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前言：
参考： RF Wireless World：
《LTE Carrier Aggregation basics》
目录：
- Why Carrier Aggregation
- Carrier Aggregation in TDD
- LTE Carrier Aggregation in FDD
- LTE Carrier Aggregation frequency bands
- RELATED LINKS
-
Advantages of carrier aggregation
- Disadvantages of carrier aggregation
一 Why Carrier Aggregation
CA 通过提高了UE 的带宽，相对非CA的UE ，提高了吞吐量。
这种技术适用于TDD&FDD
Carrier aggregation (CA) helps in increasing bandwidth allocation to the UE. Hence it will support higher data rate compare to non CA device.
It is applied for both TDD and FDD topologies as mentioned below. To know more on LTE TDD vs FDD,
二 Carrier Aggregation in TDD
The figure depicts carrier aggregation used in LTE TDD mode frame. As shown in Fig.1, here number of component carriers(CCs) and bandwidth of each component carriers are same for both uplink and downlink assignments to UE.
No. of UL(CC) <= No. of DL(CC).
UL CC 小于 DL CC,大部分产品不支持上行CC.
三 LTE Carrier Aggregation in FDD
四 LTE Carrier Aggregation frequency bands
Figure depicts LTE carrier aggregation in FDD mode. As shown in Fig.2, here no. of CCs will also be different in both uplink and downlink. They will have different bandwidths in uplink and downlink too.
In both the above cases, each CC(Component Carrier) will have a BW of any value from 1.4/3/5/10/15 or 20 MHz. It is possible to aggregate or combine at maximum upto 5 carriers, which provides max. of 100 MHz(for CC of 20MHz).
单CC 带宽是 1.4/3/5/15/20 MHz, 最高聚合5 Carriers, 所以最高带宽是20MHz.
Changes are introduced in PHY and MAC layers of LTE protocol stack to support carrier aggregation. 主要影响是 PHY, MAC,RRC 层
五 RELATED LINKS
详细的3GPP 文档解释
https://www.3gpp.org/Carrier-Aggregation-explained
TR 36.808 carrier aggregation(Base Station)
TR 36.823 carrier aggregation enhancement (UE)
六 Advantages of carrier aggregation
➨它通过组合CC来帮助增加对UE（或移动用户）的带宽分配。在3GPP中，R-10支持聚合5个CC，而R-13支持聚合32个CC。这有助于实现高下行链路和上行链路数据速率。
➨网络运营商可以将网络部署为三种类型之一：即带内连续、带内非连续和带间非连续。
➨CA有助于实现未授权和授权载波频谱的聚合。因此，它使用未经许可的波段。
➨CA可以实现CC之间的动态流量切换。
➨扩大覆盖范围对电信运营商来说不再是一个麻烦，因为他们可以根据需要扩大覆盖范围。
高频覆盖小，低频覆盖大,高低频组合
➨CA可以应用于TDD以及FDD拓扑。
➨CA功能有助于网络运营商通过优化用户体验来提高网络效率
七 Disadvantages of carrier aggregation
➨在发射端需要多路复用器来组合分量载波，在接收端需要RF滤波器来分离分量载波。这些额外的设备将增加设备和设备制造商的成本。它还增加了系统的复杂性。使用SAW和BAW类型的RF滤波器。
➨功率放大器（PA）和开关是专门为满足基于载波聚合的RF系统的要求而设计的。例如，高线性PA用于带内CA。使用端口之间具有更高隔离度的交换机
➨此功能的测试需要复杂的测试和测量硬件和软件。这增加了智能手机和设备制造商利用测试服务/设备的成本。安立（Anritsu）、罗德（Rohde）、施瓦茨（Schwarz）和安捷伦（Agilent）等测试和测量公司提供T&M解决方案来测试这一功能。
➨由于对射频链中的开关和滤波器等硬件组件的额外要求，它增加了智能手机的成本。
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