HK1171300A - Methods and systems for csi-rs transmission in lte-advance systems - Google Patents

Description

Method and system for CSI-RS transmission in LTE-ADVANCE system

Cross Reference to Related Applications

This application claims priority from U.S. provisional patent application No. 61/305,512 entitled "Methods and Systems for csi-RS Transmission in LTE-Advance Systems" filed on 17.2010, the contents of which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates generally to wireless communications, and more particularly to a method of transmitting a channel state information reference signal (CSI-RS) in a wireless communication system.

Background

In a wireless communication system, downlink reference signals are typically created to provide a reference for channel estimation used in coherent demodulation and a reference for channel quality measurements used in multi-user scheduling. In the LTE Rel-8 specification, a single type of downlink reference format, called cell-specific reference signal (CRS), is defined for both channel estimation and channel quality measurement. Features of REL-8CRS include that a base station can always broadcast CRS to all User Equipments (UEs) based on most MIMO layers/ports, regardless of the Multiple Input Multiple Output (MIMO) channel rank actually required by the UEs.

In the 3GPP LTE Rel-8 system, the transmission time is divided into 10ms long frame units, and the frames are further divided equally into 10 subframes, which are labeled as subframe #0 to subframe # 9. While the LTE Frequency Division Duplex (FDD) system has 10 adjacent downlink subframes and 10 adjacent uplink subframes in each frame, the LTE Time Division Duplex (TDD) system has a plurality of downlink-uplink allocations, the downlink and uplink subframe allocations of which are given in table 1, where the letters D, U and S represent the corresponding subframes and refer to downlink subframes, uplink subframes, and specific subframes, respectively, which contain downlink transmissions in the first part of the subframes and uplink transmissions in the last part of the subframes.

Table 1: TDD allocation configuration

In one system configuration case of LTE (so-called standard cyclic prefix, or standard CP), each subframe comprises 14 equally spaced time symbols with indices from 0 to 13. The frequency domain resources, which occupy the full bandwidth within one time symbol, are divided into subcarriers. One Physical Resource Block (PRB) is defined on a rectangular 2-D frequency-time resource region, for example, as shown in fig. 2, covers 12 adjacent subcarriers in a frequency domain and 1 subframe in a time domain, and holds 12 × 14 ═ 168 Resource Elements (REs).

Each regular subframe is divided into two parts: a PDCCH (physical downlink control channel) region and a PDSCH (physical downlink shared channel) region. The PDCCH region typically occupies the first few symbols of each subframe and carries handset-specific control channels, while the PDSCH region occupies the remaining symbols of the subframe and carries general traffic. The LTE system requires the following mandatory downlink transmissions:

primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS): these two signals are repeated every frame and used for initial synchronization and cell identity detection after the UE is powered up. The PSS transmission occurs at symbol #6 in subframe {0, 5} of FDD system with normal CP, and symbol #2 in subframe {1, 6} of TDD system; SSS transmission occurs at symbol #5 in subframe {0, 5} for FDD with normal CP and at symbol #13 in subframe {0, 5} for TDD with normal CP.

Physical Broadcast Channel (PBCH): the PBCH is also repeated every frame and is used for broadcasting of basic cell information. Its transmission occurs over { 7-10 }4 symbols in subframe # 0.

Cell-specific reference signal (CRS): CRS is used for downlink signal strength measurement and for coherent demodulation of PDSCH in the same resource block. Sometimes it can also be used for verification of cell identity over PSS and SSS. CRS transmission has the same pattern in every regular subframe and occurs on symbols 0, 1, 4, 7, 8, 11 in normal CP subframes with a maximum of four transmit antenna ports. Each CRS symbol carries two CRS subcarriers per port per resource block size in the frequency domain, as shown in fig. 2.

System Information Block (SIB): the SIB is broadcast information that is not transmitted via PBCH. It is carried on a specific PDSCH decoded by each handset. There are multiple types of SIBs in LTE, most of which have a configurable longer transmission period, except for SIB type 1(SIB 1). The SIB1 is fixedly arranged at subframe #5 in each even frame. The SIBs are transmitted in the PDSCH identified by a system information radio network temporary identity (SI-RNTI) given in the corresponding PDCCH.

Paging Channel (PCH): the paging channel is used to address the handset in idle mode or to notify the handset of system-wide events such as modification of the content in the SIB. In LTE Rel-8, the PCH may be transmitted on any subframe from the configuration selection set {9}, {4, 9} and {0, 4, 5, 9} from FDD and {0}, {0, 5}, {0, 1, 5, 6} from TDD. The PCH is transmitted in a PDSCH identified by a paging RNTI (P-RNTI) given in a corresponding PDCCH.

Note that PSS/SSS/PBCH is transmitted within the six central PRBs on the frequency domain, while SIBs and PCHs may be transmitted within any portion of at least six PRBs within the entire frequency bandwidth.

In addition to the regular subframes as shown in fig. 2, the LTE system also defines a special subframe type-multimedia broadcast over single frequency network (MBSFN) subframes. This type of subframe is defined to exclude regular data communication and CRS from the PDSCH region. In other words, this type of subframe may be used by the base station, for example, to identify a null transmission region so that the handset does not attempt to search for CRS within this region. Downlink subframes {1, 2, 3, 6, 7, 8} in FDD and downlink subframes {3, 4, 7, 8, 9} in TDD may be configured as MBSFN subframes. In this disclosure, these subframes are referred to as MBSFN-capable subframes, while the remaining downlink subframes may be referred to as non-MBSFN-capable subframes. Note that most of the basic downlink signals and channels discussed above (e.g., PSS/SSS, PBCH, SIB, and PCH) are transmitted in non-MBSFN capable subframes.

As 3GPP LTE evolves from Rel-8 to Rel-10 (also known as LTE-advance or LTE-a), it may cost a lot of overhead to maintain CRS-like reference signals on all ports due to the large number of supported antenna ports (up to 8). The downlink reference signal role is agreed to be divided into the following different RS signal transmissions:

demodulation reference signal (DMRS): this type of RS is used for coherent channel estimation and should have sufficient density and should transmit on a per UE basis.

Channel state information reference signal (CSI-RS): this type of RS is used by all UEs for channel quality measurement and can be implemented on the frequency-time domain.

Agreement in the 3GPP standards body: the DMRS pattern in each PRB is determined to be located at 24 REs, as shown in fig. 2; CSI-RS REs cannot be allocated to symbols carrying PDCCH and Rel-8CRS (i.e., CSI-RS cannot be allocated to REs on symbols labeled "CRSRE on antenna port k" and "data REs on CRS symbols" in fig. 2); the CSI-RS may only be inserted and will not beIn resource elements interpreted by Rel-8 UEs as PSS/SSS or PBCH; the same CSI-RS pattern is required between non-MBSFN subframes and MBSFN subframes. In other words, the CSI-RS pattern is designed based on the available resources in the non-MBSFN subframe; the CSI-RS transmission period per cell is an integer multiple of 5 milliseconds, and the per-period transmission of CSI-RS REs for all ports per cell is performed within a single subframe; and N_ANTRepresenting the number of CSI-RS antenna ports per cell. Average density of CSI-RS for N_ANTE {2, 4, 8} is one RE per PRB per antenna port.

Based on these protocols, the present disclosure provides further principles and methods to distribute CSI-RS signals, among other characteristics, which will become apparent from the following description. These and other implementations and examples of the cell identification method in software and hardware are described in more detail in the accompanying drawings and detailed description.

Summary of The Invention

The presently disclosed embodiments are intended to solve one or more problems associated with the prior art and to provide additional features that will be readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.

One embodiment is directed to a method of allocating resource elements for transmission of CSI-RS in an Orthogonal Frequency Division Multiplexing (OFDM) system. The method includes converting one or more resource units into a two-dimensional frequency-time domain. The one or more transformed resource elements may then be divided into units (units) of Physical Resource Blocks (PRBs), which may be, for example, one subframe. It may be determined whether at least a portion of a PRB is being used by another signal; and if at least a portion of the PRB is not currently used, it may be allocated for transmission of the CSI-RS.

The CSI-RS may be transmitted at resource element locations determined by the resource elements available to the CSI-RS in a normal or FDD downlink subframe, for example. The CSI-RS may be transmitted in a downlink subframe configured as an MBSFN or non-MBSFN subframe.

Another embodiment is directed to a station configured for allocating resource elements in an OFDM system for transmission of CSI-RS. The station comprises a conversion unit configured to convert one or more resource units into a two-dimensional frequency-time domain. The station also includes a dividing unit configured to divide the one or more transformed resource elements into elements of a PRB, a determining unit configured to determine whether at least a portion of the PRB is being used by a signal, and an allocating unit configured to allocate at least a portion of the PRB for transmission of the CSI-RS if the at least a portion of the PRB is not currently used. According to some embodiments, the station is a base station, however, one of ordinary skill in the art will recognize that any station within a wireless communication system may include the aforementioned functionality.

Yet another embodiment is directed to a non-transitory computer-readable recording medium storing instructions thereon for performing, when executed by a processor, a method of allocating resource elements in an OFDM system for transmission of CSI-RS. The method includes converting one or more resource units into a two-dimensional frequency-time domain. The one or more transformed resource elements may then be divided into units of Physical Resource Blocks (PRBs), which may be, for example, one subframe. It may be determined whether at least a portion of a PRB is being used by another signal; and if at least a portion of the PRB is not currently used, it may be allocated for transmission of the CSI-RS.

Further features and advantages of the present disclosure, as well as the structure and operation of various embodiments of the present disclosure, are described in detail below with reference to the accompanying drawings.

Brief Description of Drawings

The present disclosure, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided solely for the purpose of illustrating and depicting example embodiments of the disclosure. These drawings are provided to facilitate the reader's understanding of the disclosure and should not be construed to limit the breadth, scope, or applicability of the disclosure. It will be appreciated that for clarity and ease of illustration, these drawings are not necessarily to scale.

Fig. 1 illustrates an exemplary wireless communication system for transmitting and receiving transmissions according to one embodiment.

Fig. 2 depicts a physical resource block with CRS and DMRS according to an embodiment.

Figure 3 depicts physical resource blocks in subframe #0 with CRS, PSS/SSS and PBCH in FDD according to an embodiment.

Fig. 4 depicts physical resource blocks in subframe #0 with CRS, SSS and PBCH in TDD according to an embodiment.

Fig. 5 depicts an example of CSI-RS RE groups having different shapes and sizes, according to one embodiment.

Fig. 6 depicts a physical resource block with CRS and DMRS for N-3, according to one embodiment.

Fig. 7 depicts physical resource blocks in subframe #0 with CRS, PSS/SSS and PBCH in FDD for N-3, according to an embodiment.

Fig. 8A and 8B illustrate exemplary options regarding allocation of physical resource blocks with CRS and DMRS for N-6 according to one embodiment.

Fig. 9A and 9B show exemplary options regarding allocation of physical resource blocks in subframe #0 with CRS, PSS/SSS and PBCH in FDD for N-6, according to one embodiment.

Detailed description of exemplary embodiments

The following description is presented to enable one of ordinary skill in the art to make and use the invention. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the invention. Therefore, it is not intended that the invention be limited to the examples described and illustrated herein, but rather that the invention be given the scope consistent with the claims.

The word "exemplary" is used herein to mean "serving as an example or illustration. Any aspect or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs.

Reference will now be made in detail to aspects of the present technology, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

It is to be understood that the specific order or hierarchy of steps in the processes disclosed herein are examples of exemplary approaches. Based upon a preferred design, it should be understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented.

Fig. 1 illustrates an example wireless communication system 100 for transmitting and receiving transmissions according to one embodiment of this disclosure. System 100 may include components and elements configured to support known or conventional operating characteristics that need not be described in detail herein. The system 100 generally includes a base station 102, the base station 102 having a base transceiver station module 103, a base station antenna 106, a base station processor module 116, and a base station memory module 118. The system 100 generally includes a mobile station 104 and a network communication module 126, the mobile station 104 having a mobile transceiver module 108, a mobile station antenna 112, a mobile station memory module 120, and a mobile station processor module 122. Of course, base station 102 and mobile station 104 may include additional or alternative modules without departing from the scope of the present invention. Further, only one base station 102 and one mobile station 104 are shown in the exemplary system 100, however, any number of base stations 102 and mobile stations 104 may be included.

These and other elements of system 100 may be interconnected using a data communication bus (e.g., 128, 130) or any suitable interconnection arrangement. Such interconnection facilitates communication between the different elements of the wireless system 100. Those of skill in the art will appreciate that the various illustrative blocks, modules, circuits, and processing logic described in connection with the embodiments disclosed herein may be implemented as hardware, computer readable software, firmware, or any practical combination thereof. To clearly illustrate this interchangeability and compatibility of hardware, firmware, and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware, or software depends upon the particular application and design constraints imposed on the overall system. Those familiar with the concepts described herein may implement such functionality in a manner that is suited to each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

In the exemplary system 100, the base transceiver station 103 and the mobile site transceiver 108 each include a transmitter module and a receiver module (not shown). Additionally, although not shown in this figure, those skilled in the art will recognize that one transmitter may transmit to more than one receiver, and that multiple transmitters may transmit to the same receiver. In a TDD system, transmit and receive timing gaps exist as guard bands to prevent transitions from transmit to receive and vice versa.

In the specific example system depicted in fig. 1, the "uplink" transceiver 108 comprises a transmitter that shares an antenna with an uplink receiver. In a time-duplex mode, a duplex switch may optionally couple an uplink transmitter or receiver to an uplink antenna. Likewise, the "downlink" transceiver 103 includes a receiver that shares a downlink antenna with a downlink transmitter. In a time-duplex mode, a downlink duplex switch may optionally couple a downlink transmitter or receiver to a downlink antenna.

The mobile site transceiver 108 and the base site transceiver 103 are configured to communicate over a wireless data communication link 114. The mobile station transceiver 108 and the base station transceiver 102 cooperate using a suitably configured RF antenna arrangement 106/112 that can support a particular wireless communication protocol and modulation scheme. In an exemplary embodiment, the mobile site transceiver 108 and the base station transceiver 102 are configured to support industry standards such as third generation partnership project long term evolution (3GPP LTE), third generation partnership project 2 ultra mobile broadband (3GPP2UMB), time division synchronous code division multiple access (TD-SCDMA), and microwave access Wireless Interoperability (WiMAX), among others. The mobile site transceiver 108 and the base station transceiver 102 may be configured to support alternative or additional wireless data communication protocols, including future changes to IEEE802.16, such as 802.16e, 802.16m, and so on.

According to some embodiments, the base station 102 controls radio resource allocation and assignment, while the mobile station 104 is configured to decode and interpret the allocation protocol. Such an embodiment may be employed, for example, in a system where multiple mobile stations 104 share the same wireless channel controlled by one base station 102. However, in alternative embodiments, the mobile station 104 controls the allocation of radio resources for a particular link and may implement the role of a radio resource controller or allocator, as described herein.

The processor module 116/122 may be implemented or realized with a general purpose processor, a content addressable memory, a digital signal processor, an application specific integrated circuit, a field programmable gate array, any suitable programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. In this manner, the processor may be implemented as a microprocessor, controller, microcontroller, state machine, or the like. A processor may also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a digital signal processor core, or any other such configuration. The processor module 116/122 includes processing logic configured to perform functions, techniques, and processing tasks related to the operation of the system 100. In particular, the processing logic is configured to support the frame structure parameters described herein. In a practical implementation, the processing logic may be present at the base station and/or may be part of a network architecture that communicates with the base transceiver station 103.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in firmware, in a software module executed by the processor module 116/122, or in any practical combination thereof. A software module may reside in memory module 118/120 which may be implemented as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In this regard, memory module 118/120 may be separately coupled to processor module 118/122 such that processor module 116/120 may read information from, and write information to, memory module 118/120. As an example, processor module 116 and memory module 118, processor module 122 and memory module 120 may reside in respective ASICs. The memory module 118/120 may also be integrated with the processor module 116/120. In one embodiment, memory module 118/220 may include a cache memory for storing temporary variables or other intermediate information during execution of instructions to be executed by processor module 116/222. Memory module 118/120 may also include non-volatile memory for storing instructions to be executed by memory module 116/120.

According to an example embodiment of the invention, memory module 118/120 may include a frame structure database (not shown). The frame structure parameter database may be configured to store, maintain, and provide data needed to support the functions of the system 100 in the manner described below. Further, the frame structure database may be a local database coupled to the processor 116/122, or may be a remote database, such as a central network database or the like. The frame structure database may be configured to maintain, but is not limited to, frame structure parameters as explained below. In this manner, the frame structure database may include a look-up table for storing frame structure parameters.

The network communication module 126 generally refers to hardware, software, firmware, processing logic, and/or other components of the system 100 that allow two-way communication between the base station transceiver 103 and the network components to which the base station transceiver 103 is connected. For example, the network communication module 126 may be configured to support internet or WiMAX traffic. In a typical deployment, but not limited to, the network communication module 126 provides an 802.3 ethernet interface so that the base station transceiver 103 can communicate with a conventional ethernet-based computer network. In this manner, the network communication module 126 may include a physical interface (e.g., a Mobile Switching Center (MSC)) for connecting to a computer network.

Note that the functions described in this disclosure may be performed by either the base station 102 or the mobile station 104. The mobile station 104 may be any user equipment such as a mobile phone, and the mobile station may also be referred to as a UE.

The embodiments disclosed herein have particular application, but are not limited to, Long Term Evolution (LTE) systems, which are one of the candidates for 4 th generation wireless systems. According to one embodiment, for 3GPP LTE-a, for example, CSI-RS may be carried by one or more CRS-free symbols in the non-PDCCH region of a standard or MBSFN subframe. In some embodiments, the CSI-RS may not insert Resource Elements (REs) already occupied by Rel-8PSS/SSS or PBCH. According to an example embodiment, it may also be possible to prevent CSI-RS from interfering with, for example, SIB1 transmitted at subframe #5 and PCH that may be transmitted on any subframe from a configured subset or full set of all non-MBSFN capable subframes. Accordingly, one of ordinary skill in the art will recognize that there may be a variety of options for the locations available for CSI-RS transmission. The following are various exemplary options:

exemplary options-a:

according to one embodiment, the CSI-RS may be transmitted in a downlink subframe configured as an MBSFN subframe, such that the CSI-RS is not transmitted on, for example, subframe {0, 4, 5, 9} for FDD and subframe {0, 1, 5, 6} for TDD. According to this embodiment, there may be more available REs per PRB, providing a larger reuse factor for CSI-RS. The CSI-RS may be collision-free with the basic system signal and the common control channel.

However, MBSFN subframes may retain most of the system resources that are not available for Rel-8 PDSCH. There may be a limited number of MBSFN subframes in some TDD uplink-downlink allocations (e.g., TDD allocation #0) or even no MBSFN subframes that may be configured for CSI-RS transmission.

Exemplary option-b:

according to one embodiment, the CSI-RS may not be transmitted on subframes {0, 4, 5, 9} for FDD and subframes {0, 1, 5, 6} for TDD, but example option-b allows the CSI-RS to be transmitted in downlink subframes where MBSFN can but not be configured as MBSFN subframes.

Thus, the system-wide resource pool for the Rel-8PDSCH is not affected. The CSI-RS does not collide with the basic system signal and the common control channel. However, with subframes {0, 1, 5, 6} excluded, there may be a limited number or even no downlink subframes available for CSI-RS transmission in some TDD uplink-downlink allocations (e.g., TDD allocation # 0).

Exemplary option-c:

according to one embodiment, CSI-RS may be transmitted in any downlink subframe in FDD and TDD, and in case of collision with REs used by PSS/SSS/PBCH/SIB 1/paging, CSI-RS on this RE is not transmitted or its resource allocation avoids simultaneous PSS/SSS/PBCH/SIB 1/paging. That is, the REs may be reallocated to another resource not used by PSS/SSS/PBCH/SIB 1/paging.

According to this embodiment, CSI-RS transmission is possible in all TDD allocations. However, if there is a collision with PSS/SSS/PBCH/paging, the CSI-RS may be lost, which may be periodic or even constant for CSI-RS within e.g. six central PRBs, in case the CSI-RS period equals 10 ms. Note that collisions with PSS/SSS may be avoided, for example, if CSI-RS is not transmitted on symbols that may carry, for example, Rel-10 DMRS.

The UE may need to search for and decode a PDCCH with either SI-RNTI or P-RNTI to determine the resources allocated for SIB1 and PCH before measuring the intra-cell CSI-RS in the corresponding subframe. However, it may be difficult for the UE to know the collision situation between the CSI-RS and the SIB1/PCH in the neighboring cell, for example, if the UE needs to measure the CSI-RS inside the cell.

Exemplary option-d:

according to one embodiment, in addition to the subframe transmitting SIB1 and PCH, CSI-RS may be transmitted on any subframe in FDD and TDD, and in case of collision with REs used by PSS/SSS/PBCH, CSI-RS on this RE may not be transmitted or its resource allocation may avoid all PSS/SSS/PBCH. That is, the REs may be reallocated to another resource not used by the PSS/SSS/PBCH.

According to this embodiment, exemplary option-d makes it possible for the UE to measure CSI-RS in the neighboring cell, compared to exemplary option-c. However, the UE may still need to know the Paging Occasion (PO) configuration in the neighboring cell to avoid measuring non-existent cell-internal CSI-RS in subframes carrying PCH in the neighboring cell.

According to design features, of the above four exemplary options, option-b and option-d may be better choices for FDD, and option-d may be better choices for TDD.

In option-b, for example, CSI-RS may be transmitted on downlink MBSFN capable subframes {1, 2, 3, 6, 7, 8} for FDD and downlink MBSFN possible subframes {3, 4, 7, 8, 9} for TDD. Within these subframes, the resources available for CSI-RS transmission in each PRB are shown by the blank REs in fig. 2, and according to this embodiment, the count Z is 60 REs per PRB if the CSI-RS and DMRS can be transmitted on the same symbol, or 36 REs per PRB if the CSI-RS and DMRS cannot be transmitted on the same symbol.

In option-d, for example, any MBSFN-capable downlink subframes in both FDD and TDD may be used for CSI-RS transmission, regardless of whether any of these subframes are configured as MBSFN subframes. For these subframes, the number of REs in each PRB available for CSI-RS transmission may be the same as for option-b (see fig. 2), and Z60 and Z36 are given depending on whether CSI-RS and DMRS may be placed on the same symbol. For non-MBSFN capable subframes, exemplary possible collisions between CSI-RS and PSS/SSS/PBCH are summarized as follows:

potential collisions with PSS/SSS/PBCH in FDD may occur on the six central PRBs on subframe #0 as shown in fig. 3, for example. Figure 3 depicts physical resource blocks in subframe #0 with CRS, PSS/SSS and PBCH in FDD according to an embodiment. There may be 36 REs available for CSI-RSS transmission.

Potential collisions with PSS/SSS/PBCH in FDD may occur in the six central PRBs in subframe #0 as shown in fig. 4. Fig. 4 depicts physical resource blocks in subframe #0 with CRS, SSS and PBCH in TDD according to an embodiment. However, according to this embodiment, since subframe #0 always carries a potential subframe for PCH, CSI-RS may not be recommended to be transmitted, for example, on subframe #0 in TDD.

According to one embodiment, other non-MBSFN capable subframes in option-d that allow CSI-RS transmission may have the same resource availability as shown in fig. 2.

The REs may be divided into groups containing the same number (N) of REs according to the number and pattern of free REs available for CSI-RS transmission. Each group may contain N adjacent free REs or N separate free REs, and one CSI-RS RE may be maintained for one port per cell. Thus, is calculated as G_MAXThe maximum total number of groups Z/N may not be less than the total number of CSI-RS antenna ports per cell. Assuming that the cell identity (PCID) in LTE Rel-8 has modulo-6 operation on CRS position discrimination and a typical cellular arrangement has three cells adjacent to each other, N may be 6 or 3 according to this exemplary embodiment.

Exemplary shapes and sizes of CSI-RS RE groups with N ═ {3, 6} adjacent REs are shown in fig. 5. As depicted in fig. 5, different REs in each group may be allocated to CSI-RS ports from different cells.

Fig. 6 depicts a physical resource block with CRS and DMRS for N-3, according to one embodiment. Fig. 7 depicts physical resource blocks in subframe #0 with CRS, PSS/SSS and PBCH in FDD for N-3, according to an embodiment. As shown in fig. 6 and 7, if N ═ 3, then for the normal non-MBSFN capable subframe and subframe #0 in FDD, respectively, each adjacent RE may construct one CSI-RS RE group.

Fig. 8A and 8B illustrate an exemplary option for an N-6 allocation of physical resource blocks with CRS and DMRS, according to one embodiment. Fig. 9A and 9B illustrate an exemplary option for allocation of physical resource blocks in subframe #0 with CRS, PSS/SSS and PBCH in N-6 FDD according to one embodiment. As shown in fig. 8A-8B and 9A-9B, if N is 6, for example, every 6 neighboring REs may construct one CSI-RS RE group for a normal non-MBSFN capable subframe and subframe #0 in FDD, respectively. Further, according to exemplary embodiments, as shown in fig. 8A-8B and 9A-9B, there may be two options to define each set of six "adjacent" REs.

Note that this disclosure does not limit the value of N. Other values (e.g., 4, 8) are also within the scope of the present disclosure. Also, fig. 6-9 only show exemplary configurations of CSI-RS RE groups. Note that each set of N REs may be adjacent to each other or separated from each other. The indices of the CSI-RS RE groups also need not be in the order as shown in fig. 6-9, but for example, the indices may be the same on all PRBs in the same type of subframe.

In addition, not every CSI-RS RE group is necessary to carry CSI-RS. The actual number of CSI-RS RE groups is denoted as G: g is less than or equal to G_MAX. For example, CSI-RS RE groups that share the same time symbols as the DMRS may not be used for, e.g., CSI-RS transmissions. In this case, the number of CSI-RS RE groups G may be equal to 36/N.

It is assumed, for example, that DMRS REs may or may not be used with CSI-RS REs in the same symbol, and that this is the only type of RE with such uncertainty. According to the present embodiment, it may also be assumed that the CSI-RS supports CSI measurements on 8 antenna ports. Then, the design parameters G and N can be found in table 2.

Table 2: exemplary design parameters for CSI-RS RE allocation

Given: g (i.e., the total number of CSI-RS RE groups available to the CSI-RS) must satisfy G ≧ N_ANT(wherein N is_ANTIs the total number of CSI-RS antenna ports in a single cell), and N (i.e., the total number of available REs in each CSI-RS RE group), the kth CSI-RS port in a cell whose cell identity is PCID (0 ≦ k < N)_ANT) Is allocated to the jth RE in the ith CSI-RS RE group of the G total CSI-RS RE groups (0 ≦ j < N). Here, 0 ≦ i < G is assumed. The mapping function may be designed in such a way that:

for the mapping function f:<k，PCID；G，N>→ i since each cell has N_ANTThe fact that ≦ G CSI-RS antenna ports, the function f should be able to:

mapping different < k, PCID > s having the same PCID to different i; and

multiple < k, PCID > s with different PCIDs are mapped to the same i, and such mapping can be made uniform, which may mean that the mapping is pseudo-random.

A simple and straightforward mapping structure is given by f (k, PCID; G, N) ═ k + pseudo _ random (PCID) mod G, where mod represents the modulo operation, and pseudo _ random (PCID) is any random number generating function with a generating seed equal to the integer PCID.

For the mapping function g: < k, PCID; g, N > → j, since each cell associated with one CSI-RS RE group may have only one CSI-RS RE in the group and it does not necessarily correspond to a particular CSI-RS port, the index k may be deleted from the function parameter list, and at the same time it may be preferred to have as much inter-cell orthogonality as possible in each CSI-RS RE group, so the function G may map the PCID uniformly within the N REs per CSI-RS RE group. One exemplary mapping function is given by G (PCID; G, N) ═ PCID mod N, where mod stands for the modulo operation.

CSI-RS hopping is applicable to CSI-RS RE allocation, which means that CSI-RS REs for antenna port k of cell X may have different RE positions at different transmission time points. Such hopping may be performed in units of one CSI-RS period or a plurality of CSI-RS periods, e.g., by either intra-group hopping or inter-group hopping, or a combination of both.

For intra-group hopping, the mapping function f is not necessarily included in the hopping process; the mapping function g may for example take into account time domain jumping points. For example, the modified function G with hopping is G (PCID, T; G, N) ═ PCID + hop (T)) mod N, where hop (T) is the hopping function that converts the hopping time points into integers.

For inter-group hopping, the mapping function g is not necessarily included in the hopping process; the mapping function f may take into account time-domain jumping points. For example, the modified function f of band hopping is f (k, PCID, T; G, N) [ k + pseudo _ random (PCID) + hop (T) ] mod G, where hop (T) is a hopping function that converts the hopping time points into integers.

In some implementations of the CSI-RS allocation methods described herein, the CSI-RS RE groups may not be explicitly defined. The CSI-RS RE allocation for the kth antenna port of the cell whose cell identity is the PCID may be directly mapped to one RE in the PRB. In this case, the concept of CSI-RS REs may be mentioned implicitly, and for example, the target RE index between all available REs per PRB may be calculated as: n f (k, PCID; G, N) + G (PCID; G, N).

In the example shown in the above-described figure, the CSI-RS RE group includes REs adjacent to each other. However, embodiments of this disclosure allow REs in each CSI-RS RE group to be spaced apart in a PRB. From a mathematical point of view, there are various ways to index or order all R E in one PRB that are available for CSI-RS transmission. For the same reason, the index of the CSI-RS RE group in the PRB throughout fig. 5-8 is also for example purposes only and is not intended to limit the scope of the present disclosure. One of ordinary skill in the art will recognize that different indexing and ordering methods may be utilized.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Likewise, the various figures may depict example architectures or other configurations for the disclosure, which are done to aid in understanding the features and functionality that may be included in the disclosure. The present disclosure is not limited to the example architectures or configurations shown, but can be implemented using a variety of alternative architectures and configurations. In addition, while the present disclosure has been described above in terms of various exemplary embodiments and implementations, it is to be understood that the various features and functions described in one or more of the individual embodiments are not limited in their application to the particular embodiments in which they are described. They may instead be applied, alone or in some combination, to one or more other embodiments of the disclosure, whether or not such embodiments are described, and whether or not such features are presented as part of the described embodiments. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments.

In this document, the term "module" as used herein refers to software, firmware, hardware, and any combination of these elements for performing the relevant functions described herein. Further, for purposes of discussion, the various modules are described as discrete modules, however, as will be apparent to one of ordinary skill in the art, two or more modules may be combined to form a single module that performs the associated functions in accordance with embodiments of the present invention.

In this document, the terms "computer program product," "computer-readable medium," and the like may be used generally to refer to media such as memory storage devices or storage units. These and other forms of computer-readable media may be involved in storing one or more instructions for use by a processor to cause the processor to perform specified operations. Such instructions, generally referred to as "computer program code" (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system.

It will be appreciated that for clarity, the above description has described embodiments of the invention with reference to different functional units and processors. It will be apparent, however, that any suitable distribution of functionality between different functional units, processors or domains may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed in an open-ended sense as opposed to a limitation. As examples described above: the term "comprising" should be read as "including, but not limited to" or the like; the term "example" is used to provide an illustrative example of the term in question, and not an exclusive or limiting list thereof; and adjectives such as "conventional," "traditional," "conventional," "standard," "known," and terms of similar meaning should not be construed as limiting the described term to a given time period or to a term that is available at a given time. But rather these terms should be read to encompass conventional, traditional, normal, or standard or currently available or known technologies at a future time. Likewise, a group of terms linked with the conjunction "and" should not be read as requiring that each and every one of those terms be present in the group, but rather should be read in the meaning of "and/or" unless expressly stated otherwise. Likewise, a group of terms linked with the conjunction "or" should not be read as requiring mutual exclusivity among that group, but rather should be read in the meaning of "and/or" unless expressly stated otherwise. Furthermore, although items, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated. The presence of expansion words and phrases such as "one or more," "at least," "but not limited to," or other like phrases in some instances should not be construed to mean that the narrower case is intended or required in instances where such expansion phrases may not be present.

In addition, memory or other storage and communication components may be used in embodiments of the present invention. It will be appreciated that for clarity, the above description has described embodiments of the invention with reference to different functional units and processors. It will be apparent, however, that any suitable distribution of functionality between different functional units, processing logic units, or domains may be used without detracting from the invention. For example, illustrated functions performed by separate processing logic units or controllers may be performed by the same processing logic unit or controller. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processing logic unit. Furthermore, although individual features may be included in different claims, these may possibly be advantageously combined. The inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Furthermore, the inclusion of a feature in one category of claims does not imply that the feature is limited to this category and that the feature may be equally applicable to other claim categories, as appropriate.

Claims (31)

1. A method of allocating resource elements in an Orthogonal Frequency Division Multiplexing (OFDM) system for transmission of a channel state information reference signal (CSI-RS), the method comprising:

converting one or more resource units into a two-dimensional frequency-time domain;

dividing the one or more converted resource units into units of Physical Resource Blocks (PRBs);

determining whether at least a portion of a PRB is being used by a signal; and

allocating the at least a portion of the PRB for transmission of the CSI-RS if the at least a portion of the PRB is not currently used.

2. The method of claim 1, wherein a time-domain size of one PRB is one subframe.

3. The method of claim 1, further comprising:

transmitting the CSI-RS at resource element locations determined by resource elements available to the CSI-RS in a regular downlink subframe that includes at least one of a cell-specific reference signal (CRS), a Physical Downlink Control Channel (PDCCH), and a demodulation reference signal (DMRS).

4. The method of claim 1, further comprising:

transmitting the CSI-RS at resource element locations determined by resource elements available to the CSI-RS in a frequency division multiplexing (FDD) downlink subframe, the FDD downlink subframe including a CRS, a PDCCH, a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), and a DMRS.

5. The method of claim 3, further comprising:

transmitting the CSI-RS in a downlink subframe configured as a multimedia broadcast over a single frequency network (MBSFN) subframe.

6. The method of claim 3, further comprising:

transmitting the CSI-RS in a downlink subframe configured as a regular non-MBSFN subframe.

7. The method of claim 4, further comprising:

transmitting the CSI-RS in a downlink subframe configured as an MBSFN subframe.

8. The method of claim 4, further comprising:

transmitting the CSI-RS in a downlink subframe configured as a regular non-MBSFN subframe.

9. The method of claim 3, further comprising:

cancelling the transmission over an entire bandwidth in a subframe in which the CSI-RS collides with resource elements used by at least one of a PSS, a SSS, a Physical Broadcast Channel (PBCH), a system information block type-1 (SIB1), and paging.

10. The method of claim 3, further comprising:

cancelling the CSI-RS for the transmission on a particular resource element in which the CSI-RS collides with a resource element used by at least one of a PSS, a SSS, and a PBCH.

11. A station configured for allocating resource elements in an Orthogonal Frequency Division Multiplexing (OFDM) system for transmission of a channel state information reference signal (CSI-RS), the station comprising:

a conversion unit configured to convert one or more resource units into a two-dimensional frequency-time domain;

a dividing unit configured to divide the one or more converted resource units into units of Physical Resource Blocks (PRBs);

a determining unit configured to determine whether at least a portion of a PRB is being used by a signal; and

an allocation unit configured to allocate the at least a portion of the PRB for transmission of the CSI-RS if the at least a portion of the PRB is not currently used.

12. The station of claim 11, wherein a time-domain size of one PRB is one subframe.

13. The station of claim 11, further comprising:

a transmitter configured to transmit the CSI-RS at resource element locations determined by resource elements available to the CSI-RS in a regular downlink subframe that includes at least one of a cell-specific reference signal (CRS), a Physical Downlink Control Channel (PDCCH), and a demodulation reference signal (DMRS).

14. The station of claim 11, further comprising:

a transmitter configured to transmit the CSI-RS at resource element locations determined by resource elements available to the CSI-RS in a frequency division multiplexing (FDD) downlink subframe comprising a CRS, a PDCCH, a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), and a DMRS.

15. The station of claim 13, further comprising:

a transmitter configured to transmit the CSI-RS in a downlink subframe configured as a multimedia broadcast over a single frequency network (MBSFN) subframe.

16. The station of claim 13, further comprising:

transmitting the CSI-RS in a downlink subframe configured as a regular non-MBSFN subframe.

17. The station of claim 14, further comprising:

a transmitter configured to transmit the CSI-RS in a downlink subframe configured as an MBSFN subframe.

18. The station of claim 14, further comprising:

a transmitter configured to transmit the CSI-RS in a downlink subframe configured as a regular non-MBSFN subframe.

19. The station of claim 13, further comprising:

a cancellation unit configured to cancel the transmission over an entire bandwidth in a subframe in which the CSI-RS collides with resource elements used by at least one of a PSS, a SSS, a Physical Broadcast Channel (PBCH), a system information block type-1 (SIB1), and paging.

20. The station of claim 19, further comprising:

a cancellation unit configured to cancel the CSI-RS for the transmission on a particular resource element in which the CSI-RS collides with a resource element used by at least one of a PSS, a SSS, and a PBCH.

21. The station of claim 11, wherein the station is a base station.

22. A non-transitory computer-readable recording medium storing instructions thereon for performing, when executed by a processor, a method of allocating resource elements for transmission of a channel state information reference signal (CSI-RS) in an Orthogonal Frequency Division Multiplexing (OFDM) system, the method comprising:

converting one or more resource units into a two-dimensional frequency-time domain;

dividing the one or more converted resource units into units of Physical Resource Blocks (PRBs);

determining whether at least a portion of a PRB is being used by a signal; and

allocating the at least a portion of the PRB for transmission of the CSI-RS if the at least a portion of the PRB is not currently used.

23. The computer-readable recording medium of claim 22, wherein the time-domain size of one PRB is one subframe.

24. The computer-readable recording medium of claim 22, the method further comprising:

transmitting the CSI-RS at resource element locations determined by resource elements available to the CSI-RS in a regular downlink subframe that includes at least one of a cell-specific reference signal (CRS), a Physical Downlink Control Channel (PDCCH), and a demodulation reference signal (DMRS).

25. The computer-readable recording medium of claim 22, the method further comprising:

transmitting the CSI-RS at resource element locations determined by resource elements available to the CSI-RS in a frequency division multiplexing (FDD) downlink subframe, the FDD downlink subframe including a CRS, a PDCCH, a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), and a DMRS.

26. The computer-readable recording medium of claim 24, the method further comprising:

transmitting the CSI-RS in a downlink subframe configured as a multimedia broadcast over a single frequency network (MBSFN) subframe.

27. The computer-readable recording medium of claim 24, the method further comprising:

transmitting the CSI-RS in a downlink subframe configured as a regular non-MBSFN subframe.

28. The computer-readable recording medium of claim 25, the method further comprising:

transmitting the CSI-RS in a downlink subframe configured as an MBSFN subframe.

29. The computer-readable recording medium of claim 25, the method further comprising:

transmitting the CSI-RS in a downlink subframe configured as a regular non-MBSFN subframe.

30. The computer-readable recording medium of claim 24, the method further comprising:

cancelling the transmission over an entire bandwidth in a subframe in which the CSI-RS collides with resource elements used by at least one of a PSS, a SSS, a Physical Broadcast Channel (PBCH), a system information block type-1 (SIB1), and paging.

31. The computer-readable recording medium of claim 30, the method further comprising:

cancelling the CSI-RS from the transmission on a particular resource element in which the CSI-RS collides with resource elements used by at least one of a PSS, a SSS, a PBCH, a system SIB1, and paging.