Department of Electronics and Communications Engineering
Macro-scale THz communications
Presented by: Vitaly Petrov, Researcher
Laboratory of Electronics and Communications Engineering
Tampere University of Technology
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Part 1. THz communications. Pros and cons.
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q Growing interest towards the THz band § Suitability for bandwidth-oriented applications § Feasible for micro- and nano-scale devices
Devices miniaturization trend
Far beyond 2020
Time
Dev
ices
siz
e/D
evic
es q
uant
ity
Main-frames
PCs
Carriable electronics
IoT
IoNT
1980 1990 2000 2020
§ Adaptation of communication techniques is required § Novel research challenges raise
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Motivation for THz communications (1) Ubiquitous connectivity
Converged infrastructure for Personal Area Networking
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Motivation for THz communications (2) Data rate trends in Wireless Networks
* J. M. Jornet, “THz communications”, TUT, Oct 2015
Wide Area Paging
First Alphanumeric
Pager
GSM (2G)
UMTS (3G)
LTE (4G) LTE-A (4.5G)
Ethernet IEEE 802.3
IEEE 802.3 U IEEE 802.3 Z
IEEE 802.3 AE IEEE 802.3 BA
1 Kbps
1 Mbps
1 Gbps
1 Tbps
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020
Cellular LAN
q Wireless Terabit-per-second (Tbps) links will become a reality within the next 5 years*
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Motivation for THz communications (3) Why THz for Tbit/s links?
q Limitations of existing and emerging systems: o 2.4 and 5-6GHz spectrum:
Ø Not enough bandwidth o mmWaves spectrum:
§ One of the most significant advantages in 5G § ~7-15GHz consecutive bandwidth max § Tbit/s only with ~100bit/sec/Hz
Ø Not enough bandwidth o Visible Light Spectrum (VLC), 400-790THz
§ Very large available bandwidth Ø Inter-working and interference issues
[!] Technology has a room...
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Definition of the THz band
Frequency range Wavelengths
Industry, IEEE 802.15.3d 0.3 – 3 THz 1 mm – 100 µm
Academia 0.1 – 10 THz 3 mm – 30 µm
Smart academia 0.06 – 10 THz 5 mm – 30 µm
Current presentation Major focus: 0.1 – 3 THz Primary: 3 mm – 100 µm
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Advantages of THz band
q Very large amount of bandwidth available (~10THz) o Enabling technology for Tbit/s links
with 0.1bit/sec/Hz -> sounds feasible
q Miniaturized antennas (λ~1mm for 300GHz) o Enabling technology for interactions of
micro-scale objects (buzzword: “Nanonetworks”)
q Still penetrate visually non-transparent objects o Can work in environments, where VLC can hardly,
such as box, pocket, device with a plastic cover... [!] Is THz comm a “silver bullet”? - No
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Limitations of THz band (1) “THz gap”
q No efficient methods to generate powerful signal at ~1THz at room temperature o Too high for microwave o Too low for optical
Ø Limited power results in low communication range
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Limitations of THz band (2) Small antenna aperture
q Inherently smaller antenna’s aperture o limited communication range without huge
antenna’s gain (e.g. massive antenna arrays)
o For isotropic radiator
Ø Limited aperture results in low communication range
AEff =λ 2
4π
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Limitations of THz band (3) Molecular absorption
q Molecular attenuation is much higher than in mmWaves spectrum o Scattered spectrum
Ø Losses in environment and hardware result in low communication range
[!] Major consequence – low range
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Part 2. THz Channel Properties
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q Spatial loss § E.g. free-space loss for
omnidirectional antennas q Molecular absorption loss
§ Due to internally vibrating molecules on frequencies similar to signal ones
§ Feature of the THz Band § Coefficients è from HITRAN database
Propagation and path loss
LP f ,d( ) = 4π fdc0
!
"#
$
%&
2
( )( )df
dfLA ,1,
τ= ( ) ( )dfkdfk IGIGeedf ,,)(, ∑==
−−τ
LT f ,d( ) = LP f ,d( )+ LA f ,d( )
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Numerical estimation of losses
0 2 4 6 8 1020
40
60
80
100
120
d = 0.01m.
d = 1m.
d = 1m.
Path loss, dB
f, frequency, THz0 2 4 6 8 10
1 104
0.01
1
100d = 0.01m.
d = 1m.
Absorption loss, dB
f, frequency, THz
0 2 4 6 8
50
100
150
200 d = 0.01m.
d = 0.1m.
d = 1m.
Overall loss, dB
f, frequency, Hz
The most beneficial range is 0.1 – 1 THz
Range of minimal losses
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q Feature of the THz band § Molecules convert part of the
absorbed energy into kinetic energy
Noise in the THz band (2) Molecular absorption noise
PN f ,d( ) = kBNM f( )= kBT 1−τ f ,d( )"# $%=
= kBT 1− e−k f( )d"
#$%2 4 6 8 10
260
240
220
200
d = 0.01m.
d = 0.1m.
Molecular noise, dB
f, frequency, THz
Noise highly fluctuates through the frequencies
Range of minimal noise level
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1 104 1 10
3 0.01 0.1
1
10
100SNR, dB
d, distance, m.
q Tx/Rx hardware è SNR threshold q Application requirements è Capacity th. q (SNR + Capacity) vs distance è Estimation
of effective communication range
SNR and Capacity
1 104 1 10
3 0.01 0.1
1 1011
1 1012
1 1013
1 1014
C, Capacity, Bits/s.
d, distance, m.
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q Distance vs frequency for § SNR = 10 dB – good performance of
predicted MCSs (discussed further) § C = 2 Gpbs – sufficient for target
applications § 300 MHz bandwidth
Effective communication range
0 1 2 3 4 5 6 7 8 9 101 10
5
1 104
1 103
0.01
0.1
1SNR = 10dB (C = 1.99Gbps)
d, distance, m.
f, THz
1. THz channel is highly-frequency selective
2. Utilisation of so-called “transparency windows” is proposed
0.1 – 3 THz Best performance
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Part 3. Transparency Windows and sub-channels
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Frequency-selective channel
Window Frequency range Bandwidth Half pulse duration 1 0.10 – 0.54 THz 440 GHz 1.48 ps 2 0.63 – 0.72 THz 95 GHz 6.53 ps 3 0.76 – 0.98 THz 126 GHz 4.92 ps 4 7.07 – 7.23 THz 160 GHz 2.59 ps 5 7.75 – 7.88 THz 130 GHz 3.88 ps
0 2 4 6 8
50
100
150
200 d = 0.01m.
d = 0.1m.
d = 1m.
Overall loss, dB
f, frequency, Hz
q First transparency window is the most promising
Study 0.1 – 0.54 THz in-depth
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q ~20dB gain over 0.1 – 3 THz (!) § (10 times in amplitude, 100 in power) § Sufficient for decoding with major MCS § Suggested for transmission over
“longer” distances: ≥1 cm
First transparency window, 0.1 – 0.54 THz
0.2 0.4 0.6 0.820
40
60
80
100
120d = 0.01m.
d = 0.1m.
d = 1m.
Overall loss, dB
f, frequency, Hz
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Range/capacity trade off. Small channels
1 103 0.01 0.1 1
1
10
1000.10-0.54Thz
0.44-0.54Thz
0.49-0.54Thz
0.10-0.20Thz
0.10-0.15Thz
SNR, dB
d, distance, m.
0.01 0.11 10
8
1 109
1 1010
1 1011
1 1012
1 1013
0.10-0.54Thz
0.44-0.54Thz
0.49-0.54Thz
0.10-0.20Thz
0.10-0.15Thz
C, capacity, bits/s.
d, distance, m.
q For 10 cm distance: Frequency range (bandwidth) SNR Capacity
0.1 – 0.54 THz (440 GHz) 20 dB 500 Gbps
0.1 – 0.2 THz (100 GHz) 33 dB 300 Gbps
0.1 – 0.15 THz (50 GHz) 35 dB 200 Gbps
Enabling complex MCSs
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Range/capacity trade off. Tiny channels
0.01 0.1 1 10 1001
10
1001MHz
10MHz
100MHz
1000MHz
SNR, dB
d, distance, m.0.1 1 10
1 106
1 108
1 1010
1MHz
10MHz
100MHz
1000MHz
C, capacity
d, distance, m.
q For SNR = 10 dB, Smart metering case Frequency range (bandwidth) Range Capacity (at 1 m)
~0.1 THz (1000 MHz) 2 m 8 Gbps
~0.1 THz (10 MHz) 6 m 0.1 Gbps (100 Mbps)
~0.1 THz (1 MHz) 15 m 0.01 Gbps (10 Mbps)
Applicable for sensing applications
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Part 4. Modulation and Coding
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q Limitations of continuous-wave MCS: § Generating carrier at 1-2THz and higher § Filtering at higher frequencies § Energy efficiency Advances in physics are needed
q On/Off keying q Transmitting s(t):
§ s(t)=1 è Pulse § s(t)=0 è Silence
“Low-complex” hardware
On/Off Keying simple modulation
1 1 0 01
tt t t t t
...
v v v v
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q Asymmetric channel: pE1 ≠ pE0 q Set of threshold è optimisation problem q BER can be lower than 0.001
BER and throughput estimation for OOK
FEC codes are applicable
0 0.2 0.4 0.6 0.8 10.16
0.18
0.2
0.22
0.24
0.26
Throughput, v=0.0ps
Throughput, v=0.4ps
Throughput, v=0.8ps
Throughput, v=1.2ps
T, thoughput, Tbps
TP, relative energy detection threshold0 0.2 0.4 0.6 0.8 1
1 104
1 103
0.01
0.1
1
v=0.0ps
v=0.4ps
v=0.8ps
v=1.2ps
pE, bit error probability
TP, relative energy detection threshold
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Part 5. Envisioned applications and roadmap
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Envisioned “colonization” of THz spectrum
1. 275-325GHz by IEEE 802.15.3d Task Group o Lead by T. Kurner, TU Braunschweig, Germany o High antenna gains (20dBi+)
2. Around 1THz and 1-1.5THz by leading academic units o Graphene/CNT/plasmonic nano-antennas/etc.* o Extreme antenna gains (50dBi+)
3. Micro-scale communications with individual (~omnidirectional) antennas at 1THz+ by academia**
*J. M. Jornet and I. F. Akyildiz, "Graphene-based Plasmonic Nano-antenna for Terahertz Band Communication in Nanonetworks," IEEE JSAC, December 2013
**Akyildiz, I. F., Jornet, J. M., and Pierobon, M. "Nanonetworks: A New Frontier in Communications," Communications of the ACM, November 2011
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Envisioned application (1) Backhaul for mmWaves cell
q Backhaul rate should be higher than of the fronthaul o 275-325GHz o Static link o Alignment during the installation o Low interference with mmWaves spectrum
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Envisioned application (2) Access for Beyond-5G networks
q 100Gbit/s data rate with “THz plug” at 275-325GHz
*V. Petrov, et al. “Last Meter Indoor Terahertz Wireless Access: Performance Insights and Implementation Roadmap,” to appear in IEEE Communications Magazine, 2018 (available on arxiv).
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Envisioned application (3) Immersive Tbit/s wireless links
q Multi-Tbit/s data rate at 1-1.5THz, enabling
*V. Petrov, et al. “Last Meter Indoor Terahertz Wireless Access: Performance Insights and Implementation Roadmap,” to appear in IEEE Communications Magazine, 2018 (available on rxiv).
o Tactile Internet o Holographic Comm
o Who knows?.. [!] THz vs VLC
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Envisioned application (4) Military communications
q Interest from AirForce, DARPA, and some others o Eavesdropping is very challenging
*I. F. Akyildiz, J. M. Jornet and C. Han, "Terahertz Band: Next Frontier for Wireless Communications," Physical Communication (Elsevier) Journal, September 2014.
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Envisioned application (5) Security-sensitive communication
q Health monitoring, E-payments, etc. q Similar benefits as for military:
o Fast signal degradation with distance o Substantial bandwidth for almost any handshakes
Beneficial to study the suitability of: o PHY layer security o ID-based crypto systems
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Part 5. Challenges and open problems.
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Issue 1. Hardware limitations Challenge 1. Need for simple MCS
q Difficulties for continuous-wave MCS: o Generating carrier at 1-2THz and higher o Filtering at higher frequencies o Energy efficiency Ø Advances in physics/material science are needed
q On/Off keying MCS o Transmitting s(t):
§ s(t)=1 ! Pulse § s(t)=0 ! Silence
Ø “Low-complex” hardware Ø Low utilization of the available time*spectrum resource
1 1 0 01
tt t t t t
...
v v v v
*P. Boronin, V. Petrov, D. Moltchanov, Y. Koucheryavy, J.M. Jornet, “Capacity and Throughput Analysis of Nanoscale Machine Communication through Transparency Windows in the Terahertz Band,” Elsevier NanoComNet, 2014.
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Ø [Challenge 2.1] Limited applicability of existing system-level models for performance estimation
Issue 2. Molecular component in propagation
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Addressing Challenge 2.1 Intra-cell interference modeling in THz networks
q Random deployment in the cell
q Poisson process with pin out infinitesimal neighborhood
q – cell radius (PL) q – distance between
Tx and Rx q – distances from
interferers, q – nodes density q – minimum distance
between nodes
Rx
Tx
d0
~x2λ nodes
x
x
R
r
rdidj
d1
dN
rλ
di
d0R
i ∈ 1:N[ ]
*V. Petrov, et al., “Interference and SINR in Dense Terahertz Networks,” IEEE VTC2015-Fall, Boston, MA, USA, September 2015.
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Addressing Challenge 2.1 Intra-cell interference modeling in THz networks
q Transmit power –10dBm
q Close to normal distribution of interference (lognormal in dB scale)
q Perfect match with simulation results
q Interference level grows with the nodes density Ø Interference still plays a substantial role in
dense deployments
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Challenge 2.2 Need for frequency-specific sub-channeling and distance-aware MCS
q Sub-channels utilization with power limit is a trade off: o Rate vs Received power
q Core idea: o Occupy more band
for shorter distances o Occupy less for longer
distance transmissions Ø Not that trivial
to implement
*C. Han, A. O. Bicen, and I. F. Akyildiz, "Multi-Wideband Waveform Design for Distance-adaptive Wireless Communications in the Terahertz Band," IEEE Trans on Signal Proccessing, 2016
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Issue 3. Specific transmission/encoding energy consumption relations
q [Challenge 3] At Tbit/s rates the Tx energy/bit is significantly lower than encoding/decoding energy o “Wasting” a lot of energy on encoding/decoding
q Core idea:
o Transmitting almost raw data without encoding o Rebranding of the old concept of
cross-layer optimization Ø Finally got an application..
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Issue 4. Energy harvesting as the only solution for micro-scale devices
q [Challenge 4] Sometimes when packet arrives, node does not have energy to transmit or receive it o Protocols should be aware of this feature
q Core idea: o Initiate a transmission only when both sides have
enough energy to handle it o Problem: How to know if the receiver has enough
energy without spending energy? o Solution: Receiver-initiated protocol. Rx sends a
“Ready-to-Receive” packet to mention it is ready
*J. M. Jornet and I. F. Akyildiz, "Joint Energy Harvesting and Communication Analysis for Perpetual Wireless NanoSensor Networks in the Terahertz Band," IEEE Trans Nanotech, May 2012
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[!] Issue 5. Highly-directional antennas
q Almost the only feasible solution to compensate high pathloss at THz o Directivity at both sides is required for reliable
communication at distances higher than few meters Ø [!!!] [Challenge 5.1] Medium Access Control for THz
o Let us assume, nodes know each other’s locations § Partial solution: Receiver-initiated protocol. § Rx sends a “Clear-to-Receive” packet to
mention it is ready Ø Performance issues Ø Not realistic in dynamic environments
*Q. Xia, et al., "A Link-layer Synchronization and Medium Access Control Protocol for Terahertz-band Communication Networks,” IEEE GLOBECOM, 2015.
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Challenge 5.2 [!!!] Nodes discovery. How to find each other with directional antennas?
q Let’s assume nodes do not know each other’s locations... q Limitations of existing solutions:
o Full search beam steering o O(n2) complexity Ø Hardly feasible
o Directional + “omni”, like in 802.11ad: § O(n) complexity but low SNR at the receiver Ø Hardly feasible
o Assistance-oriented schemes (from lower freq.) § Industry resistance in IEEE, easier with cellular § Current advantage – to get “there is a neighbor”,
but where to direct the beam? Ø Partly feasible
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Challenge 5.3 Easy LoS blockage
Tx
rB
R
x
x
~x2λ nodes
rB
rB
rB
Interferer is blocked
r0
rB
rB
rB
rB
rB
Rx
Distance to Tx
Distance to interferer
Interferer is blocked
ri
ri+2
ri+1
rN
r1
1. Deployment a. Typical uniform
in a circle 2. [!] Directivity
a. Tx only b. Tx+Rx
3. [!] Blockage a. Self-blockage
4. Propagation model a. [!] With molecular
absorption V. Petrov et al., “Interference and SINR in Millimeter Wave and Terahertz Communication Systems With Blocking and Directional Antennas,” IEEE Transactions on Wireless Communications, 2017.
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Addressing Challenge 5.3 Modeling of the self-blockage process
l=0.1
l=0.3
l=0.5
l=0.7
l=0.9
10 20 30 40 50x, m.
0.2
0.4
0.6
0.8
1.0
pBHxLq Dense
deployment: a. Human at every
2m2
b. Blockage after ~5m is 80%
q Ultra-dense deployment a. Even higher
Ø Blockage significantly limits both useful signal and interference in dense deployments
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Addressing Challenge 5.3 NLoS propagation measurements
*J.Kokkoniemi, J.Lehtomäki, V. Petrov, D. Moltchanov, Y. Koucheryavy, M. Juntti, “Wideband Terahertz Band Reflection and Diffuse Scattering Measurements for Beyond 5G Indoor Wireless Networks,” EuWireless, 2016 *J.Kokkoniemi, J.Lehtomäki, V. Petrov, D. Moltchanov, M. Juntti, “Frequency Domain Penetration Loss in the Terahertz Band,” GSMM 2016
q Measuring 0.1-4THz band (device by TeraView, UK)
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Addressing Challenge 5.3 NLoS propagation simulations
*V. Petrov, et al., “Last Meter Indoor Terahertz Wireless Access: Performance Insights and Implementation Roadmap,” submitted for a magazine publication, Spring 2016
Ø 1st reflections doesn’t completely destroy the link
o Based on ray-tracing with surface tessellation o Parameterized from field measurements
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Issue 6 High nodes mobility and small cell sizes
Ø [Challenge 6.1] Fast vertical handover o Continuous coverage with THz cells is impractical o Reaction time is so low that behavior prediction
pro-active algorithms may help
Ø How to implement, if different units control different parts of the network?
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r
r
r
X
X
Long-rangeTHz IS
r
Mobile User
r
r
r
q Mobile users with opportunistic traffic offloading to ultra-high rate small cells o Quasi-omnidirectional
antennas (gain) o Random mobility model
q Both cellular and THz small cell connectivity
Issue 6 High nodes mobility and small cell sizes
Ø [Challenge 6.2] Network layer adaptation o Data pre-caching / TCP upgrade o Information/data shower concept
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Addressing Challenge 6.2 Performance gains estimation
*V. Petrov, et al., “Applicability assessment of terahertz information showers for next-generation wireless networks,” to appear at IEEE ICC, May 2016
q Comprehensive metrics (5G QoE):
o Continuous time of video playback
o Required data rate from cellular
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Issue 6 High nodes mobility and small cell sizes
Ø [Challenge 6.3] Real-time monitoring and management o 1 Tbit/s means “If a network switch is down for
0.1sec, you have just lost 100Gb of data” ! o How to control massive amount of THz APs?
q Existing solutions: o “Cellular” protocols stack is too heavy o SDN is too slow (all the decisions are made on a
remote smart node) q Two-layer SDN as a potential solution
o Latency-critical operations – on AP o Latency-tolerant – on a central node
*G. Bianchi, et al., ”OpenState: programming platform-independent stateful openflow applications inside the switch,” ACM SIGCOMM Computer Communication Review, 2014
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Part 6. Summary, open challenges and future research directions
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Summary THz commun. as a truly 5G+ technology
Ø THz band is, most probably, a next frontier for wireless communications, immediately after mmWaves
q Major advantage: o Potentially Tbit/s wireless links few meters long
q Major issues: o Hardware: “THz gap” o Propagation: Absorption and small antenna area
q Major unsolved communication challenges: q PHY: Reliable P2P interaction over the THz band
§ LoS blockage, massive scattering, high pathloss q Link: Channel access with dynamic beam steering q Network: Nodes discovery and addressing
[!] Huge room for further R&D