CN101945070B

CN101945070B - Method and device for measuring noise

Info

Publication number: CN101945070B
Application number: CN 200910054643
Authority: CN
Inventors: 徐兵; 罗新
Original assignee: Leadcore Technology Co Ltd
Current assignee: Datang Mobile Communications Equipment Co Ltd
Priority date: 2009-07-10
Filing date: 2009-07-10
Publication date: 2012-12-19
Anticipated expiration: 2029-07-10
Also published as: CN101945070A

Abstract

The invention discloses a method and a device for measuring noise, and an MIMO-OFDM system terminal receiving device. The method comprises the following steps of: measuring the noise for the first time according to frequency domain data after fast Fourier transform (FFT); estimating a channel by using the result of measuring the noise for the first time; and measuring the noise for the second time according to the frequency domain data and the channel estimation result, wherein the measured result is used for subsequent processing. The method and the device can improve the accuracy of noise measurement results and further improve the detection performance and system throughput.

Description

Noise measurement method and device

Technical Field

The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for noise measurement and a terminal receiving apparatus of a MIMO-OFDM system.

Background

A Multiple Input Multiple output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system is a communication system that simultaneously adopts MIMO technology and OFDM technology, combines the advantages of MIMO technology and OFDM technology, and becomes the mainstream trend of future mobile communication.

As shown in fig. 1, a simplified schematic diagram of a baseband receiving and processing module of a terminal in a conventional MIMO-OFDM system includes: a Fast Fourier Transform (FFT) module, a noise measurement module, a channel estimation module, a MIMO detection module, a channel decoding module, a feedback module, etc. The noise measurement module measures the noise variance, and provides the measured noise variance to the following channel estimation module to complete channel estimation in the frequency domain, such as the currently commonly used channel estimation method wiener filtering method, which requires the noise power to be used as a parameter. Meanwhile, the measurement result of the noise measurement module is also provided to the MIMO detection module, and the currently commonly used MIMO detection method, i.e., the linear Minimum Mean Square Error (MMSE) detection method, also requires noise power as a parameter input, and the accuracy of the noise power will affect the detection performance. In addition, the measurement result of the Noise measurement module is also provided to the channel decoding module to complete the decoding operation of the channel coding, since the soft bits entering the channel decoding module usually need to be weighted by using Signal-to-Noise Ratio (SNR) information, Noise variance information is also needed, and the Noise variance will affect the performance of the channel decoding. In addition, if the link adaptation technique is adopted, the terminal (UE) feeds back information such as Channel Quality Indicator (CQI) and the like, which also involves the calculation of SNR, so that noise variance information is also needed, and the accuracy of the noise variance will affect the link throughput. In summary, noise measurement is very important for MIMO-OFDM systems.

A commonly used method for estimating noise in the OFDM system at present is to estimate the noise variance by using the difference between adjacent Reference (RS) positions in the frequency domain (or in the time domain).

The method using neighboring RSs in the frequency domain direction, namely method one, can be expressed as

Where E {. denotes the desired operation. The desired operation may be replaced by averaging all reference signal estimates within a subframe

Wherein L is_RSIndicating the number of OFDM symbols containing RS in a subframe, N_RSIndicating the number of subcarriers containing RSs within one OFDM symbol.

The method for estimating the noise variance using the difference between adjacent reference signals in the time domain is similar to the above method, and can be expressed as

It can be seen that, in order to provide noise power in channel estimation, the existing methods use frequency domain data after FFT to perform measurement. However, the above method has the following disadvantages:

for method one, the assumption is made that the phase is in the frequency domainThe channel impulse responses at adjacent reference signals are the same, while for systems using discrete RS distribution, the error of this assumption is larger for some channels due to the fact that the adjacent reference signals in the frequency domain differ slightly in frequency band. For example, for the third Generation partnership project (3GPP, 3)^rdExtended classical urban channel (ETU) as specified in the Generation Partnership Project) specification, the above assumption cannot be made. At this moment there will be

Wherein E { | | Δ h_k′||²Denotes an error of channel difference noise at adjacent reference signals in the frequency domain, E { | | | n | | calculation²Represents the actual variance of the noise, the smaller the correlation of the channel on the frequency domain, the smaller E { | | | Δ h_k′||²The larger the term, the larger the error. And as the doppler spread increases, the intercarrier interference also increases, which can further increase the error.

For the second method, since it is assumed that the channel impulse responses at the adjacent reference signals in the time domain are the same, as the mobile speed of the terminal increases, the correlation at the adjacent reference signals in the time domain becomes smaller and smaller,

middle E { | | Δ h_l′||²The term will be larger and larger, i.e. the error of the noise variance estimate will be larger and larger.

In the process of implementing the invention, the inventor finds out through research that: the existing noise measurement methods are all performed by using frequency domain data after FFT, and the measurement deviation is large under some channel conditions. The larger noise variance deviation has larger influence on the MIMO detection performance, and even can cause the deterioration of the detection performance; similarly, the larger variance deviation of the noise will also affect the modules of channel decoding and feedback, and finally affect the system performance. It can be seen that the use of the existing noise measurement method cannot ensure that better detection performance is obtained under various channel conditions.

Disclosure of Invention

The embodiment of the invention provides a method and a device for measuring noise and a terminal receiving device of an MIMO-OFDM system, which can improve the accuracy of a noise measurement result and further improve the detection performance and the system throughput.

The embodiment of the invention provides the following technical scheme:

a method of noise measurement, comprising:

performing first noise measurement according to frequency domain data after Fast Fourier Transform (FFT);

performing channel estimation by using the result of the first noise measurement;

and performing second noise measurement according to the frequency domain data and the channel estimation result, and performing subsequent processing on the measurement result.

An apparatus for noise measurement, comprising:

the first noise measurement module is used for carrying out first noise measurement according to the frequency domain data after FFT;

and the second noise measurement module is used for performing second noise measurement according to the frequency domain data after the FFT and the result of performing channel estimation by using the measurement result of the first noise measurement module, and the measurement result is used for subsequent processing.

A terminal receiving apparatus of a MIMO-OFDM system, comprising:

a channel estimation module, configured to perform channel estimation using the measurement result of the first noise measurement module;

the second noise measurement module is used for carrying out second noise measurement according to the frequency domain data after FFT and the estimation result of the channel estimation module;

and the MIMO detection module is used for detecting by using the measurement result of the second noise measurement module.

According to the method and the device for measuring the noise and the terminal receiving device of the MIMO-OFDM system, the noise measurement value obtained by the existing noise measurement method is applied to the channel estimation which is not sensitive to the error of the noise estimation, and the obtained channel estimation result is used for the noise measurement again, so that the noise measurement is performed again on the existing noise measurement method, the measurement result is more accurate, and the better performance can be obtained under various channel conditions. And the accurate noise measurement result is provided for the following MIMO detection and feedback calculation, so that the detection performance and the system throughput can be improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a simplified schematic diagram of a prior art MIMO-OFDM system terminal baseband reception processing module;

FIG. 2 is a flow chart of a method for noise measurement according to an embodiment of the present invention;

fig. 3 is a diagram of RS distribution in an LTE system;

FIG. 4 is a schematic diagram of a position after rearrangement based on the RS shown in FIG. 3;

FIG. 5 is a diagram after renumbering based on the RS shown in FIG. 4;

FIG. 6 is a schematic structural diagram of a noise measurement apparatus according to a second embodiment of the present invention;

fig. 7 is a schematic structural diagram of a terminal receiving device of a MIMO-OFDM system according to a third embodiment of the present invention.

Detailed Description

The embodiment of the invention provides a noise measurement method and device suitable for an MIMO-OFDM system with excellent performance and a terminal receiving device of the MIMO-OFDM system, which can improve the accuracy of a noise measurement result and further improve the detection performance and the system throughput. Since the Long Term Evolution (LTE) system is an MIMO-OFDM system, for the sake of simplicity, the following description takes LTE as an example, but the technical solution provided by the present invention is applicable to all MIMO-OFDM systems and is not limited to the LTE system. In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples.

The inventor of the above background art has analyzed the influence of the measurement result of the noise measurement module in the terminal receiving device of the existing MIMO-OFDM system on the following modules, and the inventor has further found that the channel estimation method of wiener filtering is not very sensitive to the error of noise estimation, that is, the performance of channel estimation is not greatly influenced by the current noise measurement method, so that two noise measurements can be performed in the terminal receiving process of the MIMO-OFDM system, the first noise measurement can use the existing noise measurement method, the result of which is provided to the channel estimation module, and the second noise measurement uses the noise measurement method provided by the present invention, the result of which is provided to the modules after channel estimation.

Fig. 2 is a flowchart of a method for measuring noise according to an embodiment of the present invention. The method comprises the following steps:

step 201, performing a first noise measurement according to the frequency domain data after the FFT;

specifically, in the LTE system, a certain number of reference signals RS are inserted into each subframe in order to facilitate channel estimation by the terminal. Each RS corresponds to one OFDM symbol and one subcarrier. For each cell, the reference signal is a determination signal known to the UE, and the UE can estimate a corresponding channel response at the RS according to the received data at the RS. Since each RS occupies little time and bandwidth, each RS can be considered to experience a flat channel response; meanwhile, since the adjacent RSs have small intervals in both time and frequency, which are much smaller than the coherence bandwidth, the channel responses at the adjacent RSs can be considered to be substantially the same. Therefore, after the received signals at the RS are calibrated, the difference between the calibration signals at the adjacent RS represents the difference of noise. The noise variance can be estimated by utilizing the independent and uncorrelated characteristics of the noise at different RSs. The presently disclosed simple and easy noise variance estimation methods are also based on the received signal at the RS. The following is a brief description of the prior art:

as shown in fig. 3, which is a schematic diagram of RS distribution in an LTE system, for simplicity, only the length of one subframe (in case of a normal Cyclic Prefix (CP)) is shown in the time direction in fig. 3, only 12 subcarriers are shown in the frequency domain direction, and only RS distribution on one transmit antenna port is shown. The reference signals are located in the positions indicated in fig. 3, in practical cases, the reference signals may have different offsets in the frequency domain for different cells, and may have different distributions for different transmit antenna ports, but the relative positions of the reference signals are basically similar to those in fig. 3, and this discrete reference signal distribution method is adopted.

Let r_k，lIs the received signal at the kth subcarrier on the l OFDM symbol, wherein k is more than or equal to 0 and less than N_sc，0≤l＜N_symb，N_scIs the total number of downlink sub-carriers, N_symbIndicating the number of OFDM symbols contained in a subframe, N for normal CP_symbExtended CP is 14, N_symb12. Since only the received signal at the reference signal is of interest subsequently, for simplicity, the signals at all non-reference signal positions are removed from consideration, the resulting reference signal positions are rearranged as shown in FIG. 4, and the reference signal positions are renumbered as shown in FIG. 5, where

The position relationship in the original time-frequency resource can be seen more clearly by fig. 3, 4 and 5.

Since the transmitted signal of the reference signal position is known to the terminal, let x be_k′，l′And | x in LTE system_k′，l′Let 1 denote the frequency-domain channel impulse response for each reference signal position as h_k′，l′Then, the following relation holds

Wherein n is_k′，l′Representing the noise component, estimating n_k′，l′The variance of (c) is specified here in two ways known in the art as follows:

the method using the neighboring RSs in the frequency domain direction can be expressed as

Where E {. denotes the desired operation.

The desired operation may be replaced by averaging all reference signal estimates within a subframe

Wherein L is_RSIndicating the number of OFDM symbols containing RS in a subframe, N_RSIndicating the number of subcarriers containing RSs within one OFDM symbol. The adjacent RS in the frequency domain direction is shown by arrow 1 in fig. 3, and the adjacent RS in the time domain direction is shown by arrow 2 in fig. 3.

The method of estimating the noise variance using the difference at adjacent reference signals in the time domain is similar to the above method and can be expressed as

Since the LTE employs discrete reference signal distribution, the index values of the reference signals l' adjacent to each other in the time domain in the formula (2) are different by 2, which is specifically shown by an arrow 2 in fig. 3.

Step 202, performing channel estimation by using the result of the first noise measurement;

here, the existing MMSE channel estimation method may be adopted for channel estimation.

And 203, performing second noise measurement according to the frequency domain data and the result of channel estimation, wherein the measurement result is used for subsequent processing.

Specifically, the noise measurement method provided by the present invention is adopted here, and still referring to fig. 5, it is assumed that the frequency domain channel estimation result at the RS position (k ', l') is

The noise estimation method provided by the present invention can be expressed as follows:

where E {. denotes the desired operation, L_RSIndicating the number of OFDM symbols containing RS in a subframe, N_RSIndicates the number of subcarriers containing RSs within one orthogonal frequency division multiplexing OFDM symbol,

at RS position (k', lAs a result of the frequency-domain channel estimation of (a),

for the received signal at RS position (k ', l'), x_k′，l′Is the transmitted signal at RS location (k ', l').

Since the MIMO system is used, the measurement values at the respective transmitting antennas and receiving antennas can be averaged, and the above formula (3) can be further expressed as follows

Wherein i, j are eachIs the index of the transmit and receive antenna ports, N_T、N_RThe number of transmission antennas and the number of reception antennas are indicated, respectively.

Further, the result of the second noise measurement may be utilized to perform subsequent processing such as MIMO detection, channel decoding, and feedback calculation.

In order to better understand the technical scheme of the invention, the following is further specifically illustrated by an application example.

First, in the LTE system, frequency domain data after FFT transformation of time domain data received by a receiver may be represented as frequency domain received data assuming that processing is performed in units of one subframe

Wherein r is_lRepresenting a vector consisting of data of one OFDM symbol, N_symbIs the total number of OFDM symbols in one sub-frame, wherein

r_{l} = {[r_{0, l}, r_{1, l}, . . ., r_{k, l}, . . ., r_{N_{sc} - 1, l}]}^{T},

Wherein r is_k，lRepresenting the received data on the kth subcarrier in the ith OFDM symbol.

Secondly, according to the distribution of RS, extracting the received data at the reference signal position from the received data, and marking and numbering again after compact arrangement, which can be recorded as

Wherein

Represents a vector consisting of received data at all RSs within the i' th OFDM symbol carrying RSs,

wherein

Indicating the received data at the kth RS in the ith' OFDM symbol carrying the RS.

Then, using the above equation (1)

Or formula (2)

A first noise measurement is made.

Then, the existing MMSE channel estimation method is adopted to carry out channel estimation, and the obtained channel estimation value at the RS is assumed to be

Wherein

Represents a vector of channel estimates at all RSs within the l' th OFDM symbol carrying RSs,

wherein

Indicating the channel estimation value at the k 'th RS in the l' th OFDM symbol carrying RS.

Finally, according to the above formula (4)

And performing a second noise measurement, and performing subsequent processing including MIMO detection, feedback calculation and the like by adopting a result of the second noise estimation.

Fig. 6 is a schematic structural diagram of a noise measurement apparatus according to a second embodiment of the present invention. The device includes: a first noise measurement module 610, a second noise measurement module 620; wherein,

the first noise measurement module 610 is configured to perform a first noise measurement according to the frequency domain data after the FFT; specifically, the first noise measurement module 610 utilizes the above equation (1)

Or formula (2)

A first noise measurement is made.

The second noise measurement module 620 is configured to perform a second noise measurement according to the frequency domain data after FFT and a result of performing channel estimation by using the measurement result of the first noise measurement module 610, where the measurement result is used for subsequent processing. Specifically, the second noise measurement module 620 formula (4)

And performing a second noise measurement, and providing the obtained result of the second noise estimation for subsequent processing, such as MIMO detection, feedback calculation and the like.

Fig. 7 is a schematic structural diagram of a terminal receiving device of a MIMO-OFDM system according to a third embodiment of the present invention. The device comprises: an FFT module 710, a first noise measurement module 720, a channel estimation module 730, a second noise measurement module 740, a MIMO detection module 750, a channel decoding module 760 and a feedback module 770; wherein:

the device carries out two times of noise measurement, wherein the first time of noise measurement uses the existing method, the result is provided for a channel estimation module to use, the second time of noise measurement uses the noise measurement algorithm provided by the invention, and the result is provided for the module after channel estimation to use. Specifically, the first noise measurement module 720 performs a first noise measurement according to the frequency domain data transformed by the FFT module 710, and provides the obtained first noise measurement result to the channel estimation module 730, so that the channel estimation module 730 performs channel estimation by using the first noise measurement result and the frequency domain data transformed by the FFT module 710; the channel estimation results are provided to the second noise measurement module 740 on the one hand and to the MIMO detection module 750 on the other hand. The second noise measurement module 740 performs a second noise measurement according to the frequency domain data after FFT and the channel estimation result, and provides the obtained second noise measurement result to the MIMO detection module 750, the channel decoding module 760, and the feedback module 770, respectively.

Experiments show that the noise measurement method provided by the invention is closer to a true value than the existing method, and particularly, the performance of the method is more outstanding under the condition of high signal-to-noise ratio and is close to the performance of using ideal noise power.

It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

In addition, each functional unit in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.

The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc.

In summary, the present disclosure provides a method and an apparatus for noise measurement and a terminal receiving apparatus of MIMO-OFDM system, in which a noise measurement value obtained by using an existing noise measurement method is applied to channel estimation which is not very sensitive to an error of noise estimation, and an obtained channel estimation result is used for another noise measurement, so that the noise measurement is performed on the basis of the existing noise measurement method, so that the measurement result is more accurate, and better performance can be obtained under various channel conditions. And the accurate noise measurement result is provided for the following MIMO detection and feedback calculation, so that the detection performance and the system throughput can be improved.

The method and the device for measuring noise and the terminal receiving device of the MIMO-OFDM system provided by the present invention are described in detail above, and a specific example is applied in the present document to illustrate the principle and the implementation manner of the present invention, and the description of the above embodiment is only used to help understanding the scheme of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

Claims

1. A method of noise measurement, comprising:

performing a second noise measurement according to the frequency domain data and the channel estimation result, and performing subsequent processing on the measurement result; the second noise measurement is expressed as:

for the frequency domain channel estimation result at the RS position (k ', l'),

for the received signal at RS position (k ', l'), x_k′,l′Is the transmitted signal at RS location (k ', l').

2. The method of noise measurement according to claim 1, wherein the measurement results for subsequent processing comprise:

and performing MIMO detection by using the result of the second noise measurement.

3. The method of noise measurement according to claim 1, wherein the measurement results for subsequent processing comprise:

and performing decoding processing of channel coding by using the result of the second noise measurement, and/or performing feedback calculation by using the result of the second noise measurement.

4. The method of noise measurement according to claim 1, wherein the second noise measurement is further represented as:

where i, j are the indices of the transmit and receive antenna ports, respectively, N_T、N_RThe number of transmission antennas and the number of reception antennas are indicated, respectively.

5. An apparatus for noise measurement, comprising:

the second noise measurement module is used for carrying out second noise measurement according to the frequency domain data after FFT and the result of channel estimation by using the measurement result of the first noise measurement module, and the measurement result is used for subsequent processing; the second noise measurement module performs a second noise measurement by the following expression:

where E {. denotes the desired operation, L_RSIndicating the number of OFDM symbols containing RS in a subframe, N_RSIndicates the number of subcarriers containing RSs within one OFDM symbol,

6. The apparatus for noise measurement according to claim 5, wherein the second noise measurement module performs the second noise measurement specifically by the following expression:

7. A terminal receiving apparatus for a MIMO-OFDM system, comprising:

the second noise measurement module performs a second noise measurement by the following expression:

is the RS position

As a result of the frequency-domain channel estimation,

for the received signal at RS position (k ', l'), x_k′,l′Is the transmitted signal at RS location (k ', l');

8. The MIMO-OFDM system terminal receiving apparatus of claim 7, further comprising:

a channel decoding module, configured to perform decoding processing of channel coding by using the measurement result of the second noise measurement module; and/or

And the feedback module is used for performing feedback calculation by using the measurement result of the second noise measurement module.