decaWave DW1000, Руководство пользователя

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DW1000 User Manual
© Decawave Ltd 2017 Version 2.12 Page 34 of 242
850 kbps data rate (note that because Reed Solomon encoding is not applied to the PHR, its bit rate is
approximately 1 Mbps). If the PHR is indicating 850 kbps then the data demodulation continues at this rate,
but if the PHR is indicating 6.8 Mbps then the demodulation changes to this rate at the end of the PHR as
data demodulation begins.
4.1.5 Data Demodulation
Section 10.2 – Data modulation scheme describes the modulation scheme. In the receiver a Viterbi decoder
is used recover the data bits (this is also used for PHR reception) which are then passed through the Reed
Solomon decoder to apply any further correction it can. Every octet thus received is passed through a CRC
checker which checks the frame against the transmitted FCS.
As the data octets are received they may also be parsed by the frame filtering function if enabled, see
section
5.2– Frame filtering for more details.
Successful reception of a frame is signalled to the host via the RXDFR and RXFCG event status bits in Register
file: 0x0F – System Event Status Register. Other status bits in this register may be used to flag reception of
other parts of the frame or, events indicating failure, i.e. RXPTO (Preamble detection Timeout), RXSFDTO
(SFD timeout), RXPHE (PHY Header Error), RXRFSL (Reed Solomon error), RXRFTO (Frame wait timeout), etc.
Other related features are: -

Delayed reception – see section 4.2 – Delayed Receive .

Long receive frames – see section 3.4–Extended Length Data Frames.

Double buffering – see section 4.3 – Double Receive Buffer.

Receive message time-stamping – see section 4.1.6 – RX Message timestamp.
4.1.6 RX Message timestamp
During frame reception the SFD detection event marking the end of the preamble and the start of the PHR is
the nominal point which is time-stamped by the IC. The IEEE 802.15.4 UWB standard nominates the time
when this RMARKER arrives at the antenna as the significant event that is time-stamped.
The DW1000 digital receiver circuitry takes a coarse timestamp of the symbol in which the RMARKER event
occurs and adds a various correction factors to give a resultant adjusted time stamp value, which is the time
at which the RMARKER arrived at the antenna. This includes subtracting the receive antenna delay as
configured in
Sub-Register 0x2E:1804 – LDE_RXANTD and adding the correction factor determined by the
first path (leading edge) detection algorithm embedded in the DW1000. The resulting fully adjusted RX
timestamp is written into
Register file: 0x15 – Receive Time Stamp .
See also section 8.3 – IC Calibration – Antenna Delay .
Note: Due to an issue in the re-initialisation of the receiver, it is necessary to apply a receiver reset after
certain receiver error or timeout events (i.e. RXPHE (PHY Header Error), RXRFSL (Reed Solomon error),
RXRFTO (Frame wait timeout), etc.). This ensures that the next good frame will have correctly calculated
timestamp. It is not necessary to do this in the cases of RXPTO (Preamble detection Timeout) and