Evolved Macro-Diversity: CDMA2000 and UMTS
Macro-diversity typically means a special communication mode between a single mobile station and multiple base stations in a cellular network. It has been in CDMA standards as soft handoff since the beginning. The people in the industry usually think "soft handoff" and "macro-diversity" are interchangeable in most scenarios. Recently it has been employed for CDMA2000 BCMCS and UMTS MBS too. The basic idea is to coordinate multiple base stations to deliver the same data stream to a mobile receiver in the down links and receive the signals from a mobile station from multiple base stations. Macro-diversity is possible for CDMA soft handoff because there is no hybrid automatic repeat request (HARQ) for voice data and no fast retransmission is necessary due to the strict delay requirement of voice service. The benefits of doing soft handoff on voice service include reduced transmission power and seamless mobility. On the other hand, it also challenges the mobile station...