A heuristic approach for packing identical rectangles in convex regions

In this paper we propose a heuristic approach for the problem of packing equal rectangles within a convex region. The approach is based on an Iterated Local Search scheme, in which the key step is the perturbation move. Different perturbation moves, both combinatorial and continuous ones, are proposed and compared through extensive computational experiments on a set of test instances. The overall results are quite encouraging.     

Low Complexity Rake Receivers in Ultra-Wideband Channels

One of the major issues for the design of ultra-wideband (UWB) receivers is the need to recover the signal energy dispersed over many multipath components, while keeping the receiver complexity low. To this aim we consider two schemes for reduced-complexity UWB Rake receivers, both of which combine a subset of the available resolved multipath components. The first method, called partial Rake (PRake), combines theirs/ arriving multipath components. The second is known as selective Rake (SRake) and combines the instantaneously strongest multipath components. We evaluate and compare the link performance of these Rake receivers in different UWB channels, whose models are based on extensive propagation measurements. We quantify the effect of the channel characteristics on the receiver performance, analyzing in particular the influence of small-scale fading statistics. We find that for dense channels the performance of the simpler PRake receiver is almost as good as that of the SRake receiver, even for a small number of fingers. In sparse channels, however, the SRake outperforms the PRake significantly. We also show that for a fixed transmitted energy there is an optimum transmission bandwidth     

Measurements of the performance degradation of UMTS receivers due to UWB emissions

Results of experimental trials performed to assess the coexistence of the UMTS systems and the UWB emissions are presented. The performance degradation of the UMTS system vs. the in-channel UWB interference power has been measured in terms of the bit error rate and the noise rise.     

Analysis of UWB system capacity in a realistic multipath environment with coexistence constraints

Ultra-wideband (UWB) wireless technology is envisaged to play a key role in B3G wireless systems, guaranteeing very high bit rates, low power consumption, low costs and location capabilities. The availability of low cost and efficient devices makes UWB technology very competitive on the communications market. However, its worldwide acceptance mainly relies on coexistence issues because of the necessity of sharing the spectrum with other radio systems. The reduction, due to coexistence constraints, in the capacity of an UWB system in a realistic multipath channel is investigated. Link performance of an UWB system that exploits either partial or selective Rake combining at the receiver is evaluated over experimental impulse responses of an UWB indoor channel in an office building. Using these results, system performances are evaluated through a semi-analytical procedure in terms of outage probability and system capacity. Results on system capacity account for the limitations imposed by the current regulation, leading us to introduce the concept of `UWB systems limited by coexistence'     

The ultra-wide bandwidth indoor channel: from statistical model to simulations

We establish a statistical model for the ultra-wide bandwidth (UWB) indoor channel based on an extensive measurement campaign in a typical modern office building with 2-ns delay resolution. The approach is based on the investigation of the statistical properties of the multipath profiles measured in different rooms over a finely spaced measurement grid. The analysis leads to the formulation of a stochastic tapped-delay-line (STDL) model of the UWB indoor channel. The averaged power delay profile can be well-modeled by a single exponential decay with a statistically distributed decay constant. The small-scale statistics of path energy gains follow Gamma distributions whose parameters m are truncated Gaussian variables with mean values and standard deviations decreasing with delay. The total received energy experiences a lognormal shadowing around the mean energy given by the path-loss power law. We also find that the correlation between multipath components is negligible. Finally, we propose an implementation of the STDL model and give a comparison between the experimental data and the simulation results.