CN101599939B

CN101599939B - Method and device for estimating reference signal received power of orthogonal frequency division multiplexing system

Info

Publication number: CN101599939B
Application number: CN2009100887531A
Authority: CN
Inventors: 许百成
Original assignee: Beijing T3G Technology Co Ltd
Current assignee: Beijing T3G Technology Co Ltd
Priority date: 2009-07-10
Filing date: 2009-07-10
Publication date: 2011-09-28
Anticipated expiration: 2029-07-10
Also published as: CN101599939A

Abstract

The invention provides a method and a device for estimating the reference signal received power (RSRP) of an orthogonal frequency division multiplexing (OFDM) system. The method comprises the following steps: A. carrying out the channel estimation of a received RS (reference signal); B. obtaining the corresponding RSRP through calculation according to the channel estimation results of all the RSsin the coherent block; C. perform the weighted average to the RSRPs corresponding to all the coherent blocks within the ranges of measuring frequency bandwidth and measuring time; D. carrying out thenoise power elimination on the RSRP obtained through the weighted average. The invention realizes the unbiased estimation of the RSRP.

Description

Method and device for estimating reference signal received power of orthogonal frequency division multiplexing system

Technical Field

The present invention relates to the field of wireless communications technologies, and in particular, to a method and an apparatus for estimating Reference Signal Received Power (RSRP) of an Orthogonal Frequency Division Multiplexing (OFDM) system.

Background

In a Long Term Evolution (LTE) wireless communication system, OFDM is the physical layer technology at its core. The data stream is modulated on a plurality of orthogonal subcarriers, and the frequency spectrums of the orthogonal subcarriers can be overlapped, so that the frequency spectrum utilization rate is greatly improved.

Referring to fig. 1, in an ofdm system, transmitted information may be described by a Resource grid, which represents resources of an entire time domain and a frequency domain in the form of Resource Elements (REs), i.e., a minimum square in fig. 1, which corresponds to a subcarrier in the frequency domain and a time length of a symbol (symbol) in the time domain. All information that needs to be transmitted is carried over resource elements. A plurality of resource elements constitute one resource block, and specifically, in the case of a normal cyclic prefix, 12 (the number of subcarriers) × 7 (the number of symbols) constitutes one resource block; in the case of an extended cyclic prefix, 12 (the number of subcarriers) × 6 (the number of symbols) constitutes one resource block.

In order to demodulate data correctly, the channel conditions at each RE location need to be known. In the LTE system, the channel estimation at each RE position is obtained as follows: and inserting a known Reference Signal (RS) at a specific resource element position of each resource block to calculate the channel estimation at the RE position, and then obtaining the channel estimation at all other resource element positions by using an interpolation method. Wherein the reference signal is a random sequence generated according to a specific rule.

RSRP is one of the standard measurement items in LTE systems, which is defined and required in the standard as follows: RSRP is the linear power average of the reference signal over the considered measurement frequency bandwidth and measurement time range. Reference signal R₀(indicating that the RS signal sent by antenna port 0, carried by the RE labeled 0 in fig. 1) can be used to calculate RSRP if the terminal can accurately detect R₁Is valid, then R₁(watch)The RS signal sent by antenna port 1, carried by the RE labeled 1 in fig. 1) may also be used to calculate RSRP. If the terminal adopts the receiving diversity, the reported measurement value is not lower than the value of the RSRP corresponding to any branch in the diversity. However, no specific method of measuring RSRP is given in the standard.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method and a device for estimating the reference signal received power of an orthogonal frequency division multiplexing system, so as to achieve unbiased estimation of the reference signal received power.

In order to solve the technical problems, the invention provides the following technical scheme:

a method for estimating reference signal received power of an orthogonal frequency division multiplexing system comprises the following steps:

A. performing channel estimation on the received RS;

B. calculating according to the channel estimation results of all RSs in the coherent block to obtain corresponding RSRP;

C. carrying out weighted average on the RSRP corresponding to all coherent blocks in the measurement frequency bandwidth and the measurement time range;

D. and carrying out noise power elimination on the RSRP obtained by the weighted average.

In the estimation method, in step B, RSRP is calculated by using the following formula:

wherein, P'^(i，j，n)The corresponding RSRP of the nth coherent block transmitted by the ith antenna port and received by the jth antenna is shown, K represents the number of subcarriers occupied by the RS in the coherent block, L represents the number of OFDM symbols occupied by the RS in the coherent block,

represents the channel estimation of the kth RS signal in the nth coherent block, the kth RS signal in the frequency domain and the ith RS signal in the time domain, which are transmitted by the ith antenna port and received by the jth antenna, | · | represents the modulo operator.

In the estimation method, in step C, the weighted average is performed by using the following formula:

<math><mrow><mover><mi>P</mi><mo>&OverBar;</mo></mover><mo>=</mo><munder><mi>Σ</mi><mi>i</mi></munder><msub><mi>α</mi><mi>i</mi></msub><munder><mi>Σ</mi><mi>j</mi></munder><msub><mi>β</mi><mi>j</mi></msub><mrow><mo>(</mo><mfrac><mn>1</mn><mi>N</mi></mfrac><munder><mi>Σ</mi><mi>n</mi></munder><msup><mi>P</mi><mrow><mo>′</mo><mrow><mo>(</mo><mi>i</mi><mo>,</mo><mi>j</mi><mo>,</mo><mi>n</mi><mo>)</mo></mrow></mrow></msup><mo>)</mo></mrow><mo>,</mo><mn>1</mn><mo>≤</mo><mi>i</mi><mo>≤</mo><mi>I</mi><mo>,</mo><mn>1</mn><mo>≤</mo><mi>j</mi><mo>≤</mo><mi>J</mi></mrow></math>

wherein P represents P 'to all'^(i，j，n)RSRP after weighted averaging, I denotes the total number of transmit antenna ports used to calculate RSRP, J denotes the total number of receive antennas used to calculate RSRP, and N denotes coherence within the measurement frequency bandwidth and measurement time rangeTotal number of blocks, α_iAnd beta_jWeighting coefficients for the transmit antenna ports and the receive antennas respectively,

the above-mentioned estimation method, wherein,

in the estimation method, in step D, the following formula is adopted to perform noise power cancellation:

<math><mrow><mover><mi>P</mi><mo>^</mo></mover><mo>=</mo><mover><mi>P</mi><mo>&OverBar;</mo></mover><mo>-</mo><mfrac><msup><mi>σ</mi><mn>2</mn></msup><mi>KL</mi></mfrac></mrow></math>

wherein,

represents RSRP, σ after eliminating noise power component contained in P²Is the noise power.

The estimation method further comprises the following steps: E. and smoothing the RSRP obtained by eliminating the noise power.

In the above estimation method, in step E, the following formula is adopted for smoothing:

wherein, P_mFor the smoothed RSRP current value,

is the current value of RSRP without smoothing, P_m-1Alpha is a smoothing factor, and alpha is more than 0 and less than or equal to 1.

The above estimation method, wherein the coherent block is a block formed by all REs in the coherence time range and the coherence bandwidth range.

In the above estimation method, the coherent block is a resource block.

An apparatus for estimating reference signal received power of an orthogonal frequency division multiplexing system, comprising:

an RS channel estimator for performing channel estimation on the received RS;

the RSRP calculator is used for calculating according to the channel estimation results of all RSs in the coherent block to obtain corresponding RSRP;

the RSRP averager is used for carrying out weighted average on the RSRPs corresponding to all coherent blocks in the measurement frequency bandwidth and the measurement time range;

and the noise power eliminator is used for eliminating the noise power of the RSRP obtained by the weighted average.

The above estimation device further includes: and the RSRP smoother is used for smoothing the RSRP obtained by eliminating the noise power.

The embodiment of the invention divides the channel estimation of the reference signal into a plurality of coherent blocks, carries out RSRP estimation on each coherent block, then carries out weighted average on the estimation results of the coherent blocks on all the transceiving antennas, and finally carries out noise power elimination on the average result, thereby realizing unbiased estimation on the RSRP.

Drawings

Fig. 1 is a schematic diagram of a distribution situation of a reference signal in a resource block under a condition of a normal cyclic prefix and a number of transmit antennas less than or equal to 2;

fig. 2 is a schematic structural diagram of an apparatus for estimating reference signal received power of an ofdm system according to an embodiment of the present invention;

fig. 3 is a flowchart of a method for estimating a reference signal received power of an ofdm system according to an embodiment of the present invention.

Detailed Description

As can be seen from the theory of wireless communication, reference signals within the coherence bandwidth and coherence time range may have the same or similar channel estimates. The invention is based on this principle to accomplish the estimation of RSRP. For simplicity of the following description, a concept of a coherent block is proposed, which is a block composed of all REs within a coherence time range and a coherence bandwidth range.

Referring to fig. 2, the apparatus for estimating reference signal received power of an ofdm system according to an embodiment of the present invention mainly includes: RS channel estimator, RSRP calculator, RSRP averager, noise power canceller, and RSRP smoother (optional).

Is as followsIn the description, i represents a serial number of a transmitting antenna port; j represents the receiving antenna serial number; n represents a coherent block number; k represents the sequence number of the RS in the frequency domain in the coherent block; l represents the sequence number of the RS in the time domain in the coherent block;

the system comprises a first antenna port, a second antenna port, a first coherent block, a second coherent block and a third coherent block, wherein the first coherent block is transmitted by the first antenna port and received by the second antenna port;

to represent

Estimating a channel of (1); p'^(i，j，n)Representing the estimated RSRP of all RSs in the nth coherent block transmitted by the ith antenna port and received by the jth antenna; p represents P'^(i，j，n)Performing weighted average processing on the RSRP;

an RSRP indicating the noise power component contained in the P is removed; p represents a pair

RSRP after smoothing.

RS channel estimator

The RS channel estimator is configured to perform channel estimation on the received RS, and specifically includes:

{\hat{h}}_{k, l}^{(i, j, n)} = {\hat{r}}_{k, l}^{(i, j, n)} r_{k, l}^{(i, j, n) *}

wherein r is_k，l ^(i，j，n)Indicating the transmitted reference signal, (.)^*Representing the conjugate operator.

RSRP calculator

The RSRP calculator is configured to calculate according to channel estimation results of all RSs in the coherent block to obtain a corresponding RSRP, and specifically includes:

wherein, K represents the number of sub-carriers occupied by the RS in the coherent block, L represents the number of OFDM symbols occupied by the RS in the coherent block, and | - | represents the modulus operator.

The coherent block can be divided by using a coherent bandwidth estimation module and a coherent time estimation module in the receiver, and as a conservative implementation method, if the coherent bandwidth estimation module and the coherent time estimation module do not exist in the receiver, one resource block can be regarded as one coherent block.

RSRP averager

The RSRP averager is configured to perform weighted averaging on RSRPs corresponding to all coherent blocks in a measurement frequency bandwidth and a measurement time range to reduce an estimated error, and specifically includes:

where I denotes the total number of transmit antenna ports used to calculate RSRP (one antenna may have multiple ports, where the total number is the sum of the number of ports of all transmit antennas), J denotes the total number of receive antennas used to calculate RSRP, N denotes the total number of coherent blocks within the measurement frequency bandwidth and measurement time range considered, α_iAnd beta_jWeighting coefficients of the transmitting antenna port and the receiving antenna respectively, satisfy

As a simple embodiment, it is preferable

Noise power canceller

And the noise power eliminator is used for eliminating the noise power of the RSRP obtained by the weighted average. The RSRP value calculated by the RSRP averager is not an unbiased estimation result, and includes a noise power with a certain component, and in order to implement the unbiased estimation of RSRP, the component of the noise power needs to be eliminated, specifically:

wherein σ²Is the noise power.

RSRP smoother

And the RSRP smoother is used for smoothing the RSRP obtained by eliminating the noise power. To improve the stability of RSRP estimation, as an optimization, the current RSRP estimate and the historical values may be smoothed, i.e.,

wherein, P_mFor the smoothed RSRP current value,

is the current value of RSRP without smoothing, P_m-1Alpha is a smoothing factor (can be taken as a value according to the change condition of a channel) for the smoothed RSRP historical value, and alpha is more than 0 and less than or equal to 1.

How to divide the resources within the measurement frequency bandwidth and the measurement time range into a plurality of coherent blocks is the prior art, and as an implementation manner of the prior art, reference may be made to the chinese patent application document, which is entitled "a channel estimation method and apparatus for an orthogonal frequency division multiplexing system" and has an application number of 200910082322.4 and an application date of 2009, 4.14, which is provided by the present applicant, and only the principle thereof is briefly introduced here. As described above, coherent blocks may be divided by using a coherent bandwidth estimation module and a coherent time estimation module in a receiver, and as a conservative implementation method, if the coherent bandwidth estimation module and the coherent time estimation module do not exist in the receiver, a resource block may be regarded as a coherent block.

By coherent block is meant a block consisting of all REs within the coherence bandwidth and within the coherence time. By coherence time is meant a time interval during which the amplitude of the received signal has a strong correlation, i.e. the channel impulse response remains substantially constant during the coherence time. By coherence bandwidth is meant a frequency domain bandwidth within which the amplitude of the received signal has a strong correlation, i.e. the amplitude-frequency response of the channel remains substantially constant within the coherence bandwidth. The channel delay spread and the coherent bandwidth have a strong corresponding relation, and the larger the channel delay spread is, the narrower the coherent bandwidth is; conversely, the smaller the channel delay spread, the wider the coherence bandwidth. The term "channel delay spread" refers to the difference of propagation paths experienced by each path component of a channel, and thus has different time delays, which causes the energy of a signal to be spread in time.

The coherent bandwidth estimation module firstly utilizes the frequency domain channel estimation of the reference signal to calculate the time delay expansion tau in the wireless channel_nThen, the corresponding relation between the time delay expansion and the coherent bandwidth is carried outCalculating to obtain the coherent bandwidth

Where ζ is a mapping factor of delay spread and coherence bandwidth. The delay spread has various expression forms, and the maximum delay spread, the average delay spread, the root mean square delay spread and the like are commonly used. In either representation, the effective paths of the time domain channel impulse response are first determined. The time delay expansion can be obtained by performing inverse Fourier transform on the frequency domain channel estimation of the position of the reference signal to obtain time domain channel estimation, then obtaining an effective diameter of the time domain channel estimation, and calculating according to the effective diameter to obtain the time delay expansion of the channel.

And the coherent time estimation module calculates according to the frequency domain channel estimation at different time domain positions to obtain the coherent time of the channel. Specifically, the coherence time estimation module may include: a difference factor calculation unit for calculating a difference factor between the frequency domain channel estimation of the reference signal and an available frequency domain channel estimation adjacent in the time domain; and the coherence time calculation unit is used for determining the coherence time of the channel according to the difference factor.

Referring to fig. 3, the method for estimating the reference signal received power of the ofdm system according to the embodiment of the present invention mainly includes the following steps:

step 301: performing channel estimation on the received RS, specifically:

{\hat{h}}_{k, l}^{(i, j, n)} = {\hat{r}}_{k, l}^{(i, j, n)} r_{k, l}^{(i, j, n) *}

Step 302: calculating according to the channel estimation results of all the RSs in the coherent block to obtain the corresponding RSRP, specifically:

Step 303: performing weighted average on RSRP corresponding to all coherent blocks within a measurement frequency bandwidth and a measurement time range to reduce an estimation error, specifically:

As a simple embodiment, it is preferable

Step 304: and carrying out noise power elimination on the RSRP obtained by the weighted average. The RSRP value calculated in step 303 is not a result of unbiased estimation, and includes a noise power component, and to implement the unbiased estimation of RSRP, the noise power component needs to be eliminated, specifically:

wherein σ²Is the noise power.

Step 305: and smoothing the RSRP obtained by eliminating the noise power. To improve the stability of RSRP estimation, as an optimization, the current RSRP estimate and the historical values may be smoothed, i.e.,

wherein, P_mFor the smoothed RSRP current value,

In summary, the embodiments of the present invention implement unbiased estimation of RSRP by dividing the channel estimation of the reference signal into a plurality of coherent blocks, performing RSRP estimation on each coherent block, then performing weighted averaging on the estimation results of the coherent blocks on all the transceiving antennas, and finally performing noise power cancellation on the averaged result.

Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and those skilled in the art should understand that the technical solutions of the present invention can be modified or substituted with equivalents without departing from the spirit scope of the technical solutions of the present invention, which should be covered by the scope of the claims of the present invention.

Claims

1. A method for estimating reference signal received power of an orthogonal frequency division multiplexing system, comprising the steps of:

A. performing channel estimation on a received Reference Signal (RS);

B. calculating according to the channel estimation results of all RSs in the coherent block to obtain corresponding Reference Signal Received Power (RSRP);

D. carrying out noise power elimination on the RSRP obtained by weighted average;

in step B, RSRP is calculated using the following formula:

wherein, P'^(i，j，n)The corresponding RSRP of the nth coherent block transmitted by the ith antenna port and received by the jth antenna is shown, K represents the number of subcarriers occupied by the RS in the coherent block, L represents the number of orthogonal frequency division multiplexing OFDM symbols occupied by the RS in the coherent block,

2. The estimation method according to claim 1, wherein in step C, the weighted average is performed using the following formula:

wherein,

represents to all P'^(i，j，n)RSRP after weighted averaging, I denotes the total number of transmit antenna ports used to calculate RSRP, J denotes the total number of receive antennas used to calculate RSRP, N denotes the total number of coherent blocks within the measurement frequency bandwidth and measurement time range, α_iAnd beta_jWeighting coefficients for the transmit antenna ports and the receive antennas respectively,

3. the estimation method according to claim 2, characterized in that:

4. the estimation method according to claim 2, wherein in step D, the noise power cancellation is performed using the following formula:

wherein,

representation elimination

RSRP, σ after the noise power component contained in (1)²Is the noise power.

5. The estimation method according to claim 1, further comprising the steps of:

E. and smoothing the RSRP obtained by eliminating the noise power.

6. The estimation method according to claim 5, wherein in step E, the smoothing is performed using the following formula:

wherein, P_mFor the smoothed RSRP current value,

7. The estimation method according to claim 1, characterized in that:

the coherent block is a block composed of all resource elements REs within a coherence time range and a coherence bandwidth range.

8. The estimation method according to claim 1, characterized in that:

the coherent block is a resource block.

9. An apparatus for estimating a reference signal received power of an orthogonal frequency division multiplexing system, comprising:

an RS channel estimator for performing channel estimation on the received RS;

the noise power eliminator is used for eliminating noise power of the RSRP obtained by the weighted average;

wherein the RSRP calculator calculates the RSRP using the following formula:

wherein, P'^(i，j，n)The RSRP corresponding to the nth coherent block transmitted by the ith antenna port and received by the jth antenna is represented, and K represents the RS occupied in the coherent blockThe number of subcarriers, L represents the number of OFDM symbols occupied by RS in the coherent block,

10. The estimation apparatus of claim 9 wherein the RSRP averager performs a weighted average using the formula:

wherein,

11. the estimation apparatus of claim 10, wherein:

12. the estimation apparatus as set forth in claim 10, wherein the noise power canceller performs noise power cancellation using the following equation:

wherein,representation eliminationRSRP, σ after the noise power component contained in (1)²Is the noise power.

13. The estimation apparatus of claim 9, further comprising:

and the RSRP smoother is used for smoothing the RSRP obtained by eliminating the noise power.

14. The estimation apparatus of claim 13 wherein the RSRP smoother smoothes using the formula:

wherein, P_mFor the smoothed RSRP current value,

15. The estimation apparatus of claim 9, wherein:

the coherent block is a block composed of all REs within a coherence time range and a coherence bandwidth range.

16. The estimation apparatus of claim 9, wherein:

the coherent block is a resource block.