KR101233178B1 - Method For Transmitting Pilot Signal In Multi-Carrier Communication System, And Method For Estimating Channel - Google Patents

Abstract

The present invention relates to a pilot transmission method and a channel estimation method in a multi-carrier communication system. According to the present invention, by using one pilot for both channel estimation and channel quality measurement for data demodulation, the pilot transmission method can be simplified compared to the case where the DM pilot and the CQ pilot are transmitted separately, and when the transmission is performed separately In addition, by using both the DM pilot and the CQ pilot in the channel estimation for data demodulation, the transmission power level is set differently depending on whether the DM pilot is transmitted in the same time domain as the CQ pilot. Can be done.

Multicarrier Communication System, DM Pilot, CQ Pilot

Description

Method for Transmitting Pilot Signal In Multi-Carrier Communication System, And Method For Estimating Channel

1 is a diagram illustrating a structure of a transmitting end of a DFT-S-OFDM scheme.

2 is a diagram for explaining a general method of transmitting a CQ pilot and a DM pilot.

3 is a diagram for explaining a pilot transmission method using one pilot for both CQ and DM according to one embodiment of the present invention;

4 is a view for explaining a method for increasing transmission power level of a pilot only in a band for transmitting data according to an embodiment of the present invention.

FIG. 5 is a diagram for explaining a method of transmitting power by adjusting a power level according to whether a DM pilot is transmitted in the same time domain as a CQ pilot according to one embodiment of the present invention; FIG.

The present invention relates to a communication system using a multi-carrier, and more particularly, to a pilot transmission method and a channel estimation method in a multi-carrier communication system.

As an example of a communication method of a system using multiple carriers, Orthogonal Frequency Division Multiplexing (OFDM), DFT-S-OFDM (DFT Spreading OFDM), and Orthogonal Frequency Division Multiple Access (OFDMA)) will be described below.

The basic principle of OFDM is to divide a high-rate data stream into a large number of low-rate data streams and transmit them simultaneously using multiple carriers. Each of the plurality of carriers is called a subcarrier. Since orthogonality exists between the multiple carriers of the OFDM, the frequency components of the carriers can be detected at the receiving end even if they overlap each other. The high data rate data stream is converted into a plurality of low data rate data streams through a serial to parallel converter, and each subcarrier is included in the parallel data streams. After multiplying, the respective data strings are summed and sent to the receiving end.

A plurality of parallel data streams generated by the serial / parallel transform unit may be transmitted using a plurality of subcarriers by an inverse discrete fourier transform (IDFT), and the IDFT is inverse fast. It can be efficiently implemented using the Inverse Fast Fourier Transform (IFFT).

Since the symbol duration of the low carrier subcarrier is increased, relative signal dispersion in time due to multipath delay spread is reduced. Meanwhile, inter-symbol interference may be reduced by inserting a guard interval longer than a delay spread of a channel between OFDM symbols. In addition, if a part of the OFDM signal is copied to the guard interval and placed at the beginning of the symbol, the OFDM symbol may be cyclically extended to protect the symbol.

The DFT-S-OFDM scheme (or Single Carrier-FDMA) is as follows. In the SC-FDMA scheme, which is mainly applied to uplink, spreading is first applied to a DFT matrix in a frequency domain before generating an OFDM signal, and the result is modulated and transmitted in a conventional OFDM scheme.

1 is a diagram illustrating an embodiment of a transmitter of a DFT-S-OFDM scheme.

As illustrated in FIG. 1, the input data symbols are converted into parallel signals by the serial / parallel converter 110 and input to the DFT spreading module 120.

In SC-FDMA, a DFT matrix is distributed before transmitting a data symbol s, which can be expressed by Equation 1.

는, 데이터 심볼(s)을 분산시키기 위해서 사용된 Nb 크기의 DFT 행렬이다. 이렇게 분산된 벡터(x)에 대하여 일정한 부 반송파 할당 기법에 의해 부 반송파 매핑(subcarrier mapping)이 수행되고, IDFT 모듈에 의해 시간영역으로 변환되어 수신 측으로 전송하고자 하는 신호가 얻어진다. In Equation 1

Is an Nb-sized DFT matrix used to disperse the data symbols s. Subcarrier mapping is performed on the distributed vector x by a constant subcarrier allocation scheme, and a signal to be transmitted to the receiver is obtained by converting to the time domain by the IDFT module.

The signal transmitted to the receiving side may be represented as in Equation 2.

In Equations 1 and 2, N denotes the number of subcarriers transmitting an OFDM signal, Nb denotes the number of subcarriers for any user, and F denotes a discrete Fourier transform matrix, that is, a DFT matrix. , s denotes a data symbol vector, x denotes a vector in which data is distributed in the frequency domain, and y denotes an OFDM symbol vector transmitted in the time domain.

는 주파수 영역의 신호를 시간 영역의 신호로 변환하기 위해 사용되는 크기 N 의 DFT 행렬이다. 상술한 방법에 의해 생성된 신호 y는, 순환 전치(cyclic prefix)가 삽입되어 전송된다. 상술한 방법에 의해 전송 신호를 생성하여 수신 측으로 전송하는 방법을 SC-FDMA 방법이라 한다. DFT 행렬의 크기는 특정한 목적을 위해 다양하게 제어될 수 있다. In Equation 2

Is a DFT matrix of size N used to transform a signal in the frequency domain into a signal in the time domain. The signal y generated by the above-described method is transmitted by inserting a cyclic prefix. The method of generating a transmission signal and transmitting it to the receiving side by the above-described method is called an SC-FDMA method. The size of the DFT matrix can be variously controlled for a specific purpose.

Hereinafter, orthogonal frequency division multiple access (OFDMA) will be described. OFDMA refers to a multiple access method for realizing multiple access by providing each user with a part of subcarriers available in a modulation system using a plurality of orthogonal subcarriers. OFDMA provides each user with frequency resources called subcarriers, and each frequency resource is provided to a plurality of users independently of each other so that they do not overlap each other.

One of the essentials for data transmission on the uplink is the transmission of pilots. There are two types of pilot signals, depending on the application. Measuring channel quality ('CQ') to enable user equipment (or 'UE') scheduling and adaptive modulation and coding (AMC) CQ pilot and DM pilot for channel estimation and data demodulation during data transmission. The CQ pilot is transmitted in a predetermined time and frequency domain, and a base station (hereinafter referred to as 'Node B') can determine the channel state of the UE using the CQ pilot, and schedules the UE using this information according to a predetermined scheduling scheme. do. Therefore, for uplink scheduling of Node B, it is necessary to provide a large number of orthogonal channels in a limited time and frequency domain so that many UEs in a cell can transmit a CQ pilot. As an orthogonal channel generation method for CQ pilot transmission, time division multiplexing (TDM), frequency division multiplexing (FDM), code division multiplexing (CDM), or a combination thereof may be considered.

Meanwhile, a DM pilot for channel estimation and demodulation during data transmission is a pilot transmitted in a specific time and frequency domain when the UE is scheduled and transmits data.

For example, in 3GPP LTE, one of the standards for mobile communication, a sub-frame, which is a basic unit of transmission, includes a pilot transmission interval of two areas. Each section for transmitting the pilot is called a short block (hereinafter, referred to as 'SB'). Meanwhile, the two SBs are referred to as SB1 and SB2, respectively.

For scheduling in the frequency domain, fast scheduling in subframes and corresponding units, and AMC, it is necessary to provide an orthogonal channel so that more UEs in SB1 or SB2 can transmit CQ pilots. Accordingly, a method of multiplexing so that as many UEs as possible can transmit CQ pilots using limited frequency and time resources has been proposed. In addition, since a UE transmitting data must transmit a data pilot for channel estimation and modulation to SB1 or SB2, CQ pilots from multiple UEs and data pilots of a data transmitting UE must be efficiently multiplexed within two SBs. However, such a multiplexing technique is limited, and when two types of pilots are designed independently, it is difficult to multiplex.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide an efficient pilot transmission method by using one pilot structure as a CQ pilot and a DM pilot, and to efficiently perform a power level for pilot transmission. To provide a way.

In addition, even when the CQ pilot and the DM pilot are transmitted independently of each other, by using not only the DM pilot but also the CQ pilot in the channel estimation process for data demodulation, the transmission power level of the DM pilot is transmitted in the same time domain of the CQ pilot. It is intended to provide a method for efficiently controlling transmission power by adjusting to different depending on whether or not.

A pilot transmission method according to an embodiment of the present invention for achieving the above object is a pilot transmission method in a communication system using a multi-carrier, when the pilot for channel quality measurement and the pilot for data demodulation are transmitted in the same time domain, And transmitting one pilot for the channel quality measurement and the data demodulation.

In this case, the channel demodulation pilot is transmitted at a first level in a time domain in which only the pilot for channel quality measurement is transmitted, and the data demodulation pilot is performed in a second level in a time domain in which only the data demodulation pilot is transmitted. In the case where the channel quality measurement pilot and the data demodulation pilot are transmitted in the same time domain, the one pilot may be transmitted at the second level, and the data demodulation pilot may measure the channel quality. The pilot may be transmitted in the same structure as the pilot.

In the case where the channel quality measurement pilot and the data demodulation pilot are transmitted in the same time domain, the one pilot is at the second level in the data transmission band and the first level in a band other than the data transmission band. The first level and the second level may be a predetermined value between the base station and the user equipment or a value set through signaling between the base station and the user equipment.

On the other hand, the pilot transmission method according to another embodiment of the present invention is a pilot transmission method in a communication system using a multi-carrier, the transmission power according to whether or not the data demodulation pilot in the same time region of the channel quality measurement pilot And setting the levels differently.

In this case, the transmitting power level setting step, when transmitting the data demodulation pilot in the same time domain as the channel quality measurement pilot, compared to the transmission power level in the time domain for transmitting only the data demodulation pilot, The transmission power level may be set to be reduced and transmitted, and the transmission power level may be a predetermined value between the base station and the user equipment or a value set through signaling between the base station and the user equipment.

Finally, a channel estimation method according to another embodiment of the present invention is a channel estimation method for data demodulation in a communication system using multiple carriers, and receives a data demodulation pilot in the same time domain as a pilot for channel quality measurement. If so, characterized in that it comprises the step of performing data demodulation through the data demodulation pilot and the channel quality measurement pilot.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the 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 around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

According to the present invention, when a user equipment transmits a pilot for channel quality measurement (CQ pilot) and a pilot for channel estimation (DM pilot) for data demodulation, two objective pilots should be transmitted in the same time interval, It is proposed to transmit each pilot for two purposes in one pilot structure without multiplexing. In addition, at this time, the transmission power of the pilot may be increased (boosting) for stable data demodulation.

To this end, first, a general method of transmitting a CQ pilot and a DM pilot will be described, and accordingly, a method for using the CQ pilot and the DM pilot using one pilot structure will be described.

2 is a diagram for explaining a general method of transmitting a CQ pilot and a DM pilot.

2 (a) shows a case in which only a CQ pilot is transmitted for measuring channel quality only because there is no data transmission, and FIG. 2 (b) shows that a DM pilot is transmitted only for channel estimation for data demodulation in case of data transmission. 2 (c) illustrates a method of multiplexing and transmitting pilots for two purposes at the same time. Although FIG. 2 illustrates only an example in which each pilot signal is multiplexed with FDM on a frequency axis and transmitted, multiplexing using CDM, TDM, and the like is also possible.

In a general multi-carrier system, since pilots for each application can be generated and transmitted independently, three cases are possible as shown in FIG. As shown in (c) of FIG. 2, when multiplexing of CQ pilots and DM pilots is required, various complex aspects, such as partitioning of total system resources and transmission power, must be taken into consideration.

Therefore, in one embodiment of the present invention, when pilots are to be transmitted for two purposes of channel quality measurement and data demodulation as follows, it is proposed to configure and transmit a pilot structure without transmitting them independently.

3 is a view for explaining a pilot transmission method using one pilot for both CQ and DM according to an embodiment of the present invention.

That is, according to one embodiment of the present invention, in the case of transmitting only the CQ pilot or transmitting only the DM pilot as shown in (a) and (b) of FIG. 3, the same method as in FIG. 2 is used. When the CQ pilot is transmitted in the same time domain as the DM pilot, one pilot may be transmitted to be used for both the CQ pilot and the DM pilot, thereby reducing the complexity of multiplexing.

In addition, when the pilot is designed in accordance with the independent transmission of the pilot structure for channel quality measurement and channel estimation pilot for data demodulation, the efficiency of the design for multiplexing between UEs can be enhanced.

However, in this case, there may be a case where the power is insufficient for sufficient channel estimation for data demodulation in the data transmission region due to the characteristics of the pilot transmitted only for channel quality measurement. Accordingly, when data is transmitted, when performing channel estimation for data demodulation using the CQ pilot, it is desirable to increase the transmission power of the entire CQ pilot.

Specifically, FIG. 3A illustrates a case in which a pilot is transmitted at a power level of “a” only for channel quality measurement without data transmission, and FIG. 3B illustrates a pilot level of “b” when transmitting data. In case of transmission. In this case, the transmission power level "b" of the DM pilot is generally set larger than the transmission power level "a" of the CQ pilot.

As such, when the pilot transmission power transmitted in one time domain is increased over the entire frequency, there is no fear of increasing the PAPR separately.

Therefore, in the pilot transmission method according to an embodiment of the present invention as shown in FIG. 3C, when transmitting a pilot used for two purposes of channel quality measurement and data demodulation, the total transmission power level is " a " It is suggested to set the power level " c " This transmit power level may be the same as or different from the "b" which is the transmit power of the DM pilot, and the setting of the specific transmit power level is required by using the values promised between the user equipment and the base station or by signaling between the base station mobile stations. It is possible to set via reset (e.g., reset via power control).

For example, the base station directly signals the values of "a", "b", and "c", resets the transmission power to a power suitable for the channel situation through power control, or sets the power level of "a", "b" that has already been set. In the case of simultaneously transmitting a channel quality measurement pilot and a data demodulation pilot as a reference value, a method of signaling a value of "Δ" as a transmission power adjustment value of a pilot transmitted may be considered.

3 illustrates an example in which FDM is applied for pilot signal multiplexing, the pilot signals of a plurality of user equipments are the same even when using a scheme such as TDM, CDM (for example, using CAZAC). Multiplexing can be performed in a manner.

On the other hand, in the case of using the method described above with reference to FIG. 3, regardless of the frequency band in which data is transmitted, all data within a time domain (for example, the same subframe) in which a data demodulation pilot and a channel quality measurement pilot are simultaneously transmitted. The transmission power level of the pilot signal is set to be larger (for example, "c" in FIG. 3) than in the case where only the pilot for channel quality measurement is transmitted (for example, "b" in FIG. 3). . However, pilots used for channel estimation for data demodulation are only pilots transmitted within the data transmission frequency band, and pilots outside the data transmission band are used only for channel quality measurement. You may.

4 is a view for explaining a method of increasing the transmission power level of the pilot only in the band for transmitting data according to an embodiment of the present invention.

According to the embodiment as shown in FIG. 3, when there is no data transmission, the pilot used only for channel quality measurement is transmitted using the transmission power level of "a" as shown in FIG. Therefore, when the pilot for data demodulation and the channel quality measurement are transmitted at the same time, the pilot of one structure is used, but the transmission power level in the entire band is higher than when the pilot used for channel quality measurement is transmitted. And transmit at the transmit power level of "c".

In this case, the pilot power is wasted in the area for channel quality measurement outside the data transmission area.

Therefore, in another embodiment of the present invention, when transmitting a pilot used only for channel quality measurement because there is no data transmission as shown in FIG. 4, the pilot is transmitted to have a transmit power level of "a". (A) of FIG. 4, in the case where data transmission is performed and one identical pilot is transmitted to the pilot for data demodulation and channel quality measurement, the frequency for transmitting data as shown in (b) of FIG. Only by boosting the power to a higher transmit power level ("c") compared to the pilot transmit power level ("a") for channel quality measurement only in the band (i.e., the pilot transmitted to the subcarrier corresponding to the data transmission area) A method of transmitting a pilot at a transmit power level of "a" as in the case of transmitting a pilot and transmitting a pilot only for channel quality measurement in a section other than the data transmission band. Suggest.

When data is transmitted in this way, the power required for channel estimation for data demodulation is secured by increasing the power of a pilot transmitted only to a corresponding frequency domain, that is, a subcarrier of the corresponding frequency domain, as "c". As before, the transmission at power of "a" enables efficient transmission of the pilot without wasting power.

As in the case of FIG. 3, the power level may be set using values previously promised between the user equipment and the base station, or may be set through power control as necessary by signaling between the base station and the user equipment.

For example, the signals "a" and "c" are directly signaled, or the power control is reset to the transmission power of any one suitable for the channel situation (for example, "a"), and one set reference value ("a" Based on "), we can consider how to signal" △ "value in several steps.

In addition, the pilot transmission structure illustrated in FIG. 4 illustrates a case of using FDM, but uses TDM, FDM, or CDM (for example, CAZAC) for multiplexing between two or more multi-user devices. Regardless of whether you use it in all cases.

In the description of the above-described pilot transmission method, "one time domain" may be one subframe, or may be one short block or long block in one subframe as a narrower time domain. In the pilot transmission method according to the form, it is not necessary to be limited to any particular time domain.

On the other hand, the above-mentioned CQ pilot and DM pilot may need to be transmitted independently according to their needs. That is, the CQ information may vary in transmission period and time point according to channel conditions and system conditions, and the DM pilot is transmitted only during data transmission.

Therefore, according to another embodiment of the present invention, when the same structure of the DM pilot and the CQ pilot is used as described above and used for both channel estimation for data demodulation, the DM and CQ use are performed through one pilot. The pilot transmission power can be more efficiently controlled by using both pilots for different purposes, while maintaining the manner in which the DM pilot and the CQ pilot are transmitted separately without changing the conventional pilot transmission method as in the conventional method. How is it possible?

FIG. 5 is a diagram for describing a method of controlling and transmitting a power level according to whether a DM pilot is transmitted in the same time domain as a CQ pilot according to an embodiment of the present invention.

Specifically, FIG. 5A illustrates a case where only a CQ pilot is transmitted in one transmission time domain and FIG. 5B illustrates a case where only a DM pilot is transmitted in one transmission time domain. Shows a case where a DM pilot and a CQ pilot are simultaneously transmitted in the same time domain.

When only the DM pilot is transmitted as shown in FIG. 5B, the pilot transmit power level ("b") is compared to the pilot transmit power level ("a") when only the CQ pilot is transmitted as shown in FIG. It is necessary to set it to a high power level for channel estimation for data demodulation. In the case of transmitting only the DM pilot, sufficient transmission power is required because only the received DM pilot should be used for channel estimation for data demodulation.

In contrast, FIG. 5C shows the transmission power level compared to the pilot transmission power level ("b") when only the DM pilot is transmitted when the DM pilot is transmitted simultaneously with the CQ pilot according to one embodiment of the present invention. Lowering (e.g., "c", c <b) is shown.

In this case, since the channel estimation for data demodulation can use not only the DM pilot but also the CQ pilot, in the case of FIG. 5C, "c", which is a pilot transmission power level lower than the pilot transmission power of "b", is used. The same power can be used for channel estimation for accurate data demodulation. In addition, although the power level "c" is shown in FIG. 5C as being larger than the CQ pilot transmission power level "a", in one embodiment of the present invention, the transmission power level of the DM pilot is transmitted together with the CQ pilot. In this case, as long as the transmission power level is lowered (that is, as long as c &lt; b is satisfied), the power level " c "

As such, by adjusting the transmission power level of the DM pilot according to whether the CQ pilots are transmitted together in the same transmission time domain, power consumption used for the pilot transmission can be reduced, thereby enabling efficient power control.

In the case of FIG. 5, the transmission power levels of “a”, “b”, and “c” are also set by using values previously promised between the user equipment and the base station, or as needed by signaling between the base station and the user equipment. It is possible to set via control.

For example, signal "a", "b", and "c" values directly, or reset the specific transmit power level to the transmit power appropriate for the channel situation with power control, one of which is the reference value, Consider how to signal the difference in several steps.

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. Accordingly, 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 pilot transmission method according to the embodiment of the present invention as described above, when the CQ pilot and the DM pilot are to be transmitted at the same time, one pilot structure does not use a complex multiplexing technique to provide the functions of two different pilots. Can be replaced efficiently.

In addition, when the CQ pilot and the DM pilot are simultaneously multiplexed and transmitted simultaneously, the transmission power level of the DM pilot is lowered and transmitted, and the channel is estimated using the CQ pilot as well as the DM pilot for data demodulation. There is an effect of enabling communication.

Claims (9)

A pilot transmission method of a user equipment in a communication system using a multicarrier, And when a pilot for channel quality measurement and a pilot for data demodulation are transmitted in the same time domain, transmitting a pilot of one structure as the channel quality measurement and the data demodulation. The method of claim 1, Transmit the channel quality measurement pilot at a first level in a time domain for transmitting only the channel quality measurement pilot, Transmit the data demodulation pilot at a second level in a time domain for transmitting only the data demodulation pilot, And when the pilot for channel quality measurement and the pilot for data demodulation are transmitted in the same time domain, the pilot of one structure is transmitted at the second level. The method of claim 2, And the data demodulation pilot is transmitted as a pilot having the same structure as the pilot for channel quality measurement. The method of claim 2, When the pilot for channel quality measurement and the pilot for data demodulation are transmitted in the same time domain, the pilot of one structure is the second level in a data transmission band, and the first level in a band other than the data transmission band. Pilot transmission method. 5. The method according to any one of claims 2 to 4, And the first level and the second level are predetermined values between the base station and the user equipment, or values set through signaling between the base station and the user equipment. delete delete delete A channel estimation method for data demodulation of a base station in a communication system using multiple carriers, When receiving a pilot of one structure in the same time domain for channel quality measurement and data demodulation, performing data demodulation via the pilot of the one structure.

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