the preamble detection timeout, programmable in Sub-Register 0x27:24 – DRX_PRETOC. This may be useful
after sending a message where a response is being awaited. Here if the preamble is not detected then the
awaited response is not coming. The preamble detection time-out can be used to abandon the reception at
the earliest possible time, saving power.
The preamble detection state also has the possibility of operating in a mode called pulsed preamble
detection mode (PPDM), or SNIFF mode, programmable through Register file: 0x1D – SNIFF Mode. This is a
technique that where the receiver samples (“sniffs”) the air periodically on a timed basis, e.g. 50% or 25% of
the time, to reduce the power needed during preamble detection.
4.1.2 Preamble Accumulation
Once the preamble sequence is detected, the receiver begins accumulating correlated preamble symbols,
while looking for the SFD sequence (a particular sequence of preamble symbols, see section 10.3 –
Synchronisation header modulation scheme for details). Accumulation stops when the SFD is detected, but
may stop earlier if the accumulator grows quickly, (as is the case in close line-of-sight conditions for
instance), in this case the receiver continues receiving preamble, without accumulating, searching for the
SFD sequence.
4.1.3 SFD Detection
The detection of SFD is a key event in the reception of a frame, because it marks the start of the PHY header,
which defines the RMARKER that is time-stamped (see section 4.1.6 – RX Message timestamp), and it marks
the change from preamble demodulation to the BPM/BPSK demodulation of the PHR (and data
subsequently).
It is possible to abort reception if the SFD is not detected within a certain time after preamble is detected.
This functionality is configured via Sub-Register 0x27:20 – DRX_SFDTOC. This SFD detection timeout guards
against false detection of preamble (which has a finite chance of happening) that could otherwise lead to a
prolonged period receiving nothing. By default the SFD detection timeout is 4161 symbol times, (i.e. greater
than the largest possible preamble), but it can be set lower if it is known that all nodes in the network are
using shorter preambles. It is possible to disable the SFD detection timeout but this is not advised.
The SFD sequence is 64 symbols long for 110 kbps data rate and 8 symbols long for the other two supported
data rates of 850 kbps and 6.8 Mbps. The receiver needs to be configured to look for either the short 8-
symbol SFD or the long 64-symbol SFD. This is done via the RXM110K configuration bit in Register file: 0x04
– System Configuration.
The DW1000 also has the capability of programming non-standard SFD sequences that give improved
performance, see Register file: 0x21 – User defined SFD sequence.
4.1.4 PHR Demodulation
The main role of the PHY Header (PHR) is to convey the length of the data portion of the frame, and to
indicate the data rate being employed for data demodulation. See section 10.4 – PHY header for details of
the PHY header. For data rates of 850 kbps and 6.8 Mbps the PHR is modulated / demodulated as per the
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