加強追蹤結合混合自動重傳機制消除載波間干擾的載波干涉-正交分頻多工系統

Enhanced Chase Combining HARQ Performance of CI-OFDM with ICI Cancellation

吳其恩(Chi-En Wu)

指導教授 ： 林丁丙

國立臺北科技大學/電資學院/電腦與通訊研究所/碩士(2010年)

摘要

因為對於能夠提供高速傳輸的無線通訊系統需求日益漸增，其中正交分頻多工(Orthogonal Frequency Division Multiplexing; OFDM)被廣泛地應用在各種無線通訊系統上，它同時能夠擁有高頻寬效益以及有效抵抗多路徑效應。未來4G系統，如LTE，甚至已選擇使用正交分頻多工來傳輸資訊。
但OFDM仍有些缺點，例如我們同時使用大量載波來進行傳輸，所以會造成高峰值對均值功率比(Peak to Average Power Ratio；PAPR)，這意味著瞬間功率超出功率放大器之線性區域的可能性增加，產生非線性失真的機率會變高，所以需要較好的功率放大器，而這對於手持式裝置將會是一個負擔。
本篇論文把載波干涉(Carrier Interferometry；CI)的概念應用在OFDM，也就是將資料展頻到各個載波上的方法來抑制PAPR。並且探討載波干涉正交分頻多工(Carrier Interferometry-Orthogonal Frequency Division Multiplexing；CI-OFDM)在雷利快速衰落通道下效能分析，將資料展頻到每個載波之上在窄頻干擾(Narrowband Interference；NBI)的情況下可以有頻率分集的好處，但在多重路徑快速衰落通道下，不同資訊符元間的正交性會受到破壞，因此系統效能會受到影響。本篇論文將以理論分析此一系統在雷利快速通道下使用者的位元錯誤率，同時為了改善快速衰落造成的影響，引進了混合自動重傳請求(Hybrid Automatic Repeat Request；HARQ)來降低載波間干擾效應(Inter Carrier Interference；ICI)以提升效能。

關鍵字

正交分頻多工 ； 峰值對均值功率比 ； 載波干涉 ； 載波干涉正交分頻多工 ； 混合自動重傳請求 ； 載波干擾效應

並列摘要

Because of the increasing demands of wireless communication with high-speed transmission, and OFDM has been adopted by a wide variety of application for high spectral efficiency and reliability over multipath fading channels. In the future of 4G systems, LTE has been choosing OFDM to transmit information.
However, OFDM has some drawbacks. For example, OFDM uses a large number of subcarriers to transmit data simultaneously, which will cause the problem of PAPR. It means that we need the better power amplifier because the instantaneous power will exceed the linear region of power amplifier. It will be one burden for mobile phones.
In this thesis, we apply CI concept to OFDM to suppress the PAPR. The data in CI-OFDM system are not only transmitted on the allocated subcarrier but also spreaded on all of subcarriers. Then we analyze the performance of CI-OFDM system in the Rayleigh fast fading channel. Even though we spread them and face the problem of NBI , the symbols will still get the benefit of frequency diversity. However, CI-OFDM system is in fast fading channel today, the orthogonality between the symbols will be destroyed, then the performance will be degraded. In order to eliminate the effect of fast fading, we will use HARQ to overcome this problem and improve the performance.

並列關鍵字

OFDM ； PAPR ； CI ； CI-OFDM ； HARQ ； ICI

參考文獻

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