循環脈衝形預編碼用於正交分頻多工之新波形及收發機最佳化設計

Circularly Pulse-Shaped Precoding for OFDM: A New Waveform and Its Transceiver Optimization Design

黃彥銘(Yenming Huang)

指導教授 ： 蘇柏青

國立臺灣大學/電機資訊學院/電信工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201900478

摘要

本論文提出了一個循環脈衝形預編碼用於正交分頻多工的新波形，簡稱「CPS-OFDM」，及其收發機最佳化設計。CPS-OFDM以針對個別使用者靈活制定的預編碼器為特色，同時具備低子頻帶外散射（low out-of-subband emission）和低峰均功率比（low peak-to-average power ratio）的優點，這是第五代行動通訊系統（5G）中的各樣場景，如分散式頻譜存取、新型用戶端設備、高載波頻率通信，皆渴望的兩個主要的實體層訊號特性。與使用加窗或濾波技巧的大部分現有候選波形不同，CPS-OFDM預防了傳送訊號的區塊延展，它會造成額外的區塊間干擾和波封波動，對訊號接收和功率放大器不利。我們構想了一個循環脈衝形預編碼器的原型整形向量（prototype shaping vector）最佳化問題，用來在傳送端可控制子頻帶外散射功率和雜訊增強損害（noise enhancement penalty）的情況下，最小化瞬時功率變異量（variance of instantaneous power）。為了要解決這涉及四階目標函數的最佳化問題，利用了蓋最小化（majorization-minimization）演算法框架。藉由證明所提出之問題的凸性質（convexity），不因輸入資料而變的全域最佳解被保證可經由數次疊代計算後取得。模擬結果呈現了我們所提出的方法，對於第五代行動通訊系統的實際案例，如非同步傳輸（asynchronous transmissions）、混合系統參數（mixed numerologies），有在接收端檢測可靠度和整體頻譜效率上的優勢。

此外，在CPS-OFDM的基礎之上，許多相關的問題也被研究，以進一步在某些實際的第五代行動通訊系統場景中，提升其系統效能。對於一個需要相當高功率放大器效能的低成本機器，一個星座圖整形（constellation shaping）最佳化的方法被提出，可有效地降低CPS-OFDM訊號的立方度量（cubic metric）。為了方便採取不同系統參數的第四代和第五代行動通訊系統在同一個頻帶上共存，或更廣義地說，異質頻譜存取，提出了採用CPS-OFDM傳輸，以重新利用保護頻帶和同時用作頻譜整形的想法。

根據本論文所展示的分析推導、最佳化問題構想、及模擬結果，我們強烈地相信，所提出的CPS-OFDM與其收發機架構，將會成為第五代行動通訊系統及未來最有前途的技術之一。

關鍵字

第五代行動通訊系統 ； 新無線電 ； 新波形 ； 正交分頻多工 ； 離散傅利葉轉換散布正交分頻多工 ； 循環脈衝形預編碼器 ； 低子頻帶外散射 ； 低峰均功率比 ； 瞬時功率變異量 ； 蓋最小化 ； 立方度量 ； 星座圖整形 ； 凸最佳化 ； 收發機設計 ； 異質頻譜存取 ； 植入式廣義分頻多工 ； 頻譜整形

並列摘要

A new circularly pulse-shaped (CPS) precoding orthogonal frequency division multiplexing (OFDM) waveform, or CPS-OFDM for short, and the transceiver optimization design, are proposed in this dissertation. CPS-OFDM characterized by user-specific precoder flexibility possesses the advantages of both low out-of-subband emission (OSBE) and low peak-to-average power ratio (PAPR), which are two major desired physical-layer signal properties for various scenarios in 5G New Radio (NR), including fragmented spectrum access, new types of user equipments (UEs), and communications at high carrier frequencies. As opposed to most of the existing waveform candidates using windowing or filtering techniques, CPS-OFDM prevents block extension that causes extra inter-block interference (IBI) and envelope fluctuation unfriendly to signal reception and power amplifier (PA) efficiency, respectively. An optimization problem of the prototype shaping vector built in the CPS precoder is formulated to minimize the variance of instantaneous power (VIP) with controllable OSBE power (OSBEP) and noise enhancement penalty (NEP). In order to solve the optimization problem involving a quartic objective function, the majorization-minimization (MM) algorithmic framework is exploited. By proving the convexity of the proposed problem, the globally optimal solution invariant of incoming data is guaranteed to be attained via numbers of iterations. Simulation results reveal the advantages of the proposed scheme in terms of detection reliability and spectral efficiency for practical 5G cases such as asynchronous transmissions and mixed numerologies.

In addition, on a foundation of CPS-OFDM, several relevant problems are also studied to further improve the system performance in certain practical 5G NR scenarios. For a low-cost machine demanding a rather high PA efficiency at the transmitter, a constellation shaping optimization method is proposed to effectively reduce the cubic metric (CM) of CPS-OFDM signals. To facilitate the coexistence of 4G and 5G with different numerologies in the same band, or more generally, heterogeneous spectrum access, the idea of adopting CPS-OFDM transmission to reuse the guard bands and at the same time serve as spectrum shaping is introduced.

According to the analytical derivations, the optimization problem formulations, and the simulation results demonstrated in this dissertation, we strongly believe that the proposed CPS-OFDM along with its transceiver architecture will be one of the most promising technologies in 5G and beyond.

並列關鍵字

5G ； New Radio (NR) ； new waveform ； OFDM ； DFT-S-OFDM ； circularly pulse-shaped (CPS) precoding ； low out-of-subband emission (OSBE) ； low peak-to-average power ratio (PAPR) ； variance of instantaneous power (VIP) ； majorization-minimization (MM) ； cubic metric (CM) ； constellation shaping ； convex optimization ； transceiver design ； heterogeneous spectrum access ； embedded-GFDM ； spectrum shaping

參考文獻

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