The Relay Design In The Cooperative MIMO Relay System

Multiple inputs and multiple outputs (MIMO) relay cooperativetransmission, as an efficient solution for high data rate and ubiquitouscoverage, is a promising key technology for the next generation of wirelesscommunications. The performance of MIMO relay cooperative system isheavily dependent on the signal processing approaches adopted by relay nodes.Considering the MIMO relay cooperative system with distributed strategy,this thesis focuses on the best signal processing method at relay nodes,analyzes the mechanism of obtaining the diversity gain with multi-relays andderives a unified relaying structure. What’s more, this thesis presents athorough study of two inevitable problems in system’s practical application,and proposes corresponding solutions.Firstly, a space rotation method is proposed to exploit the causing ofmulti-relays diversity gain in MIMO relay cooperative system, and thefunction of signal processing matrices at relay nodes is clearly pointed out. Onthis basis, the thesis derives a unified relaying structure. This structure notonly guarantees the multi-relays diversity gain for the system, and alsosimplifies the design of signal processing matrices in relay nodes. Accordingto this unified relay structure, a new relaying scheme is proposed, which hasbetter system performance compared to other relaying schemes.Secondly, most research literature on the MIMO relay cooperativesystem has been conducted under the assumption that antennas in each nodeare totally uncorrelated. But it is easy to have spatial correlation amongantennas in pratice. So the assumption is extended in this thesis. Compared tothe loss of performance in the system with antennas correlated in relay nodes,the loss of performance caused by antennas correlation in the source anddestination nodes is much greater. And it is pointed out that the MF relayingscheme is most sensitive in all existed relaying schemes. Then this thesis proposes a modified-MF relaying scheme, which has a better performancethan the MF relaying scheme under spatial correlation.Most research literature on the MIMO relay cooperative system alsoassumes that the system has accurate channel state information (CSI). But CSIis always obtained by channel estimation, and channel estimation will bring inchannel estimation error. So the thesis extends this assumption and studies theeffect of channel estimation error on system performance. In order to combatthe channel estimation error, the thesis proposes an effective method from theperspective of hardware designing, which is to increase the number ofantennas in relay nodes. And simulations prove the validity of this method.