CN100521674C - Transmitting method for physical layer descending chain circuit frame of broad band wireless multimedia system - Google Patents

Abstract

The invention relates to a digit information technique of wideband wireless multimedia system, wherein it is characterized in that: it uses large base station to emit broadcast service, and uses small base station to emit communication service; the communication frame uses one N-point IFFT data block and one L-point protective distance filled by PN sequence to form OFDM mark; the broadcast frame uses one 4N-point IFFT data block and one 4L-point protective distance filled by PN sequence to form OFDM mark; the communication frame is formed by eight OFDM marks; the broadcast frame is formed by two OFDM marks; for 4N-point IFFT or FFT, it first rearranges the 4N data, then treats it with 4-butterfly transformation. The invention can be used in different band widths, as 1.25MHz, 2.5MHz, 5MHz, 10MHz, 15MHz, and 20MHz.

Description

The launching technique of the physical layer descending chain circuit frame of broad band wireless multimedia system

Technical field

The invention belongs to the digital information technology field of broad band wireless multimedia system, relate in particular to a kind of launching technique of physical layer descending chain circuit frame of broad band wireless multimedia system.

Background technology

Telecommunications network, broadcasting and television network, computer network three macroreticulars can provide to comprise comprehensive multimedia service such as voice, data, image by technological transformation.The so-called integration of three networks that Here it is.The integration of three networks is the basic orientation of future network development.

Broad band wireless multimedia system (BWM) is broadcasting and the system that communicates by letter and merge, and supports broadcasting service and communication service simultaneously.

BWM has following some feature:

1.BWM can support 6 kinds of bandwidth 1.25MHz, 2.5MHz, 5MHz, 10MHz, 15MHz, 20MHz.

2.BWM support two kinds of different operation modes during operation:

◆ big base station and little base station mode (as Fig. 1)

Big base station broadcasting service, little base station communication service can reduce like this and build the base station cost, and can utilize existing equipment more fully.

◆ complete little base station mode (as Fig. 2)

Be that little base station (legacy cellular base station) emission is all adopted in broadcasting service or communication service.

3. adopt OFDM (OFDM) technology.

Under the network architecture of big or small base station mode, system mainly contains following some feature:

1. (15km～30km), corresponding multidiameter delay is big greatly for the radio network base station range.

2. broadcasting service and communication service send in big or small base station respectively.

Take all factors into consideration above some feature, merge broadcasting and need consider the following aspects with the physical layer descending scheme of communicating by letter:

1. based on the OFDM technology.

2. for broadcasting service, because its multidiameter delay is bigger, in order to prevent the OFDM intersymbol interference, required protection is longer at interval; And for communication service, because its coverage is little, multidiameter delay is little, and the protection that needs is less at interval.

3. for broadcasting with communicate by letter, it is close that the protection of wishing both takies efficient at interval.

4. based on 2,3 two consideration, the OFDM symbol lengths that radio network needs is bigger than the OFDM symbol lengths that communication network needs.

Since broadcasting service and communication service send by large and small base station respectively, do not have communication service on the big base station, do not have broadcasting service on the little base station, so in physical layer broadcasting service and communication service is relatively independent, that is to say in the Frame the inside of using same interleaver and chnnel coding and can not contain broadcast data and communication data simultaneously.But in order to reduce terminal complexity, make it be unlikely to needs two complete equipments and receive broadcasting and communication service respectively, broadcasting and communication service need to share to greatest extent design and implementation.

6. flexible adaptation 1.25MHz, 2.5MHz, 5MHz, 10MHz, 15MHz, the demand of different bandwidths such as 20MHz.

At present also not based on this network architecture and the physical layer descending chain circuit frame structure and the corresponding launching technique that adapt to above demand.

Summary of the invention

The launching technique that the purpose of this invention is to provide a kind of physical layer descending chain circuit frame of broad band wireless multimedia system makes it can be for solving in broad band wireless multimedia system radio network and communication network in the fusion problem of physical layer.

The invention is characterized in:

This method is to realize according to the following steps in digital integrated circuit chip respectively according to the pattern of big base station and little base station:

Step (1), base station are divided into broadcasting service and communication service to the data that needs send, and broadcasting service is mail to the big base station of using 4N point length OFDM, communication service are mail to the little base station of using N point length OFDM;

Step (2), little base station form communication frame according to the following steps:

Step (2.1), little base station are for first OFDM symbol, system for filling information, described system information are meant the demodulation sign indicating number information of the necessity that will understand when the terminal of the broadcast frame information of code check, interlace mode, frame information pattern, next frame or following several frames that the sign map mode that comprises, LDPC encode receives each data;

Step (2.2), little base station are done zero padding to the communicating data block that will send and are handled, and do the IFFT computing that N is ordered then;

Step (2.3), according to the protection of the points N of IFFT and system requirements at interval occupation proportion (Tg/Tb) press the length L that following formula is determined the protection interval,

L＝N*Tg/Tb

Wherein Tb is the IFFT data block duration, and Tg is the protection interval duration, generates the protection interval of being filled by the PN sequence then;

Step (2.4), generate communication frame in the following manner: at interval and OFDM symbol that N+L is ordered of an IFFT data block composition with a protection, form a communication frame with 8 OFDM symbols, wherein the 2nd to the 8th symbol conduct data designated lane in logic is specifically designed to the communication data information that transmits;

Step (2.5), framing procedure finish back execution in step (4);

Step (3), big base station form broadcast frame according to the following steps:

Step (3.1), big base station are done zero padding to the broadcast data piece that will send and are handled, and do the IFFT computing that 4N is ordered then;

Step (3.2), according to the protection of count 4N and the system requirements of IFFT at interval occupation proportion (Tg/Tb) press the length 4L that following formula is determined the protection interval,

4L＝4N*Tg/Tb

Wherein Tb is the IFFT data block duration, and Tg is the protection interval duration, generates the protection interval of being filled by the PN sequence then;

Step (3.3), generate broadcast frame in the following manner: with a protection at interval and an IFFT data block form the OFDM symbol that 4N+4L is ordered, again with broadcast frame of 2 OFDM symbols compositions;

Step (3.4), framing procedure finish back execution in step (4);

Step (4), data are sent to generalized channel;

The pairing FFT computing of the described 4N point of above-mentioned steps (3.1) IFFT computing is carried out according to the following steps:

Step (3.1.1), 4N data that receive are carried out order rearrangement, the order rearrangement scheme is as follows:

x′(k)＝x(4k)

x′(N+k)＝x(4k+2)

x′(2N+k)＝x(4k+1)

x′(3N+k)＝x(4k+3)

K=0 wherein, 1,2 ..., N-1;

Step (3.1.2), will { x ' (k) }, { x ' (N+k) }, { x ' (2N+k) }, { x ' (3N+k) } 4 groups of data (k=0 wherein, 1,2 ..., N-1) send into N point FFT computing module in order, carry out FFT and calculate, result of calculation is x " (n); Step (3.1.3), sequence x " (n) is carried out base 4 butterfly conversion, obtains 4N point FFT result.Transform method is as follows:

$X\left(k\right)=x\&prime;\&prime;\left(k\right)+x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}+(x\&prime;\&prime;(2N+k)+x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^k$

$X(N+k)=x\&prime;\&prime;\left(k\right)-x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}+(x\&prime;\&prime;(2N+k)-x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{N+k}$

$X(2N+k)=x\&prime;\&prime;\left(k\right)+x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}-(x\&prime;\&prime;(2N+k)+x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^k$

$X(3N+k)=x\&prime;\&prime;\left(k\right)-x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}-(x\&prime;\&prime;(2N+k)-x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{N+k}$

K=0 wherein, 1,2 ..., N-1, $W_N^k=e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="C200610112440E00131.png,C200610112440E00141.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{k\&pi;}}{N}};$

IFFT carries out reverse operating according to above-mentioned steps to be realized.

The present invention supports the OFDM pattern of multiple length and the protection interval fill pattern of multiple resources occupation rate simultaneously, thereby adapts to different bandwidth and different system requirements.

Description of drawings

The network architecture of Fig. 1 .BWM system size base station mode;

The complete little base station mode of Fig. 2 .BWM (cellular network);

Fig. 3. the downlink communication data frame structure;

Fig. 4. the downlink broadcast data frame structure;

Fig. 5 .N+L point OFDM symbol and 4N+4L point OFDM symbol;

Fig. 6. the flow chart that data send;

Fig. 7 .4N point FFT implementation;

Fig. 8 .4N point FFT realization flow figure.

Specific implementation

In the present invention, frame is realized by the following method:

1. communication network is used the OFDM of N point length, and the OFDM that radio network uses 4N to order;

2. use the PN sequence to fill the protection interval of OFDM symbol;

3. the Frame of communication data contains 8 OFDM symbols, and the Frame of broadcast data contains 2 OFDM symbols, thereby makes both frame lengths identical;

4. the protection gap length of OFDM symbol is L in the communication frame, and the protection gap length in the broadcast frame is 4L.Because the OFDM symbol lengths in the broadcast frame is 4 times of OFDM symbol lengths in the communication frame, so guaranteed both identical protection occupation proportion is at interval arranged, and has solved bigger at interval than the protection of the communication network at interval problem of protection that radio network needs simultaneously;

5. first OFDM symbol available system information in the communication frame is filled.For increasing operation rate, also can fill the data message that will transmit therein;

The system information of being mentioned is meant the demodulation sign indicating number information of the necessity that will understand when terminal receives each Frame, comprises the broadcast frame information of code check, interlace mode information, frame information pattern, next frame or several frames that sign map mode, LDPC encode etc.;

The transmission method of the frame structure that proposes based on the present invention is as follows:

1. the data that send as required in the base station are determined the type of frame;

2. select IFFT to count according to frame type, the data that send are carried out this IFFT computing under counting.The 4N point IFFT that wherein broadcast frame adopted can realize by the IFFT and the FFT that the 4N dot sequency are reset and 4 N are ordered, thus the reduction complexity.

3. type and the system requirements according to frame generates the protection interval of being filled by the PN sequence;

4. according to the type group framing of frame;

5. send to generalized channel;

Realization, transmission and the processing method based on the physical layer descending frame of BWM system that the present invention proposes can realize the fusion of radio network and communication network in the BWM system.Its Frame is divided into two kinds of forms: communications data frame and broadcast data frame.These two kinds of Frames constitute as follows:

◆ the downlink communication Frame:

As shown in Figure 3, the OFDM symbol that this frame is ordered by 8 N constitutes, wherein the 1st symbol is as in logic public physic channel, be mainly used to transfer system information, when the system information that maybe needs to transmit when the system information that does not need to transmit can not be filled up the 1st symbol, also can come data information with it; The the 2nd to the 8th symbol conduct data dedicated channel in logic is used for transmitting communication data information specially.

Wherein system information is meant the demodulation sign indicating number information of the necessity that will understand when terminal receives each Frame, comprises the broadcast frame information of code check, interlace mode information, frame information pattern, next frame or several frames that sign map mode, LDPC encode etc.

◆ the downlink broadcast Frame:

As shown in Figure 4, this frame has the OFDM symbol that 2 4N order to constitute, and 2 ofdm signals wherein all are used for transmitting broadcast data information.

The OFDM symbol of above mentioning is formed by structure shown in Figure 5:

◆ N+L point OFDM symbol

Constitute by the cycle P N sequence of L point length and inverse-Fourier transform (IFFT) sequence of N point length; wherein PN is as the head of OFDM symbol; play and fill protection effect at interval, can be used for satisfying simultaneously the needs of recovered clock, the reinsertion of carrier and channel estimating.

◆ 4N+4L point OFDM symbol

Structure is identical with N point OFDM symbol, and just its protection length and counting of IFFT at interval of being filled by the PN sequence is 4 times of N point OFDM symbol.

The present invention can support the OFDM of multiple length to count.Table 1 has been listed the 1.25MHz that the OFDM symbol among the present invention is supported at the BWM system, 2.5MHz, and 5MHz, 10MHz, 15MHz, the parameter that 6 kinds of bandwidth such as 20MHz can be selected:

Table 1 OFDM symbolic parameter

Parameter	Value
		Subcarrier bundle N	128，256，512，1024，2048，4096，8192
Sample frequency	1.12 bandwidth doubly
		Useful subcarrier bundle	100，200，400，800，1600，3200，6400
The number of protection subcarrier	28，56，112，224，448，896，1792
		Protection is occupation proportion (Tg/Tb) at interval	1/4，1/8，1/16，1/32

Table 2 and table 3 are under the 20M bandwidth situation, adopt and 8192 OFDM patterns at 2048, when adopting 1/8 protection space ratio, and the parameter of frame structure proposed by the invention:

Table 2 20M bandwidth downlink communication frame parameter

Bandwidth (MHz)	20
		Sample frequency (MHz)	22.4
The OFDM symbol numbers	8
		The special-purpose OFDM symbol numbers of data	7
Public physic channel OFDM symbol numbers	1
		FFT length	2048
Carrier frequency (kHz)	10.94
		FFT symbol period (us)	91.43
PN length (adopting 1/8 pattern)	256
		PN duration (us)	11.43
OFDM symbol period (us)	102.86
		Frame length (ms)	0.8229

Table 3 20M bandwidth downlink broadcast frame parameter

Bandwidth (MHz)	20
		Sample frequency (MHz)	22.4
The OFDM symbol numbers	2
		The special-purpose OFDM symbol numbers of data	2

Public physic channel OFDM symbol numbers	0
		FFT length	4*2048
Carrier frequency (kHz)	2.734
		FFT symbol period (us)	365.7
PN length (adopting 1/8 pattern)	1024
		PN duration (us)	45.71
OFDM symbol period (us)	411.4
		Frame length (ms)	0.8229

After having established data frame structure, just can utilize corresponding Frame to carry out the downlink transfer of data, as shown in Figure 6 with above feature.Detailed process is as follows:

Step 1: the data that send as required in the base station are carried out the business classification, and the type of definite frame.If communication data, execution in step 2, if broadcast data, execution in step 6;

Step 2: if first OFDM symbol need carry out system information and fill in;

Step 3: the communicating data block that send is done zero padding handle, carry out the IFFT computing that N is ordered then.

Step 4: press the length that following formula is determined the protection interval according to the points N of IFFT and the protection interval occupation proportion (Tg/Tb) of system requirements,

L＝N*Tg/Tb

Wherein Tb is the IFFT data block duration, and Tg is the protection interval duration, generates the protection interval of being filled by the PN sequence then;

Step 5: framing.Process is that a protection interval and an IFFT data block are formed an OFDM symbol, forms a communication frame by 8 OFDM symbols.Framing procedure finishes back execution in step 9;

Step 6: the broadcast data piece that send is done zero padding handle, carry out the IFFT computing that 4N is ordered then.

Step 7: according to the protection of count 4N and the system requirements of IFFT at interval occupation proportion (Tg/Tb) press the length that following formula is determined the protection interval,

4L＝4N*Tg/Tb

Wherein Tb is the IFFT data block duration, and Tg is the protection interval duration, generates the protection interval of being filled by the PN sequence then;

Step 8: framing.Process is that a protection interval and an IFFT data block are formed an OFDM symbol, forms a broadcast frame by 2 OFDM symbols.Framing procedure finishes back execution in step 9;

Step 9: Frame is sent to generalized channel;

4N point IFFT that broadcast frame adopted in the step 6 and FFT can realize by the IFFT and the FFT that the 4N dot sequency are reset and 4 N orders, thus the reduction terminal complexity, and make terminal shared processing scheme to the full extent when two kinds of frames of processing.4N point FFT can realize according to principle shown in Figure 7.As shown in Figure 8, implementation procedure is as follows: the step 10. pair 4N data that receive are carried out order rearrangement.The order rearrangement scheme is as follows:

x′(k)＝x(4k)

x′(N+k)＝x(4k+2)

x′(2N+k)＝x(4k+1)

x′(3N+k)＝x(4k+3)

K=0 wherein, 1,2 ..., N-1;

Step 11. will { x ' (k) }, and { x ' (N+k) }, { x ' (2N+k) }, { x ' (3N+k) } 4 groups of data (k=0 wherein, 1,2 ..., N-1) send into N point FFT computing module in order, carry out FFT and calculate, result of calculation is x " (n);

Step 12. couple sequence x " (n) carries out base 4 butterfly conversion, obtains 4N point FFT result.Transform method is as follows:

$X\left(k\right)=x\&prime;\&prime;\left(k\right)+x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}+(x\&prime;\&prime;(2N+k)+x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^k$

$X(N+k)=x\&prime;\&prime;\left(k\right)-x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}+(x\&prime;\&prime;(2N+k)-x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{N+k}$

$X(2N+k)=x\&prime;\&prime;\left(k\right)+x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}-(x\&prime;\&prime;(2N+k)+x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^k$

$X(3N+k)=x\&prime;\&prime;\left(k\right)-x\&prime;\&prime;(N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}-(x\&prime;\&prime;(2N+k)-x\&prime;\&prime;(3N+k){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{2k}){\mathrm{<figure-callout\; id="4N"\; label="W"\; filenames="C200610112440E00133.png,C200610112440E00141.png"\; state="\{\{state\}\}">W</figure-callout>}}_{4N}^{N+k}$

K=0 wherein, 1,2 ..., N-1, $W_N^k=e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="C200610112440E00131.png,C200610112440E00141.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{k\&pi;}}{N}};$

IFFT carries out reverse operating according to above-mentioned steps to be realized.

Claims (2)

1, the launching technique of the physical layer descending chain circuit frame of broad band wireless multimedia system is characterized in that: this method is to realize according to the following steps in digital integrated circuit chip respectively according to the pattern of big base station and little base station:

Step (1), base station are divided into broadcasting service and communication service to the data that needs send, and broadcasting service is mail to the big base station of using 4N point length OFDM, communication service are mail to the little base station of using N point length OFDM;

Step (2), little base station form communication frame according to the following steps:

Step (2.1), little base station are for first OFDM symbol, system for filling information, described system information are meant the demodulation sign indicating number information of the necessity that will understand when the terminal of the broadcast frame information of code check, interlace mode, frame information pattern, next frame or following several frames that the sign map mode that comprises, LDPC encode receives each data;

Step (2.2), little base station are done zero padding to the communicating data block that will send and are handled, and do the IFFT computing that N is ordered then;

Step (2.3), according to the protection of the points N of IFFT and system requirements at interval occupation proportion press the length L that following formula is determined the protection interval,

L＝N*Tg/Tb

Wherein Tb is the IFFT data block duration, and Tg is the protection interval duration, generates the protection interval of being filled by the PN sequence then;

Step (2.4), generate communication frame in the following manner: at interval and OFDM symbol that N+L is ordered of an IFFT data block composition with a protection, form a communication frame with 8 OFDM symbols, wherein the 2nd to the 8th symbol conduct data designated lane in logic is specifically designed to the communication data information that transmits;

Step (2.5), framing procedure finish back execution in step (4);

Step (3), big base station form broadcast frame according to the following steps:

Step (3.1), big base station are done zero padding to the broadcast data piece that will send and are handled, and do the IFFT computing that 4N is ordered then;

Step (3.2), according to the protection of count 4N and the system requirements of IFFT at interval occupation proportion determine protection length 4L at interval by following formula,

4L＝4N*Tg/Tb

Wherein Tb is the IFFT data block duration, and Tg is the protection interval duration, generates the protection interval of being filled by the PN sequence then;

Step (3.3), generate broadcast frame in the following manner: with a protection at interval and an IFFT data block form the OFDM symbol that 4N+4L is ordered, again with broadcast frame of 2 OFDM symbols compositions;

Step (3.4), framing procedure finish back execution in step (4);

Step (4), data are sent to generalized channel;

The pairing FFT computing of the described 4N point of above-mentioned steps (3.1) IFFT computing is carried out according to the following steps:

Step (3.1.1), 4N data that receive are carried out order rearrangement, the order rearrangement scheme is as follows:

x′(k)＝x(4k)

x′(N+k)＝x(4k+2)

x′(2N+k)＝x(4k+1)

x′(3N+k)＝x(4k+3)

K=0 wherein, 1,2 ..., N-1;

Step (3.1.2), will { x ' (k) }, { x ' (N+k) }, { x ' (2N+k) }, { x ' (3N+k) } 4 groups of data, k=0 wherein, 1,2 ..., N-1 sends into N point FFT computing module in order, carries out FFT and calculates, and result of calculation is x " (n); Step (3.1.3), sequence x " (n) is carried out base 4 butterfly conversion, obtains 4N point FFT result.Transform method is as follows:

$X\left(k\right)=x\&prime;\&prime;\left(k\right)+x\&prime;\&prime;(N+k)W_{4N}^{2k}+(x\&prime;\&prime;(2N+k)+x\&prime;\&prime;(3N+k)W_{4N}^{2k})W_{4N}^k$

$X(N+k)=x\&prime;\&prime;\left(k\right)-x\&prime;\&prime;(N+k)W_{4N}^{2k}+(x\&prime;\&prime;(2N+k)-x\&prime;\&prime;(3N+k)W_{4N}^{2k})W_{4N}^{N+k}$

$X(2N+k)=x\&prime;\&prime;\left(k\right)+x\&prime;\&prime;(N+k)W_{4N}^{2k}-(x\&prime;\&prime;(2N+k)+x\&prime;\&prime;(3N+k)W_{4N}^{2k})W_{4N}^k$

$X(3N+k)=x\&prime;\&prime;\left(k\right)-x\&prime;\&prime;(N+k)W_{4N}^{2k}-(x\&prime;\&prime;(2N+k)-x\&prime;\&prime;(3N+k)W_{4N}^{2k})W_{4N}^{N+k}$

K=0 wherein, 1,2 ..., N-1, $W_N^k=e^{-j}\frac{2\mathrm{k\&pi;}}{N};$

IFFT carries out reverse operating according to above-mentioned steps to be realized.

2, the launching technique of the physical layer descending chain circuit frame of broad band wireless multimedia system according to claim 1 is characterized in that: first OFDM symbol in the described communication frame be one when system information can not be filled up this symbol and the data auxiliary channel that uses.

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