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Title: Multiplexing of mixed numerologies in OFDM/filtered-OFDM systems
Author: Mao, Juquan
ISNI:       0000 0004 8503 1841
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2019
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The flexibility in supporting heterogeneous services with vastly different technical requirements is one of the distinguishing characteristics of the fifth generation (5G) communication systems and beyond. A generic framework is developed in this thesis to address the coexistence/isolation issues of mixing multiple services over a unified physical infrastructure, where the system bandwidth is divided into several bandwidth parts (BWPs), each being allocated a distinct numerology optimized for a particular service. However, multiplexing of mixed numerologies in the same carrier comes at the cost of induced inter-numerology interference (Inter-NI). The Inter-NI can be mitigated by performing additional filtering process on top of orthogonal frequency-division multiplexing (OFDM) waveform for each numerology, namely filtered OFDM or F-OFDM. The additional filtering operation makes transmitted signal better localized in the frequency domain but worse in the time domain, which in turn causes issues within numerology, such as intra-numerology interference (Inter-NI) and filter frequency response selectivity (FFRS). With the developed analysis framework, the problems within numerology and between different numerologies are analyzed, respectively. The issues of Intra-NI and FFRS are firstly analyzed within single numerology. An Intra-NI-free and a nearly-free condition for an F-OFDM system are discussed, and an algorithm on how to select the optimal cyclic redundancy (CR) length is presented. In addition, the impact of FFRS is analyzed for both single antenna and multiple antenna cases, and a pre-equalized F-OFDM (PF-OFDM) system is proposed to tackle the issue. The level of distortion, the Intra-NI and Inter-NI, is quantified by the developed analytical metrics, each of which is a function of several system parameters. Consequently, this leads to an analysis and evaluation of these parameters for meeting a given signal distortion target. A case study utilizing the offered analysis is also presented, where an optimization problem of power allocation is formulated, and a solution is also proposed in multi-numerology systems. It is also demonstrated that a F-OFDM system better addresses the coexistence/isolation problem of mixed numerologies. The work in this thesis provides an insightful analytical guidance for the multi-service design in 5G and beyond systems.
Supervisor: Xiao, Pei Sponsor: 5GIC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral