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)

/pdf/nonlinear-time-series-analysis-1j3a35n4y3.pdf

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 deals with a multiuser detector for DS-CDMA wireless communication systems. The proposed detector's main feature lies in the joint utilization of the space and time processing techniques since adaptive antenna arrays and decorrelating multiuser receiver are supposed to be used together. Complexity growth is lowered by implementing a multiuser detection technique based on the sliding window algorithm. The DS-CDMA communication system considered resorts to QPSK modulated wideband signals so that a sliding window algorithm generalization is necessary. The simulation results shown here confirm that the proposed structure is near-far resistant even in the worst fading cases. As the sensor number increases a remarkable performance improvement takes place. Besides we show that the proposed receiver allows systems to exploit completely the array introduction while maintaining an acceptable computational complexity.

/pdf/a-low-complexity-multiuser-detector-for-asynchronous-cdma-407u3isrb0.pdf

A low-complexity multiuser detector for asynchronous CDMA QPSK systems with adaptive antenna arrays

Ultra Dense Networks (UDNs) are considered a key element to address the expected growing of communication capacity demand in an affordable and sustainable way, improving both spectral and energy efficiency. This paper focuses on the energy efficiency of a coordinated multicell multicast transmission in UDNs. In particular, a new iterative algorithm is proposed, whose goal is to maximize the energy efficiency of a single-group multicast service. Toward this goal, the cells are activated opportunistically, only when needed, using suitable transmission power. Moreover, small cells use adaptive beamforming weights in order to increase the efficiency of the radiated power. The effectiveness of the proposed method is proven in terms of energy efficiency and in comparison with different benchmark solutions. Benefits and limits of network densification are evaluated.

Energy efficient multicast beamforming in ultra dense networks

Broadband wireless communications are going to be deployed widely due to the introduction of the Universal Mobile Telecommunications System (IMT/2000), which is based on wideband-code division multiple access (W-CDMA) techniques. Adaptive blind multiuser detection, proposed for the mobile station receiver, reaches the optimum solution after a certain number of bit times. We propose the implementation on a fixed point digital signal processor (DSP) architecture of the adaptive blind algorithm based on a neural approach. A modified Kennedy-Chua (1988) neural network, based on the Hopfield model, is proposed, and its implementation on a fixed point numerical environment has been studied by means of computer simulation. Finally we discuss a medium level implementation of the algorithm on a Texas Instruments DSP.

DSP implementation of a neural network based blind multiuser receiver for DS-CDMA communication systems

The growing interest in mobile computing and communication devices leads to the necessity of wireless broadband network. Data transmission over such networks requires suitable error control schemes to guarantee high data reliability as well as efficient bandwidth utilization.

In this paper we propose an accurate yet simple analytical approach to evaluate the performance of wireless networks using gated and exhaustive polling protocols combined with the Stop and Wait (SW) or Go Back N (GBN) ARQ schemes [Bertsekas and Gallager, 2]. Moreover, simulation results concerning the performance of polling protocols combined with the Selective Repeat (SR) ARQ scheme are also shown for comparison purposes.

Protocol performance is estimated under very general assumptions, such as: AWGN or fading channels, arbitrary value of the round trip delay and arbitrary distribution of the traffic load (i.e., both symmetric or asymmetric system have been considered).

Performance Evaluation of Polling Protocols for Data Transmission on Wireless Communication Networks

In multi-path environments, Spread Spectrum multiple access techniques offer attractive properties of rejection of undesired signals and an high spectral efficiency. In this paper is presented a design method for spreading codes which employs Perfect Sequences, a class of complex sequences with singular correlation properties. The main advantage from the use of Perfect Sequences is the oppportunity of a fast DSP implementation with FFT blocks, where the analog section is extremely contained. Simulations in a multipath enviroment confirm the useful caracteristics of the proposed receiver for asyncronous trasmissions.

Romano Fantacci

Papers

A low-complexity multiuser detector for asynchronous CDMA QPSK systems with adaptive antenna arrays

Energy efficient multicast beamforming in ultra dense networks

DSP implementation of a neural network based blind multiuser receiver for DS-CDMA communication systems

Performance Evaluation of Polling Protocols for Data Transmission on Wireless Communication Networks

Fast phase sequences spreading codes for CDMA using FFT