Jaouhar Ayadi

Analysis of MIMO capacity gains for indoor propagation channels with LOS component

We analyse typical indoor propagation scenarios with respect to the capacity gain made available through the use of multiple transmit and receive antennas. In particular, we investigate propagation channels with a strong line of sight component, as evident when the transmit array is in the same room as the receive array. It is found that the capacity gain for the pure LOS component depends highly on the array geometry and the receiver location, such that the capacity gain vanishes rapidly with receiver distance. We show that the existence of stochastic scattering components is beneficial to obtain the maximum capacity gain, thus reducing the dependence on the array geometry and the receiver location. This benefit exists even for a strong LOS component. Quantitative results are provided for wireless LAN systems operating at carrier frequencies around 5 GHz.

On the multiple input multiple output capacity of Rician channels

We consider a wireless system with multiple antennas at both the transmitter and the receiver and operating in a Rician propagation environment. For fixed bandwidth and total transmitted power, the Rician channel matrix can be seen as the sum of two contributions. The first contribution is related to the deterministic component of the channel, which is given by the line-of-sight (LOS) path only. The second contribution denotes the stochastic component of the channel given by the Rayleigh fading paths, in which case the corresponding elements in the channel matrix are modeled as random variables. We focus on the averaged Rician channel capacity expression and its behavior according to the contribution of the deterministic and stochastic part of the channel. We derive an upper bound on the averaged Rician channel capacity and we show that a limit of this capacity is given by the sum of the capacities corresponding to the LOS and Rayleigh components when they are considered separately. Simulations results are given to support our claims.

UWB Transmission and MIMO Antenna Systems for Nomadic Users and Mobile PANs

Personal Area Networks (PANs) are expected to play an important role in future mobile communications and information systems. A proliferation of low data rate sensor and control devices is envisioned. These devices must be able to communicate across various networks in order to provide seamless end-to-end service. At the physical and link level, several factors are critical in order to realize a nomadic PAN: co-existence with other systems, efficient use of increasingly scarce spectrum resources and capacity, robustness in the presence of interference, as well as, the availability of low cost individual user devices. In this paper, we examine a concept for nomadic PANs employing low cost, low data rate ultra wideband (UWB) communication links between personal devices and a handset, or mobile bridge, coupled with a multiple input multiple output (MIMO) antennas for communication from a mobile bridge to other networks. Key issues are identified and potential capacity and quality-of-service (QoS) enhancements are evaluated.

Impulse radio ultra-wideband ranging based on maximum likelihood estimation

We propose a high-resolution ranging algorithm for impulse radio (IR) ultra-WideBand (UWB) communication systems in additive white Gaussian noise. We formulate the ranging problem as a maximum- likelihood (ML) estimation problem for the channel delays and amplitudes at the receiver. Then we translate the obtained delay estimates into an estimate of the distance. The ML estimation problem is a non-linear problem and is hard to solve. Some previous works focus on finding alternative estimation procedures, for example by denoising. In contrast, we tackle the ML estimation problem directly. First, we use the same transformation as the first step of Iterative quadratic maximum likelihood (IQML) and we transform the ML problem into another optimization problem that avoids the estimation of the amplitude coefficients. Second, we solve the remaining optimization problem with a gradient descent approach (pseudo-quadratic maximum likelihood (PQML) algorithm). To demonstrate the good performance of the proposed estimator, we present the numerical evaluations under the IEEE 802.15.4a channel model. We show that our algorithm performs significantly better than previously published heuristics. We also derive a reduced complexity version of the algorithm algorithm, which will be implemented on the Xinlix field-programmable gate array (FPGA) board in the future. We test the approach in a real weak line of sight (LOS) propagation environment and obtained good accuracy for the ranging.

A wideband equivalent SPICE circuit for a monopole antenna and its usefulness for UWB applications

This paper presents a transmission line based electrical equivalent schematic of a ¿/4 monopole antenna for co-simulation with electrical circuits in simulators like ELDO and SPICE. The antenna model is derived from TDR (time domain) measurements and yields fast and accurate results for the antenna impedance from DC up to 3 times the 1st resonant frequency f0.

Theoretical Limit of Impulse Radio Ultra-WideBand TOA Positioning and TDOA Positioning

In this paper, we derive the Ziv-Zakai lower bounds for Impulse Radio (IR) Ultra-WideBand (UWB) Time Of Arrival (TOA)-based positioning and Time Difference Of Arrival (TDOA)-based positioning error based on geometry of indoor environments. We present the numerical evaluations with IEEE 802.15.4a channel model and the geometry of indoor environments of interest. As our derived bounds depend on the geometry of the indoor environments, our bounds can also be used in real environments with the channel measurements from real environments.

Statistical analysis of Impulse Radio Ultra-Wideband multi-user interference based on measurments

Multiuser interference (MUI) statistical models for impulse radio ultra-wideband (IR-UWB) systems can be an important in providing an accurate estimate of the channel state. As such, it can have a major impact on the overall system performance. In the literature, MUI in the time domain is often approximated with Middleton class A and Gaussian mixture models. We use measurements from an IR-UWB testbed under office Line of Sight (LOS) environments to assess the validity of these models. We also analysis the statistical properties of MUI in the frequency domain. We expect these findings to form the basis for useful interference models.

On the use of UMTS for air-ground links

We consider a possible use of the universal mobile telecommunications system (UMTS) air interface to meet the requirements for air-ground (AG) links. Due to the available set of frequency bands, the physical layer of the UMTS standard must be revised in order to operate at the AG link carrier frequencies. We focus on the propagation considerations of the transmitted signals and the performance of the AG-UMTS system. We also discuss some related issues, such as frequency selective fading, fast fading aspects that can occur in the transmission channel and influence of these on the AG-UMTS system performance.