Communication system with portable unit

• US 4,757,553 A
• Filed: 06/12/1984
• Issued: 07/12/1988
• Est. Priority Date: 05/15/1984
• Status: Expired due to Term

• Current Assignee: K and M Electronics Incorporated, WIRELESS COMMUNICATIONS PRODUCTS LLC
• Original Assignee: James W. Crimmins
• Inventors: Crimmins, James W.
• Primary Examiner(s): PASCAL, LESLIE C
• Application Number:
  US06/619,803
• Time in Patent Office: 1,491 Days
• Field of Search: 455/607, 455/608, 455/606, 455/617, 455/69, 455/73, 370/3, 179/2 EA, 179/170 NC, 179/170 G, 379/56
• US Class Current: 398/129
• CPC Class Codes: H04M 1/737 Characterised by transmission of electromagnetic waves other than radio waves, e.g. infrared waves

Abstract

An optimized full duplex light wave communication system having a base unit and a portable unit. Two continuously operative channels exist between the base and portable units for two way communication at frequencies selected to minimize interference despite the presence of light within the environment of use at both frequencies. In addition, photo emitters and sensors are specifically configured in an assembly to minimize cross talk between sensors and emitters. A closed loop is formed around the two communication channels that it is operative to regulate the intensity of illumination received at the base photo sensors to a constant level that provides quality audio communications and minimizes portable unit battery drain. The closed loop additionally causes base station transmitter frequency tracking of any center frequency variation in the portable unit receiver.

Claims

1. A full duplex, light wave communication system, comprising:

a base unit having a light transmitter and a light receiver;

a portable unit having a light transmitter and a light receiver;

the portable unit light transmitter and base unit light receiver being operative at a first center pulse frequency and having respective light pulse modulated photo emitters and light pulse detecting photo sensors;

said base unit light transmitter and portable unit light receiver being operative at a second center pulse frequency and having respective light pulse modulated photo emitters and light pulse detecting photo sensors;

demodulating means in the base unit for demodulating a signal sent from the portable unit to the base unit and for generating a first level signal representative of the light intensity at the photo sensors of the base unit incident from photo emitters in the portable unit transmitter and representative of a change in the first center pulse frequency relative to the center frequency of the portable light receiver;

means responsive to the first level signal for shifting the second center pulse frequency transmitted by the base unit;

demodulating means in the portable unit for demodulating a signal sent from the base unit to the portable unit and generate a second level signal representative of the shift of the second center pulse frequency received at the portable unit from the base unit transmitter; and

means responsive to the second level signal for controlling the magnitude of light pulses from the portable unit light transmitter so as to maintain the light intensity at the photo sensors of the base unit at a level sufficient for optical communication between the portable unit and the base unit and for reducing the change of the second center pulse frequency.

2. The system of claim 1 and further including means for suppressing interference between the light transmitter-receiver pair operating at said first center pulse frequency and the light transmitter-receiver pair operating at said second center pulse frequency.

3. The system of claim 2 wherein said interference suppressing means includes means for establishing said first and second center pulse frequencies so that the ratio therebetween approximates the square root of two to provide maximum frequency separation between said first and second center pulse frequencies and their harmonics.

4. The system of claim 1 wherein the base unit and portable unit have infrared transmitters and infrared receivers.

5. The system of claim 4 wherein the base unit and portable unit each include means for pulse rate modulating the photo emitters with center pulse frequencies corresponding to the first center pulse frequency in the portable base unit transmitter and the second center pulse frequency in the base unit transmitter.

6. The system of claim 1 and further including:

means associated with each light transmitter for responding to an input modulating signal to provide light pulse rate modulation in accordance with the level thereof;

first nonlinear gain means at each light transmitter for varying the magnitude of the modulation signal in a manner that varies inversely with the level of the input signal; and

second nonlinear gain means in each light receiver to provide a transfer characteristic that compensates for the effect of the first nonlinear gain means;

whereby receiver output noise level at low level input signals is substantially reduced while high input signal levels are correctly reproduced at outputs of light receivers.

7. The system of claim 1

wherein said means responsive to the second level signal adjusts the portable unit light transmitter output power so as to maintain a substantially constant detectable light intensity at the base unit.

8. The system of claim 7 wherein said demodulating means in the portable unit detects frequency deviations in the center frequency of the base unit transmitter relative to the portable unit receiver center frequency.

9. The system of claim 7 wherein:

said portable unit receiver includes means for providing detection about a center frequency of photo pulses received from said base unit transmitter and to produce said second level signal indicative of the deviation between the base unit transmitter center frequency and the portable unit receiver center frequency; and

wherein said means for controlling the portable unit transmitted light magnitude controls said magnitude as a function of said deviation in center frequencies.

10. A full duplex, light wave communication system, comprising:

a base unit having a light transmitter and a light receiver;

a portable unit having a light transmitter and a light receiver;

the portable unit light transmitter and base unit light receiver being operative at a first center pulse frequency and having respective light pulse modulated photo emitters and light pulse detecting photo sensors;

said base unit light transmitter and portable unit light receiver being operative at a second center pulse frequency and having respective light pulse modulated photo emitters and light pulse detecting photo sensors;

said photo sensors and photo emitters respectively in the portable and base units being mounted in assemblies, with means for isolating photo sensors from sensing near field radiation from a photo emitter associated with the same assembly;

with photo sensors being mounted in a recessed relationship on the same assembly; and

optical wedge means for enhancing the viewing angle of recessed photo sensors.

11. The system of claim 10 wherein:

said recessed photo sensors include the photo sensors associated with said base unit; and

wherein said optical wedge means is associated with each recessed photo sensor of the base unit.

12. A full duplex, light wave communication system, comprising:

a base unit having a light transmitter and a light receiver;

a portable unit having a light transmitter and a light receiver;

the portable unit light transmitter and base unit light receiver being operative at a first center pulse frequency and having respective light pulse modulated photo emitters and light pulse detecting photo sensors;

said base unit light transmitter and portable unit light receiver being operative at a second center pulse frequency and having respective light pulse modulated photo emitters and light pulse detecting photo sensors;

said photo sensors and photo emitters respectively in the portable and the base units being mounted in assemblies, with means for isolating photo sensors from sensing near field radiation from a photo emitter associates with the same assembly;

with the photo emitters associated with said base unit being located in a recess within said base unit; and

optical wedge means for enhancing the angle over which the recessed photo emitters radiate from said base unit.

13. A full duplex infrared telephone, comprising:

a base unit having an infrared transmitter and an infrared receiver;

a portable handset having an infrared transmitter and an infrared receiver;

the portable handset infrared transmitter and base unit infrared receiver being operative at a first center pulse frequency and having respective infrared pulse modulated photo emitters and infrared pulse detecting photo sensors;

said base unit infrared transmitter and handset infrared receiver being operative at a second center pulse frequency and having infrared pulse modulated photo emitters and infrared pulse detecting photo sensors; and

means for establishing a closed loop between the respective infrared transmitter and infrared receiver of said portable handset and base unit and operative to control the photo intensity received by the base unit photo sensors and to cause said base unit transmitter to operate with a center frequency that is adjusted to correspond to any changes in the center frequency of said portable handset receiver.

14. The system of claim 13 and further including assemblies located at end locations of said handset and having in each assembly a plurality of said photo emitters and photo sensors.

15. The system of claim 13 and further including:

means for controlling a center frequency of said base unit infrared transmitter to correspond to a center frequency for said handset infrared receiver over a predetermined range of variations of said handset receiver center frequency.

16. The system of claim 15 and further including:

means associated with said base unit for coupling to and from a communication network and having an R-C balancing network for isolating signals coupled to and from said communication network.

17. The system of claim 16 wherein said coupling means includes a hybrid coupler comprising RC impedance dual and balancing circuitry between receiver and transmitter emulating inductor functions to provide a high degree of decoupling between said signals applied to and from said network.