CC2510FX Datasheet, PDF (207/253 Pages) List of Unclassifed Manufacturers – True System-on-Chip with Low Power RF Transceiver and 8051 MCU

CC2510Fx / CC2511Fx
channel requirements are fulfilled. The chip will
otherwise remain in RX. This feature is called
TX if CCA.
Four CCA requirements can be programmed:
• Always (CCA disabled, always goes to TX)
• If RSSI is below threshold
• Unless currently receiving a packet
• Both the above (RSSI below threshold and
not currently receiving a packet)
15.10.8 Link Quality Indicator (LQI)
The Link Quality Indicator is a metric of the
current quality of the received signal. If
PKTCTRL1.APPEND_STATUS is enabled, the
value is automatically appended to the end of
each received packet. The value can also be
read from the LQI status register. The LQI is
calculated over the 64 symbols following the
sync word (first 8 packet bytes). LQI is best
used as a relative measurement of the link
quality, since the value is dependent on the
modulation format.
15.11 Forward Error Correction with
Interleaving
CC2510Fx/CC2511Fx has built-in support for
Forward Error Correction (FEC). To enable
this option, set MDMCFG1.FEC_EN to 1. FEC is
employed on the data field and CRC word in
order to reduce the gross bit error rate when
operating near the sensitivity limit.
Redundancy is added to the transmitted data
in such a way that the receiver can restore the
original data in the presence of some bit
errors.
The use of FEC allows correct reception at a
lower SNR, thus extending communication
range. Alternatively, for a given SNR, using
FEC decreases the bit error rate (BER). As the
packet error rate (PER) is related to BER by:
PER = 1 − (1 − BER) ^{packet _ length} ,
a lower BER can be used to allow significantly
longer packets, or a higher percentage of
packets of a given length, to be transmitted
successfully. Finally, in realistic ISM radio
environments, transient and time-varying
phenomena will produce occasional errors
even in otherwise good reception conditions.
FEC will mask such errors and, combined with
interleaving of the coded data, even correct
relatively long periods of faulty reception (burst
errors).
The FEC scheme adopted for
CC2510Fx/CC2511Fx is convolutional coding, in
which n bits are generated based on k input
bits and the m most recent input bits, forming a
code stream able to withstand a certain
number of bit errors between each coding
state (the m-bit window).
The convolutional coder is a rate 1/2 code with
a constraint length of m=4. The coder codes
one input bit and produces two output bits;
hence, the effective data rate is halved.
15.11.1 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.
CC2510Fx/CC2511Fx employs matrix interleaving,
which is illustrated in Figure 49. The on-chip
interleaving and de-interleaving buffers are 4 x
4 matrices. 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 the
receiver, the received symbols are written into
the columns of the matrix, whereas the data
passed onto the convolutional decoder is read
from the rows 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 RFD
data register.
When FEC and interleaving is used the
minimum data payload is 2 bytes in fixed and
variable packet length mode.
CC2510Fx/CC2511Fx PRELIMINARY Data Sheet (Rev. 1.2) SWRS055A Page 207 of 252