Abstract
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.
Highlights
Discrete multitone (DMT) is a modulation technique that has been widely used in various digital subscriber lines, 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]
Researchers afterwards take into account more constraints including the transmission power spectral density (PSD) mask and the maximum allowable size of the QAM constellations [12, 13], and a common feature of these algorithms is that they all use greedy bit-loading, either during the whole allocation process or after the initial allocation
The algorithm calculates two bit allocations, that is, loop-representative bit allocation and maximum bit rate allocation, to obtain the initial bit distribution, and it performs multiple-bits loading for achieving the target rate
Summary
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] It is proposed for broadband downstream power-line communications due to its high flexibility in resources management [3]. The algorithm calculates two bit allocations, that is, loop-representative bit allocation and maximum bit rate allocation, to obtain the initial bit distribution, and it performs multiple-bits loading for achieving the target rate. When close to the target rate, a parallel bitloading procedure is used to achieve the target rate This parallel bit-loading step is computationally more efficient than the conventional greedy bit-loading algorithm.
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