WO2015180025A1

WO2015180025A1 - Methods and devices for vertical domain channel state information transmission/reception in wireless communication networks

Info

Publication number: WO2015180025A1
Application number: PCT/CN2014/078444
Authority: WO
Inventors: Gang Wang; Chuangxin JIANG; Chaofeng LI; Zhennian SUN
Original assignee: Nec Corporation
Priority date: 2014-05-26
Filing date: 2014-05-26
Publication date: 2015-12-03

Abstract

Embodiments of the present invention provide methods and devices for transmitting vertical domain channel state information CSI to support3-dimension(3D) multiple-input-multiple-output(MIMO)operation in a wireless network. The method comprising determining whether to transmit the vertical domain CSI based on a measurement of at least the vertical domain CSI, or based on a signaling from another device; and if the vertical domain CSI is determined to be transmitted, transmitting the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined transmission of the vertical domain CSI and last transmission of the vertical domain CSI is larger than the period for the specific horizontal domain CSI transmissions. Corresponding methods and devices for receiving the vertical domain CSI which is transmitted using above method are also disclosed.

Description

METHODS AND DEVICES FOR VERTICAL DOMAIN CHANNEL STATE INFORMATION TRANSMISSION/RECEPTION IN WIRELESS COMMUNICATION

NETWORKS

FIELD OF THE INVENTION

[0001] Example embodiments of the present invention relate generally to the wireless communication and, more specifically, to methods and devices for transmitting/receiving vertical domain channel state information in wireless communication networks to support 3-dimension (3D) multiple-input-multiple-output (MIMO) operation.

BACKGROUND OF THE INVENTION

[0002] In wireless communication, the demand for data rate keeps increasing but the time-frequency resources are limited, thus it is always an important object in wireless communication to increase spectrum efficiency. For this purpose, in the Long term evolution (LTE) and LTE-advanced (LTE-A) standards developed by the 3rd Generation Partnership Project (3GPP), MIMO has been introduced as a key feature to employ the degree of freedom in spatial domain.

[0003] The traditional MIMO is confined in 2-Dimensional (2D) horizontal plane, wherein one dimensional (horizontal) antenna array can provide flexible beam adaption in azimuth via horizontal domain precoding process, while in the vertical direction, fixed down-tilt is applied. 3D MIMO provides a possibility to further exploit the spatial resources by changing down-tilt of each beam adaptively according to the position of the target user, such that the user-specific elevation beamforming and spatial multiplexing on the vertical domain are both attainable. It is proposed in a Study Item of 3GPP LTE Release 12 to study user-specific beamforming and Full dimensional MIMO (i.e., 3D MIMO) with 2D antenna array (also referred to as Active Antenna System, AAS) which may improve the transmit and/or receive gain, and reduce the intra/inter-cell interference.

[0004] The research on 3D MIMO is still ongoing at the current stage in 3GPP, and how to enable vertical precoding and thereby provide spatial multiplexing in vertical domain is a problem to be solved. It may require redesign for reference signals (RSs) and channel state information (CSI) measurement and feedback schemes.

[0005] In current specification ( 36.213 cOO of 3GPP), CSI feedback schemes are designed to support 2D MIMO, and the CSI can be provided includes rank indicator (RI), precoding matrix index (PMI), and channel quality indicator (CQI), which all represent horizontal characteristic of the wireless communication channel. Moreover, to enable frequency selective scheduling, a user equipment (UE) in LTE can be requested to report wideband CSI and/or sub-band CSI via CSI feedback mode configuration. For example, in LTE release 8, for feedback model-1, the feedback process can be implemented in two steps as shown in Figure la, wherein a RI is reported in step 1 and a wideband CQI /PMI is reported in step 2 with a period Np which is much shorter than the period of RI. For feedback mode 2-1, the feedback process can be implemented in three steps as shown in Figure lb, wherein a RI is reported in step 1, a wideband CQI /PMI is reported in step 2 and one or more UE selected subband CQI is reported in step 3 with a period Np.

[0006] In LTE release 10, for 8 transmit antenna configuration, dual codebook is introduced where a precoder can be constructed based on multiplication of Wl which is long term or wideband channel information and W2 which is short term or subband channel information. Correspondingly, to support the dual codebook precoding operation, the feedback mode 1-1 of LTE release 8 is extended by introducing additional two submodes, while the feedback mode 2-1 is extended via introducing an additional precoding type indicator (PTI). Schematic examples for these extended/evolved feedback modes are illustrated in Figures 2a-2c. As shown in Figure 2a, in submode 1, Wl and W2 are fed back in different subframes, wherein Wl is feedback together with RI, while W2 is feedback together with CQI. It can be seen in Figure 2b that in submode 2, Wl, W2 and wideband CQI are transmitted in the same subframe. As shown in Figure 2c, in the evolved feedback mode 2-1, a three step process is maintained, and in step 1, a 1 bit PTI is jointly reported with RI to indicated whether next report cycle includes Wl feedback or not. Then in step 2, if PTI=0, then Wl is reported, otherwise wideband W2 and CQI are reported. In step 3, the transmission also depends on the value of PTI, i.e., when PTI=0, wideband W2 and CQI are transmitted, otherwise, subband W2 and CQI are transmitted. The lower two figures in Figure 2c illustrate different periods for Wl report which is configured vi parameter H'. These extended feedback modes also apply to 4 antenna configuration in LTE release 12.

[0007] Though the CSI feedback schemes are evolved in LTE release 10 and 12 as described above, the design of CSI feedback schemes in current 3 GPP specification can not provide feedback to support the 3D MIMO operation yet. In a US patent application No. 2014/0003240A1, entitled "Supporting measurements and feedback for 3D MIMO with data transmission optimization", filed on December 27 2012, it discloses systems and methods for 3D CSI-RS design and CSI feedback, however, there are several problems. First, it requires a different feedback structure from that of LTE release 8 since one more report step is introduced and more PUCCH resource (e.g., PUCCH forma2 resource) are consumed; second, it requires more RRC signaling for feedback configuration, e.g., for configuring period and resources for vertical PMI report; additionally, the design in the US patent application has not considered the feedback effeciency or reliability thus does not provide a balance between overhead and performance.

[0008] In the embodiments of the present invention, methods and devices which can solve the above problems and enable 3D MIMO operation with minimal signaling overhead are provided.

SUMMARY OF THE INVENTION

[0009] 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.

[0010] 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.

[0011] According to a first aspect, embodiments of the present invention provide a method for transmitting vertical domain channel state information CSI in a device to support 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the method comprises determining whether to transmit the vertical domain CSI based on a measurement of at least the vertical domain CSI, or based on a signaling from another device; and if the vertical domain CSI is determined to be transmitted, transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined transmission of the vertical domain CSI and last transmission of the vertical domain CSI is larger than the period of the specific horizontal domain CSI transmission.

[0012] In accordance with one embodiment of the invention, the method further comprises generating an indicator to indicate the determined results; and transmitting the indicator jointly with a first horizontal domain CSI, in a resource configured for the first horizontal domain CSI transmission.

[0013] In a further embodiment of the invention, generating the indicator to indicate the determined results further comprising setting a value for the indicator based on the following criterion: if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurements, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then setting a value to indicate that the vertical domain CSI is to be transmitted, otherwise, setting a value to indicate that the vertical domain CSI is not to be transmitted.

[0014] According to some embodiments of the invention, transmitting the indicator jointly with the first horizontal domain CSI comprises compressing the first horizontal domain CSI before the joint transmission with the indicator, such that the total payload to be jointly transmitted is no more than a predefined value.

[0015] In some embodiments of the invention, the first horizontal domain CSI indicates a first long-term precoding matrix and/or a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix or both the vertical domain long-term precoding matrix and a second rank.

[0016] In another embodiment of the invention, transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprises transmitting the vertical domain CSI in a resource configured for the specific horizontal domain CSI transmission, and preventing from transmitting the specific horizontal domain CSI in the same resource.

[0017] In still another embodiment of the invention, transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprises transmitting, in a resource configured for the specific horizontal domain CSI transmission, a value which is reserved not to be used by the specific horizontal domain CSI, so as to distinguish from the specific horizontal domain CSI transmission. In this case, the horizontal CSI will be prevented from transmission implicitly if the vertical CSI is reported

[0018] In some embodiments of the invention, transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprises dividing the vertical domain CSI into multiple parts, and transmitting each part jointly with the specific horizontal domain CSI in one of the resources configured for the specific horizontal domain CSI transmission.

[0019] In an further embodiment, dividing the vertical domain CSI into multiple parts further comprises dividing the vertical domain CSI into M parts, and duplicating each of the M parts N times to obtain totally MxN parts, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2.

[0020] In some embodiments of the invention, the vertical domain CSI is assigned with a priority level can equal to that of a horizontal domain long-term CSI.

[0021] According to a second aspect, embodiments of the present invention provide a method for receiving a vertical domain channel state information CSI from a second device to support a 3D-MIMO operation in a wireless network, the method comprises determining whether to receive the vertical domain CSI based on an indicator from the second device, or based on a configuration signaling previously sent to the second device; and if the vertical domain CSI is determined to be received, receiving the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined receiving of the vertical domain CSI and last reception of the vertical domain CSI is larger than the period for the specific horizontal domain CSI transmissions configured for the second device.

[0022] According to a further embodiment of the invention, the method further comprises receiving the indicator which is jointly transmitted with a first horizontal domain CSI in a resource configured for the first horizontal domain CSI transmission.

[0023] In another embodiment of the invention, the indicator is set by the second device based on following criterion: if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then setting the indicator to indicate that the vertical domain CSI is to be transmitted, otherwise, setting the indicator to indicate that the vertical domain CSI is not to be transmitted.

[0024] In accordance with some embodiments of the invention, receiving the indicator which is jointly transmitted with the first horizontal domain CSI comprises receiving the indicator and a compressed first horizontal domain CSI which are jointly transmitted, and the total payload of the joint transmission is no more than a predefined value.

[0025] In some embodiments of the invention, the first horizontal domain CSI indicates a first long-term precoding matrix and or a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix or both the vertical domain long-term precoding matrix and a second rank.

[0026] In an embodiment of the invention, receiving the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprises receiving the vertical domain CSI in a resource configured for a specific horizontal domain CSI transmission, and preventing from detecting the specific horizontal domain CSI in the same resource.

[0027] In another embodiment of the invention, receiving the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprises if receiving a value which is reserved not to be used by the specific horizontal domain CSI in the at least one of the resources configured for the specific horizontal domain CSI transmission, interpreting the value as the vertical domain CSI transmission.

[0028] In still another embodiment of the invention, receiving the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprises receiving a part of the vertical domain CSI in each resource of the at least one of the resources and, - combining the received parts to obtain a complete vertical domain CSI, wherein the vertical domain CSI is divided into multiple parts by the second device when transmitting, and each part is transmitted jointly with the specific horizontal domain CSI in one of the resources configured for the specific horizontal domain CSI transmission.

[0029] In some embodiments of the invention, the vertical domain CSI is divided into M parts and each of the M parts is duplicated N times to obtain totally MxN parts when transmitting, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2.

[0030] In some embodiments of the invention, the vertical domain CSI being received is assigned with a priority level equal to that of a horizontal domain long-term CSI.

[0031] According to a third aspect, embodiment of the present invention provides a corresponding device which implements the methods described in the first aspect.

[0032] 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

[0033] 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:

[0034] Figure la is a schematic diagram of CSI feedback mode 1-1 in LTE Release 8;

[0035] Figure lb is a schematic diagram of CSI feedback mode 2-1 in LTE Release 8;

[0036] Figure 2a is a schematic diagram of CSI feedback submode 1 of mode 1-1 in LTE Release 10 for a scenario of 8 transmit antennas;

[0037] Figure 2b is a schematic diagram of CSI feedback submode 2 of mode 1-1 in LTE Release 10 for a scenario of 8 transmit antennas;

[0038] Figure 2c is a schematic diagram of CSI feedback mode 2-1 in LTE Release 10 for a scenario of 8 transmit antennas;

[0039] Figure 3a is a schematic diagram of wireless network where an embodiment of the invention can be implemented;

[0040] Figure 3b illustrates results on a cumulative density function (cdf) statistic of unchanged time interval for an example vertical domain CSI;

[0041] Figure 4 is a flow chart of a method for transmitting a vertical domain CSI, according to an embodiment of the invention;

[0042] Figures 5a-5f are schematic illustrations showing examples of a method for transmitting a vertical domain CSI, according to an embodiment of the invention;

[0043] Figure 6 is a flow chart of a method for receiving a vertical domain CSI, according to an embodiment of the invention;

[0044] Figure 7 is a block diagram of a device for transmitting a vertical domain CSI, according to an embodiment of the invention; and

[0045] Figure 8 is a block diagram of a device for receiving a vertical domain CSI, according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS [0046] 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.

[0047] 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.

[0048] 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.

[0049] Reference is now made to Figure 3a, 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 300 comprises one or more network nodes 301, here in the form of evolved Node Bs, also known as eNode Bs or eNBs. The network nodes 301 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 301 provide radio connectivity to a plurality of user equipments (UEs) 302. 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. Though for illustrative purpose, the wireless network 300 is described to be a LTE-A 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 non-cellular network, where similar requirement for 3D CSI feedback exists and the principles described hereinafter are applicable.

[0050] In the network 300 depicted in Figure 3a, the network nodes, e.g., eNB 301 will require CSI to perform efficient scheduling. The CSI required for DL scheduling is usually reported by UEs periodically based on configuration, or reported aperiodically based on request from eNB. In LTE, the periodic CSI feedback utilizes physical uplink control channel (PUCCH) resources, and UEs are configured PUCCH resources e.g., periodicity, time offset, etc., for each type of CSI report including precoding matrix index PMI, rank indicator RI, channel quality indicator CQI. Due to different time-varying characteristic of long term PMI, short term PMI, RI and CQI, the periodicity configured for each CSI report type can be different to save signaling overhead. Currently, the feedback modes in LTE can only support 2D MIMO operations, and 3D CSI feedback, e.g., vertical domain PMI, RI, has not been considered.

[0051] If the 3D CSI feedback is to be configured in similar way as that of 2D CSI, it means additional configuration signaling, e.g., for informing a feedback periodicity and subframe offset, is required. Moreover, additional PUCCH resources will be consumed by the vertical CSI feedback. However, it is observed by the inventor that the vertical domain has the following time-varying characteristic. First, significant change will not occur in short time interval, i.e., a feedback period less than the horizontal CSI feedback is not necessary; second, the time interval between significant changes is not constant, as shown in Figure 3b, it means it will be hard to configure a proper report periodicity; third, as shown in the Table I below, when using 4 DFT codebook, both the cell average and cell edge SE decreases obviously comparing with 8 or 16 DFT codebook, then it can be contemplated that too small vertical codebook will result in throughput decrease significantly, thus, more feedback bits will be required.

Table I. Impact of vertical codebook size on spectrum effeciency

[0052] To solve the above problems in 3D CSI feedback, methods and devices are proposed in this invention. The methods and the devices in the embodiments of the present invention have the following advantages:

• If to be applied to the LTE system, it can maintain the report structure of LTE Release 8, thereby minimizes the required standard modification;

• Minimizing overhead of vertical CSI report ;

• Additional signaling to inform the vertical CSI feedback configuration may not be required;

• Introducing performance gain for cell edge UEs without additional PUCCH resources.

[0053] Reference is now made to Figure 4, which illustrates a flow chart for an example method 400, performed by a device, e.g., a UE 302 in Figure 3a, for transmitting vertical domain channel state information CSI to support a 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the method comprises the following steps. In step 401, it is determined on whether to transmit the vertical domain CSI based on a measurement of at least the vertical domain CSI, or, based on a signaling from another device, for example eNB; and if the vertical domain CSI is determined to be transmitted, in step 402, the vertical domain CSI is transmitted in at least one of the resources previously configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined transmission of the vertical domain CSI and last transmission of the vertical domain CSI is larger than the period for the specific horizontal domain CSI transmission. Here in the method 400, the dedicated signaling for the vertical domain CSI feedback resource configuration is avoided due to the fact that the vertical domain CSI are transmitted in previously configured resources for horizontal CSIs, then additional resources and corresponding configuration signaling for the additional resources are avoided. [0054] In a further embodiment of the invention, the method 400 further comprising a step 403, for generating an indicator to indicate the determined results in step 401, and a step 404, for transmitting the indicator jointly with a first horizontal domain CSI in a resource configured for the first horizontal domain CSI transmission. The indicator transmitted in step 404 enables common understanding between the device which reports the CSI and the receiver, e.g., the eNB, on whether the vertical domain CSI, is to be transmitted, and for simplicity, the indicator can be denoted as PTI-v thereafter.

[0055] In one embodiment of the invention, in step 403, a value for the indicator is set based on the following criterion (and/or the determination in step 401 is made based on the following principle): if both the first variation in a first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then set a value to indicate (and/or determine in step 401) that the vertical domain CSI is to be transmitted, otherwise, set a value to indicate (and/or determine in step 401) that the vertical domain CSI is not to be transmitted. Such implementation is based on an assumption that the vertical CSI usually changes much slower than the first horizontal CSI, then only when the first horizontal domain CSI changes more than a first threshold, and need to be updated, the transmission of the vertical CSI, i.e., the vertical domain CSI, is considered to be necessary. Such implementation also causes the interval between two adjacent transmissions of the vertical CSI to be larger than the period configured for the specific horizontal domain CSI transmissions, and in some embodiment can be larger than the maximum period for all horizontal domain CSIs. To enable this, the method 400 may comprise additional measurement step 411 not shown in the Figure 4, or the measurement is also done by the step 403, or 401.

[0056] In another embodiment, in step 403 the value of the indicator can be set based on a measurement of the vertical domain CSI only, e.g., when a significant variation on the vertical CSI is detected, the value is set to indicate that the vertical domain CSI is to be updated. Similarly, in step 401, the determination can be based on the measurement of the vertical domain CSI only, in some embodiment of the invention.

[0057] According to some embodiments of the invention, the determination in step 401 and/or the value of the indicator in step 403 can be based on a configuration signaling from another device, e.g., an eNB. In such case, the method 400 may comprise an additional signaling detection step 412, which is not shown in Figure 4, or, the operation is included in step 403 or 401.

[0058] In one embodiment of the present invention, the first horizontal domain CSI which is jointly transmitted with the PTI-v in step 404 indicates a first long-term precoding matrix, e.g., Wl of the horizontal dual codebook, and the vertical domain CSI indicates a vertical domain long term PMI, referred to as PMI-v or Wv exchange ably thereafter. One example can be found in Figure 5a, where a method according to one embodiment of the present invention is applied to improve the CSI feedback mode 2-1 of Release 10 for a scenario of 8 transmit antennas. In the example, the transmission of Wl in current mode 2-1 is replaced with the joint transmission of the indicator PTI-v and the first horizontal domain CSI (Wl, in this example) with a first period, and in this example the transmission period is 4 times long as a period of the specific horizontal domain CSI (also referred to as a second horizontal domain CSI thereafter) which includes a wide band W2 and a wideband CQI in this example, and the joint transmission can be defined to be a new report type, e.g., type 2d, to distinguish it from existing report type in current 3GPP specification. The indicator PTI-v can be 1 bit, and the size of Wl is no more than 4 bits according to current 3 GPP LTE-A specification, then the total pay load size of the type 2d report is no more than 5 bits, which guarantees a good transmission performance without additional resource occupation. Further, as shown in the Figure 5a, in each transmission cycle, the vertical domain CSI is transmitted in step 402 only when it is determined to be transmitted in step 401 and only when PTI-v=0 is transmitted in step 404. In this example embodiment, the vertical domain CSI is transmitted in one of the periodic PUCCH resources configured for the specific horizontal domain CSI, and the transmission of the specific horizontal domain CSI in same resource is avoided. The transmission of the vertical PMI can be defined to be a new report type, e.g., type 7, to distinguish it from the existing 3GPP CSI report types. It should be noted that in the lower part of Figure 5a, it only shows the change introduced by the evolved mode 2- 1 according to an embodiment of the invention, which means all other CSI transmissions can be kept the same as current mode 201 shown in the upper part of Figure 5a. Such conditional transmission in each transmission period of the vertical domain CSI makes the vertical domain CSI report have an aperiodic characteristic, which enables provision of vertical channel information without additional resource requirement and at the same time minimizes the impact to the specific horizontal domain CSI transmission, since the vertical domain CSI transmission will occupy the resource configured for the specific horizontal domain CSI (also referred to as the second horizontal domain CSI) transmission only when both PTI and PTI-v are set to be 0. It is to be noted that in this example in each of the transmission period of the vertical domain CSI, there are multiple second horizontal domain CSI transmission resources/opportunities, and as shown in Figure 5a, the vertical domain CSI transmission occupies the first one of the multiple second horizontal domain CSI resources when both PTI and PTI-v=0, however, in other embodiments, the vertical domain CSI transmission may replace any one of the multiple second horizontal domain CSI transmissions.

[0059] Though in the example of Figure 5a, the vertical domain CSI is shown to be vertical domain PMI (PMI-v, or Wv), which is just for illustration rather than limitation, it can also be other vertical CSI information, e.g., a vertical domain rank indicator RI-v, or both PMI-v and RI-v, in other embodiments of the invention.

[0060] In another embodiment of the present invention, the first horizontal domain CSI which is jointly transmitted with the vertical CSI in step 404 indicates a first rank, e.g., the RI of horizontal domain, and the vertical domain CSI indicates a vertical domain long term precoding matrix, i.e., the PMI-v, or both the PMI-v and a vertical domain rank indicator, e.g., RI-v. Such an example is shown in Figure 5c, where a method according to one embodiment of the present invention is applied to improve the CSI feedback sub-mode 2 for Release 10 for a scenario of 8 transmit antennas to support 3D CSI feedback. In this example, the indicator PTI-v is generated based on the determination results in step 401 and is jointly transmitted in step 404 with the first horizontal domain CSI which is RI, using the periodic PUCCH resource configured for RI transmission. The joint transmission of PMI-v and RI can be defined to be a new report type, e.g., type 6a. Since the indicator PTI-v can be 1 bit, and the payload of the first horizontal domain CSI (RI) is 2 or 3 bits depending on the number of antenna ports according to current 3GPP LTE-A specification, then the joint transmission of PTI-v and RI may have a payload less than 5 bits, which implies good transmission performance. As shown in the Figure 5c, the vertical domain CSI, which is wideband Wv in this example, has a third period and in each of the third period, the vertical domain CSI is only transmitted in step 402 when the it is determined to be transmitted in step 401 and correspondingly the indicator PTI-v=0 is transmitted in step 404. The transmission in step 402 occupies one of the second horizontal domain CSI resources, i.e., periodic PUCCH resources configured for the second horizontal domain CSI transmission. The second horizontal domain CSI in this example includes a Wl, a W2 and a wideband CQI, and as shown in the Figure 5c, the period of the second horizontal domain CSI is much shorter than the first and the third period, then there are multiple second horizontal domain CSI transmission opportunities in each of the third periods. Then by making the vertical domain CSI transmission only occupy one of the multiple second horizontal domain CSI transmission opportunities conditionally in each of the third period, the impact to the second horizontal domain CSI transmission is not considered to be significant. [0061] In still another embodiment of the present invention, the first horizontal domain CSI which is jointly transmitted with the indicator PTI-v in step 404 indicates both a first long-term precoding matrix and a first rank, and the vertical domain CSI indicating a vertical domain long term precoding matrix or both the vertical domain long-term precoding matrix and a second rank. One example is shown in Figure 5b, where a method according to one embodiment of the present invention is applied to improve the CSI feedback sub-mode 1 for Release 10 for a scenario of 8 transmit antennas to support 3D CSI feedback. In the example, the indicator PTI-v is jointly transmitted with the first horizontal domain CSI which is RI and Wl. The joint transmission of RI, Wl and PMI-v can be defined to be a new report type, e.g., type 5a to distinguish it from other existing report types. Since the indicator PTI-v can be 1 bit, and the payload of the first horizontal domain CSI (RI and Wl) is 5 bits according to current 3GPP LTE-A specification, then the joint transmission of PTI-v, RI and Wl conveys more than 5 bits. In one embodiment of the present invention, in order to guarantees a good transmission performance of the joint transmission, the first horizontal domain CSI can be compressed to ensure that the total payload of the joint transmission is not more than a predefined threshold. For example, the Wl can be sub-sampled to ensure that the total payload is no more than 5 bits. It should be noted that a threshold of 5 bits is just an example, and in other embodiment, any other suitable threshold value can be employed. Similarly as in Figure 5a, in the example of Figure 5b, the vertical domain CSI (wide band Wv, in this example) is transmitted with a third period which is equal to a first period of the first horizontal domain CSI, however, in each of the third period, the vertical domain CSI is transmitted in step 402 in one of the resource configured for the second horizontal domain CSI transmission only when the it is determined to be transmitted in step 401 and the PTI-v =0 is transmitted in the step 404. Here in this example, the second horizontal domain CSI includes a wide band W2 and a wideband CQI.

[0062] It should be noted that though in the examples of Figures 5a-5c, the transmission of the indicator PTI-v is shown to have a same period as the period of the first horizontal domain CSI, the interval between two transmissions of the vertical domain CSI can be much larger, e.g., be multiple of the period of the first horizontal domain CSI, since it is only transmitted when the indicator is set to be 0, and the indicator is set to be 0 only when it is determined in the step 401 that there is significant change in the vertical domain CSI, or both the vertical domain CSI and the first horizontal domain CSI need updating. Since the vertical domain has been observed to vary significantly only after a long time duration, then the time interval between two transmissions of the vertical CSI can be larger than the period configured for the second horizontal domain CSI, and in some embodiments of the invention, even larger than the maximum period configured for horizontal domain CSI transmissions.

[0063] In the examples of Figures 5a-5c, when the vertical domain CSI is transmitted in a resource configured for a specific horizontal domain CSI (also referred to as second horizontal domain CSI herein) transmission in step 402, the transmission of the specific horizontal domain CSI in same resource is avoided, and the receiver can interpret the content transmitted correctly based on the indicator PTI-v transmitted in step 404. For example, when PTI-v=0 is transmitted, then the receiver will interpret the information transmitted in step 402 to be the vertical domain CSI, otherwise, interpret it to be the second horizontal domain CSI.

[0064] The vertical domain CSI can be transmitted in a different way in another embodiment of the invention. For example, the vertical domain CSI transmitted in one resource configured for a specific horizontal domain CSI transmission can be set to a special value which is one of the values reserved not to be used by the specific horizontal domain CSI, such that, when such special value is detected, the receiver can know that it should be interpreted as the vertical CSI, rather than the specific horizontal domain CSI. One example of the reserved values is shown in Table II below, where a range for valid values of RI and Wl is restricted to be 0 to 17 and the other values between 18 and 31 are reserved. Then the reserved values can be used to represent the vertical domain CSI, and once a value between 18 and 31 is detected, the receiver can identify it as a vertical domain CSI report rather than a horizontal domain Wl+Rl report. In such case, a transmission of the indicator PTI-v is unnecessary, since the value being transmitted implies a report type. Such embodiment can be, for example, applied to improve the submode 1 of the LTE Release 10 feedback mode 1-1 to support vertical domain CSI report, and a schematic diagram is depicted in Figure 5d. If the vertical domain CSI is reported using a reserved index, the horizontal domain CSI is automatically avoided. In such case, the horizontal domain CSI can be considered to be same as the value reported last time.

[0065] Table II. Valid values for RI and W 1

Alternatively, in accordance with some embodiments of the invention, when the vertical domain CSI is determined to be transmitted in step 401, e.g., based on a configuration signaling from eNB, in step 402 the vertical domain CSI is divided into multiple groups before transmission such that each group contains a part of the vertical CSI, and each group is transmitted jointly with a specific horizontal domain CSI using one of the resources configured for the specific horizontal domain CSI transmission. Such an example is shown in Figure 5e, where a 4-bits PMI-v is divided into 4 groups with 1 bit in each group, and then each 1 bit is transmitted jointly with the horizontal domain CSI, i.e., RI and PTI in feedback mode 2-1. In such way, the payload of each joint transmission is reduced, and then a better transmission performance can be ensured and the impact to horizontal domain CSI feedback is minimized. The number of groups to divide into may be configured by eNB, predefined, or implicitly known based on some predefined rules. For example, the number of bits per group can vary depending on the payload size of the horizontal domain CSI which is to be transmitted jointly with a group of the vertical domain CSI. One example is shown in Figure 5f, where it is assumed that the horizontal RI is the horizontal domain CSI to be transmitted jointly with the PMI-v, considering that the RI is only 2 or 3 bits, the PMI-v can be divided into 2 groups with 2 bits in each group, thus the total payload of each joint transmission is still kept to be no more than 5 bits to guarantee a satisfying performance.

[0067] It should be noted that each physical channel has its transmission capacity, which can be represented by a payload size that can be transmitted with satisfying performance. For example, in LTE/LTE-A, the PUCCH type II channel used for periodic CSI feedback can convey 5 bits without introducing obvious reliability loss, thus the payload size of 5 bits can be considered as the capacity of the PUCCH type II channel. It has been observed that in current LTE-A specification (36.213 v.cOO), many CSI feedback type does not reach the PUCCH capacity. For example, the RI feedback only has a payload of 2 or 3 bits depending on the number of antenna ports. Taking subband feedback of 8ports in LTE-A as an example, the payload size is 4 bits which is still 1 bit less than the capacity can be supported by PUCCH channel. Then it will be beneficial if the remaining capacity of a PUCCH channel configured for a CSI feedback can be reused for carrying another CSI, such that avoiding dedicated resource configuration for the another CSI. The above example embodiment is just proposed based on such observation to reuse remaining capacity of an existing CSI feedback channel.

[0068] On the other hand, it should be noted that the distributed transmission of a single vertical domain CSI may increase the feedback error probability for UEs with low signal to interference plus noise power ratio (SINR), since only when every group is received correctly, the complete vertical domain CSI can be detected properly. For UEs which have very low SINR, error rate of the vertical domain CSI transmitted according to the embodiment of the invention described above may be high. Fortunately, the number of UEs with very low SINR is very small. For UEs with very low SINR, the vertical domain CSI can be fedback according to another embodiment of the invention described in the following

[0069] In one further embodiment, the vertical domain CSI is divided into multiple group by dividing the vertical domain CSI into M groups then duplicating each of the M groups N times to obtain totally MxN groups, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2. Such implementation is based on the observation that the vertical feedback interval can be much larger than that of horizontal CSI. Then such method of repeating in multiple transmissions helps to improve feedback reliability. In this case, the period of vertical CSI transmission is equal to or larger than P_h*M*N, where P_h is the period of horizontal domain CSI jointly transmitted with each group of the vertical domain CSI. It should be noted that when duplicating each of the M groups N times, it can use direct repetition, or repetition with some coding method. For example, a bit 1 can be directly repeated 4 times to be "1 1 1 1", or, it can be repeated to be "1 -1 1 -1", or can use any other suitable repetition pattern.

[0070] Besides transmission performance improvement of the vertical domain CSI, the above repetition method also enables to detect at the receiver side some transmission failure in the horizontal domain CSI which is transmitted jointly with the vertical domain CSI. For example, assuming N=4, i.e., each group of information will be transmitted for 4 times, then if the receiver detects significant difference in the four transmissions before combination, for example, the four received signals are "A A A B", then the receiver (e.g., the eNB) can judge that at least one repetition is not detected correctly, which means the second CSI transmitted together with it in the last transmission may also be corrupted. Once such transmission failure is detected, it may trigger the receiver to take some actions to improve the feedback performance of the second CSI, e.g., trigger an aperiodic CSI feedback.

[0071] In one or more embodiments of the invention, the vertical domain CSI is assigned with a priority level equal to that of a long term horizontal CSI, e.g., the priority level of vertical domain CSI is equal to the horizontal domain long term PMI. Such priority level may be used for deciding whether the vertical domain CSI should be transmitted and/or a transmission power level, in case there is resource collision with another transmission, or, in case there is no enough Tx power to support simultaneous transmission of the vertical CSI and another transmission.

[0072] It should also be noted that though in above examples, the embodiment is described in LTE environment, the embodiments of the present invention are not limited to this. For example, when the methods can be applied to other wireless networks, and the resources configured for the horizontal domain CSI can also be other channels than the PUCCH channel mentioned above.

[0073] Reference is now made to Figure 6, which illustrates a flow chart for an example method 600, performed by a device, e.g., a eNB 301 in Figure 3a, for receiving a vertical domain channel state information CSI to support a 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the vertical domain CSI is transmitted by a second device, e.g., the UE 302 in Figure 3a using the method 400 described with reference to Figures 4 and 5a-5f, then all the features of the vertical domain CSI report described with reference to Figures 4 and 5a-5f also apply here in the receiving method 600.

[0074] As shown in Figure 6, the example method comprises the following steps. In step 601, it is determined on whether to receive the vertical domain CSI based on an indicator from the second device, or based on a configuration signaling previously sent to the second device; If the vertical domain CSI is determined to be received in step 601, the vertical domain CSI is received in step 602 in at least one of the resources previously configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined receiving of the vertical domain CSI and last reception of the vertical domain CSI is larger than the period of the specific horizontal domain CSI transmission, and in some embodiments, even larger than the maximum period for all horizontal domain CSI transmissions configured for the second device. Here in the method 600, the dedicated signaling for the vertical domain CSI feedback resource configuration is avoided due to the fact that the vertical domain CSI are transmitted and received in previously configured resources for horizontal CSIs, then additional resources and corresponding configuration signaling for the additional resources are avoided.

[0075] In a further embodiment of the invention, the method 600 further comprising a step 611, for receiving the indicator which is jointly transmitted with a first horizontal domain CSI in a resource configured for the first horizontal domain CSI transmission. The indicator received in step 611 enables common understanding between the device which reports the CSI and the receiver, e.g., the eNB, on whether the vertical domain CSI, is to be transmitted, and for simplicity, the indicator can be denoted as PTI-v.

[0076] In one embodiment of the invention, the indicator received in step 611 and used for determination in step 601 is set by the second device based on the following principle: if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then set the indicator to indicate the vertical domain CSI is to be transmitted, otherwise, set the indicator to indicate the vertical domain CSI is not to be transmitted. Such implementation is based on an assumption that the vertical CSI usually changes much slower than the first horizontal CSI, then only when the first horizontal domain CSI changes more than a first threshold, and need to be updated, the transmission of the vertical CSI, i.e., the vertical domain CSI, is considered to be necessary. Such implementation also causes the interval between two adjacent transmissions of the vertical CSI to be larger than the period for the specific horizontal domain CSI transmission, and in some embodiments, even larger than the maximum period configured for all horizontal domain CSI transmissions, e.g., larger than the period of Wl for horizontal domain dual codebook, or the period of RI. In another embodiment, the indictor can be set by the second device based on a measurement of the vertical domain CSI only, e.g., when a significant variation on the vertical CSI is detected, it is set to indicate that the vertical domain CSI is to be updated.

[0077] In one embodiment of the present invention, the first horizontal domain CSI which is jointly received with the PTI-v in step 611 indicates a first long-term precoding matrix, e.g., Wl of the horizontal dual codebook, and the vertical domain CSI indicates a vertical domain long term PMI, referred to as PMI-v or Wv exchangably thereafter. One example can be found in Figure 5a, and since the transmission has been described with reference to method 400, details will not be repeated again. Though in the example of Figure 5a, the vertical domain CSI is vertical domain PMI (PMI-v, or Wv), it can also be other vertical CSI information, e.g., a vertical domain rank indicator RI-v, or both PMI-v and RI-v.

[0078] In another embodiment of the present invention, the first horizontal domain CSI which is jointly transmitted with the vertical CSI in step 404 indicates a first rank, e.g., the RI of horizontal domain. One such example is shown in Figure 5c, and details of the transmission have been presented with reference to method 400 and then will be omitted here.

[0079] In still another embodiment of the present invention, the first horizontal domain CSI which is jointly transmitted with the indicator PTI-v in step 404 indicates both a first long-term precoding matrix and a first rank. One example is shown in Figure 5b, and similarly since details has been described with reference to method 400, they will not be repeated here. It should be noted that the Wl and RI received jointly with PTI-v can be a compressed value in this example to ensure that the total payload is less than a predefined threshold.

[0080] It should be noted that though in the examples of Figures 5a-5c, the transmission of the indicator is shown to have a same period as the period of the first horizontal domain CSI, the interval between two receptions of the vertical domain CSI can be much larger, e.g., be multiple of the period of the first horizontal domain CSI, since it is only transmitted when the indicator is set to be 0, and the indicator is set to be 0 only when it is determined by the second device that there is significant change in the vertical domain CSI, or both the vertical domain CSI and the first horizontal domain CSI need updating. Since the vertical domain has been observed to vary significantly only after a long time duration, then the time interval between two transmissions of the vertical CSI can be larger than even the maximum period configured for horizontal domain CSI transmissions.

[0081] In the examples of Figures 5a-5c, when the vertical domain CSI is received in a resource configured for a specific horizontal domain CSI (also referred to as a second horizontal domain CSI) transmission in step 602, the detection of the specific horizontal domain CSI in same resource is avoided, and the content transmitted in the resource can be interpreted correctly based on the indicator PTI-v received in step 611. For example, when PTI-v=0 is detected, then the information received in step 602 is interpreted to be the vertical domain CSI, otherwise, interpreted to be a specific horizontal domain CSI.

[0082] As described with reference to method 400 and Figure 4, the vertical domain CSI can be transmitted in a different way in some embodiments of the invention. Then correspondingly, in the receiving method 600, there is also specific operation in receiving such vertical domain CSI transmission, in some embodiments. For example, if in step 602 a value, which is reserved not to be used by the specific horizontal domain CSI, is detected in the at least one of the resources configured for the specific horizontal domain CSI transmission, then it will be interpreted as the vertical domain CSI transmission. One example of such reserved value is the values 18-31 as shown in Table II. In such case, a reception of the indicator PTI-v is unnecessary, since the value being transmitted implies a report type. Such embodiment can be applied to improve the submode 1 of the LTE Release 10 feedback mode 1-1 to support vertical domain CSI report, and a schematic diagram is depicted in Figure 5d.

[0083] In another embodiment of the invention, when in step 601 the vertical domain CSI is determined to be received, in step 602, the vertical domain CSI is received by receiving a part of the vertical domain CSI in each resource of the at least one of the resources, then combining the received parts to obtain a complete vertical domain CSI. Such receiving operation corresponds to an example transmitting method embodiment where the vertical domain CSI is divided into multiple groups when transmitting, and each group contains only a part of the vertical domain CSI and each group is transmitted jointly with the specific horizontal domain CSI in one of the resources configured for the specific horizontal domain CSI transmission. Such an example can be seen in Figure 5e, and since it has been described with reference to method 400, details will be omitted here. In such embodiment, the number of groups to receive may be configured by eNB and informed to UE, or, predefined, or can be implicitly known based on some predefined rules. For example, the number of bits per group can vary depending on the payload size of the horizontal domain CSI which is to be received jointly with a group of the vertical domain CSI. One example is shown in Figure 5f, where it is assumed that the horizontal RI is the horizontal domain CSI to be transmitted jointly with the PMI-v, considering that the RI is only 2 or 3 bits, the PMI-v can be divided into 2 groups with 2 bits in each group, thus the total payload of each joint transmission is still kept to be no more than 5 bits to guarantee a satisfying performance.

[0084] In one further embodiment, the vertical domain CSI received in step 602 is divided into multiple groups before being transmitted by dividing the vertical domain CSI into M groups then duplicating each of the M groups N times to obtain totally MxN groups, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2. Such implementation is based on the observation that the vertical feedback interval can be much larger than that of horizontal CSI. Then such method of repeating in multiple transmissions helps to improve feedback reliability. In this case, the period of vertical CSI is equal to or larger than P_h*M*N, where P_h is the period of horizontal domain CSI jointly transmitted with each group of the vertical domain CSI. It should be noted that when duplicating each of the M groups N times, it can be direct repetition, or repetition with some coding method. For example, a bit 1 can be repeated 4 times to be "1 1 1 1", or, it can be repeated to be "1 -1 1 -1", or can be any other suitable repetition pattern. Then in such embodiment, the detection in step 602 may further comprise a decoding operation or a weighted combination operation based on the repetition pattern applied. For example, each of the N duplications is combined firstly based on a repetition pattern to obtain estimated M groups, then the estimated M groups are used to compose an estimated vertical domain CSI.

[0085] In further embodiment of the invention, in step 602, based on the detection of the vertical domain CSI, the receiver can also detect some transmission failure in the horizontal domain CSI which is transmitted jointly with the vertical domain CSI. For example, assuming N=4, i.e., each group of information will be transmitted for 4 times, then if the receiver detects significant difference in the four transmissions before combination, for example, the four received signals are "A A A B", then the receiver (e.g., the eNB) can judge that at least one repetition is not detected correctly, which means the second CSI transmitted together with it in the last transmission may also be corrupted. Once such transmission failure is detected, it may trigger the receiver to take some actions to improve the feedback performance of the second CSI, e.g., trigger an aperiodic CSI feedback..

[0086] In one or more embodiments of the invention, the vertical domain CSI involved in the method 600 is assigned with a priority level equal to that of a long term horizontal CSI, e.g., the priority level of vertical domain CSI is equal to the horizontal domain long term PMI. Such priority level may be used for deciding whether the vertical domain CSI should be transmitted and/or transmission power, in case there is resource collision with another transmission, or, in case there is no enough Tx power to support simultaneous transmission of the vertical CSI and another transmission.

[0087] It should also be noted that though in above examples, the embodiment is described in LTE environment, but the embodiments of the present invention are not limited to this. For example, when the methods are applied to other wireless networks, the resources configured for the first and second horizontal domain CSI can be other channels than the PUCCH channel mentioned above.

[0088] It can be understand by those skilled in the art that though the example method 400 and example method 600 are described in the context of LTE system, the embodiments of the present invention are not limited to such network scenarios and similar methods can also be applied to other wireless networks, e.g., a non-cellular network, or device-to-device communication network, as long as similar requirement for 3D CSI feedback exists.

[0089] To be noted that in some alternative implementations, the functions indicated in the block diagrams could also occur in a sequence different from what is indicated in the figure. For example, two sequentially indicated blocks could be executed substantially in parallel or sometimes in an inversed order, depending on the functions as involved.

[0090] It is also to be understood that methods described with reference to Figures 4, 5a-5c and 6 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.. [0091] Reference is now made to Figure 7, which illustrates a block diagram of a device 700 according to an embodiment of the present invention. The device 700 according to Figure 7 can be a UE 302 in Figure 3a, and may perform the example methods described with reference to Figures 4 and 5a-5f, but is not limited to these methods. Then any feature presented above, e.g., in the description with reference to Figures 4 and 5a-5f and method 400, if appropriate, can be applied to the device 700 presented below. It is to be noted that the methods described with reference to Figures 4 and 5a-5f may be performed by the device of Figure 7, but is not limited to being performed by this device 700. The device 700 may be any wireless devices, for example, a mobile phone, a laptop computer, etc.

[0092] As shown in Figure 7, the device 700 comprises at least a determination unit 701 and a vertical domain CSI transmission unit 702; the determination unit 701 is configured to determine on whether to transmit the vertical domain CSI based on a measurement of at least the vertical domain CSI, or, based on a signaling from a second device; the vertical domain CSI transmission unit is configured to transmit the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission if the vertical domain CSI is determined to be transmitted, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined transmission of the vertical domain CSI and last transmission of the vertical domain CSI is larger than the period for the specific horizontal domain CSI transmissions.

[0093] In one further embodiment, the device 700 also comprises an indicator generation unit 703, configured to generate an indicator to indicate the determined results; and an indicator transmission unit 704, configured to transmit the indicator jointly with a first horizontal domain CSI using a resource configured for the first horizontal domain CSI transmission.

[0094] In one embodiment of the invention, the indicator generation unit 703 is configured to set a value for the indicator based on the following criterion (and/or the determination unit 701 is configured to determine based on the following principle): if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then setting a value to indicate (and/or determine) that the vertical domain CSI is to be transmitted, otherwise, setting a value to indicate that the vertical domain CSI is not to be transmitted. In some example embodiments, the measurement of the vertical CSI and/or the horizontal domain CSI is performed in the determination unit 701, and in some other embodiments, it is performed by another unit not shown in the Figure.

[0095] In this embodiment, the first horizontal domain CSI may indicate a first long-term precoding matrix, and the vertical domain CSI indicates a vertical domain long term precoding matrix, or both the vertical domain long-term precoding matrix and a second rank. One example of such a first horizontal domain CSI is the Wl in Figure 5a. In another embodiment, the first horizontal domain CSI indicates a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix, or both the vertical domain long-term precoding matrix and a second rank. One example of such a first horizontal domain CSI is the RI in Figure 5c. In one further embodiment, the first horizontal domain CSI indicates both a first long-term precoding matrix and a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix, or both the vertical domain long-term precoding matrix and a second rank. One example of such a first horizontal domain CSI is the Wl and RI in Figure 5b.

[0096] In still another example embodiment, the indicator transmission unit 704 is further configured to compress the first horizontal domain CSI before the joint transmission with the indicator, such that the total payload to be jointly transmitted is no more than a predefined value. This helps to guarantee a satisfying transmission performance.

[0097] In some embodiments, the resources configured for horizontal domain CSI transmissions are periodic physical uplink control channel (PUCCH) resources.

[0098] In one further embodiment, the indicator transmission unit 704 is further configured to transmit the indicator jointly with the first horizontal domain CSI only when a need for updating the first horizontal domain CSI is detected, and the detection can be performed by another unit not shown in Figure 7, or also by the determination unit 701.

[0099] In some embodiments, the vertical CSI transmission unit 702 is configured to transmit the vertical domain CSI using a resource configured for a specific horizontal domain CSI transmission, and prevent from transmitting the specific horizontal domain CSI in the same resource. Examples can be seen in Figures 5a-5c, where the specific horizontal domain CSI indicates wideband W2 and wide band CQI, or wideband Wl, W2 and CQI.

[00100] In another embodiment of the invention, the vertical CSI transmission unit 702 is configured to transmit the vertical domain CSI by transmitting, in one resource configured for a specific horizontal domain CSI transmission, a value which is reserved not to be used by the specific horizontal domain CSI, such that distinguishing it from the specific horizontal domain CSI transmission. One example is shown in Figure 5d. In such case, when such special value is detected, the receiver can know that it should be interpreted as the vertical CSI, rather than the specific horizontal domain CSI, and in such case, the indicator PTI-v is not necessary to be transmitted.

[00101] In one further embodiment of the invention, when it is determined in the determination unit 701 based on some configuration signaling from eNB that the vertical domain CSI is to be transmitted, vertical domain CSI transmission 702 is configured to divide the vertical domain CSI into multiple groups, and transmit each group jointly with the specific horizontal domain CSI using one of the resources configured for the specific horizontal domain CSI transmission. One example of such transmission is shown in Figure 5e, where a 4-bits PMI-v is divided into 4 groups with 1 bit in each group, then each 1 bit is transmitted jointly with the horizontal domain CSI, i.e., RI and PTI in feedback mode 2-1. In such way, the payload of each joint transmission is reduced, then a better transmission performance can be ensured and the impact to horizontal domain CSI feedback is minimized. The number of groups to divide into may be configured by eNB, predefined, or implicitly known based on some predefined rules. Another example is shown in Figure 5f, where it is assumed that the horizontal RI is the horizontal domain CSI to be transmitted jointly with the PMI-v, and the PMI-v can be divided into 2 group with 2 bits in each group, thus the total payload of each joint transmission is still kept to be no more than 5 bits to guarantee a satisfying performance.

[00102] In still another embodiment, vertical domain CSI transmission 702 is configured to divide the vertical domain CSI into multiple group by dividing the vertical domain CSI into M groups then duplicating each of the M groups N times to obtain totally MxN groups, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2. Such implementation is based on the observation that the vertical feedback interval can be much larger than that of horizontal CSI. Then such method of repeating in multiple transmissions helps to improve feedback reliability. In this case, the period of vertical CSI is equal to or larger than P_h*M*N, where P-h is the period of horizontal domain CSI jointly transmitted with each group of the vertical domain CSI. It should be noted that when duplicating each of the M groups N times, it can be direct repetition, or repetition with some coding method. For example, a bit 1 can be repeated 4 times to be "1 1 1 1", or, it can be repeated to be "1 -1 1 -1", or can be any other suitable repetition pattern.

[00103] In one or more embodiments of the invention, the vertical domain CSI is assigned with a priority level equal to that of a long term horizontal CSI, e.g., the priority level of vertical domain CSI is equal to the horizontal domain long term PMI.

[00104] Reference is now made to Figure 8, which illustrates a block diagram of a device 800 according to an embodiment of the present invention. The device 800 according to Figure 8 can be a eNB 301 in Figure 3a, and may perform the example method 600 described with reference to Figure 6, but is not limited to these methods. It is to be noted that the methods described with reference to Figs. 6 may be performed by the device of Figure 8, but is not limited to being performed by this device 800. The device 800 may be any wireless devices, for example a mobile phone, a laptop computer, etc.

[00105] As shown in Figure 8, the device 800 comprises at least a determination unit 801, configured to determine on whether to receive the vertical domain CSI based on an indicator from the device, or based on a configuration signaling previously sent to the second device; and a vertical domain CSI receiving unit 802, configured to receive the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission, if the vertical domain CSI is determined to be received, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration; wherein the interval between the determined receiving of the vertical domain CSI and last reception of the vertical domain CSI is larger than the period configured for the specific horizontal domain CSI transmissions.

[00106] In one embodiment of the invention, the device 800 further comprise the indicator receiving unit 803, configured to receive an indicator which is jointly transmitted with the first horizontal domain CSI in a resource configured for the first horizontal domain CSI transmission. The indicator is used by the determination unit for determination.

[00107] In one embodiment of the invention, the indicator received by the indicator receiving unit 803 and used for determination by the determination unit 801 is set and transmitted by a second device, e.g., UE 302 in Figure 3a, based on a measurement of both the vertical domain CSI and the first horizontal domain CSI. For example, if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then the indicator is set to indicate that the vertical domain CSI is to be transmitted, otherwise, the indicator is set to indicate that the vertical domain CSI is not to be transmitted. In another embodiment, the indicator may be set by UE 302 based on measurement of the vertical CSI only. [00108] In one embodiment of the invention, the first horizontal domain CSI jointly received with the indicator in the indicator receiving unit 803 indicates a first long-term precoding matrix, e.g., the Wl in Figure 5a, and the vertical domain CSI indicates a vertical domain long term precoding matrix, e.g., PMI-v, or both the PMI-v and a vertical domain rank indicator RI-v. In another embodiment of the invention, the first horizontal domain CSI indicates a first rank, e.g., the RI in Figure 5c, and the vertical domain CSI indicates a vertical domain long term precoding matrix, e.g., PMI-v, or both the vertical domain long-term precoding matrix PMI-v and a rank RI-v. In one further embodiment, the first horizontal domain CSI indicates both a first long-term precoding matrix and a first rank, e.g., Wl and RI in Figure 5b, and the vertical domain CSI indicates a vertical domain long term precoding matrix, e.g., PMI-v, or both the vertical domain long-term precoding matrix PMI-v and a rank RI-v.

[00109] In some embodiments of the invention, the indicator receiving unit 801 is configured to receive the indicator and a compressed first horizontal domain CSI which are jointly transmitted, and the total payload of the joint transmission is no more than a predefined value. For example, the indicator being received is transmitted jointly with a RI and a compressed Wl, such that the total payload can be no more than 5 bits.

[00110] In some embodiments of the invention, the resources configured for horizontal domain CSI transmissions are periodic physical uplink control channel (PUCCH) resources.

[00111] In one further embodiment, the indicator receiving unit 803 is configured to receive the indicator jointly transmitted with the first horizontal domain CSI only when a need for updating the first horizontal domain CSI is detected. For example, the unit 803 is configured to receive the indicator only when PTI=0 has been detected, which indicates a Wl will be transmitted.

[00112] In accordance with some embodiments of the invention, the method 800 may further comprise a configuration unit 811 now shown in Figure 8, configured to signal some configuration information related to whether there is a need for the vertical CSI transmission to the second device. Then such signaling sent out in configuration unit 811 is also used by the determination unit to decide whether to receive the vertical domain CSI.

[00113] In some embodiments, the vertical domain CSI receiving unit 802 is configured to receive the vertical domain CSI in a resource configured for a specific horizontal domain CSI transmission, and prevent from detecting the specific horizontal domain CSI in the same resource. In the examples in Figures 5a-5c, the specific horizontal domain CSI includes wideband W2 and CQI, or wideband W2, Wl and CQI. The vertical domain CSI receiving unit 802 can be configured to interpret the content transmitted in the resource configured for the specific horizontal domain CSI based on the indicator PTI-v received by the indicator receiving unit 803. For example, when PTI-v=0 is received, then the information received in the resource configured for the specific horizontal domain CSI will be interpreted as the vertical domain CSI, otherwise, interpreted as the second horizontal domain CSI. In another embodiment of the invention, the vertical domain CSI receiving unit 802 can be configured to interpret the content transmitted in the resource configured for the specific horizontal domain CSI based on a configuration signaling which was sent to the UE previously.

[00114] In another embodiment, the vertical domain CSI receiving unit 802 is configured to distinguish the CSI report type based on the value of the report being received. For example, if the vertical domain CSI receiving unit 802 detects a value which is reserved not to be used by the specific horizontal domain CSI, in one resource configured for the specific horizontal domain CSI transmission, then it will be interpreted as the vertical domain CSI transmission. One example of such reserved value is values 18-31 as shown in Table II. In such case, a receiving unit for detecting the indicator PTI-v is not necessary, since the value being transmitted implies a report type. Such embodiment can be applied to improve the submode 1 of the LTE Release 10 feedback mode 1-1 to support vertical domain CSI report, and a schematic diagram is depicted in Figure 5d.

[00115] In another embodiment of the invention, the vertical domain CSI receiving unit 802 is configured to receive the vertical domain CSI by receiving a part of the vertical domain CSI in each resource of the at least one of the resources, then combining the received parts to obtain a complete vertical domain CSI. Such receiving operation corresponds to an example transmission method embodiment where the vertical domain CSI is divided into multiple groups when transmitting, and each group is transmitted jointly with the specific horizontal domain CSI using one of the resources configured for the specific horizontal domain CSI transmission. Such an example can be seen in Figure 5e, and since it has been described with reference to method 400, details will be omitted here. In such embodiment, the number of groups to receive may be configured by eNB and informed to UE, or, predefined, or can be implicitly known based on some predefined rules. For example, the number of bits per group can vary depending on the payload size of the horizontal domain CSI which is to be received jointly with a group of the vertical domain CSI. One example is shown in Figure 5f, where it is assumed that the horizontal RI is the horizontal domain CSI to be transmitted jointly with the PMI-v, considering that the RI is only 2 or 3 bits, the PMI-v can be divided into 2 groups with 2 bits in each group, thus the total payload of each joint transmission is still kept to be no more than 5 bits to guarantee a satisfying performance.

[00116] In one further embodiment, the vertical domain CSI received by the vertical domain CSI receiving unit 802 is divided into multiple group by the transmitter, through dividing the vertical domain CSI into M groups then duplicating each of the M groups N times to obtain totally MxN groups, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2. Such implementation is based on the observation that the vertical feedback interval can be much larger than that of horizontal CSI. Then such method of repeating in multiple transmissions helps to improve feedback reliability. In this case, the period of vertical CSI is equal to or larger than P_h*M*N, where P_h is the period of horizontal domain CSI jointly transmitted with each group of the vertical domain CSI. It should be noted that when duplicating each of the M groups N times, it can be direct repetition, or repetition with some coding method. For example, a bit 1 can be repeated 4 times to be "1 1 1 1", or, it can be repeated to be "1 -1 1 -1", or can be any other suitable repetition pattern. Then in such embodiment, the vertical domain CSI receiving unit 802 may be further configured to perform a decoding operation or a weighted combination operation based on the repetition pattern applied.

[00117] In another embodiment of the invention, the device 800 may further comprise an adaptation unit, which is not shown in Figure 8, configured to perform adaptive configuration based on the detection results in the vertical domain CSI receiving unit 802. For example, assuming N=4, i.e., each group of information will be transmitted for 4 times, then if the receiver detects significant difference in the four transmissions before combination, for example, the "A A A B" are detected in the vertical domain CSI receiving unit 802, then the adaptation unit can judge that at least one repetition is not detected correctly, which means the second CSI transmitted together with it in the last transmission may also be corrupted. Once such transmission failure is detected, the adaptation unit may be configured to take some actions to improve the feedback performance of the second CSI, e.g., trigger an aperiodic CSI feedback.

[00118] In one or more embodiments of the invention, the vertical domain CSI is assigned with a priority level equal to that of a long term horizontal CSI, e.g., the priority level of vertical domain CSI is equal to the horizontal domain long term PMI.

[00119] 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 be also 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 7-8 may also be implemented by a single block in other embodiments.

[00120] The exemplary embodiments can store information relating to various processes described herein, e.g., store the measured CSI, the received indicator etc.. The components of the exemplary embodiments can include computer readable medium or memories according to the teachings of the present inventions, for holding data structures, tables, records, and/or other data described herein, and/or for holding program codes to be executed by a process for performing the methods described herein .

[00121] While the present inventions have been described in connection with a number of exemplary 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 for transmitting vertical domain channel state information (CSI) in a device to support 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the method comprising:

- determining whether to transmit the vertical domain CSI based on a measurement of at least the vertical domain CSI, or based on a signaling from another device; and

- if the vertical domain CSI is determined to be transmitted, transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration;

wherein the interval between the determined transmission of the vertical domain CSI and last transmission of the vertical domain CSI is larger than the period of the specific horizontal domain CSI transmission.

2. A method of Claim 1, further comprising:

- generating an indicator to indicate the determined results; and

- transmitting the indicator jointly with a first horizontal domain CSI, in a resource configured for the first horizontal domain CSI transmission.

3. A method of Claim 2, wherein generating the indicator to indicate the determined results further comprising setting a value for the indicator based on the following criterion:

- if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurements, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then setting a value to indicate that the vertical domain CSI is to be transmitted, otherwise, setting a value to indicate that the vertical domain CSI is not to be transmitted.

4. A method of Claim 2, wherein the first horizontal domain CSI indicates a first long-term precoding matrix and/or a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix or both the vertical domain long-term precoding matrix and a second rank.

5. A method of any one of Claims 1-4, wherein transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprising:

- transmitting the vertical domain CSI in a resource configured for the specific horizontal domain CSI transmission, and preventing from transmitting the specific horizontal domain CSI in the same resource.

6. A method of Claim 1, wherein transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprising:

- transmitting, in a resource configured for the specific horizontal domain CSI transmission, a value which is reserved not to be used by the specific horizontal domain CSI, so as to distinguish from the specific horizontal domain CSI transmission.

7. A method of Claim 1, wherein transmitting the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprising:

- dividing the vertical domain CSI into multiple parts, and transmitting each part jointly with the specific horizontal domain CSI in one of the resources configured for the specific horizontal domain CSI transmission.

8. A method of Claim 7, wherein dividing the vertical domain CSI into multiple parts further comprising:

- dividing the vertical domain CSI into M parts, and duplicating each of the M parts N times to obtain totally MxN parts, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2.

9. A method for receiving a vertical domain channel state information (CSI) from a second device to support a 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the method comprising:

- determining whether to receive the vertical domain CSI based on an indicator from the second device, or based on a configuration signaling previously sent to the second device; and

- if the vertical domain CSI is determined to be received, receiving the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration;

wherein the interval between the determined receiving of the vertical domain CSI and last reception of the vertical domain CSI is larger than the period for the specific horizontal domain CSI transmissions configured for the second device.

10. A method of Claim 9, further comprising:

- receiving the indicator which is jointly transmitted with a first horizontal domain CSI in a resource configured for the first horizontal domain CSI transmission.

11. A method of Claim 10, wherein the indicator is set by the second device based on following criterion:

- if both a first variation in the first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then setting the indicator to indicate that the vertical domain CSI is to be transmitted, otherwise, setting the indicator to indicate that the vertical domain CSI is not to be transmitted.

12. A method of Claim 10, wherein the first horizontal domain CSI indicates a first long-term precoding matrix and or a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix or both the vertical domain long-term precoding matrix and a second rank.

13. A method of any one of Claims 9-12, wherein receiving the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprising:

- receiving the vertical domain CSI in a resource configured for a specific horizontal domain CSI transmission, and preventing from detecting the specific horizontal domain CSI in the same resource.

14. A method of any one of Claims 9-12, wherein receiving the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprising:

- if receiving a value which is reserved not to be used by the specific horizontal domain CSI in the at least one of the resources configured for the specific horizontal domain CSI transmission, interpreting the value as the vertical domain CSI transmission.

15. A method of Claim 9, wherein receiving the vertical domain CSI in at least one of the resources configured for a specific horizontal domain CSI transmission comprising:

- receiving a part of the vertical domain CSI in each resource of the at least one of the resources and,

- combining the received parts to obtain a complete vertical domain CSI,

wherein the vertical domain CSI is divided into multiple parts by the second device when transmitting, and each part is transmitted jointly with the specific horizontal domain CSI in one of the resources configured for the specific horizontal domain CSI transmission.

16. A method of Claim 15, wherein the vertical domain CSI is divided into M parts and each of the M parts is duplicated N times to obtain totally MxN parts when transmitting, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2.

17. A device for transmitting vertical domain channel state information (CSI) to support a 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the device comprising:

- determination unit, configured to determine whether to transmit the vertical domain CSI based on a measurement of at least the vertical domain CSI, or based on a signaling from another device; and

- vertical domain CSI transmission unit, configured to transmit the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission, if the vertical domain CSI is determined to be transmitted, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration;

wherein the interval between the determined transmission of the vertical domain CSI and last transmission of the vertical domain CSI is larger than the period for the specific horizontal domain CSI transmissions.

18. A device of Claim 17, further comprising:

- indicator generation unit, configured to generate an indicator to indicate the determined results; and

- indicator transmission unit, configured to transmit the indicator jointly with a first horizontal domain CSI, in a resource configured for the first horizontal domain CSI transmission.

19. A device of Claim 17, wherein Indicator generation unit is configured to set a value of the indicator based on the following criterion:

- if both a first variation in a first horizontal domain CSI and a second variation in the vertical domain CSI are detected via measurement, wherein the first variation indicates a need for reporting the first horizontal domain CSI and the second variation indicates a need for reporting the vertical domain CSI, then setting a value to indicate that the vertical domain CSI is to be transmitted, otherwise, setting a value to indicate that the vertical domain CSI is not to be transmitted.

20. A device of Claim 18, wherein the first horizontal domain CSI indicates a first long-term precoding matrix and/or a first rank , and the vertical domain CSI indicates a vertical domain long term precoding matrix or both the vertical domain long-term precoding matrix and a second rank.

21. A device of any one of Claims 17-20, wherein the vertical domain CSI transmission unit is configured to:

- transmit the vertical domain CSI in a resource configured for a specific horizontal domain CSI transmission, and prevent from transmitting the specific horizontal domain CSI in the same resource.

22. A device of Claim 17, wherein the vertical domain CSI transmission unit is configured to:

- transmit in one resource configured for the specific horizontal domain CSI transmission a value which is reserved not to be used by the specific horizontal domain CSI, so as to distinguish from the specific horizontal domain CSI transmission.

23. A device of Claim 17, wherein the vertical domain CSI transmission unit is configured to:

- divide the vertical domain CSI into multiple parts, and transmit each part jointly with the specific horizontal domain CSI in one of the resources configured for the specific horizontal domain CSI transmission.

24. A device of Claim 23, wherein dividing the vertical domain CSI into multiple parts further comprising:

25. A device for receiving a vertical domain channel state information (CSI) from a second device to support a 3-dimension (3D) multiple-input-multiple-output (MIMO) operation in a wireless network, the device comprising:

- determination unit, configured to determine whether to receive the vertical domain CSI based on an indicator from the device, or based on a configuration signaling previously sent to the second device; and

- vertical domain CSI receiving unit, configured to receive the vertical domain CSI in at least one of the resources previously configured for a specific horizontal domain CSI transmission, if the vertical domain CSI is determined to be received, so as to avoid dedicated signaling for the vertical domain CSI feedback resource configuration;

26. A device of Claim 25, further comprising:

- indicator receiving unit, configured to receive the indicator which is jointly transmitted with a first horizontal domain CSI in a resource configured for the first horizontal domain CSI transmission.

27. A device of Claim 26, wherein the indicator is set by the second device based on following criterion:

28. A device of Claim 26, wherein the first horizontal domain CSI indicates a first long-term precoding matrix and/or a first rank, and the vertical domain CSI indicates a vertical domain long term precoding matrix, or both the vertical domain long-term precoding matrix and a second rank.

29. A device of any one of Claims 25-28, wherein the vertical domain CSI receiving unit is configured to:

- receive the vertical domain CSI in a resource configured for a specific horizontal domain CSI transmission, and prevent from detecting the specific horizontal domain CSI in the same resource.

30. A device of Claims 25, wherein the vertical domain CSI receiving unit is configured to:

- if detecting a value which is reserved not to be used by the specific horizontal domain CSI in the at least one of the resources configured for the specific horizontal domain CSI transmission, then interpret the value as the vertical domain CSI transmission.

31. A device of Claim 25, wherein the vertical domain CSI receiving unit is configured to:

- receive a part of the vertical domain CSI in each resource of the at least one of the resources, and

- combine to obtain a complete vertical domain CSI,

32. A device of Claim 31, wherein the vertical domain CSI is divided into M parts and each of the M parts is duplicated N times to obtain totally MxN parts when transmitting, wherein M is an integer equal to or larger than 1 and N is an integer equal to or larger than 2.