Transmit diversity method for FQAM and apparatus thereof

The present invention relates to a transmit diversity method for FQAM and an apparatus therefor. According to the present invention, a transmit diversity method for FQAM and apparatus therefor are provided, the transmit diversity method comprising the steps of: modulating data into at least one FQAM symbol; interleaving a plurality of tones constituting the at least one FQAM symbol such that tones having the same index are located in adjacent resources; and transmitting the at least one interleaved FQAM symbol through at least one transceving unit.

TECHNICAL FIELD

The present invention relates to a transmit diversity method for FQAM and an apparatus thereof.

BACKGROUND ART

In typical multi-cell wireless communication systems, a Gaussian assumption has been applied to an interference signal in order to perform decoding with lower complexity. Therefore, a conventional wireless communication system has used mainly a QAM-series modulation scheme to render a characteristic of an interference signal closer to a Gaussian distribution as much as possible.

However, since a non-Gaussian channel has a greater channel capacity than a Gaussian channel, the non-Gaussian channel may offer higher decoding performance than the Gaussian channel if a suitable decoding is performed. For this reason, the development of a modulation scheme that allows an interference signal to have a non-Gaussian characteristic has been needed, so that FQAM has been proposed as a modulation scheme.

As shown inFIG. 1, FQAM is a hybrid modulation scheme for combining QAM with FSK, thus having both a higher spectral efficiency of QAM and a characteristic of FSK to form an interference signal in a non-Gaussian distribution.

Meanwhile, for more reliable communication using a plurality of antennas in a wireless communication system, transmit diversity techniques such as a space frequency block code (SFBC) and a space time block code (STBC) have been studied actively. However, since such transmit diversity techniques are induced on the assumption that a channel is unvaried within a frequency or time block, a serious degradation of performance is caused in case the channel is varied in such a block. Particularly, since a single symbol occupies a plurality of subcarriers (or OFDMA symbols) in the above-mentioned FQAM (or TQAM), simply applying the existing transmit diversity technique may invite a serious degradation of performance in a channel-varying environment. Accordingly, required for FQAM (or TQAM) is a transmit diversity technique that does not cause a serious degradation of performance even in a channel-varying environment.

DISCLOSURE OF INVENTION

Technical Problem

The object of the present invention is to provide, for FQAM (or TQAM), a transmit diversity technique that does not cause a serious degradation of performance even in a channel-varying environment.

Solution to Problem

In order to solve the above problem, a transmit diversity method of a transmitter for FQAM according to the present invention comprises steps of modulating data into at least one FQAM symbol, interleaving a plurality of tones constituting the at least one FQAM symbol such that tones having the same index are located in adjacent resources, and transmitting the at least one interleaved FQAM symbol through at least one transceiver unit.

Additionally, a transmit diversity method of a receiver for FQAM according to the present invention comprises steps of receiving at least one FQAM symbol through at least one transceiver unit, deinterleaving the at least one FQAM symbol in which a plurality of tones constituting the at least one FQAM symbol are interleaved such that tones having the same index are located in adjacent resources, and demodulating the at least one deinterleaved FQAM symbol.

Additionally, a transmitter performing a transmit diversity for FQAM according to the present invention comprises at least one transceiver unit, and a control unit configured to modulate data into at least one FQAM symbol, to interleave a plurality of tones constituting the at least one FQAM symbol such that tones having the same index are located in adjacent resources, and to transmit the at least one interleaved FQAM symbol through the at least one transceiver unit.

Additionally, A receiver performing a transmit diversity for FQAM according to the present invention comprises at least one transceiver unit configured to receive at least one FQAM symbol, and a control unit configured to deinterleave the at least one FQAM symbol in which a plurality of tones constituting the at least one FQAM symbol are interleaved such that tones having the same index are located in adjacent resources, and to demodulate the at least one deinterleaved FQAM symbol.

Advantageous Effects of Invention

A transmit diversity method for FQAM according to the present invention applies interleaving such that the same tones of FQAM symbols are located in adjacent resources, and thereby minimizes a degradation of performance due to a variation of a channel status even in FQAM having a greater frequency band of a subcarrier.

MODE FOR THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this disclosure, well known functions or structures may not be described or illustrated in detail to avoid obscuring the subject matter of the present invention. Additionally, the terms used herein are defined in view of functions in this invention and may be varied according to user or operator's intention or custom. Therefore, such a definition should be made on the basis of the contents of this disclosure.

Additionally, in this disclosure, the present invention will be described using, as an example, FQAM and a space frequency block code (SFBC). However, this invention may be also applied to TQAM and a space time block code (STBC). Further, in this disclosure, although an Alamouti code will be described exemplarily as a representative transmit diversity method, any other transmit diversity method may be also applied.

Embodiments according to the present invention are described, based on a transmitter and a receiver. The transmitter and the receiver may be a base station and a mobile station. Alternatively, the transmitter and the receiver may be a terminal, a mobile, and the like.

FIG. 2is a diagram illustrating a space frequency block of a transmitting symbol in case a space frequency block code is used in the QAM modulation scheme.

In case of using a space frequency block in a QAM modulation signal, a transmitting symbol transmitted at a transmitter is as shown inFIG. 2.

If a channel status is unvaried in respective frequency blocks201and203, a receiver may decode a space frequency code as shown in Equation 1. In the QAM modulation scheme, the size (length) of the frequency blocks201and203(namely, the number of subcarriers) is equal to the number of transmitting antennas.

However, if a channel status is varied in the respective frequency blocks201and203, a serious degradation of performance may be caused at the receiver.

FIG. 3is a diagram illustrating an example of a space frequency block of a transmitting symbol in case a space frequency block code is used in the FQAM modulation scheme.

In case of using FQAM that has four tones in a single symbol, a space frequency block of a symbol transmitted at the transmitter having two antennas is as shown inFIG. 3. For example, inFIG. 3, S12denotes the second tone of the first symbol.

Referring toFIG. 3, if the existing transmit diversity technique is used as it is in case of FQAM, the length of each frequency block301or303becomes longer in proportion to the number of tones than in case of QAM. This is expressed as “the number of transmitting antennas X the number of tones in a symbol”. As a result, case of using FQAM has a broader bandwidth of subcarrier than case of using QAM. Namely, in case of using the same transmit diversity technique under the same channel status, FQAM undergoes a greater degradation of performance due to channel variations in comparison with QAM.

Assuming that a channel status is unvaried in the frequency blocks301and303in case of FQAM, a space frequency block received at the receiver is decoded as shown in Equation 2.

Referring to Equation 2, a process of decoding a space frequency block of FQAM is performed independently for the same tone among a plurality of tones that constitute a plurality of FQAM symbols. As shown inFIG. 4, this means that no degradation of performance occurs in a decoding process if channel statuses of subcarriers corresponding to the same tones401,403,405and407of FQAM symbols in the frequency blocks301and303are equal to each other.

Using the above fact newly discovered in inducing a decoding process of an FQAM space frequency block, the present invention proposes a method of interleaving tones constituting FQAM symbols such that the same tones501,503,505and507of the FQAM symbols are located adjacently to each other in a space frequency block as shown inFIG. 5. An example of a detailed interleaving method is as shown inFIG. 5.

Referring toFIG. 5, with regard to a plurality of FQAM symbols for a plurality of antennas, this invention applies interleaving such that the same tones of FQAM symbols are located in adjacent resources (e.g., frequency, time). By allocating such interleaved tones to subcarriers, tones decoded together are transmitted through adjacent subcarriers having the same channel status. Therefore, even in FQAM having a greater frequency band of subcarrier, it is possible to minimize the degradation of performance due to a variation of a channel status.

InFIG. 5, a space frequency block is formed such that tones having the same position in the FQAM symbol are located as closely as possible. However, in a practical operation, such a space frequency block may be created and used flexibly or adaptively by using coherence bandwidth/Doppler spread of channel. Additionally, although the antennas have the same interleaving pattern in an example ofFIG. 5, it is also apparent that such antennas may use different interleaving patterns.

FIG. 6is a diagram illustrating a space frequency block of a transmitting symbol in case a space frequency block code for four antennas is used in the FQAM modulation scheme.

Referring toFIG. 6, in case of using FQAM that has four tones in a single symbol, a space frequency block of a symbol transmitted at the transmitter having four antennas is expressed as matrix having a 16*4 size as shown inFIG. 6. For example, inFIG. 6, S12denotes the second tone of the first symbol.

Referring toFIG. 6, if the existing transmit diversity technique is used as it is in case of FQAM, the length of each frequency block601,603,605or607is “the number of transmitting antennas X the number of tones in a symbol” and becomes 16. As a result, a modulation scheme in an embodiment ofFIG. 6causes a greater bandwidth of subcarrier and thereby invites a greater degradation of performance due to channel variations.

Applying the transmit diversity method according to this invention to the embodiment ofFIG. 6is as shown inFIG. 7. Referring toFIG. 7, in a space frequency block shown inFIG. 6, the transmit diversity method according to this invention interleaves tones constituting FQAM symbols such that the same tones of the FQAM symbols are located adjacently from each other. Namely, with regard to a plurality of FQAM symbols for a plurality of antennas, this invention applies interleaving such that the same tones of FQAM symbols are located in adjacent resources (e.g., frequency, time). At this time, in order to minimize interference between different tones, this invention may perform interleaving such that tone groups, disposed adjacently, are spaced apart from each other.

FIG. 8is a flow diagram illustrating a transmit diversity method for FQAM of a transmitter according to the present invention.

Referring toFIG. 8, at step801, the transmitter encodes data into a plurality of FQAM symbols for a plurality of antennas. Namely, the transmitter forms a codeword by encoding, according to a predefined coding scheme, a certain data stream to be transmitted, and maps the codeword onto a symbol that represents a position on a signal constellation.

Thereafter, at step803, the transmitter modulates the symbol according to the FQAM scheme. The FQAM modulation scheme is as discussed previously inFIG. 1.

At step805, the transmitter performs a transmit diversity, based on the symbol modulated according to the FQAM modulation scheme. For example, using a transmit diversity technique such as a space frequency block code (SFBC) or a space time block code (STBC), the transmitter forms a space frequency block or a space time block on the basis of symbol. At this time, the transmitter may form the space frequency block or the space time block by using an Alamouti code.

The space frequency block (or the space time block) is matrix formed of rows corresponding to respective antennas of the transmitter and columns having tones, as elements, of FQAM symbols and also corresponding to respective subcarriers. In the space frequency block (or the space time block), each row may be referred to as a frequency block (or a time block). In the space frequency block (or the space time block), the length of row is proportional to the number of antennas and the number of tones constituting FQAM symbols. In the space frequency block (or the space time block), the length of column corresponds to the number of antennas.

In case the transmitter has two antennas and uses FQAM modulation of four tones, the transmitter may form a space frequency block having an 8*2 size as shown inFIG. 3. Additionally, in case the transmitter has four antennas and uses FQAM modulation of four tones, the transmitter may form a space frequency block having a 16*4 size as shown inFIG. 6.

Next, at step807, the transmitter performs interleaving between tones.

According to an embodiment of this invention, the transmitter performs interleaving between tones such that tones having the same position (same index) among all tones constituting the modulated symbols are adjacent to each other. Namely, the transmitter performs interleaving such that tones corresponding to a certain position are located in adjacent resources (frequency or time). The space frequency block according to a result of interleaving is as discussed previously inFIGS. 5 and 7. At this time, the transmitter performs interleaving for each frequency block (namely, for each row) in the space frequency block. For this, the transmitter may have a plurality of tone interleavers each of which corresponds to the frequency block. The number of tone interleavers may correspond to the number of antennas.

This invention is not specially limited in a detailed algorithm for performing interleaving. For example, in various embodiments of this invention, in order to minimize interference between different tones, interleaving may be performed such that tone groups, disposed adjacently, are spaced apart from each other.

The transmitter may create and use flexibly or adaptively the space frequency block by using coherence bandwidth/Doppler spread of channel. In addition, the transmitter may apply the same interleaving pattern or different interleaving patterns to tones (i.e., respective frequency blocks) corresponding to respective antennas.

At step809, the transmitter transmits the interleaved final FQAM symbols to the receiver through a plurality of antennas.

The transmitter may perform an inverse fast Fourier transform (IFFT) for the space frequency block having the final FQAM symbols to which interleaving is applied. In the space frequency block, the transmitter may transmit a signal through a plurality of antennas corresponding to respective frequency blocks.

FIG. 9is a flow diagram illustrating a transmit diversity method for FQAM of a receiver according to the present invention.

Referring toFIG. 9, at step901, the receiver receives a signal from the transmitter. The receiver receives such signals through a plurality of antennas equipped therein. The signals received through respective antennas may form frequency blocks, which may be arranged in the order of row and thereby form a space frequency block. At this time, the length of the frequency block (the number of rows of the space frequency block) may be proportional to the number of tones constituting FQAM symbols of the received signals and the number of antennas of the receiver. Also, the number of rows of the space frequency block may be proportional to the number of the received signals, namely, the number of antennas of the receiver.

Thereafter, at step903, the receiver performs deinterleaving for the received signals. The receiver performs a fast Fourier transform (FFT) for the received signals and, based on the formed space frequency block, performs deinterleaving. At this time, the receiver performs deinterleaving for each frequency block (i.e., for each row) in the space frequency block. For this, the receiver may have a plurality of tone deinterleavers each of which corresponds to the frequency block. The number of tone deinterleavers may correspond to the number of antennas.

The signals received by the receiver may be signals for which interleaving between tones has been performed such that tones having the same position (same index) among all tones constituting the modulated FQAM symbols are adjacent to each other. Therefore, the receiver may form a space frequency block having an original array of FQAM symbols by performing inversely interleaving performed at the transmitter.

The receiver may perform deinterleaving by performing inversely an algorithm of interleaving performed at the transmitter. A detailed algorithm for performing deinterleaving is not specially limited, and the receiver may perform an algorithm for deinterleaving, based on information about an interleaving algorithm performed at the transmitter. The transmitter and the receiver may share information about interleaving and deinterleaving algorithms through upper signaling or on the basis of information earlier stored by a device manufacturer.

Next, at step905, the receiver performs a transmit diversity demodulation, based on the deinterleaved space frequency block. For example, using a transmit diversity technique such as a space frequency block code (SFBC) or a space time block code (STBC), the receiver creates an FQAM symbol based on a space frequency block. At this time, the receiver may create the FQAM symbol by using an Alamouti code. Thereafter, at step907, the receiver demodulates the created FQAM symbol according to the FQAM scheme. Then, at step911, the receiver decodes a codeword created by demodulation and thereby restores an original data stream.

FIG. 10is a block diagram illustrating the structure of a transmitter according to the present invention.

Referring toFIG. 10, the transmitter1000includes an encoder1001, a modulator1003, a transmit diversity unit1005, a tone interleaver1007, an IFFT1009, and a transceiver unit1011.

The encoder1001forms a codeword by encoding, according to a predefined coding scheme, a certain data stream to be transmitted, and maps the codeword onto a symbol that represents a position on a signal constellation.

The modulator1003modulates, according to the FQAM scheme, the symbol created by the encoder1001.

The transmit diversity unit1005performs a transmit diversity, based on the symbol modulated according to the FQAM modulation scheme. For example, using a transmit diversity technique such as a space frequency block code (SFBC) or a space time block code (STBC), the transmit diversity unit1005forms a space frequency block or a space time block on the basis of symbol. At this time, the transmit diversity unit1005may form the space frequency block or the space time block by using an Alamouti code.

The space frequency block (or the space time block) is matrix formed of rows corresponding to respective antennas of the transmitter and columns having tones, as elements, of FQAM symbols and also corresponding to respective subcarriers. In the space frequency block (or the space time block), each row may be referred to as a frequency block (or a time block). In the space frequency block (or the space time block), the length of row is proportional to the number of antennas and the number of tones constituting FQAM symbols. In the space frequency block (or the space time block), the length of column corresponds to the number of antennas.

In case the transmitter1000has two transceiver units1011and uses FQAM modulation of four tones, the transmit diversity unit1005may form a space frequency block having an 8*2 size as shown inFIG. 3. Additionally, in case the transmitter1000has four transceiver units1011and uses FQAM modulation of four tones, the transmit diversity unit1005may form a space frequency block having a 16*4 size as shown inFIG. 6.

The transmit diversity unit1005may be referred to as a space frequency block creation unit (or a space time block creation unit).

The tone interleaver1007performs interleaving between tones such that tones having the same position (same index) among all tones constituting the modulated symbols are adjacent to each other. Namely, the tone interleaver1007performs interleaving such that tones corresponding to a certain position are located in adjacent resources (frequency or time). At this time, the tone interleaver1007performs interleaving for each frequency block (namely, for each row) in the space frequency block. For this, the transmitter may have a plurality of the tone interleavers1007each of which corresponds to the frequency block. The number of the tone interleavers1007may correspond to the number of the transceiver units1011.

This invention is not specially limited in a detailed algorithm for performing interleaving. For example, in various embodiments of this invention, in order to minimize interference between different tones, interleaving may be performed such that tone groups, disposed adjacently, are spaced apart from each other.

The tone interleaver1007may create and use flexibly or adaptively the space frequency block by using coherence bandwidth/Doppler spread of channel. In addition, the transmitter may apply the same interleaving pattern or different interleaving patterns to tones (i.e., respective frequency blocks) corresponding to respective antennas.

The IFFT1009may perform an inverse fast Fourier transform (IFFT) for the space frequency block having the final FQAM symbols to which interleaving is applied.

The encoder1001, the modulator1103, the transmit diversity unit1005, the tone interleaver1007and the IFFT1009may be referred to as a single element, i.e., a control unit.

The transceiver unit1011transmits the final signal created through the above-discussed process to the receiver. According to this invention, a plurality of the transceiver units1011may be used.

FIG. 11is a block diagram illustrating the structure of a receiver according to the present invention.

Referring toFIG. 11, the receiver1100includes a transceiver unit1101, an FFT1103, a tone deinterleaver1105, a transmit diversity demodulator unit1107, a demodulator1109, and a decoder1111.

The transceiver unit1101receives at least one signal. According to this invention, a plurality of the transceiver units1101may be used. The signals received through the transceiver units1101may form frequency blocks, which may be arranged in the order of row and thereby form a space frequency block. At this time, the length of the frequency block (the number of rows of the space frequency block) may be proportional to the number of tones constituting FQAM symbols of the received signals and the number of the transceiver units1101. Also, the number of rows of the space frequency block may be proportional to the number of the received signals, namely, the number of the transceiver units1101.

The FFT1103performs a fast Fourier transform (FFT) for the received signals.

The tone deinterleaver1105performs deinterleaving, based on the formed space frequency block. At this time, the tone deinterleaver1105performs deinterleaving for each frequency block (i.e., for each row) in the space frequency block. For this, the receiver1100may have a plurality of the tone deinterleavers1105each of which corresponds to the frequency block. The number of the tone deinterleavers1105may correspond to the number of the transceiver units1101.

The received signals may be signals for which interleaving between tones has been performed such that tones having the same position (same index) among all tones constituting the modulated FQAM symbols are adjacent to each other. Therefore, the tone deinterleaver1105may form a space frequency block having an original array of FQAM symbols by performing inversely interleaving performed at the transmitter.

The tone deinterleaver1105may perform deinterleaving by performing inversely an algorithm of interleaving performed at the transmitter. A detailed algorithm for performing deinterleaving is not specially limited, and the tone deinterleaver1105may perform an algorithm for deinterleaving, based on information about an interleaving algorithm performed at the transmitter. The transmitter and the receiver may share information about interleaving and deinterleaving algorithms through upper signaling or on the basis of information earlier stored by a device manufacturer.

The transmit diversity modulator unit1107performs a transmit diversity demodulation, based on the deinterleaved space frequency block. For example, using a transmit diversity technique such as a space frequency block code (SFBC) or a space time block code (STBC), the transmit diversity modulator unit1107creates an FQAM symbol based on a space frequency block. At this time, the transmit diversity modulator unit1107may create the FQAM symbol by using an Alamouti code.

The demodulator1109demodulates the created FQAM symbol according to the FQAM scheme.

The decoder1111decodes a codeword created by demodulation and thereby restores an original data stream.

The FFT1103, the tone deinterleaver1105, the transmit diversity demodulator unit1107, the demodulator1109, and the decoder1111may be referred to as a single element, i.e., a control unit.

The principles and features of the present invention may be employed in varied and numerous embodiments without departing from the scope of the invention. Accordingly, it should be apparent to those skilled in the art that this description is provided for illustration purpose only and not for the purpose of limiting the present invention as defined by the appended claims and their equivalents.

The present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, the disclosed embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this invention to those skilled in the art. While this invention has been particularly shown and described with reference to an exemplary embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of this invention as defined by the appended claims.