Adaptive frequency hopping
Presenters : 卓訓緯 許泓崴
Professor : 王奕翔
Outline
- Jammer
- Adaptive Frequency Hopping Framework
- Link-layer
- Physical-layer
Jammer
- Slicing window searching
- Use FFT to find peak value
- Send random bits with high Tx gain
Jammer
ft
IQ rate
carrier frequency
fc
fd
f_{t} = f_{c}+f_{d}
Adaptive Frequency Hopping
Link-layer Policy
- If interrupted, change frequency
- Change frequency according to a list
- Reciever acks to detect interruption
- CRC error detection to increase robustness
- Half duplex bidirectional transmission
Packet format
preamble
8bits
sync
20bits
payload
128bits
blank
some bits
CRC
16bits
Link-layer Receiver
Rx
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
Link-layer Transmitter
Tx
Rx
Rx
ACK
after sending
if(timeout)
timer++;
else
timer = 0;
if(timer ==3)
use backup;
rcv_pkg
if(rcv_ack_num == next_ack_num)
toggle ack_num;
after comparison
send pkg with ack_num
timeout
Physical-layer
- We use existed blocks originally
- For efficiency, we build FSK modulation scheme
- We can now transmit with sampling frequency 22050 Hz, each sample 8 bits
FSK Tx
Data
Fragmentation
Add Preamble & Sync
FSK Symbol Mapping
Pulse
Shaping
Insert
Blank
USRP
Tx
FSK Rx
USRP
Rx
Detect Signal Strength
Decision
Align IQ Sample & Multiply
Collect More Sample
Align Start of Frame
Sync Word Detection
Assemble Data
FSK Demodulation
Tx IQ waveform
Rx demodulated waveform