Multi-Panel UE (MPUE) in 5G and 5G-Advanced

With the introduction of millimetre-wave spectrum in 5G NR, antenna design at the UE became significantly more complicated. At these higher frequencies, increased propagation and penetration losses mean that directional antenna arrays and beamforming are important not only at the base station but also at the device. A single directional antenna array on a smartphone, however, would provide good performance over only part of the surrounding space. Rotate the device, change the direction of the serving cell, or block the antenna with a hand, and the radio link could deteriorate rapidly.

One solution is to place several antenna panels around different parts of the device. This gives rise to the concept of the Multi-Panel User Equipment, or MPUE.

A useful definition appears in a patent on cell reselection for MPUEs. It describes a mobile UE using two or more differently oriented antenna panels, with each providing different angular coverage. Each panel can itself contain multiple closely spaced antenna elements forming an antenna array or antenna module.

In its simplest form, imagine three directional antenna panels positioned around different edges of a smartphone.

Depending on the orientation of the phone, location of the base station and blockage from the user's hand or body, one antenna panel may provide a significantly better radio path than the others.

This type of architecture is particularly interesting for 5G FR2, where directional antenna gain helps compensate for higher path and diffraction losses. Research into MPUE mobility has considered devices with several spatially distinct antenna panels, allowing the UE to exploit antenna directivity while potentially reducing interference arriving from other directions.

An important point is that MPUE should not be thought of simply as a separate type of UE defined by 3GPP.

The antenna-panel implementation has traditionally been largely hidden from the network. In Release 16, for example, antenna panel selection, activation, deactivation and switching were largely left to the UE implementation. Different MPUE hardware architectures can consequently have quite different capabilities and power-consumption characteristics.

Three MPUE assumptions have commonly been used in 3GPP-related work to represent these different hardware capabilities.

• MPUE-Assumption 1 (MPUE-A1): multiple panels are present, but only one panel can be active at a time. Switching between panels therefore introduces some activation or switching delay.
• MPUE-Assumption 2 (MPUE-A2): multiple panels can be active simultaneously, and one or more panels can be used for transmission.
• MPUE-Assumption 3 (MPUE-A3): multiple panels can be active simultaneously for reception and measurements, but only one panel is used for transmission.

These assumptions are useful because having several physical antenna panels does not automatically mean that all of them can measure, receive or transmit simultaneously. The result depends on the RF and baseband architecture inside the device.

This leads to an interesting problem for mobility. If a UE has several antenna panels pointing in different directions, which panel should be used to measure the serving and neighbouring cells?

Research from Nokia and the Vodafone Chair at TU Dresden has looked at this question in multi-beam FR2 networks, particularly comparing MPUE-A1 and MPUE-A3.

With MPUE-A1, only one panel makes measurements at a time. Measurements are therefore effectively obtained sequentially as the UE moves between its available antenna panels.

With MPUE-A3, multiple panels can make measurements simultaneously.

The difference sounds subtle, but it can have an important impact on mobility. Consider a three-panel UE moving through a network. Under MPUE-A3, measurements obtained through all three panels can remain relatively current.

Under MPUE-A1, while Panel 1 is measuring the radio environment, measurements previously obtained through Panels 2 and 3 are getting older. By the time one of those panels is used again, the UE may have moved and the surrounding radio conditions may have changed.

A handover decision can therefore potentially be based on outdated measurements.

The 2022 study Analysis and Performance Evaluation of Mobility for Multi-Panel User Equipment in 5G Networks found that the two MPUE schemes could provide significant mobility-performance gains compared with the reference traditional UE architecture used in the study. It also found that the different MPUE architectures required different mobility-parameter settings to achieve their best performance.

This is an important observation because simply adding more antenna panels does not automatically solve mobility problems. The network procedures and mobility parameters have to take account of how the particular UE actually performs its measurements.

The issue becomes even more interesting when UE-side receive beamforming is added.

Instead of merely selecting one directional antenna panel, the UE can potentially form or steer receive beams within the angular coverage of a panel.

A later study investigated three different UE-side receive-beamforming approaches for an MPUE equipped with three directional panels in a multi-beam FR2 network. In the system-level simulations used in the study, the proposed techniques reduced radio link failures by up to 53% and handover failures by up to 90%. These figures are specific to the assumptions and scenarios used in that research, but they illustrate the potential mobility benefits of combining multiple panels with UE-side beamforming.

There are also interesting implications for interference.

If the serving cell is received strongly through one UE panel while an interfering neighbouring cell lies in a substantially different direction, the directional response of the selected antenna panel can provide some spatial isolation between them.

Research into Fast Conditional Handover has similarly noted that if an MPUE can communicate using panels oriented towards its serving cell, inter-cell interference from neighbouring cells may be significantly suppressed.

A patent from Nokia takes this idea in another direction by proposing the use of spatial separation when performing cell reselection in a network supporting network slicing.

The proposed mechanism considers candidate cells and performs communication-quality measurements using one or more of the UE's antenna panels. It can then consider whether a candidate cell supporting a required network slice is sufficiently spatially separated, or orthogonal, from other candidate cells before selecting it.

It is important to stress that this is a patent proposal rather than functionality defined by current 3GPP cell-reselection procedures.

Cell reselection normally applies when the UE is in RRC_IDLE or RRC_INACTIVE, whereas most of the MPUE mobility research discussed above focuses on connected-mode handover. The patent is interesting precisely because it proposes extending the usefulness of directional MPUE measurements into the cell-reselection problem, particularly where slice availability and intra-frequency interference need to be considered.

The underlying point remains the same: for an MPUE, the radio environment seen by the device can depend not only on where the UE is located, but also on which antenna panel is observing the network and in which direction that panel is looking.

5G-Advanced takes the multi-panel concept another important step forward.

As part of the Release 18 MIMO enhancements, 3GPP introduced support for Simultaneous Transmission with Multi-Panel, or STxMP, for multi-TRP uplink operation.

This allows a capable UE to transmit simultaneously using different antenna panels towards two Transmission/Reception Points, or TRPs.

There are several possibilities.

For single-DCI STxMP Spatial Division Multiplexing (SDM) PUSCH transmission, different spatial layers of one PUSCH are separately transmitted towards the two TRPs.

For single-DCI STxMP Single Frequency Network (SFN) PUSCH transmission, the same layers of one PUSCH are transmitted towards the two TRPs. This provides transmission diversity and can improve robustness.

For multi-DCI STxMP PUSCH+PUSCH transmission, two PUSCH transmissions are transmitted towards the two TRPs.

This distinction is worth making carefully. Separate PUSCH transmissions belong to the multi-DCI PUSCH+PUSCH case; the single-DCI SDM case divides different layers of one PUSCH between the two TRPs.

Release 18 therefore represents an interesting evolution of the MPUE concept.

Initially, multiple antenna panels were largely about giving a highly directional UE better angular coverage and allowing it to select an appropriate panel as its orientation and radio environment changed.

The evolution can roughly be thought of as:

Multiple antenna panels

→ Broader angular coverage
→ Panel selection and switching
→ Panel-aware measurements
→ UE-side beamforming
→ Improved mobility and spatial interference isolation

→ Simultaneous multi-panel transmission

There are, of course, trade-offs.

Supporting several simultaneously active antenna panels may require additional RF chains and baseband processing, increasing hardware complexity and power consumption. MPUE-A1 avoids some of this complexity by using one panel at a time, but sequential measurements can become outdated and panel switching can introduce delay.

More capable architectures can provide fresher measurements and support simultaneous panel operation, but potentially at a higher implementation and energy cost.

The network and UE therefore need to balance radio performance, mobility robustness, measurement freshness, hardware capability and power consumption.

MPUE is consequently much more interesting than simply saying that a 5G smartphone contains several antenna arrays.

At FR2 in particular, the physical orientation and capabilities of those antenna panels can influence how the UE sees the network, how reliably it moves between cells and how effectively it exploits directional beamforming.

With 5G-Advanced Release 18 STxMP, multiple UE panels can now also become part of the simultaneous uplink transmission strategy towards multiple TRPs.

As mobile networks make greater use of beamforming, multi-TRP operation and increasingly sophisticated MIMO techniques, understanding the antennas and RF capabilities inside the UE becomes an increasingly important part of understanding how the overall radio network performs.

Related Posts: 

• The 3G4G Blog: High Power / Performance User Equipment (HPUE)
• The 3G4G Blog: Is 6G Our Last Chance to Make Antennas Great Again?
• Free 6G Training: MediaTek’s Device View of the Road to 6G
• Free 6G Training: 6G Terminal Vision Whitepaper by GSMA and HONOR
• Free 6G Training: Qualcomm Keynote on 'Advancing Wireless Innovations towards 6G — from a Device’s Viewpoint' from B6GS 2023
• The 3G4G Blog: What is RF Front-End (RFFE) and why is it so Important? 

Next Generation eCall Finally Moves to 4G and 5G

Back in 2022, I wrote about the transition from the original eCall system to Next Generation eCall, or NG eCall. At the time, one of the big concerns was what would happen to millions of vehicles relying on 2G and 3G as mobile operators gradually switched off these legacy networks.

Four years later, the transition is no longer something happening in the distant future. 2026 is an important year for NG eCall in Europe.

For anyone unfamiliar with eCall, it is the European emergency calling system built into vehicles. Following a serious accident, the vehicle can automatically call the European emergency number 112, or the call can be triggered manually. Along with establishing a voice connection, the vehicle sends a Minimum Set of Data (MSD) containing information such as its location, direction of travel and other relevant vehicle information. eCall has been required for new M1 and N1 vehicle types in the EU since April 2018.

The problem is that the original eCall architecture was designed around circuit-switched 2G and 3G networks. The MSD is transferred using an in-band modem during the emergency voice call.

NG eCall takes a different approach. It uses packet-switched connectivity and IMS, allowing eCall to operate over 4G LTE and 5G. At the protocol level, it becomes an IMS emergency call, with SIP used for call signalling and the eCall MSD carried as emergency-call data within the SIP-based session.

This transition became much more significant on 1 January 2026. From that date, new M1 and N1 vehicle types in the EU have to support packet-switched eCall. Public Safety Answering Points (PSAPs) that were already deployed are also required to support eCall over packet-switched 4G/5G networks from the beginning of 2026.

The standards have continued to evolve as well. Commission Delegated Regulation (EU) 2025/1871 updated the regulatory references to the newer EN 17184:2024, covering eCall high-level application protocols using IMS over packet-switched networks, and EN 17240:2024, covering end-to-end conformance testing. There are transitional arrangements during 2026, with the newer EN standards becoming mandatory for new type approvals from 1 January 2027.

There is also evidence that the ecosystem is moving from specifications to actual interoperability testing. In June 2026, ETSI organised its latest NG eCall Plugtests in Ljubljana. Testing focused on interoperability between In-Vehicle Systems (IVS) and PSAPs over 4G LTE, and importantly included access to a real Telekom Slovenije mobile network rather than relying entirely on simulated infrastructure. Testing used ETSI TS 103 683, with EN 17240:2024 conformance testing also supported.

However, moving new vehicles to NG eCall does not make the legacy problem disappear.

The existing European vehicle fleet contains a very large number of cars whose eCall systems still depend on 2G/3G. EU rules therefore require PSAPs to continue supporting circuit-switched eCall while at least one circuit-switched mobile network remains operational in the relevant Member State.

A European Commission Joint Research Centre study published in May 2026 highlights the scale of the challenge. Its modelling estimates that there could still be around 66.8 million passenger vehicles equipped with circuit-switched eCall at the end of 2027. The study considers several possible mitigation approaches, including upgrading suitable existing eCall units to 4G, using 4G-capable third-party eCall systems and providing aftermarket solutions for vehicles that cannot otherwise be upgraded.

So, in some ways, we now have two parallel eCall transitions taking place. New vehicles and emergency infrastructure are moving towards IMS-based NG eCall over 4G and 5G, while the industry still has to work out how to keep tens of millions of older vehicles able to contact emergency services as 2G and 3G networks disappear.

The short Rohde & Schwarz video below provides a good overview of how eCall and NG eCall work, followed by an explanation of how the technology can be tested from the GNSS module and telematics control unit (TCU) through to complete vehicle-level testing.