When the secondary device detects the beacon beam 24 from the primary device, the secondary device is adjusted to focus on the beacon beam 24 to establish a communication link 22. After the communication link 22 is established, communications and data 23 are transmitted and received between the two communication devices. Using the receiver 240, the one or more processors 210 of the secondary device may digitally crop the frame of the second optical system 250 such that the receiver 240 is focused on a reduced area of the frame. The cropped portion of the frame includes the pixel region where the beacon beam 24 was detected in the frame. The one or more processors 210 of the secondary device may then predict and track any motion of the beacon beam 24 and the primary device to increase signal acquisition robustness. Motion of the beacon beam 24 may be detected using the receiver 240 and the second optical system 250 of the secondary device, or may be predicted based on detected movement of the primary and/or secondary device. Prediction of beacon beam motion may also be based on detected movement of one or both of the first and second optical systems 250 of the primary and secondary devices. When motion of the beacon beam 24 is detected or predicted, cropped portion of the frame may be shifted within the frame in the direction of the beacon beam's detected or predicted motion. Signal acquisition robustness may also be increased by increasing the rate of sampling of the cropped portion of the frame.