TABLE OF CONTENTS UTRA/TDD is the TDD ( Time Division Duplex) mode of UTRA and is part of the radio access technologies in the IMT-2000 framework defined by the ITU. UTRA/TDD is based on a combination of wideband CDMA and TDMA, also known as TD-CDMA. The technical characteristics of UTRA/FDD and UTRA/TDD have been harmonized by the 3GPP community with respect to carrier spacing, chip rate and frame length. Interworking with GSM radio networks is also ensured. A similar harmonization process was carried out by 3GPP to harmonize UTRA/TDD with the radio standard TD-SCDMA ( Time-Duplex Synchronous CDMA). This was originally developed by the China Academy of Telecommunications Technology (CATT) and adopted by ITU and 3GPP as part of the UMTS Release 4 specifications. TD-SCDMA is also referred to as low-chip rate UTRA/TDD since it uses a chip rate of 1.28 Mcps in 1.6 MHz bandwidth rather than 3.84 Mcps in 5 MHz bandwidth [TR 25.834].
This chapter focuses on the air interface aspects of UTRA/TDD and more precisely on layer 1. Note that the key ideas behind upper radio layers in UTRA/TDD mode (RRC, RLC, BMC, PDCP, MAC) are equivalent to those described for the UTRA/FDD mode in previous chapters.
UTRA/TDD is a combination of TDMA and CDMA using TDD. TDD makes it possible to transmit traffic in uplink and downlink using the same frequency band - it does not require pair bands as in UTRA/FDD. As depicted in Figure...
