Patent Publication Number: US-2007097887-A1

Title: Communication method and system using time division duplex scheme and frequency division duplex scheme

Description:
PRIORITY  
      This application claims the benefit under 35 U.S.C. §119(a) of an application filed in the Korean Intellectual Property Office on Sep. 13, 2005 and assigned Serial No. 2005-85274, the contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to bidirectional communication in a communication system, and in particular, to a hybrid communication method and system using a frequency division duplex (FDD) scheme and a time division duplex (TDD) scheme.  
      2. Description of the Related Art  
      Generally, the 3 rd  generation communication system can use FDD and TDD schemes for bidirectional communication. The FDD scheme is suitable for providing voice service to users moving at high speed in a cellular environment, and the existing 2 nd  generation Global System for Mobile Communications (GSM) and Interim Standard-95 (IS-95) use the FDD scheme. Most 3 rd  generation systems also use the FDD scheme. The TDD scheme is suitable for providing data-oriented service in a fixed or low-speed nomadic/wireless LAN environment.  
      In the TDD scheme, it is not possible to design a system for reducing transmission delay while enlarging cells and increasing transmission efficiency of frames. For this reason, the TDD scheme is unsuitable for providing voice service in a high-speed moving environment. In addition, a long-length TDD frame is advantageous for increasing transmission efficiency. Each TDD frame should always include overheads such as a guard time, e.g., Tx/Rx Transition Gap (TTG) or Rx/Tx Transition Gap (RTG), and a synchronization signal. The guard time is a value determined mainly depending on the cell size, and requires a specific size. In order to increase design efficiency by reducing a percentage of the overheads, it is necessary to increase the frame length. From 7 layers based on the open system inter-connection (OSI) reference model, a media access control (MAC) layer that manages control based on a connection method of a physical transmission line also requires a long frame length in order to increase the efficiency considering a MAC overhead.  
      However, in the TDD scheme, the frame length should be small in order to reduce transmission delay and cope with high-speed movement. That is, in order to provide low-delay constraint service, a size of the TDD frame should be small. If a terminal moves, its channel characteristic undergoes a change. To determine the best modulation and coding scheme (MCS) level and power according to the time-varying channel characteristic, it is necessary to frequently exchange various control signals. For this purpose, the frame length should be short.  
      The next generation communication system should satisfy the following conditions.  
      Provide both mobile and nomadic communication environments, e.g., provide high-speed communication service to users moving at high speed in the cellular environment, and provide high-speed communication service in a nomadic fixed or low-speed environment, such as a pedestrian environment.  
      Simultaneously provide various multimedia services including voice service.  
      In order to satisfy the foregoing conditions, there is a need for a frame structure and a communication scheme having advantages of both the FDD and TDD schemes.  
     SUMMARY OF THE INVENTION  
      It is, therefore, an object of the present invention to provide a communication method and system capable of reducing transmission delay and effectively coping with high-speed movement while increasing transmission efficiency by increasing a frame length.  
      It is another object of the present invention to provide a hybrid duplex communication method and system capable of providing advantages of both a TDD and an FDD scheme.  
      According to the present invention, there is provided a communication method in a communication system, including transmitting, by a base station, downlink information to a terminal through a frequency band of a first communication scheme for a downlink period, and transmitting, by the terminal, uplink information to the base station through the frequency band of the first communication scheme or a frequency band of a second communication scheme, which is different from the frequency band of the first communication scheme, for an uplink period.  
      According to the present invention, there is provided a first embodiment of a system in a communication system, including a base station having a transmitter for transmitting downlink information to a terminal through a frequency band of a first communication scheme for a downlink period, and a receiver for receiving uplink information from the terminal through the frequency band of the first communication scheme or a frequency band of a second communication scheme, which is different from the frequency band of the first communication scheme, for an uplink period.  
      According to the present invention, there is provided a second embodiment of a system in a communication system, including a terminal having a receiver for receiving downlink information from a base station through a frequency band of a first communication scheme for a downlink period, and a transmitter for transmitting uplink information to the base station through the frequency band of the first communication scheme or a frequency band of a second communication scheme, which is different from the frequency band of the first communication scheme, for an uplink period. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
       FIG. 1  is a diagram illustrating an HDD frame/time slot structure according to the present invention;  
       FIG. 2  is a diagram illustrating the construction of a base station according to the present invention;  
       FIG. 3  is a diagram illustrating the construction of a terminal according to the present invention; and  
       FIGS. 4 and 5  are graphs illustrating overhead ratios versus a guard time length and a frame length, respectively, when a typical TDD frame structure is used. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for the sake of clarity and conciseness.  
      The present invention provides a hybrid duplex (HDD) communication method and system capable of providing advantages of both a TDD scheme and an FDD scheme. In addition, the preset invention provides a communication method and system capable of solving the problems occurring in the typical TDD scheme, while using a TDD band in the HDD scheme.  
       FIG. 1  illustrates an HDD frame/time slot structure according to the present invention.  
      Referring to  FIG. 1 , the HDD scheme transmits/receives signals using two frequency bands  102  and  104 . The first frequency band  102  is a TDD band used for transmitting/receiving signals by dividing slots  110   a  and  110   b  (hereinafter  110 ), and the second frequency band  104  is an FDD UL band used for transmission of a terminal and for reception of a base station, such as an FDD uplink (FDD UL). Transmission/reception through a TDD downlink (TDD DL) and a TDD UL using the first frequency band  102  occurs the same as in the conventional TDD communication, and transmission/reception through a TDD DL and an FDD UL using the first and second frequency bands  102  and  104  is similar to the conventional FDD communication. Therefore, the HDD scheme provides a communication scheme using both the TDD scheme and the FDD scheme.  
      Meanwhile, user signals and control signals are divided into a first group requiring low transmission delay and a second group that does not require such a low transmission delay. A length of one frame  120  is set as long as possible to reduce a loss due to various overheads and increase the efficiency. In both the TDD band  102  and the FDD UL band  104 , one frame  120  includes several slots  110 , and in the TDD band  102 , one frame  120  includes a TDD DL frame corresponding to a TDD DL period  106  and a TDD UL frame corresponding to a TDD UL period  108 . The TDD DL frame and the TDD UL frame are distinguished by a guard time, for example, a Tx/Rx Transition Gap (TTG)  122  and an Rx/Tx Transition Gap (RTG)  124 . In particular, each slot  110  in the TDD DL period  106  includes mini control slots  112  and  114  for transmitting control signals. The control signals transmitted in the TDD DL period  106  are used for converting a transmission packet format or a modulation and coding scheme (MCS) level in units of slots according to hybrid automatic repeat request (HARQ), automatic repeat request (ARQ), and adaptive modulation and coding scheme (AMC).  
      The signal requiring a transmission delay less than a transmission delay threshold set according to a communication environment is designed in units of slots, and transmitted/received through a TDD DL and an FDD UL. A feedback of the signal transmitted in a TDD DL slot or an FDD UL slot is transmitted through a corresponding FDD UL slot or TDD DL slot. Because the slot length is much shorter than the frame length, the delay condition can be simply satisfied in the TDD DL period  106 . On the contrary, the signal unaffected by the small transmission delay constraint is transmitted/received through a TDD DL and a TDD UL of the first frequency band  102 , thereby increasing the transmission rate and efficiency.  
      A detailed description will now be made of a structure of the frame  120  using specific numerical values.  
      Assuming that a frame length is T frame =10 ms and a slot length is T slot =0.4 ms, 25 slots  110  exist in one frame  120 . The TTG  122  indicating the time in which transition from the TDD DL period  106  to the TDD UL period  108  occurs is TTG=0.12 ms, and the RTG  124  indicating the time in which transition from the TDD UL period  108  to the next TDD DL period (not shown) occurs is RTG=0.04 ms. If a length of a TDD DL overhead  116  including synchronization/preamble signals, various system information, mapping information (e.g. MAP information), and control information is 1.04 ms, and a length of a TDD UL overhead  118  including various UL control information is 0.4 ms, then 1.6 ms overhead is required for one frame  120 . Therefore, 19 TDD slots (=8.4 ms) can be used for transmitting/receiving user signals through a DL/UL in one frame  120 . Likewise, even in the FDD UL band  104 , one frame  120  includes 25 slots.  
      MAP information included in the TDD DL overhead  116  represents MAP information for the full frame  120  including TDD DL, TDD UL and FDD UL. In addition, each TDD DL slot  110   a  transmits a slot-based control signal along with a user signal, and exchanges signals with FDD UL slots  110   b  by short periods of slots.  
      In the uplink, user signals and control signals are transmitted through a TDD UL or an FDD UL according to a feedback delay condition. FDD UL transmission will first be described.  
      The UL user signal requiring a transmission delay less than the transmission delay threshold is transmitted through each slot  110   b  of the FDD UL band  104  in units of slots. The feedback signal for such signal such as acknowledgement (ACK)/non-acknowledgement (NACK) can be received through the next slot  110   a  of the TDD DL period  106  before expiration of one frame. Because fast feedback is possible, the FDD UL band  104  carries the signals requiring a low transmission delay, i.e. real-time service signals such as voice over Internet protocol (VoIP) packets and video conference signals. However, when the amount of user signals that should be sent through the FDD UL is small, and thus there are FDD UL resources (frequency/time/code) left unused, the user signals unaffected by the small transmission delay constraint, can also be transmitted through the FDD UL.  
      Similarly, various UL control signals, i.e. ACK/NACK signal, channel quality indicator (CQI) signal, power control signal, MCS level signal, and channel/user information, that should be feedback very rapidly in response to the DL user signal are transmitted through each mini control slot  112  of the FDD UL band  104 .  
      Next, TDD UL transmission will be described.  
      The user signal having a feedback signal that can be received slowly in units of frames, i.e. the user signal unaffected by the small transmission delay constraint, is transmitted in the TDD UL period  108 . The non real-time service signal or the streaming service signal corresponds to this user signal. A feedback signal, such as ACK/NACK, for the UL user signal transmitted through the TDD UL is received in the TDD DL period of the next frame. Various control signals such as a CQI signal for the user signal allowing the slow feedback in units of frames (hereinafter frame-based slow feedback) are transmitted through the TDD UL overhead  118  in the TDD UL period  108 .  
      The other UL system signals such as sounding signal and ranging signal, are allowed to be transmitted through either of the TDD UL and the FDD UL, but these signals can be transmitted slowly in units of frames. Therefore, it is advantageous to transmit these signals through the TDD UL. The sounding signal is used for power measurement and channel estimation, like the pilot signal. The ranging signal, an all-1 or all-0 signal without bit transition, is used for synchronization. If the sounding signal is sent through the TDD UL, a base station can estimate a transmission channel using channel reciprocity of the TDD, and use the estimated channel characteristic for TDD DL transmission.  
      In the DL, the user signals and the control signals are transmitted in units of either frames or slots according to feedback delay condition. The transmission in units of frames (hereinafter frame-based transmission) will now be described.  
      The user signal allowing the frame-based slow feedback is transmitted in the TDD DL period  106 , and its feedback signal is received through the TDD UL overhead  118  of the TDD UL period  108  in the next frame. Control signals for one entire frame of both the TDD band and the FDD UL band, such as system information and MAP information, and various feedback control signals for a TDD UL signal, are carried by the TDD DL overhead  116  of the TDD DL period  106  in units of frames.  
      Next, transmission in units of slots (hereinafter slot-based transmission) will be described.  
      The user signal requiring low transmission delay is transmitted through each slot  110   a  of the TDD DL period  106  in units of slots, and the feedback signal, such as ACK/NACK, for the user signal is received through the mini control slot  112  of the FDD UL band  104  before expiration of one frame. MAP information valid only for the allocated slot, and various control signals, e.g., ACK/NACK signal, CQI signal, power control signal, MCS level signal and channel/user information, for the user signal requiring slot-based fast feedback, are carried by each mini control slot  114  of the TDD DL period  106  in units of slots.  
       FIG. 2  is a diagram illustrating the construction of a base station according to the present invention.  
      Referring to  FIG. 2 , a transmitter  210  controls DL transmission, and includes a mode selector  214 , a frame-based media access control (MAC) protocol data unit (PDU) generator  216 , a slot-based MAC PDU generator  218 , a TDD DL signal transmitter  220  and a transmission antenna  224 . A receiver  230  controls UL reception, and includes a reception antenna  232 , an FDD UL signal receiver  234 , a slot-based MAC PDU receiver  236 , a TDD UL signal receiver  242  and a frame-based MAC PDU receiver  244 .  
      If user information  212  is input to the transmitter  210 , the mode selector  214  determines the delay constraint of the user information  212 , whether fast feedback is required or not. If the user information  212  is required to be transmitted with a low delay, the mode selector  214  delivers the user information  212  to the slot-based MAC PDU generator  218 . However, if the user information  212  is not required to be transmitted with a low delay, the mode selector  214  transmits the user information  212  to the frame-based MAC PDU generator  216 . Feedback control information  222  received through an FDD UL band is input to the slot-based MAC PDU generator  218 . In addition, feedback control information  248  received in a TDD UL period of a TDD band is input to the frame-based MAC PDU generator  216 .  
      The slot-based MAC PDU generator  218  generates a MAC PDU of a one-slot length using the received user information  212  according to the feedback control information  222 , and transmits the generated MAC PDU to the TDD DL signal transmitter  220 . The feedback control information  222  can be used for determining information bits included in the one-slot length MAC PDU, and an MCS level and transmission power for the one-slot length MAC PDU. Various control signals associated with user information  238  received through an FDD UL band are mapped to a part corresponding to a mini control slot in the one-slot length MAC PDU. The TDD DL signal transmitter  220  modulates the one-slot length MAC PDU, and then transmits the modulated MAC PDU to a terminal via the antenna  224  along with an RF signal of a TDD band in a TDD DL period.  
      The frame-based MAC PDU generator  216  generates a MAC PDU of a TDD DL period length using the received user information  212  according to the feedback control information  248 , and transmits the generated MAC PDU to the TDD DL signal transmitter  220 . The feedback control information  248  can be used for determining information bits included in the MAC PDU of a TDD DL period length, and an MCS level and transmission power for the MAC PDU of a TDD DL period length. In addition, various control signals associated with the user information  246  received in a TDD UL period of a TDD band are mapped to a DL overhead part in the MAC PDU of a TDD DL period length. The TDD DL signal transmitter  220  modulates the MAC PDU of a TDD DL period length, and then transmits the modulated MAC PDU to the terminal via the antenna  224  along with an RF signal of a TDD band in a TDD DL period.  
      The reception antenna  232  receives an RF signal, and transmits a signal of a TDD band to the TDD UL signal receiver  242 , and a signal of an FDD UL band to the FDD UL signal receiver  234 . The FDD UL signal receiver  234  demodulates the FDD UL-band signal, and transmits the demodulated signal to the slot-based MAC PDU receiver  236 . The slot-based MAC PDU receiver  236  restores a one-slot length MAC PDU from the demodulated FDD UL-band signal, and detects user information  238  included in the one-slot length MAC PDU. In addition, the feedback control information  222  detected from the part corresponding to a mini control slot in the one-slot length MAC PDU is transmitted to the slot-based MAC PDU generator  218  of the transmitter  210 .  
      The TDD UL signal receiver  242  demodulates the TDD-band signal received in the TDD UL period, and transmits the demodulated signal to the frame-based MAC PDU receiver  244 . The frame-based MAC PDU receiver  244  restores a MAC PDU of a TDD UL period length from the demodulated TDD-band signal, and detects user information  246  included in the MAC PDU of a TDD UL period length. In addition, the feedback control information  248  detected from a UL overhead part in the MAC PDU of a TDD UL period length is transmitted to the frame-based MAC PDU generator  216  of the transmitter  210 .  
       FIG. 3  is a diagram illustrating the construction of a terminal according the present invention.  
      Referring to  FIG. 3 , a transmitter  310  controls UL transmission, and includes a mode selector  314 , a frame-based MAC PDU generator  316 , a TDD UL signal transmitter  318 , a slot-based MAC PDU generator  324 , an FDD UL signal transmitter  326  and a transmission antenna  320 . A receiver  330  controls DL reception, and includes a reception antenna  332 , a TDD DL signal receiver  334 , a mode selector  336 , a slot-based MAC PDU receiver  338  and a frame-based MAC PDU receiver  342 .  
      If user information  312  is input to the transmitter  310 , the mode selector  314  determines whether the user information  312  is susceptible to transmission delay, requiring fast feedback. If the user information  312  is susceptible to transmission delay, the mode selector  314  transmits the user information  312  to the slot-based MAC PDU generator  324 . However, if the user information  312  is not susceptible to transmission delay, the mode selector  314  transmits the user information  312  to the frame-based MAC PDU generator  316 . Feedback control information  322  received in a TDD DL period of a TDD band in units of slots is input to the slot-based MAC PDU generator  324 . In addition, feedback control information  346  received in a TDD DL period of a TDD band in units of frames is input to the frame-based MAC PDU generator  316 .  
      The slot-based MAC PDU generator  324  generates a MAC PDU of one slot length using the received user information  312  according to the feedback control information  322 , and transmits the generated MAC PDU to the FDD UL signal transmitter  326 . The feedback control information  322  can be used for determining information bits included in the one-slot length MAC PDU, and an MCS level and transmission power for the one-slot length MAC PDU. Various control signals associated with user information  340  received in the TDD DL period of the TDD band in units of slots are mapped to a part corresponding to a mini control slot in the one-slot length MAC PDU. The FDD UL signal transmitter  326  modulates the one-slot length MAC PDU, and then transmits the modulated MAC PDU to a base station via the antenna  320  along with an RF signal of an FDD band.  
      The frame-based MAC PDU generator  316  generates a MAC. PDU of a TDD UL period length using the received user information  312  according to the feedback control information  346 , and transmits the generated MAC PDU to the TDD UL signal transmitter  318 . The feedback control information  346  can be used for determining information bits included in the MAC PDU of a TDD UL period length, and an MCS level and transmission power for the MAC PDU of a TDD UL period length. Various control signals associated with the user information  344  received in a TDD DL period of a TDD band in units of frames are mapped to a UL overhead part in the MAC PDU of a TDD UL period length. The TDD UL signal transmitter  318  modulates the MAC PDU of a TDD UL period length, and then transmits the modulated MAC PDU to the base station via the antenna  320  along with an RF signal of a TDD band in a TDD UL period.  
      If there is a surplus in the FDD band, the frame-based MAC PDU generator  316  generates a MAC PDU including the user information  312  unaffected by transmission delay, and delivers the generated MAC PDU to the FDD UL signal transmitter  326 . Then, the user information  312  unaffected by the transmission delay can also be carried by an FDD-band RF signal.  
      The reception antenna  332  receives an RF signal, and transmits a signal of a TDD band to the TDD DL signal receiver  334 . The TDD DL signal receiver  334  demodulates the TDD-band signal received in the TDD DL period, and transmits the demodulated signal to the mode selector  336 . The mode selector  336  determines whether the demodulated signal includes frame-based or slot-based user information, depending on MAP information of a DL overhead included in the demodulated signal. Depending on the determination, the mode selector  336  transmits the frame-based user information to the frame-based MAC PDU receiver  342 . The frame-based MAC PDU receiver  342  restores a MAC PDU of a TDD DL period length from the demodulated signal, and detects user information  344  included in the MAC PDU of a TDD DL period length. In addition, the feedback control information  346  detected from a DL overhead part in the MAC PDU of a TDD DL period length is transmitted to the frame-based MAC PDU generator  316  of the transmitter  310 .  
      Depending on the determination, the mode selector  336  transmits the slot-based user information to the slot-based MAC PDU receiver  338 . The slot-based MAC PDU receiver  338  restores a one-slot length MAC PDU from the demodulated signal, and detects user information  340  included in the one-slot length MAC PDU. In addition, the feedback control information  322  detected from a part corresponding to each mini control slot in the one-slot length MAC PDU is transmitted to the slot-based MAC PDU generator  324  of the transmitter  310 .  
       FIGS. 4 and 5  illustrate overhead ratios versus a guard time length and a frame length, respectively, for a TDD frame structure. In an orthogonal frequency division multiplexing (OFDM) scheme, a cyclic prefix (CP) for prevention of inter-symbol interference and a pilot for channel estimation are used, and a percentage of the CP and pilot to one frame is commonly 20%. One frame includes a fixed-length synchronization signal. Herein, a synchronization signal having a fixed length of 50 μs is used.  
      Referring to  FIG. 4 , when the frame length increases to 500 μs, 1000 μs, 2000 μs, 5000 μs and 10000 μs, percentages of the total overhead including CP, pilot, synchronization signal and guard time are shown by reference numerals  402  to  410  according to a length of the guard time. As illustrated, a decrease in the frame length greatly increases a percentage of the total overhead, and in order to obtain a desired low overhead ratio, there is a need for a short guard time length. Similarly, referring to  FIG. 5 , when a guard time length increases to 25 μs, 50 μs, 75 μs, 100 μs and 150 μs, percentages of the total overhead are shown by reference numerals  502  to  510  according to a frame length.  
      That is, when the frame length is 0.5 ms, an overhead ratio for a guard time=25 μs is 35% as shown by reference numerals  402  and  502 , and an overhead ratio for a guard time=150 μs is 60% as shown by reference numerals  402  and  510 . If the guard time is 25 μs, signals generated by terminals distanced far away from a base station interfere with the signals generated by the base station or the terminals near the base station when the TDD period is changed from DL to UL, or vice-versa. In order to prevent the interference, the cell size has to be limited, decreasing the utility. On the contrary, if the guard time is set to 150 μs in order to increase the cell size large enough, the overhead ratio becomes excessive, decreasing the transmission efficiency. The overhead ratio at which a loss due to the overhead will not considerably affect the transmission performance is, for example, 25% or below. For that purpose, the frame length should be at least 5 ms, and if the frame length is 10 ms, a loss due to the overhead is very low.  
      The time required for performing two retransmissions after initial transmission in the typical FDD and TDD environments can be calculated as follows.  
      In FDD, one slot is required for initially transmitting a user signal and one slot is required for detecting the user signal, totaling two required slots. One slot is required for feeding back a NACK signal due to error detection, one slot is required for detecting the NACK signal, one slot is required for retransmitting the user signal and one slot is required for detecting the retransmitted user signal. A total of four slots are required for one retransmission. As a result, a total of 10 slots are required for initial transmission and two retransmissions of the user signal.  
      In TDD, one frame is required for initially transmitting and detecting a user signal. One frame is required for feeding back a NACK signal due to error detection, one frame is required for retransmitting the user signal, and at least two frames are required for retransmission. As a result, at least five frames are required for initial transmission and two retransmissions of the user signal.  
      To enable initial transmission and two retransmissions within 10 ms, an FDD slot should be not longer than 1 ms and a TDD frame should be not longer than 2 ms.  
      Alternatively, the frame structure according to the present invention can be designed such that the frame length is set to, for example, 10 ms, and the slot length is set to 0.5 ms or shorter. In this case, initial transmission and two retransmissions of the user signal is completed within 5 ms, decreasing the transmission delay to ½ compared with the conventional FDD or TDD, and increasing the transmission efficiency by about 20% compared with the case where the frame length is 2 ms.  
      As can be understood from the foregoing description, the HDD scheme using both the TDD band and the FDD UL band according to the present invention transmits/receives signals through a frame composed of a plurality of short slots. The HDD scheme transmits/receives the user signal and control signal requiring low transmission delay and low feedback delay within a short time of slots, thereby satisfying the required delay condition, and transmits/receives the remaining signals in units of frames in a manner that increases the transmission efficiency and flexibility.  
      In addition, the present invention enlarges the TDD frame length, thus contributing to a reduction in the loss due to various overheads. In the TDD scheme, the cell size is determined mainly depending on the guard time, so the cell size can be set large by increasing the guard time.  
      Further, the present invention can optimally use the advantages of the TDD scheme. The TDD scheme can adjust a DL-to-UL time ratio, so it can flexibly cope with a variation in the amount of DL and UL traffic. The TDD scheme can estimate channel characteristics from the signals received using reciprocal features of the DL and UL channels. The use of the characteristics of the TDD scheme in the fixed/low-speed environment contributes to an increase in the transmission efficiency using various high-end communication technologies. As a result, with the use of the characteristics of the TDD scheme, it is possible to efficiently provide data service in the low-speed environment.  
      Moreover, because the present invention transmits/receives signals in units of short slots but uses a TDD DL and an FDD UL, it can easily satisfy the low-delay condition as in the FDD scheme. As a result, the present invention is advantageous for providing real-time services such as voice service. In addition, even when the channel characteristics change rapidly due to the high-speed movement of the terminal, the present invention can provide a reliable means of communication. The present invention can efficiently apply various communication technologies including signal processing technology in the signal transmission/reception process, making it possible to attain additional performance improvement.  
      While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.