Cumulative Interference Research Articles

Cumulative and Non-Cumulative Semantic Interference in Object Naming: Evidence from Blocked and Continuous Manipulations of Semantic Context

Experiments involving blocked and continuous manipulations of the semantic naming context demonstrate that, when speakers name several taxonomically related objects in close succession, they display persistent interference effects. A review of studies using the blocked paradigm shows that, unlike the continuous paradigm, it typically does not induce cumulative interference effects in healthy speakers. This contrasts with the simulation results obtained from a model of semantic context effects recently put forward by Oppenheim and colleagues [Oppenheim, G. M., Dell, G. S., & Schwartz, M. F. (2010). The dark side of incremental learning: A model of cumulative semantic interference during lexical access in speech production. Cognition, 114, 227--262], which generates cumulative effects in both paradigms. We propose that the effects are non-cumulative in the blocked paradigm, because it allows participants to bias top-down the levels of activation of lexical-semantic representations, thereby curtailing the accumulating interference. Indeed, prior research has shown that the interference effects in the blocked paradigm are exacerbated when participants carry out a concurrent digit-retention task, loading on working memory and reducing their capacity to exert a top-down bias. In Experiment 1, combining the continuous paradigm with a digit-retention task, we demonstrate that this does not exacerbate cumulative context effects, corroborating the selective role of working memory and the associated top-down biasing mechanism in the blocked paradigm. A review of neuropsychological and neuroimaging studies demonstrates that left inferior frontal regions may play a critical role in controlling semantic interference top-down. We discuss the implications of these findings for language production research and for models of lexical-semantic encoding.

Perfusion fMRI evidence for priming of shared feature-to-lexical connections during cumulative semantic interference in spoken word production

The speed at which target pictures are named increases monotonically as a function of prior retrieval of other exemplars of the same semantic category and is unaffected by the number of intervening items. This cumulative semantic interference effect is generally attributed to three mechanisms: shared feature activation, priming and lexical-level selection. However, at least two additional mechanisms have been proposed: (1) a ‘booster’ to amplify lexical-level activation and (2) retrieval-induced forgetting (RIF). In a perfusion functional Magnetic Resonance Imaging (fMRI) experiment, we tested hypotheses concerning the involvement of all five mechanisms. Our results demonstrate that the cumulative interference effect is associated with perfusion signal changes in the left perirhinal and middle temporal cortices that increase monotonically according to the ordinal position of exemplars being named. The left inferior frontal gyrus (LIFG) also showed significant perfusion signal changes across ordinal presentations; however, these responses did not conform to a monotonically increasing function. None of the cerebral regions linked with RIF in prior neuroimaging and modelling studies showed significant effects. This might be due to methodological differences between the RIF paradigm and continuous naming as the latter does not involve practicing particular information. We interpret the results as indicating priming of shared features and lexical-level selection mechanisms contribute to the cumulative interference effect, while adding noise to a booster mechanism could account for the pattern of responses observed in the LIFG.

Effective Carrier Sensing in CSMA Networks under Cumulative Interference

This paper proposes the concept of safe carrier-sensing range under the cumulative interference model that guarantees interference-safe (also known as hidden-node-free) transmissions in CSMA networks. Compared with a previous related concept of safe carrier-sensing range under the commonly assumed but less realistic pairwise interference model, we show that the safe carrier-sensing range under the cumulative interference model is larger by a constant multiplicative factor. For example, the factor is 1.4 if the SINR requirement is 10 dB and the path-loss exponent is 4 in a noiseless case. We further show that the concept of a safe carrier-sensing range, although amenable to elegant analytical results, is inherently not compatible with the conventional power-threshold carrier-sensing mechanism (e.g., that used in IEEE 802.11). Specifically, the absolute power sensed by a node in the conventional carrier-sensing mechanism does not contain enough information for the node to derive its distances from other concurrent transmitting nodes. We show that, fortunately, a new carrier-sensing mechanism called Incremental-Power Carrier-Sensing (IPCS) can realize the carrier-sensing range concept in a simple way. Instead of monitoring the absolute detected power, the IPCS mechanism monitors every increment in the detected power. This means that IPCS can separate the detected power of every concurrent transmitter, and map the power profile to the required distance information. Our extensive simulation results indicate that IPCS can boost spatial reuse and network throughput by up to 60 percent relative to the conventional carrier-sensing mechanism under the same carrier-sensing power thresholds. If we compare the maximum throughput in the interference-free regime, the throughput improvement of IPCS is still more than 15 percent. Last but not least, IPCS not only allows us to implement the safe carrier-sensing range, but also ties up a loose end in many other prior theoretical works that implicitly used a carrier-sensing range (interference-safe or otherwise) without an explicit design to realize it.

Are Investments in Groundwater Irrigation Profitable? A Case of Rice Farms from South India1

Varghese, Shalet Korattukudy, Jeroen Buysse, Aymen Frija, Stijn Speelman, and Guido Van Huylenbroeck, 2012. Are Investments in Groundwater Irrigation Profitable? A Case of Rice Farms from South India. Journal of the American Water Resources Association (JAWRA) 1‐15. DOI: 10.1111/j.1752‐1688.2012.00690.xAbstract: This article examines the profitability of cultivating double rice under bore well irrigation, given the cumulative interference of and reduced life span of wells, and thus increases the cost of groundwater extraction and use. The overexploitation of groundwater is a common stock problem and the cultivation of water intensive crops, such as rice, further exacerbates the overdraft of groundwater. Under these circumstances, we quantify the marginal benefit of irrigation investments in rice farming by estimating the probability of having a double rice crop as a function of the investment made in wells. Using this information, we explore profit maximization behavior of farms with a mathematical programming model to derive individual economic optima of irrigation costs. The results demonstrate that the ongoing overexploitation of groundwater, and its use to cultivate an economically inefficient crop, such as rice, has resulted in low profitability at farm level. A sensitivity analysis found that even when the investment in irrigation wells is reduced by 70%, small farms are still not economically efficient, thereby confirming the Tragedy of the Commons. Raising awareness amongst farmers with regard to the economics of irrigation would facilitate the participatory implementation of control mechanisms to regulate groundwater extraction.

Immune Effects and Polychlorinated Biphenyls, Smoking and Alcohol

Polychlorinated biphenyls (PCB) have been shown to exert some immune effects. Here we analysed their effects also on immune parameters not previously studied such as TCR alpha-beta, TCR gamma-delta and regulatory T cells (Treg), taking into account the specific and cumulative interference of smoking and alcohol. The study subjects consisted of 26 male workers in a steel works factory, employed in the electrical maintenance sector, with previous exposure to a mixture of PCB (exposed subjects), and 30 male workers with no occupational exposure to PCB (controls). All subjects were given a questionnaire and peripheral venous blood samples were taken to determine serum PCB (33 congeners), total cholesterol and triglycerides, leukocytes, total lymphocytes and the T lymphocyte subpopulations (TCR alpha-beta, TCRgamma-delta, CD4+ and Treg lymphocytes). PCB, even though at a very low concentration, were significantly higher in exposed subjects than controls, and were significantly correlated with age. Monocytes% and CD4+ were significantly reduced in the exposed subjects as compared to the controls. The serum concentration of PCB positively correlated with TCR alpha-beta, and negatively with TCRgamma-delta. Treg lymphocytes showed a positive dependence on tobacco smoking, while the monocytes percentage and CD4+ showed a negative and positive dependence, respectively, on alcohol intake. Our results seem to show some effects of slight exposure to PCB in particular reducing the relative concentration of TCRgamma-delta. This effect can favour indirectly the increase in Treg induced by smoking, the anti-inflammatory or proinflammatory/fibrogenetic/angiogenetic effect of which, exerted by produced cytokines, particularly TGF-beta, deserves further clarification.

Hybrid BS-Cooperative Power Management Scheme with Self-Organized Sleep Mode in Virtual Cell-Based Femto Networks

A large-scale deployment of femtocell BSs (FBSs) causes substantial energy consumption. This paper proposes a hybrid BS-cooperative power management (HBCPM) scheme with self-organized sleep mode in virtual cell-based femto networks. Firstly, HBCPM builds a leader-member virtual cell framework, in which only one FBS is a FBS leader (FL) and others are FBS members (FMs). Then, the FL acts as an autonomous entity and is responsible for detecting active calls in the virtual cell coverage, while the FMs without active connections can entirely shut down pilot transmissions and the related processing all the time. So it is suited for self-organizing networks (SONs). Based on the proposed scheme, the state transition model is established by the semi-Markov stochastic process, and the analytic formulas of average cumulative delay and interference time as well as the energy consumption are derived. Meanwhile, three prominent-related schemes are also studied by the proposed model. With the practical long-term evolution (LTE) system parameters and three-dimensional femtocell network model, the numerical simulation and theoretical analysis match pretty well, and the tradeoff between the energy consumption and average cumulative delay is also manifested. Moreover, simulation results show that the proposed algorithm outperforms other three schemes in terms of average cumulative interference time and the energy consumption.

Maximal Scheduling in Wireless Ad Hoc Networks With Hypergraph Interference Models

This paper proposes a hypergraph interference model for the scheduling problem in wireless ad hoc networks. The proposed hypergraph model can take the sum interference into account and, therefore, is more accurate as compared with the traditional binary graph model. Further, different from the global signal-to-interference-plus-noise ratio (SINR) model, the hypergraph model preserves a localized graph-theoretic structure and, therefore, allows the existing graph-based efficient scheduling algorithms to be extended to the cumulative interference case. Finally, by adjusting certain parameters, the hypergraph can achieve a systematic tradeoff between the interference approximation accuracy and the user node coordination complexity during scheduling. As an application of the hypergraph model, we consider the performance of a simple distributed scheduling algorithm, i.e., maximal scheduling, in wireless networks. We propose a lower bound stability region for any maximal scheduler and show that it achieves a fixed fraction of the optimal stability region, which depends on the interference degree of the underlying hypergraph. We also demonstrate the interference approximation accuracy of hypergraphs in random networks and show that hypergraphs with small hyperedge sizes can model the interference quite accurately. Finally, the analytical performance is verified by simulation results.

Latency-minimizing data aggregation in wireless sensor networks under physical interference model

Minimizing latency is of primary importance for data aggregation which is an essential application in wireless sensor networks. Many fast data aggregation algorithms under the protocol interference model have been proposed, but the model falls short of being an accurate abstraction of wireless interferences in reality. In contrast, the physical interference model has been shown to be more realistic and has the potential to increase the network capacity when adopted in a design. It is a challenge to derive a distributed solution to latency-minimizing data aggregation under the physical interference model because of the simple fact that global-scale information to compute the cumulative interference is needed at any node. In this paper, we propose a distributed algorithm that aims to minimize aggregation latency under the physical interference model in wireless sensor networks of arbitrary topologies. The algorithm uses O(K) time slots to complete the aggregation task, where K is the logarithm of the ratio between the lengths of the longest and shortest links in the network. The key idea of our distributed algorithm is to partition the network into cells according to the value K, thus obviating the need for global information. We also give a centralized algorithm which can serve as a benchmark for comparison purposes. It constructs the aggregation tree following the nearest-neighbor criterion. The centralized algorithm takes O( logn) and O(log3n) time slots when coupled with two existing link scheduling strategies, respectively (where n is the total number of nodes), which represents the current best algorithm for the problem in the literature. We prove the correctness and efficiency of our algorithms, and conduct empirical studies under realistic settings to validate our analytical results.

Joint Spectrum Allocation and Power Control for Multihop Cognitive Radio Networks

We propose a new framework of joint spectrum allocation and power control to utilize open spectrum bands in cognitive radio networks (CRNs) by considering both interference temperature constraints and spectrum dynamics. We first address a simpler problem for the case of a single flow. A TDM-based power-control strategy is adopted to achieve maximum end-to-end throughput by choosing an appropriate multihop route and spectrum combination for each single flow. Then, the simpler solution is extended to the multiflow case in which interflow interference and cumulative interference temperature must be considered. Considering the overhead of switching route and spectrum, the optimal waiting time before making a switch is derived. Our in-depth simulation study has shown that the proposed algorithms utilize spectrum more efficiently than other existing algorithms.

On the Interplay Between Spatial Reuse and Network Coding in Wireless Networks

This paper studies the interplay between network coding and spatial reuse in wireless mesh networks. We present a method that attempts to maximize the system performance by exploiting effectively (and not greedily) coding opportunities through appropriate routing and achieving efficient spectrum reuse through opportunistic link scheduling. We show that judiciously selecting coding structures requires proper transmission power allocation to better manage cumulative interference in the network, and thus yield better spectrum spatial reuse and effective multi-hop system throughput. We present an optimization model for this complex design problem, which relies on the enumeration of all possible schedules and decompose it into subproblems which we can solve more efficiently. Our numerical results indicate that optimal joint coding and scheduling with proper power allocation yields a performance enhancement of more than 10% over that with maximal power transmission and more than 45% enhancement over a coding oblivious design model. Our results also revealed that network coding has only marginal benefits (~6%) in a dense network and that in such networks managing interference through proper power allocation yields very good performance.

Frequency allocation problem in a SDMA satellite communication system

Spatial Division Multiple Access (SDMA) is a principle of radio resource sharing that relies on the division of the space dimension into separated communication channels. SDMA basically relies on adaptive and dynamic beam-forming associated to a clever algorithm in charge of resource allocation. As satellite communication systems move towards an increasing number of users and a larger throughput for each of them, SDMA is one of the most promising techniques that can reach these two goals. This paper studies static Frequency Assignment Problems (FAP) in a satellite communication system involving a gateway connected to a terrestrial network and some user terminals located in a service area. Two scenarios are considered: one based on SDMA and the other based on usual spot coverage. We propose original integer linear programming formulations and greedy allocation algorithms for the FAP which involves unusual cumulative interference constraints. By considering the link budget of each user, the objective is to maximize the number of users that the system can serve. We show through computational experiments on realistic data that the FAP associated with the SDMA system can be solved efficiently, yielding substantial improvement compared to the traditional system.

Level crossing rates of interference in cognitive radio networks

The future deployment of cognitive radios (CRs) is critically dependent on the fact that the incumbent primary user (PU) system must remain as oblivious as possible to their presence. This in turn heavily relies on the fluctuations of the interfering CR signals. In this letter we compute the level crossing rates (LCRs) of the cumulative interference created by the CRs. We derive analytical formulae for the LCRs in Rayleigh and Rician fast fading conditions. We approximate Rayleigh and Rician LCRs using fluctuation rates of gamma and scaled noncentral x <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> processes respectively. The analytical results and the approximations used in their derivations are verified by Monte Carlo simulations and the analysis is applied to a particular CR allocation strategy.

Coexistence of broadband power line communication systems

Recent progress in home networks enhances the application of broadband power line communication (BPL) since it does not require any installation of new communication lines or outlets. However, high-density distribution of BPL devices may bring down the access quality. Besides, the electromagnetic field radiating from the power line may cause interference with other radio systems. Thus, the objective of this study is to investigate the impact of cumulative interference in BPL systems, especially focused on indoor environment. A 2-D model describing the BPL transmission activity is proposed. Based on transmission characteristics of the main networks, it takes into account the coexistence effect of the BPL devices. The maximum acceptable density of BPL devices and the radiation field are finally determined.

Sniffing out correct error frame model for the ns-2 simulator

Network protocols and their efficiency are extremely important to the research community. Evaluating the performance of these protocols has thus also becoming extremely important. However, it is difficult to conduct physical experiments on the performance of these systems, especially wireless networks. Therefore, network simulators, such as ns-2, QualNet and OPNET, have been widely used to evaluate the performance of network protocols, and thus the accuracy of network simulators is critical to the research community. In this paper, we consider the incorrect simulation results generated by the current ns-2 implementation employed in numerous research works. The cause which for the purposes of this paper will be called the incorrect error frame assumption (IEFA), is the incorrect handling of frames from stations located between the carrier sense and transmission ranges of the receiver in the two-ray ground propagation model. Although this model is known to be oversimplified to the extent that it does not consider such critical phenomena as cumulative interference and noise levels, it is the most popular model for simulating wireless networks. Moreover, the incorrect assumption has been widely adopted in the research community, such that the simulation scenarios are limited or the results of simulations are significantly affected by the IEFA. The issue is therefore in need of investigation and clarification. In this paper, we present a detailed description of the IEFA problem and a probabilistic analysis of the problem to determine its root cause. We suggest an implementation that fixes the IEFA and present the current bit-error model for the ns-2 simulator. We then conduct simulations to show how the problem impacts the simulation results from the MAC to the application layers.

Models and methods for frequency assignment with cumulative interference constraints

AbstractIn this paper, a realistic modeling of interferences for frequency assignment in hertzian telecommunication networks is presented. In contrast with traditional interference models based only on binary interference constraints involving two frequencies, this new approach considers the case of cumulative disruptions that are modeled through a unique non‐binary constraint. To deal with these complex constraints, we propose extensions of classical integer linear programming formulations. On a set of realistic instances, we propose hybrid constraint programming and large neighborhood search solution methods to solve minimum interference and minimum span frequency assignment problems. We compare their performances with those of existing heuristics. Finally, we show how the end‐user benefits from using the cumulative model instead of the traditional one.

Enhanced wireless mesh networking for ns-2 simulator

The ns-2 simulator has limited support for simulating 802.11 based wireless mesh networks. We have added the following new features at the MAC and PHY layer of ns-2: (i) cumulative interference in SINR (Signal to Interference and Noise Ratio) computation, (ii) an accurate and combined shadow-fading module, (iii) multi-SINR and multi-rate link support, (iv) auto rate fallback (ARF) for rate adaptation, and (v) a framework for link probing and link quality estimation as required by most mesh routing protocols. We have made these modules publicly available. In this paper, we present an overview of these new features.

Cumulative semantic inhibition in picture naming: experimental and computational studies

We report an experiment in which subjects named 120 pictures, consisting of series of five pictures drawn from each of 24 semantic categories (and intermixed with 45 fillers). The number of intervening trials (lag) between successive presentations of members of the same category varied from two to eight. Subjects' naming latencies were slowed by 30 ms for each preceding member of the category. This effect was both cumulative and linear, and unrelated to the lag elapsing since the previous presentation of a category member. These results definitively demonstrate the occurrence of cumulative interference for word retrieval by prior retrieval of other exemplars of the same semantic category—cumulative semantic inhibition. We claim that this inhibition effect could only occur if the spoken word production system possesses three specific properties (competition, priming, and sharing of semantic activation). We provide computational-modelling evidence in support of this claim. We show that no current theory of spoken word production has all of these properties. In their current form, all these theories are falsified by these results. We briefly discuss the obstacles that may be encountered by current models were they modified to account for our findings.

Dynamic channel assignment with cumulative co-channel interference

This paper studies the problem of centralized dynamic channel assignment (DCA) in wireless cellular systems under space and time-varying channel demand. The objective is to minimize the number of channels required to satisfy demand while also satisfying co-channel interference constraints. Cumulative co-channel interference constraints govern channel reuse, via a threshold decision criterion based on the carrier-to-interference ratio. The paper makes two contributions. First, it provides an empirical bound on the difference between the minimal number of channels required based only on geographic reuse distance versus the cumulative interference case in the context of linearly increasing demand. The bound is characterized using only the reuse distance. It is obtained with an Integer Programming (IP) based strategy that uses channel assignments for one demand state to assign channels for the next state. Geographic locality constraints are applied to limit reassignments. The impact of cumulative interference constraints is observed to be small for small geographic localities. Second, the paper presents a new, fast DCA heuristic that is based on the characteristic channel reuse patterns used by the IP-based strategy. The heuristic and IP-based method yield similar results for the zero blocking condition. The DCA heuristic is applied to the problem of estimating the blocking probabilities of call arrivals modeled by a two state discrete-time Markov chain and uniformly distributed holding times. The blocking performance for an ensemble of spatial load imbalance distributions is uniquely characterized using the heuristic and IP solutions.

An Assessment of the Potential Terrestrial Interference Due to Direct Broadcast Satellite Television Receivers

The potential interference of spurious, radiation from the local oscillators of direct broadcast satellite (DBS) television receivers to terrestrial 11 GHz microwave radio services is examined. Typical parameters for DBS receivers are identified and used in a computer simulation to calculate the aggregate effect of a large number of units distributed about a terrestrial repeater site. The results of the analysis show that for a local oscillator frequency of 11.2 GHz, DBS LO leakage of -70 dBW/unit, and a density of 2600/km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (1000/mi <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) the cumulative interference power would be comparable to the thermal noise level of a terrestrial radio system under realistic conditions. Methods of scaling the results for other system parameters are also presented.