Slow development in battery technology and rapid advances in ultra-capacitor design have motivated us to investigate the possibility of using capacitors as the sole energy storage for wireless sensor nodes to support ubiquitous computing. The starting point of this work is TwinStar, which uses ultra-capacitor as the only energy storage unit. To efficiently use the harvested energy, we design and implement feedback control techniques to match the activity of sensor nodes with the dynamic energy supply from environments. We conduct system evaluation by deploying sensor devices under three typical real-world settings -- indoor, outdoor, and mobile backpack under a wide range of system settings. Results indicate our feedback control can effectively utilize energy and ensure system sustainability. Nodes running feedback control have longer operational time than the ones running non-feedback control.

Processing structures required in sensing are designed to convert real-world information into useful information, and there are various restrictions and performance goals depending on physical restrictions and the target applications. On the other hand, network technologies are mainly designed for data exchange in the information world, as is seen in packet communications, and do not go well with sensing structures from the viewpoints of real-time properties, spatial continuity, etc. This indicates the need for understanding the architectures and restrictions of sensor technologies and network technologies when aiming to fuse these technologies. This paper clarifies the differences between these processing structures, proposes some issues to be addressed in order to achieve real fusion of them, and presents future directions toward real fusion of sensor technologies and network technologies.

In practical settings of wireless sensor networks, it is often feasible to consider heterogeneous deployments of devices with different capabilities. Under prescribed cost constraints, we analyze such heterogenous deployments and present how they impact the coverage of a sensor network including spatial correlation effect. We derive expressions for the heterogeneous mixture of devices that maximizes the lifetime coverage in both single-hop direct and multi-hop communication models. Our results show that using an optimal mixture of many inexpensive low-capability devices and some expensive high-capability devices can significantly extend the duration of a network's sensing performance, especially in a network with low spatial correlation.

Portable sensory devices such as sensors equipped mobile phones enable convenient sensing and monitoring of urban areas. Such devices, which are always carried by humans, are referred to as Human Probes. Instead of carrying out sensing activities independently, cooperation of Human Probes helps in realizing efficient urban sensing environments. In this paper, we propose an Architecture of Qualitative Urban Information Blending and Acquisition (Aquiba), in which the sensing activities are adjusted autonomously according to cooperation of Human Probes. Aquiba introduces a cooperative sensing approach which aims to maintain desired sensing resolution efficiently while minimizing overall energy consumption. To study the performance of Aquiba, we have conducted comprehensive simulations ranging from small- to large-scale scenarios along with applying three different movement patterns of human. The simulation results demonstrate that Aquiba is capable of providing high sensing resolution and reducing overall energy consumption.

The authors focus on the improvement of Visible Light Communication Identification (VLID) system that provides positioning information via LED light bulb, which is a part of Visible Light Communication (VLC) system. The conventional VLID system provides very low positioning estimation accuracy at room level. In our approach, neither additional infrastructure nor modification is required on the transmitter side. On the receiver side, 6-axis sensor is embedded to provide 3-axis of Azimuth and 3-axis of Tilt angulations information to perform positioning estimation. We verify the proposed system characteristics by making both empirical and numerical analysis, to confirm the effectiveness of proposed system. We define two words to justify the characteristic of the proposed system, which are Field-of-View (FOV: ψ_c) Limit and Sensitivity (R_XS) Limit. Both FOV and Sensitivity Limits have crucial impact on positioning estimation accuracy. Intuitively, higher positioning accuracy can be achieved with smaller FOV configuration in any system that has FOV. Conversely, based on system characteristics of VLID, we propose a positioning estimation scheme, namely Switching Estimated Receiver Position (SwERP) yields high accuracy even with wide FOV configuration. Cumulative Distribution Function (CDF) of error distance and Root Mean Square of Error Distance (RMSED) between experimental positions and estimated receiver positions are used to indicate the system performance. We collected 440 samples from 3 receivers' FOV configurations altogether 1320 samples within the experimental area of 1200 mm5000 mm2050 mm. The results show that with the proposed scheme, the achievable RMSEDs are in the range of 298 and 463 mm under different FOV configurations, which attained the maximum accuracy improvement over 80% comparing to the one without positioning estimation scheme. The proposed system's achievable accuracy does not depend on transmitters' orientation; only one transmitter is required to perform positioning estimation.

A Real-time Capacitor Compensation (RCC) scheme is proposed for low power and continuous communication in the wearable inductive coupling transceiver. Since inductance values of wearable inductor vary dynamically with deterioration of its communication characteristics, the inductance value is monitored and its resonance frequency is adjusted by additive parallel/serial capacitors in real time. RLC Bridge for detection of the inductance variations and the Dual-edge Sampling Comparator for recognition of the variance direction are proposed. It is implemented in a 0.18 µm CMOS technology, and it occupies a 12.7 mm² chip area. The proposed transceiver consumes only 426.6 µW at 4 Mbps data rate. The compensation time takes 4.78 µs, including 3 µs of detection and 1.78 µs for compensation process in worst case.

Developing an adaptive 3-dimensional (3D) topology control algorithm is important because most wireless nodes are mobile and deployed in buildings. Moreover, in buildings, wireless link qualities and topologies change frequently due to various objects and the interference from other wireless devices. Previous topology control algorithms can suffer significant performance degradation because they only use the Euclidean distance for the topology construction. In this paper, we propose a novel adaptive 3D topology control algorithm for wireless ad-hoc sensor networks, especially in indoor environments. The proposed algorithm adjusts the minimum transmit power adaptively with considering the interference effect. To construct the local topology, each node divides the 3D space, a sphere centered at itself, into k equal cones by using Platonic solid (i.e., regular k-hedron) and selects the neighbor that requires the lowest transmit power in each cone. Since the minimum transmit power values depend on the effect of interferences, the proposed algorithm can adjust topology adaptively and preserve the network connectivity reliably. To evaluate the performance of algorithms, we conduct various experiments with simulator and real wireless platforms. The experimental results show that the proposed algorithm is superior to the previous algorithms in terms of the packet delivery ratio and the energy consumption with relatively low complexity.

Collecting environmental sound by utilizing high-end mobile phones provides us opportunities to capture rich contextual information in real world. The gathered information can be used for various purposes, ranging from academic research to livelihood support. Furthermore, mobility of mobile phones opens a door for easily forming a dynamic sensing infrastructure, in order to gather fine-grained, but still large-scale data from both spatial and temporal perspectives. However, collecting, analyzing, storing, and sharing of sound data usually involve large energy consumption than scalar data, and like any battery-operated device, mobile phones also face the reality of energy constraints. Because people's first priorities are naturally to use mobile phones for their own purposes, there are occasions when people will not be inclined to allow their mobile phones to be used as sensing devices fearing that they will run out of batteries. Therefore, our research focuses on energy-efficient sensing, to reduce average energy consumption and to extend overall system lifetime. In this paper, we propose a node scheduling scheme for mobile nodes. By applying this scheme, optimized sensing schedules (ACTIVE/SLEEP duty cycles) will be periodically generated at each node. Following the provided schedule during sensing, energy-efficiency can be realized while original Quality of Service (i.e. coverage rate) is retained. Unlike most previous works which were based on ideal binary disk coverage model, our proposal is designed under a probabilistic disk coverage model which takes the characteristic of sound propagation into consideration. Furthermore, this is the first scheme that is adaptable to large-scale mobile sensor networks where topology dynamically changes. An accurate energy consumption model is adopted for evaluating the proposed scheme. Simulation results show that our scheme can reduce up to 48% energy consumption in an ideal environment and up to 31% energy consumption in a realistic environment. The robustness of our scheme is also verified against different type of sensing terrains and communication environments.

In clustered sensor networks, because CHs (Cluster Heads) are the collection points of data, they are likely to be compromise targets of attackers. So, they need to be changed through a CH election scheme as frequently as possible. Besides, because the compromised nodes must try to become a CH, a CH election scheme should prevent them from being a CH. This paper presents a secure CH election scheme for clustered sensor networks, which changes the CH role nodes securely by excluding the compromised nodes from CH candidates. In the proposed scheme, each node gives marks for behavior of all other nodes in the same CH election region and exchanges the mark list with them. Then, each node computes the average marks for all nodes in the region, and nodes whose average mark is less than a specific threshold are excluded from CH candidates. A CH is elected among the remaining candidates. Simulation results show that our scheme provides strong resilience against misbehavior of compromised nodes and reduces energy consumption of nodes. Another simulation results show that our scheme well operates in the environment where some packets are often lost.

The need for efficient movement and precise location of robots in intelligent robot control systems within complex buildings is becoming increasingly important. This paper proposes an indoor positioning and communication platform using Fluorescent Light Communication (FLC) employing a newly developed nine-channel receiver, and discusses a new location estimation method using FLC, that involves a simulation model and coordinate calculation formulae. A series of experiments is performed. Distance errors of less than 25 cm are achieved. The enhanced FLC system yields benefits such as greater precision and ease of use.

Two-dimensional (2D) communication is a novel physical communication form that utilizes the surface as a communication medium to provide both data and power transmission service to the sensor devices placed on the surface's top. In previous works, we developed 2D communication systems that utilize separated channels for data and power transmission. Though this assignment of different channels can achieve strong network performance, the sensor devices must be equipped with two or more interfaces to simultaneously receive the power and data signals, which significantly complicates and enlarges those devices. Moreover, when a channel is used for the power supply, it not only continually monopolizes the wireless frequency resource, it is also likely to cause interference with the other signal source in the case of the input power continually being sent out above a certain level. In this paper, we develop a novel 2D communication sensor system by using a single-carrier frequency for both power and data transmission, equipped with the wireless module for the two together in a compact body. To enable a sensor node that concurrently receives energy and data communication, we propose an enhancement scheme based on the IEEE802.15.4 MAC protocol standard. Through both computer simulation and actual measurement of the output power, we evaluate the performance of power supply and data transmission over the developed 2D communication sensor system.

This manuscript reported basic examination results of the wireless network communication performance at the coast. We consider that underwater environment condition monitoring is a sort of likely typical application for ubiquitous sensor networks. The result of the experiment shows the performance of the wireless network communication at the coastal area.

We consider a distributed transmission of data packet to a sink where the distance of a sensor node to a sink is much longer than the maximum communication range of each sensor node. We give a simple modification to the transmitter, i.e., multiplication of random phase before the transmission. Thanks to Turbo Code, it is possible to extend the transmission range as the received amplitude varies symbol by symbol for our scheme while whole data packet may be lost for the conventional scheme. In this letter, we report the experimental results of our scheme equivalently developed using visible light communication.

Recently wireless sensor networks (WSN) has risen as one of the advanced candidate technologies in order to provide more efficient structure health monitoring (SHM) solution in construction sites. In this paper, we proposed WSN monitoring framework in building sites based on 3D visualization and Augmented Reality (AR) in mobile devices. The proposed system applies 3D visualization and AR technology to camera-enabled mobile devices in WSN environment in order to gather much more information than before. Based on the proposed system, we made an experiment to validate the effectiveness of 3D and AR mode using collected data in IEEE 802.15.4-based WSN.

A new best-relay selection scheme is proposed in this letter in order to maintain a reliable cooperative communications for ubiquitous sensor networks in indoor environments. The suggested technique relies on eigenvalue decomposition to select the best relay. The simulation results confirm that the performance of the proposed approach is better than that of the previous scheme in indoor environments.

In wireless sensor networks (WSNs), geographic routing algorithms can enhance the network capacity. However, in real WSNs, it is difficult for each node to know its physical location accurately. Geographic routing with location errors may produce serious problems such as disconnected links and data transmission delays. In this letter, we present an efficient location error compensation algorithm for the geographic routing. The proposed algorithm efficiently detects and corrects the location errors and significantly enhances the network performance of geographic routing in the presence of location errors.

Ubiquitous technologies such as sensor network and RFID have enabled companies to realize more rapid and agile manufacturing and service systems. In this paper, we addresses how the huge amount of real-time events coming from these devices can be filtered and integrated to business process such as manufacturing, logistics, and supply chain process. In particular, we focus on complex event processing of sensor and RFID events in order to integrate them to business rules in business activities. We also illustrate a ubiquitous event processing system, named ueFilter, which helps to filter and aggregate sensor event, to detect event patterns from sensors and RFID by means of event pattern languages (EPL), and trigger event-condition-action (ECA) in logistics processes.

In this work, a high performance LDPC decoder architecture is presented. It is a partially-parallel architecture for low-complexity consideration. In order to eliminate the idling time and hardware complexity in conventional partially-parallel decoders, the decoding process, decoder architecture and memory structure are optimized. Particularly, the parity-check matrix is optimally partitioned into four unequal sub-matrices that lead to high efficiency in hardware sharing. As a result, it can handle two different codewords simultaneously with 100% hardware utilization. Furthermore, for minimizing the performance loss due to round-off errors in fixed-point implementations, the well-known modified min-sum decoding algorithm is enhanced by our recently proposed high-performance CMVP decoding algorithm. Overall, the proposed decoder has high throughput, low complexity, and good BER performances. In the circuit implementation example of the (576,288) parity check matrix for IEEE 802.16e standard, the decoder achieves a data rate of 5.5 Gbps assuming 10 decoding iterations and 7 quantization bits, with a small area of 653 K gates, based on UMC 90 nm process technology.

This paper presents an autonomous traffic engineering framework, named ATE, a highly efficient data dissemination mechanism for multipath data forwarding in Wireless Sensor Networks (WSNs). The proposed ATE has several salient features. First, ATE utilizes three coordinating schemes: an incipient congestion inference scheme, an accurate link quality estimation scheme and a dynamic traffic diversion scheme. It significantly minimizes packet drops due to congestion by dynamically and adaptively controlling the data traffic over congested nodes and/or poorer quality links, and by opportunistically exploiting under-utilized nodes for traffic diversion, while minimizing the estimation and measurement overhead. Second, ATE can provide with high application fidelity of the network even for increasing values of bit error rates and node failures. The proposed link quality estimation and congestion inference schemes are light weight and distributed, improving the energy efficiency of the network. Autonomous Traffic Engineering has been evaluated extensively via NS-2 simulations, and the results have shown that ATE provides a better performance with minimum overhead than those of existing approaches.

Ternary Content Addressable Memory (TCAM) is a special type of memory used in routers to achieve high-speed packet forwarding and classification. Packet forwarding is done by referring to the rules written in the routing table, whereas packet classification is performed by referring to the rules in the Access Control List (ACL). TCAM uses more transistors than Random Access Memory (RAM), resulting in high power consumption and high production cost. Therefore, it is necessary to reduce the entries written in the TCAM to reduce the transistor count. In this paper, we propose a new TCAM architecture by using Range Matching Devices (RMD) integrated within the TCAM's control logic with an optimized prefix expansion algorithm. The proposed method reduces the number of entries required to express ACL rules, especially when specifying port ranges. With less than 10 RMDs, the total number of lines required to write port ranges in the TCAM can be reduced to approximately 50%.

In this paper, we reveal inherent robustness issues of XCP (eXplicit Control Protocol), and propose extensions to XCP for increasing its robustness. XCP has been proposed as an efficient transport-layer protocol for wide-area and high-speed network. XCP is a transport-layer protocol that performs congestion control based on explicit feedback from routers. In the literature, many performance studies of XCP have been performed. However, the effect of traffic dynamics on the XCP performance has not been fully investigated. In this paper, through simulation experiments, we first show that XCP has the following problems: (1) the bottleneck link utilization is lowered against XCP traffic dynamics, and (2) operation of XCP becomes unstable in a network with both XCP and non-XCP traffic. We then propose XCP-IR (XCP with Increased Robustness) that operates efficiently even for dynamic XCP and non-XCP traffic.

Data query is one of the most important issues in wireless ad hoc networks, since the ultimate goal of these networks is to support efficient data sharing among wireless nodes. In this paper, we study the issue of data query for delay-sensitive applications in dense wireless ad hoc networks. We focus our attention on step-by-step expanding ring-based data query, which provides an upper bound on query delay to any expanding ring based query strategies. Two replication strategies including Index Replication (IR) and Data Replication (DR) are considered, to improve the delay performance of data query. We analyze the probabilistic behavior of query delay for both DR and IR by theoretical methods, and develop analytical models to approximate the minimum number of replicas required for both query strategies if an application-specified delay bound is imposed. Our work is validated through extensive simulations.

This paper proposes a medium access control (MAC) mechanism for the recently developed IEEE 802.15.4 standard, a promising candidate to become the physical (PHY) and MAC layer standard for Wireless Sensor Networks (WSNs). The main concern in WSNs is the energy consumption, and this paper presents a mechanism that adapts properly the duty cycle operation according to the traffic conditions. Various traffic adaption mechanisms have been presented for the MAC layer of the IEEE 802.15.4. However these conventional mechanisms only consider the temporal traffic fluctuations. The proposed mechanism outperforms the conventional mechanism when applied to cluster-tree based WSNs, because it considers not only the temporal fluctuations but also the spatial (geographical) fluctuations, which are intrinsic characteristics of traffic in WSNs with the cluster tree topology. Evaluations showed that the proposed mechanism achieves less energy consumption than the conventional traffic adaptation mechanism, with maintaining almost the same transmission performance.

In this paper, we discuss the validity of the multi-scale gamma model and characterize the differences in host-level application traffic with this model by using a real traffic trace collected on a 150-Mbps transpacific link. First, we investigate the dependency of the model (parameters α and β, and fitting accuracy ε) on time scale Δ, then find suitable time scales for the model. Second, we inspect the relations among α, β, and ε, in order to characterize the differences in the types of applications. The main findings of the paper are as follows. (1) Different types of applications show different dependencies of α, β, and ε on Δ, and display different suitable Δs for the model. The model is more accurate if the traffic consists of intermittently-sent packets than other. (2) More appropriate models are obtained with specific α and β values (e.g., 0.1 < α < 1, and β < 2 for Δ = 500 ms). Also, application-specific traffic presents specific ranges of α, β, and ε for each Δ, so that these characteristics can be used in application identification methods such as anomaly detection and other machine learning methods.

A stacked rectangular microstrip antenna with a shorting plate and a helical pin is proposed as a car antenna for triple band operation in ITS. The proposed antenna operates as a conventional stacked microstrip antenna at the highest frequency band. At the middle and the lowest frequency bands, the antenna radiates at low elevation angles from the helical pin and the shorting plate. In this paper, as an example of triple band antennas in the ITS, an antenna is designed that supports PHS, VICS and ETC. The proposed antennas have the proper radiation pattern for each application and are small in size.

This paper presents a method of expanding the operating frequency band of a Reverberating TEM Cell (RTC) for electromagnetic compatibility (EMC) testing. To expand the operating frequency band of an RTC, this paper places a wire septum inside the cell instead of a solid septum. The maximum usable frequency (MUF) for TEM cell operation and the lowest usable frequency (LUF) for reverberating chamber operation with the wire septum are studied and compared with a conventional solid septum. The E field strengths inside the RTC are measured and evaluated. The measurement results show that the RTC with the wire septum have similar MUF to the RTC with a solid septum at TEM mode, but have much lower LUF at a reverberating mode, which proves that the operating frequency band of the RTC can be expanded by using the wire septum.

A novel peak-to-average power ratio (PAR) control algorithm for feedback-controlled multitone-hopping code-division multiple access (FC/MH-CDMA) signals is proposed. In FC/MH-CDMA, since each chip consists of plural tones, the energy consumption due to a large PAR is not negligible at the transmitter. The proposed PAR control algorithm iteratively constructs a time-frequency code that achieves a preset, target PAR under the condition that all signals are asynchronously transmitted. A PAR of 1 dB is shown to be achievable, and the bit-error rate performance is shown to be only slightly influenced if the target PAR is set to be larger than 3 dB. The influence of quantization is also discussed in terms of its application to limited feedback channels.

In this paper, the outage probability and diversity order of opportunistic decode-and-forward (DF) cooperation are analyzed under Rayleigh fading channels, where the impacts of channel estimation error, relay selection feedback delay and the availability of the direct link between the source and the destination are considered comprehensively. The closed-form expressions of outage probability in the high signal-to-noise ratio (SNR) region are derived as well as the diversity order. The theoretical results demonstrate that the achievable diversity order is zero when channel estimation error exists, and this conclusion holds no matter whether the direct link is available, even if the relay selection feedback is delay-free. For the perfect channel estimation scenario, the achievable diversity order is related to the potential relay number K, the channel delay correlation coefficient ρ_d and the availability of the direct link. If relay selection feedback is not delayed, i.e., ρ_d = 1, the diversity order is K when the direct link is blocked, and it becomes K+1 when the direct link is available. For delayed relay selection feedback, i.e., ρ_d < 1, the diversity order achievable is only related to the availability of the direct link. In this case, if the direct link does not exist, the diversity order is 1, otherwise the diversity order of 2 can be obtained. Simulation results verify the analytical results of outage probability and diversity order.

This paper proposes a stabilized multichannel random access protocol based on slotted ALOHA for relay deployed cellular networks. To ensure the stability of random access, the proposed protocol dynamically controls the number of random access channels in a BS and a RS and the retransmission probability of the random access packets under heavy load conditions. A mathematical formula is also developed that derives an optimal partition ratio of the shared random access channels between a base station and a relay station without and with capture effect. Numerical results show that the proposed protocol can guarantee the required utilization and delay even in high offered load, which otherwise can cause bistable problem of slotted ALOHA.

With development of wireless communication technologies, users are no longer satisfied with only a single service provided per time. They are willing to enjoy multiple services simultaneously. Therefore scheduling multiple services per user becomes quite important usability issue in the area of resource management. In this paper, the multiple-service scheduling problem is firstly formulated as an integrated optimization problem based on a utility function in homogeneous service systems. Due to its NP-hard characteristic, a set of low-complexity sub-optimal algorithms is therefore proposed and used to schedule resources for multiple services per user at the downlink of Orthogonal Frequency Division Multiplexing (OFDM) systems. The proposed algorithms are capable to effectively and efficiently distribute assigned resources among multiple services for one user. Moreover the utility of our algorithms is further extended from homogeneous service systems to heterogeneous service systems. And full exploitation of multi-user diversity gain is achieved while guaranteeing quality of service (QoS). The simulation results show that the proposed algorithm outperforms traditional algorithm in terms of system best effort service throughput and fairness criterion.

Recently, broadcast services are introduced in cellular networks and macro diversity is an effective way to combat fading. In this paper, we propose a kind of distributed space-time block codes (STBCs) for macro diversity which is constructed from the total antennas of multiple cooperating base stations, and all the antennas form an equivalent multiple input multiple output (MIMO) system. This code is termed High-Dimension-Full-Rate-Quasi-Orthogonal STBC (HDFR-QOSTBC) which can be characterized as: (1) It can be applied with any number of transmit antennas especially when the number of transmit antennas is large; (2) The code is with full transmit rate of one; (3) The Maximum Likelihood (ML) decoding complexity of this code is controllable and limited to N_t/2-symbol-decodable for total N_t transmit antennas. Then, we completely analyze the structure of the equivalent channel for the kind of codes and reveal a property that the eigenvectors of the equivalent channel are constant and independent from the channel realization, and this characteristic can be exploited for a new transmission structure with single-symbol linear decoder. Furthermore, we analyze different macro diversity schemes and give a performance comparison. The simulation results show that the proposed scheme is practical for the broadcast systems with significant performance improvement comparing with soft-combination and cyclic delay diversity (CDD) methods.

In this paper, we investigate a multi-packet transmitting and receiving wireless mesh network that uses a multi-antenna set on each node in the network. In wireless mesh networks for accessing the Internet, the target of all traffic generated from distributed nodes is a gateway (GW). Therefore, many packets are concentrated around the GW and the communication channel around the GW is crowded. To prevent packet congestion around the GW, we propose setting an adaptive array antenna on the GW and the relay nodes. We also calculate an appropriate number of antenna elements considering the fair traffic over the whole region, to prevent packet congestion at each node.

The localization algorithm based on the double-thresholding (LAD) method was originally proposed for detecting and localizing narrowband (NB) signals with respect to the search bandwidth. Its weakness is that the localized signal is often split into several parts, especially when the signal-to-noise ratio (SNR) is low. This may lead to the illusion of unoccupied frequencies in the middle of the signals. In this paper, an extension of the LAD method, namely the two-dimensional LAD (2-D LAD), is proposed to solve that problem. In addition to offering low computational complexity, the proposed method is able to operate at lower SNR values than the original 1-D LAD method.

Performance analysis of a dual-hop semi-blind amplify-and-forward (AF) relay system in mixed Nakagami-m and Rician fading channels, is proposed. We derived the closed-form expression for the cumulative distribution function (CDF) of the equivalent end-to-end signal to noise ratio (SNR), based on which the exact outage probability and symbol error probability (SEP) are investigated. The theoretical analysis is validated by Monte Carlo simulation results.

We propose an opportunistic spectrum access scheme for unslotted secondary users exploiting spectrum opportunities in unslotted primary networks. An analytical model is developed to investigate the performance of the proposed scheme, and numerical results are presented to evaluate the performance in unslotted primary networks.

In PMIPv6, all packets sent by mobile nodes or correspondent nodes are transferred through the local mobility anchor. This unnecessary detour results in high delivery latency and significant processing cost. Several PMIPv6 route optimization schemes have been proposed to solve this issue. However, they also suffer from the high signaling costs when determining the optimized path. The proposed scheme which adopts the prediction algorithm in PFMIPv6 can reduce the signaling costs of the previous schemes. Analytical performance evaluation is performed to show the effectiveness of the proposed scheme.

Random scattering of sensors may cause some location not to be covered. In such a case, it is useful to make use of mobile sensors that can move to eliminate the coverage holes. Wang et al [1]. proposed self-deployment schemes of mobile sensors by using Voronoi polygon. However, some coverage holes still remain after the execution of the schemes. We propose a new self-deployment scheme using the centroid (geometric center) of each sensor's Voronoi polygon as the moving target position. The performance evaluation shows that the proposed scheme achieves better results than the existing schemes in terms of fast coverage expansion.

Wireless Sensor and Actor Networks (WSAN) are commonly used to monitor physical parameters and execute opportune actions in response to specific events. In order to achieve this goal it is necessary to implement efficient coordination and cooperation among the network nodes (i.e. sensors and actors) with the aim of reducing the energy consumption and improving the response time of the system. This work propose a clustering mechanism that organizes the sensor nodes to form clusters where the mobile actors nodes in the WSAN perform the cluster head role. The proposal considers the mobility aspect of the actor nodes and implements a mechanism to dynamically change the geographical location of the actors while trying to reduce the load in terms of the number of sensors within each cluster, all this with the aim of extending the network lifetime.

Duty-cycle MAC protocols have been proposed for wireless sensor networks (WSNs) to reduce the energy consumed by idle listening, but they introduce significant end-to-end delivery latency. Several works have attempted to mitigate this latency, but they still have a problem on handling the packet loss. The quality of the wireless channel in WSNs is quite bad, so packets are frequently lost. In this letter, we present a novel duty-cycle MAC protocol, called REMAC (Retransmission-Enhanced duty-cycle MAC), which exploits both the network layer and the physical layer information. REMAC estimates the quality of the wireless channel and properly reserves the wireless channel to handle the packet loss. It can reduce the end-to-end packet delivery latency caused by the packet loss without sacrificing the energy efficiency. Simulation results show that REMAC outperforms RMAC in terms of the end-to-end packet delivery latency.

In this letter, we present a flow-aware opportunistic routing protocol over wireless mesh networks. Firstly, a forwarder set selection mechanism is proposed to avoid potential flow contention, thus alleviating possible congestion from the increased number of flows. Secondly, a Round-Robin packet sending fashion combined with batch-by-batch acknowledgement is introduced to provide reliability and improve throughput. Evaluations show that our protocol significantly outperforms a seminal opportunistic routing protocol, MORE, under both single and multiple flow scenarios.

In this letter, we propose a revised geographic routing protocol and a scheduling algorithm to support real-time applications, which are often observed in wireless sensor networks. In order to meet real-time requirement, a specific application is modeled as an (m,k)-firm stream that has a property of weakly hard real-time system. In addition, both a priority-based scheduling and a geographic forwarding scheme based on delay, distance, and remaining slack time are newly proposed. Simulations and their analysis are followed to validate the suitability of reduced dynamic failure probability and extended network lifetime.

In this letter, the cumulative distribution function (CDF) for the maxima of the OSTBC-MIMO channel capacity in a temporal interval is estimated using the first-order Rice series approximation. As the estimation of the maxima distribution using the Rice series is applicable only to Gaussian random processes, the Gaussian-approximated probability density function (PDF) for the OSTBC-MIMO channel capacity is derived from existing exact PDF (non-Gaussian). The resulting CDF for the maxima capacity is useful to design OSTBC-MIMO systems.

A planar inverted-E (PIE) antenna that can achieve a wide impedance bandwidth is proposed. The antenna is realized by inserting a branch capacitance between the feed line and the shorting pin of a conventional planar inverted-F antenna (PIFA). Such a modification significantly enhanced the impedance bandwidth while maintaining the antenna size. The proposed antenna possesses a very wide impedance bandwidth of 1250 MHz (1650-2900 MHz) at a voltage standing wave ratio (VSWR) <3. In addition, good radiation patterns were obtained at the desired frequency bands.

In coordinated multi-cell communication, inter-cell interference (ICI) is one key factor limiting the performance of the networks, many solutions are proposed to overcome this problem, such as inter-cell interference nullification (INFN) and signal-to-leakage ratio maximization (SLRM). In this paper, one new pre-coding method is proposed from the perspective of interference controlling (INFC). This method realizes the merits of INFN and SLRM, and can flexible control interference level of networks so that it satisfies a preassigned level. Numerical simulation shows that INFC is more suitable for the multi-cell joint transmission than INFN and SLRM.

A K-exponential filter is derived and utilized for pulse shaping to reduce peak to average power ratio (PAPR) without intersymbol interference (ISI). While keeping the same bandwidth, the frequency responses of the filters vary with different values of the parameter k. The minimum PAPR is associated with a value of the parameter k when the roll-off factor α is specified. Simulations show that the PAPR can be reduced compared with the raised cosine (RC) filter in various systems. The derived pulse shaping filters also provide better performance in PAPR reduction compared with the existing filters.

This letter examines the problem of allocating the subcarrier power of the relayed signal in orthogonal frequency division multiplexing (OFDM) based dual-hop systems in which the relay terminal is operated in an Amplify-and-Forward (AF) mode and the source node transmits its signal with a uniform power distribution. In AF relaying systems, both the modulation order and the error control scheme are fixed at the relay node, and thus the potential for increasing the data rate via a suitable allocation of the subcarrier power at the relay node does not exist. Therefore, this study proposes an alternative subcarrier power allocation scheme in which the objective is to scale the power assigned to each of the relayed signal sub-carriers in such a way as to minimize the equivalent average noise power at the destination terminal.

In this paper, a novel pseudo-random noise complementary pair (PNCP) is proposed and adopted as the guard intervals in the time-domain synchronous OFDM (TDS-OFDM) system. The proposed PNCP has nearly ideal aperiodic auto-correlation property and inherits the differential property of the PN sequence. Simulations demonstrate the proposed TDS-OFDM system padded with PNCP could achieve better performance in both synchronization and channel estimation than the conventional TDS-OFDM system.

A structured codebook with various codeword configurations is proposed to overcome the sum capacity limitation in a region with finite number of users. Specifically, based on multi-user MIMO platform with a codebook of multiple orthonormal sets, called as per user unitary rate control (PU2RC), we diversify the codeword configuration of each orthonormal set and expand the corresponding codeword configuration. Numerical experiments with respect to several system parameters, such as user density and received signal to noise ratio, show that the proposed codebook offers throughput gains over the conventional system in a small to moderate number of user region.

In this paper, we investigate two receiver structures for spatially multiplexed transmission on MIMO frequency selective fading channels. Those receivers compensate the IAI (Inter-Antenna Interference) and ISI (Inter-Symbol Interference) in the time domain. We first propose the MIMO sequential equalizer in which the block of several receives symbols is processed symbol by symbol by MLD (Maximum Likelihood Detection). Next we investigate the MIMO MLSE (Maximum Likelihood Sequence Estimation) receiver in which the terminated block trellis is decoded by the Viterbi algorithm. The bit error rates of two time domain receivers are examined through computer simulations and we also compare their BER characteristics to those of the conventional MIMO SC-FDE.

In this letter, we propose a novel frequency-domain equalization (FDE) scheme for single-carrier multiple-input multiple-output (MIMO) systems over time-varying channels. Based on frequency-domain decision-feedback equalization (FD-DFE), we design a feedforward filter with constraint such that the equalization can be easily realized segment-by-segment with the help of the overlap-save (OLS) method. Since the segment length and block length can be designed independently, our proposal sets relatively short segment length to obtain good performance in time-varying environments, and very long block length to achieve high spectral efficiency. Furthermore, we present two scenarios in the design of filters for MIMO systems.

In the symbiotic cognitive radio (CR) networks, the CR users (CUs) may assist the primary transmission in a cooperation time, and obtain an incentive time for their own data transmission. In this letter, we study the throughput maximization problem in the symbiotic CR networks. Under the symbiosis and transmit power constraints, we aim to find the optimal cooperation time to assist the primary transmission and power allocations among the CUs. Given the cooperation time, the optimal power allocations can be solved by multi-level water-filling (MWF) with individual volume limits. A theoretical analysis is presented on the cooperation time and a modified bisection algorithm with low complexity is proposed to find the sub-optimal cooperation time. Simulation results show that the spectrum usage efficiency can be significantly improved as the number of CUs increases.

Recently, novel full-diversity full-rate quasi-orthogonal space-time block codes (QSTBCs) with power scaling and double-symbol maximum likelihood (ML) decoding was proposed. Specifically, the codes can achieve full-diversity through linearly combining two adequately power scaled orthogonal space-time block codes (OSTBCs). In this letter, we derive expressions for mutual information and post-processing signal-to-noise ratio (SNR) for a system with four transmit antennas. By exploiting these formulas, we propose three transmit antenna grouping (TAG) methods for a closed-loop system with low-rate feedback information. The TAG methods make it possible to provide an excellent error-rate performance even with a low-complexity zero-forcing (ZF) detection, especially in spatially correlated fading channels.