Light based communications

A method as claimed in claim 3, when a header region is identified in detected signal, the method further comprising:

• receiving a sequence of detected signals;
• identifying a plurality of portions of the payload before and after the header, over the sequence of detected signals;
• constructing the data packet by combining at least two portions of the payload from different frames or windows, based on an overlap of the at least two portions.

A method as claimed in claim 1, wherein the detected signal is detected in a capture window, and wherein the length of the capture window is less than the period of the pulse used to modulate the data onto the light signal.

A method as claimed in claim 1, wherein identifying the location of the at least one first region of the detected signal comprises:

• generating a predicted version of the header;
• and
• correlating the detected signal with the predicted version of the header, wherein the at least one first region is identified as a region with high correlation.

A method as claimed in claim 6, wherein the predicted version of the header is generated using a sampling rate of a detector that has detected the signal and a known structure of the header.

A method as claimed in claim 8, comprising:

• determining a coarse position of the header by performing a correlation using the predicted version of the header and the detected signal;
• and
• determining a fine position of the header by performing a correlation using an upsampled version of the detected signal and the predicted version of the header.

A method as claimed in claim 9, wherein the step of determining a fine position is only performed in the vicinity of positions in regions identified in the step of determining a coarse position.

A method as claimed in claim 1, wherein the detected light signal includes a plurality of channels, and the method comprises:

• selecting only a single channel to use as the detected signal.

A method as claimed in claim 1, wherein the detected signal is captured by a photosensitive device, and the data is modulated as different intensity levels on the signal.

A method as claimed in claim 1, wherein:

• the detected signal includes light from at least two sources, there being interference between the output of the light sources;
• and
• the data is encoded using an orthogonal encoding system.

A method as claimed claim 1, wherein the data comprises a unique identifier of a light source emitting the light captured in the detected signal, the method further comprising:

• receiving position data indicating a location of the light source in a global co-ordinate system;
• and
• determining a position of the device, wherein the determination of the position is based, at least in part on, the position data of the artificial light source.

A lighting system comprising:

• one or more light sources;
• one or more drivers, the one or more drivers arranged to modulate the output of the light sources to encode data on the output of the light source as light based communications, the data including a data packet having a header of known structure, and a payload.

A lighting system as claimed in claim 17, wherein the period of the pulse used to modulate the data onto the light emitted by the source is longer than a window in which the data is captured;

• and wherein the modulation depth of the data is variable in dependence on the total light output.

A computer program that, when read by a computer, causes performance of the method of claim 1.

A lighting system as claimed in claim 17, wherein a computer program is read by a computer to operate the lighting system.