Lora send but can't receive well

[hoseinaghajari]

Hi friends, I wrote codes for simple a gateway and a node. gateway send a message to node. but after 5 or 6 times send and receive, the node is hanging and not receive from gateway.
I attach the codes below:
sender:

receiver:

result is not permanent. gateway send 4 or 5 time to node but after that node can't receive anything.!!! I tried many changes in my code but at first lets discuss about this simple one. please help me. thanks.

[IoTThinks]

Read the sample examples again.
Check sender and receiveCallback examples

[IoTThinks]

If already use the examples and still can not, try to provide external powers to the LoRa.