CN101141432A

CN101141432A - Orthogonal frequency division multiplexing transmitter with modified pseudo-random noise sequence and inserted code element

Info

Publication number: CN101141432A
Application number: CNA2006101629590A
Authority: CN
Inventors: 丁海主; 郭征元
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2002-06-17
Filing date: 2002-11-06
Publication date: 2008-03-12
Also published as: CN101257474A; CN101242386A; CN101257477A; CN101257475A; CN101257473A; CN101257476A; KR20030096624A; CN100380957C; CN1870482A; CN1870483A; CN101257478A; CN101141433A; CN1464748A; CN101257479A

Abstract

Provided is an OFDM transmitter including a forward error correction coding unit for encoding the input data, an inverse fast Fourier transform(IFFT) unit for transforming the encoding data to orthogonal frequency division multiplexing symbols, a pseudo random noise insertion unit for inserting pseudo noise sequence selected from plurality of pseudo noise sequences having the sizes exceeding 255 symbols into the OFDM symbols, a pulse shaping unit for performing pulse shaping filter to the inserted OFDM symbols of pseudo noise sequence, a radio frequency up conversion unit for up converting the OFDM symbols to RF signals.

Description

Adjust PN (pseudo noise) sequence and insert OFDM transmitter in the code element

The application is to be that November 6, application number in 2002 are 200610092259.9, are entitled as the dividing an application of patent application of " adjust PN (pseudo noise) sequence and insert OFDM transmitter in the code element " applying date.

Technical field

The present invention relates generally to a kind of OFDM (OFDM) transmitter and a kind of OFDM launching technique thereof, more specifically relate to OFDM transmitter and the OFDM launching technique thereof of before Domain Synchronous (TDS) sends an OFDM code element, in described OFDM code element, inserting pseudo noise (PN) sequence and protection interval (GI).

Background technology

Generally speaking, the broadcast system of high definition TV (HDTV) can roughly be divided into image encoding unit and image modulation unit.The image encoding unit will be the data of 15～18Mbps from the digital data compression of about 1Gbps of the image source of high definition input.Described image modulation unit sends the numerical data of tens Mbps to receiving terminal by the band limited channel of about 6～8MHz.HDTV uses terrestrial broadcast system, and this system uses the very high frequency(VHF)/hyperfrequency (VHF/UHF) that is allocated for the television broadcasting purpose.

In Europe, adopted as obtaining such as the television terrestrial broadcasting method of future generation of the transmission speed that improves every bandwidth with the advantage that prevents to disturb as OFDM (OFDM) method of one of Ditital modulation method.

It is the parallel data of unit that the code element stream that ofdm system is imported serial is converted to the piece, and parallel code element is multiplexed with different sub-carrier frequencies.Such ofdm system uses multicarrier, and is very different with the existing systems of using single carrier wave.Has orthogonal attributes between the described multicarrier.By the orthogonal attributes of multicarrier, the multiplying each other of two carrier waves with generation 0 value, this is to use one of necessary condition of multicarrier.Ofdm system is realized by two conversion: one is fast Fourier transform (FFT), another is contrary fast fourier transform (IFFT), and they are easily to obtain by the definition of orthogonality between subcarrier and fast Fourier transform (FFT).

Application number is that 99907836.3 European patent discloses a kind of OFDM receiving system, and this system comprises: tuner, and the conversion of signals that will receive by antenna is an intermediate-freuqncy signal; Multiplier is converted to intermediate-freuqncy signal the ofdm signal of base band; Fft circuit will be carried out FFT to ofdm signal and handle, thus OFDM baseband demodulation ofdm signal; Equalizing circuit carries out equilibrium to the signal of handling through FFT; Decoding unit is decoded to signal.

The advantage of ofdm system is as follows:

According to the essence of TV method of terrestrially transmitting, the transmission quality of the data of TV ground transmission system depends critically upon reflected wave and in same channel or the interference between adjacent channel.Therefore the designing requirement for transmission system is very complicated.On the contrary, ofdm system is very healthy and strong for the multipath attribute.In other words, because ofdm system uses various carrier waves, therefore can prolong the code element transmission time.Therefore, transfer of data becomes for the interference signal anti-interference owing to multipath, even also like this for the echo-signal that the long period takes place.And ofdm system is also very healthy and strong to existing signal type, so it is subjected in the influence of the interference of same interchannel less.Because above-mentioned ofdm system like this, can realize a single-frequency network (SFN), by it, a broadcasting station can be carried out the broadcasting in the whole nation with a single frequency.During the transmission, the interference in same channel may be very strong, but can overcome in ofdm system, and ofdm system is healthy and strong for such data transmission environments.Owing to used the single-frequency network, can more effectively use limited frequency resource.

Ofdm signal comprises multicarrier, and each has little bandwidth.Because it is square that the shape of whole frequency spectrum comes down to, frequency efficiency is better than the single carrier wave of use.Another advantage of ofdm system is that the waveform of ofdm signal is identical with white Gauss noise.That is, because ofdm signal has and the similar waveform of white Gauss noise, therefore with such as other the broadcasting service that changes phase place (PAL), "systemme electronique couleur avec memoire" etc. with line compare, it has less interference.Owing in ofdm system, can be possible, have therefore enabled the individual-layer data transmission for the modulation of each carrier wave.

Generally, the OFDM transmitter Domain Synchronous ground that utilizes Domain Synchronous to send ofdm signal will provide the ofdm signal that produces with respect to frequency axis for the intended service of predetermined frequency band to be converted to data with respect to time shaft.Before the transmission OFDM signal, the OFDM transmitter inserted a protection interval GI so that suppress inter-signal interference before the ofdm signal that forms along time shaft, and inserted synchronizing information before the GI at interval in protection.

Fig. 1 is the figure that the structure of an ofdm signal frame is shown, and it is formed by the OFDM transmitter of a traditional TDS type during transfer of data.

The frame of ofdm signal is constructed such that GI and PN sequence are inserted in the OFDM code element that comprises the data that will send.In other words, the OFDM code element comprises the data that will send to the OFDM receiver.GI is certain zone of distributing, is used to suppress inter symbol interference.The PN sequence is the synchronizing information for each OFDM code element.The PN sequence is used to synchronously and channel estimating at the OFDM receiver.

The OFDM code element that is included in the frame of the ofdm signal that is sent by traditional OFDM transmitter is set to carry out contrary discrete Fourier transform (DFT) by a plurality of subcarriers with 3,780 points.And after the IDFT of OFDM, GI is inserted in the OFDM code element with 1/6,1/9,1/20 or 1/30 size corresponding to 3,780 points of OFDM code element.The PN sequence is inserted in the OFDM code element of inserting GI with the size corresponding to 255 code elements.

Problem is, compares with the size of the OFDM code element that is included in 3,780 points in a plurality of subcarriers, and 255 code elements of the size of PN sequence are quite little.Therefore, the OFDM receiver that receives ofdm signal with such frame be difficult to utilize the PN sequence that is included in the ofdm signal that is received carry out for the ofdm signal that is received synchronously and channel estimating.As a result, the frequent ofdm signal that received of reduction inaccurately of OFDM receiver.

Summary of the invention

Therefore, an object of the present invention is to provide a kind of OFDM (OFDM) transmitter, it can adjust the size that is inserted into the PN sequence in the OFDM code element before sending ofdm signal, so that the PN sequence in the OFDM code element that the OFDM receiver can receive based on being inserted into and carrying out more accurately synchronously and channel estimating, the present invention also provides the sending method of a kind of OFDM of correspondence.

To achieve these goals, provide a kind of OFDM transmitter, this OFDM transmitter comprises: the forward error correction coding unit is used to the data of encoding and being imported; Contrary discrete Fourier transform unit is used for described coded data is transformed to the OFDM code element; PN (pseudo noise) sequence is inserted the unit, is used for described OFDM code element and inserts the PN (pseudo noise) sequence that the size of selecting among a plurality of PN (pseudo noise) sequence surpasses 255 code elements; Pulse shaping unit is used for the OFDM code element of inserting PN (pseudo noise) sequence is carried out shaping pulse filtering; The RF up-converter unit, being used for described OFDM code element up conversion is radiofrequency signal.

Preferably, in described OFDM transmitter, described PN (pseudo noise) sequence is the PN (pseudo noise) sequence of 511 or 1023 length.

And, a kind of orthogonal frequency division multiplex ransmitting shooting method is provided, this orthogonal frequency division multiplex ransmitting shooting method comprises step: the data that coding is imported; With the contrary discrete Fourier transform (DFT) of data encoded is the OFDM code element; Insert the PN (pseudo noise) sequence that the size of selecting among a plurality of PN (pseudo noise) sequence surpasses 255 code elements in the described OFDM code element; The OFDM code element of inserting PN (pseudo noise) sequence is carried out shaping pulse filtering; With the OFDM code element up conversion of shaping pulse filtering is radiofrequency signal.

Preferably, in described orthogonal frequency division multiplex ransmitting shooting method, described PN (pseudo noise) sequence is the PN (pseudo noise) sequence of 511 or 1023 length.

Because before the described OFDM code element of transmission, described size is that the PN sequence of 511 code elements or 1,023 code element is inserted in the described OFDM code element, is used for the synchronous and channel estimating of receiving terminal, therefore, the OFDM receiver can be carried out the synchronous and channel estimating of the OFDM code element that is received more accurately.As a result, the OFDM receiver can reduce the data that received more accurately.

And, because receiver can be 511 code elements or 1 from the size being inserted into described OFDM code element, carry out the synchronous and channel estimating of the OFDM code element that is received in the PN sequence of 023 code element more accurately, therefore can reduce to insert the size of the GI that suppresses inter symbol interference.As a result, can improve the transfer rate of OFDM code element.

Description of drawings

By reference description of drawings the preferred embodiments of the present invention, above-mentioned purpose of the present invention and characteristics will become apparent, wherein:

Fig. 1 is the figure that the structure of ofdm signal frame is shown, and described ofdm signal frame is formed by a traditional TDS type OFDM transmitter between the ofdm signal transmission period;

Fig. 2 is the block diagram according to the OFDM transmitter of the preferred embodiments of the present invention;

Fig. 3 (a) is a PN generator that comprises 9 linear feedback shift registers;

Fig. 3 (b) is a PN generator that comprises 10 linear feedback shift registers;

Fig. 4 is the figure that the structure of the ofdm signal frame that is formed by Fig. 2 is shown;

Fig. 5 illustrates to be used to use the flow chart that sends the method for ofdm signal according to OFDM transmitter of the present invention.

Embodiment

Below, illustrate in greater detail the preferred embodiments of the present invention with reference to accompanying drawing.

As shown in Figure 2; according to one embodiment of the present of invention; a kind of OFDM transmitter comprises forward error correction (FEC) unit 100, contrary discrete Fourier transform (DFT) (IDFT) unit 200, and unit 300, PN generator 400, the insertion of pseudo noise (PN) sequence unit 500, pulse shaping unit 600 and radio frequency (RF) up-conversion unit 700 are inserted in protection (GI) at interval.

FEC unit 100 coding OFDM code elements are used to correct the mistake that takes place during the transmission.IDFT unit 200 is for carrying out IDFT in FEC coding unit 100 coded OFDM code elements.

When after the IDFT of IDFT unit 200, GI inserts unit 300 and insert a protection (GI) at interval in the OFDM code element, to suppress inter-signal interference.At this moment, the big small mode of GI corresponding in the IDFT unit 200 by 1/6,1/9,1/12,1/20 or 1/30 of the OFDM code element of contrary discrete Fourier transform (DFT).

As a kind of selection, GI inserts unit 300 can insert GI with the big small mode corresponding to 1/12,1/20,1/30,1/36 or 1/40.Therefore, can improve the effective ratio of transmission of the OFDM code element in the ofdm signal frame.

PN generator 400 generation length are 511 or 1023 PN sequence.

Then, PN inserts unit 500 and insert the PN sequence in is inserted the OFDM code element of GI with predetermined big small mode.At this moment, PN inserts unit 400 and insert the PN sequence that size surpasses 255 code elements in the OFDM code element of inserting GI.Preferably, PN inserts unit 400 inserts 511 code elements or 1,023 code element in the OFDM code element of inserting GI PN sequence.

The PN sequence of 511 code elements or 1,023 code element as mentioned above be inserted in the OFDM code element after, pulse shaping unit 500 comes shaping pulse filtering OFDM code element according to the predetermined roll-off factor of OFDM code element.

The OFDM code element of RF up-conversion unit 700 high frequency conversion shaping pulses is so that send them by antenna 800 and transmission channel to the OFDM receiver.

Since be used for receive a side synchronously and 511 code elements of channel estimating or the PN sequence of 1,023 code element be included in the OFDM code element that will send, so the OFDM receiver can be carried out the synchronous and channel estimating for the ofdm signal that is received more accurately.As a result, the OFDM receiver can reduce the ofdm signal that is received more accurately.

And, because inserting size in the OFDM code element is 511 code elements or 1, the PN sequence of 023 code element makes that receiving one can reach the synchronous and channel estimating of carrying out more accurately for the ofdm signal that is received, and therefore can reduce to insert the size of the GI that suppresses inter symbol interference.As a result, improved the transfer rate of OFDM code element.

Fig. 3 (a) and (b) be to be respectively to be used to produce the PN generator that length is 511 and 1023 PN sequence according to the preferred embodiments of the present invention.

Shown in Fig. 3 (a), the PN generator comprises an XOR and contains linear feedback shift register (LFSR) circuit of 9 shift register D, so it constitutes a 511PN sequencer of the present invention.

Shown in Fig. 3 (b), the PN generator comprises an XOR and contains the LFSR of 10 shift register D, therefore constituted a 1023PN sequencer of the present invention.

Fig. 4 is the figure of an example that the structure of the ofdm signal frame that is formed by Fig. 2 is shown.

As shown in Figure 4, the frame of ofdm signal comprises an OFDM code element that comprises the data that will send, and a GI and a PN sequence of being inserted into the OFDM code element.

According to the preferred embodiments of the present invention, a plurality of subcarriers of being order by N by the OFDM code element of OFDM transmitter transmission carry out contrary discrete Fourier transform (DFT).Described N point comprises 3,780 points, 2,048 points, 4,096 and 8,192 points, and 2,048 points, and 4,096 points, 8,192 the pattern of a plurality of subcarriers are respectively 2K pattern, 4K pattern and 8K pattern.

GI with corresponding to respect to the OFDM code element really the size of sizing be inserted in the OFDM code element of a plurality of subcarriers that N orders.The described size of determining with respect to the OFDM code element is 1/6,1/9,1/12,1/20 or 1/30 of an OFDM code element, perhaps also can be one of 1/12,1/20,1/30,1/36 or 1/40 of OFDM code element.

Fig. 5 is a flow chart, shows according to the preferred embodiments of the present invention and sends the method for ofdm signal by utilizing the OFDM transmitter.

At first, the OFDM code element that FEC coding unit 100 codings will send is to be corrected in the mistake (step S100) that takes place during the transfer of data.After by FEC coding unit 100 codings, IDFT (step S120) is carried out for the OFDM code element that is encoded in IDFT unit 200.

After the IDFT of OFDM code element, GI inserts unit 300 and insert GI in the OFDM code element, so that suppress inter symbol interference (step S140).At this moment, GI inserts unit 300 and inserts GI, and its size is corresponding to a definite pattern, promptly 1/6 of the OFDM code element, 1/9,1/1 2,1/20 or 1/30, or the OFDM code element 1/12,1/20,1/30,1/36 or 1/40.Therefore, can improve the transfer rate of the OFDM code element of ofdm signal frame.

PN generator 400 generation length are 511 or 1023 PN sequence (step S160).

PN inserts unit 500 and insert the PN sequence in the OFDM code element of inserting GI, and its size is for surpassing 255 code elements (step S180).Preferably, PN inserts unit 500 inserts 511 code elements or 1,023 code element in the OFDM code element of inserting GI PN sequence.

Pulse shaping unit 600 comes shaping pulse filtering to be inserted into the OFDM code element (step S200) of the PN sequence of 511 code elements or 1,023 code element according to predetermined roll-off factor.

The OFDM code element of RF up-conversion unit 700 high frequency conversion shaping pulse filtering is to come to send OFDM code element (step S220) to the OFDM receiver via transmission channel.

According to the present invention, because inserted size before the transmission OFDM code element in the OFDM code element is 511 code elements or 1, the PN sequence of 023 code element is to be used for the synchronous and channel estimating at receiving terminal, therefore can reduce to insert the size of the GI that suppresses inter symbol interference, as a result, can improve the transfer rate of OFDM code element.

Though the preferred embodiments of the present invention have been described, those skilled in the art will appreciate that to the invention is not restricted to described preferred embodiment, can make various improvement and change in the spirit and scope of the present invention of Xian Dinging in the appended claims.

Claims

1. OFDM receiver comprises:

The ADC unit, the broadcast singal that is used for receiving from tuner is converted to digital signal;

The down conversion unit, the digital signal that is used for receiving from the ADC unit downconverts to base band;

Lock unit, the PN sequence and the preamble/postamble that are used for inserting by the broadcast singal that use receives are carried out symbol timing and Frequency Synchronization;

Go to multiplexed unit, be used for the synchronous signal of quilt from lock unit output is divided into PN sequence and data block and output;

The FFT unit is used for carry out the data block behind FFT and the output transform from the data block of going the output of multiplexed unit;

The FEC unit is used for detecting according to predetermined error detection method the error of the data block after the conversion, and the error that arrives of correct detection.

2. OFDM receiver as claimed in claim 1, wherein, the size of described PN sequence surpasses 255 code elements.

3. OFDM receiver as claimed in claim 2, wherein, the size of described PN sequence is 511 or 1023 code elements.

4. OFDM method of reseptance comprises step:

To be converted to digital signal from the broadcast singal that tuner receives;

Digital signal is downconverted to base band;

Carry out symbol timing and Frequency Synchronization by using the PN sequence and the preamble/postamble that insert in the described broadcast singal that receives;

To be divided into PN sequence and data block and output by synchronous broadcast singal;

Described data block is carried out FFT, and the data block behind the output transform;

Detect error in the data block after the conversion according to predetermined error detection method, and the error that arrives of correct detection.

5. OFDM method of reseptance as claimed in claim 4, wherein, the size of described PN sequence surpasses 255 code elements.

6. OFDM method of reseptance as claimed in claim 5, wherein, the size of described PN sequence is 511 or 1023 code elements.

7. OFDM receiving system that is used to receive the broadcast singal that sends from transmitting terminal comprises:

Receiving element is used to receive the broadcast singal with PN sequence, and described PN sequence has preamble/postamble;

Lock unit is used for by using PN sequence and preamble/postamble to carry out symbol timing and Frequency Synchronization;

Demodulating unit is used for demodulation by synchronous broadcast singal.

8. receiving system as claimed in claim 7, wherein, the size of described PN sequence surpasses 255 code elements.

9. receiving system as claimed in claim 8, the size of wherein said PN sequence are 511 or 1023 code elements.

10. method of reseptance that is used to receive the broadcast singal that sends from transmitting terminal comprises step:

Reception has the broadcast singal of PN sequence, and described PN sequence has preamble/postamble;

Carry out symbol timing and Frequency Synchronization by using PN sequence and preamble/postamble;

Demodulation is by synchronous broadcast singal.

11. method of reseptance as claimed in claim 10, wherein, the size of described PN sequence surpasses 255 code elements.

12. method of reseptance as claimed in claim 11, wherein, the size of described PN sequence is 511 or 1023 code elements.

13. a receiver that is used to receive from the broadcast singal of transmitting terminal transmission comprises:

Be used to receive the receiving system of the broadcast singal with PN sequence, described PN sequence has preamble/postamble;

Be used for by using PN sequence and preamble/postamble to carry out the synchronizer of symbol timing and Frequency Synchronization;

Be used for carried out the demodulating equipment of demodulation by synchronous broadcast singal.

14. receiver as claimed in claim 13, wherein, the size of described PN sequence surpasses 255 code elements.

15. receiver as claimed in claim 14, wherein, the size of described PN sequence is 511 or 1023 code elements.

16. a receiver that is used to receive from the broadcast singal with PN sequence of transmitting terminal transmission, described PN sequence has preamble/postamble, and described receiver comprises:

Be used for by using PN sequence and preamble/postamble to carry out the lock unit of symbol timing and Frequency Synchronization;

Be used for demodulation by the demodulating unit of synchronous broadcast singal.

17. receiver as claimed in claim 16, wherein, the size of described PN sequence surpasses 255 code elements.

18. receiver as claimed in claim 17, wherein, the size of described PN sequence is 511 or 1023 code elements.

19. receiver, comprise: the conversion of signals that is used for receiving from tuner is the ADC unit of digital signal, the digital signal that is used for receiving from the ADC unit downconverts to the down conversion unit of base band, the PN sequence that is used for inserting by the signal that use receives is carried out the lock unit of symbol timing and Frequency Synchronization, be used for to be divided into from the signal of the output of lock unit the multiplexed unit that goes of PN sequence and data block and output, be used for carry out the FFT unit of the data block behind FFT and the output transform from the data block of going the output of multiplexed unit, be used for detecting the error of data block of conversion and the FEC unit of the error that correct detection arrives according to predetermined error detection method

Wherein, described PN sequence has preamble and postamble.

20. receiver as claimed in claim 19, wherein, the size of described PN sequence surpasses 255 code elements.

21. receiver as claimed in claim 19, wherein, the size of described PN sequence is 511 and 1023 code elements.