Queueing Networks of Random Link Topology: Stationary Dynamics of Maximal Throughput Schedules

In this paper, we study the stationary dynamics of a processing system comprised of several parallel queues and a single server of constant rate. The connectivity of the server to each queue is randomly modulated, taking values 1 (connected) or 0 (severed). At any given time, only the currently connected queues may receive service. A key issue is how to schedule the server on the connected queues in order to maximize the system throughput. We investigate two dynamic schedules, which are shown to stabilize the system under the highest possible traffic load, by scheduling the server on the connected queue of maximum backlog (workload or job number). They are analyzed under stationary ergodic traffic flows and connectivity modulation. The results also extend to the more general case of random server rate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47640/1/11134_2005_Article_858.pd

The Supercomputer Supernet Testbed: A WDM Based Supercomputer Interconnect

Current fiber optic networks effectively provide local connectivity among end user computing devices, and can serve as backbone fabric between LAN subnets across campus and metropolitan areas. However, combining both stream service (in which ATM excels) and low latency datagram service (in which cluster networks like Myrinet and POLO excel) has been difficult to realize. This paper describes a new wavelength division multiplexed (WDM) fiber optic network that supports both stream and datagram service and extends reach and functionality of low-latency, high bandwidth workstation clusters to a campus and MAN setting. The novel concept is based on combining the rich interconnect structure of WDM fiber optics with the fast, low-latency mesh of crossbar switches recently developed for workstation groups. This system, called the Supercomputer Supernet (SSN) achieves a high level of performance by replacing the point-to-point copper wire links with a parallel channel (WDM) fiber opt..

Fast power-up active link protection in autonomous distributed transmitter power control

In this work, we propose an enhancement to the DPC/ALP (Distributed Power Control with Active Link Protection) algorithm that allows fast power ramp-up without compromising the ALP guarantee. The original DPC algorithm was first augmented with ALP to provide absolute performance guarantees. The basis of Active Link Protection lies on constraining the rate of the new links' transmission power increase during the admission process, inducing a trade-off between the duration of the admission process and the network capacity reserved for absorbing the SINR fluctuations. Thus, to minimize the capacity loss, power-up should be slow, prolonging admission delay. In the new scheme, the power-up is accelerated when congestion is low, via test transmissions. Specifically, pairs of mini slots are interleaved between payload-carrying slots. In the first minislot, a link has the opportunity to carry out a test transmission in the wireless channel at an arbitrarily high power level, greater than what DPC/ALP allows. The purpose of this test transmission is to communicate the desired transmission power to the other links in the network neighborhood. The latter respond in the second mini-slot, indicating their distress if the first mini-slot transmissions generated excessive interference to their receivers. The absence of transmission at the second mini-slot signifies that no link has opposed, thus the link is free to use the first mini-slot's high power level in their subsequent slots, realizing the fast power ramp up. In contrast, if a transmission is sensed in the second mini-slot (emanating from one or more links in distress-typical under network congestion, when links are closely packed), the power ramp up will revert to the standard increase of DPC/ALP. © 2008 IEEE

Joint Task Migration and Power Management in Wireless Computing

We investigate a wireless computing architecture, where mobile terminals can execute their computation tasks either 1) locally, at the terminal's processor, or 2) remotely, assisted by the network infrastructure, or even 3) combining the former two options. Remote execution involves: 1) sending the task to a computation server via the wireless network, 2) executing the task at the server, and 3) downloading the results of the computation back to the terminal. Hence, it results to energy savings at the terminal (sparing its processor from computations) and execution speed gains due to (typically) faster server processor(s), as well as overheads due to the terminal server wireless communication. The net gains (or losses) are contingent on network connectivity and server load. These may vary in time, depending on user mobility, network, and server congestion (due to the concurrent sessions/connections from other terminals). In local execution, the wireless terminal faces the dilemma of power managing the processor, trading-off fast execution versus low energy consumption. We model the system within a Markovian dynamic control framework, allowing the computation of optimal execution policies. We study the associated energy versus delay trade-off and assess the performance gains attained in various test cases in comparison to conventional benchmark policies

Power Optimization in Random Wireless Networks

In this paper, we analyze the problem of power control in large, random wireless networks that are obtained by "erasing" a finite fraction of nodes from a regular d-dimensional lattice of N transmit-receive pairs. In this model, which has the important feature of a minimum distance between transmitter nodes, we find that when the network is infinite, power control is always feasible below a positive critical value of the users' signal-to-interference-plus-noise ratio (SINR) target. Drawing on tools and ideas from statistical physics, we show how this problem can be mapped to the Anderson impurity model for diffusion in random media. In this way, by employing the so-called coherent potential approximation method, we calculate the average power in the system (and its variance) for 1-D and 2-D networks. This approach is equivalent to traditional techniques from random matrix theory and is in excellent agreement with the numerical simulations; however, it fails to predict when power control becomes infeasible. In this regard, even though infinitely large systems are always unstable beyond a critical value of the users' SINR target, finite systems remain stable with high probability even beyond this critical SINR threshold. We calculate this probability by analyzing the density of low lying eigenvalues of an associated random Schrodinger operator, and we show that the network can exceed this critical SINR threshold by at least O((log N)-2/d) before undergoing a phase transition to the unstable regime. Finally, using the same techniques, we also calculate the tails of the distribution of transmit power in the system and the rate of convergence of the Foschini-Miljanic power control algorithm in the presence of random erasures. © 2016 IEEE

A characterization of max-min SIR-balanced power allocation with applications

We consider a power-controlled wireless network with an established network topology in which the communication links (transmitter-receiver pairs) are subject to some constraints on transmit powers and corrupted by the cochannel interference and background noise. The interference is completely determined by a so-called gain matrix. Assuming irreducibility of the gain matrix, we provide an elegant characterization of the max-min SIR-balanced power allocation under general power constraints. This characterization gives rise to two types of algorithms for computing the max-min SIR-balanced power allocation. It also allows for an interesting saddle point characterization of the Perron root of extended gain matrices

Power Controlled Multiple Access In Ad Hoc Networks

This work presents PCMA, a power controlled multiple access wireless MAC protocol within the collision avoidance framework. PCMA generalizes the transmit-or-defer "on/o# " collision avoidance model of current protocols to a more flexible "variable bounded power" collision suppression model. The algorithm is provisioned for ad hoc networks and does not require the presence of base stations to manage transmission power. Our initial simulation results show that PCMA can improve the throughput performance non-power controlled protocols by a factor of 2 with potential for additional scalability as source destination pairs become more localized