This Article 
 Bibliographic References 
 Add to: 
Code Placement and Replacement Schemes for WCDMA Rotated-OVSF Code Tree Management
March 2006 (vol. 5 no. 3)
pp. 224-239
Orthogonal variable spreading factor (OVSF) channelization codes are widely used to provide variable data rates for supporting different bandwidth requirements in wideband code division multiple access (WCDMA) systems. Many novel works in the literature have intensively investigated code placement and replacement schemes in OVSF code trees to reduce the code blocking probability and the code reassignment cost. In this paper, we introduce a new code tree structure, namely, a rotated-orthogonal variable spreading factor (ROVSF) code tree, whose code capacity is the same as that of the traditional OVSF code tree. This work addresses both code placement and replacement schemes in the ROVSF code tree system, where ROVSF codes can be used at the forward link of WCDMA systems. Some valuable properties of the developed ROVSF code tree are presented to develop code placement/replacement schemes with lower code blocking probability and less code reassignment cost. The main contribution of our scheme is to identify linear-code chains (LCCs) and nonlinear-code trees (NCTs) in the ROVSF code tree. This work exploits the unsequence property of linear-code chains to design a new code placement and replacement mechanism. Our code placement/replacement schemes initially attempt to allocate request codes on LCCs and, then, to allocate them to NCTs. Using LCCs with the unsequence property allows us to efficiently reduce the code blocking probability and the code reassignment cost. Extensive simulations are conducted to illustrate that our code placement/replacement results based on the ROVSF code tree actually improve the code blocking probability and the code reassignment cost.

[1] F. Adachi, M. Sawahashi, and H. Suda, “Wideband DS-CDMA for Next-Generation Mobile Communication Systems,” IEEE Comm. Magazine, vol. 36, no. 9, pp. 56-69, Sept. 1998.
[2] A. Baier, U.C. Fiebig, W. Granzow, W. Koch, P. Teder, and J. Thielecke, “Design Study for a CDMA-Based Third-Generation Mobile Radio System,” IEEE J. Selected Areas in Comm., vol. 12, no. 4, pp. 733-743, May 1994.
[3] C.M. Chao, Y.C. Tseng, and L.C. Wang, “Reducing Internal and External Fragmentations of OVSF Codes in WCDMA Systems with Multiple Codes,” Proc. IEEE Wireless Comm. and Networking Conf., vol. 1, pp. 693-698, 2003.
[4] J.C. Chen and W.S. Chen, “Implementation of an Efficient Channelization Code Assignment Algorithm in 3G WCDMA,” Proc. Nat'l Computer Symp., pp. E237-E244, 2001.
[5] W.T. Chen, Y.P. Wu, and H.C. Hsiao, “A Novel Code Assignment Scheme for W-CDMA Systems,” Proc. IEEE Vehicular Technology Conf., vol. 2, pp. 1182-1186, Fall 2001.
[6] Y.-S. Chen, T.-C. Kao, and J.-P. Sheu, “A Mobile Learning System for Scaffolding Bird Watching Learning,” J. Computer Assisted Learning, vol. 19, no. 3, pp. 347-359, Sept. 2003.
[7] Y.-S. Chen, T.-C. Kao, G.-J. Yu, and J.-P. Sheu, “A Mobile Butterfly-Watching Learning System for Supporting Independent Learning,” Proc. IEEE Int'l Workshop Wireless and Mobile Technologies in Education (IEEE WMTE 2004), pp. 11-18, Mar. 2004.
[8] R.G. Cheng and P. Lin, “OVSF Code Channel Assignment for IMT-2000,” Proc. IEEE Vehicular Technology Conf., vol. 3, pp. 2188-2192, Spring 2000.
[9] E. Dahlman, B. Gudmundson, M. Nilsson, and J. Skold, “UMTS/IMT-2000 Based on Wideband CDMA,” IEEE Comm. Magazine, vol. 36, pp. 70-80, Sept. 1998.
[10] M. Dell'Amico, M.L. Merani, and F. Maffioli, “Efficient Algorithms for the Assignment of OVSF Codes in Wideband CDMA,” Proc. IEEE Int'l Conf. Comm. (ICC '02), vol. 5, pp. 3055-3060, Apr. 2002.
[11] R. Fantacci and S. Nannicini, “Multiple Access Protocol for Integration of Variable Bit Rate Multimedia Traffic in UMTS/IMT-2000 Based on Wideband CDMA,” IEEE J. Selected Areas in Comm., vol. 18, no. 8, pp. 1441-1454, Aug. 2000.
[12] V.K. Garg, IS-95 CDMA and cdma2000: Cellular/PCS Systems Implementation. New Jersey: Prentice Hall, Dec. 1999
[13] H. Holma and A. Toskala, WCDMA for UMTS: Radio Access for Third Generation Mobile Comm., second ed. New York: John Wiley & Sons, Sept. 2002.
[14] T. Minn and K.Y. Siu, “Dynamic Assignment of Orthogonal Variable-Spreading-Factor Codes in W-CDMA,” IEEE J. Selected Areas in Comm., vol. 18, no. 8, pp. 1429-1440, Aug. 2000.
[15] Third Generation Partnership Project, Technical Specification Group Radio Access Network, “Spreading and Modulation,” technical report, http:/, 1999.
[16] T.S. Rappaport, Wireless Communications: Principles and Practice, second ed. Prentice Hall, Dec. 2001.
[17] A.N. Rouskas and D.N. Skoutas, “OVSF Codes Assignment and Reassignment at the Forward Link of W-CDMA 3G Systems,” Proc. 13th IEEE Int'l Symp. Personal, Indoor, and Mobile Radio Comm. (PIMRC '02), vol. 5, pp. 2404-2408, Sept. 2002.
[18] L.F. Tsaur and D.C. Lee, “Symbol Rate Adaptation and Blind Rate Detection Using FOSSIL (Forest for OVSF-Sequence-Set-Inducing Lineages),” Proc. IEEE Int'l Conf. Comm., vol. 6, pp. 1754-1759, 2001.
[19] Y.C. Tseng and C.M. Chao, “Code Placement and Replacement Strategies for Wideband CDMA OVSF Code Tree Management,” IEEE Trans. Mobile Computing, vol. 1, no. 4, pp. 293-302, Oct.-Dec. 2002.

Index Terms:
Wireless communication, code assignment, code reassignment, OVSF, WCDMA.
Yuh-Shyan Chen, Ting-Lung Lin, "Code Placement and Replacement Schemes for WCDMA Rotated-OVSF Code Tree Management," IEEE Transactions on Mobile Computing, vol. 5, no. 3, pp. 224-239, March 2006, doi:10.1109/TMC.2006.30
Usage of this product signifies your acceptance of the Terms of Use.