band. To obtain the gain of the VAA, the received baseband signal of the VAA must be forwarded to the master UE and processed centrally there. However, the trans- mission of the baseband signals from the VAA to the master UE requires quite a powerful UWB air interface. Here, two examples of two supplementary UEs with two antennas each are presented. It is assumed that the quantification of the baseband signal needs 12 b for one floating number of the I or Q signal. The sam- pling rates of the baseband signal are 1.28 and 5 MHz, respectively, for these two examples. To forward the baseband signals from the VAAs to the master UE, the data rate needed is calculated as follows. 2.4.1.5 MIMO OFDMA MIMO is a very promising technology to improve the spectrum efficiency. However, because the much broader frequency band will be used, more mul- tipaths will be separated, and thus the conventional single-carrier system will have much higher complexity in MIMO detection. OFDM is a good candidate to solve such problems. Due to the excellent capability of mitigating frequency- selective fading and ISI, OFDM is very suitable for high data rate transmission in wideband wireless channels. Meanwhile, the implementation of OFDM is very simple using IFFT/FFT, and AMC on every subcarrier can theoretically make full use of the spectrum. (Factually, AMC on every subcarrier will consume too much signaling; AMC usually is based on a group of subcarriers, called a chunk in 3GPP, in order to reduce the signaling consumption. The optimal size of a chunk is a trade-off between the AMC efficiency and the signaling consump- tion.) All these features make OFDM very competitive for LTE and B3G systems. Combining OFDM with MIMO, the frequency selective fading MIMO channel can be separated into many flat fading MIMO subchannels, and thus MIMO detection can be simplified. On the other hand, the dynamic range of the service data rate is quite large (e.g., from several kilobits per second to 100 Mb/s) and flexible multiple access (MA) methods are nec