Seminar on Low Power Wide Area Networks» Chirp Spreading Spectrum (CSS) LoRa Modulation Chirp f t...

RadioNetworks, DEI, Alma Mater Studiorum - Università di Bologna

Luca Feltrin

Seminar on Low Power Wide Area Networks

Technologies Overview

State of the Art

• LoRaWAN• SIGFOX• Weightless• Ingenu• ...

NB-IOT(Narrow Band)

EC-GSM(Enhanced Coverage)

a.k.a. MTC

Long RangeTechnologies for IoT

ISM BandCellular Band

Based on LTE Based on 2G New Interface

LTE Cat.0

3GPP: Rel. 12

LTE-M3GPP: Rel. 13

Motivation State of the Art LoRa NB-IOT

Outline

Extended Coverageo Large areaso Environment with poor coverage

Scenario

Basement

20 km

Long Range: ZigBee/802.15.4 o Multi-hop

Long Range: LPWANo Single -very long- hop

Long Range at Low Power

SourceRouters

Coordinator

SourceSink

Cons:• Sync required (Overhead)• More devices to mantain• Routing is complex

Pro:• Simple• Transmit power have small impact on

overall power consumption

Long range means more devices could be active atthe same time

Network Capacity

200m

20km

LPWAN 10k times bigger area

100k active devices

What do we sacrifice to have long range and lowenergy?

o For IoT it is actually OK (Machine Type Traffic)

• Sporadic Sensor Data

• Alarms

Drawbacks

Throughput

( < 200 bps )

General requirements set by 3GPP:o Coverage: More than GPRS+20dB (164 dB)o Throughput: More than 160 bpso Latency: Less than 10 secondso Battery Life: More than 10 years (5Wh battery @ MCL=164dB)o Deployment: Only SW updateo Capacity: More than 52500 devices per cell

LPWAN Requirement Summary

Details on evaluation framework in TS 45.820

3 Possible class of devices Star Topology Cloud Based Network (devices does not know about

Gateways)

LoRa - Overview

Network

gateway

gateway

User End

Frequencyo ISM bands (Europe: 868MHz and 433MHz)o Bandwidth: 125 kHz, 250kHz (and other)

Modulationo FSKo LoRa (Proprietary Standard)

LoRa - PHY

How to achieve Long Range?o Narrow Band

• Noise is filtered out

o High Sensitivity

• Processing Gain

– Spreading Spectrum Tecniques

» Chirp Spreading Spectrum (CSS)

LoRa Modulation

Chirpf

t

Bandwith

SymbolTime

Spreading Factor (SF)

o Symbol time 𝑻𝒔 =𝟐𝑺𝑭

𝑩𝑾o When SF increases, Symbol Time increases and it is easier for

the receiver to «recognize» a symbol -> better sensitivity

o 𝑮𝑷 =𝑩𝑾

𝑹𝑺= 𝟐𝑺𝑭, so if SF++ then 𝚫𝑮𝑷 ≃ 𝟑𝒅𝑩

LoRa Modulation

Spreading Factor (quasi-)orthogonality

LoRa Modulation

A

B

Useful Signal (SF=9)

Interferer (SF=12)

Prx = -100 dBm

Prx = -90 dBm C/I = -10 dB > -21.6 dB

LoRa Capture Threshold in dB

Spreading Factor (quasi-)orthogonality

LoRa Modulation

A

B

Useful Signal (SF=9)

Interferer (SF=12)

Prx = -100 dBm

Prx = -75 dBm C/I = -25 dB < -21.6 dB

Collision

LoRa Capture Threshold in dB

No Carrier Sensingo ALOHA-like Channel Accesso Duty Cycle Limit due to Regulations ( < 1%)

LoRa MAC

RX 1

GW

EDTX RX 2

1 sec

GW

EDTX RX 1 RX 2

Class B:o Beacon to synchronize the End Devices to let them open

more reception windows

Class C:o End Devices are always listening

LoRa MAC

No Carrier Sensingo ALOHA-like Channel Accesso Duty Cycle Limit due to Regulations ( < 1%)

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Succ

ess

Rat

e

Number of Nodes

Success Rate

SF=12, PL=10, ACK

SF=12, PL=10, NO ACK

SF=12, PL=100, NO ACK

SF=12, PL=100, ACK

Retransmissionso Mtype

• Confirmed – Each Uplink requires an ACK, if not received the packetis retransmitted

• Unconfirmed – the ACK is not required

LoRa MAC

RetransmissionsImprove Success Rate

Retransmissions generate too much traffic

LoRa - Performance

Each node transmits 2 packets/day

Key Featureso Integration in Cellular Network, Lower Complexity and Cost

• Simplified version of LTE, new User Equipment (UE)

o Better Coverage

• Better Sensitivity through Narrow Band

o Energy Efficiency

• Smaller Duty Cycle

NB-IOT

Smaller Duty Cycleo Extended DRX (eDRX)

• Device only listen to few paging information

• Device is registered and reachable (with a certain latency)

o Power Saving Mode (PSM)

• Device go to special power saving mode for a long period of time

• Device is registered but not reachable until it wakes up

NB-IOT

< 44 minutes

RadioNetworks, DEI, Alma Mater Studiorum - Università di Bologna

Thanks for Listening

Luca Feltrin

luca.feltrin@unibo.it