KR20080112649A

KR20080112649A - Method for accomplishing the random access procedure in lte(long-term evolution) system

Info

Publication number: KR20080112649A
Application number: KR1020070061309A
Authority: KR
Inventors: 이경열; 장수영
Original assignee: 이경열
Priority date: 2007-06-21
Filing date: 2007-06-21
Publication date: 2008-12-26

Abstract

The present invention relates to a method of performing a random access procedure in an LTE system. The method for performing a random access procedure in a mobile terminal according to the present invention comprises the steps of: extracting a RACH parameter from system information received from a base station; Determining a RACH type using the extracted RACH parameters; And performing a random access procedure by using the determined RACH type, wherein the determined RACH type is determined by an RRC layer of the mobile terminal and transferred to the physical layer of the mobile terminal to perform the random access procedure. It is characterized by. Therefore, the mobile terminal can perform a random access procedure suitable for a wireless environment.

Description

Random access procedure in mobile communication system {METHOD FOR ACCOMPLISHING THE RANDOM ACCESS PROCEDURE IN Long-Term Evolution (LTE) System}

1 is a network diagram of a conventional E-UMTS according to the present invention.

2 is a control plane of a radio protocol according to the prior art;

3 is a user plane of a wireless protocol according to the prior art.

4 is a HARQ operation defined in the 3GPP radio access network standard according to the prior art

5 is a diagram illustrating a method of inserting a CP to prevent intersymbol interference and interchannel interference.

6 is a basic RACH frame structure in LTE according to an embodiment of the present invention.

7 is an extended RACH frame structure in LTE according to an embodiment of the present invention.

8 is a repeated RACH frame structure according to an embodiment of the present invention.

* Key Drawing

340: Medium Access Control

350: Radio Link Control

610: CP (Cyclic Prefix)

620: RACH preamble

630: Guard Interval

The present invention relates to a random access method in an Evolved Universal Mobile Telecommunication System (E-UMTS), and more particularly, to a method of transmitting a preamble and receiving a message in response to the random access.

Recently, long-term evolution (hereinafter referred to as Long Term Evolution (LTE)) in which high-speed multimedia services are possible through high frequency efficiency and optimized network configuration compared to existing 3G mobile communication technologies (for example, WCDMA and HSDPA) The research on technology is being actively conducted.

The basic requirement of LTE is not only to change the existing 5MHz-limited bandwidth from 1.25MHz to 20MHz, but also to use Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO), and smart antenna technology. 100Mbps data transmission is possible by downlink.

In addition, LTE is a wireless access method capable of 50Mbps data transmission in the uplink.

In particular, the eNodeB, which is a network component of LTE, provides a hybrid automatic repeat request (HARQ) and an automatic repeat request (ARQ) function to maintain the reliability of the end-to-end transmission link and provide a desired quality of service.

Here, HARQ is provided by the eNodeB's Media Access Layer layer and ARQ is provided by the eNodeB's Radio Link Control (RLC) layer.

LTE can minimize transmission delay due to transmission of lossless packet data and packet retransmission through HARQ and ARQ functions.

In general, LTE may improve performance of a system by adaptively allocating resources (where resources include codes, modulation schemes, frequencies, etc.) according to channel environment changes.

However, the conventional random access method in the WCDMA system has a problem that it takes a long time from the random access preamble transmission of the terminal to the channel required for data transmission.

The random access procedure in the existing WCDMA is briefly described as follows.

Prior to the transmission of the RACH message, the terminal transmits a random access preamble, where the random access preamble includes a signature for identifying the terminal, to the base station to determine whether the base station can be received.

When the base station recognizes the RACH preamble, the base station transmits an acquisition indication channel (AICH) including the received signature information to the corresponding terminal.

When the terminal receives the AICH, the RACH message, where the RACH message may be a Radio Resource Control (RRC) Connection Request message for establishing a signaling radio bearer (SRB) to the base station through the PRACH channel. Send. The base station transmits the received RACH message to the Radio Network Controller (RNC).

The RNC transmits an RRC Connection Setup message including channel allocation information to the base station in response to the RRC Connection Request. The base station maps the received RRC Connection Setup message to the Secondary Common Control Physical Channel (S-CCPCH) and transmits it to the terminal.

The terminal sets a dedicated channel using the received channel allocation information and then transmits an RRC Connection Setup Complete message to the RNC through the base station through the set dedicated channel.

The random access procedure as described above is performed in a 3-way handshake method, and when the 3-way handshake is normally completed, the terminal may transmit user data to the base station and the control station.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide a method for determining a RACH type in a corresponding cell using system information received from an eNodeB in a mobile terminal, and delivering the same to a physical layer. It is done.

In addition, the present invention provides a predetermined control primitive for delivering the RACH type determined from the upper layer to the physical layer, thereby allocating the RACH resources in the physical layer, and the mobility capable of performing a random access procedure with the allocated RACH resources It is to provide a terminal.

Another object of the present invention is to provide an operation method for a case where a terminal does not receive a random access response from a base station when a terminal attempts random access, and a method for a case where a base station rejects resource allocation due to lack of resources. It is.

Other objects of the present invention will be readily understood through the following description of the embodiments.

In order to achieve the above object, according to an aspect of the present invention, a method of performing a random access procedure in a mobile terminal is disclosed.

According to an embodiment of the present invention, a method of performing a random access procedure in a mobile terminal includes: extracting a RACH parameter from system information received from a base station; Determining a RACH type using the extracted RACH parameters; And performing a random access procedure by using the determined RACH type, wherein the determined RACH type is determined by an RRC layer of the mobile terminal and transferred to the physical layer of the mobile terminal to perform the random access procedure. It is characterized by.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same components have the same number as much as possible even if displayed on different drawings.

In the following description, a network structure and a wireless protocol structure of a general Evolved Universal Mobile Communication System (E-UMTS) defined in LTE-related standards will be described with reference to the related drawings (FIGS. 1 to 3) to help understand the present invention. Let's do it.

1 is a system configuration diagram showing a network structure of an E-UMTS applied to the prior art and the present invention.

Referring to FIG. 1, the E-UMTS network may be largely composed of an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 110 and an Evolved Packet Core 120 (EPC).

The E-UTRAN 110 consists of at least one base station (hereinafter referred to as eNodeB, 130), and the eNodeB 130 provides a user plane radio protocol and a control plane radio protocol of the E-UTRAN 110.

Here, the user plane radio protocol and the control plane radio protocol will be described in detail with reference to FIGS. 2 to 3.

The EPC 120 may include a mobility management entity (hereinafter referred to as a mobility management entity (MME) 122) for managing mobility and a system architecture evolution (124) for managing transmission of actual data.

The EPC 120 and the eNodeB 130 communicate with each other using the S1 interface, and the S1 interface is an S1-MME interface and SAE 124 used to communicate with the MME 122 according to the configuration of the EPC 120. It is divided into S1-U interface which is used for communication.

An X2 interface is used for transmitting user traffic or control traffic between the eNodeBs 130.

2 and 3 are system configuration diagrams illustrating a structure of a radio interface protocol between a terminal and an E-UTRAN based on the 3GPP wireless access network standard.

2 is a structure of a control plane radio access protocol defined in the 3GPP radio access network standard.

As shown in FIG. 2, the control plane radio access protocol includes a Non Access Stratum (NAS) 210, a Radio Resource Control (RCC) 220, a Radio Link Control 230 (RLC), a Medium Access Control 240 (MAC), and the like. It may be configured as a PHY (Physical, 250) layer.

The NAS 210 layer is located in the MME 122 of the UE 140 and the EPC 120, and provides a function of transmitting and receiving transparent control messages to the eNodeB 130.

The RRC 220 layer performs a function of controlling radio resources between the UE 140 and the eNodeB 130, where the radio resources include code, frequency, power, and the like.

That is, the RRC 220 layer may control physical channels, transport channels, and logical channels for configuration, reconfiguration, and release of a radio bearer (hereinafter, referred to as RB). .

Here, RB means a service provided by a second layer, where the second layer includes the MAC 240 and the RLC 230, for data transmission between the terminal and the UTRAN.

In addition, the RRC 220 layer may provide functions such as mobility management and power control of the UE 140.

The RLC 230 layer is located above the MAC 240 layer to support reliable transmission of data.

The transmitting RLC layer performs a function of segmenting or concatenating RLC service data units (SDUs) transmitted from a higher layer in order to configure data of an appropriate size for a radio section.

The receiving RLC layer supports a function of reassembly of data to recover the original RLC SDU from the received RLC Protocol Data Units (PDUs).

Each RLC entity has a transparent mode (transparent mode, hereinafter referred to as TM), an unacknowledged mode (hereinafter referred to as UM), and an acknowledgment mode, according to the processing and transmission method of the RLC SDU. , AM).

In the LTE system, the radio interface protocol between the terminal and the eNodeB 130 may be configured as the lower three layers of the Open System Interconnection (OSI) reference model, which is widely known in a general communication system.

Here, the lower three layers may include L1 (first layer), L2 (second layer), and L3 (third layer).

Referring to FIG. 2, the first layer corresponds to a physical layer 250, and the physical layer 250 maps data received through a transport channel from the MAC 240 layer to a physical channel and wirelessly. It may perform a function of transmitting data generated by baseband processing on a radio signal received through an interface or a wireless interface to the MAC 240 layer through a transmission channel.

The second layer is composed of a MAC 240 layer and an RLC 230 layer.

In general, the MAC 240 layer may provide a data transmission service to an upper layer RLC 230 through a logical channel.

The MAC 240 layer has a function of mapping a logical channel and a transport channel, a function of measuring and reporting a traffic volume, a function of correcting a transmission error through a hybrid ARQ, and logic assigned to the same user. A priority handling function of channels, priority processing between terminals using dynamic scheduling, and a transport format selection function may be provided.

The RLC 230 layer supports end-to-end reliable data transmission and may provide an AM / UM / TM service according to the characteristics and importance of the data.

The RLC 230 layer receives an automatic retransmission (hereinafter referred to as ARQ (Automatic) by receiving a control signal indicating whether or not the corresponding packet is error, where the control signal includes an RLC ACK and an RLC NACK signal) from the pear side. Repeat reQuest) function can be performed.

The radio resource control 220 (hereinafter, referred to as RRC) layer located in the third layer plays a role of controlling radio resources allocated between the terminal and the network.

The RRC 220 layer is located in the eNodeB 130 and the UE 140, respectively, and may exchange control information with each other through a predefined RRC message.

The wireless protocol shown in FIG. 2 is composed of a PHY 250 layer, a MAC 240 layer, an RLC 230 layer, and an RRC 220 layer horizontally, and vertically for control signal transmission. It is a control plane.

3 is a structure of a user plane radio access protocol defined in the 3GPP radio access network standard.

Referring to FIG. 3, the user plane air interface protocol is horizontally composed of PHY 330, MAC 340, RLC 350, and Packet Data Convergence Protocol (hereinafter referred to as PDCP) layer. Vertically, this corresponds to a user plane for data transfer.

As shown in FIG. 3, the layers making up the user plane air interface protocol exist in both the UE 310 and the eNodeB 320.

The PHY 330, MAC 340, and RLC 350 layers included in the user plane may perform the functions described above with reference to FIG. 2.

The PDCP 360 layer is defined only in the user plane, and uses an IP header size that contains relatively large and unnecessary control information to efficiently transmit packets in a low bandwidth wireless section when transmitting IP packets such as IPv4 or IPv6. It performs header compression.

In addition, the PDCP (360) layer is located in the E-UTRAN (110) is responsible for the function of encrypting (Ciphering) the data packet.

4 is a view for explaining the HARQ operation defined in the 3GPP wireless access network standards.

More specifically, FIG. 4 illustrates a specific operation principle of HARQ applied to a downlink physical layer of a wireless packet communication system according to the present invention.

In general, the LTE system transmits data and control signals to the UE 140 in the network, where the control signals include system information, and the E-UTRAN 110 at the UE 140 and the downlink transmission channel used to transmit. There may be an uplink transmission channel for transmitting data and control signals.

The downlink transmission channel includes a broadcasting channel (BCH) for transmitting system information and a downlink shared channel (hereinafter, referred to as DL-SCH) for transmitting user data or control messages.

In addition, the downlink transmission channel further includes a multicast channel (hereinafter referred to as MCH) for transmitting data to a specific group of terminals.

The uplink transmission channel is a control message for initial call setup or a random access channel (RACH) used for synchronizing uplink time synchronization, and an uplink shared channel (UL-SCH) for transmitting user data or control messages. This).

In the following description, an embodiment of a method of performing a random access procedure in a mobile terminal according to the present disclosure will be described with reference to the drawings.

Before describing how the mobile terminal performs a random access procedure, a brief description will be given of the features of Orthogonal Frequency Division Multiplexing (OFDM), which is a wireless access scheme adopted in LTE.

In general, OFDM modulates each of two adjacent subcarriers to have a mathematically orthogonal property with each other in an overlapping period. That is, OFDM is a method of allocating subcarriers such that there is no interference of other subcarriers at the maximum value of each subcarrier.

Accordingly, the OFDM method has an advantage of higher frequency utilization efficiency than the conventional FDM method, thereby enabling high-speed data transmission.

The transmission of OFDM symbols is processed on a block-by-block basis, but since the OFDM symbols undergo a multipath delay while being transmitted in the radio interval, the same subcarrier signals arriving at different times at the receiving end may be intersected with inter-symbol interference (ISI). Can provide a cause.

In order to prevent the inter-symbol interference, the OFDM scheme inserts a guard interval (GI) between consecutive OFDM blocks.

In this case, the length of the guard interval should be longer than the maximum delay spread of the radio channel. The receiver performs data demodulation on the remaining received signals except for the guard period.

If the signal inserted in the guard interval is 0, all delay components of the previous symbol may be absorbed, and thus, inter-symbol interference may not occur, but inter-channel interference may still exist.

If all the subcarrier signals received through the wireless channel are received without delay, orthogonality is maintained in a Fast Fourier Transform (FFT) section. However, when a specific subcarrier of N subcarriers is received with a time delay, the subcarrier does not maintain an integer multiple of the fundamental frequency within the FFT period, thereby destroying orthogonality.

Thus, the transmission delay can cause interchannel interference and intersymbol interference for the same subcarrier causing distortion to other subcarriers. This problem can be solved by inserting a cyclic prefix (CP) at the guard interval position.

Referring to FIG. 5, one OFDM symbol period (T _sym , 510) is the sum of the effective symbol period (T _sub , 520) and the guard period (T _G , 530) where actual data is transmitted.

The guard interval 530 copies and inserts a signal corresponding to the last guard interval (T _last , 540) of the effective symbol interval in order to prevent the destruction of orthogonality that may be caused by the delay of the subcarrier, CP (Cyclic Prefix, 550).

When the CP 550 is inserted into the OFDM symbol period 510, even if a delay occurs in an arbitrary subcarrier, an integer multiple period of a subcarrier is maintained within an FFT period, thereby ensuring orthogonality.

Only the phase rotation due to the delay occurs in the demodulated signal, so that no interchannel interference occurs. Insertion of the guard interval may reduce bandwidth efficiency, but may prevent the bandwidth from being wasted due to retransmission due to channel interference.

The length of the guard interval is determined in consideration of the maximum delay spread of the channel, but is usually set to be less than 1/4 of the entire symbol period.

In the following description, a frame structure for each RACH type in LTE will be described with reference to related drawings (FIGS. 6 to 8) and related tables (Tables 1 to 2).

Referring to FIG. 6, the basic RACH frame structure may include a CP 610, a RACH preamble 620, and a guard interval Guard.

As shown in FIG. 6, the basic RACH interval 640 may have a length of 1 ms.

Referring to FIG. 7, the RACH frame structure has the same length as the RACH preamble 720, but the length of the CP 710 and the guard interval 730 is the same as the RACH preamble 620 of FIG. 6. It can be seen that it is somewhat longer than the structure.

Referring to FIG. 8, the repeating RACH frame structure may include a CP 810, a first RACH preamble 820, a second RACH preamble 830, and a guard interval 840. Here, the second RACH preamble 830 may be a repeated pattern of the first RACH preamble 820.

In general, there are two types of CPs in LTE, a long CP and a short CP. A short CP is called a normal cyclic prefix, and a long CP is called an extended cyclic prefix.

Two slots are transmitted in one Transmit Time Interval (TTI), and the structure of one slot includes CPs and OFDM symbols.

Referring to the frame structure of the RACH type 1 used in TDD / FDD, the short CP has the longest length of the first CP and has a feature of alleviating interference between slots. And long CP has a characteristic of being used in a deteriorated environment.

Looking at the frame structure 2 used only in TDD, the short CP has the longest length of the first CP and has a feature of mitigating interference between slots.

On the other hand, long CP is used in a deteriorated radio channel environment, and the first CP has the longest feature.

Referring to the operation of the random access (RA) in the LTE system, the bandwidth (Random Access Channel) for the RACH (Random Access Channel) is 72 subcarriers (reserved) are reserved (reserved), the RACH symbol period assigned to each subcarrier Greater than one TTI

The mobile terminal can obtain system information by decoding the BCH transmitted from the eNodeB, and can initiate a RACH-related procedure using the RACH-related information included in the acquired system information.

In LTE, one of the purposes of the random access procedure is to obtain Uplink Transmission Timing Synchronization.

For example, the eNodeB can measure the timing of a signal received from the mobile terminal, where the signal can be a RACH preamble, and send the timing measurement result to the mobile terminal. Here, the timing measurement result may be a control parameter for adjusting the uplink transmission timing.

At this time. The mobile terminal can correct the uplink transmission timing by using the timing measurement result.

Table 1 to be described below is a table defining the RACH signal structure in LTE.

Looking at the RACH signal structure used to acquire the transmission time synchronization to the uplink in detail, the RACH signal structure has a signal structure of the kind shown in Table 1 according to the supportable cell size (Table 1).

Table 1

Type RACH length RPF Supportable cell size (km) 0 1.0 ms One To 15 One 2.0 ms One To 90 2 2.0 ms 2 To 30 3 3.0 ms One To 120 4 3.0 ms 2 To 105

Table 1 may be described with reference to Table 2.

Frame structure Burst type T _RA T _CP T _PRE Type 1 Normal 30720xTs 3152xTs 24576XTs Extended 24576XTs Repeated 2x24576XTs Type 2 Normal 4340xTs 0xTs 4096xTs Extended 20736xTs 0xTs 20480xTs

Looking at the frame structure of Type 0 in Table 1 with reference to FIG. 6 as follows.

Type 0 in Table 1 is called Basic RACH. In Table 2, the frame structure is Type 1 and the burst type is Normal.

Referring to Table 2, the structure shows that the CP length T _CP is slightly longer than the guard period T _RA , and the short CP length of the next subframe is considered for the guard time. CP has a length of 102.6us, Preamble 0.8ms, Guard Time 97.4us.

Referring to FIG. 7, the frame structure of Type 1 in Table 1 is as follows.

Type 1 in Table 1 is referred to as an extended RACH, and corresponds to a case in which the frame structure is Type 1 and the burst type is extended in Table 2. The structure has a RACH duration of 2 to 3 TTI. When the RACH interval is 2TTI, CP has a size of 0.6ms, Preamble 0.8ms, Guard Time 0.6ms. That is, CP and Guard Time have the same size.

Referring to the case of Type 2 of Table 1 with reference to Figure 8 as follows.

Type 2 in Table 1 is called Repeated RACH. In Table 2, the frame structure is Type 1 and the burst type is repeated. In the above structure, the RACH Duration has 2 to 3 TTIs. In the case where the RACH Duration has 2TTI, the CP includes two Preambles having 0.2ms, the Preamble having 0.8ms, and the Guard Time has a size of 0.2ms. At this time, CP and Guard Time have the same size.

Type 3 of Table 1 corresponds to the Type 2 frame structure of Table 2, and corresponds to the case where the burst type is normal. The structure has a random access burst that starts the T _RA before the end of the UpPTS and has no CP.

Type 4 of Table 1 corresponds to the case in which the Frame Structure is Type 2 in Table 2 and the burst type is extended. In this structure, a random access burst is transmitted at the start of uplink subframe 1 and has no CP.

As described above, a method in which a mobile terminal attempts random access in LTE may vary according to the size of a cell to which the mobile terminal accesses.

At this time, the physical layer located in the mobile terminal cannot determine the type defined in Table 1 above by itself, and may determine the RACH type in the RRC layer of the mobile terminal.

The determined RACH type information may be delivered to the physical layer of the mobile terminal through a predetermined control message.

9 is a flowchart illustrating a random access procedure according to an embodiment of the present invention.

Referring to FIG. 9, the eNodeB 940 and the RRC 960 may transfer system information of a corresponding cell to the physical layer 950 of the eNodeB 940 (S902).

The physical layer 950 of the eNodeB 940 may map the received system information to the BCH and transmit it over the air (S904).

The physical layer 930 of the mobile terminal 910 may extract system information by decoding the BCH received over the radio (S906).

The physical layer 930 of the mobile terminal 910 may transfer the extracted system information to the RRC 920 of the mobile terminal 910 (S908).

The RRC 920 of the mobile terminal 910 may determine a random access type from the received system information (S910).

The RRC 920 of the mobile terminal 910 may include a random access (RA) type in the CPHY-Access-Request primitive and transmit it to the physical layer 930 of the mobile terminal 910 (S912).

The physical layer 930 of the mobile terminal 910 may configure a RACH channel based on the received RA type (S914).

The physical layer 930 of the mobile terminal 910 may transmit a random access preamble according to the RA type over the air (S916).

According to an embodiment of the present invention, the RRC layer of the mobile terminal may determine the RACH type information based on system information received from the eNodeB.

In general, it is apparent to those skilled in the art that an eNodeB can be sectorized into at least one cell, and each sector can transmit system information corresponding to that sector.

The system information is transmitted to a mobile terminal through a broadcast channel (BCH: Broadcating Channel), and may explicitly include information such as a radius of a corresponding cell and a RACH type suitable for the corresponding cell.

Here, the RACH type information may include the type of Table 1 and the frame structure and burst type information of Table 2.

The RRC layer of the mobile terminal may deliver the determined RACH type information directly to the physical layer through a predetermined control message.

For example, the RRC layer may directly transmit the RACH type information determined by using a CPHY-Config-Request primitive or a CPHY-Access-Request primitive to the physical layer. In this case, the physical layer may perform a random access procedure according to the received RACH type information.

The RRC layer according to another embodiment of the present invention may deliver the determined RACH type information to the physical layer through the RLC layer and the MAC layer, which are lower layers.

For example, if the RRC layer forwards a RLC-Config-Request primitive including the determined RACH type information to the RLC layer, the RLC layer accesses a medium including the RACH type information to the MAC layer. You can pass the MAC-Config-Request primitive.

Subsequently, the MAC layer may transmit a PHY-Config-Request primitive including RACH type information received to the physical layer.

According to another embodiment of the present invention, the mobile terminal may determine the RACH type information by using the strength of the pilot signal received from the eNodeB and the eNodeB pilot transmission power information included in the system information.

For example, the mobile terminal may calculate the distance from the cell according to the degree of attenuation of the strength of the pilot signal received from the cell relative to the pilot transmission power of the cell. That is, the mobile terminal can determine the RACH type according to the calculated distance.

In addition, the mobile terminal may additionally use uplink interference information included in the system information to calculate a distance from the corresponding cell.

Here, the uplink interference information is information indicating what the current radio channel environment of the uplink is, and the mobile terminal may determine an appropriate RACH type according to the current uplink radio channel environment.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and those skilled in the art will be able to make various modifications, changes, and additions within the spirit and scope of the present invention. Additions should be considered to be within the scope of the following claims.

As described above, the present invention has an advantage of providing a method of determining a RACH type and delivering it to a physical layer using RACH related system information received from an eNodeB in a mobile terminal.

In addition, the present invention provides a method of configuring RACH type information in a mobile terminal capable of allocating RACH resources in a physical layer by providing a predetermined control primitive for transmitting a RACH type determined from a higher layer to a physical layer. have.

Claims

In the method for determining the RACH type in the mobile terminal,

Extracting a RACH parameter from system information received from a base station;

Determining a RACH type using the extracted RACH parameters; And

Performing a random access procedure using the determined RACH type

Wherein the determined RACH type is determined by the RRC layer of the mobile terminal and is transmitted to the physical layer of the mobile terminal to perform the random access procedure.