Research On Technology Of MIMO System Receiver Under The Condition Of Unknown Space-time Scheme

Multiple input multiple output(MIMO)system is a new kind of wireless communication technology.Because of its obvious advantages in dealing with the contradiction between limit frequency resource and high speed communication,MIMO has received extensive attention and has been widely used.The research on technology of receiving for MIMO systems under the condition of unknown space-time scheme has important economic and military value.In this paper,we study the theory and method of receiving for MIMO systems based on the analysis of the MIMO systems structure,the characteristics of space-time block codes and technical requirements.The main contents and results are as follows:(1)In order to solve the problem of detecting the number of transmit antennas in MIMO systems with multi-path channel,we analyze the invalidation of presenting model and transform the MIMO multi-path channel model into virtual channel matrix to create the model of detecting the number of transmit antennas in MIMO systems with multi-path channel.Then,the result of least eigen-value of covariance in random matrix theory is applied to the proof,which shows that the least eigen-value of channel covariance,whose element obeys the Rayleigh distribution,converges in distribution to the Tracy-Widom law TW2.The effect on detecting the number of transmit antennas of this property is analyzed and an improved algorithm based on RMT,which could detect the number of transmit antennas in MIMO systems with multi-path channel,is proposed.At last,the simulation shows that compared with the RMT algorithm the improved algorithm has better performance,in the condition of low SNR and small data size.(2)To solve this problem of detecting the number of transmit antennas in MIMO systems with time-varying channel,a model is established according to the auto-correlation property of time-varying channel.The effect of disturbance term on the rank of channel covariance is analyzed and the principle of selecting the number of samples for the detection algorithm is obtained.The random matrix theory proves the distribution of the largest eigen-value of noise sample covariance matrix.By using the central limit theorem,the distribution of mean of eigen-values is acquired.An algorithm based on the mean of eigen-values is proposed to detect the number of transmit antennas in MIMO systems with time-varying channel.At last,a series of simulations confirm the validity and advantage of the proposed algorithm.(3)The recognition of space-time block code is defined as recognizing the coding type based on the received signal with a known coding set,which is a key research issue for receiving of MIMO systems under the condition of unknown space-time scheme.One of the most important algorithms is Code Parameter recognition algorithm whose penalty function could impact the performance of recognition.Considering the improved Akaike Information Criterion and the theory of hypothesis test,the choice of penalty function is discussed by numerical analysis.An improved Code Parameter recognition algorithm is proposed,which is almost no increase in computational complexity.Simulation shows that,compared with the original algorithm,the performance of improved algorithm is better for the case of low Signal to Noise Ratio and small data size.And it also has good robustness on different kinds of modulation.(4)The analysis of space-time block code parameter is defined as estimating the coding parameter based on the received signal with an unknown coding set.The model of space-time block code and the receiving signal model are discussed.The mathematic relationship between the rank of covariance matrix of receiving signals and the code parameter is revealed.Making use of the distribution of maximum eigenvalue of noise subspace in random matrix theory,the rank of covariance matrix could be exactly estimated,and then the code parameter could be obtained.Simulation results show that the proposed algorithm could not only estimate the space-time block code parameter,but also recognize the first symbol of the code under the condition of unknown coding set.(5)In order to solve the problem of detection of MIMO systems under the condition of unknown chnannel information,we implement the criterion of maximum-likelihood sequence detection and derive the formulas to get a model based on semidefinite relaxation.Due to this model the rank of SDR solution equals to the transmit antennas.Because the rank of SDR solution is greater than 1,a new method is proposed which uses the SDR solution to approximate the solution of the original problem.Besides,the proposed method could judge the number of detection sequence adaptively and reduce constrains number and the number of solving SDR.Therefore,the computation complexity of proposed method has linear relationship with the number of transmit antennas.At last,simulation results indicate that compared with Rank-1 algorithm,the proposed detector could provide the same bit error performance with decrease of computation cost.The results also validate the linear relationship between the computation complexity and the number of transmit antennas.(6)In order to solve the problem of decoding of orthogonal space-time block codes in MIMO systems under the condition of unknown chnannel information,,we constrain the inequalities between the diagonal elements of matrix and transform the scale of the matrix.A semidefinite relaxation model based on bound constrained is proposed and a kind of randomization method to approximate the decoding solution is also proposed.Through analysis,the performance of proposed method is equivalent to semidefinite relaxation model based on virtually antipodal,but the computation complexity of the method does not change with the increase of modulation order and the advantage is obvious for QAM signal whose modulation order is not less than 16.Another advantage of the method is that it could apply to QAM signal whose modulation order is not equal to 4~Q.The simulation validates the equivalent performance of two methods.Result shows that the computation complexity is much less and the advantage is more obvious with the increase of the decoding length.