Method, mobile terminal, base station, and system for reporting best companion precoding matrix index in communication system with double codebook

A method, mobile terminal, and system for reporting BCI are provided, the method comprises the steps of: obtaining a PMI W1 set and a PMI W2 to be used for a mobile terminal based on a double codebook; computing a BCI W1 set to be used for another mobile terminal based on the PMI W1 set; selecting a BCI W2 from the BCI W1 set based on the PMI W2; and reporting the BCI W1 set and the BCI W2 to a base station,

TECHNICAL FIELD

The present disclosure is related to Multiple-Input-Multiple-Output (MIMO)/beam-forming technology in a multi-user communication system.

BACKGROUND

Multi-User (MU)-MIMO is an important means to increase peak data rate and spectral efficiency in the current wireless communication. To facilitate MU-MIMO operation, advanced feedback schemes are being considered in 4G wireless standards, such as LTE-A. One of those advanced feedback schemes is BCI (best companion PMI (pre-coding matrix index)) reporting.

In LTE Rel-8, PMI is adopted for Single-User (SU)-MIMO, i.e., the UE reports the most preferred pre-coding matrix to be used for the UE itself. PMI reporting is useful. Further, with BCI reporting, the UE also reports the most preferred pre-coding matrix to be used for the possibly co-scheduled UE.

FIG. 1shows a schematic diagram that the UE feedbacks to a base station the most preferred PMI to be used for itself and the most preferred BCI to be used for possibly co-scheduled UE. As shown in theFIG. 1, a wireless communication system100may comprise a mobile terminal (UE)101and a base station103, in which the mobile terminal101reports to the base station103the most preferred PMI to be used for itself and the most preferred BCI to be used for a possibly co-scheduled UE (another mobile terminal)102. Similar to the PMI/CQI reporting pair, BCI reporting can be accompanied by a delta CQI, which indicates the CQI degradation due to the co-scheduled UE that adopts the reported BCI as its PMI.

In the LTE-advanced standardization, a double codebook structure for the PMI reporting of 8Tx antenna (eNB-base station) is agreed. The rank one pro-coding vector of the double codebook is in the form of [viTk·viT]T, where i ε {0, 1, 2, . . . 31}, and k ε {1, −1, j, −j}. The vector viis a 4×1 column vector, which can be expressed as:

vi=[1exp⁡(j⁢ⅈ·2⁢π32)exp⁡(j⁢2·ⅈ·2⁢π32)exp⁡(j⁢3·ⅈ·2⁢π32)],
where j denotes the imaginary unit.

FIG. 2shows a diagram of the agreed double codebook structure of the rank one used for the PMI reporting of 8Tx antenna. It is seen that the rank one codebook represents the combination of DFT (Discrete Fourier Transform) beam (component) and co-phasing factors. However, the reporting of DFT beam index and co-phasing factors is not to simply report the above two things. Instead, a two-level report corresponding to the double codebook is adopted: the UE firstly feedbacks a rough knowledge of PMI (a long-term/wideband component, W1), which indicates to the base station that possible pre-coding vectors are in a DFT direction {0, 1, 2, 3} when W1=0, and the co-phasing factors can be {1, −1, j, −j}. W1is a four-bit signal because there is overlapping of the possible pre-coding vectors between {W1=0} and {W1=1}. After W1is reported, the UE further reports another more accurate knowledge of PMI (a short-term/narrowband component, W2), which indicates to the base station that the exact pre-coding vector is in the set confined by W1. In theFIG. 2, the possible DFT beam indexes in case of W1=0 is from v0to v3, the possible DFT beam indexes in case of W1=1 is from v2to v5, the possible pre-coding vectors when W1=2 is from v4to v7, . . . , the possible DFT beam indexes in case of W1=14 is from v28to v31, and the possible DFT bean indexes in case of W1=15 includes v30, v31, V0, and V1.

The advantage of the double codebook is to better exploit the continuity of the pre-coding vectors in the time/frequency domain, so either the overhead can be improved comparing with a 7-bit single codebook design without significant loss of reporting accuracy.

An important feature of the agreed double codebook is that the adjacent DFT beams (in terms of index) are also adjacent in terms of their directionality.

FIG. 3shows a diagram of the directionality of the DFT beams.

As shown in theFIG. 3, when w1=0, the adjacent DFT beams v0, v1, v2, v3are also adjacent in their directionality.

Because the BCI is calculated based on the PMI assumption, how to report the BCI in conjunction with the double codebook based PMI is a problem.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a method of reporting BCI in a wireless communication system is provided, the method comprises the steps of: obtaining a PMI W1set and a PMI W2to be used for a mobile terminal based on a double codebook; computing a BCI W1set to be used for another mobile terminal based on the PMI W1set; and reporting the BCI W1set to a base station, wherein W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI.

In the above aspect, the BCI W1set is reported on a relatively long interval.

In the above aspect, the method of reporting BCI further comprises steps of: selecting a BCI W2from the BCI W1set based on the PMI W2, and reporting the BCI W2to the base station.

In the above aspect, the BCI W1set is reported on a relatively long interval, BCI W2is reported on a relatively short interval.

In the above aspect, the BCI W1set and the BCI W2are reported both on relatively short interval.

In the above aspect, the method further comprises a step of shifting the BCI W1set based on the PMI W2.

In the above aspect, the BCI W1set is reported on a long time interval, the BCI W2is reported on a short time interval.

In the above aspect, the double codebook is a combination of DFT components and co-phasing factors, the DFT components are represented by a plurality of columns of vectors, and the co-phasing factors are represented by [1, −1, j, −j].

In the above aspect, the method further comprises a step of: if the PMI W2is located on the left side column of the PMI W1set, shifting the BCI W1set to its left side, and if the PMI W2is located on the right side column of the PMI W1set, shifting the BCI W1set to its right side.

In the above aspect, the method further comprises a step of shifting the BCI W1set by one or two columns of the vectors.

In the above aspect, the method further comprises a step of confining the co-phasing factors of the BCI W1set, wherein, if the PMI W2has co-phasing factors within [1, −1], the co-phasing factors of the BCI W1set are confined to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the co-phasing factors of the BCI W1set are confined to [j, −j]. In the above aspect, the BCI W2is orthogonal to the PMI W2.

In another aspect of the present disclosure, a mobile terminal for reporting BCI to a base station in a wireless communication system is provided, the mobile terminal comprises: an obtaining unit which obtains a PMI W1set and a PMI W2based on a double codebook; a computation unit which computes a BCI W1set to be used for another mobile terminal based on the PMI W1set; and a reporting unit which reports the BCI W1set to the base station, wherein, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI.

In the above another aspect, the BCI W1set is reported on a relatively long interval.

In the above another aspect, the mobile terminal further comprises a selection unit which selects a BCI W2from the BCI W1set based on the PMI W2. The reporting unit reports the BCI W2to the base station.

In the above another aspect, the BCI W1set is reported on a relatively long interval, and BCI W2is reported on a relatively short interval.

In the above another aspect, the BCI W1set and the BCI W2are reported both on relatively short interval.

In the above another aspect, the mobile terminal further comprises a shifting unit which shifts the BCI W1set based on the PMI W2. The shifting unit shifts the BCI W1set to its left side if the PMI W2is located on the left side column of the PMI W1set, and shifts the BCI W1set to its right side if the PMI W2is located on the right side column of the PMI W1set. The shifting unit shifts the BCI W1set by one or two columns of the vectors. The shifting unit further confines the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit confines the co-phasing factors of the BCI W1set to [j, −j]. The BCI W2selected from the BCI W1set is orthogonal to the PMI W2.

In a further aspect of the present disclosure, a base station for receiving BCI (best companion PMI (pre-coding matrix index)) from a mobile terminal in a wireless communication system is provided, which comprises: a receiving unit which receives a PMI W1set, a PMI W2, and a BCI W1set from the mobile terminal, which are generated based on a double codebook; and a pre-coding unit which pre-codes data to be sent to another mobile terminal with the BCI W1set, wherein, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI.

In the above further aspect, the receiving unit further receives a BCI W2from the mobile terminal, wherein the BCI W1set is shifted by the mobile terminal based on the PMI W2, and the BCI W2is selected by the mobile terminal from the shifted BCI W1set based on the PMI W2.

In the above further aspect, the BCI W1set is received on a relatively long interval, and BCI W2is received on a relatively short interval.

In the above further aspect, the base station further comprises a shifting unit which shifts the BCI W1set based on the received PMI W2. The shifting unit shifts the BCI W1set to its left side if the PMI W2is located on the left side column of the PMI W1set, and shifts the BCI W1set to its right side if the PMI W2is located on the right side column of the PMI W1set. The shifting unit shifts the BCI W1set by one or two columns of the vectors. The shifting unit further confines the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit confines the co-phasing factors of the BCI W1set to [j, −j]. The BCI W2selected from the BCI W1set is orthogonal to the PMI W2.

In another further aspect of the present disclosure, a wireless communication system for reporting BCI from a mobile terminal to a base station is provided, wherein the mobile terminal comprises: an obtaining unit which obtains a PMI W1set and a PMI W2based on a double codebook; a computation unit which computes a BCI W1set to be used for another mobile terminal based on the PMI W1set; a selection unit which selects a BCI W2from the BCI W1set based on the PMI W2; and a reporting unit which reports the BCI W1set and the BCI W2to the base station, wherein, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI. The said base station comprises: a receiving unit which receives a PMI W1set, a PMI W2, a BCI W1set and a BCI W2from the mobile terminal, which are generated based on a double codebook; and a pre-coding unit which pre-codes data to be sent to another mobile terminal with the BCI W1set, wherein, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI.

In the above other further aspect, the mobile terminal in the wireless communication system further comprises a shifting unit which shifts the BCI W1set based on the PMI W2. The shifting unit shifts the BCI W1set to its left side if the PMI W2is located on the left side column of the PMI W1set, and shifts the BCI W1set to its right side if the PMI W2is located on the right side column of the PMI W1set. The shifting unit shifts the BCI W1set by one or two columns of the vectors. The shifting unit further confines the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit confines the co-phasing factors of the BCI W1set to [j, −j]. The BCI W2selected from the BCI W1set is orthogonal to the PMI W2.

In the above other further aspect, the base station in the wireless communication system further comprises a shifting unit which shifts the BCI W1set based on the received PMI W2. The shifting unit shifts the BCI W1set to its left side if the PMI W2is located on the left side column of the PMI W1set, and shifts the BCI W1set to its right side if the PMI W2is located on the right side column of the PMI W1set. The shifting unit shifts the BCI W1set by one or two columns of the vectors. The shifting unit further confines the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit confines the co-phasing factors of the BCI W1set to [j, −j]. The BCI W2selected from the BCI W1set is orthogonal to the PMI W2.

With the method, mobile terminal, and wireless communication system of the present disclosure, the probability that the optimal BCI W2is included in the shifted BCI W1set is increased, and the overhead for feeding-back the BCI is reduced.

The foregoing is a summary and thus contains, by necessity, simplifications, generalization, and omissions of details; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matters described herein will become apparent in the teachings set forth herein. The summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

DETAILED DESCRIPTION

The disclosure is drawn, inter alia, to methods, mobile terminals, base stations, and wireless communication systems for reporting the BCI.

FIG. 4shows a block diagram of a mobile terminal for reporting the BCI according to one embodiment of the present disclosure.

As shown in theFIG. 4, the mobile terminal400according to one embodiment of the present disclosure may comprise: an obtaining unit401, a computation unit402, and a reporting unit404which are connected with each other.

According to another embodiment of the present disclosure, the mobile terminal400may further comprise a selection unit403and/or a shifting unit405.

The mobile terminal400according to one embodiment of the present disclosure may further comprise: a central process unit (CPU)410which is used to execute relevant programs to process various kinds of data, and to control the operations of each unit included in the mobile terminal400; a read only memory (ROM)413which is used to store various programs required for the CPU410to execute various operations and controls; a random access memory (RAM)415which is used to store various data produced in the procedure of the CPU410executing operations and controls; an input/output unit (I/O)417which is used to connect with external devices, and transmit various data between the external devices and the mobile terminal400, etc. The above obtaining unit401, computation unit402, selection unit403, reporting unit404, shifting unit405, CPU410, ROM413, RAM415, and I/O unit417may be connected with each other via a data/command bus420, and transmit signals with each other.

The above units do not limit the scope of the present disclosure. According to one embodiment of the present disclosure, the functions of the obtaining unit401, computation unit402, selection unit403, reporting unit404, and shifting unit405can be realized by software in combination with the CPU410, ROM413, RAM415, and I/O unit417. Further, the obtaining unit401, computation unit402, selection unit403, reporting unit404, and shifting unit405can be realized by combining into one unit.

According to one embodiment of the present disclosure, the above units of the mobile terminal400for reporting BCI to a base station in a wireless communication system are operated as: the obtaining unit401obtains a PMI W1set and a PMI W2based on a double codebook, the computation unit402computes a BCI W1set to be used for another mobile terminal based on the PMI W1set, and the reporting unit404reports the BCI W1set to the base station, wherein, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI. Here, the other mobile terminal is possibly co-scheduled with the mobile terminal400in the wireless communication system.

FIG. 5shows a schematic diagram of the operations of the mobile terminal for reporting the BCI according to one embodiment of the present disclosure.

As shown in theFIG. 5, when the PMI W1set is generated and reported in a sub-frame (the uplink control channel) or in a report (the uplink data channel), a corresponding BCI W1set is calculated based on the generated PMI W1set, and the generated BCI W1set is reported to the base station with a sub-frame or with a report too. The BCI W1set is reported to the base station on a relatively long interval.

FIG. 6shows a schematic diagram of the operations of the mobile terminal for reporting the BCI based on the double codebook according to another embodiment of the present disclosure.

According to the present embodiment, the mobile terminal400for reporting the BCI based on the double codebook reuses the double codebook structure. In other words, the BCI reporting is based on the double codebook structure as well, where the BCI W1set is calculated based on the PMI W1set, and the BCI W2is selected from the BCI W1set based on the PMI W2.

As shown in theFIG. 6, when the PMI W1set is generated and reported in a sub-frame (the uplink control channel) or in a report (the uplink data channel), a corresponding BCI W1set is calculated based on the generated PMI W1set, and the generated BCI W1set is reported to the base station with a sub-frame or with a report too. In the subsequent sub-frame or report, the PMI W2is generated and reported to the base station. The selection unit403of the mobile terminal400selects a corresponding BCI W2from the BCI W1set based on the generated PMI W2, and the reporting unit404reports the generated BCI W2to the base station. According to the present embodiment, the reporting unit404reports the BCI W1set to the base station on a relatively long interval, and reports the BCI W2to the base station on a relatively short interval. According to the present embodiment, the BCI W1set is reported to the base station on a relatively long interval, and BCI W2is reported to the base station on a relatively short interval.

FIG. 7shows a schematic diagram of the operations of the mobile terminal for reporting the BCI according to a further embodiment of the present disclosure.

As shown in theFIG. 7, the PMI W1set is generated and reported in a sub-frame (the uplink control channel) or in a report (the uplink data channel). In the subsequent sub-frame or report, the PMI W2is generated and reported to the base station. A corresponding BCI W1set is calculated based on the generated PMI W1set, and the selection unit403of the mobile terminal400selects a corresponding BCI W2from the BCI W1set based on the generated PMI W2, and the reporting unit404reports both the generated BCI W1set and the BCI W2to the base station. According to the present embodiment, the reporting unit404reports the BCI W1set and the BCI W2to the base station both on a relatively short interval.

Hereinafter, more detailed analysis of BCI calculation process based on the double codebook will be provided.

FIG. 8shows an example of BCI calculation the double codebook according to one embodiment of the present disclosure.

As shown in theFIG. 8, the double codebook is a combination of DFT components and co-phasing factors, the DFT components are represented by a plurality of columns of vectors “v0, v1, v2, v3, . . . v31”, and co-phasing factors are represented by [1, −1, j, −j]. The resultant precoding vector corresponds to the form [v1T−v1T]T, if reported DFT beam and co-phasing factors are v1and −1, respectively, where T denotes vector transpose. The person skilled in the art should be able to generalize the above example to any combination of DFT component and co-phasing factors without any difficulty.

Similar to the PMI calculation process, the double codebook BCI calculation is a two stage process. Specifically, in the first stage, given that the reported PMI W1is 0, which is in the direction {0, 1, 2, 3} with co-phasing factors {1, −1, j, −j}, and the BCI W1set is calculated to be, for example, 4. An important observation is that BCI W1set is calculated based on the “average” of the multiple possible PMI W2sin the set W1=0. However, it is noted that the BCI W1set calculated based on the PMI W1set is rough information of the PMI, so the BCI W1set is not optimal.

In the second stage, the short-term/narrowband BCI (W2) is selected from the BCI W1set based on the knowledge of PMI W2. It should be noted that the BCI W2reported to the base station is selected from the BCI W1set based on the PMI W2, i.e., the possible BCI W2are in the direction {8, 9, 10, 11} with co-phasing factors {1, −1, j, −j}. In other words, the reported BCI W2is searched for inside the BCI W1set.

For example, in theFIG. 8, given that the PMI W2corresponds to the direction {0} and co-phasing factor {1}, which is on the left side of the “average” of the pre-coding vectors of the PMI W1set (W1=0). Because the BCI W1set is calculated based on the “average” of the pre-coding vectors of the PMI W1set, and an optimal BCI W2may be calculated based on the PMI W2, possibly the optimal BCI W2may not be in the BCI W1set. Therefore, the BCI W2selected from the BCI W1set and reported to the base station sometimes is not the optimal BCI W2, and causes performance degradation.

FIG. 9shows an example of shifting the BCI W1set in the BCI calculation according to one embodiment of the present disclosure.

To resolve the above problem of possibly the optimal BCI W2being not within the BCI W1set, the present disclosure proposes to shift the BCI W1set based on the PMI W2. Therefore, according to one embodiment of the present disclosure, the mobile terminal400further comprises a shifting unit405which shifts the BCI W1set based on the PMI W2. For example, if the PMI W2is on the left side column of the vectors of the PMI W1set, the shifting unit405shifts the BCI W1set to its left side. Similarly, if the PMI W2is on the right side column of the vectors of the PMI W1set, the shifting unit405shifts the BCI W1set to its right side. As shown in theFIG. 9, after the shifting operation, the BCI W1set indicated as W1=3 may be used as the shifted BCI W1set indicated as W1=4, though the current BCI W1set corresponds to W1=4.

As shown in theFIG. 9, given that the PMI W1set is W1=0, and the BCI W1set is calculated to be W1=4, and further given that the actual PMI W2corresponds to the direction {0} and co-phasing factor {1}, which is located on the upper-left side of the PMI W1set indicated as W1=0, then the optimal BCI W2is calculated based on the actual PMI W2to correspond to the direction {7} and co-phasing factor {−1}. In this connection, the calculated optimal BCI W2is not located within the calculated BCI W1set indicated as W1=4, so the BCI W2selected from the BCI W1set indicated as W1=4 and reported to the base station will not be the optimal BCI W2. However, according to the embodiment as shown in theFIG. 9, since the actual PMI W2is located on the left side of the averaged PMI W1set indicated as W1=0, the BCI W1set indicated as W1=4 is shifted to its left side to obtain the shifted BCI W1set, which is indicated as W1=3. After the shifting operation, the optimal BCI W2corresponding to the direction {7} and co-phasing factor {−1} is located within the shifted BCI W1set indicated as W1=3, so the optimal BCI W2can be selected from the shifted BCI W1set indicated as W1=3, and reported to the base station.

According to one embodiment of the present disclosure, the BCI W1set may be shifted by one or two columns of the vectors. For example, similar to theFIG. 9, it is possible to shift just one column to the left side if the PMI W2is on the left side of the averaged PMI W1set. In this case, the shifted BCI W1set does not correspond to any PMI W1set, but it takes a better tradeoff between the actual PMI W2and the averaged PMI W1set than the two columns shifting.

FIG. 10shows an example of shifting the BCI W1set by considering the co-phasing factors in the BCI calculation according to a further embodiment of the present disclosure.

According to a further embodiment of the present disclosure, it is possible to further confine the BCI co-phasing factors according to the actual PMI W2value. For example, the shifting unit405may further confine the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit405confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit405confines the co-phasing factors of the BCI W1set to [j, −j].

Specifically, as shown in theFIG. 10, given that the PMI W1set is W1=0, and the BCI W1set is calculated to be W1=4, and further given that the actual PMI W2corresponds to the direction {0} and co-phasing factor {1}, which is located on the upper-left side of the PMI W1set (W1=0). Since the actual PMI W2is located on the left side of the averaged PMI W1set (W1=0), so the BCI W1set (W1=4) is shifted to its left side by one column or two columns to obtain the shifted BCI W1set. According to the present embodiment, since the actual PMI W2is located on the upper side of the PMI W1set (W1=0), i.e., the actual PMI W2has co-phasing factor within [1, −1], the shifted BCI W1set is more restricted by confining the co-phasing factors to [1, −1]. Similarly, if the actual PMI W2is located on the lower side of the PMI W1set (W1=0), i.e., the actual PMI W2has co-phasing factors within [j, j], the shifted BCI W1set is more restricted by confining the co-phasing factors to [j, j]. In such a case, not only the possibility of including the optimal BCI W2in the shifted BCI W1set is increased, but also the overhead for feeding-back the BCI W2is reduced, e.g., from 4 bits to 3 bits.

In another embodiment, the BCI W2may be selected from the BCI W1set so that the BCI W2is orthogonal to the PMI W2. For example, If PMI W1set is determined as W1=0, then the possible BCI W1set are calculated as W1=4, or 8, or 12. In this case, If PMI W2is determined as having vector of v0and co-phasing factor of [1], the BCI W1set is shifted to its left side by one column. At this time, if the BCI W2is selected as orthogonal to the PMI W2, the overhead for reporting the BCI W1set will be reduced to 2 bits (original 4 bits), and the overhead for reporting the BCI W2will be reduced to 3 bits (original 4 bits).

According to one embodiment of the present disclosure, a shifting unit may not be installed in the base station side, and the schema of how to shift the BCI W1set and confine the co-phasing factors is explicitly signaled from the mobile terminal to the base station. In such a way, the reporting unit at the mobile terminal not only reports PMI W1, PMI W2, BCI W1set, and BCI W2, but also reports how the BCI W1set is shifted/confined from the original BCI W1set. Furthermore, when the reporting unit of the mobile terminal reports the BCI W1set to the base station as well as the signaling indicating shifting/confining information, both of the base station and the mobile terminal will know how to shift the BCI W1set and confine the co-phasing factors, so can select the BCI W2from the shifted BCI W1set with the same schema. However, according to another embodiment of the present disclosure, the shifting unit may be installed in the base station. In such a way, there is no explicit signaling from the mobile terminal to the base station to indicate how to shift/confine the BCI W1set. Furthermore, when the mobile terminal reports the BCI W1set to the base station, the shifting unit at the base station will derive the shifted/confined BCI W1set based on the knowledge of PMI W2. In this case (shifting unit installed at the base station), in general, the shifting units in the mobile terminal and base station should maintain the same shifting/confining rules (i.e., same PMI W2value should result the same shifting/confining in shifting units in both base station and mobile terminal). In both cases (base station shifting unit is installed or not), it is commonly understood between the mobile terminal and the base station that the reported BCI W2is selected from the shifted/confined BCI W1set but not the original BCI W1set.

FIG. 11shows a flow chart of a method of reporting the BCI in a wireless communication system according to one embodiment of the present disclosure.

As shown in theFIG. 11, in the step S1101, a PMI W1set and a PMI W2to be used for a mobile terminal are obtained based on a double codebook. In the step S1102, a BCI W1set to be used for another mobile terminal is calculated based on the PMI W1set. In the step S1103, the BCI W1set is reported to a base station. Here, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI. The BCI W1set may be reported to the base station on a relatively long interval.

According to one embodiment of the present disclosure, the above step S1101can be executed by the obtaining unit401, the above step S1102can be executed by the computation unit402, the above step S1103can be executed by the reporting unit404.

According to another embodiment of the present disclosure, the method of reporting BCI further comprises steps of selecting a BCI W2from the BCI W1set based on the PMI W2; and reporting the BCI W2to the base station. The above steps can be executed by the selection unit403and the reporting unit405, respectively. The BCI W1set may be reported on a relatively long interval, and the BCI W2may be reported on a relatively short interval. Alternatively, the BCI W1set and the BCI W2are reported both on relatively short interval.

FIG. 12shows a flow chart of a method of reporting the BCI in a wireless communication system according to another embodiment of the present disclosure.

As shown in theFIG. 12, in the step S1201, a PMI W1set and a PMI W2to be used for a mobile terminal are obtained based on a double codebook. In the step S1202, a BCI W1set to be used for another mobile terminal is calculated based on the PMI W1set. In the step S1203, a BCI W2is selected from the BCI W1set based on the PMI W2. In the step S1204, the BCI W1set and the BCI W2are reported to a base station. Here, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI.

According to one embodiment of the present disclosure, the above step S1201can be executed by the obtaining unit401, the above step S1202can be executed by the computation unit402, the above step S1203can be executed by the selection unit403, and the above step S1204can be executed by the reporting unit404.

According to another embodiment of the present disclosure, the method of reporting BCI further comprises a step of shifting the BCI W1set based on the PMI W2. The above step can be executed by the shifting unit405.

According to another embodiment of the present disclosure, the method of reporting BCI further comprises a step of reporting the BCI W1set on a long time interval, and reporting the BCI W2on a short time interval. The above step can be executed by the reporting unit404.

According to another embodiment of the present disclosure, the double codebook is a combination of DFT components and co-phasing factors, the DFT components are represented by a plurality of columns of vectors, and the co-phasing factors are represented by [1, −1, j, −j].

According to another embodiment of the present disclosure, the method of reporting BCI further comprises steps of: if the PMI W2is located on the left side column of the PMI W1set, shifting the BCI W1set to its left side, and if the PMI W2is located on the right side column of the PMI W1set, shifting the BCI W1set to its right side. The above step can be executed by the shifting unit405.

According to another embodiment of the present disclosure, the method of reporting BCI further comprises a step of: shifting the BCI W1set by one or two columns of the vectors. The above step can be executed by the shifting unit405.

According to another embodiment of the present disclosure, the method of reporting BCI further comprises a step of: confining the co-phasing factors of the BCI W1set, wherein, if the PMI W2has co-phasing factors within [1, −1], the co-phasing factors of the BCI W1set is confined to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the co-phasing factors of the BCI W1set is confined to [j, −j]. The above step can be executed by the shifting unit405.

According to another embodiment of the present disclosure, the BCI W2selected from the shifted BCI W1set, where the BCI W2is constraint to be orthogonal to the PMI W2.

FIG. 13shows a block diagram of a base station for receiving the BCI from a mobile terminal according to one embodiment of the present disclosure.

As shown in theFIG. 13, the base station1300according to one embodiment of the present disclosure may comprise: a receiving unit1301and a pre-coding unit1302which are connected with each other.

According to another embodiment of the present disclosure, the base station1300may further comprise a selection unit1306and/or a shifting unit1307.

The base station1300according to one embodiment of the present disclosure may further comprise: a central process unit (CPU)1310which is used to execute relevant programs to process various kinds of data, and to control the operations of each unit included in the base station1300; a read only memory (ROM)1313which is used to store various programs required for the CPU1310to execute various operations and controls; a random access memory (RAM)1315which is used to store various data produced in the procedure of the CPU1310executing operations and controls; an input/output unit (I/O)1317which is used to connect with external devices, and transmit various data between the external devices and the base station1300, etc. The above receiving unit1301, pre-coding unit1302, selection unit1306, shifting unit1307, CPU1310, ROM1313, RAM1315, and I/O unit1317may be connected with each other via a data/command bus1320, and transmit signals with each other.

The above units do not limit the scope of the present disclosure. According to one embodiment of the present disclosure, the functions of the receiving unit1301, pre-coding unit1302, selection unit1306, and shifting unit1307can be realized by software in combination with the CPU1310, ROM1313, RAM1315, and I/O unit1317. Further, the receiving unit1301, pre-coding unit1302, selection unit1306, and shifting unit1307can be realized by combining into one unit.

According to one embodiment of the present disclosure, the above units of the base station1300for receiving BCI from a mobile station in a wireless communication system are operated as: the receiving unit1301receives a PMI W1set, a PMI W2, and a BCI W1set from the mobile terminal, wherein the PMI W1set, PMI W2, and BCI W1set are generated based on a double codebook; the pre-coding unit1302pre-codes data to be sent to another mobile terminal with the BCI W1set, wherein, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI. Here, the other mobile terminal is possibly co-scheduled with the mobile terminal in the wireless communication system.

According to one embodiment of the present disclosure, the receiving unit1301further receives a BCI W2from the mobile terminal, wherein the BCI W1set is shifted by the mobile terminal based on the PMI W2, and the BCI W2is selected by the mobile terminal from the shifted BCI W1set based on the PMI W2. According to one embodiment of the present disclosure, the BCI W1set is received on a relatively long interval. According to one embodiment of the present disclosure, the BCI W1set is received on a relatively long interval, and BCI W2is received on a relatively short interval. According to one embodiment of the present disclosure, the BCI W1set and the BCI W2are received both on relatively short interval.

According to one embodiment of the present disclosure, the selection unit1306selects the BCI W2from the BCI W1set based on the PMI W2. Here, the BCI W2is preferred to be orthogonal to the PMI W2.

According to one embodiment of the present disclosure, the shifting unit1307shifts the BCI W1set based on the PMI W2. In the present disclosure, the double codebook is a combination of DFT components and co-phasing factors, the DFT components are represented by a plurality of columns of vectors, and the co-phasing factors are represented by [1, −1, j, −j]. According to one embodiment of the present disclosure, the shifting unit1307shifts the BCI W1set to its left side if the PMI W2is located on the left side column of the PMI W1set, and shifts the BCI W1set to its right side if the PMI W2is located on the right side column of the PMI W1set. Further, the shifting unit1307can shift the BCI W1set by one or two columns of the vectors. According to one embodiment of the present disclosure, the shifting unit1307further confines the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit confines the co-phasing factors of the BCI W1set to [j, −j].

According to one embodiment of the present disclosure, the shifting unit1307is installed in the base station, and the shifting unit405can be configured with the same schema of how to shift the BCI W1set and confine the co-phasing factors in advance. In such a way, when the mobile terminal reports the BCI W1set to the base station, both of the base station and the mobile terminal will know how to shift the BCI W1set and confine the co-phasing factors, so can select the BCI W2from the shifted BCI W1set with the same schema consistently between the base station and the mobile terminal. However, according to another embodiment of the present disclosure, the shifting unit1307may not be installed in the base station. In such a way, when the mobile terminal reports the BCI W1set to the base station, the mobile terminal will additionally report to the base station how the BCI W1set is shifted compared with original BCI W1set. In this case, the base station receiving unit not only receives PMI W1, PMI W2, BCI W1, BCI W2, but also receives the addition signaling regarding the shifting/confining schema. In both cases (shifting unit is installed or not), it is commonly understood between the mobile terminal and the base station that the reported BCI W2is selected from the shifted/confined BCI W1set but not the original BCI W1set. Thus, the base station can receive the signaling to get the preferred BCI W2, and potentially pre-code the data of the co-scheduled mobile terminal with the preferred BCI W2.

According to one embodiment of the present disclosure, in theFIG. 1, the mobile terminal101included in the wireless communication system100can be realized as the mobile terminal400according to the present disclosure, wherein the mobile terminal400comprises: an obtaining unit401which obtains a PMI W1set and a PMI W2based on a double codebook, a computation unit402which computes a BCI W1set to be used for another mobile terminal based on the PMI W1set, a selection unit403which selects a BCI W2from the BCI W1set based on the PMI W2, and a reporting unit404which reports the BCI W1set and the BCI W2to the base station. Here, W1indicates a long-term or wideband component of the PMI and BCI, and W2indicates a short-term or narrowband component of the PMI and BCI. The other mobile terminal is possibly co-scheduled with the mobile terminal in the wireless communication system.

Further, the mobile terminal400included in the wireless communication system100can further comprise a shifting unit405which shifts the BCI W1set based on the PMI W2. Specifically, the reporting unit404reports the BCI W1set on a long time interval, and reports the BCI W2on a short time interval. The double codebook is a combination of DFT components and co-phasing factors, the DFT components are represented by a plurality of columns of vectors, the co-phasing factors are represented by [1, −1, j, −j]. The shifting unit405shifts the BCI W1set to its left side if the PMI W2is located on the left side column of the PMI W1set, and shifts the BCI W1set to its right side if the PMI W2is located on the right side column of the PMI W1set. The shifting unit405may shift the BCI W1set by one or two columns of the vectors. The shifting unit405further confines the co-phasing factors of the BCI W1set, wherein if the PMI W2has co-phasing factors within [1, −1], the shifting unit confines the co-phasing factors of the BCI W1set to [1, −1], and if the PMI W2has co-phasing factors within [j, −j], the shifting unit405confines the co-phasing factors of the BCI W1set to [j, −j]. The BCI W2selected from the BCI W1set is orthogonal to the PMI W2.