Data transmission method and system thereof, portable terminal, and data receiver
In a data transmission method according to an exemplary embodiment, a data transmitter, which is capable of outputting a dummy light for judging an optical axis and a signal light having a beam spread smaller than that of the dummy light on the same optical axis, outputs the dummy light for scan so as to go across a photoreceiving part of a data receiver. When the dummy light having a predetermined optical level or more is optically received, the data receiver informs the data transmitter of reception chance and prepares for receiving the data. The data transmitter outputs the data carried by the signal light to the data receiver according to the information indicating the reception chance from the data receiver. The data receiver receives the data by optically receiving the signal light from the data transmitter.
1. A data transmission system to transmit data through open transmission, the system comprising:
a data transmitter,
wherein the data transmitter is a portable terminal; and
a data receiver,
wherein the data transmitter comprises:
a laser light source to generate a signal light;
a dummy light source to generate a dummy light for judging an optical axis;
an optical system to output the signal light and the dummy light on the optical axis, and causing a beam spread of the signal light smaller than a beam spread of the dummy light;
a receiving circuit to receive a reception OK signal from the data receiver; and
a driving circuit to drive the laser light source to output the signal light for carrying the data responsive to the reception OK signal,
wherein the data transmitter is capable of causing the optical axis of the signal light and the dummy light to scan across a photoreceiving part of the data receiver, and
wherein the data receiver comprises:
a photodetector to optically receive the dummy light and the signal light, said photodetector outputting a first electrical signal when receiving the dummy light and outputting a second electrical signal when receiving the signal light;
a level judging apparatus to judge a level of the first electrical signal from the photodetector;
a transmitting circuit to transmit the reception OK signal to the data transmitter when the first electrical signal from the photodetector has a level equal to or greater than a predetermined level responsive to a result from the level judging apparatus;
a data demodulating circuit for demodulating the second electrical signal from the photodetector when the first electrical signal from the photodetector has a level equal to or greater than the predetermined level and obtaining the data included in the second electrical signal; and
a reception result indicator to inform a user of a reception result of the data.
2. The system of claim 1 wherein optical power of the signal light is larger than optical power of the dummy light.