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Nguyen G.D.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
IEEE Transactions on Information Theory | Year: 2010

We study cellular-like wireless networks in which the cells may overlap substantially, and a common channel is used for all cells. Thus, transmissions intended for one destination (or base station) can cause interference at neighboring destinations.We assume the use of a "collision-channel" model, in which arbitrary communication and interference regions are associated with each destination. The interaction between such cells is best exemplified if the protocol of access in each cell is pure random access, i.e., Slotted Aloha. We derive a mathematical formula for the maximum achievable throughput for multiple-cell networks that satisfy a "balance" condition, which is related to (but not as stringent as) symmetry. This formula implies that the throughput achieved in a cell is affected only by the degree of overlap with adjacent cells, i.e., a cell's throughput is not affected by transmissions that are outside of its interference region. Moreover, we show that, at the point of maximum throughput, the expected channel traffic is one packet per slot in each cell, an extension of the result obtained many years ago for single-destination networks. © 2010 IEEE. Source


Kam C.,U.S. Navy | Kompella S.,U.S. Navy | Nguyen G.D.,U.S. Navy | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
IEEE Transactions on Control of Network Systems | Year: 2014

In this paper, we investigate the queue stability and throughput of a two-user cognitive radio system with multicast traffic. We study the impact of network-level cooperation, in which one of the nodes can relay the packets of the other user that are not received at the destinations. Under this approach, if a packet transmitted by the primary user is not successfully received by the destination set but is captured by the secondary source, then the secondary user assumes responsibility for completing the transmission of the packet; therefore, the primary releases it from its queue, enabling it to process the next packet. We demonstrate that the stability and throughput regions of this cooperative approach is larger than that of the noncooperative approach, which translates into a benefit for both users of this multicast system. Our system model allows for the possibility of multipacket reception (MPR), and the optimal transmission strategies for different levels of MPR capability are observed in our numerical results. In addition to achieving a larger stability region, our results show that cooperation can result in reduced average delay for both primary and secondary users. © 2014 IEEE. Source


Nguyen G.D.,United Information Technology | Kompella S.,United Information Technology | Kam C.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
2015 13th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2015 | Year: 2015

We consider a wireless network consisting of source-destination pairs, in which each source is required to transmit a given bit volume to its destination. The goal is for all the sources to transmit the given bit volumes, under a time constraint, so that the total transmission energy is minimized. Our approach is the joint optimization of link scheduling and power control for minimum energy. We show that TDMA scheduling is appropriate for this goal, in the sense that TDMA is asymptotically optimal when the time constraint approaches infinity. When the time constraint is strictly bounded, we show that TDMA is also optimal for the case of equal channel gains. © 2015 IFIP. Source


Kompella S.,United Information Technology | Nguyen G.D.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
Proceedings - IEEE INFOCOM | Year: 2012

In this paper, we consider the problem of calculating the stability region of a two-user cognitive shared channel where the secondary (lower priority) user, whose channel is modeled as a two-state Gilbert-Elliott channel, utilizes the channel state information to adapt its transmission probabilities accordingly. The analysis also takes into account the compound effects of multipacket reception at the receiver as well as the cooperative relaying capability of the secondary node, on the stability region of the cognitive network. Results clearly illustrate that the knowledge of the secondary channel state benefits not only the secondary user, but also the primary user as well. © 2012 IEEE. Source


Kompella S.,U.S. Navy | Nguyen G.D.,U.S. Navy | Kam C.,U.S. Navy | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
IEEE/ACM Transactions on Networking | Year: 2014

This paper addresses fundamental issues in a shared channel where the users have different priority levels. In particular, we study a two-user cognitive shared channel consisting of a primary (higher-priority) and a secondary user, operating in the cognitive underlay fashion, but in a novel way where interference suffered by the primary user is compensated by requiring the secondary user to cooperatively relay some of the primary's packets. We start by analyzing the case of no node cooperation, where nodes transmit their own packets to their respective destinations. We then extend the analysis to a system in which the secondary node acts as a relay for the primary user, in addition to serving its own packets. Specifically, in the cognitive cooperation case, the secondary node forwards those packets to the primary destination that it receives successfully from the primary source. In such cognitive shared channels, a tradeoff arises in terms of activating the secondary along with the primary so that both transmissions may be successful, but with a lower probability, compared to the case of the secondary node staying idle when the primary user transmits. Results show the benefits of relaying for both the primary as well as the secondary nodes in terms of the stable-throughput region. © 1993-2012 IEEE. Source

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