WO2016019555A1

WO2016019555A1 - Method and apparatus for channel state information measurement

Info

Publication number: WO2016019555A1
Application number: PCT/CN2014/083924
Authority: WO
Inventors: Gang Wang; Hongmei Liu; Zhennian SUN
Original assignee: Nec Corporation
Priority date: 2014-08-07
Filing date: 2014-08-07
Publication date: 2016-02-11

Abstract

Embodiments of the present invention provide methods and apparatus for channel state information measurement. One aspect of the invention provides a method in a device operating in a first operation mode, the method comprising transmitting a first signal with a first period; transmitting a second signal in a given time interval within the first period, with a second period smaller than the first period; determining on operation mode switching or scheduling, at least partly based on a measurement report indicative of the channel state information CSI measured based on the first signal and/or the second signal. Corresponding methods and apparatus to assist the above method are also provided. By implementing some embodiments of the invention, more accurate CSI can be provided and thus improve the scheduling efficiency and reduce interferences.

Description

METHOD AND APPARATUS FOR CHANNEL STATE INFORMATION

MEASUREMENT

FIELD OF THE INVENTION

[001] Exemplary embodiments of the present invention relate generally to the wireless communication and, more specifically, to a method and apparatus for channel state information (CSI) measurement in a wireless communication network.

BACKGROUND OF THE INVENTION

[002] The small cell network as a supplement to the macro-cellular network aiming at a boost of cell capacity and coverage has become a hot research topic, e.g., in the 3rd Generation Partnership Project (3 GPP) standardization organization.

[003] A network with co-existence of small cells and macro cells is also called Heterogeneous Network (HetNet). Though HetNet provides deployment flexibility, system capacity improvement and coverage extension, it also brings technical challenges on interference management. For example, interference between small cells is drawing more and more attention, especially in a dense small cell deployment scenario. Dense small cell deployment is an efficient way to increase the user throughput while control signaling interference is becoming more and more serious with the increase of the cell density. In order to decrease the interference and to save power, dynamic on/off of small cell has been proposed as an important feature, wherein a small cell can dynamically switch between on and off modes to adapts to the traffic status, and the switching between on and off modes may be quite frequent due to burst traffic.

[004] In 3 GPP Long Term Evolution (LTE) discussions so far, for a small cell in the off mode, it only needs to transmit very limited signals, e.g., a discovery reference signal (DRS) with at least 40ms periodicity for time/frequency synchronization, cell/transmission point (TP) identification and reference signal receive power/reference signal receive quality (RSRP/RSRQ) measurement. At present, the proposed DRS in 3GPP contains primary synchronization signal/secondary synchronization signal (PSS/SSS), common reference signal (CRS) from one antenna port and channel state information reference signal (CSI-RS) from one antenna port per cell/TP. Detailed description of PSS/SSS, CRS, and CSI-RS can be found, for example, in sections 6.10 and 6.11 of the 3 GPP specification TS. 36.211.

[005] Some disadvantages in current DRS design for a small cell in off mode have been observed. For example, a sparse transmission of the DRS makes it impossible for a user equipment (UE) to estimate the channel state information of the small cell in off mode accurately, thus impossible for the small cell to schedule the UE efficiently right after its mode switch from off to on; in addition, in a dense small cell deployment scenario, the transmission of the CSI-RS, as part of the DRS, from adjacent cells may interfere with each other, and it may further degrade the system throughput.

[006] One object of embodiments of the invention is to solve at least some of the problems. SUMMARY OF THE INVENTION

[007] Various embodiments of the invention aim at addressing at least part of the above problems and disadvantages. Other features and advantages of embodiments of the invention will also be understood from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the invention.

[008] It should be noted that though the problems to be solved by the embodiments of the invention have been described in a small cell scenario, the invention is also applicable to other wireless communication systems with similar problems, e.g., ad hoc network, or device to device (D2D) communication, where a station, an access point (AP), or a device involved in D2D may operate in an off or power saving mode.

[009] Various aspects of embodiments of the invention are set forth in the appended claims and summarized in this section. It shall be noted that the protection scope of the invention is only limited by the appended claims.

[010] According to a first aspect, embodiments of the present invention provide a method, which is performed by a device in a first operation mode, the method comprises transmitting a first signal with a first period; and transmitting a second signal in a given time interval within the first period, with a second period smaller than the first period; wherein the first signal and/or the second signal is/are used for channel state information CSI measurement by another device.

[011] In accordance with an embodiment of the invention, wherein transmitting the second signal comprises transmitting the second signal using parameter configurations derived implicitly based on the first signal, and/or an identity of the transmitter of the second signal.

[012] In accordance with another embodiment of the invention, the method further comprises receiving, from a first device, a control message, and determining on operation mode switching and/or scheduling based on the received control message, wherein the control message is generated by the first device at least partly based on a measurement report indicative of a channel state information CSI measured based on the first signal and/or the second signal.

[013] In a further embodiment of the invention, the control message indicates switching time, and/or which device to be served, and/or a resource to be used for serving a device.

[014] In still another embodiment of the invention, the method further comprises receiving, from a first device, configuration information for the transmission of the second signal, wherein the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal. In accordance with another embodiment of the invention, the configuration information indicates a given time interval within the first period via a bitmap.

[015] In accordance with one embodiment of the invention, the method further comprises receiving a measurement report from a second device indicative of a channel state information CSI measured based on the first signal and/or the second signal.

[016] According to another embodiment of the invention, the method further comprises determining on operation mode switching and/or scheduling, at least partly based on the received measurement report.

[017] According to a second aspect, embodiments of the present invention provide a method, the method comprises receiving, from a first device, a measurement report indicative of channel state information measured based on a first signal and/or a second signal transmitted by a second device in a off mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period; generating a control message on operation mode switching and/or scheduling, at least partly based on the received measurement report; and transmitting the control message to the second device.

[018] In an embodiment of the invention, the control message further indicates switching time, and/or which device to be served, and/or a resource to be used for serving a device.

[019] According to another embodiment of the invention, the method further comprises transmitting, to the second device, configuration information for the transmission of the second signal, wherein the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal. In accordance with another embodiment, the configuration information indicates a given time interval within the first period via a bitmap.

[020] In still another embodiment of the invention, the method further comprises transmitting, to the first device, a control signaling which indicates at least one of the operation mode of the second device, an identity of the second device, the configuration of the second signal, and a format for the measurement report.

[021] According to a third aspect, embodiments of the present invention provide a method, the method comprises measuring a first and/or the second signals from a first device operating in off operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period; generating a measurement report indicative of channel state information measured based on the first signal and/or the second signal, and transmitting the measurement report to the first device and/or a second device.

[022] In accordance with an embodiment of the invention, the method further comprises receiving, from the second device, a control signaling which indicates at least one of the operation mode of the first device, an identity of the first device, the configuration of the second signal, and a format for the measurement report, and measuring the second signal from the first device based on the received control signaling.

[023] In some embodiments of the invention, in a method according to any of the first to third aspects of the invention, the second signal is transmitted according to a frequency hopping pattern.

[024] In another embodiment of the invention, in a method according to any of the first to third aspects of the invention, the second signal comprises reference signals from multiple antenna ports.

[025] According to another embodiment of the invention, in a method according to any of the first to third aspects of the invention, the first signal is a discovery signal for cell or device discovery, and the second signal is a channel state information reference signal CSI-RS.

[026] According to a fourth aspect of the invention, embodiments of the present invention provide an apparatus which is configurable to perform any of the methods according to the first aspect of the invention.

[027] According to a fifth aspect of the invention, embodiments of the present invention provide an apparatus which is configurable to perform any of the methods according to the second aspect of the invention.

[028] According to a six aspect of the invention, embodiments of the present invention provide an apparatus which is configurable to perform any of the methods according to the third aspect of the invention.

[029] These and other optional embodiments of the present invention can be implemented to realize one or more of the following advantages. In accordance with some embodiments of the present invention, by transmitting a second signal with a given time interval in the first period with a second smaller period, more accurate CSI estimation can be achieved which enables more efficient scheduling and implies increase system throughput. Moreover, by transmitting the second signal with a frequency hopping pattern, it provides more flexible interference management, thus further improves the system performance.

BRIEF DESCRIPTION OF THE DRAWINGS

[030] The above and other aspects, features, and benefits of various embodiments of the invention will become more fully apparent, by way of example, from the following detailed description and the accompanying drawings, in which like reference numerals refer to the same or similar elements:

[031] Fig. 1 is a schematic diagram of wireless communication network where an embodiment of the invention can be implemented;

[032] Fig. 2a is a flow chart of a method for CSI measurement according to an embodiment of the invention;

[033] Fig. 2b is a signaling diagram of a method for CSI measurement according to an embodiment of the invention;

[034] Fig. 2c is a signaling diagram of a method for CSI measurement according to another embodiment of the invention;

[035] Fig. 3a is a schematic diagram of signal transmission for CSI measurement according to an embodiment of the invention;

[036] Fig. 3b is a schematic diagram of signal transmission for CSI measurement according to another embodiment of the invention;

[037] Fig. 3c is a schematic diagram of signal transmission for CSI measurement according to still another embodiment of the invention;

[038] Fig. 3d is a schematic diagram of signal transmission for CSI measurement according to still another embodiment of the invention;

[039] Fig. 4 is a flow chart of a method for CSI measurement according to another embodiment of the invention;

[040] Fig. 5 is a flow chart of a method for CSI measurement according to still another embodiment of the invention;

[041] Fig. 6 is a block diagram of an apparatus for CSI measurement according to an embodiment of the invention; [042] Fig. 7 is a block diagram of an apparatus for CSI measurement according to another embodiment of the invention; and

[043] Fig. 8 is a block diagram of an apparatus for CSI measurement according to still another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[044] Some preferred embodiments will be described in more detail with reference to the accompanying drawings, in which the preferred embodiments of the present disclosure have been illustrated. However, the present disclosure can be implemented in various manners, and thus should not be construed to be limited to the embodiments disclosed herein. On the contrary, those embodiments are provided for thorough and complete understanding of the present disclosure, and completely conveying the scope of the present disclosure to those skilled in the art.

[045] In the following description, numerous specific details of embodiments of the present invention are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Those of ordinary skills in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

[046] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. It shall be understood that the singular forms "a", "an" and "the" include plural referents unless the context explicitly indicates otherwise.

[047] Reference is now made to Figure 1 which is a schematic diagram of wireless communication network where an embodiment of the invention can be implemented. For illustrative purposes, the wireless communication network 100 is shown to be in a cellular structure. Those skilled in the art will appreciate, however, that embodiments of the invention also apply to non-cellular wireless communication networks, such as ad hoc network, or D2D communication network, as long as similar problems exist. The wireless communication network comprises one or more macro cells each covered by a network node 101, here for illustrative purpose, in the form of 3GPP LTE evolved Node B, also known as eNodeB or eNB. The network nodes 101 could also take the form of Node Bs, Base Transceiver Stations (BTSs), Base Station (BS) and/or Base Station Subsystems (BSSs), etc. The network nodes 101 provide radio connectivity to a plurality of user equipments (UEs) 102. The term user equipment is also known as mobile communication terminal, wireless terminal, mobile terminal, user terminal, user agent, machine-to-machine devices etc., and can be, for example, what today is commonly known as a mobile phone or a tablet/laptop with wireless connectivity or fixed mounted terminal. Moreover, the UEs may, but do not need to, be associated with a particular end user. The network 100 depicted in Fig. 1 also comprises a number of small cells, each covered by a small cell base station 103 with lower transmission power compared with a macro eNB, and correspondingly the coverage of the small cell is much smaller compared with that of the macro cell. In some embodiments, the small cells operate independently without assistance from the macro eNB 101, while in other embodiments, the small cells are controlled by a macro eNB which provides a coverage overlaps with that of the small cells. The macro eNB 101 and the small cell base station 103 may communicate via the known X2 interface, or any other suitable interfaces existing or developed in the future. In a dense small cell deployment scenario, there can be numerous small cells within coverage of same macro cell. In such case, the interference between small cells cannot be neglected; otherwise system throughput may degrade significantly. In order to decrease the interference and to save power of the small cell base stations, dynamic on/off of a small cell has been proposed as an important feature, wherein a small cell can dynamically switch between on and off modes to adapts to the traffic status, and the switching between on and off modes may be quite frequent due to burst traffic. A small cell in off mode only need to transmit very limited signals, e.g., a discovery reference signal (DRS) with at least 40ms periodicity, for time/frequency synchronization, cell/transmission point (TP) identification and reference signal receive power/reference signal receive quality (RSRP/PvSRQ) measurement. At present, the proposed DRS in 3 GPP LTE contains primary synchronization signal/secondary synchronization signal (PSS/SSS), common reference signal (CRS) from one antenna port and channel state information reference signal (CSI-RS) from one antenna port per cell/TP.

[048] Considering the possibility of fast mode switch, the on duration of a small cell may be short in time, thus it is desirable that a UE can be scheduled right after the mode switch of the small cell from off to on; however, due to the sparse transmission of DRS with a long periodicity, it is impossible for a UE to estimate the channel state information (CSI) of the small cell in off mode accurately, thus it is impossible for the small cell to schedule the UE efficiently. This may decrease the system throughput. Another factor in current DRS design that may degrade the throughput is potential interferences caused by the transmission of the CSI-RS from adjacent cells, as part of the DRS, especially for a dense small cell deployment scenario. The interference may further degrade the measurement performance and decrease the throughput accordingly.

[049] Reference is now made to Fig. 2a, which illustrates a flow chart of a method 200 for CSI measurement according to an embodiment of the invention. The method can be performed, for example, by a small cell base station 103 shown in Fig. 1 in a off mode, e.g., an off mode.

[050] The method 200 comprises a step 201 for transmitting a first signal with a first period; a step 202 for transmitting a second signal in a given time interval within the first period, with a second period smaller than the first period; wherein the first signal and/or the second signal is/are used for channel state information CSI measurement by another device

[051] In accordance with some embodiments of the invention, the method further comprises a step 203 for determining on operation mode switching and/or scheduling, at least partly based on a measurement report indicative of channel state information measured based on the first signal and/or the second signal.

[052] In accordance with some embodiments of the invention, the step 203 for determining on operation mode switching or scheduling further comprises a step 203a for receiving, from a first device, a control message, and a step 203b for determining on operation mode switching and/or scheduling based on the received control message, wherein the message is generated by the first device at least partly based on the measurement report received from a second device. In some embodiments, the first device could be a macro eNB 101 shown in Fig. 1, and the second device can be a UE 102 shown in Fig. 1. Such embodiments of the method 200 can be applied to a scenario, where the small cells, e.g., a small cell base station 103 as shown in Fig. 1, is under control of macro eNB e.g., the macro eNB 101 shown in Fig. 1, and the operation mode switching and/or scheduling is assisted by the macro eNB.

[053] In an embodiment of the present invention, the control message received in step 203 a further indicates switching time. According to another embodiment of the invention, the control message may indicate which UE should be served by the transmitter of the second signal, e.g., the small cell base station. In an example embodiment, the control message may order a mode switch implicitly, e.g., order switching to an "on" mode via indicating that there is a UE to be served by the small cell. In a further embodiment, the message may also suggest resources for the transmitter of the second signal to serve another device. The content of the control message can be determined by the first device (e.g., the macro eNB) based on the received measurement report on CSI, and in some embodiments some other factors, such as estimation on interference which may be caused by the mode switch of a specific small cell, cell- splitting gain, and/or traffic status.

[054] In another embodiment of the present invention, the method 200 further comprises a step 211 for receiving, from the first device (e.g., the macro eNB), configuration information for the transmission of the second signal. In accordance with some embodiments, the configuration information indicates at least one of the following information: a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal. The configuration information may help to reduce the interference in the transmission of the second signal then guarantee more accurate CSI measurement. In one embodiment of the invention, the configuration information received includes a bitmap which indicates a time domain position or a given time interval within the first period where transmission of the second signal is allowed. For example, for a first period of 40ms, an 8 -bits bitmap can be used to indicate when the second signal is to be transmitted. In another example, the parameter configuration received in step 211 may indicate whether the second signal should be transmitted. For example, the macro eNB may disable the second signal transmission by sending an all-zero bitmap.

[055] A signaling diagram 2000 according to some of the above embodiments of the invention is shown in Fig. 2b. However, it should be noted that the signaling shown are just for illustration purpose, which means in some embodiments, there can be additional signalings, and in some embodiments, some signaling can be omitted. As shown in Fig. 2b, the signaling procedure involves three devices which are illustrated as macro eNBs, small cell base station and UE as an example. Those skilled in the art will appreciate that the method can apply to other devices in case similar problems exist. As shown in Fig. 2b, the macro eNB firstly provides in 2001, to the small cell base station, specific parameters to be used for the transmission of the second signal, or both the first and the second signal, which are to be measured by the UE to derive CSI between the UE and the small cell. The configured transmission parameters may help to reduce interference between the signal transmissions from adjacent small cells. The small cell base station transmits, in 2002, the first signal and the second signal according to the configured parameters provided by the macro eNB, wherein a first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period. In 2003, the UE performs measurement based on the second signal, or both the first and the second signals, to derive an estimation of the CSI. The measurement can be performed by the UE periodically, or performed based on a trigger, which may be an event, e.g., link performance degradation, new traffic arrival etc., or a command transmitted by the macro eNB in 2004. Similarly, UE can report in 2005, periodically or based on a trigger provided in 2006 by the macro eNB, the measurement report indicates the CSI measured based on the second signal or, both the first and the second signals. Then at least partly based on the received measurement report, the macro eNB can send a control message in 2007 to the small cell base station, with respect to operation mode switching and/or scheduling of the small cell base station. The macro eNB can, for example, decides whether to send the control message or content of the message based on traffic status, estimation of the potential interference which may be caused by the mode switching of a specific small cell and cell splitting gain, etc..

[056] In accordance with some embodiments of the invention, the method 200 may be implemented in another way. That is, the small cell determines the operation mode switching and/or scheduling directly without assistance from the macro eNB. In such case, the step 203 for determining on operation mode switching and/or scheduling can comprise a step 203c for receiving the measurement report from a second device, e.g., the UE 102 shown in Fig 1 , and a step 203 d for determining on operation mode switching or scheduling, at least partly based on the received measurement report from the second device. It should be noted that, in some embodiments, the step 203c for receiving the measurement report from a second device may not be considered as part of the step 203 for determining operation mode switching and/or scheduling, but is a separate/independent step. In some case, the measurement report may be used for any other suitable purpose. For example in step 203d, decision on whether to switch from current "off mode to "on" mode can be made, based on both the measurement report indicating CSI, as well as the traffic status. In another example embodiment, in step 203d, based on the received measurement report or both the measurement report and some interference statistics, scheduling decision with respect to which UE to schedule and/or which resource to be used for the scheduling of UE can be made. Such embodiment of the method 200 can be applied in a scenario where the small cells operate independently without any assistance from the macro eNB. Moreover, in such a case where no assistance from a macro eNB is available, the step 202 for transmitting a second signal may comprise transmitting the second signal using parameter configurations derived implicitly based on the first signal, and/or an identity of the transmitter of the second signal according to some embodiments of the invention,. For example, the small cell may derive the transmission of the second signal implicitly based on the transmission parameters of the first signal, or, based on the transmitting point identity (TP- ID) or the small cell ID. Compared with the macro-assisted embodiments, these embodiments enable distributed scheduling and relieves the control burden of the macro eNB. It also reduces the required signaling interaction overhead between macro eNB and small cell base stations, while the performance may be sub-optimal compared with the macro-assisted scheme.

[057] In some embodiment of the invention, in step 203c, the measurement report is received periodically, and in another embodiment, the measurement report is aperiodic, and is triggered by certain event, e.g., performance degradation or new data arrival, or, triggered by a command. In some embodiments of the invention, in step 203 c, the measurement report is received via a physical random access channel (PRACH), or via a physical uplink control channel (PUCCH), but embodiments of the invention are not limited to this.

[058] In some embodiments of the invention, the step 203 of the method 200 may further comprise the operation of receiving other measurement reports from the second device, e.g., RSRP/RSRQ report, which may be measured based on the first signal or/and the second signal.

[059] Another signaling procedure 2010 according to some of the above embodiments of the invention is illustrated in Fig. 2c. It should be appreciated that, in some embodiment of the invention, some signaling can be omitted, and similarly, some additional signaling can be inserted. As shown in Fig. 2c, the signaling procedure may involve only two devices, which are illustrated as a small cell base station and a UE as an example. Those skilled in the art will appreciate that the method can apply to other devices in case similar problems exist. As shown in Fig. 2c, the small cell base station in off mode transmits a first signal and a second signal in 2011 and 2012 respectively, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period. In 2013, the UE performs measurement based on the second signal, or both the first and the second signals, to derive an estimation of the CSI. The measurement of the UE can be performed periodically, or performed based on an trigger which can be an event e.g., link performance degradation, new traffic arrival, etc. Similarly, UE can send to the small cell in 2014, periodically or based on a trigger, the measurement report indicative of the CSI measured based on the second signal or, both the first and the second signals. Then in 2015, the small cell base station may determine on mode switching and/or scheduling based on the received measurement report. In another embodiment of the invention, in 2015, the small cell base station may perform other or additional operations based on the measurement report.

[060] In an embodiment of the invention, the first signal transmitted by the device in the first operation mode is a discovery signal for cell or device discovery, and the second signal is a channel state information reference signal CSI-RS.

[061] In accordance with another embodiment of the invention, the second signal further comprises reference signals from multiple antenna ports, e.g., from 8 antenna ports, or from more or less antennas depending on the antenna configuration at the transmitter (e.g., the small cell) side and the consideration on overhead. This enables the second device (e.g., a UE) to estimate CSI for multiple antennas and enables scheduling a MIMO transmission.

[062] In an embodiment of the invention, the off mode is a mode where the device only transmit sparse signals with relatively long period, e.g, it is the off mode for small cell defined in 3 GPP LTE, in another embodiment of the invention, the off mode may be a sleeping mode or a power saving mode defined by other specifications, and the operation mode switching comprises switching to another operation mode which is a normal operation mode with more signal transmissions than the off mode.

[063] In some embodiments of the invention, in step 202, transmitting a second signal comprises transmitting the second signal according to a frequency hopping pattern. By doing so, in the second period, the second signal may be transmitted in different resources e.g., different sub-band of the cell bandwidth. Thereby enables a UE to measure the CSI based on multiple transmissions within the first period, to obtain an estimation for a wide bandwidth, e.g., for the whole cell bandwidth. This implementation allows each transmission occupy only a sub-band which enables more flexible interference management. For example, collision in transmission of the second signal from different small cells can be reduced by transmitting the second signal in different time interval within the first period, and/or, by transmitting using different frequency hopping patterns. The frequency hopping pattern can be derived implicitly by the transmitter, e.g., the small cell, or can be configured by another device, e.g., the macro eNB, e.g., via signaling step 2001 in Fig. 2b, depending on the small cell deployment scenario to which the embodiments of the invention being applied.

[064] In Fig. 3a-3d, schematic diagrams for the first and second signal transmissions according to some embodiments of the invention are presented. In these figures, the first signal is assumed to be a DRS, while the second signal is assumed to be a multiple ports CSI-RS. However, it should be noted that the embodiments of the invention are not limited to this and the first signal and the second signal can be any other suitable signals.

[065] Fig. 3a illustrates an embodiment where the first signal is transmitted with a 40ms periodicity, while the second signal is transmitted with a period of 5ms, and the transmission of the second signal occurs within a 15 ms time interval in 40 ms period. The location of the 10ms time interval where the transmission of the second signal is allowed can be determined implicitly (e.g., based on cell ID or TP ID) by the transmitter of the second device, or configured, e.g., by a macro eNB via signaling step 2001 shown in Fig. 2b.

[066] Fig. 3b illustrates an embodiment where the first signal and the second signal are transmitted with the same periodicity as shown in Fig. 3a, and the difference is that a frequency hopping pattern is applied to the transmission of the second signal, and as shown in Fig. 3b, the frequency hopping pattern in small cell 1 differs from that in small cell 2. By adopting different initial sub-bands in frequency hopping, the inter-cell interference may be reduced. Similarly, the frequency hopping pattern of the second signal can be determined implicitly (e.g., based on cell ID or TP ID) by the transmitter of the second device, or configured, e.g., by a macro eNB via step 2001 in Fig. 2b. It will be appreciated that the bandwidth for the first signal and the second signal transmissions is just shown as an example, and in other embodiments of the invention, the bandwidth occupied by the first and the second signal can differ from that shown in Fig.2b.

[067] Fig. 3 c illustrates an embodiment where the first signal and the second signal are transmitted with the same periodicity as shown in Fig. 3 a, and a hopping pattern is applied to the transmission of the second signal as in Fig.2b, the difference is that the frequency hopping transmission repeats within the first period, i.e., there are multiple transmissions in each of the sub-bands. This may provide more accurate CSI measurement at the cost of a long time interval for transmission. Similarly, the parameter for configuring the repetition can also be derived implicitly or be configured.

[068] Fig.3d illustrates an embodiment where the first signal and the second signal are transmitted with the same periodicity as shown in Fig. 3 a, the difference is that the transmission of the second signal is restricted to a very short given time interval, such that only one transmission of the second signal in the first period is available. This enables better power saving of the small cell, and UE may perform the measurement in the specified time interval based on a trigger command from the macro eNB, or based on the transmission parameter of the second cell derived from the detection of the first signal implicitly. In such case, the second signal can be transmitted in the whole cell bandwidth, or in a given sub-band thereof. Also, the second signal can comprise CSI-RS from multiple antenna ports.

[069] Reference is now made to Fig.4, which illustrates a flow chart of a method 400 for CSI measurement according to an embodiment of the invention. As shown in Fig. 4, the method 400 comprises a step 401 for receiving, from a first device, e.g., a UE, a measurement report indicative of the CSI measured by the first device based on a second signal or both a first and a second signals transmitted by a second device in a first operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period; a step 402 for generating a control message on operation mode switching and/or scheduling, at least partly based on the received measurement report; and a step 403 for transmitting the message to the second device.

[070] The method 400 can be performed by e.g., the macro eNB 101 shown in Fig. 1 and Fig. 2b, to assist the second device (e.g., the small cell base station 103 in Fig 1) in mode switching or UE scheduling.

[071] In accordance with an embodiment of the invention, the method 400 further comprises a step 404 for transmitting, to the second device, configuration information for the transmission of the second signal, which corresponds to the step 2001 in Fig. 2b. In an embodiment of the invention, the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal. In one embodiment of the invention, the at least one parameter includes a bitmap which indicates a time domain position or a given time interval within the first period where the second signal is to be transmitted. For example, for a first period of 40 ms, the 8-bits bitmap can be used to indicate when the second signal is to be transmitted. In another example, the parameter configuration may indicate whether the second signal should be transmitted. In an embodiment, the macro eNB may disable the second signal transmission by sending an all-zero bitmap.

[072] In accordance with another embodiment of the invention, the control message transmitted in step 403 further indicates time for the second device to perform the mode switch. According to another embodiment of the invention, the control message may indicate which UE the second device should serve. In an example embodiment, the control message may order a mode switch implicitly, e.g., via indicating that there is a UE to be served by the small cell. In a further embodiment, the control message may also suggest resources for the second device to serve a UE. The content of the control message is determined based on the measurement reports, and in some embodiments, together with some other factors, such as traffic status, estimation of potential interference which may be caused by the mode switching of a specific cell, and/or cell splitting gain.

[073] In some embodiment of the invention, in step 401, the measurement report is received periodically, and in another embodiment, the measurement report received is triggered by an event, e.g., link level performance degradation or new data arrival, or, triggered by a command. In some embodiments of the invention, in step 401, the measurement report is received via a physical random access channel (PRACH), or via a physical uplink control channel (PUCCH).

[074] In still another embodiment of the invention, the method 400 further comprises a step 411 for transmitting, to the first device, a control signaling which indicates at least one of the operation mode of the second device, an identity of the second device, the configuration of the second signal, and a format for the measurement report. Such control signaling from the macro eNB facilitates the UE to perform efficient measurement with reduced blind detection.

[075] In some embodiments of the invention, the step 401 of the method 400 may further comprise receiving other measurement reports from the first device, e.g., RSRP/RSRQ report which may be generated based on the measurement of the first signal and/or the second signal. Accordingly, in such embodiments, the control signaling transmitted in step 411 may also indicate the configuration for radio resource measurement (RRM).

[076] Since the method 400 is the corresponding method performed at the macro eNB side, to assist the method 200 to be performed by the small cell base station, then all the features of the first and the second signals described with reference to Fig. 2a and Figs. 3a-3d also apply here. For example, the first signal can be a DRS and the second signal can be CSI-RS. In some embodiments, the second signal further comprises reference signals from multiple antenna ports. In accordance with another embodiment, the second signal can be transmitted according to a frequency hopping pattern.

[077] Similar as what described with reference to Fig. 2a, in an embodiment of the invention, the off mode can be the off mode defined for small cell in 3GPP LTE, or a sleeping mode or a power saving mode defined by other specifications, and the operation mode switching comprises switching to a another operation mode which is a normal operation mode with more signal transmissions than the off mode.

[078] Reference is now made to Fig. 5, which illustrates a flow chart of a method 500 for CSI measurement according to an embodiment of the invention. As shown in Fig. 5, the method 500 comprises a step 501 for measuring a first and/or a second signals from a first device, e.g., a small cell base station which is in a first operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period; a step 502 for generating a measurement report indicative of channel state information measured based on the first signal and/or the second signal; and a step 503 for transmitting the measurement report to the first device, or, to a second device, e.g., a macro eNB, wherein the measurement report is to be used for determining on operation mode switching and/or scheduling.

[079] In some embodiment of the invention, in step 503, the measurement report is transmitted periodically, and in another embodiment, the measurement report is transmitted based on a trigger, which can be an event, e.g., link level performance degradation or new data rrival, or, a command from the second device. In some embodiments of the invention, in step 503, the measurement report is transmitted via a physical random access channel (PRACH), or via a physical uplink control channel (PUCCH).

[080] The method 500 can be performed by e.g., the UE shown in Fig 1 and Figs. 2b-2c, to provide CSI measurement report. Correspondingly, the step 501 corresponds to step 2003 in Fig. 2b or step 2013 in Fig. 2c, and the step 503 may correspond to the step 2005 in Fig. 2b or step 2014 in Fig. 2c.

[081] In an embodiment of the invention, the method 500 further comprises a step 504 for receiving, from the second device, a control signaling which indicates at least one of the operation mode of the first device, an identity of the first device, the configuration of the second signal, and a format for the measurement report; this step corresponds to the step 411 in Fig.4, and in such case, the step 501 further comprises measuring the second signal from the first device based on the received control signaling from the second device.

[082] In another embodiment, in step 501, the first signal is detected first, and then an identity of the cell or transmission point is obtained via the detection. After that, transmission configuration of the second signal, e.g., time/frequency resources, frequency hopping pattern, can be derived implicitly based on the obtained cell or TP identity, which will be utilized in the following measurement of the second signal.

[083] In some embodiments of the invention, the step 503 of the method 500 may further comprise transmitting other measurement reports, e.g., RSRP/RSRQ report, which can be generated based on the first signal and/or the second signal. Accordingly, in such embodiments, the control signaling received in step 504 may also indicate the configuration for radio resource measurement (RRM).

[084] All the features of the first and the second signals described with reference to Fig. 2a and Figs. 3a-3d also apply here. For example, the first signal can be a DRS and the second signal can be CSI-RS. In some embodiments, the second signal further comprises reference signals from multiple antenna ports. In accordance with another embodiment, the second signal can be transmitted according to a frequency hopping pattern.

[085] Similar as what described with reference to Fig. 2a, in an embodiment of the invention, the off mode can be the off mode defined for small cell in 3 GPP LTE, or a sleeping mode or a power saving mode defined by other specifications, and the operation mode switching comprises switching to a another operation mode which is a normal operation mode with more signal transmissions than the off mode.

[086] Reference is now made to Fig. 6, which illustrates a block diagram of an apparatus 600 for CSI measurement according to an embodiment of the invention. The apparatus 600 according to Fig. 6 may perform the methods of Figs. 2a but is not limited to this method. The method of Fig. 2a may be performed by the apparatus of Fig. 6 but is not limited to being performed by this apparatus 600. The apparatus 600 may be a small cell base station, or any other suitable devices which may in off mode or power saving mode and the CSI of which need to be estimated.

[087] As shown in Fig. 6, the apparatus 600 comprises a first transmitting unit 601, configured for transmitting a first signal with a first period when operating in a off operation mode; a second transmitting unit 602, configured for transmitting a second signal in the first operation mode in a given time interval within the first period, with a second period smaller than the first period; wherein the first signal and/or the second signal is/are used for channel state information CSI measurement by another device.

[088] In some embodiments of the invention, the apparatus 600 further comprises a determination unit 603, configured for determining on operation mode switching and/or scheduling, at least partly based on a measurement report indicative of channel state information measured based on the first signal and/or the second signal.

[089] In some embodiments of the invention, the apparatus 600 further comprises a first receiving unit 604, configured for receiving, from a first device, e.g., a macro eNB, a control message, and in such case, the determination unit 603 is further configured for determining on operation mode switching and/or scheduling based on the received control message; wherein the control message is generated by the first device at least partly based on the measurement report received by the first device from a second device, e.g., a UE. In accordance with an embodiment, the message further indicates switching time. According to another embodiment of the invention, the message may indicate which UE the apparatus 600 should serve. In an example embodiment, the message may order a mode switch implicitly, e.g., via indicating that there is a UE to be served by the small cell. In a further embodiment, the message may also suggest resources for the apparatus 600 to serve a UE.

[090] The above embodiments may be adopted, for example, when the small cell is under the control of a macro eNB and can get assistance from the macro eNB for mode switch and/or UE scheduling. In such case, the apparatus 600 may further comprise a second receiving unit 605 in an embodiment, the second receiving unit 605 is configured for receiving from the first device, e.g., the macro eNB, configuration information for the transmission of the second signal. In an example embodiment, the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal. In one embodiment of the invention, the at least one parameter includes a bitmap which indicates a time domain position or a given time interval within the first period where the second signal is to be transmitted. For example, for a first period of 40 ms, the 8-bits bitmap can be used to indicate in which 5 ms the second signal is to be transmitted. In another example, the parameter configuration may indicate whether the second signal should be transmitted. In an embodiment, the macro eNB may disable the second signal transmission by sending an all-zero bitmap.

[091] In accordance with some embodiments, the signaling procedure performed by the apparatus 600, the first device (e.g., the macro eNB 101 in Fig. 1) and the second device (e.g., the UE 102 in Fig. 1) can be depicted as shown in Fig. 2b. It can be the case when the small cell is within the coverage of a macro cell and is under the control of the macro eNB.

[092] In accordance with other embodiments, the apparatus 600 may only perform signaling exchange with the second device (e.g., a UE 102 shown in Fig. 1), as shown in Fig. 2c, especially when the small cell operates independently without assistance from the macro eNB. In such case, in an embodiment of the invention, the apparatus 600 comprise a third receiving unit 606, configured for receiving the measurement report from a second device; and in such case, the determination unit 603 is further configured for determining on operation mode switching and/or scheduling, at least partly based on the received measurement report. For example the determination unit 603 can be configured for determining on whether to switch from current "off' mode to "on" mode, based on both the measurement report indicating CSI, as well as the traffic status. In another example embodiment, the determination unit 603 can be configured for determining, with respect to which UE to schedule and/or which resource to be used for the scheduling of UE, based on the received measurement report or both the measurement report and some interference statistics. In some embodiment of the invention, the receiving unit 606 is configured for receiving the measurement report periodically, and in another embodiment, it is configured for receiving a measurement report triggered by an event, e.g., performance degradation. In some embodiments of the invention, the measurement report may be received by the receiving unit 606 via a physical random access channel (PRACH), or via a physical uplink control channel (PUCCH). [093] According to another embodiment of the invention, the second transmitting unit 602 of the apparatus 600 is further configured for transmitting the second signal using parameter configurations derived implicitly based on the first signal, and/or an identity of the transmitter of the second signal.

[094] In accordance with an embodiment of the invention, the second transmitting unit 602 is further configured for transmitting the second signal according to a frequency hopping pattern.

[095] In some embodiments of the invention, the receiving unit 606 may be further configured for receiving other measurement reports, e.g., RSRP/RSRQ report, which can be generated based on the first signal and/or the second signal.

[096] As described with the method 200, 400 and 500, in some embodiments, the off mode can be the off mode defined for small cell in 3 GPP LTE, or a sleeping mode or a power saving mode defined by other specifications, and the operation mode switching comprises switching to a another operation mode which is a normal operation mode with more signal transmissions than the off mode.

[097] Since the apparatus can perform the method 200, thus the features of the first and the second signals described with reference to Fig. 2a also apply here. For example, the second signal may comprise reference signals from multiple antenna ports. The first signal can be a discovery signal for cell or device discovery, and the second signal can be a channel state information reference signal CSI-RS.

[098] Reference is now made to Fig. 7, which illustrates a block diagram of an apparatus 700 according to an embodiment of the present invention. The apparatus 700 according to Fig. 7 may perform the methods 400 of Fig4 but is not limited to the method. The method 400 of Fig. 4 may be performed by the apparatus 700 of Fig. 7 but is not limited to being performed by this apparatus 700.

[099] As shown in Fig. 7, the apparatus 700 may comprise a receiving unit 701, configured for receiving, from a first device, e.g., a UE, a measurement report indicative of channel state information measured by the first device based on a second signal or both the first and a second signal transmitted by a second device in a first operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period which is smaller than the first period; a message generation unit 702, configured for generating a control message on operation mode switching and/or scheduling, at least partly based on the received measurement report; and a first transmitting unit 703, configured for transmitting the control message to the second device. [0100] In an embodiment of the invention, the apparatus 700 can be a macro eNB shown in Fig. 1 and Fig. 2b, and the first device can be a UE shown in Fig. 1 and Fig. 2b, while the second device can be a small cell base station shown in Fig. 1 and Fig. 2b. However, the embodiments of the invention are not limited to this, instead, the apparatus 700, the first device and the second device can be any suitable devices in any wireless communication network where similar problems solved by the embodiments of the invention exist.

[0101] In some embodiment of the invention, the receiving unit 701 is configured for receiving the measurement report periodically, and in another embodiment, it is configured for receiving a measurement report triggered by an event, e.g., performance degradation, or, a command from the apparatus 700.

[0102] In some embodiments of the invention, the measurement report may be received via a physical random access channel (PRACH), or via a physical uplink control channel (PUCCH).

[0103] In some embodiment of the invention, the message generation unit 702 is configured for generating a control message based on the received measurement report, as well as some other factors, such as, traffic status, estimation of potential interference which may be caused by the mode switching of a specific small cell, and cell-splitting gain.

[0104] In accordance with an embodiment of the invention, the apparatus 700 further comprises a second transmitting unit 704, configured for transmitting, to the second device, configuration information for the transmission of the second signal. In an embodiment of the invention, the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal. In one embodiment of the invention, the at least one parameter includes a bitmap which indicates a time domain position or a given time interval within the first period where the second signal is to be transmitted. For example, for a first period of 40ms, the 8 -bits bitmap can be used to indicate in which 5ms the second signal is to be transmitted. In another example, the parameter configuration may indicate whether the second signal should be transmitted. In an embodiment, the macro eNB may disable the second signal transmission by sending an all-zero bitmap.

[0105] In another embodiment of the invention, the control message transmitted by the first transmitting unit 703 further indicates time for the second device to switch. According to another embodiment of the invention, the message may indicate which UE the second device should serve. In an example embodiment, the message may order a mode switch implicitly, e.g., via indicating that there is a UE to be served by the small cell. In a further embodiment, the message may also suggest resources for the second device to serve a UE. [0106] According these embodiments, the apparatus 700 assists in the mode switching or scheduling of the second device. Such embodiments can be adopted in case the second device is within the coverage of the apparatus 700 and under the control of the apparatus 700.

[0107] In accordance with some embodiments, the apparatus also controls the measurement of the first device, e.g., the apparatus 700 may further comprise a third transmitting unit 705, configured for transmitting, to the first device, a control signaling which indicates at least one of the operation mode of the second device, an identity of the second device, the configuration of the second signal, and a format for the measurement report. The control signaling can help to reduce the blind detection of the first device during the CSI measurement.

[0108] In some embodiments of the invention, the receiving unit 701 can be further configured for receiving other measurement reports, e.g., RSRP/RSRQ report, which can be generated based on the first signal and/or the second signal. Accordingly in such embodiments, the control signaling transmitted by the third transmitting unit 705 may also indicate the configuration for radio resource measurement (RRM).

[0109] The apparatus 700 according to Fig. 7 may perform the methods 400 of Fig. 4, and may perform the signaling procedure with the second device as shown in Fig. 2b to enable the second device to perform the method 200. Thus, the features of the first and the second signal described with reference to Figs. 2a-2b, Figs 3a-3d, and Fig. 4 also apply here. For example, in some embodiments, the off mode can be the off mode defined for small cell in 3GPP LTE, or a sleeping mode or a power saving mode defined by other specifications, and the operation mode switching comprises switching to a another operation mode which is a normal operation mode with more signal transmissions than the off mode. The second signal may comprise reference signals from multiple antenna ports. The first signal can be a discovery signal for cell or device discovery, and the second signal can be a channel state information reference signal CSI-RS.

[0110] Reference is now made to Fig. 8, which illustrates a block diagram of an apparatus 800 according to an embodiment of the present invention. The apparatus 800 according to Fig. 8 may perform the methods 500 of Fig. 5 but is not limited to the method. The method 500 of Fig. 5 may be performed by the apparatus 800 of Fig. 8 but is not limited to being performed by this apparatus 800.

[0111] The apparatus 800 may comprise a measurement unit 801, configured for measuring a a first and/or a second signal from a first device which is in a first operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period which is smaller than the first period; a report generation unit 802, configured for generating a measurement report indicative of channel state information measured based on the first signal and/or the second signal, and a transmitting unit 803, configured for transmitting the measurement report to the first device, or, to a second device. In some embodiment of the invention, the measurement report can be used for determining on operation mode switching and/or scheduling.

[0112] It will be appreciated that the features of the first and the second signal described with reference to Figs. 2a-2c, Figs 3a-3d, and Figs. 4-5 also apply here. For example, in some embodiments, the off mode can be the off mode defined for small cell in 3GPP LTE, or a sleeping mode or a power saving mode defined by other specifications, and the operation mode switching comprises switching to a another operation mode which is a normal operation mode with more signal transmissions than the off mode. The second signal may comprise reference signals from multiple antenna ports. The first signal can be a discovery signal for cell or device discovery, and the second signal can be a channel state information reference signal CSI-RS

[0113] In an embodiment of the invention, the apparatus 800 can be a UE shown in Fig. 1 and Fig. 2b-2c, and the first device can be a small cell base station shown in Fig. 1 and Fig. 2c, while the second device can be a macro eNB shown in Fig 1 and Fig. 2b. However, the embodiments of the invention are not limited to this, instead, the apparatus 800, the first device and the second device can be any suitable devices in any wireless communication network where similar problems solved by the embodiments of the invention exist.

[0114] In an embodiment of the invention, the measurement unit 801 is configured for detecting the first signal and thereby obtaining a small cell or transmission point identity, and then deriving the transmission parameters of the second signal, which is utilized during the measurement of the second signal.

[0115] In an embodiment of the invention, the report generation unit 802 is configured for generating a measurement report indicative of channel state information measured based on the second signal, and in another embodiment, based on both the first signal and the second signal.

[0116] In some embodiment of the invention, the transmitting unit 803 is configured for transmitting the measurement report periodically, and in another embodiment, it is configured for transmitting the measurement report based on a trigger which can be an event, e.g., link level performance degradation or new traffic arrival, or, can be a command from the second device.

[0117] In some embodiments of the invention, the measurement report may be transmitted via a physical random access channel (PRACH), or via a physical uplink control channel (PUCCH). [0118] In accordance with an embodiment of the invention, the apparatus 800 further comprises a receiving unit 804, configured for receiving, from the second device, a control signaling which indicates at least one of the operation mode of the first device, an identity of the first device, the configuration of the second signal, and a format for the measurement report, and in such case, the measurement unit 801 can be further configured for measuring the second signal from the first device based on the received control signaling, and/or the transmitting unit 803 can be further configured for transmitting the measurement report to the second device based on the control signaling.

[0119] In some embodiments of the invention, the transmitting unit 803 can be further configured for transmitting other measurement reports, e.g., RSRP/RSRQ report, which can be generated based on the first signal and/or the second signal. Accordingly in such embodiments, the control signaling received by the receiving unit 804 may also indicate the configuration for radio resource measurement (RRM).

[0120] By implementing some of the above embodiments of the invention, more accurate CSI is made available, even for a small cell in off mode. It enables more efficient scheduling and reduces potential interferences, and thereby the system throughput can be improved.

[0121] The flow charts and block diagrams in the figures illustrate the likely implemented architecture, functions, and operations of the system, method, and apparatus according to various embodiments of the present invention. In this point, each block in the flow charts or block diagrams could represent a part of a module, a program segment, or code, where the part of the module, program segment, or code comprises one or more executable instructions for implementing a prescribed logic function. It should also be noted that each block in a block diagram and/or a flow chart, and a combination of the blocks in the block diagram and/or flow chart could be implemented by software, hardware, firmware, or any of their combinations. Furthermore, it will be appreciated that in some embodiments, function of a block can also be implemented by multiple blocks, and functions of multiple blocks shown in Figs. 6-8 may also be implemented by a single block in other embodiments.

[0122] The example embodiments can store information relating to various processes described herein, e.g., store the measured CSI, the received parameter configurations etc. The components of the example embodiments can include computer readable storage medium or memories according to the teachings of the present inventions and for holding data structures, tables, records, and/or other data described herein, or the program codes for implementing any of the methods according to the embodiments of the invention.

[0123] While the present inventions have been described in connection with a number of example embodiments, and implementations, the present inventions are not so limited, but rather cover various modifications, and equivalent arrangements, which fall within the purview of prospective claims. It is also obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

WHAT IS CLAIMED IS:

1. A method in a device for wireless communication, wherein the device is operating in a off mode, the method comprising:

transmitting a first signal with a first period; and

transmitting a second signal in a given time interval within the first period, with a second period smaller than the first period;

wherein the first signal and/or the second signal is/are used for channel state information CSI measurement by another device.

2. The method according to Claim 1, wherein transmitting the second signal comprising: transmitting the second signal using parameter configurations derived implicitly based on the first signal, and/or an identity of the transmitter of the second signal.

3. The method according to Claim 1, further comprising:

receiving, from a first device, a control message, and

determining on operation mode switching and/or scheduling based on the received control message, wherein the control message is generated by the first device at least partly based on a measurement report indicative of a channel state information CSI measured based on the first signal and/or the second signal.

4. The method according to Claim 3, wherein the control message indicates switching time, and/or which device to be served, and/or a resource to be used for serving a device.

5. The method according to Claim 1, wherein the method further comprising:

receiving, from a first device, configuration information for the transmission of the second signal, wherein the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal.

6. The method according to Claim 5, wherein the configuration information indicates a given time interval within the first period via a bitmap.

7. The method according to Claim 1, further comprising: receiving a measurement report from a second device indicative of a channel state information CSI measured based on the first signal and/or the second signal.

8. The method according to Claim 7, further comprising:

determining on operation mode switching and/or scheduling, at least partly based on the received measurement report.

9. A method for communication, comprising:

receiving, from a first device, a measurement report indicative of channel state information measured based on a first signal and/or a second signal transmitted by a second device in a off mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period;

generating a control message on operation mode switching and/or scheduling, at least partly based on the received measurement report; and

transmitting the control message to the second device.

10. The method according to Claim 9, wherein the control message further indicates switching time, and/or which device to be served, and/or a resource to be used for serving a device.

11. The method according to Claim 9, further comprising:

transmitting, to the second device, configuration information for the transmission of the second signal, wherein the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal.

12. The method according to Claim 11, wherein the configuration information indicates a given time interval within the first period via a bitmap.

13. The method according to Claim 9, further comprising:

transmitting, to the first device, a control signaling which indicates at least one of the operation mode of the second device, an identity of the second device, the configuration of the second signal, and a format for the measurement report.

14. A method for communication, comprising:

measuring a first and/or the second signals from a first device operating in off operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period;

generating a measurement report indicative of channel state information measured based on the first signal and/or the second signal, and

transmitting the measurement report to the first device and/or a second device.

15. The method according to Claim 14, further comprising:

receiving, from the second device, a control signaling which indicates at least one of the operation mode of the first device, an identity of the first device, the configuration of the second signal, and a format for the measurement report, and

measuring the second signal from the first device based on the received control signaling.

16. The method according to any of Claims 1 to 15, wherein the second signal is transmitted according to a frequency hopping pattern.

17. The method according to any of Claims 1 to 15, wherein the second signal comprises reference signals from multiple antenna ports.

18. The method according to any of Claims 1 to 15, wherein the first signal is a discovery signal for cell or device discovery, and the second signal is a channel state information reference signal CSI-RS.

19. An apparatus for communication, comprising:

a first transmitting unit, configured for transmitting a first signal with a first period when the apparatus is in a off mode,

a second transmitting unit, configured for transmitting a second signal in a given time interval within the first period, with a second period, which is smaller than the first period, when the apparatus is in the off mode;

20. The apparatus according to Claim 19, wherein the second transmitting unit is further configured for transmitting the second signal using parameter configurations derived implicitly based on the first signal, and/or an identity of the transmitter of the second signal.

21. The apparatus according to Claim 19, further comprising:

a first receiving unit, configured for receiving, from a first device, a control message, and a determination unit, configured for determining on operation mode switching and/or scheduling based on the received control message;

wherein the control message is generated by the first device at least partly based on a measurement report indicative of channel state information measured based on a first and/or a second signals.

22. The apparatus according to Claim 21, wherein the control message further indicates switching time, and/or which device to be served, and/or a resource to be used for serving a device.

23. The apparatus according to Claim 19, further comprising:

a second receiving unit, configured for receiving, from a first device, configuration information for the transmission of the second signal, wherein the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal.

24. The apparatus according to Claim 23, wherein the configuration information indicates a given time interval within the first period via a bitmap.

25. The apparatus according to Claim 19, further comprising:

a third receiving unit, configured for receiving a measurement report indicative of channel state information measured based on the first and/or the second signals.

26. The apparatus according to Claim 25, further comprising:

a determination unit, configured for determining on operation mode switching and/or scheduling, at least partly based on the received measurement report.

27. An apparatus for communication, comprising:

a receiving unit, configured for receiving, from a first device, a measurement report indicative of channel state information measured by the first device based on a first and/or a second signals transmitted by a second device in a off operation mode,

wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period;

a message generation unit, configured for generating a control message on operation mode switching and/or scheduling, at least partly based on the received measurement report; and

a first transmitting unit, configured for transmitting the control message to the second device.

28. The apparatus according to Claim 27, wherein the control message further indicates switching time, and/or which device to be served, and/or a resource to be used for serving a device.

29. The apparatus according to Claim 27, further comprising:

a second transmitting unit, configured for transmitting, to the second device, configuration information for the transmission of the second signal, wherein the configuration information indicates at least one of a transmission period, a time interval within the first period, a time and/or frequency resource, and a frequency hopping pattern to be used for the transmission of the second signal.

30. The apparatus according to Claim 29, wherein the configuration information indicates a given time interval within the first period via a bitmap.

31. The apparatus according to Claim 27, further comprising:

a third transmitting unit, configured for transmitting, to the first device, a control signaling which indicates at least one of the operation mode of the second device, an identity of the second device, the configuration of the second signal, and a format for the measurement report.

32. An apparatus for communication, comprising: a measurement unit, configured for measuring a first and/or a second signals from a first device operating in a off operation mode, wherein the first signal is transmitted with a first period, and the second signal is transmitted in a given time interval within the first period, with a second period smaller than the first period;

a report generation unit, configured for generating a measurement report indicative of channel state information measured based on the first signal and/or the second signal, and

a transmitting unit, configured for transmitting the measurement report to the first device, or, to a second device.

33. The apparatus according to Claim 32, further comprising:

a receiving unit, configured for receiving, from the second device, a control signaling which indicates at least one of the operation mode of the first device, an identity of the first device, the configuration of the second signal, and a format for the measurement report, and the measurement unit is further configured for measuring the second signal from the first device based on the received control signaling.

34. The apparatus according to any of Claims 19 to 33, wherein the second signal is transmitted according to a frequency hopping pattern.

35. The apparatus according to any of Claims 19 to 33, wherein the second signal comprises reference signals from multiple antenna ports.

36. The apparatus according to any of Claims 19 to 33, wherein the first signal is a discovery signal for cell or device discovery, and the second signal is a channel state information reference signal CSI-RS.