Performance Enhancement of High Order LDPC Coded Modulation Systems with Application in Mobile Backhaul Networks

Abstract

Wireless backhaul communication systems play a crucial role in the infrastructure of current cellular networks. In light of the expensive costs of fiber deployment, the importance of these links is anticipated to continue over the next few decades.Point-to-point microwave radio links (PtPMRLs) are the backbone of every wireless backhaul system. To achieve higher spectral efficiencies, the PtPMRL are designed based on the concurrent exploitation of high-order modulations and powerful forward error correcting codes. An example of such design paradigm is the high-order lowdensity-parity-check coded modulation systems (LDPC-CMSs). In this thesis two key challenges in the high-order LDPC-CMSs are overcome.In our first contribution, we consider the problem of oscillator phase hit (PH) in microwave backhaul communication links. PH results in a temporary link loss in the communication system and bears an expensive cost on the operators. In this work, we propose a two-stage solution to mitigate PH. In the first stage, we use Neyman-Pearson binary hypothesis testing to develop a low cost PH detection algorithm.In this test, a likelihood ratio test is designed and the optimal detection threshold is analytically calculated. The proposed PH detection scheme entails small real-time computations while using the existing pilot symbols in the system; thus, no extra pilot overhead is required. In the second stage, we use maximum likelihood estimation to develop a PH correction scheme. In particular, we formulate the joint estimation of phase noise (PN) and PH as a maximum likelihood estimation problem. Solving this problem results in the estimation of PN with the location and magnitude of PH. By applying the proposed correction scheme, the number of affected symbols by PH is significantly reduced. In particular, the number of remaining erroneous symbols due to PH (if any) is within the error correction capability of modern LDPC codes used iii Table of Contents viii List of Tables xi List of Figures xiii List of References 103Appendix A