TWI291817B - Method and system for residual frequency offset compensation of multi-carrier communication - Google Patents

Abstract

A residual frequency offset (RFO) compensation method and a compensation system of a multi-carrier communication system is disclosed. The compensation method of present invention includes two phase-computation steps. The first phase-computation step processes a phase variation of an OFDM data symbol each time to obtain an RFO estimator for compensating a demodulation carrier. The second-phase computation processes a plurality of OFDM data symbols each time to obtain an RFO estimator for compensating the demodulation carrier. The compensation system of the present invention includes: a Discrete Fourier Transformation (DFT) unit for performing DFT on receiving OFDM packages; a phase variation detector connecting to the DFT unit for detecting phase variations of a plurality of OFDM data symbols; and a residual frequency offset compensator connecting to the phase variation detector, which generates the desired RFO estimators in accordance with the phase variations of the plurality of OFDM data symbols and the compensation method of the present invention.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-carrier communication system, and more particularly to a method and system for residual frequency compensation of an orthogonal frequency division multiplexing communication system. [Prior Art] Since multi-carrier communication provides a large transmission bandwidth, many applications such as third-generation mobile communication and asymmetric digital-to-digital (ADSL) are implemented by multi-carrier communication technology. Among them, Orthogonal Frequency Division Multiplexing (OFDM) is a well-known communication multiplex technology. Compared to pure crossover multi-technology (FDM), the face-to-face communication system has a better bandwidth and is more versed in the fourth generation of operations. QFDM communication system application - group positive (four) fresh financial data, reverse discrete leaf conversion (Inverse

Discrete

Fourier Transform (Peng) and Parallel/Parallel Conversion (Conversion) converts the data in the frequency domain into a plurality of IDFT points in the time domain, and then the carrier generated by an oscillator is turned off to the transmitted skew. At the receiving end, the local oscillator generates the same carrier pair to receive the data of the touch, and then the DFT county. Since the receiving end demodulation variable carrier and the transmitting end modulation carrier system are generated by different oscillators, the frequency does not occur, and thus the frequency shift occurs at the receiving end. As a general rule, the receiving end estimates the frequency offset for frequency compensation by transmitting a preamble of the packet. However, whether it is the transmitting end or the receiving end, if the carrier generated by the oscillation H does not reach a stable value in the pre-phase, the frequency offset between the pre-phase estimation and the actual data portion is 1291817. The amount is different, and the residual-residual offset (ResidUal Frequency 〇ffset, _. At the receiving end, the RFO causes (inter-furrier Tn+A f , wm: er carrier Interference, ICI) effect, and improves the packet error. rate.

The first figure shows a communication system receiving end architecture. F is the carrier frequency generated by the local stitcher 100' F1 is the amount of frequency shift estimated from the preamble sequence. For the data of the packet, the carrier frequency F of the local vibration gain (10) is compensated by the frequency shift amount η, and then the OFDM data symbol (_data symb〇1) is demodulated, and then passed through the discrete Fourier transform unit. 2 for the discrete Fu Liye to turn the new te F Furier Transf〇rm, (d) to restore the data signal. In addition to the data processing operation sent to the back-end computing unit, the result of the operation is also output to the phase change detector (10), which detects the simplification data symbol by the Pilot tone inserted in the _ data symbol. Phase change. The phase change side value of the surface data symbol is sent to the processing of the back-end operation unit gamma, and the residual is also input.

The Estimation Hall recommends the calculation, and then the _estimated value ρ2. Afterwards, the modulated carrier F is compensated, and the demodulated variable carrier is changed from F + n at the beginning of _ to f + fi + f2. The second graph shows the relationship of the phase change of the _ data symbol while the demodulation variable carrier remains unchanged. If the influence of noise is excluded, basically, each point can be connected into a straight line (as shown by the dotted line). Among them, the slope of the line (four) RFQ value. For the sake of convenience, we have used English letters to represent the time interval between two consecutive data symbols, and the phase change values detected by the n-view data symbols. If η = 〇 is beautiful, the eye, the gentleman wears y ^ 丝 杂 "" n _ data symbol phase change can be calculated to get the estimated value of RF0 F F2 = ^l

nxT 7 1291817 Alternatively, the phase change estimates of the i-th and m-th OFDM data symbols are respectively (1) and θα), and the estimated value F2 of RF0 should be _ θ{τη)-θ(ί)

The size of ~{m-i)xT ( (or the interval between the i and m (10) Mf symbols) affects the accuracy of the estimation. When η is larger, the error of the detected phase change value has a smaller influence on _ (because the denominator becomes larger), so the larger the η, the more anti-noise ability. However, the larger η, the later the estimated compensation of _ is completed. For example, if η is 5, that is, the phase change value of the 5th 0FDM f symbol is used to obtain (4) the estimated value for carrier frequency compensation correction, then the 5th (the estimated value feedback to the front end compensation is the fastest) It is also the sixth OFDM data symbol to compensate.) Data symbols cannot benefit from _ compensation, and the symbol error rate cannot be effectively reduced. If n is 2, then only the 2nd data symbols are not face-rate compensated. However, φ is short-lived during its time, and the influence of the gamma-difference of the phase change of the second observation symbol on the RFC is estimated. Big. That is, the smaller the value of n is, the lower the anti-noise ability is, and the obtained RF0 estimation value is also less accurate, but the compensation result may be worse. • In summary, how to quickly and accurately estimate the compensation RF〇 at the receiving end to reduce the Ici effect is an important issue for OFDM communication systems. SUMMARY OF THE INVENTION One object of the present invention is to provide a residual frequency compensation method applied to an OFDM communication system, so that a data symbol after receiving a OFDM packet in a preamble sequence can perform RF〇 compensation as early as possible to reduce the influence of ICI. . Another object of the present invention is to provide a residual frequency compensation 1291817 method applied to an OFDM communication system, so that the touch end _ « _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Variable carrier. According to the above, the present invention provides a two-stage operation residual frequency compensation method, which is divided into two-stage operation processing--signal packet, including: in the first stage operation, each time only the current _ = symbol __ processing 'into _ __ listen, _ rectify 夂 carrier 'received in the brother-stage operation, each time to operate on a plurality of (four) symbols to obtain the corresponding residuals, and to compensate the axis to change the carrier. [Embodiment] Some embodiments of the present invention will be described in detail below. However, in addition to the detailed description, the present invention can also be widely practiced in other embodiments without limitation, which is subject to the scope of the subsequent patent application. The invention discloses a two-stage operation _ residual _ compensation method for performing the estimation of the win. The two-stage differentiation _ estimation compensation system is based on different demand considerations, in which the iw is also used to avoid the 〇 _ minus the packet towel, and the w (4) M data symbol (6) effect affects the packet error rate, and the focus of the consideration is compensation. speed. In the second stage, in order to eliminate the influence of the small fresh offset on the receiving end, the consideration is focused on the accuracy of the compensation. Assuming that the prior art is the first-time compensation for the kth 〇_ data symbol, it is known from the foregoing that the first to the kth 喔 data symbols are not compensated for the shuffling demodulation, which is affected by the (6) effect than the kth The _ _ face familiar with the practice. (4) The first-stage operation can also perform RFO compensation before 9 1291817 # k OFDM data symbols, and the k-th face f symbol can obtain the same RF0 estimation result as the prior art. The third figure shows the application of the first-P-segment RF0 estimation operation of the present invention, and (4) the relationship between the M data symbols and their phase change values. If the initial demodulation variable carrier (8)(1) is cancelled without RF0 compensation, the phase estimation value obtained from the jth and kth OFDM poor symbols should be 0 ‘(1), 0 ‘(1). However, in this example, the i, j, and k 0FM data symbols are each compensated once, so that the demodulated Lun carrier frequency changes 'so that Θ(4) and η are no longer a straight line, and after each brain compensation The slope changes. When the slanting material is smashed, the table has another _, and the carrier frequency of the scale transmission/reception end is the same. The frequency of the demodulated variable carrier is F in the end of the sequence until the i-th (fourth)_data symbol. The phase estimate of the i-th OFDM data symbol is 0 (1), so the estimated value is one F2 i = dao

After ixT ® , the compensation demodulation variable carrier is F+FHF2J. The rfo estimated value F2J of the jth OFDM data symbol is F2_j=^m

As described above, the RF〇 compensation has been performed after the i-th OFDM data symbol, and the estimated phase Θ(1) at this time is not related to the phase estimation value of the original demodulated variable carrier as a simple 0) and θ' The offset of (1) is caused by the influence of the former * _ estimated value F2 - i, and the offset caused by F2" is added back to obtain the original phase offset 0' (j). Among them, because the F2-1 is called 1291817 to the jth GFDM data symbol, the offset of the influence is (F2))x(ji)T, so <9'(j) is ~(j)= + (F2 - i)x(ji)T and the value of the new RFO F2 j is F2 / = ^ 〇{j) + (F2 __ i)x (j ^ j)T _ 9<^j) + ^ x (<j ^i)T JXT jxT - jxT then backfire 2"' compensation solution (four) carrier is just +F2"·. Then, rf〇 compensation is performed after the kth OFDM data symbol. Similarly, F2J affects the j+1th to kth 0FDM data symbols, plus the previous F2-i affects the offset of the i+1th to jth FDM data symbols, so the actual phase detection is obtained. The relationship between the value and 0'(k) should be θ 〇〇 + (F2 - i) x (H) T + (F2J) x (k - j) T and the value of the new RFO F2 - k is F2 k = hidden kxT ^k^r =

-j)T

η/ΐ\ θ{ί) Θ(/)Η / — AT7 咐)+ #心· — 〇Γ + (—— -------j 乂T

)x(k-j)T

The depreciated value F2_k obtained by kxT or more is the same as the value that is still demodulated at the carrier frequency and the first RF estimator is estimated from the material data.

The finished algorithm flow is as follows. 1. Detecting the phase of the i-th OFDM data symbol F2: changing 0(1) with ixT, obtaining the RF0 estimated value F2

Cs) 11 1291817 2. Feedback F2 compensation demodulation variable carrier 3. _ j-th 0_赖 symbol of her chopping (]·), get _ estimated value hit “θ'(7·) θ(7)沁-ΟΓ

jxT jxT

[• Feedback F2 compensation demodulation variable carrier. 5. _ k-th OFDM data symbol phase change (10)), get _ estimated value hit . '(7) + learn dr F2 = kxT 6 · feedback F2 compensation demodulation variable carrier

Τχψ )x(k- j)T

kxT It must be emphasized here that the first-p phase difference is not limited to the three compensations in the embodiment. However, the more the number of compensations, the more memory _ the previous multiple brain estimates, or the phase change values of the individual OFDM: body symbols, and the related calculations and _ estimators will become more complex. In the case of the car 乂佳实 W, the first three OFDM data symbols are taken as the first stage of the RF 〇 estimation, ie i, j, k are 1, 2, 3 respectively. In this way, by the method of the first stage of the present invention, the first few zero data symbols in the 0FM signal packet can obtain the RF〇 compensation in time and reduce the (6) effect. Furthermore, although the embodiment uses the phase change value detected during the previous liver hepatic compensation calculation to calculate the RFO estimate of the current time, it can also be obtained by calculating the RF threshold value of each feedback, the present invention. Not limited. After the first stage operation is completed, the second stage operation is entered until the end of a FDM packet. The second P Baifeng is also to eliminate the small residual frequency offset, so the selected OFDM data symbol interval is larger.

Cs) 12 1291817 'The fourth picture shows an embodiment of the second stage operation (assuming that the nth OFDM estimates the RFO value to be compensated midway through n+1 OFDM). As shown in the figure, the second-stage operation performs the -times compensation every d 〇FM data symbols, and divides the difference between the two her data symbols by the time interval between the two to obtain the _estimated value. The obtained estimated value is added to the previous brain value, and the demodulated variable carrier at the receiving end can be further corrected. If the phase difference between the two is Φ=0(η+ά)~0(η) • Therefore, the estimated compensation RF0 is

The RF0 estimate obtained by dxT is added to the RF-threshold of the first stage, and the demodulation variable carrier at the receiving end can be further corrected. Alternatively, a larger d value such as d, (d, greater than d) is substituted as a denominator to obtain a better anti-noise capability. It should be noted that the present invention is not limited to the magnitude of the d value and whether it is a fixed constant. * Generally, the larger the d value is, the lower the degree of noise is affected, and the RF0 estimation value is also more accurate. Furthermore, the phase change difference Φ may be based on a linear regression line of d OFDM data symbol phase change values (e.g., a straight line obtained by a least squares method (LMS)) to obtain a phase change difference. It should be noted that since the first stage operation has been compensated for the demodulation variable cutting wave first, basically the phase change value in the second stage operation should be as shown in the fourth picture, and the increase and decrease amplitude should be relatively flat compared to the first stage operation. (0 (n+d)« 0 (n)), however, the phase calculation limits 丨0 (η) | < , so even if 0(n+d)«0(n), it may become 0(n) +d)«0(n) +2 . "1, ί e {-1,0,1}, 8 13 1291817 So there must be a way to remove 2疋i.

In the redundancy decision, the Φ value is further subtracted or added by 2; r Φ4(ηΜ)-0(n)−2; ri,i when 丨Θ(n+d)− 0 (η) I is greater than π , we calculate cD_f root shot (four) chest (4) U is greater than /. That is: ~1,0 or 1 i=sign{0(n+d)-6>(n)} otherwise i= 0

Combining the descriptions of the first-stage and second-order operations in the above embodiments, the complete residual fresh-faced green records are compiled. Thanks to the invention of the financial method, we can quickly and accurately estimate the compensation _ to reduce the Ια effect and increase the communication _ _ performance. The above is only the preferred embodiment of the present invention (4), and the scope of the patent application is not limited to the scope of the invention; any other equivalent changes or repairs performed without departing from the spirit of the present disclosure shall be included. In the scope of the patent application. [Simple diagram of the diagram] The first picture is the receiving end architecture of the OFDM communication system; the second picture is the schematic diagram of the relationship between the OFDM data symbol and the phase change; the third picture is the first stage operation of the invention, and the (4) M data symbol and phase change relationship The schematic diagram of the second stage operation of the present invention is a schematic diagram of the relationship between the FM data symbols and the phase. 14 8 1291817 [Key component symbol description] 100 local oscillator 102 discrete Fourier transform unit 104 phase change detector 106 residual frequency estimator

Claims (1)

1291817 X. Patent application scope: 1. A residual frequency displacement compensation method for a multi-carrier communication system, including · performing-first-order financial calculations, each money--currently re-characterizing her change, obtaining-first-residual frequency estimation It is difficult to uniquely the first-residual scale-value-receiving surface-thixo-carrier, where the first------------------------------------------------------------------------------------------- The plurality of data symbols are used to obtain a second residual frequency estimate and the demodulation variable carrier is compensated by the second residual frequency estimate. 2. The residual fresh displacement compensation method of the multi-carrier communication system as described in the scope of the patent application is as follows: wherein the current data symbol and the plurality of data symbols comprise orthogonal frequency division multiplex data symbols. The residual frequency frequency displacement compensation method of the multi-carrier communication Wei described in the third item, wherein the first stage operation performs three operations, including: Obtaining the phase change 0 (i) of the i-data symbol of the first price/Bei, and compensating the demodulation variable carrier according to the formula = color standing, ixT residual frequency estimated value F2; (j), compensating the demodulation according to the formula Variable carrier; price measurement - phase change of the jth data symbol 0 F2" (/K learning X(W)r ... - obtaining the first residual frequency estimate F2 and detecting a kth data symbol The phase change θ (k) is determined according to the formula 8 16 1291817 η(ΐΓλ, θ(ϊ) eU) + —x(ji)T F2. The _ residual frequency estimate is taken ————~_ j 乂T kxT The value F2 compensates the demodulation variable carrier; where T is the time interval of two data symbols. The residual frequency displacement compensation of the multi-carrier communication line described in Item 1 is performed by The sound signal is inserted in the data symbol to obtain the phase change value. 5. The residual frequency shift compensation method of the multi-carrier communication system as described in the scope of the patent application is one of the packets before the sequence is obtained. The frequency shift compensates the carrier generated by the local oscillator to obtain the starting carrier frequency. The system of the i-th description of the money wave _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7. A multi-carrier pass-sequence residual frequency shift compensation method as described in claim 6, which causes the second stage operation to obtain the second residual estimate according to the formula F2= Measured value F2, where Θ(8) is the phase change value of the -^ teacher symbol, coffee) is the phase change value of the _th data symbol, τ is the time interval of the two data symbols, and d is a positive integer. ... ^Residual frequency displacement compensation method of the money division multiplexing communication system described in claim 7 of the patent application, in the second stage operation, the nth data symbol and the n+d data symbol 8 17 1291817 If the phase change difference is greater than π, the phase change difference is subtracted by less than -π, and the phase change difference is added by 2 7 Γ. • A residual frequency displacement compensation system for a multi-carrier communication system, which is divided into two-stage arithmetic processing, a signal packet, comprising: a discrete Fourier transform unit that receives the signal packet for discrete Fourier transform operation; The detector 'connects the discrete Fourier transform unit to detect a phase change value of one of the plurality of data symbols of the signal packet; and a residual frequency estimator connected to the phase change detector according to the phase of the plurality of data symbols The change value takes a residual frequency estimate. 10. The residual frequency displacement compensation system of the multi-carrier communication system of claim 9, wherein the multi-carrier system comprises an orthogonal frequency division multiplexing communication system. 11. The residual fresh displacement compensation system of the multi-link communication secret described in Item 9 of the application, wherein the residual frequency estimator performs a phase change value of a current data symbol each time in a first stage operation- Processing, and obtaining a residual frequency estimation value obtained by demodulating the current data symbol 7 with the initial carrier frequency to feedback the demodulation variable carrier. The shift compensation system obtains the residual 12·If the multi-carrier pass scale system of the silk frequency system described in the nth item of the full-time application is applied, the first stage operation performs 3 operations, including: detecting an i-th data symbol The phase change 0(i) compensates the demodulated variable carrier according to the formula = ^ i 乂T residual frequency estimated value F2; detects the phase change of the data symbols θ0) according to the formula 8 18 1291817 ^0 ) + x (j - {\f F2 = —— 卜 T obtains the residual frequency estimate F2 to compensate the demodulated morphing wave; detects the phase change Θ (k) of the kth cultivating symbol, and according to the formula F2 j 乂T > (k - j) T kxT obtains the residual frequency estimate F2 to compensate the demodulation variable carrier; wherein T is the time interval of two data symbols. The carrier frequency reduction surface residual frequency displacement compensation, , · charging, the residual frequency estimator in a second stage of operation... After a shipment has been 俨 $ 丨 μ * set a number of data symbols to open to a Corresponding residual frequency estimate to compensate for the demodulation variable carrier. 14. As stated in claim 13 The residual frequency displacement of the wave communication system compensates Li Tong: the operation of the second stage is based on the difference between the phase difference of the first and last two beet symbols divided by the time interval of the plurality of data symbols. 15. The residual frequency displacement compensation system of the multi-carrier communication system as described in claim 13 wherein the operation of the second-stage operation is based on the formula - '一Τ^τ一'' The side value F2, the seventh reading phase change value '(10) delete - the phase change value of the _th data symbol, τ is the time interval of the two-face number and d is a positive integer. 16. As claimed in item 15 The residual frequency displacement compensation system of the multi-carrier communication system is described in the second stage of the operation of the nth number and the symbol of the teacher 19 J291817 The position and the difference are larger than that; raf 'subtracts her variation from the difference. When it is less than _π, the phase difference is added by 2ττ. 17 • Multi-carrier communication as described in claim 9 The residual frequency offset compensation system of the system first obtains the phase change value by the sound signal inserted in the data symbol. 18. The residual frequency shift of the multi-carrier communication system as described in claim 9 a compensation system, wherein a frequency shift compensated local oscillator generates a carrier's frequency by the pre-sequence of the signal packet to obtain the starting carrier frequency. 20