Patent Description:
In Long Term Evolution (LTE) and other wireless communication standards, communication latency may be reduced by employing shorter minimum Transmission Time Intervals (TTI). The 3GPP contributions <NPL>, and <NPL> provide background information about reference signal transmission in bundled and shortened TTI communication.

In the following, any method and/or apparatus referred to as embodiments but nevertheless do not fall within the scope of the appended claims are to be understood as examples helpful in understanding the invention. A method for determining reference signal locations is disclosed. The method determines a number of Transmission Time Intervals (TTI) in a scheduled transmission of a plurality of TTI. The method further determines one or more reference signal locations based on the number of TTI. An apparatus also performs the functions of the method.

As will be appreciated by one skilled in the art, aspects of the embodiments may be embodied as a system, method or program product. The storage devices may be tangible, non-transitory, and/or nontransmission.

Many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components.

An identified module of code may, for instance, comprise one or more physical or logical blocks of executable code which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module.

More specific examples (a non-exhaustive list) of the storage device would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Code for carrying out operations for embodiments may be written in any combination of one or more programming languages including an object oriented programming language such as Python, Ruby, Java, Smalltalk, C++, or the like, and conventional procedural programming languages, such as the "C" programming language, or the like, and/or machine languages such as assembly languages.

These code may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

In this regard, each block in the schematic flowchart diagrams and/or schematic block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions of the code for implementing the specified logical function(s).

<FIG> is a schematic block diagram illustrating one embodiment of a communication system <NUM>. The system <NUM> includes a base station <NUM>, a network <NUM>, and user equipment 110a-c. The base station <NUM> may communicate with the user equipment 110a-c through the network <NUM>. The base station <NUM> may be an evolved node B (eNB) Long Term Evolution (LTE) base station. The user equipment <NUM> may be a mobile telephone, a machine-type communications (MTC) device, a tablet computer, a laptop computer, and embedded communication devices in automobiles, kiosks, appliances, and the like. The network <NUM> may be a mobile telephone network. Alternatively, the network <NUM> may be a wide-area network, a wireless network, or combinations thereof.

The base station <NUM> may communicate data to the user equipment <NUM> via a scheduled transmission. The scheduled transmission may include a plurality of Transmission Time Intervals (TTI). In one embodiment, the TTI are shortened TTI (sTTI), although for simplicity all TTI are referred to as TTI regardless of length. The TTI maybe organized in a subframe, with each subframe or Physical Resource Block (PRB) comprising a plurality of symbols as will be described hereafte.

A Physical Downlink Control Channel (PDCCH) may carry Downlink Control Information (DCI) such as information regarding a reference signal. The reference signal may encode information about the data being transferred in the scheduled transmission as well as information about the resources that the user equipment 110a-c should use for transmitting uplink data.

The latency of the network <NUM> may be decreased by shortening the TTI in a subframe. Unfortunately, as the TTI are shortened, the overhead due to the reference signals increases. The embodiments described herein reduce the overhead of the reference signals by sending the reference signals in a subset of the TTI as will be described hereafter. The embodiments according to the invention indirectly communicate the reference signal locations in the subset of TTI using a number of the TTI, as well as resource assignment messages, parameters received from a higher layer, a subframe index, a time interval between TTI, a subband size, and a Time Division Duplex (TDD) configuration to communicate the reference signal locations. The reference signals may then be communicated in the reduced set of reference signal locations. As result, the reference signal density is reduced, reducing the latency of data communication for the system <NUM>.

<FIG> is a schematic block diagram illustrating one embodiment of a subframe <NUM>. In one embodiment, the subframe <NUM> communicates data over a <NUM> millisecond (ms) time interval. Each subframe <NUM> may comprise a plurality of resource blocks <NUM>, with each resource block <NUM> occupying a unique combination of modulation frequency and time interval within the subframe <NUM>.

<FIG> is a schematic block diagram illustrating one alternate embodiment of the subframe <NUM>. For simplicity, the subframe <NUM> is depicted with seven TTI <NUM> of two Orthogonal Frequency-Division Multiplexing (OFDM) symbols each. Each combination of a TTI <NUM> and a subband <NUM> represents a resource block <NUM>. A subframe <NUM> or other organization of data may include any number of resource blocks <NUM>, TTI <NUM>, and/or subbands <NUM>.

For a particular TTI length (e.g., <NUM> symbol sTTI <NUM>), the user equipment <NUM> may assume a resource block group (RBG) size in sTTI <NUM> containing Cell-Specific Reference Signals (CRS) Resource Elements (RE) (or any other signals/channels), would be a function such as a scaling factor of the RBG size in sTTI <NUM> not containing CRS REs (or any other signals/channels). For instance, if the RBG size in non-CRS sTTI <NUM> is <NUM> resource blocks <NUM>, then the RBG size for CRS-sTTI <NUM> is <NUM> resource blocks <NUM>.

The scaling factor of RBG size for sTTI <NUM> containing CRS (or other reference symbols, like positioning, Channel State Information Reference Signals (CSI-RS), etc. or other channels to sTTI <NUM> not containing such signals, can be configured by higher layers or by physical layer, e.g., the possible set of scaling factors could be {<NUM>, <NUM>}. Instead of scaling factor, an offset can be used. For instance, an offset of "<NUM>" could mean the RBG size in the sTTI <NUM> including CRS (or other reference symbols, like positioning, CSI-RS, etc. or other channels) is one more RB larger than that of used for sTTI <NUM> without CRS (or other reference symbols, like positioning, CSI-RS, etc. or other channels). This offset may be applied when the RBG size is fixed and not signaled in the multi-TTI grant, and even if a single-TTI grant is applied. It could be configured by higher layer signaling such as Radio Resource Control (RRC) or may be fixed in the specifications.

In one embodiment, if an sTTI <NUM> with scaled or offset RBG size with respect to the RBG size of other scheduled sTTI <NUM> is present in the multi-TTI <NUM> scheduled set of sTTI <NUM> where only a subset of sTTI <NUM> contain reference signals <NUM>, in terms of reference signal usage from other sTTI <NUM>, the same precoder is assumed to be applied across all resource blocks <NUM> in RBG (irrespective to RBG size) in all sTTI <NUM> benefiting from the same reference signal <NUM> (DMRS) symbols. This approach can give flexibility to eNB to utilize resources in sTTI <NUM> without CRS for scheduling other user equipment <NUM>.

<FIG> is a schematic block diagram illustrating one embodiment of a resource block <NUM>. In the depicted embodiment, the resource block <NUM> includes a reference signal location <NUM>. A reference signal <NUM> may be transmitted in the reference signal location <NUM>. The reference signal <NUM> may encode information such as DCI about the data being transmitted in the scheduled transmission as well as information about the resources that the user equipment <NUM> should use for transmitting uplink data. The presence or absence of a reference signal <NUM> may enable some unused resources including TTI <NUM> where the reference signal <NUM> is absent to be used for data transmission.

<FIG> is a schematic block diagram illustrating one embodiment of messages. A resource assignment message <NUM>, a scheduled transmission <NUM>, and an acknowledgment message <NUM> are shown. The resource assignment message <NUM> may include downlink assignment information and/or uplink grants and may be communicated to the user equipment <NUM> over the PDCCH. The scheduled transmission <NUM> may include one or more subframes <NUM>. The acknowledgment message <NUM> may acknowledge that data in the scheduled transmission <NUM> was received.

For a particular TTI length (e.g., <NUM> symbol sTTI <NUM>), the user equipment <NUM> may assume a resource block group (RBG) size in sTTI <NUM> containing CSR RE (or any other signals/channels), would be a function such as a scaling factor of the RBG size in sTTI <NUM> not containing CRS REs (or any other signals/channels). For instance, if the RBG size in non-CRS sTTI <NUM> is <NUM> resource blocks <NUM>, then the RBG size for CRS-sTTI is <NUM> resource blocks <NUM>.

The scaling factor of RBG size for sTTI <NUM> containing CRS (or other reference symbols, like positioning, CSI-RS, etc. or other channels) to sTTI <NUM> not containing such signals, may be configured by higher layers or by physical layer, e.g., the possible set of scaling factors could be {<NUM>, <NUM>}. Instead of scaling factor, an offset can be used. For instance, an offset of "<NUM>" could mean the RBG size in the sTTI <NUM> including CRS (or other reference symbols, like positioning, CSI-RS, etc. or other channels) is one more resource blocks <NUM> larger than that of used for sTTI <NUM> without CRS (or other reference symbols, like positioning, CSI-RS, etc. or other channels). This offset may be applied when the RBG size is fixed and not signaled in the multi-TTI grant, and even if a single-TTI grant is applied. It could be configured by higher layer signaling such as Radio Resource Control (RRC) or fixed in the specifications.

In one embodiment, if an sTTI <NUM> with scaled or offset RBG size write RBG size of other scheduled sTTI <NUM> is present in the multi-TTI <NUM> scheduled set of sTTI <NUM> where only a subset of sTTI reference signals <NUM>, in terms of reference signal usage from other sTTI <NUM>, the same precoder is assumed to be applied across all resource blocks <NUM> in RBG (irrespective to RBG size) in all sTTI <NUM> benefiting from the same DMRS symbols. This approach can give flexibility to eNB to utilize resources in sTTI <NUM> without CRS for scheduling other user equipment <NUM>.

<FIG> are a schematic block diagram illustrating embodiments of reference signal locations <NUM> at predetermined TTI instances <NUM> of the plurality of TTI <NUM> within a subframe <NUM>. The predetermined TTI instances <NUM> are hereafter indicated by a crosshatch. The illustrated reference signal locations <NUM> are exemplary of reference signals being communicated within predetermined TTI instances <NUM> that are a subset of the plurality of TTI <NUM> within a subframe <NUM>, and are not limiting. The reference signal locations <NUM> and the predetermined TTI instances <NUM> may be determined through a calculation, a table lookup, and/or one or more logical tests as will be described hereafter.

One or more reference signal locations <NUM> may be determined to be in predetermined TTI instances <NUM> of the plurality of TTI <NUM>. A number of predetermined TTI instances <NUM> and/or a number of predetermined TTI instances <NUM> may be less than the number of TTI <NUM>, wherein the reference signal <NUM> is present only in the predetermined TTI instances <NUM>. According to the invention, the one or more reference signal locations <NUM> are determined to be in predetermined subband instances <NUM> of predetermined TTI instances <NUM>.

For simplicity, seven TTI <NUM> and one or two subbands <NUM> are shown. However, the embodiments may be practiced with reference signals <NUM> being communicated within other combinations of predetermined TTI instances <NUM> and predetermined subband instances <NUM>.

<FIG> shows one reference signal location <NUM> within a predetermined TTI instance <NUM> that is the first TTI 135a of a given subband <NUM> of a subframe <NUM>. In alternate embodiments, the predetermined TTI instance <NUM> for the one reference signal location <NUM> may be any TTI 135a-g of the subframe <NUM>.

<FIG> shows two reference signal locations <NUM> at two predetermined TTI instances <NUM> within a given subband <NUM> of the subframe <NUM>. Although the two predetermined TTI instances <NUM> are depicted as a first and third TTI 135a/c, the two predetermined TTI instances <NUM> may be any TTI 135a-g of the subframe <NUM>.

<FIG> shows three reference signal locations <NUM> at three predetermined TTI instances <NUM> within a given subband <NUM> of the subframe <NUM>. The three predetermined TTI instances <NUM> are depicted as the first, third, and seventh TTI 135a/c/g. However, the three predetermined TTI instances <NUM> may be any TTI 135a-g of the subframe <NUM>. For example, <FIG> shows the three reference signal locations <NUM> in predetermined TTI instances <NUM> at the first, third, and sixth TTI 135a/c/f. The predetermined TTI instances <NUM> may be periodic within a subband <NUM>. Alternatively, the predetermined TTI instances <NUM> may be aperiodic within the subband <NUM>.

<FIG> shows one embodiment of reference signal locations <NUM> for two subbands 140a-b of the subframe <NUM>. In one embodiment, the one or more reference signal locations <NUM> are determined to be in predetermined subband instances 140a-b of predetermined TTI instances <NUM>. A pattern of presence and absence of reference signal locations <NUM> may be different between each subband 140a-b for a subset of subbands <NUM> of the plurality of subbands <NUM>. For example, the presence/absence pattern of reference signal locations <NUM> may be different for each subband <NUM> of a first set of subbands <NUM>, and for each subband <NUM> of a second set of subbands <NUM>, but the second set of subbands <NUM> may include at least one presence/absence pattern of reference signal locations <NUM> from the first set of subbands <NUM>.

In the depicted embodiment, each subband 140a-b includes reference signal locations <NUM> at predetermined TTI instances <NUM> in the first TTI <NUM>. However, reference signal locations <NUM> are allocated so that predetermined TTI instances <NUM> for subsequent reference signal locations <NUM> are not located in concurrent TTI <NUM>. In one embodiment, the one or more reference signal locations <NUM> of a second predetermined subband instance 140b of a second predetermined TTI instance <NUM> are further determined based on the one or more reference signal locations <NUM> of a first predetermined subband instance <NUM> of the first predetermined TTI instance <NUM>. For example, if the third TTI 135c is selected as the second predetermined TTI instance <NUM> for the first predetermined subband instance 140a, the second TTI 135b may be selected as the second predetermined TTI instance <NUM> for a second predetermined subband instance 140b based on the selection of the third TTI 135c as the second predetermined TTI instance <NUM> for the first predetermined subband instance 140a.

In one embodiment, some predetermined TTI instances <NUM> may be different between one or more subbands <NUM> in a set of subbands <NUM>. In addition, all predetermined TTI instances <NUM> may be different between one or more subbands <NUM> in a set of subbands <NUM>. In a certain embodiment, the number of predetermined TTI instances <NUM> may be different between one or more subbands <NUM> in a set of subbands <NUM>. Table <NUM> shows additional examples of differences in predetermined TTI instances <NUM> between subbands <NUM>, where TTI <NUM> index numbers are listed for each subband <NUM>. The table is exemplary and not limiting.

The predetermined TTI instances <NUM> may be periodic between subbands <NUM>. Alternatively, the predetermined TTI instances <NUM> may be aperiodic between the subbands <NUM>.

In one embodiment, if a single transport block is sent across two or more resource block groups (or subbands), then the benefit of using different reference signal presence/absence patterns (or different predetermined TTIs) for different resource block groups (or subbands) may become smaller depending on factors such as the coding rate associated to the transport block.

<FIG> shows one embodiment of reference signal locations <NUM> for two subbands 140a-b of the subframe <NUM>. In the depicted embodiment, each subband 140a-b includes reference signal locations <NUM> at predetermined TTI instances <NUM> in the first TTI 135a. However, reference signal locations <NUM> are allocated so that predetermined TTI instances <NUM> for subsequent reference signal locations <NUM> are not located in concurrent TTI <NUM>. In the depicted embodiment, the predetermined TTI instances <NUM> for the first subband 140a are at the first, third, and seventh TTI 135a/c/g while the predetermined TTI instances <NUM> for the second subband 140b are at the first, second, and sixth TTI 135a/c/f.

<FIG> shows four reference signal locations <NUM> at four predetermined TTI instances <NUM> within a given subband <NUM> of the subframe <NUM>. The four predetermined TTI instances <NUM> are depicted as the first, third, fifth, and seventh TTI 135a/c/e/g.

<FIG> shows three reference signal locations <NUM> at three predetermined TTI instances <NUM> within a given subband <NUM> of the subframe <NUM>. The three predetermined TTI instances <NUM> are depicted as the first, fourth, and seventh TTI 135a/d/g.

<FIG> is a schematic block diagram illustrating one embodiment of allocating data <NUM> in scheduled TTI <NUM>. Some of the scheduled TTI <NUM> may include a reference signal <NUM> as well as data. In the depicted embodiment, data <NUM> for three user equipment instances 110a-c are allocated to two subbands <NUM> of the subframe <NUM>. First data 150a for a first user equipment instance 110a are allocated to the first, second, third, fourth, and sixth TTI 135a/b/c/d/f of the first subband 140a. Second data 150b for a second user equipment instance 110b are allocated to fifth and seventh TTI 135e/g of the first subband 140a and the first, second, third, and fourth TTI 135a-d of the second subband 140b. In addition, third data 150c for third user equipment instance 110c are allocated to the fifth, sixth, and seventh TTI 135e-g of the second subband 140b.

In one embodiment, first TTI 135a may need more reference signal locations <NUM> to achieve a particular channel estimation performance as the subsequent TTI <NUM> may need less reference signals <NUM> as the subsequent TTI <NUM> may reuse the reference signals <NUM> of previously scheduled TTI <NUM> if a channel doesn't change fast, such as in a low Doppler situation.

<FIG> is a schematic block diagram illustrating one embodiment of a computer <NUM>. The computer <NUM> may be embodied in the user equipment <NUM> and/or the base station <NUM>. In the depicted embodiment, the computer <NUM> includes a processor <NUM>, a memory <NUM>, and communication hardware <NUM>. The memory <NUM> may include a semiconductor storage device, a hard disk drive, an optical storage device, a micromechanical storage device, or combinations thereof. The memory <NUM> may store code and data. The processor <NUM> may execute the code and process the data.

The communication hardware <NUM> may include one or more transmitters and one or more receivers for transmitting data <NUM> between the base station <NUM> and the user equipment <NUM> through the network <NUM>. Each transmitter and/or receiver may include one or more antenna ports.

<FIG> is a schematic flow chart diagram illustrating one embodiment of a reference signal location determination method <NUM>. The reference signal location determination method <NUM> may determine one or more reference signal locations <NUM> and predetermined TTI instances <NUM> and communicate reference signals <NUM> in the predetermined TTI instances <NUM>. The method <NUM> may be performed by the base station <NUM>, user equipment <NUM>, or combinations thereof. In addition, the method <NUM> may be performed by processors <NUM> of the base station <NUM> and/or the user equipment <NUM>.

The method <NUM> starts, and in one embodiment, the processor <NUM> determines <NUM> the number of signal reference locations <NUM> as a function of the number of the plurality of TTI <NUM> for the scheduled transmission <NUM>. In addition, the number of signal reference locations <NUM> may be determined <NUM> as a function of the number of the plurality of TTI <NUM> and one or more of the subframe index, the time interval between the TTI <NUM> in the scheduled transmission <NUM>, the subband size, and the TDD configuration for the scheduled transmission <NUM>.

In one embodiment, the processor <NUM> of the base station <NUM> determines <NUM> reference signal locations <NUM> for reference signals <NUM> that are communicated in a subframe <NUM> of the scheduled transmission <NUM>. As used herein, "determines" refers to calculating, looking up, and/or making a logical decision based on one or more inputs.

The processor <NUM> may determine <NUM> the number of signal reference locations <NUM> for a scheduled message as a function of the number of the plurality of TTI <NUM> and/or predetermined TTI instances <NUM>. In one embodiment, for each number of signal reference locations <NUM> and/or predetermined TTI instances <NUM>, there is a unique number of the plurality of TTI <NUM> for the scheduled message. The number of the plurality of TTI <NUM> for the scheduled message may be determined from a lookup table.

In one embodiment, the processor <NUM> determines <NUM> the reference signal locations <NUM> by determining a number of reference signal locations <NUM> for the subframe <NUM> based on an operation standard. For example, the operation standard may specify that reference signals <NUM> be communicated in three reference signal locations <NUM> at three predetermined TTI instances <NUM> for each subband <NUM>.

In an alternative embodiment, the processor <NUM> may determine the number of reference signal locations <NUM> for the subframe <NUM> based on available bandwidth of the network <NUM>. For example, if the available bandwidth exceeds a bandwidth threshold, the processor <NUM> may determine <NUM> that a larger number of reference signal locations <NUM> may be allocated for the subframe <NUM>.

<FIG> describes an alternative embodiment for determining <NUM> the number of reference signal locations <NUM>. The embodiments for determining the number of reference signal locations <NUM> may be used singly or in combination.

The processor <NUM> may determine <NUM> the reference signal locations <NUM> based on the number predetermined TTI instances <NUM>. For example, a lookup table may specify the reference signal locations <NUM> for the predetermined TTI instances <NUM> for using the number of predetermined TTI instances <NUM> as an index.

The processor <NUM> may determine the number of signal reference locations <NUM> and/or the number predetermined TTI instances <NUM> for a scheduled transmission <NUM> as a function of the number of TTI <NUM> in the plurality of TTI <NUM>. The processor <NUM> may determine the number of predetermined TTI instances <NUM>, and/or the TTI <NUM> of the predetermined TTI instances <NUM> for a scheduled transmission <NUM> as a function of the number of TTI <NUM> in the plurality of TTI <NUM>.

In one embodiment, the processor <NUM> determines the number of signal reference locations <NUM> and/or predetermined TTI instances <NUM> for the scheduled transmission <NUM> as a function of the number of TTI <NUM> in a plurality of TTI <NUM> and one or more of the subframe index, the time interval between the TTI <NUM> in the scheduled transmission <NUM>, the subband size, and the TDD configuration for the scheduled transmission <NUM>.

According to the invention, the processor <NUM> determines <NUM> the reference signal locations <NUM> as a function of one or more of the number of TTI <NUM>, a subframe index, a time interval between the TTI <NUM> in the scheduled transmission <NUM>, a subband size, and a TDD configuration for the scheduled transmission <NUM>. The one or more reference signal locations <NUM> may be in predetermined TTI instances <NUM> of the plurality of TTI <NUM>. A number of predetermined TTI instances <NUM> may be less than the number of the plurality of TTI <NUM>. The reference signal <NUM> may be present only in the predetermined TTI instances <NUM>.

In one embodiment, the reference signal locations <NUM> are determined <NUM> to be in predetermined TTI instances <NUM> of the plurality of TTI <NUM> and a number of predetermined TTI instances <NUM> is less than the number of the plurality of TTI, wherein the reference signal <NUM> is present only in the predetermined TTI instances <NUM>. In response to one TTI <NUM> in the scheduled transmission <NUM>, the one or more reference signal locations <NUM> may be determined <NUM> to be in a first predetermined TTI instance <NUM> at the first TTI 135a of the plurality of TTI <NUM>, such as is illustrated in <FIG>. In response to three consecutive TTI <NUM> in the scheduled transmission <NUM>, the one or more reference signal locations <NUM> may be determined <NUM> to be in the first predetermined TTI instance <NUM> at the first TTI 135a and a third predetermined TTI instance <NUM> and the third TTI 135c of the plurality of TTI <NUM>, such as is illustrated in <FIG>. In response to seven consecutive TTI <NUM> in the scheduled transmission <NUM>, the one or more reference signal locations <NUM> may be determined <NUM> to be in the first predetermined TTI instance <NUM> at the first TTI 135a, the third predetermined TTI instance at the third TTI 135c, and a seventh predetermined TTI instance <NUM> at the seventh TTI <NUM> of the plurality of TTI <NUM>, such as is illustrated in <FIG>. Alternatively, In response to seven consecutive TTI <NUM> in the scheduled transmission <NUM>, the at least one reference signal <NUM> may be determined <NUM> to be in the first predetermined TTI instance <NUM> at the first TTI 135a, the third predetermined TTI instance <NUM> at the third TTI 135c, and a sixth predetermined TTI instance <NUM> at the sixth TTI 135f of the plurality of TTI <NUM>.

According to the invention, the one or more reference signal locations <NUM> are determined <NUM> to be in predetermined subband instances <NUM> of predetermined TTI instances <NUM>. The one or more reference signal locations <NUM> of a second predetermined subband instance 140b of a second predetermined TTI instance <NUM> may be determined <NUM> based on the one or more reference signal locations of a first predetermined subband instance 140a of the first predetermined TTI instance <NUM>, such as is illustrated in <FIG>.

According to the invention, the one or more reference signal locations <NUM> for a transmission layer of the scheduled transmission <NUM> of a plurality of TTI <NUM> are further determined <NUM> based on a parameter communicated in the resource assignment message <NUM>. For example, the reference signal locations <NUM> may be calculated as a function of the parameter communicated in the resource assignment message <NUM>. In addition, the number of one or more reference signal locations <NUM> for a subband <NUM> of the plurality of TTI <NUM> may be further determined <NUM> from the resource assignment message <NUM>. For example, a value in the resource assignment message <NUM> may specify the number of the one or more reference signal locations <NUM> for the subband <NUM>.

In one embodiment, a first and second plurality of TTI <NUM> with a same number of TTI <NUM> and a same rank, may have different numbers of reference signal locations <NUM> based on the resource assignment message <NUM>. For example, for the first plurality of TTI <NUM> may have a first number of reference signals <NUM> based on a first resource assignment message <NUM> and the second plurality of TTI <NUM> may have a second number of reference signals <NUM> for the second plurality of TTI <NUM> based on a second resource assignment message <NUM>.

In a certain embodiment, a given reference signal <NUM> of the one or more reference signals <NUM> is mapped to two given reference signal locations <NUM> of two TTI <NUM> of the plurality of TTI <NUM>.

The one or more reference signal locations <NUM> may be determined <NUM> to be in predetermined subband instances <NUM> of predetermined TTI instances <NUM>. The one or more reference signal locations <NUM> of a second predetermined subband instance 140b of a second predetermined TTI instance <NUM> may be determined based on the one or more reference signal locations <NUM> of a first predetermined subband instance 140a of the first predetermined TTI instance <NUM>. For example, if the first predetermined TTI instance <NUM> of a first reference signal location <NUM> the first predetermined subband instance <NUM> is at a third TTI 135c, the second predetermined TTI instance <NUM> for a second reference signal location <NUM> in the second predetermined subband instance 140b may be in the second TTI 135b based on the first predetermined TTI instance <NUM> being in the third TTI 135c, such as is illustrated in <FIG>.

In one embodiment, a first number of reference signals <NUM> for the first plurality of TTI <NUM> is different from a second number of reference signals <NUM> for the second plurality of TTI <NUM> with a same rank as the first plurality of TTI <NUM>. The difference between the number of reference signals <NUM> for the first plurality of TTI <NUM> and the number of reference signals for the second plurality of TTI <NUM> may be communicated via the resource assignment message <NUM>. For example, a first resource assignment message <NUM> for a first plurality of TTI <NUM> may be used to determine the first number of reference signals <NUM> for the first plurality of TTI <NUM> and a second resource assignment message <NUM> for a second plurality of TTI <NUM> may be used to determine the second number of reference signals <NUM> for the second plurality of TTI <NUM>.

The processor <NUM> may schedule <NUM> the scheduled transmission <NUM> of the plurality of TTI <NUM> to a user equipment <NUM>. The predetermined TTI instances <NUM> of the plurality of TTI <NUM> may contain the one or more reference signal locations <NUM> for the scheduled transmission <NUM>. In one embodiment, a given reference signal <NUM> of the one or more reference signals <NUM> is mapped to two given reference signal locations <NUM> of two TTI <NUM> of the plurality of TTI <NUM>. The two TTI <NUM> may be predetermined TTI instances <NUM>. In one embodiment the user equipment <NUM> may determine if a given reference signal <NUM> of the one or more reference signals <NUM> is mapped to two given reference signal locations <NUM> of two TTI <NUM> of the plurality of TTI <NUM> based on the resource assignment message <NUM>.

In one embodiment, a field in the DCI indicates the number of TTI <NUM> and/or the one or more reference signal locations <NUM>. In addition, a Radio Network Temporary Identifier (RNTI) may indicate the number of TTI <NUM> and/or the one or more reference signal locations <NUM>. Alternative, a fixed value for a field in multi-TTI grant indicates the number of TTI <NUM> and/or one or more reference signal locations <NUM>. In a certain embodiment, a function of a time and/or frequency wherein the multi-TTI grant is transmitted indicates the one or more reference signal locations <NUM> and/or the number of TTI <NUM>.

In one embodiment, a field in the DCI indicates if the number of scheduled TTI <NUM> is greater than <NUM>. In addition, a RNTI may indicate if the number of scheduled TTI <NUM> is greater than <NUM>. Alternative, a fixed value for a field in multi-TTI grant indicates if the number of scheduled TTI <NUM> is greater than <NUM>. In a certain embodiment, a function of a time and/or frequency wherein the multi-TTI grant is transmitted indicates if the number of scheduled TTI <NUM> is greater than <NUM>.

The processor <NUM> may transmit <NUM> a resource assignment message <NUM> to the user equipment <NUM> and the user equipment <NUM> may receive <NUM> the resource assignment message. The processor <NUM> of the user equipment <NUM> may determine <NUM> the number of the plurality of TTI <NUM> in the scheduled transmission <NUM>. The number of the plurality of TTI <NUM> may be determined <NUM> from the resource assignment message <NUM>.

In one embodiment, the processor <NUM> determines <NUM> the reference signal locations <NUM> for the scheduled transmission <NUM> based on the number of the plurality of TTI <NUM>. The processor <NUM> of the user equipment <NUM> may employ the functions and/or criteria that the processor <NUM> of the base station <NUM> employed and/or inverse functions and/or criteria from the functions and/or criteria that the processor <NUM> of the base station <NUM> employed to determine the number of the plurality of TTI <NUM>.

In one embodiment, the reference signal locations <NUM> are determined <NUM> based only on the number of TTI <NUM>. For example, the reference signal locations <NUM> may be retrieved from a lookup table that uses the number of TTI <NUM> is an index.

According to the invention, the reference signal locations <NUM> are determined <NUM> from the number of TTI <NUM> and one or more of the resource assignment message <NUM>, a parameter received from a higher layer wherein the higher layer is higher than the physical layer, the subframe index, the time interval between the TTI <NUM> in the scheduled transmission <NUM>, the subband size, and the TDD configuration for the scheduled transmission <NUM>.

In one embodiment, the one or more reference signal locations <NUM> are determined <NUM> to be in predetermined subband instances <NUM> of predetermined TTI instances <NUM>. The one or more reference signal locations <NUM> of a second predetermined subband instance 140b of a second predetermined TTI instance <NUM> may be determined <NUM> based on the one or more reference signal locations of a first predetermined subband instance 140a of the first predetermined TTI instance <NUM>, such as is illustrated in <FIG>.

In one embodiment, the one or more reference signal locations <NUM> for a transmission layer of the scheduled transmission <NUM> of a plurality of TTI <NUM> are further determined <NUM> based on a parameter received in the resource assignment message <NUM>. For example, the reference signal locations <NUM> may be calculated as a function of the parameter received in the resource assignment message <NUM>. In addition, the number of one or more reference signal locations <NUM> for a subband <NUM> of the plurality of TTI <NUM> may be further determined <NUM> from the resource assignment message <NUM>. For example, a value in the resource assignment message <NUM> may specify the number of the one or more reference signal locations <NUM> for the subband <NUM>.

In one embodiment, the one or more reference signal locations <NUM> are further determined <NUM> from a field in the DCI indicating the number of TTI <NUM> and/or one or more reference signal locations <NUM>. In addition, the number of TTI <NUM> and/or the one or more reference signal locations <NUM> may be further determined <NUM> from the RTNI. Alternative, the number of TTI <NUM> and/or the one or more reference signal locations <NUM> may be further determined <NUM> from a fixed value for a multi-TTI grant. In a certain embodiment, the number of TTI <NUM> and/or the one or more reference signal locations <NUM> are further determined <NUM> as a function of a time and/or frequency wherein a grant is transmitted.

In one embodiment, the field in the DCI indicates if the number of scheduled TTI <NUM> is greater than <NUM>. In addition, a RNTI may indicate if the number of scheduled TTI <NUM> is greater than <NUM>. Alternative, a fixed value for a field in multi-TTI grant indicates if the number of scheduled TTI <NUM> is greater than <NUM>. In a certain embodiment, a function of a time and/or frequency wherein the multi-TTI grant is transmitted indicates if the number of scheduled TTI <NUM> is greater than <NUM>.

In one embodiment, in response to different resource assignment messages <NUM> for a first and second plurality of TTI <NUM> with a same number of TTI <NUM> and a same rank, a first number of reference signals <NUM> for the first plurality of TTI <NUM> is different from a second number of reference signals <NUM> for the second plurality of TTI <NUM>. In a certain embodiment, a given reference signal <NUM> of the one or more reference signals <NUM> is mapped to two given reference signal locations <NUM> of two TTI <NUM> of the plurality of TTI <NUM>.

<FIG> and <FIG> describe additional embodiments for determining <NUM> the reference signal locations <NUM>. The embodiments for determining <NUM> the reference signal locations <NUM> may be used singly or in any combination.

In one embodiment, the data may be precoded with a given precoding matrix for a first TTI <NUM> of the predetermined TTI instances <NUM> and a second TTI <NUM> not of the predetermined TTI instances <NUM>. The base station <NUM> may transmit <NUM> the data of the scheduled transmission <NUM> to the user equipment <NUM>. The data may be transmitted on the plurality of TTI <NUM>. The reference signals <NUM> may be transmitted in the one or more reference signal locations <NUM> at the predetermined TTI instances <NUM>. The number of predetermined TTI instances <NUM> and/or corresponding reference signal locations <NUM> may be less than a number of TTI <NUM> in the scheduled transmission <NUM>. The user equipment <NUM> may receive <NUM> the data.

In one embodiment, the processor <NUM> demodulates <NUM> at least one TTI <NUM> in the scheduled transmission <NUM> using at least one reference signal <NUM> from the one or more reference signal locations <NUM>. The at least one TTI <NUM> may be demodulated <NUM> based on both a previous reference signal <NUM> and at least one of a current reference signal <NUM> and a future reference signal <NUM>. For example, scheduling information from each of the previous reference signal <NUM> a previous scheduled transmission <NUM> and a current reference signal <NUM> the current scheduled transmission <NUM> may be used to demodulate <NUM> the TTI <NUM>.

The user equipment <NUM> may transmit <NUM> an acknowledgment message <NUM> to the base station <NUM>. In one embodiment, the user equipment <NUM> transmits <NUM> an acknowledgment message <NUM> corresponding to data demodulated for each TTI <NUM> of the plurality of TTI <NUM>. The base station <NUM> may receive <NUM> the acknowledgment message <NUM> and the method <NUM> ends. The method <NUM> may be used for multi-TTI grant scheduling, and to reduce reference signal latency.

<FIG> is a schematic flow chart diagram illustrating one embodiment of a pattern assignment method <NUM>. The method <NUM> may generate patterns of reference signal locations <NUM> and assign the patterns to sub bands <NUM>. The method <NUM> may be employed in steps <NUM> and <NUM> of <FIG>. The method <NUM> may be performed by the base station <NUM>, user equipment <NUM>, or combinations thereof. In addition, the method <NUM> may be performed by processors <NUM> of the base station <NUM> and/or the user equipment <NUM>.

The method <NUM> starts, and in one embodiment, the processor <NUM> generates <NUM> a reference signal location pattern of reference signal locations <NUM>. The reference signal location pattern may include a plurality of predetermined TTI instances <NUM>. As used herein, generating refers to calculating, looking up, and/or making a logical decision based on inputs. The reference signal location pattern may be generated <NUM> based on the number of TTI <NUM>. Alternatively, the reference signal location pattern may be generating based on the number of reference signal locations, the operation standard, the available bandwidth, and/or the likelihood of interference. According to the invention, the reference signal location pattern is generated <NUM> from the number of TTI <NUM> and one or more of the resource assignment message <NUM>, a parameter received from a higher layer wherein the higher layer is higher than the physical layer, the subframe index, the time interval between the TTI <NUM> in the scheduled transmission <NUM>, the subband size, and the TDD configuration for the scheduled transmission <NUM>.

In the reference signal location pattern, the reference signal location <NUM> may be present in some TTI <NUM> and absent in other TTI <NUM> of a slot <NUM> and/or subframe <NUM>. <FIG> illustrate examples of reference signal location patterns. The processor <NUM> further assigns <NUM> reference signal location pattern to a sub band <NUM>. For example, the processor may assign <NUM> a first reference signal location pattern to a first sub band 140a. The processor <NUM> further determines <NUM> if reference signal location patterns are assigned to all sub bands <NUM>. If reference signal location patterns are not assigned to all sub bands <NUM>, the processor <NUM> may reorder <NUM> the reference signal location pattern. For example, the predetermined TTI instances <NUM> and/or reference signal locations <NUM> of the first subband 140a of <FIG> may represent a first reference signal location pattern. The first reference signal location pattern may be reordered <NUM> to generate a second reference signal location pattern represented by the predetermined TTI instances <NUM> and/or reference signal locations <NUM> of the second subband 140b of <FIG>. in another embodiment, the second reference signal location pattern represented by the predetermined TTI instances <NUM> and/or reference signal locations <NUM> of the second subband 140b of <FIG> can be determined based on one or more of The first reference signal location pattern and/or a resource assignment message <NUM>.

The processor <NUM> continues to assign reference signal location patterns to subbands <NUM> until patterns have been assigned to all subbands <NUM> and the method <NUM> ends.

<FIG> is a schematic flow chart diagram illustrating one embodiment of a reference signal presence/absence determination method <NUM>. The method <NUM> determines the predetermined TTI instances <NUM> in which the reference signal <NUM> is present and the TTI <NUM> in which the reference signal <NUM> is absent. The method <NUM> may be employed in steps <NUM> and <NUM> of <FIG>. The method <NUM> may be performed by the base station <NUM>, user equipment <NUM>, or combinations thereof. In addition, the method <NUM> may be performed by processors <NUM> of the base station <NUM> and/or the user equipment <NUM>.

The method <NUM> starts, and in one embodiment, the processor <NUM> determines if a distance between TTI <NUM> in the scheduled transmission <NUM> is less than a distance threshold. The distance may be a number of TTI <NUM> between a last previous TTI <NUM> and a current TTI <NUM>. If the distance between the TTI <NUM> is not less than the distance threshold, a predetermined TTI instance <NUM> for a reference signal location <NUM> and/or a reference signal <NUM> is determined to be present <NUM> at the current TTI <NUM>. If the distance between the TTI <NUM> is less than the distance threshold, the processor <NUM> determines if the current TTI <NUM> is an odd TTI <NUM>, such as the first, third, fifth, and/or seventh TTI 135a/c/e/g. If the current TTI <NUM> is an odd TTI <NUM>, the reference signal location <NUM> and/or reference signal <NUM> may be present <NUM> at the current TTI <NUM>.

If the current TTI <NUM> is not an odd TTI <NUM>, a predetermined TTI instance <NUM> for a reference signal location <NUM> and/or reference signal <NUM> is determined to be absent <NUM> from the current TTI <NUM> and the method <NUM> ends. As a result, the reference signal locations <NUM> may be determined based on the distance between TTI <NUM> and a position of the TTI <NUM> within a slot <NUM>.

<FIG> is a schematic flow chart diagram illustrating one embodiment of a reference signal port determination method <NUM>. The method <NUM> determines the antenna port over which the reference signal <NUM> is transmitted. The method <NUM> may be performed by the base station <NUM>, user equipment <NUM>, or combinations thereof. In addition, the method <NUM> may be performed by processors <NUM> of the base station <NUM> and/or the user equipment <NUM>.

The method <NUM> starts, and in one embodiment, the processor <NUM> determines <NUM> if the scheduled transmission <NUM> supports up to rank <NUM>. The user equipment <NUM> may report the rank to the base station <NUM>. The base station <NUM> may decode the reported rank to determine which antenna ports to use to receive transmissions from the user equipment <NUM>.

If up to rank <NUM> is not supported, the method <NUM> ends. If up to rank <NUM> is supported, the processor <NUM> determines <NUM> if a reference signal <NUM> and/or reference signal location <NUM> is at a current TTI <NUM>. If the reference signal <NUM> and/or reference signal location <NUM> is not at the current TTI <NUM>, the method <NUM> ends.

If the reference signal <NUM> and/or reference signal location <NUM> is at the current TTI <NUM>, the processor <NUM> determines <NUM> if the current TTI <NUM> is an odd TTI <NUM>. An odd TTI <NUM> has an index number of <NUM>, <NUM>, <NUM>, etc. If the current TTI <NUM> is not an odd TTI <NUM>, the processor <NUM> may communicate <NUM> the reference signal <NUM> over one or more second antenna ports of the communication hardware <NUM> and the method <NUM> ends. If the current TTI <NUM> is an odd TTI <NUM>, the processor <NUM> may communicate <NUM> the reference signal <NUM> over one or more first antenna ports of the communication hardware <NUM> and the method <NUM> ends.

<FIG> is a schematic flow chart diagram illustrating one embodiment of a reference signal number determination method. The method <NUM> may determine a number of reference signal locations <NUM> for a scheduled transmission <NUM>. The method <NUM> may be employed by step <NUM> in <FIG>. Alternatively, the method <NUM> may be employed by step <NUM> of <FIG>. The method <NUM> may be performed by the base station <NUM>, user equipment <NUM>, or combinations thereof. In addition, the method <NUM> may be performed by processors <NUM> of the base station <NUM> and/or the user equipment <NUM>.

The method <NUM> starts, and in one embodiment, the processor <NUM> determines <NUM> if the rank is less than a rank threshold. If the rank is less than the rank threshold, the processor <NUM> may decrease <NUM> reference signal locations <NUM> for a scheduled transmission <NUM> and the method <NUM> ends. For example, the processor <NUM> may decrease <NUM> the reference signal locations <NUM> to <NUM> reference signal locations <NUM>. If the rank is not less than the rank threshold, the processor <NUM> may increase <NUM> reference signal locations <NUM> for the scheduled transmission <NUM> and the method <NUM> ends. For example, the processor <NUM> may increase <NUM> the reference signal locations to <NUM> reference signal locations <NUM>.

The embodiments described herein reduce the overhead of the reference signals <NUM> by transmitting the reference signals <NUM> in reference signal locations <NUM> at predetermined TTI instances <NUM> that are a subset of the TTI <NUM> for a scheduled transmission <NUM>. As a result, the number of reference signals <NUM> is reduced, reducing the reference signal overhead.

Claim 1:
A method (<NUM>) comprising:
determining (<NUM>), by use of a processor, a number of Transmission Time Intervals, TTI, in a scheduled transmission of a plurality of TTI; and
determining one or more reference signal locations based on the number of TTI, wherein the one or more reference signal locations are further determined from the number of TTI and one or more of a parameter received from a higher layer wherein the higher layer is higher than a physical layer, a subframe index, a subband size, or a Time Division Duplex, TDD, configuration for the scheduled transmission;
wherein the one or more reference signal locations are further determined to be in one or more predetermined subband instances of one or more predetermined TTI instances.