應用於多載波系統上的傳送與接收窗框之設計

Abstract

在多載波系統中常利用到窗框(windowing) 。例如傳送器端常加上窗 框以減少漏頻(spectral leakage) ，或是減少對無線電波(radio frequency) 的干擾(此類干擾稱為egress)。窗框也有應用在接收端以減低無線電波對 多載波系統的干擾(此類干擾稱為ingress)。傳送及接收端若能有效的分 頻來減少egress 或ingress，可增加傳送的速度。 在此研究計畫中，我們將發展一個研究多載波系統窗框設計的平台。我 們將設計具有較好分頻效果的傳送及接收濾波器，以達到最少漏頻、最少干 擾，而得到較高的傳送速度。首先我們將推導一個濾波器收發的平台，以 用來設計可結合窗框的傳送器與接收器。由於理想的窗框的特徵均為頻域 上的特性，濾波器收發的平台非常適合用來分析與推演。我們會利用此一 平台來設計可減少漏頻的傳送系統，當漏頻較少時，有較多的次頻道可用來 傳送而有較高的頻寬效益。另一方面，我們也將設計有最高干擾阻絕性的 接收器，而得到較高的訊號-干擾比。在實際的實現方面，我們會發展具有 低複雜度的實現架構。此研究計畫的成果將可以利用到實際上的收發器窗框 設計，我們將研發可有效降低漏頻與干擾的多載波系統以增加傳送效能。 第一年的計畫中，我們利用濾波器組的平台已成功的推演出可維持各頻 帶正交特性的條件，此條件可利用在後續系統的設計上。我們並已找出傳 送頻譜與傳送濾波器組之間的關聯，此一關聯將有助傳送端漏頻問題的解 決。在第二年及第三年我們將在第一年發展的結果上來研究傳送及接收濾 波器的設計及實現。

Windowing is often applied to multicarrier systems to improve frequency separation among the subcarriers. At the transmitter side better frequency separation leads to a smaller out-of-band spectral leakage and also less interference to radio frequency transmission. At the receiver side better separation gives more suppression of radio frequency interference. As these are frequency based characteristics, a filterbank representation renders a natural and useful framework for formulating the problem. In this research project, we propose a unified filterbank framework to the design of windows for multicarrier systems. The approach used here will be more general: we will consider the so-called subfilters. The use of subfilters have the potential of enhancing the frequency selectivity of the transmitting/receiving filters while maintaining the orthogonality among the subchannels. The characterization of the desired transmitter and receiver--good frequency separation--lies in the frequency domain. The filterbank approach lends itself naturally to frequency domain formulation. Correspondingly, for the transmitter side spectral leakage can be reduced and for the receiver side RFI can be further suppressed. In the first year, we have established the condition for the subfilters that maintain the orthogonality among the subchannels. The condition is essential and is to be incorporated in the design of transceivers later. We have also derived the transmitted spectrum in terms of the transmitting filters. The result will be useful in considering egress emission and the design of transmitting filters. In the second and third year, we will continue on the design of transmitting and receiving filters based on the results obtained in the first year. The results from this research plan will have practical applications in the design of transmitters and receivers for multicarrier systems. We can develop useful transceivers that have less spectral leakage and RFI interference, and achieve a higher transmission rate.