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The Secret of Instantaneous CSI and Statistical CSI: Do You Know the Difference Between Them?
In wireless communications, Channel State Information (CSI) is a known channel characteristic of a communication link. This information describes how the signal propagates from the transmitter to the receiver and reflects multiple influencing factors. , such as scattering, fading, and power attenuation with distance. Understanding the acquisition and application of CSI is crucial to improving communication reliability and data transmission rate.
CSI needs to be estimated at the receiver and usually has to be quantized and fed back to the transmitter, so there may be different CSI between the transmitter and the receiver. The CSI of the transmitter is called CSIT (Channel State Information at the Transmitter), and the CSI of the receiver is called CSIR (Channel State Information at the Receiver).
Two channel status information
In the field of CSI, there are two main levels, namely instantaneous CSI and statistical CSI.
The instantaneous CSI means that the current channel status is known and can be regarded as understanding the impulse response of the digital filter. This information can be used to adjust the transmitted signal to adapt the impulse response, thereby optimizing the received signal to achieve spatial multiplexing or reduce the bit error rate.
Statistical CSI means the statistical characteristics of the known channels, including fading distribution type, average channel gain, line-of-sight components, and spatial correlation. This information can also be used for transmission optimization.
The acquisition of CSI is limited by the speed at which channel conditions change. In fast fading systems, channel conditions change rapidly under the transmission of a single signal, so the use of statistical CSI is more reasonable. In a slow fading system, however, the instantaneous CSI can be estimated relatively accurately and transmission adjustments can be made long before it becomes ineffective. In actual systems, the acquired CSI is often between the two, that is, the instantaneous CSI has a certain estimation/quantization error and is used in combination with statistical information.
CSI estimation method
Due to the changes in channel conditions, the instantaneous CSI needs to be estimated in the short term. A popular method is to use a training sequence (or pilot sequence) to estimate the channel matrix by sending a known signal.
In the training sequence, the known signal is used to obtain a channel estimate from the receiver's response, which allows the transmission process to be adjusted and optimized more effectively.
Whether it is least-squares estimation or minimum mean square error estimation (MMSE estimation), the statistical characteristics of the channel and noise must be considered to reduce the channel estimation error. In some cases, using neural networks in deep learning to estimate channel state information has been shown to achieve better performance with less guidance signals.
Data-assisted and blind estimation
CSI estimation also includes two methods: data-aided and blind estimation. In data-assisted methods, the estimation is based on known data known to both the transmitter and receiver, such as a training sequence, whereas in blind estimation, only the received data is relied upon, ignoring known information about the transmitted signal.
ConclusionData-assisted methods usually provide more accurate channel estimates, but require more bandwidth or higher management overhead.
Instantaneous CSI and statistical CSI are of fundamental significance in wireless communication networks, and their respective advantages and disadvantages affect the quality and efficiency of communication. These concepts are not only the core of wireless communication theory, but also an indispensable part of the practical application of wireless networks. In the face of growing data demands, how to choose appropriate CSI strategies to maintain the stability and speed of communications may become an important issue in future technological development?
