Professor Nathan Gomes
Nathan Gomes received a BSc (Eng) Honours degree from the University of Sussex in 1984 and a PhD from University College, London in 1988, both in Electronic Engineering. His PhD research involved the investigation of optically delivering the local oscillator to microwave diode mixers. He was awarded a European Science Exchange Programme Fellowship by the Royal Society and spent one year at the Ecole Nationale Superieure des Telecommunications, Paris. Since the end of 1989 he has been at the University of Kent where he is now a Professor of Optical Fibre Communications.
Professor Gomes leads a research team particularly focussed in the areas of fronthaul networks and radio over fibre communications. He publishes regularly in highly respected international journals such as OSA/IEEE Journal of Lightwave Technology, OSA/IEEE Journal of Optical Communications and Networks, IEEE Journal of Selected Areas in Communications, and has consistently attracted European and UK research funding. He has collaborated with industry, including companies such as Orange, BT, ADVA Optical Networking, VIAVI, in a number of these projects. Professor Gomes and members of his team have attended IEEE standards body meetings, and he is the UK-nominated expert to the IEC standards Working Group 6 on radio over fibre technologies.
Professor Gomes is EDA’s main contact to the Engineering Professors’ Council (EPC) and sits on the EPC’s Research, Innovation and Knowledge Transfer Committee.
Professor Gomes is an Academic Accreditor for the IET.
Professor Gomes’s research interests are specifically in the area of the convergence between optical fibre access networks and new and emerging wireless and mobile communication systems. This area comprises work on what is now often termed the “xhaul” or new fronthaul and middle haul of 5G and beyond mobile systems, and includes both analogue and digital radio over fibre systems. More generally, he has led work in the areas of microwave photonics and optical communications.
During the 2000s, Professor Gomes led the University of Kent contributions to the international Atacama Large Millimeter Array radio telescope project. This involved the development of a precision frequency source using an optical comb generator, the definition of the transport of the synchronization signals to the multiple radio telescopes over an optical distribution network, taking into account polarization drift effects, and the mitigation of polarization effects due to antenna cable wraps. He also led the University involvement in EU Networks of Excellence in radio over fibre technology (NEFERTITI and ISIS).
In the EU FUTON project, he led the radio over fibre systems work package and was deputy technical manager. This project was the first to demonstrate distributed MIMO/coordinated Multipoint using a radio over fibre distribution network and outlined many of the concepts of what was later termed the cloud Radio Access Network. More recently, in the EU-Japan project RAPID-5G, distributed MIMO over a radio over fibre distribution network has been demonstrated at millimetre-wave frequencies.
Professor Gomes was the coordinator and technical leader of the EU Horizon 2020 iCIRRUS and UK EPSRC NIRVANA projects, which pioneered the proposals for the use of Ethernet in new digital fronthaul architectures. The testbed developed through these projects is being used in follow-on projects, such as the EU-China 5G project 5G-DRIVE.
- EL570 Communications Principles (Communication Networks Principles)
- EL677 Digital Communication Systems (Communication Networks)
- EL822 Data Networks and the Internet
- EL873 Advanced Networking Systems and Technology
- Chartered Engineer (CEng)
- Fellow Institution of Engineering and Technology (FIET)
- Senior Member Institute of Electrical and Electronics Engineers (SMIEE)
Showing 50 of 225 total publications in the Kent Academic Repository. View all publications.
Habib, U. et al. (2019). Single Radio-over-Fiber Link and RF Chain-based 60GHz Multi-beam Transmission. Journal of Lightwave Technology [Online]. Available at: https://doi.org/10.1109/JLT.2019.2896778.An efficient multi-user transmission scheme at 60 GHz using a single-feed Leaky Wave Antenna (LWA) and hence requiring only a single Radio-over-Fiber link and single RF chain is presented. A Subcarrier Multiplexed (SCM) signal carrying the different users' data is transported over 2.2km of optical fiber and then upconverted to the 60 GHz band for transmission to multiple spatially separated users through the beam steering characteristics of the LWA. An overall sum data rate, the combined rate from all users, of 10.6 Gb/s using 16-QAM modulation serving 10 users over a transmission bandwidth of 3.05 GHz or 20 users with QPSK over 6.1 GHz span, is achieved experimentally. The theoretical sum data rates for 6.1 GHz bandwidth for different numbers of users are calculated, considering the SNR degradation due to the angularly dispersed LWA beam, showing that data rates over 30 Gb/s can be obtained. Finally, a system design that improves coverage and spectrum efficiency through operating multiple LWAs with a single RF chain is demonstrated.
Wang, J. et al. (2018). Frequency Reuse of Beam Allocation for Multiuser Massive MIMO Systems. IEEE Transactions on Wireless Communications [Online]. Available at: https://doi.org/10.1109/TWC.2018.2793227.Abstract—Massive multiple-input-multiple-output (MIMO)
has become a promising technique to provide high-data-rate
communication in fifth-generation (5G) mobile systems, thanks to
its ability to form narrow and high-gain beams. Among various
massive MIMO beamforming techniques, the fixed-beam scheme
has attracted considerable attention due to its simplicity. In this
paper, we focus on a fixed-beam based multiuser massive MIMO
system where each user is served by a beam allocated to it. To
maximize the sum data rate, a greedy beam allocation algorithm
is proposed under the practical condition that the number of
radio frequency (RF) chains is smaller than the number of users.
Simulation results show that our proposed greedy algorithm
achieves nearly optimal sum data rate. As only the sum data rate
is optimized, there are some “worst-case” users who could suffer
from strong inter-beam interference and thus experience low
data rate. To improve the individual data rates of the worst-case
users while maintaining the sum data rate, an adaptive frequency
reuse scheme is proposed. Simulation results corroborate that our
proposed adaptive frequency reuse strategy can greatly improve
the worst-case users’ data rates and the max-min fairness among
served users without sacrificing the sum data rate.
Pichorim, S., Gomes, N. and Batchelor, J. (2018). Two Solutions of Soil Moisture Sensing with RFID for Landslide Monitoring. Sensors [Online] 18:452. Available at: https://doi.org/10.3390/s18020452.Two solutions for UHF RFID tags for soil moisture sensing were designed and are described
in this paper. In the first, two conventional tags (standard transponders) are employed: one, placed
close to the soil surface, is the sensor tag, while the other, separated from the soil, is the reference for
system calibration. By transmission power ramps, the tag’s turn-on power levels are measured and
correlated with soil condition (dry or wet). In the second solution, the SL900A chip, which supports
up to two external sensors and an internal temperature sensor, is used. An interdigital capacitive
sensor was connected to the transponder chip and used for soil moisture measurement. In a novel
design for an UHF RFID tag the sensor is placed below the soil surface, while the transponder and
antenna are above the soil to improve communication. Both solutions are evaluated practically and
results show the presence of water in soil can be remotely detected allowing for their application in
Wang, G. et al. (2018). Highly efficient optical beam steering using an in-fiber diffraction grating for full duplex indoor optical wireless communication. Journal of Lightwave Technology [Online] 36:4618-4625. Available at: https://doi.org/10.1109/JLT.2018.2832200.Diffraction gratings have been widely used in wavelength-controlled non-mechanical laser beam steering for high data-rate indoor optical wireless communications (OWC). Existing free-space diffraction gratings suffer from inherent difficulties of limited diffraction efficiency, bulky configuration, high cost and significant coupling loss with optical fiber links. In this work, a new optical approach for highly efficient, compact and fiber compatible laser beam steering using an in-fiber diffraction grating is proposed and experimentally demonstrated for the first time to our best knowledge. In-fiber diffraction is made possible based on a 45° tilted fiber grating (TFG), where wavelength dependent lateral scattering is obtained due to the strongly tilted grating structure. Improved diffraction efficiency of 93.5% has been achieved. In addition, the 45° TFG works perfectly for both light emission and reception, enabling full-duplex optical wireless transmission. Utility of the 45° TFG in all-fiber laser beam steering for multi-user full duplex optical wireless communications has been verified in experiments. 1.4 m free-space full-duplex wireless transmission has been demonstrated with data rate up to 12 Gb/s per beam using 2.4 GHz bandwidth OFDM signals.
Gomes, N. et al. (2018). Boosting 5G Through Ethernet: How Evolved Fronthaul Can Take Next-Generation Mobile to the Next Level. IEEE Vehicular Technology Magazine [Online] 13:74-84. Available at: https://doi.org/10.1109/MVT.2017.2782358.Current approaches to the fronthaul for centralized- or Cloud-Radio Access Networks (C-RANs) need to be revised to meet the requirements of next-generation mobile networks. There are two major challenges: first, fronthaul signals need to be transported over public fixed access networks, such as passive optical networks (PONs), typically sharing them with other services; second, higher data rates must be catered for due to larger radio bandwidths and greater use of multi-antenna techniques, such as massive MIMO. Using Ethernet as a new transport protocol for the fronthaul allows statistical multiplexing and enables convergence between fixed and mobile services. This new approach more easily benefits from common developments being made for service level agreements, functional virtualization and software-defined networking. Higher data rates will be supported by the move to new, and possibly flexible, functional split points inside the radio access network (RAN) protocol stack of the processing located in the central and distributed units, as is being investigated by a number of bodies. However, there are technical challenges with regard to latency and packet delay variation. This article summarizes the benefits of an Ethernet-based fronthaul for the next generation of mobile networks, its main challenges and how these may be overcome.
Habib, U. et al. (2018). Analog Radio-over-Fiber Supported Increased RAU Spacing for 60GHz Distributed MIMO employing Spatial Diversity and Multiplexing. Journal of Lightwave Technology [Online]. Available at: http://dx.doi.org/10.1109/JLT.2018.2832028.The improvements in coverage through spatial diversity and increased data rates through spatial multiplexing using a distributed Multiple-Input Multiple-Output (MIMO) system are important targets for future wireless communications. Here, the appropriate separation of Remote Antenna Units (RAUs) at several user locations in a millimeter-wave system is demonstrated. An analog Radio over Fiber (RoF) fronthaul is used to achieve flexible spacing of distributed RAUs and transports two Gb/s data streams over 2.2km of fiber and up to 8m of 60 GHz wireless transmission distance. A performance comparison is performed between Single-Input Single-Output (SISO) and MIMO operation using different antenna spacing and transmission distance. Results show that the wider RAU spacing enabled by the RoF distribution provides improved results at longer distances, for both spatial diversity and for spatial multiplexing. Verification of a method for measuring each channel coefficient individually and using subsequent MIMO processing on these coefficients, enables an extension to the results showing the feasibility of 30m indoor transmission.
Assimakopoulos, P. et al. (2018). A Converged Evolved Ethernet Fronthaul for the 5G Era. IEEE Journal on Selected Areas in Communications [Online] 36. Available at: http://doi.org/10.1109/JSAC.2018.2874148.We assess the performance of two distinct functional splits based on latency/latency variation and mapping efficiency, both individually and in unison. By considering hardware-offloading possibilities for a low-layer split (especially a pre-resource mapper split) using an Option-6 software-based LTE split as an example, we show how data rate, Ethernet frame size and in general, traffic generation characteristics will be very important aspects in the design of the future Ethernet mapping function. Then, an integrated Ethernet fronthaul with legacy and new/evolved split functionality, operating at 100 Gb/s link rate is presented with state-of-the art sub-100 ns latency variation for a timing-protocol flow. This is achieved through the application of a gap-filling aggregator, used for the first time in such a mobile fronthaul application.
Nair, M. et al. (2018). Exploiting Low Complexity Beam Allocation in Multi-User Switched Beam Millimeter Wave Systems. IEEE Access [Online]:1-11. Available at: https://doi.org/10.1109/ACCESS.2018.2887003.Switched-beam systems offer a promising solution for realizing multi-user communications at
millimeter wave (mmWave) frequencies. A low-complexity beam allocation (LBA) algorithm has been
proposed to solve the challenging problem of maximizing sum data-rates. However, there are practical
limitations in mmWave systems, such as restrictions in the number of available radio frequency (RF)
transceiver chains at the base station (BS), sensitivity to sidelobe interference and the beam generation
techniques. In this paper, using generalized beam-patterns, we present the maximum sum data-rates
achievable in switched-beam mmWave systems compared to fixed-beam systems by applying LBA. Then,
the impact on maximum sum data rates of actual beam-patterns, obtained from a practical mmWave lens
antenna, which have higher and non-uniform sidelobes compared to the theoretical beams, is assessed.
Finally, as a guide for practical wireless system design, benchmarks are established for relative sidelobe levels
that provide acceptable sum data-rate performance when considering generalized beam patterns.
Steeg, M. et al. (2018). Public Field Trial of a Multi-RAT (60 GHz 5G/LTE/WiFi) Mobile Network. IEEE Wireless Communications [Online] 25:38-46. Available at: http://dx.doi.org/10.1109/MWC.2018.1800052.A public field trial showcasing an operational multi-Radio Access Technology (RAT) mobile network that was implemented in one of the largest shopping mall in Warsaw, Poland. The network supports novel 60 GHz 5G mobile access as well as legacy LTE and WiFi services All mobile access services of the network are interconnected via optical fiber to the data centers of a mobile network operator and an internet service provider. Fronthauling for the 60 GHz 5G hotspot radio access unit (RAU) and for LTE is realized by analog Radio-over-Fiber (RoF) via a fiber-optic distributed antenna system (DAS). The 60 GHz 5G radio access units (RAUs) for the enhanced mobile broadband (eMBB) use case and the WiFi access point (AP) are both backhauled via optical Gigabit Ethernet. The 60 GHz RAUs for the eMBB and hotspot use case feature 2D beam-switching and 1D beam-steering, respectively. Inter-RAT switching between the different mobile services with seamless user experience is achieved using a Mobile IP system with Fast Initial Link Setup (FILS).
Pan, C. et al. (2017). Joint User Selection and Energy Minimization for Ultra-Dense Multi-channel C-RAN with Incomplete CSI. IEEE Journal on Selected Areas in Communications [Online] 35:1809-1824. Available at: http://dx.doi.org/10.1109/JSAC.2017.2710858.This paper provides a unified framework to deal with the challenges arising in dense cloud radio access networks (C-RAN), which include huge power consumption, limited fronthaul capacity, heavy computational complexity, unavailability of full channel state information (CSI), etc. Specifically, we aim to jointly optimize the remote radio head (RRH) selection, user equipment (UE)-RRH associations and beam-vectors to minimize the total network power consumption (NPC) for dense multi-channel downlink C-RAN with incomplete CSI subject to per-RRH power constraints, each UE’s total rate requirement, and fronthaul link capacity constraints. This optimization problem is NP-hard. In addition, due to the incomplete CSI, the exact expression of UEs’ rate expression is intractable. We first conservatively replace UEs’ rate expression with its lower-bound. Then, based on the successive convex approximation (SCA) technique and the relationship between the data rate and the mean square error (MSE), we propose a single-layer iterative algorithm to solve the NPC minimization problem with convergence guarantee. In each iteration of the algorithm, the Lagrange dual decomposition method is used to derive the structure of the optimal beam-vectors, which facilitates the parallel computations at the Baseband unit (BBU) pool. Furthermore, a bisection UE selection algorithm is proposed to guarantee the feasibility of the problem. Simulation results show the benefits of the proposed algorithms and the fact that a limited amount of CSI is sufficient to achieve performance close to that obtained when perfect CSI is possessed.
Pan, C. et al. (2017). Joint Precoding and RRH selection for User-centric Green MIMO C-RAN. IEEE Transactions on Wireless Communications [Online] 16:2891-2906. Available at: http://ieeexplore.ieee.org/document/7880689/.This paper jointly optimizes the precoding matrices and the set of active remote radio heads (RRHs) to minimize the network power consumption (NPC) for a user-centric cloud radio access network (C-RAN), where both the RRHs and users have multiple antennas and each user is served by its nearby RRHs. Both users’ rate requirements and per-RRH power constraints are considered. Due to these conflicting constraints, this optimization problem may be infeasible. In this paper, we propose to solve this problem in two stages. In Stage I, a low-complexity user selection algorithm is proposed to find the largest subset of feasible users. In Stage II, a low-complexity algorithm is proposed to solve the optimization problem with the users selected from Stage I. Specifically, the re-weighted l1-norm minimization method is used to transform the original problem with non-smooth objective function into a series of weighted power minimization (WPM) problems, each of which can be solved by the weighted minimum mean square error (WMMSE) method. The solution obtained by the WMMSE method is proved to satisfy the Karush-Kuhn-Tucker (KKT) conditions of the WPM problem. Moreover, a low-complexity algorithm based on Newton’s method and the gradient descent method is developed to update the precoder matrices in each iteration of the WMMSE method. Simulation results demonstrate the rapid convergence of the proposed algorithms and the benefits of equipping multiple antennas at the user side. Moreover, the proposed algorithm is shown to achieve near-optimal performance in terms of NPC.
Aighobahi, A. and Gomes, N. (2016). Capacity and Error Performance Verification of Multi-Antenna Schemes in Radio-over-Fiber Distributed Antenna System. Journal of Lightwave Technology [Online]:1-1. Available at: http://doi.org/10.1109/JLT.2016.2565258.A radio-over-fiber distributed antenna system permits larger physical separation between antennas in a wireless system’s infrastructure; this investigation verifies that improved performance – lower error rates and higher capacities – can thus be achieved. In this paper, specific single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) algorithms are compared in an experimental radio over fiber system, using user-defined processing functions for the signals. It is shown that significantly reduced symbol error rate (SER) and modestly increased capacity is achieved for a wireless 1x2 SIMO uplink using the maximal ratio combining (MRC) processing algorithm and 2x1 MISO downlink using the Alamouti space time block coding (STBC) scheme. Further, SER is reduced for a downlink 2x2 wireless MIMO using the zero-forcing algorithm while, most importantly, greatly increased capacity is achieved through the spatial multiplexing gain.
Assimakopoulos, P., Al-Hares, M. and Gomes, N. (2016). Switched Ethernet Fronthaul Architecture for Cloud-Radio Access Networks. Journal of Optical Communications and Networking [Online] 8:B135-B146. Available at: https://doi.org/10.1364/JOCN.8.00B135.A fronthaul design for current and future mobile networks based on the transport of sampled radio signals from/to base station baseband processing units (BBUs) to/from remote radio heads (RRHs), is presented. The design is a pure-Ethernet switched architecture that uses virtual local area network (VLAN) identifiers for the RRHs and flow identifiers for the antenna ports, and is compatible with current standardization definitions. A comprehensive analysis for the limits of the Ethernet fronthaul in terms of the total number of antennas that can be supported is carried out, based on the latency imposed by the Ethernet network. The analysis assumes the transportation of control and management (C&M) and timing information (based on the precision-time protocol, PTP) but is valid for other types of background traffic (for example, that generated by the implementation of different longterm evolution (LTE) functional subdivisions, in a fronthaul with mixed processing). A low-cost testbed using “smart SFP” in-line probes is presented and
used to obtain measurements from an Ethernet fronthaul, transporting mixed traffic. The measurements show how background traffic affects hybrid-automatic repeat request (HARQ)
retransmissions, and are used to validate the analysis. The effects of contention of PTP packets is discussed and a simple solution to overcome the effects of contention is proposed.
Wang, J. et al. (2016). Low-Complexity Beam Allocation for Switched-Beam Based Multiuser Massive MIMO Systems. IEEE Transactions on Wireless Communications [Online]:1-1. Available at: http://doi.org/10.1109/TWC.2016.2613517.This paper addresses the beam allocation problem in a switched-beam based massive multiple-input-multiple-output (MIMO) system working at the millimeter wave (mmWave) frequency band, with the target of maximizing the sum data rate. This beam allocation problem can be formulated as a combinatorial optimization problem under two constraints that each user uses at most one beam for its data transmission and each beam serves at most one user. The brute-force search is a straightforward method to solve this optimization problem. However, for a massive MIMO system with a large number of beams N, the brute-force search results in intractable complexity O(NK), where K is the number of users. In this paper, in order to solve the beam allocation problem with affordable complexity, a suboptimal low-complexity beam allocation (LBA) algorithm is developed based on submodular optimization theory, which has been shown to be a powerful tool for solving combinatorial optimization problems. Simulation results show that our proposed LBA algorithm achieves nearly optimal sum data rate with complexity O(K logN). Furthermore, the average service ratio, i.e., the ratio of the number of users being served to the total number of users, is theoretically analyzed and derived as an explicit function of the ratio N=K.
Gomes, N. et al. (2015). Fronthaul evolution: From CPRI to Ethernet. Optical Fiber Technology [Online]. Available at: http://doi.org/10.1016/j.yofte.2015.07.009.It is proposed that using Ethernet in the fronthaul, between base station baseband unit (BBU) pools and remote radio heads (RRHs), can bring a number of advantages, from use of lower-cost equipment, shared use of infrastructure with fixed access networks, to obtaining statistical multiplexing and optimised performance through probe-based monitoring and software-defined networking. However, a number of challenges exist: ultra-high-bit-rate requirements from the transport of increased bandwidth radio streams for multiple antennas in future mobile networks, and low latency and jitter to meet delay requirements and the demands of joint processing. A new fronthaul functional division is proposed which can alleviate the most demanding bit-rate requirements by transport of baseband signals instead of sampled radio waveforms, and enable statistical multiplexing gains. Delay and synchronisation issues remain to be solved.
Vieira, L. and Gomes, N. (2015). Experimental demonstration of digital predistortion for orthogonal frequency-division multiplexing-radio over fibre links near laser resonance. IET Optoelectronics [Online]:1-7. Available at: http://doi.org/10.1049/iet-opt.2014.0160.Radio over fibre (RoF), an enabling technology for distribution of wireless broadband service signals through analogue optical links, suffers from non-linear distortion. Digital predistortion has been demonstrated as an effective approach to overcome the RoF non-linearity. However, questions remain as to how the approach performs close to laser resonance, a region of significant dynamic non-linearity, and how resilient the approach is to changes in input signal and link operating conditions. In this work, the performance of a digital predistortion approach is studied for directly modulated orthogonal frequency-division multiplexing RoF links operating from 2.47 to 3.7 GHz. It extends previous works to higher frequencies, and to higher quadrature amplitude modulation (QAM) levels. In addition, the resilience of the predistortion approach to changes in modulation level of QAM schemes, and average power levels are investigated, and a novel predistortion training approach is proposed and demonstrated. Both memoryless and memory polynomial predistorter models, and a simple off-line least-squares-based identification method, are used, with excellent performance improvements demonstrated up to 3.0 GHz.
Fan, Y. et al. (2015). Performance analysis of commercial multiple-input-multiple-output access point in distributed antenna system. Optics Express [Online] 23:7500. Available at: http://doi.org/10.1364/OE.23.007500.Abstract: In this paper, we experimentally investigate the throughput of IEEE 802.11n 2x2 multiple-input-multiple-output (MIMO) signals in a radio-over-fiber-based distributed antenna system (DAS) with different fiber lengths and power imbalance. Both a MIMO-supported access point (AP) and a spatial-diversity-supported AP were separately employed in the experiments. Throughput measurements were carried out with wireless users at different locations in a typical office environment. For the different fiber length effect, the results indicate that MIMO signals can maintain high throughput when the fiber length difference between the two remote antenna units (RAUs) is under 100 m and falls quickly when the length difference is greater. For the spatial diversity signals, high throughput can be maintained even when the difference is 150m. On the other hand, the separation of the MIMO antennas allows additional freedom in placing the antennas in strategic locations for overall improved system performance, although it may also lead to received power imbalance problems. The results show that the throughput performance drops in specific positions when the received power imbalance is above around 13dB. Hence, there is a trade-off between the extent of the wireless coverage for moderate bit-rates and the area over which peak bit-rates can be achieved.
Conference or workshop item
Stoehr, A. et al. (2018). Multi RAT (WiFi/ LTE/ 5G) Mobile Network featuring RoF Fronthaul, 60 GHz Beam-Switching and Mobile IP. in: 2018 European Conference on Optical Communication (ECOC). IEEE.We report on a public field trial demonstrating seamless handover in a multi Radio Access Technology mobile network supporting WiFi, LTE, and new 5G radio access in the 60 GHz band for full-duplex enhanced mobile broadband and 5G broadcast hotspots.
Elbers, J. et al. (2018). Next-Generation Optical Fronthaul in the iCirrus Project. in: Optical Fiber Communication Conference 2018. IEEE, p. M3D.1. Available at: http://dx.doi.org/10.1364/OFC.2018.M3D.1.We discuss next-generation fronthaul solutions for 5G and legacy radio access networks. Architectures, findings and experimental results from recent lab and field trial activities are reported.
Assimakopoulos, P., Birring, G. and Gomes, N. (2018). Effects of Contention and Delay in a Switched Ethernet Evolved Fronthaul for Future Cloud-RAN Applications. in: 2017 European Conference on Optical Communication (ECOC). IEEE, pp. 1-3. Available at: http://doi.org/10.1109/ECOC.2017.8346013.A Switched-Ethernet fronthaul transporting data generated by a Long-Term Evolution software base station with a MAC/PHY functional split is presented. Contention effects arising from the Ethernet fronthaul and the effects of priority-based scheduling are characterised
Gomes, N. and Assimakopoulos, P. (2018). Optical Fronthaul Options for Meeting 5G Requirements. in: International Conference on Transparent Optical Networks. IEEE. Available at: http://dx.doi.org/10.1109/ICTON.2018.8473762.New functional splits for the 5G Radio Access Network have been identified so that fronthaul will no longer need to transport sampled time-domain waveforms. However, the different functional split points place differing demands on the fronthaul transport, while also posing different constraints to 5G techniques, such as massive MIMO. According to these conflicting demands, it is likely that in many cases, more than one split point may be needed in the same radio access network.
Wang, J., Gomes, N. and Wang, J. (2018). Adaptive Frequency Reuse for Beam Allocation Based Multiuser Massive MIMO Systems. in: 2018 IEEE International Conference on Communications (ICC). IEEE. Available at: https://doi.org/10.1109/ICC.2018.8422264.Massive multiple-input-multiple-output (MIMO) is a promising technique to provide high-data-rate communication in fifth-generation (5G) mobile systems, thanks to its ability to form narrow and high-gain beams. Among various massive MIMO beamforming techniques, the fixed-beam scheme has attracted considerable attention due to its simplicity. In this paper, we focus on a fixed- beam based multiuser massive MIMO system where each user is served by a beam allocated to it. As the directions of fixed beams are predetermined and the users are randomly distributed, there could be some ``worst-case'' users, located at the edge of its serving beam, suffering from strong inter-beam interference and thus experiencing low data rate. To improve the individual data rates of the worst-case users while maintaining the sum data rate, an adaptive frequency reuse scheme is proposed. Simulation results corroborate that our proposed adaptive frequency reuse strategy can greatly improve the worst-case users' data rates without sacrificing the sum data rate.
Habib, U. et al. (2018). Radio-over-Fiber-supported Millimeter-wave Multiuser Transmission with Low-Complexity Antenna Units. in: 2018 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: http://dx.doi.org/10.1109/MWP.2018.8552904.A system for serving a large number of users at millimeter-wave (mmW) frequencies using a single Radio Frequency (RF) chain is presented. A single Remote Antenna Unit (RAU) supported by Radio over-Fiber transport is used to transmit multiple 60GHz band signals to various users located at different spatial locations using the beamsteering characteristics of a Leaky Wave Antenna (LWA). Error Vector Magnitude analysis has been performed for each user signal up to a maximum of seven users per RF chain with wireless transmission over 2m. A performance comparison for different user-signal frequency spacings has been provided to understand the limitations of the system and results show that the proposed system design with the LWA performs better than systems using waveguide and horn
antenna transmitters. A realization to double the number of served users is also presented which shows that up to 10 users can be served using half region of the LWA, with each user transmitting
1Gb/s data rate, delivering an aggregate data rate of 10Gb/s.
Yamaguchi, T. et al. (2017). Output power enhancement by optical pulse compression in photonic-based RF generation - Laser linewidth and phase noise of the RF output. in: IEICE General Conference.. Available at: https://www.awrcorp.com/news/events/event/2017-IEICE-general-conference.
Murata, H. et al. (2017). Millimeter-wave communication system using photonic-based remote antennas for configurable network in dense user environment. in: IEEE Conference on Antenna Measurements & Applications (CAMA). IEEE, pp. 24-27. Available at: https://doi.org/10.1109/CAMA.2017.8273413.Photonic-based millimeter-wave communication systems combined with conventional wireless systems have been proposed for the application in dense user environments like a large football stadium. By utilizing a narrow beam antenna for millimeter-wave asymmetric links, effective communication channels can be obtained.
Birring, G., Assimakopoulos, P. and Gomes, N. (2017). An Ethernet-Based Fronthaul Implementation with MAC/PHY Split LTE Processing. in: GLOBECOM 2017 - 2017 IEEE Global Communications Conference. IEEE, pp. 1-6. Available at: http://doi.org/10.1109/GLOCOM.2017.8254712.A testbed implementation for an Ethernet fronthaul transporting signals arising from a long-term evolution (LTE) functional subdivision (“split”) at the media-access control (MAC)/physical layer (PHY) interface is presented. Based on open LTE base station software, the testbed demonstrates significant data rate reductions compared to current fronthaul implementations that rely on In-phase and Quadrature radio sample transportation and data rates that scale with cell load. All generated traffic flows are clearly distinguishable using appropriate packet headers. A selection of test cases and their corresponding results are presented to demonstrate the operation of the fronthaul and the performance of individual flows in terms of data rates and overheads.
Gomes, N. et al. (2017). Support of Multi-antenna and Multi-user Systems Using Radio Over Fiber. in: Asia Communications and Photonics Conference 2017. OSA, p. Su4E.1. Available at: https://doi.org/10.1364/ACPC.2017.Su4E.1.Analog radio-over-fiber can efficiently support multi-antenna and multi-user techniques for future mobile communications. Experimental results demonstrate that the wider antenna separation that can be provided enhances multi-antenna scheme performance.
Wang, G. et al. (2017). Wavelength-controlled beam steering for optical wireless transmission using an in-fiber diffraction grating. in: 2017 Conference on Lasers and Electro-Optics.. Available at: http://dx.doi.org/10.1364/CLEO_SI.2017.SF1L.5.Passive beam steering for optical wireless transmission based on wavelength tuning using a novel in-fiber diffraction grating featuring compactness, high diffraction efficiency and inherent fiber-compatibility, is proposed and experimentally demonstrated for the first time.
Pan, C. et al. (2017). Joint Precoding and RRH selection for Green MIMO C-RAN. in: Global Communications Conference (GLOBECOM), 2016 IEEE. Institute of Electrical and Electronics Engineers (IEEE). Available at: http://dx.doi.org/10.1109/GLOCOM.2016.7841930.This paper jointly optimizes the precoding matrices and the set of active remote radio heads (RRHs) to minimize the network power consumption for a cloud radio access network (C-RAN) where both the RRHs and users all have multiple antennas. Both users’ rate requirements and per-RRH power constraints are considered. Due to these conflicting constraints, this optimization problem may be infeasible. We propose to solve this problem with two phases. In Phase I, a new approach is proposed to check the feasibility of the original problem. If the feasibility is guaranteed, in Phase II, a low-complexity algorithm is proposed to solve the original optimization problem. Simulation results demonstrate the rapid convergence of the proposed algorithms and the benefits of equipping multiple antennas at the user side.
Al-Hares, M. et al. (2017). Modeling Time Aware Shaping in an Ethernet Fronthaul. in: GLOBECOM 2017 - 2017 IEEE Global Communications Conference. IEEE, pp. 1-6. Available at: https://doi.org/10.1109/GLOCOM.2017.8254714.An Opnet model of a time-aware shaper (TAS) based on the IEEE 802.1Qbv standard is presented. The TAS model is assumed to be the scheduling entity in an Ethernet-based fronthaul network, comprising of Ethernet switches. The fronthaul transports different traffic flow types as envisioned in next generation Radio Access Networks (RANs), including those for a timing protocol (based on the precision time protocol) and those from the implementation of different RAN functional subdivisions. The performance of the TAS is compared to that of a strict priority regime and is quantified through the frame delay variation of the high priority traffic when this contends with lower priority traffic. The results show that with the TAS implementation, contention effects can be overcome and frame delay variation (frame jitter) can be removed. Timing instability in the significant events of the scheduler is considered and a solution to overcome this issue is proposed.
Habib, U. et al. (2017). Demonstration of radio-over-fiber-supported 60 GHz MIMO using separate antenna-pair processing. in: 2017 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: https://doi.org/10.1109/MWP.2017.8168700.Coverage at millimeter-wave (mmW) frequencies is a constraining bottleneck. Spatial diversity and spatial multiplexing multiple-input multiple-output (MIMO) improve performance over a spread of user locations and these can benefit from wider antenna spacing. Radio-over-Fiber (RoF) transport provides flexibility in deploying a number of widely-spaced Remote Antenna Units (RAUs) connected to the same Central Unit (CU). Hence, mmW systems with an integrated analog RoF fronthaul are strong candidates for use in future 5G networks. An approach to measure channel coefficients individually for MIMO processing has been demonstrated in a RoF transported 2×2 MIMO system at 60 GHz. Experimental results verify this approach through real 2×2 experiments.
Al-Hares, M. et al. (2017). Scheduling in an Ethernet Fronthaul Network. in: 2017 European Conference on Networks and Communications (EuCNC). IEEE. Available at: https://doi.org/10.1109/EuCNC.2017.7980783.This paper investigates and compares the performance of different scheduling techniques in an Ethernet fronthaul network in the presence of both time-sensitive/high priority and background traffic streams. A switched Ethernet architecture is used as the fronthaul section of a cloud radio access network (C-RAN) and a comparison of two scheduling schemes, strict priority scheduling and time-aware shaping, is carried out. The different streams are logically separated using virtual local area network identifiers and contend for the use of trunk links formed between aggregator/switch nodes. The scheduling schemes are applied in the access and trunk ports in the fronthaul, and need to handle the queue management and prioritization of the different streams. In such cases, contention induced latency variation has to be characterized, especially when the fronthaul transports precision time protocol traffic, as it directly leads to errors in timestamping. OPNET models for strict priority and time-aware schedulers have been built and employed, and simulation results are used to compare the performance of the two scheduling schemes.
Wang, G. et al. (2017). In-fibre diffraction grating based beam steering for full duplex optical wireless communication. in: International Topical Meeting on Microwave Photonics (MWP), 2017.. Available at: https://doi.org/10.1109/MWP.2017.8168644.A novel approach to achieve wavelength controlled optical beam steering using a 45° tilted fiber grating (TFG) for full-duplex indoor optical wireless transmission is proposed and experimentally demonstrated for the first time. The 45° TFG functions as an in-fiber passive diffraction device for wavelength steered light emission and reception, which enables full-duplex optical wireless transmission. The unique advantages of using an in-fiber TFG device for beam steering include high diffraction efficiency, low cost, compactness and inherent compatibility with existing fiber links. In a proof-of-concept experiment, free-space full-duplex transmission over 1.4 m with data rate of 9.6 Gb/s per beam has been demonstrated using 2.4 GHz bandwidth signals.
Al-Hares, M. et al. (2017). Traditional queuing regimes and time-aware shaping performance comparison in an Ethernet fronthaul network. in: 19th International Conference on Transparent Optical Networks (ICTON), 2017. IEEE. Available at: https://doi.org/10.1109/ICTON.2017.8025067.This paper compares the performance of traditional priority-based queuing regimes with a time-aware shaping scheduler in an Ethernet fronthaul. Different use-cases are considered for the high and low priority traffic generation, which are made to represent precision-time protocol traffic and traffic originating from different LTE functional subdivisions (function splits) respectively. It is shown that that the relative performance characteristics of the three scheduling regimes depend strongly on the utilization of the fronthaul links where contention is taking place and on the traffic generation characteristics of the different traffic sources.
Habib, U. et al. (2017). Radio-over-fiber-supported 60GHz multiuser transmission using leaky wave antenna. in: 2017 International Topical Meeting on Microwave Photonics (MWP). IEEE. Available at: https://doi.org/10.1109/MWP.2017.8305443.Simultaneous transmission to multiple users using a single-feed leaky-wave antenna (LWA) has been demonstrated. A composite signal transported through a Radio-over-Fibre (RoF) setup is upconverted to V-band frequencies and a LWA is used to direct different user data to their respective locations. An EVM analysis has been performed for two-user and three-user transmission for a range of angular locations. A performance analysis for user interference has been carried out by varying the signal spacing for 152 MHz and 305 MHz bandwidth OFDM signals, centered at 61.75 GHz after 4m of wireless transmission. The experimental results show degradation not only due to insufficient frequency spacing between the channels but also when the sidelobe interference of the neighboring data channels is higher.
Habib, U. et al. (2017). Performance Improvement for OFDM-RoF Transported 60 GHz System using Spatial Diversity and Multiplexing. in: 2017 IEEE International Conference on Communications Workshops. pp. 211-216. Available at: https://doi.org/10.1109/ICCW.2017.7962659.60 GHz system architectures with Radio over Fiber (RoF) transport and integrated transmitters/receivers provide a comprehensive solution for future mobile systems. Since 60 GHz communication relies on line-of-sight (LoS) conditions and narrow-beam antennas to compensate the high path-loss, it has limitations in terms of coverage for multiple user locations. In this paper, performance analysis of a 60 GHz integrated transmitter and receiver system supported by RoF transport has been performed experimentally at different user locations for up to 1.5m transmission distance. Extension of experimental results to prove feasibility for longer distances has been shown with a simulation model, whose results at various shorter distances have been benchmarked against the acquired experimental results at different user locations. A modified version of the Saleh Valenzuela channel has been used to model the millimeter wave (mmW) LoS indoor experimental environment. Furthermore, as a proof of concept, we present an experimental analysis demonstrating an improvement in performance of the proposed RoF based 60 GHz system using spatial diversity and multiplexing. Channel measurements at different transmitter/receiver locations and their processing have shown that an improvement (decrease from 12.5% to 10.5%) in Error Vector Magnitude (EVM) can be achieved using the Alamouti Space Time Block Coding algorithm. Then it has been shown that a two-fold data rate increase can be obtained by combining data from two transmitter locations using the Zero Forcing algorithm.
Assimakopoulos, P. et al. (2017). Ethernet-based fronthauling for cloud-radio access networks. in: 19th International Conference on Transparent Optical Networks (ICTON), 2017. IEEE. Available at: https://doi.org/10.1109/ICTON.2017.8025034.Standardization bodies such as IEEE and 3GPP, as well as other interest groups, are in the process of defining and standardizing different functional subdivisions within mobile network base stations, primarily to reduce the data rate requirements imposed on the transport architecture by 4th and 5th generation mobile systems. Ethernet is considered the leading candidate for the transport architecture as it brings benefits from structural and operational convergence in what is now termed the “xhaul” (x signifying front, mid or back). This paper reports on the performance of different functional subdivisions over a bridged Ethernet network and presents some of the main issues that occur when internetworking at the Ethernet transport level. In particular, it examines Priority-based Scheduling within an Ethernet fronthaul, which is also a subject of active standardization by IEEE.
Gomes, N. et al. (2017). Concepts and requirements for the Ethernet-based evolved fronthaul. in: 2017 IEEE Photonics Society Summer Topical Meeting. IEEE, pp. 41-42. Available at: https://doi.org/10.1109/PHOSST.2017.8012641.The use of Ethernet in the fronthaul permits convergence and exploitation of statistical multiplexing gains of the new interfaces, but minimum latency and latency variation requirements may become challenging. The techniques proposed to meet these challenges are summarized.
Gomes, N. et al. (2016). A Flexible, Ethernet Fronthaul for 5th Generation Mobile and Beyond. in: Optical Fiber Communication Conference 2016.. Available at: http://dx.doi.org/10.1364/OFC.2016.W3C.1.Using Ethernet in the fronthaul can deliver the statistical multiplexing gains offered by
the new functional splits proposed for the radio access network, but latency and delay variations
are challenges that must be overcome.
Habib, U. et al. (2016). Radio over fiber transport of mm-wave 2×2 MIMO for spatial diversity and multiplexing. in: Microwave Photonics (MWP), 2016 International Topical Meeting on. IEEE. Available at: http://dx.doi.org/10.1109/MWP.2016.7791280.DWDM-RoF transport and photonic generation of millimeter-wave MIMO signals has been demonstrated. Generation and modulation of independent data streams over different wavelengths provides allocation flexibility and centralization. EVM results show that this low-cost technique provides antenna diversity/multiplexing gain for STBC-Alamouti and Zero-Forcing algorithms based OFDM-MIMO.
Gomes, N. et al. (2016). The new flexible mobile fronthaul: Digital or analog, or both? in: International Conference on Transparent Optical Networks. IEEE, pp. 1-4. Available at: http://doi.org/10.1109/ICTON.2016.7550322.It has become apparent that current fronthaul technology cannot be simply extended to meet the projected demands of 5G and beyond mobile systems. This current technology, based on the transport of sampled radio waveforms, has been the preferred option, with analog radio over fiber reserved to relatively niche application scenarios. However, for future systems, it is recognised that different functional splits between the central location and the remote units are needed; sampled waveform transport is not scalable to these systems. We propose a flexible fronthaul, therefore, in which both digital and analog transport technologies can coexist. Using practical examples from our work, we describe where these technologies can be used in the future fronthaul.
Assimakopoulos, P. et al. (2016). Statistical distribution of packet inter-arrival rates in an Ethernet fronthaul. in: IEEE International Conference on Communications. IEEE, pp. 140-144. Available at: http://doi.org/10.1109/ICCW.2016.7503778.This paper investigates the effects of background traffic streams in the packet inter-arrival rates of an LTE traffic stream, when these streams are transported over the same Ethernet fronthaul network. Contention of background traffic with LTE traffic can occur in a Cloud-RAN that is transporting traffic streams originating from Constant Bit-Rate (CBR) sources such as the Common Public Radio Interface (CPRI) and from other non-CBR sources originating from different LTE physical layer functional subdivisions. Packet inter-arrival statistics are important in such a network, as they can be used to estimate and/or predict buffer sizes in receiving network nodes. Buffer management will also be important for traffic streams originating from functional splits (such as direct LTE MAC transport block transportation) where user plane data and control primitives have to be time aligned at the receiving node.
Al-Hares, M. et al. (2016). The effect of different queuing regimes on a Switched Ethernet fronthaul. in: International Conference of Transparent Optical Networks. IEEE, pp. 1-4. Available at: http://doi.org/10.1109/ICTON.2016.7550324.This paper investigates the effects of different queuing regimes on the mean and standard deviation of the frame inter-arrival delay of a LTE traffic stream under the presence of background Ethernet traffic. The background traffic is used to represent traffic that would be generated by different functional subdivisions in the physical layer of traditional LTE base station. In this work, a Switched Ethernet architecture is used as the fronthaul section of a Cloud Radio Access Network (C-RAN). Contention in this fronthaul becomes an important issue since different traffic streams originating from different functional subdivisions with different quality of service specifications will be transmitted over the same physical links. Trunk ports then, will have to handle the queuing management and prioritization. Handling the traffic with different queuing regimes will reflect on the latency and latency variations of the LTE traffic.
Aighobahi, A., Assimakopoulos, P. and Gomes, N. (2015). Experimental analysis of single and multiple antenna units in uplink of radio-over-fiber distributed antenna system. in: Microwave Photonics (MWP), 2015 International Topical Meeting on. pp. 1-4. Available at: http://doi.org/10.1109/MWP.2015.7356668.Increasing the number of antennas either at the transmitter or receiver has been shown to improve system reliability without occupying additional spectrum. In this paper, we experimentally investigate the error vector magnitude (EVM) of single and multiple remote antenna units (RAU) focusing on uplink transmission. We demonstrate that for 64-QAM modulation, the EVM requirement of 6.5% could be achieved with multiple separated RAUs in situations where a single RAU fails to meet this requirement. The EVM result was obtained as the transmitting device was placed at different locations in a typical office environment with OFDM signals gathered through the RAUs and brought back to a central unit for processing. The EVM results show that using multiple RAUs and an efficient signal combining technique, here, maximal ratio combining (MRC), the EVM performance could reduce by approximately 2% when the distance between the RAUs was 0.3m and further reduced by 4% and 6% when the inter-RAU distance was 2m and 4m, respectively, compared to a single RAU.
Vieira, L. and Gomes, N. (2015). Clipping and predistortion for compensation of OFDM-Radio over Fiber link distortion. in: 2015 IEEE International Conference on Communications (ICC),. IEEE, pp. 977-981. Available at: http://doi.org/10.1109/ICC.2015.7248449.A combined clipping/predistortion scheme is proposed and demonstrated for the distortion compensation of OFDM-Radio over Fiber links at baseband. In this scheme, a memory-polynomial-based predistorter and a simple amplitude clipping method are used. No specific filter is used after the clipping function, which reduces the implementation complexity. Experimental results confirm that the proposed approach gives significantly better performance compared to the digital predistortion (without clipping) approach for highly distorted OFDM RoF links. Changes in the OFDM signal's PAPR through the RoF link are analysed for the predistortion schemes with and without clipping. As a result of this, a way of optimizing the performance of the clipping/predistortion approach is proposed.
Datasets / databases
Assimakopoulos, P., Al-Hares, M. and Gomes, N. (2017). Switched ethernet fronthaul architecture for cloud-radio access networks. [Excel file]. Available at: http://dx.doi.org/10.1364/JOCN.8.00B135.A fronthaul design for current and future mobile networks based on the transport of sampled radio signals from/to base station baseband processing units to/from remote radio heads (RRHs) is presented. The design is a pure-Ethernet switched architecture that uses virtual local area network identifiers for the RRHs and flow identifiers for the antenna ports and is compatible with current standardization definitions. A comprehensive analysis for the limits of the Ethernet fronthaul in terms of the total number of antennas that can be supported is carried out, based on the latency imposed by the Ethernet network. The analysis assumes the transportation of control and management and timing information [based on the precision-time protocol (PTP)] but is valid for other types of background traffic (for example, that generated by the implementation of different Long-Term Evolution functional subdivisions in a fronthaul with mixed processing). A low-cost test bed using "smart small factor pluggable" in-line probes is presented and used to obtain measurements from an Ethernet fronthaul, transporting mixed traffic. The measurements show how background traffic affects hybrid-automatic repeat request retransmissions and are used to validate the analysis. The effects of contention of PTP packets are discussed, and a simple solution to overcome the effects of contention is proposed.
Gomes, N. et al. (2016). The new flexible mobile fronthaul: Digital or analog, or both? [datafile]. Available at: http://dx.doi.org/10.1109/ICTON.2016.7550322.It has become apparent that current fronthaul technology cannot be simply extended to meet the projected demands of 5G and beyond mobile systems. This current technology, based on the transport of sampled radio waveforms, has been the preferred option, with analog radio over fiber reserved to relatively niche application scenarios. However, for future systems, it is recognised that different functional splits between the central location and the remote units are needed; sampled waveform transport is not scalable to these systems. We propose a flexible fronthaul, therefore, in which both digital and analog transport technologies can coexist. Using practical examples from our work, we describe where these technologies can be used in the future fronthaul.
Assimakopoulos, P. et al. (2016). Statistical Distribution of Packet Inter-Arrival Rates in an Ethernet Fronthaul. [Excel file]. Available at: http://dx.doi.org/10.1109/ICCW.2016.7503778.This paper investigates the effects of background traffic streams in the packet inter-arrival rates of an LTE traffic stream, when these streams are transported over the same Ethernet fronthaul network. Contention of background traffic with LTE traffic can occur in a Cloud-RAN that is transporting traffic streams originating from Constant Bit-Rate (CBR) sources such as the Common Public Radio Interface (CPRI) and from other non-CBR sources originating from different LTE physical layer functional subdivisions. Packet inter-arrival statistics are important in such a network, as they can be used to estimate and/or predict buffer sizes in receiving network nodes. Buffer management will also be important for traffic streams originating from functional splits (such as direct LTE MAC transport block transportation) where user plane data and control primitives have to be time aligned at the receiving node.
Yigal, L. et al. (2018). Radio technologies for 5G using Advanced Photonic Infrastructure for Dense user environments - D321 Report on Beam Steerable Directive Antennas. EU-JAPAN H2020 project - RAPID5G Consortium.This deliverable reports the beam-steering architecture implementation in the RAPID 5G. Various beam-steering antenna methods are reviewed and several are chosen for implementation. The construction of the antenna for each of the chosen methods and measurement results for the constructed prototypes are reported.
Gomes, N. et al. (2019). Testbed Verification of New Fronthaul Technology for 5G Systems. in: IEEE ICC 2019 Workshops.The fronthaul for 5th generation mobile systems (and beyond) has evolved with new splits for the radio access network functions defined, and the transport for these split interfaces having very different requirements. Testing of the transport for such split interfaces is reported, and it is shown that an Ethernet fronthaul transport network, which is capable of bringing efficiency gains through statistical multiplexing, can meet stringent latency and latency variation requirements, assuming buffering and playout of the radio waveforms and that timing/synchronization signals are prioritized. An aggregation technique for a 100 Gb/s Ethernet trunk which provides for such timing signals is demonstrated. Real-time monitoring of the Ethernet fronthaul for software-defined networking control and performance optimization is also shown.