行動合作網通之無線訊號與訊息處理技術研究-子計畫一：協調型多點合作式多送多收傳收器設計

Abstract

協調式多點傳送Coordinated multipoint (CoMp)是一個多基地台合作的傳輸技術，此一技術在每一基地台都使用多送多收multi-Tx multi-Rx (MTMR) MIMO 的空間多工，這種在所有傳送端和接收端都有多根天線的系統，也被稱為MIMO X channels。此技術需要協調多個cell 間如何同時傳送和接收，這是LTE-A 無線存取技術的基礎概念。在協調式多點傳送的環境下，重要的議題為跨蜂巢干擾的協調及消除(inter-cellinterference coordination/orthogonality) 和蜂巢內干擾的消除(intra-cellorthogonality)。這個多點技術，有可能是多個cell 彼此合作，也有可能是一個cell跟其所控制的remote radio equipments (RRE)共同合作。因此目前有兩種管理inter-cell radio resource 的方式，分別為自主式和中央集權式。在中央集權式的環境下，是使用一組由光纖連結到中央基地台(eNodeB)的remote radio equipments (RREs)來共同傳送，由中央基地台統一協調RREs 完成傳送端或接收端的訊號傳送及處理。而自主式的環境下，需要用到多個eNodeB。這種方式可以利用X2 介面來做基地台間的協調。X2 介面主要應用在inter-eNodeB 越區切換(handoff)，已經在Release 8 LTE 被提過了。在此，X2 有在被考慮應用在inter-cell 的合作。 協調式多點傳送主要的目標是增加系統的容量以及提升邊界使用者的吞吐量。但是由於干擾的問題，它的使用還要配合很多因素。在下載的情況下，整體系統可依干擾及雜音情況，考慮三種操作型式：第一種是對單一使用者的聯合傳送，也稱為jointtransmission - single user (JT-SU)，這種形式下，inter-cell和intra-cell 都需要用到編碼來得到正交。第二種是動態cell選擇，在此情況下，在一個預定的時間內只有一個cell是處於運作的模式，也就是分時多工，或是使用部份頻率共用(fractionalfrequency reuse)。第三種就是協調式多點傳送，是最複雜也是最有用的。多個基地台同時對多個使用者送訊號。這種情況下，需要協調式排程和波束成型等技術的使用。多個合作的cell來共同服務多個使用者，在合作的cell內，每個使用者需要一個專屬的傳送波束權重，來降低對同一個基地台內其他使用者的干擾，很多多使用者MIMO干擾消除的研究，就是針對此一問題。在上傳時，每個基地台都收到同個傳送者的資料，所以基地台之間對單一使用者需要做maximum ratio combing (MRC) 的合併工作，假如多使用者同時存在，必須要考慮干擾消除的接收器。因此我們將研究接收器的設計，以消除內外基地台間的干擾，以及傳送端的設計，來最小化對基地台內外使用者的干擾。

Coordinated multipoint CoMp is about the multi-cell cooperative transmission techniques. It uses multi-Tx multi-Rx (MTMR) MIMO spatial multiplexing for LTE-A downlink. It is also called MIMO X channels, in which all the transmitters and receivers have multiple antennas. This technique is to coordinate among multiple cell sites for simultaneous transmission and reception. It is the basis for LTE-A radio access. Two important issues associated with CoMP are inter-cell interference coordination/orthogonality and intra-cell orthogonality. Now, there are two types of inter-cell radio resource management. They are called centralized and autonomous. In centralized environment, a group of RREs (remote radio equipment) is employed, which are connected to the central BS (eNode B) by an optical fiber. Complete coordinated transmission or reception is achieved among RREs through unified radio resource management at the central BS. In Autonomous Intercell Radio Resource Management, multiple e-Nodes are used. Direct eNode communication was already introduced into Release 8 LTE using the X2 interface (i.e., inter eNode B interface) and is mainly used for inter-eNode B handover. Now, it is considered to be extended for inter-cell cooperation. The goal is to increase system capacity and edge user throughput. In downlink, based on the interference and noise condition, basically three types of operation are considered. The first is joint transmission. In this scheme, code-book based precoding for inter-cell and intra-cell orthogonality is used. It is also called as JT-SU (joint transmission single user). The second is dynamic cell selection. In this case, only one cell is active at one time through scheduling. The third is coordinated scheduling and beamforming. In this case, multiple coordinated cells are used to serve multiple users. To minimize interference, transmit beamforming weights for each UE are generated to reduce the unnecessary interference to other UE scheduled within the coordinated cells. Many MU-MIMO related techniques are being considered for performance improvement. For uplink, multiple data are received at multiple cells, for this, MRC is used for single user case. If multiple users are considered, interference rejection combining is used. We will concentrate on both the MIMO receiver design for OCI (other cell interference) cancellation and the transmitter design for OCI minimization.