User's Manual

44 P330 Data Sheet / User Guide
DRAFT
Table 6-3: Ranging performance characteristics at maximum legal transmit power
6.4 Range Measurement Precision, Bias and Accuracy
The Range Precision, Accuracy and Bias are defined by the performance of the Decawave DW1000
chip all of which is described in the Decawave product documentation. For more detail, the reader is
encouraged to review the product information provided by Decawave.
This section will focus on discussing the precision, accuracy and bias of the DW1000 based on
empirical data and experience gathered to date.
6.4.1 Precision in LOS and NLOS Conditions
The DW1000 has a precision (standard deviation) of 10cm. This is a 3 sigma value and has been
verified both in a lab environment and in the field. Note that this is a line of sight measurement and
it assumes that the antennas of the units are clearly visible to each other that there are no obstructions
or partial blockages of the direct path and that is very little reflective surfaces which will cause
“undo” amounts of multipath. These conditions are typical of operation outdoors and are also typical
inside large areas inside building.
Operating inside buildings frequently requires transmissions through walls as well as operation in the
presence of significant reflectors. These factors will attenuate and distort the signal in a variety of
ways that will compromise the precision and bias of the resulting readings. This degradation is
generally modest, largely because serious degradation will normally be significant enough to prevent
a link from being completed. For logistical reasons, it is very difficult to quantify this degradation
especially over a wide enough number of RF environments to be statistically significant. Even so,
one can expect the precision to be generally acceptable and consistent with the chip specification.
6.4.2 Precision in Fresnel Nulls
Bal blah blah blah
6.4.3 Bias and Calibration
The DW1000 does not report range measurements with a bias of zero. This is to be expected
because the bias is a function various electrical delays in the chip, on the board, in cabling to the
antenna and in the antenna itself.
This bias needs to be calibrated out and a procedure for doing so is described in the RangeNet User’s
Guide.
The user can expect each unit to have a different bias error. The variation for most of the units is
Configuration:
Chan 2 (low band) or 5 (high band), PRF=64MHz,
Preample (128 or 1024), Data Rate = (110KHz or
6.8Mbps)
Range Conversation Time
(milliseconds)
Maximum Range
Measurement Rate (Hz)
Chan 2: High Rate (64MHz, 128, 6.8MHz) 5.5 181.8
Chan 2: Low Rate (64MHz, 1024, 110KHz) 48.0 20.8
Chan 5: High Rate (64MHz, 128, 6.8MHz) 5.5 181.8
Chan 5: Low Rate (64MHz, 1024, 110KHz) 48.0 20.8