Opportunistic Protocol Research Articles

Energy-Efficient Distributed Power Allocation With Multiple Relays and Antenna Selection

This paper proposes an iterative power allocation algorithm that maximizes the energy efficiency of a multiple-relay cooperative multiple antenna (MIMO) network. Energy efficiency is defined as the achievable spectral efficiency normalized by the total power consumption, which also accounts for the RF circuitry consumption, modeled in a wireless sensor network. Moreover, relay selection is performed using the distributed opportunistic selection protocol, while we derive closed-form expressions for outage probability and energy efficiency for a single antenna (SISO) and two MIMO scenarios: 1) based on antenna selection (AS) and 2) based on single value decomposition (SVD) beamforming. In order to evaluate the performance of the proposed algorithm, we compare it to an exhaustive search optimal power allocation method. Results show that the proposed algorithm performs very close to an exhaustive search approach and that, although MIMO SVD has the best outage performance, AS has the best energy efficiency for low and moderate source-destination distances and spectral efficiencies.

Source Selection and Content Dissemination for Preference-Aware Traffic Offloading

As mobile devices become more ubiquitous, the amount of cellular traffic for multimedia content grows explosively. Therefore, data dissemination through proximity-based opportunistic communications attracts the attention of service providers who are eager for solutions of traffic offloading. In this paper, we propose PrefCast , a preference-aware opportunistic content dissemination protocol that uses as few cellular bandwidth as possible to maximally satisfy user preferences for content objects. The efficiency of PrefCast depends on 1) how does the base-station select initial sources, and 2) how does each user forward objects within a limited contact duration. Since mobile users typically form communities and have heterogeneous preferences, PrefCast ’s base-station selects sources that efficiently produce the maximal utility to their communities. We then derive a model to predict how much utility a forwarder can contribute to future contacts. PrefCast ’s users can hence use such prediction to find their optimal forwarding schedule, which maximizes the utility contribution, in a distributed way. Our trace-based evaluation shows that, without explicit source selection, PrefCast produces a 15.7 and 22.6 percent higher average utility than the protocols that only consider contact frequency or preference of local contacts, respectively. Enabling source selection in PrefCast further improves the utility by 49.3 percent.

Connectivity-based Cross-Layer Opportunistic Forwarding for MWSNs

ABSTRACTMobile wireless sensor networks (MWSNs) consist of many sensor nodes that are randomly distributed in the environment to gather information. In MWSNs, the transmission path is affected due to node mobility and node failures. Routing protocols in MWSNs must adjust to topology changes and should determine the path with minimum overheads. Some of the existing works on the opportunistic routing minimize the energy consumption, but have large overheads and duplicate packet transmissions. In this paper, we have designed and implemented a connectivity-based cross-layer opportunistic forwarding protocol for mobile wireless sensor networks. We estimate the expected energy consumption cost for forwarding the data using prioritized forwarder list and node's connectivity metric. Connectivity metric signifies the ability of node to partition the network on its failure. To reduce retransmissions, we implement forwarding agreement mechanism among the nodes in the forwarder list, if the desired relay node has moved or failed. Our analysis shows that our protocol consumes less energy compared to conventional routing protocols. Simulation results for our protocol are compared with Energy Efficient Opportunistic Routing (EEOR), Destination Sequenced Distance Vector and ad hoc on-demand multipath distance vector protocol for energy efficiency, overheads, and packet loss. Our protocol exhibits 22% improvement in energy consumption compared to energy efficient opportunistic routing (EEOR) and also significant improvements for other performance parameters.

Opportunistic Neighbour Prediction Using an Artificial Neural Network

Device mobility is an issue that affects both MANETs and opportunistic networks. While the former employs conventional routing techniques with some element of mobility management, opportunistic networking protocols often use mobility as a means of delivering messages in intermittently connected networks. If nodes are able to determine the future locations of other nodes with reasonable accuracy then they could plan ahead and take into account and even benefit from such mobility. Location prediction in combination with geographic routing has been explored in previous literature. Most of these location prediction schemes have made simplistic assumptions about mobility. However more advanced location prediction schemes using machine learning techniques have been used for wireless infrastructure networks. These approaches rely on the use of infrastructure and are therefore unsuitable for use in opportunistic networks or MANETs. To solve the problem of accurately predicting future location in non-infrastructure networks, the authors have investigated the prediction of continuous numerical coordinates using artificial neural networks. Simulation using three different mobility models representing human mobility has shown an average prediction error of less than 1m in normal circumstances.

Improved-throughput opportunistic transmission protocol for cooperative communication systems with a preferable-link switching combining

In this article, we propose an opportunistic transmission protocol for cooperative communication systems with L relay nodes under the influence of fading channels. Unlike the protocols previously known in the literature, and given the fact that direct single-link communication outperforms multilink cooperative communication in terms of throughput for same channel conditions, we adopt the channel conditions of the direct link as a main criterion to use whether the direct link in the transmission or the indirect cooperative link. Different performance metrics are derived to demonstrate the performance of the proposed protocol along with a switching combining with a preferable link scheme. These metrics include the bit error rate (BER), outage probability, signal to interference noise ratio (SNR) gain, average throughput and the sum SNR–throughput product (SSTP). The latter performance metric is introduced to compare the maximum achievable throughput as well as the SNR range at a given quality of service (QoS). Our results show that the proposed opportunistic protocol improves the throughput as compared to the conventional cooperative communication systems for the whole range of average SNR. On the other hand, it improves the coverage range as compared to the direct link communication.

L2OR: Low-Cost Low-Complexity Opportunistic Routing for Wireless Sensor Networks

Opportunistic routing can greatly improve energy efficiency in wireless sensor networks (WSNs). An important challenge is the design of a coordination protocol to implement an effective relay selection and prioritization scheme to minimize expected cost. Many existing opportunistic routing protocols often assumed an ideal link-layer, and thus the computed forwarder list may be suboptimal. Worth noting that, the computation complexity of optimal result grows rapidly with size of candidate set when the nonideal link-layer conditions are taken into account. It is, however, not feasible for energy and processing capability constrained WSNs. To address this problem, we propose a low-cost low-complexity opportunistic routing (L2OR) protocol to achieve an energy-efficient data delivery over WSNs. Our research work begins with a thorough investigation and understanding of properties of forwarder list under nonideal link-layer conditions. On this basis, a low-complexity heuristic algorithm is designed to efficiently find a reasonable choice of forwarder list, with an objective of reducing the search space to the size of candidate set. We conduct theoretical analysis and a set of simulation experiments to evaluate the performance of our L2OR. It is shown that, when comparing to typical energy-aware opportunistic protocol, the L2OR can achieve performance improvement in terms of data transmission efficiency as well as energy consumption.

Preemptive Opportunistic MAC Protocol in Distributed Cognitive Radio Networks

A preemptive opportunistic cognitive radio (CR) medium access control (MAC) protocol, which is called PO-MAC, is proposed for distributed CR networks. PO-MAC consists of three main phases: network initialization, reporting, and contention. The primary user (PU) channel exclusively assigned to each secondary user (SU) is sensed during the sensing period, and the sensing result is then reported to all other SUs without collisions during the reporting phase. Using the sensing results, SUs can preempt and make use of free channels via a contention method during the contention phase. It is demonstrated that PO-MAC outperforms existing CR MAC protocols in terms of the end-to-end delay and throughput performance. Further, it is shown that PO-MAC effectively operates when used in real-time services such as voice over Internet protocol.

Improved opportunistic feedback with multiuser diversity for wireless systems with finite queue

A contention-based opportunistic feedback protocol has been proposed in the literature, to achieve multiuser diversity for the downlink transmission of a multiuser wireless system, with the assumption that the incoming data for the active users are infinitely backlogged. However, this assumption is not valid if the authors consider the finite-length queuing effect in practical systems. By taking not only the channel states, but also the queuing states into account, the authors propose an improved opportunistic feedback protocol with multiuser diversity, and analyse its performance with adaptive modulation and coding. Additionally, instead of solving a system of equations directly, a simple iterative method is proposed to obtain the stationary distribution of the system, where the system behaviour is modelled by a two-dimensional finite-state Markov chain. Numerical results demonstrate that the authors proposed protocol is superior to the protocol in the literature in terms of the average throughput, the average spectral efficiency and the average packet delay, when considering the queuing dynamics.

Opportunistic Cooperative Reliable Transmission Protocol for Wireless Sensor Networks

The high reliability requirement of data transmission in wireless sensor networks has been a large challenge due to the random mobility and network topoloy instability, as well as restriction of energy consumption and system life time. In this work, the relationship matirx of distance and speed was created at first. Then the binay tree of mobility and reliabiliy was proposed based on the distance relationship matrix. The optimal relay nodes with high reliabiliy were selected by seeking the binay tree. The high reliable opportunistic cooperative data transmission scheme was presnted finally. The outcome of both mathematical analysis and NS simulation indicate that the proposed mechanism is superior to the traditional data transmission mechnism such as the reliability, system throughput and energy efficiency and so on.

Análisis coste-beneficio de un programa poblacional de diagnóstico precoz de cáncer de cuello uterino diseñado para Cantabria

IntroductionCervical cancer is the second most common cancer worldwide in women, with an annual mortality of 3.6 per 100.000 women in Spain. An opportunistic screening protocol is currently being developed in Cantabria. The objective of the study is to propose a population-based screening program in Cantabria and assess its cost-benefits. Patients and methodsThe population-based program design has been carried out according to the description of the natural course of cervical cancer and its incidence and mortality in Cantabria during 2000-2009. There have been some proposals to increase participation in the program and to evaluate its quality. Costs and benefits (direct and indirect) have been analyzed in several scenarios by modifying the frequency of tests (3-5 years), the age at which the program can be accessed (21, 25 or 30 years), the coverage of the program (60-80%), and discount rates (0-3-6%). ResultsA program carried out with coverage of 80% and tests performed every 3 years generates annual costs of €893.000 (discount rate of 3%) compared to the current opportunistic protocol. Scenarios with tests performed every 5 years generate an annual benefit higher than €618.000, depending on the age of accessing the program. ConclusionsScenarios with coverage lower than 60% or with women over 30 years old having access to the program are not of interest because of the lower health benefits. However, performing tests every 5 years is more economically advantageous than every 3 years, with similar health benefits.

Cobertura y costes del cribado oportunista de detección precoz del cáncer de cuello uterino en Cantabria

ObjectiveTo analyze cervical cancer screening performed in Cantabria by evaluating the coverage and costs of screening and by calculating the available direct costs of the disease and the indirect costs of cervical cancer mortality. MethodsScreening for cervical cancer is performed in women aged between 21 and 65. According to the census for 2011 in Cantabria, there were 189.111 women in this age group. We performed a cross sectional, quantitative and qualitative study of the Pap smears performed and analyzed the direct and indirect costs of cervical cancer. ResultsBetween 2006 and 2011, 51% of women studied had one Pap smear, and 26% had two. In 2011, 31.554 Pap smears were performed in opportunistic screening in Cantabria, and the direct cost was 2,904.760 €. The annual direct cost of cervical cancer (average 2008-2010) was 567.567 €. The annual indirect costs (average 2001-2008) of cervical cancer was 386.122.02 €, in the reference scenario considered. ConclusionsOnly 26% of women in Cantabria attended screening within the intervals recommended in the current opportunistic protocol. The cost data provided in this study may be useful for future economic evaluations.

A Comparison of Opportunistic Connection Datasets

Opportunistic networking differs from conventional architectures in the lack of existing network infrastructure, which can cause intermittent connectivity or increased communication delay between nodes. From a message routing perspective, solving these problems require a different set of techniques than those used in more traditional network schemes. Forwarding algorithms in these scenarios aim to improve performance metrics such as message delivery ratio and message delay time, while trying to keep the number of message copies small. A common approach used for testing the performance of opportunistic protocols relies on existing opportunistic contact traces. These datasets are widely available on the Internet, and provide a convenient way of simulating realistic usage scenarios. As such, studying the contact patterns between nodes can lead to useful observations to take into account in future experiments. This paper presents the results of a study on four different datasets. First, the authors describe the main characteristics of each trace. Then, they propose a graphical representation of the contact behavior for each pair of nodes. Further analysis of the results in terms of connectivity distribution among nodes reveals that contacts follow a roughly lognormal distribution and that there is a small group of nodes in each set which is seemingly much more popular than the rest. Finally, the authors introduce a temporal analysis that was made over the duration of each collection experiment. It was noticeable that individual nodes have repetitive contact patterns over time, apart from some observed cyclic variation over time (namely on weekends). By modeling the data traces as time-varying graphs, a performance decrease was observed with the absence of the most popular nodes.

Performance analysis of CSMA-based opportunistic medium access protocol in cognitive radio sensor networks

Given the highly variable physical layer characteristics in cognitive radio sensor networks (CRSN), it is indispensable to provide the performance analysis for cognitive radio users for smooth operations of the higher layer protocols. Taking into account the dynamic spectrum access, this paper formulates the two fundamental performance metrics in CRSN; bandwidth and delay. The performance is analyzed for a CSMA-based medium access control protocol that uses a common control channel for secondary users (SUs) to negotiate the wideband data traffic channel. The two performance metrics are derived based on the fact that SUs can exploit the cognitive radio to simultaneously access distinct traffic channels in the common interference region. This feature has not been exploited in previous studies in estimating the achievable throughput and delay in cognitive radio networks. Performance analysis reveals that dedicating a common control channel for SUs enhances their aggregated bandwidth approximately five times through the possibility of concurrent transmissions on different traffic channels and reduces the packet delay significantly.

An Opportunistic Protocol Employing Independent Codebooks for Bidirectional Cooperative Networks

We propose an opportunistic source selection (OSS) protocol employing independent (channel) codebooks (OSS-IC), which outperforms any existing bidirectional-coded decode-and-forward (DF) protocols at high signal-to-noise ratios (SNRs). We derive the expressions of the mutual information, exact outage probability, and asymptotic outage probability for the OSS-IC protocol. We also derive a closed-form and tight approximation for the outage probability. Then, we show that the ideal relay location is the midpoint between two end-sources. Furthermore, we analytically prove that the OSS-IC protocol provides the best outage performance at high SNRs, compared with any known bidirectional-coded DF protocols, including time-division broadcast (TDBC) and physical-layer network coding (PNC). Finally, we quantify the gains of OSS-IC over those protocols at high SNRs.

Energy saving in cooperative transmission using opportunistic protocol in MANET

Energy saving in cooperative transmission using opportunistic protocol in MANET

Energy saving in cooperative transmission using opportunistic protocol in MANET

In this thesis, we study the joint problems of cooperative link and diversity in A Mobile Ad-Hoc Network (MANET) with variable wireless channels. In MANET the wireless nodes are in group and infrastructure less in nature. The major problems faced by wireless communication in real time environment are that of interference and un-reliable communication links. Much research work has been done to overcome this by using various techniques. Cooperative communication and transmission side diversity in the network are the two of the techniques that help in reducing interference and communication link failures. We have also proposed a new technique to find the optimum route as a joint problem of the transmission power at the physical layer and the link selection at the network layer that incurs the minimum cost in terms of energy, no. of hops, available bandwidth and link quality (SNR), outage probability. Analytical results show that our cooperative transmission schemes (OMCTSP) achieves average energy saving of more than 80% than direct transmission.

Opportunistic Unicast and Multicast Routing Protocol for VANET

Vehicular Ad Hoc Network (VANET) is a new paradigm of wireless network. Reliable and efficient unicast and multicast routing protocols are critical for VANETs. As a possible solution, opportunistic routing (OR) has received much attention recently. This paper focuses on the aspect of soft security by building trust opportunistic forwarding model in VANET. It incorporates the trust mechanism into OR to enhance the security of routing in resisting malicious attacks. In this paper, we proposed a trusted minimum cost opportunistic unicast routing protocol (TMCOR) and a multicast routing protocol (TMCOM). The simulation results show TMCOR and TMCOM have good throughput, average delay and security gains compared with existing protocols.

Opportunistic Retransmission in WLANs

This paper presents an efficient opportunistic retransmission protocol (PRO, Protocol for Retransmitting Opportunistically) to improve the performance of IEEE 802.11 WLANs. PRO is a link-layer protocol that allows overhearing nodes to function as relays that retransmit on behalf of a source after they learn about a failed transmission. Relays with better connectivity to the destination have a higher chance of delivering the packet than the source, thereby resulting in a more efficient use of the channel. PRO has four main features. First, channel reciprocity coupled with a runtime calibration process is used to estimate the instantaneous link quality to the destination. Second, a local qualification process filters out poor relays early. Third, a distributed relay selection algorithm chooses the best set of eligible relays among all qualified relays and prioritizes them. Finally, 802.11e Enhanced Distributed Channel Access (EDCA) is leveraged to make sure high-quality relays transmit with higher probability. PRO is designed to coexist with legacy 802.11 stations. Our extensive evaluation on both a controlled testbed and in the real world shows that PRO can improve throughput in diverse wireless environments. PRO helps the most when there is significant contention for the ether, under fading, and with user mobility.

Performance Analysis of an Opportunistic Relay Selection Protocol for Multi-Hop Networks

We analyze the performance of an interference-aware opportunistic relay selection protocol for multi-hop line networks which is based on the following simple rule: a node always transmits if it has a packet, except when its successive node on the line is transmitting. We derive analytically the saturation throughput and the end-to-end delay for two and three hop networks, and present simulation results for higher numbers of hops. In the case of three hops, we determine the throughput-optimal relay positions.

A distributed message in message aware concurrent transmission protocol in IEEE 802.11 WLANs

Abstract The IEEE 802.11 distributed coordination function (DCF) employs the carrier sense technology to avoid frame collisions. However, recent measurement studies demonstrate that the physical layer (PHY) capture effect frequently occurs; even when frames collide, one of them can be decoded successfully if its relative signal strength is high enough. Furthermore, a new wireless PHY technology, called Message In Message (MIM), adopts an advanced preamble detection function to enhance the PHY capture effect. To fully exploit MIM in multi-collision environments, frame transmission orders have to be carefully scheduled. It also requires tight time synchronization at multiple access points (APs), thus induces large overheads. In this article, we propose an opportunistic concurrent transmission protocol called D istributed O pportunistic M IM-aware C oncurrent T ransmission (DOMCT) which exploits the MIM functionality in a distributed manner obliterating the centralized control. In DOMCT, APs first prepare interference MAPs to discover the possible simultaneous MIM transmission opportunities. Detecting the inadvertent frame transmission from a neighboring AP, an AP transmits another frame intentionally if both frames can successfully be decoded at destination nodes by the MIM capture effect. Through both analysis and extensive ns-2 simulations, we show that DOMCT outperforms the legacy DCF by up to 61% and observe comparable performance to that of the centralized approach.