JP5378269B2 - Wireless communication method, wireless base station, and wireless access system - Google Patents

Description

  The present invention relates to a wireless communication method, a wireless base station, a wireless communication method for performing communication between a wireless data receiving device (wireless base station) and a plurality of wireless data transmitting devices (wireless terminal stations) connected via a wireless line. Relates to the access system.

The access method of the wireless access system used as the access system of the wired network is a centralized control method in which the transmission timing of all wireless terminals is managed by the wireless base station, and distributed control in which each wireless terminal independently determines the transmission timing and performs transmission. It can be roughly divided into two methods.
The distributed control method has a simpler base station configuration than the centralized control method. In addition, since there is no need to control the wireless terminal from the base station, a control signal is unnecessary and high throughput can be realized.

  In this distributed control method, each wireless terminal station individually determines the transmission timing, and therefore transmission packets may collide when transmission is performed at a plurality of wireless terminal stations. Particularly in a congested state, packet collisions frequently occur and reduce the throughput. Therefore, a collision avoidance algorithm is used in the distributed control method.

  In IEEE802.11, the Exponential back off algorithm is used as a collision avoidance algorithm. FIG. 10 shows the backoff operation of the collision avoidance algorithm used in IEEE802.11. When transmitting using this algorithm, a random number between 0 and a specified value (window size) is calculated, and transmission is delayed (backed off) by that value. The maximum random number for the first transmission is defined as the initial backoff window size. When packet transmission fails due to collision or the like, the window size is multiplied by x, the back-off time is calculated within that range, and transmission is delayed by that value and retransmitted. The value that increases the window size (x above) is called the persistent factor (PF). If transmission fails again, the window size is further multiplied by x, a back-off value is calculated, and transmission is performed after back-off. In the Exponential back off algorithm, this operation is repeated until transmission is successful, or until the number of retransmissions reaches a preset maximum number of retransmissions.

  As a method of providing QoS (Quality of Service) in the distributed control method using the Exponential back off algorithm, IFS (Inter Frame Space), initial backoff window size, and PF parameters are defined for each service class. There is a method of performing priority control for each class (Reference Document 1). Here, IFS is the time that must be opened from the time when the previous transmission was completed in time and the radio line changed to empty until the start of backoff, and when IFS is short, transmission priority is given. If the degree is high and the IFS is long, the priority is low.

IEEE Std 802.11-1997 (p.73-80)

In such a radio access system, it may be necessary to satisfy the following requirements (1) to (3).
(1) Wide area (a wide range is covered by one base station (for example, an area with a radius of 3.5km))
(2) Realization of super multi-dimensional multi-access (for example, more than 1 million accommodation terminals)
(3) Provision of QoS (Average transmission delay time is used as an index for defining QoS)

However, in the wireless access system as shown in (1) to (3), when the above-described method is used, there are the following problems.
a) In the assumed system based on the above requirements (1) to (3), carrier scanning may not be possible between wireless terminals, and a priority control method using IFS (Inter Frame Space) cannot be used.
b) Causes of increase in traffic added to the system include cause (i) due to increase in generated traffic of each terminal and cause (ii) increase in the number of terminals although the traffic amount per terminal does not change There are two cases. If the increase in traffic is caused by (i), transmission of low-priority terminals can be sufficiently suppressed, so the effect can be expected even with the conventional priority control method. However, in case (ii), the low-priority terminal's Since transmission cannot be sufficiently suppressed, it is difficult to provide QoS by the conventional method. Furthermore, the assumed system is a communication system aiming at realizing super multi-dimensional multi-access. The number of accommodated terminals is large, and it is predicted that traffic will frequently increase due to cause (ii).
c) Although there is a qualitative relationship between parameters (IFS, initial backoff window size, PF) used for transmission control in the conventional method and transmission delay time, the effect of each parameter on traffic control is as follows: Since it changes depending on the number of terminals accommodated in one base station, a quantitative relationship cannot be uniquely determined.

Therefore, in order to realize a wireless access system that satisfies the requirements a) to c), it is necessary to solve the following problems.
(A) Establishment of priority control method without using carrier scan and IFS
(B) Establishment of a priority control method that can provide QoS even when traffic increases due to an increase in the number of terminals
(C) Establishing a priority control method that can satisfy the conditions according to the specific index that defines QoS
(D) Establishment of an access switching method that adaptively selects an access method (distributed control method, centralized control method) according to traffic

  The present invention has been made in view of such circumstances, and an object of the present invention is to determine the communication quality of the priority class terminal device even when the number of non-priority class terminal devices increases and traffic increases. It is an object to provide a wireless communication method, a wireless base station, and a wireless access system that maintain high quality.

In order to solve the above-described problem, the present invention is a wireless communication method in a wireless access system in which a priority class terminal device and a non-priority class terminal device communicate with a wireless base station by a random access method, The radio base station can maintain the transmission delay time specified in the priority class from the transmission delay time specified in the priority class, the access parameter related to backoff of the priority class, and the effective RA slot length. And calculating an access parameter related to backoff of the non-priority class from the calculated maximum value of transmission failure probability, and notifying each terminal device of the calculated access parameter related to backoff. And

  Further, the present invention provides the above-described wireless communication method, wherein the wireless base station calculates an effective RA slot length by dividing the MAC frame length by an average number of RA slots assigned to the MAC frame, and calculates the calculated effective RA slot length. The maximum value of the transmission failure probability is calculated using the RA slot length.

The present invention also provides a wireless communication method described above, the radio base station, an initial backoff window size for the priority class and the non-priority class, priority class and non-priority class transmission probability, priority class and a non-priority class An access parameter relating to backoff is calculated from the data generation probability, the maximum number of retransmissions, and the number of terminal devices of the priority class and the non-priority class.

Further, the present invention is a radio base station in a radio access system in which a terminal device of a priority class and a terminal device of a non-priority class communicate with a radio base station by a random access method, and are defined by the priority class A transmission failure probability calculating unit that calculates the maximum value of the transmission failure probability that can maintain the transmission delay time defined in the priority class from the transmission delay time, the access parameter related to the backoff of the priority class, and the effective RA slot length; An access parameter calculation unit that calculates an access parameter related to backoff of a non-priority class from a maximum value of the calculated transmission failure probability, and a notification unit that notifies each terminal device of the calculated access parameter related to backoff It is characterized by having.

  Further, the present invention is a radio access system in which a priority class terminal device and a non-priority class terminal device communicate with a radio base station by a random access method in the above-described radio communication method, wherein the radio base station includes: A transmission for calculating the maximum value of the transmission failure probability capable of maintaining the transmission delay time specified in the priority class from the transmission delay time specified in the priority class, the access parameter of the priority class, and the effective RA slot length A failure probability calculation unit; an access parameter calculation unit that calculates an access parameter of a non-priority class from the calculated maximum value of the transmission failure probability; and a notification unit that notifies the terminal device of the calculated access parameter. And the terminal device performs backoff according to an access parameter transmitted from the radio base station, and It characterized by having a transmitter for transmitting.

  As described above, according to the present invention, even when traffic increases due to an increase in the number of terminals in the non-priority class, by selecting an optimal access parameter, while maintaining communication quality, It is possible to maximize throughput.

It is a figure which shows the structure of the radio | wireless access system by one Embodiment of this invention. It is a figure which shows the structure of the MAC frame used with the radio | wireless access system 1 in this embodiment. 2 is a block diagram illustrating functions of the wireless access system 1. FIG. It is a figure which shows the access sequence in the case of transmitting data in an uplink. It is a figure which shows the back-off sequence in random access. 10 is a flowchart for describing processing for calculating an access parameter performed by a radio base station 10; It is a figure explaining effective RA slot length. It is a figure showing the relationship between transmission failure probability and transmission delay time. It is a figure of the Markov model showing the transmission operation | movement of the radio | wireless terminal 20 in a non-saturated state. It is a figure explaining the operation | movement of the back-off of a collision avoidance algorithm.

A wireless access system according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a radio access system according to an embodiment of the present invention.
The wireless access system 1 includes one wireless base station 10 connected to the wired network 2 and a plurality of wireless terminals 20 connected to the wired network 2 via the wireless base station 10. In communication between wireless terminals 20 via wireless, an access method using a distributed control algorithm may be used.

  FIG. 2 is a diagram showing a configuration of a MAC frame used in the wireless access system 1 in the present embodiment. As an access method, TDMA / TDD (Time Division Multiple Access / Time Division Duplex) is used to realize multidimensional connection and bidirectional communication. In this figure, the length of the MAC frame is a fixed length, the first half of the MAC frame is the downlink from the base station to the terminal, and the second half is the uplink in the reverse direction.

  The downlink is composed of a broadcast area (BC) for transmitting broadcast information and a demand assignment area (DA) for transmitting unicast data. In the broadcast area, BCCH (Broadcast Control CHannel), FCCH (Frame Control CHannel), and RFCH (Random access Feedback CHannel) is transmitted. BCCH is used to broadcast system common information such as base station ID and MAC frame number, FCCH broadcasts information indicating the configuration of the MAC frame, and RFCH is the success or failure of random access in the previous MAC frame and the radio terminal 20 is notified of the random access parameters (initial backoff window size, PF) used in 20, the number of RA slots and their positions.

  The uplink is composed of a demand assign area (DA) for transmitting unicast data and a random access area composed of RA slots. Unicast data is transmitted in the demand assignment area for both downlink and uplink.

FIG. 3 is a block diagram illustrating functions of the above-described wireless access system 1.
In this figure, a radio base station 10 is composed of a central processing unit and a storage device, and an effective RA slot length calculation unit 11, a transmission failure probability calculation unit 12, an access parameter calculation unit 13, a notification signal generation unit 14, and the like. And a communication unit 15. The effective RA slot length calculation unit 11 calculates the effective RA slot number by dividing the MAC frame length by the average number of RA slots assigned to the MAC frame. The transmission failure probability calculation unit 12 calculates the transmission failure probability that can maintain the transmission delay time defined in the priority class from the transmission delay time defined in the priority class, the access parameter of the priority class, and the effective RA slot length. Calculate the maximum value. Here, the transmission failure probability calculation unit 12 uses the value calculated by the effective RA slot length calculation unit 11. The access parameter calculation unit 13 calculates a non-priority class access parameter from the calculated maximum value of the transmission failure probability. The notification signal generation unit 14 generates a notification signal for notifying each terminal device of the calculated access parameter. The communication unit 15 has a function of communicating with each wireless terminal 20 and also has a function of transmitting the notification signal generated by the notification signal generation unit 14 to the wireless terminal 20.

  The wireless terminal 20 includes a central processing unit and a storage device, and includes a communication unit 21 and a communication control unit 22. The communication unit 21 communicates with the radio base station 10. The communication control unit 22 performs back-off according to the access parameter transmitted from the radio base station 10 and performs control for transmitting a bandwidth request.

FIG. 4 is a diagram illustrating an access sequence when data is transmitted on the uplink. The access sequence is roughly divided into three phases: a bandwidth request phase, a data transmission phase, and an ACK reception phase.
In the bandwidth request phase, a bandwidth for transmitting data by random access is requested. When the random access is successful and the bandwidth request can be transmitted to the radio base station, the process proceeds to the data transmission phase.
The wireless terminal 20 waits for a data transmission band to be allocated by the wireless base station 10 in the data transmission phase. Bandwidth allocation is instructed by FCCH. When a band is allocated by the radio base station 10, the radio terminal 20 transmits data using the band and shifts to the ACK reception phase.
In the ACK reception phase, the radio terminal 20 waits for an ACK indicating that the radio base station 10 has received data normally from the radio base station 10. When the wireless terminal 20 receives the ACK from the wireless base station 10, one access sequence is completed.

"Concrete example"
In random access, backoff is performed in order to avoid collision between packets transmitted from each wireless terminal 20.
FIG. 5 is a diagram illustrating a back-off sequence in random access.
The communication unit 15 of the radio base station 10 uses the RFCH in the broadcast area at the head of the MAC frame to determine the initial backoff window size of each class, the PF, the number of RA slots in the MAC frame, and the position of the RA slot. The indicated RA slot position information is transmitted (step S10). The communication unit 21 of the wireless terminal 20 receives each MAC frame and RFCH, and updates to the latest parameter (step S11).

  Next, when transmission data is generated (step S12), the communication control unit 22 of the wireless terminal 20 calculates the number of backoff slots from the initial backoff window size (step S13). The number of backoff slots calculated here is a random number in the range of 0 to (initial backoff window size-1). The radio terminal 20 performs backoff in the RA area of the MAC frame by the calculated number of backoff slots, and then transmits a bandwidth allocation request in the RA slot via the communication unit 21 (step S14). When the number of RA slots in the MAC frame in which transmission data is generated is smaller than the calculated back-off slot number, the back-off operation is continuously performed in the next MAC frame.

  As described above, backoff performed by the radio terminal 20 is performed by the number of backoff slots calculated based on the initial backoff window size determined by the radio base station 10 and the PF.

Here, priority control can be realized by setting either one of the initial back-off window size and PF or both the initial back-off window size and PF for each class. The present invention is used in a method of setting these parameters. How to determine the initial backoff window size in the radio base station 10 will be described below.
In this example, a case will be described in which PF is a fixed value and only the initial backoff window size is dynamically changed. In the wireless access system 1 in this example, two classes (priority class and non-priority class) are provided, and the priority class provides QoS defined by “average delay time ≦ required quality threshold”.

Here, consider a case where there are two priority classes and non-priority classes as communication quality classes. The priority class defines the communication quality to be satisfied, and the non-priority class is best effort. Then, a method is considered in which the non-priority class traffic is controlled by controlling the access parameters of the non-priority class according to the generated traffic and the communication quality of the priority class is maintained.
Further, since it is necessary to always maintain the communication quality for the access parameter of the priority class, it is assumed that dynamic control is not performed in this case.

  The radio base station 10 calculates an appropriate access parameter for the non-priority class, and notifies the calculated value to each radio terminal 20 using the broadcast channel. This access parameter calculation is performed in three steps: effective RA slot length calculation, RA slot transmission failure probability calculation, and initial backoff window size (access parameter) calculation.

FIG. 6 is a flowchart illustrating a process for calculating access parameters performed by the radio base station 10.
First, the effective RA slot length calculation unit 11 of the radio base station 10 calculates the effective RA slot length from the number of RA slots allocated to the MAC frame and the MAC frame length (step S20). When the effective RA slot length is calculated, the transmission failure probability calculation unit 12 calculates the RA slot transmission failure probability p required to satisfy the specified delay time condition (step S21). Then, the access parameter calculation unit 13 calculates a non-priority class access parameter from the RA slot transmission failure probability p (step S22).

Next, the calculation of the effective RA slot length and the calculation of the transmission failure probability will be described.
FIG. 7 is a diagram for explaining the effective RA slot length. _Assuming that the average time elapsed per back-off slot in back-off operation is the effective RA slot length T _erss , the effective RA slot length T _erss is the MAC frame length with the average number of RA slots N allocated per MAC frame. The value divided by.

FIG. 8 is a diagram illustrating the relationship between the transmission failure probability and the transmission delay time.
The transmission failure probability calculation unit 12 of the radio base station 10 calculates the transmission failure probability when maintaining the quality from the transmission delay time defined in the priority class, the access parameter of the priority class, and the effective RA slot length. The maximum value of the transmission failure probability p to be satisfied is calculated by the following equation (2).

  However, Delay in equation (2) is the specified average delay time of the priority class, Wo is the initial backoff window size of the priority class, and n is the maximum number of retransmissions.

  FIG. 9 is an example of the average transmission delay time characteristic with respect to the transmission failure probability calculated as Wo = 32, N = 10, and n = 1023. For example, when the average transmission delay time is 8 seconds or less, the RA slot transmission failure probability needs to be 0.4 or less.

Next, the calculation of the initial backoff window size will be described.
FIG. 9 is a Markov model representing the transmission operation of the wireless terminal 20 in the non-saturated state. Since the initial backoff window size and the data generation probability Pg are different for each class, a Markov model also exists for each communication class.

  Here, assuming that the initial backoff window size, transmission probability, and data generation probability of the priority class and non-priority class are W0h, τh, Pgh, and W0l, τl, Pgl, respectively, each relational expression solves the Markov model. Thus, the equations (3) to (6) are obtained.

In the equation, m is the maximum number of retransmissions, nl is the number of non-priority class terminals, and nh is the number of priority class terminals. Pgh and Pgl can be calculated from the reception interval of the reception data measured by the radio base station 20.
The access parameter calculation unit 13 calculates W _0l by calculating the above equations (3) to (6). Since the determined W _0l is the appropriate back window size of the non-priority class, the notification signal generation unit 14 generates a notification signal indicating the value, and the wireless base station 10 transmits the notification signal to each terminal device via the communication unit 15. Notify them.

  According to the specific example described above, even when the traffic increases due to the increase in the number of terminals in the non-priority class, the throughput is reduced while maintaining the communication quality by selecting the optimum access parameter. It is possible to maximize.

  Further, according to the embodiment described above, a priority control method that does not use carrier scan and IFS can be established, and a priority control method that can provide QoS even when traffic increases due to an increase in the number of terminals is established. It is possible to establish a priority control method that can satisfy the conditions according to a specific index that defines QoS, and adaptively change the access method (distributed control method, centralized control method) according to traffic. The access switching method to be selected can be established.

  Further, the program for realizing the function of the radio base station 10 in FIG. 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into the computer system and executed to execute an initial backup. An off-window size may be calculated. Here, the “computer system” includes an OS and hardware such as peripheral devices.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Radio access system 10 Radio base station 11 Effective RA slot length calculation part 12 Transmission failure probability calculation part 13 Access parameter calculation part 14 Broadcast signal generation part 20 Wireless terminal 15, 21 Communication part 22 Communication control part

Claims (5)

A wireless communication method in a wireless access system in which a terminal device of a priority class and a terminal device of a non-priority class communicate with a wireless base station by a random access method,
The radio base station is
From the transmission delay time specified in the priority class, the access parameter related to backoff of the priority class, and the effective RA slot length, the maximum value of the transmission failure probability capable of maintaining the transmission delay time specified in the priority class is calculated. And
From the calculated maximum value of transmission failure probability, calculate the access parameters related to backoff of non-priority class,
The wireless communication method characterized by notifying each terminal device of the calculated access parameter related to backoff . The radio base station is
An effective RA slot length is calculated by dividing the MAC frame length by the average number of RA slots assigned to the MAC frame, and a maximum value of the transmission failure probability is calculated using the calculated effective RA slot length. The wireless communication method according to claim 1. The radio base station, priority class and the non-priority class initialization backoff window size, transmission probability of the priority class and the non-priority class, data occurrence probability of the priority class and the non-priority classes, the maximum number of retransmissions, priority class and non The wireless communication method according to claim 1 or 2, wherein an access parameter related to backoff is calculated from the number of terminal devices of each priority class. A wireless base station in a wireless access system in which a terminal device of a priority class and a terminal device of a non-priority class communicate with a wireless base station by a random access method,
From the transmission delay time specified in the priority class, the access parameter related to backoff of the priority class, and the effective RA slot length, the maximum value of the transmission failure probability capable of maintaining the transmission delay time specified in the priority class is calculated. A transmission failure probability calculation unit to
An access parameter calculation unit that calculates an access parameter related to backoff of the non-priority class from the calculated maximum value of the transmission failure probability;
A notifying unit for notifying each terminal device of the access parameter relating to the calculated backoff ;
A radio base station characterized by comprising: A wireless access system in which a terminal device of a priority class and a terminal device of a non-priority class communicate with a wireless base station by a random access method,
The radio base station is
Transmission failure to calculate the maximum value of transmission failure probability that can maintain the transmission delay time specified in the priority class from the transmission delay time specified in the priority class, the access parameter of the priority class, and the effective RA slot length A probability calculator;
An access parameter calculation unit that calculates an access parameter of a non-priority class from the maximum value of the calculated transmission failure probability;
A notification unit for notifying each terminal device of the calculated access parameter,
The terminal device
A radio access system comprising: a transmitter that performs back-off according to an access parameter transmitted from the radio base station and transmits a bandwidth request.

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