KR101423795B1 - Apparatus and method for providing adaptive channel estimation for an uplink channel - Google Patents

Abstract

The present invention relates to an apparatus and method for providing channel estimation of a wireless communication system, and more particularly, to an apparatus and method for providing an adaptive channel estimate based on a Doppler spread value for an uplink channel in an LTE system. An adaptive channel estimator for an uplink channel of a wireless communication system according to the present invention includes an SNR comparing unit for comparing an SNR estimation value of an uplink channel with a predetermined SNR threshold value and outputting a SNR comparison result, A Doppler spread comparing unit for comparing a predetermined Doppler spreading threshold value to output a Doppler spread comparing result, an estimation scheme selecting unit for selecting a channel estimation scheme for an uplink channel based on the SNR comparison result and the Doppler spread comparison result, And a channel estimator for estimating a channel value of the uplink channel based on the channel estimation method.

LTE, adaptive channel estimation, Doppler spreading

Description

ADAPTIVE CHANNEL ESTIMATION FOR UPLINK CHANNEL < RTI ID = 0.0 > [0001] < / RTI &

The present invention relates to an apparatus and method for providing channel estimation of a wireless communication system, and more particularly, to an apparatus and method for providing an adaptive channel estimate based on a Doppler spread value for an uplink channel in an LTE system.

Recently, communication standards have been developed for improving performance in terms of throughput, latency and coverage in wireless communication systems. The widely used standard is the Universal Mobile Telecommunications System (UMTS), which was developed as part of a third generation (3G) wireless communication system and is maintained by the Third Generation Partnership Project (3GPP). Among them, 3GPP LTE is a communication standard driven by 3GPP to achieve high data rate, low latency, packet optimized system performance and wide coverage in UMTS systems.

A wireless communication system such as an LTE system has a problem in that a white noise during a data transmission process, a change in received signal power due to fading, a shadowing, a Doppler effect due to a movement of a terminal and a frequent speed change, Distortion of the received signal may occur due to interference due to path signals or the like. Therefore, in order to compensate the distorted reception signal with the original signal, a channel estimation process for estimating a channel value including information on the phase and amplitude variation values of the signal is required. In this regard, the LTE system includes two Demodulation Reference Signal (DMRS) symbols for each subframe of the UL channel, and performs channel estimation using the two DMRS symbols. As a concrete channel estimation method, an average method of obtaining a channel estimation value for the remaining data symbols in the corresponding subframe by using the average value obtained by averaging the channel estimation values obtained from the two DMRS symbols in the subframe, And an interpolation method for interpolating the obtained channel information on the time axis and obtaining a channel estimation value for the remaining data symbols in the corresponding subframe is mainly used.

However, the channel estimation through the averaging method and the interpolation method depends on the Doppler spread value of the channel. In the case where the channel having a low Doppler spread value is not changed with time, the averaging scheme shows high accuracy in channel estimation, whereas a channel having a high Doppler spread value, that is, The interpolation method performs better than the average method. Therefore, there is a problem in that, in the conventional case of performing channel estimation in a fixed manner, it is not possible to provide optimized channel estimation as the amount of change in channel over time varies.

The present invention proposes an adaptive channel estimation apparatus and method for providing channel estimation according to an optimized method each time based on a Doppler spread value of a corresponding channel for an uplink channel in an LTE system.

According to one aspect of the present invention, an adaptive channel estimator for an uplink channel of a wireless communication system is provided. An adaptive channel estimator for an uplink channel of a wireless communication system according to the present invention includes an SNR comparing unit for comparing an SNR estimation value of an uplink channel with a predetermined SNR threshold value and outputting a SNR comparison result, A Doppler spread comparing unit for comparing a predetermined Doppler spreading threshold value to output a Doppler spread comparing result, an estimation scheme selecting unit for selecting a channel estimation scheme for an uplink channel based on the SNR comparison result and the Doppler spread comparison result, And a channel estimator for estimating a channel value of the uplink channel based on the channel estimation method.

According to an embodiment of the present invention, an adaptive channel estimator for an uplink channel of a wireless communication system includes a Doppler spreading threshold value calculating unit that calculates a Doppler spreading threshold value based on a function of a modulation and coding scheme (MCS) And may further include a calculation unit.

According to an embodiment of the present invention, when the SNR estimation value of the uplink channel is smaller than the predetermined SNR threshold value or the Doppler spread estimate value of the uplink channel is smaller than the predetermined Doppler spread threshold value, If the SNR estimate of the uplink channel is greater than a predetermined SNR threshold and the Doppler spread estimate of the uplink channel is greater than a predetermined Doppler spread threshold, the interpolation scheme may be selected as the channel estimation scheme.

According to an embodiment of the present invention, an adaptive channel estimator for an uplink channel of a wireless communication system includes a receiving unit for selecting one or more signals among a plurality of uplink signals received on an uplink channel, A Doppler spread value calculator for calculating a Doppler spread value of the uplink channel using an averageizer for calculating an average channel change amount by averaging the calculated channel change amount and a calculated average channel change amount, .

According to an embodiment of the present invention, the channel variation calculator includes a complex multiplier for calculating a complex multiplication value by complex-multiplying two demodulation reference signal (DMRS) symbols in a subframe of each selected signal, A phase extractor for extracting a phase component by normalizing a complex multiplication value and a cosine component extractor for extracting a cosine component from the extracted phase component.

According to one embodiment of the present invention, the receiving unit can select one or more signals based on the magnitude of the power in the time axis of the received plurality of uplink signals.

According to the present invention, in the LTE system, channel estimation is performed using a channel estimation method that is selectively optimized by using a Doppler spread value of a corresponding channel for an uplink channel, so that adaptive channel estimation based on a Doppler spread value . Therefore, according to the present invention, channel estimation accuracy of an LTE system uplink channel can be improved and data recovery performance can be improved.

Embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, detailed description of known functions and configurations will be omitted if it is determined that there is a possibility that the gist of the present invention may be unnecessarily blurred. It is to be understood that the following description is only for an embodiment of the present invention, and the present invention is not limited thereto.

1 is a diagram schematically illustrating a subframe structure 110 of an uplink channel in an LTE mobile communication system 100 and an LET mobile communication system 100 to which the present invention can be applied.

1 (a) schematically shows the configuration of the LTE mobile communication system 100. As shown in FIG. 1, the LTE mobile communication system 100 includes a base station 102 and mobile terminals 104a, 104b, and 104c. The base station 102 may provide communication services over a wireless link to a coverage area or a mobile terminal 104a, 104b, 104c in the cell where the base station 102 provides network access services. That is, the mobile terminals 104a, 104b and 104c can transmit signals to the base station 102 via the uplink channels 106a, 106b and 106c, and the base station 102 can transmit signals to the mobile terminals 104a, 104b and 104c And may transmit signals through the downlink channels 108a, 108b, and 108c. Mobile terminals 104a, 104b, and 104c may include any type of portable wireless communication device or system including, for example, a cell phone, a portable computer having wireless communication capabilities, a PDA or other device having wireless communication capability . 1 also shows that one base station 102 supports only three mobile terminals 104a, 104b, 104c, but it is to be appreciated that base station 102 may support more or fewer mobile terminals I can understand.

1B is a block diagram illustrating a structure of a subframe 110 (110a, 110b, 110c) of a signal transmitted from the mobile terminals 104a, 104b, 104c to the base station 102 through the uplink channels 106a, 106b, 106c in the LTE mobile communication system 100 ) Structure. According to the illustration, one subframe 110 includes two slots 120 and 130. Each slot 120, 130 has one DMRS symbol interval 122, 132 and six data symbol intervals 124, 126, 134, 136. Each data symbol interval 124, 126, 134, 136 may be used for transmission of control signals or data signals from the mobile terminals 104a, 104b, 104c to the base station 102. [ The DMRS symbol intervals 122 and 132 may be used for demodulation from the mobile terminals 104a, 104b and 104c to the base station 102 and for transmission of reference signals for channel estimation.

FIG. 2 is a block diagram schematically showing the configuration of a receiving unit 200 of the base station 102 shown in FIG.

2, the receiving unit 200 may include an antenna 202. [ The antenna 202 may receive RF signals transmitted from the mobile terminals 104a, 104b and 104c to the base station 102 via the uplink channels 106a, 106b and 106c. According to one embodiment, the RF signal received at the antenna 202 may be a plurality of signals by multipath. The antenna 202 may be any type of antenna including, for example, dipoles, patches, helical antennas, antenna arrays, and multiple antennas (MIMO) , But the present invention is not limited thereto. 2 also illustrates that the receiving unit 200 of the base station 102 has only one antenna, but according to another embodiment of the present invention, the receiving unit 200 of the base station 102 includes a greater number of antennas It can be understood that it can do.

The receiving unit 200 may further include a receiving unit 204. [ The receiving unit 204 performs various processing including the digital conversion processing, the quantization processing, the serial-parallel conversion processing, the Fourier transform processing, and the like on the RF signals of the uplink channels 106a, 106b, and 106c received by the antenna 202 . The receiving unit 204 may also extract two DMRS symbols for each subframe from the uplink channel signal. When the RF signal received by the antenna 202 is a plurality of signals by multipath, the receiving unit 204 takes one or more predetermined number of signals with high power in the time axis among these multipath signals, Two DMRS symbols can be extracted. However, the present invention is not limited thereto, and the receiving unit 204 may extract two DMRS symbols for each subframe for all received RF signals. Those skilled in the art will be fully understandable about the operation of the receiving unit 204 and will not be described further herein.

The receiving unit 200 may further include a Doppler spread value estimator 206. The Doppler spread value estimator 206 may receive the DMRS symbols extracted for each subframe from the uplink channel signal in the receiving unit 204. [ The Doppler spread estimator 206 may also estimate the Doppler spread value for the corresponding subframe using the received DMRS symbols. The specific configuration and operation of the Doppler spread value estimator 206 will be described in more detail below with reference to FIG.

The receiving unit 200 may further include an SNR estimator 208. [ The SNR estimator 208 may receive the processed uplink channel signal at the receiving unit 204 and estimate the SNR (signal to noise ratio) value for each signal. In one embodiment of the present invention, the SNR estimator 208 may be implemented by estimating SNR values by a data-assisted (DA) or non-data assisted (NDA) method, no. It should be appreciated that the SNR estimator 208 may be implemented in a variety of ways that may be readily implemented by those skilled in the art.

The receiver 200 may further include a channel estimator 210. The channel estimator 210 may receive the Doppler spread value estimated by the Doppler spread value estimator 206 and the SNR estimated by the SNR estimator 208 together with the uplink channel signal processed by the reception unit 204 have. The channel estimator 210 may select an appropriate channel estimation scheme for the uplink channel using the received Doppler spread value and the SNR value, and perform appropriate channel estimation accordingly. For example, the channel estimator 210 may select whether to perform the estimation based on the averaging method or the interpolation method based on the estimated Doppler spread value and the SNR value for the uplink channel signal. According to an embodiment of the present invention, when the estimated SNR value is smaller than a predetermined threshold value or when the estimated Doppler spread value is smaller than a predetermined threshold value, the channel estimator 210 estimates a corresponding uplink channel Can be performed. Also, the channel estimator 210 can estimate the uplink channel according to the interpolation method when the estimated SNR value is larger than the predetermined threshold value and the estimated Doppler spread value is larger than the predetermined threshold value. The detailed operation of the channel estimator 210 will be described in detail below with reference to the flowchart of FIG.

Although the receiving unit 204, the Doppler spread value estimator 206, the SNR estimator 208 and the channel estimator 210 are shown as separate units in FIG. 2, in yet another embodiment of the present invention, It is to be understood that the present invention can be implemented as hardware or software included in a configuration, and that all configurations can be implemented as one hardware or software.

3 is a block diagram showing a specific configuration of the Doppler spread value estimator 206 shown in FIG.

3, the Doppler spread value estimator 206 may include a complex multiplier 302. [ The complex multiplier 302 can receive the extracted DMRS symbols for each subframe of the uplink channel signal and can obtain a complex multiplication value for two received DMRS symbols for each subframe. In one embodiment, the complex multiplier 302 may select any one of the two DMRS symbols and perform a conjugate transformation. The complex multiplier 302 may then perform a complex multiplication of the conjugate transformed DMRS symbol and the non-transformed DMRS symbol to obtain a complex multiplication value for the two DMRS symbols. The complex multiplication value calculated by the complex multiplier 302 may be a value indicating a channel variation amount of the uplink channel. According to one embodiment of the present invention, a predetermined number of one or more of the plurality of signals by multipath can be selected and used for Doppler spread value estimation, and in such a case, the complex multiplier 302 multiplies The complex multiplication value of the DMRS symbols can be calculated.

The Doppler spread value estimator 206 may further include a phase extractor 304. The phase extractor 304 may receive the complex multiplication value calculated by the complex multiplier 302 and extract only the phase component from the received complex multiplication value. In one embodiment, the phase extractor 304 may extract only the phase component by removing the amplitude component from the corresponding complex multiplication value through a normalization process. The phase extractor 304 can also extract only an in-phase component, that is, a cosine component, having a large energy component from the extracted phase component. The phase component (or cosine component) extracted by the phase extractor 304 may include information on a channel change amount of the uplink channel. According to one embodiment of the present invention, a predetermined number of one or more of a plurality of signals by multipath may be selected and used for Doppler spread value estimation, and in such a case, the phase extractor 304 may calculate The phase component can be extracted. In the present embodiment, the Doppler spread value estimator 206 is shown as including the phase extractor 304, but the present invention is not limited thereto.

The Doppler spread value estimator 206 may further include an averager 306. According to an embodiment of the present invention, at least one predetermined number of signals among a plurality of signals by multipath can be selected and used for Doppler spread value estimation. The averager 306 receives the phase component signals including information on the resultant signals calculated by the phase extractor 304, i.e., the channel change amount of the uplink channel, and averages the received signals to obtain an average channel of the uplink channel The average channel change amount signal indicating the change amount can be obtained. In one embodiment, if the receiver of the base station includes a plurality of antennas, the averager 306 averages the received signals for each antenna to obtain an average channel variation for each antenna, The average channel variation amount of the channel can be obtained. In the present embodiment, the Doppler spread value estimator 206 is shown as including the averager 206, but the present invention is not limited thereto.

The Doppler spread value estimator 206 may further include a Doppler spread value calculator 308. [ The Doppler spread value calculator 308 can receive the average channel variation amount signal obtained by the averager 306 and calculate the Doppler spread value from the received signal. In one embodiment, the Doppler spread value calculator 308 calculates a Doppler spread value from the average channel variation amount signal by mapping a correlation that reflects the correlation between the amount of channel change and the Doppler spread value that can be obtained by repeated simulations Function can be used. In one embodiment, the mapping function may be stored in a table format that reflects the relationship between the average channel variation and the Doppler spread value. In another embodiment, the mapping function may be stored in the form of a partially linear function for each interval reflecting the relationship between the average channel variation and the Doppler spread value.

Although the complex multiplier 302, the phase extractor 304, the averager 306 and the Doppler spread value calculator 308 are shown as separate components in FIG. 3, in an embodiment, one or more components are included in another component It is to be understood that the present invention can be implemented as hardware or software, and that all configurations can be implemented as one hardware or software.

FIG. 4 is a flowchart illustrating the operation of the channel estimator 210 shown in FIG. 2, according to an embodiment of the present invention.

In step 402, the channel estimator 210 determines whether the estimated SNR value for the uplink channel is greater than the SNR threshold. In one embodiment, the SNR threshold can be determined by repeated simulations by selecting the maximum value of the SNR that always provides good performance for channel estimation rather than the interpolation scheme, regardless of the Doppler spread value of the channel. If it is determined in step 402 that the estimated SNR value for the uplink channel is greater than the SNR threshold, the flow proceeds to step 404. Alternatively, if the estimated SNR value for the uplink channel in step 402 is less than the SNR threshold, the flow chart proceeds to step 406. [

In step 404, the channel estimator 210 determines whether the Doppler spread value for the uplink channel is lower than the Doppler spread threshold. In one embodiment, the Doppler spreading threshold of the uplink channel may be determined using an MCS function according to the Modulation and Coding Scheme (MCS) of the channel. In one embodiment, the MCS function increases the Doppler spread value of the channel for each MCS and repeatedly performs experiments or simulations to evaluate the performance of the channel estimation by the averaging scheme and the interpolation scheme, By calculating a Doppler spread value that improves the performance of the channel estimation by the MCS and matching it with the MCS. If it is determined in step 404 that the Doppler spread value estimated for the uplink channel is lower than the Doppler spread threshold of the uplink channel, the flow chart proceeds to step 406, else the flow chart proceeds to step 408 .

In step 406, the channel estimator 210 obtains a channel estimation value of the uplink channel by the averaging method. In one embodiment, the channel estimator 210 may estimate the channel value of the uplink channel by analyzing each of the two DMRS symbols present in each subframe of the uplink signal received at the receiving unit of the base station. The channel estimator 210 then averages the estimated two channel values to obtain a channel estimate of the corresponding uplink channel.

In step 408, the channel estimator 210 obtains a channel estimation value of the uplink channel by an interpolation method. The channel estimator 210 can estimate the channel value of the uplink channel by analyzing each of the two DMRS symbols existing in each subframe of the uplink signal received at the receiving unit of the base station. Then, the channel estimator 210 can obtain the channel value of the uplink channel by interpolating the estimated two channel values on the time axis. In one embodiment, the channel estimator 210 may obtain the channel value of the uplink channel using a linear interpolation scheme, but the present invention is not limited thereto.

The blocks shown in the figures herein may be fully functional and do not require corresponding individual hardware components. For example, in one or more embodiments, two or more blocks may be implemented in software in a single digital processing device. The digital processing device may be, for example, a general purpose microprocessor, a digital signal processor (DSP), a reduced instruction set computer (RISC), a complex instruction set comptuer (CISC), a field programmable gate array (FPGS) And / or the like, and the like. In addition, the present invention may be implemented using hardware, software, firmware, and combinations thereof.

While the invention has been described in connection with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. Such modifications and variations are to be construed as being within the scope of the present invention and the appended claims.

Fig. 1 (a) schematically shows a configuration of a general LTE system; Fig.

FIG. 1 (b) schematically shows a subframe structure of an uplink channel signal; FIG.

2 is a view schematically showing the configuration of an exemplary LTE system base station receiving unit;

3 is a block diagram showing the configuration of an exemplary Doppler spread value estimator;

4 is a flow chart illustrating the operation of an exemplary channel estimator;

Description of the Related Art

Fig.

102: Base station

104:

Fig.

202: antenna

204: Receiving unit

206: Doppler spread value estimator

208: SNR estimator

210: channel estimator

3.

302: Complex multiplier

304: phase extractor

306: Average firearm

308: Doppler spread value arithmetic unit

Claims (6)

delete An adaptive channel estimator for an uplink channel of a wireless communication system, An SNR comparing unit for comparing an SNR (Signal to Noise Ratio) estimation value of the uplink channel with an SNR threshold value and outputting a SNR comparison result; A Doppler spread comparing unit for comparing a Doppler spreading estimation value of the uplink channel with a Doppler spreading threshold value and outputting a Doppler spread comparison result; An estimation scheme selecting unit for selecting a channel estimation scheme for the uplink channel based on the SNR comparison result and the Doppler spread comparison result; A channel estimator for estimating a channel value of the uplink channel based on the selected channel estimation scheme; And A Doppler spreading threshold calculating unit for calculating the Doppler spreading threshold based on a function of a modulation and coding scheme (MCS) of the uplink channel; And an adaptive channel estimator for an uplink channel of the wireless communication system. An adaptive channel estimator for an uplink channel of a wireless communication system, An SNR comparing unit for comparing an SNR (Signal to Noise Ratio) estimation value of the uplink channel with an SNR threshold value and outputting a SNR comparison result; A Doppler spread comparing unit for comparing a Doppler spreading estimation value of the uplink channel with a Doppler spreading threshold value and outputting a Doppler spread comparison result; An estimation scheme selecting unit for selecting a channel estimation scheme for the uplink channel based on the SNR comparison result and the Doppler spread comparison result; And And a channel estimator for estimating a channel value of the uplink channel based on the selected channel estimation scheme, Wherein the estimation method selection unit comprises: Selects an average scheme as the channel estimation scheme when the SNR estimate of the uplink channel is less than the SNR threshold or the Doppler spread estimate of the uplink channel is less than the Doppler spread threshold, And selecting an interpolation scheme as the channel estimation scheme when the SNR estimate of the uplink channel is greater than the SNR threshold and the Doppler spread estimate of the uplink channel is greater than the Doppler spreading threshold. Adaptive channel estimator. An adaptive channel estimator for an uplink channel of a wireless communication system, An SNR comparing unit for comparing an SNR (Signal to Noise Ratio) estimation value of the uplink channel with an SNR threshold value and outputting a SNR comparison result; A Doppler spread comparing unit for comparing a Doppler spreading estimation value of the uplink channel with a Doppler spreading threshold value and outputting a Doppler spread comparison result; An estimation scheme selecting unit for selecting a channel estimation scheme for the uplink channel based on the SNR comparison result and the Doppler spread comparison result; A channel estimator for estimating a channel value of the uplink channel based on the selected channel estimation scheme; A receiving unit for selecting one or more signals among a plurality of uplink signals received on the uplink channel; A channel variation amount calculator for calculating a channel variation amount for each of the selected signals; An averageizer for averaging the calculated channel variations to calculate an average channel variation; And And a Doppler spread value calculator for calculating a Doppler spread value of the uplink channel using the calculated average channel change amount. The adaptive channel estimator for an uplink channel of a wireless communication system, 5. The method of claim 4, Wherein the channel change amount calculator comprises: A complex multiplier for calculating a complex multiplication value by multiplying two demodulation reference signal (DMRS) symbols in a subframe of each of the selected signals; A phase extractor for normalizing the calculated complex multiplication value to extract a phase component; And a cosine component extractor for extracting a cosine component from the extracted phase component. The adaptive channel estimator for an uplink channel of a wireless communication system. 5. The method of claim 4, Wherein the receiving unit selects one or more signals based on the magnitude of power in the time axis of the received plurality of uplink signals.

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