The in-band on-channel digital-analog audio frequency broadcast signal generating method improved
Technical field
The invention belongs to DAB Technology field, specifically, relate to the production method of in-band on-channel (Time Domain Overlapping – In Band On Channel, TDO-IBOC) the digital-analog audio frequency broadcast signal of the improvement of time domain aliasing.
Background technology
Along with the fast development of TV, the Internet, mobile radio communication, traditional frequency modulation audio has been broadcasted into secondary important media method, urgently carries out digital improvement thus excites new business model and profit mode.
Existing frequency modulation digitizing technique scheme mainly contains the digital audio broadcasting (DAB in Europe, DigitalAudio Broadcasting), digital am system (DRM, Digital Radio Mondiale) and the U.S. high-fidelity broadcast (High Definition Radio, HD Radio) system.
DAB system and existing frequency modulation system are difficult to realization and seamlessly transit.And DAB broadcast receiver is expensive, be difficult to the extensive accreditation obtaining user.Therefore, its popularization is restricted, and does not accomplish the marketization and industrialization so far.
DRM digital am aims of systems is exploitation and standardization DRM expanding system, and namely the digitizing technique of VHF wave band (traditional FM broadcasting frequency range), becomes the open international standard from LW wave band to VHF wave band.The band separation △ f >=150kHz of DRM+ definition, difference power △ P >=20dB.
In-band on-channel (In-Band On-Channel, IBOC) HD Radio high-fidelity broadcast system creates set of number sideband at upper and lower two sidebands of conventional FM FM signal, it has three kinds of spectrum allocation may patterns: mixed mode, extended hybrid pattern, digital pattern, the digital signal being fixed on upper and lower two sidebands of analog signal is used to transmit, the mutual interference causing Digital and analog to broadcast and quorum sensing inhibitor problem.And the digital broadcasting being transitioned into HD Radio high-fidelity broadcast system is broadcasted by analog fm, will the bandwidth of a times be taken more.This is in the intensive area of f-m broadcast station, possibly cannot by the digitlization of all radio station.To this, HD Radio high-fidelity broadcast system have employed half-way house, when FM radio station frequency planning, ensures that the radio station of 200kHz appears in the adjacent both sides of FM radio station time different.Nonetheless, system still needs to consider the first adjacent channel interference problem.The frequency spectrum of HD Radio system digital frequency-modulation signal of analog fm signal and lower sideband in main channel is completely nonoverlapping, but exists with the first adjacent channel and mutually disturb, and is therefore difficult to be applicable to existing frequency modulation frequency range, such as the frequency modulation channel of China.
In China, frequency modulation audio broadcasting frequency scope is defined as at 87 ~ 108MHz.Domestic frequency modulation audio broadcast mode is by GBT4311 specification, and modulation frequency is spaced apart 200kHz.Except monophony and stereophonic broadcasting, go back the broadcast of specification multi-Channel Acoustic and frequency modulation data radio two class.The existing FM broadcasting of China is based on analog signal, base band idle frequency spectrum is utilized to modulate the mode of additional information although also define FM broadcasting, but additional digital sidebands smaller bandwidth, is mainly used in transmitting auxiliary data message, and analog audio information that can not be transmitting digitized.And being separated with 100kHz, 200kHz, 300kHz, 500kHz and 600kHz etc. between current domestic actual FM frequency, frequency service condition is complicated, still has dummy frequencies resource to be underutilized.Existing DAB Technology is inapplicable in China.But be greatly supplementing of frequency-modulation broadcasting by making full use of of FM Digital Realization tuned radio frequency.Therefore, need a kind of new time domain aliasing in-band on-channel (Time Domain Overlapping – In Band On Channel, TDO-IBOC) production method of modulus sound broadcasting signal and corresponding transmitting apparatus, to promote the development of the audio broadcasting of China.
Chinese invention patent application " production method of the digital-analog audio frequency broadcast signal of in-band on-channel and transmitting apparatus " (number of patent application No.201110224259) is for China's actual conditions, propose a kind of method of carrying out in-band on-channel broadcast in same analog fm broadcasting channel, simulated sound broadcast singal and digital Audio Broadcasting signal are mixed into a road signal by certain way, a real shared fm broadcast channel, do not need to repartition frequency spectrum, frequency spectrum is fully used, saves frequency spectrum resource.In the production method of FM broadcasting frequency band digital broadcast singal disclosed in this patent, time discrete mixed signal is expressed as
S=(s
0,s
1,s
2,s
3,……)
=(x
0-d
0,x
1+d
0,x
2-d
1,x
3+d
1,…..x
2m–d
m,x
2m+1+d
m…..)
Namely on adjacent vector, digital signal d is repeated
m, and time-discretely simulate FM signal phasor x with corresponding
2m, x
2m-1add and subtract mutually, i.e. x
2m– d
mand x
2m+1+ d
m, the corresponding element in corresponding vector subtracts each other or is added, as shown in Figure 1.
The mixed signal of this method gained can eliminate the interference of FM signal to digital signal at receiving terminal.
Generally available concrete grammar is:
Suppose that frequency domain digital signal is d
0, simulation FM signal phasor is x
0, x
1
(x
0-d
0)+(x
1+d
0)=(x
0+x
1)
According to correlation theory (see " An Analytic Technique to Separate CochannelFM Signals ", IEEE TRANSACTIONS ON COMMUNICATIONS, VOL.48, NO.4, APRIL2000), two FM signal sum x
0+ x
1can be decomposed by mathematical formulae and obtain x
0and x
1, and then obtain d
0.
Although method disclosed in this application for patent successfully creates the digital-analog audio frequency broadcast signal of in-band on-channel, the energy band outward leakage of signal is serious, also just means that the loss of the signal energy is after filtering more.
Summary of the invention
The object of the invention is the in-band on-channel digital-analog audio frequency broadcast signal generating method proposing a kind of improvement, analog signal and digital signal carry out time domain mixing, in 2m frame, and simulated sound broadcast singal x
2madd corresponding digital broadcast signal d
m, obtain x
2m+ d
m; In 2m+1 frame, simulated sound broadcast singal x
2m+1add corresponding digital broadcast signal d
m, obtain x
2m+1+ d
m, obtain the digital-to-analogue mixed signal transmitted in same broadcasting channel.
The in-band on-channel digital-analog audio frequency broadcast signal generating method of improvement provided by the invention, comprises the following steps:
I, simulated sound broadcast singal is obtained;
II, simulated sound broadcast singal digitlization step I obtained, obtains the simulated sound broadcast singal after corresponding digitlization;
III, reproduction digital signal in adjacent signal frame;
This method, in same broadcasting channel, while the digitized simulated sound broadcast singal that transmission above-mentioned steps II obtains, goes back transmission of one line digital signal.This digital signal is through the other audio broadcast signal of a railway digital and/or the data-signal of routine of Channel Coding and Modulation, the modulation of this digital signal is traditional OFDM (Orthogonal Frequency Division Multiplexing, OFDM) multi-carrier modulation, or single-carrier modulated, or band spectrum modulation.In adjacent simulated sound broadcast singal frame, copy time-domain digital signal, namely in 2m+1 signal frame, copy the time-domain digital signal d of order 2m signal frame
m, obtain the time-domain digital signal that a consecutive frame repeats completely, namely every two adjacent signals frames form the time-domain digital signal of one group of Data duplication.
IV, analog signal and the mixing of digital signal time domain, obtain digital-to-analogue mixed signal;
The time-domain digital signal mixing that the simulated sound broadcast singal after the digitlization that the step II of adjacent signals frame obtains and corresponding step III obtain, in 2m frame, the simulated sound broadcast singal x after digitlization
2madd corresponding time-domain digital signal d
m, obtain x
2m+ d
m; In 2m+1 frame, the simulated sound broadcast singal x after digitlization
2m+1add corresponding time-domain digital signal d
m, obtain x
2m+1+ d
m, obtain the digital-to-analogue mixed signal S transmitted in same broadcasting channel,
S=(x
0+d
0,x
1+d
0,x
2+d
1,x
3+d
1,…..x
2m+d
m,x
2m+1+d
m…..) (1)。
V, the digital-to-analogue mixed signal that obtains of step IV is after digital-to-analogue conversion, up conversion and amplification, by antenna transmission.
Only adjacent two vector signals need be subtracted each other after receiving terminal receives digital-to-analogue mixed signal S, namely
s
2m-s
2m+1=x
2m+d
m-x
2m+1-d
m=x
2m-x
2m+1(2)
Digital signal d has been eliminated in the result of subtracting each other
mcomponent, namely eliminates digital signal d
mto its interference, obtain the difference of two adjacent simulated sound broadcast singal vectors.
From s
2m-s
2m+1=x
2m-x
2m+1in obtain x
2mand x
2m+1, and then from s
2m=x
2m+ d
mor s
2m+1=x
2m+1+ d
mcut x
2mor x
2m+1, namely recover digital signal d
m.This is prior art.
Specific as follows:
Suppose that the envelope of the simulated sound broadcast singal received within the relatively short time remains unchanged, and through normalized, namely amplitude is all 1, then adjacent x
2mand x
2m+1two corresponding phase modulated signals are respectively e
j αand e
j β, so obtain:
x
2m-x
2m+1=e
jα-e
jβ=(1-e
j(α-β))e
jβ
=(1-cosθ-jsinθ)e
jβ
=Ae
j(β+δ)
In above formula
θ=α-β (4)
From the difference s of adjacent two simulated sound broadcast singal vectors
2m-s
2m+1=x
2m-x
2m+1middle separation obtains x
2mand x
2m+1, d
mprocess as follows:
Step 1: adjacent two vector signals received are subtracted each other,
s
2m-s
2m+1=(x
2m+d
m)-(x
2m+1+d
m)=x
2m-x
2m+1=Ae
j(β+δ)
Therefrom can obtain its amplitude A and phase=β+δ;
Step 2: by known amplitude A, obtains from formula (6)
Step 3: step 2 is obtained θ parameter and substitutes into formula (5), obtain
Step 4: the δ parameter that step 3 obtains is substituted into the phase bit position φ=β+δ in formula (3), obtain parameter β=φ-δ, or
Wherein, x
2mand x
2m+1being the signal received, is known;
Step 5: θ, β parameter that step 2 and 4 obtain is substituted into formula (4), obtains α=θ+β;
Step 6: β and α that step 4 and step 5 obtain is substituted into phase modulated signal e respectively
j αand e
j β, obtain x
2m=e
j αand x
2m+1=e
j β;
Step 7: from the s received
2m=x
2m+ d
mor s
2m+1=x
2m+1+ d
min cut x
2mor x
2m+1, recover digital signal d
m.
In above-mentioned steps IV, described analog signal and digital signal time domain mixing method also can be digitlization after simulated sound broadcast singal be multiplied by any nonzero integer after, and then be added with corresponding digital signal, namely in 2m frame, the simulated sound broadcast singal x after digitlization
2mbe multiplied by a j and obtain jx
2m, then add corresponding time-domain digital signal d
m, obtain jx
2m+ d
m; In 2m+1 frame, the analog broadcast signal x after digitlization
2m+1be multiplied by a k and obtain kx
2m, then add corresponding time-domain digital signal d
m, obtain kx
2m+1+ d
m, j and k is the integer of any non-zero, obtains the digital-to-analogue mixed signal S transmitted in same broadcasting channel,
S=(jx
0+d
0,kx
1+d
0,jx
2+d
1,kx
3+d
1,…..jx
2m+d
m,kx
2m+1+d
m…..) (7)。
Only adjacent two vector signals need be subtracted each other after receiving terminal receives digital-to-analogue mixed signal S, namely
s
2m-s
2m+1=jx
2m+d
m-kx
2m+1-d
m=jx
2m-kx
2m+1(8)
Subtract each other and eliminated digital signal d
mcomponent, the expression formula of adjacent two the simulated sound broadcast singals obtained is jx
2m-kx
2m+1, this numerical expression be also according to above-mentioned step 1 to step 7 method decompose obtain x
2mand x
2m+1.
In above-mentioned steps IV, the method for described analog signal and the mixing of digital signal time domain is digital signal d
mcarry out repetition with L numeral sigtnal interval, then carry out " plus-minus " or " adding " mixing with analog signal, the value of L depends primarily on time delay and the storage capacity requirement of system, and L is the positive integer of 2 to 50.
Identical with front, receiver according to above-mentioned step 1 to step 7 method remove digital signal d
m, only obtain and x
2mand x
2m+1relevant expression formula, and finally obtain d
m.
In the step I of the in-band on-channel digital-analog audio frequency broadcast signal generating method of this improvement, described simulated sound broadcast singal is simulated sound fm broadcast signal; Broadcasting channel described in step III is fm broadcast channel.
The digitlization of the simulated sound broadcast singal described in step II of the in-band on-channel digital-analog audio frequency broadcast signal generating method of this improvement is time discretization.
The Channel Coding and Modulation of the digital signal described in step III of the in-band on-channel digital-analog audio frequency broadcast signal generating method of this improvement is OFDM modulation, i.e. OFDM modulation.The Fourier transform length of described OFDM is any one in 256,512,1024 and 2028.
The digital signal described in step III of the in-band on-channel digital-analog audio frequency broadcast signal generating method of this improvement is also encoded through channel error correction, error correction coding have employed serially concatenated error correcting code, ISN adopts convolution code, its female code to be code check be 1/2 convolution code, generator polynomial is (171
otc, 131
otc), process reliability enhanced deleting by forced (puncturing), obtain the convolution code of other code check, such as 2/3,3/4,5/6 and 7/8; Outer code adopts loe-density parity-check code (Low Density Parity Check, LDPC), also can adopt other cascaded code form, such as RS code+convolution code, or BCH+ loe-density parity-check code (LDPC code) etc.
Compared with prior art, the advantage of the in-band on-channel digital-analog audio frequency broadcast signal generating method of this improvement is: 1, in a broadcasting channel, propose the method producing simulated sound broadcast singal and the complete overlapping analog-digital blended signal of digital signal spectrum, at transmitting terminal, keep compatible with existing analog broadcast channel, do not need to repartition frequency spectrum, frequency spectrum is fully used, saves frequency spectrum resource; 2, the analog-digital blended signal that this method sends is convenient to receiving terminal and is separated, and can eliminate the mutual interference of simulated sound broadcast singal and digital signal, realize the good reduction of simulated sound broadcast singal and digital signal; 3, the frequency spectrum edge of gained digital-to-analogue mixed signal is more precipitous, also means that the energy of signal in band is larger; In different bandwidth situation, the energy major part (more than 90%) that digital-to-analogue mixed signal is corresponding is all gathered in predetermined bandwidth, is with outer energy very little; At the digital-to-analogue mixed signal frequency spectrum of front patent application 201110224259 scheme gained compared with this law, be with outer energy many about 30%, also just mean front scheme digital-to-analogue mixed signal after filtering after signal energy loss how close 30%.
Accompanying drawing explanation
Fig. 1 is application number digital signal combination mode schematic diagram disclosed in the patent application of CN201110224259;
Fig. 2 is the spectrum diagram of modulus signal on same frequency modulation channel in the in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 1 of this improvement;
Fig. 3 is the in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 1 step IV digital signal combination mode of this improvement;
Fig. 4 be the in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment of this improvement when 200kHz bandwidth, the power spectral density plot that the analog-digital blended signal produced is corresponding;
Fig. 5 be comparative example when 200kHz bandwidth, the power spectral density plot that the analog-digital blended signal produced is corresponding;
Fig. 6 be the in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment of this improvement when 260kHz bandwidth, the power spectral density plot that the analog-digital blended signal produced is corresponding;
Fig. 7 be comparative example when 260kHz bandwidth, the power spectral density plot that the analog-digital blended signal produced is corresponding;
Fig. 8 is in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 3 step IV digital signal " plus-minus " compound mode of this improvement;
Fig. 9 is that in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 3 step IV digital signal of this improvement " adds " compound mode.
Embodiment
Be described in detail below in conjunction with the in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment of accompanying drawing to this improvement.
The in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 1 improved
Step is as follows:
I, simulated sound broadcast singal is obtained;
In this example, m (t) is made to represent simulated sound broadcast singal, f
cit is frequency modulated carrier.Modulating signal of frequency modulation x
fMbe expressed as
x
FM=cos[α(t)]
Wherein a (t) is the phase function that following formula provides
Here f
drepresent maximum frequency deviation, and suppose
The discrete-time signal of FM signal is made to be expressed as
X
FM=(x
0,x
1,……)
Wherein x
m=(x
0, m, x
1, m..., x
n-1, m) be m length be the vector of N.Here N is a given length, represents the sampled point number that the digital signal that repeats is corresponding.
II, simulated sound broadcast singal digitlization step I obtained, obtains the simulated sound broadcast singal after corresponding digitlization;
When adopting OFDM digital signal, N is set to the FFT length (also can be the multiple of length) of OFDM modulation in digital signal usually, by the segmentation in units of the length of FFT of FM burst.In the present embodiment, N value has 256,512,1024 and 2,028 four kinds of length.
III, reproduction digital signal in adjacent signal frame;
In this example, in same frequency modulation channel, while the digitized simulated sound fm broadcast signal that transmission above-mentioned steps II obtains, go back transmission of one line digital signal, on this frequency modulation channel, the frequency spectrum of modulus signal as shown in Figure 2.
Represent the digital signal of this example with d (t), d (t) is the audio broadcast signal after an other railway digital, or the data-signal of routine.This routine digital signal adopts traditional orthogonal frequency division multiplex OFDM modulating scheme.
Digital signal d (t) make is as follows: make D
m=(D
0, m, D
1, m..., D
k-1, m) represent modulation constellation map after frequency domain digital signal, complete OFDM multi-carrier modulation through the process of N point inverse Fourier transform, the time-domain signal obtaining D is expressed as d
m=(d
0, m, d
1, m..., d
n-1, m), d here
0, d
1..., d
n-1single scalar, as x
m, d
mrepresent that length is the vector of N.
In adjacent simulated sound broadcast singal frame, copy time-domain digital signal, namely in 2m+1 signal frame, copy the time-domain digital signal d of order 2m signal frame
m, obtain the time-domain digital signal that a consecutive frame repeats completely, namely every two adjacent signals frames form the time-domain digital signal of one group of Data duplication.
IV, analog signal and the mixing of digital signal time domain, obtain digital-to-analogue mixed signal;
The time-domain digital signal mixing that the simulated sound broadcast singal after the digitlization that the step II of adjacent signals frame obtains and corresponding step III obtain, in 2m frame, the simulated sound broadcast singal x after digitlization
2madd corresponding time-domain digital signal d
m, obtain x
2m+ d
m; In 2m+1 frame, the simulated sound broadcast singal x after digitlization
2m+1add corresponding time-domain digital signal d
m, obtain x
2m+1+ d
m, obtain the digital-to-analogue mixed signal S transmitted in same broadcasting channel,
S=(x
0+d
0,x
1+d
0,x
2+d
1,x
3+d
1,…..x
2m+d
m,x
2m+1+d
m…..)。
Namely on adjacent vector, digital signal d is repeated
m, and with corresponding time-discrete simulated sound fm broadcast signal vector x
2m, x
2m-1be added, i.e. x
2m+ d
mand x
2m+1+ d
m, the corresponding element in corresponding vector is added, digital signal d wherein
marrangement mode as shown in Figure 3.
At receiving terminal, adjacent two vector signals are subtracted each other, namely
s
2m-s
2m+1=x
2m+d
m-x
2m+1-d
m=x
2m-x
2m+1
Subtract each other in rear result and eliminated digital signal d
mcomponent, namely eliminates digital signal d from analog-digital blended signal
mto the interference of simulated sound fm broadcast signal, obtain the difference of two adjacent simulation vectors.
V, the digital-to-analogue mixed signal that obtains of step IV is after digital-to-analogue conversion, up conversion and amplification, by antenna transmission.
This routine simulated sound fm broadcast signal and digital signal are transmitted completely in same channel, compared to the HD Radio system of European DRM and the U.S., the analog-digital blended signal be made up of this method is the real same band of same frequency (Truly in-band-on-channel, TIBOC), frequency spectrum as shown in Figure 2, the frequency spectrum of simulating main FM signal and digital frequency-modulation signal is completely overlapping, and namely identical frequency modulation channel is simultaneously for the main simulated sound fm broadcast signal of transportation simulator and digital frequency-modulation signal.The actual bandwidth of digital frequency-modulation signal can adjust as required.
This method proposes more precipitous with the edge of the analog-digital blended signal frequency spectrum obtained by formula (1), and the energy of signal in band is larger.
Comparative example, adopts disclosed in Chinese invention patent application " production method of the digital-analog audio frequency broadcast signal of in-band on-channel and transmitting apparatus " (number of patent application No.201110224259)
S=(x
0-d
0, x
1+ d
0, x
2-d
1, x
3+ d
1... ..x
2m– d
m, x
2m+1+ d
m..) modulus signal is mixed.
When 200kHz bandwidth, respectively as shown in Figure 4 and Figure 5, in figure, abscissa is frequency, unit kHz, and ordinate is power spectrum density, unit is dBw/Hz for the present embodiment 1 and the power spectral density corresponding to comparative example; When wider 260kHz bandwidth, the present embodiment 1 and the power spectral density corresponding to comparative example are respectively as shown in Figures 6 and 7.Can see, under 2 kinds of bandwidth, the energy of this example correspondence is all gathered in predetermined bandwidth, is with outer energy very little; The energy band outward leakage of comparative example is serious, and after carrying out baseband filtering, through calculating, the signal many about 30% that outside the band of the signal that comparative example is corresponding, energy Ratios the present embodiment is corresponding, also just means the loss of the signal energy after filtering how close 30%.
Therefore, the modulus signal mixed method of the embodiment of the present invention has obvious improvement compared with comparative example.The in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 2 improved
Step I, II, III identical with embodiment 1 with V, in step IV, digital-to-analogue mixed signal S obtains by following formula:
S=(jx
0+ d
0, kx
1+ d
0, jx
2+ d
1, kx
3+ d
1... ..jx
2m+ d
m, kx
2m+1+ d
m..) jx
2m+ kx
2m+1also be can be decomposed by mathematical formulae to obtain x
2mand x
2m+1, in above formula, j and k is any nonzero integer, and in the present embodiment, j and k is taken as 2, namely
S=(2x
0+d
0,2x
1+d
0,2x
2+d
1,2x
3+d
1,…,2x
2m+d
m,2x
2m+1+d
m…)。
" adding ++ " adjacent in above-mentioned mixed signal S also can adopt " plus-minus+-" computing, namely
S=(jx
0+d
0,kx
1-d
0,jx
2+d
1,kx
3-d
1,…..jx
2m+d
m,kx
2m+1-d
m…..)。The in-band on-channel digital-analog audio frequency broadcast signal generating method embodiment 3 improved
Step I, II, III identical with embodiment 1 with V, in step IV, digital-to-analogue mixed signal S obtains by following formula:
S=(…x
2(m-1)+d
m-2L,….x
2(m-1)+L+d
m-L-1,x
2m+d
m-L,x
2m+1+d
m-L+1,….x
2m+L-1+d
m-1,x
2m+L+d
m…)
In the present embodiment, L gets 5,
S=(…x
2(m-1)+d
m-10,….x
2(m-1)+5+d
m-6,x
2m+d
m=5,x
2m+1+d
m-4,….x
2m+4+d
m-1,x
2m+5+d
m…)。
In like manner, digital signal d
mcan not repeat in adjacent data block, that such as repeats is spaced apart L digital signal, and then as two kinds of modes above, and analog signal carries out " plus-minus+-" or " adding ++ " process, and gained digital signal is respectively as shown in Fig. 8, Fig. 9.
Therefore, in sum, as long as the modulus signal that transmitter is launched mixed according to a kind of mathematical relationship in time domain, receiver can be made still to remove digital signal d according to this mathematical relationship
m, only obtain and x
2mand x
2m+
1relevant expression formula, thus x can be obtained by mathematical formulae decomposition
2mand x
2m+1, just finally can obtain d
m.
Above-described embodiment, be only the specific case further described object of the present invention, technical scheme and beneficial effect, the present invention is not defined in this.All make within scope of disclosure of the present invention any amendment, equivalent replacement, improvement etc., be all included within protection scope of the present invention.