Carrier Aggregation in LTE-Advanced

Carrier Aggregation (CA) is a crucial technology in LTE-Advanced (LTE-A) and LTE-Advanced Pro, enabling higher data rates, improved network capacity, and efficient use of fragmented spectrum. Introduced in 3GPP Release 10 (2011) and enhanced through Release 18 (2024), CA allows operators to combine multiple component carriers (CCs) to increase bandwidth, supporting data-intensive applications like 4K/8K streaming, AR/VR, and IoT. CA is now mainstream across global LTE and 5G non-standalone (NSA) deployments, benefiting operators, app developers, and device manufacturers with enhanced performance and scalability.

A simple diagram explaining Carrier Aggregation is here below, showing two channels being aggregated together to provide double the data capacity to the user device:

Delivering higher data rates

Carrier aggregation (CA) scales data rates by aggregating multiple carriers, each up to 20 MHz, across licensed, shared, or unlicensed spectrum. Key milestones include:

• Release 10 (2011): Supported up to 5 Component Carriers (CCs) (100 MHz total), achieving peak downlink rates of 1 Gbps with 4×4 MIMO.

• Release 12 (2014): Commercial solutions aggregated up to 3 CCs, delivering 450 Mbps (Cat 9).

• Release 13 (2016): Extended CA to 32 CCs (640 MHz), enabling multi-Gbps rates.

• Release 18 (2024): Enhanced CA for 5G-Advanced, supporting dynamic spectrum sharing (DSS) and aggregation across LTE and 5G NR for NSA deployments.

CA now supports peak rates exceeding 3 Gbps in commercial networks, with consistent 100–500 Mbps across urban areas, improving user experience for streaming, gaming, and cloud applications.

LTE Advanced with Carrier Aggregation – User Equipment (UE) capacity increases

Higher capacity for bursty applications

CA increases capacity for bursty applications (e.g. web browsing, social media, video streaming) by aggregating carriers. This can provide flexible trade-offs, as operators can prioritise higher capacity for consistent user experience or higher data rates for premium services. Aggregating multiple CCs enhances throughput, since it ensures efficient handling of peak traffics, reducing congestion in dense areas.

Benefits of Carrier Aggregation

CA transforms the LTE ecosystem, delivering value to all stakeholders:

Users:

• Higher data rates and lower latency for seamless browsing, file downloads, and 4K/8K video streaming.

• Improved performance in dense areas via small cell integration.

Operators:

• Maximised spectrum utilisation, combining fragmented bands for higher capacity.

• Support for new services like IoT, V2X, and eMBMS for broadcasting.

App Developers:

• Enables richer multimedia experiences, including AR/VR and real-time gaming.

• Leverages modern smartphones’ connectivity for innovative applications.

Manufacturers:

• Demonstrates technology leadership with CA-capable devices (e.g. Cat 9 to Cat 20 modems).

• Offers tiered devices for global markets, supporting diverse CA configurations.

LTE Carrier Aggregation basics

CA enables operators to combine multiple carriers to achieve higher bandwidths, addressing the 1 Gbps downlink target for LTE-A (Release 10) and beyond. Key aspects include:

• Spectrum Flexibility: Aggregates contiguous or non-contiguous carriers within the same band (intra-band) or across different bands (inter-band).

• FDD and TDD Support: Compatible with both Frequency Division Duplex (FDD) and Time Division Duplex (TDD), ensuring global applicability.

• Fragmented Spectrum: Combines small bands (e.g. 10 MHz) to meet high-throughput demands in spectrum-constrained regions.

Types of Carrier Aggregation

1. Intra-Band Contiguous:

   • Aggregates adjacent carriers within a single band (e.g. two 20 MHz carriers in Band 7).

   • Simplest implementation, requiring a single transceiver in the user equipment (UE).

   • Challenges include maintaining performance over wide bandwidths, particularly in UEs.

   • Base stations leverage existing multi-carrier designs, while UEs need enhanced RF frontends for wide bandwidths.

2. Intra-Band Non-Contiguous:

   • Aggregates non-adjacent carriers within the same band.

   • Requires multiple transceivers, increasing UE complexity, power consumption, and cost, but enabling flexible spectrum use.

3. Inter-Band Non-Contiguous:

   • Combines carriers across different bands (e.g. Band 1 and Band 3).

   • Addresses spectrum fragmentation, common in regions with limited band availability.

   • Increases UE complexity due to multiple transceivers and challenges like intermodulation.

   • Advanced RF designs mitigate interference, ensuring performance across fragmented bands.

Component Carriers

• Primary Component Carrier (PCC): The main carrier for control signalling, with an associated uplink PCC. Configured on a per-UE basis based on network load and conditions.

• Secondary Component Carrier (SCC): Additional carriers for data transmission, increasing throughput. Up to 31 SCCs supported (Release 13).

• Numbering: PCC is numbered zero; SCCs receive unique identifiers via RRC signalling, ensuring robust scheduling during reconfiguration.

Carrier Aggregation bandwidth classes

CA Bandwidth Class	Aggregated Bandwidth (MHz)	Number of CCs
A	≤100	1
B	≤100	2
C	100–200	2–3
D	200–300	3–4
E	300–400	4–5
F	400–640	5–32

Note: Classes D, E, and F were finalised in Releases 12–13, with Class F supporting up to 32 CCs (Release 13). 

Carrier Aggregation cross-carrier scheduling

CA requires efficient scheduling across CCs to optimise resource allocation:

• Without Cross-Carrier Scheduling:

  • Downlink assignments are valid for the carrier on which they are transmitted.

  • Uplink grants are tied to a specific downlink-uplink CC pair, configured via RRC signalling.

• With Cross-Carrier Scheduling:

  • Enabled via RRC signalling on a per-CC or per-UE basis.

  • PDCCH (control channel) indicates the target CC for PDSCH (downlink data) or PUSCH (uplink data) using a Carrier Indicator Field (CIF).

  • Enhances flexibility in dense networks, reducing control channel overhead.

Carrier Aggregation for 5G

CA is integral to both LTE-A and 5G NSA deployments:

• LTE and 5G NR Aggregation: Combines LTE and 5G NR carriers for NSA 5G, leveraging LTE’s robust coverage and NR’s high-speed mmWave or sub-6 GHz bands.

• Unlicensed Spectrum: Licensed Assisted Access (LAA) and enhanced LAA (eLAA, Release 13) aggregate licensed and unlicensed 5 GHz/6 GHz bands.

• Dynamic Spectrum Sharing (DSS): Enables LTE and 5G NR to share the same band, optimizing spectrum use during the 4G-to-5G transition.

• Release 18 (2024): Enhances CA with AI-driven scheduling, support for up to 71 GHz, and integration with non-terrestrial networks (NTN).

CableFree LTE-A Solutions

CableFree LTE-A Base Stations and CPEs support CA up to 3GPP Release 18 (2024), offering:

• Scalable Performance: Aggregates up to 7 CCs commercially, with software upgradable to 32 CCs.

• Spectrum Flexibility: Supports intra-band (contiguous/non-contiguous), inter-band, and unlicensed spectrum via LAA/eLAA.

• High Throughput: Delivers up to 3 Gbps downlink in commercial deployments, with low latency for real-time applications.

• Future-Ready: Compatible with 5G NSA, DSS, and advanced features like massive MIMO and V2X.

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