Modulation and Demodulation  

• If an input signal (=message) is imposed onto a carrier signal this process is called modulation. The modulated signal is broadcasted to the receiver. 
• Demodulation is the opposite, where the original signal (= message) is recovered from the modulated carrier wave. 

Basic modulation types 

• Modulation means how analog or digital information are encoded onto a carrier signal. 
• When analog information are encoded onto a carrier signal, three modulation types can be used: 
•  Amplitude Modulation (AM), Frequency Modulation (FM) and Phase modulation (PM)  
• When digital information are encoded onto a carrier signal, three modulation types can be used: 
• Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK). 

 

• As mentioned earlier an end node has a radio module. This radio module has a modulator which encodes information onto a carrier signal. 
• This modulated signal is transmitted and received by a gateway. 
• The gateway also has a radio module. This radio module has a demodulator which decodes the modulated signal and extracts the information. 

 

Transceivers  

• The communication between the end node and gateway is bidirectional which means the end node can send data to the gateway but it can also receive data from the gateway. 
•  If a device can both transmit and receive signals this device is also called a transceiver.  
• LoRa end nodes and gateways are transceivers. 

Modulating Digital Values 

Amplitude Shift Keying (ASK) 

 

Frequency Shift Keying (FSK) 

 

Phase Shift Keying (PSK) 

 

CHIRP SPREAD SPECTRUM (CSS)  

• Besides the 3 basic modulation types there are many other modulation types.  
• LoRa is a proprietary spread spectrum modulation scheme that is based on Chirp Spread Spectrum modulation (CSS). 
• Chirp Spread Spectrum is a spread spectrum technique that uses wideband linear frequency modulated chirp pulses to encode information. 
• Spread spectrum techniques are methods by which a signal is deliberately spread in the frequency domain. For example a signal is transmitted in short bursts, “hopping” between frequencies in a pseudo random sequence.  
• A chirp, often called a sweep signal, is a tone in which the frequency increases (up-chirp) or decreases (down-chirp) with time. 

 

Lora Modulated Signal

• These chirp signals are used as carrier signals where a message is encoded on. 
• Here is an actual LoRa modulated signal