KR20080070477A - Method for generating and transmitting symbols as transmission unit - Google Patents

Abstract

A method for generating and transmitting a transmission unit symbol is provided to transmit more information by masking and transmitting a transmission sequence on a time domain. A method for generating a transmission unit symbol includes the steps of: modulating a predetermined transmission sequence to a first direction as one of time and frequency directions, and generating a first direction modulation sequence(S201,S202); and modulating the first direction modulation sequence to a second direction as the other direction of the time and frequency directions, and generating a symbol of a transmission unit(S203,S204). The transmission unit is one of a transmission time interval or a slot of the transmission time interval. The modulation of the first direction and the modulation of the second direction are one of the spreading and scrambling of a predetermined sequence.

Description

Method for Generating And Transmitting Symbols As Transmission Unit

1 is a schematic diagram showing a configuration of a transmitting end of a typical SC-FDM communication system.

2 is a flowchart illustrating a method of generating a transmission unit symbol according to an aspect of the present invention.

3 illustrates a channel structure that may be used when transmitting only a control signal without data.

4 illustrates a channel structure that may be used when data and control signals are transmitted together.

5 is a diagram for describing a method of generating a TTI unit symbol modulated in a time and frequency direction according to a sequence modulation scheme according to an embodiment of the present invention;

6 and 7 illustrate various methods of applying hopping to the TTI unit symbol generated as shown in FIG. 5.

8 is a diagram for describing a method of generating a TTI unit symbol modulated in a time and frequency direction according to a direct modulation method according to another embodiment of the present invention;

9 is a flowchart illustrating a TTI unit symbol transmission method according to an aspect of the present invention.

FIG. 10 is a diagram for describing a method of performing time domain modulation on a transmission symbol in TTI units and transmitting the same according to an embodiment of the present invention. FIG.

11 to 14 are diagrams for explaining various ways of applying a jump to a transmission form as shown in FIG.

15 to 17 illustrate a method of inserting a pilot into a coherent TTI unit symbol generated according to an embodiment of the present invention.

18 and 19 illustrate a method of merging and using a coherent channel and a non-coherent channel according to embodiments of the present invention.

The following description of the present invention relates to a method of generating a symbol in which a predetermined transmission sequence is modulated in a time and frequency direction in a transmission unit and a method of transmitting a symbol in the above-described transmission unit.

In a Universal Mobile Telecommunications System (UMTS) communication system including 3GPP 3rd Generation Partnership Project Long Term Evolution (LTE), a transmitting end is a time unit for transmitting one or more transmission blocks, that is, higher layer transmission information simultaneously. Transmission Time Interval (“TTI”) is defined, and in the case of small packet data transmission such as VoIP, a slot included in the 1 TTI is defined as a unit for transmitting corresponding information at the same time. Such a TTI may include a plurality of OFDM symbols in the time direction. In the current 3GPP LTE, it is assumed that 14 OFDM symbols are included in 1 TTI and 2 slots are included in 1 TTI.

Meanwhile, in 3GPP LTE, specific information is transmitted in units of one OFDM symbol. For example, the SC-FDM scheme used as an uplink transmission scheme including a control signal in the 3GPP LTE scheme is as follows.

When the terminal transmits a control signal to the base station, one of the most important points is coverage. That is, the bandwidth of the signal transmitted by the terminal is not large, but the method of centralizing and transmitting power in one place is important, and it is preferable that the change width (PAPR) of the transmitted signal is also small. To this end, in 3GPP LTE, it is discussed to use SC-FDM (Single Carrier Frequency Division Multiplexing) as an uplink signal transmission.

1 is a schematic diagram illustrating a configuration of a transmitting end of a general SC-FDM communication system.

SC-FDM is a transmission scheme for improving PAPR characteristics by making a small amount of signal change, and has a wider coverage effect when the same power amplifier is used. As can be seen through the configuration of the transmitter of the SC-FDM scheme as shown in Figure 1, the biggest feature of the SC-FDM is that the transmission signal is first spread by the DFT module 101 to the DFT. This spread signal is mapped to a transmission signal (Tx Signal) in the OFDM symbol unit by the IDFT module, preferably the IFFT module 102 as shown in FIG. The generated transmission signal is concentrated and transmitted in the transmission frequency band, and the generated signal has the same effect as that transmitted through a single carrier.

Meanwhile, the transmission signal currently proposed in 3GPP LTE using the SC-FDM scheme as described above is based on the structure that information is transmitted in one OFDM symbol unit. However, since a transmission unit for transmitting a predetermined amount of information at the same time is a TTI or a slot, it may be desirable to configure a transmission signal based on this.

According to the aspect as described above, an embodiment of the present invention is to provide a method of modulating transmission information by TTI or slot unit, not by symbol unit, to generate the corresponding transmission unit symbol, and transmit the signal using the same.

In addition, the above-described scheme can be applied to a control channel for transmitting a control signal in the uplink, thereby providing a method for simultaneously transmitting more control information along with the uniformity (PAPR / CM) and cell coverage of the transmitted signal. I would like to.

A transmission unit symbol generation method according to an aspect of the present invention for achieving the above object is a method for generating a symbol in which a predetermined transmission sequence is modulated in a transmission unit in a time and frequency direction in a communication system. Generating a first directional modulation sequence by modulating in a first direction, which is one of time and frequency directions, and modulating the first directional modulation sequence in a second direction, the other of time and frequency, to TTI Generating a symbol of a unit.

In this case, the transmission unit may be any one of a transmission time interval (TTI) or a slot in the TTI, and the modulation in the first direction and the modulation in the second direction may be performed in a predetermined sequence. It can be either spreading or scrambling.

In addition, the first direction modulation is performed by multiplying the predetermined transmission sequence by a time direction modulation sequence having the transmission unit length, and the second direction modulation performs each symbol of the first direction modulation sequence within a resource block. Alternatively, the first direction modulation may be performed by multiplying the predetermined transmission sequence by a frequency direction modulation sequence having a number of subcarriers in one resource block, and performing the multiplication with the frequency direction modulation sequence. The second direction modulation may be performed by multiplying the first direction modulation sequence for each symbol in the transmission unit by a time direction modulation sequence having a TTI length.

The method may further include performing a frequency hopping for each predetermined symbol in the transmission unit symbol in the transmission unit symbol generated as described above. When the communication system is an SC-FDM communication system, the predetermined transmission sequence may be heterogeneous. The information may be a sequence mixed by discrete Fourier change (DFT) spreading.

On the other hand, according to another aspect of the present invention for achieving the above object, a transmission unit transmission method, the step of masking a predetermined transmission sequence to each symbol in the transmission unit, and the sequence masked in the symbol And transmitting in a transmission unit.

At this time, in the masking step, it may be desirable to perform masking by applying a symbol unit cyclic shift to the predetermined transmission sequence.

Further, the predetermined transmission sequence may be a symbol unit sequence, but according to the first aspect of the present invention, a time domain sequence for each subcarrier of a transmission unit symbol in which the predetermined symbol unit sequence is modulated in the transmission unit in the time and frequency directions. It may be.

In addition, according to an embodiment of the present invention, at least one of the index of the sequence masked on the symbol and the symbol unit cyclic shift applied to the sequence masked on the symbol may indicate control information, and in this case, it is included in the transmission unit. And inserting a pilot into a number of symbols corresponding to a difference between a number of symbols and a fraction of a number less than a number of symbols included in the transmission unit, wherein in the pilot insertion step, the pilot is configured to perform channel estimation. It may be desirable to be inserted at equal intervals in the central portion of the target area.

In another embodiment of the present invention, a first region in the transmission unit supports a coherent search scheme, and a second region in the TTI supports a non-coherent search scheme. The first region may be one or more of an index of a sequence masked to a symbol in the first region and a symbol unit cyclic shift applied to a sequence masked to a symbol in the first region. In this second region, symbol information of a sequence masked to a symbol in the second region may represent control information.

In addition, the sequence masked to each symbol in the transmission unit may represent control information searchable by a coherent search method, in which case a symbol for pilot transmission in the transmission unit transmitting the control information is a data transmission channel. It may be arranged to be the same as the position of the symbol for pilot transmission.

In addition, the sequence masked to each symbol in the transmission unit may represent control information searchable by a non-coherent search method, in which case the control information is a sequence used for the first direction modulation of the sequence and the It can be represented by a combination of sequences used for the second direction modulation.

In addition, the sequence masked to each symbol in the transmission unit may represent control information searchable by a non-coherent search method, in which case the control information may be represented by differential modulation in a time domain or a frequency domain of the sequence. Can be represented.

The method may further include performing frequency hopping on the modulated sequence for each predetermined symbol in the transmission unit before the transmitting step.

On the other hand, the control signal transmission method according to another aspect of the present invention is a method for transmitting a control signal in a communication system for allocating a predetermined number of subcarrier areas for the control channel at both ends or either side of the system bandwidth, Masking a predetermined transmission sequence to each symbol in a transmission unit in a predetermined number of subcarrier regions allocated for the control channel; And transmitting the sequence masked to the symbol in a transmission unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention.

As described above, an embodiment of the present invention provides a method of modulating transmission information into a transmission unit such as a TTI or a slot unit rather than a symbol unit, generating the transmission information as a corresponding transmission unit symbol, and transmitting a signal using the same. . First, a method of generating a transmission unit symbol as an aspect of the above-described embodiment is as follows.

According to an embodiment of the present invention, when a transmission signal is generated as a symbol of a predetermined transmission unit such as a TTI or a slot rather than an OFDM symbol unit, one symbol including a plurality of OFDM symbols as well as a frequency direction with respect to the generated symbol itself The transmission signal may be modulated in the time direction within the transmission unit so that the transmission signal may include additional information.

2 is a flowchart illustrating a method of generating a transmission unit symbol according to an aspect of the present invention.

First, in step S201, a predetermined sequence representing a transmission signal is modulated in either the time direction or the frequency direction (hereinafter referred to as "first direction"). If the first direction modulation is modulation in the time domain, the first direction modulation may be performed by multiplying with a time direction modulation sequence having an OFDM symbol length included in a transmission unit of a corresponding system, such as 1 TTI or 1 slot. When the modulation is modulation in the frequency domain, the modulation may be performed by multiplying a frequency direction modulation sequence having a length equal to the number of subcarriers used to transmit conventional unit information. Here, time direction modulation and frequency direction modulation refer to a process of spreading or mixing a predetermined transmission sequence in a time direction or a frequency direction.

In addition, the first directional modulation sequence used may be an exponential function sequence for applying a cyclic shift to another region and the same region when the transmission sequence is a CAZAC sequence. Sequences can be used.

Accordingly, the first direction sequence is generated in step S202. That is, the first direction sequence refers to a sequence in which the transmission sequence is modulated in one of a time direction and a frequency direction.

Thereafter, in step S203, the first direction sequence generated by step S202 is modulated in a direction other than the first direction in the time direction or the frequency direction (hereinafter referred to as "second direction"). As described above, the second directional modulation is used to transmit an OFDM symbol length included in the time domain in one TTI or a slot or one unit of information by using the first directional sequence generated in step S202 as in the above-described first directional modulation. It may be performed through a product with a second direction modulation sequence having a length equal to the number of carriers.

Accordingly, in step S204, time and frequency direction modulation symbols of a transmission unit such as a TTI or a slot are generated, and through this, additional information may be transmitted in the modulation step to each region as well as the information of the transmission sequence itself. For example, when the CAZAC sequence is used as a transmission sequence, two sequences having different cyclic shifts applied to the corresponding transmission sequence can be allocated to each UE, and each can be used to indicate ACK / NACK information. The movement may be directly applied in the process of transmitting the transmission sequence. However, when the transmission unit symbol as in the present embodiment is used, the movement may be applied in the process of performing time domain or frequency domain modulation on the transmission sequence.

The term “transmission unit” used in the embodiment of the present invention described above with reference to FIG. 2 is a concept including all of time units for transmitting transmission information such as TTI and slot at the same time. The following description focuses on the case where the above-mentioned transmission unit is TTI for convenience of description, but it is not necessary to limit the transmission unit to the TTI as described in the following embodiments.

Meanwhile, the scheme described above with reference to FIG. 2 may be applied to a control channel for transmitting a control signal in uplink using SC-FDM, and thus, the transmission signal may have a greater number of transmission signal uniformity (PAPR / CM) and cell coverage. Control information can be transmitted at the same time. In this regard, the channel structure used when transmitting a control signal in the SC-FDM scheme will be described.

There is a part to be considered when transmitting a control signal in the above-described SC-FDM scheme. First, when transmitting a control signal, different channel structures may be used as follows depending on whether or not there is data.

3 is a diagram illustrating a channel structure that may be used when only a control signal is transmitted without data.

When transmitting a control signal, when there is no data to be sent together, as shown in FIG. 3, a structure in which the control signal is divided into frequency division multiplexing (hereinafter, referred to as "FDM") and allocated to a portion of the system band may be used. Specifically, the control channel region allocated for control signal transmission without data transmission may be single at both ends of the system band as shown in FIG. 3.

The terminal transmitting only the control signal according to the control channel formed as described above may demodulate and transmit the control signal in the SC-FDM format to the allocated area. The method of transmitting a control signal in this allocated area may take the form of FDM or code division multiplexing (hereinafter, referred to as "CDM") between the control signals of the terminal in the allocated area.

4 illustrates a channel structure that may be used when data and control signals are transmitted together.

Even when data and control signals are transmitted together, some bands of the system band may be divided for FDM scheme and allocated for control channel transmission as shown in FIG. 3. In this case, the transmission scheme cannot be viewed as an SC-FDM scheme. This corresponds to a multi-carrier transmission scheme. Accordingly, even when data and control signals are simultaneously transmitted, data and control signals are transmitted together through DFT spreading in order to maintain the SC-FDM scheme and reduce the PAPR of the transmission signals. In this case, the method of combining the data and the control signal may be time division multiplexing (“TDM”), CDM, or modulation-based transmission, and FIG. 4 illustrates that the control signal and the data are transmitted in the TDM scheme.

In the structure shown in FIG. 4, a method of increasing coverage in the absence of a control signal may be similarly implemented. When it is necessary to send a control signal robustly, a method of repeatedly inserting a specific control signal in each OFDM symbol is required. to be. This can increase the power of the control signal approximately 10 * log ₁₀ (12) = 10.8 dB.

The following description of the control channel structure described above will focus on the case where a time and frequency direction modulated TTI unit symbol is applied to a control channel transmitting only a control signal without data according to each embodiment of the present invention. That is, in the basic control channel structure shown in FIG. 4, a control signal transmission structure capable of transmitting more control information without affecting the uniformity of PAPR / CM, etc. of the control signal is proposed. However, the method of generating a TTI unit symbol and transmitting a signal according to each embodiment of the present invention may not necessarily be used only for the above-described control signal transmission, and may be applied to any system using TTI as a transmission unit. .

On the other hand, when the above-described embodiment of the present invention is transmitted using a channel for transmitting only a control signal without data, a CAZAC sequence, specifically a Zadoff-Chu (ZC) CAZAC sequence, is used as a sequence used for transmitting a control signal. Do.

Hereinafter, the above-described CAZAC sequence will be described.

As the CAZAC sequence, two kinds of the aforementioned Zadoff-Chu CAZAC and GCL CAZAC are used. They are conjugated to each other and GCL CAZAC can be obtained by taking the conjugated complex number of Zadoff-Chu. Zadoff-Chu CAZAC is given by

Here k denotes a sequence index, N denotes a length of a CAZAC sequence to be generated, and M denotes a sequence ID.

On the other hand, the above-described ZC sequence is the most available sequence when the sequence length N is a prime number, and if the length of the sequence is not a prime number, it is valid only for a decimal M value relative to N (M is from 1 Up to N-1). Therefore, it is better to make the sequence to be small so as to be the length.

In case of transmitting a control signal without data in 3GPP LTE, a control channel is configured as shown in FIG. 3, and a basic allocation unit is called a resource block (RB), and the number of subcarriers is 12. No matter how the default allocation unit is set, if the value is not prime, it is recommended to generate a fractional length sequence for this length. Currently, the methods mentioned above generate a sequence with a fractional length longer than N, There are two ways to cut and write only N, and to create a sequence with a fractional length shorter than N and not use the rest or fill it with zeros. In addition, even if N is not a prime number, there is a method of generating a CAZAC sequence as it is. In this case, the number of generated sequences is very small. Signal uniformity in the time / frequency domain (PAPR, cubic metric, etc.) is a good feature.

In the following detailed description of the present invention, it is assumed that all three schemes described above can be used, and the method is selected according to the appropriate RB size and the number of symbols used in the TTI.

In addition, two methods of transmitting information through a CAZAC sequence may be considered as a method of using a CAZAC index and a method of representing information by applying a circular shift to a sequence corresponding to each CAZAC index. In addition, the cyclic shift method includes a direct cyclic shift of the applied CAZAC sequence and a domain transformation (for example, multiplying an exponential function in the frequency domain to apply a time domain cyclic shift or an exponent in the time domain). Cyclic shift using a multiplication function to apply a frequency domain cyclic shift).

Based on this, the following describes two methods (direct modulation and sequence modulation) as specific examples of the above-described embodiment of the present invention as shown in FIG. .

The direct modulation method is a method of performing OFDM modulation after performing DFT spreading on a transmission signal. That is, after performing the spreading process by the DFT spreading module 101 of FIG. 1 and performing frequency direction modulation and additional time direction modulation according to the above-described embodiment of the present invention, the TFT unit symbol is performed by the IFFT module 102. This is how you create it.

In contrast, the sequence modulation method is a method in which a specific sequence (eg, CAZAC, Walsh, Hadamad, Golay, PN, etc.) is loaded on a subcarrier. That is, the sequence itself is used as information. Circular movement may be additionally applied to this specific sequence.

Hereinafter, each method will be described with reference to the accompanying drawings.

5 is a diagram for describing a method of generating a TTI unit symbol modulated in a time and frequency direction according to a sequence modulation method according to an embodiment of the present invention.

As shown in FIG. 5, for example, the above-described specific transmission sequence such as CAZAC, Walsh, Hadamad, Golay, PN, etc. may be carried on each subcarrier. At this time, the sequence carried on each subcarrier according to the present embodiment is a time domain in which the specific transmission sequences s0 to s13 such as CAZAC, Walsh, Hadamad, Golay, and PN have a length of 1 TTI as shown in FIG. It may be a form multiplied by the modulation sequence (x0 to x13).

That is, specific sequences modulated into the time domain (s (0) x (0) to s (13) x (13)) may be mapped and transmitted to each subcarrier.

On the other hand, the above-described time domain modulation sequences (s (0) x (0) to s (13) x (13)) mapped and transmitted to each subcarrier are multiplied by the frequency domain modulation sequence c (k). You can enter In this case, the frequency domain modulation sequence c (k) may have the following exponential function form so that the transmission sequence s (n) may be cyclically moved in the time domain (n is a time domain symbol index).

Here, k may be a frequency domain subcarrier index, w ₀ may be a unit phase to which cyclic shift is applied, and S may be an index value indicating a degree of cyclic shift to be applied.

Therefore, in the time and frequency domain modulated TTI unit sequence finally generated according to the embodiment as described above, the transmission information is (1) cyclic shift of c (k), (2) transmission sequence of s (n), ( 3) can be divided into cyclic shift information of x (n).

 In the case of generating and transmitting the TTI unit symbol according to the above-described scheme, PAPR / CM and the like are not distorted at all and more transmission information can be transmitted. Meanwhile, the use of s (n) here may vary depending on the amount of data to be transmitted. That is, s (n) may have the same value for all n (in this case, the transmission information is passed to the other two options), and may use a different value.

Meanwhile, in a more specific embodiment of the present invention, diversity gain may be additionally obtained by applying frequency hopping to the TTI unit symbols generated according to the sequence modulation scheme as shown in FIG. 5.

6 and 7 are diagrams for explaining various methods of applying hopping to the TTI unit symbol generated as shown in FIG. 5.

6 and 7 apply a TTI unit symbol generated in the manner described above with reference to FIG. 5 to a control channel structure that transmits only a control signal without data, as shown in FIG. At the end, when a control signal is transmitted through a subcarrier region allocated for a control channel, a structure for transmitting a frequency domain diversity gain by changing a transmission frequency band for each predetermined symbol unit is shown. That is, the reason why the hop is applied as shown in FIGS. 6 and 7 is to obtain diversity gain through the hop when one channel is not good according to the propagation path.

Specifically, FIG. 6 illustrates changing a frequency band of each symbol for every symbol, and FIG. 7 illustrates a structure in which symbols in each region are set to be transmitted through different frequency bands by dividing 1 TTI into two. have. In each drawing, the hatching part indicates a position for transmitting control information, and the hatching part indicates a position for not transmitting control information. However, in FIG. 6 and FIG. 7, symbols generated using different sequences may be transmitted to portions hatched and not illustrated, or may be different portions of symbols generated using the same sequence. .

FIG. 8 is a diagram for describing a method of generating a TTI unit symbol modulated in a time and frequency direction according to a direct modulation method according to another embodiment of the present invention.

In the case of the direct modulation scheme, unlike the sequence modulation scheme described with reference to FIG. 5, the transmission sequence is directly loaded on a subcarrier. In the case of generating a signal as described above, the generated signal must be spread by the DFT module 101 of FIG. 1, and a sequence used as a mask at a subcarrier level is used in a spectral shaping format. do.

In this case, when the same value is applied for each OFDM symbol in the transmission sequence s (k) carried on the subcarrier, additional information (for example, from the frequency direction modulation sequence c (k) used as subcarrier directional masking) is used. , Circular movement). In addition, unlike the case described above, if different symbols are applied to subcarriers of all OFDM symbols, the frequency direction modulation sequence c (k) may be a simple scrambling sequence.

Meanwhile, according to the present embodiment, the frequency-domain modulated sequence is additionally modulated into the time domain by the time-domain modulation sequences x (0) to x (13) in the TTI unit as shown in FIG. 8. Can be.

Accordingly, in the time and frequency direction modulated TTI unit symbols generated as shown in FIG. 8, the transmission information includes (1) each subcarrier symbol s (k) as a transmission sequence, and (2) subcarrier level modulation. In addition to the sequence c (k), it may be carried by (3) a TTI unit time domain modulation sequence x (n).

In the case of the above-described direct modulation method, the hopping may be applied as shown in FIGS. 6 and 7. However, due to the subcarrier level modulation of the transmission sequence, since accurate channel estimation is required at each subcarrier level, it may be desirable not to apply the hopping or to apply the hopping according to the method shown in FIG. 7.

Meanwhile, in the TTI unit symbol generation method as described above with reference to FIGS. 5 to 8, the transmission sequence s (k) may indicate specific control information to be transmitted. In this case, the control information may indicate any control information such as ACK / NACK, CQI, etc., but may be control information in which heterogeneous control information such as ACK / NACK, CQI, etc. is mixed by DFT spreading. That is, in one specific embodiment of the present invention, a transmission sequence may be generated by mixing heterogeneous control information at the front end of the DFT spreading module of FIG. 1.

Meanwhile, the TTI unit signal transmission method according to another embodiment of the present invention will be described below.

9 is a flowchart illustrating a TTI unit symbol transmission method according to an aspect of the present invention.

In the method of transmitting a TTI unit signal according to an embodiment of the present invention as shown in FIG. 9, it is noted that simultaneously transmitting signals in a communication system is not a symbol unit but a TTI unit, so that the transmission sequence is timed within 1 TTI. Masking and transmitting the area symbols, respectively, wherein the transmission sequence transmitted may be a time direction sequence per subcarrier of the time and frequency direction modulated TTI unit symbol as described above with reference to FIG. As in the prior art, it may be an arbitrary symbol unit transmission sequence.

First, in step S901, any OFDM symbol as described above or a temporal direction sequence per subcarrier of a TTI unit symbol (hereinafter, collectively referred to as an "input sequence") of each OFDM symbol in a time domain within 1 TTI. Perform masking on the area. In this case, the input sequence may be sequentially masked to each OFDM symbol, but additional information may be transmitted by applying a cyclic shift to the order of masking the input sequence to the OFDM symbol. The cyclic shift applied in this manner is a different concept from the cyclic shift in FIGS. 5 to 8 applied in each symbol in a symbol unit cyclic shift.

Thereafter, in step S902, the time domain modulated sequence generated by step S901 is transmitted in units of TTIs. In this manner, additional information may be transmitted through time-directional modulation in the transmission sequence.

Hereinafter, the above-described scheme will be described in detail through an example of applying the control channel structure to transmit only a control signal without data in a communication system using the SC-FDM scheme.

FIG. 10 is a diagram for describing a method of performing time-domain modulation on a transmission symbol in TTI units and transmitting the same according to an embodiment of the present invention.

Specifically, FIG. 10 is an example of applying a CAZAC sequence as a transmission symbol in the time domain of a TTI unit. In FIG. Form.

Specifically, considering the structure of the OFDM symbol in 3GPP LTE, since there are a total of 14 OFDM symbols in one TTI, the length of the CAZAC sequence may be N = 14. Herein, a method of generating a transmission sequence mapped to an OFDM symbol in the time domain may include only the above-described cyclic copy and truncation methods, which generate and use a sequence based on a decimal length to secure the number of CAZAC sequences. Rather, it is possible to use N = 14 length as it is. In addition, in one embodiment of the present invention, a sequence per subcarrier of TTI unit symbols modulated in time and frequency direction as described above with reference to FIG. 2 may be used.

When such a transmission sequence is masked on a time domain OFDM symbol, cyclic shift may be applied to the time domain as shown in FIG. 10. Specifically, while the transmission sequence is sequentially masked on the first and second subcarriers of FIG. 10, the cyclic shift is applied to the transmission sequence by two OFDM symbols on the third subcarrier, and seven on the fourth subcarrier. It is shown that a cyclic shift is applied to a transmission sequence by an OFDM symbol and transmitted. The time-directional cyclic shift in TTI is performed in symbol units in the step of mapping a transmission sequence to an OFDM symbol, which is different from the cyclic shift in FIGS. 5 to 8 in which cyclic shift is applied within 1 OFDM symbol.

Therefore, one of the advantages of using CAZAC masked symbolically in the time domain according to the present embodiment is that, as described above, the number of cyclic shifts that can be used for the CAZAC sequence can be obtained by the sequence length. Unlike the cyclic shift applied within 1 OFDM symbol, this cyclic shift can maintain orthogonality with each other even when the delay spread is very large. In addition, since the sequence of 14 lengths corresponding to the number of symbols in the TTI is used, the number of applicable cyclic shifts may also be 14. In addition, since the number of root sequences according to the length is about 14, it is advantageous to secure the number of original sequences as compared with the case of using 12 subcarrier lengths in the frequency domain, thereby solving the problem of cell planning.

In addition, according to the transmission scheme of FIG. 10, additional information may be transmitted by applying symbol unit cyclic shift in the TTI to the TTI unit symbols generated according to the scheme of FIGS. 5 to 8.

In the embodiment as shown in FIG. 10, the UE can be divided into a cyclic shift or an original sequence index. Meanwhile, an embodiment of the present invention proposes a method of utilizing the cyclic shift as shown in FIG. 10 as control signal information as well as the classification of the UE. For example, two cyclic shift sequences having the same original sequence index are allocated to one UE, and ACK / NACK is transmitted to correspond to each cyclic shift value. This format may be useful when configuring the ACK / NACK channel in the control channel of FIG. 3 in FDM format.

The use of the CAZAC sequence in the FDM format was limited, and the message transmission required a pilot because the signal was generated by applying a control symbol directly to each subcarrier (ie, a coherent method). However, according to the above-described embodiment of the present invention, by masking CAZAC in the time domain as shown in FIG. 10 and directly applying different cyclic shift sequences according to control information, seven ACK / NACKs can be simultaneously transmitted per FDM resource region. It can be seen that there is (ie non-coherent).

That is, according to an embodiment of the present invention, by transmitting the control information by using the cyclic shift applied in the symbol unit in the time domain by transmitting the information by the cyclic shift itself without a pilot, the non-coherent detection method of the receiver According to another embodiment, a time domain symbol unit cyclic shift may additionally be used only for distinguishing users, and the classification of control information may support a coherent detection scheme that must be performed through channel estimation through pilot. have. A method of supporting such a coherent method and a non-coherent method will be described below with a specific example.

Meanwhile, in a specific embodiment of the present invention, frequency hopping for obtaining diversity gain may be additionally applied to the transmission method as shown in FIG. 10.

11 to 14 are diagrams for describing various methods of applying a hop to a transmission form as shown in FIG. 11.

Specifically, FIGS. 11 to 14 apply the CAZAC sequence as a transmission sequence in units of time direction symbols in the same manner as described above with reference to FIG. 10, but when the channel hops to obtain a frequency axis diversity gain, the sequence Modulation also shows how to leap together.

Two approaches can be considered here. First, as shown in FIGS. 11 and 12, the sequence length 14 may be masked as it is in the resource region where the frequency hopping is performed at a predetermined symbol interval regardless of the frequency hopping, and thus the sequence length 14 may be maintained.

On the other hand, the phenomenon that occurs due to the leap is that the channel response to the channel resources used, specifically the control channel resources may be different. Because of this, orthogonality of the sequence may be affected, and another embodiment of the present invention proposes to apply the same sequence only to OFDM symbols existing in the same resource. That is, as shown in FIGS. 13 and 14, when the position of the control signal is leap and the same subcarriers are used repeatedly, the method uses a sequence length as many times as the number of subcarriers is used. In this case, the sequence length transmitted in FIGS. 13 and 14 is half of the sequence length in FIGS. 11 and 12.

Meanwhile, in a specific embodiment of the present invention, when using frequency hopping as shown in FIGS. 13 and 14, the length of the sequence is reduced by half and the half length of CAZAC even when there is no hopping as shown in FIG. 10 for compatibility. Modulation can also be performed.

In the above-described embodiment of the present invention, it has been described that a non-coherent search method for dividing control information into only cyclic shift applied to a sequence can be supported. However, when the non-coherent search method is supported as described above, the number of information that can be transmitted may be reduced as compared to the coherent search method.

Accordingly, in a preferred embodiment of the present invention, a pilot is inserted into a control channel to retrieve control information in a coherent manner, and a pilot is inserted in consideration of securing the number of sequences and accuracy of channel estimation.

Specifically, if a sequence such as CAZAC is used, it is most advantageous to secure the number of sequences because the length thereof is a prime number. For example, when processing with 14 OFDM symbols, the sequence is inserted by inserting a pilot into one OFDM symbol. The symbol length to be applied may be set to 13 or the symbol length to which the sequence is applied may be set to 11 by inserting pilots into three OFDM symbols.

15 to 17 are diagrams for explaining a method of inserting a pilot in a coherent TTI unit symbol generated according to an embodiment of the present invention.

That is, when pilot is inserted into one OFDM symbol as shown in FIG. 15, it is preferable not to use frequency hopping. In this case, it may be advantageous for channel estimation that the OFDM symbol into which the pilot is inserted is located at the center of the transmission unit. FIG. 15 illustrates a structure in which a pilot is applied to a seventh or eighth OFDM symbol among 14 OFDM symbols in one TTI.

FIG. 16 illustrates a structure in which pilots are applied to three OFDM symbols among 14 OFDM symbols in one TTI, and frequency hopping is applied to every seven OFDM symbols. As shown in FIG. 16, when three OFDM symbols are used for pilot and frequency hopping is applied, it is preferable to arrange one pilot OFDM symbol on one side and two pilot OFDM symbols on the other side. It is preferable that the pilot OFDM symbols are arranged in the center of the hopping region, and the two pilot OFDM symbols are arranged to maintain equal intervals in the hopping region.

In addition, FIG. 17 illustrates a structure in which three OFDM symbols are used for pilot among 14 OFDM symbols within one TTI and frequency hopping is not applied. As such, when three OFDM symbols are used for pilot without frequency hopping, the three pilot OFDM symbols are preferably arranged at equal intervals in the center within 1 TTI.

In the present embodiment using the coherent search method, the length of the modulation sequence can be reduced by arranging pilots as shown in Figs. 15 to 17. When using a CAZAC sequence, the maximum number of sequences can be ensured. The channel estimation performance can be improved by arranging pilot OFDM symbols at equal intervals in the center of the transmission region.

On the other hand, if the number of OFDM symbols to be used as pilots is allocated differently, for example, when two (or three) pilots are allocated to each hopping region in FIG. 16, the length of the sequence is 10 (or each) in each hopping region. 8), the length of the sequence to be used is not a fractional length. At this time, the pilot positions are arranged at equal intervals so that the pilots can provide proper channel estimation performance to other OFDM symbols. Alternatively, the pilots may be arranged by sharing the pilot positions of the data regions. In one specific embodiment of the present invention, when the number of OFDM symbols to which the sequence is applied is not a fractional length, a sequence is generated based on the fractional length less than or equal to the number of OFDM symbols, and a cyclic duplication or 0 is inserted into the remaining part. The number of sequences of the corresponding OFDM symbol length can be secured to the maximum, and the number of usable sequences can be secured by generating a sequence based on a fractional length of the number of OFDM symbols or more and cutting the sequence portion of the number of OFDM symbols or more. .

The above description relates to a method of transmitting a control signal to support a coherent search scheme according to an embodiment of the present invention. Meanwhile, in a more specific embodiment of the present invention, the above-described coherent method and the non-coherent method may be used in combination, which will be described in detail below.

18 and 19 illustrate a method of merging and using a coherent channel and a non-coherent channel according to embodiments of the present invention.

According to the embodiment shown in Figs. 18 and 19, a method of properly combining them to solve the disadvantage of reducing the burden of pilot insertion in the coherent method and the information that can be transmitted in the non-coherent method is reduced. to provide. Specifically, one half of the control channel has a signal structure for coherent search (i.e., a structure in which the control signal symbol directly represents each symbol), and the other half has a signal structure for non-coherent search (i.e. for each symbol). Rather than representing a control signal symbol, a structure representing a signal using a sequence itself or a cyclic shift itself applied to the sequence in each subcarrier region) is used.

Accordingly, referring to FIG. 18 and FIG. 19, the upper left and lower right parts of the TTI have a structure of transmitting pilots for coherent search and the lower left and upper right parts for non-coherent search. The structure which shows this information using the sequence itself or the cyclic shift applied to the sequence is shown. Of course, in FIG. 18 and FIG. 19, the coherent region and the non-coherent region may be interchanged, and the number of symbols used for the pilot in the coherent region may also be different from that of FIGS. 19 and 19.

The TTI unit OFDM symbol generation and the TTI unit transmission method according to each embodiment of the present invention as described above can be applied in various situations, which can support both coherent and non-coherent methods.

In the following, examples of applying the above-described embodiments of the present invention to a specific communication system will be exemplarily divided into a coherent method, a noncoherent method, and a combination thereof.

First, in the case of a coherent transmission / reception scheme, since a channel estimation for channel estimation and compensation for the receiver should be possible, a pilot signal should be inserted as shown in FIGS. 15 to 17. In this case, when the pilot signal is inserted, the number of OFDM symbols that can be used for the transmission sequence in the time domain is reduced.

For example, there are 14 OFDM symbols in one subframe (i.e., within 1 TTI) in 3GPP LTE, which is currently discussed (when using a short CP), where the data portion and If the pilot of the control channel is determined with the same structure (ie, two symbols are used for pilot), twelve OFDM symbols are available for sequence transmission. Thus, x (n) of FIG. 5 or FIG. 8, which is a time domain scrambling or spreading sequence, shows a different sequence in different subcarrier regions by applying a jump when the length is not applied. If you use it will be reduced to 6. In addition, if additional reference symbols are used, the symbol length for sequence transmission is reduced by that number.

Meanwhile, in order to generate a TTI unit symbol according to an embodiment of the present invention as shown in FIG. 5 or FIG. 5, FIG. 5 or FIG. 5 is a spreading or mixing sequence on a frequency axis in the above-described time domain sequence in which a pilot is inserted. C (k) of 9 is applied.

If the control signal to be transmitted is simply a small amount of 1 bit or 2 bits such as ACK / NACK, the s (k) value, which is a transmission sequence, is fixed on the frequency axis, and as shown in FIG. Modulation can be applied to BPSK or QPSK so that the sequence multiplied by the whole indicates ACK / NACK.

If you want to convey more information (for example, CQI, PMI, etc.), you can use two methods.

First, as shown in FIG. 5, a small number of bits of control data are multiplied by QAM, and additional bits may be applied to other control OFDM symbols. Alternatively, it is possible to convert control data into QAM directly on the frequency axis and apply it to subcarriers. In this case, the c (k) sequence plays a role of mixing and may be a UE specific or a cell / node-B specific sequence.

In the above case, if the hop is applied, the sequence used in one slot (that is, half of one subcarrier) can be set differently from the sequence used in the other slot. In the case of applying MIMO diversity, diversity may be applied to a frequency axis / time axis. When applying to the frequency axis, space-frequency block coding (SFBC) is applied to FIG. 8. In the case of applying on the time axis, it can be applied to FIG. 5. That is, it can be delivered by applying block coding to different transmission sequence positions.

Next, when the non-coherent transmission / reception scheme is supported, the pilot does not need to send a pilot because the receiver does not perform channel estimation. However, in consideration of collision with the data portion, a preferred embodiment of the present invention may consider a method not used for transmission of control signals for the OFDM symbol portion with pilot. In this case, the time domain modulation sequence x (n) is reduced by the number of OFDM symbols used for pilot transmission as in the coherent scheme described above.

On the other hand, in the case of supporting the non-coherent transmission / reception scheme, since the channel estimation is not performed, the transmission of the control signal includes 1) implicit modulation and 2) explicit modulation. Can be distinguished.

In the case of implicit modulation, the control signal is not transmitted, but the control signal is classified by a sequence combination or an index. In the case of explicit modulation, the control signal is directly transmitted to the sequence. In this case, since channel estimation is impossible, it may be appropriate to use differential modulation.

Hereinafter, the implicit modulation and explicit modulation will be described in more detail.

First, in the case of implicit modulation, it is advantageous to convey a small amount of information. That is, the transmission sequence s (k) or s (n) is usually set to 1, and information is generated by a combination of c (k), which is a frequency direction modulation sequence, and x (n), which is a time direction modulation sequence. Specifically, any set of available sequences (one terminal for one bit (on-off keying) or two (sequence keying) sequence is determined) When a specific sequence is transmitted, the receiver maps and finds the sequence set information corresponding to the control signal.

When constructing a sequence set as described above, the set may be configured by simply selecting one of c (k) and x (n), or a combination of the two may be regarded as a new sequence and mapped to a control signal. For example, assuming that 12 can be used in c (k) and 7 can be used in x (n), a total of 84 (12 * 7) sequence combinations can be used. In addition, in the case of slot-by-slot hopping, sequences at the hopping position (similar to either sequence c (k) or x (n) alone, or a combination of c (k) and x (n)) are different. It can be considered to be a combination. That is, if a UE performs on-off keying in one slot, bit information in the first slot and bit information in the second slot can be extracted separately. In addition, a method in which a UE combines and detects sequence transfer information in two slots is possible. For example, considering sequence combinations A and B, [A, A]. Signals can be transmitted in four combinations: [A, B], [B, A], [B, B]. Therefore, the receiver can detect these two combinations in two slots and convert them into specific bit combinations.

Next, when an explicit modulation scheme is described, in order to be able to receive the control signal as modulation information in a non-coherent manner, a data symbol may be detected without channel estimation such as the differential modulation as described above. Should be used. Differential modulation is applied in such a way that a change in modulation value (usually a phase difference) between adjacent subcarriers on the frequency axis becomes a control signal information and a change in modulation value (phase difference between different OFDM symbols on the time axis). ) As a control signal information can be considered.

To convey more information, two-dimensional differential modulation can be considered, which is differential encoding on the frequency axis for each OFDM symbol or differential modulation information between different OFDM symbols on each subcarrier on the time axis. It is the way to have.

The diversity scheme can be applied to the non-coherent method, so that control signals are generated by applying spatial frequency block coding (SFBC) or space time block coding (STBC) on the frequency or time axis as in the case of the coherent method. It is possible.

Next, a method of using a combination of the coherent method and the non-coherent method described above according to an embodiment of the present invention will be described with reference to more specific examples.

Two representative types of control channel structures (e.g., ACK / NACK channel structures) and transmission / reception schemes, such as the coherent and noncoherent schemes described above, may be used for transmission capacity, UE capacity, and channel characteristics. Each has different characteristics. Specifically, in the coherent method, since the modulation method can be converted and supported in the transmission of small amount of information of 1 bit or 2 bits, such as ACK / NACK, the coherent method has an advantage over the non-coherent method in terms of UE capacity. have. However, in a high mobile environment with high time-varying characteristics due to a high dependency on channel estimation, it is difficult to maintain orthogonality due to deterioration in reliability of channel estimation, which results in deterioration of performance. On the other hand, in the non-coherent method, particularly the implicit modulation described above, the allocation of an additional sequence is required for every 1-bit transmission, resulting in a decrease in UE capacity for information transmission of 2 bits or more. Of course, in order to overcome this, it is possible to abandon the frequency hopping gain in the slot unit and maintain the UE capacity, but the disadvantage is that performance is degraded due to the decrease in the diversity gain. However, even in the case of a relatively high channel change, such as in a fast mobile environment, the performance is superior to the coherent method that relies on channel estimation.

As such, in order to maximize the efficiency of a small amount of control signal transmission, a coherent or non-coherent method may be selected as necessary, and a control channel configuration is required for this purpose.

In the following specific example according to the present embodiment, the resource structure for the basic control channel is considered to be leap-by-slot as shown in FIG. 16, and the number of reference signals per slot is not fixed, and 1 RB is used as the basic unit. Assume that it is configured. In addition, it is assumed that the length of the sequence of the frequency domain is 12, and that 6 sequences are used through the cyclic shift of the CAZAC of a specific index, and that the maximum length of 7 is used as the slot reference for the spreading code of the time domain. do. Of course, in the other example which concerns on this embodiment, if necessary, it can be comprised by various combinations, such as consisting of two diffusion codes of length 3 and length 4.

As a result, according to the above-described embodiment, 42 (7 * 6) orthogonal channels can be generated in one slot, and two orthogonal channels or orthogonal codes are required for one-bit transmission in case of coherent and non-coherent. Twenty-one code pairs are formed by tying two codes for each of the two codes, and the code pairs are assigned to the UE and used to easily support a mixed structure of coherent and non-coherent.

As mentioned above, various combinations are possible through the division of the spreading code in the time domain, and thus, the configuration of code pairs can be set in various ways according to channel characteristics and UE capacity, thereby maximizing the advantages of coherent and noncoherent. ACK / NACK channel configuration is possible.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can.

For example, the transmission unit symbol generation method and the transmission unit transmission method according to an embodiment of the present invention described above transmit information in a transmission unit such as TTI or slot as well as in a control channel for transmitting control information such as ACK / NACK. Can be used in any channel such as a data channel.

Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the method according to an embodiment of the present invention as described above, more information can be transmitted by generating and transmitting a symbol by performing time and frequency direction modulation in a predetermined transmission unit such as a TTI or a slot instead of a symbol unit. .

In addition, by masking and transmitting the transmission sequence in the time domain, it is possible to apply a symbol unit cyclic shift to the time domain in the case of a CAZAC sequence, thereby transmitting more information.

In addition, as described above, non-coherent search can be supported by setting the cyclic shift in the time domain to represent different control information, and in the method of supporting coherent search, appropriately adjusting the symbols to which the pilot is applied The number of available sequences can be secured and the channel estimation performance can be improved.

In addition, by applying the above-described method to a control channel that transmits only a control signal without data, it is possible to perform more efficient control information transmission without affecting signal uniformity.

Claims (21)

A method for generating a symbol in which a predetermined transmission sequence is modulated in a transmission unit in a time and frequency direction in a communication system, the method comprising: Generating a first direction modulation sequence by modulating the predetermined transmission sequence in a first direction which is either one of the time and frequency directions; And And generating a symbol of the transmission unit by modulating the first direction modulation sequence in a second direction, which is the other of the time and frequency directions. The method of claim 1, And wherein the transmission unit is one of a transmission time interval (TTI) or a slot within the transmission time interval. The method of claim 1, And wherein the modulation in the first direction and the modulation in the second direction are one of spreading and scrambling of a predetermined sequence. The method of claim 1, The first direction modulation is performed by multiplying the predetermined transmission sequence by a time direction modulation sequence having a length of the transmission unit, And wherein the second direction modulation is performed by multiplying each symbol of the first direction modulation sequence with a frequency direction modulation sequence having the number of subcarriers in one resource block. The method of claim 1, The first direction modulation is performed by multiplying the predetermined transmission sequence by a frequency direction modulation sequence having the number of subcarriers in one resource block. And wherein the second direction modulation is performed by multiplying the first direction modulation sequence for every symbol in the transmission unit by a time direction modulation sequence having a length of the transmission unit. The method according to any one of claims 1 to 5, And performing frequency hopping on the transmission unit symbol for every predetermined symbol in the transmission unit. The method according to any one of claims 1 to 5, The communication system is an SC-FDM communication system, And wherein said predetermined transmission sequence is a sequence in which heterogeneous control information is mixed by discrete Fourier transform (DFT) spreading. Masking a predetermined transmission sequence to each symbol in a transmission unit; And Transmitting the masked sequence to the symbol in transmission units. The method of claim 8, And in the masking step, masking is performed by applying a symbol unit cyclic shift to the predetermined transmission sequence. The method of claim 8, And the predetermined transmission sequence is a symbol unit sequence. The method of claim 8, The predetermined transmission sequence is, A transmission unit transmission method, wherein the transmission unit is a time-domain sequence for each subcarrier of a transmission unit symbol in which a predetermined symbol unit sequence is modulated in a time and frequency direction. The method of claim 11, The transmission unit symbol is Generating a first direction modulation sequence by modulating the predetermined symbol unit transmission sequence in a first direction which is either one of the time and frequency directions; And And modulating the first direction modulation sequence in a second direction, the other of the time and frequency directions. The method according to claim 8 or 9, And at least one of an index of the sequence masked in the symbol and a symbol unit cyclic shift applied to the symbol masked sequence indicates control information. The method of claim 13, And inserting a pilot into a number of symbols corresponding to a difference between the number of symbols included in the transmission unit and a fraction less than the number of symbols included in the transmission unit. The method of claim 14, In the pilot insertion step, And the pilots are inserted at equal intervals in the center of a region to be subjected to channel estimation. The method according to claim 8 or 9, A first region within the transmission time interval supports a coherent search scheme, a second region within the transmission time interval supports a non-coherent search scheme, In the first region, at least one of an index of a sequence masked to a symbol in the first region and a symbol unit cyclic shift applied to a sequence masked to a symbol in the first region represents control information, And wherein the second area is symbol information of a sequence masked to a symbol in the second area indicates control information. The method according to claim 8 or 9, The sequence masked to each symbol in the transmission unit represents control information searchable by a coherent search method, And a pilot transmission symbol in the transmission unit for transmitting the control information is arranged in the same position as a pilot transmission symbol of a data transmission channel. The method of claim 12, The sequence masked to each symbol in the transmission unit represents control information searchable by a noncoherent search method, And the control information is indicated by a combination of a sequence used for the first direction modulation and the sequence used for the second direction modulation of the sequence. The method according to claim 8 or 9, The sequence masked to each symbol in the transmission unit represents control information searchable by a noncoherent search method, And the control information is represented by differential modulation in the time domain or frequency domain of the sequence. The method of claim 8, Prior to the transmitting step, further comprising performing a frequency hopping of the modulated sequence for every predetermined symbol in the transmission unit. A method of transmitting a control signal in a communication system for allocating a predetermined number of subcarrier regions for a control channel at either or both ends of a system bandwidth, the method comprising: Masking a predetermined transmission sequence to each symbol in a transmission unit in a predetermined number of subcarrier regions allocated for the control channel; And And transmitting the masked sequence to the symbol in a transmission unit.

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