Browsing by Author "Chang, Min-Yao"

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Joint MMSE Transceiver Design in Amplify-and-Forward MIMO Relay Systems with Tomlinson-Harashima Source Precoding
(2010)
Tseng, Fan-Shuo
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Chang, Min-Yao
;
Wu, Wen-Rong
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傳播研究所
;
Institute of Communication Studies
Existing precoding schemes in amplify-and-forward (AF) multiple-input-multiple-output (MIMO) relay systems use linear precoders. In this paper, we consider a precoding scheme in which a Tomlinson-Harashima (TH) precoder (THP) is used at the source and a linear precoder at the relay. With a minimummean- squared-error (MMSE) receiver at destination, we propose a new joint precoders design method. Since two precoders are involved, the transceiver design, formulated as an optimization problem, is difficult to solve. To overcome the problem, we propose cascading an additional unitary precoder with the TH precoder. The unitary precoder can not only simplify the optimization problem but also improve the MMSE performance. With the specially designed unitary precoder at the source, we can then adopt the primal decomposition method to solve this problem. With the method, the original optimization problem can first be decomposed into a master and a subproblem optimization problems, and then transferred to a relay precoder optimization problem. However, the optimization is not a convex problem and the solution is not obtainable. We then propose a method being able to transfer it to a convex optimization problem. A closedform solution can then be obtained by the Karuch-Kuhn-Tucker (KKT) conditions. Simulations show that the proposed transceiver can significantly outperform existing linear transceivers.
Joint Tomlinson-Harashima Source and Linear Relay Precoder Design in Amplify-and-Forward MIMO Relay Systems via MMSE Criterion
(2011-05-01)
Tseng, Fan-Shuo
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Chang, Min-Yao
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Wu, Wen-Rong
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電機工程學系
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Department of Electrical and Computer Engineering
Existing minimum-mean-square-error (MMSE) transceiver designs in amplify-and-forward (AF) multiple-input-multiple-output (MIMO) relay systems all assume a linear precoder at the source. Nonlinear precoders in such a system have yet to be considered. In this paper, we study a nonlinear transceiver in AF MIMO relay systems in which a Tomlinson-Harashima (TH) precoder is used at the source, a linear precoder is used at the relay, and an MMSE receiver is used at the destination. Since two precoders and three links are involved, the transceiver design, which is formulated as an optimization problem, is difficult to solve. We first propose an iterative method to overcome the problem. In the method, the two precoders are separately optimized in an iterative step. To further improve the performance, we then propose a non-iterative method that can yield closed-form solutions for the precoders. This method uses the primal decomposition technique in which the original optimization can first be decomposed into a master and a subproblem optimization. In the subproblem, the optimum source precoder is solved as a function of the relay precoder. In the master problem, the optimization is then transferred to a relay-precoder-only problem. However, the optimization is not convex, and the primal decomposition cannot be directly applied. We then propose cascading a unitary precoder after the TH precoder so that the optimization in the subproblem and the master problem can be conducted. Furthermore, using a relay precoder structure, we can transfer the master problem to a convex optimization problem and obtain a closed-form solution by the Karuch-Kuhn-Tucker (KKT) conditions. Simulations show that the proposed transceivers can significantly outperform existing linear transceivers.
Robust Tomlinson-Harashima Source and Linear Relay Precoders Design in Amplify-and-Forward MIMO Relay Systems
(2012-04-01)
Tseng, Fan-Shuo
;
Chang, Min-Yao
;
Wu, Wen-Rong
;
傳播研究所
;
Institute of Communication Studies
Existing transceiver designs in amplify-and-forward (AF) multiple-input-multiple-output (MIMO) relay systems often assume the availability of perfect channel state informations (CSIs). Robust designs for imperfect CSI have less been considered. In this paper, we propose a robust nonlinear transceiver design for the system with a Tomlinson-Harashima precoder (THP), a linear relay precoder, and a minimum-mean-squared-error (MMSE) receiver. Since two precoders and imperfect CSIs are involved, the robust transceiver design is difficult. To overcome the difficulty, we first propose cascading an additional unitary precoder after the THP. The unitary precoder can not only simplify the optimization but also improve the performance of the MMSE receiver. We then adopt the primal decomposition dividing the original optimization problem into a subproblem and a master problem. With our formulation, the subproblem can be solved and the two-precoder problem can be transferred to a single relay precoder problem. The master problem, however, is not solvable. We then propose a lower bound for the objective function and transfer the master problem into a convex optimization problem. A closed-form solution can then be obtained by the Karush-Kuhn-Tucker (KKT) conditions. Simulations show that the proposed transceiver can significantly outperform existing linear transceivers with perfect or imperfect CSIs.