WO1995029566A1

WO1995029566A1 - Wireless communication system

Info

Publication number: WO1995029566A1
Application number: PCT/US1995/004069
Authority: WO
Inventors: David B. Bartholomew; A. Ray Ivie; Alma K. Schurig
Original assignee: Phonex Corporation
Priority date: 1994-04-21
Filing date: 1995-04-04
Publication date: 1995-11-02
Also published as: AU2204495A

Abstract

A system for the wireless connection of a conventional telephone instrument, such as a telephone set (150), modem (130), or facsimile machine (140), to a standard telephone line (101). The system has two units. A base unit (110) connects to the standard telephone line and communicates with one or more extension units. Extension units (120) transform the communications between themselves and the base unit into standard telephone line signals. The extension unit not only handles duplexed audio, but also senses the on-hook/off-hook status of the telephone instrument and commands the base unit to go off-hook when appropriate. The base unit detects a ringing voltage on the standard telephone line and commands the extension unit to couple a similar ringing voltage to the conventional instrument.

Description

Wireless Communication System

Background

Field of the Invention This invention relates to wireless telephone communications systems, and in particular systems that use radio transmissions to connect a conventional telephone instrument to a standard telephone line.

Description of Related Art It is often desirable to be able to use a telephone, or other telephcne-related device such as a modem, at a location away from normal telephone wiring. It may be either too expensive or too inconvenient to connect the telephone to the telephone system using normal wiring. As an alternative to normal wiring, there are a variety of systems that use a base unit connected to the standard telephone line to interface between the standard telephone line and some other communications medium, such as wireless radio or radio frequency signals on a building power line. Those signals are received by a portable extension unit.

The most common alternative to a wired telephone connection is the "cordless" telephone which uses wireless radio signals between its base unit and a handheld unit that combines a radio transceiver (transmitter and receiver) with a handset having a microphone and a speaker. Such systems operate at a low power and have a restricted range, so that licensing of the transmitters is not required.

However, the handheld unit of a cordless telephone does not permit the attachment of other telephone instruments, such as an extension telephone, a modem, or a facsimile machine. This is because the signals necessary for operating conventional telephone instruments are not present in the handheld unit. (These signals include duplexed audio at the appropriate signal levels, ringing and other control signals, and the proper response to changes in impedance indicating an off-hook condition.) In the cordless telephone, the audio output of its transceiver is connected directly to the earphone portion of the handset, while the output of the microphone portion of the handset is connected directly to the audio input of the transceiver. This simplifies the design and operation of the cordless telephone. Furthermore, rather than generating a ringing voltage similar to that used on a standard telephone line, cordless telephones produce a ringing sound through a special ringer transducer. Whether the handset is "on-hook" (not in use) or "off-hook" (in use) is not determined by sensing the impedance of a line, but by the position of a switch located on the handset. Dialing the cordless phone is performed through tones regenerated in the base. Connecting a conventional telephone instrument to a cordless phone handset would require the total redesign of the cordless phone system.

Another way of remotely connecting an extension to a standard telephone line is to use the electrical power wiring as a replacement for the normal telephone wiring between the extension as the telephone line. Obviously, powerline systems require circuitry at both the extension and the point of connection to the standard telephone line to accomplish this. Such circuitry is described in United States Patents 4,479,033 and 4,495,386, as well as the parent of this application, each of which is hereby incorporated by reference in its entirety.

There are, however, problems associated with using electrical power wiring to connect the base and extension units. It requires the extension unit to be located close to the power wiring. It could not be conveniently used in a location remote from the power wiring, such as outdoors away from buildings. Unlike a cordless phone, it is not easily mobile, but depends on a cord like a conventional telephone. But more problematic is the blocking of radio frequency signals by power transformers used to reduce the power line distribution voltage to the nominal levels found in a house or office. While this blocking may be desirable to prevent the interference of two powerline telephone systems in different locations, it can also prevent the use of a powerline system within an office building that has outlets supplied from different transformers.

Both cordless phones and powerline extension systems (to the extent a line from the same transformer is used) also can have security problems . Unauthorized persons may be able to access the base unit as if they were using a proper extension unit. There have been a number of reported incidents of people travelling through a neighborhood with a cordless telephone looking for a dialtone, produced when a base unit thinks it is talking with its extension. At that point, long distance calls can be made that will be billed to the line serving the base unit. To prevent these security problems, government agencies have been requiring security in recent cordless telephone products. But it is still possible for people to overhear conversations with similar equipment or scanners.

For background material the reader is directed to United States Patent Nos. 3,809,815, 3,809,816, 3,949,172, 4,058,678, 4,013,840, 4,218,655, 4,222,035, 4,254,403, 4,445,651, 4,514,594, 4,559,520, 4,641,322, 4,688,210, 4,701,945, 4,471,399, 4,475,193, 4,479,033, 4,523,307, 4,759,016, 4,783,780, 4,864,579, 4,901,307, 4,963,853, 4,968,970, 5,101,501 and 5,136,612 each of which is hereby incorporated by reference in its entirety.

Summary of the Invention

It is an object of this invention to provide a wireless means for connecting an extension telephone remote from standard telephone lines. Neither standard telephone wiring nor power wiring need be run to the location of the extension telephone. This is achieved by using wireless radio for the communications link between the base unit and the extension unit. This also overcomes the inability of powerline extension systems to communicate between outlets supplied by different power transformers . It is a further object of this invention to allow the attachment of normal extension telephone sets, modems, facsimile machines, or other devices that attach to standard telephone lines (collectively, conventional telephone instruments) to the extension unit. This is achieved by providing circuitry that separates the duplexed audio signal provided by the conventional telephone instrument .

Additional circuitry senses the impedance of the line connecting the conventional telephone instrument to the extension unit to sense whether the instrument is off-hook, * and that information is transmitted to the base unit to control whether the base unit takes its standard telephone line off-hook. Pulse dialing can be accomplished by treating it as rapid off-hook/on-hook signals. Circuitry is also present in the base unit to sense a ringing signal on the standard telephone line and transmit a control signal to the extension unit. The extension unit then generates a ringing voltage like that of a standard telephone line and couples it to the line connecting the conventional telephone instrument.

It is a further object of this invention to minimize the interference caused by other devices operating on frequencies near those used by this invention. It is also an object of this invention to prevent the unauthorized access of the base unit by a similar extension unit. It is also an object of this invention to prevent the unauthorized reception of the conversation being carried on. All these objects are achieved by the use of a combination of modulation techniques, including direct spread spectrum modulation based on random sequences of numbers, the use of digital modulation involving encryption/decryption and exclusive digital codes. These and other features of the invention will be more readily understood upon consideration of the attached drawings and of the following detailed description of those drawings and the presently preferred embodiments of the invention.

Brief Description of the Drawings

Fig. 1 illustrates the connection of the base unit to the standard telephone line and the connection of conventional telephone instruments to the extension unit. Fig. 2 is a block diagram showing the major sections of the base unit.

Fig. 3 is a block diagram showing the major sections of the extension unit. Fig. 4 is a schematic diagram of the subscriber line interface circuit in the extension unit .

Detailed Description of the Invention

The material (including specification, claims, drawings and abstract) of the parent application of this application, application Serial No. 07/773,009, filed October 7, 1991, is hereby incorporated by reference in its entirety.

The major components of the present invention are illustrated in Fig. 1. It comprises base unit 110 with antenna 112, which communicates using wireless radio with extension unit 120, which has antenna 122. Base unit 110 is connected to standard telephone line 101 through an appropriate jack-and-plug arrangement 102. In the United States, jack-and-plug arrangement 102 is generally a female RJ-11 connector connected to telephone line 101 and a male RJ-11 connector connected to base unit 110 through line cord 103. There are a number of signals on standard telephone line 101, including combined audio to and from base unit 110 and a ringing signal indicating that a call is being received on telephone line 101. Standard telephone line 101 can be in one of two states: on-hook, indicating that a call can be received, and off-hook, indicating that a call is currently active. The state of telephone line 101 is controlled by base unit 110. When base unit 110 presents a high DC impedance to telephone line 101, the line is on-hook. When base unit 110 presents a lower DC impedance (approximately 200 ohms in the United States) to telephone line 101, the line is off-hook. Dialing of a call can be made by repeatedly switching between off-hook and on-hook with pulse durations and idle periods between pulses that meet the specifications of the central office switch feeding standard telephone line 101.

Extension unit 120 utilizes a connector arrangement similar to jack-and-plug 102. In the United States, extension unit 120 will have an RJ-11 female connector 124 similar to the one connected to standard telephone line 101. A variety of conventional telephone instruments can be plugged into connector 124. For example, an ordinary telephone 150 having male RJ-11 connector 152 can be plugged into connector 124. Alternatively, a facsimile (FAX) machine 140 having male RJ-11 connector 142 can be plugged into connector 124. Computer terminal 134 is connected to modem 130, and modem 130 has male RJ-11 connector 132 which can be plugged into connector 124. All these conventional telephone instruments depend for their proper operation on the signals at connector 124 to be identical to those presented by a central office on a standard telephone line. In particular, there must be combined audio between extension unit 120 and the conventional telephone instrument, extension unit 120 must generate a ringing signal to indicate a call for the conventional telephone instrument, and extension unit 120 must determine whether the conventional telephone instrument is on-hook or off-hook by sensing a change in the DC impedance presented to extension unit 120 by the conventional telephone instrument. Fig. 2 is a block diagram showing the major sections of the preferred embodiment of base unit 110. Line cord 103 connects the standard telephone line to ring detect circuit 202, off-hook circuit 204, and hybrid audio circuit 206. Circuits 202, 204, and 206 collectively form the means for connecting base unit 110 to a standard telephone line.

Ring detect circuit 202 senses a high voltage (above 30 volts RMS) on line 103, and sends a signal to system controller 220 when that voltage is detected. System controller 220 further determines that a ringing signal is present on like 103 by checking to see if the high voltage is at the proper frequency (from 15.5 Hz to 68 Hz in the United States) . Off-hook circuit 204 switches line 103 from a high DC impedance to a low DC impedance (approximately 200 ohms) when commanded by system controller 220. The design of these simple circuits would be straightforward for one skilled in the telephone art.

Fig. 3 is a block diagram showing the major sections of the preferred embodiment of extension unit 120. Connector 124 connects a conventional telephone instrument to extension unit 120. To do this, it is necessary to for extension unit 120 to appear as a standard telephone line. This is achieved through ring generator 302, off-hook sense circuit 304, and hybrid audio circuit 306. Circuits 302, 304, and 306 together form a subscriber line interface circuit, or SLIC, the means for connecting extension unit 120 to a conventional telephone instrument.

Fig. 4 is a schematic diagram of the subscriber line interface circuit used in the preferred embodiment of extension unit 120. Nominal values for each component are shown on the drawing.

Ring generator 302 comprises diodes 422 and 434, transistors 424 and 430, and resistors 420, 426, 428, and 432. In response to the ring command from system controller 320, pin 3 of connector 124 is connected to a high voltage source. By cycling the ring command on and off at the desired frequency, an appropriate AC ringing voltage can be generated.

Diodes 406 and 418, transistors 408 and 410, and resistors 412, 414, and 416 form a circuit that disconnects pin 3 of connector 124 from ground whenever ring generator 302 is active.

Off-hook sense circuit 304 comprises resistor 470. The voltage drop across resistor 470 depends on the impedance between pins 3 and 4 of connector 124. This voltage allows system controller 320 to determine if the conventional telephone instrument is off-hook or on-hook. The remaining components in Fig. 4 form hybrid audio circuit 306. Capacitor 436 provides DC isolation between the telephone line at connector 124 and the hybrid circuit. Diodes 440 and 474 and transistor 438 provide a means for system controller 320 to mute the audio, such as when a ringing signal is being generated or no call is active. Resistors 442, 444, 454, and 456 and capacitors 446, 448, 450, and 452 provide a proper AC impedance match for the telephone line at connector 124 (600 ohms in the United States) .

The audio input that feeds the conventional telephone instrument feeds into hybrid audio circuit 306. Operational amplifier 468 (and its associated components resistors 458, 460, 462, 464, and 470 and capacitor 466) has as inputs the combined audio input and audio output signals to the conventional telephone instrument, and the audio input signal alone. Operational amplifier 468 subtracts the audio input signal from the combined audio input and audio output signals to produce the audio output signal.

There are a number of other circuits for hybrid audio circuit 306 that are well-known in the telephone art, including one based on transformer coupling found in many ordinary telephones . The use of an electrical circuit for ring generator 302, off-hook sense circuit 304, or hybrid audio circuit 306 different from the circuits of the preferred embodiment just described is within the scope of the claimed invention.

Referring again to Fig. 2 and Fig. 3, the remainder of the preferred embodiment of base unit 110 and extension unit 120 will be described. As can be seen, these circuits are quite similar. Antennas 112 and 122 are connected through radio frequency diplexers 240 and 340, respectively. Diplexer 240 receives a radio frequency signal from power amplifier 238, the final stage of base unit 110's transmitter subsystem, and delivers a radio frequency signal to filter 250, the first stage of base unit 110's receiver subsystem. Diplexer 340 receives a radio frequency signal from power amplifier 338, the final stage of extension unit 120' s transmitter subsystem, and delivers a radio frequency signal to filter 350, the first stage of extension unit 120's receiver subsystem.

In the preferred embodiment, the separated audio input and audio output signals from hybrid audio circuits 206 and 306 are connected to codecs (coder-decoders) 208 and 308, respectively. This permits transmission of the audio information between base unit 110 and extension unit 120 as digital codes, rather than analog signals. It is well known to persons of ordinary skill in the art to encrypt/decrypt the digital codes to provide greater privacy and security. If analog audio signals were used between base unit 110 and extension unit 120, the modulation of the radio frequency signal could be done using amplitude modulation, frequency modulation, or phase modulation, all techniques well-known in the radio art . In the preferred embodiment, the audio signals are also sent through digital compression and decompression circuits 210 and 310 to limit the range of digital codes that need to be transmitted.

There are a number of techniques that can be used to modulate the radio frequency carrier signal with the digital audio signal. In addition to amplitude modulation, frequency or phase modulation techniques such as frequency- shift keying, biphase-shift keying, quadriphase-shift keying, and minimal-shift keying can be employed. These techniques are common in the transmission of digital signals on a carrier signal. In the preferred embodiment, a more sophisticated technique is used. The audio signal modulates the carrier frequency (produced by oscillator 232 or 332) using simple frequency-shift keying at modulators 234 or 334. That modulated signal is further modulated using a code-division multiple-access technique. Code-division multiple-access techniques are described in Robert C. Dixon' s book, "Spread Spectrum Systems, 2nd Edition" published by John Wiley & Sons, which is hereby incorporated by reference.

One embodiment of the invention uses a direct spread code-division multiple-access technique. The modulated carrier signal is further modulated by CDMA modulators 236 or 336 based on a code produced by PN code generators 230 or 330.

Another embodiment of the invention uses a frequency hopping code-division multiple-access technique.

The modulated carrier signal is mixed at CDMA modulators 236 or 336 with a signal whose frequency is based on the code produced by PN code generators 230 or 330. This results in the final signal changing among a set of frequencies. An alternative means of producing a frequency hopping code-division multiple-access technique is to use frequency-agile oscillators 232 or 332, whose frequency depends on the code produced by PN code generators 230 or 330, to produce the carrier frequency that is further modulated by data modulator 234 or 334. In this case, CDMA modulators 236 or 336 are not necessary.

The received spread-spectrum signal is fed through CDMA correlators 256 and 356 to reproduce the modulated radio frequency signal, which is amplified through IF stages 256 and 356 and demodulated by data demodulators 258 and 358 using a circuit appropriate for the modulation technique used. For frequency hopping code-division multiple-access techniques, CDMA correlators 256 and 356 can be a mixer to produce a signal at the IF frequency by heterodyning the received signal with a signal based on the code from PN generators 230 or 330. To simplify the implementation of extension unit

120, it employs only a single PN (pseudo noise) code generator for both CDMA modulator 336 and CDMA correlator 354. Because the PN generators at the sending CDMA modulator and receiving CDMA correlator must be synchronized, it is not possible to use a single PN generator in base unit 110, and instead PN generators 230 and 252 are present. Both PN generators 230 and 252 produce the same sequence of random numbers. However, PN generator 230's sequence leads PN generator 252's sequence by an amount equal to twice the radio signal propagation delay between base unit 110 and extension unit 120. This means that the sequence from PN generator 230 will be in synchronization with PN generator 330 when it arrives at extension unit 110, and the sequence from PN generator 330 will be in synchronization with PN generator 352 when it arrives at base unit 110.

Data demodulator 358 in extension unit 120 also produces a signal that controls the frequency of oscillator 332 using a phase-lock technique. That assures that the frequency of oscillator 332 will be identical to oscillator 232 in base unit 110 and the three PN generators 230, 252, and 330 will remain in synchronization.

The preferred embodiment also uses time-division multiple-access to further control the transmission of information between base unit 110 and extension unit 120. Information is only transmitted when there is a digital message ready. At other times, the transmitter subsystem is inactive.

The operation of the system is as follows. When a telephone call is received on standard telephone line 101, base unit 110 senses the ringing signal with ring detect circuit 202. System controller 220 then uses the transmitter subsystem of base unit 110 to send a ringing status signal using wireless radio communications to extension unit 120. That signal is received by extension unit 120's receiver subsystem and given to system controller 320, which generates a ringing signal using ring generator 302.

There are a number of ways that the ringing status signal can be transmitted from base unit 110 to extension unit 120. It can be transmitted as a digital or analog signal on a frequency separate from that used for audio signal transmission. In the preferred embodiment, it is coded distinctly from the digitized audio data and transmitted using the same facilities as for the digitized audio data. System controller 320 in extension unit 120 recognizes this distinctive digital code and activates ring generator 302. Digitized audio signals are routed by system controller 320 to codec 310.

Each change in impedance from the conventional telephone instrument connected to extension unit 120 at connector 124 is detected by off-hook sense circuit 304. When an off-hook condition is detected, system controller 320 uses the transmitter subsystem of extension unit 120 to send an off-hook status signal using wireless radio communications to base unit 110. That signal is received by base unit 110's receiver subsystem and given to system controller 220, which generates an off-hook status on standard telephone line 101 using off-hook circuit 204. When an on-hook condition is detected, system controller 320 sends an on-hook status signal which when received by system controller 220 results in deactivating off-hook circuit 204 and in base station 110 going on-hook. A technique similar to the one described above for the ringing status signal is used for the off-hook and on-hook status signals. If the means for handling on-hook and off-hook status is sufficiently fast, pulse dialing signals from the conventional telephone instrument connected to extension unit 120 are replicated by base unit 110, allowing the use of pulse-dial telephone instruments.

Whenever the conventional telephone instrument is off-hook, the audio signal from standard telephone line 101 is separated from the combined audio signal on standard telephone line 101 by hybrid audio circuit 206 and is coupled to the transmitter subsection of base unit 110 and transmitted using wireless radio to extension unit 120. Extension unit 120' s receiver subsystem receives the audio signal which is then placed on the telephone line at connector 124 using hybrid audio circuit 306. A similar transmission path is established for the audio signal from the conventional telephone instrument to the standard telephone line. In the preferred embodiment, the audio signal is digitized before it is transmitted. As discussed above, a time-division multiple-access technique is used to activate the transmitter subsection when digitized audio (or a status signal) needs to be transmitted. The carrier signal is modulated using frequency-shift keying (FSK) and then further modulated using a direct spread code-division multiple-access technique. Corresponding techniques are employed at the receiving unit to reproduce the audio signal. It is to be understood that the above described embodiments are merely illustrative of numerous and varied other embodiments which may constitute applications of the principles of the invention. Such other embodiments may be readily devised by those skilled in the art without departing from the spirit or scope of this invention and it is our intent they be deemed within the scope of our invention.

Claims

ClaimsWe claim:

1. A wireless communications system for connecting a conventional telephone instrument to a standard telephone line using wireless radio communications, the system comprising:

(a) a base unit comprising:

(i) a first transmitter subsystem, (ii) a first receiver subsystem; and (iii) means for connecting said first transmitter subsystem and said first receiver subsystem to a standard telephone line;

(b) an extension unit comprising:

(i) a second transmitter subsystem, (ii) a second receiver subsystem, and

(iii) means for connecting said second transmitter subsystem and said second receiver subsystem to a conventional telephone instrument; wherein said first transmitter subsystem comprises means for the wireless transmission of a first radio signal and said second receiver subsystem comprises means for the reception of said first radio signal; and wherein said second transmitter subsystem comprises means for the wireless transmission of a second radio signal and said first receiver subsystem comprises means for the reception of said second radio signal .

2. A system as in claim 1, said base unit further comprising an antenna and a diplexer connecting said first transmitter subsystem and said first receiver subsystem to said antenna.

3. A system as in claim 1, said extension unit further comprising an antenna and a diplexer connecting said second transmitter subsystem and said second receiver subsystem to said antenna.

4. A system as in claim 1, said extension unit further comprising means for sensing that said conventional telephone instrument is off-hook.

5. A system as in claim 4, said base unit further comprising means for taking said standard telephone line to an off-hook condition.

6. A system as in claim 5, wherein an off-hook status signal is transmitted by said second radio signal whenever said extension unit senses that said conventional telephone instrument is off-hook, and wherein reception of said off-hook status signal by said base unit causes said base unit to take said standard telephone line to an off-hook condition.

7. A system as in claim 6, wherein said off-hook status signal is distinctive digital code.

8. A system as in claim 1, said base unit further comprising means for sensing a ringing signal on said standard telephone line.

9. A system as in claim 8, said extension unit further comprising means for generating a ringing signal to said conventional telephone instrument.

10. A system as in claim 9, wherein a ringing status signal is transmitted by said first radio signal whenever said base unit senses a ringing signal on said standard telephone line, and wherein reception of said ringing status signal by said extension unit causes said extension unit to generate a ringing signal to said conventional telephone instrument .

11. A system as in claim 1, wherein said conventional telephone instrument utilizes audio input and audio output from said extension unit combined on a single circuit between said conventional telephone instrument and said extension unit .

12. A system as in claim 11, said extension unit further comprising a hybrid audio circuit for separating said audio input from said audio output, wherein said separated audio input modulates said second transmitter subsystem and said second receiver subsystem supplies said audio output.

13. A system as in claim 12, wherein said audio input is converted to a first digital signal to modulate said second transmitter subsystem.

14. A system as in claim 13, said second transmitter subsystem comprising a carrier generator producing a carrier signal, wherein said carrier signal is modulated by said first digital signal utilizes a modulation technique selected from the following: amplitude modulation, frequency modulation, phase modulation, frequency-shift keying, biphase-shift keying, quadriphase-shift keying, and minimal-shift keying.

15. A system as in claim 14, wherein a code-division multiple-access technique is used to further modulate said carrier signal.

16. A system as in claim 15, wherein said code-division multiple-access technique is direct spread.

17. A system as in claim 15, wherein said code-division multiple-access technique is frequency hopping.

18. A system as in claim 12, said second transmitter subsystem comprising a carrier generator producing a carrier signal, wherein said carrier signal is modulated by said audio input using a modulation technique selected from the following: amplitude modulation, frequency modulation, and phase modulation.

19. A system as in claim 18, wherein a code-division multiple-access technique is used to further modulate said carrier signal.

20. A system as in claim 19, wherein said code-division multiple-access technique is direct spread.

21. A system as in claim 19, wherein said code-division multiple-access technique is frequency hopping.

22. A system as in claim 14, wherein a time-division multiple-access technique determines when said carrier signal modulated by said first digital signal is transmitted.

23. A system as in claim 12, said second receiver subsystem comprising a demodulator, wherein said demodulator's output supplies said audio output.

24. A system as in claim 23, wherein said demodulator's output is a second digital signal that is converted to said audio output.

25. A system as in claim 1, wherein said first radio signal comprises control signals and audio signals.

26. A system as in claim 25, wherein said control signals are transmitted at separate frequencies .

27. A system as in claim 25, wherein said control signals are transmitted as distinctive digital codes.

28. A system as in claim 1, wherein said second radio signal comprises control signals and audio signals.

29. A system as in claim 28, wherein said control signals are transmitted at separate frequencies.

30. A system as in claim 28, wherein said control signals are transmitted as distinctive digital codes.

31. A system as in claim 1, wherein said conventional telephone instrument is a ordinary telephone.

32. A system as in claim 1, wherein said conventional telephone instrument is a facsimile machine.

33. A system as in claim 1, wherein said conventional telephone instrument is a modem.

34. A wireless communications extension unit for connecting a conventional telephone instrument to a standard telephone line using wireless radio communications, the extension unit comprising:

(a) a transmitter subsystem,

(b) a receiver subsystem, and

(c) means for connecting said transmitter subsystem and said receiver subsystem to a conventional telephone instrument; wherein said transmitter subsystem comprises means for the wireless transmission of a first radio signal; and wherein said receiver subsystem comprises means for the wireless reception of a second radio signal.

35. An extension unit as in claim 34, said extension unit further comprising an antenna and a diplexer connecting said transmitter subsystem and said receiver subsystem to said antenna.

36. An extension unit as in claim 34, said extension unit further comprising means for sensing that said conventional telephone instrument is off-hook.

37. An extension unit as in claim 36, wherein an off-hook status signal is transmitted by said second radio signal whenever said extension unit senses that said conventional telephone instrument is off-hook.

38. An extension unit as in claim 37, wherein said off-hook status signal is distinctive digital code.

39. An extension unit as in claim 34, said extension unit further comprising means for generating a ringing signal to said conventional telephone instrument.

40. An extension unit as in claim 39, wherein reception of a ringing status signal by said extension unit causes said extension unit generates a ringing signal to said conventional telephone instrument.

41. An extension unit as in claim 40, wherein said ringing status signal is a distinctive digital code.

42. An extension unit as in claim 34, wherein said conventional telephone instrument utilizes audio input and audio output from said extension unit combined on a single circuit between said conventional telephone instrument and said extension unit.

43. An extension unit as in claim 42, said extension unit further comprising a hybrid audio circuit for separating said audio input from said audio output, wherein said separated audio input modulates said transmitter subsystem and said receiver subsystem supplies said audio output.

44. An extension unit as in claim 43, wherein said audio input is converted to a first digital signal to modulate said transmitter subsystem.

45. An extension unit as in claim 44, said transmitter subsystem comprising a carrier generator producing a carrier signal, wherein said carrier signal is modulated by said first digital signal utilizes a modulation technique selected from the following: amplitude modulation, frequency modulation, phase modulation, frequency-shift keying, biphase-shift keying, quadriphase-shift keying, and minimal-shift keying.

46. An extension unit as in claim 45, wherein a code- division multiple-access technique is used to further modulate said carrier signal.

47. An extension unit as in claim 46, wherein said code- division multiple-access technique is direct spread.

48. An extension unit as in claim 46, wherein said code- division multiple-access technique is frequency hopping.

49. An extension unit as in claim 43, said transmitter subsystem comprising a carrier generator producing a carrier signal, wherein said carrier signal is modulated by said audio input using a modulation technique selected from the following: amplitude modulation, frequency modulation, and phase modulation.

50. An extension unit as in claim 49, wherein a code- division multiple-access technique is used to further modulate said carrier signal .

51. An extension unit as in claim 50, wherein said code- division multiple-access technique is direct spread.

52. An extension unit as in claim 50, wherein said code- division multiple-access technique is frequency hopping.

53. An extension unit as in claim 45, wherein a time- division multiple-access technique determines when said carrier signal modulated by said first digital signal is transmitted.

54. An extension unit as in claim 43, said receiver subsystem comprising a demodulator, wherein said demodulator's output supplies said audio output.

55. An extension unit as in claim 54, wherein said demodulator's output is a second digital signal that is converted to said audio output.

56. An extension unit as in claim 34, wherein said first radio signal comprises control signals and audio signals.

57. An extension unit as in claim 56, wherein said control signals and said audio signals are transmitted at separate frequencies.

58. An extension unit as in claim 56, wherein said control signals and said audio signals are transmitted as distinctive digital codes.

59. An extension unit as in claim 34, wherein said second radio signal comprises control signals and audio signals.

60. An extension unit as in claim 59, wherein said control signals and said audio signals are transmitted at separate frequencies.

61. An extension unit as in claim 59, wherein said control signals and said audio signals are transmitted as distinctive digital codes.

62. An extension unit as in claim 34, wherein said conventional telephone instrument is a ordinary telephone.

63. An extension unit as in claim 34, wherein said conventional telephone instrument is a facsimile machine.

64. An extension unit as in claim 34, wherein said conventional telephone instrument is a modem.