LPWAN technologies like LoRaWAN target IoT applications with low-power and long-range wireless connectivity for battery-powered devices. LoRaWAN uses chirp spread spectrum modulation on open license-free bands below 1GHz for long ranges of 10-15km in rural areas. It has a decentralized architecture with end-devices communicating through gateways to network servers. LoRaWAN defines classes of devices from always-on Class C to scheduled receive windows for Class B. NB-IoT is a 3GPP standard for cellular IoT networks using existing LTE infrastructure to provide reliable, low-power connectivity for smart city and healthcare applications with latency under 10ms.

1. IoTSSC –
Low Power
Wide Area
Networks
(LPWAN)

2. LPWAN
• Specifically targeting IoT applications
• Battery powered devices

3. LPWAN
• Coverage (lower frequency) vs bandwidth/throughput
(WLAN/ WPAN)?
• Licensed vs unlicensed spectrum?
• Centralised vs decentralized access?
• Compatibility with cellular systems?
• Mobility support?
• Latency constraints?
• Security

4. LoRaWAN
• One of the main contenders for LPWAN dominance
• Operates in license-free ISM bands: 433, 868, 915 MHz
• Regulated (power, duty-cycle, bandwidth)
• EU: 0.1% or 1% per sub-band duty-cycle limitation
• Protocol stack works on top of a chirp spread spectrum
PHY layer (LoRa) – rates typically between 300bps –
5.5kbps + two ‘high speed’ (FSK) channels (11 and
50kb/s)
• PHY is proprietary (SemTech)
• Can work on 8 different frequencies at a time

5. LoRaWAN architecture

6. LoRa modulation
• Chirp spread spectrum - Spread Factors (SF) 7 to 12
• Moving an RF tone through time linearly - breaking
chirps in different places in terms of time and
frequency to encode a symbol.
Credits: Thomas Telkamp

7. LoRa modulation
• Robust to interference
• Symbol rate (SF bits per symbol)
𝑅𝑠 =
𝐵𝑊
2𝑆𝐹
• Bit rate
𝑅𝑏 = 𝑆𝐹
𝐵𝑊
2𝑆𝐹
• Data whitening, interleaving, FEC are then applied
• FEC k/n – for every k bits of information n bits TX

8. LoRa bit rates vs SF (BW=125kHz)
SF Chirps/symbol Bitrate
7 128 5.469kb/s
8 256 3.125kb/s
9 512 1.758kb/s
10 1024 977b/s
11 2048 537b/s
12 4096 293b/s

9. LoRa bit rates vs SF (BW=125kHz)
SF Chirps/symbol Bitrate
7 128 5.469kb/s
8 256 3.125kb/s
9 512 1.758kb/s
10 1024 977b/s
11 2048 537b/s
12 4096 293b/s
Numbers do not really match the formula. Why?

10. LoRa bit rates vs SF (BW=125kHz)
SF Chirps/symbol Bitrate
7 128 5.469kb/s
8 256 3.125kb/s
9 512 1.758kb/s
10 1024 977b/s
11 2048 537b/s
12 4096 293b/s
Numbers do not really match the formula. Why?
FEC is applied here as well. Can you guess the code rate?

11. LoRa bit rates vs SF (BW=125kHz)
SF Chirps/symbol Bitrate
7 128 5.469kb/s
8 256 3.125kb/s
9 512 1.758kb/s
10 1024 977b/s
11 2048 537b/s
12 4096 293b/s
Numbers do not really match the formula. Why?
Default code rate used is 4/5

12. LoRaWAN protocol stack

13. LoRaWAN device types
Standard defines three classes of devices defined
• Class A: Supported by all devices. Each uplink TX
followed by two short downlink receive windows.
• Class B: Extra receive windows at scheduled times
latency controlled downlink); slotted communication
• Class C: Continuously open receive widow, except when
transmitting (mains powered devices, no latency)

14. LoRaWAN frame format

15. LoRaWAN security
Two layers of security
• Network Security Key (nwkSkey) – authenticates node
in the network
• Application Security Key (appSkey) – ensures network
operator cannot inspect the data, but only service
provider can
• AES 128 used in both cases
• MIC calculated over the ‘network’ part of the message
– works as a signature

16. Device activation
1) Over The Air Activation (OTAA)
• End-device follows a join procedure.
(+) device can attach any LoRaWAN network, security
keys can be updated on a per session basis; enables
roaming
(-) App server has to answer to join requests each time a
device (re)starts, generating more downlink traffic.

17. Device activation
2) Activation By Personalization (ABP)
• The end-device already pre-registered on the network.
DevAddr and keys are stored in end-device and NS.
(+) simpler from application server point of view
(-) node tied to a particular network; vulnerable to replay
attacks

18. UoE LoRaWAN infrastructure
• Edge devices: Pycom dev boards (run micropython)
• Gateways deployed @ library, Argyle House, Bush campus
• TTN – The Things Network – open source NS stack
https://www.thethingsnetwork.org

19. Narrow Band IoT
(NB-IoT)

20. The NB-IoT paradigm
• Standardised by 3GPP (Rel 13) to enable roll out over
existing cellular infrastructure (focus on reliability)
• Target apps: smart metering, smart cities (diagnostics
and control), eHealth
• Three types of deployments:
*Wang et al. “A Primer on 3GPP Narrowband Internet of Things (NB-IoT)”

21. The NB-IoT paradigm
• Bandwidth: 180kHz (low throughput)
• Data rates: 25kb/s (downlink) and 64kb/s (uplink,
multi-tone)
• Latency <10ms
• Hybrid ARQ scheme (reliability)
• Power saving modes (base station can dictate power
control through signalling)

22. Cellular IoT (CIoT) architecture
(red) – control plane; (blue) – user plane
RAN – Radio Access Network;
S/P-GW – Serving/Packet Gateway
MME – Mobility Management Entity
SCEF - Service Capability Exposure Function (new addition)

23. Channel access - downlink
• Each NB-IoT subframe spans one physical resource
block (PRB) – 12 subcarriers
• Narrowband Primary Synchronization Signal (NPSS);
Secondary Synchronization Signal (NSSS); Physical
Broadcast Channel (NPBCH); Reference Signal (NRS);
Physical Downlink Control Channel (NPDCCH);
Physical Downlink Shared Channel (NPDSCH)

24. Channel access - uplink
• Narrowband Physical Random Access Channel
(NPRACH) – similar to LTE, but narrower channel
• Tone frequency index changes from one symbol
group to another - single-tone frequency hopping

25. Questions?