WO2015113227A1

WO2015113227A1 - Methods of small cell on/off operation based on small cell over-the-air signaling

Info

Publication number: WO2015113227A1
Application number: PCT/CN2014/071704
Authority: WO
Inventors: Pei-Kai Liao; Jing Xiao; Xiangyang Zhuang
Original assignee: Mediatek Inc.
Priority date: 2014-01-28
Filing date: 2014-01-28
Publication date: 2015-08-06

Abstract

Methods for supporting fast turn-on operation of a small cell are disclosed. In one embodiment of the invention, the method supporting fast turn-on operation of a small cell, the method comprising: receiving a signaling of activation information transmitted from a small cell basestation on a second frequency band utilized by the small cell periodically if an UE has activated a first set of UE activities for the second frequency band based on the activation signaling transmitted from a macrocell basestation on a first frequency band; determining the activation time based on the received activation information if an UE receives the signaling of activation information; and activating a second set of UE activities for the second frequency band at the determined activation time within a tolerable time period after the determined activation time.

Description

METHODS OF SMALL CELL ON/OFF OPERATION BASED

ON SMALL CELL OVER-THE-AIR SIGNALING

TECHNICAL FIELD

[0001] The disclosed embodiments relate generally to mobile communication networks, and, more particularly, to power-efficient methods.

BACKGROUND

[0002] Unlike macrocell with a coverage radius ranging from one to several kilometers, small cells are low-power radio access nodes that operate in either licensed or unlicensed spectrum with a coverage radius ranging from tens to hundreds of meters. With emerging needs for more system throughput due to the popularity of smart phones, many mobile network operators are eagerly looking for methods to enhance the utilization efficiency of available radio spectrum by either spectrum efficiency improvement in licensed band or mobile data offloading in unlicensed band. Deployment of small cells as a technology providing promising gain in radio spectrum utilization efficiency receives broad attention from mobile network operators in recent years and 3 GPP is also planning to enable this feature in the next release of LTE system.

[0003] In 3 GPP Release 11 LTE system, time-domain muting scheme together with interference cancellation receiver techniques are utilized for inter-cell interference coordination/cancellation to enable the cell range extension of picocells for better mobile data offloading from macrocell in the heterogeneous networks (HetNet), where there are deployments of both macrocells and picocells sharing the same frequency band. In addition, coordinated multi-point (CoMP) operation is also enabled to provide more system throughput gain with more tightly cooperation among base stations (eNB) in HetNet. For further improvement of system throughput, wide deployment of small cells in the mobile networks is viewed as a promising technology and feature in 3 GPP Release 12 LTE system. Small cells generally include picocells, hotspot, femtocells, and microcells in licensed band and WiFi AP in unlicensed band. In 3 GPP Release 12 LTE system, the techniques to enable the deployment of small cells in licensed band will be the main focus in RAN working groups. Due to possible acquisition of 3.5 GHz frequency bands, it enables the possibility of non-cochannel deployments for small cells to relief interference issues between macrocells and small cells. As one of considered scenarios, the signaling overhead of mobility management and the time radio access interruption due to handover can be improved by assigning the frequency band for the deployment of macrocells as a mobility layer and the other frequency band for the deployment of small cells as a capacity layer. In addition to non-cochannel deployment, further enhancements on the inter-cell interference coordination/cancellation techniques are also considered and under evaluation for cochannel deployment.

[0004] Small cell on/off operation is one of promising technique to reduce the level of inter-cell interference for better user packet throughput. However, there is trade-off between the performance impact on legacy UEs and performance improvement of UEs supporting small cell on/off operation. When the transition time between small cell on and off is large, there is even UE performance degradation to support small cell on/off operation. When the transition time between on and off is zero, there is large performance impact on legacy UEs. A better compromise is to allow a short transition time between small cell on and off so as to keep tolerable performance impact on legacy UEs and acceptable performance gain on UEs supporting small cell on/off operation. With ideal backhaul between MeNB (macrocell basestation) and SeNB (small cell basestation), CA mechanism is able to support small cell on/off operation in an efficient way. When the backhaul between MeNB and SeNB is non-ideal, existing mechanisms are not sufficient. Related mechanisms to support fast small cell on/off operation for non-ideal backhaul case are still under discussion in 3GPP RANI .

SUMMARY

[0005] Methods for UE supporting fast turn-on operation of a small cell ard disclosed.

[0006] In one embodiment, a method supporting fast turn-on operation of a small cell is disclosed, the method comprising: receiving a signaling of activation information transmitted from a small cell basestation on a second frequency band utilized by the small cell periodically if an UE has activated a first set of UE activities for the second frequency band based on the activation signaling transmitted from a macrocell basestation on a first frequency band; determining the activation time based on the received activation information if an UE receives the signaling of activation information; and activating a second set of UE activities for the second frequency band at the determined activation time within a tolerable time period after the determined activation time.

[0007] In another embodiment, a method supporting fast turn-off operation of a small cell is disclosed, the method comprising: receiving a signaling of deactivation information transmitted from a small cell basestation on a second frequency band utilized by the small cell if an UE has activated all UE activities for the second frequency band and detects the small cell basestation remains in turn-on state; determining the deactivation time based on the received deactivation information if an UE receives the signaling of deactivation information; deactivating a second set of UE activities for the second frequency band at the determined deactivation time within a tolerable time period after the determined deactivation time; and deactivating a first set of UE activities for the second frequency band within a tolerable time period if an UE receives the deactivation signaling transmitted from a macrocell basestation on a first frequency band.

[0008] Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 schematically shows a Illustration of PRBs and a PRB pair according to the embodiments of the current invention.

[0010] Figure 2 shows an exemplary diagram of carrier aggregation activation/ deactivation in LTE Release 11.

[0011] Figure 3 shows an exemplary illustration of UE behaviors in the proposed mechanism according to the embodiments of the current invention.

[0012] Figure 4 shows an exemplary illustration of downlink procedure when the downlink signaling of activation/ deactivation information from an Se B to an UE is cell-specific according to the embodiments of the current invention.

[0013] Figure 5 shows an exemplary illustration of downlink procedure when the downlink signaling of activation/ deactivation information from an SeNB to an UE is UE-specific according to the embodiments of the current invention.

[0014] Figure 6 shows an exemplary illustration of uplink procedure when the downlink signaling of activation/ deactivation information from an SeNB to an UE is cell-specific according to the embodiments of the current invention.

[0015] Figure 7 shows an exemplary illustration of uplink procedure when the downlink signaling of activation/ deactivation information from an SeNB to an UE is UE-specific according to the embodiments of the current invention.

[0016] Figure 8 shows an exemplary illustration for the transmission timing of the downlink signaling according to the embodiments of the current invention.

DETAILED DESCRIPTION [0017] Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.

[0018] To support fast small cell on/off operation, there are two main issues - 1) Existing cell detection and UE measurements for cell association requires long transmission time of CRS due to its severe interference condition in 3 GPP LTE system; 2) Existing mechanisms of carrier aggregation activation/ deactivation and handover requires tens of milliseconds to complete the procedure and are not sufficient to support fast small cell on/off operation. Introduction of discovery reference signal (DRS) resolves the first issue but it requires enhancements on procedure to enable fast small cell on/off operation for high UPT gain. Proposed solutions are described in details in the following section.

[0019] In 3GPP LTE system based on OFDMA downlink, the radio resource is partitioned into radio frames, each of which consists of 10 subframes. Each subframe has a time length of 1 ms and is comprised of 2 slots and each slot has 7 OFDMA symbols in the case of normal Cyclic Prefix (CP) and 6 OFDMA symbols in case of extended CP. Each OFDMA symbol further consists of a number of OFDMA subcarriers in frequency domain depending on the system bandwidth. The basic unit of the resource grid is called Resource Element (RE) which spans an OFDMA subcarrier in frequency domain over one OFDMA symbol in time domain. A physical resource block (PRB) consists of 12 subcarriers in frequency domain and 1 slot in time domain, which constitutes 84 REs in normal CP and 72 REs in extended CP. Two PRBs locating in the same frequency location spans in different slots within a subframe is called a PRB pair. Figure 1 illustrates two examples for both normal and extended CP.

[0020] When an UE is turned on in a cell or handovers to a cell, it performs downlink synchronization and system information acquisition before conducting random access process to get RRC-layer connected. Downlink synchronization is performed by an UE with primary and secondary synchronization signals (PSS and SSS) to synchronize the carrier frequency and align OFDM symbol boundary between the base station of a cell and an UE. Further frequency and timing fine-tune or tracking is carried out continuously with cell- specific reference signal (CRS) by an UE. CRS is a kind of common pilots which are always transmitted in whole channel bandwidth in every subframe no matter whether there is data transmission. When there is data transmission, CRS is not precoded with a MIMO precoder even if MIMO precoding is applied so CRS can also be utilized for the coherent data demodulation when there is precoding information provided to an UE. In addition to CRS, UE- specific reference signals (DMRS), which are a kind of dedicated pilots, are also specified in Release 8/9/10/11 LTE systems. Compared to CRS, DMRS is only transmitted in the radio resources where there is data transmission and it is precoded with the same MIMO precoder together with the data tones for a specific UE if MIMO precoding is applied and it is mainly utilized for coherent data demodulation. After an UE gets downlink synchronized, system information acquisition is the next step to obtain necessary information for random access and connection/ service settings. For the best trade-off between transmission overhead and connection delay, system information is divided into several blocks in LTE system, each of which has different periodicities. Master information block (MIB) is one of system information blocks and contains information of downlink cell bandwidth, system frame number (SFN), physical HARQ indicator channel (PHICH) configuration and the number of transmit antenna ports. MIB is carried in physical broadcast channel (PBCH), which is transmitted every radio frame with a fixed periodicity of 4 radio frames. After obtaining MIB, UE is able to obtain SIB1 and other SIBs for further system setting. SIB1 and other SIBs are carried in physical downlink shared channel (PDSCH), which is scheduled by downlink physical control channel (PDCCH). SIB1 is transmitted every second radio frame with a fixed periodicity of 8 radio frames while other SIBs has variable periodicity configured in SIB1.

[0021] In small cell deployments, both hotspot and hotzone are possible scenarios. In LTE Release 12, hotzone scenario is the main focus and both sparse and dense small cell deployments within a hotzone are considered for different traffic density requirements. For ubiquitous coverage, both indoor and outdoor small cell deployments are considered as well. Since user distribution may vary with time and places within a hotzone (e.g. more users in a office building during the day time and less users during the night time; higher user density in the stores on sale in a department), small cell on-off operation and load balancing among small cells may be required for network power efficiency, interference control and higher user throughput. To support the discovery of a small cell which is in non-active state (i.e. a state with no signal transmission) and the small cells which are not the small cell with the strongest received signal strength for an user (e.g. small cells with 2^nd, 3^rd or 4^th strongest received signal strength), a special reference signal, called discovery reference signal (DRS) may be needed. One of main reasons to introduce non-active state to small cell is to reduce the inter-cell interference between small cells due to the transmission of CRS when there is no data transmission. It is preferred to introduce DRS with the much less overhead than CRS. For the power efficiency of an user equipment (UE), it is also preferred to introduce DRS with which UE can discover a small cell in a short time. Faster discovery, including cell detection and measurements for cell association, of small cell with DRS also facilitates fast small cell "on" (active- state) and "off' (non-active-state) operation because a small cell doesn't need to transmit PSS/SSS and CRS for a long while for UE to detect and conduct measurements. Active-state of a small cell means that there is at least PSS/SSS and CRS transmission while non-active- state of a small cell means that there is no signal transmission except DRS transmission. Therefore, the concept of non- active-state is different from commonly known dormant- state, where there is no signal transmission at all. For convenience, "on" means active-state and "off' means non- active-state in later description. There are two deployment scenarios for small cells - 1) co-channel deployment; 2) non-cochannel deployment. In co-channel deployment, macrocells and small cells are deployed using the same carrier frequency. In non- cochannel deployment, macrocells and small cells are deployed using difference carrier frequencies. In this invention, we proposed methods to support small cell fast "on'V'off ' operation in non-cochannel deployment.

Proposed Mechanisms

[0022] Even with DRS, which facilitates faster cell detection and measurements for cell association, the transition time of a small cell from "off' to "on" and from "on" to "off' remains tens of milliseconds using existing mechanisms, e.g. carrier aggregation activation/ deactivation and handover in LTE Release 11. To further reduce the transition time, procedure enhancements are needed. In this invention, methods based on direct over-the-air communication between UE and SeNB are proposed to shorten the transition time of small cell "on'V'off' operation. Figure 2 and Figure 3 illustrate the UE activities related to the configured small cell(s), macrocell basetation (MeNB) and small cell basestation (SeNB) in the mechanisms of carrier aggregation activation/ deactivation and the proposed scheme, respectively.

[0023] From figures, the proposed mechanism decouples part or all of UE activities related to the configured small cell(s), e.g. channel state information (CSI) reporting, downlink control information (DCI) monitoring, sounding reference signal (SRS) transmission on Scell and power headroom reporting (PUR) in 3 GPP LTE system, from MeNB's Scell activation/ deactivation signaling and part or all of UE activities is controlled by SeNB's signaling. In Figure 3(a), 1^st set of UE activities related to the configured small cell(s), e.g. UE activities related to the configured small cell(s) on Pcell, synchronizes with Scell activation/ deactivation signaling from MeNB but 2^nd set of UE activities related to the configured small cell(s), e.g. UE activities related to the configured small cell(s) on Scell, can synchronize with the activation/ deactivation signaling from SeNB. In Figure 3(b), for UE power efficiency, all UE activities related to the configured small cell(s) synchronize with activation/ deactivation signaling from SeNB.

[0024] Assuming that the backhaul between MeNB and SeNB is non-ideal, it is more efficient to control UE activities related to the configured small cell(s) by SeNB signaling over the air interface when small cell operates fast "on'V'off' because the latency of signaling over the air interface is much less than that in non-ideal backhaul. Therefore, we proposed the following types of signaling over the air interface and corresponding UE behaviors to support small cell fast "on'V'off' operation in a UE power efficient way. • Downlink signaling of activation information from an Se B to an UE.

o The signaling is used to notify UE the activation information, e.g. activation time, in small cell "on'V'off ' operation.

o The signaling can be physical-layer or MAC-layer signaling.

o The signaling is carried in or together with discovery reference signal.

^■ If the signaling is carried in discovery reference signal, the information can be determined by the code sequences of the discovery reference signal.

^■ If the signaling is carried together with discovery reference signal, it is carried by a physical channel in the same time slot where the discovery reference signal exists.

^■ The signaling is transmitted during small cell "off time,

o The signaling can be either cell-specific or UE-specific.

^■ If the signaling is cell-specific, the signaled activation information means the time the small cell is turned on and an UE's receiver/ transmitter should be ready for all activities or remaining activities not activated related to the configured small cell(s), e.g. CSI reporting, DCI monitoring, SRS transmission on Scell and PHR at the signaled time.

^■ If the signaling is UE-specific, the signaled activation information means the time an UE's receiver/ transmitter should be ready for all activities or remaining activities not activated related to the configured small cell(s), e.g. CSI reporting, DCI monitoring, SRS transmission on Scell and PHR.

• Downlink signaling of deactivation information from an SeNB to an UE. o The signaling is used to notify UE the deactivation information, e.g., deactivation time, in small cell "on'V'off' operation.

o The signaling can be physical-layer or MAC-layer signaling, e.g. downlink control information (DCI) in PDCCH, MAC control element (CE) in PDSCH in 3 GPP LTE system.

o The signaling is carried in or together with discovery reference signal.

^■ If the signaling is carried in discovery reference signal, the information can be determined by the code sequences of the discovery reference signal. ^■ If the signaling is carried together with discovery reference signal, it is carried by a physical channel in the same time slot where the discovery reference signal exists.

^■ The signaling is transmitted during small cell "on" time.

" If the signaling shares the same container, e.g. discovery signal or a physical channel, with the signaling of activation time, an indication to differentiate two types of signaling is needed.

o The signaling can be either cell-specific or UE-specific.

^■ If the signaling is cell-specific, the signaled deactivation information means the time the small cell is turned off and an UE can stop all or part of activities related to the configured small cell(s), e.g. CSI reporting, DCI monitoring, SRS transmission on Scell and PHR at the signaled time.

^■ If the signaling is UE-specific, the signaled deactivation information means the time an UE can stop all or part of activities related to the configured small cell(s), e.g. CSI reporting, DCI monitoring, SRS transmission on Scell and PHR.

• Uplink acknowledgement signal from an UE to an Se B.

o The acknowledgement signal is used to acknowledge the received activation information and it is transmitted at or after the time indicated in the activation information.

o The acknowledgement signal is a physical signal, a physical channel or

MAC-layer signaling, e.g. PRACH, uplink DMRS, PUCCH or MAC CE in PDSCH in 3 GPP LTE system.

o The physical resource for the acknowledgement signal is non-contention- based and is configured by higher-layer, e.g. RRC-layer in LTE system.

· Uplink triggering signal from an UE to an SeNB.

o The triggering signal is used to trigger SeNB from "off to "on" state when there is uplink data packet in an UE.

o The triggering signal is a physical signal, a physical channel or MAC-layer signaling, e.g. PRACH, uplink DMRS, PUCCH or MAC CE in PDSCH in 3 GPP LTE system. o The physical resource for the triggering signal is non-contention-based and is configured by higher-layer, e.g. RRC-layer in LTE system.

Example Procedures

[0025] In one embodiment, the example procedures to support fast small cell "on'V'off' operation is shown in the following subsections, assuming UE's receiver/transmitter for the carrier frequency of small cells are off at the beginning. The states of an Se B can be divided into active state ("on" state), non-active state ("off' state, where there is DRS transmission only) and dormant state (completely off state, where there is no signal transmission). An Me B is able to active an SeNB from dormant state to active state and deactivate an SeNB from active state to dormant state only in this invention.

Example procedure for downlink

[0026] One example procedure for downlink is shown as follows.

• Step 1 : When receiving MAC-layer activation signaling from MeNB to activate a carrier frequency for small cells, UE turns on its receiver/ transmitter for the signaled carrier frequency and activates UE activities related to the configured small cell(s) on the carrier frequency for MeNB within a tolerable time period.

o UE can turn off its receiver/ transmitter temporarily for the carrier frequency of the configured small cell(s) for power saving when no UE activities related to the configured small cell(s) are needed.

o For example, the UE activities include CSI reporting and PHR related to the configured small cell(s) transmitted to MeNB.

• Step 2: When receiving downlink signaling of activation information from SeNB, UE activates the UE activities related to the configured small cell(s) on the carrier frequency for the corresponding SeNB(s) at the time indicated by the received activation information.

o The downlink signaling of activation information can be either cell-specific or UE-specific.

^■ UE-specific downlink signaling of activation information is more beneficial to UE power efficiency.

o For example, the UE activities include DCI monitoring, SRS transmission, CSI reporting and PUR for the configured small cell(s) transmitted to SeNB.

• Step 3 : UE transmits the uplink acknowledgement signal to SeNB at or/ and after the time indicated by the received activation information.

o UE can transmit the uplink acknowledgement signal for several times until it detects its first downlink scheduler, Se B's signal transmission, or the maximal transmission number is achieved.

o If the transmission of the uplink acknowledgement signal from the UE achieves the maximal transmission number and there is no downlink scheduler for it for a period of time after the last uplink acknowledgement signal, UE can deactivate the UE activities related to the configured small cell(s) on the carrier frequency for the corresponding Se B(s) and go back to Step 2 if UE receives downlink signaling of activation information from an Se B.

• Step 4: When receiving downlink signaling of deactivation information from SeNB, UE deactivates the UE activities related to the configured small cell(s) on the carrier frequency for the corresponding SeNB(s) at the time indicated by the received deactivation information.

o The downlink signaling of deactivation information can be either cell-specific or UE-specific.

^■ UE-specific downlink signaling of deactivation information is more beneficial to UE power efficiency.

o For example, the UE activities include DCI monitoring, SRS transmission, CSI reporting and PHR for the configured small cell(s) transmitted to SeNB.

• Step 5: Continue Step 2-4 if there are more downlink data packets from SeNB and it's in "off state.

• Step 6: When receiving MAC-layer deactivation signaling from MeNB to deactivate a carrier frequency for small cells, UE turns off its receiver/ transmitter for the signaled carrier frequency and deactivates all UE activities related to the configured small cell(s) within a tolerable time period.

[0027] Figure 5 and 6 illustrate two examples for downlink procedure when the downlink signaling of activation/ deactivation information from an SeNB to an UE is cell-specific and UE-specific, respectively.

Example procedure for uplink

[0028] One example procedure for uplink is shown as follows.

• Step 1 : When receiving MAC-layer activation signaling from MeNB to activate a carrier frequency for small cells, UE turns on its receiver/transmitter for the signaled carrier frequency and activates UE activities related to the configured small cell(s) on the carrier frequency for Me B within a tolerable time period.

o UE can turn off its receiver/transmitter temporarily for the carrier frequency of the configured small cell(s) for power saving when no UE activities related to the configured small cell(s) are needed.

• Step 2: When there is uplink data packet for transmission at the UE side, UE transmits uplink triggering signal to an SeNB to activate it if it's in "off state.

o UE can transmit the uplink triggering signal for several times until it detects its first uplink scheduler, SeNB's signal transmission, or the maximal transmission number is achieved.

• Step 3 : When receiving downlink signaling of deactivation information from SeNB and there is no more uplink data packet for transmission at the UE side, UE deactivates the UE activities related to the configured small cell(s) on the carrier frequency for the corresponding SeNB(s) at the signaled time.

^■ For example, the UE activities include DCI monitoring, SRS transmission, CSI reporting and PFIR for the configured small cell(s) transmitted to SeNB.

• Step 4: Continue Step 2-3 if there are more uplink data packets for transmission at the UE side and SeNB is in "off state.

· Step 5 : When receiving MAC-layer deactivation signaling from MeNB to deactivate a carrier frequency for small cells, UE turns off its receiver/ transmitter for the signaled carrier frequency and deactivates all UE activities related to the configured small cell(s) within a tolerable time period.

[0029] Figure 7 and 8 illustrate two examples for uplink procedure when the downlink signaling of activation/ deactivation information from an SeNB to an UE is cell-specific and UE-specific, respectively.

Example signaling

[0030] In one embodiment, the example signaling to support fast small cell "on'V'off ' operation is shown in the following subsections.

Example downlink signaling

[0031] The downlink signaling of activation/ deactivation information transmitted from an SeNB to an UE can be carried by a type of downlink control information (DCI) in a physical downlink control channel, e.g. PDCCH in 3GPP LTE system. Furthermore, the physical downlink control channel can be transmitted in the radio resources for broadcasting purpose, e.g. common search space in 3GPP LTE system, and single or one of multiple specific identifications are embedded within it for UE's identification, e.g. RNTI used to scramble the CRC bits of PDCCH in 3 GPP LTE system. The same type of DCI can carry activation information, deactivation information or both. If the type of DCI carries either activation or deactivation information, an indicator within the DCI is needed for an UE to identify. If the downlink signaling is cell-specific, the same activation/ deactivation information is broadcasted from an SeNB to all UEs. In this case, the activation/ deactivation information can determine the time the SeNB switches to "on" state or "off' state. If the downlink signaling is UE-specific, different activation/ deactivation information is either unicasted or multi-casted from an SeNB to one or a group of UEs and UE can identify whether the signaling is for it by the embedded identification configured by higher-layer to the UE. In this case, the activation/ deactivation information can determine the time an UE's receiver and transmitter should be ready for reception (for activation signaling) and transmission or turned off (for deactivation signaling) within a tolerable time period. Single DCI can carry the activation/ deactivation information for single or a group of UEs. When an SeNB is in "off' state, the downlink signaling of activation/ deactivation information is transmitted in or together with DRS. When an SeNB is in "on" state, the downlink signaling of activation/ deactivation information is transmitted in a set of time slots, which can include the time slot DRS exists, and the content doesn't change within a reconfiguration time period. Furthermore, the downlink signaling can be transmitted more than one time within a reconfiguration time period. Figure 8 illustrates an example regarding to the transmission timing of the downlink signaling. In the figure, the signaling of the activation information is transmitted in or together with DRS from an SeNB to an UE when the SeNB is in "on" state. The signaling of the deactivation information is transmitted from an SeNB to an UE with the transmission number equal to or larger than one in a set of time slots when the SeNB is in "off' state. The transmission time of the deactivation information is not limited to the time slots DRS exists.

Example uplink signaling

[0032] The uplink acknowledgement signal from an UE to an Se B can be a dedicated random access channel configured by higher-layer for the UE, e.g. PRACH in 3 GPP LTE system, or a dedicated physical uplink channel for scheduling request (SR) configured by higher-layer for the UE, e.g. PUCCH used for SR in 3 GPP LTE system. It also can be a dedicated physical uplink channel for CSI reporting configured by higher-layer for the UE, e.g. PUCCH used for CSI reporting in 3GPP LTE system, or a dedicated physical uplink signal configured by higher-layer for the UE, e.g. uplink DMRS in 3GPP LTE system. UE can transmit the uplink acknowledgement signal for several times until it detects its first downlink scheduler or the maximal transmission number is achieved. If the transmission of the uplink acknowledgement signal from the UE achieves the maximal transmission number and there is no downlink scheduler for it for a period of time after the last uplink acknowledgement signal, UE can deactivate the UE activities related to the configured small cell(s) on the carrier frequency for the corresponding Se B(s).

[0033] The uplink triggering signal from an UE to an SeNB can be a dedicated random access channel configured by higher-layer for the UE, e.g. PRACH in 3GPP LTE system, or a dedicated physical uplink channel for scheduling request (SR) configured by higher-layer for the UE, e.g. PUCCH used for SR in 3GPP LTE system. It also can be a dedicated physical uplink channel for CSI reporting configured by higher-layer for the UE, e.g. PUCCH used for CSI reporting in 3GPP LTE system, or a dedicated physical uplink signal configured by higher-layer for the UE, e.g. uplink DMRS in 3 GPP LTE system. UE can transmit the uplink triggering signal for several times until it detects its first uplink scheduler, SeNB's signal transmission, or the maximal transmission number is achieved.

[0034] Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

1. A method supporting fast turn-on operation of a small cell, the method comprising:

receiving a signaling of activation information transmitted from a small cell basestation on a second frequency band utilized by the small cell periodically if an UE has activated a first set of UE activities for the second frequency band based on the activation signaling transmitted from a macrocell basestation on a first frequency band; determining the activation time based on the received activation information if an UE receives the signaling of activation information; and

activating a second set of UE activities for the second frequency band at the determined activation time within a tolerable time period after the determined activation time.

2. The method of claim 1 wherein the signaling of activation information is UE- specific.

3. The method of claim 1, wherein the signaling of activation information is cell- specific.

4. The method of claim 1, wherein the signaling of activation information is carried by PDCCH in 3 GPP LTE system.

5. A method supporting fast turn-off operation of a small cell, the method comprising:

receiving a signaling of deactivation information transmitted from a small cell basestation on a second frequency band utilized by the small cell if an UE has activated all UE activities for the second frequency band and detects the small cell basestation remains in turn-on state;

determining the deactivation time based on the received deactivation information if an UE receives the signaling of deactivation information;

deactivating a second set of UE activities for the second frequency band at the determined deactivation time within a tolerable time period after the determined deactivation time; and deactivating a first set of UE activities for the second frequency band within a tolerable time period if an UE receives the deactivation signaling transmitted from a macrocell basestation on a first frequency band.

6. The method of claim 5 wherein the signaling of deactivation information is

UE-specific.

7. The method of claim 5, wherein the signaling of deactivation information is cell-specific.

8. The method of claim 5, wherein the signaling of deactivation information is carried by PDCCH.