High Power Nodes Research Articles

Energy-Efficient User Association Strategy for Hyperdense Heterogeneous Networking in the Fifth Generation Systems

Redesigning user association strategies to improve energy efficiency (EE) has been viewed as one of the promising shifting paradigms for the fifth generation (5G) cellular networks. In this paper, we investigate how to optimize users’ association to enhance EE for hyper dense heterogeneous networking in the 5G cellular networks, where the low-power node (LPN) much outnumbers the high-power node (HPN). To characterize that densely deployed LPNs would undertake a majority of high-rate services, while HPNs mainly support coverage; the EE metric is defined as average weighted EE of access nodes with the unit of bit per joule. Then, the EE optimization objective function is formulated and proved to be nonconvex. Two mathematical transformation techniques are presented to solve the nonconvex problem. In the first case, the original problem is reformulated as an equivalent problem involving the maximization of a biconcave function. In the second case, it is equivalent to a concave minimization problem. We focus on the solution of the biconcave framework, and, by exploiting the biconcave structure, a novel iterative algorithm based on dual theory is proposed, where a partially optimal solution can be achieved. Simulation results have verified the effectiveness of the proposed algorithm.

Mobility Aware Loose Clustering for Mobile Ad hoc Network

Mobile ad hoc network comprises of nodes that may often possess dissimilar characteristics. These characteristics include computation power, transmission range, battery backup, etc. Such heterogeneity makes the wireless channel asymmetric due to presence of some unidirectional links. The more powerful nodes enhance the scalability, coverage area, and network lifetime. However, the interference caused by the high power nodes may result in reduced throughput. An effective clustering algorithm renders longer cluster lifetime and incurs low maintenance overhead. However, the mobility of nodes adversely affects the hierarchical structure. Therefore, selecting quasi-mobile nodes for the role of cluster head is a preferred option that makes the clustering structure more stable. In the proposed algorithm, we present a stable loose clustering algorithm by considering more powerful however less mobile nodes as cluster heads. The simulation analysis confirms that our algorithm delivers more stable clusters with low maintenance effort.

Energy harvesting aware topology control with power adaptation in wireless sensor networks

In the recent years, energy harvesting technology has been integrated into wireless sensor networks for resolving the energy “bottleneck” problems caused by the limited-capacity batteries equipped in traditional sensor nodes. However, due to the limited capacity of energy buffers equipped for storing the harvested energy, excessive harvested energy is indiscreetly discarded while sensor nodes are staying at the status of energy saturation. To address this issue, we present a topology control approach, for the energy harvesting wireless sensor network, that allows each node to adaptively adjust its transmission power for utilizing the harvested energy effectively. Specifically, we first model the behaviors of sensor nodes as an ordinal potential game where the high harvesting power nodes cooperate with the low harvesting power nodes to maintain the connectivity of the whole network. And we theoretically prove the existence of a Nash equilibrium for the game. Then, a polynomial-time algorithm is proposed to achieve the Nash equilibrium. Simulation results show that our proposed scheme improves the energy availability and outperforms existing energy-aware schemes in terms of energy conservation and balanced distribution.

A Loose-Virtual-Clustering-Based Routing for Power Heterogeneous MANETs

Power heterogeneity is common in mobile ad hoc networks (MANETs). With high-power nodes, MANETs can improve network scalability, connectivity, and broadcasting robustness. However, the throughput of power heterogeneous MANETs can be severely impacted by high-power nodes. To address this issue, we present a loose-virtual-clustering-based (LVC) routing protocol for power heterogeneous (LRPH) MANETs. To explore the advantages of high-power nodes, we develop an LVC algorithm to construct a hierarchical network and to eliminate unidirectional links. To reduce the interference raised by high-power nodes, we develop routing algorithms to avoid packet forwarding via high-power nodes. Via the combination of analytical modeling, simulations, and real-world experiments, we demonstrate the effectiveness of LRPH on improving the performance of power heterogeneous MANETs.

Optimal Fractional Frequency Reuse and Power Control in the Heterogeneous Wireless Networks

Heterogeneous wireless networks have emerged as a new paradigm to meet the fast growing wireless network capacity and coverage demands. Due to the co-deployment of high power and low power nodes in the same network using the same spectrum, more advanced interference coordination and radio resource management schemes are required than in the traditional cellular network in order to achieve a high network capacity and good user experience. In this paper, we propose an optimal fractional frequency reuse and power control scheme that can effectively coordinate the interference among high power and low power nodes. The scheme can be optimized to maximize the sum of the long term log-scale throughput among all the user equipments (UEs). Towards that end, the Lagrange dual function is first derived for the proposed optimization problem. Gradient descent method is then used to search the optimal solution for the convex dual problem. Due to the strong duality condition, the optimal solution for the dual problem is also the optimal solution for the primal problem. Simulation results show that the proposed scheme can greatly improve the wireless heterogeneous network performance on system capacity and user experience.

Load Balancing Based Approach To Improve Lifetime Of Wireless Sensor Network

In wireless sensor network, clustering is used as an effective technique to achieve scalability, selforganization, power saving, channel access, routing etc.[3]. Lifetime of sensor nodes determines the lifetime of the network and is crucial for the sensing capability.[2]. Clustering is the key technique used to extend the lifetime of a sensor network. Clustering can be used for load balancing to extend the lifetime of a sensor network by reducing energy consumption. Load balancing using clustering can also increase network scalability. Wireless sensor network with the nodes with different energy levels can prolong the network lifetime of the network and also its reliability. In this paper we propose a clustering technique which will balance the load among the cluster by using some backup nodes. The backup high energy and high processing power nodes replace the cluster head after the cluster reaches to its threshold limit. This approach will increase the network lifetime and will provide high throughput.

Hetnets - a new paradigm for increasing cellular capacity and coverage [Guest Editorial

Wireless data traffic has been increasing exponentially in recent years. Driven by a new generation of devices (smart phones, MIDs, netbooks, etc.), capacity demand increases faster than spectral efficiency improvement, particularly at hotspots/areas. Also, as services migrate from voice centric to data centric, more users operate indoors, which requires increased link budget and coverage extension to provide uniform user experience. Traditional networks optimized for homogeneous traffic face unprecedented challenges to meet the demand cost effectively. Most recently, Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)-Advanced has started a new study item to investigate heterogeneous network (HetNet) deployments as an efficient way to improve system capacity as well as effectively enhance network coverage. Unlike traditional heterogeneous networks that deal with the interworking of wireless local area networks and cellular networks, which the research community has already studied for more than a decade, in this new paradigm in the cellular network domain, a HetNet is a network containing nodes with different characteristics such as transmission power and radio frequency (RF) coverage area. Low-power micro nodes and high-power macro nodes can be maintained under the management of the same operator. They can share the same frequency band, provided by the operator. In this case, joint radio resource/interference management needs to be provided to ensure the coverage of low-power nodes. In some other cases, the low- and highpower nodes can use discontinuous bands of an operator separately (e.g., through carrier aggregation) so that strong interference with each other can be avoided. Macro network nodes with large RF coverage areas are deployed in a planned way for blanket coverage of urban, suburban, and rural areas. Local nodes with small RF coverage areas aim to complement the macro network nodes for coverage extension or throughput enhancement. In addition to this, global coverage can be provided by satellites (macrocells) according to an integrated system concept. The objective of Het-Nets targets the improvement of overall capacity as well as a cost-effective coverage extension and green radio solution by deploying additional network nodes within the local area range, such as low-power micro/pico network nodes, home-evolved Node-Bs (HeNBs)/closed subscriber group (CSG) cells, and femto and relay nodes.

Advanced Key-Management Architecture for Secure SCADA Communications

Supervisory control and data-acquisition (SCADA) systems are control systems for many national infrastructures. In the past, SCADA systems were designed without security functionality because of the closed operating environment. However, the security of SCADA systems has become an issue with connection to open networks becoming more common. Any damage to the SCADA system can have a widespread negative effect to society. In this paper, we review constraints and security requirements for SCADA systems and then investigate whether the existing key-management protocols for the SCADA systems satisfy these requirements. Afterward, we propose an advanced key-management architecture fitted for secure SCADA communications. The contributions of our work are two-fold. First, our scheme supports both message broadcasting and secure communication. Second, by evenly spreading much of the total amount of computation across high power nodes (MTU or SUB-MTU), our protocol avoids any potential performance bottleneck of the system while keeping the burden on low power nodes (RTU) at minimal.

Turning heterogeneity into an advantage in wireless ad-hoc network routing

With increasing diversity of wireless devices, heterogeneity in transmission power is expected to commonly appear in ad-hoc networks. We observe that the existence of high-power nodes may adversely affect the performance of traditional ad-hoc routing protocols such as AODV and DSR. A simple fallback strategy (i.e. high-power nodes transmitting at low-power levels) may solve the problem, but may not be efficient since it ignores the extra capability of high-power nodes. In this work, we view different levels of power heterogeneity as different tiers in the network. We propose a Tier-based RoutIng Framework (TRIF) which tackles the asymmetric link problem while taking advantage of long-range transmissions by high-power nodes. In contrast to other approaches that require periodic beaconing, TRIF allows the source to discover paths with symmetric links on the fly. By avoiding dependence on periodic beaconing, TRIF requires low overhead and is robust to network dynamics. TRIF does not require changes to the MAC layer, and can be utilized by any wireless devices that support dynamic transmission power control. TRIF can be leveraged to compute the optimal transmission power level over each link in order to reduce interference. Our simulation results show that TRIF can significantly outperform traditional ad-hoc routing protocols in heterogeneous environments.

안전한 SCADA 통신을 위한 트리 기반의 효율적인 키 관리 구조

The SCADA(Supervisory Control And Data Acquisition) system is a control system for infrastructure of nation. In the past, the SCADA system was designed without security function because of its closed operating environment. However, the security of the SCADA system has become an issue with connection to the open network caused by improved technology. In this paper we review the constraints and security requirements for SCADA system and propose advanced key management architecture for secure SCADA communications. The contributions of the present work are that our scheme support both message broadcasting and secure communications, while the existing key management schemes for SCADA system don`t support message broadcasting. Moreover, by evenly spreading much of the total amount of computation across high power nodes (MTU or SUB-MTU), our protocol avoids any potential performance bottleneck of the system while keeping the burden on low power (RTU) nodes at minimal.

A novel MAC protocol and layer two transmission scheduling algorithm for WLANs

It is known that hidden-terminal is one of the main problems in ad hoc wireless networks. In addition, there are scenarios where the desired destination is located in the range of other transmitters, so that the efforts on setting up communication with this terminal will fail due to collisions that may occur between transmitted control frames and undesired received control and data frames. This phenomenon becomes a bottleneck when most of data transmissions experience packet fragmentation. In such scenarios, the desired destination becomes unreachable during the data transfer of neighboring nodes. Furthermore, another problem that arises in such networks is in the case of mobile nodes with heterogeneous power capabilities where low power nodes have a disadvantage in accessing media due to higher levels of interference from the high power nodes. Conventional protocols can not address the aforementioned problems efficiently, resulting in throughput and channel utilization degradation. Using the same PHY of IEEE 802.11 and making slight modifications in its MAC, a new medium access control scheme is presented in this paper to address such problems. The performance of the proposed approach is compared with earlier schemes through simulation-based evaluations, showing performance enhancement due to better handling of unreachability issues in the proposed MAC scheme.

On approximate optimal dual power assignment for biconnectivity and edge-biconnectivity

Topology control is one of the major approaches to achieve energy efficiency as well as fault tolerance in wireless networks. In this paper, we study the dual power assignment problem for 2-edge connectivity and 2-vertex connectivity in the symmetric graphical model. The problem has arisen from the following practical origin. In a wireless ad hoc network where each node can switch its transmission power between high-level and low-level, how can we establish a fault-tolerant connected network topology in the most energy-efficient way? Specifically, the objective is to minimize the number of nodes assigned with high power and yet achieve 2-edge connectivity or 2-vertex connectivity. Note that to achieve a minimum number of high-power nodes is harder than an optimization problem in the same model whose objective is to minimize the total power cost. We first address these two optimization problems (2-edge connectivity and 2-vertex connectivity version) under the general graph model. Due to the NP-hardness, we propose an approximation algorithm, called prioritized edge selection algorithm, which achieves a 4-ratio approximation for 2-edge connectivity. After that, we modify the algorithm to solve the problem for 2-vertex connectivity and also achieve the same approximation ratio. We also show that the 4-ratio is tight for our algorithms in both cases.

A Power Control MAC Protocol for Wireless Sensor Networks

Power control scheme is used to reduce energy consumption, but asymmetric transmit powers is the problem which can result in increased collisions and degraded throughput in the scheme. A system model following pareto distribution according to a real network situation is proposed. The performance of the power control scheme in saving energy for wireless sensor networks is studied in this paper. A power control scheme based on SMAC (sensor-MAC) for wireless sensor networks is proposed and evaluated. In the new scheme, the optimum neighbor nodes are selected by a scheduling algorithm which can improve the network topology, reduce the collisions, increase goodput, and confirm the network connectivity. The message is transmitted with the optimum power. Furthermore, the protocol provides a fair share of the medium to low power and high power nodes by the reactive mechanism. The experimental results demonstrate that the new power control MAC (media access control) protocol provides longer lifetime and higher goodput than the current important protocols.

Handling asymmetry in power heterogeneous ad hoc networks

Traditional MAC and routing protocols, which are primarily designed for homogeneous networks wherein all nodes transmit with the same power, suffer performance degradations when employed in power heterogeneous networks. The observed degradations are due to link asymmetry, which arises as high power nodes that do not sense the transmissions of low power nodes can potentially initiate transmissions that interfere with the low power communications. Link layer asymmetry in power heterogeneous networks not only disrupts the functioning of the routing protocol in use, but also results in unfairness in medium access. In this paper, we develop a cross-layer framework to effectively address the link asymmetry problem at both the MAC and the routing layers. At the MAC layer, the framework intelligently propagates low power control messages to the higher power nodes, so as to preclude them from initiating transmissions while there are low power communications in progress within their sensing range. At the routing layer, the framework facilitates the efficient use of unidirectional links. We perform extensive simulations to study the performance of our proposed framework in various settings, and show that the overall throughput in power heterogeneous networks is enhanced by as much as 25% over traditional layered approaches. In addition, we show that our schemes are also beneficial in power homogeneous settings, as they reduce the extent of false link failures that arise when the IEEE 802.11 MAC protocol is used. In summary, our framework offers a simple yet effective and viable approach for medium access control and for supporting routing in power heterogeneous ad hoc networks.

How Dense Should a Sensor Network Be for Detection With Correlated Observations?

A detection problem in sensor networks is considered, where the sensor nodes are placed on a line and receive partial information about their environment. The nodes transmit a summary of their observations over a noisy communication channel to a fusion center for the purpose of detection. The observations at the sensors are samples of a spatial stochastic process, which is one of two possible signals corrupted by Gaussian noise. Two cases are considered: one where the signal is deterministic under each hypothesis, and the other where the signal is a correlated Gaussian process under each hypothesis. The nodes are assumed to be subject to a power density constraint, i.e., the power per unit distance is fixed, so that the power per node decreases linearly with the node density. Under these constraints, the central question that is addressed is: how dense should the sensor array be, i.e., is it better to use a few high-cost, high-power nodes or to have many low-cost, low-power nodes? An answer to this question is obtained by resorting to an asymptotic analysis where the number of nodes is large. In this asymptotic regime, the Gaumlrtner-Ellis theorem and similar large-deviation theory results are used to study the impact of node density on system performance. For the deterministic signal case, it is shown that performance improves monotonically with sensor density. For the stochastic signal case, a finite sensor density is shown to be optimal

Low-power authenticated group key agreement for heterogeneous wireless networks

Heterogeneous wireless networks are gaining popularity as users can be connected to these networks without any cables and even when they are mobile. The high power nodes in heterogeneous wireless networks do not have energy constraints but the user nodes, which can be large in numbers, are usually low power energy constrained devices. Therefore, the GKA protocol used to secure group communications in these networks has to take into consideration both the low power nature of the user nodes and the network size. In this paper, we present an energy efficient and scalable authenticated GKA protocol, which uses our proposed Contributory Ring-Centralised (ContRi-Central) group model. Besides providing complexity analysis, we also show the computational and communication energy consumption costs analysis of all nodes running our proposed scheme and four other efficient GKA protocols. Both the complexity analysis and energy consumption costs analysis indicate that our proposed scheme is more efficient and suitable for heterogeneous wireless networks.

Power optimization of technology-dependent circuits based on symbolic computation of logic implications

This paper presents a novel approach to the problem of optimizing combinational circuits for low power. The method is inspired by the fact that power analysis performed on a technology mapped network gives more realistic estimates than it would at the technology-independent level. After each node's switching activity in the circuit is determined, high-power nodes are eliminated through redundancy addition and removal. To do so, the nodes are sorted according to their switching activity, they are considered one at a time, and learning is used to identify direct and indirect logic implications inside the network. These logic implications are exploited to add gates and connections to the circuit; this may help in eliminating high-power dissipating nodes, thus reducing the total switching activity and power dissipation of the entire circuit. The process is iterative; each iteration starts with a different target node. The end result is a circuit with a decreased switching power. Besides the general optimization algorithm, we propose a new BDD-based method for computing satisfiability and observability implications in a logic network; futhermore, we present heuristic techniques to add and remove redundancy at the technology-dependent level, that is, restructure the logic in selected places without destroying the topology of the mapped circuit. Experimental results show the effectiveness of the proposed technique. On average, power is reduced by 34%, and up to a 64% reduction of power is possible, with a negligible increase in the circuit delay.