JP2001333097A - Wireless communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless communication equipment that can attain a scheduling system at a low cost and early avoid congestion caused by deterioration in the channel quality. SOLUTION: The wireless communication unit H of this invention is provided with a channel quality reception section 12 that receives channel quality information sent from a wireless terminal 11 provided with a channel quality transmission section sending the channel quality of wireless communication, a channel quality management table 13 that stores the information received by the channel quality reception section 12, a packet classification section 14 that classifies arrived packets, a transmission buffer 15 that generates a queue by each packet destination host, and scheduling means 17, 18 that generate a transmission schedule sending the packets to each wireless terminal on the basis of the channel quality information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication apparatus, and more particularly, to a radio communication apparatus using a low-cost and high-speed scheduling method in consideration of radio channel quality.

[0002]

2. Description of the Related Art Conventionally, in wireless communication, compared to wired communication, there are problems specific to the wireless environment, such as fluctuations in line capacity and error ratio, and restrictions on frequency resources. For this reason, several management techniques and techniques for providing service quality for effectively utilizing resources in wireless communication have been proposed as conventional techniques.

[0003] S. Lu, V. Bharghavan and ACM SIGCOMM '97, published in August 1997
Fair Scheduling in Wireless Pack by R. Srikant
et Networks "and ACM MOBI issued in October 1999
`` Unified Architecture for the Design and Evaluati '' by T. Nandagopal, S. Luand V. Bharghavan of COM'99
on of Wireless Fair Queuing Algorithms. In these papers, as a means of providing service quality in a wireless network, a channel state dependent scheduling algorithm is proposed in which terminals with poor channel conditions wait until the channel conditions become better. They also have the function of compensating for service unfairness caused by waiting for terminals with poor channel conditions.

[0004]

However, the method of the existing technology is expensive, and the function of avoiding congestion caused by not transmitting a flow having a bad channel state is not realized. In the prior art, a scheduling algorithm model for fairly transmitting packets in a wireless environment has been proposed, but the line state is inaccurate because the line state is estimated using the characteristics of the wireless link that errors occur in bursts. is there.

[0005] Further, no specific method has been proposed for obtaining a line state in a downlink flow from a radio base station to a radio terminal. In the prior art, for a flow that cannot be sent due to a poor line condition, a fair distribution of resources is aimed at by compensating for service unfairness after the line condition is restored, but it is expensive.

The prior art proposes not to transmit a flow with poor line quality without scheduling it. However, if the flow is not transmitted, congestion will occur, and a buffer for a flow with good line quality cannot be secured. . SUMMARY OF THE INVENTION An object of the present invention is to provide a wireless communication apparatus that secures a communication capacity in consideration of channel quality for the purpose of avoiding early congestion and securing a buffer for a flow with good channel quality.

[0007]

A wireless communication apparatus according to the present invention performs wireless communication with a wireless terminal, and receives a line quality information from the wireless terminal with the wireless terminal. Quality receiving means, a line quality management table for recording line quality information between the plurality of wireless terminals received by the line quality receiving means, and communication to each of the wireless terminals with reference to the line quality management table Scheduling means for allocating capacity.

[0008] The scheduling means includes a scheduling creator for creating a distribution allocation of packets to be transmitted to each wireless terminal based on the channel quality information, and a scheduling for transmitting a packet to each wireless terminal based on the distribution allocation of the packets. And an execution unit, which is suitable for packet communication.

By providing a packet drop executing means for dropping a packet to be transmitted to each wireless terminal at a certain probability based on the line quality information of the line quality management table, it is possible to notify a source of occurrence of congestion at an early stage. it can. Since the line quality information is an SN ratio, the line quality information can be easily configured using a signal indicating the SN ratio output from existing hardware.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of a network having a wireless base station that is a wireless communication device according to an embodiment of the present invention.

In this embodiment, a radio base station and a plurality of radio terminals 11 using the radio base station are assumed. The wireless base station has a bridge function between the wired network and the wireless network, and each wireless terminal 11 can access the Internet via the wireless base station.

Each wireless base station has an area where wireless communication is possible, and the line quality differs depending on the position. Since the line capacity also changes depending on the line quality, it is necessary to consider the fluctuation of the line quality. In the present embodiment, S is used as an index of line quality.
The N ratio (signal to noise ratio: SNR) is used.

The SN ratio is calculated by the following equation (1), and the unit is (dB). SN ratio = ₁₀ Log ₁₀ [Signal power S (W) / Noise power N (W)] (1)

The SN ratio is calculated from the ratio between the received signal power and the noise power after the band-pass filter of the receiver, and is a general index for evaluating channel quality in wireless communication. FIG.
In the case where, for example, when the line condition between the wireless base station and the wireless terminal C is poor and almost no packets can be transmitted, the network resources are equally distributed to the wireless terminals A, B, and C, and the buffer reserved for the wireless terminal C And most of the transmitted data is wasted.

Therefore, in the radio base station, network resources to be allocated to the radio terminal C are limited in consideration of the line state of each radio terminal. By performing the scheduling of allocating surplus network resources generated by the restriction to the wireless terminals A and B having good line quality, it is possible to effectively use the limited network resources.

If there is a certain flow to the wireless terminal C, congestion occurs due to the limitation of network resources.
By dropping packets with a certain probability according to the line quality, it is possible to notify the source host of the occurrence of congestion at an early stage. In the present embodiment, a low-cost scheduling method for efficient network resource allocation by considering the line quality in wireless communication and an early avoidance of congestion caused by deterioration of the line quality are aimed. Provides a packet drop method.

FIG. 2 is a block diagram showing a configuration of a radio base station which is a radio communication device according to an embodiment of the present invention. This embodiment is divided into those belonging to the radio terminal 11 side and those belonging to the radio base station H side. On the wireless terminal 11 side, the line quality transmitting unit 10 periodically transmits the line quality of each wireless terminal to the wireless base station H. This is because in the case of a downlink flow from the wireless base station H to the wireless terminal 11, the wireless base station H has no means for sensing the line quality of the wireless terminal 11. Each wireless terminal 11 needs to transmit a frame including line quality information to the wireless base station H and periodically report the current line quality to the wireless base station H.

The wireless terminal 1 transmitted by the line quality transmitting unit 10
1 is received by the line quality receiving section 12 of the radio base station H, and the frame containing the line quality of the line quality management table 1 is received.
The information contained in the frame is updated to 3. The packet P arriving at the radio base station H is processed by the packet classification unit 14 in FIG. The packet classification unit 14 includes a transmission buffer 15
A queue for each destination host is created within the host, and the packets P arriving at the radio base station H are classified.

The packet drop execution unit 16 that has acquired the line quality information for the wireless terminal 11 from the line quality management table 13 drops the packet P in the transmission buffer 15 with a certain probability. Scheduling creation unit 17 that acquires line quality information for wireless terminal 11 from line quality management table 13
Is applied by the scheduling execution unit 18 to the queue for each destination host in the transmission buffer 15, so that the packet P in the transmission buffer 15 is transmitted to the destination host.

FIG. 3 shows the line quality management table 13 shown in FIG.
FIG. 3 is a diagram showing an example of the realization of. IP address 19, MAC address 20, SN ratio (line quality) of each wireless terminal
21. In the SN ratio item, a plurality of past SN ratios are stored. This is because the SN ratio fluctuates, so that the average of several SN ratios in the past is used to eliminate temporary noise.

The line quality receiving unit 12 is a
The frame including the line quality transmitted from 0 is analyzed. If the transmission source wireless terminal 11 already exists in the line quality management table 13, a new SN ratio is added. If the wireless terminal 11 is not in the table, a new entry is created. Entries that are not updated for a certain period of time are deleted.

FIG. 4 shows the packet classification unit 14 in FIG.
FIG. 4 is a block diagram showing a relationship between the transmission buffer 15 and the transmission buffer 15.
The packet classification unit 14 destination host A in the transmission buffer 15, B, queue for each C K1, K2, ..., to create a K _N, classifies the packet P arriving at the radio base station.

The packets P in each queue K are transmitted to the destination hosts A, B, and C by the scheduling execution unit 18 executing the scheduling algorithm created by the scheduling creation unit 17. The scheduling creation unit 17 refers to the line quality management table 13 and uses the relational expression between the line quality and the transmittable capacity to determine the communication capacity for each of the destination hosts A, B, and C, for example, the allocation, based on the line quality of each wireless terminal. The bandwidth is determined, and a scheduling method is created based on the allocated bandwidth. When the line quality management table 13 is updated, the scheduling method is changed at regular intervals based on the updated line quality management table 13.

The scheduling execution unit 18 periodically applies the scheduling method created by the scheduling creation unit 17 to the queue K created by the packet classifying unit 14 to transmit to the destination hosts A, B, and C. Do. By the way, the wireless environment has the following features.

The line quality varies depending on the position. -Even at the same position, line quality fluctuates due to multipath fading and the like.・ The transmission capacity and error ratio of the line also change with the fluctuation of the line quality.

Using this feature, the present embodiment formulates the relationship between the SN ratio, which is one of the indicators of the channel quality, and the communication capacity, and allocates a band to each wireless terminal 11 from the signal-to-noise ratio. Scheduling is performed based on the allocated bandwidth. With this scheduling method, it is not necessary to check the line state with the destination wireless terminal 11 every time a packet is transmitted as in the prior art, and a high-speed scheduling method based on the line quality can be provided.

Here, a description will be given of the channel quality and band allocation method. In the following, Q is quality, w is weight, m is overall communication capacity, I is Importance
value, S represents line quality, D represents a threshold, and k represents each wireless terminal.

A description will now be given of a quality and band allocation method based on the following definitions.・ Set the line quality level to 0-10. The smaller the number, the lower the quality. -The weight w for each wireless terminal is represented by 0-1. The quality Q is determined in consideration of the line quality of each wireless terminal and the Importance value assigned to each wireless terminal. For example, the more you pay for the network, the higher your Importance value will be. In addition, it is possible to use such as increasing the Importance value of data requiring real time such as voice. The quality of the wireless terminal k can be written by equation (2). Coefficient a is Importance
A value between 0 and 1 is set according to a policy of placing importance on value or line quality S.

Q (k) = (1−a) S (k) + aI (k) (2) Assume that the communication capacity of the entire wireless network is 100.

An example of communication capacity allocation in each system will be described. When the proposed allocation method is not used, the communication capacity is equally distributed to each host as shown in FIG. 5 irrespective of the line quality S and the Importance value. Next, the 0 or 1 system will be described. A threshold D is set for the quality Q, and a weight w for a wireless terminal having a quality equal to or higher than D is set to 1, and a weight w for a wireless terminal having a quality equal to or lower than D is set to 0. It works with the following algorithm.

If (Q> D) w = 1 else w = 0

FIG. 6 is a graph showing a case where D is 5. FIG. 7 shows an example of assignment when D is 5 and m is 100. In the present embodiment, the assignment is made in proportion to the weight w. Next, a method using quality dispersion will be described.

In particular, the line quality fluctuates among the qualities. Therefore, the present system uses the above-described 0 or 1 system in consideration of the vibration of the line quality. First, you need to know how the quality is distributed. The weight w is assigned by using the cumulative density function of the matching distribution. For example, assuming that the quality has a standard distribution, it can be expressed as in equation (3). The weight w can be obtained by substituting D for x, y, quality distribution for σ, and quality for Q.

[0034]

(Equation 1)

FIG. 8 is a graph showing the relationship between the quality Q and the weight w when D = 5 and σ = 1.7. FIG. 9 shows an example of assignment when D is 5 and m is 100. Then Linear
The method will be described. The quality Q that sets the weight w to 1 is Qma
Let Qmin be the quality Q at which x and weight w become 0. The algorithm of this method is shown below.

If (Q <Qmax) w = 0 else if (Q> Qmin) w = 1 else w = s (Q−Qmin) s represents a gradient of a linear expression.

FIG. 10 shows that Qmax = 8, Qmin = 2, s =
It is a graph showing the relationship between quality Q and weight w in the case of 1.6. FIG. 11 shows an example of assignment when Qmax is 8 and Qmin is 2. Next, the Piecewise-linear method will be described. Piecewise-
The linear method can determine the weight w more accurately than the linear method by finely dividing the range of the quality Q and expressing the inside of the area by a linear expression. Each threshold is set to D (i) (i = 1, 2,
.., N; n is the number of thresholds).

FIG. 12 shows that n = 4, D (1) = 2, D (2) =
4, D (3) = 6 and D (4) = 8. The actual assignment in FIG. 12 is as shown in FIG. Next, the Step method will be described.

Using the Piecewise-linear method, it is possible to gradually increase the allocated capacity according to the quality as shown in FIG. This method is considered to be useful for providing different services depending on the quality level.

FIG. 15 shows an actual assignment method of the step method in FIG. Next, a method using a theoretical value will be described. In addition, S, which is an index of the line quality,
In general, the theoretical value of the bit error rate can be obtained from the N ratio. This theoretical value differs depending on the modulation method. For example, phase shift keying (PSK) can be expressed as in equation (4). In this equation, P
e represents a bit error rate, erfc represents a capture function, E represents signal power (S) of the SN ratio, and No represents noise power (N). The equation can be simplified by applying the Liner scheme or the Piecewise-linear scheme.

Pe = １ ／ · erfc (E / No) ^1/2 (4)

Expression (5) is another example of the relational expression for obtaining the communication capacity from the SN ratio. This is to derive the communication capacity using Shannon's communication capacity theorem. In equation (5), C is the communication capacity, W is the occupied bandwidth (H
z), S is the signal power (W), N is the noise power (W), and R is the correction coefficient. Since the SN ratio is represented by equation (1), such a formulation is possible.

C = R · Wlog ₂ (1 + S / N) (5)

The formula for actually deriving the line capacity from the SN ratio is:
It is necessary to correct the difference depending on the wireless device medium, but it is not necessary to change the same wireless device medium. The scheduling creation unit in FIG. 2 creates a scheduling based on the formulation of the S / N ratio and the channel capacity, which are the channel qualities.

An example in which the formula (1) is used is shown below. First, as a property of the wireless medium, the threshold for disconnecting the line is 10 dB, and the standard deviation of the SN ratio vibration is 2. It is assumed that a queue for transmitting to the wireless terminals A, B, and C currently exists in the transmission buffer. S of the wireless terminals A, B, and C
When the N ratio is 20 dB, 10 dB, and 4 dB, respectively, the weights of the wireless terminals A, B, and C are 0.99, 0.5 by applying Equation (2).
, Becomes 0.00. The scheduling creation unit determines a scheduling method based on the weight.

As a specific scheduling algorithm in this example, for example, weighted round robin or WFQ can be used. The scheduling execution unit applies the scheduling to each queue of the transmission buffer based on the created scheduling method. In this example, bands are allocated to the wireless terminals A, B, and C and transmitted.

Next, the packet drop algorithm will be described. In the scheduling method of the present embodiment, as can be seen from the example of the above-described scheduling method, the transfer amount is limited by the line quality, and congestion occurs in the wireless base station when there is a queue to a wireless terminal with poor line quality. The transmission buffer of the radio base station is finite, and if it is consumed by packets destined for terminals with poor line quality, a buffer for a flow with good line quality cannot be secured. A similar problem exists in the scheduling method described in the existing technology. In the present embodiment, a drop algorithm that considers channel quality for the purpose of avoiding early congestion is provided.

FIG. 16 is a diagram showing one of the queues on the transmission buffer in FIG. First, the SN ratio of the queue on the transmission buffer is obtained from the line quality management table 13. A queue length threshold value t is set according to the SN ratio. As the SN ratio is higher, t is set larger, and as the SN ratio is lower, t is set smaller.

Taking FIG. 16 as an example, t moves to the right as the S / N ratio increases, and t moves to the left as the S / N ratio decreases. A two-step method is used depending on whether the queue length is longer or shorter than t. As a first step, nothing is done when the queue length is shorter than t1. As a second step, the queue length is t
When it is longer than 1, packets P arriving at the queue are dropped at a certain probability.

The second stage of the algorithm has a role of notifying the transmission source host of the occurrence of congestion due to the deterioration of the line quality by dropping randomly selected packets. In the congestion control in the transport layer such as TCP, the buffer is full and the packet P is dropped to detect the congestion. The second stage enables the early detection of the congestion. In this early detection of congestion, the threshold value t is dynamically fluctuated according to the SN ratio, so that the transmission quality is notified to the transmitting host earlier as the line quality is worse. Also, when the line quality is good, the t value increases, which indicates that congestion has occurred due to a cause different from the line quality.

The present invention is not limited to the above embodiment. There are various types of communication quality, and in addition to the SN ratio, distance, signal strength, and the like may be used. Further, the SN ratio may be the SN ratio of digital data or the SN ratio of analog data. In addition, for use, for example, it can be used as a base station for Bluetooth.

[0052]

According to the present invention, a low-cost scheduling method and early avoidance of congestion caused by deterioration of the line quality can be realized by considering the line quality in wireless communication.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of a network having a wireless base station that is a wireless communication device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a wireless base station that is a wireless communication device according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of implementing a line quality management table;

FIG. 4 is a diagram illustrating a relationship between a packet classification unit and a transmission buffer.

FIG. 5 is a diagram showing allocation when the proposed allocation method is not used.

FIG. 6 is a graph showing the relationship between the quality and the weight of the 0 or 1 system.

FIG. 7 is a diagram showing an example showing an example of allocation in the 0 or 1 system.

FIG. 8 is a graph showing the relationship between the quality and the weight of the method using the variance of the quality.

FIG. 9 is a diagram illustrating an example of allocation of a method using quality distribution.

FIG. 10 is a graph showing the relationship between the quality and the weight of the Linear system.

FIG. 11 is a diagram illustrating an example of assignment using a Linear method.

FIG. 12 is a graph showing a relationship between quality and weight using the Piecewise-linear method.

FIG. 13 is a diagram illustrating an example of assignment using the Piecewise-linear method.

FIG. 14 is a graph showing the relationship between quality and weight using the Step method.

FIG. 15 is a diagram illustrating an example of assignment using the Step method.

FIG. 16 is a diagram illustrating a queue on a transmission buffer.

[Explanation of symbols]

 Reference Signs List 10 line quality transmission unit 12 line quality reception unit 13 line quality management table 14 packet classification unit 15 transmission buffer 17 scheduling creation unit 18 scheduling execution unit 19 IP address 20 MAC address 21 line quality

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K030 GA08 HA08 JL01 JT09 KA02 LC09 MB04 MB05 5K067 AA23 BB21 CC08 DD45 EE02 EE10 EE71 HH22 HH23

Claims (4)

[Claims] 1. A wireless communication apparatus for performing wireless communication with a wireless terminal, comprising: line quality receiving means for receiving line quality information with the wireless terminal from the wireless terminal; A line quality management table that records line quality information between the plurality of wireless terminals received by the wireless terminal, and a scheduling unit that allocates a communication capacity to each of the wireless terminals with reference to the line quality management table. A wireless communication device characterized by the above-mentioned. 2. The scheduling means, wherein the scheduling unit creates a distribution allocation of packets to be transmitted to each wireless terminal based on the channel quality information, and transmits a packet to each wireless terminal based on the distribution allocation of the packets. The wireless communication device according to claim 1, further comprising: a scheduling execution unit that performs scheduling. 3. The wireless communication apparatus according to claim 1, further comprising packet drop executing means for dropping a packet to be transmitted to each wireless terminal at a certain probability based on the line quality information in said line quality management table. 4. The wireless communication apparatus according to claim 1, wherein the line quality information is an SN ratio.