JP2014138335A - Communication controller, wireless base station device and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contribute to enhancement of efficiency in the measurement of a wireless signal using a measurement gap.SOLUTION: A communication controller 1 in a wireless communication system where the coverages of a macro cell and a small cell using different frequency bands overlap, comprises: a storage unit 13 for storing the data relevant to occurrence of handover, based on the wireless measurement data relevant to the occurrence timing of handover between a macro cell and a small cell; and a search timing determination unit 14 for determining the cell search start timing in a wireless terminal device, based on the wireless measurement data and the data relevant to occurrence of handover of the wireless terminal device.

Description

  The present invention relates to a communication control apparatus, a radio base station apparatus, and a communication control method.

  In recent years, a wireless communication network called HetNet (Heterogeneous Network) is known. FIG. 5 shows a configuration example of HetNet. In FIG. 5, a macro cell 101 uses a relatively low frequency band and has a wide coverage (a range in which a communication service can be provided). The small cell 201 is arranged overlapping the macro cell 101, uses a relatively high frequency band, and has a narrow coverage.

  When the macro cell 101 and the small cell 201 use different frequency bands, the user's wireless terminal device (UE: User Equipment) 300 is connected to the wireless base station device (hereinafter referred to as a macro cell base station) 100 of the macro cell 101 and the small cell 201. The base station to be connected is switched by performing inter-band handover with the radio base station apparatus (hereinafter referred to as a small cell base station) 200. Here, for example, when the UE 300 connected to the macro cell base station 100 using the frequency band fm performs the inter-band handover to the small cell base station 200 using the frequency band fs, the UE 300 In order to find the cell 201, a radio signal is measured in the frequency band fs. In the measurement of the radio signal, the UE 300 switches the frequency band to be used from fm to fs in a measurement period called a measurement gap (see, for example, Non-Patent Document 1).

  Non-Patent Document 1 describes a measurement gap in a wireless communication system called LTE (Long Term Evolution), which is being standardized by 3GPP (3rd Generation Partnership Project). RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality) are defined as radio signal quality measured using the measurement gap.

JP 2012-34048 A

3GPP, TS36.133 3GPP, TS36.331

  In the measurement of a radio signal using the above-described conventional measurement gap, a measurement gap is periodically provided. For this reason, the UE 300 connected to the macro cell base station 100 switches the frequency band to be used from fm to fs in the measurement gap even if there is no small cell 201 in the vicinity. In addition, since the connection with the macro cell base station 100 using the frequency band fm is interrupted, there is a disadvantage that the throughput of the UE is lowered and the frequency utilization efficiency is degraded.

  However, as described in Patent Document 1, when the communication quality of the base station of one radio communication system is equal to or higher than the threshold, the communication quality of the base station of the other radio communication system is measured with respect to the radio terminal. Instructing not to do so may delay the discovery of the base station of the other wireless communication system.

  The present invention has been made in view of such circumstances, and provides a communication control apparatus, a radio base station apparatus, and a communication control method that can contribute to an improvement in efficiency in measurement of a radio signal using a measurement gap. Let it be an issue.

  In order to solve the above-described problem, a communication control apparatus according to the present invention provides a communication control apparatus in a wireless communication system in which coverage of a macro cell and a small cell using different frequency bands overlaps, between the macro cell and the small cell. A storage unit for storing handover occurrence related data based on radio measurement data related to handover occurrence timing, radio measurement data of the radio terminal device, and cell search start timing in the radio terminal device based on the handover occurrence related data And a search timing determination unit for determining.

  In the communication control device according to the present invention, the wireless measurement data is RSRP, RSRQ, wideband SINR, transmission power of a wireless terminal device, path loss, or Timing Advance information.

  In the communication control apparatus according to the present invention, the handover occurrence related data is statistical information calculated using radio measurement data of a plurality of radio terminal apparatuses.

  The communication control apparatus according to the present invention is a communication control apparatus in a radio communication system in which the coverage of a macro cell and a small cell using different frequency bands overlaps, and the path loss or Timing Advance information of the radio terminal apparatus in the macro cell or the small cell is obtained. A search timing determination unit that determines a cell search start timing in the wireless terminal device based on an acquisition unit to be acquired, the acquired path loss or Timing Advance information, and a positional relationship between the macro cell and the small cell; It is provided with.

  A radio base station apparatus according to the present invention is a radio base station apparatus including any one of the communication control apparatuses described above.

  The communication control method according to the present invention is a communication control method in a radio communication system in which the coverage of a macro cell and a small cell using different frequency bands overlap, and is related to a handover occurrence timing between the macro cell and the small cell. A storage step for storing handover occurrence related data based on the measurement data; a search timing determination step for determining a cell search start timing in the radio terminal device based on the radio measurement data of the radio terminal device and the handover occurrence related data; , Including.

  A communication control method according to the present invention is a communication control method in a radio communication system in which coverage of a macro cell and a small cell using different frequency bands overlaps, and the path loss or Timing Advance of a radio terminal device in the macro cell or the small cell An acquisition step of acquiring information, a search timing determination step of determining a cell search start timing in the wireless terminal device based on the acquired path loss or Timing Advance information, and a positional relationship between the macro cell and the small cell A communication control method comprising:

  According to the present invention, it is possible to contribute to improvement in efficiency in measurement of a radio signal using a measurement gap.

It is a block diagram which shows the structural example of the communication control apparatus 1 which concerns on 1st Embodiment of this invention. It is explanatory drawing for demonstrating the measurement gap which concerns on this invention. It is explanatory drawing for demonstrating an example of the determination method of the cell search start timing which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structural example of the communication control apparatus 2 which concerns on 2nd Embodiment of this invention. It is explanatory drawing for demonstrating the structural example of HetNet.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, LTE will be described as an example of a wireless communication method. Further, description will be made using a configuration example of HetNet shown in FIG.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration example of a communication control apparatus 1 according to the first embodiment of the present invention. In FIG. 1, the communication control apparatus 1 includes a wireless measurement data acquisition unit 11, a handover occurrence timing acquisition unit 12, a storage unit 13, and a search timing determination unit 14.

  The radio measurement data acquisition unit 11 acquires radio measurement data related to the UE 300. As radio | wireless measurement data, RSRP or RSRQ described in the nonpatent literature 1 is mentioned, for example. Examples of other radio measurement data include wideband signal to interference and noise power ratio (SINR) or transmission power of UE 300. For example, RSRP and RSRQ are defined as periodic (Periodic) and event-triggered (Event-triggered) in Non-Patent Document 2, but are regularly connected from UE 300 in the case of Event-triggered. Not reported to base station. On the other hand, the wideband SINR is regularly reported from the UE 300 to the base station to which the UE 300 is connected. The wireless measurement data acquisition unit 11 acquires the reported wideband SINR.

  In the present embodiment, as an example, the radio measurement data acquisition unit 11 uses the wideband reported from the UE 300 connected to the macro cell base station 100 as radio measurement data related to the UE 300 connected to the macro cell base station 100. The SINR is acquired. As another example, RSRP or RSRQ obtained by “Periodic report” may be used instead of the wideband SINR.

  The handover occurrence timing acquisition unit 12 is configured so that the UE 300 performs inter-band handover for each pair between base stations (in FIG. 5, for each pair of the macro cell base station 100 and the small cell base station 200). The handover occurrence timing information indicating the timing (hereinafter referred to as the handover occurrence timing) is acquired. In the present embodiment, handover occurrence timing information indicating the handover occurrence timing when the inter-band handover is performed from the macro cell base station 100 (use frequency band fm) to the small cell base station 200 (use frequency band fs) is acquired.

  The storage unit 13 stores radio measurement data (handover occurrence related data) when a handover from the frequency band fm to the frequency band fs occurs. The handover occurrence timing of the handover from the frequency band fm to the frequency band fs is indicated by the handover occurrence timing information acquired by the handover occurrence timing acquisition unit 12. The wireless measurement data is acquired by the wireless measurement data acquisition unit 11.

  For example, the handover occurrence related data is connected to the macro cell base station 100 at the handover occurrence timing when the inter-band handover is performed from the macro cell base station 100 to the small cell base station 200 and the inter-band handover is performed. Based on the wideband SINR reported from the existing UE 300.

  Specifically, for example, the timing at which the handover is performed, or the wideband SINR acquired within a predetermined period T before and after the timing is used as the handover occurrence related data. Further, statistical information such as a cumulative probability distribution calculated using handover occurrence related data accumulated for a plurality of UEs 300 may be used as handover occurrence related data.

  The search timing determination unit 14 determines the timing at which the UE 300 starts searching for a cell based on the radio measurement data related to the UE 300 and the handover occurrence related data. In this embodiment, the search timing determination part 14 determines the timing (small cell search start timing) at which the UE 300 starts searching for the small cell 201.

  For example, the handover occurrence related data is connected to the macro cell base station 100 at the handover occurrence timing when the inter-band handover is performed from the macro cell base station 100 to the small cell base station 200 and the inter-band handover is performed. Based on the wideband SINR reported from the existing UE 300. And the search timing determination part 14 determines the small cell search start timing in the said UE300 based on the wideband SINR newly reported from a certain UE300 and the handover generation related data. For example, when the wideband SINR of the UE 300 becomes the average value of the wideband SINR included in the handover occurrence related data, the small cell search start timing of the UE 300 is set. Or, when the cumulative probability distribution is held as handover-related data, the wideband SINR of the UE 300 becomes a wideband SINR (“5th percentile SINR value”) corresponding to 5% in the cumulative probability distribution. The small cell search start timing of the UE 300 is assumed. The small cell search start timing can be used as a timing for providing a measurement gap for finding a small cell 201 that can be handed over.

  FIG. 2 shows the timing t_s at which the measurement gap is provided. The UE 300 measures a radio signal in the frequency band fm of the macrocell base station 100 at timings t_m1 and t_m2. On the other hand, at timing t_s, a measurement gap T_mg is provided, and the UE 300 measures a radio signal in the frequency band fs of the small cell base station 200.

  Further, the interval of the timing t_s may be changed before and after the small cell search start timing. For example, the interval of the timing t_s may be widened before the small cell search start timing, and the interval of the timing t_s may be narrowed after the small cell search start timing. Furthermore, for example, when the 5th percentile SINR value and the 10th percentile SINR value in the cumulative probability distribution described above are set as a plurality of threshold values for determining the small cell search start timing, the wideband SINR of the UE 300 is smaller than the 5th percentile SINR value The interval of the timing t_s in the UE 300 may be narrowed stepwise between the 5th percentile SINR value and the 10th percentile SINR value and the 10th percentile SINR value.

  According to the present embodiment, the small cell search start timing determined based on the past handover occurrence timing and radio measurement data can be used as the timing for providing a measurement gap for finding the small cell 201 that can be handed over. Thereby, when measuring a radio signal using a measurement gap, the possibility that the small cell 201 exists in the vicinity of the UE 300 is increased, which can contribute to an improvement in efficiency in measuring a radio signal using the measurement gap.

  In addition, in embodiment mentioned above, although the small cell search start timing was determined, it can apply similarly, also when UE300 determines the timing (macrocell search start timing) which starts the search of the macrocell 101. FIG. In this case, radio measurement data relating to the UE 300 connected to the small cell base station 200 may be used. Further, the handover occurrence timing at which inter-band handover is performed from the small cell base station 200 to the macro cell base station 100 may be used.

  In addition, in order to increase the accuracy of cell search start timing, radio measurement data acquired by a plurality of base stations may be used. In the radio measurement data related to one base station, as illustrated in FIG. 3, there is a possibility that the radio measurement data indicated by the handover occurrence related data is acquired even in the area 210 that is not the actual small cell 201. For this reason, in the example of FIG. 3, the accuracy of the small cell search start timing can be improved by configuring the handover occurrence related data using the radio measurement data acquired by the plurality of macro cell base stations 100.

[Second Embodiment]
FIG. 4 is a block diagram showing a configuration example of the communication control apparatus 2 according to the second embodiment of the present invention. In FIG. 4, the communication control device 2 includes a path loss acquisition unit 21, a storage unit 23, and a search timing determination unit 24.

  The path loss acquisition unit 21 acquires the path loss of the UE 300 in the macro cell 101 or the small cell 201. In the present embodiment, the path loss of the UE 300 in the macro cell 101 is acquired.

An example of a path loss acquisition method will be described below. In LTE, the transmission power Pr of the UE 300 is expressed by the following equation.
Pr = min {Pmax, 10log10 (number of RBs) + P_0 + α · PL + f}
However, min {A, B} represents the smaller value of A or B.
P_r is received power from the UE 300 in the macrocell base station 100. P_0 is a target received power from the UE 300 in the macrocell base station 100, and is a preset value. α is a correction value of the path loss PL in the macrocell base station 100, and is a preset value. Pmax is an upper limit value of the transmission power of UE300. The number of RBs is the number of resource blocks (Resource Blocks) used by the UE 300. f is a parameter for closed loop transmission power control.

For this reason, when calculating the path loss PL, the number of RBs is set to 1 or a predetermined value, and the closed-loop transmission power control parameter f is set to 0. When the value of PHR (Power Head Room) is 0, the transmission power Pr is Pmax, and the path loss PL cannot be calculated. Therefore, the path loss PL is not calculated. When the number of RBs is 1 and f is 0, the path loss PL of the UE 300 can be calculated by the following equation.
PL = (P_r−P_0) ÷ α

  The above is an example of the path loss acquisition method.

  The storage unit 23 stores various data. The search timing determination unit 24 determines the small cell search start timing in the UE 300 based on the path loss PL of the UE 300.

  The path loss PL represents the distance between the macro cell base station 100 and the UE 300. Therefore, the position of the UE 300 relative to the small cell 201 can be estimated from the position of the UE 300 relative to the macro cell base station 100 based on the path loss PL and the positional relationship between the macro cell 101 and the small cell 201. Thereby, the small cell search start timing in UE300 is determined.

  Note that the path loss PL may be used as the handover occurrence related data, and the small cell search start timing may be determined based on the handover occurrence related data as in the first embodiment described above. For example, the timing at which the handover is performed, or the path loss PL acquired within a predetermined period T before and after the timing is used as the handover occurrence related data. Further, statistical information such as a cumulative probability distribution calculated using handover occurrence related data accumulated for a plurality of UEs 300 may be used as handover occurrence related data.

  Moreover, “Timing Advance information” described in Non-Patent Document 1 may be used as information other than the path loss PL. Timing advance information is information for correcting the time difference between the uplink and the downlink, and can be measured by the base station. In the method described in Non-Patent Document 1, a command for timing adjustment is transmitted from the base station to the UE. The granularity of timing to be adjusted is “2 / 30.72 us (corresponding to about 19.5 meters)”. And relatively coarse. However, since the value of “Timing advance” measured by the base station is smaller than the value of the granularity, it can be used as the small cell search start timing.

  Moreover, in order to raise the precision of a small cell search start timing, you may provide the means to estimate the direction of UE300 with respect to the macrocell base station 100. FIG. For example, the arrival direction of the radio signal from the UE 300 can be detected using a sector antenna. Then, the search timing determination unit 24 determines the small cell search start timing in the UE 300 based on the path loss PL, the arrival direction of the radio signal from the UE 300, and the positional relationship between the macro cell 101 and the small cell 201. Information indicating the positional relationship between the macro cell 101 and the small cell 201 is prepared in advance.

  According to the present embodiment, the small cell search start timing determined based on the path loss PL or Timing advance information can be used as a timing for providing a measurement gap for finding the small cell 201 that can be handed over. Thereby, when measuring a radio signal using a measurement gap, the possibility that the small cell 201 exists in the vicinity of the UE 300 is increased, which can contribute to an improvement in efficiency in measuring a radio signal using the measurement gap.

  In addition, in embodiment mentioned above, although the small cell search start timing was determined, it can apply similarly, also when UE300 determines the timing (macrocell search start timing) which starts the search of the macrocell 101. FIG. In this case, the path loss of the UE 300 in the small cell 201 may be used.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

  Note that the communication control apparatus may be provided in the base station or may be provided as an apparatus independent of the base station.

  Moreover, although LTE was mentioned as an example of a radio | wireless communication system in embodiment mentioned above, it is applicable similarly to another radio | wireless communication system. Further, the present invention can be similarly applied to wireless communication networks other than HetNet.

DESCRIPTION OF SYMBOLS 1, 2 ... Communication control apparatus, 11 ... Wireless measurement data acquisition part, 12 ... Handover generation timing acquisition part, 13, 23 ... Memory | storage part, 14, 24 ... Search timing determination part, 21 ... Path loss acquisition part, 100 ... Macrocell base Station (radio base station apparatus), 101 ... macro cell, 200 ... small cell base station (radio base station apparatus), 201 ... small cell, 300 ... UE (radio terminal apparatus)

Claims (7)

In a communication control apparatus in a wireless communication system in which the coverage of a macro cell and a small cell that use different frequency bands overlap,
A storage unit for storing handover occurrence related data based on radio measurement data related to handover occurrence timing between the macro cell and the small cell;
A search timing determination unit for determining a cell search start timing in the radio terminal device based on radio measurement data of the radio terminal device and the handover occurrence related data;
A communication control apparatus comprising:   The communication control apparatus according to claim 1, wherein the wireless measurement data is RSRP, RSRQ, wideband SINR, transmission power of a wireless terminal apparatus, path loss, or Timing Advance information.   The communication control apparatus according to claim 1, wherein the handover occurrence related data is statistical information calculated using radio measurement data of a plurality of radio terminal apparatuses. In a communication control apparatus in a wireless communication system in which the coverage of a macro cell and a small cell that use different frequency bands overlap,
An acquisition unit that acquires path loss or Timing Advance information of a wireless terminal device in the macro cell or the small cell;
Based on the acquired path loss or Timing Advance information, and the positional relationship between the macro cell and the small cell, a search timing determination unit that determines a cell search start timing in the wireless terminal device;
A communication control apparatus comprising:   A radio base station apparatus comprising the communication control apparatus according to claim 1. A communication control method in a wireless communication system in which coverage of a macro cell and a small cell using different frequency bands overlaps,
Storing the handover occurrence related data based on radio measurement data related to handover occurrence timing between the macro cell and the small cell;
A search timing determination step for determining a cell search start timing in the radio terminal device based on radio measurement data of the radio terminal device and the handover occurrence related data;
The communication control method characterized by including. A communication control method in a wireless communication system in which coverage of a macro cell and a small cell using different frequency bands overlaps,
An acquisition step of acquiring path loss or Timing Advance information of the wireless terminal device in the macro cell or the small cell;
A search timing determination step for determining a cell search start timing in the wireless terminal device based on the acquired path loss or Timing Advance information and a positional relationship between the macro cell and the small cell;
The communication control method characterized by including.

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