The introduction of several new unlicensed spectrum bands in Beyond 5G (B5G) and HetNet enables unprecedented data rates, ultra-low latency, and the capacity to support vast numbers of connected devices. However, to fully realize the potential of unlicensed spectrum bands, efficient management is essential. Traditionally, managing unlicensed bands has focused on controlling contention and interference, often using protocols like LTE-U and Listen Before Talk (LBT). Yet, because unlicensed spectrum is shared, achieving fair usage across users remains a challenge. In this paper, we present a decentralized approach for managing unlicensed spectrum in B5G HetNets. We propose a population-based spectrum sharing with soft-threshold variable to reduce hoarding and to improve fairness. The resource sharing logic is implemented through smart contract to facilitate fair and efficient spectrum sharing among coexisting base stations. Simulations comparing different methods, including fairness-enabled and inter-cell LBT approaches, reveal that our solution reduces both spectrum hoarding and rejection rates compared to solutions that do not use fair-sharing.

In this paper, we address the problem of service function chaining in a network and present a solution that tackles this problem in Software Defined Data Centers. Service function chaining can broadly be categorized into middlebox placement in a network and packet steering through middleboxes. We address packet steering in this paper. In particular, we present a One Pass Packet Steering (OPPS) approach for use in multi-subscriber environments. We show algorithms and proof of concept implementation using emulation. We examine how OPPS can benefit from Software Defined Data Center architecture to overcome challenges that occur in simple linear networks. Our results show how OPPS can utilize a lesser number of middleboxes and achieve the same hop counts as a reference model which has been described in previous work as ideal, without violating the subscriber's policy chain.

Future vehicular networks in the emerging era of 5G will be characterized by ubiquitous connectivity across heterogeneous networks (HetNets) while maintaining their required Quality of Service (QoS). 5G will introduce numerous small cells, implementing extreme densification, in order to increase capacity. In the context of vehicular networks, this translates to multiple handoffs occurring within seconds. It is critical that an efficient mobility management solution is devised for 5G vehicular networks to maintain seamless connectivity. In this paper, we investigate the use of Multiprotocol Label Switching (MPLS) based micro-mobility management to 5G vehicular visible light communication networks. MPLS has the advantage of fast and efficient packet forwarding. This paper proposes a hierarchical Integrated Services based MPLS architecture to overcome the limitations found in existing MPLS based micro-mobility schemes in terms of handoff latency, registration cost and explicit QoS support necessary for 5G vehicular communication networks.

This paper predicts the ability to externally control the firing times of a cortical neuron whose behavior follows the Izhikevich neuron model. The Izhikevich neuron model provides an efficient and biologically plausible method to track a cortical neuron's membrane potential and its firing times. The external control is a simple optogenetic model represented by a constant current source that can be turned on or off. This paper considers a firing frequency that is sufficiently low for the membrane potential to return to its resting potential after it fires. The time required for the neuron to charge and for the neuron to recover to the resting potential are fitted to functions of the Izhikevich neuron model parameters. Results show that linear functions of the model parameters can be used to predict the charging times with some accuracy and are sufficient to estimate the highest firing frequency achievable without interspike interference.

Optogenetics is an emerging field of neuroscience where neurons are genetically modified to express light-sensitive receptors that enable external control over when the neurons fire. Given the prominence of neuronal signaling within the brain and throughout the body, optogenetics has significant potential to improve the understanding of the nervous system and to develop treatments for neurological diseases. This paper uses a simple optogenetic model to compare the timing distortion between a randomly-generated target spike sequence and an externally-stimulated neuron spike sequence. The distortion is measured by filtering each sequence and finding the root mean square error between the two filter outputs. The expected distortion is derived in closed form when the target sequence generation rate is sufficiently low. Derivations are verified via simulations.

Bacteria populations rely on mechanisms such as quorum sensing to coordinate complex tasks that cannot be achieved by a single bacterium. Quorum sensing is used to measure the local bacteria population density, and it controls cooperation by ensuring that a bacterium only commits the resources for cooperation when it expects its neighbors to reciprocate. This paper proposes a simple model for sharing a resource in a bacterial environment, where knowledge of the population influences each bacterium's behavior. Game theory is used to model the behavioral dynamics, where the net payoff (i.e., utility) for each bacterium is a function of its current behavior and that of the other bacteria. The game is first evaluated with perfect knowledge of the population. Then, the unreliability of diffusion introduces uncertainty in the local population estimate and changes the perceived payoffs. The results demonstrate the sensitivity to the system parameters and how population uncertainty can overcome a lack of explicit coordination.

This paper presents an analytical comparison of active and passive receiver models in diffusive molecular communication. In the active model, molecules are absorbed when they collide with the receiver surface. In the passive model, the receiver is a virtual boundary that does not affect molecule behavior. Two approaches are presented to derive transforms between the receiver signals. As an example, two models for an unbounded diffusion-only molecular communication system with a spherical receiver are unified. As time increases in the three-dimensional system, the transform functions have constant scaling factors, such that the receiver models are effectively equivalent. Methods are presented to enable the transformation of stochastic simulations, which are used to verify the transforms and demonstrate that transforming the simulation of a passive receiver can be more efficient and more accurate than the direct simulation of an absorbing receiver.

Abstract Wireless sensor networks (WSNs) are getting popular for their deployment in unattended environments, where a registered user can log in to the network and access data collected from the desired sensor. Because of limited resources and computation power in sensor nodes, an authentication protocol should be simple and efficient. M.L. Das proposed a two‐factor authentication scheme for WSNs. Because his scheme uses only one‐way hash function and XOR operation, it is well suited for resource‐constrained environments. Because of some flaws in Das's scheme, several improved schemes have been introduced. In this paper, we show that Das's scheme and its derivatives not only have security imperfections but also do not provide key agreement. To overcome their security shortcomings, we propose a novel user authentication scheme with key agreement for WSN. We furnish security analysis of the proposed protocol to show its robustness to various attacks as well as analyze its performance to determine its efficiency. We provide protocol analysis and verification of the proposed protocol. Compared with the existing schemes, it is more robust and offers better security. Copyright © 2012 John Wiley & Sons, Ltd.

Location privacy is an important issue in vehicular networks since knowledge of a vehicle's location can result in leakage of sensitive information. A way to protect vehicles' location privacy is to have them change their pseudonyms in pre-determined regions known as mix-zones. However, selfish users may not change their pseudonyms because of the overhead occurring in this process. This could jeopardize the location privacy of those users who are in need of changing their pseudonyms. In order to encourage users to cooperate in changing their pseudonyms, we propose a method named Reputation-based Pseudonym Change for Location Privacy (RPCLP). With RPCLP, users earn reputation “credit” by implementing a change of pseudonym. Performance analysis shows that the RPCLP scheme not only motivates selfish users to cooperate with each other, but also reduces overhead while maintaining the desired location privacy.

A way to protect vehicles' location privacy under vehicular networks is to have them change their pseudonyms in pre-determined regions known as fixed mix-zones. However, pre-determined regions make pseudonym changes lack of flexibility. In this paper, we present a novel method named Pseudonym Changes based on Candidate-location-list (PCC). In PCC, a vehicle can form a mix-zone dynamically and change its pseudonym with the help of the candidate-location-list. We also provide the anonymity of our PCC and investigate it by simulations. Simulations based analysis show that our PCC has a good anonymity, low process time and high successful rate.

The low-power, low-rate ZigBee wireless sensor networks are vulnerable to the interference of collocated Wi-Fi wireless local area networks (WLAN). The results acquired through our extensive experimental studies on ZigBee-WLAN coexistence indicate that ZigBee connections may experience severe packet losses, caused by combined effect of interference and relatively long receive to transmit (RX-TX) turnaround time in ZigBee devices, even when the Wi-Fi and ZigBee devices are able to detect each other's signal and apply CSMA/CA algorithm accordingly. This paper proposes a novel Adaptive Preamble Padding with Retransmission Control (APPRC) technique for ZigBee devices to address this issue, meet certain packet loss rate (PLR) requirement, and improve packet transmission efficiency when they are suffering time varying interference from the collocated WLAN. The experimental performance evaluation results showed that the proposed APPRC technique can achieve significantly higher transmission efficiency while satisfying PLR requirements of sensing applications than packet retransmission. The technique described in this paper is patent pending.

Recent studies have shown that the low-power ZigBee based wireless sensor networks (WSN) are vulnerable to the interference generated by nodes of Wi-Fi wireless local area networks (WLAN). Mutual interference can be mitigated at nodes of either technology when energy detection (ED) is enabled in clear channel assessment (CCA). From our experimental studies on ZigBee and Wi-Fi coexistence issue, it is determined that a significant amount of ZigBee packet losses occur due to the Wi-Fi interference induced corruption of the physical layer header of ZigBee packets, which could happen even when the ED mechanisms of the Wi-Fi and ZigBee devices are able to detect each other's signal and CSMA/CA algorithms are applied accordingly. To study this phenomenon, a series of experiments were carried out, followed by thorough analysis of the recorded data. The study led to the design of a simple but effective technique named Protective Dummy-byte Preamble Padding (PDBPP) that improves the performance of ZigBee packet transmission in terms of packet loss rate (PLR) and transmission efficiency. The experimental performance evaluation results confirmed the effectiveness of PDBPP in improving PLR and transmission efficiency of a ZigBee network exposed to interference generated by collocated WLAN. Some material in this paper is part of a pending patent.

Recent studies have shown that low-power ZigBee based wireless sensor networks (WSN) are vulnerable to the interference generated by Wi-Fi nodes. In this study, the effects of energy detection (ED) mechanism in clear channel assessment (CCA) of ZigBee transmitter under 802.11g Wi-Fi interference have been evaluated through experimentation. To improve the performance of ZigBee packet transmission, a preliminary adaptive mechanism is implemented and evaluated in our testbed.

The low-power, low-rate ZigBee/IEEE 802.15.4 wireless sensor network (WSN) is vulnerable to the interference from a collocated wireless local area network (WLAN), which operates with considerably higher power in the same 2.4GHz Industrial, Scientific, and Medical (ISM) band. In this paper, a novel and effective Interference Aware Adaptive Clear Channel Assessment (IAACCA) technique is proposed to countermeasure the presence of interference with consequence to improve the performance of packet transmission between ZigBee nodes. The performance evaluation has been done through experimentation performed on a testbed implemented by the authors.

A Smart Grid is the modernization of the electricity grid using communication technology with the prime goals of reducing energy consumption as well as cost increasing reliability and creating new services for all participants. It comprises key components such as Advanced Metering Infrastructure (AMI) that includes Neighborhood area network (NAN). When multi-hopping is considered in wireless communication, especially in WiFi and ZigBee, the range of communication can be extended to communicate with the gateway collector in AMI network. Wireless mesh AMI network may have smart meters, NAN gateway, and fixed as well as mobile repeaters. Though many techniques have been developed to secure on-demand routing protocols in wireless multi-hop ad hoc networks, these protocols have shortcomings. In this paper, we propose an efficient and robust security mechanism for multipath routing protocol in wireless mesh AMI networks. We have analyzed its robustness to various attacks. The simulation results show that the proposed mechanism is better than existing secure routing protocols.

Radio Frequency Identification (RFID) technology is promising technology in ubiquitous computing area. RFID is used for various applications, ranging from inventory systems to supply chain management solutions such as vehicle fleet management. In supply chain management system, RFID tag is used to identify the object, to which it is attached, without any physical contact in various locations. This makes tags susceptible to information leak. Thus security and privacy issues remain a major issue. Suitability of public key cryptography solutions in RFID system is open research problem. In recent years, practicability of asymmetric cryptography on RFID applications has been discussed. Though EC-GPS scheme allows compact implementation on a tag, it has several flaws. In this paper, we propose robust RFID authentication scheme for supply chain process using improved EC-GPS. We have provided security proof, security analysis and performance evaluation of the proposed scheme to show its robustness.

Plug-in electric vehicles (PEVs) reduce greenhouse gas emission by using power from the electric grid. PEVs are considered distributed energy resources and mobile storage devices, which require two-way communication standards to communicate with emerging Smart Grid infrastructure. Due to frequent mobility of PEVs, inter-utility real-time data communication is critical to the operation of interconnected systems in Vehicle-to-Grid (V2G) infrastructure. Interoperability and security considerations of V2G infrastructure components are decisive for widespread deployment of PEVs. In this paper, we propose multi-domain network architecture for V2G infrastructure which includes comprehensive hybrid public key infrastructure using hierarchical and peer-to-peer cross-certifications. We present system and performance analysis of the proposed security architecture.

Due to the broadcasting nature of wireless sensor networks, it is relatively easy for an adversary to discover the sinks' location through traffic volume analysis. Traditional encryption and authentication methods are not effective to preserve privacy of a sink's location from a global adversary, capably of monitoring the traffic activity of the network. In this paper, we propose the Sink Location Privacy Protection Protocol (SLPP), which in addition to been effective in achieving its design objective it is also easy to implement. In order to confuse a local or global adversary, each node generates fake messages, the number of which is dependent on the number of the node's children. Simulation results demonstrate clearly that the SLPP protocol can hide effectively the sink's location. However, what is important and interesting is that although transmission of fake messages consumes additional energy from nodes, the network's lifetime is not impacted.

Plug-in electric vehicles (PEVs) will not only have a substantial influence on the emerging smart grid system but also create numerous challenges for the utility and customer to deal with their connections and charging. Authentication and authorization processes are critical elements to enable mass deployment of charging stations and to provide authorized customers to access the charging facility. Works on authentication system for PEV charging infrastructure are limited, and are mainly based on centralized architectures. In this paper, we propose a comprehensive decentralized authentication mechanism for PEV charging infrastructure in order to overcome shortcomings of the centralized authentication system and to provide robust authentication in multi-server environment. We present system analysis including analysis of security and functional requirements. Compared to the prevailing centralized scheme, the proposed system reduces authentication latency and is more efficient and robust.

In the paper, the uncertainty of trust is transformed into a probability vector denoting the probability distribution over possible trust levels of an entity that is hidden from observation but determined by its expected performance. We propose the use of Poisson Hidden Markov Models (PHMMs) for estimating the trust for entities in wireless environments, in which the Poisson distribution is used to describe the occurrences of behavioral patterns in peer-to-peer interactions. PHMMs allow us to explicitly consider an entity's unobserved trustworthiness that influences it's observed behaviors. As well, the hidden Markov process is associated with a Bonus-Malus System that is used to reduce the computational complexity of parameter estimations involved. An application of the model in the scenario of detection of probabilistic packet dropping attack has been investigated. The simulations demonstrate that the approach is capable of accurately estimating the (hidden) trust states probability distribution as well as the expected performance for the entities in the networks through their observed behaviors.

Using discrete-time Markov chains to analyze the performance of contention-based medium access control (MAC) protocols has been a common practice since its initial proposal by Bianchi in his seminal paper published in 2000. The way these methods work is by modeling each individual node competing for the medium in a wireless network as a Markov chain. Performance metrics of the whole system, such as throughput, delays and losses, can then be obtained from the model. However, these methods implicitly assume that Markov chains modeling individual nodes are independent from each other, which is not necessarily true in most situations. In this work we propose a more realistic model in which the whole network with all of its nodes is modeled using a single Markov chain, and in which assuming independence is no longer necessary. We reduce the complexity of the problem, both in processing and memory requirements, by taking advantage of its inherent symmetry, which allows us to work with only a few selected representative states. We evaluate how results from both types of methods compare to each other and to simulations. Our findings show that the old method has a very poor performance as compared to the new one.

A distributed trust evaluation model is presented for MANETs by which uncertainties of trust are transformed into probability vectors giving the probability distribution of trust levels. The system evolves over time as a finite-state Markov process with variant transition matrixes. We attempt to predict the trustworthiness values of entities that are determined by their inherent error patterns. The Markov process is associated to a Bonus-Malus System and controlled by the estimated error patterns of individual entities involved. As well, an iteration algorithm is designed to prevent inaccurate predictions for trust values because of the properties of Markov process. The simulation results demonstrate that our model is able to predict local trust successfully for entities in MANETs by estimating their actual error patterns accurately.

Wireless sensor networks (WSNs) are considered due to the ubiquitous nature, ease of deployment, and wide range of possible applications. WSNs can be deployed in unattended environments, where a registered user can login to the network and access data collected by the linked sensors. Authenticating users in resource constrained environments is one of the major security concerns. Since sensor nodes have limited resources and computation power, it is desirable that the authentication protocol is simple and efficient. In 2009, M. L. Das proposed a two-factor authentication for WSNs, where a user has to prove possession of both, a password and a smart card. Since his scheme utilizes only cryptographic one-way hash function and exclusive-OR operation, it is well-suited for resource constrained environments. However, Khan and Algahathbar pointed out that Das's scheme has some flaws and is vulnerable to various attacks and proposed an alternative solution. In this paper, we show that both, Das's and Khan-Algahathbar's schemes have flaws and remain vulnerable to various attacks including stolen smart card attacks. To overcome the security weaknesses of both schemes, we propose an improved two-factor user authentication that is resilient to stolen smart card attacks as well as other common types of attacks. We provide security evaluation of the proposed protocols showing its robustness to various attacks and analyzed the scheme's performance to determine its efficiency. Compared to the previous schemes, it is proven more robust and provides better security.

Privacy and security are two important issues in vehicular networks. Users wish to maintain location privacy and anonymity, meaning the identity, location/direction of move of their vehicles remains unknown to everybody with possible exception law enforcement authorities responsible by law to know and maintain such private information. In this paper, we propose a Pre-broadcast based Time Efficient Privacy (PTEP) scheme, which, instead of performing any asymmetric verification, uses Message Authentication Code (MAC) functionality and HASH operations to authenticate messages. Moreover, we use two-level key (upper-level hash chain and low-level hash chain) which assists avoiding message losses. Analysis shows that the proposed PTEP scheme superior performance in terms of packet loss rate and packet latency. In addition, it can be used to serve emergency and routine messages as well, while most of existing solutions can only work with routine messages.

As the wireless sensor network (WSN) technology evolves towards higher transmission rates, it makes sense to start considering sensing and transmission of real-time information, such as audio and video. These applications require quality of service (QoS) guarantees, not offered by current networks. The multi-hop nature of WSN makes QoS a challenging task. In addition, researchers have recently realized that cross-layer protocols achieve a far better performance than protocol layers working in isolation. These two ingredients are the focus of our work. In this paper we propose an architecture in which the MAC and routing protocols collaborate to discover and reserve routes, to organize nodes into clusters and to schedule the access to the transmission medium in a coordinated time-shared fashion. As a consequence, not only QoS is achieved but also great energy savings by eliminating collisions and considerably reducing idle listening. The resulting protocol is called QUATTRO: QUAlity-of-service-capable clusTer-based Timeshared ROuting-assisted MAC protocol. We evaluate our proposal using simulations by examining multiple scenarios in which different numbers and densities of nodes are considered. Our results show that the protocol overhead is reasonable.

The FCC has set apart a frequency band with the specific goal of improving safety and efficiency of the transportation system. Its purpose is to provide wireless communications between stations on the roadside and mobile radio units located on board of vehicles. The resulting technology is known as WAVE and is currently under development as draft standard IEEE 802.1 lp. The most time- critical messages, carrying urgent safety-related information, are transmitted over the so-called control channel (CCH). WAVE devices use the EDCA MAC protocol, defined in the 2007 version of the IEEE 802.11 standard, to compete for the transmission medium. This work analyzes the performance of EDCA under the specific conditions of the CCH of a WAVE environment. The protocol is modeled using Markov chains and results related to throughput, frame-error rate, buffer occupancy and delay are obtained under different traffic-load conditions.

Wireless local area networks (WLANs) are in a period of great expansion and there is a strong need for them to support multimedia applications. The IEEE 802.11 standard defines the way WLANs work at the physical and medium access control (MAC) level. The recently-approved IEEE 802.11e amendment proposes a MAC protocol capable of offering quality of service (QoS) guarantees. This work has to do with EDCA (Enhanced Distributed Channel Access), which is one of the mechanisms introduced in IEEE 802.11e. EDCA promises to become a widely used protocol for terminals to gain access to services with QoS guarantees. It is then extremely important to assess its performance concerning the main QoS metrics, namely throughput, delay and losses under different traffic conditions, which is exactly the goal of this work. We obtain a set of equations by modeling the system using discrete-time Markov chains, and then validate these equations using simulations.

The use of optical code division multiple access (OCDMA) techniques for contention resolution in optical burst switching (OBS) is proposed. Further a service differentiation scheme is proposed for QoS support. This novel approach achieves wider range of differentiated services than the existing offset-time-based scheme, by assigning prioritized codewords which are embedded in the signature sequence used for OCDMA. Steady-state throughput is obtained and the numerical results show that the proposed scheme provides higher throughput corresponding to the priority class assigned to the burst.

The user retrial phenomenon and its significant impact on network performance in unicast wireless systems are known and relatively well studied in the literature. However, there have been no previous studies on the impact of the user retrial phenomenon on other types of wireless networks. The objective of this paper is to extend the analysis of the user retrial phenomenon to wireless systems which, in addition to unicast service, also support a data broadcast service. This objective is realized by defining several performance measures appropriate for the analysis of hybrid unicast-broadcast systems in the presence of users' retrials. Subsequently, we derive the exact mathematical expression for each of the measures. Based on these expressions, we prove the existence of a single broadcast scheduling scheme, which ensures optimal system performance, with respect to the given set of proposed measures, the system's throughput, and the grade and quality of service. We also take a closer look at the class of hybrid unicast-broadcast systems with autonomous estimation of data item popularities, and we elaborate on the major challenges associated with such systems. Finally, we evaluate our theoretical expressions through simulation, and we discuss their robustness with respect to moderate deviations in the underlying model.

In recent years, both wireless data broadcast (WDB) and hierarchical cell structure (HCS) have attracted the attention of the scientific community, yet they have been treated as entirely separate research topics. This paper presents one of the first attempts to bring the two subjects together. In particular, the paper deals with the issue of optimized data broadcast in systems of hierarchical cellular organization. We see the following as the main contributions of the paper: 1) considerably superior performance of HCS-over single-layer- WDB system is proven; 2) an algorithm for fast identification of the optimal broadcast schedule in HCS-WDM systems is proposed. As we are moving in the era of pervasive computing, where millions of devices - many of them of mobile and nomadic nature - will be requesting network support for retrieval of information, development of efficient wireless based transfer systems become immensely important.

Virtual environments (VEs) are interactive computer simulations that immerse users in an alternate reality. Distributed VE (DVE) applications simulate the experience of real-time interaction among multiple users in a shared three-dimensional (3-D) virtual world. In this paper, we identify the network service requirements for highly interactive DVEs and show the limitations of IPv4 in satisfying them. We propose a transport system for DVE applications, which incorporates a scalable network architecture and dynamic QoS adaptation over IPv6. The network communication architecture combines the advantages of anycasting, unicasting and multicasting while the dynamic QoS adaptation assists the DVE applications in adapting to fluctuations in the network. The network-specific issues are hidden from the application by means of a networking module. The traffic measurements are performed on a DVE application using the proposed architecture.

The tremendous increase in customer bandwidth demands has led to the necessity of better utilization of available bandwidth resources. We present an artificial intelligence based pricing mechanism for control of user demand in the obtainable forwarding (OF) service in DiffServ networks. By deploying a fuzzy logic controller at the DiffServ boundary node, we are able to adjust dynamically the price per unit bandwidth, depending on customer bandwidth demands and bandwidth availability. In the case of elastic traffic, a small change in price leads to a small change in customer demand. As the decision to buy bandwidth or not lies in the hands of the customer (his grade of utility), it is difficult to estimate the parameters for the customer bandwidth utility function. The suggested fuzzy controller implements rules, easily obtainable at the boundary node, using terms such as "small change", "big increase". We present an evaluation of the utilization of dynamically changing bandwidth demand.

The paper looks at performance evaluation of a Local Multipoint Distribution Service (LMDS) system extended to support mobile users. The N-state Markov chain is used to model the LMDS wireless channel with Nakagami fading. Realistic traffic models of file transfer protocol (FTP), voice sources, and real video traces are used. Discussion of the numerical simulation results is presented.

We introduce, the use of the shot-noise analysis, brought forward by Rice (1944), as a natural tool in computing the various statistical properties of the multipath fading channels, in wireless communications. By adapting and generalizing this theory we derive the various statistical properties of the channel, including the second-order statistics, generalizations of Campbell's theorem and central-limit theorems.

The main objective of this paper is to establish that it is not efficient to use weighted fair queueing (WFQ) with a static allocation of bandwidth for the different traffic classes in a differentiated services environment and to propose an extension to WFQ, based on prediction techniques of realistic traffic models, in order to provide it with the necessary adaptability to cope with the dynamic nature of Internet traffic. We call our proposed scheme dynamic predictive weighted fair queueing (DP-WFQ). Its performance is evaluated via simulations. In addition to WFQ, our proposal is also compared to other algorithms, such as WF2Q and LTO-WFQ. Our results show the superior performance of the new algorithm in terms of the number of transmitted packets, buffer overflows, and delay.

This paper explains why the theory of effective bandwidth is in general not applicable to characterize realistic traffic sources. Moreover, we show that a static allocation of network resources (bandwidth and/or buffer space) based on large deviation theory can be highly inefficient when the real statistical behavior of traffic is taken into account. As an alternative, we propose a dynamic resource management scheme based on prediction techniques. As a specific example, we apply this scheme to a Differentiated Service (DiffServ) Internet environment, in which the goal, besides policing the incoming traffic, is to optimize the use of network resources, thus minimizing the probability of occurrence of violations of contract guarantees. The performance of the proposed scheme is evaluated via simulations and our results show the superior performance of the new algorithm in terms of buffer overflows, output link utilization, and jitter, as compared to currently used policing and shaping mechanisms.

The available bit rate (ABR) service has been proposed by the ATM Forum in 1994 and also adopted by the ITU shortly afterwards. This paper presents the performance of a rate-based ABR in the presence of bursty data applications. Based on measurements reported in the literature, we have developed a simulation tool to evaluate the performance of the rate-based ABR mechanism. The simulation model includes a complete protocol stack allowing us to study the interaction of the traffic control mechanisms implemented by protocols at different layers, i.e., TCP and ABR. Under realistic traffic models, it is shown that the rate-based ABR mechanism provides a high link utilization, minimum buffering requirements and cell transfer delays.

This comment points out some papers published before the paper of Vitetta and Taylor (see ibid., vol.43, no.11, p.2750-58, 1995). These early papers have dealt with the general problem of maximum-likelihood sequence estimation of coded/uncoded phase-shift keying (PSK) and quadrature amplitude modulation (QAM) signals in correlated Rician and Rayleigh-fading channels. These publications did not assume use of interleaving or use of optimal codes, designed for interleaved systems. The statistical properties of the multiplicative fading process have been included in the design of the receivers which were proposed, analyzed, and evaluated. The research contributions documented in these papers have also shown for the first time in the open literature the link between conventional detection techniques and the maximum-likelihood detection of signals in this type of fading channels.

Performance upper bounds for noncoherent receivers employed in conjunction with single and multi-amplitude/-phase signals, transmitted over time dispersive and Gaussian noise channels are derived. Based upon a metric which has been previously derived by the authors, we present analytical expressions and computer generated results for the performance of asymptotically optimal noncoherent detection over such channels. As a typical application of the developed theoretical analysis, we consider wideband telecommunication systems. Where time dispersion resulting in intersymbol interference (ISI) is one of the significant sources of system performance degradation. Numerical evaluation of the optimal noncoherent decoding algorithms, shows the proposed bounds to be an effective and efficient means of evaluating the performance of the noncoherent receivers under investigation. Using the derived bounds, performance evaluation results for modulation schemes such as /spl pi//4-shift DQPSK (differential quadrature phase shift keying), 8- and 16-DQAM (differential quadrature amplitude modulation), at very low bit-error rates (BER), which would otherwise pose impractically high computational loads when using Monte-Carlo error counting techniques, are readily obtained. At BER>10/sup -4/ evaluation results generated via computer simulation have verified the tightness of the bounds.>

A. Burrell et al. (1993; 1994) described an implementation efficient capacity allocation protocol for multimedia traffic (voice, video, high and low speed data). The protocol determines the capacity allocation of each traffic dynamically, and induces moving boundaries within prespecified and fixed channel frames. The channel frames are selected to satisfy the jittering constraints of all the traffic, such as voice, video and high versus low speed data. The high level protocol, in conjunction with the channel frame structure and the specifics of the transmission policy, may satisfy all traffic and QOSs and may simultaneously attain high channel utilization, for certain variability conditions of the traffic rates and at relatively low implementation cost. In the work presented, the system stability, channel utilization, traffic rejection rate and packet/cell delay are examined. Performance evaluation results are presented.>

The maximum likelihood sequence estimator for the reception of coded digital phase modulated signals with single or multiamplitude constellations, transmitted over a multiplicative, frequency-nonselective (i.e., flat) correlated fast fading Rayleigh or Rician channel and corrupted by additive white Gaussian noise (AWGN), is derived. Due to this correlation, the errors caused by fading tend to occur in bursts. In the analysis, no assumption simplifying the problem is made. For fast fading the authors consider the most general case where both phase and amplitude distortion resulting from the fading process could change significantly and thus cannot be assumed to be constant over a number of transmitted symbols. It is shown that the estimator's hardware structure consists of a combination of envelope, multiple differential and coherent detectors. With multiple differential detectors they define a receiver structure consisting of a combination of more than one distinct differential detectors each of them employing a progressively increasing (by the symbol duration) time-delay element. The outputs of these detectors are jointly processed by means of an algorithm which is presented in a recursive form. The derivation of this new receiver is general enough to accommodate trellis coded phase shift keying (PSK) and quadrature amplitude modulated (QAM) systems. Differentially encoded signals, such as the /spl pi//4-shift differential quadrature phase shift keying (DQPSK) scheme can also be incorporated. In order to reduce the overall receiver implementation complexity, several reduced complexity, near-optimal versions of the algorithm are presented. These reduced complexity receivers are based on the use of only a few multiple differential detectors. Performance evaluation results for reduced complexity trellis coded /spl pi//4-shift DQPSK, /spl pi//4-shift 8-DQAM (differential quadrature amplitude modulation) and 8-DPSK (differential phase shift keying) systems have demonstrated that the proposed receivers significantly reduce the error floors caused by fading.>

The authors study spread slotted ALOHA (SSA) techniques which combine certain characteristics of both spread spectrum and slotted ALOHA (SA) systems to achieve better performance than the constituent systems. Their results demonstrate that SSA offers significant improvements in terms of throughput, delay and network stability against excessive loading at very acceptable levels of receiver implementation complexities. Also, SSA is found to be highly robust to errors in the time of arrivals (a serious and frequently encountered problem in satellite networks) and eliminates the need to allocate guard time. Some of the candidate SSA schemes studied show great promise for practical implementation both from the performance and complexity points of view.>

The objective is to develop a general theoretical framework for a class of spread slotted ALOHA (SSA) systems. The contributions include: modeling of a generalized spread slotted ALOHA (SSA) system; derivation of computationally efficient closed form expressions for the SSA system throughput and delay taking into account receiver complexity; and presentation of numerical results to validate the derivation as well as to substantiate the superior performance of the proposed scheme. The results demonstrate that SSA schemes offer significant improvements in terms of throughput, delay, and network stability against excessive loading at very acceptable levels of receiver implementation complexities. Also, SSA is found to be highly robust to errors in the time of arrivals and eliminates the need for a guard time.>

Differential detector structures that use decision feedback to partially remove the effect of destructive intersymbol interference from minimum-shift keying (MSK) are introduced. In comparison to the conventional two-bit differential detection of GMSK (Gaussian MSK), the proposed structures provide about 4-dB E/sub b//N/sub 0/ improvement when the premodulation filter time-bandwidth product is 0.25. As the premodulation filter becomes narrower, the advantages of the proposed receivers are more pronounced. Thus the bit-error-rate performance of differential detection is brought closer to coherent detection while avoiding the problems associated with the carrier recovery.>

This paper introduces a novel class of detectors, which has a symbol-by-symbol, multisample, transversal filter-based structure. The essence of the proposed detectors is based on a noise estimationcancellation technique. By exploiting the noise correlation among the received samples, a linear minimum mean-squared estimate of the existing noise is made and subsequently cancelled. As an illustration of the detection principle, partial response signaling systems of the form1 \pm D^{m}are considered. The effects of the system bandwidth, the number of exploited samples and filtering allocation, on the system performance are thoroughly examined. It is shown that with optimum filtering allocation, the proposed detectors, while having simple structures, give substantial performance gains over conventional one-sample detectors.