KR20150095511A - Method for allocating physical random access channel - Google Patents

Abstract

A small cell base station allocates RPACH time slots for a physical random access channel (PRACH) in a subframe based on the length of the random access preamble of a terminal. The information of the allocated PRACH time slots is transmitted to the terminal through broadcasting or RRC signaling.

Description

[0001] METHOD FOR ALLOCATING PHYSICAL RANDOM ACCESS CHANNEL [0002]

The present invention relates to a physical random access channel allocation method, and more particularly, to a physical random access channel allocation method applied to a small cell.

To solve the capacity increase in the LTE based mobile communication system, the next generation mobile communication system is actively promoting the introduction of the small cell.

Small cells such as femtocells and picocells are clustered within macro cell coverage. In such a compact cell arrangement, a physical random access channel (PRACH) of a terminal included in a small cell may suffice to use a burst of a fairly short time considering the size of the cell and the low speed of the terminal.

PRACH applied to existing macro cells is divided into FDD / TDD common (formats 0, 1, 2, 3) and TDD dedicated (format 4).

The PRACH burst consists of a cyclic prefix (CP) and a preamble sequence.

Format 0 is a burst of 1 msec including a CP of 103.13 usec and a preamble sequence of 800 usec, and is generally designed to cover a cell radius up to 14 km. Therefore, format 0 transmits a burst longer than necessary in a small cell that is the mainstream of the next generation mobile communication.

Format 4 having a short burst has a limitation that the PRACH section appears in an UpPTS (Uplink Pilot Timeslot) section and is applied to a small cell having a cell radius of about 1.5 km or less, but is dedicated to TDD.

Therefore, a PRACH allocation method applied to a small cell is required.

A problem to be solved by the present invention is to provide a physical random access channel allocation method applied to a small cell.

According to an embodiment of the present invention, a method is provided in which a small cell base station allocates a Physical Random Access Channel (PRACH) for transmission of a random access preamble of a UE. The method comprising: allocating a plurality of PRACH time slots for the PRACH in a subframe based on a length of the random access preamble, and transmitting the information of the plurality of PRACH time slots to an RRC (Radio Resource Control) To the terminal.

According to the embodiment of the present invention, in a small cell environment based on the LTE mobile communication system, a plurality of PRACH transmission slots are configured in a subframe using a short RA preamble and the RA preamble is transmitted to each PRACH transmission slot, , Reduction of transmission power of the terminal, reduction of interference, and improvement of small cell discovery.

1 is a view illustrating a small cell according to an embodiment of the present invention.
2 is a diagram illustrating a PRACH allocation method according to a first embodiment of the present invention.
3 shows an RA preamble of format 4 used in a conventional macro cell.
FIG. 4 is a diagram illustrating a PRACH allocation method for transmitting an RA preamble of format 4 shown in FIG. 4 according to an embodiment of the present invention.
5 is a diagram illustrating a PRACH allocation method according to a second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification and claims, when a section is referred to as "including " an element, it is understood that it does not exclude other elements, but may include other elements, unless specifically stated otherwise.

A physical random access channel allocation method according to an embodiment of the present invention will now be described in detail with reference to the drawings.

1 is a view illustrating a small cell according to an embodiment of the present invention.

Referring to Fig. 1, the small cells 20 are arranged in a cluster form within the coverage of the macro cells 10. Fig. The small cell 20 may have a coverage of several hundred meters or less.

Since the small cell 20 satisfies the large capacity data demand of the user with efficient use of resources, the small cell 20 is used for the data traffic of the user. Also, macrocell 10 is used for signaling to provide continuous mobility management.

The UE attempts a random access (RA) procedure to request a connection setup with the target cell. PRACH means a physical channel for transmission of an RA preamble corresponding to the first stage of an RA procedure in which a UE requests to establish a connection with a target cell. The time-frequency resource at which the RA preamble is transmitted is called PRACH. The small cell 20 base station transmits information on which time-frequency resource can be used for RA preamble transmission to the UE. The transmission of information consists of broadcasting through system information or radio resource control (RRC) signaling.

The RA preamble consists of a cyclic prefix (CP) and a preamble sequence, and supports a preamble sequence in which 64 terminals can simultaneously access one base station. Thus, the RA preamble is distinguished by 64 signatures.

There are several types of events that attempt random access. The random access in the small cell environment is different from the random access in the conventional macro cell environment. The random access event is greatly reduced in the macrocell environment. For example, events such as initial connection or handover in the RRC idle state (RRC_IDLE) are not applied to small cells.

In the case of the small cell 20 having a small cell radius, the RA preamble does not need to be as long as the RA preamble of formats 0, 1, 2, and 3 used in the macrocell 10. That is, in the small cell 20, the RA preamble can be configured to be as short as the RA preamble of format 4 used in the macro cell 10. Therefore, the small cell base station 20 can allocate a plurality of PRACHs in one subframe according to the length of the RA preamble.

2 is a diagram illustrating a PRACH allocation method according to a first embodiment of the present invention.

_Referring to FIG. 2, if the length of an RA preamble applied to a small cell is defined as T _{SC_PRACH} , a small cell base station may transmit N (= 1000 / T _{SC_PRACH} ) _PRACHs for a PRACH in one subframe according to the length of an RA preamble. It is possible to allocate transmission slots (TS1-TSN). The UE can transmit the RA preamble to the small cell base station through the corresponding PRACH transmission slot.

FIG. 3 is a diagram illustrating an RA preamble of format 4 used in a conventional macro cell, and FIG. 4 is a diagram illustrating a PRACH allocation method for transmitting an RA preamble of format 4 shown in FIG. 4 according to an embodiment of the present invention .

As shown in FIG. 3, the RA preamble of format 4 used in the macrocell is composed of a preamble sequence having a CP of 14.6 microseconds (T _cp ) and a length of 133 microseconds (T _sec ), and includes a GT (Guart Time) And has a length of 157 usec.

Accordingly, six PRACH transmission slots (TS1 to TS6) can be configured in a sub-frame of 1 msec as shown in FIG. The UE can transmit the RA preamble through one PRACH transmission slot (for example, TS1) of six PRACH transmission slots (TS1 to TS6).

As described above, according to the PRACH allocation method according to the embodiment of the present invention, there is an advantage that the RA preamble of format 4 transmitted in the uplink pilot timeslot (UpPTS) period can be used as it is.

5 is a diagram illustrating a PRACH allocation method according to a second embodiment of the present invention.

5, when a small cell base station allocates six PRACH transmission slots (TS1-TS6) in one subframe according to the length of an RA preamble, a small cell base station transmits a part of six PRACH transmission slots (TS1-TS6) For example, TS1 and TS2 may be allocated for the RA use of the terminal, and the rest of the N PRACH transmission slots (for example, TS3-TS6) may be allocated for small cell discovery use.

The embodiments of the present invention are not limited to the above-described apparatuses and / or methods, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded, Such an embodiment can be readily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (1)

A method for allocating a Physical Random Access Channel (PRACH) for transmission of a random access preamble of a UE in a small cell base station,
Allocating a plurality of PRACH time slots for the PRACH in a subframe based on the length of the random access preamble, and
Transmitting information of the plurality of PRACH time slots to a mobile station through Radio Resource Control (RRC) signaling
And a physical random access channel assignment method.

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