Petar Popovski Aalborg University Denmark petarp@es.aau.dk 5G V2X - - PowerPoint PPT Presentation

principles of ultra-reliable low latency communications (URLLC)

Petar Popovski

Aalborg University Denmark petarp@es.aau.dk

5G V2X Communications @ KCL, London, June 11, 2018

5G V2X Communications @ KCL, London, June 11, 2018

• utline

▪ future connectivity landscape ▪ URLLC performance and statistics ▪ URLLC building blocks ▪ wireless network slicing in 5G

5G V2X Communications @ KCL, London, June 11, 2018

the future wireless connectivity landscape

▪ can be seen as eigenvalues for composing services, e.g. in Virtual Reality, rather than three isolated services.

5G V2X Communications @ KCL, London, June 11, 2018

future wireless connectivity landscape

5G

but a lot of (great!)

• ther wireless systems

▪ connectivity type not necessarily provided by the 5G radio interface ▪ LPWA, 802.11ah, etc.

5G V2X Communications @ KCL, London, June 11, 2018

distilled service requirements

eMBB

▪ acceleration of 4G, large payloads, active over longer periods ▪ maximize rate, moderate reliability (e.g. 10E-3)

mMTC

▪ fix low rate, unknown active subset from a massive device set ▪ maximize arrival rate, low reliability (e.g. 10E-1)

URLLC

▪ intermittent transmissions, but from a much smaller device set ▪

• ffer high reliability (e.g. 10E-5) while localized in time

5G V2X Communications @ KCL, London, June 11, 2018

the IoT modes: massive and ultra-reliable access

100 Mbps 95% of the time

• r

100 kbps 99.999% of the time

error probability data rate

reliability limit for control information 1 Mbps from 100 devices

• r

10 kbps from 10000

devices

# devices data rate

access protocol limit

5G V2X Communications @ KCL, London, June 11, 2018

adoption of ultra-reliable communication

we need to divide the applications into two groups ▪ cable replacement how would we design a system if we could trust to the wireless as much as to the wired? ▪ ”native” wireless applications which new systems can we think of once we are empowered with wireless connectivity?

5G V2X Communications @ KCL, London, June 11, 2018

MTC use cases

mMTC

▪ environmental monitoring

• f large areas

▪ large infrastructures

roads, ports, industrial plants

▪ available parking places ▪ management of object fleets vehicles, bicycles

URLLC

▪ commercial and public safety ▪ industrial control and automation ▪ smart energy and smart grid ▪ V2X and UAV control ▪ Augmented Reality (AR) and digital interaction with physical objects

5G V2X Communications @ KCL, London, June 11, 2018

a communication engineer models known unknowns

channel state noise interference

• bjective: find 𝛽 and, if 𝛽 = 1, find also 𝑦

a simple communication-theoretic model

𝑧 = ℎ ∙ 𝛽 ∙ 𝑦 + 𝑨 + 𝑗

user activity

5G V2X Communications @ KCL, London, June 11, 2018

ultra-reliability requires to ▪ model accurately the known unknowns ▪ bound the impact of the unknown unknowns ▪ the standard culprit 𝑨 seems easy ▪ interference can be arbitrarily varying

a simple communication-theoretic model

𝑧 = ℎ ∙ 𝛽 ∙ 𝑦 + 𝑨 + 𝑗

5G V2X Communications @ KCL, London, June 11, 2018

sources of uncertainty ▪ activity 𝛽 is the problem of a MAC protocol ▪ ℎ is the problem of channel estimation and channel knowledge ▪ 𝑗 is a matter of interference management and spectrum regulation

– spectrum license is paid to acquire the right to control interference.

a simple communication-theoretic model

𝑧 = ℎ ∙ 𝛽 ∙ 𝑦 + 𝑨 + 𝑗

5G V2X Communications @ KCL, London, June 11, 2018

the worst case is when there is no prior information about the user activity ▪ random access grant-free access means that the packet reception in the uplink is not conditioned on a correct downlink reception ▪ can improve latency, even reliability its uncertainty is removed by ▪ scheduling ▪ the receiver predicts the activity variable

the user activity 𝛽

5G V2X Communications @ KCL, London, June 11, 2018

URLLC performance and statistics

5G V2X Communications @ KCL, London, June 11, 2018

latency-reliability characterization

latency t

tR: time of data reception

reliability Pr(𝑢𝑆 ≤ 𝑢)

1 1-Pe diversity: time? frequency antennas interfaces

5G V2X Communications @ KCL, London, June 11, 2018

design targets

latency reliability

1

broadband rate-

• riented systems

latency reliability

1

ultra-reliable low latency communication URLLC

5G V2X Communications @ KCL, London, June 11, 2018

▪ in absence of interference, we need to characterize the lower tail of 𝛿𝑇 ▪ if 𝛿𝑇 is known, we need to characterize the upper tail of 𝛿𝐽

a simple error model

Pr 𝐹 = Pr 𝛿𝑡 1 + 𝛿𝐽 < 𝛿𝑢ℎ

SINR

5G V2X Communications @ KCL, London, June 11, 2018

▪ assume that the interference is absent. ▪ we (somehow) know that the channel is Rayleigh. ▪ the target error rate is 𝜁𝑉, average SNR is ҧ 𝛿𝑇 how do we choose the rate R?

channel uncertainty in URLLC Pr 𝐹 = Pr log2 1 + 𝛿𝑡 < 𝑆 𝑆 = log2 1 + ҧ 𝛿𝑇 ln 1 1 − 𝜁𝑉 where is the problem?

5G V2X Communications @ KCL, London, June 11, 2018

▪ the knowledge of average SNR is based on n collected samples ▪ when n is low, the rate should R be chosen very conservatively ▪ online update of the estimate and rate (or power) adaptation

channel uncertainty in URLLC

• P. Popovski et al., ”Ultra-Reliable Low Latency Communication is Difficult: A Statistical

Assessment”, in preparation

5G V2X Communications @ KCL, London, June 11, 2018

building blocks for URLLC

5G V2X Communications @ KCL, London, June 11, 2018

▪ channel models ▪ transmission of short packets ▪ high diversity ▪ lean protocol design with respect to latency

– focus on control information

▪ network architecture ▪ wireless slicing and coexistence with other services

5G V2X Communications @ KCL, London, June 11, 2018

▪ channel models ▪ transmission of short packets ▪ high diversity ▪ lean protocol design with respect to latency

– focus on control information

▪ network architecture ▪ wireless slicing and coexistence with other services

5G V2X Communications @ KCL, London, June 11, 2018

currently there is lack of experimental evidence for URC-relevant statistics of wireless channels initial analysis of common wireless channel models in URC regime ▪ block fading ▪ 𝑄𝑆 is the minimal SNR to decode data rate 𝑆 ▪ the analysis reveals the URC-behavior: Pr 𝑄

𝑆

ത 𝑄 < 𝑀 ≈ 𝜁 ≈ 𝛽 𝑄

𝑆

ത 𝑄

𝛾

wireless channel model behavior in ultra-reliable regime

5G V2X Communications @ KCL, London, June 11, 2018

two-wave model with equal amplitudes represents one of the worst cases

HTX HRX

λ ⇡

−

⇡ λ

Γ λ ⇡

−

⇡ λ

fl ⇢ ⇢ φ

• utdoor physical setup
• utdoor physical setup

5G V2X Communications @ KCL, London, June 11, 2018

indoor case dominated by diffuse components, good for high reliability

indoor physical setup

• P. Eggers, M. Angjelichinoski, and P. Popovski, ”Wireless Channel Modeling Perspectives for

Ultra-Reliable Low Latency Communications”, available on Arxiv, 2018.

5G V2X Communications @ KCL, London, June 11, 2018

an example of a short packet format

UNB (ultra narrowband) system reliability of the packet reception is a product of the reliabilities of different parts

Pr 𝑡𝑣𝑑𝑑𝑓𝑡𝑡 = Pr 𝑄𝐵 Pr 𝑡𝑧𝑜𝑑 Pr 𝐽𝐸 Pr 𝑒𝑏𝑢𝑏 …

5G V2X Communications @ KCL, London, June 11, 2018 Philippe Petit, http://www.msnbc.com/msnbc/philippe-petit-twin-towers-balancing-act-remembered#slide1

▪ repetition coding for control information inefficient ▪ the proverbial 1-bit feedback becomes questionable

5G V2X Communications @ KCL, London, June 11, 2018

communication theory and protocol information

5G V2X Communications @ KCL, London, June 11, 2018

at short blocklengths there is a penalty that keeps the rate away from capacity. AWGN SNR 0 dB fundamental theory of finite blocklength transmission

5G V2X Communications @ KCL, London, June 11, 2018

▪ low SNR ▪ 10 bytes control information ▪ 10 bytes data ▪ same amount of channel uses

probability of error 10e-3 probability of error

10e-6

gain in reliability

5G V2X Communications @ KCL, London, June 11, 2018

mixing data and control information has energy cost

M D time

M D

frequency time frequency

the notion of frame in cellular systems should be revisited

5G V2X Communications @ KCL, London, June 11, 2018

separated data and metadata useful for energy efficiency

data for Bob, Carol turns off her receiver after the metadata

Alice Bob Carol

joint data and metadata better coding of the metadata

however, everybody decodes

everything Alice Bob Carol

connection between packetization and energy efficiency

5G V2X Communications @ KCL, London, June 11, 2018

some observations

▪ basic tradeoff between energy efficiency and ultra-reliability ▪ departure from the common causal relationship metadata -> data ▪ low latency usually means sending with few channel uses (DoF)

– DoF can be increased in e.g. frequency or space

5G V2X Communications @ KCL, London, June 11, 2018

downlink communication to K users

▪ a user is active and there is a packet for her with probability q. ▪ the message for each active user is drawn randomly from a set of predefined message sizes. ▪ metadata should inform about

▪ who is active ▪ the message size.

▪

• K. F. Trillingsgaard and P. Popovski, "Downlink Transmission of Short Packets:

Framing and Control Information Revisited," in IEEE Transactions on Communications, vol. 65, no. 5, pp. 2048-2061, May 2017.

example: a theoretical treatment of downlink framing

5G V2X Communications @ KCL, London, June 11, 2018

conventional framing with pointers example: a theoretical treatment of downlink framing

ptr 2 ptr 3 UG 1 UG 2 UG 3 ptr 4 UG 4

m essages with

message sizes

messages with

alternative framing

5G V2X Communications @ KCL, London, June 11, 2018

▪ new tradeoff arises for short packets

– latency is minimized when all packets are jointly encoded; – power is minimized when each packet is encoded separately.

K=32 users

latency-energy tradeoff

5G V2X Communications @ KCL, London, June 11, 2018

massive MIMO and ultra-reliability

pros ▪ very high SNR links ▪ quasi-deterministic links, fading immunity ▪ extreme spatial multiplexing capability cons ▪ expensive CSI acquisition procedure ▪ additional protocol steps

5G V2X Communications @ KCL, London, June 11, 2018

massive MIMO/URLLC: mitigating the CSI problem

downlink beamforming based on channel structure non-coherent energy detection in the uplink

• A. Sabin-Bana, M. Angjelichinoski, E. de Carvalho and P. Popovski, ”Massive MIMO for Ultra-

reliable Communications with Constellations for Dual Coherent-noncoherent Detection”, in IEEE WSA, Bochum, 2018.

5G V2X Communications @ KCL, London, June 11, 2018

1 latency: x reliability: P(X≤x) latency distribution

Pe

timeout Transmission errors Infrastructure failures

cloning 2-out-of-3

transmission strategies

multi-interface transmission interface diversity

5G V2X Communications @ KCL, London, June 11, 2018

results based on lab measurements

▪ 1 day, 100 ms interval ▪ Wi-Fi

– achieves 10 ms for 90% of packets – but 99% requires almost 100 ms

▪ cellular: LTE and HSPA

– also requires ~100 ms for 99%

▪ cloning (1 copy per IF)

– 99% at 25 ms – 99.999% at 60 ms latency

1 2 5 10 20 50 100 200 500

l [ms]

0.99999 0.9999 0.999 0.99 0.9

RTT

LTE HSPA Wi-Fi Cloning all 2-out-of-3

interface diversity experimental results

• J. J. Nielsen, R. Liu, and P. Popovski, “Ultra-Reliable Low Latency Communication

(URLLC) using Interface Diversity”, IEEE Transactions on Communications, accepted, available at ArXiv, 2017.

5G V2X Communications @ KCL, London, June 11, 2018

* Source: Ciscus Sarasota

final remarks: protocol challenge is immensely larger

• 9. RRC Conn. Reconf. Compl.
• 8. RRC Conn. Reconfiguration
• 7. RRC Security Mode Complete
• 6. RRC Security Mode Command
• 5. RRC Conn. Setup Complete

4.b. RRC Conn. Setup 4.a. Contention resolution

• 3. RRC Conn. Request
• 2. Random access response
• 1. Random Access preamble

UE eNB

• 10. Small Data Payload

access Attempt connection establishment

5G V2X Communications @ KCL, London, June 11, 2018

summary and outlook

▪ ultra-reliable wireless has the potential to profoundly change systems and devices ▪ essential:

▪ short packet transmission ▪ communication-theoretic attention to the control information ▪ every step in the protocol needs a careful reliability design ▪ careful use of diversity

▪ large number of steps in real protocols impair reliability and latency

▪ lean protocol design

coexistence of URLLC with the other 5G services

joint work with Kasper F. Trillingsgaard, Aalborg University, Denmark Osvaldo Simeone, King’s College London, UK Giuseppe Durisi, Chalmers University, Sweden

5G V2X Communications @ KCL, London, June 11, 2018

5G V2X Communications @ KCL, London, June 11, 2018

reminder: distilled service requirements

eMBB

▪ acceleration of 4G, large payloads, active over longer periods ▪ maximize rate, moderate reliability (e.g. 10E-3)

mMTC

▪ fix low rate, unknown active subset from a massive device set ▪ maximize arrival rate, low reliability (e.g. 10E-1)

URLLC

▪ intermittent transmissions, but from a much smaller device set ▪

• ffer high reliability (e.g. 10E-1) while localized in time

5G V2X Communications @ KCL, London, June 11, 2018

the problem of slicing

slicing: share the resource while providing heterogeneous guarantees to different services

uplink scenario more challenging due to lack of coordination

eMBB mMTC URLLC

5G V2X Communications @ KCL, London, June 11, 2018

two types of slicing

eMBB mMTC URLLC idle

non-orthogonal

frequency time frequencies reserved for URLLC frequency time frequencies allocated for URLLC

• rthogonal

5G V2X Communications @ KCL, London, June 11, 2018

system model

▪ 𝐺 frequency radio resources ▪ 𝑇 minislots ▪ eMBB transmission takes one frequency resource ▪ 𝑏𝑉 is the probability of active URLLC device in a minislot ▪ an URLLC transmission spreads over 𝐺

𝑉 frequencies

▪ 𝐵𝑁 is the Poisson-distributed number of active mMTCs

radio resource at a specific frequency channel frequency channel time minislot time slot

eMBB mMTC URLLC idle

1 2 3 4 5 6 7

fic, ficients ficients ficients ⇠ Γ ⇠ Γ ⇠ Γ Γ Γ Γ

5G V2X Communications @ KCL, London, June 11, 2018

the received signal in a minislot

𝐙𝑡,𝑔 = 𝐼𝐶,𝑔𝐘𝐶,𝑔 + 𝐼𝑉,𝑔𝐘𝑉,𝑡,𝑔 + ෍

𝑛=1 𝐵𝑁

𝐼 𝑛 ,𝑔𝐘 𝑛 ,𝑡,𝑔 + 𝐚𝑡,𝑔

not a classical multiple access channel ▪ different arrivals, different decoding criteria, etc. independent Rayleigh-faded 𝐼𝑗,𝑔 if there is no transmission, 𝐘𝑗,𝑔 = 0

5G V2X Communications @ KCL, London, June 11, 2018

some more bits and pieces about the model

eMBB ▪ has a full CSI and transmits with channel inversion ▪ not transmitting w.p. 1 − 𝑏𝐶 results in outage

𝑠

𝐶,𝑔 = log2 1 + 𝐻𝐶,𝑔 tar

URLLC ▪ find maximal rate 𝑠𝑉 that satisfies 𝜁𝑉 ▪ no CSIT and no power adaptation

Pr 𝐹𝑉 = Pr 1 𝐺

𝑉

෍

𝑔=1 𝐺𝑉

log2 1 + 𝐻𝑉,𝑔 < 𝑠

𝑉

≤ 𝜁𝑉

5G V2X Communications @ KCL, London, June 11, 2018

some more bits and pieces about the model

mMTC: use of successive interference cancellation (SIC)

SNRs: 𝐻[1] ≥ 𝐻[2] ≥ ⋯ ≥ 𝐻[𝐵𝑁] SINR: 𝜏 𝑛0 =

𝐻[𝑛0] 1+σ𝑛=𝑛0+1

𝐵𝑁

𝐻[𝑛]

decoding condition: log2 1 + 𝜏 𝑛0 ≥ 𝑠

𝑁

5G V2X Communications @ KCL, London, June 11, 2018

the reliability diversity 𝜁𝑉 ≪ 𝜁𝐶 ≪ 𝜁𝑁

design that benefit from heterogeneous reliability requirements example of interfering eMBB and URLLC: (1 − 𝜁𝑉) 1 − 𝜁𝑉 1 − 𝜁𝐶

′

≥ (1 − 𝜁𝐶)

5G V2X Communications @ KCL, London, June 11, 2018

the reliability diversity 𝜁𝑉 ≪ 𝜁𝐶 ≪ 𝜁𝑁

design that benefit from heterogeneous reliability requirements example of interfering eMBB and URLLC: (1 − 𝜁𝐶) always ≤ (1 − 𝜁𝑉)

5G V2X Communications @ KCL, London, June 11, 2018

slicing for eMBB and URLLC

• rthogonal

non-orthogonal with SIC

Pr 1 𝐺

𝑉

෍

𝑔=1 𝐺𝑉

log2 1 + 𝐻𝑉,𝑔 1 + 𝐻𝐶,𝑔

tar

< 𝑠

𝑉

≤ 𝜁𝑉

5G V2X Communications @ KCL, London, June 11, 2018

slicing for eMBB and URLLC

non-orthogonal with puncturing perspective of the eMBB eMBB uses erasure code of rate 1 −

𝑙 𝑇

and thus has a decreased rate

5G V2X Communications @ KCL, London, June 11, 2018

slicing for eMBB and URLLC: results Γ𝑉 > Γ𝐶

2 4 6 8 10 12 r B ,sum 0.0 0.5 1.0 1.5 2.0 2.5 3.0 r U

• rthogonal
• rthogonal (LB)

SIC SIC (LB) puncturing puncturing (LB)

5G V2X Communications @ KCL, London, June 11, 2018

slicing for eMBB and URLLC: results Γ𝑉 < Γ𝐶

5 10 15 20 25 30 35 40 r B ,sum 0.0 0.2 0.4 0.6 0.8 1.0 1.2 r U

• rthogonal
• rthogonal (LB)

SIC SIC (LB) puncturing puncturing (LB)

5G V2X Communications @ KCL, London, June 11, 2018

slicing for eMBB and mMTC

we look into a single radio frequency resource

▪ orthogonal slicing achieved by time-sharing ▪ non-orthogonal slicing achieved by SIC

SINR: 𝜏 𝑛0 =

𝐻[𝑛0] 1+𝐻𝐶,𝑔

tar+σ𝑛=𝑛0+1 𝐵𝑁

𝐻[𝑛]

5G V2X Communications @ KCL, London, June 11, 2018

slicing for eMBB and mMTC: results three regimes

(1) small 𝑠

𝐶

(2) intermediate 𝑠

𝐶

(3) large 𝑠

𝐶

1 2 3 4 5 6 7 r B 20 40 60 80 λM SIC, ΓB = 10 dB SIC, ΓB = 20 dB SIC, ΓB = 30 dB

• rthogonal, ΓB = 10 dB
• rthogonal ΓB = 20 dB
• rthogonal, ΓB = 30 dB

5G V2X Communications @ KCL, London, June 11, 2018

summary and outlook

▪ simple model that captures the features of the 3 services ▪ non-orthogonal slicing can be beneficial, but not always ▪ reliability diversity plays a role in setting design guidelines many extensions possible ▪ use the model to analyze the slicing for all thee services ▪ multiple URLLC devices ▪ multiple mMTC channels and hopping ▪ mMTC repetitions

5G V2X Communications @ KCL, London, June 11, 2018

additional references

▪

• P. Popovski, J. J. Nielsen, C. Stefanovic, E. de Carvalho, E. Strỏm, K. F. Trillingsgaard, A.-S.

Bana, D. M. Kim, R. Kotaba, J. Park, R. B. Sørensen, "Ultra-Reliable Low-Latency Communication (URLLC): Principles and Building Blocks", IEEE Network Magazine, Special issue on 5G for Ultra-Reliable Low Latency Communications, in revision, 2017. ▪

• K. F. Trillingsgaard, and P. Popovski, “Generalized HARQ Protocols with Delayed Channel State

Information and Average Latency Constraints”, accepted for publication in IEEE Transactions on Information Theory, 2017. ▪

• A. Kalør, R. Guillaume, J. Nielsen, A. Mueller and P. Popovski, “Network Slicing in Industry 4.0

Applications: Abstraction Methods and End-to-End Analysis”, IEEE Transactions on Industrial Informatics (SS on From Industrial Wireless Sensor Networks to Industrial Internet-of-Things), 2017. ▪

• G. Durisi, T. Koch and P. Popovski, "Toward Massive, Ultrareliable, and Low-Latency Wireless

Communication With Short Packets," Proceedings of the IEEE, vol. 104, no. 9, pp. 1711-1726,

• Sept. 2016.

▪

• P. Popovski, ”Ultra-Reliable Communication in 5G Wireless Systems”, 1st International

Conference on 5G for Ubiquitous Connectivity, Levi, Finland, November 2014. ▪

• P. Popovski, K. F. Trillingsgaard, O. Simeone, and G. Durisi, ”5G Wireless Network Slicing for

eMBB, URLLC, and mMTC: A Communication-Theoretic View”, available on Arxiv, 2018.