Abstract:
There is disclosed method for reporting channel state so as to report channel state based upon CSI-RS. The method includes: a UE detecting configuration information of Channel State Information-Reference Signal (CSI-RS), determining according to detection result the number of ports required to report channel state based upon CSI-RS, the UE determining CSI-RS based PMI feedback scheme to be adopted in preset corresponding relationship between the number of ports and feedback scheme upon determining that the eNB is to map data of Physical Downlink Shared Channel (PDSCH) onto P (number) CSI-RS ports for transmission in a codebook-based precoding scheme, wherein the codebook-based precoding scheme is a scheme as represented in the formula of 
                 [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     =     W   ·   s       ,         
wherein W represents a codebook consisted of a precoding matrix, S is PDSCH data consisted of data layers whose quantity is equal to value of Rank Indication (RI) and
 
                   [           y     (   0   )               ⋮             y     (     P   -   1     )             ]           
represents a vector consisted of data on P (number) CSI-RS ports; and the UE calculating and reporting channel state information according to the determination result. The invention further discloses apparatus for performing the method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a U.S. National Stage under 35 U.S.C. §371 of International Application No. PCT/CN2011/083218, filed on Nov. 30, 2011, entitled METHOD AND DEVICE FOR REPORTING CHANNEL STATE, designating the United States and claiming the benefit of Chinese Patent Application No. 201010569722.0, filed with the Chinese Patent Office on Dec. 2, 2010 and entitled “Method and Apparatus for Reporting Channel State”, which is hereby incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of communications and particularly to method and apparatus for reporting channel state. 
     BACKGROUND OF THE INVENTION 
     Channel quality information is important base for the network side to perform a variety of adaptive adjusting and scheduling. Channel quality is quantized in Long Term Evolution (LTE) into 4-bit Channel Quality Indicator (CQI) each with an index corresponding to combination of a modulation scheme and a coding rate. To calculate CQI, a UE has to assume transmission scheme of Physical Downlink Shared Channel (PDSCH) in view of its transmission mode. For example, transmission schemes of PDSCH are assumed as illustrated in  FIG. 1  for calculation of CQI defined in LTE Release (Rel-9). 
     In each of the Transmission Modes (TMs) 4 to 6, a User Equipment (UE) has to calculate from detection of Cell-specific Reference Signal (CRS) and report its recommended Precoding Matrix Indicator (PMI), and the UE reports CQI assuming an evolved Node B (eNB) uses its reported PMI. In the TM7, a non-codebook precoding scheme is adopted, and the UE only reports CQI to the eNB, and the eNB calculates a precoding or shaping vector. In the TM8, both PMI and non-PMI feedback schemes can be supported, and the UE can generates report parameter (PMI/Rank Indication (RI)/CQI or CQI) from detection of CRS in a high-layer configured feedback scheme and specific report mode. 
     In a Long Term Evolution-Advanced (LTE-A) system, newly defined Channel State Information-Reference Signal (CSI-RS) is introduced so as to support higher-order Multiple-Input Multiple-Output (MIMO) transmission (support up to 8 data layers) as well as a multi-cell joint processing function in a subsequent release. In the TM9, a Demodulation Reference Signal (DMRS) based demodulation scheme is adopted, and CSI-RS only functions for detection instead of demodulation. Like the TM8, the eNB can configure in high-layer signaling a report mode of the UE as the PMI or non-PMI form. In the TM9, the UE configured without PMI reporting reports CQI based upon CRS, while the UE configured with PMI reporting has to generate CQI/PMI/RI or other report information from detection of CSI-RS. In this case, with the absence of a CSI-RS based feedback scheme, the UE calculating CQI can not assume which CSI-RS based transmission scheme is adopted for PDSCH and consequently can not report channel state based upon CSI-RS when calculating CQI. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention provide method and apparatus for reporting channel state so as to report channel state based upon CSI-RS. 
     A method for reporting channel state includes the steps of: 
     a UE detecting configuration information of Channel State Information-Reference Signal, CSI-RS; 
     the UE determining according to detection result the number of ports required to report channel state based upon CSI-RS; 
     the UE determining CSI-RS based Precoding Matrix Indicator (PMI) feedback scheme to be adopted by the UE according to the determined number of ports and preset corresponding relationship between the number of ports and feedback scheme upon determining that the eNB is to map data of Physical Downlink Shared Channel (PDSCH) onto P (number) CSI-RS ports for transmission in a codebook-based precoding scheme, wherein the codebook-based precoding scheme is a scheme as represented in the formula of 
                 [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     =     W   ·   s       ,         
wherein W represents a codebook consisted of a precoding matrix, S is PDSCH data consisted of data layers whose quantity is equal to value of Rank Indication (RI) and
 
                   [           y     (   0   )               ⋮             y     (     P   -   1     )             ]           
represents a vector consisted of data on P (number) CSI-RS ports; and
 
     the UE calculating and reporting channel state information according to the determination result. 
     A user equipment includes: 
     a detection module configured to detect configuration information of Channel State Information-Reference Signal (CSI-RS); 
     a ports quantity module configured to determine according to detection result the number of ports required to report channel state based upon CSI-RS; 
     a transmission mode module configured to determine CSI-RS based Precoding Matrix Indicator (PMI) feedback scheme to be adopted by the UE according to the determined number of ports and preset corresponding relationship between the number of ports and feedback scheme upon determining that the eNB is to map data of Physical Downlink Shared Channel (PDSCH) onto P (number) CSI-RS ports for transmission in a codebook-based precoding scheme, wherein the codebook-based precoding scheme is a scheme as represented in the formula of 
                 [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     =     W   ·   s       ,         
wherein W represents a codebook consisted of a precoding matrix, S is PDSCH data consisted of data layers whose quantity is equal to value of Rank Indication (RI) and
 
                   [           y     (   0   )               ⋮             y     (     P   -   1     )             ]           
represents a vector consisted of data on P (number) CSI-RS ports; and
 
     a report module configured to calculate and report channel state information according to the determination result. 
     In the embodiments of the invention, a UE determines a corresponding feedback scheme according to the number of ports required to report channel state based upon CSI-RS and reports channel state information according to the determined feedback scheme to thereby address the problem in the prior art of failing to report channel state information because a transmission scheme to be adopted by an eNB can not be determined based upon CSI-RS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of relationship between a transmission scheme and a numbered transmission mode in the prior art; 
         FIG. 2  is a flow chart of a general method for reporting channel state according to an embodiment of the invention; 
         FIG. 3  is a flow chart of a method for reporting channel state information in non-PMI feedback scheme according to an embodiment of the invention; 
         FIG. 4  is a flow chart of a method for reporting channel state information in CSI-RS based PMI feedback scheme according to an embodiment of the invention; and 
         FIG. 5  is a structural diagram of a UE according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In embodiments of the invention, a UE determines a corresponding feedback scheme according to the number of ports required to report channel state based upon CSI-RS and reports channel state information according to the determined feedback scheme to thereby address the problem in the prior art of failing to report channel state information because a transmission scheme to be adopted by an eNB can not be determined based upon CSI-RS. 
     Referring to  FIG. 2 , a flow chart of a general method for reporting channel state information according to an embodiment of the invention is as follows: 
     Step  201 : A UE detects configuration information of CSI-RS. 
     Step  202 : The UE determines according to detection result the number of ports required to report channel state based upon CSI-RS, where the configuration information of CSI-RS includes the number of ports, and the UE can obtain the number of ports from detection of the configuration information. 
     Step  203 : The UE determines a feedback scheme to be adopted according to the determined number of ports and preset corresponding relationship between the number of ports and feedback scheme. 
     Step  204 : The UE calculates and reports channel state information according to the determined feedback scheme. 
     Particularly when the number of ports required to report channel state based upon CSI-RS is equal to 1, the UE assumes that the eNB transmits over PDSCH via a single-antenna port (e.g., the port 0) without using a codebook, so the UE adopts non-PMI feedback scheme. When the number P of ports required to report channel state based upon CSI-RS is larger than 1, the UE assumes that the eNB is to map data of PDSCH onto P (number) CSI-RS ports in a codebook-based precoding scheme using a codebook, so the UE adopts a CSI-RS based PMI feedback scheme. Preferably the codebook-based precoding scheme is a scheme as represented in the formula of 
                 [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     =     W   ·   s       ,         
where W is a P×RI-dimension matrix representing a codebook consisted of a precoding matrix, particularly a codebook consisted of a precoding matrix selected from those defined in Rel-10, S is PDSCH data consisted of RI data layers, RI is a rank Indication reported by the UE, and
 
                   [           y     (   0   )               ⋮             y     (     P   -   1     )             ]           
represents a vector consisted of data on P (number) CSI-RS ports.
 
     Specifically the UE determines that the eNB is to map the PDSCH data onto the P (number) CSI-RS ports for transmission in a scheme of 
               [             a   ~       k   ,   l       (   15   )               ⋮               a   ~       k   ,   l       (     14   +   υ     )             ]     =     W   ⁡     [           a     k   ,   l       (   7   )               ⋮             a     k   ,   l       (     6   +   υ     )             ]             
and also that the eNB is to map DMRS onto the P (number) CSI-RS ports for transmission in the same scheme, where
 
                   [             a   ~       k   ,   l       (   15   )               ⋮               a   ~       k   ,   l       (     14   +   υ     )             ]           
represents
 
                     [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     ,     [           a     k   ,   l       (   7   )               ⋮             a     k   ,   l       (     6   +   υ     )             ]             
represents S,            (         =15, . . . 14+v) represents symbol transmitted over the k-th subcarrier in the l-th OFDM symbol via the p-th CSI-RS port, a k,l   (p)  (p=7, . . . 6+v) represents PDSCH data or DMRS symbol over the k-th subcarrier in the l-th OFDM symbol via the p-th port, and v represents the number of layers of PDSCH, where the UE determines that the eNB will use PMI/RI recommended by the UE in the above mentioned mapping process, and the PMI/RI corresponds to the precoding matrix W in the codebook.

     Due to a variety of feedback schemes, a report process will be introduced below in details for each feedback scheme in two embodiments. 
     Referring to  FIG. 3 , a flow chart of a method for reporting channel state information in non-PMI feedback scheme according to this embodiment is as follows: 
     Step  301 : A UE obtains configuration information of CSI-RS from system broadcast after accessing a network, where the configuration information includes time and frequency locations, period, the number of ports, etc. 
     Step  302 : The UE detects the configuration information of CSI-RS and obtains a channel transmission matrix 
               H   =     [           h   11         ⋯         h     1   ⁢   T               ⋮       ⋱       ⋮             h     R   ⁢           ⁢   1           ⋯         h   RT           ]       ,         
where h ij  represents coefficient of channel transmission between the j-th transmission antenna and the i-th reception antenna, and R and T are the numbers of reception antennas and transmission antennas respectively. In the meantime the UE can detect received interference and noise.
 
     Step  303 : The UE determines according to detection result of the step S 301  the number of ports required to report channel state based upon CSI-RS as 1. 
     Step  304 : The UE determines according to the number of ports being equal to 1 that the eNB will transmit over PDSCH via a single-antenna port. 
     Step  305 : The UE determines non-PMI feedback scheme according to the determined behavior of the eNB to transmit over PDSCH via a single-antenna port. 
     Step  306 : The UE calculates and reports CQI in the non-PMI feedback scheme, particularly calculates and reports CQI for each report unit in the frequency domain (e.g., wideband or subband). Since no codebook is required at this time, simply CQI will be reported. 
     Referring to  FIG. 4 , a flow chart of a method for reporting channel state information in CSI-RS based PMI feedback scheme according to this embodiment is as follows: 
     Step  401 : A UE obtains configuration information of CSI-RS from system broadcast after accessing a network. 
     Step  402 : The UE detects the configuration information of CSI-RS and obtains a channel transmission matrix 
             H   =       [           h   11         ⋯         h     1   ⁢   T               ⋮       ⋱       ⋮             h     R   ⁢           ⁢   1           ⋯         h   RT           ]     .           
In the meantime the UE can detect received interference and noise.
 
     Step  403 : The UE determines according to detection result of the step S 401  the number of ports required to report channel state based upon CSI-RS to be larger than 1. 
     Step  404 : The UE determines according to the number of ports being larger than 1 that the eNB will map data of PDSCH onto P (number) CSI-RS ports by 
                     [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     =     W   ·   s             
for transmission.
 
     Step  405 : The UE determines CSI-RS based PMI feedback scheme according to the determined behavior of the eNB. 
     Step  406 : The UE calculates and reports PMI for each report unit in the frequency domain CQI according to the CSI-RS based PMI feedback scheme, where the PMI represents an index in the codebook corresponding to W. 
     Step  407 : The UE calculates and reports RI for full bandwidth according to the CSI-RS based PMI feedback scheme. 
     Step  408 : The UE calculates and reports CQI, particularly calculates and reports CQI for each report unit in the frequency domain (e.g., wideband or subband), according to the CSI-RS based PMI feedback scheme and the calculated RI. When the RI is equal to 1, the UE calculates and reports one CQI in each report unit in the frequency domain, and when the RI is larger than 1, the UE calculates and reports CQI respectively for two codewords in each report unit in the frequency domain. 
     An implementation process of reporting channel state information has been learned from the foregoing description and this process is generally performed by a UE, and an internal structure and functions of the UE will be introduced below. 
     Referring to  FIG. 5 , the UE according to this embodiment includes a detection module  501 , a ports quantity module  502 , a transmission mode module  503  and a report module  504 . 
     The detection module  501  is configured to detect Channel State Information-Reference Signal (CSI-RS). The detection module  501  is further configured to obtain a channel transmission matrix 
             H   =       [           h   11         ⋯         h     1   ⁢   T               ⋮       ⋱       ⋮             h     R   ⁢           ⁢   1           ⋯         h   RT           ]     .           
In the meantime the detection module  501  is further configured to detect received interference and noise.
 
     The ports quantity module  502  is configured to determine according to detection result the number of ports required to report channel state based upon CSI-RS. 
     The transmission mode module  503  is configured to determine a feedback scheme to be adopted according to the determined number of ports and preset corresponding relationship between the number of ports and feedback scheme. The preset corresponding relationship between the number of ports and feedback scheme includes the number of ports being equal to 1 corresponding to non-PMI feedback scheme and the number of ports being larger than 1 corresponding to CSI-RS based PMI feedback scheme. The transmission mode module  503  determines according to the number of ports being equal to 1 that the eNB will transmit over PDSCH via a single-antenna port and further determines non-PMI feedback scheme; or the transmission mode module  503  determines according to the number of ports being larger than 1 that the eNB will map data of PDSCH onto P (number) CSI-RS ports for transmission in a codebook-based precoding scheme and further determines CSI-RS based PMI feedback scheme. The codebook-based precoding scheme includes a scheme represented in the formula of 
                 [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     =     W   ·   s       ,         
where W represents a codebook consisted of a precoding matrix, S is PDSCH data consisted of RI data layers, and
 
                   [           y     (   0   )               ⋮             y     (     P   -   1     )             ]           
represents a vector consisted of data on P (number) CSI-RS ports.
 
     Specifically the transmission mode module  503  determines that the eNB is to map the PDSCH data onto the P (number) CSI-RS ports for transmission in a scheme of 
               [             a   ~       k   ,   l       (   15   )               ⋮               a   ~       k   ,   l       (     14   +   υ     )             ]     =     W   ⁡     [           a     k   ,   l       (   7   )               ⋮             a     k   ,   l       (     6   +   υ     )             ]             
and also that the eNB is to map DMRS onto the P (number) CSI-RS ports for transmission in the same scheme, where
 
                   [             a   ~       k   ,   l       (   15   )               ⋮               a   ~       k   ,   l       (     14   +   υ     )             ]           
represents
 
               [           y     (   0   )               ⋮             y     (     P   -   1     )             ]     ,     [           a     k   ,   l       (   7   )               ⋮             a     k   ,   l       (     6   +   υ     )             ]           
represents S,             (         =15, . . . 14+v) represents symbol transmitted over the k-th subcarrier in the l-th OFDM symbol via the          -th CSI-RS port, a k,l   (p)  (p=7, . . . 6+v) represents PDSCH data or DMRS symbol over the k-th subcarrier in the l-th OFDM symbol via the p-th port, and v represents the number of layers of PDSCH, where the transmission mode module  503  determines that the eNB will use PMI/RI recommended by the UE in the above mentioned mapping process, and the PMI/RI corresponds to the precoding matrix W in the codebook.

     The report module  504  is configured to calculate and report channel state information according to the determined feedback scheme. When the determined feedback scheme is non-PMI feedback scheme, the reported channel state information includes Channel Quality Indicator (CQI), that is, the report module  504  calculates and reports CQI. When the determined feedback scheme is CSI-RS based PMI feedback scheme, the reported channel state information includes CQI, PMI and RI, that is, the report module  504  calculates and reports CQI, PMI and RI. Specifically when the determined feedback scheme is CSI-RS based PMI feedback scheme, the report module  504  calculates and reports PMI for each report unit in the frequency domain according to the CSI-RS based PMI feedback scheme, calculates and reports RI for full bandwidth according to the CSI-RS based PMI feedback scheme, and calculates and reports CQI according to the CSI-RS based PMI feedback scheme and the calculated RI. When the RI is equal to 1, the report module  504  calculates and reports one CQI in each report unit in the frequency domain, and when the RI is larger than 1, the report module  504  calculates and reports CQI respectively for two codewords in each report unit in the frequency domain. 
     The report module  504  includes a calculation unit and an interface unit. The calculation unit is configured to calculate the channel state information. The interface unit is configured to transmit the channels state information. The interface unit is further configured to obtain the configuration information of CSI-RS from system broadcast. 
     In the embodiments of the invention, a UE determines corresponding transmission mode according to the number of ports required to report channel state based upon CSI-RS and reports channel state information according to the determined feedback scheme to thereby address the problem in the prior art of failing to report channel state information because transmission scheme to be adopted by an eNB can not be determined based upon CSI-RS. The embodiments of the invention give a corresponding transmission mode, and particularly provide channel state information to be calculated and reported, for different number of ports. 
     Those skilled in the art shall appreciate that the embodiments of the invention can be embodied as a method, a system or a computer program product. Therefore the invention can be embodied in the form of an all-hardware embodiment, an all-software embodiment or an embodiment of software and hardware in combination. Furthermore the invention can be embodied in the form of a computer program product embodied in one or more computer useable storage mediums (including but not limited to a disk memory, an optical memory, etc.) in which computer useable program codes are contained. 
     The invention has been described in a flow chart and/or a block diagram of the method, the device (system) and the computer program product according to the embodiments of the invention. It shall be appreciated that respective flows and/or blocks in the flow chart and/or the block diagram and combinations of the flows and/or the blocks in the flow chart and/or the block diagram can be embodied in computer program instructions. These computer program instructions can be loaded onto a general-purpose computer, a specific-purpose computer, an embedded processor or a processor of another programmable data processing device to produce a machine so that the instructions executed on the computer or the processor of the other programmable data processing device create means for performing the functions specified in the flow(s) of the flow chart and/or the block(s) of the block diagram. 
     These computer program instructions can also be stored into a computer readable memory capable of directing the computer or the other programmable data processing device to operate in a specific manner so that the instructions stored in the computer readable memory create an article of manufacture including instruction means which perform the functions specified in the flow(s) of the flow chart and/or the block(s) of the block diagram. 
     These computer program instructions can also be loaded onto the computer or the other programmable data processing device so that a series of operational steps are performed on the computer or the other programmable data processing device to create a computer implemented process so that the instructions executed on the computer or the other programmable device provide steps for performing the functions specified in the flow(s) of the flow chart and/or the block(s) of the block diagram. 
     Evidently those skilled in the art can make various modifications and variations to the invention without departing from the spirit and scope of the invention. Thus the invention is also intended to encompass these modifications and variations thereto so long as the modifications and variations come into the scope of the claims appended to the invention and their equivalents.