Gorce J-M, Arditi M, Schneider M. Influence of bubble size distribution on the echogenicity of ultrasound contrast agents: A study of SonoVue™. Invest Radiol 2000;35:661–671. RATIONALE AND OBJECTIVES. To study the relative contributions of different bubble size classes to SonoVue™’s echogenicity in fundamental acoustic imaging modes. SonoVue™ is a contrast agent, previously known as BR1, with a bubble size distribution extending from approximately 0.7 to 10 μm. METHODS. A model for the acoustic response of SonoVue™ was determined and validated for a set of experimental data. This model was used to simulate the acoustic response of a standard batch of SonoVue™ as the sum of responses of nonoverlapping bubble size classes. RESULTS. The simulation was first validated for a standard SonoVue™ bubble size distribution. When this distribution was considered as five size classes with equal numbers of bubbles, it was found that bubbles smaller than 2 μm accounted for 60% of the total number but contained only 5% of the total gas volume. The simulation results indicated marked differences in the acoustic contributions from these classes, with 80% of the acoustic efficacy provided by bubbles 3 to 9 μm in diameter. The study also compared bubble distributions in number, surface, and volume, with the distribution computed in terms of acoustic efficacy. CONCLUSIONS. This study shows why bubble volume is a much better indicator of SonoVue™’s efficacy than is bubble count. A low threshold in diameter was found for SonoVue™ microbubbles at approximately 2 μm, under which size bubbles do not contribute appreciably to the echogenicity at medical ultrasound frequencies.

Modern cellular networks in traditional frequency bands are notoriously interference-limited, especially in urban areas, where base stations are deployed in close proximity to one another. The latest releases of LTE incorporate features for coordinating downlink transmissions as an efficient means of managing interference. Recent field trial results and theoretical studies of the performance of JT CoMP schemes revealed, however, that their gains are not as high as initially expected, despite the large coordination overhead. These schemes are known to be very sensitive to defects in synchronization or information exchange between coordinating base stations as well as uncoordinated interference. In this article, we review recent advanced CB schemes as alternatives, requiring less overhead than JT CoMP while achieving good performance in realistic conditions. By stipulating that in certain LTE scenarios of increasing interest, uncoordinated interference constitutes a major factor in the performance of CoMP techniques at large, we hereby assess the resilience of the state-of- the-art CB to uncoordinated interference. We also describe how these techniques can leverage the latest specifications of current cellular networks, and how they may perform when we consider standardized feedback and coordination. This allows us to identify some key road blocks and research directions to address as LTE evolves toward the future of mobile communications.

The multiresolution frequency domain parflow (MR-FDPF) approach is applied to radio wave propagation in indoor environments. This method allows for a better understanding of indoor propagation and hence greatly assists the development of WiFi-like network planning tools. The efficiency of such wireless design tools is strongly impacted by the quality of the coverage predictions which have to be estimated with a limited computational load. The usual approaches are based either on an empirical modeling relying on measurement campaigns or on geometrical optics leading to ray-tracing. While the former approach suffers from a lack of accuracy, the later one needs to balance accuracy with computational load requirements. The new approach proposed herein is based on a finite difference formalism, i.e., the transmission line matrix (TLM). Once the problem is developed in the frequency domain, the linear system thus obtained is solved in two steps: a pre-processing step which consists of an adaptive MR (multigrid) pre-conditioning and a propagation step. The first step computes a MR data structure represented as a binary tree. In the second step the coverage of a point source is obtained by up-and-down propagating through the binary tree. This approach provides an exact solution for the linear system whilst significantly reducing the computational complexity when compared with the time domain approach

Recent advances in information theory have provided achievability bounds and converses for the coding rate for the finite blocklength regime. In this paper, recent results on the non-asymptotic coding rate for fading channels with no channel state information at the transmitter are exploited to analyze the goodput in additive white Gaussian noise (AWGN) and the energy-efficiency spectral- efficiency (EE-SE) tradeoff where the fundamental relationship between the codeword length and the EE is given. Finally, the true outage probability in Ricean and Nakagami-m block fading channels is investigated and it is proved that the asymptotic outage capacity is the Laplace approximation of the average error probability in finite blocklength regime.

As 4G wireless networks are vastly and rapidly deployed worldwide, 5G with its advanced vision of all connected world and zero distance communications is already at the corner. Along with the super quality of user experience brought by these new networks, the shockingly increasing energy consumption of wireless networks has become a worrying economic issue for operators and a big challenge for sustainable development. Green Transmission Technologies (GTT) is a project focusing on the energy-efficient design of physical-layer transmission technologies and MAC-layer radio resource management in wireless networks. In particular, fundamental tradeoffs between spectrum efficiency and energy efficiency have been identified and explored for energy-efficiency-oriented design and optimization. In this article, four selected GTT solutions are introduced, focusing on how they utilize the degrees of freedom in different resource domains, as well as how they balance the tradeoff between energy and spectrum efficiency. On top of the elaboration of separated solutions, the GTT toolbox is introduced as a systematic tool and unified simulation platform to integrate the proposed GTT solutions together.

Recent years have witnessed a tremendous growth of research in the field of wireless systems and networking protocols. Consequently, simulation has appeared as the most convenient approach for the performance evaluation of such systems and several wireless network simulators have been proposed in recent years. However, the complexity of the wireless physical layer (PHY) induces a clear tradeoff between the accuracy and the scalability of simulators. Thereby, the accuracy of the simulation results varies drastically from one simulator to another. In this paper, we focus on this tradeoff and we investigate the impact of the physical layer modeling accuracy on both the computational cost and the confidence in simulations. We first provide a detailed discussion on physical layer issues, including the radio range, link and interference modeling, and we investigate how they have been handled in existing popular simulators. We then introduce a flexible and modular new wireless network simulator, called WSNet. Using this simulator, we analyze the influence of the PHY modeling on the performance and the accuracy of simulations. The results show that the PHY modeling, and in particular interference modeling, can have a significant impact on the behavior of the evaluated protocols at the expense of an increased computational overhead. Moreover, we show that the use of realistic propagation models can improve the simulation accuracy without inducing a severe degradation of scalability.