This paper studies the efficiency of Radio-frequency fingerprinting (RFF) on IEEE 802.15.4 networks using properties extracted by machine learning techniques. As a test case, we used the measurements of 33 wireless sensor devices to create a dataset with 640 complex samples from the signals' synchronization header of the frames transmitted by all sensors in two moving scenarios. This paper evaluates using an autoencoder (AE) neural network (NN) for extracting the RFF features. It addresses the challenge of identifying the performance of different AE NN architectures using varying numbers of features obtained from the AE latent state (LS). We compare the relative performance of the AE NN with varying types of NN (combining dense, convolutional, and recurrent layers) with five different LS dimensions (between 4 and 128), as well as two classifiers: a multi-layer perceptron (MLP) and a random forest (RF). An optimization for the encoder's LS, which uses the weights of the AE and a classifier NNs on an additional NN training phase, is also proposed. We show that a larger LS size does not always lead to better classification accuracy and that the AE loss is a bad predictor for the classifier performance. The best F1-score achieved was 93%, measured using the MLP classifier and the optimized one-dimensional convolutional AE with an LS dimension of 8, or 86% using the same configuration without the optimization. The RF classifier is much faster to train and still achieves an 88% F1-score for the optimized Gated Recurrent Unit (GRU) AE with an LS dimension of 16.

Unmanned aerial vehicle (UAV) systems are vulnerable to jamming from self-interested users who utilize radio devices to disrupt UAV transmissions. The vulnerability occurs due to the open nature of air-to-ground (A2G) wireless communication networks, which may enable network-wide attacks. This paper presents two strategies to identify Jammers in UAV networks. The first strategy is based on a time series approach for anomaly detection where the available signal in the resource block is decomposed statistically to find trends, seasonality, and residues. The second is based on newly designed deep networks. The combined techniques are suitable for UAVs because the statistical model does not require heavy computation processing, but is limited to generalizing possible attacks that might occur. On the other hand, the designed deep network can classify attacks accurately, but requires more resources. The simulation considers the location and power of the jamming attacks and the UAV position related to the base station. The statistical method technique made it feasible to identify 84.38% of attacks when the attacker was at a distance of 30 m from the UAV. Furthermore, the Deep network’s accuracy was approximately 99.99 % for jamming powers greater than two and jammer distances less than 2II meters.

When users exchange data with Unmanned Aerial Vehicles - (UAVs) over Air-to-Ground - (A2G) wireless communication networks, they expose the link to attacks that could increase packet loss and might disrupt connectivity. For example, in emergency deliveries, losing control information (i.e., data related to the UAV control communication) might result in accidents that cause UAV destruction and damage to buildings or other elements. To prevent these problems, these issues must be addressed in 5G and 6G scenarios. This research offers a Deep Learning (DL) approach for detecting attacks on UAVs equipped with Orthogonal Frequency Division Multiplexing - (OFDM) receivers on Clustered Delay Line (CDL) channels in highly complex scenarios involving authenticated terrestrial users, as well as attackers in unknown locations. We use the two observable parameters available in 5G UAV connections: the Received Signal Strength Indicator (RSSI) and the Signal to Interference plus Noise Ratio (SINR). The developed algorithm is generalizable regarding attack identification, which does not occur during training. Further, it can identify all the attackers in the environment with 20 terrestrial users. A deeper investigation into the timing requirements for recognizing attacks shows that after training, the minimum time necessary after the attack begins is 100 ms, and the minimum attack power is 2 dBm, which is the same power that the authenticated UAV uses. The developed algorithm also detects moving attackers from a distance of 500 m.

Decentralized PHY/MAC techniques for the uplink of Multi-Packet Reception (MPR) schemes are of great interest in future wireless communication systems (e.g., IEEE 802.11ax). In MPR schemes the average number of successful received packets depends on the radio propagation effects, the number of nodes simultaneously transmitting and the capture threshold that characterizes the PHY-layer MPR technology. In this paper we adopt a MPR capture model capable of describing the average number of successful packets simultaneously received. The capture model is then used in an optimal reservation-based medium access control (MAC), designed to operate in a decentralized way through a random access policy. This work describes the PHY/MAC cross-layer design, as well as the rationale required to understand its optimality. While the main objective of the proposed MAC is to achieve the optimal number of simultaneous transmissions that maximize the PHY-layer performance, a cost due to the MAC reservation period must also be considered in the optimization process. A model of the PHY/MAC performance is derived, which allows the optimization of the parameters that regulate the nodes' random access. Different simulation results are described and compared with numerical results obtained with the proposed PHY/MAC model. The paper ends up discussing possible solutions to implement the proposed methodology in practical wireless networks formed by a high number of competing nodes.

In this work, target localization problem in adverse indoor environments is addressed, where most (if not all) links are non-line-of-sight (NLOS). Localization accuracy in such environments is highly affected by multipath, which makes the problem very challenging. Hence, in order to enhance the localization accuracy, received signal strength (RSS) and time of arrival (TOA) integrated measurements, are considered here. Nevertheless, the derived joint maximum likelihood (ML) problem is highly non-convex and has no closed-form solution; thus, some approximations are required to solve it. We show that, for small noise power, the ML estimator can be tightly approximated by another (non-convex in general) one, given in a form of a generalized trust region sub-problem (GTRS). Hence, exact solution of the derived estimator can be readily obtained by merely a bisection procedure. The proposed algorithm is compared with the state-of-the-art (SOA) RSS/TOA algorithms, as well as its RSS-only and TOA-only complements. Our simulations validate the effectiveness of the proposed approach, outperforming the SOA algorithms in all considered scenarios, and show the benefit of the measurement fusion.

This paper studies what mechanisms a network must have to offer a very low-latency service to applications (featuring a maximum end-to-end packet delay). We assume very concrete requirements, not seen in the literature, that raise the challenge level: i) applications might be unresponsive to traffic warnings from the network; and ii) applications do not inform or require any network resources, exactly as the Internet works today (i.e., there is no admission control procedures). We present an architecture/algorithm with a minimum of state information and good scalability properties. Obviously, it is not applicable to the wide Internet. Even more, the architecture is not TCP-friendly (because control loops must be shorter than the Round Trip Time (RTT) magnitudes and oscillations, and packet losses are higher). Instead, it is appropriate to an end-to-end slice network based on a virtualization of the physical network with independent queues and line bandwidths. It is designed for interactive applications and for certain real-time ones. We use plain backpressure control supported by cooperation amongst the routers to isolate offending traffic. We are particularly concerned in situations of very high load, as they will be very common in the future. One objective is to reach a predictable network behaviour that in the limit (heavy network overload) is maintained, contrary to the current Internet. In the future, new pace-based congestion control algorithms for applications can be designed to take the most out of this type of network.

This paper deals with the cross-layer design of a decentralized medium access control (MAC) scheme to coordinate the access of multiple transmitters adopting a Multi-Packet Reception (MPR) physical (PHY) layer. Knowing that in MPR systems the average number of packets successfully decoded depends on the number of simultaneous transmissions, we propose an integrated PHY/MAC cross-layer design that explores the advantages of MPR communications in a decentralized network. The joint performance of the PHY/MAC cross-layer scheme is characterized to allow the maximization of the average number of packets successfully decoded. While the main objective of the proposed MAC is to randomly grant access to the channel in order to achieve the optimal number of simultaneous transmissions, the decentralized MAC introduces a cost due to the time required to coordinate the multiple transmitters. In a first step we characterize the throughput achieved by the cross-layer scheme, by modeling the performance of the PHY-layer and the random MAC scheme. The formal characterization of the throughput is then used to optimize the duration of the first stage of the MAC scheme. In this way, the number of transmitters is regulated to optimize the cross-layer operation, taking into consideration the features of the MPR PHY-layer and the maximum performance achieved with the proposed MAC design. Several results obtained through simulation are presented, which validate the numerical results obtained with the proposed characterization. Finally, the results confirm the advantages of the proposed PHY/MAC design.

Vehicles need to locate other vehicles and network infrastructure elements on unmanned autonomous vehicle (UAV) systems. Human passengers also need to locate and be located by the vehicles, preferentially using a portable device, such as a smartphone. This paper analyses the accuracy of several localization algorithms in the remote location of entities running WiFi access points, using measurements collected in moving vehicles using a new application developed by us. The algorithms analysed include closed form estimators and one based on second order cone programming (SOCP) relaxation, which exhibits the best accuracy and is capable of estimating the path loss exponent and the transmission power. Although, due its lower complexity, the Levenberg-Marquardt algorithm was better suited for the stand-alone Android prototype application. The results show that real-time accurate positioning of static/slow moving remote entities is possible, even though the accuracy degrades when the measuring vehicle's speed increases.

In this paper, we characterize the wireless interference of a mobile ad hoc network, where the nodes move according to the random waypoint model. The interferers are assumed to be located within an interference region that is defined as a circular region centered in a fixed node located at a given point of the mobility scenario. The main contribution of this paper is the characterization of the aggregate interference caused to the fixed node by mobile interferers located within the interference region. The distribution of the interference is analyzed taking into account the stochastic nature of the path loss due to the mobility of the nodes, as well as fast fading and shadowing effects. The derivation of the characteristic function of the aggregate interference is used in two different estimators, which successfully characterize the interference using only a small set of samples. The theoretical approach is validated through simulations, which confirm its effectiveness. Finally, we assess the accuracy of the proposed estimators, demonstrating the practical value of this paper.

Software defined networks (SDNs) reduce the complexity of implementing multi-commodity flow (MCF) optimization problems and several optimization based SDN Traffic Engineering (TE) schemes have been proposed. This approach has several limitations like the need to know or infer bandwidth demands, the number of forwarding rules needed to implement the solution and the cost of the control-loop communication between controller and switches. This usually results in systems that do not scale and need to adapt the problem formulation to an approximation of the optimal solution. In this work we propose an approach for TE in SDNs without optimization and no need for traffic demand knowledge. We propose a logically hierarchical controller architecture built on the premise of low rule space and sparse controller communication where TE is performed in two actions: the setting of stable paths in the core and the distribution of traffic among them in the access. Different algorithms can be used for these purposes. We start by studying the performance of using a shortest path algorithm for the calculation of the stable core paths and a concept from social networks analysis called betweenness centrality to measure congestion risk and support the traffic distribution decisions in the access.1

In this paper we characterize the radio frequency (RF) spectrum opportunities available in a common GSM (Global System for Mobile Communications) channel to support the operation of a cognitive radio network (CRN). In a first step, we describe the technical details involved to sample the channel using a Software Defined Radio (SDR) device. Adopting a simple Energy-based detector, we identify the two energy regions where the GSM system is active or inactive. Based on the output of the detector, we show that the distribution of the durations of busy and idle periods are approximated by geometric distributions. Finally, we validate a theoretical model for the distribution of the service time. The validation results indicate that the service time can be successfully represented by a discrete Generalized Pareto (dGP) distribution, which is confirmed by the Kolmogorov-Smirnov test. Because the throughput of the CRN is represented by the inverse of the service time, the proposed analysis provides an upper bound for the networks' throughput, indicating the maximum throughput that can be attained when a single SU transmits over a GSM cellular channel. The results presented in the paper are validated with real data, confirming the accuracy of the proposed service time model.

In this paper we propose two decentralized medium access control (MAC) schemes to coordinate the access of multiple transmitters adopting a Multi-Packet Reception (MPR) physical (PHY) layer. The proposed MAC schemes operate over a MPR-based PHY-layer and are divided in two stages. In the first stage the nodes indicate their willingness to transmit, while in the second one they jointly transmit. The MAC schemes differ by considering a Single-Packet Reception (SPR) or a MPR PHY-layer in the first stage. We analyze the throughput achieved by each MAC in a theoretical way. Several results obtained through simulation are also presented, which validate the numerical results obtained with the theoretical model. The results demonstrate the effectiveness of the proposed MAC schemes, and allow us to draw valuable conclusions about the design of distributed MPR systems.

In recent schemes proposed to the physical layer of wireless systems the receiver node has the capability of simultaneously receiving multiple transmissions, which is commonly referred to as a Multi-Packet Reception (MPR) scheme. Assuming that the transmitters are randomly located in the far-field region and a generic signal-to-interference-plus-noise ratio (SINR) threshold-based criterion is used as the packet capture model, we derive the probability of successful reception of a packet considering path loss, shadowing and fading effects. Our approach relies on the characterization of the aggregate interference caused by the transmitters, which is used in the capture model in a simplified way. The probability of successful reception of a packet is then used to approximate the average number of packets simultaneously received. The proposed analysis is evaluated for different scenarios and compared with several results obtained through simulation. The simplicity of the model, as well as its accuracy, makes it a useful tool to assist the design of future medium access control mechanisms for MPR wireless systems.

This paper presents a scalable solution for guaranteeing bandwidth to interactions/communications assuming no information is provided by the applications. The objective is to define and assess what the network can do with so little information both in terms of guaranteeing quality and preventing being throttled by overloads. The suggestion of having applications indicating their needs did not materialize in the past and it is not credible to happen in the future. Applications tend to adapt to the conditions of the network (instead of requiring resources), and can drive the network to a halt. With no explicit information, the network must firstly protect itself from being driven into an uncontrolled saturation situation with unacceptable delays, and secondly devise what kind of guarantees can still be provided to applications. In this paper, if interactions live enough time, they become flows without any disruption in traffic or initial delays for flow establishment. Traffic is aggregated in the core and all flows access the network up to a maximum rate that is calculated when they begin. When the network becomes loaded, traffic that was granted guarantees is protected. New traffic is never blocked from accessing the network and may even get guarantees.

Software Defined Networks (SDNs) provides a separation between the control plane and the forwarding plane of networks. The software implementation of the control plane and the built in data collection mechanisms of the OpenFlow protocol promise to be excellent tools to implement Machine Learning (ML) network control applications. A first step in that direction is to understand the type of data that can be collected in SDNs and how information can be learned from that data. In this work we describe a simple architecture deployed in an enterprise network that gathers traffic data using the OpenFlow protocol. We present the data-sets that can be obtained and show how several ML techniques can be applied to it for traffic classification. The results indicate that high accuracy classification can be obtained with the data-sets using supervised learning.

In this paper we propose a decentralized medium access control (MAC) scheme to coordinate the access of multiple transmitters adopting a multi-packet reception (MPR) physical (PHY) layer. MPR receivers are able to decode multiple transmissions, and depending on the technique adopted at the PHY-layer, there is an optimal number of simultaneous transmissions that maximize the number of packets successfully decoded in a simultaneous way. The proposed MAC scheme admits an MPR PHY-layer and is divided in two stages. In the first one the nodes indicate their willingness to transmit, while in the second one they jointly transmit. Adopting a generic model for the PHY-layer, we characterize the throughput achieved by the proposed MAC when both MAC and PHY layers are considered. The formal characterization of the throughput is then used to optimize the duration of the first stage of the MAC scheme in order to optimize the throughput. In this way, the number of transmitters is regulated to optimize the cross-layer operation, taking into consideration the features of the MPR PHY-layer and the maximum performance achieved with the proposed MAC design. Several results obtained through simulation are presented, which validate the numerical results obtained with the proposed characterization. The proposed scheme is a first step to develop MAC protocols specifically designed to distributed MPR systems that operate in a cross-layer and improve the exploitation of current and future MPR techniques proposed for the PHY-layer.

FTN (Faster Than Nyquist) signaling allows capacity gains but requires substantially complex equalization schemes, even for an ideal AWGN (Additive White Gaussian Noise) channel. Extending conventional FTN receivers for severely time- dispersive channels is not an option, since the receiver complexity becomes prohibitively high. In this paper we address the design of a receiver for FTN signaling over severely time-dispersive channels. To cope with the severe ISI (Inter-Symbol Interference) associated to the combined effects of FTN signaling and the time-dispersive channel we consider an iterative FDE scheme (Frequency-Domain Equalization) combined with a HARQ (Hybrid Automatic Repeat reQuest) especially designed taking into account the characteristics of FTN signals. We also present a simple, yet accurate model for the performance evaluation, considering multiple retransmissions per block. Our performance results show that we can have significant throughput gains, while maintaining essentially the receiver complexity of conventional, Nyquist-rate signaling schemes, even for severely time-dispersive channels.

Prefix-assisted direct-sequence code-division multiple access (DS-CDMA) is a viable transmission technique for high-data-rate wireless broadband systems, capable of coping with highly dispersive channels at the uplink. Packet combining (PC) ARQ with an iterative block decision feedback equalization (IB-DFE) technique can be used to cope with errors. However, extracting the IB-DFE's packet error rate (PER) for MAC-layer simulations can be time consuming. Most works that model the DS-CDMA behavior with PC ARQ use simplified asymptotic PER models in the study of the system performance, which are not precise for low signal-to-noise ratios and for a low number of mobile terminals (MTs). In this paper, the MAC performance is modeled using a discrete-time Markov chain that relies on a PER model. As an example, this paper describes a PER analytical model for an uncoded prefix-assisted DS-CDMA system with PC ARQ that considers the following inputs: the number of MTs accessing the channel, the MTs' number of transmissions, and the channel realizations for a given bit energy over noise ratio. The results show that the model portrays with better accuracy the simulations' results, compared with an alternative asymptotic model.

Multipath routing can provide a better solution for several of the current BGP's problems in the inter-domain scenario by allowing a cleaner separation between routing and traffic engineering and better failure containment. The separation between routing control logic and data forwarding, and the use of software defined networking principles open space to easier deployments of new routing protocols at the inter-domain level. This paper explores the potential of using a multipath policy based inter-domain routing algorithm based on an algebraic model. The algorithm establishes multiple paths to a destination following a policy-based architecture and works with simple destination-based hop-by-hop forwarding. We focus on the definition of algebraic models for the links, their composition and the resulting path's ranking. Our algorithm addresses the most common situations in the Internet and we include others not so common as backup links and sibling relations. We prove the correctness of the algorithm under conditions that open several implementation options and describe how it can use multipath for failure containment, using the extra paths to make each failure less important. The paper finishes with the presentation of some experimental results that illustrate the algorithm capabilities.

Ethernet is the Layer 2 infrastructure of choice for modern data center networks and service provider metro networks. These networks need to scale to a high number of end hosts and bridges, provide isolation between tenants and support host mobility with an efficient bandwidth use and reduced operating costs. Ethernet uses controlled flooding of frames and the spanning tree protocol, falling short on demands like scalability and full usage of the topology. Solutions at Layer 3 solve some of the problems but they are harder to configure, more expensive and pose difficulties to host mobility. Recent efforts try to bring some of the advantages of L3 to L2 by using equal cost multipath (ECMP) control planes to populate the bridges forwarding tables. In this paper we go beyond and propose a non-ECMP solution where the paths are selected by policy. This means that very different paths (in terms of the physical topology) can be considered equal. It provides an extra layer of flexibility in traffic distribution with a high utilization of the network in a single L2 Ethernet domain. Our design is based on routing algebra theory and its correct behaviour can be proved for both centralized and distributed implementations.

Radio Spectrum sensing has been a topic of strong research in the last years due to its importance to Cognitive Radio (CR) systems. However, in Cognitive Radio Networks (CRNs) with multiple Primary Users (PUs), the Secondary Users (SUs) can often detect PUs that are located outside the sensing range, due to the level of the aggregated interference caused by that PUs. This effect, known as Spatial False Alarm (SFA), degrades the performance of CRNs, because it decreases the SUs' medium access probability. Adopting Energy-based spectrum sensing (EBS) in each SU, this work starts to characterize the interference caused by multiple PUs located outside the sensing area. The interference formulation is then used to derive the probabilities of detection (PD) and false alarm (PFA), and closed form expressions are presented. Several results show that the probabilities PDand PFAare successfully validated through simulation. Finally, the work shows that the SFA can be almost neglected, depending on the path loss factor and on the number of samples collected by the energy detector to decide the spectrum's occupancy state.1

Random access approaches in Low Earth Orbit (LEO) satellite networks are usually incompatible with the Quality of Service (QoS) requirements for multimedia traffic, especially when hand-held terminals must operate with a very low signal-to-noise ratio. This paper proposes the Satellite Random Network Diversity Multiple Access (SR-NDMA) protocol that handles multimedia traffic under this context through the combination of a random and scheduled access scheme. The protocol uses a multi-packet receiver, for Single Carrier with Frequency Domain Equalization (SC-FDE) in the uplink, that gradually reduces the packet error rate with additional transmissions. The paper proposes analytical performance models for the throughput, delay and energy efficiency - as long as terminals have finite queues. System parameters are defined to enhance the energy efficiency while satisfying the QoS requirements for limited queue and bit-rate constraints. Results show that the proposed system is energy efficient and provides enough QoS to support multimedia services such as video telephony.

Algebra has made the tasks of defining routing algorithms and proving their correct operation very clear. However, current results in the modelling of multipath policy routing protocols only prove correct behaviour for models that exhibit a strict decrease in the preference of a path with every added link. This is very rigid for multipath routing. For instance it does not allow a link attribute to dominate the entire path classification or having equivalent paths with similar policy but a different number of links. This paper starts by defining the fundamental sufficient conditions for the correct operation of a multipath policy routing protocol with independent destination based hop-by-hop forwarding. We then study the sufficient properties that the protocol model should exhibit so that those conditions are met. We prove that correct operation is possible without the strict increase in preference, provided that the policies applied to links forming circuits in the network graph are restricted. We derive two conditions on the policies applied in the circuits of a network graph that assure correct behaviour and can serve as a tool in the design process.

Traditionally, Low Earth Orbit (LEO) satellite networks use hard handovers when a Mobile Terminal (MT) moves between the footprints of two satellites. Such approach introduces a transitory disconnection interval, which may limit the capacity to provide demanding real-time requirements. A soft- handover approach that applies distributed packet combining on a satellite diversity scenario is proposed in this paper. Considering inexpensive MT hardware and low transmission powers, the paper analyses the performance gains and the difficulties that are associated to different Doppler and time-of-arrival shifts when the MT signal is broadcast to two satellites during the short handover period where both satellite's footprint overlap. A Single-Carrier with Frequency Domain Equalization (SC-FDE) transmission technique is considered in this paper. It is shown that it is possible to have an inter-satellite handover almost without quality of service (QoS) degradation for a Satellite Network Diversity Multiple Access (S-NDMA) scheme.

Traditionally, an unsuccessful packet reception, either due to channel conditions or interference from multiple sources (collisions), is discarded and followed by a new reception of the same packet. Network diversity multiple access (NDMA) handles collisions by using time diversity multipacket reception: the base station forces terminals to transmit P copies of each packet when P terminals collide. This rigidity of having P copies is unsuitable for poor propagation conditions. It might be desirable to have more than P copies of a given packet, adopting a technique for single packet reception called hybrid-ARQ. Hybrid-ARQ effectively decreases the packet error rate. This paper proposes such mechanism for multi-packet reception, called hybrid-ARQ NDMA (H-NDMA), a gated slotted random access protocol, where the access mechanism forces the terminals involved in a collision with reception errors to transmit more than P times. Analytical models for the throughput, delay and energy per useful packet are proposed. The energy performance is analyzed for bounded average delay constraints. The proposed system's performance is evaluated for a single-carrier with frequency domain equalization (SC-FDE) scheme, and compared with the classical NDMA protocol. The comparison highlights that H- NDMA is scalable for an increasing number of terminals and network load.

This paper presents a Medium Access Control (MAC) protocol solution designed to properly handle collisions when in the presence of a multi-packet detection receiver for Single-Carrier (SC) modulations with Frequency-Domain Equalization (FDE). It is considered an iterative frequency-domain receiver that jointly performs equalization, multi-packet separation and channel decoding operations, for up to Qmaxmobile terminals transmitting in one slot. In this work, it is proposed and evaluated a p-persistent Network Diversity Multiple Access (NDMA) random MAC protocol designed to cope with a total number of mobile terminals J, for a maximum decoding capability of Qmaxsimultaneous packets. An accurate analytical model is presented to optimize two different scenarios: in the first one, a saturated network is considered and it is determined the packet transmission probability that maximizes the uplink throughput; the second represents a non-saturated network and the goal is to compute the optimal transmission probability associated to each mobile terminal that minimizes the packet transmission delay. In the end, analytical results obtained through physical and MAC layer simulations are discussed.

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Hybrid Automatic Retransmission reQuest (H-ARQ) and time diversity multipacket reception approaches, such as Network Diversity Multiple Access(NDMA), improve the system performance by requesting additional retransmissions and combining all the signals received together. However, the high round trip delay time associated to satellite networks introduces limitations in the number of retransmission requests that may be issued by the terminals to fulfill the Quality of Service (QoS) requirements. This paper considers the design of hybrid protocols combining H-ARQ and NDMA for satellite networks with demand-assigned traffic. The satellite NDMA (S-NDMA) protocol is presented and analytical models are proposed for its performance. Energy efficient QoS provisioning is also analyzed. The proposed system's performance is evaluated for a Low Earth Orbit (LEO) network with a Single-Carrier with Frequency Domain Equalization (SCFDE) scheme, and compared to H-NDMA. Results show that the proposed system is energy efficient and can provide enough QoS to support high demand services such as video telephony.

Multipacket Reception (MPR) techniques employing either Direct Sequence Code Division Multiple Access (DS- CDMA) or Network Diversity Multiple Access (NDMA) have great potential to deal with packet collisions from multiple Mobile Terminals (MTs). However, their performance evaluation in prac- tical systems is difficult because lengthy simulations are needed to obtain the packet error rates for specific channel conditions. This paper considers MPR receivers based on the Iterative Block Decision Feedback Equalization (IB-DFE) concept. An analytical tool that computes the Bit Error Rate (BER) and Packet Error Rate (PER) for DS-CDMA is proposed, where its theoretical results have a good accuracy. This analytical approach, that provides a simple and relatively fast way to compute the BER and PER performance for DS-CDMA, is then employed for a comparison with NDMA.

Diversity Combining (DC) and Multipacket Detection (MPD) are efficient techniques that cope with packet errors due to severe propagation conditions and/or collisions. To evaluate their network performance on a network simulator, an accurate characterization of the Bit Error Rate (BER) and Packet Error Rate (PER) can successfully replace the behavior of the PHY layer. This choice is better in terms of computational time than implementing a full PHY layer to be jointly simulated with the upper layers. In this paper, an analytical model is proposed to compute the BER and PER of DC, MPD and hybrid techniques, considering a Single-Carrier with Frequency-Domain Equalization (SC-FDE) scenario. The paper also considers two frequency-domain detection methods: a simple linear receiver and a powerful iterative receiver. The proposed model is simple and versatile, since it can support nonhomogeneous transmitting powers, and different channel conditions concerning retransmissions and channel randomization techniques. Several simulations show that the proposed model provides accurate BER and PER results for a wide range of scenarios.

The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high, with small error rates and delays. Packets with errors are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmissions like Automatic Repeat reQuest (ARQ) schemes, that can minimize the degradation is to combine the signals associated to different transmission attempts, usually called diversity combining techniques. This paper considers the use of Single-Carrier (SC) modulations with Frequency-Domain Equalization (FDE) and low-complexity soft combining ARQ schemes. The time diversity combining technique presented in this paper, allows packets associated to different transmission attempts to be combined in a soft way so as to improve the performance. This technique is employed in a Time Division Multiple Access (TDMA) scheme. An accurate analytical model is proposed for the evaluation of the uplink packet delay in non-saturated traffic condition, and for the system's throughput (goodput) considering a generic packet arrival process. Physical (PHY) layer (packet error rates) and system-level (goodput and packet delay considering both PHY and Medium Access Control (MAC) layers) results are presented and validated by simulations for two distinctive arrival processes: Poisson and Geometric.

Traffic Engineering (TE) aims at distributing traffic through routes to suit a specific goal. BGP addresses TE in a very specific way: it is a single path system, and mixes traffic control and route dissemination by letting attributes influence the choice of the best path. Several techniques have been proposed but due to BGP characteristics they have high complexity requirements such as the need for coordination and information about the network that is not locally available. and, in most cases, the use of tunnelling. In a previous work we proposed an inter-domain routing architecture DTIA (Dynamic Topological Information Architecture) that builds a robust multipath routing system based on the inter-AS relationships and routing policies. DTIA separates traffic control from route dissemination and seems to have less complex requirements to provide TE. The aim of this paper is to assess the ability of such a system to provide TE maintaining the complexity overhead to a minimum. We propose a simple feedback protocol to avoid congestion and achieve better traffic distribution at inter-domain level using only local available traffic information and DTIA's routing information.

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Network Diversity Multiple Access (NDMA) handles collisions by combining a multipacket detection scheme with time diversity. In NDMA, the base station (BS) forces mobile terminals (MTs) to transmit J copies of each packet when J MTs collide. Diversity combining is limited to J copies of the packets, not allowing it to adapt to severe errors due to channel noise. This paper considers a multipacket detection scheme recently proposed, which reduces the packet error rate (PER) when more than J copies of the packets are available. In this paper, an Hybrid-ARQ NDMA access mechanism is proposed. The access mechanisms forces MTs with reception errors during a collision resolution epoch to transmit more than J times. Analytical models are proposed for the goodput and delay, considering Poisson traffic. The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) scheme, and compared to classical NDMA.

Packet Combining (PC) and Multipacket Reception (MPR) techniques have great potential to deal with lost packets since both take full advantage of the signals associated to all failed transmission attempts. However, their performance evaluation in practical systems is difficult because lengthy simulations are needed to obtain the packet error rates for specific channel conditions. The paper presents an analytical tool to obtain the Bit Error Rate (BER) and Packet Error Rate (PER) performances for Packet Combining (PC), Multipacket Reception (MPR) and the hybrid of both schemes, based on Iterative Block Decision Feedback Equalization (IB-DFE) receivers for Single-Carrier with Frequency-Domain Equalization (SC-FDE). A set of simulation results show that the proposed analytical approach has accurate Bit Error Rate (BER) and Packet Error Rate (PER) results with a simple and relatively fast method.

Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, leading to performance losses. Two different approaches are considered to cope with lost packets, a low-complexity packet combining ARQ scheme (Automatic Repeat reQuest) and a multipacket detection scheme. These approaches are employed on a SC-FDE scheme (Single-Carrier with Frequency Domain Equalization). Suitable receiver structures are described, employing packet combining, multipacket detection and hybrid schemes. An accurate analytical tool is presented for predicting the performance of the different schemes.

Current applications and services for ad hoc net works heavily rely in advertisements, which are transmitted using broadcast. In the current Medium Access Control (MAC) schemes, namely in IEEE 802.11, broadcast co-exists with unicast frames. While the transmission scheme used for unicast frames is considered reliable, the IEEE 802.11 does not offer any possibility of retransmission for broadcast frames. This work presents a novel reliable MAC scheme, which is designed to maximize the network throughput. In our scheme all nodes adopt a common optimal contention window, which is based on a common view of the channel. Contrary to IEEE 802.11 we use the same contention window for both unicast and broadcast transmissions. Thus the conditional collision probability is independent of the traffic type. Departing from the optimal throughput for a saturated network, we estimate the number of nodes, which is a prime parameter to regulate the medium access control. We show that each node is suitable to estimate the number of competing nodes by using both its own medium access probability and the idle slot probability observed from the channel. Several simulation results evaluate the reliability and the throughput of our proposal, for different amounts of unicast/broadcast traffic. The results are compared to the well known IEEE 802.11 MAC, indicating that even without retransmitting the broadcast frames, the probability of successful transmission can be doubled. Moreover, the throughput of our approach outperforms IEEE 802.11 MAC and the results show it can be boosted up to 100%.

In this paper we present a performance analysis of XOR1-based flat routing protocols in high mobility conditions, considering a vehicular ad hoc network (VANET) formed in a highway scenario. First, we describe an XOR-based protocol that incorporates several adaptations of the existing XOR-based routing algorithms for wired networks, in order to cope with the network mobility. Then we propose an improved version of it, XORi, which modifies the protocol's information gathering process to accommodate the specific dynamic nature of VANETs topology. Finally, we evaluate the performance of XOR-based protocols with other topology-based routing protocols. Simulation results allow us to characterize the performance of this class of protocols through the comparison of the packet delivery ratio, end-to-end path delay and average number of path hops2. When a moderate density of nodes is considered, simulations show that XOR-based algorithms achieve almost the same packet delivery rate as link state algorithms, such as OLSR, while for high density of nodes XOR-based algorithms scale better in terms of delay when compared to source routing algorithms, such as DSR3.

In the last years, there has been an increasing interest in developing and testing Medium Access Control (MAC) protocols for ad hoc networks based on optimal methods. Several solutions do not take into account the throughput-fairness tradeoff, presenting high throughput performance but under-performing in terms of medium access fairness. This work presents a novel MAC scheme, which is designed to maximize the network throughput-fairness performance. In our scheme, all nodes adopt a common optimal contention window, which is based on a common view of the channel. Our proposal improves the access fairness because the contention window is similar to all nodes, and its behavior does not depend on previous MAC states. Departing from the optimal throughput for a saturated network, we devise a scheme to estimate the number of nodes, which is a prime parameter to regulate the medium access control. We show that each node is suitable to estimate the number of competing nodes by using both its own medium access probability and the idle slot probability observed from the channel. Several simulation results evaluate the throughput-fairness performance of our proposal with several state-of-the-art MAC protocols, such as AOB, Idle Sense, GDCF and the well known IEEE 802.11. The results indicate that our approach presents the highest value of medium access fairness among the simulated protocols, meaning that its throughput is closer to the optimal theoretical throughput obtained for a fair network.

In the last years, there has been an increasing interest in developing and testing Medium Access Control (MAC) protocols for ad hoc networks based on optimal methods. The solutions already proposed in several works are generally hard to implement because they require extensive message passing among the nodes. Moreover, a relaxation for the optimal solution is generally needed to achieve an implementable algorithm from the optimization problem solution. These disadvantages decrease the performance of the optimal-based algorithms, often translated into a less than expected throughput. This is the main reason why several MAC protocols, such as IEEE 802.11, use simple heuristics to control the access of the nodes to the medium. Generally, the adoption of heuristics in MAC protocols turns its formal performance analysis very difficult. The motivation of this work is to assess the validity of a formal method that analyzes the throughput of heuristic-based MAC protocols. This work starts to introduce the method that characterizes the node's medium access satisfaction. This method is used to compare the heuristics used to control the medium access. We describe and compare several heuristics by applying the formal analysis, which is later validated through simulations. The method here described can be applied at MAC design stage, since the designer can evaluate the performance of a given heuristic by comparison with others.

This paper considers the use of low-complexity diversity combining hybrid ARQ schemes (Automatic Repeat reQuest) on a TDMA (Time Division Multiple Access) system. Its low complexity makes it particularly interesting for battery-powered nodes of a wireless sensor network (WSN). TDMA is commonly used for WSNs applications that require high throughput or constrained packet delay. This paper analyzes the energy per useful packet, packet delay and goodput performances of the TDMA system. Analytical models were used to define a constrained energy optimization problem, where the minimum transmission power is calculated based on the goodput and delay constraints. Analytical results were validated through simulations.

Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance losses. In this paper we compare the performance of two different approaches to cope with lost packets. One alternative is a multi-packet detection approach able to separate up to Qmaxmobile terminals transmitting in one slot. The other alternative is a low-complexity soft combining ARQ scheme (Automatic Repeat reQuest) employed in a TDMA (Time Division Multiple Access) architecture. This paper evaluates the uplink non-saturated packet delay and goodput for a Poisson traffic generator. Our analytical results are validated by simulation using joint PHY (physical layer) and MAC (Medium Access Control) behavior.

This paper considers the use of a code combining hybrid ARQ scheme (Automatic Repeat reQuest) on a TDMA (Time Division Multiple Access) system. A multi-rate turbo-code is proposed to implement the H-ARQ scheme, allowing improved performances. This paper analyzes the energy per packet successfully received, the packet delay and goodput performances for the TDMA system on a HAP (High Altitude Platform). Analytical models were used to define a constrained energy optimization problem, where the minimum transmission power is calculated based on the goodput and delay constraints. Analytical results were validated through simulations for a typical HAP Network uplink channel.

This paper proposes the Mobile MH-MAC (Multimode Hybrid - Medium Access Control) protocol, an extension of MH-MAC with enhanced support for mobility on wireless sensor networks. It provides an asynchronous mode for energy efficiency during idle (unconnected) periods, and a synchronous mode for high throughput periods. Mode change is controlled by the application in a cross-layer approach. MMH-MAC was specially designed to tolerate asynchronous mobile nodes in the neighborhood of synchronous nodes, providing fast transition and interference mitigation mechanisms. Current MAC protocols rely on a passive method to associate a mobile node to a static cluster, triggered by the reception of a beacon. We propose an active approach that allows a mobile node to start sending data packets shortly after entering into data range of a static node, with negligible data loss in existing synchronous data connections. MMH-MAC was implemented in TinyOS and tested on TelosB motes and TOSSIM simulator.

Several routing protocols for Mobile Ad Hoc Networks (MANETS), including the well known Ad hoc On-Demand Distance Vector Routing (AODV) and Optimized Link State Routing (OLSR), propose the use of periodic messages (Hello messages) to detect neighbor nodes. After receiving the first Hello message from one of its neighbors, a node starts the link sensing task by setting up a sensing timer. Each time a new Hello message is received from the same neighbor, the sensing timer is restarted and the link duration is prolonged. If the sensing timer expires, it indicates a long time interval without receiving an Hello message and, consequently, the link is considered broken. The transmission frequency of the Hello messages and the expiration value of the sensing timer truly depends on node's mobility: if the nodes are moving quickly and the Hello messages are rarely transmitted, the neighbor nodes can be in communication range but they are not detected; in the same scenario, if the expiration value of the sensing timer is too high, a link is sensed broken too late. In this paper, we consider a MANET under the Random Waypoint mobility model. We investigate the relationship between the transmission frequency of the Hello messages and the sensing timer expiration value with the network node's mobility. We formally deduce the probability of link existence after β periods of transmission of the Hello message. The probability is later used to define the sensing timer expiration value, considering a given probability that the Hello message transmission fails. Finally, we evaluate our study through both numerically analysis and simulations, which confirms the effectiveness and accuracy of our approach.

This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Frequency- Domain Equalization). We consider iterative frequency-domain receivers that jointly perform equalization, multi-packet separation and channel decoding operations, for up to Qmaxmobile terminals transmitting in one slot. In this paper we propose an accurate analytical model for a p-persistent random access MAC protocol, designed to handle a total number of mobile terminals J above Qmax. It evaluates the uplink non-saturated packet delay and calculates the optimal configuration for the packet transmission probability associated to each mobile terminal that minimizes the delay. Our analytical results are validated using physical and MAC layer simulations.

This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) with low-complexity soft combining ARQ schemes (Automatic Repeat reQuest). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Its low complexity makes it particularly interesting for the uplink of wireless systems. This paper proposes an accurate analytical model for a TDMA (Time Division Multiple Access) scheme where packet combining ARQ is applied. It evaluates the uplink non-saturated packet delay and goodput for a generic message arrival process. Our analytical results are validated using physical and MAC layer simulations.

DTIA (Dynamic Topological Information Architecture), an inter-domain routing architecture, assumed the existence of "regions of domains" to offer a scalable solution for the Internet. The way regions can be connected and how traffic flow amongst them is not a trivial aspect and can jeopardize the solution proposed for intra-region traffic. This paper covers the inter-region case showing that it can be performed by using a smaller set of valid paths than for the intra-region case in the source region, but still featuring multipath to the destination and taking advantage of multi-homing. The routing is based on a monotone algebra to converge without the need to change the IP headers or introduce additional signaling or state in the network. The overall system complies with the current business model of the Internet, and it also features one tendency that has been increasingly used: the fact that Autonomous Systems (ASes) are each time more connected with direct (or semi-direct) links instead of in a pure hierarchical structure up to tier-1 ASes.

This paper proposes an architecture for inter-domain routing, called DTIA - Dynamic Topological Information Architecture. DTIA separates the issues of reachability and routing, and this paper addresses the first one. One major requirement has been not to change IP packets and the commercial relations in the Internet. DTIA is based on the knowledge of a static network formed by the Autonomous Systems (AS) and an algorithm to manage link failures. We use the concept of a region as a mechanism to sustain scale. DTIA supports the most important functionalities of BGP: some of them are built in and others can be implemented on top of the reachability level or the routing level. The main concerns we aim to solve are taking advantage of multihoming, increase the robustness in terms of convergence, reduce the churn rate and range of routing events, and due to forwarding packets by AS identifiers and topologic links (as opposed to prefix policy defined) reduce the growth of the routing table.

This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization). We consider iterative frequency- domain receivers that jointly perform the equalization, multi-packet separation and channel decoding operations. Our receivers allow a high throughput provided that the number of mobile terminals that is trying to access a given slot is equal to or below the multi-packet detection capacity Qmax. We propose a new MAC protocol that allows a total number of mobile terminals J above Qmaxby controlling the number of mobile terminals contending to transmit. The paper evaluates the uplink saturated system throughput and proposes an optimal configuration for the packet transmission probability associated to each mobile terminal. Our analytical results are validated using physical and MAC layer simulations.

The traditional approach to cope with collisions is to discard the packets involved in it and to ask for their retransmission. However, since the signal associated to a collision has important information concerning the packets involved, we can efficiently resolve collisions with proper retransmissions. In this paper we consider severely time-dispersive channels and we propose a technique that allows efficient packet separation. We employ SC-FDE schemes (single-carrier with frequency-domain equalization) and we propose an iterative frequency-domain multi-packet detection. Since our technique requires uncorrelated channels for different retransmissions, we also propose an SP technique (Shifted Packets) for retransmissions in fixed channels. Since the total number of transmissions is equal to the number of packets involved in the collision (even when the channel remains fixed for the retransmissions), our technique allows high throughputs. The analysis of our detection technique combined with the NMDA (network-assisted diversity multiple access) MAC (medium access control) protocol shows significant throughput and delay improvements for low Eb/N0values compared to a TDMA (time division multiple access) approach, where collisions are avoided. This technique is particularly appealing for the uplink of broadband wireless systems, since we consider SC-FDE schemes and the complexity is concentrated in the receiver. By employing the SP scheme we can use the same channel for the retransmissions, with only a small performance degradation.

This paper proposes an architecture for inter-domain routing, called DTIA -- Dynamic Topological Information Architecture. It is designed to address current limitations of BGP like: scalability of the routing tables, multihoming problems, churn rate, range of routing events and policy coordination. Still it supports the most important functionalities of BGP, and maintains the current Internet routing distribution model based on Inter-AS business relationships. The architecture is based on the knowledge of a static network graph formed by the Autonomous Systems (AS) and an algorithm to manage link failures. We use the concept of a region as a mechanism to sustain scale. New possible features like multi-path routing and enhanced Traffic Engineering capabilities might benefit with DTIA's usage.

Usually, packets involved in a collision are lost, requiring their retransmission. However, the signal associated to collisions has important information concerning the packets involved. In fact, with proper retransmissions we can efficiently resolve collisions. In this paper we propose a frequency-domain multi- packet detection technique for SC-FDE schemes (Single- Carrier with Frequency-Domain Equalization) that allows an efficient packet separation in the presence of successive collisions. This technique allows high throughputs, since the total number of transmissions is equal to the number of packets involved in the collision, even when the channel remains fixed for the retransmissions. Since we consider SC-FDE schemes and the complexity is concentrated in the receiver, this technique particularly appealing for the uplink of broadband wireless systems.

This paper proposes MH-MAC, a new MAC protocol for wireless sensor networks capable of handling applications that generate infrequent huge peaks of traffic. Existing protocols are not adapted to this kind of applications. Asynchronous protocols are energy efficient for the long inactive periods, but fail to cope with the bandwidth and latency requirements of the traffic peaks when more than two nodes are sending data to a common sink. Synchronous protocols that support contention free slots provide good throughput for handling the load peaks, but consume unnecessary energy maintaining clocks synchronized for very long idle periods. MH-MAC is a multimode hybrid protocol that can be configured by the application to run in asynchronous mode or in synchronous mode, with or without contention, providing the best possible trade-off. MH-MAC is a single-hop MAC, which supports multi-hop applications through a cross-layering API. The paper includes simulation results with the energy consumption, latency and throughput for the operation modes of MH-MAC, showing the asynchronous-synchronous trade-offs and the state transition overhead.

The strong research on the performance of the IEEE 802.11 standard seen lately contributes to a better understanding of the network and as a starting point for the design of future networks (specially in the ad-hoc area). Oliveira et al. proposed a model to study the IEEE 802.11 DCF delay assuming saturated or non-saturated broadcast and unicast traffic. Oliveira et al. assumes that all nodes generate frames having the same length. This paper extends Oliveira et al. supporting variable frame's length and both unicast basic and RTS/CTS multirate transmission schemes. The 802.11 MAC average time overhead per frame is deduced. Several simulations scenarios are described to validate the theoretical analysis. The validation results confirm that the MAC transmission delay is strongly dependent on the amount of broadcast traffic in the network. For high transmission data rates the MAC delay increases when the broadcast traffic also increases. However when high data rates are not possible the broadcast traffic increase can have the reverse effect.

The existing models for IEEE 802.11 DCF networks only consider unicast frames, ignoring the existence of broadcast traffic. In a real scenario, the stations are most of the times non-saturated and unicast and broadcast frames exist. These specific characteristics influence the service time which consequently affects the queue behaviour. In this paper, the authors model the total frame's delay for IEEE 802.11 DCF networks in presence of both unicast and broadcast traffic. Our theoretical analysis proposes a model able to compute the time between the instant when a new frame is inserted on the transmission queue and the instant when its transmission finishes. The time needed to serve a frame (service time) is formally deduced from the IEEE 802.11 transmission procedure, conceptually using the view of one network's node. The authors use an M/M/1/K queue model in order to model each frame's queueing delay. The authors validate the total frame's delay using several simulations and present some results. These are analysed for different scenarios of broadcast/unicast network loads and different number of nodes.

Most studies on performance of IEEE 802.11 DCF networks do not contemplate the existence of broadcast traffic. They model network behaviour in presence of unicast traffic alone. In a real scenario, broadcast frames exist, and they will influence the overall network behaviour. This work presents a new traffic generalized model for CSMA/CA saturated single-hop networks able to describe the network behaviour in presence of both unicast and broadcast frames. Interesting statistics like station transmission probability, average time needed to complete a frame transmission, and network aggregate throughput are deduced from the model. The paper compares the performance of our model with other models proposed only for unicast traffic. Our model is validated for broadcast and unicast traffic through simulations, using an IEEE 802.11 DCF network scenario. Results are presented and analysed for different scenarios of broadcast/unicast network loads, different number of nodes and different frame data lengths