WO2009079849A1

WO2009079849A1 - Method and device for receiving diversity combining in ofdm system

Info

Publication number: WO2009079849A1
Application number: PCT/CN2007/003736
Authority: WO
Inventors: Jia Qiao; Jing Zhang
Original assignee: Utstarcom Telecom Co., Ltd.
Priority date: 2007-12-21
Filing date: 2007-12-21
Publication date: 2009-07-02
Also published as: CN101953089A

Abstract

A method and device for receiving diversity combining in orthogonal frequency division multiplexing system and an orthogonal frequency division multiplexing system, wherein the method for receiving diversity combining comprises the steps as follows: comparing the signal-to-noise ratio of all the diversity branches with a threshold; if there is a diversity branch whose signal-to-noise ratio is less than the threshold, setting the channel response estimated value of one or more diversity branches to zero according to the comparison result; calculating the maximum ratio combining output according to the receiving symbol of the carrier wave and the channel response estimated value of the diversity branch.

Description

Receive diversity combining method and device for OFDM system

The present invention relates to wireless communication technologies, and in particular, to a receive diversity combining method and apparatus for an Orthogonal Frequency Division Multiplexing (OFDM) system, and an OFDM system employing the receive diversity combining apparatus.

Background technique

In order to reduce the impact of fading on the reception performance in a wireless communication system, diversity techniques are usually employed. Commonly used diversity techniques mainly include spatial diversity and polarization diversity. If the antennas of the receiver are far enough apart and the fading of the received signals is independent of each other, spatial diversity reception is typically employed. In addition, the receiver can achieve polarization diversity using a +/-45 ° or vertical/horizontal dual-polarized antenna.

At present, there are two main types of diversity combining technologies, one is the maximum ratio combining technology, and the other is the selective combining technology. In maximum ratio combining, the receiving end generally has multiple diversity branches. Before combining, the multiple signals are weighted to achieve the best performance and are in phase. After the phase adjustment, the phases are added according to the appropriate gain coefficients. Selective combining is to select the branch with the largest signal to noise ratio among the multiple diversity branches as the output.

Specifically, as shown in FIG. 1, the transmitter 100 transmits an OFDM-modulated wireless signal that is received by the antenna 201 of the receiver 200. The received signal is converted into a baseband signal by the down-converting unit 202, and then subjected to a fast Fourier transform (FFT) unit 203, and is transformed to a received symbol corresponding to each subcarrier, and the received symbols of the k subcarriers are ^

Y _k = H _k X _{k +} N _k

Among them, is the transmitted symbol, which is the channel response on subcarrier k, which is additive noise. When ^ is a known pilot sequence, the channel response can be estimated. Under the least squares criterion (LS), the channel response is estimated based on the received pilot symbols in the received signal and the pilot symbols transmitted by the transmitter.

^ = H

X _t + X where ^ refers to the pilot symbol transmitted on the kth subcarrier. Usually, ^H k ^≠H letter The higher the noise ratio, the smaller the error of the channel estimation; the lower the signal-to-noise ratio, the larger the error of the channel estimation. By interpolating, the channel response on all subcarriers including the data symbols can be estimated. Finally, the maximum ratio combining is performed on all the branch road signals, and the maximum ratio combined output is

If the weights of the other branches except the one with the best signal quality are forcibly zeroed, the degradation is selective:

•yd ^ ι

Λ k _t mrc where 4 is the branch with the best signal quality.

As mentioned earlier, the lower the signal to noise ratio, the greater the error in channel estimation. In the maximum ratio combining algorithm, the conjugate of the channel response is used as the weight. Therefore, in the case where a certain branch or some branches are in a low SNR, the performance of the maximum ratio combining is due to the error of channel estimation. And greatly reduced, and even bring a large negative gain.

For example, "Subcarrier-based selection diversity reception of DVB-T in a mobile environment (Rinne, J.; Vehicular Technology Conference, 1999. VTC 1999 - Fall. IEEE VTS 50 ^th Volume 2, 19-22 Sept. 1999 Page (s): 1043 - 1047 vol. 2), in this paper, an improved selective diversity reception method is proposed, which is incorporated herein by reference. However, such methods are directly applied to the OFDM system. Among them, its performance is not as great as the merger technology.

It is an object of the present invention to provide a receive diversity combining method for an OFDM system that effectively avoids the maximum ratio of combined negative gain due to channel estimation errors.

The above object of the present invention is achieved by the following technical solutions:

A method for receiving diversity combining for an OFDM system, comprising the following steps:

Compare the signal-to-noise ratio and threshold of all diversity branches;

Estimating the verbal response of the associated diversity branch based on the result of the comparison The value is set to zero;

The output of the maximum ratio combining is calculated based on the received symbols of the carrier and the channel response estimates of the diversity branch.

Preferably, in the above method, if the signal to noise ratio of all the diversity branches is lower than the threshold, all other than the diversity branch having the largest signal to noise ratio The channel response estimate for the diversity branch is set to zero.

Preferably, in the above method, if a signal to noise ratio of a portion of the diversity branch is less than the threshold, estimating a channel response of the corresponding diversity branch whose signal to noise ratio is less than the threshold value The value is set to zero.

Preferably, in the above method, the threshold value is determined according to a bit error rate of the channel and a signal to noise ratio.

Another object of the present invention is to provide a receive diversity combining apparatus for an OFDM system that can effectively avoid a maximum ratio combining negative gain due to channel estimation errors.

A receiving diversity combining apparatus for an OFDM system, characterized in that the apparatus is configured to perform the following steps:

Compare the signal-to-noise ratio and threshold of all diversity branches;

And determining, according to the result of the comparison, a channel response estimate of the associated diversity branch to zero;

Preferably, the channel estimation device is a digital signal processor.

It is still another object of the present invention to provide an OFDM system that effectively avoids the maximum ratio combining negative gain due to channel estimation errors.

The above object of the present invention is also achieved by the following technical solutions:

An OFDM system, comprising: at least one source end and at least one sink end, wherein the sink end comprises a receive diversity combining apparatus according to claim 9, for receiving the received end of the sink end The diversity signals are combined. The receiving diversity combining device is a digital signal processor.

Compared with the prior art, the present invention compares the signal to noise ratio of the diversity branch and a pre-preparation The threshold is set and the channel response estimate of the associated branch is set to zero based on the comparison result, thereby avoiding a significant reduction in the performance of the maximum ratio combining due to the fact that some of the branches are in a low signal to noise ratio. Finally, the present invention also has the advantage of achieving a relatively complex complexity and easy hardware implementation. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be more fully described by means of the preferred embodiments and the accompanying drawings, in which:

1 is a schematic diagram of a receiver for implementing receive diversity combining techniques in a conventional OFDM system.

2 shows a flow diagram of a preferred embodiment of a receiver in an OFDM system that can implement the receive diversity combining method of the present invention.

3 is a flow chart of a preferred embodiment of a receive diversity combining method for an OFDM system in accordance with the present invention. detailed description

In the following description, the embodiment of the present invention is described by taking an ODFM system as an example, but this does not mean that the present invention is limited to application on such a communication system. On the contrary, the present invention can also be extended to other carrier systems. .

According to the present invention, various algorithms can be used to calculate the signal-to-noise ratio, and various algorithms are used for channel estimation, and different threshold values can be set according to specific wireless environment characteristics. Exemplary generality will be given below. Algorithm, but it should be pointed out that after reading this application, those skilled in the art will recognize that other algorithms besides the specific algorithm can be employed, and that relevant or relevant designs can be selected or selected according to the characteristics of the application. The algorithm and therefore the scope of the invention and the scope of protection should not be limited by the specific algorithm.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

Figure 2 shows a schematic block diagram of a system according to the invention including, but not limited to, a transmitter and a receiver. In order to explain the spirit of the present invention more clearly and concisely, only the transmitter 100 and receiver 200 embodying the present invention are further described herein. As shown, the receiver side includes, but is not limited to, a receiving antenna 201, a down-converting unit 202, a fast Fourier transform (FFT) unit 203, a channel estimation/signal-to-noise ratio estimating unit 204, The weight generator unit 205, the multiplication unit 206, the addition unit 207, and the decoding unit 208.

The transmitter 100 is configured to transmit an OFDM modulated wireless signal. The receiver 200 receives the wireless signal through the multiplex antenna 201 and performs further processing.

The multiplex antenna 201 receives the analog RF signal and transmits it to the downconversion unit 202. The down conversion unit 202 is mainly used to convert the received analog radio frequency signal into a digital baseband signal. The FFT unit 203 is configured to perform a discrete Fourier transform on the digital baseband time domain signal to convert the time domain signal into a frequency domain signal. That is, the input digital baseband time domain signal is converted into a digital baseband frequency domain signal, and converted to a received symbol corresponding to each subcarrier. In general, the received symbol Y _{k of the kth} subcarrier

Y _k = H _k X _{k +} N _{k ( 1} ) where X _k is the transmitted symbol, H _k is the channel corresponding on subcarrier k, and N _k is additive noise.

Next, the FFT-transformed signal is sent to the channel estimation/signal-to-noise ratio estimating unit 204. The channel estimation/signal-to-noise ratio estimating unit 204 estimates the channel response based on the received pilot symbol Y _k in the received signal and the pilot symbol transmitted by the transmitter.

H _k = ^ = H _k +^- ( 2 )

Χζ χ ^ρ Then by interpolation, the channel response on all subcarriers including the data symbols can be estimated.

At the same time, the channel estimation/signal-to-noise ratio estimating unit 204 calculates the signal-to-noise ratio SNR based on the received signal strength RSSI measured on the useful subcarrier and the noise power N measured on the idle subcarrier.

Next, the channel frequency domain impulse response and the signal-to-noise ratio SNR output by the channel estimation/signal-to-noise ratio estimating unit 204 are sent to the weight generator 205. The weight generator determines whether the branch participates in the maximum ratio combining by comparing the signal to noise ratio of the diversity branch with a predetermined threshold, and if not, sets the weight to zero, otherwise, according to the channel frequency domain The weight of the branch for maximum ratio combining should be calculated.

Where M denotes the number of receiving antennas, m denotes the mth receiving antenna, i denotes the i-th OFDM symbol, k denotes the kth subcarrier, and H, _m denotes an estimation of the channel response of the kth subcarrier of the mth receiving antenna The conjugate value of the value, H,,. represents the channel response estimate of the i-th OFDM symbol of the kth subcarrier, and ^^ represents the weight.

Specifically, as shown in Fig. 3, first, the signal-to-noise ratio of all branches and the threshold value of the branch with the largest pre-signal-to-noise ratio are compared. If the signal-to-noise ratio of all branches is below the threshold, then the channel responses of all other branches except the one with the largest signal-to-noise ratio are zeroed. If only the signal-to-noise ratio of some of the branches is below the threshold and the signal-to-noise ratio of the other branches is greater than the threshold, the channel response of the branch with a signal-to-noise ratio lower than the gate P艮 is zeroed.

Finally, as shown in FIG. 2 and FIG. 3, the multiplier 206 and the adder 207 _combine according to the weight ^ _{ΛΒ 1} and the received symbol ^ to obtain

Wherein, the received pilot symbol of the i-th OFDM symbol of the kth subcarrier is represented.

Finally, the combined result is sent to decoding unit 208 for decoding to complete the channel decoding operation.

The algorithm according to the present invention may be implemented independently by hardware or software modules, or may be implemented in a coordinated manner by a number of hardware or software modules, and variations of these implementations will be apparent to those skilled in the art, and thus It is within the spirit and scope of the invention.

Other modifications will be apparent to those skilled in the art after reading the above disclosure. Such modifications may involve well-known features within the wireless communication system and its component units, and these features may be substituted for The features described are either applied in an additive manner.

In the present specification and claims, the <RTI ID=0.0>"a" </ RTI> </ RTI> preceded by a unit does not exclude a plurality of such elements. Moreover, the word "comprising" does not exclude other elements or steps other than the listed elements or steps.

Claims

Rights request

A receiving diversity combining method for an orthogonal frequency division multiplexing system, characterized in that it comprises the following steps:

Compare the signal-to-noise ratio and the gate P艮 value of all diversity branches;

If there is a diversity branch whose signal to noise ratio is less than the threshold value, the channel response estimation value of one or more of the diversity branches is set to zero according to the result of the comparison;

2. The method according to claim 1, wherein if the signal to noise ratio of all of the diversity branches is lower than the threshold, the diversity branch except the signal to noise ratio is maximized The channel response estimates for all other of the diversity branches are set to zero.

3. The method according to claim 1, wherein if a signal to noise ratio of a portion of the diversity branch is less than the threshold, the signal to noise ratio is less than the corresponding diversity of the threshold The channel's channel response estimate is set to zero.

4. The method of claim 1, wherein the signal to noise ratio is calculated from a received signal strength measured on the wanted carrier and a measured noise power measured on the idle carrier.

5. The method of claim 1, wherein the threshold value is determined according to a bit error rate of the channel and a signal to noise ratio.

6. A receiving diversity combining apparatus for an orthogonal frequency division multiplexing system, characterized in that said apparatus is configured to perform the following steps:

If there is a diversity branch whose signal to noise ratio is less than the threshold value, zeroing the channel response estimation value of one or more of the diversity branches according to the result of the comparison; according to the received symbol of the carrier and the diversity branch The channel's channel response estimate calculates the maximum ratio of the combined output.

The channel estimating apparatus according to claim 6, wherein said channel estimating means is a digital signal processor.

8. The receiving diversity combining apparatus according to claim 6, wherein if the signal to noise ratio of all of the diversity branches is lower than the threshold, the signal to noise ratio is the most The channel response estimates for all other of the diversity branches outside the large diversity branch are set to zero.

9. The receiving and combining apparatus according to claim 6, wherein if a signal to noise ratio of a portion of the diversity branch is less than the threshold, the signal to noise ratio is less than a corresponding value of the threshold The channel response estimate for the diversity branch is set to zero.

10. The receiving diversity combining apparatus according to claim 6, wherein the threshold value is determined according to a bit error rate and a signal to noise ratio of the channel.

An Orthogonal Frequency Division Multiplexing (OFDM) system, comprising: at least one source end and at least one sink end, wherein the sink end comprises a receive diversity combining apparatus according to claim 6, The received diversity signals of the sinks are combined.

The Orthogonal Frequency Division Multiplexing (OFDM) system according to claim 11, wherein the receiving and combining unit is a digital signal processor.