Glafkos Stratis

Pulse spectrum optimization for ultra-wideband communication

Ultra-wideband (UWB) communications employ very short pulses with different modulation that result in extremely wideband spectra for high data-rate links. These spectra are a function of both the spreading operation as well as the pulse shapes. We propose a pulse spectrum optimization technique based on classical filters. Non-ideal impulse characteristics are then considered and the optimum pulse derived for either minimal energy (highest spectral bandwidth). The motivation is to show that filtered pulses can achieve significant spectral control in direct baseband UWB signals for high data-rate communications.

Numerical calculation of diffraction coefficients of generic conducting and dielectric wedges using FDTD

Classical theories such as the uniform geometrical theory of diffraction (UTD) utilize analytical expressions for diffraction coefficient for canonical problems such as the infinite perfectly conducting wedge. We present a numerical approach to this problem using the finite-difference time-domain (FDTD) method. We present results for the diffraction coefficient of the two-dimensional (2-D) infinite perfect electrical conductor (PEC) wedge, the 2-D infinite lossless dielectric wedge, and the 2-D infinite lossy dielectric wedge for incident TM and TE polarization and a 90/spl deg/ wedge angle. We compare our FDTD results in the far-field region for the infinite PEC wedge to the well-known analytical solutions obtained using the UTD. There is very good agreement between the FDTD and UTD results. The power of this approach using FDTD goes well beyond the simple problems dealt with in this paper. It can, in principle, be extended to calculate the diffraction coefficients for a variety of shape and material discontinuities, even in three dimensions.

On the suitability of 802.11a/RA for high-mobility DSRC

The 802.11a standard has been considered and applied to DSRC (dedicated short-range communication) in the 5.9 GHz band. Among the parameters of the DSRC are support for data transfers during high-mobility applications. Given that the 802.11a standard was designed for relatively low speed (3 MPH) wireless LAN applications, it is necessary to analyze the suitability of the standard in outdoor high-speed mobility applications. We present an analysis of the error rate of 802.11a in high-speed mobile applications. It is shown that 802.11a/RA communication exhibits high packet error rates and consequently lower channel capacity. An example is submitted and discussed.

Pseudo-pilot OFDM scheme for 802.11a and R/A in DSRC applications

A pseudo-pilot scheme is proposed for 802.11a and 802.11R/A (roadside applications version) in DSRC (dedicated short range communication) applications. The scheme overcomes the shortcomings of the original IEEE 802.11a standard by substituting pilots in selected data slots for channel equalization; at the receiver, the pilots are removed and random data inserted. It is shown that the technique is very effective in addressing the high mobility DSRC environment with minor changes to the 802.11a and R/A physical layer.

Composite antenna pattern for realistic ray tracing simulations

The widespread adoption of wireless local area networks (WLAN) and the emerging wireless personal area networks (WPAN) has required a deeper understanding of the indoor propagation channel. As a consequence, ray analysis techniques based on geometrical optics have emerged as the tools of choice for modeling indoor and outdoor environments. In realistic scenarios, antennas will be installed within proximity to wall structures or embedded in complex environments such as vehicle interiors for telematics applications. Hence. we no longer have free space antenna patterns but composite antenna patterns. We consider here the application of the finite-difference time-domain (FDTD) technique for obtaining 3D antenna patterns in complex structures with different material properties. Simulation results are submitted and discussed.