CC2550RSTR Datasheet, PDF (24/61 Pages) Texas Instruments – Low-Cost Low-Power 2.4 GHz RF Transmitter

CC2550
sensitivity from a higher receiver bandwidth
will be counteracting factors.
15.2 Interleaving
Data received through radio channels will often
experience burst errors due to interference
and time-varying signal strengths. In order to
increase the robustness to errors spanning
multiple bits, interleaving is used when FEC is
enabled. After de-interleaving on the receiver
side, a continuous span of errors in the
received stream will become single errors
spread apart.
CC2550 employs matrix interleaving, which is
illustrated in Figure 12. The on-chip
interleaving buffer is a 4 x 4 matrix. The data
bits from the rate ½ convolutional coder are
written into the rows of the matrix, whereas the
bit sequence to be transmitted is read from the
columns of the matrix. Conversely, in a CC2500
[9] receiver, the received symbols are written
into the rows of the matrix, whereas the data
passed onto the convolutional decoder is read
from the columns of the matrix.
When FEC and interleaving is used at least
one extra byte is required for trellis
termination. In addition, the amount of data
transmitted over the air must be a multiple of
the size of the interleaver buffer (two bytes).
The packet control hardware therefore
automatically inserts one or two extra bytes at
the end of the packet, so that the total length
of the data to be interleaved is an even
number. Note that these extra bytes are
invisible to the user, as they are removed
before the received packet enters the RX FIFO
in a CC2500 [9].
When FEC and interleaving is used the
minimum data payload is 2 bytes.
Note that for the CC2500 [9] transceiver FEC is
only supported in fixed packet length mode
(PKTCTRL0.LENGTH_CONFIG=0).
Packet
Engine
FEC
Encoder
Interleaver
Write buffer
Interleaver
Read buffer
Modulator
Figure 12: General Principle of Matrix Interleaving
SWRS039B
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