The Road to 6G: Ten Physical Layer Challenges for Communications Engineers.

While the deployment of 5G cellular systems will continue well into the next decade, much interest is already being generated towards technologies that will underlie its successor, 6G. 5G will surely have a transformative impact on the way people and businesses communicate, but it is still far from supporting the Internet-of-Everything (IoE), where upwards of a million devices per km3 (both terrestrial and aerial) will require ubiquitous, reliable, low-latency connectivity.

The idea of 6G has started to circulate within the wireless research community, with the first overview articles appearing in the literature in the past two years. The common ground of these narrative articles is that 6G will try to address the shortcomings of 5G by boldly pushing the communication to higher frequency bands (mmWave and THz), creating smart radio environments through reconfigurable surfaces, and by removing the conventional cell structures – aka cell-free massive MIMO (CF MaMi).

Unfortunately, transforming these speculative academic concepts into commercially viable solutions is a very challenging process.

Our researchers Prof. Simon Cotton, Prof. Vincent Fusco, Prof. Michalis Matthaiou, Dr. Hien-Quoc Ngo, Dr. David Morales-Jimenez and Dr. Okan Yurduseven examined the fundamental innovations needed as key physical layer enablers for 6G, such as intelligent reflecting surfaces, cell-free massive MIMO,  and mmWave/THz/Free Space Optics frequency bands.

They identified 10 of the most important challenges that need to be addressed at the physical layer, to boost follow-up research in the 6G ecosystem.

Their discussion goes from fundamental electromagnetic and signal processing to transceiver design and hardware implementations, including theoretical modelling challenges, hardware implementation issues and scalability, while delineating the critical role of signal processing in the next generation of wireless communication technologies and networks.

Over the next decade, the investigation of these 10 most pressing challenges will cross-leverage expertise in signal processing, information theory, electromagnetics and physical implementation and require close cooperation between academia and industry.

Read the full analysis at: https://go.qub.ac.uk/RoadTo6G

The Road to 6G: Queen’s University Belfast – July 2021

https://gsacom.com

LinkedIn

Twitter

YouTube

Weibo

WeChat: GSA Express

© GSA 2o21

The post The Road to 6G: Queen’s University Belfast – July 2021 appeared first on GSA.

Development of innovative imaging technologies has been at the forefront of the research conducted within the electromagnetics community for decades. Today, imaging systems form an indispensable part of our daily lives, from optical cameras to LiDAR and millimetre-wave (mmW) radars with applications ranging from automotive sensors, non-destructive testing, to remote sensing and security screening to name a few. Across the electromagnetic spectrum, radiation at microwave and mmW frequencies is particularly advantageous as electromagnetic waves at these frequencies are not ionizing (unlike X-rays), can see through materials that are opaque at optical frequencies and operate in all-weather conditions.

MmW imaging radars conventionally rely on a multi-pixel based raster scanning principle to image a limited field-of-view located in front of the radar. This raster scanning requirement can be realized using several techniques, such as mechanical raster scanning shown in Fig. 1(a) and phased array based all-electronic scanning solutions depicted in Fig. 1(b). Limitations with such imaging technologies are that raster scanning can be slow (a significant challenge for real-time data acquisition) and require an excessive amount of data (a significant challenge for real-time image reconstruction).

To address these challenges, there has been an increasing shift towards unusual solutions, leveraging compression in the physical layer. Computational imaging facilitated by compressive sensing is one such technique that has recently received significant traction [1-3]. Computational imaging uses single-pixel compressive antennas to radiate wave-chaotic modes to sample the scene information using quasi-random bases as depicted in Fig. 1(c).

This quasi-random sampling replaces the raster scanning requirement. In computational imaging, the back-scattered data from the imaged scene is compressed into a single channel and an estimate of the scene information can then be retrieved by correlating the compressed back-scattered measurements and the transfer function of the wave-chaotic compressive antennas. As a result, the mmW images of the scene can be retrieved from a significantly reduced number of measurements in comparison to the raster scanning based techniques. Computational compressive imaging is an all-electronic technique, and hence does not require any mechanically moving parts. Moreover, the synthesis of quasi-random modes to facilitate compressive imaging can be achieved in real-time using a simple frequency-sweep or dynamically modulating the radiation pattern of the wave-chaotic antennas.

The development of compressive sensing theory and its recent applications in mmW imaging systems has shown to offer a significant potential to reshape the next generation imaging technologies. It is a question of “how” rather than “if” we will soon witness the transition of this technology from lab-based research efforts to real-life applications.

Compressive Imaging – Queen’s University Belfast

https://gsacom.com

© GSA 2021

The post Compressive Imaging – Queen’s University Belfast appeared first on GSA.

In response to the challenges of designing 5G-ready beamformer hardware at mmWave (re. my article of the last three months), disruptive technological trends have emerged that are likely to change the way we look at mmWave beamforming hardware, like using a multi-stage lens-based beamformer, or a channel sounding technique based on a metallic cavity with sub-wavelength holes on one side and a scatterer placed inside, or to integrate the 3D beamformer radiation patterns measured in the field with the communication models.

A fourth technique is related to a very large mmWave array hardware. Beamformers at mmWave 5G can operate at full capacity when they have a very large number of radiating antennas. Each antenna is responsible to transmit a fraction of the total available radiated power, which means that each antenna must have a direct or indirect connection to the radio power source. This leads to cumbersome hardware at mmWave frequencies, where technology is not advanced enough to withstand high loss between the radio source and the antennas.

Using sparse antenna arrays is an alternative approach where the total radiated power from the access point is the same, while the number of radiating antennas is less than in a conventional antenna array, in which adjacent antenna spacing must be no larger than λ/2 to avoid grating lobes. Surprisingly, the direction of radiation (main lobe and side lobes) using a sparse antenna array can perfectly match that of a conventional antenna array using the Compressive Sensing [1-2] technique. The randomness of antenna locations in a sparse array avoids the introduction of grating lobes while allowing adjacent antenna spacing to be greater than λ/2. This means that a larger array size can be implemented using a relatively small number of antennas.

Conclusion:

The radio infrastructure required to support mmWave 5G is not ready yet, however, the disruptive technologies are pushing the limits of engineering to make it a reality by 2025. The fastest version of 5G is in fact the mmWave 5G and we are looking forward to the benefits of its ubiquitous ultra-high-speed and very low latency.

References:

1. M. A. B. Abbasi, V. Fusco and D. E. Zelenchuk, “Compressive Sensing Multiplicative Antenna Array,” in IEEE Transactions on Antennas and Propagation, vol. 66, no. 11, pp. 5918-5925, Nov. 2018.

2. Abbasi, M. A. B., & Fusco, V. “Hardware Constraints in Compressive Sensing Based Antenna Array,” In UK-China Emerging Technologies (UCET) Conference at the University of Glasgow, UK IEEE 2019.

Disruptive Beamforming Trends – 4. QUB White Paper

© Queens University Belfast 2020

About the Authors:

Dr. M. Ali Babar Abbasi is a researcher in the Centre for Wireless Innovation and lecturer at the School of Electronics Engineering at Queen’s University Belfast, UK. Profile.

Professor Vincent Fusco (FIEEE, FREng, FIAE, MRIA, FIET) is a researcher in the Centre for Wireless Innovation, Professor of High Frequency Electronics at the School of Electronics Engineering and CTO of the Institute of Electronics, Communications and Information Technology (ECIT) at Queen’s University Belfast. Profile.

For detailed information on our mmWave 5G beamformers, please contact Norbert Sagnard, Business Development Manager at Queen’s University Belfast [E] n.sagnard(at)qub.ac.uk

https://gsacom.com

The post Disruptive Beamforming Trends – 4. QUB White Paper appeared first on GSA.

In response to the challenges of designing 5G-ready beamformer hardware at mmWave (re. my articles of the last two months), disruptive technological trends have emerged that are likely to change the way we look at mmWave beamforming hardware, like using of a multi-stage lens-based beamformer, or a channel sounding technique that uses a metallic cavity with sub-wavelength holes on one side and a scatterer placed inside.

Another solution is related to mmWave 5G field trials. Although it is always better to rely on channel measurements and field trials to test the practical limits of the mmWave 5G before commercial deployment, rigorous field trials are often not possible or too expensive to execute. Because of this limitation, the investigation of novel approaches within a network is not possible. In the past, the network planning sector and researchers often relied on a theoretical model to predict network performance. A single antenna used for the network calculations was often considered as an ideal omnidirectional radiator. This approximation was valid because of the simplicity of the system at sub-6 GHz 5G bands.

For mmWave 5G wireless, the assumption of an antenna as an ideal radiator can easily lead to the overestimation of the network performance. The least we can do is to integrate the practically measured 3D beamformer radiation patterns with the communication models. This approach is even more critical for dense urban environments, where connectivity and reliability of the entire network depend primarily upon the radiation performance of high directivity beamformers.

This new technique can reliably estimate the practical communication system performance by including the measured near-field and far-field 3D radiation patterns into the network calculations that are measured in an anechoic environment like the one shown below.

Next month, I will show one final technique for addressing these challenges and conclude my analysis on mmWave 5G beamformers.

Disruptive Beamforming Trends – 3. QUB White paper

©Queens University Belfast 2020

About the Authors:

Dr. M. Ali Babar Abbasi is a researcher in the Centre for Wireless Innovation and lecturer at the School of Electronics Engineering at Queen’s University Belfast, UK. Profile.

Professor Vincent Fusco (FIEEE, FREng, FIAE, MRIA, FIET) is a researcher in the Centre for Wireless Innovation, Professor of High Frequency Electronics at the School of Electronics Engineering and CTO of the Institute of Electronics, Communications and Information Technology (ECIT) at Queen’s University Belfast. Profile.

For detailed information on our mmWave 5G beamformers, please contact Norbert Sagnard, Business Development Manager at Queen’s University Belfast [E] n.sagnard@qub.ac.uk

https://gsacom.com

The post Disruptive Beamforming Trends – 3. QUB White paper appeared first on GSA.

Following on from the article in November 2020.

In response to the challenges of designing 5G-ready beamformer hardware at mmWave (re. my article of last month), disruptive technological trends have emerged that are likely to change the way we look at mmWave beamforming hardware.

One such example is the use of a multi-stage lens-based beamformer, in which the requirement of the complex phase shifter and power networks is avoided. As a result, many antennas can be fed using a smaller number of radio frequency chains (power amplifier, mixer, and filter). This way, beamforming gain is achievable, thanks to many antennas, while the cost of the system is kept minimal since the phase-shifting required for beamforming is done in low-cost lens structures.

A simple example of such a system is shown below, in which a 15-element antenna array is shown to be capable of generating nine independent radio beams [1]. The system is designed to operate on 28 GHz and is in line with 3GPP standards for 5G. This system is scalable to 64 or even 128 antenna elements, and still, low cost because the beamforming is possible without the requirement of complex and costly phase-shifting networks.

A second example is related to successful channel sounding in mmWave 5G bands. The classical radio channel sounder hardware that works well at sub-6 GHz bands of 5G is not efficient enough to support mmWave channels. A new technique of sounding requires much simpler beamforming hardware than the conventional fully connected antenna array and can deliver fast and accurate direction-of-arrival estimations in the mmWave bands. This technique requires only a metallic cavity with sub-wavelength holes on one side and a scatterer placed inside the cavity [2-3].

An example structure is shown Fig. 2. The cavity uses a frequency-diverse computational approach to do the direction-of-arrival estimation, which requires a single radio frequency chain, hence a low-cost solution again.

Next month, we will describe two more examples for addressing these challenges.

Disruptive Beamforming Trends – 2

https://gsacom.com

©QUB 2020

The post Disruptive Beamforming Trends – 2: Improving mmWave 5G appeared first on GSA.

5G is now a reality and the first stage of its infrastructure (sub-6 GHz) is already deployed in major cities around the world. The high data rate demand for 5G mobile users is shown to be fulfilled using the famous Multiple-Input Multiple-Output (MIMO) technology [1]. The next deployment stage of 5G is expected to utilize the millimeter-wave (mmWave) frequency spectrum, and the forthcoming base station antennas will operate at frequency bands around at 28 GHz and 39 GHz. At these high frequencies, a steerable RF beam can reliably serve a communication device in a much better way compared to an isotropic RF radiator having inefficient directivity, and this is possible by performing beamforming at the base station end, illustrated in Fig. 1.

Fig. 1. mmWave beamformer serving mobile terminals in mmWave 5G network.

Beamforming is a technique by which a radiator is made to transmit radio signals in a particular direction. A communication device that performs this function is called a beamformer. The most common and simplest type of a beamformer is an array of half-wavelength spaced antennas connected to a single radio frequency (RF) source via a network of power dividers. Such a beamformer is referred to as a corporate-feed array. More sophisticated beamformers involve a bank of phase shifters connected to each antenna element to add beam steering capability to a simple corporate-feed array. Advanced beamformers involve digitally controlled phase shifters, lens structures, intelligent and meta-surfaces, etc., which enhances the beamformer performance.

Disruptive mmWave Beamforming Technologies:

Designing 5G-ready beamformer hardware at mmWave is challenging due to three major reasons:
1.     Huge losses faced by the electromagnetic waves while propagating through the free space, hence highly directive radiation is desirable.
2.     The required network of phase-shifters and power dividers to add beam steering capabilities is lossy and expensive.
3.     The theoretical array theory supporting MIMO require each antenna to be connected separately to the baseband processing unit, making the overall system prohibitively expensive, especially when it comes to implementing a 64 or 128 element mmWave massive MIMO system.

Disruptive Beamforming Trends Improving mmWave 5G

https://gsacom.com

© QUB 2020

The post Disruptive Beamforming Trends Improving mmWave 5G appeared first on GSA.

Since the first cellular networks were trialled in the 1970s, we have witnessed an incredible wireless revolution. From 1G to 4G, the massive traffic growth has been managed by a combination of wider bandwidths, refined radio interfaces, and network densification, namely increasing the number of antennas per site. Due its cost-efficiency, the latter has contributed the most. Massive MIMO (multiple-input multiple-output) is a key 5G technology that uses massive antenna arrays to provide a very high beamforming gain and spatially multiplexing of users and hence increases the spectral and energy efficiency (see references herein). It constitutes a centralized solution to densify a network, and its performance is limited by the inter-cell interference inherent in its cell-centric design. Conversely, ubiquitous cell-free Massive MIMO refers to a distributed Massive MIMO system implementing coherent user-centric transmission to overcome the inter-cell interference limitation in cellular networks and provide additional macro-diversity. These features, combined with the system scalability inherent in the Massive MIMO design, distinguish ubiquitous cell-free Massive MIMO from prior coordinated distributed wireless systems. In this article, we investigate the enormous potential of this promising technology while addressing practical deployment issues to deal with the increased back/front-hauling overhead deriving from the signal co-processing.

One of the primary ways to provide high per-user data rates—requirement for the creation of a 5G network— is through network densification, namely increasing the number of antennas per site and deploying smaller and smaller cells. A communication technology that involves base stations (BSs)    with very large number of transmitting/receiving antennas is Massive MIMO, where MIMO stands for multiple-input multiple-output.

In the uplink (UL), all the users transmit data to the BS in the same time-frequency resources. The BS exploits the massive number of channel observations to apply linear receive combining, which discriminates the desired signal from the interfering signals. In the downlink (DL), the users are coherently served by all the antennas, in the same time-frequency resources but separated in the spatial domain by receiving very directive signals.

©2019 Queens University Belfast

https://gsacom.com

The post Ubiquitous cell-free Massive MIMO communications appeared first on GSA.

Indoor mm-Wave wireless access points will necessarily be placed relatively high on walls and ceilings to reduce shadowing and blocking effects and to improve coverage. This means that the access point will be at a range of elevation angles with respect to the user equipment.

In this research project, a series of experiments were conducted in our anechoic chamber to investigate the influence of elevation angle on non-line-of-sight (NLOS) near-body path gain at 60 GHz. The analysis of our measurement results shows that, compared to low elevation angle scenarios, high elevation angles of incidence provide a much better performance. The paper is particularly useful for network planners.

Please contact Norbert Sagnard at Queen’s University Belfast (Centre for Wireless Innovation) for detailed information on these findings [n.sagnard@qub.ac.uk].

©2019 QUB

The post The Influence of Elevation Angle on 60 GHz Near-Body Path Gain appeared first on GSA.

The utilization of unused millimetre–wave (mmWave) spectrum is inevitable, due to the unavailability of required bandwidth in the conventional RF band to support the high data demands in 5G networks. at mmWave frequencies, large antenna arrays with beamforming capabilities are required to compensate for the high path–loss. We are on the verge of a massive mmWave radio front-end deployment, and low–complexity, low–cost hardware beamforming solutions are required more than ever.

In this paper, we therefore demonstrate the capabilities of a constant–er lens in an attempt to realize a low complexity RF front–end for mmWave MU–MIMO. We present a high performance and low complexity lens-based beamformer consisting of constant dielectric material (er) with antenna feeds for multi–beams operation. We developed a prototype based on the classical synthesis approach and in line with the requirements of mmWave hybrid multi–user multiple–input multiple–output (MU–MIMO) systems. We performed a characterization at 28 GHz wherein uplink signal–to–noise–ratio of user terminals was evaluated with the zero–forcing (ZF) baseband signal processing.

With the measurements of the lens beamformer, we predicted the end–to–end system performance of hybrid MU–MIMO architecture in terms of ergodic sum spectral efficiency for 9 UE terminals. To draw a comparison, we used the performance of previously reported classical analogue Rotman lens-based beamformers connected to ULA and URA. Our results depict the superiority of the constant–er lens in terms of cost, complexity and performance. We show that the constant–er based beamformer solution is simple, yet significantly outperforms conventional antenna array beamformers with analogue phase shifter network. The capacity gains acquired with our proposed solution, when coupled to the mechanical and thermal properties of the lens beamformer, suggest that it is a useful engineering solution for mm-wave beamforming in hybrid massive MIMO systems.

This innovative approach is an evolution of our 28 GHz two-stage Roman Lens beamformer design, for which we were awarded the Grand Prize of the global Mobile World Scholar at MWC19 in Barcelona this year.

Please contact Norbert Sagnard at Queen’s University Belfast (Centre for Wireless Innovation) for detailed information [n.sagnard@qub.ac.uk].

©2019 QUB

www.gsacom.com

The post Lens Beamformer technical paper from Queens University Belfast appeared first on GSA.

Phase shifter–based hybrid beamforming has received a lot of attention at millimeter–wave frequencies for cellular communications. Nevertheless, the implementation complexity of such beamformers is rather high due to the complexities involved in designing and fabricating the required radio–frequency (RF) circuits. In contrast, lens–based RF beamformers significantly reduce the implementation complexity, as all active circuits can be replaced by a passive device. In this paper, researchers of the Centre for Wireless Innovation at Queen’s University Belfast present the sum spectral efficiency performance of an uplink multiuser multiple–input multiple–output (MU–MIMO) system with a 28 GHz Rotman lens. An asymmetric two–stage stacked design is fabricated with a 15 element (3×5) uniform rectangular array feeding 9 RF down–conversion chains towards baseband.

Zero–forcing processing is employed at baseband for interference nulling and multistream recovery. Our results show that the MU–MIMO gains are substantially more pronounced for the two–stage architecture relative to a single–stage design due to the inclusion of the elevation multipath components. They also show that the asymmetric design can help further reduce the implementation complexity, since the conventional beam selection network can be omitted from the RF front–end.

This novel approach won the Grand Prize of the global Mobile World Scholar award at MWC19 in Barcelona in February 2019. Please contact Norbert Sagnard for more info [n.sagnard@qub.ac.uk].

©2019 Queens University Belfast.

The post 28 GHz Two–Stage Rotman Lens Beamformer appeared first on GSA.