Research On MIMO Transmission Strategy With Unknown Channel Rank

In the past few decades,satellite communication has become a research hotspot after land mobile communication due to its advantages of wide coverage,unlimited geographical conditions,reliability and stability.However,with the increasing demand for data transmission,how to further increase the transmission rate of satellite communications has become the focus of research at this stage.Due to the remarkable success of MIMO technology on the land side,more and more scholars are devoted to the research of satellite MIMO systems.In satellite communication,the light-of-sight component of signal occupies a large proportion,and there are very few scatterers around the satellite,which leads to a strong correlation between the satellite MIMO channels.At present,mature satellite MIMO technologies mainly include single-satellite polarized MIMO and multi-satellite distributed MIMO systems,where the distributed MIMO system adjusts the phase by optimizing the antenna distance configuration to ensure the full rank of the channel.However,the changes in the environment caused by terminal mobility and the random disturbance of the satellite channel phase by the atmosphere will change the rank of the satellite MIMO system,which poses a huge challenge to the stability of the satellite MIMO system.In addition,due to the large transmission delay of the satellite link,the feasibility of feeding back channel state information to the transmitter is not strong.Therefore,the satellite MIMO system is faced with the problem of indeterminate rank of the channel matrix.If conservative transmission is performed according to the lowest rank of the channel,there is obviously the possibility of wasting channel freedom;if more aggressive transmission is performed according to a higher rank,then there is the current channel It may not be supported,so that the receiver cannot be successfully detected.How to find a better balance between the two,so as to achieve higher rate transmission is a problem that has certain challenges in theory and also has important practical value.In order to deal with the above problems,our core idea is to adopt opportunistic transmission,that is,when the channel rank is high,multiple data streams can be transmitted,and when the channel rank is low,it does not affect the reception of the core data stream.This is mainly achieved through opportunistic ZF(Zero Forcing,zero forcing)transmission.Specifically,this paper uses the keyhole channel model to describe the unknown channel rank,and on the premise that the channel rank is unknown but the transmitter can acquire part of the channel knowledge,an opportunistic ZF transmission strategy that does not depend on the size of the channel rank is proposed.Secondly,in order to further improve the capacity performance of the opportunistic ZF strategy at low and medium signal-tonoise ratio,combined with the probability distribution of the channel rank size,it is optimized from the perspective of data flow power allocation;finally,the channel vector ambiguity is analyzed against the opportunity The impact of the performance of the ZF transmission strategy.Through the simulation of the system capacity,it is verified that the opportunistic ZF transmission strategy has a low dependence on the channel rank size.It can adapt to the change of the channel.When the channel conditions become better,it can make full use of the spatial freedom of the MIMO system to realize the opportunistic transmission.Therefore,this strategy has a greater equivalent degree of freedom gain during the entire channel change process.And when the channel vector ambiguity is relatively low,the performance of this strategy can still be effectively guaranteed.The research results of this paper have great guiding significance and practical application value for the reliable transmission of data streams in satellite MIMO systems.