What is Carrier Aggregation in 4G and 5G Networks?

Eric Murrell

Sr. VP of Sales

I am sure you would be happier to get doubled data rates and increased bandwidth from the same network. Yes, this is what carrier aggregation (CA) does – this technique multiplies the data rates and improves network performance. But what is carrier aggregation, and how does it work?

In short, it combines multiple frequency blocks, known as component carriers (CC), to create a larger bandwidth to enhance the overall data throughput ¹²³. CA is mostly used in LTE-Advanced and 5G networks for latency reduction and spectral efficiency ⁴. So, consider this method very crucial for meeting the growing demand for high-speed data.

Carrier aggregation can be your next favorite topic that may help you learn how you can get better network experience. And that is why I am here with a long discussion throughout this article. In this article, I will explain the definition, functionality, types, and benefits of CA in modern networks.

What is Carrier Aggregation?

According to 3GPP, in carrier aggregation, a terminal receives or transmits multiple component carriers ⁵. It is a key technique as a part of LTE Advanced (LTE-A) from release 10 (in 2011) onwards. In this method, each component carrier can have a 1.4, 3, 5, 10, 15, or 20 MHz bandwidth. These carriers can be aggregated to get a maximum bandwidth.

Initially, aggregation allowed for the combination of up to five CC, which resulted in aggregated bandwidths of up to 100 MHz (5 x 20 MHz). However, 5G technology has led to devices capable of aggregating many more CCs for much higher bandwidth outputs.

Operators can implement carrier aggregation in both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) modes of LTE 6.

In TDD mode, the bandwidth and the number of each CC are usually the same for both uplinks (UL) and downlinks (DL).
In FDD mode, the number of UL CCs is either the same as or lower than the number of DL CCs.

How Does Carrier Aggregation Work?

The process of carrier aggregation involves several key components and steps.

Component Carriers

The aggregation process starts with component carriers or CCs. These are individual frequency bands allocated to a mobile network operator. By aggregating these CCs, the network creates a wider bandwidth channel to improve data transfer speeds significantly.

Frequency Bands

Frequency bands such as low, mid, and high bands are used in carrier aggregation. This flexibility allows for optimal utilization of the available spectrum. In modern implementations, CA is allowed to allocate resources dynamically. It enables the network to adapt to changing conditions and optimize performance.

Primary and Secondary Cells

When a user equipment (UE), such as a mobile device, connects to a carrier for both uplink (UL) and downlink (DL). This is known as the primary cell (PCell). This cell handles control information and RRC connection. 
Then, secondary DL carriers (one or multiple) are added. You can call them secondary cells (SCells). They carry user data but no extra information.

Here is a catch. Secondary carriers are always DL. UL is not used on these carriers. When a user (assume yourself) moves between cells, the network performs handovers. Through this process, the aggregated channels are transitioned to maintain service.

Network providers use different frequency bands as SCells to aggregate with PCell. Note that both the base station and mobile devices must support CA. The base station manages the aggregation process. On the other hand, the mobile device receives and processes the combined signal.

Types of Carrier Aggregation

We can categorize carrier aggregation into three main types based on how the CCs are combined. Each type has its characteristics and applications in mobile networks.

Intra-band Contiguous Carrier Aggregation

It involves aggregating CCs that are adjacent to each other within the same frequency band. Hence, this aggregation is the simplest one. Operators often use this contiguous carrier aggregation when they have a contiguous spectrum.

The benefit of intra-band contiguous carrier aggregation is the reduced complexity in implementation since the carriers are closely spaced. It minimizes the need for complex signal processing.

Intra-band Non-contiguous Carrier Aggregation

The second type is intra-band non-contiguous carrier aggregation. It aggregates CCs that are within the same frequency but are separated by a gap. Operators with non-contiguous spectrum allocations within the same band can use this type of CA mostly.

It allows for more flexible use of the available spectrum, though it introduces some complexity regarding signal processing and interference management.

Inter-band Carrier Aggregation

The third type is inter-band carrier aggregation. It combines CCs from different frequency bands. It offers the greatest flexibility. Again, it is beneficial for operators with a fragmented spectrum across multiple bands.

Inter-band aggregation enhances network performance by utilizing a wider range of frequencies. However, more sophisticated signal processing and coordination are needed to manage the different propagation characteristics of each band.

Implementation in Different Technologies

Network providers have already implemented carrier aggregation in various wireless communication technologies, particularly in LTE (Long-Term Evolution) and 5G (Fifth Generation) networks.

LTE and LTE-A

CA was introduced as part of LTE-Advanced (LTE-A) in Release 10 of the 3GPP specifications ⁵. It allows mobile operators to combine component carriers to create a larger bandwidth channel.

In LTE-A, up to five CCs can be aggregated, resulting in maximum bandwidth of 100 MHz. Yet LTE’s early implementations typically involved aggregating two DL carriers (mostly 10 MHz bandwidth each) across different frequency bands.

5G New Radio (NR)

Carrier aggregation continues to play a crucial role in 5G NR networks. It helps to achieve the high data rates and low latency required for advanced applications.

CA in 5G allows for the combination of different frequency bands, including low, mid, and high bands. Users get a better experience from this aggregation as 5G NR supports wider bandwidths than LTE-A.

5G carrier aggregation allows for the combination of traditional cellular bands with millimeter wave frequencies. Additionally, it introduces more advanced spectrum sharing capabilities, known as dynamic spectrum sharing (DSS), for more flexible use of aggregated carriers.

5G enables aggregation across different radio access technologies, including LTE and 5G NR, for seamless handovers and improved performance.

Challenges in Implementing Carrier Aggregation

Implementing CA in mobile networks presents several challenges. Operators and equipment manufacturers need to address them. Some of the key challenges include:

Interference Management

Interference management between different frequency bands and carriers is often complex, especially when aggregating carriers across various frequency ranges—for example, low-band and mid-band frequencies.

Spectrum Allocation Issues

Different countries and regions may have varying spectrum allocations. So, it becomes difficult to implement consistent carrier aggregation strategies globally. Plus, operators may have fragmented spectrum holdings within a single band. It complicates intra-band, non-contiguous CA implementations.

Device Compatibility

UE must support carrier aggregation. They should be able to handle multiple CCs simultaneously. However, device capabilities vary, and not even all smartphones or tablets support advanced CA configurations.

Network Complexity

Implementing CA increases the complexity of network planning and optimization. Operators need to carefully manage resource allocation across multiple frequency bands and ensure seamless handovers between cells.

Cost Considerations

Implementing and maintaining a CA-capable network comes with increased costs. Service providers need to balance the investments with possible revenue gains and better customer satisfaction.

Regulatory Challenges

Different countries have varying regulations regarding spectrum usage and aggregation. They can complicate global deployments of CA-enabled networks.

RF Design Challenges

Especially for multi-band CA, designing radio frequency (RF) components presents engineering challenges. These components can efficiently operate across different frequency bands.

Power Consumption

CA can increase power consumption in mobile devices, especially when aggregating multiple high-frequency carriers.

Backhaul Requirements

The increased bandwidth offered by CA puts additional demands on backhaul infrastructure. It requires operators to upgrade their transport networks to support higher capacities.

Carrier Aggregation vs. mmWave Technology

CA and mmWave often work together to provide enhanced network performance. These two important technologies are used in modern wireless communication systems. Here’s a comparison of these technologies:

Carrier Aggregation

As I said, CA combines multiple frequencies to create a wider bandwidth channel. Its key features are:

Combines multiple CCs within the same band or across different bands.
Supports up to five CCs (in LTE-A), each with a bandwidth of up to 20 MHz, resulting in aggregated bandwidths of up to 100 MHz.
Can operate across different frequency bands, including low, mid, and high bands.
Improves coverage and capacity by utilizing available spectrum resources efficiently.

mmWave Technology

mmWave is a 5G component. It operates in high-frequency bands, typically ranging from 24 GHz to 40 GHz. Key features of mmWave include:

Delivers multi-gigabit speeds, massive bandwidth, and ultra-high data rates.
Particularly effective in dense urban areas, cities, stadiums, and transportation hubs.
Relies on small cells, Massive MIMO, beamforming, and adaptive beam tracking to overcome range limitations.
Supports applications such as 4K/8K video streaming, VR/AR, gaming, and fixed wireless access (FWA).

Comparison Between Carrier Aggregation and mmWave Technology

Factors	Carrier Aggregation	5G mmWave
Frequency Range	Operates across various frequency bands, including sub-6 GHz and mmWave frequencies	Specifically operates in high-frequency bands (24 GHz to 40 GHz)
Speed and Capacity	Significantly improves data speeds and network capacity by combining multiple frequency bands	Offers even higher peak speeds and capacities compared to traditional cellular bands
Coverage	Enhances overall network coverage by leveraging different propagation characteristics of various frequency bands	Has limited range due to high-frequency signals but uses small cells and advanced antenna techniques to improve coverage
Use Cases	General-purpose enhancement of mobile broadband services	Ideal for high-data-throughput applications in specific environments (dense urban areas, stadiums, etc.)
Complexity	Increases network complexity but provides flexibility in spectrum usage	Requires sophisticated RF designs and advanced antenna technologies like Massive MIMO and beamforming

Frequently Asked Questions

What is 4G+ carrier aggregation?

4G+ carrier aggregation (LTE-Advanced) combines multiple frequency bands to create a larger bandwidth channel. This technology allows mobile operators to utilize a fragmented spectrum more efficiently, providing users with faster download and upload speeds. For example, LTE-Advanced can aggregate up to five component carriers, each with a bandwidth of up to 20 MHz, resulting in a maximum aggregated bandwidth of 100 MHz.

Does 5G support carrier aggregation (CA)?

Yes. In fact, CA is a critical feature in 5G networks. It enables the combination of different frequency bands, including low, mid, and high bands (mmWave). Aggregation helps to get a seamless and high-performance user experience. Also, it supports advanced applications like AR, VR, and IoT.

What is the maximum aggregated bandwidth for 5G?

Theoretically, 5G networks can support aggregation of up to 16 component carriers, each with a bandwidth of up to 100 MHz. It will result in a maximum aggregated bandwidth of 1.6 GHz. This extensive bandwidth capability allows 5G networks to deliver extremely high data rates and support a wide range of high-demand applications.

How Nybsys Solutions Support Carrier Aggregation

So, what is carrier aggregation? Isn’t it an interesting topic? Certainly, it enhances cellular network performance by combining multiple frequency bands through data rate and spectrum efficiency improvements.

Starting with LTE-Advanced, now CA has become an important matter for 5G networks. Implementing it can be sometimes challenging, yet its benefits are countless. Soon, there will be more advancements in this technique.

Nybsys offers multiple solutions that support carrier aggregation to enhance mobile network performance and efficiency. Also, these solutions are compliant with the latest 3GPP standards to ensure interoperability and futureproofing.

Particularly, our eNodeB, a critical component of LTE networks, supports CA. It combines multiple frequency bands like 1.4, 3, 5, 10, 15, and 20 MHz to increase data rates and UE capacity. Similarly, Nybsys Evolved Packet Core (EPC) for LTE and 5G Dual Packet Core framework also provides end-to-end IP connectivity and support for carrier aggregation.

If you need any suggestions or products relevant to carrier aggregation, you can contact us. We will be happy to assist you! Thank you.