1. Foreshadowing
With the continuous change of communication methods, from wired transmission methods to wireless transmission methods, the communication distance continues to expand, the quality of communication continues to improve, and the efficiency of communication continues to rise. From telephone communication that only relies on voice communication, it has now developed to video , network and other communication methods, communication technology has been developing and improving with the change of communication methods. Multiple-Input Multiple-Output (MIMO) utilizes multiple transmitting antennas and receiving antennas, and signals are transmitted between multiple transmitting and receiving antennas. This method can make reasonable use of space resources, so that the MIMO system can transmit Under the condition of constant power and constant bandwidth , the capacity of MIMO system is improved .
Bandwidth
Bandwidth refers to the frequency bandwidth occupied by the signal, which can be used to describe the channel, and can also be interpreted as the maximum frequency bandwidth of the signal effectively passing through the channel.
- Analog signal: bandwidth is also called frequency width, the unit is Hz
- Digital signal: the amount of data that the link can pass per unit of time, described by baud rate or symbol rate
Remarks: The transmission of digital signals is accomplished through the modulation of analog signals.
The advantage of the MIMO system is that the multi-transmit and multi-receive antenna system provides a large channel capacity without changing the frequency band, but it cannot solve the multipath interference in the channel. The principle of the MIMO system is to improve the communication quality and rate of MIMO by combining the antenna signals of the transmitting end and the receiving end. It is traditionally considered that multipath propagation is a defect of wireless transmission, but the main feature of MIMO system is to transform multipath propagation into a factor beneficial to users. The wireless signal transmission of the transceiver antenna of the MIMO system is relatively independent, and the data signal at the sending end is restored by using a receiver at the receiving end to process the signal.
2. MIMO system model construction
Multi-transmitting and multi-receiving antennas are the characteristics of MIMO. In the wireless communication environment, there are various interferences and losses in the wireless communication channel, such as multipath fading, shadow fading, free space propagation loss, etc., which reduce the reliability of system transmission. The signal received by the receiving end of the system has been damaged and cannot be restored. Although the single-antenna system has the characteristics of being simple and easy to implement, it is not feasible in harsh environments, so the MIMO technology of multiple transmission and multiple reception is produced.
The schematic diagram of the MIMO system is as follows:
MIMO technology has made important contributions to signal transmission in complex signal environments. The specific details are: a single data stream is transformed into several small data symbol streams through MIMO system processing, and the receiving end receives these data symbols transmitted from the channel to demodulate and restore the original signal.
In addition, OFDM technology uses the method of dividing the channel into multiple sub-channels to reduce frequency fading. In MIMO technology, it is solved by increasing the number of antennas. There are multiple antennas at the transmitting end and multiple antennas at the receiving end. Antenna to receive. The two important parts of MIMO technology are: space multiplexing technology that can improve channel capacity and space diversity technology that can improve the accuracy rate of received signals in MIMO system. By increasing the number of antennas, the capacity of the system can be improved and the waste of spectrum can be reduced. Due to the increase in the number of antennas, multiple data channels can increase the transmission rate. The transmission quality can also be improved by utilizing the diversity of the transmitting end and the receiving end, so MIMO technology is very important in wireless communication.