Semi-blind adaptive spatial equalisation for MIMO systems with high-order QAM signalling

This contribution investigates semi-blind adaptive spatial filtering or equalisation for multiple-input multiple-output (MIMO) systems that employ high-throughput quadrature amplitude modulation (QAM) signalling. A minimum number of training symbols, equal to the number of receivers (we assume that the number of transmitters is no more than that of receivers), are first utilized to provide a rough least squares channel estimate of the system's MIMO channel matrix for the initialization of the spatial equalizers' weight vectors. A constant modulus algorithm aided soft decision-directed blind algorithm, originally derived for blind equalization of single-input single-output and single-input multiple-output systems employing high-order QAM signalling, is then extended to adapt the spatial equalizers for MIMO systems. This semi-blind scheme has a low computational complexity, and our simulation results demonstrate that it converges fast to the minimum mean-square-error spatial equalization solution

Semi-blind adaptive beamforming for high-throughput quadrature amplitude modulation systems

A semi-blind adaptive beamforming scheme is proposed for wireless systems that employ high-throughput quadrature amplitude modulation signalling. A minimum number of training symbols, equal to the number of receiver antenna arrays elements, are first utilised to provide a rough initial least squares estimate of the beamformer's weight vector. A concurrent constant modulus algorithm and soft decision-directed scheme is then applied to adapt the beamformer. This semi-blind adaptive beamforming scheme is capable of converging fast to the minimum mean-square-error beamforming solution, as demonstrated in our simulation study

Generalised MBER-based vector precoding design for multiuser transmission

We propose a generalized vector precoding (VP) design based on the minimum bit error rate (MBER) criterion for multiuser transmission in the downlink of a multiuser system, where the base station (BS) equipped with multiple transmitting antennas communicates with single-receiving-antenna mobile station (MS) receivers each having a modulo device. Given the knowledge of the channel state information and the current information symbol vector to be transmitted, our scheme directly generates the effective symbol vector based on the MBER criterion using the particle swarm optimization (PSO) algorithm. The proposed PSO-aided generalized MBER VP scheme is shown to outperform the powerful minimum mean-square-error (MMSE) VP and improved MMSE-VP benchmarks, particularly for rank-deficient systems, where the number of BS transmitting antennas is lower than the number of MSs supported

On the pinning strategy of complex networks

In pinning control of complex networks, a tacit believing is that the system dynamics will be better controlled by pinning the large-degree nodes than the small-degree ones. Here, by changing the number of pinned nodes, we find that, when a significant fraction of the network nodes are pinned, pinning the small-degree nodes could generally have a higher performance than pinning the large-degree nodes. We demonstrate this interesting phenomenon on a variety of complex networks, and analyze the underlying mechanisms by the model of star networks. By changing the network properties, we also find that, comparing to densely connected homogeneous networks, the advantage of the small-degree pinning strategy is more distinct in sparsely connected heterogenous networks

The Physical Mechanism of Blood-Brain Barrier Opening Using Focused Ultrasound and Microbubbles

The key to effective treatment of neurological diseases resides in the safe opening of the blood-brain barrier (BBB), a specialized structure that impedes the delivery of therapeutic agents to the parenchyma. Despite the fact that several approaches have been successful in overcoming the BBB impermeability, none of them can induce localized BBB opening noninvasively except for focused ultrasound (FUS) in conjunction with microbubbles. The physical mechanism behind the opening, however, has not been identified. Insight into the mechanism can be critical for delineating the safety profile for in both small and large animals alike. Therefore the purpose of this dissertation is to first determine the physical mechanism of FUS-induced BBB opening in mice and then translate this approach to non-human primates. To accomplish this goal, an in vivo transcranial cavitation detection system was developed and tested, built in phantoms and in vivo, to monitor the behavior of the microbubbles in the FUS bean, and to determine the type of cavitation, i.e., the activation of bubbles in an acoustic field, during BBB opening. We showed that the inertial cavitation (IC), a collapse of a bubble, which can vary from a fragmentation of the bubble to shock wave and liquid jets depending on the pressure, thereby damaging the endothelial cells of the brain capillaries, was not required to induce BBB opening in mice. With this system, the role of microbubble properties, including the diameter and shell components, in the BBB opening were determined. When the BBB opens with stable cavitation (SC), i.e., relatively moderate amplitude changes in the bubble size, the bubble diameter is similar to the capillary diameter (i.e., at 4-5, 6-8 µm) while with inertial cavitation it is not (i.e., at 1-2 µm). The bubble may thus have to be in closer proximity to the capillary wall to induce BBB opening without IC. The BBB opening properties, such as volume and permeability, however, were not affected by the shell component of the microbubbles in mice. The connection between the physical and physiological mechanism was then investigated to identify the lowest peak rarefactional pressure BBB opening threshold at 1.5 MHz (0.18 MPa). A sufficiently long pulse (pulse length = 0.5 ms) was required for the SC to induce BBB opening at the lowest pressure. However, the tight junctions, the main formation of the BBB, were found not to be disrupted after sonication at both low (0.18 MPa) and high (0.45 MPa) pressures. Therefore, the transcellular pathway may be the main route of the FUS-induced BBB opening. Finally, the cavitation-guided BBB opening system was used to induce reversible BBB opening in non-human primates. This is a major step towards clinical feasibility. In conclusion, a transcranial cavitation detection system was developed, in order to characterize the physical mechanism, the role of the microbubbles, and the corresponding physiological response of the FUS-induced BBB opening