A radio resource allocation method for transmitting downlink control signaling in a search space, performed by a base station, BS, the method comprising: comparing time periods of a common search space and a specific search space, to obtain a time difference between the time length of the periods of the common search space and the specific search space, wherein the common search space is a time interval for at least one user equipment (UE, UE1-UE8) not under a connected mode to monitor a physical downlink control channel and the specific search space is a time interval for the at least one user equipment (UE, UE1-UE8) under the connected mode to monitor the physical downlink control channel; modifying the number of at least one valid time position for the allocation of a radio resource in the specific search space according to the obtained time difference, wherein the at least one valid time position represents a time position in the specific search space in which the physical downlink control channel is initially transmitted and which can be finally used by the at least one user equipment (UE, UE1-UE8) for monitoring, wherein a plurality of valid time positions within the specific search space do not overlap with each other and wherein the at least one valid time position is determined based on whether time positions used in the specific search space and time positions used in the common search space overlap, and modifying the number of at least one valid time position comprises: reducing the number of the valid time positions and making the time positions used by the specific search space to not overlap with the time position used by the common search space when the obtained time difference is that the period of the common search space is not smaller than the period of the specific search space; and allocating a radio resource to the at least one valid time position for transmitting a physical downlink control channel in the specific search space to the at least one user equipment (UE, UE1-UE8). comparing time periods of a common search space and a specific search space, to obtain a time difference between the time length of the periods of the common search space and the specific search space, wherein the common search space is a time interval for at least one user equipment (UE, UE1-UE8) not under a connected mode to monitor a physical downlink control channel and the specific search space is a time interval for the at least one user equipment (UE, UE1-UE8) under the connected mode to monitor the physical downlink control channel; modifying the number of at least one valid time position for the allocation of a radio resource in the specific search space according to the obtained time difference, wherein the at least one valid time position represents a time position in the specific search space in which the physical downlink control channel is initially transmitted and which can be finally used by the at least one user equipment (UE, UE1-UE8) for monitoring, wherein a plurality of valid time positions within the specific search space do not overlap with each other and wherein the at least one valid time position is determined based on whether time positions used in the specific search space and time positions used in the common search space overlap, and modifying the number of at least one valid time position comprises: reducing the number of the valid time positions and making the time positions used by the specific search space to not overlap with the time position used by the common search space when the obtained time difference is that the period of the common search space is not smaller than the period of the specific search space; and allocating a radio resource to the at least one valid time position for transmitting a physical downlink control channel in the specific search space to the at least one user equipment (UE, UE1-UE8). reducing the number of the valid time positions and making the time positions used by the specific search space to not overlap with the time position used by the common search space when the obtained time difference is that the period of the common search space is not smaller than the period of the specific search space; and allocating a radio resource to the at least one valid time position for transmitting a physical downlink control channel in the specific search space to the at least one user equipment (UE, UE1-UE8).