Direct Communication Link Research Articles

Performance Evaluation of a Power-Efficient and Robust 60 GHz Wireless Server-to-Server Datacenter Network

Datacenters have become the digital backbone of the modern world. To support the growing demands on bandwidth, datacenter networks (DCNs) consume an increasing amount of power. Additionally, the complex cabling in traditional datacenters poses design and maintenance challenges and increases the energy cost of the cooling infrastructure by obstructing the flow of chilled air. In this paper, we present a wireless server-to-server datacenter network architecture using millimeter-wave links to eliminate the need for power-hungry switching fabric of traditional fat-tree based datacenter networks. The server-to-server wireless datacenter network (S2S-WiDCN) architecture requires line-of-sight (LoS) between servers to establish direct communication links. However, in the presence of an obstruction such as an IT technician, the LoS may be blocked. To address this issue, we propose a novel obstruction-aware adaptive routing algorithm for S2S-WiDCN. We evaluate the performance of S2S-WiDCN in terms of traffic flow completion duration and throughput, with different kinds of datacenter traffic as well as in presence of obstruction to LoS links. We also compare the performance and power efficiency of S2S-WiDCN with the traditional fat tree DCN as well as a top-of-rack (ToR)-to-ToR wireless DCN.

Resilient Randomized Quantized Consensus

We consider the problem of multiagent consensus where some agents are subject to faults/attacks and might make updates arbitrarily. The network consists of agents taking integer-valued (i.e., quantized) states under directed communication links. The goal of the healthy normal agents is to form consensus in their state values, which may be disturbed by the non-normal, malicious agents. We develop update schemes to be equipped by the normal agents whose interactions are asynchronous and subject to nonuniform and time-varying time delays. In particular, we employ a variant of the so-called mean subsequence reduced algorithms, which have been long studied in computer science, where each normal agent ignores extreme values from its neighbors. We solve the resilient quantized consensus problems in the presence of totally/locally bounded adversarial agents and provide necessary and sufficient conditions in terms of the connectivity notion of graph robustness. Furthermore, it will be shown that randomization is essential both in quantization and in the updating times when normal agents interact in an asynchronous manner. The results are examined through a numerical example.

Cardinality improvement of Zero Cross Correlation (ZCC) code for OCDMA visible light communication system utilizing catenated-OFDM modulation scheme

In this paper, we proposed a new OCDMA-VLC system design utilizing new modulation scheme known as catenated-OFDM (orthogonal frequency division multiplexing) technique. The catenated-OFDM-OCDMA-VLC system is demonstrated by implementing Zero Cross Correlation (ZCC) code. ZCC code is the preferred code generation in OCDMA system as the effect of multiple access interference (MAI) can be cancelled out due to reduction in Phase Intensity Induced Noise (PIIN). In particular, the use of catenated-OFDM and its application in intensity modulation and direct detection fiber optic visible light communication link is theoretically investigated by taking into account all the noises contribute in the visible light spectrum. The theoretical results demonstrated that cardinality enhancement with doublefold, triplefold and fourfold increase in number of user for (Band = 2), (Band = 5) and (Band = 8) respectively compared to previous ZCC-VLC system designs. The results also indicates a good performance with high data rate up 10Gbps using proposed system which is predicted to be new considerable for upcoming OCDMA-VLC mobile communication system design.

Letter from Taiwan

Letter from Taiwan

Engaging customers in value co-creation or co-destruction online

PurposeThis paper aims to develop a theoretical model to understand co-creation/co-destruction of value through customer engagement in online channels. It also investigates the contributing factors.Design/methodology/approachThe qualitative approach uses the critical incidents technique to answer the research questions. The authors identify 350 critical incidents in which customers expressed online customer engagement-induced value co-creation or co-destruction experiences. The factors and resulting propositions are identified through data analysis. Data coding and analysis are facilitated by using MAXQDA 12.FindingsCo-creation through positively valenced engagement behaviors may occur when customers are delighted, feel valued, experience reciprocity, receive organizational incentives, are solicited for feedback, can count on service recovery efforts and interact with helpful, empathetic, polite and responsive employees. Co-destruction through negatively valenced engagement behaviors emerges from rude employee behaviors, indifference, confrontation with company representatives, technological failure, the lack of complaint outlets and customers’ desire for revenge.Practical implicationsSelecting and training employees to be helpful, polite, responsive and empathetic toward online visitors can trigger co-creation. Communication between firms and customers should boost customer approval and delight. Organizations can offer incentives, reliable service delivery and a recovery design to stimulate visitor participation. Soliciting feedback requires sound technological support and direct communication links with visitors.Originality/valueThis study presents the conditions and framework contributing to the duality of customer engagement-induced co-creation and co-destruction values in online channels from the customer, organizational, employee, service design and technological perspectives. It also addresses how value is co-created or co-destructed through examples.

Collaborative Multimedia Source-Protocol Coordination: A Cross-Layer QoE Study in Modern Wireless Networks

Multiple image/video source neighbors in modern wireless systems such as device-to-device (D2D) networks can significantly improve multimedia quality of experience (QoE) in content sharing. However, the exploration of multisource diversity in multimedia communications has largely been overlooked in the past. In this paper, we propose a new scheme to improve user equipment's (UE) multimedia QoE by optimizing the source traffic dispatching and resource allocation strategies from multiple UE sources in cross-layer wireless D2D networks while assuring the latency constraint. This approach results in two major contributions. First, the proposed approach optimally controls the source server traffic for each multimedia packet with regard to distortion reduction (e.g., quality contribution) and the channel conditions. Second, optimal packet retry limits are adjusted on each direct D2D communication link to achieve effective but unequal resource allocation. Simulation results show that the cross-layer collaborative source-level traffic control and protocol-level resource optimization strategy improve D2D multimedia transmission quality.

Optimal and Suboptimal Resource Sharing Schemes for Underlaid D2D Communications

Being attracted by offloading local services to adjacent users, the operator allows two proximity users to build up a direct communication link, which is a new supplementary to current cellular network and called device-to-device (D2D) communication. Due to the low power radiation and occupation of the licensed band, D2D users can share the resource with cellular users fully controlled by cellular network to improve the local frequency efficiency. Due to the combinatorial and nonconvex nature of formulated problem, solving such problem optimally is a nearly impossible task. However, we propose an upper bound computation method, which can be seen as a benchmark for resource sharing scheme design. We also propose another two suboptimal schemes, i.e., suboptimal resource sharing scheme I with parallel computation structure which can achieve optimality in the most cases, and suboptimal resource sharing scheme II with relatively low complexity at the cost of acceptable performance loss. Moreover, through extensive numerical results, we find that both suboptimal resource sharing schemes can outperform the existed works. To conclude, our work actually provide a tradeoff between complexity and performance.

Performance Analysis of Overlay Spectrum Sharing in Hybrid Satellite-Terrestrial Systems With Secondary Network Selection

In this paper, we study a hybrid satellite-terrestrial spectrum sharing system (HSTSSS) in which multiple terrestrial secondary networks cooperate with a primary satellite network for dynamic spectrum access. For complexity-aware HSTSSS design, we propose an amplify-and-forward-based overlay spectrum sharing protocol using partial and opportunistic secondary network selection schemes. The secondary network selection aims to minimize the outage probability of the primary satellite system and, thereby, to explore spectrum sharing opportunities. With the overlay approach, the selected secondary network allocates part of its power to relay the satellite signal and utilizes the remaining power to transmit its own signal. Considering Shadowed-Rician fading for satellite links, and Nakagami- ${m}$ as well as Rician fading for terrestrial links, we derive closed-form expressions for the outage probability of both primary and secondary networks, and examine their achievable diversity orders. Numerical and simulation results validate our analysis and highlight the performance gains of the proposed schemes for an HSTSSS with and without a direct satellite primary communication link.

The Soviet use of the Moscow–Washington Hotline in the Six-Day War

This article examines the role the Moscow–Washington Hotline played in the 1967 Six-Day War, focusing on the Soviet side. We argue that the Soviet Union used the Direct Communication Link much more broadly than had been intended when the Hotline was agreed on in 1963 mainly because Moscow did not assign the Hotline any special diplomatic significance. We also show that the Hotline is a poor channel for crisis negotiations, and its efficacy as a communication tool is compromised if regular diplomatic channels cannot match its speed. Finally, we challenge the existing debate in the historiography of the Six-Day War, arguing for the importance of studying the implications of Soviet behaviour rather than Soviet intentions.

Performance analysis of averaging based distributed estimation algorithm with additive quantization model

In this paper, we consider the distributed sensor fusion problem over sensor networks under directed communication links and bandwidth constraint. We investigate the impact of the additive quantization model on the proposed two-stage averaging based algorithm. Existing works on the effect of the additive model show that convergence can be guaranteed only if the quantization error variances form a convergent series. We show that the proposed algorithm achieves the performance of the optimal centralized estimate even if the quantization error variances are not vanishing. This is guaranteed by establishing a law of the iterated logarithm for weighted sums of independent random vectors. Moreover, an explicit bound of the convergence rate of the proposed algorithm is given to quantify its almost sure performance.

A Bidirectional Brain-Machine Interface Featuring a Neuromorphic Hardware Decoder.

Bidirectional brain-machine interfaces (BMIs) establish a two-way direct communication link between the brain and the external world. A decoder translates recorded neural activity into motor commands and an encoder delivers sensory information collected from the environment directly to the brain creating a closed-loop system. These two modules are typically integrated in bulky external devices. However, the clinical support of patients with severe motor and sensory deficits requires compact, low-power, and fully implantable systems that can decode neural signals to control external devices. As a first step toward this goal, we developed a modular bidirectional BMI setup that uses a compact neuromorphic processor as a decoder. On this chip we implemented a network of spiking neurons built using its ultra-low-power mixed-signal analog/digital circuits. On-chip on-line spike-timing-dependent plasticity synapse circuits enabled the network to learn to decode neural signals recorded from the brain into motor outputs controlling the movements of an external device. The modularity of the BMI allowed us to tune the individual components of the setup without modifying the whole system. In this paper, we present the features of this modular BMI and describe how we configured the network of spiking neuron circuits to implement the decoder and to coordinate it with the encoder in an experimental BMI paradigm that connects bidirectionally the brain of an anesthetized rat with an external object. We show that the chip learned the decoding task correctly, allowing the interfaced brain to control the object's trajectories robustly. Based on our demonstration, we propose that neuromorphic technology is mature enough for the development of BMI modules that are sufficiently low-power and compact, while being highly computationally powerful and adaptive.

GNU Radio Based Testbed (GRaTe-BED) for Evaluating the Communication Link of Unmanned Aerial Systems

Abstract UAS (Unmanned Aerial Systems) are commonly used in 3D (dull, dirty and dangerous) missions, because these are not endangering the operators life, while reduce maintenance costs and increase maneuvering capabilities. Despite of these advantages we should consider the possible vulnerabilities of this technology as well. Unmanned vehicles can be controlled via direct communication link, or they can work in a preprogrammed mode. Usually the preprogrammed mode is based on radio navigation systems, so we can draw a conclusion that both depend on the RF environment. In this paper I analyze a possibility to effectively evaluate the communication link of an UAS. Developers have to consider several key factors (type of operation, endurance, payload type and size, propulsion, communication link, etc.) during the development process. They are also responsible that the final product meets the predefined requirements. On the other side commercial UAS owners should have a possibility to compare and evaluate the UAS before the acquisition. Finally, operators and frequency management entities need tools to diagnose the possible sources of interference regarding the unmanned vehicles. To understand the consequences of interference in the RF spectrum we have to be able to measure the quality of the communication link in different usage scenarios. In my research I evaluate the usage of SDRs (Software Defined Radios) in RF Test and Evaluation processes. After analyzing the possibilities for a flexible testbed, I demonstrate the usability with some measurements in the GNU Radio signal processing framework.

Improved Precise Fault Diagnosis Algorithm for Hypercube-Like Systems Based on the Comparison Diagnosis Model

Multiprocessor systems are being increasingly adopted and the system reliability is an important perspective for multiprocessor systems. The fault diagnosis has become crucial for achieving high reliability in multiprocessor systems. The precise fault diagnosis diagnoses all processors correctly. In the comparison-based model, it allows a processor to perform diagnosis by contrasting the responses from a pair of neighboring processors through sending the identical assignment. On the basis of comparison-based model, Sengupta and Dahbura (“On self-diagnosable multiprocessor systems: diagnosis by the comparison approach,” IEEE Transaction on Computers, vol. 41, no. 11, pp. 1386–1396, 1992) put forward the MM* model, any processor c diagnoses two processors c1 and c2 if c has direct communication links to them. Sengupta and Dahbura also designed an O(N5)-time precise fault diagnosis algorithm to diagnose faulty processors for general topologies by using the MM* model, where N is the cardinality of processor set in multiprocessor systems. Lately, Ye and Hsieh (“A scalable comparison-based diagnosis algorithm for hypercube-like net-works,” IEEE Transaction on Reliability, vol. 62, no. 4, pp. 789–799, 2013) devised an precise fault diagnosis algorithm to diagnose all faulty processors for hypercube-like networks by using the MM* model with O(N(log2N)2) time complexity. On the basis of Hamiltonian cycle properties, we improve the aforementioned results by presenting an O(N)-time precise fault diagnosis algorithm to diagnose all faulty processors for hypercube-like networks by using the MM* model.

Secrecy Outage Probability of a Distributed Multi-Antenna Cooperative Communication System

A distributed multi-antenna cooperative communication system with amplify-and-forward mode for secure communication in the presence of an eavesdropper is considered. In the communication system, there is no direct communication link between the transmitter and the intended receiver, and all nodes except relay nodes are equipped with multi-antenna. The secrecy capacity of this multiple input multiple output multiple eavesdropper system is investigated. The communication security depends on whether the noise on wiretap channel is stronger than that on main channel or not. The secrecy outage behavior of the flat Rayleigh fading channel is discussed and a relation between the strength of the channel noise and the secrecy outage probability is obtained. It is demonstrated that the secrecy outage probability is closely related to the channel noise strength and the number of the relay nodes. The thresholds for the noises received by legitimate receiver and eavesdropper are suggested, which is useful to design the secure distributed multi-antenna cooperative communication system.

ASEAN and the ADMM-Plus: Balancing between Strategic Imperatives and Functionality

The ASEAN Defence Ministers' Meeting (ADMM) was established in 2006 to an institutionalized mechanism for the ASEAN defense establishments to strengthen trust and regional security cooperation.1 While the ADMM remains a platform for intraregional cooperation, the ADMM-Plus was inaugurated in 2010 to facilitate ASEAN's engagement with extraregional security partners (the so-called Plus countries). The ADMM-Plus aims to provide a platform for ASEAN and its eight Dialogue Partners to strengthen security and defense cooperation for peace, stability and development in the region.2 Originally, the ADMM-Plus was conceptualized to hold meetings once every three years, but the ASEAN defense ministers decided at the 6th ADMM in Phnom Penh to reduce the interval to every two years. To date, the ADMM-Plus has met three times: in 2010, 2013, and 2015.This essay discusses the strategic utility of the ADMM-Plus for ASEAN. The first part provides a cursory review of the development of the grouping and its relationship with the ADMM and the Shangri-La Dialogue. This is followed by a discussion of how ASEAN views the ADMM-Plus and an analysis of ASEAN's leadership and centrality within this multilateral framework. The essay concludes by outlining four challenges and issues for the ADMM-Plus to ponder in the immediate future.The Nexus between the ADMM and the ADMM-PlusThe fact that the ADMM was established twelve years after the ASEAN Regional Forum (ARF) demonstrated ASEAN's cautious approach toward establishing security regimes in the region. At the same time, it also underlined ASEAN's increasing comfort in tackling security-related issues. Attended and led by states' foreign affairs officials, the ARF was, until then, the sole region-wide security forum. However, its unwieldy membership-which comprises 27 countries, ranging from Australia to Vietnam and including states not usually associated with Southeast Asian security such as Mongolia, Pakistan, and Sri Lanka- reinforces the ARF's reputation as a talk shop and diminishes its functional utility for security cooperation.The ADMM added a new dimension to regional security by moving it from the diplomatic realm to one that is functional. For the first time since ASEAN's inception in 1967, the military establishment was at the fore instead of playing a supporting role. This was also the first time that the relationship among the ten ASEAN defense establishments was formalized in a regional framework. Although the ADMM arose from the ASEAN Security Community, it will not evolve into a military pact. Some of its recent achievements, such as the peacekeeping centers network, direct communications link, and logistics support framework, indicate that the ADMM is satisfied with finding modalities for ASEAN militaries to build trust through an intensification of cross-national interactions and cooperation. The development of the ADMM-Plus mimics the approach taken by the ADMM to improve institutional efficiency by reducing the number of collaborators and focusing on building a practical and jointly acceptable platform for the militaries to engage each other in an open and sustained manner.The ADMM-Plus also distinguishes itself from the Shangri-La Dialogue in that it goes beyond the diplomacy of defense and places a premium on function over ceremony. The Shangri-La Dialogue is an important part of the regional architecture and stands out primarily for its bilateral discussions and consultations. In comparison, the ADMM-Plus's scope is multilateral and regional. The two institutions perform complementary functions, but the net impact of the ADMM-Plus will be more measurable because of its singular geographic focus on Southeast Asia, whereas the Shangri-La Dialogue defines Asia in the broadest sense.Why Is the ADMM-Plus Important for ASEAN?The ADMM-Plus provides an institutionalized framework for ASEAN member states to diversify and broaden their scope for military cooperation. …

A tutorial on network coded cooperation

Network Coding (NC) can significantly help increase the efficient use of network resources. However, directly applying NC to wireless networks is not an effective design solution. Wireless channels are prone to bit errors due to fading, possibly generating erroneous decisions at the relay nodes while applying NC. Furthermore, the broadcast nature of wireless channels may provide a direct communication link between source and destination nodes. In order to combat fading channel impairments, and also to exploit the inherent spatial diversity provided through the direct link, network coded cooperation (NCC) techniques should be incorporated to the NC systems for wireless networks. This tutorial provides an overview of the state-of-the-art in the NCC systems, combining the powerful tools of NC and cooperative communication, in order to increase data transmission rates and robustness of multiple source wireless networks.

On the Degrees of Freedom of the Two-Cell Two-Hop MIMO Network With Dedicated and Shared Relays

We investigate the degrees of freedom (DoF) of the downlink of a cellular relay network. In this network, two base stations transmit to two mobile stations via relays due to the absence of a direct communication link. Each base station and mobile station is equipped with $M$ antennas. Each base station has two messages; one to each mobile station, and uses two relays to transmit to the mobile stations. The relays are half duplex, decode-and-forward and equipped with $N$ antennas each. We consider two configurations of the relays; shared and dedicated relays. In the shared relays configuration, the system has two relays that are used by both base stations. Whereas, in the dedicated relays configuration, each base station has two dedicated relays, i.e., the system has four relays. We consider all possible relaying schemes where the base stations can use the relays either simultaneously or alternately. We derive an upper bound on the DoF achievable by each relaying scheme as a function of the ratio between $N$ and $M$ . Furthermore, we propose an achievable scheme that uses interference alignment to achieve the upper bound on the DoF for the shared relays configuration, and for all values of $M$ and $N$ except for $1 in the dedicated relays configuration.

COOPERATIVE RELAY PROTOTYPE DEVELOPMENT AND PERFORMANCE MEASUREMENT

To meet the demand for high data rate, the wireless cellular system technology has grown in a steady pace in recent years. However, due to multipath fading, shadowing effects and path loss, the wireless communication links are prone to errors. To improve the communication link, at the cell edge and shadowed environment, cooperative relaying scheme has been proposed. In cooperative relaying, an additional node is placed between the source and destination terminals, to provide redundant path for data transmission. However, existing literature on cooperative relaying only investigates the system performance through theoretical simulations. The real world performance remains unknown because of the lack of prototypes for field testing and measurement. This work focuses on the development of an amplify-and-forward (AF) cooperative relaying prototype. The prototype is developed using the LabVIEW system development platform and the implementations are carried out on Universal Software Radio Peripheral (USRP). The performance of the AF based cooperative relaying prototype is measured in terms of the bit error rate (BER) and compared with the direct communication link without relay. The measured results show that cooperative relay assisted communication achieves significant improvement in terms of signal reliability, coverage distance and power efficiency.

Distributed Secret Dissemination Across a Network

Shamir's $(n,k)$ threshold secret sharing is an important component of several cryptographic protocols, such as those for secure multiparty-computation and key management. These protocols typically assume the presence of direct communication links from the dealer to all participants, in which case the dealer can directly pass the shares of the secret to each participant. In this paper, we consider the problem of secret sharing when the dealer does not have direct communication links to all the participants, and instead, the dealer and the participants form a general network. Existing methods are based on separate secure message transmissions from the dealer to each participant, requiring considerable coordination and communication in the network. We present a distributed algorithm for disseminating shares over a network, which we call the “SNEAK” algorithm, requiring each node to know only the identities of its one-hop neighbors. While SNEAK imposes a stronger condition on the network by requiring the dealer to be what we call $k$ -propagating rather than $k$ -connected as required by the existing solutions, we show that in addition to being distributed, it achieves significant reduction in the amount of communication and the randomness required. We also derive information-theoretic lower bounds on the amount of communication for secret sharing over networks, which may be of independent interest.

Connectivity Analysis of Cognitive Radio Ad-hoc Networks with Shadow Fading

In this paper, we analyze the connectivity of cognitive radio ad-hoc networks in a log-normal shadow fading environment. Considering secondary user and primary user’s locations and primary user’s active state are randomly distributed according to a homogeneous Poisson process and taking into account the spectrum sensing efficiency of secondary user, we derive mathematical models to investigate the connectivity of cognitive radio ad-hoc networks in three aspects and compare with the connectivity of ad-hoc networks. First, from the viewpoint of a secondary user, we study the communication probability of that secondary user. Second, we examine the possibility that two secondary users can establish a direct communication link between them. Finally, we extend to the case of finding the probability that two arbitrary secondary users can communicate via multi-hop path. We verify the correctness of our analytical approach by comparing with simulations. The numerical results show that in cognitive radio ad-hoc networks, high fading variance helps to remarkably improve connectivity behavior in the same condition of secondary user’s density and primary user’s average active rate. Furthermore, the impact of shadowing on wireless connection probability dominates that of primary user’s average active rate. Finally, the spectrum sensing efficiency of secondary user significantly impacts the connectivity features. The analysis in this paper provides an efficient way for system designers to characterize and optimize the connectivity of cognitive radio ad-hoc networks in practical wireless environment.