Transmitter, receiver, and method for chirp-modulated radio signals
AssigneeSemtech Corporation
InventorsOlivier Bernard André Seller, Christophe Jean Jacques Devaucelle
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Abstract
A LoRa transmitter and corresponding receiver where the detection sequence in the preamble is phase-modulated and includes an information that encodes the position in the preamble, such as a countdown index. Nodes that wake up to receive a scheduled download can determine from this information how far the end of the detection sequence is and manage their energy consumption accordingly. The phase modulation is compatible with legacy devices.
Claims14
A transmitter for chirp-modulated radio signals comprising a modulator configured to generate a radio signal that includes a plurality of chirps, each chirp being limited in time between an initial instant at which the signal has an initial instantaneous frequency and a final instant (T1) at which the signal has a final instantaneous frequency, whereby the modulator is configured to generate base chirps, in which the frequency changes monotonically from the initial instantaneous frequency to the final instantaneous frequency according to a predetermined base chirp function, and modulated chirps, whose instantaneous frequency vary according to a plurality of functions that are cyclic shifts of the base chirp function, the transmitter being configured to organize chirps in frames having a preamble and a payload comprising a set of modulated chirps carrying an element of information encoded as cyclic shift, wherein the preamble comprises a succession of base chirps, characterized in that chirps of the preamble have a phase shift encoding their position in the preamble.
A receiver for chirp-modulated radio signals comprising a demodulator for demodulating a signal that includes a plurality of chirps, each chirp being limited in time between an initial instant at which the signal has an initial instantaneous frequency and a final instant at which the signal has a final instantaneous frequency, the chirps in the signal being organized in frames having a preamble and a payload, wherein the preamble comprises a succession of base chirps in which the frequency changes monotonically from the initial instantaneous frequency to the final instantaneous frequency according to a predetermined base chirp function, and wherein the payload comprises a set of modulated chirps, which have an instantaneous frequency that varies according to a plurality of functions that are cyclic shifts of the base chirp function, an element of information being encoded as cyclic shifts in the modulated chirps, characterized in that the receiver is configured to detect the preamble, determine phase shifts of chirps in the preamble, assume that the phase shifts encode a position of the corresponding chirp in the preamble according to a predefined encoding, enter a low-power state and/or a listening state during a period dependent on said position in the preamble.
A method of downloading data from a first device to a second device in a low-power wide-area wireless network comprising
- defining a scheduled download time,
- configuring the second device to enter a listening state when, according to a time reference of the second device, is the scheduled download time,
- generating in the first device a radio signal that includes one or more frames, each frame having a plurality of chirps, each chirp being limited in time between an initial instant at which the signal has an initial instantaneous frequency and a final instant at which the signal has a final instantaneous frequency, whereby the modulator can generate base chirps, in which the frequency changes monotonically from the initial instantaneous frequency to the final instantaneous frequency according to a predetermined base chirp function, and modulated chirps, whose instantaneous frequency vary according to a plurality of functions that are cyclic shifts of the base chirp function, each frame having a preamble comprising a succession of base chirps and a payload comprising a set of modulated chirps carrying the data encoded as cyclic shift,
- detecting the preamble in the second device,
- characterized by,
- the length of the preamble being longer than an estimated incertitude in the time reference of the second device,
- determining in the second device phase shifts of chirps in the preamble and assume that the phase shifts encode a position of the corresponding chirp in the preamble according to a predefined encoding,
- causing the second device to enter a low-power state or a listening state during a period dependent on said position in the preamble,
- receiving the payload— and demodulating the data in the second device.
Dependencies are inferred from the claim text.