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271
Spectrum Sharing for Unlicensed Bands
- in IEEE DySPAN 2005
, 2005
"... We study a spectrum sharing problem in an unlicensed band where multiple sys-tems coexist and interfere with each other. Due to asymmetries and selfish system behavior, unfair and inefficient situations may arise. We investigate whether efficiency and fairness can be obtained with self-enforcing spe ..."
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Cited by 302 (4 self)
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We study a spectrum sharing problem in an unlicensed band where multiple sys-tems coexist and interfere with each other. Due to asymmetries and selfish system behavior, unfair and inefficient situations may arise. We investigate whether efficiency and fairness can be obtained with self-enforcing spectrum sharing rules. These rules have the advantage of not requiring a central authority that verifies compliance to the protocol. Any self-enforcing protocol must correspond to an equilibrium of a game. We first analyze the possible outcomes of a one shot game, and observe that in many cases an inefficient solution results. However, systems often coexist for long periods and a repeated game is more appropriate to model their interaction. In this repeated game the possibility of building reputations and applying punishments allows for a larger set of self-enforcing outcomes. When this set includes the optimal operating point, efficient, fair, and incentive compatible spectrum sharing becomes possible. We present examples that illustrate that in many cases the performance loss due to selfish behavior is small. We also prove that our results are tight and quantify the best achievable performance in a non-cooperative scenario.
Dual methods for nonconvex spectrum optimization of multicarrier systems
- IEEE TRANS. COMMUN
, 2006
"... The design and optimization of multicarrier communications systems often involve a maximization of the total throughput subject to system resource constraints. The optimization problem is numerically difficult to solve when the problem does not have a convexity structure. This paper makes progress ..."
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Cited by 201 (7 self)
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The design and optimization of multicarrier communications systems often involve a maximization of the total throughput subject to system resource constraints. The optimization problem is numerically difficult to solve when the problem does not have a convexity structure. This paper makes progress toward solving optimization problems of this type by showing that under a certain condition called the time-sharing condition, the duality gap of the optimization problem is always zero, regardless of the convexity of the objective function. Further, we show that the time-sharing condition is satisfied for practical multiuser spectrum optimization problems in multicarrier systems in the limit as the number of carriers goes to infinity. This result leads to efficient numerical algorithms that solve the nonconvex problem in the dual domain. We show that the recently proposed optimal spectrum balancing algorithm for digital subscriber lines can be interpreted as a dual algorithm. This new interpretation gives rise to more efficient dual update methods. It also suggests ways in which the dual objective may be evaluated approximately, further improving the numerical efficiency of the algorithm. We propose a low-complexity iterative spectrum balancing algorithm based on these ideas, and show that the new algorithm achieves near-optimal performance in many practical situations.
Dynamic Spectrum Management: Complexity and Duality
, 2007
"... Consider a communication system whereby multiple users share a common frequency band and must choose their transmit power spectral densities dynamically in response to physical channel conditions. Due to co-channel interference, the achievable data rate of each user depends on not only the power spe ..."
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Cited by 129 (8 self)
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Consider a communication system whereby multiple users share a common frequency band and must choose their transmit power spectral densities dynamically in response to physical channel conditions. Due to co-channel interference, the achievable data rate of each user depends on not only the power spectral density of its own, but also those of others in the system. Given any channel condition and assuming Gaussian signaling, we consider the problem to jointly determine all users ’ power spectral densities so as to maximize a system-wide utility function (e.g., weighted sum-rate of all users), subject to individual power constraints. For the discretized version of this nonconvex problem, we characterize its computational complexity by establishing the NP-hardness under various practical settings, and identify subclasses of the problem that are solvable in polynomial time. Moreover, we consider the Lagrangian dual relaxation of this nonconvex problem. Using the Lyapunov theorem in functional analysis, we rigorously prove a result first discovered by Yu and Lui (2006) that there is a zero duality gap for the continuous (Lebesgue integral) formulation. Moreover, we show that the duality gap for the discrete formulation vanishes asymptotically as the size of discretization decreases to zero.
Optimized Signaling for MIMO Interference Systems with Feedback
"... The system mutual information of a multiple-input multiple-output (MIMO) system with multiple users which mutually interfere is considered. Perfect channel state information is assumed to be known to both transmitters and receivers. Asymptotic performance analysis shows that the system mutual info ..."
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Cited by 106 (0 self)
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The system mutual information of a multiple-input multiple-output (MIMO) system with multiple users which mutually interfere is considered. Perfect channel state information is assumed to be known to both transmitters and receivers. Asymptotic performance analysis shows that the system mutual information changes behavior as the interference becomes sufficiently strong. In particular, beamforming is the optimum signaling for all users when the interference is large. We propose several numerical approaches to decide the covariance matrices of the transmitted signals and compare their performance in terms of the system mutual information. We model the system as a noncooperative game, and perform iterative water-filling to find the Nash equilibrium distributively. A centralized global approach and a distributed iterative approach based on the gradient projection method are also proposed. Numerical results show that all proposed approaches give better performance than the standard signaling which is optimum for the case without interference. Both the global and the iterative gradient projection methods are shown to outperform the Nash equilibrium significantly.
A gametheoretic approach to energy-efficient power control in multicarrier CDMA systems
- IEEE Journal on Selected Areas in Communications (JSAC
, 2006
"... Abstract—A game-theoretic model for studying power control in multicarrier code-division multiple-access systems is proposed. Power control is modeled as a noncooperative game in which each user decides how much power to transmit over each carrier to maximize its own utility. The utility function co ..."
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Cited by 89 (8 self)
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Abstract—A game-theoretic model for studying power control in multicarrier code-division multiple-access systems is proposed. Power control is modeled as a noncooperative game in which each user decides how much power to transmit over each carrier to maximize its own utility. The utility function considered here measures the number of reliable bits transmitted over all the carriers per joule of energy consumed and is particularly suitable for networks where energy efficiency is important. The multidimensional nature of users ’ strategies and the nonquasi-concavity of the utility function make the multicarrier problem much more challenging than the single-carrier or throughput-based-utility case. It is shown that, for all linear receivers including the matched filter, the decorrelator, and the minimum-mean-square-error detector, a user’s utility is maximized when the user transmits only on its “best ” carrier. This is the carrier that requires the least amount of power to achieve a particular target signal-to-interference-plus-noise ratio at the output of the receiver. The existence and uniqueness of Nash equilibrium for the proposed power control game are studied. In particular, conditions are given that must be satisfied by the channel gains for a Nash equilibrium to exist, and the distribution of the users among the carriers at equilibrium is characterized. In addition, an iterative and distributed algorithm for reaching the equilibrium (when it exists) is presented. It is shown that the proposed approach results in significant improvements in the total utility achieved at equilibrium compared with a single-carrier system and also to a multicarrier system in which each user maximizes its utility over each carrier independently. Index Terms—Energy efficiency, game theory, multicarrier code-division multiple-access (CDMA), multiuser detection, Nash equilibrium, power control, utility function. I.
Optimal linear precoding strategies for wideband noncooperative systems based on game theory – Part II: Algorithms
- IEEE Trans. Signal Process
, 2008
"... In this two-parts paper we propose a decentralized strategy, based on a game-theoretic formulation, to find out the optimal precoding/multiplexing matrices for a multipoint-to-multipoint communication system composed of a set of wideband links sharing the same physical resources, i.e., time and band ..."
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Cited by 86 (10 self)
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In this two-parts paper we propose a decentralized strategy, based on a game-theoretic formulation, to find out the optimal precoding/multiplexing matrices for a multipoint-to-multipoint communication system composed of a set of wideband links sharing the same physical resources, i.e., time and bandwidth. We assume, as optimality criterion, the achievement of a Nash equilibrium and consider two alternative optimization problems: 1) the competitive maximization of mutual information on each link, given constraints on the transmit power and on the spectral mask imposed by the radio spectrum regulatory bodies; and 2) the competitive maximization of the transmission rate, using finite order constellations, under the same constraints as above, plus a constraint on the average error probability. In Part I of the paper, we start by showing that the solution set of both noncooperative games is always nonempty and contains only pure strategies. Then, we prove that the optimal precoding/multiplexing scheme for both games leads to a channel diagonalizing structure, so that both matrix-valued problems can be recast in a simpler unified vector power control game, with no performance penalty. Thus, we study this simpler game and derive sufficient conditions ensuring the uniqueness of the Nash equilibrium. Interestingly, although derived under stronger constraints,
Iterative spectrum balancing for digital subscriber lines
- in IEEE ICC
, 2005
"... Abstract — The main performance bottleneck of modern Digital Subscriber Line (DSL) networks is the crosstalk among different lines (users). By deploying Dynamic Spectrum Management (DSM) techniques and reducing excess crosstalks among users, a network operator can dramatically increase the data rate ..."
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Cited by 81 (19 self)
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Abstract — The main performance bottleneck of modern Digital Subscriber Line (DSL) networks is the crosstalk among different lines (users). By deploying Dynamic Spectrum Management (DSM) techniques and reducing excess crosstalks among users, a network operator can dramatically increase the data rates and service reach of broadband access. However, current DSM algorithms suffer from either substantial suboptimality in typical deployment scenarios or prohibitively high complexity due to centralized computation. This paper develops, analyzes, and simulates a new suite of DSM algorithms for DSL interferencechannel models called Autonomous Spectrum Balancing (ASB), for both synchronous and asynchronous transmission cases. In the synchronous case, the transmissions over different tones are orthogonal to each other. In the asynchronous case, the transmissions on different tones are coupled together due to intercarrier-interference. In both cases, ASB utilizes the concept of a “reference line”, which mimics a typical victim line in the interference channel. The basic procedure in ASB algorithms is simple: each user optimizes the weighted sum of the achievable rates on its own line and the reference line while assuming the interferences from other users as noise. Users then iterate until the target rate constraints are met. Good choices of reference line parameters are already available in industry standards, and the ASB algorithm makes the intuitions completely rigorous and theoretically sound. ASB is the rst set of algorithms that is fully autonomous, has low complexity, and yet achieves nearoptimal performance. It effectively solves the nonconvex and coupled optimization problem of DSL spectrum management, and overcomes the bottleneck of all previous DSM algorithms.
Analysis of Iterative Waterfilling Algorithm for Multiuser Power Control
- in Digital Subscriber Lines,” EURASIP Journal on Applied Signal Processing, vol. 2006, Article ID 24012
, 2006
"... In modern digital subscriber line (DSL) systems where multiple users must coexist in the same frequency band, multiuser power control is an effective technique for reducing crosstalk interference and improving total system throughput. The popular distributed iterative waterfilling algorithm (IWFA) f ..."
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Cited by 76 (10 self)
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In modern digital subscriber line (DSL) systems where multiple users must coexist in the same frequency band, multiuser power control is an effective technique for reducing crosstalk interference and improving total system throughput. The popular distributed iterative waterfilling algorithm (IWFA) for DSL power control lets each user locally measure the total noise plus interference powers in all frequencies and optimally allocate its power across frequency tones according to a “waterfilling ” procedure to maximize its own achievable rate. Though effective and empirically convergent in extensive simulations, IWFA has only been shown to be convergent in limited cases under restrictive interference assumptions. In this paper we present an equivalent linear complementarity problem (LCP) formulation of the noncooperative Nash game resulting from the DSL power control problem. Based on this LCP reformulation, we establish the linear convergence of IWFA for arbitrary symmetric interference environment and for certain asymmetric channel conditions with any number of users. In the case of symmetric interference crosstalk coefficients, we show that the users of IWFA in fact, unknowingly but willingly, cooperate to minimize a common quadratic cost function whose gradient measures the
Optimal multiuser spectrum balancing for digital subscriber lines.
- IEEE Trans. Communications,
, 2006
"... ..."
Optimal Multi-user Spectrum Management for Digital Subscriber Lines
- IEEE TRANS. COMMUN.
, 2003
"... Crosstalk is a major issue in modern DSL systems such as ADSL and VDSL. Static spectrum management, the traditional way of ensuring spectral compatibility, employs spectral masks which can be overly conservative and lead to poor performance. In this paper we present a centralized algorithm for opti ..."
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Cited by 64 (20 self)
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Crosstalk is a major issue in modern DSL systems such as ADSL and VDSL. Static spectrum management, the traditional way of ensuring spectral compatibility, employs spectral masks which can be overly conservative and lead to poor performance. In this paper we present a centralized algorithm for optimal spectrum management (OSM) in DSL. The algorithm uses a dual decomposition to solve the spectrum management problem in an efficient and computationally tractable way. The algorithm shows significant performance gains over existing DSM techniques, e.g. in a downstream ADSL scenario the centralized OSM algorithm can outperform a distributed DSM algorithm such as iterative waterfilling by up to 135%
