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To: D. Newberry who wrote (10947)	5/28/2000 2:31:00 PM
From: mightylakers	Read Replies (1) \| Respond to of 13582

Hi DN, since you are not quite satisfied with the answer, here is the CDG white paper regarding DS and MC mode. cdg.org And here's the part about the BW efficient etc. The myths and the facts about chip rate The debate about cdma2000 and WCDMA convergence has been based on the fact that these CDMA-based proposals have certain parameter definitions that present an opportunity for compromise. The most discussed and debated parameter is the system chip rate. WCDMA uses a chip rate value of 4.096 Mbps. cdma200 uses 3.6864 Mbps. WCDMA proponents liken the higher rate to more horse power and claim the lower cdma2000 rate degrades performance. This falsity requires clarification. Deployment scenarios in various bands First, WCDMA proponents claim that the WCDMA chip rate provides as much as a 10% capacity improvement over that of cdma2000. This should be examined under a realistic scenario of how the technology will be deployed, and must include all factors affecting system performance. While some operators will deploy 3G in as little as 5 MHz of spectrum many will use allocations of 10, 15, or 20 MHz. This is important since it is the usable spectrum, in conjunction with chip rate, which affects capacity. Figures 1-3 illustrate the deployment scenarios for cdma2000 and WCDMA in 10, 15, and 20 MHz bands respectively. Even with the required guard bands as verified in today?s operational cdmaOne systems, greater overall capacity is achieved with a mixture of cdma2000 1X and 3X channels as compared with using WCDMA channels. With that configuration it can be shown that up to 13% capacity improvement is achievable in a 20 MHz deployment ( 1). . Figure 1 Deployment scenario for cdma2000 and WCDMA in a 2x 10 MHz operation Figure 2. Deployment scenario for cdma2000 and WCDMA in a 2x 15 MHz operation Figure 3. Deployment scenario for cdma2000 and WCDMA in a 2x 20 MHz operation Examining chip rate in context with other characteristics Second, chip rate alone does not determine overall system capacity. To build on the automobile analogy referenced earlier, assuming chip rate is the only factor affecting capacity is like assuming tire pressure is the only thing affecting gas mileage. One of the main parameters in determining the capacity of a CDMA system is the ratio of energy per information bit to noise power spectrum density (Eb/No) required to achieve certain QoS (Quality of Service) requirements such as frame or bit error rate. The required Eb/No value depends on frame structure, coding and modulation characteristics, diversity techniques and channel model. The small difference in chip rate between 3.6864 Mcps and 4.096 Mcps has negligible impact on the Eb/No requirement. Instead, other system designs such as channel structure (including pilot structure), power control mechanisms, diversity techniques, handoff efficiency, and base station synchronization have a much greater impact on system capacity. The impact of system design on capacity is illustrated in Table 1, where the normalized spectrum efficiency in Erlangs/MHz/cell for voice services in a vehicular environment is shown, taken from the cdma2000 and the UTRA (WCDMA) RTT ( 2 ). Table 1 also contains the simulation results from the RTT evaluation report submitted by the Chinese evaluation group. We can see that a larger chip rate does NOT translate into higher spectrum efficiency. Table 1. Spectrum efficiency for voice in a vehicular environment: cdma2000 & WCDMA System Chip Rate (Mcps) Spectrum Efficiency for Forward Link/Reverse Link * (Erlangs/MHz/ Omni cell) Self evaluation Chinese evaluation cdma2000 3.6864 36.7/29 26.4/27.2 UTRA WCDMA 4.096 17.8/22.4 18.4/22 *Higher Erlangs/MHz/Omni Cell equates to greater efficiency Consideration of power emissions Finally, what proponents of the WCDMA chip rate often overlook are the negative effects on spectrum use and power emissions by using the higher value chip rate. The CDMA air interface signal of IMT-2000 needs to fit into a 5 MHz spectrum to comply with different frequency plans around the world. For example, if deployed in a 5 MHz spectrum such as in the D, E, F North American PCS blocks, the WCDMA system as specified currently cannot meet the FCC out-of-band emission requirements. All major wireless technologies use guard bands to separate their signal spectra from those of services in adjacent bands. It is unreasonable to assume that WCDMA can operate without such guard band protection. For instance, the guard band used to separate IS-95 CDMA from TDMA/AMPS is 270 KHz on each side; the guard band used to separate DECT from adjacent service bands is 2.396 MHz to the lower band, and 1.052 MHz to the upper band. This issue is particularly significant for the PDC systems in Japan, as well as anywhere there is another service operating in the band adjacent to the IMT-2000 band. WCDMA advocates propose using more complex filters to address this. While in theory such an approach can be conceived, the required filter is hard to realize within a 5 MHz bandwidth ( 3 ). Essentially, the purported 10% capacity gain is not realizable in practical deployments that in many markets need to consider adjacent channel interference or FCC power emission requirements ? not a realistic solution for operators. In summary, chip rate is not a simple issue with a direct cause and effect relationship. More is not necessarily better. cdma2000 enables 3G services without the deployment risks and cost of WCDMA.