JP3953343B2 - Wireless packet communication device and wireless packet communication method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless packet communication device and a wireless packet communication method, and more particularly to a wireless packet communication device and a wireless packet communication method connected to an IP network.
[0002]
[Prior art]
In recent years, data communication with an IP network via a wireless communication line has been actively performed. FIG. These are figures which show an example of a structure of an IP network and a radio | wireless communications system. FIG. 1, when performing data communication with the fixed terminal 6 or the server 5, the wireless terminal 3 first transmits / receives data to / from the base station 2 through a wireless link, and further, the IP network in which the base station 2 is configured by a wired network. 1, data communication is performed with the fixed terminal 6 and the server 5.
[0003]
Generally, the fixed terminal 6 and the server 5 connected to the IP network 1 have a fourth layer (transport) of an OSI (Open System Interconnection) reference model in order to guarantee high reliability of end-to-end data transmission. TCP corresponding to the layer) is mounted. TCP is a protocol having functions such as flow control and retransmission control for controlling the transmission amount of data. Flow control can be realized by increasing or decreasing the window size indicating the number of TCP segments (data transmission units in TCP) that can be transmitted simultaneously.
[0004]
FIG. These are the figures for demonstrating the flow control in TCP mounted in the radio | wireless terminal 3, the fixed terminal 6, or the server 5. FIG. Here, the flow control will be described with the fixed terminal 6 as the transmission side TCP 10 and the wireless terminal 3 as the reception side TCP 11.
[0005]
The transmission-side TCP 10 (fixed terminal 6) can perform flow control by increasing / decreasing the number of TCP segments to be transmitted at the same time, and can increase transmission efficiency. In other words, the transmission side TCP 10 (fixed terminal 6) increases or decreases cwnd (Congestion WiNDow) 12, which is a transmission window indicating the amount of data that can be transmitted simultaneously, in units of the size of the TCP segment according to the congestion state of the network. Flow control.
[0006]
Specifically, the transmission side TCP 10 (fixed terminal 6) starts communication with the size of cwnd 12 as 1, and receives an ACK segment, which is a reception confirmation response corresponding to the transmitted TCP segment, from the reception side TCP 11 (wireless terminal 3). When received, cwnd12 is increased exponentially until the size of cwnd12 reaches a predetermined threshold (slow start mode). Then, after cwnd12 reaches a predetermined threshold value, cwnd12 is increased linearly (congestion avoidance mode). In this congestion avoidance mode, when the ACK segment having the same sequence number is received repeatedly, the transmission side TCP 10 (fixed terminal 6) determines that the network is in a light congestion state, and reduces cwnd12 to a predetermined threshold value. . If the ACK segment is not received within a predetermined time (retransmission timeout), the size of cwnd12 is set to 1.
[0007]
On the other hand, the reception side TCP 11 (wireless terminal 3) always reports an award (Advertised WiNDow) 13 indicating the number of receivable TCP segments to the transmission side TCP 10 (fixed terminal 6). The transmission-side TCP 10 (fixed terminal 6) increases / decreases cwnd12 as described above, compares cwnd12 with awnd13, and transmits the TCP segment with the smaller window size. That is, FIG. In FIG. 3, since the size of cwnd12 is 3 and the size of awnd13 is 5, three TCP segments 14 are simultaneously transmitted from the transmission side TCP 10 (fixed terminal 6).
[0008]
In this way, data transmission that makes the most of the available bandwidth between connections can be performed, and the number of TCP segments that exceed the processing capacity of the receiving side can be obtained by considering the receiving side window size. It is possible to prevent transmission, and it is possible to prevent the received TCP segment from being discarded due to insufficient buffer capacity on the receiving side.
[0009]
However, when a wireless link is included between the transmission side TCP 10 (fixed terminal 6) and the reception side TCP 11 (wireless terminal 3) as described above, the wireless link has a higher error rate than the wired link. The cwnd 12 may be reduced even for packet discards caused by transmission errors on the wireless link that occur regardless of network congestion. That is, the receiving TCP 11 (wireless terminal 3) is discarded when there are many transmission errors in the received TCP segment, and transmits the ACK segment for the previously received TCP segment without transmitting the ACK segment for the TCP segment. The transmitting TCP 10 (fixed terminal 6) receives the ACK segment redundantly, and decreases cwnd12 to a predetermined threshold value.
[0010]
Further, in order to reduce transmission errors in the radio link (that is, the link between the radio terminal 3 and the base station 2), retransmission processing between the radio links is generally performed. As a result of retransmission, the effective radio link bandwidth decreases, the number of packets waiting to be transmitted increases, and the TCP segment may be discarded in the buffer of the base station 2, which is the transmission buffer of the radio link.
[0011]
In response to such a decrease in throughput due to a transmission error peculiar to a wireless link unrelated to network congestion, the technique disclosed in Japanese Patent Laid-Open No. 2001-136209 is based on a signal transmitted from a communication destination. End-to-end in case of packet loss in the radio link by identifying the cause of discard of the packet transmitted by the device, and in the case of packet loss due to transmission error of the radio link, by reducing the window size reduction width The throughput drop has been improved.
[0012]
[Problems to be solved by the invention]
However, in the method for identifying the cause of packet discard as described above, it is necessary to change not only the device connected to the wireless link but also the TCP of the fixed terminal or server connected to the IP network. In view of the widespread use of networks and fixed terminals and servers connected thereto, there is a problem that it is difficult to realize a reduction in throughput by this method. In addition, there is a problem that packets are still discarded in the buffer of the base station apparatus when there is an effective change in the radio link band due to retransmission processing between the radio links.
[0013]
The present invention has been made in view of such points, and provides a wireless packet communication device and a wireless packet communication method capable of improving throughput in a network including a wireless link without changing the configuration of the IP network. With the goal.
[0014]
[Means for Solving the Problems]
The wireless packet communication device according to the present invention includes a determination unit that determines a maximum amount of packets that can be received based on information indicating a packet amount that is allowed to be transmitted in wireless communication, and a determined maximum amount of receivable packets. Transmitting means for transmitting information including, And the determination means includes: a reception unit that receives a packet; a calculation unit that calculates a frame error rate of the received packet; a control unit that controls a wireless band used for wireless communication; and a calculated frame error An estimation unit for estimating a maximum buffer capacity that can be used to store the received packet from a rate and a controlled radio band, and subtracting the buffer capacity in use from the estimated maximum buffer capacity Determine the maximum amount of packets that can be received Take the configuration.
[0015]
According to this configuration, a fixed terminal or server connected to the IP network is used to determine and report the maximum amount of receivable packets based on information indicating the amount of packets allowed to be transmitted in wireless communication. The source of a packet such as a packet can transmit a quantity of packets that can be transmitted in consideration of retransmissions and transmission errors that occur in the wireless link, and can prevent packet discarding that occurs in the wireless link, and change the configuration of the IP network In addition, the throughput in a network including a wireless link can be improved.
[0020]
The radio packet communication apparatus of the present invention employs a configuration in which the estimation unit estimates a maximum buffer capacity every time a radio band used by the control unit is changed.
[0021]
According to this configuration, since the maximum buffer capacity is estimated every time the radio band is changed, packet discarding can be prevented even when the effective radio link band fluctuates by performing retransmission processing between radio links. It is possible to improve throughput in a network including a wireless link without changing the configuration of the IP network.
[0044]
The wireless packet communication method of the present invention includes: Receiving a packet; calculating a frame error rate of the received packet; controlling a radio band used for radio communication; calculating the frame error rate; and receiving from the controlled radio band Estimating the maximum buffer capacity that can be used to store packets, and subtracting the buffer capacity in use from the estimated maximum buffer capacity A step of determining a maximum amount of receivable packets and a step of transmitting information including the determined maximum amount of receivable packets.
[0045]
According to this method, a fixed terminal or server connected to the IP network is used to determine and report the maximum amount of receivable packets based on information indicating the amount of packets allowed to be transmitted in wireless communication. The source of a packet such as a packet can transmit a quantity of packets that can be transmitted in consideration of retransmissions and transmission errors that occur in the wireless link, and can prevent packet discarding that occurs in the wireless link, and change the configuration of the IP network In addition, the throughput in a network including a wireless link can be improved.
[0046]
DETAILED DESCRIPTION OF THE INVENTION
The gist of the present invention is to notify information relating to the state of the radio link to TCP, which is a transport protocol, and to perform flow control using the information.
[0047]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0048]
(Embodiment 1)
FIG. 1 is a diagram showing configurations of radio communication terminal apparatus 100 and base station apparatus 200 according to Embodiment 1 of the present invention. The radio communication terminal apparatus 100 includes an application unit 110, a TCP control unit 120, an IP control unit 130, a retransmission control unit 140, a radio transmission / reception unit 150, a radio resource control unit 160, a frame error rate estimation unit 170, and an and estimation unit 180. Have. The application unit 110 creates transmission data and performs predetermined processing on the received data. The TCP control unit 120 divides transmission data into a predetermined size and adds a TCP header such as a transmission source port, a destination port, and a sequence number to generate a TCP segment. Further, the TCP control unit 120 adds a receivable andd obtained by subtracting the buffer amount actually used from the maximum awnd estimated by the awn estimating unit 180 to the TCP segment header unit. Here, the receivable andd indicates the maximum amount of packets that can be transmitted simultaneously from a packet transmission source such as a fixed terminal or a server.
[0049]
The IP control unit 130 generates an IP packet by adding an IP header such as a transmission source IP address and a destination IP address to the TCP segment. The retransmission control unit 140 divides the IP packet into a predetermined PDU (Protocol Data Unit) size and adds a PDU header. In addition, retransmission control section 140 performs error detection on the received PDU packet. The radio transmission / reception unit 150 performs predetermined radio processing such as encoding / modulation on the PDU packet, and transmits the PDU packet via the antenna.
[0050]
The radio resource control unit 160 controls the retransmission control unit 140 and the radio transmission / reception unit 150 and notifies the awn estimation unit 180 of information on the used radio band. The frame error rate estimation unit 170 estimates a frame error rate from the error detection result. The awn estimation unit 180 estimates the maximum awnd, which is the maximum buffer capacity that can be used to store a packet, from the radio band information and the frame error rate.
[0051]
On the other hand, the base station apparatus 200 includes a radio transmission / reception unit 210, a retransmission control unit 220, a transmission buffer 230, an IP control unit 240, a link layer control unit 250, and a radio resource control unit 260. The wireless transmission / reception unit 210 performs predetermined wireless processing such as demodulation and decoding on the wireless packet received via the antenna. The retransmission control unit 220 generates an IP packet from a predetermined number of PDU packets received by the wireless transmission / reception unit 210. The transmission buffer 230 temporarily stores an IP packet to be transmitted when transmitting a packet to the wireless communication terminal device 100. The IP control unit 240 links the IP packet output from the retransmission control unit 220 to a transfer destination (for example, a fixed terminal connected to an IP network) designated by an IP address by a predetermined routing protocol. 250. The radio resource control unit 260 controls the radio transmission / reception unit 210 and the retransmission control unit 220.
[0052]
Next, operations of radio communication terminal apparatus 100 and base station apparatus 200 configured as described above will be described. Here, an operation from when wireless communication terminal apparatus 100 receives a downlink PDU packet until a fixed terminal (not shown) transmits data to wireless communication terminal apparatus 100 will be described.
[0053]
First, at the time of receiving operation, the PDU packet is received by the radio transmission / reception unit 150 via the antenna, and predetermined radio processing such as demodulation is performed. Then, the PDU packet after the radio processing is output to the retransmission control unit 140, and error detection is performed by using a CRC (Cyclic Redundancy Check) added to the PDU packet. Further, the retransmission control unit 140 assembles an IP packet from a predetermined number of PDU packets, the IP control unit 130 generates a TCP segment from the IP packet, the TCP control unit 120 obtains received data from the TCP segment, The obtained data is processed by the application unit 110.
[0054]
In addition, the retransmission control unit 140 outputs an error detection result to the frame error rate estimation unit 170, and the frame error rate estimation unit 170 calculates an average frame error ratio (FER: Frame Error Ratio) for a predetermined time from the error detection result. Presumed. The estimated FER is output to the awn estimation unit 180.
[0055]
On the other hand, the radio resource control unit 160 notifies the awn estimation unit 180 of the currently used radio band.
[0056]
Then, the awn estimation unit 180 estimates the maximum awnd that is the maximum buffer capacity that can be processed by the radio communication terminal device 100 based on the FER and the radio band. The maximum awdd estimated at this time is the maximum window size that can be processed by the wireless communication terminal device 100 and is based on the FER and the wireless band. The window size can be used in consideration of fluctuations. The estimated maximum awnd is notified to the TCP control unit 120.
[0057]
Next, at the time of transmission operation, transmission data is generated by the application unit 110, and the generated transmission data is divided into a predetermined size by the TCP control unit 120, and TCP headers such as a transmission source port, a destination port, and a sequence number Is added to generate a TCP segment. Further, the TCP control unit 120 reduces the buffer capacity in which the TCP segment actually received from the maximum and notified from the awn estimation unit 180 is reduced, so that the receivable andd that can be used is a usable buffer capacity. Calculated. Here, the generated TCP segment has, for example, a data field as shown in FIG. 2, and the calculated receivable andd is recorded in the window field.
[0058]
Then, an IP header such as a source IP address and a destination IP address is added to the TCP segment by the IP control unit 130, and the obtained IP packet is divided into PDU sizes by the retransmission control unit 140, and is transmitted by the wireless transmission / reception unit 150. Sent via antenna.
[0059]
The transmitted PDU packet is received by the radio transmission / reception unit 210 via the antenna of the base station apparatus 200, and predetermined radio processing such as demodulation and decoding is performed. These processes are controlled by the radio resource control unit 260. Then, when the retransmission control unit 220 is controlled by the radio resource control unit 260, an IP packet is generated from the PDU packet, and the IP control unit 240 connects to the transfer destination (for example, connected to the IP network) specified by the IP address. To the fixed terminal) via the link layer control unit 250. The IP packet sent to the IP network is received by, for example, a fixed terminal (not shown).
[0060]
On the other hand, when data is transmitted from a fixed terminal (not shown) to the wireless communication terminal apparatus 100, first, the receivable and of the wireless communication terminal apparatus 100 is acquired from the TCP segment included in the received IP packet. Then, cwnd, which is a transmission buffer capacity of a fixed terminal (not shown) that increases or decreases depending on the congestion state of the network, is compared with the acquired receivable andd, and a TCP segment having a smaller window size is transmitted.
[0061]
The sent TCP segment is received by the wireless communication terminal device 100 via the base station device 200. At this time, the fixed terminal (not shown) does not simultaneously transmit a TCP segment that is reported from the wireless communication terminal device 100 and exceeds the window size in consideration of the state of the wireless link. For example, the state of the wireless link is inferior, Even when many retransmission packets are transmitted from the base station apparatus 200 to the radio communication terminal apparatus 100, a number of TCP segments exceeding the capacity of the transmission buffer 230 of the base station apparatus 200 are transmitted from a fixed terminal (not shown). TCP segment is not discarded. Therefore, packet discarding in the buffer of the base station apparatus 200 due to radio link fluctuation does not occur, so that an ACK segment is always transmitted normally to a fixed terminal (not shown), and cwnd in the fixed terminal is reduced regardless of congestion. There is nothing to do.
[0062]
Thus, according to the present embodiment, the receivable and in the wireless communication terminal device is estimated based on the wireless band and the frame error rate between the wireless links, and the fixed terminal connected to the IP network on the transmission side Since the packet is not discarded in the base station apparatus and the IP network configuration is not changed, the throughput in the network including the wireless link can be improved.
[0063]
In the present embodiment, the maximum awn is estimated when the radio link is set up. That is, when the wireless communication terminal device shifts from the idle state to the communication state, negotiation is performed between the base station device and the wireless communication terminal device, the wireless link band to be used is determined, and from the determined wireless link band A maximum awn is estimated.
[0064]
Further, when the radio link band is changed during the communication state, it is possible to reset the maximum andd based on the radio link band changed at that timing.
[0065]
Further, in the present embodiment, the receivable and is recorded in the window field of the TCP header of the TCP segment transmitted from the wireless communication terminal device. For example, the wireless communication terminal device receives from the fixed terminal. It may be recorded in the ACK segment for the TCP segment, and may be recorded and notified in a part of data transmitted from the wireless communication terminal apparatus to the packet transmission source.
[0097]
(Embodiment 4)
The feature of the fourth embodiment of the present invention is that when a wireless communication terminal device is about to be handed over, it reports “awn” as 0, and the fixed terminal or server that is the transmission source of the TCP segment temporarily stops the transmission of the TCP segment. Is a point.
[0098]
The configurations of the radio communication terminal apparatus and the base station apparatus according to the present embodiment are the same as those of radio communication terminal apparatus 100 and base station apparatus 200 shown in FIG.
[0099]
Next, regarding operations of radio communication terminal apparatus 100, base station apparatus 200, and fixed terminal (not shown) according to the present embodiment, FIG. It demonstrates using the sequence diagram shown in FIG.
[0100]
First, during normal communication, a TCP segment is transmitted from the fixed terminal to the base station apparatus 200, and is buffered in the transmission buffer 230 of the base station apparatus 200. Has been sent to.
[0101]
On the other hand, in wireless communication terminal apparatus 100, the reception power and reception quality of the common pilot channel transmitted from a plurality of base station apparatuses including base station apparatus 200 are measured by wireless transmission / reception section 150. The measurement result is notified to the radio resource control unit 160, and it is determined whether or not the prior handover sequence activation is requested by comparing the reception power and reception quality of pilot signals from a plurality of base station apparatuses. Here, the pre-handover sequence is, for example, a threshold value in soft handover, and is a trigger for starting a preparatory operation when the wireless communication terminal apparatus performs handover.
[0102]
When it is determined to request advance handover sequence activation, the radio resource control unit 160 notifies the retransmission control unit 140 of the determination result, and the retransmission control unit 140 transmits a signal to request advance handover sequence activation. The obtained transmission data is transmitted from the wireless transmission / reception unit 150 to the base station apparatus 200 via the antenna.
[0103]
The transmission data is received via the antenna by the radio transmission / reception unit 210 of the base station apparatus 200 and is output to the radio resource control unit 260 via the retransmission control unit 220. If the radio resource control unit 260 negotiates with a control station (not shown) or the like and a handover is possible, the time t ₁ , A pre-handover sequence is started, and a handover trigger signal indicating that a handover is about to be performed is transmitted from the wireless transmission / reception unit 210 via the antenna.
[0104]
The handover trigger signal is received by the radio transmission / reception unit 150 of the radio communication terminal apparatus 100 via the antenna, and is output to the radio resource control unit 160 via the retransmission control unit 140. When a handover trigger signal is output to radio resource control section 160, a signal indicating that a handover is to be performed is output to awn estimation section 180, and a receivable awnd is set to 0 by and estimation section 180, as in the first embodiment. The receivable and is reported to a fixed terminal (not shown).
[0105]
Then, the fixed terminal (not shown) stops the transmission of the TCP segment, and the base station apparatus 200 transmits the TCP segment buffered in the transmission buffer 230. As a result, the TCP segment buffered in the transmission buffer 230 of the base station apparatus 200 that is the handover source is transmitted before the radio communication terminal apparatus 100 is handed over, and an ACK for each TCP segment is not shown. Sent to. Therefore, it is possible to prevent the TCP segment that has been buffered in the transmission buffer 230 from being discarded after the radio communication terminal apparatus 100 is handed over, and to be handed over despite the arrival of the TCP segment to the base station apparatus 200. Accordingly, it is possible to prevent the base station apparatus 200 from discarding the packet and not transmitting the ACK to a fixed terminal (not shown). Therefore, it is possible to prevent a retransmission timeout from occurring at a fixed terminal (not shown) and reduce cwnd, and as a result, the transmission window size of the TCP segment from the fixed terminal (not shown) even after the radio communication terminal apparatus 100 is handed over. Will not decrease due to handover.
[0106]
Then, in the wireless communication terminal apparatus 100, similarly to the determination of whether or not there is a request for starting a prior handover sequence, a request for starting a handover sequence is made by comparing the received power and reception quality of pilot signals from a plurality of base station apparatuses. If it is determined whether or not to make a request, a signal for requesting activation of the handover sequence is multiplexed with the data and transmitted to the base station apparatus 200.
[0107]
The base station apparatus 200 receives the time t ₂ Start the handover sequence at time t _Three , The wireless communication terminal device 100 switches the communication partner from the base station device 200 to another base station device, so that the handover is performed.
[0108]
When the handover is completed, the radio resource control unit 160 of the radio communication terminal apparatus 100 outputs a signal indicating that the handover is completed to the awn estimation unit 180, and the awnd estimation unit 180 estimates based on the FER and the radio band. The maximum awnd to be output starts to be output to the TCP control unit 120. At this time, the maximum awnd output from the awn estimation unit 180 may have been estimated before the handover.
[0109]
Thereafter, as in the first embodiment, the receivable and is calculated, added to the TCP segment header, and reported to the fixed terminal (not shown) via the handover destination base station apparatus. When a receivable and is reported, the fixed terminal (not shown) resumes the transmission of the stopped TCP segment and starts transmitting the TCP segment to the wireless communication terminal device 100 via the handover destination base station device.
[0110]
As described above, according to the present embodiment, when the radio communication terminal apparatus is likely to be handed over, the receivable and is set to 0 and notified to the fixed terminal or server on the transmission side, and after the radio communication terminal apparatus completes the handover. In order to start notifying the receivable awn estimated again, the fixed terminal or server on the transmission side can stop the packet transmission immediately before the handover, and can resume the packet transmission after the handover is completed, thereby reducing cwnd. Thus, the packet transmission can be efficiently resumed even after the handover is completed.
[0111]
In each of the above embodiments, the wireless communication terminal device estimates the maximum awnd and transmits a receivable andd based on the estimated maximum awn. However, the application unit, the TCP control unit, and the IP control unit For example, a communication device such as a wireless communication card is configured to be attached to and detached from an information terminal device such as a computer, and the communication device estimates a maximum awnd and notifies the information terminal device of the estimated maximum awnd. The information terminal device may operate using the notified maximum and, and the communication device may transmit the calculated receivable and.
[0112]
【The invention's effect】
As described above, according to the present invention, it is possible to improve throughput in a network including a wireless link without changing the configuration of the IP network.
[Brief description of the drawings]
FIG. 1 is a block diagram showing configurations of a radio communication terminal apparatus and a base station apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing an example of a data field of a TCP segment according to the first embodiment
FIG. 3 is a sequence diagram showing operations of a radio communication terminal apparatus, a base station apparatus, and a fixed terminal according to Embodiment 4 of the present invention.
FIG. 4 is a diagram showing an example of the configuration of a conventional IP network and a wireless communication system
FIG. 5 is a diagram for explaining flow control in the conventional transmission side TCP and reception side TCP;

Claims (3)

Determining means for determining a maximum amount of receivable packets based on information indicating a packet amount allowed to be transmitted in wireless communication;
Transmission means for transmitting information including the determined maximum receivable packet amount ,
The determining means includes
A receiver for receiving the packet;
A calculation unit for calculating a frame error rate of the received packet;
A control unit that controls a wireless band used for wireless communication;
An estimated unit that estimates a calculated frame error rate and a maximum buffer capacity that can be used to store the received packet from a controlled radio band; and
Wireless packet communication apparatus characterized by determining a receivable packet maximum amount by subtracting the buffer capacity in use from the estimated maximum buffer capacity. The estimation unit includes
2. The wireless packet communication apparatus according to claim 1 , wherein a maximum buffer capacity is estimated every time a wireless band used by the control unit is changed. Receiving a packet;
Calculating a frame error rate of the received packet;
Controlling a radio band used for radio communication;
Estimating a maximum buffer capacity that can be used to store the received packet from the calculated frame error rate and a controlled radio band;
Determining the maximum amount of packets that can be received by subtracting the buffer capacity in use from the estimated maximum buffer capacity ;
Transmitting information including the determined maximum amount of receivable packets;
A wireless packet communication method comprising:

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