A new protocol uses a trigger message to identify one or more symbols transmitted between a first and a second communication device. The first device generates and transmits a trigger message to the second device. This process may be initiated based on the first device receiving a measurement initiation message from another device (e.g., such as the second device or another device within the system). Then, the first device transmits a signal that includes those one or more symbols to the second device. Before or during transmission, the first device generates a first capture of those one or more symbols. After receipt of the transmission from the first device, the second device performs a second capture of those one or more symbols identified within the trigger message. Then, any device having the first and second captures can determine a characterization of the communication pathway between the first and second devices.