KR20130054105A

KR20130054105A - Method and apparatus for assigning of control channel

Info

Publication number: KR20130054105A
Application number: KR1020120016848A
Authority: KR
Inventors: 장일두; 이희봉; 김상하; 박병성
Original assignee: 에릭슨 엘지 주식회사
Priority date: 2011-11-16
Filing date: 2012-02-20
Publication date: 2013-05-24

Abstract

PURPOSE: A control channel allocation method and an apparatus thereof are provided to extend coverage as increasing capacity of a control channel. CONSTITUTION: A base station(10) includes a macro base station, a micro base station and a relay. The macro base station manages a cell of wide range, and the micro base station manages a small network cell. The base station transmits data to terminals(20a-20d) included in a communication coverage area directly or through the relay. The base station transmits data through the relay to a terminal which is unable to be communicated directly as being located out of the communication coverage area. A terminal(20) includes a mobile phone, a portable computer having mobile communication function, a PDA having mobile communication function and a portable wireless communication device or system in a random type. The relay or the terminal transmits a signal to the base station through an uplink channel, and transmits the signal to the relay or the terminal through a downlink channel.

Description

Control channel assignment method and apparatus {METHOD AND APPARATUS FOR ASSIGNING OF CONTROL CHANNEL}

The present invention relates to the field of long term evolution (LTE), and more particularly, to a method and apparatus for allocating a control channel for effectively allocating when the number of control channels to be transmitted in a cell increases.

"This study was carried out as a result of the study of the original technology development project of the next generation communication network of the Korea Communications Commission" (KCA-2011-10913-04002)

Recently, communication standards for improving performance in terms of throughput, latency, and coverage have been developed in mobile communication systems. A widely used standard is the UMTS (Universal Mobile Telecommunications System) which was developed as part of the 3rd generation (3G) mobile communication system and is maintained by the 3rd Generation Partnership Project (3GPP). Among these, 3GPP Long Term Evolution (LTE) is a communication standard driven by 3GPP to achieve high data rate, low latency, packet optimized system performance and wide coverage in UMTS systems.

In LTE-Advanced (4th generation mobile communication) system, a base station (Macro-eNB, Pico-eNB, Femto-eNB, or Home-eNB, etc.) and a terminal (eg, a mobile station) to support higher data rates and expand serviceable coverage. In addition to direct communication between UEs, signal transmission methods using a relay node (RN) system have been studied. This technology enables high-speed data communication by reducing the signal loss by relaying signals in the path between the base station and the terminal through a relay, and extends the service area by transmitting a signal to a mobile terminal far from the base station. The relay of the LTE-Advanced mobile communication system is used to solve the shadow area in the cell, and it is installed in the cell boundary area and is used to improve the effective cell coverage expansion and throughput.

In an LTE-Advanced mobile communication system, one side transmits a subframe including a signal for transmitting to a counterpart through downlink or uplink, and each subframe includes a control channel for transmitting control information. channel) and a data channel for transmitting data. Downlink (physical layer) signal transmitted from the base station to the terminal is a physical downlink shared channel (PDSCH), a physical downlink control channel (PDCCH), a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH) Etc. In addition, the uplink physical layer signal transmitted from the terminal to the base station includes a PUSCH (Physical Uplink Shared Channel), a PUCCH (Physical Uplink Control Channel), SRS (Sounding Reference Signal).

In particular, in the area of the LTE DL (DownLink) control channel, a PHICH, DL grant and UL for a HARQ (Hybrid Automatic Retransmit Request) ACK / NACK transmission for PCFICH, UL (UpLink) PUSCH for indicating the number of symbols of the channel PDCCH for transmitting grant is allocated. In the current LTE standard, up to three orthogonal frequency division multiple access (OFDM) symbols (FRs) are controlled as shown in FIG. 1 to transmit PDCCH for each subframe (minimum transmission unit is transmission time interval (TTI)). ) Can be assigned. The control channel region is located ahead of time in one subframe.

However, in the LTE-Advanced mobile communication system, the number of UEs to be controlled per cell increases as the transmission technologies such as CA (Carrier Aggregation) / CoMP (Coordinated Multi-point operation) / enhanced DL MIMO are introduced. The capacity is expected to be insufficient, and in order to solve this problem, the capacity of a control channel such as a PDCCH must be expanded.

In addition, the coverage of the UpLink has been extended because the number of reception antennas of the base station is increased up to eight. However, since the number of transmission antennas for the control channel of the base station is limited to four, the coverage of the downlink may appear smaller than the coverage of the uplink. In addition, when the downlink PDSCH serves a terminal outside a cell using beamforming, the coverage area of the PDCCH may appear smaller than that of the PDSCH. For this reason, if the current LTE standard is maintained, improved coverage will not be managed. Therefore, the coverage of the control channel must also be expanded to manage the improved coverage.

For example, due to a problem of CA introduction, when an extension carrier is used to expand the capacity of the PDSCH, an additional control channel is required to use the extension carrier. The extended carrier is a carrier for data transmission only. Since the PDCCH for data transmission of the extended carrier is transmitted to a place other than the extended carrier, it is necessary to transmit not only its own carrier but also PDCCH information for the extended carrier. In the carrier, the capacity of the control channel may be insufficient.

In addition, as a problem according to CoMP, when there is a remote radio header (RRH) having the same cell ID in one cell, the number of terminals using one cell ID increases, but the capacity of the PDCCH is limited. To improve, the capacity of the PDCCH must be increased.

In addition, as a problem according to MU-MIMO, PDCCH is additionally required because the same time / frequency region can be serviced to one or more terminals spatially separated in one cell, but in the current standard, PDCCH is not spatially separated and served. This should be improved. That is, since the number of user terminals to be controlled in one transmission frame increases, a PDCCH for each user terminal is required.

In addition, due to a problem caused by MIMO, it is determined that uplink coverage will be expanded since the base station can support up to eight receive antennas in LTE-Advanced. However, since the PDCCH is transmitted with up to four transmission antennas, there is a possibility that the coverage of the uplink is extended more than the downlink. Therefore, in order to support extended coverage, coverage of a downlink control channel must be extended. For this purpose, the downlink control channel should also extend coverage by using eight or more antennas or using beamforming. The use of eight antennas and beamforming are currently applied only to data channels, and these techniques should be considered to be applicable to PDCCH.

For the above reasons, there is an urgent need for a method of additionally transmitting a control channel.

The present invention provides a control channel allocation method and apparatus for effectively allocating an increase in the number of control channels to be transmitted in a cell.

According to an aspect of the present invention, a method and apparatus for allocating a control channel for effectively allocating an increase in the number of control channels to be transmitted in a cell are disclosed. According to the present invention, a control channel for transmitting control information on a downlink subframe is additionally allocated to a part of a data channel region. In this case, the additionally allocated control channel may be allocated in units of a time axis OFDM symbol or in units of frequency axis resource blocks (RBs).

According to the present invention, there is an advantage in that an area other than the prescribed resource is additionally allocated for transmission of the control channel, thereby increasing the capacity of the control channel and extending the coverage.

1 is a diagram illustrating the structure of an LTE subframe (1 TTI).
2 illustrates a configuration of an exemplary mobile communication system in which the present invention may be practiced.
3 is an exemplary view showing a downlink subframe structure of an LTE-Advanced system according to an embodiment of the present invention.
4 is an exemplary view showing an assignable area when only CRS is considered according to an embodiment of the present invention.
5 is an exemplary view showing an assignable region when the CRS and the UE-specific RS are considered together according to an embodiment of the present invention.
6 is an exemplary view showing a TDM allocation method according to an embodiment of the present invention.
7 is an exemplary view showing an FDM allocation method according to an embodiment of the present invention.
8 is an exemplary view showing a hybrid allocation method according to an embodiment of the present invention.
9 is an exemplary view showing an approval assignment order in a hybrid allocation method according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

2 is a diagram illustrating a configuration of an exemplary mobile communication system in which the present invention may be implemented, and illustrates a configuration of an LTE-Advanced mobile communication system.

As shown in FIG. 2, the LTE-Advanced system includes a base station 10 and a terminal 20.

The base station 10 may be a macro base station (Macro-eNB or eNB) that manages a wide range of cells (eg, a cell area managed by an outdoor base station, such as a Macro-cell), or a small network cell (indoor base station or a femto base station). It may include a micro base station (Pico-eNB, Femto-eNB or Home-eNB, etc.), a relay (RN), etc. that manages a cell area managed by the micro base station, such as a femto-cell.

The base station 10 may provide a communication service through a wireless link to the terminal 20 in a coverage region where the base station provides a network access service. In one embodiment, the base station 10 transmits data to the terminals 20a to 20d included in the communication coverage area of the base station 10 directly or through a relay, and the communication of the base station 10. For a terminal (not shown) located outside the coverage area and unable to communicate directly, data is transmitted through a relay or the like. In addition, since the terminal located outside the communication coverage area of the base station 10 cannot directly communicate with the base station 10 due to the limitation of the transmission power, the terminal transmits data to the base station 10 through a relay or the like.

The terminal (UE) 20 may include any type of portable wireless communication device or system, including, for example, a mobile phone, a portable computer having a mobile communication function, a PDA having a mobile communication function, or another device.

The relay or the terminal 20 transmits a signal to the base station 10 through the uplink channel, and the base station 10 transmits a signal to the relay or the terminal 20 through the downlink channel. If the subframe of the downlink channel including information transmitted from the base station 10 through the relay, a control channel for transmitting control information for the relay (control channel) and a data channel (data channel) for transmitting data And a control channel for transmitting control information for the terminal 20 and a data channel for transmitting data. In addition, the subframe of the downlink channel transmitted directly from the base station 10 to the terminal 20 is configured to include a control channel for transmitting control information for the terminal 20 and a data channel for transmitting data. . Each control channel for the relay or terminal 20 is located ahead of the remaining data channels on the time axis as shown in FIG. This is to allow the relay or the terminals 20a to 20d to first receive the control channel and determine whether to perform the data channel reception operation by recognizing whether the data channel transmitted to the relay channel is transmitted. Therefore, when the relay and the terminal 20 determines that there is no data channel transmitted from the control channel, the relay and the terminal 20 do not need to receive the subsequent data channel, thereby saving power consumed in the reception of the data channel.

If carrier aggregation (CA) is applied to a plurality of carrier PCells (Primary Cells) and SCells (Secondary Cells), the downlink control information may be transmitted to an enhanced PDCCH (E-PDCCH). The S-CH may include a physical downlink shared channel (PDSCH) or a physical uplink shared channel (PUSCH) that carries user data. The E-PDCCH newly proposed in the present invention, which will be described in more detail below, can support capacity increase and coverage extension.

When one terminal 10a simultaneously services different terminals by using a multi-user MIMO (MU-MIMO) scheme, the downlink control information may be transferred to the E-PDCCH.

Downlink control when CoMP (Coordinated Multi-Point operation) is applied to one terminal 20d while sharing scheduling information or data between different sectors in one base station or between different nodes connected by X2 interface. The information may be transferred to the E-PDCCH.

In the 3GPP LTE Release 8/9/10 system, the control channel (PDCCH) and data channel (PDSCH) for the terminals 20a to 20d are allocated on the downlink in the frequency-time domain. The PDCCH is used to transmit various types of downlink control information formats according to uplink scheduling assignment information and downlink control information (DCI) such as a power control command.

The PDCCH includes common purpose such as transmission of system information, power control command, response information for random access attempt, and uplink / downlink allocation information for scheduling user request data. On the other hand, since the physical resources that can transmit the PDCCH is limited (e.g., up to 3 symbols), the capacity of the PDCCH itself may be limited accordingly. CoMP, which will be introduced in the system after LTE 11, is a technique for improving system performance by utilizing cooperation between transmission points, and techniques such as joint processing and coordinated scheduling are used. Because of this, more scheduling information will be needed than now. In addition, carrier aggregation introduced in LTE release 10 supports cross carrier scheduling, which enables scheduling of all carriers in a component carrier in a good channel state, and thus can be used in one carrier. PDCCH capacity is increased. In addition, multi-user access schemes are available for downlink antennas increased after release 10, which is also a factor of increasing PDCCH capacity.

As described above, an enhanced MIMO / MU-MIMO / CoMP / CA scheme has been proposed as a method for expanding the capacity and coverage of an LTE-Advanced mobile communication system. There is no plan to expand PDCCH transmission capacity and coverage. If the PDCCH is not improved, the capacity and coverage of the enhanced data channel are virtually impossible to use. Therefore, a method for extending the capacity and coverage of the PDCCH must be supported so that such an improvement can be actually applied.

3 is an exemplary view showing a downlink subframe structure of a long term evolution (LTE) -Advanced system according to an embodiment of the present invention.

As shown in FIG. 3, the part to be improved relates to the control channel (PDCCH) region. In order to increase the capacity of the PDCCH, there is a scheme of using a region of the PDSCH. The form of transmitting a PDCCH by defining a new resource type in an area of an existing PDSCH is called an E-PDCCH.

4 and 5 illustrate regions in which an E-PDCCH can be transmitted in one resource block (RB). FIG. 4 is an exemplary view showing an assignable region when only a CRS (cell-specific reference signal) is considered, and FIG. 5 is an exemplary view showing an assignable region when both a CRS and a UE-specific RS are considered.

Resource space allocation methods for transmitting an E-PDCCH may be broadly divided into a time division multiplexing (TDM), a frequency division multiplexing (FDM), and a hybrid allocation method.

6 is an exemplary view showing a TDM allocation method according to an embodiment of the present invention. In an embodiment, as illustrated in FIG. 6, the entire designated symbol (for example, the fourth symbol) may be used as the E-PDCCH. This method may be referred to as a TDM allocation method. In the TDM allocation scheme, the capacity of the control channel can be increased by extending the region of the E-PDCCH in units of OFDM symbols.

7 is an exemplary view showing an FDM allocation method according to an embodiment of the present invention. In another embodiment, the entire RB designated as shown in FIG. 7 may be used as the E-PDCCH. This may be regarded as an FDM allocation method for allocating an area of the E-PDCCH in units of RBs on the frequency axis. In the FDM allocation scheme, the capacity of the control channel can be increased by allocating an E-PDCCH region in units of RBs.

8 is an exemplary view showing a hybrid allocation method according to an embodiment of the present invention. In another embodiment, as shown in FIG. 8, a specific RB of a designated symbol may be used as an E-PDCCH. This can be regarded as a TDM + FDM allocation scheme (hybrid allocation scheme) for allocating the region of the E-PDCCH in units of symbols on the time axis and RB on the frequency axis. In the hybrid allocation scheme, the capacity of the control channel can be increased by extending the region of the E-PDCCH in units of OFDM symbols and RBs.

A downlink grant message and an uplink grant message may be delivered to the allocation region of the E-PDCCH. In an embodiment, the downlink grant message and the uplink grant message may be multiplexed and transmitted in the region of the extended E-PDCCH in the TDM, FDM, and hybrid allocation methods.

In the TDM allocation method, the control channel may be received using the CRS. In the FDM allocation method and the hybrid allocation method, the control channel may be received using the CRS or the UE-specific RS.

As the control channel area increases, resources for transmitting data decrease. Therefore, a method of allocating the control channel resources to the minimum should be taken. Therefore, a method of dividing and assigning a downlink grant message and an uplink grant message may be applied. In general, the number of downlink grant messages is greater than the number of uplink grant messages. Therefore, a method of transmitting only a downlink grant message should be pursued in the extended E-PDCCH region.

As a method of determining the minimum allocation unit of the E-PDCCH in the hybrid allocation method, the following methods are possible.

1.Dividing the minimum transmission area of E-PDCCH in slot unit

2. If the area of the E-PDCCH is divided into slots, an unbalance of resource amount occurs in each slot. Therefore, considering the balance of the amount of resources divided by symbol unit

When the UE-specific RS is used for reception of the control channel in the hybrid allocation method, UE-specific RSs of the first slot and the second slot may be allocated differently to support transmission of the control channel of the multi-user terminal. In this case, transmission of a control channel for a multi-user terminal to one RB is possible.

In the hybrid allocation scheme, when only an uplink grant message is transmitted to a certain RB, an unused region may occur in the front slot or the rear slot. In this case, waste of radio resources occurs. Therefore, when only the uplink grant message is transmitted, the waste of resources can be avoided by transmitting the uplink grant in the PDCCH region rather than the E-PDCCH.

9 is an exemplary view showing a grant allocation order in the hybrid allocation method according to an embodiment of the present invention.

As shown in FIG. 9, in the case where the area division of the E-PDCCH of the hybrid allocation method is used as a slot, the resource amount of the second slot is larger than that of the first slot. Therefore, in order to increase the reception performance of the control channel, it may be effective to transmit the control channel information from the second slot.

The E-PDCCH multiplexing method according to the present embodiment may be applicable to a relay-PDCCH (R-PDCCH) which is a control channel for relay of LTE-Advanced. This is because the R-PDCCH also has a common point in that it is allocated to the PDSCH region.

While the above methods have been described through specific embodiments, the methods may also be implemented as computer readable code on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission over the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the above embodiments can be easily deduced by programmers of the present invention.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

10: base station 20: terminal
FR: Control Channel Area

Claims

A control channel assignment device,
And an additional control channel for transmitting control information on the downlink subframe to a part of the data channel region in addition to the control channel region.

The method of claim 1,
And the control channel region is 3 OFDM symbols located before the data channel region on a time axis.

The method of claim 2,
The additionally assigned control channel,
A control channel allocation apparatus, allocated in units of time-base OFDM symbols.

The method of claim 2,
The additionally assigned control channel,
A control channel allocation apparatus allocated in units of frequency axis resource blocks (RBs).

The method of claim 2,
The additionally assigned control channel,
Control channel assignment apparatus, which is allocated in a combined unit of a time axis OFDM symbol and a frequency axis resource block (RB).

The method according to any one of claims 1 to 5,
And multiplexing a downlink grant message and an uplink grnat message using the additionally allocated control channel.

The method according to any one of claims 1 to 5,
And transmitting a downlink grant message using the additionally allocated control channel.

The method of claim 5,
And a control channel allocation apparatus for transmitting control information by first allocating a region having a large amount of radio resources in consideration of the additionally allocated control channel.

9. The method of claim 8,
And a UE-specific RS (user equipment-specific reference signal) different for each slot for receiving the control information.

As a control channel allocation method,
a) further allocating a control channel to a portion of the data channel region on the downlink subframe; And
b) transmitting control information via the further allocated control channel.

The method of claim 10,
And the control channel region is 3 OFDM symbols located before the data channel region on a time axis.

The method of claim 11,
The step a), the control channel allocation method for allocating the control channel in the time axis OFDM symbol unit in the data channel region.

The method of claim 11,
The step a), the control channel allocation method in the data channel region, the frequency channel resource block (RB) unit.

The method of claim 11,
The step a), the control channel allocation method for allocating the control channel in the combined unit of a time axis OFDM symbol and a frequency axis resource block in the data channel region.