Patent Publication Number: US-6665276-B1

Title: Full duplex transceiver

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to a transceiver for data communication, and more particularly to a Radio Frequency (RF) front end to a standard IF (Intermediate Frequency) modem to allow full duplex data communication at RF. 
     (2) Description of the Prior Art 
     For a full duplex communication transceiver, the transceiver&#39;s transmitter and receiver are simultaneously active, thereby allowing simultaneous data transmission and reception. Depending upon the design considerations, a full duplex transceiver&#39;s transmit and receive antennae are often the same. When transmit and receive frequencies are similar, interference is often encountered although separate transmission and receive antennae are employed. 
     Methodologies and systems for avoiding transmit and receive signal interference include U.S. Pat. No. 5,905,706 to Vidales wherein half-bit transmission and reception intervals are formed; U.S. Pat. No. 5,715,520 to Hillock, et al, for Time Division Duplex (TDD) systems to utilize a single Local Oscillator (LO) to derive two LO signals at different times, thereafter using the two LO signals to produce an intermediate and an offset signal frequency; U.S. Pat. No. 5,687,169 to Fullerton describes a pulse interleaving method and apparatus for impulse radio&#39;s ultrawide-band communications; and, U.S. Pat. No. 5,533,056 to Cripps provides a duplex transceiver binary encoder/decoder. 
     U.S. Pat. No. 5,881,369 to Dean, et al, describes a duplex receiver operational in Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes. The Dean, et al, transceiver has an up-conversion path that converts an Intermediate Frequency (IF) to a Radio Frequency (RF) in either an upper RF frequency range or a lower RF frequency range, and similarly a down-conversion path to convert the received RF frequency in either the upper or lower frequency range to a desirable IF frequency. The Dean, et al, up-conversion and down-conversion paths connect to either an upper or lower band diplexer port through a switch array. A switch controller controls the switch array based upon whether the transceiver is operating in TDD or FDD mode. The Dean, et al, invention concentrates on cellular communication requirements and demands. 
     General data communication between a transmitter and receiver are less restrictive than the cellular requirements. Higher frequency data communication allows more rapid communication rates; however, typical modems for data communication operate in the IF frequency band. 
     There is currently no apparatus or method for a full duplex transceiver at the Radio Frequency (RF) bands, wherein RF is derived from a variable IF frequency. 
     What is needed is a method and apparatus to convert an IF generator output to RF for full duplex communication. 
     SUMMARY OF THE INVENTION 
     It is a general purpose and object of the present invention to provide a configurable transceiver architecture that allows simplex, half-duplex, and full duplex operation. Another object of the present invention is to provide a transceiver architecture that accepts a variable IF as input, and generates a RF output for data communication using fixed Phase Locked Oscillators (PLOs). A further object is to provide a transceiver that receives a RF signal and converts the RF signal to an IF signal using fixed PLOs. Still yet another object is to provide such configurable transceiver architecture for single or dual antenna use, utilizing internal, external, or no diplexer, and allowing internal or external oscillator references. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     These objects are accomplished with the present invention by a RF front end to an IF generator and post-processor whereby the IF generator output is variable. The transceiver up-conversion path includes an IF Filter, the output of which is input to a mixer with the output of a fixed Phase Locked Oscillator (PLO). The mixer output is input to a band-pass filter and amplified. With a single antenna configuration, the amplifier output connects to either an internal or external diplexer that interfaces to the antenna. With a dual antenna configuration, the amplifier output interfaces directly to the transmit antenna. Similarly, the down-conversion path includes an internal or external diplexer in the single antenna configuration, a band-pass filter, a RF amplifier, a mixer that receives the RF amplifier output and the fixed PLO as inputs, an IF Filter, IF amplifier, and an attenuator for interfacing to the IF post-processor. A user-interface allows RF TX and RX frequency selection, data rate selection, and configurable options including internal or external diplexer, internal or external oscillator reference, and TX amplifier keying to allow simplex, half duplex, or full duplex communication. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts and wherein: 
     FIG. 1 is a block diagram of the RF transceiver for the preferred embodiment wherein the IF generator is a modem; 
     FIG. 2 is a block diagram of the RF transceiver up-conversion and down-conversion paths for a single antenna configuration utilizing an internal diplexer; 
     FIG. 3 is a block diagram of the RF transceiver up-conversion and down-conversion paths for a single antenna configuration utilizing an external diplexer; and, 
     FIG. 4 is a block diagram of the RF transceiver up-conversion and down-conversion paths for a dual antenna configuration. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown a block diagram  10  of the transceiver system, further detailing individual transceiver components. In the preferred embodiment, the transceiver  12  interfaces to a modem  14  that provides a varying IF to the transceiver  12 . The modem&#39;s  14  variable IF is specified through a user-interface  16  that allows a user to specify communication parameters. Communication parameters specified through the user-interface  16  include satellite or line-of-site (LOS) communication, RF transmit (TX) frequency, RF receive (RX) frequency, communication data rate, internal or external oscillator reference, and transmit power amplifier keying options. 
     An embedded controller  18  controls the user-interface  16  and initializes transceiver  12  components according to user selections. The embedded controller  18  uses the user-selected transmit (TX) and receive (RX) RF frequencies to compute respective TX and RX intermediate frequency (IF) values, and the. embedded controller  18  transfers the TX and RX IF frequency values to the modem  14 . The embedded controller  18  also uses the TX and RX RF frequencies to specify the respective TX and RX band-pass filter (BPF)  20 ,  22  coefficients through interfaces  100  and  102 . 
     The embedded controller  18  accepts a user-selected data rate from the user-interface  16 , and provides the data rate to the modem  14 . The TX amplifier  24  is additionally keyed by the embedded controller  18  through interface  104  according to user-interface designations of constant on, constant off, or request to send (RTS) control, thereby providing a mechanism that allows the transceiver to perform in full duplex, half duplex, or simplix modes. In the preferred embodiment, when satellite communication is user-specified, the embedded controller enables the internal diplexer  26  through interface  106 . 
     As will be shown in FIGS. 2,  3 , and  4 , the down-conversion path comprises an attenuator  28 . In the preferred embodiment, the attenuator  28  is digital and controlled by the embedded controller  18  through interface  108  to maintain a desired signal level at the attenuator output. The embedded controller  18  also enables the internal oscillator reference  30  through interface  112  depending upon whether the user selects (via the user interface) internal or external oscillator reference. 
     Other components comprising the transceiver  12  are the TX mixer  32 , RX Mixer  34 , TX IF Filter  36 , RX IF Filter  38 , RX Amplifier  40 , RX IF Amplifier  42 , and at least one fixed Phase-Locked Oscillator (PLO)  44 . The preferred embodiment transceiver  12  also maintains an embedded controller/user-interface interface  46  to allow user-interface control by the embedded controller, user-entered data transfer, and transmission of performance data for user-interface display; an embedded controller/IF modem interface  48  to transfer computed IF frequencies and user-entered data rates from the embedded controller  18  to the modem  14 , and received signal levels and error rates from the modem  14  to the embedded controller  18 ; an external oscillator interface  50  to allow an external oscillator reference to drive the fixed PLO(S)  44  when the internal oscillator is not selected; an external diplexer interface  52  to provide for external diplexer configurations; a single (TX/RX) antenna interface  54 ; a dual antenna interface  56 ; a TX IF interface  58  to accept TX IF signals from the modem  14 ; and, a RX IF interface  59  to transfer down-converted RX IF signals from the transceiver  12  to the modem  14 . 
     Referring now to FIG. 2, there is shown the up-conversion and down-conversion paths for a single antenna configuration using the internal diplexer. The modem  14  provides an IF frequency to the transceiver  12  as directed by the transceiver&#39;s embedded controller and based upon the user-entered, TX RF frequency and fixed PLO values  44 . The modem&#39;s  14  TX IF frequency is transferred to the transceiver  12  through the TX IF interface between the modem and transceiver  58  and input to the TX IF filter  36 . The TX IF Filter output  60  provides one input to the up-conversion (TX) mixer  32 . The fixed PLO(s)  44  provide(s) the TX mixer  32  with a second input  62 . The fixed PLO(s)  44  is selected to achieve the user-selected TX RF frequency, recalling that the TX IF provided by the modem  14  was calculated by the embedded controller  18  using the user-selected TX RF frequency and a fixed PLO  44  value. 
     In the preferred embodiment, the fixed PLO(s)  44  is driven by a relay  64  that maintains connections to the internal oscillator  30  and an external oscillator interface  50 . The relay  64  is activated depending upon the user selection for internal or external oscillator reference. Although FIG. 2 indicates a single fixed PLO  44 , multiple fixed PLOs may be utilized to provide a larger TX (and RX) RF frequency selection. 
     The IF filter output  60  and fixed PLO output  62  provide the mixer  32  with signals to achieve the desired TX RF frequency at the mixer output  66 . The mixer output  66  is input to the TX band-pass filter (BPF)  20  that is tuned by the embedded controller  18  for the appropriate TX RF frequency, and amplified  24 . In the preferred embodiment, the amplifier  24  interfaces to a relay  68 , the output of which connects to the internal diplexer  26  TX input  26   a . In the preferred embodiment, the internal diplexer  26  combined output  26   b  connects to a relay  70  for interfacing to the single antenna  54 . 
     The FIG. 2 down-conversion path includes the internal diplexer  26 , whose RX input  26   c  is connected to a relay  72  and thereafter a RX BPF  22  tuned to the user-specified RX RF frequency. The RX RF signal is then amplified  40  before input to the down-conversion path (RX) mixer  34 . A fixed PLO  44  provides the second input to the down-conversion path mixer  34  to generate an IF signal that is filtered  38  and amplified  42  before being attenuated  28  and transferred to the modem  14  using the RX IF interface  59 . 
     Referring now to FIG. 3, there is shown a single antenna configuration utilizing an external diplexer. Similar to FIG. 2, the modem  14  provides the variable TX IF to the transceiver  12  through the TX IF interface  58 , and the IF signal is filtered  36  and provided as one input  60  to the up-conversion mixer  32 . A PLO  44 , driven by either an internal oscillator reference  30  or an external oscillator through the external oscillator interface  50 , provides the second mixer input  62 . The up-conversion mixer  32  provides a TX RF signal  66  that is band-pass filtered  20 , amplified  24 , and connected through relay  68  to the TX external diplexer interface  52   a . The external diplexer TX terminal  90   a  accepts the TX signal, while the external diplexer combined terminal  90   b  returns to the transceiver  12  through the external diplexer combined interface  52   b , connecting to a relay  70  and hence the single antenna interface  54 . The external diplexer RX terminal  90   c  returns to the transceiver  12  via the RX external diplexer interface  52   c . The RX RF signal  92  begins the down-conversion path by passing through a relay  72 , RX BPF  22  tuned by the embedded controller to the user-specified RX RF frequency, and amplifier  40 . The amplified RF signal  94  is input to the down-conversion mixer  34  with a signal from a fixed PLO  44  to convert the RF signal to IF, whereupon the IF signal is filtered  38 , amplified  42 , and attenuated  28  for transmission to the modem  14  through the RX IF interface  59 . 
     Referring now to FIG. 4, there is shown a dual antenna configuration wherein a first antenna designated the TX antenna, and a second antenna designated the RX antenna, are connected to the transceiver dual antenna interface  56 . The up-conversion path connected to the TX antenna is similar to the up-conversion paths of FIGS. 2 and 3, with the omission of a diplexer. Once again, the modem  14  provides a variable TX IF to the transceiver  12  through the TX IF interface  58 , whereupon the TX IF signal is filtered  36  and input to a mixer  32  with a signal from a fixed PLO  44 . A fixed PLO  44  may be driven by an internal reference  30  or by an external oscillator through the external oscillator interface  50 . The mixer output  66  is a RF signal that is input to the TX BPF  20 , amplified  24 , and connected to the dual antenna interface&#39;s TX antenna terminal  56   a  through a relay  68 . The down-conversion path begins with the signal from the dual antenna interface&#39;s RX antenna terminal  56   b  that is sent through a relay  72 , RX BPF  22 , and RF amplifier  40 , before being input to the RX mixer  34 . The other RX mixer input is derived from a fixed PLO  44 , and the RF mixer output  96  is an IF signal that is filtered  38 , amplified  42 , and attenuated  28  before it is returned to the modem  14  via the RX IF interface  59  for post processing. 
     The advantage of the present invention over the prior art is that a RF signal can be derived from a variable IF using a fixed PLO, thereby allowing increased data rate communication. 
     What has thus been described is a RF front end to an IF generator and post-processor whereby the IF generator output is variable. The transceiver up-conversion path includes an IF Filter, the output of which is input to a mixer with the output of a fixed Phase Locked Oscillator (PLO). The mixer output is input to a band-pass filter and amplified. With a single antenna configuration, the amplifier output connects to either an internal or external diplexer that interfaces to the antenna. With a dual antenna configuration, the amplifier output interfaces directly to the antenna. Similarly, the down-conversion path includes an internal or external diplexer in the single antenna configuration, a band-pass filter, a RF amplifier, a mixer that receives the RF amplifier output and the fixed PLO as inputs, an IF Filter, IF amplifier, and an attenuator for interfacing to the IF post-processor. A user-interface allows RF TX and RX frequency selection, data rate selection, and configurable options including internal or external diplexer, internal or external oscillator reference, and TX amplifier keying to allow simplex, half duplex, or full duplex communication. 
     Although the present invention has been described relative to a specific embodiment thereof, it is not so limited. Obviously many modifications and variations of the present invention may become apparent in light of the above teachings. For example, although the preferred embodiment indicated the presence of relays in the up-conversion and down-conversion paths, the relays may be replaced by another appropriate device, or omitted entirely. The amplifier may require a pre-amplifier depending on signal and amplifier characteristics. Multiple, fixed PLOs may be utilized to offer greater ranges of TX and RX RF selection. Although the preferred embodiment indicated a fixed PLO feeding the TX and RX mixers, depending upon the user-selected TX and RX RF frequencies, the fixed PLO output to the TX and RX mixers may be different, and may be derived from a different fixed PLO. The RF signal may be any frequency range, including but not limited to UHF, VHF, etc. Although the description provided three external diplexer interface components, these interfaces may in fact represent a single component. Similarly, the dual antenna interface may be a single interface for two antennae, or dual interfaces. The TX IF interface and RX IF interface between the transceiver and modem may also be a single interface. Although the described transceiver operates in full duplex mode, the constant on, constant off, and RTS TX amplifier control options provide for simplex, half-duplex, or full duplex operation. Although the preferred embodiment indicated diplexer use only in single antenna configurations, diplexers may be utilized in the dual antenna configuration. The attenuator may be digital or analog. Any variable, IF frequency generator and post-processor can substitute for the modem. Although the transceiver architecture was shown in three basic configurations to encompass the configurable options within the preferred embodiment, a single configuration may be selected and implemented individually. 
     Many additional changes in the details, materials, steps and arrangement of parts, herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention. It is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.