[Show abstract][Hide abstract] ABSTRACT: In this letter, a Rayleigh block-fading (BF) channel, subject to an information outage probability constraint, is considered. The transmitter is assumed to have causal knowledge of the channel state information (CSI), which is exploited to intelligently allocate the power over the blocks (and hence vary the channel mutual information) to minimize the average transmitted power per block for satisfying the outage probability constraint for a given target code-rate. We first show that the optimal solution to this problem can be obtained by solving the reverse problem of minimizing the outage probability for a range of long-term power constraints through repeated uses of dynamic programming (DP), which is nevertheless prohibitively complex. Then, we develop a suboptimal allocation algorithm which still uses DP to exploit the CSI causality but at a much reduced complexity. A performance lower-bound is further derived, which permits us to see that the proposed algorithm is near-optimal, especially in the small outage probability regime. A scheme called equal-outage-probability per block (EOPPB) which compromises the performance further for reducing the complexity is also devised. To compare the methods, we evaluate both analytically and numerically their complexities and performance. The results are finally generalized to multiple-input multiple-output (MIMO) BF channels.
[Show abstract][Hide abstract] ABSTRACT: In this correspondence, a central Wishart multiple input multiple-output (MIMO) K-block fading channel with an information outage probability constraint is studied. Under this block-limited channel condition, we aim to minimize the transmit power required for attaining a given outage probability based on the statistical channel information at the transmitter (SCIT). Using Gaussian approximation to express the probability density function (pdf) of the instantaneous mutual information and by deriving analytically the mean and variance of the mutual information of the MIMO channel, the optimal power allocation can be obtained numerically by a simple one-dimensional sampling method such as dividing rectange (DIRECT).
IEEE Transactions on Communications 05/2009; DOI:10.1109/TCOMM.2009.04.070139 · 1.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we aim to develop an energy-efficient multiuser time-division multiple-access (TDMA) system in block-fading (BF), subject to individual user's quality-of-service (QoS) requirements in terms of outage probability, by jointly-adaptive time-sharing and power allocation for the users in accordance with the causal channel side information (CSI) at the transmitter. We first propose a simple closed-form power allocation solution for a single-user BF channel to attain a given outage probability constraint with causal CSI. Then, we construct an optimization problem to permit a joint consideration of power consumptions and QoS requirements of the users, which we solve to obtain a near-optimal solution for users' time-sharing. The two solutions are combined to provide a suboptimal joint solution for adaptive time-sharing and power allocation of the system. Results reveal that the proposed scheme is near-optimal and a significant energy saving of more than 15 (dB) is possible between systems with and without adaptation on time-sharing and/or power allocation.
Global Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE; 01/2009
[Show abstract][Hide abstract] ABSTRACT: In this paper, our aim is to devise energy efficient strategies for single and multiuser multiple-input multiple-output (MIMO) antenna systems with individual users' effective capacity (EC) constraints. The use of EC provides a metric to quantify the maximum achievable rate under a certain delay constraint and in particular, we formulate the problem as a cross-layer resource allocation problem that connects the link-layer parameters such as delay and source rate with the physical-layer parameters such as fading statistics and power control. The object is to minimize the transmission energy of the MIMO systems while meeting the EC constraints, with the aid of the channel statistics. By deriving a closed-form expression for the EC of a single-user link MIMO system, we address multiuser MIMO systems in the downlink, in which dynamic time (or spectrum) sharing and multiuser power control are performed if time-division multiple-access (TDMA) (or frequency-division multiple-access (FDMA)) is used. We show that the optimal resource-allocation solution can be obtained by a dynamic programming (DP) approach and more importantly, low-complexity near-optimal heuristic solutions are proposed.
Proceedings of the 69th IEEE Vehicular Technology Conference, VTC Spring 2009, 26-29 April 2009, Hilton Diagonal Mar, Barcelona, Spain; 01/2009
[Show abstract][Hide abstract] ABSTRACT: In this letter, we consider a delay-constrained wireless communication system where a delay constraint is characterized by the information outage probability in a transmission of K-block Rayleigh flat-fading channels. With multiple users, each given an individual delay requirement, this letter aims to minimize the total transmitted power by optimizing jointly the power distribution and the time sharing of a time-division (TD) multiuser system where the transmitter knows only the channel statistics (CST) but the mobile receivers (or users) have perfect knowledge of the channels. A suboptimal solution which utilizes Gaussian approximation with the mean and variance derived on the instantaneous mutual information and convex optimization, is proposed. Numerical results show that the proposed scheme performs nearly the same as the global optimum.
[Show abstract][Hide abstract] ABSTRACT: This paper addresses a time-division multiple-access (TDMA) multiuser multiple-input multiple-output (MIMO) antenna system in if-block Rayleigh flat-fading. Assuming a downlink channel where users are given individual outage probability constraints and that the transmitter knows the statistical information about the channel, we aim to minimize the overall transmit power for achieving the users' probability constraints by jointly optimizing the users' power allocation and time-sharing (i.e., the number of time slots). The proposed scheme composes of a newly derived formula for power minimization of an individual user and solving a convex problem constructed for joint consideration of the power consumptions and the probability constraints. Results demonstrate that the proposed scheme performs nearly the same as the global optimum with inappreciable difference.
Information, Communications & Signal Processing, 2007 6th International Conference on; 01/2008