This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0142035 filed in the Korean Intellectual Property Office on Oct. 20, 2014, the entire contents of which are incorporated herein by reference.
(a) Field of the Invention
The present invention relates to an apparatus and method for communication of a base station for multiple user-multiple input multiple output in a distributed antenna system. More particularly, the present invention relates to an apparatus and method for communication of a base station for improving a receiving performance gain of multiple user multiple antenna transmission in an uplink direction in a distributed antenna system.
(b) Description of the Related Art
A distributed antenna system in consideration of one of technology for maximizing average cell spectrum efficiency and maximum data transmission speed through cooperation communication is a system in which a plurality of low power Remote Radio Heads (RRH) are distributed and connected through an optic cable to be integrated and managed in a cell area of a base station.
In the distributed antenna system, a plurality of RRHs are used as receiving points of a signal that is transmitted from one terminal in an uplink direction to obtain an optimal cooperation communication reception gain. Particularly, when using a plurality of terminals and a plurality of RRHs as transmitting and receiving points, there is a merit that an uplink MU-MIMO for maximizing average cell spectrum efficiency and maximum data transmission speed in an uplink direction can be used.
However, in order to actively use an uplink MU-MIMO, a performance degradation problem due to an independent receiving delay time difference occurring through a radio channel between a plurality of terminals and a plurality of RRHs should be considered. When a plurality of RRHs use a signal that is transmitted from a terminal as a receiving point, one of a plurality of RRHs may be determined as an anchor RRH and a transmitting time point of a terminal may be adjusted based on a receiving delay time of an anchor RRH, but there is a problem that a receiving delay time of non-anchor RRHs cannot entirely equally correspond. Due to a receiving delay time difference between a plurality of terminals and a plurality of RRHs due to such a problem, degradation of receiving performance of an uplink MU-MIMO may occur.
Particularly, in an uplink LTE-A MU-MIMO, because each Demodulated Reference Signal (DMRS) that is transmitted from a plurality of terminals has a characteristic that it shares a frequency resource and a time resource and that it distinguishes a code with only Cyclic Shift (CS) and Orthogonal Cover Code (OCC), a receiving delay time difference between terminals may have a serious influence on receiving performance of an MU-MIMO.
The present invention has been made in an effort to provide an apparatus and method for communication of a base station for multiple user-multiple input multiple output (MU-MIMO) in a distributed antenna system that can improve a receiving performance gain of an uplink MU-MIMO in a distributed antenna system.
An exemplary embodiment of the present invention provides a method in which a base station that is connected to a plurality of Remote Radio Heads (RRH) that are installed within a cell performs uplink multiple user-multiple input multiple output (MU-MIMO) communication with a plurality of terminals. The method includes: acquiring an arrival time at which a signal that is transmitted from the plurality of terminals arrives at the plurality of RRHs; calculating an arrival delay time between the plurality of terminals and the plurality of RRHs using a predetermined reference time and an arrival time of the plurality of RRHs; selecting RRHs to participate in receiving the uplink MU-MIMO among the plurality of RRHs using an arrival delay time between the plurality of terminals and the plurality of RRHs; and adjusting a transmitting time of the plurality of terminals using an arrival delay time between the plurality of terminals and RRHs to participate in receiving the uplink MU-MIMO.
The selecting of RRHs may include: calculating a plurality of first arrival delay time differences between the same terminal and different RRHs using an arrival delay time between the plurality of terminals and the plurality of RRHs; selecting a first number of RRHs among the plurality of first arrival delay time differences; calculating a plurality of second arrival delay time differences between different terminals and the same RRH and a plurality of third arrival delay time differences between different terminals and different RRHs using an arrival delay time between the plurality of terminals and the first number of RRHs; and selecting a second number of RRHs to participate in receiving the uplink MU-MIMO using the plurality of second arrival delay time differences and the plurality of third arrival delay time differences.
The selecting of the first number of RRHs may include selecting the first number of RRHs having a small value among the plurality of first arrival delay time differences.
The selecting of the second number of RRHs may include selecting the second number of RRHs in which the sum of a second arrival delay time difference and a third arrival delay time difference is small for each of the first number of RRHs.
The adjusting of a transmitting time may include: calculating a first minimum arrival delay time between the first number of RRHs for each terminal using an arrival delay time between the same terminal and the first number of selected RRHs; calculating a second minimum arrival delay time between the second number of RRHs for each terminal using an arrival delay time between the same terminal and the second number of selected RRHs; and determining a transmitting time of each terminal using the calculated first minimum arrival time for each terminal and the calculated second minimum arrival delay time for each terminal.
The determining of a transmitting time may include determining a transmitting time of each terminal from the sum of a first minimum arrival time corresponding to each terminal and a second minimum arrival time corresponding to each terminal.
The adjusting of a transmitting time may further include transmitting a transmitting time of each terminal to each terminal.
Another embodiment of the present invention provides an apparatus that enables a base station that is connected to a plurality of Remote Radio Heads (RRH) that are installed within a cell to perform uplink multiple user-multiple input multiple output (MU-MIMO) communication with a plurality of terminals. The communication apparatus includes a processor and a transceiver. The processor acquires an arrival time at which a signal that is transmitted from the plurality of terminals arrives at the plurality of RRHs, calculates an arrival delay time between the plurality of terminals and the plurality of RRHs using a predetermined reference time and an arrival time of the plurality of RRHs, and selects RRHs to participate in receiving an uplink MU-MIMO using an arrival delay time between the plurality of terminals and the plurality of RRHs. The transceiver includes the plurality of RRHs and receives a signal that is transmitted from the plurality of terminals through the plurality of RRHs.
The processor may calculate a plurality of first arrival delay time differences between the same terminal and different RRHs using an arrival delay time between the plurality of terminals and the plurality of RRHs to select a first number of RRHs, and calculate a plurality of second arrival delay time differences between different terminals and the same RRH and a plurality of third arrival delay time differences between different terminals and different RRHs using an arrival delay time between the plurality of terminals and the first number of RRHs to select a second number of RRHs to participate in receiving the uplink MU-MIMO.
The processor may select the first number of RRHs having a small value among a plurality of first arrival delay time differences.
The processor may select the second number of RRHs in which the sum of a second arrival delay time difference and a third arrival delay time difference is small for each of the first number of RRHs.
The processor may determine a transmitting time of the plurality of terminals using an arrival delay time between the plurality of terminals and RRHs to participate in receiving the uplink MU-MIMO.
The processor may calculate a first minimum arrival delay time between the first number of RRHs for each terminal using an arrival delay time between the same terminal and the first number of selected RRHs, calculate a second minimum arrival delay time between the second number of RRHs for each terminal using an arrival delay time between the same terminal and the second number of selected RRHs, and determine a transmitting time of each terminal using the calculated first minimum arrival time for each terminal and using the calculated second minimum arrival time for each terminal.
The processor may determine a transmitting time of each terminal from the sum of a first minimum arrival time corresponding to each terminal and a second minimum arrival time corresponding to each terminal.
In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.
In addition, in an entire specification and claims, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, the terms “-er”, “-or”, “module”, and “block” described in the specification mean units for processing at least one function and operation and can be implemented by hardware components or software components and combinations thereof.
In an entire specification, a terminal may indicate a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), a high reliability mobile station (HR-MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), and user equipment (UE), and may include an entire function or a partial function of the MT, the MS, the AMS, the HR-MS, the SS, the PSS, the AT, and the UE.
Further, a base station (BS) may indicate an advanced base station (ABS), a high reliability base station (HR-BS), a node B, an evolved node B (eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, a relay station (RS) that performs a BS function, a relay node (RN) that performs a BS function, an advanced relay station (ARS) that performs a BS function, a high reliability relay station (HR-RS) that performs a BS function, and a small BS [a femto BS, a home node B(HNB), a home eNodeB (HeNB), a pico BS, a metro BS, and a micro BS], and may include an entire function or a partial function of the ABS, the nodeB, the eNodeB, the AP, the RAS, the BTS, the MMR-BS, the RS, the RN, the ARS, the HR-RS, and the small BS.
Hereinafter, an apparatus and method for communication of a base station for multiple user multiple antenna transmission in a distributed antenna system according to an exemplary embodiment of the present invention will be described in detail with reference to the drawings.
Referring to
The base station 100 manages a cell and supports wireless communication to a terminal within a cell. The base station 100 performs a baseband signal processing function and performs a control function of the RRHs 1101-1106 and a radio resource allocation function for transmitting and receiving to and from a terminal within a cell. A radio resource may include at least one of a time, a frequency, and a power resource.
The RRHs 1101-1106 are distributed within a cell that the base station 100 manages, and are connected to the base station 100 through an optic cable. The RRHs 1101-1106 may include at least one antenna.
According to an exemplary embodiment of the present invention, one base station 100 that is connected to the RRHs 1101-1106 forms a multiple input multiple output (MIMO) channel with a terminal within a cell, and when a plurality of terminals exist within a cell, the base station 100 may support multiple user MIMO (MU-MIMO) communication.
The MU-MIMO may include a downlink MU-MIMO and an uplink MU-MIMO. In the downlink MU-MIMO, one base station 100 performs transmission through the RRHs 1101-1106, and a plurality of terminals simultaneously perform reception. In the uplink MU-MIMO, a plurality of terminals performs transmission, and one base station 100 performs reception through the RRHs 1101-1106.
Referring to
It is assumed that four RRHs 1101-1104 are distributed within a cell.
In uplink MU-MIMO transmission, the terminals 210 and 220 perform transmission, and the base station 100 that is connected to the RRHs 1101-1104 performs reception.
Each radio channel is formed between the terminals 210 and 220 and the RRH 1101-1104, and each radio channel has an independent delay time by spatial separation of the RRHs 1101-1104. That is, a signal that is transmitted from each of the terminals 210 and 220 has independent arrival delay times T11, T12, T13, T14, T21, T22, T23, and T24 through each radio channel and arrives at the RRHs 1101-1104. The arrival delay times T11, T12, T13, T14, T21, T22, T23, and T24 represent a time difference between a predetermined RRH reference time and an arrival time at each of the RRHs 1101-1104.
In uplink MU-MIMO transmission, different arrival delay times T11, T12, T13, T14, T21, T22, T23, and T24 between the terminals 210 and 220 and the RRHs 1101-1104 deteriorate receiving performance of an uplink MU-MIMO.
A simulation parameter that is applied to
In a simulation environment of Table 1, in each terminal, in order to view an influence of an arrival delay time difference between RRHs, while fixing arrival delay times T11 and T22 to 0 sample delay and changing each of arrival delay times T12 and T21 by samples 0, 3, 10, and 20, bit error rates according to an arrival delay time difference were compared.
As can be seen through a simulation result of
In
In
As shown in
In a result of
Therefore, in uplink MU-MIMO transmission/reception, in order to minimize receiving performance degradation of an uplink MU-MIMO due to an arrival delay time difference between the terminals 210 and 220 and the RRHs 1101-1104, in an exemplary embodiment of the present invention, a method of selecting RRHs to participate in receiving an uplink MU-MIMO among a plurality of RRHs according to a determined method and adjusting a transmitting time of the terminals 210 and 220 based on the selected RRHs is suggested.
In
Three kinds of arrival delay time differences may exist. A first arrival delay time difference is an arrival delay time difference between the same terminal and different RRHs, a second arrival delay time difference is an arrival delay time difference between different terminals and the same RRH, and a third arrival delay time difference is an arrival delay time difference between different terminals and different RRHs. In this case, even if a predetermined RRH is selected by any rule, a value of the first arrival delay time difference is not changed. When a terminal adjusts a transmitting time of an uplink, the second and third arrival delay time differences may be changed.
Hereinafter, a method of selecting an RRH to participate in receiving an uplink MU-MIMO for minimizing an arrival delay time difference and a method of adjusting a transmitting time of terminals will be described in detail with reference to
Referring to
The base station 100 measures arrival times T11, T12, . . . , T1N, T21, T22, . . . , T2N in which the training signal is arrived at each of the RRHs 1101-110N (S710).
The base station 100 calculates arrival delay times ΔT11, ΔT12, . . . , ΔT1N, ΔT21, ΔT22, . . . , ΔT2N of the RRHs 1101-110N using a predetermined RRH reference time to and arrival times T11, T12, . . . , T1N, T21, T22, . . . , T2N of the RRHs 1101-110N (S720).
The base station 100 selects an RRH group including the predetermined number of RRHs in which an arrival delay time difference between the same terminal and different RRHs is smallest, as in Equation 1 using arrival delay times ΔT11, ΔT12, . . . , ΔT1N, ΔT21, ΔT22, . . . , ΔT2N between the terminals 210 and 220 and the RRHs 1101-110N (S730). Here, the predetermined number may be set to the number or more of the terminals 210 and 220.
In Equation 1, M is the number of terminals, and in an exemplary embodiment of the present invention, M is 2.
Thereafter, referring to
T1min=min(ΔT11,ΔT12,ΔT1(N-1)) (Equation 2)
T2min=min(τ21,ΔT22,ΔT2(N-1)) (Equation 3)
The base station 100 selects RRHs to participate in receiving an MU-MIMO, as in Equation 4 using arrival delay times ΔT11, ΔT12, . . . , ΔT1N, ΔT21, ΔT22, . . . , ΔT2N between the terminals 210 and 220 and the RRHs 1101-110N (S750). That is, the base station 100 may select RRHs in which an arrival delay time difference between different terminals and the same RRH and an arrival delay time difference between different terminals and different RRHs becomes a minimum as an RRH to participate in receiving an MU-MIMO.
In Equation 4, M is the number of terminals, and in an exemplary embodiment of the present invention, M may be 2, and two RRHs, for example, a first RRH and an (N−1)th RRH, may be selected based on Equation 4.
The base station 100 aligns an arrival delay time of the RRH that is selected at step S750 to correspond with a predetermined reference time, and selects a minimum arrival delay time among aligned arrival delay times (S760). The base station 100 stores an aligned arrival delay time and a selected minimum arrival delay time for each terminal. For example, as shown in
T1′min=min(ΔT11,ΔT1(N-1)) (Equation 5)
T2′min=min(ΔT21,ΔT2(N-1)) (Equation 6)
Finally, the base station 100 determines a transmitting time of the terminals 210 and 220, as in Equations 7 and 8 (S770). That is, the base station 100 may determine a transmitting time of the terminal 210 to the sum of minimum arrival delay times between the terminal 210 and RRHs that are calculated at each of steps S740 and S760, and determine a transmitting time of the terminal 220 to the sum of minimum arrival delay times between the terminal 220 and RRHs that are calculated at each of steps S740 and S760.
T1adj=T1+min+T1′min (Equation 7)
In Equation 7, T1adj represents a transmitting time of the terminal 210.
T2adj=T2min+T2′min (Equation 8)
In Equation 8, T2adj represents a transmitting time of the terminal 220.
Through the above procedure, the base station 100 selects an RRH to participate in receiving an MU-MIMO and adjusts a transmitting time of each of the terminals 210 and 220, thereby minimizing an arrival delay time difference between the terminals 210 and 220 and the selected RRH, as shown in
A simulation parameter that is applied to
As a simulation result of a BER to an SNR of a case of randomly selecting two RRHs among RRH1, RRH2, RRH3, and RRH4 and of a case of selecting two RRHs with reference to
Referring to
By performing operations that are described with reference to
The transceiver 920 receives a training signal from the terminals 210 and 220. Such a transceiver 920 may include a plurality of RRHs that are described with reference to
The memory 930 stores instructions for performing in the processor 910 or loads and temporarily stores an instruction from a storage device (not shown), and the processor 910 executes an instruction that is stored or loaded at the memory 930.
The processor 910 and the memory 930 are connected through a bus (not shown), and an input/output interface (not shown) may be connected to the bus. In this case, the transceiver 920 is connected to the input/output interface, and a peripheral device such as an input device, a display, a speaker, and a storage device may be connected to the input/output interface.
According to an exemplary embodiment of the present invention, in uplink MU-MIMO communication of a distributed antenna system, by selecting an RRH to participate in receiving an uplink MU-MIMO in consideration of a relative receiving delay time difference between a plurality of terminals and a plurality of RRHs and by adjusting a transmitting time of terminals based on the selected RRH, a receiving performance gain of the uplink MU-MIMO can be improved.
An exemplary embodiment of the present invention may not only be embodied through the above-described apparatus and/or method, but may also be embodied through a program that executes a function corresponding to a configuration of the exemplary embodiment of the present invention or through a recording medium on which the program is recorded, and can be easily embodied by a person of ordinary skill in the art from a description of the foregoing exemplary embodiment.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Number | Date | Country | Kind |
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10-2014-0142035 | Oct 2014 | KR | national |