Carrier interferometry for next generation CDMA and TDMA wireless systems: a multi-carrier framework

Abstract

In this thesis, we introduce an enabling technology called Carrier Interferometry. that has the potential to satisfy many of the requirements of next generation wireless systems. The objective of this work is not only to present the technology, but also demonstrate the benefits it offers to multiple access schemes like MC-CDMA and TDMA, and modulation schemes like FSK.

We first introduce the Carrier Interferometry (Cl) signal, the basic building block for the Carrier Interferometry approach. This signal corresponds to the superposition of N orthogonal carriers equally spaced in frequency. A theoretical analysis of the orthogonal and pseudo-orthogonal properties of this Cl signal is provided and it is shown how as a result, this signal can support many practical applications.

We apply the Cl approach to an MC-CDMA system in the form of a powerful set of complex spreading codes (referred to as Cl codes). These Cl spreading codes of length N have a unique feature which allows the CI/MC-CDMA system to (1) support N users orthogonally; (2) then, as system demand increases, codes can be selected to accommodate up to an additional N users pseudo-orthogonally. Furthermore, the performance of CI/MC-CDMA shows minimum degradation when capacity is doubled.

We also introduce the Cl signal into TDMA systems as a multi-carrier implementation of the sine pulse shape. We demonstrate that this proposed multi-carrier pulse shape along with frequency domain receiver processing, provides significant performance gains relative to TDMA systems employing traditional pulse shapes. The Cl approach in TDMA also results in a doubling of throughput via pseudo-orthogonality.

The Cl approach is also applied to fundamental FSK modulation to yield significant performance and throughput gains. We demonstrate that, by introducing a multi-carrier implementation of FSK using the Cl approach, along with a novel coherent receiver, we can successfully employ an FSK system in a frequency selective channel and exploit frequency diversity benefits.

Finally, we demonstrate how our Cl-based multi-carrier approach can be extended to the synthesis of any arbitrary pulse shape. We demonstrate a corresponding signal decomposition at the receiver side leading to dramatic performance gains.

These are definitely exciting times in the wireless world. There is a large gap emerging between public expectations for mobile communications and available technologies. The work presented in this thesis is extremely significant as we introduce a fundamental technology that can play a big part in closing this gap.