Patent Application
20140198688
An example embodiment of the present invention relates generally to wireless communication and, more particularly, to reducing self-interference in a wireless transceiver.
In traditional wireless communication systems, a transceiver may be transmitting and receiving either using different frequency bands or different time slots, e.g., in a half-duplex mode. If the transceiver were to operate simultaneously on an overlapped time and frequency resource, e.g., in a full-duplex mode, the high self-interference may saturate the receiver chain, making signal recovery difficult or even impossible. Accordingly, in the absence of effective self-interference technology, full-duplex transceivers have to date been regarded as impractical and difficult to implement in wireless communication systems.
Therefore, methods, apparatuses, and computer program products are provided according to example embodiments in order to effectively reduce self-interference. In this regard, a method, apparatus, and computer program product from the perspective of an analog baseband canceller (ABC) may determine a self-interference channel estimate, determine a reconstructed self-interference based on a signal to be transmitted and the self-interference channel estimate, and subtract the reconstructed self-interference from a received signal. According to a further embodiment, the ABC may iteratively repeat this process until the residual self-interference drops below a threshold, at which point detection of a desired signal may be initiated.
In one embodiment, a method is provided that includes determining a self-interference channel estimate, causing a reconstructed self-interference to be determined based at least in part on the self-interference channel estimate and a signal to be transmitted, and causing the reconstructed self-interference to be subtracted from a received signal. According to a further example embodiment, the method may include determining a residual self-interference based at least in part on a signal resulting from subtraction of the reconstructed self-interference from the received signal, determining whether the residual self-interference component is less than a threshold, and causing detection of a desired signal to be enabled in an instance in which the residual self-interference is less than the threshold.
In another embodiment, an apparatus is provided that includes a processing system, which may be embodied by at least one processor and at least one memory including program code. The processing system is arranged to cause the apparatus to at least determine a self-interference channel estimate, cause a reconstructed self-interference to be determined based at least in part on the self-interference channel estimate and a signal to be transmitted, and cause the reconstructed self-interference to be subtracted from a received signal. According to a further example embodiment, the apparatus may be further caused to determine a residual self-interference based at least in part on a signal resulting from subtraction of the reconstructed self-interference from the received signal, determine whether the residual self-interference component is less than a threshold, and cause detection of a desired signal to be enabled in an instance in which the residual self-interference is less than the threshold.
In a further embodiment, a computer program product is provided that includes a set of instructions, which, when executed by a processing system, causes the processing system to determine a self-interference channel estimate, cause a reconstructed self-interference to be determined based at least in part on the self-interference channel estimate and a signal to be transmitted, and cause the reconstructed self-interference to be subtracted from a received signal. The set of instructions may be embodied on a non-transitory computer readable medium storing computer program code portions therein. According to a further example embodiment, the set of instructions, when executed by the processing system, may cause the processing system to determine a residual self-interference based at least in part on a signal resulting from the subtraction of the reconstructed self-interference from the received signal, determine whether the residual self-interference component is less than a threshold, and cause detection of a desired signal to be enabled in an instance in which the residual self-interference is less than the threshold.
In another embodiment, an apparatus is provided that includes means for determining a self-interference channel estimate, means for causing a reconstructed self-interference to be determined based at least in part on the self-interference channel estimate and a signal to be transmitted, and means for causing the reconstructed self-interference to be subtracted from a received signal. According to a further example embodiment, the apparatus may further include means for determining a residual self-interference based at least in part on a signal resulting from the subtraction of the reconstructed self-interference from the received signal, means for determining whether the residual self-interference component is less than a threshold, and means for causing detection of a desired signal to be enabled in an instance in which the residual self-interference is less than the threshold.
Having thus described certain example embodiments of the present disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
As used in this application, the term “circuitry” refers to all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or access point, to perform various functions) and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.
This definition of “circuitry” applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term “circuitry” would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term “circuitry” would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or application specific integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, an access point, or other network device.
Referring now to
The conventional transceiver depicted in
The conventional transceiver of
Because of the simple design, the RF canceller 120 has a limited ability to reduce self-interference. Assuming that the distance between the transmission and reception antennas is about 10 cm, analog RF cancellation combined with the effects of path loss can achieve a reduction in self-interference of around 50 dB at a frequency of 2.4 GHz (using a near field path loss model provided by IEEE P802.15 working group for wireless personal area networks). Although analog RF cancellation may achieve about 50 dB of self-interference suppression, the RF canceller 120 is unable to deal with multipath components of self-interference and therefore leaves some self-interference un-canceled (e.g., residual self-interference). Moreover, this residual self-interference is frequently much stronger than the desired signal. To recover the desired signal, a conventional digital canceller can be utilized as depicted in
The effectiveness of including a conventional digital canceller in a transceiver, however, is still not ideal and can be seriously limited depending on the components used. To illustrate, consider the following example. There are two users being 50 meters apart from each other. Each user is using 1 transmission antenna and 1 reception antenna and the distance between the two antennas is 10 cm. The transmit power of each user is from −10 dBm to 20 dBm. The operating frequency is 2.4 GHz and the signal bandwidth is 20 MHz. In this scenario, the residual self-interference is about −55 to −25 dBm while the desired signal is about −80 to −50 dBm. Thus, the residual self-interference is still much stronger than the desired signal. As a result, a very high resolution analog-to-digital-converter (ADC) must be utilized. This effect is shown in the graph 200 of
Turning now to
The self-interference estimation module 410 may, for example, comprise an apparatus, such as the apparatus 20 that is generally depicted in
As shown in
In an example embodiment, the memory 24 may include one or more non-transitory memory devices such as, for example, volatile and/or non-volatile memory that may be either fixed or removable. The memory may be configured to store information, data, applications, instructions or the like for enabling the apparatus 20 to carry out various functions in accordance with example embodiments of the present invention. For example, the memory could be configured to buffer input data for processing by the processor 22. Additionally or alternatively, the memory could be configured to store instructions for execution by the processor. As yet another alternative, the memory may include one of a plurality of databases that may store a variety of files, contents or data sets. Among the contents of the memory, applications may be stored for execution by the processor in order to carry out the functionality associated with each respective application. In some cases, the memory may be in communication with the processor via a bus for passing information among components of the apparatus.
The processor 22 may be embodied in a number of different ways. For example, the processor may be embodied as various processing means such as one or more of a microprocessor or other processing element, a coprocessor, a controller or various other computing or processing devices including integrated circuits such as, for example, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), DSP (digital signal processor), or the like. In an example embodiment, the processor may be configured to execute instructions stored in the memory 24 or otherwise accessible to the processor. As such, whether configured by hardware or by a combination of hardware and software, the processor may represent an entity (e.g., physically embodied in circuitry—in the form of processing circuitry) capable of performing operations according to some embodiments of the present invention while configured accordingly. Thus, for example, when the processor is embodied as an ASIC, FPGA, DSP or the like, the processor may be specifically configured hardware for conducting the operations described herein. Alternatively, as another example, when the processor is embodied as an executor of software instructions, the instructions may specifically configure the processor to perform the operations described herein.
The self-interference reconstruction element 420 may comprise circuitry configured in various ways according to example embodiments. For example, the self-interference reconstruction element 420 may, as with the self-interference estimation module 410, comprise an apparatus, such as the apparatus 20 that is generally depicted in
The switching elements may, for example, respectively comprise circuitry configured to act as a switch, such as one or more transistors, relays, or the like.
Thus having described various components that the ABC 300 may comprise, attention will be directed to
In this regard, and by way of a general overview, the operations of the ABC may be conceptualized as proceeding in two phases. The first phase is a “training” phase, in which the self-interference is reconstructed. In this training phase, a full-duplex transceiver including or otherwise associated with the ABC 300 may operate as a normal half-duplex transceiver (e.g., either transmitting or receiving, but not both at the same time). In this phase, a self-interference re-construction branch of the receiver chain is active, while a desired signal detection branch is inactive. After self-interference has been reconstructed to a suitable degree, such that subtracting it from the received signal results in a suitable reduction in residual self-interference, the second phase may be entered. In this phase, the desired signal detection branch is activated and the transceiver may thus operate in a full-duplex mode, transmitting and receiving signals at the same time, with reduced self-interference.
Thus, turning to
The ABC 300 may further include means, e.g., circuitry, such as the self-interference estimation module 410, for determining a self-interference channel estimate. See operation 510. As discussed above, the self-interference estimation module 410 may itself comprise means, such as the processor 22 and memory 24 of apparatus 20 depicted in
The ABC 300 may further comprise means, e.g., circuitry, such as the self-interference reconstruction module 420, for determining a reconstructed self-interference. See operation 520. The self-interference reconstruction module 420 may itself comprise various means for determining the reconstructed self-interference, as discussed above, such as the processor 22 and memory 24 of apparatus 20 depicted in
The ABC 300 may further comprise means, e.g., circuitry, such as the self-interference reconstruction module 420, for causing the reconstructed self-interference to be subtracted from a received signal. See operation 530. That is, the self-interference reconstruction module 420 may be further configured to output the reconstructed self-interference to a first input of a subtraction element 470, the subtraction element 470 receiving the received signal at a second input and comprising circuitry configured to subtract the first input from the second input. Thus, according to embodiments, reconstructed self-interference is determined based on the self-interference channel estimate and the signal to be transmitted and then is canceled from a received signal via subtraction.
The ABC 300 may further comprise means, e.g., circuitry, such as the VGA 430, for receiving a subtracted signal resulting from the subtraction of the reconstructed self-interference from the received signal. See operation 540. According to example embodiments, the second VGA 430 may further be configured to amplify the subtracted signal and output the amplified subtracted signal to the ADC 140.
The ABC 300 may further comprise means, e.g., circuitry, such as the switching element 450, for causing the second VGA 430 to be tuned based on a power of the subtracted signal. See operation 550. For example, the ABC 300 may cause, via switching element 450, an output of the AGC element 480 to be directed to a tuning input of the second VGA 430.
The ABC 300 may further comprise means, e.g., circuitry, such as the AGC element 480, for determining a residual self-interference. See operation 560. The AGC element 480 may be further configured to determine whether the residual self-interference is less than a threshold. See operation 560. In an instance in which the residual self-interference is not less than the threshold, the ABC 300 may return to operation 510 and determine, via the self-interference estimation module 410, a self-interference channel estimate, e.g., an updated self-interference channel estimate. Thus, the self-interference channel estimate and reconstructed self-interference may continue to be updated, and the reconstructed self-interference may continue to be subtracted from the received signal, until the residual self-interference is less than the threshold.
The AGC element 480 may be further configured to, in an instance in which the residual self-interference is less than the threshold, cause the self-interference channel estimate to be fixed. See operation 570. For example, the AGC element 480 may be configured to signal to the self-interference estimation module 410 that the residual self-interference is less than the threshold. Thus, the self-interference channel estimate may be fixed at the last determined value, such that it will remain unchanged when used for subsequent reconstructions of the self-interference via the self-interference reconstruction module 420.
A receiver may also be caused to be informed of the signal to be transmitted 490 in an instance in which the residual self-interference is less than the threshold, such as via the transmission antenna 160. See operation 580. The ABC 300 may further comprise means, e.g., circuitry, such as the first switching element 440, for causing detection of the desired signal to be enabled in an instance in which the residual self-interference is less than the threshold. For example, the ABC 300 may cause, via the first switching element 440, an output of the ADC 140 to be directed to the desired signal detection branch 495, which may, for example, comprise a desired signal detection module 496 and desired signal estimation module 497.
Having thus described the operations of the ABC 300 generally, attention will now be turned to
As shown in
As shown in
One commonality between certain ones of the example embodiments discussed thus far is the use of the output of the AGC 480 to tune, e.g., control the gains of, the first VGA 460 and second VGA 430, and to use the second switching element 450 to toggle which VGA is tuned at any one time. While this switching scheme works suitably in full-duplex transceivers, it may be adapted to account for imbalances in bi-directional transmission time and to account for adaptive transmitter-side power control. With respect to the first issue, if a full-duplex transceiver using the switching scheme is going to stop its transmission, the self-interference signal may disappear from the tuning input of the first VGA 460. Consequently, its input signal power may weaken so that the gain of the first VGA 460 should be increased to reduce its noise figure impact. With respect to the second issue, the transmitter of a transceiver may adaptively change its transmit power during its transmission, making it beneficial for the AGC 480 to take own transmit power into account.
Based on these two concerns, an adapted AGC 480 scheme is presented in
Some embodiments according to the invention may provide many benefits in a wireless communication system. For example, the ABC 300 may reduce self-interference, thereby improving the overall performance of a full-duplex transceiver. Moreover, some embodiments of the present invention may achieve this without the use of an expensive, high-resolution ADC. For example, the performance realized from using an ABC 300 comprising an 8 bit ADC according to example embodiments of the present may be quite close to that realized by using a traditional digital base band cancellation and a 14 bit ADC.
As discussed above,
Accordingly, blocks of the flowchart support combinations of means for performing the specified functions and combinations of operations for performing the specified functions. It will also be understood that one or more blocks of the flowcharts, and combinations of blocks in the flowcharts, can be implemented by special purpose hardware-based computer systems which perform the specified functions, or combinations of special purpose hardware and computer instructions, or special or general-purpose circuitry, or any combination thereof.
In some embodiments, certain ones of the operations above may be modified or further amplified. Moreover, in some embodiments additional optional operations may also be included, some of which are shown in dashed lines in
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1300878.4 | Jan 2013 | GB | national |
