A dynamic channel assignment algorithm for a hybrid TDMA/CDMA-TDD interface using the novel TS-opposing technique

It has been demonstrated that code division multiple access (CDMA) provides great flexibility by enabling efficient multiuser access in a cellular env ironment. In addition, time division duplex (TDD) as compared to frequency division duplex (FDD) represents an appropriate method to cater for the asy mmetric use of a duplex channel. However, the TDD technique is subject to a dditional interference mechanisms compared to an FDD system, in particular if neighboring cells require different rates of asymmetry. If TDD is combin ed with an interference limited multiple access technique such as CDMA, the additional interference mechanism represents an important issue. This issu e poses the question of whether a CDMA/TDD air-interface can be used in a c ellular environment. The problems are eased if a hybrid time division multi ple access (TDMA)/CDMA interface (TD-CDMA) is used. The reason for this is that the TDMA component adds another degree of freedom which can be utilize d to avoid interference. This, however, requires special channel assignment techniques. A notable example of a system which uses a TD-CDMA/TDD interfa ce is the Universal Mobile Telecommunications System (UNITS). This paper pr esents a novel centralized dynamic channel assignment (DCA) algorithm for a TD-CDMA/TDD air-interface. The DCA algorithm exploits a new technique whic h is termed "TS-opposing technique." The key result is that the new DCA alg orithm enables neighboring cells to adopt different rates of asymmetry with out a significant capacity loss.