JP5891067B2 - Communication control device and communication control method - Google Patents

Description

  The present invention relates to a communication control device and a communication control method.

  In recent years, standardization of LTE (Long Term Evolution) has been promoted by 3GPP (3rd Generation Partnership Project) as a standard of the 3.9th generation mobile communication system. An MLB (Mobility Load Balancing) technique is known as a technique for performing traffic offload between base stations in the LTE (see, for example, Non-Patent Document 1).

  In MLB technology, when traffic concentrates on a specific base station, a handover parameter for adjusting the timing at which the user terminal performs handover is changed. Thereby, the user terminal connected to the specific base station can easily be handed over to a base station (adjacent base station) adjacent to the specific base station. As a result, it is expected that the traffic of a specific base station will be offloaded to neighboring base stations.

  For example, Non-Patent Document 2 describes a technique for performing traffic offload between base stations by adjusting base station parameters such as transmission power of the base station and antenna tilt angle to change cell coverage. Yes. In the traffic offload technology between base stations by changing the cell coverage, when traffic concentrates on a specific base station, the cell coverage of a specific base station is reduced and the cell coverage of an adjacent base station is increased. Thereby, among the user terminals connected to a specific base station, the user terminals in the cell coverage change part are handed over to the adjacent base station. As a result, the traffic of a specific base station is offloaded to neighboring base stations.

3GPP TS 36.300, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2” Hampel, G., et al. “The tradeoff between coverage and capacity in dynamic optimization of 3G cellular networks”, Proceeding of Vehicular Technology Conference 2003 (VTC 2003 Fall), 2003.

  According to the MLB technique described above, only the handover parameter is adjusted and the cell coverage is not changed, so there is no fear of increasing radio wave interference with neighboring base stations. However, a user terminal that has been handed over to an adjacent base station may not be able to obtain sufficient received power at the handover destination base station, and may not be able to ensure a certain communication quality. In order to guarantee a certain communication quality for the user terminal, it is conceivable to limit the adjustment range of the handover parameter. However, in this case, the traffic offload effect may not be sufficiently obtained.

  In the traffic offload technology between base stations by changing the cell coverage, a more reliable traffic offload effect can be expected by changing the cell coverage compared to the MLB technology. However, expanding cell coverage may increase radio wave interference with neighboring base stations.

  The present invention has been made in view of such circumstances, and provides a communication control apparatus and a communication control method that can appropriately use MLB technology and inter-base station traffic offload technology by changing cell coverage. This is the issue.

  In order to solve the above-described problem, the communication control apparatus according to the present invention changes a handover parameter for adjusting a timing at which a user terminal connected to a base station determined to be in a congested state is handed over, or A communication control apparatus that selects whether to change cell coverage of the base station, a traffic offload effect determination unit that determines a traffic offload effect when the handover parameter is changed, and the constant traffic offload effect When it is determined that a certain traffic offload effect cannot be obtained, and the first traffic offload control unit that changes the handover parameter, the cell coverage of the base station is determined. And a second traffic offload control unit for changing That.

  In the communication control apparatus according to the present invention, the traffic offload effect determination unit determines whether a user terminal that is a handover target can be handed over to a base station that is a handover destination when the handover parameter is changed, and handover is possible It is characterized in that it is determined whether or not a result of releasing radio resources allocated to a user terminal determined to be a certain effect.

  In the communication control apparatus according to the present invention, the traffic offload effect determination unit uses radio resources when the user terminal is handed over to the adjacent base station based on the communication quality information of the adjacent base station received from the user terminal. A rate increase is estimated, and it is determined that handover is possible when the sum of the radio resource utilization rate of the adjacent base station and the estimated radio resource utilization rate is equal to or less than a predetermined threshold value. .

  The communication control method according to the present invention changes a handover parameter for adjusting a timing at which a user terminal connected to a base station determined to be congested is handed over, or changes a cell coverage of the base station. A communication control method for selecting whether to perform the traffic offload effect when the handover parameter is changed, and when it is determined that a certain traffic offload effect is obtained, the handover parameter is And changing the cell coverage of the base station when it is determined that a certain traffic offload effect cannot be obtained.

  According to the present invention, when it is determined that the constant traffic offload effect can be obtained by the MLB technique, the MLB technique is used, and when it is determined that the constant traffic offload effect cannot be obtained by the MLB technique. By using the traffic offload technology between base stations by changing cell coverage, we can expect a more reliable traffic offload effect than MLB technology. Thereby, it can contribute to using appropriately the MLB technique and the traffic offload technique between base stations by a cell coverage change.

1 is a schematic configuration diagram of a mobile communication system according to an embodiment of the present invention. It is a block diagram of the communication control apparatus 10 which concerns on one Embodiment of this invention. It is a sequence chart for demonstrating the communication control method which concerns on one Embodiment of this invention. FIG. 4 is a flowchart of a traffic offload effect determination method according to step S4 of FIG. It is explanatory drawing for demonstrating MLB technique. It is explanatory drawing for demonstrating the traffic offload technique between base stations by a cell coverage change.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a mobile communication system according to an embodiment of the present invention. This mobile communication system is compliant with LTE. In FIG. 1, base stations BS 1, BS 2, BS 3 are connected to a core network 100. The base stations BS1, BS2, and BS3 transmit and receive data via the core network 100. Each base station BS1, BS2, BS3 forms each cell coverage 201, 202, 203 which is a geographical range where communication is possible.

  Each base station BS1, BS2, BS3 communicates wirelessly with a user terminal MS in its own cell coverage. The user terminal MS communicates with another user terminal MS via a cell coverage base station in which the user terminal MS is located, or communicates with an external network such as the Internet via the core network 100. be able to. Base stations BS1 and BS3 are adjacent base stations of base station BS2.

  FIG. 2 is a configuration diagram of the communication control apparatus 10 according to the present embodiment. The communication control device 10 is provided in each base station BS1, BS2, BS3. In FIG. 2, the communication control apparatus 10 includes a local station state determination unit 11, a traffic offload effect determination unit 12, a first traffic offload control unit 13, and a second traffic offload control unit 14.

  The own station state determination unit 11 determines whether or not the own base station is in a congested state. The traffic offload effect determination unit 12 determines the traffic offload effect when the MLB technology is used. The first traffic offload control unit 13 controls traffic offload between base stations using MLB technology. The second traffic offload control unit 14 performs control of the traffic offload between base stations using the traffic offload technology between base stations by changing the cell coverage.

  FIG. 3 is a sequence chart for explaining the communication control method according to the present embodiment. In FIG. 3, the operation of the communication control apparatus 10 of the base station BS2 is taken as an example. Hereinafter, the operation of the communication control apparatus 10 of the base station BS2 will be described with reference to FIG.

(Step S1) Each user terminal MS connected to the base station BS2 transmits an MR (Measurement Report) to the base station BS2 when an event occurs or periodically. This MR corresponds to an A2 event defined by LTE, and is transmitted when the RSRP (Received Signal Reference Power) or RSRQ (Received Signal Reference Quality) of the base station BS2 measured by the user terminal MS is below a certain value. Is done.

(Step S2) In the base station BS2, the own station state determination unit 11 of the communication control apparatus 10 determines whether or not the own base station is congested when an event occurs or periodically. Specifically, the own station state determination unit 11 determines that the own base station receives a PRB (Physical Resource Block) indicating the number of resource blocks (radio resources) used in the physical layer that exceeds a preset threshold. Is determined to be in a congested state. If it is determined that the own base station is congested, the process proceeds to step S3. If it is determined that the own base station is not congested, steps S1 and S2 are repeated.

(Step S3) In the base station BS2, the communication control apparatus 10 acquires load information from adjacent base stations (base stations BS1 and BS3). In this embodiment, PRB is acquired as load information.

(Step S4) In the base station BS2, the traffic offload effect determination unit 12 of the communication control apparatus 10 determines the traffic offload effect when the MLB technology is used. Details of step S4 will be described later. As a result of step S4, if the traffic offload effect using the MLB technique is sufficient, the process proceeds to step S5, and if insufficient, the process proceeds to step S6.

(Step S5) In the base station BS2, the first traffic offload control unit 13 of the communication control apparatus 10 performs control of the inter-base station traffic offload (change of handover parameters) using the MLB technique.

(Step S6) In the base station BS2, the second traffic offload control unit 14 of the communication control apparatus 10 controls the traffic offload between base stations using the inter-base station traffic offload technique by changing the cell coverage (cell coverage). Change).

FIG. 4 is a flowchart of the traffic offload effect determination method according to step S4 of FIG. Hereinafter, the operation of the traffic offload effect determination unit 12 of the communication control apparatus 10 will be described with reference to FIG. In this description, the following notation is used.
RSRP (k, n), RSRQ (k, n): RSRP and RSRQ values measured by UEk (user terminal k) for cell n.
PRB (n): Total PRB usage rate in cell n.
EPRB (k, n): An increase in the PRB usage rate predicted when UEk hands over to cell n.
TPRB: Total number of PRBs.
D (k): The desired bit rate of UEk after handover.
T (RSRQ (k, n)): Bit rate for each PRB. This value depends on “Modulation and Coding Scheme (MCS)” used for data transmission, and can be calculated from RSRQ (k, n) transmitted from the user terminal.
-Th _PRB : PRB usage rate threshold for off-road determination.

(Step S11) The traffic offload effect determination unit 12 lists UEs to be subjected to HO (handover) when using MLB technology among UEs (user terminals) connected to the base station. Specifically, a UE that satisfies the condition of the following equation (1) is selected based on the RSRP or RSRQ received from each UE in step S1 of FIG.
Mn−Hys> Mp (1)
However, Mn is RSRP or RSRQ of the adjacent base station measured by UE. Mp is the RSRP or RSRQ of the connected base station measured by the UE. Hys is a hysteresis when performing a handover decision, and here, a minimum value allowable by the MLB technique is set.

(Step S12) The traffic offload effect determination unit 12 determines the HO-destination base station for each UE selected in step S11. Specifically, the base station having the maximum RSRP or RSRQ is selected as the HO-destination base station among the adjacent base stations of the own base station.

(Step S13) The traffic offload effect determination unit 12 sets the value of “RSRP _n -RSRP _s ” (where n is an adjacent base station and s is its own base station) for the UE selected in step S11. Sort UEs in descending order. Thereafter, steps S14 to S18 are repeatedly executed for each UEk until the PRB usage rate (PRB (s)) of the own station becomes equal to or less than the threshold (Th _PRB ) or all UEs are deleted from the list.

(Step S14) The traffic offload effect determination unit 12 calculates an increase in the PRB usage rate (ePRB (k, n)) predicted when UEk hands over to the cell n based on the following equation (2). To do. For D (k) in Equation (2), when UEk uses a “Guaranteed Bit Rate (GBR)” bearer, the minimum guaranteed bit rate in GBR is used, and UEk is “non Guaranteed Bit Rate ( When using the “n-GBR)” bearer, the current bit rate is used from the viewpoint of ensuring the same throughput after the handover.
ePRB (k, n) = D (k) ÷ (tPBR × T (RSRQ (k, n)) (2)

(Step S15) The traffic offload effect determination unit 12 determines that the sum of the PRB usage rate (PRB (n)) of the HO-destination base station of UEk and the ePRB (k, n) calculated in step S14 is a threshold value (Th _PRB ). It is judged whether it is below. As a result, if it is determined that the value is below, the process proceeds to step S16. Otherwise, the process proceeds to step S18.

(Step S16) The traffic offload effect determining unit 12 updates the PRBs of the own base station and the HO destination base station. Specifically, ePRB (k, n) calculated in step S14 is added to the PRB (PRB (n)) of the HO-destination base station. Also, the PRB usage rate of the current UEk is subtracted from the PRB (PRB (s)) of the own base station. Furthermore, UEk is deleted from the list.

(Step S17) The traffic offload effect determination unit 12 determines whether the PRB (PRB (s)) of the base station calculated in step S16 is below a threshold value (Th _PRB ). As a result, when it is determined that the value is lower, the process of FIG. 4 is terminated, and in other cases, the process proceeds to the process after step S14 for the next UE registered in the list.

(Step S18) As a result of the determination in step S15, the traffic offload effect determination unit 12 determines that further handover to the cell n is not possible, and lists UEs that have the same UEk and UEk and HO destination base station. Delete from.

As a result of the processing of FIG. 4, when the PRB usage rate (PRB (s)) of the own base station is lower than the threshold (Th _PRB ), it is determined that the traffic offload effect using the MLB technique is sufficient. On the other hand, if all the HO target UEs are deleted from the list before the PRB usage rate (PRB (s)) of the base station falls below the threshold (ThPRB), traffic off when MLB technology is used It is determined that the load effect is insufficient.

  According to this embodiment, in a base station that is determined to be in a congested state, it is determined whether or not a user terminal that is a handover target can be handed over to a base station that is a handover destination when MLB technology is used. It is determined whether the result of releasing the PRB assigned to the user terminal determined to be a certain effect is effective, and if it is determined that a certain effect is achieved, between base stations using MLB technology If traffic offload is performed and it is determined that a certain effect is not produced, inter-base station traffic offload using inter-base station traffic offload technology by cell coverage change is performed.

  As a result, when a certain traffic offload effect can be obtained by the traffic offload between base stations using MLB technology, the traffic offload between base stations can be reduced by MLB technology without increasing the radio wave interference to surrounding base stations. Can be implemented. On the other hand, when a certain traffic offload effect cannot be obtained due to the traffic offload between base stations using the MLB technology, a more reliable traffic offload effect can be expected by changing the cell coverage.

  FIG. 5 is an explanatory diagram for explaining the MLB technology. When the base station in the congested state determines that the traffic can be offloaded, the base station changes the handover parameter so as to facilitate the handover from the own base station to the adjacent base station. In LTE, by changing Hys in the above-described formula (1), the user terminal transmits an MR of an A3 event to the base station when the state satisfying the formula (1) is continued for a certain period of time. Execute handover processing.

  A base station in a congested state can facilitate handover from its own base station to an adjacent base station by setting Hys to a value smaller than the initial value. In addition, the adjacent base station can make it difficult to perform handover from its own base station to a congested base station by setting Hys to a value larger than the initial value. Therefore, the MLB technology does not change the cell coverages 201, 202, and 203 of the base stations BS1, BS2, and BS3.

  FIG. 6 is an explanatory diagram for explaining a traffic offload technology between base stations by changing cell coverage. In FIG. 6, each base station BS1, BS2, BS3 forms cell coverage 201, 202, 203. The base station that is determined to be in a congested state decreases the transmission power or sets the antenna tilt angle large (the antenna is directed downward) so as to reduce the cell coverage. Further, in the adjacent base station, the transmission power is increased or the antenna tilt angle is set small (the antenna is directed upward) so as to expand the cell coverage. Thereby, among the user terminals connected to the base station in the congested state, the user terminals in the cell coverage change part are handed over to the adjacent base station. As a result, the traffic of the congested base station is offloaded to the adjacent base station. In the example of FIG. 6, the cell coverage 202 of the congested base station BS2 is reduced to 202a, and the cell coverages 201 and 203 of the adjacent base stations BS1 and BS3 are expanded to 201a and 203a. As a result, the user terminal MS in the cell coverage changing part of the congested base station BS2 hands over to the adjacent base stations BS1 and BS3, and the traffic of the base station BS2 is offloaded to the adjacent base stations BS1 and BS3.

  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.

DESCRIPTION OF SYMBOLS 10 Communication control apparatus, 11 Own station state determination part, 12 Traffic offload effect determination part, 13 1st traffic offload control part, 14 2nd traffic offload control part, BS1, BS2, BS3 Base station, MS user Terminal, 201, 202, 203 cell coverage

Claims (4)

A communication control apparatus that selects whether to change a handover parameter for adjusting a timing at which a user terminal connected to a base station determined to be congested is to be handed over or to change cell coverage of the base station. Yes,
A traffic offload effect determining unit for determining a traffic offload effect when changing the handover parameter;
First traffic offload control for changing the handover parameter so as to facilitate handover from the base station to a base station adjacent to the base station when it is determined that a certain traffic offload effect is obtained. And
A second traffic offload control unit that reduces cell coverage of the base station when it is determined that a certain traffic offload effect cannot be obtained;
A communication control apparatus comprising: The traffic offload effect determination unit determines whether a user terminal to be handed over can be handed over to a base station to be handed over when changing the handover parameter, and determines whether the user terminal that has been handed over can be handed over Determine whether the result of releasing the allocated radio resources has a certain effect,
The communication control apparatus according to claim 1. The traffic off-road effect determination unit
Based on the communication quality information of the adjacent base station received from the user terminal , the user terminal uses the “Guaranteed Bit Rate (GBR)” to indicate the increase in the radio resource utilization rate when the user terminal is handed over to the adjacent base station. When using a bearer, estimation is performed using the minimum guaranteed bit rate of the GBR bearer. On the other hand, when the user terminal uses a “non Guaranteed Bit Rate (n-GBR)” bearer, Estimate using current bit rate ,
When the sum of the radio resource utilization rate of the adjacent base station and the estimated radio resource utilization rate is equal to or less than a predetermined threshold, it is determined that handover is possible
The communication control apparatus according to claim 2. A communication control method for selecting whether to change a handover parameter for adjusting a timing at which a user terminal connected to a base station determined to be congested is to be handed over or to change cell coverage of the base station. Yes,
Determining a traffic offload effect when changing the handover parameter;
Changing the handover parameter so as to facilitate handover from the base station to a base station adjacent to the base station when it is determined that a certain traffic offload effect is obtained;
If certain of the traffic offload effect is determined to not be obtained, and the step of reducing the cell coverage of the base station,
The communication control method characterized by including.

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