Related art wireless multi-mode data communication methods include a method (for example, refer to JP,2002-369261,A) of switching between an autonomous mode in which data are transmitted and received autonomously, and a so-called scheduling mode in which data are transmitted and received according to requirements (i.e., scheduling) set for data transmission and reception, such as a communication timing permitted by a base station, according to a data rate and so on.
According to this communication method, when packet data is transmitted at a low data rate of about 9.6 kbps between a base station and a wireless device, for example, the transmission of the packet data is carried out with the transmission mode being switched to the autonomous mode. On the contrary, when packet data is transmitted at a high data rate between a base station and a wireless device, the transmission of the packet data is carried out with the transmission mode being switched to the scheduling mode.
In the scheduling mode, the base station transmits a signaling for notifying scheduling frequently to the wireless device. For this reason, if there is not a certain or more amount of data for each transmission, the efficiency of data transmission is reduced with respect to the number of times that the signaling is performed.
In the above-mentioned related art data communication method, the above-mentioned malfunction is removed by switching to the scheduling mode in the case of a high data rate at which the amount of data per unit time is large.
However, although the above-mentioned related art reference discloses application of a switching to either the autonomous mode or the scheduling mode based on the amount of data to the above-mentioned related art data communication method, it does not disclose any process of switching between the autonomous mode and the scheduling mode under other communication conditions.
As the communication conditions which should be used as the reference for switching between the communication modes, an amount of interference (referred to as a noise rise from here on), a delay time, or the like in the base station can be provided, for example, by taking into consideration a process of demodulating an encoded signal, and a process of handling data of which real-time nature is required.
According to the invention disclosed by the above-mentioned related art reference, no due consideration is given to flexible communication mode switching operations according to communication conditions, such as a communication mode switching operation of making a wireless device which carries out data communications in which any delay time cannot be permitted operate in the autonomous mode if possible, and making a device which carries out communications in which a delay time can be permitted operate in the schedule mode.
In uplink packet communications using a CDMA method, when interference caused by a transmission signal from a wireless device exceeds the limit of a noise rise in a base station, the base station cannot demodulate the transmission signal.
This noise rise varies dependently upon interference by other cells, transmission from other wireless devices in the same cell, etc. For this reason, it is necessary to sufficiently pay attention to the management of the noise rise in the packet communications using a CDMA method.
When a margin for the noise rise is sufficiently secured as noise rise management, it is possible to use the autonomous mode even if the amount of data to be transmitted is large. In this case, the number of times that the signaling is performed can be reduced compared with the case of the schedule mode, and there is an advantage of being able to reduce the delay time.
Thus, by appropriately dividing the margin for the noise rise resulting from various factors which vary according to the conditions of the communications traffic with respect to the noise rise margin of the base station, efficient communications dependent upon changes in the noise rise can be carried out.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a communication mode controlling method of making it possible to carry out efficient data communications dependent upon changes in a noise rise caused by changes in the load of communications between a base station and a mobile communication terminal by switching between communication modes appropriately in consideration of factors other than the amount of data.
It is another object of the present invention to provide a communication mode controlling method of being able to divide a noise rise margin between an autonomous mode and a schedule mode according to QoS (Quality of Service) by independently setting a threshold for switching between transmission modes to each terminal in consideration of QoS parameters, such as a delay time.
It is a further object of the present invention to provide a mobile communication system, an RNC, a base station, and a mobile communication terminal, which carry out efficient data communications dependent upon changes in a noise rise caused by a change in the load on communications using the above-mentioned method.