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To: SKIP PAUL who wrote (10905)	5/27/2000 4:32:00 PM
From: D. Newberry	Read Replies (2) \| Respond to of 13582

Hi Skip, It would be helpful if you could explain in non technical terms why a GSM operator would find it more economical to go via GPRS to EDGE to WCDMA as opposed to going straight to 1X-MC/HDR. Politics aside. TIA Non-technical? You really want to get me in trouble with the other techies here don't you <g>. I pulled the relevant sections from the IEEE paper that led me to draw my previous conclusions. They are listed below. I would recommend you read it over and reach your own conclusions. That being said, my interpretation of that discussion is this: First, you need to understand how CDMA works. In very very simple terms, the signal is spread out in a pseudo random manner over a fixed bandwidth. (the other end knows the psuedo random sequence for that particular signal so the signal can be captured). CDMAone uses a fairly narrow band. For 3G CDMA, however, the standards dictate that a 5MHZ spectrum be used that will allow for the 144K/384K data rates that are the goals of 3G standards. Both WCDMA and CDMA2000 ultimately achieve these design goals, but each accomplishes those goals in a different fashion. WCDMA uses a contiguous 5MHZ frequency band. This is an efficient way to achieve the 144K/384K data rates. In addition, WCDMA was designed with GSM in mind. In essence, WCDMA was designed to allow handover between CDMA and legacy GSM systems. The framing definition of the WCDMA standard was developed to be compatible with the GSM frame structure so that the relative timing between GSM and WCDMA carriers are maintained. I don't have the technical depth on this subject to make any qualifications on how significant this is to GSM carriers, but clearly the WCDMA was developed with GSM in mind. Legacy CDMAone systems use a narrower band. The WCDMA structure would then be incompatible with this narrow channel alignment, since it utilizes a single 5MHZ wideband frequency. Keep in mind that a nominal 5MHZ band is required to provide 144K/384Kbps transmission. Since CDMAone systems use narrower bands, CDMA2000 uses three of these consecutive IS-95B (CDMAone) bands to provide the necessary spectrum to achieve 3G rates. As such, CDMA2000 is optimized for legacy carriers of CDMAone systems. You might also note from the article below that this is accomplished with a 5 to 10% loss of sprectrum efficiency over WCDMA. The efficiency tradeoff is necessary to achieve backward compatibility with CDMAone. Both standards are based on the fundamentals of spread spectrum (CDMA) technology. Both utilize the Q's IPR. Each standard is a variant of CDMA that was developed for different operating environments. Hope this helps. I am still researching and learning this technology, so comments and discussion are welcome. But for now, time to mow the lawn <g> DN comsoc.org Technical Approaches In the following, we discuss the main technical approaches of WCDMA and cdma2000. These differences apply to the TTA I and TTA II as well. The main differences between WCDMA and cdma2000 systems are chip rate, downlink channel structure, and network synchronization. cdma2000 uses a chip rate of 3.6864 Mc/s for the 5-MHz band allocation with the direct spread downlink and a 1.2288-Mc/s chip rate for the multicarrier downlink [5]. WCDMA uses direct spread with a chip rate of 4.096 Mc/s. The multicarrier approach is motivated by a spectrum overlay of cdma2000 with existing IS-95 carriers. Similar to IS-95B, the spreading codes of cdma2000 are generated using different phase shifts of the same M-sequence. This is possible because of the synchronous network operation. Since WCDMA has an asynchronous network, different long codes rather than different phase shifts of the same code are used for the cell and user separation. The code structure further impacts how code synchronization, cell acquisition, and handover synchronization are performed. The nominal bandwidth for all third-generation proposals is 5-MHz. There are several reasons for choosing this bandwidth. First, data rates of 144 and 384 Kb/s are achievable within 5-MHz bandwidth for third-generation systems and can be provided with reasonable capacity. Even 2-Mb/s peak rate can be provided under limited conditions. Second, lack of spectrum calls for reasonably small minimum spectrum allocation, especially if the system has to be deployed within the existing frequency bands already occupied by the second-generation systems. Third, the large 5-MHz bandwidth can resolve more multipaths than a narrower bandwidth, thus increasing diversity and improving performance. Larger bandwidths of 10, 15, and 20 MHz have been proposed to support highest data rates more effectively. ???. Inter-operability Between GSM and WCDMA. The handover between the WCDMA system and the GSM system, offering worldwide coverage already today, has been one of the main design criteria taken into account in the WCDMA frame timing definition. The GSM compatible multiframe structure, with a superframe multiple of 120 ms, allows similar timing for intersystem measurements as in the GSM system itself. Apparently the needed measurement interval does not need to be as frequent as for GSM terminal operating in a GSM system, as intersystem handover is less critical from intra-system interference point of view. Rather, the compatibility in timing is important that when operating in WCDMA mode, a multimode terminal is able to catch the desired information from the synchronization bursts in the synchronization frame on a GSM carrier with the aid of frequency correction burst. This way the relative timing between a GSM and WCDMA carriers is maintained similar to the timing between two asynchronous GSM carriers. The timing relation between WCDMA channels and GSM channels is indicated in Fig. 36, where the GSM traffic channel and WCDMA channels use similar 120 ms multiframe structure. The GSM frequency correction channel (FCCH) and GSM synchronization channel (SCH) use one slot out of the eight GSM slots in the indicated frames with the FCCH frame with one time slot for FCCH always preceding the SCH frame with one time slot for SCH as indicated in the Fig. 36. Further details on GSM common channel structures can be found in [49]. ???????. cdma2000 Within standardization committee TIA TR45.5, the subcommittee TR45.5.4 was responsible for the selection of the basic cdma2000 concept. Like for all the other wideband CDMA schemes, the goal has been to provide data rates that meet the IMT-2000 performance requirements of at least 144 Kb/s in a vehicular environment, 384 Kb/s in a pedestrian environment, and 2048 Kb/s in an indoor office environment. The main focus of standardization has been providing 144 Kb/s and 384 Kb/s with approximately 5-MHz bandwidth. The main parameters of cdma2000 are listed in Table 5. Bandwidth and Deployment Scenarios -- In the following we highlight the channel structures of cdma2000. Currently there exist two main alternatives for the downlink: multicarrier and direct spread options. The multicarrier approach maintains orthogonality between the cdma2000 and IS-95 carriers [51]. In the downlink this is more important because the power control cannot balance the interfering powers between different layers, as it can in the uplink. As illustrated in Fig. 37, transmission on the multicarrier downlink (nominal 5-MHz band) is achieved by using three consecutive IS-95B carriers10 where each carrier has a chip rate of 1.2288 Mc/s. For the direct spread option, transmission on the downlink is achieved by using a nominal chip rate of 3.6864 Mc/s. The multicarrier approach has been proposed since it might provide easier an overlay with the existing IS-95 systems. This is because without multipath it retains orthogonality with existing IS-95 carriers. However, in certain conditions the spectrum efficiency of multicarrier is 5 to 10 percent worse than direct spread since it can resolve a smaller number of multipath components [51]. Editorial Note: I believe the DS option referenced here did not make it to standards. This is a 1998 paper. The IMT-2000 DS standard adopted is the WCDMA format.