Stepan Kucera

Asynchronous distributed power and rate control in ad hoc networks: a game-theoretic approach

This paper analyzes distributed asynchronous power and rate control for wireless ad hoc networks. Importantly, all network transmitters are considered to be independent of any management infrastructure and to have the freedom to choose their own arbitrary control rules, using as input only information on local interference and achieved carrier signal-to-interference ratio (CIR). Such an approach respects diverse user preferences of on quality of service (QoS) and allows them to adapt to local network conditions in contrast with conventional cellular systems, whose users must follow centralized control commands from serving base stations. For this purpose, we develop a general non-cooperative game-theoretic framework and characterize the resulting power and rate allocation dynamics in terms of its convergence to network-wide acceptable equilibrium states under stochastic communication channels. Chief among the attractive features of our proposed framework is the fact that it is developed in an entirely abstract way without any particular technological or architectural assumptions, which are typically made in related works. Numerical simulations prove the potential of our approach to provide for fair, robust and comparably better CIR allocation in ad hoc networks with varying topology and user density.

Adaptive channel allocation for enabling target SINR achievability in power-controlled wireless networks

This paper offers a new insight to the fundamental problem of efficient admission control in arbitrary power-controlled wireless networks with an unknown call arrival distribution. Active transmitter-receiver pairs are assumed to (i) communicate simultaneously over shared channels, (ii) define target signal-to-interference and noise ratios (SINRs) by nonlinear functions of channel interference, and (iii) use adaptive power control to maintain the actual SINR at the target level in response to interference variations. Unlike other studies, in this study, power control with limited dynamic range and both the discrete-time and the continuous-time dynamics is explicitly considered, as well as the effects of stochastic radio propagation phenomena. Without relying on a priori assumptions, we first define sufficient conditions for a channel allocation mechanism to ensure the SINR constraints in cooperation with the deployed power control mechanism. We use the concept of Lyapunov stability as a cross-layer optimization criterion. Subsequently, we focus on the widely assumed case of SINR targets being defined by linear functions of interference, and show that such targets can be achieved if hii > |Ai|¿ j¿i hij ¿i, where hij is the channel gain between the transmitter of link j and the receiver of link i, and Ai is the slope of the linear definition of the target SINR. This knowledge allows us to propose a simple distributed algorithm for implementing an admission control mechanism that (i) uses interference and pilot signal measurements as its only decision-making input, and (ii) allows links to adaptively adjust the SINR targets within the system stability bounds. This mechanism is shown to outperform the carrier sensing approach (CSMA/CA) for admission control.

Distributed Power Control for Wireless Ad Hoc Networks: A Game-Theoretic Approach Based on Best-Response Functions

This paper presents a novel framework for distributed power control for ad-hoc wireless networks. We analyze dynamic adaptive power allocation assuming that transmit power is adjusted with respect to experienced interference based on general best-response functions. For this purpose, we develop a general non-cooperative game-theoretic framework in order to characterize optimal equilibrium states and convergence of distributed power control dynamics to such states. Our work provides a more general insight to game-theoretic power control compared to most of recent works in this field. Moreover, our framework is developed in an abstract way without any technical assumption on particular modulation, coding, QoS measure definition or network architecture. To demonstrate an application of our framework, we show that stable linear best-response power control converges exponentially to a unique Nash equilibrium for any initial condition, which we confirm by numerical simulations.

Low-complexity admission control for distributed power-controlled networks with stochastic channels

This study addresses the general problem of efficient resource management in wireless networks with arbitrary time-varying topologies. Communication channels are assumed to generally accommodate multiple simultaneous transmissions. In this context, we focus our attention on the problem of distributed transmission power allocation and medium access by links (transmitter-receiver pairs) that require a guaranteed minimum signal-to-interference and noise ratio (SINR) at the receiver for a reliable data transfer. The design constraints for derived solutions consist of (i) a theoretically optimum performance, (ii) minimum complexity in implementation, and (iii) reliable feedback on target SINR feasibility to both active and inactive links. To this end, we propose adaptive algorithms that employ real-time tracking of the spectral radius of the Foschini-Miljanic matrix by means of distributed interference measurements. The algorithm design is characterized by an inherent resistant to the effects of stochastic radio propagation phenomena and an exponential convergence rate - a fact which we prove analytically. Numerical simulations confirm that our approach to admission control reaches the performance upper bounds of comparison algorithms that are based on random access, carrier-sensing, fixed channel probing, controlled power-up, or channel measurements.

A Game-Theoretic Framework for Distributed Power Control in Wireless Ad HOC Networks

This paper presents a novel game-theoretic framework for distributed adaptive power control in wireless ad-hoc networks. It first shows the equivalency of two recent approaches to this noncooperative field - the QoS utility maximization approach and the best-response approach. We then choose to follow the analytically more intuitive best-response approach and analyze in an abstract way general conditions for existence of optimal outcomes (Nash equilibria) of best-response power control dynamics. Consequently, we characterize conditions for global convergence to such states without any particular technical assumption. Our work provides a mathematically more general insight to game-theoretic power control compared to recent related works. Using the herein developed framework, we discuss CIR-based utility function maximization and show conditions for applicability of linear (linearized) best-response power control in connection with illustrative simulations

Asynchronous Distributed Power and Rate Control in Ad Hoc Networks with Stochastic Channels

This paper analyzes distributed asynchronous power and rate control for wireless ad hoc networks with stochastic channels. In contrast to conventional cellular systems, all network transmitters are assumed to be independent of any management infrastructure and, importantly, to have the freedom to choose their own arbitrary control rules, using as input only the information on local interference and achieved signal-to-interference and noise ratio (SINR). This approach respects links different local network conditions and preferences on quality of service. With the purpose of finding network-wide acceptable equilibria for such an individually defined power/rate allocation dynamics, the authors discuss an entirely general asynchronous and distributed algorithm, whereby stochastic channels are assumed. Moreover, optimum admission scheme for linear/linearized models is given. Numerical simulations show the efficiency of our approach to allocate comparably higher SINRs in random ad hoc networks with changing topologies and user density.

Predictive Techniques for Enabling Fast and Accurate Medium Access Control in Distributed Power-Controlled Networks

The goal of this study is to define a scheme for fast and accurate medium access control (MAC) in distributed power-controlled wireless networks. The system model assumes (i) arbitrary topologies, (ii) arbitrary call arrival rates, (iii) multiple links transmitting simultaneously over shared interference-limited channels, and (iv) transmitters updating their powers to maintain a predefined signal-to-interference and noise ratio (SINR) at the receiver. Departing from our own theoretical framework on the computation of the dominant eigenvalue of the network information matrix, we discuss an accurate MAC scheme that uses interference measurements as its only decision-making input. By accuracy is meant that the MAC scheme grants channel access to all links with achievable target SINRs and rejects others. In contrary to other schemes, our approach allows once-admitted links to continuously monitor the achievability of their SINR targets without any overhead. However, the initial admission decision of passive links relies on energy-consuming channel probing, which can be protracted in networks with high channel reuse. While maintaining the accuracy and reliability, we reduce the overall call admission delay and energy usage of the MAC scheme by employing simple techniques for future prediction by data estimation/extrapolation. Power control based on Kalman filtration is suggested for noise suppression. Numerical simulations demonstrate the potential of the proposed scheme.

Low-Latency Communications in LTE Using Spatial Diversity and Encoding Redundancy

Control of data delivery latency in wireless mobile networks is an open problem due to the inherently unreliable and stochastic nature of wireless channels. This paper explores how the current best-effort throughput-oriented wireless services could be evolved into latency-sensitive enablers of new mobile applications such as remote 3D graphical rendering for interactive virtual/augmented-reality overlay. Assuming that the signal propagation delay and achievable throughput meet the basic latency requirements of the user application, we examine the idea of trading excess/federated bandwidth for the elimination of non-negligible data re-ordering delays, caused by temporal transmission failures and buffer overflows. The general system design is based on (i) spatially diverse delivery of data over multiple paths with uncorrelated outage likelihoods, and (ii) forward packet protection based on encoding redundancy that enables proactive recovery of lost or intolerably delayed data without end-to-end re-transmissions. Our analysis is based on traces of real-life traffic in live carrier-grade LTE networks.

Uplink-oriented deployment guidelines and optimization in W-CDMA heterogeneous networks

The operation of wireless cellular networks can be efficiently supported by secondary small cells that are on-demand deployed in traffic hotspots within the coverage area of primary macro cells. Assuming shared communication channels and the uplink communication mode, this study defines deployment guidelines and self-configuration algorithms that enable the coexistence of both the primary and the secondary cell tiers by ensuring a predefined signal-to-interference-and-noise ratio (SINR) for all active transmissions. To this end, solutions to the problems of base station placement, cell coverage optimization, and target SINR adaptation are discussed as well as their compatibility with downlink-oriented deployment guidelines. The analytical framework is accompanied by 3GPP-compliant simulations.

Stability Emphasizing Cross-Layer Optimization of Transmit Power Allocation in Distributed Wireless Networks

This paper theoretically analyzes cross-layer optimized design of transmit power allocation in distributed interference-limited wireless networks with asynchronously acting links and stochastic communication channels, whereby the network links architecture is abstracted into three layers - a physical, a data link and a network layer. We treat the transmit power allocation process as a result of coupled interaction, in which all the three layers try to satisfy their individual requirements on power control, admission control and routing respectively. Using a best-response approach for system modeling and the notion of networks stability for its cross-layer optimization, we present simple power control and admission control algorithms for convergent iterative allocation of equilibrium transmit powers, which optimally balance the network-wide trade-off between allocated transmit powers and resulting interference. Numerical simulations evaluate the achievable stability of our scheme with theoretical bounds.