Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for improving system throughput of service generating small amount of traffic such as VoIP (Voice over IP) in 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) system. 
     2. Description of the Related Art 
     The mobile communication system has evolved into a high-speed, high-quality wireless packet data communication system to provide data services and multimedia services beyond the early voice-oriented services. Recently, various mobile communication standards, such as High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), both defined in 3 rd  Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) defined in 3 rd  Generation Partnership Project-2 (3GPP2), and 802.16 defined in IEEE, have been developed to support the high-speed, high-quality wireless packet data communication services. 
     Such recent mobile communication systems adopt Adaptive Modulation and Coding (AMC) and channel sensitive techniques to improve transmission efficiency. With AMC, the transmitter can control the data amount according to channel state. That is, when the channel state is bad, the data rate is decreased to math a predetermined error rate, and when the channel state is good, the data transmission rate is increased to match another predetermined error rate. In this way, the mobile communication system can transmit large amount of information efficiently. 
     With the channel sensitive scheduling resource management method, the transmitter can serve the user having superior channel state first selectively among multiple users and thus increase system throughput as compared to the general channel allocation and serving method. For example, the AMC and channel sensitive scheduling are the techniques for using the most appropriate modulation and coding scheme at the most efficient timing based on the partial channel state information fed back by the receiver. 
     There has been many researches done to adopt Orthogonal Frequency Division Multiple Access (OFDMA) to next generation communication systems in place of Code Division Multiple Access (CDMA) that has been used in 2 nd  and 3 rd  Generation mobile communication systems. The standardization organizations such as 3GPP, 3GPP2, and IEEE are developing standards for enhanced system based on the OFDMA or modified OFDMA. It is known that OFDMA promises to increase system capacity as compared to CDMA. One of the factors affecting the increase of system capacity in an OFDMA system is the use of frequency domain scheduling. As the channel sensitive scheduling technique uses the time-varying channel for capacity gain, it is possible to increase the capacity gain with frequency-varying channel characteristic. 
     LTE adopts Orthogonal Frequency Division Multiplexing (OFDM) in Downlink (DL) and Single Carrier Frequency Division Multiple Access (SC-FDMA) that are both capable of scheduling in frequency domain. 
     The AMC and channel sensitive scheduling are the techniques that are capable of improving the transmission efficiency in the state where the transmitter has acquired information enough on the transmit channel. In FDD (Frequency Division Duplex) mode where the transmitter cannot estimate the state of the transmit channel based on the receive channel, it is designed for the receiver to report the information on the transmit channel to the transmitter. In case of TDD (Time Division Duplex) mode where the transmit channel state can be inferred from the receive channel state, the transmit channel state report from the receiver to the transmitter can be omitted. 
     Although the mobile communication system evolves to support high speed high quality radio packet data communication, voice communication is still one of the main services. VoIP (Voice over Internet Protocol) is the service for supporting efficient voice communication in the communication system designed for radio packet data communication. The voice communication service has a characteristic in that a certain amount of traffic takes place at a certain interval and very sensitive to delay. In case of the traffic not sensitive to time delay, the scheduler can schedule the data on appropriate radio resource with temporal margin so as to expect high gain with the AMC and channel sensitive scheduling. In case of the delay sensitive traffic, however, the scheduler has to schedule the data without enough temporal margin and, as a consequence, it is difficult to expect the large gain of channel sensitive scheduling. Also, if a certain amount of traffic takes place regularly, the AMC which changes the modulation and coding scheme depending on the data amount becomes useless. In such cases, the control signals for indicating the modulating and coding scheme that are transmitted by using the AMC and channel sensitive scheduling techniques causes consummation of relatively large amount of resource as compared to the data amount to be transmitted. 
     By taking notice of these features of VoIP, a new resource allocation scheme appropriate for VoIP, referred to as SPS (Semi-Persistent Scheduling), is defined in LTE. SPS is designed to prevent the control signal from being transmitted for every data transmission such that the resource is allocated automatically at the interval of the traffic occurrence with the initially configured modulation and coding scheme until a resource release signal is transmitted. 
       FIG. 1  is diagram illustrating a resource unit defined for downlink in a LTE system. 
     Referring to  FIG. 1  LTE adopts OFDMA in downlink. The resource is allocated in unit of resource block (RB)  110 . An RB  110  is generated from 12 subcarriers on frequency axis and a subframe on time axis. A subframe has 1 msec duration and consists of 14 OFDM symbols. 10 subframes constitute a radio frame. 
     The basic unit of radio resource is resource element (RE). An RE  112  is defined by one subcarrier on frequency axis, one OFDM symbol on time axis, and one virtual antenna port on spatial axis. This means that one RE carrier a modulation signal. In case of allocating resource in unit of RE, too much information amount is required for indicating allocated resources and thus resource allocation is performed in unit of Resource Block (RB). 
       FIG. 2  is a diagram illustrating an RB composed of a plurality of REs arranged with different purposes in LTE downlink. 
     Referring to  FIG. 2 , an enhanced Node B (eNB) transmits predetermined reference signal (RS) at predetermined positions in an RB for channel estimation. A User Equipment (UE), which knows the position of the resource designated for the signal, estimates channel according to the received RB. Reference number  120  denote the RE used for common RS.  FIG. 2  shows the RB configured with common RS in case that 4 antenna ports are used. 
     One RB consists of 168 (=12×14) REs and, when the number of transmit antennas is 4, 24 REs are assigned for common RSs. In order to indicate resource allocation, Physical Downlink Control Channel (PDCCH) is transmitted in n OFDM symbols duration at the beginning of a subframe which is referred to as control region  122 . Here, n can be 1, 2, or 3. Since the control region consists of 3 OFDM symbols in the example of  FIG. 2 , n=3. The size of the control region can vary every subframe and indicated by Physical Control Format Indicator Channel (PCFICH) at the first OFDM symbol of each subframe. 
     In the control region  122 , physical ARQ Indicator Channel (PHICH) carrying ACK/NACK signal for Physical Uplink Shared Channel (PUSCH) is defined to support HARQ process. That is, the control channel region carries RS, PDCCH, PCFICH, and PHICH. Reference number  124  denotes RE designated for control signal transmission. Reference number  126  denote RE designated for PUSCH transmission carrying scheduled user data. 
     PDSCH cannot be transmitted in the control region  122 . Accordingly, in the exemplary case of  FIG. 2  where the number of transmit antenna ports is 4 and the control region consists of three OFDM symbols, the number of REs that can be used for PDSCH transmission in an RB is  116 . 
     Table 1 summarizes the number of REs available for PDSCH transmission in one RB according to the number of eNB&#39;s transmit antennas, whether the dedicated RS is defined, and length of the control region. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 # of transmit 
                   
                 Size of control 
                 Number of 
               
               
                 Condition 
                 antenna ports 
                 Dedicated RS 
                 region 
                 PDSCH REs 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 Not defined 
                 1 
                 150 
               
               
                 2 
                 1 
                 Not defined 
                 2 
                 138 
               
               
                 3 
                 1 
                 Not defined 
                 3 
                 126 
               
               
                 4 
                 1 
                 Defined 
                 1 
                 138 
               
               
                 5 
                 1 
                 Defined 
                 2 
                 126 
               
               
                 6 
                 1 
                 Defined 
                 3 
                 114 
               
               
                 7 
                 2 
                 Not defined 
                 1 
                 144 
               
               
                 8 
                 2 
                 Not defined 
                 2 
                 132 
               
               
                 9 
                 2 
                 Not defined 
                 3 
                 120 
               
               
                 10 
                 2 
                 Defined 
                 1 
                 132 
               
               
                 11 
                 2 
                 Defined 
                 2 
                 120 
               
               
                 12 
                 2 
                 Defined 
                 3 
                 108 
               
               
                 13 
                 4 
                 Not defined 
                 1 
                 136 
               
               
                 14 
                 4 
                 Not defined 
                 2 
                 128 
               
               
                 15 
                 4 
                 Not defined 
                 3 
                 116 
               
               
                 16 
                 4 
                 Defined 
                 1 
                 124 
               
               
                 17 
                 4 
                 Defined 
                 2 
                 116 
               
               
                 18 
                 4 
                 Defined 
                 3 
                 104 
               
               
                   
               
             
          
         
       
     
     The number of REs determined which is by referencing table 1 is available in case of using normal Cyclic Prefix (CP) and system bandwidth is greater than 10 RBs. This is because the number of OFDM symbols constituting a subframe using an extended CP decreases to 6 and the size of the control region is configured with 2, 3, or 4 rather than 1, 2, or 3 when the system bandwidth is equal to or less than 10 RBs. 
     Reference number  130  denotes a principle of frequency first mapping for PDSCH. The modulation symbols streams of PDSCH are arranged in ascending order direction of subcarrier indices on the frequency axis. Once all of the subcarriers in an OFDM symbol are assigned, and then subcarriers in next OFDM symbol are assigned for PDSCH resource. 
     In an RB, dedicated RS can be defined additionally. The dedicated RS means the RS, when beamforming is applied for a scheduled user, to which the same beamforming is applied as to the PDCCH. The dedicated RS is mapped to 12 REs per RB. 
       FIG. 3  is a block diagram illustrating a configuration of an eNB transmitter in a legacy LTE system. 
       FIG. 3  shows the configuration of normal eNB transmitter using spatial multiplexing (SM) in case of transmitting two codewords (CWs). 
     Transport Block (TB) denotes the information signal delivered from a higher layers to a physical layer to be transmitted through PDSCH. In case of supporting SM, up to two TBs can be transmitted on the same resource. Reference number  200   a  denotes TB 1  for the first CW, and reference number  200   b  denotes TB 2  for the second CW. 
     TB 1   200   a  and TB 2   200   b  channel coded by the channel coders  202   a  and  202   b , scrambled by the scramblers  204   a ,  204   b , and modulated by the modulators  206   a  and  206   b  so as to be converted to modulation signal streams. In case that no SM is used, TB 1   200   a  does not exist such that the processes  202   b ,  204   b , and  206   b  for TB 1   200   a  are omitted. 
     The one or two modulation signal streams are converted to modulation signal streams per spatial layer to which precoding is applied by the precoder  210  through layer mapper  208 . In case of SM the number of CWs is limited to 2 but four spatial layers are allowed an thus it is necessary to define the arrangement for this. 
     In case of using transmit diversity, the number of spatial layers is 2 or 4 while the number of CWs is 1, and precoding means the transmit diversity coding. The precoding can be categorized into one of transmit diversity coding, open-loop precoding, and closed-loop precoding. 
     The precoder  210  can converts the modulation signal streams per spatial layer to signal streams to be transmitted through respective transmission antenna ports  2116   c  and  216   d . The precoded signal streams are mapped to REs corresponding to antenna ports by RE mappers  212   c  and  212   d , converted to OFDM symbols by OFDM signal generator  214   c  and  214   d , and then transmitted through respective antenna ports  216   c  and  216   d.    
       FIG. 4  is a diagram illustrating a resource unit defined in uplink of a legacy LTE system. 
     Referring to  FIG. 4 , LTE adopts SC-FDMA in uplink, and the basic unit of radio resource is RE as in downlink. An RB  400  is generated from 12 virtual subcarriers and one subframe on time axis. The subframe has 1 msec duration and consists of 14 OFDM symbols as in downlink. The RE  402  is defined by a virtual subcarrier in an SC-FDMA symbol. 
     SC-FDMA applies Discrete Fourier Transform as precoding at step prior to OFDM signal generation. Accordingly, the RE mapped designated for a modulation symbol does not means a subcarrier but is referred as virtual subcarrier. In case of allocating resource in unit of RE, too much information amount is required for indicating allocated resources and thus resource allocation is performed in unit of Resource Block (RB). 
       FIG. 5  is a diagram illustrating resource arrangement per purpose in an RB in uplink of legacy LTE. 
     Referring to  FIG. 5 , RS can be defined in unit of RE in SC-FDMA. Accordingly, a specific SC-FDMA symbol is entirely used for RS. The uplink RS is defined in the form of dedicated RS for per-user uplink channel estimation and used for demodulation so as to be referred to as Demodulation RS (DM RS). 
     Uplink Multi-User Multiple Input Multiple Output (MU-MIMO) means uplink Space Domain Multiple Access (SDMA). If the dedicated RSs that are orthogonal between user are received, the eNB receiver applies spatial filter appropriate for the per-user spatial channel response to discriminate among PUSCHs transmitted to different users. 
     The fourth and eleventh SC-FDMA symbols of a subframe  510  are SC-FDMA symbols  514  for transmitting the dedicated RS. By transmitting the per-user orthogonal signals as dedicated RS, it is possible to support uplink MU-MIMO. Other SC-FDMA symbols  516  are the resource available for PUSCH transmission. Among the total 168 (=14×12) RBs are defined in LTE uplink, the number of REs available for PUSCH transmission is 144 (12×12) with exception of resource assigned for RS. 
     In case of the subframe including Sounding RS (SRS) transmitted for uplink channel state at eNB, the last SC-FDMA symbol of a subframe is used for SRS transmission. Accordingly, the number of PUSCH REs is 132 (=11×12) per RB. Here, the number of REs is for a normal CP subframe. In case of using the extended CP, the number of SC-FDMA symbols constituting the subframe decreases and, as a consequence, the number of RE varies. 
       FIG. 6  is a block diagram illustrating a configuration of a UE transmitter in a legacy LTE system. 
     Referring to  FIG. 6 , the TB  620  is channel coded by a channel coder  622 , scrambled by a scrambler  624 , and modulated by a modulator  626 , so as to be output as a modulation symbol stream. The modulation symbol stream is transform-precoded by a transform precoder  628  as DFT precoder, mapped to PUSCH RB by an RE mapper  630 , and then converted to SC-FDMA signal by a SC-FDMA signal generator  632  to be transmitted through a UE transmit antenna  634 . 
       FIG. 7  is a block diagram illustrating a configuration of an eNB receiver in a legacy LTE system. 
     Referring to  FIG. 7 , the signal received by the receive antenna  710  processed by a SC-FDMA signal receiver  712  and then RE-demapped by an RE demapper  714 . In case that the eNB has multiple receive antennas, it is assumed that an antenna combiner is included in the SC-FDMA signal receiver  712 . The signal separated to decode the DFT precoding applied at the UE for generating the SC-FDMA signal is processed by a transform-precoding decoder  716  as an Inverse DFT (IDFT), demodulated by a demodulator  718 , descrambled by a descrambler  720 , and channel-decoded by a channel decoder  722  so as to be recovered as the TB  724  transmitted by each user. 
       FIG. 8  is a diagram illustrating resource allocation according to channel state of UE in conventional system. 
     Referring to  FIG. 8 , two UEs  802  and  804  are connected to a eNB  800 . The UE  804  is located close to the eNB  800  as compared to the UE  802  such that the average channel state of the UE  804  is superior to that of the UE  802 . 
     If the channel response of UE  802  is good enough to apply a high order modulation and coding scheme, it is possible to allocate the resource small in amount to the UE  802  for transmitting the same data amount as the UE  804 . For example, if the 16QAM (16 Quadrature Amplitude Modulation) is applied to the UE  802  while QPSK (Quadrature Phase Shift Keying) to the UE  904 , the PDSCH or PUSCH for UE  802  carries 4 coded bits per RE while the PDSCH or PUSCH for UE  802  carries 2 coded bits per RE. If the same channel coding is applied and the same data amount is transmitted, the UE  804  needs only half of the resource allocated to the UE  804 . 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The LTE system composed of an UE having a good channel quality and an eNB is capable of reducing the resource amount to be less than an RB for providing a service generating small amount of traffic regularly such as VoIP. However, there is no resource allocation in unit less than an RB in LTE. The reason is because the use of smaller resource allocation causes the ore control signal overhead for indicating the allocated resource. In order to solve this problem, may researches are being conducted. 
     The present invention proposes a fractional RB allocation method that is capable of allocating the resource in unit smaller than an RB, resulting in improvement of VoIP capacity in LTE system. Also, the present invention introduces a method for resource mapping to enable different users to share the same resource without using SDMA and indicating fractional RB allocation. It is an object of the present invention to improve VoIP capacity by reducing the resource amount occupied by the UEs having good channel quality. 
     Solution to Problem 
     In order to solve the above problems, the resource allocation method of the present invention includes generating modulation symbols streams by performing channel coding and modulation on transport blocks corresponding to first and second data to be transmitted to respective users; multiplexing the modulation symbols stream alternately in unit of two continuous modulation symbols; and transmitting the multiplexed modulation symbol stream as mapped to corresponding resource. 
     Advantageous Effects 
     According to the present invention, it is allowed to allocate resource in unit smaller than an RB for delay sensitive service such as VoIP generating a small amount of traffic at a certain interval, resulting in increase of capacity of service such as VoIP. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is diagram illustrating a resource unit defined for downlink in a LTE system; 
         FIG. 2  is a diagram illustrating an RB composed of a plurality of REs arranged with different purposes in LTE downlink; 
         FIG. 3  is a block diagram illustrating a configuration of an eNB transmitter in a legacy LTE system; 
         FIG. 4  is a diagram illustrating a resource unit defined in uplink of a legacy LTE system; 
         FIG. 5  is a diagram illustrating resource arrangement per purpose in an RB in uplink of legacy LTE; 
         FIG. 6  is a block diagram illustrating a configuration of a UE transmitter in a legacy LTE system; 
         FIG. 7  is a block diagram illustrating a configuration of an eNB receiver in a legacy LTE system; 
         FIG. 8  is a diagram illustrating resource allocation according to channel state of UE in conventional system; 
         FIG. 9  is a block diagram illustrating a configuration of an LTE eNB transmitter having a multiplexer for supporting downlink fractional RB allocation according to an embodiment of the present invention; 
         FIG. 10  is a diagram illustrating a configuration of a first type multiplexer supporting fractional RB allocation according to an embodiment of the present invention; 
         FIG. 11  is a diagram illustrating RE mapping with the use the first type multiplexer according to an embodiment of the present invention; 
         FIG. 12  is a block diagram illustrating a configuration of a second type multiplexer according to an embodiment of the present invention; 
         FIG. 13  is a diagram illustrating RE mapping with the use the second type multiplexer in the eNB using two transmit antennas according to an embodiment of the present invention; 
         FIG. 14  is a diagram illustrating RE mapping with the use the second type multiplexer in the eNB using a single transmit antenna according to an embodiment of the present invention; 
         FIG. 15  is a diagram illustrating RE mapping with the use the second type multiplexer in the eNB using four transmit antennas according to an embodiment of the present invention; 
         FIG. 16  is a block diagram illustrating a configuation of a third type multiplexer for supporting fractional RB allocation according to an embodiment of the present invention; 
         FIG. 17  is a diagram illustrating RE mapping with the use the third type multiplexer in the eNB using four transmit antennas according to an embodiment of the present invention; 
         FIG. 18  is a diagram illustrating RE mapping with the use the third type multiplexer in the eNB using one transmit antennas according to an embodiment of the present invention; 
         FIG. 19  is a diagram illustrating RE mapping with the use the third type multiplexer in the eNB using 2 transmit antennas according to an embodiment of the present invention; 
         FIG. 20  is a diagram illustrating a principle of RE mapping of an LTE transmitter according to an embodiment of the present invention; 
         FIG. 21  is a block diagram illustrating a configuration of a fourth type multiplexer for supporting fractional RB allocation according to an embodiment of the present invention; 
         FIG. 22  is a block diagram illustrating a configuration of a UE receiver supporting the fractional RB allocation with a multiplexer according to an embodiment of the present invention; 
         FIG. 23  is a flowchart illustrating a method of downlink fractional RB allocation according to an embodiment of the present invention; 
         FIG. 24  is a diagram illustrating a principle of uplink fractional RB allocation method according to the first embodiment of the present invention; 
         FIG. 25  a diagram illustrating a principle of uplink fractional RB allocation method according to the second embodiment of the present invention; and 
         FIG. 26  is a flowchart illustrating a method of uplink fractional RB allocation according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed description of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention. 
     Terms and words used in the specification and claims must be regarded as concepts selected by the inventor as the best method of illustrating the present invention, and must be interpreted as having meanings and concepts adapted to the scope and sprit of the present invention to understand the technology of the present invention. 
       FIG. 9  is a block diagram illustrating a configuration of an LTE eNB transmitter having a multiplexer for supporting downlink fractional RB allocation according to an embodiment of the present invention. 
     Referring to  FIG. 9 , TB 1   910   a  as the first data to be transmitted to the first UE of user A and TB 2   910   b  as the second data to be transmitted to the second UE of user B are channel-coded by channel coders  912   a  and  912   b , scrambled by scramblers  914   a  and  914   b , and modulated by modulators  916   a  and  916   b  so as to be output as modulation symbol streams. The symbol streams output by modulating the first and second data are multiplexed by a multiplexer  918 . Next, the multiplexed modulation signal stream is layer-mapped by a layer mapper  920  and precoded into per-spatial layer modulation symbol streams. In case of SM, the number of CWs is limited to 2 while the number of spatial layers is allowed up to 4. In case of transmit diversity, the number of CWs is 1 while the number of spatial layers is 2 or 4 with the precoding as transmit diversity coding. The precoding can be categorized into one of a transmit diversity coding, open-loop precoding, and closed-loop coding. 
     A precoder  922  converts the modulation symbol streams per spatial layer to symbol streams to be transmitted through respective antenna ports  928   c  and  928   d . The precoded symbol streams are mapped to REs per antenna port by RE mappers  924   c  and  924   d  and converted to OFDM symbols by OFDM signal generators  926   c  and  926   d  so as to be transmitted through respective transmit ports  928   c  and  928   d.    
     Although the description is made under the assumption that the first and second data are transmitted to respective UEs, the present invention is not limited. That is, in case that a UE is configured with at least two receive antennas, the data transmitted through the respective antennas can be discriminated among the first and second data. 
     The eNB transmitter according to an embodiment of the present invention can be configured by adding the multiplexer  918  to the structure of the conventional eNB transmitter. By adding the multiplexer  918 , it is possible to transmits TBs  910   a  and  910   b  to different users, instead of two CW transmissions, through SM. Here, the multiplexer  918  is responsible for multiplexing multiple users into an RB. 
     Since the traffic amount generated by VoIP is not great, the SM operation is excluded for simplifying the explanation. Although  FIG. 9  is depicted under assumption that an RB is shared by two UEs for simplicity purpose, it is obvious that the number of UEs sharing an RB can increases if multiple UEs having good channel quality are aggregated. 
     Since the VoIP traffic is delay-sensitive, the precoding technique is used for transmit diversity. The transmit diversity is the technique to mitigate the influence of fading effect caused by irregular variation of reception electric field in electromagnetic wave environment and includes frequency diversity technique, spatial diversity technique, and transmit diversity technique. 
     The frequency diversity is the technique to transmit data on the resources located distant enough on the frequency axis. By taking notice of frequency-selective fading, the data transmitted on the resources located far enough on frequency axis experience channel responses with low correlation. In this case, even though the signal transmitted on a resource experience worst channel, the signal transmitted on the other resource is likely not to experience such worst channel. Accordingly, the possibility that the signals transmitted with the frequency diversity technique experiences the worst channel quality decreases. 
     The spatial diversity is the technique to transmit or receive data through spatially separated antennas. If the distance between antennas are far enough, the channel response correlation between the antennas decreases. Accordingly, even when the signal transmitted through an antenna experience very bad channel, the signal transmitted through the other antenna is likely to experience relatively good channel. In case of using the spatial diversity technique, the probability that all the signals experience very bad channel states decreases. 
     The transmit diversity is the technique to adopt the spatial diversity to the transmitter. LTE adopts Space Frequency Block Coding (SFBC) for the eNB having two transmit antennas and a combination of SFBC and Frequency Switched Transmit Diversity (FSTD) for the eNB having four transmit antennas. The SFBC technique is to transmit the spatial diversity-coded symbols in contiguous subcarriers rather than the same subcarrier in the contiguous time slots, and FSTD technique is to transmit the symbols extracted from a coded symbol stream while switching between antennas per frequency. 
     SFBC is the transmit diversity technique for transmitting a pair of modulation symbol ‘streams through two transmit antennas. Formula (1) expresses the SFBC transmission technique. 
     
       
         
           
             
               
                 
                   [ 
                   
                     
                       
                         
                           S 
                           
                             2 
                             ⁢ 
                             k 
                           
                         
                       
                       
                         
                           S 
                           
                             
                               2 
                               ⁢ 
                               k 
                             
                             + 
                             1 
                           
                         
                       
                     
                     
                       
                         
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     In matrix of formula (1), the columns denote subcarriers on frequency axis, and the rows denotes transmit antennas. That is, the first transmit antenna transmits {S 2k , S 2k+1 } on the two congiguous subcarriers {−S* 2k+1 , S* 2 k}, and the second transmit antenna transmits on the same subcarriers. In this manner, SFBC applys transmit diversity of the two contiguous subcarriers. 
     The combination of SFBC and FSTD is the transmit diversity technique for transmitting four contiguous modulation symbol streams {S 2k , S 2k+1 , S 2k+2 , S 2k+3 } through four transmit antennas. Formula (2) expresses the transmit diversity technique using four transmit antennas. 
     
       
         
           
             
               
                 
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     In matrix of formula (2), the columns denote subcarriers on frequency axis, and the rows denote transmit antennas. That is, the first transmit antenna transmits {S 2k , S2k+1} on two contiguous subcarriers, the third transmit antenna transmits {−S* 2k+1 , S *   2k } on the same subcarriers, the second transmit antenna transmits {S 2k+2 , S 2k+3 } on two congiguous subcarriers, and the fourth transmit antenna transmits {−S* 2k+3 , S* 2k+2 } on the same subcarriers. 
       FIG. 10  is a diagram illustrating a configuration of a first type multiplexer supporting fractional RB allocation according to an embodiment of the present invention. 
     Referring to  FIG. 10 , [S 0   (A) , . . . , S k   (A) , . . . ] denotes a modulation symbol stream to be transmitted to the first UE, and [S 0   (B) , . . . , S k   (B) , . . . ] denotes a modulation symbol stream to be transmitted to the second UE. These two symbol streams are multiplexed into a multiplex modulation symbol stream [S 0   (A) , S k   (B) , . . . , S k   (A) , S k   (B) , . . . ] by the multiplexer  918   a . The first type multiplexer  918   a  is characterized by multiplexing the modulation symbol streams of individual users alternately. 
       FIG. 11  is a diagram illustrating RE mapping with the use the first type multiplexer according to an embodiment of the present invention. 
     In  FIG. 11 , it is assumed that one transmit antenna is used and the control region is composed of three OFDM symbols at the beginning of the subframe. Accordingly, the REs denoted by reference number  1115  are not used for PDSCH transmission. In LTE downlink, the frequence first mapping scheme is adopted. Accordingly, when the first type multiplexer  918   a  depicted in  FIG. 10  is used, the REs denoted by reference number  1117  are mapped for the first UE, and the REs denoted by reference number  1119  are mapped for the second UE. Meanwhile, the modulation symbols are mapped to the REs in a sequential order jumping the RS REs. 
     The description has been directed to the modulation symbol mapping method of the eNB having one transmit antenna hereinabove. In case of using one transmit antenna, the signals destined to different UEs are transmitted on the orthogonal frequency and time so as to avoid interference between the UEs. 
     A description is made of the case where the eNB having two transmit antennas uses SFBC. In this case, the eNB transmits the modulation symbols arranged in the form of matrix (3). 
     
       
         
           
             
               
                 
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     If the UE performs channel estimation without error, the modulation symbols S k   (A)  and S k   (B)  transmitted to different UEs can be recovered without interference to each other. However, an error occurs in the channel estimation, interference takes place between the UEs. Such interference may take place due to the channel estimation error even when the UEs are not multiplexed. If there is a large difference in power between the first and second UEs, the signal of the UE allocated relatively high power interferes the signal of the UE allocated relatively low power. 
       FIG. 12  is a block diagram illustrating a configuration of a second type multiplexer according to an embodiment of the present invention. 
     Referring to  FIG. 12 , [S 0   (A) , S 1   (A) , . . . ] is a modulation symbol stream to be transmitted to the first UE, and [S 0   (B) , S 1   (B) , . . . ] is a modulation symbol stream to be transmitted to the second UE. These two symbol streams are multiplexed into a multiplex symbol stream [S 0   (A) , S 1   (A) , S 0   (B) , S 1   (B) , . . . ] by the multiplexer  918   b.    
     The second type multiplexer  918   b  can multiplex modulation symbols of each UE in pairs alternately. That is, the second type multiplexer  918   b  is characterized by grouping the modulation symbols of each UE in unit of two contiguous symbols and multiplexing the groups alternately. In this way, SFBC is applied to the modulation symbols of the same UE so as to avoid interference between UEs. 
       FIG. 13  is a diagram illustrating RE mapping with the use the second type multiplexer in the eNB using two transmit antennas according to an embodiment of the present invention. 
     Referring to  FIG. 13 , the control region is composed of the first three OFDM symbols of the subframe. Accordingly, the REs designated by reference number  1315  are not used for PDSCH transmission in RB  1310 . Since the frequence first mapping scheme is adopted in LTE downlink, if the second type multiplexer  918   b  of  FIG. 12  is used, the REs denoted by reference number  1317  are mapped for the first UE, and the REs denoted by reference number  1319  are mapped for the second UE. The second type multiplexer  918   b  of  FIG. 12  can be applied for single transmit antenna transmission. 
       FIG. 14  is a diagram illustrating RE mapping with the use the second type multiplexer in the eNB using a single transmit antenna according to an embodiment of the present invention. 
     Referring to  FIG. 14 , under the assumption of the control region composed of the first three OFDM symbols, the REs designated by reference number  1415  are not used for PDSCH transmission in RB  1410 . Assuming the frequency first mapping, the REs denoted by reference number  1417  are mapped for the first UE, and the REs denoted by reference number  1419  are mapped for the second UE. As shown in  FIG. 14 , the number of the REs  1417  mapped for the first UE is greater by 2 than the number of the REs  1419 . This is because the condition that, when using the second type multiplexer  918   b , the number of REs for PDSCH transmission should be a multiple of 4 for allocating the same amount of resource to the users is not fulfilled always. In order to achieve fair resource allocation between the users, it can be considered to change the multiplexing order at every transmission. 
     For example, the second type multiplexer  918   b  of  FIG. 12  can arrange the REs  1417  for the first UE prior to the REs  1419  for the second UE at odd-numbered transmissions and the REs  1419  for the second UE prior to the REs  1417  for the first UE at even-numbered transmissions. By taking notice of a large number of transmission durations, it is possible to expect fair resource allocation between the UEs. 
       FIG. 15  is a diagram illustrating RE mapping with the use the second type multiplexer in the eNB using four transmit antennas according to an embodiment of the present invention. 
     Referring to  FIG. 15 , under the assumption of the control region composed of the first three OFDM symbols, the REs designated by reference number  1515  are not used for PDSCH transmission in RB  1510 . Assuming the frequency first mapping, the REs denoted by reference number  1517  are mapped for the first UE, and the REs denoted by reference number  1519  are mapped for the second UE. 
     In case that the eNB using four transmit antennas adopts the combination of SFBC and FSTD for the transmit diversity, the transmission can be performed in the form of matrix (4). 
     
       
         
           
             
               
                 
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     That is, the first UE always UEs the first and third transmit antennas while the second UE uses the second an fourth transmit antennas. In this case, there is no interference between the user but the diversity order is limited to 2. 
       FIG. 16  is a block diagram illustrating a configuation of a third type multiplexer for supporting fractional RB allocation according to an embodiment of the present invention. 
     Referring to  FIG. 16 , [S 0   (A) , S 1   (A) , S 2   (A) , S 3   (A) , . . . ] is the modulation symbol stream to be transmitted to the first UE, and [S 0   (B) , S 1   (B) , S 2   (B) , S 3   (B) , . . . ] is the modulation symbol to be transmitted to the second UE. These two symbol streams are multiplexed into [S 0   (A) , S 1   (A) , S 2   (A) , S 3   (A) , S 0   (B) , S 1   (B) , S 2   (B) , S 3   (B) , . . . ] by the third type multiplexer  918   c.    
     The third type multiplexer  918   c is  characterized by multiplexing in unit of four continuous modulation symbols for the respective UEs alternately. With this scheme, the transmit diversity of combination of SFBC and FSTD are applied to the modulation symbols for the same UE so as to maintain the diversity order of 4. 
       FIG. 17  is a diagram illustrating RE mapping with the use the third type multiplexer in the eNB using four transmit antennas according to an embodiment of the present invention. 
     Referring to  FIG. 17 , under the assumption of the control region composed of the first three OFDM symbols, the REs designated by reference number  1715  are not used for PDSCH transmission in RB  1710 . Assuming the frequency first mapping adopted in LTE downlink, with the use of the third type multiplexer  918   c , the REs denoted by reference number  1717  are mapped for the first UE, and the REs denoted by reference number  1719  are mapped for the second UE. 
     According to the embodiment of  FIG. 17 , the number of REs  1717  for the first UE is greater by 4 than the number of REs  1719  for the second UE. This is because the condition that, with the third type multiplexer  918   c , the number of REs for PDSCH transmission should be a multiple of 8 for allocating the same amount of resource to the users is not fulfilled always. In order to achieve fair resource allocation between the users, it can be considered to change the multiplexing order at every transmission. 
     For example, the third type multiplexer  918   c  of  FIG. 16  arranges the REs  1717  for the first UE prior to the REs  1719  for the second UE at odd-number transmissions as [S 0   (A) , S 1   (A) , S 2   (A) , S 3   (A) , S 0   (B) , S 1   (B) , S 2   (B) , S 3   (B) , . . . ] and the REs  1719  for the second UE prior to the REs  1717  for the first UE at even-numbered transmissions as [S 0   (B) , S 1   (B) , S 2   (B) , S 3   (B) , S 0   (A) , S 1   (A) , S 2   (A) , S 3   (A) , . . . ]. By taking notice of a large number of transmission durations, it is possible to expect fair resource allocation between the UEs with this scheme. 
       FIG. 18  is a diagram illustrating RE mapping with the use the third type multiplexer in the eNB using one transmit antennas according to an embodiment of the present invention. 
     Referring to  FIG. 18 , under the assumption of the control region composed of the first three OFDM symbols, the REs designated by reference number  1815  are not used for PDSCH transmission in RB  1810 . Assuming the frequency first mapping adopted in LTE downlink, the REs denoted by reference number  1817  are mapped for the first UE, and the REs denoted by reference number  1819  are mapped for the second UE. According to the embodiment of  FIG. 18 , the number of REs  1817  for the first UE is greater by 2 than the number of REs  1819  for the second UE. With the use of multiplexing order change scheme, it is possible to achieve fair resource allocation between the users. 
       FIG. 19  is a diagram illustrating RE mapping with the use the third type multiplexer in the eNB using 2 transmit antennas according to an embodiment of the present invention. 
     Referring to  FIG. 19 , under the assumption of the control region composed of the first three OFDM symbols, the REs designated by reference number  1915  are not used for PDSCH transmission in RB  1910 . Assuming the frequency first mapping adopted in LTE downlink, the REs denoted by reference number  1917  are mapped for the first UE, and the REs denoted by reference number  1919  are mapped for the second UE. 
     With such fractional RB allocation scheme, to multiplexer can multiplex a plurality of users into a single RB. Referring to RE arrangements of  FIGS. 11 ,  13 ,  14 ,  15 ,  17 ,  18 , and  19 , it is noted that the fractional RB allocation can be implemented even through the RE arrangement is modified. 
       FIG. 20  is a diagram illustrating a principle of RE mapping of an LTE transmitter according to an embodiment of the present invention. 
     In the embodiment of  FIG. 20 , the users are mapped to different OFDM symbols on time axis in TDM (Time Division Multiplexing) manner. TDM, is to allocate resource in unit of SC-FDMA symbol on time axis. 
     In RB  2010 , the 4th, 6 th , 8 th , 10 th , 12 th , and 14 th  OFDM symbols are configured with the REs  2017  for the first UE. The 5 th , 7 th , 9 th , 11 th , and 13 th  OFDM symbols are configured with the REs  2019  for the second UE. If the REs are arranged on frequency axis in the same manner, the FDM (Frequency Division Multiplexing) is adopted. 
       FIG. 21  is a block diagram illustrating a configuration of a fourth type multiplexer for supporting fractional RB allocation according to an embodiment of the present invention. 
     Referring to  FIG. 21 , the fourth multiplexing scheme is characterized in that the fourth type multiplexer  918   d  performs CDM (Code Division Multiplexing). CDM is characterized by spreading a plurality of modulation symbol streams are spread by different codes such that the resources are allocated on code axis. 
     It is assumed that [S 0   (A) , S 1   (A) , . . . ] is the modulation symbol stream to be transmitted to the first UE, and [S 0   (B) , S 1   (B) , . . . ] is the modulation symbol stream to be transmitted to the second UE. These two symbol streams are multiplexed into [S 0   (A) +S 0   (B) , S 0   (A) −S 0   (B) , S 1   (A) +S 1   (B) , S 1   (A) −S 1   (B) , . . . ] by the multiplexer  918   d  corresponding to a 2×2 Walsh-Hadamard transformer. Since the main object to secure the orthogonality among the codes in the modulation symbol transformation at the fourth type multiplexer  918   d , it is possible to apply a certain orthogonal unitary transform rather than Wash-Hadamard transformation. 
     With the use of this CDM scheme, it is possible to avoid the interference between users that may be caused by application of the fourth type multiplexing scheme to the eNB using multiple antennas. In CDM, since all of the PDSCH REs are mapped for the signals of one UE, it is not necessary to map the user signal to the REs in different patterns for respective uses. 
       FIG. 22  is a block diagram illustrating a configuration of a UE receiver supporting the fractional RB allocation with a multiplexer according to an embodiment of the present invention. 
     Although  FIG. 22  is depicted under the assumption of the configuration of the UE having multiple receive antennas, the present invention can be applied when the UE has a single receive antenna; In case that the UE has one transmit antenna, it can be implemented only one OFDM receiver and one RE demapper. The signals received by the receive antennas  2210   c  and  2210   d  of the receiver processed by the OFDM receivers  2212   c  and  2212   d  so as to be converted to baseband signals. The converted signal is delivered to the channel estimator  2216  via the RE demappers  2214   c  and  2214   d  for extracting resource allocation indication signal, and the signal mapped to PDSCH REs are delivered to the pre-decoder  2218 . 
     In case that the precoding is applied for the transmit diversity, the pre-decoder  2218  is a transmit diversity receiver. Since the pre-decoder  2218  needs channel response, it receives channel response estimation value from the channel estimator  2216 . 
     The pre-decoded signal is demapped by a layer demapper  2220  so as to be recovered as multiplexed modulation symbol streams. The multiplexed modulation symbol streams are demultiplexed by a demultiplexer  2224  so as to extract only the modulation symbols destined to the receiver. If fractional RB allocation is not applied, the extraction process at the demultiplexer  2224  is skipped. The extracted user modulation symbol stream is processed by a descrambler  2228  and a channel decoder  2230  in sequence so as to be recovered as TB  2232 . Here, since both the demodulator  2226  and the channel decoder  2230  receives the channel response estimation value from the channel estimator  2216 . 
     In case that the fractional RB allocation is performed by changing RE arrangement rather than multiplexing, the extraction process performed by the multiplexer  2224  is skipped, and the modulation symbols destined to the UE are extracted by RE demappers  2214   c  and  2214   d.    
     In order to support downlink fractional RB allocation according to an embodiment of the present invention, one a multiplexing-based method and a RB arrangement modification-based method can be used. Discussions have been done about the problems that may occur according to the multiplexing scheme and the number of eNB&#39;s transmit antennas. Descriptions are made of the embodiments in which the fractional RB allocation is implemented with multiplexing technique. 
     &lt;First Embodiment&gt; 
     The first embodiment relates to the method for applying the first type multiplexing scheme regardless of the number of transmit antennas as described with reference to  FIG. 10 . In this method, interference may occur between UEs when the number of transmit antennas is 2 or 4. However, it is possible to maintain a specific multiplexing scheme regardless of the number of eNB&#39;s transmit antennas and achieve fair resource allocation to the two UEs with the fractional RB allocation in a subframe. 
     &lt;Second Embodiment&gt; 
     The second embodiment relates to the method for applying the second type multiplexing scheme regardless of the number of transmit antennas as described with reference to  FIG. 12 . This method guarantees no interference between the UEs and allows maintaining a specific multiplexing scheme regardless of the number of eNB&#39;s transmit antennas, however, the diversity order is limited to 2 when the number of eNB&#39;s transmit antennas is 4. 
     &lt;Third Embodiment&gt; 
     The third embodiment relates to the method for applying the third type multiplexing scheme regardless of the number of transmit antennas as described with reference to  FIG. 16 . This method guarantees no interference between the UEs and allow s maintaining a specific multiplexing scheme regardless of the number of eNB&#39;s transmit antennas. Also, this method is characterized in that the diversity order of 4 can be maintained even when the number of eNB&#39;s transmit antennas I 4. 
     &lt;Fourth Embodiment&gt; 
     The fourth embodiment relates to the method for applying the fourth type multiplexing scheme regardless of the number of transmit antennas as described with reference to  FIG. 21 . This method may cause interference between UEs but can maintain a specific multiplexing scheme regardless of the number of eNB&#39;s transmit antennas. Also, this method is characterized by fair resource allocation to the UEs with fractional RB allocation in a subframe. 
     &lt;Fifth Embodiment&gt; 
     The fifth embodiment relates to the method for applying different multiplexing schemes depending on the number of transmit antennas of the eNB. This method apply the first multiplexing scheme for the case of using one transmit antenna, second multiplexing scheme for the case of using two transmit antennas, and third multiplexing scheme for the case of using four transmit antennas. With this method, no interference takes place between the UEs. 
     &lt;Sixth Embodiment&gt; 
     The sixth embodiment relates to the method for supporting the fractional RB allocation without change of the RE arrangement as described with reference to  FIG. 20  with no introduction of new multiplexing scheme. Although this causes no interference between the users and a predetermined arrangement rule can be applied regardless of the number of eNB&#39;s transmit antennas, fair resource allocation between the users is not guaranteed. 
     The above-described embodiments can be applied to the case where dedicated RS is defined. A description is made of signaling between eNB and UE for implementing these embodiments hereinafter. 
       FIG. 23  is a flowchart illustrating a method of downlink fractional RB allocation according to an embodiment of the present invention. 
     Referring to  FIG. 23 , the eNB configures the fractional RB allocation mode for a VoIP UE having good channel state at step  2310 . Next, the eNB transmits downlink resource allocation information in PDCCH at step  2320 . In the fractional RB allocation mode, the eNB transmits PDCCH designed to support the fraction RB allocation or interpret PDCCH under the assumption of fractional RB allocation. For this purpose, the PDCCH can be interpreted as follows. 
     The first method is to modify the structure of PDCCH to notify explicitly which fractional RB is allocated. It is assumed that the fractional RB is defined so as to allocate resources for K UEs in an RB. If the number of downlink RBs is N RB , the eNB uses log 2 (K×N RB ) as RB allocation field so as to notify the UE of the allocated multiplexing pattern explicitly. Also, it is possible to notify the UE of the allocated RB and multiplexing pattern in the RB allocation field by adding a new field of log 2  (K) bits. In order to discriminate among K multiplexing patterns and the case with no fractional RB application, the eNB can use log 2 ((K+1)×N RB ) bits for the RB allocation field or add a new field of log 2  (K+1) bits while maintaining the conventional PDCCH. 
     The second method is to interpret the conventional PDCCH in different rule without modifying the configuration of PDCCH. In case that the VoIP UE is allocated a higher order MCS, the eNB interprets this as fractional RB allocation and notifies of the multiplexing pattern with bits of a field. Since the VoIP UE has low decoding burden, the eNB may use blink decoding in association with resource allocation. For example, the UE attempts decoding with the assumption of every case without explicit notification on the situation such as the case of using an RB entirely, case of using pattern A, and case of using Pattern B. In case of depending on the blind decoding, if the pattern can be changed at every transmission by taking notice of HARQ process, it is necessary to increases the size of soft buffer for storing the values used in decoding as much as the combination of the patterns. 
     Next, the eNB transmits PDSCH to the UE as indicated in PDCCH at step  2330 . The UE receives PDCCH to acquire transmission format and resource allocation information at step  2340 . Next, the UE receives PDSCH using the acquired transmission format and resource allocation information at step  2350 . 
     Until now, the eNB&#39;s resource allocation method has been explained. A description is made of the resource allocation method for data transmission from the UE to the eNB. 
     Since the UE is a transmitter in LTE uplink, the multiplexing of the UEs are not performed by the transmitter. Accordingly, it is a condition of uplink fraction RB allocation for the eNB to allocate the resources orthogonal between UEs without defying the features of SC-FDMA. 
       FIG. 24  is a diagram illustrating a principle of uplink fractional RB allocation method according to the first embodiment of the present invention. 
     Referring to  FIG. 24 , the resources orthogonal between the users are defined as different SC-FDMA symbols. Reference number  2410  denotes REs designated for dedicated RS, reference number  2420  denotes PUSCH REs for the first UE, and reference number  2430  denotes PUSCH REs for the second UE. The PUSCH REs  2420  and  2430  for the first and second UEs are arranged on time axis. The RE mapping is performed by the RE mapper in UE transmitter and RE demapper in eNB receiver. 
       FIG. 25  a diagram illustrating a principle of uplink fractional RB allocation method according to the second embodiment of the present invention. 
     Referring to  FIG. 25 , the resources orthogonal between the UEs are defined as different REs. Reference number  2510  denotes REs designated for dedicated RSs, reference number  2520  denotes PUSCH REs for the first UE, and reference number  2530  denotes PUSCH REs for the second UE. The PUSCH REs  2420  and  2430  for the first and second UEs are arranged on frequency axis. Since the SC-FDMA condition should be satisfied, the REs for a UE are arranged at the same interval. Accordingly, the RE mapping is performed by the RE mapper in UE transmitter and RE demapper in eNB receiver. 
       FIG. 26  is a flowchart illustrating a method of uplink fractional RB allocation according to an embodiment of the present invention. 
     Referring to  FIG. 26 , the eNB configures fractional RB allocation mode for the VoIP UE having good channel condition as in downlink at step  2610 . Next, the eNB transmits the uplink resource allocation information in PDCCH to the UE at step  2620 . At this time, the eNB transmits PDCCH designed to support fractional RB allocation in the fractional RB allocation mode as in downlink or interprets PDCCH under the assumption of fractional RB allocation. 
     Finally, the UE transmits PUSCH as indicated in PDCCH at step  2630 . That is, if fractional RB is allocated through PDCCH, the UE transmits PUSCH with the application of fractional RB allocation. 
     Although the description has been made with reference to particular embodiments, the present invention can be implemented with various modification without departing from the scope of the present invention. Thus, the present invention is not limited to the particular embodiments disclosed but will include the following claims and their equivalents.

Technology Category: h