rambling. First, each com- plex valued data symbol d(k,i) of equation (4.47) gets spread with a real valued chan- nelization code (k) of length Qk E {1,2,4,8,16}. We then scramble the resulting se- quence by a complex sequence V of length 16. The elements C(k) ; k = 1,...,K; q = 1,...,Qk; of the real valued channelization codes, i.e. The UMTS Network and Radio Access Technology (cc)k1 (4.49) will be taken from the set c={{,-1}. (4.50) cok belong to Orthogonal Variable Spreading Factor (OVSF) codes, which allow mixing in the same time slot channels with different spreading factors while preserving the orthogonality. We define the OVSF codes using the code tree illustrated in Figure 4.47. (k=1) CQ=4_=(1,1,1,1) (k=1) CQ=2 = (1,1) (k=2) (k=1) Q=1 = (k=3) ==1,-1,1,1,-1) (k=2) C Q=2 (1,-1) (k=4) Figure 4.47 Code-tree generating OVSF codes for channelization. Each level in the code tree defines a SF indicated by the value of Q in Figure 4.47. We may not use all codes within the code tree simultaneously in a given time slot. We can use a code in a time slot if and only if no other code on the path from the specific code to the root of the tree, or in the sub-tree below the specific code is used in this time slot. This implies that the number of available codes in a slot depends on the rate and spread- ing factor of each physical channel. The SF goes up to QMAX=16 [7]. 4.5.4 Scrambling Codes Data spreading by a real valued channelization code () of length Qk gets followed by a cell specific complex scrambling sequence V = The elements V1, i = 1,...,16 of the complex valued scrambling codes originates from the complex set Vv=={1,j,-1,-j}. = (4.51) where j denotes the imaginary unit. The UTRA Physical Layer Design We generate a complex scrambling code V from the binary scrambling codes V = of length 16 described in the Annex of [7]. The relation between the elements vand V is given by: = (j)'.v, v, e {1,-1}, i=1,...,16. (4.52) Thus, the elements Vi of the complex scrambling code V have alternating real and imaginary values.