JP5187236B2 - Mobile station, in-cell position estimation method, cell search method and program - Google Patents

Description

  The present invention relates to a mobile station, an intra-cell location estimation method, a cell search method, and a program, and more particularly, to a mobile station of a mobile communication system in which a base station transmits a reference signal (RS), and an intra-cell location estimation method. The present invention relates to a cell search method and a program.

  Orthogonal division frequency multiplexing (OFDM) and orthogonal frequency division multiplexing (OFDM), such as the next generation mobile communication system (LTE; Long Term Evolution) defined by 3GPP (3rd Generation Partnership Project) In a wireless communication system using Multiple Access), wireless communication between a mobile station and a base station is realized by mapping a data signal, a reference signal (Reference Signal), or the like to a plurality of orthogonal subcarriers. A mobile station in such a wireless communication system has a function of measuring the reception quality from the received power of the reference signal in the downlink and reporting it to the base station.

  As shown in Non-Patent Document 1, introduction of subframes (blank subframes) in which signals such as data signals and reference signals are not mapped in the downlink of LTE is being studied.

  Patent Document 1 discloses an interference and noise estimation device used for signal-to-interference and noise ratio estimation in an OFDM / OFDMA / DMT (Discrete Multi-tone Technology) system.

JP-A-2005-204307

“Specifying blank subframes for effective support of relays”, 3GPP TSG-RAN WG1 # 55 R1-084385, November 2008, [online], [February 17, 2009 search], Internet <URL: www.3gpp.org/ftp/TSG_RAN/WG1_RL1/TSGR1_55/Docs/R1-084385.zip>

  In the present invention, use of a blank subframe as proposed in the 3GPP is considered. In blank subframes, valid signals such as data signals and reference signals are not mapped to all subcarriers. Therefore, each subcarrier is not affected by the influence of the propagation path or the thermal noise of the receiver. The received power should be zero.

  However, in an actual environment, interference power is generated due to the influence of signals transmitted from base stations in other cells. Furthermore, thermal noise that cannot be ignored is generated inside the mobile station, and the received power of each subcarrier measured from the blank subframe should be interpreted as the sum of interference power and noise power from other cells. Can do.

  If the magnitude of the interference power can be estimated, it is determined whether the mobile station is located at the center of the cell or at the cell edge close to the boundary with other cells. Various measures can be taken to eliminate the influence of interference, but it is difficult to measure only the interference power.

  An object of the present invention is to provide a mobile station, a cell search method, and a program having a function of determining the position of the own station (the mobile station) in the cell using the blank subframe.

  According to a first aspect of the present invention, a blank subframe power estimation unit that calculates interference noise power of a blank subframe in which neither a reference signal nor a data signal is mapped, and the blank subframe power estimation unit A mobile station is provided that includes an in-cell position estimation unit that estimates the position of the own station in the cell from the difference between the interference noise power calculated in the above and the interference noise power obtained from the reference signal.

  According to a second aspect of the present invention, a blank subframe power estimation step for calculating interference noise power of a blank subframe in which neither a reference signal nor a data signal is mapped, and the blank subframe power estimation unit A position estimation method is provided that includes a position estimation step of estimating the position of the mobile station in the cell from the difference between the interference noise power calculated in this way and the interference noise power obtained from the reference signal.

  According to the third aspect of the present invention, the process of calculating the interference noise power of the blank subframe in which neither the reference signal nor the data signal is mapped, and the interference calculated by the blank subframe power estimation unit A program to be executed by a computer mounted on a mobile station is provided that includes a process of estimating the position of the mobile station in a cell from the difference between the noise power and the interference noise power obtained from the reference signal.

  According to the present invention, it becomes possible for the mobile station to estimate the position of the own station in the cell. For example, even if the mobile station does not have a GPS function, the cell search method is changed according to the position in the cell. Etc. can be used. Further, as one of the reception qualities, it is possible to transmit the estimated position of the mobile station in the cell to the base station, and to take measures to improve the reception characteristics of the mobile station on the base station side.

  The reason why the above effect can be obtained is as follows. Since it can be generally said that the thermal noise inside the mobile station does not vary greatly with time, the interference and noise power estimated in the blank subframe and the interference and noise power estimated in the normal subframe Can be interpreted as a fluctuation amount of the interference power.

  Since the interference power is an influence from another cell, it can be said that if the interference power is large, the mobile station is likely to be located at the cell edge instead of at the center of the cell. On the other hand, when the interference power is small, it can be said that the mobile station is likely to exist at the center of the cell.

It is a block diagram for demonstrating the outline | summary of this invention. It is a block diagram showing the structure of the mobile station of the 1st Embodiment of this invention. FIG. 2 is a diagram illustrating an LTE radio frame structure. It is an example of the determination table for changing the cell search frequency according to the amount of interference power fluctuation. It is a flowchart showing operation | movement of the mobile station of the 1st Embodiment of this invention.

  First, the outline of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the present invention effectively uses a subframe transmitted from a base station as described above, and performs a normal subframe for performing interference and noise power estimation processing from a normal subframe to which a reference signal is mapped. A reception power estimation unit 131 and a blank subframe reception power estimation unit 132 that performs interference and noise power estimation processing from the blank subframe are provided.

  The in-cell position estimation unit 16 compares the interference and noise power estimation values output from the normal subframe reception power estimation unit 131 with the interference and noise power estimation values output from the blank subframe reception power estimation unit 132. Thus, the magnitude of interference power from other cells is estimated, and the position of the mobile station in the cell is estimated.

  The estimated position of the mobile station in the cell can be used, for example, to change the cell search method in the mobile station. Thereby, reduction of the power consumption of a mobile station, improvement of cell search performance, etc. are achieved. Also, the estimated in-cell position of the mobile station can be reported on the base station side to help improve the radio service for the mobile station.

[First Embodiment]
Next, a first embodiment of the present invention that changes the cell search frequency using the in-cell position will be described in detail with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the mobile station according to the first embodiment of the present invention. In FIG. 2, elements relating to the downlink reception function of the mobile station are shown, and other elements are omitted.

  Referring to FIG. 2, the mobile station according to the first embodiment of the present invention includes a receiving unit 20 that receives a signal from a base station, a subframe determining unit 10, a physical channel / signal separating unit 11, and the like. In addition to the conversion unit 12 and the normal subframe received power estimation unit 131, the signal power addition averaging unit 14, the blank subframe received power estimation unit 132, the power estimated value storage unit 133, and the interference power fluctuation amount calculation unit 15 And an in-cell position estimation unit 16 and a cell search frequency control unit 17.

  First, a method for determining whether or not a received subframe is a blank subframe will be described. FIG. 3 is a diagram illustrating an LTE radio frame structure defined by 3GPP. In the case of LTE, one radio frame is composed of 10 subframes. It is assumed that the mobile station is notified of information on whether the received subframe is a blank subframe or a normal subframe from the transmitting base station. For example, Non-Patent Document 1 proposes that information indicating whether or not a blank subframe is included in a system information block (SIB) included in broadcast information from a base station.

  The subframe determination unit 10 determines whether the subframe received by the reception unit 20 is a blank subframe or a normal subframe based on the notification from the base station.

  When the received subframe is a normal subframe, the physical channel / signal separation unit 11 separates the signal mapped to the received subframe into a reference signal and a data signal.

  The equalization unit 12 equalizes the reference signal separated by the physical channel / signal separation unit 11 with a known signal pattern (for example, zero forcing equalization; ZF equalization).

The normal subframe reception power estimation unit 131 estimates interference and noise power N _U in units of system bandwidths using a plurality of subcarriers equalized by the equalization unit 12, and stores them in the power estimation value storage unit 133. Output.

  When the received subframe is a blank subframe, the signal power addition averaging unit 14 adds and averages the signal powers of all subcarriers in the received subframe.

Blank subframes received power estimation section 132, the signal power output from the signal power averaging section 14 estimates the interference and noise power N _B, and outputs the power estimation value storage unit 133.

  The power estimation value storage unit 133 stores the values estimated by the normal subframe reception power estimation unit 131 and the blank subframe reception power estimation unit 132. The power estimated value storage unit 133 only needs to be able to hold the latest output value. For example, when the same subframe type is continuously received, the normal subframe reception power estimation unit 131 or the blank subframe reception power estimation unit 132 overwrites the latest reception power estimation value, respectively, If the previously estimated value is discarded, the buffer size can be reduced.

The interference power fluctuation amount calculation unit 15 calculates the difference between the interference and noise power N _U estimated from the normal subframe stored in the power estimation value storage unit 133 and the interference and noise power N _B estimated from the blank subframe ( Y = N _U −N _B ) and output the interference power fluctuation amount Y to the in-cell position estimation unit 16.

  The in-cell position estimation unit 16 estimates the position of the mobile station in the cell from the sign (Sign (Y)) and the absolute value (Abs (Y)) of the interference power fluctuation amount Y, and performs a cell search based on the result. The control unit 17 is instructed to increase / decrease or maintain the cell search frequency.

  FIG. 4 is an example of a determination table using the interference power fluctuation amount Y. In the example of FIG. 4, when the sign of Y (Sign (Y)) is positive and the absolute value of Y (Abs (Y)) is larger than a preset threshold value T, the mobile station moves more to the cell edge. An instruction is given to increase the frequency of cell search. Conversely, if the sign of Y (Sign (Y)) is negative and the absolute value of Y (Abs (Y)) is greater than the threshold T, it is assumed that the mobile station has moved closer to the cell center. An instruction to lower the search frequency is given.

  Next, the operation of this embodiment will be described in detail with reference to the drawings. FIG. 5 is a flowchart showing the operation of the mobile station according to the first embodiment of the present invention. Referring to FIG. 5, first, the mobile station determines whether the currently received subframe is a blank subframe or a normal subframe (step S001).

  When the received subframe is a normal subframe, power estimation processing is performed by the physical channel / signal separation unit 11, the equalization unit 12, and the normal subframe reception power estimation unit 131 (step S002).

  On the other hand, when the received subframe is a blank subframe, power estimation processing is performed by the signal power conversion average separation unit 14 and the blank subframe reception power estimation unit 132 described above (step S003).

  The result of the power estimation process in step S002 or S003 is stored in the power estimation value storage unit 133 (step S004; power estimation value buffering).

  Next, the mobile station determines whether or not the interference power fluctuation amount Y can be calculated based on whether or not a measurement value of a type different from the currently received subframe type has already been stored in the power estimation value storage unit 133. (Step S005).

As a result of the determination, when the interference power fluctuation amount can be calculated (Yes in step S005), the interference and noise power N _U estimated from the normal subframe, and the interference and noise power N _B estimated from the blank subframe , The interference power fluctuation amount Y is calculated from the difference (Y = N _U −N _B ) (step S006).

  As a result of the determination, if it is determined that the amount of interference power fluctuation cannot be calculated (No in step S005), the process ends and prepares for the process of the next subframe (RET).

If the interference power fluctuation amount Y obtained as described above is larger than the predetermined value T (Yes in step S007), the mobile station increases the cell search frequency (step S009).
Conversely, when the interference power fluctuation amount is less than the predetermined value −T (Yes in step S008), the mobile station decreases the cell search frequency (step S010).

  As described above, in the present embodiment, the mobile station can autonomously determine its own position in the cell using the blank subframe, and the cell search frequency can be varied. Thereby, since the cell search frequency is optimized, the power consumption of the mobile station can be reduced, and the cell search performance can be improved.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and further modifications, replacements, and replacements may be made without departing from the basic technical idea of the present invention. Adjustments can be made. For example, in the first embodiment described above, it has been described that the frequency of cell search is controlled, but the same can be achieved by controlling the mobile station to increase or decrease the number of cells to be searched according to the position in the cell. An effect is obtained.

  Further, in the above-described embodiment, it has been described that the determination is made based on the sign direction of the interference power fluctuation amount Y and the absolute value. However, the threshold value for determining that the cell is near the cell center and the threshold value for determining that the cell is at the cell edge. And may be set respectively.

  Further, in the above-described embodiment, the mobile station has been described as changing the cell search process based on the position in the cell determined by itself, but the mobile station uses the cell as one index indicating the reception quality. You may make it transmit the position in the inside to a base station. In addition, the base station that has received the position in the cell changes the neighboring cell list used for the cell search according to the position of the mobile station in the cell, or uses it for other allocation of radio resources to the mobile station. It may be.

  Further, the method for measuring interference noise power in the above-described embodiment is merely an example, and various other methods for measuring interference noise power that have been proposed can be used.

  Furthermore, in the above-described embodiment, an example of LTE has been described, but a mobile communication system having a base station that transmits both a frame in which no valid signal is transmitted and other frames is transmitted. If applicable.

DESCRIPTION OF SYMBOLS 10 Sub-frame determination part 11 Physical channel / signal separation part 12 Equalization part 131 Normal sub-frame reception power estimation part 132 Blank sub-frame reception power estimation part 133 Power estimated value storage part 14 Signal power addition average part 15 Interference power fluctuation amount calculation Unit 16 in-cell position estimation unit 17 cell search frequency control unit 20 reception unit

Claims (12)

A blank subframe power estimation unit that calculates interference noise power of a blank subframe in which neither the reference signal nor the data signal is mapped,
An intra-cell position estimator that estimates the position of the own station in the cell from the difference between the interference noise power calculated by the blank subframe power estimator and the interference noise power obtained from the reference signal Bureau. From the difference between the interference noise power calculated by the blank subframe power estimation unit and the interference noise power obtained from the reference signal, the fluctuation amount of the interference power is measured,
The mobile station according to claim 1, wherein the position of the own station in a cell is estimated based on a magnitude of fluctuation amount of the interference power.   Furthermore, the mobile station of Claim 1 or 2 provided with the cell search control part which changes a cell search method based on the position of the said own station in the said estimated cell.   The mobile station according to claim 3, wherein the frequency of cell search is increased when the amount of fluctuation of the interference power is larger than a predetermined value.   The mobile station according to claim 3 or 4, wherein the frequency of cell search is decreased when the amount of fluctuation of the interference power is smaller than a predetermined value.   The mobile station according to any one of claims 3 to 5, wherein when the amount of fluctuation of the interference power is larger than a predetermined value, the number of target cells for cell search is increased.   The mobile station according to any one of claims 3 to 6, wherein the number of target cells for cell search is decreased when the fluctuation amount of the interference power is smaller than a predetermined value. Furthermore, a subframe determination unit that determines whether the received subframe is a blank subframe,
A sub signal power addition averaging unit that adds the signal power of all subcarriers in the blank subframe and outputs the sum to the blank subframe power estimation unit,
An interference power fluctuation amount calculation unit that calculates a difference value between the interference noise power calculated by the blank subframe power estimation unit and the interference noise power obtained from the reference signal;
A mobile station according to any one of claims 1 to 6.   The mobile station according to claim 1 or 2, further comprising a function of transmitting the estimated position of the own station in the cell to a base station. A blank subframe power estimation step for calculating interference noise power of a blank subframe to which neither the reference signal nor the data signal is mapped;
A position estimation step for estimating the position of the mobile station in the cell from the difference between the interference noise power calculated by the blank subframe power estimation unit and the interference noise power obtained from the reference signal. Estimation method. A blank subframe power estimation step for calculating interference noise power of a blank subframe to which neither the reference signal nor the data signal is mapped;
Cell search for estimating the position of a mobile station in a cell from the difference between the interference noise power calculated by the blank subframe power estimation unit and the interference noise power obtained from the reference signal, and changing the cell search pattern A cell search method including a control step. A process of calculating the interference noise power of a blank subframe in which neither the reference signal nor the data signal is mapped;
A process for estimating the position of the mobile station in the cell from the difference between the interference noise power calculated by the blank subframe power estimation unit and the interference noise power obtained from the reference signal is mounted on the mobile station. Program to be executed by a computer.

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