KR100835684B1 - Method for performing backoff algorithm for random access in wireless mobile communication system and Wireless mobile communication system using this - Google Patents

Abstract

A method for backing off random access and a wireless mobile communication system are disclosed.

The present invention provides a method of transmitting a ranging request message including a number of transmission attempts and a first access attempt time until a connection is successfully established by any one of a plurality of terminals, the base station receiving the ranging request message. Calculating a retransmission probability using the number of terminals successfully connected in each frame, the number of transmission attempts and the initial access attempt time, broadcasting the retransmission probability at the base station, and the terminal requesting the ranging request message. If the ranging response message corresponding to does not receive within the threshold time, transmitting the ranging request message to the base station according to the retransmission probability.

According to the present invention, an effective random access can be implemented in a wireless mobile communication system in which a base station cannot distinguish a collision from an empty channel, and only an optimized number of terminals can access a connection because the base station determines the channel status. It is possible to increase throughput while reducing the delay of accessing a base station in channel congestion, and to solve the problem of wasting resources of BEB algorithm, falling into instability, fairness problem and potential collision problem.

Description

Method for performing backoff algorithm for random access in wireless mobile communication system and Wireless mobile communication system using this}

1 illustrates a frame structure in a broadband wireless mobile communication system.

2A is a flowchart of a method for backoff of wideband random access according to the prior art.

Figure 2b shows a prior art backoff algorithm distribution interval.

3 is a block diagram of a wireless mobile communication system in accordance with the present invention.

4 is a flowchart of a method of backoff of random access according to the present invention.

5 is a flowchart illustrating a procedure for implementing backoff of random access in a base station according to the present invention.

6 is a flowchart illustrating a procedure for implementing backoff of random access in a terminal according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless mobile communication system, and more particularly to a method of backoff random access and a wireless mobile communication system.

In the mobile communication system, the wireless portable Internet is a communication method that further supports mobility in a short-range data communication method using a fixed access point, such as a conventional wireless local area network (WLAN).

In such a wireless mobile communication system, a ranging subscriber station needs a ranging function to access a base station. In a wireless mobile communication system, a ranging function is a function of adjusting a transmission power, a timing, and a frequency offset of a terminal so that a base station can correctly receive data transmitted by the terminal. For convenience of explanation, the IEEE 802.16 communication system will be described as an example.

IEEE 802.16, an international standard related to domestic mobile Internet, is called Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA). Broadband Wireless Access (BWA) communication system using a scheme. Since the IEEE 802.16 communication system adopts the OFDM / OFDMA scheme, high-speed data can be transmitted by transmitting a physical channel signal using a plurality of subcarriers.

1 illustrates a frame structure used in a broadband wireless mobile communication system.

As shown in FIG. 1, the MAC layer of IEEE 802.16 defines the ranging channel 100. Sub-channels constituting the ranging channel are specified in the UL-MAP 110 message, and terminals are allowed to collide in the ranging channel. The IEEE 802.16 ranging subsystem uses initial ranging using a random access protocol of a code division multiple access (CDMA) scheme to simultaneously access a plurality of terminals. Handoff ranging, periodic ranging, and bandwidth request. When the UE generates a message to transmit to the base station, it selects a random code from a set of pseudo-noise (PN) codes, spreads the message to be transmitted using the PN code, and transmits the message to the base station through the CDMA scheme.

The random access protocol uses a slotted ALOHA scheme. The slot aloha method is a method in which a terminal immediately accesses a slot unit to access a base station. Therefore, when one terminal attempts to access the same slot, data transmission is successful. When two or more terminals attempt to access, a collision occurs and data transmission fails. If it fails, it waits for a random time (backoff time) and tries to connect in the same way.

If the failed terminals wait for the same random time and attempt to connect, the same terminals collide again and fail. In order to avoid such continuous collision, a binary exponential backoff (BEB) algorithm, which is a terminal distribution algorithm, is used.

2A is a flowchart of a method of backoff random access in a broadband mobile communication system according to the prior art.

Figure 2b shows a prior art backoff algorithm distribution interval.

The BEB algorithm determines the backoff time for retransmission by the number of collisions of respective terminals. The BEB algorithm has a minimum contention window and a maximum contention window.

Referring to FIG. 2A, if there is data to be sent to the base station 250 for the first time by the terminal 200, the terminal 200 immediately occurs (211). However, as described above, in the random access method, a message can be transmitted using the same PN code in the same slot. At this time, the messages transmitted by the plurality of terminals conflict.

의 분산 구간(261)에서 임의의 정수를 선택하고, 이 정수가 백오프 시간(215)이 된다. 단말은 백오프 시간 동안 기다렸다가 메시지를 재전송한다(217).Terminals that send the message start a timer (213). As soon as the base station receives the message, it sends a ranging response message. If the terminal does not receive the ranging response message within a predetermined time, the terminal regards the sent message as a collision and performs the BEB algorithm. Because the crash happened once

An arbitrary integer is selected in the dispersion section 261 of, and this integer becomes the backoff time 215. The terminal waits for the backoff time and retransmits the message (217).

의 분산 구간(262)에서 임의의 정수를 선택하고, 이 정수가 백오프 시간(221)이 된다. 단말은 백오프 시간 동안 기다렸다가 메시지를 재전송한다(223).The retransmission format is also the same as the initial transmission format. The UEs operate a timer (219), and if the ranging response message is not received within a predetermined time, the UE determines the backoff time through the BEB algorithm. Because the crash happened twice

An arbitrary integer is selected in the variance interval 262 of, and this integer becomes the backoff time 221. The terminal waits for the backoff time and retransmits the message (223).

를 넘을 수 없다. 따라서 분산 구간은

(269)이 된다. 여기서

는 충돌 횟수를 의미한다. IEEE 802.16 시스템에서는 최대 충돌 횟수를 15번으로 제한하고 있다. 15번 동안에 기지국으로부터 레인징 응답 메시지(227)를 받으면 성공이고, 16번째 충돌이 발생하면 데이터는 버려지게 된다.As the collision occurs (225), the dispersion interval increases, and this dispersion interval

Can't go beyond Therefore, the variance interval

(269). here

Is the number of collisions. The IEEE 802.16 system limits the maximum number of collisions to 15. Receiving the ranging response message 227 from the base station for 15 times is successful, and if the 16th collision occurs, the data is discarded.

When the number of terminals sharing the same channel in a wireless network increases, collision between each other is inevitable. This is because the UEs do not know when other UEs competing with each other will start transmitting, which may result in a situation where multiple UEs transmit simultaneously. To reduce this inevitable collision, the random access protocol uses a terminal distribution algorithm.

The most commonly used terminal distribution algorithm is the BEB algorithm. The BEB algorithm determines the distribution intervals according to the number of collisions of respective terminals, and determines an arbitrary backoff time in the determined distribution interval. The terminal waits for the determined backoff time and immediately sends a message. If a collision occurs again, repeat the previous steps. As the collision occurs, the dispersion interval increases.

The BEB algorithm distributes the terminals very efficiently when the number of terminals is small compared to the radio channel capacity. However, as the number of terminals increases, it is extremely rare for one terminal to connect to one radio channel, and when the number of terminals further increases, all radio resources may not be available.

In addition, as the number of terminals increases, the number of terminals attempting to access the system increases. However, as described above, the number of terminals successfully connected is extremely rare or absent. In other words, the system is in an unstable state. The BEB algorithm lacks the ability to recover a system that has become unstable quickly.

In addition, in the BEB algorithm, a terminal that has undergone several collisions with an initial ranging terminal competes with each other in the same slot. A terminal that has experienced several collisions needs to access the system faster than an initial ranging terminal, but suffers more delay because the dispersion interval increases rapidly due to an increase in the binary index. This is called a 'fairness problem'.

In addition, the number of collisions is initialized to '0' in the terminal that has successfully connected the system. When the number of terminals trying to access the system is large, there is a 'potential collision problem', in which the probability of collision further increases when successful terminals access the system again.

Therefore, the conventional BEB algorithm cannot consider the radio channel situation when determining the backoff time, the efficiency decreases rapidly as the number of terminals increases, and it is not possible to quickly recover the instability of the system, and there is a potential conflict with the fairness problem between the terminals. There is such a problem.

Therefore, the first technical problem to be achieved by the present invention is to implement an effective random access in a wireless mobile communication system that can not distinguish between the collision and the empty channel in the base station, and increases the throughput while reducing the delay required for accessing the base station during channel congestion It provides a method of backoff of random access that can solve the problem of wasting resources of BEB algorithm, falling into instability, fairness problem and potential collision problem.

Another object of the present invention is to provide a wireless mobile communication system to which the random access backoff method is applied.

In order to achieve the first technical problem, the present invention comprises the steps of transmitting a ranging request message to the base station including the number of attempts and the initial access attempt until the connection is successful in any one of the plurality of terminals, the Computing a retransmission probability using the number of terminals successfully connected every frame, the number of transmission attempts and the initial access attempt time at each base station receiving the ranging request message, and broadcasting the retransmission probability at the base station And when the terminal does not receive the ranging response message corresponding to the ranging request message within a threshold time, transmitting the ranging request message to the base station according to the retransmission probability. Provide a back off method.

In addition, in order to achieve the first technical problem, the present invention is a step of transmitting a ranging request message including the number of transmission attempts until the first successful connection from any one of the plurality of terminals and the initial access attempt time to the base station When the terminal receives the ranging response message corresponding to the ranging request message within a threshold time, determining that the terminal is successful in connection; when the terminal does not receive the ranging response message within a threshold time, Receiving a retransmission probability from the base station using the number of terminals successfully connected to each frame, the number of transmission attempts and the initial access attempt time, and transmitting a ranging request message to the base station according to the retransmission probability. The back of random access in a wireless mobile communication system comprising a There is provided a method.

In order to achieve the second technical problem, the present invention provides a wireless mobile communication system including a plurality of terminals and at least one base station, wherein the plurality of terminals and the number of transmission attempts until a successful connection from any one terminal and By the transceiver and the transceiver for transmitting the ranging request message including the initial access attempt time to the base station, receiving the retransmission probability from the base station, and retransmitting the ranging request message to the base station according to the retransmission probability If a ranging response message corresponding to a ranging request message is not received within a threshold time, the transceiver includes a processor for receiving a retransmission probability of the next frame, and determines whether to retransmit the ranging request message according to the retransmission probability The base station is the number of attempts to transmit And calculating and broadcasting the retransmission probability every frame using an initial access attempt time, and when the ranging request message does not have a collision, transmitting a ranging response message to a corresponding terminal. Provide a system.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention. However, embodiments of the present invention illustrated below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below.

The present invention can be applied to any communication system to which a random access method that attempts initial access or bandwidth request through a channel shared by a plurality of terminals can be applied.

In general, a random access method distributes a plurality of terminals using a terminal distribution algorithm when a collision occurs and fails. A commonly used terminal distribution algorithm is the BEB algorithm. The BEB algorithm, however, has resources waste, instability, fairness, and potential conflict. These problems are because the terminals themselves determine the backoff time without considering the overall state of the channel.

Therefore, the present invention does not determine the backoff time at the terminal, but calculates the retransmission probability in consideration of the state of the channel at the base station, and determines whether all the terminals retransmit according to the retransmission probability. The problem of the BEB algorithm is solved by optimizing the number of terminals that attempt to access one frame.

In order to calculate the retransmission probability at the base station, it is necessary to know the state of the channel. The status of the channel should be known by the base station whether there is one terminal (ranging success), two or more (ranging failures), or not, trying to access the channel. However, because the ranging subchannel of the IEEE 802.16 system uses the OFDMA-CDMA scheme, it is not known whether the current channel is successful, failed, or empty. Only successful terminals can be known. Therefore, there are three types of information that can be obtained from the terminals that have successfully connected. The first is the number of terminals that have successfully connected in one frame, the second is the number of attempts of each of the terminals that have successfully connected in one frame, and the last is the delay of each of the terminals that have successfully connected in one frame. With this limited information, you can estimate the parameters required for control.

이다. 여기서 S는 처리량이고, G는 오퍼드 로드(offered load)이다. IEEE 802.16 시스템의 레인징 서브 시스템은 한 프레임은 PN 코드의 개수만큼 단말들이 접속에 성공할 수 있다. 따라서 IEEE 802.16 시스템의 레인징 서브 시스템의 처리량은

가 된다. C는 한 프레임 안에 있는 PN 코드 수이다. 따라서 최대 처리량은 슬롯 알로하 같이

이다. 그리고 슬롯 알로하에서 최대 처리량을 얻기 위한 offered load는 '1'이다. 따라서 IEEE 802.16의 레인징 서브 시스템에서는

이 되고, 최대 처리량을 얻기 위한 offered load는 'C'가 된다.Random access is based on slot aloha by default. Slot Aloha Throughput

to be. Where S is throughput and G is offered load. In the ranging subsystem of the IEEE 802.16 system, one frame can be connected to terminals by the number of PN codes. Therefore, the throughput of the ranging subsystem of the IEEE 802.16 system

Becomes C is the number of PN codes in a frame. So the maximum throughput is like slot aloha

to be. And the offered load to get maximum throughput in slot Aloha is '1'. Therefore, in the ranging subsystem of IEEE 802.16

And the offered load to get the maximum throughput is 'C'.

가 된다. B는 백로그드 유저(backlogged user)들의 수이고,

는 백로그드 유저들의 재전송 확률이다. 재전송 확률을 한 프레임에 엑세스하는 단말의 수가 평균적으로 'C'가 되게 조절한다. 따라서 재전송 확률

가 가장 이상적인 재전송 확률이 된다. BEB 알고리즘은 단말 접속률이

에 근접하면 불안정 상태가 된다. 하지만 앞의 재전송 확률을 갖고 재전송을 하면 최대 처리량을 유지한다. The offered load is the sum of newly generated terminals and retransmitted terminals. So the offered load

Becomes B is the number of backlogged users,

Is the retransmission probability of backlog users. The retransmission probability is adjusted so that the number of terminals accessing a frame is 'C' on average. Thus retransmission probability

Is the most ideal retransmission probability. BEB algorithm has a terminal access rate

If it approaches, it becomes unstable. However, retransmission with the previous retransmission probability maintains maximum throughput.

To calculate the retransmission probability, the base station needs to know the terminal access rate, the offered load, and the number of backlogged users. Here is how to predict the first three parameters.

The terminal access rate is predicted by the number of successful terminals. The prediction method is as follows. When the system is in a stable state, the number of terminals to connect to is the number of successful terminals. Therefore, the terminal access rate can be predicted as follows.

는 i번째 프레임에서 성공한 단말의 수이다. 단말 접속률의 오르내림을 줄이기 위해 단말 접속률을 자기 회귀 처리(autoregressive processing)를 이용한 수학식 2를 사용한다.Equation 1 shows the terminal access rate as the average of successful terminals from the km-1 th frame to the k th frame in the k th frame. Where m is the number of frames.

Is the number of successful terminals in the i-th frame. In order to reduce the rise and fall of the terminal access rate, Equation 2 using autoregressive processing is used.

는 k번째 프레임에서의 도착률에서 고주파 성분을 걸러내어 오르내림을 줄인 예측 값이다. 앞의 예측 방법은 예측 지연이 발생한다. 실제 단말 접속률이 갑작스럽게 변하는 환경에서는 예측 지연이 큰 영향을 미친다. 실제 단말 접속률이 갑작스럽게 변하면 예측 지연에 의해 실제 단말 접속률보다 작게 예측이 되고, 작게 예측된 단말 접속률은 offered load와 backlogged user 수의 예측에 영향을 미친다. 따라서 수학식 3과 같이 한 프레임에 접속을 성공하는 단말의 수가 하나도 없는 상태가 일정 시간 동안 계속되면 단말 접속률을 최대값인

로 증가시킨다.here

Is a predicted value that reduces high frequency components by filtering high frequency components from the arrival rate in the kth frame. The previous prediction method incurs a prediction delay. In an environment where the actual terminal access rate changes abruptly, the prediction delay has a great effect. If the actual terminal access rate changes abruptly, it is predicted to be smaller than the actual terminal access rate due to the prediction delay, and the small predicted terminal access rate affects the prediction of the offered load and the number of backlogged users. Therefore, as shown in Equation 3, if there is no number of terminals successfully connected to one frame for a predetermined time, the terminal access rate is maximum.

To increase.

= 0 이면

= 0

The estimated load and the number of backlogged users are predicted using Equation 4 and Equation 5 using the predicted terminal access rate.

은 n번째 프레임에서 단말들이 엑세스를 성공할 때까지의 시도 횟수이다.

은 n번째 프레임에서 엑세스를 성공한 단말들의 지연이다. 단말 접속률의 예측에서 사용한 것과 같이 오르내림을 줄이기 위해 autoregressive processing을 이용하면, 수학식 6 및 수학식 7과 같다.Where q is the number of frames,

Is the number of attempts until the terminals succeed in access in the nth frame.

Is a delay of UEs that have successfully accessed in the nth frame. When autoregressive processing is used to reduce the up and down as used in the prediction of the UE access rate, Equations 6 and 7 are used.

,

,

는 0과 1사이의 값을 갖으며, 오르내림을 조절하는 요소이다.Of Equations 2, 6 and 7

,

,

Has a value between 0 and 1 and is a factor controlling up and down.

)와 비교하고, 지연을 BEB 알고리즘의 지연과 비교하면 4가지 상황이 발생한다.In order to show an improved performance of the BEB algorithm, the base station has a database of the delay of the BEB algorithm. The retransmission probability is calculated by the terminal access rate, the offered load, and the number of backlogged users. Table 1 shows the retransmission probability according to the situation. The expected load for the situation shown in Table 1 is compared to the offered load with the maximum throughput.

), And comparing the delay with that of the BEB algorithm, four things happen.

Case

One.

2.

3.

4.

The IEEE 802.16 standard cannot transmit information for calculating the number of transmission attempts and delays from the terminal to the base station, and cannot transmit the retransmission probability from the base station to the terminal. Therefore, the IEEE 802.16 standard needs to be modified as follows. The UE should add the number of transmission attempts and the time when the first connection is attempted to the ranging request message (RNG-REQ). In addition, the base station should add the retransmission probability to the DL-MAP message.

Table 2 shows the ranging request message format transmitted from the terminal to the base station proposed in the present invention.

Table 3 shows a DL-MAP message format broadcasted by the base station proposed by the present invention to the terminal.

grammar size Explanation  RNG-REQ_Message_Format () {  Management Message Type = 4 8 bits  Downlink Channel ID 8 bits Number of Trials 4 bits Time of First Access 12 bits  TLV Encoded Information variable TLV specific  }

grammar size Explanation  DL-MAP_Message_Format {  Management Message Type = 2 8 bits  PHY Synchronization Field variable See appropriate PHY specification  DCD Count 8 bits  Base Station ID 48 bits Retransmission Probability 16 bits  Begin PHY Specific Section { See applicable PHY section  for (i = 1; i <= n; i ++) { For each DL-MAP element 1 to n  DL-MAP_IE () Variable See corresponding PHY specification  }  }  if! (byte boundary) {  Padding nibble 4 bits Padding to reach byte boundary  }  }

3 is a block diagram of a wireless mobile communication system in accordance with the present invention.

The wireless mobile communication system of FIG. 3 includes a plurality of terminals 310-380 and at least one base station 390.

The plurality of terminals 310-380 each include a transceiver 311 and a processor 312.

The transceiver 311 includes a wireless protocol processing means, an antenna for transmitting and receiving a wireless signal, and the like. The transceiver 311 transmits a ranging request message including the number of transmission attempts and the initial access attempt time until the terminal successfully accesses the base station 390. In addition, the transceiver 311 receives the retransmission probability from the base station 390. In addition, the transceiver 311 retransmits the ranging request message to the base station 390 according to the received retransmission probability. The retransmission operation of the transceiver 311 is controlled by the processor 312.

If the ranging response message corresponding to the ranging request message is not received by the transceiver 311 within the threshold time, the processor 312 causes the transceiver 311 to receive a retransmission probability of the next frame, and most recently. The ranging request message is retransmitted according to the received retransmission probability. In this case, the threshold time is a time at which the timer operates and is a time that can be appropriately determined by considering the performance of the terminal by a person having ordinary knowledge in the art.

The base station 390 calculates and broadcasts a retransmission probability every frame by using the number of transmission attempts and the initial access attempt time. In addition, the base station 390 transmits the ranging response message to the corresponding terminal when the ranging request message does not have a collision.

In the above, the system environment, the retransmission probability, and the method for estimating the terminal access rate, the offered load, and the number of backlogged users for calculating the retransmission probability have been described. The message format of uplink and downlink for predicting terminal access rate, offered load, and number of backlogged users is described.

Hereinafter, a backoff procedure of random access according to the present invention will be described in detail with reference to FIG. 4.

4 is a flowchart illustrating a method of backing off random access in a wireless mobile communication system according to the present invention.

In the same manner as the conventional backoff method, the terminal 400 immediately attempts to access the data if there is data to be sent to the base station 450 (411). However, another terminal may transmit a message by using the same PN code in the same slot. In this case, collisions may occur between the messages transmitted by the plurality of terminals.

After transmitting the message, the terminals start a timer (413). The base station 450 sends the ranging response message immediately after receiving the message. If the terminal does not receive the ranging response message within the threshold time, the terminal considers the sent message as a collision and determines whether to retransmit (419). In this case, the threshold time is a time at which the timer operates and is a time that can be appropriately determined by considering the performance of the terminal by a person having ordinary knowledge in the art.

The terminal receives several retransmission probabilities 415 while the timer is running. Whether to retransmit is determined by the terminal with the last retransmission probability 417 received. The terminal randomly selects a real number between 0 and 1. If the selected random real number is smaller than the last retransmission probability 417 (419), the retransmission 421 is performed. In this case, the messages transmitted by the plurality of terminals may conflict.

As with the initial connection attempt, the terminals sending the message start the timer 423 and receive several retransmission probabilities 425 while the timer is running. When the terminal 400 waiting for the ranging response message from the base station 450 does not receive the ranging response message until the end of the timer, that is, within the threshold time, the terminal 400 considers the transmitted message as a collision and retransmits it with the last retransmission probability 427 received. A determination is made 429.

In this case, the retransmission determination process, as described above, the UE randomly selects a real number between 0 and 1, and compares the random number selected with the last retransmission probability 427. If the probability of retransmission is greater than any real number (429), retransmission is not performed. If the retransmission is not performed, the retransmission probability 431 is received again. The new transmission retransmission probability 431 is used to determine whether to retransmit 433. As before, a random real number is selected, and the selected random real number is compared with the newly received retransmission probability 431 to determine whether to retransmit.

Until the ranging is successful, the terminal 400 receives the retransmission probability 435 and determines 437 whether to retransmit. When the terminal receives the ranging response message 441, the message sent is successful.

The base station 450 calculates retransmission probabilities 415, 417, 425, 427, 431, and 435 based on the number of successful terminals in each frame, the number of attempts obtained by the successful terminals, and the time when the first access attempt is made. The calculated retransmission probability is transmitted to all terminals. All terminals follow the ranging procedure described above. The retransmission probability is small when there are many terminals to be connected at present, and large when there are few terminals. Therefore, the number of terminals always connected to one frame is optimized.

Hereinafter, the procedures performed in the base station and the terminal according to the present invention will be described in detail with reference to FIGS. 5 and 6.

5 is a flowchart illustrating a procedure for implementing backoff of random access in a base station according to the present invention.

Referring to FIG. 5, a plurality of ranging request messages transmitted by a plurality of terminals are received at a base station (operation 501). Only when data transmitted through the ranging channel does not collide with each other, the base station normally demodulates a predetermined ranging request message transmitted from a specific terminal (step 503).

로 증가시킨다(515 과정).The UE access rate is estimated based on the number of normally received and demodulated messages (step 505). As described above, the prediction method predicts the average number of terminals that have successfully ranged for a certain number of frames. As described above, if the predicted terminal access rate is '0' (step 507), N is incremented by one (step 509). If not, the value of N is set to 0 (step 511). Here, N represents the number of frames where the prediction terminal access rate value was '0'. When N becomes a certain number of frames Q (step 513), the predicted terminal access rate is the maximum value.

(Step 515).

Next, information on the number of attempts of each terminal and the time of first access is extracted from the successfully demodulated messages (step 517).

This is used to predict the offered load and the number of backlogged users along with the expected terminal access rate (step 519).

이고

이면(523) 재전송 확률은

(525)이 되고, 나머지 상황에서 재전송 확률은

)(527)가 된다.The base station may have a delay data base (DB) of the BEB algorithm. This delay DB serves as a criterion for determining the state of the channel in Table 1. Given the situation of the channel,

ego

Back (523) retransmission probability

(525), and in the rest of the situation the probability of retransmission

(527).

The calculated retransmission probability is included in the DL-MAP message and broadcasted to all terminals by the base station (step 529). All terminals receive the retransmission probability and determine whether to retransmit.

6 is a flowchart illustrating a procedure for implementing backoff of random access in a terminal according to the present invention.

Referring to FIG. 6, the terminal transmits a ranging request message (initial ranging, handoff ranging, periodic ranging, and bandwidth request) to the base station, including the number of attempts and the time of first access through the random access. Start the timer (step 601). The base station sends a ranging response message to the terminal that has successfully received the message.

When the terminal receives the ranging response message from the base station (step 603), the terminal checks the processing result of the ranging response message (step 615). However, if the ranging response message is not received until the end of the timer, that is, within the threshold time (step 603), the base station receives the retransmission probability broadcast by the base station (step 607).

The terminal selects a random real number between 0 and 1, and compares the selected random real number with the received retransmission probability (step 609). If any real number is greater than the retransmission probability (step 609), a new retransmission probability is received (step 607).

If any real number is less than the retransmission probability, select a random slot and PN code. The ranging request message is transmitted using the selected slot and the PN code, including the number of attempts and the time of first access. At this time, operate the timer.

When the ranging response message is received from the base station until the timer expires, that is, within the threshold time (step 613), the ranging response message processing result is checked (step 615). If the timer is not received without receiving the ranging response message (step 613), a new retransmission probability is received to repeat the above process (steps 607-611). At this time, whether to retransmit is determined according to the most recently received retransmission probability.

Preferably, in the wireless mobile communication system of the present invention, a program for executing the backoff method of random access on a computer may be recorded and provided on a computer-readable recording medium.

The invention can be implemented via software. When implemented in software, the constituent means of the present invention are code segments that perform the necessary work. The program or code segments may be stored on a processor readable medium or transmitted by a computer data signal coupled with a carrier on a transmission medium or network.

The computer-readable recording medium includes all kinds of recording devices in which data is stored which can be read by a computer system. Examples of computer-readable recording devices include ROM, RAM, CD-ROM, DVD ± ROM, DVD-RAM, magnetic tape, floppy disks, hard disks, optical data storage devices, and the like. The computer readable recording medium can also be distributed over network coupled computer devices so that the computer readable code is stored and executed in a distributed fashion.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those skilled in the art that various modifications and embodiments may be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the present invention, an effective random access can be implemented in a wireless mobile communication system in which a base station cannot distinguish a collision from an empty channel, and only an optimized number of terminals can access a connection because the base station determines the channel status. At the same time, the throughput can be increased while reducing the delay of accessing a base station during channel congestion, and it is possible to solve the problem of wasting resources of BEB algorithm, falling into instability, fairness problem and potential collision problem.

Claims (12)

Transmitting a ranging request message to the base station, the ranging request message including a number of transmission attempts and an initial access attempt time until an access is successfully made by any one of a plurality of terminals; Calculating a retransmission probability by the base station receiving the ranging request message by using the number of terminals successfully connected every frame, the number of transmission attempts, and an initial access attempt time; Broadcasting the retransmission probability at the base station; And If the terminal does not receive a ranging response message corresponding to the ranging request message within a threshold time, transmitting a ranging request message to a base station according to the retransmission probability; Off way. The method of claim 1, The step of transmitting the ranging request message to the base station according to the retransmission probability And when the terminal receives the ranging response message within a threshold time, determining that the terminal is successful in accessing the wireless mobile communication system. The method of claim 1, The step of transmitting the ranging request message to the base station according to the retransmission probability Randomly selecting a real number between 0 and 1 in the terminal, and transmitting a ranging request message to a base station if the selected real number is less than the retransmission probability. Off way. The method of claim 1, The step of transmitting the ranging request message to the base station according to the retransmission probability Randomly selecting a real number between 0 and 1 in the terminal, and if the selected real number is greater than the retransmission probability, waiting for a retransmission probability of a next frame to be received in the wireless mobile communication system. Way backoff. The method of claim 1, Computing the retransmission probability Calculating a terminal access rate using the number of messages for which collision does not occur among ranging request messages received by the base station; Estimating the number of backlog users based on the number of transmission attempts and the terminal access rate, and predicting an operational load using delays of terminals successfully connected according to the initial access attempt time; And Computing the retransmission probability using an operator load, the number of backlog users, and the predicted operator load for which a maximum throughput determined according to the number of PN codes present in a frame occurs; A method of backoff random access in a wireless mobile communication system. The method of claim 5, wherein Computing the terminal access rate

If is the number of successful terminals in the i-th frame, for m frames from the km-1 th frame to the k th frame, Equation 1

(One) And calculating a terminal access rate using the random access method. The method of claim 6, Computing the terminal access rate If the number of terminals successfully connected in one frame is zero, increasing the terminal access rate to a maximum value. The method of claim 6, Predicting the offer load λE (k) is the terminal access rate of the kth frame, q is the number of frames, Tn is the number of transmission attempts until the terminals succeed in the nth frame, and Dn is the delay of the terminals that have successfully accessed in the nth frame. When Equation 4

(4) To calculate the load of the operation using Equation 5

(5) And calculating the number of backlog users using the random access method. The method of claim 8, Computing the retransmission probability

Is the load of the workload for which the maximum throughput occurs,

Is the delay of the BEB algorithm stored in the base station,

Delays of less than or equal to and successful terminals

Greater than or equal to

To calculate the retransmission probability, otherwise

Calculating a retransmission probability by using a random access backoff method in a wireless mobile communication system. Transmitting a ranging request message to the base station, the ranging request message including a number of transmission attempts and an initial access attempt time until an access is successfully made by any one of a plurality of terminals; When the terminal receives a ranging response message corresponding to the ranging request message within a threshold time, determining that the terminal has successfully connected; If the terminal does not receive the ranging response message within a threshold time, receiving, from the base station, a retransmission probability calculated by using the number of terminals successfully connected in each frame, the number of transmission attempts, and the initial access attempt time; ; And And transmitting a ranging request message to a base station according to the retransmission probability. A computer-readable recording medium having recorded thereon a program for executing the method of claim 10 on a computer. In the wireless mobile communication system comprising a plurality of terminals and at least one base station, The plurality of terminals A ranging request message including a number of transmission attempts and an initial access attempt time until a successful connection is transmitted from one terminal to the base station, a retransmission probability is received from the base station, and the ranging request is based on the retransmission probability. A transceiver for retransmitting a message to a base station; And If the ranging response message corresponding to the ranging request message is not received within the threshold time by the transceiver, the transceiver receives the retransmission probability of the next frame and whether to retransmit the ranging request message according to the retransmission probability. A processor for determining a; The base station It calculates and broadcasts the retransmission probability every frame by using the number of transmission attempts and the initial access attempt time, and transmits a ranging response message to a corresponding terminal when the ranging request message does not have a collision. Wireless mobile communication system.

Images