JP2007336583A - Transmitting apparatus, receiving apparatus, and retransmission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a packet signal retransmission system for efficiently transmitting a retransmission packet in accordance with a propagation path state in a packet communication system which changes a modulation parameter of a transmission signal adaptively to the propagation path state and retransmits a packet that cannot be received at a receiving station from a transmitting station. <P>SOLUTION: A base station (transmitting station) comprises a propagation path state comparing section and a propagation path state or a modulation parameter in the transmission of a novel packet is compared with a propagation path state or a modulation parameter in the transmission of a retransmission packet and in accordance with a result of the comparison, the modulation parameter of a packet to be retransmitted is changed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a packet signal retransmission method for efficiently transmitting retransmission packets according to a radio propagation path state (hereinafter referred to as a propagation path state) in a mobile communication system that performs packet transmission.

  In recent years, with the spread of the Internet, there is an increasing demand for providing services such as music data distribution over the Internet using a mobile communication system. In data communication, a packet transmission method is suitable for transmitting signals having various qualities and transmission rates as data of a determined capacity. Particularly, in the downlink from a base station (transmitting station) to a mobile station (receiving station), it is desired to efficiently transmit a large amount of data.

  In packet transmission, packet data is transmitted only when user data is generated, and the channel can be shared with multiple users, and wireless resources such as power, frequency, and time can be used efficiently. Can do. Further, there are techniques such as adaptive modulation, scheduler, and retransmission as means for performing efficient transmission.

<About adaptive modulation>
Since the propagation path state changes every moment, packet signal transmission according to the propagation path state is required.

  As an example, there is a method of controlling transmission power. When the propagation path state is bad, the reception power at the receiving station is guaranteed to be raised to a certain level by increasing the transmission power. However, it is conceivable that the interference characteristics with respect to other receiving stations and adjacent cells change as the transmission power changes.

  As another concept, there is a method called adaptive modulation in which the transmission power is constant and modulation parameters such as a modulation method, a coding rate, and a spreading factor are changed in accordance with a propagation path state. In general, data to be transmitted is subjected to error correction and then modulated by a multi-level modulation method. The higher the multi-value number of the modulation scheme, and the higher the coding rate, which is the ratio of the correctable block size and information bits in error correction, the larger the amount of data that can be transmitted at one time, so the resistance to transmission errors is higher. become weak. That is, when the channel condition is good, increasing the number of modulation schemes and increasing the coding rate can increase the amount of transmission data and perform data transmission with few transmission errors. On the other hand, when the propagation path state is bad, the number of modulation schemes is reduced and the coding rate is lowered, thereby reducing the amount of transmission data and performing data transmission with few transmission errors.

  Further, in a system using a spread spectrum method for modulating a transmission information waveform such as CDMA (code division multiple access), a signal spreading factor (also referred to as a process gain) can be used as a modulation parameter. In this way, by changing the modulation parameter according to the propagation path state, it is possible to adapt to the propagation path state, increase the amount of transmission data, and suppress the transmission error rate within a certain range.

<About the scheduler>
In a mobile communication system, when performing signal transmission to a plurality of users in a cell, it is important to efficiently allocate radio resources to each user. In other words, it is necessary to determine which user's packet (in the case of one user or in the case of multiple users) at which time, on which channel, with what power, and with what packet length. I must. The part that performs this work is the scheduler.

The scheduler allocates radio resources to each user based on various information. The various information includes a propagation path state for each user, transmission rate information, traffic priority, and the like, but which information is used differs depending on the system. In addition, which resource is allocated to which reference among radio resources is different depending on the system. In order to maximize the amount of transmission in the entire system or in a cell, for example, a user with the best propagation path condition such as a user near the base station (transmitting station) is selected and all radio resources are allocated. become. In order to maintain fairness among users, transmission opportunities are equally allocated. The above technique is disclosed in the following document (see, for example, Non-Patent Document 1).
<About resending>
When packet reception fails, there is a retransmission method for retransmitting a packet that failed to be received. The receiving station determines whether or not the received packet information is correctly decoded, and notifies the transmitting side of reception success / reception failure (ACK / NACK). The transmitting station stores the data information of the transmitted packet in the signal buffer, and when there is a notification of reception failure, retransmits the packet. When there is a notification of successful reception, the data information of the packet is deleted from the signal buffer.

  When performing data communication on the Internet or the like, accuracy is required after allowing a certain delay. In the case of such traffic, communication without packet discard can be performed by setting a large maximum number of retransmissions in retransmission. On the other hand, when real-time traffic such as a telephone is assumed, the maximum number of retransmissions is set to be small, assuming that a certain amount of packet discard is acceptable.

  Furthermore, there is a method of combining data on the receiving side in order to improve the reception quality of the retransmission signal. On the receiving side, the data of the packet that failed to be received and issued a retransmission request is stored in the buffer, and when the retransmitted packet is received, the data in the buffer is changed based on the difference between the data in the buffer and the retransmission data. Combining resend data. This data composition improves reception quality, and the degree of improvement increases as the number of retransmissions increases, and the success rate of packet reception increases.

  In addition, there is one that improves the transmission characteristics by notifying the transmission side of the reliability using an ACK / NACK signal (see, for example, Patent Document 1).

  In the mobile communication packet transmission system, the above-described adaptive modulation, scheduler, and retransmission techniques are used to efficiently use radio resources, adapt to the characteristics of each user or traffic, and meet the purpose of the system provider Packet transmission can be realized.

  FIG. 11 shows an example of a conventional configuration. Here, assuming downlink transmission from the base station 1 to the mobile station 2, the mobile station 2 receives the signal from the base station 1 by the radio unit 12b via the antenna 11b, and the signal demodulation unit 13b. The SIR measurement unit 21 constantly monitors the state of the propagation path in the downlink for the signal demodulated in step S1, and the SIR is multiplexed with the transmission data in the signal multiplexing unit 23 in the base station 1 and in the signal modulation unit 19b. Modulated and transmitted from the radio unit 12b via the antenna 11b. Further, the packet determination unit 22 determines whether or not the received packet information is correctly decoded. If the packet reception is successful, the packet multiplex unit 23 receives an ACK when the packet reception is successful and a NACK when the packet reception is unsuccessful. It is multiplexed with the transmission data, modulated by the signal modulator 19b, and transmitted from the radio unit 12b via the antenna 11b.

In the base station 1, the signal from the mobile station 2 is received by the radio unit 12a via the antenna 11a and demodulated by the signal demodulation unit 13a. The demodulated signal is separated into received data, SIR, and ACK / NACK in the signal separation unit 14. The scheduler unit 17 selects a user to transmit in the next packet based on information such as SIR, and notifies the transmission data control unit 18 of the selection result. The transmission data control unit 18 converts the transmission data in the signal buffer included in the transmission data control unit 18 into a signal modulation unit according to the user information notified from the scheduler unit 17 and the ACK / NACK notified from the signal separation unit 14. Send to 19. The data to be transmitted to the mobile station 2 is once stored in the signal buffer for each mobile station. The adaptive modulation control unit 16b calculates a modulation parameter suitable for each user based on the SIR, and notifies the signal modulation unit 19 of the modulation parameter. The signal modulator 19 modulates the signal using the notified modulation parameter.
Oto, et al. “Characteristic comparison of scheduling methods focusing on the throughput of each user in downlink high-speed packet access” IEICE Technical Report RCS2001-291 Japanese Patent Laid-Open No. 2002-9741 “Communication Method and Base Station Device for Performing Automatic Retransmission Request”

  As described above, in the adaptive modulation scheme in which the modulation parameter is changed according to the propagation path state and the packet signal is transmitted, when the packet that has failed to be received is retransmitted, the signal is modulated by the same modulation parameter as at the time of new transmission. Send the packet signal. However, the propagation path state is constantly changing, and the propagation path state (SIR) may fluctuate by several tens of decibels considering the movement, shadowing, and fading of the mobile station (receiving station). In addition, when there are a large number of users in a cell, the scheduler does not always transmit a retransmission packet immediately, and retransmission may occur several times. In such a case, the modulation parameter set at the time of new transmission may not match the modulation parameter adapted to the propagation path state at the time of retransmission. When the propagation path state at the time of retransmission is worse than at the time of new transmission, the probability of successful packet reception is very small even if the packet is transmitted with the same modulation parameter as at the time of new transmission. On the other hand, if the channel condition at the time of retransmission is better than at the time of new transmission, if the packet is transmitted with the same modulation parameters as at the time of new transmission, the probability of successful packet reception will be very large, but radio resources will be used excessively It will be.

  An object of the present invention is to provide a packet signal retransmission method for efficiently transmitting retransmission packets according to propagation path conditions in a mobile communication system that performs packet transmission.

In the present invention, when the transmitted packet data cannot be correctly received on the receiving side, the transmission parameter can be switched at the time of transmission of the packet data in accordance with the propagation path state in the transmission apparatus capable of executing the retransmission process Parameter control means, and transmission to be applied to the adaptive modulation control means by dividing the stored retransmission data into a plurality of packets when transmission of the amount of data at the time of new transmission is not ensured at the time of retransmission For each of the plurality of packets divided by the data control means and the transmission data control means, the modulation scheme and coding rate are controlled according to the transmission parameters switched by the parameter control means, And an adaptive modulation control means for sequentially transmitting the packets as retransmissions, using a transmitter characterized by comprising In addition, if the transmitted packet data cannot be correctly received on the receiving side, the retransmission process can be executed, the transmission parameter at the time of packet data transmission is switched according to the propagation path state, and the new transmission When transmission of the amount of data is not ensured at the time of retransmission, the stored retransmission data is divided into a plurality of packets and given to the adaptive modulation control means, and switching is performed for each of the divided packets. The receiving apparatus that receives packet data from the transmitting apparatus that transmits the plurality of packets as retransmissions in order, receives the divided plurality of packets in order, by controlling the modulation scheme and coding rate according to the determined parameters. A receiving device comprising: a radio unit that performs demodulation; and a demodulation unit that demodulates the received plurality of divided packets In addition, in the retransmission control method in the transmission apparatus capable of executing the retransmission process when the transmitted packet data is not correctly received on the receiving side, the transmission parameter when transmitting the packet data according to the propagation path state If the transmission of the amount of data at the time of new transmission is not ensured when performing retransmission, the stored retransmission data is divided into a plurality of packets, and each of the divided packets is divided Using a retransmission control method in a transmission device, characterized by controlling a modulation scheme and a coding rate according to a switched transmission parameter, and transmitting the plurality of packets as retransmissions in order, and The idea is to change the modulation parameter of the transmission signal to adapt to the propagation path state, and retransmit the packet that could not be received by the receiving station. In a packet communication system, a propagation path state comparison unit that compares a propagation path state or modulation parameter when a retransmission packet is transmitted with a propagation path state or modulation parameter when a packet that could not be received is transmitted, and SIR (signal to interference ratio) information, adaptive modulation / transmission power controller that determines modulation parameters based on propagation path condition comparison information, SIR information, signal buffer information, transmission rate information, traffic priority information And a transmission data control unit that has a signal buffer for storing new transmission data and retransmission data and that outputs data to be transmitted in the next slot. This is a packet signal retransmission method.

According to the first proposal , when a retransmission packet is transmitted, it is possible to change the modulation parameter at the time of transmission as a new packet, and transmit with a modulation parameter adapted at the time of transmission of the retransmission packet.

The second proposal is the packet signal retransmission method of the first proposal , in which the comparison result of the propagation path state comparison unit indicates that the propagation path state when the retransmission packet is transmitted or the propagation parameter when the modulation parameter is transmitted as a new packet. In the packet signal retransmission system, the transmission station postpones transmission of a retransmission packet and transmits a new packet or another retransmission packet when the path condition or the modulation parameter is worse.

According to the second proposal, when it is determined that the modulation parameter at the time of transmitting a retransmission packet is smaller than the modulation parameter at the time of transmitting a new packet, that is, the current channel state is more than the channel state at the time of new transmission. This is a bad case, and if the probability of successful reception is low even if retransmission is performed with the modulation parameter at the time of new transmission, it is possible to increase the probability of successful reception by performing packet transmission adapted to the current channel state.

The third idea is that in the packet signal retransmission scheme of the first proposal , the result of the comparison by the propagation path state comparison unit is the propagation state when the propagation path state or modulation parameter when the retransmission packet is transmitted is a new packet. When the transmission condition is worse than the path condition or the modulation parameter, the transmission station changes the modulation parameter of the retransmission packet and transmits the packet divided into a plurality of times.

According to the third proposal, when it is determined that the modulation parameter at the time of transmitting a retransmission packet is smaller than the modulation parameter at the time of transmitting a new packet, that is, the current channel state is more than the channel state at the time of new transmission. If the probability of successful reception is low even if retransmission is performed with the modulation parameter at the time of new transmission, the retransmission data is divided into multiple times and transmitted using the modulation parameter adapted to the current channel state. The probability of successful reception can be increased.

In the fourth proposal , in the packet signal retransmission method of the first proposal , the comparison result of the propagation path state comparison unit indicates that the propagation state when the retransmission packet is transmitted or the propagation parameter when the modulation parameter is transmitted as a new packet. When the path condition or the modulation parameter is better, the transmitting station transmits the next packet in the signal buffer for the same receiving station as the retransmission packet together with the retransmission packet.

According to the fourth proposal, when it is determined that the modulation parameter at the time of transmitting a retransmission packet is better than the modulation parameter at the time of transmitting a new packet, that is, the current channel state is more than the channel state at the time of new transmission. This is a good case, and when there is a high probability of successful reception when retransmission is performed with the modulation parameter at the time of new transmission, it is possible to effectively use radio resources by transmitting other signals together with the retransmission packet signal. .

According to the fifth proposal , in the packet signal retransmission scheme of the first proposal , if the propagation path state at the time of transmitting a retransmission packet is different from the propagation path state at the time of transmitting a new packet, the difference between the propagation path states is The packet signal retransmission method is characterized in that the power for transmitting a retransmission packet is adjusted so as to be a reference SIR.

According to the fifth plan , it is possible to suppress power resources that are one of radio resources.

According to the present invention, at the time of retransmission, a plurality of divided packets can be transmitted with their coding rates controlled separately. According to the above embodiment, the base station (transmitting station) includes the propagation path state comparison unit, compares the propagation path state when the new packet is transmitted with the propagation path state when the retransmission packet is transmitted, and compares the comparison. A packet signal retransmission method that prevents the reception failure of retransmitted packets, suppresses the use of excessive radio resources, and enables the efficient use of radio resources by changing the modulation parameters of the retransmitted packets according to the result Can be realized.

According to the first plan , when a retransmission packet is transmitted, it is possible to use a modulation parameter that is adapted at that time.

According to the second proposal , it is possible to increase the probability of successful reception by changing the modulation parameter of the retransmission packet.

According to the third plan , it is possible to increase the probability of successful reception by changing the modulation parameter of the retransmission packet and transmitting the retransmission packet in multiple times.

According to the fourth plan , it is possible to effectively use radio resources by transmitting other packets together with the retransmission packet.

According to a fifth proposal, it is possible to suppress the power resources.

  Hereinafter, the technique of the present invention will be described in detail with reference to the drawings.

   FIG. 1 is a basic configuration diagram of the present invention, and shows a base station (referred to as a transmitting station) 1 and a mobile station (referred to as a receiving station) 2.

  Here, assuming downlink transmission from the base station 1 to the mobile station 2, the mobile station 2 receives the signal from the base station 1 by the radio unit 12b via the antenna 11b, and the signal demodulation unit 13b. The SIR measurement unit 21 constantly monitors the state of the propagation path in the downlink for the signal demodulated in step S1, and the SIR is multiplexed with the transmission data in the base station 1 and the signal multiplexing unit 23 as SIR, and in the signal modulation unit 19b Modulated and transmitted from the radio unit 12b via the antenna 11b. Further, the packet determination unit 22 determines the received packet. When the packet reception is successful, ACK is received. When the packet reception is unsuccessful, NACK is multiplexed with the transmission data by the signal multiplexing unit 23 and the signal modulation unit 19b. And is transmitted from the radio unit 12b via the antenna 11b.

  In the base station 1, the signal from the mobile station 2 is received by the radio unit 12a via the antenna 11a, and the signal demodulated by the signal demodulating unit 13a is received by the signal demultiplexing unit 14, received data, SIR, ACK / NACK Separated. The scheduler unit 17 selects a user to transmit in the next packet based on information such as SIR, and notifies the transmission data control unit 18 of the selection result.

  The adaptive modulation / transmission power control unit 16a calculates a modulation parameter suitable for each user based on the comparison result of the SIR and the propagation path state comparison unit 15, and notifies the signal modulation unit 19a of the modulation parameter.

  In the propagation path state comparison unit 15, the current propagation path state or modulation parameter from the adaptive modulation / transmission power control unit 16a and the propagation path state or modulation when the retransmission packet from the transmission data control unit 18 is transmitted as a new packet. The parameters are compared, the comparison result is notified to the transmission data control unit 18, and the signal modulation unit 19 is notified.

  In the transmission data control unit 18, the transmission data control unit 18 includes the user information notified from the scheduler unit 17, the comparison result notified from the propagation path state comparison unit 15, and the ACK / NACK information for each user. The transmission data in the signal buffer is sent to the signal modulator 19a. The data to be transmitted to the mobile station 2 is once stored in the signal buffer for each mobile station.

  The signal modulation unit 19a modulates the signal using the comparison result notified from the propagation path state comparison unit 15 and the modulation parameter notified from the adaptive modulation / transmission power control unit 16a.

  The signal output from the signal modulation unit 19a is transmitted from the radio unit 12a via the antenna 11a as a transmission signal corresponding to the transmission power control signal notified from the adaptive modulation / transmission power control unit 16a in the multiplier 20. Is done.

   An operation of adaptive modulation in the configuration of FIG. 1 will be described.

   FIG. 2 is an operation example of adaptive modulation, and the graph shown in FIG. 2 is an SIR of a user notified from a receiving station (mobile station). FIG. 3 is an explanation of the adaptive modulation / transmission power control unit shown in FIG. 1, and compares the SIR of each user with the MCS (modulation and coding scheme) threshold (MCS will be described below), and modulation is performed. The MCS number representing the parameter is determined, and the user number and the MCS number are notified to the propagation path state comparison unit 15. When the modulation parameter at the time of packet retransmission is changed from the modulation parameter at the time of new transmission according to the comparison information in the propagation path state comparison unit 15, the changed MCS number is notified to the signal modulation unit 19a. As shown in FIG. 2, since the SIR at time T1 for a certain user is equal to or greater than the MCS threshold 2, the MCS number of the user in the next transmission slot SL1 is MCS3.

  MCS represents a modulation parameter. For example, a combination of a modulation method and a coding rate. The MCS threshold is determined from each modulation parameter and the SIR required by the modulation parameter. For example, the MCS thresholds 1 and 2 are provided, and if the SIR measured by the mobile station and notified to the base station is equal to or greater than the MCS threshold 2, the modulation parameter MCS3 is set. If it is between 2, the modulation parameter MCS2 is set. If the SIR is less than or equal to the MCS threshold 1, the modulation parameter MCS1 is set. The higher the MCS threshold, the higher the required SIR.

  Next, the operation of the scheduler in the embodiment of the present invention will be described.

   FIG. 4 shows an example of the operation of the scheduler unit shown in FIG. The scheduler determines user assignments from various perspectives. As shown in the description of the scheduler unit in FIG. 5, a user number as a user allocation result is determined based on SIR, signal buffer information, transmission rate information, and traffic priority information. In the configuration of FIG. 1, only SIR is used as shown in FIG. 4, and allocation is performed only to one user having the highest SIR (the best propagation path state). Since the SIR of user A is high at time T1, transmission is performed to user A in the next slot SL1. Similarly, since the SIR of user B is high at time T4, transmission is performed to user B in the next slot SL4.

  6 shows the configuration of the transmission data control unit shown in FIG. 1. The transmission data control unit 18 accumulates new transmission data and retransmission data in the signal buffer 181 and modulates data to be transmitted in the next slot. Send to part 19. The signal buffer 181 can be classified for each user, new / retransmission data, and traffic type. The specified value of the number of retransmissions differs depending on the user and the traffic type, and the data is discarded when the specified value is exceeded. Is also performed. In addition to the signal data, control information such as a modulation parameter at the time of new transmission and the number of retransmissions is also stored. The transmission user determination unit 182 determines a user to be transmitted in the next slot based on the user information notified from the scheduler unit 17 and the comparison result notified from the propagation path state comparison unit 15 and notifies the signal buffer 181 of the user. Also, the ACK / NACK information from each user is notified to the retransmission information control unit 183, and if the ACK is notified, the data of the corresponding user is deleted from the signal buffer 181. If NACK is notified, it is stored in the signal buffer 181 again.

  Next, an operation example of adaptive modulation in retransmission will be described.

 FIG. 7 shows an example of retransmission operation in adaptive modulation. The graph shows the SIR notified from the mobile station according to the transmission slot. In addition, the reception state at the mobile station is indicated according to the transmission slot, and is indicated by “◯” when ACK is notified and by “X” when NACK is notified. The data number transmitted in the transmission slot is shown. It is assumed that reception of data (data number 5) transmitted from the transmission slot 5 for a certain user has failed. In this case, the modulation parameter is MCS3 based on the SIR at T4 from the graph. It is assumed that the scheduler retransmits the data of data number 5 that failed to be received in the transmission slot 9. However, the modulation parameter in this case is MCS1 from the SIR at T8 from the graph, and the propagation path state is worse than that at the time of new transmission (transmission slot 5). Therefore, even if a packet of the modulation parameter MCS3 at the time of new transmission is transmitted, it is received. Is less likely to succeed. Therefore, the data of data number 5 is retransmitted with the modulation parameter MCS1 so as to adapt to the current channel state. Or, another user packet, a new packet of the same user, and another retransmission packet of the same user and having a modulation parameter of MCS1 are selected.

Next, FIG. 8 shows a processing flowchart in the case where retransmission is performed by changing the modulation parameter at the time of retransmission described above, and will be described in detail.
S1. The scheduler unit 17 determines the first candidate user and notifies the transmission data control unit 18 of the user information.
S2. Whether the transmission data control unit 18 transmits new data in the next slot in consideration of information such as whether there is data for retransmission or whether the priority of the data is high based on the notified user information To determine whether to send retransmission data.
S3. If it is determined in step S2 that retransmission data is to be transmitted, the transmission data control unit 18 notifies the channel state comparison unit 15 of channel state information at the time of new transmission known from the signal buffer 181 from the user information, and performs channel state comparison. The unit 15 acquires propagation path state information at the time of new transmission.
S4. The propagation path state comparison unit 15 acquires the MCS number that is the modulation parameter of the current propagation path state from the adaptive modulation / transmission power control unit 16a.
S5. The propagation path state comparison unit 15 compares the modulation parameter at the time of new transmission acquired in steps S3 and S4 with the modulation parameter in the current propagation path state.
S6. If it is determined in step S2 that new data is to be transmitted instead of retransmission, or if it is determined in step S5 that the modulation parameter in the current propagation path state is smaller than the modulation parameter in the new transmission, that is, the current propagation path state Is worse than the propagation path state at the time of new transmission, and if the probability of successful reception is low even if retransmission is performed with the modulation parameter at the time of new transmission, the signal modulation unit 19a transmits the current propagation from the adaptive modulation / transmission power control unit 16a. The MCS number that is the modulation parameter for the road condition is acquired and modulated.
S7. If it is determined in step S5 that the modulation parameter at the time of new transmission is smaller than the modulation parameter at the time of new transmission, that is, the current channel condition is better than the channel condition at the time of new transmission. If the probability of successful reception is high when retransmission is performed with parameters, the signal modulation unit 19a acquires and modulates the MCS number that is the modulation parameter of the propagation path state at the time of new transmission from the adaptive modulation / transmission power control unit 16a.
S8. The signal modulator 19a outputs the modulated signal to the radio unit 12 and is transmitted.

Further, a processing flowchart in the case where the retransmission is postponed depending on the current channel state at the time of retransmission is shown in FIG. 9 and will be described in detail.
Steps S1 to S5 are the same as those in FIG.
S1. The scheduler unit 17 determines the first candidate user and notifies the transmission data control unit 18 of the user information.
S2. Whether the transmission data control unit 18 transmits new data in the next slot in consideration of information such as whether there is data for retransmission or whether the priority of the data is high based on the notified user information To determine whether to send retransmission data.
S3. If it is determined in step S2 that it is retransmission, the transmission data control unit 18 notifies the channel state comparison unit 15 of channel state information at the time of new transmission known from the signal buffer 181 from the user information, and the channel state comparison unit 15 15 acquires propagation path state information at the time of new transmission.
S4. The propagation path state comparison unit 15 acquires the MCS number that is the modulation parameter of the current propagation path state from the adaptive modulation / transmission power control unit 16a.
S5. The propagation path state comparison unit 15 compares the modulation parameter at the time of new transmission acquired in steps S3 and S4 with the modulation parameter in the current propagation path state.
S6. If it is determined in step S2 that new data is to be transmitted, the signal modulation unit 19a acquires and modulates the MCS number that is the modulation parameter of the current channel state from the adaptive modulation / transmission power control unit 16a.
S7. If it is determined in step S5 that the modulation parameter at the time of new transmission is smaller than the modulation parameter at the time of new transmission, that is, the current channel condition is better than the channel condition at the time of new transmission. If the probability of successful reception is high when retransmission is performed with parameters, the signal modulation unit 19a acquires and modulates the MCS number that is the modulation parameter of the propagation path state at the time of new transmission from the adaptive modulation / transmission power control unit 16a. S8. The signal modulator 19a outputs the modulated signal to the radio unit 12a and is transmitted. S11. If it is determined in step S5 that the modulation parameter of the current propagation path state is smaller than the modulation parameter at the time of new transmission, that is, the current propagation path state is worse than the propagation path state at the time of new transmission. If the probability of successful reception is low even if retransmission is performed with parameters, the scheduler unit 17 determines the next candidate user and notifies the transmission data control unit 18 of the user information of the candidate user.
<When the channel state at the time of retransmission (current channel state) is worse than at the time of new transmission>
Another operation example when the channel state at the time of retransmission, that is, the channel state at the present time is worse than when a packet to be retransmitted is newly transmitted, that is, when reception fails, will be described.

  When it is determined in step S5 of the processing flowchart for changing and retransmitting the modulation parameter in FIG. 8 that the modulation parameter of the current propagation path state is smaller than the modulation parameter at the time of new transmission, that is, when the current propagation path state is new transmission. This is an example of operation when the modulation parameter of the retransmission packet is changed to the current modulation parameter in step S6 when the probability of successful reception is low even if retransmission is performed with the modulation parameter at the time of new transmission. .

  In this case, the data amount may exceed one packet, and at that time, the transmission data control unit 18 divides the data into a plurality of packets for transmission.

  In the example of FIG. 7, the transmission is performed with the modulation parameter MCS3 at the time of new transmission (in the case of transmission slot 5), but at the time of retransmission, the transmission slot 9 is changed to the modulation parameter MCS1 according to the current propagation path state. become. If the transmission rate in the modulation parameter MCS3 is three times the transmission rate in the modulation parameter MCS1, a transmission capacity that is three times (equivalent to three times the packet amount) is generated by setting the modulation parameter to MCS1. The packet data after the second packet is stored again in the signal buffer 181 and retransmitted at the next and subsequent slot assignments.

Regarding the above operation, in a system using, for example, CDMA (code division multiple access), a signal is transmitted using a plurality of channels, and a plurality of signals are transmitted simultaneously using a plurality of codes by a technique called multicode. It is possible. In multi-code transmission, it is possible to maintain orthogonality between codes by selecting codes, but interference occurs due to delayed waves. The greater the number of multicodes (number of simultaneous transmission channels), the greater the interference and the higher the required quality. For this reason, when the channel state at the time of retransmission is poor, the signal can be transmitted with the required quality close to the current channel state by reducing the number of multicodes while keeping the modulation parameter as it is. At this time, other multicode signals that have not been transmitted are stored again in the signal buffer 181 and retransmitted at the next and subsequent slot allocation.
<When propagation path state at retransmission (current propagation path state) is better than at new transmission>
Contrary to the example described above, an operation example in the case where the channel state at the time of retransmission (current channel state) is better than the channel state at the time of new transmission will be described.

  If it is determined in step S5 of the processing flowchart for changing and retransmitting the modulation parameter in FIG. 8 that the modulation parameter at the time of new transmission is smaller than the modulation parameter of the current propagation path state, that is, the current propagation path state is at the time of new transmission Operation in the case where it is better than the propagation path state of the packet, and when there is a high probability of successful reception when retransmitted with the modulation parameter at the time of new transmission, the operation when retransmitting the modulation parameter of the retransmission packet with the modulation parameter at the time of new transmission as it is at step S7 It is an example. In this case, radio resources are excessively used.

  Referring to the example of FIG. 7, if a new transmission is performed in the transmission slot 9, the modulation parameter is MCS1, and if retransmission is performed in the transmission slot 11, the modulation parameter corresponding to the channel state at that time is MCS2. When the transmission rate of the modulation parameter MCS2 is twice the transmission rate of the modulation parameter MCS1, retransmitting the signal modulated by the modulation parameter MCS1 means that one packet in the modulation parameter MCS1 is unused, and transmission efficiency Decrease. For this reason, if the next retransmission signal of the same user is the modulation parameter MCS1, the transmission data control unit 18 can transmit efficiently together with this signal, for example, as a multicode signal. Alternatively, new data that is the modulation parameter MCS1 can be sent together. Furthermore, it is also possible for other users to send the modulation parameter MCS1 data together.

Similarly, when the channel state at the time of retransmission (current channel state) is better than the channel state at the time of new transmission, the modulation parameter of the retransmission packet (modulation parameter at the time of new transmission) is changed to the current modulation parameter. For example, when the modulation parameter is changed from MCS1 to MCS2, the modulation parameter is increased and the transmission rate is also increased. Since the transmission amount of the signal to be transmitted is the same as that at the time of new transmission, it is possible to suppress radio resources to be used by increasing the transmission rate. For example, when the transmission rate is doubled, it is possible to take measures such as doubling the transmission power, halving the packet length, or halving the frequency band. As a result, interference with other users and other cells is suppressed.
<When the channel state at the time of retransmission (current channel state) is almost equal to the time of new transmission>
An operation example in the case where the channel state at the time of retransmission (current channel state) is substantially equal to the channel state at the time of new transmission will be described.

  Adaptive modulation / transmission power control even when it is determined that the modulation parameter of the current propagation path state is substantially equal to the modulation parameter at the time of new transmission, that is, when the current propagation path state and the propagation path state at the time of new transmission are substantially equal. The unit 16a changes the modulation parameter of the retransmission packet to a low level modulation parameter. At this time, the amount of packet data may exceed one packet, and it is divided into a plurality of packets for transmission. In the case of traffic that performs real-time transmission (for example, a telephone), the real-time property becomes important, so the specified value of the number of retransmissions is set small, and data exceeding the specified value is discarded. On the other hand, since discarding data results in degradation of service quality, it is necessary to keep the discard rate low. For this reason, the adaptive modulation / transmission power control unit 16a changes the modulation parameter of the retransmission data to a low level, thereby changing the modulation parameter to a lower possibility of causing an error and keeping the packet discard rate low. It becomes possible.

  Next, an operation example in the case of controlling transmission power at the time of retransmission will be described.

  Transmission power control is generally used to keep reception quality at a mobile station (reception side) constant. When the propagation path state is bad, the reception quality is improved by increasing the transmission power, and when the propagation path state is good, the power resource is suppressed by reducing the transmission power. In this operation example, power control is performed according to the difference between the propagation path states at the time of new transmission and at the time of retransmission. FIG. 10 shows an operation example of transmission power control. In FIG. 10, it is assumed that new transmission is performed in transmission slot 3 with modulation parameter MCS2. Assume that retransmission is performed in transmission slot 5. The modulation parameter at this point is MCS3, and if the packet is retransmitted as it is, the modulation parameter MCS2 is used, so that radio resources are excessively used. By reducing the transmission power, excessive resource use is suppressed, and interference is also suppressed for adjacent cells. Therefore, a reference SIR is set for each MCS. In the modulation parameters MCS2 and MCS3, resources are excessively used by the difference between the SIRs of the respective standards, so the adaptive modulation / transmission power control unit 16a decreases the transmission power by this difference. When retransmission is set to transmission slot 9, the modulation parameter is MCS1, and if the packet of modulation parameter MCS2 is retransmitted, the probability of successful reception is low. Here, the quality can be improved up to the SIR corresponding to the modulation parameter MCS2 by increasing the transmission power by the difference of the reference SIR. It is also possible to control the transmission power according to the difference between the SIR at the time of new transmission and the SIR at the time of retransmission.

  (Supplementary note 1) In a packet communication system that retransmits a packet that could not be received by the receiving station by changing the modulation parameter of the transmission signal in accordance with the propagation path state, the propagation path when transmitting a retransmission packet A propagation path state comparison unit that compares a state or modulation parameter with a propagation path state or modulation parameter when a packet that could not be received is transmitted, SIR (signal to interference ratio) information, propagation path An adaptive modulation / transmission power control unit that determines modulation parameters based on state comparison information, a scheduler unit that determines user assignment based on SIR information, signal buffer information, transmission rate information, and traffic priority information; A transmission data control unit having a signal buffer for storing transmission data and retransmission data, and outputting data to be transmitted in the next slot; Packet signal retransmission scheme, characterized in that it comprises a.

  (Supplementary note 2) In the packet signal retransmission method according to supplementary note 1, the comparison result of the propagation path state comparison unit indicates that the propagation path state or modulation when a retransmission packet is transmitted is a propagation path state or modulation parameter when a retransmission packet is transmitted. A packet signal retransmission system, characterized in that if it is worse than the parameter, the transmitting station postpones transmission of a retransmission packet and transmits a new packet or another retransmission packet.

  (Supplementary note 3) In the packet signal retransmission method according to supplementary note 1, the comparison result of the propagation path state comparison unit is a propagation path state or modulation when a propagation path state or modulation parameter when a retransmission packet is transmitted is a new packet. A packet signal retransmission system characterized in that, if the parameter is worse than the parameter, the transmitting station changes the modulation parameter of the retransmission packet and transmits the packet in multiple times.

  (Supplementary note 4) In the packet signal retransmission method according to supplementary note 1, the comparison result of the propagation path state comparison unit is a propagation path state or modulation when a propagation path state or modulation parameter when a retransmission packet is transmitted is a new packet. When the parameter is better, the transmitting station transmits the next packet in the signal buffer for the same receiving station as the retransmission packet together with the retransmission packet.

  (Supplementary Note 5) In the packet signal retransmission method according to Supplementary Note 1, if the propagation path state at the time of transmitting a retransmission packet is different from the propagation path state at the time of transmitting a new packet, the retransmission packet is transmitted according to the difference in the propagation path state. A packet signal retransmission method characterized by adjusting the power to be transmitted so as to be a reference SIR.

  (Supplementary note 6) In the packet signal retransmission method according to supplementary note 1, the result of the propagation path state comparison unit indicates that the propagation path state or modulation parameter when the retransmission packet is transmitted is a propagation path state or modulation parameter when the new packet is transmitted. Packet signal retransmission characterized by reducing the number of simultaneous transmission channels and transmitting in multiple times when the signal to the receiving station of the retransmission packet to be transmitted is transmitted using a plurality of channels in the worse case method.

  (Supplementary note 7) In the packet signal retransmission method according to supplementary note 1, the result of the propagation path state comparison unit indicates that the propagation path state or modulation parameter when the retransmission packet is transmitted is a propagation path state or modulation parameter when the new packet is transmitted. In a better case, a packet signal retransmission system characterized in that a modulation parameter of a signal to a receiving station of a retransmission packet to be transmitted is changed to suppress radio resources used at the time of transmission.

  (Supplementary note 8) In the packet signal retransmission method according to supplementary note 1, the result of the propagation path state comparison unit indicates that the propagation path state or modulation parameter when the retransmission packet is transmitted is a propagation path state or modulation parameter when the new packet is transmitted. If the number of retransmissions of the signal to the receiving station of the retransmitted packet to be transmitted is limited, the transmitting station may change the modulation parameter of the retransmitted packet signal and transmit it in multiple times. Packet signal retransmission system characterized by

Basic configuration of the present invention Example of adaptive modulation operation Explanation of adaptive modulation / transmission power control unit Example of scheduler operation Explanation of scheduler part Transmission data control unit description Example of retransmission operation in adaptive modulation Process flowchart for changing modulation parameter and resending Resending postponement processing flowchart Transmission power control operation example Conventional configuration

Explanation of symbols

1 Base station (transmitting station)
2 Mobile station (receiving station)
11a, 11b Antennas 12a, 12b Radio units 13a, 13b Signal demodulation unit 14 Signal separation unit 15 Channel state comparison unit 16a Adaptive modulation / transmission power control unit 16b Adaptive modulation control unit 17 Scheduler unit 18 Transmission data control unit 181 Signal buffer 182 Transmission user determination unit 183 Retransmission information control unit 19a, 19b Signal modulation unit 20 Multiplier 21 SIR measurement unit 22 Packet determination unit 23 Signal multiplexing unit

Claims (3)

When the transmitted packet data cannot be correctly received on the receiving side, in the transmitting device capable of executing the retransmission process,
Parameter control means capable of switching transmission parameters when transmitting packet data according to the propagation path state;
A transmission data control unit that divides stored retransmission data into a plurality of packets and gives it to the adaptive modulation control unit when transmission of the amount of data at the time of new transmission is not secured when performing retransmission;
For each of the divided plurality of packets given by the transmission data control means, the modulation scheme and coding rate are controlled according to the transmission parameters switched by the parameter control means, and the plurality of packets are sequentially re-sent. Adaptive modulation control means for transmitting as transmission;
A transmission device comprising:
If the transmitted packet data cannot be received correctly on the receiving side, retransmission processing can be performed, the transmission parameter for packet data transmission is switched according to the propagation path state, and the amount of data for new transmission When the transmission of the packet is not ensured when performing retransmission, the stored retransmission data is divided into a plurality of packets and given to the adaptive modulation control means, and each of the divided packets is switched. In a receiving apparatus that receives packet data from a transmitting apparatus that transmits the plurality of packets as retransmissions in order by controlling a modulation scheme and a coding rate according to parameters.
A wireless unit that sequentially receives the plurality of divided packets;
A demodulator that demodulates the received plurality of divided packets;
A receiving apparatus comprising:
In the retransmission control method in the transmission apparatus capable of executing the retransmission process when the transmitted packet data cannot be correctly received on the receiving side,
Switch the transmission parameter when transmitting packet data according to the propagation path state,
If transmission of the amount of data at the time of new transmission is not ensured when performing retransmission, the stored retransmission data is divided into multiple packets,
For each of the plurality of divided packets, the modulation scheme and the coding rate are controlled according to the switched transmission parameters, and the plurality of packets are sequentially transmitted as retransmissions.
A retransmission control method in a transmitter characterized by the above.

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