CN1334655A - Filling method of protecting gap in orthogonal frequency division multiplexing modulation system - Google Patents
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Abstract
The invention relates to information transmission, especially information communication in the Internet, digital television, data broadcast application etc. When the time delay exists in the transmission channel using orthogonal frequency division multiplexing modulation (OFDM), the PN serial instead of protecting interval (zero protecting interval) is utilized to realize the antimultipath method of transferring signal and time estimating method for the start and termination of transferring signal. Each signal frame provides pseudo random m PN serial; the convolution signal is composed of receiving signal and PN serial. The start and termination of PN serial is recognized by the receiving signal substracting the convolution signal. The PN serial is used in time recovering, carrier wave recovering, channel estimation, frame synchronization and substitution of the protecting interval in OFDM.
Description
Technical field
The invention belongs to the transmission of Information field, particularly the ICT (information and communication technology) in internet, Digital Television, data broadcasting and other related application.
Background technology
The core of communication system is how to improve efficiency of transmission and reliability in limited bandwidth.Therefore, in Digital Television or computer system, the payload of each transmission frame or valid data part should account for the big as far as possible part of transmission frame, so that improve the efficiency of transmission of system.Simultaneously, system should be able to discern and compensate the characteristic variations of transmission channel, comprises the time delays of each transmission frame, so that realize reliable transmission.
Realize above-mentioned high efficiency and high reliability, need system can be from the signal specific of Channel Transmission recovered clock, the reinsertion of carrier and the estimation characteristic of channel, and this signal is also as the protection of transmission signals at interval and frame synchronization.
Summary of the invention
The objective of the invention is by pseudorandom or pseudo noise (Pseudo Noise are provided in each transmission frame, PN) sequence satisfies the needs of recovered clock, the reinsertion of carrier and estimation channel, and the PN sequence here satisfies orthogonality and closure for algebraic operation (for example convolution, Boolean add and section internal shift).The received signal (through Channel Transmission) and the PN sequence of one or more selections are carried out convolution, obtain convolution signal.Analyze this convolution signal, can discern beginning or concluding time, the identification channel time delay of PN sequence and recover timing.The carrier frequency of received signal can be recovered from the symbol (bit, nibble, byte etc.) that constitutes the PN sequence, and realizes that signal frame is synchronous, estimates transmission channel characteristic from time delay and corresponding phase shift.Above-mentioned PN sequence is positioned at signal frame, and as the protection interval of OFDM (OFDM) modulation scheme, the protection that is equivalent among the common OFDM has become zero at interval simultaneously.All these characteristics concentrate in together, and can realize the OFDM demodulation, and obtain high efficiency and high reliability.
The present invention proposes protection fill method at interval in a kind of orthogonal FDM modulation system, under the life period time-delay situation, replaces protection at interval with the PN sequence in the signal channel of OFDM (OFDM) system, may further comprise the steps:
1) provides pseudorandom m sequence PN (t; K) (k=1 ..., K; K 〉=1) collection, the convolution signal of wherein any two sequences satisfies PN (t; I) * PN (t+ Δ t; J)=and δ (Δ t) δ (i, j), δ (Δ τ) is the δ function here, and δ (i, j)=0, unless i=j;
2) the additional sequence PN (t that selects behind at least one signal frame that will transmit; K), constitute the signal frame of filling;
3) by the signal frame of at least one filling of Channel Transmission, the transmission signals that receives may have uncontrollable time delays Δ t;
4) receive a reception version Rc (t) of transmission signals, and form convolution signal:
Here Δ t is the incremental time of selecting, and k
1And k
2Satisfy 1≤k1≤k2≤K; Form residual signal Rc (t; Rem)=Rc (t)-Rc (t; Δ t; Comp); And at least one sequence PN (t in received signal Rc (t); K) (k=k1, k1+1 ..., adjudicate on time started k2).
The method of the invention can further comprise determines described at least one sequence PN (t; K) carrier frequency.
The method of the invention can further comprise at least one parameter of using described PN sequence to estimate described transmission channel.
The method of the invention can further comprise with at least one described signal frame with described PN sequence and replaces at least one protection at interval.
The method of the invention can further comprise uses at least one PN sequence, and it has one of described filling signal frame, for described filling signal frame provides time synchronized.
The present invention proposes a kind of system that adopts protection fill method at interval in the orthogonal FDM modulation system, under the life period time-delay situation, replaces protection at interval with the PN sequence in the signal channel of ofdm system; Comprise a programmable computer, further comprise:
Pseudorandom m sequence PN is provided (t; K) (k=1 ..., K; K 〉=1) collection, the convolution signal of wherein any two sequences satisfies PN (t; I) * PN (t+ Δ t; J)=and δ (Δ t) δ (i, j), δ (Δ τ) is the δ function here, and δ (i, j)=0, unless i=j;
The additional sequence PN (t that selects behind at least one signal frame that will transmit; K), constitute the signal frame of filling;
At least transmit the signal frame of a filling by transmission channel, the transmission signals that receives may have uncontrollable time delays Δ t, and one that receives transmission signals receives version Rc (t), and forms convolution signal:
Here Δ t is the incremental time of selecting, and k
1And k
2Satisfy 1≤k1≤k2≤K; Form residual signal Rc (t; Rem)=Rc (t)-Rc (t; Δ t; Comp); And at least one sequence PN (t in received signal Rc (t); K) (k=k1, k1+1 ..., adjudicate on time started k2).
Described computer can further be programmed for determines described at least one sequence PN (t; K) carrier frequency.
Described computer can further be programmed at least one parameter of using described PN sequence to estimate described transmission channel.
Described computer can further be programmed for at least one described signal frame with described PN sequence and replace at least one protection at interval.
Described computer can further be programmed for and use at least one PN sequence, and it has one of described filling signal frame, for described filling signal frame provides time synchronized.
The present invention can realize the OFDM demodulation, and obtains high efficiency and high reliability.
Description of drawings
Figure 1A and 1B have described the optional mode of traditional OFDM frame structure.
Fig. 2 A, 2B and 2C have described the frame structure mode of utilizing the PN sequence proposed by the invention.
Fig. 3 has described the composition of frame synchronization PN sequence.
Fig. 4 has described a typical transmission signals.
Fig. 5 A and 5B have described the non-overlapped component of desirable signal frame sequence.
Fig. 6 A and 6B have described typical multipath and have disturbed (pecked line) influence to frame synchronization sequence and data division.
Fig. 7 has described the signal flow graph of implementation procedure of the present invention.
Fig. 8 and 9 has described and has been used for the system that transmits and receives of the present invention.
The specific embodiment
Usually first and second kinds of formations of OFDM frame format as shown in Figure 1A and 1B. In the form of Figure 1A, DFT (or FFT) piece 13B is positioned at after the Cyclic Prefix section 13A, and Cyclic Prefix is as the protection interval of DFT. OFDM transfers System needs to use protection interval or its equivalent, receives the multipath signal that may exist in the signal in order to offset, and prevents intersymbol Crosstalk. In the form of Figure 1B, the zero padding section is followed in DFT piece back, and this zero padding section is used as the protection interval of DFT piece,
Pseudorandom of the present invention or pseudo noise PN sequence (the m sequence of coding) are used between the protection of OFDM modulation Every in. This m sequence is the symbol sebolic addressing of certain-length, is generally the set of " 0 " and " 1 ", and it satisfies three needs: 1) number of dissimilar symbols (such as data " 0 " and " 1 ") is etc. general; 2) boolean of any two m sequences With, and be still the m sequence after the cyclic shift of Random m-sequence; 3) two m sequence MS (t; I) and MS (t; J) Convolution satisfies orthogonality condition:
MS(t＋Δt；i)*MS(t；j)＝δ(Δt)·δ(i，j) (1)
Here δ (Δ t) is that the δ function revised is (for | Δ t|＞Δ t1, δ (Δ t)=0), δ (i, j) is Kronecker δ function (=0, unless i=j). If the m sequence does not rely on call number i, perhaps call number is well-known full Foot i=j, Kronecker δ function can be ignored so. Usually the m sequence length elects 2 asJ-1, J is for just whole here Number, for example J=7,8 or 9.
Subset to all m arrangement sets all is suitable for, the m sequence PN (t of as noted above coding; J). (coding) The set of PN sequence can be adopted walsh code or similarly Haar code generation. Produce the side of walsh code or Haar code " data compression " that method is write referring to T.J.Lynch (Data Data Compression, Van Nostrand, New York, 1985, pp.79-85) and K.Smolik, J.E.Wilker " in the wireless/personal communication CDMA use " of writing (Applications of CDMA in Wireless/personal Communications, Prentice Hall, Upper Saddle River, New Jersey, 1997, pp.23-39.). Also can produce and use other set of PN sequence, As long as it satisfies equation (1).
The PN sequence is M rank m sequences, and is well-known, available Fibonacci Linear feedback shift register (Linear Feedback shift register, LFSR) realize. For LFSR and M=9, a suitable proper polynomial is:
P(x；4∶9)＝1＋X
4＋X
9 (2)
Initial mask has determined the primary condition of LFSR, thereby has determined the phase place of the PN sequence of generation. Here also can Select other suitable proper polynomial, and corresponding exponent number M.
In first kind of embodiment of the present invention shown in Fig. 2 A, the PN sequence 23A of coding comprises or replaces shown in Figure 1A Cyclic Prefix section 13A, 21A links to each other with the DFT piece. In the second embodiment of the present invention shown in Fig. 2 B, coding PN sequence 23B comprise or replace the zero padding section 11A shown in Figure 1B, 21B links to each other with the DFT piece.
In the third embodiment of the present invention shown in Fig. 2 C, the PN sequence 23B of the coding in Fig. 2 B is included in Among the frame sync segment 26C, follow by DFT piece 21C. Frame sync segment comprises an optional preamble 24C among Fig. 3, and is tight Follow PN sequence 23C thereafter and closely follow PN sequence optional rear synchronous 25C afterwards. Preamble, PN sequence and after Synchronous length is respectively F1, F2 and F3, and F1 and F3 are chosen as nonnegative integer here, and selection F2 is positive integer. Frame Sync section length is F1+F2+F3 symbol.
In the form shown in Fig. 2 C, in order to realize that preamble and rear sync section are not any selections synchronously fast and reliably . The most preferably the selection of preamble and rear synchronizing symbol to make frame that the arbitrary order set of F2 continuous symbol consists of with Step section (length is F1+F2+F3) also is the PN sequence; More particularly, being arranged in frame sync segment F1+1 among Fig. 3 arrives " original " PN sequence of F1+F2 position forms new PN sequence after passing through some or cyclic shift, as front same Step and rear synchronous. Frame sync segment if exist in signal frame, can characterize with relevant PN sequence.
Here used information transmission unit is signal frame, and it comprises shown in Fig. 2 A and the 2B frame 21A or 21B in the form, Perhaps the frame sync segment 26C in the form and frame 21C shown in Fig. 2 C. Frame 21A, 21B or 21C comprise the DFT piece And header, header has the signal code (Octets, bytes, Nibbles or bit) of fixed number, and it provides Frame source, frame destination, sequence number, frame length, data type (supervision, information, unnumbered), payload user data are big Little, flow process control, message priority, Error detection and correction, other check information etc., the most preferably frame has solid Sizing is perhaps in the magnitude range of regulation.
Suppose that Tr (t) is the frame signal of representative transmission, as shown in Figure 4. Come by separating the PN sequence relevant with analysis The identification signal frame, this need to know beginning and the end position of each PN sequence in the signal frame sequence exactly.
The signal frame sequence of desirable correction can be decomposed into two non-overlapping sequence: first sequence-PN sequence PN (t; I; Ideal) and second sequence-DFT piece DFT (t; I; Ideal), shown in Fig. 5 A and 5B.
In any case in practice, the signal frame of each transmission postpones if having time, comprises the multipath signal distortion, for PN Other data segment difference in sequence and the signal frame is come, and needs quite regularly accurate. Fig. 6 A and 6B described as Impact after the upper increase of frame synchronization shown in Fig. 5 A, the 5B and the DFT time delay. Although desirable correction PN sequence PN (t; I; Ideal) when t=`` (i), sport 0, receiving sequence PN (t; I; Rc) regular hour t`` (i)≤ Reduce to lentamente 0 in t≤t``` (i+1), as shown in Figure 6A. Similarly, although desirable DFT piece DFT (t:i: Ideal) sport 0 when t=` (i+1), the DFT of reception (t:i:Rc) is at regular hour t` (i+1)≤t Reduce to lentamente 0 in≤t```` (i+1)＜t`` (i+1), shown in Fig. 6 B. Therefore, receiving terminal want t=t` positioning time (i: Rc) and t=t`` (i:Rc) very difficult, and these time correspondences and are not had opening of the PN sequence that receives in the multipath situation Begin and end position.
H (t) is that the pulse δ (t) of transmission channel TC (has infinitely small width Delta t1Correction δ (t) function) ring Should. Signal Tr (t) receives signal Rc (t) and is expressed as signal transmission Tr (t) and pulse after transmitting by channel TC The convolution of response signal h (t):
Rc(t
2)＝Tr(t
1)*h(t
2-t
1) (3) here * represent two signal Tr (t1) and h (t2－t
1) convolution and related operation. And Tr (t) signal is
Tr (t)=PN (t; I; Ideal)+mp (t) (t ＇ (i; Rc)≤t＜t ＇ (i+1; Rc) (4) Here, mp (t) expression multipath interference components. Because the orthogonality of each PN sequence is then provable in the equation (1)
PN(t＋Δt；i；ideal)*PN(t；j；ideal)＝δ(Δt)δ(i，j) (5)
At time interval t` (i; Rc)≤t≤t`` (i; Rc) in, if PN sequence PN is (t; I; Ideal) no Depend on index i, perhaps PN sequence (i) is known, and i=j, then the Kronecker δ rope here Drawing δ (i, j) (=0 or 1) can abandon. Then equation (3) and PN sequence convolution: PN (t+ Δ t; I; Ideal) * Rc (t)=PN (t+ Δ t; I; Ideal) * { Tr (t1)*h(t
2－t
1)｝
＝PN(t＋Δt；i；ideal)*{[PN(t；i；ideal)＋mp(t)]*h(t
2-t
1)｝
＝PN(t＋Δt；i；ideal)*PN(t；i；ideal)*h(t
2－t
1)
＋PN(t＋Δt；i；ideal)*mp(t)*h(t
2－t
1)
=δ (Δ t) * h (t)+(because mp (t) and little residual) (6)
Be used for the sequence PN (t multiply each other in the following formula; I; Ideal) be known, and the impulse response h (t) of system can To calculate, therefore, can know, for channel TC, when the convolution signal of statement can be used for measuring in the equation (6) Between point (t=t` (i; Rc) and t=t`` (i; Rc)), corresponding to the desirable PN signal by channel TC transmission " edge ".
The segmentation definition that receives signal is as follows:
Thereby can cascade consist of composite signal
For the d frame signal frame sequence of analyzing, here k1 and k2 (〉=k1) be the integer of selecting. From what receive Cut composite signal Rc (t among the signal Rc (t); Δ t; Comp), obtain residual signal
Rc(t；rem)＝Rc(t)－Rc(t；Δt；comp) (9)
Following formula has been explained multipath signal clearly at each time interval t`` (i; Rc)≤t≤t`` (i+1; Rc) right in The impact of the signal that receives. From this multipath information, can identify each (time delay) DFT piece and corresponding PN order Row, thereby each signal frame in the identification signal frame sequence.
After time delays is determined or estimated, come the restoring signal carrier frequency with known symbol pattern in the signal frame PN sequence, And estimate frequency shift (FS) and/or frequency departure.
Time-delay service time and frequency shift (FS) and/or frequency departure can estimate one or more transmission letters among frame or the frame group The road characteristic.
In frequency domain, signal frame has certain bandwidth deltaf f1 In order fully to cover this bandwidth, do not produce spectral aliasing, the DFT piece At least equal the Nyquist frequency with the time domain sampling frequency of its corresponding PN sequence. In some cases, sampling rate needs Be greater than the symbol rate of signal frame.
The δ function that convolution algorithm produces in the equation (1) has time width Δ t very little but non-zero1, respective bandwidth is Δ f in its frequency domain2 The actual bandwidth Δ f that provides for signal frame1Should equal at least needed bandwidth deltaf f2。
One of method of estimating one or more transmission channel characteristics is to analyze the Fourier transform FT (f that receives signal Rc (t); Rc), its corresponding impulse response function is h (t). Desirable Fourier transform FT (f; Rc) be approximately a synchronous function:
Represent the reference frequency f of frequency domain bandwidth0Approximate the selection. Actual Fourier transform FT (f; Rc) and desirable Fu Shi become Change FT (f; Rc; Ideal) deviation can be used for estimating one or more (times change) of frame of transmission channel or frame sequence Characteristic.
In case the time delays of PN Serial relation determines and has compensated that PN just can be used for the synchronous of signal frame.
In any form shown in Fig. 2 A, 2B and the 2C, when detection or the estimation time delays relevant with frame, the PN sequence Can be used as the protection interval of DFT piece, because the symbol sebolic addressing of (1) PN sequence is known; (2) beginning of PN sequence With/concluding time is known. Thereby in frame, do not need the protection interval that provides other, in the past for the protection of the interval Part can be used for the payload user data part of frame now, and/or reduces the length of frame. Therefore, improved efficiency of transmission. Simultaneously, aforesaid information also is used for receiving the demodulation of signal.
The insertion of PN sequence and analyzed following effect in each transmission signal frame: (1) clock recovery and multipath letter frame by frame The estimation of number distortion; (2) recovery of carrier frequency; (3) estimation of one or more transport channel parameters; (4) deletion only Protection interval as the protection interval; (5) each signal frame that receives synchronously.
According to the present invention, in the situation of life period time-delay, at least one transmits letter in the signal channel of ofdm system The beginning of number section and the timing estimation flow process of end are as shown in Figure 7. In step 71, provide K (〉=1) rank pseudorandom m Sequence PN (t; K), satisfy the orthogonality of the convolution signal in equation (1) or (5). In step 72, the sequence of selection Append at least one signal frame, form the signal frame of filling. In step 73, the signal frame of at least one filling is by one The signal time uncontrollable transmission channel of delaying time. In step 74, one that receives signal transmission receives version Rc (t), For k1≤k≤k2, form convolution signal PN (t+ Δ t; K) * Rc (t; I) summation Rc (t; Δ t; Comp), as Equation (8). In step 75, form residual signal Rc (t; Rem)=Rc (t)-Rc (t; Δ t; Comp), as on an equal basis Formula (9). In step 76, analysis residual signal is in order to determine to receive at least one sequence PN (t among the signal Rc (t); K) Beginning and end.
Fig. 8 principle has been described an emission system 80 that adopts the inventive method. Connect at DFT (or FFT) conversion block 81 Receive the input data, and be converted to suitable number format. PN block 83 provides one or more PN sequences. From DFT The signal of piece 81 and 83 outputs of PN sequence blocks is given multiplexer (MUX) 85, and the MUX output signal comprises DFT alternately Piece and PN sequence. RF module 87 receives the MUX output signal, and the result after the processing gives transmitting antenna or other signal Emitter 89.
Receiving system 90, antenna or other signal receiver 91 that adopts the inventive method has been described to Fig. 9 principle Receive modulation signal, give down conversion module 93 and carry out frequency transformation. Signal frame after the down coversion, comprise the DFT piece and Additional PN sequence is given PN sequence processor 95, and it is finished, and clock recovery, carrier wave recover (option), channel is estimated The channel condition informations such as meter (option) and frame synchronization (option). Signal frame after the down coversion is also given the PN sequence and is removed mould Piece 97. After PN sequence processor 95 is finished its task, also give the PN sequence control signal that obtains and remove module 97, from signal frame, remove additional PN sequence, the DFT piece that obtains is given DFT conversion module 99. After the conversion The DFT of " original " signal frame is partly as restituted signal (data). Obtain channel status from PN sequence processor 95 Information can be analyzed separately (optionally) in order to determine channel condition information based on the signal frame that receives.
Claims (10)
1. protect fill method at interval in an orthogonal FDM modulation system, in the signal channel of OFDM (OFDM) system, under the life period time-delay situation, replace the protection interval, may further comprise the steps with the PN sequence:
1) provides pseudorandom m sequence PN (t; K) (k=1 ..., K; K 〉=1) collection, the convolution signal of wherein any two sequences satisfies PN (t; I) * PN (t+ Δ t; J)=and δ (Δ t) δ (i, j), δ (Δ τ) is the δ function here, and δ (i, j)=0, unless i=j;
2) the additional sequence PN (t that selects behind at least one signal frame that will transmit; K), constitute the signal frame of filling;
3) by the signal frame of at least one filling of Channel Transmission, the transmission signals that receives may have uncontrollable time delays Δ t;
4) receive a reception version Rc (t) of transmission signals, and form convolution signal:
Here Δ t is the incremental time of selecting, and k
1And k
2Satisfy 1≤k1≤k2≤K; Form residual signal Rc (t; Rem)=Rc (t)-Rc (t; Δ t; Comp); And at least one sequence PN (t in received signal Rc (t); K) (k=k1, k1+1 ..., adjudicate on time started k2).
2. according to the method for claim 1, it is characterized in that, further comprise and determine described at least one sequence PN (t; K) carrier frequency.
3. according to the method for claim 1, it is characterized in that, further comprise at least one parameter of using described PN sequence to estimate described transmission channel.
4. according to the method for claim 1, it is characterized in that, further comprise with at least one described signal frame replacing at least one protection at interval with described PN sequence.
5. according to the method for claim 1, it is characterized in that further comprise and use at least one PN sequence, it has one of described filling signal frame, for described filling signal frame provides time synchronized.
6. a system that adopts protection fill method at interval in the orthogonal FDM modulation system under the life period time-delay situation, replaces protection at interval with the PN sequence in the signal channel of ofdm system; Comprise a programmable computer, further comprise:
Pseudorandom m sequence PN is provided (t; K) (k=1 ..., K; K 〉=1) collection, the convolution signal of wherein any two sequences satisfies PN (t; I) * PN (t+ Δ t; J)=and δ (Δ t) δ (i, j), δ (Δ τ) is the δ function here, and δ (i, j)=0, unless i=j;
The additional sequence PN (t that selects behind at least one signal frame that will transmit; K), constitute the signal frame of filling;
At least transmit the signal frame of a filling by transmission channel, the transmission signals that receives may have uncontrollable time delays Δ t, and one that receives transmission signals receives version Rc (t), and forms convolution signal:
Here Δ t is the incremental time of selecting, and k
1And k
2Satisfy 1≤k1≤k2≤K; Form residual signal Rc (t; Rem)=Rc (t)-Rc (t; Δ t; Comp); And at least one sequence PN (t in received signal Rc (t); K) (k=k1, k1+1 ..., adjudicate on time started k2).
7. according to the system of claim 6, it is characterized in that described computer further is programmed for determines described at least one sequence PN (t; K) carrier frequency.
8. according to the system of claim 6, it is characterized in that described computer further is programmed at least one parameter of using described PN sequence to estimate described transmission channel.
9. according to the system of claim 6, it is characterized in that described computer further is programmed for at least one described signal frame with described PN sequence and replaces at least one protection at interval.
10. according to the system of claim 6, it is characterized in that described computer further is programmed for and uses at least one PN sequence, it has one of described filling signal frame, for described filling signal frame provides time synchronized.
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