In our protocol, the control messages are exchanged between the coordinator and sensor nodes by direct link. The data messages are sent in the multi-hop way from the sensors to the coordinator. An example of the schedules in a BSN with three sensors is shown in Figure 4. In the beginning the coordinator broadcasts a beacon message to synchronize all the sensor nodes. After that, the coordinator broadcasts a message to announce the starting time slot for the following sections “information exchange”, “neighboring information upload” and “schedule assignment”. All the sensor nodes receive this broadcast information and use their own identification (ID) as the shift to calculate their own transmission time slots for information exchange, neighboring information uploading, and schedule assignment. In the information exchange section, each sensor broadcasts its own information including sensor ID and transmission power in its time slot. In the rest of the time it listens for others' information. In the upload section, the sensors send the collected information and their time slot requests to the coordinator in their own time slots. They go into the sleep status for saving energy when other The frame format is shown in Figure 5a. Assume there are N sensor nodes in the network. The frame is bounded by the beacon. It is composed of mini control slots and data slots. The mini control slots include broadcast slot (slot 1), information exchange slots (slot 2 to slot N+1), neighboring information upload slots (slot N+2 to slot 2N+1), and scheduling assignment slots (slot 2N+4 to slot 3N+3). There are two slots (slot 2N+2 and slot 2N+3) reserved for the coordinator to compute the schedules of sensor nodes. The control data is exchanged using one-hop communication between the coordinator and sensor nodes, which means the sensor nodes need to use a larger transmission power to send the control data to the coordinator, but for the sensing data transmission, the sensor nodes use little transmission power to send data to the coordinator in a multi-hop way.