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Packet
Engine
FEC
Encoder
Modulator
Interleaver
Write buffer
Interleaver
Read buffer
Demodulator
FEC
Decoder
Packet
Engine
Interleaver
Write buffer
Interleaver
Read buffer
SWRS037B – JANUARY 2006 – REVISED MARCH 2015
5.10.2 Interleaving
Data received through real 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, a continuous span of errors in the received stream will
become single errors spread apart.
CC1150 employs matrix interleaving, which is illustrated in
. The on-chip interleaving buffer is
a 4 × 4 matrix. In the transmitter, the data bits are written into the rows of the matrix, whereas the bit
sequence to be transmitted is read from the columns of the matrix and fed to the rate ½ convolutional
coder. Conversely, in a CC1101 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
CC1101.
When FEC and interleaving is used, the minimum data payload is 2 bytes in fixed and variable packet
length mode.
Figure 5-10. : General Principle of Matrix Interleaving
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