower layer processing than the communication control device 300. The interface 101 functions as an interface between the access point 100 and the communication control device 300.

  The L2 processing unit 102 performs processing of a so-called layer 2 (for example, a media access control (MAC) layer, a radio link control (RLC) layer).

  The L1 processing unit 103 performs so-called layer 1 (physical (PHY) layer) processing. The radio unit 104 performs radio signal processing (for example, up-conversion for radio signal transmission, filtering, power amplification, etc., down-conversion for radio signal reception, filtering, low-noise amplification, etc.).

  The antenna 105 transmits and receives radio signals. The antenna 105 may or may not be considered part of the access point 100 element. In other words, the antenna 105 may be built in the access point 100 or may be externally attached. The number of antennas 105 may be plural.

  Note that the access point 100 and the communication control apparatus 300 can be functionally divided from a viewpoint different from FIG. For example, the interface 101 may be disposed between the L2 processing unit 102 and the L1 processing unit 103, and the L2 processing unit 102 may be included in the communication control apparatus 300. Further, the interface 101 may be disposed between the L1 processing unit 103 and the wireless unit 104, and the L2 processing unit 102 and the L1 processing unit 103 may be included in the communication control apparatus 300. Furthermore, the interface 101 may be disposed between the wireless unit 104 and the antenna 105, and the L2 processing unit 102, the L1 processing unit 103, and the wireless unit 104 may be included in the communication control device 300. That is, the access point 100 only needs to be a wireless signal transmission / reception point (for example, RRU (Remote Radio Unit) is also included).

  The access point 200 is the same as or similar to the access point 100, and includes an I / F 201, an L2 processing unit 202, an L1 processing unit 203, a radio unit 204, and an antenna 205. The description of each part of the access point 200 is omitted because it overlaps with the description of each part of the access point 100.

  The communication control apparatus 300 includes interfaces 301 and 302, RRC (Radio Resource Control) units 303 and 304, a communication control unit 305, and a switching unit 306.

  The interface 301 functions as an interface between the communication control device 300 and the access point 100. The interface 302 functions as an interface between the communication control device 300 and the access point 200.

  The RRC units 303 and 304 are controlled by a communication control unit 305 described later. The RRC units 303 and 304 perform RRC processing in LTE, for example. The RRC unit 303 allocates radio resources for the first cell ID (also referred to as Cell-ID1 in the following description). The RRC unit 304 allocates radio resources for the second cell ID (also referred to as Cell-ID2 in the following description). Further, in accordance with LTE, the RRC units 303 and 304 are connected to an external network device or the like through the S1 interface. Cell-ID1 and Cell-ID2 provide services in the same frequency band.

  The communication control unit 305 controls the RRC units 303 and 304 and the switch 306. The switch 306 connects the RRC unit 303 to one or both of the interfaces 301 and 302 or does not connect to either of them according to a command from the communication control unit 305. Further, the switch 306 connects the RRC unit 304 to one or both of the interfaces 301 and 302 or does not connect to either of them according to a command from the communication control unit 305.

  For example, the communication control unit 305 can cause both the access points 100 and 200 to use Cell-ID 1 by connecting the RRC unit 303 to both the interfaces 301 and 302. That is, as shown in FIG. 2A, the access points 100 and 200 can perform the same frequency transmission. On the other hand, the communication control unit 305 can cause the access points 100 and 200 to use Cell-ID1 and Cell-ID2 by connecting the RRC unit 303 to the interface 301 and connecting the RRC unit 304 to the interface 302, respectively. . That is, as shown in FIG. 2C, the access points 100 and 200 can provide different cells.

  Here, it is assumed that the communication control apparatus 300 changes the cell ID used by the access point 200 from Cell-ID1 to Cell-ID2 (that is, when shifting from the phase of FIG. 2A to the phase of FIG. 2C). . As described above, when the cell ID assignment shown in FIG. 2A is immediately changed to the cell ID assignment shown in FIG. 2C, the communication of the user terminals 402, 403, 404 accommodated by Cell-ID1, for example, is disconnected. End up.

  Therefore, the communication control device 300 does not immediately change from the phase of FIG. 2A to the phase of FIG. 2C, but incorporates the phase shown in FIG. 2B between them. In the phase of FIG. 2B, the access point 200 uses both Cell-ID1 and Cell-ID2. Therefore, it is possible to prompt the user terminals 402, 403, 404 to be handed over to Cell-ID2 while the communication of the user terminals 402, 403, 404 is maintained.

  However, the cell ID assignment shown in FIG. 2B means that the access point 200 transmits a radio signal defined by two cell IDs. Therefore, interference occurs between the two, and there is a possibility that communication between the access point 200 and the user terminals 402, 403, 404 becomes difficult.

  By the way, LTE radio resources are configured by resource elements defined by subcarriers and OFDMA symbols, as illustrated in FIG. The t axis is a time axis, and each grid represents a symbol (t0,..., t13). The f-axis is a frequency axis, and each grid represents a subcarrier (f0,..., f23). In LTE, a basic resource block is composed of 14 symbols × 12 subcarriers. In the example of FIG. 3, the first resource block is composed of subcarriers f0,..., F11 × symbols t0,..., T13, and the second resource block is subcarriers f12,. Symbol t0,..., T13. Strictly speaking, although there are at least six resource blocks used in LTE, FIG. 3 illustrates two resource blocks for simplicity.

  The dedicated channel region is provided for each resource block. In the example of FIG. 3, subcarriers f0,..., F11 in symbols t3,..., T13 are individual channel regions of the first resource block, and subcarriers f12, symbols t3,. ..., F23 is an individual channel region of the second resource block. The dedicated channel region of each resource block may be assigned to the same user or may be assigned to different users. On the other hand, the control channel region is provided over a large number of subcarriers in order to obtain a frequency diversity effect. Specifically, the control channel region is provided across a plurality of resource blocks. In the example of FIG. 3, all subcarriers f0,..., F23 in symbols t0,. All user terminals receive the control channel region. In the control channel region, information indicating the position of the radio resource (resource block) assigned to each user terminal is transmitted.

  The reference signal is transmitted in the resource element with hatching in FIG. The reference signal carries known data. For example, the user terminal can perform propagation path estimation or measure the reception quality of the cell by comparing the known data carried by the reference signal with the received data.

  Considering the radio resource configuration as described above, interference in the case of using a plurality of cell IDs can be avoided at least in the dedicated channel region. For example, if the communication control apparatus 300 assigns the Cell-ID1 signal to the dedicated channel region of the first resource block and assigns the Cell-ID2 signal to the dedicated channel region of the second resource block, both transmission frequencies Interference can be avoided because the bands are different. However, since the control channel region is provided across a plurality of resource blocks as described above, it is difficult to avoid interference by the above method. Therefore, as will be described later, the communication control apparatus 300 according to the present embodiment attempts to avoid interference by assigning different cell IDs in a time division manner.

  FIG. 4 illustrates an LTE radio frame configuration in a time division duplex (TDD) scheme. According to TDD, uplink (UL) transmission and downlink (DL) transmission are performed in a time division manner. The radio frame in FIG. 4 includes 10 subframes, and each subframe is given a time length of 1 msec. That is, a time length of 10 msec is given to one radio frame. The subframe number represents a logical number of the subframe. Downlink transmission is performed in subframes # 0, # 3, # 4, # 5, # 8, and # 9. In subframes # 2 and # 7, uplink transmission is performed. Subframes # 1 and # 6 are prepared for switching from downlink transmission to uplink transmission, and include a guard period (GP).

  For the radio frame configuration of FIG. 4, the communication control apparatus 300 performs cell ID assignment as shown in FIG. 5, for example. According to the cell ID assignment of FIG. 5, the access point 200 transmits a Cell-ID2 radio signal in subframe # 0, transmits a Cell-ID1 radio signal in subframe # 3, and in subframe # 4. Cell-ID2 radio signal is transmitted. That is, the cell ID used by the access point 200 is switched on a subframe basis. The cell-ID1 radio signal and the cell-ID2 radio signal are transmitted in different subframes. Therefore, interference between the two does not occur.

  For example, as shown in FIG. 2B, the access point 200 can use both Cell-ID1 and Cell-ID2 while avoiding interference. Therefore, the user terminals 402, 403, and 404 in the vicinity of the access point 200 are urged to perform handover to Cell-ID2 with respect to the user terminals 402, 403, and 404 while maintaining communication (using Cell-ID1). After these user terminals 402, 403, and 404 are handed over to Cell-ID2, the communication control device 300 causes the access point 200 to stop using Cell-ID1, as shown in FIG. 2C, for example, and Cell-ID2 Continue to use. By such a series of controls, the cell ID used by the access point 200 can be changed (from Cell-ID1 to Cell-ID2) without disconnecting the communication of the user terminals 402, 403, and 404.

  In the phase in which the access point 200 uses both Cell-ID1 and Cell-ID2 as shown in FIG. 2B, the user terminals 402, 403, and 404 near the access point 200 are handed over to Cell-ID2. In order to effectively promote the communication, the communication control apparatus 300 may perform the following additional control. For example, the communication control apparatus 300 may change in time the ratio between the number of subframes in which the access point 200 uses Cell-ID1 and the number of subframes in which Cell-ID2 is used in one radio frame. . Specifically, the communication control apparatus 300 may perform control such that the number of subframes that cause the access point 200 to use Cell-ID2 relatively increases with the passage of time. Further, the communication control apparatus 300 may change the transmission power when the access point 200 uses each cell ID over time. Specifically, the communication control apparatus 300 performs control such that the transmission power becomes relatively small when the access point 200 uses Cell-ID1 over time, or uses Cell-ID2. Control may be performed such that the transmission power at the time is relatively large.

  As described above, when the communication control apparatus according to the first embodiment changes the cell ID used by the access point, the access point uses both the cell ID before the change and the cell ID after the change. Provide a phase to use. In this phase, the communication control apparatus switches the cell ID used by the access point in units of subframes. Therefore, according to the communication control apparatus according to the present embodiment, since the subframes in which the radio signal of the cell ID before the change and the radio signal of the cell ID after the change are transmitted are different, the access point avoids interference between the two. However, both cell IDs can be used. That is, the communication of the user terminals accommodated by the cell ID before the change is not disconnected, and these user terminals are prompted to perform handover to the cell ID after the change. Therefore, the cell ID can be changed flexibly. For example, the communication control device can easily change the cell ID of the access point even in a time zone with heavy traffic such as during the daytime.

(Second Embodiment)
The communication control apparatus according to the first embodiment switches the cell ID used by the access point in units of subframes. That is, the cell ID is exclusively used in each subframe.

  Incidentally, as described above, according to the LTE specification, a reference signal is transmitted in a specific resource element. Then, the user terminal uses the signal strength of the reference signal (that is, reference signal received power (RSRP)) as an index for determining handover, for example.

  If the cell ID is exclusively used in each subframe, the reference signal defined by the unused cell ID is not transmitted. That is, for example, assuming the cell ID allocation pattern shown in FIG. 5, the reference signal defined by Cell-ID2 is not transmitted in subframe # 3. Therefore, even if the user terminal decides handover to Cell-ID2 by subframe # 0, RSRP for the user terminal Cell-ID2 decreases by subsequent subframe # 3. Therefore, there is a possibility that the user terminal determines the handover to Cell-ID1 again. Such useless handover may waste radio resources.

  Therefore, the communication control apparatus 300 according to the present embodiment causes the access point 200 to transmit a reference signal defined by an unused cell ID in each subframe. For example, in subframe # 3, access point 200 basically uses Cell-ID1, but transmits a reference signal of Cell-ID2 in a specific resource element defined by Cell-ID2. According to such control, since the user terminal can receive the Cell-ID2 reference signal in any subframe, its RSRP does not decrease. That is, the above-mentioned useless handover request can be avoided. Note that the communication control apparatus 300 may enable or disable transmission of a radio signal of a cell ID in use in a resource element that transmits a reference signal of an unused cell ID.

  Here, it is desirable to avoid collision between the resource element to which the reference signal of the unused cell ID is transmitted and the resource element to which the reference signal of the cell ID being used is transmitted. When the resource elements of the reference signal collide, there is a possibility of adversely affecting propagation path estimation, RSRP measurement, etc. at the user terminal.

  For example, according to the LTE specification, the resource element to which the reference signal is transmitted is determined by the remainder obtained by dividing the cell ID by 6. Specifically, the resource element to which the reference signal is transmitted is offset in the frequency direction by this remainder. For example, if the remainder is “0”, the reference signal is transmitted on subcarriers f0, f6, f12, and f18 at symbol t0. On the other hand, if the remainder is “1”, the reference signal is transmitted on subcarriers f1, f7, f13, and f19 in symbol t0. Note that, depending on the specifications of the wireless communication system, the resource element of the reference signal may be offset in the time direction. In such a case as well, collision can be avoided by setting the cell ID. In other words, the communication control apparatus 300 can avoid a collision by using an offset in the frequency direction or time direction of the resource element of the reference signal determined by the cell ID.

  As described above, the communication control apparatus according to the second embodiment further transmits the reference signal of the unused cell ID in each subframe when the cell ID used by the access point is switched in units of subframes. . Therefore, according to the communication control apparatus according to the present embodiment, it is possible to avoid a useless handover request due to a decrease in RSRP.

  In the present embodiment, it has been described that a reference signal of an unused cell ID is transmitted in each subframe without distinguishing both cell IDs. However, such control may be omitted for the cell ID before change (for example, Cell-ID1 in FIG. 2B) that is temporarily used for changing the used cell ID. In this case, since the RSRP of the cell ID before the change is reduced, it is easy to avoid a useless handover request. Furthermore, the user terminal using the cell ID before change can be urged to perform handover to the cell ID after change.

(Third embodiment)
The communication control apparatus according to the first embodiment switches the cell ID used by the access point in units of subframes. That is, the same cell ID may be repeatedly used in a specific subframe.

  By the way, according to the LTE specification, once every 40 msec (ie, radio frame × 4), an MIB (Master Information Block) including basic information such as the number of antennas provided in the access point and the bandwidth of the transmission signal is provided. ) Is generated. The MIB is passed from layer 2 to layer 1 as a broadcast channel (BCH; Broadcast Channel). In layer 1, four types of physical broadcast channels (PBCH) are generated by performing scrambling processing using four types of initial values on the BCH. These PBCHs are transmitted four times in the first subframe (that is, subframe # 0) of each radio frame.

  Therefore, for example, when the communication control device 300 consistently uses the cell ID assignment of FIG. 5, the cell-ID 1 PBCH is not transmitted from the access point 200 at all. Therefore, a user terminal communicating with Cell-ID1 near the access point 200 may malfunction. On the other hand, for example, when the communication control device 300 consistently uses the cell ID assignment of FIG. 6, the PBCH of Cell-ID 2 is not transmitted at all from the access point 200. Therefore, a user terminal communicating with Cell-ID1 in the vicinity of the access point 200 cannot be handed over to Cell-ID2.

  Therefore, the communication control apparatus 300 according to the present embodiment switches a plurality of cell ID allocation patterns in units of radio frames. For example, the communication control apparatus 300 switches the cell ID allocation pattern in FIG. 5 and the cell ID allocation pattern in FIG. 6 in units of radio frames.

  As described above, according to the LTE specification, the BCH is repeatedly transmitted four times in the PBCH format. By transmitting BCH four times, it is possible to withstand path loss even when the cell radius is large. In other words, when the cell radius is small, the user terminal can correctly demodulate the BCH if it receives the BCH once or twice. Therefore, if the cell ID allocation pattern is switched at least once during 40 msec, the user terminal may be able to correctly receive the BCHs of both cell IDs.

  As described above, the communication control apparatus according to the third embodiment switches the cell ID allocation pattern in units of radio frames when switching the cell ID used by the access point in units of subframes. Therefore, according to the communication control apparatus which concerns on this embodiment, the user terminal can receive BCH of several cell ID correctly.

  In the above-described embodiments, the cell ID used by the access point 100 is not particularly described. For example, if Cell-ID1 is used consistently by the access point 100, the throughput of user terminals near the access point 100 can be improved. On the other hand, the communication control apparatus 300 may change the cell ID of the access point 100 flexibly as with the access point 200.

(Fourth embodiment)
The first to third embodiments described above assume a TDD system. The fourth embodiment assumes a frequency division duplex (FDD) system. According to FDD, uplink transmission and downlink transmission are performed by frequency division. Therefore, the possibility of interference between uplink transmission and downlink transmission is very low. Also in the case of FDD, it is necessary to cause the user terminal to correctly receive BCHs having a plurality of cell IDs as in the third embodiment.

  For example, as illustrated in FIG. 7, the communication control apparatus 300 according to the present embodiment transmits Cell-ID1 radio signals to the access point 200 in even-numbered subframes # 0, # 2,. Send it. Therefore, as described above, PBCH of Cell-ID1 is transmitted in subframe # 0. Further, the communication control apparatus 300 causes the access point 200 to transmit a cell-ID2 radio signal in even-numbered subframes # 0, # 2,. Therefore, as described above, the PBCH of Cell-ID2 is transmitted in subframe # 0. However, as is apparent from FIG. 7, the subframe number for Cell-ID2 is shifted (cyclically shifted) by one subframe (1 msec) as compared to the subframe number for Cell-ID1. ). That is, subframes # 0, # 2,..., # 8 for Cell-ID2 correspond temporally to subframes # 1, # 3,. Yes. That is, since the access point 200 uses Cell-ID1 and Cell-ID2 in a time division manner, interference between the two does not occur.

  In general, with regard to FDD, a subframe number which is different for each cell ID is added to a subframe number for transmitting a radio signal (for example, a radio signal is transmitted only to even-numbered or odd-numbered subframes). By giving the number, the access point 200 can use a plurality of cell IDs in a time division manner. According to such control, the aforementioned PBCH problem can also be avoided. Furthermore, the above restriction may be switched in units of radio frames. That is, the communication control apparatus 300 may transmit a radio signal only in an even-numbered subframe in a certain radio frame and transmit a radio signal only in an odd-numbered subframe in another radio frame.

  Alternatively, the communication control apparatus 300 can cause the access point 200 to use a plurality of cell IDs in a time division manner without using an offset of the subframe number. For example, the communication control apparatus 300 may cause the access point 200 to use Cell-ID1 in the even-numbered subframe and cause the access point 200 to use Cell-ID2 in the odd-numbered subframe. If the cell ID allocation pattern is switched in units of radio frames, the aforementioned PBCH problem can be avoided.

  As described above, the communication control apparatus according to the fourth embodiment causes the access point to use a plurality of cell IDs in a time division manner. Therefore, according to the communication control apparatus according to the present embodiment, the cell ID can be flexibly changed even in the FDD wireless communication system.

  Note that the communication control apparatus 300 according to the present embodiment causes the access point 200 to use a plurality of cell IDs in a time division manner. Therefore, in order for the access points 100 and 200 to achieve the same frequency transmission, it is necessary to align the timing at which the access point 100 transmits the Cell-ID 1 radio signal with the access point 200.

(Fifth embodiment)
According to the LTE specification, broadcast information called SIB (System Information Block) is transmitted in addition to the above-described MIB. SIB is defined from SIB1 to SIB9. Of these, SIB1 is basic information indicating an operator identifier, a cycle in which another SIB is transmitted, and the like, and is transmitted in a fixed cycle. Specifically, SIB1 is transmitted in subframe # 5 of a radio frame with an even SFN (System Frame Number). Here, SFN means a logical number given to a radio frame.

  The communication control apparatus 300 according to the third embodiment described above switches the cell ID allocation pattern in units of radio frames. However, for example, if two types of cell ID allocation patterns are alternately switched, the same cell ID allocation pattern is consistently applied in even-numbered radio frames. That is, no SIB1 of one cell ID is transmitted.

  Therefore, the communication control apparatus 300 according to the fifth embodiment gives the SFN a different offset for each cell ID as shown in FIG. According to this control, the communication control apparatus 300 can cause the access point 200 to transmit the SIB1 of Cell-ID1 in the subframe # 5 of the even-numbered radio frame of Cell-ID1. On the other hand, the communication control device 300 can transmit the SIB1 of Cell-ID2 to the access point 200 in the subframe # 5 of the even-numbered radio frame of Cell-ID2. As is clear from FIG. 8, due to the SFN offset, the even-numbered radio frame of Cell-ID2 temporally corresponds to the odd-numbered radio frame of Cell-ID1, so that the access point 200 has a plurality of cell IDs. SIB1 can be transmitted in a time division manner.

  By the way, according to the LTE specification, a modification period representing a cycle in which the content of the SIB is changed is set. That is, each user terminal receives SIBs simultaneously in the SFN specified by this modification period. Therefore, when an offset different for each cell ID is given to the SFN, it is necessary to consider the value of Modification period. For example, if the access point 200 uses three types of cell IDs, the SFN offset amount of each cell ID is set to, for example, “0”, “1”, and “2”, respectively. If the modification period is “2”, the user terminal needs to receive an SIB every two radio frames for each cell ID. However, the transmission timing of the SIB of the cell ID whose offset amount is “0” and the SIB of the cell ID whose offset amount is “2” overlap. Therefore, it is necessary to set the maximum offset amount of SFN smaller than the value of Modification period.

  As described above, the communication control apparatus according to the fifth embodiment gives the SFN a different offset for each cell ID. Therefore, according to the communication control apparatus according to the present embodiment, it is possible to cause the access point to transmit SIB1 of a plurality of cell IDs in a time division manner.

  Note that the communication control apparatus 300 according to the present embodiment gives different offsets to the SFN for each cell ID. Therefore, in order for the access points 100 and 200 to achieve the same frequency transmission, it is necessary to align the SFN for Cell-ID1 between the access points 100 and 200.

(Sixth embodiment)
The communication control apparatus 300 according to the first to fifth embodiments described above causes the access point 200 to use a plurality of cell IDs in a time division manner. In other words, the access point 200 basically uses one cell ID at a given time (strictly speaking, as in the second embodiment, the access point 200 is not used at a given time. ID reference signal may be transmitted). The time division use of a plurality of cell IDs is excellent in terms of avoiding interference, but there is room for improvement in the utilization efficiency of radio resources. Therefore, the communication control apparatus 300 according to the sixth embodiment causes the access point 200 to use a plurality of cell IDs at a given time. However, as described above, when a plurality of cell IDs are used together, interference between control channel regions becomes a problem. The communication control device 300 performs control to mitigate such interference.

  Specifically, as illustrated in FIG. 9, the communication control apparatus 300 gives a time offset that differs for each cell ID to the radio resource. In the example of FIG. 9, the radio resource of Cell-ID2 is delayed by 3 symbols compared to the radio resource of Cell-ID1. According to such control, the time position occupied by the control channel area of Cell-ID2 overlaps with the time position occupied by the individual channel area of Cell-ID1. That is, the cell-ID1 control channel region (symbols t0, t1, t2) and the cell-ID2 control channel region (symbols t0, t1, t2) occupy different time positions. Therefore, interference between the two is avoided. On the other hand, the control channel region of Cell-ID2 occupies the same time position as the dedicated channel region (symbols t3, t4, t5) of Cell-ID1. Therefore, interference between the two occurs.

  For example, the communication control device 300 omits assignment of the second resource block of Cell-ID1 (that is, the resource block on the high frequency side) (does not allow transmission of the radio signal of Cell-ID1). Note that the communication control apparatus 300 may permit the transmission of the Cell-ID1 reference signal even for resource blocks that are not assigned.

  According to such control, since the radio signal of Cell-ID1 is not transmitted on the high frequency side (subcarriers f12,..., F23) in the control channel region of Cell-ID2, no interference occurs. On the other hand, interference with the radio signal of Cell-ID1 occurs on the low frequency side (subcarriers f0,..., F11) of the control channel of Cell-ID2. Here, the error resistance is enhanced by the error correction coding and the repetitive coding, and the control channel is arranged over a wide frequency band, so that a frequency diversity effect can be obtained. Therefore, if the user terminal can receive a part of the control channel region without interference, the user terminal may be able to correctly decode the entire control channel region. In the example of FIG. 9, radio resources (resource blocks) are not allocated to half of the dedicated channel region of Cell-ID1. Therefore, the user terminal can receive half of the cell-ID2 control channel region without interference. It should be noted that there is room for adjustment in the amount of radio resources that are not assigned. For example, it is also effective to increase or decrease the amount of the radio resource according to the reception environment of the user terminal. It is desirable to adjust the amount of such radio resources so that the user terminal can correctly decode the entire control channel region.

  As described above, the communication control apparatus according to the sixth embodiment gives a radio resource a different time offset for each cell ID. Furthermore, the communication control apparatus omits assignment of at least a part of resource blocks in the dedicated channel region of the cell ID. Therefore, according to the communication control apparatus according to the present embodiment, the access point can use a plurality of cell IDs at a given time. Since the control channel region of each cell ID does not interfere with the dedicated channel region of other cell IDs at least partially, the user terminal can correctly decode the entire control channel region.

  In the above description, interference mitigation between the control channel region of Cell-ID2 and the dedicated channel region of Cell-ID1 is described. Similarly, it is also possible to realize interference mitigation between the control channel region of Cell-ID1 and the dedicated channel region of Cell-ID2.

  In the above description, three symbols are exemplified as the time offset amount, but different time offset amounts may be used. For example, the communication control apparatus 300 may use a time offset of less than 3 symbols. When the amount of time offset decreases, interference between the control channel region of Cell-ID2 and the dedicated channel region of Cell-ID1 becomes a problem, but by increasing the dedicated channel region that omits the above-described radio resource allocation, The terminal can correctly decode the entire control channel region of each cell ID. Further, the time offset amount may be an integer multiple of the symbol length or may not be so.

  In the case of TDD, if the time offset amount is increased, interference may occur between uplink transmission and downlink transmission. As described above, according to the LTE specification, a subframe including a GP is prepared for switching from downlink transmission to uplink transmission (see FIG. 4). The GP absorbs the arrival time difference until the radio signal transmitted from the access point reaches the user terminal at various positions, and the power amplifier (PA; Power Amplifier) when the user terminal transitions from the reception mode to the transmission mode. ) To absorb the transient response time. However, the arrival time difference increases or decreases depending on the cell radius. For example, when the cell radius is small, the arrival time difference is shortened. Therefore, in the case of TDD, it is necessary to set the time offset amount so that the uplink subframe and the downlink subframe do not collide in consideration of the length of the GP, the cell radius, and the like.

  Unlike the first to fifth embodiments described above, the communication control apparatus 300 according to this embodiment causes the access point 200 to use a plurality of cell IDs at a given time. Therefore, the access point 200 has a heavy load because the cell-ID1 radio signal transmission process and the cell-ID2 radio signal transmission process are performed in parallel. For example, the L1 processing unit 203 is required to perform processing at a speed about twice that of the first to fifth embodiments described above.

  The solution to this problem is described below. The first measure is to divide the functions of the access points 100 and 200 and the communication control device 300 from a viewpoint different from FIG. Specifically, the interfaces 101 and 201 are disposed between the L1 processing units 103 and 203 and the wireless units 104 and 204, and the L2 processing units 102 and 202 and the L1 processing units 103 and 203 are included in the communication control apparatus 300. Is effective. According to such function division, since the radio signal generated by the L1 processing unit 103 can be distributed to the radio units 104 and 204, the processing load on the L1 processing unit 203 can be reduced. The second measure is to add an interface between the access points 100 and 200 without performing such function division. If the wireless signal generated by the L1 processing unit 103 is also distributed to the wireless unit 204 via this interface, the processing load on the L1 processing unit 203 can be reduced.

  Note that the communication control apparatus 300 according to the present embodiment gives a radio resource a different time offset for each cell ID. Therefore, in order for the access points 100 and 200 to perform the same frequency transmission, it is necessary to align the transmission timing of the Cell-ID1 radio signal between the access points 100 and 200. Specifically, it is necessary to suppress the transmission timing difference between them within the cyclic prefix.

(Seventh embodiment)
The communication control apparatus 300 according to the above-described sixth embodiment gives a radio resource a different time offset for each cell ID, and omits assignment of at least some radio resources in the dedicated channel region. The amount of radio resources for which allocation is omitted (that is, the amount of radio resources that do not transmit radio signals in the dedicated channel region) may be adjusted so that the user terminal can correctly decode the entire control channel region.

  By the way, according to the LTE specification, it is possible to adjust the strength of error resilience by increasing / decreasing the redundancy of signals in the control channel region according to the reception environment. Therefore, it can be assumed that the frequency utilization efficiency can be improved by enhancing the error tolerance of the signal in the control channel region and suppressing the amount of radio resources to be omitted.

  However, even if the error tolerance of the signal in the control channel region is enhanced, it is difficult to obtain good reception characteristics if the accuracy of the propagation path estimation of this signal is poor. That is, the reference signal required for propagation path estimation needs to be correctly received by the user terminal.

  Therefore, the communication control apparatus 300 according to the seventh embodiment gives a radio resource a different time offset for each cell ID, as shown in FIG. In the example of FIG. 10, the radio resource of Cell-ID2 is delayed by 3 symbols compared to the radio resource of Cell-ID1. According to such control, the time position occupied by the control channel area of Cell-ID2 overlaps with the time position occupied by the individual channel area of Cell-ID1. That is, the cell-ID1 control channel region (symbols t0, t1, t2) and the cell-ID2 control channel region (symbols t0, t1, t2) occupy different time positions. Therefore, interference between the two is avoided. On the other hand, the control channel region of Cell-ID2 occupies the same time position as the dedicated channel region (symbols t3, t4, t5) of Cell-ID1. Therefore, interference between the two occurs.

  The communication control apparatus 300 basically does not limit the allocation of radio resources in the dedicated channel area. However, the communication control apparatus 300 allocates a null symbol to the resource element of Cell-ID1 that overlaps the resource element to which the reference signal is transmitted in the control channel region of Cell-ID2. That is, the access point 200 does not transmit the Cell-ID1 radio signal in the resource element that transmits the reference signal in the Cell-ID2 control channel region.

  The total number of reference signals in the control channel region of the resource block is about 1% with respect to the total number of resource elements in the individual channel region. Therefore, even if 1% of the dedicated channel region is replaced by a null symbol, the error rate of the dedicated channel region signal is not greatly affected. That is, the user terminal can correctly decode the signal in the dedicated channel region.

  Note that when transmitting the radio signals in the dedicated channel regions of both cell IDs, the communication control apparatus 300 may attempt to avoid interference using adaptive array antenna technology (for example, null steering). In addition, in the transmission of the radio signal in the dedicated channel region, the communication control apparatus 300 may reduce the transmission rate and enhance error resilience as necessary so that the user terminal can accurately receive.

  As described above, the communication control apparatus according to the seventh embodiment gives a radio resource a different time offset for each cell ID. Furthermore, the communication control apparatus assigns a null symbol to the resource element of the other cell ID that overlaps the resource element to which the reference signal is transmitted in the control channel region of one cell ID. Therefore, according to the communication control apparatus according to the present embodiment, the access point can use a plurality of cell IDs at a given time. Furthermore, since the reference signal in the control channel region of each cell ID does not interfere with radio signals of other cell IDs, the user terminal can correctly decode the entire control channel region.

  In the first to seventh embodiments described above, it is assumed that the used cell ID of the access point 200 is changed from Cell-ID1 to Cell-ID2, as shown in FIGS. 2A, 2B, and 2C. It is stated. However, each embodiment is not limited to this, and can be generalized and applied in order to flexibly change the used cell ID of the communication apparatus.

(Eighth embodiment)
According to the first to seventh embodiments described above, the communication control apparatus 300 can realize a phase in which the access point 200 uses a plurality of cell IDs. By using such a phase, it is possible to reduce the number of times of handover of the user terminal and to avoid disconnection of communication of the user terminal due to handover.

  For example, as illustrated in FIG. 11A, it is assumed that the user terminal 401 communicating by Cell-ID1 moves away from the access point 100 and approaches the access point 200. At this time, the access point 200 uses Cell-ID2. As the mobile terminal 401 moves, the reception signal level of Cell-ID1 decreases in the user terminal 401, and the reception signal level of Cell-ID2 increases. Therefore, normally, the user terminal 401 requests a handover to the Cell-ID2.

  However, when a handover is realized, a dedicated control signal is exchanged between the access points 100 and 200, and a control signal for handover is exchanged also in an upper layer, so that traffic increases. Further, if the exchange of control signals by handover does not end at a specified time, the communication of the user terminal 401 may be disconnected. Such a situation is likely to occur when the user terminal 401 is moving at high speed.

Therefore, when the communication control apparatus 300 according to the eighth embodiment detects that the user terminal 401 is moving near the access point 200, for example, the communication control apparatus 300 changes the used cell ID of the access point 200 as shown in FIG. To do. Specifically, the communication control device 300 causes the access point 200 to use both Cell-ID1 and Cell-ID2. Note that the communication control apparatus 300 can avoid interference by using the first to seventh embodiments described above when the access point 200 uses both Cell-ID1 and Cell-ID2. . Various methods for detecting that the user terminal 401 is moving near the access point 200 can be assumed, but this embodiment may use any method. Alternatively, the communication control apparatus 300 may cause the access point 200 to use both Cell-ID1 and Cell-ID2 consistently. In addition, the communication control apparatus 300 may cause the access point 200 to use both Cell-ID1 and Cell-ID2 under some other conditions. According to such control, the user terminal 401 is also connected to the Cell near the access point 200. -Since communication by ID1 can be maintained, a handover request to Cell-ID2 does not occur. That is, unnecessary traffic is suppressed, and communication disconnection when handover fails can be avoided.

  Further, when the communication control apparatus 300 detects that the user terminal 401 is in an idle state when the access point 200 uses both Cell-ID1 and Cell-ID2, as illustrated in FIG. 11A. The access point 200 may stop using Cell-ID1. According to such control, the user terminal 401 is handed over to Cell-ID2. However, if the user terminal 401 is in an idle state, there is no communication disconnection problem due to handover, so communication quality is not impaired.

  As described above, the communication control apparatus according to the eighth embodiment causes an access point to use a plurality of cell IDs in order to avoid user terminal handover. Therefore, according to the communication control apparatus according to the present embodiment, a handoverless communication service can be provided to the user terminal.

(Ninth embodiment)
According to the above-described first to eighth embodiments, an undesirable handover may be required when the access point 200 uses a plurality of cell IDs.
For example, in the above-described eighth embodiment, the communication control apparatus 300 causes the access point 200 to temporarily use Cell-ID1 in order to maintain the communication of the user terminal 401. In such a situation, it is not desirable for another user terminal (for example, user terminal 404) to hand over to Cell-ID1. If such a handover is allowed, not only an unnecessary handover occurs, but it is difficult to return the used cell ID of the access point 200 to Cell-ID2 when the user terminal 401 leaves the service area of the access point 200. .

  Further, when both cell IDs are used to change the cell ID of the access point 200 from Cell-ID1 to Cell-ID2 (see, for example, FIG. 2B), the user terminal hands over to Cell-ID1. That is not desirable. If such a handover is permitted, it takes a long time to complete the change of the used cell ID of the access point 200.

  Therefore, the communication control apparatus 300 according to the ninth embodiment changes the cell ID (for example, Cell-ID1 in FIG. 11B) temporarily used for providing the handoverless service and the change of the used cell ID. Handover to a cell ID before change (for example, Cell-ID1 in FIG. 2B) that is temporarily used is rejected. For example, the RRC unit 304 or the communication control unit 305 performs control to reject the handover request to the Cell-ID1 received by the access point 200 and to remain in the Cell-ID2.

  As described above, the communication control apparatus according to the ninth embodiment rejects a handover to an undesirable cell ID. Therefore, according to the communication control apparatus according to the present embodiment, it is possible to smoothly change or return the used cell ID.

(Tenth embodiment)
The communication control apparatus 300 according to the ninth embodiment described above smoothly changes or returns a cell ID by rejecting a handover to an undesirable cell ID.
By the way, according to LTE specifications, a user terminal receives a synchronization channel when power is turned on or when a handover destination cell is searched. Specifically, the user terminal receives PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal) transmitted in subframe # 0 and subframe # 5 in FIG. The user terminal identifies the sequence used in the cell by calculating the correlation between the received PSS and SSS and a predetermined sequence. This sequence corresponds to the cell ID, and the user terminal receives the aforementioned PBCH using the identified sequence. In other words, the user terminal cannot receive PBCH unless it receives PSS and SSS and identifies the sequence corresponding to the cell ID. That is, the user terminal cannot find the cell ID unless it receives PSS and SSS.

  Accordingly, the communication control apparatus 300 changes the cell ID temporarily used for providing the handoverless service (for example, Cell-ID1 in FIG. 11B) and the change temporarily used for changing the used cell ID. For the previous cell ID (for example, Cell-ID1 in FIG. 2B), transmission of PSS and SSS from the access point 200 is omitted. According to this control, the access point 200 can use Cell-ID1 in a state where Cell-ID1 is concealed from a user terminal (for example, user terminal 404) that is not communicating with Cell-ID1. That is, a user terminal (for example, user terminal 401) that communicates with Cell-ID1 can maintain communication with Cell-ID1 even near the access point 200, and a user terminal that does not communicate with Cell-ID1 (for example, user terminal 404). ) Cannot find Cell-ID1, so unnecessary handover does not occur.

  As described above, the communication control apparatus according to the tenth embodiment omits transmission of the synchronization channel for the cell ID in order to avoid an undesired handover to the cell ID. Therefore, according to the communication control apparatus according to the present embodiment, it is possible to smoothly change or return the used cell ID.

  Each embodiment is not limited to LTE and can be applied to various wireless communication systems. For example, each embodiment may be applied to WiMAX having a control channel area addressed to all user terminals, MobileWiMAX, or other wireless communication systems. Even when each embodiment is applied to such a wireless communication system, the access point can use a plurality of cell IDs.

  The processing of each of the above embodiments can be realized by using a general-purpose computer as basic hardware. The program for realizing the processing of each of the above embodiments may be provided by being stored in a computer-readable storage medium. The program is stored in the storage medium as an installable file or an executable file. The storage medium may be a computer-readable storage medium such as a magnetic disk, optical disk (CD-ROM, CD-R, DVD, etc.), magneto-optical disk (MO, etc.), semiconductor memory, etc. Any form may be used. Further, the program for realizing the processing of each of the above embodiments may be stored on a computer (server) connected to a network such as the Internet and downloaded to the computer (client) via the network.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

100, 200 ... access point 101, 201 ... interface 102, 202 ... L2 processing unit 103, 203 ... L1 processing unit 104, 204 ... wireless unit 105, 205 ... antenna 300 ..Communication control device 301, 302... Interface 303, 304... RRC unit 305... Communication control unit 306... Switching unit 401, 402, 403, 404.

Claims (6)

A first control unit that causes a communication device to transmit a radio signal including a control channel region and a dedicated channel region of the first cell ID;
A radio signal including a control channel region and a dedicated channel region of a second cell ID different from the first cell ID is transmitted to the communication device as a time position of the control channel region of the second cell ID and the first cell ID. A second control unit for transmitting so that the time positions of the individual channel regions overlap,
The first control unit does not cause the communication device to transmit a radio signal of the first cell ID in a part of resource elements of the dedicated channel region of the first cell ID;
Communication control device.   The communication control apparatus according to claim 1, wherein the first control unit omits assignment of a part of resource blocks in the dedicated channel region of the first cell ID.   The first control unit transmits the first cell ID to the communication device in the resource element of the first cell ID that overlaps the resource element to which a reference signal is transmitted in the control channel region of the second cell ID. The communication control device according to claim 1, wherein the wireless signal is not transmitted.   The first control unit does not cause the communication device to transmit a radio signal of the first cell ID unless a user terminal that communicates with the first cell ID exists near the service area of the communication device. The communication control device according to claim 1, wherein if a user terminal that communicates using the first cell ID exists in the vicinity of a service area of the communication device, the communication device causes the communication device to transmit a radio signal of the first cell ID.   The communication control device according to claim 1, wherein the first control unit does not cause the communication device to transmit a synchronization channel of the first cell ID. A communication unit for transmitting radio signals;
A communication apparatus comprising: an interface with the communication control apparatus according to claim 1.

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