Seminar on Low Power Wide Area Networks» Chirp Spreading Spectrum (CSS) LoRa Modulation Chirp f t...
Transcript of Seminar on Low Power Wide Area Networks» Chirp Spreading Spectrum (CSS) LoRa Modulation Chirp f t...
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RadioNetworks, DEI, Alma Mater Studiorum - Università di Bologna
Luca Feltrin
Seminar on Low Power Wide Area Networks
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Technologies Overview
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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
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Motivation State of the Art LoRa NB-IOT
Outline
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Extended Coverageo Large areaso Environment with poor coverage
Scenario
Basement
20 km
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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
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Long range means more devices could be active atthe same time
Network Capacity
200m
20km
LPWAN 10k times bigger area
100k active devices
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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 )
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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
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3 Possible class of devices Star Topology Cloud Based Network (devices does not know about
Gateways)
LoRa - Overview
Network
gateway
gateway
User End
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Frequencyo ISM bands (Europe: 868MHz and 433MHz)o Bandwidth: 125 kHz, 250kHz (and other)
Modulationo FSKo LoRa (Proprietary Standard)
LoRa - PHY
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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
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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
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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
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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
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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
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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%)
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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
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LoRa - Performance
Each node transmits 2 packets/day
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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
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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
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RadioNetworks, DEI, Alma Mater Studiorum - Università di Bologna
Thanks for Listening
Luca Feltrin