Hierarchical Cellular Networks Research Articles

A recipe for new genes

Evolution Most lineages contain evolutionarily novel genes, but their origin is not always clear. Cosby et al. investigated the origin of families of lineage-specific vertebrate genes (see the Perspective by Wacholder and Carvunis). Fusion between transposable elements (TEs) and host gene exons, once incorporated into the host genome, could generate new functional genes. Examination of KARABINER , a bat gene that arose through this process, shows how the retention of part of the TE within this gene allows the transcribed protein to bind throughout the genome and act as a transcriptional regulator. Thus, TEs interacting within their host genome provide the raw material to generate new combinations of functional domains that can be selected upon and incorporated within the hierarchical cellular network. Science , this issue p. [eabc6405][1]; see also p. [779][2] [1]: /lookup/doi/10.1126/science.abc6405 [2]: /lookup/doi/10.1126/science.abf8493

An efficient bandwidth allocation scheme for hierarchical cellular networks with energy harvesting: an actor-critic approach

ABSTRACTIn this paper, we propose an efficient bandwidth allocation strategy for multiclass services in hierarchical cellular networks that consist of an operation controller, several small-cell base stations (SBSs), and a number of mobile users. Each SBS is equipped with a finite-capacity battery that is regularly recharged by a solar harvester. We aims to find the optimal bandwidth allocation policy in order to enhance the network performance in terms of user satisfaction and energy efficiency under energy harvesting and bandwidth sharing constraints. Since the arrivals of harvested energy and traffic requests are unknown due to users’ mobility and stochastic request generation, it is necessary to design a learning framework for the controller in order to predict these dynamics through interaction with the environment. For this purpose, we first formulate the resource allocation problem as the framework of a Markov decision process, and then, we employ an actor-critic algorithm to find the optimal policy under which the controller can effectively allocate the limited bandwidth to the SBSs for their data transmissions. We evaluate the performance of the proposed scheme through comprehensive simulations with different settings, and show that the proposed bandwidth allocation scheme can enhance the network’s performance in the long run.

A novel handoff algorithm for hierarchical cellular networks

In this paper, we propose a novel speed and service-sensitive handoff algorithm and analytical model for hierarchical cellular networks. First, we use the Gauss-Markov mobility model to predict the speeds of mobile stations, and divide mobile stations into three classes based on the predicted speeds: fast, medium-speed, and slow. Then, according to the mobility classification, network conditions, and service types, mobile stations will be handoff to the proper target networks prior to the deterioration of the currently operating channel. We further develop an analytical model to evaluate the performance of such a hierarchical system with different speed classes and service types. Simulations and analytical results show that the proposed handoff algorithm can significantly improve the network performance in terms of the handoff failure probability, unnecessary handoff probability, and network throughput, comparing with the traditional algorithms.

Three-dimensional electrospun nanofibrous materials: Fabrication, properties, and applications

Electrospun nanofibers, which are at the forefront of advanced fibrous materials, combine the robust mechanical strength, low density, fine flexibility, extremely high aspect ratio and ease of scalable synthesis from various materials, have been widely applied in the fields including electronics, environmental remediation, safety protections, and tissue engineering. Despite their outstanding potential, the major problem associated with electrospun nanofibers is their anisotropic lamellar deposition character, with the resultant nanofibers usually assembling into close-packed membranes (with thicknesses smaller than 100 mm) rather than into bulk three- dimensional (3D) nanofibrous materials, which have restricted their widely applications. Thus, the construction of 3D nanofibrous materials with stable structures has become a key challenge for electrospun nanofibers. Currently, researchers have successfully fabricated various 3D nanofibrous materials based on different approaches. Herein, this review summarizes the recent representative literatures on 3D construction of electrospun nanofibers by using layer-by-layer stacking, liquid- or template-assisted collection, and condition optimization. In addition, the mechanism and latest development of each 3D construction method are briefly analyzed and reviewed. However, the principle of the aforementioned methods remains the direct deposition of nanofibers; thus, the anisotropic lamellar deposition problem of electrospun fibers has not been solved. Moreover, most of these products are not real 3D-structured aerogels but rather stacks of membranes or fluffy cotton-like nanofiber deposits, which exhibit poor mechanical strength with no elastic resilience. Therefore, we subsequently summarized a novel strategy for creating fibrous, isotropically bonded elastic reconstructed aerogels with a hierarchical cellular structure and superelasticity by combining electrospun nanofibers and the fibrous freeze-shaping technique. The premise for this design is that for the first time, the intrinsically lamellar deposited electrospun nanofibers are reconstructed into 3D fibrous bulk aerogels with tunable densities and desirable shapes on a large scale. Furthermore, this fibrous aerogels exhibit the integrated properties of extremely low density (minimum of 0.12 mg/cm3), super recyclable compressibility and multifunctionality of combining the thermal insulation, sound absorption, emulsion separation and elasticity- responsive electric conduction, all originating from the synergistic effect of hierarchical cellular fibrous networks and well-bonded nanofibers. Afterwards, a brief outlook on the future development is indicated for the construction of 3D electrospun nanofibrous materials.

Resource allocation in integrated femto–macrocell networks based on location awareness

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme, macrocell uses all resource blocks along with a portion of the spectrum allocated to femtocell while both networks operate simultaneously. Closed-form expressions for downlink throughput and outage probability of femtocells are also attained as well as the throughput of macrocell network. The results demonstrate that the proposed hierarchical cellular network achieves higher throughput and lower outage probability for femtocell when compared to other hierarchical macro–femto cellular networks.

Fairness guaranteed novel eICIC technology for capacity enhancement in multi-tier heterogeneous cellular networks

Driven by surging demands for high data rate services and better user experiences, there is an increasing capacity demand in heterogeneous cellular networks. As one of the promising solutions for capacity enhancement, densely deployed small cells are proposed to provide a huge capacity gain and improve the user experience with high data rate services. However, the inter-cell interference among densely deployed cells is a big challenge that constraints the performance of capacity improvements in hierarchical multi-tier heterogeneous cellular networks. To minimize the inter-cell interference and achieve a fairness guaranteed solution among different users, a novel enhanced inter-cell interference coordination (eICIC) technology is proposed by jointly considering about the cell range expansion (CRE) scheme to minimize interferences among multi-tier cellular networks, improving the network throughput and quality of service (QoS). Optimal CRE bias and almost blank subframe (ABS) ratio solutions are achieved in this paper by considering the fairness among users at the center and cell edge. Moreover, the multi-objective decision-making problem is solved by maximizing the proportional fairness (PF) utility and area capacity in multi-tier heterogeneous cellular networks. Simulation results denote that a tradeoff between fairness and network throughput is achieved when CRE bias is from 8 to 12 dB and ABS ratio is from 4/8 to 6/8.

Agent Based Modeling on Organizational Dynamics of Terrorist Network

Modeling organizational dynamics of terrorist network is a critical issue in computational analysis of terrorism research. The first step for effective counterterrorism and strategic intervention is to investigate how the terrorists operate with the relational network and what affects the performance. In this paper, we investigate the organizational dynamics by employing a computational experimentation methodology. The hierarchical cellular network model and the organizational dynamics model are developed for modeling the hybrid relational structure and complex operational processes, respectively. To intuitively elucidate this method, the agent based modeling is used to simulate the terrorist network and test the performance in diverse scenarios. Based on the experimental results, we show how the changes of operational environments affect the development of terrorist organization in terms of its recovery and capacity to perform future tasks. The potential strategies are also discussed, which can be used to restrain the activities of terrorists.

An Adaptive Load Balance and Handoff Management Strategy for Hierarchical Infrastructure Networks

Hierarchical cellular networks that employ microcells with overlaying macrocells have been proposed to increase the traffic-carrying capacity and circuit quality. Variations in the traffic loads among cells will lessen the traffic-carrying capacity. Moreover, the handoff procedure usually takes place when the call crosses the cell boundary. An ineffective management will increase the system overheads, such as channel switch, data switch, and even network switch. The invetigation proposes an effective load balance and handoff management strategy. This strategy are implemented to solve traffic-adaption problem that can enhance the traffic-carrying capacity for variations in traffic. For the management of handoff procedure, our strategy considers the mobility of mobile hosts and the bandwidth utilization in macrocells. It can descrease the number of handoffs and, accordingly, lessen the system overhead. Furthermore, the simulation results are presented to confirm the efficiency of the proposed strategy.

Navigating the Multilayered Organization of Eukaryotic Signaling: A New Trend in Data Integration

The ever-increasing capacity of biological molecular data acquisition outpaces our ability to understand the meaningful relationships between molecules in a cell. Multiple databases were developed to store and organize these molecular data. However, emerging fundamental questions about concerted functions of these molecules in hierarchical cellular networks are poorly addressed. Here we review recent advances in the development of publically available databases that help us analyze the signal integration and processing by multilayered networks that specify biological responses in model organisms and human cells

An efficient method for loss performance modeling of hierarchical heterogeneous wireless networks

SummaryLoss performance modeling is important for the purpose of developing efficient dimensioning tools for large complicated networks. The performance modeling involves two challenging problems:(i) it is difficult to achieve in heterogeneous wireless networks, where different networks have different statistical characteristics in service and traffic models and (ii) capacity‐constrained femto‐macro overlay networks pose significant challenges due to the wide variety of bandwidth requirement of Internet services, the large number of femtocells overlaid by a macrocell, and the need for fast computations imposed by practical requirements of dynamic real‐time resource allocation. This paper proposes a new computationally efficient numerical method for the loss probability approximation in hierarchical heterogeneous wireless networks. Verified by simulations, the performance and accuracy of the proposed numerical method is evaluated in a two‐tier hierarchical cellular network and compared with an existing approximation method based on multidimensional Markov‐modulated Poisson process. Copyright © 2013 John Wiley & Sons, Ltd.

Optimal Pipeline Paging Load Balancing for Hierarchical Cellular Networks

We study load balancing of paging schemes for multitier hierarchical cellular networks, in which different tiers of cells overlay each other to provide multiple coverage in cellular service areas. Each mobile terminal (MT) can be paged in any tier of a multitier hierarchical cellular network. Paging requests are balanced in different waiting queues of different tiers, and the load balancing among them is achieved probabilistically among N tiers. The studied paging schemes are the Hierarchical Pipeline Paging scheme, the Hierarchical Sequential Paging scheme, and the Hierarchical Blanket Paging scheme. We study two optimization problems using the N-tier load balancing: 1) given a paging delay constraint, to minimize the total paging cost under the constraint that the total delay is upper bounded by a predefined total delay, and 2) given a bound on the total delay, to minimize the total paging cost under a paging delay constraint.

Efficient cell selection algorithm in hierarchical cellular networks: multi-user coordination

In a hierarchical cellular network employing universal frequency reuse, the level of both intra- and intercell interference largely depends on the selection of a serving cell for the users in the overlapping area of multiple cells. We propose an efficient cell selection algorithm that is suitable for hierarchical cellular networks. In the proposed algorithm, uplink transmit power is used as a key parameter and cells are selected on the basis of the coordination of multiple users, rather than the choice of a single user. Simulation results show that the proposed algorithm improves performance with respect to the number of supportable users and the transmit power that each user needs in order to achieve a given target SINR.

On hierarchical pipeline paging in multi-tier overlaid hierarchical cellular networks

We propose a hierarchical pipeline paging (HPP) for multi-tier hierarchical cellular networks, in which different tiers overlay with one another to provide overlapped coverage of cellular service, and each mobile terminal can be paged in any tier of a network. Paging requests (PRs) are queued in different waiting queues, and multiple PRs in each waiting queue are served in a pipeline manner. We study HPP, hierarchical sequential paging (HSP), and hierarchical blanket paging (HBP) schemes analytically in terms of discovery rate, total delay, paging delay, and cost. It is shown that HPP scheme outperforms both HBP and HSP schemes in terms of discovery rate while maintaining the same cost as HSP scheme. The HPP scheme outperforms HSP scheme in terms of total delay and has a lower total delay than HBP scheme when traffic load is high.

Performance Analysis of Sub-Rating for Handoff Calls in HCN

Hierarchical Cellular Networks (HCN) offer more efficient channel utilization and better quality of service (QoS) under the high tele-traffic condition compared to the single-tier system. One of the important measures of QoS in HCN as in any single-tier system is the handoff dropping rate. Although the existing approaches such as guard channel and queuing can reduce forced termination probability, they also result in higher new call blocking probability. The channel sub-rating strategy has found to be an effective technique to reduce the handoff force termination probability while preserving the new call blocking probability in a single-tier system. In this paper, we propose a new call admission control scheme for HCN based on the channel sub-rating. Analytic models based on 1-D Markov process in microcell and 2-D Markov process in macrocell are developed. Experimental results show that our scheme achieves lower blocking and forced termination probabilities compared to the traditional guard channel scheme. The effect of channel sub-rating on the voice quality degradation is also studied. Results demonstrate that we can establish a good balance between the forced termination probability and the voice quality degradation by varying the number of sub-ratable full-rate channels.

Optimal Positions of Relay Stations for Cluster-Based Two-Hop Cellular Network

Multihop cellular networks is an exciting and a fledgling area of wireless communication which offers huge potential in terms of coverage enhancement, data-rates, power reduction, and various other quality of service improvements. However, resource allocation in MCN is an NP-hard problem. Hence, significant research needs to be done in this field in order to efficiently design the radio network. In this paper, optimal position of relay stations in a hierarchical cluster-based two-hop cellular network is investigated. Vector algebra has been used to derive general equation for carrier-to-interference ratio (C/I) of a mobile station. It has been observed that when the transmit power of base station (BS) and the gateway (GTW)/relay station (RS) are same, the RSs should be located close to mid-point of BS and the edge of the cell. However, significantly, when the transmit power of the BS is greater than that of the GTW, then the RSs should be placed closer to the edge of the cell, in order to maximize the minimum C/I at any point in the cell. This in turn results in higher modulation technique at the physical layer, and hence, a higher data-rate to all the users in the system.

Analysis of multiservice hierarchical cellular CDMA networks for intelligent transportation systems

We consider two‐tier cellular CDMA networks supporting soft handoff for ITS (Intelligent Transportation System), where mobile users can move in only one of two directions. Both narrowband voice service and broadband services are supported in the considered system. The broadband calls are assigned to the associated macrocell in order to reduce the number of handoffs and the voice calls are assigned to the associated microcell. The handoff calls are prioritized over new calls in the system. To avoid macrocell resource under‐utilization, voice calls in microcells can be allowed to overflow to macorcells. To avoid excessive overflow from the microcells, broadband calls are prioritized over voice calls. Another way to avoid excessive overflow in macrocells is to allow overflowed voice calls to be taken back to microcells. For comparison purposes, we study three models: Model A (no overflow), Model B (overflow without takeback), and Model C (overflow and takeback). Two multi‐dimensional Markov chains are used to describe microcells and macrocells, respectively, and the analytical results for the performance measures of interest are derived, e.g., new call blocking probability, handoff failure probability, forced termination probability, and utilization. Last but not least, simulation programs are written in C to collect simulation results for verifying the analytical results.

Approximation of loss calculation for hierarchical networks with multiservice overflows

This paper studies loss calculation in hierarchical networks with multiservice overflows which have different call arrival rates, mean holding times, bandwidth requirements and share a common link. The loss calculation involves two challenging problems: 1) the computation of the two moment characterizations of multiservice overflow traffic over the shared link, 2) the calculation of the loss probabilities for multiservice non-Poisson overflow traffic in hierarchical systems. An efficient approximation method, known as multiservice overflow approximation (MOA), is proposed to enable multiservice networks designs with hierarchical architecture. Two contributions are included in the MOA method. First, an approximation based on blocking probabilities matching is proposed to compute the variances of multiservice overflows over the shared link. Second, a modified Fredericks & Hayward's approximation is used to calculate the loss probabilities of multiservice non-Poisson over flow traffic. The performance of the MOA method is evaluated in a two-tier hierarchical cellular network and compared with an existing approximation method based on multi-dimensional Markov-modulated Poisson process (MMPP). Verified by simulations, the MOA method achieves better accuracy in the general heterogeneous cases at lower computational cost than the MMPP method.

Service model and resource allocation scheme for multimedia traffic in 3G wireless systems

In this paper, we propose a multi-component teleservice model for multimedia applications. A Novel Resource Allocation Scheme for call and traffic management that exploits the multi-component teleservice is developed and analysed. The scheme was applied to hierarchical cellular structure networks. The performance is compared with the standard approach based on the single multimedia stream flow. The proposed scheme shows better performance in terms of reducing blocking and dropping probabilities.

Optimal paging load balance with total delay constraint in macrocell-microcell hierarchical cellular networks

Paging is a search process conducted in a paging area to locate a mobile terminal (MT) in terms of a cell. In this paper, we propose two paging schemes, called separated macro-micro paging (SMMP) and combined macro-micro paging (CMMP) for macrocell-microcell hierarchical cellular networks. In this kind of networks, MTs can receive signals from both macrocells and overlaid microcells. In the SMMP scheme, an MT can be paged from either the macrocell-tier or its overlaid microcell-tier. In the CMMP scheme, an MT is paged in a mix of the macrocell-tier and its overlaid microcell-tier. Optimal paging load balance between the macrocell-tier and the microcell-tier has been studied. The SMMP scheme when location probabilities are available is also studied. Analytical models are developed to evaluate the proposed schemes.

Modeling and analysis of hierarchical cellular networks with bidirectional overflow and take-back strategies under generally distributed cell residence times

The rapid growth of wireless services and mobile users drives a great interest in cellular networks with a hierarchical structure. Hierarchical cellular networks (HCNs) can provide high system capacity, efficient channel utilization and inherent load-balancing capability. In this paper, we develop an analytical model and a performance analysis method for a two-layer HCN with bidirectional overflow and take-back strategies. Mobile users are divided into two classes. The call requests (including new and handoff calls) of fast and slow users are preferably assigned to the macrolayer and microlayer, respectively. A call from a fast user or slow user can overflow to its non-preferable layer if there is no channel available. The successful overflow call can be taken back to its preferable layer if a channel becomes available. Since the commonly used exponentially distributed assumption for cell residence time and then the channel occupancy time does not hold for emerging mobile networks, we model various cell residence times by general distributions to adapt to more flexible mobility environments. The channel occupancy times are derived in terms of the Laplace transforms of various cell residence times. The handoff rates, overflow rates and take-back rates of each layer are also derived in terms of the new call arrival rates and related probabilities. The stationary probabilities (and then the performance measures) are determined on the basis of the theory of multi-dimensional loss systems.