Emrecan Demirors

Software-defined underwater acoustic networks: toward a high-rate real-time reconfigurable modem

We review and discuss the challenges of adopting software-defined radio principles in underwater acoustic networks, and propose a software-defined acoustic modem prototype based on commercial off-the-shelf components. We first review current SDR-based architectures for underwater acoustic communications. Then we describe the architecture of a new software-defined acoustic modem prototype, and provide performance evaluation results in both indoor (water tank) and outdoor (lake) environments. We present three experimental testbed scenarios that demonstrate the real-time reconfigurable capabilities of the proposed prototype and show that it exhibits favorable characteristics toward spectrally efficient cognitive underwater networks, and high data rate underwater acoustic links. Finally, we discuss open research challenges for the implementation of next-generation software-defined underwater acoustic networks.

Design of A Software-defined Underwater Acoustic Modem with Real-time Physical Layer Adaptation Capabilities

This article describes the design of a custom software-defined modem with adaptive physical layer for underwater acoustic (UWA) communications. The modem consists of a commercial software-defined radio (SDR) interfaced with a wideband acoustic transducer through amplifying circuitry. With this custom-built platform, we focus on the unique physical layer challenges of the underwater acoustic channel to demonstrate the benefits of real-time adaptation in such rapidly varying environments. We first focus on an Orthogonal-Frequency-Division-Multiplexing (OFDM) transmission scheme. In particular, for the forward link, we consider and implement a high-data rate Zero-Padded OFDM (ZP--OFDM) physical layer with a superimposed convolutional error-correction coding scheme. ZP--OFDM offers high re-configurability in terms of number of OFDM subcarriers, modulation type (e.g., BPSK, QPSK), and error-correction coding rate. Real-time adaptation at the transmitter is achieved through a robust feedback link based on a binary chirp spread-spectrum modulation (B-CSS). We demonstrate that joint real-time adaptation of system parameters such as modulation constellation and channel coding rate leads to significant data rate increase under preset bit-error-rate (BER) constraints. Moreover, in the same context, we present for the first time a seamless switch of our SDR transmitter between different signaling technologies such as OFDM and direct-sequence spread-spectrum (DS-SS).

SEANet: A Software-Defined Acoustic Networking Framework for Reconfigurable Underwater Networking

As of today, Underwater Acoustic Networks (UANs) are heavily dependent on commercially available acoustic modems. While commercial modems are often able to support specific applications, they are typically not flexible enough to satisfy the requirements of next-generation UANs, which need to be able to adapt their communication and networking protocols in real-time based on the environmental and application conditions. To address these needs, we present SEANet (Software-dEfined Acoustic Networking), a modular, evolving software-defined framework for UAN devices that offers the necessary flexibility to adapt and satisfy different application and system requirements through a well-defined set of functionalities at the physical, data-link, network, and application layers of the networking protocol stack. SEANet is based on a structured modular architecture that enables real-time reconfiguration at different layers, provides a flexible platform for the deployment of new protocol designs and enhancements, and ensures software portability for platform independence. Moreover, we present a prototype of a low-cost, fully reconfigurable underwater sensing platform that implements the SEANet framework, and discuss performance evaluation results from water tank tests.

RcUBe: Real-time reconfigurable radio framework with self-optimization capabilities

Existing commercial wireless systems are mostly hardware-based, and rely on closed and inflexible designs and architectures. Moreover, despite recent significant algorithmic developments in cross-layer network adaptation and resource allocation, existing network architectures are unable to incorporate most of these advancements. While software-defined radio (SDR) was envisioned as a new paradigm promising radical runtime adaptation through all layers of the networking protocol stack, the reality of the state-of-the-art in wireless networking practice is far from having fulfilled such promise of fast and intelligent reconfigurability and adaptability. Networking research based on the “software-defined radio” paradigm has suffered almost invariably from the lack of adequate and coherently designed abstractions to (i) define networking protocols and their cross-layer interactions across all layers of the protocol stack; (ii) define decision-making algorithms to control such interactions. To address this need, we introduce RcUBe (Real-time Re-configurable Radio), a novel architectural radio framework based on abstractions that offer real-time reconfigurability and optimization capabilities at the PHY, MAC, and network layers of the protocol stack. Unlike state-of-the-art solutions, RcUBe offers a structured methodology at variable levels of abstraction to accommodate implementations of a wide range of network architectures and protocols and complex decision-making in a modular, platform-independent way. RcUBe provides these features through a design structured into four distinct, but interacting planes, namely decision, control, data, and register plane. The broad capabilities of the proposed framework are demonstrated on a network level software-defined radio setup through a range of experiments where RcUBe is used to implement various reconfigurable functionalities of a wireless system at the PHY, MAC, and network layer.

Receiver configuration and testbed development for underwater cognitive channelization

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.

All-Spectrum Cognitive Channelization around Narrowband and Wideband Primary Stations

In this paper we design, implement, and experimentally evaluate a wireless software-defined radio platform for cognitive channelization in the presence of narrowband or wideband primary stations. Cognitive channelization is achieved by jointly optimizing the transmission power and the waveform channel of the secondary users. The process of joint resource allocation requires no a-priori knowledge of the transmission characteristics of the primary user and maximizes the signal-to- interference-plus-noise ratio (SINR) at the output of the secondary receiver. This is achieved by designing waveforms that span the whole continuum of available/device-accessible spectrum, while satisfying a peak power constraint for the secondary users and an interference temperature (IT) constraint for the primary users. We build a four-node software-defined radio testbed and experimentally demonstrate in an indoor laboratory environment the theoretical concepts of all-spectrum cognitive channelization in terms of pre-detection SINR and bit- error-rate (BER) at both primary and secondary receivers.

A hybrid MAC protocol with channel-dependent optimized scheduling for clustered underwater acoustic sensor networks

We propose a novel optimal time slot allocation scheme for clustered underwater acoustic sensor networks that leverages physical (PHY) layer information to minimize the energy consumption due to unnecessary retransmissions thereby improving network lifetime and throughput. To reduce the overhead and the computational complexity, we employ a two-phase approach where: (i) each member node takes a selfish decision on the number of time slots it needs during the next intra-cluster cycle by solving a Markov decision process (MDP), and (ii) the cluster head optimizes the scheduling decision based on the channel quality and an urgency factor. To conserve energy, we use a hybrid medium access scheme, i.e., time division multiple access (TDMA) for the intra-cluster communication phase and carrier sense multiple access with collision avoidance (CSMA/CA) for the cluster head-sink communication phase. The proposed MAC protocol is implemented and tested on a real underwater acoustic testbed using SM-75 acoustic modems by Teledyne Benthos. Simulations illustrate an improvement in network lifetime. Additionally, simulations demonstrate that the proposed scheduling scheme with urgency factor achieves a throughput increase of 28% and improves the reliability by up to 25% as compared to the scheduling scheme that neither use MDP nor optimization. Furthermore, testbed experiments show an improvement in throughput by up to 10% along with an improvement in reliability.

High data rate ultrasonic communications for wireless intra-body networks

It is well known that electromagnetic radio-frequency (RF) waves that are the basis of most commercial wireless technologies are largely unsuitable to interconnect deeply implanted medical devices. RF waves are in fact absorbed by aqueous biological tissues and prone to malicious jamming attacks or to environmental interference from pervasively deployed RF communication systems; moreover, they pose a potential safety hazard when exposure of tissues is prolonged and at high power. While existing wireless technologies can satisfy the requirements of some specific applications, the root challenge of enabling networked intra-body miniaturized sensors and actuators that communicate through body tissues is largely unaddressed. Considering these limitations, this article proposes a high data rate ultrasonic communication scheme for wireless intra-body networks. The proposed scheme can enable various applications that require high sampling rates such as neural data recording or monitoring of the digestive tract through endoscopic pills. The proposed scheme is based on Orthogonal Frequency-Division Multiplexing (OFDM), which is proven to be robust against frequency-selective channels with relatively long delay spreads like the intra-body ultrasonic channel. The proposed scheme is implemented in a prototype ultrasonic software-radio and demonstrated to achieve data rates up to 28.12 Mbit/s through synthetic phantoms mimicking the ultrasonic propagation characteristics of biological tissues.

SEANet G2: toward a high-data-rate software-defined underwater acoustic networking platform

Existing underwater acoustic networking platforms are for the most part based on inflexible hardware and software architectures that can support mostly point-to-point, low-data-rate, delay-tolerant applications. Most commercial devices do not provide neither the sufficient data rates nor the necessary flexibility to support future underwater networking applications and systems. This article discusses a new high-data rate software-defined underwater acoustic networking platform, SEANet G2, able to support higher data rates (megabit/s data rates are foreseen over short range links), spectrum agility, and hardware/software flexibility in support of distributed networked monitoring operations. The article reports on the main architectural choices of the new platform, as well as some preliminary performance evaluation results. Data rates in the order of megabit/s were demonstrated in a controlled lab environment, and, for the first time to the best of our knowledge, data rates of 522kbit/s where obtained in sea trials over short horizontal links (e.g., 10 m) for a BER lower than 10−3.

Chirp-based LPD/LPI underwater acoustic communications with code-time-frequency multidimensional spreading

Most underwater acoustic communication systems incorporate well-recognized, easily detectable narrowband signals modulated over low-frequency carriers at high transmission powers, which ultimately limits LPD/LPI performance of the communication scheme. While there have been promising works concentrating on LPD/LPI performance, they are for the most part based on direct-sequence spread spectrum (DSSS) techniques, which have been shown to be blindly detectable in previous work at relatively low SINR values. As a result, there is likely significant room to improve the LPD/LPI performance of underwater acoustic communication schemes. To this end, in this paper, we propose the preliminary design of a novel communication scheme based on transmitting chirp signals that are further spread over a multidimensional domain spanning code, time, and frequency. We evaluated the performance of the proposed scheme both with simulation and experimental studies.