Itsik Bergel

Narrowband interference suppression in time-hopping impulse-radio systems

Ultra-wideband (UWB) radio systems have drawn a lot of attention during the last few years. These systems use very low transmission power, spread over a bandwidth of several gigahertz. The very low transmission power and the large bandwidth used enable UWB radio systems to coexist with other narrowband systems over the same frequency band without interfering with the narrowband systems. Nevertheless, these narrowband systems may cause interference which jams the UWB receiver completely. Since standard narrowband interference suppression techniques are not applicable, techniques for interference suppression have to be developed. This paper presents novel narrowband interference suppression algorithms for UWB radio systems. Theoretical analysis of these algorithms reveal that they can eliminate the narrowband interference almost completely.

Narrowband interference mitigation in impulse radio

Impulse radio (IR) systems have drawn attention during the last few years. These systems are planned to coexist with narrowband systems without interfering them. Nevertheless, the narrowband systems can cause interference which may jam the IR receiver. This letter analyzes a low-complexity narrowband interference (NBI)-mitigation algorithm for IR systems, based on minimal mean-square error combining. Theoretical analysis reveals that these algorithms nearly eliminate the NBI. The concept is also extended to the case where the receiver has more correlators than channel taps.

Restoration of thermal images distorted by the atmosphere, based on measured and theoretical atmospheric modulation transfer function

Restoration of thermal images distorted by the atmosphere is presented. The method is based on atmospheric MTF analysis, both theoretical and experimental. Thermal IR atmospheric MTF measurements performed simultaneously in both atmospheric IR windows (3- to 5- and 8- to 12-μm wavelengths) are also presented. The MTFs were evaluated via point spread function measurements, under various meteorological conditions and different SNRs. Results are analyzed and shown to be in very good agreement with theoretical predictions.

The Ergodic Rate Density of ALOHA Wireless Ad-Hoc Networks

In recent years, much attention has been paid to the analysis of random wireless ad hoc networks (WANETs) that combine the effect of the physical layer and the medium access layer. However, most works have concentrated on an outage rate model which does not accurately describe the performance of modern communication systems. In this work we consider the ergodic rate density (ERD) of a random ALOHA WANET with a homogenous Poisson point process node distribution. We present two novel lower bounds on the ERD, one for general transmission and reception strategies and the other for receivers with a spatial interference cancellation capability. The bounds are simpler than previously published results for ALOHA WANETs (that have primarily considered the outage rate density). In addition, the bounds and the bounding technique are quite general and enable the derivation of closed form expressions of the ERD for various network models. The efficiency and simplicity of the bounds are demonstrated through several applications, and insights are drawn on the behavior of the network performance as function of the path-loss factor, transmission strategies and number of antennas. Simulation results demonstrate that these simple lower bounds predict the performance of ALOHA WANETs with high accuracy.

The Performance of Zero Forcing DSL Systems

DSL systems use multi-channel processing to mitigate the electromagnetic coupling between the wires in a binder and provide high data rates to multiple users. In recent years, most multichannel processing for DSL had focused on zero-forcing (ZF) processing that was proven to be near optimal. This near optimality has been observed in numerical evaluations as well as in real life systems. However, this near optimality has only been demonstrated theoretically by relatively loose bounds. In this paper we prove novel bounds on the performance of ZF processing in DSL systems. These bounds are simpler and yet tighter than currently known bounds. These novel bounds support previously published results, and further confirm the near optimality of ZF processing.

Linear Precoding Bounds for Wyner-Type Cellular Networks With Limited Base-Station Cooperation and Dynamic Clustering

This work studies the achievable average data rate in the downlink of a Wyner-type linear cellular network with limited cooperation and linear precoders. We derive upper and lower bounds on the achievable average data rate subject to an average power constraint. The bounds show that even a small number of cooperating base stations applying suboptimal (linear) precoding can approach optimal performance, and significantly increase the average user data rates as compared to those achievable with noncooperating cellular systems. We highlight the importance of dynamic clustering and of base station (BS) silencing. Dynamic clustering allows the system to build clusters that benefit some users at the expense of others, and then shifts the priority between the users. Such a scheme results in higher average rates for all users, while meeting some level of fairness. BS silencing is shown to be important for limited cooperation networks in the high SNR regime. Silencing is a simple and efficient way to reduce the interference (and hence increase the user rates) without increasing the number of cooperating BSs. The theoretical analysis is accompanied by several numerical examples in selected scenarios.

Convergence Analysis of Downstream VDSL Adaptive Multichannel Partial FEXT Cancellation

In this paper we analyze an adaptive downstream multichannel VDSL precoder that is based on error signal feedback. The analysis presents sufficient conditions for precoder convergence and an upper bound on the precoder steady state error. The paper also considers and analyzes the case of partial FEXT cancellation. The analysis shows that in some scenarios (and in particular in mixed-length binders) the use of partial FEXT cancellation is crucial to achieve precoder convergence in a reasonable time. Based on this analysis we determine that convergence is achievable in most practical channels. These bounds also allow for the proper setting of the convergence parameters. The paper presents several simulations to demonstrate the theoretical results. In these simulations, setting the precoder parameters according to the analysis leads to convergence in less than 400 OFDM symbols.

Unified Approach to Joint Power Allocation and Base Assignment in Nonorthogonal Networks

In this paper, we consider the joint power allocation and base station (BS) assignment in nonorthogonal downlink transmission code-division multiple-access (CDMA) communication systems. In addition to the popular sum-power criterion, we introduce three novel criteria that better take into account the network requirements and particularly the separate power limit of each of the BSs. In our model, we allow each user to be connected to more than one BS and show that such a scheme can improve the system capacity (while currently this mechanism is only used to support soft handoff). Nevertheless, we show that in any optimal solution, the actual number of connections used by each user is small. We propose a unified approach to optimization, which allows the use of linear programming (LP)-based iterative algorithms to solve all of the presented optimization problems. The proposed scheme is verified by simulations for several scenarios. The simulation results show that by taking into account the power constraints of each of the BSs, the system capacity can be increased by up to 33%. The results can also approximate the performance of orthogonal CDMA networks with precision that increases with system bandwidth.

Arbitrary Partial FEXT Cancellation in Adaptive Precoding for Multichannel Downstream VDSL

In this paper, we present and analyze a simplified, adaptive precoder for arbitrary partial far-end cross talk (FEXT) cancellation in the downstream of multichannel VDSL. The precoder is based on error signal feedback and is computationally efficient. Furthermore, the partial precoding makes it possible to operate the precoder at any desired complexity, and the systems performance increases with any increase in system complexity. Unlike previous works, in which each user experienced either complete FEXT cancellation or no cancellation at all, the presented precoder can mitigate the FEXT from any desired subset of interfering users for each user. We derive sufficient conditions for convergence of the adaptive precoder, for any partial cancellation scheme, and provide closed form steady state error analysis. The precoders performance and convergence properties are also demonstrated through simulations.

Upper Bound on the Ergodic Rate Density of ALOHA Wireless Ad-Hoc Networks

We present a novel upper bound on the Ergodic Rate Density (ERD) of ALOHA wireless ad-hoc networks. Our analysis uses a proper model of the physical layer together with an abstraction of higher communication layers. The novel bound is very general and supports various system models including for example, beamforming, spatial multiplexing, different fading models and different power control schemes. We also derive a closed form expression for the maximal gap between the novel bound and a known lower bound on the ERD. This maximal gap holds for any network that operates below the optimal density. This expression is simple to evaluate and only depends on the path loss factor. For example, for a path loss factor of α = 3 the novel upper bound is proved to be at most 31% higher than the lower bound (and hence also from the actual ERD). The usefulness and the generality of the novel bound is demonstrated by applications in multiple-antenna schemes. In particular, we study the optimization of the number of transmitted spatial streams in a MIMO network and derive the scaling of the ERD as the number of antennas grows. The results are further demonstrated using extensive simulations.