Optimal Subcarrier Sharing for Weighted Sum of Rates Maximization in Multiuser-OFDM Systems (original) (raw)
Related papers
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.
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.
Sum-Rate Optimization Problem for Multiuser OFDM Systems
Proceedings of the ISCIE International Symposium on Stochastic Systems Theory and its Applications, 2015
A multiuser Orthogonal Frequency Division Multiplexing (OFDM) system with perfect channel knowledge and limited power at base station is studied to maximize the average system throughput. Data rate and bit error rate (BER) can be adaptively changed with the channel variation. An efficient and low complexity algorithm for subcarrier and power allocation in OFDM systems is proposed in this paper. We consider an OFDM downlink system where each subcarrier is used by only one user. Since our resource allocation problem is non-convex, it is not easy to find an optimal solution. Our approach is to consider a user iterative water filling algorithm (IWF), which is concave, and find a numerical method to approximate the optimal solution for our non convex problem. Our results show that each subcarrier is allocated to a user by taking into account channel gains and interference caused by other users.
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.
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.
Low complexity subcarrier and power allocation for utility maximization in uplink OFDMA systems
IEEE Transactions on Wireless Communications, 2008
We consider the joint subcarrier and power allocation problem with the objective of maximizing the total utility of users in the uplink of an OFDMA system. Our formulation includes the problems of sum rate maximization, proportional fairness and max-min fairness as special cases. Unlike some previous algorithms, which are iterative and time consuming, our proposed one is non-iterative and with time complexity of only O(KN log 2 N), where K and N are the number of users and subcarriers respectively. We prove that it provides a solution that is Pareto optimal within a large neighborhood of itself. Besides, we derive an efficiently computable upper bound of the optimal solution. Simulation results show that our algorithm is nearly optimal.
Dynamic subchannel and bit allocation in multiuser OFDM with a priority user
Eighth IEEE International Symposium on Spread Spectrum Techniques and Applications - Programme and Book of Abstracts (IEEE Cat. No.04TH8738), 2004
In this paper, we consider multiuser orthogonal frequency division multiplexing (OFDM) with adaptive subcarrier allocation and adaptive modulation, especially when there is one priority user who must be provided with a fixed data rate. We develop the optimum subcarrier/bit allocation method that minimizes total transmission power employing integer programming (IP) which is NP-hard problem. To reduce the complexity, suboptimum two-step algorithm is proposed: firstly, subcarriers are allocated to the priority user and then the remaining subcarriers are distributed to other users considering the best channel gain for each subcarrier; in the second step, using the Levin-Campello algorithm, the bits are loaded into the priority user and the other users separately. Numerical results show that total transmission power of the proposed optimum/suboptimum algorithms is significantly smaller than that of fixed modulation. In addition, the difference of total transmission power between the optimum and suboptimum algorithms is within about 0.5 dB when the number of subcarriers is 64 and the required data rate of the priority user is identical to the average required data rate of each user.
Multiuser OFDM with adaptive subcarrier, bit, and power allocation
IEEE Journal on Selected Areas in Communications, 1999
Multiuser orthogonal frequency division multiplexing (OFDM) with adaptive multiuser subcarrier allocation and adaptive modulation is considered. Assuming knowledge of the instantaneous channel gains for all users, we propose a multiuser OFDM subcarrier, bit, and power allocation algorithm to minimize the total transmit power. This is done by assigning each user a set of subcarriers and by determining the number of bits and the transmit power level for each subcarrier. We obtain the performance of our proposed algorithm in a multiuser frequency selective fading environment for various time delay spread values and various numbers of users. The results show that our proposed algorithm outperforms multiuser OFDM systems with static time-division multiple access (TDMA) or frequency-division multiple access (FDMA) techniques which employ fixed and predetermined time-slot or subcarrier allocation schemes. We have also quantified the improvement in terms of the overall required transmit power, the bit-error rate (BER), or the area of coverage for a given outage probability
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.
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.