Method and Node for Supporting Network Assisted Interference Cancellation

Abstract

The present invention relates to a method for supporting network assistance interference cancellation at a first wireless device served by a first radio network node of a wireless communication network. A transmission of a second radio network node of the wireless communication network directed to a second wireless device interferes with a transmission of the first radio network node directed to the first wireless device. The method is performed in the second radio network node and comprises determining (610) whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device, and transmitting (620) the network assistance information to the first wireless device based on the determining.

Claims

1-23. (canceled)

24. A method for supporting network assistance interference cancellation at a first wireless device served by a first radio network node of a wireless communication network, wherein a transmission of a second radio network node of the wireless communication network directed to a second wireless device interferes with a transmission of the first radio network node directed to the first wireless device, the method being performed in the second radio network node and comprising: determining whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device; and transmitting the network assistance information to the first wireless device based on the determining.

25. The method according to claim 24, further comprising: obtaining information related to an efficiency of the network assisted interference cancellation at the first wireless device; and wherein the determining is based on the obtained information.

26. The method according to claim 25, wherein obtaining information related to the efficiency of the network assisted interference cancellation at the first wireless device comprises estimating an efficiency of the network assisted interference cancellation at the first wireless device, and wherein the determining to transmit the network assistance information is based on the estimated efficiency.

27. A second radio network node for a wireless communication network configured to support network assisted interference cancellation at a first wireless device served by a first radio network node of the wireless communication network, wherein the second radio network node is configured to perform a transmission directed to a second wireless device, the transmission interfering with a transmission of the first radio network node directed to the first wireless device, the second radio network node comprising: radio circuitry configured for communication with the first and second wireless devices; and processing circuitry operatively associated with the radio circuitry and configured to: determine whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device; and transmit the network assistance information to the first wireless device based on the determining.

28. The second radio network node according to claim 27, wherein the processing circuitry is configured to: obtain information related to an efficiency of the network assisted interference cancellation at the first wireless device; and determine whether to transmit the network assistance information based on the obtained information.

29. The second radio network node according to claim 28, wherein the processing circuitry is configured to: obtain information related to the efficiency of the network assisted interference cancellation at the first wireless device by estimating an efficiency of the network assisted interference cancellation at the first wireless device; and determine to transmit the network assistance information based on the estimated efficiency.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1a is a schematic illustration of a WCDMA/HSPA radio network in which the present invention may be applied.

[0027] FIG. 1b is a schematic illustration of a UTRAN in which the present invention may be applied.

[0028] FIGS. 2a-c are block diagrams schematically illustrating example deployments of heterogeneous networks.

[0029] FIG. 3a is a diagram schematically illustrating the link throughput degradation for a victim UE due to aggressor node interference.

[0030] FIG. 3b is a diagram schematically illustrating link throughput improvement when using NAIC.

[0031] FIG. 4 is a signaling diagram illustrating the message sequences used for conveying network assistance information.

[0032] FIG. 5 is a schematic illustration of wireless devices with different geometry factors.

[0033] FIGS. 6a-d are flowcharts illustrating the method in the radio network node according to embodiments.

[0034] FIGS. 7a-b are block diagrams schematically illustrating the radio network node according to embodiments.

DETAILED DESCRIPTION

[0035] In the following, different aspects will be described in more detail with references to certain embodiments and to accompanying drawings. For purposes of explanation and not limitation, specific details are set forth, such as particular scenarios and techniques, in order to provide a thorough understanding of the different embodiments. However, other embodiments that depart from these specific details may also exist.

[0036] Embodiments are described in a non-limiting general context in relation to an example scenario in a HSPA heterogeneous radio network, where an aggressor HPN transmission interferes with an LPN transmission to a wireless device. However, it should be noted that the embodiments may be applied to any network technology supporting NAIC such as the LTE technology. Furthermore, the network can be a homogeneous network deployment as well as any kind of heterogeneous network deployment where the downlink transmission of one node interferes with a downlink transmission of another node, such as any co-channel or combined cell deployment scenario.

[0037] In embodiments of the invention, the problem related to the signaling resource consumption for network assistance information signaling in a node supporting NAIC, is addressed by a solution where the power need is minimized by not transmitting the network assistance information at all times, but only when such transmission is deemed necessary. In this way the NAIC procedure applying signaling of e.g. scheduling information for the interfering transmission to the UE does not unduly deteriorate the own cell throughput performance.

[0038] NAIC is most effective if the victim UE is able to decode the data packet in the interfering transmission from the aggressor node scheduled to another UE. If the victim UE can't decode this packet, the gains of interference cancellation are usually smaller, in some cases even negligible. Hence when the victim UE cannot decode the aggressor node's transmission in current reception conditions, the power allocated to signaling over the network assisted control channel is typically wasted as there is no gain at system or link level. Therefore, it is preferable to switch off the network assisted control channel such that it isn't transmitting in such cases. The power allocated to the network assisted control channel may then be allocated to other channels. In one example scenario, the power can be allocated to data channels instead, thereby improving the throughput performance of the UE's in the aggressor cell as well as the overall system performance.

[0039] Hereinafter, different embodiments of how the aggressor node can decide whether to transmit the network assisted control channel or not are described. The decision of whether to transmit network assistance information is based on different criteria in the different embodiments.

EMBODIMENT A

[0040] In a first embodiment A, the decision of whether to transmit network assistance information is an autonomous decision by the aggressor node. The decision is based on the geometry aspects of the UE in the cell served by the aggressor node. The aggressor node determines to not transmit network assistance information on the network assisted control channel if the geometry factor of the UE it is serving is greater than a pre-configured threshold G_Th. The reason is that if the aggressor node is serving a UE with a high geometry factor, meaning that the UE is close to the aggressor node, then the UE in the cell of the victim LPN, which is typically at or beyond the cell edge of the cell served by the aggressor node, usually cannot fully decode the data packet intended for the UE in the aggressor cell. By fully decode we here mean that the information bits can be detected with no error as indicated by, e.g., a Cyclic Redundancy Check (CRC). This is further explained with reference to FIG. 5. The aggressor HPN 201 is serving UE's 211, 212, and 213 at different locations, and the LPN 202 is serving a UE 210. If G_Th is chosen such that only 211 and 212 are considered as high geometry UEs and if the aggressor HPN 201 is serving these UEs in any Transmission Time Interval (TTI), then the network assisted control channel can be switched off.

[0041] There are several different possible techniques for computing the geometry of the UE served by the HPN in the cell. One example is to determine the geometry based on CQI reports from the UE. In HSDPA and in LTE, the UE reports a periodic or an aperiodic CQI determined based on UE measurements of the pilot or reference signal transmitted by the serving node. The NodeB/eNodeB can determine the geometry factor of the UE by averaging the CQI reports over time. Alternatively, the NodeB/eNodeB can determine the geometry factor of the UE from the UE's downlink mobility measurement reports.

[0042] Another example is to determine the geometry based on uplink measurements performed by the aggressor node. From the uplink measurements, such as UE traffic channel or control channel measurements, the geometry factor of the UE may be determined based on the uplink received signal strength.

EMBODIMENT B

[0043] In a second embodiment B, the decision of whether to transmit network assistance information is also an autonomous decision by the aggressor node. The decision is based on the aggressor node's scheduling parameters used for the transmission to the UE in the serving cell of the aggressor node. This embodiment is similar to embodiment A, however, instead of finding the geometry of the currently served UE, the aggressor node bases it decision to transmit the network assisted control channel on the scheduling parameters for that UE. In analogy with the case of a UE with a high geometry factor, a UE which is allocated a less robust modulation and coding by the aggressor node means that it is unlikely that the victim UE can fully decode the data packet transmitted by the aggressor node to this UE. The decision could also be based on instantaneous or recent CQI values reported by the served UE, since the scheduled rate is closely related to the received CQI reports.

[0044] In embodiment B, the decision to transmit the assistance information will provide a more instantaneous optimization, in contrast to the embodiment A where the geometry factor is a long-term parameter.

[0045] In one example of embodiment B, the aggressor node assigns a certain modulation scheme and a certain transport block size in the i:th TTI. This means that the aggressor node assigns a number of bits equal to Mi, and a code rate equal to Ri. The aggressor node may then determine that the network assisted control channel is transmitted only when f(Mi*RI)<M_Th, where M_Th is a preconfigured threshold. In another example of embodiment B, the aggressor node can compute Mi*Ri over a period of time for a UE and decide not to transmit the network assisted control channel for the UE if the UE's scheduling factor (SF) is greater than a preconfigured threshold, where the scheduling factor is defined as

[00001]$\mathrm{SF}=\underset{i=1}{\overset{N}{.Math.}}.Math..Math.\mathrm{MiRi}/N$

where N is the number of scheduled TTIs observed.

EMBODIMENT C

[0046] In a third embodiment C, the decision whether to transmit network assistance information is a decision by the aggressor node based on knowledge about scheduling parameters and interference cancellation (IC) gains at the victim UE. In a UE applying soft IC, which may be either pre-decoding IC or post-decoding IC, the metric which is important for this embodiment is the difference between pre-decoding IC and post-decoding IC gain. To obtain significant post-decoding IC gains, it is not necessary to fully decode the packet. Even when the Signal to Interference plus Noise Ratio (SINR) is lower than that required for full decoding, the victim UE may be able to achieve high cancellation efficiencies, especially for high code rates. However, when the SINR gap exceeds a certain threshold which is transport format specific, post-decoding IC gains become negligible. As pre-decoding IC is typically possible without network assistance information while post-decoding IC requires network assistance information, the aggressor cell should only transmit the network assistance information over the network assisted control channel when post-decoding gains are likely to be higher than pre-decoding gains.

[0047] In one example embodiment, the aggressor node determines the transport format for the currently scheduled UE based on the scheduling parameters. Furthermore, the aggressor node evaluates the expected post-decoding IC gains over pre-decoding IC for that transport format and at geometries that are typical for the victim UE. The expected gains may be expressed as an improvement of cancellation efficiency, e.g. using a pre-computed look-up table, or as an improvement of SINR after IC. The aggressor node then decides to transmit the network assisted control channel if the expected gains exceed a threshold.

EMBODIMENT D

[0048] In a fourth embodiment D, the decision of whether to transmit network assistance information is a decision by the aggressor node made with assistance information from the victim LPN. In one example embodiment, the LPN serving the victim UE shares its scheduling information on a TTI level with the aggressor node through a high speed link. The aggressor node may then decide not to transmit the network assisted control channel if the scheduling information from the LPN indicates the victim UE would need a more robust coding or lower scheduling factor than those corresponding to the scheduling information used by the aggressor node.

EMBODIMENT E

[0049] In a fifth example embodiment E, the LPN serving the victim UE explicitly indicates to the aggressor node not to transmit the network assisted control channel. This may be used when the victim UE is close to the LPN. Another example is when there are no UEs in the victim cell that can benefit from the network assisted control channel, a decision made by the LPN based e.g. on a UE category or capability.

EMBODIMENT F

[0050] In a sixth embodiment F, the decision of whether to transmit network assistance information is a decision by the aggressor node made with assistance information from an RNC. The RNC regulates the offloading factor by setting the cell selection offset parameters, e.g. the cell individual offset (CIO) as defined in the 3GPP specifications. When a HPN cell is overloaded, the RNC can use CIO to increase offloading from the HPN cell to LPN cells. Thus, the aggressor HPN can learn from the RNC about the CIO settings. If the CIO setting indicates that no aggressive off-loading of the HPN is applied, it may mean that no UE's will be in the LPN range expansion area. The aggressor HPN may then decide not to transmit the network assisted control channel.

Method and Radio Network Node

[0051] FIG. 6a is a flowchart illustrating one embodiment of a method for supporting network assistance interference cancellation at a first wireless device 730 served by a first radio network node 740 of a wireless communication network. A transmission of a second radio network node 720 of the wireless communication network directed to a second wireless device 710 interferes with a transmission of the first radio network node directed to the first wireless device. The method is performed in the second radio network node 720 and comprises: [0052] 610: Determining whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device. [0053] 620: Transmitting the network assistance information to the first wireless device based on the determining. The network assistance information is transmitted to the first wireless device when it is determined to transmit.

[0054] FIG. 6b is a flowchart illustrating another embodiment of the method. The method optionally comprises: [0055] 600: Obtaining information related to an efficiency of the network assisted interference cancellation at the first wireless device.

[0056] The method also comprises: [0057] 610: Determining whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device, wherein the determining is based on the obtained information [0058] 620: Transmitting the network assistance information to the first wireless device based on the determining.

[0059] FIG. 6c is a flowchart illustrating an embodiment of the method described with reference to FIG. 6b. Obtaining 600 information related to the efficiency of the network assisted interference cancellation at the first wireless device comprises estimating 601 an efficiency of the network assisted interference cancellation at the first wireless device. In 610 it is thus determined to transmit the network assistance information based on the estimated efficiency.

[0060] In one embodiment, estimating 601 the efficiency of the network assisted interference cancellation at the wireless device may comprise determining a geometry factor of the second wireless device, and estimating that the network assisted interference cancellation at the first wireless device is efficient if the geometry factor is lower than a first threshold. One example embodiment is embodiment A described previously. The geometry factor may be determined based on at least one of channel quality measurement reports received from the second wireless device, signal quality measurement reports received from the second wireless device, and uplink measurements on channels of the second wireless device.

[0061] In another embodiment, the efficiency may be estimated 601 based on scheduling parameters used for the transmission of the second radio network node directed to the second wireless device. One example embodiment is embodiment B described previously.

[0062] In still another embodiment, estimating 601 the efficiency of the network assisted interference cancellation at the wireless device may comprise determining a gain for post-decoding interference cancellation over pre-decoding interference cancellation at the first wireless device, and estimating that the network assisted interference cancellation at the first wireless device is efficient if the gain for post-decoding interference cancellation over pre-decoding interference cancellation exceeds a second threshold. One example embodiment is embodiment C described previously.

[0063] FIG. 6d is a flowchart illustrating an alternative embodiment to the method described with reference to FIG. 6c. In this embodiment, obtaining 600 information related to the efficiency of the network assisted interference cancellation at the first wireless device, may comprise receiving 602 the information related to the efficiency of the network assisted interference cancellation at the first wireless device from another node. In one embodiment, the information related to the efficiency of the network assisted interference cancellation at the first wireless device may be received 602 from the first radio network node and may comprise scheduling parameters used for the transmission of the first radio network node directed to the first wireless device. The determining 610 may thus comprise comparing scheduling parameters used for the transmission of the second radio network node directed to the second wireless device with the received scheduling parameters used for the transmission of the first radio network node directed to the first wireless device, and determining to transmit the network assistance information based on the comparison. One example embodiment is embodiment D described previously.

[0064] In another embodiment, the information related to the efficiency of the network assisted interference cancellation at the first wireless device may be received 602 from the first radio network node, and indicates to the second radio network node not to transmit the network assistance information. One example embodiment is embodiment E described previously.

[0065] In a further embodiment, the information related to the efficiency of the network assisted interference cancellation at the first wireless device may be received 602 from an RNC controlling the first and the second radio network node. The information may comprise a level of off-loading indicating to what extent the second radio network node is offloaded by the first radio network node. It may be determined 610 to transmit the network assistance information if the level of off-loading exceeds a third threshold. One example embodiment is embodiment F described previously.

[0066] An embodiment of a second radio network node 720 for a wireless communication network is schematically illustrated in the block diagram in FIG. 7a. The second radio network node 720 is configured to support network assisted interference cancellation at a first wireless device 730 served by a first radio network node 740 of the wireless communication network. The second radio network node 720 is configured to perform a transmission directed to a second wireless device 710, the transmission interfering with a transmission of the first radio network node 740 directed to the first wireless device 730. The second radio network node 720 is configured to determine whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device. The second radio network node 720 is also configured to transmit the network assistance information to the first wireless device based on the determining. The first and the second radio network nodes may be NodeBs in a UTRAN, and the first and second wireless devices may be UEs.

[0067] In one embodiment, the second radio network node 720 may be further configured to obtain information related to an efficiency of the network assisted interference cancellation at the first wireless device, and to determine whether to transmit the network assistance information based on the obtained information.

[0068] In a further embodiment, the second radio network node 720 may be further configured to obtain information related to the efficiency of the network assisted interference cancellation at the first wireless device by estimating an efficiency of the network assisted interference cancellation at the first wireless device. The second radio network node 720 may be further configured to determine to transmit the network assistance information based on the estimated efficiency. In still another embodiment, the second radio network node 720 may be further configured to estimate the efficiency of the network assisted interference cancellation at the wireless device by determining a geometry factor of the second wireless device, and estimating that the network assisted interference cancellation at the first wireless device is efficient if the geometry factor is lower than a first threshold. In one embodiment, the second radio network node 720 may be further configured to determine the geometry factor based on at least one of channel quality measurement reports received from the second wireless device, signal quality measurement reports received from the second wireless device, and uplink measurements on channels of the second wireless device.

[0069] In another embodiment, the second radio network node 720 may be further configured to estimate the efficiency of the network assisted interference cancellation at the wireless device based on scheduling parameters used for the transmission of the second radio network node directed to the second wireless device.

[0070] In one embodiment, the second radio network node 720 may be further configured to estimate the efficiency of the network assisted interference cancellation at the wireless device by determining a gain for post-decoding interference cancellation over pre-decoding interference cancellation at the first wireless device, and estimating that the network assisted interference cancellation at the first wireless device is efficient if the gain for post-decoding interference cancellation over pre-decoding interference cancellation exceeds a second threshold.

[0071] In another embodiment, the second radio network node 720 may be further configured to obtain information related to the efficiency of the network assisted interference cancellation at the first wireless device by receiving the information related to the efficiency of the network assisted interference cancellation at the first wireless device from another node. In one embodiment, the second radio network node 720 may be further configured to receive the information related to the efficiency of the network assisted interference cancellation at the first wireless device from the first radio network node. The received information may comprise scheduling parameters used for the transmission of the first radio network node directed to the first wireless device. The second radio network node 720 may be further configured to compare scheduling parameters used for the transmission of the second radio network node directed to the second wireless device with the received scheduling parameters used for the transmission of the first radio network node directed to the first wireless device, and to determine to transmit the network assistance information based on the comparison. In another embodiment, the second radio network node 720 may be further configured to receive the information related to the efficiency of the network assisted interference cancellation at the first wireless device from the first radio network node, the received information indicating to the second radio network node not to transmit the network assistance information. In still another embodiment, the second radio network node 720 may be further configured to receive the information related to the efficiency of the network assisted interference cancellation at the first wireless device from an RNC controlling the first and the second radio network node. The received information may comprise a level of off-loading indicating to what extent the second radio network node is offloaded by the first radio network node. The second radio network node 720 may be further configured to determine to transmit the network assistance information if the level of off-loading exceeds a third threshold.

[0072] In embodiments of the invention, the second radio network node 720 may comprise a processor 722 and a memory 723. The second radio network node 720 may also comprise a radio interface circuit 721 configured to communicate with the second wireless device 710, and connected to the processor 722. The memory 723 may comprise instructions executable by the processor 722. The second radio network node 720 may thereby be operative to determine whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device. The second radio network node 720 may also be operative to transmit the network assistance information to the first wireless device based on the determining. In one embodiment, the second radio network node 720 may be operative to obtain information related to an efficiency of the network assisted interference cancellation at the first wireless device, and to determine whether to transmit the network assistance information based on the obtained information. The first radio network node 740 of the wireless communication network, also illustrated in FIG. 7b, may also comprise a radio interface circuit 741 for the communication with the first wireless device.

[0073] In an alternative way to describe the embodiment in FIG. 7a, illustrated in FIG. 7b, the second radio network node 720 comprises a determining module 725 adapted to determine whether to transmit network assistance information related to the transmission of the second radio network node to support interference cancellation at the first wireless device, and a transmitting module 726 adapted to transmit the network assistance information to the first wireless device 710 based on the determining. The modules described above are functional units which may be implemented in hardware, software, firmware or any combination thereof. In one embodiment, the modules are implemented as a computer program running on a processor.

[0074] In an alternative way to describe the embodiment in FIG. 7a, the second radio network node 720 comprises a Central Processing Unit (CPU) which may be a single unit or a plurality of units. Furthermore, second radio network node 720 comprises at least one computer program product (CPP) in the form of a non-volatile memory, e.g. an EEPROM (Electrically Erasable Programmable Read-Only Memory), a flash memory or a disk drive. The CPP comprises a computer program, which comprises code means which when run on the second radio network node 720 causes the CPU to perform steps of the procedure described earlier in conjunction with FIGS. 6a-d. In other words, when said code means are run on the CPU, they correspond to the processor 722 of FIG. 7a.

[0075] The above mentioned and described embodiments are only given as examples and should not be limiting. Other solutions, uses, objectives, and functions within the scope of the accompanying patent claims may be possible.