KR101482498B1 - Method of performing random access procedure in wireless communication system - Google Patents

Abstract

A method for performing a random access procedure in a wireless communication system includes transmitting a random access preamble randomly selected from a random access set, receiving a random access response in response to the random access preamble, Transmitting a connection request message using resource allocation information, transmitting a CQI (Channel Quality Indicator) as channel state information for a downlink channel, and receiving a contention resolution message transmitted in consideration of the CQI do. The reliability of message reception can be increased in the random access procedure, and the failure rate of the random access procedure can be lowered.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of performing random access in a wireless communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a method for performing a random access procedure in a wireless communication system.

A 3rd Generation Partnership Project (3GPP) mobile communication system based on WCDMA (Wideband Code Division Multiple Access) wireless access technology is widely deployed all over the world. HSDPA (High Speed Downlink Packet Access), which can be defined as the first evolutionary phase of WCDMA, provides 3GPP with highly competitive wireless access technology in the mid-term future. However, since the development of wireless access technology that continues to increase and compete with the requirements and expectations of users and operators continues, development of new technologies in 3GPP is required for future competitiveness.

One of the systems considered in the third generation and later systems is an Orthogonal Frequency Division Multiplexing (OFDM) system capable of attenuating the inter-symbol interference effect with low complexity. OFDM transmits a data stream on a plurality of subcarriers. The subcarriers maintain orthogonality in the frequency domain. Each orthogonal subcarrier experiences independent frequency selective fading and can eliminate inter-symbol interference through a cyclic prefix (CP).

OFDMA (Orthogonal Frequency Division Multiple Access) is a multiple access method for realizing multiple access by providing a part of available subcarriers to each user independently. OFDMA provides a frequency resource called a subcarrier to each user, and each frequency resource is provided independently to a plurality of users and is not overlapped with each other.

1 shows an example of frequency scheduling in OFDMA. The terminals A to G in the entire frequency domain are allocated the most appropriate frequency domain. The size and number of each region may vary depending on the channel state between the UE and the BS. The base station receives channel information, for example, a channel quality indicator (CQI) from each terminal, and schedules the terminals.

Meanwhile, the terminal generally performs a random access procedure to access the network. The random access procedure is performed to adjust the uplink synchronization or request the uplink radio resource allocation. The UE may perform a random access procedure in order to obtain uplink synchronization after initial downlink synchronization after the power is turned on. Alternatively, the UE may perform a random access procedure in order to allocate uplink radio resources for uplink transmission in a state where a radio resource control (RRC) connection is not established. The MS may perform a random access procedure for initial access to the target BS in the handover process.

Since the random access procedure is an initialization procedure for an uplink transmission or a network connection, if the random access procedure is delayed or fails, the service delay occurs. Therefore, there is a need for a method that can perform a random access procedure more quickly and reliably.

SUMMARY OF THE INVENTION The present invention provides a method for performing reliable random access in a wireless communication system.

A method for performing a random access procedure in a wireless communication system according to an aspect of the present invention includes the steps of transmitting a random access preamble randomly selected from a random access set, receiving a random access response in response to the random access preamble, Transmitting a connection request message using radio resource allocation information included in the random access response, transmitting a CQI (Channel Quality Indicator), which is channel state information on a downlink channel, and a contention resolution And receiving the message.

A method for performing a random access procedure in a wireless communication system according to another aspect of the present invention includes receiving a random access preamble, transmitting a random access response in response to the random access preamble, Receiving a connection request message using radio resource allocation information, receiving a CQI (Channel Quality Indicator) as channel state information for a downlink channel, and transmitting a contention resolution message in consideration of the CQI .

The reliability of message reception can be increased in the random access procedure, and the failure rate of the random access procedure can be lowered. Therefore, it is possible to prevent a service delay in initial connection or handover.

1 shows an example of frequency scheduling in OFDMA.
2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.
3 is a block diagram showing a signal generator according to the SC-FDMA scheme.
4 shows a structure of a radio frame.
5 is a diagram illustrating a resource grid for one uplink slot.
6 shows a structure of an uplink sub-frame.
7 is a flowchart illustrating a random access procedure according to an embodiment of the present invention.
8 shows an example of transmitting a CQI on the PUSCH.
9 shows another example of transmitting the CQI on the PUSCH.
FIG. 10 shows another example of transmitting the CQI on the PUSCH.
FIG. 11 shows another example of transmitting the CQI on the PUSCH.
12 shows an example of transmitting a CQI in the MAC layer.

Hereinafter, a downlink refers to communication from a base station (BS) to a user equipment (UE), and an uplink refers to communication from a terminal to a base station. In the downlink, the transmitter may be part of the base station, and the receiver may be part of the terminal. In the uplink, the transmitter may be part of the terminal, and the receiver may be part of the base station. A terminal may be fixed or mobile and may be referred to by other terms such as a Mobile Station (MS), a User Terminal (UT), a Subscriber Station (SS), a wireless device, A base station generally refers to a fixed station that communicates with a terminal and may be referred to by other terms such as a Node-B, a Base Transceiver System (BTS), an Access Point, and so on. One base station may have more than one cell.

2 is a block diagram illustrating a transmitter according to an embodiment of the present invention.

Referring to FIG. 2, a transmitter 100 includes a data processor 110, a physical resource mapper 140, and a signal generator 150. The data processor 110 performs processing on user data and a CQI (Channel Quality Indicator) to generate complex-valued symbols. The data processor 110 may implement functions of a medium access control (MAC) layer or a radio resource control (RRC) layer in addition to a physical layer. The functions of the physical layer and other layers may be implemented by a separate processor .

Physical resource mapper 140 maps complex value symbols to physical resources. A physical resource may be a resource element or a subcarrier. The signal generator 150 generates a time domain signal to be transmitted via the transmit antenna 190. The signal generator 150 may generate a time domain signal using a single carrier frequency division multiple access (SC-FDMA) scheme. The time domain signal output from the signal generator 150 may be an SC-FDMA symbol or an OFDMA Orthogonal Frequency Division Multiple Access) symbols.

Hereinafter, it is exemplified that the signal generator 150 uses the SC-FDMA scheme, but there is no limitation to the multiple access scheme to which the present invention is applied. For example, OFDMA, Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), and Frequency Division Multiple Access (FDMA).

3 is a block diagram showing a signal generator according to the SC-FDMA scheme.

3, the signal generator 200 includes a DFT unit 220 for performing a Discrete Fourier Transform (DFT), a subcarrier mapper 230, and an IFFT unit 240 for performing an Inverse Fast Fourier Transform (IFFT) ). The DFT unit 220 performs DFT on the input data to output a frequency domain symbol. The subcarrier mapper 230 maps the frequency domain symbols to the respective subcarriers, and the IFFT unit 230 performs IFFT on the input symbols to output a time domain signal.

4 shows a structure of a radio frame.

Referring to FIG. 4, a radio frame is composed of 10 subframes, and one subframe is composed of two slots. The time taken for one subframe to be transmitted is referred to as a transmission time interval (TTI). For example, the length of one subframe may be 1 ms and the length of one slot may be 0.5 ms. One slot includes a plurality of SC-FDMA symbols in a time domain and a plurality of resource blocks in a frequency domain.

The structure of the radio frame is merely an example, and the number of subframes included in a radio frame, the number of slots included in a subframe, and the number of SC-FDMA symbols included in a slot can be variously changed.

5 is a diagram illustrating a resource grid for one uplink slot.

Referring to FIG. 5, an uplink slot includes a plurality of SC-FDMA symbols in a time domain and a plurality of resource blocks in a frequency domain. Here, one uplink slot includes 7 SC-FDMA symbols and one resource block includes 12 subcarriers, but the present invention is not limited thereto.

Each element on the resource grid is called a resource element, and one resource block contains 12 × 7 resource elements. The number of resource blocks N ^UL included in the uplink slot is dependent on the uplink transmission bandwidth set in the cell.

6 shows a structure of an uplink sub-frame.

Referring to FIG. 6, the uplink subframe may be divided into a region to which a Physical Uplink Control Channel (PUCCH) for carrying uplink control information is allocated and a region to which a Physical Uplink Shared Channel (PUSCH) have. An intermediate portion of the subframe is allocated to the PUSCH, and both side portions of the data region are allocated to the PUCCH. One UE does not transmit PUCCH and PUSCH at the same time.

The PUSCH is mapped to a UL-SCH (Uplink Shared Channel), which is a transport channel, and carries user data and / or UL control information.

The uplink control information transmitted on the PUCCH includes an ACK (Acknowledgment) / NACK (Not-Acknowledgment) signal used for HARQ (Hybrid Automatic Repeat Request), a CQI (Channel Quality Indicator) indicating a downlink channel state, And a scheduling request signal which is an allocation request. The uplink control information may be transmitted on the PUCCH or PUSCH.

The PUCCH for one UE uses one resource block occupying different frequencies in each of two slots in a subframe. Two slots use different resource blocks (or subcarriers) in a subframe. It is assumed that the two resource blocks allocated to the PUCCH are frequency hopped at a slot boundary. Here, a PUCCH with m = 0, a PUCCH with m = 1, a PUCCH with m = 2, and a PUCCH with four PUCCHs with m = 3 are allocated to a subframe.

7 is a flowchart illustrating a random access procedure according to an embodiment of the present invention. The random access procedure may be performed by the UE to obtain uplink synchronization with the base station or to allocate uplink radio resources.

Referring to FIG. 7, the UE initially synchronizes with the BS in downlink synchronization (step S700). The terminal synchronizes the downlink through a primary synchronization channel and a secondary synchronization channel, which the base station periodically transmits.

The UE transmits a random access preamble randomly selected from among a random access set to which a plurality of random access preambles belong to from the base station to a base station through a physical random access channel (PRACH) (step S710). The random access set may include 64 random access preambles, and the information for generating the random access set may inform the terminal as part of the system information.

The base station receiving the random access preamble transmits a random access response to the terminal through a downlink shared channel (DL-SCH) (step S720). The random access response may include time synchronization information for uplink time synchronization correction, uplink radio resource allocation information, a random access preamble identifier, a temporary C-RNTI (Cell-Radio Network Temporary Identifier), and the like. The time synchronization information is information for the UE to adjust the uplink synchronization, and the random access preamble identifier is an identifier for the random access preamble received by the base station. The random access response is indicated by a random access identifier on the PDCCH, i.e., Random Access-Radio Network Temporary Identifier (RA-RNTI). In addition, the random access response may include radio resource allocation information for CQI transmission.

The MS transmits a connection request message to the BS through an uplink shared channel (UL-SCH) using the uplink radio resource allocation information included in the random access response (step S730). At this time, the UE transmits the connection request message and information on the downlink channel state to the CQI. Since the UE has previously acquired downlink synchronization, it can calculate a CQI by receiving a downlink channel (e.g., a broadcast channel).

Upon receiving the connection request message and the CQI, the base station allocates a suitable frequency domain to the UE according to the CQI and transmits a contention resolution message (step S740). If the UE successfully receives the collision solving message, the contention is resolved and the RRC connection is established and the random access procedure is completed.

Although the random access preamble is randomly selected from a random access set comprising 64 random access preambles, multiple terminals can simultaneously transmit the same random access preamble. This is called contention. In principle, the base station and each terminal can not know whether or not a contention occurs. After the terminal successfully receives the contention resolution message, the contention is resolved and it can be known that the terminal succeeds in accessing the base station. If the UE does not receive the collision solving message for a predetermined time, the UE transmits a new random access preamble in consideration of the random access failure. Thus, successful reception of the conflict resolution message may be essential for the quick completion of the random access procedure.

During the random access procedure, the UE transmits the CQI so that the BS can know the downlink channel state before transmitting the collision solving message. Accordingly, the best scheduling is possible for successful transmission of the collision solving message, and the reception failure rate of the collision solving message can be lowered.

Here, although the CQI is illustrated to be transmitted together with the connection request message, it may be transmitted separately from the connection request message. Also, the CQI may be transmitted at least once, periodically or aperiodically, before the base station transmits the conflict resolution message.

Various methods can be used to transmit the CQI during the random access procedure. The CQI may be configured in the physical layer and transmitted through the PUSCH, which is a physical channel, and may be configured in the MAC layer and transmitted through the UL-SCH.

8 shows an example of transmitting a CQI on the PUSCH. A reference signal (refernce signal) is assigned to a fourth SC-FDMA symbol and an eleventh SC-FDMA symbol on a subframe including 14 SC-FDMA symbols. The CQI is allocated to the resource element on the SC-FDMA symbol adjacent to the reference signal. The reliability of the CQI transmission can be increased by arranging the CQIs adjacent to the reference signal. CQIs can be distributed at equal intervals in the time domain and the frequency domain.

The number or spacing of resource elements to be allocated may vary depending on the amount of CQI, but is not limited thereto. Also, the CQI may be placed in the time domain preference, or may be arranged in the frequency domain preference. The frequency domain priority refers to allocating the CQI to the allocated resource element by first going to the frequency domain on one SC-FDMA symbol, and arranging the CQI on the next SC-FDMA symbol if the resource element is insufficient. Alternatively, the CQIs may be staggered in the time domain and the frequency domain.

9 shows another example of transmitting the CQI on the PUSCH. CQI is preferentially distributed in the time domain. That is, CQIs are allocated to subcarriers in the same position on different SC-FDMA symbols.

FIG. 10 shows another example of transmitting the CQI on the PUSCH. This is different from the embodiment of FIG. 8 or 9, and transmits the CQI over two resource blocks. CQIs can be placed at larger intervals to reduce data loss in frequency and time domain. This can achieve frequency diversity.

The interval of the resource element to which the CQI is allocated may be changed according to the number of allocated resource blocks and the amount of CQI information.

FIG. 11 shows another example of transmitting the CQI on the PUSCH. CQI is preferentially distributed in the time domain on two resource blocks.

12 shows an example of transmitting a CQI in the MAC layer. In order to transmit the CQI on the PUSCH, the data on the resource element to which the CQI is allocated should be punctured. In this case, since there is a possibility of loss of some data, the CQI in the MAC layer can be configured as a part of the MAC PDU (protocol data unit).

Referring to FIG. 12, the MAC PDU includes a MAC header and a CQI. The MAC PDU may further include a MAC SDU (service data unit) and a MAC control element. The MAC SDU is a data block from the upper layer of the MAC layer, and the MAC control element is used to transmit control information of the MAC layer, such as a buffer status report. Here, the CQI is attached to the last part of the MAC PDU, but the position of the CQI may be changed.

The subheader of the MAC header includes the CQI length to indicate whether the CQI is included in the MAC PDU. A MAC header is divided into at least one subheader, and a subheader indicates a length and a characteristic of each MAC control element and a MAC SDU. It is possible to notify whether the CQI is included through the subheader of the MAC header, and transmit the CQI including the CQI in the MAC PDU.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

Claims (4)

A method for performing a random access procedure in a wireless communication system,
Transmitting a random access preamble to a base station;
Receiving a random access response including uplink resource allocation from the base station in response to the random access preamble; And
And transmits a scheduled message and a CQI (Channel Quality Indicator) on a Physical Uplink Shared Channel (PUSCH) to the base station according to the uplink resource allocation in response to the random access response, Frame, and the CQI is a CQI of a type that is transmitted non-periodically to the base station
Way.

The method of claim 1, wherein the random access response includes at least one of a random access preamble identifier corresponding to the random access preamble, time synchronization information for synchronization correction, or a temporary C-RNTI (Cell-Radio Network Temporary Identifier)
Way.
In a wireless communication system, in a user terminal performing a random access procedure,
A wireless unit for transmitting and receiving signals; And
Connected to the wireless unit,
Transmitting a random access preamble to the base station;
Receiving, in response to the random access preamble, a random access response including uplink resource allocation from the base station;
And transmits a scheduled message and a CQI (Channel Quality Indicator) on a Physical Uplink Shared Channel (PUSCH) to the base station according to the uplink resource allocation in response to the random access response, Frame, and the CQI is set to a CQI of a type that is transmitted non-periodically to the base station
Lt; / RTI >

4. The method of claim 3, wherein the random access response includes at least one of a random access preamble identifier corresponding to the random access preamble, time synchronization information for synchronization correction, or a temporary C-RNTI (Cell-Radio Network Temporary Identifier)
User terminal.

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