Why do we need long range transmission?
- For wireless transmission over large areas, there are two options: cellular or low power wide area network LPWAN
- Cellular is expensive, power-hungry
- Cellular network covering is only 15%
draw figure of wireless technologies (L8 4)
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draw schematic of LPWAN family members (L8 5)
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benefits of LPWAN
- Long battery life
- Massive IoT
- Low-cost for end devices
- Easy deployment
- extended coverage
Examples of massive IoT services by LPWAN
- smart building
- agriculture monitoring, livestock tracking
- industrial, process monitoring and optimization
Estructure of LoRaWAN protocol stack
- Application layer: Applications
- Mac layer: LoRa MAC, MAC options
- Physical layer: class A, class B, class C, LoRa modulation, regional ISM band
Intended usage of LoRaWAN end-device classes
- class A: battery powered sensors
- class B: battery powered actuators
- class C: mains powered actuators
Diagram of LoRaWAN classes against energy efficiency and latency (L8 10)
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Frequency at which LoRa channels operate
868MHz-869MHz
LoRa frame structure (L8 14)
- Preamble: needed to synchronize receiver with transmitter
- Header: basic information
- Payload: information/data
- CRC: error detection
draw a LoRaWAN architecture (L8 16)
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Tasks of LoRa network server (traffic handling)
- To process all traffic received from gateways
- Manages radio configuration
- Message management: authentication, authorization, accounting
- Location determination (DTOA)
- manages ACKs
- manages downlink messages including multicast
Properties of LoRa modulation
- version of Chirp Spread Spectrum (bandwidth 125kHz)
- high sensitivity end nodes
- Long range communication
- strong indoor penetration
- uses entire bandwidth, making it robust to channel noise
- resistant to doppler effect, multi-path, signal weakening
what is spread spectrum modulation?
- technique used to reduce signal interference
- transmitted signal has a wider bandwidth than information signal
Draw diagram of LoRa CSS modulation (L8 20)
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represent the chirp waveform with an schematic (L8 21)
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draw schematic of chirp frequency spreading factors (L8 26)
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Draw curve of data rate vs SF (spreading factor) (L8 29)
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SF assignment mechanisms
- PHY-based
- Random assignment
- Fixed assignment
- Fairness-based
- Distance-based
How localization works in LoRA?
- Uses differential time of arrival (DTOA)
- Triangulation-based location determination
- Outdoor accuracy<50M
- Indoor accuracy<75M
Challenges of LoRaWAN
- Energy consumption
- Communication range
- Multiple access
- Error correction
- Security
