There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

Information Theory and Reliable Communication

: This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)

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Nonlinear Time Series Analysis.

This document provides updates to IEEE Std 802.16's MIB for the MAC, PHY and asso- ciated management procedures in order to accommodate recent extensions to the standard.

IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems Draft Amendment: Management Information Base Extensions

This paper investigates the use of bi-orthogonal modulations in multiuser communication systems based on ultra wide band impulse radio (UWB-IR) technology: the communication systems considered herein use Gaussian waveforms in AWGN channel and rely on the utilization of a time-hopping spreading technique. A hybrid pulse modulation is defined, which is obtained by combining pulse amplitude modulation (PAM) and pulse position modulation (PPM) techniques. Particularly, we have compared the bi-orthogonal system performance to the classical orthogonal one, also in the condition of lack of a general synchronism, possibly caused by the presence of interfering users that belong to a separate network. Moreover, we have taken into account the use of an M-ary alphabet, in the case of orthogonal and bi-orthogonal modulation schemes.

Performance of the bi-orthogonal modulation for ultra-wideband communication systems with multiple access interference

In this paper, a medium access control (MAC) technique for wireless systems that efficiently manages adaptive modulation and coding (AMC) schemes is presented with the aim of improving the downstream data rate, together with preserving quality of service (QoS) requirements. Basically, the proposed access scheme relies on physical channel monitoring and state mapping into a variable rate packet format. A suitable analytical model is proposed herein in order to predict the system performance, i.e., the average packet queuing delay or, equivalently, the average queue length. In particular, the non-stationary transmission channel is modeled as a Markov chain and each state is associated with a particular modulation and coding scheme (MCS) for a specified data rate. Comparisons between analytical predictions and simulation results are provided to validate our model and to highlight the improvement of the proposed technique with respect to a static rate allocation scheme, especially in the presence of heavy tailed traffic conditions, like those arising in remote file transfer typical of a Web connection.

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A dynamic rate allocation technique for wireless communication systems

In this paper, an innovative admission control (AC) policy for CDMA wireless networks, based on minimizing the multiple-access-interference (MAI), is introduced. According to our proposal, an incoming connection is accepted whenever the QoS constraints, for all communications, are respected, that is, the signal-to-interference-plus-noise-ratio (SINR) is kept under control. This parameter mainly depends on traffic load variations. Thus, the MAI arising from a new connection must be considered. This problem can be proactively faced by characterizing MAI and correctly estimating its value. Furthermore, two approaches are presented, named, respectively, static soft AC and dynamic soft AC; the latter involving a dynamic power management. Analytical models describing the first approach are investigated and validated by means of simulations performed on a typical uplink UMTS environment. Moreover, a remarkable gain of the second approach, in terms of dropping probability, is highlighted without, thus rendering our approach a proper candidate for variable network traffic management.

An efficient soft admission control technique for wireless communications

This paper presents a novel energy-aware communication scheme based on random network coding that is suitable for multicast and broadcast data delivery over Long Term Evolution (LTE) and LTE-Advanced networks. The proposed energy-aware transmission scheme minimises the average energy consumption of the macro base station that is required to deliver a message to all users in a multicast group in an LTE-A network. The energy saving gains and improved performance of the proposed scheme are compared to classical error control strategies. The reported analytical results clearly show a performance improvement of almost two-fold compared to the considered alternative.

Reliable multicast in LTE-A: An energy efficient cross-layer application of network coding

In this work, a combined amplitude-phase modulation communication system is considered. Amplitude modulation is used to transmit a voice signal, and phase modulation is used for data transmission. Such a scheme was studied as a possible realization of a data channel between aircraft and ground station, which can be introduced without great modifications of the actual on-board equipment. The performance of the combined modulation system is evaluated through a computer simulation.

Romano Fantacci

Papers

Performance of the bi-orthogonal modulation for ultra-wideband communication systems with multiple access interference

A dynamic rate allocation technique for wireless communication systems

An efficient soft admission control technique for wireless communications

Reliable multicast in LTE-A: An energy efficient cross-layer application of network coding

An Integrated Voice-Data Communication System for VHF Links