Uplink record with 5G Advanced modem: 550 Mbit/s on the T-Mobile USA network

The US network operator T-Mobile is the first in the world to achieve an uplink speed of 550 Mbit/s with a frequency spectrum below 6 GHz. This was announced by the US subsidiary of Deutsche Telekom. T-Mobile, network supplier Nokia and modem supplier MediaTek worked together for the live demo at a public 5G base station in Seattle. MediaTek, together with Ericsson and Telstra, attracted some attention at the beginning of the year with its 5G modem, which delivered 10 Gbit/s in receive mode for the first time.

The record stands out because many network operators traditionally focus on the receiving speed of mobile technology, although the sending direction is gradually gaining in importance and applications such as cloud synchronization or sending high-resolution videos are coming into focus.

The next big thing

Ulf Ewaldsson, President of Technology at T-Mobile, even believes that “Uplink will be the next big thing”. The company wants to pave the way for games in near-real time and professional applications such as remote maintenance with AR and VR headsets.

For the live demo, the three partners used a base station and an unspecified smartphone prototype in accordance with the 3GPP Release 17 standard with Tx Switching uplink switching. The smartphone contained the M90 modem from MediaTek, which was presented at the Mobile World Congress 2025. Nokia contributed AirScale radio and system modules as well as software functions in accordance with 5G-Advanced, a spokesperson explained when asked. The partners did not comment on the distance or the exact radio conditions.

Tx-switching is a comparatively new technology that poses challenges for smartphones in particular. At best, they can only use two antennas for the transmission direction and require modern technologies such as uplink carrier aggregation (UL-CA) and uplink MIMO (UL-MIMO) to efficiently bundle several radio bands. T-Mobile has configured a total of 135 MHz of radio spectrum in the Nokia base station for this purpose. Of this, 35 MHz was allocated to the n25 band and 100 MHz to n41.

On closer inspection, this is an almost typical Tx switching configuration: two radio bands are bundled into two operating modes, an FDD and a TDD band. Vodafone also implemented this concept in January 2024 with its UL Tx switching record of 273 Mbit/s.

However, when network operators are not chasing a record, they supply customers with FDD bands alone. Here, the transmit and receive directions are divided into different parts of the spectrum, which are the same width, for example 5, 10 or 20 MHz in each direction (frequency division duplex). As soon as a mobile device has locked onto a first FDD band, it can both send and receive data. As the receiving direction dominates for most users, part of the transmission spectrum is normally unused in FDD mode.

More demand for higher upload speeds

In TDD mode (Time Division Duplex), both directions of traffic run in one radio band, but in different time slots. Because network operators can allocate time slots as required, TDD mode is considered to accelerate the main direction of traffic: if customers are expected to be mainly downloading, they are given at least one TDD band in addition to one or more FDD bands, reserving the majority of slots for the downlink and thus drastically speeding up downloads. For the uplink record, the slot allocation is reversed and a disproportionately large number of time slots are allocated to the transmission direction.

Deutsche Telekom responded to a query from c't magazine by stating that it is observing an increasing demand for more upload capacity among its customers. The company has therefore been using “initial variants” of uplink Tx switching for a while now. “In the 3.6 GHz band, we use uplink multi-user MIMO and uplink carrier aggregation to specifically increase network capacity. Due to technical constraints, current end devices usually only bundle two uplink carriers,” said a spokesperson for the company.

Overall, the progress appears to be welcome, even though few users still rely on real-time gaming and VR headsets with mobile networks. Stationary 5G routers with uplink Tx switching are also desirable in a future everyday life, simply because they can draw the power required for the additional performance from the socket. The uplink turbo is likely to use up the limited energy supply of smartphones far too quickly. Stationary routers also seem interesting in the long term because they offer enough space for four transmission units and thus for even higher transmission speeds.

(dz)