JP2010273050A - Radio communication method, base station and mobile station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radio communication method which improves throughput of a TCP. <P>SOLUTION: A base station includes a downlink scheduler 14 which manages a retransmitting situation of a packet by each mobile station, performs control for transmitting the packet to satisfy predetermined conditions can raising transmission probability when it is recognized that retransmission of the packet to the mobile station continuously fails for over the predetermined number, and performs control for transmitting the packet by normal transmission probability when it is not recognized that retransmission of the packet to the mobile station continuously fails for over the predetermined number. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wireless communication method using TCP (Transmission Control Protocol).

  Conventional Internet communication is realized by a TCP / IP (Internet Protocol) protocol group. Currently, TCP is the majority of transport layer protocols used in Internet communication. Therefore, in Internet communication, improving the throughput provided by TCP to an application (hereinafter also referred to as TCP throughput) is an advantage for the application and the user who operates the application. Also in a wireless communication system, data is transmitted using TCP / IP in packet communication.

  By the way, in TCP, in order to escape from network congestion, mechanisms such as “slow start” and “congestion avoidance” are implemented, and the transmission data amount is controlled by changing the congestion window (cwnd) on the transmission side. These functions work effectively against network congestion, but are known to cause problems if the network includes a wireless link. The radio link has fluctuation factors such as propagation loss, shadowing, and fading fluctuation, and a transmission path error due to these factors is unavoidable. Therefore, due to the characteristics of wireless links, the probability of transmission path errors is much higher than that of wired links. In TCP, in order to recognize these errors as IP packet loss, a slow start or congestion avoidance operation is performed. However, since radio errors are not congestion, there is no point in reducing the transmission rate.

  It is known that the TCP throughput (BW) is approximately obtained by the following equation (1). In Equation (1), MSS is the maximum segment size, RTT is Round Trip Time, and p is the packet loss probability.

  From equation (1), it can be seen that reducing the packet loss probability p, that is, the packet error, or reducing the RTT leads to an improvement in TCP throughput.

  With respect to such a problem, in Patent Document 1 below, when a packet loss caused by a radio section error occurs, the receiving side notifies the transmitting side of “radio discard notification” in the TCP layer, and the TCP layer on the transmitting side immediately before A technique for retransmitting a discarded packet by using the transmission rate and the window size that have been held up to is disclosed. Thereby, since the conventional slow start function is not operated, it is possible to avoid a decrease in throughput.

  Further, Non-Patent Documents 1 and 2 below disclose a technique for implementing a retransmission protocol in a wireless section so that packet discard in upper TCP approaches 0. For example, in W-CDMA standardized by 3GPP, retransmission at an RLC (Radio Link Control) layer or a MAC layer is defined.

  In Non-Patent Document 3 below, focusing on the fact that Drop Tail buffer overflow in the FIFO queue results in bursty packet loss, Random, one of Active Queue Management, is a method for avoiding such bursty packet loss. Presents Early Detection / Discard (RED). In RED, packets are randomly discarded when the queue length of the buffer exceeds a certain threshold. As a result, the TCP slow start operation is not caused, so that a significant decrease in throughput can be avoided.

Japanese Patent Laid-Open No. 11-243419

3GPP TS25.322 V6.17.0 2008-12 3GPP TS25.321 V6.12.0 2008-05 IETF RFC2309 April. 1998

  However, in the technique disclosed in Patent Document 1, it is necessary to add a new function to TCP. Therefore, it must be adopted in the standardization of TCP, and even if it is assumed that it is standardized, in order for the function to spread, it is necessary to wait for an update of the standard OS, etc., which takes a very long time. There was a problem.

  Further, according to the techniques of Non-Patent Documents 1 and 2, since the delay is increased by performing retransmission (since the delay affects the TCP throughput), the effect of improving the TCP throughput is sufficient only by repeating the retransmission. There was a problem that it may not be obtained.

  Further, according to the technique of Non-Patent Document 3, there is a problem that if a packet loss due to a radio error is bursty, TCP slow start occurs and TCP throughput decreases. In addition, since random errors due to RED drop cwnd in half, there is a problem that TCP throughput is reduced although it is not as slow as slow start due to burst loss.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a wireless communication method capable of improving TCP throughput.

  In order to solve the above-described problems and achieve the object, the present invention is a wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication as a transmitting station or a receiving station using TCP. The transmission station manages the packet retransmission status for each of the receiving stations, and can increase the delivery probability when recognizing that retransmission of packets to the receiving station has failed continuously for a predetermined number of times. A transmission control step for performing control to transmit a packet so as to satisfy a predetermined condition.

  According to the present invention, it is possible to avoid a significant decrease in TCP throughput.

FIG. 1 is a diagram illustrating a configuration example of a base station according to the first embodiment. FIG. 2 is a diagram illustrating a configuration example of the mobile station according to the first embodiment. FIG. 3 is a flowchart showing the transmission operation of the base station in the first embodiment. FIG. 4 is a diagram illustrating an example of a correspondence relationship between a packet and a radio frame. FIG. 5 is a diagram illustrating a configuration example of a base station in the second embodiment. FIG. 6 is a flowchart showing the transmission operation of the base station in the second embodiment. FIG. 7 is a flowchart showing the transmission operation of the base station in the second embodiment. FIG. 8 is a diagram for explaining the relationship between the queue length of the transmission buffer and the priority state. FIG. 9 is a diagram illustrating an example of a simulation result of throughput with respect to the packet error rate. FIG. 10 is a diagram illustrating the relationship between the congestion window size and the queue length in the transmission buffer. FIG. 11 is a diagram illustrating a configuration example of a base station in the third embodiment. FIG. 12 is a flowchart for explaining a transmission operation of the base station in the third embodiment. FIG. 13 is a diagram illustrating a relationship between a radio error and cnwd. FIG. 14 is a diagram illustrating a configuration example of a base station in the fourth embodiment. FIG. 15 is a flowchart for explaining a transmission operation of the base station in the fourth embodiment. FIG. 16 is a diagram for explaining a delay spike generated in the wireless communication system. FIG. 17 is a diagram illustrating a configuration example of a base station according to the fifth embodiment. FIG. 18 is a flowchart showing the transmission operation of the base station in the fifth embodiment.

  Embodiments of a wireless communication method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a base station according to the present embodiment. A base station 1 in FIG. 1 includes a packet receiving unit 11 that receives a downlink reception packet from a wired section, a transmission buffer 12 that includes a plurality of queues and buffers data for each user, and a transmission buffer 12 according to an instruction of the downlink scheduler 14. A MAC frame 13 that constructs a radio frame from the data in the network, performs MAC retransmission, a downlink scheduler 14 that controls downlink data transmission, an uplink scheduler 15 that controls uplink data transmission, and a MAC unit 13 Receiving a radio frame, transmitting the radio frame as downlink transmission data to a radio section, receiving a reception PHY unit 17 for receiving uplink reception data from the radio line, and receiving uplink reception data from the reception PHY unit 17, Packet construction unit 18 for reconstructing the packet, and upstream transmission packet to the wired section It includes a packet transmission unit 19 for transmitting, the.

  FIG. 2 is a diagram illustrating a configuration example of a mobile station according to the present embodiment. The mobile station 2 in FIG. 2 constructs a radio frame from data in the transmission buffer 21 according to an instruction from the transmission buffer 21 that buffers packets received from the upper layer and the uplink radio resource control unit 23, and performs MAC retransmission. A MAC unit 22 that implements, an uplink radio resource control unit 23 that controls uplink data transmission, a transmission PHY unit 24 that receives a radio frame from the MAC unit 22 and transmits the radio frame as uplink transmission data to a radio section; A reception PHY unit 25 that receives downlink reception data from a radio section, and a packet construction unit 26 that receives downlink reception data from the reception PHY unit 25 and reconstructs a packet.

  As described above, in TCP, when a burst-like packet loss occurs, the throughput decreases significantly compared to when a random packet loss occurs. Burst packet loss due to buffer overflow can be solved by RED, but burst packet loss due to radio error cannot be solved by RED. In order to solve this, the following operation is performed.

  Next, an operation of wireless communication in a wireless communication system including the base station and mobile station configured as described above will be described. Here, only the operations of the base station 1 and the mobile station 2 will be described, but a plurality of mobile stations are connected in an actual wireless communication system.

  First, packet transmission in the downlink direction from the base station 1 to the mobile station 2 will be described. The downlink scheduler 14 of the base station 1 receives downlink radio communication quality information from the mobile station 2 via the reception PHY unit 17, and grasps the downlink radio communication quality based on the information. Further, the transmission buffer 12 notifies the downlink scheduler 14 of the buffer status for each user (mobile station). The downlink scheduler 14 determines a mobile station that performs transmission processing, a modulation method and a coding rate of transmission data, based on the downlink radio channel quality and the buffer state of the transmission buffer 12. Further, the downlink scheduler 14 manages the transmission state by the TCP ACK received via the reception PHY unit 17, manages the MAC retransmission, and controls the MAC unit 13.

  Here, for example, let us consider a case where, in the buffer for the mobile station 2 in the transmission buffer 12, delivery to the mobile station 2 by MAC retransmission fails for N consecutive packets before the leading packet (N Is a natural number). FIG. 3 is a flowchart showing the transmission operation of the base station in the present embodiment. The downlink scheduler 14 manages the retransmission status of each packet for each mobile station when performing MAC retransmission, and when delivery by retransmission fails for consecutive N packets in transmission data to the mobile station 2 (step S1: Yes), it is determined to perform the transmission operation to the mobile station by a method capable of increasing the delivery probability than usual (step S2). On the other hand, the downlink scheduler 14 transmits a continuous N number of packets by a normal method while delivery by retransmission is not failed (step S1: No) (step S3).

  The downlink scheduler 14 specifically takes the following method in order to increase the delivery probability than usual. For example, the downlink scheduler 14 grasps the wireless communication quality based on the received wireless communication quality information, and performs a transmission operation to the mobile station 2 at the MAC unit 13 at a timing with good wireless communication quality for the mobile station 2. Instruct. Further, for example, the downlink scheduler 14 controls the transmission PHY unit 16 to change the modulation scheme and error correction scheme of downlink transmission data to the mobile station 2 to a robust one. For example, the downlink scheduler 14 controls the transmission PHY unit 16 to increase the transmission power of the downlink transmission data to the mobile station 2. Further, for example, the downlink scheduler 14 instructs the MAC unit 13 to increase the upper limit value of the number of retransmissions for performing the MAC retransmission set for the mobile station 2. Further, for example, the downlink scheduler 14 instructs the MAC unit 13 to increase the upper limit value of the execution time for performing the MAC retransmission set for the mobile station 2. One or more arbitrary methods of the above methods are applied to the base station 1 (downlink scheduler 14).

  In the case of a wireless communication system in which a packet and a wireless frame that is a wireless transmission unit do not support 1: 1, the downlink scheduler 14 grasps the correspondence relationship, and the wireless frame (TB: Transport Block, The above-mentioned means are applied to the above. FIG. 4 is a diagram illustrating an example of a correspondence relationship between a packet and a radio frame. FIG. 4 shows IP packets 31, 32, 33, and 34, and TBs 35 and 36. In the example of FIG. 4, two packets correspond to one radio frame. Here, since TCP starts a slow start when four consecutive packet losses occur, a case where N = 2 is set will be described. In the example of FIG. 4, when the retransmission of the TB 35 fails, the IP packets 31 and 32 become packet loss. At this point, since two packets are lost in succession, control is performed to increase the delivery probability. Thereby, if the next packet is successfully delivered, it is possible to avoid a slow start due to the packet loss of the IP packet 33 or 34.

  Next, uplink packet transmission from the mobile station 2 to the base station 1 will be described. The uplink radio resource control unit 23 of the mobile station 2 receives the uplink radio quality information via the reception PHY unit 25, and grasps the uplink radio communication quality based on the information. In addition, the transmission buffer 21 notifies the uplink radio resource control unit 23 of the state of the buffer (data accumulation amount and the like). The uplink radio resource control unit 23 determines the modulation scheme and coding rate of transmission data based on the uplink radio channel quality and the buffer status of the transmission buffer 21. The uplink radio resource control unit 23 manages the transmission state by the TCP ACK received via the reception PHY unit 25, manages the MAC retransmission, and controls the MAC unit 22. Further, the uplink radio resource control unit 23 performs control to transmit uplink allocation request information that is information for requesting the base station 1 to allocate uplink resources.

  The uplink scheduler 15 in the base station 1 receives uplink allocation request information from a plurality of mobile stations via the reception PHY unit 17. The uplink scheduler 15 determines to which mobile station the uplink radio resource is allocated based on the uplink allocation request information, and transmits the uplink allocation information to the mobile station (mobile station 2) via the transmission PHY unit 16.

  When the uplink radio resource control unit 23 of the mobile station 2 receives the uplink allocation instruction information from the base station 1 via the reception PHY unit 25, the uplink radio resource control unit 23 controls the transmission PHY unit 24 to indicate the radio resource indicated by the uplink allocation information. Is used to transmit uplink transmission data.

  Here, the uplink radio resource control unit 23 of the mobile station 2 performs the operation of FIG. 3 as described above. The uplink radio resource control unit 23 manages the retransmission status of each packet when performing MAC retransmission. And the uplink radio | wireless resource control part 23 performs the same process as the above-mentioned, when the delivery by resending fails about M packets (M is a natural number) in the transmission buffer 21. FIG.

  That is, when the uplink radio resource control unit 23 of the mobile station 2 recognizes that the delivery of consecutive M packets has failed (step S1: Yes), the delivery probability can be increased more than usual. It determines with performing the transmission operation | movement to the base station 1 by a method (step S2). On the other hand, the uplink radio resource control unit 23 transmits in a normal manner (step S3) while not recognizing that the delivery of consecutive M packets has failed (step S1: No).

  In the above description, the function of allocating uplink radio resources has been described on the assumption that the uplink scheduler 15 in the base station 1 and the uplink radio resource control unit 23 in the mobile station 2 share the functions. The present invention can be similarly applied to a system in which all functions including the function of the uplink radio resource control unit 23 are unified by the uplink scheduler 15 in the base station 1. In such a system, the uplink radio resource control unit of the mobile station notifies the base station of the state (data accumulation amount) of the transmission buffer of the mobile station, and the base station side based on the uplink radio channel quality and the buffer status. The mobile station transmission data modulation scheme and coding rate are specified.

  In such a system, when the uplink radio resource control unit of the mobile station recognizes that delivery of M consecutive packets has failed, the base station transmits a report to that effect to the base station, and the base station Based on the above, a decision to increase the delivery probability is made, and an instruction to the mobile station for increasing the delivery probability is transmitted. Therefore, the mobile station only executes the instruction content from the base station. The instruction may include a time for continuing the processing for increasing the delivery probability, or the mobile station eliminates the bursty packet error (failed to deliver consecutive M packets). In such a case, the base station may report that fact, and the base station may transmit an instruction to cancel the control for increasing the delivery probability (return to normal control) based on the report.

  In the above embodiment, the case has been described in which the downlink scheduler 14 performs an operation for increasing the downlink delivery probability in the base station 1, and the uplink radio resource control unit 23 performs the operation for increasing the uplink delivery probability in the mobile station 2. However, control for increasing the delivery probability may be performed only for either downlink or uplink.

  As described above, in this embodiment, when the MAC retransmission fails for a predetermined number of packets and the packet cannot be delivered, control is performed to increase the delivery probability of the packet to the transmission destination, and the packet is transmitted. I decided to do it. As a result, burst errors are randomized, that is, when bursty packet errors (or signs) occur, they are collected, reducing the number of bursty packet errors caused by radio errors. It becomes possible. Therefore, it is possible to avoid causing the TCP slow start, to reduce the case where the queue becomes empty, and to avoid a significant decrease in the TCP throughput.

Embodiment 2. FIG.
In the first embodiment, in order to avoid TCP starting slow start due to occurrence of a bursty packet error and cnwd becoming small, when packet retransmission fails continuously, the delivery probability is improved. Therefore, it was decided to achieve TCP throughput. In the present embodiment, a case will be described in which when a packet error occurs, the transmission buffer is monitored and an operation of increasing the delivery probability according to the state of the transmission buffer is performed.

  In TCP, if cnwd is small, the data input rate may decrease and the transmission buffer may become empty. As a result, the radio link is not used up and throughput is reduced. In this embodiment, such a case is assumed.

  FIG. 5 is a diagram illustrating a configuration example of a base station in the present embodiment. The base station 1B of FIG. 5 includes a downlink scheduler 14B instead of the downlink scheduler 14. When the downlink scheduler 14B detects packet discard due to a radio error, the downlink scheduler 14B performs control to increase the packet delivery probability to the corresponding mobile station.

  Next, the operation of the wireless communication method in this embodiment will be described. 6 and 7 are flowcharts showing the transmission operation of the base station in the present embodiment.

  First, it demonstrates along the flowchart of FIG. When the downlink scheduler 14B of the base station 1B detects that packet discard due to a radio error has occurred, for example, for the mobile station 2 (step S11: Yes), it corresponds to the mobile station (mobile station 2) in the transmission buffer 12 The buffer is monitored over Ta time. If the buffer is emptied within Ta time (step S12: Yes), the downlink scheduler 14B determines that the TCP has performed either slow start or congestion avoidance processing, and determines the delivery probability. Control to raise is performed (step S13). The control for increasing the delivery probability is as described above. Hereinafter, a mobile station in a state where the delivery probability is increased is referred to as a priority state. On the other hand, if the buffer is not emptied within Ta time (step S12: No), the downlink scheduler 14B determines that the TCP has not performed either the slow start or the congestion avoidance process, and the process is performed. Exit. Further, when the downlink scheduler 14B does not detect packet discard due to a radio error (step S11: No), the downlink scheduler 14B does not perform any particular processing.

  As a result, the speed at which cnwd is opened in the slow start or congestion avoidance phase is increased, the data inflow rate toward the user (mobile station 2) is increased, and the time during which the buffer is emptied can be shortened.

  Next, a description will be given along the flowchart of FIG. After executing the processing of FIG. 6, the downlink scheduler 14B monitors the buffer corresponding to the mobile station in the transmission buffer 12 in the priority state over the Tb time (step S21). If this buffer has not been emptied until the time Tb elapses (step S21: Yes), the priority state is canceled and the processing performed to increase the delivery probability is returned to the original state. Control for returning to step S22 is performed (step S22). If this buffer becomes empty before the Tb time elapses (step S21: No), the downlink scheduler 14B ends the process and continues the priority state for this mobile station.

  FIG. 8 is a diagram for explaining the relationship between the queue length of the transmission buffer 12 and the priority state. When a packet loss due to a radio error occurs, the TCP enters a slow start or congestion avoidance phase in which cnwd is decreased, so the queue length starts to decrease, and eventually the queue length becomes 0 (FIG. 8: Ta Terminal part). The downlink scheduler 14B urges data to accumulate in the queue by increasing the subsequent delivery probability by the above operation. As shown in the queue length in the transmission buffer in FIG. 8, when it is determined that the data starts to accumulate again in the queue and it is no longer necessary to increase the delivery probability (FIG. 8: end portion of Tb), the downlink scheduler 14B performs the above operation. The mobile station is returned from the priority state to the normal state.

  In the above description, the downlink scheduler 14B in the base station 1 has been described. However, the uplink scheduler 15 in the base station 1 and the uplink radio resource control unit 23 in the mobile station 2 similarly execute the uplink transmission. Is possible.

  As described above, in this embodiment, when packet discard due to a radio error occurs, the transmission buffer for the corresponding mobile station is monitored thereafter, and the buffer becomes empty within a predetermined time. In this case, it is determined that TCP has performed window control (slow start or congestion avoidance), and control is performed to increase the probability of subsequent packet delivery. Further, when the state where the packet is not empty continues for a predetermined time, the control for increasing the delivery probability is canceled and the configuration returns to the normal state.

  As a result, it is possible to reduce the occurrence of a radio error by increasing the delivery probability and to prompt the TCP cnwd to be opened quickly for a mobile station that has poor radio communication quality and has undergone packet discard due to a radio error. By opening cnwd, it is possible to reduce the time that the buffer is empty, improve the transmission rate of the mobile station, and avoid a decrease in TCP throughput. Therefore, it is possible to improve the fairness between mobile stations including mobile stations with poor radio communication quality.

Embodiment 3 FIG.
In the second embodiment, when a packet error occurs, the transmission buffer is monitored, and the TCP throughput is improved by performing the operation of increasing the delivery probability according to the state of the transmission buffer. In the present embodiment, a case will be described in which the packet error rate is controlled by performing control for improving or decreasing the delivery probability based on the buffer overflow frequency.

  FIG. 9 is a diagram illustrating an example of a simulation result of throughput with respect to the packet error rate. The conditions for this simulation are RTT: 30 ms, packet length: 1000 bytes, and buffer size: 100 packets. As seen in FIG. 9, the TCP throughput is greatly improved as the packet error rate is reduced, but is not improved from the point where the link speed is approached. That is, even if the packet error rate is excessively reduced, the throughput reaches its peak. For example, in order to reduce the packet error rate, it is necessary to add a lot of redundant data for error correction, radio resources for performing retransmission, and the like. From this point of view, it is a waste of radio resources to reduce the packet error rate more than necessary.

  The reason why the throughput reaches the limit near the link speed is that the packet loss due to the overflow of the buffer becomes most. FIG. 10 is a diagram illustrating the relationship between the congestion window size and the queue length in the transmission buffer. As shown in FIG. 10, in the example of FIG. 9, the TCP throughput does not stick to the link speed because window control works due to packet loss due to buffer overflow, and data may temporarily disappear in the transmission buffer. is there. In this embodiment, such a situation is assumed.

  FIG. 11 is a diagram illustrating a configuration example of a base station in the present embodiment. The base station 1C in FIG. 11 includes a downlink scheduler 14C instead of the downlink scheduler 14 as compared with the base station 1 in FIG. The downlink scheduler 14C monitors the transmission buffer 12, calculates an average buffer overflow frequency that is a buffer overflow frequency per predetermined unit time for each mobile station, and delivers to the mobile station based on the average buffer overflow frequency. Control to increase the probability. In the present embodiment, a wireless communication system including a base station 1C and a mobile station is assumed.

  Next, operations in the radio communication system configured as described above will be described. FIG. 12 is a flowchart for explaining the transmission operation of the base station in the present embodiment. The downlink scheduler 14C calculates the average buffer overflow frequency as described above, and periodically determines whether or not the value exceeds a predetermined threshold value (step S31). When there is a mobile station whose average buffer overflow frequency exceeds a predetermined threshold (step S31: Yes), the downlink scheduler 14C performs control for increasing the delivery probability to the mobile station (step S32). On the other hand, for mobile stations whose average buffer overflow frequency is less than or equal to a predetermined threshold (step S31: No), in order to avoid that the radio error rate decreases more than necessary and the congestion window becomes too large, the delivery probability is set to Control for lowering is performed (step S33). In addition, it is good also as transmitting by a normal method instead of performing the control which reduces a delivery probability.

  As described above, in the present embodiment, the base station calculates the average buffer overflow frequency, which is the buffer overflow frequency per predetermined unit time, for each mobile station, and the average buffer overflow frequency reaches a predetermined threshold. It was set as the structure which performs control which reduces the delivery probability to the mobile station which exceeds. In addition, the delivery probability for mobile stations whose average buffer overflow frequency is equal to or lower than a predetermined threshold is increased.

  As a result, for users (mobile stations) with a high buffer overflow frequency, the packet error rate is prevented from further decreasing by lowering the delivery probability. For users (mobile stations) with a low buffer overflow frequency, The packet error rate can be lowered by increasing the delivery probability. Therefore, it is possible to obtain the maximum TCP throughput without wasting radio resources.

  In the above embodiment, the control of the downlink scheduler in the base station has been described, but the uplink transmission can be similarly realized by the uplink scheduler in the base station and the radio resource control unit in the mobile station. However, in the case of a system that is centralized in the uplink scheduler in the base station, including the function of the uplink radio resource control unit in the mobile station, the mobile station may cause occurrence of packet loss (buffer overflow) in the base station. It is necessary to notify the scheduler in the station. In this case, the base station makes a determination to increase the delivery probability based on the notification, and transmits an instruction to that effect to the mobile station. Therefore, the mobile station only executes the instruction content from the base station. As described above, the instruction may include a time for continuing the processing for increasing the delivery probability, or when the mobile station reports that the buffer overflow is resolved, the base station Based on the report, an instruction may be transmitted to cancel the control for increasing the delivery probability (return to normal control).

Embodiment 4 FIG.
In the third embodiment, the maximum TCP throughput is obtained by controlling the packet error rate by performing control for improving or decreasing the delivery probability based on the buffer overflow frequency. In the present embodiment, a case will be described in which the wireless error rate is monitored and the delivery probability is controlled based on the wireless error rate.

  FIG. 13 is a diagram illustrating a relationship between a radio error and cnwd. In FIG. 13, when there is no packet loss due to radio error (when there is only packet loss due to buffer overflow), when there is packet loss due to radio error, when RTT is large (solid line), and when RTT is small (broken line) ).

  As shown in FIG. 13, in TCP, there is a phenomenon in which the increase rate of the congestion window decreases as the RTT increases. This is because an increase in the congestion window is performed every time TCP ACK is received, and therefore, as the RTT increases, the cycle of increasing the congestion window becomes longer. As shown in FIG. 13, when there is no packet loss due to radio error (only packet loss due to buffer overflow), although the congestion window increase cycle differs depending on the RTT, the height of the congestion window does not change. There is no big difference in throughput. On the other hand, when there is a packet loss due to a radio error, a radio error often occurs again before cnwd is fully opened, and assuming that the frequency per radio error is constant, the height of the congestion window is The larger the RTT delay, the lower the throughput and the lower the throughput. In this embodiment, such a situation is assumed.

  FIG. 14 is a diagram illustrating a configuration example of a base station in the present embodiment. The base station 1D in FIG. 14 includes a downlink scheduler 14D instead of the downlink scheduler 14 as compared with the base station 1 in FIG. The downlink scheduler 14D manages the transmission status and radio errors based on the TCP ACK received via the reception PHY 17, and calculates an average radio error rate that is a radio error rate per predetermined unit time for each mobile station. Based on the average radio error rate, control for increasing the delivery probability to the mobile station is performed. In the present embodiment, a wireless communication system including a base station 1D and a mobile station (such as mobile station 2) is assumed.

  Next, operations in the radio communication system configured as described above will be described. FIG. 15 is a flowchart for explaining the transmission operation of the base station in the present embodiment. The downlink scheduler 14D calculates the average radio error rate as described above, and periodically determines whether or not the value exceeds a predetermined threshold value (step S41). When there is a mobile station whose average radio error rate exceeds a predetermined threshold (step S41: Yes), the downlink scheduler 14D performs control for increasing the delivery probability to the mobile station (step S42). On the other hand, for a mobile station having an average radio error rate equal to or less than a predetermined threshold (step S41: No), control for reducing the delivery probability is performed (step S43). Note that, instead of reducing the delivery probability, for example, transmission may be performed in a normal state.

  As described above, in this embodiment, the base station calculates an average radio error rate, which is a radio error rate per predetermined unit time, for each mobile station, and the average radio error rate has a predetermined threshold value. It was set as the structure which performs control which raises the delivery probability to the mobile station which exceeds. In addition, the delivery probability for the mobile station whose average radio error rate is equal to or less than a predetermined threshold is reduced.

  As a result, the delay is reduced by increasing the delivery probability for a user (mobile station) with many radio errors, and the delivery probability is lowered for a user (mobile station) with few radio errors. Therefore, it is possible to improve the TCP throughput of a user with many radio errors. In particular, when the user has a large RTT, it can be avoided that the average cwnd becomes too small and the throughput decreases. Although the above method increases the RTT of users who do not have a radio error as a whole, the size of the congestion window does not change when there is no radio error as described above. Has no significant effect.

Embodiment 5 FIG.
In Embodiment 4, the base station calculates, for each mobile station, an average radio error rate that is a radio error rate per predetermined unit time, and performs control to increase the delivery probability based on the average radio error rate Therefore, it was decided to improve the TCP throughput. In the present embodiment, a case will be described in which the RTT delay is smoothed by increasing the delivery probability for a retransmission packet.

  TCP starts a slow start operation when an RTT of a packet becomes larger than an RTO (Retransmission Time Out) timer value. In TCP, the RTO timer value is dynamically optimized according to the RTT of each packet to be measured. However, in a wireless communication system, when a retransmission at a wireless level occurs due to a wireless error, a rapid increase in RTT (spike delay) is caused and RTO occurs. FIG. 16 is a diagram for explaining a delay spike generated in the wireless communication system. FIG. 16 shows that a delay spike occurs where RTT is set to be smaller than the RTO timer value, and RTT exceeds the RTO timer value. In this embodiment, such a case is assumed.

  FIG. 17 is a diagram illustrating a configuration example of a base station according to the present embodiment. Compared with the base station of FIG. 1, the base station of FIG. 17 includes a transmission buffer 12E instead of the transmission buffer 12, and includes a downlink scheduler 14E instead of the downlink scheduler 14. The transmission buffer 12E detects retransmission packets accumulated in its own queue. The downlink scheduler 14E performs control to transmit the retransmission packet by a method for increasing the delivery probability. In the present embodiment, as an example, a wireless communication system including a base station 1E and a mobile station 2 is assumed.

  Next, operations in the radio communication system configured as described above will be described. FIG. 18 is a flowchart showing the transmission operation of the base station in the present embodiment. For example, the transmission buffer 12E notifies the downlink scheduler 14E of whether or not the packet at the head of the queue is a retransmission packet and the queue (or the corresponding mobile station). When the downlink scheduler 14E recognizes that the first packet in the queue is a packet waiting for retransmission based on the notification (step S51: Yes), the downlink scheduler 14E transmits the packet by a method that increases the delivery probability. The PHY unit 16 is controlled (step S52). On the other hand, when the head packet in the queue is not a retransmission waiting packet (step S51: No), the downlink scheduler 14E performs control to transmit by a normal method (step S53). The method for increasing the delivery probability is the same as described above.

  As described above, in this embodiment, when a retransmission waiting packet is transmitted, the packet is transmitted by a method for increasing the delivery probability. As a result, delivery by MAC retransmission can be confirmed quickly, and MAC retransmission can be converged quickly, so that there is an effect of reducing the delay spike and smoothing the delay. Therefore, it is possible to reduce the probability that unnecessary RTO occurs, and to improve TCP throughput.

  In the above embodiment, control of the downlink scheduler in the base station has been described. However, uplink transmission can be similarly realized by the radio resource control unit in the mobile station.

  As described above, the wireless communication method according to the present invention is useful in a wireless communication system, and is particularly suitable for a wireless communication system using TCP.

1, 1B, 1C, 1D, 1E Base station 2 Mobile station 11 Packet receiving unit 12, 12E Transmission buffer 13 MAC unit 14, 14B, 14C, 14D, 14E Downlink scheduler 15 Uplink scheduler 16 Transmission PHY unit 17 Reception PHY unit 18 Packet Construction unit 19 Packet transmission unit 21 Transmission buffer 22 MAC unit 23 Up wireless resource control unit 24 Transmission PHY unit 25 Reception PHY unit 26 Packet construction unit 31-34 IP packet 35, 36 TB

Claims (23)

A wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication as a transmitting station or a receiving station using TCP,
The transmission station manages the packet retransmission status for each of the receiving stations, and is able to increase the delivery probability when recognizing that retransmission of packets to the receiving station has failed continuously for a predetermined number of times. A transmission control step for performing control to transmit a packet so as to satisfy the condition of
A wireless communication method comprising: A wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication using TCP,
When the mobile station recognizes that retransmission of packets to the base station has failed continuously over a predetermined number, a retransmission failure reporting step for reporting the fact to the base station;
When the base station receives the report in the retransmission failure reporting step, it instructs the mobile station to transmit a packet so as to satisfy a predetermined condition that can increase the delivery probability. Steps,
A transmission control step for performing control to transmit a packet to the base station so as to satisfy the predetermined condition when the mobile station receives an instruction in the delivery probability improvement instruction step;
A wireless communication method comprising: A wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication as a transmitting station or a receiving station using TCP,
When the queue length of the transmission buffer corresponding to the receiving station becomes zero before the first time elapses after executing packet discard due to a radio error in the packet received from the receiving station In the transmission, the transmission station determines that it has performed a slow start or congestion avoidance, and performs control to transmit a packet to the reception station so as to satisfy a predetermined condition capable of increasing a delivery probability. Control steps;
When the queue length of the transmission buffer corresponding to the receiving station is not zero over the second time after executing the processing of the transmission control step, the transmitting station transmits a packet with a normal delivery probability. A normal control return step for returning to the transmission control of
A wireless communication method comprising: A wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication as a transmitting station or a receiving station using TCP,
A buffer overflow frequency calculating step for calculating, for each receiving station, an average occurrence frequency of transmission buffer overflow per unit time of the receiving station;
When there is a receiving station whose calculation result exceeds a predetermined threshold, a first transmission control for performing control to transmit a packet to the receiving station so that the transmission station has a low delivery probability Steps,
When there is a receiving station whose calculation result is a predetermined threshold value or less, the transmitting station transmits a packet to the receiving station so as to satisfy a predetermined condition that can increase the delivery probability. A second transmission control step for performing control;
A wireless communication method comprising: A wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication using TCP,
The mobile station calculates an average occurrence frequency of transmission buffer overflow per unit time for the base station, and reports a calculation result to the base station, a buffer overflow frequency reporting step;
When there is a mobile station whose calculation result exceeds a predetermined threshold in the buffer overflow frequency reporting step, the base station instructs the mobile station to perform transmission so that the delivery probability is low. A delivery probability reduction instruction step;
When there is a mobile station whose calculation result is equal to or less than a predetermined threshold in the buffer overflow frequency reporting step, the base station satisfies a predetermined condition that can increase the delivery probability for the mobile station. A delivery probability improvement instruction step for instructing to perform transmission,
A first transmission control step for performing control to transmit a packet to the base station so that a delivery probability is low when the mobile station receives an instruction in the delivery probability reduction instruction step;
When the mobile station receives an instruction in the delivery probability improvement instruction step, second control is performed to transmit a packet to the base station so as to satisfy a predetermined condition capable of increasing the delivery probability. A transmission control step of
A wireless communication method comprising: A communication method in a wireless communication system in which a base station and a mobile station perform wireless communication using TCP,
A radio error rate calculating step for calculating, for each mobile station, a probability of radio error occurring per unit time in a packet received from a mobile station operating as a receiving station by a base station operating as a transmitting station;
When there is a mobile station for which the calculation result exceeds a predetermined threshold, the base station performs control to transmit a packet to the mobile station so that the delivery probability is low. Steps,
When there is a mobile station whose calculation result is equal to or less than a predetermined threshold, the base station transmits a packet to the mobile station so as to satisfy a predetermined condition that can increase the delivery probability. A second transmission control step for performing control;
A wireless communication method comprising: A wireless communication method in a wireless communication system in which a base station and a mobile station perform wireless communication as a transmitting station or a receiving station using TCP,
When the transmitting station monitors the transmission buffer of the receiving station and detects a packet waiting for retransmission, control for transmitting the packet to the receiving station so as to satisfy a predetermined condition capable of increasing the delivery probability Performing transmission control step,
A wireless communication method comprising: The predetermined condition is
Transmitting the packet at a timing when the transmitting station determines that the radio channel quality for the receiving station is good;
Changing the modulation method or error correction method for packet transmission to the receiving station to a highly robust method;
Increasing transmission power required for transmission of packets to the receiving station;
Increasing the number of retransmissions, which is the number of retransmissions to the receiving station,
Increasing the upper limit of the execution time for performing retransmission to the receiving station;
At least one of
The wireless communication method according to claim 1, wherein the wireless communication method is a wireless communication method. The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
The packet retransmission status is managed for each mobile station, and when it is recognized that the packet retransmission to the mobile station has failed continuously over a predetermined number, the predetermined condition that can increase the delivery probability is satisfied. A downlink scheduler that controls transmission of packets,
A base station comprising: The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
When the queue length of the transmission buffer corresponding to the mobile station becomes zero after the packet is discarded due to a radio error in the packet received from the mobile station until the first time elapses Determines that a slow start or congestion avoidance has been performed, performs control to transmit a packet to the mobile station so as to satisfy a predetermined condition that can increase the delivery probability, and then When the queue length of the transmission buffer corresponding to the mobile station becomes non-zero over time, a downlink scheduler that returns to the transmission control of the packet with a normal delivery probability for the mobile station,
A base station comprising: The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
The average occurrence frequency of the transmission buffer overflow per unit time of the mobile station is calculated for each mobile station, and if there is a mobile station whose calculation result exceeds a predetermined threshold, the delivery probability is lowered. , Perform control to transmit a packet to the mobile station. On the other hand, if there is a mobile station whose calculation result is a predetermined threshold value or less, satisfy a predetermined condition that can increase the delivery probability. A downlink scheduler for controlling transmission of packets to the mobile station,
A base station comprising: The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
The probability of a radio error occurring per unit time in a packet received from the mobile station is calculated for each mobile station, and if there is a mobile station whose calculation result exceeds a predetermined threshold, the delivery probability is low. In such a case, control is performed to transmit a packet to the mobile station. On the other hand, if there is a mobile station whose calculation result is a predetermined threshold or less, a predetermined condition that can increase the delivery probability A downlink scheduler that performs control to transmit a packet to the mobile station so as to satisfy
A base station comprising: The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
When the transmission buffer of the mobile station is monitored and a packet waiting to be retransmitted is detected, control is performed to transmit a packet to the mobile station so that a predetermined condition that can increase the delivery probability is satisfied. Scheduler,
A base station comprising: The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
When the mobile station is informed that retransmission of packets to its own station has failed continuously over a predetermined number, the packet is set so as to satisfy a predetermined condition that can increase the delivery probability for the mobile station. An uplink scheduler that directs to transmit,
A base station comprising: The base station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
When receiving the average occurrence frequency of transmission buffer overflow per unit time for the own station from the mobile station, it is determined whether the average occurrence frequency exceeds a predetermined threshold, and if it exceeds a predetermined threshold, The mobile station is instructed to perform transmission so that the delivery probability is low, and if it is equal to or lower than a predetermined threshold, the mobile station is given a predetermined condition that can increase the delivery probability. An uplink scheduler that directs transmission to satisfy,
A base station comprising: The predetermined condition is
Transmitting a packet at a timing when it is determined that the radio channel quality for the mobile station is good;
Changing the modulation scheme or error correction scheme for packet transmission to the mobile station to a robust scheme;
Increasing transmission power required for transmission of packets to the mobile station;
Increasing the number of retransmissions, which is the number of retransmissions to the mobile station,
Increasing the upper limit of the execution time for performing retransmission to the mobile station,
At least one of
The base station according to any one of claims 9 to 15. The mobile station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
To manage the retransmission status of packets to the base station and satisfy a predetermined condition capable of increasing the delivery probability when recognizing that retransmission of packets to the base station has failed continuously over a predetermined number , An uplink scheduler for controlling transmission of packets,
A mobile station comprising: The mobile station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
When it is recognized that the retransmission of packets to the base station has failed continuously over a predetermined number, the fact is reported to the base station, and the delivery probability is increased based on an instruction from the base station. An uplink scheduler that performs control to transmit a packet to the base station so as to satisfy a predetermined condition that can be
A mobile station comprising: The mobile station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
When the queue length of the transmission buffer corresponding to the base station becomes zero after the first time elapses after the packet discard due to a radio error in the packet received from the base station Determines that a slow start or congestion avoidance has been performed, performs control to transmit a packet to the base station so as to satisfy a predetermined condition capable of increasing the delivery probability, and then performs a second operation. When the queue length of the transmission buffer corresponding to the base station becomes non-zero over time, an uplink scheduler that returns to packet transmission control with a normal delivery probability,
A mobile station comprising: The mobile station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
The average occurrence frequency of the transmission buffer overflow per unit time for the base station is calculated, and when the calculation result exceeds a predetermined threshold, packets are transmitted to the base station so that the delivery probability is low. In addition, when the calculation result is equal to or less than a predetermined threshold, control is performed to transmit a packet to the base station so as to satisfy a predetermined condition that can increase the delivery probability. Perform uplink scheduler,
A mobile station comprising: The mobile station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
It is possible to calculate the average occurrence frequency of transmission buffer overflow per unit time for the base station, report the calculation result to the base station, and increase the delivery probability based on an instruction from the base station An uplink scheduler that performs control to transmit a packet to the base station so that a predetermined condition is satisfied,
A mobile station comprising: The mobile station in a wireless communication system in which a base station and one or more mobile stations perform wireless communication using TCP,
The transmission buffer for the base station is monitored, and when a packet waiting for retransmission is detected, control is performed to transmit a packet to the base station so as to satisfy a predetermined condition capable of increasing a delivery probability. Scheduler,
A mobile station comprising: The predetermined condition is
Transmitting a packet at a timing when it is determined that the radio channel quality for the mobile station is good;
Changing the modulation scheme or error correction scheme for packet transmission to the mobile station to a robust scheme;
Increasing transmission power required for transmission of packets to the mobile station;
Increasing the number of retransmissions, which is the number of retransmissions to the mobile station,
Increasing the upper limit of the execution time for performing retransmission to the mobile station,
At least one of
The mobile station according to any one of claims 17 to 22.

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