Why do we need the "Great Uphill"?
Recently, operators across the country have intensively launched 5G-A packages, setting off a large-scale wave of 5G-A commercialization.
When promoting 5G-A, there is a term that often comes up in operators' pitches as the core highlight of 5G-A.
This term is - "High-capacity uplink".
Operators claim that "Compared with 5G, 5G-A offers a tenfold increase in theoretical speed, which will propel mobile communication into an era of '10 Gbps downlink and 1 Gbps uplink'. High-capacity uplink will meet the needs of user scenarios in the AI era and bring a brand-new network experience."
So, why are operators emphasizing the importance of "High-capacity uplink"? What are the technical backgrounds and market demands behind this? And how does 5G-A achieve "High-capacity uplink" technically?
In today's article, Xiaozao Jun will have an in-depth discussion on this topic with you.
Why is the traditional uplink so slow?
The so-called "High-capacity uplink" refers to a higher uplink connection speed.
As we all know, mobile terminals like mobile phones both receive data from base stations and send data to them. The former is the downlink, and the latter is the uplink.
The communication speeds of the uplink and downlink have always been unequal. The uplink speed is significantly slower than the downlink speed.
The reason is simple. Cellular mobile communication has always had a centralized architecture, where one base station serves hundreds or thousands of terminals.
The wireless transmission power of a base station is three orders of magnitude greater than that of a mobile phone, with a stronger signal and a longer propagation distance.
5G base station
It's like on a playground, where a teacher talks to N students. To make themselves heard, the teacher uses a megaphone, while the students don't have one. So, it's easy for students to hear the teacher, but difficult for the teacher to hear the students.
From the perspective of a mobile phone, not only is its transmission power low, but the number of its antennas is also limited. Generally, mobile phone antennas are configured as 2T4R (2 transmit, 4 receive) or 1T2R (1 transmit, 2 receive), which is also imbalanced.
Modern mobile communication systems are designed to favor the downlink. For example, in the frame structure configuration of 5G TDD, the ratio of uplink to downlink time slots is usually 3:7, with more downlink than uplink.
Moreover, after receiving downlink data, the mobile phone also needs to use the uplink bandwidth to send back acknowledgment messages, which further affects the uplink capacity.
Looking at specific technology generations, the theoretical uplink/downlink speeds of 4G (FDD LTE) are 50Mbps and 150Mbps respectively, and those of 5G NR are 200 - 300Mbps and 1.5 - 2Gbps respectively (depending on specific frequency bands and configurations). It can be seen that in both 4G and 5G, the uplink speed is significantly lower than the downlink speed.
Why do we need to improve the uplink?
The fact that the uplink is weaker than the downlink is determined by the centralized architecture of the communication network. In a sense, it is also a "legacy issue".
In the early stages of mobile communication development, it was mainly used for person-to-person communication, with voice calls and text messages being the main services. Although this type of communication is point-to-point, it has low requirements for communication bandwidth.
Later, with the rise of the Internet, more and more websites and content service providers emerged. The form of content also evolved from text to multimedia such as audio and video. The entire network began to adopt a centralized business architecture.
Under this architecture, most communication needs involve transmitting multimedia content from data centers to mobile terminals. This is obviously a downlink requirement, so mobile communication networks at that time focused on enhancing downlink capabilities.
Now, the times have changed dramatically.
Thanks to continuous upgrades in camera and other technologies, terminals have strong image capture capabilities, giving rise to new services such as high-definition video calls, video conferences, and video live broadcasts. These services place higher demands on the uplink capabilities of mobile communication networks. The model of network services has begun to shift from "downlink-oriented" to "equal emphasis on uplink and downlink".
In addition to mobile phones, the continuously evolving Internet of Things also has higher requirements for the uplink capacity. The service types of the Internet of Things include control and data collection. In terms of data collection, there are also a large number of video terminals (such as industrial cameras, traffic cameras, and security cameras) that need to upload data.
The scale of IoT terminals is larger, and in some industrial scenarios (such as intelligent manufacturing), the video resolution collected is extremely high, which not only requires a higher uplink speed but also a lower uplink transmission delay.
If video services only pose a preliminary test to the uplink capacity, then the rapidly emerging mobile AI will make this test even more challenging.
AI is a typical data-driven service. AI-related services, such as AI assistants, real-time translation, and image recognition, all require uploading a large amount of raw data (such as voice, video, and environmental information) to the cloud for processing. Some AI applications involve multi-modal interaction (text, voice, video, AR, etc.), which also have diverse requirements for the bandwidth, delay, and stability of the uplink.
As we can see, AI applications on the edge side are accelerating towards an Agent-centric interaction mode. In 80% of Agent interaction scenarios, the uplink demand exceeds the downlink demand.
In addition to consumer AI applications on mobile phones, industrial AI applications will pose greater challenges to the uplink capacity. A large amount of scenario data needs to be uploaded to the cloud and processed into sample data for large model training.
For example, in the Internet of Vehicles scenario, autonomous vehicles need to upload up to several gigabytes of environmental perception data per second.
In summary, under the multiple pressures of video services and AI services, it has become urgent to improve the uplink capacity of mobile communication networks. Strengthening the uplink capacity and achieving Gbps-level uplink speeds in the new-generation mobile communication technology standard 5G-A has also become a common consensus in the industry.
How to improve the uplink capacity?
So, how exactly does 5G-A achieve "High-capacity uplink"?
Actually, in the early stages of 5G, research on how to improve the uplink capacity had already begun.
For example, the SUL (Supplementary Upload) technology introduced in 5G, which uses the low-frequency LTE FDD (e.g., the 1.8GHz band) for uplink and the high-frequency NR TDD for downlink, can to some extent solve the uplink bottleneck at long distances caused by the weak transmission power of mobile phones.
SUL (Supplementary Upload)
Another example is that by appropriately modifying the frame structure and increasing the uplink time slots, the uplink speed can be increased several times. Or, using CA carrier aggregation in the uplink can also improve the uplink capacity.
In 2019, Huawei and China Telecom jointly launched the "Super uplink" technology, which solves the problems of insufficient uplink bandwidth and limited coverage through TDD/FDD coordination, high/low-frequency complementarity, and time/frequency domain aggregation.
In the 5G-A era, the industry has conducted more in-depth exploration based on these attempts.
Let's take a look at some recent developments:
Not long ago, Zhejiang Mobile, in collaboration with Huawei and other partners, completed the first large-scale field network verification of the F/A SUL (Supplementary Uplink) high-capacity uplink technology in Hangzhou.
The F/A SUL technology introduces the full uplink spectrum of the F band (1880 - 1900MHz) or A band (2010 - 2025MHz) during the downlink time slots of the anchor station (using the 4.9GHz band in this pilot), achieving "uplink on different frequencies simultaneously" and breaking through the uplink resource bottleneck of traditional TDD links.
This verification achieved a single-user uplink peak speed of over 1Gbps for commercial terminals, demonstrating the uplink capacity of the F/A SUL technology and laying the foundation for the next stage of large-scale commercial network verification.
The industry's first large-scale antenna array AAU for F/A SUL
Last month, Zhejiang Telecom, Zhejiang Unicom, and Huawei jointly completed the innovative commercial verification of a dual-frequency 8T8R base station operating at 1.8GHz + 2.1GHz, with the 5G single-user uplink speed exceeding 1.1Gbps.
The 1.8GHz + 2.1GHz dual-frequency 8T8R base station used in this commercial verification has a large bandwidth capacity of 95MHz for both uplink and downlink in frequency division duplex (FDD). Through the coordinated use of uplink carrier aggregation (CA) and single-user multiple-input multiple-output (SU-MIMO) technology, the uplink capacity of the base station has been effectively improved.
On June 19th, during the 2025 MWC Shanghai, China Telecom and Huawei jointly held a 5G-A "Intelligent Aggregation for High-capacity Uplink" joint innovation press conference. Their proposed "Intelligent Aggregation for High-capacity Uplink" technology is worthy of attention.
This technology includes three major innovations: intelligent spectrum aggregation, intelligent cell coordination, and intelligent link management. It fully exploits the uplink coverage capabilities of multiple antennas, combines distributed UCN (User-Centric Network) and real-time sharing of all time, frequency, and power resources, and introduces wireless intelligent technology to build a wireless network for AI service bearers.
5G-A "Intelligent Aggregation for High-capacity Uplink" joint innovation press conference
Intelligent spectrum aggregation means that in the past, traditional 4G/5G could not achieve flexible cross-standard spectrum allocation. After adopting this innovation, cross-standard intelligent spectrum pooling can be achieved, and part of the 4G uplink spectrum can be "borrowed" for 5G uplink use.
Intelligent cell coordination is an innovation in networking, which enables multiple network-level cells to cooperate intelligently to provide users with guaranteed deterministic delay.
Intelligent link innovation refers to the intelligent reconstruction of the uplink through intelligent channel tracking, achieving optimal spectrum efficiency.
According to the data released at the press conference, these innovations can enable the 5G-A network to have accurate prediction capabilities, reduce the delay by over 30%, increase the uplink speed by over 15%, and improve the edge experience by over 15%.
Final thoughts
Currently, the development of 5G-A in China has entered the fast lane. The three major operators have deployed 5G-A networks in more than 300 cities across 31 provinces, covering key scenarios such as core business districts, transportation hubs, and industrial parks, which are expected to support 50 million users.
Specifically, China Mobile has launched 5G-A services in over 330 cities. In 2025, China Mobile will invest 9.8 billion yuan to promote the commercialization of 5G-A and expects to have 50 million 5G-A users by the end of the year. China Unicom plans to fully launch 5G-A services in the main urban areas of 39 key cities in 2025 and start 5G-A services in key scenarios in over 300 other cities. China Telecom deployed approximately 70,000 5G-A base stations in 121 cities on a large scale in 2024. In 2025, they plan to further expand the coverage of 5G-A base stations to more than 150 key cities.
As the 5G-A network becomes more widespread, more and more users will enjoy an excellent network experience, including "High-capacity uplink". The promotion of "High-capacity uplink" is not only a technological innovation but also a positive response to future network demands. It is hoped that all parties in the industrial chain can work together to accelerate the innovation, upgrade, and application expansion of this technology, laying a solid foundation for the arrival of the mobile AI era.