Patent Publication Number: US-2020305005-A1

Title: Method and devices for signaling transmission in unlicensed band

Description:
FIELD OF THE INVENTION 
     Example embodiments of the present invention relate generally to the wireless communication, and more specifically, to method and apparatus for signaling transmission in unlicensed band. 
     BACKGROUND OF THE INVENTION 
     In wireless communication, the demand for high data rate keeps increasing and Long Term Evolution (LTE) developed by the third generation project partnership (3GPP) has been shown to be an extremely successful platform to meet such demand. In recent years, LTE has been widely deployed in many different countries/regions. LTE system has been designed to operate in dedicated and licensed frequency band to avoid interference with other systems and to guarantee satisfying communication performance. However, with the demand for high data rate keeps increasing and at the same time available licensed frequency resources shrinks, more and more cellular network operators begin to consider seriously utilization of the unlicensed spectrum as a complimentary tool to augment their service offering. 
     One alternative way for utilizing an unlicensed band is called “Licensed-Assisted Access”, which means the utilization of the unlicensed band is under control from the licensed band, e.g., an unlicensed band is configured as a secondary component carrier while a licensed carrier is configured to be primary component carrier. Such a deployment scenario enables operators and vendors to maximally leverage the existing or planned investments in LTE/EPC (Evolved Packet Core) hardware. 
     However, unlicensed band is not a dedicated band for cellular network use, and on the contrary, it is shared by various wireless communication systems including Wi-Fi. To avoid/reduce interferences between the various wireless communication systems, in some countries, access technologies employed in unlicensed band need to abide to certain regulations, e.g., Listen-Before-Talk (LBT), and channel bandwidth occupancy requirements. Fair coexistence between LTE and other technologies, such as Wi-Fi, as well as between different LTE operators appears necessary. 
     To comply with the regulations for unlicensed band, current cellular wireless communication techniques, e.g., LTE, have to be modified, if to be deployed in the unlicensed band; and at the same time current design for these communication techniques and corresponding numerologies should be reused as much as possible to reduce the cost of the product and the effort for standardization. 
     The following meanings for the abbreviations used in this specification apply: 
     AP Access point 
     BS Base Station 
     CRS Cell-specific Reference Signal 
     CSI-RS Channel state Information Reference Signal 
     eNB Evolved Node B 
     GSM Global system for mobile communications
 
LBT Listen before talk
 
     LTE Long Term Evolution 
     MIB Master Information Block 
     PSS Primary Synchronization Signal 
     SF Subframe 
     SIB System Information Block Type 1 
     SSS Secondary Synchronization Signal 
     TDM Time Division Multiplexing 
     UE User Equipment 
     SFN System Frame Number 
     WCDMA Wideband Code Division Multiple Access 
     SUMMARY OF THE INVENTION 
     To enable basic detection and measurements in unlicensed band, thus facilitate employing unlicensed band resources for cellular communication use, and at the same time allow fair utilization of the shared resources by different wireless systems, methods and apparatus have been provided herein. 
     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. 
     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. 
     According to a first aspect of the invention, embodiments of the present invention provide a method for signal transmission in a wireless communication network, the method comprises determining a signal transmission pattern, which defines time and frequency resources for transmitting at least one signal in a first frequency band; signaling, via a second frequency band, the signal transmission pattern to a first device; and transmitting the at least one signal via the first frequency band to the first device, according to the signal transmission pattern, wherein transmission of any of the at least one signal is skipped if the time and frequency resource for its transmission defined by the signal transmission pattern is detected as busy. 
     In accordance with one embodiment of the invention, the method further comprises performing channel detection in the first frequency band before transmitting each of the at least one signal, and determining whether to skip a transmission of one of the at least one signal based on the channel detection results. 
     In accordance with another embodiment of the invention, determining whether to skip a transmission of one of the at least one signal based on the channel detection results includes skipping a transmission of one of the at least one signal if the time and frequency resource for its transmission is detected as busy, and continuing the channel detection in the time and frequency resource corresponding to the skipped transmission. 
     According to one further embodiment of the invention, the signal transmission pattern defines time and frequency resources for one of a periodic transmission, an opportunistic transmission, and a combination thereof. 
     In accordance with another embodiment of the invention, the at least one signal includes at least one of a reference signal, a synchronization signal, and a control signaling. 
     In accordance with still another embodiment of the invention, the time and frequency resource for the transmission of the one of the at least one signal is detected as busy when received signal power on the same frequency resource is above a threshold, the threshold is configurable, determined based on a receiver sensitivity, or fixed. 
     In accordance with one further embodiment of the invention, the method further comprises determining whether to adopt a listen before talk (LTB) operating mode in the first frequency band; and performing the steps of determining, signaling, transmitting and skipping only when the listen before talk mode is determined to be adopted. In accordance with one embodiment of the invention, determining whether to adopt a listen before talk (LTB) operating mode in the first frequency band is based on regulation for the first frequency band and/or the device&#39;s capability, e.g., whether a eNB is capable of LBT operation. 
     In still another embodiment of the invention, the first frequency band is an unlicensed frequency band and the second frequency band is a licensed frequency band. 
     In accordance with one embodiment of the invention, the first frequency band and/or the second frequency band comprise(s) multiple carriers. In accordance with another embodiment of the invention, at least one carrier in the first frequency band and at least one carrier in the second frequency band are configured for the first device as carrier aggregation or dual connectivity. 
     In accordance with one embodiment of the invention, the operations of determining a signal transmission pattern and signaling the signal transmission pattern to the first device are performed by a second device, while transmitting the at least one signal via the first frequency band to the first device is performed by a third device different from the second device. 
     According to a second aspect of the invention, embodiments of the present invention provide a method for signal reception in a wireless communication network, the method comprises receiving, via a second frequency band, a configuration signaling indicating a signal transmission pattern to be used in a first frequency band, wherein the signal transmission pattern defines time and frequency resources for transmitting at least one signal; and receiving the at least one signal via the first frequency band, according to the signal transmission pattern. 
     In accordance with one embodiment of the invention, the signal transmission pattern defines time and frequency resources for one of a periodic transmission, an opportunistic transmission, and a combination thereof. 
     In accordance with another embodiment of the invention, the at least one signal includes at least one of a reference signal, a synchronization signal, and a control signaling. 
     In some embodiments of the invention, the first frequency band is an unlicensed frequency band and the second frequency band is a licensed frequency band. 
     In accordance with one embodiment of the invention, the first frequency band and/or the second frequency band comprise(s) multiple carriers. In accordance with another embodiment of the invention, at least one carrier in the first frequency band and at least one carrier in the second frequency band are configured for a device as carrier aggregation or dual connectivity. 
     In accordance with one further embodiment of the invention, the configuration signaling is received from a first apparatus, while the at least one signal is received from a second apparatus different from the first apparatus. 
     According to a third aspect, embodiment of the present invention provides a corresponding device which implements the methods described in the first aspect. 
     According to a fourth aspect, embodiments of the present invention provide a corresponding device which implements the methods described in the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and benefits of various embodiments of the invention will become more fully apparent, from the following detailed description and the accompanying drawings, in which like reference numerals refer to the same or similar elements. The drawings are illustrated for facilitating better understanding of the embodiments of the disclosure and not necessarily drawn to scale, in which: 
         FIG. 1  is a schematic diagram of wireless network where an embodiment of the invention can be implemented; 
         FIG. 2 a    is a flow chart of a method for signal transmission in a wireless communication network according to an embodiment of the invention; 
         FIG. 2 b    is a flow chart of a method for signal transmission in a wireless communication network according to another embodiment of the invention; 
         FIG. 2 c    is a flow chart of a method for signal transmission in a wireless communication network according to still another embodiment of the invention; 
         FIG. 3 a -3 f    are examples of the signal transmission patterns and corresponding channel detection according to an embodiment of the invention; 
         FIG. 4  is a flow chart of a method for signal reception in a wireless communication network according to an embodiment of the invention; 
         FIG. 5 a    is a block diagram of a device for signal transmission in a wireless communication network according to an embodiment of the invention; 
         FIG. 5 b    is a block diagram of a distributed device for signal transmission in a wireless communication network according to another embodiment of the invention; and 
         FIG. 6  is a block diagram of a device for signal reception in a wireless communication network according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     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. 
     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. 
     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. 
     Reference is now made to  FIG. 1  which is a diagram of an example wireless network scenario where a method according to an embodiment of the present invention can be applied. The wireless network  100  comprises one or more network nodes  101  and  103 , here in the form of evolved Node B, also known as eNode Bs or eNBs, or pico eNB, femto eNB. The network nodes  101  could also be in the form of Node Bs, BTSs (Base Transceiver Stations), BS (Base Station) and/or BSSs (Base Station Subsystems), etc. The network nodes  103  may operate with different radio access technology (RAT) and/or in different frequency band than that of network node  101 . For example, the network node  103  may be a Wi-Fi access point (AP) operating in unlicensed band, while network node  101  is a LTE eNB operating in licensed band. In another example, both the network node  101  and  103  operate in a licensed frequency band, but using different carriers. It should be noted that it is also possible for both network node  101  and  103  to operate in same carrier. The network nodes  101  and  103  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  102  may, but do not need to, be associated with a particular end user. Though for illustrative purpose, the wireless network  100  is described to be a 3GPP LTE network, the embodiments of the present invention are not limited to such network scenarios and the proposed methods and devices can also be applied to other wireless networks, e.g., a GSM or a WCDMA network. 
     In the network  100  depicted in  FIG. 1 , the network nodes, e.g., eNB  101  may firstly provide service to the UEs  102  via a carrier C 1  in a frequency band B 1 , and then when more frequency resources are required to serve an increased number of UE, or to provide an increased throughput, the eNB  101  may provide service to UEs  102  via another carrier C 2  in another frequency band B 2 , e.g., by using carrier aggregation (CA); or the eNB  101  may provide service to UEs  102  together with another network node, e.g., a pico eNB  103  which operates in another carrier C 2  in another frequency band B 2 , by using dual connectivity. In a CA scenario specified by 3GPP LTE Release 10, a UE can be configured with multiple carriers, with each carrier provided by a different network node, or with both carriers provided by same network node. The multiple carriers can belong to same or different frequency bands. Among the configured multiple carriers, one carrier is designated as primary component carrier (PCC), while others are called secondary component carriers (SCCs). In a dual connectivity scenario under discussion in 3GPP LTE for Release 12, a given UE consumes radio resources provided by at least two different network points connected with non-ideal backhaul. Furthermore, each eNB involved in the dual connectivity for a UE may assume different roles, i.e., one eNB serves as master eNB, while others serve as secondary eNBs. Those roles do not necessarily depend on the eNB&#39;s power class and can vary among UEs. Generally, a primary cell/master eNB should operate in a licensed band to guarantee accurate signaling transmission, while the secondary cell/eNB can be either licensed or unlicensed band. 
     In either CA or dual connectivity scenarios described above, in case the second band B 2  is a frequency band to be shared with other wireless network or another cell, e.g., the second band B 2  is an unlicensed band and is shared by the eNB  101  with another Wi-Fi AP  103 , the communication between the eNB  101  and the UEs  102  via the carrier C 2  in the frequency band B 2  may need to avoid interference to/from other networks/cells. In another example, the second band B 2  can be an licensed band shared by some pico eNBs  103 , and in such case, when utilizing the second band B 2  (e.g., using dual connectivity technique with eNB  101  as master eNB operating in the carrier C 1  and a pico eNB  103  as secondary eNB operating in the carrier C 2 ), interference to/from other network nodes/cells should also be taken into account. In the embodiments of the invention, methods and devices are provided to enable communication in a shared frequency band which guarantees little interference to/from other wireless network/cells. 
     Reference is now made to  FIG. 2 a    which illustrates a flow chart for an example method  200  for transmitting signal in a wireless network. The method  200  comprises a step S 201 , for determining a signal transmission pattern which defines time and frequency resources for transmitting at least one signal in a first frequency band; a step S 202 , for signaling via a second frequency band the signal transmission pattern to a first device (e.g., UE  102  shown in  FIG. 1 ); a step S 203 , for transmitting the at least one signal via the first frequency band, to the first device, according to the signal transmission pattern which is determined in the step S 201  and signaled to the UE  102  in the step S 202 , and skipping a transmission of one of the at least one signal if time and frequency resource for the transmission defined by the signal transmission pattern is detected as busy. 
     In one embodiment of the invention, the first frequency band is an unlicensed frequency band and the second frequency band is a licensed frequency band, but the invention is not limited to this. It can be appreciated that in another embodiment of the invention, both the first frequency band and the second frequency band can be licensed frequency bands, e.g., the first frequency band is a shared frequency band with other cells and serves as a secondary carrier, while the second frequency band serves as primary carrier; and in still another embodiment of the invention, they both can be unlicensed band. In accordance with one embodiment of the invention, the first frequency band and/or the second frequency band comprise(s) multiple carriers. In accordance with another embodiment of the invention, at least one carrier in the first frequency band and at least one carrier in the second frequency band are configured for the first device as carrier aggregation or dual connectivity. 
     In one embodiment of the invention, the at least one signal transmitted in the step S 203  includes at least one of a reference signal, a synchronization signal, and a control signal. For example, the at least one signal can be a CRS or a CSI-RS, a PSS and SSS, or some common control signaling like system information. 
     In one embodiment of the invention, the signal transmission pattern defines time and frequency resources for one of the following transmissions: a periodic transmission, an opportunistic transmission, and a combination thereof. 
     In  FIGS. 3 a -3 f   , some examples of the signal transmission patterns are provided. In the example of  FIG. 3 a   , it is assumed that a CRS/CSI-RS signal is transmitted periodically in the step S 203  according to a signal transmission pattern determined for it in the step S 201 . As shown in  FIG. 3 a   , the signal transmission pattern defined for the CRS/CSI-RS indicates in which subframe the CRS/CSI-RS should be transmitted. For example, the signal transmission pattern may indicate a transmission period (e.g., 5 ms in this example) and a subframe offset for transmitting the CRS/CSI-RS. With respect to the frequency resources to be used for transmitting the CRS/CSI-RS, it can be predefined, or also indicated by the signal transmission pattern, e.g., via a carrier index or a channel index. In this example, the CRS/CSI-RS is expected to be transmitted in subframes  0  and  5 ; however, in subframe  4 , the first frequency band is detected to be busy, and thus the transmission of the corresponding CRS/CSI-RS in subframe  5  is skipped. 
     In  FIG. 3 b   , an example of opportunistic transmission of the CRS/CSI-RS signal is illustrated. That is, before each transmission of the CRS/CSI-RS, a listen before talk (LBT) is performed to detect whether the channel to be used for the transmission is busy or not. In an embodiment of the invention, the detection is performed in each available subframe where there is no concurrent transmission scheduled in the same frequency band, and the CRS/CSI-RS is transmitted in next subframe whenever the channel is detected as idle. If the corresponding channel is detected as busy in a subframe, then continue performing the LBT in the next subframe instead of transmitting the CRS/CSI-RS. As a result, the CRS/CSI-RS is sent aperiodically. In the example shown in  FIG. 3 b   , the eNB detects the channel in the first frequency band (e.g., an unlicensed band) in subframe  0 , and finds it idle, and as a result the CRS/CSI-RS is transmitted in the following subframe  1 ; then before transmitting next CRS/CSI-RS, the channel detection is performed again in subframe  2 , and the channel is detected as busy. It means transmission of the CRS/CSI-RS is not allowed in subframe  3 , and then the channel detection continues till the channel is detected as idle in subframe  4 . As a result, the CRS/CSI-RS is transmitted in subframe  5 . The opportunistic transmission as shown in  FIG. 3 b    as an example provides more chance for CRS/CSI-RS transmission at the cost of more frequent channel detection. 
     In another embodiment of the invention, the signal transmission pattern determined in the step S 201  may define time and frequency resources for a combination of periodical and opportunistic transmission to balance between signaling overhead and CSI precision. In one embodiment of the invention, the periodical and opportunistic transmission patterns can be arranged in TDM way, e.g., when channel in the unlicensed band changes slowly, or the idle channel is easy to be obtained, periodical transmission can be applied; and when the channel in the unlicensed band changes quickly, or the channel is busy in most of the time, opportunistic transmission can be a better choice. Other factors, such as scheduling information of adjacent cells, or, assisting information on transmission characteristic of a Wi-Fi AP which shares the first frequency band with the eNB, can also be considered to determine a proper signal transmission pattern in step S 201 . 
     In  FIGS. 3 c  and 3 d   , another two examples of the signal transmission pattern are provided, with  FIG. 3 c    for FDD system and  FIG. 3 d    for TDD system. In these examples, it is assumed that the at least one signal to be transmitted in the step S 203  is synchronization signals comprising PSS and SSS. The determined signal transmission patterns in  FIG. 3 c    and  FIG. 3 d    for PSS/SSS are consistent with current LTE-FDD and LTE-TDD specification respectively to reuse the design of current LTE system, however, it should be noted that such patterns are just presented as examples and the embodiments of the invention are not limited to this. As shown in  FIG. 3 c   , for FDD system, both the PSS and SSS are transmitted in subframes  0  and  5 , and according to an embodiment of the invention, the LBT is performed one subframe before each transmission of the PSS/SSS, i.e., the LBT is performed in subframe  9  of previous radio frame and subframe  4  in current frame. It can be appreciated that the channel detection can also be performed in other subframes than that shown in  FIG. 3 c   , e.g., it can be executed 2 subframes before each PSS/SSS transmission.  FIG. 3 d    illustrates the signal transmission pattern for a LTE-TDD system, where the PSS is transmitted in subframes  1  and  6 , and SSS is transmitted in subframes  0  and  5  in each radio frame. The channel detection (or, LBT) is shown to be performed in the same subframes as shown in  FIG. 3 c   , however, it can be appreciated that the invention is not limited to this. 
     In accordance with one embodiment of the invention, the time and frequency resource for the transmission of the one of the at least one signal is detected as busy when received signal power on the same frequency resource is above a threshold, the threshold is configurable, determined based on a receiver sensitivity, or fixed. In an embodiment of the invention, the threshold can be determined by eNB receiver sensitivity. In another embodiment of the invention, the threshold can be fixed, e.g., be set to be −62 dBm as in 802.11. 
     In accordance with another embodiment of the invention, the channel detection described above is performed in an additional step S 204 , for performing channel detection in the first frequency band before transmitting each of the at least one signal in the step S 203 , and for determining whether to skip a transmission of one of the at least one signal based on the channel detection results, as shown in  FIG. 2 b   . In accordance with another embodiment of the invention, only the latest channel detection results is taken into account during determining, and in another embodiment of the invention, both the channel detection results and some other estimation are considered during determining, e.g., an estimation for the maximum duration of an interfering transmission from, e.g., a Wi-Fi station. 
     In another embodiment of the invention, the channel detection step S 204  is not executed before each transmission. Instead, the channel detection provides a prediction on a time duration unavailable/available for the signal transmission. That is, if the channel detection indicates that a channel in the first frequency band will be idle for a period of P ms, then a signal can be transmitted according to the signal transmission pattern within the P ms without additional channel detection between each transmission. In case the channel detection indicates that the first frequency band keep busy for a period of P ms, then all the transmission of a signal defined the signal transmission pattern within the P ms will be skipped, without additional channel detection before each skipping. 
     In still another embodiment of the invention, the channel detection step S 204  may be performed by a separate device rather than an eNB which performs the steps S 201  to S 203 . For example, the channel detection can be done by a UE, which report the detection results to the eNB based on certain configuration. In a further embodiment, the channel detection may be performed by a Wi-Fi Station or AP connected to the eNB which performs the steps S 201  to S 203 . In such case, the method may further include a receiving step not shown in FIGS.  2   a - 2   c , for receiving the channel detection results for the first frequency band. In still another embodiment of the invention, the steps S 203  and S 204  are performed by a pico eNB  103 , while the steps S 201  and S 202  are performed by a macro eNB  101 , the wherein the pico eNB  103  and the macro eNB  101  provide service to a UE via CA or dual connectivity. 
     In accordance with still another embodiment of the invention, determining whether to skip a transmission of one of the one or more signals based on the channel detection results includes skipping a transmission of one of the one or more signals if the corresponding channel is detected as busy, and continuing the channel detection in the corresponding time-frequency resource for the skipped transmission defined by the signal transmission pattern. That is, in  FIG. 3 d   , if the channel is detected as busy in subframe  4 , then in the following subframes  5  and  6 , the PSS and SSS are not allowed to be transmitted, and correspondingly, the channel detection may continue in the subframes  5  and  6 . However, if the subframes  5  and  6  are detected as idle and the PSS and SSS are scheduled there, the channel detection should be avoided in same subframes. The reason is that, to avoid in-device interference and reduce implementation complexity, concurrent transmission and reception in same frequency band should be prevented. Correspondingly, when signal is being transmitted in the first frequency band, the channel detection is not allowed in same frequency band; on the other hand, once the channel is detected as busy and the signal is not allowed to be transmitted, i.e., a transmission defined by the signal transmission pattern will be skipped, the subframe corresponding to the skipped transmission can be used for channel detection, according to the embodiment of the invention. 
     In  FIGS. 3 e  and 3 f   , another two example are provided, where it is assumed that the at least one signal to be transmitted in step S 203  is MIB and SIB1, respectively. The signal transmission patterns illustrated in  FIGS. 3 e  and 3 f    indicate periodic resources for MIB and SIB1 transmission. In these Figures, “N F ” stands for index of radio frame, “N f ” stands for index of subframe, “F” denotes the first transmission in each period, and “R” denotes a repetition of the transmission. It can be seen that MIB is assigned a transmission period of 40 ms, wherein the first transmission is scheduled in subframe  0  of radio frames for which the SFN mod 4=0, and repetitions are scheduled in subframe  0  of all other radio frames. Similarly, SIB1 is assigned a transmission period of 80 ms with repetitions made within the 80 ms. The first transmission of SIB1 is scheduled in subframe  5  of radio frames for which the SFN mod 8=0, and repetitions are scheduled in subframe  5  of all other radio frames for which SFN mod 2=0. Similarly as shown in  FIGS. 3 a -3 d   , in case a corresponding channel is detected as busy, the transmission of MIB/SIB1 is skipped. 
     In accordance with one embodiment of the invention, the method  200  further comprising a step S 205 , for determining whether to adopt a listen before talk (LTB) operating mode in the first frequency band; and, only when the LTB mode is determined to be adopted, the steps of S 201 , S 202  and S 203  depicted in  FIG. 2 a    are performed; otherwise, performing according to any prior art in step S 206 , e.g., performing normal operation as defined in current standard (e.g., LTE) for a licensed band. One example is shown in  FIG. 2 c   . In accordance with one embodiment of the invention, determining whether to adopt a listen before talk (LTB) operating mode in the first frequency band is based on regulation for the first frequency band and/or the device&#39;s capability, e.g., whether a eNB (a macro eNB  101  and/or a pico eNB  103 ) is capable of LBT operation. 
     In one embodiment of the invention, all the steps in the method  200  can be implemented, for example, by the eNB  101  shown in  FIG. 1 . One exemplary scenario can be that the eNB  101  provides service to a UE  102  via CA, by using both the first and the second frequency bands. In another embodiment of the invention, some steps in the method  200  can be implemented, for example, by the eNB  101  shown in  FIG. 1 , while other steps are implemented by another network node, e.g., a pico eNB  103  shown in  FIG. 1 . One exemplary scenario for this can be that the eNB  101  and the eNB  103  provides service to a UE  102  via dual connectivity, by using the first and the second frequency bands, respectively. In one example, steps S 201  and S 202  can be performed by the eNB  101 , while the step S 203  (or, steps S 203  to S 205 ) is performed by the eNB  103 . This may require some signaling exchange between the eNB  101  and  103 , however, the inter-eNB interfacing for signaling exchange is well known, and thus details are omitted here. Furthermore, it should he noted that these are just examples, and other implementation can also be possible, e.g., the steps S 201 , S 202  and S 205  can be performed by the eNB  101 , while the step S 203  to S 204  are performed by the eNB  103 . 
     Though some specific signal transmission patterns are presented for the CRS/CSI-RS, PSS/SSS, MIB/SIB1, it should be appreciated that the embodiments of the invention are not limited to these signals and the signal transmission patterns, and, any other signals can be transmitted in the first frequency band (e.g., an unlicensed band) following the same principle of method  200 . 
     Referring now to  FIG. 4 , which illustrates a flow chart for an example method  400  for signal reception in a wireless communication network. The method can be implemented, for example, by a UE  102  shown in  FIG. 1 . The method comprises a step S 401 , for receiving via a second frequency band (e.g., a licensed frequency band) a configuration signaling indicating a signal transmission pattern to be used in a first frequency band (e.g., an unlicensed frequency band), the signal transmission pattern defines time and frequency resources for transmitting at least one signal; and a step S 402 , for receiving the at least one signal in the first frequency band, according to the signal transmission pattern. 
     In accordance with an embodiment of the invention, the at least one signal received in step S 402  is a signal transmitted by an eNB in step S 203  according to the method  200  described with reference to  FIGS. 3 a -3 f   , and/or, the signal transmission pattern received in the step S 401  is sent by an eNB in the step S 202  according to the method  200  described with reference to  FIGS. 2 a -2 c  and 3 a -3 f   . Thus, the features described for the at least one signal and the signal transmission pattern with respect to  FIGS. 3 a -3 f    also apply in  FIG. 4 , and their details will not be repeated here. For example, the signal transmission pattern defines time and frequency resources for one of a periodic transmission, an opportunistic transmission, and a combination thereof; and the at least one signal includes at least one of a reference signal, a synchronization signal, and a control signaling. 
     In accordance with one embodiment of the invention, the first frequency band and/or the second frequency band comprise(s) multiple carriers. In accordance with another embodiment of the invention, at least one carrier in the first frequency band and at least one carrier in the second frequency band are configured for a device as carrier aggregation or dual connectivity, as described with reference to  FIGS. 2 a   - 2   c.    
     In accordance with a further embodiment of the invention, in step S 401 , the configuration signaling is received from a first apparatus (e.g., a macro eNB  101 ), while in step S 402 , the at least one signal is received from a second apparatus (e.g., a pico eNB  103 ) different from the first apparatus. 
     To be noted that in some alternative implementations, the method steps indicated in the flow charts could also occur in a sequence different from what is indicated in the figures. For example, two sequentially indicated blocks could be executed substantially in parallel or sometimes in an inversed order, depending on the functions as involved. 
     It is also to be understood that methods described with reference to  FIGS. 2 a  and 2 b    can be implemented in various ways, by software, hardware, firmware, or any of their combinations, e.g., a processor, computer programming code stored in a computer readable storage media, etc. 
     Reference is now made to  FIG. 5 a   , which illustrates a block diagram of a device  500  for signal transmission in a wireless communication network according to an embodiment of the invention. The device  500  according to  FIG. 5 a    can be an eNB  101  in  FIG. 1 , and may perform the example methods described with reference to  FIGS. 2 a -2 c   , but is not limited to these methods. Then any feature presented above, e.g., in the description with reference to  FIGS. 2 a -2 c    can be applied to the device  500  presented below. It is to be noted that the methods described with reference to  FIG. 2 a    may be performed by the device  500  of  FIG. 5 a    but is not limited to being performed by this device  500 . The device  500  may also be other network element than the eNB  101  shown in  FIG. 1 , e.g., in an embodiment of the invention, it can be a relay node, a WLAN AP, etc. 
     As shown in  FIG. 5 a   , the device  500  comprises a determination unit  501 , configured for determining a signal transmission pattern which defines time and frequency resources for transmitting at least one signal in a first frequency band (e.g., an unlicensed frequency band); a first transmission unit  502 , configured for signaling via a second frequency band (e.g., a licensed frequency band) the signal transmission pattern to a first device; and a second transmission unit  503 , configured for transmitting the at least one signal via the first frequency band, to the first device, according to the signal transmission pattern and skipping a transmission of one of the at least one signal if time frequency resource for the transmission defined by the signal transmission pattern is detected as busy. 
     In accordance with one embodiment of the invention, the first frequency band and/or the second frequency band comprise(s) multiple carriers. In accordance with another embodiment of the invention, at least one carrier in the first frequency band and at least one carrier in the second frequency band are configured for the first device as carrier aggregation or dual connectivity. 
     In accordance with one embodiment of the invention, the units  501  to  503  are configured for performing the steps  201  to  203  described with reference to  FIGS. 2 a -2 c   , respectively. 
     In another embodiment of the invention, the determined signal transmission pattern by the determination unit  501  can define time and frequency resources for one of a periodic transmission, an opportunistic transmission, and a combination thereof. For example, the signal transmission pattern can be any of the patterns described with reference to  FIGS. 3 a  to 3 f   , but is not limited to this. 
     According to one embodiment of the invention, the at least one signal transmitted by the second transmission unit  503  includes at least one of a reference signal, a synchronization signal, and a control signaling. For example, the at least one signal can be a CRS/CSI-RS, a PSS/SSS, and/or MIB/SIB1 as illustrated in  FIGS. 3 a   - 3   f.    
     In one embodiment of the invention, the device  500  further comprises a channel detection unit  504 , configured for performing channel detection in the first frequency band before transmitting each of the at least one signal, and the second transmission unit  503  is further configured for determining whether to skip a transmission of one of the at least one signal based on the channel detection results obtained by the channel detection unit  504 . In another embodiment of the invention, the second transmission unit  503  is further configured for skipping a transmission of one of the at least one signal if the corresponding channel is detected as busy by the channel detection unit  504 ; and the channel detection unit  504  is further configured for continuing the channel detection in the corresponding time and frequency resource for the skipped transmission defined by the signal transmission pattern. Such implementation is due to a consideration that to avoid in-device interference and reduce implementation complexity, concurrent transmission and reception in same frequency band should be prevented. Correspondingly, when the second transmission unit  503  is transmitting in the first frequency band, the channel detection unit  504  is not allowed to perform channel detection in same frequency band; on the other hand, once the channel is detected as busy and the second transmission unit is not allowed to transmit, i.e., a transmission defined by the signal transmission pattern will be skipped, the subframe corresponding to the skipped transmission can be used for channel detection by the channel detection unit  504 , according to the embodiment of the invention. 
     In another embodiment of the invention, the channel detection unit  504  is not configured for performing channel detection in the first frequency band before transmitting each of the at least one signal. Instead, the channel detection unit  504  is configured for providing a prediction on a time duration unavailable/available for the signal transmission. That is, if the channel detection indicates that a channel in the first frequency band will be idle for a period of P ms, then a signal can be transmitted by the second transmission unit  503  according to the signal transmission pattern within the P ms without additional channel detection performed by the channel detection unit  504  between each transmission. In case the channel detection indicates that the first frequency band keep busy for a period of P ms, then the second transmission unit  503  will be configured for skipping all the transmission of a signal defined the signal transmission pattern within the P ms, without additional channel detection performed by the channel detection unit  504  before each skipping. 
     In still another embodiment of the invention, the channel detection may be performed by a separate device rather than the channel detection unit  504  in an eNB. For example, the channel detection can be done by a UE, which reports the detection results to the eNB based on certain configuration. In a further embodiment, the channel detection may be performed by a Wi-Fi Station or AP connected to the eNB. In such case, the device  500  may further include a receiving unit not shown in  FIG. 5 a   , for receiving the channel detection results for the first frequency band. 
     In one embodiment of the invention, the time and frequency resource for the transmission of the one of the at least one signal is detected as busy when received signal power on the same frequency resource is above a threshold, the threshold is configurable, determined based on a receiver sensitivity, or fixed. In one embodiment of the invention, the threshold can be determined by the eNB based on its receiver sensitivity. In another embodiment of the invention, the threshold can be set as a fixed value, e.g., −62 dBm as in 802.11. 
     In one further embodiment of the invention, the device further comprises a mode determination unit  505 , configured for determining whether to adopt a listen before talk LTB operating mode in the first frequency band; and only when the mode determination unit  505  determines that LTB mode is determined to be adopted, the units of  501  to  504  are configured to perform corresponding functions as described above; otherwise, performing according to any prior art, e.g., performing normal operation as defined in current standard (e.g., LTE) for a licensed band. In accordance with one embodiment of the invention, determining whether to adopt a listen before talk (LTB) operating mode in the first frequency band is based on regulation for the first frequency band and/or the device&#39;s capability, e.g., whether a eNB (a macro eNB and/or a pico eNB) is capable of LBT operation. 
     In accordance with another embodiment of the invention, all the units  501  to  505  are implemented in a same device, e.g., a eNB  101  as shown in  FIG. 1 . In another embodiment of the invention, some of the units  501  to  505  are implemented in a device, while other units are implemented in another device, that is, the device  500  is a distributed system. One example of such embodiments is shown in  FIG. 5 b   , wherein the units  501  and  502  (or,  501 ,  502  and  505 ) are implemented in a macro eNB  101 , while the unit  503  (or, both  503  and  504 ) is implemented in a pico eNB  103 . However, the example in  FIG. 5 b    is just for illustrative purpose, it can he appreciated that other arrangement of the distributed device  500  is also possible. For example, all the units  503  to  505  may be implemented in a same device, e.g., in a small cell eNB. These example embodiments can be implemented, for example, in a scenario where the eNB  101  and the eNB  103  provides service to a UE  102  via dual connectivity, by using the first and the second frequency bands, respectively. It can be easily appreciated that in such case, there can be other additional units implemented in the eNB  101  and the eNB  103 , e.g., for signaling exchange between them, however, since the inter-eNB interfacing for signaling exchange is well known, the details are omitted here. 
     It should be noted that though in some embodiments the first frequency band is an unlicensed frequency band and the second frequency band is a licensed frequency band, the embodiments of the invention are not limited to this. The device  500  can be applied in any other scenarios, e.g., where both the first and the second frequency bands are licensed or unlicensed bands. One example can be that the second frequency band is a primary carrier dedicated for one cell, while the first frequency band is a shared carrier available to multiple cells or multiple networks/operators, and then for any transmission in the first frequency band, the eNB can follow the principles described above to avoid/reduce interference from/to other cells/wireless systems. 
     Reference is now made to  FIG. 6 , which illustrates a block diagram of a device  600  for signal reception in a wireless communication network. In accordance with one embodiment of the invention, the device  600  comprises a first receiving unit  601 , configured for receiving via a second frequency band a configuration signaling indicating a signal transmission pattern to be used in a first frequency band, the signal transmission pattern defines time and frequency resources for transmitting at least one signal; and a second receiving unit  602 , configured for receiving the at least one signal via the first frequency band, according to the signal transmission pattern. 
     According to one embodiment of the invention, the device  600  may perform the example methods described with reference to  FIGS. 2 a -2 c    but is not limited to these methods, Then any feature presented above, e.g., in the description with reference to  FIGS. 2 a -2 c   , if appropriate, can be applied to the device  600  presented below. It is to be noted that the methods described with reference to  FIGS. 2 a -2 c    may be performed by the device  600  of  FIG. 6  but is not limited to being performed by this device  600 . The device  600  may be, for example, a UE  102  shown in  FIG. 1 . 
     In accordance with an embodiment of the invention, the at least one signal received by the second receiving unit  602  is a signal transmitted by eNB in step  203  according to the method  200  described with reference to  FIGS. 2 a -2 c  and 3 a -3 f   , and/or, the signal transmission pattern received by the first receiving unit  601  is sent by an eNB in step  202  according to the method  200  described with reference to  FIGS. 2 a -2 c  and 3 a -3 f   . Thus, the features described for the at least one signal and the signal transmission patterns described with respect to  FIGS. 2 a -2 c  and 3 a -3 f    also apply in  FIG. 6 , and their details will not be repeated here. For example, the signal transmission pattern defines time and frequency resources for one of a periodic transmission, an opportunistic transmission, and a combination thereof; and the at least one signal includes at least one of a reference signal, a synchronization signal, and a control signaling. 
     In accordance with one embodiment of the invention, the signal transmission pattern is received by the first receiving unit  601  via a licensed band to guarantee satisfying performance, while the at least signal is received by the second receiving unit  602  via an unlicensed band; but the embodiments of the invention are not limited to this. 
     In accordance with one embodiment of the invention, the first frequency band and/or the second frequency band comprise(s) multiple carriers. In accordance with another embodiment of the invention, at least one carrier in the first frequency band and at least one carrier in the second frequency band are configured for the UE  102  as carrier aggregation or dual connectivity, as described with reference to  FIGS. 2 a   - 2   c.    
     In accordance with a further embodiment of the invention, in receiving unit  601 , the configuration signaling is received from a first apparatus (e.g., a macro eNB  101 ), while in receiving unit  602 , the at least one signal is received from a second apparatus (e.g., a pico eNB  103 ) different from the first apparatus. 
     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 can be appreciated that the methods and devices may comprise other steps/functional blocks besides those illustrated. 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 should be understood that in some embodiments, function of a block can also be implemented by multiple blocks, and functions of multiple blocks shown in  FIGS. 5 a , 5 b    and  6  may also be implemented by a single block in other embodiments. 
     The example embodiments can store information relating to various processes described herein, e.g., store the channel detection results, the received signal transmission pattern 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. 
     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 he 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.