JP2009017075A - Mobile communication system, base station device, and mobile communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an amount of receiving quality information transmitted from a mobile station device to a base station device, and to control adaptive demodulation coding performed at the base station device to follow an actual channel state of a transmission path even if a channel change on the transmission path is large. <P>SOLUTION: The mobile station device includes a receiving quality measuring portion 111 for measuring the receiving quality of a plurality of channels based on a signal received from the base station device; a receiving quality information measuring portion for calculating a relationship between the receiving qualities measured by the receiving quality measuring portion 111 at different times; and a radio transmission portion 105 for transmitting the information indicating the relationship between the receiving quality information measured by the receiving quality measuring portion 111 and the receiving quality. Meanwhile, the base station device includes a demodulation coding controlling portion 209 for controlling adaptive demodulation coding of the signal transmitted to the mobile station device based on the information indicating the relationship between the receiving quality information and the receiving quality; and a radio transmission portion 205 for transmitting the signal subjected to adaptive demodulation coding control to the mobile station device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mobile communication system, a base station apparatus, and a mobile communication method for measuring and transmitting reception quality.

  Currently, there is an increasing demand for data communication in mobile communication systems, and various techniques for obtaining high frequency utilization efficiency corresponding to the increase in communication data associated therewith have been proposed. One technique for improving frequency utilization efficiency is OFDMA (Orthogonal Frequency Division Multiple Access). This OFDMA relates to a modulation scheme technique for communication using the same frequency in all cells in a communication area composed of cells, and can realize high-speed data communication.

  In scheduling of transmission packets in the OFDMA system, the mobile station device transmits CQI (Channel Quality Indicator), which is information indicating the reception quality of the downlink state in all subcarriers, to the base station device. A method of scheduling packets based on CQIs of all subcarriers transmitted from a device is known (for example, see Non-Patent Document 1).

  Moreover, in scheduling of transmission packets in an OFDM (Orthogonal Frequency Division Multiplexing) system using a plurality of subcarriers, each channel state (frequency characteristics, that is, transmission loss depending on the frequency) in the downlink in the mobile station apparatus And the like, the information obtained by quantizing each channel state is transmitted to the base station apparatus, and the base station apparatus determines a subcarrier to be allocated to each mobile station apparatus based on the transmitted information. (For example, refer to Patent Document 1).

  FIG. 9 is a diagram for explaining a conventionally known communication method between a base station apparatus and a mobile station apparatus. The communication method shown in FIG. 9 is disclosed in Non-Patent Document 2, for example. As shown in FIG. 9, the mobile station apparatus that has received downlink downlink information used for reception quality measurement from the base station apparatus measures the reception quality of each channel based on the downlink information, and the channel of the propagation path Create a profile.

The channel profile created by the mobile station apparatus is transmitted from the mobile station apparatus to the base station apparatus as reception quality information. Based on the reception quality information, the base station apparatus performs adaptive modulation coding and frequency selection scheduling processing on the downlink information transmitted from the base station apparatus to the mobile station apparatus.
JP 2005-130491 A “Comments on frequency scheduling and joint power and rate optimization for OFDM”, 3GPP, TSG RAN WG1 Meeting # 29, R-02-1321, November 2002 “CQI design and its impact to DL performance”, 3GPP, TSG RAN WG1 Meeting # 48, R1-071002, February 2007 “Compressed CQI Reporting Scheme”, 3GPP, TSG RAN WG1 Meeting # 48, R1-070879, February 2007

  However, in the conventional technique (FIG. 9), in order for the base station apparatus to perform appropriate adaptive modulation coding and frequency selection scheduling for the mobile station apparatus, all the mobile station apparatuses divided for each region are used. It is necessary to transmit the reception quality information for each channel to the base station apparatus. For example, in the technique described in Non-Patent Document 2, reception quality information that is divided into 32 stages (5 bits) for each of the 25 divided channels is transmitted from the mobile station apparatus to the base station apparatus. In this case, it is necessary to transmit reception quality information having an information amount of 25 × 5 bits = 125 bits.

  In this regard, Non-Patent Document 3 proposes a technique for reducing the amount of information of reception quality information to be transmitted by transmitting the reception quality information and its difference information from the mobile station device to the base station device. . Hereinafter, this method will be described with reference to FIG.

  As shown in FIG. 10, the reception qualities at the frequencies f0, f1,..., Fn−1, fn at time t0 are x (t0, f0), x (t0, f1),..., X (t0, fn−1). ), X (t0, fn), and the reception quality at the frequencies f0, f1,..., Fn−1, fn at time t1 are x (t1, f0), x (t1, f1),. -1), x (t1, fn), and the reception quality at the frequencies f0, f1,..., Fn-1, fn at time t2 are x (t2, f0), x (t2, f1),. , Fn-1), x (t2, fn), the mobile station apparatus first receives the reception quality information x (t0, f0), x (t0, f1), ..., x (t0, fn- at time t0. 1) Transmit x (t0, fn) to the base station apparatus. Subsequently, difference information of reception quality at time t0 and time t1, x (t1, f0) -x (t0, f0), x (t1, f1) -x (t0, f1), x (t1, f2)- Each of x (t0, f2)... is transmitted with, for example, 3 bits (8 levels). Similarly, difference information x (t2, f0) −x (t1, f0), x (t2, f1) −x (t1, f1), x (t2, f2) − of the reception quality between time t1 and time t2. x (t1, f2)... is transmitted in 3 bits (8 levels), for example, and so on, so that the mobile station device reduces the difference information with respect to the reception quality information transmitted last time to the base station device. ) To reduce the amount of received quality information transmitted to the base station apparatus.

  However, in this method (FIG. 10), when the channel state of the propagation path changes abruptly, the reception quality information transmitted from the mobile station apparatus to the base station apparatus can follow the actual channel fluctuation of the propagation path. The problem of disappearing occurs.

  When the channel state of the propagation path changes abruptly, that is, when the modulation scheme and coding rate applied to the signal transmitted by the base station apparatus must be changed at a large level (for example, modulation scheme QPSK, coding rate 1 / 3 to the modulation scheme 16QAM and the coding rate 8/9), the reception quality information having a small amount of information (for example, 3 bits) from the mobile station apparatus has a modulation scheme and a coding rate. Since it cannot be changed at a large level, adaptive modulation and coding cannot be performed with a required modulation method and coding rate. This indicates that the adaptive modulation and coding applied to the signal in the base station apparatus cannot follow the actual channel variation of the propagation path.

  In addition, if it is attempted to increase the level of the modulation scheme and the coding rate that can be changed with the reception quality information having a small amount of information, it becomes impossible to follow the channel fluctuation of the detailed propagation path. Even if the modulation method and coding rate are changed at a large level by transmitting reception quality information with a small amount of information multiple times, this is the reception quality transmitted from the mobile station device to the base station device. This will lead to an increase in the amount of information.

  The present invention has been made in view of such problems, and the channel variation of the propagation path is large while reducing the amount of reception quality information transmitted from the mobile station apparatus to the base station apparatus. The purpose of the present invention is to provide a mobile communication system, a base station apparatus, and a mobile communication method in which adaptive modulation and coding performed in a base station apparatus can follow the channel state of an actual propagation path.

  (1) In order to achieve the above object, the present invention has taken the following measures. That is, the mobile communication system according to the present invention is a mobile communication system including a mobile station apparatus and a base station apparatus, and the mobile station apparatus receives a plurality of channels based on signals received from the base station apparatus. A reception quality measurement unit for measuring quality, a reception quality information measurement unit for calculating a relationship between reception quality measured at different times by the reception quality measurement unit, reception quality information and reception quality measured by the reception quality measurement unit A reception quality information transmission unit that transmits information indicating the relationship between the reception quality information and the reception quality to the mobile station device based on the information indicating the relationship between the reception quality information and the reception quality. A modulation code control unit that controls adaptive modulation and coding for a signal to be transmitted, and a signal transmission that transmits the signal that has been subjected to control of adaptive modulation and coding by the modulation code control unit to the mobile station apparatus It is characterized in that it comprises a part, a.

  Thus, for example, in the base station apparatus, when the relationship of reception quality is a predetermined relationship (for example, when the variation in reception quality measured at different times is large), the modulation scheme and coding rate are determined. In order to determine the modulation method and coding rate when the relationship of the reception quality does not have a predetermined relationship (for example, when the variation of the reception quality measured at different times is small) Since the base station apparatus can determine the modulation scheme and coding rate applied to the signal according to the relationship of the reception quality measured at different times by the mobile station apparatus by changing the step width of It is possible to perform adaptive modulation control following the channel variation of the propagation path. Also, the modulation scheme and coding rate applied to the signal in the base station apparatus are determined simply by transmitting the difference information of the reception quality from the mobile station apparatus and the information indicating the relationship between the reception quality to the base station apparatus. The amount of reception quality information transmitted from the station device to the base station device can be reduced. As a result, even when the channel variation of the propagation path is large while reducing the information amount of the reception quality information transmitted from the mobile station device to the base station device, the adaptive modulation and coding performed in the base station device is It becomes possible to follow the channel state of the actual propagation path.

  (2) Moreover, the mobile communication system according to the present invention is a mobile communication system including a mobile station device and a base station device, and the mobile station device has a plurality of signals based on signals received from the base station device. A reception quality measurement unit that measures the reception quality of the channel, a correlation value calculation unit that calculates a correlation value indicating a relationship of reception quality based on the reception quality measured by the reception quality measurement unit at different times, and the reception quality measurement A reception quality information transmission unit that transmits the reception quality information measured by the unit and the correlation value to the base station device, the base station device based on the reception quality information and the correlation value. A modulation code control unit that controls adaptive modulation and coding of a signal to be transmitted to a device; and a signal transmission unit that transmits a signal that has been subjected to control of adaptive modulation and coding by the modulation code control unit to the mobile station device. It is characterized in that to obtain.

  Thus, for example, in the base station apparatus, when the correlation value calculated based on the reception quality measured at different times by the mobile station apparatus is large (for example, when the mobile station apparatus is stationary), the modulation scheme is used. In order to determine the modulation method and coding rate when the correlation value is small (for example, when the mobile station apparatus is moving at high speed), the step width for determining the coding rate is changed to be small. Thus, the adaptive modulation control that follows the actual channel variation of the propagation path can be performed. Also, the modulation scheme and coding rate applied to the signal in the base station apparatus simply by transmitting the reception quality difference information and the correlation value (or information indicating the calculated correlation value) from the mobile station apparatus to the base station apparatus. Therefore, the amount of received quality information transmitted from the mobile station apparatus to the base station apparatus can be reduced. As a result, even when the channel variation of the propagation path is large while reducing the information amount of the reception quality information transmitted from the mobile station device to the base station device, the adaptive modulation and coding performed in the base station device is It becomes possible to follow the channel state of the actual propagation path.

  (3) The mobile communication system according to the present invention is a mobile communication system including a mobile station device and a base station device, and the mobile station device has a plurality of signals based on signals received from the base station device. A reception quality measurement unit that measures the reception quality of a channel, a variance value calculation unit that calculates a dispersion value indicating a relationship of reception quality based on the reception quality measured by the reception quality measurement unit at different times, and the reception quality measurement A reception quality information transmission unit that transmits the reception quality information measured by the unit and the variance value to the base station device, wherein the base station device is configured to transmit the mobile station based on the reception quality information and the variance value. A modulation code control unit that controls adaptive modulation and coding of a signal to be transmitted to a device; and a signal transmission unit that transmits a signal that has been subjected to control of adaptive modulation and coding by the modulation code control unit to the mobile station device. It is characterized in that to obtain.

  Thus, for example, in the base station apparatus, when the dispersion value calculated based on the reception quality measured by the mobile station apparatus at different times is small (for example, when the mobile station apparatus is stationary), the modulation scheme is used. In order to determine the modulation scheme and the coding rate when the variance is large (for example, when the mobile station apparatus is moving at high speed) while the step width for determining the coding rate is changed small Thus, the adaptive modulation control that follows the actual channel variation of the propagation path can be performed. Also, the modulation scheme and coding rate applied to the signal in the base station apparatus simply by transmitting the difference information of reception quality and the dispersion value (or information indicating the calculated dispersion value) from the mobile station apparatus to the base station apparatus. Therefore, the amount of received quality information transmitted from the mobile station apparatus to the base station apparatus can be reduced. As a result, even when the channel variation of the propagation path is large while reducing the information amount of the reception quality information transmitted from the mobile station device to the base station device, the adaptive modulation and coding performed in the base station device is It becomes possible to follow the channel state of the actual propagation path.

  (4) A base station apparatus according to the present invention is a base station apparatus that communicates with a mobile station apparatus, the reception quality information of a plurality of channels measured at different times by the mobile station apparatus, and the reception quality information A modulation code control unit that controls adaptive modulation and coding of a signal to be transmitted to the mobile station apparatus based on information indicating a relationship; and a signal that has been subjected to adaptive modulation and coding by the modulation code control unit And a signal transmission unit that transmits the signal.

  In this way, the modulation scheme and coding rate to be applied to the signal are determined based on the information indicating the relationship between the reception quality information and the reception quality information transmitted from the mobile station apparatus. (For example, when the variation in reception quality measured at different times is large), the step width for determining the modulation method and coding rate is greatly changed, while the relationship between the reception quality is predetermined. If the relationship is not relevant (for example, when the variation in reception quality measured at different times is small), the channel variation of the actual propagation path can be changed by changing the step width for determining the modulation method and coding rate to be small. It is possible to perform adaptive modulation control following the above. Further, since the modulation scheme and the coding rate to be applied to the signal can be determined using only the difference information of the reception quality transmitted from the mobile station apparatus and the information indicating the relationship between the reception quality, the base station apparatus can be determined from the mobile station apparatus. It is possible to reduce the amount of reception quality information to be transmitted to. As a result, even when the channel variation of the propagation path is large while reducing the information amount of the reception quality information transmitted from the mobile station device to the base station device, the adaptive modulation and coding performed in the base station device is It becomes possible to follow the channel state of the actual propagation path.

  (5) A mobile communication method according to the present invention is a mobile communication method using a mobile station apparatus and a base station apparatus, wherein the mobile station apparatus uses a plurality of channels based on a signal received from the base station apparatus. A reception quality measurement process for measuring the reception quality, a reception quality information measurement process for calculating a relationship between reception quality measured at different times in the reception quality measurement process, a reception quality information measured in the reception quality measurement process, and A reception quality information transmission step of transmitting information indicating a relationship of reception quality to the base station device, and the base station device is based on the reception quality information and information indicating the relationship of the reception quality, A modulation code control process for controlling adaptive modulation and coding for a signal to be transmitted to the mobile station apparatus, and a signal subjected to adaptive modulation and coding control in the modulation code control process are transmitted to the mobile station apparatus It is characterized by performing a No. transmission process.

  Thus, for example, in the base station apparatus, when the relationship of reception quality is a predetermined relationship (for example, when the variation in reception quality measured at different times is large), the modulation scheme and coding rate are determined. In order to determine the modulation method and coding rate when the relationship of the reception quality does not have a predetermined relationship (for example, when the variation of the reception quality measured at different times is small) Since the base station apparatus can determine the modulation scheme and coding rate applied to the signal according to the relationship of the reception quality measured at different times by the mobile station apparatus by changing the step width of It is possible to perform adaptive modulation control following the channel variation of the propagation path. Also, the modulation scheme and coding rate applied to the signal in the base station apparatus are determined simply by transmitting the difference information of the reception quality from the mobile station apparatus and the information indicating the relationship between the reception quality to the base station apparatus. The amount of reception quality information transmitted from the station device to the base station device can be reduced. As a result, even when the channel variation of the propagation path is large while reducing the information amount of the reception quality information transmitted from the mobile station device to the base station device, the adaptive modulation and coding performed in the base station device is It becomes possible to follow the channel state of the actual propagation path.

  According to the present invention, the modulation method and coding rate to be applied to the signal are determined by the base station device according to the relationship of the reception quality measured at different times by the mobile station device. Adaptive modulation control following channel fluctuation can be performed. Also, the modulation scheme and coding rate applied to the signal in the base station apparatus are determined simply by transmitting the difference information of the reception quality from the mobile station apparatus and the information indicating the relationship between the reception quality to the base station apparatus. The amount of reception quality information transmitted from the station device to the base station device can be reduced. As a result, even when the channel variation of the propagation path is large while reducing the information amount of the reception quality information transmitted from the mobile station device to the base station device, the adaptive modulation and coding performed in the base station device is It becomes possible to follow the channel state of the actual propagation path.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
First, the configuration of the mobile communication system according to the first embodiment of the present invention will be described. The mobile communication system according to the first embodiment includes a base station device and a mobile station device. FIG. 1 is a schematic block diagram illustrating configurations of a mobile station apparatus and a base station apparatus included in the mobile communication system according to the first embodiment.

  As shown in FIG. 1, the mobile station apparatus includes a transmission buffer 101, a modulation encoding unit 102, a mapping unit 103, an inverse fast Fourier transform (IFFT) unit 104, a wireless transmission unit (also referred to as a reception quality information transmission unit) 105, A transmission control unit 106, a radio reception unit 107, a fast Fourier transform (FFT) unit 108, a demodulation / decoding unit 109, and an antenna 110 are provided. The transmission control unit 106 includes a reception quality measurement unit 111, a reception quality information generation unit 112, and a correlation value calculation unit 113.

  The mobile station apparatus receives the downlink information transmitted from the base station apparatus by the radio reception unit 107, down-converts the received signal into a baseband signal, performs analog / digital conversion, and then performs the fast Fourier transform unit 108. Each subcarrier is converted into a modulation symbol. The modulation symbol converted by the fast Fourier transform unit 108 is demodulated and decoded by the demodulation / decoding unit 109 and output to the reception quality measurement unit 111 and the correlation value calculation unit 113.

  On the other hand, transmission information for the base station apparatus is input from the upper layer to the mobile station apparatus. This transmission information includes information on a base station apparatus that is a signal transmission destination, and is temporarily stored in the transmission buffer 101. Modulation coding section 102 performs modulation processing and error correction coding processing on the signal output from transmission buffer 101, and outputs a coded bit sequence to mapping section 103. Mapping section 103 maps the encoded bit sequence output from modulation encoding section 102 to a symbol sequence on each subcarrier, and outputs the result to inverse fast Fourier transform section 104.

  The inverse fast Fourier transform unit 104 performs an inverse fast Fourier transform process on the symbol sequence output from the mapping unit 103, converts it to a time-series baseband digital signal, and outputs the time-series baseband digital signal to the radio transmission unit 105. The output signal from the inverse fast Fourier transform unit 104 is digital / analog converted in the radio transmission unit 105, up-converted to a frequency suitable for transmission, and then transmitted to each base station apparatus via the antenna 110.

  Reception quality measuring section 111 measures reception quality of a plurality of channels based on signals received from the base station apparatus. In the present embodiment, the reception quality measurement unit 111 measures CINR (Carrier-to-Interference plus Noise power Ratio) as the reception quality.

  The base station apparatus includes a transmission buffer 201, a modulation encoding unit 202, a mapping unit 203, an inverse fast Fourier transform (IFFT) unit 204, a wireless transmission unit (also referred to as a signal transmission unit) 205, a wireless reception unit 206, a fast Fourier transform ( FFT) section 207, demodulation / decoding section 208, modulation code control section 209, scheduler control section 210, and antenna 211.

  Transmission information (also referred to as downlink information) is input from the upper layer to the base station apparatus. The downlink information includes information on a mobile station apparatus that is a signal transmission destination, and a signal to be transmitted to each mobile station apparatus is temporarily stored in the transmission buffer 201. Modulation code control section 209 determines the modulation scheme and coding rate to be applied to the signal based on the reception quality information and the correlation value transmitted from the mobile station apparatus, and outputs them to modulation coding section 202. Modulation coding section 202 performs modulation processing and error correction coding processing on the signal output from transmission buffer 201 based on the modulation scheme and coding rate determined by modulation code control section 209, and performs coding. The bit sequence is output to the mapping unit 203.

  Mapping section 203 maps the encoded bit sequence output from modulation encoding section 202 to the symbol sequence on each subcarrier based on the scheduling information output from scheduler control section 210, and performs inverse fast Fourier transform section 204. Output to. The inverse fast Fourier transform unit 204 performs an inverse fast Fourier transform process on the symbol sequence output from the mapping unit 203, converts the symbol sequence to a time-series baseband digital signal, and outputs the time-series baseband digital signal to the radio transmission unit 205. The output signal from the inverse fast Fourier transform unit 204 is digital / analog converted in the radio transmission unit 205, up-converted to a frequency suitable for transmission, and then transmitted to each mobile station device via the radio transmission unit 205 and the antenna 212. Sent to.

  On the other hand, the base station apparatus receives the transmission signal transmitted from the mobile station apparatus by the wireless reception unit 206. The wireless reception unit 206 down-converts the received signal into a baseband signal and performs analog / digital conversion. Fast Fourier transform section 207 converts each subcarrier output from radio reception section 206 into modulation symbols. The modulation symbol converted by the fast Fourier transform unit 207 is demodulated and decoded by the demodulation / decoding unit 208 and output to the modulation code control unit 209 and the scheduler control unit 210.

  FIG. 2 is a diagram for explaining the reception quality measured by the reception quality measurement unit 111 of the mobile station apparatus according to the first embodiment. In FIG. 2, the frequency is taken in the horizontal axis direction, the time is taken in the vertical axis direction, and the reception quality is taken in the direction orthogonal to the horizontal axis and the vertical axis. The reception quality shown in FIG. 2 indicates the reception quality in the mobile station apparatus for the signal transmitted from the base station apparatus.

2, the reception quality measurement unit 111, at time t _A, measures the reception quality indicated by the curve g1. Then, reception quality measurement unit 111, at time t _B, measures the reception quality indicated by the curve g2. Then, reception quality measurement unit 111, at time t _C, measures the reception quality indicated by the curve g3. Note that the reception quality measured by the reception quality measurement unit 111 of the mobile station apparatus can be expressed as X (t, f) as a function of time t and frequency f.

Correlation value calculation section 113 calculates a correlation value indicating the relationship between reception quality based on reception quality measured at different times (for example, time t _A and time t _B in FIG. 2) by reception quality measurement section 111. Specifically, the correlation value is calculated as follows.

ここで、式（１）におけるｎは、受信品質の相関値を測定する区間を示している。例えば、受信品質の相関値を測定する区間が５ＴＴＩ（Time Transmission Interval）であるならば、ｎ＝５となる。 The reception quality X (t, f) at the predetermined time t and the predetermined frequency f measured by the reception quality measuring unit 111 of the mobile station apparatus, and the time t−T and the predetermined frequency before the predetermined time t by the time difference T. Using reception quality X (t−T, f) at f, correlation value calculation section 113 calculates correlation value R _T (t) by the following equation (1).

Here, n in Equation (1) indicates a section in which a correlation value of reception quality is measured. For example, if the interval for measuring the correlation value of the reception quality is 5 TTI (Time Transmission Interval), n = 5.

Further, E (t) and S (t) in Equation (1) indicate the average value and standard deviation in the frequency direction of the reception quality X (t, f) at time t, respectively. The average value E (t) can be expressed as in the following formula (2). The standard deviation S (t) can be expressed as in the following formula (3).

ここで、受信品質Ｘ（ｔ，ｆ）の時間方向の変化速度が十分に緩やかであるとすると、Ｒ_Ｔ，τを測定した時刻τでの受信品質Ｘ（τ，ｆ）と、それより時刻差Ｔだけ後の時刻での受信品質Ｘ（τ＋Ｔ，ｆ）とには、大きい相関値Ｒ_Ｔ，τがあると推定できる。 Furthermore, when the measurement time length of the reception quality X (t, f) for calculating the correlation value is L (= t _C −t _A (FIG. 2)), the correlation value R _T (t) is near the time τ. The averaged one can be expressed by the following formula (4).

Here, assuming that the rate of change in the time direction of the reception quality X (t, f) is sufficiently slow, the reception quality X (τ, f) at the time τ when _{RT, τ} is measured, and the time It can be estimated that there is a large correlation value R _{T, τ} with the reception quality X (τ + T, f) at the time after the difference T.

  In addition, you may calculate a correlation value using calculation methods other than the method using Formula (1)-Formula (4) mentioned above. Further, in the present embodiment, the case where the correlation value is calculated using CINR as the reception quality has been described, but the correlation value may be calculated using other reception quality indicators.

  Next, a method for determining the modulation scheme and coding rate performed by the modulation code control section 209 based on the correlation value transmitted from the mobile station apparatus by the base station apparatus will be described. FIG. 3 is a diagram for explaining a method of determining a modulation scheme and a coding rate performed by the base station apparatus based on the correlation value transmitted from the mobile station apparatus according to the first embodiment of the present invention. .

  The base station apparatus selects a table having a different step width according to the magnitude of the correlation value of the reception quality measured at different times by the mobile station apparatus, and applies a modulation scheme and encoding applied to a signal transmitted at the step width. Change the level that determines the rate. Specifically, when the correlation value of the reception quality measured by the mobile station apparatus at different times is large, the base station apparatus selects the table A having a step width for changing the modulation scheme and the coding rate to be small. The modulation scheme applied to the signal to be transmitted with the step width and the level for determining the coding rate are changed. If the correlation value of the reception quality measured at different times is small, the base station apparatus selects a table C having a step width that greatly changes the modulation scheme and coding rate, and transmits a signal transmitted with the step width of the table C. The level for determining the modulation method and coding rate to be applied to is changed.

  Table A having a step size for changing the modulation scheme and coding rate to be small is difference information with respect to reception quality information (or reception quality information transmitted at time t0) transmitted last time by the mobile station apparatus to the base station apparatus. Is transmitted in 3 bits (8 levels), for example, with respect to the difference information 3 bits (8 levels), the base station apparatus has a step width of, for example, one step in a range from -3 to +4. The table which can determine the modulation system and code rate which are given to a signal is shown.

  Table C having a step width for greatly changing the modulation scheme and coding rate is difference information with respect to reception quality information (or reception quality information transmitted at time t0) transmitted last time by the mobile station apparatus to the base station apparatus. Is transmitted in 3 bits (8 levels), for example, with respect to the difference information 3 bits (8 levels), for example, the base station apparatus has a step width of 4 steps in a range from −12 to +16. The table which can determine the modulation system and code rate which are given to a signal is shown.

  Similarly, the table B shown in FIG. 3 shows difference information with respect to reception quality information (or reception quality information transmitted at time t0) transmitted last time by the mobile station apparatus to the base station apparatus, for example, 3 bits (8 levels). For example, the modulation method and coding rate applied to the signal by the base station apparatus are determined for the difference information of 3 bits (8 levels) with a width of 2 steps in a range from -6 to +8, for example. Shows a table that can be.

  In FIG. 3, the difference information transmitted from the mobile station apparatus is represented by 3 bits, but the difference information of the reception quality may of course be represented by any number of bits. Further, the step width corresponding to 3 bits (8 levels) may be any value or a number other than an integer.

  FIG. 4 is a diagram illustrating an example of information stored in the modulation code control unit 209 of the base station apparatus according to the first embodiment of the present invention. The mobile station device transmits a correlation value of the reception quality measured at different times to the base station device, and the base station device selects a table for determining the modulation method and coding rate based on the value, and The modulation method and coding rate applied to the signal are determined by the step width of the table. The modulation code control unit 209 of the base station apparatus stores a correlation value (for example, R12 or more) transmitted from the mobile station apparatus and a table (for example, table A) for determining the step width in association with each other. In this embodiment, two threshold values R11 and R12 are set for the correlation value. Here, R11 <R12.

  When the correlation value is equal to or greater than the predetermined threshold R12, the modulation code control unit 209 of the base station apparatus selects the table A as a table for determining the modulation scheme and coding rate. The table A is, for example, a table having a width of one step in a range from −3 to +4 with respect to the difference information of 3 bits (8 levels) as described above.

  When the correlation value is greater than or equal to the predetermined threshold R11 and less than the predetermined threshold R12, the modulation code control unit 209 of the base station apparatus uses table B as a table for determining the modulation scheme and coding rate. select. The table B is, for example, a table having a width of 2 steps in a range from −6 to +8 with respect to the 3-bit difference information as described above.

  When the correlation value is less than the predetermined threshold R11, the modulation code control unit 209 of the base station apparatus selects the table C as a table for determining the modulation scheme and coding rate. The table C is, for example, a table having a width of 4 steps in a range from −12 to +16 with respect to the difference information of 3 bits (8 levels) as described above.

  As shown above, the base station apparatus determines the modulation scheme and coding rate to be applied to the signal from the difference information of the reception quality transmitted from the mobile station apparatus and the step width of the table selected based on the correlation value. decide. Thereby, even when the channel variation of the propagation path is large, the adaptive modulation and coding applied to the signal can follow the channel state of the actual propagation path. In addition, in order to transmit only the reception quality difference information and the correlation value (or information indicating the calculated correlation value), the amount of reception quality information transmitted from the mobile station apparatus to the base station apparatus is reduced. Can do.

  FIG. 5 is a sequence chart showing processing of the mobile communication system according to the first embodiment of the present invention. As illustrated in FIG. 5, the radio transmission unit 205 of the base station apparatus transmits a signal to the mobile station apparatus via the antenna 211 (S501). The radio reception unit 107 of the mobile station apparatus receives a signal transmitted from the base station apparatus, and the reception quality measurement unit 111 measures the reception quality of a plurality of channels based on the received signal.

Then, the correlation value calculation unit 113 of the mobile station apparatus receives the reception quality (for example, the curves g1 and g2 in FIG. 2) measured by the reception quality measurement unit 111 at different times (for example, t _A and t _B in FIG. 2). Based on the above, the correlation value is calculated using the above-described equations (1) to (4). Here, a case will be described in which correlation value calculation section 113 of the mobile station apparatus obtains R13 (where R11 <R13 <R12) as the correlation value.

  Then, the radio transmission unit 105 of the mobile station apparatus obtains the difference information with respect to the reception quality information transmitted to the base station apparatus last time (or the reception quality information transmitted at time t0) and the correlation value R13 calculated by the correlation value calculation unit, It transmits to the base station apparatus via the antenna (S502).

  The radio reception unit 205 of the base station apparatus receives the reception quality difference information and the correlation value R13 information (or information indicating R13) transmitted by the mobile station apparatus. Next, the modulation code control unit 209 of the base station apparatus selects a table corresponding to the correlation value R13 calculated by the correlation value calculation unit 113 of the mobile station apparatus based on information stored in association with each other. For example, if the table shown in FIG. 3 is used, here, the modulation code control unit 209 selects the table B associated with the correlation value R13.

  Then, the modulation code control unit 209 receives the difference information of the reception quality transmitted from the mobile station apparatus and the step width determined by the table (for example, from −6 to +8 if the table shown in FIG. 3 is used) In this range, a modulation method and a coding rate to be applied to a signal to be transmitted are determined. The base station apparatus performs adaptive modulation coding on the signal with the determined modulation scheme and coding rate, and transmits the signal to the mobile station apparatus via the antenna 211 (S503).

FIG. 6 is a diagram for explaining the effect of the first embodiment according to the present invention. FIG. 6A shows reception quality characteristics measured when the mobile station apparatus moves at a low speed. The base station device transmits signals to the mobile station device at times t ₁ , t ₂ , and t ₃ . FIG. 6B shows reception quality characteristics measured when the mobile station apparatus moves at high speed. The base station apparatus transmits signals to the mobile station apparatus at times t ₄ , t ₅ , and t ₆ .

The reception quality measured by the reception quality measuring unit 111 of the mobile station apparatus varies greatly depending on the state of the propagation path from the base station apparatus to the mobile station apparatus. In the context of such a channel, the correlation value calculation unit 113 of the mobile station apparatus, the reception quality information measured at time t _1, the reception quality information measured at time t _2, the reception quality information measured at time t ₂ When the reception quality information measured at time t _3, and the reception quality information measured at time t _4, the reception quality information measured at time t _5, the reception quality information measured at time t _5, at time t ₆ The correlation value of the measured reception quality information is calculated. Instead of calculating the correlation value from the two reception qualities measured at different times, the correlation value calculation unit 113 may calculate the correlation value from the reception quality information measured over a certain interval.

When the mobile station apparatus is stationary or moving at a low speed, that is, when the channel variation of the propagation path is small, the temporal variation of the reception quality measured by the mobile station apparatus is small. The correlation value calculated in is a large value. For example, when the mobile station apparatus measures reception quality at time t ₁ , time t ₂ , and time t ₃ shown in FIG. 6A, a larger correlation value is calculated.

  In this case, in the present embodiment, the difference information of the reception quality transmitted from the mobile station apparatus and the table having a small step width selected based on the correlation value transmitted from the mobile station apparatus are used as signals. Since the modulation scheme and coding rate to be applied are determined, it is possible to determine a fine modulation scheme and coding rate following the channel variation of the propagation path.

On the other hand, when the mobile station apparatus is moving at high speed, that is, when the channel variation of the propagation path is large, the temporal variation of the reception quality measured by the mobile station apparatus is large. The correlation value is a small value. For example, when the mobile station apparatus measures reception quality at time t ₄ , time t ₅ , and time t ₆ shown in FIG. 6B, a smaller correlation value is calculated.

  In this case, in the present embodiment, the signal is applied from the table having the large step width selected based on the difference information of the reception quality transmitted from the mobile station apparatus and the correlation value transmitted from the mobile station apparatus. In order to determine the modulation scheme and coding rate, it is possible to determine the modulation scheme and coding rate following channel fluctuations with a large propagation path.

  In the above-described embodiment, the case where CINR is used as the reception quality has been described. However, the present invention is not limited to this. For example, the reception quality includes RSSI (Receive Signal Strength Indication), SNR (Signal to Noise power Ratio), SIR (Signal to Interference power Ratio), SINR. (Signal to Interference plus Noise power Ratio), CNR (Carrier to Noise power Ratio), CIR (Carrier to Interference power Ratio), etc. You may use the parameter | index which shows reception quality in relation to signal power or carrier power. In addition, as an indicator of reception quality, BER (Bit Error Rate), PER (Packet Error Rate), BLER (Block Error Rate), and the like indicating reception quality in relation to success or failure of reception An index indicating reception quality may be used in relation to the success or failure of reception.

  The channel in the present embodiment is composed of one or a plurality of subcarriers, but a plurality of channels indicated by a transmission antenna or an eigenmode in SDMA (Space Division Multiple Access) such as MIMO (Multiple Input Multiple Output), or The present embodiment may be applied to a mobile communication system using a combination of channels.

(Second Embodiment)
Next, a mobile communication system according to the second embodiment of the present invention is described. In the mobile communication system according to the second embodiment, the mobile communication system according to the first embodiment determines the modulation scheme and the coding rate according to the correlation value of the reception quality measured at different times by the mobile station apparatus. On the other hand, the mobile station apparatus is different in that the modulation scheme and the coding rate are determined according to the dispersion value of the reception quality measured at different times.

  Note that, in the mobile communication system according to the second embodiment, the base station apparatus includes the variance value calculation unit 114 instead of the correlation value calculation unit 113, and the base station apparatus according to the first embodiment. It is different. FIG. 7 is a schematic block diagram illustrating configurations of a mobile station apparatus and a base station apparatus included in the mobile communication system according to the second embodiment. In FIG. 7, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the mobile station apparatus according to the second embodiment, the variance value calculation unit 114 calculates the variance value as follows. Here, let X (t, f) be a value measured at a certain time t and a certain frequency f of the reception quality measured by the mobile station apparatus. At this time, the dispersion value in the time direction of the measured reception quality X (t, f) can be obtained as follows.

ここでＥ（ｔ，ｆ）は、区間τ±１／２Ｌ、周波数ｆにおける受信品質Ｘ（ｔ，ｆ）の時間方向の平均値を示し、以下の式（６）で表すことができる。

When the measurement time length for measuring the dispersion by the mobile station apparatus is L, the dispersion in the vicinity of time τ of X (t, f) at the frequency f can be expressed as the following equation (5).

Here, E (t, f) represents an average value in the time direction of the reception quality X (t, f) in the interval τ ± 1 / 2L and the frequency f, and can be expressed by the following equation (6).

ここで、分散Ｖ（τ）が小さい場合には、Ｖ（τ）を測定した時刻τでの受信品質Ｘ（τ，ｆ）と、それより時刻差Ｔだけ後の時刻での受信品質Ｘ（τ＋Ｔ，ｆ）とには、強い相関があり、逆に分散値Ｖ（τ）が大きい場合には、測定した受信品質Ｘ（τ，ｆ）から時刻差Ｔ後の受信品質Ｘ（τ＋Ｔ，ｆ）を推定することは困難である。 Furthermore, what averaged the dispersion | distribution V ((tau), f) in the frequency f in a frequency direction can be represented by the following formula | equation (7).

Here, when the variance V (τ) is small, the reception quality X (τ, f) at the time τ when V (τ) is measured, and the reception quality X ( There is a strong correlation with τ + T, f). Conversely, when the variance value V (τ) is large, the reception quality X (τ + T, f after time difference T from the measured reception quality X (τ, f). ) Is difficult to estimate.

  In addition, you may use the calculation method of a dispersion value other than the method using Formula (5)-Formula (7) mentioned above. In this embodiment, the case where the variance value is calculated using CINR as the reception quality is shown, but the variance value may be calculated using another reception quality index.

The modulation code control unit 209 of the base station apparatus, depending on the magnitude of the dispersion value of the reception quality measured by the reception quality measurement unit of the mobile station apparatus at different times (for example, time t _A and time t _B in FIG. 2), A table having a different step width is selected, and the modulation method and coding rate applied to the signal are determined by the step width of the table. Specifically, when the dispersion value of the reception quality measured by the mobile station apparatus at different times is small, the base station apparatus selects the table A having a step width for changing the modulation scheme and the coding rate to be small, and the table A The modulation scheme and coding rate to be applied to the signal are determined with the step width. If the dispersion value of the reception quality measured by the mobile station apparatus at different times is large, the base station apparatus selects the table C having a step width for greatly changing the modulation scheme and coding rate, and the signal with the step width of the table B is selected. The modulation method and coding rate to be applied to are determined. Here, the tables A and C are, for example, the tables shown in FIG. 3 described in the correlation value example.

  Next, a method for selecting tables having different step widths based on the variance value transmitted by the mobile station apparatus by the modulation code control unit 209 of the base station apparatus will be described.

  FIG. 8 is a diagram illustrating an example of information stored in the modulation code control unit of the base station apparatus according to the second embodiment of the present invention. The mobile station device transmits a dispersion value of the reception quality measured at different times to the base station device, and the base station device selects a table for determining the modulation method and coding rate based on the value, and The modulation method and coding rate applied to the signal are determined by the step width of the table. The modulation code control unit 209 of the base station apparatus stores a dispersion value (for example, V12 or more) transmitted from the mobile station apparatus in association with a table (for example, table C) for determining the step width. In this embodiment, two threshold values V11 and V12 are set for the variance value. Here, V11 <V12.

  When the variance value is equal to or greater than the predetermined threshold value V12, the modulation code control unit 209 of the base station apparatus selects Table C as a table for determining the modulation scheme and coding rate. When the variance value is greater than or equal to the predetermined threshold value V11 and less than the predetermined threshold value V12, the modulation code control unit 209 of the base station apparatus uses table B as a table for determining the modulation scheme and coding rate. select. When the variance value is less than the predetermined threshold value R11, the modulation code control unit 209 of the base station apparatus selects the table A as a table for determining the modulation scheme and coding rate. Here, the table A, the table B, and the table C indicate, for example, the tables shown in FIG. 3 described in the correlation value embodiment.

  As shown above, the base station apparatus uses the table selected based on the difference information of the reception quality transmitted from the mobile station apparatus and the dispersion value transmitted from the mobile station apparatus, the modulation scheme and code applied to the signal Determine the conversion rate. Thereby, even when the channel variation of the propagation path is large, the adaptive modulation and coding to be performed can follow the channel state of the actual propagation path. Also, in order to transmit only the difference information and the variance value (or information indicating the calculated variance value) of the reception quality, the amount of reception quality information transmitted from the mobile station apparatus to the base station apparatus is reduced. Can do.

  The sequence showing the processing of the mobile communication system according to the second embodiment of the present invention can be realized by the same sequence as the sequence shown in FIG. 5 shown in the first embodiment.

  In the embodiment described above, these functions or a program for realizing a part of these functions is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system. The base station apparatus or the mobile station apparatus may be controlled by executing. Here, the “computer system” includes an OS and hardware such as peripheral devices.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” dynamically holds a program for a short time, like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, it is also assumed that a server that holds a program for a certain time, such as a volatile memory inside a computer system that serves as a server or client. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and the design and the like within the scope of the present invention are also within the scope of the claims. include.

It is a schematic block diagram which shows the structure of the base station apparatus of the mobile communication system which concerns on the 1st Embodiment of this invention, and a mobile station apparatus. It is a figure for demonstrating the reception quality which the reception quality measurement part of the mobile station apparatus by 1st Embodiment measures. It is a figure explaining selection of the table for determining the modulation system and coding rate which are given to the signal by a 1st embodiment. It is a figure which shows an example of the information which the base station apparatus by 1st Embodiment memorize | stores. It is a sequence chart which shows the process of the mobile communication system by 1st Embodiment. It is a figure for demonstrating the effect by 1st Embodiment. It is a schematic block diagram which shows the structure of the base station apparatus of the mobile communication system which concerns on the 2nd Embodiment of this invention, and a mobile station apparatus. It is a figure which shows an example of the information which the base station apparatus by 2nd Embodiment memorize | stores. It is a figure for demonstrating the communication method of the conventional base station apparatus and a mobile station apparatus. It is a figure for demonstrating the measurement of the reception quality in the conventional mobile station apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Transmission buffer 102 Modulation encoding part 103 Mapping part 104 Inverse fast Fourier transform (IFFT) part 105 Wireless transmission part (Reception quality information transmission part)
106 Transmission Control Unit 107 Radio Reception Unit 108 Fast Fourier Transform (FFT) Unit 109 Demodulation Decoding Unit 110 Antenna 111 Reception Quality Measurement Unit 112 Reception Quality Information Generation Unit 113 Correlation Value Calculation Unit 114 Variance Value Calculation Unit 201 Transmission Buffer 202 Modulation Code Conversion unit 203 mapping unit 204 inverse fast Fourier transform (IFFT) unit 205 wireless transmission unit (signal transmission unit)
206 Radio reception unit 207 Fast Fourier transform (FFT) unit 208 Demodulation decoding unit 209 Modulation code control unit 210 Scheduler control unit 211 Antenna

Claims (5)

A mobile communication system comprising a mobile station device and a base station device,
The mobile station device
A reception quality measuring unit that measures reception quality of a plurality of channels based on a signal received from the base station device;
A reception quality information measurement unit for calculating a relationship between reception quality measured at different times by the reception quality measurement unit;
A reception quality information transmission unit that transmits the reception quality information measured by the reception quality measurement unit and information indicating the relationship between the reception quality to the base station device, and
The base station device
A modulation code control unit that performs adaptive modulation and coding control on a signal to be transmitted to the mobile station apparatus based on the reception quality information and information indicating a relationship between the reception quality;
A mobile communication system, comprising: a signal transmission unit that transmits a signal that has been subjected to adaptive modulation and coding control by the modulation code control unit to the mobile station apparatus. A mobile communication system comprising a mobile station device and a base station device,
The mobile station device
A reception quality measuring unit that measures reception quality of a plurality of channels based on a signal received from the base station device;
A correlation value calculation unit for calculating a correlation value indicating a relationship of reception quality based on reception quality measured at different times by the reception quality measurement unit;
A reception quality information transmission unit that transmits the reception quality information measured by the reception quality measurement unit and the correlation value to the base station device;
The base station device
A modulation code controller that controls adaptive modulation and coding for a signal to be transmitted to the mobile station apparatus based on the reception quality information and the correlation value;
A mobile communication system, comprising: a signal transmission unit that transmits a signal that has been subjected to adaptive modulation and coding control by the modulation code control unit to the mobile station apparatus. A mobile communication system comprising a mobile station device and a base station device,
The mobile station device
A reception quality measuring unit that measures reception quality of a plurality of channels based on a signal received from the base station device;
A dispersion value calculation unit that calculates a dispersion value indicating a relationship of reception quality based on reception quality measured by the reception quality measurement unit at different times; and
A reception quality information transmission unit that transmits the reception quality information measured by the reception quality measurement unit and the variance value to the base station device, and
The base station device
A modulation code control unit that controls adaptive modulation and coding for a signal to be transmitted to the mobile station apparatus based on the reception quality information and the variance value;
A mobile communication system, comprising: a signal transmission unit that transmits a signal that has been subjected to adaptive modulation and coding control by the modulation code control unit to the mobile station apparatus. A base station device that communicates with a mobile station device,
Controlling adaptive modulation and coding of signals transmitted to the mobile station apparatus based on reception quality information of a plurality of channels measured at different times by the mobile station apparatus and information indicating a relationship between the reception quality information A modulation code control unit;
A base station apparatus comprising: a signal transmission unit that transmits a signal that has been subjected to adaptive modulation and coding by the modulation code control unit to the mobile station apparatus. A mobile communication method using a mobile station device and a base station device,
The mobile station device
A reception quality measurement process for measuring reception quality of a plurality of channels based on a signal received from the base station apparatus;
A reception quality information measurement process for calculating a relationship between reception quality measured at different times in the reception quality measurement process;
Performing a reception quality information transmission step of transmitting the reception quality information measured in the reception quality measurement step and information indicating the relationship between the reception quality to the base station device;
The base station device
A modulation code control process for controlling adaptive modulation and coding for a signal to be transmitted to the mobile station apparatus based on the reception quality information and information indicating the relationship between the reception quality;
A signal transmission process for transmitting a signal, which has been subjected to adaptive modulation and coding control in the modulation code control process, to the mobile station apparatus.

Images