Charm: Exploiting Geographical Diversity Through Coherent Combining - - PowerPoint PPT Presentation

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Charm: Exploiting Geographical Diversity Through Coherent Combining - - PowerPoint PPT Presentation

Jan 30, 2024 166 likes •422 views

Charm: Exploiting Geographical Diversity Through Coherent Combining in LPWANs OR When They Go Low, We Go Lower (Power) IPSN 2018, Porto Adwait Dongare , Revathy Narayanan, Akshay Gadre, Anh Luong, Artur Balanuta, Swarun Kumar, Bob Iannucci,

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SLIDE 1

Charm: Exploiting Geographical Diversity Through Coherent Combining in LPWANs OR When They Go Low, We Go Lower (Power)

IPSN 2018, Porto

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Adwait Dongare, Revathy Narayanan, Akshay Gadre, Anh Luong, Artur Balanuta,
 Swarun Kumar, Bob Iannucci, Anthony Rowe Electrical And Computer Engineering Carnegie Mellon University, Pittsburgh PA and Silicon Valley CA

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SLIDE 2

Low-Power Wide-Area Networking (LPWAN)

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SLIDE 3

LPWAN’s potential

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10km range in line-of-sight 5+ year battery life Thousands of devices per gateway Low data rate
 (0.25 kbps – 27 kbps) Sub-GHz ISM band
 chirp spread-spectrum (CSS)

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SLIDE 4

OpenChirp In Pittsburgh

  • openchirp.io


CMU’s LoRaWAN network in Pittsburgh

  • 4 outdoor gateways + multiple

indoor gateways

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SLIDE 5

Coverage

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4km 8km 12km 16km 4km 8km 12km 0,0

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SLIDE 6

Penetration Inside Buildings

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0 % 50 % 100 % gateway

Bi-directional packet success rate

44 % 52 % 18 % 40 % 36 % 72 % 67 % 59 % 66 % 20 % 67 % 52 % 61 % 58 % 72 % 72 %

0 m 10 m 5 m

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SLIDE 7

Client Device Battery Life

  • Wireless transmissions

dominate energy usage

  • Increasing data rate and

reducing retransmissions significantly improves battery life

7 Time (s)

0.5 1 1.5 2 2.5

Current (mA)

100 200

MCU + TX
 120.7 mA MCU +
 radio sleep
 3.7 mA MCU + RX
 16.6 mA MCU sleep +
 radio sleep
 287 nA

Packets per day

10 1 10 2 10 3 10 4

Battery lifetime (years)

1 2 3 4 5 6 7 8 9 10

DR0 (980 bits/s) DR1 (1760 bit/s) DR2 (3125 bit/s) DR3 (5470 bit/s) DR4 (12500 bit/s)

Packets per hour

1 5 10 60 100

increase data rate
 2.2 →4 years halve retransmissions
 2.2 →4.5 years

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SLIDE 8

LPWANs have lots of gateways…..

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Can we use them to improve network performance?

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SLIDE 9

Coherent Combining

  • Multiple gateways hear the

same weak transmission

  • Coherent combining in the

cloud

  • e.g. Cloud Radio Access

Networks (C-RAN) in cellular communication

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client cloud gateway 3 gateway 2 gateway 1

time gateway 1 gateway 2 gateway 3

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SLIDE 10

Challenges

  • High bandwidth connectivity

to the cloud

  • Nanosecond-scale

synchronization

  • Expensive computing

resources for large number of streams

  • Latency

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SLIDE 11

Charm

  • Practical coherent combining


Leverage diversity from multiple gateway receivers

  • Software architecture
  • Scaleable two-phase protocol
  • Local packet detection
  • Hardware platform


Auxiliary low-cost SDR-like platform for gateways

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SLIDE 12

LoRaWAN

12 x y1 y2 yN RX1 RX2 RXn TX h1 h2 hN … Packet Cloud MAC Packet

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SLIDE 13

Charm: Two-Phase Protocol

13 x y1 y2 yN RX1 RX2 RXn TX h1 h2 hN … Packet? Request Joint Decoder Cloud MAC Packet?

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SLIDE 14

Charm: Local Packet Detection

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matched
 filtering

time frequency

chirp spread-spectrum packet

time frequency

known preamble

time amplitude

Uses only the preamble and sync header

threshold

preamble sync data

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SLIDE 15

Charm: Enhanced Packet Detection

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time f

subsample
 (folding)

time frequency

chirp spread-spectrum packet matched
 filtering

Uses the entire packet

time amplitude threshold

known signal pattern

time f

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SLIDE 16

Charm: Gateway Hardware

  • Semtech SX1257 frontend with

MicroSemi IGLOO FPGA

  • Outputs radio I/Q stream like

an SDR

  • Auxiliary hardware for existing

gateways and interfaces with raspberry Pi

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RPi 3 FPGA
 (IGLOO) RF frontend
 (SX1257) LNA SPI SPI ΔΣ-I/Q Ethernet RX
 antenna TX
 antenna LPRAN board

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SLIDE 17

Practical Coherent Combining With Charm

  • High bandwidth connectivity

to the cloud

  • Nanosecond-scale

synchronization

  • Expensive computing

resources for large number of streams

  • Latency

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upload samples on request local packet detection
 simplifies synchronization selective combination of sample streams LoRaWAN ~1 sec to ACK

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SLIDE 18

Benchmark: Packet Detection

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SLIDE 19

Benchmark: Improved Network And Device Performance

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Combined signal SNR
 increases logarithmically Results into improved
 battery life on client devices

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SLIDE 20

Simulation: Dense Deployment

Improvements

Increase in coverage area: 46.60%

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Charm

Data Rate Battery Life Improved region (by area) 2x 2x 35.33% 4x 4x 22.30% 8x 8x 2.26%

coverage improvement data rate improvement

LoRaWAN

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SLIDE 21

Simulation: Random Deployment

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Charm

Data Rate Battery Life Improved region (by area) 2x 2x 33.70% 4x 4x 25.82% 8x 8x 3.48%

Improvements

Increase in coverage area: 74.59%

coverage improvement data rate improvement

LoRaWAN

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SLIDE 22

Future Work

  • Collisions: can we decode

collisions?

  • Scalability: can we avoid

continuously streaming to the cloud?

  • Hardware Architecture: how

can we leverage new radio front-ends

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time time

Analog Devices
 ADALM-Pluto

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SLIDE 23

Conclusions

  • Decode weak transmissions through coherent

combining

  • Charm’s two-phase protocol
  • On-demand upload - save bandwidth
  • Local packet detection - simplify

synchronization requirements and computation

  • Selective combination - better scalability
  • SDR-like auxiliary hardware to capture I/Q streams
  • Performance
  • Improve coverage up to 98%
  • Improve battery life up to 8x
  • Effectively reduce coverage holes
  • No changes on low-power devices

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Cloud Gateway 1 Gateway 2 Client User Deployed Gateway 3

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SLIDE 24

Thank you! Q&A

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Adwait Dongare (adongare@cmu.edu)