Gregg Rasor

Model of multi-band OFDM interference on broadband QPSK receivers

A model for multi-band orthogonal frequency division multiplex (MB-OFDM) interference on in-band broadband uncoded QPSK receivers is provided. Multi-band OFDM results in periodic gated noise with power scaled to equal the total power of AWGN over the entire hop time. Since MB-OFDM can have high peak-to-average power (PAP), its impulsive characteristics are captured by the model as a function of the hop depth. Based on the proposed model, it is shown that MB-OFDM is a more harmful interference than ungated AWGN for the same effective isotropic radiated power (EIRP).

Ultra-wideband outdoor channel modeling using ray tracing techniques

An ultra-wideband (UWB) channel modeling approach using ray tracing techniques is presented. The scenario consists of a farm area with clusters of scatterers over moderately varying terrain. The channel sounding consists of power-scaled distinct frequencies whereby all relevant ray signal descriptors are captured. From this we develop a two-ray and three-ray path loss model with associated parameters. The technique is suitable for UWB channel characterisation using narrowband channel sounding in outdoor environments with small number of scatterers over moderately varying terrain.

A weighted multiple-frequency method for ultra-wideband outdoor coverage prediction

Ultra-wideband (UWB) outdoor coverage prediction using ray tracing techniques is presented. The scenario consists of a farm area with clusters of scatterers over moderately varying terrain. A multiple frequency step approach, with weighted power levels is developed and shown to he useful in coverage and reliability prediction equivalent to a two-ray path loss model. Based on the simulation results, it is shown that UWB provides up. to 100 m range under different environmental conditions. The technique presented here can be generalized to UWB channel sounding using frequency scanning.

Peak-to-average power ratio (PAPR), fractional bandwidth and processing gain of UWB schemes

This paper addresses the peak-to-average power ratio (PAPR), fractional bandwidth and processing gain of ultra-wideband (UWB) signals. First, the PAPR of UWB signals are derived and the numerical examples demonstrating PAPR values with Gaussian monocycle pulse shaping are presented. We then examine the FCC order authorizing the use of UWB signals and demonstrate that the FCC order presents a broader definition of UWB signals as compared to the original DARPA definition. Finally, we determine the processing gain for FCC compatible UWB signals subject to various data rates.

In-band interference of multi-band OFDM systems

The impact of time-frequency hopped multi-band orthogonal frequency division multiplexing (MB-OFDM) on in-band wideband receivers is considered. First, we compare direct-sequence and frequency-hopped ultra-wideband (UWB) systems in terms of power and range characteristics. We then show that in-band receivers with large bandwidths are susceptible to UWB systems, but direct sequence systems are potentially less harmful due to the large relative bandwidth. The MB-OFDM signal introduces less interference for long hop lengths, but the signal peak-to-average power rises. This makes the MB-OFDM signal appear impulsive to a victim receiver, causing destructive interference at high signal-to-noise ratios.

Constructing spectral gaps in OFDM for interference mitigation

The construction of spectral gaps via tone nulling in OFDM signaling for interference mitigation is investigated. Design formulas for the nominal gap bandwidth and gap depth are derived and shown to be in good agreement with simulation results. It is shown that the resulting gap spectrum is U-shaped with a maximum rejection depth approaching 20 dB even under ideal tone nulling; selectivity and bandwidth control are poor. In addition, to increase the rejection depth by even a modest amount, a significant number of tones must be nulled. When considering demanding spectral gap requirements, tone nulling requires significant margins and is of limited effectiveness in replacing conventional filtering for interference mitigation. I. INTRODUCTION

Improved Performance OFDM Exploiting Polarization

A new OFDM modulation technique exploiting polarization is presented. The proposed Alternating Dual Polar- ization Stages OFDM (APDS-OFDM) is comparable to conven- tional OFDM in terms of computational complexity. The main drawback of APDS-OFDM is the need for dual signal paths to implement the polarization. However, this OFDM technique offers the following improvements: Peak-to-average power is 3 dB lower per channel, less expensive frequency sources can be used, and the modulation is far less sensitive to inter-carrier interference (ICI) caused by Doppler. I. INTRODUCTION