Concordia Institute for Information Systems Engineering CIISE

Montréal, Canada

Concordia Institute for Information Systems Engineering CIISE

Montréal, Canada

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Qu L.,Ningbo University | He J.,Ningbo University | Assi C.,Concordia Institute for Information Systems Engineering CIISE
IEEE Transactions on Communications | Year: 2014

The performance of wireless multihop networks depends on the achievable channel capacity for each transmission link as well as the level of spectrum spatial reuse in the network. For the latter one, successive interference cancellation (SIC) has emerged as an advanced PHY technique with the ability of decoding two or more overlapping signals and therefore allowing multiple concurrent transmissions. Effectively managing the transmission concurrency over the shared medium ensures good quality of transmission and therefore results in higher achievable transmission data rates. In this paper, we seek to understand the benefits of SIC and its interference management capabilities in a multi-rate multihop wireless network. To characterize the network performance under these characteristics, we follow a cross-layer design approach and formulate the joint routing and scheduling problem with rate control as a mixed integer linear program with the objective to maximize the minimum flow throughput. Given its large scale and combinatorial complexity, we follow a decomposition approach using column generation to solve the problem. However, the complexity of solving exactly the pricing subproblem limits the application of the model to very small size network instances. We develop one efficient greedy method for solving exactly the pricing subproblem as well as a simulated annealing based heuristic approach with very good performance. Our results indicate that SIC benefits strongly depend on the strength of the received signals. We show that transmission links with fixed higher data rates do not necessarily yield higher SIC gains because higher transmission rates result in sparser network topologies and thus less flexible routing. Larger networks with SIC capabilities and bitrate adaptation however are most effective in controlling the interference and improving the spatial reuse and thus reap the largest benefits with gains exceeding 20% over networks only with SIC capabilities or only with rate control. © 2013 IEEE.


El-Najjar J.,Concordia University at Montréal | Assi C.,Concordia Institute for Information Systems Engineering CIISE | Jaumard B.,Concordia Institute for Information Systems Engineering CIISE
IEEE Transactions on Wireless Communications | Year: 2010

The problem of scheduling and routing tree construction in WiMAX/802.16 based mesh networks is not defined in the standard and has thus been the subject to extensive research. We consider the problem of joint routing and scheduling in WiMAX-based mesh networks, with the objective of determining a minimum schedule period that satisfies a given (uplink/downlink) traffic demand. Minimizing the length of a schedule amounts to maximizing the spectrum spatial reuse by activating concurrently as many links. This group of transmission links active concurrently is referred to as the transmission group and refers to the set of wireless links that can simultaneously transmit without violating the signal-to-interference-plus-noise ratio (SINR) requirement. Our model is referred to as maximum spatial reuse (MSR). We assume centralized scheduling at the base station and attempt to maximize the system throughput through appropriate routing tree selection and achieving efficient spectrum reuse through opportunistic link scheduling. We present an ILP optimization model for the joint problem, which relies on the enumeration of all possible link schedules. Given its complexity, we decompose the problem using a column generation (CG) approach. We present two formulations for modeling MSR, namely the link-based (CGLink) and the path-based (CGPath) formulation. These two formulations differ mainly in the number of routing decision variables. Our experimental results indicate that the path-based formulation needs much less computational (CPU) time than the link-based in order to determine the (same) optimal solution with the same spatial reuse gain. © 2006 IEEE.


Qu L.,Ningbo University | He J.,Ningbo University | Assi C.,Concordia Institute for Information Systems Engineering CIISE
IEEE Transactions on Vehicular Technology | Year: 2015

Recently, there has been strong interest in exploiting advanced physical-layer techniques to increase the capacity of multihop wireless networks. Several recent studies have emerged with a particular focus on successive interference cancelation (SIC) as an effective approach to allow multiple adjacent concurrent transmissions to coexist, enabling multipacket reception. This paper is in line with those efforts in that we attempt to understand the benefits of SIC on the throughput performance of wireless networks. We consider a cross-layer design for the joint congestion control, routing, and scheduling problem in wireless networks where nodes are endowed with SIC capabilities and under the general physical signal-to-interference-plus-noise ratio (SINR) interference model. We use duality theory to decompose the joint design problem into congestion control and routing/scheduling subproblems, which interact through congestion prices. This decomposition enables us to solve the joint cross-layer design problem in a completely distributed manner. Given that the problem of scheduling with SIC and under the SINR interference regime is NP-hard, this paper develops a decentralized approach that allows links to coordinate their transmissions and, therefore, efficiently solve the link scheduling problem. Numerically, we show that our decentralized algorithm achieves similar results to those obtained by other centralized methods (e.g., greedy maximal scheduling). We also study the performance gains SIC brings to wireless networks, and we show that flows in the network achieve up to twice their rates in most instances, in comparison with networks without interference cancelation capabilities. These gains are attributed to the capabilities of SIC to better manage the interference and promote higher spatial reuse in the network. © 1967-2012 IEEE.


Shinwari M.,Concordia Institute for Information Systems Engineering CIISE | Youssef A.,Concordia Institute for Information Systems Engineering CIISE | Hamouda W.,Concordia University at Montréal
Communications in Computer and Information Science | Year: 2013

High frequency power consumption readings produced by smart meters introduce a major privacy threat to residential consumers as they reveal details that could be used to infer information about the activities of home occupants. In this paper, we question the need to disclose high frequency readings produced at the home's level. Instead, we propose equipping smart meters with sufficient processing power enabling them to provide the utility company with a set of well-defined services based on these readings. For demand side management, we propose the collection of high frequency readings at a higher level in the distribution network, such as local step-down transformers, as this readily provides the accumulated demand of all homes within a branch. Furthermore, we study the effect of the proposed approach on consumers' privacy, using correlation and relative entropy as measures. We also study the effect of load balancing on consumers' privacy when using the proposed approach. Finally, we assess the detection of different appliances using high frequency readings collected for demand side management purposes. © Springer-Verlag Berlin Heidelberg 2013.

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