TWI352520B - Orthogonal frequency division multiplexing system - Google Patents

Description

1352520 IX. Description of the Invention: [Technical Field] The present invention relates to a channel estimation apparatus and method for an orthogonal frequency division multiplexing transmission system, and more particularly to tracking a perfect channel estimation apparatus and method Rapid changes in the channel to enhance system performance. [Prior Art] Many studies have been proposed in the wireless communication of the Orthogonal Frequency Division Multiplexing (OFDM) system. In mobile communication systems, wireless channels are usually frequency selective and time varying, although orthogonal frequency division multiplexing (〇FDM) systems have good resistance to frequency selective fading. The precondition is that the receiving end should have a good = orthogonal one transmission [_ continuation, in #· $ 4+ often in the transmission wheel (four) Γ, in order to the station (four) characteristics, the pass is the pilot signal known to the receiving end or The training signal and the pilot signal number are used for channel estimation, so in order to increase the information of the transmission channel characteristics when the pure end is used for the pilot. In the use of pilot signal transmission [_] wide 'navigation signal only use these subcarriers in the orthogonal frequency division between the specific subcarriers, the channel estimation is only for the estimation of the subcarrier information, and then Using these estimates, it is mostly the interpolation method used for the subcarriers of the non-navigable signals. However,

During operation, many orthogonal frequency division multiplexing transmissions [0FDM 5 1352520: First, please refer to the first figure, which is the block diagram of the orthogonal frequency division multiplexing transmission (OFDM) system of the present invention. After the information of the two bits is modulated, that is, the signal is corresponding (110), after the serialization of the serial data (120) becomes the serial data, the 're-insertion error detection signal (130) is obtained. The frequency domain of the modulated subcarrier signal is W. This error signal can be used to detect the error of the received signal. The modulated signal is then converted to the frequency domain by fast inverse Fourier transform (140) [IFFT]. Convert to time domain signal (141) [ time domain ] χ(«): x(n) = IDFT{x(k)} = ^ X(k)ej2nkn/N, A=0 « = 0,1,.· iV-1 (-) where # is the number of subcarriers of the Orthogonal Frequency Division Multiplexing (OFDM) system.

In order to prevent the inter-symbol interference phenomenon of the received signal, a guard interval (150) is usually inserted between the symbols of the two time-domain signals to become a transmission signal of the orthogonal frequency division multiplexing (OFDM) system. (151)xg(«):

X x(N + n\ n = -Ng, -Ng x(4 w = 0,1,···, - 1 where is the length of the insertion guard interval (150). Insert the time domain of the guard interval (150) After the signal is transmitted to the receiver (210) via the parallel channel (160) and transmitted through the transmitter (170), the signal received by the receiver can be expressed as: 7 yg(n) = («) ® h(n)+ w{n) (c) _ where is the impulse response of the channel, but it is additive

Additive White Gaussian Noise (AWGN)® is a convolution symbol for two signals. The demodulation step at the receiving end is to remove the guard interval (23〇) after serial concatenation (22〇), and then up-convert the time domain to the frequency domain through fast Fourier transform (24〇) [ IFFT]. On, become the receiving signal in the frequency domain (241) Yik):

r(k)=, DFT{y(n)}=±^y^ ~J2nbt / N moxibustion=0,1,1 (4) In the received signal, the error detection of the received signal (250) can be performed to detect Measure whether the received signal has an error. It is assumed that the length of the guard interval is greater than the length of the channel pulse (four)', so there is no (8) phenomenon between the adjacent symbols of the orthogonal splitter transmission [_Μ], so it is demodulated. The sign r(々) is: m = xik)H (k)+ I(k)+ w = (5) ^The frequency response of the channel is just formed by the Buhler effect of the transmitter and receiver. W, _ is the Fourier transform of the coffee. In the = (5), we estimate the frequency response of the channel through the channel estimation, and then pass the equalization control (2_[AGC] to get the original passback, and then receive the signal. The transmission signal is male), so the final (six) ring = worm, which is the estimated channel frequency response. The received signal/(4) is then restored to the original two-bit information output via the signal opposition (290). Please refer to the second figure again, which is a flowchart of the estimation architecture of the orthogonal frequency division multiplexing transmission (OFDM) system of the present invention, and the steps are as follows: (a) transmitting signal (371) - transmitter number A transmitted symbol is a known signal, and the receiver (210) receives the known symbol, uses the known signal for channel estimation (270) and stores channel parameters; (b) error detection (372) - at When receiving the data symbol, the receiver (210) may use the transmitter (170) to transmit the inserted error detection signal (130) to perform error detection (250) of the data symbol, and detect whether the symbol has an error; (c) Channel Estimation (373) or No Channel Estimation (375)_The above symbols are represented as reliable symbols and channel estimation is performed using this reliable symbol; (d) Update channel parameters (374)_by channel estimation ( 27〇) to update the channel parameters. One of the embodiments of the channel estimation method is that after the receiver (210) receives the signal (241) via the fast Fourier transform (240) [FFT], channel estimation (270) is required to obtain the channel response solution. Original signal, we transmit a set of orthogonal frequency division multiplexing (OFDM) symbols that are all pilot signals at the beginning of the transmission signal to estimate the unknown channel response 'in order to reduce the error of estimation'. First of all, we use The minimum mean square error [MMSE] estimation method, the orthogonal frequency division multiplexing transmission (OFDM) transmission signal starts with a set of all pilot signals such as: pilot signal « = 0,1, 2, ...,#- 1 (7) Ϊ352520 The estimation method used is to estimate the channel frequency response by the least square [LS] estimation method;

= XpY =-virtual Zfil quasi-1) _work) A(1) 4(#-1)

The rush is the received signal, and the channel response estimated by the least square [LS] estimation method is reversed; since the least square [LS] estimation method is susceptible to interference by the noise (190), it is at a minimum. The square [LS] estimation method then uses the minimum mean square error [MMSE] estimation method for more accurate channel estimation (270): ΛΗΡ, mmse

Rfffi RJ zj ntlP, LS nPJ^nPJS

(nine)

Where σ„2 is the variance of the noise (190) rfr), and the matrix of the common variance is

(10) It can be seen from equation (9) that as long as the transmitted pilot signal or training symbol is changed, the inverse matrix operation must be performed, and the complexity of the minimum mean square error [MMSE] estimation method is also improved. The average of the transmitted symbols can be used to reduce the complexity of the minimum mean square error [MMSE] estimation method, replacing the (X〆/)-1 in equation (9) with the expected value, and assuming that on the signal constellation, each The probability of a single signal is the same, so the reliable symbol channel estimation method proposed by 10 ¢ 352520 paper is better than the interpolation method. When the speed is V=50 km/hr and V=100 km/hr, we At the same time, it is found that the reliable symbol channel estimation method can track the change of the time-varying channel because of the slow change of the channel, and the BER value obtained is close to the BER result under the known channel response, and the channel changes rapidly. (speed 16 〇 km / hr), its 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 are not limited to the invention, and therefore, those skilled in the art would like to Modifications and variations of the examples are intended to be within the scope of the appended claims. In the positive-father multiplexed transmission (0FDM) system, the estimator of the channel estimation (270) requires accurate, high data rate and low complexity, and the reliable symbol estimation method proposed by the present invention is compared. The pilot signal interpolation method in the c〇iQb_type state has a higher data rate because fewer subcarriers are used to transmit additional information. At the same time, through the results of software simulation, it is better to estimate the performance of the system. In the calculation of the noise, we use singular value decomposition to estimate the frequency response of the entire channel. . In summary, the embodiment of the present invention achieves the expected use of work Φ 'and the specific structure disclosed therein, not only has not been seen in the same product ^ and has not been disclosed before the middle of the request, Cheng has fully complied with the provisions of the Patent Law If the invention patent is issued with the | ^ ' level method, it is expected to be reviewed, and the patent will be granted. 14 1352520 Error Detection Update Channel Parameters (371) Transmit Signal (372) (373) Perform Channel Estimation (374) (375) Do not perform channel estimation 16

Claims (1)

Patent application park: 1. A kind of orthogonal tool-frequency multiplex transmission system, which mainly transmits the tone, the sub-carrier, and the signal ' to convert the frequency domain signal into fast reverse Fourier transform. The domain signal inserts a guard interval between the two time domain signals, and the time domain signals are paralleled and serialized. After being transmitted by the transmitter, the receiver passes through the wireless channel to the receiver, and the receiver removes the guard interval after serializing and paralleling, and then removes the guard interval. By fast, Fourier transform converts the time domain up to the frequency domain to become the received signal, and then, by equalizing n, the original received signal is obtained, and then the signal is opposed to be restored to the original binary information output. : < . The old man is converted by the fast fan Fourier transform, can perform the error detection of receiving H 'error detection to detect whether the received subcarrier has error occurred' and the channel estimation is obtained by error detection control The frequency responder of the channel. 2. The orthogonal frequency division multi-transmission system as described in item 1 of the U-profit range, wherein 'the equalizer is an automatic gain controller. 3. As described in claim 1 An orthogonal frequency division multiplexing transmission system, wherein the error detection is a total checksum of subcarriers. 4. The orthogonal frequency division multiplexing transmission system according to claim 1, wherein the Estimate that the channel frequency response is estimated by least square (LS) estimation, and then the minimum mean square error (MMSE) is used to estimate a more accurate channel frequency response. 5. As stated in the first paragraph of the patent application scope Cross-frequency multiplex transmission system, in which 'the first symbol of the IF cross-frequency transmission (OFDM) transmission signal is the training symbol. 6. Channel estimation of the positive-father multiplex transmission The measuring device comprises: an error detecting signal, converting the binary information into a serial data "352520 channel estimating device, wherein the frequency response in the channel estimation is obtained by the equalizer to obtain the original transmitting signal; And then restore it to the original two-bit information output. 11. The channel estimation device for orthogonal frequency division multiplexing transmission according to claim 6, wherein the error is measured as a subcarrier. Total check and. 12. The channel estimation device for orthogonal frequency division multiplexing transmission according to claim 6, wherein the channel estimation first estimates the channel frequency response by least squares (LS) estimation, and then uses the minimum Mean Square Error (MMSE) estimates a more accurate channel frequency response. 13. The channel estimation device for orthogonal frequency division multiplexing transmission according to claim 6 of the patent application garden, wherein the first symbol of the orthogonal frequency division multiple transmission (OFDM) transmission signal is used in the channel estimation For training symbols. 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 Know the signal to estimate the channel and store the channel parameters; (b) Error detection—When receiving data symbols, the receiver can use the error detection signal transmitted by the transmitter to perform error sampling of data symbols 'detecting no errors in the symbol; (c) performing channel estimation - above The symbol is represented as a reliable symbol and channel estimation is performed using this reliable symbol; (d) Channel parameters are updated - channel estimation can be 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