Transmission of data by ultrasound
An ultrasonic transmission system in which, for the purpose of transmission, a signal is used which generates a broadband signal by means of code spreading and is capable of eliminating any echoes by means of correlation. The transmission system exhibits a transmitter and a receiver. In this configuration, digital information is spread to a great bandwidth in accordance with a CDMA technique, D/A converted and then transmitted by means of ultrasound via an air Preferred applications of the present invention are air interfaces having a length of a few meters. One field of application is, for example, the connection of cordless handsets or hands-free telephones to telephones.
1. A method for transmitting voice data between a head part and a base part of a hands-free telephone, which comprises:
compressing information, being the voice data, to be transmitted using compression coding;
digitizing the compressed information;
spreading the digitized information over a wider frequency band using a CDMA technique;
performing a digital to analog conversion on the spread digitized information;
converting the digital to analog converted spread information into an ultrasound signal;
transmitting the ultrasound signal via an air interface;
at a receiver component, receiving the transmitted ultrasound signal and converting the received ultrasonic signal into an analog electrical signal;
performing an analog to digital conversion on the analog electrical signal;
despreading the analog to digital converted signal using a CDMA technique; and
decoding the despread analog to digital converted signal.
2. The method according to claim 1 , which comprises reducing an effective bit rate of the information to be transmitted to about 1-10 kbit/s when performing the compression coding.
3. The method according to claim 1 , wherein in performing the step of transmitting the ultrasound signal, the ultrasound signal is transmitted at a frequency between 200 and 400 kHz.
4. The method according to claim 1 , wherein in performing the step of spreading the digitized information, the digitized information is spread to ±100 kHz.
5. A hands-free telephone comprising an ultrasonic transmission system including:
a compression coder for compression coding analog information; wherein the analog information is voice data;
a CDMA spreader for spreading digital information, which is obtained from said coded analog information, to a number of carrier frequencies using a CDMA technique;
a digital to analog converter for digital to analog converting the spread information;
an ultrasonic transducer for converting the digital to analog converted spread information into an ultrasound signal and for transmitting the ultrasound signal over an air interface; and
a receiver including:
an ultrasonic transducer for receiving the transmitted ultrasound signal and for converting the received ultrasonic signal into an electrical signal;
an analog to digital converter for analog to digital converting the electrical signal; and
a CDMA despreader for despreading the analog to digital converted signal using a CDMA technique.
6. The hands-free telephone according to claim 5 , wherein said compression coder reduces an effective bit rate to about 1-10 kbit/s.