What Is 5G Carrier Aggregation?

Carrier Aggregation Will Enable Improved Performance As Global 5G Usage Expands

The global deployment of commercial 5G networks has dramatically enhanced the mobile user experience. Still, as the 5G ecosystem continues to mature, advanced 5G Standalone (5G SA) networks will be crucial in delivering high-speed, ultra-low latency connectivity for cutting-edge applications. 5G Carrier Aggregation will be a key driver in realizing the substantial performance improvements promised by 5G SA.

Carrier Aggregation is a software function found in Radio Access Networks and user devices, enabling Mobile Network Operators (MNOs) to combine the capabilities of radio cells operating at different frequency bands to enhance the overall user experience.

While Carrier Aggregation was already a pivotal technology in LTE-Advanced networks – facilitating the transition to Gigabit-LTE with user data rates exceeding 1 Gbps – it will play an even more critical role in 5G networks. Carrier Aggregation will enable the evolution towards multi-Gigabit-5G, supporting user data rates of approximately 4 Gbps and beyond. Additionally, 5G Carrier Aggregation has the potential to enhance the geographic coverage of high data rates, expanding the accessibility of high-speed connectivity in various locations.

Carrier Capacity and Coverage

Each frequency layer, referred to as a carrier, possesses distinct characteristics related to coverage (the area around the antenna where signals remain receivable) and capacity (bandwidth, data rates, throughput).

In simple terms, carriers in higher frequency bands typically offer greater capacity, while carriers in lower bands provide broader or deeper coverage.

Firstly, lower frequencies correspond to longer wavelengths, which propagate more effectively and penetrate deeper into indoor spaces. Secondly, lower frequency bands are often used in Frequency Division Duplex (FDD) mode, featuring stronger uplink signal strength than Time Division Duplex (TDD) mode. They are used mainly for cellular allocations above 2.5 GHz. Mid-band frequencies, such as the 3.5 GHz band, offer a balanced combination of capacity and coverage.

In most global markets, national regulators have granted spectrum licenses to Mobile Network Operators (MNOs) in the form of carriers within allocated frequency bands. Multiple operators may access carriers within a specific band, and there can be several carriers per operator in a given band. Consequently, operators may have access to narrower bandwidth carriers in the low-frequency bands (sometimes as little as 10 MHz of bandwidth in allocations below 1 GHz). In mid to high-frequency bands like n78, allocations are typically larger, often reaching 100 MHz or more per operator.

Carrier Aggregation is essential to harness the full potential of 5G performance from the available spectrum resources.

It’s important to note that uplink usually limits coverage rather than downlink. However, for a stable connection, both downlink and uplink are necessary. This is where Carrier Aggregation plays a pivotal role: it enables the use of downlink for all aggregated cells while ensuring connection stability through a common uplink on the lower aggregated carrier. Particularly when aggregating low and mid bands, Carrier Aggregation amplifies data rates and enhances the range where users can benefit from these higher speeds.

Carrier Aggregation: Evolution From 3G HSPA+, to LTE-Advanced and 5G SA

Carrier Aggregation debuted during the transition from 3G to HSPA+ when individual carriers were constrained to only 5 MHz of bandwidth. As LTE advanced, Carrier Aggregation emerged as one of its most pivotal features and data rates that showcased the true potential of mobile internet. In LTE, the maximum carrier bandwidth was capped at 20 MHz, and the aggregation of multiple 20 MHz carriers paved the way for the era of Gigabit-LTE.

In the 5G landscape, Carrier Aggregation is supported for frequencies in the low and mid-band range, falling below 7 GHz (designated as Frequency Range 1 or FR1), as well as in the high band, encompassing millimeter-wave frequencies above 24 GHz (known as Frequency Range 2 or FR2). The maximum bandwidth achievable for an individual 5G carrier is 100 MHz. In the lower bands, carrier bandwidth is typically influenced by earlier regulatory decisions that catered to the requirements of preceding network generations at that particular time.

The spectrum bands allocated to operators vary depending on the market or region. In most markets, additional spectrum resources are allocated for 5G by repurposing frequency bands originally designated for 2G, 3G, or 4G or by introducing entirely new frequency bands. This strategic allocation is a response to the escalating demand for bandwidth, driven by the continual growth in data volumes handled by mobile networks.

Carrier Aggregation in 5G Networks

To expedite the deployment of 5G networks, the initial commercial implementations relied on existing LTE infrastructure in radio access and core network components, known as 5G non-Standalone (5G NSA). With 5G NSA, MNOs could enhance available bandwidth for end users by combining 4G and 5G carriers through a 4G-5G Dual Connectivity mechanism. This allowed 5G users to leverage the existing LTE Carrier Aggregation capabilities, enabling the aggregation of up to two 5G carriers alongside LTE carriers.

However, to fully harness the potential of 5G, which includes ultra-low latency, reliability, and efficiency, MNOs are now transitioning to 5G Standalone (5G SA) networks. These 5G SA networks feature a dedicated 5G Core and a highly efficient 5G air interface, eliminating the dependence on existing LTE networks.

The number of specified 5G SA Carrier Aggregation band combinations continually increases with each quarterly revision of the 3GPP specifications. This expansion of options allows for achieving multi-Gigabit 5G data rates. These specifications ensure seamless interoperability between user equipment, such as smartphones, and the 5G networks they connect to.

Notably, between 2021 and 2022, the focus of the specifications for Carrier Aggregation in 5G SA within Frequency Range 1 shifted from two-component carriers to three and four-component carriers. As the number of 5G frequency bands surpasses that of LTE-Advanced, the potential combinations for Carrier Aggregation in 5G SA have significantly grown. The increased flexibility and deployment options allow MNOs to adapt to the unique demands of different markets and enhance their 5G offerings accordingly.

Commercial smartphones that support three-component 5G Carrier Aggregation in Frequency Range 1 (FR1) are currently available and compatible with commercially deployed Nokia 5G Radio Access Network (RAN) software. These smartphones enable the aggregation of various combinations, including Frequency Division Duplex (FDD) low-bands and Time Division Duplex (TDD) mid-bands, optimizing both data throughput and network coverage.

This advanced technology, involving the aggregation of four carriers, is poised for commercial deployment. It offers network operators even greater flexibility than the three-component carrier equivalent, enhancing their ability to deliver high-performance 5G services to their customers.

Key benefits of 5G Carrier Aggregation

As the deployment of 5G Standalone (5G SA) networks gains momentum, 5G Carrier Aggregation is poised to play a pivotal role in delivering next-generation services and exceptional user experiences. With throughput speeds already reaching levels previously achievable only on optical networks—surpassing 4 Gbps for downlink and over 2 Gbps for uplink—this technology represents a substantial leap forward in real-world performance.

As the technology matures and devices become increasingly capable of handling a growing number of component carriers, performance is expected to improve further, benefiting both network operators and 5G users. Nokia remains committed to collaborating with industry and ecosystem partners to advance 5G Carrier Aggregation technology and unleash the full potential of 5G connectivity.

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