Known and novel diversity approaches in a JD-CDMA system concept developed within COST 231

Presently, standards for third generation mobile radio systems are being developed. The main requirements to be met by third generation mobile radio systems are high cellular spectrum efficiency and high flexibility. In this paper, the focus is on high cellular spectrum efficiency, which is difficult to achieve due to the time variance and frequency selectivity of the mobile radio channel and due to interference. It is known that the degrading effects of these adverse characteristics of the mobile radio channel and of interference can be mitigated by diversity. The way how diversity influences cellular spectrum efficiency is derived in general. Diversity techniques applied in mobile radio systems realize combinations of different types of diversity. As a reference point, the types of diversity used in GSM are analyzed since GSM is the most successful standard of second generation mobile radio systems worldwide. In GSM, the potential for diversity enhancement inherent in code division multiple access (CDMA) is not exploited. Within COST 231, a joint detection code division multiple access (JD-CDMA) system concept aiming at third generation mobile radio systems has been developed which introduces a CDMA feature into systems based on TDMA and FDMA like GSM and also advanced TDMA (ATDMA). The gains achievable by different types of diversity in the JD-CDMA system concept are investigated. It is shown that considerable gains can be achieved by different types of antenna diversity and by exploiting the additional diversity potential of CDMA. Therefore, third generation standards should be flexible in order to allow the use of as many types of diversity as possible to enhance the cellular spectrum efficiency.