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Hi, Soft Handoff provides gains for real-time transmission application, thus, we strongly support it being accepted in the standard. However, system complexity may increase dramatically and H-ARQ may need to be turned off to support Soft Handoff. For non-real-time transmission, the loss may outweigh the benefit by using soft Handoff. Therefore, in cdma2000 1XEV-DO system, virtual soft handoff (or soft switching) is used instead of Soft Handoff. In virtual soft handoff (or soft switching), only one BS in the active list with the best pilot strength transmits at any moment. We think it will provide the following benefit:
1. It provides diversity gain by allowing fast switching of data transmission from BS to another BS. 2. It can fit into both OFDM and OFDMA PHY layer without much change 3. Since only BS is transmitting at any given time, the schedule of the BS can be more flexible and optimized than in SHO (no data synchronization issue to worry about) 4. It can easily support data connection with H-ARQ 5. It won't take up additional air link capacity/resource as in SHO case.
We would like to propose the virtual soft handoff coexist with soft handoff in the standard to provide more flexibility.
Any opinion?
Best regards,
Irving Wang, Ph. D. Director, Standards & 3G Technologies ZTE San Diego
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