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

Multiple-input-multiple-output (MIMO) wireless systems are those that have multiple antenna elements at both the transmitter and receiver. They were first investigated by computer simulations in the 1980s. Since that time, interest in MIMO systems has exploded. They are now being used for third-generation cellular systems (W-CDMA) and are discussed for future high-performance modes of the highly successful IEEE 802.11 standard for wireless local area networks. MIMO-related topics also occupy a considerable part of today's academic communications research. The multiple antennas in MIMO systems can be exploited in two different ways. One is the creation of a highly effective antenna diversity system; the other is the use of the multiple antennas for the transmission of several parallel data streams to increase the capacity of the system. This article presented an overview of MIMO systems with antenna selection. The transmitter, the receiver, or both use only the signals from a subset of the available antennas. This allows considerable reductions in the hardware expense.

MIMO systems with antenna selection

We consider multiple-input - multiple-output (MIMO) systems with reduced complexity. Either one, or both, link ends chose the "best" L out of N available antennas. This implies that only L instead of N transceiver chains have to be built, and also the signal processing can be simplified. We show that in ideal channels, full diversity can be achieved, and also the number of independent data streams for spatial multiplexing can be maintained if certain conditions on L are fulfilled. We then discuss the impact of system nonidealities, like noisy channel estimation, correlations of the received signals, etc.

MIMO systems with antenna selection - an overview

The growth in wireless communications necessitates more efficient utilization of spectrum. The increased sharing of spectrum translates into a higher likelihood of users interfering with one another. Interference rejection techniques allow a high capacity of users within the available spectrum. This overview comprises a literature review of published papers pertaining to single-channel adaptive interference rejection in digital wireless dating primarily from 1980 to the present. Though previous overviews are referenced and summarized, the focus is on advances not covered by previous overviews (consequently, some papers are included that predate 1980 because they are not covered in previous overviews). An organizational chart (divided into spread spectrum and nonspread spectrum techniques) is shown which outlines the types of techniques covered. Interference rejection is important for several reasons. Cellular capacity is inherently interference limited, particularly by co-channel interference (CCI) and adjacent-channel interference (ACI). One solution to combat CCI and ACI is to split cells and decrease the power, but cell-splitting is expensive. Interference-rejection techniques often represent a less expensive alternative to cell-splitting. In addition, as newer communication technologies supersede older technologies, interference-rejection techniques are important in helping to facilitate compatibility during transitions between the old and new technologies.

Interference rejection in digital wireless communications

This paper presents an overview of feature-based (FB) methods developed for Automatic classification of digital modulations. Only the most well-known features and classifiers are considered, categorized, and defined. The features include instantaneous time domain (ITD) parameters, Fourier transform (FT), wavelet transform (WT), higher order moments (HOM) to name a few. The classifiers are artificial neural networks (ANN), support vector machines (SVMs), and decision tree (DT). We also highlight the advantages and disadvantages of each technique in classifying a certain modulation scheme. The objective of this work is to assist newcomers to the field to choose suitable algorithms for intended applications. Furthermore, this work is expected to help in determining the limitations associated with the available FB automatic modulation classification (AMC) methods.

An overview of feature-based methods for digital modulation classification

An automatic modulation classification algorithm for application in communications via multipath fading channels, without a priori information on channel characteristics, based on normalized sixth-order cumulants is described. In comparison with existing approaches, proposed algorithm can achieve much better classification accuracy in distinguishing BPSK from complex-valued modulation techniques. Theoretical analysis is verified via extensive simulations, under real-world channel propagation conditions.

Automatic modulation classification algorithm using higher-order cumulants under real-world channel conditions

An algorithm is described for estimation of multipath fading channels without a priori information on channel characteristics, for application in automatic modulation classification based on normalised sixth-order cumulants. Compared with existing approaches, the proposed algorithm can achieve much better classification accuracy in distinguishing complex-valued modulation techniques. Theoretical analysis is verified via extensive Monte-Carlo simulations.

Multipath channel estimation algorithm for automatic modulation classification using sixth-order cumulants

In this article we present a survey of the power control techniques for modern wireless DS-CDMA communication systems. Power control is the single most important system requirement for DS-CDMA systems. Well-defined power control is essential for proper functioning of the DS-CDMA system. In the absence of power control the effect of near⁄far phenomena is dominant, and the capacity of the DS-CDMA mobile system is very low, even lower than that of mobile systems based on FDMA. However, when the power control in DS-CDMA systems exists, it allows users to share resources of the system equally between themselves. Also, with a proper power control it is possible to lower total transmitting power of the mobiles and prolong the battery life.

Evolution of the power control techniques for DS-CDMA toward 3G wireless communication systems

In this paper an algorithm for automatic classification of unknown signal modulation formats, based on sixth-order cumulant features of received data samples, is analyzed. This algorithm is characterized with extremely low computational complexity and can be completely realized with modest digital resources. Also, it is capable to maintain significant classification performance, in the meaning of achieved probability of correct modulation format recognition, under the impact of various degradation sources: additive white noise, multipath propagation channels, or interference. These properties make the algorithm be perspective for practical implementation and potentially a good solution for wide set of military and commercial communication systems. Also, results of theoretical analysis of different properties of algorithm are presented, along with new channel estimation algorithm, proposed in literature for adoption within the system with automatic modulation classification. Some particular methods for improvement of algorithm's performance under specific propagation conditions are presented and discussed. Its performance has been compared with the best known classification algorithm, having similar implementation properties and capability to solve real-world issues, and verified through numerous Monte-Carlo simulations.

Automatic modulation classification: Sixth-order cumulant features as a solution for real-world challenges

In this paper one algorithm for automatic modulation classification under conditions of multipath channel, based on sixth-order cumulants, is considered. Performance of proposed algorithm is analysed within the two-ray multipath model. In comparison with fourth-order cumulants-based method, this algorithm can achieve much better classification accuracy in distinguishing BPSK from complex-valued constellations.

Miroslav L. Dukic

Papers

Automatic modulation classification algorithm using higher-order cumulants under real-world channel conditions

Multipath channel estimation algorithm for automatic modulation classification using sixth-order cumulants

Evolution of the power control techniques for DS-CDMA toward 3G wireless communication systems

Automatic modulation classification: Sixth-order cumulant features as a solution for real-world challenges

Algorithm for automatic modulation classification in multipath channel based on sixth-order cumulants