Patent Description:
Various communication systems may benefit from appropriate coordination of measurements for mobility or other reasons. For example, Long Term Evolution communication systems may benefit from signaling for uplink short transmission time interval transmissions.

Third generation partnership project (3GPP) long term evolution (LTE) releases <NUM> and <NUM> (Rel-<NUM>/<NUM>) may include an LTE-Advanced Pro system. More specifically, there is a Rel-<NUM> Study Item, "Study on Latency reduction techniques" RP-<NUM> and the follow-up Work Item RP-<NUM> that is based on the Study Item. The conclusions of the Study Item are captured into the 3GPP technical report (TR) <NUM> and they indicate that processing time is related to physical layer radio latency.

The changes associated with this study item and work item include introduction of shorter transmission time interval (TTI) (sTTI) operation with reduced processing times. For Frame structure type <NUM> [RAN1, RAN2, RAN4], the changes may specify support for a transmission duration based on <NUM>-symbol sTTI and <NUM>-slot sTTI for short physical downlink shared channel (sPDSCH) / short physical downlink control channel (sPDCCH) and may specify support for a transmission duration based on <NUM>-symbol sTTI, <NUM>-symbol sTTI, and <NUM>-slot sTTI for sPUCCH/sPUSCH. Down-selection is not precluded. The use of "s" in combination with other abbreviations such as PUCCH or PUSCH can refer to "short," "shorter," "shortened" or the like, without limitation.

The performance in link level throughput conventionally decreases with shorter TTI lengths. This is primarily due to the increased relative overhead from the uplink (UL) demodulation reference signals (DMRS).

<NPL>; provides design details for uplink channels for shortened TTIs.

<CIT> relates to allowing a demodulation reference signal (DMRS) pattern suitable for a terminal to be selected from among a plurality of DMRS patterns including Legacy DMRS and Reduced DMRS.

<CIT> relates to methods, apparatuses and a computer program product for signaling for uplink demodulation reference signal. The invention includes causing reception of an uplink grant message at a user equipment, evaluating the uplink grant message, and determining, based on the result of the uplink grant message, whether to apply a full demodulation reference signal pattern or a reduced demodulation reference signal pattern.

<NPL> and <CIT> describe sounding using DMRS.

<CIT> is a further prior art document in the sense of the Article <NUM>(<NUM>) EPC.

There is hereby provided a method according to claim1.

There is also provided an access node apparatus according to claim <NUM>.

Certain embodiments relate to, for example, short physical uplink shared channel (sPUSCH) operation for example with <NUM>-symbol short transmission time interval (sTTI). Certain embodiments more particularly relate to uplink (UL) demodulation reference signals, and the related signaling allowing flexible reference signal transmission.

Having multiple sTTIs using the same DMRS can help in mitigating performance loss described above. For example, having DMRS in every second or third short TTI and/or multiplexing DMRS of different user equipment (UEs) on the same resource may significantly reduce the total DMRS overhead and thus increase the throughput. Certain embodiments provide a signaling scheme for such flexible DMRS transmission.

<FIG> illustrates a transmission time arrangement for sPUSCH. As shown in <FIG>, each transmission time interval can include L symbols, in this case three symbols. There can be one or no reference symbols (RS) and either L or L-<NUM> data symbols, in this case two or three symbols. Such arrangement allows reducing DMRS overhead but a drawback of the solution is that the number of data symbols in an sTTI varies depending on whether UL DMRS are present in the given sTTI or not. As the work item in RP-<NUM> considers also <NUM>-symbol sTTI, there would be a rather drastic difference in the number of resources available depending on whether the sTTI contains UL DMRS or not (double the resources are available when RS is not present). This kind of fluctuation of the amount of resources is undesirable, as it complicates scheduler operation in terms of e.g. link adaptations, retransmissions and the related control signaling design. Instead, it would be preferable to have the sTTI always containing a constant number of resources available for data. Certain embodiments provide a solution fulfilling this design criterion.

In addition, flexibility provided by certain embodiments may be beneficial in view of UL grant transmission in downlink (DL). Detailed design of DL control signaling for sTTI does not exist yet, but UL grants for sTTI may be transmitted both on PDCCH and sPDCCH. If, as may be the case, the number of PDCCH symbols can change dynamically from <NUM> to <NUM> and a grant is decodable only after reception of the last PDCCH symbol, the timing and the number of UL grants per subframe may be variable. The signaling design for UL grants may provide efficient use of UL resources even in presence of such variations.

Certain embodiments may facilitate efficient and flexible signaling for determining DMRS and data symbol transmission for sTTI operation. This signaling may allow an access node, such as an evolved node B (eNB), to adjust the amount of overhead according to UE or eNB needs. For example, UEs with higher mobility may need to transmit a DMRS symbol close in time to the data symbols, or even transmit two DMRS symbols to allow an eNB to interpolate the channel estimates.

For example, an eNB can use an UL grant to schedule a UE to transmit according to one of the following options: only DMRS symbol alone; two data symbols without DMRS symbol; or a combination of a DMRS symbol and two data symbols. Other options are also permitted. Additionally, the UL grant may indicate delay of one or two symbols with respect to a nominal delay. The UL grant may be transmitted on PDCCH or sPDCCH.

The following features illustrated and discussed with respect to table <NUM> in <FIG>, and further illustrated and discussed with reference to <FIG> and <FIG>, are merely examples. Other implementations are also permitted.

In an example embodiment, pre-defined transmit formats are used to schedule the UE how to transmit with respect to a demodulation reference signal. <FIG> illustrates Table <NUM>, a table of combinations of transmit formats, according to certain embodiments. Table <NUM> shows <NUM> combinations of transmit formats, where Formats <NUM>-<NUM> grant UE a transmission of single DMRS symbol, Formats <NUM>-<NUM> grant UE transmission of two data symbols and the rest of the formats grant both DMRS and two data symbols. Note that this table is only an example, with intention to keep the sTTI size in terms of the number data symbols constant, and more combinations could be defined or some of the combinations could be left out. Symbol <NUM> can be the UL symbol delayed by nominal minimum processing time delay with respect to a grant received on sPDCCH.

More particularly, Table <NUM> shows sTTI formats for UL DMRS (R) and data (D) symbol transmission. As mentioned above, symbol <NUM> can correspond to a nominal time of the grant. If that is empty, as in Format <NUM> for example, this can mean that the UE has to delay transmission with respect to the nominal starting time.

<FIG> illustrates an eNB scheduling different sTTI formats within five consecutive UL subframes, according to certain embodiments. The arrows always point to "Symbol <NUM>" from Table <NUM>, namely the UL symbol delayed by nominal delay with respect to UL grant received on PDCCH or sPDCCH. The number connected to an arrow corresponds to format index in the Table of <FIG>. In this example, the eNB allocated all the UL symbols and no sTTI spans over subframe boundary. However, eNB could leave a UL symbol unused if it wishes to do so. Thus, <FIG> illustrates examples of UL grants with flexible DMRS symbol positions.

<FIG> illustrates multiplexing of two UEs in time, according to certain embodiments. In this example, UE1 is in moderate speed, which may require a DMRS symbol to be close to the data symbols. On the other hand, in this example UE2 is of low mobility and may reuse the DMRS symbols already transmitted a few symbols earlier. When DMRSs of the two UEs coincide, orthogonal DMRS sequences may be transmitted by UE1 and UE2. The DMRS orthogonality may be achieved by using different cyclic shifts or interleaved frequency division multiple access (IFDMA).

Thus, <FIG> illustrates flexible multiplexing of two UEs by transmitting overlapping orthogonal DMRSs in some symbols and data multiplexing in time.

There are alternative ways of signaling a format as shown in Table <NUM>. For example, according to a first alternative three or four bits can be reserved in UL sTTI grant for indicating one of the formats. The three-bit approach may involve some scheduling constraints.

According to a second alternative, formats can be grouped, and downlink control information (DCI) can include a switch to a group. The DCI contents for different groups can be different but the DCI size can be the same.

As an example, there could be three groups corresponding to the following: only DMRS transmission, only data transmission, and both DMRS and data transmission. When group <NUM> is indicated, MCS bits may not be needed and can be used for indicating a format within group <NUM> or for other purposes. Similarly, when group <NUM> is indicated, the bits for selection of a DMRS cyclic shift may not be needed and can be used, for example, for indicating a format within group <NUM>. Other ways of grouping are possible.

The switch to a group can be implemented explicitly by DCI bit(s) in a similar way to the way in which the differentiation of legacy DCI Format <NUM> and 1A is done. DCI Format <NUM> and 1A have the same size and one bit in the DCI indicates whether the DCI is for UL grant (Format <NUM>) or a DL assignment (Format 1A). Another way could be to apply group dependent cyclic redundancy check (CRC) scrambling of DCI, which may involve essentially reserving multiple C-RNTIs, or using a combination of group dependent scrambling and explicit bits.

In addition to the scheduling flexibility illustrated in <FIG> and <FIG>, the signaling scheme of certain embodiments can enable efficient UL resource use when the number of scheduling instances in DL varies with the number of PDCCH symbols. This is illustrated in <FIG>.

<FIG> illustrates some examples of UL grants for different numbers of PDCCH symbols, according to certain embodiments. The encoding of a DCI spreads it over all PDCCH symbols. Therefore, when an sTTI grant is given in PDCCH, its decoding can start only after receiving the last PDCCH symbol. This may involve losing one scheduling opportunity per subframe, as shown in the upper part of <FIG> for the case of three PDCCH symbols, or otherwise uneven separation between nominal scheduling times ("subframes <NUM>"), as shown in the two lower examples in <FIG>.

For these lower examples, it is assumed that even in case of two PDCCH symbols there could be seven sTTI UL grants per TTI, and different ways of adapting scheduling according to the number of PDCCH symbols is shown. However, the number of grants in case of two PDCCH symbols is still an open question and may be variously implemented. Note that the signaling scheme also allows many other ways besides the displayed ones. Nevertheless, in all cases eNB can make use of formats with delay and/or formats using <NUM> UL symbols in order to allocate all available UL symbols within subframes.

<FIG> illustrates a method according to certain embodiments. As shown in <FIG>, a method can include, at <NUM>, determining how a user equipment is to transmit with respect to a demodulation reference signal. The determination can be on a case by case basis or can be preconfigured. The determination can be made at an access node, such as an eNB.

The determination can be one or more of the following: that the user equipment is to transmit only a demodulation reference signal without data symbols; that the user equipment is to transmit a plurality of data symbols without a demodulation reference signal; or that the user equipment is to transmit a plurality of data symbols and a demodulation reference signal. In addition, determination can include discontinuous transmission of data and demodulation reference signals. Furthermore, the determination can include that the user equipment is to transmit with delay compared with the nominal time from an UL grant to start of UL transmission.

The method can also include, at <NUM>, providing uplink grant to schedule the user equipment to transmit according to the determination. The uplink grant can be configured to indicate a delay of one or two symbols with respect to a nominal delay.

The UL grant can be sent by the access node, such as eNB.

How the user equipment is to transmit with respect to a demodulation reference signal can involve transmitting according to a selected format of a set of formats, such as the format set forth in <FIG>. The selected format can be signaled in an UL grant by a set of bits, such as three or four bits, indicating the format.

The formats can be grouped and downlink control information or other signaling can include a switch to a group. Within the group, a particular format can be indicated using modulation and coding scheme bits or demodulation reference signal cyclic shift bits, as described above. The downlink control information can include bits indicative of the group or the downlink control information can be subject to group dependent cyclic redundancy code scrambling.

The method can further include, at <NUM>, receiving an uplink grant to schedule the user equipment to transmit according to a determination with respect to a demodulation reference signal. This can be the grant sent at <NUM> and the determination made at <NUM>. The method can additionally include, at <NUM>, communicating in uplink by the user equipment in accordance with the determination, for example using a format identified or otherwise indicated. The method can additionally include, at <NUM>, the access node receiving DMRS and sPUSCH data transmission corresponding to the grant sent in <NUM>.

<FIG> illustrates a system according to certain embodiments of the invention. It should be understood that each block of the flowchart of <FIG> 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 <NUM> and user equipment (UE) or user device <NUM>. The system may include more than one UE <NUM> and more than one network element <NUM>, 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.

Each of these devices may include at least one processor or control unit or module, respectively indicated as <NUM> and <NUM>. At least one memory may be provided in each device, and indicated as <NUM> and <NUM>, 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 <NUM> and <NUM> may be provided, and each device may also include an antenna, respectively illustrated as <NUM> and <NUM>. 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 <NUM> and UE <NUM> may be additionally configured for wired communication, in addition to wireless communication, and in such a case antennas <NUM> and <NUM> may illustrate any form of communication hardware, without being limited to merely an antenna.

Transceivers <NUM> and <NUM> 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. One possible use is to make a network element to deliver local content. One or more functionalities may also be implemented as a virtual application that is provided as software that can run on a server.

A user device or user equipment <NUM> 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 <NUM> may be a sensor or smart meter, or other device that may usually be configured for a single location.

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 <FIG>.

Processors <NUM> and <NUM> 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.

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 <NUM> and <NUM> 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.

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 <NUM> and/or UE <NUM>, to perform any of the processes described above (see, for example, <FIG>). 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.

Furthermore, although <FIG> illustrates a system including a network element <NUM> and a UE <NUM>, 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.

Certain embodiments have various benefits and/or advantages. For example, certain embodiments provide a constant number of data symbols per sPUSCH data transmission. Likewise, certain embodiments allow an eNB to flexibly grant DMRS positions according to needs of the UE, for example with respect to mobility. Additionally, certain embodiments provide a solution to a variable number of PDCCH symbols on subframe basis, which may cause a variable number of scheduling instances in DL as well as impacting the position of nominal "subframe <NUM>".

Claim 1:
A method to be performed by an access node (<NUM>), comprising: providing a first uplink grant comprising a first format index indicating a first transmission format for a first user equipment (<NUM>) within a sub-frame, wherein the first transmission format comprises transmission of a demodulation reference signal in a transmission time interval without data symbols in the transmission time interval; and providing a second uplink grant comprising a second format index indicating a second transmission format for the first user equipment within the sub-frame, wherein the second transmission format comprises transmission of a plurality of data symbols in another transmission time interval without transmission of a demodulation reference signal in the another transmission time interval; and providing a third uplink grant to schedule a second user equipment to transmit within the sub-frame a plurality of data symbols and a demodulation reference signal.