Patent Description:
In general, mobile communication systems have been developed to provide voice services while guaranteeing user mobility. Such mobile communication systems have gradually expanded their coverage from voice services through data services up to high-speed data services. However, as current mobile communication systems suffer resource shortages and users demand even higher-speed services, development of more advanced mobile communication systems is needed.

To meet this demand, the 3rd generation partnership project (3GPP) has been working to standardize specifications for the long term evolution (LTE) system as a next generation mobile communication system. The LTE system is expected to be commercially available in about <NUM>, and aims to realize high-speed packet based communication supporting a data rate of <NUM> Mbps. To this end, various approaches have been considered, such as reducing the number of nodes on a communication path through simplification of the network architecture and bringing wireless protocols as close as possible to wireless channels.

In the uplink of the LTE system, a base station may selectively combine and process signals received from user equipments. Hence, it is necessary to develop a scheme that enables the base station of a mobile communication system to select antennas with favorable channel states in real time and to combine and decode signals received through the selected antennas.

<CIT> describes a distributed antenna system, a distributed antenna switching method, a base station apparatus and an antenna switching device. <CIT> describes a multi-antenna station with distributed antennas. <CIT> describes an antenna diversity for wireless communication system. <CIT> describes an antenna selection method and device.

Aspects of the present disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a method and apparatus that enable a base station of a wireless communication system to select antennas for effective uplink communication with a user equipment (UE) in real time.

In accordance with an aspect of the present disclosure, a method of antenna selection for a base station is provided as defined in claim <NUM>.

In accordance with another aspect of the present disclosure, a base station is provided as defined in claim <NUM>.

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scopeof the present disclosure.

The following description is focused on advanced devolved universal terrestrial radio access (E-UTRA) (long term evolution advanced (LTE-A)) supporting carrier aggregation. However, it should be understood by those skilled in the art that the subject matter of the present disclosure is applicable to other communication systems having similar technical backgrounds and channel configurations without significant modifications departing from the scope of the present disclosure. For example, the subject matter of the present disclosure may be applied to multicarrier high speed packet access (HSPA) supporting carrier aggregation.

Descriptions of components having substantially the same configurations and functions may be omitted.

In the drawings, some elements are exaggerated, omitted, or only outlined in brief, and thus may be not drawn to scale.

Further, it is known to those skilled in the art that blocks of a flowchart (or sequence diagram) and a combination of flowcharts may be represented and executed by computer program instructions. These computer program instructions may be loaded on a processor of a general purpose computer, special purpose computer or programmable data processing equipment. When the loaded program instructions are executed by the processor, they create a means for carrying out functions described in the flowchart. As the computer program instructions may be stored in a computer readable memory that is usable in a specialized computer or a programmable data processing equipment, it is also possible to create articles of manufacture that carry out functions described in the flowchart. As the computer program instructions may be loaded on a computer or a programmable data processing equipment, when executed as processes, they may carry out operations of functions described in the flowchart.

A block of a flowchart may correspond to a module, a segment or a code containing one or more executable instructions implementing one or more logical functions, or to a part thereof. In some cases, functions described by blocks may be executed in an order different from the listed order. For example, two blocks listed in sequence may be executed at the same time or executed in reverse order.

In the description, the word "unit", "module" or the like may refer to a software component or hardware component such as a field programmable gate array (FPGA) or application specific integrated circuit (ASIC) capable of carrying out a function or an operation. However, "unit" or the like is not limited to hardware or software. A unit or the like may be configured so as to reside in an addressable storage medium or to drive one or more processors. Units or the like may refer to software components, object-oriented software components, class components, task components, processes, functions, attributes, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays or variables. A function provided by a component and unit may be a combination of smaller components and units, and may be combined with others to compose large components and units. Components and units may be configured to drive a device or one or more processors in a secure multimedia card.

<FIG> illustrates a wireless communication system including a base station (BS) and multiple antennas thereof according to an embodiment of the present disclosure.

Referring to <FIG>, the BS <NUM> may use multiple antennas <NUM> to <NUM> to send and receive signals to and from user equipments (UEs) located in the coverage thereof. A signal may include a control signal and data.

In <FIG>, eight antennas are shown in the coverage of the BS <NUM>, but the number of antennas may vary depending upon the circumstances.

The serving area of the BS <NUM> may be divided into multiple sectors. Individual antennas may be separated at regular intervals so that the sectors contain the same number of antennas. For example, two antennas may be installed in each sector.

A mobile station (MS) or user equipment (UE) <NUM> may send or receive a signal to or from the BS <NUM> through one or more antennas.

When signals from the UE <NUM> are received through the multiple antennas <NUM> to <NUM>, the BS <NUM> may select some of the antennas <NUM> to <NUM> according to channel information and combine signals received through the selected antennas for processing.

For example, when the UE <NUM> is close to the antennas TP0 (<NUM>), TP1 (<NUM>) and TP2 (<NUM>) as shown in <FIG>, signals sent from the UE <NUM> through the antennas TP0 (<NUM>), TP1 (<NUM>) and TP2 (<NUM>) to the BS <NUM> may have favorable channel states.

Hence, for the UE <NUM>, the BS <NUM> may combine and process signals received through only the antennas TP0 (<NUM>), TP1 (<NUM>) and TP2 (<NUM>) among the antennas <NUM> to <NUM>.

In general, to select antennas with high received signal strength, the BS <NUM> may measure the signal-to-noise ratio (SNR) of signals sent by the UE <NUM> at a subframe allocated to the UE <NUM> and store the measurement results in advance. When the UE <NUM> has uplink data to be sent to the BS <NUM>, the BS <NUM> may select antennas by using the stored SNR values to receive and combine data signals coming from the UE <NUM>.

In the above antenna selection scheme, the time difference between the allocated subframe and the current subframe for antenna selection may be significant. This time difference may lower the reliability of SNR values obtained at the allocated subframe. Additionally, the BS <NUM> has to store and manage the measured SNR values.

To address the above problem, the sounding reference signal (SRS) periodically sent from the UE to the BS may be utilized. However, to use the SRS, the BS has to send the UE control information via a separate resource for SRS transmission of the UE.

In addition, interference conditions may differ between SRS and physical uplink shared channel (PUSCH)/physical uplink control channel (PUCCH). For example, in the case of SRS-based antenna selection, for selected antennas, channel conditions for PUSCH/PUCCH transmission may not be good enough, unlike channel conditions for SRS transmission. That is, the BS <NUM> may fail to receive good-quality signals through the antennas selected using SRSs. Consequently, SRS-based antenna selection may degrade reception accuracy of the BS <NUM>.

Next, to solve the above problems and to efficiently select antennas, components of the BS are described with reference to <FIG>.

<FIG> is a block diagram of the BS <NUM> according to an embodiment of the present disclosure.

Referring to <FIG>, the BS <NUM> may include a transceiver unit <NUM> and a controller <NUM>.

The transceiver unit <NUM> sends and receives data for wireless communication for the BS <NUM>. The transceiver unit <NUM> may include a radio frequency (RF) transmitter for upconverting the frequency of a signal to be transmitted and amplifying the signal, and an RF receiver for low-noise amplifying a received signal and downconverting the frequency of the received signal. The transceiver unit <NUM> may forward data received through a wireless channel to the controller <NUM>, and may transmit data from the controller <NUM> through the wireless channel.

The controller <NUM> controls the BS <NUM> to select antennas for effective communication with the UE <NUM> in the uplink. For example, the controller <NUM> may measure channel information using signals received through the transceiver unit <NUM>, determine antennas having received a signal with channel information higher than equal to a preset threshold, and combine and process signals received through the determined antennas.

For channel information, the controller <NUM> may measure the SNR or received power of signals received through multiple antennas.

For real-time antenna selection, the controller <NUM> may measure the SNR or received power of signals received through multiple antennas on a subframe basis, and determine at least one antenna whose SNR or received power is greater than or equal to the threshold on a subframe basis.

In the related art, there is a time difference between the subframe for channel information measurement and the current subframe for antenna selection. However, the BS <NUM> of the present disclosure may measure channel information and select antennas according to the measurement result in real time.

For channel information, the controller <NUM> may measure noise interference power. When noise interference power is measured as channel information, the controller <NUM> may determine antennas whose channel information is less than or equal to a preset threshold and combine and process signals received through the determined antennas.

As described above, the controller <NUM> may measure the SNR, received power, or noise interference power as channel information. However, the controller <NUM> may measure any other information enabling prediction of antenna channel states for channel information.

The controller <NUM> may select antennas using measured channel information and determine at least one antenna so that signals received through the selected antennas are processed without errors.

Meanwhile, when the operating mode of the BS <NUM> is multi-user multiple input multiple output (MU-MIMO), the BS <NUM> may receive signals sent by multiple UEs <NUM> through multiple antennas.

During MU-MIMO, the BS <NUM> may use multiple antennas to send and receive signals in real time to and from multiple UEs in the coverage thereof.

In one embodiment, for each antenna, the controller <NUM> may determine the average channel information of signals received through the antenna. The controller <NUM> may determine at least one antenna whose average channel information is greater than or equal to a preset threshold. For each UE, the controller <NUM> may combine and process multiple signals received through the determined antennas.

In another embodiment, the controller <NUM> may select UEs with a large MCS index and a large number of allocated RBs for each of multiple antennas. The controller <NUM> may compare pieces of channel information of antenna signals for the selected UEs and determine at least one antenna according to the comparison result.

For example, the controller <NUM> may select a UE with the largest MCS index and the largest number of allocated RBs for each antenna among UEs sending signals. The controller <NUM> may measure channel information of a signal sent by the selected UE through each antenna. The controller <NUM> may determine antennas having received a signal whose channel information is greater than or equal to a preset threshold. The controller <NUM> may combine and process multiple signals received through the determined antennas.

The controller <NUM> may determine an antenna on the basis of channel information measured at the uplink data channel and perform channel estimation on the uplink control channel corresponding to the uplink data channel by use of a signal received via the determined antenna.

For example, the controller <NUM> may utilize an antenna, which is used to decode data received through the uplink data channel, to receive data through the uplink control channel corresponding to the uplink data channel.

In another embodiment, the controller <NUM> may assign different weights to measured channel information according to antennas having received signals. The controller <NUM> may determine antennas whose weighted channel information is greater than or equal to a preset threshold.

For example, antennas close to the UE tend to have good channel conditions. Hence, the controller <NUM> may assign a high weight to a signal received through an antenna placed in the same sector as the UE.

After selecting antennas to receive uplink signals using one of the schemes described above, the controller <NUM> may combine and process signals received through the selected antennas.

Accordingly, the BS <NUM> may select antennas with good channel conditions in real time by measuring channel information on a subframe basis.

The BS <NUM> may select antennas by use of various types of channel information indicating channel states. For example, the BS <NUM> may measure the SNRs of signals received through multiple antennas and use the SNR information as channel information. Next, a description is given of a configuration that enables the BS <NUM> to measure the SNRs of signals received through multiple antennas and to select antennas with reference to <FIG> and <FIG>.

<FIG> is a block diagram of a controller of the BS according to an embodiment of the present disclosure.

Referring to <FIG>, the controller <NUM> may include an SNR measurement section <NUM>, an antenna selection section <NUM>, and a processing section <NUM>.

The SNR measurement section <NUM> may measure SNRs of signals received through each of multiple antennas. For example, the SNR measurement section <NUM> may measure the SNR of each signal on a subframe basis.

When the operating mode of the BS <NUM> is MU-MIMO, the SNR measurement section <NUM> may compute the average of SNRs of signals received through each antenna.

The antenna selection section <NUM> may select antennas by use of the SNRs measured by the SNR measurement section <NUM>. For example, the antenna selection section <NUM> may determine a signal whose SNR is greater than or equal to a preset threshold. The antenna selection section <NUM> may select the antenna having received the determined signal.

It is possible to set the number of selectable antennas. Hence, when there are multiple signals whose SNR is greater than or equal to a preset threshold, the antenna selection section <NUM> may select a given number of antennas in descending order of SNR.

When the operating mode of the BS <NUM> is MU-MIMO and the average of SNRs of signals received through each antenna is computed by the SNR measurement section <NUM>, the antenna selection section <NUM> may select an antenna having received signals whose average SNR value is greater than or equal to a preset threshold.

In one embodiment, the SNR measurement section <NUM> may compute SNRs of signals received through each antenna and forward the SNR values to the antenna selection section <NUM>, and the antenna selection section <NUM> may compute the average of SNR values for each antenna and select an antenna having received signals whose average SNR value is greater than or equal to a preset threshold.

Alternatively, when the operating mode of the BS <NUM> is MU-MIMO, the antenna selection section <NUM> may select a UE with the largest MCS index and the largest number of allocated RBs for each of multiple antennas. The antenna selection section <NUM> may examine the SNR values of signals sent by the selected UEs, determine a signal whose SNR value is greater than or equal to a preset threshold, and select the antenna having received the determined signal.

The processing section <NUM> may process signals received through the antenna selected by the antenna selection section <NUM> in real time. For example, the processing section <NUM> may combine signals received through the selected antenna and decode the combined signal.

<FIG> is a block diagram illustrating components of the controller <NUM> according to an embodiment of the present disclosure.

Referring to <FIG>, the controller <NUM> may include an SNR measurement section <NUM>, a weighting control section <NUM>, an antenna selection section <NUM>, and a processing section <NUM>.

The SNR measurement section <NUM> may include multiple SNR measurers <NUM>-<NUM> to <NUM>-K. Each of the SNR measurers <NUM>-<NUM> to <NUM>-K may compute an SNR value of a signal received through an antenna. The configuration of the SNR measurers <NUM>-<NUM> to <NUM>-K is described in detail later.

The weighting control section <NUM> may assign weights (<NUM>-<NUM> to <NUM>-K) to the SNR values computed by the SNR measurers <NUM>-<NUM> to <NUM>-K. The weighting control section <NUM> may assign different weights (<NUM>-<NUM> to <NUM>-K) to the SNR values according to antennas having received a signal.

For example, the weighting control section <NUM> may assign a high weight to the SNR of a signal received through an antenna placed in the same sector as the UE. When the distance to the UE or an antenna is large, the weighting control section <NUM> may assign a low weight to the SNR of a signal received through the antenna.

Hence, the controller <NUM> may select an antenna for signal reception in consideration of the measured channel information and location of the UE.

The antenna selection section <NUM> may select antennas by use of measured SNR values. The antenna selection section <NUM> may select an antenna having received a signal whose weighted SNR value is greater than or equal to a preset threshold.

It is possible to set the number of selectable antennas. For example, when up to four antennas are selectable, the antenna selection section <NUM> may select four signals in descending order of weighted SNR from among signals whose weighted SNR value is greater than or equal to a preset threshold, and determine antennas having received the selected signals.

When the operating mode of the BS <NUM> is MU-MIMO, each of the SNR measurers <NUM>-<NUM> to <NUM>-K may compute SNR values of signals received through an antenna and determine the average of the SNR values.

The weighting control section <NUM> may assign weights (<NUM>-<NUM> to <NUM>-K) to averages of SNR values computed by the SNR measurers <NUM>-<NUM> to <NUM>-K. The antenna selection section <NUM> may select an antenna on the basis of weighted averages of SNR values. That is, the antenna selection section <NUM> may select an antenna having received signals whose weighted SNR average is greater than or equal to a preset threshold.

When the operating mode of the BS <NUM> is MU-MIMO, the antenna selection section <NUM> may select a UE representing channel conditions for each antenna first and compare SNR values of signals sent by the selected UEs.

For example, the SNR measurers <NUM>-<NUM> to <NUM>-K may compute SNR values of signals received through antennas, and the weighting control section <NUM> may assign different weights (<NUM>-<NUM> to <NUM>-K) to the SNR values according to the antennas having received signals.

The antenna selection section <NUM> may select a UE with the largest MCS index and the largest number of allocated RBs for each antenna. The antenna selection section <NUM> may examine the weighted SNR values of signals sent by the selected UEs, determine a signal whose weighted SNR value is greater than or equal to a preset threshold, and select the antenna having received the determined signal.

Hence, the antenna selection section <NUM> may select those UEs with good channel conditions from among UEs having sent signals through antennas first, and select antennas having received signals, whose weighted SNR value is greater than or equal to a preset threshold, from the selected UEs.

The processing section <NUM> may combine signals received through the selected antenna and decode the combined signal. The processing section <NUM> may process signals received through the antenna selected by the antenna selection section <NUM> in real time.

<FIG> is a block diagram of the SNR measurement section <NUM> according to an embodiment of the present disclosure.

Referring to <FIG>, the SNR measurement section <NUM> may include a fast Fourier transform (FFT) unit <NUM>, a signal power estimator <NUM>, a noise power estimator <NUM>, and a divider <NUM>.

When a signal is input through the transceiver unit <NUM>, the FFT unit <NUM> of the SNR measurement section <NUM> may apply fast Fourier transform to the input signal.

The signal power estimator <NUM> may estimate the signal power of the fast Fourier transformed signal. The noise power estimator <NUM> may estimate the noise power of the fast Fourier transformed signal.

The divider <NUM> may obtain an SNR value by dividing the signal power value estimated via the signal power estimator <NUM> by the noise power value estimated via the noise power estimator <NUM>. Then, the SNR measurement section <NUM> may forward the SNR value obtained via the divider <NUM> to the antenna selection section <NUM> as shown in <FIG>.

Alternatively, the SNR measurement section <NUM> may forward the SNR value obtained via the divider <NUM> to the weighting control section <NUM> as shown in <FIG>.

<FIG> is a flowchart of an antenna selection method for the BS according to an embodiment of the present disclosure.

Referring to <FIG>, at operation S500, the BS <NUM> receives signals through multiple antennas. At operation S510, the BS <NUM> measures channel information of the received signals. For example, the BS <NUM> may measure the SNR or received power of signals received through multiple antennas as channel information.

At operation S520, the BS <NUM> determines antennas having received signals whose channel information is higher than or equal to a preset threshold. For example, when a high level of channel information indicates better channel conditions as in the case of the SNR, the BS <NUM> may determine a signal whose channel information is higher than or equal to a preset threshold first and identify the antenna having received the determined signal.

At operation S530, the BS <NUM> combines and processes the signals received through the determined antennas. For example, when a preset number of antennas are determined, the BS <NUM> may combine multiple signals received through the determined antennas and decode the combined signal.

When the distance between the UE and antenna is small, it is highly probable that channel conditions are good. Hence, the BS <NUM> may perform antenna selection in consideration of the distance between the UE and each antenna.

<FIG> is a flowchart of an antenna selection method for the BS in consideration of the distance between the UE and each antenna according to an embodiment of the present disclosure.

Referring to <FIG>, at operation S600, the BS <NUM> receives signals through multiple antennas. At operation S610, the BS <NUM> measures SNR values of the received signals. In addition to the SNR, as channel information, the BS <NUM> may measure any other information enabling prediction of antenna channel states, such as received power.

At operation S620, the BS <NUM> assigns different weights to the measured SNR values according to antennas having received signals. The BS <NUM> may assign different weights to the measured SNR values according to the locations of antennas having received signals.

For example, the BS <NUM> may assign a high weight to an antenna placed in the same sector as the UE. That is, when the distance between the UE and an antenna is large, the BS <NUM> may assign a low weight to the SNR of a signal received through the antenna.

At operation S630, the BS <NUM> determines an antenna having received a signal whose weighted SNR value is greater than or equal to a preset threshold. At operation S640, the BS <NUM> combines and processes signals received through the determined antenna.

As described above, the BS <NUM> may select an antenna to receive a signal in consideration of the measured channel information and the location of the UE.

Consequently, the base station may select an antenna enabling effective uplink communication with a UE in real time among multiple antennas.

Claim 1:
A method for processing signals by a base station (<NUM>), the method comprising:
receiving signals through multiple antennas (<NUM>-<NUM>);
measuring channel information from the received signals;
selecting, if an operating mode of the base station is multi-user multiple input multiple output, MU-MIMO, user equipments, UEs, with a largest modulation and coding scheme, MCS, index and a largest number of allocated resource blocks, RBs, for each antenna;
determining antennas that received signals whose channel information is higher than or equal to a preset threshold by comparing pieces of channel information of antenna signals for the selected UEs; and
combining and processing signals received through the determined antennas.