A minimum connected dominating set (MCDS) is used as virtual backbone for efficient routing and broadcasting in ad hoc sensor networks. The minimum CDS problem is NP-complete even in unit disk graphs. Many heuristics-based distributed approximation algorithms for MCDS problems are reported and the best known performance ratio has ð4:8 þ ln 5Þ. We propose a new heuristic called collaborative cover using two principles: 1) domatic number of a connected graph is at least two and 2) optimal substructure defined as subset of independent dominator preferably with a common connector. We obtain a partial Steiner tree during the construction of the independent set (dominators). A final postprocessing step identifies the Steiner nodes in the formation of Steiner tree for the independent set of G. We show that our collaborative cover heuristics are better than degree-based heuristics in identifying independent set and Steiner tree. While our distributed approximation CDS algorithm achieves the performance ratio of ð4:8 þ ln 5Þopt þ 1:2, where opt is the size of any optimal CDS, we also show that the collaborative cover heuristic is able to give a marginally better bound when the distribution of sensor nodes is uniform permitting identification of the optimal substructures. We show that the message complexity of our algorithm is OðnÁ 2 Þ; Á being the maximum degree of a node in graph and the time complexity is OðnÞ.

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Analysis of activity-travel patterns is an important component of any activity-based transportation planning exercise. Most of the current activity-travel literature focuses on studying the characteristics of workers. In comparison, little emphasis has been placed on studying nonworker activity-travel patterns. This paper presents the results of an exploratory analysis of the activity-travel patterns of non-workers in the San Francisco Bay Area. The attributes of a nonworker's overall activity-travel pattern are examined in terms of three dimensions -number of stops of each activity type, trip chaining, and the temporal sequencing of activities. The paper concludes with a summary of the results and implications for transportation planning and policy analysis.2

Wireless ad hoc and sensor networks (WSNs) often require a connected dominating set (CDS) as the underlying virtual backbone for efficient routing. Nodes in a CDS have extra computation and communication load for their role as dominator, subjecting them to an early exhaustion of their battery. A simple mechanism to address this problem is to switch from one CDS to another fresh CDS, rotating the active CDS through a disjoint set of CDSs. This gives rise to the connected domatic partition (CDP) problem, which essentially involves partitioning the nodes V ðGÞ of a graph G into node disjoint CDSs. We have developed a distributed algorithm for constructing the CDP using our maximal independent set (MIS)-based proximity heuristics, which depends only on connectivity information and does not rely on geographic or geometric information. We show that the size of a CDP that is identified by our algorithm is at least b þ1ðcþ1Þ c À f, where is the minimum node degree of G, 2, c 11 is a constant for a unit disk graph (UDG), and the expected value of f is jV j, where ( 1 is a positive constant, and ! 48. Results of varied testing of our algorithm are positive even for a network of a large number of sensor nodes. Our scheme also performs better than other related techniques such as the ID-based scheme.

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