JP4812567B2 - Pilot signal allocation method and radio apparatus using the same - Google Patents

Description

  The present invention relates to a pilot signal assignment technique, and more particularly to a pilot signal assignment method for assigning a pilot signal to a multicarrier signal and a radio apparatus using the same.

An OFDM (Orthogonal Frequency Division Multiplexing) transmission system that has excellent resistance to multipaths and ghosts and enables mobile reception is adopted as a transmission system for terrestrial digital broadcasting and wireless LAN. This is a method of modulating data while using a plurality of subcarriers orthogonal to each other on the frequency axis. In such an OFDM signal, pilot signals are arranged at predetermined subcarrier intervals in order to make it possible to estimate transmission path characteristics in units of one transmission symbol. The pilot signal is a known signal. In addition, in order to enable estimation of transmission path characteristics in a high-speed fading environment, pilot signals are continuously arranged on the time axis (see, for example, Patent Document 1).
JP 2005-124125 A

  When the error included in the transmission path characteristic estimated on the receiving side becomes large, the reception characteristic when data is demodulated based on the transmission path characteristic is deteriorated. Therefore, it is required to arrange pilot signals on subcarriers so as to reduce an error included in the estimated transmission path characteristics. On the other hand, the radio quality such as reception strength generally varies from subcarrier to subcarrier due to the influence of frequency selective fading.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a pilot signal allocation technique for reducing an error included in transmission path characteristics estimated on the receiving side.

  In order to solve the above problems, a radio apparatus according to an aspect of the present invention allocates a pilot signal based on an acquisition unit that acquires radio quality for each of a plurality of subcarriers, and the radio quality acquired by the acquisition unit A specifying unit that specifies a subcarrier, and a transmission unit that transmits a multicarrier signal formed by a plurality of subcarriers while assigning a pilot signal to the subcarrier specified by the specifying unit. The specifying unit specifies a subcarrier to which a pilot signal is allocated so that at least one pilot signal is arranged in a block unit when a plurality of subcarriers are classified into a number of blocks smaller than the number of subcarriers.

  “Acquiring” may be measuring the radio quality in the radio device, receiving the radio quality measured in the communication target as data, and obtaining the value measured in the communication target. Originally, the wireless quality may be derived in the wireless device. That is, it suffices if the wireless quality can be confirmed. According to this aspect, since the subcarrier to which the pilot signal is allocated is specified according to the radio quality, the error included in the estimated transmission path characteristic can be reduced.

  The specifying unit specifies a subcarrier to which a pilot signal is assigned with a subcarrier arranged near the center frequency of the block as a specific target, and the acquiring unit acquires radio quality for at least each of the subcarriers to be specified May be. “Near the center frequency of a block” corresponds to the vicinity of the center of a band occupied by one block. In this case, since pilot signals are allocated to subcarriers arranged near the center frequency of the block, the pilot signals can be arranged evenly over a plurality of blocks.

  The identifying unit performs weighting on the wireless quality acquired by the acquiring unit so that the wireless quality is improved as the frequency approaches the center frequency of the block, and then identifies a subcarrier having the best wireless quality for each block. May be. In this case, since it becomes easy to assign pilot signals to subcarriers arranged near the center frequency of the block, pilot signals can be arranged evenly over a plurality of blocks.

  The wireless communication apparatus further includes a receiving unit that receives a multicarrier signal from a wireless device to be communicated. The acquisition unit measures the radio quality for each of the plurality of subcarriers from the multicarrier signal received at the reception unit, and the transmission unit uses the same frequency band as the multicarrier signal received at the reception unit, A carrier signal may be transmitted. In this case, since the wireless quality is measured by itself, the procedure for transmitting the wireless quality from the wireless device to be communicated can be omitted, and a decrease in transmission efficiency can be suppressed.

  The transmission unit may transmit the multicarrier signal as a packet signal, and may transmit the information on the subcarrier specified by the specifying unit in a period in front of the packet signal. In this case, information of the identified subcarrier can be notified to the wireless device to be communicated.

  Another aspect of the present invention is also a wireless device. This device is a multicarrier signal from a wireless device to be communicated, and when a plurality of subcarriers are classified into a number of blocks smaller than the number of subcarriers, at least one pilot signal is arranged for each block. Based on the result of the correlation processing in the correlator, the receiver that receives the received multicarrier signal, the correlator that performs correlation processing between the multicarrier signal received in the receiver, and the pilot signal in units of subcarriers An estimation unit that estimates a subcarrier to which a pilot signal is allocated in units of blocks, and a processing unit that processes a multicarrier signal received at a reception unit while using a pilot signal at a subcarrier estimated by the estimation unit; Is provided.

  The “pilot signal” to be subjected to correlation processing may be a pilot signal stored in advance, or may be a pilot signal included in the received multicarrier signal. The correlation process in the former case corresponds to a cross-correlation process, and the correlation process in the latter case corresponds to an autocorrelation process. According to this aspect, the transmission efficiency can be improved because the subcarrier to which the pilot signal is assigned is specified without receiving information on the subcarrier to which the pilot signal is assigned from the wireless device to be communicated.

  Yet another aspect of the present invention is a pilot signal allocation method. The method includes: acquiring radio quality for each of a plurality of subcarriers; identifying a subcarrier to which a pilot signal is assigned based on the acquired radio quality; and assigning a pilot signal to the specified subcarrier Transmitting a multicarrier signal formed by a plurality of subcarriers. In the identifying step, when a plurality of subcarriers are classified into a number of blocks smaller than the number of subcarriers, a subcarrier to which a pilot signal is allocated is identified so that at least one pilot signal is arranged in a block unit. .

  The specifying step specifies a subcarrier to which a pilot signal is assigned, with a subcarrier arranged near the center frequency of the block as a specific target, and the acquiring step includes at least radio quality for each of the target subcarriers to be specified May be obtained. In the step of specifying, after performing weighting for improving the radio quality as the center frequency of the block gets closer to the acquired radio quality, the subcarrier having the best radio quality is identified for each block. Good.

  The method further includes a step of receiving a multicarrier signal from a wireless device to be communicated. The obtaining step measures the radio quality for each of the plurality of subcarriers from the received multicarrier signal, and the transmitting step uses the same frequency band as the received multicarrier signal in the receiving step. A carrier signal may be transmitted. In the transmitting step, the multicarrier signal is transmitted as a packet signal, and information on the specified subcarrier may be transmitted in a period preceding the packet signal.

  Yet another embodiment of the present invention is a reception method. In this method, when a plurality of subcarriers are classified into a number of blocks less than the number of subcarriers that are multicarrier signals from a wireless device to be communicated, at least one pilot signal is arranged in units of blocks. Receiving the received multicarrier signal, executing a correlation process between the received multicarrier signal and the pilot signal in units of subcarriers, and, based on the result of the correlation process, the sub signal to which the pilot signal is assigned. Estimating a carrier on a block basis, and processing a received multicarrier signal using a pilot signal on the estimated subcarrier.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  The error included in the transmission path characteristics estimated on the receiving side can be reduced.

  Before describing the present invention in detail, an outline will be described. Embodiments of the present invention relate to a communication system including a base station device and at least one terminal device. In the communication system, one subcarrier block is composed of a plurality of subcarriers, and a multicarrier signal is composed of a plurality of subcarrier blocks. The base station apparatus executes OFDMA by assigning one subcarrier block to one terminal apparatus. Moreover, the base station apparatus may allocate a plurality of subcarrier blocks to one terminal apparatus. The base station apparatus arranges the pilot signal on a predetermined subcarrier so that the terminal apparatus can estimate the transmission path characteristics.

  When affected by frequency selective fading, the signal strength of the multicarrier signal received at the terminal device becomes a different value for each subcarrier. If a pilot signal is arranged on a subcarrier having a low signal strength, the transmission path characteristics estimated based on the pilot signal and errors included in the transmission path characteristics estimated in the terminal device are large. Become. Since the terminal apparatus demodulates data based on the estimated transmission path characteristics, the reception characteristics deteriorate when the error included in the transmission path characteristics increases. In order to cope with this, the base station apparatus according to the present embodiment executes the following processing.

  The downlink packet signal transmitted from the base station apparatus to the terminal apparatus and the uplink packet signal transmitted from the terminal apparatus to the base station apparatus are configured similarly. The base station apparatus measures radio quality, for example, EVM (Error Vector Magnitude) for each subcarrier with respect to the multicarrier signal received from the terminal apparatus. Further, the base station apparatus compares a plurality of EVMs for each subcarrier block, and determines assignment of pilot signals to subcarriers corresponding to the best EVM. The base station apparatus transmits a multicarrier signal after assigning a pilot signal to the determined subcarrier.

  FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. The communication system 100 includes a terminal device 10, a base station device 12, and a network 18. The terminal device 10 includes a terminal antenna 14, and the base station device 12 includes a base station antenna 16.

  The base station apparatus 12 connects the terminal apparatus 10 to one end via a base station antenna 16 and connects the network 18 to the other end. Further, the terminal device 10 is connected to the base station device 12 via the terminal antenna 14. The base station apparatus 12 performs communication with the plurality of terminal apparatuses 10 by assigning channels to the plurality of terminal apparatuses 10 (not shown). Specifically, the terminal apparatus 10 transmits a channel allocation request signal to the base station apparatus 12, and the base station apparatus 12 allocates a channel to the terminal apparatus 10 in response to the received request signal.

  Moreover, the base station apparatus 12 transmits information on the channel allocated to the terminal apparatus 10, and the terminal apparatus 10 executes communication with the base station apparatus 12 while using the allocated channel. As a result, the data transmitted from the terminal device 10 is output to the network 18 via the base station device 12 and finally received by a communication device (not shown) connected to the network 18. Data is also transmitted in the direction from the communication device to the terminal device 10.

  FIG. 2 shows a configuration of a multicarrier signal transmitted in communication system 100. In particular, FIG. 2 shows the spectrum of a signal in the OFDM transmission scheme. One of a plurality of carriers in the OFDM transmission system is generally called a subcarrier, but here, one subcarrier is designated by a “subcarrier number”. Here, z subcarriers from subcarrier numbers “1” to “z” are defined. Further, one signal unit composed of a plurality of subcarriers and one signal unit in the time domain is referred to as an “OFDM symbol”.

  FIG. 3 shows a configuration of a packet signal transmitted in the communication system 100. The vertical direction in FIG. 3 shows the frequency axis, and the horizontal direction in FIG. 3 shows the time axis. Also, the vertical frequency axis corresponds to the spectrum of FIG. 2, and as shown in FIG. 2, a packet signal is formed by a multicarrier signal including z subcarriers. By including a predetermined number of multicarriers in one subcarrier block in the frequency component of the packet signal, M subcarrier blocks from the first subcarrier block to the Nth subcarrier block are formed. Here, M has a value smaller than z.

  That is, a plurality of subcarriers are classified into a smaller number of subcarrier blocks than the number of subcarriers. Such a plurality of subcarrier blocks are arranged in parallel in the time direction. The base station apparatus 12 of FIG. 1 allocates at least one subcarrier block to the terminal apparatus 10 as the above-described channel. The packet signal in FIG. 3 shows the packet signal in the downlink transmitted from the base station apparatus 12 to the terminal apparatus 10 in FIG. 1, but the uplink signal transmitted from the terminal apparatus 10 to the base station apparatus 12 Since the packet signal in FIG. 6 may be configured in the same manner, description thereof is omitted here.

  FIG. 4 shows the configuration of the subcarrier block. FIG. 4 shows in detail one of the plurality of subcarrier blocks shown in FIG. Here, the vertical direction of FIG. 4 shows the frequency axis as in FIG. 3, and the horizontal direction of FIG. 4 shows the time axis as in FIG. Also, as described in FIG. 2, subcarriers included in the subcarrier block are indicated by subcarrier numbers “i” to “i + 14”. Here, the number of subcarriers included in one subcarrier block is “15”. Arrangement is made in the order of “STS”, “LTS”, “SIG”, and “data” from the beginning of the packet signal on the time axis.

  Here, “STS” is a known signal for AGC (Automatic Gain Control) setting and timing detection in the terminal device 10, and “LTS” is a known signal for estimating transmission path characteristics in the terminal device 10. , “SIG” is a control signal. Furthermore, “data” is a general term for “data 1” to “data N” in FIG. 4 and corresponds to data to be transmitted from the base station apparatus 12 to the terminal apparatus 10. “STS” is arranged in subcarrier numbers “i + 1”, “i + 5”, “i + 9”, “i + 13”, and “LTS” is subcarrier numbers “i”, “i + 2”, “i + 4”, “i + 6”. , “I + 8”, “i + 10”, “i + 12”, “i + 14”. That is, STS and LTS are arranged on different subcarriers. On the other hand, “SIG” is arranged in all subcarriers included in one subcarrier block.

  “Data” is arranged over a plurality of symbols on the time axis. FIG. 4 shows that 15 data, for example, “data 1” to “data 15” are arranged in one symbol, but in actuality, at least one of the 15 subcarriers. A pilot signal is included. For example, when a pilot signal is assigned to a subcarrier of subcarrier number “i + 7”, “pilot signal” is arranged instead of “data 8”. Also, when a pilot signal is assigned to a subcarrier with subcarrier number “i + 7”, the pilot signal is arranged in a plurality of symbols.

  FIG. 5 shows the configuration of the base station apparatus 12. The base station device 12 includes a base station antenna 16, a radio unit 20, an FFT (Fast Fourier Transform) unit 22, a demodulation unit 24, a measurement unit 26, a control unit 28, a desubchannelization unit 30, a subchannelization unit 32, A modulation unit 34, an IFFT unit 36, and a baseband processing unit 38 are included.

  As a reception process, the radio unit 20 performs frequency conversion on a radio frequency multicarrier signal received from the terminal apparatus 10 by the base station antenna 16 to generate a baseband multicarrier signal. Further, the radio unit 20 outputs a baseband multicarrier signal to the FFT unit 22. In general, a baseband multicarrier signal is formed by an in-phase component and a quadrature component, and therefore should be transmitted by two signal lines. For the sake of clarity, a single signal line is used here. Only. The radio unit 20 also includes an AGC and an A / D conversion unit.

  As a transmission process, the radio unit 20 performs frequency conversion on the baseband multicarrier signal input from the IFFT unit 36 to generate a radiofrequency multicarrier signal. Further, the radio unit 20 outputs a radio carrier multicarrier signal to the base station antenna 16. That is, the radio unit 20 transmits a radio frequency multicarrier signal from the base station antenna 16. The radio unit 20 transmits the multicarrier signal while using the same radio frequency band as the received multicarrier signal. In other words, TDD (Time Division Duplex) is used. The wireless unit 20 also includes a PA (Power Amplifier) and a D / A conversion unit. The multicarrier signal processed in the radio unit 20 is a signal obtained by converting the multicarrier signal shown in FIGS. 2 to 4 into the time domain. In addition, a guard interval may be added to the signal converted into the time domain, but description thereof is omitted here.

  The FFT unit 22 performs time-domain to frequency-domain conversion on the baseband multicarrier signal input from the radio unit 20. The FFT unit 22 outputs the multicarrier signal converted into the frequency domain to the demodulation unit 24. The multicarrier signal converted into the frequency domain has components corresponding to each of the plurality of subcarriers as shown in FIGS. Note that the FFT unit 22 executes timing synchronization, that is, FFT window setting, and also deletes the guard interval. The above-described “STS” is used for timing synchronization and the like, but since a known technique may be used, description thereof is omitted here.

  The demodulator 24 demodulates the multicarrier signal converted into the frequency domain by the FFT unit 22. Note that the transmission path characteristics are estimated for demodulation, and the above-described “LTS” is used to estimate the transmission path characteristics. Since a known technique may be used for estimating the transmission path characteristics, the description thereof is omitted here, but the transmission path characteristics are estimated in units of subcarriers. The demodulation unit 24 outputs the demodulated result to the desubchannelization unit 30.

  The desubchannelization unit 30 receives the demodulation result from the demodulation unit 24 and separates the demodulation result into units of the terminal device 10. That is, the demodulation result is composed of a plurality of subcarrier blocks as shown in FIGS. Therefore, when one subcarrier block is assigned to one terminal apparatus 10 as one channel, the demodulation result includes signals from a plurality of terminal apparatuses 10. The desubchannelization unit 30 separates such demodulation results. The desubchannelization unit 30 adds information for identifying the transmission source terminal device 10 and information for identifying the destination to the separated demodulation result, and outputs the result to the baseband processing unit 38. .

  The baseband processing unit 38 outputs the demodulation result received from the desubchannelization unit 30 to the network 18. The destination of the demodulation result is set based on information added to the demodulation result and information for identifying the destination. Here, the information for identifying the destination is indicated by, for example, an IP (Internet Protocol) address. In addition, the baseband processing unit 38 inputs data for a plurality of terminal devices 10 from the network 18. The control unit 28 outputs the input data to the subchannelization unit 32.

  The sub-channelization unit 32 performs a process reverse to that of the de-subchannelization unit 30. The sub-channelization unit 32 receives data for the plurality of terminal devices 10 from the baseband processing unit 38, assigns the data to the subcarrier blocks, and forms a multicarrier signal from the plurality of subcarrier blocks. That is, the subchannel formation unit 32 forms a multicarrier signal composed of a plurality of subcarrier blocks as shown in FIGS. The subcarrier block to which data is to be assigned is determined in advance, and an instruction related thereto is received from the control unit 28 via a signal line (not shown). The subchannel formation unit 32 outputs the multicarrier signal to the modulation unit 34.

  Modulator 34 modulates the multicarrier signal received from subchannelization unit 32. Further, the modulation unit 34 outputs the modulated multicarrier signal to the IFFT unit 36. The IFFT unit 36 performs conversion from the frequency domain to the time domain for the modulated multicarrier signal input from the modulation unit 34. The IFFT unit 36 outputs the multicarrier signal converted into the time domain to the radio unit 20 as a baseband multicarrier signal. The IFFT unit 36 also adds a guard interval, but a description thereof is omitted here.

  The measurement unit 26 measures EVM as radio quality for each of the plurality of subcarriers. That is, the measurement unit 26 measures the radio quality for each of the plurality of subcarriers from the received multicarrier signal. For this purpose, the measurement unit 26 receives from the demodulation unit 24 the multicarrier signal converted into the frequency domain by the FFT unit 22, that is, the signal before demodulation. The measurement unit 26 also receives a detected multicarrier signal, that is, a signal after demodulation, from the demodulation unit 24. The measurement unit 26 derives the EVM for each subcarrier while using the signal before demodulation and the signal after demodulation. A description of derivation of the EVM will be given later.

  The control unit 28 performs channel allocation to the terminal device 10, timing control of the entire base station device 12, and the like. Further, the control unit 28 specifies a subcarrier to which a pilot signal is allocated based on the EVM measured by the measurement unit 26. More specifically, the control unit 28 specifies a subcarrier to which a pilot signal is allocated so that at least one pilot signal is arranged in units of subcarrier blocks. Here, it is assumed that one pilot signal is arranged in one subcarrier block. The control unit 28 compares the size of the EVM for each subcarrier block. In the example of FIG. 4, the EVM sizes corresponding to each of the 15 subcarriers are compared. Further, the control unit 28 specifies a subcarrier corresponding to the minimum EVM. The control unit 28 notifies the specified subcarrier to the subchannelization unit 32.

  The subchannel formation unit 32 generates a multicarrier signal formed by a plurality of subcarriers as a packet signal while assigning a pilot signal to the subcarrier specified by the control unit 28. For example, if the control unit 28 specifies the subcarrier of the subcarrier number “i + 7” in FIG. 4, the subchannelization unit 32 allocates a pilot signal to “data 7”, “data N-7”, and the like. It is assumed that the pilot signal pattern over a plurality of symbols is defined in advance. Further, the sub-channelization unit 32 transmits the information on the subcarrier specified by the measurement unit 26 in the period preceding the packet signal. Here, the information of the subcarrier specified in the measurement unit 26 is included in “SIG” in FIG. 4.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it is realized by a program having a communication function loaded in the memory. Describes functional blocks realized by collaboration. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 6 shows the configuration of the demodulation unit 24 and the measurement unit 26. The demodulation unit 24 includes a carrier reproduction unit 50 and a detection unit 52, and the measurement unit 26 includes a remodulation unit 54 and an EVM calculation unit 56. As described above, the signal input to the demodulator 24 is a multicarrier signal converted into the frequency domain. Therefore, components corresponding to a plurality of subcarriers should be input to the demodulation unit 24 in parallel. However, here, for the sake of clarity, this is indicated by a single signal line.

  The carrier reproducing unit 50 estimates the above-described transmission path characteristics for each subcarrier. Explanation of the operation of the carrier reproducing unit 50 is omitted. In addition, the carrier reproducing unit 50 outputs a reverse characteristic of the estimated transmission path characteristic. The detecting unit 52 detects the multicarrier signal converted into the frequency domain while using the inverse characteristic of the transmission path characteristic from the carrier reproducing unit 50. Here, the detection unit 52 performs detection in units of subcarriers while associating subcarriers. The detection unit 52 outputs the detection result as the demodulation result described above.

  Remodulation unit 54 receives the demodulation result from detection unit 52, remodulates the received demodulation result in units of subcarriers, and outputs the result. Since a known technique may be used for remodulation, description thereof is omitted here. The remodulator 54 outputs the remodulated signal to the EVM calculator 56 as a reference signal. The EVM calculation unit 56 receives the multicarrier signal converted into the frequency domain and the reference signal from the remodulation unit 54. The EVM calculation unit 56 derives the EVM for each subcarrier.

FIG. 7 shows an outline of the calculation in the EVM calculation unit 56. FIG. 7 corresponds to an outline of calculation for one subcarrier. Further, the horizontal axis in FIG. 7 corresponds to the I axis, and the vertical axis corresponds to the Q axis. “IQmeasured” in the figure corresponds to a multicarrier signal converted into the frequency domain, and “IQreference” corresponds to a reference signal. The error between “IQ measured” and “IQ reference” on the I axis is shown as “Ierr” as shown in the figure, and the error between “IQ measured” and “IQ reference” on the Q axis is shown as “Qerr” as shown in the figure. It is. Here, EVM is derived as follows.

  Returning to FIG. The EVM calculation unit 56 outputs the derived EVM for each subcarrier to the control unit 28 (not shown).

  The operation of the base station apparatus 12 having the above configuration will be described. FIG. 8 is a flowchart showing a transmission procedure in the base station apparatus 12. In the initial state, the control unit 28 arranges the pilot signal at the center of the subcarrier block (S10). The sub-channelization unit 32, the modulation unit 34, the IFFT unit 36, and the radio unit 20 transmit packet signals (S12). The radio unit 20, the FFT unit 22, the demodulation unit 24, and the desubchannelization unit 30 receive the packet signal (S14). The measurement unit 26 calculates EVM for each subcarrier (S16). Based on the EVM, the control unit 28 specifies subcarriers in units of subcarrier blocks (S18). The control unit 28 instructs the sub-channelization unit 32 to allocate a pilot signal to the identified subcarrier (S20). If the data is not finished (N in S22), the process returns to step 12. If the data is finished (Y in S22), the process is finished.

  In the embodiments so far, the base station apparatus 12 includes information on the subcarriers to which the pilot signal is allocated in “SIG”. The terminal apparatus 10 acquires information included in “SIG”, identifies a subcarrier to which a pilot signal is allocated from the information, and then estimates transmission path characteristics from the pilot signal. Below, the case where the base station apparatus 12 does not include the information regarding the subcarrier which allocated the pilot signal in "SIG" is demonstrated. The terminal device 10 stores a pilot signal pattern in advance, and executes cross-correlation between the stored pilot signal and the received multicarrier signal in units of subcarriers. Moreover, the terminal device 10 estimates that a pilot signal is allocated to a subcarrier having a large correlation value. Furthermore, the terminal device 10 estimates transmission path characteristics from the pilot signal.

  The terminal device 10 here is the same type as the base station device 12 shown in FIG. However, unlike the base station apparatus 12, the terminal apparatus 10 is not connected to the network 18 and does not execute allocation of pilot signals and channel allocation to the terminal apparatus 10. FIG. 9 shows the configuration of the measurement unit 26 and the control unit 28 in the terminal device 10. The measurement unit 26 includes a correlation unit 60, and the control unit 28 includes an estimation unit 62.

  The radio unit 20 and the FFT unit 22 (not shown) are multicarrier signals from the base station device 12 (not shown), and when a plurality of subcarriers are classified into the above-described subcarrier blocks, at least one subcarrier block unit. The multicarrier signal in which the pilot signals are arranged is received. It is assumed that the terminal apparatus 10 does not recognize in advance which subcarrier is assigned the pilot signal. Therefore, after receiving the multicarrier signal converted into the frequency domain from the FFT unit 22, the demodulator 24 temporarily stores it.

  The correlation unit 60 stores pilot signal patterns in advance, and performs cross-correlation processing between the multicarrier signal converted into the frequency domain by the FFT unit 22 and the stored pilot signal pattern in units of subcarriers. A pilot signal pattern is a value defined over a plurality of symbols. The correlation unit 60 is configured by a matched filter to execute the above processing, and sets a pilot signal pattern as a tap coefficient. Such a matched filter is provided for each of the plurality of subcarriers. Note that the correlation unit 60 may execute autocorrelation processing instead of cross-correlation processing. In this case, the pilot signal pattern is configured by combining a shorter pattern a plurality of times. The delay time for autocorrelation processing is set to a cycle for forming a short pattern.

  The estimation unit 62 compares the correlation values derived by the correlation unit 60. Moreover, the estimation part 62 specifies the subcarrier corresponding to the largest correlation value per subcarrier block. The estimation unit 62 estimates that a pilot signal is assigned to the identified subcarrier. The estimation unit 62 outputs information on the estimated subcarriers to the demodulation unit 24 (not shown).

  The demodulator 24 acquires information on the subcarriers estimated by the estimator 62, and demodulates the stored multi-domain signals in the frequency domain while assuming that pilot signals are arranged on the subcarriers corresponding to the information. The demodulator 24 estimates the channel characteristics during the LTS period and updates the channel characteristics based on the pilot signal using a known technique. Note that, in the terminal device 10, the desubchannelization unit 30 and the subchannelization unit 32 (not shown) target the subchannel blocks allocated to the terminal device 10.

  According to the embodiment of the present invention, since the subcarrier to which the pilot signal is allocated is specified according to the EVM, it is possible to reduce the error included in the transmission path characteristics estimated in the terminal apparatus. Moreover, since the subcarrier to which the pilot signal is assigned is specified according to the EVM, the assignment of the pilot signal to the subcarrier having a deteriorated quality can be avoided. In addition, since the error included in the transmission path characteristics is reduced, the reception quality can be improved. Further, since the allocation is performed in units of subcarrier blocks, the channel and the allocation unit can be made the same. Further, since the allocation unit is the same, the processing can be simplified. In addition, since the EVM is measured by itself, the procedure for receiving the EVM from the terminal device can be omitted, and a decrease in transmission efficiency can be suppressed. Moreover, since the information regarding the subcarrier which allocated the pilot signal is transmitted in SIG, the information of the specified subcarrier can be notified with respect to a terminal device. Moreover, since the subcarrier to which the pilot signal is allocated is changed according to the radio environment, it is possible to suppress the deterioration of reception quality.

  In addition, the transmission efficiency can be improved because the subcarrier to which the pilot signal is assigned is specified without receiving information on the subcarrier to which the pilot signal is assigned from the base station apparatus. Moreover, since the subcarrier to which the pilot signal is assigned is specified, the pilot signal can be specified even when the subcarrier to which the pilot signal is assigned is changed at any time in the base station apparatus. Further, since a pilot signal is used, reception quality can be improved.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  In the embodiment of the present invention, the measurement unit 26 measures EVM in units of subcarriers as radio quality. However, the present invention is not limited to this. For example, the measurement unit 26 may derive the strength of the received signal as the radio quality in units of subcarriers. According to this modification, the process in the measurement unit 26 can be simplified. Further, the control unit 28 may receive the wireless quality measured by the terminal device 10 instead of receiving the wireless quality measured by the measuring unit 26. According to this modification, the present invention can be applied even when the uplink frequency and the downlink frequency are different. That is, it is only necessary to acquire the radio quality in units of subcarriers.

  In the embodiment of the present invention, the measurement unit 26 and the control unit 28 target a plurality of subcarriers included in the subcarrier block. However, the present invention is not limited to this, and for example, the control unit 28 may specify a subcarrier to which a pilot signal is assigned by specifying a subcarrier arranged near the center frequency of the subcarrier block as a specific target. Specifically, five subcarriers from the subcarrier numbers “i + 5” to “i + 9” in FIG. 4 are specified. In that case, the measurement part 26 acquires the radio | wireless quality with respect to each of the subcarrier used as a specific object at least. According to this modification, pilot signals are allocated to subcarriers arranged near the center frequency of the subcarrier block, so that pilot signals can be arranged evenly over a plurality of subcarrier blocks. In addition, since the pilot signals are evenly arranged, the influence of fading can be reduced. Also, since the subcarriers arranged near the center frequency of the subcarrier block are processed, the amount of processing can be reduced. That is, it is only necessary to specify the subcarrier to which the pilot signal is to be assigned.

  In the embodiment of the present invention, the control unit 28 compares the EVM sizes measured by the measurement unit 26 as they are. However, the present invention is not limited to this. For example, the control unit 28 performs weighting on the EVM acquired by the measurement unit 26 so that the EVN is improved as the center frequency of the subcarrier block is approached. Identification may be performed. Specifically, weighting of ¼ is performed on the subcarrier of the subcarrier number “i + 7” in FIG. 4, and the subcarrier numbers “i + 4” to “i + 6” and “i + 8” to “i + 10” Perform 1/2 weighting on the carrier. As a result, the EVM for the weighted subcarrier becomes small, so that the control unit 28 can easily specify the EVM. When the wireless quality is the strength of the received signal, weighting is performed so that the strength of the received signal is increased. Furthermore, this modification and the modification described above may be combined. According to this modification, pilot signals can be easily assigned to subcarriers arranged near the center frequency of the subcarrier block, so that pilot signals can be arranged evenly over a plurality of subcarrier blocks. That is, it is only necessary to specify the subcarrier to which the pilot signal is to be assigned.

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the multicarrier signal transmitted in the communication system of FIG. It is a figure which shows the structure of the packet signal transmitted in the communication system of FIG. It is a figure which shows the structure of the subcarrier block of FIG. It is a figure which shows the structure of the base station apparatus of FIG. It is a figure which shows the structure of the demodulation part and measurement part of FIG. It is a figure which shows the outline | summary of the calculation in the EVM calculation part of FIG. It is a flowchart which shows the transmission procedure in the base station apparatus of FIG. It is a figure which shows the structure of the measurement part and control part in the terminal device of FIG.

Explanation of symbols

  10 terminal apparatus, 12 base station apparatus, 14 terminal antenna, 16 base station antenna, 18 network, 20 radio section, 22 FFT section, 24 demodulation section, 26 measurement section, 28 control section, 30 desubchannelization section, 32 subchannelization unit, 34 modulation unit, 36 IFFT unit, 38 baseband processing unit, 100 communication system.

Claims (7)

An acquisition unit that acquires radio quality for each of a plurality of subcarriers;
Based on the radio quality acquired in the acquisition unit, a specifying unit for specifying a subcarrier to which a pilot signal is allocated;
While assigning a pilot signal to subcarriers identified in the identifying unit includes a transmission unit for transmitting a multicarrier signal formed by a plurality of sub-carriers, a,
The specifying unit classifies a plurality of subcarriers into a smaller number of blocks than the number of subcarriers, and specifies a subcarrier to which a pilot signal is allocated so that at least one pilot signal is arranged in a block unit . The wireless quality acquired in the acquisition unit is weighted so that the wireless quality improves as it approaches the center frequency of the block, and then the subcarrier with the best wireless quality is specified for each block. A wireless device. The specifying unit specifies a subcarrier to which a pilot signal is assigned, with a subcarrier arranged near the center frequency of the block as a specific target,
The radio apparatus according to claim 1, wherein the acquisition unit acquires radio quality for each of at least specific target subcarriers. A receiver that receives a multicarrier signal from a wireless device to be communicated;
The acquisition unit measures radio quality for each of a plurality of subcarriers from the multicarrier signal received by the reception unit,
And the transmission unit, while using the same frequency band and multi-carrier signal received at the reception unit, the wireless device according to claim 1 or 2, characterized in that to transmit the multicarrier signal. The transmitting section may transmit the multicarrier signal as the packet signal, in front of the period of a packet signal, any of claims 1 to 3, characterized by transmitting the information of subcarriers identified in the specific portion A wireless device according to claim 1. A wireless device that communicates with the wireless device according to claim 1,
A multi-carrier signal from the wireless device of the communication target, and when classifying a plurality of sub-carriers to fewer blocks than the number of subcarriers, the multi at least one pilot signal is arranged in blocks A receiver for receiving a carrier signal;
A correlation unit that performs correlation processing between the multicarrier signal received by the reception unit and the pilot signal in units of subcarriers;
Based on the result of correlation processing in the correlator, an estimation unit that estimates a subcarrier to which a pilot signal is assigned in units of blocks;
A processing unit for processing a multicarrier signal received by the receiving unit while using a pilot signal on a subcarrier estimated by the estimating unit;
A wireless device comprising: Obtaining radio quality for each of a plurality of subcarriers;
Identifying a subcarrier to which a pilot signal is allocated based on the acquired radio quality;
While assigning a pilot signal to the identified sub-carrier, comprising the steps of transmitting a multicarrier signal formed by a plurality of sub-carriers, a,
Wherein the step of specifying classifies a plurality of sub-carriers to fewer blocks than the number of subcarriers, such that at least one pilot signal is arranged in blocks, when specifying subcarriers to assign pilot signals , After performing the weighting so that the radio quality is improved as the frequency approaches the center frequency of the block with respect to the radio quality obtained in the obtaining step, the subcarrier having the best radio quality is identified for each block. A pilot signal allocation method characterized by the above. Obtaining radio quality for each of a plurality of subcarriers;
Identifying a subcarrier to which a pilot signal is allocated based on the acquired radio quality;
While assigning a pilot signal to the identified sub-carrier, comprising the steps of transmitting a multicarrier signal formed by a plurality of sub-carriers, a,
Wherein the step of specifying classifies a plurality of sub-carriers to fewer blocks than the number of subcarriers, such that at least one pilot signal is arranged in blocks, when specifying subcarriers to assign pilot signals , After performing the weighting so that the radio quality is improved as the frequency approaches the center frequency of the block with respect to the radio quality obtained in the obtaining step, the subcarrier having the best radio quality is identified for each block. A program that causes a computer to execute.

Images