Wieselthier Research

Silver Spring, MD, United States

Wieselthier Research

Silver Spring, MD, United States
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Kam C.,United Information Technology | 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 Military Communications Conference MILCOM | Year: 2016

We study the age of information, which is a recently introduced metric for measuring the freshness of a continually updated piece of information as observed at a remote monitor. The age of information metric has been studied for a variety of different queuing systems, and in this work, we consider the impact of buffer sizes, packet deadlines, and packet replacement on the average age of information for queuing systems. We conduct a simulation-based study in which we modeled a wide variety of queuing systems and control mechanisms in simulation and computed the average age of information. We first study the buffer size alone to see how it affects the average age, and then we look at adding a packet deadline for such a system. We consider packet deadline control in the buffer only and in both the buffer and server, and we also compare the performance with a random deadline. We observe how the buffer size and deadline are optimized for the age, and we identify general trends for how to choose values of control mechanisms under different conditions of the packet generation rate. Lastly, we study the ability to replace packets in the buffer with newly arriving packets, and we are particularly interested in whether we can achieve the performance of such a system by controlling buffer size and deadline alone, for systems in which we do not have the ability to do packet replacement. © 2016 IEEE.


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
2017 15th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, WiOpt 2017 | Year: 2017

For time critical updates, it is desirable to maintain the freshness of the received information. We address the impact of hostile interference on information freshness by formulating a non-zero-sum two-player game, in which one player is the transmitter aiming to maintain the freshness of the information updates it sends to its receiver, and the other player is the interferer aiming to prevent this. The strategy of a player is the power level transmitted by that player. We then derive the equilibria for both Nash and Stackelberg strategies. We show that both players have the same power cost at Nash equilibrium. In addition, the Stackelberg strategy dominates the Nash strategy, i.e., the Stackelberg utility function exceeds the Nash utility function. © 2017 IFIP.


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.


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.


Kam C.,United Information Technology | Kompella S.,United Information Technology | Nguyen G.D.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
IEEE International Symposium on Information Theory - Proceedings | Year: 2016

We study the age of information, which is a recently introduced metric for measuring the freshness of a continually updated piece of information as observed at a remote monitor. The age of information metric has been studied for a variety of different queuing systems. In this work, we introduce a packet deadline as a control mechanism and study its impact on the average age of information for an M/M/1/2 queuing system. We analyze the system for a fixed deadline and derive a mathematical expression for the average age. We numerically evaluate the expression and show the relationship of the age performance to that of the M/M/1/1 and M/M/1/2 systems. We show that the system with a deadline constraint can outperform both the M/M/1/1 and M/M/1/2 without such a deadline. © 2016 IEEE.


Nguyen G.D.,United Information Technology | Kompella S.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
Proceedings - IEEE Military Communications Conference MILCOM | Year: 2010

In this paper, we consider a cognitive radio network in which the secondary users are allowed to share the spectrum with the primary users as long as the interference caused by the secondary users to the primary users is below a specified level. Both the primary users and secondary users access the common channel by way of transmission schedules. The channel model includes realistic features such as receiver noise, fading, and multiuser interference. Our primary performance measure is network throughput, which is the average number of packets that are successfully received per time slot. For a given level of guaranteed performance for each primary user, our goal is to determine the transmission schedule for the secondary users that maximizes their throughput. Our method exploits the multi-packet reception capability to improve throughput performance. We show that our method for scheduling can allow significant additional throughput for the secondary users, while keeping the impact of interference to the primary users to the specified level.


Nguyen G.D.,United Information Technology | Kompella S.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
IEEE Transactions on Vehicular Technology | Year: 2015

We develop cognitive radio networking methods for a heavy-traffic model in which the channel is always occupied by primary users. This contrasts with the interference-avoidance approach for the non-heavy-traffic model, in which primary users have idle times, and secondary users are allowed to use the channel at those idle times. We use an 'underlay' approach to cognitive radio networking by allowing secondary users to share the channel with simultaneously transmitting primary users. Thus, secondary users can degrade the performance of primary users, and our goal is to ensure that the level of performance degradation is acceptable. This is accomplished by scheduling and coordinating the transmissions among users, as well as providing a safeguard for controlling the level of additional interference caused by transmissions from secondary users. We show that our methods can provide additional throughput for secondary users, while maintaining the performance of primary users at the specified level. © 2014 IEEE.


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: 2011

This paper addresses fundamental issues in a shared channel where the users have different priority levels. In particular, we characterize the stable-throughput region in a two user cognitive shared channel where the primary (higher priority) user transmits whenever it has packets to transmit while the secondary (cognitive) node transmits its packets with probability p. Therefore, in this system, the secondary link is allowed to share the channel along with the primary link, in contrast to the traditional notion of cognitive radio, in which the secondary user is required to relinquish the channel as soon as the primary is detected. The analysis also takes into account the compound effects of multi-packet reception as well as of the relaying capability on the stability region of the network. We start by analyzing the non-cooperation case where nodes transmit their own packets to their respective destinations. We then extend the analysis to a system where the secondary node cooperatively relays some of the primary's packets. Specifically, in the cooperation case, the secondary node relays those packets that it receives successfully from the primary, but are not decoded properly by the primary destination. 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. © 2011 IEEE.


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.


Nguyen G.D.,United Information Technology | Kompella S.,United Information Technology | Wieselthier J.E.,Wieselthier Research | Ephremides A.,University of Maryland University College
IEEE Transactions on Wireless Communications | Year: 2011

We study transmission strategies in a multiple-source, multiple-destination wireless network. Each source transmits packets that are intended for a particular destination. However, a transmitted packet can cause interference at other destinations. Our primary performance measure is throughput, which we define to be the average number of packets that are successfully received per intended destination per time slot. The sources are first divided into groups, based on the intended destination of their packets. In our parallel method, each group operates according to its own local protocol (e.g., TDMA), concurrently with and independently of the other groups. Our results show the impact of transmission schedules, channel fading, receiver noise, and other-user interference on network performance. We then show that, for given channel statistics and topology configurations, the network performance can be significantly improved when the groups in the network coordinate their transmissions according to an optimal schedule. Further, in many cases, even the use of randomly generated parallel schedules can provide considerably higher performance than traditional TDMA. © 2006 IEEE.

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