JP2012209613A - Communication device and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device and a communication method that can appropriately set the maximum retransmission number according to a situation.SOLUTION: A maximum number setting unit 35 updates a currently-set maximum retransmission number based on difference between an error rate of HARQ sub bursts transmitted to the device of a communication partner by the currently-set maximum retransmission number and an error rate of HARQ sub bursts transmitted to the device of the communication partner by a retransmission number larger than or smaller than the currently-set maximum retransmission number. The error rate of HARQ sub bursts by each retransmission number indicates a ratio of HARQ sub bursts about which a retransmission request has been received from the device of the communication partner to HARQ sub bursts transmitted by each retransmission number. A retransmission control unit 33 repeats retransmission within the set maximum retransmission number in response to a retransmission request from the device of the communication partner.

Description

  The present invention relates to a communication apparatus and a communication method, and more particularly to a communication apparatus having a HARQ (Hybrid Automatic Repeat Request: HARQ) retransmission function and a communication method of such a communication apparatus.

  In a radio base station system using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, a retransmission procedure called HARQ retransmission is performed when downlink data is transferred from a radio base station to a radio terminal (for example, Patent Literature 1 (see Japanese translations of PCT publication No. 2008-526089) and Patent Document 2 (Japanese translations of PCT publication No. 2009-502088).

  In HARQ retransmission, when an error occurs in downlink data on the radio, the radio base station retransmits the data. Data that is a unit of HARQ retransmission is called a HARQ sub-burst. This HARQ retransmission process is performed in the physical layer.

Special table 2008-526089 Special table 2009-502088

  By the way, in HARQ, the maximum number of retransmissions is normally set to a fixed number. For example, in a communication system adopting a WiMAX (Worldwide Interoperability for Microwave Access) system, the maximum number of retransmissions is set to four.

  However, if the communication path conditions and the performance of the wireless terminal are poor, correct data may not be obtained even if retransmission is performed up to a predetermined maximum number of retransmissions. In such a case, radio resources are wasted by repeating retransmission up to a predetermined maximum number of retransmissions. Also, correct data may be obtained by continuing retransmission beyond the predetermined maximum number of retransmissions instead of aborting the retransmission at a predetermined maximum number of retransmissions. In such a case, if retransmission is terminated at a predetermined maximum number of retransmissions, retransmission processing in the upper layer (MAC (Media Access Control) layer) is required, and it takes a long time to obtain correct data. .

  Therefore, an object of the present invention is to provide a communication device and a communication method that can appropriately set the maximum number of retransmissions according to the situation.

  In order to solve the above-described problem, the present invention provides a communication device in which retransmission is controlled in units of a predetermined amount of data blocks, and the data block transmitted to the communication partner device at the currently set maximum number of retransmissions. Depending on the difference between the error rate and the error rate of the data block transmitted to the communication partner device with the number of retransmissions greater or less than the currently set maximum number of retransmissions, the currently set maximum number of retransmissions The data block error rate at each number of retransmissions represents a ratio of data blocks that have received a retransmission request from a communication partner device among the data blocks transmitted at each number of retransmissions. Furthermore, a retransmission control unit that repeats retransmission within the set maximum number of retransmissions in response to a retransmission request from the communication partner apparatus is provided.

  According to the present invention, the maximum number of retransmissions can be appropriately set according to the situation.

It is a figure showing the structure of the radio | wireless communications system of embodiment of this invention. It is a figure which shows the structure of the wireless base station of embodiment of this invention. It is a figure showing the OFDMA frame transmitted / received by the wireless base station of embodiment of this invention. (A) is a diagram showing a DL subframe. (B) is a diagram showing a DL burst. It is a figure for demonstrating the information transmitted in HARQ resending control. It is a figure for demonstrating the resending procedure of HARQ. It is a figure for demonstrating the example of the sampling area for the setting of the maximum frequency | count of resending. It is a flowchart showing the procedure of the setting operation | movement of the maximum number of resending of 1st Embodiment. (A)-(c) is a figure showing the example of the error rate E (n-1), E (n), and E (n + 1) of a HARQ subburst. (A)-(c) is a figure showing change of the maximum number of retransmissions in the error rate of the HARQ subburst of Drawing 9 (a)-(c). It is a flowchart showing the procedure of the setting operation | movement of the maximum retransmit count of 2nd Embodiment. (A)-(c) is a figure showing the example of the change of the maximum retransmission count n and the variables k and d.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
(overall structure)
FIG. 1 is a diagram showing a configuration of a wireless communication system according to an embodiment of the present invention.

  Referring to FIG. 1, this radio communication system 1 includes a radio base station 2 and n radio terminals 3a to 3n. Hereinafter, when any one of the wireless terminals 3a to 3n is represented, it is described as the wireless terminal 3. The radio base station can communicate simultaneously with a plurality of n radio terminals. The radio base station 2 is connected to the communication control device 4 via a wired network 5. The communication control device 4 transmits downlink user data to the wireless terminals 3 a to 3 n in communication with the wireless base station 2 to the wireless base station 2 through the network 5.

  This radio communication system implements a HARQ retransmission procedure for downlink user data. That is, retransmission of downlink user data is controlled in units of HARQ subbursts, which are a predetermined amount of data blocks.

  When the wireless terminal normally receives the HARQ subburst transmitted from the wireless base station, the wireless terminal feeds back an ACK (ACKnowledgement) to the wireless base station. The radio terminal feeds back a NACK (Negative Acknowledgment) to the radio base station when the HARQ sub-burst transmitted from the radio base station cannot be normally received. When receiving the NACK, the radio base station retransmits the HARQ subburst corresponding to the NACK.

(Constitution)
FIG. 2 is a diagram showing a configuration of a radio base station according to the embodiment of the present invention.

  The radio base station 2 is an orthogonal frequency division multiple access (OFDMA) type radio base station, and includes a first antenna 10, a second antenna 11, a transmission unit 13, a reception unit 12, and a control unit. 31.

  The transmission unit 13 includes a subcarrier arrangement unit 23, a multi-antenna transmission signal processing unit 24, an IFFT unit (Inverse First Fourier Transform) 22, a CP (Cyclic Prefix) addition unit 21, an RF (Radio Frequency) unit 20, Is provided.

  The subcarrier arrangement unit 23 arranges subcarriers according to the data arrangement determined by the control unit 31 based on, for example, PUSC (Partial Usage of Subchannels).

  The multi-antenna transmission signal processing unit 24 space-time codes one data stream or spatially multiplexes a plurality of data streams.

  The IFFT unit 22 converts a plurality of subcarrier signals (frequency domain signals) output from the multi-antenna transmission signal processing unit 24 into time domain signals (OFDMA (Orthogonal Frequency Division Multiple Access) symbols) by IFFT.

  The CP adding unit 21 adds the same signal as the tail part of the OFDMA symbol to the beginning of the OFDMA symbol as a CP.

  The RF unit 20 includes an up-converter that up-converts to a radio frequency band, a power amplification circuit that amplifies the up-converted signal, and passes only the signal component in the desired band of the amplified signal to pass through the first antenna 10 and the first antenna 10. A band-pass filter that outputs to the second antenna 11.

  The receiving unit 12 includes an RF unit 15, a CP removing unit 16, an FFT unit 17, and a subcarrier arrangement unit 18.

  The RF unit 15 includes a band-pass filter that allows only a signal component in a desired band among signals output from the first antenna 10 and the second antenna 11 to pass, a low-noise amplifier circuit that amplifies the RF signal, and the RF signal that is down Includes downconverter to convert.

The CP removal unit 16 removes the CP from the signal output from the RF unit 15.
The FFT unit 17 converts the time domain signal output from the CP removal unit 16 into a frequency domain signal by FFT and demodulates the signal into a plurality of subcarriers.

  The subcarrier arrangement unit 18 extracts each subcarrier output from the FFT unit 17 based on PUSC, for example.

  The control unit 31 includes a user data management unit 34, a control information management unit 36, a retransmission control unit 33, and a maximum retransmission number setting unit 35.

  The control information management unit 36 creates map information including HARQ_DL_MAP_IE and HARQ_ACK_Region_Allocation_IE.

  The user data management unit 34 generates user data to be transmitted to the wireless terminal and holds user data received from the wireless terminal. User data to be transmitted to the wireless terminal is divided into HARQ sub-bursts that are retransmission units.

  The retransmission control unit 33 repeats retransmission within a set maximum number of retransmissions in response to a retransmission request from the wireless terminal. More specifically, the retransmission control unit 33 controls retransmission of the HARQ subburst using the HARQ scheme. When receiving the NACK from the wireless terminal, the retransmission control unit 33 retransmits the HARQ subburst corresponding to the NACK.

  The maximum retransmission number setting unit 35 transmits the error rate of the HARQ sub-burst transmitted to the wireless terminal with the currently set maximum number of retransmissions and the wireless terminal with a number of retransmissions that is larger or smaller than the currently set maximum number of retransmissions. The currently set maximum number of retransmissions is updated according to the difference from the error rate of the HARQ sub-burst transmitted to. Here, the error rate of the HARQ sub-burst at each number of retransmissions is the HARQ sub-burst transmitted at each number of retransmissions, and the HARQ sub-burst that has received a retransmission request from the wireless terminal (that is, the HARQ sub-burst in which a communication error has occurred). ) Ratio.

(flame)
FIG. 3 is a diagram showing an OFDMA frame transmitted and received by the radio base station according to the embodiment of the present invention.

  In FIG. 3, the horizontal axis is displayed in symbol units as a time axis, and the vertical axis is displayed in subchannel units as a frequency axis. The OFDMA frame includes a DL (DownLink) subframe and a UL (UpLink) subframe.

  Each of the DL subframe and the UL subframe is represented in two dimensions, a time axis given by an OFDM symbol (unit time) and a frequency axis given by a subchannel.

  There are multiple types of patterns for the number of DL subframe symbols, the number of UL subframe symbols, the number of subchannels of the DL subframe, and the number of subchannels of the UL subframe. As an example, 29 are used as the number of symbols in the DL subframe, 15 are used as the number of symbols in the UL subframe, and 30 are used as the number of subchannels in the DL subframe and the UL subframe.

(DL subframe)
FIG. 4A shows a DL subframe.

  As shown in FIG. 4A, the DL subframe includes a plurality of DL bursts. User data is arranged in each DL burst. The DL burst is composed of a plurality of slots.

FIG. 4B shows a DL burst.
As shown in FIG. 4B, the DL burst includes a plurality of HARQ subbursts. In the example of FIG. 4B, the DL burst is composed of five HARQ subbursts, HARQ subbursts # 1 to # 5. Each HARQ sub-burst is a retransmission unit in HARQ retransmission control. For example, if there is an error (error) in any data included in the HARQ subburst # 2 among the data included in the DL burst, the HARQ subburst # 2 is retransmitted.

(HARQ retransmission control)
FIG. 5 is a diagram for explaining information transmitted in HARQ retransmission control.

  HARQ_DL_MAP_IE 41 in the MAP information included in the DL subframe defines the arrangement of the HARQ subburst 42. Also, HARQ_ACK_Region_Allocation_IE43 in the MAP information included in the DL subframe defines the arrangement of ACKCH44.

  When the wireless terminal receives the HARQ subburst, the wireless terminal returns an ACK or NACK through the ACKCH 44 at a position defined by HARQ_ACK_Region_Allocation_IE43.

(Resending procedure)
FIG. 6 is a diagram for explaining a HARQ retransmission procedure.

A HARQ sub-burst as shown in FIG. 6 is transmitted from the radio base station to the radio terminal.
The wireless terminal determines whether the HARQ subburst is correct or not based on a CRC (Cyclic Redundancy Check) of the received HARQ subburst. In the example of FIG. 6, since it is determined to be an error, the wireless terminal stores each bit of the received HARQ subburst with reliability. Here, the reliability is an amount corresponding to a difference between a threshold value to be compared with an analog value input in AD conversion and a digital value obtained by converting the input analog value. Returns NACK to the radio base station when the HARQ subburst is in error.

  The radio base station that has received the NACK retransmits the HARQ subburst. The wireless terminal determines whether the HARQ subburst data is correct based on the received CRC of the HARQ subburst. In the example of FIG. 6, since it is determined again as an error, the wireless terminal stores each bit of the received HARQ subburst with reliability. The wireless terminal synthesizes a plurality of stored data with a maximum ratio based on the reliability. The radio terminal determines whether the HARQ sub-burst combined with the maximum ratio is correct. In the example of FIG. 6, since it is determined to be correct, the wireless terminal transmits ACK to the wireless base station.

The radio base station that has received the ACK ends the HARQ sub-burst retransmission.
(Sampling interval for setting the maximum number of retransmissions)
FIG. 7 is a diagram for explaining an example of a sampling interval for setting the maximum number of retransmissions.

  As shown in FIG. 7, after starting communication with an arbitrary user A, in the first sampling period SP1, the maximum number of retransmissions n is set to an initial value, and retransmission is performed within the range of the maximum number of retransmissions. Further, in a specific section SSP1 within the sampling section SP1, the maximum number of retransmissions is provisionally set to be increased by one step, and retransmission is performed within the range of the temporarily set maximum number of retransmissions.

  In the sampling period SP1, the maximum number of retransmissions n in the next sampling period SP2 is set according to the change in the error rate of the HARQ subburst transmitted to the wireless terminal at the number of retransmissions (n−1), n, (n + 1). .

  For example, if there are 100 HARQ subbursts retransmitted at the number of retransmissions n and 70 HARQ subbursts have been correctly received, the error rate at the number of retransmissions n is 0.3.

  In the sampling period SP2, in the communication in the sampling period SP1, the maximum number of retransmissions set according to the change in the error rate of the HARQ subburst transmitted to the wireless terminal at the number of retransmissions (n−1), n, (n + 1). Retransmission is performed within the range. Similarly to the sampling interval SP1, in the specific interval SSP2 in the sampling interval SP2, the maximum number of retransmissions is provisionally set to be increased by one step, and retransmission is performed within the range of the maximum number of retransmissions set temporarily. Done. In the sampling period SP2, the maximum number of retransmissions n in the next sampling period SP3 is set according to the change in the error rate of the HARQ subburst transmitted to the wireless terminal at the number of retransmissions (n-1), n, (n + 1). .

The same processing as described above is performed for subsequent sampling intervals.
(Maximum retransmission count setting operation)
FIG. 8 is a flowchart showing the procedure for setting the maximum number of retransmissions according to the first embodiment.

  Referring to FIG. 8, when the radio base station starts communication with an arbitrary user A, maximum retransmission number setting unit 35 sets maximum retransmission number n to initial value n0 (step S101).

  Next, the maximum retransmission number setting unit 35 sets a sampling interval SPi (i is sequentially increased by a natural number of 1 or more) in communication with the user A, and further increases the maximum retransmission number in the sampling interval SPi by one step. A section SSPi is set (step S102).

  If the maximum number of retransmissions n is not 0 (NO in step S103), the maximum number of retransmissions setting unit 35 determines the HARQ sub-burst error rate at the number of retransmissions of (n-1) times, n times, and (n + 1) times. E (n-1), E (n), and E (n + 1) are calculated (step S104).

  On the other hand, when the maximum number of retransmissions n is 0 (YES in step S103), the maximum number of retransmissions setting unit 35 sets the HARQ subburst error rate E (n) with n and (n + 1) retransmissions, E (n + 1) is calculated (step S105).

  When the error rate E (n-1) of the HARQ subburst at the (n-1) number of retransmissions is not greater than the threshold TH1 than the error rate E (n) of the HARQ subburst at the n number of retransmissions (NO in step S106), the maximum retransmission number setting unit 35 decreases the maximum retransmission number n by 1 (step S107).

  When the error rate E (n-1) of the HARQ sub-burst at the (n-1) times of retransmissions is larger than the error rate E (n) of the HARQ sub-burst at the number of retransmissions of n times by the threshold TH1 (step YES in S106), or when the maximum number of retransmissions n is 0, the error rate E (n) of the HARQ subburst at the number of retransmissions n times is the error rate E (HARQ subburst at the number of retransmissions (n + 1) times ( If the threshold TH2 is greater than n + 1) (YES in step S108), the maximum retransmission number setting unit 35 increases the maximum retransmission number n by 1 (step S109).

  If the error rate E (n) of the HARQ subburst at the number of retransmissions n times is not greater than the threshold TH2 than the error rate E (n + 1) of the HARQ subburst at the number of retransmissions (n + 1) (step S108) NO), the maximum number of retransmissions setting unit 35 does not change the maximum number of retransmissions n (step S110).

(Operation example)
FIGS. 9A to 9C are diagrams illustrating examples of HARQ sub-burst error rates E (n−1), E (n), and E (n + 1).

  FIGS. 10A to 10C are diagrams showing changes in the maximum number of retransmissions at the error rate of the HARQ subburst in FIGS. 9A to 9C.

  However, the initial value of the maximum number of retransmissions n, that is, the maximum number of retransmissions n in the first sampling period SP1 (excluding SSP1) is 4. The thresholds TH1 and TH2 are 7%.

  As shown in FIG. 9A, when the HARQ subburst error rate E (n-1) is 30%, E (n) = 25%, and E (n + 1) is 20%, E (n-1) -E (n) is 5%. Since the value of E (n−1) −E (n) is less than the threshold value TH1 (= 7%), NO is determined in step S106, and the maximum number of retransmissions n is decreased by 1 to 3. In the next sampling period SP2 (excluding SSP2), retransmission control is performed with the maximum number of retransmissions n being 3.

  As shown in FIG. 9B, when the HARQ subburst error rate E (n-1) is 30%, E (n) = 20%, and E (n + 1) is 10%, E (n-1) -E (n) is 10%. Since the value of E (n−1) −E (n) is equal to or greater than the threshold value TH1 (= 7%), “YES” is determined in the step S106. E (n) -E (n + 1) is 10%. Since the value of E (n) −E (n + 1) is equal to or greater than the threshold value TH2 (= 7%), “YES” is determined in the step S108. As a result, the maximum number of retransmissions n increases by 1 to 4. In the next sampling period SP2 (excluding SSP2), retransmission control is performed with the maximum number of retransmissions n being 5.

  As shown in FIG. 9C, when the HARQ subburst error rate E (n-1) is 30%, E (n) = 20%, and E (n + 1) is 15%, E (n-1) -E (n) is 10%. Since the value of E (n−1) −E (n) is equal to or greater than the threshold value TH1 (= 7%), “YES” is determined in the step S106. E (n) -E (n + 1) is 5%. Since the value of E (n) −E (n + 1) is less than the threshold value TH2 (= 7%), NO is determined in step S108. As a result, the maximum number of retransmissions n does not change and becomes 4. In the next sampling period SP2 (excluding SSP2), retransmission control is performed with the maximum number of retransmissions n being four.

  As described above, according to the present embodiment, the maximum number of retransmissions can be appropriately set according to the change in the error rate of the HARQ subburst, so that radio resources can be used effectively, It can be avoided that the time until data without error is obtained is prolonged.

[Second Embodiment]
FIG. 11 is a flowchart showing the procedure for setting the maximum number of retransmissions according to the second embodiment.

  Referring to FIG. 11, when the radio base station starts communication with an arbitrary user A, maximum retransmission number setting unit 35 sets maximum retransmission number n to initial value n0 (step S201).

  Next, the maximum retransmission number setting unit 35 sets a sampling interval SPi (i is sequentially increased by a natural number of 1 or more) in communication with the user A, and further increases the maximum retransmission number in the sampling interval SPi by one step. The section SSPi is set (step S202).

  When the maximum number of retransmissions n is not 0 (NO in step S203), the maximum number of retransmissions setting unit 35 determines the HARQ sub-burst error rate at the number of retransmissions of (n-1) times, n times, and (n + 1) times. E (n-1), E (n), and E (n + 1) are calculated (step S204).

  On the other hand, when the maximum number of retransmissions n is 0 (YES in step S203), the maximum number of retransmissions setting unit 35 determines the error rate E (n) of the HARQ subburst with n and (n + 1) retransmissions. E (n + 1) is calculated (step S205).

  When the error rate E (n-1) of the HARQ subburst at the (n-1) number of retransmissions is not greater than the threshold TH1 than the error rate E (n) of the HARQ subburst at the n number of retransmissions (NO in step S206), the maximum number of retransmissions setting unit 35 reduces the maximum number of retransmissions by the processing of the next steps S207 to S213.

  When the current sampling interval is the first sampling interval SP1 (YES in step S207), the maximum retransmission number setting unit 35 sets k to 0 (step S206).

  The maximum retransmission number setting unit 35 is a case where the current sampling interval is not the first sampling interval SP1 (NO in step S207), and if the previous change in the number of retransmissions has also decreased (YES in step S209). , K is increased by 1 (step S210).

  If the current sampling interval is not the first sampling interval SP1 (NO in step S207), and if the previous change in the number of retransmissions is not decreasing (NO in step S209), the maximum retransmission number setting unit 35 is k. Is decreased by 1 (step S211).

Next, the maximum retransmission number setting unit 35 sets the change width d to 2 ^k (step S212), and decreases the maximum retransmission number n by d (step S213).

  When the error rate E (n-1) of the HARQ sub-burst at the (n-1) times of retransmissions is larger than the error rate E (n) of the HARQ sub-burst at the number of retransmissions of n times by the threshold TH1 (step YES in S206), or when the maximum number of retransmissions n is 0, the error rate E (n) of the HARQ subburst at the number of retransmissions n times is the error rate E of the HARQ subburst at the number of retransmissions (n + 1) times When the threshold TH2 is greater than (n + 1) (YES in step S214), the maximum number of retransmissions setting unit 35 decreases the maximum number of retransmissions by the processing of the next steps S215 to S222.

  When the current sampling interval is the first sampling interval SP1 (YES in step S215), the maximum number of retransmissions setting unit 35 sets k to 0 (step S216).

  The maximum retransmission number setting unit 35 is a case where the current sampling interval is not the first sampling interval SP1 (NO in step S215), and if the previous change in the number of retransmissions has also increased (YES in step S217). , K is increased by 1 (step S218).

  The maximum number of retransmissions setting unit 35 is a case where the current sampling interval is not the first sampling interval SP1 (NO in step S15), and if the previous change in the number of retransmissions has not increased (NO in step S217). , K is decreased by 1 (step S219).

Next, the maximum retransmission number setting unit 35 sets the change width d to 2 ^k (step S220), and increases the maximum retransmission number n by d (step S221).

  When the error rate E (n) of the HARQ subburst at the number of retransmissions n times is not greater than the threshold TH2 than the error rate E (n + 1) of the HARQ subburst at the number of retransmissions (n + 1) (step S214) NO), the maximum number of retransmissions setting unit 35 does not change the maximum number of retransmissions n (step S222).

(Operation example)
12A to 12C are diagrams showing examples of changes in the maximum number of retransmissions n and the variables k and d.

  However, the initial value of the maximum number of retransmissions n, that is, the maximum number of retransmissions n in the first sampling period SP1 (excluding SSP1) is 100.

(Operation example 1)
Referring to FIG. 12A, first, assume that NO is obtained in step S206 in the first sampling period SP1. As a result, the maximum number of retransmissions n decreases as follows. In the first sampling period SP1, YES is set in step S207, so that k = 0 and d = 1, and the maximum number of retransmissions n is 99 in step S213. In the next sampling period SP2 (excluding SSP2), retransmission control is performed with the maximum number of retransmissions n being 99.

  Assume that NO in step S206 in the sampling period SP2. As a result, the maximum number of retransmissions n decreases as follows. In the sampling interval SP2, NO is determined in step S207, YES is determined in step S209, and k = 1 and d = 2 are set. In step S213, the maximum number of retransmissions n is 97. In the next sampling period SP3 (excluding SSP3), retransmission control is performed with the maximum number of retransmissions n being 97.

  Assume that NO in step S206 in the sampling period SP3. As a result, the maximum number of retransmissions n decreases as follows. In the sampling period SP3, NO is determined in step S207, YES is determined in step S209, and k = 2 and d = 4 are set. In step S213, the maximum number of retransmissions n is 93. In the next sampling period SP4 (excluding SSP4), retransmission control is performed with the maximum number of retransmissions n being 93.

  Assume that NO in step S206 in the sampling period SP4. As a result, the maximum number of retransmissions n decreases as follows. In the sampling period SP4, NO in step S207, YES in step S209, k = 3, d = 8, and the maximum number of retransmissions n is 85 in step S213. In the next sampling period SP5 (excluding SSP5), retransmission control is performed with the maximum number of retransmissions n being 85.

  In the sampling section SP5, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling period SP5, NO is determined in step S215, NO is determined in step S217, k = 2 and d = 4, and the maximum number n of retransmissions is 89 in step S221. In the next sampling period SP6 (excluding SSP6), retransmission control is performed with the maximum number of retransmissions n being 89.

  Assume that NO in step S206 in the sampling period SP6. As a result, the maximum number of retransmissions n decreases as follows. In the sampling interval SP6, NO is determined in step S207, NO is determined in step S209, and k = 1 and d = 2 are set. In step S213, the maximum number of retransmissions n is 87. In the next sampling period SP7 (excluding SSP7), retransmission control is performed with the maximum number of retransmissions n being 87.

(Operation example 2)
Referring to FIG. 12B, first, assume that NO is obtained in step S206 in the first sampling period SP1. As a result, the maximum number of retransmissions n decreases as follows. In the first sampling period SP1, YES is set in step S207, so that k = 0 and d = 1, and the maximum number of retransmissions n is 99 in step S213. In the next sampling period SP2 (excluding SSP2), retransmission control is performed with the maximum number of retransmissions n being 99.

  Assume that NO in step S206 in the sampling period SP2. As a result, the maximum number of retransmissions n decreases as follows. In the sampling interval SP2, NO is determined in step S207, YES is determined in step S209, and k = 1 and d = 2 are set. In step S213, the maximum number of retransmissions n is 97. In the next sampling period SP3 (excluding SSP3), retransmission control is performed with the maximum number of retransmissions n being 97.

  Assume that NO in step S206 in the sampling period SP3. As a result, the maximum number of retransmissions n decreases as follows. In the sampling period SP3, NO is determined in step S207, YES is determined in step S209, and k = 2 and d = 4 are set. In step S213, the maximum number of retransmissions n is 93. In the next sampling period SP4 (excluding SSP4), retransmission control is performed with the maximum number of retransmissions n being 93.

  Assume that NO in step S206 in the sampling period SP4. As a result, the maximum number of retransmissions n decreases as follows. In the sampling period SP4, NO in step S207, YES in step S209, k = 3, d = 8, and the maximum number of retransmissions n is 85 in step S213. In the next sampling period SP5 (excluding SSP5), retransmission control is performed with the maximum number of retransmissions n being 85.

  In the sampling section SP5, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling period SP5, NO is determined in step S215, NO is determined in step S217, k = 2 and d = 4, and the maximum number n of retransmissions is 89 in step S221. In the next sampling period SP6 (excluding SSP6), retransmission control is performed with the maximum number of retransmissions n being 89.

  In the sampling period SP6, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling period SP6, NO in step S215, YES in step S217, k = 3, d = 8, and the maximum number of retransmissions n becomes 97 by step S221. In the next sampling period SP7 (excluding SSP7), retransmission control is performed with the maximum number of retransmissions n being 97.

(Operation example 3)
Referring to FIG. 12C, first, assume that YES is obtained in step S206 and YES in step S214 in the first sampling period SP1. As a result, the maximum number of retransmissions n increases as follows. In the first sampling period SP1, YES is set in step S215, so that k = 0 and d = 1, and the maximum number of retransmissions n is 101 in step S221. In the next sampling period SP2 (excluding SSP2), retransmission control is performed with the maximum number of retransmissions n being 101.

  In the sampling section SP2, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling period SP2, NO is determined in step S215, YES is determined in step S217, and k = 1 and d = 2 are set. In step S221, the maximum number of retransmissions n is 103. In the next sampling period SP3 (excluding SSP3), retransmission control is performed with the maximum number of retransmissions n being 103.

  In the sampling section SP3, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling interval SP3, NO is determined in step S215, YES is determined in step S217, k = 2 and d = 4, and the maximum number of retransmissions n is 107 due to step S221. In the next sampling period SP4 (excluding SSP4), retransmission control is performed with the maximum number of retransmissions n being 107.

  In the sampling period SP4, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling interval SP4, NO in step S215, YES in step S217, k = 3, d = 8, and the maximum number of retransmissions n becomes 115 by step S221. In the next sampling period SP5 (excluding SSP5), retransmission control is performed with the maximum number of retransmissions n being 115.

  Assume that NO in step S206 in the sampling period SP5. As a result, the maximum number of retransmissions n decreases as follows. In the sampling period SP5, NO is determined in step S207, NO is determined in step S209, and k = 2 and d = 4 are set. In step S213, the maximum number of retransmissions n is 111. In the next sampling period SP6 (excluding SSP6), retransmission control is performed with the maximum number of retransmissions n being 111.

  In the sampling period SP6, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling section SP6, NO is determined in step S215, NO is determined in step S217, and k = 1 and d = 2 are set. In step S221, the maximum number of retransmissions n is 113. In the next sampling period SP7 (excluding SSP7), retransmission control is performed with the maximum number of retransmissions n being 113.

  In the sampling section SP7, it is assumed that YES is determined in the step S206 and YES is determined in the step S214. As a result, the maximum number of retransmissions n increases as follows. In the sampling period SP7, NO is determined in step S215, YES is determined in step S217, k = 2 and d = 4 are set, and the maximum number of retransmissions n is 117 in step S221. In the next sampling period SP8 (excluding SSP8), retransmission control is performed with the maximum number of retransmissions n set to 117.

  As described above, according to the present embodiment, similarly to the first embodiment, the maximum number of retransmissions can be appropriately set according to the change in the error rate of the HARQ subburst, so that the radio resources can be effectively used. It is possible to avoid the increase in the time until the error-free data is obtained. Further, according to the present embodiment, since the amount of change in the maximum number of retransmissions is set according to the previous amount of change instead of 1, the maximum number of retransmissions can be adjusted to an appropriate value in a short time. it can.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Wireless communication system, 2 Wireless base station, 3a-3n, 3 Wireless terminal, 5 Network, 10, 11 Antenna, 12 Receiving part, 13 Transmitting part, 14 Control part, 15, 20 RF part, 16 CP removal part, 17 FFT unit, 18 subcarrier allocation unit, 21 CP addition unit, 22 IFFT unit, 24 multi-antenna transmission signal processing unit, 23 subcarrier allocation unit, 31 control unit, 33 retransmission control unit, 34 user data management unit, 35 maximum retransmission Number setting part, 36 Control information management part.

Claims (10)

A communication device in which retransmission is controlled in units of a predetermined amount of data blocks,
The error rate of the data block transmitted to the communication partner device at the currently set maximum number of retransmissions, and the data block transmitted to the communication partner device at a number of retransmissions greater or less than the currently set maximum number of retransmissions A setting unit that updates the currently set maximum number of retransmissions according to a difference from an error rate of the data block, and the error rate of the data block at each number of retransmissions is a data block transmitted at each number of retransmissions Represents the ratio of data blocks that received a retransmission request from the communication partner device,
The communication device further includes:
A communication apparatus comprising a retransmission control unit that repeats retransmission within the range of the set maximum number of retransmissions in response to a retransmission request from the apparatus of the communication partner.   The setting unit has a difference between the error rate when the retransmission is performed at the currently set maximum number of retransmissions and the error rate when the retransmission is performed at the number of retransmissions immediately before the currently set maximum number of retransmissions. The communication apparatus according to claim 1, wherein when not greater than a predetermined value, the currently set maximum number of retransmissions is decreased.   The communication apparatus according to claim 2, wherein a change amount that decreases the currently set maximum number of retransmissions is one.   The amount of change that decreases the currently set maximum number of retransmissions is twice the previous amount of change when the maximum number of retransmissions is changed in a direction that decreases when the number is changed last time. 2. The communication device according to 2.   When the maximum number of retransmissions is changed in a direction that increases when the previous change is changed, the amount of change that decreases the currently set maximum number of retransmissions is ½ times the previous amount of change. The communication apparatus according to claim 2. The setting unit temporarily sets a maximum number of retransmissions that is one more than the currently set maximum number of retransmissions in a predetermined period,
The retransmission control unit repeats retransmission within the predetermined maximum number of retransmissions in response to a retransmission request from the communication partner apparatus during the predetermined period,
When the difference between the error rate when retransmitting at the currently set maximum number of retransmissions and the error rate when retransmitting at the temporarily set maximum number of retransmissions is a predetermined value or more, The communication apparatus according to claim 1, wherein the currently set maximum number of retransmissions is increased.   The communication apparatus according to claim 6, wherein the amount of change that increases the currently set maximum number of retransmissions is one.   The amount of change that increases the currently set maximum number of retransmissions is twice the previous amount of change when the maximum number of retransmissions is changed in a direction that increases when the previous change is changed. 6. The communication device according to 6.   When the maximum number of retransmissions is changed in a direction that decreases when the previous retransmission is changed, the amount of change that increases the currently set maximum number of retransmissions is ½ times the previous amount of change. The communication apparatus according to claim 6. A communication method in which retransmission is controlled in units of a predetermined amount of data blocks,
The error rate of the data block transmitted to the communication partner device at the currently set maximum number of retransmissions, and the data block transmitted to the communication partner device at a number of retransmissions greater or less than the currently set maximum number of retransmissions A step of updating the currently set maximum number of retransmissions according to a difference from the error rate of the data block, and the error rate of the data block at each number of retransmissions is the number of retransmissions of the data block transmitted at each number of retransmissions. Of these, it represents the ratio of data blocks that received a retransmission request from the communication partner device,
The communication method further includes:
A communication method comprising a step of repeating retransmission within a range of the set maximum number of retransmissions in response to a retransmission request from the communication partner apparatus.

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