JP2011041195A - Signal quality estimation apparatus, signal quality estimation method and computer program - Google Patents

Abstract

A signal quality estimation based on a received reference signal is performed in consideration of a change in radio wave propagation path state caused by movement of a wireless terminal.
Frequency characteristics estimators for estimating an uplink frequency characteristic for each RB based on a received reference signal, and the significance of a received reference signal based on a coherence time of a wireless terminal and a reference signal transmission time. A determination unit 13 that determines each time, a reception signal average level estimation unit 16 that estimates a reception signal average level, and frequency characteristics and reception based on the significant reception reference signal for an RB that has a significant reception reference signal A received signal level estimation unit that estimates a received signal level based on the average signal level and estimates a received signal level based on the received signal average level without using frequency characteristics for an RB having no significant received reference signal 18 and a signal quality calculation unit 19 that calculates the signal quality based on the received signal level.
[Selection] Figure 4

Description

  The present invention relates to a signal quality estimation device, a signal quality estimation method, and a computer program.

  In recent years, standards for new wireless communication systems have been studied by various standardization organizations (for example, 3GPP (3rd Generation Partnership Project), 3GPP2 (3rd Generation Partnership Project 2), IEEE 802.16 standardization organizations, etc.). For example, as a successor system of the third generation (3G) cellular system, LTE (Long Term Evolution: official name is “Evolved Universal Terrestrial Radio Access (E-UTRA)”. See Non-Patent Documents 1 and 2) and UMB ( Next generation cellular systems (also called 3.9G cellular systems) such as Ultra Mobile Broadband are being considered. Furthermore, an IMT-Advanced system (also referred to as a 4G cellular system), which is an evolution system of the 3.9G cellular system, is being studied.

  Some wireless communication systems under consideration adopt an Orthogonal Frequency Division Multiple Access (OFDMA) scheme. For example, LTE, UMB, WiMAX, and LTE-Advanced and IEEE 802.16m currently being studied for 4G cellular systems.

  In a wireless communication system using the OFDMA scheme (hereinafter referred to as an OFDMA system), a plurality of subcarriers within an available frequency band (hereinafter referred to as a system band) can be allocated to a wireless terminal. Moreover, the allocation content can be changed with time. Therefore, in general, in an OFDMA system, radio resources can be allocated flexibly using a two-dimensional radio resource composed of a frequency component and a time component.

  In the radio resource allocation, a modulation scheme and a coding rate suitable for signal quality are selected in adaptive modulation and coding (AMC). For the signal quality, for example, SINR (Signal-to-Interference-plus-Noise Ratio) is used. The AMC is one of important functions that influence the frequency utilization efficiency of the radio system because the throughput is maximized by appropriately operating the AMC.

  The signal quality estimation method used in AMC differs depending on the type of wireless communication system, but in an OFDMA system compliant with LTE (hereinafter referred to as LTE system), the downlink (link in the direction from the base station to the terminal) In both the estimation of the signal quality and the estimation of the signal quality of the uplink (link in the direction from the terminal to the base station), a method using a reference signal (reference signal) is generally used. In the case of the LTE system, the downlink reference signal is a cell specific reference signal (see Non-Patent Document 1, for example).

  On the other hand, uplink reference signals are a data demodulation reference signal (DeModulation Reference Signal: DM-RS) and a sounding reference signal (Sounding Reference Signal: SRS) (see, for example, Non-Patent Document 1). In the uplink, it is possible to receive a reference signal transmitted from a wireless terminal by a base station and estimate signal quality based on this received signal.

3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)” 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 8)” Hiroshi Katsuragawa, “LTE uplink reference signal”, 2008 IEICE Society Conference, BS-4-6, September 2008

  As described above, in the uplink of the LTE system, there are DM-RS and SRS as reference signals, and the signal quality can be estimated based on the received reference signal received by the base station. However, when the state of the radio wave propagation path changes due to the movement of the wireless terminal, if the signal quality is estimated based on the received reference signal without considering the change of the radio wave propagation path state, the signal quality estimation result is There is a possibility that it cannot follow the change of the state. In addition, there is a risk that signal quality estimation accuracy will vary greatly depending on the frequency and magnitude of changes in the state of the radio wave propagation path caused by the movement of the wireless terminal.

  The present invention has been made in consideration of such circumstances, and its purpose is to perform signal quality estimation based on a received reference signal in consideration of a change in radio wave propagation path state caused by movement of a wireless terminal. An object is to provide a signal quality estimation apparatus, a signal quality estimation method, and a computer program that can be performed.

  In order to solve the above-described problem, a signal quality estimation apparatus according to the present invention is a signal quality estimation apparatus that estimates uplink signal quality from a wireless terminal to a base station. A frequency characteristic estimator configured to estimate an uplink frequency characteristic of the radio terminal for each frequency band section based on a received reference signal received by the base station for a reference signal transmitted from the radio terminal; and A determination unit that determines the significance of the received reference signal for each frequency band section based on a coherence time and a transmission time from the wireless terminal related to the received reference signal or a reception time at the base station; and the base station The reception signal average level estimation unit that estimates the average level of the reception signal from the wireless terminal that is received at the frequency band section having the significant reception reference signal The received signal level is estimated based on the frequency characteristic based on the received reference signal and the average received signal level, and the reception is performed without using the frequency characteristic for a frequency band section having no significant received reference signal. A reception signal level estimation unit that estimates a reception signal level based on a signal average level, and a signal quality calculation unit that calculates the signal quality based on the reception signal level.

  In the signal quality estimation device according to the present invention, the received signal level estimation unit receives the instantaneous value of the frequency characteristic based on the significant received reference signal for the frequency band section where the significant received reference signal is present. The received signal level is calculated by adding to the average signal level.

  In the signal quality estimation apparatus according to the present invention, the reception signal level estimation unit sets the reception signal average level as a reception signal level for a frequency band section having no significant reception reference signal.

  In the signal quality estimation apparatus according to the present invention, the determination unit calculates the signal quality calculated by the signal quality calculation unit from the transmission time from the wireless terminal related to the reception reference signal or the reception time at the base station. When the time until the scheduled transmission time of an uplink radio resource allocation target frame for which radio resource allocation is performed is within the coherence time, the received reference signal is determined to be significant.

  In the signal quality estimation apparatus according to the present invention, the frequency characteristic estimation unit estimates the frequency characteristic only for the frequency band section of the received reference signal determined to be significant by the determination unit.

  In the signal quality estimation apparatus according to the present invention, the reference signal is a first reference signal that is transmitted from the radio terminal in a predetermined number of consecutive sections of the uplink frequency band, or the radio signal It is a second reference signal transmitted from the radio terminal in a section of the uplink frequency band for data signal transmission allocated to the terminal.

  In the signal quality estimation device according to the present invention, the reception signal level estimation unit prioritizes the frequency characteristic based on the first reception reference signal over the frequency characteristic based on the second reception reference signal. It is characterized by using.

  The signal quality estimation apparatus according to the present invention includes a coherence time estimation unit that estimates a coherence time of the wireless terminal.

  The signal quality estimation apparatus according to the present invention includes an interference signal level estimation unit that estimates a level of an interference signal received by the base station, and the signal quality calculation unit is based on the reception signal level and the interference signal level. And calculating the signal quality.

  A signal quality estimation method according to the present invention is a signal quality estimation method for estimating uplink signal quality from a radio terminal to a base station, and is a reference transmitted from the radio terminal for each uplink frequency band section Estimating a frequency characteristic of an uplink related to the wireless terminal for each frequency band section based on a received reference signal received by the base station, and a coherence time of the wireless terminal and the received reference signal Determining the significance of the received reference signal for each frequency band section based on a transmission time from a wireless terminal or a reception time at the base station; and a received signal from the wireless terminal received at the base station Estimating the average level, and for the frequency band segment with a significant received reference signal, the frequency characteristics based on the significant received reference signal and the reception Estimating the received signal level based on the average signal level, and estimating the received signal level based on the received signal average level without using the frequency characteristic for a frequency band segment having no significant received reference signal And calculating the signal quality based on the received signal level.

A computer program according to the present invention is a computer program for performing signal quality estimation processing for estimating uplink signal quality from a radio terminal to a base station, from the radio terminal for each division of an uplink frequency band. Based on a received reference signal received by the base station for a reference signal to be transmitted, estimating an uplink frequency characteristic for the radio terminal for each frequency band section, a coherence time of the radio terminal, and the reception reference Determining the significance of the received reference signal for each frequency band section based on a transmission time from the wireless terminal related to a signal or a reception time at the base station, and from the wireless terminal receiving at the base station Estimating the average level of the received signals for the frequency band, and for the frequency band section where there is a significant received reference signal, Estimating the received signal level based on the frequency characteristic based on the signal and the average received signal level; and for the frequency band section having no significant received reference signal, the received signal without using the frequency characteristic. A computer program for causing a computer to execute a step of estimating a received signal level based on an average level and a step of calculating the signal quality based on the received signal level.
As a result, the signal quality estimation apparatus described above can be realized using a computer.

  Advantageous Effects of Invention According to the present invention, an effect that signal quality estimation based on a received reference signal can be performed in consideration of a change in radio wave propagation path state caused by movement of a wireless terminal.

It is a conceptual diagram which shows the structure of the LTE system which concerns on one Embodiment of this invention. It is a figure which shows the structure of the uplink radio frame of the LTE system which concerns on the embodiment. FIG. 3 is a conceptual diagram showing a configuration of radio resources in one subframe shown in FIG. 2. It is a block diagram which shows the structure which concerns on Example 1 of the signal quality estimation part 1 shown in FIG. It is a flowchart which shows the procedure of the signal quality estimation method which concerns on Example 1 of this invention. It is a block diagram which shows the structure which concerns on Example 2 of the signal quality estimation part 1 shown in FIG. It is a flowchart which shows the procedure of the signal quality estimation method which concerns on Example 2 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram showing a configuration of an LTE system according to an embodiment of the present invention. In FIG. 1, a base station 100 and a radio terminal 200 perform radio communication on the uplink and the downlink, respectively.

  FIG. 2 is a diagram illustrating a configuration of an uplink radio frame in the LTE system according to the present embodiment. In FIG. 2, one radio frame (one frame length is 10 milliseconds) is composed of ten subframes (one subframe length is 1 millisecond). FIG. 3 is a conceptual diagram showing a configuration of radio resources in one subframe shown in FIG. As shown in FIG. 3, radio resources in one subframe are resource blocks (RB) having a certain frequency bandwidth (number of subcarriers: N_SC) and a certain time width (number of OFDM symbols: N_OFDM). N_RB units are connected in the frequency direction. The frequency bandwidth for N_RB RBs corresponds to the system bandwidth. One RB corresponds to one section of the uplink system band.

  The SRS is transmitted from the radio terminal 200 in a cycle for every predetermined number of consecutive RBs (SRS bandwidths). The RB included in the SRS bandwidth is the RB targeted for SRS transmission. In the RB targeted for SRS transmission, the SRS is transmitted in the last OFDM symbol in time in the subframe as shown in FIG.

  The DM-RS is transmitted from the radio terminal 200 by an RB (DM-RS transmission RB) for data signal transmission (for uplink physical layer data channel (Physical Uplink Shared Channel: PUSCH)) assigned to the radio terminal 200. Is done. In an RB to be transmitted as a DM-RS (DM-RS transmission RB), the DM-RS is transmitted using a temporally defined OFDM symbol in a subframe as shown in FIG.

  Returning to FIG. In FIG. 1, a base station 100 includes a signal quality estimation unit 1, a terminal information acquisition unit 2, a radio scheduler 3, an SRS scheduler 4, and a radio unit 5. The signal quality estimation unit 1 estimates the uplink signal quality for each radio terminal 200. The terminal information acquisition unit 2 acquires various information.

  The radio scheduler 3 performs RB allocation for each subframe used when the radio terminal 200 transmits a data signal in the uplink. The RB of the allocation result by the wireless scheduler 3 becomes the DM-RS transmission target RB (DM-RS transmission RB). The subframe transmission time is the DM-RS transmission time.

  The SRS scheduler 4 determines a rule (SRS transmission information) when the radio terminal 200 transmits an SRS on the uplink. With the SRS transmission information, the SRS bandwidth and the SRS transmission time regarding the SRS transmitted by the wireless terminal 200 can be specified.

  The radio unit 5 transmits a downlink radio signal and receives an uplink radio signal with the radio terminal 200. In addition, the radio unit 5 receives an uplink radio signal transmitted from a radio terminal subordinate to a base station other than the base station 100. An uplink radio signal transmitted from a radio terminal under another base station becomes an interference signal.

  Hereinafter, the signal quality estimation unit 1 according to the present embodiment will be described with examples.

  FIG. 4 is a block diagram illustrating a configuration according to Example 1 of the signal quality estimation unit 1 illustrated in FIG. 1. In FIG. 4, the signal quality estimation unit 1 includes an input information acquisition unit 11, a coherence time estimation unit 12, a determination unit 13, an SRS frequency characteristic estimation unit 14, a DMRS frequency characteristic estimation unit 15, a received signal average level estimation unit 16, and an interference. A signal level estimator 17, a received signal level estimator 18, and a signal quality calculator 19 are included. Hereinafter, the operation of the signal quality estimation unit 1 shown in FIG. 4 will be described in detail with reference to FIG.

  FIG. 5 is a flowchart illustrating the procedure of the signal quality estimation method according to the first embodiment of the present invention. The signal quality estimation unit 1 starts the signal quality estimation process of FIG. 5 at the signal quality estimation timing. Note that the signal quality estimation unit 1 performs signal quality estimation processing for each wireless terminal 200 to be processed by the wireless scheduler 3, but for the sake of convenience of description, the following description will be made with respect to one wireless terminal 200. .

  In FIG. 5, in step S1, the input information acquisition unit 11 acquires input information. Details of the input information will be described in each step described later.

  Next, in step S <b> 2, the coherence time estimation unit 12 estimates the coherence time of the wireless terminal 200. The coherence time can be estimated from the maximum Doppler frequency of the wireless terminal 200. The coherence time estimation unit 12 calculates a coherence time by multiplying the reciprocal of the maximum Doppler frequency (minimum Doppler period) of the wireless terminal 200 by a coherence time calculation coefficient. The maximum Doppler frequency or the minimum Doppler period of the wireless terminal 200 is supplied from the terminal information acquisition unit 2 to the coherence time estimation unit 12 via the input information acquisition unit 11. The terminal information acquisition unit 2 estimates the maximum Doppler frequency or the minimum Doppler period of the radio terminal 200 based on the uplink received signal from the radio terminal 200 received by the radio unit 5. The coherence time calculation coefficient is a positive real number of 1 or less, and is set in advance. The coherence time calculation coefficient may be changed by the operator.

  Next, in step S <b> 3, the SRS frequency characteristic estimation unit 14 and the DMRS frequency characteristic estimation unit 15 each estimate the uplink frequency characteristic related to the radio terminal 200.

  The SRS frequency characteristic estimation unit 14 estimates the uplink frequency characteristic related to the radio terminal 200 for each RB based on the SRS received signal of each RB from the radio terminal 200. As a result of this estimation, an instantaneous value of the frequency characteristic is obtained for each RB. The SRS reception signal acquired by the terminal information acquisition unit 2 is supplied from the terminal information acquisition unit 2 to the SRS frequency characteristic estimation unit 14 via the input information acquisition unit 11. The terminal information acquisition unit 2 acquires the SRS reception signal from the uplink reception signal from the wireless terminal 200 received by the wireless unit 5. The SRS is transmitted from the radio terminal 200 over the entire system band while circulating for each SRS bandwidth. For this reason, the terminal information acquisition unit 2 supplies the latest SRS reception signal for the entire system band to the SRS frequency characteristic estimation unit 14.

  The DMRS frequency characteristic estimation unit 15 estimates the uplink frequency characteristic related to the radio terminal 200 for each RB based on the DM-RS received signal of each RB from the radio terminal 200. As a result of this estimation, an instantaneous value of the frequency characteristic is obtained for each RB. The DM-RS received signal acquired by the terminal information acquisition unit 2 is supplied from the terminal information acquisition unit 2 to the SRS frequency characteristic estimation unit 14 via the input information acquisition unit 11. The terminal information acquisition unit 2 acquires a DM-RS reception signal from the uplink reception signal from the radio terminal 200 received by the radio unit 5. The DM-RS is transmitted from the radio terminal 200 by DM-RS transmission RB, but is not necessarily transmitted in the entire system band. For this reason, the terminal information acquisition unit 2 supplies DM-RS reception signals for the latest fixed period to the DMRS frequency characteristic estimation unit 15.

  Next, in step S <b> 4, the received signal average level estimation unit 16 estimates the average level of the received signal from the radio terminal 200 received by the base station 100.

Here, a method of estimating the received signal average level will be described.
The wireless terminal 200 transmits power headroom (PH) information to the base station 100. The PH information is defined by equation (1) (see Non-Patent Document 2).
PH (i) = P_CMAX− { ₁₀ log ₁₀ (M_PUSCH (i)) + P_O_PUSCH (j) + α (j) · PL + Δ_TF (i) + f (i)}, unit is dB (1)
Here, i is the identification number of the subframe, and PH (i) is the PH information of the i-th subframe. P_CMAX is the maximum transmittable power value of the wireless terminal 200. M_PUSCH (i) is the number of RBs transmitted in the i-th subframe. j is an identification number of the radio terminal 200, and P_O_PUSCH (j) is an offset power value used by the PUSCH transmission power of the j-th radio terminal 200. PL is a path loss value between the radio terminal 200 and the base station 100 (Serving Sector), and is a value including the antenna gains of the radio terminal 200 and the base station 100. α (j) is a correction coefficient for the path loss value of the j-th wireless terminal 200. Δ_TF (i) is a parameter specific to the wireless terminal in the i-th subframe. f (i) is a transmission power adjustment value of PUSCH in the i-th subframe. Parameters such as a path loss value correction coefficient (α (j)) and PUSCH transmission power offset value (P_O_PUSCH (j)) can be arbitrarily set.

By changing the equation (1), the path loss value (PL) is expressed by the equation (2).
PL = [P_CMAX−PH (i) − { ₁₀ log ₁₀ (M_PUSCH (i)) + P_O_PUSCH (j) + Δ_TF (i) + f (i)}] / α (j), unit is dB (2)

Moreover, the transmission power of PUSCH is controlled by a control equation defined by equation (3) (see Non-Patent Document 2).
P_PUSCH (i) = min {P_CMAX, 10log ₁₀ (M_PUSCH (i)) + P_O_PUSCH (j) + α (j) · PL + Δ_TF (i) + f (i)}, unit is dBm (3)
However, min {A, B} is the smaller value of A and B. P_PUSCH (i) is a transmission power value of PUSCH transmitted in the i-th subframe.

By substituting equation (2) into equation (3), the PUSCH transmission power value (P_PUSCH (i)) of wireless terminal 200 is expressed by equation (4).
P_PUSCH (i) = min {P_CMAX, P_CMAX-PH (i)}, unit is dBm (4)

  Thereby, the received signal average level estimation unit 16 calculates the PUSCH transmission power value (P_PUSCH (i) [dBm]) of the radio terminal 200 using the equation (4), and the path loss value (PL [dB]) using the equation (2). ) And subtract the path loss value (PL [dB]) from the PUSCH transmission power value (P_PUSCH (i) [dBm]) to calculate the received signal average level [dBm] of the radio terminal 200.

  The PH information (PH (i)) acquired by the terminal information acquisition unit 2 is supplied from the terminal information acquisition unit 2 to the received signal average level estimation unit 16 via the input information acquisition unit 11. The terminal information acquisition unit 2 acquires PH information (PH (i)) from the uplink reception signal from the wireless terminal 200 received by the wireless unit 5. As the maximum transmittable power value (P_CMAX) of the radio terminal 200, a default value set in advance may be used, or a value notified from the radio terminal 200 may be used. The maximum transmittable power value (P_CMAX) notified from the wireless terminal 200 is acquired by the terminal information acquisition unit 2 from the terminal information acquisition unit 2 to the received signal average level estimation unit 16 via the input information acquisition unit 11. Supplied. The terminal information acquisition unit 2 acquires the maximum transmittable power value (P_CMAX) from the uplink received signal from the radio terminal 200 received by the radio unit 5. Note that the default value of the maximum transmittable power value (P_CMAX) may be changed by the operator.

  Note that the received signal average level estimation method is not limited to the method using the above-described PH information. As another received signal average level estimation method, for example, DM-RS transmitted from the radio terminal 200 can be used. Specifically, the reception level of the DM-RS reception signal is measured for each DM-RS transmission RB, and the reception level of each DM-RS transmission RB within a certain period is averaged in the time axis direction and the frequency axis direction. This average value is taken as the received signal average level.

  In addition, when performing moving averaging when estimating the received signal average level, a coefficient for moving average is set in advance. The coefficient for moving average may be changed by an operator.

  The above is the description of the received signal average level estimation method.

Returning to FIG.
Next, in step S5, the interference signal level estimation unit 17 estimates the interference signal level for each RB based on the DM-RS received signal. The DM-RS received signal acquired by the terminal information acquisition unit 2 is supplied from the terminal information acquisition unit 2 to the interference signal level estimation unit 17 via the input information acquisition unit 11. The terminal information acquisition unit 2 acquires a DM-RS reception signal from the reception signal received by the radio unit 5.

  The Zadoff-Chu sequence used for DM-RS is different for each base station. Accordingly, the DM-RS received signal received by its own base station 100 is correlated with the DM-RS received signal using the Zadoff-Chu sequence of its own base station 100, and the radio terminal 200 under its own base station 100. The DM-RS received signal from the signal is detected, and the remainder after removing the detected signal becomes an interference signal (including a noise component). The interference signal level estimation unit 17 calculates the level of the interference signal for each RB. When moving average is performed at the time of interference signal level estimation, a coefficient for moving average is set in advance. The coefficient for moving average may be changed by an operator.

  Next, in step S6, the determination unit 13 determines the significance of the SRS reception signal from the radio terminal 200 based on the coherence time and SRS transmission time of the radio terminal 200 for each RB. The coherence time of the wireless terminal 200 is supplied from the coherence time estimation unit 12. The SRS transmission time in each RB of the wireless terminal 200 can be specified from the SRS transmission information of the wireless terminal 200. The SRS transmission information is supplied from the SRS scheduler 4 to the determination unit 13 via the input information acquisition unit 11.

  The determination unit 13 determines that the SRS reception signal of the RB is significant when the time from the SRS transmission time of a certain RB to the scheduled transmission time of the next radio resource allocation target subframe is within the coherence time. The scheduled transmission time of the next radio resource allocation target subframe is supplied from the wireless scheduler 3 to the determination unit 13 via the input information acquisition unit 11. The next radio resource allocation target subframe is an uplink radio resource allocation target frame in which radio resource allocation is performed using the signal quality calculated by the signal quality calculation unit 19 in the current signal quality estimation process.

  Next, in step S8, the reception signal level estimation unit 18 determines the reception signal level for the RB (that is, RB in which the SRS reception signal is significant) for which the determination result in step S6 is significant (YES in step S7). Is estimated. As a result of the determination in step S6, “RB having a significant SRS reception signal” is notified from the determination unit 13 to the reception signal level estimation unit 18.

  The reception signal level estimation unit 18 adds the instantaneous value of the frequency characteristic based on the SRS reception signal of the RB to the reception signal average level for the RB having a significant SRS reception signal, and adds the value of the addition result of the RB. Receive signal level. The instantaneous value of the frequency characteristic based on the SRS reception signal of each RB is supplied from the SRS frequency characteristic estimation unit 14 to the reception signal level estimation unit 18. The reception signal average level is supplied from the reception signal average level estimation unit 16 to the reception signal level estimation unit 18.

  On the other hand, in step S9, the determination unit 13 determines, based on the coherence time and DM-RS transmission time of the radio terminal 200, for each RB, for the RB in which the determination result in step S6 is not significant (step S7, NO). The significance of the DM-RS received signal from the wireless terminal 200 is determined. The DM-RS transmission time in each RB of the wireless terminal 200 is supplied from the wireless scheduler 3 to the determination unit 13 via the input information acquisition unit 11.

  When the time from the DM-RS transmission time of a certain RB to the scheduled transmission time of the next radio resource allocation target subframe is within the coherence time, the determination unit 13 determines that the DM-RS received signal of the RB is significant. Is determined.

  Next, in step S11, the reception signal level estimation unit 18 determines that the result of determination in step S9 is significant (step S10, YES) RB (that is, the SRS reception signal is not significant, but the DM-RS reception signal is significant). For a certain RB), the received signal level is estimated. As a result of the determination in step S <b> 9, “RB having a significant DM-RS reception signal” is notified from the determination unit 13 to the reception signal level estimation unit 18.

  The reception signal level estimation unit 18 adds the instantaneous value of the frequency characteristic based on the DM-RS reception signal of the RB to the reception signal average level for the RB having a significant DM-RS reception signal, and the value of the addition result Is the received signal level of the RB. The instantaneous value of the frequency characteristic based on the DM-RS reception signal of each RB is supplied from the DMRS frequency characteristic estimation unit 15 to the reception signal level estimation unit 18.

  On the other hand, in step S12, the reception signal level estimation unit 18 determines that the determination result in step S9 is not significant (step S10, NO) RB (that is, both the SRS reception signal and the DM-RS reception signal are not significant RB). On the other hand, the received signal level is estimated. As a result of the determination in step S <b> 9, “RB in which both the SRS reception signal and the DM-RS reception signal are not significant” is notified from the determination unit 13 to the reception signal level estimation unit 18.

  The reception signal level estimation unit 18 does not use the instantaneous value of the frequency characteristic of the RB with respect to the RB in which both the SRS reception signal and the DM-RS reception signal are not significant, and calculates the reception signal average level as the reception signal level of the RB. To do.

  As a result of steps S8, S11, and S12, a received signal level is obtained for each RB over the entire band of the uplink system band.

  Next, in step S13, the signal quality calculation unit 19 calculates the signal quality based on the received signal level and the interference signal level. In the present embodiment, SINR is used as signal quality. The signal quality calculation unit 19 calculates SINR for each RB. The SINR of a certain RB is a value obtained by dividing the received signal level of the RB by the interference signal level. The reception signal level of each RB is supplied from the reception signal level estimation unit 18 to the signal quality calculation unit 19. The interference signal level is supplied from the interference signal level estimation unit 17 to the signal quality calculation unit 19.

  The signal quality estimation unit 1 supplies the signal quality of each RB of the wireless terminal 200 to the wireless scheduler 3. The radio scheduler 3 uses the signal quality of each RB of each radio terminal 200 supplied from the signal quality estimation unit 1 in radio resource allocation of the next radio resource allocation target subframe. The signal quality of each RB of a certain radio terminal 200 is used for selecting an RB suitable for the radio terminal 200, selecting a modulation scheme and a coding rate in AMC, and the like.

  According to the first embodiment, the significance of the reception reference signal (SRS reception signal and DM-RS reception signal) is determined for each RB based on the coherence time of the wireless terminal 200. Then, when estimating the received signal level of each RB, the frequency characteristics based on the significant received reference signal are added to the RB having the significant received reference signal based on the average received signal level. The frequency characteristics based on the received reference signal are not taken into account for the RB having no significant received reference signal. Thereby, the effect that the signal quality estimation based on the received reference signal can be performed in consideration of the change of the radio wave propagation path state caused by the movement of the radio terminal 200 is obtained. In addition, it is possible to prevent a large variation in signal quality estimation accuracy due to the frequency and magnitude of changes in the radio wave propagation path state caused by the movement of the wireless terminal. As a result, stable signal quality estimation accuracy can be expected.

  Further, by using the frequency characteristic based on the SRS received signal with priority over the frequency characteristic based on the DM-RS received signal, it is possible to stabilize the signal quality estimation accuracy. This is because the SRS is originally designed for signal quality measurement and is constantly transmitted from the radio terminal 200 over the entire system band.

  Further, since the received signal level is estimated based on the average received signal level, it is possible to estimate the signal quality even in an RB where a significant received reference signal cannot be obtained.

  Further, since the coherence time of each wireless terminal 200 is estimated, the effect of improving the significance determination accuracy related to each wireless terminal 200 is obtained.

  FIG. 6 is a block diagram illustrating a configuration according to the second embodiment of the signal quality estimation unit 1 illustrated in FIG. 1. FIG. 7 is a flowchart illustrating the procedure of the signal quality estimation method according to the second embodiment of the present invention. 6 and 7, parts corresponding to those in FIGS. 4 and 5 according to the first embodiment are denoted by the same reference numerals.

  In FIG. 6, the configuration of the signal quality estimation unit 1 is almost the same as that of FIG. 4 according to the first embodiment, but in the second embodiment, the SRS frequency characteristic estimation unit 14 and the DMRS frequency characteristic estimation unit 15 are determined by the determination unit. The frequency characteristic is estimated only for the RB of the received reference signal determined to be significant in 13. Hereinafter, the operation of the signal quality estimation unit 1 shown in FIG. 6 will be described mainly with reference to FIG. 7 and differences from the first embodiment.

  In FIG. 7, each process is first performed in the order of steps S1, S2, S4, S5, and S6. The processes in these steps S1, S2, S4, S5 and S6 are the same as those in the first embodiment.

  Next, in step S3a, the SRS frequency characteristic estimator 14 targets only the RB for which the result of the determination in step S6 is significant (step S7, YES) (that is, the RB for which the SRS received signal is significant), and performs wireless communication. The frequency characteristics of the uplink related to terminal 200 are estimated. As a result of this estimation, an instantaneous value of the frequency characteristic is obtained for each RB for which the SRS reception signal is significant.

  Next, in step S8, the received signal level estimation unit 18 estimates the received signal level for an RB for which the SRS received signal is significant. This received signal level estimation process is the same as in the first embodiment. The instantaneous value of the frequency characteristic based on the SRS reception signal of each RB for which the SRS reception signal is significant is supplied from the SRS frequency characteristic estimation unit 14 to the reception signal level estimation unit 18.

  On the other hand, in step S9, the determination unit 13 determines, based on the coherence time and DM-RS transmission time of the radio terminal 200, for each RB, for the RB in which the determination result in step S6 is not significant (step S7, NO). The significance of the DM-RS received signal from the wireless terminal 200 is determined. This significance determination process is the same as in the first embodiment.

  Next, in step S3b, the DMRS frequency characteristic estimation unit 15 determines that the determination result in step S9 is significant (step S10, YES). RB (that is, the SRS reception signal is not significant, but the DM-RS reception signal is significant). The uplink frequency characteristics of the radio terminal 200 are estimated only for a certain RB). As a result of this estimation, an instantaneous value of the frequency characteristic is obtained for each RB for which the DM-RS received signal is significant.

  Next, in step S11, the received signal level estimation unit 18 estimates the received signal level for the RB for which the DM-RS received signal is significant. This received signal level estimation process is the same as in the first embodiment. The instantaneous value of the frequency characteristic based on the DM-RS reception signal of each RB in which the DM-RS reception signal is significant is supplied from the DMRS frequency characteristic estimation unit 15 to the reception signal level estimation unit 18.

  On the other hand, in step S12, the reception signal level estimation unit 18 determines that the determination result in step S9 is not significant (step S10, NO) RB (that is, both the SRS reception signal and the DM-RS reception signal are not significant RB). On the other hand, the received signal level is estimated. This received signal level estimation process is the same as in the first embodiment.

  Next, in step S13, the signal quality calculation unit 19 calculates the signal quality based on the received signal level and the interference signal level. This signal quality calculation process is the same as in the first embodiment.

  According to the second embodiment, the frequency characteristic estimation target RB is limited to those for which the received reference signal is significant, so that it is possible to reduce the amount of calculation required for frequency characteristic estimation.

  As described above, according to the present embodiment, it can be expected that the signal quality of each RB can be estimated with stable signal quality estimation accuracy over the entire system band. As a result, it is possible to appropriately perform uplink frequency scheduling and obtain a good frequency scheduling gain, and as a result, it is possible to contribute to improvement of user throughput and cell throughput in the uplink.

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.
For example, in the above-described embodiment, the significance of the received reference signal is determined based on the coherence time and the reference signal transmission time. However, the reference signal reception time may be used instead of the reference signal transmission time.

  In the above-described embodiment, the coherence time of each wireless terminal is estimated. However, when it can be assumed that there is no significant difference in the coherence time between wireless terminals, the coherence time common to each wireless terminal is used. May be set. In this case, the coherence time estimation unit is unnecessary.

  In the above-described embodiment, SINR is used as the signal quality. However, the signal quality is not limited to SINR and may be any signal quality based on the received signal level. For example, when the signal quality not based on the interference signal level is used, the interference signal level estimation unit is unnecessary.

Further, a program for realizing each step shown in FIG. 5 or FIG. 7 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed, whereby a signal is obtained. Quality estimation processing may be performed. Here, the “computer system” may include an OS and hardware such as peripheral devices.
“Computer-readable recording medium” refers to a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a DVD (Digital Versatile Disk), and a built-in computer system. A storage device such as a hard disk.

Further, the “computer-readable recording medium” means a volatile memory (for example, DRAM (Dynamic DRAM) in a computer system that becomes a server or a client when a program is transmitted through a network such as the Internet or a communication line such as a telephone line. Random Access Memory)), etc., which hold programs for a certain period of time.
The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.
The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

DESCRIPTION OF SYMBOLS 1 ... Signal quality estimation part, 2 ... Terminal information acquisition part, 3 ... Wireless scheduler, 4 ... SRS scheduler, 5 ... Radio | wireless part, 11 ... Input information acquisition part, 12 ... Coherence time estimation part, 13 ... Determination part, 14 ... SRS frequency characteristic estimation unit, 15 ... DMRS frequency characteristic estimation unit, 16 ... received signal average level estimation unit, 17 ... interference signal level estimation unit, 18 ... received signal level estimation unit, 19 ... signal quality calculation unit, 100 ... base station , 200 ... wireless terminal

Claims (11)

In a signal quality estimation device that estimates uplink signal quality from a wireless terminal to a base station,
Based on the received reference signal received by the base station for the reference signal transmitted from the wireless terminal for each uplink frequency band section, the uplink frequency characteristics of the wireless terminal are estimated for each frequency band section A frequency characteristic estimation unit;
A determination unit that determines the significance of the received reference signal for each frequency band section based on a coherence time of the wireless terminal and a transmission time from the wireless terminal related to the received reference signal or a reception time at the base station; ,
A received signal average level estimating unit that estimates an average level of a received signal from the wireless terminal that is received by the base station;
For frequency band sections with a significant received reference signal, the received signal level is estimated based on the frequency characteristics based on the significant received reference signal and the received signal average level, and there is no significant received reference signal. A received signal level estimating unit that estimates a received signal level based on the received signal average level without using the frequency characteristic for the frequency band section;
A signal quality calculator that calculates the signal quality based on the received signal level;
A signal quality estimation apparatus comprising:   The received signal level estimation unit adds an instantaneous value of the frequency characteristic based on the significant received reference signal to the received signal average level for a frequency band section having a significant received reference signal, and receives the received signal level. The signal quality estimation apparatus according to claim 1, wherein:   The signal quality according to claim 1 or 2, wherein the received signal level estimation unit sets the received signal average level as a received signal level for a frequency band section having no significant received reference signal. Estimating device.   The determination unit is configured to perform uplink radio resource allocation using the signal quality calculated by the signal quality calculation unit from the transmission time from the wireless terminal related to the received reference signal or the reception time at the base station 4. The received reference signal is determined to be significant when the time until the scheduled transmission time of the radio resource allocation target frame is within the coherence time. 5. Signal quality estimation apparatus.   The frequency characteristic estimation unit estimates the frequency characteristic only for a frequency band section of a received reference signal determined to be significant by the determination unit, according to any one of claims 1 to 4. Signal quality estimation apparatus.   The reference signal is a first reference signal transmitted from the wireless terminal in a predetermined number of consecutive sections of the uplink frequency band, or a data signal transmission allocated to the wireless terminal. 6. The signal quality estimation apparatus according to claim 1, wherein the signal quality estimation apparatus is a second reference signal transmitted from the radio terminal in the uplink frequency band section. 7.   The received signal level estimation unit uses the frequency characteristic based on the first received reference signal in preference to the frequency characteristic based on the second received reference signal. The signal quality estimation apparatus described in 1.   The signal quality estimation apparatus according to claim 1, further comprising a coherence time estimation unit that estimates a coherence time of the wireless terminal. An interference signal level estimation unit for estimating the level of the interference signal received by the base station;
The signal quality calculation unit calculates the signal quality based on the received signal level and the interference signal level;
9. The signal quality estimation apparatus according to claim 1, wherein the signal quality estimation apparatus is any one of claims 1 to 8. A signal quality estimation method for estimating uplink signal quality from a wireless terminal to a base station,
Based on the received reference signal received by the base station for the reference signal transmitted from the wireless terminal for each uplink frequency band section, the uplink frequency characteristics of the wireless terminal are estimated for each frequency band section Steps,
Determining the significance of the received reference signal for each frequency band section based on the coherence time of the wireless terminal and the transmission time from the wireless terminal related to the received reference signal or the reception time at the base station;
Estimating an average level of a received signal from the wireless terminal received at the base station;
Estimating a received signal level based on the frequency characteristic based on the significant received reference signal and the received signal average level for a frequency band section having a significant received reference signal;
Estimating a received signal level based on the received signal average level without using the frequency characteristic for a frequency band section having no significant received reference signal;
Calculating the signal quality based on the received signal level;
A signal quality estimation method comprising: A computer program for performing signal quality estimation processing for estimating uplink signal quality from a wireless terminal to a base station,
Based on the received reference signal received by the base station for the reference signal transmitted from the wireless terminal for each uplink frequency band section, the uplink frequency characteristics of the wireless terminal are estimated for each frequency band section Steps,
Determining the significance of the received reference signal for each frequency band section based on the coherence time of the wireless terminal and the transmission time from the wireless terminal related to the received reference signal or the reception time at the base station;
Estimating an average level of a received signal from the wireless terminal received at the base station;
Estimating a received signal level based on the frequency characteristic based on the significant received reference signal and the received signal average level for a frequency band section having a significant received reference signal;
Estimating a received signal level based on the received signal average level without using the frequency characteristic for a frequency band section having no significant received reference signal;
Calculating the signal quality based on the received signal level;
A computer program for causing a computer to execute.

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