Performance of Adaptive Beam Nulling in Multihop Ad-Hoc Networks under Jamming

Adaptive beam nulling in multihop ad hoc networks against a jammer in motion

Cooperative communication fully leverages the broadcast nature of wireless channels and exploits time/spatial diversity in a distributed manner, thereby achieving significant improvements in system capacity and transmission reliability. Cooperative diversity has been well studied from the physical layer perspective. Thereafter, cooperative MAC design has also drawn much attention recently. However, very little work has addressed cooperation at the routing layer. In this paper, we propose a simple yet efficient scheme for cooperative routing by using cooperative metrics including packet delivery ratio, throughput, and energy consumption efficiency. To make a routing decision based on our scheme, a node needs to first determine whether cooperation on each link is necessary or not, and if necessary, select the optimal cooperative scheme as well as the optimal relay. To do so, we calculate and compare cooperative routing metric values for each potential relay for each different cooperative MAC scheme (C-ARQ and CoopMAC in this study), and further choose the best value and compare it with the noncooperative link metric. Using the final optimal metric value instead of the traditional metric value at the routing layer, new optimal paths are set up in multihop ad hoc networks, by taking into account the cooperative benefits from the MAC layer. The network performance of the cooperative routing solution is demonstrated using a simple network topology.

One critical issue in multihop ad-hoc networks is the medium access control (MAC). The IEEE 802.11 MAC protocol is originally designed for fully connected, one-hop ad-hoc networks but not for multihop ad-hoc networks. In addition to the well known hidden-terminal problem, we found that IEEE 802.11 also suffers from an erroneous reservation problem which occurs when RTS-CTS exchange fails but the channel is incorrectly reserved. In this paper, we propose a jamming-based MAC (JMAC) protocol that is not only free from both the hidden-terminal and the erroneous reservation problems but also allows more concurrent transmission/receipt activities for stations within each other's transmission range. The idea behind the JMAC is to separate source stations' traffic from destination stations' traffic into different channels (i.e. dividing the shared medium into two channels), and explicitly signal the channel status by jamming the channels. Simulation results show that although the channel division incurs some cost, the advantages of being free from the erroneous reservation and the hidden-terminal problems, and the benefits of more concurrent transmissions will compensate the cost and provide higher channel utilization when data frame size is median or large. Copyright © 2004 John Wiley & Sons, Ltd.

In most profile monitoring applications, the regression parameters are unknown and must be estimated via Phase I reference samples. This study evaluates how parameter estimation affects the average run length (ARL) properties of two well-known charts in Phase II monitoring of logistic regression profiles. In this regard, the performance of T 2 and MEWMA charts established by estimated regression parameters is evaluated for both in-control and out-of-control situations. The results of simulation experiments confirm that estimation error affects the ARL properties of both T 2 and MEWMA charts. Two remedial procedures of increasing the Phase I samples and control limit modification are employed to compensate for the estimation error impact. Then, an illustrative example based on simulated data is given to indicate the impact of estimation error on detection ability of T 2 chart. Finally, a real-life example is provided to represent how estimation error increases the false alarm rate of T 2 chart.

Some ad hoc protocols allow the discovery and/or storage of multiple routes to the same destination node. The selection of the path to utilize is commonly based on the criterion of the minimum number of hops. However, other strategies could be more appropriate to improve the network performance. In this sense, this paper proposes the criterion based on the estimation of the Mean Residual Path Lifetime. In order to compute this metric, a formal description of link duration in mobile ad hoc networks is presented. The model has been verified by means of simulations enclosing different mobility and transmission conditions. From the link duration model, an analytical expression for path duration and mean residual lifetime is then derived. Finally, the authors show that selected ad hoc routing paths live longer when the proposed criterion is employedKeywordsMANETPath DurationRoute Selection

The problem we address in this paper is that of finding effective and parsimonious patterns of connectivity in sparse associative memories. This problem must be addressed in real neuronal systems, so that results in artificial systems could throw light on real systems. We show that there are efficient patterns of connectivity and that these patterns are effective in models with either spiking or non-spiking neurons. This suggests that there may be some underlying general principles governing good connectivity in such networks. We also show that the clustering of the network, measured by Clustering Coefficient, has a strong negative linear correlation to the performance of associative memory. This result is important since a purely static measure of network connectivity appears to determine an important dynamic property of the network.

An adaptive antenna places nulls in its antenna pattern in the direction of the interfering sources. Adaptive antennas are a subset of smart antennas, and have received considerable interest in the recent wireless revolution. This paper presents a successful application of a genetic algorithm with an experimental antenna for placing a null in the direction of an interference source. The experiment took place at the Air Force Research Laboratory (AFRL)/Sensors Directorate, Hanscom AFB, MA. Results show that a null can be placed down to the noise floor of the measurement system within 20 to 50 power measurements. Thus, the approach to adaptive nulling is a viable means of quickly placing a null in the sidelobes of a phased array antenna.

In this paper, the pattern nulling of a linear array for interference cancellation is derived by phase-only perturbations using memetic algorithm. It is proposed to improve the search ability of genetic algorithms. Memetic algorithm is a kind of an improved type of the traditional genetic algorithm. By using local search procedure, it can avoid the shortcoming of the traditional genetic algorithm, whose termination criteria are set up by using the trial and error method. The memetic algorithm is applied to find the pattern nulling of the proposed adaptive antenna. This design for radiation pattern nulling of an adaptive antenna can suppress interference by placing nulls at the directions of the interfering sources, i.e., to increase the Signal to Interference Ratio (SIR). This proposed method is that an innovative adaptive antenna optimization technique is also able to solve the multipath problem which exists in practical wireless communication systems. The example is provided to justify the proposed phase-only perturbations approach based on memetic algorithms. Computer simulation results are given to demonstrate the effectiveness of the proposed method.

The use of an adaptive antenna array as a means of improving the performance of a slotted ALOHA packet radio network is presented. An adaptive array creates a strong capture effect at a packet radio terminal by automatically steering the receiver antenna pattern toward one packet and nulling other contending packets in a slot. A special code preamble and randomized arrival times within each slot allow the adaptive array to lock onto one packet in each slot. The throughput and delay performance of a network with an adaptive array are computed by applying the standard Markov chain analysis of slotted ALOHA. It is shown that throughput levels comparable to carrier sense multiple access (CSMA) are attainable with an adaptive array without the need for stations to be able to hear each other. The performance depends primarily on the number of adaptive array nulls, the array resolution, and the length of the randomization interval within each slot.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

While the millimeter-wave (mmWave) communication is less susceptible against the conventional wiretapping attack due to its short transmission range and directivity, this paper proposes a new opportunistic wiretapping and jamming (OWJ) attack model in mmWave wireless networks. With OWJ, an attacker can opportunistically conduct wiretapping or jamming to initiate a more hazardous attack based on the instantaneous costs of wiretapping and jamming. We also provide three realizations of the OWJ attack, which are mainly determined by the cost models relevant to distance, path loss and received power, respectively. To understand the impact of the new attack on mmWave network security, we first develop novel approximation techniques to characterize the irregular distributions of wiretappers, jammers and interferers under three OWJ realizations. With the help of the results of node distributions, we then derive analytical expressions for the secrecy transmission capacity to depict the network security performance under OWJ. Finally, we provide extensive numerical results to illustrate the effect of OWJ and to demonstrate that the new attack can more significantly degrade the network security performance than the pure wiretapping or jamming attack.

An adaptive nulling system has been designed for a space-based radar incorporating a phased array fed Cassegrain antenna. Auxiliaries are formed by reusing elements from the main antenna array feed together with an external horn antenna. Antenna patterns for the main antenna and for the auxiliaries are calculated using a physical optics-based reflector code. Nulling performance is calculated using an Applebaum array model, and results using array element reuse and external horn auxiliaries are compared. Using both types of auxiliaries together is considered. It is found that the array element reuse auxiliaries provide sufficient sidelobe coverage in most cases. Performance is found to degrade when jammers are at far-out sidelobe locations, and when multiple jammers are present. Optimal performance may be obtained with a combination of reuse and external horn auxiliaries. >

Segment routing (SR) is a new routing paradigm to provide traffic engineering (TE) capabilities in an IP network. The main feature of SR is that no signaling protocols are needed, since extensions of the interior gateway protocol routing protocols are used. Despite the benefit that SR brings, introducing a new technology into an operational network presents many difficulties. In particular, the network operators consider both capital expenditure and performance degradation as drawbacks for the deployment of the new technology; for this reason, an incremental approach is preferred. In this paper, we face the challenge of managing the transition between a pure IP network to a full SR one while optimizing the network performances. We focus our attention on a network scenario where: 1) only a subset of nodes are SR-capable and 2) the TE objective is the minimization of the maximum link utilization. For such a scenario, we propose an architectural solution, named SR domain (SRD), to guarantee the proper interworking between the IP routers and the SR nodes. We propose a mixed integer linear programming formulation to solve the SRD design problem, consisting in identifying the subset of SR nodes; moreover, a strategy to manage the routing inside the SRD is defined. The performance evaluation shows that the hybrid IP/SR network based on SRD offers TE opportunities comparable to the one of a full SR network. Finally, a heuristic method to identify nodes to be inserted in the set of nodes composing the SRD is discussed.

Traditional portfolio optimization has often been criticized for not taking estimation risk into account. Estimation risk is mainly driven by the parameter uncertainty regarding the expected asset returns rather than their variances and covariances. The global minimum variance portfolio has been advocated by many authors as an appropriate alternative to the tangential portfolio. This is because there are no expectations which have to be estimated and thus the impact of estimation errors can be substantially reduced. However, in many practical situations an investor is not willing to choose the global minimum variance portfolio but he wants to minimize the variance of the portfolio return under specific constraints for the portfolio weights. Such a portfolio is called local minimum variance portfolio. Small-sample hypothesis tests for global and local minimum variance portfolios are derived and the exact distributions of the estimated portfolio weights are calculated in the present work. The first two moments of the estimator for the expected portfolio returns are also provided and the presented instruments are illustrated by an empirical study.

This study quantifies the number of estimates involved in firms’ accruals and examines whether it is informative about the relation between accruals and future earnings. We measure the number of estimates using the frequency of the use of the word estimate in the qualitative portions of a firm’s Notes to the Financial Statements (footnotes). Motivated by arguments regarding the impact of estimation errors in accruals, we hypothesize and find that the accruals of firms that have more estimates have a lower relation with future earnings (i.e., lower persistence) and a lower association with their past, current, and future cash flows. This paper was accepted by Suraj Srinivasan, accounting. Funding: This work was supported by Zijiang Endowment. H. Chen acknowledges the financial support from the National Natural Science Foundation of China [Grants 72150710550, 71790591, and 72121002]. J. V. Chen acknowledges the financial support from the University of Michigan, University of Illinois at Chicago, Paton Accounting Fellowship, and Harry Jones Endowment. F. Li acknowledges the financial support from SJTU SAIF Zijiang Discipline Development Fund, sponsored by the Zijiang Foundation. Supplemental Material: The internet appendix and data are available at https://doi.org/10.1287/mnsc.2022.4659 .

The one-sided cumulative count of conforming (CCC) chart is a useful method to monitor nonconforming fraction in high-quality manufacturing processes. The nonconforming fraction parameter is assumed to be known when implementing a one-sided CCC chart. In this study, we investigated the impact of estimated nonconforming fraction, [pcirc] 0, in a one-sided CCC chart. The run length distribution is derived as well as the conditional probability of a false alarm rate (CFAR), conditional average run length (CARL) and its standard deviation (CSDRL). Simulation results are conducted to evaluate the effect of [pcirc] 0 in a one-sided CCC chart. The results show that values of CFAR, CARL and CSDRL are close to the nominal values for a large sample. The impact of estimation errors was also studied. We find that CFAR decreases for large [pcirc] 0. Thus, a large value of [pcirc] 0 is suggested for fewer false alarms.