A Heuristic Optimal Discrete Bit Allocation Algorithm for Margin Maximization in DMT Systems
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Research Article A Heuristic Optimal Discrete Bit Allocation Algorithm for Margin Maximization in DMT Systems Li-Ping Zhu,1 Yan Yao,1 Shi-Dong Zhou,1 and Shi-Wei Dong2 1 Department 2 National
of Electronic Engineering, School of Information Science and Technology, Tsinghua University, Beijing 100084, China Key Laboratory of Space Microwave Technology, Xi’an Institute of Space Radio Technology, Xi’an 710100, China
Received 14 July 2006; Revised 24 December 2006; Accepted 25 December 2006 Recommended by Erchin Serpedin A heuristic optimal discrete bit allocation algorithm is proposed for solving the margin maximization problem in discrete multitone (DMT) systems. Starting from an initial equal power assignment bit distribution, the proposed algorithm employs a multistaged bit rate allocation scheme to meet the target rate. If the total bit rate is far from the target rate, a multiple-bits loading procedure is used to obtain a bit allocation close to the target rate. When close to the target rate, a parallel bit-loading procedure is used to achieve the target rate and this is computationally more efficient than conventional greedy bit-loading algorithm. Finally, the target bit rate distribution is checked, if it is efficient, then it is also the optimal solution; else, optimal bit distribution can be obtained only by few bit swaps. Simulation results using the standard asymmetric digital subscriber line (ADSL) test loops show that the proposed algorithm is efficient for practical DMT transmissions. Copyright © 2007 Li-Ping Zhu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Discrete multitone (DMT) is a modulation technique that has been widely used in various digital subscriber lines (xDSL), such as asymmetric digital subscriber line (ADSL) and very-high-speed digital subscriber line (VDSL), permitting reliable high rate data transmission over hostile frequency-selective channels [1, 2]. Recently, it is proposed for broadband downstream power-line communications due to its high flexibility in resources management [3]. A crucial aspect in the design of a DMT system is to allocate bits and power to the subchannels in an optimal way under various constraints. One of the problems that are of practical interest is margin maximization or transmission power minimization, also known as margin adaptive (MA) [4]. Many optimal or suboptimal discrete bit-loading algorithms are proposed for solving the problem. Among the algorithms in which the constraint of a target bit rate is considered, the computational complexity of the Hughes-Hartogs algorithm [5] and Chow’s algorithm [6] is relatively high. There are also a lot of computationally efficient algorithms, including the algorithms proposed by Piazzo [7, 8], the algorithm of Krongold et al. [9], and the Levin-Campello (LC) algorithms [4, 10, 11]. Researchers afterwards take into account more co
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