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Ultraviolet communication (UVC) has been regarded as a promising supplement for overloaded conventional wireless communications. One challenge lies in the communication deterioration caused by the UV-photon scattering induced inter-symbol-interference (ISI), which will be even worse when encountering multilevel pulse amplitude modulation (multi-PAM) symbols. To address the ISI, traditional coherent detection methods (e.g., maximum-likelihood sequence detection, MLSD) require high computational complexities for UV channel estimation and sequential detection space formation, thereby making them less attractive. Current non-coherent detection, which simply combines the ISI-insensitive UV signal features (e.g., the rising edge) as the 1-dimensional metric, cannot guarantee reliable communication accuracy. In this work, a novel high-dimensional (HD) non-coherent detection scheme is proposed, leveraging a HD construction of the ISI-insensitive UV signal features. By doing so, we transform the ISI caused sequential detection into an ISI-released HD detection framework, which avoids complex channel estimation and sequential detection space computation. Then, to compute the detection surface, a UV feature based unsupervised learning approach is designed. We deduce the theoretical bit error rate (BER) in terms of the signal-to-noise-ratio (SNR), and prove that the proposed HD non-coherent detection method has a lower BER than that of the current 1D non-coherent scheme. Simulation results validate our results, and more importantly, demonstrate a very-close BER with the state-of-the-art coherent MLSD (

Feature extraction of electronic nose (e-nose) output response aims to reduce information redundancy so that the e-nose performance can be improved. The use of different sensor types and sample targets can affect the optimization of feature extraction. This research used six types of metal oxide sensors, TGS 813, 822, 825, 826, 2620, and 2611 in an e-nose system to detect three types of herbal drink. Five kinds of feature extraction methods on the original response curve in a steady-state response were used, namely, baseline difference, logarithmic difference, local normalization, global normalization, and global autoscaling. The results of feature extraction were fed into a Principal Component Analysis (PCA) system. As a result, global autoscaling and normalization had the highest total sum of the first and second principal components of 96.96%, followed by local normalization (90.18%), logarithm, and baseline difference (88.92% and 79.26%, respectively). The validation of PCA results was performed using a Backpropagation Neural Network (BPNN). The highest accuracy, 97.44%, was obtained from the global autoscaling method, followed by global normalization, local normalization, logarithm, and baseline difference, with an accuracy level of 94.87%, 92.31 %, 89.74%, and 82.05%, respectively. This demonstrates that the selection of the feature extraction method can affect the classification results and improve e-nose performance.

A wireless body-centric nano-network consists of various nano-sized sensors with the purpose of healthcare application. One of the main challenges in the network is caused by the very limited power that can be stored in nano-batteries in comparison with the power required to drive the device for communications. Recently, novel rectifying antennas (rectennas) based on carbon nanotubes (CNTs), metal and graphene have been proposed. At the same time, research on simultaneous wireless information and power transfer (SWIPT) schemes has progressed apace. Body-centric nano-networks can overcome their energy bottleneck using these mechanisms. In this Letter, a nano-rectenna energy harvesting model is developed. The energy harvesting is realised by a nano-antenna and an ultra-high-speed rectifying diode combined as a nano-rectenna. This device can be used to power nanosensors using part of the terahertz (THz) information signal without any other system external energy source. The broadband properties of nano-rectennas enable them to generate direct current (DC) electricity from inputs with THz to optical frequencies. The authors calculate the output power generated by the nano-rectenna and compare this with the power required for nanosensors to communicate in the THz band. The calculation and analysis suggest that the nano-rectenna can be a viable approach to provide power for nanosensors in body-centric nano-networks.

The complexity of social-ecological systems (SES) is rooted in the outcomes of node activities connected by network topology. Thus far, in network dynamics research, the connectivity degree (CND), indicating how many nodes are connected to a given node, has been the dominant concept. However, connectivity focuses only on network topology, neglecting the crucial relation to node activities, and thereby leaving system outcomes largely unexplained. Inspired by the phenomenon of “consensus of wills and coordination of activities” often observed in disaster risk management, we propose a new concept of network characteristic, the consilience degree (CSD), aiming to measure the way in which network topology and node activities together contribute to system outcomes. The CSD captures the fact that nodes may assume different states that make their activities more or less compatible. Connecting two nodes with in/compatible states will lead to outcomes that are un/desirable from the perspective of the SES in question. We mathematically prove that the CSD is a generalized CND, and the CND is a special case of CSD. As a general, fundamental concept, the CSD can facilitate the development of a new framework of network properties, models, and theories that allows us to understand patterns of network behavior that cannot be explained in terms of connectivity alone. We further demonstrate that a co-evolutionary mechanism can naturally improve the CSD. Given the generality of co-evolution in SES, we argue that the CSD is an inherent attribute rather than an artificial concept, which underpins the fundamental importance of the CSD to the study of SES.

In this letter, we investigate the bit error rate (BER) performance of a cooperative relaying transmission scheme for wireless nanosensor networks in the Terahertz (THz) Band. We consider nanosensor networks comprising several graphene-based devices deployed at the nanoscale. Both amplify-and-forward (AF) and decode-and-forward (DF) relaying modes are studied. We consider a line-of-sight (LOS) channel model in the THz band which takes into account both spreading loss and molecular absorption loss. Given the high path loss and level of noise from significant random fluctuations through the THz channel, relay assisted schemes offer advantages in terms of significant performance improvements. To quantify the likely benefits, we derive the predicted bit error rate (BER) of the proposed scheme. We conduct a simulation of the proposed relay schemes based on the THz LOS channel model utilizing a Monte-Carlo method. The results obtained show that a performance improvement of 2.2 dB for AF and of 5 dB for DF is achievable at a target bit error rate (BER) of 10-5.

This paper discusses the effect of receiver field-of-view (FOV) on the power distribution and bandwidth performance of short-range diffuse line-of-sight (LOS) links. Monte Carlo simulation is used to investigate the performance of the links for the on-axis and off-axis scenarios in clear, coastal and turbid water. In both clear and coastal water, the receiver FOV has little influence on the on-axis power reception but has a significant effect on the off-axis power reception where there is an approximately 30 dB gain (off-axis) when the receiver FOV is increased from 10° to 180°. However, in turbid water receiver FOV significantly affects the power received both on-axis and off-axis, with gains of 15-18 dB for the same change in receiver FOV. In terms of bandwidth performance, the FOV only affects the on-axis bandwidth in clear and coastal water but not in turbid water.

Growing bandwidth demands are driving the search for increased network capacity leading to the exploration of new wavelength ranges for future communication systems. Therefore, we consider two technologies that offer increased transmission bandwidths by virtue of their high carrier frequencies, namely optical wireless and millimeter-wave transmission. After highlighting the relevant electromagnetic (EM) spectrum region, we briefly describe the applications and properties of each approach coupled with a short history of their development. This is followed by a performance comparison in two possible 5G links: outdoor point-to-point and indoor hotspots. We find that in both cases, there are regions where optical wireless communications (OWC) are better, but others where millimeter waves are to be preferred. Specifically, the former outperforms the latter over distances up to approximately 50 meters outdoors and a 10-meter hotspot radius indoors.

Quorum sensing (QS) is used to describe the communication between bacterial cells, whereby a coordinated population response is controlled through the synthesis, accumulation and subsequent sensing of specific diffusible chemical signals called autoinducers, enabling a cluster of bacteria to regulate gene expression and behaviour collectively and synchronously, and assess their own population. As a promising method of molecular communication, bacterial populations can be programmed as bio-transceivers to establish information transmission using molecules. In this work, to investigate the key features for molecular communication, a bacterial QS system is introduced, which contains two clusters of bacteria, specifically Vibrio fischeri, as the transmitter node and receiver node, and the diffusive channel. The transmitted information is represented by the concentration of autoinducers with on–off keying (OOK) modulation. In addition, to achieve better reliability, transmission efficiency and channel throughput performance, different Automatic Repeat reQuest (ARQ) protocols are taken into consideration. This configuration is investigated via simulation and the consequent results discussed. The performance of the system is evaluated in terms of transmission time, efficiency, bit error rate (BER) and channel throughput. Results show that Selective-Repeat (SR-ARQ) performs better than Go-Back-N (GBN-ARQ), while the performance of Stop-N-Wait (SW-ARQ) varies for different channel conditions, which is quite different from the performance of ARQ schemes in traditional networking areas.

The increasing amount of user equipment (UE) and the rapid advances in wireless body area networks bring revolutionary changes in healthcare systems. However, due to the strict requirements on size, reliability and battery lifetime of UE devices, it is difficult for them to execute latency sensitive or computation intensive tasks effectively. In this paper, we aim to enhance the UE computation capacity by utilizing small size coordinator-based mobile edge computing (C-MEC) servers. In this way, the system complexity, computation resources, and energy consumption are considerably transferred from the UE to the C-MEC, which is a practical approach since C-MEC is power charged, in contrast to the UE. First, the system architecture and the mobility model are presented. Second, several transmission mechanisms are analyzed along with the proposed mobility-aware cooperative task offloading scheme. Numerous selected performance metrics are investigated regarding the number of executed tasks, the percentage of failed tasks, average service time, and the energy consumption of each MEC. The results validate the advantage of task offloading schemes compared with the traditional relay-based technique regarding the number of executed tasks. Moreover, one can obtain that the proposed scheme archives noteworthy benefits, such as low latency and efficiently balance the energy consumption of C-MECs.

Inspired by the recent developments of the Internet of Things (IoT) relay and mobile edge computing (MEC), a hospital/home-based medical monitoring framework is proposed, in which the intensive computing tasks from the implanted sensors can be efficiently executed by on-body wearable devices or a coordinator-based MEC (C-MEC). In this paper, we first propose a wireless relay-enabled task offloading mechanism that consists of a network model and a computation model. Moreover, to manage the computation resources among all relays, a task offloading decision model and the best task offloading recipient selection function is given. The performance evaluation considers different computation schemes under the predetermined link quality condition regarding the selected vital quality of service (QoS) metrics. After demonstrating the channel characterization and network topology, the performance evaluation is implemented under different scenarios regarding the network lifetime of all relays, network residual energy status, total number of locally executed packets, path loss (PL), and service delay. The results show that data transmission without the offloading scheme outperforms the offload-based technique regarding network lifetime. Moreover, the high computation capacity scenario achieves better performance regarding PL and the total number of locally executed packets.

As a recently reported network property, consilience degree (CSD) indicates how well a network system integrates its topology and node activities together to serve a specific systemic goal. As is well known, many natural and man-made systems are complex networks where, besides network topology, node activity states also play an important role in determining system performance. For example, a collaborative project involving friends is more likely to succeed than one involving enemies, even though the topology of network organization is the same. The concept of CSD can quantitatively distinguish the difference between the involvement of friends and the involvement of enemies. This article reports a simulation study on the adaptive behaviors of nodes based on the selfish rule and the following-others rule, and the simulation results show that based on such adaptive behaviors of nodes, a network system will automatically evolve to a high level of system consilience. The simulation study also demonstrates that a high level of system consilience resulting from adaptive behaviors will contribute to increased system resistance to external disturbances. The generality of adaptive behaviors in reality implies that CSD is an inherent attribute of real-world network systems, and therefore, the concept of CSD has significant application potential in the study of adaptive behaviors in network systems.

A nanonetwork is comprised of nanoscale sensors and communicating devices facilitating communication at the nanoscale, which is a promising technology for application in health applications such as intra-body health monitoring and drug delivery. However, the communication performance within a nanonetwork is substantially limited by the energy loss as the Electromagnetic (EM) wave propagates along the channel. Energy harvesting for nanosensor networks can provide a way to overcome the energy bottleneck without considering the lifetime of batteries. Moreover, relaying protocols for nanoscale communications have been proposed to improve the communication performance and extend the transmission distances among nanosensors within nanonetworks. The combination of energy harvesting and a relaying protocol provides an emerging solution not only to overcome the aforementioned energy issues but also enhance the system performance. Therefore, in this paper, simultaneous wireless information and power transfer nanonetworks in the Terahertz (THz) Band (0.1-10 THz) is proposed. An amplify and forward (AF) relaying nanonetwork in this band is investigated, where the relay harvests energy from the received THz signal which is then consumed to forward the information to the destination. Performance based on both time-switching and power-splitting protocols is analyzed. The numerical results show the optimal power-splitting ratio and time switching ratio that achieves the maximum throughput at the destination as well as the impact of transmission distance on system performance. It is seen that the power-splitting protocol gives greater throughput than that of the time-switching protocol.

Optical wireless communications (OWC) are being consid-ered for use under water because sea water exhibits a win-dow of reduced absorption in the visible spectrum, particularly between 400–550nm. Recent technology has demonstrated the ability to support mid-range links (

Wireless in-body sensor networks are attracting increasing attention for numerous healthcare applications and medical services. Implant devices are widely employed to measure physiological signals inside the human body in a simple, long lifetime and continuous approach. However, due to the strict technical requirements of implant devices, there exist numerous key research challenges in this area. Considering realistic transmission power requirements based on the IEEE 802.15.6 standard safety regulations, the channel characteristics of implant to deep implant and implant to body surface communication scenarios are investigated. Furthermore, multiple vital quality of service (QoS) factors of implant communication channels are studied regarding channel capacity, bit error rate (BER), link quality and data rate. The system performance evaluation indicates that the data transmission rate can be optimized up to 10 Mbps. Furthermore, the transmission distance supported by in-body to on-body communication path is 2 meters, at 1 µW while the in-body to deep tissue region communication channel achieves less than 1 meter. The results proposed in this paper give an outlook of the intra-body networking system performance and can be applied to in-body communication system implementation research.

Molecular Communications is a promising area with significant potential applications. To enhance the reliability of the transmission process, self-orthogonal convolutional codes (SOCCs) are proposed and investigated with respect to both bit error rate (BER) and energy efficiency. The codes are compared to both an un-coded system and one that employs Hamming codes to show that they can provide a benefit for molecular communication systems. The influence of the channel memory is also analysed in this paper. In addition, taking into account the extra energy required to implement the coding, the critical distance is investigated as another performance metric for nano-to-nano device communication, nano-to-macro device communication and macro-to-nano device communication. Considering the transmission distance and the operating BER of the designed system, the designer can determine whether the use of coding is beneficial or which code better suits the system.

This chapter focuses upon the use of coding and protocols within diffusion based molecular communication systems, laying the groundwork for future development in test bed implementations. The chapter starts with an introduction that briefly discusses coding and protocols used in traditional communication systems. Following this, details of the molecular channel are given, including the energy consumption constraints and a relevant mathematical framework. This discussion then leads onto potential encoding and decoding technologies. Next, original results on the use of Hamming codes in molecular communication systems are presented with a quantitative comparison against an uncoded molecular system. The impact of specific design parameters such as the number of molecules, energy, and transmission distance on the bit error rate (BER) is considered. Finally, a protocol, based upon the use of an acknowledgement (ACK) packet is presented as a further advancement to the field that the reader may wish to consider when designing future systems.

Given several different new product development projects and limited resources, this paper is concerned with the optimal allocation of resources among the projects. This is clearly a multi-objective optimization problem (MOOP), because each new product development project has both a profit expectation and a loss expectation, and such expectations vary according to allocated resources. In such a case, the goal of multi-objective new product development (MONPD) is to maximize the profit expectation while minimizing the loss expectation. As is well known, Pareto optimality and the Pareto front are extremely important to resolve MOOPs. Unlike many other MOOP methods which provide only a single Pareto optimal solution or an approximation of the Pareto front, this paper reports a novel method to calculate the complete Pareto front for the MONPD. Some theoretical conditions and a ripple-spreading algorithm together play a crucial role in finding the complete Pareto front for the MONPD. Simulation results illustrate that the reported method, by calculating the complete Pareto front, can provide the best support to decision makers in the MONPD.

Through the implementation of a simple linearly scalable 1-W infrared (IR) transmitter, which is centrally located on the ceiling of a sports utility vehicle (SUV), and for 15 passenger configurations, an analysis into the received power, power deviation, minimum bandwidth, and maximum root-mean-square (RMS) delay spread is provided for the regions of the vehicle most likely to benefit from the deployment of intravehicle optical wireless (OW) communication systems. Several specific regions, including the areas around a passenger's legs, arms, necks, and shoulders, are shown to have beneficial channel characteristics for the use of personal electronics equipment such as laptops, tablet PCs, or wireless headphones. Similarly, a region around the headrest of the front seat is shown to have potential for the deployment of in-car entertainment solutions independent of the passenger configuration. This analysis, which is the first to introduce the concept of channel variation from multiple passenger configurations, aims to show that OW is a potential candidate for future intravehicular communication systems.

In this paper, we aim to minimize in-body sensor node energy consumption and to prolong the network lifetime by utilizing a relay strategy based on our proposed flexible quality of service (QoS) radio frequency communication module and advanced In-to-out body path loss (PL) model. A selection algorithm is derived and investigated in which the relay nodes with lower energy consumption and minimum distance to the coordinator will be chosen in each round. In this way, time division multiple access (TDMA) can be investigated to schedule data transmission from implants to the corresponding relays, and thus minimize the overall length of communication links. Moreover, a linear programming network lifetime model is proposed along with various subjective functions. Followed by constraints, simulations are conducted on a proposed topology network assuming two commercial transceivers. Results show that the existing two-relay based protocol achieves higher transmission data rates due to the availability of redundant communication pathways. However, our proposed incremental relay-based cooperative routing protocol outperforms the existing two-relay based scheme regarding total network lifetime, overall throughput, average power consumption and propagation delay.

The discovery that bacteria use signalling molecules, which are released into the environment, to communicate with each other changed our general perception of organisms inhabiting the world. Nowadays, the term quorum sensing is used to describe the phenomenon whereby a coordinated population response is controlled by exchanging specific diffusible chemical signals called autoinducers, enabling a cluster of bacteria to regulate their gene expression and behaviour collectively and synchronously. Bacteria assess their own population and coordinate their actions through the synthesis, accumulation and subsequent sensing of autoinducers. In this work, a bacterial quorum communication system is introduced, which contains two clusters of bacteria, specifically Vibrio fischeri, a gram-negative marine bacterium, as the transmitter node and receiver node, and the diffusive channel. The transmitted information is encoded into the concentration of autoinducers, with binary representation, and then, it is divided into frames for transmission. Automatic Repeat reQuest protocols are applied to achieve better reliability. In addition, this paper addresses the question of optimal frame size for data communication in this channel capacity and energy constrained bacterial quorum communication system. The optimal fixed frame length is determined for a set of channel parameters by maximising the throughput and energy efficiency matrix. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper, an analytical and accurate in-to-out (I2O) human body path loss (PL) model at 2.45 GHz is derived based on a 3D heterogeneous human body model under safety constraints. The bit error rate (BER) performance for this channel using multiple efficient modulation schemes is investigated and the link budget is analyzed based on a predetermined satisfactory BER of 10−3. In addition, an incremental relay-based cooperative quality of service-aware (QoS-aware) routing protocol for the proposed I2O WBAN is presented and compared with an existing scheme. Linear programming QoS metric expressions are derived and employed to maximize the network lifetime, throughput, minimizing delay. Results show that binary phase-shift keying (BPSK) outperforms other modulation techniques for the proposed I2O WBAN systems, enabling the support of a 30 Mbps data transmission rate up to 1.6 m and affording more reliable communication links when the transmitter power is increased. Moreover, the proposed incremental cooperative routing protocol outperforms the existing two-relay technique in terms of energy efficiency. Open issues and on-going research within the I2O WBAN area are presented and discussed as an inspiration towards developments in health IoT applications.

Wireless body area sensor networks (WBASNs) are becoming an increasingly significant breakthrough technology for smart healthcare systems, enabling improved clinical decision-making in daily medical care. Recently, radio frequency ultra-wideband technology has developed substantially for physiological signal monitoring due to its advantages such as low-power consumption, high transmission data rate, and miniature antenna size. Applications of future ubiquitous healthcare systems offer the prospect of collecting human vital signs, early detection of abnormal medical conditions, real-time healthcare data transmission and remote telemedicine support. However, due to the technical constraints of sensor batteries, the supply of power is a major bottleneck for healthcare system design. Moreover, medium access control (MAC) needs to support reliable transmission links that allow sensors to transmit data safely and stably. In this Letter, the authors provide a flexible quality of service model for ad hoc networks that can support fast data transmission, adaptive schedule MAC control, and energy efficient ubiquitous WBASN networks. Results show that the proposed multi-hop communication ad hoc network model can balance information packet collisions and power consumption. Additionally, wireless communications link in WBASNs can effectively overcome multi-user interference and offer high transmission data rates for healthcare systems.

Communication between nanoscale devices is an area of considerable importance as it is essential that future devices be able to form nanonetworks and realise their full potential. Molecular communication is a method based on diffusion, inspired by biological systems and useful over transmission distances in the nm to μ m range. The propagation of messenger molecules via diffusion implies that there is thus a probability that they can either arrive outside of their required time slot or ultimately, not arrive at all. Therefore, in this paper, the use of a error correcting codes is considered as a method of enhancing the performance of future nanonetworks. Using a simple block code, it is shown that it is possible to deliver a coding gain of ∼1.7 dB at transmission distances of 1 μ m . Nevertheless, energy is required for the coding and decoding and as such this paper also considers the code in this context. It is shown that these simple error correction codes can deliver a benefit in terms of energy usage for transmission distances of upwards of 25 μ m for receivers of a 5 μ m radius.

Molecular communications (MC) is a promising paradigm which enables nano-machines to communicate with each other. Due to the severe attenuation of molecule concentrations, there tends to be more errors when the receiver becomes farther from the transmitter. To solve this problem, relaying schemes need to be implemented to achieve reliable communications. In this letter, time-dependent molecular concentrations are utilised as the information carrier, which will be influenced by the noise and channel memory. The emission process is also considered. The relay node (RN) can decode messages, and forward them by sending either the same or a different kind of molecules as the transmitter. The performance is evaluated by deriving theoretical expressions as well as through simulations. Results show that the relaying scheme will bring significant benefits to the communication reliability.

The channel capacity and the bit error rate of ultra-wide bandwidth transmitted-reference systems are optimized with respect to time delay between the reference and the adjacent data pulses. Approximate and theoretical expressions for the signal-to-interference-plus-noise ratio are derived. Numerical results show that optimizing the receiver can provide a significant capacity improvement of up to 2.2 bits/s/GHz and a bit error rate performance gain of up to 2 dB in effective signal-to-noise ratio

This paper investigates the asymptotic BER performance of coherent optical wireless communication systems in Gamma-Gamma turbulence when applying the V-BLAST MIMO scheme. A new method is proposed to quantify the performance of the system and mathematical solutions for asymptotic BER performance are derived. Counterintuitive results are shown since the diversity gain of the V-BLAST MIMO system is equal to the number of the receivers. As a consequence, it is shown that when applying the V-BLAST MIMO scheme, the symbol rate per transmission can be equal to the number of transmitters with some cost to diversity gain. This means that we can simultaneously exploit the spatial multiplexing and diversity properties of the MIMO system to achieve a higher data rate than existing schemes in a channel that displays severe turbulence and moderate attenuation.

The fast frequency hopping optical CDMA with prime-hop codes (PHCs) provides great flexibility and increases spectral efficiency in comparison with direct sequence methods. Applying the spectrum-sliced incoherent source will further reduce the system cost. However, the dispersion in such an incoherent system becomes a limiting factor to the bit error rate. A novel adaptive PHC scheme to such systems is proposed in this article. The main impact of the scheme is to reduce the power loss and the bit error rate (BER) degradation due to higher-order dispersion. The impact of inherit beat noise in spectrum slicing systems is also alleviated. Performance comparisons between the adaptive PHC and original PHC schemes indicate that the former is more suitable for use in the considered incoherent system, accommodating up to 17% more users for a given BER. The proposed adaptive method can be universally applied to mitigate dispersion effects in the similar 2D OCDMA systems.

In underwater optical wireless communication (UOWC) channels, impulse response is widely used to describe the temporal dispersion of the received signals. In this paper, we propose a new function to model the impulse response in most realistic cases in UOWC channels. By exploiting the inherent properties of such channels, our newly proposed model is superior to the conventional weighted double gamma functions (WDGF) model in explaining the behavior of the channel. We use Monte Carlo simulation to verify that our newly proposed model has a better accuracy of numerical fitting in most cases. Therefore, this new modeling approach offers a more convenient way to evaluate the performance of different kinds of UOWC channels.\ud \ud

Generalized ultra-wide bandwidth (UWB) transmitted reference (TR) receivers proposed previously in the literature are improved with respect to the energy allocation in the data packet and the integration interval length in the correlator. The improvement refers to a best-effort technique to reduce the receiver bit error rate. Simulation results show that the improvement can provide a performance gain of up to 4.2 dB in signal-to-noise ratio. These results give useful guidance on the design of generalized UWB TR receivers.

An M-ary coded synchronous optical code-division multiple-access (O-CDMA) system with pulse-position modulation (PPM) is investigated. One novel class of optical spreading codes based on combinatorial designs is adopted in the multiplexing process. Their ideal correlation properties facilitate the discrimination between desired signals and jamming. However, the multiple-access interference (MAI) with high intensity significantly deteriorates the system performance even if the number of interferers is small. In this paper, we present an interference reduction technique for direct-detection O-CDMA to suppress the noise effect and increase the system capacity. The MAI from reference signals can be estimated by utilizing the uniform cross-correlation (CC) among its sequences and considerably cancelled out after the photodetection process. The upper bound on the error probability of optical synchronous PPM-CDMA is then derived. The proposed system is shown to be effective to improve the bit error performance and to alleviate the error floor when the number of simultaneous users and the received optical power are not appreciably small.

This paper introduces an incorporated spectral-amplitude coding (SAC) optical code-division multiple-access (OCDMA) scheme. One novel class of optical signature codes based on combinatorial designs is employed with M-ary pulse-position modulation (PPM) signaling to improve the system performance beyond the interference limit. A union upper bound on the bit error rate (BER) is derived and the performance characteristics are then discussed with a variety of system parameters. Furthermore, fuzzy logic (FL) control is proposed to provide tolerance of different degrees of reliability in multirate transmission and to achieve distinct service differentiation for multimedia applications. It is shown that the proposed system can effectively suppress noise effects and offer improved adaptation capabilities for multi-quality network requirements in comparison with systems without optimization.

The provision of acceptable service in the presence of failures and attacks is a major issue in the design of next generation dense wavelength division multiplexing (DWDM) networks. Survivability is provided by the establishment of redundant lightpaths for each connection request to protect the primary lightpaths. This paper presents a genetic algorithm (GA) solver for the routing and wavelength assignment problem with working and spare lightpaths. The proposed approach has been evaluated on both dedicated path protection and shared path protection. Simulation results show that the GA method is efficient and able to design DWDM survivable real-world optical mesh networks.

This article illustrates a microwave dielectric lens design using genetic programming (GP), which, to the best knowledge of the authors, is the first time GP has been applied to design a microwave dielectric lens. A phase-compensating single layer lens and a quarter-wave phase-compensating multilayer dielectric lens, which uses four types of materials and a zoned structure, was designed using GP. The dielectric lens shape was designed using GP strategy, with a random initial shape, to compensate for the phase error of the multilayer dielectric lens and to achieve the required performance. Standard GP (SGP) and hierarchical fair competition genetic programming (HFC-GP) was applied to obtain the solution. The results show that this novel method of microwave lens shape design using GP is both accurate and stable. In addition, the simulation results of using high frequency simulation software (HFSS) are illustrated and compared. (c) 2007 Wiley Periodicals, Inc.

Implant wireless body area networks (WBANs) are becoming increasingly significant for numerous applications in the healthcare and medical sectors. Here an in-body communication model is proposed, based on a 1 mm resolution mesh kneeling position inhomogeneous 30-year male body model in the 400 MHz medical implant communication service (MICS) band. Firstly, semi-empirical path loss models for numerous homogeneous tissues and a heterogeneous human body model are proposed. Then we investigate the bit error rate (BER) performance using the heterogeneous human body channel model. Coupled with link margin analysis, this model can be applied to future implementations and system design research work.

Underwater Wireless Sensor Networks (UWSNs) are used in applications such as mineral exploration and environmental monitoring, and must offer reliability and energy efficiency. These are related to each other in the sense that the former requires error-correction which in turn requires energy, consuming battery life in an environment where battery replacement and recharging are difficult. This chapter thus addresses the energy efficiency of three suitable error correction methods for UWSNs, namely Automatic Repeat Request (ARQ), Forward Error Correction (FEC) and Network Coding (NC). The performance of the schemes as a function of transmission distance is determined for various packet sizes by using models of attenuation and noise that represent the underwater environment. ARQ offers the lowest efficiency and NC the highest but there is a distance at which FEC becomes the best option rather than NC suggesting a hybrid FEC/NC method.

Molecule concentration is often used as the information carrier to accomplish diffusion-based molecular communications (DMC) among nano-machines. To achieve the optimal functionality, knowing the distance between the transmitter nano-machine (TN) and the receiver nano-machine (RN) is of high importance. In this paper, two distance estimation schemes are proposed based upon the RN-sensed concentration which changes with regards to the time and distance. The RN estimates the distance by means of measuring either the concentration-peak time or received concentration energy. Simulations are performed to compare the accuracy of each scheme and to discover how the diffusion channel and noise may influence the accuracy. Results show that both schemes will provide a beneficial enhancement to molecular communication systems.

This chapter discusses the structure of deterministic Ethernet which helps to improve the security and accessibility of services in a time critical communication system. Frame switching is the method of connecting frames to their destination. A disorganised frame switching network increases the fluctuation of application response times and creates weakness in a sensitive network. Dynamic frame traffic oscillation allows the frame workload to be more organised and manageable for networking by isolating external influences that disrupt network service. This concept, which we term Critical Networking, organises networks and reduces network resource wastage, such as overheads, thereby reducing application network frame delay by carefully planning the type of frame transmission and the available network resource. The frame traffic is handled by a network traffic oscillator (NTO), which creates deterministic time response in frame transmission. Both concepts when combined remove the need to assign arbitrary priority numbers in frames, and overheads for consecutive application transmissions and hides sensitive overhead information within every frame. The concept is illustrated using a simulation of real-time traffic in an airfield scenario.

Network management for optical networks faces additional security challenges that arise by using transparent optical network components in communication systems. While some available management mechanisms are applicable to different types of network architectures, many of these are not adequate for all-optical networks. These have unique features and requirements in terms of security and quality of service, thus requiring a much more targeted approach in terms of network management. In this article we consider management issues with particular emphasis on complications that arise due to the unique characteristics and peculiar behaviors of transparent network components. In particular, signal quality monitoring is still a major complication in all-optical networks. Despite new methods for detection and localization of attacks having been proposed, no robust standards or techniques exist to date for guaranteeing the quality of service in these networks. Therefore, sophisticated mechanisms that assist in managing and assessing the proper function of transparent network components are highly desirable. Accordingly, we present an algorithm for multiple attack localization and identification that can participate in some tasks for fault management of all-optical networks.\ud

The implementation of wavelength division multiplexing (WDM) in communication access networks is dependent upon the availability of low cost optical sources. One possible alternative to lasers is to employ slices of a broadband optical source obtained via optical filters, which may be tuneable. This paper considers the behaviour of such a spectrally sliced optical transmission system as a function of the bandwidth of a realistic receiver electrical filter for the first time. The treatment includes distortion from optical fibre dispersion over several kilometres of fibre. The optimum ratio between the electrical bandwidth and the optical bit rate is found to be ~0.6 for a fifth-order Bessel filter

The security characteristics of currently emerging all-optical networks display many unique features compared to traditional communication networks. In particular, network transparency raises many security vulnerabilities that differ substantially from conventional failures and should therefore be treated differently. One of the serious problems related to transparency lies in the fact that optical crosstalk is additive and can be exploited to perform service disruption attacks upon the network. Since these attacks can spread rapidly through the network, causing additional problems and triggering multiple alarms, they must be detected and identified at any point in the network where they may occur. However, to monitor all wavelength channels at several detection points into any node is likely to be very expensive. In this paper we provide formal specifications for optical crosstalk that can arise in optical cross-connect nodes. Based on these specifications, we propose an algorithm for localizing the sources of multiple attacks and identifying their nature in all-optical networks.

A new application of genetic algorithms (GAs) for feed point optimization of a coaxial probe fed E-shape microstrip patch antenna is presented. The GA shows excellent results for finding the best feed point in a given antenna structure. The method of moments is used in this paper, employing Rao-Wilton-Glisson basis functions. The simulation results show that the E-shape microstrip patch antenna performs well at similar to 2.11/GHz with the minimum return loss of approximately -17.1 dB. (c) 2006 Wiley Periodicals, Inc.

All-optical wavelength conversion based on multi-section semiconductor optical amplifiers (SOAs) in a symmetrical Mach-Zehnder interferometer (SMZI) is modeled for use in optical networks. It incorporates an enhanced SOA model that is implemented using the time domain transfer matrix approach and hence the overall numerical model determines simultaneously the wavelength and gain parameters for the wavelength converter. The overall model accurately predicts the optimal conditions for the SMZI arrangement in order to achieve the best results for the chirp, the phase inversion and the converted probe signal power. It is also demonstrated that large chirp and mismatch of the phase inversion reduces the eye opening ratio (EOR) which can seriously affect the performance of the wavelength converter to be used as a sub-system component in all-optical networks.

An analysis of the generation of harmonics for millimetre-wave signals using a Franz–Keldysh effect waveguide modulator is presented. The Franz–Keldysh electroabsorption is obtained via a method known to provide accurate results in comparison with experimental data. This is followed by an optimisation of the drive voltage in terms of the d.c. bias for a sinusoidal input. A spectrum rich in harmonics is produced and the fifth is considered in detail for device optimisation. The modulator considered is based on a large core multimode waveguide designed to yield a high coupling efficiency to single-mode fibres. The confinement factor, and hence the length, of the structure are determined via the effective index method. The resulting device could be used for the cost-effective production of millimetre-wave carriers via the harmonics generated whilst enabling the employment of electronics running at the speed of the fundamental.

A wavelength converter based on cross-phase modulation using semiconductor optical amplifiers (SOAs) in a symmetrical MZI is modelled. Since the model of the SOAs considers both amplitude and wavelength-dependent parameters simultaneously it provides an accurate prediction of the peak chirp variation for both inverting and non-inverting converted probe signals. The peak chirp variation and the eye-opening ratio are determined for ITU-T grid wavelength up- and down-conversion and they show a sharp dependence on the injection current of the SOAs. Optimal operating conditions for the wavelength converter are demonstrated in order to achieve nominal chirp on the output signal for either an inverting or non-inverting converted probe signal.

Underwater optical wireless has two distinct modes of communication depending on the choice of transmitter technology; short-ranged dispersive LED links (

The performance of duplex underwater optical wireless communication systems are limited by back-scattering of the transmitted light. This paper introduces a novel underwater wireless link design using hybrid optical/acoustic as a method to overcome it. The design comprises of highly directive, high-bandwidth optical uplinks from submersed AUVs or divers to a base station and a low bandwidth, wide-angle downlink. The limiting performance factors for the acoustic and optical aspects were found through respective channel modelling and SNRs; the maximum bitrate of the hybrid link is greater than a traditional acoustic link by a factor of 150. Main issues such as susceptibility to natural ocean variation, optical misalignment and acoustic latency are discussed.

The idea of a network traffic oscillator (NTO) is presented for dynamically adjusting to network conditions so as to ensure the best response time for all safety critical application payloads in a network. The context of the work is airport networking where the desire for greater interconnectivity coupled with Ethernet adoption makes the delivery of real-time deterministic service extremely challenging. The prevailing approach via the Enhanced Interior Gate Routing Protocol (EIGRP) is presented since it finds widespread commercial application for reliable data exchange. However, it still produces great variation in packet delivery times as a result of varying congestion and buffer delays. The NTO matches the transmission rates to the links in the network by its resonant nature an using as routing vector metric. Simulations of a typical airfield network show that the NTO delivers a reduction of over 25% in network response time for radar data transmissions with minimal response time variance. Moreover, only 1% of packets experience problematic transmission delays compared to 10% using EIGRP. The NTO thus offers real-time deterministic Ethernet performance for safety critical applications.

Performance analysis of Network Coding (NC) is becoming an increasingly important issue in today's data communication systems. This is because of its success in achieving the min-cut capacity of multicast networks, leading to throughput improvement at the destination nodes. The implementation of NC requires a thorough investigation of its impact on relevant queuing systems. In this paper, we analyze the behavior of an M/D/1 queuing system under a synchronous NC-based scenario; an intermediate node represented by a First-In-First-Out (FIFO) queue and a single server is configured so that it receives merged and coded packets from two streams. The probability density function (pdf) for the coded packets is derived. Analytical results show that the derived pdf of the coded packets follows a random general distribution, and extensive simulations are presented to verify the constructed distribution. Furthermore, measurements of the mean waiting time and server utilization for merged and coded packets in the FIFO queue are compared.

This paper provides results on an investigation concerning the application of five tailored Stop-and-Wait Automatic Repeat reQuest (SW-ARQ) schemes to a diffusion based molecular communication system. Each scheme is numerically simulated and evaluated to determine its performance with regards to average time cost and energy consumption. It is shown that all five schemes are beneficial depending upon the application scenario. Scheme 1 is the best choice for adjacent communications although, if a slightly higher energy budget can be afforded, schemes 2 and 3 will provide better performance than scheme 1 as the communication distance increases. Schemes 4 and 5 are designed to benefit scenarios with either a varying channel or for a channel with unknown parameters although will also benefit a static channel if again, further system energy can be utilised. This optimisation and trade-off between time and energy requirement for a complete successful transmission will become more important in future applications involving molecular communications where energy efficiency is a design consideration.