WIRELESS DIGITAL HIGH SPEED COMMUNICATIONS

Abstract: The present invention provides a high speed wireless link suitable for the transmission of high bit rate digital data over UHF and microwave frequencies, including the PCS band. Digital data is transmitted over an RF carrier wave by modulating the carrier wave using on-off keying. At the receiver end of the link, the digital data is extracted from the modulated carrier wave through the use of a novel envelope detection circuit comprised of a fast LED and an optical pulse detector. The circuitry used to build the resulting wireless link is substantially simpler in architecture than comparable wireless links, and can be easily built with commercially available components. The present invention is especially suited for providing broadband wireless access to the Internet and broadband communications with satellites.

Description: DESCRIPTION WIRELESS DIGITAL HIGH SPEED COMMUNICATIONS TECHNICAL FIELD This invention relates to a process and apparatus for wireless high speed multiplex communications. More specifically, this invention relates to wireless transmission of high speed multiplex digital data over high frequency radio waves, including (but not limited to) the PCS band or other bands within the ultra high frequency (UHF) and microwave spectrum. BACKGROUND ART With the growth of the Internet, and the increased reliance of businesses and consumers on the Internet, it has become critically important for users to have timely and reliable access the Internet, regardless of whether they have access to a wired connection. Thus there is an increasing demand for wireless access to the Internet over the electromagnetic spectrum. With the increase in the use of the Internet, the amount of data available has increased. Businesses and consumers are increasingly needing to use the Internet for real-time applications such as foil screen video. Thus the need for transmission rates higher than those available over telephone lines has correspondingly increased. This need for increased transmission speed has resulted in innovations such as T-l lines, cable modems, and fiber optic transmissions. Data transmitted at such rates is often referred to as "broadband" data. However, many applications for which the Internet will be used require mobile access to the Internet. Furthermore, many businesses and consumers work or live in buildings in which it would be prohibitively expensive to install the wiring or cables necessary for high speed transmission. For example, many businesses and homes are situated in historic buildings so that installation of wires or cables necessary for high speed transmission is virtually impossible. Thus, there is a need for high speed wireless transmission of Internet and other data (such as Intranet or private network data), especially to businesses and consumers located in buildings in which it is prohibitively expensive or impractical to install wires or cables. The high speed wireless transmission of data is often referred to with the umbrella term "broadband wireless". The electromagnetic spectrum has been allocated by government agencies (such as the Federal Communications Commission of the United States) into various frequency bands. Each band has been allocated for various usages, such as communications for military, maritime, and aircraft radio, cellular telephone networks, and commercial broadcast radio and television. Most of this electromagnetic spectrum has already been allocated for these various uses, with a large infrastructure having been built up around these uses. In general, the users of these bands have collectively invested billions of dollars in equipment for these uses. Thus there is a strong resistance to freeing up spectrum for new uses by changing the frequency allocations put forth by government agencies. One band that is still available for configuration is the band allocated for personal communications systems, commonly known by its acronym "PCS". The PCS "A" and "B" bands have been built out in the majority of markets and are primarily used for voice transmissions. The PCS "C" band includes the frequencies between 1895 to 1910 megahertz (MHz) and between 1975 to 1990 MHz. This band has been configured for voice transmission in certain limited markets. However, this PCS "C" band has not been built out in the majority of the more significant markets in the country, and therefore remains available for the option of data transmission. The smaller PCS "D", "E", and "F" bands also have not been built out in the majority of markets, and therefore also retain the option of being configured for data transmission. Thus, in the United States, these PCS bands are the last frequency bands widely available for use in transmitting digital data, although LMDS, MDS, and MMDS may soon be available. Although, as noted above, there are some existing users of the PCS band who have configured their equipment to use the PCS band for voice transmission (and, therefore, cannot reconfigure their equipment or abandon their existing voice transmission customers in order to convert to transmission of digital data), much of the PCS band retains the option of being used for data transmission in major markets: The PCS band also can be used to communicate with satellites. In other countries of the world, government authorities have allocated the electromagnetic spectrum somewhat differently. However there are still UHF and microwave frequency bands available for configuration to transmission of digital data. The technical background relevant to the present invention will be discussed next. Wireless equipment transmits signals by modulating (or modifying) "carrier" waves of a designated frequency. A variety of schemes for modulating a carrier wave are known. The easiest to implement is amplitude modulation (AM), in which the strength (amplitude) of the carrier is modulated. Other basic schemes include frequency modulation (FM), in which the frequency of the carrier wave is modulated by the signal, and phase modulation (PM), in which the phase of the carrier wave is modulated. Other, more complex methods of modulating a carrier wave are known, such as quadrature amplitude modulation (QAM). The book Communication Systems, 3rd Edition, by A. Bruce Carlson, and published by McGraw Hill in 1986 is a classic textbook on communications theory and is incorporated herein by reference. This book includes the theory of the above- described and other modulation schemes, circuitry for implementing these modulation schemes, and rigorous analysis of the performance of these modulation schemes in the presence of noise. Another good book containing circuits for implementing various modulation schemes is the ARRL Handbook for Radio Amateurs, published annually by the American Radio Relay League (ARRL). The Year 2000 edition of this book is also incorporated herein by reference. Consider AM modulation in further detail. Fig 1 depicts several waveforms. Shown is an unmodulated carrier wave 101 and a digital signal 103 that represents the binary data stream "10110100". When the unmodulated carrier wave 101 is AM modulated by the digital signal 103, the result is the AM modulated wave 105. When applied to the transmission of digital signals, AM modulation is also known as amplitude shift keying (ASK). Basically, the digital signal 103 modulates the carrier wave 101 by allowing transmission when the digital signal 103 is "high" or "digital one", and not allowing a transmission when the digital signal 103 is "low" or "digital zero". In other words, the carrier wave amplitude, or strength, is modulated, or shifted between foil strength and off. The AM modulated wave 105 is characterized by pulses (e.g. 107) occurring when a digital one or a sequence of digital ones is being transmitted between digital zeros. The "data rate" of the AM modulated signal 105 refers to how many raw bits of the digital signal 103 can be transmitted in a second. This type of AM modulation is also called on-off keying (OOK) because the carrier wave 101 is turned on or off according to the state of the digital signal 103. Circuitry for generating such AM modulated signals from digital signals is a well- known and established art. In general, such circuitry is simple and easy to implement. AM modulation can also be performed without using strict OOK, by reducing the carrier wave amplitude to a smaller value rather than turning it off. AM modulation can also be performed in a multilevel fashion rather than the above- described binary (two) level fashion, enabling multiple bits to be sent concurrently. However for a given transmission power limit, such schemes are more susceptible to noise than strict OOK. Demodulating, or extracting the digital signal wave 103, from the AM modulated wave at the receiver end of a wireless system is also a well-known and established art. A classical means is with an envelope detector. Fig 2 shows a classic envelope detector circuit 201, configured for reception of digital signals. This circuit is comprised of a diode 205, a low-pass circuit 207, and a threshold circuit 211. Also shown are an AM modulated carrier wave pulse 225, a rectified and filtered pulse 227, and an output digital pulse 229, which are used to discuss the operation of the envelope detector circuit 201. Suppose the AM modulated pulse 225 is presented to the envelope detector input 203. The diode 205 rectifies the input signal, allowing only the positive portion to pass through. The low-passing filter network 207 smoothes out the bumps caused by the carrier wave frequency. The rectified and filtered pulse 227 is what appears at point 209 of the envelope detector. The rectified and filtered pulse 227 is still essentially an analog signal. The threshold circuit 211 outputs a high or digital one when it's input is above a predetermined threshold, and outputs a low or digital zero otherwise. The design of such threshold circuits is a well-known and established art. The output of the threshold circuit 211 is the envelope detector output 213, and in this example will produce the pulse 229. Overall, it should be clear to those familiar with the art that using AM modulation to transmit digital data has the advantage that the circuitry for modulating the carrier wave 101, and extracting the digital signal 103 from the modulated carrier wave 105 is very simple. Those familiar with the art of transmitting digital data will know that circuits to perform a similar function with other modulation schemes such as PM, FM, or QAM, are significantly more complex. In general, the term "modulation" refers to the process of modifying a carrier wave with any signal to be transmitted in order to create a modulated carrier wave. A device or circuit that performs modulation is referred to as a "modulator". Likewise, the term "demodulation" refers to the process extracting the signal from the modulated carrier wave. A "demodulator" is any device or circuit that performs demodulation. Thus an "envelope detector" is considered a demodulator, and the process of "envelope detection" is considered a process of demodulation. The advantage of the envelope detector circuit 201 is that it is extremely simple to implement. The primary disadvantage is that the diode 205 must be able to handle the high frequency of the carrier wave. If the carrier frequency is in the AM broadcast band (0.535 to 1.6 MHz) or at HF frequencies (3 to 30 MHz), then a common germanium diode can be used as diode 205. Unfortunately, such germanium diodes are not appropriate for use as described above at frequencies such as PCS frequencies. There are other prior art circuits for AM demodulation that do not make use of a diode and thus do not have the data rate limitations outlined in the previous paragraph. However, these circuits are substantially more complex and difficult to implement than the envelope detector circuit 201 shown in Fig 2. The discussion will turn briefly towards two of these circuits. Fig 3 A shows a coherent AM demodulator circuit 301, configured for reception of digital data. The signal presented to input 303 is mixed (using mixer 307), or multiplied, with a local oscillator signal 309 produced by an oscillator 305. The mixer output 311 is then passed through a low pass filter 312 to erase remnants of the carrier wave. The low pass filter output is then passed through threshold circuit 313 to generate the demodulator output 315. In order for this circuit to function properly, two conditions must exist. First, the oscillator 305 must be oscillating at exactly the same frequency as that of the carrier wave used to generate the AM modulated signal. Second, the oscillator output 309 must be exactly in phase with the input carrier wave. To enforce both of these conditions in a real- world implementation requires a stable oscillator plus the use of additional phase- locking circuitry. This results in the real-world implementation of a synchronous detector being substantially more complex than that of the envelope detector 201. Fig 3B shows another AM demodulator 351 that does not require careful synchronization of an oscillator. It makes use of an oscillator 355 that is oscillating at a frequency very close to that of the carrier wave, however these two frequencies need not be exactly the same. The signal from the oscillator 355 is mixed (using mixer 359) with the signal provided at the input 353 to produce an in-phase intermediate frequency signal at point 361. At the same time, the signal from the oscillator 355 is also delayed by 90 degrees with a delay unit 357 and then mixed (using mixer 363) with the input 353 to produce a quadrature intermediate frequency signal at point 365. The in-phase signal 361 and quadrature signal 365 are squared respectively with square law units 367 and 369. The outputs of these square law units are summed (using summer 371), and the resulting sum signal is presented to a threshold circuit 373. The threshold circuit output becomes the output 375 of this demodulator circuit. The disadvantage of this circuit is that it requires complex circuitry to implement. In fact, the algorithm implemented by this circuit is better implemented as an algorithm in a digital computer or in a digital signal processor (DSP) chip. Amplitude modulation can also be used to transmit an analog signal, as is done in the 0.535 - 1.605 kHz (kilohertz) AM broadcast band. In this case, the carrier wave amplitude is modulated continuously between foil strength and off according to the signal being transmitted. Demodulation to extract the signal from the AM modulated carrier wave can be performed by any of the three circuits shown in figs 2, 3A, and 3B, with the change that the threshold circuit is removed, and optionally replaced with further low-pass filtering. For efficient usage of any wireless digital high speed communications system, it is highly desirable to allow multiple users to use the same frequency in communications, without having one user's signal interfering with another user's signal. Thus, there is a great need for multiplexing of wireless digital high speed communications. This need has led to the development of a wide variety of multiplexing schemes. For example, in time-division multiple-access (TDMA) schemes, different users take turns transmitting on the same frequency. In frequency- division multiple access (FDMA) schemes, different users transmit on different frequencies. Other more complex schemes such as code-division multiple-access (CDMA) are known. It is also desirable for any communications to be both robust and have penetration into a wide variety of locations. This led to the development of networks, which are comprised of a number of nodes interconnected by wired or wireless lines, also called "links". Nodes can be access points, where users have access to the network, and intermediary nodes, where data is routed through the network from source to destination. The network has a high degree of connectivity, allowing for many possible routes for data to be transmitted from source to destination. Such a network has robustness in that if one of the intermediary nodes on a route becomes inoperable during a transmission, other nodes are able to take over and provide a new route from source to destination. The need for multiple users to have robust digital communications over a single, shared network had led to the development of protocols such as the "TCP/IP" protocol. The TCP/IP protocol is the protocol used for communications in the Internet. In this protocol, data is broken into discrete packets using a process called "packetizing". Each of the packets is given a label that contains the address of the destination to which the packet is being sent. The packets are then sent through the network and reassembled at their destination. In this protocol, different packets can be sent via different routes if one or more links or nodes becomes overloaded or inoperable. The generation and implementation of networking, packetizing, and multiple access protocols is an established and well-known art. The interested reader is referred to the book An Engineering Approach to Computer Networking, by Srinivasan Keshav, and published by Addison- Wesley in 1997. This book is incorporated herein by reference. For many years, scientists and engineers have sought to create optical circuits, including optical networks and optical computers, because of the great speed with which optical signals can be processed. A substantial amount of research has been directed to creating optical circuits in order to avoid the relative slowness of RF and electronics technologies, with an emphasis on creating completely optical circuits. Two products of this research are "fast LEDs (light emitting diodes)" and "optical pulse detectors". Fast LEDs are LEDs that were engineered to have extremely short switching times, and thus can generate high speed light pulses from high speed electronic pulses. Optical pulse detectors are opto-electronic devices that generate high speed electronic pulses from high speed light pulses. These two devices are typically used in electronic interfaces to and from the above mentioned optical circuits. It is, therefore, an object of this invention to provide a process and apparatus for wireless digital high speed communications allowing high speed wireless communications of digital data. It is a further object of this invention to provide such a process and apparatus that uses readily available components and is easy and economical to manufacture. It is a still further object of this invention to provide such a process and apparatus for wireless digital high speed multiplex communications allowing high speed wireless multiplex communications of digital data. It is a still further object of this invention to provide such a process and apparatus that allows wireless digital high speed communications directly with satellites. It is a still further object of the present invention to provide a process and apparatus that allows multiple users to use the same frequency for data transmission without any interference with each other's data. It is a still further object of the present invention to provide a process and apparatus that allows the demodulation of carrier waves modulated with broadband data. It is a still further object of the present invention to provide a process and apparatus for extracting signals from a modulated carrier wave. DISCLOSURE OF INVENTION This invention provides a high speed link for transmitting digital data comprising: a transmitter, with the transmitter creating a modulated carrier wave fiOm the digital data; an RF front end, with the RF front end creating an intermediate signal from the modulated carrier wave; an LED circuit, with the LED circuit creating optical pulses from the intermediate signal; and an optical pulse detector, with the optical pulse detector extracting the digital data from the optical pulses. BRIEF DESCRIPTION OF DRAWINGS Fig 1 shows several waveforms used in the discussion of AM modulation. Fig 2 shows an envelope detector circuit and it's operation. Figs 3 A and 3B show two alternative circuits that implement demodulation of AM signals. Fig 4A shows the first preferred embodiment of the present invention. Fig 4B shows a heterodyne circuit. Fig 5 shows the second preferred embodiment of the present invention. Fig 6 shows an alternative optical pulse detector. BEST MODES FOR CARRYING OUT THE INVENTION DESCRIPTION OF THE FIRST PREFERRED EMBODIMENT Fig 4A depicts a high speed wireless link 401, which comprises the first embodiment of the present invention. This link 401 is comprised of an AM transmitter 403, a transmitting antenna 405, a receiving antenna 407, an RF front-end 409, a fast LED circuit 411, and an optical pulse detector 413. Also shown in the figure, for purposes of discussion, are a source digital signal 421, an AM modulated carrier wave 423, an electromagnetic signal 425, two possible intermediate signals 427 and 428, an optical pulse signal 429, and an output digital signal 431. The AM transmitter 403 and transmitting antenna 405 comprise the transmitter section 415 of the link. The AM transmitter 403 takes as input a digital signal 421 and generates an AM modulated carrier wave 423. The AM modulated carrier wave 423 is transmitted as an electromagnetic wave 425 by the transmitting antenna 405. The AM transmitter can be any standard system that generates an AM modulated carrier wave, via on-off keying (OOK) or amplitude shift keying (or any other technology), that is of sufficient power to be transmitted the distance between the transmitter antem a 405 and receiver antenna 407. The construction of such a transmitter section is an established and known art. The receiving antenna 407, RF front end 409, fast LED circuit 411, and optical pulse detector 413 comprise the receiver section 417. The receiving antemia 407 intercepts the electromagnetic wave 425 and provides input to the RF front-end 409. The RF front-end 409 generates an intermediate signal. The RF front-end 409 can simply be comprised of an amplifier with a band-pass filter (not shown). In this case, signal 427. depicts the intermediate signal, and the carrier frequency of the intermediate signal is the same as that of the AM modulated carrier wave 423. The RF front-end can instead be a single-stage heterodyne circuit comprised of a bandpass filter, a local oscillator, a mixer, an intermediate frequency bandpass filter, and optionally one or more stages of amplification in the configuration typically found in the art of basic radio circuitry (not shown). Fig 4B shows one possible heterodyne circuit 451 that can implement the RF front end 409. The signal at the input 453 is first filtered using bandpass filter 455. The filtered signal is mixed, using a mixer 459, with the signal generated by a local oscillator 457. The mixer output 461 is then filtered using a second bandpass filter 463, and amplified using an amplifier 465. The amplifier output forms the heterodyne circuit output 467. Careful selection of the two bandpass filters 455 and 463, and selection of the local oscillator 457 frequency, ensures that the correct modulated carrier wave is selected and other RF signals are rejected. In this latter case in which a heterodyne circuit is used, signal 428 depicts the intermediate signal. Furthermore, the carrier frequency of the intermediate signal is called the "intermediate frequency" and is different from that provided by the AM transmitter 403. Note that theoretically, intermediate signal 428 itself can be considered an AM modulated carrier wave with its own carrier frequency. The intermediate signal is then provided to the LED circuit 411. If the intermediate signal (427 or 428, as appropriate) is of sufficient strength, then the LED circuit 411 can be comprised of a fast LED, which is directly driven by the intermediate signal. Otherwise, the LED circuit 411 is comprised of an amplifier circuit and a fast LED. The LED circuit 411 generates optical pulses 429 from the intermediate signal. The optical pulse detector 413 receives the optical pulses 429 and generates the received digital signal 431, which is a reconstructed version of the original digital signal 421. The optical pulse detector output 414 is the output of the wireless link 401. The key distinction between the present invention and the prior art is in the use of the LED circuit and the optical pulse detector for envelope detection. Recall from the discussion on Fig 2 that envelope detection is typically performed with an envelope detector circuit 201, which uses a diode 205 to rectify the input signal. The diode 205 and low-pass filter 207 together produce a rectified, filtered version of the input signal at point 209, which is then converted to a digital signal by the threshold circuit 211. This is a different process from the present invention, where the rectification is performed by the fast LED in the LED circuit 411, and the output digital signal is produced by the optical pulse detector 413. There are two main advantages to using the LED circuit 411 and optical pulse detector 413 combination of the present invention. First, fast LEDs are readily available that function at the high frequencies commonly used in UHF and microwave receiving systems, such as that used in the PCS bands. Second, optical pulse detectors are readily available that convert optical pulses into digital signals compatible with standard electronic equipment. Thus, readily available components are available to implement a simple, inexpensive AM demodulator for reception of high speed wireless digital signals. The overall result is that the entire receiver section 417 can be implemented at a relatively low cost, compared to that of equivalent receiver sections used to receive digital PM- or FM- modulated carrier waves. It should be noted that this first preferred embodiment can be used to implement a wide variety of wireless links, including fixed-location to fixed- location, fixed-location to mobile, mobile to mobile, and fixed-location or mobile to satellite. It also shall be understood that even though the above description of the first preferred embodiment specifies the use of AM modulation, it does not limit the present invention to AM modulation schemes. Likewise, it shall be understood that the present invention is not limited to using an AM transmitter. The system can be configured to use other modulation schemes, and still be within the scope of the spirit of the invention. For example, if the RF front end 409 is implemented with heterodyne circuit 451, and if bandpass filter 463 is chosen so that its cutoff frequency is near the generated intermediate frequency, then FM modulation can be used instead of AM modulation. The above discussion specifies the use of AM modulation, and more specifically OOK modulation, because this is believed to be the best known mode of carrying out the invention. DESCRIPTION OF SECOND PREFERRED EMBODIMENT Recall from above that the need for a robust communication system between multiple points, with provisions for multiple users to have simultaneous access to the system, has led to the development of networking protocols such as TCP/IP. Recall that in this protocol, data is packetized into discrete packets, and each of the packets is given a label that contains the address of the destination to which the packet is being sent. The packets are then each sent through the network and reassembled at their destination. The present invention can be incorporated into a communications system that uses such protocols, including the Internet. The present invention is especially suited for providing "last mile" wireless access to the network. The present invention used in this manner comprises the second preferred embodiment. Please refer to Fig 5, which depicts how the present invention can be used to provide "last mile" interface to a network. Fig 5 depicts a "user" or data source 501, digital data 502 that is contained within the source 501, digital packets 503, a network 505, a network access point 507 connected to the source 501, and a second network access point 509. These parts are all part of the communications network 511 to which the second preferred embodiment is attached. There can be additional users and/or data sources (not shown) able to provide data to the network. Also depicted is the second preferred embodiment 521, which is comprised of a transmitter 523, a receiver 525, and a destination device 527. The transmitter 523 could be physically located on a tower for improved transmission to it's intended reception area. There can be more than one receiver and destination. Fig 5 shows one additional receiver 529 and destination 531. Likewise, even though there is only one "second network access" shown, there can be more (not shown) to provide network access to a large number of users. The entire network 511, including the second preferred embodiment 521, functions as follows: The source 501 contains a large amount of data 502 to be sent. This data is packetized into packets 503. For purposes of discussion, it is assumed that the source 501 contains circuitry and/or algorithms for packetizing the data 502 into packets 503. The implementation of such circuits and/or algorithms is an established art. As described above, each packet contains data to be send as well as a label describing the packet destination. These packets 503 are sent into the network via the network access point 507. Using standard routing protocols, the packets 503 are routed to the appropriate destination. The packets 503 are sent to the second access point 509 because this is the access point ultimately connected to the destination(s) 527 (and 531). The second access point 509 receives the packets 503 and wirelessly transmits them with the transmitter 523. This transmitter 523 is comprised of the transmitter section 415 from the first preferred embodiment. The packets are sent wirelessly over an electromagnetic wave 524 to the receiver 525. This receiver 525 is comprised of the receiver section 417 from the first preferred embodiment. The digital packets 503 are then sent to the destination 527. This destination 527 could be a laptop computer or a personal digital assistant that is being granted access to the network via the second preferred embodiment. For purposes of this discussion, destination 527 includes circuitry and algorithms to receive the packets addressed to it, to extract the digital portion of the packets 503, and to reconstruct the original digital data 502. The implementation of such circuitry and algorithms are a known and established art. This digital data 502 is then made available to the end user. In the above discussion, data transmission was discussed only in the direction from the source 501 to the destination 527. For most practical cases (as of the time of writing) this is sufficient because when accessing the Internet there is typically a greater need for downloading at a high data rate (as shown in Fig 5) than for uploading at a high data rate. Data transmission in the reverse direction can be additionally performed in the reverse direction using essentially the same techniques. The necessary modifications will be clear to those familiar with the art. In summary, the first modification is that the destination 527 additionally provides the data to be sent, and has circuitry and or algorithms for packetizing data. The second modification is that there is an additional wireless link 540, comprised of an additional transmitter section 541 (connected to device 527) and an additional receiver section 543 (connected to access node 509). This wireless link provides access to the network in the opposite direction, i.e. from device 527 to access node 509. The third modification is that transmissions in the two directions have to be configured and/or coordinated to allow data to be sent both directions simultaneously ("duplex"). This is easily accomplished with well known circuitry and/or algorithms that implement multiplexing schemes such as FDMA, TDMA, or CDMA. The fourth modification is that the original "source" 501 additionally includes circuitry and/or algorithms for selecting the packets addressed to it and reconstructing the sent data. This second preferred embodiment is considered within the scope of the present invention whether it is configured for only downloading data or only uploading data (i.e "one-way" or "one directional" link), or both downloading and uploading data (i.e. "two-way" or "two directional" link). The significance of this preferred embodiment is that it could allow wireless access to the Internet, when the Internet is the network 505 depicted in Fig 5. The wireless access provided by the second preferred embodiment 521 could be implemented over the above-described PCS spectrum, whose sub-bands C, D, E, and F are available for configuration to data transmission using the present invention. Given that the implementation of the wireless link provided by the present invention is easy to implement using off-the-shelf components, and given that circuitry and algorithms for implementing the TCP/IP protocol are readily available, a system providing broadband wireless access to the Internet can be quickly built out in the appropriate PCS bands. ALTERNATIVE EMBODIMENTS The above discussion describes just two of many different embodiments of the present invention. Next is a discussion of a number of different variations or embodiments that can be produced. Many of the following variations are "orthogonal", i.e. more than one variation can be utilized at the same time to create yet more embodiments. These variations are discussed below: Variation 1: Wired transmission of AM modulated carrier wave: In this variation, the transmitter antenna 405 and receiver antenna 407 are replaced by a connector such as a cable, a conductor, or even a waveguide, so that the output of the AM transmitter 403 is connected directly to the input of the RF front-end 409. This connector shall be referred to as a "wired connector", even when a waveguide is used, and this variation shall be referred to as providing a "wired connection" or a "wired link". In this case, the output of the AM transmitter 403 is applied directly to the RF front-end 409 (via the wired connector). The remainder of this variation functions exactly the same as in the preferred embodiment. This variation can be useful where a wired connection is practical, and where group delay within the wired connector does not degrade the signal enough to prevent operation. Variation 2: Use of light sources other than fast LEDs in the LED circuit 411: The LED circuit 411 need not specifically use a fast LED. For example, if the carrier wave is sufficiently slow in frequency, then a regular LED can be used. Likewise, any other device that generates light from electricity can is a candidate device, subject to the electrical and physical limitations of the particular device. For example, a circuit comprised of a laser diode may be usable in some circumstances. Even though the preferred embodiment specifies the use of a fast LED in the LED circuit 411, it shall be understood that the replacement of the fast LED with any device that generates light from electricity will result in an alternative embodiment that falls within the scope of the present invention. Variation 3: Variations in the optical pulse detector 413: Rather than a commercially available optical pulse detector, any circuit with a similar function can be used. For example, refer to Fig 6, which depicts an alternative optical pulse detector circuit implemented with standard electronic components. A photodiode 603 (or alternately a phototransistor) receives optical pulses 429 and conducts a current proportional to the instantaneous light intensity. A careful choice of value for resistor 605 maximizes the voltage swing across photodiode 603 for a given intensity of the optical pulses 429 and of any ambient light. Resistor 607 and capacitor 609 implement a low-pass filter for noise cancellation. These two components are optional, or could be rearranged to form a high-pass filter. A threshold circuit 611 receives the filtered signal and generates a digital output 613. Those familiar with the art will conceive other circuits that perform the same function. Even though the preferred embodiment refers to commercially available optical pulse detectors, it shall be understood that any means of converting optical pulses into electronic or digital pulses is considered an "optical pulse detector". Variation 4: Physical separation between LED circuit and optical pulse detector: In this subtle variation, the LED circuit 411 and the optical pulse detector 413 can be physically placed in different locations. For example, the receiver antenna 407, the RF front-end 409, and the LED circuit 411 can be located on the ceiling of a room, and the optical pulse detector 413 can be located in a mobile device, such as a laptop computer or a PDA (personal digital assistant). The transmitter section 415 would be located, perhaps, several kilometers away. With such a configuration, the mobile device is able to receive the transmitted high speed digital data but with a minimal amount of wireless circuitry incorporated in the mobile device itself. A further variation can be had by allowing for multiple mobile devices, each with it's own optical pulse detector, and each able to receive the optical pulses (e.g. all in "the same room"). In this latter case, all the mobile devices would have the ability to receive the same transmitted data. Variation 5: The above-described second preferred embodiment was presented as a means of providing "last mile" access to a communications network such as the Internet. It should be noted that the wireless link afforded by the second preferred embodiment for the transmission of packetized data can be used elsewhere in the network. Essentially every link, whether wired or wireless, is a candidate for application of the data transmission system described in the first and second preferred embodiments. Such variations shall be considered within the scope of the present invention. Variation 6: Use in other modulation schemes: As described at the bottom of the first preferred embodiment section, modulation schemes other than AM modulation can be used. Variation 7: Novel demodulator circuit or device: As described above, the key distinction between the present invention and the prior art is the use of the LED circuit 411 and the optical pulse detector 413 for extracting the signal from the modulated carrier wave.. The use of these components in this manner for demodulation is what enables the reception of high speed digital data via modulated carrier waves. If the optical pulse detector has a continuous response rather than a threshold response, then this combination can be used to demodulate a carrier wave that was modulated by any signal, analog or digital. Such a continuous response optical pulse detector can be implemented with the circuit 601 of Fig 6, modified by deleting the threshold device. It should also be noted that such demodulators could potentially be mass produced in a single package or even as part of an RF integrated circuit. These combinations used as envelope detectors or as AM demodulators have not been encountered in the prior art. Therefore, the use of an LED circuit 411 and an optical pulse detector 413 (whether having a threshold response or a continuous response) for the demodulation of signals, for envelope detection, or for extracting signals transmitted in a modulated carrier wave, shall all be understood as within the scope of the present invention. Furthermore, any device or integrated circuit comprising an LED circuit 411 and an optical pulse detector 413, when used for extracting signals from a modulated carrier wave, shall be considered within the scope of the present invention. Variation 8: The novel envelope detector just described can be incorporated in a receiver, including any AM receiver. An example of such a receiver is the receiver section 417 of the first preferred embodiment. Such a receiver is novel in that it makes use of the just-described novel demodulator for demodulation. Any receiver utilizing the novel demodulator for demodulation of a carrier wave shall be considered within the scope of the present invention. The above-described embodiments and variations are illustrative of the principles of the present invention. Other embodiments could be devised by those skilled in the art without departing from the spirit and scope of the present invention. INDUSTRIAL APPLICABILITY The present invention can be used for applications requiring a high speed wireless link.

Claims: CLAIMS What is claimed is: 1. A high speed link for transmitting digital data comprising: a transmitter, said transmitter creating a modulated carrier wave from said digital data; an RF front end, said RF front end creating an intermediate signal from said modulated carrier wave; an LED circuit, said LED circuit creating optical pulses from said intermediate signal; and an optical pulse detector, said optical pulse detector extracting said digital data from said optical pulses. 2. The link of claim 1 wherein said transmitter is an AM transmitter. 3. The link of claim 1 wherein said LED circuit is comprised of an LED. 4. The link of claim 2 wherein said LED circuit is comprised of an LED. 5. A process for transmitting digital data comprising the steps: (a) modulating a carrier wave with said digital data to produce a modulated carrier wave; (b) a step for processing said modulated carrier wave to produce an intermediate signal; (c) generating optical pulses from said intermediate signal; (d) reconstructing said digital data from said optical pulses. 6. The process of claim 5 wherein step (a) comprises AM modulating a carrier wave with said digital data to produce a modulated carrier wave. 7. The process of claim 5 wherein step (c) comprises providing said intermediate signal to an LED circuit to generate optical pulses. 8. The process of claim 5 wherein step (d) comprises using an optical pulse detector to reconstruct said digital data from said optical pulses. 9. The process of claim 7 wherein step (d) comprises using an optical pulse detector to reconstruct said digital data from said optical pulses. 10. A high speed link for transmitting packetized digital data comprising: a transmitter, said transmitter creating a modulated carrier wave from said packetized digital data; an RF front end, said RF front end creating an intermediate signal from said modulated carrier wave; an LED circuit, said LED circuit creating optical pulses from said intermediate signal; and an optical pulse detector, said optical pulse detector extracting said packetized digital data from said optical pulses. 11. The link of claim 10 wherein said transmitter is an AM transmitter. 12. The link of claim 10 wherein said LED circuit is comprised of an LED. 13. The link of claim 11 wherein said LED circuit is comprised of an LED. 14. A process for transmitting packetized digital data comprising the steps: (a) modulating a carrier wave with said packetized digital data to produce a modulated carrier wave; (b) a step for processing said modulated carrier wave to produce an intermediate signal; (c) generating optical pulses from said intermediate signal; (d) reconstructing said packetized digital data from said optical pulses. 15. The process of claim 14 wherein step (a) comprises AM modulating a carrier wave with said digital data to produce a modulated carrier wave. 16. The process of claim 14 wherein step (c) comprises providing said intermediate signal to an LED circuit to generate optical pulses. 17. The process of claim 14 wherein step (d) comprises using an optical pulse detector to reconstruct said digital data from said optical pulses. 18. The process of claim 16 wherein step (d) comprises using an optical pulse detector to reconstruct said digital data from said optical pulses. 19. A high speed link for transmitting packetized digital data comprising: means for creating a modulated carrier wave from said packetized digital data; means for creating optical pulses from said modulated carrier wave; and means for extracting said packetized digital data from said optical pulses. 20. The link of claim 19 wherein said means for creating optical pulses is comprised of an LED circuit. 21. The link of claim 19 wherein said means for extracting said packetized digital data is comprised of an optical pulse detector. 22. The link of claim 20 wherein said means for extracting said packetized digital data is comprised of an optical pulse detector. 23. A device for extracting a signal contained in a modulated carrier wave comprising: an LED circuit, said LED circuit creating optical pulses from said modulated carrier wave; and an optical pulse detector, said optical pulse detector producing said signal contained in said modulated carrier wave. 24. A process for demodulating a modulated carrier wave to extract a signal contained in said modulated carrier wave, comprising the steps: (a) generating optical pulses from said modulated carrier wave; and (b) reconstructing said signal from said optical pulses. 25. A process for using an LED circuit and an optical pulse detector for extracting signals from a modulated earner wave. 26. The process of claim 25 wherein said signals are digital signals. 27. The process of claim 26 wherein said digital signals are packetized digital signals.

Inventors: BARROWS GEOFFREY L, CHANTAVY BOONTHAI, MALINA JOSEPH K, BARROWS, GEOFFREY, L., CHANTAVY, BOONTHAI, MALINA, JOSEPH, K.
Applicants: BARROWS GEOFFREY L, CHANTAVY BOONTHAI, MALINA JOSEPH K, NETLESS WEB WIRELESS INC, BARROWS, GEOFFREY, L., CHANTAVY, BOONTHAI, MALINA, JOSEPH, K., NETLESS WEB WIRELESS, INC.
Application year: 2001
Main classification: H04B10
IPC codes: H03D1, H04B10, H04L27