Editing UMTS (section)

===== Technical highlights =====
TD-SCDMA uses TDD, in contrast to the FDD scheme used by [[W-CDMA]]. By dynamically adjusting the number of timeslots used for downlink and [[uplink]], the system can more easily accommodate asymmetric traffic with different data rate requirements on downlink and uplink than FDD schemes. Since it does not require paired spectrum for downlink and uplink, spectrum allocation flexibility is also increased. Using the same carrier frequency for uplink and downlink also means that the channel condition is the same on both directions, and the [[base station]] can deduce the downlink channel information from uplink channel estimates, which is helpful to the application of [[beamforming]] techniques.

TD-SCDMA also uses TDMA in addition to the CDMA used in WCDMA. This reduces the number of users in each timeslot, which reduces the implementation complexity of [[multiuser detection]] and beamforming schemes, but the non-continuous transmission also reduces [[coverage (telecommunication)|coverage]] (because of the higher peak power needed), mobility (because of lower [[power control]] frequency) and complicates [[radio resource management]] algorithms.

The "S" in TD-SCDMA stands for "synchronous", which means that uplink signals are synchronized at the base station receiver, achieved by continuous timing adjustments. This reduces the [[Interference (communication)|interference]] between users of the same timeslot using different codes by improving the [[Orthogonality#Telecommunications|orthogonality]] between the codes, therefore increasing system capacity, at the cost of some hardware complexity in achieving uplink synchronization.