This paper addresses the end-to-end average BER (ABER) performance of decode-and-forward (DF) relay free-space optical (FSO) communications over weak and strong turbulence channels with pointing errors. For the weak and strong turbulence channels, the probability distribution function (PDF) of the irradiance can be modeled by a lognormal and Gamma–Gamma distribution, respectively. Considering the effects from atmospheric attenuation, turbulence and pointing errors, we present a statistical model for the optical intensity fluctuation at the receiver. Then the end-to-end ABER performances are analyzed and derived closed-form expressions are obtained. The simulation results indicate that the derived closed-form expressions provide sufficiently accurate approximations.
This paper' summarizes recent developments in semi-smart antenna systems for geographic load balancing in cellular mobile communication systems by cooperatively changing the antenna radiation patterns and compares the performance with cooperatively down tilted antennas. Cooperative coverage is advantageous, e.g. in the presence of hotspots. For semi-smart antennas the ideal shape for a cell in the context of its neighbours is determined using the Bubble Oscillation Algorithm (BOA) and the pattern is then given to the semi-smart antenna for further radiation pattern synthesis. The adjustment process differs for different antenna systems and mostly depends on the antenna's physical capabilities on pattern shaping. This paper then considers the special case of adaptively tilting through the use of Electrical Down-Tilt (EDT) antennas, and compares the system capacity performance between EDT and semi-smart antennas for traffic load balancing. Coverage under load balancing is optimal with respect to the whole network, rather than just for individual antennas. The results show that both the adaptive approaches give benefit, with different site costs in relation to practical antenna system complexity.Index Terms -semi-smart antenna, Electrical Down-Tilt (EDT), Wideband CDMA (WCDMA), Frequency Division Duplexing (FDD).
An architecture for wireless communication between control centers and registered users in emergency situations when the cellular network is not operational is described. It is based on delay tolerant networks (DTN) and enables mobile users with multiple radio interface technologies to communicate across heterogeneous network technologies. With the help of asynchronous bundles passing from hop to hop, short message service (SMS), multimedia messaging and walkie-talkie communication services are provided. The security issues for deployment of DTN communication applications using this architecture are also described. To assess the performance of the system, results from simulations for the degree of message penetration of broadcasts into the community and the probability that a control centre receives uplink messages are presented for different user densities, routing protocols on the system. The approach has been implemented on the Android mobile platform.
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