JP2011072024A - Adaptive modulation control device, wireless communication apparatus and adaptive modulation control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To switch a modulation parameter in the middle of one transmission unit. <P>SOLUTION: An adaptive modulation control device selects any one of a plurality of modulation parameters determined from at least one of a modulation scheme and an encoding rate. The device includes: a switching control unit 203 which determines the modulation parameter is to be switched in the middle of one transmission unit and outputs a switching control signal for switching the modulation parameter; and a selection unit 204 which selects one modulation parameter and further selects a modulation parameter again when the switching control signal indicates that the modulation parameter is to be switched in the middle of one transmission unit. When selecting a modulation parameter again, the selection unit selects a modulation parameter of a lower transmission rate relative to the one modulation parameter in accordance with predetermined policies. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to modulation scheme control for selecting one of a plurality of modulation parameters in accordance with the quality of a propagation path.

  In conventionally known adaptive modulation communication, a modulation parameter (MCS: Modulation and Coding Scheme) composed of a plurality of modulation schemes, error correction coding rates, or a combination thereof is used as a reference for adaptive selection. Next, the state of the propagation path is estimated.

  In general, the state of the propagation path is estimated as a value such as a signal-to-noise ratio (SNR) from the reception state using a preamble which is a known signal inserted into a radio frame. Further, in subcarrier adaptive modulation communication in a multicarrier transmission scheme, a propagation path state for each subcarrier is estimated, and a modulation parameter is selected for each subcarrier.

  However, in an adaptive modulation system that does not consider propagation path fluctuation within the transmission unit, as shown in FIG. 19, when the propagation path state at the time when the modulation method is selected varies within the transmission unit, A situation occurs in which the reception level is lowered and the modulation scheme selected at the time of transmission does not satisfy the required quality.

  In a system to which adaptive modulation is applied, a block for estimating the maximum Doppler frequency fd is provided in order to reduce deterioration of reception quality due to fading fluctuation, and a modulation scheme having a low transmission rate is used when the Doppler frequency is estimated to be large. A method of making a selection has been proposed (Non-Patent Document 1). Further, a method has been proposed in which adaptive modulation is applied by performing propagation path estimation by extrapolation when the Doppler frequency is low, and the minimum bit rate is selected when the Doppler frequency is high (Patent Document 1).

  Below, patent document 1 is demonstrated as a prior art example of an adaptive modulation system. The block configuration of the receiver and the block configuration of the fd estimation unit 2009 when a TDD (Time Division Duplex) system is adopted in the conventional example are shown in FIGS. 20 and 21, respectively. The receiver has an fd estimation unit 2009. The received signal is band-limited by a band pass filter (BPF) 2001 and then received at an automatic gain controller (AGC) 2002 and an automatic frequency controller (AFC) 2003. The frequency is adjusted, and the quadrature demodulation block 2004 performs quadrature demodulation based on the input from the local oscillator 2005. The quadrature demodulated signal passes through a low pass filter (LPF) 2006 and is then sent to a fading distortion estimation / compensation block 2007 and an fd estimation unit 2009. From the signal whose fading is compensated in the fading distortion estimation / compensation block 2007, output data 2011 is extracted in a decision block 2008. On the other hand, the fd estimation unit 2009 estimates fd from the orthogonal demodulated signal using the configuration shown in FIG. The fd estimated value data 2010 is used for adaptive modulation during transmission.

  Further, as shown in FIG. 21, fd estimating section 2009 extracts pilot symbol data in pilot symbol data extracting section 2112, and normalized moving distance calculating section 2113 includes pilot symbol data extracting section 2112. A normalized moving distance is calculated for the output signal. The sliding average output unit 2114 outputs a sliding average based on the output signal of the normalized moving distance calculation unit 2113, and the fd estimation unit output unit 2115 outputs the output as the fd estimation unit 2009.

  Next, adaptive modulation considering fd estimated value data will be described. FIG. 22 shows a table used for modulation method selection. 22 (a), (b), and (c), the vertical axis represents the carrier power to noise power density ratio (C / N0), and the horizontal axis represents the delay dispersion σ (σ / σ) normalized by the symbol period Ts. Ts), and the modulation method is determined from C / N0 and delay dispersion based on these tables. When the fd estimated value data 2010 is at a low level, the transmission rate is improved by referring to the table (a) and applying adaptive modulation in which a modulation scheme is selected from any one of QPSK, 16QAM, and 64QAM. When the fd estimated value data 2010 is at a medium level, the table (b) is referred to, and adaptive modulation for selecting a modulation method from either QPSK or 16QAM is applied. When the fd estimated value data 2010 is at a large level, the error rate is reduced using QPSK which is the minimum rate regardless of C / N0 and delay dispersion as shown in the table (c).

  As described above, by changing the modulation method selection table in adaptive modulation according to the fd estimated value data 2010, it is possible to reduce deterioration in transmission quality when fading fluctuation is large.

  Further, in Patent Document 1, in order to improve the accuracy of modulation method selection, a technique of extrapolating propagation path information at the time of reception for a plurality of past times, which is a known technique, is used. Yes. As an example of propagation path estimation by extrapolation, FIG. 23 shows a propagation path estimation method by primary extrapolation. As shown in FIG. 23, the propagation path estimated value 2304 at the time of the k-th transmission is obtained from a straight line 2303 that connects the propagation path value 2301 in the k-1th transmission unit and the propagation path value 2302 in the k-2th transmission unit. Can be sought. In this example, the past two propagation path values are connected by a straight line, but the propagation path values in the kth transmission unit are approximated by polynomial approximation of the past propagation path values at a plurality of points. It is known that it can be estimated.

JP 2003-198426 A

Kondo, Akiba, Terai, Sunada, “A Study on Adaptive Modulation Method for Commercial Mobile Communications”, IEICE, IEICE Technical Report RCS2001-234, pp. 11-28. 65-72, January 2002

  However, in the above-described conventional example, the modulation scheme for all symbols in the transmission unit is determined based on the propagation path estimation value and the Doppler frequency at the time of transmission. A modulation scheme with a low transmission rate is selected in advance. For this reason, there is a problem in that the transmission efficiency is lowered because the low transmission rate modulation method is adopted even in the symbol at the front of the transmission unit having a high reception level. That is, as shown in FIG. 24, the SNR estimated value 2402 at the start of transmission satisfies the required SNR 2403 of MCS1 with respect to the actual SNR 2401 of the propagation path. Since the required SNR 2403 is not satisfied, the MCS 2 having a lower transmission rate must be selected. In the first half of the frame 2405, although the reception level is high, a modulation method with a low transmission rate is adopted as a whole, so that the transmission efficiency is lowered.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an adaptive modulation control device, a wireless communication device, and an adaptive modulation control method for switching modulation parameters in the middle of one transmission unit.

  (1) One aspect of an adaptive modulation control apparatus according to the present invention is an adaptive modulation control apparatus that selects any one modulation parameter from a plurality of modulation parameters determined from at least one of a modulation scheme and a coding rate, It is determined that the modulation parameter is switched in the middle of one transmission unit, a switching control unit that outputs a switching control signal for switching the modulation parameter, and one modulation parameter is selected, and further, based on the switching control signal, And a selection unit that selects a modulation parameter.

Thus, according to this adaptive modulation control apparatus, the modulation parameter used for the data symbol sequence can be switched in the middle of the frame. Thereby, the modulation parameter according to the fluctuation | variation of a propagation path condition can be selected. Also, it is possible to modulate and encode the data symbol sequence using modulation parameters that satisfy the required quality throughout the entire frame, and suppress deterioration in data transmission quality due to propagation path fluctuations within the frame. can do.
(2) Further, in the adaptive modulation control apparatus according to the present invention, the switching control unit receives at least one of propagation path fluctuation information indicating a propagation path fluctuation estimation result or movement speed information indicating a movement speed of a destination communication device. It is input as switching determination information, and based on the switching determination information, it is determined to switch a modulation parameter in the middle of one transmission unit.

In this way, switching of the modulation parameter can be determined based on either the propagation path fluctuation state or the moving speed information. As a result, it is possible to determine switching of the modulation parameter reflecting the fluctuation of the propagation path.
(3) Further, in the adaptive modulation control apparatus according to the present invention, the selection unit inputs propagation path information, and selects a modulation parameter according to the propagation path information.

In this way, the modulation parameter can be selected based on the propagation path information.
(4) In the adaptive modulation control apparatus according to the present invention, the selection unit receives modulation parameter information and selects a modulation parameter according to the modulation parameter information.

  In this way, the modulation parameter can be selected based on the modulation parameter information. Thus, the modulation parameter can be instructed by notifying the selection unit of the modulation parameter information about the modulation parameter to be selected.

  (5) In the adaptive modulation control apparatus according to the present invention, the adaptive modulation control apparatus is used in a radio communication apparatus that performs radio communication using a multicarrier communication scheme, and the selection unit is in units of one or a plurality of subcarriers. A modulation parameter is selected.

  In this way, the modulation parameter can be selected for each of a plurality of subcarriers. Thereby, it is possible to suppress a processing amount related to switching of the modulation parameter.

  (6) In the adaptive modulation control apparatus according to the present invention, the adaptive modulation control apparatus is used in a radio communication apparatus that performs radio communication using a multicarrier communication scheme, and the switching control unit includes one or a plurality of subcarrier units. Thus, it is determined that the modulation parameter is switched in the middle of one transmission unit.

  In this way, switching of the modulation parameter can be determined for each of a plurality of subcarriers. Thereby, it is possible to suppress a processing amount related to switching of the modulation parameter.

  (7) Further, in the adaptive modulation control apparatus according to the present invention, the selection unit selects any modulation parameter having a transmission rate lower than that of the one modulation parameter and the same transmission rate. .

  Thus, when the quality of the propagation path is lowered, it is possible to switch to a modulation parameter that lowers the transmission rate. As a result, it is possible to suppress the deterioration of the data transmission quality accompanying the decrease in the propagation path condition.

  (8) The adaptive modulation control apparatus according to the present invention further includes a generation unit that receives the switching control signal and generates a symbol including switching information indicated by the switching control signal.

  In this way, control information including switching information indicated by the switching control signal can be generated. As a result, the communication destination can be notified of the switching information, and the transmission destination can perform modulation / decoding based on the switching information.

  (9) In the adaptive modulation control apparatus according to the present invention, the switching information includes information on an instruction as to whether or not to switch modulation parameters.

  In this way, it is possible to notify the communication destination by the control information whether or not to switch the modulation parameter. As a result, the communication destination can perform switching control determined in advance.

  (10) In the adaptive modulation control apparatus according to the present invention, the switching information includes information of one or more positions for switching modulation parameters.

  In this way, the communication destination can be notified of the position of the data symbol sequence for switching the modulation parameter. As a result, the communication destination can change the modulation parameter at the designated position.

  (11) In the adaptive modulation control apparatus according to the present invention, the switching information includes information specifying one or more modulation parameters to be switched.

  In this way, one or more modulation parameters to be switched can be notified to the communication destination. As a result, the communication destination can switch and use one or more notified modulation parameters.

  (12) In the adaptive modulation control apparatus according to the present invention, the generation unit instructs insertion of the modulation parameter information to be switched into a modulation parameter switching start position within one transmission unit.

  Thus, the modulation parameter to be switched can be notified immediately before switching the modulation parameter.

  (13) In the adaptive modulation control apparatus according to the present invention, the switching control unit holds a position for switching a modulation parameter, detects that the one transmission unit reaches the position, and notifies the position. A signal is output, and the selection unit selects a modulation parameter again according to a predetermined selection procedure based on the switching control signal.

  In this way, the modulation parameter can be switched at a predetermined position. Also, the modulation parameter to be switched can be specified by the selection unit using a predetermined method.

  (14) In the adaptive modulation control apparatus according to the present invention, the selection unit selects a modulation parameter again according to a predetermined selection procedure based on the switching control signal.

  In this way, the modulation parameter can be switched by notifying the selection unit of the switching signal. In addition, since the selection unit can switch the modulation parameter according to a predetermined selection criterion, the amount of information notified as control information can be suppressed.

  (15) In the adaptive modulation control apparatus according to the present invention, the switching control unit holds a position for switching a modulation parameter, detects that the one transmission unit reaches the position, and notifies the position. A signal is output.

  In this way, by notifying the communication destination that the modulation parameter is switched, the modulation parameter can be switched at a predetermined position.

  (16) In the adaptive modulation control apparatus according to the present invention, the generation unit uses the information specifying one or more modulation parameters to be switched as difference information from the modulation parameter immediately before switching.

  As described above, a plurality of modulation parameters can be notified to a communication destination with a small amount of information, compared to a case where a plurality of modulation parameters are notified.

  (17) The adaptive modulation control apparatus according to the present invention is characterized in that the generation unit specifies a relative level degree of a modulation parameter compared to the modulation parameter immediately before switching.

  Thus, the modulation parameter to be switched can be specified by specifying a relative level, and the amount of information notified as control information can be suppressed.

  (18) In the adaptive modulation control apparatus according to the present invention, the selection unit selects a predetermined modulation parameter as the modulation parameter to be selected again.

  In this way, it is possible to switch to a modulation parameter predetermined by the system.

  (19) In the adaptive modulation control apparatus according to the present invention, the selection unit selects a modulation parameter having a lowest rate as a predetermined modulation parameter.

  In this way, when the propagation path condition is lowered, it is possible to switch to a modulation parameter having a predetermined minimum rate. Further, it is possible to switch to the modulation parameter of the lowest rate without notifying the modulation parameter to be switched.

  (20) The adaptive modulation control apparatus according to the present invention is characterized in that the generation unit sets information on one or more positions for switching modulation parameters to a data length to be transmitted with each modulation parameter.

  Thus, the position information of the data symbol sequence can be specified using the data length.

(21) In the adaptive modulation control apparatus according to the present invention, the switching control unit uses a Doppler frequency as an index as the switching determination information.

  In this way, it is possible to control switching of the modulation parameter using the Doppler frequency. Thereby, the switching of the modulation parameter can be controlled using the moving speed of the communication destination.

  (22) In the adaptive modulation control apparatus according to the present invention, the switching control unit switches a modulation parameter when the Doppler frequency is larger than a preset threshold value.

  As described above, when the Doppler frequency is larger than the threshold value, it is possible to control that the modulation parameter is switched by interpreting that the propagation path fluctuation is large.

  (23) In the adaptive modulation control apparatus according to the present invention, the switching control unit further inputs an adaptive modulation period, and when the product of the Doppler frequency and the adaptive modulation period is greater than a preset threshold value, The modulation parameter is switched.

  In this way, the magnitude of the propagation path fluctuation can be determined using the product of the Doppler frequency and the adaptive modulation period.

  (24) Further, another aspect of the adaptive modulation control apparatus according to the present invention is an adaptive modulation control apparatus that selects any one modulation parameter from a plurality of modulation parameters determined from at least one of a modulation scheme and a coding rate. A switching control unit that holds a position in the middle of one transmission unit for switching the modulation parameter, detects that the one transmission unit reaches the position, and outputs a switching control signal notifying the position; A selection unit that inputs propagation path information, selects one modulation parameter according to the propagation path information, and selects a modulation parameter again based on the switching control signal input from the switching control unit; It is characterized by.

  Thus, according to this adaptive modulation control apparatus, the modulation parameter used for the data symbol sequence can be switched in the middle of the frame. As a result, the modulation parameter can be switched in accordance with the quality degradation of the propagation path condition. Also, it is possible to modulate and encode the data symbol sequence using modulation parameters that satisfy the required quality throughout the entire frame, and suppress deterioration in data transmission quality due to propagation path fluctuations within the frame. can do.

  (25) In addition, according to one aspect of the wireless communication device of the invention, from the transmission-side device, propagation path information indicating a propagation path state estimation result, propagation path fluctuation information indicating a propagation path fluctuation estimation result, and modulation A receiving unit that receives at least one of modulation parameter information indicating a parameter, the adaptive modulation control device according to any one of claims 1 to 18, and a modulation parameter output from the adaptive modulation control device And a transmitter that transmits data modulated using the.

  Thus, according to this wireless communication apparatus, the modulation parameter used for the data symbol sequence can be switched in the middle of the frame. Thereby, the modulation parameter according to the fluctuation | variation of a propagation path condition can be switched. Also, it is possible to modulate and encode the data symbol sequence using modulation parameters that satisfy the required quality throughout the entire frame, and suppress deterioration in data transmission quality due to propagation path fluctuations within the frame. can do.

(26) Moreover, one aspect of the second wireless communication apparatus according to the present invention is a second wireless communication apparatus that communicates with the wireless communication apparatus according to claim 25, wherein the propagation path indicates the estimation result of the propagation path state. A transmission section that transmits at least one of information, propagation path fluctuation information indicating an estimation result of propagation path fluctuation, and modulation parameter information indicating a modulation parameter, and an adaptive modulation control apparatus provided in the wireless communication apparatus And a receiving unit that receives a signal modulated using the modulation parameter output from.

  Thus, according to the second wireless communication device, necessary information can be transmitted to a wireless communication device that is a communication destination capable of switching the modulation parameter. Thereby, the quality of the data received from the wireless communication device of the communication destination can be improved.

  (27) According to another aspect of the wireless communication apparatus of the present invention, a propagation path estimation unit that estimates a propagation path state, a propagation path fluctuation estimation part that estimates propagation path fluctuation, and claims 1 to The adaptive modulation control apparatus according to any one of 23, and a transmission unit that transmits a modulation parameter output from the adaptive modulation control apparatus to a reception-side apparatus.

Thus, according to this wireless communication apparatus, according to this wireless communication apparatus, the modulation parameter used for the data symbol sequence can be switched in the middle of the frame. Thereby, the modulation parameter according to the fluctuation | variation of a propagation path condition can be switched. In addition, it is possible to select a modulation parameter to be switched by estimating propagation path fluctuation in the own apparatus. It is possible to modulate and encode a data symbol sequence using a modulation parameter that satisfies the required quality for the entire frame, and to suppress deterioration in data transmission quality due to propagation path fluctuations in the frame. Can do.
(28) One aspect of the wireless communication method according to the present invention is an adaptive modulation control method for selecting any one modulation parameter from a plurality of modulation parameters determined from at least one of a modulation scheme and a coding rate. It is determined that the modulation parameter is switched in the middle of the transmission unit, a switching step for outputting a switching control signal for switching the modulation parameter, one modulation parameter is selected, and the modulation parameter is again determined based on the switching control signal. And a selection step of selecting.

  Thus, according to this adaptive modulation control method, the modulation parameter used for the data symbol sequence can be switched in the middle of the frame. Thereby, the modulation parameter according to the fluctuation | variation of a propagation path condition can be switched. Also, it is possible to modulate and encode the data symbol sequence using modulation parameters that satisfy the required quality throughout the entire frame, and suppress deterioration in data transmission quality due to propagation path fluctuations within the frame. can do.

  (29) In one aspect of the wireless communication method according to the present invention, the switching step switches at least one of propagation path fluctuation information indicating a propagation path fluctuation estimation result or movement speed information indicating a movement speed of a destination communication device. It is input as determination information, and based on the switching determination information, it is determined that the modulation parameter is switched in the middle of one transmission unit.

  In this way, switching of the modulation parameter can be determined based on either the propagation path fluctuation state or the moving speed information. As a result, it is possible to determine switching of the modulation parameter reflecting the fluctuation of the propagation path.

  (30) In one aspect of the wireless communication method according to the present invention, the selecting step is characterized by inputting propagation path information and selecting a modulation parameter according to the propagation path information.

  In this way, the modulation parameter can be selected based on the propagation path information.

  (31) In one aspect of the wireless communication method according to the present invention, the adaptive modulation control method is used in a wireless communication apparatus that performs wireless communication by a multicarrier communication method, and the selecting step includes one or a plurality of subcarriers. The modulation parameter is selected in units.

  In this way, the modulation parameter can be selected for each of a plurality of subcarriers. Thereby, it is possible to suppress a processing amount related to switching of the modulation parameter.

  (32) In one aspect of the wireless communication method according to the present invention, the adaptive modulation control method is used in a wireless communication apparatus that performs wireless communication by a multicarrier communication method, and the switching step includes one or a plurality of subcarriers. It is a step of determining whether to switch the modulation parameter in the middle of one transmission unit.

  In this way, switching of the modulation parameter can be determined for each of a plurality of subcarriers. Thereby, it is possible to suppress a processing amount related to switching of the modulation parameter.

  According to the present invention, it is possible to switch modulation parameters in the middle of one transmission unit. Thereby, the modulation parameter according to the propagation path quality can be selected.

It is a figure which shows the structural example of the OFDM system which concerns on 1st Embodiment. It is a figure which shows the structural example of the MCS control part in the base station which concerns on 1st Embodiment. It is a figure which shows the structural example of the MCS control part in the mobile station which concerns on 1st Embodiment. It is a figure which shows the structural example of a downlink frame which concerns on 1st Embodiment. It is a figure which shows the example of an upstream frame structure which concerns on 1st Embodiment. It is a figure which shows the example of an upstream frame structure which concerns on 1st Embodiment. It is a figure which shows an example of MCS switching according to the propagation path fluctuation | variation which concerns on 1st Embodiment. It is a figure which shows the structural example of the MCS control part in the mobile station which concerns on 2nd Embodiment. It is a figure which shows the structural example of the downlink frame which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of MCS switching according to the propagation path fluctuation | variation which concerns on 2nd Embodiment. It is a figure which shows an example of the propagation path fluctuation | variation estimation method which concerns on 2nd Embodiment. It is a figure which shows the structural example of the downlink frame which concerns on 3rd Embodiment. It is a figure which shows the structural example of the mobile station which concerns on 4th Embodiment. It is a figure which shows the structural example of the OFDM system which concerns on 5th Embodiment. It is a figure which shows the structural example of the MCS control part in the base station which concerns on 5th Embodiment. It is a figure which shows the structural example of the downlink frame which concerns on 5th Embodiment. It is a figure which shows the structural example of the MCS control part in the base station which concerns on 7th Embodiment. It is a figure which shows the structural example of a downlink frame which concerns on 7th Embodiment. It is a figure which shows the example of selection of MCS in a general adaptive modulation system. It is a figure which shows the system configuration | structure in the conventional adaptive modulation system. It is a figure which shows the structure of the fd estimation part in the conventional adaptive modulation system. It is a figure which shows the table used for the conventional modulation system selection. It is a figure which shows the propagation path estimation method by extrapolation. It is a figure which shows the example of selection of MCS in the conventional adaptive modulation system.

  Next, embodiments of the present invention will be described with reference to the drawings. In each embodiment, a mode in which a modulation parameter (MCS: Modulation and Channel Coding Scheme) is switched in the middle of transmission data in downlink transmission will be described. The modulation parameter (hereinafter also referred to as “MCS”) is a combination including at least one of a modulation scheme and a coding rate, and is defined by either the modulation scheme, the coding rate, or a combination thereof. For example, MCS1 indicates a combination in which the modulation method is QPSK and the encoding is 1/3. Further, MCS may be determined only by the modulation scheme or only by the coding rate. Therefore, the modulation parameter determines at least one of the modulation scheme and the coding rate. In wireless communication, one MCS is selected from a plurality of MCS and used. In the present specification, different MCSs are represented as MCS1, MCS2,..., MCSn (n is an integer).

(First embodiment)
In the first embodiment, a case will be described in which whether or not to change the MCS level at a predetermined position is instructed. FIG. 1 shows a configuration example of an orthogonal frequency division multiplexing (OFDM) system according to the first embodiment. Also, a configuration example of the MCS control unit 103 in the base station 100 is shown in FIG. 2, and a configuration example of the MCS control unit 124 in the mobile station is shown in FIG. However, although one base station 100 and one mobile station 120 are shown in FIG. 1, a plurality of mobile stations exist, and one mobile station 120 is shown. Also, a downlink frame configuration example and an uplink frame configuration example are shown in FIGS. 4 and 5, respectively. The frames shown in FIGS. 4 and 5 represent one transmission unit. Although the present embodiment describes the case where uplink and downlink have independent links, the present invention can also be applied to TDD (Time Division Duplex) that shares uplink and downlink with slight changes.

In FIG. 1, the data transmission unit of the base station 100 includes an encoding unit 101, a modulation unit 102, an MCS control unit 103, an IFFT (Inverse Fast Fourier Transform) unit 104, a preamble multiplexing unit 105, a radio transmission unit 106, and a preamble generation unit. 111 includes an adaptive modulation OFDM transmitter for each subcarrier composed of 111. The data reception unit of the base station includes a radio reception unit 107, a preamble separation unit 108, a demodulation unit 109, and a decoding unit 110. Data is transmitted and received via the antenna 112.

  On the other hand, the data reception unit of the mobile station 120 includes a radio reception unit 121, a preamble separation unit 122, a propagation path estimation unit 123, an MCS control unit 124 that controls demodulation and a decoding scheme, an FFT (Fast Fourier Transform) unit 125, a demodulation In addition to the subcarrier adaptive modulation OFDM receiving unit configured by the unit 126 and the decoding unit 127, a channel variation estimation unit 129 that estimates channel variation from the channel information and outputs the estimated channel estimation information is provided. Have. The data transmission unit of the mobile station includes a preamble generation unit 128, a preamble multiplexing unit 130, a modulation unit 131, an encoding unit 132, and a radio transmission unit 133. Data is transmitted and received via the antenna 134.

  IFFT (Inverse Fast Fourier Transform) is an inverse fast Fourier transform. A mobile station generates a QAM modulation symbol sequence for each subcarrier from the OFDM symbol sequence. FFT (Fast Fourier Transform) is a fast Fourier transform. An OFDM symbol sequence is generated from a QAM modulation symbol sequence for each subcarrier in the base station.

  Here, the frame configuration will be described with reference to FIGS. The configurations of the downlink frame 401 and the uplink frame 501 can be broadly classified into a preamble part that is a control information part and a data part that is a data part to be transmitted and received. The preamble part of the downlink frame 401 shown in FIG. 4 includes a channel estimation symbol (CE), an MCS switching information symbol (COI: MCS Change Over Information), and an MCS information symbol (MLI: MCS Level Information). Consists of The downlink frame 401 shown in FIG. 4 shows a configuration example in the case where MCS is switched once in the center of the data portion and all preamble portions are time-multiplexed in front of the data portion. It is not limited. For example, the control information may be notified to the mobile station using a subcarrier different from the data, or code multiplexed.

  5 includes a channel estimation symbol (CE), a channel information notification symbol (CQI: Channel Quality Indicator), and a channel variation information notification symbol (CFI: Channel Fluctuation Information). ). Hereinafter, in the present specification, explanation will be made using abbreviations of CE, COI, MLI, CQI, and CFI.

  CE is a preamble symbol multiplexed in the downlink frame 401 and the uplink frame 501. CE is a known symbol and is used for channel estimation in the base station 100 and the mobile station 120. The downlink frame 401 is used for propagation path compensation, propagation path information estimation and propagation path fluctuation estimation for each subcarrier, and the uplink frame 501 is used for propagation path compensation. For example, CE is a known pseudorandom number sequence.

  The COI is a preamble symbol that is multiplexed in the downstream frame 401. The COI is sent to the MCS switching control unit 303 of the mobile station 120 and is used to control the timing for switching the MCS when demodulating and decoding the received downlink frame 401. For example, the COI includes information “switch MCS from the 10th data symbol”. Alternatively, it is used to control whether or not to perform MCS switching.

  The MLI is a preamble symbol multiplexed in the downlink frame 401. The data is sent to the MCS control unit 124 of the mobile station 120 and used for selection of MCS at the time of demodulation and decoding. For example, the MLI includes information “MCS1 (QPSK, coding rate = 1/3)”. Alternatively, it may include information indicating a relative value of the MCS level (for example, a numerical value such as 1, 0, −1) and instructing the change of the MCS level.

  The CQI is a preamble symbol multiplexed in the uplink frame 501. This is a symbol for notifying the base station 100 of propagation path information for each subcarrier in the downlink frame. The data is sent to the MCS control unit 103 of the base station 100 and used for selection of MCS at the time of encoding and modulation. For example, the CQI includes information that “the SNR of the i-th subcarrier is 5 dB”.

  The CFI is a preamble symbol multiplexed in the uplink frame 501. This is a symbol for notifying the base station 100 of propagation path fluctuation information in a downlink frame. It is sent to the MCS switching control unit 203 of the base station 100 and is used for controlling the timing for switching the MCS when encoding and modulating the downlink frame to be transmitted. For example, the CFI includes information such as “the propagation path fluctuation in the frame is 1 dB” or “the propagation path fluctuation in the frame is severe”.

  Hereinafter, a process of transmission / reception in the base station 100 will be described with reference to FIG. In the data transmission unit of the base station 100, transmission data for each mobile station 120 is encoded and modulated by the encoding unit 101 and the modulation unit 102. At this time, the coding rate and the modulation scheme are adaptively controlled in the MCS control unit 103 based on the propagation path information notified from the mobile station 120 and the MCS switching position in the frame predetermined by the system. Details of the MCS switching control performed by the MCS control unit 103 will be described later. The modulated data symbol sequence is combined into an OFDM symbol sequence by IFFT processing in IFFT section 104, CE, COI, and MLI are multiplexed in preamble multiplexing section 105 and transmitted through radio transmission section 106.

  A signal from the mobile station received by the radio reception unit 107 is separated into a preamble symbol sequence and a data symbol sequence by a preamble separation unit 108. FIG. 5 shows an uplink frame configuration example 501. CE is used for propagation path compensation, and CQI and CFI are sent to the MCS control unit 103. Received data is extracted from the data symbol sequence through demodulation in demodulation section 109 and decoding in decoding section 110.

  Here, details of the MCS control unit 103 of the base station 100 will be described. FIG. 2 is a diagram illustrating a configuration example of the MCS control unit 103 in the base station 100. The MCS control unit 103 includes a CFI determination unit 201, a CQI determination unit 202, an MCS switching control unit 203, an MCS selection unit 204, and an MCS table 205.

  The CFI determination unit 201 determines (extracts / specifies) propagation path fluctuation information indicating the estimation result of the propagation path fluctuation from the CFI. The CQI determination unit 202 determines (extracts / specifies) the propagation path information indicating the estimation result of the propagation path condition from the CQI. The MCS switching control unit 203 performs MCS switching control based on the propagation path fluctuation information determined by the CFI determining unit 201. The MCS switching control unit 203 determines whether or not the MCS is switched based on the magnitude of the fluctuation of the propagation path fluctuation information, and notifies the judgment result as an MCS switching control signal. The MCS selection unit 204 selects the MCS by comparing the channel information determined by the CQI determination unit 202 with the MCS table 205 in accordance with the MCS switching control signal notified from the MCS switching control unit 203. The MCS table 205 divides the combination of the modulation scheme and the coding rate into a plurality of stages and holds them in correspondence with the required quality.

  The MCS switching control signal (switching control signal) is a signal for notifying the determination result of determining whether or not MCS switching is performed, and is used for switching the modulation parameter. As an example, the determination result (switching information) includes information such as the presence / absence of MCS switching, the position of MCS switching, the designation of MCS to be switched, and the number of times of MCS switching. The MCS switching signal includes a case where the determination result is notified by a pulse signal, a case where a continuously output signal is used, and the determination result is notified by a change in the value of ON / OFF (0, 1). The MCS switching control signal includes a case where information (data) is notified to the MCS selection unit 204.

  Further, the MCS selection unit 204 first selects the MCS, and then selects the MCS again based on the input MCS switching control signal. The MCS to be selected again may be different or the same as the MCS that was initially selected. For example, when switching to the MCS with the lowest quality level is specified, the MCS may be the same for subcarriers with poor propagation path quality from the beginning.

  When the propagation path fluctuation information is larger than a predetermined threshold, the MCS switching control unit 203 decides to perform MCS switching and notifies the MCS selecting unit 204 of an MCS switching control signal instructing to switch MCS. Further, the MCS switching control signal is output to the preamble generation unit 111.

  The MCS selection unit 204 uses the table 205 to select an MCS based on the required quality, and notifies the encoding unit 101 and the modulation unit 102 of an MCS control signal that identifies the selected MCS. The level of MCS is set based on the required propagation path quality using the table 205. The higher the level, the higher the communication speed, but the higher the required channel quality, and the lower the level, the lower the communication speed but the lower the required channel quality. If it is determined that the fluctuation is small based on the propagation path fluctuation information, the MCS is not switched at the MCS switching position where the MCS value is set in advance. If the fluctuation is determined to be large, the MCS is switched.

  The information of the MCS notified from the MCS control unit 103 to the encoding unit 101 and the modulation unit 102 is the predetermined MCS from the selected MCS to the MCS switched based on a predetermined switching policy when switching the MCS. It is changed at the switching position. It is assumed that the predetermined MCS switching position is held in the MCS switching control unit 203. The predetermined switching policy is, for example, to lower the MCS level by one or a plurality of levels, or to change the MCS level to a preset level (for example, a minimum rate).

  In general, in an environment in which propagation path fluctuation is severe, there is a high possibility that required quality cannot be satisfied when adaptive modulation is performed in units of frames. On the other hand, in the system according to the present embodiment, when the propagation path changes rapidly, the quality degradation in the second half of the frame can be prevented by lowering the MCS level in the frame. The preamble generation unit 111 generates a CE. In addition, MLI and CQI are generated from the MCS information notified from the MCS control unit 103. The MLI includes the value of the MCS in the first half of the data, and the COI includes information on whether or not to change the MCS in the second half of the data to the first half.

  Note that information COI indicating whether or not to switch the MCS between the first half and the second half can be omitted by using a frame configuration as shown in FIG. In that case, the MCS is always switched at the MCS switching position, so that it is possible to cope with the fluctuation of the propagation path. In this case, there is no need to notify the CFI upstream.

In this case, the MCS control unit 103 operates as follows as an example. The MCS switching control unit 203 holds a switching position in the middle of one transmission unit for switching the modulation parameter, detects that one transmission unit reaches the switching position, and outputs a switching control signal notifying the switching position. . Further, the MCS selection unit 204 receives the propagation path information, selects one modulation parameter according to the propagation path information, and selects the modulation parameter again based on the switching control signal input from the switching control unit. .

  Next, the process of transmission / reception in the mobile station 120 will be described. A signal from the base station received by the wireless reception unit 121 is first separated into a preamble symbol sequence and a data symbol sequence by the preamble separation unit 122. Of the preamble symbol sequence, CE is sent to the propagation path estimation unit 123, and COI and MLI are sent to the MCS control unit 124 for demodulation and decoding. The data symbol sequence is converted into a symbol sequence assigned to each subcarrier by FFT processing in the FFT unit 125, and then demodulated and decoded in the demodulating unit 126 and decoding unit 127 to obtain received data. At this time, MCS control section 124 notifies MCS of each data symbol to demodulation section 126 and decoding section 127.

  Next, details of the MCS control unit 124 of the mobile station 120 will be described. FIG. 3 is a diagram illustrating a configuration example of the MCS control unit 124 in the mobile station 120. The MCS control unit 124 includes a COI determination unit 301, an MLI determination unit 302, an MCS switching control unit 303, and an MCS selection unit 304.

  The COI determination unit 301 receives the COI from the preamble separation unit 122 and determines (extracts / specifies) the MCS switching information from the COI. The MLI determination unit 302 receives the MLI from the preamble separation unit 122 and determines (extracts / specifies) the MCS information from the MLI. The MCS switching control unit 303 performs MCS switching control based on the MCS switching information determined by the COI determining unit 301. The MCS selection unit 304 selects an MCS based on the MCS information notified from the MLI determination unit 302 according to the MCS switching control signal notified from the MCS switching control unit 303.

  If the MCS switching control unit 303 is instructed to switch the MCS in the latter half of the COI, the MCS switching control signal that instructs to switch the MCS at a predetermined MCS switching position (that is, the timing to switch the MCS) is selected as the MCS. Notification to the unit 304. The MCS selection unit 304 outputs an MCS according to a predetermined switching policy. Each data symbol is demodulated and decoded based on the MCS control signal notified from the MCS control unit 124.

  Specifically, when the downstream frame 401 of FIG. 4 is used, it is assumed that the following policy is determined in advance. For example, COI indicates whether or not MCS is switched, and MLI1 indicates MCS before switching. It is assumed that the MCS switching position for switching the MCS by COI is determined in advance by the system and is held by the MCS switching control unit 303. When the COI is switched, the MCS switching control unit 303 outputs an MCS switching signal to the MCS selecting unit 304 at the MCS switching position. The MCS selection unit 304 switches from MCS1 indicated by MLI1 to MCS2 and outputs the result. The MCS 2 is, for example, an MCS that is specified in advance, such as an MCS that lowers (or raises) a transmission rate by a predetermined level from the MCS 1 or an MCS at the lowest level.

  The propagation path estimation unit 123 estimates propagation path information (for example, signal-to-noise power ratio) for each subcarrier based on the CE. The estimated propagation path information for each subcarrier is notified to the preamble generation unit 128 and the propagation path fluctuation estimation unit 129. Signal-to-noise ratio (SRN) is a ratio of signal power to noise power.

  The propagation path fluctuation estimation unit 129 estimates the time fluctuation of the propagation path in the current frame from the propagation path information for each subcarrier notified from the propagation path estimation unit 123, and indicates the estimation result of the propagation path fluctuation. Is transmitted to the preamble generation unit 128. As the propagation path variation information, for example, there is a difference between the SNR in the frontmost symbol of the frame and the SNR in the last symbol of the frame.

  The preamble generation unit 128 generates a CE used for channel estimation in the base station 100. Further, preamble generation section 128 generates CQI from the propagation path information for each subcarrier sent from propagation path estimation section 123, and generates CFI from the propagation path fluctuation information sent from propagation path fluctuation estimation section 129. Next, the preamble generation unit 128 sends CQI and CFI together with the CE to the preamble multiplexing unit 130. In preamble multiplexing section 130, CE, CQI, and CFI are multiplexed on the transmission data symbol sequence encoded and modulated by encoding section 132 and modulation section 131, and transmitted via radio transmission section 133.

  Next, FIG. 7 shows an example of the relationship between propagation path fluctuations in the mobile station 120 and the data symbol sequence portion of the received downlink frame. In FIG. 7, a data symbol string 705 (in the figure, the data symbol string is described as data. The same applies hereinafter) indicates a case where MCS is not switched (conventional method), and the data symbol string 706 is an MCS in a frame. Is shown (this embodiment). As shown in the SNR 1001 of the actual propagation path in FIG. 7, the state of the propagation path (SNR is shown as an example of the state of the propagation path) changes every moment in the frame. In the conventional method, only one type of MCS of the data symbol string 705 in one frame is used, and the MCS cannot be switched in the middle of the frame. For this reason, in the conventional frame, the entire data symbol sequence 705 is transmitted only by MCS1 selected based on the received SNR estimation value 702 at the mobile station at the start of downlink frame transmission at the base station. Accordingly, when a large propagation path fluctuation in the frame as shown in FIG. 7 occurs as shown in the SNR 701 of the actual propagation path, the MCS 1 cannot satisfy the required quality from the middle of the frame. It caused deterioration in communication quality such as an increase in error rate.

  In the present embodiment, MCS switching in the middle of a frame can be performed according to the state of the propagation path. For this reason, even when the propagation path fluctuation 707 as shown in FIG. 7 occurs, transmission in the MCS that satisfies the required quality in the entire frame becomes possible. That is, the first half of the data symbol sequence 706 uses MCS1, and the second half of the data symbol sequence 706 uses MCS2. Accordingly, it is possible to suppress deterioration in quality due to propagation path fluctuation in the frame.

  In addition, when it is estimated that the propagation path may be greatly deteriorated, the base station 100 can suppress transmission power by not transmitting a symbol from the middle of the frame. Alternatively, the bit error rate can be improved by transmitting the same information as that of the first half of the data symbol sequence 706 to the second half of the data symbol sequence 706.

  Thus, according to the present embodiment, it is possible to switch the MCS used for the data symbol sequence in the middle of the frame. This makes it possible to select an MCS according to fluctuations in propagation path conditions, and it is possible to modulate and encode a data symbol sequence using the MCS that satisfies the required quality in the entire frame and transmit it. become. Therefore, it is possible to suppress deterioration of data transmission quality due to propagation path fluctuation in the frame. In particular, it is possible to suppress deterioration in data transmission quality due to a decrease in propagation path conditions. Moreover, the information amount notified by control information can be reduced (suppressed) by determining in advance the procedure for selecting the MCS switching position and the switching MCS.

  In the present embodiment, the configuration example in which the propagation path fluctuation estimation unit 129 is installed in the mobile station 120 has been described. However, the present invention is not limited to this. The propagation path fluctuation estimation unit 129 that performs the propagation path fluctuation estimation based on the CQI notified in the uplink frame is provided in the base station 100, the uplink frame does not include the CFI, and the propagation path fluctuation estimation unit 129 of the mobile station 120 An unnecessary configuration may be adopted.

  In addition, the configuration example of the MCS in FIG. 2 is an example, and a selection control unit configured by the CFI determination unit 201 and the MCS switching control unit 203, and a selection configured by the CQI determination unit 202 and the MCS selection unit 204. The structure of a part may be sufficient. In this embodiment, the switching control is performed using the propagation path fluctuation information. However, the switching of the MCS may be controlled using the moving speed information indicating the moving speed of the transmission destination communication device. When using propagation path fluctuation information or movement speed information, the switching control unit inputs at least one of propagation path fluctuation information and movement speed information as switching determination information, and based on the switching determination information, one transmission unit During the process, it is determined that the modulation parameter is switched, and a switching control signal is output at the timing of switching the modulation parameter. The selection unit receives the propagation path information, selects and outputs one modulation parameter according to the propagation path information, and differs from the one modulation parameter at the timing when the switching control signal is input from the switching control unit. Select and output modulation parameters.

(Second Embodiment)
In the second embodiment, a case where the MCS after switching is designated will be described. The block configuration of the entire system of this embodiment is the same as that of FIG. 1, but the internal configuration of the MCS control unit 124 in the mobile station is different from that of the first embodiment. FIG. 8 shows an internal configuration of the MCS control unit 124 in the mobile station in the OFDM system according to the second embodiment. FIG. 9 shows an example of a downlink frame configuration. The system according to the present embodiment is a mode in which deterioration of quality is prevented by lowering the MCS level once or a plurality of times within one frame in an environment where the propagation path fluctuation is severe. Further, when it is estimated that propagation path fluctuation is in the direction of improvement and the required quality can be satisfied even at a higher MCS level from the middle of the frame, the MCS level is set once or a plurality of times within one frame. This is an aspect in which the transmission rate is improved by increasing the transmission rate.

  Hereinafter, the present embodiment will be described based on the block diagram of the MCS control unit 124 in the mobile station 120 shown in FIG. 8 and the configuration example of the uplink frame 901 shown in FIG. Based on the CQI and CFI notified from the mobile station 120, the base station 100 encodes and modulates data with one or a plurality of MCSs according to the propagation path fluctuation estimated value. Further, one or a plurality of MLI including one or a plurality of selected MCS information is multiplexed as shown in FIG. The downlink frame 901 illustrated in FIG. 9 stores MCS1 in MLI1 and stores MCS2 in MLI2. The MLI 2 may store information for specifying the MCS 2 based on the relationship (for example, level difference) with the MCS 1 stored in the MLI 1 instead of the information for specifying the MCS 2 itself.

  In mobile station 120, CQI determination section 801 and MLI determination section 802 determine COI and MLI, respectively. The MCS switching control unit 803 controls MCS switching based on the MCS switching information determined by the COI determining unit 801. The MCS selection unit 804 stores the subsequent MCS information notified from the MLI determination unit in the MCS storage unit 805, extracts the MCS information from the MCS storage unit 805 according to the MCS switching control signal notified from the MCS switching control unit 803, The MCS control information is notified to the demodulation unit 126 and the decoding unit 127.

  For example, when the COI indicates whether or not switching is performed, the MCS switching control unit 803 outputs an MCS switching control signal to the MCS selecting unit 804 at a predetermined switching position. When the COI indicates a switching position, the MCS switching control unit 803 outputs an MCS switching control signal to the MCS selecting unit 804 at the switching position indicated by COI. First, the MCS selection unit 804 stores the MCS2 specified by the MLI2 in the MCS storage unit 805. The MCS selection unit 804 outputs MCS1, and then outputs MCS2 stored in the MCS storage unit 805 when the MCS switching control signal is input.

In the present embodiment, it is possible to estimate propagation path fluctuations and switch MCS during a frame based on the estimation. For this reason, even when a propagation path variation as shown in FIG. 7 occurs, it is possible to perform transmission using MCS that satisfies the required quality in the entire frame, and it is possible to suppress deterioration in quality due to propagation path variation in the frame. . In addition, when it is estimated that the propagation path may be greatly deteriorated, transmission power can be suppressed by not transmitting symbols from the middle of the frame. Alternatively, the bit error rate can be improved by transmitting the same information as the first half of the frame to the second half of the frame.

  FIG. 10 shows another example of the relationship between the propagation path fluctuation in the mobile station and the data symbol sequence portion of the received downlink frame. In FIG. 10, the propagation path condition is improved as indicated by the SNR 1001 of the actual propagation path. In FIG. 10, even in the conventional method using MCS1 for the data symbol string 1005, the required quality (required SNR 1003 of MCS1) can be satisfied in the entire frame, so that there is no quality degradation. However, in this embodiment, further, by notifying a plurality of MLIs, it becomes possible to switch to a higher MCS level in the middle of a frame when a propagation path fluctuation 1007 as shown in FIG. Can be made. The data symbol sequence 1006 uses MCS1 for the first half and MCS2 for the second half. In any case, the data symbol string 1006 satisfies the required quality, and in the second half, MCS2 having a higher transmission rate than MCS1 is used. It will be realized.

  In this case, the propagation path estimation value (propagation path information) and the propagation path fluctuation estimation value (propagation path fluctuation information) in the transmission unit are obtained by extrapolating a plurality of past propagation path information as shown in FIG. Also good.

  Thus, according to this embodiment, it is possible to switch the MCS used for the data symbol sequence to a desired MCS in the middle of the frame. This makes it possible to flexibly select an MCS according to fluctuations in propagation path conditions, and to modulate and encode a data symbol sequence using the MCS that satisfies the required quality in the entire frame. Is possible. Therefore, it is possible to suppress deterioration in data transmission quality due to propagation path fluctuations in the frame and improve transmission efficiency corresponding to the propagation path situation.

  Although FIG. 9 illustrates the case where two MLIs are included in the control information, the present invention is not limited to two MLIs. It is possible to include three or more MLI as control information. In this case, the MCS selection unit 804 stores a plurality of MCSs in the MCS storage unit 805. In addition, when specifying the switching position, the COI may switch the MCS for each length of the data symbol string specified by the COI by specifying the length of the data symbol string to be switched. For example, the MCS can be switched every length m (m is a positive integer).

(Third embodiment)
In the third embodiment, a case where an MLI is inserted at the MCS switching position will be described. In the second embodiment, since MLI included in a plurality of downlink frames is arranged at the head of the frame, the MCS control unit 124 demodulates all the MLIs in order to normally demodulate the data part in which the subsequent MCS is changed at the time of reception. You need to remember at once. It is also necessary to store all demodulated MCS information. Therefore, in the second embodiment, an MCS storage unit 805 is provided as shown in FIG.

However, since only one MLI is used at a time, the use efficiency of the memory for storing the MLI and MCS information cannot be said to be high. Therefore, the frame configuration is changed as shown in FIG. FIG. 12 is a diagram illustrating an example of the configuration of the downlink frame 1201 of the present embodiment. It is assumed that the MLI is arranged for each preamble portion and a data portion having a certain length thereafter. At the time of reception, the first MLI1 is used to demodulate the data part (MCS1), and the M allocated thereafter
The operation of receiving LI2 and demodulating the data part (MCS2) according to the contents is repeated. As a result, only one memory is required to store the MLI, and usage efficiency is improved.

  As described above, in the present embodiment, the memory utilization efficiency can be improved by arranging the MLI at the position of the data symbol sequence for switching the MCS in the frame.

(Fourth embodiment)
The fourth embodiment shows details of the propagation path fluctuation information symbol CFI. In the first embodiment, a fluctuation amount per time of the propagation path in all bands is required. In the case of multicarrier communication, in most cases, known data is inserted for each symbol between transmission and reception called a pilot carrier. Therefore, by observing the received power of the pilot carrier, it is possible to estimate the amount of power fluctuation per hour. A case where a pilot carrier is not used is also conceivable. In this case, it is possible to estimate the amount of power fluctuation per time by handling a carrier with a constant amplitude in each symbol in the same manner as a pilot carrier.

  FIG. 13 is a reception block diagram of the mobile device 1300 clearly illustrating this function. In FIG. 13, 1301 is a carrier selection unit, and 1302 is a power fluctuation observation unit. Components having the same reference numerals as those in FIG. 1 have the same functions as those in FIG. The carrier selection unit 1301 is a block having a function of selecting a pilot carrier when a pilot carrier is used in the system, and selecting a carrier having a constant amplitude otherwise. The power fluctuation observation unit 1302 receives the carrier selected by the carrier selection unit 1301 and measures the received power of the carrier.

  In the power fluctuation observation unit 1302, the time variation of the received power observed is passed to the preamble generation unit 128, and the preamble generation unit 128 is incorporated into the control information as CFI, and thus as the CFI incorporated into the control information. The base station 100 is notified.

  In addition, in the case where the MCS selection method of the first embodiment is a rule that lowers the MCS level, it is sufficient to notify the CFI whether or not the propagation path fluctuation is severe. In this case, a block for detecting the moving speed of the mobile device may be provided, and if the moving speed is high, it may be requested to change the MCS. It is also possible to determine the number of MCS changes according to the moving speed. The base station may use the moving speed of the mobile station instead of the propagation path fluctuation information as determination information for estimating the propagation path fluctuation.

  In the second embodiment, the amount of fluctuation per time of the propagation path for each subcarrier is required as CFI. For this purpose, it is necessary to arrange pilot carriers over all frequencies. Therefore, the pilot position is changed in symbol units (a so-called scattered pilot scheme), and propagation path fluctuations in each subcarrier are estimated in symbol units in which pilot carriers appear.

  As described above, according to the present embodiment, it is possible to estimate the propagation path variation using the received power that can be measured by the pilot carrier or the carrier corresponding to the pilot carrier.

(Fifth embodiment)
In this embodiment, in the case where the MCS selection method of the first embodiment is a rule that lowers the MCS level, the base station does not notify the base station of the CFI, and the base station moves the mobile station from the uplink received signal. An embodiment in which the speed is estimated and MCS switching control is performed will be described.

  FIG. 14 is a diagram illustrating a configuration example of the OFDM system according to the present embodiment. FIG. 15 is a diagram illustrating a configuration example of the MCS control unit 1402 in the base station 1400 according to the present embodiment. The base station 1400 shown in FIG. 14 includes a Doppler frequency estimation unit 1401 that estimates movement speed information (for example, Doppler frequency) indicating the movement speed of the mobile station 1410 from the CE of the uplink frame and / or the data symbol sequence. When the speed is high, control is performed to change the MCS. Further, the MCS control unit 1402 adopts the configuration shown in FIG. Also, the mobile station 1410 does not include the propagation path fluctuation estimation unit 129. Also, the preamble generation unit 1411 generates control information without using the propagation path fluctuation information CFI. FIG. 16 shows a configuration example of the downlink frame according to the present embodiment. The preamble generation unit 1411 generates CE and CQI as control information. In FIG. 14, components having the same reference numerals as those in FIG. 1 have the same functions as those in FIG.

  An MCS switching control unit 1501 illustrated in FIG. 15 inputs a Doppler frequency and controls switching of MCS based on the Doppler frequency. The MCS switching control unit 1501 is the same as the MCS switching control unit 1501 shown in FIG. 2 except that the Doppler frequency is used instead of the CFI. Further, the components other than the CFI determination unit 201 and the MCS switching control unit 203 shown in FIG.

  By providing the Doppler frequency estimation unit 1401, the MCS switching control unit 1501 can determine the number of MCS changes according to the moving speed of the mobile station 1410.

  In this embodiment, as shown in FIGS. 14 and 15, the mobile station 1410 does not have to be provided with a propagation path fluctuation estimation block (the propagation path fluctuation estimation unit 129 in FIG. 1). Can be reduced. Also, as shown in FIG. 16, since it is not necessary to notify the CFI in the upstream frame 1601, the upstream frame efficiency can be improved.

  Thus, in the present embodiment, the base station can estimate the fluctuation of the propagation path using the moving speed information of the mobile station. As a result, it is possible to reduce the load for estimating the propagation path fluctuation on the mobile station side and to control the number of MCS switchings on the base station side according to the moving speed of the mobile station.

  In the present embodiment, the MCS control unit 1402 has been described using the configuration example of FIG. 15, but the MCS control unit 1402 has the same configuration example as FIG. 2, and determination information serving as a reference for controlling switching is provided. Any of the CFI and the moving speed information may have a function of controlling the MCS switching. In this case, the CFI determination unit 201 determines which of the CFI and the moving speed information is input as the determination information, and notifies the MCS switching control unit 203 of the determination. The MCS switching control unit 203 performs switching control of MCS by selecting switching control based on CFI or switching control based on moving speed information based on the notified type of determination information.

  Further, the MCS control unit 1402 can also control MCS switching using at least one or both of CFI and moving speed information. The MCS switching control unit 203 can also determine whether to switch the MCS based on both the CFI and the moving speed information. For example, it is possible to set a CFI threshold value and a moving speed threshold value, and to switch the MCS when at least one of the CFI and the moving speed exceeds the threshold value.

  Further, by comparing the Doppler frequency used as an example of the moving speed information with a predetermined threshold value, it is possible to determine the magnitude of the propagation path fluctuation. It is also possible to compare the product of the Doppler frequency and the adaptive modulation period with a predetermined threshold value to determine the magnitude of propagation path fluctuation. The adaptive modulation period is a period for selecting a modulation parameter.

(Sixth embodiment)
In this embodiment, another aspect of the MCS designation method in the MLI, for example, a case where the second and subsequent MCSs are designated by a difference is shown.

  As shown in FIG. 9 or FIG. 12, in the second embodiment and the third embodiment, the number of MLI included in the downstream frame increases according to the number of times of switching of MCS, so the number of times of switching becomes too large. And frame efficiency is reduced. For example, in a system in which data is placed on 100 subcarriers and eight types of MCS are selected for each subcarrier, one MLI requires at least 300 bits.

  In the present embodiment, the second and subsequent MLI are changed so as to notify only the difference information for the MCS in the immediately preceding data symbol sequence. By this change, it is possible to suppress a decrease in downlink frame efficiency due to an increase in the number of MLI. For example, when there are three types of difference information, “increase 1 level”, “do not change level”, and “decrease 1 level”, a system that selects from 8 types of MCS for each subcarrier is necessary for one MLI. The number of bits can be reduced to 200 bits.

  When a plurality of MCSs are desired to be specified, it is possible to designate a relative level difference from MCS1 in MLI2, and the level designated in MLI2 may be changed every time the MCS is switched. For example, if (-1) is specified for MLI2, every time the MCS is switched, the MCS that is one level lower than the MCS1 is used, and the lowest level MCS is used when the MCS reaches the lowest level. You may make it do. It is also possible to specify that MCS1 is not changed by specifying 0 (zero) in MLI2.

  Thus, according to the present embodiment, the number of bits used for MLI can be reduced. Thereby, it becomes possible to suppress the amount of information of MLI included in the frame.

(Seventh embodiment)
In the seventh embodiment, a mode in which an MCS is requested from a terminal to a base station is shown. In the base station, an MCS control unit 1700 shown in FIG. 17 is used instead of the MCS control unit 103 shown in FIG. FIG. 17 shows an internal configuration of the MCS control unit 1700 in the base station in the present embodiment. In the mobile station, the functions of the propagation path fluctuation estimation unit 129 and the preamble generation unit 128 shown in FIG. 1 are different from those of the first embodiment. The configuration of the OFDM system of the present embodiment uses the same configuration example as in FIG. This will be described below.

  In the mobile station, propagation path estimation and propagation path fluctuation estimation are performed, whether to switch between MCS and MCS, and at least one of the positions to switch MCS and MCS after the change is determined. As shown in FIG. 18, MLI and COI The base station is notified of at least one of the changed MLI. Whether or not to switch the MCS and MCS to be used first by using the propagation path information for estimating the propagation path condition and the propagation path fluctuation information for estimating the propagation path fluctuation in the propagation path fluctuation estimation unit of the mobile station. , At least one of the positions to switch the MCS is determined. The preamble generation unit uses the information determined by the propagation path fluctuation estimation unit to create control information including COI and MLI. In the example of FIG. 18, one MLI is shown. However, when the MCS after the change is determined and notified to the base station as MLI2, MLI2 is added to the uplink frame 1801.

The base station encodes and modulates data with the MCS requested from the mobile station and transmits it to the mobile station. The specific operation of the MCS control unit 1700 is to input the COI from the preamble separation unit 108 to the COI determination unit 1701 and input the MLI to the MLI determination unit. The COI determination unit 1701 determines (extracts / specifies) the COI, and outputs the COI to the MCS switching control unit 1703. The MCS switching control unit 1703 performs MCS switching control based on the determined COI, and therefore the timing for switching the MCS. The MCS switching control signal is output to the MCS selection unit 1704. The MLI determination unit 1702 determines (extracts / specifies) the MLI and outputs it to the MCS selection unit 1704. The MCS selection unit 1704 selects the MCS based on the determined MLI, and selects and outputs the MCS to be switched at the timing when the MCS switching control signal is input.

  MLI or COI may be multiplexed as downlink control information notified from the base station to the mobile station. When demodulating and decoding based on the control information stored in the terminal, the control information is not multiplexed. May be. When downlink control information is multiplexed, the reliability of MLI or COI is improved. In addition, the MCS or the MCS switching position that is different from the request from the mobile station can be selected in the base station. In this case, CE, COI, and MLI are included as downlink control information. When downlink control information is not multiplexed, downlink communication efficiency is improved. In this case, CE is included as downlink control information, and COI and MLI are not included.

  Whether or not the mobile station switches between MCS and MCS, and if at least one of the changed MCS and MCS switching positions is determined, undecided elements are determined in the base station or in advance in the system The agreed value will be used.

  Thus, according to this embodiment, it is possible to notify MCS switching or switching MCS from the mobile station. Thereby, the mobile station can request a desired MCS from the base station.

  In the present embodiment, the case where the MCS control unit 1700 shown in FIG. 17 is used in place of the MCS control unit 103 shown in FIG. 2 has been described. However, the MCS control unit may accept input of CFI or COI and CQI or MLI. For example, as a function of MCS switching control (switching control unit), there is a switching determination unit that determines by inputting CFI or COI, and an MCS switching control unit that controls MCS switching by inputting a determination result. As the function (selection unit), an MCS control unit having a configuration including a selection determination unit that inputs and determines CQI or MLI and an MCS selection unit that inputs a determination result and selects MCS may be used.

  In each of the above embodiments, when an adaptive control modulation apparatus is used in a wireless communication system that uses a multicarrier communication scheme, the MCS selection unit performs a plurality of subcarriers (for each block of a plurality of subcarriers or grouped). It is also possible to select a modulation parameter for each subcarrier). This makes it possible to determine MCS switching using propagation path information, propagation path fluctuation information, or movement speed information for each of a plurality of subcarriers. For this reason, it becomes possible to suppress the amount of control information transmitted / received between the base station and the mobile station or the amount of processing related to the process of switching the modulation parameter.

DESCRIPTION OF SYMBOLS 100 Base station 101 Encoding part 102 Modulation part 103, 1402 MCS control part 104 IFFT (Inverse Fast Fourier Transform) part 105 Preamble multiplexing part 106 Radio transmission part 107 Radio reception part 108 Preamble separation part 109 Demodulation part 110 Decoding part 111 Preamble Generation unit 120 Mobile station 121 Radio reception unit 122 Preamble separation unit 123 Channel estimation unit 124 MCS control unit 125 FFT (Fast Fourier Transform) unit 126 Demodulation unit 127 Decoding unit 128, 1411 Preamble generation unit 129 Channel variation estimation unit 130 Preamble multiplexing unit 131 Modulating unit 132 Encoding unit 133 Wireless transmission unit 201 CFI determining unit 202 CQI determining unit 203, 1501 MCS switching control unit 204 MCS selecting unit 205 MCS table 301, 801 OI determination unit 302,802 MLI determination unit 303 (or 803) MCS switching control section 304,804 MCS selecting section 805 MCS storage unit 1301 carrier selecting section 1302 power fluctuation observing section 1401 Doppler frequency estimator

Claims (26)

An adaptive modulation control apparatus that selects any one modulation parameter from a plurality of modulation parameters determined from at least one of a modulation scheme and a coding rate,
A switching control unit for determining to switch the modulation parameter in the middle of one transmission unit and outputting a switching control signal for switching the modulation parameter;
A selection unit that selects one modulation parameter, and further selects the modulation parameter when the switching control signal indicates switching the modulation parameter in the middle of one transmission unit, and
An adaptive modulation control apparatus, wherein the selection unit selects a modulation parameter having a transmission rate lower than that of the one modulation parameter according to a predetermined policy when selecting the modulation parameter again.   The adaptive modulation control apparatus according to claim 1, wherein the switching control unit outputs a switching control signal for switching a modulation parameter at a predetermined switching position.   The switching control unit inputs at least one of propagation path fluctuation information indicating the estimation result of the propagation path fluctuation or movement speed information indicating the movement speed of the destination communication device as switching determination information, and based on the switching determination information, 3. The adaptive modulation control apparatus according to claim 1, wherein it is determined that the modulation parameter is switched in the middle of one transmission unit.   The adaptive modulation control apparatus according to claim 1, wherein the selection unit inputs propagation path information and selects a modulation parameter according to the propagation path information.   The adaptive modulation control apparatus according to claim 1, wherein the selection unit receives modulation parameter information and selects a modulation parameter according to the modulation parameter information. The adaptive modulation control device is used in a wireless communication device that performs wireless communication in a multicarrier communication system,
3. The adaptive modulation control apparatus according to claim 1, wherein the switching control unit determines to switch the modulation parameter in the middle of one transmission unit in units of one or a plurality of subcarriers.   The selection unit, as a modulation parameter to be selected again, selects any modulation parameter having a transmission rate lower than that of the one modulation parameter and the same transmission rate as the modulation parameter. The adaptive modulation control apparatus according to claim 6.   The adaptive modulation control apparatus according to claim 1, further comprising: a generation unit that receives the switching control signal and generates a symbol including switching information indicated by the switching control signal.   9. The adaptive modulation control apparatus according to claim 8, wherein the switching information includes information indicating whether to switch modulation parameters.   The adaptive modulation control apparatus according to claim 8 or 9, wherein the switching information includes information of one or more positions at which modulation parameters are switched.   The adaptive modulation control apparatus according to any one of claims 8 to 10, wherein the switching information includes information specifying one or more modulation parameters to be switched. The switching control unit holds a position for switching a modulation parameter, detects that the one transmission unit reaches the position, and outputs a switching control signal for notifying the position;
The adaptive modulation control apparatus according to claim 9, wherein the selection unit selects a modulation parameter again according to a predetermined selection procedure based on the switching control signal.   The switching control unit holds a position for switching a modulation parameter, detects that the one transmission unit reaches the position, and outputs a switching control signal notifying the position. The adaptive modulation control apparatus described.   The adaptive modulation control apparatus according to claim 11, wherein the generation unit uses information specifying one or more modulation parameters to be switched as difference information from a modulation parameter immediately before switching.   15. The adaptive modulation control apparatus according to claim 14, wherein the generation unit specifies a relative level degree of a modulation parameter by comparing the difference information with a modulation parameter immediately before switching.   The adaptive modulation control apparatus according to claim 1, wherein the selection unit selects a predetermined modulation parameter as the modulation parameter to be selected again.   The adaptive modulation control apparatus according to claim 16, wherein the selection unit selects a modulation parameter having a lowest rate as a predetermined modulation parameter.   The adaptive modulation control apparatus according to claim 1, wherein the switching control unit uses a Doppler frequency as an index as the switching determination information.   The adaptive modulation control apparatus according to claim 18, wherein the switching control unit switches a modulation parameter when the Doppler frequency is larger than a preset threshold value. Reception that receives at least one of propagation path information indicating a propagation path state estimation result, propagation path fluctuation information indicating a propagation path fluctuation estimation result, and modulation parameter information indicating a modulation parameter from the transmission-side apparatus. And
An adaptive modulation control device according to claim 1 or 2,
A wireless communication device comprising: a transmission unit that transmits data modulated using a modulation parameter output from the adaptive modulation control device. A propagation path estimator for estimating the propagation path state;
A channel fluctuation estimation unit for estimating the channel fluctuation;
An adaptive modulation control device according to claim 1 or 2,
A wireless communication device comprising: a transmission unit that transmits a modulation parameter output from the adaptive modulation control device to a reception-side device. An adaptive modulation control method for selecting any one modulation parameter from a plurality of modulation parameters determined from at least one of a modulation scheme and a coding rate,
A switching step of determining to switch the modulation parameter in the middle of one transmission unit and outputting a switching control signal for switching the modulation parameter;
Selecting one modulation parameter, and further selecting the modulation parameter again when the switching control signal indicates switching the modulation parameter in the middle of one transmission unit, and
In the selecting step, when selecting a modulation parameter again, a modulation parameter having a lower transmission rate than that of the one modulation parameter is selected according to a predetermined policy.   The adaptive modulation control method according to claim 22, wherein in the switching step, a switching control signal for switching the modulation parameter at a predetermined switching position is output.   In the switching step, at least one of propagation path fluctuation information indicating the estimation result of propagation path fluctuation or movement speed information indicating the movement speed of the destination communication device is input as switching determination information. The adaptive modulation control method according to claim 22 or 23, wherein switching of the modulation parameter is determined in the middle of a transmission unit.   The adaptive modulation control method according to any one of claims 22 to 24, wherein the selection step inputs propagation path information and selects a modulation parameter according to the propagation path information. The adaptive modulation control method is used for a wireless communication apparatus that performs wireless communication in a multicarrier communication system,
26. The switching step according to any one of claims 22 to 25, wherein the switching step is a step of determining to switch a modulation parameter in the middle of one transmission unit in units of one or a plurality of subcarriers. Adaptive modulation control method.

Images