se the smart antenna cannot eliminate the side lobe perfectly. If joint detection can take into account this kind of interference and eliminate it, then SDMA can obtain higher efficiency. Furthermore, if joint detection can eliminate the intercell interference from the neighboring cells, then the system capacity and spectrum efficiency will be improved greatly. Thus, the enhancement of joint detection has potential for improving the system performance. 2.4.1.3 Higher Spreading Factor and Chip Rate The potential benefits of higher chip rate include system-level gains from trunking efficiency, link-level gains from the ability to better resolve channel paths, the abil- ity to support more accurate location services, higher peak bit rate and cell through- put, and an improved ability to reject narrowband interferers. Thus, with a higher spreading factor and chip rate-for example, SF = 32 and 2.56 Mc/s-more gain from spreading processing, multipath resolution, and interference elimination can be obtained for TD-SCDMA, and better system performance can be expected. The benefit of 7.68 Mc/s for UTRA TDD has been investigated in detail. Therefore, a higher spreading factor and higher chip rate TD-SCDMA can provide a possible solution for further improving the system performance. 2.4.1.4 Virtual Antenna Array Usually, due to limited size and cost, it is difficult to mount multiple antennas at the UE. By using a virtual antenna array (VAA), several idle UEs near the master UE can cooperate to work for the master UE and construct a VAA to improve the © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology system coverage and data-transmission capability. When the distance among UEs is quite large compared to the wavelength, fading on the antennas of VAA is inde- pendent and thus the spatial multiplexing and diversity gain can be exploited to improve the system performance. The connection among UEs can be built through Bluetooth or ultrawideband (UWB) technology in a free-frequency 