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

This paper provides a tutorial introduction to the constant modulus (CM) criterion for blind fractionally spaced equalizer (FSE) design via a (stochastic) gradient descent algorithm such as the constant modulus algorithm (CMA). The topical decisions utilized in this tutorial can be used to help catalog the emerging literature on the CM criterion and on the behavior of (stochastic) gradient descent algorithms used to minimize it.

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Blind equalization using the constant modulus criterion: a review

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

In this paper, an approach of estimating signal parameters via rotational invariance technique (ESPRIT) is proposed for two-dimensional (2-D) localization of incoherently distributed (ID) sources in large-scale/massive multiple-input multiple-output (MIMO) systems. The traditional ESPRIT-based methods are valid only for one-dimensional (1-D) localization of the ID sources. By contrast, in the proposed approach the signal subspace is constructed for estimating the nominal azimuth and elevation direction-of-arrivals and the angular spreads. The proposed estimator enjoys closed-form expressions and hence it bypasses the searching over the entire feasible field. Therefore, it imposes significantly lower computational complexity than the conventional 2-D estimation approaches. Our analysis shows that the estimation performance of the proposed approach improves when the large-scale/massive MIMO systems are employed. The approximate Cramer-Rao bound of the proposed estimator for the 2-D localization is also derived. Numerical results demonstrate that albeit the proposed estimation method is comparable with the traditional 2-D estimators in terms of performance, it benefits from a remarkably lower computational complexity.

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An ESPRIT-Based Approach for 2-D Localization of Incoherently Distributed Sources in Massive MIMO Systems

A system includes a three dimensional antenna and mobile devices that wirelessly communicate with the antenna. A phase of arrival and a phase difference of arrival are calculated, and a distance between the three dimensional antenna and the mobile device is calculated. A direction between the three dimensional antenna and the mobile device is calculated. The direction calculation includes an angular spread function of multipath scattering in the communication between the three dimensional antenna and the mobile device. The direction calculation further includes an estimation of a propagation delay and an angle in the communication between the three dimensional antenna and the mobile device.

System and method for locating mobile devices

Low-complexity estimation of 2D DOA for coherently distributed sources

We consider the problem of estimating the nominal direction of arrival (DOA) of an incoherently distributed source. This problem is encountered due to the presence of local scatterers in the vicinity of a transmitter or due to signals propagating through a random inhomogeneous medium. Since the spatial covariance matrix has full rank for an incoherently distributed source, the performance of most high-resolution DOA estimation algorithms conceived under coherently distributed sources, as well as point source models, degrades when scattering is present. In addition, several DOA estimation techniques devised under a distributed source model require a high-dimensional nonlinear optimization problem. In this paper, we propose a novel method based on the conventional beamforming approach, which estimates the nominal DOA from a spatial maximum peak of the output power. The proposed method is computationally more attractive than the maximum likelihood (ML) estimator, although the performance degrades in comparison with the ML estimator, whose asymptotic performance is equivalent to the Cramer-Rao bound (CRB). We derive and compare the asymptotic performances of the proposed method and the redundancy-averaged covariance matching (RACM) method in the single-source case. The simulation results illustrate that the asymptotic performance of the proposed method is better than that of the RACM method.

A Method for the Direction-of-Arrival Estimation of Incoherently Distributed Sources

Performance of constant modulus adaptive digital filters for interference cancellation

We consider the quasi-maximum-likelihood (quasi-ML) detectors of the reverse link system that uses antenna arrays in asynchronous channels when the channel vector is time-invariant and time-varying. A channel vector estimation method based on eigendecomposition for time-invariant channels and its adaptive version suitable for the time-varying channels are also proposed. It is shown that the proposed quasi-ML detector can be regarded as a beamformer followed by a decorrelating filter and that the proposed system performs better than the conventional decorrelator scheme. It is also observed that the performance gain of the proposed scheme over the conventional decorrelator system increases as the numbers of active users and antenna arrays increase.

Analysis of quasi-ML multiuser detection of DS/CDMA systems in asynchronous channels

A class of polyphase signature sequences for direct-sequence code-division multiple-access (DS/CDMA) systems is proposed. The proposed class has zero periodic (=even) cross-correlation (CC) function and approximate maximum magnitude N//spl pi/ of odd cross-correlation (OCC), where N is the length of sequences. Although the maximum magnitude is relatively large, it is observed that the maximum magnitude has little effect on the performance of the DS/CDMA system, since its frequency is very low. The performance of the proposed sequence in DS/CDMA systems is investigated and shown to be better than that of other sequences for an asynchronous additive white Gaussian noise channel environment with and without Rayleigh multipath fading.

Jooshik Lee

Papers

Low-complexity estimation of 2D DOA for coherently distributed sources

A Method for the Direction-of-Arrival Estimation of Incoherently Distributed Sources

Performance of constant modulus adaptive digital filters for interference cancellation

Analysis of quasi-ML multiuser detection of DS/CDMA systems in asynchronous channels

A new polyphase sequence with perfect even and good odd cross-correlation functions for DS/CDMA systems