Hi everyone, I hope you enjoy today's presentation of great technology: MIMO technology.
MIMO technology refers to the use of multiple transmitting and receiving antennas at the transmitting and receiving ends, respectively, so that signals are transmitted and received through multiple antennas at the transmitting and receiving ends to improve communication quality. It can make full use of space resources, through multiple antennas to achieve multiple transmit and receive, without increasing spectrum resources and antenna transmission power, can double the LTE user rateshowing obvious advantages, is considered the core technology of next-generation mobile communications.
The transmitting end maps the data signals to multiple antennas and sends them out. The receiving end translates the signals received by each antenna into space to recover the data signals sent by the transmitting end. According to different spatial mapping methods, MIMO technology can be roughly divided into two categories: spatial diversity and spatial multiplexing. Spatial diversity refers to the use of multiple transmitting antennas to send signals with the same information through different paths, while obtaining multiple independent decays of the same data symbol at the receiver end, thus obtaining diversity to improve reception reliability. For example, in a slow Riley decay channel, one transmitting antenna and n receiving antennas are used, and the signal is sent through n different paths. If the attenuation between the antennas is independent, the maximum diversity gain of n can be obtained. For the transmit diversity technique, again the gain of multiple paths is used to improve the reliability of the system. In a system with m transmitting antennas and n receiving antennas, if the paths between the antenna pairs are independent and uniformly distributed Riley decay, the maximum diversity gain can be obtained as mn. The spatial diversity techniques commonly used in MIMO systems are Space-Time Block Code (STBC) and beamforming techniques. is an important form of coding based on transmit diversity, the most basic of which is the Alamouti scheme designed for two antennas.
The most important aspect of the STBC method is the orthogonalization of the signal vectors to be transmitted over multiple antennas. The beamforming technique uses different transmitting antennas to send the same data, forming a shaped beam directed to certain users, thus effectively increasing the antenna gain. In order to maximize the signal strength of the beam directed to the user, the beamforming technique usually needs to calculate the phase and power of the data sent from each transmitting antenna, also known as the power beamforming vector. The beamforming vector can be calculated by the maximum eigenvalue vector, MUSIC algorithm, etc. The maximum transmits diversity gain that can be obtained by beamforming technique for M transmitting antennas is M. Spatial multiplexing is a technique in which the data to be transmitted can be divided into several streams and then transmitted on different antennas to increase the transmission rate of the system. The commonly used spatial multiplexing method is the vertically layered space-time code, or V-BLAST technique, proposed by Bell Labs.
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