des, where for compressed frames, each of these codes are associated with a left alternative scrambling code and a right alternative scrambling code. The left alternative scrambling code corresponding to scrambling code k has scrambling code number k + 8192, while the right alternative scrambling code corresponding to scrambling code k has scram- bling code number k + 16 384. When we use alternative scrambling codes for com- pressed frames, left alternative scrambling code applies if n SF/2 and the right alterna- tive scrambling code applies if n SF/2. Upper layers signal the usage of alternative The UMTS Network and Radio Access Technology scrambling code in compressed frames for each physical channel. We use channeliza- tion code Cch,SF,n for non-compressed frames. The set of primary scrambling codes gets further divided into 64 scrambling code groups, each consisting of 8 primary scrambling codes. The jth scrambling code group consists of primary scrambling codes 16x8xj+1 16 X k, where j = 0,...,63 and k = 0,...,7. Each cell receives one and only one primary scrambling code allocation. The primary CCPCH and primary CPICH always use the primary scrambling code to transmit. On the other hand, the other downlink physical channels can use either the primary scrambling code or a secondary scrambling code from the set associated with the primary scrambling code of the cell to transmit. The combination of primary and secondary scrambling codes in one CCTrCH may be possible. However, if the CCTrCH has a DSCH type then all the PDSCH channelization codes that one UE may receive must be under a single scrambling code, i.e. either the primary or a secondary scram- bling code. The scrambling code sequences result from combining two real sequences into a com- plex sequence. We build each of the two real sequences as the position wise modulo 2 sum of 38 400 chip segments of two binary m sequences generated by means of two generator polynomials of degree 18. The resulting sequences thus constitute segments of a set of gold se