Method and apparatus for cordless infrared communication

• US 6,426,819 B1
• Filed: 02/17/1998
• Issued: 07/30/2002
• Est. Priority Date: 03/22/1996
• Status: Expired due to Fees

• Current Assignee: WIRELESS COMMUNICATIONS PRODUCTS LLC
• Original Assignee: WIRELESS COMMUNICATIONS PRODUCTS LLC
• Inventors: Crimmins, James W., Saulnier, James L., Gallo, Steven
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US09/024,995
• Time in Patent Office: 1,624 Days
• Field of Search: 359/135-137, 359/152, 359/167, 359/172, 370/347, 455/403, 455/426
• US Class Current: 398/99
• CPC Class Codes: H04B 10/1149 Arrangements for indoor wireless networking of information

Abstract

An infrared (IR) communication system is described in which a base unit for a cell can communicate with a plurality of infrared portable devices through distributed infrared receiver/transmitter (RT) modules over a plurality of channels using IR carrier signals. A call or signal processor, referred to as a radio exchange unit, and controlling communication of a cell, communicates with the base unit to place or receive calls with the IR portable devices. The communication occurs in standard communication frames divided into transmission and receiving segments with each segment further divided into slots and with the slots containing digital data, with each communication channel formed by a slot. Each transmission segment to an RT module is immediately followed by a responsive receiving segment. As an IR portable device moves from the vicinity of one RT module to another, the base unit automatically and seamlessly and in a robust manner hands over control to the nearer RT module by monitoring signal strength signals from various RT modules coupled to the base unit. When an IR portable device moves from one cell to another, the call processor hands over control to another base unit using standard protocols. Since an IR portable device may receive IR communication signals from several RT modules, care is taken to avoid signal interference by effectively controlling signal propagation lengths between the base unit and RT modules so that signals arriving from nearby RT modules at a common IR portable device do not have a phase difference more than a predetermined amount. The path lengths can be controlled by selecting cable lengths or by insertion of delays between the base unit and the RT modules to assure that IR signals arrive at portable devices with a minimum amount of interference.

Claims

1. An infrared receiver/transmitter (RT) module for use in a communication system using a time division multiple access communication protocol for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit which produces a repetitive frame signal having time spaced transmission and receiving segments each of which includes a plurality of time spaced respective transmission and receiving slots, comprising:

transmitter means for sending signals received from a base unit within transmission slots at an infrared carrier frequency to portable infrared devices and receiver means for sending signals received in the form of infrared signals from portable devices within receiving slots to the base unit;

a signal generator to produce characteristic signals indicative of a quality of infrared signals occurring during respective receiving slots and incident at the RT module from infrared portable devices communicating during said respective receiving slots with the base unit.

2. The RT module as claimed in claim 1 wherein said signal generator further comprises:

means for producing a control signal representative of the end of a preceding slot; and

means activated by the control signal for generating a said characteristic signal indicative of a quality of the infrared signal incident on the RT module during a receiving slot which follows the preceding slot.

3. The RT module as claimed in claim 2 wherein said receiving signals sent in different slots during receiving segments are separated by short intervals of time;

and

wherein said characteristic signal generating means comprises a fast analog to digital converter coupled to produce a predetermined number of data bits representative of the signal strength or signal-to-noise ratio of the infrared signals incident on the RT module during the short intervals.

4. The RT module as claimed in claim 3 and further including means for sending the individual data bits from the fast analog to digital converter on separate lines to said base unit.

5. An infrared receiver/transmitter (RT) module for use in a communication system using a time division multiple access communication protocol for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit which produces a repetitive frame signal having time spaced transmission and receiving segments each of which includes a plurality of time spaced respective transmission and receiving slots, comprising:

said RT module including transmitter means for sending signals received from a base unit within transmission slots at an infrared carrier frequency to portable infrared devices and receiver means for sending signals received in the form of infrared signals from portable devices within receiving slots to the base unit;

a signal strength detector to produce characteristic signals indicative of the strength of infrared signals occurring during respective receiving slots and incident at the RT module from infrared portable devices communicating during said respective receiving slots with the base unit;

means for producing a reference signal indicative of a high quality infrared signal level incident on the RT module; and

means responsive to the reference signal and a signal representative of the infrared signal incident on the RT module for producing said characteristic signals when said infrared signals incident on the RT module exceed the reference signal level.

6. An infrared receiver/transmitter (RT) module for use in a communication system using a time division multiple access communication protocol for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit which produces a repetitive frame signal having time spaced transmission and receiving segments each of which includes a plurality of time spaced respective transmission and receiving slots, comprising:

first means for sending signals received from a base unit within transmission slots at an infrared carrier frequency to portable infrared devices and second means for sending signals received in the form of infrared signals from portable devices within receiving slots to the base unit;

a signal generator, which produces characteristic signals indicative of a quality of infrared signals occurring during respective receiving slots and incident at the RT module from infrared portable devices communicating during said respective receiving slots with the base unit;

means for producing a reference signal indicative of an acceptable quality infrared signal level incident on the RT module;

means responsive to the reference signal and a signal representative of the infrared signal incident on the RT module for producing an enabling signal when said infrared signals incident on the RT module exceed the reference signal level; and

means responsive to the enabling signal and an electrical form of the infrared signals incident upon the RT module for activating the second sending means.

7. An infrared receiver/transmitter (RT) module for use in a communication system using a time division multiple access communication protocol for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit which produces a repetitive frame signal having time spaced transmission and receiving segments each of which includes a plurality of time spaced respective transmission and receiving slots, comprising:

transmitter means for sending signals received from a base unit within transmission slots at an infrared carrier frequency to portable infrared devices and receiver means for sending signals received in the form of infrared signals from portable devices within receiving slots to the base unit;

said RT module including a signal strength detector to produce characteristic signals indicative of the strength of infrared signals occurring during respective receiving slots and incident at the RT module from infrared portable devices communicating during said respective receiving slots with the base unit; and

means for sensing a calibration mode and means responsive to the sensed calibration mode for returning signals to a base unit for a measurement of the length of a cable coupling the RT module to the base unit.

8. A plurality of infrared receiver/transmitter (RT) modules for use in an infrared communication system for enabling a central control unit connected to telephone lines to communicate via a common base unit with a plurality of portable infrared devices located within a building, each of said RT modules including:

transmitter means for sending signals received from a base unit at an infrared carrier frequency to portable infrared devices and receiver means for sending signals received in the form of infrared signals from portable devices to a port in the base unit and which port is associated with a said RT module;

a signal generator to produce characteristic signals indicative of a quality of infrared signals from infrared portable devices communicating through said associated port with the base unit.

9. The plurality of infrared receiver/transmitter (RT) modules as claimed in claim 8, wherein each of said RT modules further comprises:

means for producing a reference signal indicative of a high quality infrared signal level incident on a RT module; and

means responsive to the reference signal and a signal representative of the infrared signal incident on an RT module for producing said characteristic signals when said iinfrared signals incident on the RT module exceed the reference signal level.

10. A plurality of infrared receiver/transmitter (RT) modules as claimed in claim 8 wherein each of said RT modules further comprises:

means for producing a reference signal indicative of an acceptable quality infrared signal level incident on the RT module;

means responsive to the reference signal and a signal representative of the infrred signal incident on the RT module for producing an enabling signal when said infrared signals incident on the RT module exceed the reference signal level; and

means responsive to the enabling signal and an electrical form of the infrared signals incident upon the RT module for sending received infrared signals to the base unit.

11. An infrared communication system for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit, comprising:

a base unit operatively located between the signal processing unit and the portable devices for enabling communication therebetween;

a plurality of spaced apart stationary infrared receiver and transmitter (RT) modules operatively interposed between the base unit and said portable devices for transmitting and receiving infrared signals at a desired carrier frequency with said portable units and with electrical signals with said base unit;

a plurality of cables connecting the base unit to the RT modules, each of said cables carrying transmission signals from the base unit to the RT modules and carrying received signals from the RT modules to the base unit;

with the transmission of signals through the cables between the base unit and RT modules being so controlled that signals from the base unit arrive at substantially the same time at RT modules which are near each other and with phase differences between infrared carrier signals received by a portable device from nearby RT modules not exceeding a preselected amount; and

a receiving signal selector to select a received signal from one of several RT modules responding to a portable device transmission for transfer to said signal processing unit, whereby the system'"'"'s IR connection to a portable infrared device can be effectively, automatically and instantly handed off from an RT module experiencing an unacceptable infrared input signal to an RT module having an acceptable infrared input signal.

12. The infrared communication system as claimed in claim 11, wherein said cables connected between the base unit and said nearby RT modules have substantially the same lengths.

13. The infrared communication system as claimed in claim 11, and further including a delay circuit coupled to adjust the transmission time from the base unit to the RT modules to achieve said same time arrival of infrared signals at said portable devices.

14. An infrared communication system for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit, comprising:

a base unit operatively located between the signal processing unit and the portable devices for enabling communication therebetween;

a plurality of spaced apart stationary infrared receiver and transmitter (RT) modules, interposed between the base unit and said portable devices, for transmitting and receiving infrared signals at a desired carrier frequency;

a plurality of cables connecting the base unit to the RT modules, each of said cables carrying transmission signals from the base unit to the RT modules and carrying, to said base unit received signals from RT modules responding to infrared signals from infrared portable devices and incident on the responding RT modules;

wherein said cables connected to nearby RT modules have electrical lengths which do not differ more than an equivalent electrical delay of about a quarter wavelength of the highest infrared carrier frequency employed between the nearby RT modules and portable devices so that signals from the base unit arrive at substantially the same time at RT modules which are near each other and phase differences between infrared carrier signals received by a portable device from different nearby RT modules are sufficiently low so as to reduce signal interference at the portable devices; and

a receiving signal selector to select a received signal from one of several RT modules responding to a portable device transmission for transfer to said signal processing unit.

15. The infrared communication system as claimed in claim 14 and further comprising:

means for generating control signals representative of electrical signal travel times along cables connecting the base unit to the RT modules; and

means responsive to said control signals for delaying communications between the base unit and selected RT modules so as to cause infrared carrier transmissions for nearby RT modules to be transmitted at effectively the same time and cause processing at the base unit of received signals from different responding RT modules to be at effectively the same time.

16. The infrared communication system as claimed in claim 15 and further comprising:

means in said RT modules for generating signals indicative of a quality of infrared signals from infrared portable devices and incident on the RT modules; and

wherein said signal selector includes means, responsive to signals indicative of the quality of infrared signals received by different RT modules and originating from the same portable device, for selecting those received signals representative of at least an adequate quality infrared signal at an RT module and coupling said selected received signals to said signal processing unit.

17. The infrared communication system as claimed in claim 14 and further including:

means within said RT modules for detecting the infrared signal strength incident on an RT module and producing characteristic signals indicative thereof; and

wherein said signal selector includes a priority network responsive to the characteristic signals and received signals for selecting those received signals at the base unit representative of at least an adequate infrared signal strength at an RT module.

18. The infrared communication system as claimed in claim 14 and further including:

a hub interposed between the base unit and a plurality of RT modules;

said hub having a first port for connection to the base unit and a plurality of second ports for connection to a plurality of RT modules, said hub having an interconnection network between said first port and said second ports to enable communication between said portable devices and said base unit as if the hub were an RT module;

a first cable interconnecting said base unit to the first port of the hub and a plurality of second cables connecting the second ports of the hub to said RT modules;

the combined length of the first cable and each of at least selected ones of said second cables being selected so that transmission signals from the base unit and passing through the hub arrive at nearby RT modules at a time selected to limit phase differences between infrared carrier frequency signals received by a portable device from nearby RT modules below a preselected amount.

19. The infrared communication system as claimed in claim 18 and further including:

means within the RT modules for generating characteristic signals indicative of the signal strength of infrared carrier signals incident on RT modules from portable devices and coupling the characteristic signals to said base unit along cables connected therebetween.

20. The infrared communication system as claimed in claim 19:

wherein said characteristic signal generating means in said RT modules comprises;

means for generating amplitude signals representative of the amplitude of the infrared signals incident on the respective RT modules;

means responsive to said amplitude signals for determining the presence of high quality infrared signals incident on the RT module and producing high quality signals indicative thereof;

means for transmitting said high quality signals to said base unit along a said cable;

wherein said system includes means for generating satisfactory quality signals representative of satisfactory infrared signal levels incident on respective RT modules during receiving slots; and

wherein said selection means in said base unit further comprises a priority network responsive to high quality and satisfactory quality signals and said received signals to select the best received signals from RT modules receiving an infrared communication from the same portable infrared device.

21. The infrared communication system as claimed in claim 20 wherein said characteristic signal generating means in said RT modules further comprises:

means for generating a threshold signal indicative of a satisfactory infrared signal level incident on respective RT modules; and

means responsive to said threshold signal and signals indicative of received infrared signals at the associated RT module for producing said received signals for retransmission to said base unit.

22. A base unit for use in an infrared communication system for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit, with a plurality of distributed infrared transmitter and receiver (RT) modules coupled to the base unit and interposed to enable the base unit to communicate with portable infrared devices, comprising:

a signal selection network responsive to signals sent by RT modules and originating from infrared portable devices for selecting a signal representative of at least an adequate infrared signal received by several RT modules from the same portable infrared device, whereby the system'"'"'s IR connection to said same portable infrared device can be effectively, automatically and instantly handed off from an RT module experiencing an unacceptable infrared input signal to an RT module having an acceptable infrared input signal.

23. The base unit as claimed in claim 22 wherein the base unit has a plurality of ports for connection by cables to remote RT modules, said ports having receiving lines connected to said signal selection network, which further comprises a signal selecting priority network connected to the receiving lines to enable one of the adequate quality signals received at the RT modules to be selected for coupling to the signal processing unit.

24. The base unit as claimed in claim 22 wherein the base unit has a plurality of ports for connection by cables to remote receiving an transmission RT modules, the signal selection network further comprising:

means for monitoring respective ports for deriving a control signal as indicative of which of said ports represents the best signal from RT modules responding to a transmission from a common portable infrared device; and

means responsive to said control signal for selecting the best signal received from RT modules.

25. The base unit as claimed in claim 24 and further including:

means responsive to said control signal for selecting a best signal strength indication from said RT modules.

26. The base unit as claimed in claim 24 and further comprising:

means for providing said signal processing unit with an indication of a location of the portable device yielding the best received signal.

27. A method for communicating with a plurality of infrared portable devices via a communication system for enabling a central control unit connected to telephone lines communicate through a signal processing unit, comprising the steps of:

generating transimission signals destined for the infrared portable devices via spatially distributed stationary RT modules for retransmission at carrier frequencies and delaying selected transmission signals arrive at RT modules essentially at the same time with phase differences that are less than about a quarter wavelength of the highest infrared carrier frequency employed;

sending the transmission signals over an infrared carrier to said infrared portable devices; and

passing selected received signals representative of infrared signals from infrared portable devices to a base unit and delaying selected received signals so as to enable them to be processed at said base unit at essentially the same time.

28. The method as claimed in claim 27 wherein said delaying steps comprise the steps of inserting cables between the base unit and said RT modules with lengths selected to avoid infrared signal interference.

29. The method as claimed in claim 28 wherein said delaying steps comprises the steps of:

calibrating the length of cables coupling the base unit to RT modules and generating delay signals representative of the difference in the lengths of said cables; and

delaying the transmission signals destined to RT modules along cables in accordance with said delay signals so as to cause said transmission signals to arrive at said RT modules at essentially the same time.

30. The method as claimed in claim 29 wherein said delaying step further comprises the steps of:

delaying received signals at said base unit in accordance with said delay signals so as to enable the comparing of said received signals to be done essentially at the same time.

31. The method as claimed in claim 27 and further including the step of:

comparing received signals from different nearby RT modules and selecting one of said received signal for transmission to said signal processing unit.

32. The method as claimed in claim 31 wherein said comparing step comprises the steps of:

generating characteristic signals at said RT modules and representative of the signal strength of infrared signal incident on RT modules from infrared portable devices and sending the characteristic signals to the base unit;

comparing the characteristic signals at the base unit and, in response to said latter comparing step, selecting a received signal.

33. An infrared digital and analog communication system for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit, comprising:

a base unit operatively located between the signal processing unit and the portable devices for enabling communication therebetween;

a plurality of spaced apart stationary infrared receiver and transmitter (RT) modules, interposed between the base unit and said portable devices, for transmitting and receiving infrared signals at a desired carrier frequency to and from said portable devices;

said RT modules each including a signal processor, which produces a characteristic signal representative that the intensity or the signal-to-noise ratio, of IR carrier signals from portable devices incident on respective RT module, exceeds a minimum threshold level;

a receiving signal selector in the base unit, responsive to said characteristc signals from RT moduels, to select a received signal from one of several RT modules which respond to an infrared portable device transmission for transfer of the selected received signal to said signal processing unit, whereby the system'"'"'s IR connection to a portable infrared device can be effectively, automatically and instantly handed off from an RT module experiencing an unacceptable infrared input signal to an RT module having an acceptable infrared input signal.

34. The infrared communication system as claimed in claim 33 wherein said RT module'"'"'s signal processor produces a high quality signal indicative that the IR carrier signals from a portable device incident on the respective RT module exceeds a predetermined high quality signal level.

35. The infrared communication system as claimed in claim 34 wherein said receiving signal selector in said base unit further includes a priority network responsive to respective high quality signals from different RT modules so as to select one of said high quality signals.

36. The infrared communication system as claimed in claim 33 and further including:

a hub interposed between the base unit and a plurality of RT modules;

said hub having first port for connection to the base unit and a plurality of RT modules;

said hub having a first port for connection to the base unit and a plurality of second ports for connection to a plurality of RT modules, said hub having an interconnection network between said first port and said second ports to enable communication between said portable devices and said base unit as if the hub were an RT module.

37. An infrared digital and analog communication system for enabling a central control unit connected to telephone lines to communicate with a plurality of portable infrared devices located within a building through a signal processing unit, comprising:

a base unit operatively located between the signal processing unit and the portable devices for enabling communication therebetween;

a plurality of spaced apart stationary infrared receiver and transmitter (RT) modules, interposed between the base unit and said portable infrared devices, for transmitting and receiving infrared signals at a desired carrier frequency to and from said portable infrared devices;

said RT modules each including a signal strength or signal-to-noise ratio signal processor, which produces digital amplitude signals representative of the signal strength or signal-to-noise ratio of IR carrier signals from portable infrared devices incident on the respective RT module;

means for coupling the digital amplitude signals to the base unit;

a receiving signal selector in the base unit, responsive to said digital amplitude signals from RT modules, to select the best received signal from one of several RT modules which respond to an infrared portable device transmission for transfer of the selected received signal to said signal processing unit, whereby the system'"'"'s IR connection to a portable infrared device can be effectively, automactically and instantly handed off from an RT module experiencing an unacceptable infrared input signal to an RT module having an acceptable infrared input signal.