Receiver configuration and testbed development for underwater cognitive channelization

Abstract

—We propose a receiver configuration and we develop a software-defined-radio testbed for real-time cognitive underwater multiple-access communications. The proposed receiver is fully reconfigurable and executes (i) all-spectrum cognitive channelization and (ii) combined synchronization, channel estimation , and demodulation. Online (real-time) experimental field studies using in-house built modems demonstrate our theoretical developments and show that cognitive channelization is a powerful proposition for underwater communications that leads to significant improvement of spectrum utilization. Even in the absence of interference, due to the noise characteristics of the acoustic channel, cognitive channelization offers significant performance improvements in terms of receiver pre-detection signal-to-interference-plus-noise-ratio and bit-error-rate. I. INTRODUCTION Underwater Acoustic (UW-A) communications has been an emerging research topic for the last few years due to its wide range of commercial and military applications such as tactical surveillance, marine life monitoring, and offshore exploration. The UW-A channel poses several challenges such as high path loss, noise, severe multipath, Doppler spread, high and variable propagation delay, and limited bandwidth that is both temporally and spatially varying [1]. As of today, the limited bandwidth of UW-A channel is heavily utilized by multiple " artificial " acoustic systems (i.e., sonar users) for a variety of underwater applications (e.g., echolocation, sensing) as well as shared with " natural " acoustic systems such as marine mammals. However, spectrum resources remain underutilized both spatially and temporally [2]. At the same time, existing underwater modems lack the ability for channel-awareness and are not sufficiently flexible to dynamically reconfigure their communication parameters in real-time (e.g., modulation scheme, frequency band, and wave-form). Therefore, cognitive acoustics need to overcome both practical challenges and the unique features that characterize the rapidly-varying underwater environment. In contrast to terrestrial radio networks where cognitive radio is a well-researched topic [3], [4], there are only few works that consider cognitive underwater acoustic networks [5]–[7]. In particular, work in [5] borrows different dynamic spectrum access models from terrestrial networks and investigates their potential application to heterogeneous underwater network

DOI: 10.1109/ACSSC.2014.7094734

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