d CDMA (TD-SCMDA), 1.28 megachips per second. With a stationary radio path and no multipath, a BER of 10 can be maintained with Eb/No equal to 4.1 dB, a factor of 2.6. Under these conditions, the value of a is 14.8, so a single call at this rate can withstand 14 interferers using this data rate in single-cell-sector environment. Fifteen subscribers using this service will fill a 3G car- rier with a little left over. In the forward direction, we can use orthogonal codes. If we take the bit rate times the FEC rate, then we get 96 kbps, enough for a spreading gain of 32 and too many for a spreading gain greater than 32 on a 3.6844-megachip-per-second carrier. 4 Not only does the forward direction handle twice as many data channels on the 3G carrier, but those data channels also see no interference from the other channels on the same cell sector, so those 32 channels can withstand significant interference from other sectors. If we put the user terminal in motion at 20 km/h, then the Eb/No requirement goes up 2 dB, so the capacity goes down to 10 reverse and 26 forward. The reason for the re- duction in forward capacity is multipath and Doppler interference not eliminated by the orthogonal codes. Increase the speed to 120 km/h, and the Eb/No requirement goes up another 1 dB, the capacity going down to 8 reverse and 16 forward. If we decide to use a higher channel FER and to manage the errors using ARQ, then we would have more delay but have a more efficient channel. The effective Eb/No re- quirement goes down to 3.2 dB, a factor of 2.1, even counting the extra packets. The re- verse capacity goes up to 19, whereas forward capacity remains 32 with orthogonal codes. At 20 km/h, the Eb/No requirement is 3.8 dB, and reverse capacity goes down 16, and at 120 km/h, the Eb/No requirement is 4.8 dB, so reverse capacity goes down to 13. The forward capacity remains 32 even at the higher speeds, although the resistance to other interference goes down. Lengthening the interleaving from 10 to 80 ms reduces the Eb/No about 1 dB, S