e us j = 0 in the forward direction, but TD-SCDMA uses joint detection in the reverse direction, which saves about 1 dB, so we use dB. We continue to split the Doppler difference with d = 1 dB, with some subscribers sta- tionary, d = 0 dB, and others moving, d = 2 dB. Our data subscribers are likely to be less mobile, so we set their Doppler factor to d = 0.5 dB. Because of the low-rate power control, TD-SCDMA has less channel overhead, h = 0.1 for voice channels. We consider the overhead insignificant compared with the high-speed data channel, so h = 0 for data. The lower rate of power control means more variation in power levels compared with the optimal values, so we set p = -1.5 dB in the forward direction and p = in the reverse direction, where relative radio signal path changes are greater. Like W-CDMA, the TD-SCDMA speech coder does not have four-rate speech coding for voice activity detection, so we set U to 0.6 for voice. Our data service example has U = 0.2. Without soft handoff, we can use S = 0. Finally, the multipath factor depends heavily on the radio environment, and we are figuring that the densest and busiest areas are fairly hostile, so m = 0.3 is our estimate for this chip rate. In computing the values in Table 30.6 (the same as those in Tables 30.1 and 30.2), we put these parameters into Eqs. (30.1) and (30.2). We used six-sector cells as an ap- proximation for smart antennas used in TD-SCDMA. And we used 12.5 carriers in 20 MHz for these calculations. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Capacity Issues Specific to CDMA Capacity Issues Specific to CDMA TABLE 30.6 TD-SCDMA Summary Parameter values in CDMA capacity estimation Eg/No, Direction Mchps kbits TD-SCDMA voice TD-SCDMA voice TD-SCDMA data 160.0 TD-SCDMA data 160.0 CDMA capacity estimates One-way Forward Reverse erlangs capacity capacity Erlangs Erlangs 