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Medium access control (MAC) protocols simultaneously integrating transmission power (TP) control with directional antennas have the potential to enhance both energy savings and capacity throughput in wireless multihop Mobile Ad hoc NET-works (MANETs). In this paper, we present a model to calculate future interference in networks with directional antennas, and based on this model, we derive some relations that should exist between the required TP of RTS, CTS, DATA, and ACK frames for successful data packet delivery in MANETs based on the directional version of the IEEE 802.11 distributed coordination function. From these relations, we propose a distributed power control scheme. Furthermore, we show, via simulations, that the true potentials from the proposed control scheme cannot be shown due to the imperfection of the derived model. Based on these observations, we introduce another class of power control algorithm that instead deploys a prediction filter (Kalman or extended Kalman) to estimate future interference. Simulation experiments for different topologies are used to verify the significant through- put and energy gains that can be obtained by the proposed power control schemes. [ABSTRACT FROM AUTHOR]

This paper proposes the log-shifted Ganuna (LSG) approximation to model the sum of M lognormally distributed random variables (RVs). The closed-form probability density function of the resulting LSG RV is presented, and its parameters are directly derived from those of the M individual lognormal RVs by using an iterative moment-matching technique without the need for curve fitting of computer-generated distributions. Simulation and analytical results on the cumulative distribution function (cdt) of the sum of M lognormal RVs in different conditions indicate that the proposed LSG approximation can provide better accuracy than other lognormal approximations over a wide cdf range, especially for large M and/or standard deviation. [ABSTRACT FROM AUTHOR]

In this paper, a two stage hybrid interference cancellation and equalization framework is proposed for interference cancellation in the uplink of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The first stage uses time domain equalization to suppress cochannel interference, mitigate asynchronism, and shorten the postequalization channel response to be no longer than the length of the cyclic prefix. The second stage performs low-complexity single tap equalization and detection in the frequency domain. The framework is developed specifically for spatial multiplexing and is applied to multiuser MIMO-OFDM systems with asynchronism between users as well as to single-user MIMO-OFDM systems. Various equalizer design methods are proposed that determine the coefficients directly from the training data and are compared with methods based on channel estimates. The equalizer coefficients and postequalization channel response are found by solving a joint optimization that maximizes the signal to interference-plus-noise ratio (SINR) in the frequency domain. Simulations compare various training-based methods and show the proposed methods provide good bit error rate (BER) and SINR performance in a variety of interference scenarios. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a new adaptive dual-antenna array for mitigation of both interference and multipath effects in digital mobile communications at the handset level. This proposed system employs a nonlinear adaptive algorithm in the front end of the receiver to enhance the transmission quality in confined areas. The enhancement is blind since no priori knowledge of spatial signatures or training sequences is required. Furthermore, to obtain a compact antenna array system, a miniaturized shorting post microstrip antenna that operates in the 1.9 GHz PCS band is used as a radiating element. Using this microstrip antenna, a new experimental adaptive dual-antenna array prototype was designed and implemented. To examine the expected performance of this approach, experimental measurements were carried out and the measured performances indicate that gain improvement of 7 dB can be achieved by using this approach. [ABSTRACT FROM AUTHOR]