Sum-Rate Optimization Problem for Multiuser OFDM Systems (original) (raw)
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Optimal Subcarrier Sharing for Weighted Sum of Rates Maximization in Multiuser-OFDM Systems
2007
We consider the maximization of the weighted sum of rates in a multiuser OFDM system with dynamic subcarrier allocation and subcarrier-wise adaptive modulation and power. We assume a total peak power constraint and a target bit error rate (BER). We allow each subcarrier to be shared by more than one user. This sharing implies an interference which the receivers deal with as noise. In this paper, we show that the resulting non-convex optimization problem can be decomposed into two tractable subproblems: a subcarrier assignment and a power allocation. We prove that the optimal subcarrier assignment is exclusive, i.e. each subcarrier has to be allocated to one user only. The optimal power allocation corresponds to a multilevel water-filling. Since the solutions to these two subproblems are mutually dependent, one can use exhaustive search to explicit the optimal subcarrier assignment. To avoid the burden of exhaustive search, we show that a close-to-optimal low-complexity solution is obtained if the total power is equally partitioned among the subcarriers. Finally, simulation results show that the proposed suboptimal solution yields a significant gain in terms of average weighted sum of rates compared to a traditional static subcarrier allocation.
2007
We consider the maximization of the weighted sum-rate on a multiuser-OFDM downlink with adaptive modulation and power under a total transmit power constraint and a user-wise target BER. We allow each subcarrier to be shared by more than one user. We show that this optimization problem can be decomposed into two subproblems: a subcarrier assignment and a power allocation. We prove that the optimal subcarrier assignment is exclusive, that is each subcarrier is allocated to only one user. The optimal power allocation corresponds to a multilevel water-filling. When the achievable rate region is convex, the optimality of the exclusive subcarrier assignment for arbitrary weights means that the OFDMA is the optimal sharing scheme for various performance criteria.
Maximization of the Single User Rate in OFDMA Assuming Equal Power on Allocated Subcarriers
2007 IEEE 65th Vehicular Technology Conference - VTC2007-Spring, 2007
The problem of optimal power allocation for a single user in an OFDMA system is considered for uplink, under the assumption that the total power is divided equally to a selected subset of subcarriers. This scenario suggests reduced feedback information for power control from base station to the user since only the information over modulation on each subcarrier is necessary. Assuming knowledge of the instantaneous users' channel gains, the rate optimization problem reduces to a subcarrier allocation problem, discribed by a discrete function with the set of possible allocated subcarriers as domain and the set of achievable sum rates as range. A continuous equivalent of the function is used to derive properties that also hold in the discrete case. The function is in general not concave and concavity holds only for high CNR regions-over a specified bound. In all cases however it is proved that the maximum is unique and a simple and efficient algorithm is proposed for subcarrier allocation which always provides the optimal solution concerning the subcarriers to be loaded. The cost in achievable capacity from the use of equal-power compared to actual waterfilling is calculated, which is shown to be small while the gain in frequency resources and feedback reduction is important.
IEEE Transactions on Signal Processing, 2000
This paper considers the downlink of a cellular orthogonal frequency division multi-access (OFDMA) system, in which multiple base stations (BSs) are coordinated by a centralized resource allocation algorithm. We address the problem of maximizing the weighted sum of the minimal user rates (WSMR) of coordinated cells subject to a total power constraint at each BS, in terms of jointly optimizing coordinated BSs' subcarrier and power allocation. In particular, the solution of this problem corresponds to a resource allocation that guarantees similar rates to all users in each cell. An iterative algorithm is proposed to optimize the subcarrier allocation and the power allocation alternatively, so that the WSMR keeps increasing until convergence. In each iteration, the subcarrier allocation is updated by solving a mixed integer linear program for each cell, while the power allocation is updated by solving a successive set of convex optimization problems with a duality-based numerical algorithm. The effectiveness of the algorithm is illustrated by numerical experiments.
We consider the maximization of the weighted sum-rate on a multiuser-OFDM downlink with adaptive modulation and power under a total transmit power constraint and a user-wise target BER. We allow each subcarrier to be shared by more than one user. We show that this optimization problem can be decomposed into two subproblems: a subcarrier assignment and a power allocation. We prove that the optimal subcarrier assignment is exclusive, that is each subcarrier is allocated to only one user. The optimal power allocation corresponds to a multilevel water-filling. When the achievable rate region is convex, the optimality of the exclusive subcarrier assignment for arbitrary weights means that the OFDMA is the optimal sharing scheme for various performance criteria.
Iterative waterfilling for weighted rate sum maximization in MIMO-OFDM broadcast channels
2007
Abstract We study the maximization of the weighted sum rate in Gaussian multi-input multi-output OFDM broadcast channel under a total power constraint. This problem is motivated by adaptive resource allocation policies in a multi-carrier wireless system with multiple antennas at the base station. We propose a iterative waterfilling algorithm based on dual decomposition. Two decompositions are considered, one in subcarrier domain and another in both subcarrier and user domain.
A Survey on Resource Allocation in OFDMA Using Convex Optimization
2015
Orthogonal Frequency Division Multiple Access (OFDMA) is the promising technique for ever increasing demand of high data rate services. This paper proposes the Resource allocation issues for multiuser wireless transmissions, based on orthogonal frequency division multiple Access (OFDMA) and convex optimization techniques which are widely used in the design and analysis of variety of communications problems. By using convex optimization we convert the highly non convex resource allocation problem into a sequence of convex sub problems. The proposed system will be designed, to solve the subcarrier and power allocation problems for multiuser OFDMA system. The aim of proposed system is to maximize total throughput while maintaining rate proportionality among the users and minimizing the total transmit power under the condition that the QoS requirement of each user can be guaranteed.
Joint Allocation of Subcarriers and Transmit Powers in a Multiuser OFDM Cellular Network
2006 IEEE International Conference on Communications, 2006
In the present paper, we consider the problem of joint bandwidth (subcarriers) and power allocation for the downlink of a multiuser multi-cell OFDM cellular network. This resource allocation problem is formulated as a power minimization problem, subject to meeting the target rates of all users in the network. We develop a distributed solution to find the globally optimal allocation which determines the subcarrier and power allocation dynamically. In addition, we investigate the impact of reducing the complexity by reducing the number of degrees of freedom available in the optimization. In particular, we consider a static bandwidth allocation scheme, and a static power allocation scheme. The numerical results show that the penalty on network performance due to the reduction in the available degrees of freedom is not significant.
Resource Allocation for Maximizing Weighted Sum Min-Rate in Downlink Cellular OFDMA Systems
2010 IEEE International Conference on Communications, 2010
This paper considers the downlink of a cellular orthogonal frequency division multi-access (OFDMA) system, in which multiple base stations (BS) are coordinated by a centralized resource allocation algorithm. We address the problem of maximizing the weighted sum min-rate (WSMR) subject to a total power constraint at each BS, in terms of jointly optimizing coordinated BSs' subcarrier and power allocation. In particular, this problem leads to a resource allocation that guarantees similar rates to users in each cell. An iterative algorithm is proposed to optimize subcarrier and power allocation alternatively, so that the WSMR keeps increasing until convergence. In each iteration, the subcarrier allocation is updated by solving a mixed integer linear programming problem for each cell, while the power allocation is updated by solving a successive set of convexoptimization problems with an algorithm based on Karush-Kuhn-Tucker conditions. The effectiveness of the algorithm is illustrated by numerical experiments.