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An equivalent model for a multi-input multi-output (MIMO) communication system with orthogonal space-time block codes (OSTBCs) is proposed based on a newly revealed connection between OSTBCs and Euclidean codes. Examples of distance spectra, signal constellations, and signal coordinate diagrams of Euclidean codes equivalent to simplest OSTBCs are given. A new asymptotic upper bound for the symbol error rate (SER) of OSTBCs, based on the distance spectra of the introduced equivalent Euclidean codes is derived, and new general design criteria for signal constellations of the optimal OSTBC are proposed. Some bounds relating distance properties, dimensionality, and cardinality of OSTBCs with constituent signals of equal energy are given, and new optimal signal constellations with cardinalities M = 8 and M = 16 for Alamouti's code are designed. Using the new model for MIMO communication systems with OSTBCs, a general methodology for performance analysis of OSTBCs is developed. As an example of the application of this methodology, an exact evaluation of the SER of any OSTBC is given. Namely, a new expression for the SER of Alamouti's OSTBC with binary phase shift keying (BPSK) signals is derived., Comment: 33 pages, 12 figures, 5 tables, full size journal paper, Finished in Oct. 2009, Unpublished

The pre-emphasis problem for FM radiotelephony over an additive white Gaussian noise channel is investigated. A Gaussian model and an experimentally measured frequency spectrum density for speech are used to solve the optimum filtering problem analytically. The optimum pre-emphasis characteristic is expressed in terms of the message spectral power density, the noise power density and the LaGrange multiplier. An iterative algorithm for the determination of the multiplier is presented and solved numerically for typical values of the signal-to-noise ratio. The optimum filter is unrealizable. It is approximated by a whitening filter in cascade with a two pole network. The selection of the pole positions involves a trade-off between mean square error performance and spectral compression. The transmitted signal spectra are computed numerically for three choices of pole positions and compared to those for the currently employed prefilter. The mean square error is computed and compared to the optimum mean square error for typical values of the signal-to-noise ratio. The new designs have less distortion than the present design. The roll-off rate of the spectrum in the adjacent channel region is determined to be greater than 4 for the proposed filter. This compares favourably with the rate of 2 for the current filter. Interference coefficients are defined to measure the interference between adjacent channel signals. The cases of voice-to-voice, voice-to-digital and digital-to-voice interference are investigated. Four types of data signals are considered, PAM signals with a = 0 and a = 1, MSK and PSK signals. An improvement ranging from 4 to 19 dB is noted for the new network. The improvement is greatest for the bandlimited PAM signals. The effects of a different speech model on the previous results are investigated. Spectra and interference coefficients are computed for a second speech spectral density function. A computer simulation verifies that the proposed new design offers improved performance.

The rapid growth in demand for cellular mobile communications and emerging fixed wireless access has created the need to increase system capacity through more efficient utilization of the frequency spectrum, and the need for better grade of service. In cellular systems, capacity improvement can be achieved by reducing co-channel interference. Several techniques have been proposed in literature for mitigating co-channel interference, such as adaptive antennas and power control. Also, by allocating transmitter power and communication channels efficiently (resource allocation), overall co-channel interference can be maintained below a desired maximum tolerable level, while maximizing the carried traffic of the system. This dissertation presents investigation results on the performance of base station adaptive antennas, power control and channel allocation, as techniques for capacity improvement. Several approaches are analyzed. Firstly, we study the combined use of adaptive antennas and fractional loading factor, in order to estimate the potential capacity improvement achieved by adaptive antennas. Next, an extensive simulation analysis of a cellular network is carried out aiming to investigate the complex interrelationship between power control, channel allocation and adaptive antennas. In the first part of this simulation analysis, the combined use of adaptive antennas, power control and reduced cluster size is analyzed in a cellular system using fixed channel allocation. In the second part, we analyze the benefits of combining adaptive antennas, dynamic channel allocation and power control. Two representative channel allocation algorithms are considered and analyzed regarding how efficiently they transform reduced co-channel interference into higher carried traffic. Finally, the spatial filtering capability of adaptive antennas is used to allow several users to share the same channel within the same cell. Several allocation algorithms combined with power control are analyzed. Ph. D.