H as reference, and the AICH may use the same or different channelization codes. Figure 4.27 with the corresponding 'API part' label illustrates the structure of AP-AICH. The AP-AICH has a part of 4096 chips duration to transmit the AP acquisition indicator (API), followed by a part of 1024 chips duration with no transmission. Equation (4.40b) defines the real-valued symbols ao,A1,...,A31 seen in Figure 4.27, where API, taking the values +1, -1, and 0, are the AP acquisition indicators corre- sponding to the access preamble signature S transmitted by UE and Table 20 in [1] pro- vides the sequence bs,0,...,bs,31. As in the AICH, when the AP-AICH has STTD-based open-loop transmit diversity, STTD encoding applies to each sequence separately before these sequences combine into AICH symbols ao,...,A31. The UMTS Network and Radio Access Technology 4.3.9.8 CPCH Collision Detection/Channel Assignment Indicator Channel As a physical channel, the Collision Detection Channel Assignment Indicator Channel (CD/CA-ICH) carries the CD Indicator (CDI) only if the CA is not active, or CD Indi- cator/CA Indicator (CDI/CAI) at the same time if the CA is active. Figure 4.27 illus- trates the CD/CA-ICH structure with the corresponding label, where the CD/CA-ICH transmits 4096 chips duration, followed by 1024 chips duration without transmission. The same or different channelization codes may apply to the CD/CA-ICH and AP- AICH. As in the preceding indicator channels, when the CD/CA-ICH has STTD-based open- loop transmit diversity, STTD encoding applies to each sequence sepa- rately before these sequences combined into AICH symbols ao,...,A31. Equation (4.41a) defines the real-valued symbols ao,A, shown in Figure non-active CA, where CDI, with values +1, and 0, is the CD indicator corresponding to CD preamble signature S transmitted by the UE. Table 20 in [1] lists the sequence bs,0,...,bs,31. (4.41) Equation (4.41b) defines the real-valued symbols ao,A1,...,A31 when CA is active, where the subscript Si, Sk depend on the indexes i, k ac