適用於多頻帶正交分頻多工系統之通道及多微網衍生干擾對抗技術

Abstract

由於超寬頻通訊系統具有取代家庭與辦公室內高傳輸速率之有線系統的能力而成為極具潛能的新技術。超寬頻技術可提供每秒數億位元的傳輸速率而其涵蓋的範圍可達數公尺。IEEE802.15.3a多頻段正交分頻多工(Multiband OFDM, MB OFDM)系統是眾多超寬頻技術中較新的技術之一，該系統每次傳輸只利用500 MHz的頻寬並且將該頻寬分割成數個更小的副載波，然而MB OFDM之系統效能會受到長延遲擴散通道及多微網間干擾的影響而大幅下降。在本論文中，吾人提出一種具有對抗因長延遲擴散通道產生的載波間干擾(intercarrier interference)及避免其它微網(piconet)干擾之接收機，雖然最小均方差等化器可以改善此ICI問題，然而其複雜度過高不利於被MB OFDM所採用，因此吾人提出「載波間干擾消除輔助決策法」有效改善此一問題。另一方面，為了降低多微網間之干擾， MB OFDM採用四組時頻交錯碼，吾人針對此問題提出「避免干擾傳輸法」，此方法略過被干擾的頻槽(frequency slot)，而只在不受干擾的頻槽傳輸信號，藉以達到避免干擾之目的。吾人藉由電腦模擬驗證上述架構在超寬頻環境中可有效改善位元錯誤率。

Ultra wideband (UWB) communication is a potential new technique for replacing high-speed data cables in homes and offices. UWB technology will be capable of transmitting hundreds of megabits per second over distances of several meters. Multi-band (MB) orthogonal frequency division multiplexing (OFDM) system is one of the most innovative UWB techniques. MB OFDM system utilizes only 500 MHz instantaneous bandwidth and dividing that frequency band into smaller simultaneously transmitted subcarriers. In this thesis, a MB OFDM receiver is proposed, which mitigates the intercarrier interference (ICI) induced by a long delay spread channel and avoids the interference from other piconet, respectively. Performance of a MB OFDM system is typically significantly degraded due to long delay spread channels. Although the minimum mean-square error (MMSE) equalizer can solve this problem, the matrix inverse computation is too complex for the MB OFDM system. To alleviate this problem, the decision-aided ICI canceller is designed to improve the influence of ICI. On the other hand, the four unique time-frequency interleaving codes are adopted to reduce the effect of cochannel interference (CCI) from simultaneously operating piconets (SOP). Furthermore, we proposed an interference avoidance transmission scheme which turns off the collided frequency slots and conveys signal in the interference-free frequency slots. Finally, we evaluate the performance of the proposed system and confirm that it works well in a UWB environment.