Diversity Techniques

The downlink of a wireless network where multi-antenna base stations (BSs) communicate with single-antenna mobile stations (MSs) using maximal ratio transmission (MRT) is considered here. The locations of BSs are modeled by a homogeneous Poisson point process (PPP) and the channel gains between the multiple antennas of each BS and the single antenna of each MS are modeled as spatially arbitrarily correlated Rayleigh random variables. We first present novel closed-form expressions for the distribution of the power of the interference resulting from the coexistence of one intended and one unintended MRT over the considered correlated fading channels. The derived expressions are then used to obtain closed-form expressions for the success probability and area spectral efficiency of the wireless communication network under investigation. Simulation results corroborate the validity of the presented expressions. A key result of this work is that the effect of spatial correlation on the network throughput may be contrasting depending on the density of BSs, the signal-to-interference-plus-noise ratio (SINR) level, and the background noise power.

In this paper, we present a new electromagnetic methodology that determines the covariance matrix of compact multi-port antenna (MPA) systems at the early design stage. Further insight to this field is provided, as contrary to existing methodologies, it rigorously relies on the reciprocity principle of MPA systems. Thus, the impact of propagation environment, termination conditions and MPA radiation characteristics as independent factors affecting performance is physically incorporated. Provided the availability of mathematical expressions for the cumulative distribution function (CDF) and probability density function (PDF) of received signal-to-noise ratio (SNR), performance can be then analytically studied via the diversity antenna gain (DAG) in terms of a) SNR enhancement at a specific outage probability (OP) level (that is DAG-OP) and b) average SNR reduction for achieving a specific average bit error rate (BER) (that is DAG-BER). Illustrative examples with performance evaluation of compact MPA systems are presented. The adopted diversity technique is the transmit antenna selection/maximal ratio combining (TAS/MRC), which for the first time is analytically studied employing realistic MPA systems. Comparisons with existing published results further demonstrate the validity and usefulness of the proposed methodology.

The performance of L-branch scan-and-wait combining (SWC) reception systems over arbitrarily correlated and not necessarily identically distributed Nakagami-m fading channels is analyzed and evaluated. Firstly, a fast convergent infinite series representation for the SWC output signal-noise ratio (SNR) is presented. This expression is used to obtain analytical expressions in the form of infinite series for the average error probability performance of various modulation schemes for integer values of m as well as the average number of paths estimation and average waiting time (AWT) of L-branch SWC receivers for arbitrary values of m. The numerically obtained results have shown that the performance expressions converge very fast to their exact analytical values. It was found that the convergence speed depends on the correlation and operating SNR values as well as the Nakagami m-parameter. In addition to the analytical results, complementary computer simulated performance evaluation results have been obtained by means of Monte Carlo error counting techniques. The match between these two sets of results has verified the accuracy of the proposed mathematical analysis. Furthermore, it is revealed that, at the expense of a negligible AWT, the average error probability performance of SWC receivers is always superior to that of switched-and-examine combining receivers and in certain cases to that of maximal-ratio combining receivers.