JP4523424B2 - Cell-specific rate control method, base station, and terminal - Google Patents

Description

  The present invention relates to a rate control method for each cell in a communication system composed of at least one base station and a plurality of terminals existing in a service area (cell) covered by the base station. The present invention relates to a rate control method for each cell when a transmission rate is defined.

  For example, in the W (wireless) -LAN system standardized in the following non-patent document 1, eight transmission rates (6 Mbps, 9 Mbps, 12 Mbps, 18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, 54 Mbps) are used for data transmission using a wireless line. ) Is defined. When a low transmission rate is used, noise resistance is strong and the error rate is low, while the throughput is low. When a high transmission rate is used, a high throughput can be expected, but the usable range is limited because the resistance to noise is weak.

  Further, the specific method of selecting the transmission rate is not defined in the following Non-Patent Document 1, and is left to the manufacturer that provides the product. As an example of a specific method of selecting the transmission rate, if data transmission fails continuously while using a certain transmission rate, the current transmission rate is lowered and continuously If data transmission is successful, a method of increasing the currently used transmission rate can be considered. When there are a plurality of terminals, this control is performed individually at each terminal. Such a method is described in, for example, Patent Document 1 below. In the data transmission in the W-LAN, since the ACK is returned when the receiving station correctly receives the data, the transmitting station can determine the success / failure of the data transmission by receiving / not receiving the ACK.

IEEE802.11a Japanese Patent Laid-Open No. 2003-110575 “Multi-rate radio base station apparatus”, paragraph number 31 and the like

  The W-LAN system currently defined in IEEE802.11a / 11b / 11g is supposed to be used in a stationary or quasi-stationary state. There is an increasing demand, and in this case, the following problems occur.

  For example, in a W-LAN system, a cell radius of 100 to 300 m is assumed, and when a cell with a radius of 300 m is passed at a speed of 300 km, the time that the terminal exists in the cell is only 7.2 seconds. In such a short time, there is a problem that the number of times one terminal transmits data in the same cell decreases, and it is difficult to obtain a transmission result indicated by continuous success or continuous failure. In addition, when moving at a speed of 300 km / h, the state of the radio line changes quickly, and even if a data transmission result (success or failure) is obtained, the transmission rate selected based on it is There is also a problem that it is not appropriate at the time of the next data transmission.

  The present invention has been made in view of the above, and is a cell-specific rate for selecting a transmission rate optimum for the state of a wireless line at that time from a plurality of transmission rates defined in the system. An object is to provide a control method.

  In order to solve the above-described problems and achieve the object, the rate control method for each cell according to the present invention exists in at least one base station and a service area (corresponding to a cell) covered by the base station. A rate control method for each cell when a plurality of usable transmission rates are defined in a communication system composed of a single terminal or a plurality of terminals. For example, each terminal is broadcast in a cell. A response accumulation step in which data is transmitted at a transmission rate included in the transmission rate broadcast signal and the number of ACK receptions and non-receptions corresponding to the data transmission is accumulated, and each terminal immediately before moving to another cell In addition, the number of ACK receptions and the number of non-receptions (accumulation results) accumulated during the serving cell's coverage period are passed to the base station covering the cell in communication. A cumulative result notification step, and the base station accumulates the number of received and non-received ACKs individually received from each terminal, and based on the cumulative result, the base station transmits an uplink from a plurality of defined transmission rates. And an uplink transmission rate selection step for selecting a transmission rate of the line, and a notification step in which the base station broadcasts the selection result in a transmission rate notification signal.

  According to the present invention, the base station accumulates the number of receptions and non-receptions of ACK received from the terminal, determines the uplink transmission rate based on the accumulation result, and all terminals in the same cell The determined uplink transmission rate is used, and each terminal does not perform transmission rate determination processing based on reception and non-reception of ACK in the cell coverage period.

  According to this invention, by applying the cell-specific rate control method, communication is performed at a transmission rate that is selected from a plurality of transmission rates defined in the system and that is optimal for the state of the wireless line at that time. There is an effect that it becomes possible.

  Embodiments of a cell-by-cell rate control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
In the present embodiment, a communication system is assumed in which a plurality of (including one) terminals exist in at least one base station and a service area (hereinafter referred to as a cell) covered by the base station. However, a description will be given of a process of selecting an optimum transmission rate for a wireless line state at that time from a plurality of transmission rates defined in the system when performing data transmission.

  FIG. 1-1 is a diagram illustrating a configuration example of a communication system that implements the cell-specific rate control method according to the present invention, and FIG. 1-2 is a diagram illustrating a plurality of transmission rates prepared by the system. Here, the base station 1 has a transmission rate N1 (N1 is one of the numbers 1 to M shown in FIG. 1-2), and the base station 2 has a transmission rate N2 (N2 is a number 1 to M shown in FIG. 1-2). Any one of them is notified by its own beacon signal (corresponding to the transmission rate notification signal in the claims). Note that the system as a whole supports M transmission rates as shown in FIG.

  FIG. 2 is a diagram illustrating a transmission rate acquisition sequence when the terminal 3 has moved to a cell covered by the base station 1, for example. The base station 1 periodically sends a beacon signal, and the signal includes information on a transmission rate used in the cell (transmission rate information) (steps S1 to S3). When the terminal 3 enters a cell covered by the base station 1, the terminal 3 first receives a beacon signal and acquires transmission rate information included in the signal (step S1). Thereafter, when data transmission is performed, data transmission is executed at the acquired transmission rate (step S4). As described above, in the above system, an optimum transmission rate for the cell can be obtained instantaneously immediately after moving to a new cell.

  Next, an uplink transmission rate update method will be described. FIG. 3 is a diagram illustrating an uplink transmission rate update method. For example, when the terminal 3 and the terminal 4 enter a cell covered by the base station 1, the terminal 3 and the terminal 4 acquire the transmission rate information used in the cell from the base station 1 (step S11). Each terminal transmits data at the acquired transmission rate X1 (corresponding to the transmission rate shown in FIG. 1-2) (step S12), and accumulates the number of times of receiving ACK and the number of times of not receiving ACK. . Furthermore, immediately before moving to the next cell, each terminal notifies the base station 1 of the ACK reception count and non-reception count accumulated so far (corresponding to the cell coverage period shown in the figure) (step S13). The base station 1 accumulates these ACK reception count and non-reception count, and updates the uplink transmission rate to X2 based on the accumulation result (step S14).

  Thus, in this embodiment, all terminals in the same cell use the same transmission rate determined by the base station, and the terminals are based on reception and non-reception of ACK during the cell coverage period. The transmission rate selection process is not performed.

  In FIG. 3, for convenience of explanation, updating is performed based on the number of ACK receptions and non-receptions in a very short period (cell coverage period). Update is performed based on the accumulated number of ACK receptions and non-receptions. As a result, it is possible to cope with a state in which an appropriate transmission rate cannot be determined immediately after the base station is installed, and a change in the environment around the cell that affects the wireless environment (such as building construction that generates reflected waves).

  FIG. 4 shows a configuration example of base stations (1, 2) and terminals (3, 4) for realizing the cell-specific rate control method (uplink transmission rate update method) according to the present invention. FIG. In FIG. 4, the base station includes a transmission rate update unit 11, a transmission data selection unit 12, a transmission unit 13, a reception unit 14, an ACK transmission determination unit 15, an ACK reception / non-reception count accumulation unit 16, The terminal includes a reception unit 21, a beacon analysis unit 22, a transmission data selection unit 23, a transmission unit 24, an ACK reception / non-reception count accumulation unit 25, and a cell switching determination unit 26.

  In the base station, when there is a change in the transmission rate used in response to an instruction from the transmission rate update unit 11, the transmission data selection unit 12 replaces the transmission rate information at the time of transmitting the beacon signal with new transmission rate information. On the other hand, when the terminal receives the beacon signal, the beacon analysis unit 22 acquires transmission rate information and notifies the transmission data selection unit 23 of the information. The transmission data selection unit 23 transmits data arriving from an upper layer to the transmission unit 24 and notifies the transmission rate to be used together. At this time, the transmission data selection unit 23 notifies the ACK reception / non-reception count accumulation unit 25 that the data has been transmitted (transmission notification). Thereafter, the ACK reception / non-reception count accumulation unit 25 counts ACK reception / non-reception corresponding to the above transmission. Then, when there is a notification of cell switching from the cell switching determination unit 26, the transmission data selection unit 23 is notified of the accumulated ACK reception count and the non-reception cumulative count accumulated so far. , Before switching to a new cell, the respective cumulative number is transmitted to the base station.

  As the reception processing of the base station, for example, when normal data is received, the ACK transmission determination unit 15 determines the validity of the data, and when it is determined that the data is correctly received, the transmission data selection unit 12 Instruct to send ACK. Further, when receiving information on the cumulative number of ACK reception / non-reception from the terminal, the ACK reception / non-reception number accumulating unit 16 further adds the number of times to the information accumulated from before. Then, the transmission rate update unit 11 is notified of this number of times, and the transmission rate update unit 11 performs an update process after the elapse of a specific period.

  Next, a method for updating the downlink transmission rate will be described. FIG. 5 is a diagram illustrating a method for updating the transmission rate in the downlink direction. Note that the downlink transmission rate is a transmission rate used at the time of transmission by the base station, and thus there is no need to notify the terminal in advance.

  First, the base station 1 performs data transmission, for example, at the transmission rate Y1 used so far (step S21). Then, an ACK for the above transmission is received (steps S22 and S23), and the ACK reception count and ACK non-reception count are accumulated. After that, when the specified time has passed, the transmission rate to be used in the downlink is selected based on the accumulated number of ACK receptions and ACK non-receptions so far. For example, when updating, a new transmission rate is selected. Data transmission is performed at Y2 (step S24). Although FIG. 5 shows a case where there is one terminal, in the present invention, ACK reception and non-ACK reception corresponding to data transmission to all terminals existing in the cell are counted.

  The method of independently determining the downlink and uplink transmission rates in this way is effective when, for example, the transmission powers of the base station and the terminal are different. Since the W-LAN system uses the same frequency in the downlink and uplink, it is easy to consider that the radio channel state is the same, but when the transmission power is different, the signal power level on the receiving side is different, and the downlink and uplink The appropriate transmission rate may be different.

  FIG. 6 is a diagram illustrating a configuration example of the base stations (1, 2) for realizing the downlink transmission rate update method. Here, the transmission rate of the downlink is updated using the configuration of FIG. 6, but the configuration is not limited to this, and the transmission rate of the downlink is also limited. It is good also as providing separately the structure which updates this.

  First, the transmission data selection unit 12 sends the data received from the upper layer to the transmission unit 13 together with transmission rate information applied to the data. At this time, the ACK reception / non-reception count accumulation unit 16 is notified that data transmission has been performed via the transmission unit 13. Then, the ACK reception / non-reception count accumulation unit 16 receives ACK from the terminal via the reception unit 14 and counts the ACK reception count and ACK non-reception count for the data transmission. Thereafter, the accumulated number of times is notified to the transmission rate update unit 11, and the transmission rate update unit 11 determines a new transmission rate.

  Next, an example of a rate control method when a terminal moves at a high speed in a relatively small service area covered by one base station as in the W-LAN system will be described. FIG. 7 is a diagram illustrating a specific example of the rate control method when there is a terminal moving at a specific speed or more. Here, for example, the terminal 3 moving at a speed of Z or higher per hour uses the transmission rate included in the beacon transmitted by the base station 1 (applying the uplink transmission rate update method described above), The terminal 4 moving at the speed actively changes the transmission rate in the cell by a known process (see the prior art).

  That is, for uplink data transmission, each terminal determines the transmission rate to apply based on whether the mobile station's moving speed is equal to or higher than Z or lower than Z. Specifically, when the moving speed of the local station is equal to or higher than Z, data is transmitted at the transmission rate N1 (N1 is any one of numbers 1 to M specified by the beacon), and the moving speed of the local station is less than Z. In this case, data transmission is performed based on the determination criteria of the local station, regardless of the beacon (known processing). On the other hand, for downlink data transmission, the base station determines the transmission rate to be applied by notifying the base station of the moving speed of the terminal. That is, according to this method, the transmission rate is positively switched for a terminal having a relatively slow moving speed and effective switching of the transmission rate in the cell. Thereby, the throughput of the terminal can be improved, and the improvement of the throughput of the entire system can be expected. Note that there are a method of knowing the moving speed from a speedometer of a car or a train, a method of estimating from a state of fluctuation of received power in a wireless line, and the like.

  Next, an example of a rate control method when a terminal exists in an overlapping portion of two or more cells will be described. FIG. 8 shows a specific example of a rate control method when a terminal exists in an overlapping portion of two or more cells. Here, the moving terminal 3 compares the transmission rates (applying the above uplink transmission rate update method) reported by the base stations (1, 2) with beacons in the overlapping part of the cells. Select the higher transmission rate. For example, when a terminal enters the overlapping portion between the right cell (transmission rate N2) and the left cell (transmission rate N1) in FIG. 8, the transmission rate is “N1> N2”. If so, switch to the transmission rate N1 included in the beacon transmitted in the new cell as soon as possible, and if the transmission rate is “N1 <N2,” communication in the old cell is continued as much as possible. Thus, higher throughput can be expected by performing communication in a cell that provides the highest possible transmission rate. The new cell represents a cell that can be newly provided by the movement of the terminal, and the old cell represents a cell in communication.

  As described above, in the present embodiment, by applying the rate control method, a transmission rate that is selected from a plurality of transmission rates defined by the system and that is optimal for the wireless channel state at that time point It becomes possible to communicate with.

  As described above, the cell-specific rate control method according to the present invention is useful for a communication system including at least one base station and a plurality of terminals existing in a service area covered by the base station. Is suitable for communication when a plurality of transmission rates are defined.

It is a figure which shows the structural example of the communication system which implement | achieves the rate control method according to this invention. It is a figure which shows the some transmission rate which a system prepares. It is a figure which shows the sequence of transmission rate acquisition. It is a figure which shows the update method of the transmission rate of an uplink. It is a figure which shows the structural example of a base station and a terminal. It is a figure which shows the update method of the transmission rate of a downlink direction. It is a figure which shows the structural example of a base station. It is a figure which shows the specific example of the rate control method in case the terminal which is moving above a specific speed exists. It is a specific example of the rate control method when a terminal exists in the overlapping part of two or more cells.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Base station 3, 4 Terminal 11 Transmission rate update part 12 Transmission data selection part 13 Transmission part 14 Reception part 15 ACK transmission determination part 16 ACK reception / non-reception count accumulation part 21 Reception part 22 Beacon analysis part 23 Transmission data selection Unit 24 transmission unit 25 ACK reception / non-reception count accumulation unit 26 cell switching determination unit

Claims (9)

When a plurality of usable transmission rates are defined in a communication system composed of at least one base station and a single or a plurality of terminals existing in a service area (corresponding to a cell) covered by the base station A rate control method for each cell,
A response accumulation step in which each terminal performs data transmission at a transmission rate included in a transmission rate broadcast signal broadcast in a cell, and accumulates the number of receptions and non-receptions of ACK corresponding to the data transmission,
Immediately before each terminal moves to another cell, the number of ACK receptions and the number of non-receptions (accumulation results) accumulated during the coverage period of the cell being communicated to the base station covering the cell in communication A cumulative result notification step to be notified,
The base station accumulates the number of received and non-received ACKs individually received from each terminal, and selects an uplink transmission rate from the plurality of defined transmission rates based on the accumulation result An uplink transmission rate selection step;
A notification step in which the base station broadcasts the selection result in a transmission rate notification signal;
A rate control method for each cell. Further, the base station accumulates the number of ACK receptions and non-receptions corresponding to its own data transmission, and selects a downlink transmission rate based on the accumulation result when a specified time has elapsed. Transmission rate selection step,
The cell-specific rate control method according to claim 1, comprising:   When the terminal is moving at a specific speed or higher, the terminal uses the transmission rate included in the transmission rate notification signal. When the terminal is moving at a speed lower than the specific speed, the terminal transmits the transmission rate notification signal. Regardless of this, the cell-based rate control method according to claim 1 or 2, wherein data transmission is performed based on a judgment criterion of the own station.   When the terminal exists in an overlapping part of adjacent cells, the base station covering each of the terminals compares the transmission rate broadcasted by the transmission rate broadcast signal, and selects the higher transmission rate to perform communication The rate control method for each cell according to claim 1, 2, or 3. In a base station that constitutes a communication system with a single or multiple terminals existing in a service area (corresponding to a cell) covered by the own station,
Accumulating means for further accumulating the accumulated results individually received from each terminal when the terminal has a function of transmitting the number of times of ACK received and the number of times of non-reception (accumulated result) accumulated during the serving cell's coverage period When,
An uplink transmission rate selection means for selecting an uplink transmission rate from a plurality of transmission rates defined in the system, based on a result of accumulation by the accumulation means;
Informing means for informing and including the selection result in a transmission rate informing signal;
A base station comprising: Further, a downlink transmission rate selection means for accumulating the number of ACK receptions and non-receptions corresponding to the data transmission of the own station, and selecting a downlink transmission rate based on a cumulative result when a specified time has elapsed,
The base station according to claim 5, comprising: In a terminal that constitutes a communication system with a base station and exists in a service area (corresponding to a cell) covered by the base station,
Response accumulation means for performing data transmission at a transmission rate included in a transmission rate broadcast signal broadcast in a cell, and accumulating the number of receptions and non-receptions of ACK corresponding to the data transmission;
Accumulated result notifying means for notifying the base station of the number of ACK receptions and the number of non-receptions (cumulative results) accumulated during the coverage period of the cell in communication immediately before moving to another cell;
A terminal comprising:   When moving at a specific speed or higher, the transmission rate included in the transmission rate notification signal is used. When moving at a speed lower than the specific speed, the transmission rate notification signal does not depend on the transmission rate notification signal. The terminal according to claim 7, wherein data transmission is performed based on a determination criterion of a station.   When there is an overlapping portion of adjacent cells, the base stations that cover each cell compare the transmission rates broadcasted by the transmission rate broadcast signal, and perform communication by selecting the higher transmission rate. The terminal according to claim 7 or 8.

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