Same-Aperture Any-Frequency Simultaneous Transmit and Receive Communication System
A same-aperture any-frequency simultaneously transmit and receive (STAR) system includes a signal connector having a first port electrically coupled to an antenna, a second port electrically coupled to a transmit signal path, and a third port electrically coupled to receive signal path. The signal connector passes a transmit signal in the transmit signal path to the antenna and a receive signal in the receive signal path. A signal isolator is positioned in the transmit signal path to remove a residual portion of the receive signal from transmit signal path. An output of the signal isolator provides a portion of the transmit signal with the residual portion of the receive signal removed. A signal differencing device having a first input electrically coupled to the output of the signal isolator and a second input electrically coupled to the third port of the signal connector subtracts a portion of the transmit signal in the receive signal path thereby providing a more accurate receive signal.
- 1-61. -61. (canceled)
- 62. An any-RF-frequency simultaneously transmit and receive (STAR) system, the STAR system comprising:
a) an array of radiating elements; b) an any-RF-frequency signal connector having a first port coupled to the array of radiating elements, a second port electrically coupled to a transmit signal path such that the array of radiating elements are configured to be fed an any-RF-frequency transmit signal having an unspecified RF transmit frequency, and a third port electrically coupled to a receive signal path such that the array of radiating elements provide an any-RF-frequency receive signal having an unspecified RF receive frequency to the receive signal path, the any-RF-frequency signal connector passing the any-RF-frequency transmit signal having the unspecified RF transmit frequency in the transmit signal path to the first port and passing the any-RF-frequency receive signal having the unspecified RF receive frequency in the receive signal path; c) a signal differencing device having a first input electrically coupled to the transmit signal path and a second input electrically coupled to the third port of the any-RF-frequency signal connector, the signal differencing device subtracting a portion of the any-RF-frequency transmit signal having the unspecified RF transmit frequency in the receive signal path, thereby providing a copy of the any-RF-frequency receive signal having the unspecified RF transmit frequency at an output of the signal differencing device; and d) a signal processor having a first input electrically coupled to the output of the signal differencing device and a second input electrically coupled to the transmit signal path, the signal processor processing a copy of the any-RF-frequency transmit signal having the unspecified RF transmit frequency so as to reduce a residual any frequency transmit signal in the receive signal path.
- View Dependent Claims (63, 64, 65, 66, 67, 68, 69, 70, 71)
- 72. An any-RF-frequency simultaneously transmit and receive (STAR) system, the STAR system comprising:
a) a first and second radiating element; b) a first transmit signal path and a first receive signal path electrically coupled to the first radiating element, the first transmit signal path configured to pass a first any-RF-frequency transmit signal having an unspecified RF transmit frequency to the first radiating element and the first receive signal path configured to pass an any-RF-frequency receive signal having an unspecified RF receive frequency from the first radiating element; c) a second transmit signal path electrically coupled to the second radiating element, the second transmit signal path configured to pass a second any-RF-frequency transmit signal having an unspecified RF transmit frequency to the second radiating element; b) a signal differencing device having a first input electrically coupled to the first transmit signal path and a second input electrically coupled to the first receive signal path, the first signal differencing device subtracting a portion of the first any-RF-frequency transmit signal having the unspecified RF transmit frequency in the first receive signal path, thereby providing a copy of the any-RF-frequency receive signal having the unspecified RF transmit frequency at an output of the signal differencing device; and c) a signal processor having a first input electrically coupled to the output of the signal differencing device, a second input electrically coupled to the first transmit signal path and a third input electrically coupled to the second transmit signal path, the signal processor processing a copy of the first and second any-RF-frequency transmit signal having the unspecified RF transmit frequency so as to reduce a residual any-frequency transmit signal transmitted by the first and second radiating element in the first receive signal path.
- View Dependent Claims (73, 74, 75, 76, 77, 78)
- 79. A method of any-RF-frequency simultaneously transmitting and receiving, the method comprising:
a) connecting an any-RF-frequency receive signal comprising an unspecified RF receive frequency from a port with an any-RF-frequency transmit signal comprising an unspecified RF transmit frequency from a transmit signal path so that the any-RF-frequency receive signal is passed to a receive signal path and the any-RF-frequency transmit signal is passed to the port; b) performing a subtraction of the any-RF-frequency transmit signal in the transmit signal path from the any-RF-frequency receive signal in the receive signal path, thereby removing a residual portion of the any-RF-frequency transmit signal from the receive signal path making a more accurate representation of the any-RF-frequency receive signal; and c) processing the more accurate representation of the any-RF-frequency receive signal so as to reduce a residual any-RF-frequency transmit signal in the any-RF-frequency receive signal path.
- View Dependent Claims (80, 81, 82, 83)
The section headings used herein are for organizational purposes only and should not to be construed as limiting the subject matter described in the present application in any way.
The present application claims priority to U.S. patent application Ser. No. 13/844,180 filed on Mar. 15, 2013, entitled “Same-Aperture Any-Frequency Simultaneous Transmit and Receive Communication System,” U.S. Provisional Patent Application No. 61/755,044, filed on Jan. 22, 2013, entitled “Single-Aperture, Full Duplex Communication System,” and to U.S. Provisional Patent Application No. 61/677,366 filed on Jul. 30, 2012, entitled “Signal Canceller and Simultaneous Transmit And Receive System with Signal Processing.” The entire contents U.S. patent application Ser. No. 13/844,180, and Provisional Patent Applications Nos. 61/755,044 and 61/677,366 are herein incorporated by reference.
It is generally assumed in communications that it is not possible to simultaneously transmit and receive (STAR) in the same frequency band. Recently this basic tenet has begun to be challenged by several groups that have reported prototype STAR systems. Researchers at Purdue in, for example, A. Wegener and W. Chappell, “Simultaneous transmit and receive with a small planar array,” IEEE MTT-S Tnt. Microwave Symp. Dig., Montreal, June 2012, and researchers at Stanford in, for example, J. Choi, et al., “Achieving Single Channel, Full Duplex Wireless Communication,” Proc. Int. Conf. Mobile Computing and Networking, New York, 2010 have proposed arrangements of multiple antenna elements in which the receive antenna is located in a null of the transmit antenna pattern to realize ˜40 dB of transmit-to-receive (T/R) isolation.
Signal processing was then used to extend the T/R isolation to ˜60-70 dB. A group at Rice University using single, separate transmit and receive antennas, computed the required cancelling signal and used it to cancel the transmit signal before it reached the analog-to-digital converter. See A. Sahai, B. Patel and A. Sabharwal, “Asynchronous full-duplex wireless,” Proc. Int. Conf. on Communication Systems and Networks, pp. 1-9, 2012. This group reported up to 79 dB suppression. A key limitation of these approaches is the limited bandwidth over which sufficient T/R isolation can be achieved.
The present teaching, in accordance with preferred and exemplary embodiments, together with further advantages thereof, is more particularly described in the following detailed description, taken in conjunction with the accompanying drawings. The skilled person in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating principles of the teaching. The drawings are not intended to limit the scope of the Applicant'"'"'s teaching in any way.
Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the teaching. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
It should be understood that the individual steps of the methods of the present teachings may be performed in any order and/or simultaneously as long as the teaching remains operable. Furthermore, it should be understood that the apparatus and methods of the present teachings can include any number or all of the described embodiments as long as the teaching remains operable.
The present teaching will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications and equivalents, as will be appreciated by those of skill in the art. Those of ordinary skill in the art having access to the teaching herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein.
For decades, there existed only microwave circulators to simultaneously connect the transmit and receive paths to a common antenna. Microwave circulators are passive components with three ports arranged in a waveguide ring around a ferrite disk that induces a direction-dependent phase shift, causing the two counter-circulating halves of the wave to add up constructively at the next port in one circumferential direction along the ring but destructively at the next port in the other direction. A ferrite circulator is an inherently narrow-band device because it depends on summing and differencing the RF phase of two waves. Designers have found ways to widen a ferrite circulator'"'"'s bandwidth in exchange for some loss of its perfect unidirectionality at its center design frequency. Ferrite circulators are now commercially available from multiple vendors with ˜20 dB of port 1-3 isolation over an octave-wide band.
To enable single-aperture STAR applications, separate groups of researchers recently hit upon two active circulator designs. An electronic circulator has achieved up to 40 dB T/R isolation, albeit over only about 10% bandwidth at X-band. A description of the electronic circulator'"'"'s principle of operation is described in S. Cheung, et al., “MMIC-based quadrature hybrid quasi-circulators for simultaneous transmit and receive,” IEEE Trans. Microwave Theory Tech., vol. 58, pp. 489-497, March 2010.
The second new type of device is based on photonics and hence it is referred to herein as a photonic circulator. As described herein, this new photonic component performs two additional functions beyond those of a conventional ferrite circulator. For this reason, we refer to the new photonic component as a TIPRx, for Transmit-Isolating Photonic Receiver.
Several years ago Photonic Systems, Inc., the assignee of the present application, began to investigate a more challenging yet potentially more widely applicable STAR configuration, which is STAR via the same antenna element and in the same polarization.
It is well known in the communications art that to simultaneously transmit and receive via the same aperture, one must use either time, frequency, or code multiplexing. Time multiplexing involves inserting a switch so that either the transmitter or the receiver is connected to the antenna. Frequency multiplexing involves inserting a diplexer and/or filters so that the transmit and the receive signals occupy disjoint portions of the RF spectrum. Code multiplexing uses orthogonal codes for the transmit and receive signals; the relatively limited degree of orthogonality that can be realized, however, often requires code multiplexing to be augmented with frequency multiplexing to achieve sufficient transmit-to-receive (T/R) isolation. Thus, persons skilled in the art generally agree that it is not possible to simultaneously transmit and receive via the same aperture using the same portion of the RF spectrum at the same time.
A key parameter to achieving same-aperture any-frequency STAR is the T/R isolation; systems typically would require >60 dB of T/R isolation. The system 100 of
One input of the differencing device 210 is connected to the receive path 206. Another input of the differencing device 210 is connected to the transmit signal path 205 that ideally has no residual receive signal. The isolator 208 connected to the transmit signal path 205 is designed to isolate any residual receive signal so that a clean copy of the transmit signal is applied to the differencing device 210. In operation, the differencing device 210 subtracts out the large transmit signal leaving just the receive signal.
If the transmit signal environment is sufficiently stable, it is possible to provide a transmit signal of fixed complex value to the second port of the differencing device 210. However, in many practical same-aperture any-frequency STAR systems, the transmit environment around the antenna 204 will change as a function of time, which in turn will cause the complex value of the transmit signal reflected by the antenna to change. In these situations it is desirable to include a signal processor 212 to determine the precise complex value of the transmit signal that should be fed to the second terminal of the differencing device 210 so as to minimize the residual transmit signal that is present in the receive path. A transmit signal adjustment circuit 214 is used to set the complex value of the transmit signal.
Active electronic differencing devices, such as the devices 400, 420 described in connection with
Furthermore, depending on the design of the particular photonic differencing device the photonic differencing device can have a gain that is greater or less than unity. Thus, the photonic differencing device can provide either gain or loss. When the photonic differencing device is designed to have gain, it is capable of achieving low noise figure, much like active electronic differencing devices. When the photonic differencing device is designed to have loss, it has higher noise figure, much like passive electronic differencing devices. Some types of differential optical modulators are only capable of summing two signals. In such cases, these differential modulators can realize the required differencing by offsetting the clean transmit signal by 180 degrees as described in connection with
There are two basic types of signal sources: voltage sources and current sources. An ideal voltage source is a signal source with zero internal impedance. An ideal current source is a signal source with infinite internal impedance. Such ideal signal sources are not realizable. Realizable voltage sources generally have an internal impedance that is much lower than the external impedances in the circuit. Realizable current sources generally have an internal impedance that is much larger than the external impedances in the circuit.
Numerous other types of isolators can be used in the apparatus of the present teaching. For example, in one embodiment, a directional coupler 580 is used to perform the isolation as shown in
RF isolation can also be achieved in RF amplifiers in which the reverse isolation is greater than the forward gain. An isolation technique that takes advantage of such an amplifier 590 is shown in
Another function performed by the signal processor 212 is estimating the complex value of the transmit signal that needs to be applied to the input of the differencing device 210 so as to result in minimizing the residual transmit signal at the output of the differencing device 210. The result of this estimation is a signal that is applied to the transmit signal adjustment circuit 214.
To further establish as good a balance as possible between the two inputs to the differencing device, identical connectors are used, in this case, the matched impedance type can be used. This example system uses the photonic differencing device described herein. Key advantages of this type of differencing device or subtractor are that they are extremely wide bandwidth (>4 decades) and there is high isolation between the + and − differencing ports. Voltage source isolation, with identical output impedance in the two outputs, further enhances the balance. One of the disadvantages of this system architecture is the relatively high loss incurred by the transmit signal. Because the same transmit power is supplied to both the antenna and the pseudo-antenna, there is 3 dB of loss for ideal (i.e., lossless) connectors. There is an additional 3 dB loss at each of the connectors. Thus, the total transmit loss between the output of the power amplifier and the antenna is 6 dB plus the excess loss of the connector.
To implement sampling, one can use a fast switch that is capable of connecting the input—in this case the signal coming from the antenna 1102—to the receiver for the short period of time of the sample, and then opening—i.e. disconnecting the input from the receiver. This means that for the remaining 99% of the time between samples, the sampling switch is open, and hence the receiver is not connected to the input. The fast switch connector 1100 utilizes the inter-sampling interval to connect the transmitter to the antenna 1102. There is negligible transmitter power loss since the transmitter is connected to the antenna 1102 for almost 100% of the time. With the fast switch signal connector, the transmitter and the receiver are never simultaneously connected to the antenna 1102. Hence, the transmit signal does not have the opportunity to enter the receive path. This can eliminate the need for the differencing device, isolator, signal processor and transmit signal adjuster described herein for some applications
It is important to point out that, while the fast switch is topologically similar to a conventional transmit-receive (T/R) switch in systems not designed for STAR, the function of the fast switch connector shown in
Although in some system applications, sufficient performance may be achievable using the same-aperture any-frequency STAR systems described in
In the digital domain, the digital signal processor 1202 is used to correlate the transmit signal with the differencing device 1208 output to isolate the residual transmitter component in the differencing device 1208 output. The signal processor 1202 then forms an estimate of the optimum complex value of the transmitter signal that needs to be injected into the differencing device 1208 so as to minimize the residual transmitter signal that is present at the differencing device 1208 output. The output of the signal processor 1202 includes two signals that contain the desired settings on the IQ transmit signal adjuster 1212. Since in the example shown in
Referring back to
Referring now to
In some modes of operation, the Tx signal is down-converted and run through the analog-to-digital converter 1204 and then stored in the signal processor 1202. In this way, multiple, appropriately-delayed copies of the Tx signal can be generated in the digital domain and the resulting signals can be converted back by a digital-to-analog converter 1210 to an analog signal which is then up-converted by a frequency converter, such as a mixer. Alternatively, the up-conversion can be performed digitally and then fed to a digital-to-analog converter. One powerful aspect of this approach is that the appropriate delays for each copy of the transmit signal can be determined by signal processing using well know techniques. The delays can be updated as signal conditions change.
All of the embodiments of the present teaching in
Up to this point the large signal that needed to be removed (subtracted) from the receive path was a signal to be transmitted through the same antenna that was detecting a signal to be received. The transmit signal may be differentiated from the receive signal in two key aspects: (1) the transmit signal is much more powerful than the receive signal and (2) the transmit signal does not need to be demodulated to recover the information, if any, that is being conveyed by the transmit signal. There is another class of system configurations in which a large signal that does not need to be demodulated enters the receive path. If such a large signal is benign, it is generally referred to as co-site inference. If the large signal is hostile in nature it is generally referred to as jamming. In such cases, the large signal needs to be removed so that the receiver can process, i.e. demodulate, the desired receive signal(s). Various means of removing co-site and jamming signals are well known. One common approach is to use RF filters to suppress the large signal while permitting the receive signal(s) to pass. Such techniques are effective, of course, only when the receive and co-site/jamming signals occupy disjoint frequency bands. The teaching of the present invention will now be applied to suppress co-site and jamming signals, where the frequency spectra of the receive and co-site/jamming signals may overlap.
Given that we will wish to cancel large interferers with more complicated spectral content than the simple sinusoid, we assumed in this simulation that we will need multiple bits of quantization to preserve this content. Thus, we will only be able to effectively cancel the effect of interferers much (not just 10 dB) stronger than the SOI.
The system 2000 is a generalized form of the single-element front-end described in connection with
One of the N attenuated (by at least a factor of N) copies of the transmit signal is fed to this front-end'"'"'s transmit signal adjuster 2006 exactly as was done in
Identical to the N-way RF divider 2008, this N-way RF combiner 2010 may consist, for example, of two-way traveling-wave resistive power combiners (Wilkinson power combiners) employed in a corporate tree arrangement to yield N-way combining of the RF signals. The combined copies of the transmit signals are subtracted from the signal received by this front-end'"'"'s antenna element 2002 in the differencing device 2012. As in