Soderi, Mucchi, Hämäläinen, Piva, and Iinatti
126
the transmitter marks, utilizing SS, the host signal x S utilizing its first N W over N
samples. Then x W is given by
x i
x i
W
S
( )=
( ),
,
0,
.
for 1 i N
elsewhere
W
(6.8)
Alternatively, the receiver can jam N W discontinuous samples for each symbol, but
even if this randomness requires a wide‐band jammer, for example ultra wideband
(UWB), the work presented in this chapter is still valid. With N
N
W
, the energy of the
watermark is given by
E
N
N
E
W
W
S
=
.
(6.9)
Finally, the signal is mixed to carrier frequency f c and radiated by the antenna.
Figure 6.4 shows the block diagram of the transmitter.
6.2.2 Jamming Receiver
In this chapter, the authors propose a different strategy to implement the jamming
receiver’s architecture if compared to iJAM [20]. Indeed, the proposed scheme of the
receiver works with jammed samples as well as the watermark extraction.
It is assumed that both the jamming signal and the host signal have the same energy
over N samples as
E
x i
x i
S
i
N
S
i
N
J
1
2
1
2
| ( )|
| ( )| .
(6.10)
Assuming N samples for symbol, as Bob jams M samples over N with M N , the energy
of the jamming signal is given by
E
M
N
E
J
S .
(6.11)
The receiver structure is shown in Figure 6.5. In the WBPLSec, the legitimate receiver can
jam at most M N W samples, because N W samples are the information transmitted through
the SS watermark. The received signal after the antenna is down‐converted to the baseband
by the carrier frequency f c and then processed by the original signal demodulator to recover
data exchanged through channel. Due to the jamming, the signal after the low pass filter
(LPF), that is ˆ , is corrupted and unusable alone. To stitch unjammed samples and create a
clean symbol, in parallel, the received signal is led to an additional DSSS demodulator used
to recover the watermark x W . Afterwards, as in the iJam protocol [20], the receiver replaces
corrupted samples in ˆ S
x with non‐jammed samples, which in our solution are taken from
ˆ W
x . In the end, the clean symbol x S is achieved and then demodulated.
6.2.3 Secrecy Metrics
In Section 10.1, the authors presented the standard metrics used to measure the secrecy
of communications. Regarding the notation used in Figure 6.3, Shannon defined a
126
the transmitter marks, utilizing SS, the host signal x S utilizing its first N W over N
samples. Then x W is given by
x i
x i
W
S
( )=
( ),
,
0,
.
for 1 i N
elsewhere
W
(6.8)
Alternatively, the receiver can jam N W discontinuous samples for each symbol, but
even if this randomness requires a wide‐band jammer, for example ultra wideband
(UWB), the work presented in this chapter is still valid. With N
N
W
, the energy of the
watermark is given by
E
N
N
E
W
W
S
=
.
(6.9)
Finally, the signal is mixed to carrier frequency f c and radiated by the antenna.
Figure 6.4 shows the block diagram of the transmitter.
6.2.2 Jamming Receiver
In this chapter, the authors propose a different strategy to implement the jamming
receiver’s architecture if compared to iJAM [20]. Indeed, the proposed scheme of the
receiver works with jammed samples as well as the watermark extraction.
It is assumed that both the jamming signal and the host signal have the same energy
over N samples as
E
x i
x i
S
i
N
S
i
N
J
1
2
1
2
| ( )|
| ( )| .
(6.10)
Assuming N samples for symbol, as Bob jams M samples over N with M N , the energy
of the jamming signal is given by
E
M
N
E
J
S .
(6.11)
The receiver structure is shown in Figure 6.5. In the WBPLSec, the legitimate receiver can
jam at most M N W samples, because N W samples are the information transmitted through
the SS watermark. The received signal after the antenna is down‐converted to the baseband
by the carrier frequency f c and then processed by the original signal demodulator to recover
data exchanged through channel. Due to the jamming, the signal after the low pass filter
(LPF), that is ˆ , is corrupted and unusable alone. To stitch unjammed samples and create a
clean symbol, in parallel, the received signal is led to an additional DSSS demodulator used
to recover the watermark x W . Afterwards, as in the iJam protocol [20], the receiver replaces
corrupted samples in ˆ S
x with non‐jammed samples, which in our solution are taken from
ˆ W
x . In the end, the clean symbol x S is achieved and then demodulated.
6.2.3 Secrecy Metrics
In Section 10.1, the authors presented the standard metrics used to measure the secrecy
of communications. Regarding the notation used in Figure 6.3, Shannon defined a