Multi-cell transmission diversity method and apparatus

A multi-cell transmission diversity method and apparatus that is capable of forming two virtual antennas of each cell and producing orthogonality of the virtual antennas using an improved precoding technique in an OFDM-based cellular mobile communication system is provided for improving transmission diversity gain with coherent combination of the orthogonal signals at the receiver. A multi-cell transmission diversity transmission method of a transmitter according to the present invention includes generating a first signal stream and a second signal stream by performing transmission diversity encoding on a user data; multiplexing and precoding the first signal stream and a first dedicated reference signal into a first diversity signal; multiplexing and precoding the second signal stream and a second dedicated reference signal a second diversity signal; and transmitting the first and second diversity signals simultaneously, wherein the first dedicated reference signal and the second dedicated reference signal are user-specific reference signal signals.

TECHNICAL FIELD

The present invention relates to an OFDM-based cellular mobile communication system and, in particular, to a multi-cell transmission diversity method and apparatus that is capable of forming two virtual antennas of each cell and producing orthogonality of the virtual antennas using an improved precoding technique in an OFDM-based cellular mobile communication system, thereby improving transmission diversity gain with coherent combination of the orthogonal signals at the receiver.

BACKGROUND ART

The evolution to the high speed and high quality wireless packet data communication system has transformed the voice-oriented communication service to the data and multimedia services. The High Speed Packet Access (HSPA) and Long Term Evolution (LTE) of the 3rdGeneration Partnership Project (3GPP), High Rate Packet Data (HRPD) and Ultra Mobile Broadband (UMB), and 802.16e of the Institution of Electrical and Electronics Engineers (IEEE) are the mobile communication standards developed for supporting such high speed and high quality wireless data transmission services.

These recent mobile communication technologies use sophisticated techniques such as an Adaptive Modulation and Coding (AMC) and/or channel-sensitive scheduling. The AMC is a technique to adjust the transmission amount of data according to the channel conditions. This means that the transmitter decreases the transmission data amount in bad channel condition to limit the received signal error probability to a wanted level and increases the transmission data amount in good channel condition while maintaining the signal error probability level. The channel sensitive scheduling allows the transmitter to allocate channels to multiple users selectively according to the channel condition so as to increase the system throughput. In the system using the AMC and channel-sensitive scheduling, the transmitter receives feedback from the receivers and performs transmission at the most effective timing with most appropriated modulation and coding scheme.

Meanwhile, the wireless access technology which is dominant in 2G and 3G system is evolving from Code Division Multiple Access (CDMA) to Orthogonal Frequency Division Multiple Access (OFDMA). The 3GPP and 3GPP2 have begun working on the standardization of the OFDMA-based evolved system. OFDMA is known superior to CDMA in capacity improvement.

It is one of the various factors for increasing the system capacity that the OFDMA can exploit frequency domain scheduling. In addition to the channel-sensitive scheduling, the frequency domain scheduling allows further system capacity gain in time-varying channel environments.

The AMC and channel-sensitive scheduling are technologies to improve the transmission efficiency based on the information about the transmission channels. Typically, a Frequency Division Duplex (FDD) system, in which the transmitter cannot infer the condition of its transmission channel, is designed such that the receiver reports the channel information to the transmitter. However, since the channel condition varies as time progresses in the wireless communication environment, feedback delay causes degradation of the efficiency of the AMC and channel-sensitive scheduling. This can be worse when the receiver is in high mobility state. Accordingly, there is a need for a supplementary transmission scheme to maintain the ongoing communication at least reliable level even when the channel condition feedback has become unreliable.

The technologies that are typically referred to as diversity methods are known less sensitive to the channel conditions. For instance, a frequency diversity method performs transmission through the frequency channels spaced enough on the frequency domain. Considering the frequency selective fading environment, the responses of the channels spaced enough are less correlated with each other. This means that the frequency diversity transmission can reduce the probability of any worst case of transmission failure because, even when one frequency resource experiences bad channel condition, the other frequency resource does not do.

Spatial diversity is another diversity scheme that uses multiple transmission and/or reception antennas. Assuming the transmission and/or reception antennas are spaced far enough from each other, the channel responses of the antennas are less correlated. Accordingly, the spatial diversity can decrease the probability to experience of the worst transmission condition even when one of the antennas experiences a bad channel response.

Transmission diversity is a special case of the spatial diversity applied to the transmitter. There are various transmission diversity techniques including Selective Transmission diversity, Space Time coding, Orthogonal Transmission diversity, etc.

In a cellular communication system, a base station serves mobile stations within its radio coverage, also referred to as cell, and triggers a handover of the mobile station moving out of its coverage to a neighbor base station for maintaining the ongoing call. In the cellular structure, the user located at the boundary of a cell is likely to experience the interference caused by the signal of neighbor base stations, resulting in bad channel state. Also, the closer the mobile station is to the base station, the higher the service transmission rate is.

In order to solve this problem, the 4th Generation (4G) mobile communication systems are expected to be implemented with a newly introduced technique called collaborative transmission in which the adjacent base stations transmit the same signal to a mobile station located at the cell boundary.

The collaborative transmission techniques can be classified into low level collaborative transmission technique and high level collaborative transmission technique. In the low level collaborative transmission technique, the base stations do not share the signal transmission but collaborates to make scheduling and beamforming decisions. In contrast, the high level collaborative transmission technique, the base stations collaborate for actual signal transmission as well as the scheduling and beamforming decisions. Although it increases the network traffic due to the increase of information exchanged between the base stations, the high level collaborative transmission technique is advantageous to improve the channel condition at the cell boundary since the mobile station can achieve transmission diversity gain from the transmissions of the base stations.

The transmission diversity is known to be optimized with two transmission antennas, since the recipient device can achieve the coherent combination of the received signals using the orthogonality without compromising data rate. In case that two cells, each having a single transmission antenna, are involved, it is ease to implement the high level collaborative transmission in which the both the base station transmit the same signal, resulting in transmission diversity gain. In other cases using more than two transmission antennas, however, other diversity technique, rather than the optimized transmission diversity, has to be adopted.

For instance, when three cells, each having a single transmission antenna, are involved in the collaborative transmission, another transmission diversity technique is required to achieve transmission diversity gain. Also, when two bases stations, each having multiple transmit antennas, are involved in the collaborative transmission, still another diversity technique is required.

DISCLOSURE OF INVENTION

Technical Problem

Even though the transmission diversity schemes suited for the number of involved cells and the number of transmit antennas of each cell are defined, the diversity scheme should be changed according to the change of the number of cells involved in the collaborative transmission due to the time-varying channel condition. This means that the receiver can be implemented to deal with all the kinds of transmission diversity schemes, resulting in reception complexity of the receiver.

There is therefore a need to develop a multi-cell diversity method that is capable of supporting the collaborative transmission situations irrespective of the number of involved cells and/or the number of transmit antenna(s) of each cell.

Solution to Problem

In order to overcome the problem of the prior art, the present invention provides a multi-cell transmission diversity method and apparatus that is capable of achieving transmission diversity gain with the high level collaborative transmission technique.

Also, the present invention provides a multi-cell transmission diversity method and apparatus that is capable of achieving transmission diversity gain regardless of the change of the number of cells involved in the collaborative transmission and/or the number of antenna of each cell.

In accordance with an exemplary embodiment of the present invention, multi-cell transmission diversity transmission method of a transmitter includes generating a first signal stream and a second signal stream by performing transmission diversity encoding on a user data; multiplexing and precoding the first signal stream and a first dedicated reference signal into a first diversity signal; multiplexing and precoding the second signal stream and a second dedicated reference signal a second diversity signal; and transmitting the first and second diversity signals simultaneously, wherein the first dedicated reference signal and the second dedicated reference signal are user-specific reference signal signals.

In accordance with another exemplary embodiment of the present invention, a multi-cell transmission diversity reception method of a receiver includes demultiplexing a received signal into a first signal stream, a first dedicated reference signal, a second signal stream, and a second dedicated reference signal, the first and second signal streams carrying a data signal; estimating a channel for receiving a first diversity signal using the first dedicated reference signal; estimating a channel for receiving a second diversity signal using the second dedicated reference signal; recovering the data signal using the estimated channels, wherein the first and second dedicated reference signals are user-specific reference signals.

In accordance with another exemplary embodiment of the present invention, a transmitter for supporting multi-cell transmission diversity in which multiple cells transmit the same signal to a receiver simultaneously includes a transmission diversity encoder which encodes a user data into a first signal stream and a second signal stream; a first multiplexer which multiplexes the first signal stream with a first dedicated reference signal into a first diversity signal; a second multiplexer which multiplexes the second signal stream with a second dedicated reference signal into a second diversity signal; a first precoder which performs precoding on the first diversity signal; a second precoder which performs precoding on the second diversity signal; and at least two antenna which transmit the precoded diversity signals to the receiver, wherein the first and second dedicated reference signals are user-specific reference signals.

In accordance with still another exemplary embodiment of the present invention, a receiver for supporting multi-cell transmission diversity in which multiple cells transmit the same signal to the receiver simultaneously includes a demultiplexer which demultiplexes a received signal into a first signal stream, a first dedicated reference signal, a second signal stream, and a second dedicated reference signal, the first and second signal streams carrying a data signal; a channel estimator which estimates channels for receiving a first diversity signal using the first dedicated reference signal and a second diversity signal using the second dedicated reference signal; and a transmission diversity decoder which decodes the data signal using the channels estimated by the channel estimator.

Advantageous Effects of Invention

According to the present invention, the multi-cell transmission diversity method and apparatus of the present invention allows each cell involved in the collaborative transmission to form two virtual antennas using DRS and precoders for transmission diversity, thereby achieving robust and uniform transmission diversity gain regardless of the number of cells involved in the collaborative transmission and the number of antenna of each cell. Also, the multi-cell transmission diversity method and apparatus of the present invention is capable of recovering the transmitted data with channel estimation on the virtual antennas without modification of the conventional receiver structure. Also, the multi-cell transmission diversity method and apparatus of the present invention is configured such that the corresponding virtual antennas of the individual cells involved in the collaborative transmission use the same DRSs, thereby recovering the transmitted data without differentiating between the collaborative cells.

MODE FOR THE INVENTION

FIG. 1is a schematic block diagram illustrating a multi-cell transmission diversity system according to an exemplary embodiment of the present invention.

InFIG. 1, the multi-cell transmission diversity system includes a transmitter100and a receiver110.

The transmitter100includes two transmit antennas, i.e. a first transmit antenna101and a second transmit antenna102. In order to simplify the explanation, it is assumed that the receiver110includes a single receive antenna111. In case that multiple receive antennas are used, the receiver110can be provided with corresponding numbers of combining units operating identically. The transmitter100transmits a signal through the two transmit antennas101and102, and the receiver110receives the signals experienced the respective channels h0and h1. Here, h0is the channel response between the first transmit antenna101and the receive antenna111, and h1is the channel response between the second transmit antenna102and the receive antenna111. A user data stream is modulated and coded by a modulation and coding unit103of the transmitter100and output in the form of a modulation symbol stream
S=[S0,S1, . . . ,S2N−2S2N−1].

Here, it is assumed for the purpose of transmission diversity encoding that the length of the modulation symbol stream is 2N. The modulation symbol stream is input to a transmission diversity (T×D) encoder105of the transmitter100, and the T×D encoder105outputs two symbol streams X0and X1. The operation of the T×D encoder105is described in detail with reference toFIGS. 2 and 4later. The first modulation symbol stream is transmitted through the first transmit antenna101, and the second modulation symbol stream is transmitted through the second transmit antenna101.

In order for the receiver110to estimate the channels h0and h1, the transmitter100has to transmit a reference signal (RS) per transmit antenna. A reference signal RS0107for the first channel h0is multiplexed with the first modulation symbol stream X0by a first multiplexer111of the transmitter100, and a reference signal RS1109for the second channel h1is multiplexed with the second modulation symbol stream X1by a second multiplexer113of the transmitter100.

The signal y received by receiver110is the sum of the transmitted signal100and an Additive White Gaussian Noise (AWGN). A demultiplexer121of the receiver110separates the RSs and the transmitted signal and sends the RSs to a channel estimator123and the transmitted signal to a transmission diversity (T×D) decoder125. The T×D decoder125recovers the transmitted modulation symbol stream using the channel values
ĥ0
and
ĥ1

estimated by the channel estimator123and outputs the modulation symbol stream to a demodulation and decoding unit127. The demodulation and decoding unit127performs demodulation and decoding on the modulation symbol stream to acquire the original transmission signal.

FIG. 2is a diagram illustrating the operation of the T×D encoder ofFIG. 1according to an exemplary embodiment of the present invention.

Referring toFIG. 2, the T×D encoder105performs diversity encoding on the modulation symbol stream s201and outputs two signal streams X0and X1. In the embodiment ofFIG. 2, the first symbol stream X0is identical with the input symbol stream S and the second symbol stream X1is output by encoding the input symbol stream S as expressed in Math Figure (1):
MathFigure 1
X0=S=[S0,S1, . . . ,S2N−2S2N−1]
X1=[−S1*,S0*, . . . ,−S2N−2*S2N−1*]  [Math.1]

where S* is a conjugate value of S and, if
S=a+jb,
S*=√{square root over (−1)}.

FIG. 3is a diagram illustrating the configuration of the T×D decoder of the receiver ofFIG. 1for processing the signal encoded as shown inFIG. 2.

When two contiguous symbols y2n211and y2n+1213of a received symbol stream are input to the T×D decoder125, the T×D decoder125recovers the transmitted symbols S2nand S2n+1using the estimated channel values
ĥ0

Assuming ideal channel estimation of
ĥ0=h0
and
ĥ1=h1,

the recovered symbols
Ŝ2n
and
Ŝ2n+1

This means that the transmitted symbols SI, and S2n+1 are recovered successfully, and the expected Signal-to-Noise Ratio (SNR) is expressed as Math Figure (4):

Here, Psdenotes energy allocated for transmitted symbol stream S, and
σz2

denotes the variance of AGWN z. If the symbol stream is transmitted through the first transmit antenna101or the second transmit antenna102without use of the transmission diversity, the expected SNRs for the respective antennas are
|h0|2γ
and
|h1|2γ.

In order to prevent the performance degradation on the channel without knowledge about the channels of the transmit antennas, it is required to avoid the worst channel condition. According to equation (4), the SNR with the transmission diversity is not less than the least value of the SNR with a signal transmit antenna.

FIG. 4is a diagram illustrating the operation of the T×D encoder ofFIG. 1according to another exemplary embodiment of the present invention.

In Math Figure (5), Alamouti encoding is used.

FIG. 5is a diagram illustrating the configuration of the T×D decoder of the receiver ofFIG. 1for processing the signal encoded as shown inFIG. 4.

When two contiguous symbols y2n321and y2n+1323of a received symbol stream are input to the T×D decoder125, the T×D decoder125recovers the transmitted symbols S2nand S2n+1using the estimated channel values
ĥ0
221and
ĥ1
223fed by the channel estimator123(n=0, 1, . . . , N−1).

The received symbols y2n211and y2n+1and the recovered symbols
Ŝ2n
and
Ŝ2n+1

Assuming ideal channel estimation of and
ĥ0=h0
and
ĥ1=h1,

the recovered symbols
Ŝ2n
and
Ŝ2n+1
can be expressed as Math Figure (7):
MathFigure 7
ŝ2n=(|h0|2+|h1|2)s2n+h0*z2n+h1z2n+1*
ŝ2n+1=(|h0|2+|h1|2)s2n+1+h1*z2n−h0z2n+1*  [Math.7]

This means that the transmitted symbols SI, and S2n+1are recovered successfully, and the expected Signal-to-Noise Ratio (SNR) is expressed as MathFIG. 4). Accordingly, the transmission diversity methods described with reference toFIGS. 2 and 4are identical in performance.

The above described transmission diversity methods are optimized for the system using two transmit antennas from the viewpoint of the receiver by using coherent combination of the received signals using their orthogonality without compromising data rate. In case that two cells are involved in the collaborative transmission and each cell uses one transmit antenna, it is possible to adopt the high level collaborative transmission in which the cells are transmitting the same signal simultaneously. In other cases where the total number of transmit antennas of the cells involved in the transmission is greater than 2, a new transmission diversity scheme is required rather than the above described ones. For instance, in case that three cells, each having a single transmit antenna, are involved in the collaborative transmission, another transmission diversity scheme has to be used to achieve the optimized diversity gain. Also, in case that more than two cells, each having multiple transmit antennas, are involved in the collaborative transmission, still another transmission diversity scheme has to be used to achieve the optimized diversity gain.

Even when all the transmission diversity schemes optimized for the different number of cells involved in the collaborative transmission and the total number of transmit antennas, it is required to change the transmission diversity scheme used in the collaborative transmission according to the change of the number of cells due to the variation of the channel conditions. This means that the receiver has to be implemented to support the different types of transmission diversity schemes, resulting in increase of reception diversity.

In the present invention, a multi-cell transmission diversity method and apparatus that is capable of achieving transmission diversity gain regardless of the change of the number of cells involved in the collaborative transmission and/or the number of antenna of each cell.

FIG. 6is a diagram illustrating a multi-cell transmission diversity system using virtual antennas for the collaborative transmission according to an exemplary embodiment of the present invention.

InFIG. 6, the User Equipment (UE)405is configured to support the high level cooperative transmission so as to receive the signal transmitted by the two cells cell A401and cell B403. In the embodiment ofFIG. 6, each cell is provided with two virtual antennas. That is, the cell A401includes a virtual antenna0411(first virtual antenna) and a virtual antenna1413(second virtual antenna), and the cell B403includes a virtual antenna0415(first virtual antenna) and a virtual antenna1417(second virtual antenna). When the cells401and403are transmitting the signal to the UE405collaboratively in high level collaborative transmission mode, the UE405receives the signals transmitted by the cells401and403without distinguishing between the first virtual antennas411and415and between the second antennas413and417. Although it is depicted that just two cells401and403are involved in the collaborative transmission, more than two cells can be involved in the collaborative transmission according to the system design and the channel conditions.

FIG. 7is a diagram illustrating a channel model between a cell and a UE in the multi-cell diversity system ofFIG. 6.

Referring toFIG. 7, a precoder505performs precoding on a transmission signal x507with different precoding weight values for M antennas501to503. The signal is weighted by the weight value W0for the first antenna501and the weight value WM-1for the last antenna503. That is, the first antenna501transmits the signal W0x, and the last antenna503transmits the signal Wm-1x. The signals weighted with different weight values propagate through different channels h0and h1509and then received through a receive antenna511. The transmit antennas501and503are used for transmitting the same transmission signal x507and are equivalent to the structure as shown inFIG. 8.FIG. 8is a diagram illustrating an equivalent form of the channel model ofFIG. 7. As shown inFIG. 8, the transmission signal x507can expressed as it is transmitted signal transmitted by a single transmit antenna521and received by the signal receive antenna511. Here, the equivalent channel g can be expressed as Math Figure (8):

The UE has to estimate the channel to demodulate the transmitted signal successfully. That is, the UE can demodulate the transmitted signal with the successful estimation on the equivalent channel. In case that the virtual antennas are configured with the precoder505as shown inFIG. 7, the equivalent channel g can be estimated using two different methods.

In the first method, the UE knows the weight values {w0, . . . , wM-1} In more detail, the cell transmits the different RSs through the respective transmit antennas501to503, and the UE estimates the channels {h0, . . . , hM-1} using the RSs transmitted by the cell. Simultaneously, the cell transmits the weight values {w0, . . . , wM-1} in the control information such that the UE can estimate the equivalent channel g by combining the estimated channels {h0, . . . , hM-1} and the weight values {w0, . . . , wM-1}.

In the second method, the RS is inserted into the signal before the signal is precoded by the precoder505rather than transmitting different RSs through the respective antennas501and503. In this case, since the RS is precoded along with the transmission signal x507, the UE can estimate the equivalent channel g using the RS.

Since the RS is transmitted inserted onto the resource allocated per user in the second method, this RS is defined as Dedicated Reference Signal (DRS). Also, since it is transmitted for the purpose of the channel condition measurement and report can be observed by all the users, the RS per transmit antenna is defined as Common Reference Signal (CRS).

The DRS is multiplexed with the precoded signal stream for forming a virtual antenna. The UE can estimate the channels of the individual virtual antennas using the corresponding DRSs and recovers the transmitted signal. In contrast, the CRS is multiplexed with the precoded signals as the cell- and antenna-specific RS. The UE measures the channel conditions using the CRS and feeds back the measurements to the cell(s). As aforementioned, the DRS and CRS are different from each other in their features and purposes.

The first method requires to transmit any separate control signal for informing the UE of the precoding weight values {w0, . . . , wM-1} but is advantageous to reuse the CRS. In contrast, the second method has to define additional DRS but is advantageous since there is no need of the addition control signal for informing the UE of the precoding weight values {w0, . . . , wM-1}.

In the embodiments of the present invention, the transmission diversity gain is achieved by using the virtual antennas as described with reference toFIGS. 7 and 8. By defining two pairs of the transmit antennas of two cells as shown inFIG. 6, it is possible for the two cells to transmit the same signal precoded for the transmission diversity.

FIG. 9is a diagram illustrating configurations of a pair of cells involved in a collaborative transmission for the multi-cell diversity transmission system according to an exemplary embodiment of the present invention. In the embodiment ofFIG. 9, the virtual antennas are implemented with the DRS and precoders615,617,655, and657.

If a user data stream is fed to the cell A601and the cell B603, each the two cells generates a modulation symbol stream s by means of a Forward Error Correction and modulation unit103. The modulation symbol stream s is input to the T×D encoder105and output in the forms of two coded symbol streams x0and x1. Here, the coded symbol stream x0is the signal to be transmitted by a virtual antenna0, and the coded symbol stream x1is the signal to be transmitted by another virtual antenna1. In order for a recipient UE to estimate an equivalent channel, each cell sends antenna-specific DRSs for the corresponding virtual antennas. For this purpose, a first multiplexer of each cell multiplexes a first DRS (DRS0) with the coded symbol stream x0. Simultaneously, a second multiplexer of each cell multiplexes a second DRS (DRS1) with the coded symbol stream x1. In this case, the virtual antennas0of the cells601and603are allocated the same DRS611(DRS0), and the virtual antennas1of the cells601and603are allocated the same DRS613(DRS1).

Next, the each cell configures the two virtual antennas. The precoder615configures the virtual antenna0of the cell A601, and the precoder655configures the virtual antenna0of the cell B603. The precoder617configures the virtual antenna1of the cell A601, and the precoder657configures the virtual antenna1of the cell B603.

Although the precoders are used for differentiating between the virtual antennas of each cell, the present invention is not limited thereto. For instance, the precoders are used for differentiating between the frequency/time resources allocated for the transmissions. Since the recipient UE estimates an equivalent channel using the DRSs611and613, it is possible to receive the transmitted symbol streams x0and x1distinguishably irrespective of the type of the precoders used in the cells.

The precoded symbol streams can be transmitted through the individual virtual antennas along with a CRS. InFIG. 9, a CRS621
(CRS0A)

is allocated for a 0th virtual antenna631of the cell A601and another CRS623
(CRSM−1A)

is allocated for a (MA−1)th virtual antenna633of the cell601. Here, MA denotes a number of transmit antennas of the cell A601. Similarly, a CRS661
(CRS0B)

is allocated for a 0th virtual antenna671of the cell B603, and another CRS663
(CRSMA−1B)
is allocated for a (MB−1)th virtual antenna633of the cell B603. Here, MB denotes a number of transmit antennas of the cell B603.

As described with reference toFIG. 9, the multi-cell transmission diversity method of the present invention is capable of achieving the transmission diversity gain when the number of transmit antennas of each cell is more than two transmit antennas regardless of the number of cells involved in the collaborative transmission. The multi-cell transmission diversity method of the present invention is advantageous to reuse the conventional transmission diversity receiver structure.

A description is made of the reusability of the conventional transmission diversity receiver structure with reference to the structure of the receiver ofFIG. 1. The signal y received through the receive antenna111is the sum of the transmitted signal100and the AWGN z.

The demultiplexer121of the receiver110demultiplexes the first symbol stream, the first DRS, the second symbol stream, and the second DRS from the received signal. The first and second DRSs are fed to the channel estimator123, and the first and second symbol streams are fed to the T×d decoder125.

Also, the demultiplexer121can demultiplex the CRS from the received signal.

The channel estimator123estimates the channel on which the first precoded signal is received by using the first DRS and feeds the estimation result to the T×D decoder125. The channel estimator123also estimates the channel on which the second precoded signal is received by using the second DRS and feeds the estimation result to the T×D decoder125.

The channel estimator123also measures the channel condition using the CRS extracted by the demultiplexer121and feeds back the measurement results to the transmitter through a transmit antenna (not shown).

The T×D decoder125recovers the received modulation symbols using the channel estimation result fed by the channel estimator123.

The demodulation and decoding unit127recovers the transmitted signal from the output of the T×D decoder125.

FIG. 10is a flowchart illustrating a transmission procedure of a multi-cell transmission diversity method according to an exemplary embodiment of the present invention.

Referring toFIG. 10, the transmitter first performs channel coding and modulation on the data signal destined to a receiver (S1010). Next, the transmitter performs transmission diversity precoding on the modulation symbol (S1020). As a result of the precoding, the first symbol stream x0and the second symbol stream x1are produced. Next, the transmitter multiplexes the first symbol stream with the first DRS (DRS0) and then performs a first type precoding on the multiplexed signal for forming the virtual antenna0(S1030). Sequentially, the transmitter multiplexes the second symbol stream with the second DRS (DRS1) and then performs a second type precoding on the multiplexed signal for forming the virtual antenna1(S1040). Finally, the transmitter performs summing of the precoded signals per transmit antenna and transmit the summed signals through the transmit antennas (S1050).

FIG. 11is a flowchart illustrating a reception procedure of a multi-cell transmission diversity method according to an exemplary embodiment of the present invention.

Referring toFIG. 11, the receiver first demultiplexes a received signal into DRSs and data signal (S1110). Next, the receiver estimates an equivalent channel of the virtual antenna0formed with the first type precoding by using the first DRS (DRS0) (S1120). Sequentially, the receiver estimates an equivalent channel of the virtual antenna1formed with the second type precoding by using the second DRS (DRS1) (S1130). The receiver performs transmission diversity decoding on the data signals using the estimated equivalent channels (S1140). Finally, the receiver performs demodulation and channel decoding on the transmission diversity-decoded signal to recover the transmitted signal (S1150).

As described above, the multi-cell transmission diversity method and apparatus of the present invention allows each cell involved in the collaborative transmission to form two virtual antennas using DRS and precoders for transmission diversity, thereby achieving robust and uniform transmission diversity gain regardless of the number of cells involved in the collaborative transmission and the number of antenna of each cell. Also, the multi-cell transmission diversity method and apparatus of the present invention is capable of recovering the transmitted data with channel estimation on the virtual antennas without modification of the conventional receiver structure. Also, the multi-cell transmission diversity method and apparatus of the present invention is configured such that the corresponding virtual antennas of the individual cells involved in the collaborative transmission use the same DRSs, thereby recovering the transmitted data without differentiating between the collaborative cells.