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Understanding Spatio-Temporal Uncertainty in Medium Access with ALOHA Protocols

Affan Syed, Wei Ye, Bhaskar Krishnamachari, and John Heidemann
USC/Information Sciences Institute

Abstract

The goal of this paper is to gain deep understanding of how location-dependent propagation latency affects medium access control (MAC) by using ALOHA as a case study. MAC protocols in underwater acoustic networks suffer from latency that is five orders-of-magnitude larger than that in radio networks. Existing work on analyzing MAC throughput in RF networks, where the propagation latency is negligible, generally makes assumptions that render propagation latency irrelevant. As a result, only transmit time is considered as being uncertain in contention-based protocols. We introduce the spatial dimension of uncertainty that is inherent to varying locations of transmitters, resulting in unequal propagation latency to a receiver, where collision occurs. We show through simulation that the benefit of synchronization in slotted ALOHA is lost due to such latency. We propose a modification that adds guard bands to transmission slots to handle spatial uncertainty. We then perform simulation and first order analysis on this modified MAC to find its optimal operating parameters.

Availability

This paper is available in several formats: abstract web page with pointers and cites, PDF, paper copies can be obtained by mail to the authors. Copyright terms for this paper appear below.

Reference

Syed07b: Affan Syed, Wei Ye, Bhaskar Krishnamachari, and John Heidemann. Understanding Spatio-Temporal Uncertainty in Medium Access with ALOHA Protocols. In Proceedings of the Second ACM International Workshop on UnderWater Networks (WUWNet) , pp. 41-48. Montr\'eal, Quebec, Canada, ACM. September, 2007. <http://doi.acm.org/10.1145/1287812.1287822>.

@inproceedings{Syed07b,
	author = "Affan Syed and Wei Ye and Bhaskar
 Krishnamachari and John Heidemann",
	title = "Understanding Spatio-Temporal Uncertainty in Medium Access with {ALOHA} Protocols",
	booktitle = "Proceedings of the Second ACM International Workshop on UnderWater Networks ({WUWNet}) ",
	year = "2007",
	publisher = "{ACM}",
	address = "Montr{\'e}al, Quebec, Canada",
	month = "September",
	pages = "41--48",
	keywords = "ALOHA, underwater MAC",
	doi = "http://doi.acm.org/10.1145/1287812.1287822",
	myorganization = "USC/Information Sciences Institute",
	copyrightholder = "{ACM}",
	url = "http://www.isi.edu/~johnh/PAPERS/Syed07b.html",
	pdfurl = "http://www.isi.edu/~johnh/PAPERS/Syed07b.pdf",
}

Copyright

This paper is copyright © 2007 by ACM. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee.