Understanding Duty Cycle Coding Rate Packet Structure in LoRa-11

LoRa and LoRaWAN – Part 5: Understanding Duty Cycle Coding Rate Packet Structure in LoRa Protocol Leave a comment

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Understanding Duty Cycle Coding Rate Packet Structure in LoRa

Duty Cycle

In the previous section, we explored Spreading Factors and ADR in LoRaWAN. Duty Cycle indicates what portion of time a resource or channel is actively in use. For example: If a device operates on a channel for 10 time units but transmits for only 2 units, its Duty Cycle = 20%.

Understanding Duty Cycle Coding Rate Packet Structure in LoRa-2

Single Channel

Calculation is simple: Transmitted time ÷ Total time → 2 / 10 = 20%

Multiple Channels

Things get more complex. Suppose the device transmits on 3 different channels, each with 2 units transmitted per 10 units → 20% per channel. Total transmission: 6 units out of 10 → Overall device Duty Cycle = 60%

In simple terms: Adding more channels allows the device to be active longer overall, even if per-channel limits are respected.

Understanding Duty Cycle Coding Rate Packet Structure in LoRa-3

Europe: Sub-bands Matter

In European frequency plans, channels are grouped into sub-bands. Duty Cycle is calculated per sub-band, not just per channel.

Example continuation:

  • 3 channels, each 20% Duty Cycle
  • But they belong to 2 sub-bands:
    • Sub-band 1: 2 units / 10 → 20%
    • Sub-band 2: 4 units / 10 → 40%

Key point: Regulations in Europe define separate Duty Cycle caps per sub-band (e.g., 1%, 0.1%, 10%). → You must track usage per sub-band to stay compliant.

This ensures fair spectrum sharing and reduces interference in dense networks.

Understanding Duty Cycle Coding Rate Packet Structure in LoRa-4

Maximum Duty Cycle

In many countries, radio device Duty Cycle is restricted by regulators. The most common limit is 1% — meaning a device may transmit only 1% of the time on a given channel. Always check local regulations, as limits vary.

In Europe, these are defined by ETSI EN300.220-2 V3.2.1 (2018-06), Section 4.3.3. The standard specifies maximum Duty Cycle per sub-band:

Sub-band Frequency Range Max Duty Cycle
K 863 – 865 MHz 0.1%
L 865 – 868 MHz 1%
M 868 – 868.6 MHz 1%
N 868.7 – 869.2 MHz 0.1%
P 869.4 – 869.65 MHz 10%
Q 869.7 – 870 MHz 1%

Additionally, LoRaWAN specifications impose Duty Cycle limits on Join channels (used for OTAA). In most regions, Join channels are limited to 1% Duty Cycle.

Forward Error Correction (FEC) and Coding Rate

LoRa improves reliability using Forward Error Correction (FEC). How it works: Before transmission, redundant bits are added to the payload. If noise or interference corrupts the message (e.g., flipping 0→1 or 1→0), the receiver uses these extra bits to detect and correct errors.

Coding Rate (CR) defines the ratio of real data to total transmitted bits. LoRaWAN supports four standard coding rates:

Coding Rate Data Bits Total Bits Redundant Bits Use Case
4/5 4 5 1 Fastest, least robust
4/6 4 6 2 Balanced
5/7 5 7 3 More robust
4/8 4 8 4 Most robust, slowest

Example: CR = 5/7 → For every 5 real data bits, the encoder sends 7 bits total → 2 redundant.

In simple terms:

  • Lower Coding Rate (e.g., 4/8) → More redundancy → Stronger error resistance → Lower data rate
  • Higher Coding Rate (e.g., 4/5) → Less redundancy → Faster data rate → Less error tolerance

This gives flexibility: Use high CR in good conditions for speed. Use low CR in noisy or distant links for reliability.

Understanding Duty Cycle Coding Rate Packet Structure in LoRa-5

LoRa Physical Layer Packet Format

LoRa uses two packet formats for data transmission: Explicit and Implicit.

Explicit Mode

The LoRa packet includes the following components:

  • Preamble
    • Used for receiver-transmitter synchronization.
    • Standard length: 8 symbols (per LoRaWAN Regional Parameters).
    • Radio automatically adds 4.25 symbols → Total: 12.25 symbols.
  • PHDR (Physical Header)
    • Optional — only in Explicit mode.
    • Contains payload size and CRC status.
  • PHDR_CRC (Header CRC)
    • Optional field.
    • Provides error detection/correction for the header.

PHDR and PHDR_CRC are encoded with Coding Rate = 4/8.

  • PHYPayload
    • Contains the entire MAC-layer frame.
    • Maximum size varies by Data Rate (DR) and regional regulations.
  • CRC
    • Optional field for uplink payload error detection.

PHYPayload and CRC are encoded with one of the Coding Rates: 4/5, 4/6, 4/7, or 4/8

The entire frame is transmitted using one of the Spreading Factors (SF7 to SF12).

The LoRa physical layer is designed for flexibility (optional CRC, configurable header) and high reliability in IoT communications — balancing efficiency, robustness, and regional compliance.

Preamble PHDR PHDR_CRC PHYPayload CRC

Physical structure of an uplink packet

Preamble PHDR PHDR_CRC PHYPayload

Physical structure of a downlink packet

 

Implicit Mode The header is removed from the packet. Reason:

  • Payload size and Coding Rate are predefined or fixed
  • No need to send extra header to convey this information

Key Example: Beacons in LoRa

  • Gateways use Implicit mode to send time synchronization information
  • Packet structure is known in advance → removing header makes the packet shorter and simpler

Summary

Mode Header When to Use
Explicit Yes Variable payload size or Coding Rate
Implicit No Fixed payload size and Coding Rate (e.g., beacons)

 

Preamble
BCNPayload

Physical structure of a beacon

FAQ – Understanding Duty Cycle Coding Rate Packet Structure in LoRa

What is Duty Cycle in LoRa?
+

The Duty Cycle defines the percentage of time a device transmits on a channel. For example, 2 seconds of transmission in 10 seconds total equals a 20% Duty Cycle.

How is Duty Cycle calculated across multiple channels or sub-bands?
+

For multiple channels, the total Duty Cycle is the sum of each channel’s usage. In Europe, it’s calculated per sub-band with specific regulatory limits (e.g., 1%, 0.1%, 10%).

What is Coding Rate (CR) and why is it important?
+

Coding Rate adds redundancy to transmitted data for error correction. Lower CR (like 4/8) gives stronger protection but slower speed; higher CR (like 4/5) increases data rate but reduces robustness.

What are Explicit and Implicit packet modes in LoRa?
+

Explicit Mode includes a header with payload size and CRC. Implicit Mode omits the header when payload size and coding rate are fixed — reducing packet size and transmission time.

When should Explicit or Implicit mode be used?
+

Use Explicit Mode for variable payloads or changing Coding Rates. Use Implicit Mode for fixed-size transmissions, such as gateway beacons or time-synced messages.

Resources

Compare generations, choose the right hardware, and future-proof your network in one go.
Dive into Part 6: Introduction and Comparison of LoRaWAN Concentrators and Transceivers Across Generations –
to select optimal devices and scale with confidence.

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