KR20140077647A - Method for selection of transmitter in multi-cell communication system - Google Patents

Abstract

There is provided a method of selecting a base station to participate in cooperation based on the strength of a received signal so as to smoothly calculate a precoding vector when there are three or more base stations sharing information. According to an embodiment of the present invention, a base station to share information among all base stations of a multi-cell MIMO network is determined, so that it is possible to improve performance compared to a non-cooperative network and to realize performance close to a fully cooperative network.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for selecting a transmitter in a multi-cell communication system,

The present invention relates to a method for selecting a base station sharing information with one another in a multi-cell communication system.

BACKGROUND ART In a wireless communication network such as a cellular based mobile communication system or a local area network (LAN), transmission of a large amount of data, such as multimedia data, has increased, and a multi-input multi-output (MIMO) . The MIMO technique is a technique of using a spatial domain by introducing a plurality of antennas. The MIMO technique improves the transmission rate using spatial multiplexing, reduces the error rate using spatial diversity, reduces the signal-to- signal-to-noise ratio (SNR) gain, and co-channel interference reduction.

Spatial multiplexing transmits independent information through a plurality of antennas. When transmitting using m antennas, the transmission rate can be increased to m times without increasing additional bandwidth or power as compared with a single antenna system. The network operator can introduce channel coding to the transmitting end and introduce an interference cancellation algorithm at the receiving end to ensure a constant error correction performance. The Bell Labs Layered Space-Time Architecture (BLAST) is a representative method.

Space diversity is a scheme similar to channel coding, which transmits redundant signals representing the same information to multiple antennas to reduce the error rate of the system. Using space-time coding, multiple transmit antennas spread the information and combine the receive antennas with the extra signals as appropriate. At this time, a plurality of reception antennas can be used for improving the performance, and a diversity gain and a coding gain can be obtained without lowering the transmission rate because the space is used. In an exemplary manner, space-time trellis codes and Alamouti transmit diversity are available.

The smart antenna improves the SNR at the receiving end and can reduce the cochannel interference in a multi-user environment. By implementing beamforming through an adaptive antenna array, the beam shape of the transmit and receive antennas can be adjusted in a certain direction and suppressed from unwanted directions.

However, when the MIMO technique is applied to a multi-cell communication network, when the number of transmitters is three or more, complexity greatly increases and it is difficult to calculate a precoding vector.

Therefore, the embodiment of the present invention provides a method of selecting a base station to participate in cooperation so that a precoding vector can be smoothly calculated even when there are three or more base stations (transmitters) sharing information.

Thus, in accordance with a feature of the present invention, a method for selecting a transmitter to participate in cooperation among a plurality of transmitters in a multi-cell communication system is provided. Wherein the transmitter selection method comprises the steps of: determining a threshold value for the strength of a signal transmitted from the plurality of transmitters and transmitting the determined threshold value to a receiver; determining, from among the plurality of transmitters, Receiving a transmitter index of the at least one first transmitter from the receiver, and calculating a precoding vector based on the at least one first transmitter.

As described above, according to the embodiment of the present invention, since the base stations to share information among all the base stations of the multi-cell MIMO network are determined, the performance can be improved compared to the non-cooperation network and performance close to the fully cooperative network.

1 is a diagram showing a general beam forming or precoding method.
2 illustrates a transmitter and a receiver pair according to an embodiment of the present invention.
3 and 4 are views illustrating a multi-cell MIMO network according to an embodiment of the present invention.
5 is a flowchart illustrating a method of selecting a transmitter for sharing information in a transmitter according to an exemplary embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, a terminal is referred to as a mobile terminal (MT), a mobile station (MS), a subscriber station (SS), a portable subscriber station (PSS) an access terminal (AT), a user equipment (UE), and the like, and may include all or some of functions of MT, MS, SS, PSS,

In addition, a base station (BS) includes a node B, an evolved node B, an eNodeB, an access point (AP), a radio access station (RAS) a base transceiver station (BTS), a mobile multihop relay (MMR) -BS, or the like, and may include all or some of functions of a Node B, an eNodeB, an AP, a RAS, a BTS, and an MMR-BS.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise. Also, the terms " part, "" module," " module, "and " block" refer to units that process at least one function or operation, Lt; / RTI >

1 is a diagram showing a general beam forming or precoding method.

Referring to FIG. 1, a transmitter to which a MIMO technique is applied multiplies a data vector s by a precoding matrix W to generate a transmission signal vector x, and then transmits a transmission signal vector through a channel H. The receiver receives the signal in the form of added noise (n) (y = H * x + n)

In the MIMO technique, a transmitter transmits a signal using a beam forming or precoding method. The beamforming or precoding scheme is a method for obtaining a gain when a signal is received by performing preprocessing on data to be transmitted based on the channel information fed back from the terminal (or the channel information measured by the transmitter in the time division multiplexing system). For example, in a radio channel environment including k transmission antennas and n reception antennas, a transmission signal vector x (nx1 (k) is multiplied by a precoding matrix W (nxk vector) Vector).

At this time, the beam forming or precoding method can be determined based on the channel information and the data information to be transmitted. A maximum ratio transmission (MRT) scheme for maximizing a signal from a specific user and a zero-forcing (ZF) scheme for eliminating another signal are representative schemes of beam forming or precoding schemes.

The MRT scheme uses a complex conjugate transpose matrix of channel H as a precoding matrix. The received signal y can be expressed by Equation (1).

The ZF scheme mainly uses an inverse matrix (H ^H (HH ^H ) ^-1 ) as a precoding matrix. The received signal y can be expressed by Equation (2).

At this time, it is assumed that there are two or more base stations serving as transmitters in the downlink of the multi-cell MIMO network. It is also assumed that some base stations among two or more base stations have channel information and transmission data information in order to apply a beam forming or precoding scheme.

2 illustrates a transmitter and a receiver pair according to an embodiment of the present invention.

Referring to FIG. 2, a multi-cell MIMO network includes two transmitters having three antennas and two receivers having one antenna. In this case, the problem of selecting a base station to share information with each other does not occur, and two base stations always share information. Therefore, in order to implement beamforming or precoding, it is necessary to determine the matrix w _kj .

If information is shared between the transmitter 1 and the transmitter 2 to know data to be transmitted to the receiver 1 and the receiver 2, respectively, the signal x _j transmitted from the transmitter j can be expressed by Equation (3).

In Equation 3,

Is the transmit power from transmitter j to receiver k, and w _kj is the precoding vector from transmitter j to receiver k

Lt;

Denotes a symbol transmitted to the receiver k. Each transmitter can satisfy Equation (4) which is a power constraint of an average transmission signal.

On the other hand, the reception signal at the receiver k can be expressed by Equation (5).

In Equation (5)

Is the channel between transmitter j and receiver k,

Is the noise measured at receiver k.

At this time, the signal interference to noise ratio (SINR) at the receiver k can be expressed by Equation (6).

At this time, the SINR is maximized

, The channel between the transmitter and the receiver is regarded as a combination of two interference channels,

. ≪ / RTI >

3 and 4 are views illustrating a multi-cell MIMO network according to an embodiment of the present invention.

Considering the downlink of the multi-cell MIMO network with reference to FIG. 3, each base station may share information (channel information or data information to be transmitted) and calculate a better performance precoding vector using the shared information . At this time, when the MIMO technique is used, each base station can transmit data only to the terminals included in its cell region or to the terminals included in the adjacent cell region.

When transferring single louder than words of data contained in their cell region is, assuming that the transmission power p _k, k SINR at the receiver may be expressed as equation (8).

At this time,

Is a precoding vector of transmitter k, and one subscript is used because each transmitter has no data to send to the other receiver.

If the transmitter k knows the precoding vector (data information to be transmitted) of the transmitter different from all the channel information, SINR is maximized as in Equation (9)

Can be selected.

If the transmitter k does not know the precoding vector of another transmitter, the virtual SINR is maximized as shown in Equation (10)

Can be selected.

In the case of transmitting data to a terminal included in a neighboring cell area, the SINR at the receiver k is expressed by Equation (11) when the power allocated to data transmitted from the transmitter j to the receiver k is P _kj .

At this time, if the precoding vector of another transmitter is known, the SINR is maximized

Can be selected.

However, if the transmitter k does not know the precoding vector of the other transmitter, the virtual SINR is maximized

.

At this time, it is possible to select an optimal beam forming or precoding method by sharing information in all transmitters, but sharing information in all transmitters is limited. That is, when there are three or more transmitters, there is a problem that the amount of data to be exchanged is large and the time may be delayed. Even if all the information is shared, the complexity in calculating the precoding vector may increase.

5 is a flowchart illustrating a method of selecting a transmitter for sharing information in a transmitter according to an exemplary embodiment of the present invention.

In the embodiment of the present invention, a precoder vector is calculated after selecting some transmitters to share information. The transmitter to share information is determined based on the strength (or path loss value) of the signal received at receiver k. Each receiver k measures the strength of the received signal and transmits the index of the transmitter that transmitted the received signal to the transmitter of the cell area in which it is located. The transmitter that receives the index selects the set S _k of transmitters that will share information among the transmitters of the index. A base station that greatly affects a mobile station in a cellular-based mobile communication system may be limited to a base station located near a mobile station as shown in FIG.

5, the transmitters k and transmits the threshold T _k of the signal strength to the maximum number of other transmitters N _k and the threshold value set up T _k, and (S501), the receiver of the signal strength to share the transmitter k information (S502).

Receiver k measures the strength (R _kj ) of the received signal from transmitter j (s 503) and transmits the index of the transmitter that transmitted the signal whose signal strength is greater than T _k to transmitter k (S 504, S 505).

Then, the transmitter k stores the received index information, and (S506), if the total number of stored transmitter index N _k or less (S507), the sender of the index, and the elements of S _k, the transmitter is still receiving a transmitter index And stores it.

However, the total number of indexes stored in the transmitter is greater than N _k, to align the transmitter contained in S _k in signal strength order (S508). Thereafter, the transmitter calculates a precoding vector based on the sorted S _k (S509), and transmits the data signal to the receiver using the calculated precoding vector (S510).

At this time, the precoding vector may be determined by a method of maximizing the SINR or the virtual SINR. That is, the precoding vector can be determined by an MRT method, a ZF method, or a mixed method of MRT and ZF. However, the transmitter included in the calculation is limited to the elements of S _k .

For example, when one base station transmits data only in a single cell included in a cell region, if the base station k knows all the channel information and the precoding vector (data information to be transmitted) of another base station, SINR is maximized To do

Can be selected.

As described above, according to the embodiment of the present invention, a base station (a base station to participate in cooperation) to which information is to be shared among all base stations of a multi-cell MIMO network is determined, have.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (1)

CLAIMS 1. A method for selecting a transmitter to participate in cooperation among a plurality of transmitters in a multi-cell communication system,
Determining a threshold value for the strength of a signal transmitted from the plurality of transmitters, and transmitting the threshold to a receiver,
Receiving, from a plurality of transmitters, a transmitter index of at least one first transmitter that has transmitted a signal greater than the threshold;
Calculating a precoding vector based on the at least one first transmitter
/ RTI >

Images