Understand 5G-A multi-frequency coordination—“3CC” in one minute

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Speaking of "3CC", we must mention its more popular name - "3 legs". In the communications industry, we often talk about the concepts of "adding legs" and "deleting legs". So, what are "legs"?

The "legs" are actually the communication carrier frequency bands. The "three legs" contained in 3CC correspond to three component carriers (CC), such as 2.1G/3.4G/3.5GHz.

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The combination of three component carriers of 3CC is also called "T+T+F". Naturally, there must be 2CC corresponding to 3CC. There are many combinations of 2CC, the most common ones are "F+F, F+T and T+T".

• TDD-NR frequency band: including 3.4GHz/3.5GHz, etc.
• FDD-NR frequency band: frequency band refarming or spectrum sharing can be used to coexist with existing 4G networks, such as 800M, 900M, 2.1G, etc.

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First of all, as to why 3CC is used, it must be because a single carrier has some disadvantages. We all know that the frequency bands used by 5G are relatively high, such as 4.9GHz and 3.5GHz, which belong to the medium and high frequency bands. The advantage of high frequency bands is that the bandwidth resources are large, but the corresponding transmission loss is also higher and the penetration loss is greater. For example, the path loss of 3.5GHz is about 4.4dB higher than that of 2.1GHz. This leads to a shorter coverage distance and insufficient coverage depth of a 5G single carrier. This is reflected at the user level in the low cell edge rate, poor network performance, and poor perception.

For places with dense traffic, such as high-speed rail stations, airports, and central business districts, there are many partition scenarios. When outdoor macro base stations are used for coverage, the penetration loss is relatively large. Elevators, underground parking lots, and other areas in such scenarios are generally blind spots. In addition, the bandwidth of the FDD frequency band is generally small. For example, the bandwidth of 2.1GHz is only 40M, which is insufficient compared to the 100M of TDD-3.4/3.5GHz.

We all know the principle of "1+1+1>1". 3CC can combine three carriers to achieve a bandwidth of more than 200M+, which is much higher than a single carrier in terms of speed and capacity. It can effectively improve the coverage distance and coverage depth, and maximize user perception.

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3CC is based on traditional carrier aggregation technology (CA), which aggregates two or more component carriers to obtain a larger bandwidth. After the UE is configured with carrier aggregation, it can send and receive data with multiple cells at the same time, deeply coordinate high and low frequency multi-carrier capabilities, and further improve the user's perceived rate and experience.

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• Improve throughput: CA can integrate continuous or non-continuous frequencies to achieve the superposition of available bandwidth, thereby increasing terminal throughput and improving the speed experience.
• Improve resource utilization: CA's primary and secondary cells can achieve more flexible scheduling, thereby making full use of the idle resources of each carrier to form efficient diversion to ensure maximum resource utilization.
• Improve coverage: Under carrier aggregation, relevant control information can be sent through the main carrier, thereby taking advantage of the uplink coverage of the main carrier to improve the overall coverage of the cell.

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In April 2021, ZTE took the lead in completing the DL 3CC CA verification of 2.1G+3.4G+3.5G, and the single-user peak rate increased by 226% compared with the 3.5GHz single carrier.

In 2024, ZTE will conduct field performance testing and verification of 3CC, and cooperate with operators to create key coverage scenarios for 3CC contiguous areas.

In March 2024, ZTE conducted a 3CC contiguous area test in a certain bureau, and its indoor depth coverage was increased by up to 15%+, and the indoor edge rate was increased by 110%+; the outdoor downlink road rate was increased by 50%+. ZTE will continue to cooperate with operators to create a high-speed experience in 3CC contiguous areas, further improve network performance, and provide users with a better perceived experience.

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