As explained before, it is anticipated that MIMO and software radio technologies may play a key role in 4G systems. The use of a MIMO system could significantly increase the data rate but on compared to 3G it could also increase the computational complexity by 1-2 orders of magnitude, depending on the number of antennas. There are several different flavors of MIMO based systems such as MIMO-OFDM (Orthogonal Frequency Division Multiplexing) and MIMO MC-CDMA (Multi-Carrier Code Division Multiple Access). A simplified block diagram of a MIMO-OFDM receiver is shown in Figure 7. MIMO-OFDM combines OFDM and MIMO techniques to realize good spectral efficiency and high throughout. It can transmit OFDM modulated data from multiple antennae simultaneously. The receiver first performs OFDM demodulation then does MIMO decoding to extract data from all the transmit antennae and sub-channels.
In software defined radio technology, a large portion of the radio frequency functionality such as the intermediate frequency (IF) stage, bit-stream processing, modulation/demodulation, and source processing are performed in software running as opposed to the traditional approach of using RF circuits. SDR provides the opportunity to implement multi-mode terminals that can operate at several different frequency ranges. New services and advanced signal processing techniques can be easily implemented and tested using the SDR approach. Its re-programmability allows it to download algorithms on demand, and intelligently adapt radio interfaces to different applications and environments. Both MIMO and SDR are computationally intensive techniques with well structured data-flow and are amenable to stream processing.