MIMO techniques for future generation cellular systems (4G)

: The Multiple-Input Multiple-Output (MIMO) techniques are widely proposed as the key technique to enhance the radio channel capacity of cellular systems. This technology can enhance the link quality by using diversity MIMO schemes and/or improve the spectrum efficiency by enabling multi-stream transmission MIMO schemes Ideally, in cellular systems, switching between those two kinds of MIMO schemes is desired for different users or same user experiences different channel conditions, which is called adaptive MIMO. To fully utilize these potential features, MIMO technology should be combined with flexible link adaptation (LA) mechanisms which can map high SINR values into high user data rates and simple receiver structure system which can afford the MIMO signal processing complexity. OFDM is hot candidate for 4G because of its simper receiver structure without complex time equalization. The biggest advantage of the introduction of OFDM is that it can divide the frequency selective channel to a set of parallel of frequency flat channels based on the assumption that the length of CP is greater or equal to the length of the channel impulse response and the channel is invariant within one OFDM symbol time. That is why it is natural for people to think of the possibility of introducing MIMO together with the OFDM. The marriage of MIMO and OFDM is natural and beneficial since OFDM enables support of more antennas and larger bandwidth with a simple equalization and MIMO can increase the capacity (coverage or link quality in other sense) at no cost in frequency. The target of this study is to evaluate the performance of advanced MIMO in 4G scenarios. And hopefully include adaptive MIMO in LA layer as well. In order to do that, more comprehensive studies will be done in both link and system level, in which the more realistic MIMO channel model will be used and imperfections in Tx/Rx will be considered. The effect of different Link Adaptation (LA) and Hybrid Automatic Repeat reQuest (H-ARQ) algorithms will be included in the next step. (Na Wei, Troels B. Sørensen, Preben E. Mogensen & Troels E. Kolding, Nokia Networks)