Code-Multiplexing-Based One-Way Detect-and-Forward Relaying Schemes for Multiuser UWB MIMO Systems

In this paper, we consider decode-and-forward (DF) one-way relaying schemes for multiuser impulse-radio ultrawideband (UWB) communications. We assume low-complexity terminals with limited processing capabilities and a central transceiver unit (i.e., the relay) with a higher computational capacity. All nodes have a single antenna differently from the relay in which multiple antennas may be installed. In order to keep the complexity as low as possible, we concentrate on noncoherent transceiver architectures based on multiuser code-multiplexing transmitted-reference schemes. We propose various relaying systems with different computational complexity and different levels of required channel knowledge. The proposed schemes largely outperform systems without relay in terms of both bit error rate (BER) performance and coverage

Performance Analysis of Multiple Input Multiple Output Free Space Optical Communication Systems

The Free Space Optical (FSO) communication i.e. optical communication without fibers is slowly becoming quite popular as fiber and its installation cost as well as difficulties involved becomes zero. The FSO communication is already making its impact in deep space communication and is expected to replace the existing optical fiber communication systems in the near future. In order to further speed up the optical communication, the Multiple Input/Multiple Output (MIMO) technology from microwave MIMO systems is being investigated. The characteristics of the Multiple Input/Multiple Output Free Space Optical communication systems using APD receivers have been discussed. The APD-based receivers for MIMO FSO systems under normal working conditions are designed and the characteristics of the components, such as InGaAs APDs, GaAs MESFET transimpedance amplifiers, a matched filter and an equalizer, etc., are considered. The probabilistic analysis of a FSO channel, APDs and noise in the FSO systems has been carried out. The main contributions in this dissertation are: obtaining the detailed closed-form expressions for the upper bounds of the error probabilities, analyzing the impacts of different parameters in MIMO FSO systems, and thorough analysis of a more complex model of the MIMO FSO system involving Webb distribution for APD-based optical receiver, the probabilistic analysis of the detection for pulse position modulation signaling and the transmitted symbol matrix for MIMO FSO equal gain combining systems. Using this detailed analysis the average symbol error probability, average bit error probability and average pairwise probability are also obtained. The equations have been derived by using the Fourier series analysis method. The modified Gauss-Chebyshev method for error probability calculation is also proposed. Results for average SEP and average BEP under different parameters are obtained and the impact of these parameters on MIMO FSO systems is also discussed