Digital Signal Processing Reference
In-Depth Information
The task of signal decoding is to reconstruct the original message from the baseband
coded
received signal
and to recognise any
transmission errors
and flag them as such.
6.1 Coding in the Baseband
Binary ones and zeros can be represented in various
line codes
. RFID systems normally
use one of the following coding procedures: NRZ, Manchester, Unipolar RZ, DBP
(differential bi-phase), Miller, differential coding on PP coding (Figure 6.2).
NRZ code
A binary 1 is represented by a 'high' signal and a binary 0 is rep-
resented by a 'low' signal. The NRZ code is used almost exclusively with FSK or
PSK modulation.
Manchester code
A binary 1 is represented by a negative transition in the half
bit period and a binary 0 is represented by a positive transition. The Manchester code
is therefore also known as
split-phase coding
(Couch, 1997).
The Manchester code is often used for data transmission from the transponder to
the reader based upon load modulation using a subcarrier.
NRZ coding:
1
0
1
1
0
0
1
0
Manchester coding:
(bi-phase)
1
0
11
00
1
0
Unipolar RZ coding:
1
0
1
1
0
0
1
0
DBP
1
0
1
1
0
0
1
0
Miller coding:
1
0
1
1
0
0
1
0
Modified Miller
coding:
1
0
1
1
0
0
1
0
Differential coding:
1
0
1
1
0
0
1
0
1
Figure 6.2
Signal coding by frequently changing line codes in RFID systems
Search WWH ::
Custom Search