Research Article Max-Min Fair Link Quality in WSN Based on SINR Ada Gogu, 1 Dritan Nace, 2 Supriyo Chatterjea, 3 and Arta Dilo 3 1 Polytechnic University of Tirana, 1010 Tirana, Albania 2 Universit´ e de Technologie de Compi` egne, 60205 Compi` egne Cedex, France 3 University of Twente, 7500 AE Enschede, Te Netherlands Correspondence should be addressed to Ada Gogu; agogu@fi.edu.al Received 5 March 2014; Revised 21 May 2014; Accepted 23 May 2014; Published 23 June 2014 Academic Editor: Michał Pi´ oro Copyright © 2014 Ada Gogu et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis paper addresses frst the problem of max-min fair (MMF) link transmissions in wireless sensor networks (WSNs) and in a second stage studies the joint link scheduling and transmission power assignment problem. Given a set of concurrently transmitting links, the MMF link transmission problem looks for transmission powers of nodes such that the signal-to-interference and noise ratio (SINR) values of active links satisfy max-min fairness property. By guaranteeing a “fair” transmission medium (in terms of SINR), other network requirements may be directly afected, such as the schedule length, the throughput (number of concurrent links in a time slot), and energy savings. Hence, the whole problem seeks to fnd a feasible schedule and a power assignment scheme such that the schedule length is minimized and the concurrent transmissions have a fair quality in terms of SINR. Te focus of this study falls on the transmission power control strategy, which ensures that every node that is transmitting in the network chooses a transmission power that will minimally afect the other concurrent transmissions and, even more, achieves MMF SINR values of concurrent link transmissions. We show that this strategy may have an impact on reducing the network time schedule. 1. Introduction Wireless sensor networks (WSNs) are presently used in a wide range of applications. Tey are usually deployed as a standalone system or as part of a larger, more sophisticated system, such as the Internet-of-Tings. However, this tech- nology has stringent requirements mainly related to energy and wireless transmission medium. Te power allocated to sensor nodes in a network is fundamentally constrained; nonetheless they have to transmit their data which costs suf- cient energy. Because of interference, the concurrent wireless transmissions may be easily corrupted, which increases the number of packet retransmissions. Tis may cause energy depletion and delays in the network. Existing solutions such as transmission power control and blacklisting PCBL [1], adaptive transmission power control ATPC [2], and adaptive and robust topology control ART [3] use parameters like received signal strength indicator (RSSI) or packet receive rate (PRR) to evaluate the quality of a link. However, RSSI or PRR may not capture the efect of interference in particular scenarios as will be further detailed. In addition, we consider the SINR parameter and solve the problem of fair SINR link transmission. Hence, for a set of activated links, the problem seeks to fnd the power of the transmitting nodes such that the SINR value is fair at each receiver. Fairness is a key consideration in WSN scenarios in order to maintain a balanced view of the network and, in this case, to give the same priority to each of the concurrent transmissions. Tis increases the number of potential concurrent links scheduled in the same time slot and therefore reduces the schedule length. However, the feasibility of this problem is tightly coupled with the given set of activated links and therefore the scheduling. Tis is a typical example that shows how the optimization problems in WSN may ofen lead to cross-layer ones. Te cross-layer optimization problem comes to be the joint link scheduling and power assignment (JLSPA) that seeks to fnd an efcient link scheduling scheme, in which the power of sender nodes is set variable, such that certain requirements are satisfed. In a time-driven WSN, sensor nodes need to send their data periodically according to a regular trafc pattern. Tis period is usually known as a round of data gathering. Hindawi Publishing Corporation Journal of Applied Mathematics Volume 2014, Article ID 693212, 11 pages http://dx.doi.org/10.1155/2014/693212