JP2010288302A - Wireless communication method, wireless communication system, base station and mobile unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a random access control method capable of improving throughput and delay characteristics, while suppressing the quantity of radio resources used. <P>SOLUTION: In a random access control method, a base station determines whether a transmission line is in a normal state or in a congested state, on the basis of whether there is the collision of packets and uses a specific channel to transmit a CS indicative of the normal state or the congested state; meanwhile, when a mobile unit is unable to recognize own transmission success, even after the lapse of a predetermined time, on the other hand, the mobile unit extracts the CS on the specific channel, determines a CW size indicating a maximum value of CW on the basis of the CS, determines the CW on the basis of the CW size and transmits a retransmission packet, on the basis of the CW. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a random access control method used in a wireless communication system.

  First, as an example of a random access control method used in a wireless communication system, there is a method described in Patent Document 1 below. In this method, the same back-off window size determined by the base station is reported to a plurality of terminals, and dynamically adjusted so as to make the collision rate constant, thereby improving the overall throughput. Specifically, if the collision counter value that is the basis for the collision rate is small (when not congested), the back-off window size is decreased, and vice versa (when congested), the back-off window size is increased. This is broadcast from the base station to all terminals. Each terminal performs random access within the range of the instructed backoff window size.

  Note that in general distributed control by “binary exponential back-off” (wireless LAN, etc.), the window size of a user who has been trying for a long time tends to increase. There was a problem that the size tends to be relatively small. However, if the random access control method described above is used, even users who have recently appeared have the same opportunity for trials. Fairness can be improved.

  Next, a random access control method in the mobile satellite communication system described in Non-Patent Document 1 below will be described. For example, the mobile station understands whether or not its own random access has succeeded by receiving PE (Partial Echo) included in the physical channel for forward link control. If the PE of the local station cannot be received even after the timer time has elapsed, the IW included in the physical channel for forward link control is waited for the elapse of random delay (CW: Contention Window) within 25 frames (= 1 second). Check whether Idle or Busy at / B, and if it is Idle and “Persistent = 1.0”, immediately perform a retransmission process (backoff control). However, in the case of “Persistent = 0.5”, retransmission is performed only with a probability of 0.5 even if it is Idle.

JP 2002-374262 A

ARIB STD-T49

  However, in Patent Document 1, the base station dynamically adjusts the back-off window size, that is, the CW width, and notifies the mobile device of the CW width itself. There was a problem of becoming.

  Further, in Non-Patent Document 1, the random control width (CW) in the back-off control is constant, and in the case of Idle, it is fixed at “Persistent = 1.0”, so that traffic tends to increase. In some cases, convergence may take time.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a random access control method capable of improving throughput and delay characteristics while suppressing the amount of radio resources used.

  In order to solve the above-described problems and achieve the object, a random access control method according to the present invention is a random access control method in a radio communication system including a base station and a plurality of mobile devices that communicate with the base station. The base station, for example, determines whether the transmission path is in a normal state or a congestion state based on the presence or absence of a packet collision, and uses a specific channel to determine the normal state or the congestion state. A control signal transmission step of transmitting a CS (Contention Status) indicating, on the other hand, if the mobile station cannot recognize its own transmission success even after a predetermined time has elapsed, A control signal extraction step for extracting CS, and a transmission parameter determination step for determining a CW size indicating the maximum value of backoff time (CW) based on the CS. And flop, and wherein the CW determining step of determining a CW, to perform a retransmission step of transmitting a retransmission packet based on the CW based on the CW size.

  According to the present invention, the collision probability can be controlled by adjusting the CW size and the persistent value according to the congestion state of the transmission path. In addition, the delay characteristic can be improved.

FIG. 1 is a diagram illustrating a configuration example of a base station that implements a random access control method according to the present invention. FIG. 2 is a diagram illustrating a configuration example of a mobile device that implements the random access control method according to the present invention. FIG. 3 is a diagram illustrating a configuration example of an AC. FIG. 4 is a diagram illustrating a random access control method at the time of retransmission in the second embodiment. FIG. 5 is a diagram illustrating a probability distribution for each number of traffic. FIG. 6 is a diagram showing a table representing the distribution of states 0 to 3 when SEG and CW _Max are fixed values and various values are entered in λ. FIG. 7 is a diagram illustrating a configuration example of the congestion detection unit according to the fourth embodiment. FIG. 8 is a diagram illustrating a CS determination method according to the fifth embodiment.

  Hereinafter, embodiments of a random access control method, a base station, and a mobile device according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a base station that implements a random access control method according to the present invention. This base station detects whether a packet collides with the interface unit 1 that is an interface with the network side and the wireless unit 2 that is an interface with the mobile device side, and is in a transmission permitted state or a transmission prohibited state. A collision detection unit 3 that outputs information (Idle / Busy) indicating the above, a congestion detection unit 4 that determines whether or not there is a congestion state, and outputs a result (CS: Contention Status), and a physical channel for forward link control And a transmission unit 5 that transmits the AC (Access Channel) including the CS and I (transmission permitted) / B (transmission prohibited).

  FIG. 2 is a diagram showing a configuration example of a mobile device that realizes the random access control method according to the present invention. This mobile device includes a radio unit 11 that is an interface with the base station side, a data receiving unit 12 that receives a signal on a physical channel for forward link control, an interface unit 13, and an AC on a physical channel for forward link control. A CW size determining unit 14 that determines a CW size based on the CS included in the (Access Channel), and a Persistent value determining unit 15 that determines a Persistent value based on the CS included in the AC on the physical channel for forward link control, A back-off time determination unit 16 that determines a back-off time based on the CW size determined above, a transmission buffer 17 that stores transmission packets in accordance with a known packet transmission process, a back-off time determined above, Persistent And a data transmission unit 18 that transmits a retransmission packet according to the value and the I / B.

  In the case of the initial transmission, the I / B is confirmed by the same processing as in the prior art. If it is idle, the packet is transmitted according to the Persistent value, and if it is busy, the packet transmission is stopped. If the transmission is successful, the local station receives its own PE (Partial Echo) from the base station. On the other hand, when the PE of the local station cannot be received even after the timer time has elapsed, that is, when transmission fails, the random access control method of the present embodiment described later is executed.

  Next, a random access control method (a method using a control channel) at the time of retransmission according to the present embodiment in the base station and mobile device configured as described above will be described.

  First, in the base station, the collision detection unit 3 detects whether or not a packet has collided in the wireless transmission path. If there is no collision, information indicating the Idle state (Idle) is indicated. If there is a collision, the Busy state is indicated. Information (Busy) is output.

  Next, the congestion detection unit 4 determines whether or not the transmission path is congested based on the information (Idle / Busy) obtained from the collision detection unit 3, and sets the result as CS (0: normal, 1: congestion). Output.

  Then, in the transmission unit 5, based on the information obtained from the collision detection unit 3 and the congestion detection unit 4, CS and 0 in which 0 (normal) or 1 (congestion) is set in the AC on the physical channel for forward link control. Inform the mobile device including the I / B for which (transmission prohibited) or 1 (transmission permitted) is set. FIG. 3 is a diagram illustrating a configuration example of the AC according to the present embodiment. In the present embodiment, it is a bit for notifying a mobile station whether it is in a congested state or a normal state to a conventional AC composed of I / B, PE, TA (time alignment), and CRC. CS is added. In the present embodiment, CS is 1-bit information. For example, CS represents a congestion state, and 0 represents a normal state. In addition, although the example which adds CS to the head of conventional AC is described in FIG. 3, the position where CS is added is arbitrary, and may be added anywhere as long as the mobile device can be confirmed.

  On the other hand, if the mobile station cannot receive its own PE even after the timer time elapses, the mobile device first extracts the I / B and CS included in the AC on the physical channel for forward link control in the data receiving unit 12. . Then, information (Idle / Busy) indicating whether the transmission line is idle or busy is output to the data transmission unit 18, and the transmission line is in a normal state (CS = 0) or a congestion state (CS = 1). Is output to the CW size determination unit 14 and the Persistent value determination unit 15.

  Next, the CW size determination unit 14 determines the CW size indicating the maximum value of CW based on the information obtained from the data reception unit 12 indicating whether the transmission path is in the normal state or the congestion state. . Specifically, “CW size = x” is set in the normal state, and “CW size = y” is set in the congested state. However, x and y are fixed integer values and satisfy “y> x”.

  Note that the CW size determination process by the CW size determination unit 14 is not limited to this. For example, the current CW size is added by a (arbitrary integer) in the normal state, and the current CW in the congestion state. A process of subtracting the size by b (arbitrary integer) may be performed. In this case, a and b may be “a = b” or “a ≠ b”.

  Next, the back-off time determination unit 16 determines the back-off time (CW) based on the CW size determined by the CW size determination unit 14.

  Further, the Persistent value determining unit 15 determines the Persistent value based on the information obtained from the data receiving unit 12 indicating whether the transmission path is in the normal state (CS = 0) or the congestion state (CS = 1). To decide. For example, “Persistent value = k” is set in the normal state, and “Persistent value = l” is set in the congested state. However, k and l are values from 0 to 1 and satisfy “k> l”.

  The persistent value determining process by the persistent value determining unit 15 is not limited to this. For example, in the normal state, the current persistent value is added by c (arbitrary value) in the range of 0 to 1, and the congestion state is determined. In this case, the current persistent value may be subtracted by d (arbitrary value) in the range of 0 to 1. In this case, the above c and d may be “c = d” or “c ≠ d”.

  Then, in the data transmitting unit 18, when the Idle / Busy obtained from the data receiving unit 12 is Idle, the backoff time obtained from the backoff time determining unit 16 and the persistent value obtained from the persistent value determining unit 15 are set. Based on this, the packet to be retransmitted stored in the transmission buffer 17 is read and transmitted.

  As described above, in the present embodiment, CS, which is a bit for notifying the mobile device whether it is in a congestion state or a normal state, is added to the conventional AC on the physical channel for forward link control. It was. As a result, the collision probability can be controlled by adjusting the CW size and the persistent value according to the congestion state of the transmission path, so that the throughput can be greatly improved as compared with the prior art while suppressing the increase in radio resources to 1 bit. Can do. In addition, since the CW size and the Persistent value can be adjusted according to the congestion state of the transmission path and the waiting time until retransmission can be controlled, the retransmission delay can be greatly reduced as compared with the prior art.

  In the present embodiment, CS is expressed by 1 bit, but can be expressed by a plurality of bits. In this case, the CW size and the Persistent value can be finely adjusted. When CS is expressed by a plurality of bits, the CW size and the persistent value do not need to be monotonously increased or decreased in the order of low load, medium load, and high load. For example, the CW size may be small for low and high loads and large for medium loads. If it is a Persistent value, it may be large at low and high loads and small at medium loads.

  Further, in the Idle after the Busy continues, there is a high possibility that the packet collides. Therefore, in the Persistent value determination process by the Persistent value determination unit 15, the Persistent value may be forcibly set to less than 1.

  Also, when there is congestion, sending a short packet with random access increases the probability of collision, so the mobile device retains some transmission data and sends it as a long packet (Long Packet). It is good to do.

  Also, if the transmission path status with the base station is different for each mobile station, there is a possibility that a mobile station with a good transmission path will always succeed in random access, resulting in unfairness between mobile stations. There is. In such a case, the mobile device may adjust the CW size and the Persistent value according to the magnitude of the received power or the failure probability. Specifically, when the received power is low or the random access failure probability is high, processing for decreasing the CW size and / or processing for increasing the persistent value is executed. On the other hand, in the opposite case, processing for increasing the CW size and / or processing for decreasing the Persistent value is executed.

Embodiment 2. FIG.
In the first embodiment described above, the random access control method using the control channel has been described. In the present embodiment, a random access control method using the packet communication channel will be described. In the present embodiment, since I / B is not included in AC, Persistent control is not performed for the mobile device, that is, Persistent value determination unit 15 does not exist. The configurations of the other base stations and mobile devices are basically the same as those shown in FIGS. 1 and 2 of the first embodiment.

  Here, an outline of processing different from the first embodiment will be briefly described. First, in the base station shown in FIG. 1, the transmission unit 5 of the present embodiment embeds an AC (Access Channel) including CS, PE, TA, and CRC on the packet communication channel and transmits the packet. Further, unlike the first embodiment described above, the mobile device shown in FIG. 2 does not have the Persistent value determining unit 15, the data receiving unit 12 receives a signal on the packet communication channel, and the CW size determining unit. 14 determines the CW size (the maximum value of CW) based on the CS included in the AC on the packet communication channel, and the data transmission unit 18 transmits the retransmission packet according to the back-off time determined based on the CW size. To do. As described above, since the transmitter transmits without including the I / B in the AC, the mobile device according to the present embodiment does not have a function of detecting the I / B and does not perform the persistent control. It has become.

  Next, the random access control method (method using a packet communication channel) at the time of retransmission according to the present embodiment in the base station and mobile device configured as described above will be described in detail. Here, processing different from that of the first embodiment will be described.

  In the base station of the present embodiment, the transmission unit 5 embeds AC including CS in addition to PE, TA, CRC on the packet communication channel based on the information obtained from the congestion detection unit 4, Send to the mobile device. FIG. 4 is a diagram showing a random access control method (a method using a packet communication channel) at the time of retransmission in the second embodiment, in which a packet communication channel is used as a channel for performing random access control. This is a difference from the first embodiment. Unlike the control channel, the packet communication channel does not have AC. Therefore, in this embodiment, 4TS (TS1 to Ts4) is stealed in each frame in the superframe, and AC is embedded therein and transmitted. Further, as shown in FIG. 4, TS0 immediately before AC is, for example, “SSC = all 1”.

  Further, in the present embodiment, CS is 1-bit information, as described above. When CS is 1, it indicates a congestion state, and when it is 0, it indicates a normal state. Although FIG. 4 shows an example in which CS is arranged at the head of AC, the position of CS is arbitrary, and it may be arranged anywhere on the packet communication channel as long as the mobile device can confirm.

  On the other hand, after transmitting a packet, if the mobile station of the present embodiment cannot receive its own PE even after a predetermined timer time has elapsed, the mobile station of the present embodiment first uses the AC on the packet communication channel in the data receiving unit 12. Confirm CS included in. Then, information indicating whether the transmission path is in the normal state (CS = 0) or the congestion state (CS = 1) is output to the CW size determination unit 14. Thereafter, in the same process as in the first embodiment, the CW size determination unit 14 determines the CW size, and the backoff time determination unit 16 performs the backoff based on the CW size determined by the CW size determination unit 14. Determine the time (CW).

  Then, the data transmission unit 18 reads and transmits the packet to be retransmitted stored in the transmission buffer 17 based on the backoff time obtained from the backoff time determination unit 16.

  As described above, in the present embodiment, an AC including CS, which is a bit for notifying the mobile device whether it is in a congested state or a normal state, is embedded in the packet communication channel, and I decided to send it. As a result, the CW size can be adjusted according to the congestion state of the transmission path and the collision probability can be controlled, so that the throughput and delay characteristics can be greatly improved as compared with the prior art while suppressing the increase in radio resources to 1 bit. Can do.

  In the present embodiment, CS is expressed by 1 bit, but can be expressed by a plurality of bits. In this case, the CW size can be finely adjusted.

Embodiment 3 FIG.
Next, in the first and second embodiments described above, an algorithm when the congestion detection unit 4 of the base station determines the CS will be described in detail.

  In general, the traffic generation per unit time can be approximated by a Poisson distribution. The Poisson distribution can be expressed by the following equation (1). X represents a random variable (0, 1, 2, 3,..., N,...), And λ represents an average of Poisson distribution.

  For example, when λ = 1, the probability distribution is as shown in FIG. Considering this as the occurrence of traffic, where the horizontal axis is the number of simultaneous accesses X and the vertical axis is the probability P, the probability of 0 traffic (no access) is about 37% and 1 traffic (no simultaneous access). Similarly, the probability is about 37%, the probability of two traffics (with simultaneous access) is about 18%, and so on.

In the case of random access, if two or more traffics occur, there is a high possibility that both will collide and result in random access failure. Therefore, by counting the following states, the parameter λ ′ for determining the shape of the Poisson distribution Can be estimated.
State 0: Idle state (no access, ie X = 0)
State 1: Success state (only one case is accessed, that is, X = 1)
State 2: Collision state (2 or more accesses overlapped and failed, X ≧ 2)

On the other hand, for example, in the known access method called ICMA-PE, a mobile device that has secured the access right can exclusively transmit continuously, so state 3 shown below is defined.
Status 3: Reserved status (because a specific mobile station is transmitting exclusively (because it is busy), access is not possible)

  That is, since the state 3 originally belongs to any of the states 0 to 2, the actual parameter λ (≠ λ ′ is simply obtained by simply counting the states 0 to 2 and taking the average. ) Cannot be determined.

  Therefore, in the present embodiment, the base station estimates the actual parameter λ (≠ λ ′) by the following method based on the count results in the states 0 to 3.

First, as input parameters, λ (average value of Poisson distribution), SEG (time during which a mobile device that has secured the access right exclusively transmits) and CW _Max (maximum value when randomly delaying when colliding), And the distribution of the states 0 to 3 when the values “λ = λ _x ”, “SEG = SEG _z ”, and “CW _Max = CW _y ” are set are obtained by Monte Carlo simulation.

For example, SEG and CW _Max are fixed values, and various values are put into λ to obtain the distribution of the states 0 to 3, and a table as shown in FIG. 6 is obtained in advance.

Then, the congestion detection unit 4 obtains the occurrence probabilities P _0x , P _1x , P _2x , and P _3x of the states 0 to 3 based on the count results of the states 0 to 3 over a predetermined Δt time. Λ _i closest to the occurrence probability obtained above is determined as the actual λ. Here, λ _i is defined as the smallest square error shown in the following equation (2).
E = (P _0i -P _0x ) ² + (P _1i -P _1x ) ² + (P _2i -P _2x ) ² + (P _3i -P _3x ) ² (2)

  Thereafter, the congestion detection unit 4 compares λ determined above with a preset threshold value, and, for example, determines that the congestion state (CS = 1) when λ is larger than a specific threshold value. .

  As described above, in the present embodiment, the congestion detection unit approximates the traffic generation per unit time with the Poisson distribution and determines the CS based on the average value λ of the Poisson distribution. Thereby, in the mobile device, the CW size can be adjusted according to the congestion state of the transmission path, and the collision probability can be controlled. As a result, throughput and delay characteristics can be improved as compared with the conventional case.

Embodiment 4 FIG.
Subsequently, in the fourth embodiment, an algorithm different from that in the third embodiment when the congestion detection unit 4 of the base station determines the CS will be described.

FIG. 7 is a diagram illustrating a configuration example of the congestion detection unit 4 according to the fourth embodiment. The congestion detection unit 4 according to the present embodiment includes delay units 21-0 to 21- (N-1), multipliers 22-0 to 22-N, and an adder 23, and a state X (m) ... State X (m− _N ) is multiplied by weights h ₀ , h ₁ , h ₂ ,..., H _N (h ₀ > h ₁ > h ₂ >...> H _N ), and each multiplication result Are added, and the addition result is output as the filter result Y (m).

The congestion detection unit 4 first assigns points P ₀ , P ₁ , and P ₂ (P ₀ <P ₁ <P ₂ ) to the above-described three states (state 0, state 1, and state 2), respectively. Then, filtering is performed with the above configuration, and for example, when the filter result Y (m) exceeds a predetermined threshold value, it is determined that the congestion state (CS = 1). Thereafter, the filter process is continued while gradually shifting the N states recently, and it is determined whether or not the state is a congestion state every time the filter result Y (m) is obtained.

  In addition, regarding the state 3 described above, it is uncertain which one of the states 0 to 2 falls, but random access may be concentrated in the slot immediately after the reservation state continues for a long time. The weight immediately after the M continues for more than M (arbitrary integer) slots is multiplied by a predetermined coefficient ρ.

  Thus, in the present embodiment, the congestion detection unit is configured by the filter, and CS is determined based on the filter result Y (m). Thereby, in the mobile device, the CW size can be adjusted according to the congestion state of the transmission path, and the collision probability can be controlled. As a result, throughput and delay characteristics can be improved as compared with the conventional case.

  Note that in the Idle after Busy continues, there is a high possibility of packet collision, so the weight in the collision state may be set lower than usual.

Embodiment 5 FIG.
Subsequently, in the fifth embodiment, an algorithm different from those in the third and fourth embodiments when the congestion detection unit 4 of the base station determines the CS will be described.

  FIG. 8 is a diagram illustrating a CS determination method according to the fifth embodiment. Specifically, the above three states (state 0, state 1, and state 2) are represented by three events of Idle, success, and failure, respectively. The CS is determined from the state transition shown in FIG. Here, S0 and S1 are in a normal state (CS = 0), and S2 and S3 are in a congestion state (CS = 1).

  For example, the initial state (idle state) is set to S0 (normal state), and random access occurs in this state. If it succeeds or fails, the state transits to S1 (normal state), and the state of S1 is maintained during the success. In the state of S1, when N1B times or more out of N1A times fail, the state transits to S2 (congestion state). Further, in the state of S2, in the case of success or failure, this state is maintained, and when it becomes Idle in this state, the state transits to S3 (congestion state). Further, in the state of S3, when N2B times or more of N2A times becomes Idle, the state transits to S0 (normal state).

  Note that state 3 described above is considered to be idle or successful stochastically. Specifically, for example, each state (S0 to S3) has a threshold value, generates a uniform random number, and if the value exceeds the threshold value, it succeeds, otherwise it is regarded as Idle. , Perform state transition.

  As described above, in this embodiment, the above three states (state 0, state 1, state 2) are divided into three events of Idle, success, and failure, respectively, and CS is determined from the state transition shown in FIG. It was decided to decide. Thereby, in the mobile device, the CW size can be adjusted according to the congestion state of the transmission path, and the collision probability can be controlled. As a result, throughput and delay characteristics can be improved as compared with the conventional case.

  As described above, the random access control method according to the present invention is useful for mobile communication systems, and is particularly suitable as a random access control method during packet retransmission.

DESCRIPTION OF SYMBOLS 1 Interface part 2 Radio | wireless part 3 Collision detection part 4 Congestion detection part 5 Transmission part 11 Radio | wireless part 12 Data reception part 13 Interface part 14 CW size determination part 15 Persistent value determination part 16 Back-off time determination part 17 Transmission buffer 18 Data transmission part 21-0 to 21- (N-1) delay device 22-0 to 22-N multiplier 23 adder

Claims (12)

A base station and a mobile station, wherein the mobile station retransmits data transmitted to the base station to the base station.
A back-off signal transmission step in which the base station transmits a back-off time determination signal for the mobile device to set a maximum back-off time for each predetermined unit;
A back-off time setting step in which the mobile device sets a maximum value of a back-off time based on the back-off time determination signal;
A wireless communication method comprising: The wireless communication method according to claim 1, wherein the predetermined unit is a unit of encoding the back-off time determination signal. A radio station employed by the base station in a radio communication system that transmits after a lapse of a backoff time when the mobile station retransmits data transmitted to the base station to the base station. A communication method,
The mobile device transmits a back-off time determination signal for setting the maximum value of the back-off time to the mobile device that sets the maximum value of the back-off time based on the back-off time determination signal for each predetermined unit. Backoff signal transmission step,
A wireless communication method comprising: The wireless communication method according to claim 3, wherein the predetermined unit is an encoding unit of the back-off time determination signal. A wireless communication system including a base station and a mobile device, wherein the mobile device employs a wireless communication system that transmits after a back-off time elapses when the mobile device retransmits data transmitted to the base station to the base station. A communication method,
A back-off signal receiving step for receiving a back-off time determination signal for the mobile station to set a maximum value of the back-off time, which is transmitted by the base station for each predetermined unit;
A back-off time setting step for setting a maximum value of the back-off time based on the received back-off time determination signal;
A wireless communication method comprising: The wireless communication method according to claim 5, wherein the predetermined unit is a unit of encoding the back-off time determination signal. A wireless communication system including a base station and a mobile device, wherein the mobile device retransmits data transmitted to the base station to the base station when a back-off time has elapsed;
The base station comprises back-off signal transmitting means for transmitting a predetermined unit of back-off time determination signal for the mobile device to set a maximum back-off time,
The mobile device includes backoff time setting means for setting a maximum value of backoff time based on the backoff time determination signal.
A wireless communication system. The wireless communication system according to claim 7, wherein the predetermined unit is a unit of encoding the back-off time determination signal. A base station and a mobile station, wherein the mobile station retransmits data transmitted to the base station to the base station, the base station in a radio communication system that transmits after a back-off time,
The mobile device transmits a back-off time determination signal for setting the maximum value of the back-off time to the mobile device that sets the maximum value of the back-off time based on the back-off time determination signal for each predetermined unit. Back-off signal transmission means,
A base station comprising: The base station according to claim 9, wherein the predetermined unit is an encoding unit of the back-off time determination signal. A base station and a mobile device, wherein the mobile device retransmits data transmitted to the base station to the base station, the mobile device in a wireless communication system that transmits after the lapse of a backoff time,
Backoff signal receiving means for receiving a backoff time determination signal for the mobile station to set a maximum backoff time, which is transmitted by the base station for each predetermined unit;
Based on the received backoff time determination signal, backoff time setting means for setting the maximum value of the backoff time;
A mobile device comprising: The mobile unit according to claim 11, wherein the predetermined unit is an encoding unit of the back-off time determination signal.

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