在本碩士論文中，我們探討兩個主題關於第三代行動通訊(3G)，第一個主題是多碼配置(Placement)與重配置(Replacement)的議題。由於WCDMA可以支援高傳輸速率以及可變傳輸速率服務，因為其採用了正交變數展頻因子(Orthogonal Variable Spreading Factor, OVSF)碼來作通道碼，而目前有兩種分配OVSF碼的方法，單碼(Single-Code)和多碼(Multi-Code)，在第一個主題中，我們採用的是多碼分配,為了解決碼碎裂(Code Fragmentation)問題以及降低過多的碼重配置次數，我們提出了一個碼樹(OVSF Code Tree)劃分策略(High Rate Right Most, HRRM)來管理我們的碼樹。另外，我們也將連線需求頻寬做一個調整，使OVSF碼的傳輸速率符合某一個單位的倍率，此方法為UBMC (Unit-Based Multi-Code)。UBMC可以讓每個使用者使用較少的OVSF碼就能滿足需求，也能降低碼碎裂的次數。與現有的多碼配置機制,如最左優先配置(Left-Most)以及擁擠優先配置(Crowded-First)相比較，透過模擬我們可以說明，HRRM以及UBMC兩者配合將有較少的碼碎列情形以及碼重配置次數。在第二個主題裡，我們探討的是SIP (Session Initiation Protocol)在VoIP (Voice Over IP)上的應用。因為SIP將作為3G標準中控制信號通訊協定，也是未來多媒體通訊的技術標準，同時又因為現今VoIP網路電話的興起，所以我們為了要深入了解SIP的信令格式與傳遞規則以及實現一個網路電話環境，於是我們在本論文第二個主題中，建置SIP Server,建立一個SIP Based的網路電話環境，除了使用者在網際網路內能夠互通，也能與傳統電信網路雙向互連，我們也觸及與第三方SIP Server相容性之互通測試。

In this thesis, we discuss two topics about the third generation (3G) mobile communications. In the first topic, we focus on the multi-code placement and replacement issue. Since WCDMA systems use orthogonal variable spreading factor (OVSF) codes as channelization codes, it can support high-rate transmission and variable-bit-rate services. For the OVSF codes, there are two approaches to assign codes, i.e., single-code and multi-code. To solve the code fragmentation problem and to reduce the number of code reassignments, we propose a tree partition policy for managing the OVSF code tree based on the multi-code approach. Furthermore, we modify the multi-code rate using a unit-based method, which enables each multi-code to have fewer codes but a slightly higher rate than what is requested, so as to decrease the number of code fragments. Compared with the left-most and crowded-first algorithms, it turns out that the tree partition policy and the unit-based multi-code method perform better through extensive simulations. In the second topic, we emphasize applications of voice over IP (VoIP) using the session initiation protocol (SIP). It is well known that SIP can be used for singnaling in the 3G cellular systems and has become the standard of the multimedia services in the Internet. Besides, VoIP is very popular in recent years since people can use VoIP phones to communicate, too. Therefore, we want not only to understand how SIP works but also to estabilish a VoIP telephony environment. We shall implement SIP servers so that SIP user agents (UAs) or public-switched telephone network (PSTN) calls can commuincate with each other through the SIP servers. Via a thorough test, we carefully examine the connecting compatibility bwtween our SIP servers and SIP servers of other companies.

[1]Y.C.Tseng and C.M.Chao, ``Code placement and replacement strategies for wideband CDMA OVSF code tree Management,'' IEEE Transactions on Mobile Computing, vol. 1, no. 4, pp. 293--302, Oct.--Dec. 2002.
[2]W.T.Chen, Y.P.Wu, and H.C.Hsiao, ``A novel code assignment scheme for W-CDMA
systems,'' in Proc. IEEE VTC '01, pp. 1182--1186, Oct. 2001.
[3]T.Minn and K.Y.Siu, ``Dynamic assignment of orthogonal variable-spreading-factor codes in W-CDMA,'' IEEE Journal on Selected Areas in Communications, vol. 3, no. 8, pp. 1429--1440, Aug. 2000.
[4]R.Assarut, K.Kawanishi, U.Yamamoto, Y.Onozato, and M.Matsushita, ``Region division assignment of orthogonal variable-spreading-factor codes in W-CDMA,'' in Proc. IEEE VTC '01, pp. 1884--1888,Oct. 2001.
[5]R.Assarut, K.Kawanishi, U.Yamamoto, and Y.Onozato, ``Performance evaluation of orthogonal variable-spreading-factor code assignment schemes in W-CDMA,'' in Proc. IEEE ICC '02, PP. 3050--3054, April.--May. 2002.
[6]A.Rouskas and D.Skoutas, ``OVSF codes assignment and reassignment at the forward link of W-CDMA 3G systems,'' in Proc. IEEE PIMRC '02, pp. 2404--2408, Sept. 2002.
[7]J.C.Chen and W.S.E.Chen, ``Queue-aided BLRU scheme for orthogonal variable-spreading-facotr code assignment in 3G WCDMA,'' in Proc. IEEE PIMRC '03, pp. 74--78, Sept. 2003.
[8]Y.S.Chen and H.C.Chang, ``Multi-code placement and replacement schemes for W-CDMA rotated-OVSF code tree,'' in Proc. IEEE CASS '04, pp. 345--348, May.--June. 2004.
[9]M.D.Amico, F.Maffioli, and M.L.Merani, ``A tree partitioning danamic policy
for OVSF codes assignment in wideband CDMA,'' IEEE Transactions on Wireless Communications, vol. 3, no. 4, pp. 1013--1017, Nov. 2004.
[10]R.G.Cheng and P.Lin, ``OVSF code channel assignment for IMT-2000,''
in Proc. IEEE VTC '00, pp. 2188--2192, May. 2000.
[11]F.Shueh and W.S.E.Chen ``Code assignment for IMT-2000 on forward radio link,'' in Proc. IEEE VTC '01, pp. 906--910, May. 2001.
[12]L.H.Yen and M.C.Tsou, ``An OVSF code assignment scheme utilizing multiple rake combiners for W-CDMA,'' Computer Communications, vol. 27,
no. 16, pp. 1617--1623, Oct. 2004.
[13]C.M.Chao, Y.C.Tseng, and L.C.Wang, ``Reducing internal and external fragmentation of OVSF codes in WCDMA systems with multiple codes,'' in Proc. IEEE WCNC '03, pp. 693--698, March. 2003.
[14]A.Rouskas and I.Athanasakis, ``Assignment of multiple OVSF codes at the downlink in WCDMA,'' in Proc. IEEE PIMRC '04, pp. 454--458, Sept. 2004.
[15]F.Adachi, M.Sawahashi, and K.Okawa, ``Tree-structured generation of orthogonal spreading codes with different lengths for forward link of DS-CDMA mobile radio,'' Electronics Letters, vol. 33, no. 1, pp. 27--28, Jan. 1997.