Group-Wise Scrambling Diversity for Broadcast and Multicast Services in OFDM Cellular System

Broadcast and multicast services in OFDM cellular system provide the ability to transmit the same information from multiple base stations. For the services, cyclic delay diversity (CDD) is one of the promising diversity schemes, since it can be easily applied to any number of base stations. However, there is a problem in that CDD increases frequency selectivity and makes channel estimation more difficult. In this paper, we propose a new diversity scheme that can overcome the problem of CDD. In the proposed scheme, subcarriers are divided into several subcarrier-groups. By rotating phase of each subcarrier-group independently among base stations, the frequency selectivity of the whole band is increased as in the case of CDD. On the other hand, unlike in the case of CDD, the frequency selectivity within each subcarrier-group is not changed. Utilizing this property, channel estimation carried out within each subcarrier-group can avoid the problem of CDD.