LTE Carrier Aggregation basics

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This tutorial section on LTE basics covers following sub topics:
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This page describes LTE carrier aggregation basics in TDD and FDD mode. It mentions LTE carrier aggregation types and carrier aggregation frequency bands.

Why Carrier Aggregation

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, visit our page on LTE TDD Vs FDD modes and go through LTE frame structure in both of these modes.

Carrier Aggregation in TDD

carrier aggregation TDD fig1
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).

LTE Carrier Aggregation in FDD

carrier aggregation FDD fig2
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). Changes are introduced in PHY and MAC layers of LTE protocol stack to support carrier aggregation.

Types of Carrier Aggregation

carrier aggregation types fig3
As shown in fig.3 there are major three types, based on how CCs are allocated from frequency pool to the UE;Whether allocated frequency is within one band or different bands and spacing between them.

Spacing between two CCs = 300KHz X N, Where N is any integer. Below section mentions LTE carrier aggregation frequency bands for intra band and inter band in both TDD and FDD modes.

LTE Carrier Aggregation frequency bands

Intra-band contiguous CA:

CA_40 (2300 to 2400MHz in UL), (2300 to 2400M in DL), TDD
CA_1 (1920 to 1980M in UL) ,(2110 to 2170M in DL), FDD

Inter Band Non Contiguous(FDD)

CA_1, 1920-1980MHz(UL),2110-2170(DL)
CA_3, 1710-1785M(UL),1805-1880(DL)
CA_4, 1710-1755(UL), 2110-2155M(DL)
CA_5, 824-849(UL), 869-894 (DL)
CA_7, 2500-2570(UL), 2620-2690(DL)
CA_13, 777-787(UL), 746-756(DL)
CA_17, 704-716(UL), 734-746(DL)


For more detailed information for changes in PHY/MAC to support carrier aggregation pls. visit following links and 3GPP standards.
TR 36.808 carrier aggregation(Base Station)
TR 36.823 carrier aggregation enhancement (UE)

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