後三代行動通訊處理器設計(3/3)

在後三代（Beyond 3G）行動通訊系統當中，我們期望這個系統能夠讓許多分散的使用 者在相當不確定的無線通道中傳輸較高速的資料。因此在設計無線傳輸介面時，很重要的 ㄧ件事是讓系統具有高容量的多用戶存取設計來滿足突發型的多媒體資料封包並符合不同 的服務品質（QoS）。 多載波分碼多工（MC-CDMA）是滿足後三代行動系統需求中相當有希望的技術。它 結合了多載波傳輸技術的優點（例如：對於頻率選擇衰減效應的穩健性）以及分碼多工系 統（CDMA）的多用戶存取能力。而且多載波分碼多工相當適合多速率的多媒體資料傳輸。 在這個三年期的計畫當中，我們研究並提出了一個新的在頻域做直接序列分碼多工系 統（DS-CDMA）的多用戶偵測。而正交分頻多工（OFDM）的相位同步化也是我們研究的 問題之一。然後我們提出了在多載波分碼多工系統中（特別是多調分碼多工（MT-CDMA）） 的多用戶偵測設計並且估量了它的效能。為了要使得在多載波分碼多工系統中的射頻資源 分配（RRA）更有效率，我們還提出了綜合傳輸速率、子載波（sub-carrier）、以及傳輸功 率分配的演算法，此演算法還同時具有線性最小均方差（LMMSE）的多用戶偵測技術。除 了考量後三代通訊系統設計的物理層，我們也考量了無線隨意式網路（wireless ad hoc network）的群組問題，這種網路結構將會在下一代無線通訊系統中相當普遍。In the “Beyond 3G” mobile communication systems, it is expected to be capable of delivering higher data rate service for distributed users in extremely unpredictable wireless channel. Thus it would be very important to design air interface that has high capacity multiple-access schemes to transmit burst-type multimedia data packet with different quality-of-service (QoS). Multi-carrier code-division multiple-access (MC-CDMA) has been a promising technique to meet the demand of “Beyond 3G” systems. It combines advantages of multi-carrier transmission such as robustness to frequency-selective fading and multiple-access capabilities of CDMA. In addition, MC-CDMA is suitable for multi-rate multimedia data transmission. In this three-year project, we investigated a novel frequency domain approach for multi-user detection in DS-CDMA systems. Phase synchronization for well-known multi-carrier technique, orthogonal frequency-division multiplexing (OFDM), was studied. Multi-user detection scheme of multi-rate MC-CDMA where we focused on multi-tone CDMA (MT-CDMA) was proposed and the corresponding performance evaluation was given. To make the radio resource allocation (RRA) in MC-CDMA more efficient, we further propose a joint rate, sub-carrier and power allocation algorithm with LMMSE multi-user detection. In addition to the physical layer consideration in “Beyond 3G” receiver design, we also consider wireless ad hoc network clustering issues which may be a widespread network topology in the future generation wireless communication systems