Seminar on Low Power Wide Area Networks

Transcription

1 Seminar on Low Power Wide Area Networks Luca Feltrin RadioNetworks, DEI, Alma Mater Studiorum - Università di Bologna

2 Technologies Overview

3 State of the Art Long Range Technologies for IoT Cellular Band ISM Band Based on LTE Based on 2G New Interface LTE Cat.0 3GPP: Rel. 12 LTE-M 3GPP: Rel. 13 EC-GSM (Enhanced Coverage) NB-IOT (Narrow Band) LoRaWAN SIGFOX Weightless Ingenu... a.k.a. MTC

4 Outline Motivation State of the Art LoRa NB-IOT

5 Scenario Extended Coverage o Large areas o Environment with poor coverage Basement 20 km

6 Long Range at Low Power Long Range: ZigBee/ o Multi-hop Cons: Sync required (Overhead) More devices to mantain Routing is complex Coordinator Routers Source Long Range: LPWAN o Single -very long- hop Sink Pro: Simple Transmit power have small impact on overall power consumption Source

7 Network Capacity Long range means more devices could be active at the same time LPWAN 10k times bigger area 100k active devices 200m 20km

8 Drawbacks What do we sacrifice to have long range and low energy? Throughput ( < 200 bps ) o For IoT it is actually OK (Machine Type Traffic) Sporadic Sensor Data Alarms

9 LPWAN Requirement Summary General requirements set by 3GPP: o Coverage: More than GPRS+20dB (164 db) o Throughput: More than 160 bps o Latency: Less than 10 seconds o Battery Life: More than 10 years (5Wh MCL=164dB) o Deployment: Only SW update o Capacity: More than devices per cell Details on evaluation framework in TS

10 LoRa - Overview 3 Possible class of devices Star Topology Cloud Based Network (devices does not know about Gateways) User End Network gateway gateway

11 LoRa - PHY Frequency o ISM bands (Europe: 868MHz and 433MHz) o Bandwidth: 125 khz, 250kHz (and other) Modulation o FSK o LoRa (Proprietary Standard)

12 LoRa Modulation How to achieve Long Range? o Narrow Band Noise is filtered out o High Sensitivity Processing Gain Spreading Spectrum Tecniques» Chirp Spreading Spectrum (CSS) Chirp Bandwith f Symbol Time t

13 LoRa Modulation Spreading Factor (SF) o Symbol time T s = 2SF BW o When SF increases, Symbol Time increases and it is easier for the receiver to «recognize» a symbol -> better sensitivity o G P = BW R S = 2 SF, so if SF++ then ΔG P 3dB

14 LoRa Modulation Spreading Factor (quasi-)orthogonality LoRa Capture Threshold in db Useful Signal (SF=9) A Prx = -100 dbm Interferer (SF=12) B Prx = -90 dbm C/I = -10 db > db

15 LoRa Modulation Spreading Factor (quasi-)orthogonality LoRa Capture Threshold in db Useful Signal (SF=9) A Prx = -100 dbm Collision Interferer (SF=12) B Prx = -75 dbm C/I = -25 db < db

16 LoRa MAC No Carrier Sensing o ALOHA-like Channel Access o Duty Cycle Limit due to Regulations ( < 1%) GW ED TX RX 1 RX 2 1 sec GW ED TX RX 1 RX 2

17 LoRa MAC No Carrier Sensing o ALOHA-like Channel Access o Duty Cycle Limit due to Regulations ( < 1%) Class B: o Beacon to synchronize the End Devices to let them open more reception windows Class C: o End Devices are always listening

18 Success Rate LoRa MAC Retransmissions o Mtype Confirmed Each Uplink requires an ACK, if not received the packet is retransmitted Unconfirmed the ACK is not required % Success Rate 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Number of Nodes Retransmissions Improve Success Rate SF=12, PL=10, ACK SF=12, PL=10, NO ACK SF=12, PL=100, NO ACK SF=12, PL=100, ACK Retransmissions generate too much traffic

19 LoRa - Performance Each node transmits 2 packets/day

20 NB-IOT Key Features o 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

21 NB-IOT Smaller Duty Cycle o Extended DRX (edrx) Device only listen to few paging information Device is registered and reachable (with a certain latency) < 44 minutes 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

22 Thanks for Listening Luca Feltrin RadioNetworks, DEI, Alma Mater Studiorum - Università di Bologna