Abstract:
A communication device of handling at least one cyclic prefix (CP) comprises a storage unit for storing instructions and a processing means coupled to the storage unit. The processing means is configured to execute the instructions stored in the storage unit. The instructions comprise performing a first communication operation with a BS according to at least one first CP which has at least one first format; receiving a control signal indicating at least one second CP which has at least one second format or indicating no CP from the BS, wherein the at least one first format is different from the at least one second format; and performing a second communication operation with the BS according to the at least one second CP or using no CP according to the control signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/148,764, filed on Apr. 17, 2015, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of handling a cyclic prefixes for a wireless communication system. 
         [0004]    2. Description of the Prior Art 
         [0005]    A long-term evolution (LTE) advanced (LTE-A) system includes advanced techniques, such as carrier aggregation, licensed-assisted access (LAA) using LTE, etc. The LTE-A system employs orthogonal frequency-division multiplexing (OFDM) with cyclic prefix(es) (CP(s)) as a transmission scheme for downlink (DL) transmission and single-carrier frequency-division multiple access (SC-FDMA) with CP(s) as a transmission scheme for uplink (UL) transmission. However, it is not known what transmission scheme(s) for the UL transmission and the DL transmissions will be used in a 5G system developed by 3GPP. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention therefore provides devices for handling CPs with various formats to solve the abovementioned problem. 
         [0007]    A communication device of handling at least one cyclic prefix (CP) comprises a storage unit for storing instructions and a processing means coupled to the storage unit. The processing means is configured to execute the instructions stored in the storage unit. The instructions comprise performing a first communication operation with a BS according to at least one first CP which has at least one first format; receiving a control signal indicating at least one second CP which has at least one second format or indicating no CP from the BS, wherein the at least one first format is different from the at least one second format; and performing a second communication operation with the BS according to the at least one second CP or using no CP according to the control signal. 
         [0008]    A base station of handling at least one cyclic prefix (CP) comprises a storage unit for storing instructions and a processing means coupled to the storage unit. The processing means is configured to execute the instructions stored in the storage unit. The instructions comprise performing a first communication operation with a communication device according to at least one first CP which has at least one first format; transmitting a control signal indicating at least one second CP which has at least one second format or indicating no CP to the communication device, wherein the at least one first format is different from the at least one second format; and performing a second communication operation with the communication device according to the at least one second CP or using no CP according to the control signal. 
         [0009]    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 
         [0010]      FIG. 1  is a schematic diagram of a wireless communication system according to an example of the present invention. 
           [0011]      FIG. 2  is a schematic diagram of a communication device according to an example of the present invention. 
           [0012]      FIG. 3  is a flowchart of a process according to an example of the present invention. 
           [0013]      FIG. 4  is a schematic diagram of OFDM symbols with CPs according to an example of the present invention. 
           [0014]      FIG. 5  is a schematic diagram of OFDM symbols with CPs according to an example of the present invention. 
           [0015]      FIG. 6  is a schematic diagram of OFDM symbols with CPs and non-OFDM symbols according to an example of the present invention. 
           [0016]      FIG. 7  is a schematic diagram of OFDM symbols with CPs and non-OFDM symbols according to an example of the present invention. 
           [0017]      FIG. 8  is a schematic diagram of OFDM symbols with/without CPs and non-OFDM symbols according to an example of the present invention. 
           [0018]      FIG. 9  is a flowchart of a process according to an example of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      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. In  FIG. 1 , the network and the communication devices are simply utilized for illustrating the structure of the wireless communication system  10 . Practically, the network may be an evolved universal mobile telecommunication system Terrestrial Radio Access Network (E-UTRAN) including at least one evolved Node-B (eNB), or may be a 5G network including at least one 5G base station (BS) which employs orthogonal frequency-division multiplexing (OFDM) and/or non-OFDM for communication with the communication devices. In general, a BS may also be used to refer any of the eNB and the 5G BS. 
         [0020]    A communication device maybe a user equipment (UE), a machine type communication (MTC) device, a mobile phone, an electronic book, a portable computer system, a vehicle, or aircraft. In addition, 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. 
         [0021]      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 means  200  such as a microprocessor or Application Specific Integrated Circuit (ASIC), a storage unit  210  and a communication interfacing unit  220 . The storage unit  210  may be any data storage device that may store a program code  214 , accessed and executed by the processing means  200 . Examples of the storage unit  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 unit, non-transitory computer-readable medium (e.g., tangible media), etc. The communication interfacing unit  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 means  200 . 
         [0022]    In the following embodiments, a UE is used to represent a communication device in  FIG. 1  to simplify the illustration of the embodiments. 
         [0023]      FIG. 3  is a flowchart of a process  30  according to an example of the present invention. The process  30  may be utilized in a UE, to handle at least one cyclic prefix (CP). The process  30  may be compiled into the program code  214  and includes the following steps: 
         [0024]    Step  300 : Start. 
         [0025]    Step  302 : Perform a first communication operation with a BS according to at least one first CP which has at least one first format. 
         [0026]    Step  304 : Receive a control signal indicating at least one second CP which has at least one second format or indicating no CP from the BS, wherein the at least one first format is different from the at least one second format. 
         [0027]    Step  306 : Perform a second communication operation with the BS according to the at least one second CP or using no CP according to the control signal. 
         [0028]    Step  308 : End. 
         [0029]    According to the process  30 , the UE may initiate a first communication operation with a BS according to at least one first CP which has at least one first format. Then, the UE may receive a control signal indicating at least one second CP which has at least one second format or indicating no CP from the BS, wherein the at least one first format is different from the at least one second format. Accordingly, the UE may perform a second communication operation with the BS according to the at least one second CP or using no CP according to the control signal. That is, at the beginning of the communication, the UE communicates with the BS by using the at least one first CP. The UE can communicate with the BS by using the at least one second CP or without using any CP, after receiving the control signal. Thus, the UE can communicate with the BS regularly, because the rule for switching the use of the CP can be determined according to the process  30 . 
         [0030]    Realization of the process  30  is not limited to the above description. 
         [0031]    An example is illustrated according to the process  30  as follows. A BS transmits a first DL transmission by using a first set of CPs with first format(s) in a first timeslot (or a first subframe). Correspondingly, the UE receives the first DL transmission from the BS by using the first set of CPs with the first format(s) in the first timeslot (or the first subframe). The UE transmits a first UL transmission to the BS by using the first set of CPs with the first format(s) in a second timeslot (or a second subframe). Then, the BS may transmit a control signal for indicating the UE to use a second set of CPs with second format(s) for a third timeslot (or a third subframe). Accordingly, the UE transmits a second UL transmission by using the second set of CPs with the second format(s) in the third timeslot (or the third subframe) according to the control signal, or receives a second DL transmission by using the second set of CPs with the second format(s) in the third timeslot (or the third subframe) according to the control signal. The above format(s) maybe length(s) of the CP(s), or may be the number of the CP(s) (e.g., m CPs) within n symbols. For example, the second format(s) may be length(s) of the second set of CPs, and are different from the first format(s) which may be the length(s) of the first set of CPs. For example, different format(s) may be different m values and/or different n values. Multiple symbols may share a CP, if a non-orthogonal waveform is used for the symbols. The non-orthogonal waveform may be generated according to a universal filtered multi-carrier (UFMC) depending on a filter length. 
         [0032]    The first DL transmission may include any information such as data and/or control information, and is not limited herein. For example, the first DL transmission may include system information which includes at least one of a cell identity, DL bandwidth configuration, UL bandwidth configuration, random access configuration, cell reselection configuration, frequency band information. After the UE receives the system information, the UE may tune its radio frequency (RF) receiver according to the DL bandwidth configuration, may tune its RF transmitter according to the UL bandwidth configuration, may perform random access according to the random access configuration, may perform cell reselection according to the cell reselection configuration, or may determine a frequency band supported by the BS according to the frequency band information. In one example, the first DL transmission may include a data packet (e.g., Medium Access Control (MAC) Protocol Data Unit (PDU)). In one example, the first DL transmission may be transmitted in a DL slot/subframe/frame including a plurality of OFDM symbols or a plurality of non-OFDM symbols, wherein the CP(s) (e.g., the first set of CPs and/or the second set of CPs) with the corresponding format(s) is inserted into the plurality of OFDM symbols or the plurality of non-OFDM symbols. 
         [0033]    The first UL transmission may include any information such as data and/or control information, and is not limited herein. For example, the first UL transmission may include a preamble for a random access or a MAC PDU including an Internet Protocol (IP) packet. In another example, the first UL transmission may be transmitted in a UL slot/subframe/frame including a plurality of OFDM symbols or a plurality of non-OFDM symbols, wherein the CP(s) (e.g., the first set of CPs and/or the second set of CPs) with the corresponding format(s) is inserted into the plurality of OFDM symbols or the plurality of non-OFDM symbols. 
         [0034]    The control signal may be any message such as a radio resource control (RRC) message, a MAC control element in a MAC PDU, a MAC control PDU or a physical layer signaling (e.g., DL control information), and is not limited herein. In addition, the control signal may indicate the second format(s) of the second set of CP, filter length(s) and/or subband bandwidth(s) (e.g., for the UFMC). The second format(s) of the second set of CP, the filter length(s) and/or the subband bandwidth(s) may be separately or jointly indicated in the control signal. In addition, the control signal may further indicate a modulation and coding scheme (MCS). The UE may generate the second UL transmission according to the control signal, or may process the second DL transmission according to the control signal. The control signal may also indicate a timeslot/subframe number to which the second format(s) or no CP is applied. 
         [0035]    The BS may determine content of the control signal according to a capability of the UE, wherein the capability may include the second format(s) of the second set of CP, the filter length(s), the subband bandwidth(s), and/or the MCS. In this situation, the UE may transmit the capability to the BS, e.g., before step  304 . Besides the capability, the BS may determine the second format(s) of the second set of CP, the filter length(s), and/or the subband bandwidth(s) according to measurement result(s) (e.g., measurement value(s)) indicating signal strength(s), signal quality(ies), and/or channel state(s)/quality(ies). The measurement result(s) may be obtained by the BS, or may be received from the UE. 
         [0036]    In one example, the BS may determine no CP, a short CP or fewer CPs for the second UL transmission, if the measurement result(s) indicates that UL channel(s)/frequency(ies)/subband(s)/subcarrier(s) is good enough (e.g., the measurement results(s) is greater than threshold(s)). Similarly, the BS may determine no CP, a short CP or fewer CPs for the second DL transmission, if the measurement results(s) indicates that DL channel(s)/frequency(ies)/subband(s)/subcarrier(s) is good enough. In another example, the BS may determine a filter length/subband bandwidth for the second UL transmission, if the measurement result(s) indicates that UL channel(s)/frequency(ies)/subband(s)/subcarrier(s) is good enough (e.g., the measurement results(s) is greater than threshold(s)). Similarly, the BS may determine a filter length/subband bandwidth for the second DL transmission, if the measurement result(s) indicates that DL channel(s)/frequency(ies)/subband(s)/subcarrier(s) is good enough. 
         [0037]    If the UE does not receive the control signal, the UE may use the first set of CPs with the first format(s) for receiving the second DL transmission or for transmitting the second UL transmission. 
         [0038]    In one example, the first communication operation may be performed via a first part of a bandwidth (e.g., at a carrier frequency), and the second communication operation may be performed via a second part of the bandwidth. An example can be illustrated jointly with the process  30  as follows. A BS transmits a synchronization signal, a reference signal and/or system information in the first part of the bandwidth by using the at least one first CP. Correspondingly, a UE receives the synchronization signal, the reference signal and/or the system information in the first part of the bandwidth by using the at least one first CP. Then, the BS transmits a control signal in the first part of the bandwidth by using the at least one first CP. The control signal indicates use of the at least one second CP, or indicates no CP for the second part of the bandwidth. Correspondingly, the UE receives the control signal by using the at least one first CP. Thus, the UE can apply the at least one second CP to communicate with the BS via the second part of the bandwidth according to the control signal. 
         [0039]    The UE may simultaneously communicate with the BS in the first part of the bandwidth by using the at least one first CP, and in the second part of the bandwidth by using the at least one second CP or no CP according to the control signal. 
         [0040]    The system information mentioned above may include a frequency band indicator, a system bandwidth, cell information, a random access configuration, etc. Control information including a RRC configuration, MAC PDU(s)/element(s), a hybrid automatic repeat request (HARQ) feedback may also be transmitted in the first part of the bandwidth, because a reliable transmission is needed for the system information and/or the control information. Data packets such as IP packets may be transmitted in the second part of the bandwidth. 
         [0041]      FIG. 4  is a schematic diagram of OFDM symbols with CPs according to an example of the present invention. A time slot  420  may include multiple OFDM symbols, and CPs of first format(s) are inserted in the OFDM symbols. A time slot  440  may include multiple OFDM symbols, and CPs of second format(s) are inserted in the OFDM symbols. A UE/BS may transmit the time slot  420  and/or the time slot  440  to the BS/UE. The UE and the BS may know positions of the time slots  420  and  440 , so the UE and the BS know which format(s) is applied to the CPs. In one example, the positions may be represented by frame numbers, subframe numbers and/or time slot numbers which are configured by the BS or specified in a standard. In one example, the UE/BS may know about the position of the time slot  440  according to information received in the time slot  420 . In one example, the first two OFDM symbols in each of the time slot  420  and/or  440  may be used by the UE/BS for transmitting control signal(s) which indicates which format(s) is applied to the CPs of the rest OFDM symbols. 
         [0042]      FIG. 5  is a schematic diagram of OFDM symbols with CPs according to an example of the present invention. A time slot  520  may include multiple OFDM symbols, and CPs of first format(s) are inserted in the OFDM symbols. A time slot  540  may include multiple OFDM symbols, and CPs of second format(s) are inserted in the first two OFDM symbols. A UE/BS may transmit the time slot  520  and/or the time slot  540  to the BS/UE. The UE and the BS may know positions of the time slots  520  and  540 , so the UE and the BS knows only 2 CPs are inserted in the first 2 OFDM symbols and no CP is inserted in the rest five OFDM symbols. In one example, the positions may be represented by frame numbers, subframe numbers and/or time slot numbers which are configured by the BS or specified in a standard. In one example, the UE/BS may know about the position of the time slot  540  according to information received in the time slot  520 . In one example, the first two OFDM symbols in the time slot  520  and/or  540  may be used by the UE/BS for transmitting control signal(s) which indicates which no CPs is applied to the rest OFDM symbols. 
         [0043]      FIG. 6  is a schematic diagram of OFDM symbols with CPs and non-OFDM symbols according to an example of the present invention. A UE/BS may transmit the time slot  620  and/or the time slot  640  to the BS/UE. The UE and the BS may know positions of the time slots  620  and  640 , so the UE and the BS knows only 2 CPs are inserted in the first 2 OFDM symbols and no CP is inserted in the rest five symbols. In one example, the positions may be represented by frame numbers, subframe numbers and/or time slot numbers. In one example, the UE/BS may know about the position of the time slot  640  according to information received in the time slot  620 . In one example, the first two OFDM symbols in the time slot  620  and/or  640  may be used by the UE/BS for transmitting control signal(s) indicating that no CP is applied to the rest five symbols. The control signal(s) may include filter length(s) and/or subband bandwidth(s). Accordingly, the UE/BS may apply the filter length(s) and/or the subband bandwidth(s) to demodulate/decode the non-OFDM symbols for a UFMC operation. The information or the control signal(s) may indicate that the rest five symbols are OFDM symbols (i.e., the time slot  640  in  FIG. 5 ) or non-OFDM symbols (i.e., the time slot  740  in  FIG. 6 ). 
         [0044]      FIG. 7  is a schematic diagram of OFDM symbols with CPs and non-OFDM symbols according to an example of the present invention. A UE/BS may transmit the time slot  720  and/or the time slot  740  to the BS/UE. The UE and the BS may know positions of the time slots  720  and  740 , so the UE and the BS knows no CP is inserted in the time slot  740 . In one example, the positions may be represented by frame numbers, subframe numbers and/or time slot numbers which are configured by the BS or specified in a standard. In one example, the UE/BS may know about the position of the time slot  740  according to information received in the time slot  720 . In one example, the first two OFDM symbols in the time slot  720  may be used by the UE/BS for transmitting control signal(s) indicating that no CP is applied to the time slot  740 . The information or the control signal(s) may include filter length(s) and/or subband bandwidth(s). Accordingly, the UE/BS may apply the filter length(s) and/or the subband bandwidth(s) to demodulate/decode the non-OFDM symbols for a UFMC operation. The information or the control signal(s) may indicate that the time slot  740  include OFDM symbols with CPs or non-OFDM symbols. 
         [0045]    The time slot  420 / 520 / 620 / 720  may be used for transmitting system information or control information (e.g., radio resource configuration), and the time slot  440 / 540 / 640 / 740  may be used for transmitting data such as a MAC PDU. The “time slot” is used as a unit for illustrating the examples above, and the examples can be applied to other time units such as “subframe”. 
         [0046]      FIG. 8  is a schematic diagram of OFDM symbols with/without CPs and non-OFDM symbols according to an example of the present invention. A UE/BS may transmit blocks  820 ,  840  and/or  860  to the BS/UE. The UE may initially receive a first part of spectrum, i.e., frequencies  830 , and decode/demodulate the OFDM symbols which have CPs inserted. The UE and the BS may know positions of the blocks  820 . In one example, the UE/BS may know about the positions of the blocks  840  and/or  860  according to information received in the block  820  in the time slot (e.g., control signal  880 ). The control signal indicates that one CP is applied to a part of bandwidth  850  in the time slot, or indicates that no CP is applied to a part of bandwidth  810  in the time slot. The control signal may include filter length(s) and/or subband bandwidth(s). Accordingly, the UE/BS may apply the filter length(s) and/or the subband bandwidth(s) to demodulate/decode the non-OFDM symbols for a UFMC or FBMC (Filter Bank Multicarrier) operation. 
         [0047]      FIG. 9  is a flowchart of a process  90  according to an example of the present invention. The process  90  may be utilized in a BS, to handle at least one CP. The process  90  may be compiled into the program code  214  and includes the following steps: 
         [0048]    Step  900 : Start. 
         [0049]    Step  902 : Perform a first communication operation with a UE according to at least one first CP which has at least one first format. 
         [0050]    Step  904 : Transmit a control signal indicating at least one second CP which has at least one second format or indicating no CP to the UE, wherein the at least one first format is different from the at least one second format. 
         [0051]    Step  906 : Perform a second communication operation with the UE according to the at least one second CP or using no CP according to the control signal. 
         [0052]    Step  908 : End. 
         [0053]    The process  90  may be realized by the BS to communicate with the UE realizing the process  30 . Detailed operations and variations of the process  90  can be referred to the previous description, and are not narrated herein. 
         [0054]    In addition, the BS may transmit the control signal, because the BS is going to transmit data of a type to the UE or the BS knows that the UE has data of a type to transmit, e.g., by receiving a buffer status report from the UE which indicates the data of the type is available. Moreover, according to the previous example, the BS may simultaneously communicate with the UE in the first part of the bandwidth by using the at least one first CP with the at least one first format, and in the second part of the bandwidth by using the at least one second CP with the at least one second format or no CP according to the control signal. 
         [0055]    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 . 
         [0056]    To sum up, a UE and a BS can dynamically use CP(s) with various format(s) for communicating with each other according to the present invention. The UE and the BS can dynamically use various filter length(s) or subband bandwidth(s) for communicating with each other when using UFMC. An abovementioned control signal indicating the format(s) of the CP(s) may be replaced by a control signal indicating a filter length and/or a subband bandwidth. For example, at least one first CP with at least one first format may be replaced by a first filter length and/or a first subband bandwidth, and at least one second CP with at least one second format may be replaced by a second filter length and/or a second subband bandwidth. Furthermore, the UE and the BS may communicate with each other by simultaneously using OFDM symbols with CPs with various formats or by using OFDM and non-OFDM in different time slots and/or different parts of a bandwidth (e.g., at a carrier frequency). The UE/BS may transmit reference signal(s) in OFDM symbols for the BS/UE to measure signal strength(s)/quality(ies). The OFDM symbols or non-OFDM symbols above may be transmitted via orthogonal waveforms or non-orthogonal waveforms. 
         [0057]    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.