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The proliferation of IoT devices comes with many challenges among which security is one of the most serious issues. In order to address the security issue for low-end IoT devices, ARM recently proposed the Platform Security Architecture (PSA), which provides execution isolation to safely manage and protect the computing resources of low-end IoT devices. However, developers implementing IoT services for PSA-based IoT devices need to follow complex development procedures and understand the PSA hardware, which dramatically increases the development time and cost of PSA-based IoT devices. This paper analyzes vulnerabilities that may arise from general purpose low-end IoT devices to derive the security requirements and essential security services for PSA-based IoT devices, and proposes a secure platform model based on the analysis results. The proposed secure platform model consists of system security services and application security services based on the basic PSA model and essential trusted sub-systems, and it is designed to be flexible and applicable to various types of PSA-based IoT devices. In addition, it provides secure platform services APIs to enable easy and fast development of IoT services. To evaluate the proposed secure platform model, two proof-of-concept implementations are provided by using both the basic PSA model with Secure Element (SE) and a reference device for ARM’s PSA. Finally, a case study shows that the development of IoT services can be done easily and quickly using the proposed security platform model.

A cognitive radio (CR) is a promising technology to solve the emerging spectrum crisis, especially for applications where thousands of wireless sensor nodes are deployed. Since continuous spectrum sensing will greatly reduce the lifetime of a network composed of energy-restricted CR nodes, an accurate method for predicting spectrum occupancy is necessary to improve energy efficiency. This paper proposes a hidden Markov model (HMM)-based cooperative spectrum sensing (CSS) that predicts the status of a network environment. The traditional prediction algorithms for cooperative spectrum sensing assume that all CR nodes have the same network environment. However, the channel availability of various CR nodes can be quite different, and thus the traditional algorithms will lead to low prediction accuracy in a complex radio environment. The proposed methods learn the historical spectrum sensing results and help the network to make an energy-efficient spectrum sensing decision. More specifically, the hidden state of HMM is set to different areas, where primary users (PUs) perform different activities. A Baum-Welch (BW) algorithm is employed to estimate the parameters of the HMM based on the past spectrum sensing results, and then the parameters are fed to a forward algorithm for the predicting of PUs' activity. Based on the prediction, secondary users (SUs) are classified into either ”interfered by PU” or ”not interfered by PU. ” The nodes selected as ”interfered by PU” will not perform spectrum sensing to reduce unnecessary energy consumption. The performance of the proposed method is evaluated using the simulations under different traffic conditions. The simulation results show that, compared with the conventional HMM-based methods, the effectiveness of the proposed algorithm in energy efficiency and spectrum utilization improved by about 13% and 15%, respectively.

Recently, cluster computer environments using multiple CPUs or multiple GPUs have been widely used to accelerate computation such as in the field of big data or artificial intelligence. In this paper, we propose an automatic computing device selection scheme between CPU and GPU by estimating the expected execution time based on trained deep learning model. Based on the experimental results, our scheme can select the computing device dynamically to reduce the execution time and maximize the computing efficiency.

To investigate the diagnostic value of computed tomography (CT) urography findings of anterior nutcracker syndrome (NCS).The study included patients with left renal vein (LRV) compression at the aortomesenteric portion at CT urography who underwent renal venography or cystoscopy. Patients with a renocaval pressure gradient of ≥3 mmHg on renal venography or bloody urine jetting from the left ureteral orifice on cystoscopy were defined as the NCS group; the remaining patients comprised the non-NCS group. CT findings were analysed using the jetting of contrast medium flow from the LRV to the inferior vena cava (jetting sign), aortomesenteric distance, presence of collateral veins, and a dilatation ratio of LRV diameter at the aortomesenteric portion (arterial phase/delayed phases). Clinical findings, including age, gender, and body-mass-index, were also analysed. CT features and clinical findings were compared between the NCS and non-NCS groups. Diagnostic performance of CT parameters was assessed using receiver operating characteristic curve analysis.A total of 70 patients (21 men, mean age 44.4 ± 17.2 years) with NCS (n=13) and non-NCS (n=57) were included. Younger age (40 years), presence of the jetting sign, and a lower dilatation ratio of LRV diameter between the arterial and delayed phases (1.7) were found to be significant independent factors for predicting the NCS group (OR 24.5, 18.9, 19.4, respectively, p0.05 for all). The combination of the presence of the jetting sign and a dilatation ratio of LRV diameter of1.7 obtained the highest AUC of 0.88.The jetting sign and the dilatation ratio of LRV diameter between the arterial and delayed phases can both be very useful in the diagnosis of anterior nutcracker syndrome during CT urography.

Recent IoT services are being used in various fields such as smart homes, smart factories, smart cars and industrial systems. These various IoT services are implemented through hyper-connected IoT devices, and accordingly, security requirements of these devices are being highlighted. In order to satisfy the security requirements of IoT devices, various studies have been conducted such as HSM, Security SoC, and TrustZone. In particular, ARM proposed Platform Security Architecture (PSA), which is a security architecture that provide execution isolation to safely manage and protect the computing resources of low- end IoT devices. PSA can ensure confidentiality and integrity of IoT devices based on its structural features, but conversely, it has the problem of increasing development difficulty in using the security functions of PSA. To solve this problem, this paper analyzes the security requirements of an IoT platform and proposes secure platform based on PSA. To evaluate the proposed secure platform, a PoC implementation is provided based on hardware prototype consisting of FPGA. Our experiments with the PoC implementation verify that the proposed secure platform offers not only high security but also convenience of application development for IoT devices.

The cognitive radio (CR) technology allows secondary users (SUs) to occupy the licensed bands opportunistically without causing interferences to primary users (PUs). SUs perform spectrum sensing to detect whether PUs are busy or idle. Therefore, spectrum sensing directly affects the performance of the PU protection and the secondary throughput. The sensing time is a critical parameter for spectrum sensing performance, and the optimum sensing time is a tradeoff between the spectrum sensing performance and the secondary throughput. In this paper, a novel spectrum sensing scheme is proposed to maximize both sensing accuracy and network energy efficiency. In order to provide a better protection for the PU, another spectrum sensing is adaptively performed according to the first sensing result. In other words, SU will perform spectrum sensing again to confirm that the PU is indeed idle when the first sensing result indicates the PU is idle. Due to the energy constraint in CR sensor networks, this adaptive sensing interval can also be adjusted according to the varying activity of the PU to maximize the network energy efficiency. Finally, our simulation study validates that the proposed scheme improves both the spectrum sensing performance and the energy efficiency compared with other existing methods.

Wireless body area network (WBAN) is a communication technology, which aims providing both medical and consumer electronics services through sensor devices in, on, or around a human body. Due to the absence of the IEEE 802.15.6-based RF modules, the IEEE 802.15.4, a typical low-power communication technology of which requirements are similar, is considered to implement WBANs. In the case where a lot of WBANs coexist, meanwhile, collisions and signal attenuations may lead to their communication performance degradation. However, the IEEE 802.15.4 does not provide any solutions to solve coexistence problems, and thus, coexistence mitigation schemes for the IEEE 802.15.4-based WBANs are necessary. In this paper, we perform preliminary experiments to identify aspects of coexistence problem among the coexisting IEEE 802.15.4-based WBANs. Based on the results of preliminary experiments, we also propose a hybrid channel access scheme to mitigate coexistence problems in WBANs. The proposed scheme can be classified into two phases. In the first phase, the proposed scheme provides probabilistic collision avoidance on the contention-free period. When the pre-defined requirements of reliability cannot be satisfied with performing the first phase, the proposed scheme performs the second phase, which helps to mitigate collision or interference through changing channel access method. To evaluate the performance of the proposed scheme, we implement our scheme and perform experiments by comparing with an IEEE 802.15.4-based WBAN.

The recent ASCE report card gave a "D" grade for the state of drinking water infrastructure in the U.S. and reported that there are about 240,000 water main failures annually. Some of these failures result in significant economic, environmental and societal consequences that are difficult to predict for the purpose of accurate risk assessment and subsequent rehabilitation planning. This study analyzed the overall consequences of 20 large diameter water main failures in the U.S., majority of which have occurred in the last seven years, with an objective of identifying factors that aggravate the consequences to be able to reasonably predict them for rehabilitation decision making. It has been found that the overall cost of the failure consequences dependedon several factors that include but not limited to pipeline size, relative elevation and the type of land use, population density, utility response and repair time, and operating pressure. Direct repair of the failed pipeline, followed by property damage and then travel delays, accounted for 35%, 22% and 21% of the overall failure cost on average, respectively. It has also been found that the direct costs which the water utility pays for accounted for only about 41% while the indirect costs which are usually borne by the society accounted for the remaining 59%. While consideration of the overall failure costs as part of rehabilitation planning may increase the investment needs of water utilities, it remains to be investigated as to how much more investment will be required, who would pay for it and how willing are the water utilities in adopting the overall failure cost approach.

In a wireless body area network (WBAN), high data reliability and long operating time are important requirements. The retransmission process of the default Automatic Repeat reQuest (ARQ) mechanism in IEEE 802.15.4 is a suitable method to ensure the data reliability of WBAN communications, where frame loss can occur frequently. However, retransmitting the entire DATA frame is energy inefficient due to the fact that the most of payload data within lost frames are only partially corrupted. Therefore, this paper proposes the automatic segment repeat request scheme for the IEEE 802.15.4-based WBANs. The proposed scheme partitions the data payload into segments when the channel condition is bad, and retransmits only the corrupted segment(s). This reduces the size of the retransmitted frames, which improves frame reception rate and decreases the amount of transmitted traffic, and thus energy consumption. Our experiments using a real IEEE 802.15.4-based WBAN test bed show that the proposed method provides higher transmission reliability and lower power consumption than the default IEEE 802.15.4 ARQ mechanism.

A Wireless body area network (WBAN) is a communication network that provides both medical and consumer electronics services by using sensors in/on/around a human body. In general, a WBAN environment suffers from frequent link loss due to interferences among sensors scattered over a body. In addition, the channel condition can frequently change by postural body movement, which increases packet drops, retransmissions, and eventually power consumption. This paper presents an Analytical Hierarchy Process (AHP)-based flexible relay node selection scheme that considers a multitude of decision factors, such as average SNR, remaining energy ratio, and traffic load. Moreover, the proposed scheme can adaptively satisfy the requirements of WBAN in various scenarios. Our simulation study shows that the proposed method provides high communication reliability and low power consumption.

인지 무선 기술은 보조 사용자가 (SUs) 주 사용자 (PUs)에 간섭을 주지 않고 기회주의적 방식으로 라이선스 스펙트럼을 사용할 수 있는 기술이다. 인지 라디오의 핵심 기술은 스펙트럼 센싱이다. 그러나 인지 무선 센서 네트워크에서 에너지 효율적인 스펙트럼 센싱 기법에 대한 연구는 많지 않다. 본 논문에서는 클러스터 기반의 인지 무선 센서 네트워크를 위한 에너지 효율적인 협력 스펙트럼 센싱 노드 선택 기법을 제안한다. 제안하는 기법에서, 허위 경보 확률 및 에너지 소비를 최적화하기 위하여 클러스터내 스펙트럼 센싱 노드들의 수를 최소화하게 된다. 시뮬레이션 결과를 통하여 본 논문에서 제안한 최적의 스펙트럼 센싱 노드 수를 적용하므로 스펙트럼 센싱 효율성이 향상되었고, 또한 네트워크의 에너지 효율성도 보장된 것을 검증하였다.

In densely located loosely coupled wireless charger environments, cross-connection errors can occur when wireless chargers operate at the same time within the same wireless communication range. In this work, an effective algorithm is proposed to prevent cross-connection error. The algorithm based on the cross-connection abatement technique with the received signal strength indicator of out-band BLE communication has improved using an in-band magnetic field signal controlled by a pulse-width-modulation-like waveform. The experimental results obtained from a proper test set in a RF shield room verify that the wireless charging system using the proposed algorithm provides wireless charging services without cross-connection errors.

In wireless sensor networks, clustering schemes have been adopted as an efficient solution to prolong the network lifetime. In these schemes, the performance of energy-efficient data transmission is affected the cluster ratio (CR). This paper analyzes the optimal CR from the perspective of network energy efficiency, and its impact on the network lifetime. In order to provide a generic analytic model, various data propagation cases are mathematically analyzed. In addition, the network lifetime is extended by jointly optimizing the network transmission count and link reliability. Our simulation results show that the optimal CR derived based on the proposed analytical model enhances the energy efficiency and effectively increases the network lifetime.

WBAN(Wireless Body Area Network) operating around the human body aims at medical and non-medical service at the same time. and it is the short-range communication technology requiring lo w-power, various data rate and high reliability. Various studie s is performing for IEEE 802.15.4, because IEEE 802.15.4 can provide high compatibility for operate WBAN among communication standa rd satisfiable these requirements. Meanwhile, in the case of coexi sting many IEEE 802.15.4-based WBAN, signal interference and co llision are the main cause that is decreasing data reliability. but IEE E 802.15.4 Standard does not consider about coexistence of many networks. so it needs improvement. In this paper, To solve abou t this problem, identify coexistence problem of IEEE 802.15.4-b ased WBAN by preliminary experiments. and propose a scheme to mitiga te the reliability decrease at multiple coexistence WBAN. The proposed scheme can be classified in two steps. The first step is avoidance to collision on the CFP through improving data tra nsmission. The second step is mitigation collision through converting chan nel access method. Proposed scheme is verified the performance by performing comparison experiment with Standard-based WBAN.

To provide scalability, wireless sensor network has cluster-based architecture. Wireless sensor network can be implemented based on the IEEE 802.15.4 which is exploited in 2.4GHz ISM frequency band. Since this frequency band is used for various data communication, network status of wireless sensor networks frequently changes according to wireless environment. Thus, wireless channel selection to avoid reduction of transmission efficiency is required. This paper estimates network status using the information that a cluster-head collects in a cluster. Through objective function with throughput, RSSI level and reliability as input parameters, this paper proposes proper wireless channel selection. Simulation results show that the proposed method maintains transmission efficiency even though network status changes.

In public environments where LC wireless charging pads and charging devices are dense, cross-connection errors between the wireless charging pads and charging devices can occur within the same short-range wireless communication range. In this work, an effective cross-connect abatement technique using a received signal strength indicator (RSSI) signal and an in-band magnetic field signal modulated by a pulse with modulation (PWM)-like waveform is proposed to prevent cross-connection errors. The experimental results in dense LC wireless charging pad environments show that the proposed technique provides stable wireless charging services without cross-connection errors.

Cognitive radio technology can enable secondary users (SUs) to occupy licensed bands in a non-interference way. SUs perform spectrum sensing to determine the presence of primary user (PU). Spectrum sensing period and transmission time are the critical parameters for the sensing performance and the secondary throughput, respectively. In this paper, a joint optimization of sensing period and transmission time is proposed for cognitive radio sensor network (CRSNs). The joint optimization model is established by taking the network energy efficiency and interference caused by SU's traffic into consideration. By using the optimization model, we try to figure out the optimal sensing period and transmission time which can guarantee the network energy efficiency and maximize the network throughput jointly. The performance of the proposed optimization model is evaluated through a set of simulations, and the existence of the optimal sensing period and transmission time is verified.

Clustering schemes have been adopted as an efficient solution to prolong network lifetime and improve network scalability. In such clustering schemes cluster ratio is represented by the rate of the number of cluster heads and the number of total nodes, and affects the performance of clustering schemes. In this paper, we mathematically analyze an optimal clustering ratio in wireless sensor networks. We consider a multi-hop to one-hop transmission case and aim to provide the optimal cluster ratio to minimize the system hop-count and maximize packet reception ratio between nodes. We examine its performance through a set of simulations. The simulation results show that the proposed optimal cluster ratio effectively reduce transmission count and enhance energy efficiency in wireless sensor networks.

The RS(Relay Station) has become an important radio resource in next generation wireless communication systems. The optimal number of RSs is one of the crucial issues in configuring a cost-effective RS-based network architecture. In this letter, we present an analytic model to describe the impact of the number of RSs on the channel capacity of two-hop relay network. From the mathematical analysis, the optimal number of RSs is obtained to satisfy QoS requirements of users considering various levels of MCS(Modulation and Coding Scheme). In addition to the mathematical analysis to determine the feasibility of the analytic model, we also examine its performance through a set of simulations. The simulation results show the validity of the proposed analytic model.

By cognitive radio technology, secondary users (SUs) can use licensed bands opportunistically without causing interferences to primary users (PUs). Spectrum sensing is performed by SUs to detect that PUs are present or not. Therefore, spectrum sensing is a key technology for cognitive radio (CR), and sensing time is a critical parameter for spectrum sensing performance. The longer sensing time can result in a higher sensing accuracy. However, it will lead to occupying data transmission period, and consuming higher energy in spectrum sensing. In this paper, a novel spectrum sensing scheme is proposed to guarantee both of the sensing accuracy and energy efficiency. In the proposed scheme, SU will dynamically decide to perform spectrum sensing one or two periods according to the sensing result of the current frame for guaranteeing the sensing accuracy. Furthermore, in order to guarantee the network energy efficiency, the spectrum sensing time is optimized through the mathematical model of the secondary network. Simulation results validate that the energy efficiency and miss detection probability of SU can be improved significantly by the proposed scheme.

Wireless Body Area Networks (WBANs) have received a lot of attention as a promising technology for medical and healthcare applications. A WBAN should guarantee energy efficiency, data reliability, and low data latency because it uses tiny sensors that have limited energy and deals with medical data that needs to be timely and correctly transferred. To satisfy this requirement, many multi-radio multi-channel MAC protocols have been proposed, but these cannot be implemented on current off-the-shelf sensor nodes because they do not support multi-radio transceivers. Thus, recently single-radio multi-channel MAC protocols have been proposed; however, these methods are energy inefficient due to data duplication. This paper proposes a TDMA-based single-radio, multi-channel MAC protocol that uses the Unbalanced Star+Mesh topology to satisfy the requirements of WBANs. Our analytical analysis together experiments using real sensor nodes show that the proposed protocol outperforms existing methods in terms of energy efficiency, reliability, and low data latency.

A Wireless Body Area Networks (WBAN) is a communication network that provides both medical and consumer electronics (CE) services by using sensor devices in, on, or around a human body. To provide reliable communication with low power consumption for in-body communication, the IEEE 802.15.6 provides Medical Implant Communication Service (MICS) band and defines its communication policy. However, MICS band communication suffer from the coexistence problem, which causes significant performance degradation due to high-density deployment and network-level mobility of WBANs. In addition, existing coexistence mitigation schemes in IEEE 802.15.6 do not consider the MICS band. To overcome the coexistence problem, numerous studies have been conducted for multi-channel usage in WBANs, but they just include simple channel selection schemes which do not provide reliable channel selection. This paper proposes an Adaptive Channel Estimation and Selection Scheme (ACESS) for coexistence mitigation in WBANs. The proposed method maintains a history table and predicts the conditions of available channels based on two-state Markov chain with an exponentially controlled channel history, which can control the sensitivity of prediction. Our simulation study show that the proposed scheme can improve communication performance in terms of Packet Reception Ratio (PRR) under coexistence environments with multiple WBANs.

In a heterogeneous wireless environment, a variety of Radio Access Technologies (RATs) coexist. Since the number of RATs is anticipated to increase in the near future, it is desirable to have radio and network resources managed in a cooperative manner using the Common Radio Resource Management (CRRM) strategy. In order to make RAT-specific radio resources manageable in CRRM, this paper proposes the Analytical Hierarchy Process (AHP) based resource management scheme that efficiently allocates resources among heterogeneous wireless networks. The proposed AHP-based method is simple and flexible enough to be used in any network environment and can consider a multitude of decision factors. In addition, the proposed scheme uses a radio bandwidth model, which properly reflects transmission rates under given channel conditions, as the actual radio resources to be allocated. The model considers the AMC (Adaptive Modulation and Coding) scheme that is widely used in current broadband wireless access technologies, and thus, packet service characteristics, such as response time, can be analyzed. This is in contrast to existing work that focuses only on circuit service characteristics (e.g., blocking probability). The effectiveness and flexibility of the proposed method are demonstrated by implementing a number of existing methods and performing extensive simulation study on several different scenarios.

In a heterogeneous wireless environment, a variety of Radio Access Technologies (RATs) coexist. Since the number of RATs is anticipated to increase in the near future, it is desirable to have radio and network resources managed in a cooperative manner using the Common Radio Resource Management (CRRM) strategy. In order to make RAT-specific radio resources manageable in CRRM, this paper proposes the Analytical Network Process (ANP) based resource management scheme that efficiently allocates resources among heterogeneous wireless networks. The proposed ANP-based method is flexible enough to be used in any network environment and can consider a multitude of decision factors. In addition, the proposed scheme uses a radio bandwidth model, which properly reflects transmission rates under given channel conditions, as the actual radio resources to be allocated. The model considers the AMC (Adaptive Modulation and Coding) scheme that is widely used in current broadband wireless access technologies, and thus, packet service characteristics, such as response time, can be analyzed. The effectiveness and flexibility of the proposed method are demonstrated by implementing a number of existing factors on heterogeneous networks environment.

Wireless body area network(WBAN) provide communication service in the vicinity of the body. Since WBANs utilize both MICS frequency band for implant medical applications and ISM frequency band for medical and consumer electronics(CE) applications. Therefore, MAC protocols in WBAN should be designed considering flexibility between medical and CE applications. In this paper, we identify the requirements of WBAN MAC protocols and propose a WBAN MAC protocol which satisfies the requirements. In other to provide transmission flexibility for various applications. we present the dynamic CFP allocation and opportunity period. Extensive simulation result show that the proposed protocol achieves improved throughput and latency in WEAN environment cimpared with IEEE 802.15.4.

Wireless body area networks (WBANs) provide medical and/or consumer electronics (CE) services within the vicinity of a human body. In a WBAN environment, immediate and reliable data transmissions during an emergency situation should be supported for medical services. In this letter, we propose a flexible emergency handling scheme for WBAN MAC protocols. The proposed scheme can be applied to superframe-structured MAC protocols such as IEEE 802.15.4 and its extended versions. In addition, our scheme can be incorporated into the current working draft for IEEE 802.15.6 standards. Extensive simulations were performed and the low latency of emergent traffics was validated.

Many energy aware routing algorithms and protocols have been proposed for wireless sensor networks recently to achieve aims like minimum energy consumption, maximized network lifetime, reduced communication latency and overhead etc. The problem of hotspot can not be well addressed under many routing algorithms since some nodes which are on the shortest path or close to the base station tend to deplete their energy quickly and consequently cause network partition. In this paper, we propose a Ring-based Energy Aware Routing (REAR) algorithm for wireless sensor networks which can achieve both energy balancing and energy efficiency for all sensor nodes. Our algorithm considers not only the hop number and distance but also the residual energy of the next hop node during routing process. Simulation results validate that our algorithm outperforms some other routing algorithms in the aspects of energy consumption and network lifetime etc.

In this work we propose an energy-efficient transmission strategy for wireless sensor networks that operate in a strict energy-constrained environment. Our transmission algorithm consists of two components: a binary-decision based transmission and a channel-aware backoff adjustment. In the binary-decision based transmission, decision on whether to transmit or not is absolutely dependent on the current channel conditions. Specifically, transmission is initiated only when the channel quality exceeds a specified threshold, so that unsuccessful transmissions causing a waste of energy are avoided whenever possible. Using the Markov decision process (MDP) formulation we obtain the optimum threshold for successful transmission. A channel-aware backoff adjustment, the second component of our proposal, is introduced to favor nodes with better channel conditions. By intelligently combining these two ingredients our transmission algorithm attempts to maximize energy efficiency. Extensive simulations are performed to verify the performance of our proposal over fading wireless channels. Numerical results show that our transmission algorithm outperforms the existing approaches in terms of energy efficiency, thereby further prolonging the network lifetime.

Reliable data transmission is desirable in wireless sensor networks due to the high packet loss rate during multi-hop transmissions. To reliably transmit data for event-driven applications, packet loss recovery mechanism is needed. For loss recovery, sensor nodes need to keep packets in their buffers until transmissions successfully complete. However, since sensor nodes have limited memory, packets cannot be buffered for a long period of time. This letter proposes an efficient buffer management technique that caches data packets for appropriate amount of time to minimize the resource requirements and at the same time provide reliable data transmission among sensor nodes.

WBANs provide communication services in the vicinity of the human body. Since WBANs utilize both MICS frequency band for implant medical applications and ISM frequency band for medical and consumer electronics (CE) applications, MAC protocols in WBAN should be designed considering flexibility between medical and CE applications. In this letter, we identify the requirements of WBAN MAC protocols and propose a WBAN MAC protocol which satisfies the requirements. In order to provide transmission flexibility for various applications, we present the dynamic CFP allocation and opportunity period. Extensive simulation results show that the proposed protocol achieves improved throughput and latency in WBAN environment compared with IEEE 802.15.4.

Energy efficient routing is one of the key design issues to prolong the lifetime of wireless sensor networks (WSNs) since sensor nodes can not be easily re-charged once they are deployed. During routing process, the routes with only few hops or with too many hops are not energy efficient. Hop-based routing algorithms can largely improve the energy efficiency of multi-hop routing in WSNs because they can determine the optimal hop number as well as the corresponding intermediate nodes during multi-hop routing process under medium or high density network. In this paper, we not only focus on studying the relationship between energy consumption and hop number from theoretical point of view but also provide a practical selection criterion of the sub-optimal hop number under practical sensor network so as to minimize the energy consumption. We extend the theoretical deduction of optimal hop number and propose our Hop-based Energy Aware Routing (HEAR) algorithm which is totally distributed and localized. Simulation results show that our HEAR algorithm can reduce the average energy consumption about 10 times compared to the direct transmission algorithm and 2 to 10 times than other algorithms like LEACH and HEED under various network topologies.

This paper aims to combine adaptive modulation and coding with layered video coding to improve the quality of video services to users experiencing differing radio conditions, in the context of broadcast and multicast standards such as MBMS and BCMCS. We propose an optimal radio resource allocation algorithm which maximizes a general performance metric for a video session in polynomial time. We show that system-wide optimal resource allocation can be obtained by combining our algorithm with a simple two-step decomposition of the system. In some configurations frequent re-allocations of resource are required, so we also present a sub-optimal allocation algorithm which runs in near linear time. Simulation results show better video quality than existing resource allocation schemes over a range of conditions, and also suggest that the difference between the performance of optimal and suboptimal solutions is less than 3%.

Nowadays, wireless packet data services are provided over Wireless MAN (WMAN) at a high data service rate, while 3G cellular networks provide wide-area coverage at a low data service rate. The integration of mobile WiMAX and 3G networks is essential, to serve users requiring both high-speed wireless access as well as wide-area connectivity. In this paper, we propose a cross-layer optimization scheme for a vertical handover between mobile WiMAX and 3G cellular networks. More specifically, L2 (layer 2) and L3 (layer 3) signaling messages for a vertical handover are analyzed and reordered/combined, to optimize the handover procedure. Extensive simulations using ns-2 demonstrate that the proposed scheme enhances the performance of a vertical handover between mobile WiMAX and 3G networks: low handover latency, high TCP throughput, and low UDP packet loss ratio.

In this paper, we investigate the critical low coverage problem of position aware localized efficient broadcast in mobile ad hoc ubiquitous sensor networks and propose a generic framework for it. The framework is to determine a small subset of nodes and minimum transmission radiuses based on snapshots of network state (local views) along the broadcast process. To guarantee the accuracy of forward decisions, based on historical location information nodes will predict neighbors' positions at future actual transmission time and then construct predicted and synchronized local views rather than simply collect received "Hello" messages. Several enhancement technologies are also proposed to compensate the inaccuracy of prediction and forward decisions. To verify the effectiveness of our framework we apply existing efficient broadcast algorithms to it. Simulation results show that new algorithms, which are derived from the generic framework, can greatly increase the broadcast coverage ratio.

Ubiquitous sensor networks (USNs) are comprised of energy constrained nodes. This limitation has led to the crucial need for energy-aware protocols to produce an efficient network. We propose a sleep scheduling scheme for balancing energy consumption rates in a single hop cluster based network using Analytical Hierarchy Process (AHP). We consider three factors contributing to the optimal nodes scheduling decision and they are the distance to cluster head (CH), residual energy, and sensing coverage overlapping, respectively. We also propose an integrated sleep scheduling and geographical multi-path routing scheme for USNs by AHP. The sleep scheduling is redesigned to adapt the multi-hop case. For the proposed routing protocol, the distance to the destination location, remaining battery capacity, and queue size of candidate sensor nodes in the local communication range are taken into consideration for next hop relay node selection. The proposed schemes are observed to improve network lifetime and conserve energy without compromising desired coverage. In the multi-hop case, it can further reduce the packet loss rate and link failure rate since the buffer capacity is considered.

The cdma2000 1timesevolution-data-only (EV-DO) mobile communication system provides broadcast and multicast services (BCMCS) to meet an increasing demand for multimedia data services. Currently, broadcast and multicast streams are scheduled using a slot-based static algorithm which cannot support dynamic environments where broadcast content is added or removed online. We propose a dynamic packet-scheduling algorithm that works with a retransmission scheme to enable a scalable and adaptive service across the cdma2000 1timesEV-DO BCMCS environments. Since it is integrated with earliest deadline first real-time scheduling, the proposed algorithm not only adapts efficiently to dynamic contexts but also satisfies the real-time requirements of broadcast streams. Furthermore, by exploiting the fine granular scalability features of the MPEG-4 Part 2 standard, our scheme can avoid abrupt playback quality degradation by protecting the base layer using a retransmission technique and can also adapt more flexibly to an environment in which the resource requirements of video streams change dynamically. Simulation results show a significant improvement in average playback quality while quantitatively validating the efficiency of our approach.

Applying cognitive radio technologies to wireless sensor networks (WSNs) explores new possibilities for network architectures. The cognitive radio technology enables opportunistic access of unlicensed sensor nodes to licensed bands without influencing primary users (PUs). Spectrum sensing is a key technology to identify the presence of PUs. Benefit from the diversity of different sensors, Cooperative spectrum sensing (CSS) can provide a more reliable sensing result compared with individual spectrum sensing. However, due to limited energy of batteries in cognitive radio sensor networks (CRSNs), more energy consumed by CSS will result in a short network lifetime. In this paper, a novel sensing nodes selection scheme is proposed to improve energy efficiency of cooperative spectrum sensing for cluster-based CRSNs. A novel optimization technique is employed to optimize the number of spectrum sensing nodes in a cluster. The optimized results can efficiently maximize the detection probability and minimize false alarm probability. In addition to this, the proposed scheme can efficiently balance the energy consumption among different sensors to some extent. Through a set of simulation, it is verified that the proposed scheme can obtain a good sensing performance with less sensor nodes and energy consumption, and thus, prolong the network lifetime.

The coexistence problem occurs when a single wireless body area network (WBAN) is located within a multiple-WBAN environment. This causes WBANs to suffer from severe channel interference that degrades the communication performance of each WBAN. Since a WBAN handles vital signs that affect human life, the detection or prediction of coexistence condition is needed to guarantee reliable communication for each sensor node of a WBAN. Therefore, this paper presents a learning-based algorithm to efficiently predict the coexistence condition in a multiple-WBAN environment. The proposed algorithm jointly applies PRR and SINR, which are commonly used in wireless communication as a way to measure the quality of wireless connections. Our extensive simulation study using Castalia 3.2 simulator based on the OMNet++ platform shows that the proposed algorithm provides more reliable and accurate prediction than existing methods for detecting the coexistence problem in a multiple-WBAN environment.

A Wireless Body Area Network (WBAN) which consists of wireless sensors in/on/around human body requires high reliability for medical data. The coexistence problem which occurs when multiple-WBANs occupy the same channel at the same time declines the performance of the network. It is an important issue because this problem causes the collision of data among WBANs. For that reason, the IEEE 802.15.6 which was established for WBAN standardization defined guidelines to solve this problem, but these guidelines did not provide detailed methods. To solve this problem, there are also a few related works by using graph coloring algorithm as a general theory to assign limited resources but they cannot satisfy the requirements of WBAN. In this paper, we propose a distributed multi-coloring algorithm to mitigate coexistence problems among WBANs. The proposed algorithm shows short transmission-cycle per WBAN through multiple coloring with a color sequence and the efficiency of the proposed scheme is verified by the numerical results which outperform existing works in multiple WBANs environment.

In a wireless sensor network, sensor nodes are deployed in an ad hoc fashion and they deliver data packets using multihop transmission. However, transmission failures occur frequently in the multihop transmission over wireless media. Thus, a loss recovery mechanism is required to provide end-to-end reliability. In addition, because the sensor nodes are very small devices and have insufficient resources, energy-efficient data transmission is crucial for prolonging the lifetime of a wireless sensor network. This paper proposes a transmission power control mechanism for reliable data transmission, which satisfies communication reliability through recovery of lost packets. The proposed method calculates packet reception rate (PRR) of each hop to maintain end-to-end packet delivery rate (PDR), which is determined based on the desired communication reliability. Then, the transmission power is adjusted based on the PRR to reduce energy consumption. The proposed method was evaluated through extensive simulations, and the results show that it leads to more energy-efficient data transmission compared to existing methods.

Video can be encoded into multiple-resolution format in nature. A multi-resolution or scalable video stream is a video sequence encoded such that subsets of the full resolution video bit stream can be decoded to recreate lower resolution video streams. Employing scalable video enables a video server to provide multiple resolution services for a variety of clients with different decoding capabilities and network bandwidths connected to the server. The inherent advantages of the multi-resolution video server include: heterogeneous client support, storage efficiency, adaptable service, and interactive operations support. For designing a video server, several issues should be dealt with under a unified framework including data placement/retrieval, buffer management, and admission control schemes for deterministic service guarantee. In this paper, we present a general framework for designing a large-scale multi-resolution video server. First, we propose a general multi-resolution video stream model which can be implemented by various scalable compression techniques. Second, given the proposed stream model, we devise a hybrid data placement scheme to store scalable video data across disks in the server. The scheme exploits both concurrency and parallelism offered by striping data across the disks and achieves the disk load balancing during any resolution video service. Next, the retrieval of multi-resolution video is described. The deterministic access property of the placement scheme permits the retrieval scheduling to be performed on each disk independently and to support interactive operations (e.g. pause, resume, slow playback, fastforward and rewind) simply by reconstructing the input parameters to the scheduler. We also present an efficient admission control algorithm which precisely estimates the actual disk workload for the given resolution services and hence permits the buffer requirement to be much smaller. The proposed schemes are verified through detailed simulation and implementation.

The paper investigates the pattern of soil stress around a pipeline installed under the river using a non-linear three-dimensional finite element method (FEM). This study compares von Mises soil stresses occurring in native soil adjacent to river crossing pipeline between traditional open trench (OT) and horizontal directional drilling (HDD) pipe installation methods. The MohrCoulomb theory is utilized to describe soil behavior in the finite element models. The entire model is assumed to be elasto-plastic. The whole research considers saturated native soil in one month after construction. Additionally, design parameters (i.e. depth of cover and annular space) in HDD method are examined for understanding their influence on soil stress occurring around original soil. The paper investigates how critical design parameters (i.e. density and diameter) in the annular space affect the pattern of maximum von Mises soil stresses occurring in native soil adjacent to pipeline installed under the river. Finally this study found that when the OT method is used for pipeline crossing under the river, stress occurring in the soil cover is greater than when the HDD method is used. In addition, the diameter of the annular space in HDD method could impact on total soil stress occurring in the soil overburden.

WBAN(Wireless Body Area Network) which has received a lot of attention for developing medical and entertainment services is standardized by IEEE 802.15 Task Group 6(TG6). WBAN should be guaranteed low data latency because medical data must be timely and correctly transferred. Since the standard considers only a single-channel, it has problems such as intervention and large latency. To solve these problems, a lot of multi-channel TDMA MAC protocols have been proposed. However, multi-radio multichannel MAC protocols cannot be implemented on current off-the-shelf sensor modules because they have a single-radio transceiver. Furthermore, existing single-radio MAC protocols duplicate data, which may lead to energy inefficiency. In this paper, we propose a single-radio multi-channel TDMA MAC protocol which can support low data latency, high reliability, and energy efficiency. To achieve above goals, the proposed protocol employs an inventive topology, i.e., star plus mesh topology. In addition, we implement our protocol on real sensor modules, ZigbeX-I and ZigbeX-II based on IEEE 802.15.4 packet frame and superframe so that we can verify the performance in real environment.

A multi-channel approach for MAC protocols is one of the most significant issues in recent research trend of WSNs. Numerous studies on multi-channel MAC protocols have focused on how to select and allocate channels efficiently to links or nodes. However, existing studies do not consider interferences from different communication technologies in the same band such as IEEE 802.11 in ISM band. In addition, these studies use traditional channel scanning methods and it can cause huge performance degradation in terms of latency, throughput, and energy consumption due to the increased number of channel scanning. To alleviate the problem, we propose an efficient channel scanning algorithm which reduces the number of channel scanning in cluster-based WSN. Based on the proposed channel scanning algorithm, we also propose a priority-based channel allocation algorithm to provide efficient channel allocation for both traffic load and estimation of channel condition. Through extensive simulations, we validate that our scheme exhibits low communication overhead and high channel utilization.

Nowadays, backplane bus-based multiprocessor systems often utilize the standard network protocol such as TCP/IP for communication between processors on the backplane bus. In such systems, it is common for the backplane bus to emulate the standard MAC protocols such as CSMA/CD. This paper aims to analyze the delay performance of the MAC emulation-based backplane network by constructing queueing models based on detailed bus operations. For this purpose, we choose BusNet as a target protocol. BusNet is an ANSI standard network protocol and its specification contains basic operations commonly used in most backplane buses. We investigate the throughput-delay characteristics in terms of packet size, block transfer scale, and arbitration scheme. We also compare the packet delay in BusNet with the IEEE 802.3 CSMA/CD network which BusNet is expected to be compatible with. The simulation result shows how an optimal block transfer scale can be determined in respect of the performance trade-off between BusNet and other real-time traffics.

Due to the high packet loss rate during multi-hop transmissions in wireless sensor networks, more reliable end-to-end data transmission is desirable. Because wireless sensor network applications require various levels of communication reliability (CR), the end-to-end data transmission should satisfy the desired CR of the applications. In this letter, we propose a flexible loss recovery mechanism for sensor network applications with various CRs. The proposed scheme caches data packets at intermediate nodes over routing paths computed by CR to retransmit lost packets during multi-hop transmissions. Because the proposed scheme presents a tradeoff between end-to-end delays and memory requirements dependent on CR, it can be used flexibly in various sensor network applications.

This paper addresses the design problems concerning a large-scale, parallel video-on-demand server that consists of multiple clusters of nodes connected by a high performance interconnection network. In order to efficiently control the flow of video streams, we propose two scheduling algorithms for data retrieval and communication. First, we present a disk scheduling algorithm called round scheduling which fully utilizes disk bandwidth, minimizing the disk idle time while the server retrieves data blocks. Second, a communication scheduling algorithm is developed to guarantee conflict-free communication over the multistage interconnection network that is topologically equivalent to the Omega network. We also show some simulation results on the server configuration. Analysis of tradeoffs between the server utilization and the start-up latency helps to determine the proper number and size of server clusters for a set of given nodes.