Biological systems can share and collectively process information to yield emergent effects, despite inherent noise in communication. While man-made systems often employ intricate structural solutions to overcome noise, the structure of many biological systems is more amorphous. It is not well understood how communication noise may affect the computational repertoire of such groups. To approach this question we consider the basic collective task of rumor spreading, in which information from few knowledgeable sources must reliably flow into the rest of the population. In order to study the effect of communication noise on the ability of groups that lack stable structures to efficiently solve this task, we consider a noisy version of the uniform PULL model. We prove a lower bound which implies that, in the presence of even moderate levels of noise that affect all facets of the communication, no scheme can significantly outperform the trivial one in which agents have to wait until directly interacting with the sources. Our results thus show an exponential separation between the uniform PUSH and PULL communication models in the presence of noise. Such separation may be interpreted as suggesting that, in order to achieve efficient rumor spreading, a system must exhibit either some degree of structural stability or, alternatively, some facet of the communication which is immune to noise. We corroborate our theoretical findings with a new analysis of experimental data regarding recruitment in Cataglyphis niger desert ants.
The computational study of abstract systems composed of simple individuals that interact using highly restricted and stochastic interactions has recently been gaining considerable attention in the community of theoretical computer science. Popular models include population protocols @cite_28 , which typically consider constant size individuals that interact in pairs (using constant size messages) in random communication patterns, and the beeping model @cite_36 , which assumes a fixed network with extremely restricted communication. Our model also falls in this framework as we consider the @math model @cite_25 @cite_21 @cite_22 with constant size messages. So far, despite interesting works that consider different fault-tolerant contexts @cite_19 @cite_7 , most of the progress in this framework considered noiseless scenarios.
@cite_22 @cite_7 @cite_28 @cite_36 @cite_21 @cite_19 @cite_25
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Distributed computing models typically assume reliable communication between processors. While such assumptions often hold for engineered networks, e.g., due to underlying error correction protocols, their relevance to biological systems, wherein messages are often distorted before reaching their destination, is quite limited. In this study we aim at bridging this gap by rigorously analyzing a model of communication in large anonymous populations composed of simple agents which interact through short and highly unreliable messages. We focus on the rumor-spreading problem and the majority-consensus problem, two fundamental tasks in distributed computing, and initiate their study under communication noise. Our model for communication is extremely weak and follows the push gossip communication paradigm: In each synchronous round each agent that wishes to send information delivers a message to a random anonymous agent. This communication is further restricted to contain only one bit (essentially representing an opinion). Lastly, the system is assumed to be so noisy that the bit in each message sent is flipped independently with probability 1 2-e, for some small Ae >0. Even in this severely restricted, stochastic and noisy setting we give natural protocols that solve the noisy rumor-spreading and the noisy majority-consensus problems efficiently. Our protocols run in O(log n e2) rounds and use O(n log n e2) messages bits in total, where n is the number of agents. These bounds are asymptotically optimal and, in fact, are as fast and message efficient as if each agent would have been simultaneously informed directly by the source. Our efficient, robust, and simple algorithms suggest balancing between silence and transmission, synchronization, and majority-based decisions as important ingredients towards understanding collective communication schemes in anonymous and noisy populations. In this work, we study the problem of constructing interactive protocols that are robust to noise, a problem that was originally considered in the seminal works of Schulman (FOCS '92, STOC '93), and has recently regained popularity. Robust interactive communication is the interactive analogue of error correcting codes: Given an interactive protocol which is designed to run on an error-free channel, construct a protocol that evaluates the same function (or, more generally, simulates the execution of the original protocol) over a noisy channel. As in (non-interactive) error correcting codes, the noise can be either stochastic, i.e. drawn from some distribution, or adversarial, i.e. arbitrary subject only to a global bound on the number of errors. We show how to simulate any interactive protocol in the presence of constant-rate noise, while incurring only a constant blow-up in the communication complexity (CC). Our simulator is randomized, and succeeds in simulating the original protocol with probability at least @math . Background Digital networks, mobile devices, and the possibility of mining the ever-increasing amount of digital traces that we leave behind in our daily activities are changing the way we can approach the study of human and social interactions. Large-scale datasets, however, are mostly available for collective and statistical behaviors, at coarse granularities, while high-resolution data on person-to-person interactions are generally limited to relatively small groups of individuals. Here we present a scalable experimental framework for gathering real-time data resolving face-to-face social interactions with tunable spatial and temporal granularities. Methods and Findings We use active Radio Frequency Identification (RFID) devices that assess mutual proximity in a distributed fashion by exchanging low-power radio packets. We analyze the dynamics of person-to-person interaction networks obtained in three high-resolution experiments carried out at different orders of magnitude in community size. The data sets exhibit common statistical properties and lack of a characteristic time scale from 20 seconds to several hours. The association between the number of connections and their duration shows an interesting super-linear behavior, which indicates the possibility of defining super-connectors both in the number and intensity of connections. Conclusions Taking advantage of scalability and resolution, this experimental framework allows the monitoring of social interactions, uncovering similarities in the way individuals interact in different contexts, and identifying patterns of super-connector behavior in the community. These results could impact our understanding of all phenomena driven by face-to-face interactions, such as the spreading of transmissible infectious diseases and information. Numerous massive data sets, ranging from flows of Internet traffic to logs of supermarket transactions, have emerged during the past few years. Their overwhelming size and the typically restricted access to them call for new computational models. This thesis studies three such models: sampling computations, data stream computations, and sketch computations. While most of the previous work focused on designing algorithms in the new models, this thesis revolves around the limitations of the models. We develop a suite of lower bound techniques that characterize the complexity of functions in these models, indicating which problems can be solved efficiently in them. We derive specific bounds for a multitude of practical problems, arising from applications in database, networking, and information retrieval, such as frequency statistics, selection functions, statistical moments, and distance estimation. We present general, powerful, and easy to use lower bound techniques for the sampling model. The techniques apply to all functions and address both oblivious and adaptive sampling. They frequently produce optimal bounds for a wide range of functions. They are stated in terms of new combinatorial and statistical properties of functions, which are easy to calculate. We obtain lower bounds for the data stream and sketch models through one-way and simultaneous communication complexity. We develop lower bounds for the latter via a new information-theoretic view of communication complexity. A highlight of this work is an optimal simultaneous communication complexity lower bound for the important multi-party set-disjointness problem. Finally, we present a powerful method for proving lower bounds for general communication complexity. The method is based on a direct sum property of a new measure of complexity for communication complexity protocols and on a novel statistical view of communication complexity. We use the technique to obtain improved communication complexity and data stream lower bounds for several problems, including multi-party set-disjointness, frequency moments, and Lp distance estimation. These results solve open problems of Alon, Matias, and Szegedy and of Saks and Sun.