14. Acoustic Modems

14.1. Time definitions

Variable	Description
\(T_{\text{p}}\)	Poll duration
\(\tau_{\text{p}}\)	Propagation delay (travel time of poll)
\(T_{\text{wp}}\)	Processing delay receiver (process poll, generate response and switch from receiving to transmission mode)
\(T_{\text{r}}\)	Response duration
\(T_\text{TWR}\)	Measured two-way-ranging time, with \(T_\text{TWR} = t_\text{r} - t'_\text{p}\)
\(\tau\)	Time of flight (TOF), with \(\tau = \frac{T_\text{TWR} - T_\text{wp}}{2} = \frac{\tau_\text{p} + \tau_\text{r}}{2}\)
\(T_\text{wr}\)	Processing delay agent
\(\tau_\text{r}\)	Travel time of response

Broadcast algorithm: Single broadcast poll packet from agent, which is received by all anchors. Responses are transmitted sequentially, implemented e.g. by using different \(T_{\text{wp},i}\) for each anchor \(i\). Unique offset \(T_{\text{wp},i}\) is called ranging delay.

Alternating algorithm: Send individual poll to each anchor