Now, exemplary embodiments of the present invention will be described by referring to the drawings.
In the cellular system, a plurality of carriers are available for communication between a base station and a mobile station. The carriers include uplink carriers and downlink carriers. Different carriers are used in the Frequency Division Duplexing on uplink and downlink. The OFDM (Orthogonal Frequency Division Multiplexing) is used for modulation.
The carriers are divided in a transmission time unit. In packet transmission from a mobile station to a base station, a carrier is selected, a transmission time is allocated in the transmission time unit, and a data block is transmitted during the transmission time. The base station notifies the mobile station of control information of the selected carrier and the transmission time using a control link set between the base station and the mobile station.
Each data block is attached with an error detection code with which a receiver determines whether or not there is an error in receiving a data block. If there is an error, the receiver transmits a NACK (Non-Acknowledgement) signal to a sender and retains the received data block. Otherwise, if there is no error, the receiver transmits an ACK (Acknowledgement: delivery acknowledgement) signal. If the sender receives the NACK signal, it retransmits the same data block while the receiver combines the retransmitted data block and the retained data block to get a data block to be received. This enables to properly receive a data block in a less number of retransmissions.
Each of the base stations 1 and 2 measures interference power of each carrier used in the cellular system at pre-determined measurement time intervals. Then, each of the base stations 1 and 2 calculates a frequency rate Rintf being a ratio of times that the interference power is more than a pre-determined threshold Tintf of interference power to the number of measurements of the interference power during a pre-determined notification time interval set longer than the measurement time interval. The frequency rate corresponds to a time rate being a ratio of time that the interference power is more than the Tintf to the notification time interval. Each of the base stations 1 and 2 notifies the base station controller 5 of the frequency rate Rintf at notification time intervals. The measurement of the interference power of each carrier can be made while a data block is transmitted on the carrier, but the measurement is made herein while a data block is not transmitted on the carrier.
Each of the base stations 1 and 2 further calculates a retransmission probability Rretx of a data block on each of the carriers used for uplink transmission of the data block at the notification time intervals, and notifies the base station controller 5 of the retransmission probability Rretx and the frequency rate Rintf. The retransmission probability Rretx of a data block is calculated as a value of the times that the base station transmitted a NACK signal to the mobile station divided by the times of transmission of ACK signals and NACK signals. The retransmission probability is also called a communication quality. In this retransmission control, since the same data block may be retransmitted for a number of times, only transmission of a new data block can be accounted into the calculation of a retransmission probability.
Each of the base stations 1 and 2 calculates and notifies the frequency rate Rintf and the retransmission probability Rretx for each cell and each carrier. However, a base station corresponds to a cell herein, so that a calculation for each cell will be described hereinafter as a calculation in a base station corresponding to the cell.
The first exemplary embodiment of the present invention will be described below in detail. In the first exemplary embodiment, the base station controller 5 determines a change between an available state or an unavailable state in all carriers.
Referring to
Referring to
In an initial state of the cellular system at the start-up, all the carriers are in an available state.
Referring to
Next, referring to
The base station controller changes an available or unavailable state of each of the carriers and notifies the base station of the information of the change, while the base station updates an available or unavailable state of the carrier based on the notification and uses a carrier in an available state for communication.
An example of the operation of the first exemplary embodiment of the present invention will be described with reference to
Meanwhile, the base station 1 measures interference power of a carrier c2. The mobile stations 6 and 7 cannot use the carrier c2 if a frequency rate Rintf of the carrier c2 is higher than Rintf_High since the mobile station 8 uses the carrier c2 in the cell 4. If the Rintf is lower than the Rintf_Low, the mobile stations 6 and 7 can use the carrier c2.
Next, a second exemplary embodiment of the present invention will be described. In the second exemplary embodiment, high priority carriers and low priority carriers are defined for each cell. The base station controller determines a change between an available state and an unavailable state only for low priority carriers. Other details are same as the first exemplary embodiment including the configuration diagram of the cellular system in
In the second exemplary embodiment, a plurality of carriers available in the entire cellular system are grouped into the carrier groups f1, f2 and f3. The carrier group f1 has a high priority in the cell 3 and the carrier group f2 has a high priority in the cell 4. The carrier group f3 has a high priority in a cell not shown. Carrier groups of high priority are deployed in cells not shown such that different carrier groups have a high priority in neighboring cells as shown in
In the second exemplary embodiment, carriers of high priority in each cell are always in an available state regardless of the measurement of interference power or a retransmission probability in the base station. On the other hand, an available or unavailable state is determined for carriers of low priority using the same procedure as the first exemplary embodiment.
An example of the operation of the second exemplary embodiment will be described with reference to
Meanwhile, the base station 1 measures the interference power of the carrier c2 since the carrier c2 is a low priority carrier in the cell 3. The carrier c2 is used by the mobile station 8 in the cell 4; the mobile stations 6 and 7 cannot use the carrier c2 if the frequency rate Rintf is higher than Rintf_High, and the mobile stations 6 and 7 can use the carrier c2 if the Rintf is lower than Rintf_Low.
Next, a third exemplary embodiment of the present invention will be described. In the third exemplary embodiment of the present invention, as shown in a configuration diagram of a cellular system in
In the first exemplary embodiment, the base station controller determines an available or unavailable state of the carriers, while in the third exemplary embodiment, the base station determines the state. The other details are same as the first exemplary embodiment.
Referring to
Next, referring to
An example of the operation of the third exemplary embodiment can be described with reference to
Next, a fourth exemplary embodiment of the present invention will be described. In the fourth exemplary embodiment of the present invention, as shown in the configuration diagram of the cellular system in
In the second exemplary embodiment, the base station controller determines an available or unavailable state of the carriers of low priority, while in the fourth exemplary embodiment, the base station determines the state. The other details are same as the second exemplary embodiment. The carriers of low priority are changed between an available and unavailable state similarly to the third exemplary embodiment shown in the flow diagrams in
An example of the operation of the fourth exemplary embodiment can be described with reference to
The operation according to each of the above embodiments can be realized by a program prestored in a recording medium such as an ROM being read and executed by a computer (CPU).
An exemplary advantage according to the invention is that a carrier can be used efficiently in packet transmission by avoiding interference with other cells.
While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.
Number | Date | Country | Kind |
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2006/185054 | Jul 2006 | JP | national |