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? 

IET Lecture by Prof. Andy Sutton: Point to Point Microwave Radio Systems

Point to point microwave radio systems have been with us for more than eighty years, yet they rarely attract much attention in an era where fibre dominates network planning and satellite systems continue to develop at pace. At a recent IET Anglian Coastal Local Network event, Prof. Andy Sutton delivered an excellent lecture that brought these fixed radio links back into the spotlight. His talk explored the history, engineering and future of microwave and millimetre wave links, reminding us why they remain essential for transmission networks in the UK and around the world.

The story begins with the national microwave radio network of the 1970s, with the BT Tower at its centre. These early deployments supported long links across the country and laid the foundation for many of the design principles still used today. While the landscape has changed significantly, the fundamentals of fixed radio communication continue to be shaped by spectrum availability, propagation characteristics and careful engineering.

Microwave links depend on a wide range of bands, from the lower 6 GHz region through to 80 GHz E-band. The choice of frequency affects everything from link length to susceptibility to atmospheric absorption. As Andy explained, a link designer must consider not just free space path loss, but also Fresnel zone clearance, rainfall intensity and antenna characteristics. The slides included a worked example that showed the impact of frequency and distance on the radius of the Fresnel zone and highlighted the need for adequate clearance to maintain availability over time.

The talk moved on to modern access radio systems, where compact rooftop nodes and all-outdoor radios have become common. These systems rely on careful use of vertical and horizontal polarisations, often enabled through XPIC technology. XPIC allows separate data streams to coexist on the same frequency using orthogonal polarisations, effectively doubling link capacity when conditions allow. This is paired with adaptive coding and modulation, which enables the radio to shift modulation schemes according to link quality. The result is a more resilient and efficient link compared to older fixed-modulation systems.

Capacity planning is a balancing act that involves radio channel bandwidth, modulation choice and the number of aggregated carriers. Wider channels and higher order modulation support multi-gigabit throughput, although this introduces penalties in transmit power and receiver sensitivity. The trade-offs are central to radio design and determine the type of equipment used, whether through a separate indoor and outdoor unit or an integrated all-outdoor system.

Andy also covered the practical elements of radio link planning, such as antenna selection, path profiling, waveguide losses and typical link budget calculations. A link planning example using a 32 GHz radio demonstrated the relationship between transmit power, antenna gain, free space loss and fade margin for a target availability of 99.99 percent. The discussion tied together the theoretical foundations with real-world engineering and illustrated how access radios are designed for street-level backhaul scenarios.

The lecture then moved to millimetre wave systems, particularly E-band radios that operate around 70 and 80 GHz. These links offer enormous capacity over shorter distances and are increasingly used for dense urban backhaul and enterprise connectivity. The slides included examples of network topologies showing how microwave and fibre can be combined to meet different deployment objectives.

A substantial part of the presentation focused on trunk or core microwave radio systems. These high-capacity, high-availability links support long distances and historically formed the backbone of national networks. Although demand for trunk links has reduced as fibre has spread, they still exist in challenging environments. In the UK, many trunk links remain operational in Scotland and island regions where terrain and geography limit fibre deployment. The lecture covered branching networks, duplexers, waveguide installations and space diversity techniques, all of which contribute to the reliability of long-haul links.

Looking ahead, research continues into new frequency bands, wider channels, higher modulation schemes and improved radio hardware. These advances will support even greater capacities, with millimetre wave links expected to reach 100 Gbps over short distances. Microwave radio may no longer be the headline technology it once was, but the field continues to push boundaries and remains an essential part of modern communication networks.

Andy’s lecture was a comprehensive tour of the past, present and future of point to point microwave systems. For anyone working in transmission, mobile networks or wireless engineering, it served as a valuable reminder of the depth of innovation in this area and its continued relevance in the broader ecosystem.

If you would like to explore the material in more detail, the slides from the event are available here and the video can be seen here. Both are well worth a look.

Related Posts:

• Connectivity Technology Blog - 5G Demystified; the What, When and Where by Prof. Andy Sutton, BT
• The 3G4G Blog - Prof. Andy Sutton: Backhauling the 5G Experience - Jan 2020
• The 3G4G Blog - Prof. Andy Sutton: 5G Radio Access Network Architecture Evolution - Jan 2019
• The 3G4G Blog: 5G Network Architecture, Design and Optimisation - Jan 2018
• The 3G4G Blog: 5G Network Architecture and Design Update - Jan 2017
• The 3G4G Blog - CWHeritage Talk: The History of Synchronization in Digital Cellular Networks 

Prof. Ted Rappaport Keynote at EuCNC & 6G Summit 2023 on 'Looking Towards the 6G Era - What we may expect, and why'

Prof. Ted Rappaport has featured a few times in our blog posts (see here and here). Today we look at his recent keynote at the EuCNC & 6G Summit 2023 on the topic 'Looking Towards the 6G Era - What we may expect, and why'. The abstract of the talk says:

Recent work has shown that the fundamentals of the radio propagation channel will enable mobile communications all the way to 900 GHz, offering bandwidths of tens of GHz. An amazing fact that is all but disregarded is that the three fundamental technological breakthroughs of 5G, namely millimeter wave technology, small cell densification, and massive multiple-input multiple-output (massive-MIMO) antenna systems, are paving the way for the next several decades of the wireless industry. This talk demonstrates how the 5G era will futureproof wireless networks as we enter the 6G era and beyond — an era of wireless cognition and human-style computing. In fewer than 20 years, wireless networks will carry information at the computation speed of the human brain. Yet, how will engineers ensure that we build these networks with sustainability and power efficiency in mind? This talk offers some solutions and promising areas of exploration to ensure the future 6G era is lightning fast yet kind to planet earth.

Next G Alliance has a nice short report looking at 'Terminology for Frequency Ranges'. Handy and useful charts - https://t.co/kfJFxcdUDo via @atisupdates @NextGAlliance #Free5Gtraining #3G4G5G #ATIS #NGA #5G #B5G #6G #Frequency #Spectrum #Bands #mmWave #cmWave #THz pic.twitter.com/Nyoh1X0asX

— Free 5G Training (@5Gtraining) July 25, 2023

Recently I had a discussion about mmWave, sub-THz, THz, etc. This chart in the Tweet above is handy with deciphering the 5G/6G spectrum terminology.

Prof. Rappaport covered quite a few topics on spectrum above 100 GHz and made a strong case for mmWave and Terahertz. The mmWave adoption for 5G hasn't yet taken off so we will have to see how enthusiastic the industry is for even higher frequencies. The other keynotes from the conference (see references below) argued for cmWave as the mid-band for 6G. We will have to wait and see where all this discussion goes.

The talk is embedded below:

Related Posts: 

• Free 6G Training: Recent Advances on Terahertz (THz) communications
• The 3G4G Blog - 6G: Above 100 GHz and Terahertz (THz) Frequencies
• The 3G4G Blog: Spectrum for 5G NR beyond 52.6 GHz
• Free 6G Training: Ericsson's Keynote at EuCNC & 6G Summit 2023 on '6G – Connecting a cyber-physical world'
• Free 6G Training: Nokia's and Docomo's Joint Keynote at EuCNC & 6G Summit 2023 on '6G getting into next gear'
• Free 6G Training: Huawei's Keynote at EuCNC & 6G Summit 2023 on 'On the Convergence Route for 6G'
• Free 6G Training: EuCNC & 6G Summit 2023 Panel Session on 'Sustainability challenges and opportunities for 6G'
• Free 6G Training: Samsung's 6G Spectrum Whitepaper Discusses Candidate Bands
• Free 6G Training: Do we need more Bandwidth or Higher Bandwidth Efficiency?
• Free 6G Training: 7 Defining Features of Terahertz (THz) Wireless Communications Systems 

New 5G NTN Spectrum Bands in FR1 and FR2

Release-17 includes two new FR1 bands for NTN; n255 (a.k.a. NTN 1.6GHz) and n256 (a.k.a. NTN 2GHz). The picture is from a slide in Rohde & Schwarz presentation available here. Quoting from an article by Reiner Stuhlfauth, Technology Manager Wireless, Rohde & Schwarz:

Currently, several frequency ranges are being discussed within 3GPP for NTN. Some are in the FR1 legacy spectrum, and some beyond 10 GHz and FR2. The current FR1 bands discussed for NTN are:

• The S-band frequencies from 1980 to 2010 MHz in uplink (UL) direction and from 2170 to 2200 MHz in downlink (DL) direction (Band n256).
• The L-band frequencies from 1525 to 1559 MHz DL together with 1626.5 to 1660.5 MHz for the UL (Band n255).1

These frequency ranges have lower path attenuation, and they’re already used in legacy communications. Thus, components are available now, but the bands are very crowded, and the usable bandwidth is restricted. Current maximum bandwidth is 20 MHz with up to 40-MHz overall bandwidth envisaged in the future [TR 38.811].

As far as long-term NTN spectrum use is concerned, 3GPP is discussing NR-NTN above 10 GHz. The Ka-band is the highest-priority band with uplinks between 17.7 and 20.2 GHz and downlinks between 27.5 and 30 GHz, based on ITU information regarding satellite communications frequency use.2 Among current FR2 challenges, one is that some of the discussed bands fall into the spectrum gap between FR1 and FR2 and that NTN frequencies will use FDD duplex mode due to the long roundtrip time.

6G Unified networks: Multi-Layer Multi-Dimension Multi-Band (ML-MD-MB) Topology via @RohdeSchwarz highlights the future 6G Satellite and Terrestrial Network Convergence Vision#3G4G5G #5G #B5G #6G #NTN pic.twitter.com/DHVIP9kw8J

— Zahid Ghadialy (@zahidtg) May 20, 2023

Worth highlighting again that the bands above, including n510, n511 and n512 are all FDD bands due to the long round trip times.

The latest issue of 3GPP highlight magazine has an article on NTN as well. Quoting from the article:

The NTN standard completed as part of 3GPP Release 17 defines key enhancements to support satellite networks for two types of radio protocols/interfaces:

• 5G NR radio interface family also known as NR-NTN
• 4G NB-IoT & eMTC radio interfaces family known as IoT-NTN

These critical enhancements including adaptation for satellite latency and doppler effects have been carefully defined to support a wide range of satellite network deployment scenarios and orbits (i.e., LEO, MEO and GEO), terminal types (handheld, IoT, vehicle mounted), frequency bands, beam types (Earth fixed/Earth moving) and sizes. The NTN standard also addresses mobility procedures across both terrestrial and non-terrestrial network components. Release 17 further includes Radio Frequency and Radio Resource Management specifications for terminals and satellite access nodes operating in two FR1 frequency ranges allocated to Mobile Satellite Services (i.e., n255 and n256).

You can read it here.

Related Posts: 

• The 3G4G Blog: 3GPP 5G Non Terrestrial Networks (NTN) Standardization Update
• Connectivity Technology Blog: 5G NR-NTN Demos make a Debut at MWC 2023
• Connectivity Technology Blog: Direct-to-Mobile Communications Using LEO Satellites gets a Step Closer
• Connectivity Technology Blog: TIP has launched 'Non-Terrestrial Connectivity Solutions' Group
• The 3G4G Blog: An Introduction to Non-Terrestrial Networks (NTN)
• Free 6G Training: Non-Terrestrial Networks (NTN) & Satellites - Taking 6G to the Stars
• The 3G4G Blog: How Many People are Still Unconnected in 2023 and Why? 

Qualcomm Explains 5G Millimeter Wave (mmWave) Future & Integrated Access and Backhaul (IAB)

We have covered various topics in our blog posts on millimeter wave spectrum and even going beyond 52.6 GHz in FR2. A Qualcomm webinar from back in January expands on many of the topics that I looked superficially in various posts (links at the bottom).

The following is edited from the Qualcomm blog post:

5G NR in unlicensed spectrum (NR-U) was standardized in Release 16 and it is a key enabler for the 5G expansion to new use cases and verticals, providing expanded spectrum access to mobile operators, service providers, and industry players. At the same time, we are starting to push the mmWave boundary to even higher bands toward the sub-Terahertz (i.e., >100 GHz) range. Expected in Release 17, 5G NR will support spectrum bands up to 71 GHz, leveraging the 5G NR Release 15 scalable numerology and flexible framework. This opens up 5G to operate in the globally unlicensed 60 GHz band, which can fuel a broad range of new applications and deployments.

One daunting challenge that mobile operators will face when expanding 5G mmWave network coverage is the cost of deploying additional base stations for mmWave, which usually requires new fiber optics backhaul installations. Release 16-defined IAB allows a base station to not just provide wireless access for its user devices (e.g., smartphones) but also the ability to backhaul wirelessly via neighboring base stations using the same mmWave spectrum. IAB opens the door to more flexible densification strategies, allowing mobile operators to quickly add new base stations to their networks before having to install new fiber to increase backhaul capacity. 

Release 16 established foundational IAB capabilities, such as dynamic topology adaptation for load balancing and blockage mitigation, and Release 17+ will further enhance IAB by bringing new features like full-duplex operation, topology redundancy, and ML-based network management.

Beyond IAB, there is a rich roadmap of other new features that can further improve 5G mmWave system performance and efficiency. The webinar embedded below is presented by Ozge Koymen, Senior Director, Technology, Qualcomm Technologies, Inc. It covers the following topics:

• Qualcomm's vision for 5G mmWave and the new opportunities it poises to bring for the broader ecosystem
• mmWave capabilities and enhancements coming in Release -16 and beyond
• Qualcomm’s role in mobilizing and democratizing 5G mmWave to usher in new experiences
• Latest update on the global commercial rollout of 5G mmWave networks and devices

Slides of the presentation are available here.

Related Posts:

• Free 6G Training: Spectrum for 5G, Beyond 5G and 6G research
• The 3G4G Blog: A mmWave Special Cell in Open RAN Environment
• The 3G4G Blog: Spectrum for 5G NR beyond 52.6 GHz
• The 3G4G Blog: 5G Integrated Access and Backhaul (IAB) Enhancements in Rel-17
• The 3G4G Blog: Carrier Aggregation (CA) and Dual Connectivity (DC)
• The 3G4G Blog: The Politics of Standalone vs Non-Standalone 5G & 4G Speeds 

A mmWave Special Cell in Open RAN Environment

NR RRC signaling messages exchanged for establishing a 5G radio connection, in particular the NR RRC Reconfiguration and NR RRC CG Config messages, contain a parameter called "SpCellID", which refers to the Special Cell ID. 

The concept of the Special Cell already exists in 3GPP LTE Advanced standards. Here a Special Cell is set of physical cells with same or different carrier frequency and physical cell ID (PCI) that overlap in a certain geographical area and thus, are combined for data transmission to/from UEs located in this area.

This concept now also gains high importance for 5G NR mmWave spectrum and here is why:

Many 5G mmWave radio transmitters can only handle a maximum bandwidth of 100 MHz, but the radio sector shall be covered with total bandwidth of e.g. 600 MHz. To achieve this six mmWave radio transmitters are installed in parallel at the same spot covering the same footprint. 

Each transmitter is identified on the radio interface by its own dedicated NR ARFCN (carrier frequency) and PCI. Thus, from UE point of view the sector is covered with 6 dedicated NR cells that all together form a Special Cell.

When a UE gets radio resources assigned in this 5G sector one of  the 6 cells is the Primary Cell, which NR CGI (Cell Global Identity) is then used as Special Cell ID in layer 3 signaling messages. All other cells act as Secondary Cells.

In an Open RAN environment the F1AP protocol allows perfect analysis of the SpCell resource allocation since it contains the SpCellID as well as all SCellIDs to be setup in the call. 

If the gNB-DU fails to allocated resources for a particular Secondary Cell this will also be signaled together with a failure cause value on F1AP as illustrated in the figure below. Also radio link failures occurring within the Special Cell will be signaled on F1AP including a cause value that provides deeper insight than  protocol causes seen on X2AP (in case of 5G NSA connections) or NGAP (in case of 5G SA connections). 

(click on image to enlarge)