One of the essential challenges for MIMO or massive MIMO systems is achieving accurate channel state information (CSI) at the base station side with reasonable reporting overhead. 3GPP systems - like LTE or NR - rely for this purpose on codebook solutions, where the latest 3GPP Release 15 has standardized a so called Type II reporting mode. For future NR Releases a shift to explicit time domain CSI has been proposed as an option to support more advanced precoding methods like coherent cooperative multi point or non linear precoding. Effective reporting of explicit time domain CSI is possible in combination with compressed sensing, achieving higher performance and/or lower overhead compared to the Type II CSI feedback. Explicit CSI - in contrast to the implicit reporting of precoding matrix indicators (PMI) - is closely related to the physical radio channel and promises high accuracy, favorably scalability to larger bandwidth, and eventually might support channel prediction. The iterative orthogonal matched pursuit (OMP) algorithm is often used to calculate the sparse representation of the explicit time domain CSI. Here, we will propose a less complex so called time shifting approach and will discuss the pros and cons compared to the OMP algorithm.
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