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A serious shortcoming of current downlink power control methods is that their performance may be severely degraded when the downlink channel information is known imprecisely at the transmitter. In this paper, a computationally and implementationally simple centralized downlink power control method is proposed for cellular wireless communication systems using code division multiple access (CDMA) or space division multiple access (SDMA). Our method provides a substantially improved robustness against imperfect knowledge of the wireless channel by means of maintaining the required quality of service for the worst-case channel uncertainty. In the SDMA case, the proposed technique can be straightforwardly combined with any of the existing transmit beamforming methods. Simulation results validate substantial robustness improvements achieved by our approach.

This paper proposes a simple and practical passive system for detection and direction finding of a far-field signal source. The proposed system receives signal emitted from a far away source using a set of similar directional antennas. The envelope of the received signals are used both to detect the existence of a pulse and to estimate it's bearing angle. We determine a set of design constraints on the employed antennas pattern such that the processing algorithm be simple and practical which operates in a wide frequency range at each instant. We evaluate the required constrains on the shape of antenna's pattern and we study the performance of the proposed algorithm. It is shown that simple antennas can be efficiently utilized in this system. Index Terms--Angle of arrival (AOA), antenna beam-pattern, detection, direction finder (DF), direction of arrival (DOA), electronic intelligent (Elint), electronic support measure (ESM), localization.

The performance of multiple-input multiple output channel estimation methods are studied using training sequences. The popular least squares (LS) and minimum mean-square-error (MMSE) approaches are considered and new scaled LS and relaxed MMSE techniques are proposed that require less knowledge of the channel second-order statistics and have better performance than the conventional channel estimators, therefore offering attractive tradeoffs, in terms of performance and prior knowledge of channel parameters.

Estimating the signal direction of arrival (DOA) using a compact system is of great interest in various civil, military, airborne, and communication applications. The signal DOA can be estimated using the arriving delays at multiple collocated sensors. In this paper, the Cramer–Rao bound (CRB) of the DOA estimation based on measuring the time difference of arrival by $N$ pairs of collocated sensors is derived. Then, the optimum sensor arrangement for minimizing the DOA estimation error is obtained and finally a discrete Fourier transform-based solution for estimating the signal DOA is presented. Using computer studies, it is observed that the proposed estimator is unbiased and its mean square error almost coincides with the CRB. [ABSTRACT FROM PUBLISHER]