d adapts its phase and amplitude relations to achieve an improvement of 8 dB in signal to in- terference (S/I) over omnidirectional antennas. This is referred to as space division multiple access (SDMA) because it takes advantage of the distance in space among user terminals to reduce interference. 10.4.6 TD-SCDMA dynamic channel allocation While the time slots and code division control intracell interference, TD-SCDMA mini- mizes its intercell interference using four multiple access technologies: TDMA is used by allocating traffic to the least-interfered time slots. FDMA is used by allocating traffic to the least-interfered radio carrier because multiple 1.6-MHz carriers can fit in a radio spectrum of several megahertz. Space division multiple access (SDMA) is enabled through the use of adaptive phased ar- rays, that is, smart antennas. CDMA is used by allocating traffic to the least-interfered code, with 16 codes per time slot. These allocations are done dynamically to optimize radio resources according to the in- terference at the moment. 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. Worldwide CDMA Standards Standards for Cellular Systems 10.4.7 TD-SCDMA joint detection and power control Joint detection (JD), also known as multiuser detection (MUD), is a mathematically complex technology that filters out same-sector CDMA interference more effectively than the PN-code multiplication used in other current CDMA standards. JD uses a training sequence within each time slot so that the receiver can estimate the parame- ters of the radio channel. In TD-SCDMA, the emphasis on time division multiplexing allows the CDMA component to operate at a lower spreading gain. Having only 16 pos- sible codes allows the receiver to do the calculations. The high number of codes used in other 3G CDMA systems would require huge computer processors to perform t