Abstract:
A base station (BS) for sharing downlink (DL) demodulation reference signals (DMRSs) between the DL data and the DL control signals comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored in the storage device. The instructions comprise transmitting a DL control signal on a first layer in a first time-frequency resource to the communication device; transmitting a DL data, associated with the DL control signal on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, to the communication device; and transmitting a set of DMRSs for the DL control signal and the DL data to the communication device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/339,106 filed on May 20, 2016, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0002]    The present invention relates to a device and a method used in a wireless communication system, and more particularly, to a device and a method of sharing downlink demodulation reference signals between data and a control signal. 
       2. Description of the Prior Art 
       [0003]    A long-term evolution (LTE) system provides high data rate, low latency, packet optimization, and improved system capacity and improved coverage. The LTE system is evolved continuously to increase peak data rate and throughput by using advanced techniques, such as carrier aggregation (CA), dual connectivity, licensed-assisted access, etc. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network. The core network may include a mobility management and a Quality of Service (QoS) control of the at least one UE. 
         [0004]    Transmissions of downlink (DL) data in wireless communication systems are typically performed in two steps. A DL control signal is first transmitted from an eNB to a UE, and carries information for receiving DL data. After correctly receiving the DL control signal, the UE understands where and how to receive the DL data. In addition, demodulation reference signals (DMRSs) are needed to be used as a reference to correctly receive the DL control signal and the DL data. However, when single-user (SU) multi-input multi-output (MIMO) (SU-MIMO) spatial multiplexing (SM) is operated, it is still unknown how to use the DMRSs for receiving the DL control signal and the DL data efficiently. Thus, sharing the DMRSs between the DL data and the DL control signal is an important problem to be solved. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention therefore provides a communication device for sharing DL demodulation RSs (DMRSs) between DL data and a DL control signal to solve the abovementioned problem. 
         [0006]    ABS for sharing DL DMRSs between the DL data and the DL control signals comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored in the storage device. The instructions comprise transmitting a DL control signal on a first layer in a first time-frequency resource to a communication device; transmitting a DL data, associated with the DL control signal on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, to the communication device; and transmitting a set of DMRSs for the DL control signal and the DL data to the communication device. 
         [0007]    A communication device for sharing DL DMRSs between the DL data and the DL control signals comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored in the storage device. The instructions comprise receiving a DL control signal on a first layer in a first time-frequency resource from a BS; receiving a DL data, associated with the DL control signal, on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, from the BS; and receiving a set of DMRSs for the DL control signal and the DL data from the BS. 
         [0008]    A BS for sharing DL DMRSs between the DL data and the DL control signals comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored in the storage device. The instructions comprise allocating a first time-frequency resource for transmitting a DL control signal to a communication device; allocating a second time-frequency resource for transmitting a DL data to the communication device, wherein the first time-frequency resource and the second time-frequency resource are adjacent; transmitting the DL control signal on a first layer in the first time-frequency resource to the communication device; transmitting the DL data in the second time-frequency resource via a plurality of layers of SU-MIMO SM, to the communication device; rate matching around the first time-frequency resource occupied by the DL control signal, when transmitting the DL data signal via the plurality of layers of the SU-MIMO SM; and transmitting a set of DMRSs for the DL control signal and the DL data to the communication device. 
         [0009]    A communication device for sharing DL DMRSs between the DL data and the DL control signals comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored in the storage device. The instructions comprise receiving a DL control signal in a first time-frequency resource from a BS; receiving a DL data in a second time-frequency resource via a plurality of layers of SU-MIMO SM, from the BS, wherein the first time-frequency resource and the second time-frequency resource are adjacent; receiving the DL data by rate matching around the first time-frequency resource occupied by the DL control signal; and receiving a set of DMRSs for the DL control signal and the DL data from the BS. 
         [0010]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram of a wireless communication system according to an example of the present invention. 
           [0012]      FIG. 2  is a schematic diagram of a communication device according to an example of the present invention. 
           [0013]      FIG. 3  is a flowchart of a process according to an example of the present invention. 
           [0014]      FIG. 4  is a schematic diagram of a time-frequency resource allocation according to an example of the present invention. 
           [0015]      FIG. 5  is a schematic diagram of a time-frequency resource allocation according to an example of the present invention. 
           [0016]      FIG. 6  is a flowchart of a process according to an example of the present invention. 
           [0017]      FIG. 7  is a schematic diagram of a time-frequency resource allocation according to an example of the present invention. 
           [0018]      FIG. 8  is a schematic diagram of a time-frequency resource allocation according to an example of the present invention. 
           [0019]      FIG. 9  is a flowchart of a process according to an example of the present invention. 
           [0020]      FIG. 10  is a flowchart of a process according to an example of the present invention. 
           [0021]      FIG. 11  is a flowchart of a process according to an example of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  is a schematic diagram of a wireless communication system  10  according to an example of the present invention. The wireless communication system  10  is briefly composed of a network and a plurality of communication devices. The network and a communication device may communicate with each other via one or more carriers of licensed band(s) and/or unlicensed band(s). 
         [0023]    In  FIG. 1 , the network and the communication devices are simply utilized for illustrating the structure of the wireless communication system  10 . The network may be a narrowband (NB) internet of things (IoT) network or an evolved universal terrestrial radio access network (E-UTRAN) including at least one evolved Node-B (eNB) and/or at least one relay in a long-term evolution (LTE) system, a LTE-Advanced (LTE-A) system or an evolution of the LTE-A system. The eNB or the relay may be termed as a base station (BS). The network may be a fifth generation (5G) network including at least one 5G BS which employs orthogonal frequency-division multiplexing (OFDM) and/or non-OFDM (e.g., filtered OFDM (F-OFDM), Generalized Frequency Division Multiplexing (GFDM), Universal Filtered Multi-Carrier (UFMC) or Filter Back Multi-Carrier (FBMC)), and a transmission time interval (TTI) shorter than 1 ms (e.g. 100 or 200 microseconds). In general, a BS may also be used to refer any of the eNB and the 5G BS. 
         [0024]    A communication device may be a user equipment (UE), a machine type communication (MTC) device, a mobile phone, a laptop, a tablet computer, an electronic book, a portable computer system, a vehicle, or an aircraft. In addition, the network and the communication device can be seen as a transmitter or a receiver according to direction (i.e., transmission direction), e.g., for an uplink (UL), the communication device is the transmitter and the network is the receiver, and for a downlink (DL), the network is the transmitter and the communication device is the receiver. 
         [0025]      FIG. 2  is a schematic diagram of a communication device  20  according to an example of the present invention. The communication device  20  may be a communication device or the network shown in  FIG. 1 , but is not limited herein. The communication device  20  may include a processing circuit  200  such as a microprocessor or Application Specific Integrated Circuit (ASIC), a storage device  210  and a communication interfacing device  220 . The storage device  210  may be any data storage device that may store a program code  214 , accessed and executed by the processing circuit  200 . Examples of the storage device  210  include but are not limited to a subscriber identity module (SIM), read-only memory (ROM), flash memory, random-access memory (RAM), hard disk, optical data storage device, non-volatile storage device, non-transitory computer-readable medium (e.g., tangible media), etc. The communication interfacing device  220  is preferably a transceiver and is used to transmit and receive signals (e.g., data, messages and/or packets) according to processing results of the processing circuit  200 . 
         [0026]    In the following embodiments, a UE is used to represent a communication device in  FIG. 1 , to simplify the illustration of the embodiments. 
         [0027]      FIG. 3  is a flowchart of a process  30  according to an example of the present invention. The process  30  can be utilized in a BS (e.g., in the network shown in  FIG. 1 ), for sharing DL DMRSs between data and control signals. The process  30  includes the following steps: 
         [0028]    Step  300 : Start. 
         [0029]    Step  302 : Transmit a first DL control signal in a first time-frequency resource and a first DL data in a second time-frequency resource to a first UE. 
         [0030]    Step  304 : Transmit a first set of DMRSs for the first DL control signal and the first DL data. 
         [0031]    Step  306 : Transmit a second DL control signal in the first time-frequency resource and a second DL data in a third time-frequency resource to a second UE. 
         [0032]    Step  308 : End. 
         [0033]    According to the process  30 , the BS transmits a first DL control signal in a first time-frequency resource and a first DL data in a second time-frequency resource to a first UE. Then, the BS transmits a first set of DMRSs for the first DL control signal and the first DL data. The first set of DMRSs may be allocated between the first DL control signal and the first DL data. The BS transmits a second DL control signal in the first time-frequency resource and a second DL data associated with the second DL control signal in a third time-frequency resource to a second UE. In other words, the first DL control signal can share the first set of DMRSs with the second DL control signal, because the first DL control signal and the second DL control signal are transmitted in the same time-frequency resource. Thus, the DMRSs can be shared between the DL controls and the DL data. 
         [0034]    Realization of the process  30  is not limited to the above description. The following examples may be applied to the process  30 . 
         [0035]    In one example, a distance between the first time-frequency resource and the second time-frequency resource is shorter than a predetermined value. That is, the first time-frequency resource and the second time-frequency resource are in neighborhood of each other. In one example, the first DL data is transmitted via a plurality of layers of single-user (SU) Multi-input Multi-output (MIMO) (SU-MIMO) spatial multiplexing (SM). In one example, the first DL control signal is transmitted via a layer of SU-MIMO SM. 
         [0036]    In one example, the first set of DMRSs is transmitted in the first time-frequency resource, the second time-frequency resource, or both of the first time-frequency resource and the second time-frequency resource. The number of DMRS ports is the same as the number of layers of MIMO SM, with one DMRS port on each layer. 
         [0037]    In one example, the first DL control signal and the second DL control signal are separated according to a principle of multi-user (MU) MIMO (MU-MIMO). In one example, the third time-frequency resource is chosen such that a DL channel state experienced by the second UE in the first time-frequency resource and the third time-frequency resource are similar, such that sharing the first set of DMRSs between the second DL control signal and the second DL data allows a reception with an acceptable error probability for the second DL data. 
         [0038]      FIG. 4  is a schematic diagram of a time-frequency resource allocation  40  according to an example of the present invention. The BS transmits a first DL control signal  410  to a first UE in a first time-frequency resource  400 , and transmits a first DL data  412  to the first UE in a second time-frequency resource  402 . A distance between the first time-frequency resource  400  and the second time-frequency resource  402  is shorter than a predetermined value. The base station transmits a set of DMRSs  414  for the first DL control signal  410  and the first DL data  412 . The set of DMRSs  414  is transmitted in the first time-frequency resource  400 , the second time-frequency resource  402  or both of the first time-frequency resource  400  and the second time-frequency resource  402 . In addition, the BS may transmit a second DL control signal  420  to a second UE in the same time-frequency resource as that of the first DL control signal (i.e., the first time-frequency resource  400 ). The BS transmits a second DL data  422  to a second UE in a third time-frequency resource  406 . In other words, the set of the DMRSs  414  may be shared between the DL data and the DL control signals for the first UE and the second UE. 
         [0039]    In one example, the BS indicates in the second DL control signal whether a second set of DMRSs is transmitted along with the second DL data to the second UE. In this case, the third time-frequency resource is not required to have a similar channel state as that of the first time-frequency resource for the second UE. In one example, the second set of DMRSs is transmitted to the second UE, if the first set of DMRSs is not comprised in the third time-frequency resource. If the second DL data is transmitted in the third time-frequency resource that does not comprise at least part of the first set of DMRSs, the second set of DMRSs are transmitted along with the second DL data. Otherwise, the first set of DMRSs is shared with the second DL data. 
         [0040]    In one example, the second UE receives the second DL control signal by performing a blind detection on a plurality of known time-frequency resource positions (i.e., candidates). When a correct decoding of the second DL control signal is performed, the second UE understands whether the second set of DMRSs transmitted along with the second DL data, or whether the first set of DMRSs used for demodulating the second DL control signal is also used for demodulating the second DL data. In addition, a resource allocation, a modulation coding scheme (MCS), and a MIMO transmission scheme (e.g., the number of the plurality of layers) may also be specified in the second DL control signal. The second UE collects the time-frequency resource that carries the second DL data, and performs decoding based on parameters provided in the second DL control signal. 
         [0041]      FIG. 5  is a schematic diagram of a time-frequency resource allocation  50  according to an example of the present invention. The time-frequency resource allocation  50  is applied in a LTE-A system with a technique of a latency reduction. A first shortened Physical DL Control Channel (sPDCCH)  510  and a first shortened Physical DL Shared Channel (sPDSCH)  512  are transmitted to a first UE. The first sPDCCH  510  is transmitted in a first time-frequency  500 . The first sPDSCH  512  is transmitted in a second time-frequency resource  502 . The first time-frequency resource  500  is comprised in the second time-frequency resource  502 . A set of DMRSs  514  may be transmitted within the first sPDCCH  510 , and shared with the first sPDSCH  512 . The set of DMRSs  514  may be transmitted in the first time-frequency resource  500 , the second time-frequency resource  502  or both of the first time-frequency resource  500  and the second time-frequency resource  502 . The first sPDSCH  512  is transmitted via a plurality of layers of SM. A second sPDCCH  520  is transmitted in the same time-frequency resource as that of the first sPDCCH  510  (i.e., the first time-frequency resource  500 ) to a second UE. The first sPDCCH  510  and the second sPDCCH  520  are separated at the first UE and the second UE, respectively, according to a principle of multi-user (MU) MIMO (MU-MIMO). A second sPDSCH  522  is transmitted in a third time-frequency resource  504  to the second UE. The third time-frequency resource  504  is adjacent to the second time-frequency resource  502 . The second sPDSCH  522  may also be transmitted via a plurality of layers of SM, if the number of layers is supported by the number of DMRS ports. After correctly receiving the second sPDCCH  520 , the second UE receives and demodulates the second sPDSCH  522  according to the set of DMRSs  514 . A BS may also indicate dynamically in the second sPDCCH  520  whether there is a dedicated set of DMRSs for the second sPDSCH  522 . The BS may also transmit a dedicated set of DMRSs with sPDSCH, if the associated sPDCCH is not comprised in the sPDSCH, as in the case for the second sPDSCH  520 . 
         [0042]      FIG. 6  is a flowchart of a process  60  according to an example of the present invention. The process  60  can be utilized in a BS (e.g., in the network shown in  FIG. 1 ), for sharing DL DMRSs between data and control signals. The process  60  includes the following steps: 
         [0043]    Step  600 : Start. 
         [0044]    Step  602 : Transmit a DL control signal on a first layer in a first time-frequency resource to the UE. 
         [0045]    Step  604 : Transmit a DL data, associated with the DL control signal, on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, to the UE. 
         [0046]    Step  606 : Transmit a set of DMRSs for the DL control signal and the DL data to the UE. 
         [0047]    Step  608 : End. 
         [0048]    According to the process  60 , the BS transmits a DL control signal on a first layer in a first time-frequency resource to the communication device. Then, the BS transmits a DL data, associated with the DL control signal, on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, to the UE. The BS transmits a set of DMRSs for the DL control signal and the DL data. In other words, the DL data is not only transmitted in the second time-frequency resource but also in the first time-frequency resource on the second layer that is occupied but not utilized by the DL control signal. Thus, the time-frequency resource for transmitting the DL data is increased. 
         [0049]    Realization of the process  60  is not limited to the above description. The following examples may be applied to the process  60 . 
         [0050]    In one example, the DL control signal and the DL data are transmitted via a plurality of layers of SU-MIMO SM. In one example, the first time-frequency resource and the second time-frequency resource are adjacent. In one example, the first time-frequency resource and the second time-frequency resource are disconnected. 
         [0051]    In one example, the set of DMRSs is transmitted in the first time-frequency resource, the second time-frequency resource, or both of the first time-frequency resource and the second time-frequency resource. The number of DMRS ports is the same as the number of the plurality of layers in MIMO SM, with one DMRS on each layer. 
         [0052]    In one example, the DL control signal on the first layer in the first time-frequency resource and the DL data on the second layer on the first time-frequency resource are transmitted by using a precoder, and the precoder is also used for transmitting the set of DMRSs. 
         [0053]    In one example, at least one DMRS in the set of DMRSs and the DL control signal are transmitted according to (e.g., using) a first modulation format. In one example, at least one DMRS in the set of DMRSs and the DL data are transmitted according to (e.g., using) a second modulation format. 
         [0054]      FIG. 7  is a schematic diagram of a time-frequency resource allocation  70  of according to an example of the present invention. The time-frequency resource allocation  70  is applied to transmissions on two layers. The BS transmits a DL control signal  720  on a first layer  700  in a first time-frequency resource  710  to a UE. ABS transmits a DL data  722 , associated with the DL control signal  720 , on the first layer  700  in a second time-frequency resource  712 , and on a second layer  710  in the first time-frequency resource  710  and the second time-frequency resource  712 , to the UE. In the present example, the first time-frequency resource  710  is completely overlapped with the second time-frequency resource  712 . A set of DMRSs  724  is transmitted on one or more layer(s) in the first time-frequency resource  710 , the second time-frequency resource  712  or both of the first time-frequency resource  710  and the second time-frequency resource  712 . After correctly receiving the DL control signal  720  on the first layer  700  in the first time-frequency resource  710 , the UE receives the DL data  722  on the second layer  702  in the first time-frequency resource  710 , and on the first layer  700  and the second layer  702  in the second time-frequency resource  712 . 
         [0055]    In one example, in LTE-A systems, a time-frequency resource is computed in units of resource elements (REs). The eNB may transmit a larger transport block (TB) since there are more available REs, or may use a more robust MCS if a transport block size (TBS) is to be held unchanged as compared with an original situation without the process  60 . It should be noted that in the current LTE systems, the TBS is known to the UE by looking up a predetermined table with the MCS and the number of allocated resource blocks (RBs) as the table indices, both of which are indicated in the DL control signal. A new TBS table can be constructed to account for additional REs available from the process  60 . 
         [0056]    In one example, the UE receives the DL control signal by performing a blind detection on a plurality of known time-frequency resource positions (i.e., candidates). When a correct decoding of the DL control signal is performed, the UE understands necessary parameters to correctly receive the associated DL data. The parameters comprise resource allocation, MCS, and MIMO transmission scheme (e.g., the number of the plurality of layers). The time-frequency resource allocated for the DL control signal may be comprised partly or completely in the time-frequency resource of the DL data, as indicated in the DL control signal. 
         [0057]    In one example, a field may also exist to indicate to the UE whether the process  60  is applied or not. In the case that the process  60  is not applied, the UE proceeds to collect a time-frequency resource that carries the DL data, not including the time-frequency resource occupied by the DL control signal. Then, the UE performs a decoding based on parameters provided in the DL control signal. In the case that the process  60  is applied, the UE receives the DL control signal on a first layer. The UE receives the DL data from a second layer in a first time-frequency resource, and from the first layer and the second layer in a second time-frequency resource, as indicated in the DL control signal. The first time-frequency resource may be comprised partly or completely in the second time-frequency resource. The UE performs the decoding based on the parameters provided in the DL control signal. To perform an error control decoding on the DL data, the UE may need to know the TBS and the actual code rate. The TBS is known to the UE by looking up the abovementioned predetermined table. The actual code rate is known to the UE by calculating the total number of coded bits, which is the number of REs used for carrying the DL data multiplied by the modulation order. For example, a total number of coded bits of 10*4=40 bits can be obtained according to 10 REs and 16 QAM. 
         [0058]      FIG. 8  is a schematic diagram of a time-frequency resource allocation  80  according to an example of the present invention. The time-frequency resource allocation  80  is applied to transmission on two layers of a LTE-A system with a technique of a latency reduction. A sPDCCH  820  is transmitted on a first layer  800  in a first time-frequency resource  810 . A sPDSCH  822  is transmitted on a second layer  802  in the first time-frequency resource  810 , and on the first layer  800  and the second layer  802  in the second time-frequency resource  812 . The first time-frequency resource  810  is comprised in the second time-frequency resource  812 . A set of DMRSs  824  is transmitted with the sPDCCH  820 , and shared with the sPDSCH  822 . The set of DMRSs  824  may be transmitted in the first time-frequency resource  810 , the second time-frequency resource  812  or both of the first time-frequency resource  810  and the second time-frequency resource  812 . The sPDSCH  822  is transmitted via both of the first layer  800  and the second layer  802  of SM, while the sPDSCH  820  is transmitted via only the first layer  800  of SM. After correctly receiving the sPDSCH  820  on the first layer  800  in the first time-frequency resource  810 , the UE receives the sPDSCH  822  on the second layer  802  in the first time-frequency resource  810 , and on the first layer  800  and the second layer  802  in the second time-frequency resource  812 . 
         [0059]    The processes  30  and  60  may be combined by letting the BS dynamically indicate in the DL control signal to a first UE whether the process  60  has been applied or not. In the case that the process  60  is not applied, the process  30  may be applied to a second UE and this application is transparent to the first UE. It should be noted that MU-MIMO can be applied to both of the processes  30  and  60 , and this application is transparent to the UEs. 
         [0060]      FIG. 9  is a flowchart of a process  90  according to an example of the present invention. The process  90  can be utilized in a UE, for sharing DL DMRSs between data and control signals. The process  90  includes the following steps: 
         [0061]    Step  900 : Start. 
         [0062]    Step  902 : Receive a DL control signal on a first layer in a first time-frequency resource from a BS. 
         [0063]    Step  904 : Receive a DL data, associated with the DL control signal, on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, from the BS. 
         [0064]    Step  906 : Receive a set of DMRSs for the DL control signal and the DL data from the BS. 
         [0065]    Step  908 : End. 
         [0066]    According to the process  90 , the UE receives a DL control signal on a first layer in a first time-frequency resource from a BS. Then, the UE receives a DL data, associated with the DL control signal, on a second layer in the first time-frequency resource and on the first layer and the second layer in a second time-frequency resource, from the BS. The UE receives a set of DMRSs for the DL control signal and the DL data from the BS. In other words, the DL data is not only received in the second time-frequency resource but also in the first time-frequency resource on the second layer that is occupied but not utilized by the DL control signal. Thus, the time-frequency resource for receiving the DL data is increased. 
         [0067]    Realization of the process  90  is not limited to the above description. The previous examples related to a BS may imply corresponding operations of the UE. In addition, the following examples may be applied to the process  90 . 
         [0068]    In one example, the first time-frequency resource and the second time-frequency resource are adjacent. In one example, the first time-frequency resource and the second time-frequency resource are disconnected. 
         [0069]    In one example, the set of DMRSs is received in the first time-frequency resource, the second time-frequency resource, or both of the first time-frequency resource and the second time-frequency resource. 
         [0070]    In one example, the DL control signal and the DL data are received by using at least one DMRS in the set of DMRSs. 
         [0071]      FIG. 10  is a flowchart of a process  100  according to an example of the present invention. The process  100  can be utilized in a BS (e.g., in the network shown in  FIG. 1 ), for sharing DL DMRSs between data and control signals. The process  100  includes the following steps: 
         [0072]    Step  1000 : Start. 
         [0073]    Step  1002 : Allocate a first time-frequency resource for transmitting a DL control signal to a UE. 
         [0074]    Step  1004 : Allocate a second time-frequency resource for transmitting a DL data to the UE, wherein the first time-frequency resource and the second time-frequency resource are adjacent. 
         [0075]    Step  1006 : Transmit the DL control signal in the first time-frequency resource to the UE. 
         [0076]    Step  1008 : Transmit the DL data in the second time-frequency resource via a plurality of layers of SU-MIMO SM, to the UE. 
         [0077]    Step  1010 : Rate match around the first time-frequency resource occupied by the DL control signal, when transmitting the DL data signal via the plurality of layers of the SU-MIMO SM. 
         [0078]    Step  1012 : Transmit a set of DMRSs for the DL control signal and the DL data to the communication device. 
         [0079]    Step  1014 : End. 
         [0080]    According to process  100 , the BS allocates a first time-frequency resource for transmitting a DL control signal to a UE. Then, the BS allocates a second time-frequency resource for transmitting a DL data to the UE, wherein the first time-frequency resource and the second time-frequency resource are adjacent. That is, the first time-frequency resource may be surrounded by (or comprised in) the second time-frequency resource. The BS transmits the DL control signal in the first time-frequency resource to the UE. The BS transmits the DL data in the second time-frequency resource via a plurality of layers of SU-MIMO SM, to the UE. The BS rate matches around the first time-frequency resource occupied by the DL control signal, when transmitting the DL data signal via the plurality of layers of the SU-MIMO SM. That is, the DL data is not transmitted in the first time-frequency resource. The BS transmits a set of DMRSs for the DL control signal and the DL data to the UE. 
         [0081]    Realization of the process  100  is not limited to the above description. The following examples may be applied to the process  100 . 
         [0082]    In one example, the set of DMRSs is transmitted in the first time-frequency resource, the second time-frequency resource, or both of the first time-frequency resource and the second time-frequency resource. 
         [0083]    In one example, the DL data and the set of DMRSs are transmitted by using a precoder, and the precoder is also used for transmitting the DL control signal. 
         [0084]    In one example, at least one DMRS in the set of DMRSs and the DL control signal are transmitted according to (e.g., using) a first modulation format. In one example, at least one DMRS in the set of DMRSs and the DL data are transmitted according to (e.g., using) a second modulation format. 
         [0085]    In one example, The UE receives the DL control signal by searching over a plurality of predetermined time-frequency resources. The plurality of predetermined time-frequency resources comprise the first time-frequency resource. The UE obtains a first information of the second time-frequency resource by decoding and reading a content of the DL control signal found in the first time-frequency resource. The UE also obtains a second information of the fact that the DL data signal is rate matched around the first time-frequency resource. 
         [0086]    In one example, the DL data signal is always rate matched around the time-frequency resource occupied by the control signal. In this case, the UE understands that the DL data is rate matched (not transmitted) in the first time-frequency resource after obtaining the first information of the second time-frequency resource. The UE also understands the fact that the first time-frequency resource is overlapped with the second time-frequency resource. The UE finally receives the DL data signal in the second time-frequency resource from the content of the DL control signal. 
         [0087]      FIG. 11  is a flowchart of a process  110  according to an example of the present invention. The process  110  can be utilized in a UE, for sharing DL DMRSs between data and control signals. The process  100  includes the following steps: 
         [0088]    Step  1100 : Start. 
         [0089]    Step  1102 : Receive a DL control signal in a first time-frequency resource from a BS. 
         [0090]    Step  1104 : Receive a DL data in a second time-frequency resource via a plurality of layers of SU-MIMO SM, from the BS, wherein the first time-frequency resource and the second time-frequency resource are adjacent. 
         [0091]    Step  1106 : Receive the DL data by rate matching around the first time-frequency resource occupied by the DL control signal, from the BS. 
         [0092]    Step  1108 : Receive a set of DMRSs for the DL control signal and the DL data from the BS. 
         [0093]    Step  1110 : End. 
         [0094]    According to process  110 , the UE receives a DL control signal in a first time-frequency resource from a BS. Then, the UE receives a DL data in a second time-frequency resource via a plurality of layers of SU-MIMO SM, from the BS, wherein the first time-frequency resource and the second time-frequency resource are adjacent. The UE receives the DL data by rate matching around the first time-frequency resource occupied by the DL control signal, from the BS. The UE receives a set of DMRSs for the DL control signal and the DL data from the BS. 
         [0095]    Realization of the process  110  is not limited to the above description. The previous examples related to a BS may imply corresponding operations of the UE. In addition, the following examples may be applied to the process  110 . 
         [0096]    In one example, the set of DMRSs is received in the first time-frequency resource, the second time-frequency resource, or both of the first time-frequency resource and the second time-frequency resource. 
         [0097]    In one example, the DL control signal and the DL data are received by using at least one DMRS in the set of DMRSs. 
         [0098]    Those skilled in the art should readily make combinations, modifications and/or alterations on the abovementioned description and examples. The abovementioned description, steps and/or processes including suggested steps can be realized by means that could be hardware, software, firmware (known as a combination of a hardware device and computer instructions and data that reside as read-only software on the hardware device), an electronic system, or combination thereof. An example of the means may be the communication device  20 . Any of the above processes and examples above may be compiled into the program code  214 . 
         [0099]    To sum up, the present invention provides a device and a method for sharing DL DMRSs. According to the present invention, a BS can utilize time-frequency resource(s) more efficiently by transmitting additional DL control signals or DL data via layer(s) of the time-frequency resource(s). Thus, the problem in the art is solved. 
         [0100]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.