Transmission resource allocation method and related apparatus and communication system

The invention discloses a transmission resource allocation method and a related apparatus and a communication system, wherein the transmission resource allocation method includes that an access device informs a user device a second uplink and downlink matching change period, wherein the second uplink and downlink matching change period is shorter than a system message change period. The access device sends a first message to the user device, wherein the first message is carrying an uplink and downlink matching instruction corresponding to the second uplink and downlink matching change period, so that the user device updates an uplink and downlink matching used by the user device according to the uplink and downlink matching instruction. The transmission resource allocation method and the related apparatus and the communication system have the advantages that flexibility of the transmission resource allocation and spectrum resource utilization are improved.