LoRa and LoRaWAN

Energy – Range Dilemma

 Free space/Log-normal path loss
Free Space Path loss
𝑃𝑇 𝐺𝑇 𝐺𝑅 𝜆2
Friss 𝑃𝑟 𝑑 = 4𝜋 2 𝑑2 𝐿

L(fs) = 32.45 + 20log(d) + 20log(f)

d (km); f (MHz); L (dB)

Lower energy means shorter range !!!

Fresnel zone
 The Fresnel zone is an elliptical shaped body around the direct line of
sight path between the end node and the gateway.

𝑟 = 8.657 ∗ 𝐷/𝑓

Any obstacle within this volume, for example buildings, trees, hilltops or ground can weaken the
transmitted signal even if there is a direct line of sight between the end node and the gateway.
Link Budget
 A link budget is the sum of all of the gains and losses from the
transmitter, through the medium (aka free space), to the receiver in a
telecommunication system. It is a way of quantifying the link
performance.
RSSI
 The Received Signal Strength Indication (RSSI) is the received signal
power in milliwatts and is measured in dBm.

Typical LoRa RSSI values are:

RSSI minimum = -120 dBm.
If RSSI=-30dBm: signal is strong.
If RSSI=-120dBm: signal is weak.

The RSSI is measured in dBm and is a negative value.

The closer to 0 the better the signal is.
SNR
 Signal-to-Noise Ratio (SNR) is the ratio between the received power
signal and the noise floor power level.

Typical LoRa SNR values are between: -20dB and +10dB

A value closer to +10dB means the received signal is less corrupted.
LoRa can demodulate signals which are -7.5 dB to -20 dB below the noise floor.

𝑆
𝐶 = 𝐵 𝑙𝑜𝑔2(1 + )
𝑁

If the bandwidth is bigger (spread), we can use a smaller SNR and still get good data rates
Or
We can cope with higher SNR and are very resilient to narrowband interferers
LPWAN
 LoRaWAN is one of the most prominent LPWAN technology
operating in the Industrial, Scientific and Medical (ISM) band, alongside
with SigFOX and NB-IoT, among others

- Long range, low-power, low-cost, and low throughput

- A very long range of LPWA technologies enables devices to spread and move over large
geographical areas.
LPWAN
Design goals and techniques
❑ Long range ❑Low Cost
 Use of Sub-1GHz band: ❑ Reduction in hardware complexity
 433, 868, 915/920 MHz ❑ Minimum infrastructure
❑ Using license-free or owned licensed bands
 Modulation Techniques
Narrowband: < 25KHz

❑Scalability
 Spread spectrum techniques: CSS, DSSS ❑ Diversity techniques
❑ Densification
❑ Adaptive Channel Selection and Data Rate
❑ Ultra low power operation
 Topology ❑Quality of Service
 Single hop vs. multi-hop
 Duty Cycling
 Lightweight Medium Access Control
 ALOHA
 Offloading complexity from end devices
LoRa and LoRaWAN

LoRa is strictly physical layer, and is proprietary. Chip

manufacturers include Semtech, Microchip and Hope RF.

LoRaWAN is an open standard that adds the MAC,

networking and application layers that provide required
functionalities like managing medium access, security
and so on.

LoRaWAN exploits the LoRa physical layer. It is an open

standard developed by the LoRa Alliance
LoRa and LoRaWAN

End Devices

LoRa signals

IP traffic, encrypted for security

LoRaWAN Architecture

HAL: Hardware Abstract Layer

PHY: Physical Layer
SPI: Serial Peripheral Interface
LoRa and LoRaWAN
LoRaWAN
In order to allow end-devices to receive downlink frames, three different classes are
defined based on energy consumption

All end-devices are booted in

this mode. It allows the lowest
energy consumption possible
since the end-device only gets to
receive downlink traffic in one of
two reception slots after each
transmission.

Beacons. A Class A end-device

can decide to switch to Class B.
The purpose is to make an end-
device available to receive
downlink frames at other
predictable times, in addition to
RX1 and RX2.
Continuous listening allows
devices to constantly be in
receive mode, except when an
uplink frame has to be sent.
LoRaWAN
 The maximum duty-cycle, defined as the maximum percentage of time
during which an end-device can occupy a channel, is a key constraint
for networks operating in unlicensed bands.
 Therefore, the selection of the channel must implement pseudo-
random channel hopping at each transmission and be compliant with
the maximum duty-cycle.
 E.g,
 The duty-cycle is 1% in EU 868 for end-devices.
 Time on Air (ToA) = 530ms => affer sending a message, we have to wait
99x530ms = 52.47s before sending a new message.

channel hopping
LoRaWAN
Gateways listen in 8 frequencies simultaneously, in every
spreading factor at each frequency
Collisions prevented by maximum duty cycle limitations
per frequency. If nevertheless, there is a collision, the
strongest packet prevails.
Depending on the SF in use, LoRaWAN data rate ranges
from 0.3 kbps to 125 kbps

In Europe, duty cycles are regulated by section 7.2.3 of the ETSI EN300.220 standard. This
standard defines the following sub-bands and their duty cycles:
g (863.0 – 868.0 MHz): 1%
g1 (868.0 – 868.6 MHz): 1%
g2 (868.7 – 869.2 MHz): 0.1%
g3 (869.4 – 869.65 MHz): 10%
g4 (869.7 – 870.0 MHz): 1%
Activation mode
 In order to participate in a LoRaWAN network, each end-device has
to be activated in one of the two following manners:
 Over-The-Air-Activation (OTAA) requires an end device join-request
uplink frame and a network server join-accept downlink frame if the end-
device is permitted to join the network. This type of activation is the most
secure.
 Activation By Personalization (ABP) directly ties an end-device to a
specific network, bypassing the join procedure. The end-device is assumed to
have the required information for participating in the network when started.
EUI: Extended Unit Identifier
Lora packet format

 The time on air, or packet duration, is simply then the sum of the
preamble and payload duration

𝑇𝑝𝑎𝑐𝑘𝑒𝑡 = 𝑇𝑃𝑟𝑒𝑎𝑚𝑏𝑙𝑒 + 𝑇𝑃𝑎𝑦𝑙𝑜𝑎𝑑

Forward Error Correction (FEC)

Technique of adding redundant (parity) bits to the

transmission so that errors can be recovered at the
reception.
The coding rate refers to the proportion of
transmitted bits that actually carry information.

Coding rate can be 6/8, 4/8, etc…

So if CR is 4/8 we are transmitting twice as many bits
as the ones containing information.
Advantages of LoRaWAN
 Long battery life for devices and sensors due to low power
consumption
 Low cost implementation due to low cost hardware and unlicensed
spectrum
 Long range coverage and in-building penetration
 Less complexity in programming
 Offers a secure transmission network
 Scalable network to support future upgrades
 Ease of access and connectivity to the cloud applications
 Remote management and control access
 Highly intelligent architecture
Applications
 Smart City: LoRa WAN will be inevitable technology in future smart
city applications together with Internet of Things
 Smart lighting
 Air quality and pollution monitoring
 Smart parking and vehicle management
 Facilities and infrastructure management
 Fire detection and management
 Waste management
 Industrial Applications: LoRa WAN is suitable for wide range of
industrial applications.
 Radiation and leak detection
 Smart sensor technology
 Item location and tracking
 Shipping and transportation
Applications
 Smart home applications: In future, billions of smart devices and home
appliances will be connected to internet.
 Enhanced home security
 Home automation for IoT enables smart appliances
 Healthcare: LoRa is one of the best solutions for connecting
healthcare devices efficiently
 Health monitoring devices and management
 Wearable technology
 Agriculture: LoRa technology can be used in smart agriculture and
farming applications.
 Smart farming and livestock management
 Temperature and moisture monitoring
 Water level sensors and irrigation control
Direct Sequence Spread Spectrum (DSS)

Spreading technique used in WiFi

Time domain Frequency Domain

LoRa modulation
Chirp Spread Spectrum
 Bandwidth (BW): difference between the upper and lower
frequencies occupied by the chirp: 125 kHz, 250 kHz, 500 kHz.
 Spreading Factor (SF): number of bits per symbol
 Chirp rate (Sample rate Rs): first derivative of chirp frequency
Rs = BW/2SF
 Nominal bit rate
4
𝑅𝑏 = 𝑆𝐹 ∗ 4 +𝑆𝐹𝐶𝑅
2
 Where: 𝐵𝑊
 SF: spreading factor (7 .. 12)
 CR: Coding rate (1 .. 4)
 BW: modulation bandwidth (Hz)
Chirp Modulation
 In binary chirp modulation, binary data is transmitted by mapping the
bits into chirps of opposite chirp rates.
 E.g
 Over bit period "1" is assigned a chirp with positive rate c
 Over bit period "0" is assigned a chirp with negative rate −c
Time
Adaptive Data Rate (ADR) at 125 kHz BW

Spreading Factor Signal/Noise bit rate ms per 10 byte packet

7 -7.5 5469 56
8 -10 3125 103
9 -12.5 1758 205
10 -15 977 371
11 -17.5 537 741
12 -20 292 1483

Sensitivity is proportional to S/N, since the detection is

determined by the amount of energy per bit