Robust OFDM Modem for a Swarm of Underwater Autonomous Vehicles

Abstract

In this article, a filter bank is coupled with a CFAR detector to guarantee an efficient frame detection in presence of Doppler shift. This work is realized in scope of the NEMOSENS project, which aims to produce autonomous underwater vehicles (AUVs) able to communicate and move in a network thanks to UA modems. Many adverse phenomenons occur in the context of underwater acoustic. Most harmful effects for underwater acoustic communication (UAC) are the multi-path nature of the environment, the Doppler spread and the noise variability. The proposed method reduces the number of lost frames and gives a rough estimate of delay and Doppler shift. The followed approach is supported by simulations with simplified hypotheses, but the interest of this approach is also shown in real sea experiments.

Optimization of Acoustic Communication Links for a Swarm of AUVs: The COMET and NEMOSENS Examples

“…So, in this section, we present the physical layer aspect regarding the AUV's communication. We first describe the OFDM modem embedded in each AUV [22][23][24]. We then present a method that takes advantage of the knowledge of the network geometry to automatically adapt some of the OFDM parameters.…”

“…For this modulation type, no channel equalization is required [21]. As a consequence, no pilot symbols are needed for channel equalization, reducing the overall system overhead [24]. These modulated symbols are mapped into the subcarriers through the multiplication by an IDFT matrix.s…”

“…In the locking mode, the signal of interest is detected and synchronized. The signal detection utilizes a maximum likelihood (ML) approach [24]. In this approach, a bank of matched filters is used for a joint estimation of the signal delay and of the Doppler factor.…”