In MIMO systems, a transmitter sends multiple streams through multiple transmitting antennas. The transmission flows pass through a channel consisting of all the NtNr paths between the Nt transmitting antennas and Nr receiving antennas. The receiver obtains the signal vector received by the multiple receiving antennas and decodes the received signal vectors into original information. A flat fade MIMO system can be modeled as “Say no to plagiarism”. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original test = Hx + wWhere x and y are transmitted and received signal vectors, respectively, and H and w are the channel matrix and noise vector. , respectively. xa has a dimension of Nt _x1, y has a dimension of Nr x 1 and H has a dimension of Nr x Nt. The ergodic channel capacity of MIMO systems in the presence of perfect instantaneous information on the channel state is given by where (:) H denotes the Hermitian transposition, _ is the ratio between the power of the transmit signal and the power of the noise, and CCSIperfect is the capacity of the MIMO system when perfect channel state information is available. Q is the optimal covariance of the signal and is given by Q = VSVH. If the transmitter has no information about the channel state, it can select the signal covariance Q to maximize the channel capacity in the worst case, which means Q = 1 Nt I and, therefore, exploit the advantages. proposed by MIMO systems, diversity coding is used. In this paper, a special type of space-time block code (STBC), invented by Alamouti in 1998, is used. It was first designed for a two-emission antenna system and is represented in matrix form: where * denotes a complex conjugate. c1 and c2 are the symbols to be transmitted at two different times by two antennas. It takes two time slots to transmit two symbols. In the first time interval, two symbols x1 and x2 (in OFDM language) are transmitted simultaneously from two transmitting antennas. During the second time slot, ????x_2 is transmitted from the first transmitting antenna and x_1 is transmitted from the second transmitting antenna. The Alamouti coding system for a two-transmit, two-receive system is shown in Figure 4.16. Using the optimal decoding scheme described below, the bit error rate (BER) of this STBC is equivalent to the 2Nr maximum branch ratio (MRC) combination. Keep in mind: this is just a sample. Get a personalized item from our expert now. writers.Get a Custom EssayThis is the result of perfect orthogonality between symbols after receiving processing - there are two copies of each symbol transmitted and Nr copies received. Where Nr is the number of receiving antennas. This is a very special thing for STBC. It is the only orthogonal STBC that achieves rate 1. That is, it is the only STBC capable of achieving its full diversity gain without having to sacrifice its data rate. Strictly speaking, this is only true for complex modulation symbols. Since almost all constellation diagrams rely on complex numbers. However, this property generally gives Alamouti's code a significant advantage over higher-order STBCs, even though they achieve better performance in terms of error rate..