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To: DaveMG who wrote (19630)12/13/1998 10:54:00 AM
From: Clarksterh  Read Replies (1) of 152472
 
Dave - 'Multi-carrier' is a reference to how a current IS-95 system is upgraded to CDMA-2000 in a frequency planning sense:

1) If tomorrow CDMA-2000 were approved, but no new spectrum were allocated, the current PCS operator cannot just drop 9 (for example) contiguous IS-95 chip rates and move to three contiguous 3.6x chip rate systems. The current handset do not recognize 3.6x chip rates nor would they recognize all of the CDMA-2000 protocols - i.e. they are not forward compatible.

2) But this is not an insurmountable problem. By using a multiple of the same chip rate they can switch over gradually. Thus, initially the service providers would start handing out CDMA-2000 phones which would work even though there was no CDMA-2000 carrier. The CDMA-2000 phones would be backwards compatible with IS-95 and thus would work, although without any of the 3g capabilities. When there were enough CDMA-2000 phones in use, the service providers could designate that one of the IS-95 channels is now CDMA-2000, albeit without the full performance because the chip rate is too low. There is no need to find more spectrum since it uses exactly the same amount of spectrum as the carrier it replaced.

3) As more and more users migrate to CDMA-2000, from IS-95, the service provider can turn over other IS-95 carriers until eventually there are three contiguous CDMA-2000 narrow channels (each with their own carrier). The service provider can now merge all of these together into one carrier with a 3.6x chip rate because it is a multiple of the original IS-95 chip rate. This merging is very efficient since it uses exactly the same amount of spectrum, but now provides full 3g service.

Clark

PS I suspect that there is yet another benefit, besides ease-of-upgrade, of the 'multiple carriers' scenario. For narrowband communications (i.e. normal phones) the slower chip rate may actually be more efficient in some scenarios (such as rake receivers dealing with multipath). Thus, even after everything is CDMA-2000 there may still be cases where there are three CDMA-2000 narrowband channels instead of one 3.6x chip rate channel.

Clark
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