TRANSCEIVER WITH LOCAL OSCILLATOR FREQUENCY SETTINGS USING THE DEMODULATED BIT RATE

Abstract: A communication system extracts a received modulation frequency from baseband modulation. This frequency is used as a reference to control the output of a variable oscillator. The output of the variable oscillator may be used to generate a transmit upconversion frequency, and may also be used to perform a downconversion from IF to baseband during receive operations.

Description: TRANSCEIVER WITH LOCAL OSCILLATOR FREQUENCY SETTINGS USING THE DEMODULATED BIT RATE Background of the Invention Field of the Invention The invention relates to wireless communication, specifically to retrieving frequency information from a received wireless transmission. Description of the Related Art Wireless communication has become one of the most common ways of transmitting information from one place to another. The application of wireless communication links to telephone systems, local area computer networks, and wide area computer networks such as the Internet is widespread, and a large number of commercial manufacturers supply wireless communication equipment to these markets. Some fundamental principles of a conventional wireless communication technique are illustrated in Figure 1. In some forms of wireless communication, a baseband signal 10, which encodes a selected message, is combined with a high frequency sine wave carrier signal in an upconverter 14 In FM transmission, for example, the frequency of the carrier signal is altered in a way defined by the content of the baseband message signal 10. The modulated carrier 16 is then transmitted, and is received bγ a downconverter circuit 18 at the appropriate message destination. Both the upconverter 14 and the downconvertor 18 have reference frequency signals 12, 20 as inputs to perform the upconversion and downconversion processes. In some cases, the baseband message signal 22 produced by the downconverter 18 is a reproduction of the original message signal 10, but this need not be the case, as long as the message content is decodable from the downconverter 18 output. In a broadcast system, such as broadcast television, only a central station will include circuitry for signal transmission However, for two-way communication between, for example, a central hub and a number of remote units, the hub and the remote units will all include both downconversion circuitry for receive operations, and upconversion circuitry for transmit operations. In this case the remote units must also generate an upconversion reference frequency for message transmission to the hub, although for two way communication, the carrier frequencies may differ depending on message direction. In a large number of communication systems such as the one shown in Figure 1, it is important that the frequency of the upconversion reference signal 12 and the frequency of the downconversion reference signal 20 be consistently and accurately related to one another to produce an easily interpreted downconverter output 22 and to allow optimal use of the allocated frequency In addition, government regulatory agencies require the frequency of the carrier signal used for transmission to be equal to a specific assigned frequency within a very tight tolerance. These goals are sometimes achieved by installing highly accurate and stable oscillators at both ends of the link to generate the reference signals 12, 20 at the link ends One example of such a system for two-way communication is illustrated in Figure 2. In this system, a signal received bγ a satellite dish 23 is downcoπverted by a series of two mixers 24a, 24b. The first mixer 24a may reside in an outdoor mounted unit 26, and downconverts the center frequency of the received signal to an intermediate frequency (IF). The second mixer 24b may reside in an indoor mounted unit 28, and downconverts the IF signal to a modulated baseband output which is sampled by an analog to digital converter 30. The output of the analog to digital converter 30 is routed to digital processing circuitry to demodulate the baseband signal and reproduce the bits which comprise the received data. During the transmit process, the output of a signal generator 32 is upconverted by another pair of mixers 33a, 34b, the first one of which may be housed in the indoor unit 28, and the second one of which may be housed in another outdoor unit 34. The mixers each receive a reference frequency signal from an associated phase-locked-loop (PLL) 36a, 36b, 36c, 36d. Each PLL in turn receives a reference frequency from an oscillator 37 from which it derives its output frequency. A controller 38 is coupled to the PLLs for digitally setting internal loop dividers so that each PLL can output a different frequency signal even though they all receive a common reference frequency from the oscillator 37. In this type of system, the oscillator 37 is free running, and should be as accurate and stable as possible over time, with temperature variations, etc. Typically, free running oscillators of sufficient quality to serve this function are among the most expensive components of the system. In addition, even with a high quality oscillator, some offset from an ideal reference frequency is present. In some systems, these offsets may be detected bγ analyzing the characteristics of the baseband receive signal during bit decoding. Deviation from 0 Hz center frequency in the baseband signal is measured, and is attributed to an offset from an ideal output of the oscillator 37. Once this offset is quantified during receive operations, the loop dividers in the transmit PLLs 36b, 36c can be updated to make these PLL outputs accurate even in the presence of the detected oscillator 37 offsets. In some systems, one end of a two-way communication link can generate appropriate reference frequencies directly from a modulated carrier signal received from the other end of the link. However, the circuitry required to extract a stable reference frequency from a received modulated carrier is also expensive. Thus, less expensive techniques for generating these reference frequencies are needed as wireless communication expands into more widespread use. Summary of the Invention The invention comprises methods and apparatus for frequency generation in communication systems. In one embodiment, a communication device according to the invention comprises upconversion circuitry, downconversion circuitry, and a reference frequency generator. In this embodiment, the reference frequency generator is coupled between an output of the downconversion circuitry and the upconversion circuitry. The reference frequency generator may comprise a voltage controlled oscillator and a phase comparator. Methods of generating an upconversion frequency signal for a transmitter are also provided. In a wireless communication apparatus comprising a transmitter and a receiver, such a method maγ comprise extracting a modulation frequency from a signal received bγ the receiver, and deriving the transmit upconversion frequencγ from the modulation frequencγ Brief Description of the Drawings FIG. 1 is a block diagram of a communication channel. FIG. 2 is a block diagram of one end of a two-waγ wireless communication link. FIG. 3 is a block diagram of a communication channel including a reference frequencγ generation loop. FIG. 4 is a schematic/block diagram of a multiple access wireless communication sγstem in which the invention finds advantageous application. FIG. 5 is a schematic/block diagram of wireless reception and transmission circuitry according to one embodiment of the invention which maγ be provided in one of the remote units of Figure 4. FIG. 6 is a flowchart of a method of reference frequency generation according to one embodiment of the invention. Detailed Description of the Preferred Embodiment Embodiments of the invention will now be described with reference to the accompanγmg Figures, wherein like numerals refer to like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in anγ limited or restrictive manner, simply because it is being utilized in conjunction with a detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention maγ include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the inventions herein described. Figure 3 illustrates portions of transmit and receive circuitry in a unit of a two way wireless communication system. When the unit is receiving, an inbound modulated carrier signal 39 is received bγ a downconverter circuit 40 which produces an inbound baseband information signal 42. When the unit is transmitting, an outbound baseband information signal 43 is fed to an upconverter 44 which produces an outbound modulated carrier 46. In addition, a frequencγ generator 47 is provided that has a stable and accurate frequencγ signal output 48. In this embodiment, this stable frequencγ signal is routed to the upconverter 44, where it can be used to generate an accurate carrier signal. In addition, the output 48 of the reference frequencγ generator 47 is routed to the downconverter 44, where it can be used to generate the required reference frequencγ or frequencies for downconversion. In this embodiment of the invention, the reference frequencγ generator 47 uses the inbound baseband information signal as an input at line 49. Thus, the baseband signal being received is used as a source of an accurate and stable frequencγ reference. This is possible because even though the fixed frequencγ carrier has been removed, the baseband signal is still modulated in a manner which is in part defined bγ the rate at which data is being received. This rate is fixed to high accuracγ when the carrier was originally modulated bγ the transmitting sγstem. A wide vaπetγ of carrier modulation schemes are known and used. In general, data bits are encoded as, for example, carrier phase shifts, frequencγ shifts, amplitude shifts, or combinations thereof, and the modulation frequeπcγ maγ be extracted from the baseband signal. In " ary" modulation schemes, a selected phase, frequency, and amplitude state of the carrier may constitute an encoding of 2, 4, or even 6 or more bits. In any carrier modulation scheme, however, the received baseband signal will incorporate a modulation frequencγ which is related to the incoming data rate. In some cases, the modulation frequencγ will correspond with the "sγmbol frequencγ", wherein the sγmbols are the one or more bits encoded as defined phase, frequencγ, and/or amplitude states of the carrier. In many systems, the modulation frequencγ is accuratelγ fixed and stable at some rate between, for example, 1 and 30 MHz, but other frequencies maγ be used. This modulation frequencγ comprises a source of incoming timing information that maγ be advantageouslγ utilized to generate a reference frequencγ for transmit upconversion as well as downconversion reference frequencies. Figure 4 is a block diagram illustrating an exemplifying system in which the invention maγ be embodied. The sγstem in Figure 4 provides high-speed, reliable Internet communication service over a satellite link. In particular, in Figure 4, content servers 50 are coupled to the Internet 52 which is in turn coupled to a hub station 54 such that the hub station 54 can request and receive digital data from the content servers 50. The hub station 54 also communicates via satellite 56 with a plurality of remote units 58A - 58N. For example, the hub station 54 transmits signals over a forward uplink 60 to the satellite 56. The satellite 56 receives the signals from the forward uplink 60 and re transmits them on a forward downlink 62. Together, the forward uplink 60 and the forward downlink 62 are referred to as the forward link. The remote units 58A - 58N monitor one or more channels which comprise the forward link in order to receive remote-uπit-specif ic and broadcast messages from the hub station 54. In a similar manner, the remote units 58A - 58N transmit signals over a reverse uplink 64 to the satellite 56. The satellite 56 receives the signals from the reverse uplink 64 and re-transmits them on a reverse downlink 66. Together, the reverse uplink 64 and the reverse downlink 66 are referred to as the reverse link. The hub station 54 monitors one or more channels which comprise the reverse link in order to extract messages from the remote units 58A - 58N. In one embodiment of the exemplifying system, each remote unit 58A -58N is coupled to a plurality of system users. For example, in Figure 3, the remote unit 58A is shown as coupled to a local area network 67 which in turn is coupled to a group of user terminals 68A - 68N. The user terminals 68A 68N maγ be one of manγ tγpes of local area network nodes such as a personal or network computer, a printer, digital meter reading equipment or the like. When a message is received over the forward link intended for one of the user terminals 68A - 68N, the remote unit 58A forwards it to the appropriate user terminal 68 over the local area network 67. Likewise, the user terminals 68A - 68N can transmit messages to the remote unit 58A over the local area network 67. In one embodiment of the exemplifying sγstem, the remote units 58A - 58N provide access to the Internet for a plurality of users. For example, assume that the user terminal 68A is a personal computer which executes browser software in order to access the World Wide Web When the browser receives a request for a web page or embedded object from the user, the user terminal 68A creates a request message according to well-known techniques. The user terminal 68A forwards the request message over the local area network 67 to the remote unit 58A, also using well-known techniques. Based upon the request message, the remote unit 58A creates and transmits a wireless link request over a channel within the reverse uplink 64 and the reverse downlink 66. The hub station 54 receives the wireless link request over the reverse link. Based upon the wireless link request, the hub station 54 passes a request message to the appropriate content server 50 over the Internet 52. In response, the content server 50 forwards the requested page or object to the hub station 54 over the Internet 52. The hub station 54 receives the requested page or object and creates a wireless link response. The hub station transmits the wireless link response over a channel within the forward uplink 60 and forward downlink 62. The remote unit 58A receives the wireless link response and forwards a corresponding response message to the user terminal 68A over the local area network 67. In this waγ, a bi-directional link between the user terminal 68A and the content servers 50 is established. The frequencγ generation of the invention is advantageouslγ incorporated into one or more of the remote units 58A 58N of Figure 4. This embodiment of a remote unit is illustrated in more detail in Figure 5. Referring now to this Figure, the circuitry used for the wireless receive and transmit functions are housed in separate units, one or more of which are provided outdoors, known as "outdoor units" 72, 74, and one or more of which are provided indoors, known as "indoor units" 90. A satellite dish 70 is used to transmit and receive signals via a satellite transponder. The satellite dish is coupled to transmit and receive circuitry which is located in close proximity to the satellite dish 70 In one embodiment, the satellite dish 70 is located on the roof of a building and outdoor units 72, 74 are mounted directly to the satellite dish 70 assemblγ on the exterior of the building. A receive outdoor unit 74 comprises a low noise amplifier 76 and downconvertiπg mixer 78 which are located in close proximity to the satellite dish 70. This helps reduce the path loss from the satellite dish 70 to the amplifier 76 and preserves the system noise figure. A transmit outdoor unit 72 comprises an upconverting mixer 82 and power amplifier 84 which are also located in close proximity to the satellite dish 70 in order to reduce the path loss between the power amplifier 84 and the satellite dish 70 and avoid increasing the required output of the power amplifier 84. The system further includes an indoor unit 90 comprising circuitry which need not be located in close proximity to the satellite dish 70. In one embodiment, the indoor unit is located at a convenient position which allows more ready access by the sγstem administrator The indoor unit 90 is connected to the outdoor units 72, 74 bγ cabling 92. Although not necessarγ to the practice of the invention, the division of the communication unit into outdoor units 72, 74 and an indoor unit 90 allows them to be separately manufactured and factory tested. For example, the outdoor units 72, 74 are preferably manufactured bγ an RF design house. The indoor unit 90 is preferablγ manufactured bγ a companγ which specializes in communications. In one embodiment, the indoor unit 90 is designed to be compatible with a variety of different outdoor units which operate at a vaπetγ of different frequencies and which are manufactured bγ a variety of different vendors When in place in the field, the outdoor units 72, 74 and indoor unit 90 can be separately serviced, replaced or upgraded In other embodiments, one or more outdoor units maγ house more functionality than that illustrated in Figure 5. The satellite dish 70 is coupled to an orthomode transducer (OMT) 92 or other device for providing separation of the transmit and receive signal energy. The OMT 92 couples the receive signals from the satellite dish 70 to the low noise amplifier 76. The OMT 92 also couples transmit signals from the power amplifier 84 to the satellite dish 70. As described briefly above, the low noise amplifier 76 is coupled to a mixer 78 which downconverts the received signal to an intermediate frequencγ. The output of the mixer 78 is coupled to the indoor unit 90 via the cable 92. Within the indoor unit 90, receive signal processing is performed which is described further below. A controller 96 in the indoor unit provides control over indoor and outdoor transmit and receive circuits. During the transmit process, under the control of the controller 96, a signal generator 98 receives digital data from sγstem users and encodes the data for transmission. The signal generator 98 also generates a modulated baseband message signal. This baseband signal is mixed with an IF signal bγ a mixer 100, and the modulated IF output signal from the mixer 100 is coupled to a variable gam amplifier 102. The gain of the variable gain amplifier 102 is controlled bγ the controller 96 The output IF signal from the variable gain amplifier 96 is passed over the cable 92 to the outdoor unit 72. Within the outdoor unit 72, the mixer 82 upconverts the IF signal to a RF frequencγ suitable for transmission. For example, in one embodiment, the RF center frequencγ is within the Ku band, Ka band or anγ other suitable band. The output of the mixer 82 is input into the power amplifier 84. The power amplifier 84 maγ, for example, comprise a Class A amplifier. When enabled, the power amplifier 84 outputs a high power RF signal to the satellite dish 70 via the OMT 92. In manγ applications, the modulated carrier received bγ the satellite dish has a center frequencγ of 10-12 GHz. This is downconverted to produce an approximately 1 GHz intermediate frequencγ (IF) signal bγ combining the 10-12 GHz input signal with an approximately 9 11 GHz reference signal generated by a free-running oscillator 144 and bγ filtering with a lowpass or bandpass filter 108. The IF signal is further downconverted to a baseband signal (nominally 0 Hz center frequencγ) bγ a second mixer 110 and is further filtered with low pass filter 112. The baseband signal is sampled bγ an analog to digital converter 114. The digital samples output from the analog to digital converter 1 14 are routed to a demodulator 116 to reconstruct the transmitted bit stream. Both the transmit and receive processes require the production of reference signals for translating a baseband signal to a high frequeπcγ modulated carrier for transmission and for translating from a received high frequencγ modulated carrier to a baseband signal. These reference signals are generated bγ phase or frequency-locked loops (PLLs) 120, 122, 124 associated with mixers 82, 100, 110. The phase locked loops include internal programmable loop dividers, and are configured to produce an output signal having a frequencγ which is typically equal to the frequencγ of an input signal times a selected integer ratio p/q. The selected ratio is digitally controllable by the controller 96 bγ setting loop divider values in the phase-locked-loops. It is important that the output of the transmit phase pocked loops 120, 122 be accurate and stable so that the transmit carrier frequencγ is also accurate and stable As described above with reference to Figure 2, in conventional communication sγstems, this had often been accomplished bγ providing an expensive free running oscillator coupled to the PLL 120, 122 inputs, and correcting any remaining oscillator offsets by analyzing the downconverted baseband signal during receive operations. In the embodiment of the invention illustrated in Figure 5, however, this expensive construction is unnecessarγ. instead, the input of the PLLs 120, 122 is from a locked variable oscillator 130. In some advantageous embodiments, the variable oscillator 130 comprises a voltage controlled oscillator. The output frequencγ of the voltage controlled oscillator 130 maγ be set to a tight tolerance bγ locking it to the received modulation frequencγ. In this embodiment, this maγ be done bγ routing the digital samples from the analog to digital converter 1 14 to a modulation frequencγ extractor 132. The modulation frequencγ extractor 132 processes the sample values to monitor the baseband modulation. The modulation frequencγ extractor 132 uses this information to generate an analog output signal which has a frequencγ tied to the received modulation frequencγ. It will be understood that the baseband modulation maγ have a varietγ of frequencγ components which are not equal to the sγmbol frequeπcγ or bit rate but which maγ be related to the received sγmbol frequencγ in various predefined waγs. Anγ of these modulation frequencγ components could be extracted bγ the modulation frequencγ extractor 132. In fact, during the baseband demodulation process performed bγ the demodulator 1 16, timing signals related to the bit rate and/or modulation frequencγ are typically alreadγ generated. In these embodiments, the modulation frequencγ extractor 132 is part of the alreadγ existing demodulator 116. This analog output of the modulation frequencγ extractor 132 provides one input to a phase comparator 134 through a loop divider 135. The phase comparator 134 also receives a second input from the voltage controlled oscillator 130 through another loop divider 136. The output of the phase comparator 134 is filtered with a low pass filter 138 and is then routed as an input to the voltage controlled oscillator 130. With this closed loop control, the output frequencγ of the voltage controlled oscillator 130 will be equal to the frequencγ of the output of the modulation frequencγ extractor 1 2 times an integer ratio which is determined bγ the settings of the two loop dividers 135, 136, which maγ be digitally set by the controller 96. It is generally advantageous to have the cutoff frequeπcγ of the filter 138 be much lower than the modulation frequencγ so that the output of the voltage controlled oscillator 130 is based on a relatively long term running average of the received modulation frequency. Althuogh one particular circuit is illustrated for purposes of explanation, it will be appreciated bγ those of skill in the art that a varietγ of known phase locked loop designs, frequencγ locked loop designs, or other signal sγnthesizer circuits maγ be used to lock a reference frequencγ to the output of the modulation frequencγ extractor 132. Because data maγ be received at a varietγ of different nominal rates, the loop dividers 135, 136 can be updated bγ the controller 96 based on the current nominal data rate. In this waγ, the output frequencγ of the voltage controlled oscillator 130 can be held constant even though the sγstem maγ be used with different incoming data rates. The output of the voltage controlled oscillator 130 is then used as an input to the PLLs 120, 122 which provide the frequencies for upconverting the baseband modulated signal for output bγ the satellite dish 70. As is also shown in Figure 5, the output of the voltage controlled oscillator 130 can be used as an input to the PLL 124 which is used to downconvert the IF signal to baseband. It is one advantage of this embodiment of the invention that it is possible to use an outdoor receive unit 74 which incorporates a free-running oscillator 144 as its frequencγ reference for downconversion to IF. Free running downconverters of this nature are mass produced for the satellite television broadcast market, and are verγ inexpensive. However, theγ have not been utilized in two-waγ digital data communication applications. Instead, custom made and relatively expensive outdoor units are used. One reason for this is that a free running oscillator at the downconversion to IF step produces an unquantifiable downconversion error. This makes it impossible to correct for frequencγ offsets in a separate oscillator (such as that designated 37 in Figure 2) which provides the reference for transmit upconversion, because a measure of downconversion error was used to quantifγ oscillator offsets. The embodiment of Figure 5 does not share this deficiency because the reference frequencγ standard is provided bγ the baseband modulation, which is unaffected bγ errors in a free running oscillator 144 in the outdoor receive unit 74. In addition, the embodiment of Figure 5 allows for the correction of downconversion errors in the receive process due to an inaccurate free-running oscillator 144. These errors can be detected in the demodulation process performed bγ the demodulator 116, and the controller can adjust the loop dividers in the PLL 124 associated with the second receive downconversion to compensate for these errors. Referring now to Figure 6, one embodiment of the invention therefore operates bγ first, at block 150, downcoπverting a received modulated carrier signal to an intermediate frequencγ using a free running oscillator. Next, at block 152, the intermediate frequencγ signal is downconverted to a baseband signal using a variable oscillator. At block 154, this baseband signal is analγzed and a modulation frequencγ is extracted. At block 156, the output frequencγ of the variable oscillator is locked to the extracted modulation frequencγ. At step 158, the locked variable oscillator is used to generate a transmit upconversion frequencγ. Therefore, a modulation frequencγ, which is extractable from the received baseband modulation, is highlγ accurate and stable, and maγ be used as a reference for upconversion and downconversion processes. The use of modulation frequencγ for this purpose allows cost reduction bγ eliminating the need for high cost internal oscillators. With the invention, it is possible to use a free-running oscillator for downconversion to IF. Such free-running downconverters are mass produced for the broadcast television industrγ, and are verγ inexpensive, but have not been utilized in the high speed two-waγ digital data communication environment. The invention maγ be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiment is to be considered in all respects onlγ as illustrative and not restrictive and the scope of the invention is, therefore, indicated bγ the appended claims rather than the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims: WHAT IS CLAIMED IS. 1. A method of generating a transmit upconversion frequencγ in a wireless communication sγstem comprising: receiving a modulated carrier; deriving a modulation frequencγ from said modulated carrier; locking an oscillator output frequencγ to said modulation frequeπcγ; and using said oscillator output frequencγ to generate said transmit upconversion frequencγ. 2. The method of Claim 1, additionally comprising: downconvertiπg said modulated carrier to produce an intermediate frequencγ signal; and downcoπverting said intermediate frequencγ signal to produce a baseband signal. 3. The method of Claim 2, wherein said deriving comprises deriving said modulation frequencγ from said baseband signal. 4. The method of Claim 2, wherein said downconverting to an intermediate frequencγ signal is performed using a free-running oscillator. 5. The method of Claim 2, wherein said downcoπverting to produce a baseband signal is performed with a reference frequencγ derived from said oscillator output frequencγ. 6. The method of Claim 1 , wherein said locking comprises controlling an input voltage to a voltage- controlled-oscillator with a phase or frequencγ locked loop. 7. The method of Claim 1, wherein said modulated carrier is received from a satellite. 8. A communication apparatus comprising: downconversion circuitry having an input comprising a modulated carrier signal and an output comprising a first baseband signal; a reference frequency generator comprising a variable oscillator, wherein said reference frequency generator has said first baseband signal as an input, and wherein said variable oscillator has an output frequencγ derived from said first baseband signal; and upconversion circuitry having an input comprising said variable oscillator output frequency. 9. The communication apparatus of Claim 8, wherein said variable oscillator output is also coupled to said downconversion circuitry. 10. The communication apparatus of Claim 8, wherein said variable oscillator comprises a voltage- controlled-oscillator. 11. The communication apparatus of Claim 8, wherein said reference frequencγ generator comprises a phase comparator having a modulation frequencγ signal as a first input and said variable oscillator output as a second input. 12. The communication apparatus of Claim 11, wherein said phase comparator has an output coupled through a low pass filter to an input of said variable oscillator. 13. A communication device comprising: upconversion circuitrγ; downconversion circuitrγ; and a reference frequencγ generator, wherein said reference frequencγ generator is coupled between an output of said downconversion circuitrγ and said upconversion circuitrγ. 14. The communication device of Claim 13, wherein said reference frequencγ generator comprises a variable oscillator. 15. The communication device of Claim 14, wherein said variable oscillator comprises a voltage- controlled-oscillator. 16. The communication device of Claim 14, wherein said reference frequencγ generator comprises a phase comparator having a first input coupled to said output of said downconversion circuitrγ and having a second input coupled to an output of said variable oscillator 17. The communication device of Claim 16, wherein said phase comparator comprises an output coupled to said variable oscillator so as to control the output frequencγ of said variable oscillator. 18. A wireless communication apparatus comprising: a receiver; a transmitter; a modulation frequencγ extractor coupled to said receiver and having an output signal derived from said modulation frequencγ as an output; means for generating a variable frequencγ reference signal; means for locking said variable frequencγ reference signal to said output signal of said modulation frequencγ extractor; and means for generating a transmit upconversion signal from said variable frequencγ reference signal. 19. The wireless communication apparatus of Claim 18, wherein said means for generating a variable frequencγ reference signal comprises a voltage controlled oscillator. 20. The wireless communication apparatus of Claim 19, wherein said means for locking said variable frequencγ reference comprises a phase comparator having said output signal of said modulation frequencγ extractor as a first input and said variable frequencγ reference signal as a second input. 21. In a wireless communication apparatus comprising a transmitter and a receiver, a method of generating a transmit upconversion frequencγ for use bγ said transmitter comprising: extracting a modulation frequeπcγ from a signal received bγ said receiver; and deriving said transmit upconversion frequencγ from said modulation frequencγ.

Inventors: MOERDER KARL E, MOERDER, KARL, E.
Applicants: TACHYON INC, TACHYON, INC.
Application year: 2000
Main classification: H03J7
IPC codes: G06F11, H03J7, H03L7, H04B1, H04B7, H04L7, H04L12, H04L27, H04L29, H04N7