Two-tiered Wireless Sensor Networks Research Articles

Study and Design of Privacy-Preserving Range Query Protocol in Sensor Networks Based on the Integration Reversal 0-1 Encoding with Bloom Filter

In the current research on data query for two-tiered WSN, the privacy-preservation range query is one of the hotspots. However, there are some problems in the existing researches in two-tiered wireless sensor networks such as high computational and communication costs for security comparison items and high energy consumption of sensing nodes. In this paper, a privacy-preservation range query protocol based on the integration reversal 0-1 encoding with Bloom filter is researched and designed. In the sensing data submission stage, the optimized reversal 0-1 encoding, HMAC algorithm, AES encryption algorithm and variable-length Bloom filter are used for generating the maximum–minimum comparison encoding and constructing a shorter verification index chain to reduce computational and communication costs of sensing nodes; in the private data range query stage, the base station uses the HMAC algorithm to convert the plaintext query range into the ciphertext query range and sends it to the storage node. In the storage node, the bitmap encoding information of the verification index chain is calculated with the comparison rule of the reversal 0-1 encoding and it is returned to the base station together with the verification index chain and the data ciphertext that compliance with the query rule; in the data integrity verification stage, the integrity of the query results using the verification index chain and bitmap encoding is verified at the base station. In the experimental section, the Cortex-M4 development board equipped with the Alios-Things operating system as sensing node and the Cortex-A9 development board equipped with the Linux operating system as storage node are implemented in this protocol, which is compared with the existing protocols in three aspects: the number of data collected in each cycle, the length of data and the number of data dimensions. The experimental results show that the energy consumption of this protocol is lower under the same experimental environment.

Constrained K-means and Genetic Algorithm-based Approaches for Optimal Placement of Wireless Structural Health Monitoring Sensors

Optimal placement of wireless structural health monitoring (SHM) sensors has to consider modal identification accuracy and power efficiency. In this study, two-tier wireless sensor network (WSN)-based SHM systems with clusters of sensors are investigated to overcome this difficulty. Each cluster contains a number of sensor nodes and a cluster head (CH). The lower tier is composed of sensors communicating with their associated CHs, and the upper tier is composed of the network of CHs. The first step is the optimal placement of sensors in the lower tier via the effective independence method by considering the modal identification accuracy. The second step is the optimal placement of CHs in the upper tier by considering power efficiency. The sensors in the lower tier are partitioned into clusters before determining the optimal locations of CHs in the upper tier. Two approaches, a constrained K-means clustering approach and a genetic algorithm (GA)-based clustering approach, are proposed in this study to cluster sensors in the lower tier by considering two constraints: (1) the maximum data transmission distance of each sensor; (2) the maximum number of sensors in each cluster. Given that each CH can only manage a limited number of sensors, these constraints should be considered in practice to avoid overload of CHs. The CHs in the upper tier are located at the centers of the clusters determined after clustering sensors in the lower tier. The two proposed approaches aim to construct a balanced size of clusters by minimizing the number of clusters (or CHs) and the total sum of the squared distance between each sensor and its associated CH under the two constraints. Accordingly, the energy consumption in each cluster is decreased and balanced, and the network lifetime is extended. A numerical example is studied to demonstrate the feasibility of using the two proposed clustering approaches for sensor clustering in WSN-based SHM systems. In this example, the performances of the two proposed clustering approaches and the K-means clustering method are also compared. The two proposed clustering approaches outperform the K-means clustering method in terms of constructing balanced size of clusters for a small number of clusters. Doi: 10.28991/CEJ-2022-08-12-01 Full Text: PDF

Problem Characteristics and Dynamic Search Balance-Based Artificial Bee Colony for the Optimization of Two-Tiered WSN Lifetime with Relay Nodes Deployment.

Lifetime optimization is one of the key issues among the many challenges of wireless sensor networks. The introduction of a small number of high-performance relay nodes can effectively improve the quality of the network services. However, how to deploy these nodes reasonably to fully enhance the network lifetime becomes a very difficult problem. In this study, a modified and enhanced Artificial Bee Colony is proposed to maximize the lifetime of a two-tiered wireless sensor network by optimal deployment of relay nodes. First, the dimension of the problem is introduced into the candidate search equation and the local search is adjusted according to the fitness of the problem and number of iterations, which helps to balance the exploration and exploitation ability of the algorithm. Second, in order to prevent the algorithm from falling into local convergence, a dynamic search balance strategy is proposed instead of the scout bee phase in the original Artificial Bee Colony. Then, a feasible solution formation method is proposed to ensure that the relay nodes can form the upper-layer backbone of the network. Finally, we employ this algorithm on a test dataset obtained from the literature. The simulation results show that the proposed algorithm for two-tiered wireless sensor network lifetime optimization can obtain higher and stable average network lifetime and more reasonable relay node deployment compared to other classical and state-of-the-art algorithms, verifying the competitive performance of the proposed algorithm.

A Security Multi-Dimensional Range Query Protocol Based on Left 0-1 Encoding in Two-Tiered Wireless Sensor Networks

In this research on range query technology for two-tiered wireless sensor networks, the existing researches still need improvement in privacy security and communication cost of the sensor node. In this paper, a security multi-dimensional range query protocol is proposed. The left 0-1 encoding mechanism (a new and optimized encoding mechanism), HMAC algorithm, and BASE64 encoding are employed to optimize the calculation of comparison factor. The encryption index chain is constructed by using AES algorithm to replace the long encryption constraint chain, so as to lower the energy consumption of computation and communication. The base station can verify the authenticity and integrity of query results on the basis of continuity of storage time and encryption index chain. The experiment has been conducted in the real systems. The protocol is compared and analyzed with the latest proposed Communication-Efficient Secure Range Queries (CSRQ). The results have shown that the proposed protocol can gain a better performance in terms of four aspects, i.e., the length of sensing data, the number of data collected in each cycle, the number of data dimensions and the number of sensor nodes in each unit. Meanwhile, compared with CSRQ, the communication cost of the proposed protocol is reduced by at least 10%.

An Efficient Privacy and Integrity-Preserving Range Query Scheme over Unsorted Data in IoT Two-tiered Wireless Sensor Networks

In most existing privacy-preserving range-query schemes, sorting data items is extremely critical for enabling integrity verification over query results. In two-tiered WSNs, the data is collected by several sensors and send to a central node called the storage node. If data is not sorted, it is hard for the sink to verify query result integrity without sending all data items to the sink. To preserve data privacy on the storage node, the sensors must do sorting, and data is encrypted before it’s sent to the storage nodes since storage nodes are more vulnerable to adversary attacks than the sensor nodes. However, sensors are resource-constrained, yet the sorting process is resource-consuming. The higher the number of data items collected, the larger the number of resources required to sort the elements. In this paper, on top of proposing a scheme that assumes that the data is sorted, we also propose a scheme we call Probabilistic Verification Neighborhood chaining (PvNC) for both sorted and unsorted data that still preserves data and range-query privacy and to a great extent guarantee data integrity. Experimental results show that sensor nodes use less power using our PvNC for unsorted data than the existing schemes that require data to be sorted.

Energy-Efficient Node Deployment in Heterogeneous Two-Tier Wireless Sensor Networks With Limited Communication Range

We study a heterogeneous two-tier wireless sensor network in which N heterogeneous access points (APs) collect sensing data from densely distributed sensors and then forward the data to M heterogeneous fusion centers (FCs). This heterogeneous node deployment problem is modeled as an optimization problem with the total power consumption of the network as its cost function. The necessary conditions of the optimal AP and FC node deployment are explored in this paper. We provide a variation of Voronoi Diagram as the optimal cell partition for this network and show that each AP should be placed between its connected FC and the geometric center of its cell partition. In addition, we propose a heterogeneous two-tier Lloyd algorithm to optimize the node deployment. Furthermore, we study the sensor deployment when the communication range is limited for sensors and APs. Simulation results show that our proposed algorithms outperform the existing clustering methods like Minimum Energy Routing, Agglomerative Clustering, Divisive Clustering, Particle Swarm Optimization, Relay Node placement in Double-tiered Wireless Sensor Networks, and Improved Relay Node Placement, on average.

A Novel Tree‐Based Genetic Algorithm for the Multicast Protocol in Two‐Tiered WSNs

Genetic algorithms (GAs) serve as a class of powerful tools to search for an effective multicast routing scheme among multiple cluster header nodes, which strongly affects the lifetime of two-tiered Wireless sensor networks (WSNs). This paper proposes a novel Genetic algorithm (GA) with a new crossover mechanism called Leaf crossover for the multicast routing among upper tier nodes in two-tiered WSNs, which outperforms the existing popular tree-based GAs by not requiring the global network link information, encoding/decoding or repair operations. Our simulation study indicates that the proposed algorithm could prolong the lifetime of multicast service, increase the packet delivery ratio as well as converge fast by comparison with existing GAs.

A Physarum-Inspired Algorithm for Minimum-Cost Relay Node Placement in Wireless Sensor Networks

Relay node placement, which aims to connect pre-deployed sensor nodes to base stations, is essential in minimizing the costs of wireless sensor networks. In this paper, we formulate the new Node-Weighted Partial Terminal Steiner Tree Problem (NWPTSTP) for minimum-cost relay node placement in two-tiered wireless sensor networks. The objective is to minimize the sum of heterogeneous production and placement costs of relay nodes and the sum of outage probabilities of transmission routes in a routing tree simultaneously. This extends the previous work that considers the costs of relay nodes to be homogeneous. After formulating NWPTSTP for this purpose, we prove that it can be transformed to the existing node-weighted Steiner tree problem. Subsequently, we conduct some theoretical analyses on the emerging Physarum-inspired algorithms to reveal their potential of computing Steiner trees. Based on these analyses, we propose a new Physarum-inspired algorithm for solving NWPTSTP. We conduct computational trials to show that: 1) in comparison to a state-of-the-art approximation algorithm for solving the node-weighted Steiner tree problem, our Physarum-inspired algorithm can produce better solutions in a smaller amount of time; and 2) in comparison to two state-of-the-art relay node placement algorithms, our Physarum-inspired algorithm can design wireless sensor networks with 25% lower relay cost and similar quality of service (specifically, 5% shorter network lifetime, 2% longer delay, and 0% loss of goodput). This indicates the usefulness of our Physarum-inspired algorithm for minimum-cost relay node placement in budget-limited scenarios.

SLS-STQ: A Novel Scheme for Securing Spatial–Temporal Top-$k$ Queries in TWSNs-Based Edge Computing Systems

A novel network paradigm of edge computing, namely, two-tiered wireless sensor networks (TWSNs), has been proposed by researchers in recent years for its high scalability and robustness. However, in the TWSNs-based edge computing systems, the storage nodes, which are located at the upper layer of the systems, are prone to be attacked by adversaries because they play a key role in bridging sensor nodes and Sink, which may lead to the disclosure of all the data stored on them as well as some other potentially devastating results. In this article, we study the integrity-and-privacy preservation problem for spatial–temporal Top- $k$ queries in the TWSNs-based edge computing systems and propose a sequence-encryption-based lightweight scheme named sequence-encryption-based lightweight scheme for securing spatial–temporal Top- $k$ queries (SLS-STQ) to solve the problem. In SLS-STQ, three algorithms, namely, the report preparation algorithm, the query processing algorithm, and the integrity verification algorithm, are designed for the sensor nodes, the storage nodes, and Sink, respectively. The theoretical analysis shows that SLS-STQ is able to achieve both integrity validation and privacy preservation with low computational complexity, and the simulation results show that SLS-STQ is much more efficient than the related state-of-the-art schemes.

A novel privacy- and integrity-preserving approach for multidimensional data range queries in two-tiered wireless sensor networks

To address the problem of storage nodes in wireless sensor networks being vulnerable to attack, this article proposes a new range query protocol, WQuery, based on multidimensional data privacy and integrity protection. To ensure the privacy of multidimensional data, the WQuery protocol encodes multidimensional sensing data and user query requests based on a bucket-partitioning scheme and sequential encryption mechanism at the sensor node and sink node. Therefore, the storage nodes cannot sense the real value of sensing data and query requests under the premise of correctly executing the request. To ensure the integrity of the multidimensional data query results, WQuery includes an integrity verification scheme based on the new tree-to-destination data structure. The scheme translates the actual query scope of a user request into a matched set of bucket labels and verifies the integrity of query results through the tree-to-destination data structure. Simulation results show that the tree-to-destination scheme is flexible, easy to implement, and highly secure, thereby effectively reducing energy consumption.

AN-Aided Secure Beamforming in Power-Splitting-Enabled SWIPT MIMO Heterogeneous Wireless Sensor Networks

In this paper, we investigate the physical layer security in a two-tier heterogeneous wireless sensor network (HWSN) depending on simultaneous wireless information and power transfer (SWIPT) approach for multiuser multiple-input multiple-output wiretap channels with artificial noise (AN) transmission, where a more general system framework of HWSN only includes a macrocell and a femtocell. For the sake of implementing security enhancement and green communications, the joint optimization problem of the secure beamforming vector at the macrocell and femtocell, the AN vector, and the power splitting ratio is modeled to maximize the minimal secrecy capacity of the wiretapped macrocell sensor nodes (M-SNs) while considering the fairness among multiple M-SNs. To reduce the performance loss of the rank relaxation from the SDR technique while solving the non-convex max–min program, we apply successive convex approximation (SCA) technique, first-order Taylor series expansion and sequential parametric convex approximation (SPCA) approach to transform the max–min program to a second order cone programming (SOCP) problem to iterate to a near-optimal solution. In addition, we propose a novel SCA-SPCA-based iterative algorithm while its convergence property is proved. The simulation shows that our SCA-SPCA-based method outperforms the conventional methods.

A Source Coding Perspective on Node Deployment in Two-Tier Networks

Multi-tier networks have many applications in different fields. We define a novel two-tier quantizer that can be applied to different node deployment problems including the energy conservation in two-tier wireless sensor networks consisting of $N$ access points (APs) and $M$ fusion centers (FCs). We aim at finding an optimal deployment of APs and FCs to minimize the average weighted total, or Lagrangian, of sensor and AP powers. For one FC, $M=1$ , we show that the optimal deployment of APs is simply a linear transformation of the optimal $N$ -level quantizer for density $f$ , and the sole FC should be located at the geometric centroid of the sensing field. We also provide the exact expression of the AP-Sensor power function and prove its convexity. For more than one FC, $M>1$ , we provide a necessary condition for the optimal deployment. Furthermore, to numerically optimize the AP and FC deployment, we propose three Lloyd-like algorithms and analyze their convergence. Simulation results show that our algorithms outperform the existing algorithms.

Delay constrained relay node placement in two-tiered wireless sensor networks: A set-covering-based algorithm

As Wireless Sensor Networks (WSNs) are widely used in time-critical applications, e.g., factory automation and smart grid, the importance of Delay Constrained Relay Node Placement (DCRNP) problem is becoming increasingly noticeable. Considering the benefits in terms of energy efficiency and scalability brought by the two-tiered topology, this paper studies the DCRNP problem in two-tiered WSNs. To address the NP-hardness, a Two-phase Set-Covering-based Algorithm (TSCA) is proposed to approximately solve this problem. To be specific, in the first phase, a Connectivity-aware Covering Algorithm (CCA) places Relay Nodes (RNs) to fully cover distributed sensor nodes with respect to delay constraints, and meanwhile CCA tries to reduce the number of connected components in the topology constructed in this phase so as to save the RNs deployed to build network connectivity. In the second phase, the network connectivity is built in obedience to delay constraints by a Set-Covering-based Algorithm (SCA) through an iterative manner, which formulates the deployment of RNs at each iteration as the set covering problem and solves this problem using a classic set covering algorithm. In addition, the elaborated analysis of time complexity and approximation ratio of the proposed algorithms is given out. Finally, extensive simulations demonstrate that TSCA can significantly save deployed RNs in comparison to existing algorithms.

SER: Secure and efficient retrieval for anonymous range query in wireless sensor networks

A two-tiered wireless sensor network, where storage nodes take charge of storing sensitive data and processing queries with respect to the sensing nodes and querists, incurs a security breach. This is because the important role of storage nodes may be (1) instructed by attackers to return fake and/or incomplete data in response to querists’ queries or (2) compromised by attackers to arbitrarily expose mass of valuable data or launch choice attacks to make authorized querists miss valuable data and disturb their decisions. Additionally, attackers may launch DoS attacks via wireless channels to storage nodes. To address the above issues, we propose a secure and efficient retrieval scheme for wireless sensor networks, namely SER, which mainly prevents attackers from gaining the valuable information stored on storage nodes, detects the compromised storage nodes when they misbehave, and efficiently verifies the querists’ privileges without knowing their identities. In addition to privacy and system analyses, we demonstrate the feasibility and efficiency of SER through experiments conducted on TelosB prototype sensor platform equipped with IEEE 802.15.4 TI wireless transceiver, and conduct comparisons with state-of-the-art methods.

Secure MAX/MIN Queries in Two-Tiered Wireless Sensor Networks

In wireless sensor networks, secure MAX/MIN query processing is a challenging issue, and it is useful in fields, where security is necessary. In this paper, we propose a secure MAX/MIN query processing method in two-tiered wireless sensor networks. To the best of our knowledge, it is the first work that can achieve data privacy protection and query result integrity verification simultaneously. Three schemes, naive secure MAX/MIN query (NSMQ), complicated secure MAX/MIN query (CSMQ), and OSMQ, are designed to achieve secure MAX/MIN queries. In NSMQ, we present an intuitive and baseline solution that makes the master nodes return all the ciphertext as the query result. However, it may incur high query communication cost. To address this limitation, a CSMQ scheme is designed, which introduces the comparable factors (c-factors) based on 0–1 encoding verification to find the accurate encrypted query result from the stored ciphertext of the master nodes even when their real values are unknown. Then, a broadcasting method is introduced to generate minor-node-sets as the proofs for verifying the integrity of the query results. CSMQ can significantly reduce the query communication cost, but its in-cell communication cost is high because of the extra data submission and broadcasting. To balance the in-cell and query communication cost, OSMQ, as an optimized version of CSMQ, is proposed to address the minor-node-set compression and random c-factor selection. The proposed schemes are built upon symmetric encryption and hash-based message authentication coding primitives. OSMQ can prevent compromised master nodes from obtaining the plaintext of private data and force them to return integrity-satisfying query results to avoid being detected. Extensive theoretical and experimental studies have been conducted to demonstrate the efficacy and efficiency of the proposed schemes.

Virtual movement of relay nodes for two-tier wireless sensor networks in tunnels

In wireless sensor networks, node placement plays a significant role in terms of meeting design goals, such as cost effectiveness, connectivity, lifetime, and data latency. In tunnel environments, the energy consumption of sensor nodes and relay nodes is imbalanced because of the long and narrow shape of tunnels. In this article, to reduce the use of extra batteries and the number of forwarding times for a message, we propose a new approach to assist in the placement of relay nodes for two-tier wireless sensor networks in a tunnel environment. The approach proposed is based on the principle that working relay nodes can change approximately at the same time during network operation. It seems the relay nodes move to a new place when they are instead by dormant relay nodes. The approach provides a novel method that has been proved to find optimal places to deploy relay nodes in tunnel environment. Moreover, the approach balances the energy consumption of entire sensor nodes and prolongs the lifetime of entire networks significantly, which is shown in simulations.

VP2RQ: Efficient verifiable privacy-preserving range query processing in two-tiered wireless sensor networks

In the field of wireless sensor networks, the secure range query technique is a challenging issue. In two-tiered wireless sensor networks, a verifiable privacy-preserving range query processing method is proposed that is based on bucket partition, information identity authentication, and check-code fusion. During the data collection process, each sensor node puts its collected data into buckets according to the bucket partition strategy, encrypts the non-empty buckets, generates the check-codes for the empty buckets, and fuses them. Then, the check-codes and the encrypted buckets are submitted to the parent node until they reach the storage node. During query processing, the base station converts the queried range into the interested bucket tag set and sends it to the storage node. The storage node determines the candidate-encrypted buckets, generates the check-code through code fusion, and sends them to the base station. The base station obtains query results and verifies the completeness of the result with the check-code. Both the theoretical analysis and experimental results show that verifiable privacy-preserving range query is capable of protecting the privacy sensor data, query result, and query range, which also supports the completeness verification of the query result. Compared to existing methods, verifiable privacy-preserving range query performs better on communication cost.

PSH: A Pruning and Substitution Based Heuristic Algorithm for Relay Node Placement in Two-Tiered Wireless Sensor Networks

Delay constrained relay node placement (DCRNP) problem minimizes the quantity of deployed relays that are employed to build at least one path between the sink and each sensor, while guaranteeing that the delay constraints for the built paths are fulfilled. Published literature only focus on the DCRNP problem in single-tiered wireless sensor networks (WSNs). Considering the benefits in terms of network scalability and energy consumption by the two-tiered network topology, this paper studies the DCRNP problem in two-tiered WSNs and proposes a pruning-and-substitution-based-heuristic (PSH) algorithm to solve the DCRNP problem. PSH consists of two phases, i.e., the covering phase and the connecting phase. In the covering phase, a shortest-path-based algorithm (SPA) is proposed to deploy relays at a subset of predetermined deployment locations such that each sensor is covered by at least one relay, meanwhile ensuring the obedience of delay constraints. Then, in the connecting phase, a tree-based connecting algorithm (TCA) is proposed to build the high-tier network connectivity. TCA first builds a shortest path tree to connect the relays deployed by SPA to the sink, and then, saves the deployed relays by gradually pruning or substituting them by the relays placed at the locations that several feasible paths pass through. The time complexity and the approximation ratio of this work are explicitly analyzed and extensive simulations are implemented to demonstrate its effectiveness.

Range-Free Mobile Actor Relocation in a Two-Tiered Wireless Sensor and Actor Network

Two-tiered wireless sensor and actor networks (WSANs) have been proposed to enhance network capabilities, where a set of resource-rich mobile nodes (termed actors ) form a connected backbone to relay sensing data from static sensors to the sink and sometimes are requested by sensors to perform a particular action. Such a two-tiered WSAN facilitates scalability and can efficiently reduce the energy consumption incurred by conventional hop-by-hop relaying via only sensors. However, relocating actors to achieve both connectivity and load balance is a challenge, especially when there is no location information of the nodes. Connectivity ensures that the actors are connected, whereas load balance ensures that actors collect and originate a similar amount of sensory data from the sensors. In this article, we formulate the Connected and Balanced Mobile Actor Relocation (CBMAR) optimization problem to address both connectivity and load balance and prove that the problem is NP-hard. We thus propose a dual-mode distributed actor relocation protocol that does not rely on any location information of nodes to relocate actors. The idea is to locally form virtual Voronoi cells of actors (termed covering cells ) based on the lower-tiered topology, where each actor locally recruits its own sensor members to form its own covering cell. By maintaining the covering cell, each actor locally relocates itself toward a sensor along the lower-tiered topology. Extensive simulation results show that the protocol can achieve both objectives of connectivity and load balance with low moving and communication overheads.

CSRQ: Communication-Efficient Secure Range Queries in Two-Tiered Sensor Networks.

In recent years, we have seen many applications of secure query in two-tiered wireless sensor networks. Storage nodes are responsible for storing data from nearby sensor nodes and answering queries from Sink. It is critical to protect data security from a compromised storage node. In this paper, the Communication-efficient Secure Range Query (CSRQ)—a privacy and integrity preserving range query protocol—is proposed to prevent attackers from gaining information of both data collected by sensor nodes and queries issued by Sink. To preserve privacy and integrity, in addition to employing the encoding mechanisms, a novel data structure called encrypted constraint chain is proposed, which embeds the information of integrity verification. Sink can use this encrypted constraint chain to verify the query result. The performance evaluation shows that CSRQ has lower communication cost than the current range query protocols.