This paper focuses on the interaction and integration of several critical components of a Mobile Ad-Hoc Network (MANET) using smart antenna systems. A MANET is a wireless network where the communicating nodes are mobile and the network topology is continuously changing. One of the central motivations for this work comes from the observed dependence of the overall network throughput on the design of the adaptive antenna system and its underlying signal processing algorithms. In fact, a major objective of this work is to study and document the overall efficiency of the network in terms of the antenna pattern and the length of the training sequence used by the beamforming algorithms. This study also considers in sufficient detail problems dealing with the choice of direction of arrival algorithm and the performance of the adaptive beamformer in the presence of antenna coupling effects. Furthermore, the paper presents strategies and algorithms to combat the effects of fading channels on the overall system.

This correspondence studies antenna selection for wireless communications systems that employ multiple transmit and receive antennas. We assume that 1) the channel is characterized by quasi-static Rayleigh flat fading, and the subchannels fade independently, 2) the channel state information (CSI) is exactly known at the receiver, 3) the selection is available only at the receiver, and it is based on the instantaneous signal-to-noise ratio (SNR) at each receive antenna, and 4) space-time codes are used at the transmitter. We analyze the performance of such systems by deriving explicit upper bounds on the pairwise error probability (PEP). This performance analysis shows that 1) by selecting the set of antennas that observe the largest instantaneous SNR, one can achieve the same diversity gain as the one obtained by using all the receive antennas, provided that the underlying space-time code has full spatial diversity, and 2) in the case of rank-deficient space-time codes, the diversity gain may be dramatically reduced when antenna selection is used. However, we emphasize that in both cases the coding gain is reduced with antenna selection compared to the full complexity system. Based on the upper bounds derived, we describe code design principles suitable for antenna selection. Specifically, for systems with two transmit antennas, we design space-time codes that perform better than the known ones when antenna selection is employed. Finally, we present numerical examples and simulation results that validate our analysis and code design principles. Index Terms-Antenna selection, diversity, multiple-input multipleoutput (MIMO) systems, multiple-antenna communications, pairwise error probability (PEP), space-time coding, wireless communications.

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Abstract-A reconfigurable antenna (RA) capable of steering its beam into the hemisphere corresponding too }, and of changing 3-dB beamwidth, whereo } for broadside direction is presented. The RA operating in 5 GHz band consists of a driven patch antenna with a parasitic layer placed above it. The upper surface of the parasitic layer has two pixelated metallic strips, where each strip has four pixels. The pixels connected via PIN diode switches enable to change the current distribution on the antenna providing the desired modes of operation. A prototype RA was characterized indicating an average gain of 8 dB. Measured and simulated impedance and radiation patterns agreed well. The proposed RA offers an efficient solution by using less number of switches compared to other RAs. The system level simulations for a 5G orthogonal frequency division multiple access system show that the RA improves capacity/coverage trade-off significantly, where the RA modes and users are jointly determined to create proper beamwidth and directivity at the access point antennas. For a hotspot scenario, the presented RA provided 29% coverage and 16% capacity gain concurrently.

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