Further transmission features are described in the following sections:
Transmit message time-stamping – see section 3.2 –Transmission timestamp.
Delayed transmission – see section 3.3 – Delayed Transmission.
Long transmit frames – see section 3.4 – Extended Length Data Frames.
High Speed transmit – see section 3.5 – High Speed Transmission.
3.2 Transmission timestamp
During frame transmission the start of the PHR (PHY header) is the event nominated by the IEEE 802.15.4
UWB PHY standard for message time-stamping. The time the first symbol of the PHR launches from the
antenna (defined as the RMARKER) is the event nominated as the transmit time-stamp.
The DW1000 digital transmit circuitry takes note of the system clock counter as the RAW transmit
timestamp at the point when it begins sending the PHR. It then adds to this the transmit antenna delay
(configured in Register file: 0x18 – Transmitter Antenna Delay) to get the antenna adjusted transmit time-
stamp that it writes to the TX_STAMP field of Register file: 0x17 – Transmit Time Stamp.
See also section 8.3 – IC Calibration – Antenna Delay.
3.3 Delayed Transmission
For delayed transmission, the transmit time is programmed into Register file: 0x0A – Delayed Send or Receive
Time and then the delayed transmission is initiated by setting both TXDLYS and TXSTRT controls in Register
file: 0x0D – System Control Register.
One of the design goals of delayed transmission was that the specified transmission time would be
predictable and aligned with the Transmit timestamp. This was achieved in that the transmission time
specified is the time of transmission of the RMARKER (not including the TX antenna delay), that is the raw TX
time, TX_RAWST in Register file: 0x17 – Transmit Time Stamp before the antenna delay is added. This
allows for the time of transmission of a message to be pre-calculated and embedded in the message being
transmitted.
NOTE: The low-order 9 bits of the delayed Transmit value programmed into Register file: 0x0A – Delayed
Send or Receive Time are ignored giving a time resolution of 8 ns, or more precisely 4 ÷ (499.2×10
6
). To
calculate the time of transmission of the RMARKER at the antenna, the low 9 bits of the delayed TX time
should be zeroed before adding the TX antenna delay.
In performing a delayed transmission, the DW1000 calculates an internal start time for when to begin
sending the preamble to make the RMARKER raw timestamp agree with the programmed transmit time.
The DW1000 remains in idle state until the system time (Register file: 0x06 – System Time Counter) reaches
the correct point to turn on the transmitter and begin preamble.
One use of delayed transmission (and reception), is in symmetric double-sided two-way ranging, (described
in APPENDIX 3: Two-Way Ranging), where it is important to keep the response times the same at both ends
to reduce the error in range estimate. Minimising the response time also reduces this error, and in working
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