S2-LP datasheet(57/90 Pages) STMICROELECTRONICS

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S2-LP

Packet handler engine

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The automatic filtering can be programmed to discard packet below certain threshold

settings. These kind of filtering are general purpose and can be used with any packet

format.



Carrier Sense: The carrier sense (CS) functionality detects if any signal is being

received, the detection is based on the measured RSSI value. There are 2 operational

modes for carrier sensing: static and dynamic. In static CS mode, the CS is high when

the measured RSSI is above the RSSI threshold specified and is low when the RSSI

is 3 dB below the threshold. In dynamic CS mode, the CS is high if the signal is above

the threshold and a fast power increase of 6, 12, or 18 dB is detected. The CS is also

used internally for the demodulator to start the AFC and timing recovery algorithms

and for the CSMA procedure (only static CS mode).



PQI: It is possible to set a PQI threshold in such a way that, if PQI is below the

threshold, the packet demodulation is automatically aborted.



SQI: It is possible to set a SQI threshold in such a way that, if SQI is below the

threshold, the packet demodulation is automatically aborted. When the SQI threshold

is set at 0, a perfect match is required. It is recommended mandatory to always enable

the SQI check.

7.8

Data coding and integrity check

7.8.1

FEC

The device provides hardware support for error correction and detection.

Error correction can be either enabled or disabled according to link reliability and power

consumption needs.

Convolution coding (rate 1/2) and interleaving (FEC) can optionally be applied to the data.

FEC can be enabled by setting the FEC_EN register. When FEC is enabled the number of

transmitted bits is roughly doubled hence the on-air packet duration in time is roughly

double as well. The data rate specified in section always applies to the on-air transmitted

data.

FEC is applied to all the fields of BASIC and STack packet format, except Preamble, Sync

and Postamble. While is applied to all the fields except Preamble and Sync for the

802.15.4g packet format.

For the 802.15.4g packet format, two different coding schemes can be selected depending

on the setting of the FEC_TYPE_4G register. In particular if FEC_TYPE_4G = 0 then the

NRNSC encoder is selected, otherwise the RSC one is selected. Please note that the

NRNSC encoder for 802.15.4g is the same as the one used in Basic and STack formats

with logical inversion of the output symbols.

When FEC is enabled then the transmitter automatically selects the secondary SYNC

word. On receiver side, a FEC coded frame is recognized by the reception of such

secondary SYNC word and FEC is automatically activated independently of the setting of

the FEC_EN register.

Use of FEC coding is exclusive with Manchester and Three-out-of-six coding.

7.8.1.1

Interleaving

In order to improve the effectiveness of convolutional encoding, matrix interleaving is

applied to the encoded data at the output of the convolutional encoder.

The symbols from the output of the encoder are written raw-wise into a 4x4 matrix buffer

starting from the upper-left cell and read column-wise starting from the lower-right cell.

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