realizing next-generation backhaul ... - mm-wave 5g and thz 6g · w. khawaja, o. ozdemir, y....
TRANSCRIPT
Realizing Next-Generation Backhaul/Fronthaul and
Fixed-Wireless Access Networks Through
Reconfigurable Intelligent Surfaces
Konstantinos Ntontin Research Associate
Institute of Informatics and Telecommunications, National Centre for Scientific Research “Demokritos”,
Marco Di Renzo CNRS, Research Director at CentraleSupélec,
Fotis Lazarakis Research Director
Institute of Informatics and Telecommunications, National Centre for Scientific Research “Demokritos”
1
Contents
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results
Challenges Ahead
Conclusions
2
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results
Challenges Ahead
Conclusions
3
Wireless backhauling
Current mobile access networks rely on sub-6 GHz bands, for instance LTE/LTE-A. Offer peak data rate slightly above 1 Gbps
Small-cell market penetration increases rapidly. Challenge for operators to backhaul the generated traffic between core network and all the cells
Capacity-wise, fiber connection between core network and each cell as ideal case. Practically impossible due to cost of fiber deployment
Operators have pushed for wireless backhauling as a solution. 50% market share in 2025. Majority of links in 7-100 GHz range. Area of intense research from vendors
M. Paolini, L. Hiley, and F. Rayal, Small-cell backhaul:Industry trends and market overview, Senza Fili Consulting, 2013
ABI Research, Mobile Backhaul Options: Spectrum Analysis and Recommendations, September 2018
1
1
4 2
2
Wireless backhauling typical scenario
Portion of the cells, either macro or small, are fiber connected to the core network
Remaining cells connected to the core network through the fiber-connected ones
Core network
Fiber-connected cell
Wirelessly-connected cell
User
Fiber connection
Wireless connection
5
Wireless fronthauling
Cloud-RAN architecture more suitable for future 5G and beyond networks.
Baseband processing centralized in baseband units (BBUs)
Cells called remote radio heads (RRHs). They include only the RF circuitry and
antennas. BBU-RRH connections constitute the fronthaul
Cloud-RAN enables smaller energy footprint due to reduction of equipment needed
Similar to backhauling, fiber cost creates the need for wireless fronthauling. The 7-
100 GHz range also currently used
6
Wireless fronthauling typical scenario
Core network
Fiber-connected RRH
Wirelessly-connected RRH
User
Fiber connection
Wireless connection
BBU
7
Fixed-wireless access (FWA)
FWA provides broadband services to homes and enterprises
Attractive for the several cases where fiber cannot reach, due to cost, users’ premises
Multitude of bands in 7-100 GHz used for FWA, as in the backhaul/fronthaul cases
Common access protocols: time division multiple access (TDMA) and joint TDMA-space division multiple access (SDMA)
K. Laraqui et al., 5G & Fixed Wireless Access, Ericsson, White Paper, February 2016
3
3
8
3
FWA scenario
Base
station
User
equipment
Primarily based on LOS links
Rate degradation with increasing number of fixed users
9
Background recap
Bringing fiber to every site/user premise is still many years away due to cost
Big money invested from vendors in wireless broadband solutions for
backhaul/fronthaul and FWA networks. High market share
Majority of bands currently used for such networks are in the 7-100 GHz range
(low end millimeter-wave spectrum)
10
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results (Pending)
Challenges Ahead
Conclusions
11
User demands increasing
Continuous increase in data-rate demands from mobile and fixed users
Cannot be covered by conventional solutions, such as MIMO. Bandwidth in sub-6 GHz bands is bottleneck
CISCO VNI: Global Mobile Data Traffic Forecast Update, 2017-2022, February 2019
4
4
12
Going up the spectrum
For 5G mobile access networks, circumventing the sub-6 GHz bandwidth bottleneck means migrating to the millimeter-wave range. Successful trials at 28, 38, and 73 GHz
To accommodate the generated mobile traffic, backhaul/fronthaul networks should also go up the spectrum. That means beyond 100 GHz
Same need for beyond-100 GHz links holds for FWA networks. Due to increasing rate demands and number of users, which can limit significantly the rate per user
T. S. Rappaport, Spectrum frontiers: The new world of millimeter-wave mobile communication, Invited Keynote Presentation, The Federal Communications Commission (FCC) Headquarters, Mar. 2016
J. Edstam et al., Microwave backhaul evolution-reaching beyond 100 GHz, Ericsson, White Paper, February 2017
ECC, Point-to-Point Radio Links in the Frequency Ranges 92-114.25 GHz 130-174.8 GHz, Technical Report, September 2018
5
5
6,7
6
7
13
Current beyond-100 GHz research activity
Increasing interest from vendors in the D-band (130-174.8 GHz). Huawei,
Ericsson, NEC, and NOKIA have performed trials
D-band prototype from Ceragon presented at Mobile World Congress 2018.
100 Gbps achieved
Several H2020 and national projects on the area: ARIADNE, DREAM,
ULTRAWAVE, ThoR, TERRANOVA, WORTECS, TERAPAN, BRAVE
ETSI, millimetre Wave Transmission (mWT); Analysis of Spectrum, License Schemes and Network Scenarios in the D-band, Technical
Report, August 2018
https://www.ceragon.com/blog/100gbps-single-box-radio-inconceivable
8
9
8
9 14
Great challenge
All trials in the beyond-100 GHz spectrum consider LOS links. No NLOS measurements
NLOS communication possible in 7-100 GHz. Highly questionable for beyond 100 GHz
Due to envisaged massive street-level small-cell deployment and continuous increase of FWA subscribers, several backhaul/fronthaul and FWA links are inevitably going to be NLOS in a metropolitan area
Without practical NLOS solutions, no reliability→Death of future ultra high capacity networks
https://www.ceragon.com/what-you-need-to-know-about-5g-wireless-backhaul_2019
https://www.lightningbroadband.com.au/news/nlos-wireless-broadband-lb23721/
10,11
10
11
15
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results
Challenges Ahead
Conclusions
16
Relays and non-reconfigurable passive reflectors
Most well-known solutions: relays and non-reconfigurable passive reflectors (dielectric mirrors)
Alternative routes through LOS hops
Core network
Fiber-connected RRH
Wirelessly-connected RRH
User
Fiber connection
Wireless connection
BBU
Relay
Dielectric mirror
17
Relays
Pros:
Electrical beamsteering through multiple antennas
Power amplification
Cons:
Rate reduction in the HD case. Loop-back self-interference in the FD case
Dedicated power supply needed. Substantial cost of RF electronics at very high frequencies (mixers, PAs, LNAs)→Not a viable solution for wide-scale deployment
W. Khawaja, O. Ozdemir, Y. Yapici, I. Guvenc and Y. Kakishima, “Coverage Enhancement for mm Wave Communications using Passive Reflectors," 2018 11th Global Symposium on Millimeter Waves (GSMM), Boulder, CO, USA, 2018
12 18
12
Non-reconfigurable passive reflectors
Pros:
Large life span
Low maintenance cost
Low initial investment costs: No active electronic components needed
Cons:
No electrical beamsteering. Reflection angle obeys to Snell’s law. Mechanical steering (rotation) can induce substantial latency
Natural question: Would it be possible to control the reflection angle?
Affirmative answer through the novel paradigm of Reconfigurable Intelligent Surfaces
19
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results
Challenges Ahead
Conclusions
20
What is a reconfigurable intelligent surface
(RIS)?
Artificial surface of EM material. Can shape the wavefront of the impinging wave
Based on metasurfaces, which is 2D equivalent of metamaterials. Thickness<<λ
Sub-wavelength array by sub-wavelength metallic/dielectric particles, called meta-atoms
Based on meta-atom structure, functions realized on the impinging waves are:
Reflection and refraction at arbitrary angles (not obeying classical Snell’s law)
Absorption
Polarization change
In the reconfigurable case, meta-atom structure modified based on external stimuli.
Enabled by phase-switching components between meta-atoms, such as CMOS/MEMS
Prototypes of reconfigurable metasurfaces have been realized
F. Liu, et al., “Intelligent metasurfaces with continuously tunable local surface impedance for multiple reconfigurable functions”,
Physical Review Applied, vol. 11, Apr. 2019.
13
13 21
RIS Illustration
22
Comparison with relaying
Substantial energy gains over relaying expected:
Relays need dedicated power supply (mixers, PAs, LNAs)
RISs need a small amount of energy (non-dedicated power supply) for
enabling reconfigurability. Can be secured by energy harvesting
Substantial achievable-rate gains observed for a point-to-point
scenario under ideal RIS functionality
14
K. Ntontin, M. D. Renzo, J. Song, F. Lazarakis, J. de Rosny, D.-T. Phan-Huy, O. Simeone, R. Zhang, M. Debbah, G. Lerosey,
M. Fink, S. Tretyakov, and S. Shamai, “Reconfigurable Intelligent Surfaces vs. Relaying: Differences, Similarities, and
Performance Comparison”, IEEE Wireless Commun. Magazine, submitted, September 2019: https://arxiv.org/abs/1908.08747
14 23
Performed trials
Trial of NTT Docomo with Metawave at 28 GHz. Only known published trial
Significant rate enhancement based on non-reconfigurable metasurface reflector
https://www.nttdocomo.co.jp/english/info/media_center/event/mwc19/pdf/about_docomo_5g.pdf
15
15
24
The VisorSurf project
VisorSurf is an ongoing H2020-EU.1.2.1.-FET Open project
(http://www.visorsurf.eu/). Total budget close to 6 million euros
Its objective is the development of a full stack of hardware and software
components for the creation of RISs, called HyperSurfaces
First and only project on the design and manufacturing of RISs for modifying
the propagation environment
25
The ARIADNE project
ARtificial Intelligence Aided D-Band Network for 5G long term Evolution
(ARIADNE) is a H2020-ICT-2018-2020 project
First H2020 project on the potential of metasurfaces for aiding beyond-100 GHz
backhaul/fronthaul and FWA networks. Total budget around 6 million euros
Based on the following 3 pillars:
The development of new radio technologies for communications using the
beyond-100 GHz D-band frequency range
The leveraging of metasurfaces for shaping the propagation environment
The employment of machine learning and artificial intelligence techniques for
the reconfiguration of the metasurfaces and, consequently, the propagation
environment, based on required metrics
26
The ARIADNE consortium
27
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results
Challenges Ahead
Conclusions
28
A future wireless fronthaul scenario
LOS and NLOS links
If LOS→D-band operation
If NLOS→3 options:
Switching to <100 GHz
Alternative LOS routing
through half-duplex and
decode-and-forward
relaying
Alternative LOS routing
through RISs
TDMA protocol
Core network
Fiber-connected RRH
Wirelessly-connected RRH
User
Fiber connection
Wireless connection
BBU
Relay
RIS
29
Simulation parameters
RISTx
Rx
nd
Relay
TxRx
nd
30
10% links are NLOS
Average rate:
All links LOS (Best
performance): 28 Gbps
RIS case: 27.3 Gbps
Relaying case: 26.5 Gbps
28 GHz case: 25.3 Gbps
31
40% links are NLOS
32
Average rate:
All links LOS (Best
performance): 28 Gbps
RIS case: 25.3 Gbps
Relaying case: 22 Gbps
28 GHz case: 17.1 Gbps
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results (Pending)
Challenges Ahead
Conclusions
33
Challenges ahead (1/2)
Physics-based modelling: Currently, simplified models about interaction of
metasurfaces with impinging waves. Accurate and tractable models needed
Experimental validation: The developed analytical models should be validated
Information- and communication-theoretic models: Propagation environment
subject to optimization. Novel information-/communication-theoretic models needed
34
Challenges ahead (2/2)
High-bandwidth design: Design of metasurfaces operating in the high bandwidth
of beyond-100 GHz bands
Constrained system design: RISs should be nearly passive. Low-complexity
protocols should be developed for channel sensing, so to program the RIS operation
Reliability issues: RISs may become prone to failure by the integration of
advanced circuitry enabling reconfigurability. Potential sources of errors need to be
identified and tackled
H. Taghvaee, S. Abadal, J. Georgiou, A. Cabellos-Aparicio and E. Alarcón, "Fault Tolerance in Programmable Metasurfaces: The Beam Steering
Case," 2019 IEEE International Symposium on Circuits and Systems (ISCAS), Sapporo, Japan, 2019
16
16 35
Background
Problem
Conventional Solutions
Disruptive Solution: Reconfigurable Intelligent Surfaces
Indicative Simulation Results
Challenges Ahead
Conclusions
36
Conclusions
Last-mile fiber costs, so vendors heavily invest on wireless backhaul/fronthaul and FWA
Near future need for beyond-100 GHz operation and NLOS solutions
Relaying and dielectric mirrors conventional NLOS solutions, but both not viable
RISs as disruptive solution. Trial of NTT Docomo with Metawave showcased the
potentials. 2 H2020 projects already on the area
Potential for important rate gains in realistic network setups
Several challenges ranging from electromagnetic and information-theoretic modeling to
practical designs operating in the high-bandwidth regimes of beyond-100 GHz networks
37
Backup Slides
39
Market share and bands used
7-100 GHz range is the vast majority of wireless backhaul. Primarily, LOS links
Wireless backhaul share of 57% in 2017. Slightly reduced by 2025 (50%)
ABI Research, Mobile Backhaul Options: Spectrum Analysis and Recommendations, September 2018
2
2
40