DW1000 User Manual
© Decawave Ltd 2017
Version 2.12
Page 217 of 242
Table 60: Preamble parameters
Mean PRF (MHz)
#Chips Per Symbol
Preamble Symbol Duration (ns)
16 nominal
496
993.59
64 nominal
508
1017.63
The standard defines PSR settings of 16, 64, 1024 and 4096. The DW1000 supports these (although it will
not receive frames with preamble length below 64 symbols) and in addition supports PSR settings of 128,
256, 512, 1536 and 2048.
The preamble sequence has a property of perfect periodic autocorrelation
11
which in essence allows a
coherent receiver to determine the exact impulse response of the RF channel between transmitter and
receiver. This brings two important benefits. Firstly, it allows the receiver make use of the received energy
from multiple paths, turning multipath from an interference source into a positive affect extending operating
range. Secondly, it lets the receiver resolve the channel in detail and determine the arrival time of the first
(most direct) path, even when attenuated, which brings precision advantages for RTLS applications.
The SFD marks the end of the preamble and the precise start of the switch into the BPM/BPSK modulation of
the PHR. The time-stamping of this event is very deterministic in terms of symbol times and it is this in
conjunction with determining the first arriving ray within that symbol time that allows the accurate time-
stamping needed for precision RTLS applications.
The standard specifies the SFD, which consists of the preamble symbols either not sent, or sent as normal or
sent inverted (i.e. positive and negative pulses reversed) in a defined pattern 8 symbol times long for data
rates other than 110 kbps, and 64 symbols long for the 110 kbps mode.
The length-8 SFD sequence is: 0, +1, 0, -1, +1, 0, 0, -1
The length-64 SFD sequence is: 0, +1, 0, -1, +1, 0, 0, -1, 0, +1, 0, -1, +1, 0, 0, -1, -1, 0, 0, +1, 0, -1, 0, +1, 0, +1,
0, 0, 0, -1, 0, -1, 0, -1, 0, 0, +1, 0, -1, -1, 0, -1, +1, 0, 0, 0, 0, +1, +1, 0, 0, -1, -1, -1, +1, -1, +1, +1, 0, 0, 0, 0, +1,
+1
The DW1000 has the capability for user programmability of SFD sequence, and thus has the possibility to
improve upon the SFD sequence in the standard, if a non-standard SFD sequence is programmed it will be
impossible to interwork with a device expecting the standard SFD sequence.
10.4 PHY header
The PHY header (PHR) is modulated using the BPM/BPSK modulation scheme defined in section 10.2 above,
but it does not employ the Reed Solomon code used for data, instead is employs a 6-bit SECDED (Single error
correct, Double error Detect) parity check sequence as part of its 19-bit length.
11
V. P. Ipatov, “Ternary sequences with ideal autocorrelation properties,” Radio Eng. Electron. Phys., vol. 24, pp. 75–79, 1979