CN102447665A - Method for reducing peak-to-mean ratio of DTMB embedded multi-service system - Google Patents

Abstract

The invention discloses a method for reducing peak-to-mean ratio of DTMB embedded multi-service system, comprising firstly increasing degree of an extension mapping set to make multiple standard QAM constellation points belong to a preimage of an E-QAM constellation point; then during the extension mapping, selecting randomly constellation points which are not extension mapped to be fixed in a set consisting of some constellation points; considering adjacent constellation points as an extension set to make the extended frequency domain mark become random and correlation be better controlled; when the constellation point becomes random, increasing bit error rate. According to the maximum likelihood judgment rule, the Euclidean distance reduction between adjacent constellation points will result in BER performance deterioration. In order to balance the performances, the Euclidean distance is maximally reduced when the correlation is weakened. The method can maintain the bit error rate at a relatively tolerable range when reducing the peak-to-mean ratio of the system to ensure the practicability, thereby improving the practicability of the system.

Description

A kind of method that reduces the embedded multiservice system peak-to-average force ratio of DTMB

Technical field

The present invention relates to the digital TV Broadcasting Techniques field, relate in particular to the method for the embedded multiservice system peak-to-average force ratio of a kind of DTMB of reduction.

Background technology

Along with people's supports multiple services broadcast system to obtain increasing attention to the continuous increase of the professional diversity demand of data, and wherein economical and practical development approach is based on the embedded design again of ground TV broadcast system.Consider system compatibility, in multi-service embedded processing process, the low order mapping of equal value that comes from the high-order mapped extension is a kind ofly more preferably to select.This kind algorithm can run into high peak-to-average force ratio in practical application (peak-to-average power ratio, problem PAPR) has had a strong impact on systematic function, even causes system in reality, to use.

Summary of the invention

To in the embedded multiservice system of Chinese terrestrial DTV transmission standard exist higher peak all than; The objective of the invention is to propose the method for the embedded multiservice system peak-to-average force ratio of a kind of DTMB of attenuating; Make this system peak-to-average than reducing greatly, can be applied to actual environment better.

A kind of method that reduces the embedded multiservice system peak-to-average force ratio of DTMB comprises:

At first increase the degree of the set of expansion mapping, make the constellation point of a plurality of standard QAM belong to the primary image of an E-QAM constellation point, the correlation between the E-QAM frequency domain symbol is just weakened, and has promptly reached the purpose that reduces peak-to-average force ratio;

Secondly can in the set that some constellation point is formed, select at random during the expansion mapping and be not that expansion is mapped to fixing constellation point; Close constellation point is regarded as an expanded set makes the frequency domain symbol after the expansion become at random, correlation is better controlled;

Yet but brought the increase of bit error rate (BER) when making constellation point become at random; According to the maximum likelihood decision criteria, the Euclidean between adjacent constellation point is apart from reducing to cause the BER mis-behave; In order to take into account both performances, maximization minimum Eustachian distance in attenuation of correlation property.

Optional, the degree of the optional constellation point set of expansion mapping equals Standard Map mode constellation point number, and this moment, its correlation was identical with former constellation mapping mode, and peak-to-average force ratio reaches the mean value of original system.

Optional, E-QAM mapping mode at random is a lot: in the expansion mapping of E-4QAM, available mode is as follows at 64QAM: the set of establishing the ring notes is E-4QAM-R (1), and this mode is represented extended bit B ₄B ₃B ₁B ₀Option set be combined into { (0000,0101,0001,0100) }, constellation point is { (± 5, ± 5), (± 7, ± 5), (± 5, ± 7), (± 7, ± 7) }; The set that rectangle frame is annotated is made as E-4QAM-R (2), and this mode is illustrated in extended bit B ₄B ₃B ₁B ₀Option set be combined into { (1111,0111,0101,1101) }, constellation point set is { (± 3, ± 3), (± 3, ± 5), (± 5, ± 3), (± 5, ± 5) }; Similarly expand the set E-4QAM-R (3) of the constellation point of the also useful rectangle constellation point sign of option set; Constellation point set E-4QAM-R (4) with triangle constellation point sign; Enclose the constellation point of notes with irregular polygon and gather E-4QAM-R (5), and the completely random extended method E-4QAM-R (6) under the extreme case.

Optional, wait under the general situation and judge the standard MQAM mapping bit error probability that calculates with maximum-likelihood criterion, use P _bExpression; Wherein Q (x) is the truncation distribution of standard Gauss,

E _bBe energy per bit, N ₀Be noise power;

$P_b=\frac{2(L-1)}{L{\log }_{2}L}Q\left(\sqrt{\frac{6{\log }_{2}L}{2(L^2-1)}}\frac{E_b}{N_0}\right).$

Optional, seeing that 64QAM is identical with the E-4QAM of expansion at random to the fixing expansion of E-16QAM gained constellation point position feature, thereby need not increase the degree of optional set, needing only and suitably select constellation point, its peak-to-average force ratio just can effectively reduce.

Beneficial effect of the present invention: reducing system peak-to-average, keep bit error rate through the present invention in a tolerable relatively scope, improved the practicality of system than when guaranteeing practicality.The method that the present invention proposes can directly apply to actual working environment and not bring additional complexity and time-delay.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art; To do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below; Obviously, the accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills; Under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.

Fig. 1 is the embedded multi-service transmission system of DTMB;

Fig. 2 is a 64QAM expansion mapping sketch map of the present invention;

Fig. 3 is a 16QAM expansion mapping sketch map of the present invention.

Embodiment

To combine the accompanying drawing in the embodiment of the invention below, the technical scheme in the embodiment of the invention is carried out clear, intactly description, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills are not making the every other embodiment that is obtained under the creative work prerequisite, all belong to the scope of the present invention's protection.

Common multiservice system mostly have channel fading big, the time characteristics that accelerate, and require low threshold level and low-power consumption, thereby system design must guarantee backward compatibility and satisfy different service quality (quality of service, QoS) demand.

The present invention adopts the embedded multi-service data transmission system of Chinese terrestrial DTV transmission standard (DTMB).For guaranteeing the compatibility of itself and DTMB receiver, adopt based on the identity code transmission package (packet identifier, strategy is differentiated in multi-service PID); In order to satisfy different QoS requirements, (quadrature amplitude modulation QAM) expands and next low order mapping mode of equal value and different coding efficient from the high-order orthogonal amplitude modulation(PAM) in use.For simplicity, suppose to have high low bit rate two-way code stream, for example mobile video is professional and professional this system transmissions that adopts of HDTV.Fig. 1 has provided the system block diagram of this situation.The data service of low bit rate through the expansion of precoding constellation mapping, data format is adaptive and the PID scrambling after, with the follow-up DTV broadcasting system of the high sign indicating number multiplexing entering of fast television services through scrambling.Because produce the associative operation that the main cause of very high peak-to-average force ratio is the mapped extension part, the present invention will pay close attention to the constellation extension mapping block.

Higher peak-to-average force ratio can have a strong impact on the performance of system in practical application; At fixed point OFDM (orthogonal frequency division multiplexing; OFDM) in the system; High peak-to-average force ratio produces follows Discrete Fourier Transform among the OFDM often (discrete Fourier transform, saturated overflowing DFT) is further worsened systematic function together.

(1) reason of peak-to-average force ratio generation

Ofdm signal be the separate complex variable of N with, formula (1) be a kind of method for expressing of common ofdm signal.X in the formula (k) representes frequency domain symbol, and x (n) representes time-domain symbol.Under the extreme case, if all subcarriers have identical instantaneous phase, then the instantaneous amplitude of composite signal be all subcarrier amplitude peaks and.If N has the subcarrier stack of unit power, for synthetic ofdm signal, its average power is N, and peak power equals N under the observing time sufficiently long situation ², so the peak-to-average power ratio of ofdm signal is N; If all subcarriers all have separate instantaneous phase, according to central-limit theorem, when number of sub carrier wave was enough big, the distribution of ofdm signal trended towards Gauss and distributes, and the Rayleigh that its amplitude satisfies formula (2) distributes.σ ²It is the variance of this distribution.

$X\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}x\left(n\right)\exp (-j\frac{2\mathrm{\π}}{N}\mathrm{nk})---\left(1\right)$

$f\left(r\right)=\frac{r}{{\mathrm{\σ}}^2}\exp (-\frac{r^2}{2{\mathrm{\σ}}^2})---\left(2\right)$

Accumulation distribution complementary function (complementary cumulative distribution function according to peak-to-average force ratio; CCDF); The accumulation distribution complementary function that can be met the ofdm signal peak-to-average force ratio of Gauss distribution satisfies formula (4), and wherein Q (x) is the truncation distribution of standard Gauss.

CCDF(PAPR ₀)＝P(PAPR＞PAPR ₀) (3)

CCDF(r ₀)＝2Q(r ₀) (4)

Yet; If in embedding multiservice system, adopt the method for fixing expansion mapping; Then its frequency domain symbol phase place and amplitude all are fixed, and the amplitude distribution of its ofdm signal will no longer satisfy formula (2) but fixed overlay simply, and the convergence in probability that high peak-to-average force ratio occurs is in 1.

Seeing that system according to the invention frequency domain symbol phase supposes independently and is false that need are sought the character of this kind sequence from another angle.The peak-to-average force ratio of multicarrier system is higher to be to cause each subcarrier capacity volume variance great disparity because the energy of subcarrier can't be allocated in advance, and multi-carrier modulation essence is of equal value with DFT, from the DFT viewpoint of measures, and the peak-to-average force ratio of the proper corresponding time-domain symbol of correlation of frequency domain symbol.

The degree of correlation of Schroeder proof signal time domain or frequency domain is corresponding with the peak-to-average force ratio in another territory.The stronger peak-to-average force ratio in another territory of the degree of correlation of signal in a territory is just high more.It is exactly the degree of correlation that will reduce frequency domain symbol that multicarrier system reduces peak-to-average force ratio.

In order to obtain better anti-fading property, this embedded system signal only is mapped to the bit error performance (be similar to hard seat mapping preceding precoding) of certain several constellation point to obtain low order QAM mapping of equal value (E-QAM) of standard high-order QAM.In this step,, increased the degree of correlation of signal undoubtedly if adopt fixing expansion (the E-MQAM constellation point is the constellation point of M fixing high-order QAM) strategy.For example, (64QAM expands to E-16QAM:{ (± 3, ± 5), (± 5, ± 3) to said fixedly mapping mode; (± 5, ± 5), (± 3, ± 3) }; 64QAM expands to { (± 5, ± 5) }, and 16QAM is to E-4QAM{ (± 3, ± 3) } the high peak-to-average force ratio that caused is that real system is intolerable.

(2) shine upon based on the expansion at random of E-QAM

The peak-to-average force ratio of reduction system need reduce the degree of correlation of frequency-region signal, promptly increases the randomness of frequency-region signal.Dynamic constellation extension technology (adaptive constellation extension, ACE) a solution of can yet be regarded as.Yet the increase of the complexity that the ACE algorithm brings and time-delay are that system is difficult to bear.

If increase the degree of the set of expansion mapping, make the constellation point of a plurality of standard QAM belong to the primary image of an E-QAM constellation point, the correlation between the E-QAM frequency domain symbol is just weakened, and has promptly reached the purpose that reduces peak-to-average force ratio.When mapping expansion can be selected at random in the set that some constellation point is formed and be not that expansion is mapped to fixing constellation point.Close constellation point is regarded as an expanded set makes the frequency domain symbol after the expansion become at random, correlation is better controlled.The degree of the optional constellation point set of expansion mapping equals Standard Map mode constellation point number under the egregious cases, and this moment, its correlation was identical with former constellation mapping mode, and peak-to-average force ratio reaches the mean value of original system.

E-QAM mapping mode at random is a lot: in the expansion mapping of E-4QAM, available mode is as shown in Figure 2 at 64QAM.If the set that ring is annotated is E-4QAM-R (1), this mode is represented extended bit B ₄B ₃B ₁B ₀Option set be combined into { (0000,0101,0001,0100) }, constellation point is { (± 5, ± 5), (± 7, ± 5), (± 5, ± 7), (± 7, ± 7) }; The set that rectangle frame is annotated is made as E-4QAM-R (2), and this mode is illustrated in extended bit B ₄B ₃B ₁B ₀Option set be combined into { (1111,0111,0101,1101) }, constellation point set is { (± 3, ± 3), (± 3, ± 5), (± 5, ± 3), (± 5, ± 5) }; Similarly expand the set E-4QAM-R (3) of the constellation point of the also useful rectangle constellation point sign of option set; Constellation point set E-4QAM-R (4) with triangle constellation point sign; Enclose the constellation point of notes with irregular polygon and gather E-4QAM-R (5), and the completely random extended method E-4QAM-R (6) under the extreme case (the option set merging is not limited to cited).

The fixing expansion of comparing, part constellation extension mapping at random can reduce peak-to-average force ratio.Yet, but brought bit error rate (bi t-error-rate, increase BER) when making constellation point become at random.According to the maximum likelihood decision criteria, the Euclidean between adjacent constellation point is apart from reducing to cause the BER mis-behave.Judge the standard MQAM mapping bit error probability that calculates with maximum-likelihood criterion under the general situation such as formula (5) is, use P _bExpression.Wherein Q (x) is the truncation distribution of standard Gauss, E _bBe energy per bit, N ₀Be noise power.

$P_b=\frac{2(L-1)}{L{\log }_{2}L}Q\left(\sqrt{\frac{6{\log }_{2}L}{2(L^2-1)}}\frac{E_b}{N_0}\right)---\left(5\right)$

With 64QAM expansion E-4QAM-R (1) is the bit error rate that example is calculated this kind E-4QAM.Suppose general appearance such as each constellation symbol,, can get its mistake to do than probability if do not consider that shining upon the signal power that causes by expansion increases

$P_b=\frac{1}{2}[Q\left(\sqrt{\frac{14}{3}\frac{E_b}{N_0}}\right)+Q\left(\sqrt{\frac{50}{21}\frac{E_b}{N_0}}\right)]---\left(6\right)$

Because E-4QAM-R (1) has selected the constellation point of outermost to form set, thereby the average power of expansion mapping back its average power overgauge QAM.For reflecting the capacity usage ratio of this constellation extension better, need to consider the increase of the signal power brought by its mapping mode, its power is carried out normalization, then can obtain BER characteristic suc as formula (7), its order of diversity is still approaching with standard 4QAM.

$P_b=\frac{1}{2}[Q\left(\sqrt{\frac{98}{37}\frac{E_b}{N_0}}\right)+Q\left(\sqrt{\frac{50}{37}\frac{E_b}{N_0}}\right)]---\left(7\right)$

Likewise; 16QAM also has different expansion mapping modes to E-4QAM, constellation point set E-4QAM-R (7) that for example rectangle frame is annotated among Fig. 3 and the set E-4QAM-R (8) that identifies with

.

In view of 64QAM is identical with the E-4QAM of expansion at random to the fixing expansion of E-16QAM gained constellation point position feature, thereby need not increase the degree of optional set, as long as suitable selection constellation point, its peak-to-average force ratio just can effectively reduce.Optional mapping mode also has the set E-16QAM-R (1) that represents such as rectangle constellation point among Fig. 2, the E-16QAM-R (2) of circular constellations point representative etc.

In like manner can know, the filler in the pattern matched also should randomization so that the frequency domain degree of correlation is low as far as possible.

The present invention proposes and realizes a kind of planisphere extended method at random.This method is kept bit error rate in a tolerable relatively scope reducing system peak-to-average than when guaranteeing practicality, has improved the practicality of system.The method that the present invention proposes can directly apply to actual working environment and not bring additional complexity and time-delay.

More than to the method for the embedded multiservice system peak-to-average force ratio of a kind of DTMB of reduction that the embodiment of the invention provided; Carried out detailed introduction; Used concrete example among this paper principle of the present invention and execution mode are set forth, the explanation of above embodiment just is used for helping to understand method of the present invention and core concept thereof; Simultaneously, for one of ordinary skill in the art, according to thought of the present invention, the part that on embodiment and range of application, all can change, in sum, this description should not be construed as limitation of the present invention.

Claims (5)

1. a method that reduces the embedded multiservice system peak-to-average force ratio of DTMB is characterized in that, comprising:

At first increase the degree of the set of expansion mapping, make the constellation point of a plurality of standard QAM belong to the primary image of an E-QAM constellation point, the correlation between the E-QAM frequency domain symbol is just weakened, and has promptly reached the purpose that reduces peak-to-average force ratio;

Secondly can in the set that some constellation point is formed, select at random during the expansion mapping and be not that expansion is mapped to fixing constellation point; Close constellation point is regarded as an expanded set makes the frequency domain symbol after the expansion become at random, correlation is better controlled;

Yet but brought the increase of bit error rate (BER) when making constellation point become at random; According to the maximum likelihood decision criteria, the Euclidean between adjacent constellation point is apart from reducing to cause the BER mis-behave; In order to take into account both performances, maximization minimum Eustachian distance in attenuation of correlation property.

2. the method for claim 1 is characterized in that, the degree of the optional constellation point set of expansion mapping equals Standard Map mode constellation point number, and this moment, its correlation was identical with former constellation mapping mode, and peak-to-average force ratio reaches the mean value of original system.

3. according to claim 1 or claim 2 method, it is characterized in that E-QAM mapping mode at random is a lot: in the expansion mapping of E-4QAM, available mode is as follows at 64QAM: establishing the set that ring annotates is E-4QAM-R (1), and this mode is represented extended bit B ₄B ₃B ₁B ₀Option set be combined into { (0000,0101,0001,0100) }, constellation point is { (± 5, ± 5), (± 7, ± 5), (± 5, ± 7), (± 7, ± 7) }; The set that rectangle frame is annotated is made as E-4QAM-R (2), and this mode is illustrated in extended bit B ₄B ₃B ₁B ₀Option set be combined into { (1111,0111,0101,1101) }, constellation point set is { (± 3, ± 3), (± 3, ± 5), (± 5, ± 3), (± 5, ± 5) }; Similarly expand the set E-4QAM-R (3) of the constellation point of the also useful rectangle constellation point sign of option set; Constellation point set E-4QAM-R (4) with triangle constellation point sign; Enclose the constellation point of notes with irregular polygon and gather E-4QAM-R (5), and the completely random extended method E-4QAM-R (6) under the extreme case.

4. the method for claim 1 is characterized in that, waits under the general situation and judges the standard MQAM mapping bit error probability that calculates with maximum-likelihood criterion, uses P _bExpression; Wherein Q (x) is the truncation distribution of standard Gauss, E _bBe energy per bit, N ₀Be noise power;

$P_b=\frac{2(L-1)}{L{\log }_{2}L}Q\left(\sqrt{\frac{6{\log }_{2}L}{2(L^2-1)}}\frac{E_b}{N_0}\right).$

5. the method for claim 1; It is characterized in that,, thereby need not increase the degree of optional set seeing that 64QAM is identical with the E-4QAM of expansion at random to the fixing expansion of E-16QAM gained constellation point position feature; As long as suitably select constellation point, its peak-to-average force ratio just can effectively reduce.

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