Abstract: The performance analysis of diversity schemes in wireless communications typically involves the assumption of a variation of an instantaneous value of the received signal, i.e. fading of signal envelope, due to the multipath propagation. Fading is one of the main causes of the receiver performance degradation. Diversity combining technique which consists of receiving redundantly the same information-bearing signal over two or more fading channels, then combining these multiple replicas at the receiver in order to increase the overall received signal-to-noise ratio (SNR) is commonly used. Diversity technique is certainly one of the most frequently used methods for combating the deleterious effect of channel fading.
Since the selection combining (SC) and switch and stay combining (SSC) do not require signal cophasing and fading envelope estimation, they are very often implemented in practice. The SC is combining technique where the strongest signal is chosen among L branches of diversity system. In the case of dual branch SSC, the first branch stay selected as long as its instantaneous signal-to-noise ratio (SNR) is greater than predetermined switching threshold, even if the instantaneous SNR in the second branch maybe has a larger value at that time. The consideration of SSC systems in the literature has been restricted to low-complexity mobile units where the number of diversity antennas is typically limited to two.
The Rayleigh fading is a simple channel model frequently used to model multipath fading with no direct line-of-sight (LOS) path exists between the transmitter and receiver antennas. It also applies to the propagation of reflected and refracted paths through the troposphere and ionosphere and to ship-to-ship radio links.
Considering Nakagami-m distribution multipath scattering with relatively large delay-time spreads, with different clusters of reflected waves are described. In that way good fits to collected data in indoor and outdoor mobile-radio environments are provided.
Slow fading can be caused by events such as shadowing, where a large obstruction such as a hill or large building obscures the main signal path between the transmitter and the receiver. The amplitude change caused by shadowing is often modeled using a log-normal distribution with a standard deviation according to the log-distance path loss model.
The probability density functions of the SSC/SC combiner output signal at two time instants in the presence of Rayleigh, Nakagami-m and log-normal fading are determined in closed form. The probability density function of the SSC/SC combiner output signal at two time instants is important when the decision is based on multiple samples. The outage probability is numerically calculated using PDF. The graphically shown results emphasize better performances of the SSC/SC combiner apropos classical SSC and SC combiners at one time instant.

Brief Biography of the Speaker:
Dragana S. Krstic was born in Pirot, Serbia. She received the BSc, MSc and PhD degrees in electrical engineering from Faculty of Electronic Engineering, Department of Telecommunications, University of Nis, Serbia, in 1990, 1998 and 2006, respectively. Her field of interest includes telecommunications theory, optical communication systems, wireless communication systems, satellite communication systems etc. She works at the Faculty of Electronic Engineering in Nis since 1990. She participated in more Projects which are supported by Serbian Ministry of Science. She has written or co-authored about 140 papers, published to International/National Conferences and Journals. She has also reviewed more articles in IEEE Transactions on Communications; IEEE Communications Letters; ETRI journal; C&EE Journal; Electronics and Electrical Engineering (Elektronika ir Elektrotechnika) and other journals. She is the reviewer of the papers for many conferences and the member of technical program committees and international scientific committees of several scientific conferences.