Multiuser margin optimization in digital subscriber line (DSL) channels

Abstract

Abstract-This paper presents efficient multiuser margin optimization algorithms suitable for multicarrier digital subscriber line (DSL) systems using Dynamic Spectrum Management (DSM). The favorable monotonicity and fairness properties of multiuser margin are employed to formulate a box-constrained nonlinear least squares (NLSQ) problem for multiuser margin maximization, which is efficiently solved by using a scaled-gradient trust-region approach with Broyden Jacobian update. Based on this NLSQ formulation, a multiuser harmonized margin (MHM) optimization algorithm for resource allocation is developed. A Newton-Raphson method is also developed for fast margin estimation and used within the MHM. The MHM algorithm converges efficiently to a solution for the best common equal margin to all users, while explicitly guaranteeing their target rate requirements. (This is the reason for the term harmonized.) Furthermore, its predominantly distributed structure can be implemented in DSL/DSM scenarios with only Level 1 coordination. Simulation results of various cases verify the convergence to the unique optimal solution within 5-10 iterations.Index Terms-Broyden update, digital subscriber line (DSL), dynamic spectrum management (DSM), iterated water-filling, loading algorithms, margin adaptive, trust region methods.

An hybrid evolutionary multiobjective algorithm for multiuser margin maximization in DSL

“…A comparison is made against a baseline algorithm called Newton-Raphson margin estimation (NRME), published in [5]. A comparison is made against a baseline algorithm called Newton-Raphson margin estimation (NRME), published in [5].…”

“…However, because DSL transceivers are restricted with respect to the transmitted power, bit rate and noise margin become conflicting requirements [5]. It works as a safety margin applied to the transmit signal, which is translated into longer distances between constellation points for improved robustness.…”

“…It works as a safety margin applied to the transmit signal, which is translated into longer distances between constellation points for improved robustness. However, because DSL transceivers are restricted with respect to the transmitted power, bit rate and noise margin become conflicting requirements [5]. This tradeoff suggests that bit allocation and noise margin parameters should be jointly optimized.…”

“…This tradeoff suggests that bit allocation and noise margin parameters should be jointly optimized. There are techniques such as the Automatic Margin Adaptation (AMA) that dynamically increases the noise margin when many errored frames or some other instability indicator is detected at the receiver [5]. Nevertheless, AMA never brings down the noise margin again and suffers from the problem known as 'stuck-at low rate' [6], which can occur for example when the modem initializes with line conditions near to its worst-case noise scenario and then EVOLUTIONARY ALGORITHM FOR MULTIUSER MARGIN MAXIMIZATION IN DSL 195 continues to use an excessively and unnecessary high target margin even when the line conditions improve significantly.…”

A new mathematical analysis of the cyclic prefix effect on removing ISI and ICI in DMT systems

“…If the length of the CP is equal or longer than the length of the channel impulse response minus one, then the demodulation can be implemented by means of an FFT, followed by a (complex) 1-tap frequency domain per tone equalizer (FEQ) to compensate for the channel magnitude and phase effects [5], [6]. A long CP, however, results in a large overhead with respect to the data rate [6]. The DMT block diagram is shown in Fig.…”