This article considers the joint problem of packet scheduling and self-localization in an underwater acoustic sensor network with randomly distributed nodes. In terms of packet scheduling, our goal is to minimize the localization time, and to do so we consider two packet transmission schemes, namely a collision-free scheme (CFS), and a collision-tolerant scheme (CTS). The required localization time is formulated for these schemes, and through analytical results and numerical examples their performances are shown to be dependent on the circumstances. When the packet duration is short (as is the case for a localization packet), the operating area is large (above 3 km in at least one dimension), and the average probability of packet-loss is not close to zero, the collision-tolerant scheme is found to require a shorter localization time. At the same time, its implementation complexity is lower than that of the collision-free scheme, because in CTS, the anchors work independently. CTS consumes slightly more energy to make up for packet collisions, but it is shown to provide a better localization accuracy. An iterative Gauss-Newton algorithm is employed by each sensor node for self-localization, and the Cramér Rao lower bound is evaluated as a benchmark.

Random Access Compressed Sensing (RACS) is an efficient method for data gathering from a network of distributed sensors with limited resources. RACS relies on integrating random sensing with the communication architecture, and achieves overall efficiency in terms of the energy per bit of information successfully delivered. To address realistic deployment conditions, we consider data gathering over a fading and noisy communication channel. We provide a framework for system design under various fading conditions, and quantify the bandwidth and energy requirements of RACS in fading. We show that for most practical values of the signal to noise ratio, energy utilization is higher in a fading channel than it is in a non-fading channel, while the minimum required bandwidth is lower. Finally, we demonstrate the savings in the overall energy and the bandwidth requirements of RACS compared to a conventional TDMA scheme. We show that considerable gains in energy -on the order of 10 dB- are achievable, as well as a reduction in the required bandwidth, e.g., 2.5-fold decrease in the bandwidth for a network of 4000 nodes.

Random Access Compressed Sensing (RACS) is an efficient method for data telemetry from a network of distributed sensors deployed in a challenging field environment with limited resources. RACS relies on integrating sensing with the communication architecture, in order to achieve overall efficiency in terms of the energy per bit of information successfully delivered to the fusion center. Targeting realistic deployment conditions, we consider data gathering over a Ricean fading channel and in the presence of communication noise. We provide a framework for system design and study the energy and bandwidth requirements of the network. We then show that compared to a conventional TDMA network with ARQ, RACS achieves significant energy and bandwidth savings. For example, for a network of 4000 nodes, we observe 10 dB gain in the energy as well as a 2.5-fold reduction in the required bandwidth.

Inspired by the theory of compressed sensing and employing random channel access, we propose a distributed energy-efficient sensor network scheme denoted by Random Access Compressed Sensing (RACS). The proposed scheme is suitable for long-term deployment of large underwater networks, in which saving energy and bandwidth is of crucial importance. During each frame, a randomly chosen subset of nodes participate in the sensing process, then share the channel using random access. Due to the nature of random access, packets may collide at the fusion center. To account for the packet loss that occurs due to collisions, the network design employs the concept of sufficient sensing probability. With this probability, sufficiently many data packets - as required for field reconstruction based on compressed sensing - are to be received. The RACS scheme prolongs network life-time while employing a simple and distributed scheme which eliminates the need for scheduling.

Reconfigurable antennas offer a promising solution to the problem of space limitation in high-performance wireless communication over handset devices. In this paper, we propose a novel transmission scheme capable of extracting the maximum diversity gains of a Multiple-Input Multiple-Output (MIMO) communication system employing reconfigurable antennas at the transmitter, the receiver or at both ends of the wireless link, without the need for feedback. For a MIMO communication system using reconfigurable antennas at the transmitter, we propose a state-switching scheme in combination with an appropriate three-dimensional block code in order to extract the maximum possible level of diversity. When reconfigurable antennas are placed at the receiver end, we propose a state-selection scheme and prove that the proposed scheme is capable of achieving maximum diversity gains. Moreover, the state-selection method is able to obtain selection gain in addition to diversity gain. As shown, both state-switching and state-selection schemes can be combined together when reconfigurable antennas are used at both ends of the wireless link. Furthermore, we discuss and quantify the effects of switching delay on the performance of both state-switching and state-selection schemes. Finally, we provide simulation results to validate the performance of the proposed schemes. To demonstrate the gains of our schemes in realistic propagation conditions, we also conduct simulations using an actual reconfigurable antenna known as the PIXEL antenna.

In this paper, we propose a novel Multiple-Input Multiple-Output (MIMO) wireless communication system employing reconfigurable PIXEL antennas at the receiver. We design a Space-Time-State Block Coding scheme for the PIXEL-based reconfigurable MIMO system and propose optimal and ad hoc state-selection algorithms that achieve maximum diversity gains. Moreover, we prove that in state-selection schemes, contrary to antenna selection, there is no benefit in selecting more than one state. Furthermore, we discuss the gains of state-selection over the state-switching scheme proposed in [1]. Finally, we evaluate the theoretical findings through simulations. These simulations are conducted using a realistic channel model, that takes into account the radio-electric characteristics (radiation pattern, gain, efficiency, etc.) of the PIXEL antennas.

In this paper, we present an open-loop reconfigurable multiple-input multiple-output system, employing ORIOL antennas at both ends of the communication system. The ORIOL is a compact dual-polarized reconfigurable antenna introduced in [1]. First, we provide a realistic model for our communication system based on measurements conducted using ORIOL antennas. Then, we analytically discuss the performance limits of the practical system and derive the maximum achievable diversity gains. Furthermore, we design a specific space-time block code that is capable of achieving such maximum diversity gains, without any feedback from the receiver. Finally, we evaluate the theoretical findings through measurements and simulations.

In this paper, we propose a novel class of Space-Frequency and Space-Time-Frequency block codes based on Quasi-Orthogonal designs, over a frequency selective Rayleigh fading channel. The proposed Space-Frequency code is able to achieve rate-one and full space and multipath diversity gains available in the MIMO-OFDM channel. As simulation results demonstrate, the code outperforms the existing Space-Frequency block codes in terms of bit error rate performance. By coding across the three dimension of space, time and frequency, we propose a Quasi-Orthogonal Space-Time-Frequency code that is capable of achieving rate-one and exploiting all of the spatial, multipath and temporal diversity gains offered by the channel. In case of a channel which is quasi-static over adjacent OFDM symbol durations, we propose a Space-Time-Frequency code that benefits from a reduced maximum likelihood decoding complexity.

In this paper, we propose a novel class of Space-Frequency and Space-Time-Frequency block codes based on Quasi-Orthogonal designs, over a frequency selective Rayleigh fading channel. The proposed codes are able to achieve rate one and full diversity by exploiting the space and multipath diversity gains available in the MIMO-OFDM channel. As the simulation results show, our codes outperform the existing Space-Frequency block codes in terms of bit error rate performance. Additionally, the proposed Space-Time-Frequency code benefits from a reduced maximum likelihood decoding complexity, which is a huge simplification compared to the existing codes. We also discuss the conditions under which the maximum likelihood decoding for our proposed Quasi-Orthogonal Space-Frequency code is simplified as well.

In this paper, we first introduce a quasi-orthogonal space-time block coding scheme over multiple antenna block fading channels. The proposed code exploits temporal diversity due to the mobile nature of the block fading channel as well as spatial diversity due to multiple antennas. We then propose a beamforming strategy over temporally correlated channel blocks. It is assumed that the channel undergoes Doppler frequency shift and an AR1channel model is adopted to track the channel temporal correlation coefficients at the transmitter. Using the combination of transmit beamforming and quasi-orthogonal block coding over adjacent channel blocks, we accomplish to achieve the available array gains on top of notable diversity gains and coding gains, compared to the standard solutions in the conventional wireless communication schemes. In our model, the knowledge of the channel statistics at the transmitter side is based on the approximation of the Jakes' model and does not require frequent feedback updates from the receiver. Simulation results show the superiority of our scheme to the existing coding schemes with knowledge of the channel statistics at the transmitter