LTE及LTE-A多使用者多輸出入傳輸之強韌預編碼研究

Abstract

在第四代行動通訊系統中為了達到高傳輸率的要求，因而產生多使用者多輸出入之技術。對於一個有大量使用者的蜂巢細胞，高傳輸率可藉由在同樣的頻帶資源裡同時傳送獨立的資料給多使用者而達到。而在閉路傳收系統裡基地台將從使用者方得到偏好的預編碼以及調變與編碼方法，有了足夠的通道狀態資訊後，多輸出入預編碼技術將可增加多使用者傳輸率。然而，通道狀態資訊如果不精確，上述的的傳輸方式將不再適用。此外，使用者回饋的資訊是建立在單一使用者的量測，所以使用者間的干擾將被忽略，因而造成傳輸率的衰減。為了達到高多使用者傳輸率以及使用者間的干擾，基地台必須用回饋的資訊重新估算預編碼以及調變與編碼方法。這篇論文提出一達到高傳輸率之多使用者多輸出入方法，同時研究重算調變與編碼的方法所來的成果與複雜度。此外，我們也介紹了預等化的方法來更加改善傳輸率。另外我們也使用低複雜度的回饋機制來減少省用者硬體複雜度。模擬結果顯示利用調變與編碼方法重算可提高傳輸率，預等化技術也將更加提高成效。

Multi-user MIMO (MU-MIMO) techniques were born due to the urge of high data rates and spectral efficiency in mobile communication systems. For scenarios with a large number of users to be served in one cell, high capacity gains can be achieved by transmitting independent data streams to different users sharing the same time-frequency resources through the use of MIMO precoding. In a closed-loop transmission configuration in LTE, the base station (BS) receives from each user the preferred precoding vector and modulation and coding scheme (MCS). With enough channel state information (CSI) at the transmitter, MIMO precoding allows to increase multi-user throughput gain. However, without a correct CSI vector selection, the transmission scheme might be not suitable. Moreover the user feedback is reported in the sense of single-user measurement, so users are not aware of other users’ interference in MU-MIMO transmission. Hence the interference between users can seriously degrade the overall network data rate. To achieve the highest multi-user throughput gains and avoid user interference, the BS needs to recalculate the precoding vector and MCS for each user. The goal of this study is to investigate how to maximize MU-MIMO throughput and examine complexity of state-of-the-art methods for recalculation of MCS. Furthermore we also introduce pre-equalization to improve data rate for LTE-A scenarios. Additionally, we apply a low-complexity feedback scheme that would reduce the feedback calculation adaptively. The simulation shows that throughput gain can be achieved with proposed MCS recalculation, and pre-equalization would further improve it in high interference scenarios.