QSP Quasi-Systematic Precoding
QSP (Quasi-Systematic Precoding) is a technique used in wireless communication systems to mitigate the interference caused by multi-user transmissions. It is primarily employed in multi-user multiple-input multiple-output (MU-MIMO) systems, where multiple users simultaneously transmit data to a common base station.
In MU-MIMO systems, the base station is equipped with multiple antennas, allowing it to communicate with multiple users simultaneously by transmitting different data streams over the same frequency and time resources. However, due to the spatial proximity of the users and the limited wireless channel resources, the transmitted signals from different users can interfere with each other at the receiver.
Precoding is a signal processing technique used to mitigate this interference by shaping the transmitted signals before they are transmitted from the base station antennas. It exploits the channel state information (CSI) to pre-multiply the data symbols by a precoding matrix, which optimally aligns the signals in a way that minimizes the interference at the receiver.
QSP is a particular form of precoding that combines the advantages of both systematic and non-systematic precoding techniques. In systematic precoding, a subset of the transmitted symbols, known as the systematic symbols, are transmitted directly without any precoding. The remaining symbols, called the parity symbols, are precoded to mitigate interference. On the other hand, non-systematic precoding precodes all symbols, including both systematic and parity symbols.
In QSP, the precoding operation is performed in such a way that a subset of the symbols is transmitted directly (systematic symbols), while the remaining symbols are precoded (non-systematic symbols). The systematic symbols can be considered as the most important symbols that are preserved without any precoding to enhance their reliability and simplify the receiver design. The non-systematic symbols are precoded to mitigate interference and improve the overall system performance.
The precoding matrix used in QSP is designed based on the channel state information to exploit the spatial diversity and channel conditions. The goal is to maximize the signal-to-interference-plus-noise ratio (SINR) at the receivers, which improves the overall system capacity and reliability.
QSP offers several benefits over other precoding techniques. By preserving the systematic symbols, it reduces the complexity of the receiver design, as these symbols can be directly decoded without any precoding matrix operations. It also provides enhanced flexibility in choosing the precoding matrix, as it can be optimized separately for systematic and non-systematic symbols. Moreover, QSP achieves good interference mitigation capabilities while maintaining a reasonable computational complexity.
In conclusion, QSP (Quasi-Systematic Precoding) is a precoding technique used in multi-user MIMO systems to mitigate interference caused by simultaneous transmissions. It combines systematic and non-systematic precoding to preserve the most important symbols while precoding the rest to enhance system performance. QSP improves the reliability, capacity, and complexity of MU-MIMO systems, making it an effective solution for wireless communication.