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