Development of path loss model for 802.11n in large conference rooms

In this paper, a path loss (PL) model for 802.11n in large conference rooms is determined, based on PL measurements. The PL can be described accurately by a one-slope model with one standard deviation. PL exponents varying from 1.2 to 1.7 are found. Based on this PL model, the effect of frequency (2.4 vs 5 GHz), configuration (SISO vs MIMO (spatial diversity)), bandwidth (20 vs 40 MHz) and transmit power on number of access points, total power consumption and possible (physical) throughputs is investigated. According to the determined PL model, a higher range (by tuning the transmit power) requires less access points, as well as a lower total power consumption, due to a PL exponent lower than 2

Performance degradation due to multipath noise for narrowband OFDM systems: channel-based analysis and experimental determination

The performance of OFDM systems over a multipath channel can strongly degrade due to the propagation delay spread. The distortion of the received signal over the fast Fourier transform window is referred to as multipath noise. This work aims to analytically determine the performance loss due to multipath noise as a function of OFDM and channel parameters for narrowband OFDM systems. First, it is investigated whether it is possible to describe the multipath noise, varying over different OFDM packets due to the temporal variation of the channel, by an effective noise factor F-delay, from which the loss factor is directly determined. Second, the theory of room electromagnetics is applied to develop a closed-form expression for F-delay as a function of the OFDM and reverberation parameters. This analytical method is validated with excellent agreement. Finally, the loss factor is determined for IEEE 802.11 based on channel measurements in two large conference rooms, providing values up to 19 dB for an 800 ns cyclic prefix length

Analysis of 802.11 OFDM in high multipath environments

The performance loss of 802.11 OFDM systems due to propagation delay spread has been analyzed as a function of OFDM parameters for a wide range of reverberation times. This analysis gives physical insight and solutions for the OFDM design to suppress the performance degradation

A numerical semiconductor model applicable to organic solar cells

Excitons are marginally important in classical semiconductor device physics, and their treatment is not included in standard solar cell modelling. However, in organic semiconductors and solar cells, the role of excitons is essential, as the primary effect of light absorption is exciton generation, and free electrons and holes are created by exciton dissociation. First steps to include excitons in solar cell modelling were presented by Green and Zhang. We extended their model (2006), including the space charge region, exciton surface dissociation, recombination at the contacts, and non-uniform bulk dissociation. This model showed that it IS possible to apply the standard semiconductor device modelling frame to situations were excitons are dominant, but the model was not general, and did not cover parameters relevant for organic solar cells. We now extended the numerical semiconductor model to more general situations (e.g., it is now not any more limited to a one sided n+p junction), and made it suitable for the application on organic solar cells (e.g. lower diffusion lengths). Organic solar cell behaviour is calculated as a function of the ratio of generated excitons to free eh-pairs, of the exciton dissociation mechanisms and of the diffusion length. Our numerical simulations show that a cell can work decently when there is enough exciton dissociation (wherever this be in the cell) and when both the electron and the exciton diffusion lengths exceed the “unit cell” thickness

Performance loss due to multipath propagation for IEEE 802.11 systems

In this work, we developed an analytical estimation of the performance loss due to multipath propagation for a narrowband OFDM system. The propagation characteristics required for this loss estimation, are experimentally determined by virtual SIMO measurements in a large conference room where repeated reception problems were reported for an IEEE 802.11 system, as well as in 2 other large conference rooms for comparison. The resulting losses due to multipath are calculated for IEEE 802.11a/n and related to the propagation characteristics

A numerical semiconductor model applicable to organic solar cells

status: publishe