WO2013044432A1

WO2013044432A1 - Timing control in flexible time division duplex configuration

Info

Publication number: WO2013044432A1
Application number: PCT/CN2011/080159
Authority: WO
Inventors: Jing HAN; Chunyan Gao; Erlin Zeng; Haiming Wang; Wei Hong
Original assignee: Renesas Mobile Corp
Current assignee: Renesas Electronics Corp
Priority date: 2011-09-26
Filing date: 2011-09-26
Publication date: 2013-04-04
Anticipated expiration: 2014-03-26

Abstract

There are provided measures for timing control in flexible time division duplex configuration. Such measures may exemplarity comprise configuring a change from a first uplink-downlink configuration to a second uplink- downlink configuration out of a set of flexible uplink-downlink configurations of a frame structure for time division duplex communication on the basis of flexible subframe patterns, and controlling a timing of one or more boundary subframes in at least one of the first and second uplink-downlink configurations, said boundary subframes being those subframes in one of the first and second uplink-downlink configurations having an associated feedback or grant subframe in the other one of the first and second uplink- downlink configurations.

Description

TIMING CONTROL IN FLEXIBLE TIME DIVISION DUPLEX

CONFIGURATION

Field of the invention

The present invention relates to timing control in flexible time division duplex configuration , More specifically, the present invention relates to measures (including methods, apparatuses and computer program products) for timing control in flexible time division duplex configuration.

Background

In the field of communication systems, including wireless and/or cellular communication systems, various techniques are known for concurrently utilizing a physical channel for both transmitting and receiving operations, i.e. for communication in both transmitting and receiving directions from the viewpoint of a system entity in questions. One of these known channel utilization techniques is Time Division Duplex (TDD) in which transmitting and receiving channels utilize a common frequency spectrum while being temporally separated from each other.

The TDD technique is effective by offering flexible deployments without requiring a pair of spectrum resources, which is especially beneficial in wireless communication systems having limited spectrum resources. Further, the TDD technique is effective by allowing an asymmetric uplink-downlink (UL-DL) resource allocation in that a different number of resources (e.g. blocks, frames, subframes or the like) are allocated for uplink and downlink communications. In view of these features, TDD is currently utilized in various communication systems, including wireless and/or cellular communication systems, e.g. LTE and LTE- A.

In connection with an asymmetric UL-DL resource allocation in TDD, seven different semi-statically configured UL-DL configurations are currently specified. The resource allocations, which may be realized by these specified UL-DL configurations, provide between 40% and 90% of DL subframes, i.e. DL capacity. A currently proposed mechanism for adapting UL/DL allocations is based on a system information change procedure. However, such semi- static resource allocation may not match the instantaneous traffic situation, leading to inefficient resource utilization, especially in cells with a small number of users where the traffic situation changes more frequently.

For this reason, a flexible (or dynamic) TDD configuration would be expected to be beneficial for achieving more efficient resource utilization in TDD.

However, no such flexible (or dynamic) TDD configuration has been proposed or specified so far. Rather, such flexible (or dynamic) TDD configuration would lead to various problems due to the thus introduced flexibility in resource allocation .

Figure 1 shows schematic diagrams illustrating problems in terms of flexibility in the context of conventional TDD UL-DL configurations. In Figure 1, a TDD configuration under consideration is assumed to have ten subframes (SF), wherein any one of the subframes represents a downlink (DL) subframe denoted by D, an uplink (UL) subframe denoted by U or a special subframe denoted by S. In connection with Figure 1, a full flexibility in TDD UL-DL configurations is assumed, i.e. it is allowed that any UL (DL) subframe could be changed to a DL (UL) subframe, respectively.

As shown under a) in Figure 1, a problematic issue in terms of flexibility in the context of conventional TDD UL-DL configurations resides in potential timing collisions at the terminal or user equipment (UE) side and the access node or base station (eNB) side. Such problem is caused by the fact that an UL subframe before another adjacent UL subframe should not be changed to a DL subframe because a guard period is needed between a DL subframe and an UL subframe. Namely, if SF#8 is changed to from an UL subframe to a DL subframe, then the receiving of SF#8 and the transmitting of SF#9 will be overlapped at UE side. This collision might for example be avoided via muting some OFDM symbols in SF#8 or SF#9 and using the thus muted OFDM symbols as a guard period. However, the efficiency would be greatly reduced by such approach.

Another problem in this regard is that, if a DL subframe is changed to an UL subframe, then CRS measurement of legacy UEs will be impacted, since there is actually no CRS after the changing. Rather, a legacy UE will still think that the current subframe is a DL subframe and will measure CRS in the predefined location . As shown under b) in Figure 1, a problematic issue in terms of flexibility in the context of conventional TDD UL-DL configurations relates to HARQ timing design for subframes at a changing boundary between two different TDD UL-DL configurations. Namely, assuming that a specified TDD Configuration 1 and a specified TDD configuration 0 are used in two subsequent periods, an UL subframe (e.g. a PUSCH) in SF#8 of the TDD Configuration 1 would have to have a DL feedback DL subframe in the TDD Configuration 0. In the illustrated example, the dotted line represents the original PHICH timing for the TDD configuration 1, but in the subsequent configuration period with the TDD configuration 0, SF#4 is an UL subframe. Accordingly, the PHICH timing needs to be changed somehow, e.g. to the solid line timing.

However, in such a case, there are no specified measures for mapping/timing the feedback in the subsequent TDD UL-DL configuration. A similar issue also happens for UL feedback for DL subframes and UL grant timing for UL subframes.

Another problem in this regard is that, if a HARQ timing depending on each specific TDD UL-DL configuration, which might be an approach for addressing the aforementioned problem, more HARQ timing would be needed to be implemented, which would increase the complexity of both UE and eNB implementation and operation. In view thereof, there exist problems in terms of providing flexibility for a TDD configuration as well as providing an appropriate timing control for a flexible TDD configuration.

Thus, there is a need to further improve timing control in flexible time division duplex configuration.

Summary

Various exemplary embodiments of the present invention aim at addressing at least part of the above issues and/or problems and drawbacks.

Various aspects of exemplary embodiments of the present invention are set out in the appended claims. According to an exemplary aspect of the present invention, there is provided a method comprising configuring a change from a first uplink- downlink configuration to a second uplink-downlink configuration out of a set of flexible uplink-downlink configurations of a frame structure for time division duplex communication on the basis of flexible subframe patterns, and controlling a timing of one or more boundary subframes in at least one of the first and second uplink-downlink configurations, said boundary subframes being those subframes in one of the first and second uplink- downlink configurations having an associated feedback or grant subframe in the other one of the first and second uplink-downlink configurations,

According to an exemplary aspect of the present invention, there is provided an apparatus comprising at least one processor, at least one memory including computer program code, and at least one interface configured for communication with at least another apparatus, the at least one processor, with the at least one memory and the computer program code, being configured to cause the apparatus to perform configuring a change from a first uplink-down!ink configuration to a second uplink- downlink configuration out of a set of flexible uplink-downlink configurations of a frame structure for time division duplex communication on the basis of flexible subframe patterns, and controlling a timing of one or more boundary subframes in at least one of the first and second uplink-downlink configurations, said boundary subframes being those subframes in one of the first and second uplink-downlink configurations having an associated feedback or grant subframe in the other one of the first and second uplink- downlink configurations.

According to an exemplary aspect of the present invention, there is provided a computer program product comprising computer program code which, when the program is run on a computer (such as a computer of an apparatus according to the aforementioned apparatus-related aspect of the present invention), is configured to execute the method according to the aforementioned method-related aspect of the present invention.

According to an exemplary aspect of the present invention, there is provided a computer-readable storage medium on which the computer program product according to the aforementioned aspect is embodied.

Any one of the aforementioned aspects of the present invention may be modified or developed in various ways, as will be evident from the following description of exemplary embodiments with reference to the accompanying drawings.

By way of exemplary embodiments of the present invention, there is provided timing control in flexible time division duplex configuration (in/for cellular communication systems). More specifically, by way of exemplary embodiments of the present invention, there are provided measures and mechanisms for timing control in flexible time division duplex configuration (in/for cellular communication systems). Thus, improvement is achieved by methods, apparatuses and computer program products enabling timing control in flexible time division duplex configuration (in/for cellular communication systems). Brief description of drawings

For a more complete understanding of exemplary embodiments of the present invention, reference is now made to the following description taken in connection with the accompanying drawings in which :

Figure 1 shows schematic diagrams illustrating problems in terms of flexibility in the context of conventional TDD UL-DL configurations,

Figure 2 shows a flowchart iilustrating a procedure according to exemplary embodiments of the present invention,

Figure 3 shows a signaling diagram illustrating a procedure according to exemplary embodiments of the present invention, Figure 4 shows a schematic diagram illustrating types of boundary subframes in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention,

Figure 5 shows a schematic diagram iliustrating an example of DL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention,

Figure 6 shows a schematic diagram illustrating an example of UL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention,

Figure 7 shows a schematic diagram iliustrating another example of UL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention, Figure 8 shows a schematic diagram illustrating another example of UL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention, Figure 9 shows a table illustrating a potential collision scenario in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention,

Figure 10 shows a schematic diagram illustrating a potential UL grant scenario in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention, and

Figure 11 shows a block diagram illustrating exemplary apparatuses according to exemplary embodiments of the present invention.

Description of exemplary embodiments

Exemplary aspects of the present invention will be described herein below. More specifically, exemplary aspects of the present are described hereinafter with reference to particular non-limiting examples and to what are presently considered to be conceivable embodiments of the present invention. A person skilled in the art will appreciate that the invention is by no means limited to these examples, and may be more broadly applied. It is to be noted that the following exemplary description mainly refers to specifications being used as non-limiting examples for certain exemplary network configurations and deployments. In particular, for the applicability of thus described exemplary aspects and embodiments, LTE- (including LTE- Advanced-) related cellular communication networks are used as non- limiting examples. As such, the description of exemplary aspects and embodiments given herein specifically refers to terminology which is directly related thereto. Such terminology is only used in the context of the presented non-limiting examples, and does naturally not limit the invention in any way. Rather, any other communication systems, network configurations or system deployments, etc. may also be utilized as long as compliant with the features described herein.

Hereinafter, various embodiments and implementations of the present invention and its aspects or embodiments are described using several alternatives. It is generally noted that, according to certain needs and constraints, all of the described alternatives may be provided alone or in any conceivable combination (also including combinations of individual features of the various alternatives).

According to exemplary embodiments of the present invention, in general terms, there are provided mechanisms, measures and means for timing control in flexible time division duplex communication (in/for cellular communication systems).

As described hereinafter, exemplary embodiments of the present invention are generally applicable to any cellular communication system utilizing TDD, for example LTE/LTE-A-based communication systems. Accordingly, exemplary embodiments of the present invention are considered to be specifically applicable for example for LTE Release 11 onwards, including e.g . layered heterogeneous network deployments, deployments involving different carriers deployed in the same frequency band (such as in the context of carrier aggregation), and the like. Basically, exemplary embodiments of the present invention are applicable both in an isolated cell scenario (without co-channel interference) and a multi-cell scenario (with co-channel interference). Due to the more fluctuating traffic in the isolated cell scenario, exemplary embodiments of the present invention could provide for even more gain in such isolated cell scenario.

In the following, exemplary embodiments of the present invention are described with reference to methods, procedures and functions, as well as with reference to structural arrangements and configurations. For the purpose of explaining exemplary embodiments of the present invention, the seven different semi-statically configured UL-DL configurations, which are specified in the context of LTE TDD systems for realizing an asymmetric resource allocation (in 3GPP TS 36.211 VIO.0.0), are taken as a basis.

In Table 1 below, these specified UL-DL configurations are shown, wherein D indicates a DL subframe, U indicates an UL subframe, and S indicates a special subframe (which denotation is also used in the drawings) .

Hereinafter, the TDD configuration changing period is assumed to be 10ms, i.e. each subframe corresponds to a time of 1ms.

Table 1

Figure 2 shows a flowchart illustrating a procedure according to exemplary embodiments of the present invention.

As shown in Figure 2, a corresponding procedure according to exemplary embodiments of the present invention comprises an operation of configuring (210) a change from a first (old) UL-DL configuration to a second (new) UL- DL configuration out of a set of flexible UL-DL configurations of a frame structure for TDD communication on the basis of flexible subframe patterns, and an operation of controlling (220) a timing of one or more boundary subframes in at least one of the first (old) and second (new) UL-DL configurations, said boundary subframes being those subframes in one of the first (old) and second (new) UL-DL configurations having an associated feedback or grant subframe in the other one of the first (old) and second (new) UL-DL configurations. As shown in Figure 2, the operation of timing control according to exemplary embodiments of the present invention comprises specifying a timing to be set for a boundary subframe being subjected to timing control and setting the specified timing for the boundary subframe being subjected to timing control. According to exemplary embodiments of the present invention, the timing control (for individual ones of boundary subframes) may be carried out based on a (real-time or on-line) determination or a look-up of the timing to be set or a combination thereof. That is, the timing to be set may be determined (for the boundary subframes to be timing- controlled) depending on a type of subframe being subject to the timing control based on at least one of respective properties of the first (oid) and second (new) UL-DL configurations and timings thereof, or the timing to be set (for the boundary subframes to be timing-controlled) may be looked up in a predefined !ook-up table (which is produced and stored in advance) depending on a type of subframe being subject to the timing control, or the timing to be set may be determined, as outlined above, for one of the boundary subframes to be timing-controlled and looked-up, as outlined above, for the other ones of the boundary subframes to be timing-controlled.

Figure 3 shows a signaling diagram illustrating a procedure according to exemplary embodiments of the present invention.

As shown in Figure 3, the aforementioned procedure according to exemplary embodiments of the present invention is operable at both the eNB (i.e. access node or base station) side and the UE (i.e. terminal or user equipment) side. When being executed at the eNB side, the configuration operation in the corresponding procedure comprises establishing (the two relevant UL-DL configurations and) a change there-between and transmitting the established change receiving (and the two relevant UL-DL configurations) to the UE side, before locally executing the timing control operation based thereon. When being executed at the eNB side, the configuration operation in the corresponding procedure comprises receiving (the two relevant UL-DL configurations and) a change there-between from the eIMB side and setting up the received change (and the two relevant UL- DL configurations), before locally executing the timing control operation based thereon.

Accordingly, a flexible TDD configuration established at the network side may be dynamically indicated to and used at the terminal side. Next, details regarding the configuration operation according to exemplary embodiments of the present invention are explained.

Generally, according to exemplary embodiments of the present invention, flexible UL-DL configurations of a frame structure for flexible TDD communication may be configured on the basis of flexible subframe patterns according to the following rules.

Flexible subframe patterns according to exemplary embodiments of the present invention are based on TDD configurations broadcasted in SIB1.

Firstly, it is defined that only UL subframes of any specified UL-DL configuration could be set as flexible subframes, i.e. only UL subframes determined by a specified TDD configuration can be dynamically changed between DL subframes and UL subframes, respectively.

This rule is effective in terms of backward compatibility. This is because, when an UL subframe is changed to a DL subframe in a cell, the impact to legacy UEs could be avoided by scheduling restriction to avoid a new transmission, e.g. by "always ACK" scheme to avoid non-adaptive retransmission, and by adjusting configuration parameters to avoid configuring SRS/SR/CQI on these flexible subframes. Then, legacy UEs could also be operated on these bands with flexible TDD configuration.

Secondly, it is defined that no new TDD configuration is introduced in addition to the currently specified TDD configurations, i.e. no matter how DL/UL subframes are changed, the resulting TDD configuration after change is still one of the existing seven TDD configurations.

This rule is effective in terms of avoiding the need for a new design of HARQ timings and new process definitions for a potentially new (i.e. currently unspecified) TDD configuration before or after the change, thus reducing complexity.

In view of the above, flexible subframe patterns according to exemplary embodiments of the present invention comprise subframe patterns of a predefined number of (i.e. the seven) specified UL-DL configurations, in which at least one specified UL subframe is flexibly modifiable (changeable) to represent an UL subframe or a DL subframe, while an accordingly modified (changed) subframe pattern still represents a subframe pattern of one of the predefined number of specified UL-DL configurations.

Accordingly, the flexible subframe patterns according to exemplary embodiments of the present invention result in a restricted flexibility of UL- DL configurations of frame structure for TDD communication, i.e. in a restricted flexibility of TDD communication.

As a result of a flexible subframe configuration on the basis of the aforementioned rules, the flexible subframe patterns for each TDD configuration broadcasted in SIB1 are defined as shown in Table 2 below wherein D indicates a DL subframe, U indicates an UL subframe, S indicates a special subframe, and F indicates a flexible subframe (which could be configured as an UL subframe or a DL subframe).

Table 2

In view of the TDD configuration as shown in Table 2, the TDD Configuration 0 could for example be modified in that SF#3, SF#4, SF#8 and SF#9 are configured as UL subframes so as to represent the specified TDD Configuration 0, or in that SF#3 and SF#8 are configured as UL subframes while SF#4 and SF#9 are configured as DL subframes so as to represent the specified TDD Configuration 1, or in that SF#3, SF#4, SF#8 and SF#9 are configured as DL subframes so as to represent the specified TDD Configuration 2, or in that SF#3, SF#4 and SF#8 are configured as UL subframes while SF#9 is configured as DL subframes so as to represent the specified TDD Configuration 6.

Since, according to the above rules, the flexibility is restricted in existing TDD configurations and also only UL subframes could be set as flexible subframes, the possibility of flexible TDD configurations is also restricted. Accordingly, there results a total of 18 changing possibilities between the specified TDD configurations, which are listed in Table 3 below.

Table 3

Next, details regarding the timing control operation according to exemplary embodiments of the present invention are explained.

Generally, according to exemplary embodiments of the present invention, timings of certain boundary subframes may be controlled on the basis of the TDD configurations of restricted flexibility as defined above according to the following rules. Thereby, it may be ensured that any potential misunderstanding of timings between eNB and UE is avoided in the context of a TDD configuration change.

Accordingly, new timing rules and/or tables based thereon are defined for boundary subframes, wherein the boundary subframes are those subframes in one of the first (old) and second (new) UL-DL configurations having an associated feedback or grant subframe in the other one of the first (old) and second (new) UL-DL configurations, i.e. those subframes with associated subframes spanning over the changing boundary between the (old) and second (new) UL-DL configurations.

Herein, a changing boundary is defined as the boundary between two different TDD configurations during flexible subframe change. The TDD configuration before this boundary, i.e. the first TDD configuration, is referred to as the old TDD configuration, and the TDD configuration after this boundary, i.e. the second TDD configuration, is referred to as new the TDD configuration. In respective drawings, the changing boundary is indicated by a vertical dashed line between SF#9 of the old TDD configuration and SF#0 of the new TDD configuration.

Herein, those DL/UL subframes in the old TDD configuration, whose UL/DL feedbacks (according to the old timing) are located in the new TDD configuration, as well as those UL subframes in the new TDD configuration, whose UL grants (according to the old timing) are located in the old TDD configuration, are referred to as boundary subframes. Figure 4 shows a schematic diagram illustrating types of boundary subframes in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention.

In Figure 4, an example is assumed, in which the specified TDD Configuration 1 is changed to the specified TDD configuration 0. In this example, subframes #5, #6, #7, #8, and#9 are changing boundary subframes in the old TDD configuration, while subframes #2 and #3 are changing boundary subframes in the new TDD configuration.

Specifically, the subframes #5, #6 and #9 in the old TDD configuration are DL/S subframes with the associated UL feedback subframes #2 and #3 in the new TDD configuration, as indicated by dotted blocks and arrows, the subframes #7 and #8 in the old TDD configuration are UL subframes with the associated DL feedback subframes #1 and #4 in the new TDD configuration, as indicated by solid blocks and arrows, and the subframes #2 and #3 in the new TDD configuration are UL subframes with the associated UL grant subframes #5 and #6 in the old TDD configuration, as indicated by chain-dotted blocks and arrows.

The subsequently explained rules of timing control according to exemplary embodiments of the present invention may generally be applied in a separate or combined manner. While typically one of the rules will be applied at a time, it is feasible to combine two or more rules in any conceivable manner, e.g. for subsequent changing boundaries, for different subframes at a single changing boundary, or the like. The rule/rules to be applied as well as, if applicable, a way for their application may be selected/ decided at the network side (e.g. the eNB). That is, the eNB may select/ decide the rule/rules and its/their manner of application and indicate this election/decision to the UEs in its coverage area e.g. by a dedicate signaling such as RRC signaling so as to semi-statically configure the rule/rules and its/their manner of application for timing. A first basic rule of timing control according to exemplary embodiments of the present invention relates to a TDD configuration dependent (HARQ) timing design for boundary subframes. This rule may comprise at least one of setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the first uplink-downlink configuration, when a number of uplink subframes in the second uplink-downlink configuration is greater than a number of uplink subframes in the first uplink-downlink configuration, and setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the second uplink-downlink configuration, when a number of uplink subframes in the second uplink- downlink configuration is not greater than a number of uplink subframes in the first uplink-downlink configuration.

This rule may also comprise at least one of setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the first uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is greater than a number of downlink subframes in the first uplink-downlink configuration, and setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the second uplink-downlink configuration, when a number of downfink subframes in the second uplink-downlink configuration is not greater than a number of downlink subframes in the first uplink- downlink configuration.

Accordingly, for DL HARQ timing (uplink feedback timing) of boundary subframes, the HARQ timing of the old TDD configuration may be used for one or more boundary subframes, if the uplink subframes number of the new TDD configuration is greater than that of the old TDD configuration, and otherwise the HARQ timing of the new TDD configuration may be used for one or more boundary subframes. Further, for UL HARQ timing (downlink feedback timing and uplink grant timing) of boundary subframes, the HARQ timing of the old TDD configuration may be used for one or more boundary subframes, if the downlink subframes number of the new TDD configuration is greater than that of the old TDD configuration, and otherwise the HARQ timing of the new TDD configuration may be used for one or more boundary subframes,

Figure 5 shows a schematic diagram illustrating an example of DL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention. The illustrated example is based on the first basic rule of timing control according to exemplary embodiments of the present invention.

In the illustrated example for DL HARQ timing of Figure 5, the old TDD configuration is the specified TDD configuration 1 and the new TDD configuration is the specified TDD configuration 0, i.e. changing pattern #1 is applied. Accordingly, subframes #5, #6 and #9 in the old TDD configuration are DL boundary subframes. Since the UL subframe number in the new TDD configuration (i.e. 6) is greater than that in the old TDD configuration (i.e. 4), the old TDD configuration timing (i.e. the HARQ timing of the specified TDD configuration 1) is used for the UL feedback timing of subframes #5, #6 and #9 in the old TDD configuration.

Figure 6 shows a schematic diagram illustrating an example of UL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention. The illustrated example is based on the first basic rule of timing control according to exemplary embodiments of the present invention.

In the illustrated example for UL HARQ timing of Figure 6, the old TDD configuration is the specified TDD configuration 1 and the new TDD configuration is the specified TDD configuration 0, i.e. changing pattern #1 is applied. Accordingly, subframes #7 and #8 in the old TDD configuration and subframes #2 and #3 in the new TDD configuration are UL boundary subframes. Since the DL subframe number in the new TDD configuration (i.e. 2) is smaller than that in the old TDD configuration (i.e. 4), the new TDD configuration timing (i.e. the HARQ timing of the specified TDD configuration 0) is used for the DL feedback timing of subframes #7 and #8 in the old TDD configuration and the UL grant timing of subframes #2 and #3 in the new TDD configuration. A second basic rule of timing control according to exemplary embodiments of the present invention relates to a TDD configuration dependent (HARQ) timing design for boundary subframes, and may be regarded as a complementary rule to the aforementioned first basic rule. This rule may comprise at least one of setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the second uplink-downlink configuration, when a number of uplink subframes in the second uplink-downlink configuration is greater than a number of uplink subframes in the first uplink-downlink configuration, and when a timing according to the second uplink-downlink configuration is usable and exhibits less delay than a timing according to the first uplink- downlink configuration, and setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the first uplink- downlink configuration, when a number of uplink subframes in the second uplink-downlink configuration is not greater than a number of uplink subframes in the first uplink-downlink configuration, and when a timing according to the first uplink-downlink configuration is usable and exhibits less delay than a timing according to the second uplink-downlink configuration .

This rule may also comprise at least one of setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the second uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is greater than a number of downlink subframes in the first uplink-downlink configuration, and when a timing according to the second uplink-downlink configuration is usable and exhibits less delay than a timing according to the first uplink-downlink configuration, and setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the first uplink-downlink configuration, when a number of downlink subframes in the second uplink- downiink configuration is not greater than a number of downlink subframes in the first uplink-downlink configuration, and when a timing according to the first uplink-downlink configuration is usable and exhibits less delay than a timing according to the second uplink-downlink configuration.

Accordingly, after the old/new TDD configuration timing is determined (or although the old/new TDD configuration timing would be determined) according to the aforementioned first basic rule, if another timing (i.e. the new/old TDD configuration timing) could also be used and has lower delay, i.e. a corresponding DL/UL subframe exists for the other timing and occurs prior to (i.e. in an earlier subframe position than) a respective DL/UL subframe of the previously determined timing, the other timing may be used instead of the previously determined timing for one or more boundary subframes.

Figure 7 shows a schematic diagram illustrating another example of UL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention. The illustrated example is based on the second basic rule of timing control according to exemplary embodiments of the present invention.

In the illustrated example for UL HARQ timing of Figure 7, the old TDD configuration is the specified TDD configuration 6 and the new TDD configuration is the specified TDD configuration 1, i.e. changing pattern #9 is applied. Accordingly, subframe #8 in the old TDD configuration is an UL boundary subframe. According to the first basic rule for UL HARQ timing, the DL feedback timing for subframe #8 in the old TDD configuration would use the new TDD configuration timing. However, since subframe #4 in the new TDD configuration still exists and the new TDD configuration timing could also be used and has lower delay, then according to the complementary rule for UL HARQ timing the DL feedback timing for subframe #8 will use the new TDD configuration timing. That is, although the DL subframe number in the new TDD configuration (i.e. 4) is greater than that in the old TDD configuration (i.e. 3), the new TDD configuration timing (i.e. the HARQ timing of the specified TDD configuration 1) is used for the DL feedback timing of subframe #8 in the old TDD configuration, as the old TDD configuration timing (i.e. the HARQ timing of the specified TDD configuration 6) would provide for a delayed DL feedback timing (in subframe #5 instead of subframe #4 in the new TDD configuration) . A third basic rule of timing control according to exemplary embodiments of the present invention relates to a new (HARQ) timing design for boundary subframes.

This rule may comprise setting a timing of an uplink feedback subframe associated with a downlink boundary subframe to the first available uplink feedback subframe after a predetermined time period in the other one of the first and second uplink-downlink configurations.

This rule may also comprise setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe to the first available downlink feedback subframe after a predetermined time period in the other one of the first and second uplink- downlink configurations. Accordingly, the HARQ timing for one or more boundary subframes, i.e. the UL feedback timing, DL feedback timing and UL grant timing for boundary subframe, may map to the first available (i.e. the nearest) DL/UL subframe after a predetermined time period such as e.g. 4ms. Figure 8 shows a schematic diagram illustrating another example of UL subframe timing control in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention. The illustrated example is based on the third basic rule of timing control according to exemplary embodiments of the present invention. In the illustrated example for UL HARQ timing of Figure 8, the old TDD configuration is the specified TDD configuration 0 and the new TDD configuration is the specified TDD configuration 2, i.e. changing pattern #2 is applied . For subframe #9 in the old TDD configuration, the DL feedback timing of the old TDD configuration timing (i.e. the HARQ timing of the specified TDD configuration 0) would be 6 ms, but upon application of the third basic rule, the DL feedback timing for subframe #9 in the old TDD configuration is 4ms. That is, the DL subframe firstly appearing in the new TDD configuration after the predetermined time period is used as a DL feedback subframe for the UL subframe #9 in the oid TDD configuration.

As mentioned above, the operation of timing control according to exemplary embodiments of the present invention, i.e. the timing control according to any one of the aforementioned basic rules according to exemplary embodiments of the present invention, could equally be carried out by way of actual (real-time or on-line) determination operations (including e.g. identifying and/or comparing respective properties (e.g. the number of DL/UL subframes) of the old and new TDD configurations and timings thereof) or by way of actual (reai-time or on-line) look-up of/in a predefined table, which is pre-stored in a respective memory, storage or database, wherein such table is predefined accordingly (i.e. on the basis of properties (e.g . the number of DL/UL subframes) of the old and new TDD configurations and timings thereof). In case of a look-up based timing control according to exemplary embodiments of the present invention, a corresponding look-up could be based on a corresponding table depending on a type of subframe being subject to timing control. There may be three corresponding tables for DL HARQ (UL feedback) timing, UL HARQ (DL feedback) timing and UL HARQ (UL grant) timing for each one of the aforementioned basic rules.

Such approach could be efficient in view of the limited number of changing possibilities between TDD configurations according to the restricted flexibility, as evident from Table 3 above, particularly in connection with the first and second basic rules. In the following, exemplary tables for the first and second basic rules are given, in which the respective timings to be set are set out by changing pattern indices according to Table 3 above.

Table 4 below relates to DL HARQ (UL feedback) timing according to the first basic rule.

Table 4

Table 5 below relates to UL HARQ (DL feedback) timing according to the first basic rule.

Table 5 It is noted that the symbol * indicates that there is no boundary subframe re!ated to UL HARQ (DL feedback) in the respective changing pattern, thus no UL HARQ (DL feedback) timing being defined. Table 6 below relates to UL HARQ (UL grant) timing according to the first basic rule.

Table 6

It is noted that the symbol ** indicates, when there are two timings defined for a specific subframe, the first value is for UL grant with UL index=0, and the second value is for UL grant with UL index=l. Table 7 below relates to DL HARQ (UL feedback) timing according to the second basic rule.

Table 7

Table 8 below relates to UL HARQ (DL feedback) timing according to the second basic rule.

Table 8

It is noted that the symbol * indicates that there is no boundary subframe related to UL HARQ (DL feedback) in the respective changing pattern, thus no UL HARQ (DL feedback) timing being defined.

Table 9 below relates to UL HARQ (UL grant) timing according to the second basic rule.

Table 9 It is noted that the symbol ** indicates, when there are two timings defined for a specific subframe, the first value is for UL grant with UL index=0, and the second value is for UL grant with UL index=l.

According to exemplary embodiments of the present invention, the following operability or functionality may also be provided.

On the one hand, exemplary embodiments of the present invention provide for operability or functionality for resolving a possible PHICH collision, which might arise when applying the aforementioned first basic rule for timing control.

Figure 9 shows a table illustrating a potential collision scenario in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention.

As evident from Figure 9, a possible PHICH collision problem might occur between the specified TDD configuration 0 and the specified TDD configuration 6. Such possible PHICH collision problem is indicated by the encircled subframe timings in the respective TDD configurations.

Namely, for the specified TDD configuration 0, when applying the aforementioned first basic rule for timing control, PHICH for PUSCH in SF#3 and SF#4 are not in the same group, i.e. exhibit different timings. Therefore, a distinction by way of the parameter I_PHICH is to be applied. The parameter I_PHICH is defined to be 1 for the specified TDD configuration 0 with PUSCH transmission in subframe #4 or #9, and to be 0 otherwise When the specified TDD configuration 6 changes to the specified TDD configuration 0, i.e. changing pattern #7 is applied, PHICH for SF#4 of new (up-to-date) UEs with the TDD configuration 6 and PHICH for SF#3 of legacy UEs with the TDD configuration 0 will be mapped to the same subframe, namely SF#0 of the new TDD configuration . That is, they will be mapped to the same PHICH group and thus have a collision problem, since IPHI_CH for the TDD configuration 6 is always 0.

According to exemplary embodiments of the present invention, such possible PHICH collision could be resolved by always following the I_PHIC_H value for the specified TDD configuration 0 at the relevant changing boundary, or in that the elMB does not schedule the same UL PRB index, or in that the eNB using a proper cyclic shift of DMRS allocates the PHICH to the different group, for example.

On the other hand, exemplary embodiments of the present invention provide for operability or functionality for resolving possible uplink grant infeasibility, i.e. the issue that some uplink subframe could not be scheduled .

Figure 10 shows a schematic diagram illustrating a potential UL grant scenario in the context of TDD UL-DL configurations according to exemplary embodiments of the present invention. In particular, the illustrated example relates to the issue that some uplink subframe could not be scheduled unless a new uplink grant is designed.

As shown in Figure 10, when the specified TDD configuration 0 is changed to the specified TDD configuration 6, i.e. changing pattern #6 is applied, without designing an extra new UL grant timing or without adding an UL index in SF#0 in the new TDD configuration, SF#4 in the new TDD configuration could not be scheduled.

According to exemplary embodiments of the present invention, such possible uplink grant infeasibility could be resolved by re-explaining (re- define or modify) an UL index for the specified TDD configuration 0, More specifically, when an UL grant in subframe #6 in the specified TDD configuration 0 is scheduling subframes #2 and #3 in the new TDD configuration, an UL index could indicate subframes #2 and #3 in the new TDD configuration. While as another example, if an UL grant in subframe #6 in the specified TDD configuration 0 is scheduling subframes #3 and #4 in the new TDD configuration, an UL index could indicate subframes #3 and #4 in the new TDD configuration.

According to exempiary embodiments of the present invention, such possible uplink grant infeasibility could also be resolved by adding an UL index into the first subframe, i.e. SF#0, in the specified TDD configuration 6. Then, the subframe #0 in the specified TDD configuration 6 could schedule both subframes #4 and #7 at the same time. Namely, an UL index in subframe #0 in the specified TDD configuration 6 could indicate subframes #4 and #7 therein.

The above-described procedures and functions may be implemented by respective functional elements, processors, or the like, as described below. While in the foregoing exemplary embodiments of the present invention are described mainly with reference to methods, procedures and functions, corresponding exemplary embodiments of the present invention also cover respective apparatuses, network nodes and systems, including both software and/or hardware thereof.

Respective exemplary embodiments of the present invention are described below referring to Figure 11, while for the sake of brevity reference is made to the detailed description of respective corresponding methods and operations according to Figures 2 to 8.

In Figure 11 below, which is noted to represent a simplified block diagram, the solid line blocks are basically configured to perform respective operations as described above. The entirety of solid line blocks are basically configured to perform the methods and operations as described above, respectively. With respect to Figure 11, it is to be noted that the individual blocks are meant to illustrate respective functional blocks implementing a respective function, process or procedure, respectively. Such functional blocks are implementation-independent, i.e. may be implemented by means of any kind of hardware or software, respectively. The arrows and lines interconnecting individual blocks are meant to illustrate an operational coupling there-between, which may be a physical and/or logical coupling, which on the one hand is implementation-independent (e.g. wired or wireless) and on the other hand may also comprise an arbitrary number of intermediary functional entities not shown. The direction of arrow is meant to illustrate the direction in which certain operations are performed and/or the direction in which certain data is transferred.

Further, in Figure 11, only those functional blocks are illustrated, which relate to any one of the above-described methods, procedures and functions. A skilled person will acknowledge the presence of any other conventional functional blocks required for an operation of respective structural arrangements, such as e.g. a power supply, a central processing unit, respective memories or the like. Among others, memories are provided for storing programs or program instructions for controlling the individual functional entities to operate as described herein.

Figure 11 shows a block diagram illustrating exemplary apparatuses according to exemplary embodiments of the present invention. In view of the above, the thus described apparatuses 10 and 20 are suitable for use in practicing the exemplary embodiments of the present invention, as described herein. The thus described apparatus 10 may represent a (part of a) terminal such as a mobile station MS or user equipment UE, as described above, and may be configured to perform a procedure and/or exhibit a functionality as described in conjunction with any one of Figures 2 to 8. The thus described apparatus 20 may represent a (part of a) network entity being operable on a cellular system, i.e. a base station BS, a base transceiver station BTS or an access node, such as for example a NodeB, an eNB, or the like, and may be configured to perform a procedure and/or exhibit a functionality as described in conjunction with any one of Figures 2 to 8. Referring to Figure 3 above, the apparatus 10 may take the role or act as the UE, and the apparatus 20 may take the role or act as the eNB.

As shown in Figure 11, according to exemplary embodiments of the present invention, a terminal 10 comprises a processor 11, a memory 12, and an interface 13, which are connected by a bus 14 or the like, and a network entity 20 comprises a processor 21, a memory 22, and an interface 23, which are connected by a bus 24 or the like. The terminal 10 and the network entity 20 may communicate with each other through a link or connection 30.

The memory 12 and/or 22 may store respective programs assumed to include program instructions or computer program code that, when executed by the processor 11 and/or 21, enables the respective electronic device or apparatus to operate in accordance with the exemplary embodiments of the present invention. Further, the memory 12 and/or 22 may store one or more of the aforementioned look-up tables, respectively.

The processor 11/21 and/or the interface 13/23 may also include a modem or the like to facilitate communication over a (hardwire or wireless) link, respectively. The interface 13/23 may include a suitable transceiver coupled to one or more antennas or communication means for (hardwire or wireless) communications with the linked or connected device(s), respectively. The interface 13/23 is generally configured to communicate with at least one other apparatus, i.e. the interface thereof.

In general terms, the respective devices/apparatuses (and/or parts thereof) may represent means for performing respective operations and/or exhibiting respective functionalities, and/or the respective devices (and/or parts thereof) may have functions for performing respective operations and/or exhibiting respective functionalities.

When in the subsequent description it is stated that the processor (or some other means) is configured to perform some function, this is to be construed to be equivalent to a description stating that at least one processor, potentially in cooperation with computer program code stored in the memory of the respective apparatus, is configured to cause the apparatus to perform at least the thus mentioned function. Also, such function is to be construed to be equivalently implementable by specifically configured means for performing the respective function (i.e. the expression "processor configured to [cause the apparatus to] perform xxx-ing" is construed to be equivalent to an expression such as "means for xxx-ing"). According to exemplary embodiments of the present invention, an apparatus representing the terminal 10 or the network entity 20 comprises at Ieast one processor 11/21, at Ieast one memory 12/22 including computer program code, and at Ieast one interface 13/23 configured for communication with at least another apparatus. The at Ieast one processor 11/21 is configured (to cause the apparatus 10/20) to perform : configuring a change from a first (old) UL-DL configuration to a second (new) UL-DL configuration out of a set of flexible UL-DL configurations of a frame structure for TDD communication on the basis of flexible subframe patterns, and controlling a timing of one or more boundary subframes in at Ieast one of the first (old) and second (new) UL-DL configurations, said boundary subframes being those subframes in one of the first (old) and second (new) UL-DL configurations having an associated feedback or grant subframe in the other one of the first (old) and second (new) UL-DL configurations.

According to exemplary embodiments of the present invention, the flexible subframe patterns may comprise subframe patterns of a predefined number of specified UL-DL configurations, in which at Ieast one specified UL subframe is flexibly modifiable to represent an UL subframe or a DL subframe, while an accordingly modified subframe pattern still represents a subframe pattern of one of the predefined number of specified UL-DL configurations. According to exemplary embodiments of the present invention, the processor 11/21 may be further configured (to cause the apparatus 10/20) to perform setting a timing of an uplink feedback subframe associated with a downlink boundary subframe and/or setting a timing of a downlink feedback subframe associated with an uplink boundary subframe and/or setting a timing of an uplink grant subframe associated with an uplink boundary subframe, as explained in connection with any one of Figures 4 to 8 above.

According to exemplary embodiments of the present invention, the processor 11/21 may be further configured (to cause the apparatus 10/20) to perform determining the timing to be set depending on a type of subframe being subject to said timing control based on at least one of respective properties of the first and second uplink-downlink configurations and timings thereof, and/or looking up the timing to be set in a predefined look-up table, which is stored in the at least one memory, depending on a type of subframe being subject to said timing control.

According to exemplarily embodiments of the present invention, the processor 11/21, the memory 12/22 and the interface 13/23 can be implemented as individual modules, chipsets or the like, or one or more of them can be implemented as a common module, chipset or the like, respectively.

According to exemplarily embodiments of the present invention, a system may comprise any conceivable combination of the thus depicted devices/apparatuses and other network elements, which are configured to cooperate as described above.

In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device.

Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention. Such software may be software code independent and can be specified using any known or future developed programming language, such as e.g. Java, C++, C, and Assembler, as long as the functionality defined by the method steps is preserved. Such hardware may be hardware type independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Fie!d-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components. A device/apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device/apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor. A device may be regarded as a device/apparatus or as an assembly of more than one device/apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

Apparatuses and/or means or parts thereof can be implemented as individual devices, but this does not exclude that they may be implemented in a distributed fashion throughout the system, as iong as the functionality of the device is preserved. Such and similar principles are to be considered as known to a skilled person.

Software in the sense of the present description comprises software code as such comprising code means or portions or a computer program or a computer program product for performing the respective functions, as well as software (or a computer program or a computer program product) embodied on a tangible medium such as a computer-readable (storage) medium having stored thereon a respective data structure or code means/portions or embodied in a signal or in a chip, potentially during processing thereof.

The present invention also covers any conceivable combination of method steps and operations described above, and any conceivable combination of nodes, apparatuses, modules or elements described above, as long as the above-described concepts of methodology and structural arrangement are applicable.

In view of the above, the present invention and/or exemplary embodiments thereof provide measures for timing control in flexible time division duplex configuration. Such measures may exemplarily comprise configuring a change from a first uplink-downlink configuration to a second uplink- downlink configuration out of a set of flexible uplink-downlink configurations of a frame structure for time division duplex communication on the basis of flexible subframe patterns, and controlling a timing of one or more boundary subframes in at least one of the first and second uplink-downlink configurations, said boundary subframes being those subframes in one of the first and second uplink-downlink configurations having an associated feedback or grant subframe in the other one of the first and second uplink- downlink configurations.

Stated in other words, referring to exemplary embodiments of the present invention, there are provided measures for flexible TDD configurations (i.e. TDD configuration changes) and a timing control/design especially at a changing boundary of a TDD configuration change. Also, there are provided measures for a timing control/design which adapts to dynamic/flexible TDD configurations (i.e. TDD configuration changes). Thereby, measures for a flexible TDD communication (with asymmetric UL-DL resource allocations) are provided.

Even though the present invention and/or exemplary embodiments are described above with reference to the examples according to the accompanying drawings, it is to be understood that they are not restricted thereto. Rather, it is apparent to those skilled in the art that the present invention can be modified in many ways without departing from the scope of the inventive idea as disclosed herein. List of acronyms and abbreviations

ARQ Automatic Repeat Request

CQI Channel Quality Indicator

CRS Cell-specific Reference Signal

DL Downlink

DMRS Demodulation Reference Signal

eNB evolved Node B (E-UTRAN base station)

E-UTRAN Evolved Universal Terrestrial Radio Access Network HARQ Hybrid Automatic Repeat Request

LTE Long Term Evolution

LTE-A Long Term Evolution Advanced

OFDM Orthogonal Frequency Division Multiplexing

PDCCH Physical Downlink Control Channel

PCFICH Physical Control Format Indicator Channel

PHICH Physical Hybrid ARQ Indicator Channel

PRB Physical Resource Block

PUSCH Physical Uplink Shared Channel

RNC Radio Network Controller

RRC Radio Resource Control

SF Sub-Frame

SIB System Information Block

SR Scheduling Request

SRS Sounding Reference Signal

TDD Time Division Duplex

UE User Equipment

UL Uplink

Claims

What is claimed is:

1. A method comprising

configuring a change from a first uplink-downlink configuration to a second uplink-downlink configuration out of a set of flexible uplink-downlink configurations of a frame structure for time division duplex communication on the basis of flexible subframe patterns, and

controlling a timing of one or more boundary subframes in at least one of the first and second uplink-downlink configurations, said boundary subframes being those subframes in one of the first and second uplink- downlink configurations having an associated feedback or grant subframe in the other one of the first and second uplink-downiink configurations.

2. The method according to claim 1, wherein

the flexible subframe patterns comprise subframe patterns of a predefined number of specified uplink-downlink configurations, in which at least one specified uplink subframe is flexibly modifiable to represent an uplink subframe or a downlink subframe, while an accordingly modified subframe pattern still represents a subframe pattern of one of the predefined number of specified uplink-downlink configurations.

3. The method according to claim 1 or 2, wherein said timing control comprises at least one of

setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the first uplink-downlink configuration, when a number of uplink subframes in the second uplink- downlink configuration is greater than a number of uplink subframes in the first upiink-downlink configuration, and

setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the second uplink-downlink configuration, when a number of uplink subframes in the second uplink- downlink configuration is not greater than a number of uplink subframes in the first uplink-downlink configuration.

4. The method according to claim 1 or 2 or 3, wherein said timing control comprises at least one of

setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the first uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is greater than a number of downlink subframes in the first uplink-downlink configuration, and

setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the second uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is not greater than a number of downlink subframes in the first uplink-downlink configuration.

5. The method according to claim 1 or 2, wherein said timing control comprises at least one of

setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the second uplink-downlink configuration, when a number of uplink subframes in the second uplink- downlink configuration is greater than a number of uplink subframes in the first uplink-downlink configuration, and when a timing according to the second uplink-downlink configuration is usable and exhibits less delay than a timing according to the first uplink-downlink configuration, and

setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the first uplink-downlink configuration, when a number of uplink subframes in the second uplink- downlink configuration is not greater than a number of uplink subframes in the first uplink-downlink configuration, and when a timing according to the first uplink-downlink configuration is usable and exhibits less delay than a timing according to the second uplink-downlink configuration.

6. The method according to claim 1 or 2 or 5, wherein said timing control comprises at least one of

setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the second uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is greater than a number of downlink subframes in the first uplink-downlink configuration, and when a timing according to the second uplink-downlink configuration is usable and exhibits less delay than a timing according to the first uplink- downlink configuration, and

setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the first uplink-downlink configuration, when a number of downlink subframes in the second upiink-downlink configuration is not greater than a number of downlink subframes in the first uplink-downiink configuration, and when a timing according to the first uplink-downlink configuration is usable and exhibits less delay than a timing according to the second uplink-downlink configuration .

7. The method according to claim 1 or 2, wherein said timing control comprises

setting a timing of an uplink feedback subframe associated with a downlink boundary subframe to the first available uplink feedback subframe after a predetermined time period in the other one of the first and second uplink-downlink configurations.

8, The method according to claim 1 or 2 or 7, wherein said timing control comprises

setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe to the first available downlink feedback subframe after a predetermined time period in the other one of the first and second uplink-downlink configurations.

9. The method according to any one of claims 3 to 8, wherein said timing control is carried out by means of at least one of

determining the timing to be set depending on a type of subframe being subject to said timing control based on at least one of respective properties of the first and second uplink-downlink configurations and timings thereof, and looking up the timing to be set in a predefined look-up table depending on a type of subframe being subject to said timing control.

10. The method according to any one of claims 1 to 9, wherein at least one of the following applies :

the method is operable at or by a terminal or user equipment or an access node or base station of a cellular communication system,

the timing of one or more boundary subframes comprises a hybrid automatic repeat request timing, and

the time division duplex communication is to be carried out in a cellular communication system in accordance with a LTE-based specification .

11. The method according to claim 10, wherein

when the method is operable at or by an access node or base station of a cellular communication system, said configuring comprises establishing a change between the first and second uplink-downlink configurations and transmitting the established change to a terminal or user equipment of the cellular communication system.

12. The method according to claim 10, wherein

when the method is operable at or by a terminal or user equipment of a cellular communication system, said configuring comprises receiving a change between the first and second uplink-downlink configurations from an access node or base station of the cellular communication system and setting up the received change.

13. An apparatus comprising

at least one processor,

at least one memory including computer program code, and

at least one interface configured for communication with at least another apparatus,

the at least one processor, with the at least one memory and the computer program code, being configured to cause the apparatus to perform : configuring a change from a first uplink-downlink configuration to a second uplink-downlink configuration out of a set of flexible uplink-downlink configurations of a frame structure for time division duplex communication on the basis of flexible subframe patterns, and

controlling a timing of one or more boundary subframes in at least one of the first and second uplink-downlink configurations, said boundary subframes being those subframes in one of the first and second uplink- downiink configurations having an associated feedback or grant subframe in the other one of the first and second uplink-downlink configurations.

14. The apparatus according to claim 13, wherein

the flexible subframe patterns comprise subframe patterns of a predefined number of specified uplink-downiink configurations, in which at least one specified uplink subframe is flexibly modifiable to represent an uplink subframe or a downlink subframe, while an accordingly modified subframe pattern still represents a subframe pattern of one of the predefined number of specified uplink-downlink configurations,

15. The apparatus according to claim 13 or 14, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform at least one of:

setting a timing of an uplink feedback subframe associated with a downlink boundary subframe according to the first uplink-downlink configuration, when a number of uplink subframes in the second uplink- downlink configuration is greater than a number of uplink subframes in the first uplink-downlink configuration, and

16. The apparatus according to claim 13 or 14 or 15, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform at least one of: setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the first uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is greater than a number of downlink subframes in the first uplink-downlink configuration, and

17. The apparatus according to claim 13 or 14, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform at least one of:

18. The apparatus according to claim 13 or 14 or 17, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform at least one of: setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the second uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is greater than a number of downlink subframes in the first uplink-downlink configuration, and when a timing according to the second uplink-downlink configuration is usable and exhibits less delay than a timing according to the first uplink- downlink configuration, and

setting a timing of a downlink feedback subframe or an uplink grant subframe associated with an uplink boundary subframe according to the first uplink-downlink configuration, when a number of downlink subframes in the second uplink-downlink configuration is not greater than a number of downlink subframes in the first uplink-downlink configuration, and when a timing according to the first upiink-downiink configuration is usable and exhibits less delay than a timing according to the second uplink-downlink configuration.

19. The apparatus according to claim 13 or 14, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform:

20. The apparatus according to claim 13 or 14 or 19, the at least one processor, with the at least one memory and the computer program code, being further configured to cause the apparatus to perform :

21. The apparatus according to any one of claims 15 to 20, the at least one processor, with the at least one memory and the computer program code, being further configured to carry out said timing control by causing the apparatus to perform at least one of: determining the timing to be set depending on a type of subframe being subject to said timing control based on at least one of respective properties of the first and second uplink-downlink configurations and timings thereof, and

looking up the timing to be set in a predefined look-up table, which is stored in the at least one memory, depending on a type of subframe being subject to said timing control.

22. The apparatus according to any one of claims 13 to 21, wherein at least one of the following applies:

the apparatus is operable as or at a terminal or user equipment or an access node or base station of a cellular communication system,

the time division duplex communication is to be carried out in a cellular communication system in accordance with a LTE-based specification.

23. The apparatus according to claim 22, wherein

when the apparatus is operable as or at an access node or base station of a cellular communication system, the at least one processor, with the at least one memory and the computer program code, is further configured to cause the apparatus to perform establishing a change between the first and second uplink-downlink configurations and transmitting the established change to a terminal or user equipment of the cellular communication system.

24. The apparatus according to claim 22, wherein

when the apparatus is operable as or at a terminal or user equipment of a cellular communication system, the at least one processor, with the at least one memory and the computer program code, is further configured to cause the apparatus to perform receiving a change between the first and second uplink-downlink configurations from an access node or base station of the cellular communication system and setting up the received change.

25. A computer program product comprising computer-executable computer program code which, when the program is run on a computer, is configured to cause the computer to carry out the method according to any one of claims 1 to 12.

26. The computer program product according to claim 25, embodied as a computer-readable storage medium.