WO2014194460A1

WO2014194460A1 - Interference coordination and interference cancellation

Info

Publication number: WO2014194460A1
Application number: PCT/CN2013/076654
Authority: WO
Inventors: Wei Bai; Lili Zhang; Pengfei Sun; Haiming Wang; Chunyan Gao; Na WEI; Jing HAN; Wei Hong
Original assignee: Broadcom Corporation
Priority date: 2013-06-03
Filing date: 2013-06-03
Publication date: 2014-12-11

Abstract

At least one preamble is dedicated for interference probing. An aggressor access node (macro eNB) sends a command to a user equipment (UE) to transmit the dedicated preamble on a physical random access channel (PRACH). A victim access node (pico eNB) detects the transmitted preamble, and if this UE is the source of uplink interference to the victim access node it informs that to the macro access node which may then use interference coordination and interference cancellation to mitigate further uplink interference. In some embodiments the victim access node decides what is the transmit power for the UE to use for the dedicated preamble on the PRACH, and informs it to the macro access node which instructs the UE of the transmit power to use. In one example embodiment the victim access node calculates an offset from SRS/PUSCH transit power and informs the macro access node of the offset.

Description

INTERFERENCE COORDINATION AND INTERFERENCE

CANCELLATION

TECHNICAL FIELD:

[0001 ] The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to interference coordination and interference cancellation (ICIC) on wireless channels using a random access channel. BACKGROUND:

[0002] The Third Generation Partnership Project (3 GPP) has inspired much detailed research into co-channel interference coordination and interference cancellation (ICIC in general, or elCIC for the Evolved UMTS Terrestrial Radio Access E-UTRAN system)) among different wireless network nodes operating in a heterogeneous network (HetNet). One effective resolution has involved the concept of almost blank sub frames (ABS), which are coordinated between the higher power macro cell and the nearby lower power pico cell. One of several ways to use ABSs for ICIC is for the macro cell to not schedule data transmissions in the ABSs, leaving the ABSs available for the pico cell's use free of interference from the macro cell. The types of transmissions that are allowed in an ABS by the macro cell in the above scenario are agreed in advance and generally are much less prone to interfere with the pico cell's communications than would normal data transmissions with the macro cell, (for example, such as synchronization signals, cell specific reference signals CRS and multicast-broadcast signal frequency networks MBSFNs).

[0003] Now there is research into carrier-based ICIC (CB-ICIC) to resolve issues that past research into ICIC does not address. Specifically, conventional ICIC assumes the source of the interference is known, typically a particular UE located in a border area between the macro and pico cells as shown in Figure 1 which is a scenario from 3 GPP TR 03.024. The problem concerns uplink interference; a macro user equipment (MUE) may severely interfere with the uplink quality of a pico eNB when the MUE is located in the vicinity of pico eNB while being served by macro eNB. Conventional ICIC cannot yet be employed because in the Figure 1 scenario the MUE is not aware of the existence of the pico eNB and thus interferes with the uplink of the pico eNB. An alternative uplink interference scenario between the macro and the pico eNBs is characterized by the asymmetry between the uplink coverage of the MUE and the downlink coverage of the pico eNB. An MUE that is not able to detect the pico eNB's signal may cause uplink interference to the pico eNB. The uplink interference area can be normally depicted as a circled area, the center of which is on a line extending between the macro and pico eNBs and shown in Figure 1 as the area 101 . [0004] To enable normal ICIC techniques to be effective somehow the MUE causing the interference must be detected or otherwise identified. The teachings below provide a practical solution for how this may be done so that conventional or yet to be developed ICIC techniques can be used to mitigate the uplink interference. SUMMARY:

[0005] In a first example embodiment of the invention there is a method for controlling a user equipment. In this embodiment the method comprises: reserving at least one preamble dedicated for interference probing; and in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing, causing the UE to transmit the dedicated preamble on a physical random access channel (PRACH).

[0006] In a second example embodiment of the invention there is an apparatus for controlling a user equipment and the apparatus comprises a processing system. The processing system itself comprises at least one processor, and at least one memory including computer program code. In this embodiment the processing system is configured to cause the apparatus to at least: reserve at least one preamble dedicated for interference probing; and in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing, cause the UE to transmit the dedicated preamble on a physical random access channel (PRACH). [0007] In a third example embodiment of the invention there is a computer readable memory tangibly storing a set of computer readable instructions that are executable on a data processing system for controlling a user equipment. The computer readable instructions comprise:

· code for reserving at least one preamble dedicated for interference probing; and

• code for causing the UE to transmit the dedicated preamble on a physical random access channel (PRACH) in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing.

[0008] In a fourth example embodiment of the invention there is an apparatus for controlling a user equipment, and this apparatus comprises storing means for reserving at least one preamble dedicated for interference probing; and control and communication means for causing the UE to transmit the dedicated preamble on a physical random access channel (PRACH) in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing. In one example the storing means may be a computer readable memory, and the control and communication means may be a transmitter with a digital processor running executable software stored on the computer readable memory.

[0009] In a fifth example embodiment of the invention there is a method for operating a serving network access node. In this embodiment the method comprises: commanding a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing; informing a victim network access node of the dedicated preamble; and managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node. [0010] In a sixth example embodiment of the invention there is an apparatus for operating a serving network access node and the apparatus comprises a processing system. The processing system itself comprises at least one processor, and at least one memory including computer program code. In this embodiment the processing system is configured to cause the apparatus to at least: command a user equipment (UE) to transmit on a physical random access channel (P ACH) a preamble dedicated for interference probing; inform a victim network access node of the dedicated preamble; and manage wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node.

[001 1 ] In a seventh example embodiment of the invention there is a computer readable memory tangibly storing a set of computer readable instructions that are executable on a data processing system for operating a serving network access node. The computer readable instructions comprise:

• code for commanding a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing;

• code for informing a victim network access node of the dedicated preamble; and

• code for managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node

[0012] In an eighth example embodiment of the invention there is an apparatus for operating a serving network access node. In this embodiment the apparatus comprises: communication means for commanding a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing; communication means for informing a victim network access node of the dedicated preamble; and control means for managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node. In one example the communication means may be a transmitter, and the control means may be a digital processor running executable software stored on a memory.

[0013] In a ninth example embodiment of the invention there is a method for operating a victim access node. In this embodiment the method comprises: receiving from a serving access node an indication of a preamble dedicated for interference probing; monitoring a physical random access channel (PRACH) for a transmission comprising the dedicated preamble; and if the dedicated preamble is detected on the PRACH, indicating to the serving access node whether a UE that transmitted the dedicated preamble on the PRACH is a source of uplink interference to the victim access node.

[0014] In a tenth example embodiment of the invention there is an apparatus for operating a victim access node and the apparatus comprises a processing system. The processing system itself comprises at least one processor, and at least one memory including computer program code. In this embodiment the processing system is configured to cause the apparatus to at least: in response to receiving from a serving access node an indication of a preamble dedicated for interference probing, monitoring a physical random access channel (PRACH) for a transmission comprising the dedicated preamble; and indicate to the serving access node, if the dedicated preamble is detected on the PRACH, whether a UE that transmitted the dedicated preamble on the PRACH is a source of uplink interference to the victim access node.

[0015] In an eleventh example embodiment of the invention there is a computer readable memory tangibly storing a set of computer readable instructions that are executable on a data processing system for operating a victim access node. The computer readable instructions comprise:

• code for monitoring a physical random access channel (PRACH) for a transmission comprising a dedicated preamble in response to receiving from a serving access node an indication of the preamble which is dedicated for interference probing; and

· code for indicating to the serving access node, if the dedicated preamble is detected on the PRACH, whether a UE that transmitted the detected preamble on the PRACH is a source of uplink interference to the victim access node.

[0016] In a twelfth example embodiment of the invention there is an apparatus for operating a victim access node. In this embodiment the apparatus comprises: communication means for receiving from a serving access node an indication of a preamble dedicated for interference probing; communication means for monitoring a physical random access channel (PRACH) for a transmission comprising the dedicated preamble; and processing and communications means for indicating to the serving access node, if the dedicated preamble is detected on the PRACH, whether a UE that transmitted the dedicated preamble on the PRACH is a source of uplink interference to the victim access node. In one example the communication means for receiving from the serving access node may be a modem, the communication means for monitoring the PRACH may be a receiver, and the processing and communications means may be a digital processor running executable software stored on a memory in conjunction with the modem.

[0017] These and other aspects are detailed below with more particularity.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0018] Figure 1 is a conceptual schematic diagram illustrating a non-limiting example of an uplink interference scenario in a macro-pico heterogeneous network environment in which these teaching may be practiced.

[0019] Figure 2 is a table illustrating hexa-decimal R TI values in which a new dedicated PRA-R TI is used to scramble a PDCCH that commands a UE to transmit a dedicated preamble according to some non-limiting embodiments of these teachings.

[0020] Figure 3 is a non-limiting example of a design of the code point for a PDCCH format 1A used to trigger a UE to transmit a dedicated preamble according to some non-limiting embodiments of these teachings.

[0021 ] Figures 4-6 are logic flow diagrams that each illustrate the operation of a method, a result of execution of by apparatus, and execution of computer instructions comprising code embodied on a computer readable memory, in accordance with some example embodiments of this invention.

[0022] Figure 7 is a simplified block diagram of a UE in communication with a macro cell and in the vicinity of a pico cell, and illustrates example electronic devices suitable for use in practicing some embodiments of this invention. DETAILED DESCRIPTION:

[0023] The non-limiting examples detailed herein are in the context of a UE operating in a radio network utilizing the E-UTRAN radio access technology (including LTE and LTE- Advanced), but this is only one example in order to provide a practical context for describing the inventive concepts detailed herein. These teachings may be utilized with other types of radio access technologies, such as for example UTRA, including Wideband Code Division Multiple Access (WCDMA) and High Speed Packet Access (HSPA), Global System for Mobile Communications (GSM), and the like. The specific names of messages, channels, operating states and various network entities in the examples below follow the nomenclature for E-UTRA networks, and these names also are not limiting to the broader teachings presented below but are for clarity of explanation.

[0024] As noted in the background section above, it is important to detect or otherwise identify the MUE in the uplink interference area that is the cause of the uplink interference. The MUE is not aware itself that it is the source of the interference to the pico eNB since the MUE is not aware of the existence of the pico eNB. Several broad techniques to identify this interfering MUE are summarized below.

[0025] One detection option is to have the pico eNB send an overload indicator to the macro eNB. Based on its recent scheduling decisions the macro eNB will know which UEs were transmitting at what time. Comparing this schedule against the pico eNB's overload indicator can allow the macro eNB to compute which MUE was transmitting when the pico eNB's uplink was overloaded. Another is to use the actual geographical location of the MUE relative to the pico eNB, if the MUE's location information is available to the macro eNB. Another possibility is for the pico eNB to listen for uplink channel soundings (sounding reference signals or SRSs) sent from various MUEs, assuming the macro eNB would signal these channel sounding configurations to the pico eNB so it can identify a given UE from channel soundings that the pico eNB hears. A more complex arrangement has the macro eNB providing to the pico eNB the uplink radio resources that the macro eNB allocates to its various MUEs (for example the transmission time intervals, the allocated physical resource blocks, the demodulation reference signal configurations, and possibly further parameters such as each MUE's timing advance), and from this information for all the active MUEs the pico eNB can determine which is the interfering MUE and inform the macro eNB of its findings.

[0026] Each of these has its disadvantages and the example embodiments detailed herein take a quite different approach. As will be detailed below, in some embodiments the macro eNB selects one or more MUEs to begin a contention-free random access channel (RACH) procedure. Since it is contention free the MUE will not randomly choose a preamble to send on the RACH but will select one that is reserved or otherwise dedicated for the purpose of detecting co-channel interfering UEs. Both the reserved preamble and the RACH on which the MUE sends it are known in advance to both the macro eNB and the pico eNB, and so both can recognize this preamble on the RACH as having the purpose of detecting a UE rather than for establishing a connection which is the conventional purpose of a RACH procedure.

[0027] In one example embodiment the pico eNB informs the macro eNB of what is to be the dedicated preamble, and the macro eNB orders a selected one or ones of its MUEs which may be or become a source of uplink interference to the pico eNB to begin a contention- free RACH procedure using the dedicated preamble. If the pico eNB can detect the dedicated preamble on the RACH, then the pico eNB knows that the UE that sent that dedicated preamble is the source of interference or could become a source of interference to the pico eNB. The pico eNB reports to the macro eNB when it saw the dedicated preamble on the RACH and the macro eNB can then know which MUE is the source or potential source of uplink interference with the pico eNB. Or in another embodiment the macro eNB can inform the pico eNB which MUEs are ordered to begin a RACH procedure with the dedicated preamble and when (that is, on what radio resources the preamble is to be sent), which gives the pico eNB enough information to itself identify which is the suspect MUE and report the particular suspect MUE to the macro eNB directly. [0028] The dedicated physical RACH (PRACH) preamble and the resource on which it is to be sent may in some embodiments be forwarded similar to the information forwarding normally done for a conventional handover operation. But for the above solution for identifying which MUE is the potential source of interference there are further issues to resolve. Namely the conventional RACH procedure, whether contention based or contention free, are for the purpose of the UE to establish a radio connection with the network but in the interference mitigation scenario the interfering MUE may already have such a connection with the macro cell. In fact, if the MUE has such an active connection it is the uplink transmissions on that connection that are the very source of the interference. For this reason, according to some example embodiments of these teachings the RACH procedure used for interference probing is abbreviated as compared to the conventional connection-establishing RACH procedures; namely, this contention free RACH procedure that the UE initiates at the network's direction is terminated after the MUE sends the dedicated interference-probing preamble; the subsequent steps of the conventional RACH procedure are simply not necessary to the interference probing purpose. Such interference probing can be done in different deployments, for example when the MUE has an active connection with the macro eNB and the victim eNB is already experiencing interference, or as another example when the MUE does not yet have such a connection established with the macro eNB but for some reason interference is anticipated such as location of the MUE or the macro eNB having an incoming voice call or data for the MUE that is currently in an idle mode.

[0029] In a conventional contention free RACH procedure, once the UE is triggered to transmit a preamble, the UE ' s transmission power is normally set according to the some parameters signaled by the eNB. But simply extending this to the macro-pico eNB scenario would leave the pico eNB with no knowledge of the used transmission power at the MUE, meaning the pico eNB may not accurately derive which detected signal strength of this preamble transmission as the interference. This is because the pico eNB in this example is expected to somehow derive the potential interference due to some UE that is present on the physical uplink shared channel (PUSCH) but the UE's transmit power for the preamble on the RACH is not the same as its transmit power on the PUSCH so the pico eNB would have some difficulty in understanding the interference accurately, even if it detects the dedicated preamble from a particular MUE on the RACH. For this reason some example embodiments below simplify the procedure and resolve the above transmit power issue for a more complete solution for detecting the source of uplink interference.

[0030] In this example similar to the example above there is configured an ICIC dedicated PRACH resource, and any UE is only allowed to transmit this preamble when it is ordered to do so by the UE's serving eNB. In some embodiments, the UE's transmit power of this dedicated preamble is pre-defined (for example, in the serving cell's system information), or it may be explicitly signaled by the macro eNB via dedicated signaling.

[0031 ] To summarize some of the above points before detailing further example embodiments, the aggressor cell eNB (which in the above example is the macro eNB) configures a dedicated PRACH resource for its serving UEs. This resource configuration could in different implementations be configured with system information, or with dedicated radio resource control (RRC) signaling. In an alternative example the ICIC dedicated preamble is pre-defined in a published radio standard as being reserved for the above interference proving purpose in which case the macro eNB, the pico eNB and the UE may not need to coordinate it amongst themselves or otherwise configure the preamble via signaling since each entity will know it from the published radio standard. Regardless of how these entities know what is the dedicated preamble, the UE is not allowed to trigger a RACH procedure with this dedicated resource without the eNB requesting the UE to do so. This means that from the UE's perspective, during preamble and PRACH resource selection the UE will only see that dedicated preamble resource as being available when the UE is commanded by the macro eNB to perform a contention free RACH for interference probing purposes (for example, such a command may order the UE to select the dedicated PRACH preamble). In some embodiments, once the UE receives the preamble order from its serving eNB to transmit in such a dedicated PRACH resource the UE will not expect a random access response (RAR) message after the UE transmits this dedicated preamble.

[0032] Another advantage of having a RACH preamble dedicated for this interference probing purpose is that because the UE is not allowed to transmit this dedicated preamble on a PRACH resource without the eNB's prior request/command, the eNB could re-use that resource for PUSCH transmissions if needed. That is, the preamble may be dedicated for the interference probing purpose only on the RACH, and so can be used on other channels for other purposes. [0033] As an alternative implementation the eNB could schedule the dedicated preamble dynamically with the physical downlink control channel (PDCCH). In this case it is possible for the eNB to configure only the preamble related configuration, such as for example the root index. In one example of this the eNB may use the resource allocation (RA) field in the PDCCH to allocate the resource for preamble transmission. A new radio network temporary identifier (RNTI) for this PDCCH could be used as the indication to the pico eNB that this is a 'special' PDCCH used for interference probing purposes.

[0034] Whether the dedicated PRACH resource is broadcasted in system information (such as system information block 2 SIB2 for example) or configured per UE via dedicated signaling or pre-defined in a published radio standard, in one example implementation the eNB could re-use the current RACH order; that is, PDCCH format 1A which is defined in 3 GPP TS 36.212. [0035] For the alternative PDCCH implementation noted above the new RNTI can be used to scramble the PDCCH (for example, PRA-RNTI). As one non-limiting example Figure 2 is a table illustrating hexa-decimal RNTI values where the new dedicated PRA-RNTI 201 used to scramble the PDCCH has a hexadecimal value between 003D and FFF3. Regardless of the specific value, in one implementation the PDCCH format 1 A may be used to trigger the UE to send the interference probing preamble, and Figure 3 is a non-limiting example of a design of the code point fields for this embodiment where the PDCCH is used to indicate to the UE to transmit the dedicated interference probing preamble.

[0036] As noted above, the transmit power of this dedicated preamble transmission could be pre-defined, or it can be configured explicitly by the macro eNB in different implementations. For example, the macro eNB can configure the transmission power of this dedicated interference probing preamble to be the same as a sounding reference signal on the physical uplink shared channel (S S on the PUSCH), possibly with a power offset. Such an offset may be configured by the macro eNB, so that for example if the offset refers to power on the PUSCH there may be defined a reference PUSCH format which the offset is used to adjust for the dedicated preamble transmission. Alternatively, there may be defined a nominal power for the dedicated preamble which the macro eNB can configure, taking into account the interference measurement purpose of this preamble so that the UE would then simply follow the conventional power control mechanism to decide what transmit power to use with the dedicated preamble.

[0037] Following is one non-limiting example of such a power offset. In some example embodiments the eNB could configure the UE to transmit the dedicated interference probing preamble with SRS/PUSCH transmission power as adjusted with a configured offset P offset, according to:

,c ( (w) + 101og₁₀( _{SRS c})

+ PUSC C ) + «_c ) · PL_C + f_c [ⁱ)

[0038] In one non-limiting embodiment the eNB may also include a transmission power control (TPC) command for preamble transmission in the PDCCH format 1 A, to further adjust the UE's dedicated preamble transmission power.

[0039] Some embodiments of these teachings provide the technical effect of reducing the unnecessary steps from the conventional connection-establishment RACH procedure, which may prove to save significant amounts of signaling overhead and UE battery power. Additionally, some embodiments of these teachings may provide the technical effect of aiding the pico e B to obtain more accurate interference measurements by enabling the pico eNB to know in advance the appropriate transmit power of the interference probing preamble. [0040] Figure 4 presents an example for controlling a UE to operate according to some of the teachings detailed herein, and may be performed by the UE itself or by one or more components thereof such as a processor running executable software stored on a computer readable memory disposed within the UE (for example, a modem). At block 402 there is reserved within the UE at least one preamble dedicated for interference probing. The UE may do this by storing the preamble in its local memory but leaving it unavailable for purposes not related to interference probing, so for example such a preamble would be available for a RACH procedure by which the UE seeks to establish or re-establish a network connection. Then at block 404, in response to the UE receiving a command from a serving network access node such as the macro eNB to transmit the preamble dedicated for interference probing, the UE is caused to transmit the dedicated preamble on a physical random access channel PRACH.

[0041 ] In one example embodiment there is a set of preambles dedicated for interference probing which are configured for the UE, and the dedicated preamble that is transmitted by the UE is indicated to the UE in system information or in radio resource control (RRC) signaling. In another example the UE terminates a RACH procedure after transmitting the dedicated preamble.

[0042] In a still further example the command to transmit the dedicated preamble is received in a physical downlink control channel (PDCCH). In a particular embodiment the command to transmit the dedicated preamble comprises the PDCCH being scrambled with a radio network temporary identifier (RNTI) that is dedicated for interference probing, and in a further implementation the dedicated preamble is received from the serving network access node in a resource field of the PDCCH.

[0043] In another example embodiment the dedicated preamble is transmitted on the PRACH at a transmit power that is predefined for interference probing, and in one example above the predefined transmit power is based on transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH). In a more particular embodiment of this the predefined transmit power is offset from the transmit power used by the UE for transmitting the SRS or the PUSCH, where the offset is configured for the UE via signaling from the serving network access node.

[0044] Figure 5 presents one example for controlling a serving network access node such as the macro eNB in the above examples or whatever other access node is the aggressor node. Similar to Figure 4, the process of Figure 5 may be performed by the serving network access node itself or by one or more components thereof such as a processor running executable software stored on a computer readable memory disposed within the serving network access node. At block 502 the serving network access node commands a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing. Then at block 504 the serving network access node informs a victim network access node such as the pico eNB in the above example of the dedicated preamble, and at block 506 the serving network access node manages wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node.

[0045] In one example the serving network access node configures the UE with a set of preambles dedicated for interference probing and indicating to the UE the dedicated preamble to transmit via system information or via radio resource control (RRC) signaling.

[0046] In another example, after receiving the dedicated preamble from the UE the serving network access node terminates a RACH procedure of which the preamble transmission is a part by not transmitting in reply a random access response (RAR). [0047] In another example embodiment the command to transmit the dedicated preamble is sent by the serving network access node to the UE on a physical downlink control channel (PDCCH). In a particular embodiment the command to transmit the dedicated preamble comprises the PDCCH being scrambled with a radio network temporary identifier (RNTI) that is dedicated for interference probing. And in another particular embodiment the serving network access node provides the dedicated preamble to the UE in a resource field of the PDCCH.

[0048] In a further example embodiment, managing the wireless communications with the UE using ICIC with the victim network access node as in block 506 is contingent upon the victim network access node indicating to the serving/aggressor access node that the UE is a likely source of uplink interference.

[0049] In a still further example there is indicated to the UE a predefined transmit power at which the dedicated preamble is to be transmitted. In one example embodiment of this the predefined transmit power is based on transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH). In a particular embodiment of this example the predefined transmit power is offset from the transmit power used by the UE for transmitting the SRS or the PUSCH, where the offset is configured for the UE via signaling from the serving network access node. As detailed further below with respect to Figure 6, in some embodiments the offset is computed by the victim eNB wand the macro eNB provides to the UE the offset that the macro eNB receives from the victim eNB.

[0050] Figure 6 presents one example for controlling a victim access node such as the pico eNB in the above examples or whatever other access node is the victim node. Similar to Figure 5, the process of Figure 6 may be performed by the victim access node itself or by one or more components thereof such as a processor running executable software stored on a computer readable memory disposed within the victim access node. At block 602 the victim access node/eNB receives from a serving access node an indication of a preamble dedicated for interference probing. In one example this may be received at a modem of the victim eNB over an X2 interface. In response to block 602 the victim eNB at block 604 then monitors a PRACH for a transmission comprising the dedicated preamble, for example using its wireless receiver. And finally at block 606, if the victim eNB detects the dedicated preamble on the PRACH, it indicates to the serving access node whether a UE that transmitted the dedicated preamble on the PPvACH is a source of uplink interference to the victim access node. This indication to the serving eNB may also be sent over a X2 interface. [0051 ] In one example embodiment, the indication of block 606 whether the UE that transmitted the dedicated preamble on the PPvACH is the source of uplink interference to the victim access node is based on the victim eNB evaluating the dedicated preamble that is detected against a transmit power that is predefined for interference probing. [0052] It may not be optimum for the UE to follow the conventional mechanism for determining its transmit power on the PPvACH since this may not be the most useful for the victim eNB to detect potential uplink interference for SRS and/or PUSCH. For this reason, in one non-limiting example embodiment it is the victim eNB that calculates or otherwise decides the offset from the SRS/PUSCH transmission power that the UE should apply for its PRACH transmission power. In this example the victim eNB then provides the offset it decides to the macro/aggressor eNB (such as via the X2 interface for an implementation in an LTE network), and the macro/aggressor eNB provides it to the UE. The UE may then add this offset to the preamble transmission power to arrive at the transmission power it should use to send the interference proving dedicated preamble on the PRACH. The victim eNB may still calculate the offset according to a reference SRS/PUSCH format but this may be invisible to the UE since the victim eNB is deciding the offset internally in this example. For this example embodiment the victim eNB further sends to the serving access node an indication of transmit power to be used for transmitting the dedicated preamble on the PRACH, and the victim eNB also uses the indicated transmit power to determine the predefined transmit power for interference probing. And in a more specific example of this embodiment the indicated transmit power comprises an offset and the predefined transmit power for interference probing is determined by applying the offset to transmit power used by the UE for transmitting a SRS or a PUSCH.

[0053] The logic diagrams of Figures 4, 5 and 6 may be considered to illustrate the operation of a method, and a result of execution of a computer program stored in a computer readable memory, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate, whether such an electronic device is the UE or the serving eNB or the victim eNB or one or more components thereof such as a modem, chipset, or the like. The various blocks shown in Figures 4, 5 and 6 may also be considered as a plurality of coupled logic circuit elements constructed to carry out the associated function(s), or specific result of strings of computer program code or instructions stored in a memory.

[0054] Such blocks and the functions they represent are non-limiting examples, and may be practiced in various components such as integrated circuit chips and modules, and the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

[0055] Such circuit/circuitry embodiments include any of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of circuits and software (and/or firmware), such as: (i) a combination of processor(s) or (ii) portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as one or more network access nodes, to perform the various functions summarized at Figures 4, 5 and 6 and (c) 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 specification, including in any claims. As a further example, as used in this specification, 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" also covers, for example, a baseband integrated circuit or an application specific integrated circuit (ASIC) or a similar integrated circuit for a UE or a network device/radio network access node which operates according to these teachings.

[0056] Reference is now made to Figure 7 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing some embodiments of this invention. In Figure 7 a radio access network access node shown as a macro cell 22 is adapted for communication over a first wireless component carrier or frequency band 21 A with an apparatus, such as a mobile terminal or UE 20. The access node 22 may be any access node such as an eNB or a NodeB (including frequency selective repeaters and remote radio heads) of any wireless network, such as E-UTRAN/LTE/LTE-Advanced, UTRAN, HSDPA, WCDMA, GSM, GERAN, and the like. For completeness Figure 7 also shows a second radio access node implemented as a local area or pico cell 24 and which is adapted for communication over a second wireless component carrier or frequency band 2 IB, though in the above scenario the link 2 IB is not bi-directional with the UE but rather is where the uplink interference lies. There may also be a control interface 23 between these cells directly, which in E-UTRAN is implemented as an X2 interface over which the cells coordinate the dedicated preamble and transmit power for the UE as detailed above.

[0057] The operator network of which the macro and pico cells 22, 24 are a part may also include a network control element or other higher network entity such as a radio network controller RNC in the case of a UTRAN and WCDMA/HSDPA network, or a mobility management entity MME for the case of LTE/LTE- Advanced networks in which case the MME may also serve as the serving gateway S-GW as shown at Figure 4. This higher network entity 26 generally provides connectivity with the core cellular network and with further networks (e.g., a publicly switched telephone network PSTN and/or a data communications network/Internet).

[0058] The UE 20 includes processing means such as at least one data processor (DP) 20A, storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C, and communication means such as a transmitter TX 20D and a receiver RX 20E for bidirectional wireless communications with the macro cell 22 using the operative radio access technology. All of the relevant wireless communications are facilitated via one or more antennas 20F, though the antennas may or may not be a part of apparatus carrying out these teachings, for example when such apparatus are one or more components of the UE rather than the entire UE itself. Also stored in the MEM 20B at reference number 20G are the computer code or algorithms for the UE to operate according to exemplary embodiments above by learning the preamble that is dedicated for interference probing and/or the transmit power for sending that preamble, according the teachings detailed above by non-limiting example. [0059] The macro cell 22 also includes processing means such as at least one data processor (DP) 22A, storing means such as at least one computer-readable memory (MEM) 22B storing at least one computer program (PROG) 22C, and communication means such as a transmitter TX 22D and a receiver RX 22E for bidirectional wireless communications with the UE 20 on the first frequency band or carrier. All the wireless communications are via one or more antennas 22F, which for an eNB are typically implemented as an antenna array. The macro cell 22 stores at block 22G its own computer software code or algorithms to cause the macro cell 22 to operate as detailed above by commanding the UE 20 to transmit a dedicated preamble, which in some of the example embodiments above is done at a predetermined transmit power.

[0060] The pico cell 24 is similar to the macro cell, and includes processing means such as at least one data processor (DP) 24A, storing means such as at least one computer-readable memory (MEM) 24B storing at least one computer program (PROG) 24C, and communication means such as a transmitter TX 24D and a receiver RX 24E for wireless communications via one or more antennas 24F. Similar to the macro cell 22, the pico cell 24 stores at block 24G its own computer software code or algorithms to cause the pico cell 24 to operate as detailed above by listening for the dedicated preamble and/or using the predetermined transmit power to know whether this UE is the source of uplink interference to the pico eNB 24, as detailed above.

[0061 ] Also at Figure 7 is shown a higher network entity 26 above the radio access node 22. In UTRAN (for example, HSDPA and WCDMA) this higher network entity 26 may be a radio network controller RNC, whereas in LTE/LTE -Advanced this entity 26 may be a MME and/or a S-GW as noted above. However implemented, the higher network entity 26 includes processing means such as at least one data processor (DP) 26A, storing means such as at least one computer-readable memory (MEM) 26B storing at least one computer program (PROG) 26C, and communication means such as a modem 26F for bidirectional communications with the macro cell 22 and with other access nodes under its control or coordination over the data and control link 27.

[0062] While not particularly illustrated for the UE 20 or the cells 22, 24, those devices are also assumed to include as part of their wireless communicating means a modem and/or a chipset and/or an antenna chip which may or may not be inbuilt onto a radiofrequency (RF) front end module within those devices 20, 22, 24 and which also operates according to the teachings set forth above. [0063] At least one of the PROGs 22C, 24C in each of the cells 22, 24 is assumed to include a set of program instructions that, when executed by the associated DP 22A, 24A, enable the device to operate in accordance with some embodiments of this invention, as detailed above. The UE 20 and the macro cell 22 also have software stored in their respective MEM 20B/22B to implement certain aspects of these teachings, as detailed above. In these regards the example embodiments of this invention may be implemented at least in part by computer software stored on the MEM 20B, 22B, 24B, 26B which is executable by the DP 22A, 24A of the respective cell 22, 24 and/or by the DP 20A of the UE 20 and/or by the DP 26A of the higher network entity 26; or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware) in any one or more of these devices 20, 22, 24, 26. In this manner the respective DP with the MEM and stored PROG may be considered a data processing system. Electronic devices implementing some embodiments of the invention need not be the entire devices as depicted at Figure 4 or may be one or more components of same such as the above described tangibly stored software, hardware, firmware and DP, a system on a chip SOC, an application specific integrated circuit ASIC, a digital signal processor DSP, a modem, an antenna module, or a RF front end module as noted above. [0064] In general, the various embodiments of the UE 20 can include, but are not limited to personal portable digital assistance devices having wireless communication capabilities, including but not limited to cellular and other mobile phones (including smart phones), navigation devices, laptop/palmtop/tablet computers, digital cameras and music devices, Internet appliances, USB dongles and data cards, machine-to-machine communication devices, and the like.

[0065] Various embodiments of the computer readable MEMs 20B, 22B, 24B, 26B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 20A, 22A, 24A, 26A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.

[0066] Various modifications and adaptations to the foregoing example embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the example embodiments have been described above in the context of the E-UTRAN systems, as noted above the example embodiments of this invention are not limited for use with only these particular types of wireless radio access technology networks. [0067] Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

WHAT IS CLAIMED IS:

1. A method for controlling a user equipment, the method comprising:

reserving at least one preamble dedicated for interference probing; and in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing, causing the UE to transmit the dedicated preamble on a physical random access channel (PRACH).

2. The method according to claim 1 , wherein there is a set of preambles dedicated for interference probing which are configured for the UE, and the dedicated preamble that is transmitted by the UE is indicated to the UE in system information or in dedicated radio resource control (RRC) signaling received from the serving network access node.

3. The method according to claim 1 or 2, the method further comprising:

terminating a RACH procedure after transmitting the dedicated preamble.

4. The method according to any of claims 1-3, wherein the command to transmit the dedicated preamble is received in a physical downlink control channel (PDCCH).

5. The method according to claim 4, wherein the command to transmit the dedicated preamble comprises the PDCCH being scrambled with a radio network temporary identifier (RNTI) that is dedicated for interference probing.

6. The method according to claim 4 or 5, wherein the dedicated preamble is indicated in a resource field of the PDCCH.

7. The method according to any of claims 1-6, wherein the dedicated preamble is transmitted on the PRACH at a transmit power that is predefined for interference probing.

8. The method according to claim 7, wherein the predefined transmit power is based on transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH).

9. The method according to claim 8, wherein the predefined transmit power is offset from the transmit power used by the UE for transmitting the SRS or the PUSCH, where the offset is configured for the UE via signaling from the serving network access node.

10. An apparatus for controlling a user equipment in which the apparatus comprises a processing system and the processing system comprises at least one processor, and at least one memory including computer program code;

wherein the processing system is configured to cause the apparatus to at least:

reserve at least one preamble dedicated for interference probing; and in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing, cause the UE to transmit the dedicated preamble on a physical random access channel (PRACH).

11. The apparatus according to claim 10, wherein there is a set of preambles dedicated for interference probing which are configured for the UE, and the dedicated preamble that is transmitted by the UE is indicated to the UE in system information or in dedicated radio resource control (RRC) signaling received from the serving network access node.

12. The apparatus according to claim 10 or 11, wherein the processing system is configured to cause the apparatus to further:

terminate a RACH procedure after transmitting the dedicated preamble.

13. The apparatus according to any of claims 10-12, wherein the command to transmit the dedicated preamble is received in a physical downlink control channel (PDCCH).

14. The apparatus according to claim 13, wherein the command to transmit the dedicated preamble comprises the PDCCH being scrambled with a radio network temporary identifier (RNTI) that is dedicated for interference probing.

15. The apparatus according to claim 13 or 14, wherein the dedicated preamble is indicated in a resource field of the PDCCH.

16. The apparatus according to any of claims 10-15, wherein the dedicated preamble is transmitted on the PRACH at a transmit power that is predefined for interference probing.

17. The apparatus according to claim 16, wherein the predefined transmit power is based on transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH).

18. The apparatus according to claim 17, wherein the predefined transmit power is offset from the transmit power used by the UE for transmitting the SRS or the PUSCH, where the offset is configured for the UE via signaling from the serving network access node.

19. The apparatus according to any of claims 10-18, wherein the apparatus comprises the user equipment.

20. A computer readable memory tangibly storing a set of computer readable instructions that are executable on a data processing system for controlling a user equipment, wherein the computer readable instructions comprise:

code for reserving at least one preamble dedicated for interference probing; and code for causing the UE to transmit the dedicated preamble on a physical random access channel (PRACH) in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing.

21. The computer readable memory according to claim 20, wherein the dedicated preamble is transmitted on the PRACH at a transmit power that is predefined for interference probing.

22. An apparatus for controlling a user equipment, the apparatus comprising: storing means for reserving at least one preamble dedicated for interference probing; and

control and communication means for causing the UE to transmit the dedicated preamble on a physical random access channel (PRACH) in response to the user equipment (UE) receiving a command from a serving network access node to transmit the preamble dedicated for interference probing.

23. A method for operating in a serving network access node, the method comprising:

commanding a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing;

informing a victim network access node of the dedicated preamble; and managing wireless communications with the UE using interference

coordination and interference cancellation (ICIC) with the victim network access node.

24. The method according to claim 23, the method further comprising configuring the UE with a set of preambles dedicated for interference probing and indicating to the UE the dedicated preamble to transmit via system information or via dedicated radio resource control (RRC) signaling.

25. The method according to claim 23 or 24, the method further comprising:

after receiving the dedicated preamble from the UE, terminating a RACH procedure of which the preamble transmission is a part by not transmitting in reply a random access response (RAR).

The method according to any of claims 23-25, wherein the command to transmit the dedicated preamble is sent to the UE on a physical downlink control channel (PDCCH).

27. The method according to claim 26, wherein the command to transmit the dedicated preamble PUSCH comprises the PDCCH being scrambled with a radio network temporary identifier (RNTI) that is dedicated for interference probing.

28. The method according to claim 26 or 27, wherein the serving network access node indicates the dedicated preamble to transmit to the UE in a resource field of the PDCCH.

29. The method according to any of claims 23-28, wherein managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node is contingent upon the victim network access node indicating that the UE is a source of uplink interference.

30. The method according to any of claims 23-29, the method further comprising: indicating to the UE a predefined transmit power at which the dedicated preamble is to be transmitted.

31. The method according to claim 30, wherein the predefined transmit power is based on transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH).

32. The method according to claim 31, wherein the indication of the predefined transmit power sent to the UE comprises an offset to be applied to the transmit power used by the UE for transmitting the SRS or the PUSCH, where the offset is configured for the UE via signaling from the serving network access node.

33. An apparatus for controlling a serving network access node in which the apparatus comprises a processing system and the processing system comprises at least one processor, and at least one memory including computer program code; wherein the processing system is configured to cause the apparatus to at least:

command a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing;

inform a victim network access node of the dedicated preamble; and manage wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node.

34. The apparatus according to claim 34, wherein the processing system is configured to cause the apparatus further to:

configure the UE with a set of preambles dedicated for interference probing and indicate to the UE the dedicated preamble to transmit via system information or via dedicated radio resource control (RRC) signaling.

35. The apparatus according to claim 33 or 34, wherein the processing system is configured to cause the apparatus further to:

after receiving the dedicated preamble from the UE, terminate a RACH procedure of which the preamble transmission is a part by not transmitting in reply a random access response (RAR).

36. The apparatus according to any of claims 33-35, wherein the command to transmit the dedicated preamble is sent by a serving network access node to the UE on a physical downlink control channel (PDCCH).

37. The apparatus according to claim 36, wherein the command to transmit the dedicated preamble PUSCH comprises the PDCCH being scrambled with a radio network temporary identifier (RNTI) that is dedicated for interference probing.

38. The apparatus according to claim 36 or 37, wherein the dedicated preamble is indicated to the UE in a resource field of the PDCCH.

39. The apparatus according to any of claims 33-38, wherein managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node is contingent upon the victim network access node indicating that the UE is a likely source of uplink interference.

40. The apparatus according to any of claims 33-39, wherein the processing system is configured to cause the apparatus further to:

indicate to the UE a predefined transmit power at which the dedicated preamble is to be transmitted.

41. The apparatus according to claim 40, wherein the predefined transmit power is based on transmit power used by the UE for transmitting a sounding reference signal

(SRS) or a physical uplink shared channel (PUSCH).

42. The apparatus according to claim 41, wherein the indication of the predefined transmit power sent to the UE comprises an offset to be applied to the transmit power used by the UE for transmitting the SRS or the PUSCH, where the offset is configured for the UE via signaling from the serving network access node.

43. The apparatus according to any of claims 33-42, wherein the apparatus comprises an enhanced Node B.

44. A computer readable memory tangibly storing a set of computer readable instructions that are executable on a data processing system for controlling a serving network access node, wherein the computer readable instructions comprise:

code for commanding a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing;

code for informing a victim network access node of the dedicated preamble; and code for managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node.

45. The computer readable memory according to claim 44, wherein the computer readable instructions further comprise:

code for indicating to the UE a predefined transmit power at which the dedicated preamble is to be transmitted.

46. An apparatus for operating a serving network access node, the apparatus comprising:

communication means for commanding a user equipment (UE) to transmit on a physical random access channel (PRACH) a preamble dedicated for interference probing;

communication means for informing a victim network access node of the dedicated preamble; and

control means for managing wireless communications with the UE using interference coordination and interference cancellation (ICIC) with the victim network access node.

47. A method for operating a victim access node, the method comprising:

receiving from a serving access node an indication of a preamble dedicated for interference probing;

monitoring a physical random access channel (PRACH) for a transmission comprising the dedicated preamble; and

if the dedicated preamble is detected on the PRACH, indicating to the serving access node whether a UE that transmitted the dedicated preamble on the PRACH is a source of uplink interference to the victim access node.

48. The method according to claim 47, wherein indicating whether the UE that transmitted the dedicated preamble on the PRACH is the source of uplink interference to the victim access node comprises evaluating the dedicated preamble that is detected against a transmit power that is predefined for interference probing.

49. The method according to claim 47 or 48, the method further comprising: causing the victim access node to send to the serving access node an indication of transmit power to be used for transmitting the dedicated preamble on the PRACH, and using the indicated transmit power to determine the predefined transmit power for interference probing.

50. The method according to claim 49, wherein the indicated transmit power comprises an offset decided by the victim access node, and the predefined transmit power for interference probing is determined by applying the offset to transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH).

51. An apparatus for controlling a victim access node in which the apparatus comprises a processing system and the processing system comprises at least one processor, and at least one memory including computer program code;

wherein the processing system is configured to cause the apparatus to at least:

in response to receiving from a serving access node an indication of a preamble dedicated for interference probing, monitoring a physical random access channel

(PRACH) for a transmission comprising the dedicated preamble; and

indicate to the serving access node, if the dedicated preamble is detected on the

PRACH, whether a UE that transmitted the dedicated preamble on the PRACH is a source of uplink interference to the victim access node.

52. The apparatus according to claim 51 , wherein the indication whether the UE that transmitted the dedicated preamble on the PRACH is the source of uplink interference to the victim access node is based on evaluating the dedicated preamble that is detected against a transmit power that is predefined for interference probing.

53. The apparatus according to claim 51 or 52, wherein the processing system is configured to cause the apparatus further to:

send to the serving access node an indication of transmit power to be used for transmitting the dedicated preamble on the PRACH, and use the indicated transmit power to determine the predefined transmit power for interference probing.

54. The apparatus according to claim 53, wherein the indicated transmit power comprises an offset decided by the processing system, and the predefined transmit power for interference probing is determined by applying the offset to transmit power used by the UE for transmitting a sounding reference signal (SRS) or a physical uplink shared channel (PUSCH).

55. The apparatus according to any of claims 51-54, wherein the apparatus comprises an enhanced Node B.

56. A computer readable memory tangibly storing a set of computer readable instructions that are executable on a data processing system for controlling a victim access node, wherein the computer readable instructions comprise:

code for monitoring a physical random access channel (PRACH) for a transmission comprising a dedicated preamble in response to receiving from a serving access node an indication of the preamble which is dedicated for interference probing; and

code for indicating to the serving access node, if the dedicated preamble is detected on the PRACH, whether a UE that transmitted the detected preamble on the PRACH is a source of uplink interference to the victim access node.

57. The computer readable memory according to claim 56, wherein the computer readable instructions further comprise:

code for sending to the serving access node an indication of transmit power to be used for transmitting the dedicated preamble on the PRACH, and

code for determining from the indicated transmit power the predefined transmit power for interference probing.

58. An apparatus for operating a victim access node, the apparatus comprising: communication means for receiving from a serving access node an indication of a preamble dedicated for interference probing;

communication means for monitoring a physical random access channel

(PRACH) for a transmission comprising the dedicated preamble; and

processing and communications means for indicating to the serving access node, if the dedicated preamble is detected on the PRACH, whether a UE that transmitted the dedicated preamble on the PRACH is a source of uplink interference to the victim access node.