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Energy consumption is a significant issue for data forwarding in Delay-Tolerant Network (DTN), where nodes are energy-constrained as they are driven by batteries. During their limited lifetime, these nodes have to spend a huge amount of energy since they perform forwarding, receiving, and temporarily storing messages, searching for the neighboring nodes for message forwarding, etc. The remaining energy of a node is expected to be higher as it increases the possibility of successful message delivery. Hence, awareness of energy expenditure is necessary for the routing strategies in DTN. This issue instigated us to evaluate the impact of node remaining energy on social-based routing protocols for the DTN scenario. Apart from the conventional DTN forwarding techniques, social-based forwarding protocols have involved an emerging concept that considers nodes’ social relations and behaviors to make routing decisions for efficient message transmission. In this paper, we have analyzed the energy efficiency of several social-based routing approaches, such as Social-aware Content-based Opportunistic Routing Protocol (SCORP), dLife, dLifeComm, and Bubble Rap with their corresponding performance evaluations regarding the performance metrics: average remaining energy, delivery ratio, average delay, and transmission cost. Opportunistic Network Environment (ONE) simulator is used as the simulation tool, where all the simulations are performed by (i) varying the number of nodes in each group with a fixed message Time-To-Live (TTL), and (ii) changing the message TTL, while the number of nodes per group is kept constant. From the outcome of simulations, it is observed that SCORP has the highest energy efficiency and shows the best performances for average delay and transmission cost.

Delay-Tolerant Network (DTN) is a resource-bound networking system which consists of many intermittently connected, movable devices known as nodes. Energy can be considered as an important resource for DTN scenarios since these nodes have limited energy. In order to perfect network enforcement, it is necessary to exploit the energy of the nodes efficiently. In DTN, most of the node energy is consumed because of mobility, scanning neighbors to deliver message and message transmission. Node energy has a significant role for successful transmission of messages. Higher energy of a node means that it has a high possibility to route its message with success across the network. So, for effective message routing it is mandatory to select an energy efficient routing mechanism in DTN environment. This point makes us interested to study the consumption of node energy in DTN scenarios. Within this research, the study of energy issue is focused for DTN routing approaches: Epidemic, Resource Allocation Protocol for Intentional DTN (RAPID), MaxProp, Probabilistic Routing Protocol using History of Encounters and Transitivity (PRoPHET), Spray and Wait, and Spray and Focus with their comparative performance analysis on behalf of four performance criteria: average remaining energy of node, delivery ratio, average latency, and transmission cost. Simulations are performed in Opportunistic Network Environment (ONE) simulator by varying node density while keeping message Time-To-Live (TTL) fixed and further, message TTL is changed while node density is kept fixed. We have found that Spray and Wait is the most energy efficient DTN routing scheme, whereas Spray and Focus yields the best performance in terms of delivery ratio, average latency and transmission cost.

Delay-Tolerant Networks are used to enable communication in challenging environments where nodes are intermittently connected, and an end-to-end path does not exist all the time between source and destination, e.g., Intermittently Connected Mobile Networks (ICMNs). Therefore, network environments, where the nodes are characterized by opportunistic connectivity, are appropriately modeled as Delay-Tolerant Networks (DTNs). In this paper, we have investigated the performance of DTN routing protocols, namely Epidemic, PRoPHET, and Spray-and-Wait (Binary version) in an ICMN scenario. Their performances are analyzed in terms of delivery probability, average latency, and overhead ratio of varying message generation rates and number of mobile nodes, respectively. In addition, the impacts of varying buffer size and Time-to-Live (TTL) on their performances are investigated. For evaluating these performance metrics, we have used Opportunistic Network Environment (ONE) simulator as the simulation tool. The outcome of this work shows that for the ICMN scenario, the best DTN routing technique is Binary Spray-and-Wait, whereas Epidemic routing exhibits the worst performance in terms of all the metrics considered here.

In opportunistic environments data forwarding is challenging where connectivity is intermittent because of network partitioning, dynamic topologies and long delays. Traditional routing protocols of Delay Tolerant Network (DTN) exploit "Store-Carry-and-Forward" strategy in these cases. But the pitfall of this approach is the selection of perfect relay node and the determination of best data transmission moment in dense and urban areas. To route data in such dynamic, heterogeneous networks social-based routing is an emerging technique that concerns social behaviors and interactions of nodes. Here, we look into the performances of customary routing protocols of DTN, such as Epidemic, Spray-and-Wait (SNW), PRoPHET with two social-aware routing protocols: SCORP and dLife by conducting simulations in Opportunistic Network Environment (ONE) simulator through three criteria, that are: delivery ratio, average latency and transmission cost with necessary simulation settings. The performances are evaluated by varying node density and message Time-To-Live (TTL). From the outcomes of this experiment, it can be said that dLife acts best for delivery ratio but worst for average latency. On the other hand, SNW has best performance for average latency, Epidemic shows lowest performance for both delivery ratio and transmission cost, where SCORP as well as SNW show best performances for transmission cost.

High peak-to-average power ratio (PAPR) is one of the major operational problems for orthogonal frequency division multiplexing (OFDM) system that may cause non-linear distortion leading to high bit error rate (BER). In this paper, we performed comparative study of four different phase sequences when applied in selected mapping (SLM) technique on the basis of PAPR, associated computational overhead, BER and bandwidth compactness. From simulation results, we demonstrated that the Riemann phase sequence achieved good PAPR reduction with minimum computational complexity, good BER performance with acceptable spectral efficiency.

High Peak to Average Power Ratio (PAPR) is one of the major drawbacks for Orthogonal Frequency Division Multiplexing (OFDM) transmitted signal. Among the PAPR reduction techniques, Selected Mapping (SLM) technique is one of the promising one but results in added computational complexity. In this paper, we applied Greatest Common Divisor (GCD) sequence based SLM method using our proposed reverse searching technique. The proposed scheme is named lightweight as it is very simple to implement and offers improved performance through significant reduction in PAPR and computational complexity. Additionally, we explored side information free transmission with GCD default index that achieves higher throughput but sacrifices slight PAPR reduction.

In Delay-Tolerant Network (DTN), there exists a lack of direct path from source to destination, and it is also featured by extremely high bit error rate, unwanted delay, limited resource, etc. For such network, we have investigated the effects of buffer size and mobility models on the optimization of the number of message copies for multi-copy routing protocols such as Spray-and-Focus (SNF) and Spray-and-Wait (SNW). This investigation is essential for providing us with the insight on the number of message copies that would provide better delivery, lower latency and lower overhead considering the effects of buffer size and mobility models in scalable delay-tolerant networks. In this investigation, we have considered three performance metrics, namely delivery probability, average latency, and overhead ratio. Simulation is done using Opportunistic Network Environment (ONE) simulator, which is designed basically for evaluating the performance of DTN routing strategies. Here we have considered three mobility models, namely Shortest Path Map Based (SPMB) movement, Random Walk, and Random Direction. Simulation results show that for increasing buffer size and number of nodes on these considered mobility models for a particular value of number of message copies, indicated by L, SNF routing exhibits satisfactory performance, especially in the case of SPMB movement using only L = 2 copies. Since our purpose is to provide a satisfactory performance, i.e., higher delivery, lower latency and lower overhead, SNW routing shows overall good performance using L = 10 copies. Therefore, it would be a good optimization using Shortest Path Map Based movement model using L = 2 copies for SNF routing, and L = 10 copies for SNW in scalable DTN scenario, where there may be a high possibility of varying buffer size with number of mobile nodes.

In Orthogonal Frequency Division Multiplexing (OFDM) system, high value of Peak-to-Average Power Ratio (PAPR) is an operational problem that may cause non-linear distortion resulting in high Bit Error Rate (BER). Selected Mapping (SLM) is a well known PAPR reduction technique that shows good performance but inflicts added computational overhead. In this paper, using Riemann sequence based SLM method, we apply reverse searching technique to find out low PAPR yielding phase sequences with significant reduction in computation complexity. In addition, we show side-information free transmission is possible that supports higher throughput with very little sacrifice in PAPR reduction. simulation results show that the proposed method achieves reduced computational complexity as well as side information free transmission with low PAPR.

High Peak-to-Average Power Ratio (PAPR) is one of the main drawbacks that may limit practical applications of Orthogonal Frequency Division Multiplexing (OFDM) System. Based on the well known Selective Mapping (SLM) method of PAPR reduction, in this paper, we propose a new phase sequence generation technique from Condex matrix that can achieve better PAPR reduction compared to the generally used Bauml sequence. From the simulation results, we show that our proposed phase sequence achieves 4.0 dB higher PAPR reduction compared to original SLM method and also reduces the computational overhead about 59 percent.

Intermittently Connected Mobile Networks (ICMNs) are sparse wireless networks where most of the time an end-to-end path does not exist from source to destination. These networks are characterized by opportunistic connectivity, long and variable delay, asymmetric data rate and high error rate. Hence, they can be appropriately modeled as Delay-Tolerant Networks (DTNs). In this paper, the performance of replication-based DTN routing protocols, namely Epidemic, PRoPHET, MaxProp, RAPID, Binary Spray-and-Wait, and Spray-and-Focus has been investigated in an ICMN scenario against varying message generation rates and number of mobile nodes, respectively. The performance is analyzed on the basis of three metrics: Delivery Probability, Average Latency, and Overhead Ratio. Opportunistic Network Environment (ONE) simulator is used as the simulation tool for evaluating these performance metrics. The outcome of this work shows that for the ICMN scenario and given simulation setting, the best DTN routing technique is Spray-and-Focus, whereas Epidemic routing exhibits the worst performance in terms of all the metrics considered here.

Reduction of high Peak-to-Average Power Ratio (PAPR) is a very important issue in Orthogonal Frequency Division Multiplexing (OFDM) system. In this contribution, we propose a new phase sequence that can be used in Selective Mapping (SLM) technique; a well known PAPR reduction method. Generated from Greatest Common Divisor (GCD) Matrix, we show that our proposed phase sequence possesses better PAPR reduction capability compared to the Bauml sequence often used in SLM technique. From simulation results, we demonstrate that the proposed sequence achieves 3.2 dB higher PAPR reduction compared to SLM method with Bauml sequence and also reduces the computational overhead about 65 percent.

The underwater acoustic channel features long and variable propagation delay, high bit error rate and limited bandwidth. Moreover, underwater mobile networks consisting of Autonomous Underwater Vehicles (AUVs) for surveillance and monitoring applications often suffer from intermittent connectivity as nodes move around the area of operations. Therefore, this scenario is appropriately modeled as a Delay-Tolerant Network (DTN). In this paper, we investigate two classes of DTN routing protocols: Spray-and-Wait (SNW) and the Resource Allocation Protocol for Intentional DTN (RAPID), together with a standard flooding protocol for underwater mobile networks, and their performance is analyzed in terms of packet delivery ratio, average end-to-end delivery delay and throughput, in different load conditions across various node mobility scenarios. Our results show that RAPID performs better than other DTN routing protocols in terms of packet delivery ratio at higher load conditions irrespective of node mobility, whereas the Binary version of SNW has the best performance in terms of average delivery delay.

Impedance and radiation characteristics of offset-fed slot antenna have been investigated for the reception of digital terrestrial TV broadcasting at 600 MHz including the effects of human hands and LCD (liquid crystal display) panel. First, the impedance characteristics of center-fed slot antenna have been obtained using finite difference time domain (FDTD) method. Then the impedance characteristics of offset-fed slot antenna have been simulated until the optimum feed point is achieved. According to the optimum results of the simulations, actual offset-fed slot antenna has been constructed on 300 mm times 210 mm copper plate. Then the impedance and radiation characteristics of the antenna have been simulated including the effect of human hands using FDTD method. It has been assumed that a metallic plate has the similar effect on the impedance and radiation characteristics of the antenna as that of the LCD panel of notebook computers. Therefore, the impedance and radiation characteristics of the antenna have been obtained including the effect of a metallic plate using FDTD method. Finally, experimental results have been obtained for the input impedance including the effects of the metallic plate and LCD panel, and compared for justification.

Impedance and radiation characteristics of offset-fed slot antenna have been investigated for the reception of digital terrestrial TV broadcasting at 600 MHz including the effects of human hands. The proposed antenna is suitable for embedding at the back of notebook computers' display. First, the impedance characteristics of center-fed slot antenna have been obtained using finite difference time domain (FDTD) method. Then the impedance characteristics of offset-fed slot antenna have been simulated until the optimum feed point is achieved. According to the optimum results of the simulations, actual offset-fed slot antenna has been constructed on 300 mm times 210 mm copper plate, and experimental results have been obtained for the input impedance. Finally the impedance and radiation characteristics of the antenna have been simulated including the effect of human hands using FDTD method. And a self-adaptive feed circuit for offset-fed slot antennas in parallel is proposed utilizing the effects of human hands on the radiation characteristics

Impedance and radiation characteristics of offset-fed slot antenna have been investigated for the reception of digital terrestrial TV broadcasting at 600 MHz including the effects of human hands. The proposed antenna is suitable for embedding at the back of notebook computers' display. First, the impedance characteristics of center-fed slot antenna have been obtained using finite difference time domain (FDTD) method. Then the impedance characteristics of offset-fed slot antenna have been simulated until the optimum feed point is achieved. According to the optimum results of the simulations, actual offset-fed slot antenna has been constructed on 300 mm /spl times/ 210 mm copper plate, and experimental results have been obtained for the input impedance. Finally, the impedance and radiation characteristics of the antenna have been simulated including the effect of human hands using FDTD method.