Modulation for point-to-point microwave radio links

Abstract

The drastic increase of traffic in cellular networks due to the introduction of mo- bile broadband technologies such as HSPA and LTE has created a need to improve the data throughput in the back-hauling networks and thus over the microwave links. The scarcity and the high cost of spectrum have influenced telecommunication fraternity to come up with spectrally efficient communication systems. The techniques like line-of- sight MIMO and Dual Polarization-multiplexing have enabled the increase in spectral ef- ficiency. Though the above techniques have improved the spectral efficiency significantly, further improvements have to be considered. Dual polarization-multiplexing and spatially-separated line-of-sight MIMO techniques have given rise to parallel streams for communication. The existing systems modulate and demodulate these parallel streams independently. In this thesis, the idea of using the parallel streams together for modulation and detection (joint modulation and detection) is considered. This allows the signal space to move from two to higher dimensions. In this thesis the modulation formats in four-dimensional (4-D) space are examined. Further, the same idea has been extended to eight dimensions. The performance of modulation formats in four and eight dimensions are compared with the standard QAM constellations. The introduced modulation formats are shown to be power and spectrally efficient. The performance of the modulation formats is studied for AWGN and partially coherent AWGN channel models and capacity curves are plotted. Finally, we have discussed low complexity detectors for the joint modulations which make the modulation formats practically feasible.