JP5541500B2 - Multi-carrier communication interference power estimation method and receiver - Google Patents

Description

  The present invention relates to an interference power estimation method and receiver for multicarrier communication.

  In a mobile communication system, it is required to efficiently use limited radio resources. In recent years, adaptive link control in which a base station adaptively changes a transmission format such as a coding rate and a modulation scheme based on propagation path state information estimated by a mobile station has been used in response to such a request ( Patent References 1 to 6).

  For example, Patent Document 6 discloses a technique related to subcarrier allocation according to a propagation path estimation result. In Patent Document 6, in order to obtain channel quality information, received signal power, interference signal power, noise power, ratio of received signal power and interference signal power, ratio of received signal power and noise power, or interference power and noise are described. It is shown that the ratio of the combined power of the power and the received signal power is used for channel estimation. However, Patent Document 6 does not describe how to obtain these parameters.

  Further, in Patent Document 7, although adaptive link control is not performed based on propagation path state information, in order to solve the problem that the spread spectrum method does not function well when subjected to frequency selective fading, It is disclosed that the orthogonality of spreading processing is maintained by measuring received power with a signal received on the station side and assigning a spreading code to each subcarrier group. However, the technique disclosed in Patent Document 7 is such that when a mobile station receives a signal by assigning a spreading code, each subcarrier can be received with equal power, and the mobile station performs propagation path quality. It does not estimate information.

  The adaptive link control is performed by the base station based on the propagation path state information reported from the mobile station. For this reason, if the estimation accuracy of the quality information reported from the mobile station is poor, the effect of adaptive link control is diminished, and improvement in system throughput cannot be expected.

  For example, even in LTE (Long Term Evolution) defined by 3GPP (3rd Generation Partnership Project), adaptive link control in which mobile station apparatus performs adaptive transmission / reception control by transmitting propagation path state information to the base station apparatus is adopted. Has been. In addition, in order to perform more effective link control, mobile stations are required to report channel state information in units (subbands) obtained by dividing an effective bandwidth (full band) into a plurality of units. . A subband is a band obtained by bundling a plurality of subcarriers, and a system band is configured by a plurality of subbands that do not overlap each other.

  The propagation path state information is generally generated based on a signal-to-interference power ratio (SIR). Therefore, in order for a mobile station to report a highly accurate propagation path state, it is necessary to estimate interference power and signal power with high accuracy. Generally, a pilot signal (RS: Reference Signal in LTE) is used for estimating interference power and signal power. First, the interference power of the pilot signal is estimated, and the signal power is estimated by subtracting the estimated interference power from the reception power of the pilot signal.

  The estimation of the interference power of the pilot signal can be performed in units of subbands, but all pilot signals mapped to the entire system band can also be used for interference power estimation. The standard specification stipulated by 3GPP requires the mobile station to “report” the transmission path state information for each subband, and the mobile station determines the SIR immediately before conversion to the transmission path state information. It is arbitrary whether to ask. Therefore, it is not always necessary to obtain interference and signal power for each subband. For example, the SIR can be obtained for each subband by calculating a common value for the entire band using the pilot signal for the entire system bandwidth and obtaining the signal power for each subband. If the interference power is not significantly different for each subband, it is assumed that the estimation accuracy is improved because the number of available pilots is larger when the interference power is obtained over the entire band.

  However, when the interference power is estimated in the entire system band, that is, in the full band, interference of other cells when the mobile station is located at the cell edge, interference from another network such as a pico cell, femto cell, etc., interference from other channels There is a possibility that different interference occurs for each subband due to the influence or the like. In such a case, if the interference power is estimated based on the average in the full band, there is a possibility that the interference power estimation accuracy in units of subbands is deteriorated.

  On the other hand, if the interference power is estimated in units of subbands using only the pilot signal included in the subband, the interference power for each subband can be estimated without being affected by the subband subjected to another interference. However, since the number of pilot signals used for estimation is limited as compared with the case where estimation is performed in all bands, there is a possibility that the estimation accuracy is degraded.

JP 2006-229503 A JP 2008-118656 A JP 2008-141313 A JP 2008-294631 A JP 2009-017341 A JP 2006-148220 A WO2006-114932

  An object of the present invention is to provide an interference power estimation method and a receiver capable of estimating interference power in multicarrier communication with high accuracy.

  According to the first aspect of the present invention, the received power of a known signal included in a plurality of subcarriers in each subband is measured in each of a plurality of subbands obtained by dividing the effective bandwidth, and the measured received power is measured. Provided is a multicarrier communication interference power estimation method characterized in that a plurality of subbands are grouped into a plurality of groups based on a value, and the interference power is estimated for each of the plurality of subbands in each group. Is done.

  Of the plurality of subbands, subbands in which the frequency fluctuation amount of the known signal between subcarriers is larger than a predetermined value are preferably excluded from grouping targets.

  According to the second aspect of the present invention, a known signal separation unit that separates known signals included in a plurality of subcarriers from user-specific information, and an equalization process that equalizes the known signals separated by the known signal separation unit A reception power measurement unit that measures the reception power of each of the plurality of subbands obtained by dividing the effective bandwidth, and a reception power measurement obtained by the reception power measurement unit. A grouping unit that divides a plurality of subbands into a plurality of groups based on a value, an interference power estimation unit that estimates interference power for each subband in the group for each group divided by the grouping unit, and received power measurement A signal power estimator that estimates the signal power of each of the plurality of subbands from the value and the interference power estimate obtained by the interference power estimator Receiver is provided, characterized in that it comprises a channel quality information generating unit that generates a channel quality information from more estimated signal power and the interference power estimate.

  For each of a plurality of subbands, a frequency error measurement unit that measures a frequency error from a difference between adjacent signals among equalized known signals, and a subband in which the frequency error measured by the frequency error measurement unit is greater than a predetermined threshold Preferably, the grouping unit excludes the subbands determined to have a large frequency error from the grouping target by the frequency error threshold determination unit.

  According to the present invention, interference power in multicarrier communication can be estimated with high accuracy.

It is a block block diagram which shows the receiver which concerns on the 1st Embodiment of this invention. It is a block block diagram which shows the receiver which concerns on the 2nd Embodiment of this invention. It is a block block diagram which shows the receiver which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows the flow of a process after the receiver shown in FIG. 3 receives a downstream signal until it performs subband grouping. 4 is a flowchart showing a flow of processing from estimation of interference power by the receiver shown in FIG. 3 to generation of propagation path state measurement information. It is a figure which shows the structural example of a subband, a resource block, and a resource element (subcarrier). It is a figure explaining an example of a grouping process. It is a figure explaining estimation of the interference power of a group unit. It is a figure explaining the estimation of the interference electric power per subband.

[First Embodiment]
FIG. 1 is a block configuration diagram showing a receiver according to the first embodiment of the present invention. This receiver is used as a receiver of a mobile station apparatus for multicarrier communication, and includes a known signal separation unit 1, an equalization processing unit 2, a reception power measurement unit 3, a grouping unit 4, an interference power estimation unit 5, and a signal power estimation. Unit 6 and propagation path quality information generation unit 7.

  The known signal processing unit 1 separates known signals, for example, pilot signals, included in a plurality of subcarriers from user-specific information. The equalization processing unit 2 equalizes the known signal separated by the known signal separation unit 1. The reception power measurement unit 3 measures the reception power of the equalization known signal obtained by the equalization processing unit 2 for each of a plurality of subbands obtained by dividing the effective bandwidth. The grouping unit 4 divides a plurality of subbands into a plurality of groups based on the received power measurement value obtained by the received power measurement unit 3. For each group divided by the grouping unit 4, the interference power estimation unit 5 estimates the interference power for the entire subband in the group. The signal power estimation unit 6 estimates the signal power of each of the plurality of subbands from the reception power measurement value obtained by the reception power measurement unit 3 and the interference power estimation value obtained by the interference power estimation unit 5. The propagation path quality information generation unit 7 generates propagation path quality information from the signal power estimated by the signal power estimation unit 6 and the interference power estimation value.

  The grouping by the grouping unit 4 is performed as follows, for example. First, the received power measurement values obtained by the received power measuring unit 3 are rearranged in ascending order or descending order. Then, based on the rearranged received power measurement values, grouping is performed for each subband in which the received power is determined to be the same value by the threshold value for dividing into groups.

  Here, the received power measurement value of a known signal is used as an index for sub-group grouping in interference power estimation. The reason is as follows. First, the amplitude of interference follows a Gaussian distribution. That is, it is random. Because of this randomness, it is necessary to ensure the number of samples in order to ensure the estimation accuracy of interference power. On the other hand, the received power can be measured by the square calculation of the received signal. For this reason, in the estimation of the interference power and the measurement of the received power, the received power is higher in accuracy even though the signals used for obtaining each are the same. When all known signals transmitted with the same symbol are transmitted with the same transmission power, if the reception power is the same, it can be determined that the interference power is also the same. Therefore, the subbands having the same reception power are grouped, and the interference power is estimated on the assumption that the interference power is the same in the group.

  The signal power estimation unit 6 can estimate the signal power for each subband by subtracting the interference power estimation value from the received power measurement value. The propagation path quality information generation unit 7 calculates a signal-to-interference power ratio (SIR) for each subband from the interference power estimation value and the signal power estimation value for each subband, and performs a propagation path from the SIR by table lookup or the like. The state information is converted and reported to the base station using the uplink communication channel.

[Second Embodiment]
FIG. 2 is a block diagram showing a receiver according to the second embodiment of the present invention. This receiver includes a frequency error measurement unit 8 and a frequency error threshold determination unit 9 in addition to the configuration of the receiver according to the first embodiment of the present invention shown in FIG.

  The frequency error measurement unit 8 measures the frequency error from the difference between adjacent signals among the equalization known signals. The frequency error threshold determination unit 9 determines a subband in which the frequency error measured by the frequency error measurement unit 8 is greater than a predetermined threshold. Then, the grouping unit 4 determines that the interference power largely fluctuates between subcarriers for subbands determined to have a large frequency error by the frequency error threshold determination unit 9, and excludes them from grouping targets.

[Third Embodiment]
FIG. 3 is a block diagram showing a receiver according to the third embodiment of the present invention. Here, a mobile station receiver that receives LTE downlink will be described in detail. The receiver shown in FIG. 3 includes an FFT (Fast Fourier Transform) unit 10, a demapping unit 11, an RS equalization processing unit 12, an RS received power measurement unit 13, a frequency error measurement unit 14, a frequency error threshold determination unit 15, a reception A power sort processing unit 16, a subband grouping unit 17, an interference power estimation unit 18, an interference power time averaging unit 19, a signal power estimation unit 20, a signal-to-interference power ratio calculation unit 21, and a propagation path quality information generation unit 22 are provided.

  The demapping unit 11 corresponds to the known signal separation unit 1 in the first and second embodiments. The RS equalization processing unit 12 corresponds to the equalization processing unit 2 in the first and second embodiments. The RS received power measuring unit 13 corresponds to the received power measuring unit 2 in the first and second embodiments. The frequency error measurement unit 14 corresponds to the frequency error measurement unit 8 in the second embodiment. The frequency error threshold value determination unit 15 corresponds to the frequency error threshold value determination unit 9 in the second embodiment. The received power sort processing unit 16 and the subband grouping unit 17 correspond to the grouping unit 4 in the first and second embodiments. The interference power estimation unit 18 and the interference power time averaging unit 19 correspond to the interference power estimation unit 5 in the first and second embodiments. The signal power estimation unit 20 corresponds to the signal power estimation unit 6 in the first and second embodiments. The signal-to-interference power ratio calculation unit 21 and the channel quality information generation unit 22 correspond to the channel quality information estimation unit 7 in the first and second embodiments.

  In the receiver shown in FIG. 3, FFT section 10 obtains subcarriers for each symbol by performing FFT conversion on the signals received by the respective receiving antennas. The demapping unit 11 separates, from the subcarrier obtained by the FFT unit 10, a subcarrier to which a data signal unique to each user is mapped and a signal to which a reference signal (RS) that is a known signal is mapped, Get RS. The RS equalization processing unit 12 equalizes the RS and cancels the pilot pattern. The above processing is performed in units of slots. The format of LTE downlink subframes and slots is defined in 3GPP TS 36.211, and will not be described here.

  The RS received power measurement unit 13 measures the received power of the pilot signal for each subband using both the first RS and the second RS of the RS equalized by the RS equalization processing unit 12. In addition, since RS is always transmitted with the same transmission power, the RS reception power measurement unit 13 performs time averaging of reception power over the nearest AI [slot] in subband units.

  The frequency error measurement unit 14 uses the RS equalized by the RS equalization processing unit 12 as an input, and measures the frequency error in subband units for control of the subsequent subband grouping process. When the frequency error in subband units measured by the frequency error measurement unit 14 is larger than the threshold T, the frequency error threshold determination unit 15 removes the subband from the target to be grouped by the subsequent subband grouping processing unit 17. Set a flag so that.

  The received power sort processing unit 16 sorts the received power measurement values in units of subbands, and groups the subbands that can be determined to be equivalent values using the sorting result and the threshold value X. The subband grouping processing unit 17 determines the reception power sorted by the reception power sorting processing unit 16 as an equivalent value based on the threshold value X for the subbands other than the subband flagged by the frequency error threshold determination unit 15. Divide each subband into several groups. It is not always necessary to perform grouping, and it is possible to set the threshold value X = 0 and not perform grouping.

  The interference power estimation unit 18 estimates the interference power of the slot to be processed by using the RS included in the group in the unit grouped by the subband grouping unit 17. The interference power time averaging unit 19 averages the interference power calculated by the interference power estimation unit 18 for each subband over AI [slot]. When the interference power value of the current slot calculated by the interference power estimation unit 18 deviates by more than X [dB] from the time average interference power value calculated by the interference power time average unit 19, the interference power estimation is performed as the time average interference power. It is also possible to use the interference power of the unit 18. The signal power estimation unit 20 estimates the signal power by subtracting the interference power estimation value obtained by the interference power estimation unit 18 from the reception power measurement value obtained by the RS reception power measurement unit 13.

  The signal-to-interference power ratio calculation unit 21 calculates the SIR using the interference power estimation value and the signal power estimation value obtained by the interference power time averaging unit 19 and the signal power estimation unit 20, respectively. The propagation path state information generation unit 22 generates propagation path state information with reference to the SNR and the propagation path state information conversion table.

[Description of operation]
The detailed operation of the receiver shown in FIG. 3 will be described with reference to FIGS. FIG. 4 is a flowchart showing a flow of processing from when the receiver shown in FIG. 3 receives a downlink signal to when subband grouping is performed. FIG. 5 is a flowchart showing the flow of processing from the estimation of interference power by the receiver shown in FIG. 3 to the generation of propagation path state measurement information. FIG. 6 is a diagram illustrating a configuration example of subbands, resource blocks, and resource elements (subcarriers). FIG. 7 is a diagram illustrating an example of grouping processing. FIG. 8 is a diagram for explaining estimation of interference power in units of groups. FIG. 9 is a diagram illustrating estimation of interference power in units of subbands.

  Here, an example will be described in which the system bandwidth is 10 MHz, the CP (Cyclic Prefix) is Normal, the CQI report mode is PUSCH1-2, Transmission mode 4 (Closed-loop spatial multiplexing), and two transmission antennas. Since the number of subbands S is 9 (subbands # 0 to # 8) and the number of resource blocks is 50, the number of resource blocks included in one subband is 4, excluding subband # 8. One resource block is composed of 12 resource elements (subcarriers) (see FIG. 6).

  The RS equalization processing unit 12 demaps all RSs (the first RS and the second RS of the transmission antennas # 1 and # 2) mapped at intervals of 6 resource elements from the signal obtained by FFT of the reception signal, and performs ZF (Zero). (Forcing) equalization processing is performed (step S1). The RS received power measurement unit 13 calculates RS received power using the equalized RS for each subband (loop L1) (step S2). Here, it is assumed that the RS received power is obtained by the time average of the latest AI [slot] of the processing target slot, and the average power is stored in the RAM (step S3). If the number of signals that can be received is less than AI [slot], averaging is performed for the number of slots that can be received. In addition, the frequency error estimation measurement unit 14 takes the difference from the RS equalized signal mapped adjacently on the frequency axis using the equalized RS for each subband (loop L1) in parallel, A frequency fluctuation amount is calculated (step S4).

  Next, the following processing is performed to perform grouping processing for dividing the subband into G groups.

  First, the received power sort processing unit 16 performs processing for sorting the received power measurement values for each subband calculated in the process of the loop L1 (steps S2 to S4) in ascending order (step S5), and stores it in the RAM (i = 0, ..., 8).

  The subband grouping unit 17 sequentially reads the received power after sorting stored in the RAM from the maximum value in order to group the subbands having the same RS reception power measurement value, that is, the interference power is equivalent (i = i) It is determined whether or not the difference from the received power of the next point (i = i + 1) is within X [dB] (step S6). If the difference is within X [dB] (Yes in step S6), the process proceeds to the next process. As the next processing, the frequency error threshold value determination unit 15 determines whether or not the frequency fluctuation amount of the subband (i) currently processed is larger than the threshold value T by checking the frequency fluctuation amount of the subband (i) currently processed. (Step S7). If the frequency fluctuation amount is smaller than the threshold value T (Yes in step S7), the subband grouping unit 17 can add the subband to the previous group (step S8). If the frequency fluctuation amount is larger than the threshold T (No in step S7), the subband grouping unit 17 has a large fluctuation in interference level even within the subband, and the subband should be a grouping target. Therefore, it is excluded from the grouping process target. If the difference is larger than X [dB] in step S6 (No in step S6), the subband grouping unit 17 collects up to the reception power currently being processed as one group (step S10), and the next point (i + 1). After the subband, the process proceeds to the grouping process to the next group. Steps S6 to S10 are executed until all subbands are processed (loop L2).

  In the processing of the loop L2, for example, it is assumed that the reception power and frequency error of each subband can be calculated as shown in FIG. In this case, eight subbands are subgroups # 1, # 2, # 5 and # 8, subbands # 0, # 3, # 4 and # 6, and subband # 7 (groups # 0 to # 7). # 3). In this example, there are no ungrouped subbands.

When the processing of the loop L2 is completed, the interference power estimation unit 18 uses the equalized RS signal included in each group for each group grouped by the processing of the loop L2, for example, as shown in FIG. Electric power is calculated (loop L3, step S11). At this time, all the interference powers of the subbands included in the same group have the same value. For example, as shown in FIG. 7, assuming that subbands # 0 to # 7 are divided into groups # 0 to # 3, interference power _{IG = 0} obtained in group # ₀ is subbands # 1, # The interference powers I _{S = 1} , I _{S = 2} , I _{S = 5} , and I _{S = 8} are respectively set to 2, # 5, and # 8. Further, the interference power I _{G = 1} obtained in the group # 1 is the interference power I _{S = 0} , I _{S = 3} , I _{S = 4 of} the subbands # 0, # 3, # 4, and # 6, respectively. I _{S = 6} . Further, the interference power I _{G = 2} obtained in the group # 2 is set as the interference power I _{S = 7 of the} subband # 7.

The interference power time averaging unit 19 uses the interference power estimation value calculated in the processing of the loop L3, and performs time average processing of interference power for A _I [slot] on a subband basis, as shown in FIG. (Loop L4, Step S12). That is, the interference power estimate _{I s} subbands #s the slot #n, the interference power estimate _{I s} subbands _#s, by dividing the sum of _n of the n = _{0 to A} I -1 in _{A I} Desired.

  The signal power estimation unit 20 calculates a signal power estimation value for each subband by subtracting the interference power estimation value from the received power measurement value for each subband. Subsequently, the signal power estimation unit 20 calculates the ratio of the transmission power of the PDSCH (Physical Downlink Shared Channel) to which the RS notified by the higher level signaling and the user-specific data are mapped, and the signal power estimation value calculated in the loop L2. From this, the signal power estimation value of PDSCH is calculated (step S13). The signal-to-interference power ratio calculation unit 21 estimates the SIR for each subband from the interference power estimation value and the PDSCH signal power estimation value (step S14). The propagation path quality information generation unit 22 generates propagation path state measurement information using the SIR-CQI conversion table (step S15). Steps S13 to S15 are performed for each subband (loop 15).

[Description of effects]
In the embodiment of the present invention described above, in a multicarrier communication system using adaptive link control, when it is necessary to report a propagation path state in units of subbands, which is a unit in which a plurality of subcarriers are bundled, the interference level is Group subbands that are equivalent. As a result, even when the mobile station undergoes frequency selective fading, the accuracy of interference power estimation for each subband is improved, the SIR estimation accuracy for each subband is improved, and propagation path state information reported from the mobile station to the base station The effect of improving the accuracy of the is obtained. Also, even when a certain subband receives a large amount of interference, it is possible to avoid degradation of the accuracy of the channel state information by excluding that subband from the grouping target.

[Other embodiments]
In the above description, especially the third embodiment, application to LTE has been described as an example. The present invention is not necessarily limited to this, and can be applied to all mobile communication systems that need to report channel state information in units obtained by dividing a system band into several in a multicarrier communication system. . Further, it is not always necessary to use all the reference signals for calculating received power, and the calculation may be performed using either the first RS or the second RS.

  In addition, although a pilot signal (including RS) has been described as an example of a known signal used for estimating interference power, other signals such as a synchronization channel may be used.

  In addition, the case where the subband grouping process is performed every slot has been described as an example, but when the estimated error (variation amount) in the time direction is used to determine that the variation amount is small, the grouping process is not performed. It is also possible to apply dynamic control.

  Also, by adding the calculation of the frequency error in the entire system bandwidth, if the amount of fluctuation is less than a certain value, the reception power, frequency error calculation, and interference power grouping are performed for each subband. It is also possible to perform control for obtaining interference power and signal power by using pilots of the entire system bandwidth.

DESCRIPTION OF SYMBOLS 1 Known signal separation part 2 Equalization process part 3 Reception power measurement part 4 Grouping part 5 Interference power estimation part 6 Signal power estimation part 7 Channel quality information generation part 8 Frequency error measurement part 9 Frequency error threshold value determination part 10 FFT part 11 Demapping unit 12 RS equalization processing unit 13 RS received power measurement unit 14 Frequency error measurement unit 15 Frequency error threshold determination unit 16 Received power sort processing unit 17 Subband grouping unit 18, interference power estimation unit 19 Interference power time averaging unit 20 Signal power estimation unit 21 Signal to interference power ratio calculation unit 22 Channel quality information generation unit

Claims (2)

Measure the received power of the known signals contained in the multiple subcarriers in each subband in each of the multiple subbands that divided the effective bandwidth.
Based on the measured received power value, the subbands are sorted in ascending order of the received power value to group the plurality of subbands that are received power within a predetermined difference value into a plurality of groups, and Among subbands, subbands whose frequency variation of the known signal is larger than a predetermined value between subcarriers are excluded from the grouping target,
In each of the plurality of groups, interference power is estimated for all subbands in the group, and a signal-to-interference power ratio of each subband is estimated based on the estimated interference power estimation value. Interference power estimation method for carrier communication. A known signal separation unit for separating known signals included in a plurality of subcarriers from user-specific information;
An equalization processing unit for equalizing the known signal separated by the known signal separation unit;
For the equalization known signal obtained by the equalization processing unit, a received power measurement unit that measures the received power for each of a plurality of subbands obtained by dividing the effective bandwidth;
For each of the plurality of subbands, a frequency error measurement unit that measures a frequency error from a difference between adjacent signals among the equalization known signals;
A frequency error threshold determination unit that determines a subband in which the frequency error measured by the frequency error measurement unit is greater than a predetermined threshold;
Based on the received power measurement value obtained by the received power measurement unit, the subbands are sorted in ascending order of the received power value, and the plurality of subbands that are received power within a predetermined difference value are divided into a plurality of groups , A grouping unit that excludes the subbands determined to have a large frequency error by the frequency error threshold determination unit from the grouping target ;
For each group divided by the grouping unit, an interference power estimation unit that estimates interference power over the entire subband in the group;
A signal power estimator that estimates the signal power of each of the plurality of subbands from the received power measurement value and the interference power estimate obtained by the interference power estimator;
A receiver comprising: a channel quality information generating unit that generates channel quality information from the signal power estimated by the signal power estimating unit and the interference power estimation value.

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