LTE is the next generation of all-IP mobile communication system designed and developed by 3GPP. It offers unprecedented data transmission speed and low latency to support a variety of applications and services. However, compared to wireline networks, efficient QoS provisioning for diversified applications in wireless access networks such as LTE is challenging due to unreliable and resource-constrained radio interface. In this paper, we investigate an important problem of downlink resource allocation in recently enhanced LTE-Advanced systems where a newly added feature carrier aggregation provides more flexibility in radio resource management in addition to the existing resource block level packet scheduling. The resource allocation problem can be formulated as a complex combinatorial problem with multiple constraints and is solved every time slot. We decompose this highly complex optimization problem and construct a two-tier resource allocation framework which incorporates dynamic component carrier assignment and backlog based scheduling schemes with intelligent link adaptation. An efficient algorithm is developed to dynamically allocate component carriers to users to achieve load balancing. We also present novel backlog based scheduling policies and weighted-CQI based link adaptation scheme to obtain significantly better throughput and delay fairness. Performance of the proposed schemes is evaluated against the static round-robin component carrier assignment, the well-known proportional fairness scheduling rule and the existing link adaptation scheme. Extensive simulation results demonstrate that our schemes offer both better throughput and delay performance as well as user fairness.

As the next generation of all-IP mobile communication system, LTE offers unprecedented data transmission speed and low latency for a variety of applications and services. However efficient QoS provisioning for wireless networks is challenging due to unreliable and resource-constrained radio interface. In this paper, we investigate the important downlink scheduling problem in LTE networks with a focus on video streaming applications. Unlike the conventional scheduling rules which exploit the network layer metrics, our scheme is directly targeted on optimizing the application-layer video quality within the required end-to-end delay bound. The video quality optimized scheduling is formulated as a complex combinatorial optimization problem with an exponentially-growing search space. To solve this complex optimization problem, we exploit the GA (genetic algorithm) based metaheuristic approach. The intrinsic strength of population based solution of GA offers a superior advantage for this type of scheduling problems. Performance of the proposed crosslayer design and the GA solution is evaluated against the well-known M-LWDF scheduling rule and a trajectory method. The simulation results demonstrate the effectiveness of the GA based quality-optimized approach. It can enhance the video quality significantly and satisfy the delay bound.

The dynamic and shared nature of wireless medium imposes an adverse barrier to supporting QoS for video streaming applications in wireless networks. In this paper, we investigate a case study of video streaming in a wireless mesh network to obtain important observations on the factors which impact video quality in multihop wireless mesh networks. Based on our analysis of the case study, we propose the solutions for enhancing video streaming experience in wireless mesh networks from a cross-layer perspective which leverage the information across network (routing) layer and link (MAC) layer. The MAC layer retransmission count is exploited to guide the interface queue management for video packets. In addition, this retransmission count is also used as a metric to construct a retransmission-aware QoS routing scheme for video streams. In our approach, the upper layers are aware of the dynamic network status via retransmission count, so timely QoS decision can be made to enhance video quality effectively. Simulation results demonstrate the proposed solutions improve video streaming quality significantly compared with the existing schemes.

Interference among concurrent transmissions complicates QoS provisioning for multimedia applications in wireless mesh networks. In this paper we propose MARIA (mesh admission control and QoS routing with interference awareness), a scheme towards enhancing QoS support for multimedia in wireless mesh networks. We characterize interference in wireless networks using a conflict graph based model. Nodes exchange their flow information periodically and compute their available residual bandwidth based on the local maximal clique constraints. Admission decision is made based on the residual bandwidth at each node. We implement an on-demand routing scheme that explicitly incorporates the interference model in the route discovery process. It directs routing message propagations and avoids "hot-spots" with severe interference. Simulation results demonstrate that by taking interference into account MARIA outperforms the conventional approach. It finds routes with less interference and enhances the performance significantly. We use video as an example application and MARIA improves the quality of delivered videos, with up to 7.3 dB average PSNR gain.

Supporting multimedia services in wireless mesh networks is receiving more attention from the research community. While wired networks have mature infrastructure and protocols providing QoS for multimedia, supporting multimedia in multihop wireless mesh networks faces greater technical challenges. The unreliable nature and shared media of multihop communications make the deployment of multimedia applications in wireless mesh networks a difficult task. To identify and understand the issues and problems of providing multimedia in multihop wireless mesh networks, we take video streaming as an example, setting up a real testbed to conduct extensive experiments in various scenarios and analyze its performance. In contrast to simulation or network-layer statistics based studies, our investigation is directly focused on video quality in multihop scenarios. The results better represent real networks and reveal interesting aspects of video performance in multihop wireless mesh networks, which we believe is helpful in designing efficient QoS solutions for multimedia services in the wireless mesh networks.

We used molecular dynamics (MD) simulations to explore the transport of single cations through the channel of the muscle nicotinic acetylcholine receptor (nAChR). Four MD simulations of 16 ns were performed at physiological and hyperpolarized membrane potentials, with and without restraints of the structure, but all without bound agonist. With the structure unrestrained and a potential of -100 mV, one cation traversed the channel during a transient period of channel hydration; at -200 mV, the channel was continuously hydrated and two cations traversed the channel. With the structure restrained, however, cations did not traverse the channel at either membrane potential, even though the channel was continuously hydrated. The overall results show that cation selective transport through the nAChR channel is governed by electrostatic interactions to achieve charge selectivity, but ion translocation relies on channel hydration, facilitated by a trans-membrane field, coupled with dynamic fluctuations of the channel structure.

For media streaming in ad hoc networks, service replication has been demonstrated to be a quite effective countermeasure to streaming interruptions caused by fragile paths and dynamic topology. In this paper, we study the problem of joint routing and server selection for double description (DD) video streaming in ad hoc networks. We formulate the task as a combinatorial optimization problem and present tight lower and upper bounds for the achievable distortion. The upper bound provides a feasible solution to the formulated problem. Our extensive numerical results show that the bounds are very close to each other for all the cases studied, indicating the near-global optimality of the derived upper bounding solution. Moreover, we observe significant gains in video quality achieved by the proposed approach over existing server selection schemes. This justifies the importance of jointly considering routing and server selection for optimal MD video streaming

The initial coupling between ligand binding and channel gating in the human alpha7 nicotinic acetylcholine receptor (nAChR) has been investigated with targeted molecular dynamics (TMD) simulation. During the simulation, eight residues at the tip of the C-loop in two alternating subunits were forced to move toward a ligand-bound conformation as captured in the crystallographic structure of acetylcholine binding protein (AChBP) in complex with carbamoylcholine. Comparison of apo- and ligand-bound AChBP structures shows only minor rearrangements distal from the ligand-binding site. In contrast, comparison of apo and TMD simulation structures of the nAChR reveals significant changes toward the bottom of the ligand-binding domain. These structural rearrangements are subsequently translated to the pore domain, leading to a partly open channel within 4 ns of TMD simulation. Furthermore, we confirmed that two highly conserved residue pairs, one located near the ligand-binding pocket (Lys145 and Tyr188), and the other located toward the bottom of the ligand-binding domain (Arg206 and Glu45), are likely to play important roles in coupling agonist binding to channel gating. Overall, our simulations suggest that gating movements of the alpha7 receptor may involve relatively small structural changes within the ligand-binding domain, implying that the gating transition is energy-efficient and can be easily modulated by agonist binding/unbinding.

We study the problem of multipath routing for double description (DD) video in wireless ad hoc networks. We follow an application-centric cross-layer approach and formulate an optimal routing problem that minimizes the application layer video distortion. We show that the optimization problem has a highly complex objective function and an exact analytic solution is not obtainable. However, we find that a meta-heuristic approach such as genetic algorithms (GAs) is eminently effective in addressing this type of complex cross-layer optimization problems. We provide a detailed solution procedure for the GA-based approach. Simulation results demonstrate the superior performance of the GA-based approach versus several other approaches. Our efforts in this work provide an important methodology for addressing complex cross-layer optimization problems, particularly those involved in the application and network layers

Multiple description (MD) coding has a great potential for multimedia communications in wireless ad hoc networks. In this paper, we study the important problem of joint routing and server selection for MD video in ad hoc networks. We take a cross-layer approach to formulate the task as a combinatorial optimization problem and present tight lower and upper bounds for the achievable distortion. The upper bound also provides a feasible solution to the formulated problem. Our extensive numerical results show that the bounds are very close to each other for all the cases studied, indicating the near-global optimality of the derived upper bounding solution. Moreover, we observe significant gains in video quality achieved by the proposed approach over existing server selection schemes. This justifies the importance of jointly considering routing and server selection for optimal MD video streaming in wireless ad hoc networks. The proposed algorithms are computationally efficient and can be easily incorporated into existing routing protocols.

As developments in wireless ad hoc networks continue, there is an increasing expectation with regard to supporting content-rich multimedia communications (e.g., video) in such networks, in addition to simple data communications. The recent advances in multiple description (MD) video coding have made it highly suitable for multimedia applications in such networks. In this paper, we study the important problem of multipath routing for MD video in wireless ad hoc networks. We follow an application-centric cross-layer approach and formulate an optimal routing problem that minimizes the application layer video distortion. We show that the optimization problem has a highly complex objective function and an exact analytic solution is not obtainable. However, we find that a meta-heuristic approach such as genetic algorithms (GAs) is eminently effective in addressing this type of complex cross-layer optimization problems. We provide a detailed solution procedure for the GA-based approach, as well as a tight lower bound for video distortion. We use numerical results to demonstrate the superior performance of the GA-based approach and compare it to several other approaches. Our efforts in this work provide an important methodology for addressing complex cross-layer optimization problems, particularly those involving application and network layers.

We consider the problem of multicasting multiple description (MD) video in wireless ad hoc networks. We follow an application-centric, cross-layer approach with the objective of minimizing video distortion. The contribution of this paper is twofold. First, we propose a practical MD video multicast scheme that uses multiple trees to achieve an improved error resilience performance. The proposed scheme also takes into account highly diverse wireless link bandwidths by using scalable coding for each description, thus further improving the overall video quality. Second, we formulate the optimized multicast routing as a combinatorial optimization problem and propose an efficient genetic algorithm (GA)-based metaheuristic solution procedure. Performance comparison with existing approaches show significant gains for a wide range of network operating conditions.