Patent Application
20150173087
An example embodiment of the present invention relates generally to communications technology and, more particularly, to interference suppression.
As communication with mobile terminals increases, network operators endeavour to improve the utilization of their spectrum. One technique for improving the utilization of their spectrum is to increase the network density, such as by more densely deploying the network with smaller cells. In some examples, increasing the network density through the addition of macro sites or smaller cells, such as in the context of heterogeneous network deployments, may lead to increased interference conditions and thus may result in the degradation of the quality of service.
Another technique for improving the spectrum efficiency in time domain duplex (TDD) systems is to enable more dynamic selection of the switching point between downlink and uplink transmissions. As such, additional downlink allocations may be enabled in instances in which the communication with mobile terminals is downlink heavy. Another technique for increasing spectrum efficiency is to offload traffic from the network, such as by allowing mobile terminals to communicate directly with one another, such as in accordance with device-to-device (D2D) communications in a long-term evolution (LTE®) or LTE-advanced (LTE-A) network. In this instance, the mobile terminals may communicate directly with one another, thereby allowing the evolved Node B (eNB) and other network resources to utilize the spectrum for other transmissions simultaneous with the D2D communication between the mobile terminals.
However, each of these techniques for increasing the utilization of the spectrum may increase the interference. For example, in an instance in which the network density is increased, the signal quality at the receiver will become increasingly limited by interference. In addition, in an instance in which the switching point between downlink and uplink transmissions is dynamically selected in a TDD system, downlink transmissions may interfere with uplink transmissions and, conversely, uplink transmissions may interfere with downlink transmissions. Still further, in an instance in which D2D communications are supported, the D2D communication between the mobile terminals may interfere with communication between the mobile terminals and the eNBs.
A variety of techniques have been introduced in an effort to suppress interference. For example, Release 8 of the LTE® specification describes inter-cell interference coordination (ICIC) mechanisms that are primarily based upon the exchange of some interference and/or load information between the base stations over an X2 interface. Beginning with Release 10, the Third Generation Partnership Project (3GPP) has introduced enhanced ICIC (eICIC), which is intended to protect certain subframes from certain types of interference, such as the most disruptive forms of interference. In other words, eICIC is a time-domain ICIC technique that builds on the X2-based signaling of almost blank subframe (ABS) patterns among network nodes participating in the coordination.
In a heterogeneous network, macro nodes typically act as a dominant interference source for pico-nodes within their coverage. For time domain multiplexing (TDM) eICIC, the macro nodes may mute their transmissions, except for common reference signals (CRS) during one or several subframes indicated by the ABS patterns. As such, the pico-nodes may benefit from lower interference conditions and traffic offloading to the pico-nodes may be made possible, thereby increasing the overall cell throughput.
While eICIC may be applicable to a variety of interference scenarios, eICIC may not readily scale to situations in which there are multiple sources of interference since eICIC was designed essentially for a scenario in which a single source of interference was heavily interfering with another cell. eICIC also operates on a subframe level in which the protected subframes are set semi-statically since the configuration of restricted resources for mobile terminal measurements, such as radio resource management (RRM), radio link monitoring (RLM), radio resource control (RRC), etc., involve RRC signaling that may cause significant overhead if performed too frequently. While network nodes involved in eICIC may exchange ABS pattern information over the X2 interface in a dynamic fashion, the resource partitioning remains limited to the time dimension with eICIC, thereby not providing frequency domain multiplex (FDM) partitioning.
In another effort to reduce interference, Release 11 of the 3GPP specification specifies coordinated multi-point transmission/reception (CoMP), which aims at coordinating transmissions/reception between cells/access points/eNodeBs in order to reduce interference. Cells/access points/eNodeBs may also be in control of multiple transmission points under their coverage. However, Release 11 of the 3GPP specification does not contemplate coordination between access points, as there is no standardized information exchange via X2 interfaces or otherwise.
However, CoMP techniques for reducing interference require centralized control and scheduling and, as such, are not particularly applicable to situations in which the interference arises from several access points, particularly if the access points are from different network vendors. Also, CoMP techniques generally require substantial feedback of channel state information (CSI) such that CoMP techniques do not typically scale very well for denser network deployments in which more than one source of interference is to be suppressed. Furthermore, CoMP techniques are also less useful in regards to resolving interference between the uplink and downlink transmissions in a TDD system and in regards to mitigating interference arising from D2D communications.
Until the Release 10 specification, the baseline assumption, in terms of minimum performance requirements defined in RAN4 specifications, regarding the receiver of a mobile terminal was that the receiver was embodied by a simple minimum mean squared error (MMSE) receiver without co-channel interference rejection capabilities (IRC). While more advanced receivers may be implemented, such as maximum likelihood (ML) detection which can also take into account the interference structure, there have been no performance requirements for the more advanced receivers and, hence, no guarantee from a network perspective that all mobile terminals will perform well in conditions with heavy spatially coloured interference. In the Release 11 specification, however, performance requirements for MMSE-IRC receivers are being developed. In this regard, MMSE-IRC receivers are able to suppress a number of sources of interference, depending upon the number of receive antennas of the mobile terminal. For example, the most common LTE® mobile terminal includes two receive (Rx) antennas and, as such, is able to suppress one rank-1 complex-valued source of interference while receiving a rank-1 complex-valued transmission from its own cell or access point, thereby continuing to be limited in the number of sources of interference that may be suppressed. Additionally, the network must also take into account machine-type communication (MTC) devices that may be only equipped with a single receive antenna port, thereby being incapable of suppressing interference.
In receivers having, but not limited to, IRC, the use of real valued modulation may enable additional degrees of freedom for interference suppression. In this regard, real-valued signals may be received and then decoded by the receiver of a mobile terminal using an IQ split receiver, such as a widely linear receiver or non-linear receivers (e.g. maximum likelihood or serial/parallel interference cancellers), thereby enabling improved interference suppression. In an LTE® network, however, current LTE® specifications support only complex constellations, such as multiple quadrature amplitude modulation (M-QAM), such that a mobile terminal equipped with two receive antennas can efficiently mitigate interference from at most one complex-valued rank-1 source of interference so long as the desired transmission is also rank-1 complex-valued. By employing real-valued modulated transmissions, the degrees of freedom in the receiver would be increased since the intended transmission would occupy one dimension from among the four that would be available in an instance in which the receiver had two receive antennas, that is, the four dimensions defined by the two I/Q branches for each of the two receive antennas. However, the benefits of these receivers are only applicable when the signals transmitted by the mobile terminal as well as the sources of interference utilize real-valued modulation, which is challenging in regards to an LTE® network, which is configured to support complex valued modulation.
A method, apparatus and computer program product are therefore provided in accordance with an example embodiment of the present invention in order to suppress interference, such as interference attributable to increased network density, interference attributable to interference between uplink and downlink transmissions in a TDD system and/or interference attributable to D2D communications. In one embodiment, the method, apparatus and computer program product may provide for the coexistence of real-valued and complex-valued modulation while enabling improved interference suppression, such as by utilizing widely linear receivers. In this regard, the method, apparatus and computer program product of an example embodiment may coordinate the real-valued and complex-valued modulation in order to facilitate enhanced interference suppression.
According to the invention, there is provided the method of claim 1.
According to the invention, there is also provided the apparatus of claim 8.
According to the invention, there is also provided the computer program product of claim 17.
According to the invention, there is also provided the apparatus of claim 18.
According to the invention, there is also provided the method of claim 19.
According to the invention, there is also provided the apparatus of claim 26.
According to the invention, there is also provided the computer program product of claim 42.
According to the invention, there is also provided the apparatus of claim 43.
Having thus described some example embodiments of the invention 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 server, 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 server, a cellular network device, or other network device.
A method, apparatus and computer program product of one example embodiment of the present invention coordinate the type of modulation to be utilized such that the signals transmitted between an access point and a mobile terminal as well as the dominant form of interference have the same type of modulation, such as either real-valued modulation or complex-valued modulation. In regards to the interference, the dominant form of interference may be created by a single source of interference, e.g., a single interferer, or by two or more sources of interference, e.g., two or more interferers. For example, in regards to CoMP techniques, there may be multiple interferers brought about by transmissions between two or more mobile terminals and two or more access points. In another example, the dominant form of interference may arise within the coverage of a single access point/cell (e.g. in single-cell multi-user multiple input, multiple output (MIMO) or intra-site CoMP transmission). As another example, in regards to D2D communications, there may be multiple interferers as a result of interference created by D2D communications with a plurality of pairs of mobile terminals. As such, the mobile terminal may suppress the interference by, for example, utilizing widely linear reception. In one embodiment in which the interference is real-valued, the coordination of the type of modulation to be utilized involves an access point determining that the mobile terminal is also scheduled on physical resource blocks (PRBs) for real-valued modulation, such as pulse amplitude modulation (PAM). On the other hand, if the dominant form of interference is complex-valued, the mobile terminal may also be scheduled with complex-valued modulation. By coordinating the type of modulation for the signals transmitted between an access point and a mobile terminal with the modulation type of the interference, the mobile terminal may receive the signals and separate the in-phase (I) and quadrature (Q) branches and then perform widely linear processing of the received signal in order to suppress interference, thereby increasing the degrees of freedom for interference suppression and correspondingly improving interference rejection capabilities. For example, a mobile terminal having two receive (Rx) antennas may suppress up to three sources of interference assuming real-valued modulations are in use. In another example, a mobile terminal having one receive (Rx) antenna may suppress up to two sources of interference if these use real-valued modulations.
While the method, apparatus and computer program product may be utilized in conjunction with mobile terminals configured to communicate in a variety of networks, a network in which the method, apparatus and computer program product of an example embodiment may be deployed is illustrated in
An apparatus 20 that may be embodied by or included within one or more of a mobile terminal 10, an access point 14 or other network entity is shown in
In an example embodiment, the processing circuitry 22 may include a processor 24 and memory 26 that may be in communication with or otherwise control a communication interface 28 and, at least in instances in which the apparatus 20 is embodied by a mobile terminal 10, a user interface 30. As such, the processing circuitry may be embodied as a circuit chip (e.g., an integrated circuit chip) configured (e.g., with hardware, software or a combination of hardware and software) to perform operations described herein. However, in some embodiments taken in the context of the mobile terminal, the processing circuitry may be embodied as a portion of a mobile terminal. Alternatively, in embodiments taken in the context of an access point 14 or other network entity, the processing circuitry may be embodied as a portion of the access point or other network entity.
The user interface 30 (if implemented in embodiments of the apparatus 20 embodied by a mobile terminal 10) may be in communication with the processing circuitry 22 to receive an indication of a user input at the user interface and/or to provide an audible, visual, mechanical or other output to the user. As such, the user interface may include, for example, a keyboard, a mouse, a joystick, a display, a touch screen, a microphone, a speaker, and/or other input/output mechanisms. In one embodiment, the user interface includes user interface circuitry configured to facilitate at least some functions of the mobile terminal by receiving user input via, for example, a display or touch screen, and providing output.
The communication interface 28 may include one or more interface mechanisms for enabling communication with other devices and/or networks. In some cases, the communication interface may be any means such as a device or circuitry embodied in either hardware, or a combination of hardware and software that is configured to receive and/or transmit data from/to the network and/or any other device or module in communication with the processing circuitry 22. In this regard, the communication interface may include, for example, an antenna (or multiple antennas) and supporting hardware and/or software for enabling communications with a wireless communication network and/or a communication modem or other hardware/software for supporting communication via cable, digital subscriber line (DSL), universal serial bus (USB), Ethernet or other methods.
In an example embodiment, the memory 26 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 24. 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 24 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), or the like. In an example embodiment, the processor may be configured to execute instructions stored in the memory 26 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 embodiments of the present invention while configured accordingly. Thus, for example, when the processor is embodied as an ASIC, FPGA 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.
Referring now to
In one embodiment, the apparatus 20 embodied by the access point 14 may include means, such as the processing circuitry 22, the processor 24, the communication interface 28 or the like, for receiving an indication of a modulation preference from the mobile terminal 10. See block 40 of
The apparatus 20 embodied by the access point 14 may also include means, such as the processing circuitry 22, the processor 24, the communication interference 28 or the like, for providing for communication with the mobile terminal 10 in accordance with the one of real-valued modulation or complex-valued modulation that was determined. See block 46 of
As shown in block 44 of
In one embodiment in which an access point 14 is configured to coordinate multi-point transmission and/or reception, an apparatus 20 embodied by the access point may determine whether communication between the access point and a mobile terminal 10 should be subjected to real-valued modulation or complex-valued modulation as shown in block 50 and as described above in conjunction with block 42 of
Although the determination as to the type of modulation to be employed for communication between the access point 14 and the mobile terminal 10 may be accomplished in various manners, the apparatus 20 embodied by the access point of one embodiment that coordinates multi-point transmission and/or reception may include means, such as the processing circuitry 22, the processor 24, the communication interface 28 or the like, for determining whether the communication between the access point and the mobile terminal should be subjected to real-valued modulation or complex-valued modulation based upon path loss differences between the cells or access points. By way of example, if path loss differences between serving and interfering cells are small, such as below a threshold, it is likely that real valued modulation could be useful. Alternatively, if one interfering cell has significantly lower path loss than another (indicating a dominant interferer), it would be beneficial to be coordinated to use real valued modulation.
In another embodiment depicted in
From the perspective of the mobile terminal 10, an apparatus 20 is provided that includes means, such as the processing circuitry 22, the processor 24 or the like, for configuring the mobile terminal for communication in accordance with a type of modulation selected from real-valued modulation or complex-valued modulation. See block 76 of
In one embodiment, for example, the apparatus 20 embodied by the mobile terminal 10 may include means, such as the processing circuitry 22, the processor 24, the communication interface 28 or the like, for receiving an indication of the type of modulation from the access point 14. See block 74 of
Although the access point 14 may determine the type of modulation to be employed for communication between the access point and the mobile terminal 10 in a manner independent of input from the mobile terminal, the apparatus 20 embodied by the mobile terminal of one embodiment may include means, such as the processing circuitry 22, the processor 24, the communication interface 28 or the like, for causing an indication of a modulation preference to be provided to the access point. See block 72 of
In one example, the apparatus 20 embodied by the mobile terminal 10 may include means, such as the processing circuitry 22, the processor 24, the communication interference 28 or the like, for determining the type of modulation, such as a modulation preference, based upon a signal to interference plus noise ratio (SINR). See block 70 of
In one embodiment in which the mobile terminal 10 is also capable of D2D communications, the apparatus 20 embodied by the mobile terminal may include means, such as a processing circuitry 22, the processor 24, the communication interface 28 or the like, for receiving an indication of the type of modulation, such as real-valued modulation or complex-valued modulation, to be utilized for a device for D2D communications with another mobile terminal. See block 78 of
By configuring the type of modulation to be utilized for communication between the access point 14 and the mobile terminal 10 to be of the same type as the dominant form of interference, such as interference due to densely configured networks, interference between uplink and downlink transmissions in a TDD system, interference attributable to D2D communications and/or interference attributable to coordinated or uncoordinated transmissions, the mobile terminal, such as the communication interface 28 of the mobile terminal, may mitigate interference by separating the I and Q branches and performing widely linear processing utilizing, for example, a widely linear receiver. Indeed, in one embodiment in which the mobile terminal includes at least two receiver antennas, the degrees of freedom of the receiver may be increased to four dimensions of which one is utilized for the intended transmission with the access point and the others may be utilized to suppress interference. Other type of receivers such as maximum likelihood (ML) detection can also take into account the interference structure, and therefore one is not limited to the class of linear receivers. As such, the method, apparatus and computer program product of an example embodiment may facilitate improved interference suppression, while continuing to support communications between the mobile terminal and the network, such as via an access point.
Accordingly, blocks of the flowcharts 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.
In some embodiments, certain ones of the operations above may be modified or further amplified as described below. Moreover, in some embodiments additional optional operations may also be included as shown, for example by the 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 |
|---|---|---|---|
| 1209741.6 | May 2012 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB13/54472 | 5/30/2013 | WO | 00 |
