0 ms Multiple Switching Point Symmetric DL/UL 10 ms Multiple Switching Point, Asymmetric DL/UL 10 ms Single Switching Point, Asymmetric DL/UL Figure 4.41 The TDD frame structure. 4.4.2 Dedicated Physical Channel (DPCH) 4.4.2.1 Downlink and Uplink Physical Channel Spreading We map DCH onto the dedicated physical channel. The two step spreading of the data The UTRA Physical Layer Design part in the physical channels include channelization and scrambling operations. The first operation transforms every data symbol into a number of chips, thereby increasing the bandwidth of the signal. We call this number of chips per data symbol the Spreading Factor (SF). The second operation scrambles the spread signal through a scrambling code [7]. Downlink physical channels use SF = 16 as described in [7], and operation with a single code with SF = 1 can apply to downlink physical channels. To support higher data rates we can utilize multiple parallel physical channel transmission using different channeli- zation codes. Uplink physical channels have SF ranging from 16 down to 1. In multi-code transmis- sion a UE simultaneously uses two physical channels per time slot maximum. These parallel physical channels transmit using different channelization codes [7]. 4.4.3 Burst Types The two types of dedicated physical channel bursts, i.e. Burst1 (B1) and Burst2 (B2), consist of two data symbol fields, a midamble and a guard period. Burst1 because of its longer midamble of 512 chips, suits the uplink better by allowing up to 16 channel es- timations. Burst2, which has only 256 chips, applies more to the downlink. We can summarize the burst use as follows: Burst1 Burst2 Uplink Independent of the number of active When bursts within a time slot are users in one time slot allocated to < 4 users Downlink Independent of the number of active Independent of the number of active users in one time slot users in one time slot Burst1 has data fields of 976 chips, whereas Burst2 has data fields of 1104 chips. The corresponding number of symbols depen