What is difference between Chip and Chirp in LoRaWAN, LoRa
This page mentions difference between chip and chirp in LoRaWAN or LoRa system.
The terms are associated with chirp spread spectrum (CSS) modulation technique. It uses wideband linear frequency modulated chirp pulses in order to encode baseband information.
Chirp Spread Spectrum is used in space and military communications due to its long range, low transmit power and less interference.
Symbol, Spreading Factor and Chip
The chirps are cyclically shifted and it is frequency jumps which determines data encoding on chirps.
Let us understand use of spreading factor in Lora to encode message.
Example: Symbol consisting og 1011111 (representing decimal of 95).
Here number of raw bits to be encoded by one symbol is 7
Hence Spreading Factor = 7
The symbol has 2SF values. For SF= 7, we have range from 0 to 127.
The symbol value is encoded on sweep signal (up-chirp) i.e. sweep signal is divided in 27 = 128 chips. This is shown in the figure below.
As mentioned above spreading factor defines two values:
• The number of raw bits which can be encoded by that symbol and
• Each symbol can hold 2SF chips.
Following table mentions different spreading factors supported by LoRaWAN along with chips/symbol, SNR limit, time on air and bit rate for each of them. These values are for LoRa bandwidth of 125 KHz.
|Spreading factor||Chips/Symbol||SNR Limit||Time on air (10 byte packet)||Bit Rate|
|7||128||-7.5||56 ms||5469 bps|
Difference between chirp and chip in LoRaWAN
➨A symbol houses 2SF chips.
➨Chirps refers to ramp from Flow to Fhigh for up-chirp and from Fhigh to Flow for down-chirp.
LoRaWAN related links
The LoRaWAN Wireless tutorial covers following sub topics:
LoRaWAN Smart Parking LoRaWAN sensor design LoRaWAN smart healthcare system LoRaWAN smart water metering LoRaWAN architecture LoRaWAN Interface Types LoRaWAN roaming types LoRa tutorial LoRa Frequency Bands LoRa protocol stack LoRa MAC layer LoRaWAN classes LoRa features LoRa Transceiver module