Signal transmission system using multiple antenna and signal transmission method thereof

The present invention relates to a multiple antenna transmission system and a signal transmission method In the signal transmission method using multiple antennas, a plurality of subcarrier symbols are grouped as a plurality of groups including first and second tiles that are basic resource management units including two or more subcarriers included in a set frequency domain, phases of subcarrier symbols included in a first tile are shifted to be a first phase shifting value, and phases of subcarrier symbols included in a second tile are shifted to be a second phase shifting value that is different from the first phase shifting value.

TECHNICAL FIELD

The present invention relates to a multiple antenna transmission system and a signal transmitting method using the multiple antenna transmission system.

BACKGROUND ART

In a multiple antenna communication system, a diversity gain and receiving complexity are important standards for designing a signal transmitting apparatus. Among multiple antenna transmission methods for obtaining a maximum diversity gain, a cyclic delay diversity transmission method has been proposed. In this method, the same signal is transmitted through the same subcarrier to all transmitting antennas, and different cyclic delays are provided to the respective antennas. That is, since the different delay times are provided for the respective transmitting antennas when transmitting the signal by using the multiple antennas, frequency diversity is artificially added. Accordingly, when one channel encoding frame is transmitted through a plurality of subcarriers in a multi-carrier system such as an orthogonal frequency division multiplexing (OFDM) system, receiving quality may be improved by using the frequency diversity added by a channel decoding unit.

When cyclic delay diversity is realized at a frequency domain, τtdenotes a cyclic delay value corresponding to an antenna t, fhdenotes a subcarrier frequency, and a phase shifting value is given as
Φ=−2 πτt·fh.

In this case, when it is assumed that a pilot signal is transmitted by using the cyclic delay diversity transmission method, a trade-off effect may occur between a frequency diversity gain and channel estimation performance according to the cyclic delay value. That is, when the cyclic delay value increases, the frequency diversity gain increases, but the channel estimation performance is deteriorated. In addition, since the frequency diversity gain may not be obtained when the cyclic delay value is decreased to be lower than a predetermined value to increase the channel estimation performance, the purpose of using the multiple antennas may be lost. Therefore, a transmission method for simultaneously maximizing the channel estimation performance and the frequency diversity gain is highly required.

DISCLOSURE OF INVENTION

Technical Problem

The present invention has been made in an effort to provide a multiple antenna transmission system for simultaneously maximizing channel estimation performance and a frequency diversity gain, and a signal transmission method using the multiple antenna transmission system.

Technical Solution

In an exemplary signal transmission method using multiple antennas according to an embodiment of the present invention, a plurality of subcarrier symbols are grouped as a plurality of groups including first and second tiles that are basic resource management units including two or more subcarriers included in a set frequency domain, phases of subcarrier symbols included in a first tile are shifted to be a first phase shifting value, and phases of subcarrier symbols included in a second tile are shifted to be a second phase shifting value that is different from the first phase shifting value.

An exemplary multiple antenna transmission system according to an embodiment of the present invention includes two or more phase shifting units, two or more inverse fast Fourier transform (IFFT) units, and two or more antennas. The two or more phase shifting units include a plurality of phase shifter groups respectively corresponding to a plurality of tiles that are basic resource management units including two or more subcarriers included in a set frequency domain. The two or more IFFT units multiplex an output signal of one corresponding phase shifting unit, and convert the output signal to be a time domain signal. The two or more antennas transmit the output signal of one corresponding IFFT unit.

ADVANTAGEOUS EFFECTS

According to the exemplary embodiment of the present invention, the multiple antenna transmission system for increasing the frequency diversity gain and improving the channel estimation performance at the receiving terminal, and the signal transmission method using the multiple antenna transmission system may be realized.

MODE FOR THE INVENTION

It will be understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In addition, the terms “Module”, “Unit” and “Block” used herein respectively mean one unit that processes a specific function or operation, and may be implemented by hardware or software and a combination thereof.

A multiple antenna transmission system according to an exemplary embodiment of the present invention and a signal transmitting method using the multiple antenna transmission system will be described with reference to the figures.

While the multiple antenna transmission system generally includes two or more antennas, only two antennas ANT #1and ANT #2are illustrated in the exemplary embodiment of the present invention for convenience of description. In addition, in an orthogonal frequency division multiplexing (OFDM) system, a plurality of subcarriers included in a predetermined frequency domain are grouped to be used as basic units of one resource management, and the basic units will be referred to as “tiles” InFIG. 1andFIG. 2, when S(fi) denotes an input symbol to be transmitted to correspond to a subcarrier fiand a phase shifting value established at each phase shifter is—Φ,the phase shifting value is shown as exp(−j Φ) in each phase. That is, the corresponding phase shifter multiplies the input symbol by exp(−jΦ). Further, τ0and τ1respectively denote cyclic delay values respectively corresponding to the antenna ANT #1and the antenna ANT #2.

FIG. 1is a block diagram representing a signal transmitting method using conventional multiple antennas.

As shown inFIG. 1, a conventional multiple antenna transmission system includes first and second phase shifting units10and20, first and second inverse fast Fourier transformers (IFFT)30and40, and a plurality of antennas ANT #1and ANT #2.

The first phase shifting unit10includes phase shifter groups10a1, . . . , and10aNfor processing input symbols respectively corresponding to N tiles Tile #1to Tile #N. Each phase shifter group includes first to Mthphase shifters for respectively performing phase shifting operations for M subcarriers. The first to Mthphase shifters shift a phase of the input symbol according to different phase shifting values established in each phase shifter and transmit the input symbol to the first IFFT30.

The second phase shifting unit20includes phase shifter groups20a1, . . . , to20aNfor processing input symbols respectively corresponding to the N tiles Tile #1to Tile #N. Each phase shifter group includes first to Mthphase shifters for respectively performing phase shifting operations for M subcarriers. The first to Mthphase shifters shift a phase of the input symbol according to different phase shifting values established in each phase shifter and transmit the input symbol to the first IFFT40.

The first IFFT30multiplexes the phase shifted symbol input from the plurality of phase shifters of the first phase shifting unit10to shift the phase shifted symbol to a time domain signal, and transmits the time domain signal to the antenna ANT #1. The second IFFT40multiplexes the phase shifted symbol input from the plurality of phase shifters of the second phase shifting unit20to shift the phase shifted symbol to the time domain signal, and transmits the time domain signal to the antenna ANT #2. The antennas ANT #1and ANT #2transmit the received signals to a receiving terminal.

That is, the respective phase shifting values of the first to Mthphase shifters respectively included in the phase shifter groups11a1, . . . , and11aNrespectively corresponding to the N tiles Tile #1to Tile #N included in the first phase shifting unit10are set to be different from each other, and the cyclic delay diversity transmission method is applied such that symbols having phases that are shifted by the same tile respectively have different phase shifting values, which is applied to the second phase shifting unit20as well. Accordingly, since the cyclic delay is increased over a predetermined level, the channel estimation performance at the receiving terminal for performing a channel estimation operation for each unit is deteriorated.

A signal transmitting method for maximizing the frequency diversity gain by improving the signal transmitting method in the conventional multiple antenna transmission system shown inFIG. 1without deteriorating the channel will be described with reference toFIG. 2.

FIG. 2is a block diagram representing a signal transmitting method using multiple antennas according to the exemplary embodiment of the present invention.

The multiple antenna transmission system according to the exemplary embodiment of the present invention shown inFIG. 2includes first and second phase shifting units110and120, first and second inverse fast Fourier transformers (IFFTs)130and140, and a plurality of antennas ANT #1and ANT #2.

The first phase shifting unit110for shifting a phase of an input symbol transmitted to the antenna ANT #1to transmit the input symbol to the first IFFT130includes first to Nthphase shifter groups110a1to110aNcorresponding to first to Nthtiles to process the input symbol corresponding to the N tiles Tile #1to Tile #N. Here, the first phase shifter group110a1includes first to Mthphase shifters110a1−1 to110aN−M for respectively shifting phases of M input symbols included in the first tile Tile #1, and the second to Nthphase shifter groups110a2to110aNrespectively includes M phase shifters. In addition, the M phase shifters in the first to Nthphase shifter groups110a1to110aNshift the phase of the input signal according to the phase shifting value and transmit the input signal to the first IFFT130.

The second phase shifting unit120for shifting the phase of the input symbol transmitted to the antenna ANT #2to transmit the input symbol to the second IFFT140includes first to Nthphase shifter groups120a1to120aNrespectively corresponding to the first to Nthtiles Tile #1to Tile #N to process the input symbols corresponding to the N tiles Tile #1to Tile #N. Here, the first phase shifter group120a1includes first to Mthphase shifters120a1−1 to120aN−M for shifting the phases of M input symbols included in the first tile Tile #1, and the second to Nthphase shifter groups120a2to120aNrespectively include M phase shifters. In addition, the M phase shifters in the first to Nthphase shifter groups120a1to120aNshift the phase of the input symbol according to the same phase shifting value and transmit the input symbol to the second IFFT140.

The first IFFT130multiplexes the phase-shifted symbol to convert it to a time domain signal, and transmits the signal to the antenna ANT #1. The second IFFT140multiplexes the phase-shifted symbol to the time domain signal and transmits the signal to the antenna ANT #2. The antennas ANT #1and ANT #2transmit the received signal to a receiving terminal.

In a signal transmission method using the multiple antennas according to the exemplary embodiment of the present invention, one symbol is transmitted through the different antennas ANT #1and ANT #2. Four input symbols S(fY0), S(fY0+M−1), S(fYn), and S(fYn+M−1) shown inFIG. 2in the signal transmission method of the conventional multiple antenna transmission system will now be described.

The phase of the symbol S(fY0) is shifted through the first phase shifter110a1−1 of the first phase shifter group110a1in the first phase shifting unit110and the first phase shifter120a1−1 of the first phase shifter group120a1in the second phase shifting unit120. The phase of the symbol S(fY0+M−1) is shifted through the M phase shifter110a1−M of the first phase shifter group110a1in the first phase shifting unit110, and the M phase shifter of the first phase shifter group120a1in the second phase shifting unit120. The phase of the symbol S(fYn) is shifted through the first phase shifter110aN−1 of the Nthphase shifter group110aN in the first phase shifting unit110and the first phase shifter120aN−1 of the Nthphase shifter group120aN in the second phase shifting unit120. In addition, the phase of the symbol S(fYn+M−1) is shifted through the Mthphase shifter110aN−M of the Nthphase shifter group110aNin the first phase shifting unit110and the M phase shifter110aN−M of the Nthphase shifter group120aNin the second phase shifter group120.

That is, the phases of the respective symbols are respectively shifted by the different phase shifting units110and120, and accordingly the phases are respectively shifted to different values to be transmitted through the antennas ANT #1and ANT #2.

Different from the conventional multiple antenna transmission system shown inFIG. 1, in an input symbol process in the multiple antennas transmission system according to the exemplary embodiment of the present invention shown inFIG. 2, respective phase shifting values of the first to Nthphase shifter groups110a1to110aNand120a1to120aNcorresponding to the N tiles Tile #1to Tile #N of the first and second phase shifting units110and120are set to be the same. That is, the phase shifting values in the phase shift group corresponding to one tile in one phase shifting unit among the first and second phase shifting units110and120are set to be the same, and therefore the input symbols in one tile in the signal transmitted through one antenna are shifted to the same phase values to be transmitted.

Different from the conventional multiple antenna transmission system shown inFIG. 1, in an input symbol process in the multiple antennas transmission system according to the exemplary embodiment of the present invention shown inFIG. 2, respective phase shifting values of the first to Mthphase shifter groups110a1to110aNand120a1to120aNcorresponding to the N tiles Tile #1 to Tile #N of the first and second phase shifting units110and120are set to be the same. That is, the phase shifting values in the phase shift group corresponding to one tile in one phase shifting unit among the first and second phase shifting units110and120are set to be the same, and therefore the input symbols in one tile in the signal transmitted through one antenna are shifted to the same phase values to be transmitted.

In addition, inFIG. 2, the phase shifting value of the phase shifter corresponding to a tile h among the phase shifters in the first to Nthphase shifter groups110a1to110aNand120a1to120aNof the first and second phase shifting units110and120is −2πfkhτt. In this case, fkhmay be set to be fYhthat is a frequency of a subcarrier having the lowest frequency among the subcarriers in the tile, or it may be set to be fYh+Mh−1that is a frequency of a subcarrier having the highest frequency among the sub-carriers in the tile. In addition, fkhmay be set to be (fYh+fYh+Mh−1)/2 that is an intermediate value between the frequency of the subcarrier having the highest frequency and the frequency of the subcarrier having the lowest frequency.

In addition, τtdenotes a cyclic delay value allocated for each antenna, and is required to be set to sufficiently obtain a frequency diversity gain. The cyclic delay value of each antenna is set as follows. When the number of transmitting antennas is T, the cyclic delay values respectively corresponding to the first to Tthantennas are τ0, τ1, . . . and τT−1, and τ0<τ1< . . . <τT−1, τt−τt−1(here, t=1, . . . , and T) are required to be designed to be greater than a maximum multipath delay value of a radio channel. Accordingly, the frequency diversity gain between tiles may be maximized since the channel estimation performance at the receiving terminal is not affected and a difference between cyclic delay values of antennas may be sufficiently increased.

In the signal transmission method using the multiple antennas according to the exemplary embodiment of the present invention, the cyclic delay diversity method is used between the different tiles, and the same phase shifting value is used between subcarrier input symbols corresponding to one tile in the same phase shifter group rather than using the cyclic delay diversity method. Accordingly, since the cyclic delay is maintained to be lower than a predetermined level, the channel estimation performance at the receiving terminal may be increased. In addition, since the difference between cyclic delay values of antennas may be sufficiently increased, the channel estimation performance at the receiving terminal may be improved while the frequency diversity gain may be maximized.

The above-described methods and apparatuses are not only realized by the exemplary embodiment of the present invention, but, on the contrary, are intended to be realized by a program for realizing functions corresponding to the configuration of the exemplary embodiment of the present invention or a recording medium for recording the program.