DW1000 User Manual
© Decawave Ltd 2017
Version 2.12
Page 215 of 242
10 APPENDIX 1: The IEEE 802.15.4 UWB physical layer
This appendix gives an introduction to the modulation scheme and frame structure of the UWB physical
layer as specified in the IEEE 802.15.4 – 2011 standard and as implemented by the DW1000 transceiver IC.
This is useful in understanding the operation of the DW1000 transceiver and its configuration options.
10.1 Frame structure overview
The UWB communications are based around the transmission and reception of frames. Figure 31 shows the
general structure of the UWB frame. It begins with a synchronisation header consisting of the preamble and
the SFD (start of frame delimiter), after which the PHY header (PHR) defines the length (and data rate) of the
data payload part of the frame.
Figure 31: UWB PHY Frame structure
10.2 Data modulation scheme
The UWB used in 802.15.4 is sometimes called impulse radio UWB because it is based on high speed pulses
of RF energy. During the PHR and Data parts of the frame, information bits are signalled by the position of
the burst, in a modulation scheme termed burst position modulation (BPM).
Figure 32:- BPM/BPSK data and PHR modulation
Each data bit passes through a convolution encoder to generate a “parity” bit used to set the phase of the
burst as either positive or negative, this component of the modulation is termed binary phase-shift keying
(BPSK). Figure 32 shows how the convolutional encoder contributes to this BPM/BPSK modulation. A
coherent receiver (i.e. one tracking carrier timing and phase) such as the one in the DW1000 can determine
this burst phase and use it in a Viterbi decoder to get an additional 3 dB of coding gain, thereby extending
the operational range of the modulation
Preamble
SFD PHR
Data
IEEE STD: 64, 1024 or 4096 symbols
IEEE STD: 8 or 64 symbols
19 bits
IEEE STD: Up to 127 coded octets
Systematic
Convolution Encoder
Systematic (position) bit determines which
half of the symbol contains the burst
D
D
Parity (sign) bit determines whether
the burst is inverted or not
Burst here
= 0
unused
guard
interval
Burst here
= 1
unused
guard
interval
One symbol interval (or bit time)
+
Data in
