processor 208 a storage device 210 a program code 212 and a transceiver 214 of the wireless communications transmission device 200 in the wireless communications transmission device 200 the control circuit 206 executes the program code 212 stored in the storage device 210 with the central processor 208 and then controls operations of the wireless communication transmission device 200 the wireless communications transmission device 200 can receive signals input by users through the input device 202 or output signals through the output device 204 the transceiver 214 is used for receiving or transmitting radio signals in a structure of a communications protocol the transceiver 214 is known as a part of layer one whereas the control circuit 206 is an application of layer two and layer three please refer to fig3 fig3 is a schematic diagram of the program code 212 in fig2 the program code 212 comprises an application program layer 300 a layer three interface 302 a layer two interface 306 and a layer one interface 318 when transmitting signals the layer two interface 306 stores a plurality of service data units sdus 308 which are submitted from the layer three interface 302 in a buffer 312 then the layer two interface 306 generates a plurality of protocol data units pdus 314 according to the sdus 308 stored in the buffer 312 and outputs the pdus 314 generated to a destination through the layer one interface 318 for improved robustness of data transmission when in am the program code 212 receives a status report unit 310 or a piggybacked status report unit 310 of a receiver from the layer one interface.