WO2017134336A1

WO2017134336A1 - Short transmission time interval backwards compatible arrangement

Info

Publication number: WO2017134336A1
Application number: PCT/FI2017/050016
Authority: WO
Inventors: Esa Tiirola; Klaus Hugl; Kari Juhani Hooli; Timo Lunttila
Original assignee: Nokia Technologies Oy
Priority date: 2016-02-04
Filing date: 2017-01-17
Publication date: 2017-08-10

Abstract

Various communication systems may benefit from backwards compatibility with legacy communication systems. For example, certain wireless communication systems may benefit from a short transmission time interval arrangement for backwards compatible time division long term evolution, supporting coexistence with legacy signals. A method can include dividing a subframe of a first configuration into at least two parts for transmitting and/or receiving data according to a type of a second configuration. The method can also include determining the type of the second configuration to be used contingent upon whether uplink traffic is configured in the subframe for devices operating according to the first configuration. The method can further include transmitting and/or receiving data in at least one of the at least two parts of the subframe according to the determined type of second configuration.

Description

TITLE:

Short Transmission Time Interval Backwards Compatible Arrangement

CROSS-REFERENCE TO RELATED APPLICATION:

[0001] This application is related to and claims the benefit and priority of U.S. Provisional Patent Application No. 62/291,239, filed February 4, 2016, the entirely of which is hereby incorporated herein by reference.

BACKGROUND:

Field:

[0002] Various communication systems may benefit from backwards compatibility with legacy communication systems. For example, certain wireless communication systems may benefit from a short transmission time interval arrangement for backwards compatible time division long term evolution, supporting coexistence with legacy signals.

Description of the Related Art:

[0003] Long term evolution (LTE)-Advanced Pro may be part of 3GPP LTE Rel-13/14. There is a Rel-13 Study Item (SI) "Study on Latency reduction techniques," described in third generation partnership project (3GPP) report (RP) 150465. The entirely of RP- 150465 is hereby incorporated herein by reference.

[0004] As mentioned in RP- 150465, the study area includes resource efficiency, including air interface capacity, battery lifetime, and control channel resources. Both frequency division duplex (FDD) and time division duplex (TDD) modes are considered in the study item.

[0005] One aspect for consideration is transmission time interval (TTI) shortening and reduced processing times. It is considered that there TTI lengths may be between 0.5ms and one orthogonal frequency division multiplexed (OFDM) symbol. The TTI length may take into account impact on reference signals and physical layer control signaling.

[0006] Figure 1 provides a table summarizing latency performance in legacy TD-LTE (LTE TDD). Figure 1 is drawn from 3GPP technical report (TR) TR 36.912, the entirety of which is hereby incorporated herein by reference. [0007] User plane latency may be defined in many ways. One definition commonly used in 3GPP studies refers to the one-way transit time between a service data unit (SDU) packet being available at the Internet protocol (IP) layer in the user terminal/base station and the availability of this packet as a protocol data unit (PDU) at the IP layer in the base station/user terminal. User plane packet delay can include delay introduced by associated protocols and control signaling, assuming the user terminal is in the active state. International mobile telecommunication (IMT)- Advanced systems may need to achieve a user plane latency of less than 10 ms in unloaded conditions for small IP packets for both downlink and uplink. In the meanwhile, 5G requirements are also discussed in 3GPP and user plane latency of less than 1 ms is a common requirement in those discussion. That can be seen as one motivation behind Rel-13/14 latency studies aiming at to reduce gap between LTE- Advanced Pro and 5G requirements.

[0008] As shown in Figure 1, latency can include many components, such as evolved Node B (eNB) and user equipment (UE) processing time, TTI duration and hybrid automatic repeat request (HARQ) re-transmission time. In principle, some latency components shown in Table 1 can be scaled linearly according to TTI length similarly in both FDD and TDD duplex mode, for example UE and eNB processing. On the other hand, in time division duplex (TDD) mode, there can be an extra latency component called frame alignment which can be caused by the fact that UE/eNB may need wait before reception/transmission of certain signal because the cell is currently serving in "the wrong link direction". For this reason, latency performance in TD LTE can vary according to TDD uplink (UL) - downlink (DL) configuration and the subframe index. When shortening the TTI length, limited switching point periodicity may become a bottleneck for considerable latency reduction, when compared to FDD-based latency reduction. This is due to the fact related latency components (such as frame alignment time and HARQ Re-transmission) do not scale linearly with TTI length.

[0009] Figure 2 illustrates time division duplex uplink/downlink configurations. For ease of reference, these seven configurations can be considered to be "legacy" configurations by comparison to certain embodiments of the present invention. As can be seen in Figure 2, some of the configurations contain more uplink subframes and some contain more downlink subframes. For example, configurations 0, 6, and 1 are the most uplink heavy, while configurations 5 and 2 are the least uplink heavy.

[0010] Figure 3 illustrates a table of HARQ acknowledgement (HARQ-ACK) timing in legacy-LTE. When considering a latency component caused by HARQ-ACK feedback, shown as HARQ Re-transmission delay in Figure 1, it can be helpful to understand the concept of a downlink association set, as illustrated in the table in Figure 3. The DL association set can define for each UL subframe n the timing and the order in which the HARQ feedback for each DL/Special subframe is transmitted.

[0011] For example, with UL-DL configuration #0, in UL subframe #n=2 the physical uplink control channel (PUCCH) may carry the HARQ-ACK for DL subframe which was 6 subframes earlier. The HARQ delay in this case is 6 subframes. Similarly, for UL-DL configuration 1 , in UL subframe #2 the HARQ-ACK may be signaled for DL subframes that were 7 and/or 6 subframes earlier, and the PUCCH resources are filled in this specific order (first HARQ-ACK for DL subframe n-7, then for DL subframe n- 6). In other words, the table in Figure 3 illustrates the HARQ-ACK feedback delay in milliseconds associated with each DL subframe. As can be seen the delay ranges from 4 ms up to 13 ms.

SUMMARY:

[0012] According to a first embodiment, a method can include dividing a subframe of a first configuration into at least two parts for transmitting and/or receiving data according to a type of a second configuration. The method can also include determining the type of the second configuration to be used contingent upon whether uplink traffic is configured in the subframe for devices operating according to the first configuration. The method can further include transmitting and/or receiving data in at least one of the at least two parts of the subframe according to the determined type of second configuration.

[0013] In a variant, the subframe can include one of an uplink subframe, a special subframe, or a downlink subframe.

[0014] In a variant, the first configuration can include a legacy configuration and the second configuration can include a short transmission time interval configuration.

[0015] In a variant, the method can include aligning a downlink pilot time slot length to be approximately one slot in length.

[0016] In a variant, a length of a short transmission time interval can vary according to a type of the subframe in the first configuration and/or an immediately following subframe in the first configuration.

[0017] In a variant, the method can include aligning a length of a short transmission time interval with a length of a downlink pilot time slot.

[0018] In a variant, a length of the short transmission time interval can be one slot minus a switching gap configured to permit switching of transmission direction.

[0019] In a variant, the uplink traffic can include at least one of a hybrid automatic repeat request acknowledgement or a physical uplink shared channel or a sounding reference signal or a physical uplink control channel.

[0020] In a variant, a hybrid automatic repeat request acknowledgment feedback for a short transmission time interval shared channel is transmitted or received only on a second part of the at least two parts.

[0021] According to a second embodiment, a method can include determining, for a subframe of a first configuration, a type of a second configuration, wherein the subframe of the first configuration is divided into at least two parts for transmitting and/or receiving data according to the type of the second configuration. The method can also include transmitting and/or receiving data in at least one of the at least two parts of the subframe according to the determined type of second configuration.

[0022] The second embodiment can also include any of the variants of the first embodiment and can be configured to operate in conjunction with the first embodiment.

[0023] According to third and fourth embodiments, an apparatus can include means for performing the method according to the first and second embodiments respectively, in any of their variants.

[0024] According to fifth and sixth embodiments, an apparatus can include at least one processor and at least one memory and computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to perform the method according to the first and second embodiments respectively, in any of their variants.

[0025] According to seventh and eighth embodiments, a computer program product may encode instructions for performing a process including the method according to the first and second embodiments respectively, in any of their variants.

[0026] According to ninth and tenth embodiments, a non-transitory computer readable medium may encode instructions that, when executed in hardware, perform a process including the method according to the first and second embodiments respectively, in any of their variants.

[0027] According to eleventh and twelfth embodiments, a system may include at least one apparatus according to the third or fifth embodiments in communication with at least one apparatus according to the fourth or sixth embodiments, respectively in any of their variants.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0028] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0029] Figure 1 provides a table summarizing latency performance in legacy TD-LTE.

[0030] Figure 2 illustrates time division duplex uplink/downlink configurations.

[0031] Figure 3 illustrates a table of HARQ acknowledgement (HARQ-ACK) timing in legacy-LTE.

[0032] Figure 4 illustrates a new uplink/downlink configuration for short transmission time interval use, according to certain embodiments.

[0033] Figure 5A illustrates subframe structure types 1 and 2, according to certain embodiments.

[0034] Figure 5B illustrates two categories of type 3 subframes, according to certain embodiments.

[0035] Figure 6 illustrates short transmission time interval configuration from TD-LTE, according to certain embodiments.

[0036] Figure 7 illustrates DL HARQ timing for a low latency configuration, according to certain embodiments. [0037] Figure 8 illustrates PUSCH timing for a low latency configuration, according to certain embodiments.

[0038] Figure 9 illustrates a method according to certain embodiments.

[0039] Figure 10 illustrates a system according to certain embodiments.

DETAILED DESCRIPTION:

[0040] Both FDD and TDD duplex modes may benefit from configurations to avoid or reduce latency. Initially, latency performance in TDD mode may be worse compared to FDD, due to the fact that in TDD both data and control signals may suffer from additional frame alignment time caused by the duplexing, as can be seen from Figure 1, discussed above. Furthermore, in TDD mode air interface latency may vary significantly according to TDD DL/UL configuration as well as the subframe index within the radio frame.

[0041] Additionally, backwards compatibility may be a specific issue to consider in TDD mode, because it may not be possible to change HARQ/scheduling timing for legacy UEs. Furthermore at least one legacy TDD DL/UL configuration may need to be applicable for legacy UEs served on such a carrier. The same applies to radio resource management (RRM) measurements: due to legacy burden, DL subframes cannot conventionally be used as UL subframes. For that reason, the room for latency reduction in a backwards compatible TDD cell conventionally may appear much smaller than in FDD.

[0042] The achievable latency reduction gains may depend on the TDD DL/UL configuration of the legacy 1ms TTI operation. For example, in UL/DL configuration #5, which is DL heavy, the possibilities for major latency reduction may conventionally be limited since there is just one UL subframe of 1ms length in the radio frame. Moreover, legacy DL subframes (or at least symbols containing Cell Specific Reference signals) cannot conventionally be used as UL in a backward compatible manner.

[0043] Certain embodiments may address latency reduction by adopting shorter HARQ- feedback, adopting shorter scheduling latencies, and/or changing the TTI length for operation of LTE TDD. Moreover, certain embodiments may facilitate or provide smooth coexistence between legacy TDD and short TTI (STTI) operation. Thus, certain embodiments may facilitate major latency reduction in a backwards compatible TD- LTE system. Additionally, certain embodiments may support short TTI in a reasonable manner, on top of a backwards compatible TD-LTE system.

[0044] Figure 4 illustrates a new uplink/downlink configuration for short transmission time interval use, according to certain embodiments. For example, the configuration shown in Figure 4 (labelled as "STTI") may be used by UEs configured to apply STTI. The illustrated TDD configuration has inbuilt support of smooth coexistence with legacy UEs following SIB1 defined UL/DL configuration.

[0045] In certain embodiments, STTI length is defined to be about one slot in the configuration. The length can be different from one slot by, for example, an amount of time required for switching from downlink to uplink. This slightly shorter length option is shown, for example, in the gap between D6 and D7 in both places in the STTI row of Figure 4.

[0046] Each, or at least one, UL subframe of the legacy configuration can be defined to be an additional special subframe for UEs following STTI configuration. Thus, for example, in certain embodiments the legacy subframes configured for downlink may be configured for downlink usage also by UEs following STTI configuration. On the other hand, at least one uplink subframe can be, in essence, reserved for special usage by UEs following STTI configuration (for example, subframes 3 and 8 in Figure 4).

[0047] Furthermore, both legacy special subframes (S) and additional special subframes (additional S) can be defined to have the following functionalities for STTI UEs.

[0048] The first slot of additional S can be either DL with STTI (Type 1), or UL with STTI (Type 2). Figure 5A illustrates subframe structure types 1 and 2, according to certain embodiments. The first slot of legacy S may always be DL for STTI and Downlink Pilot Time Slot (DwPTS) for legacy. This is shown in subframes 1 and 6 in Figure 4.

[0049] In certain embodiments, the second slot of both legacy S and additional S may always be UL with STTI. This is similarly shown in subframes 1 and 6 in Figure 4.

[0050] The UL with STTI, type 2, can be capable of carrying both physical uplink shared channel (PUSCH) and physical uplink control channel (PUCCH).

[0051] In certain embodiments, STTI PDSCH HA Q-ACK timing for STTI operation can be defined solely based on a second slot of special subframe(s) independent of whether type 1 or type 2 additional S is used. Consequently, HARQ-ACK feedback for STTI PDSCH may be transmitted only on the second slot of special subframes. The second slot can be a common denominator of type 1 and type 2 additional S and can therefore simplify the HARQ-Ack procedure. This use of the second slot may also ensure reasonable PDSCH HARQ-ACK feedback times.

[0052] In certain embodiments, a guard period (GP) length is set to be 1 symbol for UEs following STTI configuration. This approach is illustrated in Figure 4.

[0053] The above-described features may optionally be complemented by further features. For example, if certain subframe is defined to be a special subframe, either legacy S or additional S, in the STTI configuration and the subframe does not contain PDSCH HARQ-ACK at all, it may also be possible to support a third type of subframe structure on those subframes. There can be two categories of type 3 subframes.

[0054] Figure 5B illustrates two categories of type 3 subframes, according to certain embodiments. As shown in Figure 5B, type 3a can contain a switching gap for DL2UL switching when the next subframe/slot is in UL phase. Otherwise, for example when the next subframe/slot is in DL phase, type 3b may be applied.

[0055] DL subframes of legacy configuration can be used as downlink subframes also for UEs following STTI configuration. For example, DL with STTI can be used in both the first and second slot, as shown in subframes 0 and 5 in Figure 4. UEs with STTI can apply PDSCH with 7 symbols, 6 symbols, or even 14 symbols, as will be discussed below.

[0056] In certain embodiments, legacy UEs can be configured to apply an UL heavy configuration in the cell, such as configuration 0 or 1 or 6, as illustrated in Figure 2. DwPTS length can be set to be 6 symbols, for example. Accordingly, legacy UEs can be configured also with 2 symbol uplink pilot time slot (UpPTS) and 6 symbol GP.

[0057] UEs configured to follow STTI configuration may be configured to apply power control (PC) / channel state information (CSI) principles defined for enhanced interference mitigation and traffic adaptation (eEVITA). Such configuration can include defining CSLPC sets in slot level instead of subframe level, defining multiple slot/subframe sets for CSI measurement/reporting, and/or defining multiple slot/subframe sets for UL power control. Related enhancements to X2 signaling may also be needed and applied.

[0058] Depending on the eNB scheduling decision for legacy UEs, UL subframe may or may not contain PUCCH and/or PUSCH for legacy UEs. In order to facilitate smooth coexistence between legacy UEs and STTI UEs, for UL legacy subframes which may contain legacy PUCCH/PUSCH, certain embodiments may employ a dynamic switching between the type 1 / type 2 subframe types and also type 3 if configured. This dynamic switching may take place when operating in the STTI configuration. Dynamic switching between typel / type2 may relate only to additional S. In certain embodiments, the dynamic switching may more particularly apply only to the first slot of additional S. In the absence of legacy UL signals in an UL subframe, dynamic switching between type 1 and type 2 may be used also for dynamic traffic adaptation for UEs configured to apply STTI configuration. In case legacy UL signals are present in an UL subframe, type 2 can be selected for STTI UEs.

[0059] For example, considering subframe #4 in Figure 4, depending on the PDSCH scheduling for legacy UEs on subframe #0 (see Figure 3), and PUSCH scheduling, subframe #4 may or may not contain PDSCH HARQ-ACK and/or PUSCH for legacy UEs. Thus, the following options may be available for an eNB. If legacy HARQ-ACK and legacy PUSCH are not present in subframe #4, than the eNB can select type 1 or type 2, or even type 3 if configured. Alternatively, if legacy HARQ-ACK is present or legacy PUSCH is scheduled in subframe #4, then the eNB can select type 2

[0060] Selection between type 1 and type 2 may be done based on eNB scheduling decision. For example, the selection can be based on the presence of legacy signal and/or based on instantaneous traffic needs.

[0061] Indication of the 'additional S' subframe type, such as type 1, type 2, or type 3 if configured, for sTTI UEs may or may not include explicit signaling in common/dedicated DCI. If additional S subframe type is not explicitly indicated, the UE may derive the subframe type implicitly.

[0062] From a UE operation point of view, determining the subframe type implicitly can be quite straightforward. If UE has valid STTI PUSCH scheduling grant for the first slot of the special subframe, the UE does not perform PDCCH blind detection there. Instead, the UE can just transmit PUSCH according to scheduling grant.

[0063] Otherwise, if there is no UL scheduling grant detected, the UE can assume type 1 or type 3 for the first slot of an additional S subframe and can perform (E)PDCCH blind detection accordingly. If type 3 subframe is configured, the UE can perform (E)PDCCH blind detection also for the second slot.

[0064] With asynchronous HA Q in both UL and DL, this kind of dynamic selection of STTI type between type 1 and type 2 on the first part of additional S can be done without any impact to the HARQ-ACK timing.

[0065] In the following, UL/DL configuration options for STTI are illustrated in more detailed examples.

[0066] In an example, UL-DL configuration #0 can be selected as the configuration for legacy UEs. Other legacy UL-DL configurations can be considered as well, such as UL- DL configuration #1 and configuration #6. However, the room for practical latency reduction may be smaller in configurations that have fewer UL slots. This configuration #0 can correspond to SIB1 indicated UL/DL configuration.

[0067] Subframes [0, 1, 5, 6] may be used to serve legacy UEs in the DL direction. For that reason, subframes [0, 5] can be considered as regular, fixed DL subframes without any flexibility. This no flexibility restriction can apply at least to legacy signals which are always on, such as PSS/SSS, CRS, PDCCH, PCFICH, PHICH. Additionally, subframes [1, 6] can be special subframes with a fixed special subframe configuration (configuration defined by SIB1). Again a no flexibility restriction can apply at least to legacy DwPTS signals which are always on (such as PSS/SSS, CRS, PDCCH, PCFICH, PHICH) on special subframes. Flexibility on subframes [1, 6] can relate to the higher layer configured special subframe configuration with a predetermined split among DwPTS, GP and UpPTS.

[0068] Subframes [2, 4, 7, 9] may contain PUCCH for legacy UEs (see Figure 3) and PUSCH for legacy UEs. Thus, subframes [2, 4, 7, 9] can always be used as type 2 additional S subframes for low latency UEs, with UL STTI in both the first and second slot.

[0069] If subframes [2, 4, 7, 9] are free from legacy UL signals, it may be possible to apply those subframes also as type 1 low-latency special subframes containing both UL and DL.

[0070] The presence of PUCCH (or UCI in general) and PUSCH in these subframes may be up to an eNB scheduler decision. The scheduling decision may depend on, for example PDSCH scheduling (creating HARQ-ACK according to Figure 3). The scheduling decision may also depend on periodic CSI configuration and possible carrier aggregation configuration, indicating that PUCCH may locate in another carrier, called primary cell.

[0071] In this example, subframes [3, 8] may only contain PUSCH for legacy UEs. Thus, subframes [3, 8] can always be used as type 2 additional S subframes for low latency UEs, with UL STTI in both the first and the second slot. If those subframes are free from legacy PUSCH signals, it may be possible to apply those subframes as type 1 low-latency special subframes containing both UL and DL. The presence of legacy PUSCH in subframes [3, 8] can be is up to eNB scheduler decision. If subframes 3 and 8 are not applied for conveying PDSCH HARQ-ACK for STTI UEs, it is also possible to apply type 3 subframe(s) there, if configured.

[0072] Figure 6 illustrates short transmission time interval configuration from TD-LTE, according to certain embodiments. As shown in Figure 6, TDD UL-DL configuration #0 can be taken as the starting point, as the number of UL subframes is largest among the seven configurations illustrated in Figure 2. Other options may be configurations #1 and #6, in view of them being UL heavy configurations.

[0073] If there are UEs in the cell that support Rel-12 eEVITA feature, it may be beneficial to switch eEVITA feature ON for those UEs. This can reduce the need for scheduler restrictions due to PUCCH and provide more opportunities for STTI usage.

[0074] More particularly, Figure 6 shows flexible subframes for eEVITA, in the case where UL/DL configuration #5 is selected as DL reference configuration.

[0075] In the example shown in Figure 6, special subframe handling can be applied for legacy UEs. DwPTS length can be set to be 6 symbols, UpPTS length to 2 symbols and a guard period can be set to be six symbols, and special UpPTS handling can be employed.

[0076] For example, in a first case, legacy UEs may not be scheduled for UpPTS at all. Consequently, UpPTS may not be used at all. In a second case, the system may support multiplexing of legacy UpPTS with UL STTI of different length. This can be done by means of FDM (and/or TDM), for example.

[0077] Subframe configuration for low latency UEs can specially address subframes [1, (2), 3, 4, 6-9], which are either UL subframes or special subframes according to SIBl configuration. These subframes can facilitate short-TTMow latency operation having an opportunity for bi-directional communication within the subframe.

[0078] A specific special subframe configuration can facilitate bi-directional communication, as will be discussed below. Other splits between DL STTI, GP and UL STTI can be considered as well. DwPTS length of 6 symbols is supported by current TD-LTE. Thus, DL STTI length can be set to be 6 symbols. Furthermore, GP length of 1 symbol may be sufficient for an anticipated operation scenario for TD-LTE with short TTI. Thus, one symbol may be allocated to GP. Furthermore, UL STTI symbol can be set to be 7 symbols. UL STTI contains an opportunity for conveying both PUCCH and PUSCH. DL STTI and UL STTI can be considered as short TTI, approximately 0.5 ms in length.

[0079] As mentioned above, different symbol split for DL STTI, GP and UL STTI can also be supported. For example, another possible split option is [6DL, 2GP, 6UL]. Other splits are also permitted. Generally speaking, STTI may involve definition of new special subframe formats with different split for DwPTS (DL sTTI), GP and UpPTS (UL sTTI).

[0080] Different example configuration options for short TTI are illustrated in Figure 6. Subframes 0 and 5, which may be fixed DL subframes, can be considered either as 1ms subframes or -0.5 ms subframes for low latency UEs. Option 1 in Figure 6 considers subframes 0 and 5 as 1ms DL subframes. Option 2 considers those same subframes as approximately 0.5 ms DL subframes of 7 symbols. For legacy UEs these subframes can be used as fixed DL subframes

[0081] Subframes 1 and 6, which are special subframes of UL/DL Configuration #0, can be used as special subframes for legacy UEs and low latency UEs. The discussion above explains how, for example, type 1 additional S subframe can be applied for low latency UEs in such cases.

[0082] Subframes 2 and 7 can be considered additional special subframes for STTI UEs, which may or may not contain legacy UL. They can be considered either as 1ms subframes or -0.5 ms subframes for low latency UEs.

[0083] Option 1 in Figure 6 considers these subframes as 1ms UL subframes. Option 2, by contrast, considers these subframes as each two 0.5 ms UL subframes, namely type 2 additional special subframe. When legacy signal is not present, it is possible to use these subframes as type 1 additional special subframes. In addition to exemplary subframe lengths shown in Figure 6, eNB may be able to dynamically select also legacy format for UEs configured to apply STTI configuration. In these cases, STTI transmission/reception may be seen as a legacy signal from short TTI usage point of view.

[0084] Subframes 3, 4, 8, and 9 can be considered additional special subframes for low latency UEs, which do not contain legacy UL. These subframes can contain Type 1 additional special subframe with the split DL6+GP+UL7, as mentioned above. Legacy UE UL multiplexing may not be possible in these subframes. Based on scheduler decision, these subframes may also be used as type 2 or type 3 subframes, if configured.

[0085] Legacy PUCCH may or may not be present in the carrier supporting short TTI. For example, if the current TDD carrier is used only as secondary cell, then PUCCH may not be present there. Nevertheless, Figure 6 assumes that legacy PUSCH/PUCCH is present in subframes 2 and 7.

[0086] Certain embodiments can be implemented by defining a new latency optimized TDD UL/DL configuration. This low latency configuration may contain predefined values for any or each of the following: DL STTI length, UL STTI length, GP length, special subframes including legacy S and additional S, PDSCH HARQ timing, and PUSCH scheduling timing. Low latency PUSCH can apply asynchronous HARQ. Thus, there may be no need for a separate PHICH channel.

[0087] Legacy UEs and low latency UEs may be multiplexed using FDM within a subframe, in the case when link direction is the same for both legacy UE and low latency UE(s). Otherwise, eNB may apply scheduler restrictions, in effect providing TDM between two modes. In order to improve coexistence, legacy mode can be used as a fallback solution for UEs configured to operate according to low latency mode. UE may monitor two set of C-RNTIs at the same time: one set according to legacy mode and another set according to low latency mode.

[0088] Figure 7 illustrates DL HARQ timing for a low latency configuration, according to certain embodiments. More particularly, Figure 7 provides an example of DL HA Q-Ack timing on top of a configuration as described above. In this example, minimum HARQ timing is set to be 1.5 ms. Thus, in certain embodiments, a specific HARQ/scheduling timing defined for short TTI scenario can be applied.

[0089] Figure 8 illustrates PUSCH timing for a low latency configuration, according to certain embodiments. More particularly, Figure 8 shows an example of PUSCH scheduling timing on top of a configuration as described above. Also in this example, the minimum scheduling timing can be set to be 1.5 ms. The upper part of the figure illustrates scheduling timing with type 1 subframes, while the lower part illustrates scheduling timing with type 2 subframes. PUSCH scheduling may involve multi-TTI scheduling, as well as scheduling with variable scheduling timing. Furthermore, the actual scheduling latency may depend on the subframe carrying the UL grant, as shown in Figure 8.

[0090] Figure 9 illustrates a method according to certain embodiments. As shown in Figure 9, a method can include, at 910, dividing a subframe of a first configuration into at least two parts for transmitting and/or receiving data according to a type of a second configuration. The first configuration can be a legacy configuration, such as any of the seven configurations shown in Figure 2. The second configuration can be a short transmission time interval configuration, such as the configuration illustrated in Figure 4. The short TTI configuration may be defined separately for each legacy configuration. The two parts can be of equal or unequal lengths. The subframe can be an uplink subframe, a special subframe, or a downlink subframe. The same process can be applied to multiple subframes of a configuration.

[0091] The method can also include, at 920, determining the type of the second configuration to be used contingent upon whether uplink traffic is configured in the subframe for devices operating according to the first configuration. For example, any of types 1, 2, 3a, or 3b may be used to divide the subframe, using, for example, the approach described above. The uplink traffic can be at least a hybrid automatic repeat request acknowledgement, a physical uplink control channel, a physical uplink shared channel, a sounding reference signal, a PRACH preamble, or any combination of those.

[0092] The method can also include, at 925, signaling the type of the second configuration to be used to a user equipment. The signaling can be explicit or implicit signaling, as mentioned above.

[0093] The method can further include, at 930, transmitting and/or receiving data in at least one of the at least two parts of the subframe according to the determined type of second configuration.

[0094] The method can include, at 915, aligning a downlink pilot time slot length to be approximately one slot in length. The method can also include, at 917, aligning a length of a short transmission time interval with a length of a downlink pilot time slot.

[0095] A length of a short transmission time interval can vary according to a type of the subframe in the first configuration or an immediately following subframe in the first configuration. In certain embodiments, a length of the short transmission time interval can be one slot minus a switching gap configured to permit switching of transmission direction. The switching gap length may be defined with the granularity of OFDMA/SC-FDMA symbol (including CP).

[0096] A hybrid automatic repeat request acknowledgment feedback for a short transmission time interval shared channel can be transmitted or received only on a second part of the at least two parts. For example, a hybrid automatic repeat request acknowledgment feedback for a short transmission time interval shared channel may be transmitted only on a second slot of special subframes.

[0097] The above features may be performed by a network element such as an evolved node B (eNB). The method may also include features that may be performed by a device such as a user equipment (UE).

[0098] For example, a method can include, at 940, determining, for a subframe of a first configuration, a type of a second configuration, wherein the subframe of the first configuration is divided into at least two parts for transmitting and/or receiving data according to the type of the second configuration. The division of the subframe into the two parts can be based on the criteria described above. [0099] The method can further include, at 950, transmitting and/or receiving data in at least one of the at least two parts of the subframe according to the determined type of second configuration.

[0100] Figure 10 illustrates a system according to certain embodiments of the invention. It should be understood that each block of the flowchart of Figure 9 may be implemented by various means or their combinations, such as hardware, software, firmware, one or more processors and/or circuitry. In one embodiment, a system may include several devices, such as, for example, network element 1010 and user equipment (UE) or user device 1020. The system may include more than one UE 1020 and more than one network element 1010, although only one of each is shown for the purposes of illustration. A network element can be an access point, a base station, an eNode B (eNB), or any other network element.

[0101] Each of these devices may include at least one processor or control unit or module, respectively indicated as 1014 and 1024. At least one memory may be provided in each device, and indicated as 1015 and 1025, respectively. The memory may include computer program instructions or computer code contained therein, for example for carrying out the embodiments described above. One or more transceiver 1016 and 1026 may be provided, and each device may also include an antenna, respectively illustrated as 1017 and 1027. Although only one antenna each is shown, many antennas and multiple antenna elements may be provided to each of the devices. Other configurations of these devices, for example, may be provided. For example, network element 1010 and UE 1020 may be additionally configured for wired communication, in addition to wireless communication, and in such a case antennas 1017 and 1027 may illustrate any form of communication hardware, without being limited to merely an antenna.

[0102] Transceivers 1016 and 1026 may each, independently, be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that may be configured both for transmission and reception. The transmitter and/or receiver (as far as radio parts are concerned) may also be implemented as a remote radio head which is not located in the device itself, but in a mast, for example. It should also be appreciated that according to the "liquid" or flexible radio concept, the operations and functionalities may be performed in different entities, such as nodes, hosts or servers, in a flexible manner. In other words, division of labor may vary case by case.

[0103] A user device or user equipment 1020 may be a mobile station (MS) such as a mobile phone or smart phone or multimedia device, a computer, such as a tablet, provided with wireless communication capabilities, personal data or digital assistant (PDA) provided with wireless communication capabilities, portable media player, digital camera, pocket video camera, navigation unit provided with wireless communication capabilities or any combinations thereof. The user device or user equipment 1020 may be a sensor or smart meter, or other device that may usually be configured for a single location.

[0104] In an exemplifying embodiment, an apparatus, such as a node or user device, may include means for carrying out embodiments described above in relation to Figure 9.

[0105] Processors 1014 and 1024 may be embodied by any computational or data processing device, such as a central processing unit (CPU), digital signal processor (DSP), application specific integrated circuit (ASIC), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), digitally enhanced circuits, or comparable device or a combination thereof. The processors may be implemented as a single controller, or a plurality of controllers or processors. Additionally, the processors may be implemented as a pool of processors in a local configuration, in a cloud configuration, or in a combination thereof.

[0106] For firmware or software, the implementation may include modules or units of at least one chip set (e.g., procedures, functions, and so on). Memories 1015 and 1025 may independently be any suitable storage device, such as a non-transitory computer-readable medium. A hard disk drive (HDD), random access memory (RAM), flash memory, or other suitable memory may be used. The memories may be combined on a single integrated circuit as the processor, or may be separate therefrom. Furthermore, the computer program instructions may be stored in the memory and which may be processed by the processors can be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language. The memory or data storage entity is typically internal but may also be external or a combination thereof, such as in the case when additional memory capacity is obtained from a service provider. The memory may be fixed or removable.

[0107] The memory and the computer program instructions may be configured, with the processor for the particular device, to cause a hardware apparatus such as network element 1010 and/or UE 1020, to perform any of the processes described above (see, for example, Figure 9). Therefore, in certain embodiments, a non- transitory computer-readable medium may be encoded with computer instructions or one or more computer program (such as added or updated software routine, applet or macro) that, when executed in hardware, may perform a process such as one of the processes described herein. Computer programs may be coded by a programming language, which may be a high-level programming language, such as objective-C, C, C++, C#, Java, etc., or a low-level programming language, such as a machine language, or assembler. Alternatively, certain embodiments of the invention may be performed entirely in hardware.

[0108] Furthermore, although Figure 10 illustrates a system including a network element 1010 and a UE 1020, embodiments of the invention may be applicable to other configurations, and configurations involving additional elements, as illustrated and discussed herein. For example, multiple user equipment devices and multiple network elements may be present, or other nodes providing similar functionality, such as nodes that combine the functionality of a user equipment and an access point, such as a relay node.

[0109] Certain embodiments may have various benefits and/or advantages. For example, certain embodiments may provide a clean solution for TDD latency reduction on top of legacy TDD. Moreover, certain embodiments may provide smooth coexistence between legacy UEs/STTI UEs. In certain embodiments, for example, STTI configuration can be optimized separately for each subframe.

[0110] Certain embodiments also have inbuilt support for dynamic traffic adaptation for STTI UEs. Flexible traffic adaptation can be achieved using, for example, dynamic selection of Typel/Type 2 (and Type 3 if configured) 'additional special' subframes.

[0111] Certain embodiments may get considerable latency reduction on top of legacy TD-LTE carrier, especially for scheduling and HA Q/timing. The achievable latency reduction may be advantageous, particularly taking into account that certain embodiments can support simultaneous LTE Rel-8 UEs on the same carrier.

[0112] System overhead due to new configuration can be minimized. This overhead may be up to 5 OFDMA symbols/radio frames due to UL/DL switching for Type 1 'additional special' subframes.

[0113] Furthermore, certain embodiments may permit the use of a TDD system having two different TDD switching periodicities (one for legacy and one for low latency UEs) in use in parallel.

[0114] Certain embodiments may have various characteristics. For example, certain embodiments may restrict the selection of the type (type 1, 2 or 3a/3B) so that when there is no legacy HARQ-ACK/PUSCH the eNB has all the options (if all are configured) but when there is legacy HARQ-ACK present or PUSCH scheduled, the eNB has to choose type 2. Such a forced selection of type 2 may ensure that only UL traffic is transmitted.

[0115] Thus, in certain embodiments a TDD configuration for STTI UEs can be provided in which STTI length is defined to be one slot. In the configuration, UL subframes free from legacy PUCCH can be used as additional special subframes. STTI can apply HARQ/scheduling timing as described above, and asynchronous HARQ in both UL/DL.

[0116] One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.

[0117] List of Abbreviations 0118] 3 GPP Third Generation Partnership Program

0119] ACK Acknowledgement

0120] C-RNTI Cell Radio Network Temporal Identifier

0121] CRS Common Reference Signal

0122] D7 DwPTS block with seven OFDMA symbols

0123] DL, D Downlink

0124] DwPTS Downlink Pilot Time Slot

0125] eIMTA Enhanced Interference Management and Traffic Adaptation (3GPP term to characterize WI, which defines dynamic TDD feature in LTE Rel-12. 0126] eNB Enhanced NodeB

0127] FDD Frequency Division Duplexing

0128] FDM Frequency Division Multiplexing

0129] FS2 Frame Structure 2

0130] GP Guard Period

0131] HARQ Hybrid Automatic Retransmission request

0132] LTE Long Term Evolution

0133] OFDM Orthogonal Frequency Division Multiplexing

0134] PCFICH Physical Control Format Indicator Channel

0135] PDSCH Physical Downlink Shared Channel

0136] PHICH Physical HARQ- ACK Indicator Channel

0137] PSS Primary Synchronization Sequence

0138] PUCCH Physical Uplink Control Channel

0139] RAN Radio Access Network

0140] Rel Release

0141] S Special Subframe

0142] SI Study Item

0143] SIB System Information Block

0144] SSS Secondary Synchronization Sequence

0145] TD Time Division

0146] TDD Time Division Duplexing [0147] TDM Time Division Multiplexing

[0148] TSG Technical Steering Group

[0149] TTI Transmission Time Interval

[0150] U7 UpPTS block with seven SC-FDMA symbols

[0151] UCI Uplink Control Information

[0152] UE User Equipment

[0153] UL, U Uplink

[0154] UpPTS Uplink Pilot Time Slot

[0155] WG Working Group

[0156] WI Work Item

Claims

WE CLAIM:

1. A method, comprising:

dividing a subframe of a first configuration into at least two parts for transmitting and/or receiving data according to a type of a second configuration;

determining the type of the second configuration to be used contingent upon whether uplink traffic is configured in the subframe for devices operating according to the first configuration; and

transmitting and/or receiving data in at least one of the at least two parts of the subframe according to the determined type of second configuration.

2. The method according to claim 1, wherein the subframe comprises one of an uplink subframe, a special subframe, or a downlink subframe.

3. The method according to claim 1 or claim 2, wherein the first configuration comprises a legacy configuration and the second configuration can include a short transmission time interval configuration.

4. The method according to any of claims 1 to 3, further comprising:

aligning a downlink pilot time slot length to be approximately one slot in length.

5. The method according to any of claims 1 to 4, wherein a length of a short transmission time interval varies according to a type of the subframe in the first configuration and/or an immediately following subframe in the first configuration.

6. The method according to any of claims 1 to 5, further comprising:

aligning a length of a short transmission time interval with a length of a downlink pilot time slot.

7. The method according to any of claims 1 to 6, wherein a length of the short transmission time interval comprises one slot minus a switching gap configured to permit switching of transmission direction.

8. The method according to any of claims 1 to 7, wherein the uplink traffic comprises at least one of a hybrid automatic repeat request acknowledgement or a physical uplink shared channel or a sounding reference signal or a physical uplink control channel.

9. The method according to any of claims 1 to 8, wherein a hybrid automatic repeat request acknowledgment feedback for a short transmission time interval shared channel is transmitted or received only on a second part of the at least two parts.

10. A method, comprising:

determining, for a subframe of a first configuration, a type of a second configuration, wherein the subframe of the first configuration is divided into at least two parts for transmitting and/or receiving data according to the type of the second configuration; and

11. The method according to claim 10, wherein the subframe comprises one of an uplink subframe, a special subframe, or a downlink subframe.

12. The method according to claim 10 or claim 11, wherein the first configuration comprises a legacy configuration and the second configuration can include a short transmission time interval configuration.

13. The method according to any of claims 10 to 12, further comprising:

14. The method according to any of claims 10 to 13, wherein a length of a short transmission time interval varies according to a type of the subframe in the first configuration and/or an immediately following subframe in the first configuration.

15. The method according to any of claims 10 to 14, further comprising:

16. The method according to any of claims 10 to 15, wherein a length of the short transmission time interval comprises one slot minus a switching gap configured to permit switching of transmission direction.

17. The method according to any of claims 10 to 16, wherein the uplink traffic comprises at least one of a hybrid automatic repeat request acknowledgement or a physical uplink shared channel or a sounding reference signal or a physical uplink control channel.

18. The method according to any of claims 10 to 17, wherein a hybrid automatic repeat request acknowledgment feedback for a short transmission time interval shared channel is transmitted or received only on a second part of the at least two parts.

19. An apparatus, comprising:

means for performing the method according to any of claims 1-9 or 10-18.

20. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform a process, the process comprising the method according to any of claims 1-9 or 10-18.

21. A computer program product encoding instructions for performing a process, the process comprising the method according to any of claims 1-9 or 10-18.

22. A non-transitory computer readable medium encoded with instructions that, when executed in hardware, perform a process, the process comprising the method according to any of claims 1-9 or 10-18.