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A new cross-layer proportional fair scheduling algorithm suited for delay tolerant traffic in both saturated and non-saturated regimes is presented. Unlike the classical proportional fair scheduling algorithm where the instantaneous rate is normalized by the past average throughput, in the proposed algorithm the normalization is done with respect to the past maximal values. And unlike cumulative distribution function (CDF) based fair scheduling, the knowledge of the CDF of users' rates is not required in the proposed solution. In saturated regime, the proposed algorithm outperforms the classical ones. Moreover, in the non-saturated regime it even outperforms the multiuser diversity scheduling in term of spectral efficiency and classical fair schedulers in term of fairness.

In this work, we study fundamental limitation to the performance of time-delay estimation schemes of IR-UWB signals. We are specially interested in deriving lower bound on the mean square error (MSE). As UWB systems are expected to operate at low signal-to-noise ratio (SNR) (80211.15.4 low-power low rate standard), the improved Ziv-Zakai lower bound (IZZLB) [1] is then more suited to characterize the lower bound on the MSE, than the Cramer-Rao lower bound (CRLB). We express then the lower bound on MSE of maximum likelihood estimator based on perfect knowledge of the 2nd order statistics of the received signal by mean of the IZZLB.