From the start the use of the Time Division Duplex (TDD) operation was part of the Universal Terrestrial Radio Access (UTRA) operation to deal with the unpaired spectrum allocations. In Release 99, the 3.84 Mcps TDD mode was included together with the first WCDMA release in the specifications. For the next release, Release 4, the 1.28 Mcps TDD mode was added, known more widely as TD-SCDMA. The motivation for the adoption for a smaller chip rate was the expected equipment complexity especially related to the use of adaptive antenna and joint processing solutions on the network side and thus it was intended to achieve low enough sampling rates together with a low enough chip rate. Later on still another TDD mode with 7.68 Mcps was added. While the 3.84 Mcps and 7.68 Mcps TDD modes failed to achieve significant market deployment, the 1.28 Mcps TDD, or TD-SCDMA, based on the Release 5 version with 3 carrier operation, is widely used and is partly under construction in China. The commercial operation during 2009 is following a few years of a test period and the issuing of 3G licenses in China in early 2009. TD-SCDMA is covered mainly in Release 5 and later versions of the 3GPP 25.221 to 25.225 specifications [1–5]. Only the physical layer specifications are specific to TD-SCDMA (or TDD modes in general), the higher layer specifications are the same as in FDD. This chapter will focus in covering the TD-SCDMA operation. First, ...