"why should a Global standard be harmonized to a minority (i.e., the chip rate for IS-95 operators, as there are not that many compared to TDMA based systems)?"
Why not? Since it has nothing to do with TDMA, and thus there is no "synchronization" to worry about there, why not include the estimated 100 million CDMA subscribers that will be around by the time 3G is important? Also, it is a superior system.
"I heard from a reliable source that in a Korean conference recently a cdma2000 champion said that the BST connection could be asynchronous. Is this the give (if it is true)?"
QCOM has covered this in their white paper:
Principle # 3 - Synchronous base station transmission of a shared, time-shifted code-division continuous pilot should be used on each forward beam
CDMA technology has successfully benefited by keeping base stations synchronized to a common time reference. The Global Positioning Satellite System (GPS) has been utilized for this purpose in cdmaOne deployments. Alternative methods for synchronization are also being investigated and some proposals have been made for use in cdma2000 systems.
The competing W-CDMA proposal stipulates asynchronous base station operation. The rationale for proposing asynchronous systems over synchronous systems has been stated to be 1) to avoid GPS based synchronization methods and 2) to overcome the alleged difficulty of providing an external synchronization source for micro base stations or pico base stations in buildings or underground subway stations. QUALCOMM has participated in discussions on the merits of synchronous versus asynchronous base station approaches. It is well known that, however implemented, synchronized operation yields better CDMA system performance with less mobile station complexity (for example, in handoff scenarios). Further, GPS is the simplest, most economical, accurate and omnipresent source of timing for synchronization and frequency maintenance. Synchronization schemes other than GPS have been proposed and can be deployed to remove any GPS related issues. However, some companies are still insisting on asynchronous operation to the exclusion of synchronous operation.
Conclusion: QUALCOMM believes that the third generation standard should be based upon synchronous operation. While there are several possible approaches for synchronous systems, the cdmaOne approach works very well and has been extensively deployed. Further adoption will maintain compatibility and minimize developmental risks, while achieving low cost.
In addition, QUALCOMM believes that Code-Division Multiplexed (CDM) pilots perform better and provide greater flexibility for cell/sector wide beams, for spot beams covering portions of cells/sectors, and for adaptive beams directed at a single mobile station, than the Time-Division-Multiplexed (TDM) pilots currently being proposed for W-CDMA. The W-CDMA proposal uses a dedicated TDM pilot per mobile station, resulting in lower system capacity and exhaustion of forward link codes utilized to support various services. The CDM approach, therefore, yields greater capacity and flexibility.
Conclusion: QUALCOMM believes that technology modifications that yield performance and cost benefits should be adopted wherever possible. Changing from CDM pilots to the W-CDMA approach of TDM pilots has thus far not demonstrated any performance or cost benefit, but to the contrary, adversely impacts capacity and flexibility. QUALCOMM advocates full public comparative testing to prove the purported advantages of this technology modification. |
