跳到主要內容

臺灣博碩士論文加值系統

(44.200.27.215) 您好!臺灣時間:2024/04/24 18:24
字體大小: 字級放大   字級縮小   預設字形  
回查詢結果 :::

詳目顯示

我願授權國圖
: 
twitterline
研究生:陳俊任
研究生(外文):CHUN JEN, CHEN
論文名稱:WCDMA系統中消除OVSF所造成內部與外部破碎問題之最佳化演算法
論文名稱(外文):Optimal algorithms in eliminating internal and external fragmentation of OVSF codes in WCDMA system with single code
指導教授:李端興李端興引用關係
指導教授(外文):Duan-Shin Lee
學位類別:碩士
校院名稱:國立清華大學
系所名稱:資訊工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2003
畢業學年度:91
語文別:英文
論文頁數:71
中文關鍵詞:3GOVSF外部破碎內部破碎WCDMA
外文關鍵詞:3GWCDMAOVSFcode blockingfragmentation
相關次數:
  • 被引用被引用:0
  • 點閱點閱:170
  • 評分評分:
  • 下載下載:0
  • 收藏至我的研究室書目清單書目收藏:0
在下一代3G無線通訊系統裡,可預期的將會有大量封包資料,為了提供混和語音資料的多媒體應用,系統將必須能提供不同的資料需求速度給不同的使用者,依照使用者傳送的資料種類,如:realtime traffic、best effort traffic等,給予不同的服務品質保證,以規劃較好的頻譜使用效率。在direct-sequence(DS)WCDMA中,每位使用者將被給予一個相互正交且唯一的碼(code sequence),不同於以往IS-95 2G CDMA系統只使用single orthogonal constant-spreading-factor(OCSF),UMTS/IMT2000對不同資料速度需求提出兩種方式:multi-code CDMA(MC-CDMA)和 single orthogonal variable-spreading-factor CDMA(OVSF-CDMA),而OVSF-CDMA因為只使用單一收發器比MC-CDMA降低硬體設計複雜度,又較為一般所採納。
然而,OVSF-CDMA系統先天上有些限制急待克服,其中較為嚴重的問題就是:OVSF code blocking(不同於capacity blocking),因為每位使用者的抵達與離開,符合某種統計的特性,這將使得在這個區域內的OVSF code tree變得破碎,因為分配給每個使用者的碼都是彼此正交的,所以會有可能產生:系統capacity大於使用者需求、但卻因為得不到適合的code,必須拒絕使用者進入系統的情形。這種情形對較高資料需求的使用者而言,更為嚴重。根據模擬結果顯示,假使不做任何重分配正交碼的動作,OVSF-CDMA的頻譜使用效率將損失大約20%,這是非常嚴重的問題,相當於是對每四個已進入系統的正交碼,其中一個便要做重分配才能達到最大的頻譜使用效率。
我們針對過去完全偏向考慮『分配』或『重分配』的作法,提出了兩個全面性考量的最佳化演算法,分別用以解決外部破碎(code blocking)及內部破碎(coarsely quantized data rate)的問題。在保證對每一個使用者都是最小『重分配次數』下,依然能考慮OVSF code tree的結構,減低對未來使用者『分配』的成本,並且加入了用啟發式搜尋來找最佳解的方法,免除了疲憊式計算的負擔,也不需要離線式的手動建立輔助表格,能自己動態產生輔助表格。我們所提出的演算法,能完全消除OVSF可能帶來的code blocking及coarsely quantized data rate 問題,相信對未來推動3G研發實作,能夠有其實質上的應用。

This paper completely eliminates the external and internal fragmentation of OVSF codes at the forward link in 3G WCDMA system. Only assigning a single OVSF code for each user is more preferable than assigning multiple OVSF codes for each user. Since it is an evolution from second-generation wireless CDMA system such as IS-95 and costs less in hardware design and complexity. However, OVSF-CDMA (with single code) has two severe constraints: code blocking (due to fragmenting OVSF code tree by scattered codes) and coarsely quantized data rates (due to that allocated rates are larger than guaranteed rates). To resolve the phenomenon of code blocking (external fragmentation), we contrives two innovative region division algorithms (DRDA, VRDA). Both of the two algorithms entirely eradicate the above external fragmentation, i.e., guarantee no code blocking, and provide flexible region size for rapidly altering arrival rates distribution, without losing fairness. Additionally, VRDA is the first mechanism that not only optimizes the number of OVSF codes that must be reassigned to support a new call but also takes the posterior potential code blocking possibility into account in long-term circumstances. On the other hand, to resolve the phenomenon of coarsely quantized data rates (internal fragmentation), we introduce the concept of group and share codes between group members. Our simulation results demonstrate that V-RDA performs more superiorly, in reducing income/spectrum loss, and number of reassignments, than previously proposed schemes, such as DCA, RDA, CONV, perform. Conclusively, combining VRDA and sharing codes mechanism , i.e., VRDA+, optimizes the bandwidth utilization of allocated/guaranteed rates.

Contents
I Introduction and Motivation 1
II OVSF codes in W-CDMA 6
III External fragmentation 18
IV Internal fragmentation 44
V Performance evaluation and simulation model 50
VI Conclusions and future works 63
VII Appendix 64

[1] 3gpp tr 25.922, v3.2.0, radio resource management strategies, june. 2000.
[2] 3gpp ts 23.107, v3.3.0, qos concept and architecture, june. 2000.
[3] 3gpp ts 25.213(v3.5.0), spreading and modulation(fdd), technical specification(release
1999), technical specification group radio access network, 3gpp, mar. 2001.
[4] K.; Yamamoto U.; Onozato Y. Assarut, R.; Kawanishi. Performance evaluation of
orthogonal variable-spreading-factor code assignment schemes based on umts/imt-2000
in w-cdma. Vehicular Technology Conference, 2002. Proceedings. VTC 2002- Fall. 2002
IEEE 56th, 3:1585 — 1589, 2002.
[5] Y.-C. Tseng C.-M. Chao and L.-C. Wang. Reducing internal and external fragmentations
of ovsf codes in wcdma systems with multiple codes. IEEE Wireless Communications
and Networking Conf. (WCNC), 2003.
[6] M. Nilsson E. Dahlman, B. Gudmundson and J. Skold. Umts/imt-2000 based on wideband
cdma,. IEEE Commun. Mag., 36:70 — 80, 1998.
[7] R. Fantacci and S. Nannicini. Multiple access protocol for integration of variable bit
rate multimedia tra±c in umts/imt-2000 based on wideband cdma. IEEE Journal on
Selected Areas in Communications, 18(8):1441 — 1454, 2000.
[8] Rai Jain. The Art of Computer Systems Performance Analysis: Techniques for Experimental
Design, Measurement, Simulation, and Modeling. John Wiley and Sons,
1991.
[9] T.; Siu K.-Y. Kam, A.C.; Minn. Supporting rate guarantee and fair access for bursty
data tra±c in w-cdma. IEEE Journal on Selected Areas in Communications, 19(11):2121
— 2130, November 2001.
[10] R. Padovani. Reverse link performance of is-95 based cellular systems,. IEEE Personal
Commun., 1:28 — 34, 1994.
[11] D.N. Rouskas, A.N.; Skoutas. Ovsf codes assignment and reassignment at the forward
link of w-cdma 3g systems. Personal, Indoor and Mobile Radio Communications, 5:2404
—2408, 2002.
[12] Thit Minn; Kai-Yeung Siu. Dynamic assignment of orthogonal variable-spreading-factor
codes in w-cdma. IEEE Journal on Selected Areas in Communications, 18(8):1429—1440,
Augest 2000.
[13] Y.-C. Tseng and C.-M. Chao. Code placement and replacement strategies for wideband
cdma ovsf code tree management. IEEE Trans. on Mobile Computing, 1(4):293—302,
Oct.-Dec. 2002.
[14] T. S.P. Yang Yang; Yum. Nonrearrangeable compact assignment of orthogonal variable
spreading factor codes for multi-rate tra±c. Vehicular Technology Conference 2001 Fall.
IEEE VTS 54th, 2:938 — 942, 2001.

QRCODE
 
 
 
 
 
                                                                                                                                                                                                                                                                                                                                                                                                               
第一頁 上一頁 下一頁 最後一頁 top
無相關期刊