Parametrization of unitary matrices using Givens rotations has been used for limited feedback in multiple-input multiple-output (MIMO) systems. Feedback based on these rotations has been adopted in IEEE 802.11n and other upcoming standards. However, the probability distributions of Givens rotations is not known for correlated channels, forcing the use of uniform quantization. In this paper, novel probability density function (PDF) models, based on beta and wrapped Cauchy distributions, are proposed for Givens rotations in correlated MIMO channels. Empirical distributions and goodness-of-fit tests show that the proposed distributions characterize the spatial correlation behavior with good accuracy. Moreover, it is shown that the distributions known in the literature for uncorrelated MIMO channels are only special cases. Distributions of Givens rotations are useful to understand the behavior of singular vectors of correlated channels. In this paper, the PDF models are utilized for bit allocation and optimized codebook design. Simulations show that precoding using the proposed codebooks achieves significant performance improvement, in terms of mean square error and sum rate, as compared to using uniform codebooks. It is also shown that the bit allocations proposed in this paper reduce to that of IEEE 802.11n standard when the MIMO channel is not spatially correlated.

In this paper, we consider a wireless sensor network (WSN) with sensors simultaneously reporting their decision to a fusion center (FC) equipped with multiple antennas. A Gaussian mixture channel model is used to obtain a general fading characterization of the channels ensemble between the sensors and the FC. Energy detection is studied as an appealing low-complexity sub-optimal alternative to the (computationally expensive) optimal test based on log-likelihood ratio. Closed-form theoretical performance is obtained for the energy test and furthermore asymptotic analysis for both tests is derived in order to provide a detailed characterization of large-system scenarios. Finally, the simulation results are provided to confirm the theoretical results and compare performance trends of the two tests.

In this paper, a path-loss model for the open-sea environment is proposed, in which different propagation phenomena including effective reflection, shadowing, divergence, and diffraction, related to the sea surface and earth curvature in the open-sea environments, are taken into account. The channel model is parameterized and validated by experimental results from our measurement campaign at 2 GHz over a distance range of 45 km in calm, cold Norwegian ocean waters. Model and measurements show excellent agreement in terms of the root mean square error. By evaluating the channel model parameters like mean-square surface slope and standard deviation of surface height related to the sea surface roughness, it can be concluded that the effects of shadowing and scattering on the reflected rays will influence the fading amplitude within the distance range where the Line-Of-Sight (LOS) is tangential to the surface of the earth. It is also found that the diffraction loss starts to influence the path-loss results beyond the distance of 0.6 × the first Fresnel zone clearance. The amplitude probability density function (PDF) of fading is studied as well. By using the Akaike information criterion for model selection, it is found that the amplitude PDF can be modeled as Weibull distribution at short distances and very large distances. The two-wave with diffuse power distribution, Rician distribution, and Rayleigh distribution dominate at distances between 9 and 45 km. The correlation coefficient between the signal amplitudes at two antennas that are vertically separated by 3 m was studied, and found to be close to zero when the transmitter is below the horizon. This indicates the potential to employ multi-antenna techniques for maritime communication systems.

In a Bayesian linear model, suppose observation y = Hx + n stems from independent inputs x and n which are Gaussian mixture (GM) distributed. With known matrix H, the minimum mean square error (MMSE) estimator for x , has analytical form. However, its performance measure, the MMSE itself, has no such closed form. Because existing Bayesian MMSE bounds prove to have limited practical value under these settings, we instead seek analytical bounds for the MMSE, both upper and lower. This paper provides such bounds, and relates them to the signal-to-noise-ratio (SNR).

This paper considers the analytical performance of primary users (PUs) subject to interference due to secondary users (SU) in an underlay cognitive radio system over Rayleigh fading. In particular, we focus on a more general spatial configuration where the interfered PU, not only located at the center of the cell, is having a protective region which is free of SUs and the SUs are distributed over a finite area in contrast to the commonly used infinite area assumption. We first characterize the statistical properties of the aggregate interference at the PU due to SUs, by deriving new exact closed form expressions for the moment generating function, cumulants, first, second and third moments and first order expansions of the cumulative distribution functions corresponding to propagation scenarios with path loss factors, two and four. We then investigate the PU performance by presenting new analytical expressions for the outage probability, amount of fading as well as the diversity order and coding gain. Our results indicate that the PU can achieve the full diversity gain given a non-zero protective region around the PU.

In this paper, we study the performance of the energy detector when considered for binary hypothesis decision fusion in underwater acoustic wireless sensor networks with a multiple-access reporting channel. Energy detection is appealing in terms of computational complexity and limited system knowledge requirements, i.e., channel state information, signal-to-noise ratio, and local performance of the sensors are not needed at the receiver side, then the interest for performance assessment over underwater acoustic channels arises. Here, we demonstrate that energy detection may be applied with good results to underwater sensor networks. The impact on the performance of various design parameters is considered, including sampling frequency, number of transmitting sensors, and number of receiving elements (hydrophones).