CN101018105A - A classified modulating mobile digital multimedia broadcast signal transmission system and method - Google Patents

Abstract

The disclosed mobile digital multimedia broadcast signal transmission system comprises: two channel decoders to receive 1st and 2nd data flow to decode and interlace data and converse into bit flow, a constellation mapper to combine two bit flow and map them into QAM mode signal flow, an OFDM signal forming module, a framing module to add beacon into OFDM signal and form transmission frame, an up-conversion module to up converse the frame and generate RF signal, a changing module for channel width to control said decoder and forming module and framing module. This invention can satisfy different business requirements.

Description

A kind of classified modulating mobile digital multimedia broadcast signal transmission system and method

Technical field

The present invention relates to the mobile digital multi-media broadcast field, relate in particular to signal transmission system and method in a kind of mobile digital multi-media broadcast.

Technical background

OFDM (OFDM) is a kind of known multi-carrier modulation method, and its main thought is: channel is divided into some orthogonal sub-channels, converts high-speed data signal to parallel low speed sub data flow, be modulated on each subchannel and transmit.Orthogonal signalling can separately can reduce the phase mutual interference ICI between the subchannel like this by adopt correlation technique at receiving terminal.Signal bandwidth on each subchannel is less than the correlation bandwidth of channel, so can regard the flatness decline as on each subchannel, thereby can eliminate intersymbol interference.And because the bandwidth of each subchannel only is the sub-fraction of former channel width, it is relatively easy that channel equalization becomes.OFDM has been used in the several wireless system standards at present, for example European digital audio and digital video broadcast system (DAB, DVB-T, DVB-H), 5GHz high data rate WLAN (IEEE802.11a, HiperLan2, MMAC) system etc.

In that some have adopted in the multi-media broadcasting system of OFDM at present, also there are some defectives and unsatisfactory place.Mobile Multimedia Broadcasting is the mobile transmission system at handheld terminal, main challenge is that design supports low-power consumption, high dynamic terminal equipment to receive various speed and categorical data stream, and multi-media broadcasting system of the prior art only uses unified code rate and interleaving mode to handle to data flow, so, when receiver ambient signal of living in is bad, can only solve the quality problems of multi-medium data such as image, and the transfer of data of different quality grade can not be provided according to different demands for services by the approach that increases the receiver power consumption; In addition, in the frame structure of some multi-media broadcasting systems, do not have independently synchronization signal designs, increased the lock in time and the synchronization accuracy of receiver; Moreover scrambler design has only a kind ofly in these broadcast systems, also is unfavorable for single frequency network.

For solution comprises many defectives that the problems referred to above are interior again, need a better mobile digital multi-media broadcast transfer scheme.

Summary of the invention

In view of this, the object of the present invention is to provide the transfer system and the method for signal and communication in a kind of mobile digital multimedia broadcast system.

In order to achieve the above object, it is as follows to the invention provides scheme:

A kind of mobile digital multimedia broadcast signal transmission system, its characteristics are that it comprises:

Two groups of channel encoders receive first, second group data stream respectively and will be converted to bit stream after the encoded and interleaving treatment of data flow;

Constellation mapper, be used for two groups of bit streams of described two groups of channel encoders output in conjunction with after be mapped as the symbols streams of QAM pattern;

The OFDM symbol forms module, and the symbols streams that is used for forming according to described constellation mapper forms the OFDM symbol;

Become frame module, be used for described OFDM symbol is added beacon to form transmission frame;

The up-conversion module is used for described transmission frame is carried out the radiofrequency signal that up-conversion is used to launch with generation.

Further, in above-mentioned first, second group data stream, first group data stream is represented the dibit or four bits of energy maximum, and second group data stream is represented other low-yield bits;

Further, above-mentioned QAM pattern is 16QAM, 64QAM pattern;

Further, when above-mentioned QAM pattern is the 16QAM pattern, b0b1 is distributed to first group data stream, b2b3 is distributed to second group data stream;

Further, when the QAM pattern is the 64QAM pattern, b0b1 is distributed to first group data stream, b2b3b4b5 distributes to second group data stream; Perhaps b0b1b2b3 is distributed to first group data stream, b4b5 distributes to second group data stream;

Further, when being mapped as the symbols streams of QAM pattern, can increase the energy of two bits of energy maximum in 16QAM and the 64QAM modulation; At first carry out 16QAM or 64QAM modulation according to common mode, the amplitude to I road signal and Q road signal increases a numerical value 1 or 3 (suppose that the I of 16QAM or the amplitude of Q are 1,3, the I of 64QAM or the amplitude of Q are 1,3,5,7) respectively then, and sign is constant;

Further, described each channel encoder all includes outer encoder, external interleaver, inner encoder and inner encoder, and first and second group data stream is handled back output through outer encoder, external interleaver, inner encoder and inner encoder successively;

Further, described each channel encoder can have different code rates and interleaving mode;

Further, described two-way channel encoder can be different, and every path channels encoder can include only outer encoder, external interleaver, inner encoder and the interior part unit of compiling in the interleaver;

Further, described outer encoder adopts binary system BCH code or RS sign indicating number;

Further, described external interleaver can interweave by a checking symbol at the RS sign indicating number, and the information symbol to the RS sign indicating number does not interweave;

Further, described inner encoder can adopt LDPC sign indicating number or QC-LDPC sign indicating number;

Further, the subcarrier of described OFDM symbol formation module and the corresponding relation of data and pilot tone are: (1) effectively subcarrier number is 0～3075 (when the channel width position is 8MHz) or 0～627 (when the channel width position is 2MHz); (2) insert scattered pilot, in even number OFDM symbol (0 beginning), effective subcarrier that numbering satisfies 8*K (K is an integer) form is a scattered pilot; In odd number OFDM symbol, effective subcarrier that numbering satisfies 8*K+4 (K is an integer) form is a scattered pilot; (3) add continuous pilot; (4) modulate effectively-1537～1538 in the corresponding IFFT conversion of subcarrier 0～3075 difference, or-313～314 in the corresponding IFFT conversion of 0～627 difference;

Further, described scattered pilot can selectively increase the 2-4dB transmitting power;

Further, described beacon comprises two identical synchronizing signals and identification signal of transmitter.

The present invention is by adopting the mode of dual input hierarchical modulation, two bits or four bits with the energy maximum in to the QAM modulation separate with all the other bits, modulate different code streams respectively, these two code streams can have different code rates and interleaving mode, the energy that can also increase simultaneously two bits of energy maximum carries out different modulation at the data code flow of different-energy, make that receiving function reaches better reception, and can be the transfer of data that different demands for services provides the different quality grade; Moreover the insertion of synchronizing signal has been accelerated the synchronizing speed of receiver and precision and can be used for channel estimating in the beacon infrastructure; Also have, the present invention selectively increases transmitting power and is used to improve the receiver channel estimation performance in scattered pilot, make that the channel estimating of receiving terminal is more accurate, and the demodulation performance of receiving terminal also improves a lot.

Come the present invention with embodiment with reference to the accompanying drawings and include but not limited to that above-mentioned plurality of advantages is described in more detail.

Description of drawings

Fig. 1 is the block diagram of a kind of execution mode of mobile digital multimedia broadcast signal transmission system of the present invention;

Fig. 2 is the block diagram of the channel coding module of mobile digital multimedia broadcast signal transmission system of the present invention;

Fig. 3 A, 3B are respectively 16QAM and 64QAM pattern constellation mapping schematic diagram;

Fig. 4 is data subcarrier, scattered pilot and the continuous pilot subcarrier allocation figure at the OFDM symbol;

Fig. 5 is the concrete structure that linear feedback shift is deposited;

Fig. 6 is B _fOFDM sub-carrier structure figure during=8MHz;

Fig. 7 is B _fOFDM sub-carrier structure figure during=2MHz;

Fig. 8 is that time slot is divided and frame assumption diagram;

Fig. 9 is a beacon infrastructure;

Figure 10 is the structure chart of OFDM symbol;

Figure 11 is RS coding and single fisherman's knot composition.

Embodiment

According to an aspect of the present invention, the present invention proposes a kind of a kind of execution mode of mobile digital multimedia broadcast signal transmission system, it is described specifically to please refer to Fig. 1.Generally speaking, described mobile digital multimedia broadcast signal transmission system comprises that two groups of channel encoders 10,11, constellation mapper 20, OFDM symbol form module 30, become frame module 40, up-conversion module 50.Described two groups of channel encoders 10,11 receive first, second group data stream respectively and data flow are converted to bit stream after the encoded and interleaving treatment.Be mapped as the symbols streams of QAM pattern after two groups of bit streams combinations that described constellation mapper 20 is used for described two groups of channel encoders are exported.Described OFDM symbol forms module 30 and is used for forming the OFDM symbol according to the symbols streams of described constellation mapper formation.Described one-tenth frame module 40 is used for described OFDM symbol is added beacon to form transmission frame.Described up-conversion module 50 is used for described transmission frame is carried out the radiofrequency signal that up-conversion is used to launch with generation.

According to another aspect of the present invention, the present invention proposes a kind of a kind of execution mode of mobile digital multi-media broadcast signal transmission method, described a kind of mobile digital multi-media broadcast signal transfer approach comprises: a) receive first, second group data stream respectively and will be converted to bit stream after the encoded and interleaving treatment of data flow; B) with two groups of bit streams of described two groups of channel encoders output in conjunction with after be mapped as the symbols streams of QAM pattern; C) symbols streams that forms according to described constellation mapper forms the OFDM symbol; D) described OFDM symbol is added beacon to form transmission frame; E) described transmission frame is carried out launching after the up-conversion.

Below mainly successively the embodiment of each functional module is described in detail according to the pass order of signal flow.

1.1 chnnel coding

Specifically please referring to Fig. 2, each channel encoder all includes outer encoder 101, external interleaver 102, inner encoder 103 and inner encoder 104, and first and second group data stream is handled back output through outer encoder, external interleaver, inner encoder and inner encoder successively.Described first group data stream and second group data stream can be to be formed by same data distribution, and wherein group data stream is represented the dibit of energy maximum, and second group data stream is represented other low-yield bits.In a specific embodiment, described data flow can be a video data stream.

1.1.1 outer coding and outer interweaving

Described outer encoder can adopt binary system BCH code or RS sign indicating number.The binary system BCH code can adopt the shortened code (240,216) of (255,231).The RS sign indicating number can adopt code length be 240 bytes RS (240, K) shortened code, (255, M) systematic code produces by brachymemma this yard, wherein M=K+15 by original RS.(240, K) sign indicating number provides 4 kinds of patterns to RS, is respectively K=240, K=224, K=192, K=176.

Shortened code (240, K) can encode in the following way: at K input information byte (m ₀, m ₁..., m _K-1) 15 complete " 0 " bytes of preceding interpolation, be configured to original (255, M) list entries of systematic code (0 ... 0, m ₀, m ₁..., m _K-1), coding back generated codeword (0 ... 0, m ₀, m ₁..., m _K-1, p ₀, p ₁..., p _255-M-1), from code word, leave out the byte of interpolation again, promptly obtain the shortened code (m of 240 bytes ₀, m ₁..., m _K-1, p ₀, p ₁..., p _255-M-1)

The external interleaver structure can be block interleaver, and the columns of external interleaver can be fixed as 240, and interleave depth is by line number M _IDetermine.

Work as B _fDuring=8MHz, the line number of external interleaver is by the byte-interleaved pattern of system's appointment and the LDPC code check decision of inner encoder; Work as B _f=2MHz, the line number of external interleaver is by the LDPC code check of constellation mapping pattern and inner encoder, shown in following table one.External interleaver parameter MI, wherein, B _fThe expression baseband bandwidth.

Table one

		1/2 LDPC sign indicating number	3/4 LDPC sign indicating number
				B f＝8MHz	Interlace mode	1	MI＝24	MI＝36
Interlace mode 2	MI＝72	MI＝108
			Interlace mode 3		MI＝144	MI＝216
Interlace mode 4	MI＝288	MI＝432
			B f＝2MHz		BPSK	MI＝36	MI＝54
QPSK	MI＝72	MI＝108
				16QAM	MI＝144	MI＝216

This shows, increased the shorter option that interweaves when interweaving outside, can lower the memory demand of reception like this, reduce power consumption simultaneously.

1.1.2 in-line coding and interweaving

Inner encoder can adopt LDPC sign indicating number or QC-LDPC sign indicating number, and the coding configuration as shown in Table 2.

Table two

Code check	The information bit length K	Code word size N
			1/2	4608 bits	9216 bits
3/4	6912 bits	9216 bits

LDPC output code word C={c ₀, c ₁..., c ₉₂₁₅By input information bits S={s ₀, s ₁..., s _K-1And check bit P={p ₀, p ₁..., p _9215-KComposed as follows:

$c_{\mathrm{COL}\_\mathrm{ORDER}\left(i\right)}=\left\{\begin{array}{cc}{p}_i& 0\≤i\≤9215-K\\ s_{i+K-9216}& 9216-K\≤i\≤9215\end{array}\right.$

The information bit of 1/2LDPC piece is corresponding to the TS bag of 3 188 bytes, and the information bit of 3/4LDPC piece is corresponding to the TS bag of 4.5 188 bytes.

Inner encoder can also adopt QC-LDPC coding, because the performance of the performance of QC-LDPC sign indicating number and common LDPC sign indicating number quite or lower slightly, still has very low implementation complexity.The complexity of its realization of decoding has only 1/4 of common LDPC sign indicating number decoding complexity, even lower.And LDPC decoding occupies the proportion about 1/3 in the demodulator circuit of receiving terminal, and simplification LDPC decoding has very large meaning to the cost and the power consumption of receiving terminal.Radio communication and the broadcast system of most of at present employing LDPC all adopt the QC-LDPC sign indicating number basically.

Bit input interleaver behind the LDPC coding interweaves.Interleaver adopts M _b* I _bBlock interleaver, M _bAnd I _bValue as shown in Table 3.

Table three

	M b	I b
			B f＝8MHz	384	360
B f＝2MHz	192	144

The output of interleaver and slot synchronization, first bit that promptly transmits in the time slot are defined as first bit of bit interleaver output all the time.

Memory requirements when interior interleaving block can adopt the design of squarish can reduce the receiver deinterleaving.

1.2 constellation mapping

Be mapped as the symbols streams of QAM pattern after two groups of bit streams combinations that described constellation mapper is used for described two groups of channel encoders are exported.Described QAM pattern is 16QAM, 64QAM or 256QAM pattern.Utilize hierarchical modulation that the quality of different brackets is provided at different service requests.Because first group data stream is represented the dibit of energy maximum, second group data stream is represented other low-yield bits, please specifically referring to shown in Fig. 3 A, when the QAM pattern is the 16QAM pattern, bit-order is b0b1b2b3, b0b1 can be distributed to first group data stream, b2b3 is distributed to second group data stream; Please specifically referring to shown in Fig. 3 B, when the QAM pattern was the 64QAM pattern, bit-order was b0b1b2b3b4b5, b0b1 can be distributed to first group data stream, and b2b3b4b5 distributes to second group data stream; When the QAM pattern is the 256QAM pattern, b0b1 is distributed to first group data stream, b2b3b4b5b6b7b8b9b10b11b12b13b14b15 is distributed to second group data stream.Constellation mapper can also adopt BPSK, QPSK pattern in addition.

Various sign map add the power normalization factor (the normalization factor  of QPSK, the normalization factor of 16QAM

, the normalization factor of 64QAM

), make the average power advolution of various sign map.

So far as can be seen, two bits and all the other bits to energy maximum in 16QAM and the 64QAM modulation separate in the present invention, modulate different code streams respectively, and these two code streams can have different code rates and interleaving mode.Can increase simultaneously the energy of two bits of energy maximum in 16QAM and the 64QAM modulation.At first carry out 16QAM or 64QAM modulation according to common mode, then the amplitude of I road signal and Q road signal (seeing also Fig. 2 and Fig. 3) is increased a numerical value 1 or 3 respectively and (suppose that the I of 16QAM or the amplitude of Q are 1,3, the I of 64QAM or the amplitude of Q are 1,3,5,7), sign is constant.The transfer of data of different quality grade can be provided for different demands for services like this.

1.3 the OFDM symbol forms

Described OFDM symbol is loaded into effective subcarrier and forms the OFDM symbol after forming the symbols streams of module 40 with scattered pilot and the output of continuous pilot insertion constellation mapping module.After being loaded into effective subcarrier, the symbols streams of constellation mapping module output forms data subcarrier.

Each OFDM symbol comprises N _vIndividual effective subcarrier, N _vValue is:

$N_V=\left\{\begin{array}{cc}3076,& B_f=8\mathrm{MHz}\\ 628,& B_f=2\mathrm{MHz}\end{array}\right.$

Remember in each time slot on n the OFDM symbol i effectively subcarrier be X _n(i), i=0,1 ... N _v-1; 0≤n≤52.The subcarrier of OFDM symbol is distributed to data subcarrier, scattered pilot and continuous pilot according to mode shown in Figure 4.

1.3.1 continuous pilot

B _fDuring=8MHz, comprise N1 continuous pilot in each OFDM symbol; B _fDuring=2MHz, each OFDM symbol comprises N2 continuous pilot.

The partial continuous pilot tone is used to transmit transmission parameter signaling, and modulation system is BPSK, and transmission parameter signaling comprises timeslot number; the byte interleaver device sync id, configuration change indication, front and back protection length option; the external encode and the option that interweaves, the in-line coding and the option that interweaves, scattered pilot option etc.

1.3.2 scattered pilot

Scattered pilot sends known symbol 1+0j.In each time slot in n OFDM symbol the subcarrier number m value rule of scattered pilot correspondence as follows:

B _f＝8MHz：

if mod(n，2)＝＝0 if mod(n，2)＝＝1

Option one $m=\left\{\begin{array}{c}8P+1,p=\mathrm{0,1},\·\·\·191\\ 8p+3,p=\mathrm{192,193},\·\·\·383\end{array}\right.$ $m=\left\{\begin{array}{c}8P+5,p=\mathrm{0,1},\·\·\·191\\ 8p+7,p=\mathrm{192,193},\·\·\·383\end{array}\right.$

if mod(n，2)＝＝0 if mod(n，2)＝＝1

Option 2 $m=\left\{\begin{array}{c}8P+1,p=\mathrm{0,1},\·\·\·191\\ 8p+6,p=\mathrm{192,193},\·\·\·383\end{array}\right.$ $m=\left\{\begin{array}{c}8P=5,p=\mathrm{0,1},\·\·\·191\\ 8p+10,p=\mathrm{192,193},\·\·\·383\end{array}\right.$

The inserted mode of option 2 can be simplified the design of receiving terminal scattered pilot interpolation filter.B _f＝2MHz：

if mod(n，2)＝＝0 if mod(n，2)＝＝1

$m=\left\{\begin{array}{c}8P+1,p=\mathrm{0,1},\·\·\·38\\ 8p+3,p=\mathrm{39,40},\·\·\·77\end{array}\right.$ $m=\left\{\begin{array}{c}8P+5,p=\mathrm{0,1},\·\·\·38\\ 8p+7,p=\mathrm{39,40},\·\·\·77\end{array}\right.$

Scattered pilot can selectively increase the 2-4dB transmitting power and be used to improve the receiver channel estimation performance, can make the channel estimating of receiving terminal more accurate, and the demodulation performance of receiving terminal is improved more than the 0.5dB.

1.3.3 data subcarrier

Subcarrier in each OFDM symbol except that scattered pilot and continuous pilot is a data subcarrier.The data symbol of data subcarrier after according to the front and back sequential delivery constellation mapping of subcarrier, OFDM symbol.Have 138330 (B in each time slot _f=8MHz) or 27666 (B _f=2MHz) individual data subcarrier, wherein preceding 138240 (B _f=8MHz) or 27648 (B _f=2MHz) individual subcarrier is used to carry the data complex symbol after the constellation mapping, last 90 (B _f=8MHz) or 18 (B _f=2MHz) individual symbol is filled 0+0j.

1.3.4 scrambler

To data subcarrier, scattered pilot and continuous pilot etc., all by a multiple pseudo random sequence P _c(i) scrambler.Multiple pseudo random sequence P _c(i) generating mode is as follows:

$P_c\left(i\right)=\frac{\sqrt{2}}{2}[(1-2S_i\left(i\right))+j(1-2S_q\left(i\right))]$

Wherein, S _i(i) and S _q(i) be that 12 bit shift register produce pseudo random sequence, produce that corresponding generator polynomial is: x by linear feedback shift register shown in Figure 5 ¹²+ x ¹¹+ x ⁸+ x ⁶+ 1.The initial value of shift register provides 8 kinds of different options, as shown in Table 4:

Scrambler shift register initial value

Table four

Option	Initial value
		0	0000 0000 0001
1	0000 1001 0011
		2	0000 0100 1100
3	0010 1011 0011
		4	0111 0100 0100
5	0000 0100 1100
		6	0001 0110 1101
7	0010 1011 0011

The concrete structure that the linear feedback shift of scrambler is deposited please refer to Fig. 5.Scrambler passes through complex symbol on effective subcarrier and multiple pseudo random sequence P _c(i) carrying out complex multiplication realizes.During single frequency network, the adjacent transmitters in the service area adopts different scrambling codes to the data scrambling, utilizes identification signal of transmitter and scrambling code information to help receiver and selects the signal of " the best " transmitter emission to receive.

1.3.4 OFDM modulated carrier

OFDM subcarrier Y behind insertion pilot tone and the scrambler _n(i), 0≤i≤N _SBe mapped as the OFDM symbol by IFT:

$S_n\left(t\right)=\frac{1}{N_S}\underset{i=0}{\overset{N_S-1}{\mathrm{\Σ}}}{Z}_n\left(i\right)e^{j2\mathrm{\πi}{\left(\mathrm{\Δf}\right)}_S(t-T_{\mathrm{CP}})},$ 0≤t≤(T _S+T _CP)，0≤n≤52

Wherein:

S _n(t) be n OFDM symbol in the time slot

N _SBe OFDM symbol sub-carrier number, value is:

$N_S=\left\{\begin{array}{cc}4096,& B_f=8\mathrm{MHz}\\ 1024,& B_f=2\mathrm{MHz}\end{array}\right.$

(Δ f) _SBe the subcarrier spacing of OFDM symbol, value is 2.44140625kHz.Z _n(i) be data carried by data on i subcarrier in n the OFDM symbol, mapping relations are as follows

B _f＝8MHz：

$Z_n\left(i\right)=\left\{\begin{array}{cc}{Y}_n(i-1),& 1\≤i\≤1538\\ Y_n(i-1020),& 2558\≤i\≤4095\\ 0,& i=0\mathrm{or}1539\≤i\≤2557\end{array}\right.$

B _f＝2MHz：

$Z_n\left(i\right)=\left\{\begin{array}{cc}{Y}_n(i=1),& 1\≤i\≤314\\ Y_n(i-396),& 710\≤i\≤1023\\ 0,& i=0\mathrm{or}315\≤i\≤709\end{array}\right.$

B _f=8MHz and B _fOFDM sub-carrier structure during=2MHz respectively as shown in Figure 6 and Figure 7.

1.4 framing

Described one-tenth frame module 40 is used for described OFDM symbol is added beacon to form transmission frame.

1.4.1 the time domain frame structure of described transmission frame

Physical layer signal was 1 frame in per 1 second, was divided into 40 time slots.The length of each time slot is 25ms, comprises 1 beacon and 53 OFDM symbols.Time slot division and frame structure are as shown in Figure 8.

The reason of dividing slot transmission is to adopt different slot transmission at data flow of different nature (video, audio frequency, control information and emergent broadcasting information etc.), to make things convenient for the flexible configuration of media access layer (MAC).

1.4.2 beacon

Beacon infrastructure comprises 2 identical synchronizing signals and identification signal of transmitter (TxID) as shown in Figure 8.

A) synchronizing signal

Described synchronizing signal S _b(t) be the limited pseudo-random signal of frequency band, length is designated as T _b, value is 204.8 μ s.Synchronizing signal is produced by following formula:

$S_b\left(t\right)=\frac{1}{N_b}\underset{i=0}{\overset{N_b-1}{\mathrm{\Σ}}}{X}_b\left(i\right)e^{j2\mathrm{\πi}{\left(\mathrm{\Δf}\right)}_{b}t},$ 0≤t≤T _b

Wherein: N _bBe the sub-carrier number of synchronizing signal, value is as follows:

$N_b=\left\{\begin{array}{cc}2048,& B_f=8\mathrm{<figure-callout\; id="512"\; label="MHz"\; filenames="A20061013199600211.png"\; state="\{\{state\}\}">MHz</figure-callout>}\\ 512,& B_f=2\mathrm{MHz}.\end{array}\right.$

(Δ f) _bBe the subcarrier spacing of synchronizing signal, value is 4.8828125kHz.

X _b(i) be the pseudo-random signal of BPSK modulation, pseudo random sequence is produced by ten single place shift registers.

The insertion of synchronizing signal has been accelerated the synchronizing speed of receiver and precision and can be used for channel estimating.

B) identification signal of transmitter

Identification signal of transmitter S _ID(t) be the limited pseudo-random signal of frequency band, be used to identify different transmitters.S _ID(t) length is designated as T _ID, value is 36.0 μ s.Identification signal of transmitter is produced by following formula:

$S_{\mathrm{ID}}\left(t\right)=\frac{1}{N_{\mathrm{ID}}}\underset{i=0}{\overset{N_{\mathrm{ID}}-1}{\mathrm{\&Sigma;}}}{X}_{\mathrm{ID}}\left(i\right)e^{j2\mathrm{\&pi;i}{\left(\mathrm{\&Delta;f}\right)}_{\mathrm{ID}}(t-T_{\mathrm{IDCP}})},$ 0≤t≤T _ID

Wherein: N _IDBe the sub-carrier number of identification signal of transmitter, value is as follows:

$N_b=\left\{\begin{array}{cc}256,& B_f=8\mathrm{MHz}\\ 64,& B_f=2\mathrm{MHz}\end{array}\right.$

(Δ f) _IDBe the subcarrier spacing of identification signal of transmitter, value is 39.0625kHz.

X _ID(i) pseudo-random signal of modulating for BPSK.

Sender unit identification sequence TxID (k) length is 191 bit (B _f=8MHz) or 37 bit (B _f=2MHz).The Cyclic Prefix of sender unit identification (IDCP) length T _IDCP=10.4uS

1.4.3OFDM symbol

The OFDM symbol is by Cyclic Prefix (CP), and OFDM symbol body and selectable protection (GI) at interval constitute.As shown in figure 10.The protection blank signal is overlapped through windowing by the protections of the front and back between adjacent OFDM (GD) and forms, as shown in Figure 9.

T ₀Be symbol body length, T ₁Be circulating prefix-length, T _GDBe front and back protection length.T ₀, T ₁And T _GDValue list in table five:

Table five

Option	T0(μs)	T1(μs)	TGD(μs)
				1	409.6	51.2	2.4
2	409.6	53.6	0

1.5 up-conversion

Described up-conversion module 50 is used for described transmission frame is carried out the radiofrequency signal that up-conversion is used to launch with generation.

The baseband signal of framing produces radiofrequency signal through behind the quadrature up-conversion, and radiofrequency signal is described by following formula:

S(t)＝Re{exp(j×2πf _ct)×[Frame(t)F(t)]}

Wherein, S (t) is a radiofrequency signal

f _cBe carrier frequency

Frame (t) is the baseband signal after the framing

F (t) is the emission filter impulse response.

The above only is preferred embodiment of the present invention, and is in order to restriction the present invention, within the spirit and principles in the present invention not all, any modification of being done, is equal to replacement etc., all should be included within protection scope of the present invention.

Claims (16)

1. a mobile digital multimedia broadcast signal transmission system is characterized in that it comprises

Two groups of channel encoders receive first, second group data stream respectively and will be converted to bit stream after the encoded and interleaving treatment of data flow;

Constellation mapper, be used for two groups of bit streams of described two groups of channel encoders output in conjunction with after be mapped as the symbols streams of QAM pattern;

The OFDM symbol forms module, and the symbols streams that is used for forming according to described constellation mapper forms the OFDM symbol;

Become frame module, be used for described OFDM symbol is added beacon to form transmission frame;

The up-conversion module is used for described transmission frame is carried out the radiofrequency signal that up-conversion is used to launch with generation.

2. mobile digital multimedia broadcast signal transmission system according to claim 1 is characterized in that, wherein first group data stream is represented the dibit or four bits of energy maximum, and second group data stream is represented other low-yield bits.

3. mobile digital multimedia broadcast signal transmission system according to claim 2 is characterized in that, described QAM pattern is 16QAM, 64QAM pattern.

4. mobile digital multimedia broadcast signal transmission system according to claim 3 is characterized in that, when the QAM pattern is the 16QAM pattern, b0b1 is distributed to first group data stream, and b2b3 is distributed to second group data stream.

5. mobile digital multimedia broadcast signal transmission system according to claim 3 is characterized in that, when the QAM pattern is the 64QAM pattern, b0b1 is distributed to first group data stream, and b2b364b5 is distributed to second group data stream.

6. mobile digital multimedia broadcast signal transmission system according to claim 3 is characterized in that, when the QAM pattern is the 64QAM pattern, b0b1b2b3 is distributed to first group data stream, and b4b5 is distributed to second group data stream.

7. according to claim 4 and 5 described mobile digital multimedia broadcast signal transmission systems, it is characterized in that, when being mapped as the symbols streams of QAM pattern, can increase the energy of two bits of energy maximum in 16QAM and the 64QAM modulation.At first carry out 16QAM or 64QAM modulation according to common mode, the amplitude to I road signal and Q road signal increases a numerical value 1 or 3 (suppose that the I of 16QAM or the amplitude of Q are 1,3, the I of 64QAM or the amplitude of Q are 1,3,5,7) respectively then, and sign is constant.

8. mobile digital multimedia broadcast signal transmission system according to claim 1, it is characterized in that, described each channel encoder includes outer encoder, external interleaver, inner encoder and the interior interleaver of compiling, and first and second group data stream is handled the back through outer encoder, external interleaver, inner encoder and inner encoder successively and exported.

9. mobile digital multimedia broadcast signal transmission system according to claim 8 is characterized in that, described each channel encoder can have different code rates and interleaving mode.

10. mobile digital multimedia broadcast signal transmission system according to claim 8, it is characterized in that, described two-way channel encoder can be different, and every path channels encoder can include only outer encoder, external interleaver, inner encoder and the interior part unit of compiling in the interleaver.

11. mobile digital multimedia broadcast signal transmission system according to claim 8 is characterized in that, described outer encoder adopts binary system BCH code or RS sign indicating number.

12. with 11 described outer encoder and external interleavers, it is characterized in that according to Claim 8 described external interleaver can interweave by a checking symbol at the RS sign indicating number, the information symbol to the RS sign indicating number does not interweave.

13. mobile digital multimedia broadcast signal transmission system according to claim 8 is characterized in that, the inner encoder in the described channel encoder can adopt LDPC sign indicating number or QC-LDPC sign indicating number.

14. mobile digital multimedia broadcast signal transmission system according to claim 1, it is characterized in that described OFDM symbol forms the subcarrier of module and the corresponding relation of data and pilot tone is: (1) effectively subcarrier number is 0～3075 (when the channel width position is 8MHz) or 0～627 (when the channel width position is 2MHz); (2) insert scattered pilot, in even number OFDM symbol (0 beginning), effective subcarrier that numbering satisfies 8*K (K is an integer) form is a scattered pilot; In odd number OFDM symbol, effective subcarrier that numbering satisfies 8*K+4 (K is an integer) form is a scattered pilot; (3) add continuous pilot; (4) modulate effectively one 1537～1538 in the corresponding IFFT conversion of subcarrier 0～3075 difference, or-313～314 in the corresponding IFFT conversion of 0～627 difference;

15. mobile multimedia broadcast signal transmission system according to claim 14 is characterized in that, described scattered pilot can selectively increase the 2-4dB transmitting power.

16. mobile multimedia broadcast signal transmission method according to claim 1 is characterized in that, described beacon comprises two identical synchronizing signals and identification signal of transmitter.

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