TW200915751A - Orthogonal frequency division multiplexing system and its channel estimating appliance and method - Google Patents

Abstract

The present invention relates to an orthogonal frequency division multiplexing system and its channel estimating appliance and method, which essentially transmit the signals of error detection for sub-carrier waves by a transmitter, and check the receiving signals from a receiver to strengthen the accuracy of information to determine whether to perform channel estimation or measurement. This invention takes advantage of the least-square estimation (LS) for preliminary estimation, the minimum mean square error estimation (MMSE) for obtainment of more accurate channel estimation and the singular value decomposition for reducing the arithmetic complexity of the minimum mean square error estimation in sequence. According to the aforesaid channel estimations, optimum system efficiency thereof can be obtained in the speedy time-varying channels.

Description

200915751 IX. Description of the invention: [Technical field of invention] The present invention relates to a channel estimation apparatus and method for an orthogonal frequency division multiplexing transmission system, in particular, a tracking device and method with perfect channel estimation Rapid changes in the channel to enhance system performance. [Prior Art] According to the Orthogonal Frequency Division Multiplexing (OFDM) system, many studies have been proposed in wireless communication. In mobile communication systems, the wireless channel is usually frequency selective and time varying. Although the orthogonal frequency division multiplexing (OFDM) system has good ability to resist frequency selective fading, the prerequisite is The condition is that the receiver must have a good channel estimation system to improve the performance of the system. Especially when the system is in a fast time-varying wireless channel, the receiver needs a better dynamic channel estimation mechanism to assist in demodulation. Correct orthogonal frequency division multiplexing transmission (boring) signals for better system performance. In the prior art, in order to understand the unknown channel characteristics, the number I adds a pilot signal or a training signal, and the pilot signal connects (4) the known signal information, so the channel can be estimated by the pilot signal at the receiving end. When the channel characteristics are tasted 4, in order to increase the bandwidth of the transmission, the pilot signal only transmits (_) between a few specific subcarriers, channel estimation = estimation of the channel hiding for these subcarriers, and then The subcarrier information obtained is estimated by the (10) pilot carrier channel characteristics of the pilot money, and the methods used are mostly interpolation. However, in the prior art, many channel estimation methods for orthogonal frequency division multiplexing transmission (200915751) systems are developed under the assumption of slow fading channels, which usually assume that the channel is in several positive The amount of change in the cross-frequency multiplex transmission (0FDM) symbol time is not large, so after the first channel estimation (usually using the training symbol for channel estimation), it can be used until the training symbol is not used. The channel characteristics previously estimated are used for material detection. In fact, in a wideband wireless channel, the channel is likely to have a significant change in the sign of an orthogonal frequency division multiplexing (OFDM). Therefore, the channel characteristics of the two symbols before and after the difference will be different. The estimated channel is used for data detection of the next symbol, sometimes producing a large error, which reduces the performance of the receiving system, so a better channel estimation method is needed to get better in the fast changing channel environment. System performance. In view of this, the inventors have developed a channel estimation method for orthogonal frequency division multiplexing transmission system according to the prior art to achieve the purpose of improving reception efficiency and reducing detection error, so as to improve the existing orthogonal frequency division multiplexing. The missing of the transmission [0FDM]. SUMMARY OF THE INVENTION In order to achieve the above object, the channel estimation method of the orthogonal frequency division multiplexing transmission system of the present invention is implemented by the following technologies: Mainly, the error detection signal of the subcarrier is transmitted by the transmitting end, and then the receiving end is checked. Whether the received signal is correct or not to enhance the correctness of the data, and whether it is necessary to perform channel estimation; by the above channel estimation method, the system performance is better in a fast time-varying channel. . [Embodiment] In order to make the technical content, the object of the invention and the effects thereof achieved by the present invention more comprehensive and clear disclosure, in the following embodiments, the details of 200915751 are as follows: First, please refer to the first figure. The block diagram of the orthogonal frequency division multiplexing transmission (OFDM) system of the present invention is mainly characterized in that the information of the two bits is modulated by the transmitting end, that is, the signal corresponding to (110), and then juxtaposed by serial transmission. (120) After becoming the serial data, insert the error detection signal (130) [error detection] to become the modulated subcarrier signal iW in the frequency domain [freqUenCy domain], and the error signal can be used to detect the received signal. Error 'This tuning signal (8) then converts the frequency domain signal (8) into a time domain signal (141) via the fast inverse Fourier transform (140) [IFFT] [ time domain ] χ(η): χ(η) = IDFT {x{k)}=Y^x(k)ej2idmlN ^ λ=0 π = 0,1,··.,#_ΐ (1) where water is the subcarrier of the orthogonal frequency division multiplexing (OFDM) system number. In order to prevent the interference (inter-Symb〇l interference) between the symbols of the receiving number, a guard interval (15〇) is usually inserted between the symbols of the two time domain signals to become an orthogonal frequency division multiplexing (OFDM) system. Transmission signal (151) χ >):

X x(N + n\ n = -Ng)

Anl « = 0, where the meaning is the length of the insertion guard interval (150). The time domain signal inserted into the guard interval (150) is transmitted through the transmitter (17〇) and then transmitted through the wireless channel (180) to the receiver (210). The receiver receives the signal through the parallel transmission (16〇). Representation: 200915751 ^(w)= h(n)+ w(n) (iii) where is the impulse response of the channel, and w(«) is additivity

Additive White Gaussian Noise (AWGN)' ® is the conv〇lution symbol of two signals. The demodulation step at the receiving end is to remove the guard interval (230) after the parallel column (220), and then up-convert the time domain to the frequency domain through fast Fourier transform (240) [IFFT]. Frequency domain receiving signal (241) Y(k) · ]2π]ίη/Ν ^ η=0 ^ = 〇, 1,··· , Ν-l (4) The receiving signal can be executed in the receiving signal 呛) Error detection 25〇) to detect whether the received signal has an error, assuming that the length of the guard interval is greater than the length of the channel pulse, so the orthogonal frequency division multiplexing transmission will not follow the adjacent symbols. There is a phenomenon of ISI, so the demodulated symbol 呛) is:

Hk)= X(k)H(k)+ I(k)+w(k), k = 0,l,^,Nl (five: # ι 1, middle ^(6) is the frequency response of the channel, the price is Both the transmitter and the receiver are similar to each other, and _ is the Fourier transform of the coffee. 1. In equation (5), we estimate the frequency response of the channel by channel estimation (270), and then obtain it by equalizer (28GA) or automatic cover = (28Gy AGC). The original transmission, so the last _ to receive the signal (6) is 1 (six) 200915751 where 圮 (6) is the estimated channel frequency response. The receiving signal (8) is then restored to the original two-bit information by the signal opposition (10) Output. Ming-- and referring to the second figure, the flow chart of the estimation architecture of the orthogonal frequency division multiplexing transmission [_M] system of the present invention is as follows: (a) transmitting signal (371) - transmitter - The transmitted symbol is a known

The signal 'receiver' (21G) receives this known symbol and uses this known signal for channel estimation (270) and stores it in Fuzhou Moxibustion. (6) Error ❹ K372) - In the "Material ^, Receiver (10)), use Transmitter (17G) transmits the error signal (1) 所) the wrong debt test (25〇) of the beet symbol, cross-measures whether the symbol has an error; (c) performs channel estimation (373) or does not execute Channel Estimation (375)—The above symbols are represented as reliable symbols and channel estimates are made using this reliable symbol; (4) Channel parameters (10) are updated—by channel estimation (10)) the channel parameters can be updated. In the embodiment, when the receiver (21()) receives the signal (10), the channel is estimated by the fast (four) conversion (10)) [fft]m (27G) 'to get the channel response to return the original signal, we are transmitting the signal The beginning of the transmission - the group is all (four) signal orthogonal frequency division multiple input [0FDM] symbol to estimate the unknown channel response, for the error, first, we use the minimum mean square error / orthogonal frequency division multiplexing The transmission [coffee] transmission signal starts with - the group is all ^ ’ Signals such as: Scoop voyage (7)

Xp(^hpilot signal neQD,...,N~1 9 200915751 The estimation method used is to estimate the channel frequency response by least square [LS] estimation method; =[^,ω(〇) ^/>, Ω(1)··. ι)]Γ = Χ;!7 —“r(o) r(i) 冲) coffee-i) 丫 where r(〇 is the received signal, and the least square [LS] estimation method The estimated channel response is also due to the least square [LS] estimation method susceptible to noise (190) interference, so the least squares error [MMSE] estimation method is used after the least square [Ls] estimation method. For more accurate channel estimation (270):

Where < is the variance of the noise (190) rW, and its mound coefficient matrix is eight or eight

It can be seen from the private (9) that as long as the transmission of the y number eight changes 'there must be the operation of the inverse matrix, the minimum] the complexity of the estimation method is also improved a lot; the operation 'minimum mean square error MMSE 'Less; can use the value to find the flat

On the live seat map, the probability of occurrence of each job number is on the current seat map. As long as the pilot signal or training symbol is transmitted, the time ΙΓ > ν is set in the news, so get tQr ή. 10 200915751 = Qiu ~(4)| / ' where I is the identity matrix, and γ is defined according to the definition of (signal-to-noise ratio), and equation (9) is simplified as \-ι 食 p=Rhh

lP, LS (11) where Θ = ♦ (〇邱~(*)| is a constant whose value depends on the value of the signal constellation for the 16-QAM system is one (7) 9. If the book and snr are at - start The time is known, so it only needs to be calculated once. ^^ The volume can be avoided. Although (11) can avoid the operation of the repeated inverse matrix, ^ is the overall complexity of the 2 detector, and its complexity is still It is quite high. Because the channel correlation matrix (reporting matrix) requires a complex, "method operation", in order to reduce the number of multiplication operations, a singular matrix decomposition is proposed, and the heterogeneous [SVD] decomposition decomposes the channel correlation matrix into (10). b) fe ...1 μ0, μι,..·, "λμ, dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia dia Estimation equation

SNR ^HH ~ UAXJ where U is a row orthogonal matrix and its row vector is

HP=U

UhH

PyLS (13) where ~ is a pair of angular matrices, the content of which is , public = 0,1,·..,#-1

Male)=iW X(k)+~^~ SNR (The working block diagram of the fourteen channel estimation method is shown in the third figure. See the fourth figure again, which is the orthogonal frequency division of the present invention. Multiplex 200915751 2 OFDM system reliable symbol overnight = 7 augmented channel estimation (27 °) time === (CheCkSUn 〇 carrier transmits the total sum of CLHecksuni), because the transfer sum value The u and μ can get a larger data bandwidth at the receiving end, and the data for the first-time channel (7) of the pilot symbol is still the estimated channel U 270), and the subsequent symbol contains the summed message. , in the reception = it is correct - if the data is correct through the sum of the sum of the words - the symbol is a reliable symbol, so use this symbol for general channel estimation (270), here I Cong E channel estimation The method is used to obtain the channel parameters of the current channel (270) and (4) for the next channel, and then re-estimate the channel until the correct symbol is received; The frequency division multiplexing transmission (〇FDM) symbol is used for the channel estimation (270) action, and can also Tracking changes in time-varying channels, while improving system performance (please refer to Figure 5). The following is the simulation verification of the channel estimation method of the orthogonal frequency division multiplexing transmission system of the present invention. First, we will set the analog parameters of the orthogonal frequency division multiplexing transmission (OFDM), and the orthogonal frequency division is more. The modulation of the transmission [〇FDM] system uses 16-QAM, and the center frequency of the carrier is 2.4 GHz, and the bandwidth is 20 MHz. The total number of subcarriers is n=64, of which 61 subcarriers transmit general data 'another 3 The subcarrier transmits a check sum message; the green channel model is a time-varying multipath channel of the Jakes' model; assuming that the Guard intervals are greater than the channel's maximum path delay, 12 200915751, the system has no ISI phenomenon. Next, the time-varying channel is used to estimate the channel using different channel estimation methods at different speeds, and it is better than the car's performance. When it is at the transmitting end, an orthogonal frequency division multiplexing transmission [0FDM] 〕 The symbol is evenly inserted into the pilot signal, and the channel frequency is estimated for receiving the navigation signal. Then, the complete channel is calculated by the _ method, and the number of the interpolation pilot signals in the simulation is 1M times the original signal. It can be seen that the interpolation method is completely different from the che-ck sum method, so we use MATLAB to simulate the difference in performance. During the simulation, we compare the mean square error (MSE) of the channel response between the estimated value and the true value. This mean square error is defined as

MSE Cheng | Township ~ Qiu〗 (Fifteen: Ming - and refer to the figure shown in Figure 6 for the transmission of four hundred transmission [_] symbols (generally a transmission packet for the class ~ a ^ multi-work off in the channel has changed顾顾可# The symbolic estimation method traces to the time-varying channel: ^ It can be seen that the reliable symbol estimation method can be pen speed (V=5GWh/:; - and refers to (four) seven graphs, for comparison in different The channel and the actual channel ^1〇〇1^ and V=1嶋/hr), the comparison of the reliable symbol channel to Na, the method that can be known from the figure is lower than the interpolating method of the interpolated ^. We pick b at different speeds - and see the eighth picture, MSE = MSE = speed in the figure shows the method of reliable symbol estimation in the non-sequence test ability is lower than the (four) method, the surface is reliable In the channel warehouse, please refer to the coating 160 km / hr, shown in Figure XX, for the moving speed in V, 1, 〇〇, E "fSNR performance comparison" shown by the figure of ice 13 200915751 The efficiency of the ### channel estimation method is better than the interpolation method. When the speed is V=50 km/hr and V=i〇〇km/hr, we simultaneously send & reliable symbol pass Because the channel changes slowly, the estimation method can easily track the change of the time-varying channel, and the BER value is close to the BER result under the known channel response, and the channel changes quickly (speed ι6〇km/ Hr)' performance is also acceptable. The above-mentioned invention examples are only for describing the principle and function of the channel estimation method of the orthogonal frequency division multiplexing transmission (OFDM) of the present invention, and do not limit the present invention. Modifications and variations of the above examples are intended to be within the scope of the appended claims. In the Orthodox Crossover Multiplex Transmission (0FDM) system, the requirements for channel estimation (270) are required. It is an accurate, high data rate and low complexity estimator. The reliable symbol estimation method in this month is compared to the C-type pilot signal interpolation method because fewer subcarriers are used to transmit additional There is a high data rate, and at the same time, through the results of software simulation, the reliable symbol estimation method is also better in system performance; in computing, the complexity, in order to reduce the complexity of the operation We use singular value decomposition to estimate the frequency response of the entire channel. As described in ''τ', the embodiment of the present invention can achieve the expected use of the work and the specific structure disclosed, not only has not been seen in similar products. Before the public's request, Cheng e fully complied with the provisions of the Patent Law and the invention of the invention patent towel, please ask for the review, and grant the patent, then the real sense of virtue. 14 200915751 Simple description of the schema] Block diagram f of the system of the present invention: Flow chart of the channel estimation method of the system of the present invention. Figure 3: Working block diagram of the hidden channel estimation method =® Reliable character: The working block diagram of the channel estimation method f: Flow chart of the reliable symbol estimation method of the present invention. FIG. 6 is a comparison diagram of the MSE of the channel estimation of the present invention. FIG. 7 is a channel and an actual channel of the invention (IV).

MSE vs SNR

Figure 8 is a comparison of the present invention at different speeds, at different speeds. Figure IX. The present invention is a comparison of the performance of BERif SNR at moving speed. [Main component symbol description] <The present invention > (110) Signal Correspondence (130) Insert Error Detection Signal (141) Time Domain Signal (151) Transmitter Signal (170) Transmitter (190) Noise (220) Tandem Rotation (240) Fast Fourier Transform (250) Error Detection (270) Channel Estimation (280B) Automatic Gain Control (120) Tandem Rotation (140) Fast Inverse Fourier Transform (150) Insertion Protection Interval (160) Parallel Array (180) Wireless Channel (210) Receiver (230) Remove guard interval (241) Receive signal (260) Parallel to serial (280A) Equalizer (290) Signal opposition

15 200915751 (371) Transmit signal (372) (373) Perform channel estimation (374) (375) Do not perform channel estimation Error detection Update channel parameters 16

Claims (1)

200915751 X. Patent application scope: 1. An orthogonal frequency division multiplexing transmission system, which mainly transmits a modulated subcarrier signal by a transmitting end, and converts a frequency domain signal into a time domain signal by a fast inverse Fourier transform. The guard interval is inserted between the domain signals and the time domain signals are arranged side by side. After the transmitter transmits, the receiver passes through the wireless channel to the receiver. The receiver removes the guard interval after serialization and then removes the guard interval. Then the fast Fourier transform takes time. The domain is converted to the receiving signal in the frequency domain, and then the original receiving signal is obtained through the equalizer, and then restored to the original two-bit information output by the signal echo, which is characterized by: the received signal converted by the fast Fourier transform, The receiving signal can be executed, and the error detection "detects whether the received subcarrier is faulty by error detection" and the channel estimation is obtained by the error detection control. g : Called, the orthogonal frequency division multiplex transmission system described in item i of Li Fanyuan, ▲ 忒 equalizer is the automatic gain controller. V. Please refer to the orthogonal frequency division multiplexing transmission system described in item 1. 4) If the application is “the general inspection of the subcarriers, the orthogonal frequency division described in the channel 1, 1! After the transmission system, the rate response, and then the least squares (10) estimate estimates the channel sea channel frequency response using the minimum mean square error (_) to estimate more accurate (4) The orthogonal frequency division multiplexing transmission system described in item C1 The first of the 6 is a singularity: the crossover frequency and the multi-passing _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 200915751 and insert the error detection signal to become the modulation subcarrier a in the frequency domain. This error signal can be used to detect the error of the received signal. κ A fast inverse Fourier transform, the modulated subcarrier signal is Fast anti-Fourier transform, which converts the frequency domain signal into a time domain signal; and a transmitter transmits the time domain signal via the wireless channel; a receiver 'receives the signal transmitted by the transmitter for demodulation processing ; a fast Fourier transform, will The signal is converted to the frequency domain signal to be 'received in the frequency domain'; 'an error detection is used to detect whether the received subcarrier is faulty or not, and is used to estimate the frequency response of the transmission channel. The test can be controlled by the error detection. 7. The channel estimation device for orthogonal frequency division multiplexing transmission according to claim 6, wherein the binary information in the error detection signal is The signal corresponding method is used for modulation processing, and then is serialized into a serial data by serial transmission. 8. The channel estimation device for orthogonal frequency division multiplexing transmission according to item 6 of the patent application scope, wherein the fast reverse Insert the guard interval between the symbols of the two time domain signals in the Fourier transform to prevent interference between the symbols of the received signals and to make the time domain signals pass through the parallel array. 9. As described in claim 6 The channel estimation device of the orthogonal frequency division multiplexing transmission, wherein the signal received by the receiver is serially converted and collocated to remove the guard interval inserted between the symbols of the two time domain signals. Application According to the sixth aspect of the invention, the orthogonal frequency division multiplexing transmission according to the sixth aspect of the invention provides a channel estimation device, wherein the frequency response in the channel estimation is obtained by the equalizer to obtain the original transmission signal, and then the original transmission signal is restored to the original The two-bit information output device. 11. The channel estimation device for orthogonal frequency division multiplexing transmission according to claim 6, wherein the error detection is a total check sum of subcarriers. The channel estimation device for orthogonal frequency division multiplexing transmission according to item 6 of the patent application scope, wherein the channel estimation first estimates the channel frequency response by least squares (LS) estimation, and then uses the minimum mean square error (MMSE) Estimate a more accurate channel frequency response. 13. A channel estimation device for orthogonal frequency division multiplexing transmission as described in claim 6 wherein the channel is estimated by orthogonal frequency division. The first symbol of the multi-transport (0FDM) transmission signal is the training symbol. 14. A channel estimation method for orthogonal frequency division multiplexing transmission, the steps of which: (a) transmitting a signal, the first symbol transmitted by the transmitter is a known signal, and the receiver receives the known symbol and uses the The signal is estimated and the channel parameters are stored. (b) Error detection. When receiving the data symbol, the receiver can use the error detection signal transmitted by the transmitter to perform error detection of the data symbol, and the symbol is detected without error. (c) Perform channel estimation. The above symbols are represented as reliable symbols and channel estimation is performed using this reliable symbol; (d) Channel parameters are updated - channel estimation is performed to update channel parameters. 15. The channel estimation method for orthogonal frequency division multiplexing transmission according to claim 14, wherein the known signal is a full pilot signal. 19