Patent Publication Number: US-2010111004-A1

Title: Method of transmitting data employing data operation pattern

Description:
TECHNICAL FIELD 
     The present invention relates to wireless communication, and more particularly, to a method of transmitting data based on a predicted traffic pattern in a wireless communication system. 
     BACKGROUND ART 
     Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technique are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with wireless access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, proper power consumption of a user equipment, and the like are defined as requirements. 
     In order to efficiently transmit or receive data between a network and a user equipment, scheduling is necessary. Scheduling is basically performed by the network. The network informs the user equipment of its decided scheduling information. Scheduling information includes information on allocation of radio resources. 
     A user equipment requests scheduling information from the network in order to transmit or receive data. After scheduling information is received from the network, the user equipment transmits or receives data according to the scheduling information. 
     However, if the user equipment must receive scheduling information from the network whenever data is received or transmitted, repetitive signaling is required. Hence, overall capacity can be reduced due to such signaling. 
     There are various types of data and a specific size of data can be transmitted for a specific time period. For example, VoIP (Voice Over Internet Protocol) refers to a series of communication services in which voice data is converted into a data packet, enabling voice call as in a telephone call. In general, a specific size of data is transmitted for a specific time period. In the case of VoIP, scheduling information is previously set between a network and a user equipment so that a specific size of data can be transmitted for a specific time period. 
     In order to increase data transmission efficiency, a data compression technique is used. If data is compressed, the size of compressed data is smaller than that of original data, which enables more data to be transmitted. However, if data is compressed, the size of original data is changed, which makes it impossible to employ conventional scheduling information in which a specific size of data is transmitted for a specific time period. 
     Accordingly, there is a need for a method which is able to transmit data while minimizing signaling although data compression is performed. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present invention provides a method of transmitting data, in which radio resources are allocated on the basis of a predicted data operation pattern and the data is transmitted through the radio resources. 
     Technical Solution 
     In one aspect, a method of transmitting data in a wireless communication system is provided. The method includes configuring a data operation pattern for a plurality of data blocks with variable size, generating the plurality of data blocks according to the data operation pattern and transmitting the plurality of data blocks. 
     In another aspect, a method of transmitting data in a wireless communication system is provided. The method includes transmitting a message including a data operation pattern, the data operation pattern comprising information on generating a plurality of data blocks with variable size, generating the plurality of data blocks according to the data operation pattern and transmitting the plurality of data blocks. 
     In still another aspect, a method of receiving data in a wireless communication system is provided. The method includes receiving a message including a data operation pattern, the data operation pattern comprising information on generating a plurality of data blocks with variable size and receiving the plurality of data blocks according to the data operation pattern. 
     In still another aspect, a user equipment includes a RF (Radio Frequency) unit for transmitting and receiving radio signals and a processor coupled to the RF unit and configured to transmit a request for allocating radio resources according to a data operation pattern, the data operation pattern comprising information on generating a plurality of data blocks with variable size, generate the plurality of data blocks according to the data operation pattern and transmit the plurality of data blocks through the allocated radio resources. 
     Advantageous Effects 
     Although a data generating time or size is irregular, data can be transmitted without the need for additional signaling by predicting or deciding the pattern of the data. Although a data generating time or size is not constant, additional signaling is not required every transmission. It is effective in transmission of VoIP packets employing the header compression scheme. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a wireless communication system. 
         FIG. 2  is a block diagram showing constitutional elements of a user equipment. 
         FIG. 3  is a block diagram showing control plane of the radio interface protocol. 
         FIG. 4  is a block diagram showing user plane of the radio interface protocol. 
         FIG. 5  illustrates a dynamic scheduling scheme in downlink transmission. 
         FIG. 6  illustrates static scheduling scheme in uplink transmission. 
         FIG. 7  illustrates static scheduling scheme in uplink transmission. 
         FIG. 8  shows a change in the header size of a RTP/UDP/IP packet when ROHC is applied. 
         FIG. 9  shows a change in the header size of the RTP/UDP/IP packet generated when ROHC is used. 
         FIG. 10  is a block diagram illustrating a method of transmitting data in accordance with an embodiment of the present invention. 
         FIG. 11  is a flowchart illustrating a method of transmitting data in accordance with an embodiment of the present invention. 
         FIG. 12  is a flowchart illustrating a method of transmitting data in accordance with an embodiment of the present invention. 
     
    
    
     MODE FOR THE INVENTION 
       FIG. 1  is a block diagram showing a wireless communication system. This may be a network structure of an E-UMTS (Evolved-Universal Mobile telecommunications System). The E-UMTS system may be referred to as an LTE (Long-term Evolution) system. The wireless communication system can widely be deployed to provide a variety of communication services, such as voices, packet data, and the like. 
     Referring to  FIG. 1 , an E-UTRAN (Evolved-UMTS Terrestrial Radio Access 
     Network) includes base stations (BS)  20 . A user equipment  10  can be fixed or mobile and can be referred to as another terminology, such as a MS (Mobile Station), a UT (User Terminal), a SS (Subscriber Station), wireless device, or the like. The base station  20  generally is a fixed station that communicates with the user equipment  10  and can be referred to as another terminology, such as an e-NB (evolved-NodeB), BTS (Base Transceiver System), access point, or the like. There are one or more cells within the coverage of the base station  20 . An interface for transmitting user traffics or control traffics can be used between base stations  20 . Hereinafter, downlink means a communication from the base station  20  to the user equipment  10 , and uplink means a communication from the user equipment  10  and the base station  20 . 
     The base station  20  provides the user equipment  10  with termination points of a user plane and a control plane. The base stations  20  can be connected with each other through an X 2  interface, and adjacent base stations  20  can have a network of a meshed structure where the X 2  interface always exists. 
     The base station  20  is connected to an EPC (Evolved Packet Core), further specifically, to an aGW (access Gateway)  30  through an S 1  interface. The aGW  30  provides a termination point of session and mobility management function of the user equipment  10 . A plurality of nodes of the base stations  20  and the aGWs  30  can be connected to each other in a many-to-many relation through the S 1  interface. The aGW  30  can be divided into a part for processing user traffics and a part for processing control traffics. In this case, the part for processing traffics of a new user and the part for processing a control traffic can communicate with each other through a new interface. The aGW  30  also can be referred to as an MME/UPE (Mobility Management Entity/User Plane Entity). 
     Layers of the radio interface protocol between the user equipment and the base station can be classified into L 1  (a first layer), L 2  (a second layer), and L 3  (a third layer) based on the lower three layers of the Open System Interconnection (OSI) model that is well-known to communication systems. The physical layer belonging to the first layer provides information transfer service using a physical channel. A radio resource control (RRC) layer belonging to the third layer serves to control radio resources between the user equipment and the network. The user equipment and the network exchange RRC messages via the RRC layer. The RRC layer can be distributed among network nodes, such as the base station, the aGW, and the like. Or the RRC layer can be located only in the base station or the aGW. 
       FIG. 2  is a block diagram showing constitutional elements of a user equipment. A user equipment  50  includes a processor  51 , memory  52 , an RF unit  53 , a display unit  54 , and a user interface unit  55 . The memory  52  coupled with the processor  51  stores operating systems, applications, and general files. The display unit  54  displays a variety of information on the user equipment and may use a well-known element, such as an LCD (Liquid Crystal Display), OLED (Organic Light Emitting Diode), or the like. The user interface unit  55  can be configured with a combination of well-known user interfaces such as a keypad, touch screen, and the like. The RF unit  53  coupled to the processor  53  transmits and/or receives radio signals. 
     Functions of layers of the radio interface protocol can be implemented in the processor  51 . The processor  51  can provide control plane and user plane. 
     The radio interface protocol includes a physical layer, a data link layer, and a network layer in horizontal plane, and user plane for transmitting user data and control plane for transferring control signals in vertical plane. 
       FIG. 3  is a block diagram showing control plane of the radio interface protocol.  FIG. 4  is a block diagram showing user plane of the radio interface protocol.  FIGS. 3 and 4  show the structure of the radio interface protocol between the user equipment and the E-UTRAN based on the 3GPP radio access network specification. 
     Referring to  FIGS. 3 and 4 , a physical layer, i.e., the first layer, provides an information transfer service to upper layers through a physical channel. The physical layer is connected to the MAC (Medium Access Control) layer, i.e., an upper layer of the physical layer, through a transport channel. Data are moved between the MAC layer and the physical layer through the transport channel. The transport channel can be divided into a dedicated transport channel and a common transport channel. Between different physical layers, i.e., the physical layer of a transmitter and the physical layer of a receiver, data are moved through the physical channel. 
     The MAC layer provides a service to a RLC (Radio Link Control) layer, i.e., an upper layer of the MAC layer, through a logical channel. The MAC layer maps a logical channel to a transport channel and performs logical channel multiplexing by which a plurality of logical channels maps to a single transport channel. The MAC layer is coupled with the RLC layer through the logical channel. The logical channel can be classified to a control channel for transmitting information on the control plane and a traffic channel for transmitting information on the user plane. 
     The RLC layer in the second layer adjusts the size of data to facilitate data transmission in lower layers by performing segmentation and concatenation of data. The RLC layer provides various operation modes to guarantee quality of service (QoS) at each radio bearer (RB). The RLC layer can perform automatic repeat and request (ARQ) for reliable data transmission. 
     A PDCP (Packet Data Convergence Protocol) belonging to the second layer performs header compression function. When transmitting an Internet Protocol (IP) packet such as an IPv4 packet or an IPv6 packet, the header of the IP packet may contain relatively large and unnecessary control information. The PDCP layer reduces the header size of the IP packet so as to efficiently transmit the IP packet. 
     A RRC (Radio Resource Control) layer belonging to the third layer is defined only on the control plane. The RRC layer serves to control the logical channel, the transport channel, and the physical channel in association with configuration, reconfiguration, and release of Radio Bearers (RBs). The RB is a service provided by the second layer for data transmission between a user equipment and a E-UTRAN. The RB means a logical path provided by the first and second layers of the radio protocol to transfer data between a user equipment and the E-UTRAN. Establishing the RB means a procedure of specifying characteristics of the radio protocol layers and channels needed to provide a specific service and setting specific parameters and an operation method of each layer and channel. 
     Hereinafter, a scheduling method in accordance with an embodiment of the present invention is disclosed. 
     Scheduling is basically performed by a network (for example, a base station). The network informs a user equipment of its decided scheduling information. The user equipment first receives scheduling information from the network in order to transmit or receive data, and transmits or receives data according to the received scheduling information. Scheduling information is information necessary to transmit data in a radio interface, and can include (1) identifier information such as a user equipment identifier or a group identifier, (2) radio resource assignment information such as time and frequency, (3) duration of assignment, that is, a valid duration of assigned radio resources, (4) multi-antenna information pertaining to MIMO (Multiple Input Multiple Output) or beam forming, (5) modulation information such as QPSK (Quadrature Phase Shift Keying), (6) payload size such as packet size, (7) information of a HARQ (Hybrid Automatic Repeat Request) process number, a redundancy version, and asynchronous HARQ such as a new data indicator, (8) synchronous HARQ information such as a retransmission sequence number. 
     In general, scheduling is largely classified into dynamic scheduling and static scheduling. In accordance with the dynamic scheduling scheme, downlink scheduling information or uplink scheduling information is received whenever data is transmitted. Data is transmitted according to received downlink scheduling information or uplink scheduling information. In accordance with the static scheduling scheme, in an initial stage where a network and a user equipment establishes a RB, scheduling information for transmitting a number of data is previously set through a RRC message, etc. The user equipment (or the network) transmits or receives data by employing the preset scheduling information when transmitting or receiving data. 
       FIG. 5  shows the dynamic scheduling scheme in uplink transmission. 
     Referring to  FIG. 5 , a user equipment checks whether there is data to be transmitted to a base station every TTI (Transmission Time Interval). The TTI refers to a time unit in which data is transmitted (scheduled) at once. If, as a result of the check, there exists data to be transmitted, the user equipment requests radio resources from the base station. If the radio resource request is received from the user equipment, the base station determines whether available resources exist. If, as a result of the determination, available resources exist, the base station allocates proper radio resources to the user equipment. The user equipment transmits data according to the allocated radio resources. 
       FIG. 6  shows the dynamic scheduling scheme in downlink transmission. 
     Referring to  FIG. 6 , a base station checks whether there is data to be transmitted to a user equipment every TTI. If, as a result of the check, there exists data to be transmitted, the base station allocates downlink radio resources to the user equipment and transmits data to the user equipment according to the allocated radio resources. The user equipment receives data according to the allocated radio resources. 
     The dynamic scheduling scheme must request and be allocated radio resources whenever data is transmitted and, therefore, requires lots of signaling. The method of transmitting or receiving data by employing scheduling information every time when data is transmitted is advantageous when various sizes of data, such as web browsing, are transmitted irregularly, but is disadvantageous in that signaling is increased since scheduling information is required every time. 
       FIG. 7  shows the static scheduling scheme in uplink transmission. 
     Referring to  FIG. 7 , a base station and a user equipment exchange uplink scheduling information. The user equipment transmits data having a preset packet size on a preset transmission time according to uplink scheduling information. Here, data having a constant size is transmitted uplink at  3  TTI intervals. 
       FIG. 8  shows the static scheduling scheme in downlink transmission. 
     Referring to  FIG. 8 , a base station and a user equipment exchange downlink scheduling information. The base station transmits data having a preset packet size on a preset transmission time according to downlink scheduling information. Here, data having a constant size is transmitted downlink at  3  TTI intervals. 
     If data having a constant size is transmitted on a constant time such as VoIP, it may not be said that the dynamic scheduling scheme where signaling is performed every transmission uses radio resources inefficiently. Thus, it can be said that the static scheduling scheme is suitable to transmit data having a constant size on a constant time. 
     Meanwhile, as described above, the PDCP layer performs header compression. 
     Header compression is a scheme of reducing the header size based on the fact that most IP packets belonging to the same packet stream are not changed. The header compression scheme is a method of reducing the overhead of IP headers by storing fields whose values are not changed in the compressor of a transmitter and the decompressor of a receiver in the form of a context and then transmitting only changed fields after the context is formed. In the initial stage of header compression, the compressor transmits the full header packet in order to form a context with respect to a corresponding packet stream in the decompressor. Thus, there is no profit due to header compression. However, after the context is formed in the decompressor, the compressor can transmit only compressed header packets and, therefore, a profit thereof is significant. 
     ROHC (Robust Header Compression), that is, one of the header compression schemes is used to reduce header information of real-time packets such as RTP (Real-time Transport Protocol)/UDP (User Datagram Protocol)/IP (Internet Protocol). The RTP/UDP/IP packet refers to a packet to which pertinent headers of data coming down from an upper side are attached after the data passes through RTP and UDP and IP, and includes various and lots of header information through which data is transferred to a destination via an Internet and then recovered. In general, the header size of the RTP/UDP/IP packet 40 bytes in IPv4 (IP version 4) and 60 bytes in IPv6 (IP version 6). If the header is compressed using ROHC, the size of the header can be reduced to 1 to 3 bytes. 
       FIG. 9  shows a change in the header size of the RTP/UDP/IP packet generated when ROHC is used. In general, the full header includes additional information for forming a context and has a size slightly larger than that of a normal header. 
     Referring to  FIG. 9 , when a packet stream is first transmitted, the full header is transmitted in order to form a context since the context is not formed both in the compressor and the decompressor. If some degree of the full header is transmitted (it is assumed that the number of the full header that is transmitted at the initial stage is N 1 ), the context is formed. A compressed header is then transmitted. However, the context may be damaged due to causes, such as packet loss, during the transmission of the header. Thus, it is necessary to transmit the full header at proper intervals. It is assumed that the number of the compressed header that is transmitted between the full headers is N 2  and the number of the full header that is transmitted at the intermediate stage is N 3 . The full header and the compressed header are transmitted repeatedly at constant TTI intervals. 
     A VoIP packet is a representative packet of the RTP/UDP/IP type and is transmitted as a constant size on a constant time. Thus, it can be said that the above static scheduling method is effective. However, if the header compression scheme is used in order to reduce the header size of the VoIP packet, the size of the header is changed as shown in  FIG. 9 , so a packet having a different size is generated. This makes it difficult to use the static scheduling method used only for transmission of data having a constant packet size. 
     A VoIP packet requires header compression. A VoIP packet has a header size too larger than that of real data. For example, the entire header size of the RTP/UDP/IP packet used in VoIP is 40 bytes in the case of IPv4 and 60 bytes in the case of IPv6, whereas the size of a pure data portion called payload is at most 15 to 20 bytes. Thus, it can be said that header compression for reducing the size of the header is indispensable. If the header is compressed using ROHC, the header size can be reduced from 40 or 60 bytes to 1 to 3 bytes. Consequently, in VoIP, header compression is indispensable. Hence, there is a need for a method that does not generate lots of signaling like static scheduling while header compression is applied in order to support VoIP effectively. 
     There is presented a pattern scheduling method of previously deciding a pattern of transmitted data in any data stream and allocating radio resources according to the pattern. That is, a user equipment and a network set a traffic pattern for data generation when a RB is set up and transmit or receive data according to the set pattern without the need for additional scheduling information when real data is transmitted and received. 
       FIG. 10  is a block diagram illustrating a method of transmitting data in accordance with an embodiment of the present invention. 
     Referring to  FIG. 10 , in the case of uplink transmission, a RRC  320  of a user equipment is an entity which sets a data operation pattern of a data generator  310  when establishing a RB or receives information about the data operation pattern set by the data generator  310 . The data generator  310  is an entity, which directly generates data or processes received data in order to generate a new type of data, and can include, for example, a codec or header compressor, etc. In the case of downlink transmission, a RRC  220  of a network sets a data operation pattern of a data generator  210  when establishing a RB or receives information about the data operation pattern set by the data generator  210 . 
     When setting the data operation pattern, the user equipment or the network can decide parameters of the data generators  210  and  310  and directly control the data operation pattern. Alternatively, the data generators  210  and  310  may decide the data operation patterns themselves and inform the RRC  320  of the user equipment or the RRC  220  of the network of the parameters. The data operation pattern related parameters can include a data generating time, a generated data size and the like, and may also include various pieces of information such as the number of data having a specific size, which is generated, the cycle of data having a specific size, which is generated, and the type of a data size that is generated on a specific time. 
     The RRC  320  of the user equipment and the RRC  220  of the network exchange information about the data operation patterns. The parameters of the set data operation pattern can be exchanged through a RRC message. The RRC  320  of the user equipment and the RRC  220  of the network set lower layers, such as PHY, MAC, RLC and PDCP, by employing the information about the set data operation pattern. 
     If data transmission begins, the data generators  210  and  310  of the transmitter generate data according to a previously set data operation pattern. That is, the data generators  210  and  310  of the transmitter generate data having a preset size on a preset time and transmit the data through a radio interface. The receiver also receives data based on preset information. 
     In the case where ROHC is applied to VoIP, if the presented scheduling method is used, scheduling can be performed effectively while reducing signaling. In VoIP, basically, packets having a constant size (55 to 60 bytes or 75 to 80 bytes) are generated at constant time intervals (for example, 20 ms). If header compression is performed, a generating time is not changed, but the size of the generated packet is changed. However, if several parameters of ROHC are previously set, the size pattern of a generated packet can be predicted, so the pattern scheduling method can be used. 
     A parameter that decides a pattern is various. However, if parameters, such as the number N 1  of the full header that is transmitted in the initial stage, the number N 2  of the full header that is transmitted between the full headers, the number N 3  of the full header that is transmitted in the intermediate stage, etc. in  FIG. 9  are decided and previously exchanged, VoIP packets can be transmitted or received effectively even without other scheduling information. Time information, such as a transmission time or cycle of the full header and a transmission time of the compressed header, can also be used as parameters. 
       FIG. 11  is a flowchart illustrating a method of transmitting data in accordance with an embodiment of the present invention. 
     Referring to  FIG. 11 , a user equipment requests radio resources from a base station (S 410 ). A radio resource request message can include a data operation pattern. The data operation pattern can include a transmission time of data to be transmitted, the size of data, and soon. The transmission time of the data may be varied depending on the type of data. 
     The base station allocates radio resources according to the data operation pattern (S 420 ). 
     The user equipment sequentially transmits first to N-th data (N&gt;1) according to the data operation pattern by employing the allocated radio resources (S 430 ). Although the sizes of the first to N-th data are changed differently due to header compression, the user equipment can transmit plural data without the need for additional signaling by previously exchanging the data operation patterns. 
     Here, it has been described that the data operation pattern is transmitted with it being included in the radio resource request message. However, the data operation pattern can be transmitted to the base station through an additional message. 
       FIG. 12  is a flowchart illustrating a method of transmitting data in accordance with an embodiment of the present invention. 
     Referring to  FIG. 12 , a base station prepares a data operation pattern, allocates radio resources according to the data operation pattern, and transmits the radio resources to a user equipment (S 510 ). 
     The base station sequentially transmits first to Nth data (N&gt;1) according to the data operation pattern by employing the allocated radio resources (S 520 ). Although the sizes of the first to N-th data are changed differently due to header compression, the base station can transmit plural data without the need for additional signaling by previously exchanging the data operation patterns. 
     Here, it has been described that the data operation pattern is transmitted with it being included in the radio resource allocation message. However, the data operation pattern can be transmitted to the base station through an additional message. 
     The functions described in connection with the embodiments disclosed herein may be performed by implemented by hardware, software or a combination thereof. The hardware may be implemented by a microprocessor, a controller, an application specific integrated circuit (ASIC) and a processor. Design, development and implementation of the software are well known to those skilled in the art based on the detailed description. 
     As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims. Therefore, all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are intended to be embraced by the appended claims.