WO2015168864A1

WO2015168864A1 - Method and device for cooperative interference management in small cell networks

Info

Publication number: WO2015168864A1
Application number: PCT/CN2014/076897
Authority: WO
Inventors: Gang Wang; Zengfeng ZHANG; Lingyang Song
Original assignee: Nec Corporation
Priority date: 2014-05-06
Filing date: 2014-05-06
Publication date: 2015-11-12

Abstract

Embodiments of the present invention provide methods and devices for cooperative interference management in small cell networks. The wireless network including a plurality of coalitions, wherein each coalition consists of one or more devices capable of cooperating with each other, and the method comprising discovering coalitions in the wireless network, selecting, from the discovered coalitions, one or more potential coalitions to join and assigning an associated coalition to each resource unit, respectively, wherein the associated coalition is one of the selected potential coalitions and each resource unit is to be shared in collision-free mode by all devices in the associated coalition assigned to it. Corresponding devices are also disclosed.

Description

METHOD AND DEVICE FOR COOPERATIVE INTERFERENCE MANAGEMENT IN SMALL CELL NETWORKS

FIELD OF THE INVENTION

[0001] Example embodiments of the present invention relate generally to the wireless communication and, more specifically, to a method and devices for cooperative interference management in small cell networks.

BACKGROUND OF THE INVENTION

[0002] Due to the recent booming of the wireless internet, it is expected that the demand for high-speed wireless data service will keep on fast soaring in the near future. Among those advanced technologies proposed to meet the challenging demand, reducing the cell size is one of the most prominent one. In the past 50 years, the wireless network capacity has been increased by thousands of times from smaller cells. Therefore, the small cell network as a supplement to the macro-cellular network aiming to boost cell capacity and coverage has become a hot research topic, e.g., in 3rd Generation Partnership Project (3GPP) standardization.

[0003] A network with co-existence of small cells and macrocells is also called Heterogeneous Network (HetNet), which is characterized in a multiple-tier structure. Though HetNet provides deployment flexibility, system capacity improvement and coverage extension, it also brings technical challenges on interference management. For example, introduction of small cell base stations in a macrocell may interfere with the macrocells user equipments (UEs), and the transmission from macro base station may interfere with small cell UEs as well. Many works have been conducted to avoid or ameliorate such cross-tier interference, while the small cell co-tier interference, i.e., interference between small cells, has not been properly studied in the previous HetNet work.

[0004] In U.S. patent application No. 2012/0230267 Al filed on Sep. 13, 2012, entitled "Femtocell resource management for interference mitigation", methods and systems for managing resources in femtocells have been disclosed. One method includes categorizing the clients into two classes based on measurements. Class 1 clients have throughput benefits from reusing the spectrum while Class 2 clients have throughput benefits from interference mitigation via resource isolation. Such method can reduce interference, however, it is a centralized solution with high complexity and cooperation between femtocells has not been considered. In another U.S. patent application No. 2012/8285322 B2 filed on Oct. 9, 2012, entitled "Minimizing inter-femtocell downlink interference," a method for minimizing interference for mobile devices operating in a communication network has been disclosed. The method uses a priority order to determine the power that assigned to the base station for each femtocell. In this method, cooperation between small cells is still not well considered.

[0005] Considering that in dense small cell deployment, the co-tier small cell interference can be very high, especially in downlink, some embodiments of the present invention propose methods and devices to reduce the interference and improve the system performance in a cooperative way. SUMMARY OF THE INVENTION

[0006] Various embodiments of the invention aim at addressing at least part of the above problems and disadvantages. Other features and advantages of embodiments of the invention will also be understood from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the invention.

[0007] Various aspects of embodiments of the invention are set forth in the appended claims and summarized in this section. It shall be noted that the protection scope of the invention is only limited by the appended claims.

[0008] According to a first aspect, embodiments of the present invention provide a method, which comprises discovering coalitions in the wireless network, selecting, from the discovered coalitions, one or more potential coalitions to join and assigning an associated coalition to each resource unit, respectively, wherein the associated coalition is one of the selected potential coalitions and each resource unit is to be shared in collision-free mode by all devices in the associated coalition assigned to it.

[0009] In an example embodiment, selecting, from the discovered coalitions, one or more potential coalitions to join comprises, for each coalition S of the discovered coalitions, or, for each coalition S in a subset of the discovered coalitions, calculating a corresponding power cost which indicates the total required power for each device in the coalition S to communicate with a farthest device in the same coalition S, and selecting the coalition S as a potential coalition if the calculated power cost is no larger than a predefined threshold.

[0010] In an example embodiment, the selected potential coalitions including a coalition formed by only the first device. [0011] In an example embodiment, assigning an associated coalition to each resource unit respectively comprises determining a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized and assigning the target coalition determined in the last iteration as the associated coalition for corresponding resource unit.

[0012] In an example embodiment, determining a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized further comprises estimating at least a first sum rate, a second sum rate and a third sum rate based on an initial associated coalition for each resource unit before the first iteration, wherein the first sum rate is a sum rate of each associated coalition, the second sum rate is a sum rate of all selected potential coalitions and the third sum rate is a sum rate of the first device, and recording the first sum rate, the second sum rate and the third sum rate as history sum rates, and, in each iteration, selecting one of the potential coalitions as target coalition for each resource unit, such that updated first sum rate, second sum rate and third sum rate are equal or larger than their corresponding history sum rates if the selected target coalition is used as new associated coalition for the corresponding resource unit, and recording the updated first sum rate, second sum rate and third sum rate corresponding to the selected target coalition as history sum rates. In a further embodiment, assigning an associated coalition to each resource unit, respectively further comprises comparing the selected target coalition for each resource unit obtained in current iteration with that in last iteration, and if the selected target coalition for each resource unit in current iteration is same as that in last iteration, determining that the iteration converges, assigning the selected target coalition for each resource unit as associated coalition to corresponding resource unit and stopping the iteration; otherwise, conducting next iteration.

[0013] In some example embodiments, the method is performed by a small cell base station and the method further comprises receiving signaling from at least a second device to facilitate the assignment of associated coalition to each resource unit, wherein the signaling including at least one of the following: a sum rate of a coalition to which the second device belongs; information related to transmission power required to communicate with a farthest device in the coalition to which the second device belongs; the number of resource units which are shared by devices in the coalition to which the second device belongs; and an identifier of the coalition to which the second device belongs.

[0014] According to a second aspect, embodiments of the present invention provide a method in a second device for cooperative interference management in a wireless network including a plurality of coalitions wherein each coalition consists of one or more devices capable of cooperating with each other, the method comprising: sending signaling to a first device to facilitate the first device to perform assignment of associated coalition to each of its resource unit according to one of the methods described above, and wherein the signaling including at least one of the following: sum rate of a coalition to which the second device belongs; information related to transmission power required to communicate with a farthest device in the coalition to which the second device belongs; the number of resource units which are shared by devices in the coalition to which the second device belongs; and identifier of the coalition to which the second device belongs.

[0015] According to a third aspect, embodiment of the present invention provides a corresponding device which implements the methods described in the first aspect.

[0016] According to a fourth aspect, embodiments of the present invention provide a corresponding device which implements the methods described in the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other aspects, features, and benefits of various embodiments of the invention will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which like reference numerals refer to the same or similar elements:

[0018] FIG.1 is a diagram of an example wireless network where a method according to an embodiment of the present invention can be applied;

[0019] FIG.2A is a flow chart for an example method in a SB S for cooperative interference management in a wireless network according to an embodiment of the present invention;

[0020] FIG.2B is a flow chart for another example method in a SBS for cooperative interference management in a wireless network according to an embodiment of the present invention

[0021] FIG.3 illustrates a flow chart of a method for sending signaling to facilitate the interference management according to an embodiment of the present invention;

[0022] FIG.4 illustrates a block diagram of a device for interference management according to an embodiment of the present invention;

[0023] FIG. 5 illustrates a block diagram of a device for sending signal to the device shown in Fig.4 for interference management according to an embodiment of the present invention; and [0024] FIG. 6A-6D show simulation results of a method for interference management according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0025] Some preferred embodiments will be described in more detail with reference to the accompanying drawings, in which the preferred embodiments of the present disclosure have been illustrated. However, the present disclosure can be implemented in various manners, and thus should not be construed to be limited to the embodiments disclosed herein. On the contrary, those embodiments are provided for thorough and complete understanding of the present disclosure, and completely conveying the spirit of the present disclosure to those skilled in the art.

[0026] In the following description, numerous specific details of embodiments of the present invention are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Those of ordinary skills in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

[0027] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. It shall be understood that the singular forms "a", "an" and "the" include plural referents unless the context explicitly indicates otherwise.

[0028] Fig. l is a diagram of an example wireless network scenario where a method according to an embodiment of the present invention can be applied. As illustrated in Fig. 1, a wireless network can include several macrocell base stations, denoted as MBSs herein, and a plurality of small cell base stations, denoted as SBSs. Each SBS serves one or more small cell UEs referred to as SUEs which are not shown in the Figure. Such a wireless network as illustrated in Fig. l is known as HetNet which has a two-tier structure. Typically, to avoid cross-tier interference, the frequency band(s) allocated to small cells can be different from that allocated to macrocells, and thus in the embodiments of the present invention, we only focus on management of co-tier small cell interference while cross-tier interference is assumed to be negligible compared with co-tier interference.

[0029] For small cells disposed close to each other, the interference is expected to be high which will result in degraded performance in each of the small cells. In one embodiment of present invention, to avoid co-tier interference, several SBSs cooperate with each other for interference management by forming a coalition. In a coalition, all small cell base stations involved can coordinate with each other on radio resource utilization, transmission power, etc., and thereby prevent from utilizing same radio resource concurrently and avoid interference. In one example embodiment, the transmissions on same frequency from different SBSs in a coalition S can be scheduled in a time division multiple access (TDMA) mode, thus collisions in the transmissions are avoided. In another example embodiment, the transmissions from different SBSs in a coalition S can be scheduled in a frequency division multiple access (FDMA) mode, i.e., each SBS transmit with different frequency, and similarly, interference within the coalition S can be eliminated by avoiding collision in transmission. One example of coalition is shown in Fig. 1, e.g., coalition Si formed by SBS 1, SBS 2 and SBS3. However, it should be noted that in particular small cell deployment scenario, a small cell, e.g., SBS 6 in Fig .1, may experience interference from multiple neighbor small cells, e.g., SBS 4 and SBS 5, and it is possible that though the multiple neighbor cells are all close to the small cell, they are far from each other. In such case, it is not reasonable to make the small cell and the interfering multiple neighbor small cells to be in one coalition since the multiple neighbor small cells, e.g., SBS 4 and SBS 6, are too far from each other to cooperate.

[0030] In one embodiment of present invention, a method is proposed to also take the above scenario into account. The method enables a small cell base station to join one or more coalitions based on need, by assigning a coalition to each of resource unit respectively, wherein the assigned coalition to the each resource unit can be same or different. As a result, the coalitions in the wireless network can overlap, e.g., as shown in Fig. 1, by applying a method according to one embodiment of the present invention, the SBS 6 is associated with S₂ and S₃ concurrently, and it results in the overlapping of coalition S₂ and coalition S₃. The resource unit represents the minimum indivisible resource of SBS, which can be, for example, a physical resource block or a subchannel or any other radio resource unit depending on the wireless communication technology used in the small cell network. For each resource unit, in its assigned coalition, it will be shared by all SBSs in the same coalition in a collision-free manner, e.g., in a TDMA mode.

[0031] Fig. 2A illustrate a flow chart for an example method 200 in a small cell base station SBS for cooperative interference management in a wireless network according to an embodiment of the present invention, wherein the wireless network including a plurality of small cell base station coalitions with each coalition consisting of one or more small cell base stations capable of cooperating with each other. As shown in Fig. 2A, the method starts from step 201, where the SBS discovers coalitions in the wireless network; then in step 202, the SBS select from the discovered coalitions one or more potential coalitions to join; in the following step 203, the SBS assigns an associated coalition to each of its resource unit, respectively, wherein the associated coalition is one of the selected potential coalitions and each resource unit will be shared in a collision-free mode by all devices in the associated coalition assigned to it.

[0032] In an embodiment of the present invention, SBS will initiate the method 200 when it powers up. In another embodiment of the present invention, SBS may initiate the method 200 when it detects significant interference variation or performance degradation. In still another embodiment of the present invention, SBS may initiate the method 200 upon request from a central control station in the wireless network.

[0033] In an embodiment of the present invention, in step 201, the SBS discovers existing coalitions in the wireless network by listening to beacon signals transmitted from the coalitions. For example, the SBS discovers a coalition by listening to a beacon transmitted by a master SBS in the coalition. In another example, the SBS discovers a coalition by listening to beacons transmitted by all SBS in the coalition. The coalition discovery can also be performed based on any other signaling, e.g., pilot, designed for this purpose. The signaling detected during coalition discovery can indicate information related to the discovered coalition, for example but not limited to, the coalition identifier/ID, coalition size, members of the coalition and, power limitation in the coalition, etc., in some embodiments.

[0034] After coalition discovery, the SBS may select from the discovered coalitions some preferred coalitions to join in step 202, and these coalitions are called potential coalition herein. In an example embodiment, the selection is determined based on some predefined power restriction, pathloss restriction or coalition size restrictions, etc. In one embodiment, in step 202, for each of the discovered coalitions S, or, for each coalition S in a subset of the discovered coalitions, SBS calculates a corresponding power cost P_s which indicates the total required power to form such a coalition. As one non-limiting example, the power cost can be calculated by estimating the required power for each SBS in the coalition S to communicate with a farthest SBS in same coalition as shown in the following Equation 1,

[0035] Equation 1:

where P_{i j*} is the power required for SBS i to broadcast the information to the farthest SBS j* in same coalition S. Then the SBS determines whether it is possible/allowable to form the coalition S by comparing the calculated power cost with a power limit, e.g., a power threshold Pii_m. For example, if P_s≤P_lim , the SBS can determine that it can join the coalition S being evaluated, then select S as one of its potential coalitions. Similar evaluation can be performed on other discovered coalitions.

[0037] In one embodiment, the SBS can evaluate all the discovered coalitions, and in another embodiment, the SBS may choose to only evaluate some of the discovered coalitions from which it has detected in step 201 very high received signal power, e.g., the received signal power exceeds a threshold. The evaluation can result in one or more potential coalitions being selected. In one embodiment, the selected potential coalitions include a coalition formed by only the SBS itself.

[0038] In one embodiment, in step 203, the SBS select from the potential coalitions an associated coalition for each of its resource unit and assign it to corresponding resource unit. It means, different resource units may be used for interference management in different coalitions. For example, a resource unit RUi is assigned an associated coalition Si, and a resource unit RU₂ is assigned an associated coalition S₂, then the SBS will use RUi for interference management in coalition Si, i.e., share RUi with other SBS in Si in a collision-free manner to avoid interference, and use RU₂ for interference management in S₂.

[0039] The assignment of associated coalition for each resource unit can be implemented in various ways, e.g., the SBS can divide all its available resource units to several groups and assign a different associated coalition to each group of resource units respectively, or, the SBS can determine how many resource units to be associated with a coalition based on distribution of SUEs to be served in its coverage, e.g., if most of the SUEs to be served are close to a coalition A, while only few SUEs locate close to a coalition B, then the SBS can assign the coalition A as an associated coalition to most of its resource units, while assign the coalition B as an associated coalition to the remaining few resource units. [0040] In some further embodiments of the present invention, the assignment of associated coalition to each resource unit in step 203 is implemented by determining a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized, and assigning the target coalition to each resource unit obtained in the last iteration as the associated coalition for the each resource unit.

[0041] Reference is now made to Fig.2B, which illustrates a flow chart of method 200 according to some embodiments of the present invention. In the example flow chart in Fig.2B, the step 203 can be implemented by some further steps 204-206. As shown in Fig.2B, in one embodiment, to determine the assignment iteratively, the SBS will firstly estimate, in step 204, at least a first sum rate, a second sum rate and a third sum rate based on an initial associated coalition for each of its resource unit before the first iteration, wherein the first sum rate indicates a sum rate of each associated coalition, the second sum rate indicates a sum rate of all potential coalitions to the SBS and the third sum rate indicates a sum rate of the SBS, for example, the first sum rate U(S,CS) for each associated coalition S can be obtained based on the following Equation 2:

[0042] Equation 2:

wherein the ■ ^ i ) J a&a

j ,j denotes the overall interference suffered by an SUE that is served by SBS i on resource unit k, and the interference is from other coalitions in the wireless network, and CS denotes the set of all the coalitions in the wireless network. In above

Equation 2,

denotes the total number of resource units available to SBS i, and g_u ^k denote the transmit power and the channel gain respectively, and <j² is the noise power. In one embodiment, the channel gain g i ca be an averaged value derived based on the channels status for multiple SUEs in the small cell served by SBS i and in another embodiment, g^k _t can be a value derived based on the channel status between a particular SUE and the SBS i.

[0044] With the results of the first sum rate, i.e., sum rate of each associated coalition, the second sum rate v(CS) and the third sum rate P¹ (CS) can be obtained accordingly, e.g., based on the following Equation 3 and 4, respectively: [0045] Equation 3:

where v(S_j , CS) means the sum rate of a potential coalition S_j to the SBS, e.g., a coalition which the SBSs can join without destroying the predefined power restriction, and v(5^. , CS) can be obtained, for example, by using Equation 2, i.e., v(5 ^. , CS) = U(S CS) . The parameter / in Equation 3 denoted the total number of potential coalitions.

[0046] Equation 4:

wherein X¹ (5, CS) = <$ (£, CS) means the payoff of SBS i receives from a coalition S, and wherein df represents the fraction of the resource that SBS i dedicates to coalition S in the whole resource pool which is contributed by all the member of the coalition for interference management.

[0048] These values, i.e., the first sum rate, the second sum rate and the third sum rate are recorded by the SBS as history sum rates in step 204. In one embodiment, in each iteration, these values are updated, and a comparison is performed between the history values and the updated values. For example, in step 205, for each iteration, the SBS selects one potential coalition from the potential coalitions and make it a target coalition for a resource unit RUi, such that updated first, second and third sum rates derived based on the selected target coalition are all equal or larger than their corresponding history sum rates. For example, if with a potential coalition, the updated first sum rate is equal to or larger than the history first value, and both the updated second and updated third sum rates are larger than the history second and third sum rates respectively, then this potential coalition can be selected as a target coalition. In one embodiment, the selected target coalition can be the same coalition corresponding to the history sum rates, i.e., the updated first, second and third sum rates are all same as their corresponding history sum rates. This may happen, for example, when no other potential coalition, which can guarantee that at least one of the updated first, second and third sum rates are larger than their corresponding history sum rates, and all of the updated first, second and third sum rates are no less than their corresponding history sum rates, is available. After determination of the target coalition, the updated first sum rate, second sum rate and third sum rate corresponding to the selected target coalition are recorded as history sum rates which will be used for comparison during target coalition selection for next resource unit.

[0049] In one example embodiment, the method 200 further comprises the step 206 of convergence checking, where after each iteration, the SBS checks whether the iteration converges. In some embodiments, the convergence checking is implemented by comparing the selected target coalition for each resource unit in current iteration with that in last iteration. For example, if the selected target coalition for each resource unit in current iteration is same as that in last iteration, it is determined that the iteration converges and the selected target coalition for each resource unit is assigned as associated coalition to corresponding resource unit and the iteration is stopped; otherwise, next iteration is conducted. Such convergence checking can also be implemented based on a counter in another embodiment, where iteration is terminated if number of the iteration reaches a predefined threshold value.

[0050] In some embodiment, the method 200 may apply some predefined rules to the assignment of the associated coalition for each resource unit. One example of such rules can be that each resource unit can not be assigned a same coalition twice. This helps to guarantee a convergence of iteration. In such embodiment, the method 200 may also comprise the step of recording all history associated coalitions assigned to each resource unit

[0051] In still another embodiment, the method 200 further comprises the step 207 as shown in Fig.2B, for receiving signaling from at least another SBS j to obtain information to facilitate the assignment of the associated coalition for each resource unit. For example, the signaling including at least one of the following:

[0052] - sum rate of a coalition to which the SBS j belongs;

[0053] - information related to transmission power required to communicate with a farthest device in the coalition to which the SBS j belongs;

[0054] - the number of resource units which are shared by members in the coalition to which the SBS j belongs; and

[0055] - identifier of the coalition to which the SBS j belongs.

[0056] The received signaling may contribute to any of the steps in method 200 described above, e.g., the receive information may be used during calculation of the power cost or, during the calculation of the first, second, or third sum rates.

[0057] In one embodiment, the operation of receiving signaling from a SBS j can be triggered by a determination to start method 200 at the SBS i. In another embodiment the operation of receiving signaling from a SBS j is performed periodically. In further embodiment, the operation of receiving signaling from a SBS j can also be ordered by a central controller in the wireless network.

[0058] The signaling received by the SBS i in step 207 can be from a master SBS in a coalition in an example embodiment, and can be from any SBS in a coalition or a central controller in the wireless network which may collect required information from all the coalitions and forward to the SBS i, in another embodiment. The signaling can be received via a control channel between SBS i and the SBS j which sends the signaling. The control channel can be, for example, a X2 interface, or any other suitable control channels capable of conveying such signaling.

[0059] In one embodiment, the method 200 can further comprise receiving reports from SUEs which it serves to acquire information related to, for example but not limited to, interference level or signal to interference power, or channel status, which may trigger the start of the method 200, and/or may be used in the sum rate calculation, e.g., in the calculation of Equation 2.

[0060] Fig. 3 illustrates a flow chart of method 300 in a SBS j which sending signaling to another SBS i to facilitate the interference management according to an embodiment of the present invention. The involved SBSs are in a wireless network including a plurality of coalitions with each coalition including one or more SBSs capable of cooperating with each other, and in one example the method 300 comprises sending signaling in step 301 to a SBS i to facilitate the SBS i to perform assignment of associated coalition to each of its resource unit, e.g., using the method 200 described above, wherein the signaling can include at least one of the following:

[0061] - sum rate of a coalition to which the SBS j belongs;

[0062] - information related to transmission power required to communicate with a farthest device in the coalition to which the SBS j belongs;

[0063] - the number of resource units which are shared by members in the coalition to which the SBS j belongs; and

[0064] - identifier of the coalition to which the SBS j belongs.

[0065] In one embodiment, the operation of sending signaling from a SBS j can be performed in response to a request received from another SBS i or central controller, in step 311, and in another embodiment the operation of sending signaling from a SBS j is performed periodically. In further embodiment, the operation of the SBS j sends signaling to a central controller in the wireless network which will later forward the information to a SBS i.

[0066] The signaling can be sent via a control channel between SBS j and another SBS receiving the signaling. The control channel can be, for example, a X2 interface, or any other suitable control channels capable of conveying such signaling.

[0067] It can be understand by those skilled in the art that though the example method 200 and example method 300 are described in the context of SBS in a small cell network, the embodiments of the present invention are not limited to such network scenarios and similar methods can also be applied to other wireless networks, e.g., a non-cellular network, or device-to-device communication network, where similar requirement for interference management exists, and correspondingly, the method can be implemented by a wireless station STA, or a device, for example, a mobile phone, a laptop computer, etc. instead of the SBS described above.

[0068] As can be appreciated by those skilled in the art, though steps of the method 200 are shown in particular order, these step in some embodiment can be performed in an order different from what has been shown. It is also to be understood that methods described with reference to Figs. 2A-2B and Fig.3 can be implemented in various ways, by software, hardware, firmware, or any of their combinations, e.g., a processor, computer programming code, etc.

[0069] Reference is now made to Fig.4, which illustrates a block diagram of a device 400 according to an embodiment of the present invention. The device 400 according to Fig. 4 may perform the example methods described with reference to Fig. 2A-2B but is not limited to these methods. The methods described with reference to Fig. 2A-2B may be performed by the device of Fig. 4 but is not limited to being performed by this device 400. The device 400 may be a small cell base station or part of a small cell base station in some embodiment, but can also be other devices, for example a STA, a mobile phone, a laptop computer, etc., in other embodiments.

[0070] The device 400 comprises a discovery module 401, a selection module 402, and an assignment module 403. The discovery module 401 is configured to discover coalitions in the wireless network. The selection module 402 is configured to select, from the discovered coalitions, one or more potential coalitions to join, and the assignment module 403 is configured to assign an associated coalition to each resource unit, respectively, wherein the associated coalition is one of the selected potential coalitions and each resource unit will be shared in a collision-free mode by all devices in the associated coalition assigned to it. [0071] In an embodiment of the present invention, the modules 401-403 of the device 400 are configured to perform the method 200 when the device 400 powers up. In another embodiment of the present invention, the modules 401-403 of the device 400 are configured to perform the method 200 based on input from another module of the device 400, e.g., a interference detection module which requests the modules 401-403 to perform the method 200 when it has detected significant interference variation or performance degradation. In still another embodiment of the present invention, the modules 401-403 of the device 400 are configured to perform the method 200 based on a request from an external input, e.g., based on request from central control station in the wireless network.

[0072] In an embodiment of the present invention, the discovery module 401 is configured to discover existing coalitions in the wireless network by listening to beacon signals transmitted from the coalitions. For example, the discovery module 401 discovers a coalition by listening to a beacon transmitted by a master SBS in the coalition. In another example, the discovery module 401 discovers a coalition by listening to beacons transmitted by all SBS in the coalition. The discovery module 401 can also be configured to perform coalition discovery based on any other signaling, e.g., pilots, designed for this purpose. The signaling detected by the discovery module 401 can indicate information related to the discovered coalition, for example but not limited to, the coalition identifier/ID, coalition size, members of the coalition and, power limitation in the coalition, etc., in some embodiments.

[0073] In one embodiment of the present invention, the selection module 402 is configured to select, from the discovered coalitions output from the discovery module 401, one or more potential coalitions. In an example embodiment, the selection is determined based on some predefined power restriction, pathloss restriction or coalition size restriction, etc. In one embodiment, the selection module 402 is configured to, for each of the discovered coalitions S, or, for each coalition S in a subset of the discovered coalitions, calculate a corresponding power cost P_s which indicates the total required power to form such a coalition. As one non-limiting example, the power cost can be calculated by estimating the required power for each SBS in the coalition S to communicate with a farthest SBS in same coalition as shown in Equation 1.

[0074] In one embodiment, the selection module 402 is configured to evaluate all the discovered coalitions, i.e., to select potential coalitions from all the discovered coalitions, and in another embodiment, the selection module 402 is configured to evaluate only some of the discovered coalitions from which very high received signal power has been detected by the discovery module 401, e.g., the received signal power exceeds a threshold. The evaluation can result in one or more potential coalitions being selected. In one embodiment, the selected potential coalitions include a coalition formed by only the device 400 itself.

[0075] In one embodiment, the assignment module 403 is configured to select from the potential coalitions one associated coalition for each resource unit and assign it to corresponding resource unit. It enables different resource unit to be used for interference management in different coalitions. In one example, if a resource unit RUi is assigned an associated coalition Si, and a resource unit RU₂ is assigned an associated coalition S₂, then the RUi will be used for interference management in coalition Si, i.e., RUi will be shared with other SBS in Si in a collision-free manner to avoid interference, and RU₂ will be used for interference management in S₂.

[0076] The assignment module 403 can be configured to perform the assignment of associated coalition for each resource unit in various ways, e.g., the assignment module 403 can be configured to divide all available resource units to several groups and assign a different associated coalition to each group of resource units respectively, or, the assignment module 403 can be configured to determine how many resource units to be associated with a coalition based on distribution of SUEs in its coverage, e.g., if most of the SUEs to be served are close to a coalition A, while only few SUEs locate close to a coalition B, then the assignment module 403 can be configured to assign the coalition A as an associated coalition to most of its resource units, while assign the coalition B as an associated coalition to the remaining few resource units.

[0077] In some further embodiments of the present invention, the assignment module 403 can be configured to implement the assignment of associated coalition to each resource unit by determining a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized, and assigning the target coalition obtained in the last iteration as the associated coalition for corresponding resource unit.

[0078] In an embodiment of the present invention, in order to determine the assignment iteratively, the device may also comprise a initialization module 404, which is configured to estimate at least a first sum rate, a second sum rate and a third sum rate based on an initial associated coalition for each resource unit before the first iteration is performed, wherein the first sum rate is a sum rate of each associated coalition, the second sum rate is a sum rate of all potential coalitions to the SBS and the third sum rate is a sum rate of the SBS. For example, the first sum rate, the second sum rate and the third sum rate can be obtained based on Equations 2-4, respectively. These values, i.e., the first sum rate, the second sum rate and the third sum rate are recorded by the initialization module 404 in one embodiment, or by another separate recording module in another embodiment.

[0079] In an embodiment of the present invention, the device 400 further comprise the iteration module 405 which is configured to, for each iteration, select one potential coalition from the potential coalitions and make it a target coalition for a resource unit RUi, such that updated first, second and third sum rates derived based on the selected target coalition are all equal or larger than their corresponding history sum rates; and module 405 is also configured to record the updated first sum rate, second sum rate and third sum rate corresponding to the selected target coalition as history sum rates which will be used for comparison during target coalition selection for next resource unit. For example, if with a potential coalition, the updated first sum rate is equal to or larger than the history first value, and both the updated second and updated third sum rates are larger than the history second and third sum rates respectively, then the iteration module 405 is configured to select this potential coalition as a target coalition. In one embodiment, the target coalition selected by the iteration module 405 can be the same coalition corresponding to the history sum rates, i.e., the updated first, second and third sum rates are all same as their corresponding history sum rates. This may happen, for example, when no other potential coalition, which can guarantee that at least one of the updated first, second and third sum rates are larger than their corresponding history sum rates, and all of the updated first, second and third sum rates are no less than their corresponding history sum rates, is available.

[0080] In one example embodiment, the device 400 further comprises the convergence checking module 406 configured to checking whether the iteration converges. For example, the convergence checking module 406 is configured to check, after each iteration, whether the selected target coalition for each resource unit in current iteration is same as that in last iteration, and if they are the same, the convergence checking module 406 determines that the iteration converges and correspondingly assigns the selected target coalition for each resource unit as its associated coalition and stopping the iteration; otherwise, conducting next iteration. In another embodiment, such convergence checking module 406 can be configured to operate based a counter, for example, it will stop iteration if number of iteration reaches a predefined threshold value.

[0081] In some embodiment, the device 400 may apply some predefined rules to the operation performed in the module 403-406. One example of such rules can be that each resource unit can not be assigned a same coalition twice. This helps to guarantee a convergence of iteration. In such embodiment, the device 400 may also comprise a module of recording all history associated coalitions assigned to each resource unit, or, the recoding is performed by one of the module 403-406.

[0082] In still another embodiment, the device 400 further comprises the receiving module 407, which is configured to receive signaling from at least one device j in a discovered coalition to facilitate the operation of assigning associated coalition to each resource unit, wherein the signaling including at least one of the following:

[0083] - sum rate of a coalition to which the device j belongs;

[0084] - information related to transmission power required to communicate with a farthest device in the coalition to which the device j belongs;

[0085] - the number of resource units which are shared by members in the coalition to which the device j belongs; and

[0086] - identifier of the coalition to which the device j belongs.

[0087] The received signaling may contribute to operation performed in any of the modules 402-406, e.g., the receive information may be used during calculation of the power cost or, during the calculation of the initial/updated first, second, or third sum rate.

[0088] In one embodiment, the operation of receiving module 407 can be triggered by a determination in another module to start method 200. In another embodiment the receiving module 407 is configured to perform the signaling receiving periodically. In further embodiment, the receiving module 407 is configured to start the signaling receiving upon an order from a central controller in the wireless network.

[0089] The signaling can be received via a control channel between device 400 and another device sending the signaling. The control channel can be, for example, a X2 interface, or any other suitable control channels capable of conveying such signaling.

[0090] The receiving module 407 can be configured to detect signaling from a master SBS in a coalition in an example embodiment, and can be configured to detect signaling from any SBS in a coalition, or a central controller in the wireless network which may collect required information from all the coalitions and forward to the SBS i, in another embodiment.

[0091] In some embodiments, the device 400 can further comprise another module configured to receive reports from SUEs which it serves to acquire information related to, for example but not limited to, interference level or signal to interference power, or channel status, which may trigger the operation in module 401-4070, and/or may be used in the sum rate calculation, e.g., in module 404 and 405. In one embodiment, the function of receiving report from SUEs can also be implemented by one of the module 401-407.

[0092] Reference is now made to Fig.5, which illustrates a block diagram of a device 500 according to an embodiment of the present invention. The device 500 according to Fig. 5 can perform the method described with reference to Fig.3, and for example may send signaling to the device 400 as illustrated in Fig.4. The device 500 comprises sending module 501, configured to send signaling to another device to facilitate the another device to perform assignment of associated coalition to each of its resource unit according to the method described with reference to Fig .2A-2B, and wherein the signaling including at least one of the following:

[0093] - sum rate of a coalition to which the device 500 belongs;

[0094] - information related to transmission power required to communicate with a farthest device in the coalition to which the device 500 belongs;

[0095] - the number of resource units which are shared by devices in the coalition to which the device 500 belongs; and

[0096] - identifier of the coalition to which the device 500 belongs.

[0097] In one embodiment, the device 500 may further comprise a receiving module 511 configured to receive a request received from the another device or from a central controller, before a signaling sending operation is performed in the module 501; in another embodiment the operation of sending signaling in module 501 is performed periodically. In further embodiment, the sending module 501 is configured to send signaling to a central controller in the wireless network which will later forward the signaling to another device.

[0098] The signaling can be sent via a control channel between device 500 and another SBS receiving the signaling. The control channel can be, for example, a X2 interface, or any other suitable control channels capable of conveying such signaling.

[0099] In some embodiments of the present invention, the devices 400 and 500 are small cell base stations (SBSs), however, the embodiments of the present invention are not limited to such network scenarios and the functions and corresponding of devices 400 and 500 can also be implemented in or by any other wireless communication devices capable of performing the processes of the exemple embodiments, e.g., when the methods described with reference to Figs. 2 and 3 are applied in a non-cellular network, or device-to-device communication network, where similar requirement for interference management exists, the devices 400 and 500 can correspondingly be wireless station STAs, or terminals, for example, a mobile phone, a laptop computer, etc. instead of the SBSs described above.

[00100] As can be appreciated by those skilled in the art, the blocks illustrated in Figs. 4-5 and the corresponding functions can be implemented in various ways, e.g., by software, hardware, firmware, or any of their combinations. Furthermore, it should be understood that in some embodiments, function of a block can also be implemented by multiple blocks, and functions of multiple blocks shown in Figs 4-5 may also be implemented by a single block in other embodiments.

[00101] To show the advantage of the proposed method, simulations are conducted. The simulation parameters can be found in Table 1 below and results are shown in Figure 6A-6D. During the simulation, the proposed method, denoted as OCF, is compared with two convention schemes, i.e., a non-overlapping coalition scheme denoted as CF scheme, and a non-cooperative scheme.

Table 1 Simulation parameters

[00102] Fig. 6A illustrates that the proposed overlapping coalition formation scheme for cooperative interference management makes the SBSs self-organize to reach the final stable network structure, where the circles module the coalitions formed. It can be seen that the SBS 5 is associated with two coalitions by assign different coalitions to different resource units, and thus enables better interference management. Figure 6B illustrates System throughput with different number of SBSs. It can be seen the proposed OCF scheme obtains high system throughput. Figure 6C illustrates system throughput with different number of iterations, and it shows that although the proposed OCF scheme requires a few additional iterations to reach the convergence, the OCF performs obviously better than the coalition formation scheme in terms of system sum rate. Figure 6D illustrates individual throughput which related to the sum rate of the single SBS. As shown in the figure 6D, the proposed OCF scheme also makes the individual performance of the SUEs better.

[00103] The embodiments of the invention described hereinbefore in association with Figures 1 to 5 may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment of the invention.

[00104] The example embodiments can store information relating to various processes described herein, e.g., store the history sum rates, the updated sum rate, and the history associated coalitions for each resource unit, etc. The components of the example embodiments can include computer readable medium or memories according to the teachings of the present inventions and for holding data structures, tables, records, and/or other data described herein.

[00105] While the present inventions have been described in connection with a number of example embodiments, and implementations, the present inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of prospective claims. It is also obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

WHAT IS CLAIMED IS:

1. A method in a first device for cooperative interference management in a wireless network including a plurality of coalitions, wherein each coalition consists of one or more devices capable of cooperating with each other, the method comprising:

- discovering coalitions in the wireless network;

- selecting, from the discovered coalitions, one or more potential coalitions to join; and

- assigning an associated coalition to each resource unit, respectively, wherein the associated coalition is one of the selected potential coalitions and each resource unit is to be shared in collision-free mode by all devices in the associated coalition assigned to it.

2. A method of Claim 1, wherein selecting, from the discovered coalitions, one or more potential coalitions to join comprising:

- for each coalition S of the discovered coalitions, or, for each coalition S in a subset of the discovered coalitions, calculating a corresponding power cost which indicates the total required power for each device in the coalition S to communicate with a farthest device in same coalition S; and

- selecting the coalition S as a potential coalition, if the calculated power cost is no larger than a predefined threshold.

3. A method of Claim 1, wherein the selected potential coalitions include a coalition formed by only the first device.

4. A method of Claim 1, wherein assigning an associated coalition to each resource unit, respectively, comprising:

determining a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized; and

assigning the target coalition determined in the last iteration as the associated coalition for corresponding resource unit.

5. A method of any of Claim 4, wherein determining a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized further comprising:

- estimating at least a first sum rate, a second sum rate and a third sum rate based on an initial associated coalition for each resource unit before the first iteration, and recording the first sum rate, the second sum rate and the third sum rate as history sum rates, wherein the first sum rate indicates a sum rate of each associated coalition, the second sum rate indicates a sum rate of all selected potential coalitions and the third sum rate indicates a sum rate of the first device; and

- in each iteration, for each resource unit, selecting one of the potential coalitions as target coalition, such that updated first, second and third sum rates derived based on the selected target coalition are all equal or larger than their corresponding history sum rates, and recording the updated first, second and third sum rates as history sum rates.

6. A method of Claim 5, wherein assigning an associated coalition to each resource unit, respectively further comprising:

- comparing the selected target coalition for each resource unit obtained in current iteration with that in last iteration, and if they are the same, determining that the iteration converges, assigning the selected target coalition for each resource unit as associated coalition to corresponding resource unit, and stopping the iteration; otherwise, conducting next iteration.

7. A method of any of Claims 1-6, wherein the first device is a small cell base station and the method further comprising:

- receiving signaling from at least a second device to facilitate the assignment of associated coalition to each resource unit,

wherein the signaling including at least one of the following:

- a sum rate of a coalition to which the second device belongs;

- information related to transmission power required to communicate with a farthest device in the coalition to which the second device belongs;

- the number of resource units which are shared by devices in the coalition to which the second device belongs; and

- an identifier of the coalition to which the second device belongs.

8. A method in a second device for cooperative interference management in a wireless network including a plurality of coalitions, wherein each coalition consists of one or more devices capable of cooperating with each other, the method comprising:

- sending signaling to a first device to facilitate the first device to perform assignment of associated coalition to each of its resource unit according to a method of any of Claims 1-7, wherein the signaling including at least one of the following: - a sum rate of a coalition to which the second device belongs;

- an identifier of the coalition to which the second device belongs.

9. A device for cooperative interference management in a wireless network including a plurality of coalitions, wherein each coalition consists of one or more devices capable of cooperating with each other, the device comprising:

- discovery module, configured to discover coalitions in the wireless network;

- selection module, configured to select, from the discovered coalitions, one or more potential coalitions to join; and

- assignment module, configured to assign an associated coalition to each resource unit, respectively, wherein the associated coalition is one of the selected potential coalitions and each resource unit is to be shared in collision-free mode by all devices in the associated coalition assigned to it.

10. A device of Claim 9, wherein the selection module is further configured to:

- for each coalition S of the discovered coalitions, or, for each coalition S in a subset of the discovered coalitions, calculate a corresponding power cost which indicates the total required power for each device in the coalition S to communicate with a farthest device in same coalition S; and

- select the coalition S as a potential coalition, if the calculated power cost is no larger than a predefined threshold.

11. A device of Claim 9, wherein the selected potential coalitions include a coalition formed by only the device itself.

12. A device of Claim 9, wherein the assignment module is further configured to:

- determine a target coalition for each resource unit iteratively, such that sum rate of the wireless network is maximized; and - assign the target coalition determined in the last iteration as the associated coalition for corresponding resource unit.

13. A device of any of Claim 12, wherein the assignment module further comprising:

- initialization module, configured to estimate at least a first sum rate, a second sum rate and a third sum rate based on an initial associated coalition for each resource unit before the first iteration, and record the first sum rate, the second sum rate and the third sum rate as history sum rates, wherein the first sum rate indicates a sum rate of each associated coalition, the second sum rate indicates a sum rate of all selected potential coalitions and the third sum rate indicates a sum rate of the first device; and

-iteration module, configured to, in each iteration, for each resource unit, select one of the potential coalitions as target coalition, such that updated first, second and third sum rates derived based on the selected target coalition are all equal or larger than their corresponding history sum rates, and record the updated first, second and third sum rates as history sum rates.

14. A device of Claim 13, wherein the assignment module further comprising:

- convergence checking module, configured to compare the selected target coalition for each resource unit obtained in current iteration with that in last iteration, and if the selected target coalition for each resource unit in current iteration is same as that in last iteration, determine that the iteration converges, assign the selected target coalition for each resource unit as associated coalition to corresponding resource unit and stop the iteration; otherwise, conduct next iteration.

15. A device of any of Claims 9-14, wherein the device is a small cell base station and the device further comprising:

- receiving module, configured to receive signaling from at least a second device to facilitate the assignment of associated coalition to each resource unit, wherein the signaling including at least one of the following:

- a sum rate of a coalition to which the second device belongs;

- the number of resource units which are shared by devices in the coalition to which the second device belongs; and - an identifier of the coalition to which the second device belongs.

16. A device for cooperative interference management in a wireless network including a plurality of coalitions, wherein each coalition consists of one or more devices capable of cooperating with each other, the device comprising:

- sending module, configured to send signaling to a first device to facilitate the first device to perform assignment of associated coalition to each of its resource unit according to a method of any of Claims 1-7,

wherein the signaling including at least one of the following:

- a sum rate of a coalition to which the second device belongs;

- an identifier of the coalition to which the second device belongs.