Packet 1

Packet 1 Repeat

Packet 2

Packet 2 Repeat

Window 1

Window 2

Packet 1

Packet 2

Packet 3

Packet 4

Window 1

Window 4

Window 3

Window 2

Detect

Preamble

Concatenate Next Window

Detect Buffer Length

Cut Until Preamble Length

Get

Packet

Cut Out a Packet Size

True

False

Sufficient

Less than preamble length

Link-layer  Receiver

Detect Preamble

Rx
CRC

Rx
ACK

Tx

rcv_pkg

timeout

OK

failed

if(rcv_ack_num == ack_num)
toggle ack_num;

after comparison

send ack with ack_num

Use backup frequency