A localization algorithm based on the use of a hybrid approach is discussed in this paper. Bishop et al. suggest the use of both time difference of arrival (TDOA) and angle of arrival (AOA). This approach is based on the assumption that a number of sensors N exist (N being greater than or equal to two) that can each individually estimate both the azimuth bearing to a target and the time of signal arrival.

Section 1 presents a justification of why such an approach is promising, and may result in achieving both more reliable and more robust results. After that, the application of the algorithm in two-dimensional (2D) and three-dimensional (3D) cases is described. Some previous implementations of hybrid algorithms are discussed in Section 3. The main theoretical results related to the proposed algorithms (two theorems and a corollary) are formulated and proven in Section 4. A constrained optimization approach, applicable to both the 2D and 3D cases, is described in Section 5. Examples are given in Section 6. The results from the numerical experiments clearly show that the algorithm proposed by Bishop et al., called the geometrically constrained optimization approach, incorporating a weighted least squares cost function (GCLS), generally performs better than the other algorithms used in the comparisons; the text explains why this is so. Short conclusions are given in Section 7. Appropriate stopping criteria for the GCLS algorithm are derived in Appendix A.

This paper is well written, and the results proven may successfully be used in attempts to make the localization process both more accurate and more robust.