Description of Related Art. A power line and wireless RF audio signal communication systems have been proposed and are well known in the prior art.

Typically, such systems do not employ frequency division multiplexing techniques to transmit two audio channels to a remote location over a common RF carrier, whether and AC power line or a wireless RF channel.

The reader is referred to the following U. S. patent documents for general background material. Each of these patents is hereby incorporated by reference in its entirety for the material contained therein.

U. S. Patent Nos. 604, and 5,321,514 describe a spread spectrum system that provides bidirectional digital communication on a vacant television channel for simultaneous use by more than 75,000 subscribers using time and frequency division multiplex signals locked to horizontal and vertical sync pulses of an adjacent channel host TV station.

U. S. Patent No. 4,955,050 describes a system configuration of wireless PBX and communication method therefor with high user facility.

U. S. Patent No. 4,980,665 describes a repeater for receiving data transmitted thereto via a first transmission medium, transmitting that data over AC power lines to a remote location and re-transmitting that data from the remote location via a second transmission medium.

U. S. Patent No. 5,201,066 describes a radio-telephone system employing a manner of changing a channel and a privacy digital code and interstoring them between by wireless and a method of changing the privacy digital code.

U. S. Patent Nos. 5,237,612 and 5,241,598 describe a system for the validation and verification of base stations and mobile stations within a cellular radio communications network.

U. S. Patent No. 5,305,132 describes a light frequency communication system and method of using the system.

U. S. Patent No. 5,375,174 describes a wireless remote active noise canceling headset including residual microphones mounted on the headset with speakers located adjacent to the residual microphones and an algorithm driven synchronous controller to operate said headset.

U. S. Patent No. 5,473,675 describes a modem, capable of simultaneously coupling voice and data signals, that connects to local digital terminal equipment (DTE) and a local telephone to a communications link.

U. S. Patent No. 5,483,695 describes an FM receiver that comprises a local oscillator, a heterodyning stage and a demodulator stage.

U. S. Patent No. 5,544,164 describes a Wide Area Network Asynchronous Transfer Mode compliant cell based communications system that is capable of

delivering high data rate cells from a plurality of terminal devices to support a multiplicity of simultaneous terminal device applications for homes and businesses.

U. S. Patent Nos. 5,664,019, and 5,757,929 describe a personal communications apparatus using a garment-based audio interface.

U. S. Patent No. 5,594,789 describes a system and method of implementing purchasing and other transactions in an integrated multimedia communication system by utilizing an intelligent peripheral of an advanced intelligent telephone network.

U. S. Patent No. 5,612,974 describes a convolutional encoder that is accomplished by provided by a first register, a plurality of logic gates, a simpler, a second register and a sequencer.

U. S. Patent No. 5,621,800 describes an integrated circuit that provides multiple communication functions that are accomplished by providing an integrated circuit that includes memory, which stores an audio code algorithm, echo cancellation information, a modem processing algorithm and audio data.

U. S. Patent No. 5,652,903 describes a DSP co-processor that is used on an integrated circuit that provides multiple communication functions.

U. S. Patent No. 5,659,698 describes a circular buffer address generation unit.

U. S. Patent No. 5,694,454 describes a communication system that provides analog message re-transmission on demand, and which comprises a base station and at least one portable communication transceiver.

U. S. Patent Nos. 5,748,103 and 5,767,791 describe a two-way medical telemetry system.

Summary of the Invention

It is desirable to provide a system for communicating two-channel (stereo) signals for wireless speaker system. Moreover, it is desirable to provide a means for transmitting and receiving two audio channels to a remote location using frequency division multiplexing on a common radio frequency (RF) carrier.

Accordingly, it is the primary object of this invention to provide a system and method of communicating two channels of audio information on a common carrier channel.

Another object of this invention is to provide a system and method for the communication of audio channels for wireless speaker systems.

A further object of this invention is to provide a system and method for communicating audio signals to a remote location using frequency division multiplexing techniques.

It is another object of this invention to provide a system and method for communicating audio signals using power line carrier techniques.

It is a still further object of this invention to provide a system for communicating two audio signals over a single RF channel where the source of the audio signals can be a stereo receiver, a compact disk player, a stereo video cassette recorder, a digital video disk or the like.

It is a further object of this invention to provide a system for communicating two audio signals over a single RF channel that is compatible with a RF wireless data link.

A further object of this invention is to provide a system for communicating two audio signals over a single RF channel that is compatible with AC power line channels.

Additional objects, advantages, and other novel features of this invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of this invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Still other objects of the present invention will become readily apparent to those skilled in the art from the following description wherein there is shown and described the preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out this invention. As it will be realized, this invention is capable of other different embodiments, and its several details, and specific electronic circuits, are capable of modification in various aspects without departing from the invention. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive.

To achieve the foregoing and other objectives, and in accordance with the purposes of the present invention, two audio channels are connected to a two-channel modulator, which in turn communicates with a transmitter for transmitting over the "wireless"link. A receiver receives the signal transmitted over the"wireless"link and outputs the signal to a two-channel demodulator, which presents two independent audio channels to a sound generator, such as speakers or headphones.

Brief Description of the Drawings The accompanying drawings incorporated in and forming a part of the specification, illustrate a preferred embodiment of the present invention. Some, although not all, alternative embodiments are described in the following description.

In the drawings: Figure 1 is a top level system block diagram showing the major sections of the invention.

Figure 2 is a block diagram providing additional detail of the two-channel modulator unit of the preferred embodiment of the invention.

Figure 3 is a block diagram providing additional detail of the demodulator unit of the preferred embodiment of the invention.

Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.

Detailed Description of the Invention Figure 1 shows the top-level system block diagram of the major sections of the preferred embodiment of the invention. Two audio channel signal generators 101 and 102 are the source of the audio signals processed and communicated in this invention.

These signal generators 101,102 typically are the left and right audio channels of a stereo device, such as a stereo receiver, compact disc (CD), stereo video cassette recorder (VCR) or the like. Alternative communication devices could made use of this invention without necessarily being related audio signals. The audio signals provided by the signal generators 101,102 are received by a two-channel modulator 103, which combines the two channels via frequency division multiplexing into a

single waveform and sends this composite signal to a transmitter 104. The transmitter 104 generates the radio frequency (RF) carrier that is modulated by the composite signal from the two-channel modulator 103. This modulated carrier 105 is transmitted from the transmitter 104 to the receiver 106 via an AC power line channel, or alternatively, through an over the air channel. The received RF signal is demodulated to produce the composite signal by the receiver 106 and send to a two- channel demodulator 107, where it is separated into the two audio channels 108 and 109 using frequency division multiplexing techniques. These separated channels 108, 109 can be used with a headphone set or other listening device, such as a set of powered speakers. This invention provides that multiple receivers 106 can be receive signals from a given transmitter 104. For example, a receiving set 110 can be used in each room of a household, each receiving and producing the same two audio sources 108,109 from the same transmitter set 111.

Figure 2 shows the block diagram of the preferred two-channel modulator 103 of this invention. The two audio channels 101,102 are received by the modulator 103. Audio channel 1 101 is mixed with a local oscillator frequency produced by local oscillator 201 in a mixer 202 that translates the baseband signal to a higher frequency passband signal 207. This passband signal 207 is filtered in a low pass filter 203 to provide a filtered signal 208 having any undesired signals produced by any non-linearities in the mixer 202 eliminated. The frequency signal 209 of the local oscillator 201 is high enough that all frequency components of the upconverted signal are greater than the highest desired frequency component of the audio signals in audio channel 2 102. The frequency signal 209 of the local oscillator 201 is received by a

divider 204 for dividing the signal by two, the output 210 of which is delayed by a delay unit 205. This divided and delayed signal 211, commonly called the pilot tone signal, is used to regenerate the local oscillator frequency in the receiver 106 for coherent detection. The three signals: the output of the low pass filter 203, the output of the delay unit 205 and audio channel 2 102 are combined in the summer 206. The summer 206 produces the single composite signal that is used to modulate the RF carrier frequency of the transmitter 104.

Figure 3 shows the block diagram of the preferred two-channel demodulator 107 of this invention. The received composite signal 311 from the receiver 106 is presented to three devices: a first band pass filter 307, a second band pass filter 301 and a low pass filter 310. The second band pass filter 301 produces a pilot tone signal 313 by filtering out the other signals present, the output of this band pass filter 301 feeds into a carrier recovery loop 302 providing its 312 pilot tone. The carrier recovery loop 302 uses a phase comparator 303 to compare the phase of the incoming signal, or pilot tone, 313 from the second band pass filter 301 with a reference signal 314, produced by a divide by 2 circuit 304 which in turn receives a reference signal 315 from a voltage controlled oscillator (VCO) 305, and produces an error signal 312.

The error signal 312 is fed into a loop filter 306, thereby producing a filtered error signal 316a, which is provided to the VCO 305 to complete the feedback loop. This technique phase locks the VCO 305 with the input frequency and provides a coherent reference 315 for the input to a mixer 308. The composite signal 311 is also passed through the first band pass filter 307, which produces the passband signal 316 containing signal from audio channel 1 101 and which is the other input to the mixer

308. The mixer 308 downconverts the passband signal 316 to the baseband. The output 317 of the mixer 308 is fed into a low pass filter 309, which reduces the spurious signals and reproduces the baseband signal of audio channel 1. The composite signal 311 is also fed through a second low pass filter 310 to filter out the pilot signal and the passband signal. The resulting output from the second low pass filter 310 is the reproduced audio channel 2 signal.

The foregoing description is of a preferred embodiment of the invention and has been presented for the purposes of illustration and as a description of the best mode of the invention currently known to the inventors. It is not intended to be exhaustive or to limit the invention to the precise form, connections, or choice of components disclosed. Obvious modifications or variations are possible and foreseeable in light of the above teachings. This embodiment of the invention was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable on of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when they are interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.