Craig M. Barnhart
United States Naval Research Laboratory
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Featured researches published by Craig M. Barnhart.
IEEE Transactions on Communications | 1994
Jeffrey E. Wieselthier; Craig M. Barnhart; Anthony Ephremides
The issues of routing and scheduling the activation of links in packet radio networks are highly interdependent. The authors consider a form of the problem of routing for the minimization of congestion as a step toward the study of the joint routing-scheduling problem. They formulate this as a combinatorial-optimization problem, and they use Hopfield neural networks (NN) for its solution. The determination of the coefficients in the connection weights is the most critical issue in the design and simulation of Hopfield NN models. They use the method of Lagrange multipliers, which permits these coefficients to vary dynamically along with the evolution of the system state. Extensive software simulation results demonstrate the capability of their approach to determine good sets of routes in large heavily congested networks. >
Wireless Networks | 1995
Craig M. Barnhart; Jeffrey E. Wieselthier; Anthony Ephremidis
In this paper, we investigate the admission-control problem for voice traffic in fixed-route circuit-switched wireless networks. We consider coordinate-convex admission-control policies and a “blocked-calls-cleared” mode of operation, in conjunction with the usual assumptions on the voice process statistics. These conditions result in a product-form stationary distribution for the voice state of the system, which facilitates the evaluation of network performance. However, to determine the optimal policy a large state space must be searched. We develop a recursive procedure to accelerate the evaluation of a large number of different admission-control policies, and a descent-search method to reduce significantly the number of policies that must be evaluated in searching for the optimal one. The numerical examples we present indicate that reduced blocking probability (or increased throughput) can be obtained by administering active admission control. The degree of improvement is highest in moderately overloaded traffic conditions, but it is typically small in low-capacity networks (at all loads). However, in applications where the performance measure associates different revenues or costs with the various call types, considerable improvement can be obtained when admission control is used.
international conference on computer communications | 1993
Craig M. Barnhart; Jeffrey E. Wieselthier; Anthony Ephremides
Admission-control schemes for voice traffic in circuit-switched multihop radio networks are studied. The problem formulation is based on the methodology of multiple-service, multiple-resource (MSMR) modeling, and only those admission-control policies that yield a coordinate convex state space are considered. This restriction, in conjunction with reasonable modeling assumptions, results in a product-form stationary distribution for the system state. A recursive procedure to accelerate the evaluation of a large number of different admission-control policies and a descent-search method to minimize the number of policies that must be evaluated in searching for the optimal one are developed. Numerical examples indicate that performance can be improved by administering admission control, but the improvement is typically small unless different revenues or costs are associated with the various call types.<<ETX>>
Discrete Event Dynamic Systems | 1995
Jeffrey E. Wieselthier; Craig M. Barnhart; Anthony Ephremides
In this paper we apply the ideas of ordinal optimization and the technique of Standard Clock (SC) simulation to the voice-call admission-control problem in integrated voice/data multihop radio networks. This is an important problem in networking that is not amenable to exact analysis by means of the usual network modeling techniques. We first describe the use of the SC approach on sequential machines, and quantify the speedup in simulation time that is achieved by its use in a number of queueing examples. We then develop an efficient simulation model for wireless integrated networks based on the use of the SC approach, which permits the parallel simulation of a large number of admission-control policies, thereby reducing computation time significantly. This model is an extension of the basic SC approach in that it incorporates fixed-length data packets, whereas SC simulation is normally limited to systems with exponentially distributed interevent times. Using this model, we demonstrate the effectiveness of ordinal-optimization techniques, which provide a remarkably good ranking of admission-control policies after relatively short simulation runs, thereby facilitating the rapid determination of good policies. Moreover, we demonstrate that the use of crude, inaccurate analytical and simulation models can provide highly accurate policy rankings that can be used in conjunction with ordinal-optimization methods, provided that they incorporate the key aspects of system operation.
international conference on computer communications | 1994
Jeffrey E. Wieselthier; Craig M. Barnhart; Anthony Ephremides
The authors study the voice-call admission control problem in integrated voice/data multihop radio networks. They develop an efficient simulation model based on the use of the standard clock (SC) approach, which permits the simultaneous simulation of a large number of admission-control policies, thereby reducing computation time significantly. They then demonstrate the effectiveness of ordinal-optimization techniques, which provide a remarkably good ranking of admission-control policies after relatively short simulation runs, thereby facilitating the rapid determination of good policies. Moreover, they demonstrate that the use of crude and inaccurate analytical and simulation models can provide highly accurate policy rankings that can be used in conjunction with ordinal-optimization methods, provided that they incorporate the key aspects of system operation.<<ETX>>
conference on decision and control | 1994
Craig M. Barnhart; Jeffrey E. Wieselthier; Anthony Ephremides
In this paper we apply the standard clock (SC) and ordinal-optimization techniques to the voice-call admission-control problem in integrated networks, which is a problem of considerable interest to the communications community. We actually had to extend the SC model to incorporate deterministic events, namely the fixed packet lengths of data packets. Our ordinal-optimization studies show that crude models are often adequate to predict the relative performance of different control policies, even though they may provide poor estimates of actual system performance. The accuracy of these rankings suggests that simple analytical models can be used to reduce the search space to just a few policies whose performance can then be evaluated accurately via simulation, thus decreasing computation time dramatically.<<ETX>>
international conference on computer communications | 1991
Jeffrey E. Wieselthier; Craig M. Barnhart; Anthony Ephremides
The problem of routing is addressed for the minimization of congestion as a first step toward the solution of the joint routing-scheduling problem in packet radio networks. This is formulated as a combinatorial-optimization problem, and a Hopfield neural network model is developed for its solution. The method of Lagrange multipliers is used, which permits these coefficients to vary dynamically along with the evolution of the system state. Extensive software simulation results demonstrate the ability of this approach to determine good sets of routes in large, heavily-congested networks.<<ETX>>
conference on decision and control | 1992
J.E. Weiselthier; Craig M. Barnhart; Anthony Ephremides
Admission control in circuit-switched multihop radio networks is addressed. The problem formulation is based on the multiple service, multiple resource (MSMR) model developed by S. Jordan and P. Varaiya (1991). A recursive procedure is used to evaluate the performance associated with different coordinate convex policies, coupled with a descent-search technique for performance optimization. Empirical evidence supports the conjecture that throughput and blocking probability are unimodal functions of the admission-control policy. The major observation is that the exercise of admission control achieves minimal performance improvement as long as all call types are weighted equally. However, it has been shown that admission control is useful in cases of unequally weighted call types.<<ETX>>
military communications conference | 1991
Craig M. Barnhart; Jeffrey E. Wieselthier; Anthony Ephremides
The authors address the problem of link activation or scheduling in multihop packet radio networks, a contention-free form of channel access that is appropriate for many military communication applications. This problem, in almost all of its forms, is a combinatorial-optimization problem of high complexity. They approach this problem by the use of a Hopfield neural network model in which the method of Lagrange multipliers is used to dynamically vary the values of the coefficients used in the connection weights. Extensive software simulation results demonstrate the effectiveness of this approach in producing schedules of optimal length. Issues associated with the extension of this approach to the joint routing/scheduling problem are discussed.<<ETX>>
Wireless Networks | 1996
Jeffrey E. Wieselthier; Craig M. Barnhart; Anthony Ephremides
In this paper we consider the evaluation of data-packet delay in wireless integrated voice/data networks. In networks that support voice in the classical circuit-switched fashion, the voice occupancy process satisfies a product-form solution under reasonable modeling assumptions. Although this product-form solution provides an accurate characterization of equilibrium voicetraffic behavior, it does not directly provide a method to evaluate data-packet delay. However, examination of each link separately in a manner that incorporates interaction with the rest of the network permits us to take advantage of the wireless nature of the network and obtain a three-flow characterization of each link, which also satisfies a product-form solution and is hence termed a “mini-product-form” solution. By matching the values of these flows to the average values obtained from the product-form solution of the entire network, we obtain a three-dimensional Markov chain characterization of the voice occupancy state on the link, which permits a simpler evaluation of data-packet delay. A further reduction is possible by converting the three-dimensional chain to a single-dimensional one. Performance results demonstrate that these models provide satisfactory delay estimates that also appear to be upper bounds on delay.