RU2396714C1 - Method for distribution of reference signals in system with multiple inputs and multiple outputs (mimo) - Google Patents

Abstract

FIELD: information technologies. ^ SUBSTANCE: method includes preparation of multiple subframes for multiple antennas, besides one subframe includes multiple OFDM-symbols in time area and multiple subcarriers in frequency area, at the same time reference signal in one subframe and reference signal in the other subframe are arranged so that reference signals do not overlap in a single subframe, besides reference signal of one subframe and reference signal of the other subframe are serially arranged in adjacent OFDM-symbols or in adjacent subcarriers. ^ EFFECT: improved quality of information transfer. ^ 11 cl, 91 dwg

Description

FIELD OF THE INVENTION

[1] The present invention relates to wireless data transmission, in particular to a method for distributing reference signals in an antenna system with many inputs and many outputs (MIMO).

State of the art

[2] A multi-input multi-output (MIMO) system is defined as a system that improves data transmission efficiency by using many transmit antennas and many receive antennas. A MIMO system can be implemented using, for example, such a MIMO scheme as spatial multiplexing and spatial diversity. In accordance with the principle of spatial multiplexing, various streams are simultaneously transmitted via a plurality of transmit antennas, and thus fast transmission is achieved without the need to increase the system bandwidth. In accordance with the principle of spatial diversity, the same streams are transmitted through multiple transmit antennas to obtain diversity.

[3] To reproduce the signal transmitted by the transmitter, the receiver must estimate the channel. Channel estimation is defined as the process by which a distorted signal is restored by compensating for signal distortion due to attenuation. In general, reference signals are necessary for channel estimation, which are known to both the transmitter and the receiver.

[4] The reference signals can be distributed using either the first circuit in which the reference signals are distributed over the entire frequency band or the second circuit in which the reference signals are distributed over a part of the frequency band. The reference signals when using the first circuit are distributed more densely than when using the second circuit. If the first scheme is used, then the channel estimation can be carried out more accurately. On the other hand, in the second scheme, a higher data rate can be achieved than in the first scheme. In the second scheme, the reference signals are almost not distributed, which can degrade the channel estimate.

[5] In a MIMO system, multiple channels independently provide multiple channels. The reference signals should be distributed taking into account multiple channels. In addition, in accordance with the rank, the MIMO system can operate either in a single codeword mode or in a multiple codeword mode. With an increase in the number of transmitting antennas, the number of reference signals may increase. However, this can adversely affect the data transfer rate.

[6] Therefore, a technology is needed in which reference signals can be efficiently distributed taking into account multiple antennas.

Disclosure of invention

Technical solution

[7] The present invention provides a method for distributing reference signals for an antenna system with many inputs and many outputs (MIMO) over a wireless connection.

[8] In accordance with one aspect of the invention, there is provided a method for distributing reference signals for a subframe in a multi-input multi-output (MIMO) wireless communication system. A subframe includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain and a plurality of subcarriers in a frequency domain. The method includes distributing a plurality of first reference signals for a first antenna to a first OFDM symbol during a subframe for a first antenna at constant intervals in a frequency domain, distributing a plurality of second reference signals for a second antenna to a first OFDM symbol during a subframe for a second antenna at constant intervals in the frequency domain, provided that the plurality of second reference signals do not overlap with the plurality of first reference signals, the distribution of the plurality of third reference signals for the third antenna in the second OFD The M symbol during the subframe for the third antenna at constant intervals in the frequency domain, wherein the second OFDM symbol is adjacent to the first OFDM symbol, and the distribution of the plurality of fourth reference signals for the fourth antenna to the second OFDM symbol during the subframe for the fourth antenna from the condition that the plurality of fourth reference signals does not overlap with the plurality of third reference signals.

[9] In accordance with another aspect of the present invention, a method for placing reference signals in a wireless communication system is provided. The method includes preparing a plurality of subframes for a plurality of antennas, wherein one subframe comprises a plurality of OFDM symbols in a time domain and a plurality of subcarriers in a frequency domain, arranging a reference signal for one subframe and arranging a reference signal for another subframe so that it does not overlap with the reference signal for one subframe, wherein the reference signal for one subframe and the reference signal for another subframe are sequentially placed in adjacent OFDM symbols or in adjacent subcarriers.

[10] In accordance with another aspect of the invention, a method for placing reference signals in a wireless communication system is provided. The method comprises arranging a plurality of reference signals for a selected signal and arranging a plurality of reference signals for a multi-user signal such that the intervals in the frequency domain of the plurality of reference signals for a multi-user signal are shorter than the intervals of the plurality of reference signals for a selected signal.

[11] In accordance with another aspect of the invention, there is provided an apparatus for a multi-input multiple output (MIMO) wireless communication system based on orthogonal frequency division multiplexing (OFDM). The device includes a plurality of transmit antennas, a multiplexer for distributing the plurality of reference signals across the plurality of transmitting antennas so that they do not overlap with each other, at least two reference signals from the plurality of reference signals are sequentially arranged in adjacent OFDM symbols or in adjacent subcarriers, and an OFDM modulator for modulating a plurality of reference signals.

[12] In accordance with another aspect of the invention, there is provided an apparatus for an orthogonal frequency division multiplexing (OFDM) wireless communication system. The device includes at least one receiving antenna and a channel estimator for estimating a channel using a plurality of reference signals for a plurality of transmitting antennas, while the plurality of reference signals do not overlap and at least two reference signals from the plurality of reference signals sequentially placed in adjacent OFDM symbols or in adjacent subcarriers.

[13] In accordance with another aspect of the invention, there is provided a reference signal structure for providing channel estimation information in an OFDM-based MIMO wireless communication system. The reference signal structure includes a plurality of reference signals for a plurality of non-overlapping antennas, wherein at least two reference signals from a plurality of reference signals are sequentially arranged in adjacent OFDM symbols or in adjacent subcarriers.

Brief Description of the Drawings

[14] The features, nature and advantages of the present invention will become more apparent from the following detailed description in conjunction with the drawings, in which throughout the same elements are denoted by the same positions.

[15] Figure 1 is a block diagram of a transmitter having multiple antennas;

[16] FIG. 2 is a block diagram of a receiver having multiple antennas;

[17] figure 3 shows an example of a distribution of reference signals when using two transmitting antennas;

[18] figure 4 shows an example of a distribution of reference signals when using four transmitting antennas;

[19] figure 5 shows an example of a distribution of reference signals;

[20] figure 6 shows another example of a distribution of reference signals;

[21] figure 7-19 shows examples of the distribution of reference signals for a multi-user signal;

[22] FIGS. 20-82 show examples of reference signal distributions in accordance with an embodiment of the present invention;

[23] on Fig-91 shows examples of the distribution of reference signals for a multi-user signal.

The implementation of the invention

[24] Additional features and advantages of the invention will be set forth in the following description, and may be partially understood from the description or practice of the invention. It should be understood that the previous general description and the following detailed description of the present invention are illustrative and explanatory and are intended to further explain the claimed invention.

[25] The technology described below can be used in various communication systems. Communication systems designed to provide various data services (for example, voice, packet data, etc.) are widespread. The technology can be used for both downlink and uplink. In general, a downlink means transmitting data from a base station (BS - base station) to a user equipment (UE), and an uplink means transmitting data from a subscriber's equipment UE to a BS. The base station BS in the General case is a stationary station that exchanges data with the subscriber equipment UE, and may be called another term, for example, a node B, a base transceiver system (BTS) and an access point. The subscriber equipment of the UE may be stationary or movable. The subscriber equipment of the UE may also be called another term, for example, a mobile station (MS - mobile station), a user terminal (UT - user terminal), a subscriber station (SS-subscriber station) and a wireless device.

[26] A communication system can be either a system with many inputs and many outputs (MIMO), or a system with many inputs and one output (MISO - multiple-input single-output). A MIMO system includes multiple transmit antennas and multiple receive antennas. A MISO system includes multiple transmit antennas and one receive antenna.

[27] There are no restrictions in a multiple access modulation scheme. A multiple access modulation scheme may be a well-known single carrier modulation scheme (e.g., TDMA (time division multiple access), CDMA (code division multiple access), SC-FDMA ( single carrier-frequency division multiple access - or a multi-carrier modulation method (for example, orthogonal frequency division multiplexing).

[28] Channel estimation can be effectively performed by the receiver when the reference signals are distributed according to the following conditions.

[29] First, the reference signals must be distributed so that the receiver can distinguish between reference signals transmitted by multiple transmitting antennas. This is because the reference signals are used by the receiver to estimate the channel. The reference signals can be distributed so as not to overlap each other in the time and / or frequency domain for the respective transmitting antennas, so that the receiver can distinguish the reference signals. Alternatively, when the reference signals are orthogonal to each other in the code domain, the reference signals may overlap each other in the time and / or frequency domain. To achieve orthogonality in the code domain, an orthogonal code having excellent autocorrelation or cross-correlation can be used in the reference signals. Examples of an orthogonal code may include a constant amplitude zero auto-correlation (CAZAC) sequence and a Walsh code.

[30] Secondly, the channel divergence should be negligible in the region where the reference signals are located. A channel in such an area is used to decode data distributed next to the reference signals. If the channel varies greatly in such an area, the channel estimation error can become significant.

[31] In embodiments of the invention, the reference signals can be shifted by a certain interval along the time axis or by a certain interval along the frequency axis. That is, for each subframe for the respective transmitting antennas, the reference signals can generally be shifted by a certain time interval and / or a certain frequency interval while maintaining the interval between the reference signals.

[32] The reference signal may be a reference signal for a user or a reference signal for a multi-user signal. The multi-user signal may be a broadcast signal and / or a multicast signal. A broadcast signal is sent to all users within a specific zone (e.g., cell and / or sector). A multicast signal is sent to a specific group of users. A unicast signal is sent to a specific user. An example of a multi-user signal may be a signal of a broadcast / multicast mobile service (MBMS - mobile broadcast / multicast service). When transmitting an MBMS signal, the same signal is transmitted from all cells (or base stations).

[33] Various examples of reference signal allocation in a MIMO system having four transmit antennas will now be described. The reference signals will be distributed in accordance with the following principles. First, the number of reference signals for the first and second antennas in the subframe is greater than the number of reference signals for the third and fourth antennas in the subframe. Secondly, the percentage of all reference signals in the subframe is below a predetermined value. Thirdly, the reference signals for each transmitting antenna do not overlap with each other.

[34] A subframe includes multiple OFDM symbols in the time domain and multiple subcarriers in the frequency domain. A subframe is a resource grid that is defined for each transmit antenna. The transmission time interval (TTI) can be defined as the time required to transmit a single subframe. A frame may include multiple subframes. For example, one frame may include ten subframes.

[35] A subframe can be divided into two areas: a control channel and a data channel. A control channel is an area carrying control data. A data channel is an area carrying user data. For example, a first OFDM symbol, a second OFDM symbol, and a third OFDM symbol may be assigned to a control channel, and other OFDM symbols may be assigned to a data channel. Although the number of OFDM symbols for the control channel is less than the number of OFDM symbols for the data channel, the reliability of the control channel should be higher than the reliability of the data channel. To transmit a control channel, only a portion of the plurality of antennas can be assigned. For the control channel, a first antenna and a second antenna may be used. In this case, the reference signals for the third antenna and the reference signals for the fourth antenna cannot be assigned to the OFDM symbols of the control channel, since the third antenna and the fourth antenna are not used for the control channel.

[36] Figure 1 is a block diagram of a transmitter having multiple antennas.

[37] As shown in FIG. 1, the transmitter 100 includes a channel encoder 120, a converter 130, a MIMO processor 140, a multiplexer 150, and an OFDM modulator 160. The channel encoder 120 encodes an input stream in accordance with a predetermined coding scheme and then generates an encoded word . A converter 130 converts the encoded word into a symbol reflecting a position in the signal constellation. Since there are no restrictions on the modulation scheme of converter 130, the modulation scheme can be m-position phase shift keying (m-PSK - m-phase shift keying) or m-position quadrature amplitude modulation (m-QAM - m-quadrature amplitude modulation). Examples of m-position phase shift keying (m-PSK) include BPSK (binary phase shift keying), quadrature phase shift keying (QPSK), and 8-position phase shift keying (8-PSK). Examples of m-position quadrature amplitude modulation (m-QAM) include 16-position quadrature amplitude modulation (16-QAM), 64-position quadrature amplitude modulation (64-QAM) and 256-position quadrature amplitude modulation (256-QAM). The MIMO processor 140 processes the displayed symbol using the MIMO scheme in accordance with the transmit antennas 190-1, ..., 190-Nt (Nt> 1). For example, the MIMO processor 140 may perform precoding based on the encryption book.

[38] A multiplexer 150 distributes a subcarrier of an input symbol and reference signals. The reference signals are distributed over the respective transmit antennas 190-1, ..., 190-Nt. The reference signals, also called pilot signals, are used for channel estimation or data demodulation and are recognized by the transmitter 100 and receiver 200 shown in FIG. OFDM modulator 160 modulates the multiplexed symbol and accordingly provides an OFDM symbol. OFDM modulator 160 may perform an inverse fast Fourier transform (IFFT) on the multiplexed symbol and optionally add a cyclic prefix to it (CP). The OFDM symbol is transmitted through the respective transmit antennas 190-1, ..., 190-Nt.

[39] Figure 2 is a block diagram of a receiver having multiple antennas.

[40] As shown in FIG. 2, the receiver 200 comprises an OFDM demodulator 210, a channel estimator 220, a MIMO post processor 230, an inverter 240, and a channel decoder 250. Signals received from receiving antennas 290-1, ..., 290- Nr are subjected to fast Fourier transform (FFT) by the OFDM demodulator 210. The channel estimator 220 obtains a channel estimate using the reference signals. The MIMO post-processor 230 performs post-processing equivalent to the processing performed by the MIMO processor 140. The inverter 240 performs the inverse conversion of the input symbol into a coded word. Channel decoder 250 decodes the encoded word so that it is restored to the original data.

[41] Next, the distribution of the reference signals will be described.

[42] FIG. 3 illustrates an example of a reference signal distribution using two transmit antennas. In general, data can be transmitted in a block from a subframe for respective transmit antennas according to an OFDM modulation scheme. For example, the subframe shown in FIG. 3 includes seven OFDM symbols, with a transmission time interval (TTI) of 0.5 milliseconds (ms). However, the concept of the present invention is not limited thereto, and therefore, the subframe and the transmission time interval (TTI) can be configured in various forms.

[43] As shown in FIG. 3, reference signals are allocated respectively for a subframe of a first antenna and a subframe of a second antenna. D is a data symbol for data transfer, R ₁ is a first reference signal for a first antenna, and R ₂ is a second reference signal for a second antenna. The first reference signal R ₁ may be equal to or different from the second reference signal R ₂ .

[44] Each of the elements of the resource grid forming the subframe is called the resource element. For example, the resource element q (k, l) is located in the kth OFDM symbol and the 1st subcarrier. The data symbol D, the first reference signal R ₁ and the second reference signal R ₂ are carried in one resource element.

[45] Regarding the subframe of the first antenna, the reference signals are distributed across seven OFDM symbols. To make the description clearer, hereinafter seven OFDM symbols will be referred to as the first OFDM symbol, the second OFDM symbol, ..., and the seventh OFDM symbol from the beginning of the transmission time interval (TTI), respectively.

[46] In the first OFDM symbol, the first reference signals R ₁ may be distributed in an interval of six subcarriers. Similarly, in the fifth OFDM symbol, the second reference signals R ₂ can be distributed in an interval of six subcarriers. In the fifth OFDM symbol, all of the second reference signals R _{2 are} shifted by an amount of three subcarriers from the positions in which the first reference signals R _{1 are located} in the first OFDM symbol. In the subframe, the matrix (R ₁ , D, D, D, D, D) is repeated in the first OFDM symbol, and the matrix (D, D, D, R ₂ , D, D) is repeated in the fifth OFDM symbol.

[47] As for the second antenna, the reference signals are distributed according to the same scheme as in the first antenna. In the first OFDM symbol, the first reference signals R _{1 are} distributed in an interval equal to six subcarriers. In the fifth OFDM symbol, the negative second -R ₂ reference signals are distributed in an interval of six subcarriers. Negative second reference signals —R ₂ are obtained by inverting the second reference signals R ₂ . In the fifth OFDM symbol, all negative second reference signals -R _{2 are} shifted by three subcarriers from the positions at which the first reference signals R ₁ in the first OFDM symbol are located. That is, the matrix (R ₁ , D, D, D, D, D) is repeated in the first OFDM symbol, and the matrix (D, D, D, -R ₂ , D, D) is repeated in the fifth OFDM symbol.

[48] Since the reference signals in the first and second antennas are distributed in the same way, an orthogonal code can be used so that the receiver can distinguish the reference signals for the respective transmit antennas. The orthogonal code may be a constant amplitude sequence with zero autocorrelation (CAZAC sequence) or a Walsh sequence having remarkable autocorrelation or cross-correlation.

[49] FIG. 4 illustrates an example of a reference signal distribution using four transmit antennas. Reference signals are allocated for each subframe for the respective transmit antennas. Here, N is a null symbol, R ₁ is a first reference signal, R ₂ is a second reference signal, and D is a data symbol. A null character can be defined as a character that does not carry data. A null symbol may be generated when data is not assigned to a subcarrier, or when the subcarrier to which data is assigned later disappears.

[50] With respect to the first antenna, reference signals are distributed in an interval of six subcarriers. In other words, the reference signals are placed with five subcarriers between them. Five subcarriers may include four data symbols D and one null symbol. Thus, the first OFDM symbol is repeated with the matrix (R ₁ , D, D, N, D, D). A null symbol is assigned to a resource element in which reference signals for the third and fourth antennas are described, described below. The reference signals are not allocated in the second, third, and fourth OFDM symbols. Instead, data symbols D are allocated to them. Reference signals may be allocated in an interval of six subcarriers in a fifth OFDM symbol. In the fifth OFDM symbol, all reference signals are shifted by an amount of three subcarriers from the positions at which the reference signals are located in the first OFDM symbol. The sixth and seventh OFDM symbols are assigned data symbols instead of reference signals.

[51] With respect to the second antenna, the reference signals are distributed in the same manner as for the first antenna. The reference signals for the first and second antennas are distributed so as to overlap each other in the same OFDM symbols and subcarriers. In order to distinguish between reference signals for the first antenna and reference signals for the second antenna, an orthogonal code having excellent autocorrelation or cross-correlation can be used in the receiver. By using the orthogonality of the reference signals R ₁ and R ₂ transmitted through the first antenna and the reference signals R ₁ and -R ₂ transmitted through the second antenna, the receiver can separate one of these reference signals from others.

[52] With respect to the third antenna, the reference signals are distributed as follows. The reference signals R _{1 are} allocated in the first OFDM symbol in an interval of six subcarriers. Similarly, the reference signals R _{2 are} allocated in the fifth OFDM symbol in an interval of six subcarriers. In the fifth OFDM symbol, all the reference signals R _{2 are} shifted by an amount of three subcarriers from the positions at which the reference signals in the first OFDM symbol are located. Thus, the matrix (N, D, D, R ₁ , D, D) is repeated in the first OFDM symbol, and the matrix (R ₂ , D, D, N, D, D) is repeated in the fifth OFDM symbol. For the fourth antenna, the reference signals are distributed in the same manner as for the third antenna. The reference signals are distributed in an interval equal to six subcarriers in the first and fifth OFDM symbols. To distinguish between reference signals for the third antenna and reference signals for the fourth antenna, an orthogonal code may be used at the receiver.

[53] Although the above distribution of the reference signals is exemplified, the concept of the present invention is not limited thereto, and therefore, the reference signals can be shifted by a certain interval along the time axis or by a certain interval along the frequency axis. That is, for each subframe of the respective transmit antennas, the reference signals can generally be shifted by a certain time interval and / or a certain frequency interval while maintaining the interval between the reference signals. Since, in the general case, the reference signals can be shifted as described above, without the need to redistribute the reference signals, channel estimation can be performed for multiple cells, multiple sectors, and multiple users.

[54] Meanwhile, the reference signals for a particular antenna may be partially or fully used (or not used) in accordance with changes in the channel over time in a multiple of subframes.

[55] In the above description, the reference signals overlap each other when at least two antennas are used. Overlapping reference signals retain their orthogonality in the code domain through the use of orthogonal code.

[56] FIG. 5 illustrates an example of a reference signal distribution. R is a reference signal, and a space of a resource element means a data symbol or a null symbol.

[57] As shown in FIG. 5, a plurality of reference signals R are allocated in an interval equal to two subcarriers in a third OFDM symbol. The plurality of R reference signals are also allocated in an interval equal to two subcarriers in the seventh OFDM symbol, which is four OFDM symbols away from the third OFDM symbol. The reference signals R in the third and seventh OFDM symbols are spaced from each other. The plurality of R reference signals are allocated in an interval equal to two subcarriers in the eleventh OFDM symbol, which is four OFDM symbols away from the seventh OFDM symbol.

[58] Each reference signal R may be a reference signal for a multi-user signal. Here, the multi-user signal may be a broadcast signal and / or a multicast signal. A broadcast signal is sent to all users of a specific area (for example, cells and / or sectors). A multicast signal is sent to a specific group of users. A unicast signal is sent to a specific user. An example of a multi-user signal may be a Broadcast / Multicast Mobile Service Signal (MBMS signal). When transmitting an MBMS signal, the same signal is transmitted from all cells (or base stations). Therefore, all base stations use the same reference signal.

[59] When using the MBMS signal, the reference signals R can be placed with a narrow interval between them to minimize frequency selectivity due to delay spread. In addition, the reference signals are densely spaced on the time axis to minimize time selectivity.

[60] In accordance with some MIMO methods, such as cyclic delay diversity (CDD) and beam generation, it is assumed that the user equipment receives reference signals through a single transmit antenna. Therefore, the base station (BS) does not need to transmit reference signals by classifying the reference signals for each transmit antenna.

[61] FIG. 6 illustrates another example of a distribution of reference signals.

[62] As shown in Fig.6, the reference signals are placed with a relatively wider spacing between them in the frequency domain compared with Fig.5. With such a distribution, an advantage can be obtained if the frequency selectivity is relatively low, or if the subcarrier bandwidth is relatively small. The subcarrier bandwidth may be half the subcarrier bandwidth shown in FIG.

[63] FIG. 7 illustrates an example of a reference signal allocation for a multi-user signal. Here, R ₁ is the reference signal for the first antenna, R ₂ is the reference signal for the second antenna.

[64] As shown in FIG. 7, the reference signals R _{1 are} allocated in an interval equal to two subcarriers in the third OFDM symbol. That is, the reference signals R ₁ are located with one subcarrier between them. Therefore, the matrix (R ₁ , N) is repeated in the third OFDM symbol, where N is the zero symbol. The reference signals R _{1 are} distributed in an interval equal to two subcarriers in the seventh OFDM symbol, which is four times the OFDM symbol from the third OFDM symbol. The reference signals R ₁ in the third and seventh OFDM symbols are spaced from each other.

[65] The reference signals R ₂ in the same OFDM symbol are distributed alternately with the reference signals R ₁ . That is, one reference signal R ₂ is located between two reference signals R ₁ with the same interval in the frequency domain.

[66] FIG. 8 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[67] As shown in FIG. 8, the reference signals R ₁ for the first antenna are distributed in an interval of four subcarriers in the third OFDM symbol. That is, the reference signals R ₁ are located with three subcarriers between them. Therefore, the matrix (R ₁ , D, N, D) is repeated in the third OFDM symbol, where the space of the resource element means D and N. The reference signals R _{1 are} distributed in the interval equal to four subcarriers in the seventh OFDM symbol, which is separated by four OFDM symbols from the third OFDM symbol. The reference signals R ₁ in the third and seventh OFDM symbols are spaced from each other.

[68] The reference signals R ₂ for the second antenna are arranged alternately with the reference signals R ₁ in the same OFDM symbols at the same interval as the reference signals R ₁ . That is, one reference signal R ₂ is located between two reference signals R ₁ with the same interval in the frequency domain.

[69] FIG. 9 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[70] As shown in Fig.9, the reference signals R ₁ for the first antenna are distributed in the interval equal to two subcarriers in the third OFDM symbol. That is, the reference signals R ₁ are located with one subcarrier between them. Therefore, the matrix (R ₁ , N) is repeated in the third OFDM symbol. The reference signals R _{1 are} distributed in an interval equal to two subcarriers in the seventh OFDM symbol, which is four times the OFDM symbol from the third OFDM symbol. The reference signals R ₁ in the third and seventh OFDM symbols are spaced in the frequency domain from each other.

[71] The reference signals R ₂ for the second antenna are allocated in the same frequency domain as in the case of the reference signals R ₁ in OFDM symbols (for example, in the fourth OFDM symbol, in the eighth OFDM symbol, etc.) which are adjacent to OFDM symbols in which the reference signals R ₁ are distributed. That is, the frequency signals R _{2 are} distributed at the same interval as the frequency signals R ₂ .

[72] FIG. 10 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[73] As shown in FIG. 10, the reference signals R ₁ for the first antenna are distributed in an interval equal to four subcarriers in the third OFDM symbol. That is, the reference signals R ₁ are located with three subcarriers between them. Therefore, the matrix (R ₁ , D, N, D) is repeated in the third OFDM symbol. The reference signals R _{1 are} distributed in an interval equal to four subcarriers in the seventh OFDM symbol, which is spaced apart by an amount of four OFDM symbols from the third OFDM symbol. The reference signals R ₁ in the third and seventh OFDM symbols are spaced from each other.

[74] The reference signals R ₂ for the second antenna are allocated in the same frequency domain as in the case of the reference signals R ₁ in OFDM symbols (for example, in the fourth OFDM symbol, in the eighth OFDM symbol, etc.) which are adjacent to OFDM symbols in which the reference signals R ₁ are distributed. That is, the frequency signals R _{2 are} distributed in the frequency domain with the same interval as the frequency signals R ₂ .

[75] FIG. 11 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[76] As shown in FIG. 11, the reference signals R ₁ for the first antenna are distributed in an interval equal to two subcarriers in the third OFDM symbol. That is, the reference signals R ₁ are located with one subcarrier between them. Therefore, the matrix (R ₁ , N) is repeated in the third OFDM symbol. The reference signals R _{1 are} distributed in an interval equal to two subcarriers in the seventh OFDM symbol, which is four times the OFDM symbol from the third OFDM symbol. The reference signals R ₁ in the third and seventh OFDM symbols are spaced from each other.

[77] The reference signals R ₂ for the second antenna overlap the reference signals R ₁ in the same OFDM symbols in the same frequency domain. The reference signals R ₁ and R ₂ can maintain orthogonality in the code domain by using the orthogonal code.

[78] FIG. 12 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[79] As shown in FIG. 12, the reference signals R ₁ for the first antenna are distributed in an interval equal to four subcarriers in the third OFDM symbol. That is, the reference signals R ₁ are located with three subcarriers between them. Therefore, the matrix (R ₁ , D, N, D) is repeated in the third OFDM symbol. The reference signals R _{1 are} distributed in an interval equal to four subcarriers in the seventh OFDM symbol, which is spaced apart by an amount of four OFDM symbols from the third OFDM symbol. The reference signals R ₁ in the third and seventh OFDM symbols are spaced from each other.

[80] The reference signals R ₂ for the second antenna overlap the reference signals R ₁ in the same OFDM symbols and in the same frequency domain. The reference signals R ₁ and R ₂ can maintain orthogonality in the code domain by using the orthogonal code.

[81] FIG. 13 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[82] As shown in FIG. 13, the reference signals R ₁ for the first antenna are allocated in an interval of three subcarriers in the third OFDM symbol. The reference signals R ₂ for the second antenna are adjacent to the reference signals R ₁ and are distributed at the same interval as the reference signals R ₁ . Therefore, the matrix (R ₁ , R ₂ , D) is repeated in the third OFDM symbol.

[83] Both the reference signals R ₁ and the reference signals R _{2 are} allocated in OFDM symbols that are spaced apart by an amount of three OFDM symbols starting from the third OFDM symbol.

[84] FIG. 14 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used. 14-19, R means a reference signal for a multi-user signal, and T means a reference signal for a dedicated user signal. That is, examples with different types of reference signals will be given below.

[85] As shown in FIG. 14, the reference signals T ₁ for the first antenna and the reference signals T ₂ for the second antenna are allocated in the first OFDM symbol. In addition, the reference signals T ₁ and T _{2 are} also allocated in the fourth OFDM symbol. The reference signals R ₁ for the first antenna and the reference signals R ₂ for the second antenna are allocated in OFDM symbols that are four OFDM symbols away from the third OFDM symbol.

[86] FIG. 15 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[87] As shown in FIG. 15, the reference signals R ₁ for the first antenna and the reference signals R ₂ for the second antenna are distributed at a wider interval than in the example in FIG. 14.

[88] FIG. 16 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[89] As shown in FIG. 16, in comparison with the example in FIG. 4, the reference signals R ₁ for the first antenna and the reference signals R ₂ for the second antenna are allocated respectively in the interval of three subcarriers in the third OFDM symbol. The reference signals R ₂ are adjacent to the reference signals R ₁ and are distributed in the same range as the reference signals R ₁ .

[90] FIG. 17 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[91] As shown in FIG. 17, compared to the example in FIG. 14, reference signals T ₁ for the first antenna and reference signals T ₂ for the second antenna are allocated only in the first OFDM symbol.

[92] FIG. 18 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[93] As shown in FIG. 18, the reference signals R ₁ for the first antenna and the reference signals R ₂ for the second antenna are distributed at a wider interval than in the example of FIG. 17.

[94] FIG. 19 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[95] As shown in FIG. 19, compared to the example in FIG. 16, reference signals T ₁ for the first antenna and reference signals T ₂ for the second antenna are allocated only in the first OFDM symbol.

[96] In the embodiments of FIGS. 14-19, reference signals for multiple users can be transmitted by a single transmit antenna. Since it is assumed that the subscriber equipment (UE) receives the reference signals of one transmitting antenna using cyclic delay diversity (CDD) or beamforming methods, the base station (BS) does not need to transmit reference signals after classifying the reference signals for all transmitting antennas.

[97] Various examples of reference signal distribution in a MIMO system having four transmit antennas will now be described. The reference signals will be distributed in accordance with the following principles.

[98] (1) The reference signals R ₁ for the first antenna described in the example of FIG. 3 also retain their positions in the MIMO system containing four transmit antennas.

[99] (2) Among all the signals used, the percentage of all reference signals is below a predetermined value. When the percentage of all reference signals increases, the receiver can accordingly accurately estimate the channel by receiving a plurality of reference signals. However, the higher the percentage, the lower the data rate. Suppose the percentage is below about 15 or 20 percent. In this case, if the reference signals are distributed efficiently, the degradation of channel estimation indices can be minimized.

[100] (3) The reference signals for each transmit antenna do not overlap. That is, the reference signals for each transmit antenna do not overlap either in the time domain or in the frequency domain.

[101] FIG. 20 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention. T ₁ is the reference signal for the first antenna, T ₂ is the reference signal for the second antenna, T ₃ is the reference signal for the third antenna, T ₄ is the reference signal for the fourth antenna. An empty resource element may be a data symbol or a null symbol.

[102] As shown in FIG. 20, one subframe contains fourteen OFDM symbols. However, this is just one example, and therefore, the number of OFDM symbols constituting one subframe may vary. Although one subframe is illustrated for convenience, the reference signals for each antenna are allocated for each subframe of the respective antennas. That is, the reference signals T _{1 are} allocated in a subframe for the first antenna. The reference signals T _{2 are} allocated in a subframe for the second antenna. The reference signals T _{3 are} allocated in a subframe for the third antenna. The reference signals T _{4 are} allocated in a subframe for the fourth antenna. To make the description clearer, suppose that fourteen OFDM symbols are defined as a first OFDM symbol, a second OFDM symbol, ..., and a fourteenth OFDM symbol from the beginning of a transmission time interval (TTI).

[103] The reference signals T _{1 are} distributed in an interval equal to six subcarriers in the first and eighth OFDM symbols. In addition, the reference signals T _{1 are} also distributed in an interval equal to six subcarriers in the fifth and twelfth OFDM symbols. The reference signals T ₁ distributed in the fifth and twelfth OFDM symbols are all shifted by an amount of three subcarriers from the reference signals distributed in the first and fifth OFDM symbols.

[104] The reference signals T _{2 are} distributed in an interval equal to six subcarriers in the first, fifth, eighth and twelfth OFDM symbols. In the first and fifth OFDM symbols, all the reference signals T _{2 are} shifted by an amount of three subcarriers from the positions at which the reference signals T _{1 are located} . In the fifth and twelfth OFDM symbols, all the reference signals T ₂ are located at the same positions as the reference signals T ₁ .

[105] The reference signals T _{2 are} distributed in the interval equal to 12 subcarriers in the first, fifth, eighth and twelfth OFDM symbols. In the first OFDM symbol, all the reference signals T _{2 are} shifted by one subcarrier from the positions at which the reference signals T _{1 are located} . The reference signals T ₂ in the fifth, eighth and twelfth OFDM symbols are distributed in an interval equal to twelve subcarriers and are shifted by one subcarrier in comparison with where the reference signals of other antennas are located.

[106] The reference signals T _{4 are} distributed in an interval equal to twelve subcarriers in the first, fifth, eighth and twelfth OFDM symbols. All reference signals T _{4 are} shifted by one subcarrier from the positions at which the reference signals T _{3 are located} .

[107] The reference signals T ₁ and T ₂ are more densely distributed than the reference signals T ₂ and T ₄ , so that the first and second antennas, which are used more often than other antennas, may have a better channel estimation measure.

[108] In general, more control signals are carried in OFDM symbols located before the third OFDM symbol. The reference signals T ₁ through T _{4 are} distributed so that the matrix (T ₁ , T ₃ , T ₄ , T ₂ , D, D, T ₁ , D, D, T ₂ , D, D) is repeated in the first OFDM symbol and the matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , T ₂ , T ₄ , T ₁ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₁ , D, D, T ₂ , T ₃ , T ₄ , T ₁ , D, D, T ₂ , D, D) is repeated in the eighth OFDM symbol, and the matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , D, D, T ₁ , T ₃ , T ₄ , T ₂ ) is repeated in the twelfth OFDM symbol. Data symbols D may be allocated where these reference signals are not located. In this case, the percentage of data symbols D is about 86 percent.

[109] The percentage of data symbols in a subframe may be different in accordance with the characteristics of the system. The following is an example of 14 OFDM symbols per transmission time interval (TTI), but this is not a limitation. One transmission time interval (TTI) may include 12 or more OFDM symbols.

[110] The reference signal distribution diagram shown is presented with relative signal positions and, therefore, does not indicate absolute positions. The distribution pattern of the reference signals can be shifted in the time domain and / or in the frequency domain, while the intervals between the reference signals are maintained.

[111] In a subframe, a null symbol may be allocated to a resource element in which reference signals of other antennas are located. For example, in the subframe for the first antenna, the null symbol may be allocated to the resource element in which the reference signals for the second to fourth antennas are located.

[112] At least one of the reference signals for the respective antennas may be a reference signal for a multi-user signal. In a subframe, a reference signal for a multi-user signal may not be allocated to OFDM symbols including a dedicated control signal, but may be allocated to other OFDM symbols. For example, if the first and second OFDM symbols include dedicated control signals, reference signals for a multi-user signal may be allocated starting from the third OFDM symbol.

[113] FIG. 21 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[114] As shown in FIG. 21, reference signals T ₁ and T _{3 are} distributed sequentially in a first OFDM symbol together with one data symbol. An empty resource element may be a data symbol or a null symbol. The reference signals T ₂ and T _{4 are} distributed sequentially after the data symbol D. Accordingly, the matrix (T ₁ , T ₃ , D, T ₂ , T ₄ , D) can be repeated.

[115] In the fifth OFDM symbol, the reference signal T ₂ is arranged such that two data symbols D and the reference signal T ₁ follow it. Two data symbols D are placed again so that after them comes the reference signal T ₂ . Accordingly, the matrix (T ₂ , D, D, T ₁ , D, D) can be repeated.

[116] The eighth OFDM symbol may have a pattern similar to that of the first OFDM symbol, and therefore, the matrix (T ₁ , T ₄ , D, T ₂ , T ₃ , D) can be repeated. The twelfth OFDM symbol may comprise the same pattern as the fifth OFDM symbol.

[117] The percentage of D data symbols is about 86%.

Therefore, the percentage of reference signals is about 14%. Accordingly, the reference signals for the respective antennas do not overlap and, therefore, the receiver can evaluate the corresponding channels.

[118] FIG. 22 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[119] As shown in FIG. 22, the first, third, and fourth reference signals T ₁ , T ₃ , T ₄ , and T ₂ are all allocated in the first OFDM symbol. An empty resource element may be a data symbol or a null symbol. Then, two data symbols D are arranged such that another reference signal T ₁ follows them. Two data symbols are placed again so that another reference signal T ₂ follows them. Then two data symbols are placed so that after them are the reference signals T ₁ , T ₃ , T ₄ and T ₂ , in that order. Accordingly, the matrix (T ₁ , T ₃ , T ₄ , T ₂ , D, D, T ₁ , D, D, T ₂ , D, D) can be repeated in the first OFDM symbol.

[120] In the fifth OFDM symbol, the reference signal T ₂ is arranged such that two data symbols and a reference signal T ₁ follow it. Then two data symbols are placed so that after them are the reference signals T ₂ , T ₃ , T ₄ and T ₁ , in that order. Then two data symbols are placed again, and this combination can be repeated. Accordingly, the matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , T ₃ , T ₄ , T ₁ , D, D) can be repeated in the fifth OFDM symbol.

[121] The eighth OFDM symbol has the same reference signal distribution as the first OFDM symbol. The twelfth OFDM symbol has the same reference distribution as the fifth OFDM symbol.

[122] Data symbols occupy 85% of the total area. Consequently, reference signals occupy about 15%. Accordingly, the receiver can estimate the channels by using reference signals transmitted from the respective transmit antennas.

[123] FIG. 23 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[124] The matrix (D, T ₁ , T ₃ , T ₄ , T ₂ , D) is repeated in the first OFDM symbol. The matrix (T ₄ , T ₁ , D, D, T ₂ , T ₃ ) is repeated in the eighth OFDM symbol. The matrix (D, T ₂ , D, D, T ₁ , D) is repeated in the fifth and twelfth OFDM symbols.

[125] FIG. 24 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[126] The matrix (D, T ₁ , D, D, T ₂ , D) is repeated in the first and eighth OFDM symbols. The matrix (D, T ₂ , T ₃ , T ₄ , T ₁ , D) is repeated in the fifth OFDM symbol. The matrix (T ₄ , T ₂ , D, D, T ₁ , T ₃ ) is repeated in the twelfth OFDM symbol.

[127] FIG. 25 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[128] The matrix (D, T ₁ , T ₃ , T ₄ , T ₂ , D) is repeated in the first and eighth OFDM symbols. The matrix (T ₄ , T ₂ , D, D, T ₁ , T ₃ ) is repeated in the fifth and twelfth OFDM symbols.

[129] FIG. 26 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[130] The matrix (T ₁ , T ₃ , D, T ₂ , T ₄ , D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₄ , D, T ₁ , T ₃ , D) is repeated in the fifth and twelfth OFDM symbols.

[131] FIG. 27 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[132] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the second and ninth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the sixth and thirteenth OFDM symbols.

[133] FIG. 28 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[134] The matrix (T ₁ , D, T ₃ , T ₂ , D, T ₄ ) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, T ₄ , T ₁ , D, T ₃ ) is repeated in the fifth and twelfth OFDM symbols.

[135] FIG. 29 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[136] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[137] FIG. 30 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[138] The matrix (T ₁ , D, D, T ₂ , D, D, T ₃ , D, D, T ₄ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D, T ₁ , D, D, T ₂ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[139] FIG. 31 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[140] The matrix (T ₁ , T ₃ , D, T ₂ , D, D, T ₁ , T ₄ , D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₄ , D, T ₁ , D, D, T ₂ , T ₃ , D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[141] FIG. 32 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[142] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ , D, D, D, D, D, T ₄ , D, D, D, D, D) is repeated in the second and ninth OFDM symbols.

[143] The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₄ , D, D, D, D, D, T ₃ , D, D, D, D, D) is repeated in the sixth and thirteenth OFDM symbols.

[144] FIG. 33 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[145] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first OFDM symbol. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the eighth OFDM symbol. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the twelfth OFDM symbol.

[146] FIG. 34 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[147] The matrix (T ₁ , D, D, T ₃ , D, D, T ₂ , D, D, T ₄ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₄ , D, D, T ₁ , D, D, T ₃ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[148] FIG. 35 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[149] The matrix (T ₁ , D, T ₃ , T ₂ , D, D, T ₁ , D, T ₄ , T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, T ₄ , T ₁ , D, D, T ₂ , D, T ₃ , T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[150] FIG. 36 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[151] The matrix (T ₁ / T ₃ , D, D, T ₂ / T ₄ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ / T ₄ , D, D, T ₁ / T ₃ , D, D) is repeated in the fifth and twelfth OFDM symbols. Here, the reference signals T ₁ and T _{3 are} distributed in the same subcarrier and in the same time domain. The reference signals T ₁ and T ₃ maintain their orthogonality by using an orthogonal code characterized by the presence of autocorrelation and cross-correlation. This applies to the reference signals T ₂ / T ₄ .

[152] FIG. 37 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[153] The matrix (T ₁ , T ₃ / T ₄ , D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T, T ₃ / T ₄ , D) is repeated in the fifth and twelfth OFDM symbols. The reference signals T ₃ and T _{4 are} distributed in the same subcarrier and in the same time domain and maintain their orthogonality by using an orthogonal code characterized by the presence of autocorrelation and cross-correlation.

[154] FIG. 38 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[155] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ / T ₄ , D, D, D, D, D) is repeated in the second and ninth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (D, D, D, T ₃ / T ₄ , D, D) is repeated in the sixth and thirteenth OFDM symbols.

[156] FIG. 39 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[157] The matrix (D, T ₁ , D, T ₃ / T ₄ , T ₂ , D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ / T ₄ , T ₂ , D, D, T ₁ , D) is repeated in the fifth and twelfth OFDM symbols.

[158] FIG. 40 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[159] The matrix (T ₁ , T ₃ , D, T ₂ , T ₄ , D) is repeated in the first OFDM symbol. The matrix (T ₁ , T ₄ , D, T ₂ , T ₃ , D) is repeated in the eighth OFDM symbol. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[160] FIG. 41 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[161] The matrix (T ₄ , T ₁ , D, T ₃ , T ₂ , D) is repeated in the first OFDM symbol. The matrix (T ₃ , T ₁ , D, T ₄ , T ₂ , D) is repeated in the eighth OFDM symbol. The matrix (D, T ₂ , D, D, T ₁ , D) is repeated in the fifth and twelfth OFDM symbols.

[162] Fig. 42 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[163] The matrix (T ₁ , T ₃ , D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₄ , D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[164] FIG. 43 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[165] The matrix (T ₁ , T ₃ , T ₄ , T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[166] FIG. 44 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[167] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₃ , D, T ₁ , T ₄ , D) is repeated in the fifth OFDM symbol. The matrix (T ₂ , T ₄ , D, T ₁ , T ₃ , D) is repeated in the twelfth OFDM symbol.

[168] Fig. 45 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[169] The matrix (D, T ₁ , D, D, T ₂ , D) is repeated in the first and eighth OFDM symbols. The matrix (T ₄ , T ₂ , D, T ₃ , T ₁ , D) is repeated in the fifth OFDM symbol.

The matrix (T ₃ , T ₂ , D, T ₄ , T ₁ , D) is repeated in the twelfth OFDM symbol.

[170] Fig. 46 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[171] The matrix (T ₁ , D, T ₃ , T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, T ₄ , T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[172] FIG. 47 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[173] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₃ , T ₄ , T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[174] FIG. 48 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[175] The matrix (T ₁ , T ₃ , D, T ₂ , T ₄ , D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[176] Fig. 49 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[177] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₃ , D, T ₁ , T ₄ , D) is repeated in the fifth and twelfth OFDM symbols.

[178] Fig. 50 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[179] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the second and ninth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[180] Fig. 51 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[181] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the second OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the ninth OFDM symbol.

[182] In the first, fifth, and twelfth OFDM symbols, the reference signals T ₁ and T _{2 are} spaced apart for each antenna in the frequency domain. In the second and ninth OFDM symbols, the reference signals T ₃ and T _{4 are} spaced from each other for each antenna in the frequency domain. Accordingly, selectivity in the frequency domain can be provided.

[183] The reference signals T ₁ and T _{2 are} allocated in the first OFDM symbol. The reference signals T ₃ and T _{4 are} allocated in a second OFDM symbol adjacent to the first OFDM symbol. When the reference signals for several antennas are distributed over two consecutive OFDM symbols, the lower the rank, the higher the efficiency. For example, if in some MIMO methods the rank is unity, then the same data is transmitted by four antennas. In this case, the channel estimate can be more efficiently obtained if the reference signals are distributed in two consecutive OFDM symbols.

[184] In addition, reference signals for at least two antennas are transmitted through the same frequency domain in two consecutive OFDM symbols. Therefore, the channel estimate can be obtained with fewer errors than in the case in which the reference signals are excessively spaced when they are concentrated in the frequency domain and in the time domain.

[185] Only a portion of the reference signals for all antennas is allocated in one OFDM symbol. For example, among the reference signals for four antennas, only reference signals for two antennas can be distributed. Thus, for each antenna, it is possible to further increase the power where the power is distributed among the reference signals. By increasing the power of the reference signals, the receiver can more effectively estimate the channel.

[186] In some receivers, the first few OFDM symbols are decoded (eg, three OFDM symbols). If the decoding result does not match the data stored in the receiver, then the transmitted OFDM symbols are not buffered. This mode is called the microsleep mode. In this case, the first few OFDM symbols should include reference signals for all antennas. The short standby mode can also be implemented when the reference signals for all antennas are allocated in the first and second OFDM symbols.

[187] FIG. 52 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[188] The matrix (T ₁ , D, T ₃ , T ₂ , D, T ₄ ) is allocated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols.

[189] FIG. 53 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[190] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, T ₃ , T ₁ , D, T ₄ ) is allocated in the fifth and twelfth OFDM symbols.

[191] FIG. 54 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[192] A matrix (T ₁ , D, D, T ₂ , D, D) is allocated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the sixth and thirteenth OFDM symbols.

[193] FIG. 55 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[194] The matrix (T ₁ , D, D, T ₂ , D, D) is allocated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is allocated in the sixth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is allocated in the thirteenth OFDM symbol.

[195] FIG. 56 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[196] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols. The matrix (T ₃ / T ₄ , D, D) is allocated in the second and ninth OFDM symbols.

[197] Fig. 57 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[198] The matrix (T ₁ , T ₃ / T ₄ , D, T ₂ , T ₃ / T ₄ , D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols.

[199] Fig. 58 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[200] The matrix (T ₁ , T ₃ / T ₄ , D, T ₂ , D, D) is allocated in the first and eighth OFDM symbols. The matrix (T ₂ , T ₃ / T ₄ , D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[201] FIG. 59 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[202] The matrix (T ₁ , D, D, T ₂ , D, D) is allocated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols. The matrix (T ₃ / T ₄ , D, D, D, D, D) is allocated in the second, sixth, ninth and thirteenth OFDM symbols.

[203] FIG. 60 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[204] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ / T ₄ , D, D) is repeated in the sixth and thirteenth OFDM symbols.

[205] Fig. 61 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[206] The matrix (T ₁ , D, T ₃ / T ₄ , T ₂ , D, T ₂ / T ₄ ) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[207] FIG. 62 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[208] The matrix (T ₁ , D, T ₃ / T ₄ , T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, T ₃ / T ₄ , T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols.

[209] FIG. 63 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[210] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the third and tenth OFDM symbols. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the seventh and fourteenth OFDM symbols.

[211] FIG. 64 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[212] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is allocated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the third OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the tenth OFDM symbol.

[213] FIG. 65 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[214] The matrix (D, T ₁ , D, D, D, D) is repeated in the first OFDM symbol. The matrix (T ₄ , T ₁ , D, D, T ₂ , T ₃ ) is repeated in the eighth OFDM symbol. The matrix (D, T ₂ , D, D, T ₁ , D) is repeated in the fifth and twelfth OFDM symbols.

[215] When a short-term standby mode is applied in which a control signal is distributed in an OFDM symbol located in an initial time sequence on a time axis, the control signal may be transmitted via one or two antennas. If the control signal is transmitted through the first antenna, the reference signals for the first antennas may be allocated in the first OFDM symbol.

[216] FIG. 66 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[217] The matrix (T ₁ , D, D, D, D, D) is repeated in the first OFDM symbol. The matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , T ₃ , T ₄ , T ₁ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₁ , D, D, T ₂ , T ₃ , T ₄ , T ₁ , D, D, T ₂ , D, D) is repeated in the eighth OFDM symbol. The matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , D, D, T ₁ , T ₃ , T ₄ ) is repeated in the twelfth OFDM symbol.

[218] If the control signal is transmitted through the first antenna in the short-term standby mode, the reference signals for the first antenna are distributed in OFDM symbols located in the initial time sequence on the time axis. For example, if a control signal is transmitted through a first antenna, reference signals for the first antennas may be allocated in the first OFDM symbol.

[219] FIG. 67 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[220] The matrix (D, T ₁ , D, D, T ₂ , D) is allocated in the first OFDM symbol. The matrix (T ₄ , T ₁ , D, D, T ₂ , T ₃ ) is allocated in the eighth OFDM symbol. The matrix (D, T ₂ , D, D, T ₁ , D) is allocated in the fifth and twelfth OFDM symbols. If the control signal is transmitted through the first and second antennas in the short-term standby mode, the reference signals for the first and second antennas are distributed in OFDM symbols located in the initial time sequence on the time axis.

[221] FIG. 68 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[222] If the control signal is transmitted through two antennas in the short-term standby mode, the reference signals are distributed as follows. The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first OFDM symbol. The matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , T ₃ , T ₄ , T ₁ , D, D) is allocated in the fifth OFDM symbol. The matrix (T ₁ , D, D, T ₂ , T ₃ , T ₄ , T ₁ , D, D, T ₂ , D, D) is allocated in the eighth OFDM symbol. The matrix (T ₂ , D, D, T ₁ , D, D, T ₂ , D, D, T ₁ , T ₃ , T ₄ ) is allocated in the twelfth OFDM symbol. If the control signal is transmitted through the first and second antennas in the short-term standby mode, the reference signals for the first and second antennas are distributed in OFDM symbols located in the initial time sequence on the time axis.

[223] FIG. 69 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[224] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fourth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the ninth OFDM symbol.

[225] A subframe can be divided into two areas: a control channel and a data channel. A control channel is an area carrying control data. A data channel is an area carrying user data. For example, a first OFDM symbol, a second OFDM symbol, and a third OFDM symbol may be assigned to a control channel, and other OFDM symbols may be assigned to a data channel. Although the number of OFDM symbols of the control channel is less than the number of OFDM symbols of the data channel, the reliability of the control channel should be higher than the reliability of the data channel. To transmit a control channel, only a portion of the plurality of antennas can be assigned. For the control channel, the first and second antennas may be used. In this case, the reference signals for the third antenna and the reference signals for the fourth antenna cannot be assigned to the OFDM symbols of the control channel, since the third and fourth antennas are not used for the control channel.

[226] FIG. 70 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[227] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the sixth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the ninth OFDM symbol.

[228] In order to improve the accuracy of the channel estimate, in the channel, the reference signals for the third antenna and the reference signals for the fourth antenna follow the reference signals for the first antenna and the reference signals for the second antenna.

[229] FIG. 71 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[230] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fourth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the eleventh OFDM symbol.

[231] In successive subframes, the interval for reference signals for the third antenna and for the fourth antenna may be continuously maintained.

[232] Fig. 72 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[233] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the sixth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the tenth OFDM symbol.

[234] FIG. 73 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[235] The matrix (T ₁ D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fourth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the tenth OFDM symbol.

[236] FIG. 74 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[237] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the sixth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the eleventh OFDM symbol.

[238] FIG. 75 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[239] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fifth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the sixth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the thirteenth OFDM symbol.

[240] FIG. 76 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[241] The matrix (T ₁ , D, D, T ₂ D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the third OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the ninth OFDM symbol.

[242] FIG. 77 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[243] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the ninth OFDM symbol.

[244] FIG. 78 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[245] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the third OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the eleventh OFDM symbol.

[246] FIG. 79 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[247] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the tenth OFDM symbol.

[248] FIG. 80 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[249] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the third OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the tenth OFDM symbol.

[250] FIG. 81 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[251] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the eleventh OFDM symbol.

[252] FIG. 82 illustrates an example of a reference signal allocation in accordance with an embodiment of the present invention.

[253] The matrix (T ₁ , D, D, T ₂ , D, D) is repeated in the first and eighth OFDM symbols. The matrix (T ₂ , D, D, T ₁ , D, D) is repeated in the fourth and twelfth OFDM symbols. The matrix (T ₃ , D, D, T ₄ , D, D) is repeated in the fifth OFDM symbol. The matrix (T ₄ , D, D, T ₃ , D, D) is repeated in the thirteenth OFDM symbol.

[254] FIGS. 65-82 illustrate examples of a reference signal allocation in which reference signals are allocated in a first OFDM symbol. If the number of OFDM symbols used in the short-standby mode increases, the reference signals may be allocated in other OFDM symbols, for example, in the second and third OFDM symbols.

[255] FIG. 83 illustrates an example of a reference signal allocation for a multi-user signal.

[256] In FIG. 83, R is a reference signal for a multi-user signal. The reference signal R can be used for any antenna. In the case of using two antennas, R may mean either a reference signal for the first antenna or a reference signal for the second antenna. An empty resource element may be a data symbol or a null symbol.

[257] In one subframe, the reference signals T ₁ for the first antenna are distributed in an interval of six subcarriers in the first OFDM symbol. That is, the reference signals T _{1 are} distributed so that between them there are five subcarriers. The reference signals T ₂ for the second antenna are distributed at the same interval as the first reference signals T ₁ so as not to overlap the reference signals T ₁ in the same OFDM symbols. That is, the reference signals T ₂ are located between the two reference signals T ₁ with the same interval as the first reference signals T ₁ .

[258] The reference signals R are distributed starting from positions where the allocated control signals are not distributed, for example, from the third OFDM symbol. That is, the reference signals R are distributed in an interval equal to two subcarriers in the third OFDM symbol. The reference signals R are distributed in an interval equal to two subcarriers in the seventh OFDM symbol, which is spaced apart by four OFDM symbols from the third OFDM symbol. The reference signals R in the third and seventh OFDM symbols are spaced from each other. The reference signals R are distributed in an interval equal to two subcarriers in the eleventh OFDM symbol, which is four times the OFDM symbol from the seventh OFDM symbol.

[259] FIG. 84 illustrates another example of a reference signal allocation for a multi-user signal.

[260] Compared with the example of FIG. 83, in FIG. 84, reference signals T ₁ and T ₂ for the first and second antennas are allocated in the fourth OFDM symbol. When a dedicated control signal is distributed in an area in which a multi-user signal is transmitted, the error rate of the dedicated control signal may decrease.

[261] FIG. 85 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used. This is the case when four antennas are used and at least one of them transmits a multi-user signal.

[262] As shown in FIG. 85, in one subframe, reference signals T _{1 are} distributed in an interval of six subcarriers in the first OFDM symbol. The reference signals T _{2 are} distributed in the same interval as the first reference signals T ₁ so as not to overlap the first reference signals T ₁ in the same OFDM symbols. That is, the reference signals T ₂ are located between two reference signals T ₁ in the same interval as the first reference signals T ₁ . In addition, in one subframe, the reference signals T _{3 are} distributed in an interval equal to six subcarriers in the first OFDM symbol. The reference signals T _{4 are} distributed in the same interval as the third reference signals T ₃ so as not to overlap the third reference signals T ₃ in the same OFDM symbols.

[263] The reference signals R are distributed, starting from positions where the allocated control signal is not distributed, for example, from the third OFDM symbol. The reference signals R can be transmitted through at least one of the four antennas: from the first to the fourth antenna. The reference signals R are distributed in an interval equal to two subcarriers in the third OFDM symbol. The reference signals R are distributed in an interval equal to two subcarriers in the seventh OFDM symbol, spaced from the third OFDM symbol by an amount of four OFDM symbols. The reference signals R in the third and seventh OFDM symbols are spaced from each other.

[264] The reference signals T ₁ and T _{2 are} distributed in the fourth OFDM symbol. When a dedicated control signal is distributed in an area in which a multi-user signal is transmitted, the error rate of the dedicated control signal may decrease.

[265] FIG. 86 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used. This is the case when four antennas are used and at least one of them transmits a multi-user signal.

[266] As shown in FIG. 86, the first and second reference signals R ₁ and R _{2 are} allocated in OFDM symbols starting from the third OFDM symbol in an interval of four OFDM symbols. The third and fourth reference signals R ₃ and R _{4 are} allocated in OFDM symbols starting from the fifth OFDM symbol in an interval equal to four OFDM symbols.

[267] FIG. 87 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[268] As shown in FIG. 87, the first and second reference signals R ₁ and R _{2 are} allocated in OFDM symbols starting from the third OFDM symbol in an interval of four OFDM symbols. The third and fourth reference signals R ₃ and R _{4 are} allocated in OFDM symbols starting from the fifth OFDM symbol in an interval equal to four OFDM symbols. Each of the reference signals from the first R ₁ to the fourth R _{4 is} distributed in the frequency domain in the interval equal to six subcarriers.

[269] FIG. 88 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[270] As shown in FIG. 88, the first and second reference signals R ₁ and R _{2 are} allocated in OFDM symbols starting from the third OFDM symbol in an interval of four OFDM symbols. The third and fourth reference signals R ₃ and R _{4 are} allocated in OFDM symbols starting from the fifth OFDM symbol in an interval equal to four OFDM symbols.

[271] The reference signals T ₁ through T ₄ for the first to fourth antennas are allocated in the first and second OFDM symbols. In addition, the reference signals T ₁ and T _{2 are} allocated in the fourth OFDM symbol.

[272] FIG. 89 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[273] As shown in FIG. 89, the first and second reference signals R ₁ and R _{2 are} allocated in OFDM symbols starting from the third OFDM symbol in an interval of four OFDM symbols. The third and fourth reference signals R ₃ and R _{4 are} allocated in OFDM symbols starting from the fifth OFDM symbol in an interval equal to four OFDM symbols. The reference signals from the first R ₁ to the fourth R _{4 are} distributed in the frequency domain in the interval equal to six subcarriers.

[274] The reference signals T ₁ through T ₄ for the first to fourth antennas are allocated in the first and second OFDM symbols. In addition, the reference signals T ₁ and T _{2 are} allocated in the fourth OFDM symbol.

[275] FIG. 90 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[276] As shown in FIG. 90, the first and second reference signals R ₁ and R _{2 are} allocated in OFDM symbols starting from the third OFDM symbol in an interval of four OFDM symbols. The third and fourth reference signals R ₃ and R _{4 are} allocated in OFDM symbols starting from the fifth OFDM symbol in an interval equal to four OFDM symbols.

[277] The reference signals T ₁ through T ₄ for the first to fourth antennas are allocated only in the first and second OFDM symbols.

[278] FIG. 91 illustrates another example of a reference signal allocation for a multi-user signal when multiple antennas are used.

[279] As shown in FIG. 91, the first and second reference signals R ₁ and R _{2 are} allocated in OFDM symbols starting from the third OFDM symbol in an interval equal to four OFDM symbols. The third and fourth reference signals R ₃ and R _{4 are} allocated in OFDM symbols starting from the fifth OFDM symbol in an interval equal to four OFDM symbols. The reference signals from the first R ₁ to the fourth R _{4 are} distributed in the frequency domain in the interval equal to six subcarriers.

[280] The reference signals T ₁ through T ₄ for the first to fourth antennas are allocated only in the first and second OFDM symbols.

[281] The reference signals for multiple antennas are effectively distributed. The degradation of channel estimation or data demodulation can be prevented.

[282] Since the present invention can be embodied in several forms without going beyond its essence or essential characteristics, it should be understood that the above embodiments are not limited to any details of the previous description, unless otherwise expressly agreed, but they must be interpreted broadly sense within the essence and scope defined by the attached claims. Therefore, it is understood that all changes and modifications that fall within the boundaries and boundaries of the indicated claims, or equivalents of such limits and boundaries are covered by the attached claims.

Claims (11)

1. A method for distributing reference signals in a subframe in a multi-input multi-output (MIMO) wireless data transmission system comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain and transmitted by a plurality of subcarriers in a frequency domain, comprising:
distributing a plurality of first reference signals for the first antenna to the first OFDM symbol;
distributing a plurality of second reference signals for the second antenna to the first OFDM symbol;
distributing a plurality of third reference signals for the third antenna into a second OFDM symbol adjacent to said first OFDM symbol;
and
distributing a plurality of fourth reference signals for the fourth antenna to a second OFDM symbol;
wherein
a plurality of first reference signals and a plurality of second reference signals are not adjacent and do not overlap;
a plurality of third reference signals and a plurality of fourth reference signals are not adjacent and do not overlap; and
each of the many first, second, third and fourth reference signals is distributed at constant intervals in the frequency domain. 2. The method according to claim 1, in which at least two of the many first, second, third and fourth reference signals have different densities in the subframe. 3. The method according to claim 1, in which the locations in the frequency domain of the plurality of third reference signals are the same as the locations of the plurality of first reference signals, and the locations in the frequency domain of the plurality of fourth reference signals are the same as the locations many second reference signals. 4. The method according to claim 1, in which the locations in the frequency domain of the plurality of fourth reference signals are the same as the locations of the plurality of first reference signals, and the locations in the frequency domain of the plurality of third reference signals are the same as the locations many second reference signals. 5. The method according to claim 1, additionally containing:
distributing a plurality of additional first reference signals for the first antenna to the third OFDM symbol at the same constant intervals as the first reference signals;
distributing a plurality of additional second reference signals for the second antenna to the third OFDM symbol at the same constant intervals as the second reference signals;
wherein
the third OFDM symbol is not adjacent to the first OFDM symbol or the second OFDM symbol; and
many additional first reference signals and many additional second reference signals are not adjacent and do not overlap. 6. The method according to claim 5, further comprising:
distributing a plurality of additional first reference signals for the first antenna to the fourth OFDM symbol at the same constant intervals as the first reference signals;
distributing a plurality of additional second reference signals for the second antenna to the fourth OFDM symbol at the same constant intervals as the second reference signals;
wherein
the fourth OFDM symbol is not adjacent to any of the first, second, or third OFDM symbols; and
many additional first reference signals and many additional second reference signals are not adjacent and do not overlap. 7. The method according to claim 6, in which each of the first, third and fourth OFDM symbols has a shift in the frequency domain, comparable to the previous or subsequent OFDM symbol and equal to half the constant interval between two consecutive first reference signals. 8. The method according to claim 6, further comprising:
distributing a plurality of additional third reference signals for the third antenna to the fifth OFDM symbol at the same constant intervals as the third reference signals;
distributing a plurality of additional fourth reference signals for the fourth antenna to the fifth OFDM symbol at the same constant intervals as the fourth reference signals;
wherein
the fifth OFDM symbol is not adjacent to any of the first, second, or third OFDM symbols and is adjacent to the fourth OFDM symbol; and
many additional third reference signals and many additional fourth reference signals are not adjacent and do not overlap. 9. The method of claim 8, in which the second OFDM symbol and the fifth OFDM symbol have a shift in the frequency domain equal to half the constant interval between two consecutive third reference signals. 10. The method according to claim 1, in which the first OFDM symbol is located near the beginning of the transmission time interval (TTI), and the TTI contains at least two OFDM symbols. 11. The method of claim 10, further comprising placing a null symbol for one antenna to overlap with a reference signal for another antenna.

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