Nicholas Bambos

Radio link admission algorithms for wireless networks with power control and active link quality protection

Presents a distributed power control scheme, which maintains the signal/interference ratios (SIRs) of operational (active) links above their required thresholds at all times (link quality protection), while new users are being admitted; furthermore, when new users cannot be successfully admitted, existing ones do not suffer fluctuations of their SIRs below their required thresholds values. The authors also present two admission/rejection control algorithms, which exercise voluntary drop-out of links inadmissible to the network so as to reduce interference and possibly facilitate the admission of other links.

Mobile power management for wireless communication networks

For fixed quality-of-service constraints and varying channel interference, how should a mobile node in a wireless network adjust its transmitter power so that energy consumption is minimized? Several transmission schemes are considered, and optimal solutions are obtained for channels with stationary, extraneous interference. A simple dynamic power management algorithm based on these solutions is developed. The algorithm is tested by a series of simulations, including the extraneous-interference case and the more general case where multiple, mutually interfering transmitters operate in a therefore highly responsive interference environment. Power management is compared with conventional power control for models based on FDMA/TDMA and CDMA cellular networks. Results show improved network capacity and stability in addition to substantially improved battery life at the mobile terminals.

Mobile power management for maximum battery life in wireless communication networks

We address the problem of how a mobile node in a wireless network should vary its transmitter power so that energy consumption is minimized, subject to fixed quality-of-service constraints. Optimal solutions are obtained for channels with stationary, extraneous interference. A simple dynamic power management algorithm based on these solutions is developed. The algorithm is tested by a series of simulations, including the extraneous-interference case and the more general case where multiple, mutually interfering transmitters operate in a therefore highly responsive interference environment. Results show improved network capacity and stability in addition to substantially improved battery life at the mobile terminals.

Admission control schemes for wireless communication networks with adjustable transmitter powers

When new mobiles are admitted in some channel of a wireless communication network traditional power control algorithms cannot foresee the effect that new admissions have on the signal-to-interference ratios (SIR) of active mobiles already using the channel, and may cause fluctuations of their SIR below acceptable levels during the process. The authors present two algorithms that manage transmission power and channel admissions jointly to maintain the SIR of all links above some quality factor /spl gamma/ at all times. This joint control of power and channels results in high channel reuse.<<ETX>>

Power control based admission policies in cellular radio networks

The problem of limiting the cochannel interference between transmitter-receiver pairs in a cellular network to acceptable levels, while accommodating as many transmissions as possible, is addressed. The controllable network parameters, are the transmission powers of the base stations, and possibly of mobiles too, in the cells. Efficient adaptive control of the powers guarantees quality of service above a certain threshold at all times, given the continuously changing traffic of communication requests in the network. The quality criterion used in this study is the carrier-to-interference ratio (C/I) at the receiver.<<ETX>>

On distributed power control for radio networks

Due to co-channel interference, the carrier to interference ratios (C/I) of some mobiles in a wireless network may drop below a desired quality threshold /spl gamma/, either upon admission of a new mobile or if channel conditions vary. By using dynamic, local measurement of the power gains between base stations and mobiles, we develop a new distributed algorithm for power control which operates by adjusting the transmitted powers from the base stations so as to maintain the C/I of every link above the desired threshold.<<ETX>>

Channel probing for distributed access control in wireless communication networks

Power control in wireless networks is useful for minimizing channel congestion (hence increasing network capacity). In this work, we show how the distributed power control algorithm with active link protection (DCP-ALP) can be used as a channel probing tool that allows a new link trying to access a channel to quickly and autonomously determine whether it can be admitted to it (i.e. whether there is a feasible power configuration for the transmitters such that the link quality requirements on all links are met), which significantly improves the capacity and access time of the network.

On the stationary dynamics of parallel queues with random server connectivities

We investigate the stationary dynamics of a system comprised of K parallel queues and a single server. The connectivities of the server to the various queues are randomly modulated by a stochastic process, taking values 1 (connected) or 0 (severed). At any given time, only the currently connected queues can be served. Such models capture the essential features of several practical situations of unreliable service, appearing in wireless communication networks with extraneous interference, flexible manufacturing systems with failing components etc. We focus on the problem of allocating the server to the connected queues in order to maximize the capacity (throughput) of the system. We analyze two simple dynamic server allocation policies which are shown to stabilize the system under the highest possible loading. Several applications are discussed. The system is studied under stationary ergodic input job flows and modulation processes.

Power-induced time division on asynchronous channels

Time division multiple access offers certain well-known advantages over methods such as spread spectrum code division. Foremost is the interference immunity provided by dedicated time slots. Partly offsetting this is TDMAs need for network-wide synchronization. Viewing arbitrary time intervals as potential TDMA time slots, we ask whether it is possible to obtain some of the benefit of time division without incurring the synchronization cost. In particular, we address the question of whether a TDMA-like state can be induced on asynchronous channels in such a way as to reduce interference and energy consumption. Through analysis and simulation we find conditions under which it is beneficial to use time division, and then show how autonomous power management may be used as a mechanism to induce a form of time division. In this context a backlog-sensitive power management system is presented.

ON QUEUES WITH PERIODIC INPUTS

We consider a single-server queue with a periodic and ergodic input. It is shown that if the traffic intensity is less than 1, then the waiting time process is asymptotically periodic. Limit theorems associated with the asymptotic behavior of the queue are also proven. The results are then extended to acyclic networks of queues with periodic inputs. Particular cases of these results had been previously obtained for a single queue with periodic Poisson arrival input process and with independent and identically distributed service times.