Q2. What are the key innovations of proposed schemes within this category?
The key innovations of proposed schemes within this category lie in how they address localization inaccuracy due to measurement errors and transmission losses as well as the need for time synchronization.
Q3. What is the main reason why the range-based localization is preferred?
as replacement of batteries for submerged modems is difficult, short-range, low-power communication to achieve reasonable data transmission rates is preferred, which may limit the localization coverage.•
Q4. How does the author calculate a confidence value for a reference node?
To alleviate the effects of error propagation, when an ordinary node obtains its estimated position from a set of reference nodes, it computes a confidence value, η, where 0 < η ≤ 1, by normalizing the position error with the sum of the Euclidean distance between itself and the reference nodes (see Eqn (2)).
Q5. What are the main characteristics of a localization scheme?
In general, localization schemes in terrestrial wireless sensor networks can be classified into three categories: geometric analysis approach, proximity approach and scene analysis approach (Hightower and Borriello, 2001).
Q6. What are the advantages of using static references?
In general, schemes that rely solely on static references achieve better localization accuracy at the expense of higher deployment costs.
Q7. What are the main manufacturers of USBL systems?
Manufacturers of USBL systems include Nautronix, Sonardyne, IXSEA (GAPS pre-calibrated Ultra-Short BaseLine), Applied Acoustics (EASYTRAK USBL), LinkQuest (TrackLink USBL), Tritech (Micron Nav), Kongsberg (HiPAP - High Precision Acoustic Positioning), and EvoLogics (USBL Acoustic Modem).
Q8. What are the challenges that need to be overcome for underwater localization schemes?
The authors identified several of the challenges that need to be overcome for underwater localization schemes to be fast and accurate, have low communication costs, provide wide coverage and be feasible.
Q9. How many independent range measurements are required to localize anodes?
In general, to localize anode in d-dimensional space, the number of independent range measurements required should be at least d +
Q10. What is the use of the baseline transponders?
The baseline transponders can also be mounted in fixed relative positions on a moving platform like a ship for applications like In-Water Ship Hull Inspections and other specialized tasks.
Q11. How does the author estimate distance from a reference node?
Each ordinary node S estimates its distance, li, from a reference node Ri (i) based on ToA approach upon receiving its beacon or (ii) using 3D Euclidean distance estimation if they are more than one-hop apart.
Q12. What are the key innovations of the proposed schemes?
Unlike the singlestage schemes, the key innovations of proposed schemes within this category lie in (i) how ordinary nodes qualify as new reference nodes and (ii) which new reference nodes are used for localization so as to trade-off between minimizing error propagation and delay while maximizing coverage and energy efficiency.
Q13. What are the drawbacks of the DNR-aided localization scheme?
To minimize error propagation, localized ordinary nodes can qualify as new reference nodes only if they are below the maximum depth of the DNR beacons.
Q14. What is the effect of asymmetric signal attenuation on the accuracy of distance measurements?
This may affect localization accuracy, as some distance measurements may have become obsolete by the time the node position is estimated.•
Q15. What are the challenges of deploying a reference node in the underwater environment?
While node deployment in terrestrial networks is relatively straightforward, the corresponding deployment in underwater environment encounters the following challenges:•