多使用者多重天線系統預編碼器設計

Abstract

在多使用者的傳輸通道裡，基地台將要給所有使用者的信號加總起來再一起傳送出去，雖然這種傳輸架構可以增加傳輸容量，但使用者在接收端除了會收到基地台要給自己的資料，也會收到基地台要給其他使用者的資料，即為通道干擾，為了能在傳送端就先對這些通道干擾做處理，基地台在資料傳送之前先對資料做預編碼(Precoding)，讓每個使用者可以在受到最小通道干擾的情況下，正確收到自己想要的資料，此外，在使用者的總接收天線數多於傳送天線數的時候，基地台可利用預編碼器(Precoder)來選出一組讓總通道容量達到最大的接收者。學者專家們近年來已經提出了數種預編碼器的設計方法，在使用者只用一根天線接收(MU-MISO)的情況下，我們找出了幾種現有的方法來討論與比較，分析每種設計方法的概念、運算量、對接收端增加的複雜度以及可達到的通道效能。針對通道效能較差的PU2RC與JTRUS這兩種設計方法，我們藉由做第二次使用者安排，來提升通道容量的效能，在使用者間通道干擾與系統總通道容量之間找出一個平衡點，當做是否要增加使用者的門檻。在使用者使用多根天線接收(MU-MIMO)的情況下，我們也找出了幾種現有的設計方法來做介紹，並對這些方法的運算複雜度、預編碼器型式、可達到的通道容量等方面來做比較與分析。

In multi-user MIMO channel downlink transmission, the base station sums the data for each user and then transmits. Although transmitting data simultaneously to multiple users can increase channel capacity, every user would receive the data for him as well as data for others, which is co-channel interference. In order to cancel the co-channel interference previously, the base station precodes the data before transmitting. As a result, every user can receive data intended for him correctly with interference as little as possible. Besides, when total receiving antennas are more than the transmitting antennas, the base station can use the precoder to select a group of users that maximizes the channel capacity. In recent years, a number of precoder designing solutions have been proposed. For MU-MISO channel, we introduce some existing precoder designing solutions and discuss the concept of the process, computation complexity and so on. Since PU2RC and JTRUS have worse performance at channel capacity, we improve the two solutions by performing second time user scheduling. We make the tradeoff between interference and capacity to find a threshold value for base station to decide whether or not to add additional receiver. For MU-MIMO channel, we introduce some existing precoder designing solution and compare their computation complexity, form of precoder, achievable capacity and so on.