WO2015081570A1 - Procédé d'ordonnancement d'équipement d'utilisateur dans un réseau hétérogène - Google Patents

Procédé d'ordonnancement d'équipement d'utilisateur dans un réseau hétérogène Download PDF

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Publication number
WO2015081570A1
WO2015081570A1 PCT/CN2013/088808 CN2013088808W WO2015081570A1 WO 2015081570 A1 WO2015081570 A1 WO 2015081570A1 CN 2013088808 W CN2013088808 W CN 2013088808W WO 2015081570 A1 WO2015081570 A1 WO 2015081570A1
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Prior art keywords
user equipment
small cell
cell
scheduling
macro
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PCT/CN2013/088808
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English (en)
Inventor
Zhenning Shi
Liang Liu
Daqing Gu
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Orange
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Priority to PCT/CN2013/088808 priority Critical patent/WO2015081570A1/fr
Priority to PCT/IB2014/003040 priority patent/WO2015082999A2/fr
Publication of WO2015081570A1 publication Critical patent/WO2015081570A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/12—Wireless traffic scheduling
    • H04W72/1215—Wireless traffic scheduling for collaboration of different radio technologies

Definitions

  • the present invention generally relates to scheduling in a cellular network, more particularly for the uplink transmission in a heterogeneous cellular network.
  • Wireless networks have witnessed the proliferation of smart communication terminals and drastic growth in the network traffic from data services.
  • heterogeneous networks have been proposed, where small cells are introduced, as a complement to macro cells. Such small cells allow to significantly offload the traffic from macro cells, and to extend the network coverage.
  • access nodes (or hotspots) of such small cells may use the short transmission range for exchanging data with user equipment, thus increasing local capacities at hotspots.
  • HetNet heterogeneous network
  • LTE Long Term Evolution
  • the uplink interference may substantially jeopardize the received signal quality of small cells and, in turn, the transmission performance.
  • closed -loop power control is adopted in the small cell uplink, users will reactively increase the transmission power to maintain the signal-to-interference-plus-noise ratio (SI NR). Nevertheless, this may add to the co-channel interference in the uplink of macro cells and may aggravate the already weak macro cell uplink channels.
  • SI NR signal-to-interference-plus-noise ratio
  • a solution could consist of allocating some sub-bands for the exclusive use of macro cells to avoid cross-tier interference. This may significantly enhance the received signal quality of both macro cells and small cells, but at the cost of limiting the spectrum access in small cells.
  • the resource allocation is performed in a cooperative fashion by a central scheduling unit for a set of cooperating BSs.
  • M ulti-cell Channel State Information (CSI) of all U Es associated with the set of cooperating BSs can be periodically exchanged in order to predict the experienced inter-cell interference level if a certain UE would be scheduled on certain physical resource blocks. This information is then considered in the scheduling decisions for minimizing the inter-cell interference, leading to an interference- aware scheduling.
  • CSI Channel State Information
  • the presented method relates to a method for scheduling user equipment in a heterogeneous network comprising at least one macro cell and at least one small cell having at least partially overlapping coverage, the method being run by a scheduling unit for said at least one macro cell and comprising the steps of: scheduling user equipment served by said macro cell and allocating radio resources to said scheduled user equipment, determining a set of at least one of said scheduled user equipment prone to cause interference in the uplink on at least one of said small cell(s), called a victim small cell, sending, through a backhaul link between said scheduling unit for said macro cell and a scheduling unit for said victim small cell, a coordination message co mprising information on said at least one scheduled user equipment prone to cause interference on said victim small cell and on radio resources allocated to it.
  • the invention relies on a novel and inventive approach of the scheduling in a heterogeneous network.
  • the macro cell schedules users and allocates resource blocks to scheduled users, for example based on a performance metric optimization.
  • the macro cell identifies, among its scheduling information, the information that could be useful to small cells to carry out a coordinated interference-aware scheduling, and forwards it to the affected small cells, in an effort to assist the latter to develop optimal resource allocation strategy.
  • Such a method has little impact on macro cells, as it does not compromise the performance of macro users, nor changes the scheduling of users served by the macro cell.
  • it defines a minimal set of exchange signaling between macro and small cells, sent through a backhaul link between the access nodes of both the macro cell and the small cell, which allows the small cell to take into account the user scheduling information in the macro cells to mitigate the inter-cell interference.
  • Such a method advantageously relies o n a coordinated scheduling scheme, which works between macro cells and small cells, without a need to introduce in the heterogeneous network a central scheduling unit that would perform scheduling for all small and macro cells.
  • small cell designate any cell, which is smaller than a conventional macro cell served by a macro base station, as described in the LTE standard: for example, such a small cell may be a pico cell for in-building coverage, or a femto cell served by an access point, which is called a Home Node B (HeN B).
  • HeN B Home Node B
  • an heterogeneous network as described in this document usually comprises macro eNodes B (eNBs), which are deployed for initial coverage of the network by macro cells, and pico access nodes or HeNBs, which serve small cells, and are added to the network for capacity growth and better user experience.
  • eNBs macro eNodes B
  • HeNBs pico access nodes or HeNBs
  • such a method also comprises a step of predicting a transmission channel condition between said user equipment and an access node to said macro cell, and said step of allocating radio resources to said scheduled user equipment relies on an optimization metric taking account of said predicted transmission channel condition.
  • such a method also comprises an additional step of scheduling said user equipment served by said macro cell and of allocating radio resources to said newly scheduled user equipment at a time when said coordination message has been received by said scheduling unit for said victim small cell.
  • a re -scheduling mechanism is implemented at macro-cell nodes to compensate for the backhaul latency and optimize the scheduling performance by considering the instantaneous channel conditions of macro cell in a further scheduling step.
  • the macro-cell scheduling unit performs additional scheduling at the time when small cell receive th e coordination message and performs user scheduling.
  • the macro cell can exploit the most recent Channel State Information (CSI) in user assignment and fully utilize the multi -user diversity to maximize the network performance.
  • said step of determining comprises a step of receiving from said scheduled user equipment propagation loss values towards an access node to said macro cell and towards an access node to at least one small cell in the neighborhood of said scheduled user equipment.
  • macro cell users measure the signal powers received from the serving macro -cell and form detectable small cells in the neighborhood on reference channels ; they then estimate the propagation loss towards the access nodes to theses cells, and report them periodically to the macro serving cell, which uses them to determine the set of interfering cell edge users, along with the most affected small cells.
  • said coordination message comprises: an index of said at least one scheduled user equipment prone to cause interference on said victim small cell; an index of a Resource Block Group where said at least one scheduled user equipment prone to cause interference on said victim small cell is assigned; an estimated power received by said victim small cell from said at least one scheduled user equipment prone to cause interference on said victim small cell.
  • Such a coordination message defines the minimal set of exchange signaling, which must be provided by the macro cell to the small cells, in order to allow them performing an interference aware scheduling and to help them in resource allocation .
  • the invention also concerns a method for scheduling user equipment in a heterogeneous network comprising at least one macro cell and at least one small cell having at least partially overlapping coverage, the method being run by a scheduling unit for said small cell and comprising the steps of: receiving at least one coordination message, through a backhaul link between said scheduling unit for said small cell and a scheduling unit for said at least one macro cell, said coordination message comprising information on at least one user equipment scheduled by said scheduling unit for said macro cell and prone to cause interference on said small cell, called an interfering macro user equipment, said coordination message also comprising information on radio resources allocated to said interfering macro user equipmentby said scheduling unit for said macro cell, performing interference aware scheduling of user equipment served by said small cell and allocating radio resources to said scheduled user equipment, on the basis of said coordination messages received from said at least one macro cell.
  • the invention relies on a novel and inventive approach of coordinated scheduling in a heterogeneous network.
  • the small cell collects coordination messages sent by macro-cells, such messages informing the small cell on the users, which will generate interference in the uplink on such or such resource block group.
  • the small cell scheduling unit may advantageously use th is information to adapt its own scheduling to mitigate inter-cell interference in the uplink.
  • Such a method thus relies on a scheduling scheme with coordination between macro cells and small cells to combat the uplink interference seen by small cell users while not compromising the performance of macro users.
  • Such a scheme utilizes the multi-user spatial diversity to optimize the channel capacity while causing no additional complexity to the small cell access node.
  • a central scheduling unit which would perform scheduling for both the macro cells and the small cells.
  • such a method also comprises a step of determining a constrained channel space (CCS) for a sub channel / of a bandwidth used by said small cell, said constra ined channel space taking as its elements channel state information from said interfering macro user equipment for said sub channel / to an access node of said small cell.
  • CCS constrained channel space
  • said step of performing interference aware schedul ing of user equipment served by said small cell and allocating radio resources to said scheduled user equipment comprises the sub-steps of: determining a set of user equipment having a transmission channel towards said access node of said small cell, which is pseudo-orthogonal to said constrained channel space for said sub channel /; assigning said sub channel / to a user equipment in said set, which optimizes a predetermined metric.
  • Such a solution allows the small cell to identify a set of users which are pseudo- orthogonal to the Constrained Channel Space (CCS), and then to choose the best channel- conditioned user from this set of users. By doing this, the selected user is subdue to a minimum amount of interference from macro-associated users.
  • CCS Constrained Channel Space
  • said step of performing interference aware scheduling of user equipment served by said small cell and allocating radio resources to said scheduled user equipment comprises the sub-steps of: for each user equipment served by said small cell, computing an instantaneous data rate for said sub channel / by taking into account an estimated interference generated by said interfering macro user equipment; assigning said sub channel / to the user equipment with the maximum instantaneous data rate.
  • Another objective of the invention is a scheduling unit for a macro cell in a heterogeneous networkcomprising at least one macro cell and at least one small cell having at least partially overlapping coverage, said scheduling unit comprising: a scheduler for scheduling user equipment served by said macro cell and for allocating radio resources to said scheduled user equipment, a computing unit for determining a set of at least one of said scheduled user equipment prone to cause interference in the uplink on at least one of said small cell(s), called a victim small cell, a sending unit for sending, through a backhaul link between said scheduling unit for said macro cell and a scheduling unit for said victim small cell, a coordination message comprising information on said at least one scheduled user equipment prone to cause interference on said victim small cell and on radio resources allocated to it.
  • the invention also relates to a scheduling unit for a small cell in a heterogeneous networkcomprising at least one macro cell and at least one small cell having at least partially overlapping coverage, said scheduling unit comprising: a receiving unit for receiving at least one coordination message, through a backhaul link between said scheduling unit for said small cell and a scheduling unit for said at least one macro cell, said coordination message comprising information on at least one user equipment scheduled by said scheduling unit for said macro cell and prone to cause interference on said small cell, called an interfering macro user equipment, said coordination message also comprising information on radio resources allocated to said interfering macro user equipmentby said scheduling unit for said macro cell, a scheduler for performing interference aware scheduling of user equipment served by said small cell and for allocating radio resources to said scheduled user equipment, on the basis of said coordination messages received from said at least one macro cell.
  • Another objective of the invention is a method for scheduling user equipment in a heterogeneous network comprising at least one macro cell and at least one small cell having at least partially overlapping coverage,the method comprising the steps of: scheduling user equipment served by said macro cell and allocating rad io resources to said scheduled user equipment, determining, in a scheduling unit for said macro cell, a set of at least one of said scheduled user equipment prone to cause interference in the uplink on at least one of said small cell(s), called a victim sm all cell, sending, through a backhaul link between said scheduling unit for said macro cell and a scheduling unit for said victim small cell, a coordination message comprising information on said at least one scheduled user equipment prone to cause interference on said victim small cell and on radio resources allocated to it; in a scheduling unit for said victim small cell, performing interference aware scheduling of user equipment served by said victim small cell and allocating radio resources to said scheduled user equipment, on the basis of said coordination messages received from said at least one macro cell.
  • Another objective of the invention is a communication system over a heterogeneous network comprising at least one macro cell and at least one sma ll cell having at least partially overlapping coverage, said communication system comprising user equipment receiving and transmitting data from and to access nodes to said macro cell(s) and said small cell(s), said communication system also comprising a scheduling unit for said at least one macro celland a scheduling unit for said at least one small cell, said scheduling unit for said macro cell comprising: a scheduler for scheduling user equipment served by said macro cell and for allocating radio resources to said scheduled user equipment, a computing unit for determining a set of at least one of said scheduled user equipment prone to cause interference in the uplink on at least one of said small cell(s), called a victim small cell, a sending unit for sending, through a backhaul link between said scheduling unit for said macro cell and said scheduling unit for said victim small cell, a coordination message comprising information on said at least one scheduled user equipment prone to cause interference on said victim small cell and on radio resources allocated to it, and said
  • the invention concerns also twocomputer programs, in particular computer programs on or in an information medium or memory, suitable for implementing the methods of the invention.
  • These programs can use any programming language, and be in the form of source code, object code, or of intermediate code between source code and object code such as in a partially compiled form, or in any other desirable form for implementing the configuration method according to the invention.
  • the information medium may be any entity or device capable of storing the programs.
  • the medium can comprise a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or else a magnetic recording means, for example a diskette (floppy disk) or a hard disk.
  • the information medium maybe a transmissible medium such as an electrical or optical signal, whichmaybeconveyed via an electrical or opticalcable, by radio or by othermeans.
  • the programs according to the invention may in particular be downloaded from a network of Internet type.
  • FIG. 1 represents a heterogeneous network N in which the methods of the invention are run
  • FIG. 2 represents the different steps of a method for coordinated scheduling in the heterogeneous network of figure 1, according to an embodiment of the invention
  • FIG. 3 shows a spatial visualisation ofthe scheduling of user equipment according to embodiments of the method of figure 2
  • FIG. 4 represents the time flow of the scheduling scheme according to an embodiment of the invention
  • FIG. 5 shows the time flow of the scheduling scheme according to another embodiment of the invention.
  • FIG. 6 representsa scheduling unit for a macro cell running some of the steps of the method for coordinated scheduling described by figure 2
  • FIG. 7 representsa scheduling unit for a small cell running some of the steps of the method for coordinated scheduling described by figure 2.
  • Figure 1 represents a network N in which the methods of the invention are run.
  • the network N is for example a heterogeneous LTE network, comprising several macro cells and several small cells showing overlapping coverage.
  • the network N on figure 1 shows only one macro cell MC, covered by an access node AN1.
  • the network N also comprises two small cells SCI and SC2, which coverage is included in the coverage of the macro cell MC.
  • Each small cell SCI, SC2 is covered by an access node, respectively AN2, AN3.
  • Each access node AN1, AN2, AN3, comprises at least one antenna for radio signal transmission.
  • Several mobile devices such as mobile phones, laptops or tablets for example, are attached to the access nodesof network N.
  • mobiles devices SUEl and SUE2 are respectively attached to access nodes AN2 and AN3 of small cells SCI and SC2.
  • a transmission channel is established between the mobile device SUEl and the access node AN2, as well as between the mobile device SU E2 and the access node AN3.
  • Small cells SCI and SC2 thus serve respectively mobile devices SUEl and SUE2.
  • the coverage area of the small cell SCI, SC2 is artificially enlarged, in such a way that the U E should connect to the small cell even if the macro cell downlink coverage is stronger.
  • Such an artificial enlargement is called a Range Extension Zone, shown as REZ1 for small cell SCI and REZ2 for small cell SC2.
  • Other mobile devices M UEl to M UE4 are also located in the coverage area of the macro cell MC.
  • RSRP Reference Signal Receive Power
  • LTE network measurement which provides cell-specific signal strength metric. This measurement can be used to rank different LTE cells according to their signal strength, and hence serves as an input for handover and cell reselection.
  • RSRP is defined for a specific eel I as the linear average over the power contributions (in Watts) of the Resource Elements (REs), which carry cell- specific reference signal within the considered measurement frequency bandwidth.
  • mobile devices M UEl to M UE4 are all campping on the macro cell MC.
  • mobile device M UEl is located in a so-called imbalance region I R, at the boundary between the macro cell MC and the small cell SCI. Therefore, M U El transmission power has to be tuned high to compensate for the weak channel link between itself and the access node AN1 of the serving macro cell MC. This may create strong interference in the uplink of small cell SCI and compromise the user performance, for example for the mobile device SUEl.
  • Such a strong interference is illustrated in figure 1 by a dashed arrow going from user equipment M UE1 to access node AN2 of small cell SCI.
  • Other mobile devices M UE2 and SUE2 may also generate some interference on small cell SCI, also illustrated by dashed arrows between mobile devices SUE2, M U E2 and access node AN2. However, such interference is typically weaker than that generated by mobile device M UE1.
  • an embodiment of the invention consists of a scheduling scheme with coordination between macro cell MC and small cells SCI and SC2 to combat the uplink interference seen by small cell users SUEl and SUE2 while not compromising the performance of macro users M UE1 to MUE4.
  • the scheme utilizes the multi-user spatial diversity to optimize the channel capacity while causing no additional complexity to small cell access nodes AN2 and AN3.
  • Figure 2 represents the different steps of a method for coordinated scheduling in the heterogeneous network N of figure 1.
  • M C macro cell level
  • SC small cell level
  • Such a method relies on a coordinated scheduling between the small cell and the macro cell, where the small cell MAC (i.e. the Medium Access Control layer in the small cell base station protocol) takes into account the user scheduling information in the macrocells to mitigate the inter-cell interference.
  • the small cell MAC i.e. the Medium Access Control layer in the small cell base station protocol
  • a scheduling unit for macro cell MC schedules users and allocates resource blocks to scheduled users based on a predetermined performance metric optimization.
  • a performance metrics denoted as ⁇ ( ⁇ ) is used to select users in good channel conditions with fairness consideration.
  • a second step DET. INTE F. UE 11 the macrocell scheduling unit needs to determine on the scheduling information that is most critical to the coordinated scheduling over the heterogeneous network N and forwards it to the affected small cells, in an effort to assist the latter to develop optimal resource allocation strategy.
  • This step can be realized in a sequence of operations as follows:
  • Macro cell users measure the signal powers received from the access node AN1 serving the macro cell MC and from the access nodes to detectable small cells in the neighbourhood on reference channels, e.g. RSRP. They then estimate the propagation loss towards these access nodes.
  • reference channels e.g. RSRP.
  • Macro cell users periodically report these propagation loss values to the access node AN1 of the serving macro cell MC, which reflect their positions relative to the serving cell MC as well as to small cells SC.
  • the macrocell scheduling unit determines the set of cell edge users and the most affected small cells as
  • ⁇ is a parameter used in macro cell user power control module, as described in the specification standard 3GPP TR36.942 "Evolved Universal Terrestrial Radio Access (E- UTRA); Radio Frequency (RF) Systems Scenarios" .
  • a PL and PL are system-defined thresholds on differential pathloss and small cell pathloss to determine if the macro- connected users are in the proximity of small cells. Appendix lgives an example of deriving A PL and c PL .
  • the set I m denotes macro-connected users that severely impact small cells and S m represents the set of affected small cells.
  • the macro cell scheduling unit determines the scheduling information, which should be sent to the victim small cells S m , in order to assist them in performing a cross-tier interference-aware scheduling. To this end, the macro cell scheduling unitlooks up the set I m to see if user // assigned on resource block group/ is in the set of cell edge users, which are defined as those who will cause significant interference to one or more small cells in the uplink.
  • Table 1 below shows a set of coordination messages, also called macro-assisted scheduling messages, which are sent by the macro cell scheduling unit to small cells, which receive them in a fourth step RX COORD. MSG 13.
  • small cells S j and s 5 are affected by macro-connected users i ⁇ and i $ , respectively, and they should receive macro-assisted scheduling messages in step RX COORD. MSG 13 to help them in resource allocation.
  • Such a coordination message may comprise:
  • the small cell scheduling unit hence collects the coordination messages sent by macrocells and develops a constrained channel space (CCS) for all resource block groups.
  • CCS constrained channel space
  • Such a constrained channel space CCS takes as its elements the channel state information (CSI) of the scheduled macro cell users that are close to the small cell access nodes.
  • CCS consists of channels between identified interfering macro cell UEs and small cell access nodes.
  • the small cell access node hence uses the coordination messages sent by macro cells to know which macro cell UE will be transmitting and causing interference. It may then estimate the channel of interfering macro cell UEs in the following exemplary way.
  • small cell scheduling unit sent to small cell scheduling unit the information of macro UEs who are (i) scheduled in the next transmission and (ii) considered as strong interferer to small cell node (i.e., identified as interferer);
  • small cell scheduling unit gets information of (2), it can extract the UE index of identified interfering macro cell UE. It then looks up in the reference signals obtained at (1) to find the reference signals of the macro UE;
  • Small cell access node estimates the channel between the interfering macro cell UE and the small cell access node with the reference signal obtained in (3).
  • the CCS for subchannel/ is denotedas .
  • the small cell scheduling unit then performs a cross-tier inference- aware scheduling (CTIAS) with this information.
  • CTIAS cross-tier inference- aware scheduling
  • CTIAS-I an algorithm called CTIAS-I, which is detailed as below:
  • the small cell scheduling unit determinesa pre-selected user set by choosing users that are pseudo-orthogonal to CCS ⁇ ⁇ , i ⁇ U s where U s is the user set of the small cell, h ; is the uplink channel for user ; ' .
  • the channel state is the fast fading channel elements only with unit variance, that is,
  • the small cell scheduling unit then assigns the RBG to a user in set U j with the best optimization metric. For example, PF-scheduling leads to
  • P j being the transmit power of user j determined according to specific power control procedures methods.
  • the small cellscheduling unit implements an algorithm called CTIAS-II, which is detailed below:
  • V ( ⁇ U S ) the small cell scheduling unit computes the instantaneous data rate by taking into account the estimated cross-tier interference as
  • V[ is a diagonal matrix containing all interference power of macro-connected users received by the small cell.
  • the small cell scheduling unit assigns the RBG to the user with the maximum optimization metric.
  • Figure 3 represents a spatial visualisation of the interfering macro-user channel w.r.t. those of small cell users. More precisely, in figure 3, the vectors indicate the channel direction in the spatial domain while the length of vectors represents the channel strength.
  • the dashed arrow 35 denotes the CCS, that is to say, the channel of the macro cell user UEl, considered as an interferer, towards the small cell access node.
  • Arrows referenced 31, 32, 33 and 34 respectively show the channels of small cell users referenced UEl, UE2, UE3, UE4 towards the small cell access node.
  • the small cell scheduling unit has no information of the interferer channel, and will logically assign the resource block to U E 1 as it has the best channel condition. Nevertheless, the cross-tier interference 36, which corresponds to the projection of dashed arrow 35 onto arrow 31 (showing the channel of the small cell user UEl towards the small cell access node), is quite significant and in turn degrades the transmission rate of U E 1.
  • small cell tends to select the user with the best tradeoff between the desired signal strength and cross-tier interference, which results in U E 4. It should be noted that, with macro-user information, both CTIAS-1 and CTIAS-2 take cross- tier interference as the constraint in scheduling, to enhance the small cell user experience.
  • the method for coordinated scheduling in a heterogeneous network described above in relation with figures 1 to 3 works well for a network with an ideal backhaul linking the access nodes of macro cells and small cells.
  • some legacy networks show non-ideal backhauls, and it may be necessary to compensate for the backhaul latency, in order to enable implementation of the method according to the invention.
  • Figure 4 actually shows the time flow diagram for the scheduling scheme of figure 2.
  • the macro cell scheduling unit implements step SCH. UE 10, and schedules the macro cell users. Due to a backhaul delay D 0 , the macro-assisted message exchange occurs at a time T+D 0 . Due to a small cell processing delay, the small cell only performs interference aware scheduling CTIAS 14 at time T+Di. Hence, there exists a latency of n between the macro cell scheduling time T and the user data transmissionMC Tx 40 (macro UE packet transmission) and SC Tx 41 (small cell UE packet transmission).
  • the latency of 2 is dominated by the time interval D 0 of coordination message exchange between macro cells and small cells, which is subject to the backhaul, which carries coordinated message.
  • centralized RAN architecture e.g. Cloud RAN
  • inter-BBU BaseBandUnit
  • the performance of the proposed scheme according to an embodiment of the invention can be optimized with negligible backhaul delay denoted as D 0 .
  • the backhaul delay 0 may become significant in somescenarii of legacy networks and degrades the system performance.
  • the coordinated scheduler efficiency may decrease as the backhaul latency D 0 increases.
  • FSS frequency selective scheduling
  • MAX C/l Carrier-to- interference
  • PF Proportional Fair
  • the macro cell scheduling unit uses channel prediction to overcome the sub optimalityof the coordinated scheduling caused by backhaul latency. Hence, in step SCH.
  • the macro cell scheduler does not assign the radio resources to users with the best channel condition (or the best relative channel condition) but rather to those who are predicted to have the best channel condition at the time T+D 2 of transmission MC Tx 40, to compensate for the channel mismatch caused by the backhaul latency D 0 .
  • Any known channel predictor may be used, such as the one described by Alexandra Duel- Hallen in “Fading Channel Prediction for Mobile Radio Adaptive Transmission Systems, " IEEE Proceedings, 2007. However, it is important to underline that the accuracy of the chosen channel predictor may affect the decision of macro cell user assignment, and in sequel the scheduling of small cells.
  • an additional macro cell scheduling CTIAS-RS MC 51 is performed at the time when the small cell receives the coordination message X COORD. MSG 13 and performs user scheduling CTIAS-RS SC 50.
  • the macrocell scheduling unit can exploit the most recent CSIs in user assignment and may fully utilize the multi-user diversity to maximize the network performance.
  • the macro cell scheduling unit performs a scheduling step SCH.
  • UE 10 to schedule user equipment and allocate radio resources to the scheduled users at time T.
  • the macro cell scheduling unit determines the set of macro cell users which may generate severe interference on victim small cells, and send a coordination message to the victim small cell, which is received in step RX COORD. MSG 13 at time T+D 0 .
  • the small cell scheduling unit performs a cross-tier interference-aware scheduling, with an additional re-scheduling feature at the macro cell level, CTIAS-RS SC 50, at a time T +
  • the macro cell scheduling unit may alter the user assignment decisions for a number of RBGs where the previously assigned user CSI has substantially degenerated. Nevertheless, this may impact the small cells as the newly assigned users may bring the unexpected interference to small cell scheduled users that are best matched to the macro-connected users chosen in the first scheduling step SCH.
  • UE 10 the re-scheduler is designed with a number of specific considerations on maximizing macrocell and small cell performance at the same time.
  • the re-scheduler implements the following steps: a) Select i) e J m ⁇ I m ⁇ with the best optimization metric ⁇ ( ⁇ ) ) . b) Select i j e I m according to max z( j) , (8)
  • step CTIAS-RS MC 51 it can be ensured that the re-selected users in step CTIAS-RS MC 51 have the best (relative) CSI while being also spatially aligned with the user channel in the first scheduling step SCH.
  • Figures 6 and 7 respectively show the structure of the macro cell scheduling unit and of the small cell scheduling unit implementing the methods of coordinated scheduling as described above.
  • the macro cell scheduling unit shown on figure 6 comprises a receiving unit Rx. 60 for receiving propagation loss values, which are periodically reported by macro cell users, and which correspond to the propagation loss between the macro cell users and the access nodes to small cells located in the neighborhood.
  • It also comprises a scheduler SCH. 61, which performs scheduling of user equipment and allocation of radio resources to the scheduled UE. Such a scheduler 61 may also perform rescheduling of user equipment, according to the embodiment of the invention shown in figure 5.
  • the macro cell scheduling unit of figure 6 may also comprise a channel prediction unit PRED. 64, which predicts the channel condition of users at a future time, in order to take account of the backhaul latency, as described above.
  • a channel prediction unit PRED. 64 provides the predicted channels to the scheduler SCH. 61, so that the scheduler SCH. 61 does not assign the radio resources to users with the best channel condition (or the best relative channel condition) but rather to those who are predicted to have the best channel condition at the time T+D 2 .
  • the macro cell scheduling unit of figure 6 also comprises a computing unit ⁇ 62 for determining a set of scheduled user equipment prone to cause interference in the uplink on one or several victim small cell(s), and which receives at its input information from the scheduler SCH 61.
  • a computing unit 62 determines the set of cell edge users and the most affected small cells, and determines the scheduling information which should be included in a coordination message, which will be sent to small cells by a sending unit Tx. 63.
  • the small cell scheduling unit shown on figure 7 comprises a receiving unit x. 70 for receiving coordination messages from macro cell scheduling units, through a backhaul link linking them in the network.
  • coordination messages comprise information on interfering macro user equipment, and on radio resources allocated to themby the macro cell scheduling unit.
  • the small cell scheduling unit shown on figure 7 also comprises a scheduler SCH. 71 for performing interference aware scheduling of user equipment served by the small cell and for allocating radio resources to them, on the basis of the coordination messages received from the receiving unit 70.
  • the scheduler SCH. 71 encompasses all the means necessary for performing the various CTIAS algorithms described above in relation with the previous figures.
  • the various embodiments of the invention described throughout this document hence enable global scheduling in the heterogeneous uplink.
  • the scheduler coordinates the transmission of users in macrocells and overlaid small cells such that the cross-tier interference can be eliminated in the uplink;
  • the scheduler enables small cells to utilize multi-user diversity to enhance the small cell user transmissions while not compromising the performance of macro cell users;
  • the scheduler can be readily implemented in RAN centralization architectures and work jointly with other multi-point technologies to maximize the benefits;
  • the invention comprises enabling mechanisms to enhance user performance in this scenario. With this invention the user experience in small cells can be greatly enhanced disregarding the interference from macro cells.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

La présente invention concerne un procédé d'ordonnancement d'un équipement d'utilisateur (UE) dans un réseau hétérogène comprenant des macrocellules et des petites cellules ayant une couverture se chevauchant. Le procédé comprend les étapes consistant à : ordonnancer des UE desservis par la macrocellule et leur attribuer des ressources radio, déterminer, dans un ordonnanceur de la macrocellule, un ensemble d'UE ordonnancés enclins à provoquer une interférence dans la liaison montante sur une petite cellule victime, envoyer, par le biais d'une liaison terrestre entre l'ordonnanceur de la macrocellule et un ordonnanceur de la petite cellule victime, un message de coordination comprenant des informations concernant l'UE enclin à provoquer une interférence sur la petite cellule victime et sur les ressources radio lui étant attribuées ; dans l'ordonnanceur de la petite cellule victime, exécuter un ordonnancement tenant compte de l'interférence de l'UE desservi par la petite cellule victime et attribuer des ressources radio à l'UE ordonnancé, sur la base des messages de coordination reçus de la macrocellule.
PCT/CN2013/088808 2013-12-06 2013-12-06 Procédé d'ordonnancement d'équipement d'utilisateur dans un réseau hétérogène WO2015081570A1 (fr)

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PCT/CN2013/088808 WO2015081570A1 (fr) 2013-12-06 2013-12-06 Procédé d'ordonnancement d'équipement d'utilisateur dans un réseau hétérogène
PCT/IB2014/003040 WO2015082999A2 (fr) 2013-12-06 2014-12-04 Procédé d'ordonnancement d'un équipement utilisateur dans un réseau hétérogène

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CN105898757B (zh) * 2016-05-09 2019-02-26 南京邮电大学 一种无线回程链路异构物联网中的频谱资源分配方法
CN117879778A (zh) * 2017-08-10 2024-04-12 株式会社Ntt都科摩 终端、系统及测量方法
CN110213731B (zh) * 2019-04-29 2020-07-03 中国科学院计算技术研究所 一种基于智能定价的群体用户网络选择方法及系统
FR3105672A1 (fr) * 2019-12-20 2021-06-25 Orange Procédé d’allocation de fréquences d’émission de signaux radio entre une ou plusieurs entités de communication, permettant une réduction des interférences entre ces entités de communication utilisant 5 le même canal en fréquence
FR3105671A1 (fr) * 2019-12-20 2021-06-25 Orange Procédé d’allocation de fréquences d’émission de signaux radio entre une ou plusieurs entités de communication, permettant une réduction des interférences entre ces entités de communication utilisant le même canal en fréquence

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