Robustness maximization of parallel multichannel systems
Résumé
Bit error rate (BER) minimization and SNR-gap maximization, two robustness optimization problems, are solved, under average power and bit-rate constraints, according to the waterfilling policy. Under peak-power constraint the solutions differ and this paper gives bit-loading solutions of both robustness optimization problems over independent parallel channels. The study is based on analytical approach, using generalized Lagrangian relaxation tool, and on greedy-type algorithm approach. Tight BER expressions are used for square and rectangular quadrature amplitude modulations. Integer bit solution of analytical continuous bit-rates is performed with a new generalized secant method. The asymptotic convergence of both robustness optimizations is proved for both analytical and algorithmic approaches. We also link the SNR-gap maximization problem to the conventional power minimization problem and prove that the duality does not holds in all cases. Based on a defined dissimilarity measure, bit-loading solutions are compared over Rayleigh fading channel for multicarrier systems. Simulation results confirm the asymptotic convergence of both resource allocation policies. In non asymptotic regime the resource allocation policies can be interchanged depending on the robustness measure and the operating point of the communication system. The low computational effort of the new resource allocation algorithm based on the analytical approach leads to a good trade-off between performance and complexity.
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