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

With the convergence of mobile and fixed communication networks, mobile users are increasingly demanding applications offering the same quality of service (QoS) as provided by wired access. High-speed time division duplex access mode is typical of high-speed mobile communication systems in order to simultaneously handle real-time, interactive, and best effort traffic classes. This paper proposes a medium access control (MAC) protocol that makes efficient use of radio resources for access. The proposed protocol, named dynamic-time division duplexing (D-TDD), is based on a multiple-access TDD air interface capable of supporting uplink and downlink traffic asymmetries. Validation of the D-TDD good performance was achieved by comparison with an ideal scheme and a different MAC protocol recently proposed in the literature on this subject.

An efficient demand-assign medium access control protocol for high-speed wireless networks

Green communications have a growing expansion to efficiently reduce energy consumption in wireless networks and to extend the battery life in portable devices. The paper proposes a joint Multiple Input Multiple Output (MIMO) antennas configurations and Network Coding (NC) scheme for energy saving purpose. Starting from the analysis of the reliability gain of NC for a multicast scenario proposed by Ghaderi et alii, the proposed approach leads towards the optimization of an integrated MIMO-NC system by considering a trade-off between overall complexity and performance. In particular, we optimize jointly the delivery delay of the information flow to a group of users and the number of used receive antennas to decrease energy consumption at the receiver. This goal is achieved by minimizing a suitable objective function derived by assuming that each node of the broadcast/multicast group has to be able to decode the information flow with a target probability, depending on the propagation conditions, the block and packet length, the number of interested users and the number of receive antennas. Numerical results are presented with the aim of highlighting the advantages of the proposed optimized MIMO-NC scheme in comparison with the classic solution.

Adaptive network coded MIMO schemes for group reliable multicast green communications

This paper deals with a multiuser cancellation detection scheme combined with antenna arrays, for Wideband Code Division Multiple Access (WCDMA) communication systems where different traffic load and different data rate are considered. The proposed receiver, defined as Space Time-Selective Parallel Interference Cancellation detector, is supposed to be used at the base station of a WCDMA communication system. Asynchronous users and multipath fading phenomena are considered in our analysis. The proposed receiver basic assumption is to divide signals into two different groups according to the received power level. The reliable ones are directly detected and cancelled from the whole received signal, by each sensor, before making the decision on not reliable signals, without any further processing delay. Performance evaluation has been carried out in terms of Pe (bit error probability) by means of computer simulations. In particular, it is shown here that the proposed receiver exhibits a good behavior and lowers the computational complexity in comparison with previously proposed alternatives.

Selective parallel interference cancellation for wcdma communications with antenna array

In the last decade, code division multiple access (CDMA) has gained even more importance due to its capabilities of wider band occupancy without any time constraints. A lot of the recent implemented systems for wireless communications, as Universal Mobile Telecommunication System (UMTS) or IEEE 802.11b wireless local area network (WLAN), use the CDMA approach to allow the simultaneous access of multiple users. One of the main drawbacks of CDMA systems is the so called multiple access interference (MAI). In the literature, several multiuser receivers were developed. Among them, receivers that perform mean square error minimization are very attractive for their very simple implementation. On the other hand, neural networks have gained recently an increasing importance due to their capabilities in solving many engineering problems, involving minimization of errors or some other cost functionals. In this paper, an advanced MMSE receiver based on the use of neural networks is proposed, where at every bit time neural network achieves the optimum values for the coefficient set of receiving filter, thus minimizing the error rate.

Proposal of an advanced MMSE multiuser receiver for a DS-CDMA environment using neural networks

This paper deals with a radio?based communication network with a single radio channel shared by several data terminals for transmissions to a single hub station. In particular, the communication system considered is a potential provider of wireless LAN?like services. The focus is on the capacity of combining a preemptive polling?based multiple access scheme with a Selective Repeat ARQ technique to counteract the effect of the nonstationary transmission channel. The nonstationary transmission channel has been modeled as a two?state Markov chain with parameters related to actual propagation conditions. Typical outdoor/indoor environments have been considered. The main idea is that of making the service interruption of the preemptive polling scheme dependent on the propagation conditions of the transmission channel by monitoring the outcome of the data packet transmission attempts. A performance comparison clearly reveals the superiority of this preemptive polling scheme with respect to the classical cyclic polling scheme.

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Romano Fantacci

Papers

An efficient demand-assign medium access control protocol for high-speed wireless networks

Adaptive network coded MIMO schemes for group reliable multicast green communications

Selective parallel interference cancellation for wcdma communications with antenna array

Proposal of an advanced MMSE multiuser receiver for a DS-CDMA environment using neural networks

A preemptive polling protocol for applications in wireless LANs