Kaushik Mondal

Demand-Aware Network Designs of Bounded Degree

Traditionally, networks such as datacenter interconnects are designed to optimize worst-case performance under arbitrary traffic patterns. Such network designs can however be far from optimal when considering the actual workloads and traffic patterns which they serve. This insight led to the development of demand-aware datacenter interconnects which can be reconfigured depending on the workload. Motivated by these trends, this paper initiates the algorithmic study of demand-aware networks (DANs), and in particular the design of bounded-degree networks. The inputs to the network design problem are a discrete communication request distribution, D, defined over communicating pairs from the node set V, and a bound, d, on the maximum degree. In turn, our objective is to design an (undirected) demand-aware network N = (V,E) of bounded-degree d, which provides short routing paths between frequently communicating nodes distributed across N. In particular, the designed network should minimize the expected path length on N (with respect to D), which is a basic measure of the efficiency of the network. We show that this fundamental network design problem exhibits interesting connections to several classic combinatorial problems and to information theory. We derive a general lower bound based on the entropy of the communication pattern D, and present asymptotically optimal network-aware design algorithms for important distribution families, such as sparse distributions and distributions of locally bounded doubling dimensions.

Path planning algorithms for mobile anchors towards range-free localization

The objective of path planning for a mobile anchor is to find the path of minimum length that the anchor traverses to localize all sensors. The challenge is to design a movement strategy which reduces path length while meeting the requirements of a good range-free localization technique. A novel deterministic movement strategy is proposed in this paper that reduces path length and uses an existing range-free localization scheme which yields good positional accuracy. The mobile anchor moves in a hexagonal pattern to localize all the sensors which form a connected network. We compare performance of our algorithm with an existing path planning algorithm in terms of both path length and localization accuracy. Simulation results show that even in presence of irregular radio propagation, our algorithm achieves full localization. We have proposed another movement strategy for a mobile anchor using same hexagonal pattern to localize all the sensors lying in a rectangular region. Improvement in path length is shown theoretically compared to existing path planning schemes. Proposed a distributed range-free movement strategy for mobile anchor to localization sensors in a connected network.Improvements in terms of both path length and localization accuracy are shown.Proposed another movement strategy for mobile anchor, localizes all the sensors lying in a rectangular region.Improvement of path length is shown theoretically compared to the existing methods.

Localization in presence of multipath effect in wireless sensor networks

Localization in an urban area is a challenging problem due to the blocking of Line-of-Sight (LOS) signal by various obstacles and also the multipath effect arising out of reflections and scattering of signals. Assuming that there are a few anchor nodes which know their positions accurately and which transmit ultrasonic signals, we propose here a technique to find the position of other sensor nodes based on receiving these ultrasonic signals reflected by some reflectors. Our proposed technique can calculate the position of a node correctly by receiving two reflected signals (Non-Line-of-Sight (NLOS)) from an anchor. We, however, assume that a signal is reflected at most once before reaching a node and the two reflecting surfaces are non-parallel to each other.

Range-free mobile node localization using static anchor

In this paper we have proposed a deterministic, range-free, distributed localization algorithm for mobile sensor nodes with static anchors. Mobile node calculates its approximate line of movement and corresponding position based on received beacons from two different anchors. The positional error can be further reduced by updating the approximate line of movement on receiving beacons from more anchors. We also have incorporated irregular radio propagation in our model. We have compared performance of our algorithm with existing localization algorithms. Simulation results show 80% improvement in performance of our proposed algorithm over the existing algorithms in terms of positional accuracy.

Fault-Tolerant Gathering of Mobile Robots with Weak Multiplicity Detection

There has been a wide interest in designing distributed algorithms for tiny robots. In particular, it has been shown that the robots can complete certain tasks even in the presence of faulty robots. In this paper, we focus on gathering of all non-faulty robots at a single point in presence of faulty robots. We propose a wait-free algorithm (i.e., no robot waits for other robots and algorithm instructs each robot to move in every step, unless it is already at the gathering location), that gathers all non-faulty robots in the semi-synchronous model without any agreement about the coordinate system and with weak multiplicity detection (i.e., a robot can detect if there are more than one robots at a point, but not their exact number) in the presence of at most n - 1 faulty robots for n ≥ 3. We show that the required capability for gathering robots is minimal in the above model, since relaxing it further makes gathering impossible to solve. Also, we introduce an intermediate scheduling model in between the asynchronous (i.e., no instantaneous movement or computation) and the semi-synchronous (i.e., both instantaneous movement and computation) as ASYNCIC, the asynchronous model with instantaneous computation. Then we propose another algorithm in ASYNCIC model for gathering all non-faulty robots with weak multiplicity detection without any agreement on the coordinate system in the presence of at most ⌊n/2⌋-2 faulty robots for n ≥ 7 starting from any configuration with at most one multiplicity excluding C* (0), C* (1/k), C* (1/2) and C* (1/2 + 1/k).

Range-Free Mobile Sensor Localization and a Novel Obstacle Detection Technique

Mobile sensor localization is a challenging problem in wireless sensor networks. Due to mobility, it is difficult to find exact position of the sensors at any time instance. The aim of localization is to minimize positioning errors of the mobile sensors. In this paper we propose two range-free distributed localization algorithms for mobile sensors with static anchors. Both the algorithms depend on selection of beacon points. First we assume that mobile sensors move straight during localization which helps us to provide an upper bound on localization error. Certain applications may not allow sensors to move in a straight line. Obstacles may also obstruct path of sensors. Moreover beacon point selection becomes difficult in presence of obstacles. To address these issues, we propose another localization algorithm with an obstacle detection technique which selects correct beacon points for localization in presence of obstacles. Simulation results show improvements in performance over existing algorithms.

Path Planning Algorithm for Mobile Anchor in Connected Sensor Networks

Path planning is an important issue for localization with mobile anchor in wireless sensor networks as movement of the mobile anchor consumes more energy compared to static anchor. Most of the works available in the literature either looks into the aspect of reducing path length of the mobile anchor or tries to increase localization accuracy. In this paper we propose a cost-effective movement strategy i.e., path planning for a mobile anchor which reduces path length and at the same time localization can be done using localization scheme [3], which yields good accuracy. Simulation results show improvement over existing work [4] in terms of both path length and localization accuracy.

Analysis of Multiple-Bound Signals Towards Localization: A Theoretical Approach

In presence of obstacles, localization is a real challenge since multi-path effect takes place due to reflections and/or scattering of signals. There are works in the literature which discard multiple-bound signals received by sensors using statistical methods and then localize sensors using remaining signals. In literature, to the best of our knowledge, there is no deterministic way to know the number of reflections/bounds of a particular signal, so researchers have to rely on statistical methods for localization. In this paper, we analyze multiple-bound signals based on the information gathered by different ranging techniques viz. AOA, TOA, RSSI and make use of a multiple-bound signal where number of reflections are not known, to localize sensor deterministically.