|摘要: ||隨著網路資訊的蓬勃發展與各種有線及無線通訊技術成熟的今日，人們對於網路的依賴與需求也日益劇增，網路通訊技術正在改變人們的溝通、生活及工作模式，WiMAX (IEEE 802.16e) 與LTE (Long Term Evolution)等規約的相繼定訂，都是為了能提供使用者更多且更快的網路服務的。|
本論文針對次世代行動通訊系統中提供更好的效能來討論，並分為三部份，其中第一個部份與第二個部份針對骨幹網路 (Backbone) 作討論，第三個部份針對無線網路 (Wireless) 的部份作討論。
第一個部份，第三代和第四代移動通信中，分碼多工存取 (Code-Division Multiple Access , CDMA) 技術為其重要的技術基礎。CDMA技術具有許多優於其它技術的特點，如在提高系統的容量方面具有顯著的優勢，能夠有效解決移動通信系統之中的抗干擾和抗多徑衰落的問題， CDMA技術與光纖通信能充分發揮其技術本身的優點。
由於傳統發射同步型光分碼多工存取(Optical Code-Division Multiple Access, OCDMA) 同步訊框的設計中，在接收端所收到的功率均假設為同等的大小，也就是在彼此各使用者之間所產生的相互干擾量的能量為相同，但在實際的傳輸情況下，由於在距離的遠近影響了耦合器所接收信號的大小，因此在實際的系統中，必須加入接收端所收信號強弱的變異來考量設計出符合現況的架構。針對此一情形第一部份提出接收同步型訊框格式設計來提升OCDMA 系統的效能。
第三個部份，次世代行動通訊系統中，要讓使用者在戶外及移動下，能夠提供用戶與室內相同甚至更好的網路品質，但在移動及戶外的環境下，訊號經過通道時會受到衰減及雜訊等影響，包括障礙物阻擋所產生之遮蔽衰落(Shadow Fading)、高速移動所產生的都普勒位移和多重路徑所產生之快速衰落(Fast Fading)，以及基地台及移動台所產生之同頻道間干擾問題 (Co-channel Interference, CCI) 與（Other-cell Interference, OCI），這些都會影響到訊號的接收品質，為了能在上述的通道中能得到更好的效能我們在第三個部份提出幾種Pilot與干擾的解決方法。
With the emerging and prosperous development of network information and various communication technology developments in wire and wireless systems, people are increasingly demanding for more network application services and the network service becomes an indispensable service in human’s daily life. With the consecutive introduction of the standards of WiMAX (IEEE 802.16e) and Long Term Evolution (LTE) systems, they will provide the users with higher speed, better service quality.
In this dissertation it will study and discuss the next generation mobile communication systems and their capabilities of providing better system efficiency. It consists of three parts in this dissertation, in the first and second parts we will study the optical fiber networks in backbone and then in part 3 we will discuss pilot design in the mobile wireless communications.
In Part one, Code-division multiple access (CDMA) technology plays an important role in the development of backbone. It possess in CDMA the characteristic better than other techniques such as it has the advantages of providing wide transmission bandwidth, effectively solving the interference and multipath fading problems in mobile wireless communications. The combination of CDMA and the fiber optical communication can enhance the advantages of both techniques.
In the synchronous frame design of the conventional synchronous transmission system, it always assumes that at the receiver end it will receive the same amount of powers from all users, i.e. it assumes that the interference powers of mutual interferences among users are constant, however in actual communication environment, the distance between each user and the receiver is different and this distance difference affects the signal strength received at the optical coupler, it needs in the design of system structure to consider the actual variation in the receiving signal strength so as to have the system structure to meet the actual communication environment. We introduce in the first part the design of a system structure to generate synchronous frames at the receiving end so as to increase the system efficiency.
In Part two, due to it provides the advantages of wide bandwidth and low loss in the fiber optical, the utilization of optical fiber will be the choice for the future transmission medium to provide wide transmission bandwidth and various kinds of services. The maturity of the optical fiber network technology has increased the developments of various optical fiber devices, the prices reduction in the optical amplifiers and laser sources etc. have promoted the wide usage of optical fiber networks. In the laser devices development it is an important issue to have the laser device to provide a stable and wideband wavelength because a stable wavelength can provide more wavelengths to users and enables the increase in the network or system efficiency, stability so that it can meet the requirements of providing high mobility and high data transmission rate in the network. In the Part two of this dissertation we will study the stability of laser sources so as to meet the network requirements of high mobility and high data transmission rate in the network.
In Part three, in the Next Generation mobile communication system, it will provide the users in outdoor and moving environment with the same or better service qualities as the indoor users. When a user is in the moving and outdoor environment, his signal will suffer the fading and noise effects when it transmits through the channel, these effects including the Shadowing Fading as the signal encounters the blocking obstructions, the Doppler Effect due to fast moving and the Fast Fading due to the multipath effect, the Co-channel Interference (CCI) and the Other-cell Interference (OCI) generating from using the same channel frequency in the transmission between the base station and the mobile station, and consequently the receiving signal quality will be affected by these adverse effects. We will in Part three recommends the design of several pilot signals and measures to solve interference issue so as to provide better system performance when signal passes through the channel suffering the above-mentioned fading and noise effects.