WO2018083375A1

WO2018083375A1 - Methods and apparatuses for configuring flexible downlink demodulation reference signal patterns for shorter transmission time interval

Info

Publication number: WO2018083375A1
Application number: PCT/FI2017/050735
Authority: WO
Inventors: Ankit Bhamri; Karol Schober
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2016-11-04
Filing date: 2017-10-24
Publication date: 2018-05-11
Anticipated expiration: 2019-05-04

Abstract

Systems, methods, apparatuses, and computer program products providing a flexible reference signal pattern definition for shorter transmission time interval (TTI) are provided.

Description

METHODS AND APPARATUSES FOR CONFIGURING FLEXIBLE DOWNLINK DEMODULATION REFERENCE SIGNAL PATTERNS FOR SHORTER TRANSMISSION

TIME INTERVAL

BACKGROUND:

Field:

[0001] Embodiments of the invention generally relate to wireless or mobile communications networks, such as, but not limited to, the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E- UTRAN), LTE-Advanced (LTE-A), LTE-Advanced Pro, LTE-M, and/or 5G radio access technology. Some embodiments may relate to methods and apparatuses for providing flexible reference signal pattern.

Description of the Related Art:

[0002] Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) refers to a communications network including base stations or Node Bs, and, for example, radio network controllers (RNC). UTRAN allows for connectivity between the user equipment (UE) and the core network. The RNC provides control functionalities for one or more Node Bs. The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS). In case of E-UTRAN (enhanced UTRAN), no RNC exists and radio access functionality is provided by an evolved Node B (eNodeB or eNB) or many eNBs. Multiple eNBs are involved for a single UE connection, for example, in case of Coordinated Multipoint Transmission (CoMP) and in dual connectivity.

[0003] Long Term Evolution (LTE) or E-UTRAN provides a new radio access technology and refers to the improvements of UMTS through improved efficiency and services, lower costs, and use of new spectrum opportunities. In particular, LTE is a 3GPP standard that provides for uplink peak rates of at least, for example, 75 megabits per second (Mbps) per carrier and downlink peak rates of at least, for example, 300 Mbps per carrier. LTE supports scalable carrier bandwidths from 20 MHz down to 1.4 MHz and supports both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD).

[0004] As mentioned above, LTE may also improve spectral efficiency in networks, allowing carriers to provide more data and voice services over a given bandwidth. Therefore, LTE is designed to fulfill the needs for high-speed data and media transport in addition to high-capacity voice support. Advantages of LTE include, for example, high throughput, low latency, FDD and TDD support in the same platform, an improved end-user experience, and a simple architecture resulting in low operating costs. [0005] Certain releases of 3 GPP LTE (e.g., LTE Rel-10, LTE Rel-11, LTE Rel-12, LTE Rel- 13) are targeted towards international mobile telecommunications advanced (IMT-A) systems, referred to herein for convenience simply as LTE- Advanced (LTE-A).

[0006] LTE-A is directed toward extending and optimizing the 3GPP LTE radio access technologies. A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A is a more optimized radio system fulfilling the international telecommunication union-radio (ITU-R) requirements for IMT -Advanced while keeping the backward compatibility.

[0007] 5^th generation wireless systems (5G) refers to the new generation of radio systems and network architecture. 5G is expected to provide higher bitrates and coverage as well as decreased latency than the current LTE systems. Some estimate that 5G will provide bitrates one hundred times higher than LTE offers. 5G is also expected to increase network expandability up to hundreds of thousands of connections. The signal technology of 5G is anticipated to be improved for greater coverage and further reduced latency as well as spectral and signaling efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0008] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0009] Fig. 1 illustrates an example of several shortened TTI (sTTI) with 2-symbol length within a legacy downlink (DL) TTI;

[0010] Fig. 2a illustrates a block diagram of an apparatus, according to one embodiment;

[0011] Fig. 2b illustrates a block diagram of an apparatus, according to another embodiment;

[0012] Fig. 3a illustrates a flow diagram of a method, according to one embodiment; and

[0013] Fig. 3b illustrates a flow diagram of a method, according to another embodiment.

DETAILED DESCRIPTION:

[0014] It will be readily understood that the components of the invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of embodiments of systems, methods, apparatuses, and computer program products providing flexible reference signal pattern definition for shorter transmission time interval (TTI), as represented in the attached figures, is not intended to limit the scope of the invention, but is merely representative of some selected embodiments of the invention. [0015] The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, the usage of the phrases "certain embodiments," "some embodiments," or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearances of the phrases "in certain embodiments," "in some embodiments," "in other embodiments," or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0016] Additionally, if desired, the different functions discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions may be optional or may be combined. As such, the following description should be considered as merely illustrative of the principles, teachings and embodiments of this invention, and not in limitation thereof.

[0017] Embodiments of the invention relate to LTE-Advanced Pro system, which will be a part of 3 GPP LTE Release 14 and Release 15. More specifically, certain embodiments may address latency reduction and relate to Release 13 Study Item "Study on Latency reduction techniques" (RP- 150465) and the follow-up Release 14 Work Item (RP-161299). Relevant areas of the study item include resource efficiency, including air interface capacity, battery lifetime, control channel resources, specification impact and technical feasibility. Both FDD and TDD duplex modes are considered. The objectives of the Release 14/15 Work Item include shortened TTI (sTTl) operation with reduced processing times, including: specifying support for a transmission duration based on 2- symbol sTTl and 1-slot sTTl for sPDSCH/sPDCCH, specifying support for a transmission duration based on 2-symbol sTTl, 4-symbol sTTl, and 1-slot sTTl for sPUCCH/sPUSCH, and studying any impact on CSI feedback and processing time.

[0018] User-specific reference signals for physical downlink shared channel (PDSCH) demodulation are part of the LTE standard since Release 8, where one port dedicated/user-specific reference signal (DRS) were introduced in transmission mode 7 of TDD. In a later Release, all the later introduced closed-loop downlink (DL) multiple input multiple output (MIMO) transmission modes employ user-specific demodulation reference signals (DMRS) supporting up to 8 ports. The main advantage of DM-RS based PDSCH operation is the scalability with number of MIMO layers transmitted to a user. Contrary, cell-specific reference signals (CRS) scale with number of transmit antennas, which becomes impractical for large transmit antenna arrays. Furthermore, user-specific demodulation reference signals (DMRS) allow implicit signaling of the used multi-antenna spatial precoder used for PDSCH transmission. It has been agreed in 3GPP that shorter TTI (sTTI) downlink operation will support DM-RS PDSCH operation.

[0019] Moreover, the PDSCH transmission in Multicast/Broadcast Single Frequency Network (MBSFN) subframes is limited to using DMRS based DL transmission modes only. This is another important reason why DMRS based DL transmission modes (i.e., DMRS based PDSCH demodulation) need to be supported also for shorter TTI length enabling lower latency LTE operation.

[0020] Further, in 3GPP TR 36.881, it has been recommended to support both CRS based transmission modes (TM) and DMRS based TMs for downlink (DL) sTTI transmission and no change for CRS definition is envisioned. Further, the 2-symbol sTTI design operating on both CRS and DMRS has been prioritized.

[0021] It has been agreed that with the shortening of TTI length, the DMRS pattern will be redesigned for TTI shorter than 1 -slot, as well as scheduling granularity being more course. One of the main reasons for considering new DMRS pattern is the absence of legacy DMRS for some shorter TTIs (sTTIs) that are shorter than one slot. Legacy DMRS are currently transmitted in orthogonal frequency division multiplexing (OFDM) symbols [6 7] and [12 13], as illustrated in Fig. 1. In particular, Fig. 1 illustrates an example of several shortened downlink TTIs with 2-symbol length within a legacy downlink subframe. As an example, when legacy DL TTI is split into, for instance, 7 DL sTTIs each having 2 symbols: sTTIs # 0, 1, 4 and 5 have no legacy DMRS ports, sTTIs # 2 and 3 share a legacy DMRS port, and sTTIs #6 contains full DMRS port.

[0022] Thus, the need to define a new DMRS pattern for sTTI is quite evident, but there are certain problems that should be considered in designing the new DM-RS pattern. These problems include scheduling flexibility, DMRS overhead, legacy CRS collision, channel state information reference signals (CSI-RS) collision, and estimator complexity. With respect to scheduling flexibility, for DMRS-based transmission with TTI length shorter than 1 -slot, it is not possible to reuse legacy DMRS because the DMRS would not be present in every sTTI. As a consequence, scheduling restriction would need to be imposed which jeopardize the benefits of TTI shortening. For full scheduling flexibility, it would be required to transmit DMRS in every TTI since they are user- specific signals. With respect to DMRS overhead, enabling full scheduling flexibility would consequently result in increased DMRS overhead due to more frequency transmission of DMRS in time, which again jeopardize the benefits of TTI shortening. Therefore, the new DMRS patterns should be designed such that the overhead can be reduced in frequency domain, while performance of channel estimation is not significantly impacted. Regarding legacy CRS collision, another issue that should be considered while designing new DMRS patterns is the location of legacy CRS ports. A primary criterion is to avoid any collision with legacy CRS ports. Legacy CRS will be transmitted wideband regardless of the sTTI lengths or position within a subframe. Therefore, a new DMRS pattern for a 2-symbol sTTI length needs to be designed to avoid collision with legacy CRS ports in all scenarios. In addition, with respect to CSI-RS collision, the sTTI DMRS pattern will need to avoid collisions with CSI-RS ports, which can be configured by an eNB and transmitted wideband in the given positions within the subframe. An eNB could avoid configuring CSI-RS ports which would collide with the sTTI DMRS pattern; however these restrictions could complicate the deployment of sTTI in the networks in transmission modes employing the CSI-RS such TM10 (CoMP). Therefore, the new DMRS pattern for 2-symbol sTTI should also avoid collisions with configured CSI-RS ports. In addition to solving the issues above, the complexity of the receiver should also be considered. It would be unacceptable to generate a different channel estimation filter for each sTTI with different DMRS pattern. Therefore, the DMRS pattern should not vary for different sTTIs within a subframe.

[0023] Therefore, embodiments of the invention described herein provide a solution that serves the purpose of defining new DM-RS patterns providing the reasonable performance and also overcoming the issues discussed above. For example, an embodiment relates to DMRS for significantly shortened PDSCH (sPDSCH), such as 2-symbol sPDSCH. One embodiment is directed to configuring flexible DMRS patterns for sTTI DL operation, reducing the DMRS overhead while at the same time providing reliable channel estimates needed for demodulation.

[0024] Due to shortening the sTTI (in terms of number of OFDM symbol), the frequency allocations becomes wider. At the same time, control overhead becomes an issue and the minimum scheduling granularity needs to change from 1 -physical resource block (PRB) pair to a block of physical resource blocks (PRBs), a resource block group (RBG). This RBG size may be dependent on system bandwidth (BW), size of the band used by sTTI as well as on sTTI length. Furthermore, DMRS need to be placed as well into OFDM symbols containing CRS and CSI-RS; therefore DMRS pattern has to match around existing CRS and CSI-RS.

[0025] Accordingly, an embodiment provides a flexible pattern definition which may be dependent on RBG/bundling size, number of signalled DMRS within a bundle and CRS and CSI-RS shifts in a cell and is valid irrespective of position and length of sTTI.

[0026] According to one embodiment, the nominal position for DMRS resources is initially calculated and the DMRS is transmitted on the nominal position if no collision is seen with legacy

CRS and CSI-RS. The nominal position may be based on a number of principles that provide better tracking and estimation of channel, including: DMRS resources at the edge/boundary of PRB bundle, and/or equal spacing between DMRS resources in frequency.

[0027] In an embodiment, if there is a collision with either CRS or CSI-RS, then the DMRS resources may be shifted from their nominal position. [0028] In order to configure flexible DL DMRS configuration for sTTI operation, according to an embodiment, the steps discussed below are followed across all sTTIs within a subframe at the same time to ensure same pattern within the subframe. First, an eNB configures (RRC) or signals (DCI ) the PRB bundle size and number of DMRS resources per OFDM symbol in each

PRB bundle Average spacing between the DMRS resources within a PRB

bundle is calculated according to the following equation:

where is the number of subcarriers within a resource block.

[0029] Based on the DMRS spacing, the nominal position of DMRS resources for each PRB bundle is given as: a. First DMRS resource is fixed at the first subcarrier of the PRB bundle, b. Second DMRS resource is also fixed at the last subcarrier of the PRB bundle, c. The remaining DMRS resources are spread between the first and last subcarrier:

where m" represents the nominal position of DMRS resources for each PRB bundle. Nominal DMRS resource position for any RBG with index i can be written as:

[0030] Once the nominal DMRS resource position is calculated for a given OFDM symbol, any collision with legacy CRS and CSI-RS should be avoided by shifting that specific DMRS resource. In one embodiment, the following steps may be followed for each DMRS resource:

a. Let be the legacy CRS position that is given in section 6.10.1.2 of 3GPP TS

36.211

b. Let be the CSI-RS position that is given in section 6.10.5.2 of 3GPP TS

36.211

c. Let ¾3_$¾5 be the flexible DMRS position that is given as

i. When there is no collision with either legacy CRS or CSI-RS

ii. When there is collision with legacy CRS or CSI-RS and the nominal DMRS position is not on the last subcarrier position within a PRB bundle

iii. When there is collision with legacy CRS or CSI-RS and the nominal DMRS position is on the last subcarrier position within a PRB bundle

[0031] The overall resource mapping equation for flexible DMRS can be written as:

[0032] Fig. 2a illustrates an example of an apparatus 10 according to an embodiment. In an embodiment, apparatus 10 may be a node, host, or server in a communications network or serving such a network. For example, apparatus 10 may be a network node or access node for a radio access network, such as a base station, node B or eNB, or an access node of 5G radio access technology. It should be noted that one of ordinary skill in the art would understand that apparatus 10 may include components or features not shown in Fig. 2a.

[0033] As illustrated in Fig. 2a, apparatus 10 includes a processor 22 for processing information and executing instructions or operations. Processor 22 may be any type of general or specific purpose processor. While a single processor 22 is shown in Fig. 2a, multiple processors may be utilized according to other embodiments. In fact, processor 22 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

[0034] Apparatus 10 may further include or be coupled to a memory 14 (internal or external), which may be coupled to processor 22, for storing information and instructions that may be executed by processor 22. Memory 14 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memory 14 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, or any other type of non- transitory machine or computer readable media. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 22, enable the apparatus 10 to perform tasks as described herein.

[0035] In some embodiments, apparatus 10 may also include or be coupled to one or more antennas 25 for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 may further include or be coupled to a transceiver 28 configured to transmit and receive information. For instance, transceiver 28 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 25 and demodulate information received via the antenna(s) 25 for further processing by other elements of apparatus 10. In other embodiments, transceiver 28 may be capable of transmitting and receiving signals or data directly.

[0036] Processor 22 may perform functions associated with the operation of apparatus 10 which may include, for example, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication resources.

[0037] In an embodiment, memory 14 may store software modules that provide functionality when executed by processor 22. The modules may include, for example, an operating system that provides operating system functionality for apparatus 10. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 may be implemented in hardware, or as any suitable combination of hardware and software.

[0038] In one embodiment, apparatus 10 may be a network node or access node, such as a base station, node B, or eNB, or an access node of 5G, for example. According to one embodiment, apparatus 10 may be controlled by memory 14 and processor 22 to define a flexible pattern for sTTI, where the defined pattern is dependent on RBG/bundling size, number of signaled reference signals (e.g., DMRS) within a bundle, and CRS and CSI-RS shifts in a cell. According to one embodiment, the defined flexible pattern is a DMRS pattern. In an embodiment, the sTTI length may be less than or equal to 7 symbols. However, the defined flexible pattern is valid and beneficial irrespective of sTTI length.

[0039] According to an embodiment, to define a flexible pattern for sTTI, apparatus 10 may be controlled by memory 14 and processor 22 to calculate a nominal position for DMRS resources, and to transmit the DMRS on the nominal position if no collision is seen with legacy CRS and CSI-RS. In one embodiment, the nominal position is based on DMRS resources at the edge/boundary of PRB bundle and/or based on equal spacing between DMRS resources in frequency. For example, according to an embodiment, apparatus 10 may be controlled by memory 14 and processor 22 to configure (RRC) or signal (DCI ) the PRB bundle size and number of DMRS resources

per OFDM symbol in each PRB bundle Average spacing between the DMRS resources

within a PRB bundle is calculated according to the following equation:

where, is the number of subcarriers within a resource block.

[0040] Based on the DMRS spacing, the nominal position of DMRS resources for each PRB bundle is given as: (a) first DMRS resource is fixed at the first subcarrier of the PRB bundle, (b) second DMRS resource is also fixed at the last subcarrier of the PRB bundle, (c) the remaining DMRS resources are spread between the first and last subcarrier:

where represents the nominal position of DMRS resources for each PRB bundle. Nominal DMRS resource position for any RBG with index i can be written as:

[0041] If there is a collision with either CRS or CSI-RS, apparatus 10 may be controlled by memory 14 and processor 22 to shift the DMRS resources from their nominal position. More specifically, once the nominal DMRS resource position is calculated for a given OFDM symbol, any collision with legacy CRS and CSI-RS may be avoided by shifting that specific DMRS resource. In one embodiment, for each DMRS resource, is the legacy CRS position that is given in section

6.10.1.2 of 3 GPP TS 36.211, is the CSI-RS position that is given in section 6.10.5.2 of

3 GPP TS 36.211 , is the flexible DMRS position that is given as:

i. When there is no collision with either legacy CRS or CSI-RS,

ii. When there is collision with legacy CRS or CSI-RS and the nominal DMRS position is not on the last subcarrier position within a PRB bundle,

iii. When there is collision with legacy CRS or CSI-RS and the nominal DMRS position is on the last subcarrier position within a PRB bundle,

[0042] The overall resource mapping equation for flexible DMRS may then be written as:

[0043] In an embodiment, apparatus 10 may then be controlled by memory 14 and processor 22 to transmit the DMRS on the flexible DMRS position,

[0044] Fig. 2b illustrates an example of an apparatus 20 according to another embodiment. In an embodiment, apparatus 20 may be a node or element in a communications network or associated with such a network, such as a UE, mobile device, mobile unit, or other device. For instance, in some embodiments, apparatus 20 may be UE in LTE, LTE-A, or 5G. It should be noted that one of ordinary skill in the art would understand that apparatus 20 may include components or features not shown in Fig. 2b.

[0045] As illustrated in Fig. 2b, apparatus 20 includes a processor 32 for processing information and executing instructions or operations. Processor 32 may be any type of general or specific purpose processor. While a single processor 32 is shown in Fig. 2b, multiple processors may be utilized according to other embodiments. In fact, processor 32 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

[0046] Apparatus 20 may further include or be coupled to a memory 34 (internal or external), which may be coupled to processor 32, for storing information and instructions that may be executed by processor 32. Memory 34 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memory 34 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, or any other type of non- transitory machine or computer readable media. The instructions stored in memory 34 may include program instructions or computer program code that, when executed by processor 32, enable the apparatus 20 to perform tasks as described herein.

[0047] In some embodiments, apparatus 20 may also include or be coupled to one or more antennas 35 for transmitting and receiving signals and/or data to and from apparatus 20. Apparatus 20 may further include a transceiver 38 configured to transmit and receive information. For instance, transceiver 38 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 35 and demodulate information received via the antenna(s) 35 for further processing by other elements of apparatus 20. In other embodiments, transceiver 38 may be capable of transmitting and receiving signals or data directly.

[0048] Processor 32 may perform functions associated with the operation of apparatus 20 including, without limitation, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 20, including processes related to management of communication resources.

[0049] In an embodiment, memory 34 stores software modules that provide functionality when executed by processor 32. The modules may include, for example, an operating system that provides operating system functionality for apparatus 20. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 20. The components of apparatus 20 may be implemented in hardware, or as any suitable combination of hardware and software.

[0050] As mentioned above, according to one embodiment, apparatus 20 may be a mobile device, such as a UE. In this embodiment, apparatus 20 may be controlled by memory 34 and processor 32 to receive, from a network node (e.g., eNB), a configuration of the DL sTTI length according to the flexible DL DMRS configuration discussed in detail above. In an embodiment, the sTTI length may be less than or equal to 7 OFDM symbol. However, the received flexible DMRS pattern configuration may be valid irrespective of sTTI length. In one embodiment, apparatus 20 may be controlled by memory 34 and processor 32 to receive, for example in DCI, the PRB bundle size and number of DMRS resources per OFDM symbol in each PRB bundle.

[0051] Fig. 3 a illustrates an example flow diagram of a method, according to one embodiment. In some embodiments, the method of Fig. 3a may be performed by a network node or access node for a radio access network, such as a base station, node B or eNB, or an access node of 5G radio access technology. The method may be directed to defining a flexible pattern for sTTI, where the defined pattern is dependent on RBG/bundling size, number of signaled reference signals (e.g., DMRS) within a bundle, and CRS and CSI-RS shifts in a cell. According to one embodiment, the defined flexible pattern is a DMRS pattern. In an embodiment, the sTTI may be less than or equal to 7 symbol TTI. However, the defined flexible pattern is valid and beneficial irrespective of sTTI length.

[0052] As illustrated in Fig. 3a, the method may include, at 300, calculating the desired spacing between the DMRS resources within a bundle that is based on the number of DMRS in the PRB bundle and the size of the bundle, as discussed in connection with the equations above. The method may then include, at 310, calculating a nominal position for DMRS resources. In one embodiment, the calculating of the nominal position may be based on DMRS spacing calculated at 300 and the principles of placing DMRS resources at the edge/boundary of PRB. The method may then include, at 320, determining whether a collision is seen with legacy CRS and CSI-RS based on the nominal position. If no collision is seen with legacy CRS and/or CSI-RS, then the method may include, at 330, transmitting the DMRS on the nominal position. If there is a collision with legacy CRS and/or CSI-RS, then the method may include, at 340, shifting the DMRS resources from their nominal position to avoid any collision with legacy CRS and/or CSI-RS. In an embodiment, the shifting includes shifting the DMRS resources to the flexible DMRS position given by ¾¾;¾ϊ according to the equations outlined above. In one embodiment, the method may further include, at 350, transmitting the DMRS on shifted positions. [0053] Fig. 3b illustrates an example flow diagram of a method, according to another embodiment of the invention. In some embodiments, the method of Fig. 3b may be performed by a UE. The method may include, at 360, receiving, from a network node (e.g., eNB), a configuration of the DL sTTI . In an embodiment, the sTTI length may be less than or equal to 7 OFDM symbols. However, the received flexible DMRS pattern configuration may be valid and beneficial irrespective of sTTI length. In one embodiment, the method may also include, at 370, receiving, for example in DCI or RRC configured, the PRB bundle size and number of DMRS resources per OFDM symbol in each PRB bundle. The method may also include, at 380, determining the nominal DMRS positions based on the PRB bundle size and number of DMRS resources per OFDM symbol in each PRB bundle, and performing DMRS position shift to avoid collision with CRS and CSI-RS. The method may also include, at 390, performing channel estimation based on the determined DMRS pattern.

[0054] In view of the above, embodiments of the invention provide several technical improvements and/or advantages. For example, certain embodiments are able to avoid collision with resources. Also, embodiments result in better spacing between DMRS resources

within a PRB bundle, as certain embodiments configure number of DMRS resources per OFDM symbol within a PRB bundle rather than the average DMRS spacing For

example, according to an embodiment, if the is signalled to be 4 for a PRB bundle size of

3, average spacing is calculated to be 12 based on step 2 and the DMRS resources within a PRB bundle are [0 12 24 35]. Thus, embodiments result in optimally spaced DMRS resources. Also, certain embodiments are able to generate the same pattern across all sTTIs within a subframe and therefore ensure that single channel estimation filter can be used for all of them. As such, embodiments of the invention can improve performance and throughput of network nodes including, for example, base stations/eNBs and UEs. Accordingly, the use of embodiments of the invention result in improved functioning of communications networks and their nodes.

[0055] In some embodiments, the functionality of any of the methods, processes, or flow charts described herein may be implemented by software and/or computer program code or portions of it stored in memory or other computer readable or tangible media, and executed by a processor. In some embodiments, the apparatus may be, included or be associated with at least one software application, module, unit or entity configured as arithmetic operation(s), or as a program or portions of it (including an added or updated software routine), executed by at least one operation processor. Programs, also called program products or computer programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and they include program instructions to perform particular tasks. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it. Modifications and configurations required for implementing functionality of an embodiment may be performed as routine(s), which may be implemented as added or updated software routine(s). Software routine(s) may be downloaded into the apparatus.

[0056] Software or a computer program code or portions of it may be in a source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers. The computer readable medium or computer readable storage medium may be a non- transitory medium.

[0057] In other embodiments, the functionality may be performed by hardware, for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software. In yet another embodiment, the functionality may be implemented as a signal, a non- tangible means that can be carried by an electromagnetic signal downloaded from the Internet or other network.

[0058] According to an embodiment, an apparatus, such as a node, device, or a corresponding component, may be configured as a computer or a microprocessor, such as single-chip computer element, or as a chipset, including at least a memory for providing storage capacity used for arithmetic operation and an operation processor for executing the arithmetic operation.

[0059] One embodiment is directed to a method, which may include calculating a spacing between the DMRS resources within a bundle based on the number of DMRS in the PRB bundle and the size of the bundle, calculating nominal positions for DMRS resources based on the calculated spacing between the resources and the principle of placing DMRS resources at the edge/boundary of PRB. The PRB bundle size and number of DMRS resources per OFDM symbol in each PRB bundle can be configured, signaled or fixed in specification. The method may then include determining whether a collision is seen with legacy CRS and CSI-RS based on the nominal position. When no collision is detected with legacy CRS and/or CSI-RS, then the method may include transmitting the DMRS on the nominal position. When there is a collision with legacy CRS and/or CSI-RS, then the method may include shifting the DMRS resources from their nominal position to avoid any collision with legacy CRS and/or CSI-RS. In an embodiment, the shifting includes shifting the DMRS resources to a flexible DMRS position. [0060] Another embodiment is directed to an apparatus including at least one processor, and at least one memory including computer program code. The at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to calculate a spacing between the DMRS resources within a bundle based on the number of DMRS in the PRB bundle and the size of the bundle, calculating nominal positions for DMRS resources based on the calculated spacing between the resources and the principle of placing DMRS resources at the edge/boundary of PRB. The PRB bundle size and number of DMRS resources per OFDM symbol in each PRB bundle can be configured, signaled or fixed in specification. The at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to determine whether a collision is seen with legacy CRS and CSI-RS based on the nominal position. When no collision is detected with legacy CRS and/or CSI-RS, then the apparatus may be controlled to transmit the DMRS on the nominal position. When there is a collision with legacy CRS and/or CSI-RS, then the apparatus may be controlled to shift the DMRS resources from their nominal position to avoid any collision with legacy CRS and/or CSI-RS. In an embodiment, the shifting includes shifting the DMRS resources to a flexible DMRS position.

[0061] Another embodiment is directed to an apparatus, which may include calculating means for calculating a spacing between the DMRS resources within a bundle based on the number of DMRS in the PRB bundle and the size of the bundle, calculating means for calculating nominal positions for DMRS resources based on the calculated spacing between the resources and the principle of placing DMRS resources at the edge/boundary of PRB. The PRB bundle size and number of DMRS resources per OFDM symbol in each PRB bundle can be configured, signaled or fixed in specification. The apparatus may also include determining means for determining whether a collision is seen with legacy CRS and CSI-RS based on the nominal position. When no collision is detected with legacy CRS and/or CSI-RS, then the apparatus may include transmitting means for transmitting the DMRS on the nominal position. When there is a collision with legacy CRS and/or CSI-RS, then the apparatus may include shifting means for shifting the DMRS resources from their nominal position to avoid any collision with legacy CRS and/or CSI-RS. In an embodiment, the shifting means includes means for shifting the DMRS resources to a flexible DMRS position.

[0062] 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.

Claims

We Claim:

1. A method, comprising:

calculating a spacing between demodulation reference signals (DMRS) resources within a bundle based on a number of DMRS in a physical resource block (PRB) bundle and the size of the bundle;

calculating at least one nominal position for the DMRS resources based on the calculated spacing between the DMRS resources and a principle of placing DMRS resources at the edge/boundary of PRB; and

determining whether there is a collision with legacy cell-specific reference signals (CRS) and/or channel state information reference signals (CSI-RS) based on the at least one calculated nominal position.

2. The method according to claim 1, wherein, when no collision is detected with legacy CRS and/or CSI-RS, the method further comprises transmitting the DMRS on the at least one nominal position.

3. The method according to claim 1, wherein, when there is a collision with legacy CRS and/or CSI- RS, the method further comprises shifting the DMRS resources from the nominal position to avoid any collision with legacy CRS and/or CSI-RS.

4. The method according to claim 3, wherein the shifting comprises shifting the DMRS resources to a flexible DMRS position.

5. The method according to claim 1, wherein the PRB bundle size and number of DMRS resources per orthogonal frequency division multiplexing (OFDM) symbol in each PRB bundle are configured, signaled or fixed in a specification.

6. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to

calculate a spacing between demodulation reference signals (DMRS) resources within a bundle based on a number of DMRS in a physical resource block (PRB) bundle and the size of the bundle; calculate at least one nominal position for the DMRS resources based on the calculated spacing between the DMRS resources and a principle of placing DMRS resources at the edge/boundary of PRB; and

determine whether there is a collision with legacy cell-specific reference signals (CRS) and/or channel state information reference signals (CSI-RS) based on the at least one calculated nominal position.

7. The apparatus according to claim 6, wherein, when no collision is detected with legacy CRS and/or CSI-RS, the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to transmit the DMRS on the at least one nominal position.

8. The apparatus according to claim 6, wherein, when there is a collision with legacy CRS and/or CSI-RS, the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to shift the DMRS resources from the nominal position to avoid any collision with legacy CRS and/or CSI-RS.

9. The apparatus according to claim 8, wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus to shift the DMRS resources from the nominal position by shifting the DMRS resources to a flexible DMRS position.

10. The apparatus according to claim 6, wherein the PRB bundle size and number of DMRS resources per orthogonal frequency division multiplexing (OFDM) symbol in each PRB bundle are configured, signaled or fixed in a specification.

11. A computer program, embodied on a non-transitory computer readable medium, wherein the computer program, when executed by a processor, is configured to control the processor to perform a process, comprising:

calculating at least one nominal position for the DMRS resources based on the calculated spacing between the DMRS resources and a principle of placing DMRS resources at the edge/boundary of PRB ; and determining whether there is a collision with legacy cell-specific reference signals (CRS) and/or channel state information reference signals (CSI-RS) based on the at least one calculated nominal position.