Shu (Marloon) Wang

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...

One key feature of any mobile communication system is to provide a mobility mechanism for mobiles to do fast and seamless switching between serving cells. There are many different handover mechanisms for achieving this goal. They include soft handover, which is mostly used for voice services, and hard handover, which is designed for data services. Hard handovers can be further classified as network-controlled handovers and mobile-based handovers. The interesting thing is if you look at the basic handover or handoff procedures I will explain in the next, you may feel a long-time debate on which entity , base stations or mobiles, should control handover or handoff. Traditionally there is no standardized direct connection between two BTS's, even they both belong to the same BSC. Therefore, there usually are a long outage for a mobile do hard handover. For example, the default forward traffic channel MAC handover scheme of CDMA2000 EV-DO Rev. 0 usually results in 100~200ms ou...