Multi-user MIMO transmissions in wireless communication systems

Abstract

An apparatus and method for providing control information in a Multi User-Multiple Input Multiple Output (MU-MIMO) wireless communication system is provided. The method includes receiving a plurality of Resource Elements (REs) including downlink Control information (DCI), determining, using the DCI, a set of REs to which a plurality of downlink Reference signals (DRSs) may be mapped, determining remaining REs as REs to which data is mapped, and demodulating the data using a precoding vector of a DRS corresponding to the MS.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

In Equation (1), N_DRS indicates the total number of DRSs in the scheduled band. By using Eq. (1), the value of δ_power-offset will more accurately reflect situations in which there are three or more DRSs in a scheduled band. In an exemplary implementation, Eq. (1) may be used for any DCI format for MU-MIMO in which the total number of DRSs (which corresponds to total number of layers) is included. For example, Eq. (1) may be used with any of DCI format 1F, 1H, 2H, etc. where the field N_DRS or N_L is provided.

Sixth Exemplary Embodiment

In an exemplary embodiment of the present invention, a relationship for the power ratio between the data RE (per layer) and the DRS RE (per-layer), denoted as γ, is provided. As will be evidenced below, while the power ratio γ is applicable to all modulations, it is particularly applicable for 16QAM and 64QAM modulations. Moreover, the power ratio γ is applicable to both Single User (SU)-MIMO and MU-MIMO operations.

FIG. 18 is a flowchart illustrating a method of determining a power ratio γ according to an exemplary embodiment of the present invention.

Referring to FIG. 18, in step 1801, the MS determines the multiplexing that is used for DRS signaling. That is, the MS determines if either TDM or FDM, CDM, or a hybrid of CDM with TDM or FDM is used. If it is determined in step 1801 that either TDM or FDM is used for DRS signaling, the MS proceeds to step 1803 and determines if N_DRS is known. That is, the MS determines if the field N_DRS is provided in signaling received from the BS. If the MS determines in step 1803 that the field N_DRS is known, then the MS proceeds to step 1805 and sets the power ratio γ[dB]=−10 log₁₀(N_DRS). On the other hand, if the MS determines in step 1803 that the value of N_DRS is not known, then the MS proceeds to step 1807 and determines if M is known. That is, the MS determines if a value of M is provided from the BS in the DCI signaling or otherwise. If it is determined in step 1807 that the value of M is known, then the MS proceeds to step 1809 and sets the power ratio γ[dB]=−10 log₁₀(M). Alternatively, if it is determined in step 1807 that the value of M is not known by the MS, the MS proceeds to step 1811 and sets the power ratio γ[dB]=0 dB. In an alternative exemplary implementation, the BS may set the power ratio of γ[dB]=0 dB despite that the values of N_DRS and M are known. In that case, the BS would provide information regarding the power ratio γ[dB]=0 dB to the MS.

If it is determined in step 1801 that DRS signaling is made using pure CDM, that is, all DRS are CDMed together in the same set of REs, then the MS proceeds to step 1811 and sets the power ratio γ[dB]=0 dB.

Lastly, if it is determined in step 1801 that DRS signaling is made using a hybrid of CDM and either FDM or TDM, for example as illustrated in FIG. 15, the MS proceeds to step 1813 and determines if N_DRS is known. That is, the MS determines if the field N_DRS is provided in signaling received from the BS. If it is determined in step 1813 that the value of N_DRS is known, the MS sets the power ratio γ[dB]=−10 log₁₀(N_DRS)+10 log₁₀(N_SF), wherein N_SF is the Walsh code spreading length. On the other hand, if it is determined in step 1813 that the value of N_DRS is not known, the MS proceeds to step 1817 and determines if the value of N_SET is known. If the value of N_SET is known to the MS, the MS proceeds to step 1809 and sets the power ratio γ[dB]=−10 log₁₀(N_SET), wherein N_SET is number of CDMed set as discussed above. On the other hand, if the value of N_SET is not known, the MS proceeds to step 1811 and sets the power ratio γ[dB]=0 dB. In an alternative exemplary implementation, the BS may set the power ratio of γ[dB]=0 dB despite that the values of N_DRS and N_SET are known. In that case, the BS would provide information regarding the power ratio γ[dB]=0 dB to the MS. In yet another exemplary implementation as illustrated below, for a transmission with odd rank, a combination of two equations can be used to determine the power ratio γ[dB].

FIGS. 19A through 19C illustrate a combination of two downlink power control equations for a rank-3 transmission according to an exemplary embodiment of the present invention

Referring to FIG. 19A, a first CDM DRS set that is allocated two layers (L0 and L1) and a second CDM DRS that is allocated one layer (L2) is illustrated. The use of different numbers of layers allows for different power assignments for the CDM DRS of each level which in turn allows for unequal error protection. For example, as illustrated in FIG. 19A, each layer (L0 and L1) of the first CDM DRS is allocated an EPRE value of P/2 whereas the layer (L2) of the second CDM DRS is allocated an EPRE value of P. In an exemplary implementation, the two layers (L0 and L1) of the first CDM DRS are allocated power according to the equation γ[dB]=−10 log₁₀ (N_DRS)+10 log₁₀(N_SF), whereas the single layer (L2) of the second CDM DRS set uses the equation γ[dB]=−10 log₁₀ (N_SET). As illustrated in FIG. 19B, a first CDM DRS may include a single layer (L0) which is allocated an EPRE of P, while a second CDM DRS may include two layers (L1 and L2) which are allocated an EPRE of P/2. Similarly to the example of FIG. 19A, the two layers (L1 and L2) of the second CDM DRS may be allocated power according to the equation γ[dB]=−10 log₁₀(N_DRS)+10 log₁₀(N_SF), whereas the single layer (L)) of the first CDM DRS may use the equation γ[dB]=−10 log₁₀(N_SET). Finally, as illustrated in FIG. 19C, a CDM DRS may be allocated three layers (L0, L1, and L2) such that each layer is allocated an EPRE value of P/3.

In addition, if either N_DRS or N_SET in the DCI format is also used for the purpose of indicting power offset, then the existing field “Downlink Power Offset” may be removed.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

1. A method for determining a power ratio of Resource Elements (REs) transmitted by a Mobile Station (MS), the method comprising:

determining a type of multiplexing used for multiplexing the Dedicated Reference signals (DRS) REs;

if the type of multiplexing is determined to be one of Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM), determining if the number of DRSs transmitted by the BS is known;

if the number of transmitted DRSs is known, setting the physical downlink Shared Channel (pdsch) data to DRS power ratio to correspond to the number of transmitted DRSs; and

if the number of transmitted DRSs is not known, determining if the maximum number of DRSs that may be transmitted is known;

if the maximum number of DRSs that may be transmitted is known:

setting the power ratio to correspond to a maximum number of DRSs that may be transmitted; and

otherwise setting the power ratio to 0 dB.

2. The method of claim 1, wherein the setting of the power ratio to correspond to the number of transmitted DRSs comprises using the equation:

γ[dB]=−10log₁₀(N_DRS),

where γ[dB] comprises the power ratio and N_DRS comprises the number of transmitted DRSs.

3. The method of claim 1, wherein the setting of the power ratio to correspond to the maximum number of DRSs that may be transmitted comprises using the equation:

γ[dB]=−10 log₁₀(M),

where γ[dB] comprises the power ratio and M comprises the maximum number of DRSs that may be transmitted.

4. The method of claim 1, wherein, if the type of modulation is determined to be Code Division Multiplexing (CDM), setting the power ratio to 0 dB.

5. A method for determining a power ratio of Resource Elements (REs) transmitted by a Mobile Station (MS), the method comprising:

determining a type of multiplexing used for multiplexing Dedicated Reference signal (DRS) REs;

if the type of multiplexing is determined to be one of Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM), determining if the number of DRSs transmitted by a Base Station (BS) is known;

if the number of transmitted DRSs is known, setting physical downlink Shared Chanel (pdsch) data to DRS power ratio to correspond to the number of transmitted DRSs;

if the number of transmitted DRSs is not known, determining if the maximum number of DRSs that may be transmitted is known;

if the type of multiplexing is determined to be a hybrid of CDM and one of FDM and TDM, determining if the number of DRSs transmitted by the BS is known; and

if the number of transmitted DRSs is known, setting the power ratio to correspond to the number of transmitted DRSs and a spreading length used for the CDM.

6. The method of claim 5, wherein, if the total number of DRS sets that are transmitted is known:

setting the power ratio to correspond to the total number of DRS sets that are transmitted; and

otherwise setting the power ratio to 0 dB.

7. The method of claim 6, wherein the setting of the power ratio to correspond to the number of transmitted DRSs and a spreading length used for the CDM comprises using the equation:

γ[dB]=−10 log₁₀(N_DRS)+10 log₁₀(N_SF),

where γ[dB] comprises the power ratio, N_DRS comprises the number of transmitted DRSs, and N_SF comprises the spreading length used for the CDM.

8. The method of claim 5, wherein, if the type of multiplexing is determined to be a hybrid of CDM and one of FDM and TDM, determining if the number of CDMed DRS sets and the number of DRSs transmitted by the BS are known, and determining if the number of total transmission layers is an odd number and that is greater than 1; and

if the number of total transmission layers is an odd number and the transmission layers are split into two CDMed DRS sets, applying different power ratios to the layers in the two CDMed DRS sets.

9. The method of claim 8, wherein, if it is determined that three transmission layers are split into two CDMed DRS sets, applying the power ratio to the set with 2 layers as:

γ[dB]=−10 log₁₀(N_DRS)+10 log₁₀(N_SF),

and applying the power ratio to the set with 1 layer as:

γ[dB]=10 log₁₀(N_SET).

10. A method for determining a power ratio of Resource Elements (REs) transmitted by a Mobile Station (MS), the method comprising:

determining a type of multiplexing used for multiplexing Dedicated Reference signal (DRS) REs;

if the type of multiplexing is determined to be one of Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM), determining if the number of DRSs transmitted by a Base Station (BS) is known;

if the number of transmitted DRSs is known, setting physical downlink Shared Chanel (pdsch) data to DRS power ratio to correspond to the number of transmitted DRSs;

if the number of transmitted DRSs is not known, determining if the maximum number of DRSs that may be transmitted is known;

if the type of multiplexing is determined to be a hybrid of CDM and one of FDM and TDM, determining if the number of CDMed DRS sets transmitted by the BS is known; and

if the number of CDMed DRS sets is known, setting the power ratio to correspond to the number of CDMed DRS sets.

11. The method of claim 10, wherein the setting of the power ratio to correspond to the total number of DRS sets that are transmitted comprises using the equation:

γ[dB]=−10 log₁₀(N_SET),

where γ[dB] comprises the power ratio and N_SET comprises the total number of DRS sets that are transmitted.

12. A method for transmitting a signal in a communication system, the method comprising:

determining a ratio of physical downlink shared channel (pdsch) energy per resource element (EPRE) to mobile specific reference signal EPRE based on a number of layers;

transmitting downlink control information including Hybrid Automatic Repeat reQuest (HARQ) information, mobile specific reference signal information, modulation and coding scheme information per a transport block, and new data indicator information per the transport block; and

transmitting data on the pdsch according to the determined ratio and based on the downlink control information.

13. The method of claim 12, wherein the number of layers is equal to a number of mobile specific reference signals.

14. The method of claim 12, wherein indices of mobile specific reference signals indicated by the mobile specific reference signal information are consecutive.

15. The method of claim 12, wherein an L^th layer is associated with an index of mobile specific reference signal, i_DRS+L−1.

16. The method of claim 12, wherein a mobile specific reference signal is defined by applying code division multiplexing and frequency division multiplexing.

17. The method of claim 12, wherein the data is mapped onto resource elements other than cell specific reference signal resource elements and mobile specific reference signal resource elements.

18. An apparatus for transmitting a signal in a communication system, the apparatus comprising:

control circuitry configured to determine a ratio of physical downlink shared channel (pdsch) energy per resource element (EPRE) to mobile specific reference signal EPRE based on a number of layers; and

a transmitter configured to transmit downlink control information including Hybrid Automatic Repeat reQuest (HARQ) information, mobile specific reference signal information, modulation and coding scheme information per a transport block, new data indicator information per the transport block, and to transmit data on the pdsch according to the determined ratio and based on the downlink control information.

19. The apparatus of claim 18, wherein the number of layers is equal to a number of mobile specific reference signals.

20. The apparatus of claim 18, wherein indices of multiple mobile specific reference signals indicated by the mobile specific reference signal information are consecutive.

21. The apparatus of claim 18, wherein a L^th layer is associated with an index of mobile specific reference signal, i_DRS+L−1.

22. The apparatus of claim 18, wherein a mobile specific reference signal is defined by applying code division multiplexing and frequency division multiplexing.

23. The apparatus of claim 18, wherein the data is mapped onto resource elements other than cell specific reference signal resource elements and mobile specific reference signal resource elements.

24. A method for receiving a signal in a communication system, the method comprising:

receiving downlink control information including Hybrid Automatic Repeat reQuest (HARQ) information, mobile specific reference signal information, modulation and coding scheme information per a transport block, new data indicator information per the transport block;

obtaining a ratio of physical downlink shared channel (pdsch) energy per resource element (EPRE) to mobile specific reference signal EPRE based on a number of layers; and

receiving data that has been transmitted on the pdsch according to the obtained ratio and based on the downlink control information.

25. The method of claim 24, wherein the number of layers is equal to a number of mobile specific reference signals.

26. The method of claim 24, wherein indices of mobile specific reference signals indicated by the mobile specific reference signal information are consecutive.

27. The method of claim 24, wherein an L^th layer is associated with an index of mobile specific reference signal, i_DRS+L−1.

28. The method of claim 24, wherein a mobile specific reference signal is defined by applying code division multiplexing and frequency division multiplexing.

29. The method of claim 24 wherein the data is mapped onto resource elements other than cell specific reference signal resource elements and mobile specific reference signal resource elements.

30. An apparatus for receiving a signal in a communication system, the apparatus comprising:

a receiver configured to receive downlink control information including Hybrid Automatic Repeat reQuest (HARQ) information, mobile specific reference signal information, modulation and coding scheme information per a transport block, new data indicator information per the transport block; and

control circuitry configured to obtain a ratio of physical downlink shared channel (pdsch) energy per resource element (EPRE) to mobile specific reference signals (RSs) based on a number of layers,

wherein the receiver is configured to receive data that has been transmitted on the pdsch according to the obtained ratio and based on the downlink control information.

31. The apparatus of claim 30, wherein the number of layers is equal to a number of mobile specific reference signals.

32. The apparatus of claim 30, wherein indices of multiple mobile specific reference signals indicated by the mobile specific reference signal information are consecutive.

33. The apparatus of claim 30, wherein a L^th layer is associated with an index of mobile specific reference signal, i_DRS+L−1.

34. The apparatus of claim 30, wherein a mobile specific reference signal is defined by applying code division multiplexing and frequency division multiplexing.

35. The apparatus of claim 30, wherein the data is mapped onto resource elements other than cell specific reference signal resource elements and mobile specific reference signal resource elements.