WO2014140678A1

WO2014140678A1 - Joint uplink and downlink operation for dynamic time division duplex long term evolution system

Info

Publication number: WO2014140678A1
Application number: PCT/IB2013/001248
Authority: WO
Inventors: Joydeep Acharya; Sudhanshu Gaur; Long GAO
Original assignee: Hitachi, Ltd.
Priority date: 2013-03-15
Filing date: 2013-03-15
Publication date: 2014-09-18

Abstract

Exemplary embodiments provide techniques to properly choose an uplink/downlink (UL/DL) configuration for base stations to minimize the chances of UL DL interference while keeping the configurations aligned to traffic conditions. In one embodiment, a time division duplex (TDD) system includes an apparatus, a first base station having a first UL/DL configuration, and a second base station having a second UL/DL configuration which is not identical to the first UL/DL configuration. The apparatus comprises a processor, a memory, and a configuration determination module which is operable to: judge whether the first and second UL/DL configurations are close or not based on a preset condition; and if it is judged that the first and second UL/DL configurations are close, decide, based on the first and second UL/DL configurations, a common UL/DL configuration to be used by the first and second base stations instead of the first and second UL/DL configurations.

Description

JOINT UPLINK AND DOWNLINK OPERATION FOR DYNAMIC TIME DIVISION DUPLEX LONG TERM EVOLUTION SYSTEM

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to wireless systems and, more particularly, to joint uplink (UL) and downlink (DL) operation for dynamic time division duplex (TDD) long term evolution (LTE) systems.

[0002] TDD LTE systems allow base stations to choose the

uplink/downlink (UL/DL) configurations based on the nature of UL and DL user traffic. In future LTE small cell systems, it is possible that two base stations in close vicinity have very different UL and DL traffic characteristics. If the base stations choose UL/DL configurations based only on traffic, this could greatly increase interference in subframes where one of the base stations is transmitting in the downlink and the other is in uplink reception mode. We call this the UL DL interference.

BRIEF SUMMARY OF THE INVENTION

[0003] Exemplary embodiments of the invention provide techniques to properly choose a UL/DL configuration for both base stations to minimize the chances of UL DL interference while still keeping the configurations aligned to traffic conditions. Further, if the different configurations are chosen by the two base stations, scheduling guidelines need to be established to reduce the resulting uplink-downlink interference.

[0004] This invention includes two parts. In the first part, we propose a method by which two base stations in the same vicinity can cooperate to decide what UL/DL configuration to use for TDD LTE. This is based on their own traffic characteristics and trying to minimizing the UL DL interference. In the second part, we provide the design of a joint UL DL scheduler

recommendation module, which provide inputs to the schedulers at the two base stations for dealing with the UL DL interference. This invention solves the problem of dynamic UL/DL configuration selection and UL DL interference mitigation in dynamic TDD systems. As a result, this invention will enable dynamic TDD systems where the UL/DL configurations in TDD LTE systems do not have to remain static.

[0005] An aspect of the present invention is directed to an apparatus in a time division duplex (TDD) system which includes the apparatus, a first base station having a first uplink/downlink (UL/DL) configuration, and a second base station having a second UL/DL configuration which is not identical to the first UL/DL configuration. The apparatus comprises a processor, a memory, and a configuration determination module which is operable to: judge whether the first and second UL/DL configurations are close or not based on a preset condition; and if it is judged that the first and second UL/DL configurations are close, decide, based on the first and second UL/DL configurations, a common UL/DL configuration to be used by the first and second base stations instead of the first and second UL/DL

configurations.

[0006] In some embodiments, judging whether the first and second

UL/DL configurations are close or not comprises: calculating a first ratio n_A of

UL to DL subframes for the first UL/DL configuration; calculating a second ratio n_B of UL to DL subframes for the second UL/DL configuration; calculating the difference in the first and second ratios of UL to DL subframes |n_A - n_B|; and determining that the first and second UL/DL configurations are close if the difference |n_A - n_B| is less than a preset threshold. Deciding a common UL/DL configuration comprises one of: (i) choosing the first UL/DL

configuration as the common UL/DL configuration; (ii) choosing the second UL/DL configuration as the common UL/DL configuration; or (iii) choosing a third UL/DL configuration, which is close to both the first and second UL/DL configurations, as the common UL/DL configuration.

[0007] In specific embodiments, the apparatus further comprises a joint UL-DL scheduler preprocessing module, wherein if it is judged that the first and second UL/DL configurations are not close, the configuration

determination module is operable to inform the first base station to keep the first UL/DL configuration and to inform the second base station to keep the second UL/DL configuration; and the joint UL-DL scheduler preprocessing module is operable, based on the first and second UL/DL configurations and information of respective UEs (user equipment) which are associated, respectively, with the first and second base stations, to develop a set of recommendations for UL and DL scheduling for the first and second base stations to manage UL DL interference caused by the first and second UL/DL configurations that are not close.

[0008] In some embodiments, the set of recommendations include, for cell edge UEs that are associated with the first and second base stations: a first recommendation not to schedule cell edge UE transmission in

corresponding subframes for the first and second base stations which are different from each other in terms of UL or DL; and a second

recommendation, for corresponding subframes for the first and second base stations which are identical in terms of UL or DL, to schedule cell edge UE UL transmissions via CoMP (Coordinated Multipoint) if the corresponding subframe is UL for both the first and second base stations and to schedule cell edge UE DL transmissions via CoMP if the corresponding subframe is DL for both the first and second base stations.

[0009] In specific embodiments, the set of recommendations include, for cell edge UEs associated with the first base station which are located close in physical position to any cell edge UE associated with the second base station and for cell edge UEs associated with the second base station which are located close in physical position to any cell edge UE associated with the first base station, based on a preset closeness criterion: a first recommendation not to schedule cell edge UE transmission in corresponding subframes for the first and second base stations which are different from each other in terms of UL or DL; and a second recommendation, for corresponding subframes for the first and second base stations which are identical in terms of UL or DL, to schedule cell edge UE UL transmissions via CoMP

(Coordinated Multipoint) if the corresponding subframe is UL for both the first and second base stations and to schedule cell edge UE DL transmissions via CoMP if the corresponding subframe is DL for both the first and second base stations.

[0010] In accordance with another aspect of the invention, a time division duplex (TDD) system comprises a first base station having a first uplink/downlink (UL/DL) configuration; a second base station having a second

UL/DL configuration which is not identical to the first UL/DL configuration; and an apparatus. The apparatus includes a processor, a memory, and a configuration determination module which is operable to: judge whether the first and second UL/DL configurations are close or not based on a preset condition; and if it is judged that the first and second UL/DL configurations are close, decide, based on the first and second UL/DL configurations, a common UL/DL configuration to be used by the first and second base stations instead of the first and second UL/DL configurations.

[0011] In some embodiments, the apparatus is provided in one of: (i) one of the first or second base stations; (ii) a core network of the TDD system which is coupled with the first and second base stations; or (iii) a central controller of the TDD system which is coupled with the first and second base stations as first and second remote radio heads. The first base station determines the first UL/DL configuration based on traffic characteristics of the first base station. The second base station determines the second UL/DL configuration based on traffic characteristics of the second base station.

[0012] Another aspect of this invention is directed to a method for joint uplink (UL) and downlink (DL) operation in a time division duplex (TDD) system which includes a first base station having a first uplink/downlink (UL/DL) configuration, and a second base station having a second UL/DL configuration which is not identical to the first UL/DL configuration. The method comprises: a processor judging whether the first and second UL/DL configurations are close or not based on a preset condition; and if it is judged that the first and second UL/DL configurations are close, deciding, based on the first and second UL/DL configurations, a common UL/DL configuration to be used by the first and second base stations instead of the first and second UL/DL configurations. [0013] These and other features and advantages of the present invention will become apparent to those of ordinary skill in the art in view of the following detailed description of the specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows an example of a frame with different UL/DL configurations available for TDD LTE.

[0015] FIG. 2 shows an example of two base stations employing different UL/DL configurations in dynamic TDD.

[0016] FIG. 3 shows an example of a new UL DL interference situation that can arise with dynamic TDD.

[0017] FIG. 4 shows an example of downlink ML) (Multi-User) CoMP (Coordinated Multipoint) to jointly transmit to both user equipment UE A and UE B simultaneously from both base stations BS A and BS B.

[0018] FIG. 5 shows an example of uplink MU CoMP to jointly receive from both UE A and UE B simultaneously at both base stations.

[0019] FIG. 6 shows an example of a flow diagram illustrating the process flow of a TDD configuration determination module and how it interacts with the base stations.

[0020] FIG. 7 shows an example of a flow diagram illustrating the process flow of a generic joint UL-DL scheduler preprocessing module and how it interacts with the base stations.

[0021] FIG. 8 shows an example of a first design of a joint UL-DL scheduler preprocessing module and how it interacts with the base stations. [0022] FIG. 9 shows an example of a second design of a joint UL-DL scheduler preprocessing module and how it interacts with the base stations.

[0023] FIG. 10 shows Table 1 which highlights the main feature of the two designs of the joint UL-DL scheduler preprocessing modules of FIGS. 8 and 9.

[0024] FIG. 1 1 shows Table 2 which lists the possible physical implementation of the two logical modules (TDD configuration determination module and joint UL-DL scheduler preprocessing module) and features of the different physical realizations of the two logical modules.

[0025] FIG. 12 shows an example of implementing the two modules (TDD configuration determination module and joint UL-DL scheduler preprocessing module) in one of the base stations.

[0026] FIG. 13 shows an example of implementing the two modules in the core network.

[0027] FIG. 14 shows an example of implementing the two modules in the central controller for the RRH (remote radio head) case.

[0028] FIG. 15 shows an example of a cell edge UE determination module.

[0029] FIG. 16 shows an example of a module to determine if two cell edge UEs in adjacent base stations are close.

DETAILED DESCRIPTION OF THE INVENTION

[0030] In the following detailed description of the invention, reference is made to the accompanying drawings which form a part of the disclosure, and in which are shown by way of illustration, and not of limitation, exemplary embodiments by which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. Further, it should be noted that while the detailed description provides various exemplary embodiments, as described below and as illustrated in the drawings, the present invention is not limited to the embodiments described and illustrated herein, but can extend to other embodiments, as would be known or as would become known to those skilled in the art. Reference in the specification to "one embodiment," "this embodiment," or "these

embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, and the appearances of these phrases in various places in the specification are not necessarily all referring to the same embodiment. Additionally, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details may not all be needed to practice the present invention. In other circumstances, well-known structures, materials, circuits, processes and interfaces have not been described in detail, and/or may be illustrated in block diagram form, so as to not unnecessarily obscure the present invention.

[0031] Furthermore, some portions of the detailed description that follow are presented in terms of algorithms and symbolic representations of operations within a computer. These algorithmic descriptions and symbolic representations are the means used by those skilled in the data processing arts to most effectively convey the essence of their innovations to others skilled in the art. An algorithm is a series of defined steps leading to a desired end state or result. In the present invention, the steps carried out require physical manipulations of tangible quantities for achieving a tangible result. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals or instructions capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, instructions, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as

"processing," "computing," "calculating," "determining," "displaying," or the like, can include the actions and processes of a computer system or other information processing device that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system's memories or registers or other information storage, transmission or display devices.

[0032] The present invention also relates to an apparatus for performing the operations herein. This apparatus may be specially

constructed for the required purposes, or it may include one or more general- purpose computers selectively activated or reconfigured by one or more computer programs. Such computer programs may be stored in a computer- readable storage medium, such as, but not limited to optical disks, magnetic disks, read-only memories, random access memories, solid state devices and drives, or any other types of media suitable for storing electronic information. The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs and modules in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform desired method steps. In addition, the present invention is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. The

instructions of the programming language(s) may be executed by one or more processing devices, e.g., central processing units (CPUs), processors, or controllers.

[0033] Exemplary embodiments of the invention, as will be described in greater detail below, provide apparatuses, methods and computer programs for joint uplink (UL) and downlink (DL) operation for dynamic time division duplex (TDD) long term evolution (LTE) systems. This invention will be particularly helpful in LTE-Advanced systems employing small cells and dynamic TDD such as Rel-1 1 LTE onwards. It proposes a method to choose

UL/DL configurations for dynamic TDD systems and also proposes a method to reduce the UL DL interference seen in such systems.

[0034] FIG. 1 shows an example of a frame with different UL/DL configurations available for TDD LTE. In TDD LTE, a base station can choose different configurations of UL and DL subframes in a radio frame. See 3GPP TS 36.21 1 V1 1 .0.0, "Evolved Universal Terrestrial Radio Access (E- UTRA); Physical Channels and Modulation," 2012-10. Examples of such configurations are given in FIG. 1 . As shown, some configurations such as Configuration 0 have more UL subframes and are more suited for systems where there is more uplink traffic while configurations such as Configuration 5 have more DL subframes and are suited more for systems with more downlink traffic.

[0035] Till LTE Rel-10, base stations were predominantly macro base stations, covering a wide area with users of different traffic types. The network operator usually would choose a TDD configuration for all its macros in a given region. With the advent of LTE Rel-1 1 , the focus has shifted from large coverage macros to small cells which cater to localized traffic demand. Thus it is possible in LTE Rel-1 1 and beyond that an operator chooses a UL/DL configuration to adapt to the localized traffic characteristics. See RWS-120006, "Views on Rel-12 and onwards for LTE and UMTS," Huawei Technologies, HiSilicon, RAN workshop on Rel-12 and onwards, Ljubljana, Slovenia, 1 1 th-12th June, 2012. This is also sometimes called dynamic TDD. A macro base station has a higher (typically substantially higher) transmission power/coverage than a small cell. One typical network deployment involves a large macro coverage area with many pico cells (called small cells) present in it. In such an example, the small cells are within the macro coverage area of the macro base station.

[0036] FIG. 2 shows an example of two base stations employing different UL/DL configurations in dynamic TDD. The two base stations, BS A and BS B, have corresponding associated UE (user equipment), UE A and UE B, respectively.

[0037] FIG. 3 shows an example of a new UL DL interference situation that can arise with dynamic TDD. This new kind of interference can arise when base stations employ different UL/DL configurations. Consider that UE A and UE B are both cell edge UEs of base stations A and B, respectively, and they are physically located close to each other as shown in FIG. 3.

Consider subframe 9 in which cell A is in UL mode and cell B is in DL mode. Thus the transmissions are UE A→ BS A and BS B→ UE B. For the UE A → BS A uplink communication, the interference is due to transmission from BS B. This is not severe as the interfering source (BS B) is far away from the receiver (BS A). However, consider the other communication process, i.e., BS B→ UE B. The interference at UE B is due to transmission from UE A. Since the UEs are close to each other, this interference could be very severe. Note that this interference arises only when both UE A and UE B are located close to each other. This implies that both of them are cell edge (but the converse is not true).

[0038] Note that if two subframes of the two base stations are in the same mode (e.g., subframe 0 where both are downlink or subframe 8 where both are uplink), this kind of interference is avoided. A UE in UL mode in subframe 8 is still interfered by other UEs in UL mode and a UE in DL mode in subframe 0 is interfered by other base stations in DL mode. However, interference from other UEs or base stations in the same mode is easier to control. 3GPP already has several interference management mechanisms such as elCIC, etc. to deal with this. [0039] In fact, if two subframes of the two base stations are in the same mode, interference can also be totally avoided by CoMP (Coordinated Multipoint) Transmission/Reception technology where base stations cooperate to transmit/receive from multiple UEs at the same time. For example, in subframe 0, downlink CoMP can be used to serve both UEs simultaneously by both the base stations. FIG. 4 shows an example of downlink ML) (Multi-User) CoMP to jointly transmit to both UE A and UE B simultaneously from both base stations BS A and BS B. For subframe 8, similarly, UL CoMP can be used for joint reception from multiple UEs simultaneously, as shown in FIG. 5. FIG. 5 shows an example of uplink MU CoMP to jointly receive from both UE A and UE B simultaneously at both base stations. There is a tradeoff involved here:

[0040] (1 ) An isolated base station should choose a UL/DL configuration to match the traffic characteristics (UL or DL) of its associated UEs.

[0041] (2) When there are other base stations in the area, this may lead to large UL DL interference, negating the gains from choosing the UL/DL configuration to match the traffic characteristics. Furthermore, if base stations choose configurations that are similar but are not necessarily matched to the traffic characteristics, then interference can be managed by CoMP

technology.

[0042] (3) Hence the base stations should choose their UL/DL configurations by keeping in mind both factors, namely, matching traffic characteristics of its UEs and potential interference management by CoMP technology. [0043] In this invention, we thus propose two methods: (1 ) to properly choose UL/DL configurations; and (2) to handle the UL DL interference if it still remains.

[0044] FIG. 6 shows an example of a flow diagram illustrating the process flow of a TDD configuration determination module and how it interacts with the base stations, BS A and BS B. In FIG. 6, the process flow of the proposed TDD configuration determination module has the following steps:

[0045] (1 ) Base stations A and B determine their respective UL/DL configurations C_A and C_B (initial TDD configurations) based only on their own traffic characteristics and transmit this to the TDD configuration determination module. Note that the TDD configuration determination module is a logical module for purposes of this description. In actual implementation, the functionalities of this module can be implemented by one of the base stations (having a processor/controller and a memory), or this module could reside in the core network (having a processor/controller and a memory), or the base stations could be remote radio heads (RRHs) that are controlled by a central controller and this central controller can implement the TDD configuration determination module.

[0046] (2) The TDD configuration determination module checks if CA

= CB. If so, the procedure of TDD configuration determination ends (in the sense that C_A new = CA and CB, new = CB and the information is sent to BS A and BS B via X2 interface). If both base stations want to choose the same configuration, there is no UL DL interference and other interference can be handled by known and standardized methods. [0047] (3) If C_A and C_B are different, the TDD configuration determination module checks how different they are. This is determined by the difference in the ratios of UL to DL subframes for C_A and C_B. Let these ratios be called n_A and n_B. If the difference |n_A - n_B| is less than a threshold Th, it means that the configurations are close. For example, assume BS A reports configuration 4 and BS B reports configuration 5. Thus, n_A = 2/7 and n_B = 1 /8 and |n_A - n_B| = 0.16. If Th is chosen to be say 0.3, then in this case, C_A and C_B are deemed to be close. In another example, assume that BS A reports configuration 1 for which n_A = 1 , and hence the difference |n_A - n_B| is 0.875. In this case, with the threshold at 0.3, the two configurations C_A and C_B are deemed to be different.

[0048] (4) If the two configurations C_A and C_B are close (such as configurations 4 and 5), then there is a module (denoted by function f) that chooses a common configuration m which is close to both C_A and C_B. An example could be choose m = min(C_A, C_B). Thus in the given example, configuration 4 would be chosen for both base stations. The logic is that since C_A and C_B are close, a common configuration m can be found which is reasonably aligned to the traffic characteristics of both cells. Another example could be to choose a third configuration which is close to both C_A and C_B. Let

C_A = 3 and C_B = 5 then choose m = 4. Choosing a common configuration m ensures that there is no subsequent UL DL interference.

[0049] (5) If the two configurations are different, then choosing any common configuration m to avoid UL DL interference is not good as a common configuration would not be reasonably aligned to the traffic characteristics of one or both cells. In that case, the proposed TDD configuration determination module keeps the same TDD configurations C_A and CB. This will lead to UL DL interference which will be handled by our next proposal.

[0050] (6) The final configurations decided by this module are termed C_A, new and CB, new- The configuration information is sent to BS A and BS B via X2 interface and used to initialize TDD configurations in BS A and BS B, respectively.

[0051 ] In the case when the TDD configuration determination module assigns different UL/DL configurations to the two base stations, then the UL

DL interference will arise in certain subframes. This interference can be managed by intelligent scheduling. For example in FIG. 3, this interference can be avoided in scheduling either the UE A→ BS A type or the BS B→ UE

B type transmission in a given time slot. Note that the first is an uplink transmission while the second is a downlink transmission. Hence the UL and

DL scheduling decisions in the two cells have to be jointly coordinated.

[0052] FIG. 7 shows an example of a flow diagram illustrating the process flow of a generic joint UL-DL scheduler preprocessing module and how it interacts with the base stations, BS A and BS B. The possibility of such scheduling to mitigate UL/DL interference has been mentioned in TR 36.828 under the name SDIM, but no details have been provided. See 3GPP TR

36.828, "Further enhancements to LTE Time Division Duplex (TDD) for

Downlink-Uplink (DL-UL) interference management and traffic adaptation,"

June 2012. This invention thus provides an implementation of SDIM as mentioned in TR 36.828. This module inputs certain information about the final UL/DL configurations of the two base stations (that were determined by the TDD configuration determination module in the previous step) and also information about the associated UEs (such as information if a given UE is cell edge/cell center and information about the position of the UE in its serving cell). This information is passed to the information processing module for processing via X2 interface. Based on this processing, a subsequent module called the scheduling recommendation module develops a set of

recommendations for UL and DL scheduling which would manage the UL DL interference. These recommendations are then fed back to the schedulers of the individual base station schedulers via X2 interface.

[0053] Whether a UE is cell edge or cell center can be determined based on a preset criterion (e.g., distance or some other parameter from the associated base station to the UE). FIG. 15 shows an example of a cell edge

UE determination module for determining whether a UE is a cell edge UE or not. For each base station, the module calculates the link gains of all UEs connected to a base station (this is done for all base stations). For base station j, the module determines UE i to be cell edge if the link gain is below a preset threshold Th, i.e., if S(i,j) < Th. The cell edge UE determination module may be provided in the joint UL-DL scheduler preprocessing module.

[0054] Note that similar to the TDD configuration determination module, the joint UL-DL scheduler preprocessing module is a logical module for purposes of this description. In actual implementation, the functionalities of this module can be implemented by one of the base stations, or this module could reside in the core network, or the base stations could be remote radio heads (RRHs) that are controlled by a central controller and this central controller can implement the joint UL-DL scheduler preprocessing module. [0055] FIG. 8 shows an example of a first design of a joint UL-DL scheduler preprocessing module and how it interacts with the base stations. The information processing module first determines which corresponding subframes are different for the two base stations (i.e., corresponding subframes where BS A has UL and BS B has DL or vice versa). It stores this set of subframes as S. It then determines which are the cell edge UEs in both base stations. The scheduling recommendation module then has the following two recommendations:

[0056] (1 ) Do not schedule any cell edge UE transmission (UL and DL) in subframes in set S.

[0057] (2) In other corresponding subframes, the base stations have common configurations. Schedule the cell edge UE UL transmissions if the corresponding subframe is UL for both base stations and transmit via CoMP.

Schedule the cell edge UE DL transmissions if the corresponding subframe is

DL for both base stations and transmit via CoMP.

[0058] The following illustrates the functionality of the joint UL-DL scheduler preprocessing module by an example. Let the final TDD configurations be C_A, new = 1 and C_B, new = 5. This produces the set S = {3, 7,

8}. In these subframes, we do not schedule either UE A→ BS A type or BS B

→ UE B type transmissions. In subframe 2 where both base stations are in

UL mode, UE A type UEs can transmit to both BS A and BS B by UL CoMP.

In subframes {0,4,5,9} where both base stations are in DL mode, both base stations can transmit to UE B type UEs by DL CoMP. Note that FIG. 3 shows only two UEs A and B. In a real system, there will generally be a plurality of

UEs of type UE A and a plurality of UEs of type UE B. [0059] Note that this joint UL-DL scheduler preprocessing module can be further optimized. In the subframes of set S, all cell edge UEs were recommended to be prevented from being scheduled. In reality, UEs A and B can be cell edge but not close to each other. In this case, there is no problem of scheduling them simultaneously. This would not create UL DL interference and will actually improve the system performance. Hence a second joint UL- DL scheduler preprocessing module has been proposed in FIG. 9.

[0060] FIG. 9 shows an example of a second design of a joint UL-DL scheduler preprocessing module and how it interacts with the base stations. In this second design, the joint UL-DL scheduler preprocessing module also considers the position information of the UEs along with whether they are cell edge or not. The information processing module, in addition to the functions of determining subframes and determining cell edge UEs as in FIG. 8, also determines, from position information of the UEs, the set of those cell edge UEs in base stations A and B which are located close to each other in physical position and hence would create UL DL interference if co-scheduled. The scheduling recommendation module recommends not scheduling only these set of UEs together.

[0061] The closeness between UEs can be determined based on a preset closeness criterion (e.g., a preset distance or some other parameter between a cell edge UE associated with a first BS and a cell edge UE associated with a second BS, such that the two are considered close to each other if a threshold of the preset parameter is reached). FIG. 16 shows an example of a module to determine if two cell edge UEs in adjacent base stations are close. The module determines cell edge UE A in base station A and cell edge UE B in base station B, which is adjacent to base station A by the cell edge UE determination module (see FIG. 15). The module estimates the angle of arrival (AoA) of the two UEs based on LTE reference signals such as Demodulation Reference Signal (DMRS). They are call AoA A and AoA B for the two cell edge UEs A and B, respectively. The module adjusts the AoAs of the two UEs by the antenna main lobe direction of the two base stations. If the directions (in angles) are t_A and t_B, the module defines new angles, p_A = AoA A - t_A and p_B = AoA B - t_B, respectively. The module determines that UE A and UE B are close in location if the absolute difference in the angles is less than a preset threshold p_Th, i.e., if |p_A - p_B| < p_Th. This module for determining closeness may be provided in the joint UL-DL scheduler preprocessing module.

[0062] FIG. 10 shows Table 1 which highlights the main feature of the two designs of the joint UL-DL scheduler preprocessing modules of FIGS. 8 and 9. The first design (FIG. 8) is simple to implement, and has less feedback overhead and delay from base stations to the module, but has relatively less efficient scheduling recommendations than the second design. The second design (FIG. 9) has more efficient scheduling recommendations than the first design, but has more feedback overhead and delay as extra position information of all UEs have to be fed to the module.

[0063] FIG. 1 1 shows Table 2 which lists the possible physical implementation of the two logical modules (TDD configuration determination module and joint UL-DL scheduler preprocessing module) and features of the different physical realizations of the two logical modules. Implementing the module(s) in one of the base stations would result in less feedback delay and X2 interface is sufficient, but the functional complexity of the base station increases. Implementing the module(s) in the core network means that the base station functionalities would stay the same and higher complexity could be handled by the core network, but it would result in higher feedback delay and S1 interface to the core network will be needed. Implementing the module(s) in the central controller for RRH case would result in less feedback delay and fiber/X2 interface is sufficient, but the functional complexity of the central controller increases and this implementation is applicable only in the RRH case.

[0064] FIGS. 12-14 contain figures corresponding to the three cases shown in Table 2 of FIG. 1 1 . FIG. 12 shows an example of implementing the two modules (TDD configuration determination module and joint UL-DL scheduler preprocessing module) in one of the base stations BS A. BS A and BS B are coupled via X2 based backhaul. FIG. 13 shows an example of implementing the two modules in the core network. The core network is coupled via S1 based backhaul to BS A and BS B. FIG. 14 shows an example of implementing the two modules in the central controller for the RRH (remote radio head) case. The central controller BS is coupled via fiber based backhaul to RRH A and RRH B.

[0065] Of course, the communications systems shown in FIGS. 3 and

12-14 and the functional block diagrams illustrated in FIGS. 6-9 are purely exemplary of systems in which the present invention may be implemented, and the invention is not limited to a particular hardware or software configuration. The computers and storage systems implementing the invention can also have known I/O devices (e.g., CD and DVD drives, floppy disk drives, hard drives, etc.) which can store and read the modules, programs and data structures used to implement the above-described invention. These modules, programs and data structures can be encoded on such computer-readable media. For example, the data structures of the invention can be stored on computer-readable media independently of one or more computer-readable media on which reside the programs used in the invention. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include local area networks, wide area networks, e.g., the Internet, wireless networks, storage area networks, and the like.

[0066] In the description, numerous details are set forth for purposes of explanation in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that not all of these specific details are required in order to practice the present invention. It is also noted that the invention may be described as a process, which is usually depicted as a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged.

[0067] As is known in the art, the operations described above can be performed by hardware, software, or some combination of software and hardware. Various aspects of embodiments of the invention may be implemented using circuits and logic devices (hardware), while other aspects may be implemented using instructions stored on a machine-readable medium (software), which if executed by a processor, would cause the processor to perform a method to carry out embodiments of the invention. Furthermore, some embodiments of the invention may be performed solely in hardware, whereas other embodiments may be performed solely in software. Moreover, the various functions described can be performed in a single unit, or can be spread across a number of components in any number of ways. When performed by software, the methods may be executed by a processor, such as a general purpose computer, based on instructions stored on a computer-readable medium. If desired, the instructions can be stored on the medium in a compressed and/or encrypted format.

[0068] From the foregoing, it will be apparent that the invention provides methods, apparatuses and programs stored on computer readable media for joint UL and DL operation for dynamic TDD LTE systems.

Additionally, while specific embodiments have been illustrated and described in this specification, those of ordinary skill in the art appreciate that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments disclosed. This disclosure is intended to cover any and all adaptations or variations of the present invention, and it is to be understood that the terms used in the following claims should not be construed to limit the invention to the specific

embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with the established doctrines of claim interpretation, along with the full range of equivalents to which such claims are entitled.

Claims

WHAT IS CLAIMED IS:

1 . An apparatus in a time division duplex (TDD) system which includes the apparatus, a first base station having a first uplink/downlink (UL/DL) configuration, and a second base station having a second UL/DL

configuration which is not identical to the first UL/DL configuration, the apparatus comprising a processor, a memory, and a configuration

determination module which is operable to:

judge whether the first and second UL/DL configurations are close or not based on a preset condition; and

if it is judged that the first and second UL/DL configurations are close, decide, based on the first and second UL/DL configurations, a common UL/DL configuration to be used by the first and second base stations instead of the first and second UL/DL configurations.

2. The apparatus according to claim 1 , wherein judging whether the first and second UL/DL configurations are close or not comprises:

calculating a first ratio n_A of UL to DL subframes for the first UL/DL configuration;

calculating a second ratio n_B of UL to DL subframes for the second UL/DL configuration;

calculating the difference in the first and second ratios of UL to DL subframes |n_A - n_B|; and

determining that the first and second UL/DL configurations are close if the difference |n_A - n_B| is less than a preset threshold.

3. The apparatus according to claim 1 , wherein deciding a common UL/DL configuration comprises one of:

(i) choosing the first UL/DL configuration as the common UL/DL configuration;

(ii) choosing the second UL/DL configuration as the common UL/DL configuration; or

(iii) choosing a third UL/DL configuration, which is close to both the first and second UL/DL configurations, as the common UL/DL configuration.

4. The apparatus according to claim 1 , further comprising a joint UL-DL scheduler preprocessing module, wherein if it is judged that the first and second UL/DL configurations are not close,

the configuration determination module is operable to inform the first base station to keep the first UL/DL configuration and to inform the second base station to keep the second UL/DL configuration; and

the joint UL-DL scheduler preprocessing module is operable, based on the first and second UL/DL configurations and information of respective UEs (user equipment) which are associated, respectively, with the first and second base stations, to develop a set of recommendations for UL and DL scheduling for the first and second base stations to manage UL DL interference caused by the first and second UL/DL configurations that are not close.

5. The apparatus according to claim 4, wherein the set of

recommendations include, for cell edge UEs that are associated with the first and second base stations:

a first recommendation not to schedule cell edge UE transmission in corresponding subframes for the first and second base stations which are different from each other in terms of UL or DL; and

a second recommendation, for corresponding subframes for the first and second base stations which are identical in terms of UL or DL, to schedule cell edge UE UL transmissions via CoMP (Coordinated Multipoint) if the corresponding subframe is UL for both the first and second base stations and to schedule cell edge UE DL transmissions via CoMP if the

corresponding subframe is DL for both the first and second base stations.

6. The apparatus according to claim 4, wherein the set of

recommendations include, for cell edge UEs associated with the first base station which are located close in physical position to any cell edge UE associated with the second base station and for cell edge UEs associated with the second base station which are located close in physical position to any cell edge UE associated with the first base station, based on a preset closeness criterion:

corresponding subframe is DL for both the first and second base stations.

7. A time division duplex (TDD) system comprising

a first base station having a first uplink/downlink (UL/DL) configuration; a second base station having a second UL/DL configuration which is not identical to the first UL/DL configuration; and

an apparatus including a processor, a memory, and a configuration determination module which is operable to:

8. The TDD system according to claim 7, wherein judging whether the first and second UL/DL configurations are close or not comprises:

calculating a second ratio n_B of UL to DL subframes for the second UL/DL configuration; calculating the difference in the first and second ratios of UL to DL subframes |n_A - n_B|; and

9. The TDD system according to claim 7, wherein deciding a common UL/DL configuration comprises one of:

(i) choosing the first UL/DL configuration as the common UL/DL configuration;

10. The TDD system according to claim 7, wherein the apparatus further comprises a joint UL-DL scheduler preprocessing module, wherein if it is judged that the first and second UL/DL configurations are not close,

1 1 . The TDD system according to claim 10, wherein the set of

corresponding subframe is DL for both the first and second base stations.

12. The TDD system according to claim 10, wherein the set of

recommendations include, for cell edge UEs associated with the first base station which are located close in physical position to any cell edge UE associated with the second base station and for cell edge UEs associated with the second base station which are located close in physical position to any cell edge UE associated with the first base station, based on a preset closeness criterion: a first recommendation not to schedule cell edge UE transmission in corresponding subframes for the first and second base stations which are different from each other in terms of UL or DL; and

corresponding subframe is DL for both the first and second base stations.

13. The TDD system according to claim 7, wherein the apparatus is provided in one of:

(i) one of the first or second base stations;

(ii) a core network of the TDD system which is coupled with the first and second base stations; or

(iii) a central controller of the TDD system which is coupled with the first and second base stations as first and second remote radio heads.

14. The TDD system according to claim 7,

wherein the first base station determines the first UL/DL configuration based on traffic characteristics of the first base station; and

wherein the second base station determines the second UL/DL configuration based on traffic characteristics of the second base station.

15. A method for joint uplink (UL) and downlink (DL) operation in a time division duplex (TDD) system which includes a first base station having a first uplink/downlink (UL/DL) configuration, and a second base station having a second UL/DL configuration which is not identical to the first UL/DL configuration, the method comprising:

a processor judging whether the first and second UL/DL configurations are close or not based on a preset condition; and

if it is judged that the first and second UL/DL configurations are close, deciding, based on the first and second UL/DL configurations, a common UL/DL configuration to be used by the first and second base stations instead of the first and second UL/DL configurations.

16. The method according to claim 15, wherein judging whether the first and second UL/DL configurations are close or not comprises:

17. The method according to claim 15, wherein deciding a common UL/DL configuration comprises one of: (i) choosing the first UL/DL configuration as the common UL/DL configuration;

18. The method according to claim 15, further comprising, if it is judged that the first and second UL/DL configurations are not close:

informing the first base station to keep the first UL/DL configuration and informing the second base station to keep the second UL/DL configuration; and

developing, based on the first and second UL/DL configurations and information of respective UEs (user equipment) which are associated, respectively, with the first and second base stations, a set of

recommendations for UL and DL scheduling for the first and second base stations to manage UL DL interference caused by the first and second UL/DL configurations that are not close.

19. The method according to claim 18, wherein the set of

a first recommendation not to schedule cell edge UE transmission in corresponding subframes for the first and second base stations which are different from each other in terms of UL or DL; and a second recommendation, for corresponding subframes for the first and second base stations which are identical in terms of UL or DL, to schedule cell edge UE UL transmissions via CoMP (Coordinated Multipoint) if the corresponding subframe is UL for both the first and second base stations and to schedule cell edge UE DL transmissions via CoMP if the

corresponding subframe is DL for both the first and second base stations.

20. The method according to claim 18, wherein the set of

corresponding subframe is DL for both the first and second base stations.