A base station for communicating to a mobile station that transmits an uplink signal in accordance with a SC-FDMA scheme or an OFDMA scheme includes an adjustment amount range setting unit configured to set an adjustment amount for adjusting a transmit timing of the uplink signal to have different ranges depending on types of a channel transmitted by the mobile station.A communication scheme succeeding to W-CDMA and HSDPA, that is, LTE (Long Term Evolution), is discussed in a standardization group 3GPP for the W-CDMA.
Thus, the present invention addresses the above-mentioned problem.
One object of the present invention is to provide a base station, a mobile communication system, a mobile station and a communication control method that can control the transmit timing in uplink transmissions properly with limited signaling overhead by defining different adjustment amount ranges of transmit timings adapted for the communication initiation state and ongoing communication state.
For the above downlink signaling, an amount of the transmit timing adjusted in the mobile station may be defined as follows, the adjustment amount=(minimum unit of the adjustment amount)×k, where k is −K However, the above-mentioned background art has some problems as follows.
In the state where communications are to be initiated or substantially the same state as the communication initiation due to established communications but ongoing off-communications (which are collectively referred to as “the communication initiation state” hereinafter), the transmit timing may be controlled based on an adjustment amount range different from the adjustment amount range for the transmit timing during communications.
In order to overcome the above problem, one aspect of the present invention relates to a base station for communicating to a mobile station wherein the mobile station transmits an uplink signal in accordance with a SC-FDMA scheme or an OFDMA scheme, the base station comprising: an adjustment amount range setting unit configured to set an adjustment amount for adjusting a transmit timing of the uplink signal to have different ranges depending on types of a channel transmitted by the mobile station when the base station indicates the adjustment amount to the mobile station.
According to the aspect, it is possible to indicate the adjustment amount for adjusting the transmit timing to the mobile station with an optimal number of signaling bits for channel types of uplink signals.
The OFDM is a scheme where a frequency band is divided into smaller frequency bands (subcarriers) and data is transmitted in these frequency bands.
According to the OFDM, it is possible to achieve faster transmission and improve frequency utilization efficiency by arranging the subcarriers in the frequency band densely without mutual interference while allowing overlapping of the subcarriers.
Specifically, since the transmit timing of a mobile station may significantly deviate from a proper timing in the communication initiation state, a larger adjustment amount range may be required to control the transmit timing.
On the other hand, since the transmit timing of the mobile station may not deviate from the proper timing relatively during communications, a smaller adjustment amount range may be required to control the transmit timing.
In the case where a mobile station is currently communicating to the base station, the base station may control the transmit timing based on the receive timing of a pilot signal transmitted from the mobile station.